JPH08166706A - Charging device - Google Patents

Abstract

(57) [Summary] [Purpose] The surface potential of the photoconductor is kept constant without being affected by changes in the temperature and humidity of the ambient environment and film loss of the photoconductor. [Structure] At least two kinds of voltages are selectively applied from a power source 4 to a charging roller 2 which is in contact with or in proximity to a moving photosensitive member 1, and a first applied voltage Vin to the charging roller 2 is applied.
The current Ir1 generated by 1 and the second applied voltage Vin2
The current Ir2 generated by is measured by the current measuring means 11. The current value is input and stored by the control means 10, and is based on the voltage applied to the charging roller 2, the current measured by the current measuring means 11 and the resistance value Rr from the power source 4 to the charging area of the charging roller 2 measured in advance. And a charging roller 2 for performing a calculation to set the photoconductor 1 to a desired potential in the drawing process.
The optimum voltage Vin_opt to be applied to the
The power supply 4 is controlled so that in_opt is applied to the charging roller 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by an electrophotographic method such as a copying machine, a facsimile machine, a printer, etc., and more particularly, to a body to be charged including a drum or a belt-shaped photoreceptor. The present invention relates to a charging device that charges by a charging member that is in contact with or close to a charged body.

[0002]

2. Description of the Related Art In recent years, ozone is strictly regulated, and in charging, instead of the scorotron method, which generates a large amount of ozone, charging is performed by bringing a charging member such as a roller, a brush, or a blade into contact with or close to an object to be charged, A charging method with reduced ozone generation has been proposed.

Conventionally, the charging member has been applied with a constant DC voltage or with a DC voltage superposed with an AC voltage or an AC current.

[0004]

[Problems to be Solved by the Invention]

(First Problem) However, in the method of applying a constant DC voltage to the charging member, the surface potential of the charged body may change due to the influence of ambient temperature and humidity. As a result, the image density output by the image forming apparatus changed. Hereinafter, a photosensitive member will be described as an example of the member to be charged.

The allowable range of the potential fluctuation on the surface of the photoconductor is a value determined by the fluctuation of halftone density to be imaged and can be obtained as follows. First, an electrophotographic image forming apparatus forms an image having an average reflection density within a range of 0.4 to 0.9 within a circle having a diameter of at least 10 mm on the screen. Suppose that the average reflection density at this time is D1. The inventors used the Macbeth densitometer RD914 as an example of various reflection density measuring means. D1 is a value obtained by randomly measuring 30 reflection densities in a circle having a diameter of 50 mm with a Macbeth densitometer RD914, and taking an average, which is a value of 0.4 or more and 0.9 or less. During measurement of the reflection density, 10 sheets of white paper were overlaid on the back side of the image to be measured, and the light scattering conditions from the back side of the paper were kept constant.

Next, while drawing conditions other than the surface potential of the photoconductor are kept constant, only the surface potential of the photoconductor is gradually changed for printing. When the surface potential of the photoconductor changes, the image density also changes, but when the average reflection density in a circle with a diameter of 10 mm or more on the screen after changing the density changes by 0.07 or more compared with the original average reflection density D1. Then, the variation amount ΔVo_th of the surface potential of the photoconductor is obtained. This ΔVo_th is the allowable range of the surface potential fluctuation of the photoconductor in the image forming apparatus. Here, the variation 0.07 in the reflection density is a threshold value at which the variation in the density is detected as a result of the visual evaluation by the inventors. The visual evaluation was performed on 35 subjects under a standard light source according to a known subjective evaluation method, and a threshold value was obtained by a known statistical processing method.

As a result of a comparative examination of the threshold value of the density change and the development characteristics of the electrophotography currently put into practical use, the density change is detected when the surface potential of the photoconductor changes by 35 V or more.
A remarkable change in concentration was observed at a surface potential change of 50 V or more.
That is, as a result of visual evaluation, the permissible range ΔVo_th of the surface potential fluctuation of the photoconductor was 35V.

As a result of intensive investigations by the inventors on the cause of fluctuations in charging characteristics due to ambient temperature and humidity, it has been found that the resistance value from the power source to the surface of the photosensitive member in contact with the charging region of the charging member has an effect. Here, the charging area of the charging member is
Of the surface of the charging member and the gap between the charging member and the photoconductor, this is a region where the charge relating to the charging of the photoconductor is transferred.

Hereinafter, the resistance value from the power source to the surface of the photosensitive member in contact with the charging area will be referred to as charging resistance Rr. The charging resistance Rr is
The resistance of the charging member and the resistance of the air layer in the charging region from the surface of the charging member to the surface of the photoconductor are dominant.

As an example of the charging member, a charging member having a structure in which carbon and various conductive molecules are dispersed in a flexible material such as urethane will be shown. FIG. 2 is a diagram showing the structure of a charging roller as a charging member used in the embodiment of the present invention. Reference numeral 2 is a charging roller, which is a roller-shaped urethane core around a core metal having a length of 29 cm and a diameter of 6 mm and having a thickness of 3 mm. Urethane is not formed on both ends of the core metal 8 mm. The charging roller 2 is held by both ends of a cored bar on which urethane is not formed. Further, a voltage is applied from one end of the cored bar.

FIG. 3 is a schematic view of the photoconductor used in the embodiment of the present invention. In FIG. 3, 1 is a photoconductor,
An aluminum photoreceptor having a length of 30 cm, a diameter of 30 mm, and a wall thickness of 1 mm is coated with an organic photoreceptor having a film thickness of 26 μm. The relative dielectric constant ε of the organic photoconductor was 3.0.

The charging resistance Rr of the charging roller 2 is 7 ° C. and humidity 2
It was about 10 MΩ in an atmosphere environment of 0%. Further, it was about 2 MΩ under an atmosphere environment of 30 ° C. and 80% humidity. That is,
The charging resistance Rr fluctuated by 8 MΩ due to the fluctuation of the atmospheric environment.

Next, the influence of the fluctuation of the charging resistance Rr on the charging potential of the photoconductor was examined. For the sake of explanation, when the photosensitive member is charged from 0 V to the optimum surface potential Vo_opt during image formation, the voltage applied to the charging member is Vin_opt, and the current flowing through the charging member is Ir_opt.

Of the applied voltage Vin_opt, the voltage of Rr × Ir_opt is lost due to the resistance component of the charging member and the resistance component of the air layer in the charging region, and does not contribute to the charging of the photoconductor. In the charging method in which a constant voltage is applied, a value obtained by previously compensating for the voltage loss in the charging resistance may be set as the optimum applied voltage.

However, depending on the ambient environment, the charging resistance Rr
When fluctuates by ΔRr, the optimum applied voltage during printing is
It changes by ΔRr × Ir_opt. In the charging method in which a constant voltage is applied, this fluctuation in the optimum applied voltage causes an error in the photosensitive member surface potential. The fluctuation of the charging resistance Rr due to the atmospheric environment is: | ΔRr × Ir_opt | ≧ ΔVo_th ………………………………… (1) However, | | is an absolute value symbol When the above condition is entered, a change in image density occurs. From the characteristics of electrophotography currently in practical use, ΔVo_th = 35V.

In actual measurement, the current for bringing the photoconductor to a desired potential was about 5 μA. Therefore, the product of the variation of the charging resistance Rr and 8 MΩ × 5 μA = 40 V changed depending on the temperature and humidity of the atmosphere environment. It is the first object of the present invention to solve this problem in the conventional charging device.

(Second Problem) Next, the following charging control method that can be derived from the charging mechanism of the photoconductor was tried. Since the photoconductor at the time of non-exposure can be regarded as a dielectric, when the current flowing through the charging member when charging the photoconductor having a surface potential of 0 V to the potential Vo is Ir, | Vo | = k · | Ir | ………………………………………… (2) However, | | has a proportional relationship that is an absolute value symbol. Where d is the thickness of the photoconductor,
When ε is the relative permittivity of the photoconductor, ε0 is the dielectric constant of the vacuum, L is the length of the charged surface of the photoconductor in the axial direction of the photoconductor, and vp is the moving speed of the photoconductor, the coefficient k is k = d / (ε0 × ε × L × vp) ………………………………………… (3) is given in advance. Hereinafter, k may be called a charging coefficient, and the current flowing through the charging member at the time of charging the photoconductor may be called a charging current. In addition, the charging start voltage between the photosensitive member and the charging member is V
Let th.

The prototype control device applies a voltage Vin1 having an absolute value of Vth or more and the same polarity as the optimum surface potential Vo_opt of the photoconductor in the image forming process to the charging member before the image forming process to make the charging member. Measure the flowing current value.
According to (Equation 2), the measured current value Ir1 is multiplied by a coefficient k,
The surface potential Vo1 of the photoconductor is estimated. Desired surface potential Vo_
The absolute value Vin_opt of the optimum voltage applied to the charging member to obtain opt is (Equation 4) Vin_opt = | Vo_opt | + | Vin1 | -k ・ | Ir1 | ……………… (4) However, | | Calculate with absolute value symbol.

However, when the voltage Vin_opt actually calculated by (Equation 4) was applied, the surface potential of the photoconductor had an error of 35 V or more from the target potential and could not be put to practical use. Less than,
The measured value is shown. The charging roller shown in FIG. 2 was used as the charging member. Further, an outline of the photoconductor is shown in FIG. In FIG. 3, the photosensitive member is such that an organic photosensitive member having a film thickness of 26 μm is applied on the surface of an aluminum tube having a length of 30 cm, a diameter of 30 mm and a wall thickness of 1 mm. The relative dielectric constant ε of the organic photoconductor was 3.0.

FIG. 5 is a block diagram of a charging tester for measuring the surface potential of the photosensitive member 1. Reference numeral 1 is a photosensitive member, 2 is a charging roller, 3 is static elimination light, 4 is a constant voltage power source, 11 is a current measuring means, Reference numeral 41 is a surface potential measuring probe, and 42 is a surface potential meter. Surface electrometer
Reference numeral 42 indicates the surface potential of the photoconductor 1 measured by the surface potential measuring probe 41.

The charging coefficient k obtained from the equation (3) from the film thickness and the dielectric constant of the photoconductor 1 is k = 100 (V / μA). The current flowing into the charging member when the temporary applied voltage Vin = -900V was applied during non-image formation was 2.6 μA. Therefore,
The optimum applied voltage to set the photoconductor to the target potential of -450V is
From Equation 4, Vin_opt = -1060V is calculated. However, when -1060V was actually applied to the charging member, the surface potential of the photoconductor became -404V. That is, the target potential is -450V
There was a deviation of more than 35V. The cause was the voltage loss at the charging resistance Rr.

The charging current for obtaining a desired potential is Ir_op.
When t is set, there is a voltage drop of Rr × Ir_opt due to the charging resistance during charging. When the charging resistance Rr and the charging current Ir_opt satisfy the following relationship: | Rr × Ir_opt | ≧ ΔVo_th ……………………………… (5), the image density changes. .

In order to prevent voltage loss in the charging resistance Rr, it is desirable that the resistance value of the charging member be as small as possible. However, the charging member that is brought into contact with or close to the photosensitive member needs to have a resistance value of a certain value or more. The reason is,
This is because if the charging member has a low resistance, discharge is locally concentrated and abnormal discharge occurs, so that uniform charging cannot be performed. Also, in the process of long-term use, when the photoconductor surface is damaged and the conductive layer is exposed on the photoconductor surface called a pinhole,
With a low-resistance charging member, abnormal discharge occurs toward the pinhole, and uniform charging cannot be performed. In order to prevent these abnormal discharges, the charging member cannot have a low resistance. For example, in the case of a charging member for charging a photosensitive member of B4 width, it is desirable that the resistance value from the voltage application terminal of the charging member to the surface of the charging member in contact with the charging area is 1 MΩ or more.

Specifically, when actually measured, the current required to charge the surface potential of the photosensitive member to the target potential of −450 V in the photosensitive member of FIG. 3 was about 4.5 μA. On the other hand, in the case of the charging roller shown in FIG. 2, the charging resistance was about 10 MΩ from the core metal to the surface of the photosensitive member in contact with the charging area. Therefore, the voltage drop due to the resistance component of the charging roller is 45V when 4.5 μA flows. This 45V does not contribute to charging and causes a control error. The second object of the present invention is to solve this problem.

(Third Problem) When the image forming apparatus is used for a long period of time, the film of the photoconductor wears and the film thickness changes. as a result,
The charging coefficient k of the photoconductor changes. The degree of wear of the photoconductor depends on the hardness of the photoconductor. With an amorphous silicon photoconductor having high hardness, the abrasion of the photoconductor film is so small that it does not matter. On the other hand, in the case of a selenium photoconductor or an organic photoconductor having a low hardness, the film thickness of the photoconductor is reduced after long-term use. The abrasion of the photoconductor includes a cleaning blade in contact with the photoconductor, paper and paper dust, toner and additives contained in the toner, and these act in combination to scrape the surface of the photoconductor.

When the same applied voltage is applied to the charging member, if the initial charging potential of the photoconductor is Vo_opt and the charging potential of the photoconductor after long-term use is Vo_run, the potential difference between them is ΔVo_t.
When h or more, that is, | Vo_opt-Vo_run | ≧ ΔVo_th ……………………………… (6), the halftone density changes.

The charging characteristics of the photoconductor after long-term use measured by the inventors are shown below. In the experiment, the organic photoreceptor shown in FIG. 3 and the charging roller shown in FIG. 2 were used. First, a new photoconductor 1 (photoconductor film thickness: 26 μm) was mounted on the charging tester shown in FIG. 5, and allowed to stand for 3 days in a constant temperature and constant humidity environment of room temperature 7 ° C. and humidity 20% to fully adapt to the environment. . afterwards,
When −1100 V was applied to the charging roller 2 while the charge eliminating light 3 was turned on, the surface potential of the photoconductor 1 was −440 V and the charging current was
It was 4.4 μA.

Next, the same photoconductor 1 was used as a commercially available electrophotographic image forming apparatus (Fax Panafax B6 manufactured by Matsushita Electric Transmission Co., Ltd.).
It was attached to 6) and 100,000 continuous running tests were conducted.
The cleaning blade, the transfer roller, the paper, the toner, and the additives contained in the toner are in contact with the photoconductor, and these act in a complex manner to abrade the surface film of the photoconductor. The film thickness of the photoconductor 1 before the continuous paper passing test is
Although it was 26 μm, the film thickness after continuous sheet feeding test 100,000 sheets was 18 μm
Met.

The photosensitive member 1 having a film thickness of 18 μm was mounted on the charging tester shown in FIG. 5, and allowed to stand for 3 days in a constant temperature and constant humidity environment of room temperature of 7 ° C. and humidity of 20% to allow it to fully adapt to the environment. After that, when -1100 V was applied to the charging roller 2 while turning on the static elimination light 3,
The surface potential of the photoconductor 1 was −480 V and the charging current was 6.9 μA. The difference of 40 V from the surface potential of the new photoconductor is due to the reduction of the film thickness of the photoconductor. It is a third object of the present invention to solve the problem of the conventional charging device that applies a constant voltage.

(Fourth Problem) Ideally, all the current applied from the power source to the charging member is used for charging the photosensitive member.
However, as a result of intensive studies by the inventors, there was a case where a part of the current flowing through the charging member had a current that did not contribute to the charging of the photoconductor. Hereinafter, a current that does not contribute to charging will be referred to as a leak current. The generation of leak current is unstable, and it is difficult to investigate the cause and take countermeasures. Further, the leak current changed depending on the temperature and humidity of the atmosphere environment of the charging member, and the leak current increased especially in the case of high temperature and high humidity. The measurement results of the leak current are shown below.

Five charging testers shown in FIG. 5 are prepared, and the charging roller 2 shown in FIG. 2 and the photoconductor 1 shown in FIG. 3 are installed in each of them. It was left to stand for a day to fully adapt to the environment.

After that, without turning on the static elimination light 3, the voltage Vin = -1100V whose absolute value is equal to or higher than the charging start voltage Vth and whose polarity is the same as the optimum surface potential Vo_opt of the photoconductor 1 in the image forming process.
Was applied to charge. The surface potential of the photoconductor 1 before the start of charging was 0V.

When the photoconductor 1 rotates for 5 or more turns, the photoconductor 1
The surface potential of was stable and became a constant value. However, in one of the five charging testers, a current of about 0.4 μA continued to flow through the charging member even after the surface potential was stabilized. This charging tester is named charging tester A. Apparently, the current 0.4 μA flowing after the surface potential of the photoconductor 1 is stabilized does not contribute to the charging and is a leak current. In the remaining four charging testers, no current flowed to the charging member after the charging was stabilized.

Next, the above-mentioned five charging devices were set at room temperature and 33 ° C. humidity.
The sample was left in an environment of 80% constant temperature and humidity for 3 days to fully adapt to the environment. After that, the voltage Vin = − without turning on the static elimination light 3
Charging was performed by applying 1100V. Photoreceptor 1 before charging starts
Had a surface potential of 0V.

When the photoconductor 1 rotates for more than 5 turns, the photoconductor 1
The surface potential of was stable and became a constant value. However, in the charging tester A, even after the surface potential is stabilized, the charging member has 0.6
The current of μA continued to flow. This current of 0.6 μA is a leak current because it does not contribute to the charging of the photoconductor 1. Also,
In another charging tester, after the surface potential was stabilized, a current of about 0.2 μA continued to flow to the charging member. This 0.2 μA current is also a leak current because it does not contribute to the charging of the photoconductor 1. In the remaining three charging testers, no current flowed to the charging member after the charging was stabilized.

As described above, there are individual differences in the leak current, and although the charging tester was made to have the same specifications, it did or did not occur. Moreover, the value of the leak current changed depending on the ambient temperature and the humidity. The causes of this leakage current are (a) leakage current of the power source, (b) leakage current in the middle of the current path from the power source to the charging member, (c) leakage current from the holder holding the charging member, (d) There are many causes such as discharge from the charging member to the peripheral members, and (e) current used for ionizing the air around the charging member.

The inventors vigorously tried to analyze the leak current in the charging tester and the image forming apparatus, but the leak current is unstable and may occur due to individual differences in the apparatus.
Further, the image forming apparatus in which the leak current once occurred may not detect the occurrence of the leak current on another day. The inventors have tried various measures, but it has been very difficult to identify the cause of these leak currents and take effective measures.

In the present invention, when the leak current is mixed in the current used for determining the applied voltage or the applied current in the image forming process, the proportional relationship between the charging current and the surface potential is broken, and the optimum applied voltage determined. Error occurs. In particular,
The product of the charging coefficient k of the photoconductor and the leak current Ir_L (k · Ir_
When the absolute value of (L) is equal to or greater than ΔVo_th, that is, when | k · Ir_L | ≧ ΔVo_th ………………………………………… (7) The output image has uneven density. Based on the visual evaluation by the inventors, ΔVo_
th = 35V. It is the fourth object of the present invention to solve this problem.

(Fifth Problem) As a result of intensive studies by the inventors, a transient state was observed in the charging current. The electrification tester of FIG. 5 was left for 3 days in a constant temperature and constant humidity environment of room temperature 20 ° C. and humidity 50% to allow it to fully adapt to the environment. During standing, no voltage is applied to the charging roller 2, the photoconductor 1 is rotated, and the static elimination light 3 is not irradiated. Hereinafter, for the sake of explanation, a state in which no voltage is applied to the charging member, the photosensitive member is stopped, and the charge eliminating unit is not operating will be referred to as an uncharged state.

Then, the photosensitive member 1 is rotated at the peripheral speed vp,
A voltage Vin_5 having an absolute value equal to or higher than the charging start voltage Vth and the same polarity as the optimum surface potential Vo_opt of the photoconductor 1 in the image forming process was applied to the charging member while irradiating the charge removing light 3. After the application of the voltage Vin_5 was started, the photoconductor 1 was rotated three times or more, and then the photoconductor surface potential Vo_51 and the charging current Ir51 flowing through the charging roller 2 were observed. Hereinafter, this is called the first charging.

Further, the above charging tester was left for 12 hours in the same environment of constant temperature and temperature of 20 ° C. and humidity of 50%. It was in a non-charged state during standing. Immediately after leaving for 12 hours, the direct current voltage Vin_5 was applied to the charging member again to perform charging. Hereinafter, this is called the second charging.

As a result of the measurement, in the second charging, the charging current flowing through the charging member is unstable from the start of charging until the photosensitive member makes one revolution, and the absolute value thereof is the charging current in the first charging. It was larger than Ir51. Further, the absolute value of the charging potential of the photoconductor in the second charging was smaller than the absolute value of the photoconductor surface potential Vo_51 in the first charging.

However, in the second charging, when the photosensitive member 1 was continuously charged for two turns or more, the charging current was stable and coincided with Ir51. At the same time, the charging potential of the photoconductor 1 was stabilized and coincided with Vo_51.

The measured values are shown below. After incorporating the photoconductor 1 of FIG. 3 and the charging roller 2 of FIG. 2 into the charging tester of FIG.
It was left for 3 days in a constant temperature and constant humidity environment of room temperature 20 ° C and humidity 50%, and was sufficiently acclimated to the environment. It was in a non-charged state during standing.

After that, the photosensitive member 1 was rotated at a peripheral speed of 33 mm / sec, a voltage of −1100 V was applied to the charging roller 2 while the discharging light 3 was turned on, and charging was started. The charging current from the start of charging until the photoconductor 1 rotates once is 4.9 μA, and the photoconductor rotation 1
Charging current is 4.4μA between the two and more laps, 3 rotations of the photoconductor
After the first lap, the charging current was stable and was 4.4 μA, which was the same as the second lap. On the other hand, the surface potential of the photoconductor is 406V until the photoconductor 1 makes one revolution, 436V from the first revolution to the second revolution of the photoconductor, and the charging potential is stable after the third revolution of the photoconductor and the second revolution. the same
It was 436V.

That is, the charging current flowing from the start of charging until the photosensitive member 1 makes one rotation is 0.5 μA larger than the charging current when the photosensitive member 1 makes one rotation or more. However, the absolute value of the charging potential was smaller by 30 V until the photoconductor 1 completed one revolution than when the photoconductor 1 completed one revolution. That is, the charging current immediately after being left uncharged for 3 days contained a current component that did not contribute to the charging of the photoconductor. These are transient states due to the photoreceptor. Since the charging coefficient k of the photoconductor 1 is 100 (V / μA),
From (Equation 2), the difference of 0.5 μA at the time of measurement resulted in a control error of 50V.

In general, in the charging step immediately after being left in the uncharged state for one hour or more, the current Ir11 flows from the start of charging until the photosensitive member makes one revolution, and the current Ir12 flows when the photosensitive member makes one revolution or more. At this time, if the optimum applied voltage at the time of image formation is calculated from the current Ir11 according to (Equation 4), an error from the target potential by the product of the charging coefficient k of the photoconductor, k.multidot. (Ir11-Ir12), occurs. When the potential error is ΔVo_th or more, the density of the formed image changes. Here, ΔVo_th is 35V as a result of visual evaluation by the inventors. The fifth object of the present invention is to solve this problem.

(Sixth Problem) Further, the inventors of the present invention have made extensive studies and found that when a rotating roller-shaped charging member (hereinafter also referred to as a charging roller) is used as the charging member, charging is started from the start of charging. A transient state was observed in the charging current generated until the roller made one revolution.

That is, the charging tester shown in FIG. 5 was left in a constant temperature and constant humidity environment for 3 days to allow it to fully adapt to the environment. It was in a non-charged state during standing. Then, rotate the photoconductor 1 at the peripheral speed vp.
Then, the voltage Vin_6 whose absolute value is equal to or higher than the charging start voltage Vth and whose polarity is the same as the optimum surface potential Vo_opt of the photoconductor 1 in the image forming step is applied to the charging member while being rotated by. After the charging roller 2 has rotated three times or more after the start of applying the voltage Vin_6, the photoreceptor surface potential Vo_61 and the charging current Ir61 flowing through the charging roller 2 were observed. This is called the third charging. After the third charging, after left for 10 minutes, the charging member was charged again by applying the DC voltage Vin_6. This is called the fourth charging. In the fourth charging, the charging roller 2 is set to 1 from the start of charging.
The charging current flowing through the charging member is unstable until it goes around, and its absolute value is larger than the absolute value of the charging current Ir61 of the third charging. Further, the absolute value of the charging potential of the photoconductor of the fourth charge is equal to the surface potential V of the photoconductor of the third charge.
It was smaller than the absolute value of o_61.

However, in the fourth charging, when the voltage Vin_6 was continuously applied to the charging roller 2 for two or more turns, the charging current became stable and coincided with Ir61. At the same time, the charging potential of the photoconductor 1 was stabilized and coincided with Vo_61.

After the above phenomenon was recognized, the charging experiment was repeated under different conditions, and the inventors obtained the following findings. That is, when the non-charged state is 1 minute or less, the charging current flowing from the start of charging until the charging roller 2 makes one revolution does not differ from the charging current after the second revolution of the charging roller. However, if the non-charged state is for 3 minutes or more, the charging current flowing from the start of charging until the charging roller 2 makes one revolution is unstable, and its absolute value is the absolute value when the charging roller 2 makes one revolution or more. It is larger than the absolute value of the charging current. at the same time,
The absolute value of the charging potential of the photoconductor 1 from the start of charging until the charging roller 2 makes one revolution is smaller than the absolute value of the charging potential when the charging roller 2 rotates one revolution or more.

Further, regardless of the length of time that the non-charged state continues, after the voltage is applied to the charging roller 2 and the charging roller 2 rotates at least one revolution, the charging current becomes stable. At the same time, the surface potential of the photoconductor becomes stable.

As the measured values, the photoconductor 1 shown in FIG. 3 and the charging roller 2 shown in FIG. 2 were installed in the charging tester shown in FIG.
The apparatus was left in an environment of 50% humidity for 3 days to allow the apparatus to fully adapt to room temperature and humidity. It was in a non-charged state during standing. After that, a voltage of −1100 V was applied to the charging roller 2 and charging was performed while the charge eliminating light 3 was turned on. When the uncharged state is 1 minute,
The charging current was stable from the start of charging, and was 4.4 μA, and the surface potential of the photosensitive member was −430V.

Next, when the uncharged state is 3 minutes, the charging current from the start of charging to one rotation of the charging roller 2 is 4.6.
μA, the charging potential of the photoconductor 1 is −430 V, the charging current of the charging roller 2 is 1 μm to 2 turns, the charging current is 4.4 μA, the surface potential of the photoconductor 1 is −440 V, and the charging roller 2 rotates 3 or more turns. Then, the charging current is 4.4 μA and the surface potential of the photoconductor is −
It was 440V. That is, when the uncharged state is 3 minutes,
The charging current and the surface potential of the photosensitive member 1 became stable after the charging roller 2 rotated one round or more from the start of charging. This is a transient state of the charging current caused by the charging roller 2.

In general, it is desirable that the current flowing from the start of charging to one round of the charging roller is Ir13 in the charging step immediately after leaving the battery in an uncharged state for 3 minutes or more, and preferably for 1 hour or more to improve reliability. The current that flows when the circuit makes one turn or more is Ir14. At this time, when the optimum applied voltage at the time of image formation is obtained from the current Ir13 according to (Equation 4), the charging coefficient k of the photoconductor is
And the product of k and (Ir11-Ir12) causes an error from the target potential. When the potential error is ΔVo_th or more, the density of the formed image changes. Here, ΔVo_th is 35V as a result of visual evaluation by the inventors. The sixth object of the present invention is to solve this problem.

(Seventh Problem) Further, the inventors of the present invention have conducted extensive experiments and found that when the charging current is measured using a rotating charging roller as a charging member, noise is generated in the measured current in one rotation cycle of the charging roller. I found out that The causes of noise are (a) uneven resistance generated in the manufacturing process of the charging roller,
(B) uneven contact with the photoconductor due to unevenness of the charging roller surface,
(C) Dirt and wear of the charging roller due to long-term use, and (d) eccentricity of the charging roller.

Generally, the charging coefficient k of the photosensitive member and the current I
When the peak-to-peak current of the noise component of r is ΔIr_pp,
As a result of intensive studies by the inventors, it was found that when the absolute value of the product of k and ΔIr_pp is 35 V or more, a density change occurs in the formed image. If there is an error in the current used to determine the applied voltage or applied current in the drawing process, an error will also occur in the determined optimum applied voltage. This is the seventh subject of the present invention.

(Eighth Problem) The applied voltage or applied current in the drawing process is determined prior to the drawing process. As one method, it can be carried out immediately before printing. However, in this charging method, the photosensitive member is rotated about 1 to 5 times to measure the charging current. For example, in the case of a photoconductor with a diameter of 30 mm and a peripheral speed of 33 mm / sec, it takes about 5 rotations
It takes 15 seconds. Among electrophotographic image forming apparatuses, in copiers and printers where users are often on standby,
It is desirable that the time from the drawing command to the end of the drawing process is as short as possible. It is an eighth object of the present invention to solve this.

(Ninth Problem) The voltage and current used to determine the applied voltage or applied current in the drawing process are the voltage and current applied or generated when the photosensitive member having a surface potential of 0 V is charged. The surface potential of the photoreceptor immediately before charging is 0V
Therefore, it is necessary to remove the charge before measuring the charge. However, when the charge eliminating unit is the charge eliminating light, the polarity of the potential capable of eliminating the charge is limited to the polarity in which the photoconductor exhibits photoconductivity.

However, the transfer means corresponding to the reversal development in the electrophotographic method is used for the image carrier (for example,
The charge applied to the paper is the opposite polarity of the voltage at which the photoconductor has photoconductivity. When the photoconductor is charged by the transfer means to a polarity having no photoconductivity, the photoconductor potential cannot be set to 0 V by the neutralization light, and the bias remains. The bias also applies to the charging current measured due to this influence, resulting in a measurement error. If the measured current has an error, the determined optimum applied voltage also has an error. The ninth problem of the present invention is to solve this problem.

On the other hand, the charging method in which a voltage in which an alternating current is superimposed on the direct current bias is applied causes a problem that the superimposed alternating current produces annoying noise noise and is not suitable for an office environment where quietness is required.

The present invention solves these problems and provides a charging device for charging a photoconductor to a target potential.

[0063]

In order to solve the above problems, the charging device of the present invention has the following structure. (1) a body to be charged, a charging member in contact with or close to the body to be charged, a power supply for applying a voltage to the charging member, a current measuring means for measuring a current flowing from the power supply to the charging member, Based on the current measured by the current measuring means and the resistance value Rr from the power source to the charging area of the charging member, the optimum voltage Vin_opt to be applied to the charging member for setting the charged body to a desired potential is determined. And a control means for controlling the power supply.

(2) A member to be charged which is moved by a known driving means, and a charging member which is in contact with or close to the member to be charged,
A power source that selectively applies at least two types of voltages to the charging member, and a current Ir1 generated by moving the member to be charged and a first applied voltage Vin1 to the charging member.
And current measuring means for measuring the current Ir2 generated by the second applied voltage Vin2 to the charging member, and the current value measured by the current measuring means is inputted and stored, and the voltage applied to the charging member, the current Calculation is performed based on the current measured by the measuring means and the resistance value Rr measured in advance from the power source to the charging area of the charging member, and applied to the charging member to bring the charged body to a desired potential in the image forming step. A control means for determining the optimum voltage Vin_opt to be controlled and controlling the power supply.

(3) At least two kinds of voltages are selectively applied to the charged member which circulates at a speed vp by a known driving means, the charging member which comes into contact with or comes close to the charged member, and the charging member. A power source, a static eliminator for neutralizing the body to be charged, a current measuring unit for measuring a current flowing through the charging member, and a control unit for controlling the power source and the static eliminator. Occurs when the power source applies the first voltage Vin1 to the charging member in a state where the charging region of the charging member is in contact with the surface of the member to be charged, which is circulated and moved by vp and is discharged by the discharging unit. Current Ir1 is measured, and then the current Ir2 generated when the second applied voltage Vin2 is applied to the charging member in the above state is measured. Before the point From the area which receives the neutralization effect of the discharging means, TJR the time required to move to the charging area of the charging member, the measurement end time of the current Ir2 T
When it is set to 2, the charge removal by the charge removal unit is stopped after the time (T2-Tjr) in the state where the second applied voltage Vin2 is applied to the charging member, and the charge removal is not performed on the surface of the charged body that is being discharged. Assuming that the time at which the boundary with the surface of the body to be charged contacts or is closest to the charging region of the charging member is T3, from time T3 until the body makes one revolution,
The current Ir3 flowing through the charging member is measured, and the control means performs the calculation based on the currents Ir1, Ir2 and Ir3 measured by the current measuring means to set the charged body to a desired potential in the drawing process. An optimum voltage Vin_opt applied to the charging member is determined and the power source is controlled.

(4) At least two kinds of voltages are selectively applied to the charging member that circulates at a speed vp by a well-known driving unit, the charging member that is in contact with or close to the charging member, and the charging member. A power source, a static eliminator for neutralizing the body to be charged, a current measuring unit for measuring a current flowing through the charging member, and a control unit for controlling the power source and the static eliminator. Occurs when the power source applies the first voltage Vin1 to the charging member in a state where the charging region of the charging member is in contact with the surface of the member to be charged, which is circulated and moved by vp and is discharged by the discharging unit. Current Ir1 is measured, and then the current Ir2 generated when the second applied voltage Vin2 is applied to the charging member in the above state is measured. Before the point From the area which receives the neutralization effect of the discharging means, TJR the time required to move to the charging area of the charging member, the measurement end time of the current Ir2 T
When it is set to 2, the charge removal by the charge removal unit is stopped after the time (T2-Tjr) in the state where the second applied voltage Vin2 is applied to the charging member, and the charge removal is not performed on the surface of the charged body that is being discharged. Assuming that the time at which the boundary with the surface of the body to be charged contacts or is closest to the charging region of the charging member is T3, from time T3 until the body makes one revolution,
The current Ir3 flowing through the charging member and the current Ir4 flowing through the charging member when the charged body makes one or more turns from time T3 are measured, and the control means measures the currents Ir1 and Ir2 measured by the current measuring means. , Ir3 and Ir4 are calculated to determine the optimum voltage Vin_opt to be applied to the charging member to bring the charged body to a desired potential in the drawing process, and to control the power supply.

(5) A charged body which is circulated and moved at a speed vp by a known driving means, a charging member which is in contact with or close to the charged body, and a power source which applies a voltage to the charging member.
The charging means includes a discharging means for discharging the charged body, a current measuring means for measuring a current flowing through the charging member, and a control means for controlling the power supply and the discharging means. The current measuring means circulates at a speed vp. The power source is applied to the charging member while the charging region of the charging member is in contact with the surface of the member to be charged that has moved and has been discharged by the discharging unit.
Current Ir1 generated when the voltage Vin1 is applied, and one point on the body to be charged that circulates at a speed vp is charged from the area subjected to the charge removal from the charge removal means to charge the charging member. When the time required to move to the region is Tjr and the measurement end time of the current Ir1 is T2,
With the applied voltage Vin1 applied to the charging member,
After (T2-Tjr), the static elimination by the static elimination means is stopped,
Assuming that the time at which the boundary between the surface of the charged body that has been discharged and the surface of the body that has not been discharged contacts or is closest to the charging area of the charging member is T3, the charged body makes one round from time T3. In the meantime, the current Ir3 flowing through the charging member is measured, and the control means performs calculation based on the currents Ir1 and Ir3 measured by the current measuring means to bring the charged body to a desired potential in the drawing process. For determining the optimum voltage Vin_opt to be applied to the charging member for controlling the power source.

(6) An object to be charged which circulates at a speed vp by a known driving means, a charging member which is in contact with or close to the object to be charged, and a power supply which applies a voltage to the charging member.
The charging means includes a discharging means for discharging the charged body, a current measuring means for measuring a current flowing through the charging member, and a control means for controlling the power supply and the discharging means. The current measuring means circulates at a speed vp. The power source is applied to the charging member while the charging region of the charging member is in contact with the surface of the member to be charged that has moved and has been discharged by the discharging unit.
Current Ir1 generated when the voltage Vin1 is applied, and one point on the body to be charged that circulates at a speed vp is charged from the area subjected to the charge removal from the charge removal means to charge the charging member. When the time required to move to the region is Tjr and the measurement end time of the current Ir1 is T2,
With the applied voltage Vin1 applied to the charging member,
After (T2-Tjr), the static elimination by the static elimination means is stopped,
Assuming that the time at which the boundary between the surface of the charged body that has been discharged and the surface of the body that has not been discharged contacts or is closest to the charging area of the charging member is T3, the charged body makes one round from time T3. In the meantime, the current Ir3 flowing through the charging member and the current Ir4 flowing through the charging member when the charged body makes one revolution or more from time T3 are measured, and the control means measures the current measuring means. Current Ir1, Ir3
And Ir4 to perform an operation to determine the optimum voltage Vin_opt applied to the charging member to bring the charged body to a desired potential in the drawing step, and control the power supply.

(7) In the charging device of the above (1) to (6), the charging member is rotated by a known driving means including power transmission from the body to be charged, and the time for the charging member to rotate once is Tr.
Then, the current measuring means has a cutoff frequency of 1 /
It is characterized in that it has a low-pass filter of Tr or less.

(8) Further, in the charging device of the above (1) to (6), the current used for determining the voltage Vin_opt is at least one revolution of the body to be charged since the voltage was applied to the charging member. It is characterized in that it is the electric current after

(9) Further, in the charging device of the above (1) to (6), the current used for determining the voltage Vin_opt is applied to the rotating charging member by a known driving means including driving from the member to be charged. From the time when the voltage changes, the current is the current after the charging member has rotated at least one revolution.

(10) In the charging device described in (9) above, the time when the voltage changes includes the time when the voltage application to the charging member is started.

(11) A photoconductor that circulates by known driving means, a charging member that comes into contact with or close to the photoconductor, a power source that applies a voltage to the charging member, and a current flowing through the charging member are measured. Current measuring means, static elimination light for discharging the photoconductor by exposure, developing means for developing on the photoconductor, transfer means for transferring an image on the photoconductor to an image carrier, and voltage for the transfer means. Or a transfer power source for applying at least one of the currents, the photosensitive member is moved, and the current generated when a voltage is applied to the charging member in a state in which the charge removal light is turned on is used to draw an image. In the image forming apparatus that determines the voltage applied to the charging member in the step, one point on the moving photosensitive member is required to move from the transfer area of the transfer unit to the charging area of the charging member. When the measurement start time of the electric current generated in the charging member is T7 and the measurement end time is T8, at least between the time (T7-Ttr) and the time (T8-Ttr). The voltage applied to the transfer means is ground or a voltage having a polarity in which the photoconductor exhibits photoconductivity, or an absolute difference between the surface potential of the photoconductor charged by the charging member and the voltage applied to the transfer means. The value is a voltage equal to or lower than the charging start voltage between the photoconductor and the transfer unit, or the transfer unit is electrically floated.

(12) In the charging device of (2), (3), (4), (5) or (6) above, the member to be charged is a photoconductor and the discharging unit is an exposing unit. It is what

(13) In the charging device according to any one of (1) to (10), the current used for determining the voltage applied to the charging member in the image forming step is the current flowing from the body to be charged to the ground. It is a feature.

(14) In the charging device of (11) above, the charging current to be measured is a current flowing from the photosensitive member to the ground.

(15) Above (1) to (6), (8), (9) or (11)
In the above charging device, the charging member has a roller shape.

(16) In the charging device of (1) to (6), (8) or (11) above, the charging member has a blade shape.

(17) In the charging device of (1) to (11) above,
The charging member has a brush shape.

(18) In the charging device of the above (2), (3), (4), (5) or (6), the current is measured at a constant time.

(19) In the charging device of (2), (3), (4), (5) or (6), the current is measured from immediately after the power is turned on to immediately before the start of the first drawing process. It is characterized by performing.

(20) In the charging device of (2), (3), (4), (5) or (6) above, the current is measured immediately before the drawing process.

(21) In the charging device of the above (2), (3), (4), (5) or (6), the current is measured immediately after the drawing process.

(22) In the charging device of (2), (3), (4), (5) or (6), the current is measured from immediately after the power is turned on to immediately before the start of the first drawing process. Or at regular time intervals,
Alternatively, it is characterized in that two or more kinds are combined immediately after the drawing process.

(23) In the charging device of (1) to (10) above,
The member to be charged has a drum shape.

(24) In the charging device of (1) to (10) above,
The member to be charged has a belt shape.

(25) In the charging device of (11) above, the photoconductor is drum-shaped.

(26) In the charging device described in (11) above, the photoconductor is belt-shaped.

(27) In the charging device of (3), (4), (5) or (6) above, a transfer means for transferring the image on the surface of the body to be charged to the image carrier is provided, and the charge removing means is the transfer means. It is characterized in that the means also serves.

[0090]

The present invention has the following actions with respect to the above (first subject) to (9th subject) due to the above-mentioned configuration.

For (first problem), the above (3), (4),
With the configurations of (5) and (6), the charging resistance is sequentially measured, and the optimum applied voltage to the charging member is determined while making corrections.

Regarding (second problem),
With the configurations of (1), (2), (3), (4), (5), and (6), the optimum applied voltage to the charging member is determined while correcting the charging resistance value.

Regarding (third problem),
With the configurations of (2), (3) and (4), the charging member is continuously measured while the proportional coefficient k between the current flowing through the charged body including the photoconductor and the surface potential of the charged body including the photoconductor potential is sequentially measured. Determine the optimum applied voltage to.

Regarding (fourth problem), the above (4)
With the configurations of (6) and (6), the optimum applied voltage to the charging member is determined while correcting the leakage current.

Regarding (fifth problem), the above (8)
With this configuration, the optimum applied voltage to the charging member is determined without erroneously measuring the transient current caused by the photoconductor.

Regarding (sixth problem), the above (9)
With the configurations of (10) and (10), the optimum applied voltage to the charging member is determined without erroneously measuring the transient current caused by the rotating roller-shaped charging member.

Regarding (seventh problem), the above (7)
With this configuration, the noise caused by the rotating roller-shaped charging member is removed, and the optimum applied voltage to the charging member is determined.

Regarding (eighth problem), the above (21)
With the configurations of (22) and (22), the measurement step of the present invention is not executed at least between after the drawing instruction and the start of the drawing step.

Regarding (9th problem), the above (11)
With the above configuration, the photoconductor potential before charging is always 0V,
The current is measured and the optimum applied voltage to the charging member is determined.

[0100]

Embodiments will be described in detail below with reference to the drawings. (First Embodiment) First, FIG. 2 shows a structure of a charging roller as a charging member used in an embodiment of the present invention. In FIG. 2, reference numeral 2 is a charging roller, which is a roller-shaped core metal having a length of 29 cm and a diameter of φ6 mm, which is made of conductive material and has a thickness of 3 mm. No urethane is formed on both ends of the core metal 8 mm each. Charging roller 2
Is held at both ends of the core metal with no urethane formed,
A voltage is applied from one end of the cored bar.

FIG. 3 shows the structure of the photosensitive member 1 as the member to be charged used in the embodiment of the present invention. length
An organic photoreceptor having a film thickness of 26 μm is applied to the surface of an aluminum tube having a diameter of 30 cm, a drum diameter of 30 mm, and a wall thickness of 1 mm.

Since the photoconductor at the time of non-exposure can be regarded as a dielectric, when the photoconductor having a surface potential of 0 V is charged to Vo, the charging potential Vo is proportional to the current Ir flowing through the charging member. Less than,
The current flowing through the charging member during charging may be referred to as a charging current.

FIG. 4 is a diagram showing the charging characteristics of the photoconductor.
In FIG. 4, the horizontal axis represents the absolute value of the current Ir flowing into the photoconductor, and the vertical axis represents the absolute value of the charging potential Vo of the photoconductor. FIG.
Is the proportional coefficient between the absolute value of the current Ir and the absolute value of the charging potential Vo, and the proportional coefficient k is named the charging coefficient. In the case of charging a photoreceptor having an initial surface potential of 0 V, multiplying the absolute value of the charging current Ir by k gives the absolute value of the charging potential Vo.

Prior to the determination of the voltage applied to the charging member in this embodiment, the resistance value from the power source to the surface of the photosensitive member where the charging member contacts the charging area is measured in advance. Hereinafter, a method of measuring the charging resistance Rr will be described with reference to FIG.

FIG. 5 shows a charging tester, which is used to measure the charging resistance Rr in this embodiment. 1 is a photoconductor, 2 is a charging roller,
3 is static elimination light, 4 is a constant voltage power source, 11 is current measuring means, 41
Is a surface potential measuring probe, and 42 is a surface potential meter. The surface potential meter 42 is the photoreceptor 1 measured by the surface potential measuring probe 41.
Display the surface potential of the.

Assuming that the charging start voltage between the charging roller 2 and the photoconductor 1 is Vth, a voltage Vtest whose absolute value is Vth or more and whose polarity is the same as the optimum surface potential Vo_opt of the photoconductor 1 in the image forming process is supplied to the power source 4. Is applied to the charging roller 2. At this time, the current flowing through the charging roller 2 is measured by the current measuring means 11. The charging resistance Rr is obtained by the following procedure.

(A) The photoconductor is rotated in the direction of the arrow at the peripheral speed vp. (A) Photoreceptor 1 with no voltage applied to charging roller 2
To turn on the neutralization light 3 and set the surface potential of the photoconductor to 0V.
To (C) The voltage Vtest is applied to the charging roller 2 with the neutralization light 3 turned on. After rotating the photoconductor 1 at least three times or more, the flowing current Ir_test and the surface potential Vo_t1 of the photoconductor are measured. (D) After turning off the static elimination light 3, at least the photoconductor 1 is set to 3
The surface potential Vo_t2 of the photoconductor 1 when it is rotated for more than one revolution is measured. (E) When the charging current flows, the voltage decreases due to the charging resistance Rr. Therefore, when charging while removing the charge, the photoconductor 1
The absolute value Vo_t1 of the surface potential of is: Vo_t1 = | Vtest | −Vth− (Rr × | Ir_test |) (8) On the other hand, the absolute value Vo_t2 of the surface potential of the photoconductor 1 when it is charged without being discharged is Vo_t2 = | Vtest | −Vth .................................... (9). Therefore, the charging resistance Rr is (Equation 10) Rr = | Vo_t2-Vo_t1 | / | Ir_test | …………………… (10) However, ||

In the actual measurement, Vtest = −1100V was applied to the charging roller 2. The surface potential Vo_t1 of the photoconductor 1 was −436 V and the charging current Ir_t1 was 4.4 μA when the charge eliminating light 3 was turned on. When the charge eliminating light 3 was turned off, the surface potential Vo_t2 of the photoconductor 1 was -476V. Therefore, the charging resistance Rr was determined to be 9.1 MΩ from (Equation 10). In this embodiment,
This Rr is used to determine the voltage applied to the charging member as follows.

FIG. 1 shows a schematic structure of an image forming apparatus according to the first embodiment of the present invention. The image forming apparatus of this embodiment is of an electrophotographic type in which an image is formed on a photoconductor and then transferred to paper. In FIG. 1, reference numeral 1 denotes a drum-shaped photosensitive member, which has the configuration shown in FIG. The photoconductor 1 is rotated at a peripheral speed vp = 33 mm / s in the arrow direction by a drive motor (not shown). Reference numeral 2 denotes a charging roller as a charging member which is brought into contact with the photoconductor, and is rotated by a frictional force with the photoconductor 1.

Reference numeral 35 denotes a laser light source as an image writing means. The emitted laser light is reflected by the mirror 36 and then is irradiated on the surface of the photoconductor 1 to form a latent image on the photoconductor 1. 31
Develops the latent image on the photoconductor 1 with toner in a developing device. Reference numeral 32 denotes a transfer roller as a transfer unit, and 37 denotes a transfer power source, which has a function of selecting whether +2 μA is applied to the transfer roller 32 or an electric float state is selected. The transfer roller 32 transfers the toner on the photoconductor 1 onto the paper 34. During transfer, +2 μA is applied from the transfer power supply 37 to the transfer roller 32. A cleaning blade 33 scrapes off the toner remaining on the photoconductor 1. Reference numeral 3 denotes a static elimination light as a static elimination means, which irradiates the photoconductor 1 to set the surface potential to 0V.

A power source 4 selectively applies two or more kinds of DC voltages having different values to the charging roller 2. In this embodiment, two kinds of direct current voltages of Vin1 = -900V and Vin2 = -1100V are selectively applied to the charging roller 2. Further, at the time of image formation, a voltage in the range of -800V to -1300V is selected in 5V steps and applied to the charging roller 2.

A current measuring means 11 measures the current flowing from the power source 4 to the charging roller 2. Reference numeral 10 denotes a control means, which has a function of inputting a current value measured by the current measuring means 11, a function of storing the input value, a function of performing an arithmetic operation on the input and the stored value, a power source 4 and a transfer power source 37. It has a function to control. The operation of the control means 10 will be described below.
This will be described with reference to FIG.

FIG. 6 is a timing chart showing the operation of the control means 10. Time elapses in the direction of the horizontal axis arrow. Rotation of photoconductor from above, voltage V applied to charging roller 2
in, lighting (on) or extinguishing (off) of the static elimination light 3, the absolute value Ir of the charging current flowing through the charging roller 2, the current applied to the transfer roller 32 by the transfer power supply 37, and the photoconductor at the developing position by the developing device 31. The surface potential Vo of No. 1 is shown. Since it is complicated to display it as it is, the photoreceptor surface potential Vo in FIG.
Time Trd required for one point on the moving photoreceptor 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31
Just advanced. Further, the time required for the charging roller 2 to make one rotation is Tr, and the time required for the photosensitive member 1 to make one rotation is Tp. The charging time of the charging roller 2 is Tr and Tp.
, The diameter of the photosensitive member 1, and the peripheral speed vp of the photosensitive member 1.

In FIG. 6, prior to the image forming process, the photoconductor 1
Before the start of rotation, the transfer power supply 37 is set in a floating state, and the transfer roller 32 does not charge the photoconductor 1.
The voltage Vin1 is applied to the charging roller 2 at time T1 after a time sufficient for the rotation of the photoconductor 1 to be sufficiently stabilized. V
Since the current value is unstable from the time T1 when in1 is applied until the charging roller 2 makes one revolution (time T1 + Tr), it is ignored.
The current value Ir1 after the charging roller 2 has rotated one round or more is measured. This is the first measurement.

After the first measurement, the voltage Vin applied to the charging roller 2
Apply 2. Of the current flowing at this time, from immediately after Vin2 is applied to when the charging roller 2 makes one revolution (time T
Since the current flowing through the charging roller 2 in r) is unstable, ignore it.
The current value Ir2 after the charging roller 2 has rotated one revolution or more is measured. This is the second measurement.

The control means 10 determines the optimum absolute value Vin_opt of the applied voltage at the time of image formation from the measured values Ir1 and Ir2 and the previously measured charging resistance Rr. And the absolute value is Vin
The power supply 4 is controlled so that it is closest to _opt and the polarity becomes the same voltage as the optimum surface potential Vo_opt of the photoconductor 1 in the drawing process. Development is possible from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential, and the image forming process starts. In the image forming process, the control means 10 controls the transfer power supply 37 to set the transfer voltage to +2 μA and transfers the paper 34.

A method of determining the applied voltage Vin_opt at the time of drawing will be described with reference to FIG. FIG. 7 is a flow chart showing the operation of the control means 10. The optimum applied voltage is determined by the following procedure. (a) After the photosensitive member starts rotating, Vin1 is applied to the charging roller 2 before the image forming process. (b) Corresponding to the applied voltage Vin1, from the power source 4 to the charging roller 2
The current Ir1 flowing through the device is measured by the current measuring means 11, and the measured current value is inputted and stored in the control means 10. (c) The power supply 4 is controlled to set the voltage applied to the charging roller 2 to Vin2. (d) Corresponding to the applied voltage Vin2, from the power source 4 to the charging roller 2
The current Ir2 flowing in the current is measured by the current measuring means 11, and the measured current value is inputted and stored in the control means 10.

(E) The sum k + Rr of the charging coefficient k of the photoconductor 1 and the charging resistance Rr is estimated from (Equation 11) from the input measured current. k + Rr = | Vin1−Vin2 | / | Ir1−Ir2 | (11) (f) The optimum absolute value Ir_opt of the charging current is calculated from the previously obtained charging resistance Rr and the target potential Vo_opt of the photoconductor 1. Calculate with (Equation 12). Ir_opt = | Vo_opt | / k = | Vo_opt | / {| Vin1-Vin2 | / | Ir1-Ir2 | -Rr} (12) (g) The absolute value Vin_opt of the optimum applied voltage at the time of printing is Vin_opt = ( k + Rr) × | Ir_opt−Ir1 | + | Vin1 | (13) or Vin_opt = (k + Rr) × | Ir_opt−Ir2 | + | Vin2 | (14).

Based on the above procedure, the applied voltage Vin1 = -9
The measured values at 00V and Vin2 = -1100V are shown. A new photoconductor (photoconductor film thickness 26μm) while turning off the static elimination light 3
When the current value flowing when charging is measured, Ir1 = 2.6 μA for Vin1 and Ir2 = for Vin2, respectively.
It was 4.4 μA. Assuming that the unit of potential is V and the unit of current is μA, k + Rr was 111.1 (V / μA) from (Equation 11). On the other hand, the pre-measured charging resistance Rr was 9.1 MΩ, and therefore the value of the charging coefficient k was k = 102.1 (V / μA).

When the target potential at the time of image formation of the photoconductor 1 was -450 V, the optimum current value was 4.4 μA from (Equation 12), and the absolute value of the optimum applied voltage was 1101 V from (Equation 13). Since the output voltage of the power supply 4 is in 5V steps, the absolute value is closest to 1101V and the polarity is the same as the optimum surface potential Vo_opt of the photoconductor 1 in the image forming process, ie, -1100V is actually applied to the charging roller 2 for verification. It was As a result, the surface potential of the photoconductor 1 was -440V, which was close to the target value.

Next, after running 100,000 sheets, the film thickness is 18μ.
The measured values when the photosensitive member having m is charged with the applied voltage Vin1 = -900V and Vin2 = -1100V are shown. When the values of the currents that flow when charging the static elimination light 3 while lighting it are measured, they are Ir1 = 4.4 μA and Ir2 = 6.9 μA, respectively. Assuming that the charging coefficient at a film thickness of 18 μm is k ′, k ′
+ Rr became 80.0 (V / μA) from (Equation 11). Charging resistance R
Since r was 9.1 MΩ, the charging coefficient k ′ was 71.0 (V / μA).

Assuming that the target potential of the photosensitive member 1 is −450V,
The optimum current value for the charging roller 2 is 6.3μ from (Equation 12).
A, and the optimum absolute value of the applied voltage to the charging roller 2 was 1055V. When a voltage of -1055V, which is the same as the optimum surface potential of the photoconductor in the image forming process, is applied to the charging roller 2, the surface potential of the photoconductor is -438V, which is close to the target potential. As described above, according to this example, the surface potential of the photoconductor could be set to the target value without being affected by the change in the film thickness of the photoconductor.

(Comparative Example 1) As a comparison, the case where the charging resistance Rr was not taken into consideration in the first example was tried. In this case, Rr =
It is regarded as 0, and k + Rr in (Equation 11) is set as k. In the case of a new photoconductor (photoconductor film thickness 26 μm), assuming that the unit of potential is V and the unit of current is μA, from the assumption of Rr = 0,
(k + Rr) = k = 111.1 (V / μA). Applied voltage Vi
Substituting n1 = −900V and charging current Ir1 = 2.6 μA into (Equation 4), the absolute value of the optimum applied voltage with respect to the target potential −450V was calculated as Vin_opt ″ = 1061V. Photosensitive member 1 when applied to charging roller 2
Has a surface potential of -403V, which is 47V away from the target value of -450V.

Next, in the case of charging the photoconductor in which the film thickness of the photoconductor became 18 μm after running 100,000 sheets, k = 80.0,
Substituting Vin1 = -900V and Ir1 = 4.4 μA into (Equation 4),
The optimum absolute value of the applied voltage for the target potential of -450V is
Vin_opt "= 996V. However, actually, -996V
Is applied to the charging roller 2, the surface potential of the photoconductor 1 is -387V, which is 63V from the target value of -450V. In any case, the amount of deviation from the target potential was large and it was not possible to put it into practical use.

(Second Embodiment) If the film thickness of the photoconductor does not decrease, the current value may be measured once. Here, the case where the film thickness of the photoconductor does not decrease means that the photoconductor film having high hardness is used, or the surface of the photoconductor is coated with high hardness, or the life of the photoconductor is short and the film thickness of the photoconductor is short. This is the case, for example, when it is determined in the specifications that the photoconductor should be replaced before the reduction occurs.

Since the photosensitive member at the time of non-exposure can be regarded as a dielectric member, when the photosensitive member having a surface potential of 0 V is charged to Vo, as shown in FIG.
As shown in, the current Ir flowing in the photoconductor is proportional to the charging potential Vo. FIG. 4 is a diagram showing the charging characteristics of the photoconductor, where the horizontal axis is the absolute value of the current flowing into the photoconductor and the vertical axis is the charging potential of the photoconductor. The slope k of the straight line is a proportional coefficient between the current Ir and the charging potential Vo. Hereinafter, the proportional coefficient k will be referred to as a charging coefficient. When the photoconductor having an initial surface potential of 0 V is charged, the charging current I
When r is multiplied by k, the electric potential becomes Vo. An experiment for obtaining the charging coefficient k will be described with reference to FIG.

FIG. 5 shows a charging tester, which is used to measure the charging coefficient k of the photoconductor 1 in this embodiment. Reference numeral 1 is a photoconductor, 2 is a charging roller, 3 is static elimination light, 4 is a constant voltage power source, 11 is current measuring means, 41 is a surface potential measuring probe, and 42 is a surface electrometer. The surface potential meter 42 displays the potential of the surface of the photoconductor 1 measured by the surface potential measuring probe 41.

Assuming that the charging start voltage between the charging roller 2 and the photosensitive member 1 is Vth, the power source 4 charges the same voltage Vt3 as the optimum surface potential of the photosensitive member 1 in absolute value Vth or more and polarity in the image forming process. It is applied to the roller 2. At this time, the current flowing from the power source 4 to the charging roller 2 is measured by the current measuring means 11. The coefficient k of the photoconductor 1 is obtained by the following procedure.

(A) The charge removal light 3 is turned on while rotating the photoconductor 1 at the peripheral speed vp in the direction of the arrow, and the surface potential of the photoconductor 1 before charging is set to 0V. After that, with the neutralization light 3 turned on, a voltage Vt3 that is equal to or higher than the charging start voltage Vth is applied to the charging roller 2, and at least after the photoconductor 1 has rotated three or more times,
The current Ir_t3 flowing through the charging roller 2 and the surface potential Vo_t3 of the photoconductor 1 are measured.

(B) The charging coefficient k of the photoconductor 1 is obtained by (Equation 15). k = | Vo_t3 / Ir_t3 | ………………………………………… (15) However, | | is an absolute value symbol. In actual measurement, charging was performed when Vt3 = −1100V was applied to the charging roller 2. The current Ir_t1 was 4.4 μA, and the surface potential Vo_t3 of the photoconductor 1 at this time was −436 V. Therefore, the charging coefficient k of the photoconductor 1 was found to be k = 99.1 (V / μA).

Further, as in the first embodiment, in this embodiment, the charging resistance Rr is measured in advance before the potential control during image formation. Since the measuring method is the same as that of the first embodiment, it is omitted here. Since the same charging roller as in the first embodiment is used, the charging resistance Rr is 9.1 MΩ as in the first embodiment.

In this embodiment, k obtained as described above
And Rr, the applied voltage to the charging member is determined by the following procedure. The configuration of the image forming apparatus of the present embodiment is the first
Similar to the embodiment described in (1), the structure shown in FIG. 1 can be used. The difference from the first embodiment is the operation of the control means 10.

The operation of the control means 10 will be described with reference to FIG. FIG. 8 is a timing chart showing the measurement of the charging current performed prior to the drawing process. Time elapses in the direction of the horizontal axis arrow. Further, rotation of the photoconductor from above, voltage Vin applied to the charging roller 2, turning on or off of the static elimination light 3, absolute value Ir of the charging current flowing through the charging roller 2, transfer power source 37 is the transfer roller. The current applied to 32 and the surface potential Vo of the photoconductor 1 at the developing position by the developing device 31 are shown. Since it is complicated to display it as it is, Fig. 8
The surface potential Vo of the photosensitive member is shown by advancing by the time Trd required for one point on the moving photosensitive member 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. Further, the time required for the charging roller 2 to make one rotation is Tr, and the time required for the photosensitive member 1 to make one rotation is Tp. Time Tr,
Tp is obtained in advance from the diameter of the charging roller 2, the diameter of the photoconductor 1 and the peripheral speed vp.

In FIG. 8, the photosensitive member 1 is placed prior to the drawing process.
Before the start of rotation, the transfer power supply 37 is set in a floating state, and the transfer roller 32 does not charge the photoconductor 1.
The voltage Vin1 is applied to the charging roller 2 at time T1 after a time sufficient for the rotation of the photosensitive member 1 to sufficiently stabilize. Of the current flowing at this time, time T1 when Vin1 is applied
From the time until the charging roller 2 makes one revolution (time T1 + Tr)
Since the current value is unstable, it is ignored, and the current value Ir1 after the charging roller 2 rotates for one rotation or more is measured.

The control means 10 determines the optimum absolute value Vin_opt of the applied voltage at the time of image formation from the measured value Ir1 and the previously measured charging resistance Rr. Next, the power supply 4 is controlled so that the absolute value is closest to Vin_opt and the polarity is the same voltage as the optimum surface potential of the photoconductor 1 in the image forming process. The image forming process starts from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential. In the image forming process, the control means 10 controls the transfer power supply 37 to set the transfer voltage to +2 μA and transfers the paper 34.

A method of determining the applied voltage Vin_opt at the time of drawing will be described with reference to FIG. FIG. 9 is a flow chart showing the operation of the control means 10. The applied voltage at the time of drawing is determined by the following procedure. (a) After the photoconductor rotates, the power source 4 is controlled and Vin1 is applied to the charging roller 2 before the image forming process. (b) From the power supply 4 to the charging roller 2 corresponding to the applied voltage Vin1
The current Ir1 flowing through the device is measured by the current measuring means 11, and the measured current value is input to the control means 10.

(C) From the applied voltage Vin1, the input measured current Ir1 and the previously measured charging coefficient k of the photosensitive member 1, the absolute value Ir_opt of the optimum current for setting the photosensitive member 1 at the target potential Vo_opt is calculated by the formula (16). ). Ir_opt = | Vo_opt | / k …………………………………… (16) (d) The optimum absolute value Vin_opt of the applied voltage obtained from the charging resistance Rr is Vin_opt = (k + Rr) X (Ir_opt-Ir1) + | Vin1 | ... (17)

Based on the above procedure, the current value flowing when charging a new photoconductor (photoconductor film thickness 26 μm) with an applied voltage Vin1 = −900 V while turning on the static elimination light 3 is Ir1 = It was 2.6 μA. On the other hand, the previously obtained charging resistance was Rr = 9.1 MΩ, and the charging coefficient was k = 99.1 (V / μA). When the target potential at the time of image formation of the photoconductor 1 is -450V, the optimum current value Ir_opt is 4.5 μA from (Equation 16), and the absolute value Vin_opt of the optimum applied voltage is 1106V from (Equation 17).

Since the output voltage of the power supply 4 is in 5V steps,
When a voltage of −1105 V, whose absolute value is closest to 1106 V and whose polarity is the same as the photoconductivity of the photoconductor, is actually applied to the charging roller 2, the surface potential of the photoconductor 1 becomes −445 V, which is close to the target value. As described above, according to this embodiment, the surface potential of the photoconductor can be set to the target value.

(Comparative Example 2) As a comparison, a case where the charging resistance Rr is not taken into consideration in the second embodiment will be tried. When charging a new photoconductor (film thickness of the photoconductor 26 μm), the applied voltage Vin1 = −900 V, the charging current Ir1 = 2.6 μA, and the optimum absolute value of the applied voltage with respect to the photoconductor target potential −450 V are calculated from (Equation 4). Vin_opt ″
= 1092V. However, when Vin = −1092V is actually applied to the charging roller 2, the surface potential of the optical body 1 is −430V.
Became. The value after being shifted by 20 V from the target value was inferior to the present invention in accuracy after control.

(Third Embodiment) If the resistance value of the charging member changes due to the atmospheric environment or changes with time, it cannot be assumed that the charging resistance Rr is constant. Therefore, the charging resistance R during drawing
It is necessary to find r sequentially. In fact, in the case of a urethane charging roller having a high hygroscopic property, the resistance value tends to remarkably decrease in a high humidity environment.

Hereinafter, a charging device according to a third embodiment of the present invention will be described with reference to the drawings. The charging roller shown in FIG. 2 is used as the charging member, and the photosensitive member having the structure shown in FIG. 3 is used. FIG. 10 shows a schematic configuration of an image forming apparatus according to the third embodiment of the present invention. FIG.
Those having the same name as are given the same reference numerals. The image forming apparatus of this embodiment is also an electrophotographic type in which an image is formed on a photoconductor and then transferred to paper.

In FIG. 10, reference numeral 1 denotes a photoconductor, which is rotated at a peripheral speed vp = 33 mm / sec in the arrow direction by a drive motor (not shown). Reference numeral 2 denotes a charging roller as a charging member which is brought into contact with the photoconductor, and is rotated by a frictional force with the photoconductor 1. Reference numeral 35 denotes a laser light source as an image writing means. The emitted laser light is reflected by the mirror 36 and then is irradiated on the surface of the photoconductor 1 to form a latent image on the photoconductor 1. 31 is a developing device, which is a photoconductor 1.
The upper latent image is visualized with toner. Reference numeral 32 denotes a transfer roller as a transfer unit, and 37 denotes a transfer power source, which has a function of selecting whether +2 μA is applied to the transfer roller 32 or an electric float state is selected. The transfer roller 32 transfers the toner on the photoconductor 1 onto the paper 34, but at the time of transfer +
2 μA is applied from the transfer power source 37 to the transfer roller 32. 33
Is a scraping blade that scrapes off the toner remaining on the photoconductor 1. 3 is static elimination light as static elimination means, 5
Has a function of controlling the turning on and off of the static elimination light 3 in response to a command from the control means 10 by the static elimination power source of the static elimination light 3. The static elimination light 3 irradiates the photoconductor 1 at the time of lighting, and sets the surface potential to 0V.

A power source 4 selectively applies two or more kinds of DC voltages having different values to the charging roller 2. In this embodiment, there is a function of selectively applying two kinds of direct current voltage of Vin1 = -900V and Vin2 = -1100V to the charging roller 2 in accordance with a command from the control means 10, and further from -800V to -1 at the time of image formation.
A voltage in the range of 300 V is selected in 5 V steps and applied to the charging roller 2.

A current measuring means 11 measures the current flowing from the power source 4 to the charging roller 2. The control means 10 has a function of inputting the current value measured by the current measuring means 11, a function of storing the input value, a function of performing an arithmetic operation on the input and the stored value, a power source 4, a static elimination power source 5, and a transfer. Power 37
It has a function to control.

The operation of the control means 10 will be described with reference to FIG. FIG. 11 is a timing chart showing the operation of the control means, and time elapses in the direction of the arrow on the horizontal axis. Further, rotation of the photoconductor from above, voltage Vin applied to the charging roller 2, turning on or off the static elimination light 3, absolute value Ir of charging current flowing through the charging roller 2, transfer power source 37.
Indicates the electric current applied to the transfer roller 32 and the surface potential Vo of the photoconductor 1 at the developing position by the developing device 31, respectively.
Since it is complicated to display it as it is, the photosensitive member surface potential Vo in FIG. 11 is advanced by the time Trd required for one point on the moving photosensitive member 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. Indicated. Further, the time required for the charging roller 2 to make one rotation is Tr, and the time required for the photosensitive member 1 to make one rotation is Tp. The times Tr and Tp are obtained in advance from the diameter of the charging roller 2, the diameter of the photoconductor 1 and the peripheral speed vp.

In FIG. 11, the photoconductor 1 is placed prior to the drawing process.
Before the start of rotation, the transfer power supply 37 is set in a floating state, and the transfer roller 32 does not charge the photoconductor 1.
The voltage Vin1 is applied to the charging roller 2 at time T1 after a time sufficient for the rotation of the photosensitive member 1 to sufficiently stabilize. V
Since the current value is unstable from the time T1 when in1 is applied until the charging roller 2 makes one revolution (time T1 + Tr), it is ignored.
The current value Ir1 after the charging roller 2 makes one revolution or more is measured. This is the first measurement.

After measuring Ir1, the applied voltage of the power source 4 is set to Vin.
Change to 2. Immediately after Vin2 is applied and until the charging roller 2 completes one revolution (time Tr), the current flowing through the charging roller 2 is unstable and is ignored, and the current value Ir2 after the charging roller 2 has completed one revolution is measured. To do. This is the second measurement.

Next, the measurement end time of Ir2 is set to T2, and the time required for one point on the moving photosensitive member 1 to move from the area where the static elimination light 3 acts to the charging area of the charging roller 2 is set to Tjr. Then, the static elimination light 3 is turned off after the time (T2-Tjr).

In this embodiment, after the Ir2 measurement, the voltage applied to the power source 4 remains Vin2, and the static elimination light 3 is turned off. After the static elimination light 3 is turned off, the time at which the boundary between the surface of the photoconductor on which the charge is removed and the surface of the photoconductor on which the static electricity has not been discharged contacts the charging member
Set to 3. The time T3 is obtained in advance from the positional relationship between the peripheral speed vp of the photoconductor 1, the static elimination light 3 and the charging roller 2. Current Ir3 flowing through the charging member from time T3 to (T3 + Tp)
To measure.

The control means 10 controls the measured values Ir1, Ir2 and I
The charging resistance Rr is obtained from r3, and the optimum absolute value Vin_opt of the applied voltage at the time of drawing is determined. Next, the power supply 4 is controlled so that the absolute value is closest to Vin_opt and the polarity is the same voltage as the optimum surface potential of the photoconductor 1 in the image forming process. The image forming process starts from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential. Entering the drawing process, control means 10
Controls the transfer power supply 37 to set the transfer voltage to +2 μA, and the paper 34
Transfer to.

A method of determining the applied voltage Vin_opt at the time of drawing is shown.
Explain in 12. FIG. 12 is a flowchart showing the operation procedure of the control means 10, and the following operation is performed. (a) After the photoconductor 1 starts rotating, the power source 4 is controlled and Vin1 is applied to the charging roller 2 before the image forming process. Further, the static elimination light 3 is turned on. (b) From the power supply 4 to the charging roller 2 corresponding to the applied voltage Vin1
The current Ir1 flowing through the device is measured by the current measuring means 11, and the measured current value is inputted and stored in the control means 10. (c) The voltage applied to the charging roller 2 is controlled to V by controlling the power supply 4.
set to in2.

(D) The current measuring means 11 measures the current Ir2 flowing from the power source 4 to the charging roller 2 in response to the applied voltage Vin2, and the measured current value is inputted and stored in the control means 10. (e) The charge removal light 3 is turned off while the applied voltage is Vin2. (f) The current measuring means 11 measures the current Ir3 flowing through the charging member from the time T3 to the time T3 + Tp, and the control means
10 enter and remember. (g) The charging resistance Rr is obtained by the following procedure.

First, a method of deriving the charging resistance Rr will be described with reference to FIG. FIG. 5 shows a charging tester, which was used in this embodiment to guide the method of deriving the charging resistance Rr. First, the photoconductor 1 is rotated at the peripheral speed vp. The static elimination light 3 is lit while the voltage is not applied to the charging roller 2,
The surface potential of all one round is set to 0V. Next, neutralization light 3
Turn off. A voltage Vin whose absolute value is equal to or higher than the charging start voltage Vth of the charging roller 2 and the photosensitive member 1 and whose polarity is the same as the polarity of the optimum surface potential of the photosensitive member 1 in the image forming process is applied to the charging roller 2. The absolute value of the surface potential of the photoconductor 1 increases stepwise for each rotation of the photoconductor 1 from the start of charging, and asymptotically approaches the saturation potential | Vin | -Vth value. The surface potential of the photoconductor 1 is measured by the surface potential measuring probe 41.

The time on the photosensitive member between the charging roller 2 and the surface potential measuring probe 41 divided by the peripheral speed vp of the photosensitive member 1 is Trp, and the time required for the photosensitive member 1 to make one rotation is Trp.
Let p. Time when the time Trp has elapsed from the charging start time Tst
At (Tst + Trp), the surface potential measuring probe 41 starts measuring the surface potential of the photoconductor 1 after charging.

Measurement voltage Vo (1), V of the surface potential probe 41
o (2) and Vo (3) are defined as follows. Time (Tst
+ Trp) to time (Tst + Trp + Tp), that is, the absolute value of the surface potential of the photoconductor 1 from the start of charging until the photoconductor 1 completes one turn is Vo (1), and from time (Tst + Trp + Tp) to time (Tst + Trp + 2.Tp). ), That is, between the start of charging and the rotation of the photosensitive member 1 for one rotation or more and less than two rotations.
The absolute value of the surface potential of is Vo (2), which is generally the time (Tst + Tr
From (p + n · Tp) to time (Tst + Trp + (n + 1) · Tp), that is, the photoconductor 1 is n or more turns (n + 1) from the start of charging.
Let Vo (n) be the absolute value of the surface potential of the photosensitive member 1 until it rotates less than one turn.

The current Ir measured by the current measuring means 11 is
(1), Ir (2) and Ir (n) are defined as follows.
From the time Tst to the time (Tst + Tp), that is, from the start of charging until the photoconductor 1 makes one revolution, the absolute value of the current flowing through the charging roller 2 is Ir (1), and from the time (Tst + Tp) to the time (T
st + 2 · Tp), that is, the absolute value of the current flowing through the charging roller 2 during the rotation of the photosensitive member 1 from one rotation to less than two rotations is Ir (2), which is generally the time (Tst + n · Tp). )
From time (Tst + (n + 1) · Tp) to the time when the photoconductor 1 rotates more than n rotations and less than (n + 1) rotations from the start of charging, the absolute value of the current flowing through the charging roller 2 is Ir (n). To do. Further, when the charging coefficient of the photoconductor 1 is k, the charging start voltage between the charging roller 2 and the photoconductor 1 is Vth, and || is an absolute value symbol, the following three equations hold.

Vo (n) = | Vin | −Vth−Rr × Ir (n) (18) Vo (n) -Vo (n-1) = k × Ir (n) …………………………………… (19) Vo (0) = 0 ……………………………………………… (20) These are Ir (n) Solving for

[0159]

[Outside 1]

Solving for Rr, Rr = (│Vin│-Vth) × Ir (2) / (Ir (1)) ² ............ (22) (Equation 22) It is the charging resistance Rr required by the tester.

This is applied to the image forming apparatus of this embodiment. The current Ir (1) matches the charging current Ir2, and the current Ir (1)
(2) matches the charging current Ir3. Also, the applied voltage Vin
Was Vin2. Therefore, the charging resistance Rr in the image forming apparatus is obtained by (Equation 23). Rr = (| Vin2 | −Vth) × Ir3 / (Ir2) ² (23) where the charging start voltage Vth is (Equation 24) Vth = | Ir1 × Vin2-Ir2 × Vin1 | / | Ir1-Ir2 | ... Use the value obtained by (24).

(H) From the input measured currents Ir1 and Ir2,
The sum of the charging coefficient k of the photoconductor 1 and the charging resistance Rr is estimated by (Equation 25). k + Rr = | Vin1−Vin2 | / | Ir1−Ir2 | (25) The optimum charging current Ir_opt is calculated from the charging resistance Rr obtained in (g) above and the target potential Vo_opt of the photoconductor 1 (equation See step 26). Ir_opt = Vo_opt / k = Vo_opt / {| Vin1-Vin2 | / | Ir1-Ir2 | -Rr} (26) (i) The absolute value Vin_opt of the optimum applied voltage to the charging roller 2 at the time of image formation is Vin_opt = (K + Rr) * (Ir_opt-Ir1) + | Vin1 | ... (27) or Vin_opt = (k + Rr) * (Ir_opt-Ir2) + | Vin2 | ... (28)

Based on the above procedure, a new photoconductor (thickness 26 μm on the surface) was installed in the charging tester shown in FIG. 5, left at room temperature of 20 ° C. and humidity of 50% for 3 days, and then the applied voltage was changed. When charging with the static elimination light 3 turned on at Vin1 = -900V and Vin2 = -1100V, the flowing current value is Ir1.
= 2.6 μA and Ir2 = 4.4 μA. If the potential unit is V and the current unit is μA from (Equation 25), the value of k + Rr is 111.
Vth = 611V was obtained from 1 (V / μA) and (Equation 24).

Next, with the applied voltage Vin2 = -1100V, the static elimination light 3 is turned off, and Ir calculated by the procedure (f) above is obtained.
The value of 3 was 0.4 μA. From (Equation 23), the charging resistance Rr is
It was determined that Rr = 10.1 MΩ. Therefore, the charging coefficient k of the photoconductor 1 was 101.0 (V / μA). Set the target potential of the photoconductor to -45.
Assuming 0 V, the optimum charging current Ir_opt is 4.5 μA from (Equation 26).
Met. From (Equation 27), the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor to −450V was calculated to be 1111V.

For verification, when a voltage of -1110V having the same polarity as that of the photoconductor 1 exhibiting photoconductivity is applied to the charging roller 2 by the 5V step power source 4, the photoconductor 1 has the same absolute value. Has a surface potential of -447V, which is close to the target potential.

Next, after running 100,000 sheets, the photoconductor in which the thickness of the photoconductor became 18 μm was incorporated into the charging tester shown in FIG. 5, and left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%. After that, when the values of the currents flowing when the charge removal light 3 was charged with the applied voltage Vin1 = -900V and Vin2 = -1100V were actually measured, they were Ir1 = 4.4 μA and Ir2 = 6.9 μA, respectively. If the potential unit is V and the current unit is μA from (Equation 25), the value of k + Rr is 80.0 (V / μA), and from (Equation 24), Vth =
It was requested to be 548V.

Next, with the applied voltage Vin2 = -1100V, the static elimination light 3 is turned off, and Ir obtained by the procedure of the above (f) is determined.
The value of 3 was 0.8 μA. From (Equation 23), the charging resistance Rr is R
It was determined that r = 9.3 MΩ. Therefore, the charging coefficient k of the photoconductor 1 is
It was 70.7 (V / μA). When the target potential of the photoconductor is -450 V, the optimum charging current Ir_opt was 6.4 μA from (Equation 26). From (Equation 27), the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor to −450V was calculated to be 1058V.

For verification, the power supply 4 with 5V step
When a voltage of -1060V, which is the closest in absolute value to _opt and has the same polarity as the photoconductor exhibits photoconductivity, is applied to the charging roller 2, the surface potential of the photoconductor 1 becomes -442V, which is a value close to the target potential. .

Further, a new photoconductor (surface film thickness: 26 μm)
Built in the electrification tester shown in Fig. 5, room temperature 33 ℃, humidity 80
Applied voltage Vin1 = -900 after left for 3 days in the environment of
When the current values that flow when charging is performed while the static elimination light 3 is turned on at V and Vin2 = −1100 V, the respective values are Ir1 =
It was 2.8 μA and Ir2 = 4.8 μA. From (Equation 25), if the unit of potential is V and the unit of current is μA, the value of k + Rr is 100.0.
(V / μA), Vth = 620V was obtained from (Equation 24).

Next, with the applied voltage Vin2 = -1100V, the static elimination light 3 is turned off, and Ir calculated by the procedure of (f) above is obtained.
The value of 3 was 0.1 μA. From (Equation 23), the charging resistance Rr is
Rr = 2.1 MΩ is required. Therefore, the charging coefficient k of the photoconductor 1 was 97.9 (V / μA). The target potential of the photoconductor is -450
Assuming V, the optimum charging current Ir_opt is 4.6 μA from (Equation 26).
Met. From (Equation 27), the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor to −450V was obtained as 1080V.

For verification, when −1080V whose absolute value is closest to Vin_opt is applied to the charging roller 2 by the 5V step power source 4, the surface potential of the photosensitive member 1 becomes −451V, which is a value close to the target potential. As described above, according to this embodiment, the surface potential of the photoconductor can be set to the target value without being affected by the change in the surface film thickness of the photoconductor and the change in the resistance value of the charging member.

Comparative Example 3 In the third example, the charging resistance Rr
I tried not to consider. In this case, since it is assumed that Rr = 0, (k + Rr) is erroneously adopted instead of k in (Equation 4). Here, k ″ = (k + Rr) is set.

A new photoconductor (film thickness of 26 μm on the surface) is kept at room temperature for 20 minutes.
When left in an environment of 50 ° C and 50% humidity for 3 days, k ″ = 111.
1, applied voltage Vin1 = -900V, charging current Ir1 = 2.6μA
Substituting into (Equation 4), the absolute value of the optimum applied voltage Vin_opt ″
= 1061V. However, when −1061V was actually applied to the charging roller 2, the surface potential of the photoconductor 1 became −404V. It could not be put to practical use because there was a deviation of 46V from the target value.

Next, when the photoreceptor having a thickness of 18 μm after running 100,000 sheets was left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%, k ″ = 90.0, applied voltage Vin1 =
Substituting −900 V and charging current Ir1 = 4.4 μA into (Equation 4), the absolute value of the optimum applied voltage was Vin_opt ″ = 998 V. However, when −998 V was actually applied to the charging roller 2, the surface of the photoconductor 1 was changed. The potential was -387 V. Target value and 6
It could not be put to practical use because there was a deviation of 3V.

Furthermore, a new photoconductor (surface film thickness: 26 μm)
When left in an environment of room temperature 33 ° C and humidity 80% for 3 days,
k ″ = 100.0, applied voltage Vin1 = −900V, charging current Ir1
When substituting 2.8 μA into (Equation 4), the absolute value of the optimum applied voltage was Vin_opt ″ = 1070 V. However, actually −1070 V
Is applied to the charging roller 2, the surface potential of the photoconductor 1 becomes −
It became 440V. The error from the target value was larger than that in the third example.

(Fourth Embodiment) When the film thickness of the photoconductor does not decrease, the current value is measured twice. When the film thickness of the photoconductor does not decrease, when using a photoconductor film with high hardness, or when applying a coating with high hardness to the surface of the photoconductor,
Alternatively, there is a case where the photoreceptor has a short life and it is specified in the specifications that the photoreceptor should be replaced before the film thickness is reduced.

In this embodiment, the charge coefficient k of the photoconductor 1 is obtained in advance. Since the method of obtaining the charging coefficient k is the same as that of the second embodiment, it will be omitted. In the actual measurement, the charge coefficient k of the photoconductor 1 was k = 99.1 (V / μA), as in the second embodiment.

The structure of the image forming apparatus of the fourth embodiment is the same as that of the third embodiment as shown in FIG. The difference from the third embodiment is the operation of the control means 10. The operation of the control means 10 will be described with reference to FIG. FIG. 13 is a timing chart showing the measurement of the current value performed prior to the drawing process. Time elapses in the direction of the horizontal axis arrow.

In FIG. 13, the rotation of the photosensitive member 1, the applied voltage Vin to the charging roller 2, the static elimination light 3 turned on (on) or off (off), the absolute value Ir of the charging current flowing through the charging roller 2, The current applied to the transfer roller 32 by the transfer power source 37 and the surface potential Vo of the photoconductor 1 at the developing position by the developing device 31 are shown. Since it is complicated to display it as it is, Fig. 13
The surface potential Vo of the photosensitive member is shown by advancing by the time Trd required for one point on the moving photosensitive member 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. Also, the time required for the charging roller 2 to make one rotation is Tr,
Let Tp be the time required for one revolution of the. Time Tr, T
p is obtained in advance from the diameter of the charging roller 2, the diameter of the photoconductor 1 and the peripheral speed vp.

In FIG. 13, prior to the image forming process, the photoconductor 1
The transfer power source 37 is set in a floating state before the rotation starts, and the transfer roller 32 does not charge the photoconductor 1.
The voltage Vin1 is applied to the charging roller 2 at time T2 after a lapse of a time period in which the rotation of the photoconductor 1 is sufficiently stabilized. Vin
From the time T1 when 1 is applied until the charging roller 2 makes one revolution (time T1 + Tr), the current value is unstable and is ignored. After applying Vin1, the current Ir1 is measured after the charging roller 2 makes one revolution or more. This is the first measurement.

Next, the measurement end time of Ir2 is set to T2, and the time required for one point on the moving photosensitive member 1 to move from the action area of the static elimination light 3 to the charging area of the charging roller 2 is set to Tjr. Then, the static elimination light 3 is turned off after the time (T2-Tjr).

In the present embodiment, before the end of Ir1 measurement and at the time
After (T2-Tjr), the applied voltage of the power source 4 remains Vin1 and the static elimination light 3 is turned off. It is assumed that the time when the boundary between the surface of the photoconductor on which the charge has been removed and the surface of the photoconductor on which the charge has not been removed contacts the charging member after the charge-eliminating light 3 is turned off is T3. Time T3 is
It is obtained in advance from the peripheral speed vp of the photoconductor 1 and the positional relationship between the charge eliminating light 3 and the charging roller 2.

A current Ir3 flowing through the charging member is measured from time T3 to (T3 + Tp). This is the second measurement.

The control means 10 obtains the charging resistance Rr from these measured values Ir1 and Ir3 and determines the optimum absolute value Vin_opt of the applied voltage at the time of image formation. Next, the absolute value is Vin_opt
The power source 4 is controlled so that the polarity is the closest to the above, and the polarity becomes the same voltage as the optimum surface potential of the photoconductor 1 in the drawing process. The image forming process starts from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential. Enter the drawing process, control means
10 controls the transfer power supply 37 to set the transfer voltage to +2 μA, and the paper 3
Transfer to 4.

A method of determining the applied voltage Vin_opt at the time of drawing is shown.
Explain in 14. FIG. 14 is a flowchart showing the operation procedure of the control means 10, and the following operation is performed. (a) After the photoconductor starts rotating, the power source 4 is controlled and Vin1 is applied to the charging roller 2 before the image forming process. (b) The current Ir1 flowing from the power supply 4 to the charging roller 2 with respect to the applied voltage Vin1 is measured by the current measuring means 11, and the measured current value is input and stored by the control means 10.

(C) The static elimination light 3 is turned off while the applied voltage is Vin1. (d) From time T3 to (T3 + Tp), the current measuring means 11 measures the current Ir3 flowing through the charging member, and the control means 10
Is input and memorized.

(E) The charging resistance Rr is obtained by the following procedure as in the third embodiment. The following two relationships hold for Rr and Vth. Rr = (| Vin1 | −Vth) × Ir3 / (Ir1) ² (29) Here, the charging start voltage Vth is the value obtained by (Equation 30). Vth = | Vin1 | − (k + Rr) × Ir1 (30) Solving these two simultaneous equations for Rr and Vth,
The charging resistance Rr is calculated.

(F) Charge coefficient k of the photoconductor 1 given in advance
Then, the optimum charging current Ir_opt is obtained from (Equation 31) from the target potential Vo_opt at the time of drawing the image of the photoconductor 1. Ir_opt = Vo_opt / k ………………………………………… (31) (g) Absolute value is closest to Vin_opt in (Equation 32) and voltage polarity of the photoconductor 1 in the drawing process. Vin_opt = (k + Rr) × (Ir_opt−Ir1) + | Vin1 | ... (32) The power supply 4 is controlled so that the applied voltage has the same polarity as the polarity of the optimum surface potential.

Based on the above procedure, a new photoconductor (surface film thickness: 26 μm) was installed in the charging tester shown in FIG. 5 and left for 3 days at room temperature of 20 ° C. and humidity of 50%. Applied voltage V
The current value flowing when charging was performed while turning on the static elimination light 3 at in1 = −1100 V was Ir1 = 4.4 μA. Next, turn off the static eliminator 3 while the applied voltage remains -1100V, and follow the procedure above.
The value of Ir3 obtained in (d) was 0.4 μA.

Simultaneous equations of (Equation 29) and (Equation 30) and the previously determined charge coefficient k of the photosensitive member 1 = 99.1 (V / μA)
When the charging resistance Rr and the charging start voltage Vth are obtained from Rr =
It was 10.1 MΩ and Vth = 630V. Assuming that the target potential of the photoconductor is −450 V, the optimum absolute value Ir_opt of the charging current was 4.5 μA from (Equation 31). From (Equation 32), the absolute value Vi of the optimum applied voltage for setting the potential of the photoconductor to −450 V
n_opt was determined to be 1111V.

For verification, when a voltage of -1110V having the same polarity as the photoconductivity of the photoconductor is applied to the charging roller 2 with the 5V step power source 4 having the closest absolute value to Vin_opt, the photoconductor 1
Has a surface potential of -447V, which is close to the target potential.

Further, a new photoconductor (film thickness of 26 μm on the surface) was installed in the charging tester shown in FIG. 5, and the room temperature was 33 ° C. and the humidity was 80%.
It was left for 3 days in the environment. Applied voltage Vin1 = -1100V
The value of the current that flows when the charging light 3 is charged while being turned on was Ir1 = 4.4 μA. Next, the applied voltage is -1100V
Then, the static elimination light 3 was turned off, and the value of Ir3 obtained in the above step (d) was 0.1 μA.

Simultaneous equations of (Equation 29) and (Equation 30) and the previously determined charge coefficient k of the photosensitive member 1 = 99.1 (V / μA)
When the charging resistance Rr and the charging start voltage Vth are obtained from Rr =
It was 2.3 MΩ and Vth = 654V. Set the target potential of the photoreceptor to −
If it is 450 V, the optimum absolute value Ir of the charging current is calculated from (Equation 31)
_opt was 4.5 μA. From (Equation 32), the potential of the photoconductor is
The absolute value Vin_opt of the optimum applied voltage for setting to 450V is 111
It was determined to be 0V.

For verification, when -1110V whose absolute value is closest to Vin_opt is applied to the charging roller 2 by the 5V step power source 4, the surface potential of the photoconductor 1 becomes -447V, which is a value close to the target potential. As described above, according to this embodiment, the surface potential of the photoconductor can be set to the target value without being affected by the change in the resistance value of the charging member.

(Comparative Example 4) In the fourth example, the surface potential of the photosensitive member after the control is different between the temperature and the humidity of the atmospheric environment unless the change in the resistance value of the charging roller as the charging member is taken into consideration. Caused an error of maximum (9.1 MΩ-2.3 MΩ) × 4.5 μA = 30V.

(Fifth Embodiment) The first to fourth embodiments are effective when there is no current leakage, but the material for holding the charging member or the coating material, or dew condensation in a high humidity atmosphere environment In some cases, the current flowing through the charging member may be leaked. In this case, the applied voltage is determined in consideration of the leak amount.

A charging device according to the fifth embodiment of the present invention will be described below with reference to the drawings. 2 was used as the charging member, and the photoconductor of FIG. 3 was used as the photoconductor. The image forming apparatus of this embodiment has substantially the same configuration as that of FIG. 10, but the operation of the control unit 10 is different.

FIG. 15 is a timing chart showing the measurement of the current value performed prior to the drawing process. Time elapses in the direction of the horizontal axis arrow. Further, from above, the rotation of the photosensitive member 1, the voltage Vin applied to the charging roller 2 and the lighting of the neutralization light 3 (o
n) or off, the absolute value Ir of the charging current flowing through the charging roller 2, the current applied by the transfer power source 37 to the transfer roller 32, the surface potential V of the photoconductor 1 at the developing position by the developing device 31.
o are shown respectively. Since it is complicated to display as it is, the photosensitive member surface potential Vo in FIG. 15 is advanced by the time Trd required for one point on the moving photosensitive member 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. Indicated.
In addition, the time required for the charging roller 2 to rotate once is T
Let r be the time required for the photoreceptor 1 to make one revolution.
The times Tr and Tp are obtained in advance from the diameter of the charging roller 2, the diameter of the photoconductor 1 and the peripheral speed vp.

In FIG. 15, the photoconductor 1 is placed prior to the drawing process.
Before the start of rotation, the transfer power supply 37 is set in a floating state, and the transfer roller 32 does not charge the photoconductor 1.
After allowing a sufficient time for the rotation of the photoconductor 1 to stabilize, time T
The voltage Vin1 is applied to the charging roller 2 at 1. From time T1 when Vin1 is applied to when the charging roller 2 makes one revolution (time T1 + Tr), the current value is unstable and is ignored. After applying Vin1, the current value Ir1 after the charging roller 2 makes one revolution or more is measured. This is the first measurement.

After measuring Ir1, the voltage applied to the charging roller 2 is changed to Vin2. The current flowing through the charging roller 2 from immediately after the application of Vin2 until the charging roller 2 completes one revolution (time Tr) is unstable and is ignored. After applying Vin2, the current value Ir2 after the charging roller 2 has rotated one round or more is measured. This is the second measurement.

Next, the measurement end time of Ir2 is set to T2, and the time required for one point on the moving photosensitive member 1 to move from the action area of the static elimination light 3 to the charging area of the charging roller 2 is Tjr. Then, the static elimination light 3 is turned off after the time (T2-Tjr). In the present embodiment, after the measurement of Ir2, the charge removal light 3 is turned off while the applied voltage of the power supply 4 remains at Vin2. It is assumed that the time when the boundary between the surface of the photoconductor on which the charge has been removed and the surface of the photoconductor on which the charge has not been removed contacts the charging member after the charge-eliminating light 3 is turned off is T3. At time T3, the peripheral speed vp of the photoconductor 1 and the static elimination light 3
And the positional relationship between the charging roller 2 and the charging roller 2. Time T
The current Ir3 flowing through the charging roller 2 is measured from 3 to (T3 + Tp). From time (T3 + Tp) to (T3 + 2 ・
The current Ir4 flowing through the charging roller 2 is measured up to Tp).

The charging resistance Rr is obtained from the measured values Ir1, Ir2, Ir3 and Ir4, and the optimum absolute value Vi of the applied voltage at the time of printing is Vi.
Determine n_opt. Next, the power supply 4 is controlled so that the absolute value is closest to Vin_opt and the polarity is the same voltage as the optimum surface potential of the photoconductor 1 in the image forming process. The image forming process starts from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential. In the image forming process, the control means 10 controls the transfer power supply 37 to set the transfer voltage to +2 μA and transfers the paper 34.

A method of determining the applied voltage Vin_opt at the time of drawing is illustrated.
Explain in 16. FIG. 16 is a flowchart showing the operation procedure of the control means 10, and the operation is performed in the following order. (a) After the photoconductor 1 starts rotating, the power source 4 is controlled and Vin1 is applied to the charging roller 2 before the image forming process. (b) The current Ir1 flowing from the power supply 4 to the charging roller 2 with respect to the applied voltage Vin1 is measured by the current measuring means 11, and the measured current value is input and stored by the control means 10. (c) The voltage applied to the charging roller 2 is controlled to V by controlling the power supply 4.
set to in2. (d) From the power supply 4 to the charging roller 2 corresponding to the applied voltage Vin2
The current Ir2 flowing in the current is measured by the current measuring means 11, and the measured current value is inputted and stored in the control means 10.

(E) The static elimination light 3 is turned off while the applied voltage is Vin2. (f) The current measuring means 11 measures the current Ir3 flowing through the charging member from the time T3 to (T3 + Tp), and the control means 10
Is input and memorized. (g) The current measuring means 11 measures the current Ir4 flowing through the charging member from the time (T3 + Tp) to (T3 + 2.Tp).
The control means 10 inputs and stores it.

(H) The charging resistance Rr is obtained by the following procedure. First, a method of deriving the charging resistance Rr will be described using the charging tester of FIG. The photoconductor 1 is rotated at the peripheral speed vp.
With the voltage applied to the charging member, the surface potential of the entire circumference of the photoconductor 1 is set to 0 V by the static elimination light 3. Next, the static elimination light 3 is turned off. A voltage Vin whose absolute value is equal to or higher than the charging start voltage Vth of the charging roller 2 and the photosensitive member 1 and whose polarity is the same as the polarity of the optimum surface potential of the photosensitive member 1 in the image forming process is applied to the charging roller 2. The absolute value of the surface potential of the photoconductor 1 increases stepwise for each rotation of the photoconductor 1 from the start of charging, and asymptotically approaches the saturation potential | Vin | -Vth. The surface potential of the photoconductor 1 is measured by the surface potential measuring probe 41.

Trp is the time obtained by dividing the distance between the charging roller 2 and the surface potential measuring probe 41 on the photoconductor by the peripheral speed vp of the photoconductor 1, and T is the time required for the photoconductor 1 to make one rotation.
Let p. Time when the time Trp has elapsed from the charging start time Tst
At (Tst + Trp), the surface potential measuring probe 41 starts measuring the surface potential of the photoconductor 1 after charging.

Measurement voltage Vo (1), V of the surface potential probe 41
o (2) and Vo (3) are defined as follows. Time (Tst
+ Trp) to time (Tst + Trp + Tp), that is, the absolute value of the surface potential of the photoconductor 1 from the start of charging until the photoconductor 1 completes one turn is Vo (1), and from time (Tst + Trp + Tp) to time (Tst + Trp + 2.Tp). ), That is, between the start of charging and the rotation of the photosensitive member 1 for one rotation or more and less than two rotations.
The absolute value of the surface potential of is Vo (2), which is generally the time (Tst + Tr
From (p + n · Tp) to time (Tst + Trp + (n + 1) · Tp), that is, the photoconductor 1 has been rotated for more than n rounds (n + 1).
Let Vo (n) be the absolute value of the surface potential of the photosensitive member 1 until it rotates less than one turn.

Further, the current Ir measured by the current measuring means 11
(1), Ir (2) and Ir (n) are defined as follows. From time Tst to time (Tst + Tp), that is, from the start of charging until the photoconductor 1 completes one revolution, the absolute value of the current flowing through the charging roller 2 is Ir (1), and from time (Tst + Tp) to time (Tst
+ 2 · Tp), that is, the absolute value of the current flowing through the charging roller 2 during the period from the start of charging until the rotation of the photosensitive member 1 is more than one revolution and less than two revolutions, Ir (2) is generally the time (Tst + n · Tp). ) To time (Tst + (n + 1) · Tp), that is, photoconductor 1
Let Ir (n) be the absolute value of the current flowing through the charging roller 2 from the start of charging to the rotation of n cycles or more and less than (n + 1) cycles. Further, when the charging coefficient of the photoconductor 1 is k, the charging start voltage between the charging roller 2 and the photoconductor 1 is Vth, and || is an absolute value symbol, the following three equations hold.

Vo (n) = | Vin | −Vth−Rr × Ir (n) ………………………… (33) Vo (n) −Vo (n-1) = k × Ir (n) ……………………………… (34) Vo (0) = 0 ………………………………………………… (35) These are Ir (n ),

[0210]

[Outside 2]

Solving for Rr, Rr = (| Vin | −Vth) × Ir (2) / (Ir (1)) ² ………… (37) (Equation 37) is the charging of FIG. It is the charging resistance Rr required by the tester.

Taking the leak current Ir4 into consideration, the current Ir (1) is equal to (Ir2-Ir4) and the current Ir (2) is (Ir3-Ir4). ) Matches. Also,
The applied voltage Vin was Vin2. Therefore, the charging resistance Rr
Is calculated by (Equation 38). Rr = (| Vin2 | -Vth) * (Ir3-Ir4) / (Ir2-Ir4) ² (38) Here, the charging start voltage Vth is Vth = | (Ir1-Ir4) in consideration of the leak current Ir4. × Vin2− (Ir2−Ir4) × Vin1 | / | Ir1−Ir2 | ... (39) The value calculated by (Equation 39) is used.

(I) The sum of the charging coefficient k of the photoconductor 1 and the charging resistance Rr is estimated from the input measured currents Ir1 and Ir2 by (Equation 40). k + Rr = | Vin1−Vin2 | / | Ir1−Ir2 | (40) The optimum charging current Ir_opt is calculated from the charging resistance Rr obtained in (h) above and the target potential Vo_opt of the photoconductor 1 (equation See 41). Ir_opt = Vo_opt / k + Ir4 = Vo_opt / {| Vin1-Vin2 | / | Ir1-Ir2 | -Rr} + Ir4 (41) (j) The absolute value Vin_opt of the optimum applied voltage to the charging roller 2 at the time of image formation is Vin_opt = (k + Rr) * (Ir_opt-Ir1) + | Vin1 | ... (42) Alternatively, Vin_opt = (k + Rr) * (Ir_opt-Ir2) + | Vin2 | ... (43)

Based on the above procedure, a new photoconductor (film thickness of 26 μm on the surface) was installed in the charging tester shown in FIG. 5, left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%, and then applied voltage. When Vin1 = −900V and Vin2 = −1100V, the current value flowing when charging the static elimination light 3 while charging is measured,
Ir1 = 3.0 μA and Ir2 = 4.8 μA, respectively.

Next, with the applied voltage Vin2 = -1100V, the static elimination light 3 is turned off, and the values of Ir3 and Ir4 obtained by the steps (f) and (g) are Ir3 = 0.8 μA and Ir4 = 0. .
It was 4 μA. That is, the leak current is 0.4 in this measurement.
μA was present.

Using the above measurement data, if the unit of potential is V and the unit of current is μA from (Equation 40), the value of k + Rr is
111.1 (V / μA), Vth = 611V was calculated from (Equation 39). Further, the charging resistance Rr was calculated as Rr = 10.1 MΩ from (Equation 38), and the charging coefficient k of the photoconductor 1 was 102.0 (V / μA).

Assuming that the target potential of the photoconductor is −450 V,
From 41), the optimum charging current Ir_opt was 4.9 μA. (Equation 42)
From this, the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor to −450V was calculated to be 1110V.

For verification, when -1110V whose absolute value is closest to Vin_opt is applied to the charging roller 2 by the 5V step power supply 4, the surface potential of the photosensitive member 1 becomes -447V, which is a value close to the target potential.

Next, after running 100,000 sheets, the photoconductor in which the film thickness of the photoconductor became 18 μm was incorporated into the charging tester shown in FIG. 5 and left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%. After that, when the applied voltage Vin1 = −900V and Vin2 = −1100V, the current values flowing when charging the static-eliminating light 3 while lighting it were measured, and they were Ir1 = 4.8 μA and Ir2 = 7.3 μA, respectively.

Next, with the applied voltage Vin2 = -1100V, the static elimination light 3 is turned off, and the values of Ir3 and Ir4 obtained by the steps (f) and (g) are Ir3 = 1.2 μA and Ir4 = 0. .
It was 4 μA.

Using the above measurement data, if the unit of potential is V and the unit of current is μA from (Equation 40), the value of k + Rr is
80.0 (V / μA), Vth = 548V was calculated from (Equation 39).
Furthermore, the charging resistance Rr was calculated as Rr = 9.3 MΩ from (Equation 38), and the charging coefficient k of the photoconductor 1 was 70.7 (V / μA).

Assuming that the target potential of the photosensitive member is −450V, (Equation
From 41), the optimum charging current Ir_opt is 6.8 μA. From (Equation 42), the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor to −450V was calculated to be 1058V.

For verification, when -1060 V, whose absolute value is closest to Vin_opt, was applied to the charging roller 2 by the 5 V step power supply 4, the surface potential of the photoconductor 1 was -442 V, which was a value close to the target potential.

Further, a new photoconductor (surface film thickness: 26 μm)
Built in the electrification tester shown in Fig. 5, room temperature 33 ℃, humidity 80
Applied voltage Vin1 = -900 after left for 3 days in the environment of
When V and Vin2 = -1100V, the current values flowing when charging the static-eliminating light 3 while lighting it are actually measured.
= 3.4 μA and Ir2 = 5.4 μA.

Next, with the applied voltage Vin2 = -1100V, the static elimination light 3 is turned off, and the values of Ir3 and Ir4 obtained by the steps (f) and (g) are Ir3 = 0.7 μA and Ir4 = 0. .
It was 6 μA.

Using the above measurement data, if the unit of potential is V and the unit of current is μA from (Equation 40), the value of k + Rr is
Vth = 620V was calculated from 100.0 (V / μA) and (Equation 39). Furthermore, the charging resistance Rr was determined from (Equation 38) to be Rr = 2.1 MΩ, and the charging coefficient k of the photoconductor 1 was 97.9 (V / μA).

Assuming that the target potential of the photosensitive member is −450V,
From 41), the optimum charging current Ir_opt was 5.2 μA. (Equation 42)
From this, the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor to −450V was obtained as 1080V.

For verification, when −1080V whose absolute value is closest to Vin_opt is applied to the charging roller 2 by the 5V step power source 4, the surface potential of the photoconductor 1 becomes −451V, which is a value close to the target potential. As described above, according to this embodiment, the surface potential of the photoconductor can be set to the target value without being affected by the change in the surface film thickness of the photoconductor, the change in the resistance value of the charging member, and the leak current.

(Comparative Example 5) In the fifth example, a case was examined in which the leak current was not taken into consideration. New photoconductor (surface film thickness 26
(μm) is left in an environment of room temperature of 20 ° C. and humidity of 50% for 3 days, Ir1, Ir2 and Ir3 are set to (Formula 23) and (Formula 24) of the third embodiment.
To obtain Vth and Rr. Value is Vt
h ″ = 611 V and Rr ″ = 17.0 MΩ. (Equation 41) and
From (Equation 42), the optimum applied voltage Vin_opt = 1142V with respect to the target potential −450V of the photoconductor 1 is obtained. But actually -11
When 42V was applied to the charging roller 2, the surface potential of the photoconductor 1 was -477V, which was a value shifted from the target potential by 27V.

Next, when a photoreceptor having a thickness of 18 μm after running 100,000 sheets was left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%, Ir1, Ir2 and Ir3 were changed to a third value. Vth and Rr were determined by substituting them into (Equation 23) and (Equation 24) of the example. The values were Vth ″ = 548 V and Rr ″ = 13.4 MΩ, respectively. From (Expression 41) and (Expression 42), the target potential of the photoconductor 1 is −45.
The optimum applied voltage Vin_opt = 1089V with respect to 0V.
However, when -1089V was actually applied to the charging roller, the surface potential of the photoconductor 1 was -469V, which was a value deviated from the target potential by 19V.

Furthermore, a new photoconductor (surface film thickness: 26 μm)
When left at room temperature 33 ° C and humidity 80% for 3 days,
Vth and Rr were calculated by substituting r1, Ir2 and Ir3 into (Equation 23) and (Equation 24) of the third embodiment. The value is Vth ″ = 620
V, Rr ″ = 11.5 MΩ. From (Equation 41) and (Equation 42), the optimum applied voltage Vi for the target potential −450 V of the photoconductor 1
It became n_opt = 1146V. However, when -1146 V is actually applied to the charging roller 2, the surface potential of the photoconductor 1 is -515.
It became V. The value was deviated from the target potential by 65 V, which was not practical.

(Sixth Embodiment) When the current flowing through the charging member has a leak due to dew condensation or the like and the film thickness of the photosensitive member is not reduced, the measurement of the current value can be simplified to three times. When there is no decrease in the film thickness of the photoconductor, when the photoconductor film with high hardness is used, or when the surface of the photoconductor is coated with high hardness, or the life of the photoconductor is short, the film thickness decreases. This is the case when it is decided in advance that the photoconductor should be replaced.

When a photoreceptor having a surface potential of 0 V is charged to Vo, Vo is proportional to the current Ir. This relationship is shown in FIG.
In FIG. 4, the horizontal axis represents the charging current Ir and the vertical axis represents the photoreceptor surface potential Vo. The proportionality coefficient is set to k, and k is named a charging coefficient. When charging the photoreceptor with the initial surface potential of 0 V,
Multiplying the charging current Ir by k gives the charging potential Vo.

In this embodiment, the charge coefficient k of the photoconductor 1 is obtained in advance. Since the method of obtaining the charging coefficient k is the same as that of the second embodiment, it will be omitted. Since the photosensitive member is the same as that of the second embodiment, the charging coefficient k of the photosensitive member 1 was k = 99.1.

The structure of the image forming apparatus of this embodiment is basically shown in FIG. 10 as in the third embodiment. The difference from the third embodiment is the operation of the control means 10. The operation of the control means 10 will be described with reference to FIG.

FIG. 17 is a timing chart showing the operation of the control means 10. Time elapses in the direction of the horizontal axis arrow.
Further, the rotation of the photoconductor 1, the voltage Vin applied to the charging roller 2, the turning on or off of the static elimination light 3, the absolute value Ir of the charging current flowing through the charging roller 2, and the transfer power source 37 are transferred from above. The current applied to the roller 32 and the surface potential Vo of the photoconductor 1 at the developing position by the developing device 31 are shown. Since it is complicated to display it as it is, the photoconductor surface potential Vo in FIG.
Is shown by advancing by the time Trd required for one point on the moving photoconductor 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. Further, the time required for the charging roller 2 to make one rotation is Tr, and the time required for the photosensitive member 1 to make one rotation is Tp. The times Tr and Tp are obtained in advance from the diameter of the charging roller 2, the diameter of the photoconductor 1, and the peripheral speed vp of the photoconductor 1.

In FIG. 17, the photoconductor 1 is placed prior to the drawing process.
After the rotation, the transfer power source 37 is floated, and the transfer roller 32 does not charge the photoconductor 1. The voltage Vin1 is applied to the charging roller 2 after a lapse of a time sufficient for the rotation of the photoconductor 1 to be sufficiently stabilized. Of the current flowing at this time, the time Tr from immediately after the application of Vin1 to the full rotation of the charging roller 2 is unstable, so the current value is ignored, and the current value Ir1 after the charging roller 2 makes one round or more is measured. .

Next, the measurement end time of Ir1 is set to T2, and the time required for one point on the moving photosensitive member 1 to move from the working area of the static elimination light 3 to the charging area of the charging roller 2 is set to Tjr. Then, the static elimination light 3 is turned off after the time (T2-Tjr).

In this example, before the end of Ir1 measurement and at the time
After (T2-Tjr), the applied voltage of the power source 4 remains Vin1 and
The static elimination light 3 is turned off. It is assumed that the time when the boundary between the surface of the photoconductor on which the charge has been removed and the surface of the photoconductor on which the charge has not been removed contacts the charging member after the charge-eliminating light 3 is turned off is T3. The time T3 is obtained in advance from the peripheral speed vp of the photoconductor 1 and the positional relationship between the charge eliminating light 3 and the charging roller 2.

A current Ir3 flowing through the charging member is measured from time T3 to (T3 + Tp). Further time (T3 + T
The current Ir4 flowing through the charging member is measured from p) to (T3 + 2Tp).

The control means 10 controls the measured values Ir1 and Ir3.
Then, the charging resistance Rr at the time of image formation is obtained from Ir4 and Ir4, and the absolute value Vin_opt of the applied voltage is determined. Next, the absolute value is Vin_opt
Power supply 4 that is closest to the charging roller 2 and has the same polarity as the optimum surface potential of the photoconductor 1 in the drawing process.
Control. The image forming process starts from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential. In the drawing process, the control means 10 operates the transfer process by setting the transfer power source to +2 μA.

A method of obtaining the charging resistance Rr from the measured values Ir1, Ir3 and Ir4 and determining the applied voltage Vin_opt at the time of image formation will be described with reference to FIG. FIG. 18 is a flowchart showing the operation procedure of the control means 10, and the operation is performed in the following order.

(A) After the photoconductor 1 starts to rotate, the power source 4 is controlled and Vin1 is applied to the charging roller 2 before the image forming process. (b) The current Ir1 flowing from the power supply 4 to the charging roller 2 with respect to the applied voltage Vin1 is measured by the current measuring means 11, and the measured current value is input and stored by the control means 10. (c) The control means 10 instructs the static elimination power source 5 to turn off the static elimination light 3 with the applied voltage being Vin1. (d) From time T3 to (T3 + Tp), the current measuring means 11 measures the current Ir3 flowing through the charging member, and the control means 10
Is input and memorized. (e) The current Ir4 flowing through the charging member is measured by the current measuring means 11 from time (T3 + Tp) to (T3 + 2Tp), and the control means 10 inputs and stores it.

(F) The charging resistance Rr is obtained by the same procedure as in the fifth embodiment. That is, the following two relationships are established for Rr and Vth. Rr = (| Vin1 | −Vth) × (Ir3−Ir4) / (Ir1−Ir4) ² (44) Here, the charging start voltage Vth used is the value calculated by (Equation 45). Vth = | Vin1 | − (k + Rr) × (Ir1−Ir4) ……………… (45) Solving these two simultaneous equations for Rr and Vth,
The charging resistance Rr is calculated.

(G) Charge coefficient k of the photoconductor 1 given in advance
Then, the optimum absolute value Ir_opt of the charging current is obtained from (Equation 46) from the absolute value Vo_opt of the target potential at the time of image formation of the photoconductor 1. Ir_opt = Vo_opt / k + Ir4 (46) (h) The optimum absolute value Vin_opt of the applied voltage to the charging roller 2 at the time of image formation is Vin_opt = (k + Rr) × (Ir_opt −Ir1) + | Vin1 | ……… Calculate by (47).

Based on the above procedure, a new photoconductor (film thickness of 26 μm on the surface) was installed in the charging tester shown in FIG. 5 and left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%, and the device was fully charged. After adjusting to the environment, the following experiment was started. Applied voltage V
The current value Ir1 flowing when charging was performed while lighting the neutralization light 3 at in1 = −1100 V was Ir1 = 4.8 μA. Next, the applied voltage remains −1100 V, the static elimination light 3 is turned off, and the values of the currents Ir3 and Ir4 obtained in the above steps (d) and (e) are as follows.
Ir3 = 0.8 μA and Ir4 = 0.4 μA, respectively.

Simultaneous equations of (Equation 44) and (Equation 45) and the previously determined charge coefficient k of the photosensitive member 1 = 99.1 (V / μA)
When the charging resistance Rr and the charging start voltage Vth are obtained from Rr =
It was 10.1 MΩ and Vth = 620V. When the target potential of the photoconductor 1 is -450 V, the optimum absolute value Ir_opt of the charging current is 4.9 μA from (Equation 46). From (Equation 47), the absolute value Vin_op of the optimum applied voltage for setting the potential of the photoconductor 1 to −450V
t is required to be 1110V.

For verification, when -1110V whose absolute value is closest to Vin_opt is applied to the charging roller 2 by the 5V step power source 4, the surface potential of the photoconductor 1 becomes -447V, which is a value close to the target potential.

Further, a new photoconductor (surface film thickness: 26 μm) was installed in the charging tester shown in FIG. 5, and the room temperature was 33 ° C. and the humidity was 80%.
After allowing the apparatus to stand in the environment for 3 days to allow the apparatus to fully adapt to the environment, the following experiment was performed. The current value Ir1 that flows when charging is performed while turning on the static elimination light 3 with the applied voltage Vin1 = −1100 V was Ir1 = 5.4 μA. Next, the applied voltage is −1100
Turn off the static eliminator 3 with V as it is, and follow steps (d) and (e) above.
The values of the currents Ir3 and Ir4 obtained by the above are respectively Ir3 = 0.
It was 7 μA and Ir4 = 0.6 μA.

When the charging resistance Rr and the charging start voltage Vth are calculated from the simultaneous equations of (Expression 44) and (Expression 45) and the previously determined charging coefficient k = 99.1 (V / μA) of the photoconductor 1, Rr = 2 .
It was 3 MΩ and Vth = 654V. The target potential of the photoconductor 1
If it is 450V, the optimum absolute value Ir of the charging current is calculated from (Equation 46).
_opt was 5.1 μA. From (Equation 47), the absolute value Vin_opt of the optimum applied voltage for setting the potential of the photoconductor 1 to −450 V is 1
It was asked to be 070V.

For verification, when −1070 V whose absolute value is closest to Vin_opt is applied to the charging roller 2 by the 5 V step power supply 4, the surface potential of the photoconductor 1 becomes −441 V, which is a value close to the target potential. As described above, according to this embodiment, the surface potential of the photoconductor can be set to the target value without being affected by the change in the resistance value of the charging member and the leak current.

(Comparative Example 6) In the sixth example, a case was examined in which the leak current was not taken into consideration. New photoconductor (surface film thickness 26
(μm) is left for 3 days in an environment of room temperature of 20 ° C. and humidity of 50%, and the charging currents Ir1, Ir3, Ir4 are calculated by the equation (29) of the fourth embodiment.
And (Equation 30) to obtain Vth and Rr. The values obtained from the measured values are Vth ″ = 450V and Rr ″ = 22.6MΩ, respectively.
Met.

From (Equation 46) and (Equation 47), the optimum applied voltage Vin_opt = 1064V with respect to the target potential -450V of the photoconductor 1 is obtained. However, when -1064V is actually applied to the charging roller, the surface potential of the photoconductor 1 becomes -407V, which is 4V below the target potential.
The value was deviated by 3V. The difference from the target value was so large that it could not be put to practical use.

Further, the charging currents Ir1, Ir3 and Ir4 when a new photoconductor (surface film thickness 26 μm) was left for 3 days in an environment of room temperature 33 ° C. and humidity 80% were calculated from the equation (29) of the fourth embodiment. ) And (equation 30)
To obtain Vth and Rr. The values obtained from the measured values were Vth ″ = 428 V and Rr ″ = 16 MΩ, respectively.

From (Equation 46) and (Equation 47), the optimum applied voltage Vin_opt = 997V with respect to the target potential -450V of the photoconductor 1 was obtained. However, when −997 V was actually applied to the charging roller, the surface potential of the photoconductor 1 became −370 V, which was a value deviated from the target potential by 80 V. The difference from the target value was so large that it could not be put to practical use.

(Seventh Example) As a result of intensive studies by the inventors, the following phenomenon was observed in the first measurement, and it was found that the current measurement had an error.

The photosensitive member of FIG. 3 (surface film thickness: 26 μm) and the charging roller of FIG. 2 were incorporated into the charging tester shown in FIG.
An experiment was conducted after leaving the apparatus as a whole in an environment of 20 ° C. and a humidity of 50% for 3 days to fully adapt it to the environment. Applied voltage Vin =-
The current value flowing when charging was performed while turning on the static elimination light 3 at 1100V. The data obtained are shown in Figures 19 (a) and (b).

19A and 19B, the horizontal axis represents time, the voltage Vin applied to the charging roller 2 from above in the vertical direction, the absolute value Ir of the charging current flowing in the charging roller 2, and the developing position by the developing device 31. The surface potential Vo of the photoconductor 1 is shown. Since it is complicated to display it as it is, the surface potential Vo in FIGS. 19A and 19B is required for one point on the moving photoconductor 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. It is shown by advancing only time Trd. The distance on the surface of the photoconductor 1 between the charging roller 2 and the developing device is divided by the peripheral speed vp of the photoconductor 1 and advanced by the time Trd. Further, the time required for the charging roller 2 to make one rotation is Tr, and the time required for the photosensitive member 1 to make one rotation is Tp. The times Tr and Tp are the diameter of the charging roller 2, the diameter of the photoconductor 1, and the peripheral speed vp of the photoconductor 1.
Is obtained in advance from.

For the sake of explanation, the time when the voltage Vin1 is applied to the charging member is Ts1 and the time when the voltage application to the charging member is finished before the time Ts1 is closest to Ts1.
And The charging process started at time Ts1 is called the current charging, and the charging process completed at time Ts2 is called the previous charging. Between time Ts1 and time Ts2, the charging roller 2 does not charge the photoconductor 1. Hereinafter, for the sake of explanation, a state in which no voltage is applied to the charging member, the photosensitive member is stopped, and the charge eliminating unit is not operating is called an uncharged state. At this time, the time differences ΔTs and ΔTs = Ts1−Ts2 are the times when the uncharged state continues. If the charging roller 2 and the photoconductor 1 are completely new, ΔTs = infinity.

As a result of the experiment, the time ΔT that the non-charged state lasted
The measured current changed depending on s. In Fig. 19 (a), △
When Ts = 30 seconds or less, the current Ir11 flowing through the charging member from the time Ts1 until the photoconductor makes one revolution (Ts1 or more and less than Ts1 + Tp) and the period from the time Ts1 to one photoperiod or more and less than two revolutions ( The current Ir22 flowing through Ts1 + Tp or more and less than Ts1 + 2 · Tp) has the same value. However, in Figure 19 (b)
When Ts = 3 minutes or more, the absolute value of the current Ir11 'flowing through the charging member from the time Ts1 to one rotation of the photosensitive member is the current Ir22 flowing from the start of charging to one rotation or more and less than two rotations of the photosensitive member. Was greater than the absolute value of ′. In addition, the current that flows after the photosensitive member has rotated more than two turns since the start of charging is Ir2.
It was the same as 2 '. Further, Ir22 and Ir22 'have the same value.

The measured value shows that when ΔTs = 30 seconds, Ir11
= Ir22 = 4.4 μA, which was the same value. However, △ Ts
= 3 minutes, Ir11 '= 4.9 µA, Ir22' = 4.4 µA, and the absolute value of Ir11 'was larger by 0.5 µA. Also △
Ir22 ″ when Ts = 3 minutes coincided with Ir11 and Ir22 when ΔTs = 30 seconds or less, and Ir22 ″ = 4.4 μA.

Further, when the surface potential Vo of the photosensitive member is ΔTs = 30 seconds in FIG. 19 (a), the charging potential Vo11 of the photosensitive member 1 from time Ts1 to one rotation of the photosensitive member and the time The surface potential Vo12 of the photoconductor when the photoconductor makes one turn or more from Ts1 has the same value, and Vo11 = Vo12 = -436V.

On the other hand, in the case of ΔTs = 3 minutes in FIG. 19B, the photoconductor 1 from the time Ts1 to one revolution of the photoconductor 1
Charging potential Vo11 ′ = − 406V, and the photosensitive member is set to 1 from time Ts1.
Surface potential Vo12 '=-436V of the photoconductor when rotating more than one turn
The absolute value of Vo11 'was smaller by 30V. The surface potential Vo12 'when ΔTs = 3 minutes coincided with the photoreceptor surface potential Vo11 when ΔTs = 30 seconds.

From the above experimental results, it was found that when the uncharged state continues for 3 minutes or more, a transient state occurs from the start of charging to one round of the photosensitive member. That is,
In this period, although the absolute value Ir of the charging current is large, the absolute value of the photoconductor potential is small, and the proportional relationship between the charging current and the photoconductor potential is not established.

Therefore, in the present invention, the charging current is measured after the photosensitive member has rotated one or more turns since the start of charging. Hereinafter, a charging device according to a seventh exemplary embodiment of the present invention will be described with reference to the drawings. Similar to the first embodiment, in this embodiment, the charging resistance Rr was measured in advance before the potential control during image formation. The method of measurement is the same as that of the first embodiment, and is omitted here. Since the charging roller of FIG. 2 is used, the charging resistance R
The measured value of r was 9.1 MΩ as in the first embodiment. In this example, the voltage applied to the charging member was determined as follows using this Rr.

The image forming apparatus of this embodiment has the same structure as that of the first embodiment except for the operation of the control means 10.
How to obtain the current value input by the control means 10 will be described with reference to FIG. FIG. 20 is a timing chart showing the operation of the control means 10. Time elapses in the direction of the horizontal axis arrow. In addition, the rotation of the photosensitive member 1, the voltage Vin applied to the charging roller 2, and the static elimination light 3 are turned on or off (from the top).
f) shows the absolute value Ir of the charging current flowing through the charging roller 2, the current applied by the transfer power source 37 to the transfer roller 32, and the surface potential Vo of the photoconductor 1 at the developing position by the developing device 31. Since it is complicated to display it as it is, the photosensitive member surface potential Vo in FIG. 20 is advanced by the time Trd required for one point on the moving photosensitive member 1 to move from the charging area of the charging roller 2 to the developing area of the developing device 31. Indicated. In addition, the charging roller 2
Let Tr be the time required to make one revolution of the photosensitive drum, and Tp be the time required to make one revolution of the photosensitive member 1.

In FIG. 20, the photoconductor 1 is placed prior to the drawing process.
The transfer power source 37 is set in a floating state before the rotation starts, and the transfer roller 32 does not charge the photoconductor 1.
After allowing sufficient time for the rotation of the photoconductor 1 to stabilize,
At time T1, the voltage Vin1 is applied to the charging roller 2. Of the current flowing at this time, the time Tr from the time T1 when Vin1 is applied to the charging roller 2 to make one revolution and the time Tp to make one revolution of the photosensitive member 1 are ignored because the current value is unstable. The current value is measured after a longer time of Tp, whichever is longer. In this embodiment, the diameter of the photoconductor 1 is larger than the diameter of the charging roller 2 and Tr <Tp.
Becomes Therefore, the charging current Ir1 is measured after the time Tp from the time T1 when Vin1 is applied to the charging roller 2 to the photoconductor 1 completes one cycle (that is, after the time T1 + Tp). This is the first measurement.

After measuring Ir1, the applied voltage of the power source 4 is set to Vin.
Change to 2. Of the current that flows at this time, the current that flows through the charging roller 2 during the time Tr from immediately after applying Vin2 to when the charging roller 2 makes one revolution is unstable and is ignored, and the current after the charging roller 2 has rotated one revolution or more is ignored. Measure the value Ir2.
This is the second measurement.

The control means 10 determines the absolute value Vin_opt of the applied voltage at the time of image formation from these measured values Ir1 and Ir2 and the previously measured charging resistance Rr. Next, the absolute value is Vin
The power source 4 is controlled so that it is closest to _opt and the polarity is the same as the optimum surface potential of the photoconductor 1 in the image forming process.
The image forming process starts from the time when the surface potential Vo of the photoconductor 1 at the developing position reaches the target potential. In the drawing process, the control means 10 operates the transfer process by setting the transfer power source to +2 μA.

The first method of determining the optimum applied voltage Vin_opt
Similar to the embodiment of FIG. FIG. 7 is a flowchart showing the operation procedure of the control means 10, and the operation is performed in the following order. (a) After the photoconductor 1 starts rotating, the power source 4 is controlled and Vin1 is applied to the charging roller 2 before the image forming process. (b) The current Ir1 flowing from the power source 4 to the charging roller 2 after time T1 + Tp corresponding to the applied voltage Vin1 is measured by current measuring means.
The control unit 10 inputs and stores the measured current value by the control unit 11. (c) The voltage applied to the charging roller 2 is controlled to V by controlling the power supply 4.
set to in2. (d) From the power supply 4 to the charging roller 2 corresponding to the applied voltage Vin2
The current Ir2 flowing in the current is measured by the current measuring means 11, and the measured current value is inputted and stored in the control means 10.

(E) The sum of the charging coefficient k of the photoconductor 1 and the charging resistance Rr is estimated from (Equation 48) from the input measured current. k + Rr = | Vin1-Vin2 | / | Ir1-Ir2 | (48) (f) The optimum absolute value Ir_opt of the charging current is calculated from the charging resistance Rr obtained in advance and the target potential Vo_opt of the photoconductor 1. Calculate with (Equation 49). Ir_opt = | Vo_opt | / k = | Vo_opt | / {| Vin1-Vin2 | / | Ir1-Ir2 | -Rr} (49) However, the polarity of the electric current is such that the photoconductor has photoconductivity. .

(G) Absolute value Vin_o of the optimum applied voltage at the time of printing
pt is calculated by (Equation 50), and Vin_opt = (k + Rr) × | Ir_opt-Ir1 | + | Vin1 | (50) or Vin_opt = (k + Rr) × | Ir_opt-Ir2 | + | Vin2 | ) The power supply 4 is controlled so that the absolute value is closest to Vin_opt and the polarity is the same voltage as the optimum surface potential of the photoconductor 1 in the image forming process.

Based on the above procedure, the current value flowing when charging a new photoconductor (photoconductor film thickness 26 μm) with applied voltages Vin1 = −900V and Vin2 = −1100V while turning on the static elimination light 3 is measured. Then, Ir1 = 2.6 μA and Ir2 =
It was 4.4 μA. Therefore, assuming that the unit of potential is V and the unit of current is μA, k + Rr is calculated from (Equation 48) to 111.1 (V /
μA). On the other hand, the charging resistance Rr measured in advance is 9.1.
It was MΩ. Therefore, the value of k was 102.0 (V / μA). When the target potential at the time of image formation of the photoconductor 1 is -450 V, the optimum current value was calculated from (Equation 49) to be 4.4 μA, and the optimum absolute value of the applied voltage was 1101 V from (Equation 50).

For verification, the output voltage of the power supply 4 is in 5V steps. Therefore, when the voltage −1100V whose absolute value is the closest to 1101V is actually applied to the charging roller 2, the surface potential of the photoconductor 1 becomes −440V, which is the target value. A close value was obtained.

[0275] Next, after running 100,000 sheets, the film thickness is 18
The photoconductor having a size of μm was charged with the applied voltage Vin1 = -900V and Vin2 = -1100V while turning on the static elimination light 3. When the charging current is measured, Ir1 = 4.4 μA and Ir2 = 6.
It was 9 μA. The charge coefficient of the photoconductor 1 having a film thickness of 18 μm is k ′
Then, k '+ Rr is 80.0 (V / μA) from (Equation 48). Since the charging resistance Rr measured in advance is 9.1 MΩ, k '
= 70.9 (V / μA). Set the target potential of photoreceptor 1 to -450
Assuming V, the optimum current value for the charging roller 2 is (Equation 4
6.3 μA when calculated from 9). Further, the optimum absolute value of the applied voltage to the charging roller 2 is 1055V from (Equation 50). For verification, when −1055 V was actually applied to the charging roller 2, the surface potential of the photoconductor became −440 V, which was close to the target potential.

As described above, according to the present embodiment, of the charging currents used for determining the optimum applied voltage, the charging current after the photosensitive member has been rotated by one or more turns from the start of charging is measured to obtain correct charging. The current could be measured and the surface potential of the photoconductor could be set to the target value.

(Comparative Example 7) For comparison, an attempt was made to measure the charging current generated from the start of charging until the photosensitive member made one revolution. After leaving the photoconductor 1 in the non-charged state for 1 hour or more, the first example was tried. However, the first measurement was carried out from the start of charging of the photoconductor 1 to the one revolution of the photoconductor 1. The second measurement is the same as in the first embodiment.

The measured value is shown. In the first embodiment, the charging roller 2 shown in FIG. 2 and the charging roller 2 shown in FIG.
Incorporate the photoconductor 1 of. Charge tester at room temperature 20 ℃ and humidity 50%
The sample was allowed to stand for 3 days in a constant temperature and constant humidity environment to fully adapt to the environment. Voltage applied to charging roller 2 Vin1 = -900V, Vin
When 2 = -1100V, the charging current Ir11 in the first measurement
= 4.9 μA, and the charging current Ir2 in the second measurement was 6.9 μA. The charging resistance Rr is known and Rr = 9.1 MΩ.

From (Equation 11), k + Rr = 100.0 (V / μA). Therefore, the charging coefficient k of the photoconductor 1 is 90.1 (V /
μA) is estimated. From (Equation 12), the absolute value Ir_opt of the charging current for setting the photoconductor 1 at the target potential is 5.0 μA. Furthermore, from (Equation 13), the optimum applied voltage Vin_opt =
It became 910V.

However, when Vin = −910V is actually applied to the charging roller 2, the surface potential of the photoconductor 1 is −270V.
Met. There was a difference of 180 V from the target potential, which was not practical.

(Eighth Example) As a charging current to be measured,
In the first to seventh embodiments, the current flowing from the power source 4 to the charging roller 2 is used, but the charging current to be measured may be the current flowing from the photoconductor to the ground. At the same timing as the current flowing from the power source 4 to the charging roller 2 during charging, the current flows from the photoconductor 1 to the ground. At this time, from the power source 4 to the charging roller 2
And the value of the current flowing from the photoconductor 1 to the ground are also equal. This is from ground to power supply 4, charging roller 2,
This is because the path through which the current flows from the photoconductor 1 to the ground is a closed circuit.

Since the first to seventh embodiments including the control of the transfer power source can be applied to the procedure of measurement and control, description thereof will be omitted, and only the charging current portion will be described with reference to FIGS. 21 (a) and 21 (b). ).

FIG. 21 (a) shows the structure of the charging current measurement location in the charging device. The photoconductor 1, the charging roller 2, the discharging light 3, the power source 4 and the control means 10 are the same as those in the first embodiment, and 12 is a current measuring means. The current measuring means 12 measures the current flowing from the photoconductor to the ground and inputs it to the control means 10. The timing of inputting the measurement current, the operation of the peripheral members, and the processing procedure of the control means 10 are from the first to the seventh.
This is the same as the above embodiments.

A concrete example of the current measuring means 12 is shown in FIG. In FIG. 21 (b), 13 is a low-pass filter and 14 is an amplifier. A charging current measuring resistor of 10 kΩ is inserted between the photoconductor 1 and the ground, and the charging current is obtained from the voltage generated at both ends. The charging current is 10 kΩ and the voltage across the resistor is 10
The value is divided by kΩ.

In the first embodiment, the charging current flowing to charge the photoconductor 1 to the target potential was in the range of about 4 to 10 μA. Therefore, a voltage of 0.04 to 0.1 V was generated across the 10 kΩ resistor inserted between the photoconductor 1 and the ground. That is, 0.05 to 0.1 V of the applied voltage during charging was lost by the 10 kΩ resistance. However, −800
This loss has no effect on the applied voltage in the range of V to -1200V. The voltage across the 10 kΩ resistor passes through a low-pass filter 13 to remove high frequency noise components, and is further amplified by an amplifier 14 and input to the control means 10.

For verification, in the first to seventh embodiments, the current measuring means 11 was replaced with the current measuring means 12, and the optimum applied voltage at the time of image formation was determined from the charging current from the photoconductor 1 to the ground. As a result, the surface potential of the photoconductor 1 could be set to the target value as in the first to seventh embodiments. As described above, the object of the present invention can be achieved even with the configuration in which the current flowing from the photoconductor 1 to the ground is measured.

(Ninth Embodiment) When the charging member is a rotating charging roller, noise was generated in the measured current at a cycle of one round of the charging roller. When the noise is actually measured, when the charging roller 2 is made new, the charging current flowing when charging the photoconductor 1 to −450 V has an average peak amplitude ΔI of 4.5 μA.
Noise with r_pp of about 0.5 μA was superimposed. Further, the current noise has a periodicity and is repeated at a cycle Tp in which the charging roller 2 rotates once. As a result of the study by the inventors, it has been clarified that this current noise is caused by uneven contact with the photoconductor 1 due to uneven resistance and surface unevenness that the charging roller 2 initially has.

As a countermeasure, in this embodiment, the optimum applied voltage at the time of image formation is determined from the average charging current during one rotation of the charging roller. As its configuration, a low-pass filter whose cutoff frequency is equal to or less than the reciprocal of the time taken for the charging roller to make one turn is inserted in the means for measuring the charging current. Hereinafter, description will be given with reference to the drawings.

FIG. 22 (b) shows a concrete structure of the charging current measuring means, in which 1 is a photoconductor, 2 is a charging roller, 3 is static elimination light, 4 is a power source, and 10 is control means. A 10 kΩ resistor is inserted between the power supply 4 and the ground. The photoconductor 1 and the charging roller 2 rotate in the direction of the arrow at a peripheral speed of 33 mm / sec. The control means 10 has a function of measuring the voltage of a resistor inserted between the power source 4 and the ground. In addition, as a function of the control means 10 (not shown), a function of controlling the power supply 4 and a function of calculating (Equation 11), (Equation 12), (Equation 13) and (Equation 14) in the first embodiment. Is equipped with.

When the time required for the charging roller 2 to make one rotation is Tp, Tp = 1.14 seconds, so the cycle of the charging roller 2 was 0.87 Hz. Therefore, the cutoff frequency of the low-pass filter inserted before the current measurement of the control means 10 was set to 0.87 Hz or less.

As a low-pass filter satisfying the above conditions, FIG. 22A shows an example of a low-pass filter having a cutoff frequency of 0.8 Hz. FIG. 22 (a) shows an analog second-order low-pass filter. The frequency characteristics are shown in FIG.
The horizontal axis represents frequency and the vertical axis represents gain. This low-pass filter passes frequency components below 0.8 Hz, but significantly attenuates frequency components above 0.8 Hz.

In FIG. 22B, the power source 4 is the charging roller 2
A DC voltage was applied to. The voltage generated across the resistance of 10 kΩ between the photoconductor 1 and the ground is input to the control means 10 after passing through the low-pass filter. The control means 10 sets the voltage to 10k.
The charging current Ir is obtained by executing the operation of dividing by Ω.

The charging currents Ir1 and Ir2 are measured at the timing shown in FIG. 6 as in the first embodiment. Further, the optimum applied voltage Vin_opt at the time of drawing is determined by the procedure shown in FIG. 7 as in the first embodiment.

For verification, applied voltage Vin1 = −900V, V
The measured value at in2 = -1100V is shown. When the values of the currents that flow when charging the photoconductor 1 while turning on the discharge light 3 are measured, Ir1 = 2.6 μA and Vi for Vin1 respectively.
Ir2 was 4.4 μA for n2. Assuming that the unit of potential is V and the unit of current is μA, k + Rr is
It was 1.1 (V / μA). On the other hand, the charging resistance Rr measured in advance was 9.1 MΩ. Therefore, the value of the charging coefficient k was k = 102.1 (V / μA).

When the target potential at the time of image formation of the photoconductor 1 was -450 V, the optimum current value was (Formula 12) to 4.4 μA, and the optimum applied voltage absolute value was (Formula 13) to 1101 V. Since the output voltage of the power supply 4 is in 5V steps, the absolute value is closest to 1101V and the polarity is the same as the optimum surface potential Vo_opt of the photoconductor 1 in the image forming process, ie, -1100V is actually applied to the charging roller 2 for verification. It was As a result, the surface potential of the photoconductor 1 was -440V, which was close to the target value.

(Comparative Example 8) As a comparison, the case where the low-pass filter was not inserted before the current measuring means was tried. In this case, noise was generated in the measured current in the cycle of one round of the charging roller. FIG. 24 shows the charging current measuring means in Comparative Example 8. In FIG. 24, 1 is a photoconductor, 2 is a charging roller, 3 is static elimination light, 4 is a power source, and 10 is a control means. A 10 kΩ resistor is inserted between the power supply 4 and the ground. The control means 10 has a function of measuring the voltage of a resistor inserted between the power source 4 and the ground. In addition, as a function of the control means 10 not shown, a function of controlling the power supply 4 and a first
(Equation 11), (Equation 12), (Equation 13) and (Equation 1
It has a function to calculate 4).

The charging roller 2 shown in FIG. 2 is used, and the photoreceptor 1 shown in FIG. 3 is used. The photoconductor 1 and the charging roller 2 have a peripheral speed of 33 in the direction of the arrow.
Rotate at mm / sec. In FIG. 24, the power source 4 is the charging roller 2
A DC voltage was applied to. The current flowing at that time is calculated from the voltage generated across the resistance of 10 kΩ between the photoconductor 1 and the ground.
It was calculated by converting voltage / 10 kΩ.

As a result of actual measurement, when the charging roller 2 is made new, the charging current flowing when the photosensitive member 1 is charged to −450 V has an average peak-to-peak amplitude ΔIr_pp of about 0.5 μA with respect to 4.5 μA on average.
μA noise was superimposed. Further, the current noise has a periodicity, which is repeated at a cycle Tp in which the charging roller 2 rotates once.

Since the charging coefficient k of the photosensitive member 1 is about 100, a control error of kΔIr_pp = 50V has occurred as predicted from (Equation 4). In addition, the current noise tended to increase with long-term use. As a result of a running test of 100,000 sheets, the current noise was 0.8 μA. After investigating the cause of the increase in current noise, we found that toner, additives to toner,
Further, since the paper dust adheres to the charging roller 2, the charging roller 2
This was because the surface resistance value of No. 1 was uneven. Further, when the surface of the charging roller 2 was observed after running 100,000 sheets of paper, abrasion marks were found. Wear of the charging roller 2 was also a cause of current noise. The charging coefficient k of the photoconductor 1 is about
Since it is 100, as predicted from (Equation 4), k · ΔIr_p
A control error of p = 80V occurred.

(Tenth Embodiment) It is desirable that the time from the drawing command to the end of the drawing process is as fast as possible. FIG. 25 shows the
In the block diagram of the image forming apparatus of the tenth embodiment, 10 is a control means, 15 is a time management means, and 16 is an abnormal situation detection means.
The control means 10 includes (Equation 11) and (Equation 1) in the first embodiment.
It has a function to calculate 2), (Equation 13) and (Equation 14).
Further, the control means 10 is provided with a means for inputting an execution start signal for the calculation and a means for inputting an abnormal signal.

The time management means 15 has a clock function for knowing the current time, a function for storing time, a function for comparing the magnitude of the time difference, a function for detecting the input of a drawing command, and an image forming apparatus during the drawing process. It is provided with a means for detecting whether or not it is during the drawing process.

FIG. 26 is a flow chart showing the operation of the time management means 15, and the operation of the control means shows that an instruction to start execution is issued to the control means 10. Time management means 15
Does not stop until the power is turned off or an abnormal signal is input, after the power is turned on.

First, after the power is turned on, an execution start command is issued to the control means 10. Next, the current time is stored in Tset, and then the current time is stored in Now. Next, it is judged whether or not a drawing command is detected after the time Tset, and if the drawing command is detected, the process waits until the drawing process is completed, and immediately after the drawing process is finished, an execution start command is issued to the control means 10. If no drawing command is detected, the difference between Now and Tset is calculated, and (Tnow
If the value -Tset) is equal to or less than the predetermined time TL, then Know is reset to the current time and the image command detection is repeated. In this example, TL is 30 minutes. If (Tnow-Tset) is larger than the predetermined time TL, an execution start command is issued to the control means 10.

Further, the abnormal situation detecting means 16 comprises means for detecting an abnormality in the image forming apparatus and means for outputting an abnormal signal to the control means 10. When an abnormality of the device such as a paper jam or an abnormal stop of the motor is detected, an abnormality signal is immediately output to the control means 10. When the control unit 10 receives the abnormal signal, the control unit 10 immediately interrupts the current process and executes the emergency stop mode shown in FIG.

FIG. 27 is a flow chart showing the processing of the control means 10 in the emergency stop mode. When the abnormal signal is input, the power supply 4 that has applied the voltage to the charging member is turned off, the transfer power supply 37 is then floated, and the charge removal light 3 is turned off.

As a result of adding this procedure to the voltage control of the present invention, the control means 10 does not execute the current measurement between the user's drawing command and the end of the drawing, and the waiting time of the user is not increased. There wasn't. Further, since the control means 10 executes the voltage control operation at least once in 30 minutes, it is possible to sufficiently follow the changes in the atmospheric environment and the changes in the temperature and humidity due to the warming up of the drawing apparatus itself so that the exposure at the time of drawing is performed. The body potential was able to reach the target value.

In the first to eighth embodiments, the static elimination light is used as the static elimination means. However, the static elimination means may be an exposure by the image writing means or the transfer means during the current measurement period. The transfer means may be used in combination as the charge removing means by adjusting the applied voltage of.

Further, although the charging roller is used as the charging member in the first to eighth embodiments, the charging member may have a conductive block shape or a conductive brush. . Further, a conductive blade or a conductive belt-shaped charging member may be used.

Further, in the first to eighth embodiments, the drum-shaped photoconductor is used as the photoconductor, but a belt-shaped photoconductor may be used instead.

In the first to eighth embodiments, the transfer power supply 37 is configured to select +2 μA and the float state. However, the transfer power supply 37 is grounded instead of the float state. Alternatively, it may be a voltage having the same polarity as the polarity of the photoconductor exhibiting photoconductivity, or a voltage whose absolute value is equal to or lower than the voltage at which charging is started between the photoconductor and the transfer unit.

In the first to eighth embodiments, the transfer power source 37 is in the float state before the photosensitive member 1 rotates, but one point on the moving photosensitive member 1 is the transfer roller 32.
When the time required to move from the action area of the charging roller 2 to the charging area of the charging roller 2 is Ttr, the measurement start time of the current generated in the charging roller 2 is T7, and the measurement end time is T8, at least the time (T7-Ttr ) To the time (T8-Ttr), the transfer roller 2 is in a floating state or grounded,
Alternatively, it may be a voltage having the same polarity as the polarity of the photoconductor exhibiting photoconductivity, or a voltage whose absolute value is equal to or lower than the voltage at which charging is started between the photoconductor and the transfer unit.

Further, in the ninth embodiment, the low pass filter is provided before the current measuring means, but the low pass filter may be provided between the current measuring means and the control means.

In the first to eighth embodiments, the power supply during non-printing and the power supply during printing are the same.
A power supply for drawing may be separately provided, and the power supply for non-drawing may be switched to the power supply for drawing before the start of drawing. The power source for drawing at this time may be a voltage source that outputs the determined optimum voltage or a current source that outputs the optimum current.

In the first to eighth embodiments, the voltage applied during non-printing is a DC voltage. However, the voltage during non-printing includes at least DC voltage and includes AC voltage or AC current. The current measuring means may be provided with a low-pass filter that removes the alternating-current component with the superimposed voltage.

[0315]

As described above, according to the present invention,
It has the following effects. (First Effect) Since the charging resistance Rr is sequentially measured and the optimum applied voltage to the charging member is determined while making a correction, the charging resistance Rr is not affected by changes in the charging resistance due to ambient temperature and humidity,
The photoconductor can be set to a target potential.

(Second Effect) Since the charging resistance Rr is used to determine the optimum voltage to be applied to the charging member while making a correction, the photosensitive member is not affected by the voltage loss at the charging resistance Rr. It can be set to the target potential.

(Third Effect) Since the proportional coefficient k between the current flowing in the photoconductor and the photoconductor potential is measured and the optimum voltage applied to the charging member is determined by using the charging resistance Rr, the film of the photoconductor is determined. The photoreceptor can be set to the target potential without being affected by wear.

(Fourth Effect) Even if the current flowing through the charging member during the charging process includes a leakage current component, the optimum applied voltage to the charging member is determined while correcting the influence of the leakage current. Therefore, the photoconductor can be set to the target potential.

(Fifth Effect) Since the transient current of the photoconductor, which was an error factor, is not measured, the photoconductor can be stably set to the target potential.

(Sixth Effect) Since the transient current of the rotating roller-shaped charging member, which was an error factor, is not measured, the photosensitive member can be stably controlled to the target potential.

(Seventh Effect) Since the noise caused by the rotating roller-shaped charging member is removed, the photosensitive member can be stably set to the target potential.

(Eighth Effect) Since the measuring step of the present invention is not executed after the drawing command until the end of the drawing, the user of the image forming apparatus does not have to wait for the start of drawing.

(Ninth Effect) Since the photoconductor potential before charging is always 0 V, there is no error in the measurement current and the photoconductor can be stably set to the target potential.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to first and second embodiments of the present invention.

FIG. 2 is a schematic configuration diagram of a charging roller used in an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a photoconductor used in an example of the present invention.

FIG. 4 is a diagram showing a relationship between a charging current and a surface potential in a photoconductor used in an example of the present invention.

FIG. 5 is a schematic configuration diagram of a charging tester for measuring charging characteristics of a charging member and a photoconductor.

FIG. 6 is a timing chart of current measurement in the first embodiment of the present invention.

FIG. 7 is a flowchart showing a voltage determination procedure in the first embodiment of the present invention.

FIG. 8 is a timing chart of current measurement according to the second embodiment of the present invention.

FIG. 9 is a flowchart showing a voltage determination procedure in the second embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of an image forming apparatus in third, fourth, fifth and sixth embodiments of the present invention.

FIG. 11 is a timing chart of current measurement in the third embodiment of the present invention.

FIG. 12 is a flowchart showing a voltage determination procedure in the third embodiment of the present invention.

FIG. 13 is a timing chart of current measurement according to the fourth embodiment of the present invention.

FIG. 14 is a flowchart showing a voltage determination procedure in the fourth embodiment of the present invention.

FIG. 15 is a timing chart of current measurement in the fifth embodiment of the present invention.

FIG. 16 is a flowchart showing a voltage determination procedure in the fifth embodiment of the present invention.

FIG. 17 is a timing chart of current measurement according to the sixth embodiment of the present invention.

FIG. 18 is a flowchart showing a voltage determining procedure in the sixth embodiment of the present invention.

FIG. 19 is a diagram (a) showing the relationship between the charging current and the photoreceptor surface potential when the time difference between the previous charging and the current charging is 30 seconds in the seventh embodiment of the present invention, the previous charging and the current charging. FIG. 6B is a diagram (b) showing the relationship between the charging current and the surface potential of the photoconductor when the time difference from the charging is 3 minutes.

FIG. 20 is a timing chart of current measurement according to the seventh embodiment of the present invention.

FIG. 21 is a schematic configuration diagram (a) of a current measurement point in the eighth embodiment of the present invention, 10 kΩ inserted between the photoconductor and the ground.
FIG. 4B is a schematic configuration diagram (b) of an apparatus that measures a charging current from a voltage generated across a resistance.

22A is a circuit diagram of a low-pass filter having a cutoff frequency of 0.8 Hz according to the ninth embodiment of the present invention, and FIG. 22B is a diagram showing a current measurement point provided with the low-pass filter.

FIG. 23 is a diagram showing frequency characteristics of a low pass filter according to a ninth embodiment of the present invention.

FIG. 24 is a diagram showing a current measurement point without a low-pass filter according to a ninth embodiment of the present invention.

FIG. 25 is a schematic configuration diagram of an apparatus for managing the timing of operation of control means in the tenth embodiment of the present invention.

FIG. 26 is a flow chart showing a procedure for operating control means in the tenth embodiment of the present invention.

FIG. 27 is a flowchart of the emergency stop mode of the control means in the tenth embodiment of the present invention.

[Explanation of symbols]

1 ... Photosensitive member, 2 ... Charging roller, 3 ... Static elimination light, 4 ...
Power supply, 5 ... static elimination power supply, 10 ... control means, 11, 12 ... current measuring means, 13 ... low-pass filter, 14 ... amplifier,
15 ... Time management means, 16 ... Abnormal situation detection means, 31 ... Developing device, 32 ... Transfer roller, 33 ... Cleaning blade, 34 ... Paper, 35 ... Laser light source, 36 ... Mirror, 37
… Transfer power supply, 41… Surface potential measurement probe, 42… Surface potential meter.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akiyuki Naka, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hisanori Nagase, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (27)

[Claims] 1. A body to be charged, a charging member in contact with or close to the body to be charged, a power supply for applying a voltage to the charging member, and a current measuring unit for measuring a current flowing from the power supply to the charging member. The optimum voltage Vin_opt applied to the charging member for setting the charged body to a desired potential is determined based on the current measured by the current measuring unit and the resistance value Rr from the power source to the charging area of the charging member. A charging device comprising a control means for controlling the power source. 2. A member to be charged which is moved by a known driving means, a charging member which is in contact with or close to the member to be charged, a power source which selectively applies at least two kinds of voltages to the charging member, and the member to be charged. A current measuring unit that moves the charged body and measures a current Ir1 generated by the first applied voltage Vin1 to the charging member and a current Ir2 generated by the second applied voltage Vin2 to the charging member, and the current measuring unit. The measured current value is input and stored, and calculation is performed based on the voltage applied to the charging member, the current measured by the current measuring means, and the resistance value Rr measured in advance from the power source to the charging region of the charging member. And a control means for determining the optimum voltage Vin_opt to be applied to the charging member to bring the charged body to a desired potential in the drawing step and controlling the power supply. A charging device according to claim and. 3. A power source for selectively applying at least two kinds of voltages to the charging member, which is circulated and moved at a speed vp by a known driving unit, a charging member which is in contact with or close to the charging member, and a charging member. And a discharging means for discharging the charged body, a current measuring means for measuring a current flowing through the charging member, and a control means for controlling the power source and the discharging means. This occurs when the power source applies the first voltage Vin1 to the charging member while the charging region of the charging member is in contact with the surface of the member to be charged, which is circulated and moved by the discharging unit. The current Ir1 is measured, and subsequently, the current Ir2 generated when the second applied voltage Vin2 is applied to the charging member in the above state is further measured, and further, one point on the charged body that circulates at the speed vp. But the above From the area which receives the neutralization effect of the conductive means, TJR the time required to move to the charging area of the charging member, the measurement end time of the current Ir2 T2
Then, in the state where the second applied voltage Vin2 is applied to the charging member, the static elimination by the static elimination means is stopped after the time (T2-Tjr), and the surface of the body to be discharged and the non-charged surface of the body to be charged are removed. Assuming that the time at which the boundary with the surface of the charged body comes into contact with or is closest to the charged area of the charging member is T3, from the time T3 until the charged body makes one revolution,
The control means measures the current Ir3 flowing through the charging member, and the control means performs calculation based on the currents Ir1, Ir2 and Ir3 measured by the current measurement means to bring the charged body to a desired potential in the drawing process. A charging device characterized by determining an optimum voltage Vin_opt applied to a charging member and controlling the power supply. 4. A power source for selectively applying at least two types of voltages to the charging member, which is circulated and moved at a speed vp by a known driving unit, a charging member which is in contact with or close to the charging member, and a charging member. And a discharging means for discharging the charged body, a current measuring means for measuring a current flowing through the charging member, and a control means for controlling the power source and the discharging means. This occurs when the power source applies the first voltage Vin1 to the charging member while the charging region of the charging member is in contact with the surface of the member to be charged which is circulated and moved by the discharging unit. The current Ir1 is measured, and subsequently, the current Ir2 generated when the second applied voltage Vin2 is applied to the charging member in the above state is further measured, and further, one point on the charged body that circulates at the speed vp. But the above From the area which receives the neutralization effect of the conductive means, TJR the time required to move to the charging area of the charging member, the measurement end time of the current Ir2 T2
Then, in the state where the second applied voltage Vin2 is applied to the charging member, after the time (T2-Tjr), the static elimination by the static elimination means is stopped, and the surface of the body to be discharged and the non-charged surface Assuming that the time at which the boundary with the surface of the charged body comes into contact with or is closest to the charged area of the charging member is T3, from the time T3 until the charged body makes one revolution,
The current Ir3 flowing through the charging member and the current Ir4 flowing through the charging member when the charged body makes one or more turns from time T3 are measured, and the control means measures the currents Ir1 and Ir2 measured by the current measuring means. , Ir3 and Ir4 are calculated to determine the optimum voltage Vin_opt to be applied to the charging member to bring the charged body to a desired potential in the image forming step, and control the power supply. 5. A member to be charged that circulates at a speed vp by a known driving unit, a charging member that contacts or approaches the member to be charged, a power supply that applies a voltage to the charging member, and the member to be charged. A charge removing unit for removing charge, a current measuring unit for measuring a current flowing through the charging member, and a control unit for controlling the power source and the charge removing unit, the current measuring unit circulatingly moving at a speed vp and removing the charge. The current Ir1 generated when the power source applies the first voltage Vin1 to the charging member in a state where the charging area of the charging member is in contact with the surface of the body to be charged that has been discharged by the means,
Further, the time required for one point on the body to be charged, which circulates at a speed vp, to move to the charging area of the charging member from the area subjected to the discharging effect from the discharging means is T.
When the measurement end time of jr and the current Ir1 is T2, the time (T2−
Tjr) and thereafter, the static elimination by the static elimination means is stopped, and the time when the boundary between the surface of the charged body that has been discharged and the surface of the charged body that has not been discharged contacts or is closest to the charging area of the charging member is designated as T3. Then, the current Ir3 flowing through the charging member from time T3 until the charged body makes one turn.
Then, the control means performs an operation based on the currents Ir1 and Ir3 measured by the current measuring means to calculate an optimum voltage Vin_opt to be applied to the charging member to bring the charged body to a desired potential in the image forming step. A charging device characterized by determining and controlling the power supply. 6. A charging target member that circulates at a speed vp by a known driving unit, a charging member that contacts or approaches the charging target member, a power source that applies a voltage to the charging member, and the charging target member. A charge removing unit for removing charge, a current measuring unit for measuring a current flowing through the charging member, and a control unit for controlling the power source and the charge removing unit, the current measuring unit circulatingly moving at a speed vp and removing the charge. The current Ir1 generated when the power source applies the first voltage Vin1 to the charging member in a state where the charging area of the charging member is in contact with the surface of the body to be charged that has been discharged by the means,
Further, the time required for one point on the body to be charged, which circulates at a speed vp, to move to the charging area of the charging member from the area subjected to the discharging effect from the discharging means is T.
When the measurement end time of jr and the current Ir1 is T2, the time (T2−
Tjr) and thereafter, the static elimination by the static elimination means is stopped, and the time when the boundary between the surface of the charged body that has been discharged and the surface of the charged body that has not been discharged contacts or is closest to the charging area of the charging member is designated as T3. Then, the current Ir flowing through the charging member from the time T3 until the charged body makes one turn.
3, and the current Ir4 flowing through the charging member when the charged body makes one or more turns from time T3, and the control means calculates based on the currents Ir1, Ir3 and Ir4 measured by the current measuring means. The charging device is characterized by determining the optimum voltage Vin_opt applied to the charging member for making the charged body a desired potential in the image forming step and controlling the power supply. 7. The charging member is rotated by a known driving means including power transmission from an object to be charged, and when the time for one rotation of the charging member is Tr, the current measuring means has a cutoff frequency of 1 7. The charging device according to claim 1, further comprising a low-pass filter having a ratio of / Tr or less. 8. The current used for determining the voltage Vin_opt is a current after at least one revolution of the charged body since the voltage was applied to the charging member. The charging device according to item 1. 9. The current used to determine the voltage Vin_opt is at least one revolution of the charging member from the time when the voltage applied to the rotating charging member by a known driving means including driving from the member to be charged changes. The charging device according to any one of claims 1 to 6, wherein the current is a current after rotation. 10. The time when the voltage changes includes the time when the voltage application to the charging member is started.
The charging device described. 11. A photosensitive member that circulates by known driving means, and a charging member that comes into contact with or comes close to the photosensitive member,
A power source for applying a voltage to the charging member, a current measuring means for measuring a current flowing through the charging member, a destaticizing light for destaticizing the photoconductor by exposure, a developing means for developing on the photoconductor, A transfer unit for transferring the image on the body to the image carrier and a transfer power source for applying at least one of voltage or current to the transfer unit are provided, and the photosensitive member is moved to turn on the neutralization light. In the image forming apparatus that determines the voltage applied to the charging member in the image forming process by using the current generated when the voltage is applied to the charging member in the above state, one point on the moving photoconductor is the transfer point. The time required to move from the transfer area of the means to the charging area of the charging member is Ttr, the measurement start time of the current generated in the charging member is T7, and the measurement end time is T8.
, At least from time (T7-Ttr) to time (T8
-Ttr), the voltage applied to the transfer means is
Ground, or a voltage of the polarity that the photoconductor exhibits photoconductivity,
Or, the absolute value of the difference between the surface potential of the photoconductor charged by the charging member and the voltage applied to the transfer unit is a voltage equal to or lower than the charging start voltage between the photoconductor and the transfer unit, or The charging device is characterized in that the transfer means is electrically floated. 12. The charged body is a photoconductor, and the discharging means is an exposing means.
Or the charging device according to 6. 13. The current used for determining the voltage applied to the charging member in the image forming step is a current flowing from the body to be charged to the ground.
The charging device according to item 1. 14. The charging current to be measured is a current flowing from the photoconductor to the ground.
The charging device described. 15. The charging device according to claim 1, wherein the charging member has a roller shape. 16. The charging device according to claim 1, wherein the charging member has a blade shape. 17. The charging device according to claim 1, wherein the charging member has a brush shape. 18. The charging device according to claim 2, wherein the current is measured at a constant time. 19. The charging device according to claim 2, wherein the current is measured immediately after the power is turned on and immediately before the start of the first image forming process. 20. The charging device according to claim 2, wherein the current is measured immediately before the drawing process. 21. The charging device according to claim 2, wherein the current is measured immediately after the image forming step. 22. The measurement of the current is a combination of two or more kinds from immediately after the power is turned on to immediately before the start of the first drawing process, at regular time intervals, or immediately after the drawing process. The charging device according to 2, 3, 4, 5 or 6. 23. The charging device according to claim 1, wherein the member to be charged has a drum shape. 24. The charging device according to claim 1, wherein the member to be charged has a belt shape. 25. The charging device according to claim 11, wherein the photoconductor has a drum shape. 26. The charging device according to claim 11, wherein the photoconductor has a belt shape. 27. A charging device according to claim 3, 4, 5 or 6, further comprising a transfer means for transferring the image on the surface of the body to be charged onto the image carrier, and the discharging means also serves as the discharging means. apparatus.