JPH05333673A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the change in image density and line width at the rise of a developer by changing the developing bias to be impressed to a developer carrying member. CONSTITUTION:The standby time TA of a fixing device is counted by a timer a from a power switch on and is compared with the reference time T1 in a phase 1. Whether there is a need for shifting the DC component VDC of the developing bias or not is then discriminated and the timer A is reset at the time of TA>T1. The DC component VDC of the developing bias is set higher by 30V than the set value and the number of sheets of prints is counted by a paper counter in a phase 2. The DC component VDC of the developing bias is set higher by 20V than the set value and the number of sheets of prints is counted in a phase 3. The DC component VDC of the developing bias is set higher by 10V than the set value and the number of sheets of prints is counted in a phase 4. The paper counter is reset when 200 sheets are attained. DC component VDC of the developing bias is set at the set value when the 200 sheets are attained.

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 such as a copying machine of an electrophotographic type or an electrostatic recording type, a laser beam printer, an LED printer or the like, and more particularly, to a latent image formed on an image carrier. The present invention relates to an image forming apparatus that develops a visible image by attaching an agent.

[0002]

2. Description of the Related Art In forming an image by a known electrophotographic process, the electrostatic latent image formed on an image bearing member is visualized by using insulating colored particles (hereinafter referred to as toner) as carrier particles or developing. It is generally carried out by transferring the charged toner onto the image carrier by charging the toner by friction with the surface of the agent carrier and further applying an appropriate bias potential to the surface of the developer carrier. is there.

Therefore, the latent image visualization (hereinafter referred to as development) in the electrophotographic image forming apparatus is an application of the electrostatic phenomenon, and is therefore influenced by the ambient environment, particularly humidity. In order to reduce this effect, for example, various charge control agents such as azo chromium-containing complexes are internally added to the negatively charged toner, and the fluidity is increased to increase the stability of triboelectric charging, Further, in order to increase the amount of electric charge, externally added silica or the like treated with aminosilane is used to stabilize the charging.

By the way, in an electrophotographic image forming apparatus, a direct current (DC) component and an alternating current (AC) component are superimposed on a developer carrier when developing an electrostatic latent image formed on the image carrier. A bias voltage is often applied. This is because the toner in the developer (toner) layer having a uniform thickness formed on the developing sleeve, which is usually used as the developer carrier, is jetted to the photoconductor drum which is usually used as the image carrier by the force of the electric field. This is to make it happen. In other words, the toner on the developing sleeve is finally transferred to the photosensitive drum while being moved between the photosensitive drum and the developing sleeve to develop the toner.

As described above, when the developing bias in which the direct current component and the alternating current component are superposed is used, that is, when the developing bias has the alternating current component, the direct current component can be made lower than in the case of only direct current. The toner particles adhering to the photoconductor drum are supplied not only from the toner particles on the developing sleeve at the position corresponding to the latent image but also from the periphery thereof, which is advantageous in that density unevenness due to the edge effect is reduced. ..

[0006]

However, even if the charge control agent is internally added, the fluidity of the toner is improved, and the aminosilane-treated silica or the like is externally added, it is extremely difficult to control the static electricity caused by the triboelectrification. Difficult to do. The actual charging of the toner on the developing sleeve, which is usually used as a developer carrier, depends on the interaction between the powders including the external additive, such as the frictional charging of the powders and the repeated transport on the developing sleeve. The toner is complicated because it is affected by so-called charge-up and the like in which the amount of charge of the toner is increased. In particular, when the apparatus starts up, the average amount of charge generally changes in an increasing direction and reaches a saturated state of the amount of charge after printing several tens to several hundreds of sheets. For the sake of convenience, the process until the charge amount of the toner on the developing sleeve reaches an apparent equilibrium state is called the rising of the developer (toner). During this period, the image density (particularly halftone) and the line width gradually increase. There is a problem that the impression received from the printed image is different before and after the toner rises because it becomes thick or thick.

Further, when a developing bias in which a direct current component and an alternating current component are superposed is used, if the developing bias is turned off when the toner is a bias component which flies to the photosensitive drum, fogging occurs on the photosensitive drum. However, there is a problem in that it adheres to a transfer material (recording material) guide member such as a guide roller to stain the back of the transfer material, or stains the transfer charger to cause transfer blanking and transfer unevenness. In addition, when it adheres to a transfer member such as a transfer roller or a transfer material carrier such as a transfer drum, it also causes backside smearing of the transfer material. The degree of backside stain is more noticeable on thinner paper such as the second original. Further, as the toner particles have a smaller diameter, the amount of fog toner also increases.

The cause of the above fog is that when the alternating electric field between the developing sleeve and the photosensitive drum is suddenly cut off, the toner attracted from the developing sleeve toward the photosensitive drum cannot be returned to the developing sleeve side again. It is known that the toner adheres to the photosensitive drum. In order to prevent this, the alternating electric field of the developing bias is given a predetermined time constant to be attenuated, and the toner reciprocating between the developing sleeve and the photosensitive drum is gradually reduced to leave the toner left on the photosensitive drum. It has already been proposed to reduce the amount (see, for example, JP-A-64-70777).

However, when the cost of the high-voltage transformer, which is considerably expensive among the components of the apparatus, is reduced, the toner after the developing bias is turned off is disturbed and the toner flying from the developing sleeve to the photosensitive drum is developed again. The force of pulling back to the sleeve suddenly weakened, and there was the problem that fogging occurred.

Accordingly, one object of the present invention is to change the developing bias applied to the developer carrying member,
An object of the present invention is to provide an image forming apparatus capable of preventing an image density and a line width from being changed due to a rise of a developer and a change in a consumed developer amount and always obtaining an output image having a stable density and a line width.

Another object of the present invention is to provide an image forming apparatus that develops a latent image by forming an alternating electric field, in which fogging does not occur even if a low cost high voltage transformer is used. That is.

[0012]

The above object is achieved by an image forming apparatus according to the present invention. In summary, according to the first aspect of the present invention, a latent beam that irradiates a light beam on an image carrier based on an image signal corresponding to image information to form an electrostatic latent image on the image carrier. A thin layer of a developer is formed on the surface of the developer carrying member and the image forming means, and a bias potential is applied to the developer carrying member to transfer the developer carried on the surface of the developer carrying member to the image carrying member. A developing device for transferring the electrostatic latent image formed on the surface of the image carrier to the surface of the image bearing member, and a time measuring means for measuring the waiting time of the fixing device, and the waiting time of the fixing device measured. The image forming apparatus is characterized in that the bias potential applied to the developer carrying member is changed according to the number of print output sheets when the time is longer than a certain reference time.

In a second aspect, the present invention provides
A latent image forming unit that irradiates a light beam on the image carrier based on an image signal corresponding to image information to form an electrostatic latent image on the image carrier, and a thin developer layer on the surface of the developer carrier. By forming a layer and applying a bias potential to the developer carrying body, the developer carried on the surface of the developer carrying body is transferred to the surface of the image carrying body, and the static electricity formed on the surface of the image carrying body is transferred. A developing device that visualizes an electrostatic latent image, and calculates and calculates a light emission time versus the amount of consumed developer based on the light emission time of light irradiated by the latent image forming means, and the calculated amount of consumed developer is sequentially calculated. An image forming apparatus comprising: a unit for accumulating and storing, and changing a bias potential applied to the developer carrier according to an integrated value of the consumed developer amount.

Furthermore, in the third aspect, the present invention irradiates a light beam on an image carrier charged based on an image signal corresponding to image information to form an electrostatic latent image on the image carrier. The electrostatic latent image is formed and an alternating electric field is formed between the image carrier and the developer carrier to transfer the developer carried on the developer carrier to the image carrier, In the image forming apparatus configured to image, among the components of the alternating electric field that act to attenuate the alternating electric field with a predetermined time constant and pull back the developer from the image carrier to the developer carrier. The image forming apparatus is characterized in that the level of the component immediately before the final component which is equal to or higher than the threshold level that contributes to development is equal to or higher than the threshold level.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

First, a first embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In addition,
In this embodiment, the case where an image signal from an external device is converted into an image signal for a laser printer and supplied to an electrophotographic laser printer to form an image will be described. Read by the conversion element,
It goes without saying that the present invention can be applied to other image forming apparatuses such as a copying machine that forms an image by converting this into an image signal for a laser printer and supplying the image to a laser driver. Yes.

FIG. 1 is a schematic configuration diagram showing a main part of a first embodiment of the present invention. An image signal corresponding to image information from an external device 1 such as a host computer is sent to an interface 2, Is supplied to the laser driver 4 after being converted into an image signal for a laser printer including a laser control signal (BD (beam detect) signal for determining writing timing, APC (auto power control) signal for controlling power, etc.) and a video signal. To be done. on the other hand,
A CPU (Central Processing Unit) 3 controls the laser driver 4 via the interface 2, and also electrically controls the other devices as a whole.

The semiconductor laser 5 is driven by the laser driver 4 and outputs intensity-modulated laser light. This laser light is scanned by the polygon mirror 6 and f-
It is guided onto the photosensitive drum 9 via the θ imaging lens 7 and the folding mirror 8. Here, since the surface of the photosensitive drum 9 is uniformly charged by the primary charger 10, an electrostatic latent image is formed by being exposed to laser light.

This electrostatic latent image reaches the developing area facing the developing device 11 containing the one-component developer, that is, the toner 12 by the rotation of the photosensitive drum 9 in the direction of the arrow in the figure, and the development as the developer carrying member is carried out. The toner supplied by the sleeve 14 is developed and visualized by so-called reversal development that adheres to the exposed portion of the photosensitive drum 9. The developed image, that is, the developed image on the photoconductor drum 9 is transferred onto the recording material 16 such as transfer paper by the action of the transfer charging device 17, and the recording material 16 is actuated by the action of the separating / electrifying device 18. Drum 9
After being separated from the recording material 16 by a fixing device (not shown)
The upper visible image is fixed, and a print image corresponding to the image signal is obtained. Further, the residual toner remaining on the photosensitive drum 9 is removed by the cleaner 19. Incidentally, the developing device 1
A toner agitating / conveying member 13 is provided inside 1.
Further, the magnet 15 is included in the developing sleeve 14,
It is fixed.

In the electrophotographic image forming apparatus, so-called rising of the density and the line width occurs to a greater or lesser extent, as described above. FIG. 2 shows how the line width (2 dots, 5 spaces) rises with respect to the number of prints (A4 size) in the laser beam printer having the configuration shown in FIG. As can be seen from FIG. 2, the line width at the time of starting the development or at the time of being sufficiently left (in this example, left overnight) (1
The line width at the time of rising is about 20 μm thicker (about 90 μm).

The line width visualized in this laser printer is linear with respect to the development contrast (the potential difference between the DC component of the developing bias applied to the developing sleeve 14 and the developing portion potential on the photosensitive drum 9). It has changed to (linear). The relationship is shown in FIG. In the figure, the characteristic A shown by the solid line is the characteristic of the development contrast vs. line width before the rising of the toner, and the characteristic B shown by the broken line is the characteristic of the development contrast vs. the line width when the toner is rising. As is clear from these characteristics, it is understood that the development contrast may be changed by about 40 V (about 40 V may be increased) in order to correct the change in the line width of about 20 μm caused by the rising of the toner.

In this embodiment, attention is paid to this point, and it is determined from the power switch ON of the apparatus whether or not the developing bias needs to be raised (raised) in advance in consideration of the rising of the toner. It is done from the time until becoming a print ready. The reason for this is:
As described above, the phenomenon of rising of the density and the line width occurs when the apparatus is operated after not being used for a long time, and generally tends to be a problem in the morning after being left overnight. Therefore, if the print is done in the morning,
Or, it is necessary to judge whether the operation is to be carried out suddenly after a long standby state or after the paper jam processing.

In the present embodiment, this determination is made by storing the waiting time T _A of the fixing device and determining whether the stored waiting time T _A is longer or shorter than the reference time T ₁ . By selecting an appropriate value (30 seconds in this embodiment) as the reference time T ₁ , it can be determined that the fixing roller has risen from a sufficiently cooled state (room temperature) when T _A > T ₁ , which is practical. Above, you can safely assume that you are in the first condition in the morning. On the other hand, when T _A ≦ T ₁ , it can be practically considered that the power supply to the heater of the fixing roller is interrupted due to a paper jam or the like. Further, specifically, the relationship between the value for increasing the developing bias and the number of copies is from the first sheet to the fifth sheet in this embodiment.
30V until 0th sheet, 2 from 51st sheet to 100th sheet
The developing contrast is controlled to be 0 V, 10 V from the 101st sheet to the 200th sheet, and the developing contrast is increased with respect to the set developing bias value.

This control procedure is shown in FIG. In brief, in the phase 1, it is necessary to count the waiting time T _A of the fixing device after the power switch is turned on by the timer A and shift the DC component V _DC of the developing bias in comparison with the reference time T _1. If it is necessary to determine whether or not the shift is performed (T _A > T ₁ ), the timer A is reset. Next, in phase 2, the DC component V _DC of the developing bias is raised by 30 V above the set value, and the number of prints is counted by the paper counter. In phase 3, the DC component V _DC of the developing bias is raised by 20 V above the set value. , And the number of printed sheets is counted, and in the phase 4, the DC component V _DC of the developing bias is made higher than the set value by 10 V, and the number of printed sheets is counted to 20.
When the number of sheets reaches 0, the paper counter is reset and the DC component V _DC of the developing bias is set to the set value.

FIG. 4 shows the relationship between the number of sheets passed and the line width in the laser beam printer of the present embodiment in which the above-described development bias control has been performed. As is clear from the characteristics of FIG. 4, the laser beam printer to which the present invention is applied has a significantly improved change in the line width at the start-up, and therefore an output image having a stable line width and image density can be formed at all times. ..

However, the actual image density or line width varies depending on the print pattern (printing density, paper size) and the paper passing mode (continuous paper feeding or intermittent paper feeding). Therefore, in the above-described embodiment, the developing bias change amount (every 10 V) and the timing (50th, 100th, and 200th sheets) are selected so that the density and the line width can be converged even if the sheet passing mode or the print pattern is changed. did. Further, although the present invention is applied to the laser beam printer using the known one-component jumping development in the above-mentioned embodiment, in the image forming apparatus using the other development system including the two-component development, the start-up in the development system is performed. It is natural that the change amount of the developing bias and the timing are appropriately changed in order to improve the characteristics, and therefore, these changes and modifications are all included in the scope of the present invention.

Although the developing bias is controlled by the number of prints in the above embodiment, the number of prints is multiplied by a coefficient according to the size of the print paper (recording material), and when the value exceeds a certain threshold value, If the developing bias is changed as in the case of the embodiment, there is an advantage that the change of the line width and the image density can be corrected more finely.

For example, in the above embodiment, since the developing bias is controlled by the number of prints, the rotation number of the developing sleeve and the toner consumption amount are nearly doubled for the A3 portrait size print with the same number of A4 landscape size prints. Nevertheless, there was the inconvenience that the developing bias could be changed with the same number of prints.

Therefore, based on A4 vertical size paper,
3 vertical size 1.4 times, A4 horizontal size 0.9 times, B5
The vertical size is multiplied by a coefficient such as 0.8 times, the value obtained by multiplying the number of prints by the coefficient is counted, and when the count value exceeds a certain threshold, the developing bias is changed. The above inconvenience can be eliminated. This allows
Even when mixed and used with various paper sizes,
Changes in density and line width can be kept smaller,
Fine control is possible. It should be noted that the above coefficient should be set to an appropriate value in accordance with the characteristics of the apparatus main body, for example, the distance between sheets and the length of front rotation and the length of rear rotation, and is not limited to the above value.

Further, in an electrophotographic image forming apparatus, particularly an image forming apparatus equipped with a developing device for performing one-component development, the toner (usually 300
(-700 g) is used up, the phenomenon of so-called selective development in which the above-mentioned toner rises in the short term and the toner more suited to the developing conditions is consumed first in the long term progresses. Therefore, the image density and the line width tend to be thicker or thicker from the initial stage up to 2000 to 3000 sheets depending on the characteristics of the developer and the developing structure, but after that, the image density and the line width gradually become thinner or thinner until the developer is used up. The phenomenon occurs.

Therefore, for example, a new paper counter is provided in order to correct the density change and the line width change in units of 1000 sheets, and the density change value and the line width change value for every 1000 sheets are changed in the above-mentioned developing bias. If this is fed back, there is an advantage that changes in density and line width can be corrected more finely.

For example, in a developing device for performing one-component development, the density and the line width gradually increase from the initial stage up to about 3000 sheets, so that the first 1000 sheets are compared with the developing bias correction value. Is 1.0, 10
Multiply 0.9 from the 01st to 2000th sheets, and 0.8 from the 2001th to 3000th sheets. After that, the density and line width tend to decrease gradually, so 3
0.9 from the 001th sheet to the 4000th sheet, 1.0 from the 4001st sheet to the 5000th sheet, and so on.
The developing bias correction value is multiplied by a coefficient obtained by adding 0.1 for every 000 sheets, and this is increased to 1.2 as a limit.
As a result, it becomes possible to perform correction even with respect to the density and line width variation that change due to the above-described selective development.
The unit of the number of prints for correction is 100.
The number is not limited to 0, and the coefficient to be multiplied is not limited to the above value.

Next, a second embodiment of the present invention will be described with reference to FIGS.

Also in this embodiment, the case where an image signal from an external device is converted into an image signal for a laser printer and is supplied to an electrophotographic laser printer to form an image will be described. An image forming apparatus such as an electrophotographic system or an electrostatic recording system such as a copying machine that reads an image with a photoelectric conversion element such as a CCD, converts the image signal into an image signal for a laser printer, and supplies the image signal to a laser driver. Needless to say, the present invention can also be applied.

FIG. 6 is a schematic configuration diagram showing a main part of the second embodiment of the present invention. An image signal corresponding to image information from an external device 1 such as a host computer is sent to the interface 2, Is supplied to the laser driver 4 after being converted into an image signal for a laser printer including a laser control signal (BD (beam detect) signal for determining writing timing, APC (auto power control) signal for controlling power, etc.) and a video signal. To be done. on the other hand,
The CPU 3 uses the interface 2 to drive the laser driver 4
And electrically control the entire other device.

In the present embodiment, a laser emission time / consumed toner amount calculation means 30 for calculating the consumed toner amount from the above video signal is provided, and a signal corresponding to the calculated consumed toner amount is sent to the CPU 3. Then, the developing bias is controlled. This procedure will be described later. It should be noted that the semiconductor laser 5 is driven to form an electrostatic latent image on the photosensitive drum 9, and the latent image is developed to form a visible image, which is transferred to the recording material 16 and fixed to obtain a print image. Since the configuration, operation, etc. are the same as those in the first embodiment,
Elements and members corresponding to those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted unless necessary.

As described in the description of the first embodiment,
In the electrophotographic image forming apparatus, the so-called rising of the density and the line width occurs more or less.
As shown in FIG. 2 described above, the line width at the time of start-up is about 20 μm thicker than the line width (about 190 μm) at the start of development or when it is sufficiently left. Further, as shown in FIG. 3 described above, the line width visualized in the laser printer having the configuration shown in FIG. 6 changes linearly with respect to the development contrast, and the line width of about 20 μm generated by the rising of the toner. In order to correct the change, the development contrast may be changed by about 40V (higher by about 40V).

By the way, when it is attempted to stabilize the line width and the density by controlling the developing bias, the rise of the line width and the density in the electrophotographic image forming apparatus is consumed not only in the number of passed sheets. It must be taken into consideration that it largely depends on the amount of toner.

In FIG. 7, 400 dpi (dots / inch)
The laser printer continuously prints a pattern of 1 dot and 3 spaces and outputs a line width measurement sample on the way. A solid line C shows a change in line width with respect to the number of passed sheets (A4 size) when the print image of No. 2 is continuously printed and a line width measurement sample is output in the middle. As is clear from the characteristics of FIG. 7, the line width and the density also change depending on the consumed toner amount. Therefore, in the present embodiment, the consumed toner amount is calculated from the laser emission time, and the calculated consumed amount is calculated. The developing bias is controlled based on the toner amount. Here, the operation of the laser emission time / consumed toner amount calculation means 30 in this embodiment will be described with reference to FIGS. 9 and 10.

FIG. 9 is a laser emission characteristic diagram, in which the vertical axis represents laser emission intensity and the horizontal axis represents time. The time t _S indicates the time required for the laser beam LB to perform one scan, and shows the state in which the laser beam LB is emitted and irradiated during the time t ₁₁ to time t ₁₂ and the time t ₂₁ to time t _22. .. Further, the laser emission intensity at the time t ₁₁ and the time t ₂₁ is higher than the laser emission intensity at the time t ₁₂ and the time t _22. Generally, the semiconductor laser 5 continuously oscillates to raise the temperature of the semiconductor chip and emit light. This is because it has a characteristic that efficiency is reduced.

FIG. 10 is a graph showing the relationship between the laser emission time and the consumed toner amount in bit format. The vertical axis represents the consumed toner amount per unit time, and the horizontal axis represents the laser emission time t. The same parts as those in FIG. 9 are designated by the same reference numerals.

In this figure, a _{1 to} a _i represent the toner consumption amount per unit time, and t _{1 to} t _i represent the time in which the toner consumption amount a _{1 to} a _i per unit time changes stepwise. Represent. In this embodiment, the image forming apparatus has a resolution of 16 pels / mm, and the developing bias applied on the metal developing sleeve 14 has a frequency of 1500H.
z, a peak-peak value is a rectangular wave AC bias of 1500 V superimposed with a DC bias of -500 V, a process speed is 80 mm / sec, and a dry one-component magnetic developer (toner) is used. Well-known jumping development is performed.

First, when the laser beam is irradiated from the semiconductor laser 5 of the optical scanning system, which is the latent image forming means, to the photosensitive drum 9, the laser emission time versus the consumed toner amount calculating means 30.
Calculates the toner consumption amount based on the light emission time. Next, the laser emission time vs. consumed toner amount calculation means 30
For example, as shown in FIG. 9, the laser emission time consumed by the emission of the laser beam from the time t ₁₁ to the time t ₁₂ and the time t ₂₁ to the time t ₂₂ is shown in FIG. It is represented by an area surrounded by the per-consumption toner amount characteristic data, the laser emission time (t ₁₂ -t ₁₁ ) and the laser emission time (t ₂₂ -t ₂₁ ). That is,
The laser emission time (t ₁₂ −t ₁₁ ) is t ₂ <t ₁₂ −t ₁₁ <t.
Because represented by _3, the laser emission time to the toner consumption amount W, the laser emission time (t ₁₂ -t ₁₁₎ and t, the laser emission time to consume toner amount W is calculated by the following equation (1) ..

[0044]

[Equation 1] Therefore, the laser emission time versus the consumed toner amount W at an arbitrary laser emission time t is calculated based on the following equation (2).

[0045]

[Equation 2]

In this way, the laser emission time and the consumed toner amount calculation means 30 sequentially add the laser emission time and the consumed toner amount, and the development is performed according to the added laser emission time and the consumed toner amount Ws. Bias value is controlled.

This control procedure is shown in FIG. In brief, in the phase 1, the waiting time T _A of the fixing device from the power switch being turned on until the printer becomes ready for printing
Is counted by the timer A and compared with the reference time T ₁ to determine whether or not the DC component V _DC of the developing bias needs to be shifted, and the shift needs to be performed (T _A > T
₁ ) Sometimes, reset timer A. Next, in phase 2, the DC component V _DC of the developing bias is set to 30 V higher than the set value, and in the next step, the consumed toner amount is calculated for each laser emission in order to reduce this shift amount, and the integrated value is calculated. The comparison is performed until the value (W _S ) reaches the set toner amount (W ₁ ). In phase 3, the DC component V _DC of the developing bias is reduced to a value 20 V higher than the set value, and the same operation as in phase 2 is repeated. In phase 4, the DC component V _DC of the developing bias is reduced to a value 10 V higher than the set value, the same operation as in phase 2 or phase 3 is repeated, and the integrated value (W _S ) of the consumed toner amount is set to the set toner amount (W _S ). Integrated value (W _S ) when W ₁ ) is exceeded
To reset the DC component V _DC of the developing bias to a set value.

FIG. 4 shows the relationship between the number of sheets passed and the line width in the laser beam printer of this embodiment in which the above-described developing bias control has been performed. As is clear from the characteristics of FIG. 4, the laser beam printer to which the present invention is applied has a significantly improved change in the line width at the start-up, and therefore an output image having a stable line width and image density can be formed at all times. ..

Also in this embodiment, in consideration of the rise of the toner, whether or not to shift the developing bias is determined by waiting for the fixing device from turning on the power switch of the device to being ready for printing as described above. Time (T _A )
I did it from. The reason for this has been described in the description of the first embodiment, and will not be repeated here. The reference time T ₁ was set to 30 seconds also in this embodiment.

In the laser beam printer of the present embodiment which has been subjected to the above-described development bias control, the relationship between the number of sheets passed and the line width is the same as that shown in FIG. 4, and the change in the rise of the line width is greatly improved. Was done. Further, FIG. 8 shows a change in the line width with respect to the number of passed sheets when the print pattern changes (that is, when the consumed toner amount changes). In FIG. 8, a characteristic D indicated by a broken line is a case where a pattern of 1 dot and 3 spaces is continuously printed and a line width measurement sample is output on the way.
Characteristic C shown by a solid line is when a printed image of 1 dot 20 space is continuously printed and a line width measurement sample is output in the middle. From the characteristics of FIG. 8, it can be seen that according to the present embodiment, changes in the line width and the density due to the consumed toner amount are sufficiently corrected, and a stable output image with a stable line width and density can always be obtained.

As described above, according to the present embodiment, not only is it possible to suppress the change of the line width and the density depending on the number of prints, but it is also possible to correct the line width and the density change due to the change of the print pattern. ..

As described above, in an electrophotographic image forming apparatus, particularly an image forming apparatus equipped with a developing device for performing one-component development, the toner (usually 300 to 700 g) in the toner hopper is used up. In the meantime, the phenomenon of so-called selective development progresses in the short term in which the above-mentioned toner rises, and in the long term, the toner more suited to the developing conditions is first consumed. Therefore, depending on the characteristics of the developer and the developing structure, the image density and line width may be 2000 to
Up to 3000 sheets, there is a tendency to become thicker or thicker, but thereafter, a phenomenon occurs in which the developer becomes thinner or thinner until the developer is used up.

Therefore, for example, a new paper counter is provided to correct the density change and the line width change in units of 1000 sheets, and the density change value and the line width change value for every 1000 sheets are used to change the above-mentioned developing bias. If this is fed back, there is an advantage that changes in density and line width can be corrected more finely.

For example, in a developing device for one-component development, the density and the line width gradually increase from the initial stage up to about 3000th sheet, so that the first 1000th sheet with respect to the developing bias correction value. Is 1.0, 10
Multiply 0.9 from the 01st to 2000th sheets, and 0.8 from the 2001th to 3000th sheets. After that, the density and line width tend to decrease gradually, so 3
0.9 from the 001th sheet to the 4000th sheet, 1.0 from the 4001st sheet to the 5000th sheet, and so on.
The developing bias correction value is multiplied by a coefficient obtained by adding 0.1 for every 000 sheets, and this is increased to 1.2 as a limit.
As a result, it becomes possible to perform correction even with respect to the density and line width variation that change due to the above-described selective development.
The unit of the number of prints for correction is 100.
The number is not limited to 0, and the coefficient to be multiplied is not limited to the above value.

Next, a third embodiment of the image forming apparatus according to the present invention will be described.

FIG. 12 is a schematic sectional view showing the structure of an image forming apparatus according to the third embodiment of the present invention, and FIG. 13 shows the sequence of developing bias at the paper interval and at the end of printing. First, the operation of the electrophotographic image forming apparatus of this embodiment will be described with reference to FIG.

The photosensitive drum 51 rotating in the direction of arrow A in the figure is uniformly charged by the charging member 52. After that, an electrostatic latent image is formed on the surface of the photosensitive drum 51 by an image signal 60 from a light source such as a laser or an LED, and the electrostatic latent image is formed at a developing position facing the developing sleeve 53 which is a developer carrier. When it comes, it is developed. Then, the developed visible image (toner image) is transferred to the transfer material 61 by the transfer member (roller) 54. Transfer material 61
Is conveyed to the transfer nip portion between the transfer member 54 and the photosensitive drum 51 along the paper guide 56 at a timing with the toner image on the photosensitive drum. After the toner image is transferred to the transfer material 61, the transfer material 61
Is separated from the surface of the photosensitive drum, passes through a fixing device 58 including a fixing roller and a pressure roller along a paper guide 57, and the toner image is fixed and fixed and is discharged to the outside of the apparatus.
On the other hand, the toner remaining on the photosensitive drum 51 is removed by the cleaning member 59, and the same process is repeated again.

In this embodiment, the photosensitive drum 51 is 37.
It rotates at a speed of 7 mm / sec, and a charging roller is used as the charging member 52 to cover the surface of the photosensitive drum 51 by about 6 mm.
It is charged to 00V. Further, the image signal 60 uses a laser to form an electrostatic latent image on the surface of the photosensitive drum. Regarding the potential on the photosensitive drum, the potential V _D (dark potential) of the charged portion which is not irradiated with laser is −590 to −60.
0 V, and the potential _VL (bright potential) of the laser-irradiated portion is -135 to -140 V.

In the developing process, the bias source 62 is used.
From the developing sleeve 53, a developing bias in which an AC voltage and a DC voltage are superimposed is applied, but the AC component has a frequency of 1.8K.
A rectangular wave having a frequency of Hz, peak-peak voltage V _PP = 1.6 KV and a duty ratio of 50% is used, and the DC component is set to -470V. The relationship between the developing bias, the surface potential of the developing sleeve 53, and the potentials of the image portion and the non-image portion on the photosensitive drum 51 is as shown in FIG.

As described above, by applying the developing bias having the AC component from the bias source 62 to form the alternating electric field between the photosensitive drum 51 and the developing sleeve 53,
As shown in FIGS. 14 and 15, the toner reciprocates between the photosensitive drum 51 and the developing sleeve 53, and finally adheres to the image portion (electrostatic latent image) to be developed.

Here, when the normal negative polarity toner is used and the AC component of the developing bias is suddenly turned off in the bias state of the hatched portion A in FIG. 13, the developing sleeve 53
-600V of potential has become a -1270V, the potential on the photosensitive drum 51 which faces this dark potential (V _D)
Therefore, the negatively charged toner is attracted toward the photosensitive drum 51, which has a relatively positive potential.
Since it becomes as shown in 4, it becomes a fogging. Next, FIG.
Similarly, when the AC component of the developing bias is suddenly turned off in the bias state of the shaded portion B, the normal toner is pulled back to the developing sleeve 53 as shown in FIG. However, since the toner particles also have positive polarity (reversed toner) due to charging of the toner particles, the reversal toner has a negative potential with respect to the potential + 330V of the developing sleeve 53. It is attracted toward the body drum 51, and becomes a reverse fog like a normal fog.

Therefore, it is proposed that the AC component of the developing bias is not turned off rapidly but is attenuated to gradually reduce the amount of toner that reciprocates between the developing sleeve 53 and the photosensitive drum 51. There is such a problem.

FIG. 16 shows a waveform of an AC bias that decays after the conventional developing bias is turned off, and it appears particularly when a low-cost high-voltage transformer is used as the bias source 62. The potential indicated by the dotted line in the figure is the developing bias potential (alternating electric field forming potential) considered to be the minimum required to contribute to the development, and is the photosensitive drum potential (dark potential −600 V) ± T (T chopstick). Threshold level). As shown in the figure, among the bias components that pull the toner back toward the developing sleeve 53, the bias component of L _n−1 , which is one level before the final bias component L _n , which is a level above −600 + T, is indicated by a dotted line. Since it is smaller than the threshold value level T, the toner that has jumped from the developing sleeve 53 to the photosensitive drum 51 immediately before that by the reverse bias component L _m cannot be returned to the developing sleeve 53 again. In addition, the bias component L _n-1 in the opposite direction after the bias component L _{n-1
Since m + 1} is smaller than the threshold level T, the toner does not fly to the photoconductor drum 51, but since L _m > L _{n, the} bias component of the toner that has flown to the photoconductor drum 51 with the bias component L _m. The toner that has not been pulled back to the developing sleeve 53 by L _n−1 cannot be pulled back to the developing sleeve 53 by the bias component L _n , resulting in fog.

[0064] In this embodiment, as shown in FIG. 17, the bias component L _n-1 of the previous bias component L _n larger than the threshold level T, the photosensitive drum in the reverse direction of the bias component L _m The toner that has flown to 51 is bias components L _n-1 and L
It is arranged such that it is pulled back to the developing sleeve 53 again at _n . Here, since the reverse bias component L _{m + 1} between the bias components L _n-1 and L _n is less than the threshold level T, the toner does not fly from the developing sleeve 53 to the photosensitive drum 51, Further, after the bias component L _{m + 2,} the alternating electric field is weakened, and the amount of toner that reciprocates between the developing sleeve and the photosensitive drum is reduced to a negligible amount, so that fog does not occur. Therefore, a low-cost transformer can be used as the bias source 62.

The above can be said not only for the normal negatively charged toner but also for the reverse toner charged with the opposite polarity. In that case, the normal toner may be blown from the developing sleeve to the photosensitive drum. Since the bias component becomes a bias component that pulls the reverse toner from the photosensitive drum back to the developing sleeve, the explanation will be given with reference to FIG. 17, and the component corresponding to the bias component L _n becomes L _m (the last which is _equal to or higher than the threshold level T). If the bias component L _m-1 immediately before the bias component L _m-1 is equal to or higher than the threshold level T, the reversal toner that has flown from the developing sleeve to the photosensitive drum by the bias component L _n-3 is returned to the developing sleeve. Since it can be pulled back, reversal fogging can be prevented. Therefore, it is possible to prevent the transfer unevenness due to the transfer charger dirt and the backside dirt of the transfer material.

Although the present invention is applied to the image forming apparatus using the roller transfer in the third embodiment, the present invention is also applicable to the image forming apparatus using the corona transfer which is more commonly used. The invention is applicable. Next, a fourth embodiment in which the present invention is applied to an image forming apparatus using corona transfer will be described.

FIG. 18 shows a schematic structure of a fourth embodiment of the present invention. A corona charger 71 is used as a charging member, a corona transfer device 72 is used as a transfer member, and a transfer material 61 is used as a transfer area. The structure is the same as that of the image forming apparatus of the third embodiment shown in FIG. 12 except that the feeding roller 73 is provided. Is omitted.

Also in this embodiment, as in the third embodiment, when the developing bias is turned off, an alternating electric field is formed between the photosensitive drum 51 and the developing sleeve 53 as shown in FIG. Of the AC components of the developing bias, the bias before the final bias component L _n , which is a bias component that pulls the toner back from the photosensitive drum 51 to the developing sleeve 53 and is a level (threshold level T) or more that can contribute to the development. The component L _{n-1 is} also set to a threshold level T or higher to prevent fogging. By preventing the fog, it is possible to prevent the transfer guide member from being smeared by the fog toner and the transfer charger from being smeared. Further, the backside of the transfer material, the transfer unevenness due to the smearing of the transfer charger, and the transfer loss can be prevented.

In the third and fourth embodiments, the case where the rectangular wave is used as the AC component of the developing bias has been described, but the same effect can be obtained by using the sine wave or the triangular wave. For example, when a sine wave is used as the AC component, the AC bias is simply attenuated to obtain the result shown in FIG. 19. A bias for returning the toner from the photosensitive drum to the developing sleeve during the attenuation after the AC bias is turned off. Of the components, the level that contributes to development (threshold level T)
Bias component L before the last bias component L _n above
_{Since n-1} becomes less than the threshold level T, fogging occurs due to the above reason. Therefore, in this case as well, as shown in FIG. 20, the bias component L _n before the last bias component L _n is
_n-1 is made larger than the threshold level T. As a result, the toner flying from the developing sleeve to the photosensitive drum by the bias component L _m in the reverse direction is applied to the bias component L _n-1.
And L _n can be pulled back onto the developing sleeve again, so that fogging can be prevented. Bias component L
_{After m + 1,} the alternating electric field also weakens, and the amount of toner that flies to the photoconductor drum also becomes very small, so there is no fog. In each of the above embodiments, the developing method may be either reversal development or normal development. The point is that while the alternating electric field between the developing sleeve and the photosensitive drum is turned off and then attenuated, as shown in FIG. As shown, of the electric field components that pull the toner back from the developing sleeve to the photosensitive drum, the component before the final component that is equal to or higher than the threshold level that contributes to the development may be the threshold level or higher. With this configuration, the toner flying from the developing sleeve toward the photosensitive drum can be sufficiently pulled back, and the fog toner does not adhere to the photosensitive drum.

In each of the above-described embodiments, the case where the present invention is applied to the electrophotographic image forming apparatus has been described.
It is needless to say that the present invention can be applied to an image forming apparatus of another type such as an electrostatic recording type and the same operational effect can be expected.

[0071]

As described above, according to the image forming apparatus of the present invention, the bias applied to the developer carrying member is changed according to the rising time of the fixing device and the number of printed sheets. It is possible to reliably correct the changes in the image density and the line width at the rising edge of, and therefore it is possible to always output an image having a stable image density and line width.

Further, according to the image forming apparatus of the present invention, based on the light emission time of the light irradiated by the latent image forming means,
Since the developer consumption amount is sequentially integrated and the bias applied to the developer carrier is changed according to the integrated value, the developer per unit number of sheets is changed by changing the size of the recording material or the print pattern. Even if the consumption amount changes, it can be corrected with certainty, and therefore, it is possible to always output an image with stable image density and line width.

Further, according to the image forming apparatus of the present invention,
Of the components of the alternating electric field that pull back the developer from the image carrier to the developer carrier while the alternating electric field between the developer carrier and the image carrier is turned off and then attenuated, the final level that is equal to or higher than the level that contributes to the development. Since the component in the same direction, which is one before the component, is set to a level that contributes to this development or more, the fog that flies from the developer carrying member to the image carrying member can pull back the developer to the developer carrying member again, and the fog Can be prevented. Thus, by using a low-cost high-voltage transformer, fogging can be prevented even if the alternating electric field between the developer bearing member and the image bearing member is not attenuated smoothly. Further, there is an effect that the transfer guide guide can be prevented from becoming dirty and the device can be manufactured at low cost. In addition, even when a transfer roller or the like is used, it is possible to prevent the fog developer from adhering to the transfer roller, and the back stain of the transfer material is eliminated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a main part of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a graph showing the number of printed sheets versus line width characteristics in a conventional electrophotographic image forming apparatus.

FIG. 3 is a graph showing development contrast vs. line width characteristics in an electrophotographic image forming apparatus.

FIG. 4 is a graph showing the number of printed sheets versus line width characteristics in the image forming apparatus of the first embodiment of the present invention.

FIG. 5 is a flowchart illustrating a control operation of the image forming apparatus according to the first embodiment of this invention.

FIG. 6 is a schematic configuration diagram showing a main part of a second embodiment of the image forming apparatus according to the present invention.

FIG. 7 is a graph showing a sheet width versus line width characteristic for explaining that a rise in line width is different due to a difference in print pattern.

FIG. 8 is a graph showing the number of passed sheets versus line width characteristics when the print pattern is changed in the image forming apparatus of the second embodiment of the present invention.

FIG. 9 is a laser emission characteristic diagram.

FIG. 10 is an explanatory diagram showing a relationship between a laser emission time and a consumed toner amount.

FIG. 11 is a flowchart illustrating a control operation of the image forming apparatus according to the second embodiment of the present invention.

FIG. 12 is a schematic cross-sectional view showing a configuration of a main part of a third embodiment of the image forming apparatus according to the present invention.

FIG. 13 is a waveform diagram for explaining a developing bias used in the third embodiment of the present invention.

FIG. 14 is an explanatory diagram showing the behavior of toner according to the phase of the AC component of the developing bias.

FIG. 15 is an explanatory diagram showing the behavior of toner according to the phase of the AC component of the developing bias.

FIG. 16 is a diagram showing a conventional decay waveform of an AC component when the AC component of the rectangular wave of the developing bias is turned off.

FIG. 17 is a diagram showing an attenuation waveform when the AC component of the rectangular wave of the developing bias is turned off in the third embodiment of the present invention.

FIG. 18 is a schematic cross-sectional view showing the configuration of the main parts of a fourth embodiment of the image forming apparatus according to the present invention.

FIG. 19 is a diagram showing a conventional attenuation waveform of an AC component when the AC component of the sine wave of the developing bias is turned off.

FIG. 20 is a diagram showing an attenuation waveform when the AC component of the sine wave of the developing bias is turned off in the image forming apparatus embodying the present invention.

[Explanation of symbols]

1 external equipment 2 interface 3 CPU 4 laser driver 5 semiconductor laser 9 photosensitive drum 11 developing device 14 developing sleeve 16 recording material 30 laser emission time vs. toner consumption calculating means 51 photosensitive drum 52 charging member 53 developing sleeve 54 transfer member 60 image signal 61 transfer material 62 bias source

Front Page Continuation (72) Inventor Hiroki Kisu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (5)

[Claims] 1. A latent image forming means for irradiating an image carrier with a light beam based on an image signal corresponding to image information to form an electrostatic latent image on the image carrier, and a surface of a developer carrier. A thin layer of a developer is formed on the surface of the image carrier, and a bias potential is applied to the developer carrier to transfer the developer carried on the surface of the developer carrier to the surface of the image carrier. A developing device that visualizes the electrostatic latent image formed on the image forming device, and a time measuring unit that measures the waiting time of the fixing device, and when the measured waiting time of the fixing device is longer than a certain reference time, An image forming apparatus, wherein the bias potential applied to the developer carrying member is changed according to the number of printed sheets. 2. The image forming apparatus according to claim 1, wherein the bias potential applied to the developer carrying member is changed according to an integrated value of numerical values corresponding to the size of the recording material for each print. 3. A latent image forming means for irradiating a light beam on the image carrier based on an image signal corresponding to image information to form an electrostatic latent image on the image carrier, and a surface of the developer carrier. A thin layer of a developer is formed on the surface of the image carrier, and a bias potential is applied to the developer carrier to transfer the developer carried on the surface of the developer carrier to the surface of the image carrier. A developing device that visualizes the electrostatic latent image formed on the image forming device, and the amount of developer consumed versus the amount of light emitting time calculated and calculated based on the light emission time of the light irradiated by the latent image forming means, and the calculated consumption An image forming apparatus, comprising: a unit for sequentially accumulating and storing a developer amount, and changing a bias potential applied to the developer carrier according to the accumulated value of the consumed developer amount. 4. The light emitting time of the light irradiated by the latent image forming means when the timed waiting time of the fixing device is longer than a reference time when the timed waiting time of the fixing device is longer than the reference time. Development bias control for calculating and calculating the amount of consumed developer based on the light emission time, sequentially accumulating the calculated amount of consumed developer, and changing the bias potential applied to the developer carrier according to the integrated value. The image forming apparatus according to claim 3, wherein the image forming apparatus executes. 5. An electrostatic latent image is formed on the image bearing member by irradiating a light beam onto the charged image bearing member based on an image signal corresponding to image information, In an image forming apparatus, an alternating electric field is formed between an image carrier and a developer carrier to transfer the developer carried on the developer carrier to the image carrier to visualize the image, Of the component of the alternating electric field that acts to attenuate the alternating electric field with a predetermined time constant and pull back the developer from the image carrier to the developer carrier, the threshold level or more that contributes to development The level of the component immediately before the final component that is
An image forming apparatus having a threshold level or higher.