JP2001134066A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that a good image is output even under a condition that a carrier phenomenon is easily generated. SOLUTION: Relating to the image forming device provided with a developer carrier carrying a two-component developer while rotational speed and applied voltage are controlled and a photoreceptor forming a toner image using toner fed from the developer carrier while surface potential is controlled, it is characterized by that at least one of the rotational speed of the developer carrier, a DC component of the applied voltage or the surface potential of the photoreceptor is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for forming an image by electrophotography, and more particularly to control of development conditions.

[0002]

2. Description of the Related Art As an image forming method for forming an image by electrophotography, an image forming method of converting an electric signal into light using a laser light source or a light emitting diode light source, exposing a photoreceptor to form an image, That is, a so-called digital image forming method has become widespread, and a digital copying machine employing this digital image forming method has become widespread. In the developing step in the digital image forming method, a reversal developing method of developing an electrostatic latent image using toner having the same polarity as the charging polarity of the photoconductor is generally used.

In the reversal developing method using a two-component developer, the polarity of the charge of the photosensitive member is opposite to the polarity of the carrier which is a component of the developer, and a developing bias is applied to the developer carrier of the developing means. Otherwise, an undesirable phenomenon occurs in which the carrier is electrostatically attracted to the charged area of the photoconductor and adheres to the photoconductor. Conventionally, in order to prevent this phenomenon, a bias voltage for attracting carriers to the developer carrier, that is, a developing bias is applied to the developer carrier during a period in which the charged portion of the photoconductor passes. .

Usually, the value of the developing bias is set to a value slightly lower than the highest potential value of the photoconductor surface potential. With such a value of the developing bias, the portion of the electrostatic latent image having the highest potential value, that is, the toner does not adhere to the unexposed portion, and the portion of the electrostatic latent image having a value lower than the developing bias, that is, The toner is prevented from adhering to the exposed portion and the carrier is prevented from adhering to the photoreceptor, so that good reversal development is performed.

[0005]

However, in some cases, carrier development occurs in which the carrier adheres to the photoreceptor. When the carrier development occurs, the carrier C having a larger particle diameter than the toner becomes the toner T developed on the photoreceptor surface Ph and the recording material, as shown in the schematic diagram of FIG. The contact with S1 is hindered, resulting in a kind of transfer failure. Such a transfer failure can confirm the output image with the naked eye, and adversely affects the image quality.

First, the mechanism of carrier development will be briefly described. When the toner attached to the carrier is developed and moves to the photoconductor, for example, in the case of a reversal developing method using a two-component developer with a positively charged carrier and a negatively charged toner, a positive charge is generated in the carrier and the developer is A current flows between the carrier and the carrier, and the current causes a reverse charge (counter charge) in which the carrier is negatively charged. Then, similarly to the case where the negatively charged toner moves from the developer carrying member to the photoreceptor under the developing electric field, the carrier having the counter charge easily moves from the developer carrying member to the photoreceptor. In the case of a magnetic carrier, carrier development occurs when the electrostatic force received by the carrier from the developing electric field exceeds the magnetic restraining force (adhering the carrier to the developer carrying member).

FIG. 8 schematically illustrates carrier development, so that the dimensional ratio and shape of the carrier C and the toner T may be different from the actual case, and the cross section of the photoconductor surface is not a curved surface. It is shown in a plane cross section.

Next, conditions under which carrier development easily occurs will be briefly described. (1) A case where most of the toner attached to one carrier moves to the photoconductor by development.

For example, when a large amount of negatively charged toner is electrostatically adsorbed on a positively charged carrier and a large amount of the toner moves to the photosensitive member, such a carrier is easily reversely charged. Then, carrier development occurs.

(2) The carrier surface is provided with a coat layer having a high insulating property. However, when the carrier is used for a long period of time, the coat layer is peeled off, the insulating property is lost, the resistance of the developer is reduced, and a current is supplied to the carrier. , The reverse charge is likely to occur, and carrier development is likely to occur.

(3) Under a high humidity environment, the resistance of the developer decreases, and the current easily flows to the carrier.
Reverse charging easily occurs and carrier development easily occurs.

(4) When the developing device is continuously driven, for example, when a large amount of copying is performed, the charge amount per unit weight (Q / M level) of the toner changes according to the continuous driving time. If the Q / M level changes, as in (1), the carrier is easily reversely charged, and carrier development occurs.

(5) When the developing device is continuously driven, for example, when a large amount of copying is performed, the ambient temperature of the developer increases, and the fluidity of the developer deteriorates. When the fluidity of the developer deteriorates, it becomes difficult to replace the developer between the position of the developer carrier and the position where the triboelectric charging is performed, and the toner concentration at the position of the developer carrier decreases, and Development tends to occur.

Accordingly, it is a first object of the present invention to provide an image forming apparatus which can output a good image even under conditions where carrier development is likely to occur.

Further, when a recording material having a higher rigidity than paper, such as an OHT medium or a gloss sheet, is used, there is a problem that an area where transfer failure occurs when carrier development occurs increases. For example, when the OHT sheet OHT is used, compared with the case where the recording paper P is used as the recording material,
As shown in FIG. 9, the carrier C attached to the photoconductor Ph inhibits the contact between the OHT sheet OHT and the toner T over a wide area. Area B indicates an area inhibited by the OHT sheet OHT, and area A indicates an area inhibited by the recording paper P. In the hindered range, the toner T is difficult to be transferred, so that a circular image defect occurs.

FIG. 9 is a schematic diagram for schematically explaining the difference between the effect of the recording paper and the recording material having higher rigidity than the recording paper when carrier development occurs. Range differences may be different from the real world.

Accordingly, a second object of the present invention is to suppress the range in which image defects are affected even when using a highly rigid recording material in which image defects are likely to occur in a wide range under conditions in which carrier development has occurred. And

[0018]

SUMMARY OF THE INVENTION A first object of the present invention is to provide:
The problem can be solved by the image forming apparatus according to the first, second, fourth, fifth, or sixth aspect. That is, the image forming apparatus according to claim 1,
A developer carrier that controls the rotation speed and the applied voltage to carry the two-component developer, and a photoconductor that controls the surface potential and forms a toner image with the toner supplied from the developer carrier. In the image forming apparatus, at least one of the rotation speed of the developer carrier, the DC component of the applied voltage, and the surface potential of the photoconductor is changed.

According to the image forming apparatus of the first aspect,
A good image can be output even under conditions where carrier development is likely to occur.

Further, in the image forming apparatus according to the second aspect of the present invention, the rotational speed and the applied voltage are controlled to carry the two-component developer, and the surface potential is controlled so that the developer carrying is controlled. An image forming apparatus including a photosensitive member that forms a toner image with toner supplied from a body, wherein the developer carrier of the developer carrier is determined according to an output value of a humidity sensor that detects an atmospheric humidity of the two-component developer. At least one of a rotation speed, a DC component of the applied voltage, and the surface potential of the photoconductor is changed.

According to the image forming apparatus of the second aspect,
A good image can be output even under conditions in which carrier development is likely to occur due to changes in the atmospheric humidity.

According to a fourth aspect of the present invention, there is provided the image forming apparatus, wherein the rotation speed and the applied voltage are controlled to carry a two-component developer, and the surface potential is controlled to provide the developer carrier. And a photoreceptor that forms a toner image with the toner supplied from the image forming apparatus, the developer carrier of the developer carrier is detected in accordance with an output value of a toner density sensor that detects a toner density contained in the two-component developer. It is characterized in that the rotation speed is changed.

According to the image forming apparatus of the fourth aspect,
It is possible to output a good image even under conditions where the toner density changes and carrier development is likely to occur.

According to a fifth aspect of the present invention, there is provided the image forming apparatus, wherein the rotation speed and the applied voltage are controlled to carry a two-component developer, and the surface potential is controlled to control the developer carrier. And a photoreceptor that forms a toner image with the toner supplied from the image forming apparatus, the developer carrier of the developer carrier is stored in accordance with a cumulative driving time stored as a cumulative driving time of the developer carrier. It is characterized by changing the rotation speed.

According to the image forming apparatus of the fifth aspect,
A good image can be output even under conditions where the cumulative driving time is prolonged and carrier development is likely to occur.

According to a sixth aspect of the present invention, there is provided the image forming apparatus, wherein the rotation speed and the applied voltage are controlled to carry the two-component developer, and the surface potential is controlled so that the developer is carried. An image forming apparatus comprising: a photosensitive member that forms a toner image with toner supplied from a body; an output value of a toner concentration sensor that detects a toner concentration contained in the two-component developer; and an atmosphere of the two-component developer. The rotation speed of the developer carrier, the DC component of the applied voltage, and the DC voltage of the photoconductor according to at least two of the output value of the humidity sensor that detects humidity and the cumulative driving time of the developer carrier. It is characterized in that at least one of the surface potentials is changed.

According to the image forming apparatus of the sixth aspect,
A good image can be output even under conditions where carrier development is likely to occur due to changes in toner concentration, atmospheric humidity, cumulative driving time, and the like.

Further, a second object of the present invention is to provide a seventh aspect of the present invention.
The problem can be solved by the image forming apparatus described in 3 or 14. That is, the image forming apparatus according to claim 7, wherein the rotation speed and the applied voltage are controlled to supply the two-component developer, and the surface potential is controlled to be supplied from the developer carrier. An image forming apparatus comprising: a photosensitive member that forms a toner image with the toner; and changing at least one of the rotation speed of the developer carrier, the DC component of the applied voltage, and the surface potential of the photosensitive member. And a mode switching unit for switching to a special mode for forming an image.

According to the image forming apparatus of the present invention,
Under conditions in which carrier development has occurred, it has become possible to suppress the range affected by image defects even when using a highly rigid recording material in which image defects are likely to occur over a wide range.

The image forming apparatus according to claim 13 is
A developing device having a developer carrier that controls the rotation speed and the applied voltage to carry the two-component developer, and a toner charging unit that charges toner contained in the two-component developer; and a surface potential is controlled. And a photoreceptor that forms a toner image with the toner supplied from the developer carrying member, wherein the rotation speed of the developer carrying member is changed according to a continuous operation time of the toner charging unit. , And at least one of a DC component of the applied voltage and the surface potential of the photoreceptor is changed.

According to the image forming apparatus of the thirteenth aspect, under the condition that the carrier development has occurred, even if a highly rigid recording material in which the image defect is apt to occur in a wide range is used, the range in which the image defect is affected is reduced. It became possible to control.

Further, the image forming apparatus according to claim 14 is
A developer carrying member that controls the rotation speed and the applied voltage to carry the two-component developer, a developing device including: a toner charging unit that charges toner contained in the two-component developer; and the developer carrying member. An image forming apparatus comprising: a photosensitive member whose surface potential is controlled to form a toner image with the toner supplied from the developer carrier; and an output of a humidity sensor for detecting an atmospheric humidity of the two-component developer. And changing at least one of the rotation speed of the developer carrier, a DC component of the applied voltage, and the surface potential of the photoconductor in accordance with a value and a continuous operation time of the toner charging unit. And

According to the image forming apparatus of the present invention, under the condition in which the carrier development occurs, the range in which the image defect affects the image defect even when a highly rigid recording material in which the image defect easily occurs in a wide range is used. It became possible to control.

[0034]

FIG. 1 is a front sectional view showing the structure of an image forming apparatus according to an embodiment of the present invention.

In FIG. 1, the image forming apparatus main body A includes an image forming section 1, an image processing section 2, an image writing section 3, a high voltage power supply section 4, a sheet feeding and conveying section 5, a fixing device 6, a sheet discharging section 7, A re-conveying unit (ADU) 8 for duplex copying is provided.

A scanner SC and an automatic document feeder DF are mounted on the upper part of the image forming apparatus main body A. A paper discharge tray 7C is provided on the upper left side of the paper discharge unit 7 of the image forming apparatus main body A, and a paper post-processing device (not shown) can be connected thereto.

Document d supplied from automatic document feeder DF
Is photoelectrically converted by the CCD image sensor C1 provided in the scanner unit SC.

The analog signal photoelectrically converted by the CCD image sensor C1 is sent to the image writing section 3 as a digital signal which has been subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the image processing section 2. Can be

In the image writing section 3, output light from the semiconductor laser is applied to the photosensitive drum 10 of the image forming section 1 to form a latent image. In the image forming section 1, before the formation of the latent image, charging and exposure processes are performed, and subsequent to the formation of the latent image, processes such as development, transfer, separation, and cleaning are performed. The image is transferred to the recording paper S transported from the printer or the OHT sheet transported from the manual paper feed unit 5A. As the recording paper S passes through the fixing device 6, the toner image is fixed, and the recording paper S is discharged from the paper discharge unit 7 to the paper discharge tray 7C. Alternatively, the single-sided image-processed recording sheet S sent to the re-conveying unit 8 by the sheet discharge path switching plate 7A is subjected to double-sided image processing again in the image forming unit 1, and then discharged by the sheet discharging rollers 7B of the sheet discharging unit 7. The sheet is discharged to the paper tray 7C.

FIG. 2 is a partial cross-sectional view of the image forming section 1 and its peripheral portion in the image forming apparatus according to the embodiment of the present invention.

In FIG. 2, reference numeral 10 denotes a photosensitive drum, and a belt-shaped photosensitive member may be used in addition to the illustrated drum-shaped photosensitive member. In the present embodiment, an organic photoconductor (OP) in which an organic photoconductive layer is formed on a conductive substrate is used.
C photoreceptor) is used, but an a-Si photoreceptor having an a-Si layer formed on a conductive substrate may be used. Further, in the embodiment, a negatively chargeable organic photoreceptor is used,
Either a positively chargeable or negatively chargeable photoconductor may be used.

The charging means 12 includes a corona discharge wire 12a
And a grid electrode 12b, and a scorotron charger for controlling the photoconductor surface potential by a bias voltage (hereinafter referred to as a grid voltage) applied to the grid electrode 12b is used.

As the charging means 12, besides the scorotron charger, a corotron charger, a brush charger, a magnetic brush charger, a roller charger and the like can be used. For an organic photoreceptor, a scorotron charger is desirable. As the scorotron charger and the discharge electrode of the corotron charger, a saw-tooth electrode, a pin electrode, and the like can be used in addition to the corona discharge wire 12a. The charging unit 12 of the present embodiment is a negative charging unit that charges the photosensitive drum 10 to a negative electrode.

The image writing unit 3 is an example of an exposure unit that scans and exposes the photosensitive drum 10 with dot light. In the present embodiment, a semiconductor laser, a collimator, a rotating polygon mirror, fθ
A scanning exposure unit that includes a lens, a cylindrical lens, and the like, and that performs main scanning in the rotation axis direction of the photosensitive drum 10 using dot light is used.

As the image writing section 3, an apparatus using a light emitting diode array as a light source can be used. As an exposing means using the light emitting diode array as a light source, the image writing section 3 is linearly arranged in the rotation axis direction of the photosensitive drum 10. Scanning exposure means including an LED array and a condenser lens is used.

The developing means 14 is a developing means for performing reversal development using a two-component developer containing a toner and a carrier. The developing means 14 serves as a developer carrier for transporting a developer containing a negatively charged toner and a positively charged carrier to a development area. , A screw 47a, 47b for stirring the two-component developer to charge the toner by frictional charging, and an impeller 47c for supplying the stirred two-component developer to the developing sleeve 41.
The screws 47a and 47b are an example of the toner charging unit of the present invention, and are friction charging units having an action of stirring and frictionally charging the toner and the carrier in the two-component developer.

The transfer electrode 15 is a discharge electrode for transferring the toner image on the photosensitive drum 10 to the recording paper S. Separation electrode 1
Reference numeral 6 denotes a discharge electrode for separating the recording paper S from the photoconductor. The separating claw 17 is a unit for measuring the separation of the recording sheet S that has not been separated from the photosensitive drum 10 by the action of the separating electrode 16, and constitutes a separating unit together with the separating electrode 16. Reference numeral 6 denotes a fixing device for thermally fixing the toner image on the recording paper S by a built-in heater, and reference numeral 20 denotes a cleaning device for cleaning residual toner on the photoconductor.

The photosensitive drum 10 rotates in the direction indicated by the arrow, and an electrostatic latent image is formed on the photosensitive drum 10 by charging by the charging means 12 and exposure by the image writing unit 3 according to the rotation of the photosensitive drum 10. Is done. The formed electrostatic latent image is developed by the developing means 14 to form a toner image on the photosensitive drum 10. The toner image on the photoreceptor drum 10 is supplied from the paper feeder 5 and is transferred onto the recording paper S conveyed at a timing adjusted by the registration rollers 5B. The recording paper S to which the toner image has been transferred is separated from the photosensitive drum 10 by a separating unit, and is subjected to a fixing process by the fixing device 6. The photosensitive drum 10 that has passed the transfer position is cleaned by the cleaning device 20.

FIG. 3 is a front sectional view of the toner supply device 60 and the toner replenisher 40. The toner supply device 60 conveys the new toner in the toner bottle 61, and
From the toner supply unit 40.

The toner bottle 61 is a resin-made toner container which is detachable by a user's operation. In the case of newly replenishing the toner, when the user mounts the toner bottle 61 filled with the new toner at a predetermined position of the toner supply device 60, the new toner is automatically replenished. The toner container for supplying the new toner is not limited to the bottle shape, and various shapes can be used.

The toner replenishing device 40 includes the cleaning device 2
0 (see FIG. 2) and a toner recycle unit that mixes, agitates, and transports the new toner supplied from the toner supply device 60 to the developing unit 14. The toner replenisher 40 includes a first casing 43 and a second casing 43.
The toner hopper includes a casing 42, an agitating / conveying unit including a first conveying member 44, a second conveying member 45, and a third conveying member 46, and a remaining toner detection sensor 143.

The rotating shaft 48 to which the first transport member 44 and the second transport member 45 are fixed is driven and rotated by a driving means (not shown) to transport the toner inside the first casing 43 leftward in the figure.

The first conveying member 44 has a spiral screw shape having a predetermined helical angle with respect to the center line of the rotating shaft 48, and mainly conveys collected toner carried out from the cleaning device 20 in the direction of the rotating shaft.

The second conveying member 45 is formed by a plurality of elliptical plates having a predetermined inclination angle with respect to the center line of the rotating shaft 48, and is mainly collected by the new toner supplied from the toner supply device 60 and the cleaning device 20. Stir and transport with toner. The plurality of elliptical plates have a shape in which about half is cut out, and have good stirring properties.

An opening 43A is formed near the right end of the first casing 43 in the drawing. Cleaning device 20
Is fed into the toner replenisher 40 through the opening 43A and is conveyed leftward in the figure.

The new toner supplied from the toner supply device 60 falls from the opening 43 B, and is mixed with the recovered toner in the first casing 43 while rotating the second transport member 45.
Through the opening 50A and the second casing 42
Sent inside.

The third transport member 46 comprises a rotating shaft 46A and a spiral screw 46B. The rotation shaft 46A is
It is driven and rotated by a driving unit (not shown), and conveys the toner inside the second casing 42 rightward in the figure.

The toner dropped from the opening 50A travels rightward in the figure by the rotating third conveying member 46,
It is discharged from a discharge port 42A at the bottom of the second casing 42,
It is sent into the developing means 14.

FIG. 4 is a control block diagram showing an electrical configuration of the image forming apparatus according to the embodiment of the present invention.

The semiconductor laser 31 included in the image writing section 3 (see FIG. 2) emits light at an intensity corresponding to the laser drive current, and forms an electrostatic latent image on the charged photosensitive drum 10.
The modulation circuit 32 outputs a light emission signal for controlling the light emission timing of the semiconductor laser 31 to the laser output control circuit 33 by pulse width modulation of the digital signal output from the image processing unit 2. The laser output control circuit 33 compares the voltage obtained by detecting the light output of the semiconductor laser 31 with a reference voltage, and controls the current value of the laser drive current by automatic light output control for keeping the light output constant, that is, APC control. Then, the drive current whose current value is controlled is supplied to the semiconductor laser 31 at the timing of the light emission signal. Here, the light output is controlled to be constant by the APC control, but this does not mean that the light output is fixed to a single intensity, but can be controlled to an arbitrary intensity.
This means that a stable light output can be obtained at the selected intensity.

The surface potential control circuit 121 is a circuit for controlling a grid voltage applied to the grid electrode 12b in accordance with a command from the main CPU 30, which is a main control means. A technique of controlling the grid voltage to prevent unevenness of the surface potential of the photoreceptor surface and insulation breakdown is well known, and is actively employed in a photoreceptor using negatively charged OPC.

If the surface potential of the photosensitive member is high, the toner tends to be easily separated from the carrier if other conditions are the same. Therefore, control for lowering the surface potential is performed to avoid carrier development.

In the embodiment, since the scorotron charger is used as the charging electrode, the grid voltage is controlled to control the surface potential of the photosensitive drum 10, and it depends on the type of the charger. It is desirable to employ a surface potential.

The developing bias control circuit 140 includes a main CPU
This is a circuit for controlling the voltage of the developing bias applied to the developing sleeve 41 in accordance with the command of 30. When the voltage value of the DC component of the developing bias is high, the toner tends to separate from the carrier if other conditions are the same. Therefore, in order to avoid carrier development, control is performed to lower the voltage value of the DC component of the developing bias.

The developing device drive motor 14M is a stepping motor whose rotation speed is controlled by the rotation speed control circuit 141. The developing sleeve 41 is a drive transmission system (not shown)
, And is rotated at a rotation speed corresponding to the rotation speed of the development device drive motor 14M. The rotation speed control circuit 141 has a main CP
This is a circuit for controlling the rotation speed of the developing device drive motor 14M according to a command from U30. If the rotation speed of the developing sleeve 41 is low, the toner tends to be easily separated from the carrier if other conditions are the same. Therefore, in order to avoid carrier development, control for increasing the rotation speed of the developing sleeve 41 is performed.

The humidity sensor 151 is a humidity detecting means for detecting the atmospheric humidity of the developer inside the developing device, and is installed in the developing device. The humidity sensor 151 is the image forming unit 1
It is recommended to install in a location that can detect the same level of humidity as the developer atmosphere, such as the inside of the developer unit, the inside of the toner hopper, the toner recycling path, etc. More preferred.

The humidity sensor 15 that can be used in the present invention
As a specific example, a humidity sensor 151 generally used in the industry can be used. For example, a dew point hygrometer, an electric resistance type hygrometer, a thermal conductivity type hygrometer, or the like is used as a measurement medium. Sensors can be mentioned.

The temperature sensor 152 is a temperature detecting means for detecting the ambient temperature of the developer inside the developing device, and is installed in the developing device. The temperature sensor 152 is the image forming unit 1
It is recommended to install in a location that can detect the same level of humidity as the developer atmosphere, such as the inside of the developer unit, the inside of the toner hopper, the toner recycling path, etc. More preferred.

The temperature sensor 15 that can be used in the present invention
As a specific example of (2), a temperature sensor commonly used in the relevant industry can be used.
C temperature sensor, infrared sensor, and the like.

The toner density sensor 142 includes a coil unit for detecting a change in the magnetic permeability of the developer to detect a change in the toner density, and is a toner density detecting means for outputting a detection signal corresponding to the toner density. . In general, the magnetic permeability of a developer depends on the density of a magnetic material in the developer, and when the concentration of the toner is high, the concentration of the carrier, which is a magnetic material, decreases, and the magnetic permeability decreases. The image forming apparatus according to the present embodiment operates the toner replenisher 40 in response to the detection signal of the toner density sensor 142 that changes using such a change in the magnetic permeability, and discharges the toner consumed by the image formation. Supply properly. The toner replenishing device 40 and the toner density sensor 142 constitute a toner density control unit for appropriately maintaining the toner density.

The toner remaining amount detecting sensor 143 has an optical detecting section for detecting the remaining amount of toner of the toner replenisher 40 (see FIG. 3) which is an example of the toner supplying means of the present invention.
A toner remaining amount detecting unit that outputs a detection signal corresponding to the toner remaining amount in the toner replenisher 40 (hereinafter also referred to as a toner hopper). The image forming apparatus according to the present embodiment supplies the new toner to the toner hopper from the toner bottle 61 when the toner is consumed by the image formation, mixes the new toner and the collected toner inside the toner hopper, and 1
4 When the new toner in the toner bottle 61 is depleted, only the toner remaining in the toner hopper is supplied to the developing unit 14.

When image formation is performed with the toner bottle 61 depleted of toner attached, the toner inside the toner hopper also depletes. When this state is reached, the remaining toner detection sensor 143 determines that the remaining amount of toner accumulated in the toner hopper serving as the toner supply unit is in a depleted state, and outputs a corresponding detection signal.

As described above, even if the toner supply means is depleted, an image can be formed by the toner remaining in the developing means 14 and the toner slightly remaining in the toner hopper, but the toner concentration of the developer is not reduced. As a result, carrier development is likely to occur.

The continuous operation time determination circuit 145 measures the continuous operation time of the image forming apparatus, and executes control for changing the developing condition when the continuous drive time reaches a predetermined time. When the continuous pause time reaches a predetermined time, the measurement value of the continuous operation time is initialized. The continuous operation time determination circuit 145 measures a continuous drive time and a pause time as described below.

The continuous operation time determination circuit 145 controls the temperature sensor 152 so that the output signal of the temperature sensor 152 is transmitted.
Is connected to The internal temperature of the image forming apparatus tends to increase due to the image forming operation and decrease while the image forming operation is stopped. When the image forming operation is continuously performed, the internal temperature does not decrease. Is well known to rise considerably. If the internal temperature rises considerably, it can be inferred that the image forming apparatus has been operated continuously, so the main CPU 30 changes the developing conditions according to the temperature range of the internal temperature.

The number of discharged recording materials is substantially proportional to the continuous operation time of the image forming apparatus. The continuous operation time determination circuit 145 counts the number of discharged recording materials, and when the number reaches the predetermined number, determines that the continuous operation time has reached the predetermined time, and changes the developing condition.

The page counter 146 is an example of a counting unit according to the present invention, and counts the number of recording materials discharged to the discharge tray 7C through the discharge unit 7. The count value of the number of recording materials is treated as a value indicating a continuous operation time (hereinafter also referred to as a continuous operation time measurement value). If a jam detection sensor (not shown) does not output a detection signal, the executed printing is performed normally. When it is completed, it can be estimated that the recording material is discharged to the paper discharge tray 7C. Therefore, the counting is continued unless the jam detection sensor operates during the execution of printing. The page counter 146 may be configured to count the number of recording materials discharged to the discharge tray 7C by an optical sensor, a contact sensor, or the like.

When the count value of the page counter 146 reaches the set value, the main CPU 30 changes the developing condition.
At the time of the change, the main CPU 30 changes the development condition according to the range of the number of output pages.

In the case of executing a so-called image forming job in which printing of a large number of sheets is performed as a series of operations, when the output of the last page is completed, the measurement of the number of pages is temporarily stopped and the measurement of the pause time is performed. To start. However, the counted number of pages is saved. Continuous operation time judgment circuit 14
When the pause time measurement value (hereinafter also referred to as a pause time measurement value) reaches a set time (threshold value), the counted number of pages is discarded, and the next image formation is counted from the initial value. If the next image formation or image formation job is started before reaching the threshold value, the count value is added to the stored page number.

The fixing control circuit 147 turns on / off a heater built in the fixing device 6 in accordance with a command from the main CPU 30.
Controls FF. When the continuous stop time reaches a predetermined time, the fixing control circuit 147 outputs an initialization signal. The fixing control circuit 147 and the page counter 146 are connected so that an initialization signal can be transmitted. When the initialization signal is output, the measured value of the page counter 146 returns to the initial value. In the present embodiment, when the stop time lasts for 8 hours, an initialization signal is output.

The developer life monitoring circuit 144 is a circuit for monitoring the life of the carrier contained in the two-component developer, and monitors the life of the carrier based on the history of the number of copies. Like the page counter 146, the developer life monitoring circuit 144 stores a count value obtained by counting the number of recording materials discharged to the discharge tray 7C as accumulated page number data in the nonvolatile memory as needed. The accumulated page number returns to the initial value when the carrier is updated, for example, when the developing unit 14 is replaced. Since the carrier receives stress during the development process and the triboelectric charging process, peeling of the coat layer etc. occurs,
This is called carrier fatigue. The career life is
It is an index indicating the degree of fatigue accumulated by using the carrier for a long period of time. Since the carrier is subjected to stress during the development process and the charging process, the life of the carrier can be indicated by the cumulative value of the driving time of the developing unit 14. It is possible.

Further, since the cumulative value of the driving time of the developing means 14 is proportional to the cumulative number of pages of the output recording material, the present embodiment is configured to monitor the life of the carrier based on the cumulative number of pages.

When the main power of the image forming apparatus is turned on, the developer life monitoring circuit 144 reads the accumulated page number data from the non-volatile memory, adds the accumulated number of sheets after the power is turned on, and stores the accumulated page number data in the non-volatile memory. Store in memory.

The life of the developer may be monitored by counting the number of rotations of the developing sleeve 41 with an encoder or the like.

In the usage of the image forming apparatus, an OHT sheet (Overhead Projector) is used as a recording material.
Transparency) may be used. OH
T-sheets usually have higher rigidity (paper stiffness) defined by JIS-P8143 than recording paper used in copiers and printers, and therefore, when carrier development occurs, OHT sheets are larger than recording paper. Is more likely to confirm the image defect.

The recording material type detection sensor 153 includes a light emitting unit that irradiates a recording material such as a recording sheet S or an OHT sheet conveyed from the manual paper feed unit 5A, and a light receiving unit that receives light reflected by the recording material. Processes the response output of the photoelectric sensor and the reflection type photoelectric sensor that changes according to the amount of light received by the light receiving unit. There is no recording material, there is a light-transmitting recording material such as an OHT sheet, and non-transparent recording such as recording paper S And a reflection type photoelectric sensor control circuit that outputs a recording material state signal corresponding to the three states of presence of the material.

The recording material type detection sensor 153 is not limited to the reflection type photoelectric sensor, and may be configured using a transmission type photoelectric sensor.

The mode changeover switch 148 operates in a normal mode using paper as a recording material, and operates as an OH
This is a switch for switching operation in a special mode using a T-sheet, and is an example of mode switching means directly operated by a user. Since the developing conditions for the normal mode and the switching mode are changed as described later, the recording material type detection sensor 1
It is used to switch the operation mode regardless of the detection result of 53.

The image forming apparatus according to the present embodiment having the above-described configuration has the following conditions for developing conditions corresponding to the atmospheric humidity of the two-component developer, the toner concentration of the two-component developer, the life of the two-component developer, and the like. The image formation is executed with the changes as shown.

[0090]

[Table 1]

Table 1 is a table showing development conditions according to the detection result of the humidity sensor 151. The atmospheric humidity is the atmospheric humidity of the two-component developer. The development bias, the rotation speed of the development sleeve, and the charging potential of the photoconductor are development conditions, and are items that are changed according to the detected atmospheric humidity. The item of the developing bias indicates the voltage value of the DC component applied to the developing sleeve 41. The item of the rotational speed of the developing sleeve indicates the rotational speed of the developing sleeve 41 driven by the developing device drive motor 14M by the number of rotations per minute. The item of the photoconductor charging potential is the photoconductor drum 10
Is the surface potential of the unexposed portion, and is indicated by a voltage value.

The image forming apparatus according to the present embodiment is an example of reversal development using a negatively charged photosensitive member, toner, and positively charged carrier. Control is performed to reduce the absolute value of the DC component, increase the rotation speed of the developing sleeve, and reduce the absolute value of the photosensitive member charging potential. Therefore, as the atmospheric humidity increases, each developing condition is changed as shown in Table 1 to execute image formation. Therefore, according to the image forming apparatus of the present embodiment, it is possible to output a good image even under conditions where carrier development is likely to occur due to an increase in atmospheric humidity.

[0093]

[Table 2]

Table 2 is a table showing development conditions according to the detection result of the toner density sensor 142. What is toner density?
This is the density expressed as a percentage by weight of the toner in the two-component developer. In Table 2, the item “toner density” indicates a relative change amount with respect to the toner density in a state where the toner is sufficiently supplied. Indicates that the concentration was reduced by 0.5%. The item of the rotation speed of the developing sleeve is a developing condition.
Is the same as

The image forming apparatus according to the present embodiment is configured to change the developing conditions as shown in Table 2 and execute image formation as the toner density decreases. Therefore, according to the image forming apparatus of the present embodiment, it is possible to output a good image even under conditions where carrier development is likely to occur due to an increase in atmospheric humidity.

[0096]

[Table 3]

Table 3 is a table showing development conditions according to the count value of the page counter 146. The count value is a value indicating the number of sheets of recording paper S output by image formation performed continuously or continuously with a very short pause period, and this count value is set to the Q / M level. It is a corresponding index. The items of the developing bias, the rotating speed of the developing sleeve, and the charging potential of the photosensitive member are the developing conditions, which are the same as those in Table 1.

The image forming apparatus according to the present embodiment is configured to execute image formation by changing the developing conditions as shown in Table 3 as the count value increases. Therefore, according to the image forming apparatus of the present embodiment, it is possible to output a good image even under the condition in which the carrier development in which the Q / M value is changed easily occurs.

[0099]

[Table 4]

Table 4 is a table showing development conditions corresponding to the cumulative number of pages. Here, the cumulative number of pages refers to the number of copies output by the image forming apparatus in units of 1000 sheets (1000 sheets =
1 kilocopy = 1 kcopy). Each item of the developing bias and the photoconductor charging potential is a developing condition, which is the same as in Table 1.

The image forming apparatus according to the present embodiment is configured to execute image formation by changing the developing conditions as shown in Table 4 as the number of accumulated pages increases. Therefore, according to the image forming apparatus of the present embodiment, it is possible to output a good image even under the condition that the carrier life is advanced and carrier development is likely to occur.

The main CPU 30 changes the developing conditions according to the atmospheric humidity, toner concentration, carrier life, etc. of the two-component developer detected by each sensor and the count value of the page counter 146. In response to this, the surface potential control circuit 121 indicates the photoconductor surface potential, the developing bias control circuit 140 indicates the DC component of the developing bias, and the rotation speed control circuit 141 indicates the rotation speed of the developing sleeve 41 in the above-described tables. Control as follows.

[0103]

[Table 5]

Table 5 is a table showing development conditions corresponding to the operation modes of the image forming apparatus. Here, the normal mode is an operation mode of the image forming apparatus corresponding to an image forming condition in a state where the recording material type detection sensor 153 detects the presence of a non-transmissive recording material. The special mode is an operation mode of the image forming apparatus corresponding to an image forming condition in a state where the recording material type detection sensor 153 detects the presence of the light transmitting recording material. The items of the developing bias, the rotating speed of the developing sleeve, and the charging potential of the photosensitive member are the developing conditions, which are the same as those in Table 1.

The image forming apparatus according to the present embodiment is configured to change the developing conditions as shown in Table 5 and execute image formation according to the type of recording material on which an image is to be formed. Therefore,
According to the image forming apparatus of the present embodiment, it is possible to suppress the range of the influence of the image defect even when using a highly rigid recording material in which the image defect easily occurs in a wide range under the condition that the carrier development occurs.

In the above-described change of the developing condition, the main CPU 30 instructs the change of the developing condition according to the type of the recording material, and the surface potential control circuit 121 changes the photosensitive member surface potential and the developing bias control circuit 140 in response to the change. Indicates the DC component of the developing bias, and the rotational speed control circuit 141 controls the rotational speed of the developing sleeve 41 as shown in Table 5 above.

When the developing conditions are changed as shown in Tables 1 to 5, the density characteristics of the actually output image change with respect to the light emission signal output from the modulation circuit 32. This characteristic is stored as a plurality of density conversion curves,
When the development conditions are changed, the main CPU 30 instructs the image processing unit 2 to set the light output by the APC control to a predetermined intensity. The intensity of light output by APC control is
The intensity corresponding to the changed development condition is selected.

Next, an image forming apparatus according to a second embodiment of the present invention will be described with reference to a control block diagram showing an electrical configuration. The image forming apparatus according to the second embodiment fixes the control value of the light output by the laser output control circuit 33 and uses it in the image processing unit 2 as compared with the image forming apparatus of the first embodiment. The development potential is adjusted by switching the conversion table.

Therefore, description overlapping with the first embodiment will be omitted. In the control block diagram of FIG. 5, the image processing unit 2 outputs a digital signal that has been subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like, as described above. At the time of these processes, the image processing unit 2 selects and sets one density conversion curve from the non-volatile memory in which the data of the plurality of density conversion curves are written, and performs the error diffusion method based on the set density conversion curve. Multi-value processing is performed by well-known image processing such as.

As a matrix used in the error diffusion method,
A service table and a correction table are provided. The normal table is referred to when operating in a normal mode using paper as a recording material, and the correction table is referred to when operating in a special mode using a highly rigid recording material such as an OHT sheet as a recording material. As shown in Tables 1 to 5, the correction table is set to characteristics for correcting a density conversion curve that changes when the development conditions are changed. The service table and the correction table are stored in a non-volatile memory, and are read out by the image processing unit 2 when referred to. The output light from the semiconductor laser of the image writing unit 3 is subjected to PWM control, and the dot writing PWM table is changed by a common table or a correction table so that the writing of each dot by the output light is performed in a state where the density conversion curve is reflected. Be executed.

The correction table may be stored as a matrix used for the image processing operation by the direct error diffusion method, or may be stored as difference data from the matrix of the common table and used in the special mode before being used for the image processing operation. It is also possible to adopt a configuration in which a matrix to calculate

The number of correction tables is not limited to one, and it is more preferable to prepare a plurality of correction tables and switch between the plurality of correction tables according to the atmospheric humidity, the developer life, and the toner concentration.

FIG. 6 is a flowchart for explaining development condition control in the image forming apparatus of the present embodiment.

When the development condition control starts, step 11
Then, it is determined whether the recording material is paper or an OHT sheet (S11). Next, in step 12, the humidity sensor 151 and the toner concentration sensor 142 read the ambient humidity of the two-component developer and the toner concentration (S12). In step 13, the accumulation corresponding to the accumulated value of the rotation time of the developing sleeve 41 is performed. Read time data (S
13), the rotation speed of the developing sleeve 41 and the developing potential are derived from the developing condition control table corresponding to the special mode (S14).

Next, in step 14, the dot writing PWM table is changed from the gradation correction value table corresponding to the special mode (S14), and the development condition control ends. Thereafter, image formation is performed under these developing conditions.

The above-described development condition control is performed according to a schedule set by the user when the image forming apparatus can perform scheduling by using a built-in clock or a built-in calendar when the power is turned on or after a predetermined time has elapsed since the power was turned on. Or each time image formation of each page is executed, or each image formation job in which a series of image formations are continuously executed.
It may be executed in accordance with the timing at which image formation is executed.

FIG. 7 is a flowchart illustrating a second example of developing condition control in the image forming apparatus according to the present embodiment.

When the image forming operation starts, step 21
Then, the continuous operation time determination circuit 145 returns the continuous operation time measurement value and the pause time measurement value to the initial values (S21). When the image forming operation is started, measurement of the continuous operation time is started, and the continuous operation time is calculated based on the measured value in step 22 (S22). According to the continuous operation time, the developing condition is changed in step 23 (S23), and the image forming or the image forming job is executed according to the changed developing condition.

When the image forming or the image forming job is completed, the image forming apparatus shifts to an input of an instruction by a user, that is, a so-called job waiting state (S24). In the job waiting state, the measurement of the pause time is started after initialization of the pause time in step 25, and the measurement of the continuous operation time is temporarily stopped (S25). In step 26, the pause time reaches the threshold (set time). Then (S26), in step 27,
The continuous operation time and the pause time are returned to the initial values (S27).

On the other hand, if the user inputs an image forming job after shifting to the job waiting state, step 22 is executed.
Then, the measurement of the continuous operation time suspended in step 25 is restarted.

As described above, the image forming apparatus according to the present embodiment has a configuration in which each developing condition is changed according to the continuous operation time to execute image formation. Therefore, according to the image forming apparatus of the present embodiment, it is possible to output a good image even under conditions where carrier development is likely to occur due to continuous operation. In addition, since the measurement of the continuous operation time is initialized according to the pause time, it is possible to change the image forming conditions after accurately determining whether or not carrier development is likely to occur in the image forming apparatus.

[0122]

According to the image forming apparatus of the first, second, fourth, fifth, or sixth aspect of the present invention, it is possible to output a good image even under conditions where carrier development is likely to occur. Was.

According to the image forming apparatus of the present invention, under the condition that carrier development occurs,
Even when a recording material having high rigidity in which image defects easily occur in a wide range is used, it is possible to suppress the range affected by the image defects.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of an image forming unit in the present image forming apparatus and a peripheral portion thereof.

FIG. 3 is a front sectional view of a toner supply device and a toner supply device.

FIG. 4 is a control block diagram illustrating an electrical configuration of the image forming apparatus.

FIG. 5 is a control block diagram illustrating an electrical configuration of an image forming apparatus according to a second embodiment.

FIG. 6 is a flowchart illustrating development condition control in the image forming apparatus.

FIG. 7 is a flowchart illustrating a second example of developing condition control in the image forming apparatus according to the present embodiment.

FIG. 8 is a schematic diagram showing a state in which carrier development has occurred.

FIG. 9 is a schematic diagram schematically illustrating a difference in influence between a recording sheet and a recording material having higher rigidity than the recording sheet when carrier development occurs.

[Explanation of symbols]

 3 Image Writing Unit 12 Charging Means 14 Developing Means 14M Developing Device Drive Motor 41 Developing Sleeve 47a, 47b Screw 121 Surface Potential Control Circuit 141 Rotation Speed Control Circuit 142 Toner Density Sensor 143 Toner Remaining Detection Sensor 144 Developer Life Monitoring Circuit 145 Continuous Operating time judgment circuit 146 Page counter 148 Mode changeover switch 151 Humidity sensor 152 Temperature sensor 153 Recording material type detection sensor

Continued on the front page F-term (reference) 2H027 DA11 DA14 DA39 DA45 DB01 DC02 DC11 DC14 DD02 DD07 DE02 DE04 DE10 EA01 EA02 EA04 EA05 EB03 EC06 EC10 ED03 ED08 ED09 ED25 EE03 EE04 EE08 EH03 FA22 FA30 FA35 FA37 GB11 FB19 2 CA19 CA26 2H073 BA02 BA13 BA25 BA33 BA36 CA03 2H077 AA03 AA12 AB02 AB13 AB14 AB15 AC03 AD06 AD35 AE02 BA03 DA10 DA15 DA18 DA22 DA24 DA34 DA42 DA54 DA62 DA78 DB03 DB08 DB10 DB12 DB13 DB14 EA01 GA17

Claims (17)

[Claims] 1. A developer carrier for carrying a two-component developer by controlling a rotation speed and an application voltage, and a toner image being formed by toner supplied from the developer carrier by controlling a surface potential. An image forming apparatus comprising: a photoconductor that performs at least one of the rotation speed of the developer carrier, a DC component of the applied voltage, and the surface potential of the photoconductor. apparatus. 2. A developer carrier for carrying a two-component developer by controlling a rotation speed and an applied voltage, and a toner image being formed by toner supplied from the developer carrier by controlling a surface potential of the developer carrier. The rotation speed of the developer carrier, the DC component of the applied voltage, and the output voltage of a humidity sensor that detects the atmospheric humidity of the two-component developer. An image forming apparatus, wherein at least one of the surface potentials of the photoconductor is changed. 3. The image forming apparatus according to claim 2, wherein when the atmospheric humidity is high, the rotation speed is increased and the absolute value of the developing potential is reduced. 4. A developer carrier for carrying a two-component developer by controlling a rotation speed and an applied voltage, and a toner image formed by toner supplied from the developer carrier by controlling a surface potential of the developer carrier. An image forming apparatus including a photosensitive member, wherein the rotation speed of the developer carrier is changed according to an output value of a toner concentration sensor that detects a toner concentration contained in the two-component developer. Image forming device. 5. A developer carrier for carrying a two-component developer by controlling a rotation speed and an applied voltage, and forming a toner image by a toner supplied from the developer carrier by controlling a surface potential of the developer carrier. An image forming apparatus comprising: a photosensitive member, wherein the rotation speed of the developer carrier is changed in accordance with a cumulative driving time stored as a cumulative driving time of the developer carrier. Forming equipment. 6. A developer carrier for carrying a two-component developer by controlling a rotation speed and an applied voltage, and a toner image formed by toner supplied from the developer carrier by controlling a surface potential of the developer carrier. And an output value of a toner concentration sensor for detecting the concentration of toner contained in the two-component developer, and an output value of a humidity sensor for detecting the atmospheric humidity of the two-component developer. Changing at least one of the rotation speed of the developer carrier, the DC component of the applied voltage, and the surface potential of the photoconductor in accordance with at least two of the cumulative driving time of the developer carrier. Characteristic image forming apparatus. 7. A developer carrier for carrying a two-component developer by controlling a rotation speed and an application voltage, and a toner image formed by toner supplied from the developer carrier by controlling a surface potential of the developer carrier. A special mode for forming an image by changing at least one of the rotation speed of the developer carrier, a DC component of the applied voltage, and the surface potential of the photoconductor. An image forming apparatus comprising a mode switching unit for switching to a mode. 8. The special mode is set according to an output value of an optical sensor for detecting whether or not a transfer material to which a toner image formed on the photoconductor is transferred is a transparent sheet material. The image forming apparatus according to claim 7, wherein the switching is performed. 9. An image forming apparatus according to claim 7, wherein said mode switching means is a manual switching means for manually switching to said special mode. 10. The humidity sensor for detecting the atmospheric humidity of the two-component developer, wherein the rotation speed of the developer carrier in the special mode, the DC component of the applied voltage, and the surface potential of the photoconductor are 10. The image forming apparatus according to claim 7, wherein control is performed so as to change the output value in accordance with at least one of an output value and an accumulated driving time stored as an accumulated driving time of the developer carrier. apparatus. 11. A gradation correction value table for exposing the photoconductor in accordance with a light emission signal, and using a gradation correction value table for correcting a change in density gradation in the special mode when the mode is switched to the special mode. 11. The image forming apparatus according to claim 7, wherein the light emission signal is controlled by controlling the light emission signal. 12. An exposure means for exposing the photoconductor in accordance with an exposure intensity signal, wherein when the mode is switched to the special mode, a correction value for correcting a change in density gradation in the special mode is converted to an exposure intensity signal. 11. The image forming apparatus according to claim 7, wherein the light emission signal is controlled. 13. A developing device comprising: a developer carrier that controls a rotation speed and an applied voltage to carry a two-component developer; and a toner charging unit that charges toner contained in the two-component developer. A photosensitive member that forms a toner image with toner supplied from the developer carrier with the surface potential controlled, wherein the developer carrier is charged in accordance with a continuous operation time of the toner charging unit. An image forming apparatus, wherein at least one of the rotation speed of the body, the DC component of the applied voltage, and the surface potential of the photoconductor is changed. 14. A developer carrying member that carries a two-component developer by controlling a rotation speed and an applied voltage, a toner charging unit that charges toner contained in the two-component developer, and the developer carrying member. An image forming apparatus comprising: a developing device having a developing unit; and a photoconductor, which controls a surface potential and forms a toner image with the toner supplied from the developer carrier, detects an atmospheric humidity of the two-component developer. The rotation speed of the developer carrier, the DC component of the applied voltage, and at least one of the surface potential of the photoconductor are determined in accordance with the output value of the humidity sensor and the continuous operation time of the toner charging unit. An image forming apparatus characterized by changing. 15. The image forming apparatus according to claim 13, further comprising a counting unit that counts the number of printed sheets output by the image forming apparatus, wherein the continuous operation time is determined based on the number of printed sheets. apparatus. 16. The apparatus according to claim 1, further comprising a temperature sensor for detecting an ambient temperature of the two-component developer, wherein the continuous operation time is determined based on the ambient temperature.
16. The image forming apparatus according to 3, 14, or 15. 17. A transfer device for transferring a toner image formed on the photoconductor to recording paper, and a heat fixing device for thermally fixing the toner image transferred to the recording paper, wherein the thermal fixing device is continuously stopped. 15. The image forming apparatus according to claim 14, wherein the continuous operation time is initialized according to time.