JPH11184182A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a defective image such as belt-like fogging and uneven density, the waste and deterioration of developer and the deterioration of a photoreceptor by impressing a developing bias for a prescribed time after stopping the supply of a driving force for rotating a photoreceptor. SOLUTION: When a process driving motor driving signal is shifted to be low, a counting operation is started by a CPU 310 based on a program, after a lapse of prescribed time, a PCL control signal, a CEL control signal and a developing bias control signal are shifted to be low. The idle rotation of the photoreceptor drum 131 is stopped when the counting operation is finished. That is, while the photoreceptor drum 131 is idly rotated, a precharge exposure device PCL and a charging exposure device CEL are continuously turned on, and the developing bias is also impressed. Thus, the occurrence of uneven density is prevented. Besides, before starting the following copying operation, such a failure is prevented that the toner is developed in a shape like a belt even in the case the potential of a white base part becomes higher than that of a ground because of the fatigue of the photoreceptor drum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for developing an electrostatic latent image formed on a rotating photosensitive member by using toner.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a photosensitive drum is often driven by a motor. After the completion of the image formation, the CP for controlling the operation of the entire image forming apparatus
U issues a control signal to control the switching of the motor from on to off. When a control signal for turning off the motor is issued, the power supply to the motor is immediately stopped, but the photosensitive drum continues idling due to inertia and then stops.

The surface potential of the photoreceptor at the time when the idling stops has a large surface potential and can be classified into three states. That is, the region where the charged electrode and the transfer electrode were charged to a high potential by the high voltage discharge before the idling stopped, and the potential was erased by exposure with the pre-charging exposure device (PCL) and the charge erasing device (CEL). State region, and other regions where the surface potential is rough.

When the output of the control signal for turning off the motor and the turning off of the PCL are performed at the same time, and then image formation is performed, the following problem occurs.

During the operation for forming an image, a portion having a rough surface potential after cleaning is exposed and discharged when passing through the PCL, so that the surface potential of the photosensitive drum after passing through the PCL is uniform. It is almost at ground potential. However, if the photoconductor drum idles after the PCL is turned off at the time of stopping, a part of the region where the surface potential is rough passes immediately below the PCL without being neutralized. When the next image formation is started, an area that has passed just below the PCL without being neutralized passes through the charging electrode, and at this time, uneven charging occurs. If a toner image is formed in the area where the charging unevenness has occurred, density unevenness is observed in the printed image, and this may be one of the causes of deterioration of the photoconductor due to a memory effect.

In order to solve this problem, a technique is known in which exposure by PCL is continued until the idling of the photosensitive member stops.

[0007]

However, even when this technique is used, the toner adheres in a belt shape in a direction orthogonal to the transfer paper conveying direction, and fogging is sometimes observed. Also,
In some cases, density unevenness may be observed even after the control signal for turning off the motor is output, even though exposure is continued with PCL.

[0008] Two facts have been identified as causes of the phenomenon in which the toner is developed in a belt shape.

First, in a normal image forming apparatus, when a control signal for turning off the motor is output, the developing bias applied to the sleeve of the developing unit is immediately turned off, and the potential of the sleeve drops to the ground potential. On the other hand, since the potential of the photoreceptor surface is higher than the ground potential (potential of the sleeve after stopping) even after exposure with the light amount of the white background portion of the original, the direction of the developing electric field of the fatigued photoreceptor Is the direction in which the toner moves from the sleeve to the photoconductor. If the photoconductor drum idles under such a condition of the developing electric field, toner adheres to an area where the photosensitive drum has idled and passed through the developing device, and in the next image forming process, the adhered toner is transferred to the transfer electrode, the separation electrode, Alternatively, the transfer paper adheres to a guide plate or the like that guides the transfer paper to the transfer area, and is observed as toner contamination.

Second, in a normal image forming apparatus, when a control signal for turning off the motor is output, the CEL is also turned off.
When the CEL is turned off, the photosensitive drum idles while being charged to the developing potential by the charging electrode. The area not exposed by the CEL is subjected to high-density development (fogging) in a band shape in the next image formation.

The above-mentioned band-like fogging is a problem as an image defect, and also has a problem that a developer such as toner is wasted. Furthermore, since the photosensitive member is temporarily stopped while being charged, there is a problem that deterioration is accelerated.

These problems arise in an image forming apparatus in which the supply of the driving force of the photosensitive drum is stopped independently of the driving of the transport mechanism for transporting the transfer paper, in order to prevent the deterioration of the developer and the photosensitive member. Or when the photosensitive drum is stopped immediately after the separation is completed. Examples of the image forming apparatus include a photosensitive drum, a PCL, a CEL, a charging electrode,
There is an image forming apparatus in which a developing device and a cleaning mechanism are housed in an integrated cartridge so that they can be taken out from the main body of the image forming apparatus, and are provided with a motor for driving each part of the cartridge and a motor for driving each part of the main body. When the image forming apparatus outputs a control signal to turn off the motor for driving the photoconductor immediately after the completion of cleaning or separation, a portion where the surface of the photoconductor remains rough without being exposed to the PCL is left as it is, The above problems appear.

It is therefore an object of the present invention to prevent the occurrence of image defects such as band-like fogging and density unevenness in an image forming apparatus, to prevent waste and deterioration of a developer, and to prevent deterioration of a photosensitive member. .

[0014]

The object of the present invention has been attained by an image recording apparatus according to the present invention. That is, the image recording apparatus according to claim 1 includes a rotatable photoconductor,
Photoreceptor driving means for supplying a driving force to the photoreceptor to rotate the photoreceptor, latent image forming means for forming an electrostatic latent image on the photoreceptor, and a developing electric field generated by applying a developing bias to the charged toner Developing means for developing a toner image corresponding to the electrostatic latent image by applying the developing bias to the photosensitive member for a predetermined period after the supply of the driving force is stopped. It is characterized by having a control means for performing the control.

The object of the present invention can also be solved by the image forming apparatus according to the present invention. That is, the image forming apparatus according to claim 2, wherein a rotatable photoconductor, a photoconductor driving unit that supplies a driving force to the photoconductor to rotate the photoconductor, and a charging unit that charges a surface of the photoconductor. Outside exposure means for exposing outside the image area by switching the exposure width according to the width of the image area provided on the photoconductor, forming an electrostatic latent image on the photoconductor, An image forming apparatus that develops a toner image corresponding to (e), comprising a control unit that switches the exposure width of the out-of-region exposure unit to the maximum width for a predetermined period of time after the supply of the driving force is stopped, and performs exposure. And

These image forming apparatuses are preferably provided with a temperature acquiring means for acquiring a temperature near the photoconductor, and the control means preferably changes the predetermined time according to the temperature acquired by the temperature acquiring means.

The object of the present invention can also be solved by the image forming apparatus according to the fourth aspect. That is, the image forming apparatus according to claim 4, wherein the photoconductor is rotatable, a photoconductor driving unit that supplies a driving force to the photoconductor to rotate the photoconductor, and the photoconductor is exposed to light over the entire width of the photoconductor. A pre-charging exposure unit for discharging the body, and a charging unit for charging the surface of the photoreceptor removed by the pre-charging exposure unit, and forming an electrostatic latent image on the charged photoconductor to form the electrostatic latent image. In the image forming apparatus that develops a toner image corresponding to the above, a temperature acquisition unit that acquires a temperature near the photoconductor, and a predetermined time after the supply of the driving force is stopped according to the temperature acquired by the temperature acquisition unit. It is characterized by having control means for exposing the pre-charging exposure means over time.

These image forming apparatuses include a transport unit that transports a transfer material onto which the toner image is transferred, a transport drive unit that drives the transport unit, and a drive unit that drives the photosensitive member independently of the drive of the transport unit. And a drive control means for stopping the supply of the driving force of the means.

In these image forming apparatuses, the predetermined time is preferably a time from when the supply of the driving force is stopped to when the idling of the photosensitive member is stopped.

[0020]

FIG. 1 is a front sectional view showing the entire structure of a copying machine 100 according to an embodiment of the present invention.

The copying machine 100 according to the present embodiment executes an electrophotographic process to form an image corresponding to a document on transfer paper. The copying machine 100 includes an automatic document feeder (hereinafter abbreviated as RADF), a reading and scanning unit 120, an image forming unit 130, a transfer mechanism 140, and the like.

When the user sets a plurality of originals on the original set table 111 and presses a copy start button, the RADF causes each page of the originals to be transferred to the original feed roller 11.
The sheet is sequentially fed at 7 and is automatically conveyed to a predetermined position on the platen glass 121. In addition, the read original is discharged onto the document discharge table 116 or the original is turned upside down and fed onto the platen glass 121.

The reading scanning unit 120 includes a platen glass 121 on which a document is placed, and an exposure lamp 122 and a first mirror 12 below the platen glass 121 and in the apparatus main body.
3, a second mirror 124, a third mirror 125, a reflection mirror 127, and an imaging lens 126.

The exposure lamp 122 emits light and irradiates the original placed on the platen glass 121. The light reflected on the original surface becomes exposure light, and is reflected by each of the mirrors 123, 124, 12
5. The light is reflected by the reflection mirror 127 through the imaging lens 126 and is imaged on the photosensitive drum 131. A latent image is formed by the formed image of the exposure light. Further, the copying machine 100 can perform variable-magnification copying, and forms a latent image by changing the position of the imaging lens 126 and the optical path length to change the magnification of the image formed on the surface of the photosensitive drum 131.

The image forming unit 130 includes a photosensitive drum 131
, A pre-charging exposure device PCL, a charging device 132, a charging erasing exposure device CEL, a developing device 200, a transfer device 134, and a separator 135.
And a cleaning device 136 and a fixing device 137, and execute each process after the exposure process of the electrophotographic process. Photoreceptor drum 131, pre-charging exposure device PC
L, charge erasing exposure device CEL, charging device 132, developing device 2
The cleaning device 136 and the cleaning device 136 are housed in a cartridge so that they can be integrally removed from the main body when performing jam processing or maintenance of each process member.

The photosensitive drum 131 is negatively charged O
PC (Organic PhotoConducto)
r) A drum coated with a photoreceptor. Photoconductor drum 13
1 is driven by a process drive motor M2 (see FIG. 2).

The charger 132 is a scorotron charger connected to a high voltage power supply, and uniformly charges the photosensitive drum 131 to a predetermined voltage prior to a latent image forming process.

The charge erasing exposure device CEL uses a so-called LED array in which a plurality of LEDs are linearly arranged.
An area (non-image area) where a latent image is not formed on the surface of the photosensitive drum 131 is exposed. When the charged photosensitive drum 131 passes through the charge erasing exposure device CEL in a state where a part of the plurality of LEDs included in the charge erasing exposure device CEL emits light and the others are turned off, the surface of the photosensitive drum 131 is exposed. There are regions where the charged potential is erased and regions where the potential is not erased. Since the toner does not adhere to the region where the potential is erased even by the operation of the developing device 200, the LED that emits light according to the magnification and the size of the transfer paper to be used and the LED that is turned off
By selecting ED, the charging potential in the area where the latent image is not formed is set to approximately 0 V (also referred to as ground potential) to prevent unnecessary development.

The developing device 200 stirs the two-component developer in which the toner and the carrier are controlled to a predetermined concentration (% by weight) with stirring screws 227 and 228 to charge the toner to a predetermined charge, and rotates outside the magnet roller. A magnetic brush is formed on the outer periphery of the developing sleeve 223 to be
3 to the photosensitive drum 131
Is visualized as a toner image in a development area opposed to. The developing sleeve 223 is connected to a high voltage power supply 340. In the present embodiment, the developing device 200 is driven by a process drive motor M2.

The transfer unit 134 includes a scorotron discharger connected to a high-voltage power supply 340 (see FIG. 2). The transfer unit 134 superimposes the transfer paper on the toner image electrostatically supported on the photosensitive drum 131, and the back side of the transfer paper. And discharges the toner on the transfer paper.

The separator 135 includes a scorotron discharger connected to a high-voltage power supply 340 (see FIG. 2), and separates the transfer paper by removing electricity from the transfer paper electrostatically attracted to the photosensitive drum 131. Things.

Both the transfer unit 134 and the separator 135 can be replaced with a corotron discharger or the like.

The cleaning device 136 presses the cleaning blade against the surface of the rotating photosensitive drum 131 even after the transfer process, and removes and cleans the toner remaining on the surface of the photosensitive drum 131.

The pre-charging exposure unit PCL includes a photosensitive drum 131.
The remaining charge is removed. Photoconductor drum 1
On the surface of 31, there is a region in which electric charges due to the discharge of the transfer unit 134 and the separator 135 remain, or there is an area where the influence of the discharge is small, so that the potential greatly differs depending on the site. Since the pre-charging exposure device PCL performs exposure over the entire width of the photosensitive drum 131, the surface potential thereof is uniformly set to substantially the ground potential.

Exposure device CEL for charge erasing and exposure device P before charging
In the description of CL, it has been described that the surface potential of the photoconductor drum 131 becomes substantially ground potential by exposure, but this is not limited to the case where the photoconductor becomes fatigued. When the photosensitive drum 131 becomes fatigued, the potential is erased only to a potential higher than the ground potential even if the potential is erased by exposure. When a developing bias set on the premise that the surface of the photosensitive drum 131 is erased to the ground potential by exposing the white background portion to light by exposing the charge erasing exposing device CEL and the pre-charging exposing device PCL, The toner may adhere to a white background portion or a non-image area.

The fixing device 137 is a device for fixing the toner image on the transfer paper by applying heat and pressure to the transfer paper carrying the toner image. The fixing device 137 is in charge of a fixing process of an electrophotographic process as one of members constituting the image forming unit 130, and also includes a fixing mechanism 137.
It is also part of zero.

The exhaust device 138 is a device for exhausting air staying inside the copying machine 100. The exhaust device 138 includes a fan, generates an air current by rotation of the fan, and generates heat by the exposure lamp 122 and the fixing device 137.
The heated high-temperature air is discharged outside the machine to prevent heating.

The transport mechanism 140 transports the transfer paper to the transfer section in synchronization with the toner image formed on the photosensitive drum 131 and discharges the transfer paper from the fixing device 137. The paper feed cassettes 141, 142, 143 Paper feed rollers 141a, 142a, 143 for taking out and transferring the transfer paper from
a, guide members 141b, 142b, 143b, carry-out rollers 141c, 142c, 143c, a pre-shutter sensor 250, a registration shutter 145, an accumulation reversing unit 149, and a fixing device 137.

The registration shutter 145 protrudes by an exciting operation of a solenoid (not shown) to stop feeding the transfer paper. Thereby, the skew of the transfer sheet is corrected, and the synchronization with the toner image formed on the photosensitive drum 131 is ensured.

The pre-shutter sensor 250 comprises, for example, an actuator and a photocoupler. The actuator is supported by a shaft, and rotates when the transfer paper passes. Thus, the optical path of the photocoupler is blocked. Therefore, the output of the photocoupler is turned on / off depending on whether or not the transfer paper has passed.

The paper cassettes 141, 142, and 143 are universal cassettes that can store transfer papers of various sizes.

The transport mechanism 140 has the above-described structure, and is driven by the transport drive motor M1 (see FIG. 2), so that transfer sheets of a designated size are firstly transferred from the paper feed cassettes 141, 142, 143 one by one. Paper feed rollers 141a, 142
a, 143a, and unloading rollers 141c, 1
42c, 143c and guide members 141b, 142b,
The sheet is conveyed to the image transfer section via 143b. The transfer paper is sent onto the photosensitive drum 131 by a registration shutter 145 that operates in synchronization with the toner image on the photosensitive drum 131. This transfer paper has a transfer device 1
The toner image on the photoconductor drum 131 is transferred by the operation of the photoconductor drum 131, is separated from the photoconductor drum 131 by the static elimination action of the separator 135, and then is sent to the fixing device 137, where the heating roller 137a and the pressure roller 137b Then, in the case of one-sided copying, the sheet is discharged to a discharge tray 139 outside the apparatus by a discharge roller.

On the other hand, when performing duplex copying on transfer paper,
The transfer paper is conveyed to the circulating conveyance section 148 and the stacking and reversing section 149
Is stored in. When a predetermined number of transfer papers are stored in the stacking and reversing unit 149, they are carried out by the reversing paper feed roller 149a. The conveyed transfer paper is conveyed and conveyed again to the position of the registration shutter 145, and is conveyed so as to coincide with the toner image formed on the photosensitive drum 131, and recording is performed.

The copy condition input panel 150 is provided with an input unit for an operator to select a copy condition and a display unit for displaying the currently selected copy condition. Copier 10
The copy conditions included in 0 include selection of image quality switching, magnification selection of variable-size copying, selection of the number of copies, and the like, and other copying conditions.

FIG. 2 is a block diagram showing a control circuit according to the present embodiment.

The control circuit in this embodiment controls the driving state of each process member in order to record an image copied by executing an electrophotographic process.

The CPU 310 is an example of control means for executing overall control relating to the electrophotographic process. CPU31
0 is a ROM 311, a nonvolatile RAM 312, a copy condition input panel 150, a main power supply 330, and a high voltage power supply 34.
0, a transport driving motor M1, a process driving motor M2, a pre-charging exposure device PCL, a charging erasing exposure device CEL, and a contact type temperature sensor 313.

When the main power supply 330 of the copying machine 100 is turned on, the CPU 310 reads out a predetermined overall control program, timing data, lighting width data and the like from the ROM 311 and develops them. The timing data indicates the ON / OFF of the transport drive motor M1 and the process drive motor M2 during the copying operation.
The timing of turning off, the timing of turning on (on) and extinguishing (off) the pre-charging exposure device PCL and the charge erasing exposure device CEL, and the timing of starting and stopping the application of the developing bias are set. Details of each timing will be described later.

The transport drive motor M1 includes first transport rollers 141a, 142a, 143a constituting the transport mechanism 140,
Reverse feeding roller 149a and unloading rollers 141c, 142
c, 143c, 149c, and a driving source such as a transport roller 144 and a heating roller 137a. The transport drive motor M1 is an example of a transport drive unit.

The process drive motor M2 is an example of the photosensitive member driving means of the present invention, and includes a photosensitive drum 131, a developing sleeve 223, a supply roller 225, and a stirring screw 22.
7. A driving source for the developing device 200 including the stirring screw 228. The photosensitive drum 131 and the developing sleeve 22
3, supply roller 225, stirring screw 227, 228
May be shared by a plurality of motors.

The high voltage power supply 340 supplies electric power to the charger 132, the developing sleeve 223, the transfer unit 134, and the separator 135. The main power supply 330 is connected to the high voltage power supply 340 and the CP.
U310, transport drive motor M1, and process drive motor M
2, a charge erasing exposure device CEL, and a pre-charge exposure device PCL and R
AM 312, temperature sensor 313, and copy condition input panel 1
Supply power to 50. The main power supply 330 starts supplying power by turning on / off the main switch ms,
Stop. The power supply line is a power supply line from the main power supply 330 to the high voltage power supply 340, but a power supply line from the main power supply 330 to other components is omitted. Is also supplying power.

The CPU 310 controls the copy condition input panel 15
In response to a copy start signal from 0, execution of the copying operation is started. The conveyance driving motor M
1 starts driving, and the transport mechanism 140 starts transporting the transfer paper. The process drive motor M2 starts to be driven later than the transport drive motor M1, and the photosensitive drum 131, the developing sleeve 223, the supply roller 225, the stirring screw 2
27, the stirring screw 228 and the like also start rotating.

The temperature sensor 313 is in contact with the surface of the photosensitive drum 131 on which the OPC is not applied, and outputs a signal that changes according to the temperature of the photosensitive drum 131 to the CPU 310. . The sensor that detects the temperature may be a sensor that contacts the photosensitive drum 131 or a sensor that does not contact the photosensitive drum 131. A sensor that directly detects the temperature of the photosensitive drum 131 may detect the temperature around the photosensitive drum 131 or the temperature of the cleaning blade. A sensor for detection may be used.

Next, the timing of the operation of each constituent member during the copying operation in the copying machine 100 will be described with reference to FIG. FIG. 3 is a timing chart for explaining the operation of the copying machine 100, and shows an example in which three consecutive copying operations are performed. The horizontal axis indicates time, and shows the state transition of the control signal for controlling each component. PCL control signal is H
At the time of i, the pre-charging exposure device PCL is turned on, and turned off when the status changes to Low. When the developing bias control signal is Hi, the developing bias is applied, and when the state changes to Low, the application is stopped. Exposure device CE for charge erasure when CEL control signal is Hi
L is turned on, and turned off when transitioning to Low. The lighting width of the charge erasing exposure device CEL is switched according to the lighting width data provided from the CPU 310.

The image area moves as the photosensitive drum 131 rotates, and each member operates in accordance with the timing at which the image area passes. For example, the timing at which the tip of the image area passes through the charge erasing exposure device CEL and the pre-charge exposure device PC
The timing of passing through L is not simultaneous. In this figure, the item of the image area is not a state transition of the signal, and for convenience, when the leading end of the image area passes through the charge erasing exposure device CEL, H
It is denoted by i, and is denoted by Low when its tail end passes. The image area used in the first copy operation is c
The image area used in the first and second copy operations is denoted by c2, and the image area used in the third copy operation is denoted by c3.

As soon as the copy start signal is received, the transport drive motor drive signal transits to Hi (t1). The transport drive motor M1 starts rotating when the transport drive motor drive signal becomes Hi. When the transport drive motor M1 starts rotating, each part of the transport mechanism 140 starts operating and the transfer paper is transported.

On the other hand, when receiving the copy start signal, the process drive motor drive signal transits to Hi after waiting for a predetermined period (t2). When the process drive motor drive signal becomes Hi, the photosensitive drum 131 starts rotating.

When the rotation of the photosensitive drum 131 is stabilized,
Although not shown in FIG. 3, reading scanning of the document by the reading scanning unit 120 is started. And the photosensitive drum 13
With one rotation, a latent image is formed in a range from the front end to the tail end of the image area. The size of the image area matches the magnification selected in the copying operation at that time and the size of the transfer paper to be used.

At time t2, the PCL control signal, C
The EL control signal and the developing bias control signal transition to Hi,
The lighting width data instructs lighting in the entire width. When the pre-charging exposure device PCL is at the timing of t2, that is, the photosensitive drum 13
If the light is turned on when the rotation of the charging device 1 starts, the charging device 1
The potential of the region passing through 32 is uniformly erased to substantially the ground potential. Therefore, the surface of the photoconductor drum 131 is charged to a uniform potential by the next charging process in the charger 132, and the occurrence of density unevenness after development can be prevented. Similarly, if the charge erasing exposure device CEL is turned on at the timing of t2,
The potential other than the image area on the surface of the photosensitive drum 131 is erased, and the potential is uniformly set to substantially the ground potential. Therefore, even if a portion other than the image area passes through the developing device 200, the toner does not adhere to this area.

As described above, the pre-charging exposure device PCL and the charge erasing exposure device CEL are turned on, and at the timing of t2, the application of the developing bias is started to generate the developing electric field. Therefore, development can be performed as the portion of the image area where the latent image is formed passes through the developing sleeve 223.

When the tip of the image area c1 passes through the charge erasing exposure device CEL as the photosensitive drum 131 rotates, the CEL control signal transits to Low (t3). If the transfer paper having a small width is used instead of the transfer paper having the maximum width usable in the copying operation of the copying machine 100, the lighting width data is switched to switch the exposure width of the charge erasing exposure unit CEL.

When the rear end of the image area c1 passes through the charge erasing exposure device CEL, the CEL control signal transits to Hi (t4). Also at this time, the lighting width data instructs lighting in the entire width.

When one copy operation is completed in this way, the second and subsequent copy operations are subsequently performed. 2
When the leading end of the image area c2 used in the second copy operation passes through the charge erasing exposure device CEL, the CEL control signal becomes Lo.
The state changes to w (t5), and when the rear end of the image area c2 passes, the CEL control signal changes to Hi (t6).

When the leading end c3 of the image area used in the third copy operation passes through the charge erasing exposure unit CEL, the CEL control signal transits to Low (t7).

In the third copying operation, when the tail end of the image area c3 passes through the charge erasing exposure device CEL, the CEL control signal transits to Hi (t8). According to the lighting width data given at this time, the charge erasing exposure device CEL lights up in the entire width.

The tail end of the image area c3 is a charge erasing exposure device C
After passing through the EL, the developing sleeve 223, the transfer device 134, and the separator 1
Pass 35. When the tail end of the image area c3 passes through the separator 135, the transfer paper is separated from the photosensitive drum 131, and is not in contact with the photosensitive drum 131. When the tail end of the transfer paper is separated from the photosensitive drum 131, the process drive motor drive signal transitions to Low (t
9). When the process drive motor drive signal transitions to Low, the photosensitive drum 131 idles and stops after a while.

When the process drive motor drive signal transits to Low, the CPU 310 starts counting by a program, and after a predetermined time elapses, the PCL control signal, the CEL control signal, and the developing bias control signal transit to Low (t1).
0).

The count of the CPU 310 counts a period given by the timing data. The timing data is data corresponding to a period from the transition of the process drive motor drive signal to Low until the idling of the photosensitive drum 131 stops. Therefore, the idling of the photosensitive drum 131 has stopped when the counting is completed at the timing of t10. Further, during the period from t9 to t10, that is, during the idling of the photosensitive drum 131, the pre-charging exposure device PCL and the charging erasing exposure device CEL continue to be turned on, and the developing bias is applied. At the start of the next copying operation, the lighting of the pre-charging exposure device PCL and the charging erasing exposure device CEL and the application of the developing bias are performed simultaneously with the start of the rotation of the photosensitive drum 131. As a result, the process drive motor drive signal becomes L
In the period from the transition to ow to the transition to Hi due to the start of the next copy operation, the region of the potential at which the toner can be developed does not pass through the pre-charging exposure device PCL, and the toner is developed in a belt shape. Can be prevented. Further, between the transition of the process drive motor drive signal to Low and the transition to Hi at the start of the next copy operation, the region of the potential at which the toner can be developed does not pass through the charge erasing exposure device CEL. In addition, the occurrence of density unevenness can be prevented. Further, even when the photoreceptor is fatigued and the potential of the white background becomes higher than the ground potential, the process drive motor drive signal is low.
From the transition to ow to the transition to Hi at the start of the next copy operation, it is possible to prevent the toner from being developed in a belt shape.

On the other hand, during the counting by the CPU 310 and after the counting is completed, the transport drive motor drive signal is in the Hi state, and the transport mechanism 140 transports the transfer paper separated from the photosensitive drum 131 to the fixing device 137, and the fixing device 137. The transfer paper on which the toner image has been fixed in 137 is discharged to a discharge tray 139. When the transfer sheet is discharged to the discharge tray 139, the transport drive motor drive signal transitions to Low (t11).

In the copying machine 100 according to the present embodiment, when the transfer paper is separated from the photosensitive drum 131, the rotation of the process drive motor M2 is stopped, so that the photosensitive drum 131 and the developing sleeve 223 are stopped. Fatigue can be prevented from progressing. In addition, since the rotation of the photosensitive drum 131 is also stopped, the progress of the fatigue of the photosensitive member can be prevented.

Further, the process drive motor M2 or the transport drive motor M1 may be eliminated, a clutch mechanism may be provided between the photosensitive drums 131, and the drive start timing of the photosensitive drums 131 may be determined by connecting / disconnecting the clutch. .
For example, in an example including a main motor that drives the transport mechanism 140 and a clutch that intermittently drives the main motor and the photoconductor,
The main motor is a transport driving unit, and the photoconductor driving unit is constituted by the main motor and the clutch.

The timing of t9 may be the same as when the tail end of the transfer paper is separated from the photosensitive drum 131, or may be slightly delayed. The timing of t11 may be the same as the transfer paper is discharged to the discharge tray 139 or may be slightly delayed.

Next, another example of the timing of the operation of each component during the copying operation of the copying machine 100 will be described with reference to FIG. In the example of FIG. 4, the pre-charging exposure device PCL and the charge erasing exposure device C
Except for changing the timing of turning off the EL and the timing of stopping the application of the developing bias, the operation is almost the same as that of the example of FIG.

The first and second copy operations are executed by the copy start signal, and when the third copy operation is started, the temperature of the surface of the photosensitive drum 131 is detected at timing t7. As for the temperature, the signal of the temperature sensor 313 is expressed as CP.
It is determined and detected in U310. The CPU 310 replaces the timing data with a value corresponding to the detected temperature. Accordingly, the timing at which the pre-charging exposure device PCL and the charging erasing exposure device CEL are turned off and the application of the developing bias is stopped depends on the temperature of the photosensitive drum 131. In the present embodiment, the pre-charging exposure device PCL and the charging erasing exposure device CEL
Is turned off, and the temperature at which the timing for stopping the application of the developing bias is detected is 0 ± 12.5 ° C.
a, t10b at 25 ± 12.5 ° C, 50 ± 12.5
The time at ° C. was shown as t10c. However, in the display in the figure, 0
C, 25 C, and 50 C, and only the temperature at the center of the range is shown.

The cleaning device 136 uses a cleaning blade made of silicon rubber in contact with the photosensitive drum 131. The friction between the cleaning blade and the surface of the photosensitive drum 131 changes according to the temperature in the vicinity of the photosensitive drum 131, and the friction decreases when the temperature is high,
The idling time increases, and at low temperatures, the friction increases and the idling time shortens. When the temperature near the photoconductor drum 131 is high and the idling time is long, the timing for turning off the pre-charging exposure device PCL and the charging erasing exposure device CEL and the timing for stopping the application of the developing bias are delayed. It is possible to prevent the toner from being developed and uneven density from appearing. If the temperature near the photosensitive drum 131 is low and the idling time is short, the timing for turning off the pre-charging exposure device PCL and the charging erasing exposure device CEL and the timing for stopping the application of the developing bias are advanced. And the progress of fatigue of the photoreceptor due to discharge or electric discharge can be delayed. By changing the timing of turning off the pre-charging exposure device PCL and the charging erasing exposure device CEL and the timing of stopping the application of the developing bias in accordance with the idling time that changes depending on the temperature condition, the toner is developed in a belt shape. In addition, it is possible to prevent density unevenness from appearing, and to further delay the progress of fatigue of the photoconductor.

As in the example shown in FIG. 4, the pre-charging exposure device PCL and the charge erasing exposure device CEL are turned off in accordance with the temperature in the vicinity of the photosensitive drum 131, and the timing for stopping the application of the developing bias is set. In addition, it is possible to reliably prevent the density unevenness and the phenomenon in which the toner is developed in a belt shape, and to further finely delay the progress of the fatigue of the photoconductor.

The temperature range may be set finer, the pre-charge exposure unit PCL and the charge erasing exposure unit CEL may be turned off, and the timing for stopping the application of the developing bias may be set.

[0078]

According to the image forming apparatus of the present invention, image defects such as band-like fogging do not occur, the developer is not wasted, and the deterioration of the photosensitive member can be prevented.

Further, according to the image forming apparatus of the present invention, the deterioration of the developer and the photoreceptor can be delayed, and the occurrence of image defects such as band-like fogging can be prevented.

Further, according to the image forming apparatus of the present invention, even if the peripheral temperature of the photosensitive drum rises and falls, image defects such as band-like fogging and density unevenness do not occur and deterioration of the photosensitive drum can be delayed. it can.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing the entire configuration of a copying machine 100.

FIG. 2 is a block diagram illustrating a control circuit.

FIG. 3 is a timing chart illustrating an operation of the copying machine 100.

FIG. 4 is a timing chart illustrating another example of the operation timing of each component.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 copier 120 reading and scanning unit 131 photoreceptor drum 132 charger 140 transport mechanism 200 developing unit 310 CPU 313 temperature sensor M1 transport drive motor M2 process drive motor PCL pre-charging exposure unit CEL charging exposure unit

Claims (6)

[Claims] A rotatable photoreceptor; a photoreceptor driving unit for supplying a driving force to the photoreceptor to rotate the photoreceptor; a latent image forming unit for forming an electrostatic latent image on the photoreceptor; And a developing unit for developing the toner image corresponding to the electrostatic latent image by causing the developed toner to adhere to the photoconductor by a developing electric field generated by application of a developing bias. An image forming apparatus having a control unit for applying the developing bias for a predetermined period after the image forming apparatus stops. A rotatable photoreceptor, a photoreceptor driving unit for supplying a driving force to the photoreceptor to rotate the photoreceptor, a charging unit for charging a surface of the photoreceptor, and an image provided on the photoreceptor. Exposing means for exposing outside the image area by switching the exposure width according to the width of the area, forming an electrostatic latent image on the photoconductor and developing a toner image corresponding to the electrostatic latent image An image forming apparatus comprising: a control unit configured to switch an exposure width of the out-of-region exposure unit to a maximum width for exposure for a predetermined period after the supply of the driving force is stopped; 3. The apparatus according to claim 1, further comprising a temperature acquisition unit for acquiring a temperature near the photoconductor, wherein the control unit changes the predetermined time according to the temperature acquired by the temperature acquisition unit. Or the image forming apparatus according to 2. 4. A rotatable photoreceptor, a photoreceptor driving unit for supplying a driving force to the photoreceptor to rotate the photoreceptor, and a pre-charge exposure for exposing the photoreceptor by exposing the photoreceptor over its entire width Means, and charging means for charging the surface of the photoreceptor removed by the pre-charging exposure means, forming an electrostatic latent image on the charged photoreceptor and developing a toner image corresponding to the electrostatic latent image A temperature acquisition unit for acquiring a temperature in the vicinity of the photoconductor, and the pre-charging exposure unit for a predetermined time after the supply of the driving force is stopped in accordance with the temperature acquired by the temperature acquisition unit. An image forming apparatus comprising control means for exposing a light. 5. A transport unit for transporting a transfer material onto which the toner image is transferred, a transport drive unit for driving the transport unit, and a driving force of the photoconductor drive unit independently of the drive of the transport unit. 5. The image forming apparatus according to claim 1, further comprising a drive control unit for stopping supply. 6. The apparatus according to claim 1, wherein the predetermined time is a time from when the supply of the driving force is stopped to when the idling of the photoconductor is stopped. Image forming apparatus.