JPH07134454A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an image defect which is caused by sticking objects on a photoreceptor in the case where an electrifying member and the photoreceptor are left as it is, in contact with each other, in an image forming device using a contact electrifier. CONSTITUTION:Prior to image formation, prerotation is carried out to drive the photoreceptor, and the sticking objects are removed by the friction of a cleaning blade, etc., at that time. Time T required for the prerotation is automatically adjusted according to time Ts during which the photoreceptor has been stopped. A dummy toner pattern is formed on the photoreceptor during the prerotation, and the sticking objects are efficiently removed by the abrasive action of the toner. An amount of sticking toner pattern, its area, or the rotating speed of the photoreceptor are adjusted according to the time Ts.

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 having a contact charging member in which a charging member for charging the photosensitive member is in contact with the photosensitive member.

[0002]

2. Description of the Related Art In a general electrophotographic image forming apparatus represented by the Carlson process, a corona discharge method which is a non-contact charging method is used to uniformly charge a photosensitive member. However, since the corona discharge device applies a high voltage to a 30 to 100 μm tungsten wire called a corona wire to perform discharge, air is ionized to form a large amount of ozone and nitrogen oxide. The ozone and the like are not only harmful to the human body, but also damage the photoconductor and the machine. Further, ozone is particularly remarkably generated when a negative discharge is performed, and in recent years the photoconductor has become an organic photoconductor for negative charging, and environmental standards for the generated gas discharged from the image forming apparatus have become strict. In addition, it is a serious problem. On the other hand, in the contact charging method in which the charging member is brought into contact with the photosensitive member to perform charging,
There are advantages that the voltage applied to the charging member is small and the amount of ozone generated is very small. An image forming apparatus using a roller-shaped contact charging member has already been commercialized.

However, under the present circumstances, this contact charging method has no choice but to change its way to a corona wire in terms of uniformity of charging. In order to improve the uniformity of charging, for example, in Japanese Patent Laid-Open No. 63-149668, an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage when a DC voltage is applied is superimposed on the charging member. Is proposed to improve the charging uniformity.

As described above, the charging performance by the contact charging method is improved, but there are other problems. That is, the contact charging member is always in contact with the photoconductor, but if the charging member and the photoconductor are left in contact with the photoconductor being stopped, the contact portion on the photoconductor may be removed from the surface of the charging member. It becomes a state of being contaminated by the adherence of. Almost no contaminants on the photoconductor can be visually confirmed, but since less toner adheres to the contaminated part than the surface of other photoconductors during development,
As a result, a white streak (white spot) image corresponding to the contaminated portion appears in the output image, resulting in an image defect. Further, when the image forming operation is continued, toner or paper powder adheres to the charging member, and as a result, the surface property of the member (mainly releasability from the photoconductor) is changed, which also causes There is a problem that the appearance of white lines changes.

In order to solve such a problem, for example, in JP-A-4-157485 and JP-A-1-207768, the charging member is separated from the photoconductor when the photoconductor is stopped,
A technique has been proposed for preventing the charging roller from being left in pressure contact with the photosensitive member. Further, Japanese Patent Laid-Open No. 1-204081 proposes to improve the releasability from the photoconductor by coating the surface of the charging roller.

[0006]

However, if a support mechanism and a drive mechanism for retracting the charging roller are installed, it becomes difficult to downsize the apparatus and an increase in cost is inevitable. Further, even if the releasability is improved, it is not possible to completely prevent image defects.

In view of these problems, the present invention, in an image forming apparatus using a contact charging device, causes image defects due to deposits on the photosensitive member when the charging member and the photosensitive member are left in contact with each other. The problem is to suppress

[0008]

In order to solve the above-mentioned problems, in the present invention, a photosensitive member (1) for forming an image and an image forming surface of the photosensitive member are installed so as to be in contact with each other, and An image forming apparatus comprising a contact charging unit (2) for charging the photosensitive member, and at least another contact member (3, 4, 6) other than the contact charging unit contacting the image forming surface of the photosensitive member. A time measuring means (12) for measuring a time during which the contact charging means is in contact with the photoconductor while the photoconductor is stopped; A control means (7) is provided for executing the pre-rotation operation and thereafter starting the image forming process, and automatically adjusting the time of the pre-rotation operation in accordance with the time output by the timing means.

According to a second aspect of the present invention, the control means is configured to form a toner pattern (SB) on the image forming surface of the photoconductor during the pre-rotation operation.

Further, in the invention of claim 3, the control means forms a toner pattern on the image forming surface of the photoconductor during the pre-rotation operation, and at the same time, the toner pattern toner is formed. The amount of adhesion is automatically adjusted (SC) according to the time output by the timing means.

Further, in the invention of claim 4, the control means forms a toner pattern on the image forming surface of the photoconductor and the toner pattern during the pre-rotation operation. The size of the area is automatically adjusted (S6B, SD) according to the time output by the timing means.

Further, in the invention of claim 5, the control means automatically adjusts the rotational speed of the photoconductor during the pre-rotation operation in accordance with the time output by the timing means (S).
F)

The symbols shown in parentheses are the reference numerals of corresponding elements in the embodiments described later, but each constituent element of the present invention is a concrete element in the embodiments. It is not limited to only.

[0014]

In the present invention, the pre-rotation operation for driving the photoconductor (1) for forming an image is executed prior to the execution of the normal image forming process. At this time, since the contact members (developing sleeve, transfer belt, transfer roller, cleaning blade, cleaning fur brush, etc.) other than the contact charging means (for example, the charging roller 2) are in contact with the photoconductor,
By the friction between the contact member (particularly the cleaning blade) and the surface of the photoconductor, the deposit on the photoconductor existing at the contact portion between the charging roller and the photoconductor is removed. If the normal image forming process is started after the deposits are removed, the generation of white stripes can be suppressed.

If the pre-rotation operation is performed for a long time, the deposits on the photoconductor are sufficiently removed, so that the occurrence of white stripes can be prevented. Takes longer. The amount of adhered matter on the photoconductor and the difficulty of removing it are due to the fact that when the photoconductor is not rotating,
It changes according to the time (Ts) during which the photoconductor and the contact charging means are in contact with each other (empirically, white streaks worsen if the contact and leaving time is long). Therefore, in the present invention, in order to minimize the time of the pre-rotation operation and surely prevent the generation of white stripes, the photoconductor and the contact charging means are in contact with each other when the photoconductor is not rotating. Measured time Ts (for example, the elapsed time from the end of the previous image forming process to the start of the present image forming process), and the minimum necessary time is set based on this time Ts, and only that time is set. Perform pre-rotation operation. As a result, the removal work can be efficiently performed, white lines on the image can be prevented, and the image quality can be maintained.

In the image forming apparatus according to the second aspect, the toner pattern is further formed on the photosensitive member during the pre-rotation operation. As a result, the toner (resin particles) is present between the contact member (particularly the cleaning blade) and the photoconductor during the pre-rotation operation, so that the adhered substances are efficiently removed by the polishing effect.

In the image forming apparatus of the third aspect, the toner pattern is formed on the photosensitive member during the pre-rotation operation, and the adhesion amount of the toner pattern is automatically adjusted according to the measured time Ts. That is, when there is a large amount of adhered matter on the photoconductor and it is difficult to remove it, the adhered quantity of the toner pattern is increased and the polishing effect is enhanced, so that the adhered matter is efficiently removed in a relatively short time and the white stripe Suppress the occurrence. When the amount of deposits on the photoconductor is relatively small, the toner deposit amount is reduced in order to suppress unnecessary toner consumption.

According to another aspect of the image forming apparatus of the present invention, the toner pattern is formed on the photosensitive member during the pre-rotation operation, and the size (area) of the toner pattern is automatically determined according to the number of times the image forming process is executed. Adjust to. That is, when the amount of deposits on the photoconductor is large and it is difficult to remove the deposits, the area of the toner pattern is increased and the polishing effect is increased to efficiently remove the deposits in a relatively short time.
Suppress white lines. When the amount of deposits on the photoconductor is relatively small, the toner is
Reduce the amount of adhesion.

In the image forming apparatus of the fifth aspect, the drive speed of the photosensitive member during the pre-rotation operation is automatically adjusted according to the number of times the image forming process is executed. That is, a contact member (such as a cleaning blade) depending on the driving speed of the photoconductor
Since the ability to remove deposits due to friction between the and the surface of the photoconductor can be adjusted, when the amount of deposits on the photoconductor is large and it is difficult to remove the deposits, the capability of removing deposits can be increased in a relatively short time. Efficiently removes deposits and suppresses white lines.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of the peripheral portion of a photoconductor of a copying machine embodying the present invention. This will be described with reference to FIG. During the image forming process, the photoconductor 1, which is an image carrier, is rotationally driven in a clockwise direction in the drawing at a predetermined peripheral speed. The roller-shaped charging roller 2 installed at a position in constant contact with the photoconductor 1 makes the surface of the photoconductor 1 uniform to a predetermined potential by the DC voltage supplied from the voltage application power source 8 in the image forming process. Charge. The charging roller 2 is
A pressure spring (not shown) is constantly in pressure contact with the photoconductor 1 with a predetermined pressing force, and the photoconductor 1 is driven to rotate as the photoconductor 1 rotates.

The image forming process other than charging is the same as that of a general copying machine. That is, the surface of the charged photoconductor is exposed to image light and the potential distribution corresponding to the light and shade of the image,
That is, an electrostatic latent image is formed, and the electrostatic latent image is visualized by a toner in the developing device 3, and the visible toner image on the photoconductor is transferred onto a predetermined transfer paper by the action of the transfer roller 4. After that, the photoconductor 1 is cleaned of foreign matters such as transfer residual toner and paper dust by the cleaning device 5, and is prepared for the next image forming process.

A predetermined DC voltage is applied as a bias voltage to the developing sleeve in the developing device 3 from a developing bias applying power source. The cleaning device 5 is provided with a cleaning blade 6 that comes into contact with the surface of the photoconductor 1. Further, a photoconductor driving device 10 including an electric motor is connected to the central axis of the photoconductor 1, and the photoconductor driving device 10 drives the photoconductor 1 to rotate. Photoconductor driving device 10
Are controlled by the photoconductor drive control unit 11.

The central processing unit 7 includes a microcomputer and executes various controls including an image forming process. The central processing unit 7 includes a voltage applying power source 8, a developing bias applying power source 9, and a photoconductor drive control unit 1.
It is connected to 1. Further, the central processing unit 7 includes
The programmable timer 12 is connected. The programmable timer 12, under the control of the central processing unit 7, executes setting of various operation modes, presetting of counting contents, reading of counting contents, updating of counting contents, and the like when a set time has elapsed. Can be output. The programmable timer 12 is used, for example, to measure the time Ts during which the charging roller 2 is in contact with the surface of the photoconductor 1 while the photoconductor 1 is stopped.

The outline of the processing executed by the central processing unit 7 is shown in FIG. The operation of the central processing unit 7 will be described with reference to FIG.

When the power is turned on, initialization is executed in step S1 and then a standby process in step S2 is executed. In this standby process, reading the signals output by various sensors,
Reading of key inputs to an operation unit (not shown), control of various elements such as a heater, and identification of various states of the device are executed.

At the time of initialization, the clear of the photoconductor 1 is performed.
After executing the timing operation, the timer 12 is set in the timing mode, the count value is cleared, and the timing operation of the timer 12 is started. Therefore, the timer 12 measures time while executing the standby process. Further, the photosensitive member 1 is rotationally driven during the cleaning operation, but during the standby process, the photosensitive member 1 is rotated.
The rotation drive of is stopped.

In the next step S3, it is checked whether or not the fixing temperature has reached the target temperature, for example, to identify whether or not the preparation for the copy process is completed. If the preparation is not completed, the process returns to step S2. When the preparation for the copy process is completed, steps S3 to S
Go to 4.

In step S4, it is discriminated whether or not there is a start instruction, for example, whether or not the start key of the operation section is pushed. If there is no start instruction, step S2
Returning to step S5, when the start instruction is detected, step S5
Proceed to.

In step S5, the value output by the timer 12, that is, the time during which the photoconductor 1 is stopped (the time during which the charging roller 2 is in contact with the surface of the photoconductor in the stationary state) Ts is read. In the following step S6, the mode of the timer 12 is reset, the time T determined based on the contact stop time Ts read in S5 is set in the timer 12, and the timer T is set.
To

In the next step S7, a predetermined drive start signal is output to the photoconductor drive control section 11 to start the rotational drive of the photoconductor 1 at a predetermined speed. This is a pre-rotation operation performed prior to the image forming process, and at this time, no image is formed. However, during this pre-rotation operation, residual toner, paper dust, and the like adhering to the portion of the photosensitive member 1 that was in contact with the charging roller 2 during the stationary period, are cleaned by the cleaning blade 6 and the photosensitive member 1. It is removed by the action such as friction of the contact part with.

The duration of the pre-rotation operation is determined by the time T set in the timer 12. That is, when the timer 12 time-overs after starting the pre-rotation operation, in response to the signal output by the timer 12, the process proceeds from step S8 to the next step S9 to start a normal image forming process (copy process). To do. In this case, the image forming process may be started after the rotation of the photoconductor 1 is stopped.
The image forming process may be performed while the rotation of the photoconductor 1 is continued.

The basic contents of the image forming process are the same as those of a general copying machine. However, in the charging process, instead of corona discharge, the charging roller 2 in contact with the photoconductor 1 is used.
Carried out by

When the image forming process of step S9 is completed, the process proceeds to the next step SA. In step SA, after resetting the operation mode of the timer 12, the count value is cleared and the time counting operation is started. After that, the process returns to the standby process of step S2 and the operation is repeated. Therefore, the contact stop time measured by the timer 12 thereafter corresponds to the waiting time from the end of the image forming process to the start of the next image forming process, that is, the time during which the photoconductor 1 is not rotating.

Next, the second embodiment will be described. The basic configuration of this embodiment is the same as that of FIG. 1, and only the operation of the central processing unit 7 is changed. The contents of the processing of the central processing unit 7 are shown in FIG. Note that, in FIG. 3, the same step numbers are assigned to the same processing steps as in FIG. The part of the processing changed from FIG. 2 will be described with reference to FIG.

In this embodiment as well, the pre-rotation operation of the photosensitive member is executed in step S7.
In step SB, a toner pattern is formed on the surface of the photoconductor during the pre-rotation operation. In fact, given a latent image potential V _P to the photosensitive member by the charging roller, dummy electrostatic latent image on the photosensitive member - pattern - is down is formed. Then, when the developing bias V _BP is applied to the developing device 3, at the position of the developing device,
A potential difference (development potential) of V _P -V _BP occurs. Therefore, when the dummy pattern is developed by the developing device, the dummy pattern is
Toner adheres to the pattern position, and a visible image (toner pattern) is formed on the photoconductor.

As a result, the toner (resin particles) is present between the contact member (especially the cleaning blade) and the photosensitive member during the pre-rotation operation, so that the polishing effect causes
The deposits on the photoconductor are efficiently removed.

Next, a third embodiment will be described. The basic configuration of this embodiment is the same as that of FIG. 1, and only the operation of the central processing unit 7 is changed. The contents of processing of the central processing unit 7 are shown in FIG. Note that in FIG. 4, the same step numbers are assigned to the same processing steps as in FIG. The part of the processing changed from FIG. 3 will be described with reference to FIG.

Also in this embodiment, the pre-rotation operation of the photoconductor is executed in step S7, and the toner pattern is formed on the surface of the photoconductor during the pre-rotation operation in step SB. At step SC, the toner adhesion amount for the toner pattern is automatically adjusted. That is, by adjusting the development potential V _P -V _BP of the developing bias V _BP and the latent image potential V _P, the toner of the toner pattern - are adjusted adhesion amount. Actually, either one of the voltage applied to the charging roller (latent image potential V _P ) and the voltage applied to the developing device (developing bias V _BP ) is based on the contact stop time Ts measured by the timer 12. The value is being adjusted.

Next, a fourth embodiment will be described. The basic configuration of this embodiment is the same as that of FIG. 1, and only the operation of the central processing unit 7 is changed. The contents of processing of the central processing unit 7 are shown in FIG. Note that, in FIG. 5, the same step numbers are assigned to the same processing steps as in FIG. The part of the processing changed from FIG. 3 will be described with reference to FIG.

Also in this embodiment, the pre-rotation operation of the photoconductor is executed in step S7, and the toner pattern is formed on the surface of the photoconductor during the pre-rotation operation in step SB. The size of the toner pattern formed during the pre-rotation operation is automatically adjusted. Actually, the latent image forming length in the circumferential direction on the photoconductor is adjusted by changing the time for applying the voltage to the charging roller 2.
The size of the toner pattern is determined based on the contact stop time Ts measured by the timer 12. In addition, in step S6B, the timer 12 has two types of time T1.
(Voltage application time) and T2 (time for pre-rotation operation) are set, and when T1 elapses, control is performed so that formation of the toner pattern is completed.

Next, a fifth embodiment will be described. The basic configuration of this embodiment is the same as that of FIG. 1, and only the operation of the central processing unit 7 is changed. The content of the processing of the central processing unit 7 is shown in FIG. Note that in FIG. 6, the same step numbers are assigned to the same processing steps as in FIG. The part of the processing changed from FIG. 3 will be described with reference to FIG.

Also in this embodiment, the pre-rotation operation of the photoconductor is executed in step S7, and the toner pattern is formed on the surface of the photoconductor during the pre-rotation operation in step SB. The rotation speed of the photoconductor during the pre-rotation operation is automatically adjusted based on the contact stop time Ts measured by the timer 12. That is, before the driving of the photoconductor is started, the drive speed of the photoconductor is set according to Ts in step SF. When the normal image forming process is started, the drive speed of the photoconductor is reset to a normal predetermined speed in step SG.

[0043]

As described above, according to the present invention, the time Ts during which the contact charging means contacts the photoconductor and the photoconductor is stopped.
Is measured and the minimum required time (T, T1, T2) is set based on the time Ts, and the pre-rotation operation can be executed for that time, so the time of the pre-rotation operation is minimized. In addition, it is possible to reliably prevent the generation of white lines.

Further, in the image forming apparatus according to the second aspect, since the toner pattern is formed on the photosensitive member during the pre-rotation operation, the toner (resin particles) intervening between the contact member (particularly the cleaning blade) and the photosensitive member. ) The polishing effect of
The deposit can be efficiently removed.

According to the image forming apparatus of claim 3,
Furthermore, the amount of toner pattern adhered is changed according to the measured contact stop time Ts, and the polishing effect of the toner is automatically adjusted, so that the adhered substances can be reliably removed and wasteful consumption of toner is prevented. You can.

According to the image forming apparatus of claim 4,
The size of the toner pattern is changed according to the measured contact stop time Ts, and the polishing effect of the toner is automatically adjusted, so that the adhered substances can be reliably removed and the wasteful consumption of the toner can be prevented. .

In the image forming apparatus of the fifth aspect, the driving speed of the photosensitive member during the pre-rotation operation is changed according to the measured contact stop time Ts, so that the adhered matters are efficiently removed and the image quality is maintained. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration around a photoconductor of a copying machine according to an embodiment.

FIG. 2 is a flowchart showing the operation of the CPU 7 of FIG.

FIG. 3 is a flowchart showing the operation of the CPU 7 of the second embodiment.

FIG. 4 is a flowchart showing the operation of the CPU 7 of the third embodiment.

FIG. 5 is a flowchart showing the operation of the CPU 7 of the fourth embodiment.

FIG. 6 is a flowchart showing the operation of the CPU 7 of the fifth embodiment.

[Explanation of symbols]

1: Photoconductor 2: Charging roller 3: Developing device 4: Transfer roller 5: Cleaning device 6: Cleaning blade 7: Central processing unit 8: Voltage application power supply 9: Development bias power supply 10: Photoconductor driving device 11: Photoconductor Drive control unit 12: Timer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kentaro Matsumoto 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Inventor Nobuo Kikuchi 1-chome, Nakamagome, Ota-ku, Tokyo No. 3-6 Inside Ricoh Company (72) Inventor Koichi Yamazaki 1-chome Nakamagome 1-chome, Ota-ku, Tokyo No. 3-6 Inside Ricoh Company Ltd. (72) Sadao Takahashi 1-chome Nakamagome, Ota-ku Tokyo No. 3-6 In Ricoh Company

Claims (5)

[Claims] 1. A photoconductor for forming an image, a contact charging means for charging the photoconductor in a state in which the photoconductor is provided so as to be in contact with the photoconductor, and an image forming surface of the photoconductor. In an image forming apparatus comprising at least another contact member other than the contact charging means for contacting with:
A time measuring means for measuring a time during which the contact charging means is in contact with the photoconductor while the photoconductor is stopped; and a pre-rotation operation of the photoconductor when an instruction to start the image forming process is given. An image forming apparatus comprising: a control unit that executes the image forming process, starts the image forming process thereafter, and automatically adjusts the time of the pre-rotation operation according to the time output by the time measuring unit. apparatus. 2. The image forming apparatus according to claim 1, wherein the control unit forms a toner pattern on the image forming surface of the photoconductor during the pre-rotation operation. 3. The control means forms a toner pattern on the image forming surface of the photoconductor during the pre-rotation operation, and at the same time, the toner adhesion amount of the toner pattern is measured by the time measuring means. Automatically adjusts according to the output time,
The image forming apparatus according to claim 2. 4. The control means forms a toner pattern on the image forming surface of the photoconductor at the time of the pre-rotation operation, and determines the size of the area for forming the toner pattern. The image forming apparatus according to claim 2, wherein the image forming apparatus automatically adjusts according to the time output by the time measuring means. 5. The image forming apparatus according to claim 1, wherein the control unit automatically adjusts the rotation speed of the photoconductor during the pre-rotation operation in accordance with the time output by the timing unit.