JPH08305242A - Image forming device - Google Patents

Abstract

PURPOSE: To eliminate a charging phenomenon on an image carrier which occurs if waiting time is not less than a fixed time. CONSTITUTION: A timer 17 accumulates waiting time from the completion of image formation in which a toner image is transferred onto a transfer material to the start of the next image formation process. When waiting time such that toner images are continuously transferred onto the transfer material is detected to be within a fixed time, for example, the start time of charging by a post charger 7 and a separation charger 9 for charging a photoconductor 1 is set by a CPU 16 to just before the transfer material is conveyed into a transfer nip part. When the waiting time is detected to be not less than the fixed time, the CPU 16 sets the start time of charging to a time after the position of contact between a cleaning roller 12 and the photoconductor 1 has passed through a primary charger 3 and before this position has passed through the post charger 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine having an AC charger, a laser beam printer and a facsimile.

[0002]

2. Description of the Related Art A conventional electrophotographic image forming apparatus, for example, a negative / positive microreader printer is shown in FIG.
As shown in FIG. 3, a pre-exposure unit 2, a primary charging device 3, a positive developing device 5, are sequentially arranged around a photosensitive member 1 having a negative charging characteristic such as an OPC photosensitive drum along the rotation direction of the photosensitive member 1.
A negative developing device 6, a post charger 7, a transfer charger 8, a separation charger 9 and a cleaner 10 are provided, and a fixing device (not shown) is provided downstream of the transfer material (not shown) after the transfer of the visible image in the conveying direction. Is provided. Cleaner 10
Includes a cleaning blade 11 and a cleaning member (cleaning roller) 12, and the cleaning roller 12 is configured by covering a core metal 13 with urethane rubber 14.

The primary charger 3 uniformly charges the photoconductor 1, and the image pattern transmitted through the film original is projected on the photoconductor 1 uniformly charged by the primary charger 3. An electrostatic latent image is formed. To this electrostatic latent image, chromatic fine powder (toner) having an electrostatic charge is attached and developed as a visible image. In this case, the photoconductor 1
Methods of developing a visible image on the top include a negative mode for obtaining a positive print from a negative film original and a positive mode for obtaining a positive print from a positive film original. In the negative mode, a portion on the surface of the photoconductor 1 corresponding to the image portion of the negative film original is strongly exposed, and a negative image is formed using the negative developing device 6 to form a positive image. It is a thing. On the other hand, in the positive mode, a portion on the surface of the photoconductor 1 corresponding to the bright background portion of the positive film original is strongly exposed, and a positive image is formed by developing with a positive toner positively charged using the positive developing device 5. To do.

The post charger 7 charges a visible image on the photosensitive member 1 by superposing an alternating current (AC) bias on a direct current (DC) bias having the same polarity as the toner. So that it can be easily transferred to a transfer material such as. Then, the transfer material is brought into close contact with the visible image on the photoreceptor 1, and a charge having a polarity opposite to that of the toner is applied from the back side of the transfer material by the transfer charger 8 such as a corona charger to electrostatically transfer the image. After that, the transfer material is subjected to an alternating current (AC) charge by a separation charging device 9 including a corona charging device to remove the charge, and is peeled off from the photoconductor 1. Next, the transfer material is conveyed to a fixing device (not shown) to fix a visible image by heat or the like, and then discharged to the outside of the apparatus main body.

In the transfer step, 100% of the toner on the photoconductor 1 is not always transferred to the transfer material, and for example, about 10% of the toner remains on the surface of the photoconductor 1 after the transfer. Therefore, as shown in FIG. 4, the residual toner (waste toner) 15 on the photoconductor 1 is removed by the cleaning blade 11.
Scraped off by the cleaning roller 12
Be recovered by.

Next, the charging sequence of the image forming apparatus will be described with reference to FIG. When copying (image formation) is started, the photoconductor 1 starts to rotate. The primary charging is started from the timing of one rotation earlier than the tip position of the image forming area of the photoconductor 1. Immediately before the tip of the transfer material passes through the transfer charger 8, the post charger 7, the transfer charger 8 and the separation charger 9 start the charging operation.
After the trailing end of the transfer material passes through the separation charging device 9, the charging operations of 8 and 9 are completed.

By the way, with the recent increase in the speed of printer engines, the voltage in each charging step tends to increase.
Therefore, if the photoconductor 1 is directly charged when the transfer material is not fed, fatigue of the photoconductor 1 increases, which adversely affects long-term image stability and life of the photoconductor 1.
Post charging, transfer charging, and separation charging are performed by the sequence described above. As a result, it is possible to reduce power consumption and reduce charged products such as ozone.

[0008]

However, since the cleaning roller 12 in the conventional image forming apparatus is in contact with the photosensitive member 1, the cleaning roller 12 rotates with the rotation of the photosensitive member 1 to cause frictional electrification. The urethane rubber 14 on the surface of 12 is negatively charged. Therefore, if the cleaning roller 12 that is strongly negatively charged and the photoconductor 1 are left in contact with each other for a certain period of time after the completion of copying, a positive charge is induced on the surface of the photoconductor 1. A so-called positive charging memory (charging phenomenon) occurs.

That is, the photosensitive member 1 having a negative charging polarity can easily be neutralized by the pre-exposure unit 2 when the surface thereof is negatively charged, but can be neutralized when the surface is negatively charged. Since it is difficult to charge, a positive charging memory remains. Therefore, as shown in FIG. 5, after the copying is restarted, there is a potential valley for a while.

When such a charging memory occurs, in the positive mode, a portion of the surface of the photosensitive member 1 which is higher than the surface potential on the negative side is developed and the density becomes high. Therefore, the photosensitive member charged positively by the contact of the cleaning roller 12 The area 1 has a lower potential than the surrounding area, and the image density on the print becomes lighter as shown in FIG. 6A.

On the other hand, in the negative mode, since the portion of the photosensitive member 1 having a low surface potential is developed, the memory portion positively charged by the contact of the cleaning roller 12 is originally the background portion as shown in FIG. 6B. Black streaks are generated in areas that should be white, and the quality of the printed image is degraded.

Since the microreader printer processes both the negative mode and the positive mode as described above, the charging memory exists regardless of whether the charging memory is positive or negative. For this reason, there is a problem that an image defect occurs regardless of which mode the image processing is performed.

Therefore, the present invention has been made in order to solve the above-mentioned problems, and an image for eliminating the charging phenomenon on the image carrier, which occurs when the waiting time is a certain time or more, is provided. An object is to provide a forming device.

[0014]

In order to achieve the above object, an image forming apparatus according to the present invention comprises an image carrier having a charging characteristic of a predetermined polarity, and an image carrier rubbed against the image carrier. A cleaning member for removing transfer residual toner on the surface of the carrier, wherein the triboelectrification polarity of the cleaning member and the charging characteristic of the image carrier due to the rubbing with the image carrier have the same polarity, An AC charger that charges the image carrier to the same polarity as the charging characteristics of the image carrier, a timer that integrates the waiting time after the image forming operation of transferring the toner image to the transfer material, and the image forming again. When the waiting time is a first waiting time within a certain time, the charging start timing of the AC charger is set immediately before the transfer material reaches the transfer nip portion, and the waiting time is set. Second wait time is over a certain time If it is between the charging start timing of the AC charger, and a control means for setting earlier than the charging start timing of the first waiting time, it is characterized.

As an example, the AC charger is a post charger.

As another example, the AC charger is a separation charger.

As another example, the AC charger is a pre-cleaning static eliminator.

Preferably, the control means passes the post-charger after the contact position between the cleaning member and the image carrier passes the primary charger at the charging start timing of the second waiting time. I set it before.

[0019]

According to the above construction, the timer integrates the waiting time from the end of image formation for transferring the toner image onto the transfer material to the start of the next image formation. If the cleaning member contacts the same position of the image carrier during the waiting time within a certain time, the control means sets the charging start timing of the AC charger for charging the image carrier to the transfer nip portion. Set just before delivery. Further, if the cleaning member contacts the same position of the image carrier for a certain time or more during the waiting time, the control unit sets the charging start timing earlier than when the waiting time is within a certain time. In this case, the AC charger charges the image carrier to the same polarity as the cleaning member. As a result, the AC discharge from the AC charger removes the charging phenomenon formed by the image carrier and the cleaning member being in contact with each other at the same position for a certain time or longer.

[0020]

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

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention,
FIG. 2 is a sequence diagram showing the operation of FIG. 1. In this embodiment, a printer using a negatively chargeable OPC photosensitive member as an image carrier will be described as an example. The image forming unit of the printer is configured as shown in FIG. That is,
A CPU 16 that is a control unit is connected to the post charger 7 and the separation charger 9 that are a plurality of AC chargers that charge the photoreceptor 1 that is an image carrier. Also, CPU1
To 6 is connected a timer counter 17 for integrating the waiting time from the end of image formation to the start of the next image formation. Since the charging start timing of the post charger 7 and the separation charger 9 differs depending on the length of the waiting time, the length of the waiting time is integrated by the timer counter 17. The CPU 16 controls the charging start timings of the post charger 7 and the separation charger 9, and also controls the charging start timings of the primary charger 3 and the transfer charger 8. The charging start timing of the primary charger 3 is controlled corresponding to the start of an image forming operation (copy operation) in which the primary charger 3 uniformly and primarily charges the photoconductor 1, and the charging start timing of the transfer charger 8 is also controlled. Is controlled corresponding to the time when the transfer charger 8 operates immediately before the transfer material is carried into the transfer nip portion. In FIG. 1, the same or equivalent components as those in FIG. 3 are designated by the same reference numerals, and duplicate description will be omitted.

Next, the operation will be described. During the image forming operation (during copying operation), the cleaning roller 12 is strongly rubbed against the photoconductor 1, and the surface of the cleaning roller 12 is negatively charged due to friction. Then, after the copy operation is completed, the timer counter 17 starts the integration of the waiting time after the copy is completed. When the cleaning roller 12 and the photoreceptor 1 are left in contact with each other for 20 to 40 minutes, the photoreceptor 1 in contact with the cleaning roller 12
A strong charging phenomenon occurs in the surface area of the, and a positive charging memory area charged to about +30 V is generated. On the other hand, if the contact state between the cleaning roller 12 and the photoconductor 1 is less than 20 minutes, a weak positive charging region is generated in the surface region of the photoconductor 1 in contact with the cleaning roller 12, but this level Then there is little effect.

When the copy operation is started again,
The CPU 16 detects the value of the timer counter 17 (standby time). Then, according to the standby time detected by the CPU 16, the CPU 16 outputs a command in which the timing of starting AC charging is changed. That is, as shown in FIG. 2, for example, when the standby time is longer than a predetermined time of more than 20 minutes (second standby time), the CPU 16 operates the primary charger 3 immediately after the start of copying to start discharging. Then, the charging memory area is primarily charged. Next, when the charging memory area, which is primarily charged with the rotation of the photoconductor 1, approaches the post charger 7, the CPU 16 starts the charging operation of the post charger 7 and the separation charger 9.

The photosensitive member 1 is rotated about one and a half times before image formation, and the charging memory area passes through the post charging device 7 and the separation charging device 9 twice during this period to receive AC charging. Then, immediately before the leading edge of the transfer material is carried into the transfer nip portion where the photoconductor 1 and the transfer charger 8 come into contact with each other, the transfer charger 8 starts the charging operation, and when the transfer material passes through the transfer nip portion. The toner image formed on the surface of the photoconductor 1 is transferred. When the trailing edge of the transfer material passes through the separation charger 8, the post charger 7, the transfer charger 8 and the separation charger 9 complete the charging operation.

When an image is formed again within a fixed time of less than 20 minutes (first waiting time), or when an image is formed on the transfer material of the second and subsequent sheets of continuous copy,
In the non-sheet passing area where the transfer material does not pass through the transfer charger 8, the post charger 7 and the separation charger 9 are in an off state where they do not perform a charging operation, and immediately before the front end of the transfer material passes through the transfer charger 8. The charging operation of the post charger 7, the transfer charger 8 and the separation charger 9 is started. After the copy operation is completed, the CPU 16 resets the timer counter 17 and integrates the waiting time again.

In this embodiment, the post-charger and the separation charger are used for description. However, in the case of alternating-current charging, the charge phenomenon occurring on the image carrier during the waiting time can be removed by, for example, a pre-cleaning charge eliminator. You may use it.

Further, in the above-mentioned embodiments, the image bearing member is described as a negative OPC photosensitive member, but the present invention is not limited to this, and it can be applied to, for example, an amorphous silicon photosensitive member or a cadmium sulfide photosensitive member. It is a thing.

Further, although the printer for both negative and positive has been described as the printer of the above embodiment, the same effect can be obtained by the printer for exclusive use of the negative or the printer for exclusive use of the positive.

[0029]

As described above, according to the present invention,
A timer integrates the waiting time from the end of image formation for transferring the toner image to the transfer material to the start of the next image formation, and the control means charges the image carrier when the waiting time is within a fixed time. Set the charging start time of the AC charger just before the transfer material is loaded into the transfer nip,
Further, when it is longer than the fixed time, the charging start time is set earlier than the fixed start time, so that the charging phenomenon of the image carrier caused by the contact with the cleaning member for the fixed time or longer can be removed. .

In addition, during the second and subsequent sheets of continuous copying and during continuous use without waiting time, AC charging is output only in the paper passing area, which saves energy and reduces the generation amount of charging products such as ozone. The effect of alleviating the deterioration of the image carrier can be obtained.

[Brief description of drawings]

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

FIG. 2 is a sequence diagram illustrating an operation of the above.

FIG. 3 is a schematic configuration diagram showing an example of a conventional image forming apparatus.

FIG. 4 is an enlarged cross-sectional view showing an extracted cleaner portion of the above.

FIG. 5 is a sequence diagram illustrating an operation of the above.

FIG. 6 is a diagram illustrating a transfer material on which an image is formed, and FIG. 6A is a diagram illustrating an image defect state of the transfer material in a positive mode;
(B) is a figure explaining the image defect state of the transfer material by negative mode.

[Explanation of symbols]

 1 Image Carrier (Photoreceptor) 7 AC Charger (Post Charger) 9 AC Charger (Separation Charger) 12 Cleaning Member (Cleaning Roller) 16 Control Means (CPU) 17 Timer

Claims (5)

[Claims] 1. An image carrier, comprising: an image carrier having a charging characteristic of a predetermined polarity; and a cleaning member which is rubbed against the image carrier to remove transfer residual toner on the surface of the image carrier. In an image forming apparatus in which the triboelectrification polarity of the cleaning member and the charging characteristic of the image carrier due to the friction with the image carrier are the same, the image carrier is charged to the same polarity as the charging property of the image carrier. An alternating current charger that causes the transfer material, a timer that accumulates the standby time after the image forming operation for transferring the toner image onto the transfer material, and a first standby time within which the standby time is within a fixed time when the image is formed again. In the case of, the charging start timing of the AC charger is set immediately before the transfer material reaches the transfer nip portion, and when the waiting time is a second waiting time of a certain time or more, the AC When to start charging the charger And a control means for setting earlier than the charging start timing of the first waiting time, that the image forming apparatus according to claim. 2. The image forming apparatus according to claim 1, wherein the AC charger is a post charger. 3. The image forming apparatus according to claim 1, wherein the AC charger is a separation charger. 4. The image forming apparatus according to claim 1, wherein the AC charger is a pre-cleaning static eliminator. 5. The control means passes the post-charger after the contact position between the cleaning member and the image carrier passes the primary charger at the charging start timing of the second waiting time. The image forming apparatus according to claim 1, wherein the image forming apparatus is set before the setting.