JPH11174784A - Electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a mechanism eliminating a soiling matter stuck on an electrifying roller surface of a contact system roller electrifying device, possible to maintain a cleaning effect over a long period at a low cost without making an image forming sequence complicated. SOLUTION: This device, allowed to electrify a photoreceptor surface by holding the electrifying roller 2 in contact with the photoreceptor 1, in order to remove the soiling matter stuck on the electrifying roller 2 surface, is allowed to apply speed difference between the photoreceptor 1 and the electrifying roller 2 during the cleaning sequence thereof, and to apply DC bias opposite to the image forming time on the electrifying roller 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an electrophotographic image forming apparatus such as a copying machine and a laser beam printer. More specifically, the present invention relates to a charging member to which a voltage is applied. The present invention relates to a charging device that charges a member to be charged by contacting the charging device.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus for forming an image through an electrophotographic process of charging, exposing, developing, transferring, cleaning and fixing using a photosensitive drum as an image carrier is well known.

As a charging device such as an electrophotographic image forming device, there is a corotron system in which a high voltage of 5 to 6 kV is applied to a tungsten wire to perform corona discharge to charge a member to be charged. However, since this method handles high voltage,
The power supply is expensive and has safety concerns. Therefore, in recent years, a contact charging method has been adopted in which charging is performed while a conductive charging member is in contact with a member to be charged. A surface of about 0.5 [kV] can be charged by applying a voltage of 1 to 2 [kV] to a roller-shaped conductive charging member and rotating it in contact with a photosensitive drum which is an object to be charged. The roller charging method has attracted attention because it has advantages such as a relatively low voltage to be handled and an extremely small amount of ozone generated as compared with the corotron method.

In general, a cleaning member is provided on the upstream side in the moving direction of the peripheral surface of the member to be charged at the position where the charging member is provided.
A cleaning blade is used to remove residual toner from the surface of the charged body after transfer.However, paper dust adhered to the charged body at the time of transfer and minute external additives separated from the toner are removed. The agent cannot be completely removed.

In the charging roller system, since the charging roller is always in contact with the member to be charged, paper powder and toner external additives that have passed through the cleaning blade adhere to and contaminate the surface of the charging roller. Adversely affect operation.
In order to prevent this, a mechanism for removing paper powder or toner external additives attached to the charging roller surface with a sponge material or the like is required.

[0006]

However, in the cleaning mechanism of the charging roller made of a sponge material as in the above-mentioned conventional example, paper powder and external additives such as toner are clogged in bubbles of the sponge material. There is a problem that the cleaning effect is reduced, and a streak-like mark remains on the surface of the charging roller due to unevenness of the surface of the sponge material, and it is difficult to uniformly clean. In order to solve these problems in the charging roller cleaning mechanism, the apparatus itself has to be complicated and becomes expensive.

An object of the present invention is to provide a cleaning mechanism for the charging roller having a simple structure and a low cost.
Another object of the present invention is to provide a charging device capable of maintaining a cleaning effect for a long time.

[0008]

In order to achieve the above object, the invention according to the present application provides a charging member in the form of a rotatable roller to which a voltage is applied by contacting the surface of the member to be charged. In the charging device, the charging member rotates in the direction in which the peripheral surface moves in the same direction at the same peripheral speed with respect to the rotation of the member to be charged during the operation of charging the member to be charged. It is characterized in that the charging member rotates with a peripheral speed difference with respect to the rotation of the charging member.

In addition, the peripheral speed of the charging member during the operation of not charging the member to be charged may be lower than the peripheral speed of the member to be charged,
The polarity of the voltage applied to the charging member during the operation of not charging the member to be charged may be opposite to that during the image forming operation.

In the above configuration, the charging member rotates in the same direction at the same peripheral speed as the rotation of the charged body during the operation of charging the charged body, and the rotation of the charged body during the operation of not charging the charged body. On the other hand, the means for rotating the charging member in the same direction with a peripheral speed difference is that the member to be charged rubs against the surface of the charging roller which is contaminated by paper powder or an external additive of toner,
It acts to move the contaminants attached to the charging roller to the member to be charged. Such a configuration allows the charging roller cleaning mechanism to be inexpensive and maintain the cleaning effect for a long period of time without complicating the image forming sequence.

In addition, the peripheral speed of the charging member is made slower than the peripheral speed of the member to be charged during the operation in which the member to be charged is not charged, and the peripheral speed of the charging member and the member to be charged is changed in this state. Means for reversing the polarity of the voltage applied to the member from the operation of charging the member to be charged acts to make it difficult for toner and the like to adhere to the charging roller, and further improves the cleaning effect.

[0012]

(Embodiment 1) FIG. 1 is an embodiment of the present invention and is a schematic view of a cross section of an image forming apparatus using a contact charging system. Hereinafter, a specific description will be given based on this drawing. This image forming apparatus has a photosensitive drum 1 which is a member to be charged, and a charging roller 2 which is rotatable in contact with an outer peripheral surface thereof.

The photosensitive drum 1 is an image carrier as a member to be charged. The photosensitive drum used in this embodiment is a conductive base layer of aluminum or the like, and OPC or a-S formed on the outer peripheral surface thereof.
An electrophotographic photosensitive member having a photoconductive layer such as i. The photosensitive drum 1 has an arrow A around the rotation axis 1a during the image forming operation.
, Is driven to rotate at a predetermined peripheral speed.

The charging roller 2 is in contact with the outer peripheral surface of the photosensitive drum 1, and is attached to a cored bar 2 a which is a rotating shaft of the charging roller 2.
When a predetermined DC bias or a DC + AC bias is applied by the power supply 3, the outer peripheral surface of the photosensitive drum 1 is uniformly charged with a predetermined polarity and potential. The charging roller 2 comprises a central core 2a, a conductive layer 2b formed on the outer periphery thereof, and a resistance layer 2c formed on the outer peripheral surface thereof. Pressure is applied in the radial direction of the photosensitive drum 1 toward the shaft 1a. During the image forming operation, the charging roller 2 is rotated and rotated around the rotation shaft 2a in the direction of arrow B at the same peripheral speed as the photosensitive drum 1.

The outer peripheral surface of the photosensitive drum 1 uniformly charged by the charging roller 2 is then exposed by a semiconductor laser, an LED, or the like, or slit exposure of a document image (in this embodiment, a semiconductor laser beam scanning exposure 4). ), An electrostatic latent image is formed.

The electrostatic latent image is then transferred to a developing sleeve 5a inside a developing unit 5 containing toner as a developer.
The toner is attached to the photosensitive drum 1 and is visualized by the rotation of.

This toner image is represented by an arrow A on the photosensitive drum 1.
Is moved to the transfer unit 6 by the rotation in the direction of. A transfer material 7 is conveyed to the transfer unit 6 by a paper feeder (not shown) at a timing coincident with the toner image formed on the photosensitive drum 1 in synchronization with the rotation of the photosensitive drum 1. In the present embodiment, a transfer roller 8 is provided in the transfer unit 6, and the photosensitive drum 1 is moved in the direction of arrow C in FIG.
The toner image on the photosensitive drum 1 is transferred to the front side of the transfer material 7 by rotating at a peripheral speed equal to the rotation of the transfer material 7 and performing charging of a polarity opposite to that of the toner from the back of the transfer material 7.

The transfer material 7 onto which the toner image has been transferred is separated from the photosensitive drum 1 and transported to a fixing device (not shown) to fix the image.

The photosensitive drum 1 after the transfer of the toner image
The front surface is cleaned by removing contaminants such as toner not transferred by the cleaning device 9, and the surface is further discharged by the discharging exposure device 10, and the image forming operation is repeated.

In the present embodiment, the charging roller 2 and the photosensitive drum 1 are separately rotated, and the charging roller 2 can rotate at a plurality of peripheral speeds.
The moving direction of the peripheral surface of the charging roller 2 at the contact portion with the photosensitive drum 1 is the same as the moving direction of the peripheral surface of the photosensitive drum 1.

At the time of image forming operation, the photosensitive drum 1 rotates at a peripheral speed equal to the direction A in FIG. 1 and the charging roller 2 rotates at a peripheral speed equal to the direction B in the drawing. The photosensitive drum 1 may be driven and rotated without providing the second drive system.

As the image forming operation is repeated, fine particles of the paper powder and fine external additives that have not been removed by the cleaning device 9 adhere to the surfaces of the charging roller 2 and the transfer roller 8. Images cannot be obtained. Therefore, it is necessary to provide a cleaning sequence for cleaning the contaminated charging roller 2 and transfer roller 8. Further, this sequence is preferably performed when 100 to 500 images have been formed since the start of the apparatus or the previous cleaning. Hereinafter, a timing chart of the cleaning sequence will be described with reference to FIG.

When the cleaning sequence starts during the non-imaging operation, the photosensitive drum 1 starts rotating in the direction A in FIG. 1 at the same peripheral speed as in the normal image forming operation, as shown in FIG. . On the other hand, at the same time, as shown in FIG.
Start rotating at a peripheral speed of 30%. At this time, no voltage is applied to the charging roller 2. It is desirable that the time for executing the cleaning sequence is set to the time for the charging roller 2 to rotate 3 to 10 times. When the cleaning sequence is completed, the rotation of the photosensitive drum 1 and the charging roller 2 is stopped as shown by C and D in FIG. 2A, and the process waits until a signal for starting the image forming operation comes next.

When an image forming operation start signal is received, the photosensitive drum 1 starts rotating at a predetermined peripheral speed in the direction of arrow A in FIG. 1 as shown by E in FIG. On the other hand, the charging roller 2 is shown in FIG.
As shown by F in FIG. 3A, the photosensitive drum 1 starts rotating at a peripheral speed equal to that of the predetermined photosensitive drum 1 in the direction of arrow B in FIG.

As described above, during the cleaning sequence,
If the direction of movement of the peripheral surface at the contact portion between the charging roller 2 and the photosensitive drum 1 is reversed to give a peripheral speed difference, the surface of the charging roller 2 contaminated with paper powder, toner external additives, and the like is removed. The rubbing of the roller 1 acts to move the contaminants adhering to the charging roller 2 to the photosensitive drum 1, and the contaminants adhering to the photosensitive drum 1 are collected by the cleaning device 9 as they are. Do not need. Also, since no bias is applied to the charging roller 2 during the cleaning sequence, the toner is less likely to adhere, and thus the cleaning effect is improved. Such a configuration makes the cleaning mechanism of the charging roller 2 inexpensive and can maintain the cleaning effect for a long time without complicating the image forming sequence.

(Embodiment 2) In the first embodiment, no voltage is applied to the charging roller 2 during the cleaning sequence of the charging roller 2, but as shown in FIG. A DC voltage having a polarity opposite to that of the toner and a voltage that does not charge the photosensitive drum 1 (2 to 500 [V]) may be applied to the roller 2.

Such a structure acts to make it easier for contaminants such as minute toners adhering to the surface of the charging roller 2 to separate from the charging roller 2 during the cleaning sequence of the charging roller 2, and further to improve the cleaning effect. Has the effect of improving.

Embodiment 3 In Embodiment 3, during the cleaning sequence of the charging roller 2, the photosensitive drum 1 and the charging roller 2 rotate at a constant speed with a peripheral speed difference. As shown in FIG. 2C, the rotation speeds of the photosensitive drum 1 and the charging roller 2 may be changed at the same timing during the cleaning sequence while the peripheral speed of the photosensitive drum 1 is always higher than the peripheral speed of the charging roller 2.

Such a structure acts to give an impact to contaminants such as minute toners adhering to the surface of the charging roller 2 and has an effect of further improving the cleaning effect.

Although the embodiment has been described with respect to the charging roller 2, the present invention can be similarly applied to the transfer roller 8.
Cleaning is performed in a non-paper passing state.

[0031]

As described above, according to the first and second aspects of the present invention, the contaminants adhering to the charging roller are moved to the member to be charged, and the cleaning mechanism for the surface of the charging roller complicates the image sequence. It is inexpensive and can maintain the cleaning effect for a long period of time.

Further, according to the third aspect, it is possible to make it difficult for contaminants to adhere to the charging roller, and to further improve the cleaning effect.

According to the fourth aspect of the present invention, a contaminant such as minute toner adhering to the surface of the charging member acts to give an impact, and further has an effect of improving the cleaning effect.

[Brief description of the drawings]

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

FIG. 2 is a timing chart of the image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 1a ... Rotating shaft 2 ... Charging roller 2a ... Core 2b ... Conductive layer 2c ... Resistive layer 3 ... Power supply 4 ... Semiconductor laser beam scanning exposure 5 ... Developing device 5a ... Developing sleeve 6 ... Transfer part 7 ... Transfer material 8 transfer roller 9 cleaning device 10 static elimination exposure device

Claims (4)

[Claims] 1. A charging device for charging a surface of a member to be charged by bringing a rotatable roller-shaped charging member to which a voltage is applied into contact with the surface of the member to be charged. On the other hand, when the charging member rotates in the direction in which the peripheral surface moves in the same direction at the same peripheral speed, and the charging member rotates with a peripheral speed difference with respect to the rotation of the charging member during an operation in which the charging member is not charged. A charging device characterized by the above-mentioned. 2. The charging device according to claim 1, wherein the peripheral speed of the charging member during the operation of not charging the member to be charged is lower than the peripheral speed of the member to be charged. 3. The method according to claim 1, wherein the polarity of the voltage applied to the charging member during the operation of not charging the member to be charged is opposite to the polarity of the voltage during the operation of charging the surface of the member to be charged. Charging device. 4. The charging device according to claim 2, wherein the peripheral speeds of the charging member and the member to be charged are changed.