JPH11184213A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of image quality such as the electrification irregularity and the image density irregularity of an image carrier and to prolong the life of an electrifying member and a cleaning member by providing a position changing means changing the relative position of the electrifying member and the image carrier according to a condition based on image formation. SOLUTION: A photoreceptor durum 2 and an electrifying roller 3, and the roller 3 and the cleaning member 1 are required to be prevented from always abutting on each other at the same position when the same image is consecutively formed. Thus, the roller 3 is operated in a main scanning direction which is in parallel with the shaft direction of the drum 2 at an optional interval and with optional moving amount by the position changing means, so that the respective relative positional relation of the drum 2 and the roller 3, and the roller 3 and the member 1 can be changed. Thus, the relative position of the roller 3 and the drum 2 is moved in parallel, so that the roller 3 can be brought into uniformly contact with the drum 2, and also the local deterioration of the drum 2 can be prevented.

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 such as a copying machine or a printer using an electrophotographic system, and more particularly to a technique for maintaining a good function of a charging device for charging an image carrier.

[0002]

2. Description of the Related Art Conventionally, an image bearing member such as a copying machine as an image forming apparatus using an electrophotographic system is provided with a charging device used for charging before image exposure. As such a charging device, a non-contact charging type device utilizing a discharge phenomenon like a scorotron charger is generally used in many cases.

In recent years, a contact charging system in which a conductive charging member is brought into direct contact with a photoreceptor serving as an image carrier and a charging voltage is applied to the charging member to perform charging is also used.

In this contact charging method, for example, a roller member made of conductive rubber is brought into contact with an image carrier (photosensitive drum or the like) as a charging member, and is rotated by the rotation of the photosensitive drum. By supplying a voltage, the photosensitive drum is uniformly charged.

In this contact charging method, since the charging member comes into contact with the image carrier, toner and the like are easily stained, and this stain can cause charging unevenness. Therefore, a cleaning means for rubbing the surface of the roller member to scrape dirt may be added.

Referring to FIG. 2, a schematic configuration and operation of an image forming apparatus (copier) using a charging device provided with a charging member cleaning means will be described.

[0007] A charging roller 3 as a charging member is disposed in contact with the photosensitive drum 2 as an image carrier. A charging voltage is applied to the charging roller 3 from a high voltage power supply 4.

Reference numeral 9 denotes an image exposure A according to image information of a document or the like.
An exposure device such as a laser scanner for exposing the image, 5 a developing device, 6 a transfer device, 7 a cleaning device, and 8 a fixing device.

Transfer paper P is fed from a paper feeding device (not shown), and is conveyed to a fixing device 8 through a transfer area.

Reference numeral 1 denotes a cleaning member for cleaning the roller 3, which is configured to be pressed against the charging roller 3.

In this copying machine, when a start button (not shown) is pressed, a main motor (not shown) rotates and the photosensitive drum 2 which is connected and driven rotates.

The charging roller 3 pressed against the photosensitive drum 2 rotates following the photosensitive drum 2. The photosensitive drum 2 includes a photosensitive layer 2a, and a grounded conductive substrate 2b made of aluminum or the like that supports the photosensitive layer 2a. In this example, the photosensitive layer 2a is a negatively charged OPC.

In image formation, first, the photosensitive drum 2
In order to charge the surface of the photosensitive drum 2 to a uniform potential, an applied voltage is applied by the charging roller 3 to a predetermined potential.

In this embodiment, in order to obtain a more uniform potential, the residual charge on the photosensitive drum 2 is reset by a pre-exposure device (not shown) before charging, and then the photosensitive drum 2 is uniformly charged. .

Next, an image is exposed on the charged photosensitive drum 2 to form an electrostatic latent image, and then a developing process of developing with the toner of the developing device 5 is performed. Here, the image exposure method may be analog exposure or exposure using laser oscillation light oscillated based on digital image information. In addition, the charging polarity of the toner of this embodiment is the same as the charging polarity of the photosensitive drum 2, and the reversal developing method is used.

Further, the toner image formed on the photosensitive drum 2 through the developing process is transferred to the transfer paper P fed synchronously by the transfer device 6, and the transfer paper P having passed through the transfer process is The toner is conveyed to the fixing device 8 by the conveyance belt 10, and the toner on the transfer paper P is fixed.

On the other hand, the residual toner on the photosensitive drum 2 is removed by the cleaning device 7.

[0018]

However, if a copying machine or the like using the above-mentioned contact charging system is used for a long time, if the cleaning member (cleaning device 7) is not provided for the charging member (charging roller 3), it is natural. Dirt impairs charging.

Alternatively, charging unevenness may not occur depending on the contamination by the fine powder, but since the fine powder is laminated and the overall electric resistance increases, the potential applied to the image carrier (photosensitive drum 2) is increased. Is reduced, and in this case, the charging function is reduced.

Further, when a toner lump or other foreign matter adheres, a local charging failure occurs at the adhered portion.

For this purpose, a cleaning member is provided in contact with the charging member and a mechanism for removing the adhered substance is implemented. However, since the cleaning member is continuously pressed to the same position, the charging member is damaged by long-term use. Or it may be worn, and in this case, charging failure may also occur.

There is also a system which implements a mechanism for reducing the damage of the image carrier by the charging member by separating the charging member from the image carrier except during image formation.
As described above, since the cleaning member is pressed against the charging member, the charging member may be damaged or worn by long-term use. In this case, charging failure may occur.

As described above, even the charging device provided with the cleaning means may result in poor charging.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to maintain the function of a charging device in a satisfactory manner, and to improve the charging unevenness of an image carrier and the charging unevenness caused by the unevenness. It is an object of the present invention to provide an image forming apparatus capable of preventing deterioration in image quality such as uneven image density and extending the life of a charging member and a cleaning member thereof.

[0025]

In order to achieve the above object, according to the present invention, there is provided a rotating image carrier, charging means for charging the image carrier, and charging the image carrier. Exposure means for exposing, developing means for converting the electrostatic latent image formed on the image carrier by the exposure into a visible image, and the visible image on the recording material from the image carrier at a transfer position And a transfer unit for transferring an image. The charging unit includes a charging member that is in contact with the image carrier, and a relative position between the charging member and the image carrier is determined based on image formation. It is characterized by comprising a position changing means for changing according to conditions.

It is also preferable that the position changing means moves the relative position between the charging member and the image carrier in parallel with the axial direction of the image carrier.

A cleaning unit for cleaning the charging member in a state where the charging member is separated from the image carrier by the separation unit; a moving direction of the charging member by the separation unit is a tangential direction of the image carrier; Is also preferably parallel to

Preferably, the position changing means changes the relative position between the charging member and the image carrier in a state where the charging member is separated from the image carrier.

The cleaning means has a contact area of a predetermined width parallel to the axial direction and the tangential direction of the image carrier with respect to the charging member, and the cleaning means for cleaning the charging member by the position changing means and the separating means. It is also preferable to change the position in the contact area according to a condition based on image formation.

[0030]

(Embodiment 1) An embodiment of the present invention will be described below. An image forming apparatus (copier) employing an electrophotographic method to which the present invention is applied will be described with reference to FIGS.

First, the schematic structure of the image forming apparatus will be described with reference to FIG. A charging roller 3 serving as a charging member that functions as a charging unit is disposed in contact with the photosensitive drum 2 serving as an image carrier. A charging voltage is applied to the charging roller 3 from a high voltage power supply 4.

Reference numeral 9 denotes an image exposure A according to image information of a document or the like.
Exposure means such as a laser scanner for exposing the image, 5 a developing device as a developing device, 6 a transfer device as a transfer device, 7
Denotes a cleaning device for cleaning the photosensitive drum 2, and 8 denotes a fixing device.

Transfer paper P is fed from a paper feeding device (not shown), and is conveyed to a fixing device 8 through a transfer area.

A cleaning member 1 for cleaning the roller 3 is configured to be pressed against the charging roller 3.

In the copying machine to which the present invention is applied, when a start button (not shown) is pressed, a main motor (not shown) rotates and the photosensitive drum 2 which is connected and driven rotates.

The charging roller 3 pressed against the photosensitive drum 2 rotates following the photosensitive drum 2. The photosensitive drum 2 includes a photosensitive layer 2a, and a grounded conductive substrate 2b made of aluminum or the like that supports the photosensitive layer 2a. In this example, the photosensitive layer 2a is a negatively charged OPC.

In image formation, first, the photosensitive drum 2
In order to charge the surface of the photosensitive drum 2 to a uniform potential, an applied voltage is applied by the charging roller 3 to a predetermined potential.

In this embodiment, in order to obtain a more uniform potential, the residual charge on the photosensitive drum 2 is reset by a pre-exposure device (not shown) before charging. Charge.

Next, after the charged photosensitive drum 2 is exposed to an image to form an electrostatic latent image, a developing process of developing with the toner of the developing device 5 is performed. Here, the image exposure method may be analog exposure or exposure using laser oscillation light oscillated based on digital image information. Further, the charging polarity of the toner of this embodiment is
And the reversal development method is used.

Further, the toner image formed on the photosensitive drum 2 through the development process is transferred to the transfer paper P fed synchronously by the transfer device 6, and the transfer paper P after the transfer process is transferred to the transfer paper P. The toner is conveyed to the fixing device 8 by the conveyance belt 10, and the toner on the transfer paper P is fixed.

On the other hand, the residual toner on the photosensitive drum 2 is removed by the cleaning device 7.

In the first embodiment, when the same image is continuously formed (an image is formed on a plurality of transfer materials P by inputting a single image formation start signal by a copy button or the like from outside the image forming apparatus). Case), in order to prevent the photosensitive drum 2 and the charging roller 3 and the charging roller 3 and the cleaning member 1 from abutting at the same position at all times, the charging roller 3 is moved to an arbitrary distance and an arbitrary amount by a position changing means (not shown). To move in the main scanning direction (direction of the arrow A1 in FIG. 1) parallel to the axial direction of the photosensitive drum 2, and the relative positions of the photosensitive drum 2 and the charging roller 3, and between the charging roller 3 and the cleaning member 1, This is to change the positional relationship.

Further, in this embodiment, the number of sheets of paper or the like used as the transfer material P is managed as a condition based on image formation, and the contact position by the position changing means is changed every time the number of sheets exceeds a predetermined number according to the flowchart shown in FIG. A moving operation is being performed. The number of transfer materials P is counted by a counter.

In the flowchart of FIG. 3, when the start button is pressed in sequence S401 (hereinafter simply referred to as S401...), The counter of the number of copies is reset in S402.

Image formation is performed in S403, and the number of image formation is counted accordingly (S404).

If it is determined in S405 that the number of continuously formed images is larger than the predetermined number (1), the process proceeds to S40.
9, a contact position moving operation is performed, and the process returns to S402.

If it is determined in step S404 that the number of continuously formed images is not larger than the predetermined number (1), the process proceeds to step S408, where the count of the counter is determined, and the predetermined number is determined. If it is larger than (2), the contact position movement operation is performed in S409, and the process returns to the upstream of S402.

If the determination of the count number of the counter in S408 is smaller than the predetermined number (2), the process proceeds to S40.
Return to the top of 3.

In this embodiment, the predetermined number (1) is 5
0 sheets and the predetermined number (2) are 500 sheets. The predetermined number (1) is the number of transfer materials in the case where images are continuously formed on a plurality of transfer materials P as in continuous copying, and the predetermined number (2) is the transfer material P that forms an image as an apparatus. Is the cumulative number of sheets. Here, the predetermined number is explicitly described as above, but it goes without saying that the predetermined number is set to an appropriate value depending on the type of the transfer material P, the developer, and the type of the charging roller 3 to be used.

For example, when an image is to be formed continuously on 500 transfer materials P first, the 50th and 100th transfer materials P
Charge roller 3 every 50th sheet, such as the 150th sheet
To move. On the other hand, when an image is formed one by one on the 500 transfer materials P by pressing the copy button 500 times, the charging roller 3 is moved when forming an image on the 500th transfer material P.

This is because, when images are formed on the same number of transfer materials P, the adhesion of dirt on the charging roller 3 is more remarkable in the case where images are formed continuously than in the case where images are formed one by one. Become.

In the case of forming an image one by one, each time the photosensitive drum 2 is rotated after the image is formed, the charging roller 3 is rotated.
Some of the dirt adhering to the photosensitive drum 2 moves to the photosensitive drum 2 and is cleaned by the cleaning device 7 for the photosensitive drum 2. In the case of continuous image formation, the same image is continuously formed at the same position in the thrust direction. Therefore, the accumulated amount of the image forming portion gradually increases locally.

When images are formed continuously on the same number of transfer materials P, the time required for the rotation of the charging roller 3 after rotation is shorter than when the images are formed one by one, and thus the contamination is less. The above-mentioned predetermined number (1)
Is preferably smaller than the predetermined number (2), and the moving frequency is increased.

The timing of the voltage applied to the charging roller 3 is different from that of the non-image area before and after the image area of the photosensitive drum 2 such as during pre-rotation and post-rotation. , The AC voltage and the DC voltage are turned off, but the area to be a non-image area corresponding to the space between sheets during continuous image formation is the area to be an image area because the space between the sheets is shortened. Similarly, it is turned on together with the AC voltage and the DC voltage.

Here, the moving amount of the charging roller 3 is about 2 to 4 mm in the main scanning direction for the purpose of preventing lamination of scratches and attached matter formed by fine powder or developer.

After moving in one direction to the maximum movement limit position, the movement is made to return in the opposite direction, and thereafter, the movement becomes repetitive. In addition, in consideration of the fact that the amount of movement at one time is a repetitive movement, it is ideal to set the amount of movement in the one reciprocation so that the contact position before one reciprocation does not abut. And the maximum movable amount of the charging roller 3.

Therefore, the entire surface of the charging roller 3 comes into uniform contact, and it is possible to prevent local accumulation of dirt due to contact of the same portion with the photosensitive drum 2 and embedding of dirt and the like by the cleaning member 1. Accordingly, it is possible to prevent deterioration in image quality such as uneven charging of the charging roller 3 and uneven image density caused by the uneven charging, and maintain high-quality image formation.

Further, by combining the cleaning member 1 with a member having a function of performing an operation such as separation at intervals according to the use situation, it is needless to say that the effect of the present embodiment can be further improved. Nor.

(Embodiment 2) In the second embodiment, the charging roller 3 is separated from the photosensitive drum 2 and
The present invention is applied to a copying machine provided with a mechanism for cleaning the charging roller 3 by contacting the cleaning member 1 which is separated from the cleaning member 1 by a predetermined distance.

In this copying machine, a separating means (not shown) for separating the charging roller 3 from the photosensitive drum 2 in order to prevent the photosensitive drum 2, the charging roller 3 and the cleaning member 1 from always contacting at the same position. ).

FIG. 4 is a diagram showing a state in which the charging roller 3 is separated from the photosensitive drum 2 and is in contact with the cleaning member 1 to perform cleaning. The charging roller 3 is indicated by arrows A1,
It moves in the direction of A2 and performs charging and cleaning.

The direction of arrow A2 is an arbitrary direction parallel to the tangential direction of the photosensitive drum 2, and when the cleaning member is arranged at a position as shown in FIG. Tangent direction from.

When the charging roller 3 is separated from the photosensitive drum 2 in the direction of the arrow A2 by the separating means, the charging roller 3 is moved in the main scanning direction (the direction of the arrow A1) at an arbitrary interval and a moving amount, and is cleaned. This is to make contact with the member 1.

In the second embodiment, the automatic cleaning operation of the charging roller 3 is performed at intervals according to the use environment and use condition of the copying machine as conditions based on image formation.

When the cleaning method of the present embodiment is compared with the cleaning method of the present embodiment, since the charging roller 3 is separated from the photosensitive drum 2 for cleaning, there is an effect of reducing the wear of the surface of the photosensitive drum 2.

However, when separated from the cleaning member 1, the fine particles and the like scraped off by the cleaning member 1 may be stacked on the charging roller 3 by a detachment operation.

Further, by repeatedly contacting the cleaning member 1 at the same position, damage over time due to the contact also causes uneven charging.

Therefore, similarly to the above embodiment, the same position of the photosensitive drum 2 and the charging roller 3 is continuously performed during the cleaning operation.
The charging roller 3 may be moved so that the same position of the charging roller 3 and the cleaning member 1 does not abut.

Here, in order to always maintain a uniform charging operation, the charging roller 3 is not moved when it is in contact with the photosensitive drum 1, but is moved only when it is in contact with the cleaning member 1.

The contact area 1a of the cleaning member 1 has a certain width W1 in the sub-scanning direction, and the movement of the charging roller 3 with respect to the cleaning member 1 is changed in the main scanning direction and also in the sub-scanning direction. Thereby, the cleaning effect can be further improved.

[0071]

As described in the embodiments of the present invention, by maintaining good functions of the charging device, it is possible to maintain high-quality image formation, and at the same time, to maintain the charging member and its cleaning. An image forming apparatus capable of extending the life of a member is provided.

By moving the relative position of the charging member and the image carrier parallel to the axial direction of the image carrier, the charging member is brought into uniform contact with the image carrier, and at the same time, the local position of the image carrier is improved. Deterioration can be prevented.

Further, the contact area of the cleaning means can be used effectively, and the cleaning effect can be further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram near a charging roller according to a first embodiment.

FIG. 2 is an explanatory cross-sectional configuration diagram illustrating a configuration of an image forming apparatus.

FIG. 3 is a flowchart illustrating a contact position moving operation.

FIG. 4 is a configuration diagram near a charging roller according to a second embodiment.

FIG. 5 is a configuration diagram near a charging roller according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cleaning member (cleaning means) 2 Photoconductor drum (image carrier) 3 Charging roller (charging member) 4 High voltage power supply 5 Developing device (developing device) 6 Transfer device (transfer device) 7 Cleaning device 8 Fixing device 9 Exposure device 10 Conveyor belt P Transfer paper

Claims (5)

[Claims] A rotating image carrier; a charging unit for charging the image carrier; an exposing unit for exposing the charged image carrier; and an exposing unit formed on the image carrier by the exposure. A developing unit for converting the electrostatic latent image into a visible image, and a transfer unit for transferring the visible image from the image carrier to a recording material at a transfer position. The image forming apparatus includes a charging member that contacts the image carrier, and a position changing unit that changes a relative position between the charging member and the image carrier according to a condition based on image formation. apparatus. 2. The image forming apparatus according to claim 1, wherein the position changing unit moves a relative position between the charging member and the image carrier in parallel with an axial direction of the image carrier. 3. A cleaning device for cleaning the charging member in a state where the charging member is separated from the image carrier by a separation device, wherein a moving direction of the charging member by the separation device is a direction of movement of the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is parallel to a tangential direction. 4. The image forming apparatus according to claim 3, wherein the position changing unit changes a relative position between the charging member and the image carrier when the charging member is separated from the image carrier. apparatus. 5. The cleaning means has a contact area of a predetermined width parallel to the axial direction and tangential direction of the image carrier with respect to the charging member, and the cleaning means has a predetermined width. The image forming apparatus according to claim 3, wherein a position of the cleaning unit in the contact area is changed according to a condition based on image formation.