JP2005128168A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus provided with an electrifying roller in which a nip area is stably enlarged and which is downsized. <P>SOLUTION: The image forming apparatus 1 is provided with a laser exposure unit 7, an image forming part 2, a paper feed conveyance part, a transfer conveyance unit 4, and a fixing part. In the image forming part 2, a developing unit 3, an electrifying roller 10, and a photoreceptor drum cleaning unit 6 are arranged along the periphery of the photoreceptor drum 5. The electrifying roller 10 acts to control the surface of the photoreceptor drum 5 to a predetermined potential at the time of the image formation, and is provided with a cylindrical sleeve, a cylindrical elastic body which is disposed within the sleeve and has an outer diameter that is smaller than the inner diameter of the sleeve, and a rotary shaft inserted in the central axis of the elastic body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus provided with a roller charging roller for charging a photosensitive drum.

In an electrophotographic image forming apparatus such as a laser printer, a laser fax machine, or a digital copying machine, the photosensitive drum is almost uniformly charged, and the photosensitive drum is exposed to form an electrostatic latent image corresponding to the image signal. After formation, the toner charged by the developing device is supplied onto the photosensitive drum to be visualized, and the toner image is transferred to a recording medium such as transfer paper, and then fixed by a fixing device to form an image. Yes.
Conventionally, in such an image forming apparatus, a roller by a roller charging method (hereinafter referred to as a charging roller) is used in order to charge the surface of the photosensitive drum almost uniformly. For example, in Patent Document 1, a support member made of an elastic body may be inserted into a seamless tube in which a resin having flexibility and a resin having heat resistance are blended with resin (inserted and bonded). The invention of a charged roller is disclosed.
JP-A-8-328358 (page 3-6, FIG. 2)

However, if the outer diameters of the photosensitive drum and the charging roller are reduced in an attempt to reduce the size of the conventional image forming apparatus, the charging roller is bent by pressing, and the contact between the charging roller and the photosensitive drum (hereinafter, referred to as the following) (This is called a nip.)
As the outer diameter of the charging roller decreases, the nip area decreases. As a result, the time during which charges can move from the charging roller to the photosensitive drum is reduced by the discharge between the charging roller and the photosensitive drum. That is, the surface potential of the photosensitive drum decreases as the outer diameter of the charging roller and the photosensitive drum decreases and as the rotation speed of the charging roller and the photosensitive drum increases. Therefore, when the hardness of the elastic body constituting the charging roller is lowered and the pressure is increased to increase the nip area, the rotating shaft of the charging roller is bent and the central portion of the charging roller comes into contact with the photosensitive drum. The problem of disappearing arises. Therefore, a lower limit naturally exists in the outer diameter dimension of the charging roller.
In addition, the charging roller described in Patent Document 1 has a problem in that the outer peripheral surface of the support member and the inner peripheral surface of the seamless tube are in close contact with each other, which requires labor for processing, cannot be mass-produced, and costs increase. was there.
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus including a charging roller that can stably increase the nip area and can be downsized. Objective.

In order to achieve the above object, in the image forming apparatus according to the present invention, a conductive or semiconductive cylindrical sleeve that abuts the photosensitive drum, and an outer diameter within the sleeve that is smaller than the inner diameter of the sleeve. And a charging roller having a conductive or semiconductive cylindrical elastic body and a conductive rotating shaft that passes through the central axis of the elastic body.
Here, a rubber material is desirable as the elastic body, and a foamed elastic body having a low hardness and a softness, such as foamed urethane rubber, is particularly suitable. Further, the sleeve may be any sleeve as long as it has a certain degree of hardness and can maintain its shape, and examples thereof include nylon resin and fluorine resin.
The thickness of the sleeve is about 0.5 mm or less so as not to lose flexibility and flexibility. The inner diameter of the sleeve is set to be approximately 0.5 mm or more larger than the outer diameter of the elastic body, preferably about 1 mm.
In the present invention, a charging roller is realized in which a flexible cylindrical elastic body having an outer diameter smaller than the inner diameter of the sleeve and a low hardness is provided in a flexible cylindrical sleeve. Thereby, even if the contact pressure to the photosensitive drum is low, the nip area can be stably increased by collapsing the sleeve and the elastic body. In addition, since the contact pressure to the photosensitive drum may be low, the charging roller can be reduced in size.
Further, in the present invention, since the outer diameter of the elastic body is smaller than the inner diameter of the sleeve, there is no need to press-fit or bond the elastic body into the sleeve as in the prior art at the time of manufacturing the charging roller. A charging roller excellent in mass productivity can be realized.

In the image forming apparatus according to the present invention, it is preferable that an electric resistance value between the charging roller and the photosensitive drum is 500 kΩ or more and 5 MΩ or less.
This is because when the electric resistance value between the charging roller and the photosensitive drum is 500 kΩ or less, it is not possible to stably discharge between the charging roller and the photosensitive drum, and the charging roller and the photosensitive drum This is because if the electric resistance value between the photosensitive drums is 5 MΩ or more, the power supply cannot catch up.

In the image forming apparatus according to the present invention, a conductive or semiconductive cleaning brush or a conductive or semiconductive first cleaning roller for cleaning the outer surface of the sleeve is provided on the outer surface of the sleeve. It may be in contact with.
Conventionally, in order to manage the pressure applied when the cleaning brush or cleaning roller abuts, the supporting member (bearing) of the cleaning brush or cleaning roller must be suspended by a spring, and because of the frictional force of the abutting portion, The driving torque of the photosensitive drum has also increased.
In the present invention, due to the elasticity of the sleeve, a uniform and stable contact state can be realized at a pressure lower than the pressure of the spring without being suspended by a conventional spring. As a result, a simple mechanism in which the cleaning brush or the support member (bearing) of the cleaning roller is fixed can be realized, and the driving torque of the photosensitive drum can be reduced.
In addition, in the present invention, since the cleaning brush or the first cleaning roller can be brought into contact with an arbitrary position on the outer surface of the sleeve, the toner adhering to the sleeve can be removed, and the image forming apparatus can be used. The cleaning brush or the first cleaning roller can be installed at a position that is optimal for downsizing.

In the image forming apparatus according to the present invention, on the photosensitive drum, on the upstream side of the sleeve, abuts on the outer surface of the sleeve and the photosensitive drum, and the outer surface of the sleeve and the photosensitive member. A conductive or semiconductive second cleaning roller for cleaning the surface of the drum may be provided.
Here, the counter-rotation direction side of the photosensitive drum is the upstream side, and the rotation direction side is the downstream side.
In the present invention, the cleaning of the charging roller and the cleaning of the photosensitive drum can be processed by one cleaning roller by bringing the second cleaning roller into contact with the outer surface of the sleeve and the photosensitive drum.

  According to the present invention, it is possible to realize an image forming apparatus including a charging roller that can stably increase the nip area and can be downsized.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described based on the drawings.
FIG. 1 is a schematic diagram illustrating a schematic configuration of a main part of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a partially enlarged schematic view of the charging roller and the photosensitive drum for explaining the first embodiment of the image forming apparatus according to the present invention.
The image forming apparatus 1 according to the present embodiment scans and exposes a laser beam modulated according to an image signal, and can perform printing on a printing medium such as paper or a plastic sheet by a dry electrophotographic method. It can be used as a printer, laser fax, digital copier, or a part thereof.
As shown in FIG. 1, the image forming apparatus 1 includes a laser exposure unit 7, an image forming unit 2, a paper feed conveyance unit (not shown), a transfer conveyance unit 4, and a fixing unit (not shown).

  The laser exposure unit 7 scans the laser beam 7a imaged on the minute spot on a straight line parallel to the rotation axis of the photosensitive drum 5 in a fixed direction at the exposure position B on the photosensitive drum 5. .

The image forming unit 2 includes a developing unit 3, a photosensitive drum cleaning unit 6, and a charging roller 10 arranged along the outer periphery of the photosensitive drum 5 that rotates in the direction of the arrow in FIG.
Hereinafter, when expressing the relative position on the photosensitive drum 5, the rotation direction side is referred to as a downstream side, and the counter rotation direction side is referred to as an upstream side.

The developing unit 3 frictionally charges the powder toner T having a predetermined color to be negatively charged, and is exposed to a positive potential relative to the non-exposed portion by exposure. The toner T is supplied to the photosensitive drum 5 so that the toner T adheres to the photosensitive drum 5.
In the developing unit 3, the toner T, a stirring blade 3d that stirs and charges the toner T, a supply roller 3b that conveys the charged toner T to the developing roller 3a side, and a toner T that is supplied by the supply roller 3b And a developing roller 3a for transporting the toner to the surface of the photosensitive drum 5 and a developing blade 3c for regulating the layer thickness of the toner T on the developing roller 3a to a constant thickness. Is provided. The stirring blade 3d, the supply roller 3b, and the developing roller 3a rotate in the direction of the arrow in FIG.

The transfer / conveying unit 4 abuts the transfer belt 9 that can be rotationally driven in one direction by a plurality of rollers (not shown) arranged on the inner periphery, and the transfer belt 9 contacts the photosensitive drum 5 at the transfer position D. And a transfer belt cleaning unit 11 having a space for scraping off deposits on the surface of the transfer belt 9 by abutting a cleaning blade 11a on the transfer belt 9 and collecting the scraped deposits. .
The material of the transfer belt 9 is such that the toner T on the photosensitive drum 5 can be sucked by the transfer voltage applied to the transfer roller 8 in contact with the back surface when facing the photosensitive drum 5 with the print medium 12 interposed therebetween. A dielectric sheet is used.
The transfer roller 8 is formed, for example, by a roller part made of conductive or semiconductive synthetic rubber or the like on a metal rotating shaft, and a high voltage power source for transfer (not shown) is connected to the rotating shaft. The surface potential can be controlled.

  The photosensitive drum cleaning unit 6 is provided with a space for collecting the scraped toner T while scraping off the toner T on the surface of the photosensitive drum 5 by contacting the cleaning blade 6a with the photosensitive drum 5.

The charging roller 10 is for setting the surface potential of the photosensitive drum 5 to a predetermined potential during image formation. The charging roller 10 is a cylindrical sleeve 10b and a circle within the sleeve 10b and having an outer diameter smaller than the inner diameter of the sleeve 10b. A columnar elastic body 10a and a rotating shaft 10c that passes through the central axis of the elastic body 10a are provided.
The sleeve 10b is formed of a nylon resin imparted with conductivity or semiconductivity, and the sleeve 10b has an inner diameter of 9 mm and a thickness of about 0.5 mm.
The elastic body 10a is made of foamed urethane rubber imparted with conductivity or semiconductivity, and has a cell diameter of about 0.1 mm and an apparent hardness of about 20-30. The outer diameter of the elastic body 10a is 8 mm.
The rotating shaft 10c is made of a conductive metal having an outer diameter of 5 mm, and both ends of the rotating shaft 10c are supported by bearings 13 described later.
The sleeve 10 b is deformed by being pressed between the elastic body 10 a and the photosensitive drum 5 by the pressing force acting on the bearing portion 13, and has a predetermined nip width that sandwiches the position A on the surface of the photosensitive drum 5. Abut. The elastic body 10a is also deformed by the pressing force, and is inscribed in the sleeve 10b with a predetermined nip width across the contact position A. The electrical resistance value between the charging roller 10 and the photosensitive drum 5 is set to 500 kΩ or more and 5 MΩ or less.

FIG. 3 is a partial cross-sectional view of the charging roller bearing portion.
Both ends 10 d of the rotating shaft 10 c of the charging roller 10 have a smaller outer diameter than the intermediate portion, and are supported by holes 13 b provided in the bearing portion 13.
A pressing force of about 250 g is applied to the bearing portion 13 in the center direction of the photosensitive drum 5 by a spring (not shown). Further, a DC voltage is applied to the bearing portion 13 so as to discharge at the contact position A between the charging roller 10 and the photosensitive drum 5.
The end of the elastic body 10 has a structure that fits about 2.5 mm inside the end of the sleeve 10b. On the other hand, on the sleeve 10b side of the bearing portion 13, a convex portion 13a is formed around the hole 13b. The clearance between the end of the sleeve 10b and the projection 13a is about 0.2 mm, and the end of the sleeve 10b and the projection 13a slide to prevent the sleeve 10b from meandering in the horizontal direction.

Next, the operation of the image forming apparatus 1 according to the present embodiment will be described.
Since the general operation of the image forming apparatus 1 is common to the operation of a known printer or the like, the description thereof will be omitted as appropriate, and the description will focus on the operation associated with the rotation of the photosensitive drum 5.
When the photosensitive drum 5 is rotationally driven in the direction indicated by the arrow in FIG. 1 by a driving means (not shown), the charging roller 10 that contacts the photosensitive drum 5 at the position A is in the direction indicated by the arrow in FIG. Followed rotation. During this time, the vicinity of the position A on the surface of the photosensitive drum 5 is negatively charged almost uniformly by the discharge between the charging roller 10 and the photosensitive drum 5.
When the photosensitive drum 5 rotates from the contact position A to the exposure position B, the print image area is exposed by the laser exposure unit 7, and the exposed portion loses its surface potential due to discharge of electric charge. As a result, the surface potential difference between the exposed portion and the non-exposed portion is recorded on the surface of the photosensitive drum 5, and a so-called electrostatic latent image is formed.
When the photosensitive drum 5 rotates from the exposure position B to the development position C, the toner T selectively moves from the developing roller 3a to the photosensitive drum 5 based on the electrostatic latent image formed on the surface of the photosensitive drum 5. Then, a visible image is formed with the toner T on the surface of the photosensitive drum 5.
Further, at the same time as the photosensitive drum 5 rotates and moves to the transfer position D, the print medium 12 is conveyed on the transfer belt 9, and the visible image formed by the toner T formed on the surface of the photosensitive drum 5 is the print medium 12. Is transcribed. The visible image by the toner T transferred onto the printing medium 12 is melted and fixed on the printing medium 12 by a fixing device (not shown), and a series of printing operations is completed.
The toner T remaining on the photosensitive drum 5 without being transferred is removed by the photosensitive drum cleaning unit 6 at the position E on the photosensitive drum 5 and cleaned before being charged again by the charging roller 10. .

In the image forming apparatus 1 according to the present embodiment, a charging roller 10 in which a flexible cylindrical sleeve 10b is provided with a flexible cylindrical elastic body 10a having an outer diameter smaller than the inner diameter of the sleeve 10b and having a low hardness. Realized. Thereby, even if the contact pressure to the photosensitive drum 5 is low, the nip area can be stably increased by collapsing the sleeve 10b and the elastic body 10a. In addition, since the contact pressure to the photosensitive drum 5 may be low, the charging roller 10 can be downsized.
In the image forming apparatus 1 according to the present embodiment, since the outer diameter of the elastic body 10a is smaller than the inner diameter of the sleeve 10b, the elastic body 10a is press-fitted into the sleeve 10b or bonded when the charging roller 10 is manufactured. Therefore, the charging roller 10 that is inexpensive and excellent in mass productivity can be realized.

FIG. 4 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a second embodiment of the image forming apparatus according to the present invention.
As shown in FIG. 4, in the second embodiment of the image forming apparatus 1 according to the present invention, the first cleaning roller 21 is in contact with the outer peripheral surface position F of the sleeve 20 b of the charging roller 20.
The first cleaning roller 21 is made of a material that has conductivity or semi-conductivity and in which a gap for holding the toner T is formed on the surface and inside thereof. Specific examples of suitable materials include nylon fibers having conductivity or semi-conductivity, or porous foams made of conductive or semi-conductive synthetic fibers.
In the image forming apparatus 1 according to the present embodiment, due to the elasticity of the sleeve 20b, there is no need to suspend a support member (bearing) (not shown) of the first cleaning roller 21 with a spring, and the pressure is lower than the pressure of the spring. In addition, a stable contact state can be realized. As a result, a simple mechanism in which the support member (bearing) of the first cleaning roller 21 is fixed can be realized, and the driving torque of the photosensitive drum 5 can be reduced.
In addition, in the image forming apparatus 1 according to the present embodiment, since the first cleaning roller 21 can be brought into contact with an arbitrary position on the outer surface of the sleeve 20b, the toner T adhering to the sleeve 20b can be removed. The first cleaning roller 21 can be installed at a position that is optimal for downsizing the image forming apparatus 1.

FIG. 5 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a third embodiment of the image forming apparatus according to the present invention.
As shown in FIG. 5, in the third embodiment of the image forming apparatus 1 according to the present invention, the cleaning brush 31 is in contact with the position G on the outer peripheral surface of the sleeve 30 b of the charging roller 30.
The cleaning brush 31 is made of a material having conductivity or semi-conductivity and having a space for holding the toner T on the surface and inside thereof. As a specific material, nylon fiber in which carbon fine particles are dispersed and contained is suitable, and the nylon fiber is woven into a velvet shape or planted and used as a brush.
The image forming apparatus 1 according to the present embodiment also has the same effects as the second embodiment.

FIG. 6 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a fourth embodiment of the image forming apparatus according to the present invention.
As shown in FIG. 6, in the fourth embodiment of the image forming apparatus 1 according to the present invention, a second cleaning roller 41 is installed on the upstream side of the position A where the charging roller 40 and the photosensitive drum 5 abut, While being in contact with the outer peripheral surface of the sleeve 40 b of the charging roller 40 at the position H, it is in contact with the surface of the photosensitive drum 5 at the position I.
The second cleaning roller 41 is made of a material that has conductivity or semi-conductivity and in which a gap for holding the toner T is formed on the surface and inside thereof. The specific material is the same as that of the first cleaning roller 21.
In the image forming apparatus 1 according to this embodiment, the second cleaning roller 41 is brought into contact with the outer surface of the sleeve 40 b and the photosensitive drum 5, thereby cleaning the charging roller 40 and cleaning the photosensitive drum 5. Can be processed with a roller.

  As described above, the embodiments of the image forming apparatus according to the present invention have been described. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. For example, in the above-described embodiment, the example in which the toner is negatively charged and attached to the exposed portion of the photosensitive drum and developed is described. Yes. In the above-described embodiment, the example of the monochromatic printer has been described. However, the present invention can be similarly applied to a color image forming apparatus.

1 is a schematic diagram illustrating a schematic configuration of a main part of an embodiment of an image forming apparatus according to the present invention. 1 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a first embodiment of an image forming apparatus according to the present invention. It is a fragmentary sectional view of a charging roller bearing part. FIG. 4 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a second embodiment of the image forming apparatus according to the present invention. FIG. 6 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a third embodiment of the image forming apparatus according to the present invention. FIG. 10 is a partially enlarged schematic view of a charging roller and a photosensitive drum for explaining a fourth embodiment of the image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image formation part 3 Developing unit 4 Transfer conveyance unit 5 Photosensitive drum 6 Photosensitive drum cleaning unit 7 Laser exposure unit 8 Transfer roller 9 Transfer belt 10, 20, 30, 40 Charging roller 11 Transfer belt cleaning unit 12 Printing medium 21 First cleaning roller 31 Cleaning brush 41 Second cleaning roller T Toner

Claims (4)

A conductive or semiconductive cylindrical sleeve that abuts the photoreceptor drum;
A conductive or semiconductive cylindrical elastic body in the sleeve and having an outer diameter smaller than the inner diameter of the sleeve;
An image forming apparatus comprising: a charging roller having a conductive rotation shaft that passes through the central axis of the elastic body.   The image forming apparatus according to claim 1, wherein an electric resistance value between the charging roller and the photosensitive drum is 500 kΩ or more and 5 MΩ or less.   A conductive or semiconductive cleaning brush or a conductive or semiconductive first cleaning roller for cleaning the outer surface of the sleeve is in contact with the outer surface of the sleeve. The image forming apparatus according to claim 1.   On the photosensitive drum, upstream of the sleeve, abuts against the outer surface of the sleeve and the photosensitive drum, and cleans the outer surface of the sleeve and the surface of the photosensitive drum. The image forming apparatus according to claim 1, further comprising a conductive second cleaning roller.

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