JPH07121002A - Image forming device - Google Patents

Abstract

PURPOSE:To precisely hold the gap between a photoreceptor drum and an electrifying member, in an electrifier charging the surface of the photoreceptor drum in such a manner that the electrifying member comes close to it. CONSTITUTION:Annular spacer rollers 30 are attached to the peripheries of the photoreceptor drum 1 on its both ends in an axial direction and each of them has a small diameter part 30a having a thickness of Ga inside and a large diameter part 30b having a thickness of Gb (Gb>Ga) outside. A gently curved proximity electrifying plate 2 is pressed on the photoreceptor drum 1 by a compression spring 12. At this time, projections 2f and 2g projected outside from the upstream and downstream sides 2a and 2b of the proximity electrifying plate 2 are made to abut on the small and large diameter parts 30a and 30b respectively. Thus, the gaps of Ga and Gb between the surface of the photoreceptor drum 1 and the proximity electrifying plate 2 can be precisely held on the upstream side 2a and on the downstream side 2b, respectively.

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 which charges a surface of an image carrier by applying an oscillating voltage to a charging member which is arranged close to the image carrier.

[0002]

2. Description of the Related Art Contact charging devices and non-contact charging devices are known as devices for charging an object to be charged. The former contact charging device is one in which a charging member to which a voltage is applied is brought into contact with or close to a member to be charged to directly transfer the charge to the member to be charged, and the surface to be charged is charged to a predetermined potential. . The contact charging device has a lower applied voltage required to charge the surface to be charged to a predetermined voltage than, for example, a corona discharge device that has been widely used as a non-contact type charging device. The amount of ozone generated during the charging process is very small, and therefore a special device for removing ozone (for example, an ozone removal filter)
It is not necessary to install, and therefore the exhaust system configuration of the device can be simplified, maintenance-free,
It has advantages such as

Therefore, in recent years, as a charging member of a contact charging device, a charging roller in which a conductive rubber or the like is formed in a cylindrical shape on the outer periphery of a metal cored bar has been used. The charging roller is rotatably supported, and is pressed by a rotating drum type photosensitive drum, which is a member to be charged, by a spring or the like, and is driven to rotate as the photosensitive drum rotates.

Further, a voltage obtained by superposing an oscillating voltage having a peak-to-peak voltage which is more than twice the charging start voltage and a DC voltage is applied to the charging roller from a power source through a cored bar, whereby the photosensitive drum The surface is uniformly charged.

However, the above charging roller has the following problems. It is necessary to have a structure in which the cored bar is covered with conductive rubber and a high resistance layer for preventing current leakage from the charging roller to the photosensitive drum (member to be charged) is provided on the surface of the conductive rubber.
Manufacturing takes time. When the charging roller is used in a laser beam printer or the like, that is, in an image forming apparatus that forms an image by writing image information by line scanning, for example, when a horizontal line pattern image is output, it is applied to the charging roller. When the unevenness of the potential on the surface of the photosensitive drum determined by the frequency of the AC component to be generated and the gap between the horizontal lines are close to each other, interference fringes occur. In order to avoid the occurrence of the above-mentioned interference fringes, it is necessary to make the potential unevenness on the photosensitive drum smaller than the size of the pixels (dots) of the image forming apparatus. Therefore, the method of increasing the frequency has been adopted. However, due to the applied AC voltage, the charging roller vibrates at a frequency about twice that AC frequency, and emits noise with the cylindrical photosensitive drum as a resonator to the outside of the apparatus main body. At this time, if the frequency of the AC voltage is high, the noise is also high.

Therefore, the present applicant proposes a charging member configured so that the charging surface passes through the contact position between the contact charging member and the member to be charged and the charging surface is located closer to the member to be charged than the tangent line drawn to the member to be charged. is doing.

This charging member brings a conductor (proximity charging plate) as an electrode plate into contact with or close to the photosensitive drum so that its charging surface faces the surface of the photosensitive drum. ) If the conductor is shaped and fixed at a predetermined position so that it is located on the photosensitive drum side with respect to the tangent line drawn from the position toward the downstream side in the moving direction of the photosensitive drum. It can be simplified more.

As a specific example of the above-mentioned proximity charging plate, the width from the upstream side to the downstream side in the rotation direction of the photosensitive drum is set to 12 mm, and it is formed long along the axial direction of the photosensitive drum. The lower surface of the proximity charging plate, that is, the charging surface facing the surface of the photosensitive drum, is gently curved following the shape of the surface of the photosensitive drum. The gap between the upstream side of the proximity charging plate and the surface of the photosensitive drum is 0 to 130 μm,
In addition, the gap between the downstream side of the proximity charging plate and the surface of the photosensitive drum is 4
It is set to 00 to 500 μm. By doing so, the gap between the surface of the photosensitive drum and the charging surface gradually increases from the upstream side to the downstream side. Through this proximity charging plate, the surface of the photosensitive drum can be favorably charged without generating charging noise or interference fringes.

[0009]

However, according to the above-mentioned conventional technique, in order to charge the image carrier satisfactorily, the gap between the image carrier and the charging member to be brought into contact with (close to) the image carrier. Must be held with high precision, and for this purpose, there has been a problem that component precision and assembly precision must be improved.

Therefore, the present invention provides an image forming apparatus in which the gap between the image carrier and the charging member is accurately maintained and good charging is performed without particularly improving the parts accuracy and the assembly accuracy. The purpose is to do.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, in which a charging member of a charging device is brought close to an image carrier and at least an oscillating voltage is applied to the charging member. In the image forming apparatus in which the image carrier is charged, the charging member has a charging surface facing the outer peripheral surface of the image carrier through a minute gap, and the charging surface is the minute gap. At a position closer to the image carrier than the tangent line drawn to the outer peripheral surface of the image carrier, and mounting an annular spacer member on the outer peripheral surface of the image carrier, and bringing the charging member into contact with the spacer member. Is characterized by holding the minute gap.

In this case, spacer members having at least two types of thickness are attached to the outer peripheral surface of the image carrier, and the charging members are brought into contact with these spacer members so that the minute gaps are held at at least two places. You may

The spacer member may be a sliding member.

[0014]

According to the above construction, the annular spacer member is mounted on the outer peripheral surface of the image carrier, and the charging member is brought into contact with the spacer member so that a minute gap required for uniform charging of the image carrier is formed. Accurately hold only by the thickness of. That is, the minute gap between the outer peripheral surface of the image carrier and the charging member is determined by the thickness of the spacer member, and is not directly influenced by the processing accuracy or assembly accuracy of other components other than the spacer member.

Further, by using a spacer member as a sliding member interposed between the image carrier and the charging member,
It is possible to prevent wear of the image carrier and the charging member.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a longitudinal sectional view showing the vicinity of an image carrier of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer by an electrophotographic process using a proximity charging plate as a charging member of the image carrier.

This laser beam printer is provided with a rotary drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image bearing member. The photosensitive drum 1 includes an organic photoconductor (OP) as a photosensitive layer on the outer peripheral surface of a drum base body 1a made of aluminum.
C) The layer 1b is provided and has an outer diameter of 30 mm. The photosensitive drum 1 is rotatably supported and is rotationally driven in the direction of arrow R1 at a peripheral speed Vps by a driving unit (not shown).

A proximity charging plate 2 as a charging member is arranged above the photosensitive drum 1. The proximity charging plate 2 is an electrode plate made of a metal plate, a conductive plastic, a conductive rubber, or the like, is formed to be long in the axial direction of the photosensitive drum 1, and the photosensitive drum 2 is provided on the surface facing the surface of the photosensitive drum 2. A charging surface 2c that is gently curved in an arc shape is formed along the rotation direction of. The configuration for disposing the proximity charging plate 2 at a predetermined position with respect to the surface of the photosensitive drum 1 will be described in detail later. A bias voltage (Vdc + Vac) obtained by superimposing an alternating current having a frequency f on the direct current is applied to the proximity charging plate 2 by the power supply 5, and the surface of the photosensitive drum 1 is charged to a predetermined potential.

An electrostatic latent image is formed by the exposure device 6 on the surface of the photosensitive drum 1 which has been charged. The exposure device 6 is
A constant print density Dd corresponding to a time-series electric digital pixel signal of a target image input from a host device such as a computer, a word processor, and an image reading device (not shown)
The laser light image-modulated by pi is output. As described above, the surface of the photosensitive drum 1 that has been charged is exposed to the main scanning in the drum generatrix direction by the laser light output from the scanner controlled by the controller, and the main scanning and the rotation of the photosensitive drum 1 in the direction of arrow R1 are performed. By the sub-scan based on the above, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1. Next, the latent image is toner-developed by the developing sleeve 7 of the developing device, and the developed image is introduced from a paper feeding unit (not shown) to the transfer unit between the photosensitive drum 1 and the transfer roller 9 at an appropriate timing. Transfer material P
Will be transcribed against. The transfer material P that has passed through the transfer section is separated from the surface of the photosensitive drum 1 and is conveyed to an image fixing section (not shown). After the transfer of the toner image, the surface of the photosensitive drum 1 is cleaned by a cleaning blade 10 of a cleaning device to remove adhering contaminants such as untransferred toner, and is repeatedly used for image formation.

The proximity charging plate 2 is arranged so that its charging surface 2c faces the surface (outer peripheral surface) of the photosensitive drum 1. Furthermore, in order to perform good charging, it is necessary to keep the gap between the charging surface 2c and the surface of the photosensitive drum 1 (OPC layer 1b) constant, and the gap is the rotation direction of the photosensitive drum 1 (arrow R).
One direction) is different between the upstream side 2a and the downstream side 2b. Specifically, according to an experiment by the applicant, the gap Ga between the upstream side 2a of the proximity charging plate 2 and the surface of the photosensitive drum 1 is set to 0 to 0.
It has been confirmed that good charging is performed when the gap Gb between the downstream side 2b and the surface of the photosensitive drum 1 is set to 400 to 500 μm. The width W of the proximity charging plate 2 from the upstream side 2a to the downstream side 2b is 1
It is set to 2 mm.

The surface of the photosensitive drum 1 and the proximity charging plate 2 described above.
In order to keep the gaps Ga and Gb constant, the charging device has a configuration described below.

As shown in FIG. 2, the back surface 2 of the proximity charging plate 2
A cut-and-raised portion 2e is provided at d. The cut-and-raised part 2e is connected to a compression spring 12 attached to a housing 11 of the image forming apparatus main body, and at the same time, the housing 11
Is fitted to the inner side 11a. The compression spring 12 presses the proximity charging plate 2 toward the surface of the photosensitive drum 1. As shown in FIG.
The columnar protrusions 2f and 2g as shown in FIG. 3 are provided, and these protrusions 2f and 2g are pressed against the annular spacer roller 30 mounted on the outer peripheral surface at both axial end portions of the photosensitive drum 1. Note that FIG. 3 illustrates only one end of the proximity charging plate 2.

The spacer roller 30 has a structure as shown in FIG.
It has a stepped structure, and the thicknesses of the small diameter portion 30a and the large diameter portion 30b are set to 80 ± 50 μm and 450 ± 50 μm, respectively. The protrusion 2f is in contact with only the outer peripheral surface of the small diameter portion 30a of the spacer roller 30, and the protrusion 2g is in contact only with the outer peripheral surface of the large diameter portion 30b.

With the above-described structure, the gap Ga between the surface of the photosensitive drum 1 and the upstream side 2a of the proximity charging plate 2 is 80 ± 50 μm, which is the same as the thickness of the small diameter portion 30a.
On the downstream side 2b of the surface of the photosensitive drum 1 and the proximity charging plate 2.
The gap Gb between and is 450 ± 5, which is the same as the wall thickness of the large diameter portion 30b.
Precisely maintained at 0 μm.

At this time, the positioning of the proximity charging plate 2 in the circumferential direction and the longitudinal direction (the circumferential direction and the axial direction of the photosensitive drum 1) is performed by cutting and raising the proximity charging plate 2 and the housing 11 of the image forming apparatus main body. And the spacer roller 30 is positioned in the longitudinal direction by the proximity charging plate 2
The protrusion 2f is abutted against the step portion 30c of the spacer roller 30.

At this time, when the material of the spacer roller 30 is made of a sliding member, that is, a member having a small friction coefficient between the spacer roller 30 and the photosensitive drum 1 and the proximity charging plate 2, the photosensitive drum 1 and the proximity roller are closed. Charge plate 2
It is possible to effectively prevent unnecessary wear. In addition, in the above-described embodiment, the spacer roller 30 has a small diameter portion 30.
Although the a and the large-diameter portion 30b are formed, the present invention is not limited to this, and the spacer roller and the large-diameter portion 3 including only the small-diameter portion 30a.
It goes without saying that the spacer roller consisting of only 0b may be formed separately and, for example, the two may be combined during assembly. <Embodiment 2> Also, as shown in FIG.
0 may be formed integrally with other members. In the embodiment shown in FIG. 4, the gear flange 1c which is the drive transmission means for rotationally driving the photosensitive drum 1 and the spacer roller 30 are integrally formed. According to this configuration, it is possible to reduce the number of parts. <Third Embodiment> The spacer member 30 may be formed of a sheet member. 31a and 31b are sheet members having a thickness of 80 μm and 450 μm, respectively. In this embodiment, a PET sheet having high slidability is used. By winding and sticking these sheet members 31a and 31b around the photosensitive drum 1, it is possible to provide the same function as that of the spacer rollers of the above-described first and second embodiments.

In this case, if the sheet members 31a and 31b are too long and overlap each other on the outer peripheral surface of the photosensitive drum 1, the proximity charging plate 2 and the photosensitive drum 1 are overlapped with each other.
Since the gap between and will widen, in order to prevent this,
The sheet member must be shorter than the outer peripheral length of the photosensitive drum 1. At this time, if the cuts 32a and 32b of the sheet members 31a and 31b are at right angles to the circumferential direction of the photosensitive drum 1, a step is formed in this portion and the gap becomes small. Therefore, in this embodiment, the above-mentioned cut line 32 is formed.
By slanting a and 32b, the gap between the image carrier 1 and the proximity charging plate 2 is kept constant.

[0028]

As described above, according to the present invention,
An annular spacer member is attached to the outer peripheral surface of the image carrier, the charging member is brought into contact with the spacer member, and a gap between the image carrier and the charging member is secured based on the thickness of the spacer member. This gap can be accurately held and good charging can be performed without particularly improving the precision or the assembly precision.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the configuration of a charging device according to a first exemplary embodiment.

FIG. 2 is an enlarged vertical cross-sectional view illustrating an optical description of the charging device according to the first exemplary embodiment.

FIG. 3 is a top view showing a relationship between a proximity charging plate and a spacer roller according to the first embodiment.

FIG. 4 is a top view showing a relationship between a proximity charging plate and a spacer roller according to a second embodiment.

FIG. 5 is a sheet member (spacer member) in the third embodiment.
The top view which shows the structure of.

[Explanation of symbols]

 1 image carrier (photosensitive drum) 2 charging member (proximity charging plate) 2c charging surface 30 spacer member (spacer roller) 30a small diameter portion 30b large diameter portion 31a spacer member (sheet member) 31b spacer member (sheet member) Ga, Gb minute Gap (gap)

Claims (3)

[Claims] 1. An image forming apparatus in which a charging member of a charging device is brought close to an image carrier and at least an oscillating voltage is applied to the charging member to charge the image carrier, wherein the charging member is , Having a charging surface facing the outer peripheral surface of the image carrier through a minute gap, and arranging the charged surface closer to the image carrier than a tangent line drawn to the outer peripheral surface of the image carrier in the minute gap. In addition, the image forming apparatus is characterized in that an annular spacer member is mounted on the outer peripheral surface of the image carrier, and the minute gap is held by bringing the charging member into contact with the spacer member. 2. A spacer member having at least two types of thickness is attached to the outer peripheral surface of the image carrier, and the charging member is brought into contact with these spacer members to hold the minute gap at at least two locations. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the spacer member is a sliding member.