JPH0844146A - Contact electrifying device - Google Patents

Abstract

PURPOSE:To prevent a photoreceptor from being deteriorated at an early stage and to stabilize electrification potential. CONSTITUTION:By making the length of an electrifying roller 21 which comes in contact with the belt photoreceptor 1 and electrifies the contact surface longer than the width of the photoreceptor 1, irregular electrification potential on both side parts in the width direction of the photoreceptor 1 is prevented; and both ends of the roller 21 are supported by the projected part 37a of the bearing 31 of a driving roller which drives the photoreceptor 1, whereby the roller 21 is allowed to press-contact with the photoreceptor 1 by gravity so as to equalize contact pressure and uniformize the electrification potential further.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging device in an image forming apparatus such as an electrostatic copying type copying machine, printer or facsimile.

[0002]

2. Description of the Related Art As a contact charging device of this type,
For example, the one disclosed in JP-A-2-39169 is known.

This is a contact charging device in which a charging roller to which a voltage is applied is pressed against an image carrier, which is a member to be charged, with a predetermined pressing force to charge the image carrier, and the charging roller is not in contact with the image bearing surface. By providing a pressure contact releasing means for holding the image bearing member, it is possible to prevent the image carrier from being contaminated and the charging roller from being deformed.

Further, in the above apparatus, the length of the charging roller is made smaller than the width of the image bearing member, and the cam member is operated by using a solenoid, a link machine, a spring or the like as the pressure contact releasing means to charge the roller. The roller is brought into contact with and separated from the image carrier.

[0005]

However, in such a conventional contact charging device, a complicated driving mechanism is required to bring the charging roller into and out of contact with the image carrier, so that the device is large in size. As a result, the production cost will rise as well. Further, since the length of the charging roller is smaller than the width of the image carrier, the charging potential on both ends in the width direction of the image carrier becomes unstable, and both ends of the charging roller are mechanically attached to the surface of the image carrier. There is a risk that the image bearing member will be deteriorated in an early stage due to a general stress. The present invention has been made in view of the above points, and it is an object of the present invention to prevent early deterioration of an image carrier and to stabilize the charging potentials at both end portions of the image carrier.

[0006]

In order to achieve the above object, the present invention provides a contact charging device comprising an image carrier and a charging roller which contacts the image carrier and charges the contact surface thereof. The present invention provides a contact charging device in which the length of the charging roller is larger than the width of the image carrier.

Further, it is preferable that both ends of the charging roller contacting the image bearing member are formed of insulating members. In these contact charging devices, both ends of the charging roller are connected to the image bearing member. It is more preferable to support it by a part of the bearing of the driving roller to be driven.

[0008]

The contact charging device according to the present invention is configured as described above, and the length of the charging roller is made larger than the width of the image carrier to stabilize the charging potential at both ends in the width direction of the image carrier. Therefore, it is possible to form a stable image.

If both ends of the charging roller are made of insulating members, deterioration of the image carrier caused by stress between the both ends of the charging roller and the image carrier and mechanical friction can be prevented. By supporting both ends of the charging roller with a part of the bearing of the image carrier driving roller, the contact pressure between the charging roller and the image carrier can be equalized, and the charging potential of the image carrier can be made more uniform. Will be possible.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. 1A and 1B are explanatory views showing an embodiment of the present invention, in which FIG. 1A is a front sectional view thereof, FIG. 1B is a side sectional view taken along line XX of FIG. a) A front sectional view showing a part of the figure in an enlarged manner, FIG. 2 is an explanatory view showing the overall configuration of a digital copying machine embodying the present application, and FIG. 3 is an illustration showing only the configuration of the image forming magazine system. It is a figure.

First, the structure and operation of a digital copying machine embodying the present invention will be briefly described with reference to FIG. This digital copying machine includes a manuscript table 100, an automatic document feeder 200 for supplying a manuscript on the manuscript table 100, an optical unit 300 for reading the supplied manuscript, an image forming magazine 400 using a belt photoconductor, and a transfer paper P. A paper feeding unit 500 including a manual paper feeding unit 501 and a cassette bank paper feeding unit 502 for sending to the image forming magazine 400, a fixing unit 600 for fixing the image transferred on the transfer paper P, and a fixed transfer paper. It has a paper discharge unit 700 for discharging P, and a double-sided unit 800 for temporarily stacking the transfer paper to form a double-sided image on the transfer paper P and sending it again to the image forming step.

As shown in FIG. 3, the image forming magazine 400 includes a belt photosensitive member 1 serving as an image carrier, a charging unit 2 for negatively charging the belt photosensitive member 1, and a belt photosensitive member 1 as indicated by an arrow A.
Belt drive unit 3 and belt photoconductor 1
This is a photoconductor / development / cleaning unit in which a development / toner magazine 4 for developing the upper latent image and a cleaning unit 5 for removing excess toner on the belt photoconductor 1 are integrally formed. From the reference point in the direction, it can slide about 10 mm to the right and about 1 mm to the left in the figure.

The belt drive unit 3 includes a drive roller 3
1, a transfer assist roller 32, a pressure roller 33, a driven roller 34, a pair of front and rear positioning plates 35 that pivotally support the transfer assist roller 32 and the driven roller 34, respectively, and a position between the positioning plate 35 and the pressure roller 33. And a pressure spring 36 for urging the pressure roller outward.

The charging roller 21 is provided in the vicinity of the driving roller 31 and has a length longer than that of the driving roller 31 and longer than that of the belt photosensitive member 1 as shown in FIG. Journals 31 provided at both ends of the drive roller 31
a is a bearing 37 provided on the side plate 30 of the belt drive unit 3.
The journals 21a provided on both ends of the charging roller 21 are supported by bearings 38 mounted on the side plate 30 with some vertical play, and are partially preloaded by the weight of the charging roller 21 or partially. Both end portions of the drive roller 31 can be brought into contact with the projecting portion 37a which is a part of the bearing 37 of the drive roller 31 (see (c) of FIG. 1).

Then, the charging roller 21 and the driving roller 3
1 can be separately driven by a drive motor (not shown) via a gear or the like, and the charging roller 21 is supported by the protrusion 37a of the bearing 37 by its own weight.
At the same time as setting the contact position with the belt photosensitive member 1, play is provided between the bearing 38 of the charging roller 21 and the side plate 30 so that the contact pressure of the charging roller 21 with respect to the belt photosensitive member 1 is constant.

As shown in FIG. 1C, the end surface 31 of the driving roller 31 is provided on both sides of the belt photosensitive member 1 in the width direction.
The side guide 11 regulated by b and the end face 37b of the bearing 37 is attached to prevent the side guide 11 from being offset.
Further, the developing / toner magazine 4 shown in FIG. 3 has a developing roller 41 for forming a visible image by attaching toner to the electrostatic latent image formed on the belt photosensitive member 1 by exposure.
The cleaning unit 5 has a cleaning blade 51 for scraping off excess toner adhering to the belt photosensitive member 1, and a waste toner collecting rod 53 for feeding the scraped toner to a waste toner collecting tank 52.

Next, the operation of the embodiment having the above structure will be described. Simultaneously with the start of the image forming process, the driving roller 31 rotates in the clockwise direction to move the belt photosensitive member 1 in the direction of arrow A, and is negatively charged by the charging roller 21 rotating in the counterclockwise direction in synchronization with this. The negatively charged belt photosensitive member 1 is exposed at an exposure position E (see FIG. 3) to form a latent image, which is developed by the developing roller 41 to be visualized.

Further, after transfer is performed in synchronization with the transfer paper P (FIG. 2) by a transfer charger portion (not shown), the transfer paper P is separated from the belt photosensitive member 1 by curvature separation, and the fixing process is performed. After that, it is discharged to the outside. On the other hand, the belt photosensitive member 1 from which the transfer paper P is separated is cleaned by the cleaning unit 5.
After the cleaning blade 51 cleans the surface, the charge is removed by a discharge lamp (not shown) to prepare for the next image forming process, but the excess toner scraped from the belt photosensitive member 1 is discarded toner recovery rod 53. And is collected in the waste toner collecting tank 52. Copying is performed by repeating the series of image forming processes described above.

Here, the charging roller 21 is a driving roller 31.
And the protrusion 37 of the bearing 37 of the drive roller 31 is provided instead of the bearing 38 of the charging roller 21.
Therefore, the charging roller 21 is in pressure contact with the belt photosensitive member 1 always maintaining a constant and stable contact pressure by its own weight or a partial preload. Therefore, the belt photosensitive member 1 is evenly charged by the voltage applied to the charging roller 21 at the timing when the image forming process is started, and the charging roller 21 is charged at the same time when the image forming process is completed.
Stop applying voltage to the.

Further, since the length of the charging roller 21 is made larger than the width of the belt photosensitive member 1, it is possible to stabilize the charging potential at both ends of the belt photosensitive member 1 in the width direction, and a high quality image can be obtained. Can be formed.

Next, FIG. 4 is an enlarged sectional view showing a part of the charging roller 22 in another embodiment of the present invention. In this embodiment, a journal is formed on both ends of a cylindrical charging roller 22 (only one of which is shown in FIG. 4) having a fitting portion 22b fitted to its inner diameter portion and a circumferential groove 22c following the fitting portion 22b. 22a is fixed, and an insulating member 23 made of resin or the like is embedded in the circumferential groove 22c so that its outer diameter is the same as the outer diameter of the charging roller 22. Each position is set so as to contact the outer peripheral surface of. The rest of the configuration is the same as in FIG.

According to this embodiment, in addition to the effects of the first embodiment, there is no leakage of electric charge between the charging roller 22 and both ends of the belt photosensitive member 1, and the mechanical force between the two does not occur. Since the stress is also weakened, it is possible to prevent the deterioration of the belt photosensitive member 1 due to the stress.

In the above embodiment, an example in which the latent image formed on the belt photosensitive member is negatively and positively developed has been described, but positive and positive development may be used without any problem, and excess toner adhered to the belt photosensitive member is scraped off. A trailing blade may be used instead of the cleaning blade, and
The belt photosensitive member forming the image carrier may be a drum photosensitive member. Further, these photoconductors may be a cartridge type or a separate unit type.

Further, in the above embodiment, the embodiment in which the present invention is applied to the digital copying machine has been described. However, the present invention is not limited to this, and an analog copying machine or a printer or a facsimile using an electrostatic copying method can be used without any trouble. It can be carried out.

[0025]

As described above, in the contact charging device according to the present invention, the length of the charging roller is set to be larger than the width of the image bearing member, so that charging unevenness may occur on both sides of the image bearing member in the width direction. And the charging potential on the entire surface is stabilized.

In the above apparatus, if both ends of the charging roller are made of insulating members, the leakage of charges at both sides of the image carrier in the width direction and deterioration of the image carrier due to mechanical stress can be prevented. Further, in these devices, by supporting both ends of the charging roller by the bearing portion of the image carrier driving roller, the contact pressure between the charging roller and the image carrier is made uniform, and the charging potential is further uniformed. Can be realized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the overall configuration of a digital copying machine embodying the present invention.

FIG. 3 is an explanatory diagram showing a configuration of only the image forming magazine system.

FIG. 4 is an enlarged sectional view showing a part of a charging roller according to another embodiment of the present invention.

[Explanation of symbols]

 1: Belt photosensitive member (image bearing member) 2: Charging unit 3: Belt driving unit 4: Developing / toner magazine 5: Cleaning unit 21, 22: Charging roller 23: Insulating member 31: Driving roller 37: Bearing of driving roller 37a : Bearing protrusion

Claims (3)

[Claims] 1. A contact charging device comprising an image carrier and a charging roller that contacts the image carrier and charges its contact surface, wherein the length of the charging roller is larger than the width of the image carrier. A contact charging device characterized in that 2. The contact charging device according to claim 1, wherein
A contact charging device, characterized in that both ends of the charging roller, which are in contact with the image carrier, are formed of insulating members. 3. The contact charging device according to claim 1, wherein both ends of the charging roller are supported by a part of bearings of a driving roller that drives the image carrier. .