JPH10307483A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form an image, without degrading transferability, even if a thick paper is used by adjusting the contact pressure of a transfer belt with a photoreceptive drum, in accordance with the thickness of a paper sheet to be used. SOLUTION: When carriers are interposed between the photoreceptive drum 5 and the paper sheet 8 and space is formed by the carriers, the space is larger as the paper 8 is thicker, when the carriers have the same size, so that the transferability of toner from the drum 5 to the paper 8 is degraded. Therefore, when the space can be suppressed as small as possible, the degradation of the transferability can be suppressed as low as possible. Consequently, in the thickness of the paper 8 causing the degradation of the transferability, the positioning stopper 6 of an eccentric cam is rotated to reduce eccentricity. Thus, the contact pressure (f) and contact width of the transfer belt 1 with the drum 5 are great, the space of the carriers is small and the degree of closely sticking the paper 8 to the photoreceptor 5 is highly attained to improve the transferability.

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 provided with a transfer belt provided so as to be able to contact a photosensitive drum surface.

[0002]

2. Description of the Related Art Conventionally, a photosensitive drum rotatably supported, a transfer belt provided so as to be in contact with the surface of the photosensitive drum and having a sheet conveying surface, and a transfer belt provided on the back side of the sheet conveying surface of the transfer belt. And a transfer device for transferring the toner image formed on the photosensitive drum onto a sheet on a transfer belt, the contact pressure of the transfer belt with respect to the photosensitive drum is always set to be constant. .

[0003]

When a magnetic brush two-component developing system is used as a developing system of an image forming apparatus, the developing device of this system is provided with a magnetic roller, and the toner is held on a carrier by electrostatic force. Then, a magnetic brush is formed on the magnetic roller. Since the magnetic brush rotates while contacting the photosensitive drum and forms a toner image on the photosensitive drum, the carrier rarely contacts the photosensitive drum due to the centrifugal force or electrostatic force of the magnetic roller when forming the toner image by contacting the magnetic brush. May adhere.

The carrier on the photosensitive drum has a size of about 20 μm, but forms a small space between the photosensitive drum and the paper to be brought into close contact with each other when a toner image is transferred onto the paper. May deteriorate transferability to paper and adversely affect images. This phenomenon occurs when the contact pressure between the transfer belt and the photosensitive drum is constant, because the rigidity of the paper itself increases as the thickness of the paper increases. Appears prominently.

An object of the present invention is to provide an image forming apparatus capable of forming a stable image without deteriorating transferability even when thick paper is used.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a photosensitive drum rotatably supported, a transfer belt provided so as to be in contact with the surface of the photosensitive drum, and having a sheet conveying surface; A transfer device that is disposed on the back side of the sheet conveying surface and that transfers a toner image formed on the photosensitive drum to a sheet on a transfer belt, wherein a contact pressure of the transfer belt with respect to the photosensitive drum is used. This is achieved by having a contact pressure adjustment mechanism that adjusts according to the thickness of the paper to be adjusted.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, during a printing operation, a transfer belt 1 is exposed to light by abutting a positioning ring 4 attached to both ends of a driven roller shaft 3 with a constant force p around a shaft center of a driving roller 2 as a fulcrum. Drum 5
Contact pressure.

The stopper 6 is an eccentric cam, which is driven and rotated by a stepping motor 7 according to the thickness of the paper 8 to change the contact pressure of the transfer belt 1 with respect to the photosensitive drum 5.

FIG. 2 is a schematic diagram showing a mechanism of improving the transferability. Carrier c between photosensitive drum 5 and sheet 8
Are interposed, thereby forming a space b. If the size of the carrier c is the same, the space b becomes larger as the paper thickness of the paper 8 is larger (or as the stiffness is higher), and the transferability of the toner from the photosensitive drum 5 to the paper 8 is deteriorated. Will be. Therefore, the photosensitive drum 5 and the sheet 8
If the space b can be minimized even if the carrier c is interposed between them, the deterioration of transferability can be minimized. For this purpose, when the thickness of the sheet 8 that deteriorates transferability is increased, the contact pressure f and the contact width a of the transfer belt 1 with respect to the photosensitive drum 5 can be reduced by rotating the stopper 6 for positioning the eccentric cam to reduce the amount of eccentricity. Is increased, the space defined by the carrier c is reduced, the adhesion between the photosensitive drum 5 and the paper 8 is increased, and the transferability is improved.

[0010]

As described above, according to the present invention, it is possible to provide an image forming apparatus capable of performing stable image formation without deteriorating transferability even when thick paper is used.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing one embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a state during transfer.

[Explanation of symbols]

1 is a transfer belt, 2 is a transfer belt driving roller, 3 is a transfer belt driven roller, 4 is a positioning ring, 5 is a photosensitive drum, 6 is a positioning stopper (eccentric cam), 7 is a stepping motor, and 8 is paper. .

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Soyasu 1060 Takeda, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Koki Co., Ltd.

Claims (1)

[Claims] A photosensitive drum rotatably supported, a transfer belt provided to be in contact with the surface of the photosensitive drum, and having a paper transport surface; and a transfer belt disposed on the back side of the paper transport surface of the transfer belt. A transfer device for transferring a toner image formed on the photosensitive drum onto a sheet on a transfer belt, wherein a contact pressure of the transfer belt with respect to the photosensitive drum is adjusted according to a thickness of the sheet to be used. An image forming apparatus, comprising: