JPH0736288A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which separates a transfer material, after the transfer of a toner image, from a photoreceptor by means of curvature without a separation claw and the decrease in development efficiency, whereby the simplification and miniaturization of the device is possible. CONSTITUTION:The image forming device is equipped with a drive roller 1 having a fixed curvature radius R1, a flexible photosensitive belt 2 whose circumference is longer than that of the drive roller and which is fitted over the outside of the roller and rotates as it follows the rotation of the roller, a developing roller 41 and a cleaning blade 61 both of which, while allowing the rotation of the belt 2, forms a projecting loose part 21, having a curvature radius R2 smaller than the curvature radius of the drive roller 1, in the belt 2, and a transfer device 5 facing the projecting loose part 21.

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.

[0002]

2. Description of the Related Art In an image forming apparatus, the surface of a photosensitive member is usually charged by a charging device, and an electrostatic latent image corresponding to an original image is formed by exposing the charged area to an image from an optical system. The image is developed by a developing device to form a visible toner image, the toner image is transferred to a transfer material by a transfer device, and is fixed by a fixing device. After the transfer of the toner image, the toner remaining on the photoconductor is removed by the cleaning device, and the residual charge is erased by the eraser.

The photoreceptor is generally in the form of a rigid drum. The radius of curvature of the drum is set to a certain size in order to secure a developing nip as large as possible in order to improve the developing efficiency when the electrostatic latent image is developed by the developing device.

[0004]

However, in the case of such a rigid photosensitive drum, as described above, the radius of curvature of the photosensitive drum is made as large as possible in order to increase the developing efficiency. As the size of the transfer material increases, it becomes difficult to separate the transfer material after the toner image is transferred from the photosensitive member, particularly, the separation using the curvature of the photosensitive drum (curvature separation), and the transfer material separating claw becomes indispensable. This hinders simplification and downsizing of the device. If the diameter of the photosensitive drum is reduced in order to omit the separation claw, the developing nip is reduced and the developing efficiency is lowered.

Therefore, according to the present invention, the separation of the transfer material after the transfer of the toner image from the photosensitive member can be performed by the curvature separation without the separation claw without lowering the developing efficiency, which simplifies and downsizes the apparatus. An object of the present invention is to provide an image forming apparatus capable of performing the above.

[0006]

An image forming apparatus of the present invention which solves the above-mentioned problems has a driving roller having a constant radius of curvature, and a peripheral length longer than the peripheral length of the driving roller and fitted onto the roller. A flexible photoconductor belt that rotates following the rotation of the roller, and means for forming a protruding slack portion on the belt that allows the rotation and has a radius of curvature smaller than the radius of curvature of the drive roller. And a transfer device facing the protruding slack portion.

As the means for forming the protruding slack portion, a fixed arrangement in which the photosensitive belt is sandwiched and squeezed from both sides in the vicinity of the drive roller to form the protruding slack portion, or a spring-biased guide member, a rotatable member are used. A roller, a combination of these, and the like are conceivable, but a developing device and a cleaning device arranged before and after the transfer device may be used.

The transfer device in the device of the present invention may be fixedly arranged like a wire electrode type corona discharge device, or may be a rotatable transfer roller.
Further, the charging device may be a corona discharge device or a charging roller.

[0009]

According to the image forming apparatus of the present invention, the photosensitive belt wound around the driving roller is partly projected from the driving roller by the projecting slack forming means.
And, it is loosened so that its radius of curvature becomes smaller than that of the drive roller. The transfer device is provided in the protruding slack portion. This portion has a smaller radius of curvature than the portion supported by the drive roller, and therefore the transfer material after the toner image has been transferred in this transfer area is curvature-separated from the photosensitive belt without a separation claw.

The developing device is provided on a portion of the photosensitive belt that is supported by the drive roller from behind and has a large radius of curvature, or on a flexible portion that is connected to the protruding slack portion away from the rear support by the drive roller. Alternatively, a developing nip that is provided at the boundary between these portions and that achieves a desired developing efficiency is secured.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows one embodiment, and FIG. 2 shows another embodiment. The image forming apparatus shown in FIG. 1 includes a driving roller 1.
A flexible photoconductor belt 2 is wound around this. The drive roller 1 is driven by an unillustrated motor by an arrow C in the figure.
It is driven to rotate in the CW direction, its radius of curvature is R1, and the roller surface has a surface roughness capable of driving the belt 2 by frictional force. In the present example, the photosensitive belt 2 is formed by vapor-depositing an aluminum film on the surface of a polyester film and forming a photosensitive layer on the aluminum film. The photosensitive belt 2 is wound around the roller 1 with the photosensitive layer facing outward.

A charging device 3, a developing device 4, a transfer device 5, a cleaning device 6 and an eraser 7 are arranged in this order outside the periphery of the photosensitive belt 2. A part 21 of the photosensitive belt 2 is sandwiched and squeezed from both sides by the developing roller 41 of the developing device 4 and the cleaning blade 61 of the cleaning device 6 arranged in the vicinity of the driving roller 1 to form a protruding slack portion. The developing roller 41 is driven to rotate in the direction of the arrow CW in the drawing and is in contact with the photosensitive belt 2, which contributes to the formation of the protruding slack portion 21. Further, the cleaning blade 61 is in contact with the belt 2 from the direction in which the load is applied to the belt 2 in the rotating direction. In this example, the belt is in contact with the belt from the direction opposite to the traveling direction of the belt, which contributes to the formation of the protruding slack portion 21. Further, by forming the protruding slack portion as described above, the belt 2 is wound around the drive roller 1 so as to be fastened, and the belt slip is prevented.

The radius of curvature R2 of the projecting slack portion 21 thus formed is sufficiently smaller than that R1 of the drive roller 1 (thus, the radius of curvature of the belt portion supported by the roller 1). The transfer device 5 is provided in this portion 21. Generally speaking, the larger center angle θ1 formed by the portion 2a where the belt 2 starts to separate from the drive roller 1 and the portion 2b where the belt 2 starts to contact the drive roller 1 has a relation of θ1> θ2 with respect to the remaining center angle θ2. Then, θ2 <180 °, and R
1> R2 is set. The peripheral speed ratio of the developing roller 41 to the belt 2 is 1.0 or more.

The transfer device 5 comprises a corona discharge device in the illustrated example. A timing roller pair 8 is provided on the left side of the device 5 in the drawing, and a paper feeding unit (not shown) is provided on the left side of the timing roller pair 8. A fixing device 9 is arranged on the right side of the transfer device 5 in the figure. An optical system 10 is arranged above the photoconductor belt 2.

According to this image forming apparatus, the driving roller 1
The photoconductor belt 2 also rotates in response to the rotation of the optical disk 1 and the surface thereof is charged by the charging device 3, and the optical system 1 is charged in the charging area.
Image exposure corresponding to the original image is performed from 0 to form an electrostatic latent image. This latent image is developed by the developing device 4 into a visible toner image, and is sent to a transfer area where the belt protruding slack portion 21 and the transfer device 5 face each other.

On the other hand, the transfer paper S is pulled out from a paper supply unit (not shown) and reaches the timing roller pair 8, and is fed to the transfer area in synchronization with the toner image on the belt 2 by the roller pair 8. In the transfer area, the toner image that has arrived here is transferred onto the transfer paper S by the transfer device 5. The transfer sheet S onto which the toner image has been transferred is curvature-separated from the photosensitive belt 2, and then the toner image is fixed by the fixing device 9 and discharged.

The developer remaining on the belt 2 after the toner image is transferred is scraped off by the cleaning blade 61, and the residual charge is erased by the eraser 7. In the image forming apparatus described above, the developing roller 41 of the developing device 4 is in contact with the flexible belt portion having no back support between the drive roller 1 and the belt protruding slack portion 21 with a large developing nip width. The development efficiency is good, and high-quality image development is performed by utilizing the near electric field. Further, since the developing roller 41 is in contact with the flexible belt portion having no back support, the developer clogging hardly occurs.

Further, since the radius of curvature R2 of the belt protruding slack portion 21 is sufficiently smaller than the radius of curvature R1 of the driving roller 1, and hence the radius of curvature of the belt portion supported thereby,
The transfer paper S after the toner image transfer is curvature-separated from the photoconductor belt 2 without a separation claw. As described above, since the separation claw is unnecessary, the configuration of the entire apparatus is simplified, the labor for setting the separation claw is saved, and the cost can be reduced accordingly.

Further, since the cleaning blade 61 is in contact with the belt portion in the flexible state where there is no rear support between the drive roller 1 and the belt projecting slack portion 21, the setting can be roughly performed and the setting can be made. It's easy. Further, even if the contact pressure is weak, the belt 2 is well adapted to the belt 2, and the cleaning effect can be sufficiently enhanced while the abrasion is suppressed.

The developing device 4 and the cleaning device 6 may be arranged with respect to the belt portion which is supported by the driving roller 1 from behind. In this case, the radius of curvature of the drive roller 1 may be set to a size that can secure a developing nip for efficient development. Further, in this case, means such as a rotating roller and a guide member for forming the belt protruding slack portion 21 may be separately arranged.

Further, the developing device 4 and the cleaning device 6
It is also conceivable to arrange the photosensitive belt 2 at the position 2a where the photosensitive belt 2 starts to separate from the drive roller 1 and at the position 2b where the photosensitive belt 2 starts contacting again. Next, the image forming apparatus shown in FIG. 2 will be described. This device has substantially the same configuration as the device shown in FIG. 1 except for the following points. 1 is different from the device shown in FIG. 1 in that instead of the photoconductor belt 2, a light-transmitting, slightly long photoconductor belt 20 is used, and instead of the cleaning device 6, the cleaning device 60 is replaced by an eraser 7. The eraser 70 is used instead of the above, and the rotating roller 100 that forms another belt protruding slack portion 22 together with the cleaning blade 601 of the cleaning device 60.
Is adopted.

In this example, the eraser 70 is arranged inside the protruding slack portion 22 in a simplified state that does not require a reflector such as a reflector. As described above, by adopting the flexible photoconductor belt 20, the arrangement of the eraser or the like can be changed, and the degree of freedom in device design is increased accordingly. Θ1> θ described in the apparatus of FIG.
The relationship of 2, θ2 <180 ° and R1> R2 can be applied to this example.

In each of the image forming apparatuses described above, a corona discharge device is used as the transfer device 5, but a transfer roller that rolls in contact with the photosensitive belt 2 may be used.

[0024]

According to the present invention, the separation of the transfer material after the transfer of the toner image from the photosensitive member can be performed by the curvature separation without the separation claw without lowering the developing efficiency, which simplifies the apparatus. An image forming apparatus that can be downsized can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Driving roller 2, 20 Photosensitive belt 21, 201 Projected slack portion of photosensitive belt 3 Charging device 4 Developing device 41 Developing roller 5 Transfer device 6, 60 Cleaning device 61, 601 Cleaning blade 7, 70 Eraser 8 Timing roller pair 9 Fixing device 10 Optical system S Transfer paper

Claims (1)

[Claims] 1. A drive roller having a constant radius of curvature, and a flexible photosensitive member which has a peripheral length longer than that of the drive roller and is externally fitted to the roller, and which rotates following the rotation of the roller. A body belt, means for forming a protruding slack portion having a radius of curvature smaller than that of the drive roller while allowing the belt to rotate, and a transfer device facing the protruding slack portion. A characteristic image forming apparatus.