JPH05100584A - Image transfer device - Google Patents

Abstract

PURPOSE:To decrease the defect in separation between a photosensitive drum and a sheet at the time of transfer. CONSTITUTION:A transfer device 13 is used for transferring an image held on a rotating photosensitive drum 9 to a sheet and provided with a transfer roller 31, a motor and a transfer roller moving means. The transfer roller 31 can be brought into pressure-contact with the photosensitive drum 9 and separated therefrom. The coefficient muK of the transfer roller 31 against the sheet is smaller than the coefficient muD of the photosensitive drum 9 against the transfer sheet. The motor drives the transfer roller 31 so that the peripheral speed of the transfer roller 31 is higher than that of the photosensitive drum 9. The transfer roller moving means allows the transfer roller 31 to be in pressurized-contact with the photosensitive drum 9 in accordance with the timing of transfer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transfer apparatus, and more particularly to an image transfer apparatus for transferring an image carried on a rotating carrier of an image forming apparatus such as a copying machine onto a transfer sheet such as paper.

[0002]

2. Description of the Related Art An image transfer apparatus for transferring a toner image formed on a photosensitive drum, which is an image carrier, to a sheet, which is a transfer sheet, is used in an image forming apparatus such as a copying machine. In this type of image transfer apparatus, conventionally, a corona discharge is used to apply an electric charge having a polarity opposite to that of the toner to the paper to transfer the toner image to the paper. However, when corona discharge is used, ozone is generated, which adversely affects the environment.

Therefore, an image transfer device using a transfer roller instead of corona discharge is already known (see, for example, Japanese Patent Application Laid-Open Nos. 1-196087 and 1-265282). In this device, a bias voltage having a polarity opposite to the charge of the toner on the photosensitive drum is applied to the transfer roller. Then, with respect to the paper supplied between the photoconductor drum and the transfer roller, the toner image on the photoconductor drum is pressed by pressing the paper against the photoconductor drum by the transfer roller and bias voltage applied to the transfer roller. Is transferred to the paper.

[0004]

In the image transfer device using the transfer roller, the diameter of the transfer roller is smaller than the diameter of the photosensitive drum, so that the paper is easily attracted to the photosensitive drum and the separation of the paper deteriorates. In particular, when passing a blank sheet on which the toner is not transferred, the separation is extremely bad, which causes jam frequently.

An object of the present invention is to reduce defective separation between the image carrier and the transfer sheet during transfer.

[0006]

An image transfer apparatus according to the present invention is for transferring an image carried on a rotating image carrier to a transfer sheet, and comprises a transfer roller, a driving unit, and a transfer roller moving unit. And means. The transfer roller can be pressed against and separated from the image carrier, and the coefficient of friction with respect to the transfer sheet is smaller than the coefficient of friction of the image carrier with respect to the transfer sheet. The driving unit drives the transfer roller so that the peripheral speed of the transfer roller is higher than the peripheral speed of the image carrier. The transfer roller moving means presses the transfer roller against the image carrier at the transfer timing.

[0007]

In the image transfer device according to the present invention, at the time of non-transfer,
The transfer roller is separated from the image carrier by the transfer roller moving means, and the transfer roller is brought into pressure contact with the image carrier by the transfer roller moving means during transfer when the transfer sheet is carried in. Further, the transfer roller is driven by the driving unit so that the peripheral speed of the transfer roller is faster than that of the image carrier, and the coefficient of friction of the transfer sheet is smaller than that of the image carrier. Therefore, the transfer sheet is sent at the same speed as the peripheral speed of the image carrier. On the other hand, the transfer roller and the transfer sheet rotate at a high speed in a slipped state to separate the image carrier from the transfer sheet.

Since the image carrier and the transfer roller are separated apart from each other during transfer, the surface of the image carrier is not damaged.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a copying machine adopting an embodiment of the present invention. In FIG. 1, a document table 2 is fixed to the upper surface of a copying machine main body 1, and an openable and closable document holder 3 is arranged on the document table 2. A bypass tray 4 and a pair of paper feed cassettes 5 and 6 are detachably mounted on the right side of the copying machine body 1 in the figure.

Inside the copying machine main body 1, an exposure device 8 for reading a document is provided above the main body. The exposure device 8 is composed of a light source, a mirror, a lens and the like. A photoconductor drum 9 on which an electrostatic latent image is formed is arranged in the center of the copying machine body 1. Around the photosensitive drum 9, a main charging device 10 that charges the photosensitive drum 9 to a predetermined electric charge, a blank lamp 11 that erases charging of an unnecessary area on the photosensitive drum 9, and an electrostatic charge on the photosensitive drum 9. A developing device 12 for developing the latent image with toner, and a transfer device 1 for transferring the toner image on the photosensitive drum 9 to a sheet.
3, and a cleaning device 14 for removing the residual toner on the photosensitive drum 9.

Bypass tray 4 and paper feed cassettes 5 and 6
And the image forming section 1 including the photosensitive drum 9 and the like.
5 and downstream of the image forming section 15 thereof, a paper transport path 17 for transporting a paper and a paper discharge transport path 1 respectively.
8 are provided. A registration roller 21 is provided on the upstream side of the photosensitive drum 9 in the paper transport path 17. The registration roller 21 is for adjusting the timing of discharging the paper between the photoconductor drum 9 and the transfer device 13. The discharge transport path 18 is mainly used for the transport conveyor 2
And a fixing device 19 for fixing the discharged transfer image on the sheet on the downstream side (left side in the drawing).
And a discharge roller 20 for discharging the sheet fixed by the fixing device 19 to the outside.

As shown in FIG. 2, the transfer device 13 has a case 30 which rotates in the direction of arrow X about the rotation center O1. A transfer roller 31 is rotatably supported on the upper portion of the case 30 about a rotation center O2.
The transfer roller 31 is made of an elastic body having a specific resistance of about 10 ⁶ Å · cm. Further, the friction coefficient μ _K of the transfer roller 9 with respect to the paper is determined by the photosensitive drum 9
Of the transfer roller 3 smaller than the friction coefficient μ _D
1 is smaller than the friction coefficient μ _P for the photosensitive drum 9.
The upper portion of the transfer roller 31 is in pressure contact with the lower surface of the photosensitive drum 9.

As shown in FIG. 3, a pulley 35a is attached to one end of the rotary shaft of the transfer roller 31. A pulley 35b is attached to the output shaft of the motor 36. A belt 37 is wound around the pulleys 35a and 35b. The rotational driving force of the motor 36 is transmitted to the transfer roller 31 via the belt 37, and the transfer roller 31 rotates at a peripheral speed higher than the peripheral speed of the photosensitive drum 9 (for example, 1.5 times).

As shown in FIG. 2, the transfer roller 31 is connected to a bias power source 43 and is applied with a voltage having a polarity opposite to that of the toner (eg, + 1000V DC voltage).
In the case 30, below the transfer roller 31, a fur brush 32 that is in pressure contact with the lower surface of the transfer roller 31 is arranged. The fur brush 32 is rotationally driven by a driving mechanism (not shown) to clean the transfer roller 31. The tip of the blade 33 fixed to the inner wall surface of the case 30 bites into the lower portion of the fur brush 32. The blade 33 is for scraping off the toner attached to the fur brush 32 from the fur brush 32.

As shown in FIGS. 2 and 3, a cam 34 rotatable about a rotation center O3 is arranged on the lower surface of the case 30. The rotating shaft 38 of the cam 34 is connected to a stepping motor 39 via a coupling 38a. The cam 34 is rotated by the stepping motor 39, which causes the transfer device 13 to rotate in the X direction. The rotation position of the cam 34 is determined according to the thickness of the paper. Further, during non-transfer, the rotational position of the cam 34 is a position where the photoconductor drum 9 and the transfer roller 31 are separated from each other as shown by a chain double-dashed line in FIG. In addition, each center O
1, O2 and O3 are parallel to each other.

This copying machine has a control unit 4 as shown in FIG.
It has 0. The control unit 40 includes a CPU, ROM, RA
It includes a microcomputer such as M. An operation panel 41 arranged on the upper surface of the copying machine main body 1 including various switches and an LED display unit is connected to the control unit 40. Further, the control unit 40 includes a bias power source 43, each part of the image forming unit 15 except the transfer device 13, a motor 36 for rotating the transfer roller 31, a stepping motor 36 for rotating the cam 34, and a sheet conveying path 17. , A jam detection unit 42 including a jam detection sensor (not shown) provided in the paper transport path 17 and the paper discharge transport path 18, and other input / output units are connected. ing.

Next, the operation of the above embodiment will be described based on the control flow chart shown in FIG. When the copy operation is started by pressing the print button in the operation panel 41, in step S1, the primary feeding for feeding the paper via the paper feeding path 17 from the selected paper feeding cassette to the registration roller 21. Paper is made. In step S2,
It is determined whether or not a jam (paper jam) has occurred in the primary paper feed. This determination is made based on the state of each sensor of the jam detection unit 42. If it is determined that the jam has not occurred, the process proceeds to step S3. In step S3, the image forming unit 15 performs an image forming process.

In this image forming process, the exposure device 8 reads the image information from the original placed on the original table 2.
An electrostatic latent image is formed on the photosensitive drum 9 based on the read image information. The electrostatic latent image formed on the photosensitive drum 9 is visualized with toner by the developing device 12 after the unnecessary portion is removed by the blank lamp 11.

When image formation is performed, in step S4,
Register at the timing of aligning the leading edge of the image with the leading edge of the paper.
Secondary paper feed that drives the stroller 21 to perform transfer and discharge
Is executed. In step S5, the transfer roller 31
A bias voltage is applied by the bias power supply 43. Step
In step S6, the motor 39 is driven to move the cam 34 to the paper thickness.
The transfer roller 31 to the photosensitive drum.
Roll it by pressing it to the ram 9 so that the specified nip width is obtained.
Start copying. The transfer roller 31 is sensed by the motor 36.
It is driven to rotate at a peripheral speed higher than that of the optical drum 9.
To be pressed against the photosensitive drum 9 at the transfer timing.
The paper is pinched. At this time, the friction coefficient μ _DMore friction coefficient
μ_KIs small, the paper and the transfer roller 31 slip
Are in contact with each other. In addition, the photosensitive drum 9 and the paper
They are in contact with each other without deviation. For this reason, transfer deviation may occur.
You can move the paper without
The paper can be separated from the ram 9.

In step S7, a waiting time of a predetermined time corresponding to the length of the toner image formed on the photosensitive drum 9 is waited. When the predetermined time has elapsed, the process proceeds to step S8.
In step S8, the application of the bias voltage is finished and the transfer is finished. In step S9, the motor 39 is driven and the cam 34 is rotated to move the transfer roller 31 to a position separated from the photosensitive drum 9. In step S10, it is determined whether a jam has occurred in the secondary paper feeding. If no jam has occurred, the process proceeds to step S11. In step S11, the paper discharge conveyance path 18 and the fixing device 1
9 and the discharge roller 20 are driven to discharge the paper to the outside.

On the other hand, if it is determined in step S2 or S10 that a jam has occurred, the process proceeds to step S12. In step S12, each part is stopped. Step S
At 13, the jam display LED in the operation panel 41 is turned on to notify the operator that a jam has occurred. When the process in step S9 or step S13 ends, the process proceeds to the next process.

As described above, the transfer roller 31 is driven at a peripheral speed higher than the peripheral speed of the photosensitive drum 9, and the transfer roller 31 is pressed against and separated from the photosensitive drum 9 so that the paper is transferred at the time of transfer. The surface of the photosensitive drum 9 can be reliably separated from the photosensitive drum 9 and the surface 9 of the photosensitive drum is not transferred.
Can be prevented from being damaged. [Other Embodiments] (a) Although the transfer roller is moved by using the cam in the above embodiment, a member other than the cam may be used. (B) In the above embodiment, an example in which the image transfer device is used in a copying machine is shown, but the present invention can be applied to other image forming devices such as a laser printer. (C) In the above embodiments, the photoconductor drum was described as an example of the image carrier, but the image carrier may be a transfer drum or a transfer belt used in a color copying machine.

[0023]

In the image transfer device according to the present invention, the transfer roller is brought into pressure contact with the image carrier at the time of transfer, and is driven so that the peripheral speed thereof is faster than the peripheral speed of the image carrier. Therefore, the transfer roller is in contact with the paper while rotating at a high speed in a slipped state, so that defective separation of the paper from the image carrier can be reduced. Further, since the transfer roller is separated from the image carrier during non-transfer, the image carrier is not damaged.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a copying machine adopting an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a transfer device.

FIG. 3 is a partially cutaway front view showing a drive system of a transfer roller.

FIG. 4 is a block diagram showing the configuration of a control system.

FIG. 5 is a flowchart showing a control operation.

[Explanation of symbols]

 9 Photoreceptor Drum 13 Transfer Device 31 Transfer Roller 34 Cam 36 Motor 39 Stepping Motor 40 Control Unit

Claims (1)

[Claims] 1. An image transfer device for transferring onto a transfer sheet carried by a rotating image carrier, wherein the friction coefficient of the image carrier is smaller than that of the transfer device. Further, a transfer roller that can be pressed into contact with and separated from the image carrier, a driving unit that drives the transfer roller so that the peripheral speed of the transfer roller is faster than the peripheral speed of the image carrier, and a transfer roller that matches the transfer timing. An image transfer device comprising: a transfer roller moving unit that presses the transfer roller against the image carrier.