JPH05100583A - 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 the rotating photosensitive drum 9 to a sheet and provided with a transfer roller 31 and a driving means including a motor 26 and a torque limiter 35. The coefficient muK of the friction of the transfer roller 31 against the sheet is smaller than the coefficient muD of the friction of the photosensitive drum 9 against the sheet and the transfer roller 31 is in pressurized contact with the photosensitive drum 9. The driving means drives the transfer roller 31 in accordance with the timing of transfer so that the peripheral speed of the transfer roller 31 is higher than that of the photosensitive drum 9.

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 used for an image forming apparatus such as a copying machine and for transferring an image carried on a rotating image carrier to a transfer sheet. ..

[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 device 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 and a driving means. ing. The transfer roller has a smaller coefficient of friction with respect to the transfer sheet than that of the image carrier with respect to the transfer sheet, and is in pressure contact with the image carrier. The driving unit drives the transfer roller so that the peripheral speed of the transfer roller becomes faster than the peripheral speed of the image carrier in accordance with the transfer timing.

[0007]

In the image transfer device according to the present invention, when the transfer sheet is sandwiched between the image carrier and the transfer roller during transfer,
The driving unit drives the peripheral speed of the transfer roller to be higher than the peripheral speed of the image carrier. At this time, since the friction coefficient between the image carrier and the transfer sheet is larger than the friction coefficient between the transfer roller and the transfer sheet, the transfer sheet is sent in synchronization with the image carrier. On the other hand, the transfer roller rotates at high speed in a slip state with respect to the transfer sheet to separate the image carrier from the transfer sheet.

When the image carrier and the transfer roller are in contact with each other, the peripheral speeds of the image carrier and the transfer roller are the same, so that the surface of the image carrier is not damaged by the high speed rotation of the transfer roller.

[0009]

Embodiment 1 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, one end of the rotary shaft of the transfer roller 31 is connected to an output shaft of a motor 36 via a torque limiter 35. This torque limiter 35
The rotation driving force of the motor 36 is connected / disconnected according to the set torque. The set torque of the torque limiter 35 is set to be smaller than the torque when the friction coefficient is μ _P and larger than the torque when the friction coefficient is μ _K. That is, when the transfer roller 31 and the photoconductor drum 9 are in direct contact with each other without the intervening paper, the torque limiter 35 operates, the rotational driving force of the motor 36 is not transmitted to the transfer roller 31, and the transfer roller 31 It rotates together with the photosensitive drum 9. Further, when the paper is interposed between the photoconductor drum 9 and the transfer roller 31, the frictional force is reduced, so the rotational driving force of the motor 36 causes the transfer roller 31 to be faster than the peripheral speed of the photoconductor drum 9 (for example, 1. It is driven to rotate (5 times faster), and the paper is reliably separated.

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. At the bottom of the fur brush 32, the case 30
The tip portion of the blade 33 fixed to the inner wall surface of the is cut into. The blade 33 is for scraping off the toner attached to the fur brush 32 from the fur brush 32.

On the lower surface of the case 30, a cam 34 rotatable about the rotation center O3 is arranged. This cam 3
The transfer device 13 rotates in the X direction by rotating 4 around the center O3. The rotation position of this cam 34 is
Determined according to the paper thickness. In addition, each center O1,
O2 and O3 are parallel to each other. This copying machine has a control unit 40 as shown in FIG. The control unit 40 is C
It includes a microcomputer including PU, ROM, RAM and the like. The control unit 40 includes various switches and LEDs
An operation panel 41 including a display unit is connected. Further, the control unit 40 includes a bias power source 43, each unit of the image forming unit 15 excluding the transfer device 13, a motor 36 for rotationally driving the transfer roller 31, each unit of the paper transport path 17, each unit of the paper discharge transport path 18, 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.

Next, the operation of the above embodiment will be described based on the control flow chart shown in FIG. Operation panel 41
When the copy operation is started by pressing the print button in the inside, in step S1, the primary paper feed for feeding the paper through the paper feed path 17 from the selected paper feed cassette to the registration roller 21 is performed. Be seen. In step S2, it is determined whether or not a jam (paper jam) has occurred in the primary paper feed. This determination can be 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 document placed on the document 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 by toner by the developing device 12 after the unnecessary portion is removed by the blank lamp 11.

After the image formation, in step S4, the registration roller 21 is driven at the timing of aligning the leading edge of the image with the leading edge of the sheet, and the secondary sheet feeding for transferring and discharging is executed. In step S5, a bias voltage is applied to the transfer roller 31 by the bias power supply 43 to start transfer. At this time, the torque limiter 35 operates while the transfer roller 31 and the photosensitive drum 9 are in direct contact with each other without the intervening paper, and the transfer roller 31 and the photosensitive drum 9 move together regardless of the rotation of the motor 36. Turn around. Further, when the paper is interposed between the photoconductor drum 9 and the transfer roller 31, the frictional force is reduced, so the transfer roller 31 is rotationally driven faster than the peripheral speed of the photoconductor drum 9 by the rotational driving force of the motor 36. Make sure the paper is separated.

In step S6, 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 S7. In step S7, the application of the bias voltage is finished and the transfer is finished. In step S8, it is determined whether or not a jam has occurred in the secondary sheet feeding. If no jam has occurred, the process proceeds to step S9. In step S9, the paper discharge conveyance path 18, the fixing device 19, and the discharge roller 20.
To discharge the paper to the outside.

On the other hand, if it is determined in step S2 or S8 that a jam has occurred, the process proceeds to step S10. In step S10, each part is stopped. At step S11, the jam display LED in the operation panel 41 is turned on,
Notify the operator that a jam has occurred. When the process in step S9 or S11 ends, the process proceeds to the next process.

As described above, in the first embodiment, the rotational drive force of the motor 36 is turned on and off by the torque limiter 35. Thus, at the time of transfer, the peripheral speed of the transfer roller 31 can be made faster than the peripheral speed of the photosensitive drum 9 to ensure the separation of the paper. At other times, since the transfer roller 31 rotates together with the photosensitive drum 9, it is possible to prevent the surface of the photosensitive drum 9 from being damaged by the transfer roller slipping on the photosensitive drum 9. Second Embodiment In the first embodiment, the rotational driving force of the motor 36 is connected / disconnected by the torque limiter 35, but in the second embodiment, it is connected / disconnected by the electromagnetic clutch 37.

As shown in FIG. 6, an electromagnetic clutch 37 is attached to one end of the rotary shaft of the transfer roller 31. The electromagnetic clutch 37 is for transmitting the rotational driving force of the motor 36 to the transfer roller 31. The electromagnetic clutch 37 is turned on at the time of transfer to transmit the rotational driving force of the motor 36 to the transfer roller 31, and the electromagnetic clutch 37 is turned off at the time other than the time of transfer, and the rotational driving force of the motor 36 is not transmitted to the transfer roller 31. ..

As in the first embodiment, the motor 36 drives the transfer roller 31 so that the peripheral speed of the transfer roller 31 is faster than the peripheral speed of the photosensitive drum 9. The copying machine of the second embodiment is
It has a control unit 40a as shown in FIG. Control unit 4
A clutch 37 is connected to 0a in addition to the same parts as in FIG. The controller 40a outputs a command for turning on the clutch 37 during transfer, and outputs a command for turning off the clutch 37 during non-transfer. Other configurations are similar to those of the first embodiment, and the description thereof will be omitted.

Next, the operation of the second embodiment will be described. Example 2
In the copying machine, the steps S21 to S25 in FIG.
Then, the same operation as steps S1 to S5 of FIG. 5 is performed. In step S26, a command for turning on the clutch 37 is output. Further, in steps S27 and S28, step S
6, the same operation as S7 is performed, and the command to turn off the clutch 37 is output in step S29. Thereafter, step S30
The operations of to S33 are the same as the operations of steps S8 to S11 of FIG.

As described above, in the second embodiment, the clutch 37
By turning on and off, the rotational driving force of the motor 36 is turned on and off. That is, at the time of transfer, the clutch 37 is turned on and the rotational driving force of the motor 36 is transmitted to the transfer roller 31. As a result, the peripheral speed of the transfer roller 31 is made faster than the peripheral speed of the photosensitive drum 9, and the separation of the paper is ensured. On the other hand, at times other than the transfer, the rotational driving force of the motor 36 is not transmitted to the transfer roller 31 and the transfer roller 31 is rotated around the photosensitive drum 9 so that the surface of the photosensitive drum 9 is not damaged. Third Embodiment In the first and second embodiments, the torque limiter 35 and the clutch 37 are used to connect and disconnect the rotational driving force of the motor 36. In the third embodiment, as shown in FIG. 9, a stepping motor is used as the motor 36, and the rotation speed of the motor 36 is switched between high speed and low speed in two stages. Here, at the time of high speed rotation, the peripheral speed of the transfer roller 31 is made faster than the peripheral speed of the photosensitive drum 9,
When rotating at low speed, the peripheral speed is the same. A coupling 38 is attached to one end of the rotation shaft of the transfer roller 31. The output shaft of the motor 36 is attached to the coupling 38. That is, the transfer roller 31 is the motor 3
Directly connected to 6. Other configurations are the same as those in the first and second embodiments, and the description thereof will be omitted.

Next, the operation of the third embodiment will be described. In the third embodiment, as shown in FIG. 10, the same operation as the operation shown in the second embodiment (FIG. 8) is performed. However, the motor 46 is switched from low speed to high speed in step S46, and the motor 36 is switched from high speed to low speed in step S49. That is, at the time of transfer, the peripheral speed of the transfer roller 31 is made higher than the peripheral speed of the photosensitive drum 9, and at the time other than the transfer, the peripheral speed is made the same. As a result, the same effects as those of the first and second embodiments can be obtained. Other Embodiments (a) In the above embodiments, the present invention is applied to a copying machine, but the present invention can also be applied to other image forming apparatuses such as laser printers. (B) In the above-mentioned embodiment, the case of transfer 5 _d from the photosensitive drum has been described as an example, but the present invention can be applied to the case of transferring from a transfer drum or transfer belt used for color copying or the like to a sheet.

[0027]

In the image transfer device according to the present invention, the coefficient of friction of the transfer roller with respect to the transfer sheet is smaller than the coefficient of friction of the image carrier with respect to the transfer sheet, and it is adjusted according to the peripheral speed transfer timing of the transfer roller. Since the peripheral speed of the image carrier is higher than that of the image carrier, damage to the image carrier during separation of the image carrier and the transfer sheet and pressure contact between the image carrier and the transfer roller is improved.

[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 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.

FIG. 6 is a diagram corresponding to FIG. 3 of the second embodiment.

FIG. 7 is a diagram corresponding to FIG. 2 of the third embodiment.

FIG. 8 is a diagram corresponding to FIG. 5 of the second embodiment.

FIG. 9 is a diagram corresponding to FIG. 3 of the third embodiment.

FIG. 10 is a diagram corresponding to FIG. 5 of the third embodiment.

[Explanation of Codes] 9 Photoreceptor Drum 13 Transfer Device 31 Transfer Roller 35 Torque Limiter 36 Motor 37 Clutch 40, 40a Control Unit

Claims (1)

[Claims] 1. An image transfer device for transferring an image carried on a rotating image carrier to a transfer sheet, wherein a friction coefficient of the image carrier with respect to the transfer sheet is higher than a friction coefficient of the image carrier with respect to the transfer sheet. A transfer roller that is small and is in pressure contact with the image carrier, and a drive unit that drives the transfer roller so that the peripheral speed of the transfer roller becomes faster than the peripheral speed of the image carrier at the timing of transfer. Image transfer device equipped.