JPH05107938A - Transferring and separating device - Google Patents

Abstract

PURPOSE:To reduce faulty separation between a photosensitive drum and a paper while keeping transferring efficiency. CONSTITUTION:The transferring and separating device 13 transfers an image carried on the photosensitive drum 9 on the paper, separates the paper from the photosensitive drum 9 after transferring, and is provided with a transferring roller 31, a DC power source 39, an AC power source 38, and a controlling part. The transferring roller 31 press-contacts to the photosensitive body 9. The DC power source 38 impresses a DC voltage on the transferring roller 31. The AC power source 38 impresses an AC voltage on the transferring roller 31. The controlling part controls the AC power source 38 and the DC power source 39 in a state where the AC voltage is impressed for a specified time after the paper is inserted in a press-contacting position, and then the DC voltage is impressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a transfer / separation device, and more particularly,
The present invention relates to a transfer separation device that transfers toner carried by regular development on an image carrier to a transfer sheet and separates the transfer sheet from the image carrier after transfer.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine uses a transfer / separation device for transferring a toner image formed on a photosensitive drum, which is an image carrier, onto a sheet, which is a transfer sheet. There is. In this type of transfer separation device, conventionally,
A transfer charger and a separation charger are used that apply a charge having an opposite polarity to the toner and an AC voltage to the paper by corona discharge. However, when corona discharge is used, ozone is generated, which adversely affects the environment.

Therefore, there is already known a transfer separation device using a transfer roller and a discharging means instead of corona discharge (for example, Japanese Patent Laid-Open No. 1-2696969). In this apparatus, a DC bias voltage having a polarity opposite to that of the toner charge on the photosensitive drum is applied to the transfer roller. Further, a charge eliminating needle is provided in the vicinity of the downstream side of the transfer roller to eliminate charge from the paper. In this apparatus, a reversal developing method is adopted in which an electric field is formed by a developing electrode at a location where the charge on the photoconductor drum is released, and toner is attached thereto. There, a sheet of paper supplied between the photosensitive drum and the transfer roller is pressed by the transfer roller against the sheet of the photosensitive drum and a DC bias voltage having a polarity opposite to that of the toner applied to the transfer roller is applied. The toner image on the photosensitive drum is transferred. Further, the sheet is neutralized by the static elimination needle.

In the reversal developing method, since the adhesion of toner to the photosensitive drum is weak, it is possible to transfer with a low bias voltage. Further, for the same reason, the suction force between the paper and the photoconductor drum is weak, and the paper can be easily separated from the photoconductor drum simply by neutralizing the paper with the neutralizing needle. However, this configuration is difficult to be adopted in the regular developing method in which toner is attached to the photosensitive drum where electric charges exist. This is for the following reason.

In the regular developing method, toner having a charge having a polarity opposite to that of the latent image charge is electrostatically adhered to the photosensitive drum. Therefore, unless the bias voltage is increased, the transfer efficiency is deteriorated and a predetermined image is formed. Unable to get density image. However, when the bias voltage is increased, the static elimination needle alone cannot sufficiently eliminate the static electricity on the sheet, resulting in poor sheet separation. In particular, when passing a sheet close to a blank sheet with a small amount of toner, the separation is extremely bad, which causes jam frequently.

An object of the present invention is to reduce the separation failure between the image carrier and the transfer sheet while maintaining the transfer efficiency.

[0007]

A transfer / separation device according to the present invention transfers an image carried on an image carrier to a transfer sheet and separates the transfer sheet from the image carrier after transfer. A roller, a DC supply means, an AC supply means, and a control means are provided. The transfer roller is in pressure contact with the image carrier. The DC supply means applies a DC voltage to the transfer roller. The AC supply means applies an AC voltage to the transfer roller. The control unit controls the AC supply unit and the DC supply unit so that the AC voltage is applied for a predetermined time after the transfer sheet is inserted in the pressure contact position and then the DC voltage is applied.

[0008]

In the transfer / separation device according to the present invention, when the transfer sheet is inserted into the pressure contact position between the image carrier and the transfer roller, a predetermined time (for example, a time during which the non-image forming portion at the leading end of the transfer sheet passes) is exchanged An AC voltage is applied to the transfer roller from the supply means, and then a DC voltage is applied from the DC supply means to perform the transfer operation.

Here, from the start of transfer to the actual transfer, the leading edge of the transfer sheet is neutralized by the AC voltage, and the leading edge of the transfer sheet is easily separated from the photosensitive drum. Therefore, the separation failure can be reduced while maintaining the transfer operation.

[0010]

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 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.

An exposure device 8 for reading a document is provided in the upper part of the inside of the copying machine main body 1. 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 a latent image with toner, and a transfer separation device 1 for transferring the toner image on the photosensitive drum 9 to a sheet and separating the sheet from the photosensitive drum 9.
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. Photoreceptor drum 9 in paper transport path 17
A registration roller 21 is provided on the upstream side of.
The registration roller 21 is for adjusting the timing of carrying out the paper between the photoconductor drum 9 and the transfer separation device 13. The paper discharge transport path 18 is mainly a transport conveyor 22.
Consists of. A fixing device 19 for fixing the transferred image on the discharged paper, and a paper for fixing the paper fixed by the fixing device 19 to the outside, on the downstream side (the left side in the drawing) of the paper discharge conveyance path 18. A discharge roller 20 is provided.

As shown in FIG. 2, the transfer separation device 13 is
A case 30 that rotates in the direction of arrow X around the rotation center O1
have. A transfer roller 31 is provided on the case 30.
Are rotatably supported about a rotation center O2. The transfer roller 31 is made of an elastic material such as urethane rubber having a non-resistance of 10 ⁷ Å · cm and a hardness of 17 ° (Shore A scale). The upper portion of the transfer roller 31 is in pressure contact with the lower surface of the photosensitive drum 9. The transfer roller 31 is connected to the bias power source 36. The bias power supply 36 includes an AC power supply 38 capable of applying an AC voltage and a DC power supply 39 capable of applying a DC voltage.
And a switch 37 for switching them, and can selectively output an AC voltage and a DC voltage.

Within the case 30, below the transfer roller 31, there is disposed a fur brush 32 which comes into pressure contact with the lower surface of the transfer roller 31. The fur brush 32 is rotationally driven by a drive mechanism (not shown), and the transfer roller 3
1 Clean the top. 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.

On the lower surface of the case 30, a cam 34 rotatable about the rotation center O3 is arranged. This cam 3
By rotating 4 around the center O3, the transfer separation device 13 rotates in the X direction. The rotation position of the cam 34 is determined according to the thickness of the paper. In addition, each center O
1, O2 and O3 are parallel to each other. This copying machine has a control unit 40 as shown in FIG. Control unit 40
Includes a microcomputer including a CPU, a ROM, a RAM and the like. An operation panel 41 arranged on the upper surface of the copying machine body 1 is connected to the control section 40. The operation panel 41 includes various switches and an LED display unit. Further, the control unit 40 includes a bias power supply 36, a motor 43 for rotating the transfer roller 31, and the sheet conveyance path 1.
7 and the jam detection unit 42 formed of a jam detection sensor provided in the discharge conveyance path 18 and other input / output units are connected.

Next, the operation of the above embodiment will be described based on the control flowchart shown in FIG. When the copy operation is started by pressing the print button in the operation panel 41, in step S1, the primary paper feed for feeding the paper from the selected paper feed cassette to the registration rollers 21 via the paper feed path 17 is performed. Done. 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 section 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 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,
The registration roller 21 is driven at the timing when the leading edge of the image is aligned with the leading edge of the sheet, and the secondary sheet feeding for transferring and discharging is performed. In step S5, the switch 37 of the bias power supply 36 is switched to the AC power supply 38 side, the AC power supply 38 is turned on, and an AC bias voltage is applied to the transfer roller 31. As a result, the paper is discharged, and the leading edge of the paper is separated from the photosensitive drum 9. In step S6, the elapse of a predetermined time is awaited. This time is 5mm from the leading edge of the paper.
It is set by the time until the non-image portion between the degrees passes the pressure contact position.

When a predetermined time has elapsed, the process proceeds to step S7. In step S7, the switch 37 is switched to the DC power supply 39 side, the DC power supply 39 is turned on, and the bias voltage is switched from AC to DC. As a result, transfer is started, and the toner attached to the photoconductor drum 9 is transferred to the paper.
In step S8, a predetermined time period 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 S9. In step S9, the DC power supply 39 is turned off, the application of the bias voltage is completed, and the transfer is completed. Step S10
Then, it is determined whether or not 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, the fixing device 19, 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. In step S13, 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 S11 or S13 ends, the process proceeds to the next process.

As described above, when the AC voltage is applied to the non-image portion of the leading edge of the sheet to remove the electric charge at that portion and the leading edge of the sheet is separated from the photosensitive drum 9, the sheet is once separated from the photosensitive drum 9. The paper is gradually separated from the photosensitive drum 9 without being adsorbed again. Therefore, separation can be performed smoothly. [Other Embodiments] (a) In the above embodiments, the case where the present invention is applied to a copying machine has been described as an example, but the present invention is also applicable to other image forming apparatuses such as a laser printer. (B) In the above embodiment, an example in which toner is transferred from a photosensitive drum has been shown, but the present invention can be applied to the case where toner is transferred from a transfer drum or transfer belt used in a color copying machine.

[0023]

In the transfer separation device according to the present invention, an alternating voltage is applied to the leading edge of the transfer sheet to promote separation, and a direct current voltage is applied after that, so that the leading edge of the transfer sheet can be reliably separated. It is possible to reduce improper separation while maintaining the transfer efficiency.

[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 separation device.

FIG. 3 is a block diagram showing the configuration of a control system.

FIG. 4 is a flowchart showing a control operation.

[Explanation of symbols]

 9 Photosensitive Drum 13 Transfer Separator 31 Transfer Roller 36 Bias Power Supply 37 Switch 38 AC Power Supply 39 DC Power Supply 40 Control Section

Claims (1)

[Claims] 1. A transfer separation device for transferring toner carried by regular development on an image carrier to a transfer sheet, and separating the transfer sheet from the image carrier after transfer, which is in pressure contact with the image carrier. A transfer roller, a direct current supply means for applying a direct current voltage to the transfer roller, an alternating current supply means for applying an alternating current voltage to the transfer roller, and the alternating voltage for a predetermined time after the transfer sheet is inserted into a press contact position. And a control unit for controlling the AC supply unit and the DC supply unit so as to apply the DC voltage thereafter.