JPH07234593A - Transfer device - Google Patents

Abstract

PURPOSE:To resolve defective transfer by providing a charge removing member kept in conducting contact with a transfer sheet on a transfer belt upstream the transfer position of an image carrier in the conveying direction of the trans fer sheet. CONSTITUTION:A charge removing member 7 has a function as a guide member for guiding a transfer material to a transfer section in addition to a function as a member for controlling the current value. The tip of a transfer material delivered from a resist roller 9 is sent between a conducting brush 7B and a transfer belt 2 along the curved plate (main body) of the charge removing member 7. The transfer material is stuck to the transfer belt 2 while charges are removed by the conducting brush 7B. The charges of the transfer material are removed immediately before the transfer position (the position having the shortest distance between a photoreceptor 1 and the transfer belt 2). The charges of the toner on the photoreceptor 1 are not neutralized by an electric discharge before the transfer, and no defective transfer occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device mainly composed of a transfer belt for transferring a toner image on an image carrier onto a transfer material in image formation. This type of transfer device is used, for example, in a copying machine and a printer.

[0002]

2. Description of the Related Art One of the transfer devices of this type has been proposed by the present applicant in Japanese Patent Application No. 3-278187. This transfer device is provided downstream of a position (transfer position) where the transfer belt comes into contact with a photoconductor, which is an image carrier, in order to compensate for variations in transfer characteristics due to temperature, humidity, time-series characteristic changes of the transfer belt, and the like. A transfer voltage is applied to the transfer belt, the transfer belt is discharged further downstream, and a current I ₁ flowing in the transfer voltage application path is applied.
And controls the amount of current flowing in the photoreceptor from difference or the transfer belt charge eliminating current I ₂ constant.

[0003]

It has been found that the above-mentioned prior art has the following problems: (1) Since the electric potential of the transfer belt is high at a position upstream of the transfer position, discharge before transfer occurs. The toner charge on the photoconductor may be neutralized and transfer failure may occur. (2) Since the charge removing member is in contact with the inside of the transfer belt,
For example, if the transfer material (recording paper) has a large electrical resistance,
Since the current easily flows to the charge eliminating member and the charge eliminating current I ₂ tends to increase, which reduces the current value flowing through the photoconductor, the current I ₁ in the transfer voltage applying path must be increased to compensate for this. I have to. This requires a large capacity power supply. Since the electrical resistance of the transfer material changes depending on the water content and the thickness, it is necessary to prepare a large-capacity power source corresponding to the highest expected resistance value.

An object of the present invention is to improve the above problems (1) and (2).

[0005]

SUMMARY OF THE INVENTION The present invention has a transfer belt having a predetermined resistance value and a voltage application means for applying a transfer voltage to the transfer belt, and electrostatically attracts a transfer material to a toner on an image carrier. In a transfer device that transfers an image to a transfer material and conveys the transfer material, a destaticizing member that is in conductive contact with the transfer material on the transfer belt is provided upstream of the transfer position of the image carrier with respect to the transfer direction of the transfer material. Characterize.

[0006]

Since the transfer material moving toward the transfer position is discharged by the discharging member, the toner charge on the photoconductor is not neutralized by the discharge before the transfer, and the transfer failure is eliminated. That is, the problem (1) is solved. Further, since the discharging current I ₂ flows through the transfer material, its value is limited to a small value, and it becomes unnecessary to increase the current I ₁ of the transfer voltage applying path. That is, the problem (2) is solved.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0008]

FIG. 1 shows an embodiment of the present invention. In the figure, an image forming unit (charging device, image exposing device and developing device) (not shown) is provided on the photosensitive drum 1 which is an image carrier.
A toner image is formed on the sheet, and is transferred onto the transfer material (recording paper) fed from right to left in FIG. 1 by the transfer belt 2. The transfer material onto which the toner image has been transferred is sent to a fixing device (not shown) and undergoes fixing processing. The surface of the photoconductor dry 1 that has completed the transfer is cleaned and neutralized by the static eliminator and the cleaning device.

The transfer belt 2 is stretched around a driving roller 3 and a driven roller 4 with an appropriate tension. A transfer current controller 5 is supplied with a transfer voltage of a set level from a transfer bias power supply device (not shown), and has a transfer current control function described later. The transfer voltage is applied to the transfer belt 2 via the roller 6. The roller 6 rotates together with the rotation of the transfer belt 2. Reference numeral 7 denotes a charge removing member for removing charge from the transfer belt 2, and the tip contacting the transfer belt 2 is constituted by a conductive bristle brush 7B in this embodiment. The main body of the charge removing member 7 is a curved plate so that the front end of the transfer material fed by the registration roller 9 faces the upper surface of the transfer belt 2.

Reference numeral 8 denotes a cleaning blade for abutting and scraping off the waste toner on the transfer belt 2, which guides the scraped toner to a recovery tank portion (not shown). The drive roller 3 is driven at the same linear velocity as the photoconductor 1 from a drive source (not shown) (the material is rubber such as EPDM so as not to slip). The driven roller 4 is a metal such as stainless steel, and is electrically floated (equipment
Insulation state (without insulation).

A toner 9 has a transfer material (starting end) fed from a sheet feeding device (not shown) formed on the photoreceptor 1.
A pair of registration rollers for sending the image to the transfer position at a timing so as to be superposed on the image (the starting end of the image for one sheet). Reference numeral 10 is a lower guide member for guiding the transfer material.

The operation of the above configuration will be described.
Electric charges having a polarity opposite to that of the toner on the photoconductor drum 1 are applied to the transfer belt 2 to perform transfer. In this embodiment, (+) charged toner is attached to the photosensitive drum 1 whose surface is charged to -800 V, and the surface potential of the photosensitive drum is lowered by a pre-transfer charge eliminating lamp (not shown), and then applied to the applying roller 6. (-) A high voltage is applied to transfer the toner onto the transfer material. By applying a high voltage to the transfer belt 2, the transfer material is electrostatically adsorbed to the transfer belt 2 and is conveyed to the downstream side (drive roller 3 side) together with the transfer belt 2 and transferred at the position of the drive roller 3. The transfer material is automatically separated from the transfer belt 2 by the curvature separation of the material due to the waist of the material, and is fixed by a fixing device (not shown) and discharged to the outside of the device.

The transfer belt 2 has a surface of 1 × 10 ⁹ to
The resistance value is 1 × 10 ¹² Ω, and the inner surface is 1 × 10 ^{7 to} 5 × 1.
Among the 0 ⁸ Ω are using the things of the resistance value. The transfer of the toner image on the photoconductor 1 by the transfer belt 2 onto the transfer material is controlled as follows. That is, the transfer voltage output from the transfer power supply circuit (constant voltage output circuit) not shown is applied to the transfer current controller 5. The controller 5 applies a transfer voltage to the transfer belt 2 via the roller 6, and thereby the current value flowing from the roller 5 to the transfer belt 2 is set to I ₁ and the charge is removed via the transfer belt 2. If the current returning from the member 7 is I ₂ , I ₁ −I ₂ = Iout, Iou
The value of the output current value I ₁ is controlled so that t = IoutT (command value). By electrically floating the transfer belt 2 and all the members in contact with the transfer belt 2, Iout becomes a current value flowing to the photoconductor drum 1 side by the transfer.

The current I ₁ is detected by the current sensor 51 and the current I ₂ is detected by the current sensor 52, and the difference between the current values I ₁ -I ₂ = Iout
The operational amplifier 53 calculates (transfer current flowing through the photoconductor 1). The operational amplifier 54 causes the transfer current I flowing to the photosensitive member 1 to flow.
Deviation (error amount) of out from command value IoutT IoutT
-Iout is calculated and given to the current controller 55. The current controller 55 has a current value I such that I ₁ = I ₁ T + Iout T−Iout.
_The current flowing to the roller 6 is controlled to 1. This allows
A current I ₁ having a level around the command value I ₁ T and at which I ₁ -I ₂ = Iout becomes the command value Iout T flows from the transfer current controller 5 to the transfer belt 2 via the roller 6.

The discharging member 7 has a function as a guide member for guiding the transfer material to the transfer portion, in addition to the function as a member for controlling the current value as described above. That is, the leading end of the transfer material sent out from the registration roller 9 is sent between the conductive brush 7B and the transfer belt 2 along the curved plate (main body) of the charge removing member 7, where the charge is removed by the conductive brush 7B. Adsorb to the transfer belt 2. Therefore, the transfer material is discharged immediately before the transfer position (the position where the distance between the photoconductor 1 and the transfer belt 2 is the shortest), so that the electric charge of the toner on the photoconductor 1 may be neutralized by the discharge before the transfer. No transfer failure occurs.

There is a charge eliminating member on the opposite side of the roller 6 with respect to the transfer position, and the current flowing from the roller 6 to the transfer belt 2 first flows to the photoconductor 1. Therefore, the charge eliminating member 7 also passes through the transfer material. Since the charge is removed by the conductive brush 7B at the tip of the lever, the current I ₂ flowing through the charge removing member 7 is relatively small. Therefore, the static elimination current I ₂ does not significantly decrease Iout,
The power capacity of the transfer power circuit may be relatively small.

Since the discharging member 7 also serves as the transfer material guide plate, the above-described effect of preventing transfer failure can be obtained without increasing the number of parts.

A current I flowing from the roller 6 to the transfer belt 2
₁And the current I flowing through the static elimination member 7₂Controls the difference Iout of
Iout due to uneven resistance of the transfer belt 2
It is possible to always perform good transfer without fluctuation.
It In addition, the transfer characteristic is set to the command value I ₁Of T and / or IoutT
It can be adjusted properly by adjustment.

[0019]

EFFECTS OF THE INVENTION Since the transfer material toward the transfer position is discharged by the discharging member, the toner charge on the photoconductor is not neutralized by the discharge before the transfer, and the transfer failure is eliminated.
Further, since the discharging current flows through the transfer material, its value is limited to a small value, and it becomes unnecessary to increase the current capacity of the transfer voltage applying path.

[Brief description of drawings]

FIG. 1 is a drawing showing a main part of an embodiment of the present invention, part of which shows a longitudinal section of a mechanical element, and part of which shows an electric circuit.

[Explanation of symbols]

 1: Photosensitive drum 2: Transfer belt 3: Driving roller 4: Followed roller 5: Transfer current controller 6: Roller 7: Eliminating member 7B: Conductive brush 8: Cleaning blade 9: Registration roller 10: Lower guide member

Claims (3)

[Claims] 1. A transfer belt having a predetermined resistance value and a voltage applying means for applying a transfer voltage to the transfer belt. The transfer material is electrostatically attracted to transfer the toner image on the image carrier to the transfer material. A transfer device for transporting a material, comprising: a discharging member, which is in conductive contact with the transfer material on the transfer belt, upstream of the transfer position of the image carrier in the transport direction of the transfer material. 2. The transfer device according to claim 1, wherein the charge removing member includes a guide portion for guiding the transfer material on the upstream side to a transfer position where the transfer belt and the image carrier are in contact with each other. 3. The transfer device according to claim 1, wherein the voltage applying means includes means for controlling a difference between a current I ₁ supplied to the transfer belt and a current I ₂ flowing through the charge removing member to be constant.