JPH09114274A - Transferring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove toner stuck on a transfer roller to the minimum, while preventing the extension of non-transferring time and generation of the toner cloud. SOLUTION: This device is, a transferring device capable of making a sheet allowed to pass through a nip which is a transferring area between a photoreceptor drum and the transfer roller, to apply bias voltage having the polarity opposite to that of the toner image on the photoreceptor drum, onto the transferring roller, during the passing of the sheet, and to transfer the toner image onto the sheet thereby. At this time, in performing one cycle transferring for consecutively transferring a specific number of sheets, the device is composed so that the bias voltage is applied on the transfer roller even at the non- transferring time occurring between sheets, that the polarity of applying bias voltage is alternately switched for each transferring, and so that the toner having either polarity is alternately shifted onto the photoreceptor drum at the each non-transferring time.

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 utilizing an electrophotographic process such as a copying machine and a printer, which transfers a toner image formed on the surface of an image carrier to a sheet which is a recording medium. Regarding

[0002]

2. Description of the Related Art The above-mentioned transfer device conveys a sheet at a nip, which is a transfer area formed between a photosensitive drum, which is an image carrier, and a conductive transfer roller. In general, a transfer voltage is applied to a transfer roller to give a transfer charge, and the toner image developed on the photosensitive drum is transferred onto a sheet. However, since the transfer roller is constantly in pressure contact with the photoconductor, there is a problem that the fog toner of the photoconductor is adsorbed and stained, and the stain on the transfer roller adheres to the sheet back surface or the sheet end surface.

As a technique for solving this problem, a method of removing the toner adhering to the transfer roller by returning it to the photosensitive drum is described in JP-A-63-286878. As shown in FIG. 4A, when performing one-cycle transfer in which a plurality of sheets are transferred while being continuously fed, the same polarity as the toner, that is, ( -) Apply a bias voltage of polarity to the transfer roller. As a result, the (-) toner attached to the transfer roller is returned to the photosensitive drum, and the transfer roller is cleaned. However, some of the toner remaining on the surface of the photoconductor drum has a (+) polarity, but toner of the opposite polarity may adhere to the surface of the transfer roller during non-transfer. When the bipolar toner adheres to the transfer roller in this manner, all the toner cannot be returned from the transfer roller to the photosensitive drum in the method described in the above publication, and the removal effect is insufficient. .

In view of this, in Japanese Patent Application Laid-Open No. 3-69978, as shown in FIG. 4B, a bipolar bias voltage is alternately applied at the time of non-transfer, whereby bipolar toner is applied to the photosensitive drum. The method of returning to is proposed.

[0005]

However, in the method described in the latter publication, a bias voltage of both polarities is applied to the transfer roller during non-transfer, so the non-transfer time inevitably becomes long, and As a result, there is a drawback that the total time for one-cycle transfer becomes long and the productivity becomes poor. Further, when the toner is retransferred from the transfer roller to the photosensitive drum, the toner is scattered and a so-called toner cloud is generated, which inevitably pollutes the inside of the apparatus. In the method described in any of the above publications,
Since the polarity of the bias voltage is switched every time one sheet is transferred, there remains a problem that the degree of occurrence of toner cloud increases.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a transfer device capable of effectively removing toner from a transfer roller while suppressing the extension of the non-transfer time and the generation of a toner cloud. .

[0007]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and is an image carrier for developing a toner image on an electrostatic latent image formed on the surface thereof, and the image carrier. A transfer member that is disposed facing the body and forms a transfer area between the image carrier and a transfer member, and allows a sheet to pass through the transfer area; and while the sheet is passing, a bias voltage having a polarity opposite to that of the toner image is applied to the transfer member. In a transfer device that transfers the toner image onto a sheet by applying the toner, a predetermined number of sheets are passed through the transfer area one by one to perform one-cycle transfer in which transfer and non-transfer are alternately repeated. A feature is that a bias voltage is applied to the transfer member even during non-transfer, and the polarity of the applied bias voltage is alternately switched every transfer.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. A. Configuration of One Embodiment FIG. 1 shows the whole of an electrophotographic copying machine which is an image forming apparatus in which a transfer device of one embodiment of the present invention is incorporated. The copying machine 1 has a photosensitive drum 2 as an image carrier as a center, and a charging device 3, a latent image forming device 4, a developing device 5, a paper feeding device 6, a transfer device 7, and a fixing device 8 around the photosensitive drum 2. The cleaning device 9 is arranged in a clockwise direction in FIG. Of these devices, the charging device 3, the developing device 5, and the cleaning device 9 are housed in the casing 10 together with the photosensitive drum 2.

The photosensitive drum 2 is rotated in the direction of arrow A by a drive source such as an electric motor (not shown). The charging device 3 is composed of a corotron or the like, and the surface of the photosensitive drum 2 is charged to a normal (-) polarity by the charging device 3 first, and then the latent image forming device 4 charges the electrostatic latent area in the charging area. An image is formed. The latent image forming device 4 includes a polygon mirror 11, a lens 12, and a reflection mirror 13, converts an input image signal into laser light, and the laser light is reflected by the polygon mirror 11 and the lens 12.
Then, the surface of the photosensitive drum 2 is exposed by being reflected by the reflection mirror 13. As a result, an electrostatic latent image corresponding to the image signal is formed on the surface of the photosensitive drum 2.

The developing device 5 includes a developing roller 14 and a toner tank 15 in which the toner T is stored. The toner tank 15 constitutes a part of the casing 10. By the developing device 5, the toner T attached to the peripheral surface of the developing roller 14 is developed on the surface of the photosensitive drum 2 to form a toner image. This toner image is transferred by the transfer device 7 onto the surface of the sheet S fed from the paper feeding device 6.

The sheet feeding device 6 has a cassette (not shown) for stacking and accommodating a large number of sheets S, a sheet feeding roller 16, and a registration roller 17. The sheet S is transferred from the cassette to the sheet feeding roller 16 by the sheet feeding device 6.
After being pulled out one by one, the leading ends are aligned by the registration roller 17 and then sent to the transfer device 7.

The transfer device 7 is provided with a conductive transfer roller 19 which is disposed so as to face the photoconductor drum 2 and forms a nip 18 which is a transfer area between the photoconductor drum 2 and the transfer roller 19. It has the electric power feeding means 20 which charges an electric charge. By the transfer device 7, the photosensitive drum 2 is attached to the surface of the sheet S sent from the paper feeding device 6 to the nip 18.
The toner image formed on the surface of is transferred.

The sheet S on which the toner image is transferred by the transfer device 7 reaches the fixing device 8 via the conveyance guide 21. The fixing device 8 is composed of a combination of a heating roller 22 and a pressure roller 23.
While passing through the space 3, pressure is applied while being heated, whereby the toner image is fixed on the surface of the sheet S. With this, the printing on the sheet S is completed, and the sheet S is ejected.

The cleaning device 9 is composed of a cleaning blade or the like, and scrapes off the toner remaining on the surface of the photosensitive drum 2 and drops it into the toner recovery tank 24. The tank 24 constitutes a part of the casing 10.

The above is the schematic configuration and operation of the copying machine 1. Next, the transfer device 7 according to the present invention will be described in detail. FIG. 2 shows the configuration of the transfer device 7. As described above, the transfer device 7 has the conductive transfer roller 19 arranged so as to face the photoconductor drum 2 and the power feeding means 20 for supplying the transfer voltage to the transfer roller 19, and further, the number of copies. ,
A controller 32 is provided which controls the output timing and the polarity of the bias voltage applied to the transfer roller 19 in response to conditions such as the gap between sheets.

The power supply means 20 applies a bias voltage having a reverse polarity (+) polarity to the toner image on the photosensitive drum 2 to the transfer roller 19 during transfer. While the sheet S is nipped and conveyed between the transfer roller 19 to which the bias voltage is applied from the power feeding means 20 and the photoconductor drum 2, that is, while the sheet S is being conveyed by the nip 18, the toner image on the photoconductor drum 2 is transferred to the sheet S. It is designed to be transferred to.

The controller 32 operates in one-cycle transfer for continuously copying a plurality of sheets S,
The polarity of the bias voltage applied to the transfer roller 19 is shown in FIG.
As shown in, the basic control is to switch every transfer. In addition to this basic control, the following functions OP
1 and OP2 are added. OP1-Bias voltage of both polarities is alternately applied to the transfer roller 19 during the non-transfer period between the sheet S and the sheet S, that is, when the non-transfer period is longer than a certain time. When the number of sheets S in the OP2-1 cycle transfer is a certain number or more, the polarity of the bias voltage applied to the transfer roller 19 at the time of non-transfer is constant, and when the number of sheets is more than the certain number, each transfer is performed. Invert alternately.

B. Operation and Effect of One Embodiment According to the transfer device 7 having the above-described configuration, the sheet S moves to the nip
Before reaching, the transfer output is first applied with the (-) polarity, and after a certain period of time, switched to the (+) polarity, and after a certain period of time, the sheet S reaches the nip 18 and starts the transfer operation. .

Here, for example, when one-cycle copying is performed in which five sheets S are continuously fed and copied, the polarity of the bias voltage applied to the transfer roller 19 at the time of non-transfer is switched every transfer. To be That is, as shown in FIG. 3, a negative polarity (−) opposite to the transfer polarity is applied between the first sheet and the second sheet, and a negative polarity (−) is applied between the second sheet and the third sheet. The (+) polarity is continuously applied, the (−) polarity is applied by switching between the third and fourth sheets, and the same (+) polarity as that at the time of transfer is again applied between the fourth and fifth sheets. To be done.

When the (-) polarity opposite to the transfer voltage is applied during non-transfer, the toner T having the (-) polarity attached to the surface of the transfer roller 19 is transferred to the photosensitive drum 2. When a voltage having the same (+) polarity as the transfer voltage is applied, the toner T having the (+) polarity is transferred to the transfer roller 1 this time.
9 surface. In this way, the polarity of the bias voltage applied to the transfer roller 19 at the time of non-transfer is alternately switched, so that a plurality of sheets S are transferred during transfer.
The toner T having both polarities is alternately returned to the surface of the photoconductor drum 2 every time the toner T is not transferred. As a result, the bipolar toner T adhering to the surface of the transfer roller 19 is removed, and the occurrence of the problem of the toner T adhering to the back surface of the sheet S is suppressed as much as possible.

Further, the bias voltage applied to the transfer roller 19 at the time of non-transfer is either (+) or (-), not bipolar, so that the non-transfer time does not become long. For this reason, the extension of the time required for one-cycle copying is suppressed, thereby improving the productivity. In addition, since the polarity is switched once every two times of non-transfer, the number of times the toner T is transferred is reduced, and as a result, contamination inside the machine due to the toner cloud is suppressed.

Next, OP1 and OP2 will be described. OP1 is operated when the non-transfer time is relatively long such that a bipolar bias voltage can be applied to the transfer roller 19. For example, if the interval between transfers is relatively long during double-sided copying,
As shown in FIG. 4B, bipolar bias voltages are applied to the transfer roller 19. Therefore, the toner T having both polarities is transferred to the photoconductor drum 2 during one non-transfer, and the toner removing effect is improved. Since non-transfer is set to be long in advance, even if a bipolar bias voltage is applied during non-transfer, the application does not extend the non-transfer time.

In OP2, for example, 1 cycle copying is 2 to 2.
When the number of times of non-transfer is small with about 3 sheets, the polarity is not changed. For this reason, the toner on the transfer roller 19 is not removed between transfers, but since the number of transferred sheets is small, the amount of toner T adhered to the back surface of the sheet S is small, and immediately before the copy operation (cycle-in) and the end of the copy operation. A sufficient toner removing effect can be obtained only by switching the polarity at the time of (cycle out). Further, since there is no polarity switching between transfers, there is an advantage that the generation of a toner cloud can be prevented. When the number of sheets S to be copied exceeds a certain number, the above-mentioned basic control, that is, the switching of the polarity is performed for each transfer.

The present invention is not limited to the above-described embodiment, but can be applied to other image forming apparatuses using an electrophotographic process such as a printer and a facsimile.

[0025]

As described above, according to the first aspect of the present invention,
According to the invention described in (4), when continuously transferring a plurality of sheets, the polarity of the bias voltage applied to the transfer roller at the time of non-transfer is switched alternately. The occurrence of the problem that the toner is removed and the toner adheres to the back surface of the sheet is suppressed as much as possible. Further, since the bias voltage applied to the transfer member at the time of non-transfer is either (+) or (-), not bipolar, the non-transfer time is not extended and the time required for one cycle transfer is suppressed. As a result, productivity is improved. Furthermore, since the polarity of the bias voltage is switched once every two times of non-transfer, contamination inside the machine due to the toner cloud is suppressed. According to the second aspect of the present invention, when the non-transfer time is relatively long in advance, the bias voltage of both polarities is applied during the non-transfer time, so that the effect of removing the toner adhering to the transfer member is improved. improves. According to the third aspect of the present invention, since the polarity of the bias voltage applied to the transfer member is constant when the number of sheets in one-cycle transfer is equal to or less than a certain number, a useless toner cloud is formed. Occurrence is suppressed. According to the fourth aspect of the present invention, the number of sheets in one cycle transfer is equal to or less than a predetermined number. In addition, when the non-transfer time is longer than a fixed time, the polarity of the bias voltage is switched at each non-transfer time, so that the toner adhering to the transfer member is removed while suppressing the extension of the time required for one-cycle transfer.

[Brief description of the drawings]

FIG. 1 is an overall side view of a copying machine in which a transfer device according to an embodiment of the present invention is incorporated.

FIG. 2 is a side view of the transfer device according to the embodiment.

FIG. 3 is a time chart showing a polarity switching pattern of a bias voltage applied to a transfer roller.

4A is a time chart showing a conventional example of a polarity switching pattern, and FIG. 4B is a time chart showing another conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Copier (image forming apparatus), 2 ... Photosensitive drum (image carrier), 7 ... Transfer device, 18 ... Nip (transfer area), 1
9 ... Transfer roller, S ... Sheet.

Claims (4)

[Claims] 1. An image carrier on which a toner image is developed on an electrostatic latent image formed on a surface thereof, and a transfer member which is arranged so as to face the image carrier and forms a transfer area between the image carrier and the image carrier. A transfer device that transfers the toner image onto the sheet by applying a bias voltage having a polarity opposite to that of the toner image to the transfer member while the sheet is passing through the transfer area. When performing one-cycle transfer in which a number of the sheets are passed through the transfer area one by one and the transfer and the non-transfer are alternately repeated, a bias voltage is applied to the transfer member even in the non-transfer, A transfer device characterized in that the polarity of the applied bias voltage is alternately switched every transfer. 2. The transfer device according to claim 1, wherein when the non-transfer time is longer than a certain time, a bipolar bias voltage is switched and applied to the transfer member every non-transfer time. 3. When the number of sheets in the one-cycle transfer is less than a certain number, the polarity of the bias voltage applied to the transfer member during the non-transfer is constant, and when the number of sheets is more than the certain number, each transfer is performed. 2. The transfer device according to claim 1, wherein the transfer device is alternately reversed. 4. When the number of sheets in the one-cycle transfer is less than a certain number and the non-transfer time is longer than a certain time, a bipolar bias voltage is switched and applied to the transfer member every non-transfer time. Claim 1 characterized by the above.
The transfer device described.