JPH0822153A - Image forming device - Google Patents

Abstract

PURPOSE:To surely prevent the soiling of a transfer member and staining on the rear side of a transfer paper caused by a normally developed toner image, without using complex control at a low cost. CONSTITUTION:This image forming device having an electrifier 2 electrifying an image carrier 1, an exposing device forming an electrostatic latent image, an erasing lamp 3 erasing it, a developing device 4 for actualizing it and the transfer member 6 for transferring the actual image to the transfer paper is provided with a transfer paper detecting means 10 detecting the leading and tailing edges of the transfer paper before the transfer is performed and an image control means 12 calculating the length of the transfer paper from the result of the detection of the transfer paper detecting means 10 and executing control to form a nonimage region in the prescribed area of the tailing edge of the transfer paper in accordance with its length.

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 having a contact type transfer device which is used in a copying machine, a printer, a facsimile or the like and which transfers a transfer member by contacting it with an image carrier.

[0002]

2. Description of the Related Art Conventionally, as a method of a transfer device for transferring a toner image, which is a visualized electrostatic latent image formed on an image carrier, onto a transfer paper, a corona discharge is utilized to form an image on the image carrier. There is a corona discharge type transfer device of the type that causes the toner image to fly to the transfer paper, and a contact type transfer device of the type that contacts the image carrier and the transfer device to transfer the toner image to the transfer paper. Of this,
In the former corona discharge type transfer device, since the transfer device and the image carrier do not come into contact with each other, the toner image forming region of the image carrier need not be limited by the trailing edge of the transfer paper.

[0003]

However, in the image forming apparatus using the above-mentioned conventional contact type transfer apparatus,
Since the transfer member (transfer roller, transfer belt, etc.) is in contact with the image carrier, if there is a toner image in the part of the image carrier that corresponds to after the trailing edge of the transfer paper, it will directly contact the transfer member surface. When they come into contact with each other and stain the surface, they adhere to the back side of the next transfer sheet and cause back stain. In particular, when cleaning the surface of the transfer member by controlling the bias voltage, if the regular developing toner of the image carrier is applied to the surface of the transfer member by applying the transfer bias voltage, the cleaning becomes very difficult. Therefore, in JP-A-56-126876, as shown in FIG. 3, a contact / separation mechanism 7 including a solenoid 7a and an arm 7b for contacting and separating the transfer roller 6 with respect to the photosensitive drum 1 is provided. It is disclosed that the leading edge and the trailing edge of the transfer sheet are detected, and the transfer roller 6 is brought into contact with and separated from the transfer mechanism 6 by the contact / separation mechanism 7 according to the detection result to prevent the transfer sheet from being soiled. However, in this method, since the contacting / separating mechanism 7 must be separately provided, there is a problem that the cost becomes high.

Further, Japanese Patent Laid-Open No. 51-9840 discloses a method of applying a bias having a reverse polarity to that at the time of transfer when transfer paper does not exist in the transfer area of the image carrier. However, the control of the conveyance of the transfer paper is not 100% accurate, and if a deviation occurs in the conveyance, the toner image will squeeze out after the trailing edge of the transfer paper. However, there was a problem that the transfer paper is stained and the back surface of the transfer paper is stained. Therefore,
The present invention solves the above-mentioned conventional problems and can reliably prevent the transfer member from being smeared by the normally developed toner image and the backside of the transfer paper without using complicated control. An object is to provide an image forming apparatus having a low cost and a simple structure.

[0005]

According to a first aspect of the present invention, a charger for uniformly charging an image carrier, an exposure device for forming an electrostatic latent image on the image carrier, and an image carrier. An image forming apparatus including an erase lamp for erasing an electrostatic latent image formed on a body, a developing device for visualizing the electrostatic latent image, and a transfer member for transferring the visible image onto a transfer sheet. In, a transfer paper detection means for detecting the front end and the rear end of the transfer paper before transfer,
An image control unit that calculates the length of the transfer sheet from the detection result of the transfer sheet detection unit and controls so as to form a non-image area in a predetermined area at the trailing end of the transfer sheet according to the length of the transfer sheet. In addition, according to claims 2, 3, 4, and 5, the image control means includes a step of charging the charger, a step of erasing the latent image of the erase lamp, a step of developing the developing device, and the exposure device. 7. The non-image area is formed by controlling any one of the exposure steps of 1., and the image control means according to claim 6, wherein the image control means includes the charging step of the charger and the erase step. The non-image area is formed by controlling at least two of the latent image erasing process of the lamp, the developing process of the developing device, and the exposing process of the exposing device.

[0006]

Therefore, according to the first, second, third, fourth, and fifth aspects, the leading edge and the trailing edge of the transfer sheet before the transfer is detected by the transfer sheet detecting means, and the detection signal is input to the image control means. In the image control means, the length of the transfer paper is calculated from the detection result, and one of the image forming processes such as the charging process of the charger is controlled according to the length of the transfer paper, A non-image area is formed in a predetermined area at the rear end of the transfer paper. As a result, the regular developing toner does not come into direct contact with the transfer member and the backside of the transfer paper is prevented. Also,
In the present invention, the image control means controls at least two of the charging process of the charger, the latent image erasing process of the erase lamp, the developing process of the developing device, and the exposing process of the exposing device in combination, The non-image area is formed more accurately.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, in the vicinity of the periphery of the photosensitive drum 1,
Alternatively, the charger 2, the erase lamp 3, the developing device 4, the pre-transfer charge eliminating device 5, the transfer roller 6 serving as a transfer member, the cleaning device 8, the charge eliminating device 9 and the like are arranged in contact with each other. Further, on the transfer path of the transfer sheet P, the registration roller 11 is provided on the upstream side of the transfer roller 6, and the transfer sheet detection sensor 1 is a transfer sheet detection unit for detecting the transfer sheet P on the upstream side of the roller 11.
0 is arranged. The transfer paper detection sensor 10 is connected to a unit control circuit 12 which is an image control means. The transfer paper detection sensor 10 may be of a mechanical type or an optical type.

In this configuration, image information is formed as an electrostatic latent image on the photosensitive drum 1 by the exposure light 13 from an exposure device (not shown), and this electrostatic latent image is visualized on the photosensitive drum 1 by the developing device 4. To be imaged. On the other hand, the transfer paper P fed from a paper supply unit (not shown) has its leading edge and trailing edge detected by the transfer paper detection sensor 10, and is sent to the transfer roller 6 by the registration roller 11 at the same timing. After the toner image is transferred between the drum 1 and the transfer roller 6 by pressure contact, the toner image is fixed by a fixing device (not shown) and discharged.

Regarding the detection operation of the transfer paper detection sensor 10, when the front end of the transfer paper P is detected, the signal is input to the unit control circuit 12, and in the same circuit 12, the rear end detection signal of the transfer paper P is detected. The time until it is detected is counted, and the length of the transfer sheet P in the traveling direction is calculated with high accuracy from this value. Further, in the circuit 12, according to the calculation result, the charging process by the charger 2
The latent image erasing process by the erase lamp 3, the developing process by the developing device 4, and the exposing process by the exposing device are controlled by any one or a combination of at least two of them.
As shown in FIG. 2, an arbitrary area at the rear end of the transfer paper P is set to be the non-image area Ps.

That is, not only the Ps portion of the transfer paper P is set as the non-image area, but the portion on the photosensitive drum 1 corresponding to the portion after the Ps portion to the front of the image portion of the next transfer paper is not formed. An image area, that is, an area without a toner image. Therefore, the toner image on the photosensitive drum 1 does not directly contact the transfer roller 6. As described above, an arbitrary unit is controlled according to the length of the transfer paper P so that the normally developed toner image area of the photosensitive drum 1 does not protrude from the rear end of the transfer paper P.

[0011]

As described above, the first and second aspects of the present invention are as follows.
According to Nos. 3, 4, and 5, the transfer paper detecting means for detecting the front end and the rear end of the transfer paper before the transfer, and the length of the transfer paper are calculated from the detection result of the transfer paper detecting means, Since a non-image area is formed in a predetermined area at the rear end of the transfer paper according to the length of the image, image control means for controlling one of the image forming steps is provided. Due to
It is possible to reliably prevent toner stains on the transfer member (transfer roller or the like) due to the regular development toner and back stains on the transfer paper.

According to a sixth aspect of the present invention, the image control means performs at least two of the charging step of the charger, the latent image erasing step of the erase lamp, the developing step of the developing device, and the exposing step of the exposing device. By controlling in combination, the non-image area is formed, so that the non-image area can be formed with higher accuracy, and toner stains on the transfer member (transfer roller etc.) due to regular developing toner and back stain on the transfer paper. Can be reliably prevented.

[Brief description of drawings]

FIG. 1 is an overall schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a non-image area of a transfer sheet.

FIG. 3 is an overall schematic configuration diagram showing a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charger 3 Erase lamp 4 Developing device 6 Transfer member 10 Transfer paper detection means 12 Image control means

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Claims (6)

[Claims] 1. A charging device for uniformly charging an image carrier, an exposure device for forming an electrostatic latent image on the image carrier, and an erase for erasing the electrostatic latent image formed on the image carrier. In an image forming apparatus including a lamp, a developing device that visualizes the electrostatic latent image, and a transfer member that transfers the developed image to a transfer sheet, a front end and a rear end of the transfer sheet before transfer are provided. The length of the transfer paper is calculated from the transfer paper detecting means for detecting and the detection result of the transfer paper detecting means, and a non-image area is formed in a predetermined area at the rear end of the transfer paper according to the length of the transfer paper. An image forming apparatus comprising an image control means for controlling the above. 2. The image forming apparatus according to claim 1, wherein the image control means forms the non-image area by controlling a charging process of the charger. 3. The image forming apparatus according to claim 1, wherein the image control means controls the latent image erasing process of the erase lamp to form the non-image area. 4. The image forming apparatus according to claim 1, wherein the image control unit forms the non-image area by controlling a developing process of the developing device. 5. The image forming apparatus according to claim 1, wherein the image control unit forms the non-image area by controlling an exposure process of the exposure device. 6. The image control means controls at least two of a charging step of the charger, a latent image erasing step of the erase lamp, a developing step of the developing device, and an exposing step of the exposure device in combination. The image forming apparatus according to claim 1, wherein the non-image area is formed by performing the process.