JPH09179384A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of preventing from lowering of the image quality, by eliminating a failure of concentration of the electric charge, escape of the electric charge or the like, caused by such as toner that is stuck on a cleaning blade and partially shifted on contact electrifying means after stuck on the image carrier, in the image forming device provided with the electrifying means of a roller electrifying system. SOLUTION: This device is provided with the contact electrifying means 1 arranged on the periphery of the image carrier 0 for electrifying the image carrier 0, exposing means 4 for forming a latent image on the image carrier 0 being electrified by the contact electrifying means 1, developing means 5 for developing by feeding the toner on the latent image on the image carrier 0, transferring means 6 for transferring the toner image on a transfer paper and cleaning means 7 for removing the toner remaining on the image carrier, and in addition equipped with an attaching/detaching mechanism 2 for attaching/detaching the contact electrifying means 1 corresponding to the image carrier. The device is composed so as to bring the contact electrifying means 1 into contact with the image carrier 0 surface, in timing for matching with the time after the image carrier part, with which the cleaning means 7 is held in contact at stopping time of the image carrier 0, is allowed to pass the position of the contact electrifying means 1 by rotation of the image carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electrophotographic image forming apparatus such as a copying machine, a laser beam printer, a laser beam facsimile, etc., and more particularly to a contact roller such as a charging roller. The present invention relates to an image forming apparatus that prevents the streak-like toner, which is likely to occur in an image forming apparatus using the means, from adhering to the contact charging means and the resulting deterioration in image quality.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a charging wire system using corona discharge has been conventionally used as a charging means for uniformly charging a photoconductor. However, since there are problems such as deterioration of the environment due to ozone generation, deterioration of the photoconductor, and image defects due to dirt on the charge wire,
Recently, a charging method using a contact charging means (charging roller) for reducing ozone has been used. In this contact charging method, by applying a bias while pressing the charging roller against the peripheral surface of the photoconductor,
The surface of the photoconductor is uniformly charged. In an image forming apparatus having a contact charging system, conventionally, a charging roller is always in contact with the photoconductor to contaminate the photoconductor by adhering foreign matter such as toner adhering to the roller surface to the photoconductor, resulting in white spots or the like. It has been confirmed that this causes a problem on the image. In order to solve such a problem, Japanese Patent Application Laid-Open No. 03-130787 discloses a technique in which a mechanism for bringing a charging roller into contact with and separating from a photoconductor is mounted so that the charging roller is brought into contact only during charging. . Further, it is impossible to completely remove the transfer residual toner by the cleaning means for removing the untransferred toner on the surface of the photoconductor.
Therefore, the toner that has passed through the cleaning means stains the charging roller, and if the stain is uneven, image defects due to uneven charging occur. In order to solve such a problem, in JP-A-02-272589, a cleaning means (felt or the like) for removing the toner on the charging roller prevents uneven charging. JP Hei 3
A similar technique is disclosed in Japanese Patent Laid-Open No. -100766. However, the structures described in the above publications complicate the mechanism and increase the cost.

[0003]

As described above, in the conventional contact charging type image forming apparatus, when the contact charging means is in contact with the image carrier for a long time, the components constituting the contact charging means are transferred to the image carrier. However, there is a problem that the image quality is deteriorated due to poor transfer of electric charges to that portion. To solve this problem, after the image carrier is rotated, the contact charging means is brought into contact with the image carrier immediately before the start of image formation (immediately before the latent image is written by the exposure means) and is separated apart from the time of image formation. There is an image forming apparatus having a configuration. By the way, the cleaning blade used as the cleaning means for the image carrier is
When the image carrier is driven to rotate, the toner removed from the photoconductor is held on the surface near the tip, but when the image carrier stops, the adhered toner linearly adheres to the photoconductor. There is. In the conventional image forming apparatus, when the image carrier is stopped, contact charging is performed before the linear toner transferred from the cleaning blade onto the image carrier passes through the position of the contact charging unit. Since the means was in contact with the image bearing member, the toner adhered linearly adheres to the contact charging means, and the charging performance of the toner-adhered portion deteriorates. There is a problem that the image quality is deteriorated by developing a horizontal black streak. Incidentally, in the method other than the reversal development, the toner-adhered portion causes partial white spots at an invisible level, but does not largely deteriorate the image quality. The present invention has been made in view of the above, and in an image forming apparatus provided with a charging device of a roller charging system, the toner or the like attached to the cleaning blade is partially attached to the contact charging device after being attached to the image carrier. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing the deterioration of image quality by eliminating the problems such as the concentration of electric charges and the loss of electric charges that are generated by the positive transfer.

[0004]

In order to achieve the above object, the present invention provides a contact charging means arranged around an image carrier to charge the image carrier, and an image charged by the contact charging means. Exposure means for forming a latent image on a carrier, developing means for supplying a toner to the latent image on the image carrier to develop it, transfer means for transferring the toner image to a transfer paper, and image carrier In the reversal development type image forming apparatus, which comprises a cleaning means for removing the toner remaining on the body and also has a contact / separation mechanism for contacting / separating the contact charging means with respect to the image carrier, Is brought into contact with the image bearing member after the portion of the image bearing member which was in contact with the cleaning means when the image bearing member was stopped passed the position of the contact charging means by the rotation of the image bearing member. It is characterized by

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in the drawings. FIG. 1 is a schematic diagram showing a main part configuration of an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are operation explanatory diagrams of a contact charging means. In the image forming unit of the image forming apparatus of the present invention, as shown in FIG. 1, a contact charging unit (charging roller) 1 is configured to be contactable / separable with respect to an image carrier 0 by a contact / separation mechanism 2 and contact charging is performed. The means 1 charges the image carrier 0 by applying the bias from the bias applying means 3.
The image forming operation is similar to that of an ordinary electrophotographic type, and after the latent image is formed on the carrier 0 by the exposure means 4 (analog optical system, laser writing device, etc.), the latent image is developed by the developing means 5. Is developed into a toner image, and this toner image is transferred to the transfer means 6
(Transfer roller, transfer belt 6b) transfers to transfer paper and then fixes. After the transfer step, the toner remaining on the image carrier 0 is removed by the cleaning means (blade etc.) 7. Further, the charge on the image carrier 0 is removed by the charge eliminating lamp 8 to prepare for the next charging. An image is formed on the transfer sheet by this series of operations.

The contacting / separating mechanism 2 rotatably supports a rotating shaft of the contact charging means 1 as a charging roller at one end thereof, and an arm 11 rotatably supported by a shaft 10 at a central portion thereof in a vertical direction. A spring 12 for urging the arm 11 in the press contact direction, and a cam 13 for rotating the other end of the arm 11 in the retreat direction against the spring 12 or for press contact.
And The cam 13 is rotationally driven about an eccentric shaft 13a by a driving unit (not shown). And FIG.
As shown in (a), when the outer peripheral edge portion near the eccentric shaft 13a faces the other end of the arm 11, the contact charging means 11 is pressed against the image carrier 0 by the force of the spring 12, The contact charging means 11 is separated from the image carrier 0 against the force of the spring 12 when the outer peripheral edge far from 13a opposes and presses the other end of the arm 11. The contact / separation mechanism 2 is driven by a drive source (not shown), and the operation of the drive source is controlled by a controller (not shown). In this embodiment, the contact charging means 1 is brought into pressure contact with the image carrier 0 via the arm 11 which is pressed by the pressure spring (compression) 12, and the image carrier is brought into contact with the image carrier 0 by frictional force. Although the example in which the body 0 is driven and rotated is shown, the contact charging means 1 may be driven by a separate driving means. The contact charging means 1 is brought into contact with or separated from the image carrier 0 by a cam 13 driven by a clutch-gear. FIG. 1 shows a state in which the contact charging means 1 is in contact with the image carrier 0.

FIGS. 3 (a), 3 (b) and 3 (c) are explanatory views of the operation of the cleaning blade 15 which is a component of the cleaning means 7, and show the image bearing member in the tip of the cleaning blade. The fine particle toner that cannot be completely removed is attached to the downstream side surface of the rotational direction 0 (T1). Normally, the amount of toner that cannot be completely removed by the cleaning blade and passes through the cleaning blade 15 is a very small amount that does not lead to deterioration of image quality. During the image forming operation, the cleaning blade 15 made of an elastic material is lifted to the downstream side in the rotational direction of the image carrier 0 by the frictional force with the image carrier 0 as shown in FIG. 3 (a). Holds the posture. The adhered toner (T1) drops on the image carrier 0 by a small amount, but the image quality is not deteriorated because the amount is very small. When the image forming operation is stopped and the frictional force from the image carrier 0 is released, the cleaning blade 15 is moved to the position shown in FIG.
As shown in, the contact point drops from point A during operation to point B.
In other words, the contact point of the cleaning blade moves to the upstream side in the rotation direction of the image carrier, so that the cleaning blade
Since the contact angle θ of the window 15 with respect to the image carrier 0 becomes small, and the posture of lying slightly with respect to the image carrier 0, the adhesion toner (T1) is inevitably relatively large on the image carrier 0. The amount is transferred.

FIG. 4 is a diagram showing the timing of contacting the contact charging means 1 with the image carrier 0 in the present invention. When the image forming operation is stopped, the cam 13 having a larger diameter is used as shown in FIG. 2 (b). By pushing the arm 11, the pressure from the pressure spring 12 is released, and the contact charging means 1 is separated from the image carrier 0. When the machine operates again, the cam 13 is rotated after the toner (T2) attached to the image carrier 0 has passed the position of the contact charging means 1 as shown in FIGS. As in (a), the timing is set so that the contact charging means 1 contacts the image carrier 0. With this configuration, the toner T2 is prevented from adhering to the contact charging means 1.

Incidentally, in the prior art, as shown in FIGS.
As shown in FIGS. 6 (a) and 6 (b), since the contact charging means 1 contacts the image carrier 0 before the adhesion toner T2 passes through the position of the contact charging means 1 as shown in (c). -T2 further adheres linearly on the contact charging means 1, and due to the deterioration of the charging performance of the adhered portion, the corresponding image carrier position is linearly developed,
There is a problem that a black streak of one pitch of the contact charging means is formed on the transfer paper. However, according to the present invention, it is clear that such a problem does not occur.

[0010]

As described above, according to the present invention, the timing at which the contact charging means configured so as to move forward and backward is brought into contact with the image bearing member is the image bearing which the cleaning means was in contact with when the image bearing member was stopped. Since the body part has passed the contact charging means position, the toner adhered to the image carrier at the position immediately after the cleaning means does not adhere to the contact charging means, thereby preventing the image quality from being deteriorated by the adhered toner. Therefore, good image quality can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a main part configuration of an image forming apparatus according to an embodiment of the present invention.

2A and 2B are operation explanatory views of an example of a contacting / separating mechanism.

3 (a), (b) and (c) are diagrams showing a state in which toner is transferred from a cleaning blade to an image carrier.

4 (a), (b) and (c) are diagrams showing the pressure contact timing of the contact charging means according to the present invention.

5 (a), (b) and (c) are diagrams showing the pressure contact timing of the contact charging means according to the conventional example.

6 (a) and 6 (b) are views showing defects of the conventional example.

[Explanation of symbols]

0 image carrier, 1 contact charging means (charging roller), 2
Contact / separation mechanism, 3 bias applying means, 4 exposure means 4, 5
Developing means, 6 transfer means (transfer roller, transfer belt), 7 cleaning means (blade, etc.), 8 static elimination lamp, 10 axis, 11 arm, 12 spring,
13 cams, 15 cleaning blades.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Hiroshi Saito 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Inside Ricoh Company (72) Inventor Toshiyuki Uchida 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd.

Claims (1)

[Claims] 1. A contact charging unit arranged around the image carrier to charge the image carrier, an exposing unit to form a latent image on the image carrier charged by the contact charging unit, and the image. Developing means for supplying a toner to the latent image on the carrier to develop the latent image,
A transfer means for transferring the toner image onto a transfer paper; and a cleaning means for removing the toner remaining on the image carrier,
In a reversal development type image forming apparatus having a contacting / separating mechanism for contacting / separating the contact charging means to / from the image carrier, the timing of contacting the contact charging means on the image carrier is set to An image forming apparatus characterized in that an image carrier portion which is in contact with the cleaning means at the time of stop is after passing the position of the contact charging means by the rotation of the image carrier.