JPH0642099B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a movable developing device having a plurality of developing devices and moving a desired developing device to a developing position for development. In particular, the present invention can be preferably applied to an image forming apparatus for two colors or three or more monochromatic colors or full colors.

2. Description of the Related Art In recent years, in a color image forming apparatus or the like, a plurality of developing devices are mounted on, for example, a rotating body for the purpose of downsizing an image carrier such as a photosensitive drum, and thus downsizing the entire apparatus. A rotary developing device, that is, a moving developing device has been proposed in which a desired developing device is moved to a developing position facing the image bearing member by driving the body to perform the developing.

In a color image forming apparatus to which a rotary developing device is applied, in developing a latent image formed on a photosensitive drum, a desired developing device of the developing device is provided before the latent image on the photosensitive drum passes a developing position. To the development position and then development is performed, after which the developing device is prevented from moving out of the development position.

In such a developing process, for example, in a developing device for performing magnetic brush development using a developing roller, since the developer is attached to the developing roller, the developing device reaches the developing position while moving to the developing position. The developer may come into contact with the photosensitive drum before, and the toner may adhere to the outside of a desired developing area. Similarly, when the developing device is avoided after the development, the developer adhered to the developing roller during movement may contact the photosensitive drum, and the toner may adhere outside the desired developing area.

As described above, the undesired toner attached to the outside of the developing area of the photosensitive drum may contaminate the area of the transfer drum on which the transfer paper is not wound in an image forming apparatus that transfers the transfer paper to the transfer drum. In addition, the transfer charger will also be contaminated.

The present inventor, as a result of research and experiment, installed an electrode connected to a bias power source in a portion other than a rotating body carrying a developing device,
A developing bias is applied to the developing roller by bringing a contact provided on the rotating body into contact with the electrode, and the supply of the developing bias is started before the developing device reaches the developing position, and the developing bias is applied to the developing device. It has been found that the above-mentioned conventional problems can be solved by configuring the electrical connection between the electrode and the contactor so that the power supply is stopped at a position after moving from the developing position to a predetermined distance after moving. The present invention is based on such a new finding.

SUMMARY OF THE INVENTION In view of the above drawbacks, an object of the present invention is to develop a developing bias to a developing device in a movable developing device having a plurality of developing devices and moving a desired developing device to a developing position to perform development. By applying the voltage from when the developing device approaches the developing position to after the predetermined distance after the developing device leaves the developing position, contamination of the transfer drum and the transfer charging device is prevented and a high quality image is obtained. It is to provide an image forming apparatus capable of performing the above.

Means for Solving Problems The above object is achieved by the image forming apparatus according to the present invention.
In summary, the present invention relates to an image forming apparatus having a plurality of developing devices and having a movable developing device for moving a desired developing device to a developing position to develop a latent image on an image carrier. The image forming apparatus is characterized in that the developing bias is applied from before the developing device reaches the developing position until after a predetermined distance after the developing device leaves the developing position.

Embodiment Next, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 2 is a main sectional view of a full-color electrophotographic copying machine to which the present invention can be applied. In this embodiment, the photosensitive drum 1, which is a latent image carrier, rotates in the arrow direction. A charging device 2, an exposure optical system 3, a rotary developing device 4, a transfer unit 5, and a cleaning device 6 are arranged around it. The optical system 3 has a document scanning section 3a and a color separation filter section 3b. The rotary developing device 4 includes a yellow developing device 4Y using yellow toner, a magenta developing device 4M using magenta toner, a magenta developing device 4C using cyan toner,
A black developing device 4B that uses black toner is integrally provided. Each developing device is Japanese Patent Publication No. Sho 55-
As disclosed in Japanese Patent No. 20579, the scattering of toner is prevented by the action of a magnetic field, and the toner is detachably held by the rotating body 4a as shown in the drawing, and is rotationally moved together with the rotating body 4a about the central shaft 4b, and then sequentially to the developing position. Is located in. On the other hand, the transfer section 5 has a transfer drum 5b having a gripper 5a and a transfer charger 5c arranged inside thereof.

A full-color image is formed by sequentially transferring color toners onto a transfer material supported on the transfer drum 5 as in a conventional copying machine. The transfer material is supplied from the cassette 7, and the transfer material which has completed the transfer process is separated by the separating means 8 and reaches the tray 10 through the adhesion-resistant device 9.

FIG. 1 shows a sectional view of a rotary type developing device.
Since the developing devices mounted on the printer have the same structure, only the yellow developing device 4Y located at the developing position is shown in FIG. As shown in the figure, the developing device 4Y is provided with a developing container 11, and the inside of the developing container 11 is divided into two chambers by a partition plate 12.
3 and 14 are provided. The developer D is reciprocally circulated in the developing container 11 by the screws 13 and 14. on the other hand,
In the present embodiment, the developing roller means 17 includes a fixed magnet roller 17a magnetized as shown in the drawing, and the magnet roller 17a.
It is composed of a developing sleeve 17b which is attached to the periphery of a so as to be rotatable in the direction of the arrow in the drawing and which conveys the developer. The amount of the developer drawn up by the S ₁ pole due to the rotation of the developing sleeve 17b is regulated by the doctor blade 18 and is conveyed as N ₁ pole → S ₂ → N ₂ → S ₃ pole. The N ₁ pole is the main developing pole, and the developer that is erected here develops the electrostatic latent image on the photosensitive drum 1, and then the developing on the developing sleeve 17b by the repulsive magnetic field of the S ₃ pole and the S ₁ pole. The agent drops into the developing container. Here, a developing bias power source 51 is provided in a portion other than the rotating body, for example, in the main body of the apparatus, and the bias power source 51 is provided through a lead wire 53 to the central portion of the pole changing body, for example, the fixed central axis 4b of the rotating body. Is electrically connected to an electric mold 54 having a predetermined length. In the present embodiment, the fixed electrode is arranged so as to extend in an arc shape over the range of angles (θ ₁ , θ ₂ ) from the development center position. Further, in this embodiment, the contactor 55 is provided on the side of the developing device that rotates together with the rotating body.
Is provided, the contact 55 contacts the electrode 54, and is electrically connected to the developing sleeve 17b through the lead wire 56. Therefore, the developing bias can be applied to the developing sleeve 17b from the power source 51 through the electrode 54, the contact 55, and the like.

FIG. 3 shows the developing roller 17, the electrode 54 and the contact 5 when the developing device approaches the developing position and separates from the developing position.
5, the electrode 54 follows the movement locus of the developing device 4Y, and here, from θ ₁ before reaching the developing position to the developing device, as will be better understood with reference to FIG. The contact 55 and the electrode 54 start contacting with the movement of 4Y and move while maintaining contact, and when the developing device is separated from the electrode 54 by θ ₂ after the development, the contact 55 and the electrode 5
In No. 4, the contact of the contact is separated.

According to the invention, theta ₁ to the front bordering the developing position and the contacts 55 and the electrode _54, since it is electrically connected within the scope of theta ₂ in the separating direction, the developer on the developing sleeve, By applying a developing bias before and after the developing position, it is possible to prevent toner from adhering to areas other than the latent image forming area on the photosensitive drum.

In the description of the above embodiment, the image forming apparatus having the rotary developing device in which a plurality of developing devices are mounted on the rotating body is described, but the principle of the present invention is as shown in FIG. 4, for example. Further, a developing device having a configuration in which the developing device 4 including the developing devices 4Y, 4M, 4C, and 4B is linearly moved to the left, right, up, and down to position a desired developing device at the developing position, is shown in FIG. The developing device 4 including the developing devices 4Y, 4M, 4C, and 4B can be similarly applied to a developing device having a configuration in which a desired developing device is arranged at the developing position by rotational movement and linear movement.

As described above, according to the present invention, by applying the developing bias to the developing device before and after the developing position, the developer on the developing sleeve prevents toner from adhering to areas other than the latent image forming area on the photosensitive drum. Therefore, the contamination of the transfer drum, the transfer charger, etc. can be minimized, and an image forming apparatus capable of obtaining a high quality image can be provided.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a rotary developing device portion of an image forming apparatus according to the present invention. FIG. 2 is a sectional view of a color electrophotographic copying machine according to the present invention. FIG. 3 is an explanatory diagram illustrating the relationship between the developing roller, the electrodes, and the contacts when the developing device approaches the developing position and separates from the developing position. 4 and 5 (A) and 5 (B) are schematic views for explaining another embodiment of the present invention. 1: image carrier 4: rotary developing device 17: developing roller 51: bias power source 54: electrode 55: contactor

Claims (2)

[Claims] Claim: What is claimed is: 1. An image forming apparatus comprising a plurality of developing devices, wherein the desired developing device is moved to a developing position to develop a latent image on an image bearing member. An image forming apparatus, wherein the bias is applied from before the developing device reaches the developing position until after the developing device leaves the developing position and moves for a predetermined distance. 2. A fixed electrode having a predetermined length, which is electrically connected to a bias power source provided outside the developing device, and each developing device is provided with a contact electrically contacting the electrode. The apparatus according to claim 1, wherein each of the developing devices is electrically connected to the bias power source by contact between the contactor and the electrode.