JPH0721673B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus,
In particular, one or a plurality of developing devices are provided around an image bearing member such as an electrophotographic photosensitive member, and each developing unit is in the vicinity of the image bearing member and a developing operation position for developing a latent image on the image bearing member. And an image forming apparatus that is movable between a developing inoperative position separated from the image carrier. The present invention can be suitably applied not only to an image forming apparatus for two colors or three or more monochromatic colors, so-called multi-color, but also to an image forming apparatus for full color. In the present specification, the image forming apparatus includes a color copying apparatus, various color printing apparatuses such as a color printer that constitutes an output unit such as a computer and a facsimile, and an ordinary image forming apparatus that is not a color printing apparatus. I shall.

2. Description of the Related Art Recently, the demand for color copying and printing has rapidly increased not only in special fields but also in the field of general office work, and there has been a demand for a color image forming apparatus which has good operability and can obtain good image quality. ing. In particular, it may be required to copy or print a single-color original of two colors or three or more colors, and sometimes a full-color original in a desired color, and even in a full-color image forming apparatus such as a multi-color image forming apparatus. In response to the demand, it is required that selective copying or printing operation can be efficiently performed with two or three or more single colors.

In order to satisfy such a demand, a conventional color image forming apparatus has a plurality of developing devices each having a different developer around an image carrier such as an electrophotographic photosensitive member, and each developing device has an image forming apparatus. It is configured to be movable between a developing operation position which is close to the support and develops a latent image on the image support, and a development non-operation position which is separated from the image support.

The selected developing device is moved to the developing operation position to visualize the latent image on the image carrier, and at this time, the developing device provided in the developing device to bring the developing device into a good developing operation state. It is necessary to bring the agent carrier, for example, the developing sleeve and the image carrier, for example, the photosensitive drum, close to each other with a certain gear gap.
Although various methods are conceivable, usually, for example, a method of arranging abutting rollers coaxially with the developing sleeve at both ends of the developing sleeve and abutting the roller against the photosensitive drum is adopted. At this time, other developing devices that have not been selected are retracted from the photosensitive drum for reasons such as color mixing prevention,
It is placed in the development inoperative position.

However, the movement of the developing device as described above gives a shock to the photosensitive drum, and accordingly, the developing device is moved to the developing position just before the development without considering the timing of exposure, transfer, etc., and at the end of the development. If the method is carried out by moving the developing unit to a non-operating position, the rotation of the photosensitive drum may be affected by the impact when the developing unit is moved, and image blurring often occurs.

An object of the present invention is to set the timing of moving the developing unit to the developing position or the developing inoperative position other than during image exposure to during image transfer in order to eliminate the above-mentioned drawbacks. That is, it is an object of the present invention to provide an image forming apparatus capable of obtaining a good image with less image blurring by inhibiting the exposure process from the start to the end of the transfer process.

Means for Solving the Problems The present invention is summarized as follows: an exposure step of exposing an image bearing member;
The developing device includes a developing process of developing a latent image formed on the image carrier by the developing device by the exposing process and a transferring process of transferring the developed image developed by the developing process onto a transfer material. In an image forming apparatus in which the developing device is movable between a developing operation position for developing the image carrier and a developing inoperative position separated from the image carrier, the developing device is abutted against the image carrier when in the developing operation position. The developing device is prohibited from moving from the developing operation position to the developing inoperative position and from the developing inoperative position to the developing operation position from the start of the exposure process to the end of the transfer process. An image forming apparatus characterized by the above.

Next, an embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings.

The image forming apparatus according to the present invention includes at least an image exposure step for forming a latent image, a developing step for visualizing the latent image, and a transfer step for transferring the developed development image onto a transfer material. Although it can be suitably embodied by an apparatus, in the present embodiment, it is assumed that the apparatus is applied to a color electrophotographic copying apparatus for obtaining a two-color image of black and red. Further, such a color electrophotographic copying apparatus includes various electrostatic latent image forming processes, for example, so-called NP process or primary charging-color process including various steps of primary charging / secondary charging / color separation exposure / overall exposure. Although a so-called Carlson process including various steps of decomposition exposure can be used, this embodiment describes an electrophotographic copying apparatus to which the Carlson process is applied.

FIG. 1 is a schematic sectional view of a color electrophotographic copying apparatus for obtaining a two-color image of black and red.

First, the overall structure of the color electrophotographic copying apparatus will be described. An image carrier is arranged at the approximate center of the copying apparatus, and in this embodiment, a photosensitive drum 1 having an electrophotographic photosensitive layer formed on its surface is arranged. The photosensitive drum 1 has a rotation center O in a known manner.
It is rotatably and detachably attached to a rotary support shaft (not shown) having a shaft, and is driven by a drive motor (not shown). In this embodiment, the photosensitive drum 1 is assumed to rotate in the direction of arrow X, that is, clockwise in FIG.

The primary charger 2 is located substantially above the photosensitive drum 1, the developing devices 3 and 4 are located on the right side of the photosensitive drum 1 in FIG. 1, and the transfer discharger 10 and the photosensitive drum 1 are located substantially below the photosensitive drum 1.
The cleaning device 11 is arranged on the left side in FIG. Further, an optical system 5 is arranged above the electrophotographic copying apparatus so that an original image is projected onto the photosensitive drum 1 by an exposure unit located between the primary charger 2 and the developing unit 3. Is composed of. The optical system 5 may utilize any optical system.
Further, a blank exposure device 6 for erasing the electric charge of unnecessary portions outside the image area and a potential sensor 7 for measuring the surface potential of the photosensitive drum 1 are provided between the exposure unit and the developing unit 3, and A light source 12 for erasing the residual charge on the photosensitive drum 1 is provided between the charger 2 and the cleaning device 9.

Since the color copying machine described here is a color electrophotographic copying machine for obtaining a two-color image of black and red as described above, it has developing devices 3 and 4 as developing devices. Is not limited to this configuration, and may be one or may have three or more developing devices.

The operation of the color electrophotographic copying machine configured as described above will be briefly described.

The photosensitive drum 1 starts rotating in the direction of arrow X when the operation starts, and is charged by the primary charger 2 (charging step). The charged photosensitive drum 1 further rotates, and an optical image is subjected to slit exposure by the function of the optical system 5 in the exposure section (exposure step), and an electrostatic latent image of each color is formed on the photosensitive drum 1.
At this time, the blank exposure device 6 erases electric charges in unnecessary portions outside the image area, and the potential sensor 7 causes the photosensitive drum 1 to be erased.
The surface potential of is measured. The latent image on the photosensitive drum 1 is then brought by the rotation of the photosensitive drum 1 to a developing area where the developing devices 3 and 4 are arranged, and the electrostatic image on the photosensitive drum 1 is picked up by one selected developing device. The latent image is visualized as a toner image (developing process).

The toner image on the photosensitive drum is transferred to a transfer material P fed from a paper feeding device (not shown) in a transfer area where the transfer discharger 8 is arranged (transfer step). The transfer material P carrying the toner image is then conveyed to a fixing device (not shown) and fixed.

The photosensitive drum 1 is subjected to the actions of the cleaning device 9 and the light source 10 and then performs the next image forming process again.

Next, the developing devices 3 and 4 will be described. The developing devices may have any configuration. However, in order to simplify the description in this specification, a developing device that basically has the same structure and carries and conveys a developer is described. The rolls 3a and 4a are provided. Further, as shown in FIG. 2, the developing devices 3 and 4 are rotated by the developing device moving means, for example, the eccentric rollers 8 and 9, so that the developing operation position (the one-dot chain line position) and the non-developing position are changed. It is configured to be movable to the operating position (solid line position). The position regulation of the developing operation position is achieved by, for example, an abutting roller (not shown) provided in the usual manner as described above.

The developing rolls 3a and 4a include, for example, a fixed magnet (not shown) and a developing sleeve (not shown) that surrounds the magnet and rotates. The developing sleeve may be made of a non-magnetic material such as aluminum or stainless steel.

With the above configuration, for example, the developing device 3 stores red toner, and the developing device 4 stores black toner.

FIG. 3 is an outline of the time chart of each unit from the start of copying to the end of copying.

The operation of the copying apparatus configured as above will be described.

First, whether to use the first developing device 3 or the second developing device 4 is selected, and when the copying operation is started, one of the developing devices is moved to the developing operation position by the operation of the eccentric roller and is selected. A developing bias is applied only to the developing sleeve of the developing device, and the developing state is set.

The photosensitive drum 1 starts rotating before the developing device moves to the developing operation position. After that, the photosensitive drum 1 is positively charged by the charger 2. Next, the potential sensor 7 measures the dark potential on the surface of the photoconductor and feeds it back to the target potential. The charger 2 is charged by a high voltage transformer (not shown).
The voltage applied to is controlled.

In this apparatus, the developing device moves to the developing operation position while these potentials are controlled. After that, a predetermined copy operation, that is, scanning of the original by the optical system 5 and feeding of the transfer paper are started. Further, in this apparatus, the developing device at the developing position is moved to the developing inoperative position after the predetermined transfer is completed. Therefore, according to the present invention, the developing device is not moved during the image exposure process and the transfer process, that is, from the start of the exposure process to the end of the transfer process.

According to the present invention, even when one developing device is provided, the developing device is separated from the photosensitive drum at a time other than the developing time in order to prevent the developer from scattering, and the developing sleeve is provided by a shutter or the like. When it is configured to cover the above, it is possible to obtain a good image with little image blur in the same direction as described above.

EFFECTS OF THE INVENTION As described above, in the image forming apparatus according to the present invention, the timing of moving the developing device to the developing position or the developing inoperative position is set from the time of image exposure to the time of image transfer as described above. Then, by simple means, in other words, by prohibiting the movement of the developing device from the start of the exposure process to the end of the transfer process, the image (latent image, toner image) on the image carrier is prevented. ) Is prevented from being disturbed, and a good image with little image blur can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a copying machine having a plurality of developing devices. FIG. 2 is a schematic cross-sectional view showing a moving mode of the developing device. FIG. 3 is a time chart showing the relationship between the timing of movement of the developing device to the developing operation position and the developing non-operation position and the ON / OFF states of other units. 3, 4: Developing device 8, 9: Developing device moving means

Claims (1)

[Claims] 1. An exposure process for exposing an image carrier, a developing process for developing a latent image formed on the image carrier by the developing device with a developing device, and a developed image transferred by the developing process is transferred. An image forming apparatus having a transfer step of transferring to a material, the developing device being movable between a developing operation position for developing the image carrier and a developing inoperative position separated from the image carrier, The developing device is positioned so as to abut against the image carrier when it is in the developing operation position, and the movement of the developing device from the developing operation position to the developing inoperative position and from the developing inoperative position to the developing operation position is prevented. An image forming apparatus, which is prohibited from the start of the exposure process to the end of the transfer process.