JPS61231572A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain images having a small image blur by setting the timing of the movement of a developing device to a development position or nonde velopment position except during image exposure or image transfer operation. CONSTITUTION:A selection about which of the 1st developing device 3 and the 2nd developing device 4 is used is made firstly and the selected developing device moves to the development position through the operation of an eccentric roller at the start of copying operation, and a developing bias is applied to only the developing sleeve of the selected developing device and the device becomes ready for development. A photosensitive drum 1 begins to rotate before the developing device reaches the development position. Then, the photosensitive drum 1 is charged electrostatically by an electrostatic charger 2. Then, the dark part potential on the surface of the photosensitive body is measured by a potential sensor 7 and fed back to obtain a target potential, so that a high voltage transformer controls the voltage applied to the charger 2. The develop ing device moves to the development position while said potential control is performed.The developing device is moved to the nondevelopment position after specific transfer operation is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic image forming apparatus,
In particular, one or more developing units are provided around an image bearing member such as an electrophotographic photoreceptor, and each developing unit is located close to the image bearing member at a developing operation position where the latent image on the image bearing member is developed. The present invention relates to an image forming apparatus that is movable between the image forming apparatus and a developing non-operating position that is separated from the image carrier. In this specification, the term "image forming apparatus" refers to various types of color printers such as color copying apparatuses, computers, and color printers that constitute the output section of facsimile machines. The term "printing apparatus" includes printing apparatuses, and even ordinary image forming apparatuses other than color printing apparatuses.

Recently, the demand for color copying and printing has increased rapidly not only in specialized fields but also in general office fields, and color image forming devices that are easy to operate and can obtain good image quality are in demand. . In particular, there are cases where it is required to copy or print monochrome originals with two or more colors, sometimes even full-color originals, in a desired color. In response to demand, it is required to be able to selectively copy or print in two or more single colors efficiently.

In order to satisfy such requirements, conventional color image forming apparatuses arrange a plurality of developing devices each having a different developer around an image bearing member such as an electrophotographic photoreceptor, and each developing device has an image forming device. It was configured to be movable between a developing operating position, which is close to the image carrier and develops the latent image on the image carrier, and a developing non-operating position, which is remote from the image carrier.

The selected developing device is moved to the developing operating position and the latent image on the image carrier is visualized. It is necessary to bring the agent carrier, such as a developing sleeve, and the image carrier, such as a photosensitive drum, close to each other with a certain gap therebetween.

Various methods can be considered for this, but a common method is, for example, to arrange abutting rollers coaxially with the developing sleeve at both ends of the developing sleeve and abutting the rollers against the photosensitive drum. At this time, the other developing devices that were not selected are evacuated from the photoreceptor drum for reasons such as preventing color mixture.
It is placed in the developing non-operating position.

However, the above-mentioned movement of the developing device applies a shock to the photosensitive drum, so the developing device is simply moved to the developing position immediately before developing without considering the timing of exposure, transfer, etc.
If a method was adopted in which the developer was moved to a non-developing position at the end of development, the rotation of the photoreceptor drum would be affected by the shock generated when the developer was moved, often resulting in image blurring.

In order to eliminate the above-mentioned drawbacks of the conventional art, the present invention is designed to change the timing of the movement of the developing device to the developing position or to the non-developing position other than during the image exposure process or during image transfer. An object of the present invention is to provide an image forming apparatus which can obtain a good image with less image blur by setting the above.

. To summarize, the present invention includes at least an image exposure step for forming a latent image;
In an image forming apparatus having a developing step for making the latent image visible, and a transfer step for transferring the developed image to a transfer material, one or more images are provided around the image carrier carrying the latent image and the developed image. A plurality of developing units are arranged, and each developing unit has a developing operating position close to the image carrier and developing a latent image on the image carrying member, and a developing non-operating position separated from the image carrier. and is characterized in that the movement from the development operation position to the development non-operation position and from the development non-operation position to the development operation position is performed except during the image exposure process or the transfer process. It is an image forming apparatus.

Next, an embodiment of an 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 converting the latent image into a W4 image,
Although it can be suitably implemented in an image forming apparatus having a transfer step of transferring the developed image to a transfer material, in this embodiment, a color electrophotographic copying apparatus for obtaining a two-color image of black and red is used. The following description assumes that this device is applied to. In addition, such a color electrophotographic copying apparatus performs one type of electrostatic latent image forming process, for example, the so-called NP process or primary charging process, which includes the steps of primary charging, secondary charging, seven-color separation exposure, and full-surface exposure. Includes various steps of color separation exposure.

Although the so-called Carlson process and others may be used, in this embodiment, an electrophotographic copying apparatus to which the Carlson process is applied will be described.

FIG. 1 shows a schematic cross-sectional view of a color electrophotographic copying apparatus for obtaining two-color images of black and red.

First, the overall structure of a color electrophotographic copying apparatus will be described. An image carrier, in this embodiment, a photosensitive drum l having an electrophotographic photosensitive layer formed on its surface is disposed approximately in the center of the copying apparatus. The photosensitive drum l has a rotation center 0 in a well-known manner.
It is rotatably and removably attached to a rotation support shaft (not shown) having a rotary support shaft (not shown), and is driven by a drive motor (not shown). In the first embodiment, it is assumed that the photosensitive drum l rotates in the direction of arrow X, that is, clockwise in FIG.

A primary charger 2 is located approximately directly above the photosensitive drum 1, and developing devices 3 and 4 are located on the right side of the photosensitive drum 1 in FIG. A transfer discharger lO and a photosensitive drum l are placed approximately directly below the photosensitive drum l.
A cleaning device fill is disposed on the left side in FIG. Further, an optical system 5 is disposed above the electrophotographic copying apparatus, and an optical system 5 is arranged in the upper part of the electrophotographic copying apparatus to transfer the J[stripe image to the primary charger 2 and the developer 3.
The image is projected onto the photosensitive drum l at an exposure section located between the two. Optical system 5 can use any optical system. Further, a blank exposure device 6 for erasing charges in unnecessary parts outside the image area and a potential sensor 7 for measuring the surface potential of the photosensitive drum 1 are provided between the exposure section and the developing device 3. A light source 12 is provided between the charger 2 and the cleaning device 9 for erasing residual charges on the photosensitive drum l.

Since the color copying apparatus described here is a color electrophotographic copying apparatus for obtaining two-color images of black and red as described above, it has a developing device 3.4 as a developing device. is not limited to this configuration, and may have one developing device or three or more developing devices.

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

The photosensitive drum 1 begins to rotate in the direction of the arrow X when the operation starts, and is charged by the primary charger 2 (charging process). The light image is exposed to slit light (M light process)
, electrostatic latent images of each color are formed on the photosensitive drum l. At this time, the blank exposure device 6 erases charges in unnecessary portions outside the image area, and the potential sensor 7 measures the surface potential of the photosensitive drum l. The Hs image on the photosensitive drum 1 is then brought to a developing area in which a developing device 3.4 is arranged by rotation of the photosensitive drum 1, and the electrostatic latent image on the photosensitive drum 1 is produced by one selected developing device. is visualized as a toner image (
development process).

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

After the photosensitive drum 1 is subjected to the action of the cleaning device 9 and the light source 1O, the next image forming process is performed again.

Next, the developing device 3.4 will be explained. Although this developing device can have any configuration, in order to simplify the explanation in this specification, it basically has the same structure, and is a developing device that carries and conveys the developer. It is assumed that rolls 3a and 4a are provided. Furthermore, as schematically illustrated in FIG. 2, the developing unit 3.4 can be moved between a developing operating position (dotted chain line position) and a developing operating position by rotating the developing unit moving means 1, for example, an eccentric roller 8.9. (line position). The position regulation of the developing operation position is as follows.
This is accomplished, for example, by an abutment roller (not shown) provided in the usual manner as described above.

The developing rolls 3a, 4a are composed of, for example, a fixed magnet (not shown) and a rotating developing sleeve (not shown) surrounding the magnet. The developer sleeve may be made of a non-magnetic material such as aluminum or stainless steel.

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

FIG. 3 is a schematic 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 explained.

First, it is selected whether to use the first developing device 3 or the second developing device 4, and when the copying operation starts, either of the developing devices is moved to the developing operating position by the operation of the eccentric roller, and the selected developing device is moved to the developing operating position by the operation of the eccentric roller. A developing bias is applied only to the developing sleeve of the developing device to enable development.

The photosensitive drum 1 has started rotating before the developing device moves to the developing operating position. Thereafter, the photoreceptor drum l is charged more positively than the charger -2.The dark potential on the surface of the photoreceptor is measured by the potential sensor 7 and fed back to the target potential.
The voltage applied to is controlled.

In this apparatus, the developing unit moves to the developing operating position while these potential controls are being performed. Thereafter, predetermined copying operations, ie, scanning of the original by the optical system 5 and feeding of the transfer paper, are started. Furthermore, in one apparatus, the developing device at the developing position is moved to the developing non-operating position when a 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.

According to the present invention, even when one developing device is provided, the developing device is separated from the photoreceptor drum at times other than during development in order to prevent developer from scattering, etc., and the developing device is separated from the photosensitive drum by a shutter or the like. If the structure is such that the image is covered, a good image with less image blur can be obtained using the same method as described above.

i turbulence difference 1 As explained above, the image forming apparatus according to the present invention sets the timing of the movement of the developing unit to the developing position or to the developing non-operating position at times other than during the image exposure process or during image transfer. A good image with less image blur can be obtained by a simple method such as setting the image to .

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a copying apparatus having a plurality of developing devices. FIG. 2 is a schematic cross-sectional view showing how the developing unit moves. FIG. 3 is a time chart showing the relationship between the timing of movement of the developing device to the developing operating position and developing non-operating position and the ON/OFF states of other units. 3.4: Developing device 8.9: Developing device moving means

Claims (1)

[Claims] 1) An image forming apparatus having at least an image exposure step for forming a latent image, a developing step for making the latent image visible, and a transfer step for transferring the developed image to a transfer material. One or more developing devices are disposed around an image bearing member that carries a developed image, and each developing device is located in a developing operation position close to the image bearing member and developing the latent image on the image bearing member. and,
It is movable between a development non-operation position separated from the image carrier, and movement from the development operation position to the development non-operation position and movement from the development non-operation position to the development operation position is performed during the image exposure step or An image forming apparatus characterized in that the image forming apparatus performs operations other than during a transfer process.