JPH03118567A - Image forming device - Google Patents

Abstract

PURPOSE:To shorten the moving time and to improve accuracy in positioning a developing unit by correcting the position of a developing unit only when the unit is in a correction position of the shortest moving route when a currently used developing unit is switched to another. CONSTITUTION:When the color of picture information to be processed is cyan, for instance, a shift requesting signal indicating the shift of a developing part 4 so that a developing unit 4c facing the photosensitive body of a photosensitive drum 5 is switched to a developing unit 4a containing cyan toner is outputted. Since a reference point 4x is in the shortest route of the developing unit 4c and the developing unit 4a, an optical sensor 13 detects the reference point 4x to correct the position of the developing part 4. After this position correction ends, the developing part 4 is further shifted so that the developing unit 4a faces the photosensitive body of the photosensitive drum 5. Consequently, the color of a toner image is cyan when a transfer sheet passes by a transfer part.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement in an image forming apparatus such as a copying machine or a laser beam printer that is equipped with a plurality of developing units, and more specifically, to improving the positioning accuracy of the developing units. The present invention relates to an image forming apparatus that can maintain high quality images and form high quality images.

[Prior art]

In an image forming apparatus such as a copying machine or a laser beam printer that is equipped with a plurality of developing devices, color image processing or the like is performed by switching the developing devices.

Usually, there are four developing devices to be switched: the three primary colors for color image processing, and black.

These four developing devices are moved together, and the developing device facing the photoreceptor is sequentially switched to perform image forming processing such as developing processing.

Then, the position of the developing device is corrected at a predetermined correction position during movement so as to accurately face the photoreceptor, thereby preventing abnormalities such as "variations in developed density" of the processed image.

In conventional image forming apparatuses, a normal AC or DC motor is used as a motor for moving the developing device.

Also, since the positioning accuracy is poor with the above motor alone,
In order to increase this accuracy, a mechanical stub mechanism is further added.

In addition, in order to make the corrections during the movement more reliable, every time one developer is switched to another, the same developer is moved to the correction position, the position is corrected, and then the same developer is switched. It is possible to do so.

[Problem to be solved by the invention]

As mentioned above, the conventional image forming apparatus requires a stop mechanism in addition to the motor, which not only increases the cost, but also relies on mechanical braking force to position the developing device. As the moving speed increases, the positioning accuracy deteriorates.

Also, each time you switch from one developer to another,
If the above-mentioned correction is made every time, it would take too much time to move the developing unit to correct its position, so it was difficult to use the above-mentioned method in a conventional image forming apparatus.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an image forming apparatus that can form high-quality images by increasing the positioning accuracy of a developing device without requiring extra travel time.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a plurality of developing devices, moves the developing devices together to switch the developing device facing the photoreceptor, and changes the position of the developing device to a predetermined position during movement. In an image forming apparatus configured to perform correction at a correction position, the developing device is moved by a positionable motor, and when switching from one developing device to another, the predetermined position is placed on the shortest movement path. This image forming apparatus is characterized in that the position of the developing device is corrected only when there is a correction position, and the developing device is switched via the shortest path.

Examples of the motor capable of positioning include a stepping motor and a DC servo motor.

[Effect]

In this image forming apparatus, since the developing device is moved by a motor that can be positioned, the rotation of the motor itself is controlled with high accuracy, and the positioning accuracy can be made higher than in the conventional system.

In addition, when switching from one developer to another, the position of the developer is corrected only if there is a predetermined correction position on the shortest movement path, so mechanical problems such as gears and backlash Even if a positioning error occurs due to factors, it is corrected and the positioning accuracy of the developing device is maintained at a high level.

Therefore, high quality images can be formed.

Further, since the position correction is performed on the shortest moving route, there is no wasted time, and the correction is performed immediately.

〔Example〕

Hereinafter, embodiments embodying the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

In addition, the following example is an example embodying the present invention,
It is not intended to limit the technical scope of the present invention.

Fig. 1 is a schematic cross-sectional view showing a copying machine as an example of an image forming apparatus to which the present invention can be applied, Fig. 2 is a block diagram of the copying machine, and Fig. 3 is the position of the developing unit of the copying machine. FIG. 4 is a flowchart showing the correction process, and is a schematic explanatory diagram showing examples of switching states of the respective developing units of the copying machine.

This copying machine 1 shown in FIG. 1 includes an upper cassette 2 and a lower cassette 3 provided for feeding paper. A developing unit 4. which integrally has 4c and 4a in a developing device 411+4 for developing processing. Photosensitive drum for forming a copy image5. and light R1 for reading the image information of the original
5, etc., has a manual feed tray 6 on one side, and has an ejection tray 7, etc. on the other side for ejecting a transfer sheet such as copy paper after copy processing has been completed.

The respective developers S4*, 4b, 4c, and 4a contain toner for developing three primary colors (cyan, magenta, yellow) and black, for example.

Further, as shown in FIG. 4, a light shielding plate 24 is attached to the developing section 4, which provides a reference point 4X for positioning the developing section 4 in order to correct the position of the developing section 4.

The developing unit 4 is moved, and the developing unit 4 is moved to the position where the reference point 4X is detected by the optical sensor 13 (FIG. 4) provided on the main body side of the copying machine 10 (the position shown in FIG. 4 fat) as described later. When the developing section 4 is present, the position of the developing section 4 is corrected.

This copying machine 1 has a document table 8 on its top surface (Fig. 1).
, a document (not shown) is placed on this document table 8.

As shown in FIG. 2, the control circuit of this copying machine 1 is mainly composed of a control section 9 consisting of a microcomputer CPU, etc., and an input section 10 for giving various input instructions to the control section 9. A display section 11 that displays the operating status of the copying machine l. A step motor 12 for moving the developing section 4 (FIG. 1). The reference point 4 of the developing section 4. an optical sensor 13 for detecting c. Also connected is an image forming section 14 that drives the photosensitive drum 5 (FIG. 1) and performs image forming processing such as copy processing.

In accordance with the operation of the input section 10, the copying machine 1 performs a copying process of the document placed on the document table 8 based on a predetermined sequence stored in the memory M of the control section 90.

Next, with reference to FIG. 3, steps Sl, S2, . . . are shown in FIG.
This will be explained using FIGS. 2 and 4.

When a document is placed on the document table 8 and the input section 10 is operated to start, for example, color copy processing, the light R15 (
1), and the light reflected by the document is received by a light receiving section 16, which is comprised of a color sensor or the like.

The received color image information is separated into three primary colors and data processed, and light is emitted from the light source 17 based on the image information, and the surface of the photoreceptor drum 5 is exposed via the mirror 18 etc. according to the image information. scanned.

Since the photosensitive drum 5 receives exposure while rotating, an electrostatic latent image corresponding to the original image is formed on its surface.

The image information is image data of, for example, "yellow" among the three primary colors, and the developing device of the developing section 4 facing the photoreceptor of the photoreceptor drum 5 currently contains, for example, black toner. If the developer is 4-, then the 4th developer
In Figure (el), a movement request signal is output to move the developing unit 4 so as to switch to the developing unit 4c containing "yellow" toner corresponding to the color information of the image data (
Sl) At this time, between the developing device 4d and the developing device 4°,
Since there is no reference point 4K for correcting the position of the developing section 4 (
S2), the developing unit 4 is moved by the positionable step and the ping motor 12 (S5), and the developing device 4c is moved to face the photoreceptor of the photoreceptor drum 5 (56) (FIG. 4 fdl).
, the electrostatic latent image is developed into a "yellow" toner image.

As described above, the developing section 4 is moved by the positionable stamping motor 12 and positioned so that the developing device 4e of the developing section 4 faces the photoreceptor, so there is no need for a conventional stop mechanism or the like. In addition, since the stepping motor 12 itself is rotationally controlled with high accuracy by pulse control, its positioning accuracy is higher than in the past, and the toner image becomes a high quality image.

On the other hand, the upper cassette 2. The transfer sheet fed through the lower cassette 3° or the manual feed tray 6 is sent to the photosensitive drum 5 through a conveyance roller 19, etc., and the toner image is transferred thereto as it passes through the transfer section 20.

The transfer sheet onto which the toner image has been transferred is further rotated by the rotating drum 21 and sent to the photosensitive drum 5 again.

If the color of the image information to be processed next is, for example, "cyan", the developing device 4c facing the photoconductor of the photoconductor drum 5 is the developing device 4c containing "cyan" toner.
A movement request signal for moving the developing section 4 so as to switch to □ is output (Sl).

In this case, on the shortest path between the developing device 4c and the developing device 41 (
That is, it is a path of 4C-4+, -41, for example, 4cm4
Since the reference point 48 is located on the path (not a path such as 4b→41) (S2), when the developing section 4 is moved on the shortest path, the reference point 48 is located on the optical sensor 13.
is detected and the position of the developing section 4 is corrected (33).
(Figure 4(a)) When this position correction is completed (34),
The developing section 4 is further moved (S5), and then the developing device 48 is opposed to the photoreceptor of the photoreceptor drum 5 (S6) (
Figure 4(C)). Therefore, the color of the toner image transferred when the transfer sheet passes through the transfer section 20 is "cyan".

In this copying machine 1, when switching one developing device to another as described above, the above-mentioned correction position is reached only when a predetermined correction position W, (above reference point 4.) is on the shortest path. The position of the developing section 4 is corrected.

Therefore, even if a positioning error occurs due to mechanical factors such as gears or backlash, it is immediately corrected, so that the positioning accuracy of the developing device of this developing section 4 is maintained at a high level. Since the position correction is performed on the shortest route, there is no wasted time.

Thereafter, similar development and transfer processing is performed for other colors as well.

Therefore, the image formed on the transfer sheet is free from "density variations" and becomes beautiful.

When the transfer process is completed, the transfer sheet passes through the conveyor belt 22, undergoes a fixing process at a fixing roller 23, and is then discharged onto the discharge tray 7.

In this embodiment, the stenciling motor 12 is used as a positioning motor, but a motor having similar performance, such as a DC servo motor, may also be used.

Further, in the above embodiment, the shortest path is taken as an example of a switching path between "yellow" of the developing device S4c and "cyan" of the developing device 41, and the position of the developing section 4 is corrected when passing through a correction point on all the shortest paths. Although a case has been described in which the shortest path is used, it is also possible to use the shortest path only when moving between arbitrary developing units 1, for example, between adjacent developing units.

For example, in the example shown in FIG. 4, the reference point 4K of the developing unit 40 is adjacent to the developing unit 4. ．． 4I, so in this case the shortest path is to move from 4□ to 4 or from 4b to 4a
This is the case when moving to . If the reference point 48 is located at another position 5, for example between the adjacent developing devices 4b+4c, the shortest path will similarly be the case of movement 4b-4C or movement 4C-4+.

As mentioned above, if adjacent developing units are selected to determine the shortest path, even if the developing unit 4 is moved at low speed in order to improve the positioning accuracy of the developing unit 4, this positioning and position correction can be done in a short time. This makes it possible to further improve efficiency.

〔Effect of the invention〕

According to the present invention, a plurality of developing devices are provided, and the developing device is moved integrally to switch the developing device facing the photoreceptor, and the position of the developing device is corrected at a predetermined correction position during movement. In the image forming apparatus, when the developing device is moved by a positionable motor and the one developing device is switched to another developing device, only when the predetermined correction position is on the shortest movement path. There is provided an image forming apparatus characterized in that the position of the developing device is corrected and switching of the developing device is performed via the shortest path.

Therefore, the positioning accuracy of the developing device can be increased compared to the conventional method, and the positioning accuracy of the developing device can be maintained at a high level without including wasted time.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing a copying machine as an example of an image forming apparatus to which the present invention can be applied, Fig. 2 is a block diagram of the copying machine, and Fig. 3 is the position of the developing unit of the copying machine. FIG. 4 is a flowchart showing the correction process, and is a schematic explanatory diagram showing examples of switching states of the respective developing units of the copying machine. [Explanation of symbols] 1... Copying machine 4... Developing section 1 4i, 41. ．． 4c, 4a...Developer 4X...Reference point (correction position) 5...Photosensitive drum 9...Control unit 2...Stamping motor (motor) 3...Optical sensor

Claims (1)

[Claims] 1. An image forming apparatus comprising a plurality of developing devices, in which the developing devices are integrally moved to switch the developing device facing the photoreceptor, and the position of the developing device is corrected at a predetermined correction position during movement. In the apparatus, the developing device is moved by a positionable motor, and when switching from one developing device to another, the developing device is moved only when the predetermined correction position is on the shortest movement path. An image forming apparatus characterized in that the position is corrected and the developing device is switched via the shortest path.