JPH06250474A - Image forming device - Google Patents

Abstract

PURPOSE:To restrain the deterioration of image quality to the minimum even when the fluctuation of image width in the shaft direction of a photosensitive body is caused by the eccentricity or the strain of the photosensitive body in an image forming device. CONSTITUTION:In this image forming device, plural image forming parts 1a to 1d are juxtaposed, paper is allowed to successively pass to the transfer position of each image forming medium, and the images formed on the photosensitive bodies 7a to 7d in the respective image forming parts are successively transferred on the paper. The device is provided with driving sources respectively driving the respective photosensitive bodies independently, displacement gages 13a to 13d for measuring the eccentricity amount of each photosensitive body, and a controller independently controlling the respective driving sources in synchronization with the passing timing of the paper on the basing of information on the measured eccentricity amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color electronic copying machine, and more particularly to an image forming apparatus for preventing color misregistration in the axial direction of a photoconductor due to eccentricity of an image forming medium. Is.

[0002]

2. Description of the Related Art For example, in a tandem type color electronic copying machine, a plurality of image forming sections are arranged along a sheet conveying path, and a different color is produced each time a sheet passes through each image forming section. Sequentially transferred, finally 3 colors or 4
A color image is obtained by superimposing colors.

Each image forming section is composed of a drum-shaped photosensitive member which functions as an image forming medium, and a charging device, an exposure device, a developing device and the like which are arranged around the photosensitive member. The surface of the photoconductor is uniformly charged by the charging device, and then exposed by the exposure device in a pattern corresponding to the image to be output, so that an electrostatic latent image is formed on the surface of the photoconductor. This electrostatic latent image is developed by a developing device to form a toner image, and this toner image is transferred onto a sheet. The toner remaining on the surface of the photoconductor after the transfer is removed by the cleaning device.

As an exposure apparatus, as shown in FIG. 6, it is called a laser scanner in which a laser beam from a laser light source 31 is reflected by a polygon scanner 32 and an optical path is bent by a mirror 33 to expose the surface of a photoconductor 34. The device is used. In this laser scanner, the polygon scanner 32 rotates in the direction of the arrow to perform main scanning in the axial direction of the photoconductor 34, and the photoconductor 34 is scanned.
Is rotated in the arrow direction, the sub-scanning is performed in the direction orthogonal to the axial direction of the photoconductor 1.

Now, assuming that the photoconductor 34 has no eccentricity,
The scanning width in the main scanning direction on the surface of the photoconductor 34 by the laser beam is always constant. However, in reality, it is difficult to eliminate the eccentricity of the photoconductor, and some eccentricity remains.

Now, assuming that the photoconductor 34 is eccentric, the optical path length from the laser light source 31 to the surface of the photoconductor 34 is, as shown by the alternate long and short dash line in FIG. It will be longer than when there is no eccentricity (shown by the solid line). The laser beam from the laser light source 31 is
Since the light is reflected by the polygon scanner 32 and spread in a fan shape, the scanning width on the surface of the photoconductor 34 becomes wider as the optical path length becomes longer. On the contrary, as shown by the broken line in FIG. 7, when the major axis portion is main-scanned, the scanning width on the surface of the photoconductor 34 becomes narrow. That is, an image magnification difference occurs due to the eccentricity of the photoconductor 34. Therefore, the width of the electrostatic latent image formed on the surface of the photoconductor 34 in the axial direction of the photoconductor changes periodically. Therefore, when the toner image obtained by developing this electrostatic latent image is transferred onto the paper, the width of the image transferred onto the paper P is the length of the circumference of the photoconductor 34 as shown by the solid line in FIG. It changes in a wave shape with the period as the period.

In the color image forming apparatus, as described above, the color images are formed by transferring the toner images of the respective colors to the same position on the paper in the plurality of image forming units. When forming an image in each of the image forming sections, as described above, it is affected by the eccentricity of the photoconductor,
Since the eccentric states of the photoconductors are different from each other, the changing shape of the width of the image formed in each image forming portion is different. For example, as shown in FIG. 8, the changing shape of the width of the image transferred to the paper P in the first image forming unit is the shape indicated by the solid line, while the image transferred in the next image forming unit is The changing shape of the width of is the shape shown by the broken line. That is, the image formed on the paper P is
Although a periodic width variation occurs, the phase and direction of this variation are independent for each image forming unit. Therefore, in the worst case, the same position on the image shifts to the outside in the image of a certain color, while it shifts to the inside of the image of another color, and the color shift becomes very noticeable.

Incidentally, such a periodic color shift occurs not only when the photoconductor is eccentric, but also when the photoconductor is distorted into an elliptical shape, for example.

Generally, when forming a color image,
If the position of the image of each color is misaligned even slightly, color misregistration (misregistration) occurs and the image quality deteriorates significantly.
For this reason, in order to accurately transfer the image to the same position on the paper in each image forming unit, it is necessary to use the image forming method disclosed in Japanese Patent Laid-Open No. 62-59977.
JP-A-63-78163, JP-A-63-78163
78164, Japanese Patent Laid-Open No. 63-113477,
JP-A-63-113478 and JP-A-1-1789
As disclosed in Japanese Patent Laid-Open No. 78, it is known to control the rotation of the photoconductor and arrange each member of the color image forming apparatus at a position satisfying a specific condition.

[0010]

However, in the conventional examples described in the above-mentioned respective publications, the positions of the respective colors on the paper are aligned by aligning the phases of image expansion and contraction by the photoconductors with respect to the transport direction of the paper. This is for the purpose, and it is not possible to correct the width variation in the direction orthogonal to the sheet conveying direction.

Therefore, according to the present invention, in an image forming apparatus,
An object of the present invention is to minimize deterioration of image quality even when the image width varies in the axial direction of the photoconductor due to eccentricity or distortion of the photoconductor.

[0012]

In order to achieve the above object, the present invention provides an image forming apparatus for forming an image of each color on an image forming medium and sequentially transferring the images of each color on a moving body in an overlapping manner. Of the eccentricity state, and a control device for controlling the transfer timing of each color image based on the eccentricity state information measured by the measurement device.

[0013]

The amount of eccentricity of the image forming medium is measured in advance, and at the time of image formation, the transfer timing is controlled in accordance with the passage of a moving body such as a sheet. As a result, the periodic fluctuation of the width of the image due to the eccentricity of the image forming medium has the same period and the same direction for all the color images. Therefore, the shift in the width direction of each image becomes small, and the color shift when forming a color image by superimposing single-color images becomes inconspicuous.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment in which the image forming apparatus of the present invention is applied to a tandem type color electrophotographic copying machine. Four image forming portions 1a to 1d forming different colors are linearly arranged, and the transfer belt 2 is provided along these image forming portions 1a to 1d. The transfer belt 2 is wound around rolls 3a and 3b, one of which is a drive roll, and when the transfer belt 2 is rotated in the direction of the arrow, four image forming portions 1a to 1d are formed on the paper.
Are sequentially transported along. Paper feed trays 4 a and 4 b are provided below one end of the transfer belt 2, and the paper sent from either of the paper feed trays is adsorbed by the transfer belt 2 and the image forming units 1 a. Pass through 1d sequentially. In the first image forming unit 1a, for example, a yellow toner image is transferred onto a sheet. Subsequent image forming unit 1b
Similarly, in 1d to 1d, the magenta, cyan, and black toner images are transferred to the same position on the sheet in an overlapping manner.
The sheet on which the four color toner images have been transferred is separated from the transfer belt 2, undergoes a fixing process by the fixing device 5, and is then discharged to the paper discharge tray 6.

Next, the details of the image forming units 1a to 1d will be described. Since the structures of the image forming units are the same, the image forming unit 1a will be described as an example.

The image forming section 1a includes a drum-shaped photoconductor 7a.
And a charging device 8, an exposure device 9, a developing device 10, a transfer device 11, a cleaning device 12 and the like which are sequentially arranged around the photoconductor 7a. Further, in this embodiment, a displacement gauge 13a for detecting displacement of the position of the surface of the photoconductor 1 is provided near the surface of the photoconductor 7a.
Also in the other image forming sections 1b to 1d, the respective photoconductors 7a to 7a.
7d are provided with similar displacement gauges 13b to 13d, and the displacement gauges 13a to 13d correspond to the image forming units 1a to 1d, respectively.
They are arranged at the same position with respect to 1d. The outputs of these displacement gauges 13a to 13d are, as will be described later, the photoconductor 7
Used to control the rotational phase of a-7d.

As the displacement gauges 13a to 13d, the photoconductor 7 is used.
An electrostatic or optical displacement meter for measuring the distance between the surfaces of the photoconductors 7a to 7d and the displacement meters 13a to 13d in a non-contact state so as not to affect the surfaces of a to 7d. It is desirable to use.

In the image forming section 1a, the photoconductor 7
The surface of a is uniformly charged by the charging device 8 and then exposed by the exposure device 9 in a pattern corresponding to the image to be output, so that an electrostatic latent image is formed on the surface of the photoconductor 7a. This electrostatic latent image is developed by the developing device 10 to form a toner image,
This toner image is transferred onto the paper. Photoconductor 7 after transfer
The toner remaining on the surface of a is removed by the cleaning device 12 to prepare for the next image forming cycle.

The exposure device 9 is of the laser scanner type described above in the section of the prior art, and each image forming unit 1
Modulation signals obtained by subjecting the image signals corresponding to the original image obtained by the image reading unit 14 to predetermined image processing by the image processing unit 15 are sequentially sent to a to 1d in synchronization with the timing of image formation.

Next, the photoconductor 7 of each of the image forming portions 1a to 1d.
The rotation drive mechanisms a to 7d will be described.

FIG. 2 is a block diagram showing a control circuit for rotationally driving the photoconductors 7a to 7d. Note that FIG.
Shows only a part necessary for explaining the present invention, and in fact, many input devices and output devices other than this are connected.

Outputs of the displacement gauges 13a to 13d provided in the image forming units 1a to 1d are taken into a CPU (central processing unit) 17 through an interface 16 and the photoconductors of the image forming units 1a to 1d. The eccentric states of 7a to 7d are detected.

FIG. 3 is a graph showing the variation in the distance between the surface of the photoconductor 7a and the displacement gauge 13a detected by the displacement gauge 13a of the image forming section 1a. That is, when the short diameter of the eccentric photoreceptor 7a faces the displacement meter 13a (angle θ ₁ ), the distance becomes maximum, and the long diameter becomes the displacement meter 13a.
The distance is the minimum when facing (angle θ ₂ ).
Therefore, the eccentric state of the photoconductor 7a can be detected by the displacement meter 13a. The eccentric states of the photoconductors 7b to 7d can be similarly detected in the other image forming units 1b to 1d. The CPU 17 uses the detected eccentric states of the photoconductors 7a to 7d to detect the photoconductors 7a to 7d.
7d rotation control is performed.

That is, the output of the CPU 17 is supplied to the drive circuits 19a to 19d provided in the image forming units 1a to 1d through the interface 18, and the drive circuit 1 is supplied.
9a to 19d, the photoconductor 7 of each image forming portion 1a to 1d.
The motors 20a to 20d that rotationally drive the a to 7d are controlled. The rotation of the motors 20a to 20d is connected to the shafts of the photoconductors 7a to 7d via a reduction mechanism (not shown), and the rotation of the motors 20a to 20d causes the photoconductors 7a to 7d to rotate.
7d also rotates. As the motors 20a to 20d, pulse motors that rotate by a predetermined fixed angle each time a drive pulse is supplied from the motor drive circuits 19a to 19d are used. Further, paper sensors 22a to 22d corresponding to the image forming units 1a to 1d are provided along the paper conveyance path of the transfer belt 2.

Next, the rotation control of the photoconductors 7a to 7d will be described in detail.

First, the CPU 17 uses the interface 1
8 and the drive circuits 19a to 19d, each motor 20a
.About.20d are rotated and each of the photoconductors 7a to 7d is rotated at least once to detect the eccentric state of each of the photoconductors 7a to 7d. Photoconductors 7a to 7d are provided near the photoconductors 7a to 7d.
Reference phase sensors 21a-2 for detecting the rotational phase of
1d is provided, and the time when the reference positions of the photoconductors 7a to 7d have passed is detected. Note that, here, the reference phase sensors 21a to 21d are provided at an angle corresponding to the transfer position. Since pulse motors are used as the motors 20a to 20d, the photoconductors 7a to
From the time when the reference position of 7d passes the reference phase sensors 21a to 21d, the drive circuit 19a to 19d drives the motor 20
The rotation angle of the photoconductors 7a to 7d can be known by counting the number of drive pulses supplied to a to 20d by the CPU 17. Therefore, it is possible to know what angle the long diameter portion or the short diameter portion of the photoconductors 7a to 7d is at with respect to the reference position.

FIG. 4A shows an example of the eccentricity of the photoconductors 7a and 7b detected in this way. In the photoconductor 7a, the angle of the major axis portion with respect to the reference position R is θ _a , the angle of the major axis part shows an example where theta _b for the body 7b reference position R. Note that, in FIG. 4, the eccentric state is illustrated in an extremely exaggerated manner for easy understanding.

Here, in the present embodiment, each photosensitive member 7
The motor 20 so that the angles of the long diameter portion or the short diameter portion of a to 7d with respect to the reference surface, for example, the surface of the transfer belt 2 are equal.
Each of a to 20d is previously rotated by a predetermined angle. For example, the photoconductors 7a to 7d are rotated so that the long diameter portions of the photoconductors 7a to 7d face the transfer belt 2.

Explaining the photoconductors 7a and 7b as an example, as shown in FIG. 4B, after the reference phase sensor 21a detects the reference position for the photoconductor 7a,
Further, the photoconductor 7a is rotated by the angle θ _a to stop the photoconductor 7a, and the reference position of the photoconductor 7b is detected by the reference phase sensor 21b. Then, the photoconductor 7b is further rotated by the angle θ _b. Set to the stopped state. The rotations of the photoconductors 7b and 7c are similarly controlled.

The transfer belt 2 is used for image formation.
When a sheet is conveyed by the sheet sensors 22a to 22d and the sheet sensors 22a to 22d sequentially detect that the sheet reaches a position before the transfer position of each of the image forming units 1a to 1d by a certain distance,
The rotations of the photoconductors 7a to 7d are sequentially started, and the formation of images on the photoconductors 7a to 7d is sequentially started. As a result, when the leading edge of the paper reaches the transfer position, the photoconductor 7a
The leading edge of the toner image formed on 7d corresponds to the leading edge of the sheet, and the toner images are transferred to the same position on the sheet in an overlapping state.

When the toner image is transferred onto the paper in each of the image forming sections 1a to 1d, the width of the image formed on the paper in the main scanning direction becomes wavy due to the eccentricity of the photoconductors 7a to 7d. Although it fluctuates, the phase of this fluctuation in the width in the main scanning direction is
Since the image forming units 1a to 1d are in agreement and the direction of variation is the same, the difference in the width of the image of each color is small. Therefore, the color misregistration of the color image becomes inconspicuous, and the image quality is improved. FIG. 5 shows the two images formed by the two image forming units by a solid line and a broken line, respectively, and shows that the difference in width between the images of the respective colors is small.

In the above-described embodiment, the photosensitive member is placed in the standby state with the long diameter portion of the photosensitive member facing the transfer belt. However, the present invention is not limited to this. It suffices if the phase and the direction of the fluctuation of the width of the captured image in the main scanning direction are the same. For example, the photoconductor may be placed in a standby state at an arbitrary rotation phase, and the photoconductor may be rotated to a certain angle between the detection of the sheet and the start of transfer.

Further, the phases of the photoconductors may be matched with each other in consideration of the distance between the photoconductors, and the phases may be simultaneously raised and simultaneously lowered so that the phases are always constant.

Further, in the embodiment shown in FIG. 1, the transfer belt is used so that there is no color shift on the paper, but the present invention is also applied to an image forming apparatus using an intermediate transfer member. be able to. That is, the position of the image transferred to the intermediate transfer member may be detected to control the phase of the photosensitive member so that the registrations on the intermediate transfer member are matched.

Although the displacement sensor is used to measure the eccentricity of the photoconductor in the above-mentioned embodiment, the eccentricity of the photoconductor may be measured by another means. For example, an image is transferred from the photoconductors 7a to 7d onto the conveyor belt 2, the image is read by a CCD image sensor or the like, and the variation in the magnification in the axial direction of the photoconductor is known, whereby the eccentric phase of the photoconductor is calculated, and the magnification is calculated. You may make it match the phase of a fluctuation.

[0037]

According to the present invention, since the rotational phase of the photoconductor is controlled according to the eccentricity state of the photoconductor, the variation phase of the width of each color image formed on the paper becomes the same, and the photoimage of the color image is exposed. Color shift in the body axis direction can be suppressed to a small level.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment in which an image forming apparatus of the present invention is applied to a tandem type color electrophotographic copying machine.

FIG. 2 is a block diagram showing a control circuit for rotationally driving a photoconductor.

FIG. 3 is a graph showing a variation in the distance between the surface of the photoconductor and the displacement meter detected by the displacement meter of the image forming unit.

FIG. 4 is an explanatory diagram showing an example of an eccentric state of a photoconductor.

FIG. 5 is an explanatory diagram showing a variation state of the width of each color image formed by the image forming apparatus of the present invention.

FIG. 6 is a schematic diagram showing the structure of a laser scanner type exposure apparatus.

FIG. 7 is an explanatory diagram showing a state in which an image magnification difference occurs due to eccentricity of a photoconductor.

FIG. 8 is an explanatory diagram showing a variation state of a width of each color image formed by a conventional image forming apparatus.

[Explanation of symbols]

1a to 1d ... Image forming part, 2 ... Conveyor belt, 3a, 3b
... rolls, 4a, 4b ... paper feed tray, 5 ... fixing device, 6
... Paper discharge tray, 7a to 7d ... Photoconductor, 8 ... Charging device, 9
... exposure device, 10 ... developing device, 11 ... transfer device, 12 ...
Cleaning device, 13a to 13d ... Displacement sensor, 14
... image reading unit, 15 ... image processing device, 16 ... interface, 17 ... CPU, 18 ... interface,
19a to 19d ... Drive circuit, 20a to 20d ... Motor,
22 ... Paper sensor, 31 ... Laser light source, 32 ... Polygon mirror, 33 ... Mirror, 34 ... Photoconductor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Kasama 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Toshio Anzai 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (2)

[Claims] 1. An image forming apparatus for forming an image of each color on an image forming medium and transferring the images of each color in sequence on a moving body, and a measuring device for measuring an eccentric state of the image forming medium, and measuring by the measuring device. An image forming apparatus, comprising: a control device that controls the transfer timing of each color image based on the information of the eccentricity state. 2. A plurality of image forming media are juxtaposed, a moving body is sequentially passed through a transfer position of each image forming medium, and images formed on each image forming medium are sequentially transferred onto the moving body. In an image forming apparatus, a drive source that independently drives each image forming medium, a measuring device that measures the amount of eccentricity of each image forming medium, and the moving body based on information about the amount of eccentricity measured by the measuring device. An image forming apparatus comprising: a control device that independently controls each of the drive sources in accordance with the passage timing of the image forming device.