JP2000321844A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high-quality image whose positional deviation is small while restraining cost required for a memory by constituting so that at least one of the moving distance of the surface of a 1st photoreceptor, the moving distance of the surface of a 2nd photoreceptor and the moving distance of the surface of an intermediate transfer body can be adjusted. SOLUTION: Assuming that the moving distance of the surface of the photoreceptor 11 from an exposure point P1 on the photoreceptor 11 to a transfer point P3 to an intermediate transfer belt 10 is L1, the moving distance of the surface of the photoreceptor 12 from an exposure point P2 on the photoreceptor 12 to a transfer point P4 to the belt 10 is L3, and the moving distance of the surface of the belt 10 between the transfer points P3 and P4 is L2, L1 to L3 satisfy the relation of L1+L2=L3. In this device, at least one of L1 to L3 can be adjusted. Thus, the positional deviation of a toner image superposed on an intermediate transfer medium is corrected by adjusting any of L1 to L3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for forming an image based on image information, and more particularly to a color image forming apparatus having two photosensitive members.

[0002]

2. Description of the Related Art Conventionally, the following two systems are mainly used in a color image forming apparatus such as a color copying machine and a color printer. On the other hand, one photoreceptor is provided, and four developing units of yellow, magenta, cyan, and black are switched and sequentially operated on the one photoreceptor, and an image forming process is repeated four times to form a color image. This is a color image forming apparatus of a multi-rotation process to be formed. The other is a tandem-type color image forming apparatus provided with four image forming stations each including a photoreceptor and a developing device for each of yellow, magenta, cyan, and black.

The former has a problem that, although small, the printing time required for one image is long and the number of prints per unit time is small. On the other hand, in the latter case, although the number of prints per unit time is large, since each image forming station requires an image forming process device such as a charger and a laser scanner unit, the size of the device is increased.
There is a problem of cost increase.

In view of the above, two types of image forming apparatuses have conventionally been used, in which the number of prints per unit time is larger than that of a multi-rotation process apparatus, and which can be made smaller and less expensive than a tandem type apparatus. A color image forming apparatus including a photoconductor has been developed. For such a color image forming apparatus, for example, a technique disclosed in the following publication is known.

In the technique disclosed in Japanese Patent Application Laid-Open No. 2-1273, first, a first color image and a second color image are formed on two photosensitive members, respectively, and are sequentially transferred to a sheet on a transfer drum. This is a technique of forming a color image by forming a third color image and a fourth color image on each of the photoconductors and similarly transferring the images to a sheet on a transfer drum.

The technique disclosed in Japanese Patent Application Laid-Open Nos. 4-204871 and 10-177286 is to first form an image of a first color and a second color on two photoconductors, respectively. The images are sequentially transferred to the respective photoreceptors, and then the images of the third and fourth colors are formed on the respective photoconductors, similarly transferred to the intermediate transfer belt, and the images stacked on the intermediate transfer belt are transferred to paper. This is a technique for forming a color image.

The technique disclosed in Japanese Patent Application Laid-Open No. Hei 10-31342 relates to a color image forming apparatus having two photosensitive members, in which the moving distance of the surface of the photosensitive member from the exposure position to the transfer position on one of the photosensitive members is L1. L3 is the moving distance of the surface of the photosensitive member from the exposure position to the transfer position on the other photosensitive member, and L3 is the moving distance of the surface of the intermediate transfer medium between the transfer positions on the intermediate transfer medium onto which the images on these photosensitive members are transferred. When L2 is set, the respective components are arranged so as to satisfy a relationship of L1 + L2 = L3.

According to the above arrangements, the first color image and the second color image formed on the two photosensitive members based on the image data read by the same scan are transferred to the same position on a sheet or an intermediate transfer belt. To overlap
Delay memory is required.

In other words, after the transfer target (paper or intermediate transfer belt) has passed through the transfer position of the first color image, it is necessary to fill in the time difference until it reaches the transfer position of the second color image. It is necessary to temporarily store a part of the color image data in the delay memory, read out the image data from the delay memory after a predetermined time has elapsed, and write the second color image on the photoconductor. Therefore, the delay memory and its peripheral devices have caused an increase in the price of the entire apparatus.

On the other hand, according to the above configuration, since the positional relationship of the images is adjusted in advance by devising the arrangement of the units as described above, the delay memory can be eliminated. For this reason, a low-cost image forming apparatus can be provided.

[0011]

However, the above configuration has the following problems. For example, in the case of a drum-shaped photoconductor, its diameter error,
In the case of a belt-shaped photoconductor, members constituting each unit have an error due to dimensional accuracy, such as a circumferential length error. Also, there is an error between the units due to the positional accuracy of the attachment.

Since it is impossible to completely eliminate such an error, it is inevitable that L1 + L2 = L3 described above cannot be accurately realized. Such a problem can be solved by providing an adjustment memory in advance in anticipation of an image shift due to an error, and changing the timing of writing to the photoconductor in accordance with the shift amount. However, the above measures reduce the cost reduction effect due to the elimination of the delay memory.

Specifically, in an image forming apparatus having a resolution of 600 [dpi], when a transfer position shift of 1 [mm] is assumed, a memory for about 24 [lines] × 8000 [dots / line] is required. , 1 [byte / dot] requires 192 [kilobytes] of adjustment memory.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and mechanically adjusts the shift of the image transfer position for each color, and reduces the capacity of the adjustment memory to the limit of the mechanical adjustment. Accordingly, an object of the present invention is to provide an image forming apparatus capable of forming a high-quality image with small image displacement while suppressing the cost required for the memory.

[0015]

According to a first aspect of the present invention, there is provided a color image forming apparatus for solving the above-mentioned problems.
A first image process, comprising: a first photoreceptor; first exposing means for exposing the first photoreceptor to form an electrostatic latent image; and first developing means for developing the electrostatic latent image into a toner image Department,
A second image processing unit having a first photoconductor, a second photoconductor corresponding to the first exposure unit and the first development unit, a second exposure unit and a second development unit, and formed on the first and second photoconductors An intermediate transfer medium for transferring the formed toner image to form a laminated image, transferring the laminated image to paper to form a color image, and moving the laminated image from a position exposed by the first exposure unit of the first photoconductor. The moving distance of the surface of the first photoconductor to the first transfer position for transferring the toner image to the intermediate transfer medium is L1, and the second transfer of the toner image to the intermediate transfer medium from the exposure position of the second photoconductor by the second exposure unit. When the moving distance of the surface of the second photosensitive member from the transfer position to the transfer position is L3, and the movement distance of the surface of the intermediate transfer medium from the first transfer position to the second transfer position is L2, color image formation satisfying a relationship of L1 + L2 = L3 is performed. In the apparatus, the L Is characterized in that at least one of L2, L3 are configured to be adjustable.

According to the above configuration, the toner image superimposed on the intermediate transfer medium caused by the deviation of the relationship of L1 + L2 = L3 due to the shape error of the photosensitive member or the intermediate transfer medium or the error of the mounting position thereof. The displacement of the (laminated image) can be corrected by adjusting any of L1, L2, and L3. This correction can also cope with occurrence of the above-mentioned error due to aging of the apparatus. Therefore, even when the exposure of both photoconductors is performed in line in the sub-scanning direction, the positions of the toner images transferred from the respective photoconductors can be matched.

As a result, the delay memory conventionally used can be made unnecessary, or the capacity of this memory can be significantly reduced as compared with the prior art. Therefore, in the present color image forming apparatus, it is possible to form a high-quality color image with small color shift while suppressing an increase in the cost of the apparatus.

A color image forming apparatus according to a second aspect of the present invention is the color image forming apparatus according to the first aspect,
The intermediate transfer medium is in the form of an endless belt stretched by a support member, and the first and second photoconductors face the surface of the intermediate transfer medium and extend from a direction intersecting the stretching direction of the intermediate transfer medium. It is characterized by being provided so as to sandwich the transfer medium and having a first displacement mechanism for displacing the intermediate transfer medium in the direction in which the intermediate transfer medium is stretched.

According to the above arrangement, the intermediate transfer medium is moved to the first position.
By displacing in the stretching direction by the displacement mechanism, each transfer position, which is a contact point with each photoconductor, is displaced with respect to the intermediate transfer medium, and L2, that is, the moving distance by which the intermediate transfer medium moves between each transfer position is determined. Can be adjusted. That is, the intermediate transfer medium is, for example, an endless belt stretched by two rollers, and is in a state of being folded back by each roller. L2 can be adjusted by fixing each of the photoconductors provided with the intermediate transfer medium interposed therebetween and displacing the intermediate transfer medium in the direction in which the intermediate transfer medium is stretched (moving direction).

By adjusting L2, the relationship of L1 + L2 = L3 can be realized as described above, and the displacement of the stacked image can be mechanically corrected. Here, the first displacement mechanism is a mechanism for displacing the intermediate transfer medium in the direction in which the intermediate transfer medium is stretched, that is, a mechanism that can linearly move the intermediate transfer medium. The linear movement can be mechanically realized with a very simple configuration, and can be configured by, for example, a combination of a slide mechanism and a drive mechanism. That is, in performing the mechanical adjustment, the configuration can be simplified.

Therefore, in the present color image forming apparatus,
It is possible to form a high quality color image by correcting the color misregistration of the color image while suppressing the cost for performing the mechanical adjustment.

According to a third aspect of the present invention, there is provided a color image forming apparatus according to the first aspect.
The image forming apparatus further includes a second displacement mechanism for displacing an exposure position on the photoconductor by at least one of the first exposure unit and the second exposure unit.

According to the above arrangement, the arrangement of the exposure means is changed by the second displacement mechanism, and the exposure position on the photoreceptor is changed. The moving distance of the photosensitive member from the position to the transfer position where the toner image is transferred to the intermediate transfer medium can be adjusted.

That is, by the second displacement mechanism, for example,
When the angle of the exposure unit is changed, or when the exposure unit is linearly moved, the optical axis of the light emitted by the exposure unit moves, and the exposure position on the photoconductor irradiated with the light moves. L1 or L3 will be adjusted. By adjusting L1 or L3, the relationship of L1 + L2 = L3 can be realized as described above, and the displacement of the stacked image can be mechanically corrected. Here, the second displacement mechanism can be constituted by a simple mechanism such as a rotation mechanism or a mechanism for linear movement.

Therefore, in the present color image forming apparatus,
In performing the mechanical adjustment, the configuration can be simplified, and the color shift of the color image can be corrected to form a high-quality color image while suppressing an increase in the cost of the apparatus.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the second or third aspect, a test pattern forming means for forming a test pattern image on the first and second photosensitive members. Detecting means for detecting a stacked image in which both of the test pattern images are transferred onto the intermediate transfer medium and calculating a shift amount between the two test pattern images; and An adjusting means for controlling the displacement mechanism is provided to reduce the displacement amount.

According to the above arrangement, the test pattern forming means forms one test pattern image on each of the photoreceptors in which the positional deviation of the laminated image is easily detected, and transfers the image to the intermediate transfer medium to remove the positional deviation. It can be detected by the detecting means. Then, based on the detected displacement, the displacement mechanism can be operated by adjusting means to adjust the displacement so as to reduce the displacement.

These can be automatically controlled, and an automatic adjustment can be performed when an adjustment button or the like is installed and pressed. That is, the operator does not need to make manual adjustments. In addition, the above-described adjustment is performed every time the normal copying operation is performed a predetermined number of times, or the above-described adjustment is performed when the displacement of the stacked image is always detected in the normal copying operation and the displacement becomes larger than a predetermined value. For example, it is also possible to allow the apparatus itself to manage the adjustment of the positional deviation.

Therefore, in the present color image forming apparatus,
A high-quality color image can be formed without troublesome adjustment work.

A color image forming apparatus according to a fifth aspect of the present invention is the color image forming apparatus according to any one of the first to fourth aspects, wherein the exposure timing of at least one of the first exposure means and the second exposure means is provided. And an exposure timing control means for performing fine adjustment in order to reduce the amount of deviation of each toner image on the intermediate transfer medium transferred from the first and second photoreceptors, respectively. I have.

According to the above construction, the displacement of the laminated image is mechanically adjusted by one of the displacement mechanisms, and the exposure timing is controlled by the exposure timing control means to perform fine adjustment beyond the mechanical adjustment limit. It can be performed.

In order to control the exposure timing, it is necessary to temporarily store the image data corresponding to the time for delaying the exposure timing in the delay memory. Therefore, the longer the time for delaying the exposure timing, the larger the memory capacity is required. Become. However, in the above configuration, the fine adjustment can be adjusted by the exposure timing after adjusting the positional shift of the stacked image to the mechanical limit, so that the required memory capacity can be reduced.

Therefore, in the present color image forming apparatus,
While suppressing the increase in memory capacity and cost,
It is possible to form a higher-quality color image in which fine adjustment of the misalignment of the laminated image, which cannot be mechanically adjusted, is performed.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] The following will describe one embodiment of the present invention with reference to FIGS. FIG. 2 is an overall configuration diagram of a digital color copying machine 1 as a color image forming apparatus according to an embodiment of the present invention, and shows a schematic configuration inside the copying machine viewed from the front of the apparatus. The digital color copier 1 mainly includes a main unit 2 and a scanner unit 3 disposed above the main unit 2.
It is composed of

First, the configuration of the scanner section 3 will be described.
The scanner unit 3 has a document table 4 on which a document is placed. The image of the document placed on the document table 4 is read by a reading optical system 5 installed below the document table 4 and converted into an electric signal. The reading optical system 5 has a first scanning unit 5a, a second scanning unit 5b, an optical lens 5c, and a CCD line sensor 5d as a photoelectric conversion element that reciprocate in parallel along the original placing surface of the original table 4. are doing.

The first scanning unit 5a has an exposure lamp for exposing the surface of a document image and a first mirror for reflecting a reflected light image from the document in a predetermined direction. It reciprocates in parallel at a predetermined scanning speed while maintaining a constant distance from the mounting surface.

The second scanning unit 5b has second and third mirrors for further reflecting the reflected light image from the document reflected by the first mirror of the first scanning unit 5a in a predetermined direction. , Reciprocating in parallel with the first scanning unit 5a while maintaining a constant speed relationship.

The optical lens 5c includes a second scanning unit 5b
Is reduced by condensing the reflected light image from the document reflected by the third mirror, and the reduced light image is formed at a predetermined position on the CCD line sensor 5d.

The CCD line sensor 5d sequentially photoelectrically converts the formed light image and outputs it as an electric signal. The CCD line sensor 5d is a three-line color CCD capable of reading a black-and-white image or a color image and outputting line data separated into R (red), G (green), and B (blue) color components. . The document image information converted into an electric signal by the CCD line sensor 5d is
Further, the image data is transferred to an image processing unit described later and subjected to predetermined image data processing.

In the digital color copying machine 1, the scanner unit 3 has a double-sided automatic document feeder (RADF: Reversin).
g Automatic Document Feeder) 6 is installed. The RADF 6 is mounted on the document table 4 with a predetermined positional relationship with respect to the document mounting surface of the document table 4 so as to be openable and closable with respect to the document table 4.

The operation of the RADF 6 is as follows. First, the document is conveyed to a position where one side of the document faces the reading optical system 5 at a predetermined position on the document table 4. Subsequently, after the reading of the image on one surface is completed, the document is reversed, and the document is similarly conveyed to a position where the other surface faces the reading optical system 5 at a predetermined position on the document table 4. Then, after both sides of the image have been read for one document, the document is discharged and a double-sided conveyance operation is performed for the next document. The operation of the RADF 6 for transporting the original and reversing the original is controlled in relation to the operation of the digital color copying machine 1 as a whole.

Next, the main body 2 will be described. The main body 2 includes an image forming unit 7 therein, and an operation panel (not shown) is provided on an upper surface thereof.

The image forming section 7 is provided with a belt unit 8 in which an intermediate transfer belt 10 is stretched around rollers (supporting members) 9a and 9b substantially at the center, and is vertically moved so as to sandwich the belt unit 8. The two image processing units (first
Two photoconductors (first photoconductor) 11 and photoconductor (second photoconductor) 12 constituting an image processing unit 71 and an image processing unit (second image processing unit) 72 are provided. Each of the photoconductors 11 and 12 has a roller 50a
It is a belt-like body stretched around 50b.

The photoreceptor 11 installed above the belt unit 8 forms images of two colors, yellow (Y) and magenta (M), and rotates in the direction of arrow B in the figure. Around the photoconductor 11, a charger 13, a laser scanner unit (hereinafter, referred to as LSU) 15, developing devices (first developing devices) 17 and 18, and a cleaning device 2
1 are provided, and form an image processing unit 71 as a whole.

The charger 13 charges the entire surface of the photoreceptor 11, and the LSU 15 performs exposure on the charged surface of the photoreceptor 11 based on image data sent from an image processing unit to be described later. Form a latent image. Developing device 17
Reference numeral 18 denotes a device for visualizing the electrostatic latent image formed on the photoconductor 11 with a developer (toner).
Has a yellow developer, and the developing device 18 has a magenta developer. The cleaning device 21
Before the photoconductor 11 is charged by the charger 13, the toner remaining on the photoconductor 11 is removed.

The LSU 15 is a semiconductor laser device for emitting dot light modulated in accordance with image data, a polygon mirror for scanning laser light from the semiconductor laser device in the main scanning direction, and a photosensitive laser beam for scanning. Body 11
It is composed of an fθ lens, a mirror, and the like that form an image on the surface. Here, the LSU 15 forms a yellow electrostatic latent image and a magenta electrostatic latent image.

On the other hand, the photoreceptor 12 installed below the belt unit 8 has black (BK) and cyan (C)
, And rotates in the direction of arrow B in the figure.
Around the photoconductor 12 as well as the photoconductor 11 described above,
Charger 14, laser scanner unit (second exposure means, LSU) for forming electrostatic latent images of two colors of black and cyan
16, a developing device (second developing device) 19 having a black developer, a developing device (second developing device) 20 having a cyan developer, a cleaning device 22, and the like are provided. 72 are formed.

Each of the developing devices 17, 18, 19,
The developing method in 20 is a contact developing method in which development is performed by contacting the photoconductors 11 and 12 or
Any of the non-contact development systems in which development is performed without contact with the developer may be used. However, in the case of the contact developing system, the developing device 17
A mechanism for moving the photoconductors 11, 12 to and away from the photoconductors 11, 12 or a developing device 17, 18, 19, 20
Since a mechanism such as a shutter for taking in and out the developer is required, from the viewpoint of cost and design flexibility,
A non-contact development system is desirable.

On the inner surface side of the intermediate transfer belt 10, transfer units 23 and 24 are provided at positions where the intermediate transfer belt 10 comes into contact with the photoconductors 11 and 12, respectively. The transfer devices 23 and 24 transfer the toner images formed on the photoconductors 11 and 12 to the intermediate transfer belt 10.

The toner image on the surface of the intermediate transfer belt 10 is transferred onto a sheet 39 conveyed from a sheet cassette 38, which will be described later, on the outer periphery of the belt unit 8 on the roller 9b side of the intermediate transfer belt 10. A transfer transfer member 37 for transferring the image is provided.

The transfer conveying member 37 is provided so as to be able to be separated from and brought into contact with the intermediate transfer belt 10. The transfer / conveying member 37 is brought into contact with the surface of the intermediate transfer belt 10 only when the toner image is transferred from the intermediate transfer belt 10 to the paper 39.

Here, the digital color copying machine 1 is configured to maintain the following relationship. That is, a transfer point (first transfer position) P from the exposure point P1 on the photoconductor 11 to the intermediate transfer belt 10
L1 is the moving distance of the surface of the photoconductor 11 up to 3 and the exposure point P2 on the photoconductor 12 is
The moving distance of the surface of the photoreceptor 12 to the transfer point (second transfer position) P4 to L0 is L3, and the transfer point P3 · P
The distance of movement of the surface of the intermediate transfer belt 10 between
Assuming that L1, L2 and L3 are L1 + L2 =
The relationship of L3 is satisfied.

Thus, even when the exposure to the photoconductors 11 and 12 is performed by the LSUs 15 and 16 in synchronization, the photoconductors 11 and 12 can be provided without providing a large-capacity delay memory.
And the toner image transferred from the photoconductor 12 to the intermediate transfer belt 10 can be superimposed on the intermediate transfer belt 10.

Although not particularly shown in FIG. 2, the intermediate transfer belt after the transfer of the toner image is located downstream of the contact portion of the transfer / transport member 37 in the rotation direction of the intermediate transfer belt 10. A cleaning device for cleaning the surface is provided.

A paper cassette 38 for storing paper 39 as a material to be transferred is provided below the image forming unit 7. The paper cassette 38 is provided with a pickup roller 36 and a paper feed roller pair 29 for feeding paper 39 in the cassette. The fed sheet 39 is transported upward along the paper guide 34 by the transport roller pair 35. A pair of registration rollers 33 is provided at a stage preceding the transfer / conveying member 37 to adjust the timing for adjusting the position of the toner image on the intermediate transfer belt 10 to the position of the sheet 39.

A fixing device 32 for fixing the toner image transferred onto the paper 39 by the transfer / conveying member 37 is provided above the transfer / conveying member 37, and a fixing device 32.
Roller pair 31 for discharging paper 39 processed by
Is installed. Further, on the upper surface of the main body 2, a paper discharge tray 30 that stores the paper 39 discharged by the paper discharge roller pair 31 is installed.

Next, the image processing section will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of the image processing unit. The image processing unit mainly includes an image data input unit 40, an image data processing unit 41, an image data output unit 42, a central processing unit (hereinafter, referred to as a CPU) 44, and external interface units 46 and 47. .

The image data input section 40 includes a CCD line sensor 5d, a shading correction circuit 40b, a line matching section 40c, a sensor color correction section 40d, and an MTF correction section 40.
e and a gamma correction unit 40f.

The CCD line sensor 5d reads a black-and-white original image or a color original image, and outputs line data of three lines that are separated into red (R), green (G), and blue (B) color components. Shading correction circuit 40b
Corrects the line image level of the line data output from the CCD line sensor 5d. Line matching unit 40
c is constituted by a line buffer or the like, and corrects a shift of line data. The sensor color correction unit 40d corrects the color data of the line data. The MTF correction unit 40e calculates C
The correction is performed so that the change in the signal in each pixel of the CD line sensor 5d has a sharp edge. And the γ correction unit 4
0f performs visibility correction by correcting the brightness of the image.

The image data processing section 41 includes a monochrome data generation section 41a (for monochrome original image), an input processing section 41b,
Region separation unit 41c, black generation unit 41d, color correction circuit 41
e, a zoom processing circuit 41f, a spatial filter 41g, a halftone processing section 41h, and a print data input section 41i.

The monochrome data generating section 41a is a RG which is a color image signal input from the image data input section 40.
Monochrome data is generated from the B signal. Input processing unit 4
1b converts an RGB signal into a YMC signal corresponding to the image forming unit 7 mounted on the digital color copying machine 1, and performs clock conversion. The region separating unit 41c determines whether the input image data is a character, a halftone photograph, or a photographic paper photograph, and separates each region. The black generation unit 41d performs undercolor removal processing based on the YMC signal output from the input processing unit 41b to generate black in a color image.

The color correction circuit 41e adjusts each color of the color image signal based on each color conversion table. The zoom processing circuit 41f and the spatial filter 41g convert the magnification of the input image information based on the set magnification.
The halftone processing unit 41h expresses gradation such as multi-level error diffusion and multi-level dither. The print data input unit 41i
It serves as an input unit for print data input from an external interface unit 47 described later.

Here, after the above-described color correction circuit 41e, the zoom processing circuit 41f, the spatial filter 41g, the halftone processing section 41h, and the print data input section 41i
Two systems are provided corresponding to the two LSUs 15 and 16.

The two-system operation is based on the YMC signal based on the RGB signal obtained in the first document reading operation (scan) in the image data input unit 40.
A first system on the left in the figure outputs yellow image data to the image data output unit 42, and a second system on the right in the figure outputs black image data generated by the black generation circuit 41d as image data. Output to the unit 42. Then, in the subsequent second scan, similarly, the first system outputs magenta image data to the image data output unit 42, and the second system outputs cyan image data to the image data output unit 42. Output.

The image data output unit 42 includes two line memory buffers 42a and a laser controller 42b corresponding to the first system and the second system in the image data processing unit 41, respectively. And two LSUs 15 and 16.

The line memory buffer 42a adjusts the output timing of the image data of each color sent from the halftone processing section 41h. The laser controller 42b performs pulse width modulation of the image data of each color sent from the halftone processing unit 41h. The LSUs 15 and 16 perform laser recording on the photoconductors 11 and 12 based on pulse width modulation signals corresponding to image data of each color output from each laser controller 42b.

In the digital color copying machine 1, since the mechanical alignment described later is possible, the memory capacity of each line memory buffer 42a is, for example, 8
About [kilobytes] to 24 [kilobytes] is sufficient.

The first system LSU 15 performs laser recording with a pulse modulation signal corresponding to yellow image data in the first scan in the image data input unit 40, and converts the magenta image data into magenta image data in the second scan. Laser recording is performed with the corresponding pulse modulation signal. on the other hand,
The LSU 16 of the second system performs laser recording with a pulse modulation signal corresponding to black image data in the first scan in the image data input unit 40, and responds to cyan image data in the second scan. Laser recording is performed using a pulse modulation signal.

The CPU 44 controls the image data input section 40, the image data processing section 41, the image data output section 42, and the external interface sections 46 and 47 to be described later based on a predetermined sequence.

The external interface unit 46 is a communication interface means for receiving image data from an external image input processing device (communication portable terminal, digital camera, digital video camera, etc.) provided separately from the digital color copying machine 1. It is. Note that the image data input from the external interface unit 46 is also once input to the image data processing unit 41 to perform each processing, thereby achieving a data level that can be handled by the image forming unit 7 of the digital color copying machine 1. After the conversion, the image data is output to the image data output unit 42 in the same manner as described above.

Further, the external interface unit 47
A printer interface for inputting image data created by a personal computer, etc.
X is a monochrome or color FAX interface for receiving the received image data. The image data input from the external interface unit 47 is already
Since it is a YK signal, it is subjected to processing such as a halftone processing section 41h from the middle of the image data processing section 41 and output to the image data output section 42.

Next, the digital color copying machine 1 having the above configuration
In, about the operation when forming a color image,
This will be described below with reference to FIGS.

The reading optical system 5 performs a total of two scans when reading a document. The image read in the first scan is formed as an optical image on the CCD line sensor 5d via the optical lens 5c. The CCD line sensor 5d photoelectrically converts this into an image signal corresponding to each of the colors R, G, and B, and sends it to the image processing unit in FIG.

The image data that has been subjected to the above-described image processing in the image processing unit is sent to the image data output unit 42, and the first system LSU 15 irradiates a laser beam modulated based on the yellow image data. , The second LSU
From 16, a laser beam modulated based on black image data is emitted. Writing of these LSUs 15 and 16 is performed in line synchronization in the sub-scanning direction.

The surfaces of the photoconductors 11 and 12 are:
Each of the chargers 13 and 14 is associated with the rotational movement in the B direction.
Is uniformly charged when passing through the position opposite to. The charged surface is irradiated with laser light from each of the LSUs 15 and 16 at each of the exposure points P1 and P2, so that the photoconductor 11
, A black electrostatic latent image is formed on the other photoreceptor 12, respectively.

Then, the yellow electrostatic latent image on the photoreceptor 11 is visualized when passing through the position facing the developing device 17, and becomes a yellow toner image. This toner image is transferred to the intermediate transfer belt 10 by the operation of the transfer device 23 when passing through the transfer point P3.

On the other hand, the black electrostatic latent image on the photoreceptor 12 is also visualized when passing through the position facing the developing device 19 and becomes a black toner image in the same manner as described above, and when passing through the transfer point P4. Is transferred to the intermediate transfer belt 10 by the operation of the transfer unit 24.

Here, as described above, the distances L1 and L1
Since L2 and L3 are designed to satisfy the relationship of L1 + L2 = L3, at the transfer point P4, the black toner image is transferred onto the yellow toner image previously transferred onto the intermediate transfer belt 10 in a superimposed manner. Is done. At this time, the transfer conveying member 37 is separated from the intermediate transfer belt 10, and the transfer to the paper 39 is not performed.

Next, the reading optical system 5 performs a second scan, and in the second scan, the developing device 18 and the developing device 20 use the photoconductor 11 in the same manner as described above.
Then, a magenta electrostatic latent image and a toner image are formed on the photosensitive member 12 and are transferred to the intermediate transfer belt 10.

Here, the magenta toner image is transferred to be superimposed on the yellow and black toner images that have been previously transferred, and the cyan toner image is transferred to be superimposed on the yellow and black toner images. The image is further superimposed and transferred on the magenta toner image. This allows
A four-layered laminated image formed by laminating four color toner images is formed on the surface of the intermediate transfer belt 10.

Each time the toner image of each color formed on the surface of the photoreceptors 11 and 12 is transferred to the intermediate transfer belt 10, the residual toner is removed by the cleaning devices 21 and 22. The electricity is removed by an electric device (not shown) to prepare for the next image formation.

In this way, the four-layered laminated image transferred and superimposed on the intermediate transfer belt 10 is transported to the vicinity of the transfer transport member 37 as the intermediate transfer belt 10 rotates. Then, when passing through the position facing the transfer / conveying member 37, the image is transferred to the sheet 39 fed from the sheet cassette 38 by the action of the transfer / conveying member 37.

Subsequently, the sheet 3 on which the above-mentioned laminated image has been transferred
9 is conveyed to the fixing device 32 by the action of the transfer conveying member 37. The image transferred to the paper 39 is fixed on the paper 39 by the fixing device 32 to be a color image. Thereafter, the paper 39 is discharged to the discharge tray 30 by the discharge roller pair 31.

Next, the adjustment of the position when the toner image is transferred onto the intermediate transfer belt 10 will be described. In the present digital color copying machine 1, the distance, L1, L
Each unit is positioned so that the relationship between L2 and L3 is L1 + L2 = L3. Therefore, the photoconductor 11
When the exposure to 12 is performed in synchronization, the image transferred at the transfer point P3 and the image transferred at the transfer point P4 naturally coincide with each other and overlap.

However, as described in the section of the problem to be solved by the invention, there is an error due to dimensional accuracy in members constituting each unit such as a circumferential length error of the photoconductors 11 and 12. In addition, since there is an error between the units due to the positional accuracy of the attachment, the above-described relationship of L1 + L2 = L3 cannot necessarily be realized accurately. As a result, slight misregistration occurs in each toner image, and such misregistration appears as color misregistration, thereby deteriorating image quality. Such a displacement is caused by LSU15
The correction can be made by adjusting the writing start timing in the 16 sub-scanning directions. However, in order to correct the positional deviation only by this method, a large memory capacity of the line memory buffer 42a is required, and the delay memory is omitted. This reduces the cost reduction effect.

Therefore, the digital color copying machine 1 is configured so that mechanical adjustment can be performed so that the memory for adjusting the writing timing can be accommodated with a smaller capacity. Hereinafter, the method will be described in detail with reference to FIG.

The configuration shown in FIG. 1 corresponds to the above L1, L2, L
3 is provided with an adjustment mechanism by changing L2. FIG. 1 is a partial configuration diagram including the belt unit 8 and its peripheral portion in FIG. Components having the same functions as those described with reference to FIG. 2 or FIG. 3 are denoted by the same reference numerals, and description thereof is partially omitted.

Image forming section 7 of digital color copying machine 1
In both cases (see FIG. 2), two photoconductors 11 and 12 are provided so as to sandwich the belt unit 8 in a direction orthogonal to the longitudinal direction of the belt unit 8. Here, the photoconductors 11 and 12 do not necessarily need to be arranged at positions facing each other, but may be arranged so as to sandwich the belt unit 8.

The above-mentioned L2 can be changed by displacing the belt unit 8 in the longitudinal direction A and the reverse A direction (stretching direction, left-right direction in FIG. 1). Thus, L2 can be adjusted so as to satisfy the relationship of L1 + L2 = L3.

A displacement mechanism (first displacement mechanism) for displacing the belt unit 8 in the A direction and the reverse A direction can be roughly classified into a slide mechanism 60 and a drive mechanism 61.

The belt unit 8 is attached to a belt unit support frame 53. Specifically, the rotation shafts of two rollers 9 a and 9 b that stretch the intermediate transfer belt 10 are installed on the belt unit support frame 53. Therefore, the belt unit 8 moves integrally with the belt unit support frame 53.

A slide mechanism 60 is provided on the belt unit support frame 53. The slide mechanism 60 is formed by pins 52, 52 which are loosely fitted into elongated holes 53a, 53a formed in the belt unit support frame 53.

The long holes 53a are formed on the left and right sides of the belt unit support frame 53, one for each, and the longitudinal direction of the long holes 53a and the longitudinal direction of the belt unit support frame 53 are parallel to each other. On the other hand, the pin 52
Are provided on the back side of the belt unit support frame 53, and two are installed on a main body frame (not shown) on which the photoconductors 11 and 12 and the transfer units 23 and 24 are installed.

The elongated hole 53a and the pin 52 are connected to the pin 52 when the intermediate transfer belt 10, the photoconductors 11 and 12 and the like are at the designed position (a position satisfying L1 + L2 = L3 when the above errors are not taken into account). Are positioned substantially at the center of the long hole 53a in the longitudinal direction, and are arranged in a positional relationship for supporting the belt unit 8.

With such a configuration, the belt unit support frame 53 can be displaced in the A direction and the reverse A direction within the longitudinal dimension of the elongated hole 53a with respect to the main body frame on the back surface.

A driving mechanism 61 is provided on the main body frame side (the main body frame itself or a member fixed to the main body frame). The drive mechanism 61 includes a tension spring 54, a cam 5
5 and a shaft 55a.

The tension spring 54 has one end fixed to the main body frame and the other end fixed to the belt unit support frame 53. The cam 55 is generally known, has a circular outer periphery here, and has a shaft 55a fixed at a position eccentric from the center thereof. The cam 55 also rotates when the shaft 55a is rotated by driving means (not shown) such as a motor.

The tension spring 54 causes the belt unit support frame 53 to abut on the cam 55 by its elastic force. By rotating the cam 55 in this state, the contact position is displaced in the A direction and the reverse A direction. As a result, the belt unit support frame 53 can be displaced in the A direction and the reverse A direction by the action with the slide mechanism 60 described above. Therefore, the amount of displacement of the belt unit support frame 53 can be controlled by the rotation angle of the cam 55.

By displacing the belt unit support frame 53 by such a displacement mechanism, the belt unit 8 that moves integrally with the belt unit support frame 53 is displaced.
Can be moved in the A direction and the reverse A direction. As a result, the moving distance L2 of the intermediate transfer belt 10 between the transfer point P3 and the transfer point P4 can be changed. The transfer units 23 and 24 are respectively provided with the photoconductors 11 and
12, the transfer points P3 and P4 are determined, and are provided on the belt unit support frame 53 side.

Here, the slide mechanism 60 and the drive mechanism 61 are not limited to the above specific examples. Hereinafter, each specific example will be further described.

The slide mechanism 60 may be a combination of a rail and wheels that rotate and move on the rail, a slide mechanism that has a bearing inside and moves linearly, a combination of a shaft and a bearing that has a bearing, and the like. Is also good. These can be selected according to cost, position / motion accuracy, rigidity, and the like.

As the driving mechanism 61, a mechanism using an elastic body such as rubber instead of the above-mentioned tension spring 54, a mechanism converting a rotary motion into a linear motion using a screw mechanism, a mechanism using hydraulic pressure or air pressure, And so on. These can also be selected according to cost, position / motion accuracy, rigidity, controllability, and the like.

The method of adjusting L2 has been described in the present embodiment. After performing this adjustment, L1 +
In order to realize L2 = L3, for example, the following process using the configuration shown in FIG. 4 may be performed.

FIG. 4 is a block diagram showing the structure of the test pattern forming means 90 and the adjusting means 91. In the test pattern forming means 90, the CPU 44
, And sends the data to the image data output unit 42. In the image data output unit 42, the LSUs 15 and 16 write test patterns on the photoconductors 11 and 12, and form electrostatic latent images of the test patterns. This is visualized by one of the developing devices 17 or 18 and the developing device 19 or 20 for developing the photoconductors 11 and 12, respectively. Here, the test pattern image is a predetermined pattern that makes it easy to detect a positional shift amount of a preset stacked image.

In the adjusting means 91, the visualized image transferred on the surface of the intermediate transfer belt 10 is read for each color by the optical sensor (detecting means) 80, and the position of each test pattern image (toner image) is read. The shift amount is obtained by the CPU 44. The cam drive motor 82 is controlled by the CPU 44 to drive the cam drive motor 82 so as to correct the displacement based on the position shift amount obtained here, thereby performing the above-described cam rotation angle control.

On the other hand, even if the above-described mechanical adjustment is performed, there is a possibility that a displacement of several lines exceeding the limit of the mechanical adjustment remains. In this case, a line memory buffer (exposure timing control means) 42a is used to
By adjusting the timing of the exposure to the substrate, the displacement can be further suppressed.

More specifically, the following adjustments are made by the CPU 44 according to the relationship among L1, L2 and L3. L1 +
If L2> L3, the data is temporarily stored in the second line memory buffer 42a for a time corresponding to the distance of (L1 + L2) -L3, and transmitted to the laser controller 42b. Conversely, when L1 + L2 <L3, the data is temporarily held in the first line memory buffer 42a for a time corresponding to the distance of L3- (L1 + L2), and the laser controller 42
b.

In this case, however, the required capacity of the line memory buffer 42a can be set extremely small, as compared with the case where no mechanical adjustment is performed, since the displacement is very small. Therefore, an apparatus capable of producing a high-quality image with small color shift can be provided at a low price.

The above configuration is the digital color copying machine 1 in which the photoconductors 11 and 12 are formed of a belt. Here, the photoconductors 11 and 12 may be formed of a drum-shaped body. FIG. 5 shows the digital color copying machine 1 in this case. FIG. 5 is an overall configuration diagram of the digital color copying machine 1 having the drum-shaped photoconductors 11 and 12, and shows a schematic configuration inside the copying machine viewed from the front of the apparatus.

This digital color copying machine 1 has a photoconductor 1
The components other than 1 and 12 have the same configuration as the digital color copying machine 1 shown in FIG. 2, and the components having the same functions are denoted by the same reference numerals. Further, in the embodiment of the present invention, the digital color copying machine 1 shown in FIG.
Can be treated as equivalent to the digital color copying machine 1. Here, the description has been made mainly with respect to the digital color copying machine 1 of FIG. 2, but the same applies to the digital color copying machine 1 of FIG.

In this embodiment, the digital color copying machine 1 shown in FIGS. 2 and 5 has a configuration in which the longitudinal direction of the belt unit 8 is horizontal.
The belt unit 8 may be arranged so as to have a longitudinal direction in the vertical direction.

[Embodiment 2] Another embodiment of the present invention will be described below with reference to FIG. The color image forming apparatus according to the present embodiment has the above described L1, L2, L
3 is provided with an adjusting mechanism by changing L1 or L3. FIG. 6 is a partial configuration diagram including the photoconductor 11 and its peripheral portion in FIG. In addition,
Components having the same functions as the components described in FIG. 2 or FIG. 3 are denoted by the same reference numerals, and the description thereof is partially omitted.

The image forming section 7 of the digital color copying machine 1 according to the present embodiment (see FIG. 2) has two photosensitive members 11 and 12 so as to sandwich the belt unit 8 as in the above embodiment. There is no particular need to install.

In this embodiment, the exposure point P1 or P2 is moved by moving the LSU 15 or LSU 16, respectively.
3 can be varied. As a result, the above L1
It can be adjusted so as to satisfy the relationship of + L2 = L3. Here, the movement of the LSUs 15 and 16 may be either one or both. In the following, LS
A case where U15 is moved will be described.
The same applies to the case where 6 is moved.

As a displacement mechanism for moving the LSU 15 and changing L1, a mechanism for changing the angle by rotating the LSU 15 about a certain point (second displacement mechanism),
There is a mechanism (second displacement mechanism) that translates U15 almost parallel to the surface of the exposure point P1. Here, the former specific example will be described with reference to FIG.

The LSU 15 is configured to be rotatable in the Z direction in the figure around a rotation shaft 15a connecting the LSU 15 and the main body frame. On the other hand, a cam 57 is provided below the LSU 15, and the cam 57 is rotated by driving means (not shown) via a shaft 57a.

The LSU 15 is in contact with the cam 57 by its own weight, and is supported by the cam 57 and the rotating shaft 15a. The contact with the cam 57 is performed by using the drive mechanism 6 of the above-described embodiment (FIG. 1) using an elastic body such as a spring or rubber.
1 may be used. Here, by rotating the cam 57, the LSU 15 is rotated in the Z direction. As a result, the exposure point P1 is
In the up-down direction at L, and L1 can be changed.

Although the mechanism for rotating the LSU 15 has been described above, the LSU 15 is connected to the photosensitive member 1 as described above.
The mechanism may be a mechanism that translates substantially parallel to one exposure surface, and in that case, the slide mechanism 60 and the drive mechanism 61 described in the above embodiment (FIG. 1) can be used. .

Further, the mechanism for moving the LSU 15 main body has been described above. However, the mechanism for moving the exposure point P1 by moving an optical system such as a mirror or a lens inside or outside the LSU 15 is described. Is also good.

In the present embodiment, as described in the first embodiment, a test pattern can be formed, and mechanical adjustment or adjustment of exposure timing can be performed based on the test pattern. In addition, this embodiment,
The present invention is also applicable to the digital color copying machine 1 having the drum-shaped photoconductor shown in FIG.

The specific embodiments or examples described in the detailed description of the invention are only for clarifying the technical contents of the present invention, and are limited to only such specific examples. It should not be construed narrowly.

[0122]

As described above, the color image forming apparatus according to the first aspect of the present invention includes the intermediate transfer medium and the first and second intermediate transfer media.
In a color image forming apparatus having an image processing unit and satisfying a relationship of L1 + L2 = L3, at least one of L1, L2, and L3 is adjustable.

By adjusting any of L1, L2, and L3, the relationship of L1 + L2 = L3 can be realized. Even when exposure is performed in both image processing units in line synchronization in the sub-scanning direction. The positions of the toner images transferred from the respective photoconductors can be aligned, and the positional deviation of the stacked image can be mechanically corrected.

As a result, the need for a delay memory is eliminated.
Alternatively, the capacity can be significantly reduced as compared with the related art. Therefore, the present color image forming apparatus has an effect that it is possible to form a high-quality color image with a small color shift while suppressing an increase in the cost of the apparatus.

The color image forming apparatus according to claim 2 of the present invention, as described above, is sandwiched between the first and second photosensitive members in the color image forming apparatus according to claim 1,
The image forming apparatus includes a first displacement mechanism that displaces an endless belt-shaped intermediate transfer medium stretched by a support member in a stretching direction.

Thus, by displacing the intermediate transfer medium by the first displacement mechanism, it is possible to adjust the above L2, that is, the moving distance of the intermediate transfer medium between each transfer position on the intermediate transfer medium. Therefore, the relationship of L1 + L2 = L3 can be realized as described above, and the displacement of the stacked image can be mechanically corrected. Further, the first displacement mechanism may be any mechanism for linear movement, and the above adjustment can be performed by a simple mechanism.

As a result, the present color image forming apparatus forms a high quality color image with a small color shift while suppressing the cost required for the memory and the cost required for the mechanism for performing the mechanical adjustment. It has the effect of being able to do so.

According to a third aspect of the present invention, in the color image forming apparatus according to the first aspect, the second displacement mechanism for displacing the exposure position on the photoreceptor by the exposing means is provided. It is a configuration provided with.

As a result, the arrangement of the exposure means is changed by the second displacement mechanism, and the exposure position on the photosensitive member is displaced.
L1 or L3, that is, the moving distance of the photoconductor from the exposure position to the transfer position on the photoconductor can be adjusted. That is, when the arrangement of the exposure unit is changed by the second displacement mechanism, the optical axis of the light for exposure emitted by the exposure unit moves, and the exposure position on the photoconductor irradiated with the light moves. That is, L1 or L3 is adjusted.

Therefore, as described above, L1 + L2
= L3 can be realized, and the displacement of the stacked image can be mechanically corrected. Also, the second displacement mechanism can be realized by a simple mechanism such as a rotation mechanism or a mechanism for linear movement. As a result, the present color image forming apparatus can form a high-quality color image with small color shift while suppressing the cost required for the memory and the cost required for the mechanism for performing the mechanical adjustment. This has the effect.

According to a fourth aspect of the present invention, there is provided a color image forming apparatus according to the second or third aspect, wherein the test pattern forming means for forming a test pattern, and And a detecting means for detecting the amount of deviation between the two test patterns transferred to the test pattern, and an adjusting means for adjusting the amount of deviation based on the detected amount of deviation so as to reduce the amount of deviation.

In this way, a test pattern is formed by the test pattern forming means, the amount of deviation between the two test patterns is detected by the detecting means, and adjustment is performed by the adjusting means so as to reduce the amount of deviation using a displacement mechanism. By performing the above operation by automatic control or the like, it is possible to adjust so as to reduce the displacement of the stacked image. As a result, the present color image forming apparatus is not bothered by the adjustment work,
There is an effect that a high-quality color image with small color shift can be formed.

According to a fifth aspect of the present invention, there is provided a color image forming apparatus according to any one of the first to fourth aspects, wherein the exposure timing is controlled to perform fine adjustment by controlling the exposure timing. This is a configuration including timing control means.

Thus, by performing the mechanical adjustment as described above and further controlling the exposure timing, it is possible to perform a fine adjustment beyond the limit of the mechanical adjustment. Here, since the control of the exposure timing may be equivalent to the fine adjustment, the memory used for this can be realized with a small capacity. Therefore, this color image forming apparatus
While suppressing the increase in memory capacity and cost,
There is an effect that it is possible to form a higher-quality color image in which fine adjustment is performed with respect to misalignment of a stacked image of about several lines that cannot be mechanically adjusted.

[Brief description of the drawings]

FIG. 1 is a partial configuration diagram of a digital color copying machine showing a belt unit and a peripheral portion thereof according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of a digital color copying machine as a color image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of an image processing unit of the digital color copying machine in FIG. 1;

FIG. 4 is a block diagram showing a configuration of a test pattern forming unit and an adjusting unit of the digital color copying machine of FIG. 1;

FIG. 5 is an overall configuration diagram of another digital color copying machine as a color image forming apparatus according to an embodiment of the present invention.

FIG. 6 is a configuration diagram showing a configuration of a photosensitive member and a peripheral portion thereof according to another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 8 belt unit 9a roller (supporting member) 9b roller (supporting member) 10 intermediate transfer belt (intermediate transfer medium) 11 photoconductor (first photoconductor) 12 photoconductor (second photoconductor) 15 LSU (first exposure unit) 15a rotating shaft 16 LSU (second exposure unit) 17 developing device (first developing unit) 18 developing device (first developing unit) 19 developing device (second developing unit) 20 developing device (second developing unit) 39 paper 40 Image data input unit 41 Image data processing unit 42 Image data output unit 42a Line memory buffer (exposure timing control means) 44 CPU 52 Pin 53 Belt unit support frame 53a Slot 54 Tension spring 55 Cam 57 Cam 57a Shaft 60 Slide mechanism 61 Drive Mechanism 71 Image processing unit (first image processing unit) 72 Image processing unit (second image processing unit) Image processing unit) 80 optical sensor (detecting means) 81 Memory 82 cam driving motor 90 test pattern forming unit 91 adjusting means

Continued on the front page F term (reference) 2H027 DA27 EC03 ED04 ED24 EE02 EE05 HB07 HB16 ZA07 2H030 AA01 AA07 AB02 AD17 BB02 BB23 BB42 BB53 BB56

Claims (5)

[Claims] A first photoconductor, a first exposing unit configured to expose the first photoconductor to form an electrostatic latent image, and a first developing unit configured to develop the electrostatic latent image into a toner image. A first image processing unit having a first photoconductor, a second photoconductor corresponding to the first exposure unit and the first developing unit, a second image processing unit having a second exposure unit and a second developing unit, and a first image processing unit. And an intermediate transfer medium for transferring a toner image formed on the second photoconductor to form a stacked image, and transferring the stacked image to paper to form a color image. The moving distance of the surface of the first photosensitive member from the exposure position by the first exposure means to the first transfer position for transferring the toner image to the intermediate transfer medium is L1, and the toner image is intermediate from the exposure position of the second photosensitive member by the second exposure means. Second photoconductor surface up to a second transfer position for transferring to a transfer medium When the moving distance of the surface of the intermediate transfer medium from the first transfer position to the second transfer position is L2, the color image forming apparatus satisfying the relationship of L1 + L2 = L3. Wherein at least one of the color image forming apparatuses is configured to be adjustable. 2. The intermediate transfer medium is in the form of an endless belt stretched by a support member, wherein first and second photoconductors face a surface of the intermediate transfer medium, and a direction in which the intermediate transfer medium is stretched. 2. The image forming apparatus according to claim 1, further comprising a first displacement mechanism disposed so as to sandwich the intermediate transfer medium from a direction intersecting the first transfer mechanism and displacing the intermediate transfer medium in a direction in which the intermediate transfer medium is stretched. The color image forming apparatus as described in the above. A second exposure means for displacing an exposure position on the photoconductor by at least one of the first exposure means and the second exposure means;
The color image forming apparatus according to claim 1, further comprising a displacement mechanism. 4. A test pattern forming means for forming a test pattern image on first and second photoreceptors, detecting a laminated image in which both of the test pattern images are transferred onto the intermediate transfer medium, Detecting means for calculating the amount of deviation between the two test pattern images; and adjusting means for controlling the displacement mechanism so as to reduce the amount of deviation between the two test pattern images on the intermediate transfer medium. The color image forming apparatus according to claim 2. 5. A shift amount of each toner image on the intermediate transfer medium transferred from the first and second photosensitive members by controlling exposure timing of at least one of the first exposure unit and the second exposure unit. 5. The color image forming apparatus according to claim 1, further comprising an exposure timing control unit for performing fine adjustment so as to reduce the size of the image.