JP4817226B2 - Color image forming apparatus and color misregistration correction method thereof - Google Patents

Description

  The present invention has a configuration in which an image is individually formed on a photoconductor for each color by scanning a laser beam by an exposure unit for the photoconductor for each color, and the image is enlarged / reduced in the main scanning direction. The present invention relates to a color image forming apparatus and a color misregistration correction method that cause color misregistration due to misregistration in a mode in which the magnification changes according to the position in the main scanning direction.

  A so-called tandem type color image forming apparatus in which process units for respective colors of yellow, magenta, cyan, and black are arranged along an intermediate transfer belt so that toner images of the respective colors are superimposed on the intermediate transfer belt. Widely used.

  In this type of tandem color image forming apparatus, after images are individually formed on the photosensitive drums for the respective colors, the images for the respective colors are sequentially superimposed on the intermediate transfer belt. If the image is misaligned, color misregistration occurs in the image superimposed on the intermediate transfer belt, and the image quality is deteriorated.

There are various types of such color misregistration. In order to suppress the color misregistration caused by the misregistration of the mode in which the image is enlarged / reduced in the main scanning direction, enlargement / reduction is also performed. There is known an image forming apparatus in which necessary correction is performed in order to suppress color misregistration caused by misregistration in a mode in which the magnification of the image changes in accordance with the position in the main scanning direction (Patent Document 1). 2).
JP 2004-109876 A Japanese Patent Application Laid-Open No. 2004-219592

  However, in the case of color misregistration caused by misregistration in a mode in which the magnification of the image is changed according to the position in the main scanning direction, it cannot be uniformly corrected over the entire region in the main scanning direction. Furthermore, there is a limit to performing high-accuracy correction with a small number of area divisions as in the prior art, and the demand for higher image quality cannot be fully satisfied. Further, it is desirable to avoid an increase in calculation burden accompanying an improvement in correction accuracy, because it leads to a deterioration in feeling of use due to an increase in processing time and an increase in manufacturing cost due to an increase in the speed of the control unit.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to enlarge / reduce the image in the main scanning direction, and to mainly use the enlargement / reduction magnification. Color image forming apparatus configured to be able to correct color misregistration caused by misregistration in a manner that changes according to the position in the scanning direction with high accuracy without significantly increasing the calculation burden, and the color misregistration thereof It is to provide a correction method.

In order to solve such a problem, according to the present invention, as shown in claim 1, each color for individually forming an image on the photoconductor for each color by scanning of the laser beam by the exposure means for the photoconductor for each color A color image forming apparatus that forms a color image using each process unit, and when a correction execution condition including color misregistration correction is satisfied, the process unit performs registration at a plurality of positions in the main scanning direction for each color. A pattern image forming unit that forms a pattern image and transfers the pattern image onto the intermediate transfer belt, and the resist pattern image for each color formed by the pattern image forming unit is positioned near both ends in the main scanning direction and a pattern image detection means for detecting a total three points of the center position of the main scanning direction, the resist pattern by the pattern image detection means A color shift amount obtaining unit that the color shift amount obtaining for each color at each position by the detection timing of the image, the amount of color shift obtained by the color shift amount obtaining means as a linear magnification change in the main scanning direction Converting to a magnification in the main scanning direction, setting a correction magnification according to the position in the main scanning direction by linear interpolation based on the converted magnification in the main scanning direction, and changing the exposure timing of the laser beam by the exposure means Thus, the image forming apparatus includes a correction control unit that performs correction processing of the color misregistration amount.

According to this, the acquired color misregistration amount is converted into a main scanning direction magnification as a magnification change in the main scanning direction, and the correction magnification is set based on the converted main scanning direction magnification, so that the image is scanned in the main scanning direction. The color shift caused by the positional shift in the mode in which the magnification is enlarged / reduced in the direction and the magnification of the enlargement / reduction changes according to the position in the main scanning direction is corrected with high accuracy without increasing the calculation burden. be able to.
The main scanning direction magnification can be easily calculated based on an approximate expression in the main scanning direction magnification at an arbitrary position in the main scanning direction. Since the correction magnification is set based on this, correction can be performed with high accuracy. Also, if the main scanning direction magnification at each position in the main scanning direction is calculated based on a first-order approximate expression set assuming that the main scanning direction magnification changes linearly , the calculation burden can be reduced. High-speed processing is possible.

In this case, a predetermined resist pattern is imaged on the photoconductor for each color, and the image of the resist pattern for each color is detected by an image sensor as a detecting means , and the amount of color shift in the main scanning direction for each color is determined. Get it . Further, the correction control means may correct the exposure timing of the exposure means based on the set correction magnification in order to suppress the color shift in the main scanning direction for each color caused by the change in the main scanning direction magnification .

  There are various factors in the color misregistration caused by the misregistration in which the enlargement / reduction magnification changes depending on the position in the main scanning direction, but the state where the photosensitive drum is inclined mainly from the normal position with respect to the LSU. Therefore, it can be considered that the magnification in the main scanning direction changes linearly according to the position in the main scanning direction.

Further, in the color image forming apparatus, the pattern image detecting unit detects at a total of three points, that is, a position near both ends in the main scanning direction and a center position in the main scanning direction. It is necessary and sufficient to set a calculation formula for converting the color misregistration amount to the main scanning direction magnification at each position in the main scanning direction, and by reducing the number of sensors for detecting the color misregistration amount. An increase in manufacturing cost can be suppressed.

  In this case, the correction amount for each block may be obtained using the main scanning direction magnification at the center position of each block as a representative value of the block.

In the color misregistration correction method for a color image forming apparatus according to the present invention, as described in claim 2 , an image is individually formed on the photoconductor for each color by scanning the laser beam by the exposure means for the photoconductor for each color. In a color image forming apparatus that forms a color image using a process unit for each color, when a correction execution condition including color misregistration correction is satisfied, a resist pattern is formed at a plurality of positions in the main scanning direction for each color by the process unit. An image is formed, transferred onto an intermediate transfer belt, and the transferred resist pattern image for each color is displayed at a total of three points including the positions near both ends in the main scanning direction and the center position in the main scanning direction. And detecting the amount of color misregistration at each position for each color according to the detection timing of the detected resist pattern image. The shift amount in terms of the main scanning direction magnification of a linear magnification change in the main scanning direction, by setting the correction factor corresponding to the position of the main scanning direction by linear interpolation on the basis of the conversion has been the main scanning direction magnification The correction process of the color misregistration amount is performed by changing the exposure timing of the laser beam by the exposure unit.

According to this, the acquired color misregistration amount is converted into a main scanning direction magnification as a magnification change in the main scanning direction, and the correction magnification is set based on the converted main scanning direction magnification, so that the image is scanned in the main scanning direction. The color shift caused by the positional shift in the mode in which the magnification is enlarged / reduced in the direction and the magnification of the enlargement / reduction changes according to the position in the main scanning direction is corrected with high accuracy without increasing the calculation burden. be able to.
The main scanning direction magnification can be easily calculated based on an approximate expression in the main scanning direction magnification at an arbitrary position in the main scanning direction. Since the correction magnification is set based on this, correction can be performed with high accuracy. Also, if the main scanning direction magnification at each position in the main scanning direction is calculated based on a first-order approximate expression set assuming that the main scanning direction magnification changes linearly , the calculation burden can be reduced. High-speed processing is possible.

According to the present invention, by converting the obtained amount of color misregistration in the main scanning direction magnification as the magnification change of the linear main scanning direction, a main by linear interpolation on the basis of the conversion has been the main scanning direction magnification Since the correction magnification is set according to the position in the scanning direction , the image is enlarged or reduced in the main scanning direction, and the enlargement / reduction magnification changes depending on the position in the main scanning direction. The color shift to be performed can be corrected with high accuracy without increasing the calculation burden.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a color image forming apparatus to which the present invention is applied. The color image forming apparatus includes an image forming unit 1 that forms an image on a recording sheet through processes of charging, exposure, development, transfer, and fixing. The recording paper stored in the cassette is sequentially fed through the paper feeding path A, and the recording paper on which a required image is formed by the image forming unit 1 is discharged onto the tray of the paper discharging unit 3 through the paper discharging path B. The

  The image forming unit 1 includes a plurality of process units (image forming units) 11 to 14 that form toner images for the respective color components of yellow, magenta, cyan, and black, and the photosensitive drums 11a of the process units 11 to 14. And an LSU (laser scanning unit, exposure means) 16 that scans a light beam for exposure with respect to the image forming planes ˜14a.

  In each of the process units 11 to 14, an electrostatic latent image is formed by scanning an exposure light beam from the LSU 16 on the image forming surfaces of the photosensitive drums 11a to 14a uniformly charged by a charger. The electrostatic latent images on the photosensitive drums 11a to 14a are developed with toner supplied from a developing device, and single color toner images for each color component are formed on the image forming surfaces of the photosensitive drums 11a to 14a.

  Further, the image forming unit 1 displays an intermediate transfer belt 23 wound around a pair of support rollers 21 and 22 and toner images for each color formed on the photosensitive drums 11a to 14a of the process units 11 to 14, respectively. The primary transfer rollers 24 to 27 for each color to be transferred to the intermediate transfer belt 23 and the toner images for each color are sequentially transferred by the primary transfer rollers 24 to 27 so that the toner superimposed on the intermediate transfer belt 23 is superposed. And a secondary transfer roller 28 for transferring the image onto the recording paper. The recording paper on which the toner image superimposed by the secondary transfer roller 28 is transferred is transported to the fixing device 19 where the toner image is fixed on the recording paper by heat and pressure.

  A registration roller 31 for aligning the toner image on the intermediate transfer belt 23 and the recording paper is provided on the upstream side of the secondary transfer portion 29 by the nip portion between the secondary transfer roller 28 and the support roller 21. Accordingly, the recording paper feed timing is adjusted based on the detection result of the registration sensor for recording paper (not shown).

  Also, in the vicinity of the secondary transfer unit 29, a registration sensor that detects a color shift caused by a positional shift of a toner image for each color that has been imaged by each of the process units 11 to 14 and transferred onto the intermediate transfer belt 23. 32 and a belt origin sensor 33 for determining the origin position of the intermediate transfer belt 23 are disposed. The origin sensor 33 is disposed opposite to the belt origin mark provided on the side edge outside the image forming area of the intermediate transfer belt 23, and the origin position of the intermediate transfer belt 23 is determined with reference to the belt origin mark. Detect.

  FIG. 2 is a schematic diagram showing a procedure for detecting a color shift by the registration sensor shown in FIG. The positional deviation of the toner image for each color is performed by causing the resist sensor 32 to read the resist patterns 41 and 42 formed by the process units 11 to 14 and transferred onto the intermediate transfer belt 23. The registration sensors 32 are provided at a total of three positions, in the vicinity of both edge portions of the intermediate transfer belt 23 and in the center position in the width direction of the intermediate transfer belt, and the corresponding main scanning direction of the intermediate transfer belt. Resist patterns 41 and 42 are formed at positions in the (width direction), respectively.

  Here, the images of the patterns 41a to 41d and 42a to 42d for the respective colors of yellow, magenta, cyan, and black formed by the process units 11 to 14 are sequentially transferred onto the intermediate transfer belt 23, and the black pattern From the detection timings of 41a and 42a and the detection timings of cyan patterns 41b and 42b, magenta patterns 41c and 42c, and yellow patterns 41d and 42d, yellow, magenta and cyan based on black A relative displacement amount for each color is obtained.

  In addition, the first pattern 41 and the second pattern 42 are opposite to each other in the inclination direction. When the first and second patterns 41 and 42 have different detection timing shifts, the main scanning direction is used. It is possible to confirm that there is a positional shift in the sub-scanning direction when the detection timing shift is the same in both the first and second patterns.

  FIG. 3 is a block diagram illustrating a schematic configuration of a main part related to control in the image forming apparatus illustrated in FIG. 1. The image forming apparatus includes a host controller 51 that comprehensively controls the operation of the image forming apparatus and an engine controller 52 that controls various operations for image formation on recording paper, and is connected to a network. The host controller 51 performs necessary image processing based on the print data received in response to the print request from the PC 53, and the engine controller 52 performs image formation processing based on the image data obtained thereby.

  The engine controller 52 includes an electrophotographic process control unit 54 that comprehensively controls the electrophotographic process in the image forming unit 1 shown in FIG. 1, a fixing control unit 55 that controls a fixing operation by the fixing device 19, and a paper feeding unit. Controls a series of correction operations including color misregistration correction, a sheet feeding / conveying control unit 56 for controlling sheet feeding and conveying operations by 2 and other conveying rollers, an LSU control unit 57 for controlling laser scanning by the LSU 16 and the like. An image correction controller (correction control means) 58, a printed sheet counter 59 for counting the number of printed sheets, and an engine CPU 60 for comprehensively controlling the operations of these units.

  A registration sensor 32 and a belt origin sensor 33 are connected to the image correction controller 58 via an AD converter 61. These sensors 32 and 33, the image correction controller 58, the LSU control unit 57, the engine CPU 60, and the print The number counter 59 constitutes an image correction control unit (image correction control means) 62. The image correction control unit 62 executes the correction operation when a predetermined correction execution condition is satisfied, for example, when the power is turned on or when the count value of the print sheet counter 59 reaches a predetermined number (for example, 300 sheets). .

  FIG. 4 is a conceptual diagram showing a state of image enlargement / reduction due to an attachment error between the LSU and the photosensitive drum shown in FIG. In the LSU 16, after a light beam from a built-in light source (not shown) is deflected by a deflector, a lens group that forms an image of the light beam on the scanned surface of the photosensitive drums 11a to 14a, and the light beam are exposed. The image forming surface of the photosensitive drums 11a to 14a is irradiated through a scanning optical element such as a folding mirror guided to the surface to be scanned of the body drum, and this light beam is spread in a fan shape in the main scanning direction.

  For this reason, when the photosensitive drums 11a to 14a are displaced from the normal positions with respect to the LSU 16, images are formed on the scanned surfaces of the photosensitive drums 11a to 14a in a state where the images are enlarged or reduced in the main scanning direction. As shown in (A) and (B), when the photosensitive drums 11a to 14a are displaced in a tilted state from the normal positions, the enlargement / reduction magnification changes according to the position in the main scanning direction.

  In the example shown in (A), the image is reduced in a region where the surface to be scanned is located in front of the normal position with respect to the LSU 16 (direction in which the surface to be scanned approaches LSU) due to the inclination of the photosensitive drums 11a to 14a. In the region where the surface to be scanned is located on the rear side of the normal position, the image is enlarged, and in this case, the end side is located on the rear side from the start side of the main scan. The magnification gradually increases in accordance with the scanning direction (right direction in the figure).

  In the example shown in (B), since the entire scanned surface of the photoconductive drums 11a to 14a is located behind the normal position, the image is formed in an enlarged state over the entire main scanning width. On the contrary, when the entire surface to be scanned is located in front of the normal position, the image is formed in a reduced state over the entire main scanning width.

  Such a change in magnification in the main scanning direction causes an image position shift for each color, that is, a color shift. In order to suppress this, the main scan direction of the image for each color is detected from the detection timing of the resist pattern shown in FIG. Position deviation amount (color deviation amount) is obtained, and based on the magnification correction amount (correction magnification) for each color obtained from the position deviation amount, the exposure timing in the LSU 16, specifically in the main scanning direction, is obtained. Processing for correcting the writing start position and the writing clock frequency (lighting timing of the light source in the LSU 16) is performed.

  FIG. 5 is a conceptual diagram for explaining the outline of color misregistration correction in the image forming apparatus shown in FIG. By detecting the resist patterns 41a to 41d and 42a to 42d shown in FIG. 2 with the resist sensor 32, the color misregistration amount at each resist sensor 32 is obtained, and the color misregistration amount at each position in the main scanning direction. Changes in a curve as shown in FIG. On the other hand, since the color shift phenomenon in which the enlargement / reduction magnification changes according to the position in the main scanning direction is mainly caused by the inclination of the photosensitive drums 11a to 14a with respect to the LSU 16, as shown in FIG. The magnification in the main scanning direction is considered to change linearly according to the position in the main scanning direction.

Therefore, the relationship between the magnifications ML, MC, and MR at each sensor position is expressed by a linear expression (approximate expression), which is expressed by the following expression.
MR + ML = MC × 2 (Formula 1)
Furthermore, the color misregistration amount at each position in the main scanning direction is an integral value of a linear expression indicating a magnification, and the difference between the color misregistration amount ΔXR at the right sensor position and the color misregistration amount ΔXL at the left sensor position. Is equivalent to the sum of the area LC and the area CR shown in (B), and is expressed by the following expression by the magnification ML / MC / MR at each sensor position and the separation distance PLR between the left and right sensors.
ΔXR−ΔXL = MC × 2 × PLR / 2 (Formula 2)
ΔXR−ΔXL = (ML + MR) × PLR / 2 (Formula 3)
The difference between the color shift amount ΔXC at the center sensor position and the color shift amount ΔXL at the left sensor position corresponds to the area LC shown in FIG.
ΔXC−ΔXL = (ML + MC) × PLR / 4 (Formula 4)

From the above equations, the magnifications ML, MR, and MC at the left, right, and center sensor positions are expressed as follows, and the color shift amounts ΔXL, ΔXR, and ΔXC at each sensor position are The magnification ML / MR / MC at the position can be obtained.
MC = (− ΔXL + ΔXR) / PLR (Formula 5)
MR = (ΔXL−4 × ΔXC + 3 × ΔXR) / PLR (Formula 6)
ML = (− 3 × ΔXL + 4 × ΔXC−ΔXR) / PLR (Expression 7)

  Based on these mathematical formulas, the magnification ML, MR, and MC at each sensor position are obtained, and the magnification at any position between the sensor positions is linear in the main scanning direction according to the position in the main scanning direction. Can be obtained by linear interpolation. When the magnification at the required position in the main scanning direction is obtained in this way, the magnification correction value at each position in the main scanning is obtained based on the value of the magnification.

  FIG. 6 is a diagram illustrating an example of color misregistration correction in the image forming apparatus illustrated in FIG. The correction magnification (magnification correction value) is obtained for each block divided into a plurality in the main scanning direction, and correction processing is performed in the block based on a fixed correction magnification. At this time, the correction magnification for each block is set based on the magnification at the center position of each block.

  When the amount of color shift before correction changes as shown in (A), as shown in (B), a correction magnification is set for each block, and when correction processing is performed with this correction magnification, The shift amount is as shown in (C), and although a color shift slightly appears in each block, a practically sufficient accuracy can be obtained.

  FIG. 7 is a conceptual diagram illustrating a modification of color misregistration correction in the image forming apparatus shown in FIG. In the example described with reference to FIG. 5, the magnification calculation formula for obtaining the magnification ML, MR, and MC at each sensor position has a sufficiently high accuracy in practice. Since it does not take into consideration that the separation distance PLR of the sensor changes, the error increases as the value of the correction magnification increases, and when the accuracy needs to be further increased, the following calculation formula It is good to use.

As described above, the magnification MC at the center sensor position obtained based on the linear expression (approximate expression) is expressed by the following expression.
MC = (ΔXR−ΔXL) / PLR (Formula 5)
On the other hand, the magnification MC2 at the center sensor position obtained by manual calculation in consideration of the change in the separation distance PLR between the left and right sensors due to the positional deviation in the main scanning direction is expressed by the following equation.
MC2 = 1−PLR / (ΔXR−ΔXL + PLR) (Formula 8)

Here, the error component ΔMC is expressed by the following equation.
ΔMC = MC2-MC (Formula 9)
The corrected magnifications MC ′ · MR ′ · ML ′ taking this error component ΔMC into consideration are obtained by adding the error component ΔMC to the magnifications MC · MR · ML at the respective sensor positions shown in the above formulas 5, 6 and 7. It can be as follows:
MC ′ = (− ΔXL + ΔXR) / PLR + ΔMC
= 1−PLR / (ΔXR−ΔXL + PLR) (Formula 10)
MR ′ = (ΔXL−4 × ΔXC + 3 × ΔXR) / PLR + ΔMC
= (ΔXL-4 × ΔXC + 3 × ΔXR) / PLR + 1−PLR / (ΔXR−ΔXL + PLR) − (ΔXR−ΔXL) / PLR (Formula 11)
ML ′ = (− 3 × ΔXL + 4 × ΔXC−ΔXR) / PLR + ΔMC
= (− 3 × ΔXL + 4 × ΔXC−ΔXR) / PLR + 1−PLR / (ΔXR−ΔXL + PLR) − (ΔXR−ΔXL) / PLR (Formula 12)

  The phenomenon that the image is enlarged or reduced in the main scanning direction on the scanned surfaces of the photosensitive drums 11a to 14a is caused by the photosensitive drums 11a to 14a being inclined from the normal position as described above. In addition to this, even when the position accuracy of a scanning optical element such as a folding mirror incorporated in the LSU 16 is insufficient, the light beam position of the LSU 16 is relatively inclined.

In this embodiment, as described above, the correction operation for the magnification error in the main scanning direction is performed as the color misregistration correction method in the color image forming apparatus. However, this can also be applied to a single color image. In this case, the above formulas may be replaced as follows.
△ XC = 0
ΔXR applies the following values.
In the image on the recording paper, a value obtained by subtracting the theoretical distance from the actual image distance on the recording paper at the central position in the main scanning direction (corresponding to the sensor C position) and the right position in the main scanning direction (corresponding to the sensor R position). And
The following values are applied to ΔXL.
In the image on the recording paper, ΔXL is a value obtained by subtracting the actual image distance on the recording paper from the theoretical distance between the central position in the main scanning direction (corresponding to the sensor C position) and the left position in the main scanning direction (corresponding to the sensor L position). And

  If this calculation example is applied to a monochromatic image, even when the light beam position accuracy of the LSU 16 is insufficient, the calculation burden for correcting the magnification error in the main scanning direction can be reduced. However, high-speed processing is possible, and an increase in manufacturing cost can be suppressed.

  The color image forming apparatus and the color misregistration correction method according to the present invention are arranged so that the image is enlarged / reduced in the main scanning direction, and the enlargement / reduction magnification is changed according to the position in the main scanning direction. The resulting color misregistration has the effect of being able to correct with high accuracy without increasing the computational burden so much, and the individual photoconductors for each color are individually scanned by the laser beam by the exposure means for the photoconductor for each color. It is useful as a color image forming apparatus configured to form an image, such as a color printer or a color copying machine.

Schematic sectional view showing an image forming apparatus to which the present invention is applied Schematic diagram showing the point of detecting color misregistration by the registration sensor shown in FIG. 1 is a block diagram showing a schematic configuration of a main part related to control in the image forming apparatus shown in FIG. FIG. 1 is a conceptual diagram showing a state of image enlargement / reduction due to an attachment error between the LSU and the photosensitive drum shown in FIG. 1 is a conceptual diagram for explaining an outline of color misregistration correction in the image forming apparatus shown in FIG. FIG. 3 is a diagram illustrating an example of color misregistration correction in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a conceptual diagram illustrating a modification example of color misregistration correction in the image forming apparatus illustrated in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation parts 11-14 Process unit 11a-14a Photosensitive drum 23 Intermediate transfer belt 32 Registration sensor (Color misregistration detection means)
41a to 41d, 42a to 42d Registration pattern 58 Image correction controller (correction control means)
59 Print counter

Claims (2)

A color image forming apparatus that forms a color image using a process unit for each color that individually forms an image on the photoconductor for each color by scanning with a laser beam by an exposure unit for the photoconductor for each color,
Pattern image forming means for forming a resist pattern image at a plurality of positions in the main scanning direction for each color by the process unit when a correction execution condition including color misregistration correction is satisfied, and transferring the image onto an intermediate transfer belt When,
Pattern image detecting means for detecting the resist pattern image for each color formed by the pattern image forming means at a total of three points, that is, a position near both ends in the main scanning direction and a center position in the main scanning direction ;
Color shift amount acquisition means for acquiring the color shift amount at each position for each color at the detection timing of the resist pattern image by the pattern image detection means,
The color misregistration amount acquired by the color misregistration amount acquisition unit is converted into a main scanning direction magnification as a linear magnification change in the main scanning direction, and the main scanning direction is obtained by linear interpolation based on the converted main scanning direction magnification. A correction control unit configured to perform correction processing of the color misregistration amount by setting a correction magnification according to the position of the image and changing an exposure timing of the laser beam by the exposure unit. apparatus. In a color image forming apparatus that forms a color image using a process unit for each color that individually forms an image on the photoconductor for each color by scanning laser light by an exposure unit for the photoconductor for each color,
When correction execution conditions including color misregistration correction are satisfied, a resist pattern image is formed at a plurality of positions in the main scanning direction for each color by the process unit, and this is transferred onto an intermediate transfer belt.
The transferred resist pattern image for each color is detected at a total of three points in the vicinity of both ends in the main scanning direction and the center position in the main scanning direction ,
The amount of color misregistration at each position is obtained for each color according to the detection timing of the detected resist pattern image,
The obtained color misregistration amount is converted into a main scanning direction magnification as a linear magnification change in the main scanning direction , and correction according to the position in the main scanning direction is performed by linear interpolation based on the converted main scanning direction magnification. A color misregistration correction method comprising: setting a magnification, changing an exposure timing of laser light by the exposure unit, and performing the correction processing of the color misregistration amount.

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