JPH103188A - Color image forming equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To positively correct the position even a fluctuating dot positional deviation of resist having a specific period and irregularities in a pitch as well. SOLUTION: Plural image forming means 1K-1Y are arranged along a carrying belt 7 and resist position correcting resist marks are formed on the carrying belt by the respective image forming means, to detect a resist positional deviation by a detecting sensor 10 and correct the resist position of each image forming means. A resist position correcting part 20 extracts a stationary resist positional deviation component and a variable resist positional deviation component having a specific period, from the result of the detection of the resist marks, to correct the position with respect to each of the extracted resist positional deviations. Thus, not only a stationary resist positional deviation is corrected but also the position are positively corrected in a variable resist positional deviation having the specific period and the irregularities in the pitch as well.

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 in a copying machine, a printer, a facsimile machine and the like.

[0002]

2. Description of the Related Art FIG. 14 is a diagram showing a main part of an example of a conventional color image forming apparatus. As is well known, different colors (yellow (Y), magenta (M), cyan (C) ), Black (K)) image forming units 1Y, 1M, 1C, and 1K are arranged in a line along the transport belt 7 that transports the recording paper 11. Conveyor belt 7
Is driven by a driving roller, one of which is driven to rotate, and the other is driven rollers 8 and 9 which are driven rollers that are driven to rotate, and is driven to rotate in the direction of the arrow by the rotation of the conveying roller. Below the conveyor belt 7, a paper feed tray 12 in which recording paper 11 'is stored is provided. The recording paper 11 at the uppermost position among the stored recording papers 11 ′ is fed at the time of image formation and is attracted onto the transport belt 7 by electrostatic attraction. The sucked recording paper 11 is transported to the first image forming unit (yellow) 1Y, where a yellow image is formed.

The first image forming section 1Y includes a photosensitive drum 2
And a charging device 3Y, an exposure device 4Y, a developing device 5Y, a cleaning device 6Y, and the like arranged around the photosensitive drum. The surface of the photosensitive drum 2Y is
After being uniformly charged, the exposure unit 4Y exposes the laser light 16Y corresponding to the image of each color to form an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 5Y,
A toner image is formed on the photosensitive drum 2Y. The toner image is transferred by the transfer device 13Y at a position (transfer position) where the toner image contacts the recording paper on the photosensitive drum and the conveyance belt, and a single color (yellow) image is formed on the recording paper. After the transfer, the photosensitive drum is cleaned of the toner remaining on the drum surface by the cleaning device 6Y, and is ready for the next image formation.

The recording paper 11 onto which the monochromatic image (yellow) has been transferred by the first image forming section 1Y is conveyed by the conveying belt 7 to the second image forming section (magenta) 1M. Here, similarly, the toner image (magenta) formed on the photosensitive drum 2M is transferred onto the recording paper in a superimposed manner. The recording paper further includes a third image forming unit (cyan) 1
C, the toner image is conveyed to the fourth image forming unit (black) 1K, and the similarly formed toner image is transferred to form a color image. The recording paper on which the color image has been formed after passing through the fourth image forming unit is peeled off from the transport belt 7, fixed by the fixing device 14, and then discharged onto the paper discharge tray 15.

FIG. 15 shows an exposure unit 4 (4Y, 4M, 4C, 4C).
4K) and a photoreceptor drum 2 (2Y, 2M, 2C, 2K). Image signals corresponding to a single-color image pattern obtained by color-separating a color image into four-color image patterns are sequentially sent from the image processing unit 40 (FIG. 14) to the laser light source 31 in accordance with the image forming timing. The laser light source 31 generates the laser light 16 in synchronization with the image signal. The laser light 16 is reflected by the rotating polygon mirror 30, then reflected by the reflection mirror 32, and scans the photosensitive drum 2 in a direction parallel to the rotation axis (main scanning direction: arrow A direction). This laser beam
At the same time as the main scanning, the scanning in the direction perpendicular to the main scanning direction (sub-scanning direction: arrow B direction) is also performed by the rotation of the photosensitive drum.

FIG. 6 is a perspective view of the exposure device and the photosensitive drum portion of the image forming apparatus shown in FIG. In the above-described conventional optical writing system, in order to correct the inclination of the reflection mirror 32,
An actuator 33 that can drive the reflection mirror 32 in the direction of the arrow is provided, and the inclination of the laser beam is corrected by driving the actuator 33.

In the above-described color image forming apparatus, if the installation interval, the installation position, the installation angle, etc. between the respective image forming units deviate from the ideal position, the output image will have a color shift (registration position shift) and the output image quality will be poor. Had been lowered. Therefore,
Before performing normal image formation, each image forming unit forms a registration mark on the conveyor belt, obtains a registration position deviation amount of each color from a detection result of the registration mark, and performs a registration position correction method. I have.

FIG. 16 is a schematic diagram for explaining this registration position correction method. Each image forming unit 1 (1Y, 1
M, 1C, 1K) form registration marks 18 of each color on the conveyor belt 7. Formed resist mark 18
Is detected by the registration mark detection sensor 10 disposed further downstream of the most downstream image forming unit 1K, and is used to determine the amount of deviation of the registration position of each color. The pattern for the registration mark is shown in FIG.
0 is stored in the memory. A controller (not shown) that controls the entire image forming apparatus reads a pattern (1) for a registration mark from this memory before normal image formation, and generates an image signal so as to generate a registration mark in each image forming unit. Send.

Each of the image forming units 1 (1Y to 1K) forms a registration mark 18 on the conveyor belt 7 by this signal, and the formed registration mark 18 is detected by a registration mark detection sensor 10. The detection signal detected by the registration mark detection sensor 10 is sent to the registration position correction unit 20. The registration position correction unit 20 performs signal processing on the input detection signal to determine the amount of positional deviation of each color, and based on the determined amount of positional deviation, outputs a correction signal to the image processing unit 40 and each image forming unit 1 (1Y, 1Y). 1M, 1C, 1K). The image forming unit 40 corrects the write timing of each color image signal to be sent to the image forming unit based on the correction signal. Further, in the image forming unit 1, based on the correction signal,
Scanning angle (tilt) of the laser beam that scans the photosensitive drum 2
Is corrected.

Before explaining the method of correcting the registration position of the color image forming apparatus, the color shift (register position shift) of the color image forming apparatus of the type in which the image forming units are juxtaposed.
I will explain the factors. FIG. 17 is a schematic diagram for explaining the cause of the color shift. In FIG. 17, the direction of arrow A indicates the position of the output image in the main scanning direction, and the direction of arrow B indicates the position in the sub-scanning direction. The solid line indicates the position of an ideal (regular) image, and the broken line indicates the position of the image deviated from the ideal value. FIG. 17A shows a case where a position shift has occurred in the direction of arrow B from the normal write start position (position shift in the sub-scanning direction), which is caused by a shift in the write start timing of each image forming unit. . FIG. 17B shows a case where a position shift has occurred in the direction of arrow A from the normal writing position (position shift in the main scanning direction), which is caused by a shift in the scanning start timing in the main scanning of each image forming unit. Is what you do. FIG. 17C shows a case in which the photosensitive drum is shifted obliquely with respect to the normal main scanning direction (skew). The photosensitive drum is shifted due to a shift in the mounting angle of the exposure device or the inclination of the rotating shaft of the photosensitive drum. This is because the scanning line of the laser beam that scans the drum is tilted. FIG.
(D) shows a case where a magnification error occurs in the normal writing direction, which is caused by an error in the optical path length between the laser light source and the peripheral surface of the photosensitive drum.

Next, a specific method of the resist position correction method will be described. FIG. 18 is a block diagram for explaining a registration position correction method performed by the registration position correction unit 20. The detected registration mark detection signal is input to the registration position correction unit 20. Since this detection signal contains various noise components, the signal processing unit 21 removes a signal component unnecessary for position shift detection. Further, the position deviation amount 23a in the sub-scanning direction, the position deviation amount 23b in the main scanning direction, the magnification error 23c, and the skew amount 23d are calculated based on this signal. In calculating these displacement components, the pattern formation of the registration mark may be changed as appropriate so that each displacement amount can be easily calculated. The calculated position shift amounts are subjected to signal processing so as to correct the position shifts, and are output as correction signals.

A position correcting section 24a in the sub-scanning direction shown in FIG.
Outputs a correction signal to the image processing unit 40 to correct the image writing timing in the sub-scanning direction. The position correction unit 24b in the main scanning direction similarly outputs a correction signal to the image forming unit 40, and corrects the write timing in the main scanning direction. Similarly, the magnification error correction unit 24c
The correction signal is output to the image processing unit 40 to correct the frequency of the write clock. The skew correction unit 24d outputs a correction signal to the image forming unit 1. The image forming unit (the exposure unit 4), based on the input correction signal,
2 is corrected, and the scanning inclination of the laser beam that scans the photosensitive drum is corrected. In FIG. 15, the reflection mirror 32
In order to correct the inclination of the laser beam, an actuator 33 capable of driving the reflection mirror in the direction of arrow C is provided, and the inclination of the laser beam scanning is corrected by driving the actuator.

The registration mark correction is performed by detecting a positional shift of the remaining three registration marks with respect to a reference registration mark (for example, black). The shift of the yellow, magenta, and cyan resist positions with respect to the black resist position is detected.
The registration position is corrected so that the registration positions of the three colors are adjusted based on the detection result. That is, yellow, magenta,
By performing the processing shown in FIG. 18 for each color of cyan, the resist positions of the remaining three colors match the black resist positions.
As described above, before forming a normal color image, a registration mark is formed and detected, and registration position correction is performed.
In the subsequent image formation, a color image free from color misregistration is obtained.

[0014]

The conventional registration position correcting method in the color image forming apparatus of the type in which the image forming units are juxtaposed has been described above. Conventionally, the registration position correction is limited to the correction of the constant registration position deviation. However, in actuality, the registration position deviation detected by the registration mark detection sensor, the mounting accuracy of each unit, and the environmental temperature fluctuation. However, the present invention is not limited to such a situation that the resist position is constantly shifted. That is,
A variable registration position shift having a specific cycle caused by a change in the rotation speed of each photosensitive drum or a change in the transport speed of the transport belt is also included. This sometimes resulted in a dot position shift of each color.

The present invention has been made in view of the above-mentioned circumstances, and not only corrects a steady registration position deviation performed in the prior art, but also has a variable fluctuation having such a specific period. It is intended to obtain a high-quality color image with no registration position deviation more positively than conventional stationary position correction only by positively correcting the position with respect to a large dot position deviation and pitch unevenness. .

[0016]

According to a first aspect of the present invention, a plurality of image forming means disposed along a conveyor belt form a registration mark for register position correction on the conveyor belt, and the formed registration marks are formed on the conveyor belt. In a color image forming apparatus including a detection sensor that reads a registration mark and a registration position correcting unit that detects a registration position deviation based on an output of the detection sensor and corrects a registration position of each image forming unit, An image processing means for storing a pattern of a second registration mark for correcting a variable registration position deviation, in addition to a first registration mark pattern for correcting a registration position deviation, and a detection result of each registration mark. Extract and extract the steady resist position shift component and the variable resist position shift component having a specific period. A resist position correcting means for correcting the position of each resist position shift is provided, so that not only a steady resist position shift is corrected but also a variable resist position shift having a specific cycle. Is corrected so as to obtain a high-quality color image with no registration position deviation.

According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, the first registration mark and the second registration mark are generated independently. A stable resist position shift component and a variable resist position shift component can be reliably extracted, and highly accurate resist position correction can be performed by independently performing resist position correction.

According to a third aspect of the present invention, in the color image forming apparatus according to the first or second aspect, the image processing means first outputs the pattern of the second registration mark, and the registration position correcting means outputs the second registration mark pattern. The image forming unit outputs the pattern of the first registration mark, and the registration position correction unit corrects the steady position deviation based on the pattern. By correcting steady-state displacement, and then performing steady-state displacement correction, performing steady-state displacement detection in a state where there is no variable displacement, thereby achieving high accuracy. Position deviation can be detected, and as a result, steady position deviation can be corrected with high accuracy.

According to a fourth aspect of the present invention, there is provided a color image forming apparatus for forming a color image by arranging a plurality of image forming means along a conveyor belt, wherein each of the image forming means comprises a registration mark for correcting a registration position. Is formed on the conveyor belt,
A color image forming apparatus including a detection sensor that reads the formed registration mark, detecting a registration position shift based on an output of the detection sensor, and including a registration position correction unit that corrects a registration position of each image forming unit. Means for extracting a steady registration position shift component and a variable registration position shift component having a specific period from the detection result of the registration mark, and registration position correction for correcting the position of each extracted registration position shift. In addition to correcting steady-state registration position deviation, it actively performs position correction with respect to variable registration position deviation and pitch unevenness having a specific cycle. It is intended to obtain a high-quality color image with no further registration position deviation than in the case of only regular position correction. .

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, a registration mark for detecting a steady registration position deviation component and a variable registration position deviation component having a specific synchronization are detected. The feature is that each of the registration marks is independently generated, thereby independently generating a registration mark for detecting a constant registration position deviation and a registration mark for detecting a variable registration position deviation, thereby providing a constant registration mark. The resist position shift component and the variable resist position shift component can be reliably extracted, and highly accurate resist position correction can be performed by independently performing the resist position correction.

According to a sixth aspect of the present invention, in the fourth or fifth aspect of the present invention, after performing the resist position correction for the variable resist position deviation, a steady resist position deviation component is detected, and On the basis of this, the registration position correction is performed for the steady registration position deviation, and the variable position deviation is corrected, and then the fixed position deviation correction is performed. In such a case, steady positional deviation detection is performed in a state where no positional deviation is detected, so that accurate positional deviation detection can be performed, and as a result, the accuracy of fixed positional deviation correction is performed with high accuracy. is there.

According to a seventh aspect of the present invention, there is provided a color image forming apparatus for forming a color image by arranging a plurality of image forming means provided with a photoreceptor along a conveyor belt. A registration sensor is formed on the conveyor belt for forming a registration mark for correction, and a detection sensor for reading the formed registration mark is provided. A registration position shift is detected based on an output of the detection sensor, and the image forming position of each image forming unit is corrected. In the color image forming apparatus provided with a position correcting means, the position correcting means detects a steady registration position deviation component from the detection result of the registration mark, and corrects the registration position based on the detection result. The position correction value means detects a variable dot position deviation component having a specific cycle, and corrects the dot position in the sub-scanning direction based on the detection result. A second correction means is provided, which not only corrects a regular registration position deviation, but also positively corrects a variable dot (registration) position deviation having a specific cycle. Is performed to obtain a high-quality color image with no registration position deviation as compared with the conventional steady position correction alone.

According to an eighth aspect of the present invention, in the invention of the seventh aspect, after the position is corrected by the second position correcting means, the position is corrected by the first correcting means. After correcting the fluctuating dot position shift, by performing steady registration position shift correction, steady position shift detection is performed in a state where there is no fluctuating position shift. The displacement can be detected, and as a result, the accuracy of the steady position displacement correction is also performed with high accuracy.

According to a ninth aspect of the present invention, in the invention of the seventh or eighth aspect, the detection of the variable dot displacement component having a specific cycle, which is performed by the second position correcting means, is performed by a photoconductor and / or It is based on the detection result of the speed fluctuation of the conveyor belt, so that the speed fluctuation of the photosensitive drum or the conveyor belt is directly detected (the fluctuation of the position of the photosensitive drum or the speed of the conveyor belt is changed. Since the ratio due to the fluctuation is large and the speed fluctuations are directly detected), the detection accuracy is high and the repetition period is made clear.

According to a tenth aspect of the present invention, there is provided an image forming means for irradiating an exposure beam reflected by a rotary polygonal mirror on a photosensitive drum to form and develop an electrostatic latent image, and the image forming means is provided on a conveyor belt. A plurality of toner images of a plurality of colors formed by the respective image forming apparatuses are transferred to transfer paper on a conveyor belt to form a color image. Detecting the speed fluctuation of the drum and / or the conveyor belt and controlling the rotation speed of each rotary polygon mirror in accordance with the detected speed fluctuation, whereby the speed fluctuation of the photosensitive drum irradiated with the exposure beam is obtained. , The rotation speed of the rotary polygon mirror is controlled based on the above, the pitch unevenness in the sub-scanning direction is eliminated, and a high-quality color image with no deviation of the dot position is obtained.

An eleventh aspect of the present invention is characterized in that, in the tenth aspect of the present invention, the rotation speed of the rotary polygon mirror is controlled in accordance with the detected low-frequency component of the speed fluctuation of the photosensitive drum and / or the transport belt. Thus, the rotation speed of the rotary polygon mirror is controlled based on the low-frequency component of the speed fluctuation of the photosensitive drum, and the speed control of the rotary polygon mirror is gradually performed, so that the rotation speed can be reliably controlled. It is like that.

According to a twelfth aspect of the present invention, in the tenth aspect, the reference frequency for determining the writing timing of the exposure beam in the main scanning direction is controlled according to the speed fluctuation of the photosensitive drum and / or the conveying belt. Thus, in the speed control of the rotary polygon mirror according to the seventh aspect, a dot position shift in the main scanning direction is eliminated, and a high-quality color image free from position shift in both the main scanning and the sub-scanning is obtained.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is an overall structural view for explaining an embodiment of a color image forming apparatus according to the present invention. In FIG. 1, different colors are used as in the prior art shown in FIG. The image forming unit 1 (1Y, 1M, 1C, 1K) for forming an image of (yellow, magenta, cyan, black)
The recording papers 11 are arranged in a line along the transport belt 7 that transports the recording paper 11. The transport belt 7 is bridged by transport rollers 8 and 9, one of which is a driving roller that rotates and the other is a driven roller that is driven and rotated.
Is driven to rotate in the direction of the arrow. Below the conveyor belt 7, a paper feed tray 12 in which recording paper 11 'is stored is provided.

The image forming section 1 includes a photosensitive drum 2 (2Y,
2M, 2C, 2K) and a charger 3 arranged around the same.
(3Y, 3M, 3C, 3K) and an exposure unit 4 (4Y, 4M,
4C, 4K), developing unit 5 (5Y, 5M, 5C, 5K),
The exposure device 4 includes a cleaning device 6 (6Y, 6M, 6C, 6K).
6M, 16C, and 16K) are emitted to the photosensitive drum 2. These image forming units 1 are controlled by an image processing unit 40 and a registration position correcting unit 20. On the downstream side of the conveyor belt 7, the fixing device 1
4 and a paper discharge tray 15 are provided. A registration mark detection sensor 1 is provided on the upper surface of the downstream end of the conveyor belt 7.
0 is installed.

The recording paper 11 at the uppermost position among the stored recording papers 11 'is fed at the time of image formation, and is attracted onto the transport belt 7 by electrostatic attraction. The sucked recording paper 11 is conveyed to the first image forming unit (yellow) 1Y, where a yellow image is formed. That is, after the surface of the photosensitive drum 2Y is uniformly charged by the charger 3Y, the laser beam 1 corresponding to each color image is exposed by the exposure device 4Y.
Exposure is performed at 6Y to form an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 5Y, and the photosensitive drum 2Y
A toner image is formed thereon.

The toner image is transferred by the transfer unit 13Y at a position (transfer position) where the toner image is in contact with the photosensitive drum 2Y and the recording paper 11 on the conveyor belt 7, and a single color (yellow image) is formed on the recording paper 11. After the transfer, the photosensitive drum 2Y is cleaned of the toner remaining on the drum surface by the cleaning device 6Y to prepare for the next image formation.

As described above, the recording paper 11 on which the monochromatic image (yellow) has been transferred by the first image forming section 1Y is conveyed by the conveying belt 7 to the second image forming section 1M. Here, similarly, the toner image (magenta) formed on the photosensitive drum 2M is transferred onto the recording paper 11 in a superimposed manner. The recording paper 11 is further conveyed to the third image forming unit 1C and the fourth image forming unit 1K, and similarly formed toner images are transferred to form color images. The recording paper 11 on which a color image has been formed after passing through the fourth image forming unit 1K is
After being separated from the transport belt 7 and fixed by the fixing device 14, the sheet is discharged to a sheet discharge tray 15.

According to the present invention, the operation and configuration of the register position correction unit 20 and the image processing unit 40 are the same as those shown in FIG.
Therefore, these will be described below. In FIG. 1, the image processing unit 40 stores two types of registration mark patterns in an internal memory. One of the two patterns (resist mark pattern (1)) is the same as the conventional technique,
It is used to perform position correction for a steady registration position deviation. The other pattern (registration mark pattern (2)) is a registration mark pattern for detecting a fluctuating registration position deviation.

The color image forming apparatus generates a registration mark before normal image formation, and performs registration position correction based on the detection result of the registration mark. In the present invention, first, a registration mark pattern (2) is generated. The registration mark pattern (2) is a pattern for correcting a variable registration position deviation having a cycle due to a periodic speed change of a drive system such as a photosensitive drum. That is, position fluctuation is corrected by rotationally driving the photosensitive drum 2 and the conveying rollers 8 and 9 having a large periodic position fluctuation factor. Therefore, it is desirable that the registration mark pattern (2) is a registration mark having a length corresponding to the circumference of the rotating body that is driven to rotate. In this specific example, a registration mark slightly longer than the circumference of the photosensitive drum 2 is generated.

FIG. 4 shows an example of the generated registration mark 41. The registration mark 41 is ideally a pattern in which lines are formed at equal intervals in the sub-scanning direction.
If there is a fluctuating resist position shift, the pitch interval of each line fluctuates. By measuring this pitch change, a fluctuating position shift amount can be detected. It is assumed that the variable positional deviation is a continuous function having a specific period that matches the period of the photosensitive drum.

FIG. 2 is a block diagram showing the internal processing of the registration position correction unit 20. In the figure, reference numeral 22 denotes a second signal processing unit, 25 denotes a position deviation fluctuation amount storage unit, and 26 denotes a position fluctuation correction unit. In addition, the same reference numerals as those in FIG. 18 are given to the portions that operate in the same manner as the conventional technology shown in FIG.

First, the correction operation based on the conventional registration mark pattern (1) will be described. The registration position correction unit 20 receives the detected registration mark detection signal. Since this detection signal contains various noise components, the signal processing unit 21 removes unnecessary signal components for position shift detection. Further, from this signal, the sub-scanning position shift calculating unit 23a, the main scanning position shift calculating unit 23b, the magnification error calculating unit 23c, and the skew calculating unit 23d are used.
The position deviation amount in the sub-scanning direction, the position deviation amount in the main scanning direction, the magnification error, and the skew amount are calculated.

In calculating these displacement components, the pattern formation of the registration mark may be changed as appropriate so that each displacement amount can be easily calculated. The calculated position shift amounts are subjected to signal processing so as to correct the position shifts, and the sub-scanning position correcting unit 24a, the main scanning position correcting unit 24b, the magnification error correcting unit 24c, and the skew correcting unit 2
4d outputs a correction signal.

The position correcting section 24a in the sub-scanning direction in FIG.
The correction signal is output to the image processing unit 40 to correct the image writing timing in the sub-scanning direction. Similarly, the position correction unit 24b in the main scanning direction outputs a correction signal to the image processing unit 40, and corrects the write timing in the main scanning direction. Similarly, the magnification error correction unit 24c outputs a correction signal to the image processing unit 40 and corrects the frequency of the write clock. The skew correction unit 24d outputs a correction signal to the image forming unit 1. Image forming unit (exposure unit 4)
Corrects the inclination of the reflection mirror 32 based on the input correction signal, and corrects the inclination of the scanning of the laser beam that scans the photosensitive drum 2.

Next, the correction operation based on the registration mark pattern will be described. The processing of the registration mark pattern (2) is performed in the lower blocks 22, 25, 2 in FIG.
6 is performed. The detection signal of the registration mark pattern (2) is input to the signal processing unit 22, where the signal is processed. The signal processing unit 22 obtains a change in pitch interval from the detected pattern signal, and calculates a periodic position change. The calculated periodic position fluctuation data is temporarily stored in the position deviation fluctuation amount storage unit 25 which is an internal memory.
The stored data indicating the positional deviation fluctuation is output from the storage unit in synchronization with the cycle, and sent to the position fluctuation correction unit 26. The position fluctuation correction unit 26 finely adjusts the angle of the reflection mirror 32 of the (exposure unit) of the image forming unit shown in FIG. 3 in synchronization with the periodic position fluctuation.

FIG. 3 is a perspective view of the exposure device and the photosensitive drum portion of the image forming apparatus shown in FIG.
Image signals corresponding to a single-color image pattern obtained by color-separating a color image into four-color image patterns are sequentially sent from the image processing unit 40 in accordance with the image forming timing. The laser light source 31 generates the laser light 16 in synchronization with the image signal. The laser light 16 is reflected by the rotating polygon mirror 30 and then reflected by the reflection mirror 32 to move the photosensitive drum 2 in a direction parallel to the rotation axis (main scanning direction: arrow A direction).
Scan. The laser beam also scans in the direction perpendicular to the main scanning direction (sub-scanning direction: arrow B direction) by the rotation of the photosensitive drum 2 at the same time as the main scanning. The actuator 33 drives the reflection mirror 32 in the direction of arrow C in order to correct the inclination of the scanning of the laser beam described above.

Further, in the configuration of the exposure device and the photosensitive drum shown in FIG. 3, an actuator 35 is provided to finely adjust the angle of the reflection mirror 32. Actuator 35
By slightly rotating the reflection mirror 32 in the direction of arrow D, the sub-scanning position of the laser beam that scans the photosensitive drum 2 can be changed. Since the angle adjustment of the reflection mirror 32 is constantly performed at the time of image formation, it is possible to correct the periodic displacement of the drive system such as the photosensitive drum.

The registration mark pattern (2)
Is performed prior to the above-described correction based on the registration mark pattern (1), and after correcting the variable positional deviation based on the registration mark pattern (2), the correction based on the registration mark pattern is performed in the same manner as in the related art. (1)
Is generated, and the above-described steady position shift correction is performed. At this time, steady positional deviation detection is performed in a state where there is no variable positional deviation, so that positional deviation detection with higher accuracy than in the related art can be performed. In other words, the accuracy of the steady-state positional deviation correction is also high.

As described above, according to the present invention, not only a steady registration position deviation is corrected, but also a position registration is positively corrected for a variable registration position deviation having a specific period. It is possible to obtain a high-quality color image with a small registration error with respect to the technology.

[Embodiments of Claims 7 to 9] FIG. 5 is a block diagram for explaining another embodiment of the present invention.
FIG. 14 shows a portion that operates in the same manner as the prior art shown in FIG.
In the embodiments of the present invention, the following description will be made focusing on the new portions by attaching the same reference numerals as in the case of FIG. Hereinafter, an embodiment of the present invention in a color image forming apparatus, and a method of correcting a registration position performed before normal image formation will be described.

As shown in FIG. 5, in the present invention, the rotation axis of the photosensitive drum 2 (2K, 2C, 2M, 2Y) in the image forming section 1 (1K, 1C, 1M, 1Y) is used. Speed detection 17 (17
K, 17C, 17M, 17Y). The speed detectors 17 are attached to the respective photosensitive drums, and detect speed fluctuations of the corresponding rotating shafts of the photosensitive drums. When the speed of the photosensitive drum changes, the exposure unit 4 (4
K, 4C, 4M, and 4Y) are output because the writing position shifts in accordance with the speed fluctuation or the transfer position shifts when the toner image formed on the photosensitive drum is transferred to the transfer paper 11. This appears as a dot position shift or pitch unevenness in the sub-scanning direction of the color image. In addition, the positional deviation and the pitch unevenness of the output image appear as a function having a specific cycle substantially coincident with the rotation cycle of the photosensitive drum.
In FIG. 5, the rotation detection of the photosensitive drum is detected by the speed detection unit, and this detection signal is output to the registration position correction unit 20.

FIG. 6 is a block diagram showing the internal processing of the registration position correction unit 20. The detection signal of the fluctuation of the rotation of the photosensitive drum is processed in the lower block of FIG. First, the input detection signal is input to the signal processing unit 27, where the signal is processed. The signal processing unit 27 removes a noise component and a high-frequency component from the detected speed fluctuation signal, and calculates only a periodic rotation fluctuation component of a low-frequency component. The calculated periodic speed fluctuation data is temporarily stored in the speed fluctuation amount storage unit 28 which is an internal memory. The stored speed fluctuation data is output from the storage unit in synchronization with the rotation position of the photosensitive drum, and sent to the position fluctuation correction unit 29. In the position fluctuation correction unit 29, the reflection mirror 32 of the image forming unit 1 (the exposure unit 4 thereof) is synchronized with the periodic speed fluctuation.
Finely adjust the angle of (Fig. 3).

As shown in FIG. 3, the relationship between the exposure device and the photosensitive drum is provided with an actuator 35 for finely adjusting the angle of the reflection mirror 32. Actuator 35
By slightly rotating the reflection mirror 32 in the direction of arrow D, the sub-scanning position of the laser beam that scans the photosensitive drum 2 can be changed. That is, the position variation correction unit 2
Numeral 9 operates to adjust the angle of the reflection mirror 32 based on the stored speed fluctuation data so as to correct a variable positional deviation of a specific cycle of the output image. FIG.
The processing in the speed detector 17 (17K, 17C,
17M, 17Y). This variable dot position correction is always performed at the time of normal image formation or at the time of steady position correction described below, and the position correction is always performed using the data stored in the speed fluctuation amount storage unit 28 once. .

While correcting such a variable dot position shift, a registration mark pattern (1) is generated in the same manner as in the prior art, and steady position shift correction is performed. At this time, since steady position shift detection is performed in a state where there is no fluctuating position shift, the position shift detection can be performed with higher accuracy than in the related art. That is, the accuracy of the steady positional deviation correction is also performed with high accuracy.

As described above, the present invention not only corrects a steady registration position deviation, but also positively corrects a variable dot position deviation having a specific period. It is possible to obtain a high-quality color image with a small registration error with respect to the technology.

In the above, the embodiment in which the speed fluctuation of the rotating shaft of the photosensitive drum is detected and the dot position is periodically corrected has been described. However, the conveying rollers 8 and 9 for driving the conveying belt 7 to rotate. Similarly, a speed detector for detecting rotation fluctuation may be provided on the rotating shaft, and the position may be corrected based on the detection result. Further, the photosensitive drum 2 (2K, 2C, 2M, 2
The same applies to the case of detecting the speed fluctuation of the drum surface and the conveying speed of the conveying belt in Y) and correcting the position based on the detection result.

The present invention has the advantage over the inventions according to claims 1 to 6 that the means for detecting a variable positional deviation is straightforward. The largest variation in the dot displacement of the output color image is caused by the variation in the speed of the photosensitive drum or the conveyance belt. Therefore, rather than extracting a variable position shift from the resist pattern, if the source of the variable position shift is directly detected as in the present invention, the detection accuracy is high, and the repetition period is also clear. As a result, variable positional deviation correction can be performed with high accuracy, and a high-quality color image can be obtained.

FIG. 7 is a diagram showing a main part of an embodiment of the present invention. FIG. 7 shows a part of the structure of an image forming section 1. Image forming unit 1
(1K, 1C, 1M, 1Y) to individually correct the exposure position with respect to the speed fluctuation of each photosensitive drum of the image forming unit.

In FIG. 7, the photosensitive drum 2 (2K, 2
C, 2M, 2Y) is provided with an encoder 50 for detecting its rotation speed. The encoder 50 generates a pulse signal (encoder signal ENC) in accordance with the rotation of the photosensitive drum 2, and detects the frequency of the pulse to detect the pulse signal.
Rotation speed can be obtained. The encoder signal ENC output from the encoder 50 is input to a frequency / speed converter (F / V converter) 51, which converts the encoder signal ENC into a speed signal V1 and converts the rotation signal into a rotation control circuit 52. Output to The rotation control circuit 52 generates a pulse PLS according to the input speed signal V1 and outputs it to the motor drive circuit 36. The motor drive circuit 36 rotates the polygon motor 37 in synchronization with the pulse signal PLS, and rotates the polygon mirror 30 at a rotation speed corresponding to the rotation speed fluctuation of the photosensitive drum 2.

Here, the speed signal V1 inputted to the rotation control circuit 52 is caused by, for example, a speed fluctuation of a drive motor for driving the photosensitive drum and an eccentricity of the photosensitive drum as shown in FIG. From two components, a relatively large speed variation (low frequency component) such as a speed variation and a relatively small speed variation (high frequency component) such as a speed variation caused by pitch unevenness of a gear driving the photosensitive drum. Has become. In addition, the speed fluctuation of the high-frequency component includes noise and the like included in the detection signal of the speed detection. This speed signal V1 is
For example, by passing only low-frequency components using the low-pass filter 52a shown in FIG. 9, a speed signal V2 as shown in FIG. 8B is obtained. Although FIG. 8 shows the speed fluctuation on the vertical axis in an enlarged manner, the actual fluctuation is very small.

The speed signal V from the low-pass filter 52a
2 is input to the reference pulse generator 52c. When the speed signal V2 from the low-pass filter is faster than the average speed V0 of the photosensitive drum as shown by V2 (a) in FIG. 8B, the reference pulse generator 52c is shown in, for example, FIG. 10A. Thus, the pulse period PLS (a) is made shorter than the average pulse PLS (average) for the average speed V0. Reducing the period of the reference pulse input to the motor drive circuit 36 means increasing the rotation speed of the polygon motor 37, and the writing timing is also increased. Conversely, when the speed signal V2 from the low-pass filter is slower than the average speed V0 of the photosensitive drum as shown by V2 (b) in FIG. 8B, the reference pulse generator 52C outputs the signal shown in FIG.
As shown in (1), the period of the pulse PLS (b) is lengthened, and the rotation speed of the polygon motor is reduced.

The reference pulse generator 52c is a generator for generating a reference pulse PLS of the rotation speed of the polycon motor by dividing the high-speed or reference clock signal from the reference clock generator 52b. It is constituted by a digital circuit capable of changing the frequency division ratio for frequency division corresponding to the speed V2. Further, in the above description, only two cases, that is, a case where the detection speed is high and a case where the detection speed is low, have been described. However, the rotation speed of the polygon motor is sequentially controlled according to the detected speed fluctuation, so that the writing in the sub-scanning direction is performed. The position can be corrected.

When the speed of the polygon motor is controlled in accordance with the speed fluctuation of the photosensitive drum, the scanning speed in the main scanning direction also changes in accordance with the rotation speed of the polygon motor. For example, as shown in FIG. The reference frequency for determining the light writing timing may be controlled according to the rotation speed of the photosensitive drum. The speed signal V1 indicating the speed fluctuation on the photosensitive drum 2 is input to the image frequency control circuit 60. The image frequency control circuit 60 changes the image frequency, which is the data writing frequency in the main scanning direction, according to the speed signal V1, and outputs the same as the clock signal WCLK to the LD drive circuit 61. The LD drive circuit 61 receives the synchronization detection signal DET from the synchronization detection sensor 34. LD
The drive circuit 61 determines the write timing in the main scanning direction based on the synchronization detection signal DET, and
The writing timing for each dot in the main scanning direction is determined based on K. The LD drive circuit 61 converts the image signal output from the image processing unit 40 according to these timings into
This is a drive signal for driving the LD. The LD 31 sends a laser beam to the photosensitive drum 2 in accordance with the drive signal to perform exposure.

Here, in the image frequency control circuit 60, for example, as shown in FIG. 12, the input speed signal V1 is input to the low-pass filter 60a, and the speed signal V3 consisting of only the low frequency component of the speed signal V1 is extracted. I do. Speed signal V3
Is input to a clock generator 60b that determines an image frequency, and the clock generator 62b generates a clock signal WCLK based on the speed signal V3. Here, the clock generator 60b
FIG. 13 shows that the speed of the polygon motor is increased when the speed signal V3 indicates a speed higher than the average speed V0.
As shown in (A), the write frequency is also increased (the cycle of the clock signal WCLK is shortened). Conversely, when the speed signal V3 indicates a speed lower than the average speed V0, the polygon motor rotates slowly.
As shown in FIG. 3B, the write frequency is reduced (the cycle of the clock signal WCLK is lengthened). The clock signal is generated from the clock generator by using a frequency synthesizer or V
CO or the like is used.

As described above, the rotation speed of the photosensitive drum is detected, and the rotation speed of the polygon motor is
The method of controlling the image frequency has been described. Similarly,
It is also possible to detect a speed fluctuation of the conveyor belt and control the rotation speed and the image frequency of the polygon motor according to the speed fluctuation. To detect the speed fluctuation of the transport belt, an encoder is attached to the rotating shaft of the transport roller, and the speed is detected using the encoder signal, similarly to the method of detecting the speed variation of the photosensitive drum.

The moving speed of the belt on the conveyor belt 7 may be directly detected. This method is effective when the speed fluctuation of the conveyor belt is large and the positional deviation or pitch unevenness caused by the speed fluctuation is large. Further, when the above-described correction is simultaneously performed on two speed fluctuations, that is, the speed fluctuation of the photosensitive drum and the speed fluctuation of the transport belt, a more effective correction can be performed.

As described above, by using the correction method of the present invention together with the steady registration position deviation correction method used in the prior art, it is possible to obtain a high-quality color image with less positional deviation than in the prior art. I can do it.

[0063]

According to the first aspect of the present invention, a plurality of image forming means arranged along the conveyor belt form registration marks for register position correction on the conveyor belt and read the formed register marks. In a color image forming apparatus including a detection sensor and a registration position correcting unit that detects a registration position deviation based on an output of the detection sensor and corrects a registration position of each image forming unit, a steady registration position deviation correction is performed. Image processing means for storing a second registration mark pattern for correcting a variable registration position deviation in addition to the first registration mark pattern, While extracting the resist position shift component and the variable resist position shift component with a specific period,
It is characterized by having a resist position correcting means for correcting the position of each of the extracted resist positional deviations, so that it not only corrects a steady positional deviation of the resist, but also
A variable registration position shift having a specific period is also corrected, and a high-quality color image free from registration position shift can be obtained.

According to a second aspect of the present invention, in the color image forming apparatus of the first aspect, the first registration mark and the second registration mark are generated independently. It is possible to reliably extract the steady resist position shift component and the variable resist position shift component, and perform the resist position correction with high accuracy by independently performing the resist position correction.

According to a third aspect of the present invention, in the color image forming apparatus of the first or second aspect, the image processing means first outputs the pattern of the second registration mark, and the registration position correcting means outputs the second registration mark pattern. The image forming unit outputs the pattern of the first registration mark, and the registration position correction unit corrects the steady position deviation based on the pattern. After correcting the fluctuating position deviation, the stationary position deviation correction is performed, so that the stationary position deviation detection is performed without the fluctuation position deviation. Position deviation can be detected, and as a result, steady position deviation correction can be performed with high accuracy.

According to a fourth aspect of the present invention, there is provided a color image forming apparatus for forming a color image by arranging a plurality of image forming means along a conveyor belt. Is formed on the conveyor belt,
A color image forming apparatus including a detection sensor that reads the formed registration mark, detecting a registration position shift based on an output of the detection sensor, and including a registration position correction unit that corrects a registration position of each image forming unit. Means for extracting a steady registration position shift component and a variable registration position shift component having a specific period from the detection result of the registration mark, and registration position correction for correcting the position of each extracted registration position shift. Means, it not only corrects the steady registration position deviation, but also actively corrects the position deviation and the pitch unevenness with a specific period, and performs the conventional correction. Than the case of only stationary position correction,
Further, it is possible to obtain a high-quality color image without a registration position shift.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, a registration mark for detecting a steady registration position deviation component and a variable registration position deviation component having a specific synchronization are detected. The feature is that each of the registration marks is generated independently, so that a registration mark for detecting a steady registration position deviation and a registration mark for detecting a variable registration position deviation are generated independently, thereby providing a constant registration mark. The extraction of the resist position shift component and the variable resist position shift component is ensured, and highly accurate resist position correction can be performed by independently performing the resist position correction.

According to a sixth aspect of the present invention, in accordance with the fourth or fifth aspect of the present invention, after performing the resist position correction for the variable resist position deviation, a steady resist position deviation component is detected, and Based on the feature, the registration position correction is performed for the steady registration position deviation, so that after the variable position deviation is corrected, by performing the fixing position deviation correction, the variable position deviation is corrected. Without
It is possible to perform steady positional deviation detection and perform accurate positional deviation detection, and as a result, it is possible to perform fixed positional deviation correction with high accuracy.

According to a seventh aspect of the present invention, there is provided a color image forming apparatus for forming a color image by arranging a plurality of image forming means provided with a photoreceptor along a conveyor belt. A registration sensor is formed on the conveyor belt for forming a registration mark for correction, and a detection sensor for reading the formed registration mark is provided. A registration position shift is detected based on an output of the detection sensor, and the image forming position of each image forming unit is corrected. In the color image forming apparatus provided with a position correcting means, the position correcting means detects a steady registration position deviation component from the detection result of the registration mark, and corrects the registration position based on the detection result. The position correction value means detects a variable dot position deviation component having a specific cycle, and corrects the dot position in the sub-scanning direction based on the detection result. Since the second correction means is provided, not only the steady registration position deviation is corrected, but also the variable dot (registration) position deviation having a specific period is positively corrected. Is performed, and a high-quality color image having no registration position deviation can be obtained as compared with the conventional case of only stationary position correction.

The invention of claim 8 is characterized in that, in the invention of claim 7, the position correction by the first correction means is performed after the position correction by the second position correction means. After correcting the variable dot position deviation,
By performing the steady registration position deviation correction, the stationary position deviation detection is performed in a state where there is no variable position deviation, and the position deviation detection with high accuracy can be performed.
As a result, the accuracy of the steady positional deviation correction can be performed with high accuracy.

According to a ninth aspect of the present invention, in the invention of the seventh or eighth aspect, the detection of the variable dot displacement component having a specific cycle, which is performed by the second position correcting means, is performed by a photoconductor and / or Since the detection is performed based on the detection result of the speed fluctuation of the conveyor belt, the speed fluctuation of the photosensitive drum or the conveyor belt is directly detected (variable displacement is caused by the speed of the photoconductor drum or the speed of the conveyor belt). Since the ratio due to the fluctuation is large and those speed fluctuations are directly detected), the detection accuracy is high and the repetition period becomes clear.

According to a tenth aspect of the present invention, there is provided an image forming means for irradiating an exposure beam reflected by a rotary polygonal mirror on a photosensitive drum to form and develop an electrostatic latent image, wherein the image forming means is provided on a conveyor belt. A plurality of toner images of a plurality of colors formed by the respective image forming apparatuses are transferred to transfer paper on a conveyor belt to form a color image. Since the speed fluctuation of the drum and / or the conveyor belt is detected and the rotation speed of each rotary polygon mirror is controlled according to the detected speed fluctuation, the speed fluctuation of the photosensitive drum irradiated with the exposure beam is characterized. Control the rotation speed of the rotating polygon mirror based on the
It is possible to obtain a high-quality color image without deviation of dot positions.

According to an eleventh aspect of the present invention, in the tenth aspect, the rotation speed of the rotary polygon mirror is controlled in accordance with the detected low-frequency component of the speed fluctuation of the photosensitive drum and / or the transport belt. Therefore, the rotation speed of the rotating polygon mirror is controlled based on the low-frequency component of the speed fluctuation of the photosensitive drum, and the speed control of the rotating polygon mirror is gradually performed, so that the rotation speed can be reliably controlled. .

According to a twelfth aspect of the present invention, in the tenth aspect, the reference frequency for determining the writing timing of the exposure beam in the main scanning direction is controlled according to the speed fluctuation of the photosensitive drum and / or the conveying belt. So,
In the speed control of the rotary polygon mirror according to the tenth aspect, a dot position shift in the main scanning direction is eliminated, and a high-quality color image with no position shift in both the main scanning and the sub-scanning can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram for explaining an embodiment of a color image forming apparatus according to the present invention.

FIG. 2 is a block diagram showing internal processing of a registration position correction unit 20.

FIG. 3 is a diagram illustrating a relationship between an exposure device and a photosensitive drum.

FIG. 4 is a diagram illustrating an example of a generated registration mark.

FIG. 5 is an overall configuration diagram for explaining another embodiment of the present invention.

FIG. 6 is a block diagram illustrating internal processing of a registration position correction unit 20.

FIG. 7 is a main part configuration diagram for explaining another embodiment of the present invention.

FIG. 8 is a diagram showing an output voltage waveform (V ₁ ) of the frequency / speed variation converter 51.

FIG. 9 is a diagram illustrating details of a rotation control circuit.

FIG. 10 is a diagram for explaining an output signal (PLS) of a reference pulse generator.

FIG. 11 is a diagram for explaining the operation of the LD drive circuit.

FIG. 12 is a diagram illustrating details of an image frequency control circuit.

FIG. 13 is a diagram for explaining an output signal (WCLK) of a clock generator.

FIG. 14 is a main part configuration diagram for explaining an example of a conventional color image forming apparatus.

FIG. 15 is a diagram illustrating an example of a configuration diagram illustrating a relationship between an exposure device and a photosensitive drum.

FIG. 16 is a schematic diagram for explaining a registration position correction method.

FIG. 17 is a schematic diagram for explaining a color shift factor.

FIG. 18 is a block diagram illustrating a registration position correction method performed by a registration position correction unit.

[Explanation of symbols]

1 (1K, 1C, 1M, 1Y) ... image forming unit, 2 (2
K, 2C, 2M, 2Y) Photosensitive drum, 3 (3K, 3)
C, 3M, 3Y) ... charger, 4 (4K, 4C, 4M, 4)
Y): Exposure unit, 5 (5K, 5C, 5M, 5Y): Developing unit, 6 (6K, 6C, 6M, 6Y): Cleaning device, 7: Conveying belt, 8, 9: Conveying roller, 10: Registration mark Detection sensor, 11: recording paper, 12: paper feed tray, 13 (13K, 13C, 13M, 13Y): transfer device, 14: fixing device, 15: paper discharge tray, 16 (16K,
16C, 16M, 16Y) laser light, 20: resist position corrector, 30: polygon mirror, 31: laser light source (LD), 32: reflection mirror, 33: actuator,
34: Synchronous detection sensor, 35: Actuator, 37 ...
Polygon motor, 40 ... Image processing unit.

Claims (12)

[Claims] 1. A detection sensor for forming a registration mark for correcting a registration position on a conveyance belt by a plurality of image forming means arranged along the conveyance belt and reading the formed registration mark, and the detection sensor. And a registration position correcting means for detecting a registration position shift based on the output of the first register and correcting the registration position of each image forming means in the color image forming apparatus. Image processing means for storing, in addition to the mark pattern, a second registration mark pattern for correcting a variable registration position deviation;
A resist position correcting means for extracting a steady resist position shift component and a variable resist position shift component having a specific period from the detection result of each resist mark, and correcting the position of each extracted resist position shift. A color image forming apparatus comprising: 2. The color image forming apparatus according to claim 1, wherein said first registration mark and said second registration mark are generated independently. 3. The color image forming apparatus according to claim 1, wherein said image processing means firstly executes said second image processing.
The registration position correcting means corrects the variable positional deviation based on this pattern, and then the image forming means outputs the first registration mark pattern, and the registration position correction The color image forming apparatus corrects a steady positional deviation based on the pattern. 4. A color image forming apparatus for forming a color image by arranging a plurality of image forming means along a conveyor belt, wherein each image forming means forms a registration mark for register position correction on the conveyor belt. A color image forming apparatus comprising: a detection sensor for forming and detecting a formed registration mark; detecting a registration position shift based on an output of the detection sensor; and correcting the registration position of each image forming unit by a registration position correcting unit. In the apparatus, means for extracting a steady registration position deviation component and a variable registration position deviation component having a specific period from the detection result of the registration mark, and corrects the position of each extracted registration position deviation. A color image forming apparatus comprising a registration position correcting unit. 5. A color image forming apparatus according to claim 4, wherein a registration mark for detecting a steady registration position shift component and a registration mark for detecting a variable registration position shift component having a specific synchronization. A color image forming apparatus wherein marks are generated independently. 6. A color image forming apparatus according to claim 4, wherein a steady registration position deviation component is detected after performing a registration position correction for a variable registration position deviation, and based on the detection result. A color image forming apparatus that performs registration position correction for a steady registration position deviation. 7. A color image forming apparatus for forming a color image by arranging a plurality of image forming means provided with a photoreceptor along a conveying belt, wherein each of the image forming means includes a registration mark for correcting a registration position. Formed on the conveyor belt, and provided with a detection sensor that reads the formed registration mark,
In a color image forming apparatus including a position correcting unit that detects a registration position shift based on an output of the detection sensor and corrects an image forming position of each image forming unit, the position correcting unit detects a registration mark based on a registration mark detection result A first position correction value means for detecting a steady registration position shift component and correcting the registration position based on the detection result, and detecting a variable dot position shift component having a specific period and detecting the same. A color image forming apparatus comprising: a second correction unit that corrects a dot position in a sub-scanning direction based on a result. 8. The color image forming apparatus according to claim 7, wherein the position correction is performed by the first correction unit after performing the position correction by the second position correction unit. . 9. The color image forming apparatus according to claim 7, wherein the detection of the variable dot misalignment component having a specific cycle performed by the second position correction means is performed by a photoconductor and / or a conveyor belt. A color image forming apparatus that performs the detection based on a detection result of a speed fluctuation of the color image. 10. An image forming means for irradiating a photosensitive drum with an exposure beam reflected by a rotary polygon mirror to form and develop an electrostatic latent image, and comprising a plurality of said image forming means along a transport belt. In the color image forming apparatus which is arranged and transfers a plurality of color toner images formed by the respective image forming apparatuses to transfer paper on a conveyor belt to form a color image, the photosensitive drum and / or the conveyor A color image forming apparatus comprising: detecting a speed fluctuation of a belt; and controlling a rotation speed of each rotary polygon mirror in accordance with the detected speed fluctuation. 11. The color image forming apparatus according to claim 10, wherein the rotation speed of the rotary polygon mirror is controlled in accordance with the detected low-frequency component of the speed fluctuation of the photosensitive drum and / or the conveyance belt. Image forming device. 12. The color image forming apparatus according to claim 10, wherein a reference frequency for determining a writing timing of the exposure beam in the main scanning direction is controlled according to a speed variation of the photosensitive drum and / or the transport belt. Color image forming apparatus.