JP2000284561A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image being free from color smear by the image forming device of a tandem type. SOLUTION: This image forming device repeatedly formes combination of resist patterns of the respective color so that a formation area thereof becomes one round portion on a transfer belt. These resist pattern are detected, respectively obtaining data of color smear quantity of cyan, magenta can yellow with regard to the black are obtained one round portion of the belt, and a component derived from the rotary irregularity of a photoreceptor drum from data of the color smear quantity and a component derived from the travelling irregularity of the transfer belt are extracted and preserved. At the image forming time, a phase of the photoreceptor drum and the transfer belt (step S61) are detected, the color slippage data of the above respective component are made in alignment with a phase thereof (step S62), a correction pulse that timing for each scanning line to the photoreceptor of each color is corrected is generated, so as to eliminate the compounded color smear (step S63), and respective LED array is driven in accordance with the correction pulse (step S64).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called tandem type image forming apparatus which has a plurality of image forming units, and forms a color image by multiplex-transferring an image formed by these image forming units onto a recording sheet or the like. In particular, the present invention relates to a technique for preventing the occurrence of the color shift.

[0002]

2. Description of the Related Art In general, in a color image forming apparatus, an original image is separated into colors to generate image data of each reproduced color of cyan (C), magenta (M), yellow (Y), and black (K). A color image is formed by forming a toner image of each color on a photosensitive drum based on each image data, and superimposing and transferring these on a recording sheet.

Therefore, if the transfer position of the image of each color is shifted, a color shift occurs on the recording sheet, and the quality of the reproduced image is extremely deteriorated. In particular, a plurality of image forming units for forming images of each color are arranged in parallel in the conveying direction of the recording sheet conveyed on the transfer belt, and the images of each color are multiplex-transferred onto the recording sheet while shifting the image forming timing. In a so-called tandem-type image forming apparatus that obtains a color image by using an image forming apparatus, each color image is formed by a separate image forming unit, so that color misregistration is likely to occur. .

In order to prevent such a color shift from occurring,
Conventionally, in a tandem-type image forming apparatus, a registration mark of a predetermined shape is formed on a transfer belt by each image forming unit, and these are detected by an optical sensor to calculate a positional shift amount between the registration marks. A so-called registration correction is performed, in which the image is corrected based on the amount of displacement to correct the writing position of the entire image of each color.

The amount of color misregistration (the amount of color misregistration due to the optical system) due to the variation in the mounting position of the optical element in the optical system or the variation in the optical characteristics of the optical element itself for each color is considered to be constant during image formation. Therefore, the color shift is eliminated by forming a resist pattern of each color one by one on the transfer belt and correcting the writing position of the image of each color as a whole based on the positional shift amount.

However, in practice, color shifts due to periodically occurring speed fluctuations (driving system factors) such as uneven rotation of each photosensitive drum and uneven running of the transfer belt also occur.
The above-described resist correction method cannot eliminate the color misregistration caused by these. On the other hand, Japanese Patent Application Laid-Open No. H10-148992 discloses a method of obtaining a color misregistration correction amount for each color in consideration of the factors of the driving system. That is, a resist pattern of each color is repeatedly formed on the transfer belt for one rotation of the transfer belt,
This is detected by a photoelectric sensor, and the amount of color misregistration corresponding to the rotation phase of the transfer belt is obtained. The color misregistration amount obtained by averaging the color misregistration amounts for one round of the transfer belt is used as a representative value, and the difference between this representative value and the color misregistration amount corresponding to the above-described rotation phase is obtained. It is stored as difference data in association with the orbiting phase.

At the time of actual registration correction, a small number of registration patterns are formed within a short range between image forming areas (between recording sheets conveyed by a transfer belt), and obtained by the registration patterns. The obtained color shift amount is obtained, and this color shift amount is calculated from the difference data.
By correcting with a pattern having the same phase as the pattern detection timing at the time of the registration correction, the unevenness of the belt and the unevenness of the rotation of the photosensitive drum (hereinafter, referred to as “drive unevenness”) even though the registration pattern has a short width. A color shift amount that is not affected by the above is determined. Here, the obtained color shift amounts are cyan for the image of the reference color (black),
Based on the representative value of the displacement amount of the entire image of each color of magenta and yellow, the formation position of the image of each color is corrected based on the displacement amount.

[0008]

However, according to the above-described registration correction method, it is possible to obtain a representative value of the positional deviation amount which is less affected by driving unevenness for each color image. Even if the writing position of the entire corresponding image is uniformly corrected by the representative value, there is a problem that color misregistration cannot be completely eliminated in an actually formed color image.

It is considered that this is because the driving unevenness actually occurs when an image for one page is formed on a transfer belt or a recording sheet conveyed by the transfer belt. That is, the fluctuation of the writing position due to the uneven rotation of the photosensitive drum, the shift of the transfer position due to the uneven movement of the transfer belt, and the like occur continuously during the formation of an image of one page of the original. Since the generated phase is different for each color image, a color shift occurs.

The present invention has been made in view of the above problems, and has as its object to provide a tandem-type image forming apparatus capable of forming an excellent reproduced image without causing color misregistration. I do.

[0011]

In order to solve the above-mentioned problems, the present invention comprises a plurality of image forming means for forming images of different colors, and converts each color image formed by each image forming means. An image forming apparatus for forming an image by performing multiple transfer onto a transfer belt or a transfer material conveyed by the transfer belt, wherein the image forming apparatus controls each of the image forming means and repeats a set of resist patterns of each color to form a transfer belt. Control means to be formed thereon, color shift information obtaining means for detecting the plurality of sets of resist patterns and obtaining information regarding the color shift amount of each color for each set, and periodicity from the information regarding the color shift amount. A color misregistration component extracting means for extracting a plurality of color misregistration components, and continuously correcting the color misregistration components based on the extracted color misregistration components so that color misregistration does not occur during image formation by the multiple transfer. It is characterized in that it comprises a color shift correction means.

Further, according to the present invention, each of the image forming means has an image carrier and a writing means for writing an image on the image carrier, and the color misregistration correcting means has a function of causing each color misregistration component. A color shift component synthesizing unit for detecting a phase and synthesizing a color shift component in the phase for each color; and a writing unit for writing an image of a corresponding color based on the synthesized color shift component to the image carrier. The color shift is corrected by continuously controlling the writing position for each scanning line.

According to the present invention, each of the image forming means includes an image carrier and a writing means for writing an image on the image carrier, and the color misregistration component is caused by uneven running on a writing surface of the image carrier. And the color misregistration correction means, based on information on each color misregistration component, of the image bearing member driving means and the transfer belt driving means, based on the information on each color misregistration component. The color shift is corrected by continuously controlling the driving speed, which is a factor, so that the color shift component is eliminated.

Further, according to the present invention, each of the image forming means includes an image bearing drum and a writing means for writing an image on the image bearing drum. And the color shift component extracting means sets the rotation cycle of each image carrier drum and the rotation cycle of the transfer belt as a basic cycle based on the information on the color shift amount. A color shift component is extracted.

Further, according to the present invention, each of the image forming means includes an image carrier drum and a writing device for writing an image on the image carrier drum, and each of the image carrier drums has a rotational force of a driving source. Are transmitted through a drive belt, and the factors causing the color shift components are uneven driving of each image carrier drum by the drive belt and uneven running of the transfer belt. The component extracting means extracts, from the information on the amount of color misregistration, a color misregistration component whose basic cycle is the cycle of each drive belt and the cycle of the transfer belt.

Further, according to the present invention, the control means preferably controls the length corresponding to the color shift component having the longest basic cycle among the plurality of color shift components to be extracted by the color shift component extracting means. Only, a set of the resist patterns of the respective colors is repeatedly formed on the transfer belt.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below with reference to a tandem type color digital copying machine (hereinafter simply referred to as "copying machine"). Embodiment 1 (1) Overall Configuration of Copying Machine FIG. 1 is a diagram showing the overall configuration of copying machine 1. As shown in FIG. 1, the copying machine 1 includes an image reader section 10 for reading a document image roughly divided into sections, and a printer section 20 for printing the read image on a recording sheet and reproducing it.

The image reader section 10 is a known one which reads an image of an original placed on an original glass plate (not shown) by moving a scanner, and is obtained by irradiation of an exposure lamp provided in the scanner. Document image
Image data composed of multi-valued digital signals of red (R), green (G), and blue (B) after being converted into electric signals by a color image sensor (hereinafter simply referred to as a “CCD sensor”) and then subjected to A / D conversion. Get.

The image data for each color component obtained by the image reader unit 10 undergoes various data processing in the control unit 30, and is further subjected to cyan (C), magenta (M), yellow (Y), and black (K). ) Is converted into image data of each reproduction color (hereinafter, each reproduction color of cyan, magenta, yellow, and black is represented by C, M, Y, and K, and the number of a component related to each reproduction color is represented by C , M, Y, K as subscripts).

The image data is stored in the image memory 103 (see FIG. 4) of the control unit 30 for each reproduced color, and is read out for each scanning line at a timing described later in synchronization with the supply of the recording sheet, and LED arrays 52M-5
This is a 2K drive signal. The printer unit 20 forms an image by a well-known electrophotographic method. The printer unit 20 includes a recording sheet conveying unit 40 configured by stretching a transfer belt 41 around a drive roller 42 and a driven roller 43, and a transfer belt 41. M, C, M, C, which are arranged at predetermined intervals from the upstream side in the recording sheet conveyance direction (hereinafter simply referred to as “upstream side”) to the downstream side in the conveyance direction (hereinafter simply referred to as “downstream side”).
Image forming units 50M to 50K for respective colors of Y and K, and a paper feed unit 60 for feeding a recording sheet upstream of the recording sheet conveying unit 40
And a fixing unit 70 disposed on the downstream side.

Each of the image forming sections 50M to 50K includes a photosensitive drum 51M to 51K and an LED array 52M to 52K for exposing and scanning the surface of the photosensitive drum, and a known charging charger, developing device, and transfer charger. , A cleaner (each not shown), etc., and main parts of an image forming unit 50K for executing image formation with black toner and image forming units 50C to 50K for executing image formation with color toner for easy maintenance, respectively. It is configured as a unit, and is configured to be detachable from the apparatus main body in units of each unit.

The paper feed unit 60 controls the timing of feeding the paper feed cassettes 61 to 63 for accommodating recording sheets of different sizes, the pickup rollers 64 to 66 for feeding out the recording sheets from the paper feed cassettes, and the transfer belt 41. And a registration roller 67 for removing the toner. Each of the photoconductor drums 51M to 51K includes an LED array 52M to 5M.
After the toner remaining on the surface is removed by a cleaner before receiving exposure by 2K, the toner is uniformly charged by the charging charger. Body drum 51M-51K
An electrostatic latent image is formed on the surface of the substrate.

Each of the electrostatic latent images is developed by a developing unit of each color, whereby M, C, Y, and K toner images are formed on the surfaces of the photosensitive drums 51M to 51K. Is transferred onto the recording sheet conveyed by the recording sheet conveying unit 40 sequentially by the electrostatic action of the transfer charger disposed on the back side of the recording sheet.

At this time, the image forming operation of each color is executed with a timing shifted from the upstream side to the downstream side so that the toner image is transferred to the same position of the conveyed recording sheet in a superimposed manner. You. The recording sheet on which the toner images of each color have been multiplex-transferred is conveyed to the fixing unit 70 by the transfer belt 41. The fixing roller 71 of the fixing unit 70 is provided with an internal heater, and the recording sheet is pressurized by high heat here, and the toner particles on the surface are fused and fixed on the sheet surface, and then discharged onto the paper discharge tray 72. Is done.

At a position substantially below the drive roller 42, there is provided a cleaning blade 49 which comes into contact with the surface of the transfer belt 41 and removes the toner of the registration mark transferred to the transfer belt 41 when a positional deviation amount described later is detected. Have been. An operation panel 80 is provided at an easy-to-operate position on the front surface of the image reader unit 10, from which the operator performs key inputs such as an instruction to start copying, setting of the number of copies, and designation of a print mode. . The operation panel 80 is provided with a display unit composed of a liquid crystal display panel or the like, and displays a copy mode set by an operator and various messages.

(2) Driving Mechanism in Image Forming Unit FIG. 2 is a diagram showing a configuration of a driving mechanism for the photosensitive drums 51M to 51K and the transfer belt 41. In this drive mechanism, two drive motors 53 and 54 are used as drive sources. The drive motor 53 is in charge of driving the photosensitive drum 51 </ b> K for black and the transfer belt 41.
Reference numeral 4 is responsible for driving the photosensitive drums 51M to 51Y of the color unit. More specifically, the rotational force of the drive motor 53 is transmitted to the drive roller 42 via gears 531 to 535, while a timing pulley 536 is mounted coaxially with the axis of the gear 533. A timing belt 513K is suspended between a timing pulley 511K attached to the shaft of the photosensitive drum 51K, and the photosensitive drum 51K is also driven to rotate.

On the other hand, the rotational force of the drive motor 54 is
The data is transmitted to the timing pulley 544 via 41 to 543. The timing pulley 544 and the photosensitive drum 5
Timing belts 513M, 513C, and 513Y are suspended between timing pulleys 511M, 511C, and 511Y attached to the shafts of 1M, 51C, and 51Y, respectively.
1Y are simultaneously driven to rotate at the same rotation speed.

Of course, the gear ratio of each gear and the diameter of each timing pulley are set so that the peripheral speed of each photosensitive drum is equal to the traveling speed of the transfer belt. Reference numerals 512M to 512K in the drawing denote tension pulleys for applying tension to the respective timing belts, and are urged by urging means (not shown) in a direction to push the timing belts outward.

Each of SE1 to SE4 is a reflection type photoelectric sensor having a light emitting element such as an LED and a light receiving element such as a photodiode inside. SE1 is an origin sensor that detects an origin mark M1 provided inside the transfer belt 41, and SE2 and SE3 are origin marks M attached to the timing pulleys 511K and 511Y.
2, an origin sensor for detecting M3. By counting clocks from the detection of each origin, each phase can be detected. SE4 is a registration sensor for detecting a registration pattern formed on the surface of the transfer belt 41.

As described above, in the present embodiment, since the black image forming unit and the color image forming unit are driven separately, when the original is a black and white original, the black image forming unit and the black image forming unit are separately driven. If only the transfer belt is driven to execute the monochrome print mode and the original is a color original,
Further, the color image forming unit can be driven to execute the color print mode. As a result, it is not necessary to uselessly drive the color image forming unit when printing a black-and-white image to prevent wear of the photosensitive drums and consumption of the color toner.

When the monochrome print mode is executed, the photosensitive drum in the color image forming unit is stopped, but the transfer belt 41 runs, so that the photosensitive drum is prevented from being worn at the contact portion. Therefore, when executing the monochrome print mode, the photosensitive drums 51M to 51M
It is desirable that the transfer belt 41 be separated from K.

FIG. 3 is a diagram showing an example of a configuration for that purpose. As shown in the figure, the driven roller 43 is rotatably held at the right end of a swing frame 46 which is held so as to be able to swing up and down around a rotation shaft 421 of the drive roller 42. The oscillating frame 46 is moved up and down by a solenoid 47. When the color print mode is executed, the oscillating frame 46 is pushed up to the position indicated by the solid line in FIG. 51M ~
51K is brought into contact with the recording sheet conveying surface of the transfer belt 41.

On the other hand, when executing the monochrome print mode, the rod 471 of the solenoid 47 is retracted,
The swing frame 46 swings downward. At this time, since the auxiliary roller 45 is supported by a main body frame (not shown), only the transfer surface of the transfer belt on the upstream side of the auxiliary roller 45 is inclined downward (retracted position) as shown by a broken line in the drawing. The transfer surface of the transfer belt 41 can be separated from the photosensitive drums 51 </ b> M to 51 </ b> Y which are not involved in black image formation by moving. Thus, even when the photosensitive drums 51M to 51Y are stopped in the monochrome print mode, no friction occurs between the transfer belt 41 and the photosensitive drums 51M to 51Y without adversely affecting image formation. It is possible to prevent unnecessary consumption of the surface and its peripheral members.

The bearing of the tension roller 44 is urged in a direction indicated by an arrow in the drawing by an urging device (not shown) using an elastic member such as a spring.
Is changed between the retracted position and the non-retracted position.
1 is configured to be kept substantially constant.
Further, if the transfer charger is attached to the swing frame 46, the transfer charger moves downward together with the swing operation of the swing frame 46, which hinders the transfer charger from retracting the transfer belt 41 downward. Never.

Whether to execute the monochrome print mode or the color print mode is specified by the operator from the operation panel 80 at the time of copying, or the image data of the original read by the control unit 30 is analyzed. In this case, whether the original is a black-and-white original or a color original may be determined to determine which mode is to be executed. The latter function is an automatic color selection function (AC
Known as S).

(3) Configuration of Control Unit 30 Next, the configuration of the control unit 30 will be described with reference to FIG. The control unit 30 includes a main control unit 100, an image reader control unit 200, and a printer control unit 300. The image reader unit control unit 200 moves the scanner of the image reader unit 10 and turns on / off the exposure lamp.
Control is performed to read the original.

The printer unit controller 300 includes the printer unit 2
0, and controls the sheet feeding operation from the sheet feeding cassettes 61 to 63 and the operations of the image forming units 50M to 50K and the recording sheet conveying unit 40 in a unified manner while maintaining synchronization. , And execute image formation. Main control unit 10
0 indicates signal processing of image data of a document obtained by the CCD sensor, and instructs the image reader unit control unit 200 and the printer unit control unit 300 on control timing and the like.

Each control unit has a CPU and a ROM inside, and based on a control program stored in the ROM,
Execute each control. Of these, the main control unit 1
00 is a CPU 101, an image signal processing unit 102, an image memory 103, an LED array driving unit 104, a RAM 10
5, a ROM 106, an EEPROM 107, and the like.

The image signal processing unit 102 converts each of the R, G, and B electrical signals obtained by scanning the original to generate image data composed of multi-valued digital signals, and further performs shading correction and edge enhancement processing. After such correction, image data of C, M, Y, and K reproduction colors is generated and output to the image memory 103, and the image data is stored for each reproduction color.

The LED array driving unit 104 includes a CPU 10
Under the control of 1, the image data is read from the image memory 103 for each scanning line, and each LED array is driven at a timing for eliminating the color shift. Details will be described later. The RAM 105 temporarily stores various control variables, the number of copies, a print mode, and the like set from the operation panel 80, and provides a work area for executing a program.

In the ROM 106, the image reader 10
And a control program for instructing the printer unit 20 to execute a copy operation in unified manner, a program for correcting color misregistration, and the like, and print data of registration marks of each color. The EEPROM 107, which is a nonvolatile writable memory, stores correction data obtained in a resist pattern detection operation described later.

The LED array drive unit 104 includes LED array drive units 104M to 104M as shown in FIG.
Although K has the same configuration, each drive unit has the same configuration. Therefore, only the configuration of the LED array drive unit 104M will be described in detail below. LED array drive unit 104
M is an oscillator 1041, a clock counter 104
2, monostable multivibrators 1043, 1044, programmable counter 1045, image reading unit 1046,
It includes a shift register 1047, a latch register 1048, and an LED driver 1049.

The oscillator 1041 generates a basic clock, and the clock counter 1042 divides the frequency of the basic clock to generate a shift clock and a latch signal for determining the readout timing for each pixel. In addition, the programmable counter 1045 calculates the basic clock and CP
A strobe signal is generated by a control signal from U101. The image reading unit 1046 sequentially reads image data from the image memory 103 for each of a plurality of scanning lines, and sends the image data to the shift register 1047.

Each time the shift clock is received from the clock counter 1042, the shift register 1047 reads out one pixel at a time from the image reading unit 1046 and stores it in an internal register in order. Since a latch signal is sent from the clock counter 1042 via the monostable multivibrator 1043, the latch register 1048 receives the latch signal and latches one scan line of image data stored in the shift register 1047.

On the other hand, the programmable counter 1045
Is the basic clock from the oscillator 1041 and the CPU 1
A correction pulse in which the generation timing of the strobe signal is changed based on the write timing correction data from 01 (described later) is generated and sent to the LED driver 1049 via the monostable multivibrator 1044. LED driver 1
Each time the strobe signal is received, the density data value of the corresponding pixel of the latch register 1048 is set to LE.
It converts the signal into a D drive signal and drives each LED element of the LED array 52M.

The timing correction data is generated so as to eliminate a color shift due to driving unevenness, and details will be described in the following (4). Note that the write timing for each scan line of the black image is executed in accordance with the reference pulse, so that the programmable counter 1045 may be a normal counter that divides the basic clock to generate the reference pulse.

(4) Content of Color Shift Correction Processing Next, the details of the color shift correction processing will be described. In the color misregistration correction processing, first, data of color misregistration amounts of cyan, magenta, and yellow with respect to black is obtained from a resist pattern formed for one rotation of the transfer belt. A component caused by unevenness and a component caused by uneven running of the transfer belt are extracted. Then, the color shift data of each of the above components is combined in accordance with the phases of the photosensitive drum and the transfer belt during image formation to obtain the correction data, and the photosensitive colors of the respective colors are removed so as to eliminate the combined color shift. This is achieved by correcting the write timing for each scanning line on the body drum.

The following is an explanation. (4-1) Formation of Resist Pattern FIG. 6A shows the transfer belt 41 when the color misregistration amount is detected.
FIG. 3 is a diagram illustrating an example of a registration mark formed thereon.
Linear registration marks of K, Y, C, and M are printed in parallel with a direction (main scanning direction) orthogonal to the sheet conveying direction (sub-scanning direction) of the transfer belt 41 at an interval of 1 mm in the order of the colors. Each LED array is driven and formed at a certain timing (the number of clocks) (the formed set of four registration marks is hereinafter referred to as a “unit resist pattern”). The LED array of each color is driven at a timing such that the unit resist pattern is further formed every 10 mm, and the width of the formed LED array along the belt running direction is almost the same as or slightly larger than the circumference of one transfer belt. It is formed repeatedly.

(4-2) Generation of Color Misregistration Data by Detecting Resist Pattern Each resist pattern formed on the transfer belt 41 by the photosensitive drums 51M to 51K is detected by the registration sensor SE4 together with the rotation of the transfer belt 41. Then, the detection signal is sent to the CPU 301. CPU301
Calculates the amount of color misregistration of C, M, and Y with respect to K for each set of unit resist patterns based on the detection signal. In practice, clocks of a predetermined frequency are counted, and the distance between the respective resist patterns is specified by the number of clocks (time) when the respective resist marks are detected.

In the interval indicated by the number of clocks,
When multiplied by the traveling speed of the transfer belt 41, it can be expressed in units of distance. Assuming that the distance between the K registration mark and the C registration mark is determined to be 2.03 mm in a unit distance for a certain unit resist pattern, as described above, the K and C registration marks originally have a timing of 2 mm. It should be controlled to form
The color shift amount is 2 (mm) −2.03 (mm) = −
0.03 (mm). In this way, for each unit resist pattern, the color shift amount of each of the C, M, and Y registration marks with respect to K is calculated, and the value converted into the number of clocks is used as the origin sensor SE1 of the transfer belt and the photosensitive member. The origin sensor SE2 of the drum 51K (or the origin sensor SE3 of the photosensitive drum 51Y. In the color print mode, since each photosensitive drum rotates at the same speed, the detection value of either sensor may be adopted). When the data is plotted on a graph in association with the origin detection timing, data (hereinafter, simply referred to as “color shift data”) indicating a change in the amount of color shift of each color as shown in FIG. it can.

The horizontal axis represents the time required for the transfer belt 41 to make one revolution. The time when the origin mark M1 is detected is defined as the belt origin, and the time when the origin mark M2 is detected is defined as the drum (PC) origin. The vertical axis represents the relative color shift amount of each color with respect to black (indicated by the number of clocks as described above). When the color shift is positive, the image of the color is more in the sub-scanning direction than the black image. It indicates that the color is formed earlier, and a negative value indicates that the color is misaligned in the opposite direction. A (Y), A
(M) and A (C) indicate color misregistration data for yellow, magenta, and cyan, respectively.

Of course, since the number of unit resist patterns formed during one rotation of the photosensitive drum is limited, in practice, data that changes continuously as shown in FIG. I can't get it. The CPU 101 interpolates between the detected data by an appropriate interpolation method such as a quadratic interpolation method to a density required to execute the timing correction described below,
The color misregistration data A (Y), A (M), A (C) are temporarily stored in the RAM 105.

(4-3) Extraction and synthesis of color misregistration components having different periods The color misregistration data A (Y), A (M), A obtained above
(C) is data in which color shifts caused by a plurality of color shift occurrence factors are superimposed. Since the peripheral speed of each photosensitive drum and the traveling speed of the transfer belt are the same, the phase relationship between them should not change in principle. However, in practice, the phase difference between when the color misregistration is detected and when the image is formed is changed. The relationship does not completely match, and the transfer belt may shift during jam (paper jam) processing. If it is necessary to form a resist pattern for one round of the transfer belt and collect color misregistration data each time, not only does the consumption of toner increase, but also image formation must be waited for color misregistration detection. Must.

Therefore, in the present invention, the transfer belt 1 is newly extracted by extracting the above-mentioned color shift data for each of the causes of the color shift and synthesizing those color shift components in accordance with the phase relationship at the time of image formation. The trouble of forming a resist pattern for the circumference is eliminated. Extraction of color misregistration component caused by uneven rotation of photoreceptor drum Since color misregistration caused by unevenness of rotation usually occurs for each rotation of the photoconductor drum, the generation cycle is the same as the cycle of one rotation of the photoconductor drum. You may consider them the same. In the present embodiment, each photosensitive drum rotates n times while the transfer belt makes one rotation. By averaging the color misregistration data detected in each of the n rotations, the transfer belt It is possible to extract a color shift component caused only by the rotation unevenness of the photosensitive drum excluding the influence of the running unevenness. FIG. 7A shows the data of the color misregistration component derived only from the photosensitive drum (hereinafter, simply referred to as “drum component color misregistration data”) B (Y), B
(M), the example of B (C) is shown.

FIG. 6B shows the color misregistration data resulting from both the photosensitive drum and the transfer belt. Therefore, the drum component color misregistration data B (Y), FIG.
B (M) and B (C) are repeated according to the PC origin, and each color shift data A (Y), A (M),
If subtracted from A (C), data of a color misregistration component that depends only on the running unevenness of the transfer belt (hereinafter, simply referred to as “belt component color misregistration data”) should be obtained. The data thus obtained is the belt component color misregistration data D shown in FIG.

Each of the photosensitive drum component color shift data B (Y), B (M), B (C) and the belt component color shift data D obtained in this manner are stored in the EEPROM 107.
Stored within. Combination processing of each color shift component When forming an image, the transfer belt 4 is detected by the origin sensor SE1.
Origin sensor SE2 after detecting the origin mark M1
, The time Tbp until the origin mark M2 attached to the timing pulley 511K of the photosensitive drum 51K is detected. The time Tbp indicates the phase difference between the transfer belt 41 and each of the photosensitive drums 51M to 51K. Based on the phase difference, the drum component color shift data B (Y), B
(M), B (C) and the belt component color shift data D are synthesized.

FIG. 8 schematically shows how the color shift components are combined. Therefore, each drum component color misregistration data shows only five times of the PC rotation cycle.
First, the drum component color shift data B (Y) and B (Y) for one rotation of the photosensitive drum shown in FIG.
(M), B (C) The data of the color misregistration component is read, and the data is repeatedly connected so as to have a length equal to or more than one rotation of the transfer belt (FIG. 8A). Similarly, the belt component color shift data D is read out from the EEPROM 107, and is read out as shown in FIGS. 8A and 8B.
The data of FIG. 8A and FIG. 8B are superimposed so that the origin position of the second photosensitive drum component color misregistration data is shifted from the origin position of the transfer belt data by exactly tbp. The composite data as shown in FIG.

The combined data becomes accurate color misregistration correction data E (Y), E (M), E (C) for each color reflecting the current phase relationship between the transfer belt and the photosensitive drum. (4-4) Write Timing Correction Processing Next, based on the correction data E (Y), E (M), and E (C), the programmable counter 1045 (FIG. 5) uses the LED array 52 of each color for each scanning line. Is corrected.

FIG. 9 is a schematic diagram for explaining timing correction for writing a cyan image. 9A shows correction data synthesized according to the current phase relationship between the photosensitive drum and the transfer belt obtained in the above (4-3), and FIG. 8C and FIG. The same is shown. The writing time of the cyan image instructed from the printer unit control unit 300 to the photosensitive drum is t1.
From time to t2, based on the cyan correction data corresponding to the phase at that time, a pulse (timing correction pulse) in which the write timing of the scanning line is corrected as shown in FIG. 9B is formed.

That is, the correction is performed by adding or subtracting the color shift amount of the correction data at the pulse generation timing of the reference pulse indicating the normal writing timing executed when there is no color shift to the generation time of the reference pulse. Get the pulse. For example, the color shift amount is h3 at P3 of the reference pulse, and since h3 is positive, as described above, in this case, the cyan image precedes the black image by the color shift amount. Therefore, it is necessary to draw a cyan scan line with a delay corresponding to the time. Therefore, a correction pulse P3 'is obtained by correcting the reference pulse P3 in a direction delayed by the correction amount h3. On the other hand, in a portion where the correction amount is negative, a process is performed to advance the drawing timing of the cyan scanning line by the correction amount from the reference pulse.

Thus, the programmable counter 1
Numeral 045 continuously corrects the write timing by generating a timing correction pulse train obtained by correcting the reference pulse train and sending it to the LED driver 1049 via the monostable multivibrator 1044. (5) Operation of Registration Correction Control First, the control operation of the entire copying machine will be briefly described based on the flowchart of FIG.

When the apparatus is powered on, first, the RAM
Initial settings are performed to clear the contents of 105, initialize various registers, and set each unit to the initial mode (step S1). Subsequently, the internal timer is started in step S2. This main routine is executed by the internal timer.
The processing time of the routine is set. Next, the operation panel 8
An input is received from 0, a copy mode is set, and input / output processing for controlling display contents on the display unit of the operation panel 80 is executed as necessary (step S3). afterwards,
A process of acquiring color misregistration data for each component of each color is executed (step S4), and subsequently, a document reading process of reading a document image by the image reader unit 10 is executed (step S4).
5). Next, correction data is generated by synthesizing the color misregistration data of each component obtained in step S4, and the respective photosensitive drums 51M to 51K are corrected while correcting the timing based on the data.
Then, a process of writing an image to the device is executed (step S6). Then, other processes such as a transfer process and a fixing process are executed to form a color image on the recording sheet (Step S7).
Thereafter, the process returns to step S2 after waiting for the end of the internal timer (step S8).

It should be noted that the color misregistration data acquisition processing in step S4 is not executed every time an image is formed.
It is executed every predetermined number of times of image formation or every time the power is turned on. FIG. 11 is a flowchart showing a subroutine of the color shift data acquisition processing.

The CPU 101 reads out the print data of the registration mark of each color from the ROM 106, and outputs the LED arrays 52 M to 52 M of each color via the LED array driving unit 104.
K is driven, and the printer unit 20 is driven via the printer unit control unit 300.
As shown in (a), a unit resist pattern is repeatedly formed for one rotation of the transfer belt 41 (step S4).
1).

Then, the resist pattern is detected by the resist sensor SE4, and the relative displacement of the C, M, and Y resist marks with respect to the K resist mark is calculated as the color displacement for each color unit resist pattern. The data of the variation amount of the color misregistration amount of each color corresponding to the phase of the transfer belt (the color misregistration data A (Y), A in FIG. 6B)
(M), A (C)) are obtained (step S42).

The color shift data A (Y), A
(M) and A (C) are averaged for each PC cycle (that is, for each section in which the origin mark M2 is detected by the origin sensor SE2), and the drum component color shift caused only by the fluctuation factor of each photosensitive drum Data B (Y), B (M),
Obtained as B (C) (step S43). Next, based on the color misregistration data A (Y), A (M), A (C) and the drum component color misregistration data B (Y), B (M), B (C), only the transfer belt 41 is used. A process of extracting a color shift component (belt component color shift data) to be performed is executed (step S4).
4).

That is, the color shift data A (Y), A
From (M) and A (C), respectively, B (Y) and B
Data B (Y, 1 to n + 1), B (M, 1 to n + 1), B generated by repeating (M) and B (C) (n + 1) times
(C, 1 to n + 1) is converted to color shift data A (Y), A
(M) and A (C) are detected and subtracted so as to have the same phase relationship between the transfer belt and the photosensitive drum, thereby obtaining belt component color shift data D (Y), D (M),
Since D (C) can be obtained, these three are averaged to obtain belt component color shift data D.

The generated drum component color shift data B (Y), B (M), B (C) and belt component color shift data D are stored in the EEPROM 107 (step S45). FIG. 12 is a flowchart showing a subroutine for executing the writing process (step S6) based on the stored data.

First, the photosensitive drum 51K and the transfer belt 4
1 is detected (step S61). On the other hand, drum component color misregistration data B (Y), B (M), and B (C) are generated by repeating (n + 1) times, respectively, and are generated in accordance with the detected phase.
To generate correction data E (Y), E (M), and E (C) (step S62).

The CPU 101 sets the correction data E
(Y), E (M), and E (C) according to the data of the portion corresponding to the write timing.
04, a timing correction pulse is generated (step S6).
3), based on the correction pulse, an LED array 5 of each color.
The color shift is eliminated by driving 2M, C, and Y (step S64). The black write timing is executed according to the reference pulse.

<Second Embodiment> In the first embodiment,
The color shift was corrected by controlling the write timing for each scan line based on the correction data. The cause of the color shift is that the drum component color shift data is related to the rotation of the black photosensitive drum 51K. Other M, C, Y photoconductor drums 51M, 51C, 51Y
, And the belt component color misregistration data can be regarded as running unevenness of the transfer belt 41 itself.

Therefore, in the second embodiment, LE
Without changing the timing of writing by the D array 52,
The drive speed of each of the photosensitive drums 51M to 51Y and the transfer belt 41 is controlled to eliminate color misregistration.
For that purpose, first, it is necessary to drive each driven part independently. FIG. 13 is a schematic perspective view showing an example of the configuration, in which a stepping motor 345M is provided on the rotation axis of each of the photosensitive drums 51M to 51K and the axis of the drive roller 42, respectively.
345K, 325 drive shafts are directly connected. Each rotating shaft and stepping motors 345M to 345
K is held in the main body frame, but these are not shown in the figure for simplicity.

FIG. 14 is a diagram showing a configuration of a printer controller 300 for implementing the present embodiment.
A CPU 301, a ROM 302 for storing a control program in the printer controller 300, a RAM 303 serving as a work area when the control program is executed,
0, a driving unit 3 for controlling the driving of the fixing roller 71 of the fixing unit 70 and the fixing temperature.
60, and an image forming section driving section 370 for driving a stepping motor of each section of the image forming section.

The image forming section driving section 370 includes the pulse generating section 31
0, 330M to 330K, driver unit 320,
340M to 345K. A drive circuit of the stepping motor 325 that drives the transfer belt 41 is configured by a pulse generator 310 and a driver unit 320.
Similarly, a stepping motor 3 for driving each photosensitive drum
45M to 345K are the corresponding pulse generators 3
30M-330K and driver unit 340M-
The drive is controlled by 340K. Since the configuration and operation of each pulse generator and driver unit are exactly the same, only the pulse generator 310 and driver unit 320 will be described here.

When driving the transfer belt 41, the CPU 301 acquires the current phase of the transfer belt 41 via the main control unit 100. This phase can be specified by the elapsed time from the detection of the origin mark M1 of the transfer belt 41 as described above. E according to the phase
From the EPROM 107, the belt component color shift data D (FIG. 7)
(B)) is read and given to the pulse generator 310. Based on the belt component color misregistration data D, the pulse generation unit 310 corrects the reference input pulse for obtaining the predetermined system speed by the same method as described with reference to FIG. Send to unit 320. The excitation phase control unit of the driver unit 320 instructs the power amplifying unit to switch the phase to be excited every time the input pulse is received, and the power amplifying unit amplifies the voltage applied from the voltage control unit. By giving a drive pulse to the phase specified by the excitation phase control unit, speed control according to the corrected frequency of the input pulse is realized. The current detection unit detects the current value of the drive pulse and feeds it back to the voltage control unit, so that the magnitude of the drive pulse applied to the excitation phase is kept constant and the rotation torque is stabilized. It has become.

The pulse generators 330M to 330Y receive drum component color shift data B (Y), B (M), B
(C) is given according to the rotation phase, and based on each data, the pulse generators 330M to 330Y correct the reference input pulse in the same manner as the pulse generator 310. Note that no correction data is given to the pulse generation unit 330K, and only the reference input pulse is generated, so that the configuration can be simpler than the pulse generation units 330M to 330Y.

As described above, the photosensitive drums 51M to 51K and the transfer belt 41 are independently driven, and the speed is controlled by the corresponding color misregistration data except for the photosensitive drum 51K. It is possible to eliminate unevenness and running unevenness (more precisely, uneven rotation and uneven running relative to the rotation of the black photosensitive drum 51K), and to obtain an excellent reproduced image without color shift. .

In this embodiment, since the timing pulley is not provided coaxially with the photosensitive drum, the origin mark is placed outside the image forming area on the end surface or the peripheral surface of the photosensitive drum. In addition, since the photosensitive drum 5 is driven independently,
It is necessary to provide an origin mark and an origin sensor also in 1M and 51Y, and to acquire drum component color shift data in accordance with the phase of each photosensitive drum.

In the case of a stepping motor, since the number of input pulses required to make one rotation is fixed, if the number of pulses is N, a counter that counts input pulses and resets each time it reaches N is set. If provided, the phase can be indicated by the count value, so that the origin mark and the origin sensor may be omitted. If the number of input pulses required to make one rotation of the transfer belt is counted in advance, the origin mark and the origin sensor can be omitted as described above.

Further, in the present embodiment, a stepping motor having excellent speed controllability is used as a drive source, but it goes without saying that the drive motor is not limited to this. <Modifications> It is needless to say that the technical scope of the present invention is not limited to the above-described embodiment. For example, the following modifications can be considered.

(1) In the first and second embodiments,
Although the LED array is used as the exposure scanning means of the photosensitive drum, a laser beam can be used.
In the first embodiment, the drive timing for each scanning line of the LED array is corrected. However, when a laser beam is used, the correction of the writing position of the scanning line on the photosensitive drum is performed in the following manner. Will do.

That is, a folding mirror is provided in the optical path of the laser beam, and the angle of the folding mirror is changed so that the irradiation position of the laser beam on the photosensitive drum moves in the sub-scanning direction. As a drive mechanism for changing the angle of the mirror, a drive mechanism capable of high-speed response and capable of precise angle adjustment is employed. As such, for example, a known laminated piezoelectric actuator formed by laminating piezoelectric elements is used, and the amount of displacement is enlarged by a displacement enlarging mechanism utilizing the principle of leverage to drive the mirror to swing. A method can be considered.

The color shift can be prevented by changing the irradiation position of the laser beam in the sub-scanning direction based on the correction data. Instead of providing a folding mirror, it is also possible to move the irradiation position of the beam by transmitting the laser beam through a parallel glass plate and controlling the inclination of the glass plate with respect to the traveling direction of the beam.

(2) In each of the above embodiments, the rotation period of the photosensitive drum and the rotation period of the transfer belt are determined based on the color misregistration data A (Y), A (M), and A (C). Although the color shift component is extracted, the color shift component having periodicity is not limited to this. For example, in the first embodiment, each photosensitive drum is driven to rotate via a timing belt. However, if there is a variation in the shape, particularly the thickness, of such a belt member (including a wire or the like) depending on the position, Causes the driving speed to fluctuate, causing color shift. In this case, the basic cycle of the occurrence of the color misregistration is the circulation cycle of the belt member. If the length of each belt is different, its circulating cycle is also different. Therefore, it is necessary to provide a means for detecting the phase (in the above example, the origin sensor and the origin mark) in each transfer belt.

(3) In the above embodiment, the monochrome print mode and the color print mode can be switched. When the monochrome print mode is executed, only the photosensitive drum 51K rotates. When executing the color print mode, the photosensitive drum 51
The phase relationship between K and the other photosensitive drums 51M to 51C is
It is different from when each color shift data was collected. Since the color misregistration data is a relative misregistration amount of another color image with respect to the black image, if the phase relationship is different, the color misregistration data once collected will no longer be meaningful.

In this case, a resist pattern for one round of the transfer belt may be formed again and color shift data of each component may be obtained again. However, in a use environment where the monochrome print mode and the color print mode are frequently switched. However, the amount of toner consumed is enormous and maintenance costs increase. Therefore, after the monochrome print mode and before the color print mode is executed, it is preferable to execute processing for matching the phase relationship between the photosensitive drum 51K and the other photosensitive drums 51M to 51C with the phase relationship at the time of collecting color shift data. As this method, the phase relationship between the photosensitive drum 51K and the photosensitive drum 51Y when the color misregistration data is collected is stored, and the photosensitive drum 51K or the photosensitive drums 51M to 51M is started before the execution of the color print mode. May be adjusted so as to be in the phase relationship by rotating. In this case, the phase relationship between the photosensitive drum 51K and the photosensitive drum 51Y can be specified by, for example, the time from when the origin sensor SE2 detects the origin mark M2 to when the origin sensor SE3 detects the origin mark M3. .

(4) In the above embodiment, only the color misregistration in the sub-scanning direction has been described. However, the present invention can be applied to a case where there is a periodic variation in the color misregistration also in the main scanning direction. As an example, meandering of the transfer belt can be considered,
In this case, as the shape of the registration mark, a registration mark having a hatched portion such as a V-shape or an X-shape is used so that a color shift in the main scanning direction can be detected. In addition, since the fluctuation cycle may exceed the rotation cycle of the transfer belt, it is necessary to form a resist pattern at least longer than the length. In this case, it is easy to continuously correct the writing position in the main scanning direction. For example, in laser beam exposure, the timing of generating a main scanning synchronization signal that determines the timing of reading image data for each scanning line is changed in the main scanning direction. What is necessary is just to change based on the obtained correction data.

(5) In the above embodiment,
Although a tandem-type color copying machine has been described as an example, the present invention is not limited to this, and can be applied to other tandem-type color printers and image forming apparatuses such as color facsimile machines.

[0089]

As described above, according to the image forming apparatus of the present invention, a set of resist patterns of each color is repeatedly formed on the transfer belt, and these are detected, and each set of colors is detected for each set. Information about the amount of color misregistration of
A color misregistration component extracting unit extracts a plurality of color misregistration components having periodicity from the information on the color misregistration amount. Then, based on the extracted color shift components, the color shift correcting means continuously corrects the color shift so as not to occur at the time of image formation by the multiple transfer. It is possible to execute highly accurate color misregistration correction that faithfully reflects a change in the phase of a component.

Further, the present invention detects a phase of a factor causing each color shift component, synthesizes a color shift component in the phase for each color, and, based on the synthesized color shift component, an image of a corresponding color. The writing position on the image carrier by the writing means for writing the image data is continuously controlled for each scanning line. Therefore, the pitch between the scanning lines is corrected so that the color deviation is eliminated, and the accurate color deviation is corrected. Correction can be achieved.

Further, according to the present invention, the driving speed of the driving means for each image carrier and the driving means for the transfer belt, which is a factor of the color shift component, is determined based on the information of each color shift component. Since the control is continuously performed so as to eliminate the color shift, the drive unevenness itself which has caused the color shift can be eliminated, and the color shift can be accurately eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the configuration of a tandem-type digital color copying machine according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a driving mechanism of a photosensitive drum and a transfer belt in an image forming unit of the copying machine.

FIG. 3 is a diagram illustrating a mechanism for separating a transfer belt from a color photosensitive drum when executing a monochrome print mode.

FIG. 4 is a block diagram showing a configuration of a control unit in the copying machine.

FIG. 5 is a diagram showing a circuit configuration of an LED driving unit in a main control unit of the control unit.

FIG. 6A is a diagram illustrating an example of a resist pattern formed at the time of color misregistration correction, and FIG. 6B is a diagram illustrating a change amount of a color misregistration amount of each color detected by the phase change according to a phase.

7A is a diagram illustrating a change in color misregistration amount (drum component color misregistration data) caused by eccentricity of each photosensitive drum, and FIG.
FIG. 7 is a diagram illustrating a change in color misregistration amount (belt component color misregistration data) due to uneven running of the transfer belt.

FIG. 8 is a diagram illustrating a state in which drum component color misregistration data and belt component color misregistration data are combined in accordance with the phase relationship between the photosensitive drum and the transfer belt.

9A is a diagram illustrating color misregistration correction data obtained by synthesizing the color misregistration amounts of FIGS. 7A and 7B in accordance with the phases of the photosensitive drum and the transfer belt, and FIG. A state in which the write timing for each scanning line is corrected based on the data of the color shift amount of the portion corresponding to the timing of the cyan image write, (c) shows an example of a normal write timing when the write timing is not corrected, FIG.

FIG. 10 is a flowchart showing the operation of the entire copying machine.

FIG. 11 is a flowchart illustrating a subroutine of color misregistration data acquisition processing in step S4 of the flowchart in FIG. 10;

FIG. 12 is a flowchart illustrating a subroutine of an image writing process in step S6 of the flowchart in FIG. 10;

FIG. 13 is a diagram illustrating a configuration example in a case where a transfer belt and each photosensitive drum are driven independently in Embodiment 2.

FIG. 14 is a diagram illustrating a driving circuit of a stepping motor for driving a transfer belt and each photosensitive drum, particularly, a printer controller in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image reader part 20 Printer part 30 Control part 50M-50K Image formation part 51M-51K Photoconductor drum 52M-52K LED array 80 Operation panel 100 Main control part 101 CPU 102 Image signal processing part 103 Image memory 104 LED array drive part 200 Image reader controller 300 Printer controller SE1-SE3 Origin sensor SE4 Registration sensor M1-M3 Origin mark

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kimio Hara 1-47-1 Furuno, Nakamura-ku, Nagoya City 23rd floor of Nagoya International Center Building Apro Co., Ltd. F-term (reference) 2H027 DA17 DA20 DA38 DA50 EB04 EC03 EC06 EC20 ED02 ED16 ED24 EE02 EE03 EE04 EE07 EF09 2H030 AA01 AB02 AD12 AD17 BB02 BB16 BB23 BB42 BB44 BB56

Claims (6)

[Claims] 1. An image forming apparatus comprising: a plurality of image forming means for forming images of different colors, wherein multiple images of each color formed by the respective image forming means are transferred onto a transfer belt or a transfer material conveyed by the transfer belt. An image forming apparatus that forms an image by using a control unit that controls each of the image forming units to repeatedly form a set of resist patterns of each color on a transfer belt; and detects the plurality of sets of resist patterns. A color misregistration information acquiring unit that acquires information about the color misregistration amount of each color for each set; and a color misregistration component extraction unit that extracts a plurality of periodic color misregistration components from the information about the color misregistration amount. An image forming apparatus comprising: a color misregistration correction unit configured to continuously correct, based on each of the extracted color misregistration components, color misregistration during image formation by the multiple transfer. Apparatus. 2. Each of the image forming units includes an image carrier and a writing unit that writes an image on the image carrier, and the color misregistration correction unit detects a phase of a factor causing each of the color misregistration components. A color misregistration component synthesizing unit for synthesizing a color misregistration component in a phase for each color, and scanning a writing position on an image carrier by a writing unit for writing an image of a corresponding color based on the synthesized color misregistration component. 2. The image forming apparatus according to claim 1, wherein the color misregistration is corrected by continuously controlling each line. 3. Each of the image forming units includes an image carrier and a writing unit that writes an image on the image carrier.
The color shift component is caused by uneven running of the writing surface of the image carrier or uneven running of the transfer belt. The color shift correcting unit drives each image carrier based on information of each color shift component. The color shift is corrected by continuously controlling the driving speed of the means and the driving means of the transfer belt that causes the color shift component so that the color shift component is eliminated. The image forming apparatus according to claim 1. 4. Each of the image forming means includes an image bearing drum and a writing means for writing an image on the image bearing drum, and the factor causing the color misregistration component is uneven rotation of each image bearing drum. And the unevenness of the transfer belt. The color misregistration component extracting means, based on the information on the color misregistration amount, a color misregistration component having a rotation cycle of each of the image bearing drums and a rotation cycle of the transfer belt as a basic cycle. The image forming apparatus according to claim 1, wherein the image is extracted. 5. Each of the image forming means includes an image bearing drum and a writing means for writing an image on the image bearing drum, and each of the image bearing drums transmits a rotational force of a driving source via a driving belt. The factors that cause the color misregistration component while being rotated by transmitting the image are the unevenness in the drive of each image carrier drum by the drive belt and the unevenness of the transfer belt. 4. The image forming apparatus according to claim 1, wherein a color misregistration component having a basic period of the rotation period of each of the drive belts and the rotation period of the transfer belt is extracted from the information on the color deviation amount. apparatus. 6. The color shift component extracting means, wherein the color shift component extracting means comprises a plurality of color shift components, each of which has a length corresponding to a color shift component having a longest basic cycle. 6. The image forming apparatus according to claim 1, wherein a set of resist patterns is repeatedly formed on the transfer belt.