JP2000284569A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image being free from color smear by efficiently renewing the color smear data even if the phase relation between photoreceptor drums is changed in the image forming device of a tandem type. SOLUTION: This image forming device is, let respectively detecting resist pattern of each color formed of the lot of one round of a transfer belt 1, obtaining data of the color smear of each color with regard to the black for the lot of the transfer belt 1 one round portion, and extracting component derived from irregular rotation of the photoreceptor drum and the component derived from the irregular rotation of the transfer belt from these color smear data. The device is, let compounding color smear data of the above respective component in matching with respective phase of the photoreceptor drum and the transfer belt in the image forming (S68), and correcting the write-in timing for each scanning line on the photoreceptor drum of the respective color so as to eliminate the compounded color smear (S69 and S70). In the case, the phase between black and another color is changed in the image writing-in, by forming the resist pattern by the length of the photoreceptor drum one round portion (S63), by deducting the color slippage for the length derived from the belt of the same phase as formation of that pattern therefrom (S65), the data are renewed by determining the color smear data depending on only the photoreceptor drum (S65 and S66).

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 caused by the optical system) due to the variation in the mounting position of the optical element in the optical system of each color or the variation in the optical characteristics of the optical element itself 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, and the above-described resist The 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, and this is detected by the photoelectric sensor, and a color shift amount (color shift data) corresponding to the rotation phase of the transfer belt is obtained. . This transfer belt 1
The color misregistration amount obtained by averaging the color misregistration amounts for the circumferences is used as a representative value, and the difference between this representative value and the color misregistration amount according to the above-described circulation phase is obtained and associated with the circulation phase of the transfer belt. And stored as difference data.

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 the registration patterns are detected. The deviation amount obtained by the correction is corrected by using the difference data having the same phase as the pattern detection timing at the time of registration correction of the difference data. Rotation unevenness (hereinafter,
It is generically referred to as “driving unevenness”. ) Is to be determined. Here, the obtained color misregistration amount is a representative value of the misregistration amount of the entire image of each color of cyan, magenta, and yellow with respect to the image of the reference color (black), and is based on the misregistration amount. The entire forming position is corrected.

[0008]

When the above-described color misregistration correction method is used, it is necessary to accurately determine the color misregistration amount of each color image in consideration of uneven rotation of the photosensitive drum and uneven movement of the transfer belt. Becomes possible. However, when the phase relationship between the photosensitive drum for black and the photosensitive drum for another color is different from that at the time of acquiring the color shift data, there is a disadvantage that the difference data based on the color shift data can no longer be used. Was.

For example, a paper jam (jam) occurs in the transport system of the apparatus, and the phase relationship between the photosensitive drum for black and the photosensitive drum for another color changes due to the jam processing. Also, in order to prevent wasteful consumption when printing a black and white original, only the black photosensitive drum is driven and the color photosensitive drum is stopped. (Hereinafter, referred to as "monochrome print mode") to a mode for printing a color original using all photosensitive drums (hereinafter, referred to as "color print mode").
, The phase relationship between the photosensitive drum for black and the photosensitive drum for color changes.

Since the color misregistration data is obtained as a relative displacement amount of each color image with respect to the black image, the phase between the respective photosensitive drums at the time of image formation is
If the phase differs from the phase at the time of acquisition of the color shift data, accurate color shift correction cannot be performed, and the color shift data collected by forming a registration mark for one round of the transfer belt becomes meaningless. As a method for solving such a problem, it is conceivable to update the data by forming a registration mark again for one round of the transfer belt and reacquiring the color misregistration data every time the jam is cleared or the print mode is switched.
In particular, switching of the print mode is frequently performed, and each time a registration mark must be formed for one rotation of the transfer belt, not only the consumption of toner increases but also the life of the photosensitive drum and the peripheral members thereof increases. In addition, the user has to wait while forming the registration mark and collecting data, thereby increasing the time loss.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and creates information on the amount of color misregistration by detecting a large number of registration marks. It is an object of the present invention to provide a tandem-type image forming apparatus capable of updating data of a specific color misregistration component while minimizing material consumption.

[0012]

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 a transfer belt, wherein each image forming unit is controlled to repeat a set of resist patterns of each color a plurality of times. First control means for forming on the transfer belt, color shift information obtaining means for detecting the plurality of sets of resist patterns and obtaining information on the color shift amount of each color for each set, and information on the color shift amount A color misregistration component extracting means for extracting a color misregistration component having a first cycle and a color misregistration component having a second cycle longer than the first cycle; Update Updating means, and a color shift correcting means for correcting based on the color shift component having the first cycle and the color shift component having the second cycle so as not to cause color shift at the time of image formation by the multiple transfer. The updating means includes a second control means for controlling each of the image forming means so as to repeatedly form the resist pattern set for a time equal to or longer than a first cycle and shorter than a second cycle; The color shift component having the first cycle is obtained from the information regarding the color shift amount obtained by detecting the resist pattern by the color shift information obtaining means and the color shift component having the second cycle, and the data is updated. It is characterized by doing.

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 the color shift component having the first cycle is The updating means is provided with phase detecting means for detecting that the rotational phase between the respective drums has changed, and the updating means includes a phase detecting means for detecting a change in the rotational phase. Is detected, the data of the color shift component having the first cycle is updated.

Further, the present invention is characterized in that the first cycle is a rotation cycle of the image carrier drum, and the second cycle is a rotation cycle of the transfer belt.

[0015]

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"). (1) Overall Configuration of Copying Machine FIG. 1 is a diagram showing the overall configuration of the 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 a document placed on a document glass plate (not shown) by moving a scanner, and is obtained by irradiation of an exposure lamp provided on 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 is subjected to 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. 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 units 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, a known charging charger, a developing device, and a 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 supply unit 60 controls the paper supply cassettes 61 to 63 for storing recording sheets of different sizes, the pickup rollers 64 to 66 for feeding out the recording sheets from the paper supply cassettes, and the timing of feeding the recording sheets to 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 at a shifted timing from the upstream side to the downstream side so that the toner image is transferred in a superimposed manner at the same position on the conveyed recording sheet. 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 toner of a 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 therein. 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 this 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 the direction of the arrow in the figure 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 known as the automatic color selection function (ACS).

(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 control unit 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 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 the 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.

The ROM 106 stores the image reader section 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 driving unit 104 includes LED array driving 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 a read 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 sequentially in an internal register. 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 the 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.

On the other hand, the phase relationship between the photosensitive drum 51K for black and the photosensitive drums 51M to 51Y for color is monitored, and when the phase relationship changes, the color shift data due to uneven rotation of the photosensitive drum is updated. After that, the color shift correction is executed based on the updated color shift data. 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 a resist pattern Each resist pattern formed on the transfer belt 41 by the photosensitive drums 51M to 51K is detected by the resist 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 amount of color misregistration 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 drum. The origin sensor SE2 of the body 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 plotted on a graph in association with the timing of each origin detection, data indicating a change in the amount of color misregistration of each color as shown in FIG.
That. ) Can be obtained.

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, 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 Each 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 the two should not change in principle, but in practice, the phase relationship between the detection of the amount of color misregistration and the time of image formation Do not completely match, and the transfer belt may be displaced during jam (paper jam) processing. If it is necessary to form a resist pattern for one round of the transfer belt and acquire color misregistration data each time, not only will toner consumption increase, but also image formation must be waited for color misregistration detection. Must.

Therefore, in the present invention, the color shift data is extracted for each of the causes of the color shift, and the color shift components are synthesized in accordance with the phase relationship at the time of image formation, thereby newly forming the transfer belt 1. 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) and 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.

The thus obtained photosensitive drum component color misregistration data B (Y), B (M), B (C) and belt component color misregistration data D are respectively 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 the 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. (4-5) Updating Process of Drum Component Color Misregistration Data In the present embodiment, the monochrome print mode and the color print mode can be switched. When the monochrome print mode is executed, the photosensitive drum 51 is executed.
Since only K rotates, the next time the color print mode is executed, the phase relationship between the photosensitive drum 51K and the other photosensitive drums 51M to 51C will be different from when the respective color shift data is acquired. 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 acquired color misregistration data no longer has any meaning.

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. In this case, toner consumption becomes enormous, maintenance costs increase, and a user's waiting time also occurs. Also,
Such a change in the phase relationship between the photosensitive drums often occurs not only when the print mode is switched, but also during jam processing and maintenance of the photosensitive drums.

To solve such a problem, after the monochrome print mode and before the color print mode is executed, the phase relationship between the photosensitive drum 51K and the other photosensitive drums 51M to 51C is determined by the phase relationship at the time of acquiring the color shift data. However, in practice, the phase relationship of each photosensitive drum once changed due to the inertial force of each photosensitive drum, the braking accuracy of the drive motor, etc., may be used when acquiring data. It is not easy to completely match the positional relationship. In particular, when an inexpensive DC motor is used as the drive motor, since the controllability of the positioning is poor, it takes a long time to execute precise phase matching, and is enumerated as one of the conventional problems described above. There is a risk that the time loss will be further increased.

Therefore, in the present invention, each photosensitive drum 51
When the phase relationship between M and 51K changes, a unit resist pattern is formed for the length of one rotation of the photosensitive drum, and based on this, the drum component color shift data B (Y), B
(M) and B (C) are updated. That is, the unit resist pattern is repeatedly formed by the length of one rotation of the photoconductor drum by the photoconductor drums 51M to 51K, and this is detected by the registration sensor SE4. Data of the color shift amount of the C and Y registration marks is obtained. Here, the obtained color misregistration data for one rotation of the photoconductor drum is supposed to be the color misregistration of the first rotation after the time tbp 'elapses after the detection of the belt origin (origin mark M1) shown in FIG. If the data is data, the data also includes the amount of color misregistration caused by belt running unevenness. Therefore, as is, the data of the drum component color misregistration data B (Y), B (M), B (C) It cannot be adopted as update data. However, in (4-3) above, the belt component color shift data D
From the belt component color misregistration data D, from the portion corresponding to the phase in which the registration mark is formed, that is, from the portion whose phase is deviated by the time tbp 'from the detection of the belt origin, until the photosensitive drum makes one rotation. Is extracted and subtracted from the above-described color shift data for one rotation of the photosensitive drum to obtain color shift data due to only the rotation unevenness of each photosensitive drum, that is, drum component color shift data. Can be.

The newly obtained data is stored in an EEPROM
The data is stored in the register 107 and the drum component color shift data is updated. In the subsequent color shift correction, the updated data is used. As described above, according to the updating method, only by forming the resist pattern for one rotation of the photosensitive drum, appropriate update data can be obtained based on the current phase relationship, so that toner consumption and time loss at the time of updating are minimized. be able to.

(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, initialization is performed to clear the contents of the RAM 105, initialize various registers, and set each unit to the initial mode (step S1). Then, step S2
To start the internal timer. An internal timer sets the processing time of one of the main routines. Next, an input is received from the operation panel 80, 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). Thereafter, a process of acquiring color shift 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 S5). Next, correction data is generated by synthesizing the color misregistration data of each component obtained in step S4, and a process of writing an image to each of the photosensitive drums 51M to 51K is performed while correcting the timing based on the correction data. (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.

First, in step 41, the CPU 10
1 detects the current phase relationship between the photosensitive drum 51K for black and the photosensitive drums 51M to 51Y for other colors. Note that, in the present embodiment, the photoconductor drums 51M to 51Y for color are driven at the same rotation speed via the timing belt by the same drive source.
There is no phase difference between the color photoconductor drums, and only the phase relationship between the photoconductor drum 51K and one of the color photoconductor drums (photoconductor drum 51Y in this embodiment) is detected. It is good.

This phase relationship can be specified by the time tpc1 from the detection of the origin mark M2 by the origin sensor SE2 to the detection of the origin mark M3 by the origin sensor SE3. Next, the CPU 101 reads out the print data of the registration mark of each color from the ROM 106 and outputs the LED arrays 52M to 52M of each color via the LED array driving unit 104.
52K as well as the printer unit 20 via the printer unit control unit 300, so that the
As shown in (a), a unit resist pattern is repeatedly formed for one rotation of the transfer belt 41 (step S4).
2).

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 unit resist pattern of each color. 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 S43).

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 S44). 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).
5).

The color shift data A (Y), A (M), A
From (C), B (Y), B (M), B (C)
B (Y, 1 to 1)
n + 1), B (M, 1 to n + 1), B (C, 1 to n +
1) is subtracted so that the phase relationship between the transfer belt and the photosensitive drum when the color shift data A (Y), A (M), and A (C) are detected is subtracted, so that one round of the transfer belt Belt component color misregistration data D (Y), D
(M) and D (C) can be obtained, and the three are averaged to obtain belt component color shift data D (FIG. 7).
(B)).

The generated drum component color misregistration data B (Y), B (M), B (C) and belt component color misregistration data D are stored in the EEPROM 107 (step S46), and the main routine shown in FIG. Return to
FIG. 12 is a flowchart showing a subroutine for executing the writing process (step S6) based on the stored data.

First, in step 61, the CPU 10
Reference numeral 1 denotes a time tpc2 from the detection of the origin mark M2 by the origin sensor SE2 to the detection of the origin mark M3 by the origin sensor SE3. The phase relationship with the body drums 51M to 51Y is detected. Whether or not the phase relationship between the photosensitive drums has changed from the phase relationship at the time of acquiring the color misregistration data, that is, tpc1 =
It is determined whether it is tpc2 (step S62).

If there is no change, there is no need to update the color misregistration data, so the flow proceeds to step S67. In this step S67, the phase between the photosensitive drum 51K and the transfer belt 41 is detected. On the other hand, the drum component color shift data B (Y), B (M), and B (C) are respectively (n
+1) times repeated data is generated and combined with the belt component color shift data D in accordance with the detected phase to generate correction data E (Y), E (M), and E (C) ( Step S68).

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).
9), based on the correction pulse, the LED array 5 of each color
The color shift is eliminated by driving 2M, C, and Y (step S70).

The black write timing is executed according to the reference pulse. On the other hand, if it is determined in step S62 that the phase relationship between the photosensitive drums has changed, the respective drum component color shift data B (Y), B (M), B
Since (C) needs to be updated, first, a unit resist pattern is repeatedly formed on the transfer belt 41 by the length of one rotation of the photosensitive drum by the photosensitive drums 51M to 51K (step S63). And the color shift data A '(Y), A' (M), A 'for only one rotation
(C) is calculated and read (step S64).

Then, each color shift data A '(Y), A'
From (M) and A ′ (C), of the belt component color shift data D already obtained, the data having the same phase as that of the acquired color shift data is subtracted to obtain new drum component color shift data B. (Y), B (M), and B (C) (step S65), whereby the drum component color shift data B (Y), B (M),
The value of B (C) is updated (step S66), and based on the updated data and the belt component color misregistration data D, the image writing is executed while correcting the timings of steps S67 to S70, and then the process of FIG. Return to the main routine.

In the present method, the synthesizing process and the extracting process are performed by adjusting the phases of the data. However, since the electrical phase adjustment on the data can be performed instantaneously, the time loss and the like for this are reduced. This can be performed with no precision and with high accuracy. <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 above embodiment, the LED array is used as the exposure scanning means for the photosensitive drum, but a laser beam may be used. LED
In the case of exposure using an array, the drive timing for each scanning line may be corrected as described above to correct color misregistration. However, when a laser beam is used, the light is transferred to the photosensitive drum in the following manner. The correction of the write position of the scan line is executed.

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 respectively determined from 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 above 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, this is used. Since the driving speed fluctuates, it causes 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 color shift was corrected by controlling the write timing for each scanning line based on the correction data. The cause of the color shift is the drum component color shift data. With respect to the other M, C, with respect to the rotation of the black photosensitive drum 51K,
The Y rotation of the photosensitive drums 51M, 51C, and 51Y can be regarded as relative rotation unevenness, and the belt component color misregistration data D can be regarded as relative movement unevenness of the transfer belt 41.

Therefore, without changing the writing timing by the LED array 52,
The color misregistration can also be eliminated by controlling the driving speeds of M to 51Y and the transfer belt 41. For that purpose, first, it is necessary to drive each photosensitive drum and the transfer belt independently. For example, each photoconductor drum 51M-
Each part is independently driven by directly connecting the drive shaft of the stepping motor to the rotating shaft of 51K and the shaft of the drive roller 42, respectively. Then, the belt component color deviation data D and the drum component color deviation data B (Y), B (M), B
Based on (C), a reference input pulse (an input pulse set to a frequency for driving at a predetermined system speed) to be sent to a drive circuit of another corresponding stepping motor except for a stepping motor that drives the photosensitive drum 51K. Are respectively corrected in the same manner as in the case of generating the correction pulse shown in FIG. 9, the corrected input pulse is input to the drive circuit of each stepping motor, and each rotation speed is controlled in accordance with its rotation phase. I do.

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, thereby causing a color misregistration. Rotation unevenness and running unevenness (more precisely, the black photosensitive drum 51K
(Rotational unevenness or running unevenness) itself with respect to the rotation of the image, and an excellent reproduced image without color shift can be obtained.

In this case, regarding the necessity of updating the drum component color shift data (see step S62 in FIG. 12), the phase change of each of the photosensitive drums 51M to 51Y with respect to the black photosensitive drum 51K is individually determined. It is better to judge. (4) In the above embodiment, only the color shift in the sub-scanning direction has been described. However, the present invention can also be applied to a case where there is a periodic change in the color shift amount in the main scanning direction. As an example,
The transfer belt may meander, etc., but 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) When creating update data,
A resist pattern having a length corresponding to one rotation of the photosensitive drum is formed. However, if the length is longer than one rotation of the transfer belt, the effect of saving toner and reducing time loss can be obtained to some extent. . (6) In the above embodiment, when forming an image,
Black photosensitive drum 51K and other photosensitive drum 5
When a change in the phase relationship between 1M and 51Y is detected, the data update process is executed. However, even when the phase relationship is not directly detected, when there is an operation with a high probability that the phase relationship changes, the machine is updated. The data update process may be executed in a targeted manner. For example, control may be performed such that the data update mode processing is executed when the apparatus is started, when the mode is switched from the monochrome print mode to the color print mode, or when the jam processing is completed. Means for detecting these (update time detecting means) can be easily configured by a known technique.

(7) 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, the first control means controls each image forming means to repeatedly form a set of resist patterns of each color to form the transfer belt. The first cycle and the second cycle longer than the first cycle are obtained from the information about the color shift amount by the color shift component extracting means by detecting these and detecting information about the color shift amount of each color for each set. Is extracted. Then, based on each of the extracted color shift components, the color shift correcting means corrects the color shift so that color shift does not occur at the time of image formation by the multiple transfer. It is possible to execute highly accurate color misregistration correction.

Further, the updating means repeatedly forms the resist pattern set for a time equal to or longer than the first cycle and shorter than the second cycle, and detects the color shift amount obtained by detecting the resist pattern. The data is updated by obtaining the color shift component having the first cycle from the information about the color shift component having the second cycle and the color shift component having the second cycle already obtained.

In order to obtain a color misregistration component having the longer second period, the first control means needs to register the resist pattern on the transfer belt at least for a length corresponding to a time longer than the second period. However, according to the above-described updating means, the resist pattern is not formed until the length becomes equal to or longer than the length corresponding to the long second period. The color shift component having the first cycle can be obtained from the resist pattern thus obtained.

As a result, the update time of the color misregistration component having the first cycle can be shortened, and the time loss and toner consumption for updating can be reduced, or the consumption of the image forming unit can be reduced. Further, according to the present invention, the color shift component having the first cycle depends on the rotation unevenness of each image carrier drum, and the updating unit determines that the rotation phase between the respective drums has changed. Since the data of the color shift component having the first cycle is updated upon detection, the color shift component that is most likely to fluctuate can be updated at an appropriate time in the image forming apparatus. Color misregistration correction can be executed.

[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;

[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

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA09 DA38 DA50 DE07 EB06 EC03 ED04 2H030 AA01 AB02 AD17 BB16 BB56 5C077 LL19 MM27 MP08 PP23 PP33 PP38 PP39 PP43 PP78 PQ04 PQ24 TT03 TT06 5C079 HB03 MA03 LA03 9A001 BB01 BB02 BB03 BB04 DD13 EE05 HH21 HH23 HH28 HH31 JJ35 KK16 KK29 KK31 KK37 KK42 LL02 LL05

Claims (3)

[Claims] A plurality of image forming means for forming images of different colors, wherein multiple images of each color formed by each 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 first 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 a plurality of times; Color shift information acquiring means for detecting information on the amount of color misregistration of each color by detecting the resist pattern of each color, and a color misregistration component having a first cycle and a first cycle based on the information on the amount of color misregistration. A color shift component extracting means for extracting a color shift component having a longer second cycle, an updating means for updating data of the color shift component having the first cycle, and a color shift component having the first cycle When A color shift correction unit that corrects, based on a color shift component having a cycle of 2, during image formation by the multiple transfer so as not to cause a color shift. A second control unit for controlling each of the image forming units so as to repeatedly form the set of the resist patterns for a time shorter than the period of 2, and detecting the resist patterns by the color misregistration information acquiring unit. An image forming apparatus characterized in that data is updated by obtaining a color shift component having the first cycle from information on the obtained color shift amount and the color shift component having the second cycle. 2. Each of the image forming units includes an image carrier drum and a writing unit that writes an image on the image carrier drum, and the color misregistration component having the first cycle is applied to each image carrier. The update means includes phase detection means for detecting that a rotation phase between the drums has changed, and the change in the rotation phase has been detected by the phase detection means. 2. The image forming apparatus according to claim 1, wherein the data of the color shift component having the first cycle is updated. 3. The image forming apparatus according to claim 2, wherein the first cycle is a rotation cycle of the image carrier drum, and the second cycle is a rotation cycle of the transfer belt.