JPH11272032A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of correcting positional deviation with higher accuracy while restraining the labor of an operator as small as possible. SOLUTION: When a variable N(copy counting) attains 1,000(sheets) ('Y' at S1), a 1st resist pattern is formed on the surface of a transfer belt so as to calculate the positional deviation 1 (S10 to S12). After forming a 2nd resist pattern on a recording sheet, the recording sheet is set on an original glass plate and read so as to calculate the positional deviation 2 (S13 to S16). After a difference between the obtained positional deviation 1 and 2 is calculated as correction data and stored in an EEPROM, the variable N is reset (S17 to S19). When the variable N does not attain 1,000 ('N' at S1), the positional deviation 1 is calculated (step S20 to S22), it is corrected based on the correction data so as to calculate the positional deviation 1', and then the variable N is incremented by 1 (S23 and S24). An image writing position is corrected based on the positional deviation 1' thus obtained (S25).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, and more particularly to an improvement in a technique for correcting a color shift of a color image formed by superposing a plurality of color images.

[0002]

2. Description of the Related Art For example, in a tandem type full-color image forming apparatus, photosensitive drums of cyan (C), magenta (M), yellow (Y), and black (K) are moved along a transfer surface of a transfer belt. The toner image formed on the peripheral surface of the photosensitive drum by the image forming unit is sequentially superimposed on a recording sheet conveyed by a transfer belt and transferred to form a multicolor image. I have.

[0003] Such a tandem type image forming apparatus includes:
Since the photosensitive drums are individually provided in correspondence with the toners of the respective color components, there is a great advantage that a full-color image can be formed at a high speed with one pass of paper. However, on the other hand, it is necessary to multiply transfer the toner images of the respective color components onto the recording paper without color shift. For that purpose, it is important to align the images of the respective colors. However, since the transfer belt is stretched over a plurality of rollers and rotated by transmitting rotational driving force, the displacement of the transfer belt gradually in the axial direction due to variations in the diameter of each roller, elongation of the transfer belt itself, and the like. As a result, a slight skew or meandering is caused in the traveling direction, so that the transfer position of each color is shifted to cause a color shift.

In order to solve such a problem, for example, in a conventional tandem type image forming apparatus, a resist pattern of each color is sequentially formed on a transfer belt every time an image is formed, and the formation position is determined by a photoelectric sensor. The position shift amount of each color is detected to determine the position shift amount, and the color shift amount is prevented by correcting the position shift amount at the time of writing an image to each photosensitive drum (hereinafter, the position shift amount of each color is detected. This is called “position shift detection”, and correcting the position shift amount is called “position shift correction”.

[0005]

However, even if a resist pattern is formed on a transfer belt to correct the positional deviation as in the prior art, the color deviation has not always been eliminated. This is considered to be caused by a slight shift (transport shift) between the traveling speed of the transfer belt and the moving speed of the recording sheet.

That is, the electrostatic characteristics of the transfer belt deteriorate with time, and the sheet attraction force decreases. When the recording sheet is conveyed in such a state, the recording sheet is not firmly adsorbed on the transfer belt, and a conveyance deviation occurs. Will happen. Such a tendency is remarkable especially in the case of a thick recording sheet which is stiff and hard to adhere to the transfer belt surface. Further, in a recent miniaturized image forming apparatus, the distance between the transfer position of the reproduced color in which the transfer is performed first, for example, the transfer position of cyan (C) and the timing roller is very short. , The trailing edge may still be applied to the timing roller. In such a case, if there is any difference in the sheet conveying speed between the transfer belt and the timing roller, when the trailing end of the recording sheet is restrained by the timing roller, the recording sheet is further conveyed and is further conveyed. The movement speed is different from the state where the restraint is released, and also in this case, the conveyance shift occurs.

As described above, if the recording sheet is conveyed with a shift on the transfer belt, the color shift cannot be prevented no matter how much the resist pattern is formed on the transfer belt and the position shift is corrected. Therefore, Japanese Patent Application Laid-Open No. 6-261177
In the publication, a resist pattern of each color is formed on a recording sheet, an operator sets the recording sheet on a document glass plate of an image reader section, and the resist pattern formed on the recording sheet is subjected to a CCD image sensor. A method is disclosed in which the image data is read and the positional deviation is corrected based on the image data obtained by the reading. According to this method, the resist pattern is directly transferred onto the recording sheet, and the amount of displacement is calculated based on the output of the CCD image sensor having high reading resolution. Accurate misregistration correction can be performed.

However, in this method, the operator must set the recording sheet on the image reader every time the position shift is corrected. In the formation of a color image, it is desirable to correct the misregistration as frequently as possible in order to prevent color misregistration. Work efficiency is extremely reduced, and a large amount of recording sheets are wasted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and a high-quality image can be obtained by performing higher-accuracy positional displacement correction without requiring the operator as much as possible. It is an object to provide an obtained image forming apparatus.

[0010]

In order to achieve the above object, the present invention forms an image of each color on a plurality of image carriers by image writing means based on image data read by image reading means. Is transferred to a transfer material conveyed by a transfer material conveying body to form a multi-color image, controlling the image writing means,
Control means for forming a first resist pattern on the transfer surface of the transfer material transporter and a second resist pattern on the transfer material for each color; First calculating means for detecting the first resist pattern, and calculating the relative positional shift amount of the first resist pattern of each color based on the detection result; and a transfer material on which the second resist pattern is formed. Is calculated by the first calculating means and the second calculating means for calculating the relative displacement amount of the second resist pattern of each color based on the image data obtained by reading the image data by the image reading means. A correction data storage unit for obtaining a difference between the positional deviation amount and the positional deviation amount calculated by the second calculating unit for each corresponding color and storing the difference as correction data; The calculated position shift amount is corrected by the correction data, characterized by comprising an image writing position correcting means for correcting the image writing position by said image writing means based on the correction results.

Further, the formation range of the first or second resist pattern in the sub-scanning direction is set so that the variation in the amount of displacement caused by driving unevenness of the transfer material transporting body falls within a predetermined range. It is characterized by being. Also,
The first or second resist pattern is formed such that at least a black resist pattern does not overlap a resist pattern of another color.

The image reading means is capable of optically enlarging and reading an original image.
Tentatively calculates the relative positional deviation amount of each color based on the image data of the second resist pattern of each color on the transfer material that is read in an enlarged manner, and divides the calculation result by the enlargement magnification. Thus, the amount of displacement of the second resist pattern of each color is obtained.

[0013]

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 a copying machine 1 according to the present embodiment. As shown in FIG. 1, the copying machine 1 includes an image reader unit 10 for reading a document image roughly divided into:
A printer section 20 for printing and reproducing the image read by the image reader section 10 on a recording sheet.

The image reader section 10 is of a known type that reads an image of an original placed on an original glass plate (not shown) by moving a scanner. The original image is composed of red (R) and green (G). ), Blue (B), and is converted into electric signals by a CCD color image sensor (not shown).
G and B image data are obtained.

The image data for each color component obtained by the image reader unit 10 undergoes various data processing in the control unit 30, and further undergoes 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 an image memory 33 (see FIG. 2) in the control unit 30 for each color, and after being subjected to necessary image correction for positional deviation correction, synchronized with the supply of the recording sheet S. The data is read out for each scanning line and becomes a drive signal for the laser diode. The printer unit 20 forms an image by a well-known electrophotographic method. The printer unit 20 faces a recording sheet transport unit 100 in which a transfer belt 103 is stretched around a drive roller 101 and a support roller 102, and faces the transfer belt 103. C arranged at a predetermined interval 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”).
The image forming units 40C to 40K for the respective colors of M, Y, and K, a sheet feeding unit 50 arranged on the upstream side of the recording sheet conveying unit 100, and a known fixing unit 81 arranged on the downstream side.

Each of the image forming sections 40C to 40K includes an exposure scanning section 70C to 70K and an image processing section 60C to 60K, respectively.
It is composed of The exposure scanning units 70C to 70K
A laser diode 46C to 46K that emits a laser beam in response to a drive signal output from the control unit 30; and a polygon mirror for deflecting the laser beam and exposing and scanning the photosensitive drums 41C to 41K in the main scanning direction. 47C ~
47K or the like.

The image processing units 60C to 60K include photosensitive drums 41C to 41K, charging chargers 42C to 42K disposed around the photosensitive drums 41C to 41K, and a developing device 43.
C to 43K, cleaners 44C to 44K, and transfer rollers 45C to 45K. The paper supply unit 50 includes a paper supply cassette 51 for storing the recording sheet S, a pickup roller 52 for feeding out the recording sheet S from the paper supply cassette 51, and a timing for feeding the recording sheet S to the transfer belt 103. And a timing roller 53.

The laser diodes 46C to 46K of the exposure scanning units 70C to 70K receive the driving signals from the control unit 30 to emit laser beams, respectively, and the laser beams of the polygon mirrors 47C to 47K rotate at a constant speed. The light is reflected and deflected by the mirror surface, and the respective surfaces of the photosensitive drums 41C to 41K are exposed and scanned. Photoconductor drums 41C-4
1K is charged uniformly by charging chargers 42C to 42K after the residual toner on the surface is removed by cleaners 44C to 44K before receiving the exposure, and is further irradiated with an eraser lamp (not shown) to eliminate the charge. When the laser beam is exposed to light in such a uniformly charged state, electrostatic latent images are formed on the surfaces of the photosensitive drums 41C to 41K.

Each electrostatic latent image is developed by a developing unit 43 of each color.
M to 43K, thereby developing the photosensitive drum 4
C, M, Y, and K toner images are formed on the surfaces 1C to 41K, and are sequentially transferred onto the recording sheet S conveyed by the recording sheet conveying unit 100. 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 S in a superimposed manner.

The recording sheet S on which the toner images of each color are multiplex-transferred is conveyed to a fixing unit 81 by a transfer belt 103, where the recording sheet S is pressed with high heat, and the toner particles on the surface are fused to the sheet surface. And fix it, and then the discharge tray 8
2 is discharged. An operation panel 90 is provided at an easy-to-operate position on the front of the image reader unit 10, and includes a numeric keypad for inputting the number of copies, a start key for instructing the start of copying, a selection key for selecting enlargement / reduction copying, Setting keys for setting various copy modes,
A display unit or the like for displaying a mode set by the setting key or the like by a message is provided.

A photoelectric sensor 80 is disposed at the most downstream edge of the transfer belt 103. In the present embodiment, the transfer belt 103 uses an opaque material. Therefore, as the photoelectric sensor 80, a reflective photoelectric sensor having a light-emitting element such as a light-emitting diode and a light-receiving element such as a photodiode is used. You. The detection light emitted from the light emitting element of the photoelectric sensor 80 is transferred to the transfer belt 1
03 is reflected by the detection area on the surface and received by the light receiving element,
Thereby, the first color of each color formed on the transfer belt 103 is formed.
A resist pattern (see FIG. 3) is detected.

When the transfer belt 103 is transparent, a transmission type photoelectric sensor is used, and a light emitting element and a light receiving element are arranged to face each other with the transfer belt 103 interposed therebetween. (2) Configuration of Control Unit 30 Next, the configuration of the control unit 30 will be described with reference to FIG. As shown in the figure, the control unit 30 includes a CPU 31, an image processing unit 32, an image memory 33, a displacement correction unit 34,
Laser diode drive unit 35, RAM 36, ROM 37
And an EEPROM 38 and the like.

The image processing unit 32 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, edge enhancement processing, and the like. After making the correction
Image data of reproduced colors of C, M, Y, and K is generated and output to the image memory 33, and the image data is stored for each color. At this time, the number of pages of the read document and the storage position (address) in the image memory 33 are associated with each other in the RAM.
36 is stored in the management table.

The displacement correcting unit 34 generates a corrected image by changing the storage position of each pixel of the image data in accordance with an instruction from the CPU 31. Laser diode drive unit 35
Drives each laser diode based on the corrected image data. The RAM 36 stores, in addition to the management table, a displacement amount calculated based on a displacement detection operation described later, and further temporarily stores various control variables, the number of copies, a print mode, and the like set from the operation panel 90. .

In the ROM 37, a control program relating to a scanning operation in the image reader unit 10 and an image forming operation in the printer unit 20, printing data of first and second registration patterns to be described later, a control program relating to detection of misregistration, and an image A program and the like for correcting positional deviation are stored. EEPROM38
CPU 31 based on a displacement detection operation described later.
And a count table for storing the copy count and the like. The EEPROM 38 may be another nonvolatile memory, for example, an SRAM backed up by a battery.

The CPU 31 receives input from various sensors including the photoelectric sensor 80, reads a necessary program from the ROM 37, performs data processing in the image processing unit 32, writes / reads image data in the image memory 33, and A smooth copy operation is performed by controlling the misregistration detection operation of each color and the correction contents of the image data in the misregistration correction unit 34, or integrally controlling the operations of the image reader unit 10 and the printer unit 20 with timing. Let it run.

FIG. 3 is a diagram showing an example of a resist pattern (hereinafter, referred to as a "first resist pattern") formed on the transfer belt 103 at the time of the displacement detection operation. Each of the first resist patterns 111C to 111K has a V-shape and includes a first linear portion orthogonal to the transport direction and a second linear portion forming an angle of 45 ° with the first linear portion, and is transferred for each color. Formed on a belt. Print data for forming the first resist patterns 111C to 111K is stored in advance in the ROM 37 (see FIG. 2).
Based on the printing data, the transfer belt 1 is controlled by the exposure scanning units 70C to 70K and the image processing units 60C to 60K.
The first resist patterns 111C to 111K are formed on the substrate 03. At this time, in a state where the color shift does not occur in the transfer images on the photosensitive drums 41M to 41K, the position in the direction (main scanning direction) orthogonal to the transport direction A is the same and the direction parallel to the transport direction A ( In the sub-scanning direction), they are formed with a distance D from each other.

Each linear portion of the first resist patterns 111C to 111K formed by being transferred from the photosensitive drums 41C to 41K onto the transfer belt 103 corresponds to the transfer belt 103.
Is detected by the photoelectric sensor 80 on the detection line indicated by the broken line in FIG.
Sent to 1. The CPU 31 receives the detection signal from the photoelectric sensor 80 and obtains the amount of positional deviation of each color in the main scanning direction and the sub-scanning direction from the resist patterns 111C to 111K formed on the transfer belt 103 as follows.

FIG. 4 is a diagram showing a waveform of a detection signal received from the photoelectric sensor 80. Detection signals 121 to 128
Are waveforms obtained when the linear portions of the resist patterns 111C to 111K are sequentially detected from the downstream side in FIG. Since the light receiving sensor in the photoelectric sensor 80 has a constant sensing width, the waveform of the detection signal has a peak, and therefore, it is difficult to determine the exact position of each linear portion.

Then, the CPU 31 determines the center position (or peak position) of the detected value as a reference position from the detected signal value by a method of calculating the center of gravity or the like, and determines the position as the first linear portion of each resist pattern on the detection line. (Ky to Cn at the lower part of the waveform of the detection signal indicate the reference positions of the respective linear portions. In the same figure, for example, “Ky” is used. Indicates the first linear portion of the black resist pattern as “K
"n" indicates the second linear portion of the black resist pattern. The same applies to other colors. ).

The CPU 31 includes a clock generation circuit therein, and includes a first linear portion of each resist pattern 111,
The number of clocks at the time of detection of each reference position of the second linear portion is stored in the RAM 36, and the difference between these values is calculated to calculate the difference between the first linear portion detection and the second linear portion detection in each of the resist patterns 111C to 111K. Times Tk to Tc and times Tky, Tkm, and Tkc required from detection of the first linear portion of the resist pattern 111K to detection of the first linear portions of the other resist patterns 111Y to 111C are obtained.

Here, assuming that the traveling speed of the transfer belt 103 during image formation is V, the registration pattern 111
The distance between K and the first linear portion of the resist pattern 111Y is V · Tky, and similarly,
K first linear portion and resist patterns 111M and 111C
Are the distances between the first straight portions V. Tkm and V.
Tkc.

As described above, in a state where there is no color shift, the interval between the respective resist patterns 111C to 111K should be D. Therefore, the respective resist patterns 111Y and 11Y based on the resist pattern 111K are used as a reference.
The displacement amounts of the first linear portions 1M and 111C (that is, the displacement amounts in the sub-scanning direction) are D1ky and D1ky, respectively.
If 1 km and D1kc are obtained, they can be obtained by the following equations.

D1ky = DV · Tky D1km = 2D−V · Tkm D1k = 3D−V · Tkc On the other hand, each resist pattern 111 on the detection line
The distances (hereinafter, simply referred to as “line intervals”) between the first linear portion and the second linear portion in C to 111K are Dk and Dk, respectively.
Assuming Dy, Dm, and Dc, these values are calculated by the following equations using the times Tk to Tc required from the detection of the first linear portion to the detection of the second linear portion in each of the resist patterns 111C to 111K. Desired.

Dk = V · Tk Dy = V · Ty Dm = V · Tm Dc = V · Tc Therefore, the black line spacing Dk and the other color line spacing D
The differences from y, Dm, and Dc are D2ky and D2k, respectively.
Assuming m and D2kc, the following equations are obtained.

D2ky = Dk-Dy D2km = Dk-Dm D2kc = Dk-Dc As described above, the first linear portion of each of the resist patterns 111C to 111K is orthogonal to the transport direction (sub-scanning direction), Since the straight line portion forms an angle of 45 ° with the first straight line portion, the difference between the line interval in the black resist pattern on the detection line and the line interval of the other colors is the black image in the main scanning direction. This is equivalent to the amount of positional deviation in the main scanning direction between the writing position and the image writing position for another color.

As described above, the position shift amounts (D1ky, D1k) of the image writing positions of other colors in the sub-scanning direction with reference to the black image writing position.
m, D1kc) and the amount of displacement (D2ky, D2km, D2kc) in the main scanning direction are calculated by the CPU 31. Further, the copying machine 1 forms a resist pattern not only on the transfer belt 103 but also on the recording sheet S, and calculates the amount of positional deviation from the resist pattern (hereinafter, formed on the recording sheet S). The resist pattern to be formed is referred to as a “second resist pattern”.)

As described above, when a slight shift (conveyance shift) occurs between the traveling speed of the transfer belt 103 and the moving speed of the recording sheet S, the recording sheet S is transferred to the transfer belt 103.
When the sheets are conveyed with a shift, the transfer positions of the respective colors may shift to cause a color shift. In such a case, even if the first resist pattern is formed on the transfer belt 103 and the image writing position is corrected, the color shift cannot be prevented.

Therefore, the recording sheet S is actually conveyed to form a second resist pattern of each color on the recording sheet S. The recording sheet S is set on the original glass plate 11 and formed for each color. By reading the registered second resist pattern, the CPU 31 calculates the relative displacement amount of each color as follows. FIG. 5 shows the recording sheet S
Second resist pattern 200C for each color formed above
It is a figure showing an example of 200K composition.

Second resist patterns 200C to 200K
Are linear portions 201C to 20C parallel to the main scanning direction for each color.
1K, and linear portions 202C to 202K parallel to the sub-scanning direction.
Consists of Second resist pattern 200C to 200K
Is previously stored in the ROM 37 (see FIG. 2), and based on the print data, the exposure scanning units 70C to 70K and the image processing unit 60C
Each of the patterns 200C to 200K is formed on the recording sheet S conveyed at a speed of 60K to 60K. At this time, in a state where no color misregistration occurs in the transferred images on the photoconductor drums 41M to 41K, each of the linear portions 201C to 201K, 20
In 2C to 202K, they are formed with a distance d from each other.

The operator operates the second resist pattern 200C.
The recording sheet S on which ~ 200K is formed is placed on the original glass plate 1.
1 is placed at the original reading position, and the image reader 10
To read. The R, G, and B electrical signals read by the image reader unit 10 are transmitted to the image processing unit 3 as described above.
The image data is converted into image data of C, M, Y, and K reproduction colors for each pixel in 2 and stored in the image memory 33 for each reproduction color.

Based on such image data, the CPU 31
Calculates the relative displacement amount of each color of the second resist pattern as follows, for example. First, the CPU 31
Stores image data of each reproduction color at an address corresponding to the position of the detection lines 203 and 204 in FIG.
, And store them in the internal line memory.

FIG. 6 is a waveform diagram showing a change in the density of image data on the detection line 204 stored in the line memory. The horizontal axis corresponds to the number of addresses (the number of pixels) in the sub-scanning direction. I have. The waveforms 211C to 211K indicate the densities of the linear portions 201C to 201K on the detection line 204, and the CPU 31 obtains the addresses of the centroid positions 212C to 212K in each waveform by a known calculation process. Thereby, each linear portion 201C of C, M, Y, and K
The actual distance can be obtained by multiplying the distance (the number of pixels) on the pixel plane between and 201K by the pixel interval (63.5 μm when read at the same magnification at a pixel density of 400 dpi). It can be easily calculated. As mentioned above,
Since each of the straight portions 201C to 201K is formed at an interval of just d when there is no color shift,
Based on the calculated value and the value of d, relative to the second resist pattern of the other three colors in the sub-scanning direction with respect to the black (K) image writing position in the same manner as in the case of the first resist pattern. The target position shift amount can be calculated.

The amount of displacement in the main scanning direction is similarly calculated based on the image data on the detection line 203. The data of the calculated positional deviation amount of the second resist pattern is temporarily stored in the RAM 36. In the above, the R, G, and B electric signals read by the image reader unit 10 are converted into C,
After converting the image data into the image data of each of the M, Y, and K reproduction colors, the intervals between the second resist patterns 200C to 200K of each color were obtained. The R, G, and B electric signals were detected for each of the detection lines 203 and 204. Store the synthesized data in line memory,
Distance information between the colors may be obtained.

The second resist patterns 200C-2C
It is desirable that each of the straight portions 201C to 201K of 00K be formed within a range as short as possible in the sub-scanning direction. That is, there is a certain limit in the processing accuracy of the drive roller 101, and even if there is even a slight eccentricity, the traveling speed of the transfer belt 103 that rotates while being stretched over the drive roller 101 varies (drive unevenness). At this time, if the formation positions of the respective linear portions 201C to 201K are separated from each other in the sub-scanning direction, the formation positions are more susceptible to drive unevenness, so that the respective linear portions are close to each other in the sub-scanning direction. It is desirable to form them.

More specifically, the color misregistration appears remarkably when it is displaced from the image forming position by two pixels for each color in pixel units.
Each of the linear portions 201C to 201K is such that the variation of the writing position in the sub-scanning direction from 0C to 200K is less than 2 pixels each other.
The range in the sub-scanning direction in which K is formed, that is, the distance d1
If (see FIG. 5) is determined, it is possible to minimize at least the adverse effect of the driving unevenness on the detection of the positional deviation.

A specific value of d1 that satisfies such a condition can be obtained in advance by an experiment. For example, when the diameter of the driving roller 101 is 30 mm, 1/5 to 1 to 1 of the peripheral length of the driving roller is considered. By making the size of / 10,
Good results could be obtained. It is desirable that the first resist patterns 111C to 111K are similarly formed within the range of the distance d1 in the sub-scanning direction.

In order to make the formation range of the resist pattern in the sub-scanning direction as small as possible, especially for the second resist pattern, C, M, and C, excluding black (K), are used.
The initial condition may be set so that the Y resist pattern is formed to partially overlap. The overlapped portion is different from the original C, M, and Y colors, but can be distinguished by the CCD color image sensor, so that the displacement amount can be calculated. As for the first resist patterns 111C to 111K, if an image sensor capable of reading color information equivalent to the CCD color image sensor is used instead of the photoelectric sensor 80, C, M, and Y can be overlapped.

By forming the second resist patterns 200C to 200K on the recording sheet as described above, the pattern image becomes clearer, and these are read by the CCD sensor of the image reader unit 10 to detect the amount of displacement. As a result, the detection accuracy is significantly improved as compared with the case where the photoelectric sensor 80 detects the positional deviation amount of the first resist pattern on the transfer belt 103, and there is no problem of transport deviation.

However, in order to always form the second resist patterns 200C to 200K only on the recording sheet and to detect the amount of displacement, an operator's act of placing the recording sheet on the original glass plate 11 is required. It becomes necessary, and the more the frequency of the positional deviation correction increases, the more trouble becomes, and the more wasteful the recording sheet becomes. Therefore, in the present invention, the difference between the amount of positional deviation based on the second resist pattern and the amount of positional deviation based on the first resist pattern is obtained in advance and stored as correction data. The amount of misregistration due to the first resist pattern on the transfer belt 103 is detected and corrected based on the correction data to be executed (hereinafter, the first resist pattern 111 on the transfer belt 103 is used).
The position shift amount based on C to 111K is referred to as “position shift amount 1”,
Second resist patterns 200C to 200 on recording sheet
The displacement amount calculated based on K is referred to as “displacement amount 2”. ). (3) Control Operation of Position Shift Detection by Control Unit 30 FIG. 7 is a flowchart showing a control operation of position shift detection. Note that this flowchart is configured to execute the positional deviation correction each time a color image is formed once, and to update the above-described correction data every 10,000 times.

First, the CPU 31 determines whether or not the variable N has reached a predetermined value 1000 (sheets) when forming an image (step S1). Here, the variable N is a copy count that is incremented by 1 in step S24 every time image formation is performed, and the value is stored in a count table in the EEPROM 38. To obtain the value of the variable N.

When it is determined that the variable N has reached 1000 (“Y” in step S 1), the CPU 31 firstly places the first resist patterns 111 C to 111 C for each color on the transfer belt 103.
111K is formed, the displacement amount 1 is calculated, and the RAM 3
6 (steps S10 to S1).
2). After that, the recording sheet S is fed from the sheet cassette 51, and the second resist patterns 200C to 200K of each color are formed on the recording sheet S. When the recording sheet S is discharged from the copying machine 1, the CPU 31 operates the operation panel 18
A message saying "Please set the recording sheet on which the resist pattern is copied on the original glass plate and press the start key" is displayed on the upper display section.

Second resist patterns 200C to 200K
Is set on the original glass plate 11 by the operator, and when the start key is pressed, CP
The U31 controls the image reader unit 10 to read the original image at the same magnification, calculates the displacement 2 and stores it in a predetermined storage position in the RAM 36 (steps S13 to S1).
6). Then, the CPU 31 reads out the stored positional deviation amounts 1 and 2, finds these differences for each color, and stores them as correction data in a correction table in the EEPROM 38 (steps S17 and S18). The value of the difference corresponds to a shift amount (conveyance shift amount) of the movement of the recording sheet and the transfer belt 103 caused when the recording sheet is conveyed by the transfer belt 103.

Next, the CPU 31 resets the variable N stored in the count table in the EEPROM 38 (step S19) and returns. On the other hand, if the variable N is 1
000 is not reached (step S
1 and “N”), the first resist patterns 111C to 111K of the respective colors are formed on the transfer belt 103, and the positional shift amount is 1
Is calculated and stored in a predetermined storage location of the RAM 36 (steps S20 to S22). And the CPU 31
36, the correction data is read out from the correction table in the EEPROM 38 for each corresponding color, and the difference indicated by the correction data is added to the correction data to correct the correction data to calculate the positional shift 1 '. (Step S2
3). Then, after incrementing the variable N by 1 (step S24), the CPU 31 sends the displacement amount 1 'to the displacement correction unit 34. The displacement correcting unit 34
Based on the displacement amount 1 ', the address of the image data read from the image memory 33 is changed and stored in the corrected image memory to generate a corrected image, thereby correcting the image writing position (step S25). And return.

As described above, the position difference 1 ′ is obtained by adding the previously obtained difference to the calculated position difference 1 to obtain the position deviation 1 ′ during the period until the variable N reaches 1000. It is unlikely that a slight speed difference between the transfer belt 103 and the timing roller 53 or a decrease in the attraction force of the transfer belt 103 is newly generated. If the position difference 1 is corrected using the calculated difference, Actual recording sheet S
This is because it is considered that the positional deviation amount can be obtained with almost the same accuracy as the positional deviation amount 2 obtained by forming the second resist pattern thereon. As a result, the control for calculating the positional deviation amount 2 using the recording sheet S can be performed only once every 1000 (sheets) in the copy count, so that the operator sets the recording sheet S on the original glass plate 11. The work is remarkably reduced, and the recording sheet S is not wasted. In addition, the copy count is 1000
Until (sheets) are reached, each time image formation is performed, the position shift amount 1 is calculated and corrected using the difference, so that the position shift amount substantially equal to that when the recording sheet S is used is obtained. This makes it possible to correct the image writing position by calculation, and to perform higher-accuracy positional deviation correction than in the conventional case in which a resist pattern is simply formed on the surface of the transfer belt 103 to perform positional deviation correction. be able to. (4) Modifications It is needless to say that the present invention is not limited to the above embodiment, and the following modifications can be considered.

(4-1) In the above embodiment, the recording sheet S set on the original glass plate 11 in step S15 in FIG. 7 is read at the same magnification (100%), and the second resist patterns 200C to 200C for each color are read. 200K misalignment 2
However, the recording sheet S may be read by increasing the optical reading magnification, for example, to 200%. This makes it possible to calculate the positional deviation amount 2 with higher accuracy without increasing the resolution at the time of reading by the scanner. That is, the second resist patterns 200C to 200C in which the center of gravity of the linear portion of each color is twice as large.
Since the calculation is performed based on 200K, it is equal to the case where the resolution is doubled for a resist pattern of substantially the same size, and the calculation accuracy is improved as compared with the case of the same size. here,
The CPU 31 first calculates the position of the center of gravity of the enlarged pattern, calculates the temporary position shift amount 2 for each color from this, and divides this by the enlargement magnification (2 times) to obtain the true position shift amount 2. Is calculated.

(4-2) In the above embodiment, when the variable N (copy count) reaches the predetermined value 1000 in step S1 of FIG. 7, the displacement amount 1 and the displacement amount 2 are calculated. The variable N is not limited to this value. For example, a period (timing) in which a decrease in the attraction force of the transfer belt 103 occurs is derived from experimental data, and the number of copies to be performed during this period is calculated in advance. Therefore, this may be set as a predetermined value.

During the continuous copying, the variable N is set to a predetermined value of 10.
If the number reaches 00, steps S10 to S19 may be performed after the end of the continuous copying. In this way, the copying operation is not interrupted during the continuous copying, so that the usability is improved for the user. Further, the condition for calculating the positional deviation amount 1 and the positional deviation amount 2 is not limited to the copy count, and may be, for example, when the power of the copier 1 is turned on or when paper jam occurs.

(4-3) In the above embodiment, the displacement detection operation is performed every time image formation is performed once. However, the displacement detection operation does not need to be performed every time, for example, every 10 times. May be performed. In this case, in addition to the variable N, a copy count that is incremented by 1 every time an image is formed is provided as a variable M.

The CPU 31 calculates the calculated positional deviation amount 1 '
Is stored in the EEPROM 38, and the variable M is 10
Until the first resist pattern 111C-
After the variable N in step S24 (FIG. 7) is incremented by 1 without forming the 111K on the transfer belt 103 and calculating the displacement amount, each color is determined based on the stored displacement amount 1 '. The address of the image data is changed to correct the image writing position. When the image formation is performed and it is detected that the variable M has reached 10, the operations of the above steps S20 to S23 are performed, a new displacement amount 1 'is calculated, and the previous data stored in the EEPROM 38 is updated. After that, the variable M is reset.

(4-4) In the above embodiment, the shapes of the first resist patterns 111C to 111K and the second resist patterns 200C to 200K are different from each other. It may be formed on the sheet S. (4-5) In the above embodiment, when the variable N reaches 1000, first the first resist patterns 111C to 111K are formed on the transfer belt 103, and then the second resist patterns 200C to 200K are formed on the recording sheet S. Although 200K is formed, the order may be reversed.

(4-6) The first resist patterns 111C to 111K in the above embodiment have a configuration in which a first linear portion and a second linear portion forming an angle of 45 ° with the first linear portion are connected. However, the present invention is not limited to such a configuration, and a linear portion parallel to the sub-scanning direction and a linear portion forming a certain angle with the straight line may be included. Also, the angle need not be limited to 45 °.

The first resist pattern 111 of each color is used.
C-111K and second resist pattern 200C-2
If a plurality of 00Ks are provided on the transfer belt 103 and the recording sheet S, respectively, and the positional deviation is corrected based on the average value of these detection values, the accuracy is improved. (4-7) In the above-described embodiment, a full-color tandem-type copying machine has been described.
The present invention can also be applied to a copying machine using a transfer drum instead of 03.

Further, the present invention is not limited to a full-color copying machine, but can be applied to other electrophotographic image forming apparatuses capable of reading a document image.

[0066]

As described above, according to the present invention, the difference between the displacement calculated by the first calculator and the displacement calculated by the second calculator is stored as correction data as correction data. Means, a first resist pattern of each color is formed on a transfer material transporting body, the amount of displacement is calculated, and this is corrected based on the correction data. It is not necessary to frequently read the resist pattern formed on the upper surface by the image reading means and calculate the positional deviation amount.
Thereby, the labor of the operator is remarkably reduced, and the displacement can be suppressed without wasting the transfer material, so that a high-quality reproduced image can be obtained.

Further, since the formation range of the first or second resist pattern of each color in the sub-scanning direction is set, the driving unevenness of the transfer material conveyance body when the first or second resist pattern of each color is formed. Can be reduced. Also, in order to make the formation range of the first or second resist pattern as small as possible in the sub-scanning direction,
Since at least the black resist pattern is formed so as not to overlap the resist pattern of another color, it is possible to further reduce an error caused by driving unevenness of the transfer material transporting body.

Further, since the second resist pattern of each color is optically enlarged and read by the reading means, the amount of displacement of the second resist pattern of each color can be calculated with high accuracy without increasing the reading resolution. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a tandem-type copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram of a control unit installed in the copying machine.

FIG. 3 is a diagram showing an example of a first resist pattern formed on the surface of a transfer belt.

FIG. 4 is a diagram showing a waveform of a detection signal detected by a photoelectric sensor.

FIG. 5 is a diagram illustrating an example of a second resist pattern formed on the surface of the transfer belt.

FIG. 6 is a waveform diagram showing a change in density of image data on a detection line stored in a line memory.

FIG. 7 is a flowchart illustrating a position shift detection operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image reader part 11 Original glass plate 30 Control part 31 CPU 32 Image processing part 33 Image memory 34 Position shift correction part 35 Laser diode drive part 36 RAM 37 ROM 38 EEPROM 41C-40K Photoconductor drum 53 Timing roller 60C-60K Image process Unit 70C to 70K Exposure scanning unit 80 Photoelectric sensor 90 Operation panel 100 Recording sheet conveying unit 102 Drive roller 103 Transfer belt 111C to 111K First resist pattern 121 to 128 Detection signal waveform 200C to 200K Second resist pattern 201C to 201K, 202C to 202K Linear section 203, 204 Detection line 211C to 211K Signal waveform 212C to 212K Center of gravity position

Claims (4)

[Claims] An image writing unit forms an image of each color on a plurality of image carriers based on image data read by an image reading unit, and transfers these to a transfer material conveyed by a transfer material conveyance unit. An image forming apparatus which forms a multi-color image by controlling the image writing means, and a first resist pattern on a transfer surface of a transfer material transfer body and a second resist pattern on a transfer material for each color. A first resist pattern of each color formed on the transfer surface of the transfer material transfer body, and a relative displacement amount of the first resist pattern of each color based on the detection result. Based on image data obtained by reading a transfer material on which the second resist pattern has been formed by an image reading means, A second calculating means for calculating a relative positional shift amount of the second resist pattern, and a second calculating means for calculating a relative positional shift amount calculated by the first calculating means.
Correction data storage means for obtaining a difference from the displacement amount calculated by the calculation means for each corresponding color and storing the difference as correction data; and calculating the displacement amount calculated by the first calculation means based on the correction data. An image forming apparatus comprising: an image writing position correction unit that corrects an image writing position by the image writing unit based on the correction result. 2. A forming range of the first or second resist pattern in the sub-scanning direction is set so that a variation in a displacement amount caused by driving unevenness of the transfer material transporting body is within a predetermined range. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the first or second resist pattern is formed such that at least a black resist pattern does not overlap a resist pattern of another color. . 4. The image reading means is capable of optically enlarging and reading an original image, and the second calculating means is capable of reading a second resist of each color on the enlarged and read transfer material. A method for temporarily calculating a relative displacement amount of each color based on image data of a pattern, and dividing the calculation result by the enlargement magnification to obtain a displacement amount of a second resist pattern of each color. Item 2. The image forming apparatus according to Item 1.