JP2002014507A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress color slurring caused by the uneven driving of a driving roller and to accurately measure only static color slurring amount so as to obtain a color image whose color slurring is suppressed to be small by the correction of the color slurring by contriving a method for forming a pattern for measuring color slurring on a carrying belt. SOLUTION: The plural patterns for measuring the color slurring, that is, the parallel lines of four colors Y, M, C and Bk are formed on the carrying belt, and the phases of the adjacent patterns are made reverse in such a case. When the patterns are formed in the ratio of one pattern to a half cycle, the color slurring (positional deviation) between Y and M is larger than the static color slurring amount in the first pattern and smaller than it in the second pattern, and the first and the second patterns have the reverse phases, so that the color slurring amount caused by the driving roller is cancelled by averaging the color slurring amount between the patterns, and only the static color slurring amount between Y and M is obtained. The same operation is performed for the color slurring amount between M and C and that between the C and Bk.

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 using an electrophotographic process, and more particularly to a color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus for forming a color image at high speed, yellow (Y), magenta (M), cyan (C), A photosensitive drum is arranged for each color of black (K), and the toner images of each color formed on the photosensitive drum are sequentially superimposed on a recording material conveyed by a conveyance belt and transferred, or are sequentially superimposed on an intermediate transfer belt. An in-line type is known, in which a color image is transferred onto a recording material conveyed to an intermediate transfer belt and then collectively transferred to a recording material.

One of the main problems in the in-line type color image forming apparatus is a color shift between colors of a color image. The components of the color shift include a shift in the scanning direction (main scanning direction) by the laser, a shift in the belt moving direction (sub-scanning direction), expansion and contraction of an image in the main scanning direction, and an angular shift in the main scanning direction.

[0004] The deviation of each color is adjusted so as to be below the allowable value at the time of shipment of the apparatus. Due to distortion, displacement of the photosensitive drum due to replacement of a cartridge, or the like, color displacement exceeding an allowable value may occur.

Therefore, a plurality of color misregistration measurement patterns are formed at predetermined intervals on a conveyor belt or an intermediate transfer belt, and these patterns are detected by an image detection sensor, and the color misregistration amount is calculated based on the detection result. The correction of the image forming position is performed based on the calculation result.

A pattern for measuring color misregistration is shown in FIG.
As shown in the figure, yellow (Y), magenta (M), cyan (C), and black (Y) formed at equal intervals L1 = L2 = L3 in the moving direction with lines in the width direction perpendicular to the belt moving direction. Bk) are four color lines.

As shown in FIG. 8, a pattern for measuring the color misregistration of a set of four colors is arranged on a belt 61 in, for example, two rows at intervals in the width direction and at equal intervals K 1 = K2
= K3 = K4 = K5... And the positions of the lines of each color in these patterns are measured by the image detection sensors 90 and 91 arranged on the belt 61, and the distance between the lines of each color in each pattern is measured. Is measured, and the amount of misregistration between each color,
That is, the amount of color shift between the colors is obtained. This is performed for all the patterns, and the average value of the color shift amount for each color is obtained.
From this, the amount of color misregistration for each color is obtained, and based on the amount of color misregistration, the image writing position (the position where the exposure of the image on the photosensitive drum starts) is corrected.

[0008] By such color misregistration correction, the amount of color misregistration can be suppressed to within an allowable value, and a color image of optimum image quality can be always maintained.

[0009]

However, with respect to the period of driving unevenness due to the driving rollers and gears of the recording material conveying belt and the intermediate transfer belt, the period of rotation unevenness of the photosensitive drum, and the like, the distance K between the color misregistration measurement patterns is determined. Is an integral multiple, the influence of driving unevenness and rotational unevenness also appears on the average value of the color misregistration amounts measured a plurality of times.

That is, the color misregistration (position misregistration) includes, in addition to the color misregistration (static color misregistration) caused by a static factor such as an error in the image writing start position, the driving of a driving roller such as the transport belt. There is a color shift (dynamic color shift) due to a dynamic factor caused by the occurrence of a position shift (speed variation) in the transport belt due to unevenness and rotation unevenness of the photosensitive drum. The color shift of the factor is superimposed and appears.

As shown in FIG. 9, the color shift due to a static factor is a color shift having a constant color shift amount (position shift amount) represented by a straight line with a slope of 0, but the color shift due to a dynamic factor. The shift is, for example, a color shift represented by a sine wave whose color shift amount (position shift amount) periodically fluctuates in the rotation cycle of the drive roller if the dynamic factor is the drive roller.

Therefore, the color shift due to the dynamic factor changes at the timing of the measurement. Therefore, the color shift amount at which the color shift due to the dynamic factor overlaps is measured for a plurality of patterns. Even if the writing position of the image is corrected based on the result, the color shift due to the static factor cannot be corrected, and the color shift amount after correction does not converge so small that accurate correction cannot be performed.

In order to solve this problem, it is necessary to measure only the amount of color shift caused by static factors without including the color shift caused by dynamic factors. The color shift due to dynamic factors is
There is no other way but to reduce the drive unevenness of the drive roller such as the conveyor belt and the rotation unevenness of the photosensitive drum, and there is no fundamental solution.

An object of the present invention is to measure a color misregistration amount of each color of a color misregistration measurement pattern formed on a recording material conveying member or an intermediate transfer member, and to devise a method of forming a pattern when correcting color misregistration. In this way, the amount of color misregistration due to driving unevenness of the driving roller and the unevenness of rotation of the photosensitive drum can be suppressed, and only the static color misregistration can be accurately measured. An object of the present invention is to provide an image forming apparatus capable of obtaining a quality color image.

[0015]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A plurality of image forming means for forming a plurality of color toner images; a recording material conveying belt for carrying and conveying the recording material; an image detecting means for detecting a color misregistration measurement pattern formed on the conveying belt; A color misregistration correction mechanism having control means for performing color misregistration correction based on the result, wherein the color misregistration measurement pattern on the transport belt is formed without overlapping straight lines of each color in the transport belt movement direction. An image forming apparatus comprising a plurality of lines, and a plurality of lines provided along the transport belt moving direction, wherein the control unit corrects color misregistration based on a detection result by the image detection unit. The color misregistration measurement pattern is an image forming apparatus in which adjacent patterns are formed in opposite phases.

According to the present invention, the average value of the color shift amounts for each color is obtained from the detection result, and the image exposure position of each color is corrected based on the average value of the color shift amounts for each color. . When the positional deviation of the recording material transport belt has a plurality of periodic components, the time interval for forming each color line on the recording material transport belt by each of the image forming means is set to the largest amplitude of the plurality of periodic components. It was set to 1 / integer of the cycle of the large cycle component. After forming the n-th pattern (n is an integer of 1 or more) of the plurality of patterns on the recording material transport belt, the (n + 1) -th pattern is changed to the largest amplitude of the plurality of periodic components. It is formed from the opposite phase of the periodic component having the next largest amplitude after the periodic component.

Further, the present invention is based on a plurality of image forming means for forming a toner image, an intermediate transfer member, an image detecting means for detecting a color misregistration measurement pattern formed on the intermediate transfer member, and a method based on the detection result. A color misregistration correction mechanism having a control unit for performing color misregistration correction. The color misregistration measurement pattern on the intermediate transfer body is formed without overlapping straight lines of respective colors in the intermediate transfer body moving direction. Line,
And a plurality are provided along the intermediate transfer body moving direction,
In the image forming apparatus, wherein the control unit corrects color misregistration based on a detection result by the image detection unit, the plurality of color misregistration measurement patterns are formed such that adjacent patterns have opposite phases. An image forming apparatus characterized in that:

[0018]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view showing an embodiment of the image forming apparatus of the present invention. In this embodiment, the image forming apparatus is configured as a color laser printer.

The printer has a recording material transport belt 61 therein.
Along the image forming portions Pa, Pb, P of yellow (Y), magenta (M), cyan (C), and black (Bk).
c, Pd, and the image forming units Pa, Pb, Pc, Pd
Has rotatable photosensitive drums (drum-shaped electrophotographic photosensitive members) 21, 22, 23, and 24 as image carriers, and has charging rollers 31, 32, 33, 3 around them.
4, scanner units 11, 12, 13, 14, developing units 41, 42, 43, 44, transfer rollers 51, 52, 5,
3, 54, and cleaning blades 71, 72, 7
3, 74 are provided.

The transport belt 61 is a recording material transporting member for carrying paper as a recording material and transporting it to each image forming unit. The transport belt 61 is installed around a driven roller 62 and a driving roller 63 so as to be rotatable in the direction of the arrow. Have been. Conveyor belt 61
The manual feed tray 82 and its pickup roller 64 are provided on the upstream side of the image forming portion Pa at the uppermost stream in the recording material conveyance direction.
b, followed by a registration roller 65 and a suction roller 66. Below the conveyor belt 61, a paper feed cassette 81 and its pickup roller 64a
Is installed. On the downstream side of the most downstream image forming unit Pd, the image detection sensors 90 and 91 and then the fixing device 8
5 are installed.

In order to form a four-color full-color image with this color laser printer, first, each of the image forming sections Pa to
The surfaces of the Pd photosensitive drums 21 to 24 are charged to a desired potential by respective charging rollers 31 to 34, and image exposure is performed by the scanner units 11 to 14, and the photosensitive drums 21 to 24 are exposed.
The electrostatic latent images for yellow, magenta, cyan, and black are formed on the surface of the toner image, and the latent images are developed by developing units 41 to 44 to form yellow, magenta, cyan, and black toner images.

Next, the toner image of each color formed on each of the photosensitive drums 21 to 24 is held on a transport belt 61b, and is sequentially conveyed to a transfer section facing each of the photosensitive drums 21 to 24 as a recording material. Then, the images are transferred by being superimposed one by one by the transfer rollers 51 to 54. The paper is fed from a paper feed cassette 81 or a manual feed cassette 82 by a pick-up roller 81a or 82a.
5 and is held on the conveyor belt 61 via the suction roller 66.

Next, the paper on which the four color toner images have been transferred is separated from the transport belt 61 and sent to a fixing device 85, where it is heated and pressed to melt and mix and fix the four color toners. After a full-color permanent image is formed, the paper is discharged outside the printer.

The present color laser printer is provided with a color misregistration correction mechanism. Before forming an image on a sheet, the photosensitive drums 21 to 24 are charged and exposed to form a latent image of a color misregistration measurement pattern. Is formed, the latent image is developed, and the toner image of the obtained pattern is directly transferred to the conveyor belt 61, thereby forming a pattern for measuring color shift on the surface of the conveyor belt 61 and measuring the amount of color shift. Then, the color misregistration is corrected.

In this embodiment, the pattern for measuring the color shift is a line in the width direction perpendicular to the moving direction of the conveyor belt 61, as described with reference to FIGS. Yellow (Y), magenta (M), cyan (C), black (B) formed at predetermined time intervals in the moving direction.
k) A plurality of line patterns of one set of four colors are formed in two rows at intervals in the width direction of the belt 61 in the moving direction.

Correspondingly, two image detecting sensors 9 are provided at an upper position on the downstream side of the image forming portion Pd for the final color of the conveyor belt 61 with a space in the width direction of the conveyor belt 61.
0 and 91 are arranged. As shown in FIG. 2, the sensors 90 and 91 irradiate the surface of the transport belt 61 with light and receive the reflected light. , 91
, The pattern is detected as a light intensity distribution based on a change in the amount of light received from the pattern, and is output as a voltage.

The output voltage is input to the image position detection circuit 104 of the control circuit board 100 of the color misregistration correction mechanism.
The position detection circuit 104 detects the position of each color line of each pattern from the input voltage waveform, and outputs the detection result to the control circuit 1.
Enter 03. The control circuit 103 measures the interval between the colors, that is, the amount of color shift between the colors from the position of the line of each color. This is performed for all the patterns, the average value of the color shift amounts for each color is calculated, and the difference between the average value of the color shift amounts (interval between the colors) for each color and a desired value is calculated. Of color shift.

The control circuit 103 controls the photosensitive drums 21 by the scanner units 11 to 14 based on the amount of color misregistration.
The exposure start position of the image to -24, i.e., the image writing position (writing timing) is corrected and changed, and the changed image writing is performed to form an image, and the color image finally formed on the paper The color misregistration of each color is eliminated.

In this embodiment, at this time, the parallel lines of the four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) in the color misregistration measurement pattern correspond to the lines between the respective colors. Is set to 1 / integer of the period T of the drive roller 63 for driving the transport belt 61, and the adjacent patterns have opposite phases, as shown in FIG. For example, the interval L is set to 1/8 of the cycle T, and the pattern is formed at a rate of one pattern in a half cycle.

According to this, the color shift (positional shift) between Y and M is larger than the static color shift amount in the first pattern and smaller than the static color shift amount in the second pattern. Since the phases are exactly opposite between the first and second times,
By averaging in the second and the second pattern, Y−
From the amount of color misregistration between M, the amount of dynamic color misregistration caused by the driving roller can be canceled and removed, and only the amount of static color misregistration can be obtained.

Similarly, with respect to the color misregistration amount between M and C and the color misregistration amount between C and Bk, the dynamic color misregistration amount is canceled out by averaging the two values to obtain the static color misregistration amount. Only the shift amount can be obtained.

As shown in FIG. 3, if four patterns are formed over two periods, the amount of color misregistration between the colors is averaged by the first to fourth patterns to reduce the amount of static color misregistration between the colors. It can be determined with further improved accuracy.

Accordingly, the difference between the color shift amount between the colors obtained as described above and the desired value of the color shift amount for each color is calculated to easily determine the color shift amount of each color with high accuracy. It can be obtained without any extra cost. Then, by changing the timing of writing the images on the photosensitive drums 21 to 24 so as to eliminate the color shift amount based on the color shift amount, a color image with less color shift can be obtained.

Embodiment 2 FIG. 4 is an explanatory diagram for explaining another embodiment of the present invention.

In this embodiment, a plurality of displacement components are superimposed, resulting in a displacement of the transport belt (driving unevenness of the transport belt), and a color shift accompanying the displacement.

In the example shown in FIG. 4, the drive unevenness of the transport belt in the cycle Tb is formed by overlapping the drive unevenness of the drive roller in the cycle Tk with the unevenness due to the rotation of the photosensitive drum in the cycle Tb.

In such a case, a dominant positional shift cycle component, that is, a cycle Tk of drive unevenness of the drive roller having the largest amplitude is adopted, and a line between the four color lines in the color shift measurement pattern is used. The interval L is defined as an integer fraction of the period Tk,
In FIG. 4, at least two patterns are formed at a rate of one pattern in a half cycle, which is 1/8.

According to this, the positional shift between Y and M, that is, the color shift between Y and M is larger than the static color shift amount in the first pattern and the static color shift amount in the second pattern. And the phase is exactly opposite between the first and second times, the color shift between Y and M is averaged by the first and second patterns to obtain the color difference between Y and M. From the shift amount, the dynamic color shift amount by the drive roller can be canceled out and removed, and only the static color shift amount can be obtained.

Similarly, with respect to the amount of color misregistration between MC and the amount of color misregistration between C and Bk, the dynamic color misregistration is canceled out by averaging the two values to obtain the static color misregistration. Only the shift amount can be obtained.

Therefore, also in this embodiment, extra cost is increased by calculating the difference between the color shift amount between the colors obtained as described above and the desired value of the color shift amount between the colors. It is possible to easily obtain the color misregistration amount of each color with high accuracy without occurrence, and to obtain a color image with little color misregistration by changing the writing timing of the image on the photosensitive drum based on the color misregistration amount. it can.

Embodiment 3 FIG. 5 is an explanatory view for explaining still another embodiment of the present invention.

In this embodiment, a plurality of displacement components are superimposed to cause a displacement (color misregistration) of the transport belt, that is, uneven driving of the transport belt. Of these, two displacement components are dominant. Is the case.

FIG. 5 shows an example in which the driving unevenness due to the driving roller having the cycle Tk and the unevenness due to the rotation of the photosensitive drum having the cycle Tb are the main components of the driving unevenness of the transport belt having the cycle Tb. Among them, the drive unevenness due to the drive roller has a larger amplitude and is the most dominant positional shift period component.

In this embodiment, in this case, the interval L between the lines is 1 / integer of the period Tk of the driving unevenness due to the driving roller, which is the most dominant positional deviation period component. , Y and Bk were formed.

The color shift between the first Y-Bk, the second Bk-Y, and the third Y-Bk of this pattern is detected, and the color shift between the three Y-Bk is averaged. As a result, the amount of dynamic color misregistration due to the driving roller
Only the static color shift amount between k can be obtained. This is set as a first color shift amount measurement value between Y and Bk.

Further, the second same color misregistration measurement pattern is caused by the rotation of the photosensitive drum, which is the second dominant misregistration cycle component, from the writing position of the first pattern (time t = 0). It is arranged at a position separated by an odd multiple of a half period of the period Td, that is, at a position having an opposite phase. That is, the position is t = Td / 2 × (2n + 1). Usually n
= 1, and t = 3Td / 2, as shown in FIG. However, 3Td / 2 is made longer than one color shift pattern.

As before, the first pattern of the second pattern
By averaging the color misregistration amounts between the third and third Y-Bk, the dynamic color misregistration amount due to the driving roller is canceled, and
Only the static color shift amount between −Bk can be obtained. This is defined as a second color shift amount measurement value between Y and Bk.

The first measured value of color misregistration between Y-Bk and the second measured value
The average of the measured values of the color misregistration amounts is referred to as a third measured value of the color misregistration value. Become. Of course, the amount of dynamic color misregistration due to the driving roller has already been removed.

Similarly, two color misregistration measurement patterns for M and Bk and two color misregistration measurement patterns for C and Bk are formed as shown in FIG.
The amount of color shift between M and Bk and the amount of color shift between C and Bk are measured for each pattern, and the same averaging operation is performed. And the amount of color misregistration between C and Bk can be made to offset unevenness due to rotation of the photosensitive drum.

According to the present embodiment, as described above, from the amount of color misregistration between the colors, the driving unevenness of the driving roller, which is the dominant periodic component, and the photosensitive unevenness due to the driving unevenness of the conveying belt (positional shift of the conveying belt). The unevenness due to the rotation of the drum can be removed, and the amount of color misregistration between the colors, that is, the amount of static color misregistration of each color can be obtained with higher accuracy.

According to the present embodiment, the amount of color misregistration of each color is easily obtained with high accuracy without changing the cost, and the timing of writing an image on the photosensitive drum is changed. A color image can be obtained.

In each of the above embodiments, a case has been described in which a color misregistration measurement pattern is formed on a recording material transport belt and the pattern is detected to correct the color misregistration. The present invention can also be applied to an intermediate transfer type image forming apparatus in which the toner image on the drum is temporarily transferred to an intermediate transfer body such as an intermediate transfer drum before transferring the color misregistration measurement pattern to the intermediate transfer body. By detecting the pattern and correcting the color misregistration, the same effect can be obtained.

[0054]

As described above, according to the present invention,
Adjacent patterns of the color misregistration measurement pattern formed on the recording material conveyance belt or intermediate transfer body are formed so that they have opposite phases, so color misregistration due to driving unevenness of the drive roller or rotation unevenness of the photosensitive drum etc. The amount can be suppressed, and only the static color shift amount can be accurately measured. Based on this, good color shift correction can be performed, and a high-quality color image with less color shift can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating a measurement and control system of a color misregistration measurement pattern formed on a recording material conveyance belt of the image forming apparatus of FIG. 1;

FIG. 3 is a conceptual diagram showing a method of forming a color misregistration measurement pattern in the embodiment of FIG.

FIG. 4 is a conceptual diagram illustrating a method for forming a color misregistration measurement pattern according to another embodiment of the present invention.

FIG. 5 shows Y and B in still another embodiment of the present invention.
It is a conceptual diagram which shows the formation method of the color misregistration measurement pattern about k.

FIG. 6 shows Y and Bk, M and B by the formation method of FIG.
FIG. 9 is a conceptual diagram illustrating a state where a color misregistration measurement pattern for k, C, and Bk is formed.

FIG. 7 is a conceptual diagram illustrating an example of a color misregistration measurement pattern.

FIG. 8 is a conceptual diagram showing a conventional method for forming a color misregistration measurement pattern on a transport belt.

FIG. 9 is a conceptual diagram illustrating a shift amount due to a static factor and a shift amount due to a dynamic factor of a color shift amount according to a conventional pattern forming method.

[Explanation of symbols]

 11-14 Scanner unit 21-24 Photosensitive drum 41-44 Developing device 51-54 Transfer roller 61 Recording material transport belt 90-91 Image detection sensor 103 Control circuit 104 Image position detection circuit

Claims (8)

[Claims] A plurality of image forming means for forming toner images of a plurality of colors; a recording material conveyance belt for carrying and conveying the recording material; and an image detection unit for detecting a color misregistration measurement pattern formed on the conveyance belt. And a color misregistration correction mechanism having a control means for performing color misregistration correction based on the detection result. The color misregistration measurement pattern on the transport belt overlaps straight lines of respective colors in the transport belt moving direction. The image forming apparatus includes a plurality of lines that are formed in the same direction, and is provided along the moving direction of the conveyor belt, and the control unit corrects a color shift based on a detection result by the image detection unit. An image forming apparatus, wherein the plurality of color misregistration measurement patterns are formed such that adjacent patterns have opposite phases. 2. An image exposure position of each color is corrected based on an average value of color shift amounts for each color from the detection result, based on the average value of color shift amounts for each color. Image forming device. 3. When the positional shift of the recording material transport belt has a plurality of periodic components, the time interval for forming each color line on the recording material transport belt by each of the image forming means is set to a plurality of periodic components. 3. The image forming apparatus according to claim 1, wherein the period of the period component having the largest amplitude is a fraction of an integer. 4. After forming an n-th pattern (n is an integer of 1 or more) among a plurality of patterns on the recording material transport belt, an (n + 1) -th pattern is formed from the plurality of periodic components. 4. The image forming apparatus according to claim 3, wherein the image is formed from the opposite phase of the periodic component having the largest amplitude after the periodic component having the largest amplitude. 5. An image forming means for forming a toner image, an intermediate transfer member, an image detecting means for detecting a color shift measuring pattern formed on the intermediate transfer member, and a color shift based on the detection result. A color misregistration correction mechanism having a control means for performing correction, the color misregistration measurement pattern on the intermediate transfer body, a plurality of lines formed without superimposing straight lines of each color in the intermediate transfer body movement direction An image forming apparatus comprising: a plurality of color misregistrations, wherein the control means corrects a color misregistration based on a detection result by the image detection means; The image forming apparatus, wherein the patterns for use are formed such that adjacent patterns have opposite phases. 6. The method according to claim 5, wherein an average value of the color shift amounts for each color is obtained from the detection result, and the image exposure position of each color is corrected based on the average value of the color shift amounts for each color. Image forming device. 7. When the positional shift of the intermediate transfer body has a plurality of periodic components, the time interval at which each image forming unit forms a line of each color on the intermediate transfer body is set to a time interval of the plurality of periodic components. 7. The image forming apparatus according to claim 5, wherein the period of the periodic component having the largest amplitude is a fraction of an integer. 8. After forming an n-th pattern (n is an integer of 1 or more) of the plurality of patterns on the intermediate transfer member, the (n + 1) -th pattern is changed to the one of the plurality of periodic components. 8. The image forming apparatus according to claim 7, wherein the image is formed from the opposite phase of the periodic component having the largest amplitude next to the periodic component having the largest amplitude.