JP2020086068A - Image formation apparatus and image formation method - Google Patents

Abstract

To provide an image formation apparatus that stably makes it successful to detect a pattern for color shift correction.SOLUTION: An image formation apparatus has: pattern forming means which forms a correction pattern group on an endless rotary body so as to calculate a correction value to be used to correct a shift in position for superposing respective color images; group pattern detecting means which detects a group pattern included in the correction pattern group; and correction value calculating means which calculates a correction value. The group pattern is constituted including: a first pattern as a straight-line pattern orthogonal to a conveying direction of a correction pattern; and a second pattern as a straight-line pattern orthogonal to the conveying direction or an inclined-line pattern inclined thereto, the second pattern being arranged between two first patterns arranged at positions apart from each other in the conveying direction. The pattern forming means forms, when using the correction value to form the correction pattern group, shifts a formation position of the second pattern included in the group pattern from a center position.SELECTED DRAWING: Figure 15

Description

The present invention relates to an image forming apparatus and an image forming method.

In a tandem type color image forming apparatus, which is a type of color image forming apparatus that forms an image on a recording medium, a plurality of individual color images (toner images) are sequentially formed and transferred to a transfer body. To form a color image. The toner image is formed by adhering a developing material (toner) of a different color for each photoconductor to an electrostatic latent image formed by optical writing control on a plurality of photoconductors provided individually.

In the tandem type color image forming apparatus, when the toner images are superposed on the transfer body, if the superposition of the toner images is deviated (a "displacement" occurs in which the transfer position is displaced), the toner images of the respective colors are deviated. A color image is formed, and a so-called "color shift" occurs. Since the color misregistration deteriorates the quality of the color image, the tandem color image forming apparatus uses a technique of suppressing the misregistration (position misregistration) of the toner images.

The positional deviation of the superposition of the toner images occurs due to multiple factors. The main one of them is a periodic fluctuation of the rotation speed of an endless rotary member such as a transfer member. Therefore, the color misregistration occurs with a periodic change.

In the tandem type color image forming apparatus, it is necessary to use a technique for correcting the deviation of the transfer position of the toner image in order to suppress the color deviation accompanied by the periodical change as described above. The color shift is corrected by correcting the shift of the transfer position. In the present specification, this technique is referred to as “color shift correction technique”.

As a conventionally known color misregistration correction technique, a correction pattern having a Z-shaped form is formed on a transfer body, and by detecting this, the variation ratio of the sub-scanning magnification of the correction target color to the reference color is determined. A color misregistration correction technique used is known (for example, refer to Patent Document 1). In addition, the position where the correction pattern is formed on the transfer body is set to a different position in the main scanning direction orthogonal to the transport direction, and the pattern of the correction pattern is reversed from the transport direction. There is known a technique of correcting a color shift by detecting the color shift (for example, see Patent Document 2).

The techniques disclosed in Patent Document 1 and Patent Document 2 form a color misregistration correction pattern on a transfer body, and an optical sensor detects this to calculate a misregistration amount of a pattern formation position or a formation interval. The correction value is calculated so as to suppress this. In the following, the color misregistration correction pattern may be simply referred to as a pattern.

In the related art, the edge of the pattern is detected based on the timing of the fall/rise of the output voltage of the optical sensor that detects the pattern, and the correction value of the color misregistration is calculated based on the information of this edge. Therefore, if the information on the edge of the detected pattern is not correct, the color misregistration correction fails, so that the pattern detection must be made stable and successful. In this case, factors such as failure of pattern detection include scratches and stains on the transfer body (intermediate transfer belt). There is a demand for a technique capable of calculating a correct color misregistration correction value based on the detected pattern even if these scratches and stains are present.

In the color misregistration correction technique, an edge control method and a polling control method are known as methods for detecting an edge of a pattern. The edge interrupt control method is a method of detecting an edge based on the timing when the output voltage of the optical sensor decreases, and thus can be constructed with a simple configuration, but it is difficult to remove noise when the optical sensor erroneously detects. On the other hand, the polling control method is a method in which a counter based on an operation clock of a control unit interrupts a control process, acquires an output voltage of an optical sensor, and detects an edge. Therefore, in the polling control method, when an erroneous detection by the optical sensor occurs, the color misregistration correction value can be normally calculated by discarding only the information on the edge of the section. Therefore, the polling control method is more suitable for stable and successful color misregistration correction than the edge interrupt control method.

In addition, if the color misregistration correction patterns are formed with a sufficiently wide interval, the relationship between the output voltage acquisition timing of the optical sensor in the polling control method and the timing at which the optical sensor detects the pattern can be taken into consideration. , Pattern detection can be successful. However, in order to improve the accuracy of color misregistration correction, it is necessary to shorten the formation interval of the color misregistration correction pattern. When the formation interval of the color misregistration correction pattern is shortened, the "interruption position", which is the relative positional relationship between the transfer body surface and the optical sensor when the interrupt control to the optical sensor in the polling control method occurs, The relationship with the pattern formation position on the body surface becomes important.

That is, when the formation interval of the color misregistration correction pattern is shortened in order to correct the color misregistration and improve the color matching accuracy, adverse effects due to the "registration misregistration" and the "skew misregistration" occur. The registration shift is a position shift in the sub-scanning direction, which is the conveyance direction of the pattern formed on the transfer body, or in the main-scanning direction orthogonal to the sub-scanning direction. The skew shift is a position shift due to an inclination with respect to the transport direction. When these registration shifts and skew shifts occur, the formation position of the color shift correction pattern deviates from the ideal position, and therefore the interrupt position and the pattern formation position in the polling control method may overlap. If the pattern formation position and the interrupt position overlap, it becomes an obstacle to stable and successful pattern detection.

As described above, the conventional technique has a problem that if the formation interval of the color misregistration correction pattern is shortened, the color misregistration correction pattern cannot be normally detected and the color misregistration correction fails.

An object of the present invention is to provide an image forming apparatus that stably and successfully detects a color misregistration correction pattern.

In order to solve the above technical problem, one embodiment of the present invention is an image forming apparatus that forms a color image by superposing each color image developed by a developer of each color by rotational driving of a plurality of endless rotary members. Then, in order to calculate a correction value used for correcting the displacement of the position where the respective color images are superimposed on one of the endless rotary members, a correction pattern including a plurality of combination patterns composed of a plurality of correction patterns Pattern forming means for forming a group on the endless rotating body, set pattern detecting means for detecting a set pattern included in the correction pattern group formed on the endless rotating body, and detection by the set pattern detecting means Correction value calculation means for calculating a correction value based on the result, wherein the combination pattern is a linear pattern orthogonal to the conveyance direction of the correction pattern by the rotational driving of the endless rotary body. Two first patterns that include one pattern and a second pattern that is either a linear pattern that is orthogonal to the transport direction or a diagonal pattern that is inclined with respect to the transport direction, and that are arranged at positions separated in the transport direction. The second pattern is disposed between the pattern forming means and the pattern forming means forms the correction pattern group using the correction value calculated based on the detection result of the combination pattern detecting means. At this time, the formation position of the second pattern included in the set pattern is formed so as to be shifted from the central position of the set pattern.

According to the present invention, it is possible to stably and successfully detect a color misregistration correction pattern.

1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a diagram showing an arrangement relationship between an optical writing control device according to the present embodiment and a photoconductor. FIG. 3 is a hardware configuration diagram of the image forming apparatus according to the present embodiment. FIG. 3 is a functional block diagram of the image forming apparatus according to the present embodiment. FIG. 3 is a functional block diagram of the optical writing control device according to the present embodiment. FIG. 3 is a diagram showing a positional relationship among a pattern position detection sensor, a transfer body, and a correction pattern group according to the present embodiment. The figure which shows an example in the output voltage waveform of the pattern position detection sensor which concerns on this embodiment. FIG. 6 is a diagram illustrating the relationship between the magnification of the misregistration correction pattern and the color matching accuracy according to the present embodiment. 6 is a graph illustrating an example of a correlation between a magnification of a misregistration correction pattern formation interval and color matching accuracy according to the present embodiment. The figure which shows the example of the positional offset correction pattern which concerns on this embodiment. FIG. 4 is a diagram showing a relationship between a position shift correction pattern forming mode and an interrupt control position according to the present embodiment. (A) An output voltage waveform diagram based on an ideally formed pattern, and (b) an output voltage waveform based on a pattern when a main-scan registration error occurs, in accordance with detection of a misregistration correction pattern according to the present embodiment. FIG. 6C is an output voltage waveform diagram based on a pattern when a main-scanning registration deviation and a sub-scanning registration deviation occur. The figure which shows the relationship between the misregistration correction pattern and interrupt control position which concern on this embodiment. The output voltage waveform which shows the relationship between the misregistration correction pattern and the interrupt control position according to the present embodiment. FIG. 6 is a diagram illustrating an example of a method of forming a positional deviation correction pattern according to the present embodiment. 6A and 6B are diagrams showing a method of displacing the positional deviation correction pattern according to the present embodiment, in which (a) an example in which the same displacement amount is used in the sub-scanning direction and (b) an example in which different displacement amounts are used in the sub-scanning direction. 3 is a flowchart illustrating an embodiment of an image forming method according to the present invention. 6A and 6B are diagrams illustrating another example of the method of forming the positional deviation correction pattern according to the present embodiment.

[Summary of the Invention]
Embodiments of an image forming apparatus and an image forming method according to the present invention will be described below. The present invention has a main feature in the method of forming the “color shift correction pattern” that is formed in order to correct the “color shift” caused by the shift of the overlay position of the toner images. The color misregistration correction pattern according to the present invention exhibits the effect of stably detecting the color misregistration correction value and successfully calculating the color misregistration correction value.

The color misregistration correction pattern is obtained by applying a developing material (toner) to the electrostatic latent image formed on the photoconductor by the optical writing control technique and transferring the developed toner image to the intermediate transfer belt, which is a transfer body. It is formed as a combination of patterns on the intermediate transfer belt. Here, the toner image is formed in four colors of CYMK (cyan color, yellow color, black color, and magenta color) for forming an image. Therefore, the image forming apparatus according to the present invention includes the photoconductors corresponding to the four colors.

An edge interrupt control method and a polling control method are mainly known as control methods for detecting a color misregistration correction pattern as in the image forming apparatus according to the present invention.

The edge interruption control method is a method in which a pattern detection operation is executed using a timing when an optical sensor detects a color misregistration correction pattern and the output voltage of the optical sensor decreases.

The polling control method is a method in which the control for detecting the output voltage of the optical sensor is interrupted at a predetermined clock timing based on the clock of the processor that controls the operation for calculating the color misregistration correction value. Therefore, in the polling control method, when an erroneous detection of the optical sensor occurs, the color misregistration correction value can be normally calculated by discarding the detection result (edge information) in that section.

The present invention can be applied to the edge interrupt control system, but in the following description of the present embodiment, the polling control system will be used as an example.

The present invention shifts the formation position of the color misregistration correction pattern so that the "interruption position" when detecting the color misregistration correction pattern using the polling control method does not overlap the formation position of the color misregistration correction pattern. This is one of the points.

The “interruption position” according to the present embodiment detects the target on which the color misregistration correction pattern is formed and the color misregistration correction pattern when the interrupt control for detecting the color misregistration correction pattern occurs. The position is defined by the relative relationship with the detection position of the sensor. The color misregistration correction pattern is formed on the surface of the transfer body as described later. Since this surface moves as time passes, the detection position of the detection sensor moves relatively. Therefore, the interruption position corresponds to the position on the surface of the transfer body where the detection position of the sensor is projected when the interruption control for the sensor occurs.

For example, when the formation position of the color misregistration correction pattern deviates from the ideal position due to “registration misregistration” or “skew misregistration” of each color, the interrupt position may overlap the pattern detection position. Then, the color misregistration correction pattern cannot be correctly detected. Therefore, when the process for calculating the color misregistration correction value is executed, the color misregistration is performed so as to shift the pattern formation position based on the previously executed color misregistration correction result (registration correction value and skew correction value for main scanning and sub scanning). The correction pattern forming operation is controlled. Alternatively, the amount of registration deviation and skew deviation of main scanning and sub-scanning is estimated in advance with a maximum value, and the pattern formation operation is controlled by shifting the formation position of the color deviation correction pattern based on this maximum value. To do.

According to the image forming apparatus and the like according to the present invention having the above characteristics, the interrupt position by polling control and the formation position of the color misregistration correction pattern do not overlap each other, and the color misregistration correction pattern can be detected stably. Therefore, the success rate of color misregistration correction can be improved.

Further, in the color shift correction pattern used in the color shift correction control technique according to the present invention, the target of which the formation position is shifted is the central oblique line pattern or the horizontal line pattern forming the color shift correction pattern. That is, the formation position of the reference line pattern (reference line pattern) is not displaced. As a result, the formation interval of the reference pattern (horizontal line pattern) made of the reference color does not change. Therefore, according to the present invention, the accuracy of color misregistration correction can be improved. The formation interval is an interval in which a set of patterns in the color misregistration correction pattern (a set of patterns in which a correction target pattern is formed between two reference line patterns (horizontal line patterns)) is repeatedly formed. Say. For example, the interval between the reference line pattern included in the first set of patterns and the reference line pattern included in the next set of patterns is referred to as a “pattern formation interval”.

[Definition of terms]
Here, terms used in this embodiment will be described. In the color misregistration correction control according to the present embodiment, the control of the operation for detecting the color misregistration correction pattern is based on polling control. The "interruption position" by the polling control is the control for acquiring the output voltage of the optical sensor by the interrupt control, and at the timing when the output voltage of the optical sensor is acquired by the interrupt control, the pattern detection spot of the optical sensor is the transfer member. Corresponding to the position on the surface of. Therefore, the interrupt position must be different from the position where the color misregistration correction pattern is formed on the transfer body. If the interrupt position overlaps the pattern formation position, the pattern cannot be detected accurately. Here, the timing of obtaining the output voltage of the optical sensor is the timing of counter control based on the operation clock.

The “Z pattern” and the “three patterns” are types of graphic patterns drawn by the toner images that form the color misregistration correction pattern according to the present embodiment. The "Z pattern" and "three patterns" will be described with reference to FIG. In the present embodiment, the “Z pattern” is the first set pattern 521 and the “three patterns” is the second set pattern 522. Each of the first set pattern 521 and the second set pattern 522 is configured by a combination of the reference line pattern 510, which is two linear patterns, and one correction target pattern. Hereinafter, a plurality of first set patterns 521 and second set patterns 522 will be referred to as a correction pattern group 500 that is an embodiment of a color misregistration correction pattern.

The correction target first pattern 511, which is the correction target pattern included in the first set pattern 521, is an oblique line pattern represented by a line inclined with respect to the transport direction when formed on the transfer body. The first set pattern 521 is formed by arranging the correction target first pattern 511, which is one diagonal pattern, between the two reference line patterns 510. The first set pattern 521 has a form similar to the letter Z of the alphabet, and thus is referred to as a “Z pattern”.

The correction target second pattern 512, which is the correction target pattern included in the second set pattern 522, is a horizontal line pattern represented by a line orthogonal to the transport direction when formed on the transfer body. The second set pattern 522 is formed by disposing the correction target second pattern 512, which is one horizontal line pattern, between the two reference line patterns 510. Since the second set pattern 522 has a form similar to the Chinese numeral "three", this is called "three pattern".

The reference line pattern 510 is a linear pattern in a direction orthogonal to the sub-scanning direction corresponding to the direction in which the patterns are conveyed (moving direction) on the transfer body on which the toner images are superimposed. The correction pattern group 500 is formed for each toner color of the correction target first pattern 511 and the correction target second pattern 512 because it is used for correcting the formation position of the toner image of each color. The color is the same regardless of the color to be corrected.

All of the correction target patterns (correction target first pattern 511, correction target second pattern 512) included in the first set pattern 521 and the second set pattern 522 are “centered” in the area surrounded by the two reference line patterns 510. In position". Here, the “center position” means a position corresponding to the center position in the sub-scanning direction and the center position in the main scanning direction. The “center position in the sub-scanning direction” refers to a position corresponding to the middle of the formation distance in the sub-scanning direction of the two reference line patterns 510 included in the correction pattern group 500. Further, the “center position in the main scanning direction” means a position corresponding to an imaginary line connecting the midpoints of the lengths of the two reference line patterns 510 included in the correction pattern group 500 in the main scanning direction. ..

In the image forming apparatus according to the present invention, when attention is paid to the correction pattern group 500 used for one color misregistration correction process, the correction target first pattern 511 and the correction target second pattern 512 included therein are the same. Formed in color. Further, the reference line patterns 510 are all formed in the same color.

As described above, the same color is used for the reference line pattern 510 used for one color misregistration correction process, so that the phase component in the misregistration of the correction pattern group 500 caused by the fluctuation in the rotation speed of the endless rotary body is common. Can be turned into. If the phase component of the positional deviation is shared, the accuracy of color misregistration correction can be improved.

Further, if the reference line patterns 510 are formed in different colors, it is necessary to provide a certain pattern formation interval when changing the color of the reference line patterns 510. However, by setting the reference line patterns 510 to be a common color, the pattern formation intervals can be reduced. Can be narrowed. Thereby, the total length of the correction pattern group 500 can be shortened.

In adjacent groups (first pattern pair 521, second pattern pattern 522, first pattern pattern 521 and second pattern pattern 522) adjacent to each other, the correction target pattern (correction target first pattern) included in at least one group. The color and shape of the correction target pattern 511 and the correction target second pattern 512) are formed to be the same as the color and shape of the correction target pattern of the set of interest in the color misregistration correction process. This makes it possible to effectively suppress the influence of the speed fluctuation of the endless rotary body in the color misregistration calculation.

[Embodiment of Image Forming Apparatus]
First, an image forming apparatus including the optical writing device according to the present invention will be described. FIG. 1 is a configuration diagram showing a configuration of a multi-function peripheral (MFP) as an embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, the MFP 100 is one of endless rotary members, and an image forming unit 106 corresponding to each color is arranged along an intermediate transfer belt 105 which is a transfer member to which an image of each color is transferred. There is. The MFP 100 shown in FIG. 1 is called a tandem type. The intermediate transfer belt 105 is a conveyance device for a recording medium on which an image is formed, and the rotation direction of the intermediate transfer belt 105 is the conveyance direction of the correction pattern group 500 formed on the intermediate transfer belt 105.

The image forming unit 106 is an electrophotographic process unit and has a configuration used for forming an image of each color. Specifically, a yellow image forming unit 106Y used for forming a yellow image, a magenta image forming unit 106M used for forming a magenta image, a cyan image forming unit 106C used for forming a cyan image, and a black image. And a black image forming unit 106K used for forming the image. Hereinafter, these are collectively referred to as the image forming unit 106. The image forming unit 106 is arranged along the rotational movement direction of the intermediate transfer belt 105 (conveying direction of the transferred image). The image forming unit 106 has the same internal configuration except that the color of the developer (toner) used when developing the electrostatic latent image is different.

Hereinafter, the yellow image forming unit 106Y will be described in detail, but a specific description regarding each component corresponding to another color will be described with reference to M, instead of Y attached to each component of the yellow image forming unit 106Y. Only the symbols distinguished by C and K are shown in the figure, and the description is omitted.

The intermediate transfer belt 105 is an intermediate transfer unit, and is an endless belt member spanning a driving roller 108 and a driven roller 107, that is, an endless rotary member. Each color image is transferred from the image forming unit 106 to the intermediate transfer belt 105 to form a full-color image. The drive roller 108 is rotationally driven by a drive motor and a drive gear. The driven roller 107 is rotated by the intermediate transfer belt 105 that is rotated by the driving force of the driving roller 108. The drive roller 108, the drive motor that drives the drive roller 108, and the driven roller 107 that rotates according to the drive of the drive roller 108 function as a drive unit that rotates the intermediate transfer belt 105 that is an endless moving unit.

A transfer roller 119 is arranged at a position facing the drive roller 108 with the intermediate transfer belt 105 interposed therebetween. The transfer roller 119 constitutes a secondary transfer unit that applies pressure so as to press the paper 104, which is a recording medium, against the intermediate transfer belt 105. The paper 104 supplied from the paper feed tray 101 is pressed against the intermediate transfer belt 105 by the pressure of the transfer roller 119 and conveyed, and the color image formed on the intermediate transfer belt 105 is transferred onto the paper 104.

The yellow image forming unit 106Y includes a photoconductor drum 109Y as a photoconductor, a charging roller 110Y that is a charging roller arranged around the photoconductor drum 109Y, an optical writing control device 111, a developing device 112Y, and a photoconductor cleaner. It is composed of a static eliminator 113Y and the like. The optical writing control device 111 is configured to irradiate the photoconductor drums 109Y, 109M, 109C, and 109K (hereinafter collectively referred to as “photoconductor drum 109”) corresponding to each color with light.

At the time of image formation, the outer peripheral surface of the photoconductor drum 109Y is uniformly charged by the charging roller 110Y in the dark, and then writing is performed by the light from the light source corresponding to the yellow image from the optical writing control device 111. , An electrostatic latent image is formed. The developing device 112Y visualizes this electrostatic latent image with yellow toner, and as a result, a yellow toner image is formed on the photosensitive drum 109Y.

This toner image is transferred to the intermediate transfer belt 105 by the function of the transfer device 115Y at a position (transfer position) where the photoconductor drum 109Y and the intermediate transfer belt 105 are in contact with or closest to each other. By this transfer, a yellow toner image is transferred onto the intermediate transfer belt 105. After the transfer of the toner image is completed, the photoconductor drum 109Y wipes off the unnecessary toner remaining on the outer peripheral surface by the photoconductor cleaner, the charge is removed by the charge remover 113Y, and the photoconductor drum 109Y stands by for the next image formation.

As described above, the yellow toner image transferred onto the intermediate transfer belt 105 by the yellow image forming unit 106Y is conveyed to the next magenta image forming unit 106M by the roller driving of the intermediate transfer belt 105. This conveyance direction is the sub-scanning direction, is orthogonal to the sub-scanning direction, and the width direction of the intermediate transfer belt 105 (depth direction in FIG. 1) is the main scanning direction. In the magenta image forming unit 106M, a magenta toner image is formed on the photosensitive drum 109M by the same process as the image forming process in the yellow image forming unit 106Y, and the toner image is changed to the already formed yellow toner image. Transcribed so that they overlap.

The toner image on which the yellow toner image and the magenta toner image transferred to the intermediate transfer belt 105 are superimposed is further conveyed to the next cyan image forming unit 106C and black image forming unit 106K. By the same operation, the cyan toner image formed on the photoconductor drum 109C and the black toner image formed on the photoconductor drum 109K are transferred to the toner images (yellow and magenta colors). Is superimposed on the superposed toner image). In this way, a color intermediate transfer image is formed on the intermediate transfer belt 105.

The sheets 104 stored in the sheet feed tray 101 are sent out in order from the uppermost sheet, stopped once by the registration rollers 103, and the transfer position of the image from the intermediate transfer belt 105 is adjusted according to the image forming timing in the image forming unit 106. Sent to. The intermediate transfer image formed on the intermediate transfer belt 105 is transferred onto the paper 104 at a position where the conveyance path comes into contact with the intermediate transfer belt 105 or at a position closest to the intermediate transfer belt 105 to form a color image. The sheet 104 on which the image is formed is further conveyed, the image is fixed by the fixing device 116, and then the sheet is ejected to the outside of the MFP 100.

In the MFP 100 having the above configuration, the error in the axial distance between the photoconductor drums 109Y, 109M, 109C, and 109K, the parallelism error between the photoconductor drums 109Y, 109M, 109C, and 109K, and the LEDA 130 in the optical writing control device 111. Due to the installation error of, the timing error of writing the electrostatic latent image on the photoconductor drums 109Y, 109M, 109C, and 109K, the toner images of the respective colors that should originally overlap do not overlap, and the misalignment between the colors ( (Color shift) occurs. Therefore, due to the influence of the fluctuation in the rotation speed of the endless rotary body included in the MFP 100, the position of the toner image superposition is displaced, which causes the color misregistration of the image formed on the recording medium.

The MFP 100 includes a pattern position detection sensor 117 for detecting a color misregistration correction pattern formed to correct color misregistration. The pattern position detection sensor 117 is, for example, an optical sensor (TM sensor) that uses reflection of light. The pattern position detection sensor 117 is a sensor that reads the alignment mark transferred as a toner image onto the intermediate transfer belt 105 by the photosensitive drums 109Y, 109M, 109C, and 109K. The pattern position detection sensor 117 includes a light emitting element that emits light that illuminates the pattern image drawn on the surface of the intermediate transfer belt 105, and a light receiving element that receives reflected light from the pattern image. As shown in FIG. 1, the pattern position detection sensor 117 is installed on the downstream side of the photosensitive drums 109Y, 109M, 109C and 109K in the transport direction of the sheet 104, and the intermediate transfer belt 105 transports the sheet 104. A plurality of substrates are supported on the same substrate along a direction (so-called main scanning direction) orthogonal to the direction.

In the pattern position detection sensor 117, the output voltage based on the light reflected by the correction pattern group 500 is the output voltage that the light emitted from the light emitting element is reflected on the surface of the intermediate transfer belt 105 and is received by the light receiving element. Will be larger than. By detecting the output voltage of the pattern position detection sensor 117, the formation position of the correction pattern group 500 formed on the intermediate transfer belt 105 can be detected. On the other hand, the formation position of the correction pattern group 500 on the intermediate transfer belt 105 can be specified based on the toner image formation timing in the optical writing control device 111. Therefore, by using the detection result of the correction pattern group 500 by the pattern position detection sensor 117, the color misregistration amount, which is the misregistration of the formation position of the toner image of each color, can be calculated. Details of the pattern position detection sensor 117 and aspects of color misregistration correction will be described later. It should be noted that MFP 100 includes a configuration for realizing an information processing function including CPU 10 described later, and operates under the control of such a configuration.

In addition, the MFP 100 removes the toner of the alignment mark drawn by the toner image transferred to the intermediate transfer belt 105 to prevent the paper 104 conveyed by the intermediate transfer belt 105 from becoming dirty. 118 is provided. As shown in FIG. 1, the belt cleaner 118 is a cleaning blade that is arranged on the downstream side of the drive roller 108 and on the upstream side of the photosensitive drum 109, and is pressed against the intermediate transfer belt 105. The belt cleaner 118 is a developer removing unit that scrapes off the toner attached to the surface of the intermediate transfer belt 105.

[Outline of optical writing device]
Next, the optical writing control device 111 installed in the MFP 100 according to this embodiment will be described. FIG. 2 is a diagram showing a positional relationship between the optical writing control device 111 and the photosensitive drum 109 according to the present embodiment. As shown in FIG. 2, the irradiation light emitted to each of the photoconductor drums 109Y, 109M, 109C, and 109K of each color is LEDA (Light-emitting diode Array) 130Y, 130M, 130C, and 130K (hereinafter, generally referred to as a light source). It is irradiated from LEDA 130).

The LEDA 130 is configured by arranging LEDs, which are light emitting elements, in the main scanning direction of the photosensitive drum 109. The control unit included in the optical writing control device 111 controls the ON/OFF state of each LED arranged in the main scanning direction for each main scanning line based on drawing information input from the controller 20 described later. By doing so, the surface of the photoconductor drum 109 is selectively exposed to form an electrostatic latent image.

[Hardware configuration of image forming apparatus]
Next, an example of the hardware configuration of the control system of the image forming apparatus including the optical writing device according to the present invention will be described with reference to FIG. The control system of the MFP 100 according to the present embodiment includes an image processing engine that executes image formation, in addition to the same configuration as a PC (Personal Computer) that is an information processing device. That is, the MFP 100 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 11, a ROM (Read Only Memory) 12, an image processing engine 13, an HDD (Hard Disk Drive) 14, and an I/F. An (Interface) 15 is connected via a system bus 18. Further, an LCD (Liquid Crystal Display) 16, an operation unit 17, and a pattern position detection sensor 117 are connected to the I/F 15.

The CPU 10 is a control unit and controls the operation of the entire MFP 100. The RAM 11 is a volatile storage medium that can read and write information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. Image processing engine 13 includes a configuration that operates to actually perform image formation in MFP 100.

The HDD 14 is a non-volatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The I/F 15 connects and controls the system bus 18 and various hardware and networks. LCD 16 is a visual user interface for the user to check the state of MFP 100. The operation unit 17 is a user interface such as a keyboard and a mouse for the user to input information to the MFP 100.

In such a hardware configuration, a program stored in a recording medium such as the ROM 12 or the HDD 14 is read out to the RAM 11, and the CPU 10 performs an operation according to the program, thereby configuring a software control unit. A combination of the software control unit configured in this way and hardware constitutes a functional block that realizes the function of the MFP 100 according to the present embodiment. Note that the hardware configuration illustrated in FIG. 3 is an example, and the hardware configuration of the MFP 100 according to the present embodiment is not limited to the configuration of FIG. 1 as long as the hardware can realize the functional configuration described below. ..

[Functional configuration of image forming apparatus]
Next, the functional configuration of the MFP 100 according to the present embodiment will be described with reference to FIG. FIG. 4 is a block diagram showing the functional arrangement of the MFP 100 according to this embodiment. The MFP 100 includes a controller 20, an ADF (Auto Document Feeder) 21, a scanner unit 22, a paper discharge tray 23, a display panel 24, a paper feed table 25, a print engine 26, a paper discharge tray 27, and a network I/F 28. Have.

The controller 20 also includes a main control unit 30, an engine control unit 31, an input/output control unit 32, an image processing unit 33, and an operation display control unit 34. Further, the MFP 100 is configured as a multi-function peripheral having the scanner unit 22 and the print engine 26. In FIG. 4, electrical connections are indicated by solid arrows, and flows of the recording medium are indicated by broken arrows.

The display panel 24 is an output interface for visually displaying the state of the MFP 100, and is also an input interface (operation unit) as a touch panel when the user directly operates the MFP 100 or inputs information to the MFP 100. The network I/F 28 is an interface for the MFP 100 to communicate with other devices via a network, and an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface is used.

The controller 20 is composed of a combination of software and hardware. Specifically, a control program such as the ROM 12, the non-volatile memory, and the HDD 14 is loaded into a volatile memory (hereinafter referred to as a memory) such as the RAM 11 and a software control unit configured by the calculation of the CPU 10 according to the programs. The controller 20 is configured by hardware such as an integrated circuit. The controller 20 functions as a control unit that controls the entire MFP 100.

The main control unit 30 plays a role of controlling each unit included in the controller 20, and gives an instruction to each unit of the controller 20. The engine control unit 31 plays a role as a drive unit that controls or drives the print engine 26, the scanner unit 22, and the like. The input/output control unit 32 inputs signals and commands input via the network I/F 28 to the main control unit 30. In addition, the main control unit 30 controls the input/output control unit 32 to access other devices via the network I/F 28.

Under the control of the main control unit 30, the image processing unit 33 generates drawing information based on the print information included in the input print job. The drawing information is information for the print engine 26, which is an image forming unit, to draw an image to be formed in the image forming operation. The print information included in the print job is image information converted into a format recognizable by the MFP 100 by a printer driver installed in an information processing device such as a PC. The operation display control unit 34 displays information on the display panel 24 or notifies the main control unit 30 of information input via the display panel 24.

When the MFP 100 operates as a printer, the input/output control unit 32 first receives a print job via the network I/F 28. The input/output control unit 32 transfers the received print job to the main control unit 30. Upon receiving the print job, the main control unit 30 controls the image processing unit 33 to generate drawing information based on the print information included in the print job.

When the drawing information is generated by the image processing unit 33, the engine control unit 31 controls the print engine 26 based on the generated drawing information and forms an image on the recording medium conveyed from the paper feed table 25. Run. That is, the print engine 26 functions as an image forming unit. The recording medium on which the image is formed by the print engine 26 is ejected to the paper ejection tray 27.

The image information generated by the image processing unit 33 is stored in the HDD 14 or the like as it is according to a user's instruction, or is transmitted to an external device via the input/output control unit 32 and the network I/F 28. That is, the ADF 21 and the engine control unit 31 function as an image input unit.

Further, when the MFP 100 operates as a copying machine, the image processing unit 33 generates drawing information based on the imaging information received by the engine control unit 31 from the scanner unit 22 or the image information generated by the image processing unit 33. Based on the drawing information, the engine control unit 31 drives the print engine 26 as in the case of the printer operation.

[Control block of optical writing device]
Next, a control block of the optical writing control device 111 according to the present embodiment will be described with reference to FIG. FIG. 5 is a diagram showing the functional configuration of the optical writing control unit 120 that controls the optical writing control device 111 according to the present embodiment, and the relationship between the LEDA 130 and the pattern position detection sensor 117.

As shown in FIG. 5, the optical writing control unit 120 according to the present embodiment includes a light emission control unit 121, a counting unit 122, a sensor control unit 123, a correction value calculation unit 124, a reference value storage unit 125, and a correction value storage unit. Including 126. The optical writing control unit 120 functions as an optical writing control device that controls the LEDA 130 that is a light source to form an electrostatic latent image on the photoconductor.

Like the controller 20 of the MFP 100, the optical writing control unit 120 is configured by loading a control program stored in the ROM 12 or the HDD 14 into the RAM 11 and operating according to the arithmetic processing of the CPU 10.

The light emission control unit 121 is a light source control unit that controls the LEDA 130 based on image information input from the engine control unit 31 of the controller 20. That is, the light emission control unit 121 also functions as a pixel information acquisition unit. The light emission control unit 121 realizes optical writing on the photoconductor drum 109 by causing the LEDA 130 to emit light at a predetermined line cycle.

The line cycle in which the light emission control unit 121 controls the light emission of the LEDA 130 is determined by the output resolution of the image forming apparatus 1. However, as described above, when the magnification is changed in the sub-scanning direction according to the ratio with the sheet conveyance speed, the light emission control is performed. The unit 121 adjusts the line cycle to perform scaling in the sub-scanning direction.

In addition, the light emission control unit 121 drives the LEDA 130 based on the drawing information input from the engine control unit 31, and also controls the light emission of the LEDA 130 in order to draw the correction pattern group 500 in the above-described drawing parameter correction processing. To do.

As described with reference to FIG. 2, a plurality of LEDA 130 are provided corresponding to each color. Therefore, as shown in FIG. 5, a plurality of light emission control units 121 are also provided so as to correspond to the plurality of LEDAs 130, respectively. The correction value generated as a result of the positional deviation correction processing in the drawing parameter correction processing is stored as the color deviation correction value in the correction value storage unit 126 shown in FIG.

The light emission control unit 121 corrects the timing for driving the LEDA 130 based on the past color misregistration correction value stored in the correction value storage unit 126. Further, since the light emission control unit 121 corrects the position of the image in the main scanning direction, when the LEDA 130 emits light based on the image information for each main scanning line, the information of each pixel forming the image information for one line , LEDA 130 is adjusted based on the color misregistration correction value stored in the correction value storage unit 126.

To correct the drive timing of the LEDA 130 by the light emission control unit 121, specifically, delay the timing at which the LEDA 130 is driven to emit light based on the drawing information input from the engine control unit 31, that is, shift the line. Is realized by On the other hand, since the drawing information is sequentially input from the engine control unit 31 in accordance with a predetermined cycle, in order to shift the line and delay the light emission timing, the input drawing information is held, It is necessary to delay the read timing.

Therefore, the light emission control unit 121 has a line memory which is a storage medium for holding the drawing information input for each main scanning line, and stores the drawing information input from the engine control unit 31 in the line memory. Hold by. In addition, as the correction of the drive timing of the LEDA 130, fine adjustment of the light emission timing for each line cycle is performed in addition to the adjustment for each line cycle. The light emission control unit 121 constitutes a pattern forming unit.

In the color misregistration correction value process, the counting unit 122 starts counting at the same time when the light emission control unit 121 controls the LEDA 130 to start the exposure of the photosensitive drum 109K. The counting unit 122 acquires a detection signal output by the sensor control unit 123 detecting the correction pattern group 500 based on the output signal of the pattern position detection sensor 117. That is, the counting unit 112 executes interrupt control based on the operation clock of the CPU 10 and acquires a detection signal (output voltage of the pattern position detection sensor 117) from the sensor control unit 123. Further, the counting unit 122 inputs the count value at the timing when the detection signal is acquired to the correction value calculating unit 124. That is, the counting unit 122 functions as a detection timing acquisition unit that acquires the detection timing of the correction pattern group 500.

The sensor control unit 123 is a control unit that controls the pattern position detection sensor 117, and as described above, the misregistration correction pattern formed on the intermediate transfer belt 105 is generated based on the output signal of the pattern position detection sensor 117. , The pattern position detection sensor 117 is judged to have reached the position and a detection signal is output. That is, the sensor control unit 123 functions as a detection signal acquisition unit that acquires a pattern detection signal from the pattern position detection sensor 117.

Further, the sensor control unit 123 acquires the signal intensity of the output signal of the pattern position detection sensor 117 and inputs the signal intensity to the correction value calculation unit 124 when performing the density correction using the density correction pattern. Further, the sensor control unit 123 adjusts the detection timing of the density correction pattern according to the detection result of the misregistration correction pattern. The sensor control unit 123 constitutes a set pattern detection means.

The correction value calculation unit 124 uses the count value acquired from the count unit 122 and the signal intensity of the detection result of the density correction pattern acquired from the sensor control unit 123 to correct the positional deviation stored in the reference value storage unit 125. And a correction value is calculated based on the reference value for density correction. That is, the correction value calculation unit 124 functions as a reference value acquisition unit and a correction value calculation unit. The reference value storage unit 125 stores reference values for use in such calculations. The correction value is calculated based on the “deviation direction” and the “deviation amount” of the misregistration correction pattern. The correction value calculation unit 124 constitutes a correction value calculation means.

[Relationship between correction pattern group 500 and detection voltage]
Next, the relationship between the correction pattern group 500 according to the present embodiment and the output voltage of the pattern position detection sensor 117 will be described. FIG. 6 is a diagram showing the positional relationship between the pattern position detection sensor 117 according to the present embodiment, the intermediate transfer belt 105, and the correction pattern group 500 formed on the intermediate transfer belt 105. In FIG. 6, a plurality of pattern position detection sensors 117 are arranged in parallel at positions separated from each other in the main scanning direction. The correction pattern group 500 is formed at the “position detected by the pattern position detection sensor 117” when moved in the sub-scanning direction. The “position detected by the pattern position detection sensor 117” is a position where the light emitted from the light emitting element of the pattern position detection sensor 117 strikes, that is, a position corresponding to the “detection spot range”. The detection spot range corresponds to the pattern detection position by the pattern position detection sensor 117. The light receiving element receives the reflected light from the position, and as a result, the magnitude of the output voltage from the pattern position detection sensor 117 is determined.

When the correction pattern group 500, which is a color misregistration correction pattern, reaches the detection spot range of the pattern position detection sensor 117, the reflected light weakens, and the output voltage of the pattern position detection sensor 117 drops. When the correction pattern group 500 passes through the detection spot range of the pattern position detection sensor 117, the reflected light intensifies, so that the output voltage of the pattern position detection sensor 117 rises. The formation position of the correction pattern group 500 is detected by detecting the change in the output voltage of the pattern position detection sensor 117.

The background of the intermediate transfer belt 105 has a high light reflectance, but if the surface is broken, twisted, or scratched, the component of the regular reflection light weakens, and the output voltage of the pattern position detection sensor 117 drops. , The correction pattern group 500 may be erroneously detected. If the position where the correction pattern group 500 is not detected is detected as the formation position of the correction pattern group 500, the color misregistration cannot be corrected normally. To avoid this, the MFP 100 according to the present embodiment uses a polling control method that monitors whether or not the correction pattern group 500 is normally detected at regular intervals.

By the polling control, the number of patterns included in the correction pattern group 500, which should be input at regular intervals, is compared with the number of patterns derived from the number of actually detected edges. Assuming that the pattern group 500 is normally detected, the detection result is used for the color misregistration correction value calculation process. If the number of patterns that should be input does not match the number of patterns based on the detected edge number, it is determined that the detection of the correction pattern group 500 has failed, and the detection result is not used in the color misregistration correction value calculation process. In the MFP 100 according to this embodiment, the success or failure of pattern detection is determined for each monitored period. As a result, the correction pattern group 500, which is the color misregistration correction pattern, can be detected stably.

In the MFP 100 according to the present embodiment, normally, when the space between the adjacent reference line patterns 510 of the first set pattern 521 included in the correction pattern group 500 passes the detection spot range of the pattern position detection sensor 117, the pattern is detected. Interrupt control for detecting the output voltage of the position detection sensor 117 is executed. That is, in FIG. 6, the “interruption position” indicated by using the virtual line 530 represents the position where the interrupt control is started when the detection spot passes. This interrupt control is performed at predetermined intervals. Therefore, the output voltage of the pattern position detection sensor 117 is detected in the predetermined section of the virtual line 530 and the next virtual line 530. This predetermined section corresponds to the pattern detection section. The correction pattern group 500 is detected at the pattern formation interval A as shown in FIG. 6 within the pattern detection section. When forming the same pattern, the section including the pattern formation interval B shown in FIG. 6 corresponds to the pattern detection section.

As already described, the virtual line 530 corresponds to the “interruption position” according to this embodiment. Therefore, in the example of FIG. 6, both the reference line pattern 510 and the correction target first pattern 511 forming the first set pattern 521 are formed such that their formation positions do not overlap with the interruption position.

FIG. 7 is a diagram exemplifying how the output voltage of the correction pattern group 500 shown in FIG. 6 changes. Both the output voltages of the pattern position detection sensor 117R arranged on the right side in the conveyance direction and the pattern position detection sensor 117L arranged on the left side in the conveyance direction have the same waveform.

In FIG. 7, the output voltage drops and rises at the timing T1 when the reference line pattern 510 of the first first set pattern 521 is detected, and then the output voltage changes at the timing T2 when the correction target first pattern 511 is detected. It is descending and rising. After that, the output voltage drops and rises at the timing T3 when the reference line pattern 510 is detected. In this way, the output voltage of the pattern position detection sensor 117 is acquired from the virtual line 530 and monitored. The first pattern 511 to be corrected has a longer period of time from the fall of the output voltage to the rise and return of the output voltage, as compared with the reference line pattern 510. By detecting this, it is detected that it is the first set pattern 521.

Then, at timing T4, the next interrupt control is executed. Then, the first set pattern 521 is detected by counting the number of times the output voltage fluctuates as at timings T5, T6, and T7. Then, at the subsequent timing T8, the next interrupt control is executed, and the pattern detection process is repeated. In this way, the interval defined by the ideally formed correction pattern group 500 interrupt timing (T4, T8, etc.) is set to be wider than the pattern formation interval.

In the color misregistration correction technique according to the present embodiment, for example, with reference to FIGS. 8 and 9, the relationship between the scaling factor τ and the color matching accuracy when repeatedly forming the first set pattern 521 (Z pattern) is described. explain. FIG. 9 schematically shows how each line pattern is formed in the case where the position where the circumferential length of the endless rotary body that periodically causes speed fluctuations is divided into n positions is the position where the correction pattern is formed. .. By defining the pattern intervals when repeatedly forming the same line pattern as illustrated in FIG. 8, it is possible to effectively prevent the influence of the periodic speed fluctuation due to the endless rotary body that occurs when the color misregistration correction value is calculated. Can be suppressed to

As shown in FIG. 9, the larger the interval magnification τ when the first set pattern 521 is repeatedly formed, the more difficult it becomes to suppress the influence of the periodic velocity fluctuation. The component of the periodic velocity fluctuation that cannot be suppressed is directly proportional to the interval magnification τ. As is apparent from FIG. 9, in order to suppress the influence of the periodical speed fluctuation in the calculation of the color misregistration correction value, in other words, in order to improve the color matching accuracy, it is preferable to narrow the correction pattern formation interval. It is suitable.

FIG. 9 shows an example of the correction pattern group 500 according to this embodiment in which the magnification τ of the formation interval is minimized. The correction target first pattern 511 of the correction target color located in the center of the first set pattern 521, and the second set pattern 522 of the correction target color located in the center of the second set pattern 522 are between adjacent correction patterns. The same color and the same shape are repeatedly formed. The reference line pattern 510 is formed so as to be commonly used by the adjacent correction target patterns. By forming the correction pattern group 500 in this manner, the magnification τ of the formation interval can be minimized and highly accurate color misregistration correction can be realized.

In the description of the present embodiment, when the correction pattern group 500 is illustrated, the pattern drawn in yellow is shown by “dotted line”. In addition, the pattern drawn in black is shown by "solid line". Also, the pattern drawn in cyan is shown by "dashed line". The pattern drawn in magenta color is shown by "broken line".

[Relationship between pattern formation position and interrupt position]
Here, the pattern shape when the formation interval between the adjacent set patterns of the first set pattern 521 and the second set pattern 522 configuring the correction pattern group 500 is narrowed (when the magnification τ is 2), and the polling The relationship with the interrupt position in the control method will be described.

As shown in FIG. 11, as a method of forming the correction pattern group 500, adjustment is performed so that the virtual line 530 indicating the interrupt position corresponds to each of the two sets of the first set pattern 521 (the second set pattern 522). .. As described above, narrowing the correction pattern formation interval allows more accurate color misregistration correction, but limits interrupt positions. Therefore, in the MFP 100 according to the present embodiment, adjustment is performed so that the virtual line 530 indicating the interrupt position and the pattern detection position do not overlap.

[First example of influence of color shift and overlapping of interrupt positions]
Next, an example of the influence of color misregistration and the overlap of interrupt positions in polling control will be described with reference to FIG. FIG. 12A is an example of the output voltage waveform of the pattern position detection sensor 117 when the correction pattern group 500 is ideally formed by the pattern forming method shown in FIG. In the correction pattern group 500 illustrated here, the reference line pattern 510 and the correction target first pattern 511 (correction target second pattern 512) are line patterns of different colors. Since FIG. 12A shows the output voltage waveform of the pattern position detection sensor 117 when the ideal initial pattern is detected, the timing (T1 to T9) for detecting the position of each line pattern and the interrupt position are shown. Corresponding interrupt timings (W1, W2) do not overlap and the pattern formation interval A(B) is properly determined. In this case, all patterns are normally detected.

FIG. 12B shows the pattern position detection sensor 117 in the correction pattern group 500 formed after the main scanning registration shift has occurred from the ideal initial state in the pattern formation manner as shown in FIG. It is an example of an output waveform. In this case, the detection timing (T1, T3, T5, T7, T9,...) Of the horizontal line pattern (reference line pattern 510) does not change. However, the detection timing (T2, T4, T6, T8...) Of the diagonal pattern (first correction target pattern 511) changes. Specifically, as shown in FIG. 12B, the detection interval from the diagonal line pattern detection timing to the horizontal line pattern detection timing is short.

FIG. 12C shows a pattern forming method as shown in FIG. 11 in the correction pattern group 500 formed after the main scanning registration shift and the sub-scanning registration shift from the ideal initial state. It is an example of the output waveform of the pattern position detection sensor 117. In this case, the detection timing (T1, T3, T5, T7, T9,...) Of the horizontal line pattern (reference line pattern 510) also changes, and further the detection timing (T2) of the diagonal line pattern (correction target first pattern 511). , T4, T6, T8...) also changes. Specifically, as shown in FIG. 12C, the detection timing of the diagonal line pattern to the detection timing of the horizontal line pattern is the same as in the case of FIG. 12B, but the interrupt timing (W1 , W2).

Occurrence of main-scan registration deviation and sub-scan registration deviation may cause the interrupt position and the pattern detection position to overlap. Then, each line pattern forming the correction pattern group 500 cannot be normally detected. The color misregistration correction technique corrects the main-scanning registration deviation and the sub-scanning registration deviation. Therefore, in consideration of the effects of the main scanning registration deviation and the sub-scanning registration deviation that occur between the time when the color misregistration correction value is calculated and the time when the next color misregistration correction is executed, the interrupt position and the pattern formation position do not overlap. Need to be adjusted. Note that FIG. 12 does not accurately represent the amount of deviation of each detection timing, but illustrates the state of deviation from the ideal timing.

[Second example of influence of color shift and overlapping of interrupt positions]
Next, an example of the influence of the color shift and the overlap of the interrupt position in the polling control will be described with reference to FIGS. 13 and 14. FIG. 13 exemplifies a case where “skew deviation” occurs in addition to the main scanning registration deviation and the sub-scanning registration deviation, assuming the correction pattern group 500 as shown in FIG. 11.

In this case, the pattern detection position is further displaced from that illustrated in FIG. 12, and the interrupt position and the pattern formation position overlap. For example, FIG. 14 shows an example of the output voltage waveform of the pattern position detection sensor 117 based on the example of FIG. FIG. 14 is a superposition of all the output voltage waveforms illustrated in FIG. 12, in which the dotted line represents the output voltage waveform shown in FIG. 12A, and the alternate long and short dash line represents the output voltage waveform shown in FIG. 12B. , The solid line corresponds to the output voltage waveform shown in FIG.

As shown in FIG. 14, at the timing R shown by an ellipse, the pattern detection timing by the pattern position detection sensor 117 (117R) and the interrupt timing W2 overlap due to the influence of the main scanning registration shift, the sub scanning registration shift, and the skew shift. .. That is, the detection position and the interrupt position of the correction pattern group 500 overlap. If such an overlap occurs, in the example of FIG. 14, detection of all the diagonal line patterns will fail, and calculation of the color misregistration correction value and color misregistration correction processing will fail. As a result, stable color shift correction cannot be performed. That is, if the formation interval when the same pattern is repeatedly formed, such as the correction pattern group 500, is narrowed, the pattern detection may fail due to the influence of color misregistration.

According to the color misregistration correction technique executed in the image forming apparatus according to the present invention, which will be described below, the color misregistration correction is performed even when the color misregistration occurs due to the main scanning registration deviation, the sub scanning registration deviation, the skew deviation, or the like. The pattern can be detected successfully. Thereby, stable color misregistration correction can be performed.

In the embodiment of the image forming apparatus (MFP 100) according to the present invention, when calculating the skew correction, the left and right sides of the pattern position detection sensor 117 are aligned with the virtual center line connecting the center positions of all colors. The correction value is calculated. At this time, since the virtual center line itself may have a skew component, even if color misregistration correction is executed, the positions on the left and right of the pattern position detection sensor 117 where patterns are formed are displaced in the sub-scanning direction (skew). It may shift). In other words, since the skew deviation component generated in the virtual center line remains in the skew deviation generated when the color deviation correction pattern is formed, the pattern detection position and the interrupt position do not overlap even if the skew deviation occurs. Must be adjusted.

For example, the main-scanning resist deviation and the sub-scanning resist deviation are about 100 μm, while the skew deviation may be 500 μm or more. Therefore, the influence of the skew shift in the color shift correction is large.

[First Embodiment of Image Forming Apparatus According to the Present Invention]
Next, an example of how to form the correction pattern group 500 used in the color misregistration correction technique that can be executed in the MFP 100 that is an embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. In the following description, as a comparative example for clarifying the characteristics of the correction pattern group 500 according to the present embodiment, the correction pattern formed by the conventional technique is referred to as “conventional correction pattern group 600”.

In the description of this embodiment, the reference color is “black”, and the color that is the target of color misregistration correction (correction target color) is “magenta”. Of course, the present embodiment is applicable even if a color (cyan color, yellow, black) that is not used as a correction target color in the following description is used as a correction target color. The reference color is not limited to black, and another color (eg, yellow) may be used as the reference color.

The correction pattern group 500 according to the present embodiment and the conventional correction pattern group 600 are compared as illustrated in FIG. As is apparent from FIG. 15, by shifting the formation position of the correction target first pattern 511 sandwiched between the two reference line patterns 510 (the same applies to the correction target second pattern 512 hereafter), the present embodiment is realized. Overlapping of the formation position of the correction pattern group 500 and the interrupt position due to polling control is avoided. Further, even if the formation position of the correction target first pattern 511 is deviated, the formation interval of the reference line pattern 510 is not changed. In this case, the “shift amount G1” of the pattern formation position is determined based on the detection result of the correction pattern group 500 in the color misregistration correction process executed immediately before.

For example, in the color misregistration correction executed immediately before, due to the components of the virtual center line of black and magenta and the skew misalignment, the magenta oblique line pattern (correction target first pattern 511) and the black horizontal line pattern (reference line pattern 510). ) Is assumed to be shortened by 300 μm, the formation position of the magenta shaded pattern (correction target first pattern 511) is adjusted so that the formation interval between the correction target first pattern 511 and the reference line pattern 510 increases by 300 μm. Shift.

In this case, the target for shifting the formation position may be the reference line pattern 510, but black is commonly used as a reference color when performing color misregistration correction for colors other than magenta (cyan, yellow, national strength). Considering this, it is preferable to shift the magenta color pattern that is the correction target color.

As described above, the MFP 100 according to the present exemplary embodiment stabilizes the detection of the color misregistration correction pattern and corrects the color misregistration by shifting the formation position of the specific pattern forming the correction pattern group 500. realizable.

In the color misregistration correction executed immediately before, what should be referred to is skew misregistration. Others (main scanning and sub scanning registration shift) may be omitted. Note that the pattern detection result in the color misregistration correction executed immediately before is not used on the assumption that the components of the main scanning and sub-scanning registration misregistration and the skew misregistration that occur when forming the color misregistration correction pattern are accurately estimated. The pattern formation position may be shifted based on a predetermined value. For example, if the maximum deviation between the main scanning registration deviation and the sub-scanning registration deviation in the MFP 100 is 250 μm and the maximum skew deviation is 300 μm, the formation interval is increased by 800 μm to stabilize the detection of the color deviation correction pattern. You can

In addition, when the correction target color is one color and the skew deviation occurs between the two colors as compared with the case where the skew deviation is corrected, when the skew deviation occurs between the two colors, the deviation of the formation position due to the skew deviation is larger. Become. In this case, the effect is greater when the two correction target patterns located before and after the interrupt position have different colors.

The detection position of the pattern largely changes because the diagonal pattern (first correction target pattern 511) does not shift the formation position of the horizontal line pattern (second correction target pattern 512), and the diagonal pattern (first correction target pattern 511) It is also possible to shift only the formation position of.

Further, in the case of the diagonal pattern (correction target first pattern 511), as shown in FIG. 15, not only the formation position is shifted in the sub-scanning direction, but the pattern formation position in the main scanning direction may be shifted.

When the reference color and the correction target color are the same color, the formation position does not have to be shifted. This is because in the case of the same color, the influence of the shift is relatively smaller than in the case of the two colors, so that the interrupt position can be easily determined. Therefore, in the present embodiment, the effect is more likely to be obtained when the two-color putters are present in front and rear.

Next, how to shift the formation position of the correction target first pattern 511 when forming the correction pattern group 500 according to the present embodiment will be described. As shown in FIG. 16A, the formation positions of the correction target first patterns 511 included in the correction pattern group 500 detected by each of the pattern position detection sensors 117 arranged in the main scanning direction are the same. (Equal to) to form. Thereby, the calculation formula for calculating the color misregistration correction value can be simplified.

As illustrated in FIG. 16A, if the formation positions of the correction pattern groups 500 formed at positions separated in the main scanning direction are similarly shifted, the stability of pattern detection may be impaired. This is because, for example, the influence of skew shift is likely to occur, and the shift of the main scanning magnification tends to cause only one pattern position detection sensor 117 to shift from the center position of the pattern. Therefore, the pattern formation for more stably detecting the correction pattern will be described.

As shown in FIG. 16B, in the correction pattern group 500 formed at positions separated in the main scanning direction, the correction target first pattern 511 (correction target The formation positions of the two patterns 512) may be shifted. That is, in the correction pattern groups 500 of respective columns formed at different positions in the main scanning direction, different displacement directions or displacement amounts may be set for the respective columns. By finely adjusting for each column, it is possible to realize a stable pattern detection while simplifying the calculation formula for calculating the color misregistration correction value.

[Embodiment of Image Forming Method]
Next, an embodiment of the image forming method according to the present invention will be described. FIG. 17 is a flowchart showing the flow of color misregistration correction processing executed by the MFP 100 according to this embodiment.

First, when a color misregistration correction execution request is generated, the light emission control unit 121 reads the color misregistration correction value stored in the correction value storage unit 126, and controls the optical writing operation using the LEDA 130. As a result, a correction pattern group 500, which is a color misregistration correction pattern, is formed on the intermediate transfer belt 105 (S1701). In step S1701, the pattern formation position shift amount is determined based on the color misregistration correction value calculated in the previous color misregistration correction process. Then, the formation position of the correction target first pattern 511 (correction target second pattern 512) is shifted according to the formation position shift amount.

The deviation amount in the main scanning direction of the pattern of the correction target color (correction target first pattern 511, correction target second pattern 512) with respect to the reference color pattern (reference line pattern 510) is defined as “X”, and the formation position in the main scanning direction. When the shift amount is “α”, the shift in the main scanning direction is represented by “X+α”.

Further, the shift amount in the sub-scanning direction of the pattern of the correction target color (correction target first pattern 511, correction target second pattern 512) with respect to the reference color pattern (reference line pattern 510) is set to “Y”, and is set in the sub-scanning direction. When the formation position shift amount is “β”, the shift in the sub-scanning direction is represented by “Y+β”.

After S1701, the pattern position detection sensor 117 detects the correction pattern group 500 formed on the intermediate transfer belt 105 (S1702). Since the pattern formation position is shifted, the correction pattern group 500 can be stably detected in S1702, and the pattern detection determination succeeds (S1703/YES). If the pattern detection determination is not successful (S1703/NO), the process ends.

Subsequent to S1703, the correction value calculation unit 124 calculates the deviation amount in the main scanning direction and the deviation amount in the sub scanning direction using the result of detection of the correction pattern group 500 this time (S1704). The former is "M" and the latter is "S". In this case, the correction pattern group 500 detected in S1702 is shifted by the amount corresponding to the above “α” in the main scanning direction, so the main scanning direction shift amount X is obtained by adding α from M to α. It can be calculated by (or subtracting). This equation is shown in Equation 1 below.

Further, since the correction pattern group 500 detected in S1702 is displaced in the sub-scanning direction by the amount corresponding to the above “β”, the sub-scanning direction deviation amount Y is obtained by adding β from S ( Or subtraction). This equation is shown in Equation 2 below.

Subsequently, the main scanning direction shift amount X and the sub scanning direction shift amount Y calculated in S1704 are stored in the correction value storage unit 126 as the latest (S1705). As described above, in the image forming method according to the present embodiment, the color misregistration correction value can be easily calculated by adding (subtracting) only the portion formed by shifting the formation position of the pattern.

[Second Embodiment of Image Forming Apparatus According to the Present Invention]
Next, another example of a method of forming a correction pattern used in the color misregistration correction technique that can be executed in the MFP 100 that is an embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings.

FIG. 18 shows an example of the correction pattern group 500a according to this embodiment. Also in the description of the present embodiment, the reference color is “black”, and the color that is the target of color misregistration correction (correction target color) is “magenta”. Of course, this embodiment is also applicable to a color (cyan color, yellow, black) that is not used as a correction target color in the following description as a correction target color. The reference color is not limited to black, and another color (eg, yellow) may be used as the reference color.

The correction pattern group 500a shown in FIG. 18 exemplifies a state in which the first set pattern 521 (Z pattern) is repeatedly formed. Here, it is assumed that the upward-sloping diagonal pattern is formed first, and then the downward-sloping diagonal pattern is formed. Then, it is assumed that the pattern position detection sensor 117 is formed so as to deviate from the detection position in the main scanning direction (detection spot in the pattern position detection sensor 117).

Originally, it is desirable that the formation position of the correction pattern group 500a be aligned with the detection position of the pattern position detection sensor 117. However, in some cases, the formation position of the correction pattern group 500a in the main scanning direction may not be adjusted. The present embodiment aims to stably detect the pattern even in such a case.

As in the case of the correction pattern group 500a, if the method of forming the first pattern 511 to be corrected is a rightward diagonal line pattern and a leftward diagonal line pattern, the respective detection timings deviate from the timings when the center of the pattern is detected. become. Then, the margin of the interrupt position changes due to the deviation of the detection timing. Here, when the margin of the interrupt position increases, the pattern can be detected normally. On the other hand, when the margin at the interrupt position is reduced, the pattern may not be detected normally.

Therefore, the correction pattern group 500 according to the present embodiment is formed by shifting the formation position of each pattern at the detection position of the pattern position detection sensor 117 so that the detection timing of the pattern of each color and the interrupt position do not overlap. To be done.

Based on the example shown in FIG. 18, the pattern forming position is shifted only for the upward-sloping diagonal line pattern in which the margin of the interrupt position is reduced (lost). Here, the shift amount of the pattern formation position is determined using the detection result of the color misregistration correction process executed immediately before.

For example, in the color misregistration correction process executed immediately before, when it is known that the pattern formation position deviates from the detection position of the pattern position detection sensor 117 by “−3 dot”, only the upward-sloping diagonal line pattern corresponds to “3 dot”. The pattern formation position is shifted so that a margin for pattern detection timing can be secured.

On the other hand, in the color misregistration correction process executed immediately before, when it is known that the formation position of the pattern deviates from the detection position of the pattern position detection sensor 117 by “+3 dot”, only the upward-sloping diagonal line pattern corresponds to “3 dot” pattern. The pattern formation position is shifted so as to secure a margin of detection timing.

In the color misregistration correction processing executed immediately before, what should be referred to are main scanning registration misalignment and skew misalignment. Therefore, it is not necessary to correct other deviations (sub-scanning registration deviations).

Note that, as shown in FIG. 18, in the portion other than the detection position of the pattern position detection sensor 117, the respective patterns forming the correction pattern group 500a are not related to the detection processing relating to the color misregistration correction. Therefore, the color misregistration correction process can be stably performed even if some of the patterns overlap.

1: Image forming apparatus 10: CPU
11: RAM
12: ROM
13: Image processing engine 14: HDD
15: I/F
16: LCD
17: Operation unit 18: System bus 20: Controller 22: Scanner unit 23: Paper discharge tray 24: Display panel 25: Paper feed table 26: Print engine 27: Paper discharge tray 28: Network I/F
30: Main control unit 31: Engine control unit 32: Input/output control unit 33: Image processing unit 34: Operation display control unit 100: MFP
101: paper feed tray 103: registration roller 104: paper 105: intermediate transfer belt 106: image forming unit 107: driven roller 108: drive roller 109: photoconductor drum 111: optical writing control device 112: count unit 116: fixing unit 117: pattern position detection sensor 118: belt cleaner 119: transfer roller 120: optical writing control section 121: light emission control section 122: count section 123: sensor control section 124: correction value calculation section 125: reference value storage section 126: correction Value storage unit 500: Correction pattern group 510: Reference line pattern 511: Correction target first pattern 512: Correction target second pattern 521: First set pattern 522: Second set pattern 530: Virtual line 600: Conventional correction pattern group

JP, 2003-107842, A JP, 2014-032291, A

Claims (17)

An image forming apparatus for forming a color image by superposing each color image developed by a developer of each color by rotationally driving a plurality of endless rotary members,
In order to calculate a correction value used to correct the displacement of the position where the respective color images are superimposed on one of the endless rotary members, a correction pattern group including a plurality of combination patterns composed of a plurality of correction patterns is Pattern forming means for forming an endless rotary body,
A set pattern detection means for detecting a set pattern included in the correction pattern group formed on the endless rotary body,
Correction value calculation means for calculating a correction value based on the detection result in the group pattern detection means,
Have
The combination pattern is a first pattern that is a linear pattern that is orthogonal to the transport direction of the correction pattern by the rotational drive of the endless rotary body,
A second pattern, which is either a linear pattern orthogonal to the carrying direction or a diagonal pattern inclined with respect to the carrying direction, is provided between the two first patterns arranged at positions separated in the carrying direction. It is configured by arranging the second pattern,
The pattern forming means, when forming the correction pattern group using the correction value calculated based on the detection result by the combination pattern detection means, determines the formation position of the second pattern included in the combination pattern. It is formed by shifting from the central position of the pair pattern,
An image forming apparatus characterized by the above. The pattern forming means forms the first pattern and the second pattern included in one set of patterns in different colors,
The image forming apparatus according to claim 1. The pattern forming means forms the correction pattern group such that first patterns included in adjacent set patterns of the set patterns included in the correction pattern group are overlapped with each other.
The image forming apparatus according to claim 1. The pattern forming means,
The second pattern included in the set pattern is formed by shifting in the transport direction.
The image forming apparatus according to claim 1. The pattern forming means,
Forming the second pattern included in the set pattern by a diagonal pattern,
The image forming apparatus according to claim 1. The pattern forming means,
The second pattern included in the combination pattern is formed by shifting in a direction orthogonal to the transport direction,
The image forming apparatus according to claim 5. The pattern forming means forms the paired patterns with the same displacement amount as the direction of shifting the formation positions of the second patterns included in all the paired patterns,
The image forming apparatus according to claim 1. When the pattern forming means forms the correction pattern groups in parallel at positions separated in the direction orthogonal to the carrying direction, the second pattern formation position included in one correction pattern group and another The formation positions of the second patterns included in the correction pattern group are formed so as to be different from each other in the transport direction,
The image forming apparatus according to claim 1. When the pattern forming means forms the correction pattern groups in parallel at positions separated in the direction orthogonal to the carrying direction, the second pattern formation position included in one correction pattern group and another Forming positions of the second pattern included in the correction pattern group are all shifted in the same direction in the transport direction,
The image forming apparatus according to claim 1. The pattern forming means forms all the first patterns included in the correction pattern group with the same reference color,
The image forming apparatus according to claim 1. The reference color is black,
The image forming apparatus according to claim 10. The pattern forming unit calculates the formation position of the second pattern included in the combination pattern, based on the displacement direction and the displacement amount at the formation position of the second pattern detected by the combination pattern detection unit. Determine based on the correction value,
The image forming apparatus according to claim 1. A skew deviation is included in the deviation direction and the deviation amount used in the calculation of the correction value,
The image forming apparatus according to claim 12, wherein. The deviation direction and the deviation amount used for the calculation of the correction value include the deviation in the main scanning direction,
The image forming apparatus according to claim 12, wherein. The combination pattern detection means monitors that the correction pattern group is normally detected at regular intervals,
The image forming apparatus according to claim 1. The correction value calculation means adds a shift amount of the formation position of the correction pattern group to the correction value calculated in the past to newly calculate a correction value,
The image forming apparatus according to claim 1. An image forming method for forming a color image by superposing each color image developed by a developing material of each color by rotational driving of a plurality of endless rotary members,
In order to calculate a correction value used to correct the displacement of the position where the respective color images are superimposed on one of the endless rotary members, a correction pattern group including a plurality of combination patterns composed of a plurality of correction patterns is Formed into an endless rotating body,
Detects a set pattern included in the correction pattern group formed on the endless rotary body,
Calculate a correction value based on the detection result of the set pattern,
The combination pattern is a first pattern that is a linear pattern that is orthogonal to the transport direction of the correction pattern by the rotational drive of the endless rotary body,
A second pattern, which is either a linear pattern orthogonal to the carrying direction or a diagonal pattern inclined with respect to the carrying direction, is provided between the two first patterns arranged at positions separated in the carrying direction. It is configured by arranging the second pattern,
When the correction pattern group is formed using the correction value calculated based on the detection result of the formed and detected set pattern, the formation position of the second pattern included in the set pattern is set to the set position. Form from the center position of the pattern,
An image forming method characterized by the above.