JP2011008168A - Image forming apparatus, color misregistration correction method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus more properly detecting an abnormal point in data for correction, when a drawing position on an image carrier is corrected by using a correction pattern, and also to provide a technique related to the image forming apparatus.

SOLUTION: The image forming apparatus is equipped with: a detection means which detects a plurality of representative points in a pattern for detecting a color shift formed on the image carrier (for instance, an intermediate transfer belt) by using a plurality of image forming sections; and an abnormal point determination means which determines whether a deviation amount ▵Z between a detection position and a theoretical position is within a predetermined allowable range TL, in each of the plurality of representative points Q(n) and whether each of the plurality of representative points Q(n) is the abnormal point. The predetermined allowable range TL is set based on an allowable value CB relating to the periodical fluctuations of the deviation amount.

COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer and a technology related thereto.

  There is an image forming apparatus such as an electrophotographic system that forms a color image. Such an image forming apparatus includes, for example, a plurality of image forming units, an intermediate transfer belt that superimposes and supports an image of each color formed by each of the plurality of image forming units, and the intermediate transfer belt. And a transfer unit that transfers the image to a sheet. More specifically, images of four colors (yellow, magenta, cyan, and black) formed on the photosensitive drums of the four image forming units are each temporarily transferred to the intermediate transfer belt and superimposed on the intermediate transfer belt. Is done. Thereafter, such a superimposed image (color image) is further transferred onto the paper. In this way, a color image is formed on the paper.

  By the way, in such an image forming apparatus, due to various causes, the above four-color images may “shift” from each other on the intermediate transfer belt, that is, “color shift” may occur. Such color misregistration may be caused by, for example, component parts being changed and part dimensions changing slightly, or component parts (for example, a photosensitive drum and an intermediate transfer belt) being expanded or contracted due to environmental changes. It can be caused by

  On the other hand, there is a technique for detecting such “color misregistration” and correcting the drawing position on the intermediate transfer belt. For example, in Patent Documents 1 and 2, after a color misregistration detection pattern is drawn on an intermediate transfer belt, the color misregistration detection pattern is detected by using a detection means (sensor), and based on the detection result. It is shown that the amount of color misregistration is calculated.

  In addition, in such calculation of the color misregistration amount, misdetection of the color misregistration detection pattern may occur due to various factors. Since such erroneous detection adversely affects the calculation result of the color misregistration amount, it is preferable to exclude data relating to erroneously detected points (also referred to as abnormal points).

  Therefore, Patent Document 2 describes a technique for excluding abnormal points detected in such pattern correction from correction target data. In Patent Document 2, the presence / absence of an abnormality is determined using a predetermined inequality that includes both two uncertain elements (maximum value and minimum value). More specifically, in determining whether the maximum value is within the allowable range, an inequality that is affected by the magnitude of the minimum value is used. In determining whether the minimum value is within the allowable range, an inequality that is affected by the magnitude of the maximum value is used.

JP 2003-66677 A JP 2004-85954 A

  However, the abnormality determination process in Patent Document 2 is performed when determining whether one of the two uncertain elements (specifically, the maximum value and the minimum value) is abnormal. Therefore, it is not necessarily an appropriate determination process.

  Therefore, the present invention provides an image forming apparatus capable of more appropriately detecting an abnormal point in correction data when correcting a drawing position on an image carrier using a correction pattern, and a technique related thereto. The issue is to provide.

  In order to solve the above problems, the invention of claim 1 is an image forming apparatus, comprising: a plurality of image forming units; an image carrier that carries images formed by each of the plurality of image forming units; Using a plurality of image forming units, pattern formation control means for forming a color misregistration detection pattern on the image carrier, and detecting positions of a plurality of representative points in the pattern formed on the image carrier And determining whether or not a deviation amount between the detection position and the theoretical position is within a predetermined allowable range with respect to each of the plurality of representative points, based on a detection result by the detection means and the detection result by the detection means, Based on an abnormal point determination unit that determines whether each representative point is an abnormal point, a detection result by the detection unit, and a determination result by the abnormal point determination unit, the image is superimposed on the image carrier. Comprising a color shift amount calculating means for calculating color shift amount of a plurality of color images, the said predetermined tolerance is characterized in that it is determined based on the allowable values for periodic variation of the shift amount.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the invention, the abnormal point determination unit includes the deviation amount of the target representative point of the plurality of representative points and the deviation relating to the plurality of representative points. When the difference from the average value of the amounts exceeds a predetermined value, it is determined that the deviation amount related to the target representative point does not fall within the predetermined allowable range, and the target representative point is determined to be the abnormal point. It is characterized by.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect of the invention, the color misregistration amount calculating means calculates the color misregistration amount by excluding the abnormal point. .

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect of the present invention, the color misregistration amount calculating means is configured to provide the color misregistration on condition that the number of abnormal points is smaller than a predetermined value. A quantity update process is executed.

  According to a fifth aspect of the present invention, there is provided a color misregistration correction method for correcting a color misregistration between a plurality of color images formed on an image carrier by a plurality of image forming units of an image forming apparatus. A step of detecting a color misregistration detection pattern formed on the image carrier; and b) based on a detection result of the pattern, a deviation amount between a detection position and a theoretical position is determined for a plurality of representative points of the pattern. Determining whether or not each of the plurality of representative points is an abnormal point; and c) determining whether or not each of the plurality of representative points is an abnormal point on the image carrier by the plurality of image forming units. Calculating each color misregistration amount of a plurality of formed color images based on the detection result of the pattern, and the predetermined permissible range is determined based on a permissible value related to periodic variation of the misregistration amount. And said In step c), the characterized in that said color shift amount without data is used for detecting the position relating to the determined representative point and the an abnormality point out of the plurality of representative points are calculated.

  The invention according to claim 6 includes: a) obtaining detection data of a color misregistration detection pattern formed on the image carrier by a plurality of image forming units; and b) detecting the color misregistration based on the detection data. Each of the representative points of the pattern is determined whether or not the deviation amount between the detection position and the theoretical position is within a predetermined allowable range, and whether each of the plurality of representative points is an abnormal point is determined. A program for causing a computer to execute a step of calculating, based on the detection data, a color shift amount of a plurality of color images formed on the image carrier by the plurality of image forming units. The predetermined permissible range is determined based on a permissible value related to the periodic variation of the deviation amount, and in step c), the abnormal point is the abnormal point among the plurality of representative points. The color shift amount without data detection position relates to the determined representative point is used is characterized in that it is calculated.

  The invention according to claim 7 is an image forming apparatus using a plurality of image forming units, an image carrier that carries an image formed by each of the plurality of image forming units, and the plurality of image forming units. Pattern forming control means for forming a color misregistration detection pattern on the image carrier, detection means for detecting positions of a plurality of representative points in the pattern formed on the image carrier, and the detection Based on the detection result by the means, it is determined whether or not the deviation amount between the detection position and the theoretical position is within a predetermined allowable range for each of the plurality of representative points, and each of the plurality of representative points is an abnormal point. An abnormal point determination means for determining whether or not, an approximate curve acquisition means for acquiring an approximate curve that approximates a periodic variation of the deviation amount based on the plurality of representative points, and a detection result by the detection means, A color misregistration amount calculating unit that calculates each color misregistration amount of a plurality of color images formed on the image carrier based on a determination result by the abnormal point determination unit, the abnormal point determination unit When the difference between the deviation amount of the attention representative point of the plurality of representative points and the deviation amount at a position corresponding to the attention representative point on the approximate curve exceeds a predetermined value, the attention representative point It is determined that the deviation amount with respect to the value does not fall within the predetermined allowable range, and it is determined that the attention representative point is an abnormal point.

  The invention according to claim 8 is a color misregistration correction method for correcting a color misregistration between a plurality of color images formed on an image carrier by a plurality of image forming units of an image forming apparatus, and a) A step of detecting a color misregistration detection pattern formed on the image carrier; and b) obtaining an approximate curve that approximates a periodic variation in the amount of deviation between the detection positions of a plurality of representative points and the theoretical position in the pattern. And c) determining whether or not the deviation amounts relating to the plurality of representative points are within a predetermined allowable range, and determining whether each of the plurality of representative points is an abnormal point. D) calculating each color shift amount of a plurality of color images formed on the image carrier by the plurality of image forming units based on the detection result of the pattern, and c) In this case, when the difference between the shift amount of the target representative point of the plurality of representative points and the shift amount at the position corresponding to the target representative point on the approximate curve exceeds a predetermined value, the target It is determined that the deviation amount relating to the representative point does not fall within the predetermined allowable range, and it is determined that the target representative point is an abnormal point.

  The invention of claim 9 includes: a) obtaining detection data of a color misregistration detection pattern formed on an image carrier by a plurality of image forming units; and b) a plurality of representative points in the color misregistration detection pattern. Obtaining an approximate curve that approximates the periodic fluctuation of the deviation amount between the detected position and the theoretical position; and c) determining whether or not the deviation amounts relating to the plurality of representative points are within a predetermined allowable range. Determining and determining whether each of the plurality of representative points is an abnormal point; and d) color shifts of a plurality of color images formed on the image carrier by the plurality of image forming units. A program for causing a computer to execute a step of calculating an amount based on the detection data, wherein in step c), the first representative point of the plurality of representative points is calculated. When the difference between the amount and the shift amount at the position corresponding to the target representative point on the approximate curve exceeds a predetermined value, it is determined that the shift amount regarding the target representative point does not fall within the predetermined allowable range. Then, it is determined that the representative representative point is an abnormal point.

  According to the first to sixth aspects of the present invention, each representative point is determined depending on whether or not each representative point is within a predetermined allowable range determined based on the allowable value related to the periodic variation of the deviation amount. Since it is determined whether or not the representative point is an abnormal point, it is possible to appropriately detect the abnormal point.

  According to the invention described in claims 7 to 9, an approximate curve that approximates the periodic variation of the shift amount is acquired, and the shift amount and approximate curve of the target representative point among the plurality of representative points. In the above, when the difference from the deviation amount at the position corresponding to the target representative point exceeds a predetermined value, it is determined that the target representative point is an abnormal point, so that the abnormal point can be detected appropriately.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment. FIG. 3 is a cross-sectional view illustrating a schematic configuration near an intermediate transfer belt. FIG. 3 is a diagram illustrating a control unit (controller) functional block of the image forming apparatus. It is a figure which shows an example of the pattern for color misregistration detection. It is a conceptual diagram which shows the reading operation | movement of the pattern for color misregistration detection. FIG. 4 is a diagram illustrating a state in which a pattern is accurately drawn on an intermediate transfer belt. FIG. 6 is a diagram illustrating a state in which each representative point in a pattern is drawn with a deviation from each target position on the intermediate transfer belt. It is a figure which shows the dispersion | variation for every position of the deviation | shift amount regarding a certain color group. 4 is a flowchart illustrating a color misregistration amount calculating operation according to the first embodiment. It is a flowchart which shows the operation | movement which concerns on 2nd Embodiment. It is a figure which shows the dispersion | variation for every position of the deviation | shift amount regarding a certain color group. FIG. 10 is a functional block diagram of a control unit of an image forming apparatus according to a third embodiment. It is a figure which shows the dispersion | variation for every position of the deviation | shift amount regarding a certain color group. It is a flowchart which shows the operation | movement which concerns on 3rd Embodiment. It is a flowchart which shows the operation | movement which concerns on 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<1. First Embodiment>
<1-1. Equipment overview>
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an apparatus that develops an electrostatic latent image on a photosensitive drum to form an image. Here, as an image forming apparatus, an electrophotographic print output apparatus, more specifically, a tandem full color print output apparatus is illustrated.

  The image forming apparatus 1 prints an image based on image data transmitted from another information processing apparatus (such as a personal computer) connected via a network or the like by using a printing mechanism to be described later. Functions as a printer. The image forming apparatus 1 also functions as a color copying apparatus by printing out image data relating to a document read by the upper scanner unit 3 (optical reading device) using the printing mechanism.

  As shown in FIG. 1, the image forming apparatus 1 includes a plurality (specifically, four) of imaging units (also referred to as image forming units) 10. Specifically, the image forming apparatus 1 includes a yellow imaging unit 10Y, a magenta imaging unit 10M, a cyan imaging unit 10C, and a black imaging unit 10K. Each imaging unit 10 is an electrophotographic image of each color component (specifically, each component of Y (yellow), M (magenta), C (cyan), K (black)) in the final output image). It is formed by a method and transferred to an intermediate transfer belt (also referred to as an intermediate transfer member) 21. Then, the image of each color component superimposed on the intermediate transfer belt 21 is further transferred onto a sheet-like paper (also referred to as a transfer material) PA, so that a full-color image is formed on the paper PA. The intermediate transfer belt 21 is also expressed as an image carrier that temporarily carries each toner image (color image) transferred from each photoconductor 11 (described later).

  The four imaging units 10 (10Y, 10M, 10C, and 10K) are arranged in the lower linear portion mainly at the lower portion of the lower linear portion of the intermediate transfer belt 21 that is wound around the driving roller 23 and the winding roller 24. Are arranged in series. Each imaging unit 10 includes a photoconductor 11, a charger 12, an exposure device 13, a developing device 14, a first transfer device (primary transfer device) 15, an eraser (static eliminating device) 16, and a cleaner 17. Yes. Specifically, in each imaging unit 10, a charger 12, an exposure device 13, a developing device 14, a first transfer device 15, and an eraser 16 so as to surround the outer periphery of a substantially cylindrical photoconductor (photosensitive drum) 11. The cleaner 17 is arranged clockwise in this order. Among these, the first transfer device (specifically, the transfer roller (primary transfer roller)) 15 is disposed at a position facing the photoconductor 11 with the intermediate transfer belt 21 therebetween.

  The electrostatic latent image formed on the photoreceptor 11 is visualized as a toner image by the developing device 14 and transferred onto the intermediate transfer belt 21 by the first transfer device 15. More specifically, a toner image of each color is formed on each photoconductor 11 by each of the four imaging units 10. Then, the toner images (color images) of the respective colors are transferred so as to be superimposed on the intermediate transfer belt 21, and a full color toner image is formed on the intermediate transfer belt 21.

  The intermediate transfer belt 21 moves in the direction of the arrow AR <b> 1 by driving the driving roller 23. A second transfer device (transfer roller (secondary transfer roller)) 43 is provided at a position facing the driving roller 23 with the intermediate transfer belt 21 therebetween. In response to voltage application by the transfer roller 43, a toner image (full color toner image or the like) formed on the intermediate transfer belt 21 is transferred to the paper PA.

  A fixing unit (fixing device) 50 is provided on the downstream side in the transport direction of the paper PA that has passed through the positions of the driving roller 23 and the transfer roller 43. The fixing unit 50 fixes the toner image formed on the paper PA to the paper PA by applying heat to the paper PA.

  Further, a paper discharge tray 61 is provided on the downstream side of the fixing unit 50 in the transport direction.

  In addition, a plurality of paper feeding units 30 are provided below the imaging units 10 and the transfer rollers 43 (upstream on the transport path). Each paper feed unit 30 includes a paper feed tray 31, a pickup roller 32, a paper feed roller 33, and a suction roller 34, and can supply paper PA toward the timing roller 41 and the transfer roller 43. .

<1-2. Functional block>
FIG. 3 is a diagram illustrating functional blocks of the control unit (controller) 100 of the image forming apparatus 1. As shown in FIG. 3, the control unit 100 includes a pattern formation control unit 111, a data acquisition unit 112, an abnormal point determination unit 115, a color misregistration amount calculation unit 116, a correction amount calculation unit 117, a correction control unit 118, and the like. The processing part is provided. Note that the control unit 100 is physically configured by a CPU, a semiconductor memory, and the like, and the processing units 111 to 118 and the like described above are executed by executing a predetermined program PG (not shown) in the CPU or the like. Realize functionally.

  The pattern formation control unit 111 is a control unit that forms a color misregistration detection pattern (hereinafter also simply referred to as a pattern) PT (see FIG. 4) on the intermediate transfer belt 21 using a plurality of imaging units 10.

  The data acquisition unit 112 is a processing unit that acquires correction data DT and the like detected by a detection sensor 71 described later. The data DT includes data related to detection positions of a plurality of representative points (described later) on the pattern PT. The data acquisition unit 112 also calculates a deviation amount ΔZ between the detection position and the theoretical position for each of the plurality of representative points on the pattern PT.

  The abnormal point determination unit 115 determines whether or not the deviation amount ΔZ between the detection position and the theoretical position for a plurality of representative points is within a predetermined allowable range, and each representative point is “abnormal point” (its It is a processing unit that individually determines whether or not the detection position is abnormal.

  The color misregistration amount calculation unit 116 is a processing unit that calculates the color misregistration amount of each color group based on the misregistration amounts of a plurality of representative points belonging to each color group (described later). In other words, the color misregistration amount calculation unit 116 calculates the color misregistration amount of each color toner image corresponding to each color group.

  The correction amount calculation unit 117 is a processing unit that calculates a correction amount for correcting color misregistration based on the color misregistration amount determined by the color misregistration amount calculation unit 116.

  The color misregistration correction control unit 118 is a processing unit that corrects color misregistration by adjusting the output timing of each imaging unit 10 based on the correction amount calculated by the correction amount calculating unit 117. In other words, the color misregistration correction control unit 118 controls the timing for transferring the toner image of each color to the intermediate transfer belt 21 and the like.

<1-3. Basic operation of color misregistration calculation>
<Pattern configuration>
FIG. 2 is a cross-sectional view showing a schematic configuration in the vicinity of the intermediate transfer belt 21.

  As shown in FIG. 2, the four imaging units 10 (10Y, 10M, 10C, 10K) are disposed below the intermediate transfer belt 21. The imaging unit 10 can output a normal image and can also output a pattern image (hereinafter also simply referred to as a pattern) PT (see FIG. 4) for color misregistration detection.

  FIG. 4 is a diagram illustrating an example of a color misregistration detection pattern PT. In this embodiment, a case where two rows of patterns PT are drawn on the intermediate transfer belt 21 along the traveling direction (also referred to as sub-scanning direction) of the intermediate transfer belt 21 is illustrated.

  Each pattern PT is classified into a plurality of color groups GP (specifically, four color groups of black group GPk, yellow group GPy, magenta group GPm, and cyan group GPc). Each color group GP has a plurality of line segments extending in the width direction of the intermediate transfer belt 21. Each color group GP also has a line segment that runs obliquely at an angle of about 45 degrees with respect to the width direction of the intermediate transfer belt 21.

  FIG. 4 shows how the line segments LK, LC, LM, LY belonging to the four color groups GPk, GPc, GPm, GPy are sequentially formed on the intermediate transfer belt 21 in this order in the sub-scanning direction. Has been.

  The part relating to each color group GP in the pattern PT is output by the corresponding imaging unit 10. For example, the line segment LK relating to the black group GPk is output by the imaging unit 10K and transferred onto the intermediate transfer belt 21. Similarly, the line segment LC related to the cyan group GPc in the pattern PT is output by the imaging unit 10C and transferred onto the intermediate transfer belt 21. The line segment LM related to the magenta group GPm in the pattern PT is output by the imaging unit 10M and transferred onto the intermediate transfer belt 21. Further, the line segment LY related to the yellow group GPy in the pattern PT is output by the imaging unit 10Y and transferred onto the intermediate transfer belt 21.

  The image output from each imaging unit 10 is transferred toward each target position on the intermediate transfer belt 21 in synchronization with the rotation operation of the intermediate transfer belt 21 in the direction of the arrow AR1 (see FIG. 2). An image (transfer image) transferred onto the intermediate transfer belt 21 proceeds from the left side to the right side in FIG. 2 (from the lower side to the upper side in FIG. 4) on the lower side of the intermediate transfer belt 21. Therefore, the color misregistration detection pattern PT proceeds in this direction.

<Pattern detection>
As shown in FIG. 2, a detection sensor 71 is provided on the lower side of the intermediate transfer belt 21 and on the right side of the four imaging units 10 (in other words, on the front side in the traveling direction of the transferred image). The detection sensor 71 is configured as a light emitting / receiving optical sensor having a light emitting unit and a light receiving unit, for example. The light receiving unit of the detection sensor 71 receives light emitted from the light emitting unit of the detection sensor 71 and reflected on the intermediate transfer belt 21. The difference in reflectance on the intermediate transfer belt 21 is reflected in the amount of light received by the light receiving unit of the detection sensor 71. For this reason, the detection sensor 71 detects the above-described pattern PT, and more specifically, reads the position in the sub-scanning direction of the line constituting the pattern PT (in other words, the position of each representative point of the pattern PT). Is possible. In this embodiment, two detection sensors 71 (specifically 71A and 71B) are located at different positions in a direction (direction perpendicular to FIG. 2) orthogonal to the conveyance direction (sub-scanning direction) of the intermediate transfer belt 21. Is provided. Then, as shown in FIG. 4, the pattern PT drawn along the sub-scanning direction on the front edge of FIG. 2 on the intermediate transfer belt 21 is read by one detection sensor 71A. In addition, the pattern PT drawn along the sub-scanning direction on the inner edge of FIG. 2 on the intermediate transfer belt 21 is read by the other detection sensor 71B.

  In the following, for simplification, a detection operation of one pattern PT by one sensor 71A (or 71B), a color misregistration amount calculation operation based on the detection result, and the like will be described. The same applies to the operation of detecting the other pattern PT by the other sensor. If the color shift amounts calculated based on the two sensors 71A and 71B are different from each other, one color shift amount may be determined as the final color shift amount. Alternatively, an average value or the like of both color misregistration amounts may be determined as the final color misregistration amount.

  In the following, for the sake of simplicity, an example will be described in which the positions in the sub-scanning direction of the plurality of line segments arranged in parallel in the pattern PT are detected as the positions of the representative points in the pattern PT. More specifically, the case where the position in the sub-scanning direction of the line segment belonging to each color group is detected as the position of each representative point of each color group is illustrated. As will be described later, the color misregistration amount of each color group is obtained based on the position of each representative point of each color group.

<Reading operation>
FIG. 5 is a conceptual diagram showing a pattern PT reading operation. The upper part of FIG. 5 shows a state in which a plurality of line segments L extending in the vertical direction of the figure are arranged in parallel with each other along the horizontal direction of the figure, and the lower part of FIG. An output signal SG of the detection sensor 71 when detecting L is shown corresponding to the position of each line segment.

  The position of each line segment L on the intermediate transfer belt 21 can be detected by acquiring an output signal value SG (also simply referred to as an output value) SG as shown in FIG.

  For example, since the reflectance of light in the black line segment is lower than the reflectance of light of the background color (here, white) on the intermediate transfer belt 21, the output value of the detection sensor 71 in the black line segment is The output value of the detection sensor 71 in the background area (white area) is smaller. Therefore, as shown in FIG. 5, when the detection sensor 71 reads the vicinity of the black line segment of the intermediate transfer belt 21, the detection sensor 71 outputs a concave pulse waveform. The center position of the bottom of this pulse waveform is detected as the position of the black line segment. The output time of the detection sensor 71 can be associated with the position on the intermediate transfer belt 21 by conversion processing based on the conveyance speed of the intermediate transfer belt 21 and the like.

  The same applies to the line segments of other colors, and the positions of the line segments of the respective colors are obtained by the pattern detection operation using the detection sensor 71. Since the reflectance of the black line segment is different from the reflectance of the line segment of other colors, the magnitude relationship of the output values of the detection sensor 71 between the corresponding parts (the bottom of the pulse waveform) is used. It is possible to distinguish between black line segments and other color line segments.

  As described above, the position of each line segment L of each color (position on the intermediate transfer belt 21) can be obtained.

  FIG. 6 is a diagram illustrating a state in which each line segment L is drawn at each target position on the intermediate transfer belt 21, and FIG. 7 is a diagram in which each line segment L is shifted from each target position on the intermediate transfer belt 21. It is a figure which shows the state currently drawn. 6 and 7, the actual drawing position Q (thick line) of each line segment L is shown in the upper stage, and the theoretical position P (thin line) of each line segment L is shown in the lower stage.

  As shown in FIG. 7, each line segment in the pattern PT is actually drawn with a deviation from the respective target position (theoretical position). Such a deviation amount ΔZ of the drawing position Q with respect to the target position (theoretical position) P is detected using the detection sensor 71. Specifically, a deviation amount between the detection position of the line segment by the detection sensor 71 and the theoretical position of the line segment is detected as a deviation amount of the drawing position with respect to the target position (theoretical position).

  Further, these shift amounts ΔZ are acquired for each color group GP. Specifically, the shift amount ΔZ from the theoretical position of each line segment L is acquired in relation to the theoretical position P of each line segment L. For example, regarding the black group GPk, the relationship between the theoretical position P of each black line segment LK and each shift amount ΔZ regarding each black line segment LK is acquired. Similarly, regarding the yellow group GPy, the relationship between the theoretical position P of each yellow line segment LY and each shift amount ΔZ related to each yellow line segment LY is acquired. The same applies to the magenta group GPm and the cyan group GPc.

  Basically, the color shift amount for each color group GP may be obtained based on the shift amount ΔZ for each color group. For example, the average value of the shift amount ΔZ of each color group GP can be obtained as the final color shift amount ZF of the color group GP. Then, the color misregistration amount ZF is determined as a correction amount, and a correction operation at the time of image formation or the like may be executed. According to this, it is possible to appropriately correct the drawing position of the specific color image corresponding to the specific color group GP.

  However, in calculating the color misregistration amount ZF of each color group GP, it is preferable to eliminate the influence of the “abnormal point” as described above. Hereinafter, an abnormal point detection operation and the like will be described in detail.

<1-4. Fluctuation factor of deviation amount Δ>
FIG. 8 is a diagram illustrating a shift amount ΔZ related to a certain color group GP (for example, black group GPk). FIG. 8 shows the relationship between the theoretical position P of each line segment belonging to this group and the shift amount ΔZ. The horizontal axis in FIG. 8 indicates the position (or time) in the traveling direction (sub-scanning direction) on the intermediate transfer belt 21, and the vertical axis in FIG. 8 indicates the detection position of each line segment in the pattern and each line segment. The deviation amount ΔZ from the theoretical position is shown. In FIG. 8, the detection data regarding the shift amount ΔZ (= D (n)) at each theoretical position P (n) is indicated by black circles.

  As shown in FIG. 8, the shift amount ΔZ regarding a plurality of line segments of a specific color within a specific color group GP is acquired in a state having variations.

  Here, attention is focused on such factors of “variation”. Such “variation” factors include periodic factors and non-periodic factors.

  In FIG. 8, a large number of black circle data strings are shown on a predetermined periodic curve (sine curve curve). As described above, the deviation amount ΔZ basically basically varies periodically with respect to the position P. As such a variable element (also referred to as a periodic variable element), for example, rotation unevenness of the drive roller 23, more specifically, a deviation from a perfect circle of the outer circumferential circle in the cross section of the substantially cylindrical drive roller 23 (details) Are due to roundness tolerance).

  On the other hand, in addition to such a periodic variation factor, the shift amount ΔZ may be caused by a sudden factor (non-periodic factor) such as a disturbance. For example, a deviation amount ΔZ accompanied by a sudden change may occur due to a sudden vibration accompanying a cleaning operation by the cleaner 17 or a vibration caused by an external force applied by an operator. These deviations may occur during exposure of the photosensitive member 11 by the exposure device 13 or transfer to the intermediate transfer belt 21.

  In particular, the shift amount ΔZ based on such a sudden factor such as disturbance is often larger than the shift amount ΔZ based on the above-mentioned periodic factor. In short, data affected by a disturbance or the like greatly protrudes from a data string accompanied by a shift amount ΔZ caused by a periodic variation factor. When the final color shift amount ZF is calculated using data including a relatively large shift amount ΔZ (for example, as an average value of all the shift amounts ΔZ), the color shift amount ZF is shifted from an appropriate value. . More specifically, as shown in FIG. 8, when the representative point Q (n) is the abnormal point Q (n), the final data is obtained using all data including the deviation amount ΔZ of the abnormal point Q (n). When the color misregistration amount ZF is calculated, the color misregistration amount ZF shifts to a value ZF1 that deviates from the original value ZF0. As described above, data affected by disturbances or the like has an adverse effect on the calculation of the color misregistration amount ZF.

  Therefore, in this embodiment, an allowable range TL (specifically, TL1) regarding a relatively small “variation” due to a periodic variation factor is determined, and “variation” within the allowable range TL1 is allowed. On the other hand, when a relatively large “variation” that does not fall within the allowable range TL1 is detected, that is, when the deviation amount ΔZ does not fall within the allowable range TL1, a representative point corresponding to the deviation amount ΔZ is displayed. Detected as “abnormal point”. In other words, data relating to one or more representative points (abnormal points) affected by such disturbance is determined as “abnormal data”. Then, by preventing the data relating to the abnormal point from being involved in the calculation of the color misregistration correction amount, the adverse effect of the abnormal point on the color misregistration correction is avoided. In particular, it is possible to detect abnormal points appropriately by taking into account periodic fluctuations in the deviation amount ΔZ.

<1-5. Abnormal point detection operation>
Hereinafter, the abnormal point detection operation will be described more specifically.

  In the first embodiment, the abnormal point is determined based on the following equation (1). Hereinafter, the shift amount ΔZ related to the nth target representative point Q (n) among the plurality of representative points is also expressed as a value D (n). That is, the shift amount D (n) is the shift amount ΔZ with respect to the theoretical position P (n) of the representative representative point Q (n).

  Specifically, the abnormal point determination unit 115 (FIG. 3) determines whether or not the inequality of Expression (1) is satisfied for each representative point Q (n) belonging to a certain color group GP. Here, the value Dave is a plurality of deviation amounts D (i) related to a plurality of representative points Q (i) (i = 1,..., N; where N is the number of representative points) belonging to the color group GP. Is the average value. The value C1 is an appropriate constant. This value C1 is a threshold value determined based on, for example, the maximum shake amount of the drive roller 23. Specifically, the value C1 is appropriately set to a value CB theoretically calculated from tolerances regarding the roundness of the drive roller 23, and the like. It is determined as a value obtained by adding the margin value ΔC1 (C1 = CB + ΔC1). Here, since the threshold value C1 is determined in consideration of periodic fluctuations related to the shift amount such as the maximum shake amount of the driving roller 23, uncertain elements (such as the maximum value and the minimum value) are used as in Patent Document 2 described above. Therefore, the threshold value (V2) can be determined more appropriately than when the threshold value (V2) is determined.

  When the inequality of Expression (1) holds, it is determined that the corresponding representative point Q (n) is an abnormal point. Specifically, when the difference between the deviation amount D (n) relating to the representative representative point and the average value Dave relating to the plurality of representative points exceeds a predetermined value C1, the deviation amount D (n) falls within a predetermined allowable range (normal range). ) It is determined that it does not fall within TL1, and it is determined that the target representative point Q (n) is an abnormal point. As described above, a range having a predetermined width (predetermined value) C1 in both positive and negative directions with respect to the average value Dave of the deviation amounts regarding a plurality of representative points is set as the allowable range (normal range) TL1, and falls within the allowable range TL1. It is determined that the amount D (n) is abnormal data.

  On the other hand, when the inequality of Expression (1) is not satisfied, it is determined that the corresponding representative point Q (n) is a normal point.

  In this embodiment, when no abnormal point is detected for a plurality of representative points belonging to a certain color group, the color shift amount ZF of the color group is updated using a plurality of shift amounts D (i). . Specifically, an average value of a plurality of shift amounts D (n) of a certain color group is determined as a new color shift amount ZF of the color group. On the other hand, when an abnormal point is detected, the color shift amount ZF is not updated, and the previously calculated value (color shift amount ZF) is used as it is as the color shift amount ZF of the color group. As a result, the influence of abnormal points on color misregistration correction can be eliminated.

<1-6. Detailed operation>
FIG. 9 is a flowchart showing a color misregistration amount calculating operation and the like according to the first embodiment. Next, the color misregistration amount calculating operation and the like will be described in more detail with reference to FIG. Note that the operation of FIG. 9 is executed at an appropriate timing periodically (for example, every several hours or days) or irregularly (for example, immediately after power-on).

  First, as shown in step S <b> 11, a pattern PT is printed on the intermediate transfer belt 21 using the imaging unit 10. Specifically, each color toner image formed on each color photoconductor 11 is transferred to the intermediate transfer belt 21 to form the above-described pattern PT (see FIG. 4) on the intermediate transfer belt 21. . Such a pattern PT printing operation is executed by the pattern formation control unit 111.

  Next, as shown in step S <b> 12, the pattern PT formed on the intermediate transfer belt 21 is detected by the detection sensor 71. Data representing the detection result of the pattern PT is acquired by the data acquisition unit 112.

  In the following, the operation for each color group GP is executed. Therefore, first, in step S13, a color group GP to be processed (for example, a black group GPk) is selected from the four color groups GP.

  Next, it is determined whether or not there is an abnormal point among the plurality of representative points belonging to the color group GP.

  Specifically, first, a representative point to be determined is selected from a plurality of representative points in step S15.

  In step S16, it is determined whether the representative point to be determined is an abnormal point. Specifically, when the inequality relationship of the above equation (1) is established, the representative point is determined to be an abnormal point, and when the inequality relationship of the above equation (1) is not established, It is determined that the representative point is not an abnormal point (that is, a normal point).

  If it is determined that the point is not an abnormal point, the process proceeds from step S17 to step S19, and it is determined whether the determination process for all representative points in the color group GP has been completed. When it is determined that an unprocessed representative point remains, the process returns from step S19 to step S15, and the same operation is repeated again. When it is determined that the determination process for all the representative points in the color group GP is completed, the process proceeds from step S19 to step S21, and the color misregistration amount ZF for the color group GP is calculated. The color shift amount ZF is calculated as, for example, an average value of the shift amounts ΔZ (= D (i)) regarding all the representative points in the color group GP. Since a new color misregistration amount is calculated by the color misregistration amount calculation process in step S21, the process in step S21 is also expressed as a color misregistration amount update process. Thereafter, the process proceeds from step S21 to step S22.

  On the other hand, if it is determined in step S17 that a certain representative point is an abnormal point, the process proceeds to step S20, and the update processing of the color misregistration amount ZF is not executed for the color group GP. It is determined. Thereafter, the process proceeds to step S22 without proceeding to step S21 (in other words, the color misregistration amount is not updated). That is, the color misregistration amount ZF is maintained without being changed. Such a process is also expressed as a process for calculating the color misregistration amount ZF without using data of a detection position related to an abnormal point among a plurality of representative points.

  In step S22, it is determined whether or not the processing relating to all color groups GP has been completed. It is determined whether or not an unprocessed color group GP remains.

  When the unprocessed color group GP remains, the process returns to step S13, the next color group GP (for example, cyan group GPc) is selected, and the above-described operation is repeated.

  In this way, the color misregistration amount is updated for each color group (that is, for each color image).

  Thereafter, in the image forming operation, a correction operation for correcting the color misregistration amount is performed. Specifically, the writing timing of each color image is adjusted according to the amount of color misregistration associated with each color image. Thereby, the color misregistration between the four toner images on the intermediate transfer belt 21 is corrected, and an appropriate image is generated. In particular, for a color group whose color misregistration amount has not been updated (see step S20), the color misregistration amount before update is used as it is, and a color misregistration correction operation is performed. According to this, it is possible to perform the color misregistration correction operation by eliminating the influence of abnormal points.

  According to the operation as described above, each representative point Q (n) depends on whether or not each representative point Q (n) exists within a predetermined allowable range TL1 determined based on the allowable value CB regarding the periodic fluctuation of the deviation amount. Since it is determined whether or not the representative point Q (n) is an abnormal point, it is possible to appropriately detect the abnormal point in the correction data DT.

  In step S21, the color misregistration amount is calculated without using the data of the detection position regarding the representative point determined to be an abnormal point among the plurality of representative points. Therefore, it is possible to reliably eliminate the influence of abnormal points when calculating the color misregistration amount.

  In addition, although the case where the presence or absence of the update process of the color misregistration amount is determined for each color group is illustrated here, the present invention is not limited to this. For example, when it is determined that any representative point in at least one of the four color groups GP is an abnormal point, the color misregistration amount update process for all the color groups is not executed. It may be.

<2. Second Embodiment>
The second embodiment is a modification of the first embodiment. Below, it demonstrates centering on difference with 1st Embodiment.

  In the first embodiment, the case where the previous color shift amount is used as it is without updating the color shift amount when an abnormal point is detected is illustrated, but the present invention is not limited to this. For example, only the abnormal point among a plurality of representative points may be excluded from the color shift amount calculation target, and the color shift amount related to the color group may be calculated. In the second embodiment, such a modification will be described.

  FIG. 10 is a flowchart showing an operation according to the second embodiment. The flowchart of FIG. 10 differs from the flowchart of FIG. 9 in that step S18 is provided instead of step S20 and that the process proceeds to step S19 after step S18. In step S18, a process of excluding abnormal points from the color shift amount calculation target is executed.

  When an abnormal point is detected for a certain color group in step S17, data relating to the abnormal point is excluded from calculation target data for the color misregistration amount relating to the color group in step S18. Thereafter, after determining whether all the representative points are abnormal points or normal points, in step S21, using the data regarding the representative points excluding the abnormal points excluded in step S18, the color misregistration amount ZF. Is newly calculated. For example, as shown in FIG. 11, it is determined that the third representative point Q (3), the fifth representative point Q (5), and the sixth representative point Q (6) are abnormal points. In this case, the average value ZF21 of the shift amount D (j) of the other representative points Q (j) (where j = 1, 2, 4, 7,...) Is calculated as the color shift amount ZF. Is done. According to this, the value ZF21 close to the original value ZF0 is calculated as the color misregistration amount ZF, not the value ZF2 greatly influenced by the abnormal point Q (j).

  In the subsequent image forming operation, a correction operation is performed using the newly calculated color shift amount ZF (ZF21).

  Even with such processing, it is possible to appropriately detect an abnormal point and to appropriately eliminate the influence of the abnormal point. In particular, in the color misregistration correction process, the previous calculated value is not used as it is as the color misregistration amount ZF, but the newly calculated appropriate value ZF21 is used. Is executed more reliably.

<3. Third Embodiment>
The third embodiment is a modification of the second embodiment. Below, it demonstrates centering on difference with 2nd Embodiment.

  FIG. 12 is a functional block diagram of the control unit 100 (100C) of the image forming apparatus according to the third embodiment, and FIG. 13 is a diagram illustrating a position P () of a deviation amount ΔZ (= D (n)) related to a certain color group. It is a figure which shows the dispersion | variation for every n). FIG. 14 is a flowchart showing the color misregistration amount calculating operation according to the third embodiment.

  In the third embodiment, the periodic variation of the deviation amount ΔZ (= D (i)) is approximated in advance by a periodic approximate curve (specifically, a sine curve). Specifically, it is approximated by an approximate curve AP: ΔZ = B · sin θ (see FIG. 13). Here, the value B represents the amplitude of the sine curve, and the value θ represents the phase of the sine curve. The value θ is expressed using a period T (or angular velocity ω), an initial phase value, and the like. As the period T of the sine curve, it is preferable to determine in advance a value corresponding to the period length of a predetermined periodic variation factor (for example, the circumferential length of the drive roller 23).

  The approximate curve AP is obtained based on the shift amount ΔZ (= D (i)) of all the representative points Q (i). In addition, the process which calculates | requires such approximate curve AP is performed by the approximate curve acquisition part 114 (refer FIG. 12) in the control part 100 in step S14 (refer FIG. 14). The approximate curve AP is obtained for each color group GP.

  Then, the abnormal point is determined based on the following equation (2).

  Specifically, the abnormal point determination unit 115 determines whether or not the inequality of Expression (2) is satisfied for each representative point Q (n) belonging to a certain color group GP in Step S16 (FIG. 14). To do. Here, the value (B · sin (θ (n))) is a value (deviation amount ΔZ) at the theoretical position P (n) corresponding to the target representative point Q (n) on the approximate curve AP (see FIG. 13). It is also expressed as an estimated value (estimated deviation amount) of the deviation amount ΔZ in consideration of periodic fluctuation factors. Note that the phase θ (n) of the sine (sine) function in Expression (2) is calculated based on the position P (n) and an appropriate conversion expression. The value C2 is an appropriate constant.

  The approximate curve AP expressed by the equation: ΔZ = B · sin θ is acquired as, for example, a curve (sine curve curve) representing a periodic variation caused by a tolerance regarding the roundness of the drive roller 23. The difference value (left side of equation (2)) between the deviation amount D (n) at each representative point Q (n) and the deviation amount (estimated deviation amount) at the corresponding position on the approximate curve AP is an appropriate margin. Whether or not each representative point Q (n) is an abnormal point is determined depending on whether or not it is larger than the value ΔC2 (= C2).

  More specifically, when the inequality of Expression (2) is established, it is determined that the representative point Q (n) is an abnormal point. In other words, the difference between the deviation amount D (n) of the target representative point Q (n) of the plurality of representative points and the estimated deviation amount (B · sin (θ (n))) by the approximate curve AP is a predetermined value. When it exceeds C2, it is determined that the deviation amount D (n) related to the target representative point Q (n) does not fall within a predetermined allowable range (normal range) TL (specifically TL2). At this time, it is determined that the target representative point Q (n) is an abnormal point. Thus, a range having a predetermined width (predetermined value) C2 with respect to the estimated deviation amount (B · sin (θ (n))) for each position P (n) is set as the allowable range (normal range) TL2. The deviation amount D (n) that does not fall within the allowable range TL2 is determined to be an abnormal value.

  On the other hand, when the inequality of Expression (2) is not satisfied, it is determined that the representative point Q (n) is a normal point.

  According to the operation as described above, the deviation amount D (n) of the attention representative point among the plurality of representative points and the deviation amount (estimated deviation amount) at the position corresponding to the attention representative point on the approximate curve AP. When the difference exceeds the predetermined value C2, it is determined that the target representative point is an abnormal point, so that the abnormal point can be detected appropriately.

  In particular, in the third embodiment, the approximate curve AP is obtained in advance, and the estimated deviation amount at each position P on the approximate curve AP is compared with the actual deviation amount. Then, an appropriate allowable range TL2 is set for the estimated deviation amount for each position on the approximate curve AP obtained in advance, and the determination operation is executed. That is, an appropriate allowable range TL2 is set for each position on the approximate curve AP. Therefore, it is possible to detect an abnormal point more appropriately. For example, in FIG. 13, even when the representative point Q (6) due to a sudden factor is an abnormal point having a relatively small deviation amount ΔZ, the representative point Q (6) can be appropriately detected as an abnormal point. .

  In particular, in the third embodiment, since the periodic variation factor is considered in advance by the approximate curve AP, the threshold value C2 (ΔC2) is set as a relatively smaller value than the threshold value (V2) in Patent Document 2. Can be done. Therefore, it is possible to accurately detect abnormal points.

<4. Fourth Embodiment>
The fourth embodiment is a modification of the third embodiment. Below, it demonstrates centering on difference with 3rd Embodiment.

  In the above third embodiment, the case where only the abnormal points are excluded from the plurality of representative points belonging to a certain color group and the color misregistration amount for the color group is calculated is illustrated, but the present invention is not limited to this. . For example, as in the first embodiment, when an abnormal point is detected, the previous color shift amount may be used as it is without updating the color shift amount.

  FIG. 15 is a flowchart showing an operation according to the fourth embodiment. The flowchart in FIG. 15 differs from the flowchart in FIG. 14 in that step S20 (see FIG. 9) is provided instead of step S18, and that step S20 is followed by step S22.

  Even with such processing, it is possible to appropriately detect an abnormal point and to appropriately eliminate the influence of the abnormal point.

<5. Modified example>
Although the embodiments of the present invention have been described above, the present invention is not limited to the contents described above.

  For example, in the first and fourth embodiments, the amount of color misregistration is determined on the condition that no abnormal point is detected (in other words, the number of abnormal points is smaller than N (where N = 1)). Although the case where the update process is executed is illustrated, the present invention is not limited to this. Specifically, the color misregistration amount update process may be executed on condition that the number of abnormal points is smaller than N (where N is a predetermined number of 2 or more). In other words, when the number of abnormal points is larger than N, the color misregistration amount update process is not executed, and the color misregistration amount before the update is determined again as the “color misregistration amount”. Also good.

  Further, in each of the above embodiments, the description has been made on the assumption that the shift amount D (n) relating to each representative point Q (n) is appropriately detected one by one, but the present invention is also applicable to other situations. Is possible. For example, there may be a case where erroneous detection occurs at a plurality of positions in the vicinity of a certain representative point Q (n) in the pattern PT due to the influence of adhered dust or the like on the pattern PT. In such a case, appropriate data is selected in advance from the detection data at the plurality of positions, and the shift amount corresponding to the selected detection data is set as the shift amount D (n) of the representative point Q (n). You may make it determine as.

  Moreover, in each said embodiment, although the case where the rotation nonuniformity of the drive roller 23 was considered as a periodic fluctuation factor was illustrated, it is not limited to this. For example, periodic variation factors such as uneven rotation of the photosensitive drum may be considered. Alternatively, periodic variation factors such as thickness unevenness of the intermediate transfer belt 21 may be considered. In the second embodiment, the case where the periodic variation is approximated by a sine curve is illustrated, but the present invention is not limited to this, and approximate curves of various shapes according to various factors may be used.

  In each of the above embodiments, the case where the pattern PT is drawn on the intermediate transfer belt 21 is illustrated, but the present invention is not limited to this. For example, the pattern PT may be drawn on the paper PA as the image carrier, and the position of the representative point of the pattern PT on the paper PA may be detected.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10, 10Y, 10M, 10C, 10K Imaging unit 21 Intermediate transfer belt 23 Drive roller 43 Transfer roller 50 Fixing part 71, 71A, 71B Detection sensor AP Approximate curve GP, GPk, GPc, GPm, GPy Color group L , LK, LC, LM, LY Line segments PA paper PT pattern Q Representative point TL, TL1, TL2 Tolerable range ZF Color deviation amount ΔZ, D Deviation amount (from the detection position of each representative point to the theoretical position)

Claims (9)

An image forming apparatus,
A plurality of image forming units;
An image carrier that carries an image formed by each of the plurality of image forming units;
Pattern formation control means for forming a color misregistration detection pattern on the image carrier using the plurality of image forming units;
Detecting means for detecting positions of a plurality of representative points in the pattern formed on the image carrier;
Based on the detection result by the detection means, it is determined whether or not the deviation amount between the detection position and the theoretical position is within a predetermined allowable range for each of the plurality of representative points, and each of the plurality of representative points is Abnormal point determination means for determining whether or not an abnormal point;
Color shift amount calculation means for calculating each color shift amount of a plurality of color images formed on the image carrier based on the detection result by the detection means and the determination result by the abnormal point determination means;
With
The image forming apparatus according to claim 1, wherein the predetermined allowable range is determined based on an allowable value related to a periodic variation of the shift amount. The image forming apparatus according to claim 1.
The abnormal point determination means relates to the target representative point when a difference between the shift amount of the target representative point of the plurality of representative points and an average value of the shift amount regarding the plurality of representative points exceeds a predetermined value. An image forming apparatus comprising: determining that the deviation amount does not fall within the predetermined allowable range, and determining that the representative representative point is the abnormal point. The image forming apparatus according to claim 1, wherein:
The image forming apparatus, wherein the color misregistration amount calculating means calculates the color misregistration amount by excluding the abnormal point. The image forming apparatus according to claim 1, wherein:
The image forming apparatus, wherein the color misregistration amount calculation unit executes the color misregistration amount update process on condition that the number of abnormal points is smaller than a predetermined value. A color misregistration correction method for correcting color misregistration between a plurality of color images formed on an image carrier by a plurality of image forming units of an image forming apparatus,
a) detecting a color misregistration detection pattern formed on the image carrier;
b) Based on the detection result of the pattern, it is determined whether or not the deviation amount between the detection position and the theoretical position is within a predetermined allowable range with respect to the plurality of representative points of the pattern. Determining whether each is an abnormal point;
c) calculating each color shift amount of a plurality of color images formed on the image carrier by the plurality of image forming units based on the detection result of the pattern;
With
The predetermined permissible range is determined based on a permissible value related to the periodic variation of the deviation amount,
In the step c), the color misregistration amount is calculated without using data of a detection position relating to a representative point determined to be the abnormal point among the plurality of representative points. Correction method. a) obtaining detection data of a color misregistration detection pattern formed on the image carrier by a plurality of image forming units;
b) Based on the detection data, it is determined whether or not a deviation amount between the detection position and the theoretical position is within a predetermined allowable range with respect to a plurality of representative points of the color misregistration detection pattern, and the plurality of representatives Determining whether each of the points is an abnormal point; and
c) calculating each color shift amount of a plurality of color images formed on the image carrier by the plurality of image forming units based on the detection data;
A program for causing a computer to execute
The predetermined permissible range is determined based on a permissible value related to the periodic variation of the deviation amount,
In the step c), the color misregistration amount is calculated without using data of a detection position relating to a representative point determined to be the abnormal point among the plurality of representative points. An image forming apparatus,
A plurality of image forming units;
An image carrier that carries an image formed by each of the plurality of image forming units;
Pattern formation control means for forming a color misregistration detection pattern on the image carrier using the plurality of image forming units;
Detecting means for detecting positions of a plurality of representative points in the pattern formed on the image carrier;
Based on the detection result by the detection means, it is determined whether or not the deviation amount between the detection position and the theoretical position is within a predetermined allowable range for each of the plurality of representative points, and each of the plurality of representative points is Abnormal point determination means for determining whether or not an abnormal point;
An approximate curve acquisition means for acquiring an approximate curve that approximates the periodic variation of the shift amount based on the plurality of representative points;
Color shift amount calculation means for calculating each color shift amount of a plurality of color images formed on the image carrier based on the detection result by the detection means and the determination result by the abnormal point determination means;
With
When the difference between the deviation amount of the attention representative point of the plurality of representative points and the deviation amount at a position corresponding to the attention representative point on the approximate curve exceeds a predetermined value, the abnormal point determination unit An image forming apparatus comprising: determining that the deviation amount relating to the target representative point does not fall within the predetermined allowable range, and determining that the target representative point is an abnormal point. A color misregistration correction method for correcting color misregistration between a plurality of color images formed on an image carrier by a plurality of image forming units of an image forming apparatus,
a) detecting a color misregistration detection pattern formed on the image carrier;
b) obtaining an approximate curve that approximates the periodic variation of the deviation amount between the detection position of the plurality of representative points and the theoretical position in the pattern;
c) determining whether or not the deviation amounts relating to the plurality of representative points are within a predetermined allowable range, and determining whether each of the plurality of representative points is an abnormal point;
d) calculating each color shift amount of the plurality of color images formed on the image carrier by the plurality of image forming units based on the detection result of the pattern;
With
In step c), when the difference between the deviation amount of the target representative point of the plurality of representative points and the deviation amount at a position corresponding to the target representative point on the approximate curve exceeds a predetermined value A color misregistration correction method comprising: determining that the amount of deviation regarding the target representative point does not fall within the predetermined allowable range, and determining that the target representative point is an abnormal point. a) obtaining detection data of a color misregistration detection pattern formed on the image carrier by a plurality of image forming units;
b) obtaining an approximate curve that approximates a periodic variation in a deviation amount between a detection position of a plurality of representative points and a theoretical position in the color misregistration detection pattern;
c) determining whether or not the deviation amounts relating to the plurality of representative points are within a predetermined allowable range, and determining whether each of the plurality of representative points is an abnormal point;
d) calculating each color shift amount of a plurality of color images formed on the image carrier by the plurality of image forming units based on the detection data;
A program for causing a computer to execute
In step c), when the difference between the deviation amount of the target representative point of the plurality of representative points and the deviation amount at a position corresponding to the target representative point on the approximate curve exceeds a predetermined value A program for determining that the amount of deviation regarding the target representative point does not fall within the predetermined allowable range and determining that the target representative point is an abnormal point.