JP2016051028A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can perform normal color shift correction control even when an unexpected incorrect detection is made.SOLUTION: An image forming apparatus performs color shift correction control of forming each of detection patterns in a plurality of colors, detecting each of the formed detection patterns in the plurality of colors, and correcting color shift on the basis of each of detection values of the detected detection patterns in the plurality of colors. In the color shift correction control, when the detection values of the detection patterns in the plurality of colors fall out of a predetermined color shift range, color shift is corrected by temporarily using the limit value of the color shift range, and subsequent color shift correction control is performed on the basis of detection values of the detection patterns in the plurality of colors after the correction.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus that corrects a color shift of a color image in which images of a plurality of colors are superimposed.

  In an image forming apparatus such as a copying machine, a multifunction peripheral, or a printer, an image carrier is usually rotated at a predetermined peripheral speed by a drive unit such as a motor, and the image carrier is applied to the image carrier by an image forming process such as electrophotography. An image (for example, a toner image) is formed at the same timing, and the image formed on the image carrier is transferred to a transfer member.

  Specifically, in an image forming apparatus that forms a color image, images of a plurality of different colors (for example, black, cyan, magenta, and yellow color components) are respectively synchronized with a plurality of image carriers corresponding to the images. A plurality of color images formed on the plurality of image carriers are transferred onto a transfer member such as an intermediate transfer member or a recording material (for example, a recording sheet such as a recording sheet), and the transfer member serves as an intermediate transfer member. In this case, the image is further transferred to a recording material.

  In such an image forming apparatus, if the positions of the images of a plurality of colors are not aligned, color misregistration occurs and a good image cannot be obtained, resulting in a decrease in image quality.

  For this reason, as a conventional image forming apparatus, detection patterns of a plurality of colors are formed, detection patterns of the formed colors are detected, and color misregistration is performed based on detection values of the detected detection patterns of the plurality of colors. Correction (specifically, formation of a multi-color image so that the detected values of the detected patterns of the multi-colors become predetermined predetermined reference values, that is, the positions of the multi-color images are aligned) There is an image forming apparatus that performs color misregistration correction control. Here, as a method for executing correction of the formation positions of a plurality of color images, a method of adjusting the writing timing when writing images on a plurality of image carriers can be exemplified.

  However, in such color misregistration correction control, during the detection of the detection pattern, for example, drive transmission such as a drive gear that transmits rotational drive from the drive unit that drives the image carrier to the image carrier. A sudden false detection may occur due to a sudden factor such as a drive transmission failure of a part (specifically, a so-called gear jump in which the drive gear is idle). Then, since the image forming apparatus cannot recognize whether or not a sudden erroneous detection has occurred, the color misregistration is corrected with a detection value different from the original detection value. Misalignment correction control cannot be performed. In addition, if the corrected detection pattern mark overlaps with another mark, each mark in the detection pattern cannot be detected corresponding to each color, and thereafter the detection pattern mark in the overlapped state is returned. Color misregistration correction control cannot be performed. This is particularly noticeable when the interval between adjacent marks in the detection pattern is narrowed in order to detect the detection pattern in a short time.

  With respect to this point, Patent Document 1 discloses that when the color misregistration amount of the correction pattern is detected in order to correct the color misregistration of the image, if the color misregistration amount exceeds the detectable range, or the detected color misregistration amount. Discloses an image forming apparatus that returns to a detectable or correctable color misregistration amount by automatically changing a setting value for controlling the color misregistration state when the color misregistration range is exceeded.

  However, Patent Document 1 does not disclose anything about performing original color misregistration correction control in the case of sudden erroneous detection.

JP 2007-102189 A

  Therefore, the present invention forms a color detection pattern, detects each of the formed color detection patterns, and corrects the color shift based on the detected values of the detected color detection patterns. An object of the present invention is to provide an image forming apparatus that performs correction control, and is capable of performing original color misregistration correction control even when a sudden erroneous detection is performed.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found the following and completed the present invention.

  That is, color misregistration correction control that forms detection patterns of a plurality of colors, detects the detection patterns of the plurality of colors formed, and corrects color misregistration based on the detected values of the detected detection patterns of the plurality of colors. In an image forming apparatus that performs the above, the detection value of the detection pattern is usually within a certain color shift range (for example, 0 to 10 dots) within a day due to changes in the surrounding environment (for example, temperature change). Within the range.

  When the detection value of the detection pattern is out of the color misregistration range, for example, the image carrier is driven while the detection pattern is being detected even though the detection value is originally within the color misregistration range. Sudden misdetection due to a sudden factor such as a drive transmission failure of a drive transmission unit such as a drive gear that transmits rotational drive from the driving unit to the image carrier (specifically, a so-called gear jump in which the drive gear idles) In addition to the case where the detection value is different from the original detection value, the detection value actually deviated from the normal color misregistration range, for example, the image forming apparatus itself is moved or some impact is applied to the image forming apparatus. It is appropriate to perform irregular proper detection after the state of the image forming apparatus changes due to irregular factors such as an external force applied to the image forming apparatus. The case where the detection value by the detection is detection value deviates from the normal color shift range can be exemplified. That is, in the case of sudden erroneous detection, the original detection value is usually within the color misregistration range, and it is not necessary to perform color misregistration correction control with the misdetected detection value. When the appropriate detection is performed, the detection value by the proper detection is out of the color misregistration range, and it is necessary to perform the color misregistration correction control with the detection value by the proper detection deviating from the color misregistration range.

  From this point of view, when the detection value of the detection pattern is out of the color misregistration range, an attempt is made to correct the color misregistration using the limit value of the color misregistration range. Then, the detection value of the detection pattern of the plurality of colors after correcting the color misregistration using the limit value of the color misregistration range is a case where a sudden erroneous detection is performed and an irregular proper detection is performed. Thus, the values of the different properties relating to the color misregistration correction are obtained. As a result, the image forming apparatus can recognize whether a sudden erroneous detection has been performed or an irregular proper detection has been performed. Therefore, by performing the next color misregistration correction control based on the detected values of the detection patterns of the plurality of colors after correction, even if a sudden erroneous detection is performed, the original color misregistration correction is performed. Control can be performed.

  The present invention is based on such knowledge, each of which forms a detection pattern of a plurality of colors, detects each of the formed detection patterns of the plurality of colors, and based on the detected values of the detected detection patterns of the plurality of colors. An image forming apparatus that performs color misregistration correction control for correcting color misregistration, wherein the color misregistration correction control is performed when detection values of the detection patterns of the plurality of colors are out of a predetermined color misregistration range. First, the color misregistration is corrected using the limit value of the color misregistration range, and the next color misregistration correction control is performed based on the detection values of the detection patterns of the plurality of colors after the correction. An image forming apparatus is provided.

  In the present invention, it is possible to exemplify an aspect in which the limit value of the color misregistration range is a value smaller than the interval between adjacent marks of the plurality of color detection patterns.

  In the present invention, the detection value of the detection pattern of the plurality of colors after correcting the color misregistration using the limit value of the color misregistration range is corrected to the side opposite to the correction side by the detection value detected last time. In the case of the detected value, an example of returning to the state before correction and retrying the color misregistration correction control can be exemplified.

  In the present invention, the detection value indicates that the detection values of the detection patterns of the plurality of colors after correcting the color misregistration using the limit value of the color misregistration range are corrected to the correction side based on the previously detected detection value. In this case, a mode in which the color misregistration correction control for correcting the color misregistration using the limit value of the color misregistration range can be exemplified.

  In the present invention, a mode in which the upper limit of the number of retries for returning to the state before the correction and retrying the color misregistration correction control is set to a predetermined retry limit number can be exemplified.

  In the present invention, it is possible to exemplify a mode in which the detection value of the detection pattern is set to a predetermined value when the number of retries exceeds the retry limit number.

  In the present invention, it is possible to exemplify an aspect in which a predetermined notification content is notified when the retry count exceeds the retry limit count.

  In the present invention, it is possible to exemplify an aspect of storing history information including the number of retries for returning to the state before correction and retrying the color misregistration correction control.

  According to the present invention, it is possible to perform original color misregistration correction control even when a sudden erroneous detection is performed.

1 is a front view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a plan view illustrating a schematic configuration of a detection pattern detection unit that detects detection patterns of a plurality of colors formed on an intermediate transfer belt in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a block diagram schematically showing a control configuration of a control unit in the image forming apparatus shown in FIG. 1. It is explanatory drawing for demonstrating the color misregistration correction control which concerns on this Embodiment, Comprising: (a) is a figure which shows the detection pattern before correction | amendment in the case of performing a sudden misdetection by a sudden factor. Yes, (b) is a diagram showing a detection pattern after correction in the case of sudden false detection due to a sudden factor, and (c) is a correction in the case of irregular proper detection It is a figure which shows the previous detection pattern, (d) is a figure which shows the detection pattern after correction | amendment in the case of performing irregular proper detection. 4 is a flowchart illustrating a control example of color misregistration correction control according to the first embodiment by a control unit illustrated in FIG. 3. 4 is a flowchart illustrating a control example of color misregistration correction control according to a second embodiment by a control unit illustrated in FIG. 3. It is a flowchart which shows the control example of the color misregistration correction control which concerns on 3rd Embodiment by the control part shown in FIG. It is a flowchart which shows the example of control of the color misregistration correction control which concerns on 4th Embodiment by the control part shown in FIG.

  Embodiments according to the present invention will be described below with reference to the drawings.

[Entire configuration of image forming apparatus]
FIG. 1 is a front view showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention.

  The image forming apparatus 100 is a tandem color image forming apparatus, and a plurality (four in this example) of photosensitive drums 3b, 3c, 3m, and 3y (an example of an image carrier) arranged in parallel along a predetermined direction. ) And images of a plurality of different colors (in this example, black, cyan, magenta, and yellow color components) are respectively formed on the corresponding photosensitive drums 3b, 3c, 3m, and 3y in accordance with the timing. A plurality of color images respectively formed on the body drums 3b, 3c, 3m, and 3y are transferred onto an intermediate transfer belt 7 (an example of an intermediate transfer body) that acts as a transfer member, and further, a recording sheet that acts as a transfer member Transfer to P (an example of a recording material).

  The image forming apparatus 100 has a copying function of reading an image of the original G and forming an image on a recording sheet P such as recording paper. The image reading apparatus 200 for reading the image of the original G and an image on the recording sheet P are provided. And an image forming apparatus main body 300 having an image forming unit 330 for forming the image forming apparatus.

  The image forming apparatus main body 300 includes a sheet supply unit 310, a sheet conveying unit 320, and a sheet discharge unit 340 in addition to the image forming unit 330.

  The image data handled in the image forming unit 330 corresponds to a color image using each color of black, cyan, magenta, and yellow, or to a monochrome image using a single color (for example, black). Therefore, in the image forming unit 330, the photosensitive drums 3b, 3c, 3m, and 3y, the chargers 5b, 5c, 5m, and 5y, the developing devices 2b, 2c, 2m, and 2y (here, the developing unit), and the intermediate transfer device Four intermediate transfer sections 6b, 6c, 6m, and 6y (here, intermediate transfer rollers) and four drum cleaning devices 4b, 4c, 4m, and 4y in FIG. 8 are provided so as to form four types of images corresponding to the respective colors. , Each of which is associated with black, cyan, magenta and yellow, the end code b is associated with black, the end code c is associated with cyan, the end code m is associated with magenta and the end code y is associated with yellow, and four images Station is configured.

  The intermediate transfer device 8 includes an intermediate transfer belt cleaning device 9, an intermediate transfer belt driving roller 21, a driven roller 22, and a tension roller 23 in addition to the intermediate transfer portions 6b, 6c, 6m, and 6y and the intermediate transfer belt 7. . Roller members such as the intermediate transfer belt drive roller 21, the intermediate transfer portions 6b, 6c, 6m, and 6y, the driven roller 22, and the tension roller 23 support the intermediate transfer belt 7 in a stretched manner. Move around in the moving direction C.

  The image forming apparatus main body 300 rotates the photosensitive drums 3b, 3c, 3m, and 3y while rotating the endless intermediate transfer belt 7 in a predetermined movement direction C to perform image formation, thereby charging the chargers 5b and 5c. , 5m, and 5y uniformly charge the surfaces of the photosensitive drums 3b, 3c, 3m, and 3y to a predetermined potential, and the photosensitive drums 3b, 3c, and 3c are irradiated with laser beams corresponding to the toner images of the respective colors from the laser exposure apparatus 1. The surface of 3m, 3y is exposed to form an electrostatic latent image on the surface, and the electrostatic latent image on the surface of the photosensitive drums 3b, 3c, 3m, 3y is developed by the developing devices 2b, 2c, 2m, 2y. Then, toner images are formed on the surfaces of the photosensitive drums 3b, 3c, 3m, and 3y, respectively. As a result, toner images of a plurality of colors (four colors in this example) are formed on the surfaces of the photosensitive drums 3b, 3c, 3m, and 3y. Thereafter, residual toner on the surfaces of the photosensitive drums 3b, 3c, 3m, and 3y is removed and collected by the drum cleaning devices 4b, 4c, 4m, and 4y.

  Subsequently, in the intermediate transfer device 8, the photosensitive drums 3b, 3c, 3m, and 6m are moved by the intermediate transfer portions 6b, 6c, 6m, and 6y to which the transfer bias is applied while the intermediate transfer belt 7 is moved in the moving direction C. The toner images of the respective colors formed on the 3y surface are sequentially transferred to the intermediate transfer belt 7 and superimposed to form a color toner image on the intermediate transfer belt 7. As a result, a color toner image is formed on the surface of the intermediate transfer belt 7. Thereafter, the residual toner on the surface of the intermediate transfer belt 7 is removed and collected by the intermediate transfer belt cleaning device 9. In the image forming apparatus 100, the residual toner removed and collected by the drum cleaning devices 4b, 4c, 4m, and 4y and the intermediate transfer belt cleaning device 9 is accommodated in a waste toner cartridge (not shown). Yes.

  On the other hand, in the sheet supply unit 310, the recording sheets P stacked on the sheet feed cassette 311 are pulled out from the sheet feed cassette 311 by the sheet supply roller unit 312 and conveyed to the image forming unit 330 through the sheet conveyance path 321 in the sheet conveyance unit 320. To do. The paper feed cassette 311 is an detachable member that can be attached to and detached from the image forming apparatus main body 300, and is an example of a sheet storage unit that stores the recording sheet P.

  In the sheet conveyance path 321, a registration roller 322, each conveyance roller 324, and a discharge roller 325 are provided. The registration roller 322 temporarily stops the recording sheet P, aligns the leading end of the recording sheet P, and then color toner in the transfer nip region between the intermediate transfer belt 7 and the transfer roller 11a in the secondary transfer device 11. The conveyance of the recording sheet P is started in accordance with the image transfer timing. That is, the recording sheet P conveyed from the sheet supply unit 310 to the image forming unit 330 through the sheet conveyance path 321 in the sheet conveyance unit 320 is nipped and conveyed in the transfer nip region between the intermediate transfer belt 7 and the transfer roller 11a. Meanwhile, the color toner image on the surface of the intermediate transfer belt 7 is transferred onto the recording sheet P by the transfer roller 11a to which the transfer bias is applied.

  The recording sheet P is sandwiched between the heating roller 121 and the pressure roller 122 of the fixing device 12 and heated and pressed to fix the color toner image on the recording sheet P, and further toward the sheet discharge unit 340. And is discharged to a discharge tray 341 in the sheet discharge unit 340 through a discharge roller 325.

  When image formation is performed not only on the front surface of the recording sheet P but also on the back surface, the recording sheet P having the toner image fixed on the front surface by the fixing device 12 is directed in the reverse direction toward the reverse path 323 by the discharge roller 325. Then, the recording sheet P is turned upside down by the reversing path 323, and the recording sheet P is guided again to the registration roller 322, and a toner image is formed on the back surface of the recording sheet P in the same manner as the front surface of the recording sheet P. After fixing, the recording sheet P is discharged to a discharge tray 341 in the sheet discharge unit 340.

  The image forming apparatus 100 further includes a detection pattern detection unit 80 that detects a plurality of color detection patterns PT (so-called registration adjustment patterns) on the intermediate transfer belt 7 in the intermediate transfer device 8. The detection pattern detection unit 80 is provided in the vicinity of the intermediate transfer belt 7. The detection pattern detection unit 80 is disposed so as to face the surface of the intermediate transfer belt 7. The detection pattern detection unit 80 is located on the most downstream side and the most upstream side of the photosensitive drum (in this example, the black photosensitive drum 3b) in the moving direction C of the intermediate transfer belt 7. (In this example, it is arranged upstream of the yellow photosensitive drum 3y).

[Configuration of detection pattern detector]
FIG. 2 is a plan view showing a schematic configuration of a detection pattern detection unit 80 that detects detection patterns PT of a plurality of colors formed on the intermediate transfer belt 7 in the image forming apparatus 100 shown in FIG.

  In this example, the detection pattern detection unit 80 includes a detection pattern detection sensor (a so-called registration sensor) that is a reflective optical sensor having a light emitting unit 80a and a light receiving unit 80b. The detection pattern detection unit 80 detects the reflected light reflected from the light emitting unit 80a on the surface of the intermediate transfer belt 7 and the reflected light reflected from the light emitting unit 80a on the detection patterns PT of a plurality of colors by the light receiving unit 80b. It is supposed to be.

  The detection patterns PT of a plurality of colors can be formed at one or more locations in the main scanning direction Y on the intermediate transfer belt 7. The detection pattern detection unit 80 can be provided at a position corresponding to a plurality of color detection patterns PT formed at one or more locations in the main scanning direction Y of the intermediate transfer belt 7.

  In the present embodiment, the detection patterns PT of a plurality of colors are formed at two locations in the main scanning direction Y on the intermediate transfer belt 7. Therefore, the detection pattern detection unit 80 is provided with detection pattern detection units 80 (first detection patterns) provided at positions corresponding to the detection patterns PT and PT of a plurality of colors formed at two locations in the main scanning direction Y of the intermediate transfer belt 7. A detection pattern detection unit 81 and a second detection pattern detection unit 82). Note that, when the detection patterns PT of a plurality of colors are detected at a plurality of locations in the main scanning direction Y of the intermediate transfer belt 7 as in the present embodiment, the value is, for example, an average value of values detected at a plurality of locations. It can be.

[Detection pattern]
The multiple-color detection pattern PT (see FIG. 2) is an image pattern of multiple colors (in this example, cyan, black, magenta, and yellow) corresponding to each toner image formed at each image station.

  The detection patterns PT of a plurality of colors have a cyan mark CM, a black mark BM, a magenta mark MM, and a yellow mark YM arranged in parallel in the main scanning direction Y and sequentially in the sub-scanning direction X, and predetermined in the main scanning direction Y. It is composed of a cyan mark cm, a black mark bm, a magenta mark mm, and a yellow mark ym that are inclined at an angle (for example, 45 °) and are sequentially arranged in the sub-scanning direction X.

  Here, the cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM parallel to the main scanning direction Y are used as a sub-scanning direction correction detection pattern PT1 for correcting color misregistration in the sub-scanning direction X. The cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym inclined with respect to the main scanning direction Y are used as a main scanning direction correction detection pattern PT2 for correcting color misregistration in the main scanning direction Y. ing.

  The sub-scanning direction correction detection pattern PT1 and the main scanning direction correction detection pattern PT2 are formed in the sub-scanning direction X by one set or plural sets (two sets in this example).

  The cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM of the detection pattern PT1 for sub-scanning direction correction have the same shape (specifically, a rectangle that is long in the main scanning direction Y). The distance d1 between the cyan mark CM and the black mark BM is equal to the distance d2 between the black mark BM and the magenta mark MM, but is different from the distance d3 between the magenta mark MM and the yellow mark YM. (Narrower than the interval d3). The cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym of the detection pattern PT2 for main scanning direction correction have the same shape (specifically, two sides inclined in the main scanning direction Y are in the sub scanning direction X). Parallelogram longer than two parallel sides).

  Specifically, the longitudinal width h1 in the main scanning direction Y of the cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM is 172 dots, and the cyan mark CM, black mark BM, magenta mark MM, and yellow mark The lateral width h2 in the sub-scanning direction X of YM is 28 dots. Further, the interval d1 between the cyan mark CM and the black mark BM is 62 dots, and the interval d2 between the black mark BM and the magenta mark MM is 62 dots, and between the magenta mark MM and the yellow mark YM. The interval d3 is 104 dots, and the interval d4 between the sub-scanning direction correction detection pattern PT1 and the adjacent sub-scanning direction correction detection pattern PT1 is 105 dots. The pitch p1 between the detection pattern PT2 for correction in the main scanning direction is 3071 dots, and the distance d5 from the centers of the detection patterns PT and PT formed at two locations in the main scanning direction Y is 1654 dots. Yes. Here, the dot diameter is 42.33 μm in this example.

[Control unit]
FIG. 3 is a block diagram schematically showing a control configuration of the control unit 400 in the image forming apparatus 100 shown in FIG.

  As shown in FIG. 3, the control unit 400 includes a processing unit 410 composed of a microcomputer such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a rewritable nonvolatile memory. And a storage unit 420 including a storage device.

  The control unit 400 controls the operation of various components by causing the processing unit 410 to load and execute a control program stored in advance in the ROM of the storage unit 420 onto the RAM of the storage unit 420. . The RAM of the storage unit 420 provides the processing unit 410 with a work work area and an area as an image memory for storing image data.

[About color misregistration correction control]
In the present embodiment, the control unit 400 forms detection patterns PT of a plurality of colors, detects the detection patterns PT of the formed colors, and based on the detection values of the detected detection patterns PT of the plurality of colors. Thus, color misregistration correction control for correcting color misregistration is performed.

  Specifically, the control unit 400 has a predetermined detection value in the sub-scanning direction X of the detected detection pattern PT1 for sub-scanning direction correction (cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM). The formation positions of the toner images of the plurality of colors in the sub-scanning direction X are corrected so that the reference values DSyc, DSyb, DSym, DSyy are equal, that is, the positions of the toner images of the plurality of colors are aligned in the sub-scanning direction X. Further, the control unit 400 determines a predetermined reference value in which the detected value in the main scanning direction Y of the detected main scanning direction correction detection pattern PT2 (cyan mark cm, black mark bm, magenta mark mm, and yellow mark ym) is predetermined. The formation positions of the multi-color toner images in the main scanning direction Y are corrected so as to be DSxc, DSxb, DSxm, DSxy, that is, the positions of the multi-color toner images in the main scanning direction Y are matched. Here, in this example, the correction of the formation positions of the toner images of a plurality of colors in the sub-scanning direction X and the main scanning direction Y is performed by applying electrostatic latent images to the plurality of photosensitive drums 3c, 3b, 3m, and 3y, respectively. This is done by adjusting the writing timing in the sub-scanning direction X and main scanning direction Y when writing.

  Specifically, the control unit 400 includes a detection pattern forming unit 411 that forms detection patterns PT of a plurality of colors, and a detection pattern detection unit 412 that detects detection patterns PT of a plurality of colors formed by the detection pattern formation unit 411. The color shift for calculating the correction amounts Hc, Hb, Hm, Hy for correcting the color shift of the toner images of the plurality of colors from the detection values of the detection patterns PT of the plurality of colors detected by the detection pattern detection unit 412. A correction amount calculation unit 413 and a color misregistration correction execution unit 414 that changes the formation positions of a plurality of color toner images based on the correction amounts Hc, Hb, Hm, and Hy calculated by the color misregistration correction amount calculation unit 413 are provided. It is configured.

  The control unit 400 is operated manually or at predetermined intervals when the image forming apparatus 100 is in a factory shipment state or when the image forming apparatus 100 is on standby (when a normal image forming operation is not performed). Color misregistration correction control is automatically performed.

  Image data indicating the detection patterns PT of a plurality of colors is stored in advance in the storage unit 420 (see FIG. 3).

  The detection pattern forming unit 411 instructs the image forming unit 330 to form detection patterns PT of a plurality of colors on the intermediate transfer belt 7 when performing color misregistration correction control.

  The image forming unit 330 reads image data indicating the detection patterns PT of a plurality of colors from the storage unit 420 according to an instruction from the detection pattern forming unit 411 and transmits the image data to the laser exposure apparatus 1. Next, the image forming unit 330 detects each of the detection patterns PT in the image forming regions of the photosensitive drums 3c, 3b, 3m, and 3y by scanning beams corresponding to the toner images of the respective colors emitted from the laser diodes of the laser exposure apparatus 1. Forming an electrostatic latent image. Next, the image forming unit 330 develops the electrostatic latent images on the photosensitive drums 3c, 3b, 3m, and 3y by the developing devices 2c, 2b, 2m, and 2y, and the photosensitive drums 3c, 3b, 3m, and Cyan mark CM and cyan mark cm, black mark BM and black mark bm, magenta mark MM and magenta mark mm, yellow mark YM and yellow mark ym are formed on 3y, respectively. Further, the image forming unit 330 includes a cyan mark CM and a cyan mark cm, a black mark BM and a black mark bm, a magenta mark MM and a magenta mark mm, and a yellow mark YM and a yellow mark on each of the photosensitive drums 3c, 3b, 3m, and 3y. ym is transferred to the intermediate transfer belt 7, and a detection pattern PT of a plurality of colors is formed on the intermediate transfer belt 7 (see FIG. 2).

  The detection pattern detection unit 80 (81, 82) is a detection pattern PT of a plurality of colors formed on the intermediate transfer belt 7 by the detection pattern forming unit 411 and conveyed in the sub-scanning direction X as the intermediate transfer belt 7 rotates. Is detected respectively. The detection pattern detection unit 80 (81, 82) transmits detection data of the detected detection patterns PT of a plurality of colors to the detection pattern detection unit 412.

(Color shift correction of detection pattern for sub-scanning direction correction)
When the detection pattern detection unit 412 receives the detection data sent from the detection pattern detection unit 80, the cyan mark CM, the black mark BM, and the magenta mark MM that are parallel to the main scanning direction Y in the detection pattern PT1 for sub-scanning direction correction. The formation positions of the cyan mark CM, the black mark BM, the magenta mark MM, and the yellow mark YM in the sub-scanning direction X are calculated based on the detection timing of the yellow mark YM.

  Further, the detection pattern detection unit 412 detects a detected value (a positional deviation in the sub-scanning direction X) of the calculated positions of the calculated cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM in the sub-scanning direction X. Amount CMx, BMx, MMx, YMx) is detected for each of the cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM, and the detected value (positional deviation amounts CMx, BMx, MMx, YMx in the sub-scanning direction X) Is stored in the storage unit 420 (see FIG. 2).

  For example, a normal relative distance in the sub-scanning direction X from a predetermined reference position is set in advance for each of the cyan mark CM, the black mark BM, the magenta mark MM, and the yellow mark YM. The detection pattern detection unit 412 obtains a detection distance in the sub-scanning direction X from the reference position for each of the cyan mark CM, black mark BM, magenta mark MM, and yellow mark YM, and detects the normal relative distance and the detection distance in the sub-scanning direction X. Are detected as misregistration amounts CMx, BMx, MMx, and YMx.

  The color misregistration correction amount calculation unit 413 uses the detection values (position misregistration amounts CMx, BMx, MMx, YMx in the sub-scanning direction X) detected by the detection pattern detection unit 412 to determine the colors of the toner images of a plurality of colors in the sub-scanning direction X. Deviation correction amounts Hxc, Hxb, Hxm, and Hxy are calculated, and the calculated color shift correction amounts Hxc, Hxb, Hxm, and Hxy in the sub-scanning direction X are stored in the storage unit 420 (see FIG. 2).

  The color misregistration correction execution unit 414 applies the color misregistration correction amounts Hxc, Hxb, Hxm, and Hxy in the sub-scanning direction X calculated by the color misregistration correction amount calculation unit 413 to the photosensitive drums 3c, 3b, 3m, and 3y. The writing timing in the sub-scanning direction X when writing the electrostatic latent image is adjusted.

  As a result, the control unit 400 can superimpose the toner images of the plurality of colors in a state where the positions in the sub-scanning direction X of the toner images of the plurality of colors formed on the intermediate transfer belt 7 coincide with each other. The color shift can be eliminated or almost eliminated.

(Color shift correction of detection pattern for main scanning direction correction)
When the detection pattern detection unit 412 receives the detection data sent from the detection pattern detection unit 80 (81, 82), the cyan mark inclined with respect to the main scanning direction Y in the main scanning direction correction detection pattern PT2. Based on the detection timing of cm, black mark bm, magenta mark mm and yellow mark ym, the formation position of cyan mark cm, black mark bm, magenta mark mm and yellow mark ym in the sub-scanning direction X is calculated.

  In addition, the detection pattern detection unit 412 calculates the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym in the sub-scanning direction X and the cyan calculated in advance and stored in the storage unit 420. Based on the positional deviation amounts CMx, BMx, MMx, YMx of the mark CM, the black mark BM, the magenta mark MM, and the yellow mark YM in the sub-scanning direction X, the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym Detection values (position displacement amounts cmy, bmy, mmy, ymy in the main scanning direction Y) with respect to the normal formation position of the formation position in the main scanning direction Y are detected, and the detected detection values (position displacement amounts cmy in the main scanning direction Y). , Bmy, mmy, ymy) are stored in the storage unit 420.

  Here, since the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym are inclined with respect to the main scanning direction Y, the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym are sub-scanned. When a certain distance is shifted in the direction X, the main scanning direction Y is also shifted by a certain distance, and when the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym are shifted by a certain distance in the main scanning direction Y, they are also constant in the sub-scanning direction X. Deviation by the distance, and therefore one deviation is integrated corresponding to both deviations. Therefore, the cyan mark CM, the black mark BM, the magenta mark MM, and the yellow mark are determined from the positional shift amounts cmx, bmx, mmx, and ymx of the cyan mark cm, black mark bm, magenta mark mm, and yellow mark ym in the sub-scanning direction X. By subtracting the displacement amounts CMx, BMx, MMx, YMx of YM in the sub-scanning direction X, the displacement amounts cmy, bmy, y in the main scanning direction Y of the cyan mark cm, black mark bm, magenta mark mm, and yellow mark ym. mmy and ymy can be calculated.

  For example, a normal relative distance in the sub-scanning direction X from a predetermined reference position is set in advance for each of the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym. The detection pattern detection unit 412 obtains a detection distance in the sub-scanning direction X from the reference position for each of the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym, and detects the normal relative distance and the detection position in the sub-scanning direction X. Are detected as misregistration amounts cmx, bmx, mmx, ymx, and sub-scanning of the cyan mark CM, black mark BM, magenta mark MM and yellow mark YM is performed from the detected misregistration amounts cmx, bmx, mmx, ymx. By subtracting the positional deviation amounts CMx, BMx, MMx, and YMx in the direction X, the positional deviation amounts cmy, bmy, y in the main scanning direction Y of the cyan mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym are obtained from the obtained values. mmy and ymy are detected.

  The color misregistration correction amount calculation unit 413 uses the detection values (position misregistration amounts cmy, bmy, mmy, ymy in the main scanning direction Y) detected by the detection pattern detection unit 412 to change the colors of the toner images of a plurality of colors in the main scanning direction Y. The shift correction amounts Hyc, Hyb, Hym, and Hyy are calculated, and the calculated color shift correction amounts Hyc, Hyb, Hym, and Hyy in the main scanning direction Y are stored in the storage unit 420 (see FIG. 2).

  The color misregistration correction execution unit 414 uses the color misregistration correction amounts Hyc, Hyb, Hym, and Hyy in the main scanning direction Y calculated by the color misregistration correction amount calculation unit 413 to the photosensitive drums 3c, 3b, 3m, and 3y. The writing timing in the main scanning direction Y when writing the electrostatic latent image is adjusted.

  As a result, the control unit 400 can superimpose the toner images of the plurality of colors in a state where the positions in the main scanning direction Y of the toner images of the plurality of colors formed on the intermediate transfer belt 7 coincide with each other. The color shift can be eliminated or almost eliminated.

(About sudden false detection)
By the way, in the color misregistration correction control, as described above, during the detection of the detection pattern PT, for example, the photosensitive drums 3c, 3b, 3m, and 3y are driven by a drive unit (not shown) to drive the photosensitive drums. Due to a sudden factor such as a drive transmission failure of a drive transmission unit (not shown) such as a drive gear that transmits rotational drive to the body drums 3c, 3b, 3m, and 3y (specifically, a so-called gear jump in which the drive gear is idle) Sudden false detection may occur. Then, since the control unit 400 cannot recognize whether or not a sudden erroneous detection has occurred, the color misregistration correction is performed with a detection value different from the original detection value. Color misregistration correction control cannot be performed. In addition, if the corrected mark of the detection pattern PT overlaps another mark (for example, the adjacent mark), each mark of the detection pattern PT cannot be detected corresponding to each color, and after that, the overlapping state Therefore, the color misregistration correction control cannot be performed by returning the mark of the detection pattern PT. This is particularly noticeable when the intervals d1, d2, d3 (see FIG. 2) between adjacent marks of the detection pattern PT are narrowed in order to detect the detection pattern PT in a short time.

  In this regard, the color misregistration correction control according to the present embodiment is the following color misregistration correction control.

  FIG. 4 is an explanatory diagram for explaining the color misregistration correction control according to the present embodiment. FIG. 4A is a diagram showing a detection pattern PT before correction in the case where sudden false detection is performed due to a sudden factor, and FIG. 4B is a sudden false detection due to a sudden factor. It is a figure which shows detection pattern PT after correction | amendment in the case of having performed. FIG. 4C is a diagram showing the detection pattern PT before correction when irregular proper detection is performed, and FIG. 4D is after correction when irregular proper detection is performed. It is a figure which shows this detection pattern PT.

  In the following description, the cyan mark CM in the sub-scanning direction correction detection pattern PT1 will be mainly described as an example. 4A to 4D, a broken line cyan mark CMa indicates a normal position, and a solid line cyan mark CM indicates a displacement from the normal position. Further, in FIG. 4A, a chain line cyan mark CMb indicates a sudden erroneous detection.

  As described above, the detection value of the detection pattern PT is usually within a certain color shift range Ra (for example, from 0 to 10 dots) within a certain day due to changes in the surrounding environment (for example, temperature change). (For example, the positional deviation amount CMxa of the cyan mark CM: see FIG. 4A).

  When the detection value of the detection pattern deviates from the normal color misregistration range Ra such as a change due to a change in the surrounding environment (for example, temperature change), the detection pattern PT is detected even though it is originally within the color misregistration range Ra. During the process, for example, a detection value that is different from the original detection value (original cyan mark CM misregistration amount CMxa: see FIG. 4A) due to a sudden erroneous detection due to a sudden factor, for example. In addition to the case of misdetected cyan mark CMb misregistration amount CMx (see FIG. 4A), the detected value actually deviating from the normal color misregistration range Ra, for example, the image forming apparatus 100 itself is moved. Alternatively, the state of the image forming apparatus 100 may be different due to irregular factors such as an external force applied to the image forming apparatus 100, such as an impact applied to the image forming apparatus 100. The detection value obtained by performing irregular proper detection after the change of the value and the detection value by the proper detection (the positional deviation amount CMx of the cyan mark CM by the proper detection: see FIG. 4C) deviates from the normal color shift range Ra There is a case. In other words, when a sudden erroneous detection is performed, the original detection value (original positional deviation amount CMxa: see FIG. 4A) is usually within the color misregistration range Ra, and the erroneously detected detection value ( While it is not necessary to perform color misregistration correction control with misdetected misregistration amount CMx (see FIG. 4A), when irregular proper detection is performed, a detection value (position by proper detection) is detected. The deviation amount CMx (see FIG. 4C) is out of the color misregistration range Ra, and it is necessary to perform color misregistration correction control with a detection value (positional deviation amount CMx due to proper detection) deviating from the color misregistration range Ra. There is.

  From this point of view, when the detection value of the detection pattern PT deviates from the color shift range Ra (in this example, the range from 0 to 10 dots), the limit value Rm (in this example, the upper limit value) of the color shift range Ra is once set. Try to correct the color misregistration using 10 dots. As a result, the detection values of the detection patterns PT of the plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra are the cases where a sudden erroneous detection is performed and when irregular proper detection is performed. Thus, the values of the different properties relating to the color misregistration correction are obtained.

  That is, in the case of sudden erroneous detection, the corrected positional deviation amount CMxb shown in FIG. 4B is the limit value of the color deviation range Ra from the original positional deviation amount CMxa shown in FIG. A value obtained by subtracting Rm can be used. For example, when the original positional deviation amount CMxa shown in FIG. 4A is 2 dots, the corrected positional deviation amount CMxb shown in FIG. 4B is the original positional deviation amount shown in FIG. The value obtained by subtracting 10 dots of the limit value Rm of the color shift range Ra from 2 dots of CMxa is -8 dots. On the other hand, when irregular proper detection is performed, the corrected misregistration amount CMxc shown in FIG. 4 (d) is changed from the misregistration amount CMx by proper detection shown in FIG. 4 (c) to the color misregistration range Ra. It is possible to obtain a value obtained by subtracting the limit value Rm. For example, when the misregistration amount CMx by proper detection shown in FIG. 4C is 12 dots, the corrected misregistration amount CMxc shown in FIG. 4D is the position by proper detection shown in FIG. The value obtained by subtracting 10 dots of the limit value Rm of the color shift range Ra from 12 dots of the shift amount CMx is +2 dots. That is, the corrected detection value (positional deviation amount CMxb) when sudden erroneous detection is performed and the corrected detection value (positional deviation amount CMxc) when irregular appropriate detection is performed. The direction of the correction direction of the color misregistration correction control is different.

  As a result, the image forming apparatus 100 can recognize whether a sudden erroneous detection has been performed or an irregular proper detection has been performed. Accordingly, the detection values of the detection patterns PT of the corrected colors PT (corrected cyan mark CM positional deviation amount CMxb: see FIG. 4B, or corrected cyan mark CM positional deviation amount CMxc: FIG. 4 (d)), the original color misregistration correction control can be performed even if a sudden erroneous detection is performed.

(First embodiment)
Therefore, the color misregistration correction control according to the present embodiment performs predetermined color misregistration determined by the detection values (position misalignment CMx: see FIGS. 4A and 4C) of the detection patterns PT of a plurality of colors. When out of the range Ra (in this example, the range from 0 to 10 dots), the color misregistration is corrected by using the limit value Rm (10 dots in this example) of the color misregistration range Ra. The next color based on the detection values of the subsequent detection patterns PT of a plurality of colors (corrected positional deviation amount CMxb: see FIG. 4B or corrected positional deviation amount CMxc: see FIG. 4D). It is configured to perform deviation correction control.

  In the present embodiment, the limit value Rm of the color misregistration range Ra is set to a value smaller than the intervals d1, d2, d3 (see FIG. 2A) between adjacent marks of the detection patterns PT of a plurality of colors.

  In this example, the interval d1 between the cyan mark CM and the black mark BM is equal to the interval d2 (specifically 62 dots) between the black mark BM and the magenta mark MM. Although the distance d3 (specifically, 104 dots) from the yellow mark YM is different (which is narrower than the distance d3), the limit value Rm of the color misregistration range Ra is a detection pattern PT of a plurality of colors. Is set to a value (specifically, 10 dots) smaller than the minimum interval (specifically, 62 dots) of the distances d1, d2, d3 between adjacent marks.

  By the way, when a sudden erroneous detection is performed, if the original detection value (original positional deviation amount CMxa: see FIG. 4A) is within the color misregistration range Ra, the original detection is performed. The value (original misregistration amount CMxa) is within the color misregistration range Ra. For this reason, the detection values of the detection patterns PT of a plurality of colors after correcting the color shift using the limit value Rm of the color shift range Ra (corrected positional shift amount CMxb: see arrow in FIG. 4B) are: This detection value indicates that correction is performed on the opposite side to the correction side based on the previously detected detection value (misdetected misregistration amount CMx: see arrow in FIG. 4A). In this case, it can be determined that a sudden erroneous detection has been performed, and the state before the correction (initial state) can be restored to retry (redo) the color misregistration correction control. However, the condition for satisfying such a configuration is that the original detection value (original positional deviation amount CMxa: see FIG. 4A) is within the color deviation range Ra (in this example, 0 dot <CMxa <10). When it is in the dot).

  From this point of view, in the present embodiment, the color misregistration correction execution unit 414 in the control unit 400 detects the detection values of the detection patterns PT of a plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra. If the detected value indicates that the correction is performed on the opposite side to the correction side based on the detection value detected last time, the configuration is such that the color misregistration correction control is retried (restarted) by returning to the state before the correction (initial state). ing. In other words, the color misregistration correction execution unit 414 uses the limit value Rm of the color misregistration range Ra to correct the color misregistration before detecting the positive / negative sign of the detection values of the detection patterns PT of the plurality of colors (in this example, erroneous detection). Misregistration amount CMx: Refer to FIG. 4A, specifically +12, or misregistration amount CMx by appropriate detection: Refer to FIG. 4C, specifically, a positive sign of +12). If the detected value of the detection pattern PT of the plurality of colors after correcting the color misregistration using the limit value Rm is different from the sign of the detected value (in this example, the positional deviation amount CMxb after correction: FIG. 4B) For reference (specifically, in the case of a minus sign of −8), the state before the correction (initial state) is restored and the color misregistration correction control is retried (restarted).

  On the other hand, when irregular proper detection is performed, the detection value by proper detection (the positional deviation amount CMx by proper detection: see FIG. 4C) is out of the color misregistration range Ra. Therefore, the detection values of the detection patterns PT of a plurality of colors after correcting the color shift using the limit value Rm of the color shift range Ra (corrected positional shift amount CMxc: see arrow in FIG. 4D) are: This is a detection value indicating correction to the correction side based on the detection value detected last time (position shift amount CMx by proper detection: see arrow in FIG. 4C). In this case, it is possible to repeat the color misregistration correction control for determining that irregular proper detection has been performed and correcting the color misregistration using the limit value Rm of the color misregistration range Ra.

  Here, as a technique different from the technique according to the present embodiment, the color misregistration correction control is performed once again when the detection values of the detection patterns PT of a plurality of colors are out of the color misregistration range Ra. Although it is conceivable to retry (retry), when irregular proper detection is performed, color misregistration correction is performed using detection values obtained by proper detection deviating from the normal color misregistration range Ra as they are. As a result, the color misregistration correction accuracy deteriorates. That is, when the color misregistration correction amount is relatively large (for example, when the correction amount exceeds 10 dots, which is the limit value Rm of the color misregistration range Ra), the color misregistration correction amount is relatively small. Compared to the color misregistration correction performed in this case (for example, when the correction amount is 10 dots or less, which is the limit value Rm of the color misregistration range Ra), the correction accuracy of the color misregistration is deteriorated by the larger correction amount.

  From this point of view, in the present embodiment, the detection values of the detection patterns PT of the plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra are corrected to the correction side based on the previously detected detection value. In the case of the detected value indicating the color misregistration, the color misregistration correction control for correcting the color misregistration using the limit value Rm of the color misregistration range Ra is repeated. In other words, the color misregistration correction execution unit 414 uses the limit value Rm of the color misregistration range Ra to correct the color misregistration before detecting the positive / negative sign of the detection values of the detection patterns PT of the plurality of colors (in this example, erroneous detection). Misregistration amount CMx: Refer to FIG. 4A, specifically +12, or misregistration amount CMx by appropriate detection: Refer to FIG. 4C, specifically, a positive sign of +12). If the detected value of the detection pattern PT of the plurality of colors after correcting the color shift using the limit value Rm is equal to the sign of the detected value (in this example, the positional deviation amount CMxc after correction: see FIG. 4D, specific Specifically, in the case of a positive sign of +2, color misregistration correction control for correcting the color misregistration using the limit value Rm of the color misregistration range Ra is repeated.

  In the present embodiment, the history information M (for example, the history of the retry count Cd) including the retry count Cd (retry count) for returning to the state before correction (initial state) and retrying (retrying) color misregistration correction control, History of detection value of detection pattern PT, history of correction amount of color misregistration, history of repetition number Cr of repeating color misregistration correction control for correcting color misregistration using limit value Rm of color misregistration range Ra, history of storage date, etc. Are stored in the storage unit 420 (see FIG. 3).

  FIG. 5 is a flowchart illustrating a control example of color misregistration correction control according to the first embodiment by the control unit 400 illustrated in FIG. 3. In the flowchart shown in FIG. 5, the number of repetitions Cr and the number of retries Cd are reset (set to 0) prior to performing color misregistration correction control.

  In the color misregistration correction control shown in FIG. 5, first, the control unit 400 forms detection patterns PT of a plurality of colors on the intermediate transfer belt 7 by the detection pattern forming unit 411 (step S10), and the detection pattern forming unit 411 The formed detection patterns PT of a plurality of colors are respectively detected by the detection pattern detection unit 412 (step S20), and a plurality of color toner images are detected from the detection values of the detection patterns PT of the plurality of colors detected by the detection pattern detection unit 412. A correction amount for correcting the color misregistration is calculated by the color misregistration correction amount calculation unit 413 (step S30).

  Next, when the color misregistration correction execution unit 414 changes the formation position of the toner images of a plurality of colors based on the correction amount calculated by the color misregistration correction amount calculation unit 413, the control unit 400 performs steps from Step S40 to Step S40. The process of S70 is performed.

  That is, the control unit 400 determines whether or not the number of repetitions Cr is 0 (step S40), and when the number of repetitions Cr is 0 (step S40: Yes), the detection value of the detection pattern PT (for example, , Misregistration amount CMx: see FIGS. 4A and 4C), it is determined whether or not the color misregistration range Ra (the range from 0 to 10 dots in this example) is out (step S50). When the detection value of the detection pattern PT is out of the color misregistration range Ra (step S50: Yes), 1 is added to the number of repetitions Cr (step S51). At this time, history information M including the number of retries Cd (in this example, a history of the number of retries Cd, a history of detection values of the detection pattern PT, a history of correction amount of color misregistration, a history of the number of repetitions Cr, a history of storage date, etc. (History information) is stored in the storage unit 420.

  Next, the control unit 400 corrects the color misregistration using the limit value Rm (10 dots in this example) of the color misregistration range Ra (step S52), and proceeds to step S10. Specifically, in step S52, the color misregistration correction amount with respect to the limit value Rm of the color misregistration range Ra is calculated by the color misregistration correction amount calculation unit 413, and based on the correction amount calculated by the color misregistration correction amount calculation unit 413. Then, the color misregistration correction execution unit 414 corrects the color misregistration.

  On the other hand, when the number of repetitions Cr is 1 or more in step S40 (step S40: No), the control unit 400 detects the detection pattern PT after correcting the color shift using the limit value Rm of the color shift range Ra. Detected value (for example, corrected positional deviation amount CMxb: see arrow in FIG. 4B) is a previously detected value (for example, misdetected positional deviation amount CMx: see arrow in FIG. 4A). Or a detected value of the detection pattern PT after correction of color misregistration using the limit value Rm of the color misregistration range Ra (for example, after correction) 4) (refer to the arrow in FIG. 4D) is corrected to the correction side based on the detection value detected last time (for example, the positional deviation amount CMx by appropriate detection: see the arrow in FIG. 4C). Determine whether the detected value is That (step S60).

  The control unit 400 corrects the detection value of the detection pattern PT after correcting the color shift using the limit value Rm of the color shift range Ra in step S60 to the opposite side from the correction side based on the previously detected detection value. If it is the detected value (step S60: Yes), 1 is added to the retry count Cd (step S61). At this time, history information M including the number of retries Cd (in this example, a history of the number of retries Cd, a history of detection values of the detection pattern PT, a history of correction amount of color misregistration, a history of the number of repetitions Cr, a history of storage date, etc. (History information) is stored in the storage unit 420.

  Next, the control part 400 returns to the state (initial state) before correction | amendment (step S62), and transfers to step S10. Here, “return to the state before correction (initial state)” specifically refers to returning the number of repetitions Cr to 0, and using the limit value Rm of the color shift range Ra as the color shift correction amount. Means to return to the correction amount before correcting.

  Further, the control unit 400 detects that the detected value of the detection pattern PT after correcting the color shift using the limit value Rm of the color shift range Ra in step S60 is corrected to the correction side based on the previously detected detection value. If it is a value (step S60: No), the process proceeds to step S50.

  If the detection value of the detection pattern PT is within the color shift range Ra in step S50 (step S50: No), the control unit 400 corrects the color shift using the detection value of the detection pattern PT (step S30). The color misregistration correction execution unit 414 corrects the color misregistration based on the correction amount calculated in (Step S70), and the color misregistration correction control process is terminated.

  Here, in the first embodiment, the cyan mark CM in the sub-scanning direction correction detection pattern PT1 has been described, but other black marks BM, magenta marks MM and yellow marks YM, and cyan in the main scanning direction correction detection pattern PT2. The same applies to the mark cm, the black mark bm, the magenta mark mm, and the yellow mark ym. Further, in the first embodiment, the case of shifting to the plus side (right side in FIG. 4) is exemplified, but the case of shifting to the minus side (left side in FIG. 4) will be described similarly only by reversing the positive / negative sign. be able to. In this case, the limit value Rm of the color misregistration range Ra is a lower limit value. The same applies to the second to fourth embodiments described later.

(Second Embodiment)
By the way, in the case where irregular proper detection is performed, if the detection value by the proper detection (the positional deviation amount CMx by the proper detection: see FIG. 4C) is too large, the color misregistration correction amount becomes the color misregistration correction control. The allowable range (for example, 100 dots) will be exceeded.

  From this point of view, in the present embodiment, the control unit 400 is configured to set the upper limit of the number of repetitions Cr to a predetermined repetition limit number of times Crs. Here, as the repetition limit number Crs, a quotient value obtained by dividing the allowable range of color misregistration correction control by the limit value Rm of the color misregistration range Ra can be exemplified. For example, when the allowable range of color misregistration correction control is 100 dots, the value of the quotient (100 dots in this example) divided by the limit value Rm (10 dots in this example) of the allowable range of color misregistration correction control Ra 10 times in the example).

  In addition, when the erroneous misdetection is continuously generated and the color misregistration correction control is retried (restarted) after returning to the state before the correction (initial state), the sudden misdetection has a good reproducibility (continuous). If this occurs, color misregistration correction control due to sudden erroneous detection is continuously performed.

  From this point of view, in the present embodiment, the control unit 400 is configured to set the upper limit of the retry count Cd to a predetermined retry limit count Cds (retry limit count). Here, as the retry limit number Cds, a number of times that is no longer sudden (for example, about five times) can be exemplified.

  FIG. 6 is a flowchart illustrating a control example of color misregistration correction control according to the second embodiment by the control unit 400 illustrated in FIG. 3. The flowchart shown in FIG. 6 is the same as the flowchart shown in FIG. 5 except that step S501 is provided between step S50 and step S51 and step S601 is provided between step S60 and step S61 in the flowchart shown in FIG. The same thing. Therefore, in the flowchart shown in FIG. 6, the same processes as those in the flowchart shown in FIG.

  In the color misregistration correction control shown in FIG. 6, when the detection value of the detection pattern PT is out of the color misregistration range Ra in step S50 (step S50: Yes), the control unit 400 sets the repetition count Cr to the repeat limit count. It is determined whether or not Crs has been exceeded (step S501). If the number of repetitions Cr does not exceed the number of repetitions Crs (step S501: No), the process proceeds to step S51, while the number of repetitions Cr is the number of repetitions. If it exceeds Crs (step S501: Yes), the color misregistration correction control process is terminated.

  Further, the control unit 400 corrects the detected value of the detection pattern PT after correcting the color misregistration using the limit value Rm of the color misregistration range Ra in step S60 to the opposite side to the correction side based on the previously detected detection value. If it is a detected value (step S60: Yes), it is determined whether or not the retry count Cd exceeds the retry limit count Cds (step S601), and the retry count Cd does not exceed the retry limit count Cds. In the case (step S601: No), the process proceeds to step S61. On the other hand, if the retry count Cd exceeds the retry limit count Cds (step S601: Yes), the color misregistration correction control process is terminated.

(Third embodiment)
In the present embodiment, the control unit 400 determines a detection value of the detection pattern PT (a positional deviation amount CMxa: see FIG. 4A) in advance when the retry count Cd exceeds the retry limit count Cds. The configuration is set to CMxd. Here, as the predetermined value CMxd, a positional deviation amount according to the ambient temperature of the image forming apparatus 100 can be exemplified. Note that the amount of misregistration corresponding to the ambient temperature of the image forming apparatus 100 can be set in advance through experiments or the like.

  FIG. 7 is a flowchart illustrating a control example of color misregistration correction control according to the third embodiment by the control unit 400 illustrated in FIG. 3. The flowchart shown in FIG. 7 is the same as the flowchart shown in FIG. 6 except that steps S602 and S603 are provided between step S601 and the end of processing in the flowchart shown in FIG. Therefore, in the flowchart shown in FIG. 7, the same processes as those in the flowchart shown in FIG.

  In the color misregistration correction control illustrated in FIG. 7, when the number of retries Cd exceeds the retry limit number Cds in step S601 (step S601: Yes), the control unit 400 detects the detected value of the detection pattern PT (the positional deviation amount CMxa). (See FIG. 4A) is set to a predetermined value CMxd (step S602), and the color misregistration is corrected using the detection value of the detection pattern PT (detection value set to the predetermined value) (step S602). S603), the color misregistration correction control process is terminated. Specifically, in step S603, the color misregistration correction amount corresponding to the predetermined value CMxd is calculated by the color misregistration correction amount calculating unit 413, and the color misregistration is calculated based on the correction amount calculated by the color misregistration correction amount calculating unit 413. The color misregistration is corrected by the misregistration correction execution unit 414.

(Fourth embodiment)
In the present embodiment, the control unit 400 is configured to notify a predetermined notification content Md that is determined in advance when the retry count Cd exceeds the retry limit count Cds. The notification content Md is stored in advance in the storage unit 420 (see FIG. 3). Here, as a mode of notifying the predetermined notification content Md when the retry count Cd exceeds the retry limit count Cds, the image forming apparatus 100 is informed that there is a possibility that some problem relating to color misregistration has occurred. A mode in which a message or voice is output from a display unit or a speaker, and / or a notification content Md is output as external data can be exemplified.

  Further, in the present embodiment, the control unit 400 is configured to notify a predetermined notification content Mr set in advance when the number of repetitions Cr exceeds the number of repetitions Crs. The notification content Mr is stored in advance in the storage unit 420 (see FIG. 3). Here, as a mode of notifying the predetermined notification content Mr when the repetition count Cr exceeds the repetition limit count Crs, a message notifying that the color misregistration correction amount exceeds the allowable range of the color misregistration correction control, For example, the voice may be output from the display unit or the speaker, and / or the notification content Mr may be output as external data.

  FIG. 8 is a flowchart illustrating a control example of color misregistration correction control according to the fourth embodiment by the control unit 400 illustrated in FIG. 3. The flowchart shown in FIG. 8 is the same as the flowchart shown in FIG. 7 except that step S502 is provided between step S501 and the end of the process, and step S604 is provided between step S603 and the end of the process. The same thing. Therefore, in the flowchart shown in FIG. 8, the same processes as those in the flowchart shown in FIG.

  In the color misregistration correction control illustrated in FIG. 8, when the number of repetitions Cr exceeds the number of repetitions Crs in step S501 (step S501: Yes), the control unit 400 notifies a predetermined notification content Mr (for example, color Color misregistration correction is performed by outputting a message or sound notifying that the amount of misregistration correction exceeds the allowable range of color misregistration correction control from the display unit or the speaker or / and outputting the notification content Mr as external data). The control process ends.

  Further, the control unit 400 corrects the color misregistration using the detection value of the detection pattern PT (detection value set to a predetermined value) (step S603), and then notifies the predetermined notification content Md (for example, the image forming apparatus). 100. Output a message or voice informing that there is a possibility that some trouble related to color misregistration has occurred in the display unit 100 or / or a speaker, or / and further output the notification content Md as external data) to correct the color misregistration. The control process ends.

  In the flowchart shown in FIG. 8, steps S602 and S603 out of steps S602 to S604 may be deleted, and only step S604 may be provided.

(About 1st Embodiment to 4th Embodiment)
As described above, according to the first to fourth embodiments, the color misregistration correction control is performed once when the detection values of the detection patterns PT of a plurality of colors are out of the color misregistration range Ra. By correcting the color misregistration using the limit value Rm of the range Ra, the detection values of the detection patterns PT of the plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra are suddenly erroneous. Different values are used for color misregistration correction when the detection is performed and when the irregular proper detection is performed. Therefore, the image forming apparatus 100 may detect whether a sudden erroneous detection has occurred, or It is possible to recognize whether regular proper detection has been performed. Then, by performing the next color misregistration correction control based on the detection values of the detection patterns PT of the plurality of colors after correction, even if a sudden erroneous detection is performed, the original color misregistration correction control is performed. Can be performed.

  In the first to fourth embodiments, the limit value Rm of the color misregistration range Ra is set to a value smaller than the intervals d1, d2, and d3 between adjacent marks of the detection patterns PT of a plurality of colors.

  By doing this, it is possible to effectively prevent the correction amount for correcting the color misregistration from being greater than or equal to the distances d1, d2, d3 between adjacent marks of the detection patterns PT of a plurality of colors. It is possible to effectively prevent overlapping with another mark (for example, an adjacent mark). As a result, even if a sudden erroneous detection is performed, each mark of the detection pattern PT can be detected corresponding to each color without the corrected mark of the detection pattern PT overlapping another mark. In addition, after that, it is possible to avoid the inconvenience that it becomes impossible to perform the color misregistration correction control by returning the mark of the detection pattern PT in the overlapped state. This is particularly effective when the intervals d1, d2, and d3 between adjacent marks of the detection pattern PT are narrowed in order to detect the detection pattern PT in a short time.

  In the first to fourth embodiments, the detection values of the detection patterns PT of the plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra are corrected by the detection value detected last time. When the detected value indicates that the correction is performed on the opposite side, the color misregistration correction control is retried (restarted) by returning to the state before the correction (initial state).

  By doing this, when the original detection value is in the range inside the color misregistration range Ra, the detection pattern PT of the plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra. When the detection value is a detection value indicating that correction is performed on the side opposite to the correction side based on the detection value detected last time, the image forming apparatus 100 can recognize that a sudden erroneous detection has occurred. Therefore, in this case, since there is usually a low probability of a sudden erroneous detection reoccurring, the color misregistration correction control is performed by retrying (redoing) the color misregistration correction control after returning to the state before the correction (initial state). Thus, it is possible to perform the detection with the original detection value without performing the detection with the erroneously detected detection value.

  In the first to fourth embodiments, the detection values of the detection patterns PT of the plurality of colors after correcting the color misregistration using the limit value Rm of the color misregistration range Ra are on the correction side based on the previously detected detection values. In the case of a detected value indicating correction, color misregistration correction control for correcting color misregistration using the limit value Rm of the color misregistration range Ra is repeated.

  In this way, the detection value indicating that the detection value of the detection pattern PT of the plurality of colors after correcting the color shift using the limit value Rm of the color shift range Ra is corrected to the correction side based on the detection value detected last time. In some cases, it can be recognized that irregular proper detection has been performed. In this case, by repeating the color misregistration correction control for correcting the color misregistration using the limit value Rm of the color misregistration range Ra, the color misregistration correction control is not performed using the detection value of the detection pattern PT as it is, but the color misregistration correction control is performed. Is set to a relatively small value such as a limit value Rm (10 dots in this example) of the color misregistration range Ra or a value inside the color misregistration range Ra (greater than 0 dots and less than 10 dots in this example). The color misregistration correction control can be performed in a plurality of times, which makes it possible to accurately perform the color misregistration correction control by proper detection that deviates from the normal color misregistration range.

  In the second to fourth embodiments, the upper limit of the number of repetitions Cr is set to the number of repetitions limit Crs.

  In this way, the number of repetitions Cr can be limited to the number of repetitions limit Crs. Therefore, even when irregular proper detection is performed, even if the detection value by proper detection is too large, the color misregistration range Ra. The color misregistration correction control for correcting the color misregistration by using the limit value Rm can be repeated at the limit number of times Crs (that is, stopped halfway). As a result, the amount of color misregistration correction can be within an allowable range.

  In the second to fourth embodiments, the upper limit of the retry count Cd is set to the retry limit count Cds.

  In this way, the retry count Cd can be limited to the retry limit count Cds. Therefore, even if sudden false detection occurs with good reproducibility (continuously), the color due to sudden false detection The deviation correction control can be ended (that is, stopped halfway) at the retry limit count Cds.

  Further, in the third embodiment and the fourth embodiment, when the number of retries Cd exceeds the number of retries limit Cds, the detection value of the detection pattern PT is set to a predetermined value (for example, a positional deviation corresponding to the ambient temperature of the image forming apparatus 100). Amount).

  By doing so, it becomes possible to set the detection value of the detection pattern PT to a predetermined value when sudden erroneous detection occurs with good reproducibility (continuously).

  In the fourth embodiment, the notification content Md is notified when the retry count Cd exceeds the retry limit count Cds.

  In this way, it is possible to notify the user or service person that there is a possibility that some problem relating to color misregistration has occurred in the image forming apparatus 100.

  In the fourth embodiment, the notification content Mr is notified when the number of repetitions Cr exceeds the number of repetitions limit Crs.

  In this way, it is possible to notify the user or service person that the amount of color misregistration correction exceeds the allowable range of color misregistration correction control.

  In the first to fourth embodiments, history information including the number of retries Cd (for example, the history of the number of retries Cd, the history of the detection value of the detection pattern PT, the history of the color misregistration correction amount, the number of repetitions Cr, and the like) History information such as history and history of storage date and time) is stored in the storage unit 420.

  By doing so, it becomes possible to grasp the past situation in which sudden erroneous detection or irregular appropriate detection in the image forming apparatus 100 has been performed.

  The present invention is not limited to the embodiment described above, and can be implemented in various other forms. Therefore, such an embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is shown by the scope of claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Laser exposure apparatus 2b-2y Developing apparatus 3b-3y Photosensitive drum 4b-4y Drum cleaning apparatus 5b-5y Charger 6b-6y Intermediate transfer part 7 Intermediate transfer belt 8 Intermediate transfer apparatus 9 Intermediate transfer belt cleaning apparatus 12 Fixing apparatus 21 Intermediate transfer belt drive roller 22 Follower roller 23 Tension roller 80 Detection pattern detection unit 80a Light emission unit 80b Light reception unit 81 First detection pattern detection unit 82 Second detection pattern detection unit 100 Image forming apparatus 200 Image reading apparatus 300 Image forming apparatus main body 310 Sheet supply unit 320 Sheet conveyance unit 330 Image forming unit 340 Sheet discharge unit 400 Control unit 410 Processing unit 411 Detection pattern formation unit 412 Detection pattern detection unit 413 Color misregistration correction amount calculation unit 414 Color misregistration correction execution unit 420 Storage unit BM Black mark CM Cyan Mark MM Magenta mark YM Yellow mark CMx Position shift amount CMxa Original position shift amount CMxb Position shift amount after correction CMxc Position shift amount after correction CMxd Predetermined value Cd Retry count Cds Retry limit count Cr Repeat count Crs Repeat limit count M History information Md Notification content Mr Notification content PT Detection pattern PT1 Sub-scanning direction correction detection pattern PT2 Main scanning direction correction detection pattern Ra Color shift range Rm Limit value X Sub-scanning direction Y Main scanning direction bm Black mark cm Cyan mark mm Magenta Mark ym Yellow mark d1-d3 Interval between marks

Claims (8)

Color misregistration correction control is performed in which detection patterns of a plurality of colors are formed, the detection patterns of the plurality of colors formed are detected, and color misregistration is corrected based on the detected values of the detected detection patterns of the plurality of colors. An image forming apparatus,
The color misregistration correction control corrects the color misregistration once using a limit value of the color misregistration range when detection values of the detection patterns of the plurality of colors deviate from a predetermined color misregistration range. An image forming apparatus that performs the next color misregistration correction control based on detection values of the detection patterns of the plurality of colors after correction. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein a limit value of the color misregistration range is a value smaller than an interval between adjacent marks of the detection patterns of the plurality of colors. The image forming apparatus according to claim 1, wherein:
This detection value indicates that the detection value of the detection pattern of the plurality of colors after correcting the color shift using the limit value of the color shift range is corrected to the opposite side to the correction side based on the previously detected detection value. In this case, the image forming apparatus is configured to retry the color misregistration correction control by returning to a state before correction. An image forming apparatus according to any one of claims 1 to 3, wherein
When the detection value of the detection pattern of the plurality of colors after correcting the color misregistration using the limit value of the color misregistration range is a detection value indicating correction to the correction side by the detection value detected last time, An image forming apparatus that repeats the color misregistration correction control for correcting the color misregistration using a limit value of the color misregistration range. The image forming apparatus according to claim 3 or 4, wherein:
This detection value indicates that the detection value of the detection pattern of the plurality of colors after correcting the color shift using the limit value of the color shift range is corrected to the opposite side to the correction side based on the previously detected detection value. In this case, return to the state before correction and retry the color misregistration correction control,
An image forming apparatus, wherein the upper limit of the number of retries for returning to the state before the correction and retrying the color misregistration correction control is set to a predetermined predetermined number of retries. The image forming apparatus according to claim 5, wherein
An image forming apparatus, wherein the detection value of the detection pattern is set to a predetermined value when the number of retries exceeds the retry limit number. The image forming apparatus according to claim 5, wherein:
An image forming apparatus, wherein a predetermined notification content is notified when the number of retries exceeds the retry limit number. An image forming apparatus according to any one of claims 3 to 7,
This detection value indicates that the detection value of the detection pattern of the plurality of colors after correcting the color shift using the limit value of the color shift range is corrected to the opposite side to the correction side based on the previously detected detection value. In this case, return to the state before correction and retry the color misregistration correction control,
An image forming apparatus storing history information including a retry count for returning to the state before the correction and retrying the color misregistration correction control.

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