JP5915455B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, in a tandem image forming apparatus including a plurality of photosensitive drums, it is necessary to accurately superimpose toner images formed on the respective photosensitive drums on an intermediate transfer belt. However, there may be a case where a color misregistration (hereinafter referred to as “color misregistration”) occurs on the paper due to a positional accuracy or diameter deviation of each photoconductor drum, a positional accuracy deviation of the optical system, or the like. As a type of color misregistration, color misregistration caused by a shift in the writing position in the main scanning direction (a direction orthogonal to the traveling direction of the intermediate transfer belt) (see FIG. 7A), hereinafter referred to as “main scanning direction writing position shift”. ), Color shift (see FIG. 7B, hereinafter referred to as “sub-scan direction write position shift”) caused by a shift in the writing position in the sub-scanning direction (traveling direction of the intermediate transfer belt), and the entire main scanning direction. Color shift due to magnification error (see FIG. 7C, hereinafter referred to as “overall magnification error”), color shift due to partial magnification error in the main scanning direction (see FIG. 7D), hereinafter referred to as “partial magnification error” Color misregistration due to image tilt in the sub-scanning direction (see FIG. 7E, hereinafter referred to as “image tilt (skew)”), and color misregistration due to image curvature in the sub-scanning direction (FIG. 7F). See, "Image curvature (bow)" below Say) is known. 7A to 7F, the solid line and the dotted line represent the ideal image forming position and the actual image forming position, respectively, and d1, d2, d3, d4, d5, and d6 are the image forming position and the actual image, respectively. The amount of misregistration with the formation position, that is, the color misregistration amount is represented.

  In order to prevent such color misregistration, a color misregistration correction pattern (hereinafter referred to as a “resist pattern”) is printed on the outer peripheral surface of the intermediate transfer belt when printing is not performed on paper (for example, when the image forming apparatus is turned on). Based on the detection result of the resist pattern formed above, color misregistration correction (hereinafter referred to as “resist correction”) is performed.

  As a technique related to registration correction, by using detection marks provided at regular intervals in the sub-scanning direction of the intermediate transfer belt, the shift of the intermediate transfer belt in the main scanning direction is detected, A technique for correcting the image forming position in the main scanning direction has been proposed (see, for example, Patent Document 1).

JP 2010-217300 A

  By the way, the cause of color misregistration is that when printing on paper, the intermediate transfer belt expands or contracts due to changes in temperature and humidity in the apparatus, and the speed of the intermediate transfer belt changes due to the impact of the paper entering the secondary transfer nip. Etc. As described above, when the state of the intermediate transfer belt changes during printing on a sheet, a new color shift (at least one of the above-described six types of color shifts) is performed even though registration correction is performed during non-printing on the sheet. There was a problem that would occur.

  In the technique described in Japanese Patent Laid-Open No. 2004-260688, when printing on a sheet, partial magnification error in the main scanning direction and color misregistration due to image curvature are not targeted for correction, and the above six types of color misregistration due to the state change of the intermediate transfer belt are not corrected. It is not possible to detect and correct everything. For this reason, it has been difficult to prevent color misregistration caused by a change in the state of the intermediate transfer belt as a countermeasure against the problem of color misregistration.

  An object of the present invention is to provide an image forming apparatus capable of correcting a color shift caused by a change in state of an intermediate transfer belt during printing on a sheet.

An image forming apparatus according to the present invention includes:
A plurality of image forming units for forming toner images of respective colors;
An intermediate transfer belt on which a toner image of each color formed by the plurality of image forming units is transferred onto an outer peripheral surface to form a superimposed color image;
A first detector for detecting a first resist pattern formed on the outer peripheral surface of the intermediate transfer belt;
A correction amount calculation unit that calculates a color misregistration correction amount based on a detection result of the first detection unit;
A first storage unit for storing the calculated color misregistration correction amount;
A first resist pattern is formed on the outer peripheral surface of the intermediate transfer belt, the first resist pattern is detected by the first detection unit, and the color misregistration correction amount is calculated based on the detection result of the first detection unit. The color registration adjustment mode for correcting the image forming conditions of the plurality of image forming units based on the calculated color misregistration correction amount and the color misregistration correction amount stored in the first storage unit. A control unit that controls execution of an image forming mode in which a color image is formed on a sheet by correcting the formation position of each color image by the plurality of image forming units;
In an image forming apparatus having
A second resist pattern provided in advance on the inner peripheral surface of the intermediate transfer belt;
A second detector for detecting the second resist pattern;
A second storage unit that stores, as reference data, a detection result of the second detection unit during execution of the color registration adjustment mode;
A difference amount calculation unit that calculates a difference amount between the data detected by the second detection unit and the reference data in the execution of the image forming mode after the color registration adjustment mode is executed;
The control unit, when executing the image forming mode after executing the color registration adjustment mode, based on a correction amount obtained by adding the difference amount to the color misregistration correction amount, each color by the plurality of image forming units. A color image is formed on a sheet by correcting the image formation position.

  According to the present invention, the color misregistration correction resist pattern formed on the inner peripheral surface of the intermediate transfer belt, which is a surface on which a color image is not formed, is printed on a sheet (in the image forming mode). It is possible to detect a color shift caused by a change in the state of the intermediate transfer belt and perform registration correction in consideration of the color shift. Further, since the resist pattern can be arranged at an arbitrary position on the inner peripheral surface of the intermediate transfer belt, partial magnification error in the main scanning direction and color misregistration due to image curvature can be corrected. As described above, it is possible to provide an image forming apparatus capable of correcting a color shift caused by a change in the state of the intermediate transfer belt when printing on a sheet.

1 is a longitudinal sectional view of an image forming apparatus in the present embodiment. 3 is a control block diagram of the image forming apparatus in the present embodiment. FIG. FIG. 4 is a diagram illustrating a state in which a resist pattern is formed on an intermediate transfer belt. FIG. 4 is a diagram illustrating a state in which a resist pattern is formed on an intermediate transfer belt. It is a figure which shows the calculation method of the color shift amount in this Embodiment. 5 is a flowchart showing a registration correction operation of the image forming apparatus in the present embodiment. It is a figure which shows the kind of color shift in a prior art.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
[Configuration of Image Forming Apparatus 100]
An image forming apparatus 100 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. The image forming apparatus 100 primarily transfers the C (cyan), M (magenta), Y (yellow), and K (black) toner images formed on the photosensitive drum to the intermediate transfer belt, and then the intermediate transfer belt. After the four color toner images are superimposed on each other, the image is formed by secondary transfer onto a sheet.

  Further, the image forming apparatus 100 has a tandem method in which photosensitive drums corresponding to four colors of CMYK are arranged in series in the running direction of the intermediate transfer belt, and each color toner image is sequentially transferred to the intermediate transfer belt in one procedure. It has been adopted.

  As shown in FIG. 2, the image forming apparatus 100 includes a control unit 101, an image reading unit 110, an operation display unit 120, an image processing unit 130, an image forming unit 140, a conveyance unit 150, a fixing unit 160, and a first detection unit. A resist sensor 180 that functions and a resist sensor 190 that functions as a second detection unit are provided. The control unit 101 also functions as a correction amount calculation unit and a difference amount calculation unit.

  The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and the like. The CPU 102 reads a program corresponding to the processing content from the ROM 103 and develops it in the RAM 104, and centrally controls the operation of each block of the image forming apparatus 100 in cooperation with the developed program. At this time, various data stored in the storage unit 172 (for example, print data of each color resist pattern) is referred to. The storage unit 172 functions as a first storage unit and a second storage unit.

  The image reading unit 110 includes an automatic document feeder 111 called an ADF (Auto Document Feeder), an image scanning device 112, and the like.

  The automatic document feeder 111 conveys the document D placed on the document tray by the conveyance mechanism and sends it out to the image scanning device 112. The automatic document feeder 111 can continuously read images (including both sides) of the document D when a large number of documents D are placed on the document tray.

  The image scanning device 112 optically scans a document conveyed on the contact glass from the automatic document feeder 111 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 112a, and a document image is read. The image reading unit 110 generates input image data based on the reading result by the image scanning device 112. The image processing unit 130 performs predetermined image processing on the input image data.

  The operation display unit 120 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 121 and the operation unit 122. The display unit 121 displays various operation screens, image status display, operation status of each function, and the like in accordance with a display control signal input from the control unit 101. The operation unit 122 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 101.

  The image processing unit 130 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. The image forming unit 140 is controlled based on the image data subjected to the digital image processing.

  The image forming unit 140 forms an image with each color toner of Y component, M component, C component, and K component based on the input image data, and an intermediate transfer member 142 for forming an image with the image forming units 141Y, 141M, 141C, 141K. Etc.

  The Y component, M component, C component, and K component image forming units 141Y, 141M, 141C, and 141K have the same configuration. For convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and in order to distinguish them, Y, M, C, or K is added to the reference numerals. In FIG. 1, only the components of the image forming unit 141Y for the Y component are denoted by reference numerals, and the reference numerals are omitted for the other components of the image forming units 141M, 141C, and 141K.

  The configuration of the image forming unit 141 will be described using the image forming unit 141Y. The image forming unit 141Y includes an exposure device 1411, a developing device 1412, a photosensitive drum 1413, a charging device 1414, a drum cleaning device 1415, and the like.

  The photosensitive drum 1413 has, for example, an undercoat layer (UCL), a charge generation layer (CGL), a charge transport layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). An organic photo-conductor (OPC) in which CTL (Charge Transport Layer) is sequentially stacked.

  The charging device 1414 uniformly charges the surface of the photoconductive drum 1413 to a negative polarity. The exposure device 1411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 1413 with laser light corresponding to the image of each color component, so that an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 1413. .

  The developing device 1412 stores a developer for each color component (for example, a two-component developer composed of toner and a magnetic carrier), develops the electrostatic latent image on the surface of the photosensitive drum 1413, and supplies toner for each color component. By adhering, the electrostatic latent image is visualized to form a toner image.

  The drum cleaning device 1415 has a drum cleaning blade that is in sliding contact with the surface of the photosensitive drum 1413. Transfer residual toner remaining on the surface of the photosensitive drum 1413 after the primary transfer is scraped off and removed by a drum cleaning blade.

  The intermediate transfer body 142 includes an intermediate transfer belt 1421, a primary transfer roller 1422, a secondary transfer roller 1423, a driving roller 1424, a driven roller 1425, a belt cleaning device 1426, and the like.

  The intermediate transfer belt 1421 is an endless belt, and is stretched around a driving roller 1424 and a driven roller 1425. Intermediate transfer belt 1421 travels at a constant speed in the direction of arrow A by the rotation of drive roller 1424. When the intermediate transfer belt 1421 is brought into pressure contact with the photosensitive drum 1413 by the primary transfer roller 1422, each color toner image is sequentially superimposed and primarily transferred onto the intermediate transfer belt 1421. When the intermediate transfer belt 1421 is pressed against the sheet S by the secondary transfer roller 1423, the toner image primarily transferred to the intermediate transfer belt 1421 is secondarily transferred to the sheet S.

  The belt cleaning device 1426 has a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 1421. Transfer residual toner remaining on the surface of the intermediate transfer belt 1421 after the secondary transfer is scraped off and removed by a belt cleaning blade.

  The fixing unit 160 fixes the toner image on the sheet S by heating and pressurizing the conveyed sheet S at the fixing nip portion. The fixing unit 160 passes the sheet S through a fixing nip portion formed by pressing a pair of fixing members, and applies heat from a heat source to the toner image transferred onto the sheet S, whereby the sheet A toner image is fixed on S.

  The transport unit 150 includes a paper feed unit 151, a transport mechanism 152, a paper discharge unit 153, and the like. In the three paper feed trays 151a to 151c constituting the paper feed unit 151, the paper S identified based on the basis weight, size, etc. of the paper is stored for each preset type.

  The sheets S stored in the sheet feeding trays 151a to 151c are sent out one by one from the top, and are conveyed to the image forming unit 140 by a conveyance mechanism 152 including a plurality of conveyance rollers such as a registration roller 152a. Then, in the image forming unit 140, the toner image on the intermediate transfer belt 1421 is secondarily transferred onto one side of the sheet S all at once, and a fixing process is performed in the fixing unit 160. The sheet S on which the image has been formed is discharged out of the image forming apparatus 100 by a sheet discharge unit 153 provided with a sheet discharge roller 153a.

  The resist sensor 180 is a reflective optical sensor that includes a light emitting element such as a light emitting diode and a light receiving element such as a photodiode. The registration sensor 180 is disposed at a position downstream of the photosensitive drum 1413K and upstream of the secondary transfer roller 1423 in the traveling direction of the intermediate transfer belt 1421 so as to face the outer peripheral surface of the intermediate transfer belt 1421. Has been. The registration sensor 180 includes three registration sensors 180a, 180b, and 180c. As shown in FIG. 3A, the registration sensors 180a, 180b, and 180c are disposed at predetermined intervals at both ends and the center of the intermediate transfer belt 1421 in the main scanning direction.

  In the color registration adjustment mode, the registration sensor 180 corrects color misregistration of each color on the paper S (registration correction), and forms a first resist pattern for color misregistration correction formed on the outer peripheral surface of the intermediate transfer belt 1421. 200, 201, 202, 203 are detected. In the color registration adjustment mode, for example, when the image forming apparatus 100 is turned on, or when the number of prints reaches a predetermined number, execution of the color registration adjustment mode is selected by the user via the operation unit 122. Such as when.

  The first resist patterns 200, 201, 202, and 203 are formed by the image forming unit 141Y, the image forming unit 141M, the image forming unit 141C, and the image forming unit 141K, respectively, under the control of the control unit 101.

  The resist sensor 190 is a reflective optical sensor that includes a light emitting element such as a light emitting diode and a light receiving element such as a photodiode. The registration sensor 190 is disposed at a position downstream of the driving roller 1424 and upstream of the driven roller 1425 in the traveling direction of the intermediate transfer belt 1421 so as to face the inner peripheral surface of the intermediate transfer belt 1421. Yes. The registration sensor 190 includes three registration sensors 190a, 190b, and 190c. As shown in FIGS. 3A and 4, the registration sensors 190a, 190b, and 190c are disposed at predetermined intervals at both ends and the center of the intermediate transfer belt 1421 in the main scanning direction.

  The registration sensor 190 is provided in advance on the inner peripheral surface of the intermediate transfer belt 1421 in order to correct a color shift caused by a change in the state of the intermediate transfer belt 1421 when an image forming mode for forming a color image on a sheet is executed. The second resist patterns 210, 211, 212, and 213 are detected. The change in the state of the intermediate transfer belt 1421 includes the expansion or contraction of the intermediate transfer belt 1421 due to changes in temperature and humidity in the image forming apparatus 100, and the speed of the intermediate transfer belt 1421 due to the impact of the sheet S entering the secondary transfer nip portion. Fluctuations and the like.

  The first resist pattern 200 and the second resist pattern 210 correspond in the sense that they are first detected by the resist sensors 180 and 190. The first resist pattern 201 and the second resist pattern 211 correspond in the sense that they are detected second by the resist sensors 180 and 190. The first resist pattern 202 and the first resist pattern 212 correspond in the sense that they are detected third by the resist sensors 180 and 190. The first resist pattern 203 and the second resist pattern 213 correspond in the sense that they are detected last by the resist sensors 180 and 190. The detection position of the registration sensor 180 and the detection position of the registration sensor 190 are separated by a distance L in the traveling direction of the intermediate transfer belt 1421.

  As shown in FIG. 3B, each of the first resist patterns 200 to 203 and the second resist patterns 210 to 213 includes a line segment L1 parallel to the main scanning direction of the intermediate transfer belt 1421 and the main scanning direction. On the other hand, five marks M constituted by a line segment L2 having a predetermined angle (for example, 45 °) are continuously formed in the sub-scanning direction of the intermediate transfer belt 1421.

  Note that five marks M are formed for each of the first resist patterns 200 to 203 and the second resist patterns 210 to 213 because the image forming position of each resist pattern is detected and corrected accurately. It is to do. In addition, for each of the first resist patterns 200 to 203 and the second resist patterns 210 to 213, three in the main scanning direction of the intermediate transfer belt 1421 are formed in the main scanning direction writing position shift and the sub scanning direction writing position. This is because the registration correction is executed for all of the shift, the overall magnification error, the partial magnification error, the skew, and the bow color shift.

  The control unit 101 controls the image forming units 141Y, 141M, 141C, and 141K to execute the first registration in the color registration adjustment mode for correcting the image forming conditions of the image forming units 141Y, 141M, 141C, and 141K. The patterns 200 to 203 are formed on the outer peripheral surface of the intermediate transfer belt 1421, respectively. Based on the detection results of the first resist patterns 200 to 203 by the registration sensor 180, the control unit 101 calculates the correction amount (hereinafter referred to as “color shift”) from the color shift amounts of the C color, the M color, and the Y color with respect to the K color. Correction amount ”). The control unit 101 records the calculated color misregistration correction amount in the storage unit 172.

  FIG. 5 shows how the first resist patterns 200 and 201 detect the color shift of the C color with respect to the K color. For example, after detecting the main scanning direction image 200aa of the resist pattern 200a located on the left side of the K-color first resist pattern 200 by the resist sensor 180a, the resist located on the left side of the C-color first resist pattern 201 is registered. Based on the time T1 until the registration sensor 180a detects the main scanning direction image 201aa of the pattern 201a and the traveling speed of the intermediate transfer belt 1421, the distance between the main scanning direction image 200aa and the main scanning direction image 201aa (hereinafter referred to as “actual measurement”). Distance)). By calculating the difference between this measured distance and the distance (design value) between the main scanning direction image 200aa and the main scanning direction image 201aa, the sub-scanning direction writing position shift amount between the K color image and the C color image Can be calculated.

  Also, the time T2 from when the diagonal image 200ab of the K-color resist pattern 200a is detected by the resist sensor 180a until the detection of the diagonal image 201ab of the C-color resist pattern 201a by the resist sensor 180a is detected first. Based on the relationship with the time T1, the positional relationship between the K color image and the C color image in the main scanning direction can be grasped. For example, when T1 = T2, there is no color shift in the main scanning direction. When T2 is shorter than T1 as indicated by Ta in the figure, it can be seen that the C color image is shifted to the left side from the K color image as indicated by the broken line 214 in the figure. Further, it is possible to grasp the main scanning direction writing position deviation amount between the K color image and the C color image from the time difference between T1 and Ta.

  Further, the difference (T3) between the time when the registration sensor 180a detects the main scanning direction image 200aa and the time when the registration sensor 180c detects the main scanning direction image 200ba of the resist pattern 200b located on the right side of the first resist pattern 200. ), The skew amount of the K color image can be detected. From the difference between the time when the registration sensor 180a detects the main scanning direction image 201aa and the time when the registration sensor 180c detects the main scanning direction image of the resist pattern located on the right side of the first resist pattern 201, the C color image The amount of skew can be detected. Therefore, the skew amount between the K color image and the C color image can be calculated by calculating the difference between the skew amount of the K color image and the skew amount of the C color image.

  Further, as can be understood from FIG. 7F, the time when the registration sensor 180a detects the main scanning direction image 200aa (or the time when the registration sensor 180c detects the main scanning direction image 200ba) and the registration sensor 180b The bow amount of the K-color image can be calculated from the difference from the time when the main scanning direction image of the resist pattern 200 located in the middle of one resist pattern 200 is detected. The time when the resist sensor 180a detects the main scanning direction image of the resist pattern 201 located on the left side of the first resist pattern 201 (or the main scanning direction image of the resist pattern 201 located on the right side of the first resist pattern 201 The amount of bow of the C color image can be calculated from the difference between the detected time) and the time when the registration sensor 180b detects the main scanning direction image of the resist pattern 201 located in the middle of the first resist patterns 201. . Therefore, by calculating the difference between the bow amount of the K color image and the bow amount of the C color image, the bow amount between the K color image and the C color image can be calculated.

  Further, as can be understood from FIG. 7C, compared to the ideal image formation position in the first resist pattern 200 of K color, the resist pattern located in the middle of the first resist pattern 200 is located on the right side. When the registration pattern misalignment occurs in the main scanning direction in the resist pattern, the amount of misalignment in the main scanning direction writing position of the resist pattern located on the right side can be calculated as an overall magnification error amount of K color. Compared with the ideal image formation position in the C-color first resist pattern 201, the writing position shift in the main scanning direction is caused by the resist pattern located in the middle of the first resist pattern 201 and the resist pattern located on the right side. In this case, the main scanning direction writing position deviation amount of the resist pattern located on the right side can be calculated as the C-color overall magnification error amount. Therefore, the total magnification error amount between the K color image and the C color image can be calculated by calculating the difference between the total magnification error amount of the K color image and the total magnification error amount of the C color image.

  Further, as can be understood from FIG. 7D, the main scanning is performed with the resist patterns positioned on the left side and the right side of the first resist pattern 200 as compared with the ideal image forming position in the first resist pattern 200 of K color. When the direction writing position deviation does not occur, the main scanning direction writing position deviation amount of the resist pattern located in the middle can be calculated as the K partial magnification error amount. Compared with the ideal image forming position in the first resist pattern 201 of the C color, if there is no deviation in the main scanning direction writing position in the left and right resist patterns of the first resist pattern 201, the position is in the middle The amount of misregistration in the main scanning direction of the resist pattern to be calculated can be calculated as the C partial magnification error amount. Therefore, the partial magnification error amount between the K color image and the C color image can be calculated by calculating the difference between the partial magnification error amount of the K color image and the partial magnification error amount of the C color image.

  Similarly for the M and Y colors other than the C color, the M-color and Y-color writing position deviation amounts for the K color, the sub-scanning direction writing position deviation amount, the overall magnification error amount, the partial magnification error amount, A skew amount and a bow amount can be calculated.

  After calculating the color misregistration correction amount, the control unit 101 performs image forming units 141Y, 141M, and 141C so that there is no color misregistration of the C, M, and Y colors with respect to the K color according to the calculated color misregistration correction amount. , 141K image forming conditions are corrected.

  For example, when correcting the main scanning direction writing position deviation, the main scanning direction in the image forming units 141Y, 141M, 141C, and 141K is based on the C, M, and Y main scanning direction writing position deviation amounts for the K color. The writing position of K color, C color, M color, and Y color is aligned. Alternatively, pixel-by-pixel correction processing is performed on the C, M, Y, and K image data to align the writing positions of the K, C, M, and Y colors.

  Further, when correcting the sub-scanning direction writing position deviation, the sub-scanning direction in the image forming units 141Y, 141M, 141C, and 141K is based on the sub-scanning direction writing position deviation amounts of the C, M, and Y colors with respect to the K color. The writing position of K color, C color, M color, and Y color is aligned. Alternatively, correction processing in the sub-scanning direction is performed on image data of C color, M color, Y color, and K color to align the writing positions of K color, C color, M color, and Y color.

  When correcting the skew, the exposure apparatus is adjusted by adjusting the inclination of the exposure apparatus 1411 of the image forming units 141Y, 141M, 141C, and 141K based on the skew amounts of the C, M, and Y colors with respect to the K color. The inclination degree in the scanning direction of the laser light emitted from 1411 is adjusted. Alternatively, correction processing in units of pixels is performed on the C color, M color, Y color, and K color image data so that the skew amounts of the C color, M color, and Y color with respect to the K color are eliminated.

  When correcting the bow, the mirrors (various mirrors such as a polygon mirror) provided in the exposure device 1411 of the image forming units 141Y, 141M, 141C, and 141K based on the bow amounts of the C, M, and Y colors with respect to the K color. ) To adjust the curved shape. Alternatively, correction processing in units of pixels is performed on the C color, M color, Y color, and K color image data so that the bow amounts of the C color, M color, and Y color for the K color are eliminated.

  When correcting the overall magnification error, the rotation of the polygon mirror provided in the exposure device 1411 of the image forming units 141Y, 141M, 141C, and 141K is based on the overall magnification error amounts of the C, M, and Y colors for the K color. Change the number. Alternatively, correction processing in units of pixels is performed on the C color, M color, Y color, and K color image data so that the overall magnification error amount of the C color, M color, and Y color for the K color is eliminated.

  When correcting the partial magnification error, a mirror (polygon mirror) provided in the exposure device 1411 of the image forming units 141Y, 141M, 141C, and 141K based on the partial magnification error amounts of the C, M, and Y colors for the K color. Change the tilt of the mirrors). Alternatively, correction processing in units of pixels is performed on the C color, M color, Y color, and K color image data so that the partial magnification error amounts of the C color, M color, and Y color for the K color are eliminated.

  In addition, when the color registration adjustment mode is executed, the control unit 101 records the detection results of the second resist patterns 210 to 213 by the registration sensor 190 in the storage unit 172 as reference data.

  In addition, the control unit 101 performs reference data stored in the storage unit 172 from the detection results of the second resist patterns 210 to 213 by the registration sensor 190 when the image forming mode is executed after the color registration adjustment mode is executed. Is subtracted to calculate the amount of difference between the detection result and the reference data. The difference amount represents color misregistration (belt behavior data) resulting from a change in the state of the intermediate transfer belt 1421 when the image forming mode is executed. The control unit 101 adds the calculated difference amount to the color misregistration correction amount. Then, the control unit 101 determines the formation positions of the respective color images by the image forming units 141Y, 141M, 141C, and 141K so that the color shifts of the C, M, and Y colors with respect to the K color are eliminated based on the added correction amount. to correct. This correction processing is performed in the same manner as when correcting the image forming conditions of each color image by the image forming units 141Y, 141M, 141C, and 141K based on the detection results of the first resist patterns 200 to 203 by the registration sensor 180. it can. When the image forming mode is executed, it is expected that the amount of color misregistration due to the change in the state of the intermediate transfer belt 1421 is expected to constantly change. Therefore, the calculation of the difference amount, the addition processing for the color misregistration correction amount, and the formation of each color image The process of correcting the position is repeated.

[Registration Correction Operation of Image Forming Apparatus 100]
Next, the registration correction operation of the image forming apparatus 100 in the present embodiment will be described with reference to the flowchart of FIG.

  First, the control unit 101 determines whether or not to execute the color registration adjustment mode (step S100). As a result of this determination, if the color registration adjustment mode is not executed (step S100, NO), the process proceeds to step S260.

  On the other hand, when the color registration adjustment mode is being executed (step S100, YES), the control unit 101 controls the image forming units 141Y, 141M, 141C, and 141K to transfer the first resist patterns 200 to 203 to the intermediate transfer belt. Each is formed on the outer peripheral surface of 1421 (step S120). Next, the resist sensor 180 detects the first resist patterns 200 to 203 (step S140).

  Next, the control unit 101 calculates color misregistration correction amounts for the C, M, and Y colors for the K color based on the detection result of the registration sensor 180 (step S160). Next, the control unit 101 records the calculated color misregistration correction amount in the storage unit 172 (step S180). Next, the control unit 101 corrects the image forming conditions of the image forming units 141Y, 141M, 141C, and 141K so that the C, M, and Y color shifts with respect to the K color are eliminated according to the color shift correction amount. (Step S200).

  In the present embodiment, the processes in steps S220 and S240 are performed in parallel with the processes in steps S120 to S200.

  In step S <b> 220, the registration sensor 190 detects the second resist patterns 210 to 213 provided in advance on the inner peripheral surface of the intermediate transfer belt 1421. Next, the control unit 101 records the detection results of the second resist patterns 210 to 213 by the registration sensor 190 in the storage unit 172 as reference data (step S240).

  After the processes of S200 and S240 are completed, the control unit 101 determines whether or not the image forming mode is being executed (step S260). If the result of this determination is not execution of the image forming mode (step S260, NO), the processing returns to before step S260.

  On the other hand, if the image forming mode is being executed (step S260, YES), the registration sensor 190 detects the second resist patterns 210 to 213 provided in advance on the inner peripheral surface of the intermediate transfer belt 1421 (step S280). . Next, the control unit 101 subtracts the reference data stored in the storage unit 172 from the detection results of the second resist patterns 210 to 213 by the registration sensor 190, thereby obtaining a difference amount between the detection result and the reference data. Calculate (step S300).

  Next, the control unit 101 adds the difference amount calculated in step S300 to the color misregistration correction amount (step S320). Next, the control unit 101 determines the color image formation positions by the image forming units 141Y, 141M, 141C, and 141K so that the color shifts of the C, M, and Y colors with respect to the K color are eliminated based on the added correction amount. Is corrected (step S340).

  Finally, the control unit 101 determines whether or not there is image formation for the next page (step S360). If the result of this determination is that there is no image formation for the next page (step S360, NO), the image forming apparatus 100 ends the processing in FIG. On the other hand, if there is image formation for the next page (step S360, YES), the process returns to before step S260.

[Effects of the present embodiment]
As described above in detail, in this embodiment, the second resist patterns 210 to 213 provided on the inner peripheral surface of the intermediate transfer belt 1421, the resist sensor 190 that detects the second resist patterns 210 to 213, and the color sensors. A storage unit 172 that stores the detection result of the registration sensor 190 at the time of execution of the registration correction mode as reference data, and data detected by the registration sensor 190 in the execution of the image forming mode after execution of the color registration adjustment mode; A difference amount calculation unit that calculates a difference amount from the reference data is provided, and the control unit 101 performs correction by adding the difference amount to the color misregistration correction amount when executing the image forming mode after executing the color registration correction mode. Based on the amount, the formation positions of the respective color images by the plurality of image forming units 141Y to 141K are corrected. Color on paper - to form an image.

  According to the present embodiment configured as described above, in the image forming mode, the second resist patterns 210, 211, 212, formed on the inner peripheral surface of the intermediate transfer belt 1421 that is a surface on which a color image is not formed. A color shift (difference Z) due to a change in the state of the intermediate transfer belt 1421 can be detected from the detection result of 213, and registration correction can be performed in consideration of the color shift. Therefore, there is no need to interrupt the print job. As described above, it is possible to correct the color misregistration caused by the state change of the intermediate transfer belt 1421 in the image forming mode.

[Modification]
In the above embodiment, when the difference amount calculated in the image forming mode becomes larger than a predetermined value, the color image forming process may be stopped and the color registration adjustment mode may be executed. With this configuration, even when color misregistration due to a factor (disturbance) other than a change in the state of the intermediate transfer belt 1421 occurs in the image forming mode, it is possible to quickly perform registration correction in consideration of the factor.

  In the above embodiment, the registration sensor 190 corresponds to the distance L between the detection position of the registration sensor 180 and the detection position of the registration sensor 190 in the traveling direction of the intermediate transfer belt 1421 (see FIG. 3). The detection timings of the second resist patterns 210, 211, 212, and 213 may be changed so that the detection timing of 180 and the detection timing of the registration sensor 190 are the same. With this configuration, when printing on paper, the registration sensor 180 is used as if the color shift caused by the state change of the intermediate transfer belt 1421 is detected, and the registration correction considering the color shift is further performed. It can be performed with high accuracy.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 102 CPU
103 ROM
104 RAM
DESCRIPTION OF SYMBOLS 110 Image reading part 120 Operation display part 121 Display part 122 Operation part 130 Image processing part 140 Image formation part 150 Conveyance part 160 Fixing part 172 Memory | storage part 180,180a, 180b, 180c, 190,190a, 190b, 190c Registration sensor 141Y, 141M, 141C, 141K Image forming unit 200, 201, 202, 203 First resist pattern 210, 211, 212, 213 Second resist pattern 1421 Intermediate transfer belt

Claims (4)

A plurality of image forming units for forming toner images of respective colors;
An intermediate transfer belt on which a toner image of each color formed by the plurality of image forming units is transferred onto an outer peripheral surface to form a superimposed color image;
A first detector for detecting a first resist pattern formed on the outer peripheral surface of the intermediate transfer belt;
A correction amount calculation unit that calculates a color misregistration correction amount based on a detection result of the first detection unit;
A first storage unit for storing the calculated color misregistration correction amount;
A first resist pattern is formed on the outer peripheral surface of the intermediate transfer belt, the first resist pattern is detected by the first detection unit, and the color misregistration correction amount is calculated based on the detection result of the first detection unit. The color registration adjustment mode for correcting the image forming conditions of the plurality of image forming units based on the calculated color misregistration correction amount and the color misregistration correction amount stored in the first storage unit. A control unit that controls execution of an image forming mode in which a color image is formed on a sheet by correcting the formation position of each color image by the plurality of image forming units;
In an image forming apparatus having
A second resist pattern provided in advance on the inner peripheral surface of the intermediate transfer belt;
A second detector for detecting the second resist pattern;
A second storage unit that stores, as reference data, a detection result of the second detection unit during execution of the color registration adjustment mode;
A difference amount calculation unit that calculates a difference amount between the data detected by the second detection unit and the reference data in the execution of the image forming mode after the color registration adjustment mode is executed;
The control unit, when executing the image forming mode after executing the color registration adjustment mode, based on a correction amount obtained by adding the difference amount to the color misregistration correction amount, each color by the plurality of image forming units. An image forming apparatus, wherein a color image is formed on a sheet by correcting the image forming position.   The image forming apparatus according to claim 1, wherein a plurality of the second resist patterns are formed in a main scanning direction of the intermediate transfer belt.   The image forming apparatus according to claim 1, wherein the control unit executes the color registration adjustment mode when the difference amount is larger than a predetermined value.   A plurality of the second resist patterns are formed in the main scanning direction of the intermediate transfer belt, and the detection unit detects the detection position of the first detection unit and the detection of the second detection unit in the sub-scanning direction of the intermediate transfer belt. The detection timing of the second resist pattern is changed according to the distance to the position so that the detection timing of the first detection unit and the detection timing of the second detection unit become the same timing. The image forming apparatus according to claim 1.

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