Image forming apparatus and program

Abstract

To correct a color shift by forming an image of a patch for correcting the color shift on a sheet so that the color shift is hardly conspicuous.SOLUTION: An acquiring unit (controller 101) configured to acquire a read image obtained by reading an image forming surface of the recording media PM on which a color image is formed, a controller 101 configured to form an image of a registration patch P3 outside a job image forming region of the recording media PM, and a correcting unit (controller 101) configured to correct an image forming position in the image forming unit 151 based on the read image including the registration patch P3, the registration patch P3 including a reference color patch P31 and at least one measuring target color patch formed of a color material of each measuring target color, the reference color patch P31 and the measuring object color patch do not overlap each other at least in the main scanning direction at their respective ends, and the correction part performs correction on the basis of the relative positions of the reference color patch and the measuring object color patch.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, electrophotographic image forming devices are known in which an electrostatic latent image formed on a photosensitive member is developed with toner to form a toner image, the formed toner image is transferred to an intermediate transfer member (primary transfer), the toner image transferred to the intermediate transfer member is transferred to paper (secondary transfer), and the paper is heated and pressurized to form an image on the paper.Color image forming devices use toners of multiple colors, and it is necessary to accurately overlay the toner images formed on the photosensitive members of each color on the intermediate transfer member. However, in such image forming devices, for example, when the temperature of the machine body rises due to continuous operation, the transport speed of the intermediate transfer body increases, which can cause the transfer position of the toner image on the paper to shift, resulting in color misalignment.

[0003] In relation to this, Patent Document 1 describes an image forming apparatus in which the secondary transfer unit is set to a pressed state when a main scanning correction process is performed as color registration correction, and the secondary transfer unit is set to a separated state when image position correction for components other than the main scanning direction is performed as color registration correction. Furthermore, Patent Document 2 describes an image forming device that changes the interval at which paper is transported and also changes the position of the registration marks for detecting color shift and the transfer paper area where the image is formed, based on the fluctuation period of color shift calculated based on the rotational distance of the intermediate transfer body and each photosensitive drum. Furthermore, Patent Document 3 describes an image forming apparatus that reads formed color registration marks and calculates and corrects the amount of correction based on the intervals between a reference color mark and marks of other colors. Furthermore, Patent Document 4 describes a color image forming apparatus that is capable of detecting registration even during image formation, and that is capable of performing registration correction with high precision even when the printing rate at the time of registration detection differs from the printing rate at the time of registration correction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-208154 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-31739 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-322722 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-102168 Summary of the Invention [Problem to be solved by the invention]

[0005] However, color registration marks (patches) have good visibility when color misregistration occurs, but there is a problem in that color misregistration that is at a non-defective level is easily noticeable. However, the inventions described in Patent Documents 1 to 4 do not describe any specific means for making the color shift of the patches less noticeable.

[0006] The present invention has been made in consideration of such problems, and aims to provide an image forming apparatus that can correct color shift by forming patches on paper for color shift correction, in which the occurrence of color shift is less noticeable. [Means for solving the problem]

[0007] In order to solve the above problem, the image forming apparatus of the invention described in claim 1 comprises: An image forming apparatus comprising a plurality of image forming units that form images using color materials based on image data, and that forms a color image on a recording medium by superimposing images of each color formed by the respective image forming units, an intermediate transfer member for forming a color image by superimposing the images of the respective colors formed by the image forming units; a transfer unit that transfers the color image formed on the intermediate transfer body onto the recording medium; a detection unit for detecting a resist patch image formed on the intermediate transfer body; an acquisition unit that acquires a read image by reading the image forming surface of the recording medium on which the color image is formed; a control unit that forms an image of the resist patch outside a job image forming area of ​​the recording medium; a correction unit that corrects image forming positions in the plurality of image forming units based on the read image including the registration patch acquired by the acquisition unit; a setting unit that sets reference values ​​for image forming positions in the plurality of image forming units based on the detection results of the detection unit; Equipped with the resist patch has a reference color patch formed by a color material of a reference color and at least one measurement target color patch formed by a color material of each measurement target color, and the reference color patch and the measurement target color patch do not overlap each other at least in the main scanning direction at their respective ends; the control unit causes the resist patch to be image-formed on the intermediate transfer body before forming an image related to a job; The correction unit calculates a correction value based on the reference value and the relative positions of the reference color patch and the measurement target color patch in the read image, and performs correction. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an image forming apparatus that can correct color misregistration by forming patch images for correcting color misregistration on paper, in which the occurrence of color misregistration is less noticeable. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration of an image forming apparatus according to a first embodiment. [Figure 2A] 3A and 3B are diagrams illustrating an example of a recording medium on which a job image and a patch image are formed in the first embodiment. [Figure 2B]FIG. 3 is a diagram illustrating an example of a gradation patch according to the first embodiment. [Figure 2C] FIG. 3 is a diagram illustrating an example of a gradation patch according to the first embodiment. [Figure 2D] 3A to 3C are diagrams illustrating examples of resist patches according to the first embodiment. [Figure 2E] 3A to 3C are diagrams illustrating examples of resist patches according to the first embodiment. [Figure 3] 5 is a flowchart showing the flow of image forming processing in the first embodiment. [Figure 4] 10 is a flowchart showing the flow of pre-job reference value setting processing according to the first embodiment. [Figure 5] 5 is a flowchart showing the flow of a registration correction process according to the first embodiment. [Figure 6A] FIG. 3 is a diagram showing an example of a read image according to the first embodiment. [Figure 6B] FIG. 4 is a diagram showing an example of a read image after gradation processing in the first embodiment. [Figure 6C] FIG. 10 is a diagram illustrating an example of a color separation image of R in the first embodiment. [Figure 6D] FIG. 10 is a diagram showing an example of a color separation image of G in the first embodiment. [Figure 6E] FIG. 10 is a diagram illustrating an example of a color separation image of B in the first embodiment. [Figure 6F] FIG. 3 is a diagram showing an example of a primary color candidate area image according to the first embodiment. [Figure 6G] FIG. 3 is a diagram illustrating an example of a primary color region image according to the first embodiment. [Figure 7A] 3A to 3C are diagrams illustrating examples of resist patches according to the first embodiment. [Figure 7B] 3A to 3C are diagrams illustrating examples of resist patches according to the first embodiment. [Figure 7C] 3A to 3C are diagrams illustrating examples of resist patches according to the first embodiment. [Figure 8] 3A and 3B are diagrams illustrating an example of a recording medium on which a job image, a patch, and an eye mark are image-formed according to the first embodiment. [Figure 9] 3A and 3B are diagrams illustrating an example of a recording medium on which a job image and a patch image are formed in the first embodiment. [Figure 10] 5A and 5B are diagrams illustrating examples of deviation amounts from registration reference values ​​in color misregistration according to the first embodiment and their regression equations. [Figure 11] FIG. 10 is a diagram illustrating a configuration of an image forming unit according to a second embodiment. [Figure 12] 10A and 10B are diagrams illustrating examples of resist patches according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the scope of the invention is not limited to the illustrated examples.

[0011] First Embodiment [Configuration of Image Forming Apparatus] First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described. Fig. 1 is a diagram showing the main configuration of an image forming apparatus 100. As shown in Fig. 1, the image forming apparatus 100 is an apparatus that continuously forms images on a roll-shaped recording medium PM.

[0012] As shown in FIG. 1, the image forming apparatus 100 is configured to include a control unit 101, a communication unit 102, an operation display unit 103, a memory unit 104, a paper feed unit 105, a conveying unit 106, a winding unit 107, an image forming unit 150, a second image scanner 160 which is a detection unit, a fixing unit 170, a first image scanner 180 which is a reading unit, and the like.

[0013] The control unit 101 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The CPU of the control unit 101 reads a program corresponding to the processing content from the ROM, loads it into the RAM, and centrally controls the operations of each unit of the image forming apparatus 100 in cooperation with the loaded program.

[0014] The communication unit 102 is configured by a communication control card such as a LAN (Local Area Network) card, and transmits and receives various data to and from external devices connected to a communication network such as a LAN or WAN (Wide Area Network).

[0015] The operation display unit 103 includes a display unit 103a such as a liquid crystal display or an organic EL display, and an input unit 103b configured with various operation keys, a touch panel overlaid on the screen of the display unit 103a, a numeric keypad, etc. The operation display unit 103 displays various information on the display unit 103a, and converts user input operations to the input unit 103b into operation signals and outputs the signals to the control unit 101.

[0016] The storage unit 104 is configured by, for example, a non-volatile semiconductor memory (so-called flash memory), a hard disk drive, etc. The storage unit 104 stores various data including various setting information related to the image forming apparatus 100, job information (job setting information and job image data), etc. The storage unit 104 also stores image data of a toner consumption patch P1, image data of a gradation patch P2, and image data of a registration patch P3, which will be described later. The storage unit 104 also stores a pre-job registration reference value that is set in a pre-job reference value setting process, which will be described later. The storage unit 104 also stores an in-job registration reference value that is set in the first registration correction process (described later) after the start of image formation.

[0017] The paper feed unit 105 includes a paper feed roll 105a and a paper feed roller 105b. A continuous recording medium PM, such as a roll of film, roll paper, or fabric, is wound around the paper feed roll 105a. The paper feed roll 105a rotates at a speed corresponding to the conveyance speed of the recording medium PM in accordance with instructions from the control unit 101, and sends the recording medium PM to the conveyance path. The paper feed roller 105b stretches the recording medium PM with an appropriate tension while sending the recording medium PM toward the image forming unit 150. Note that the recording medium PM does not have to be a continuous medium that can be rolled up; in that case, the individual recording media PM may be fed and discharged in order. The conveying unit 106 has a conveying path and a plurality of conveying roller pairs such as registration roller pairs, and conveys the recording medium PM fed from the paper feeding unit 105 within the image forming apparatus 100. The winding unit 107 has a winding roll 107a and a winding roller 107b. The winding roller 107b sends out the recording medium PM on which an image has been formed toward the winding roll 107a. The winding roll 107a rotates at a speed corresponding to the conveying speed of the recording medium PM in accordance with instructions from the control unit 101, and winds up the recording medium PM on which the image has been formed.

[0018] The image forming unit 150 prints an image on a recording medium PM based on the job setting information and image data, and generates a printed matter. The image forming section 150 includes an image forming unit 151, a roller 152, an intermediate transfer belt 153 as an intermediate transfer member, a secondary transfer roller 154, and the like. In this embodiment, the image forming section 150 has image forming units 151 for each color: Y (yellow), M (magenta), C (cyan), K (black), and S (spot color; white in this embodiment), and is capable of printing using white toner in addition to images using the usual Y, M, C, and K toners. In the image forming section 150, toner images of each color are formed by the image forming units 151 and sequentially transferred onto the intermediate transfer belt 153, where the five color toner images are superimposed. The intermediate transfer belt 153 is an endless belt wound around multiple rollers, and rotates in the direction of the arrow shown in Figure 1 in accordance with the rotation of each roller. Secondary transfer roller 154 transfers the toner image on intermediate transfer belt 153 onto recording medium PM fed from paper feed unit 105. More specifically, the recording medium PM and intermediate transfer belt 153 are sandwiched in a transfer nip N formed by secondary transfer roller 154 being pressed against roller 152, and when a predetermined transfer voltage is applied to secondary transfer roller 154, the toner forming the toner image on secondary transfer roller 154 is attracted to the recording medium PM and transferred to the recording medium PM, thereby forming (printing) an image. Roller 152 and secondary transfer roller 154 form a transfer unit.

[0019] The secondary transfer roller 154 is configured to be separable from the roller 152 . In a pre-job reference value setting process described later, the secondary transfer roller 154 is separated from the roller 152, and the toner image on the intermediate transfer belt 153 is transported without being transferred to the recording medium PM. In this case, the second image scanner 160 detects the toner image transported without being transferred to the recording medium PM downstream of the transfer nip portion N. The second image scanner 160 also outputs the detection result to the control unit 101. After being detected by the second image scanner 160, the toner image is removed from the intermediate transfer belt by a cleaning unit (not shown). The second image scanner 160 is configured by, for example, a color scanner.

[0020] The fixing unit 170 fixes the toner image printed on the recording medium PM to the recording medium PM using heat and pressure. In FIG. 1, the image forming unit 150 is illustrated as an image forming unit of a so-called electrophotographic type, but the printing type is not limited to this, and the image forming unit may be of another printing type, such as an inkjet type, in which the image formation position shifts when the temperature inside the image forming apparatus 100 rises.

[0021] The first image scanner 180 reads the image-formed surface of the recording medium PM that has been printed by the image forming unit 150 and fixed by the fixing unit 170, and outputs the read image data (read image) to the control unit 101. The first image scanner 180 is configured, for example, by a color scanner. The first image scanner 180 is disposed downstream of the fixing unit 170, and is configured to read the image while the recording medium PM is being transported.

[0022] The control unit 101 also acquires a read image obtained by reading the image forming surface of the recording medium PM on which a color image is formed. Here, the control unit 101 functions as an acquisition unit. Furthermore, the control unit 101 controls the image forming unit 150 to form an image of a resist patch P3 outside a job image forming area (to be described later) on the recording medium PM. Here, the control unit 101 functions as a control unit. Furthermore, the control unit 101 corrects the image forming positions in the multiple image forming units 151 based on the read image including the registration patch P3 read by the first image scanner 180. Here, the control unit 101 functions as a correction unit. Furthermore, the control unit 101 sets a reference value (pre-job registration reference value) for the image forming position in the multiple image forming units 151 based on the detection result by the second image scanner 160. Here, the control unit 101 functions as a setting unit. The control unit 101 also identifies the type of the gradation patch P2 based on the form of each of the measurement target color patches, which will be described later. Here, the control unit 101 functions as an identification unit.

[0023] Here, the toner consumption patch P1, gradation patch P2, and registration patch P3 that are formed on the recording medium PM by the control unit 101 controlling the image forming unit 150 will be described. Figure 2A is a diagram showing an example of a recording medium PM on which a job image, a toner consumption patch P1, gradation patches P2a and P2b (when gradation patches P2a and P2b are not distinguished, they will be referred to as gradation patch P2 below) for correcting the density gradation in the image to be formed, and resist patches P3a to P3d (when gradation patches P3a to P3d are not distinguished, they will be referred to as resist patch P3 below) are image-formed. 2A, area A is the job image forming area where the job image is formed. Area B is outside the job image forming area on both sides of the job image forming area in the main scanning direction, and is the area where toner consumption patch P1, gradation patch P2, and registration patch P3 are image-formed. By forming the toner consumption patch P1, gradation patch P2, and registration patch P3 in area B, it is possible to ensure a larger area A, which is the job image forming area. The toner consumption patch P1 is a patch for consuming old toner when printing a job that consumes a small amount of toner.

[0024] 2B shows gradation patch P2a. Gradation patch P2a has a boundary line P21 that indicates the leading edge of gradation patch P2 in the transport direction of recording medium PM and is a detection mark for detecting gradation patch P2a, a boundary line P22 that indicates the boundary between the first gradation patch portion P25 and the second gradation patch portion P24, a boundary line P23 that indicates the trailing edge of gradation patch P2 in the transport direction of recording medium PM and is a detection mark for detecting gradation patch P2a, the first gradation patch portion P25, and the second gradation patch portion P24. The first gradation patch portion P25 is made up of a plurality of color gradation patches in which the gradation values ​​of Y, M, C, and K are varied in stages. The second gradation patch portion P24 is made up of a plurality of color gradation patches each having a secondary color or tertiary color made up of a plurality of color toners among Y, M, C, and K, with gradation values ​​that are gradually changed. 2C shows gradation patch P2b. Like gradation patch P2a, gradation patch P2b has boundaries P21 to P23, a first gradation patch portion P25, and a second gradation patch portion P24, but the positions of the first gradation patch portion P25 and the second gradation patch portion P24 are opposite to those of gradation patch P2a, with boundary line P22 sandwiched between them.

[0025] Figure 2D shows identical resist patches P3a and P3c, and Figure 2E shows identical resist patches P3b and P3d. The resist patch P3 has a reference color patch P31 and a measurement target color patch portion P33. The measurement target color patch portion P33 is disposed at a predetermined distance from the reference color patch P31. Here, the reference color is, for example, K, and the measurement target colors are Y, M, and C. The measurement target color patch section 33 has at least one patch for each measurement target color. In the examples shown in Figures 2D and 2E, the measurement target color patch section 33 has two patches for each measurement target color. If there is only one patch for each measurement target color, the accuracy of calculating the correction value in the registration correction process described below may be low, so it is preferable that there are two or more patches for each measurement target color. Furthermore, if there are too many patches for each measurement target color, it may be impossible to distinguish between patches and noise in the registration correction process, so it is preferable that the number of patches for each measurement target color is enough to enable the patches to be distinguished from noise.

[0026] Furthermore, the patches in the measurement target color patch section 33 differ from one another in size and shape. Furthermore, the positions of the patch ends of each patch in the measurement target color patch section 33 are configured to be different in the X axis (main scanning) and Y axis (sub-scanning) directions shown in FIGS. 2D and 2E. With the resist patch P3 configured in this way, when color shift occurs in the measurement target color patch portion 33, the color shift is less noticeable and the user is less likely to notice the occurrence of color shift. Therefore, when color shift at a non-defective level occurs, the user can be prevented from noticing the occurrence of color shift. Furthermore, in each patch of the measurement target color patch unit 33, the distance between the patch ends of patches of the same color, at least in the Y-axis direction, is a distance that is not an integer multiple of the reading resolution of the first image scanner 180. Furthermore, on the side of the reference color patch P31 in the X-axis direction, a step is provided in the Y-axis direction that is smaller than the reading resolution of the first image scanner 180. This allows the interpolation resolution to be improved and the registration patch P3 to be read accurately, even if the reading resolution of the first image scanner 180 is not sufficient to read the registration patch P3. Furthermore, the minimum line width of the reference color patch P31 and the measurement color patch P33 is 10 pixels or more at 600 dpi (dots per inch). This allows the first image scanner 180 to accurately read the outlines of the reference color patch P31 and the measurement color patch P33, even if the image formation characteristics of the image forming unit 150 change due to environmental changes or other factors. The above minimum line width is a preferred example based on the printing characteristics of a typical electrophotographic system. It can be appropriately set depending on the characteristics of various image forming devices and the size of the area available for image formation on the resist patch P3 (image formation area). For example, when the surface quality of the recording medium is rough, such as in textile printing, it is preferable to set the minimum line width to a larger value. However, when printing with an image forming device designed for high-quality printing, such as for artistic photo albums, a smaller minimum line width may be set. There is no particular upper limit to the minimum line width; it may be set appropriately within the image formation area of ​​the resist patch P3 for design purposes.

[0027] Returning to FIG. 2A, enlarged sections 1 to 4 will be described. The enlarged portion 1 shows a portion of the resist patch P3a and the gradation patch P2a. The resist patch P3a is arranged so that the upward direction of the Y axis shown in FIG. 2D coincides with the direction opposite to the conveyance direction of the recording medium PM. The reference color patch P31 and the boundary line P21 are also arranged so that they overlap. A portion of the resist patch P3b and the gradation patch P2a is shown in enlarged portion 2. The resist patch P3b is arranged so that the upward direction of the Y axis shown in FIG. 2E coincides with the conveyance direction of the recording medium PM. The resist patch P3b is also arranged so that the reference color patch P31 and the boundary line P23 overlap. The enlarged portion 3 shows a portion of the resist patch P3c and the gradation patch P2b. The resist patch P3c is arranged so that the upward direction of the Y axis shown in FIG. 2D coincides with the direction opposite to the conveyance direction of the recording medium PM. The resist patch P3c is also arranged so that the reference color patch P31 and the boundary line P21 overlap. The enlarged portion 4 shows a portion of the resist patch P3d and the gradation patch P2b. The resist patch P3d is arranged so that the upward direction of the Y axis shown in FIG. 2E coincides with the conveyance direction of the recording medium PM. The resist patch P3d is also arranged so that the reference color patch P31 and the boundary line P23 overlap. In other words, the reference color patch P31 also serves as a detection mark in the gradation patch. By arranging the reference color patch P31 so that it overlaps with the boundary line P21 or P23 in this way, the area in which the gradation patch P2 and the registration patch P3 are image-formed can be made smaller. Furthermore, by arranging identical resist patches P3a and P3c at the leading edge of the gradation patch P2 in the transport direction of the recording medium PM, and identical resist patches P3b and P3d at the trailing edge of the gradation patch P2 in the transport direction of the recording medium PM, the control unit 101 can identify the leading and trailing edges of the gradation patch P2 in the transport direction of the recording medium PM based on the read image including the resist patch P3.

[0028] 2A indicates the reading range of the first image scanner 180. As shown in Fig. 2A, the gradation patch P2 and the registration patch P3 are formed as images on the recording medium PM within a range that is surely within the range IS.

[0029] [Operation of Image Forming Apparatus] Next, the operation of image forming apparatus 100 will be described. 3 shows a flowchart of the image forming process executed by the image forming apparatus 100. The image forming process is executed by a program stored in the control unit 101 of the image forming apparatus 100.

[0030] In the image forming process, first, the control unit 101 executes a pre-job reference value setting process (step S1). FIG. 4 shows a flowchart of the pre-job reference value setting process.

[0031] In the pre-job reference value setting process, first, the control unit 101 separates the secondary transfer roller 154 from the roller 152 (step S11). Next, the control unit 101 acquires image data of the resist patch P3 from the memory unit 104, controls the image forming unit 150 to form an image of the resist patch P3 (step S12), and transports the toner image of the resist patch P3 formed on the intermediate transfer belt 153. Next, the control unit 101 controls the second image scanner 160 to detect the toner image of the registration patch P3 and receives the detection result (step S13). Next, the control unit 101 sets the detection result received in step S13 as a pre-job registration reference value by storing it in the storage unit 104 (step S14). Next, the control unit 101 presses the secondary transfer roller 154 against the roller 152 (step S15), and ends this process. In addition, instead of the second image scanner 160, a reflective optical sensor incorporating a light-emitting element such as a light-emitting diode and a light-receiving element such as a photodiode may be used to form an image of a patch that can be detected by the optical sensor instead of the resist patch P3, and set the pre-job resist reference value.

[0032] Returning to the description of the image forming process shown in FIG. Next, the control unit 101 acquires the image data of the job, the image data of the toner consumption patch P1, the image data of the gradation patch P2, and the image data of the resist patch P3 from the memory unit 104, and controls the image forming unit 150 to form the image of the job and each patch on the recording medium PM (step S2). Next, the control unit 101 determines whether or not the registration patch P3 has been detected based on the image read on the recording medium PM by the first image scanner 180 (step S3). If the resist patch P3 is not detected (step S3; NO), the control unit 101 moves the process to step S3. Furthermore, if the registration patch P3 is detected (step S3; YES), the control unit 101 executes the registration correction process (step S4). FIG. 5 shows a flowchart of the registration correction process.

[0033] In the registration correction process, first, the control unit 101 performs gradation conversion on the read image data read by the first image scanner 180 (step S41). Specifically, the control unit 101 performs gradation conversion on the read image as shown in Fig. 6A so that the white color of the recording medium PM becomes the brightest color in RGB (Red, Green, Blue) information and the high-density portion of the registration patch P3 becomes the darkest color in the RGB information. Fig. 6B shows an example of the gradation-converted read image. Next, the control unit 101 separates the scanned image data that has been tone-converted in step S41 into R, G, and B filters to generate color-separated image data (step S42). Fig. 6C shows an R color-separated image. Fig. 6D shows a G color-separated image. Fig. 6E shows a B color-separated image. Next, the control unit 101 extracts primary color candidate regions from the color separation image data generated in step S42. For example, the control unit 101 extracts a region with high density in all of the R, G, and B separation image data as a K (black) candidate region. The control unit 101 also extracts a region with high density only in the B separation image data as a Y (yellow) candidate region. The control unit 101 also extracts a region with high density only in the G separation image data as an M (magenta) candidate region. The control unit 101 also extracts a region with high density only in the R separation image data as a C (cyan) candidate region. The control unit 101 then generates primary color candidate region image data from each extraction result (step S43). FIG. 6F shows an example of a primary color candidate region image. The method for generating primary color candidate area image data is not limited to the above method. For example, an image forming apparatus having more colors of toner, such as six colors, may have orange and blue toners in addition to YMCK toners. In this case, it may be difficult to separate toner images with similar hues using only the high density criterion of a single color in the RGB separation image data. In such a case, in addition to determining that a specific color among the RGB has the highest density, the hue angle may be calculated from the RGB separation image data to identify the toner colors that make up the patch. Next, the control unit 101 performs morphology processing on the primary color candidate region image data generated in step S43 to remove noise and generate primary color region image data (step S44). Fig. 6G shows an example of the primary color region image.

[0034] Next, the control unit 101 calculates the position of each measurement target color patch relative to the position of the reference color patch P31 of the registration patch P3 in the primary color region image data generated in step S44 (step S45). Specifically, when there are two patches for each measurement target color, the control unit 101 calculates the center of gravity of each patch, and then calculates the center of gravity of two patches of the same color based on the calculated center of gravity. The control unit 101 also calculates the center of gravity of the reference color patch P31. Then, the control unit 101 calculates the relative positions of the centers of gravity of the two patches of the same color relative to the center of gravity of the reference color patch P31. Here, the control unit 101 sets the calculated value as the in-job registration reference value by storing it in the storage unit 104 during the first registration correction process after the start of image formation. Here, the control unit 101 may calculate the relative position between the area of ​​the reference color patch P31 and the center of gravity of two patches of the same color. The position of the area of ​​the reference color patch P31 is calculated by identifying the position of the edge of the side of the reference color patch P31 in the X-axis direction by edge extraction. Next, the control unit 101 calculates a registration correction value from the difference between the pre-job registration reference value set in the pre-job reference value setting process and the value calculated in step S45 (step S46). Next, the control unit 101 corrects the image data of the job based on the registration correction value calculated in step S46, and forms the image of the corrected job (step S47), thereby completing this process.

[0035] In this way, since the center of gravity of each patch is calculated as the patch position of the measurement target color, there is a degree of freedom in the shape of each patch. Therefore, patch shapes that make color shifts less noticeable can be designed and used for registration correction. Furthermore, since there is a degree of freedom in the layout of patches of the measurement target color, predetermined information may be added to the layout of the patch. The predetermined information may be, for example, information indicating the type of gradation patch P2 adjacent to registration patch P3 (such as identification information for YMCK single color, RGB3C standard intermediate color, or other user-defined intermediate color). This allows the control unit 101 to identify the type of gradation patch P2 based on the scanned image including registration patch P3. 7A to 7C show examples of resist patches P3 having patches with different shapes from those shown in FIGS. 2D and 2E. The example shown in FIG. 7A differs from the examples shown in FIGS. 2D and 2E in that the reference color patch P31 is arranged below the measurement target color patch portion P33 in the Y-axis direction. In the example shown in FIG. 7B, the shape of each measurement target color patch is not rectangular as in FIGS. 2D and 2E, but is composed of curved lines. The example shown in FIG. 7C differs from the examples shown in FIGS. 2D and 2E in that the measurement target color patch portion P33 is also arranged above the reference color patch P31 in the Y-axis direction.

[0036] Returning to the description of the image forming process shown in FIG. Next, the control unit 101 determines whether or not the image formation of the job is completed (step S5). If the image formation of the job is completed (step S5; YES), the control unit 101 ends this process. If the image formation of the job is not completed (step S5; NO), the control unit 101 shifts the process to step S3. In step S3, if the registration patch P3 is detected, the control unit 101 executes the second registration correction process after the start of image formation (step S4). In step S46 of the second registration correction process after the start of image formation, the control unit 101 calculates a registration correction value by adding together the difference between the pre-job registration reference value and the value calculated in step S45, and the difference between the in-job registration reference value set in the first registration correction process after the start of image formation and the value calculated in step S45. This is also true for the third and subsequent registration correction processes after the start of image formation.

[0037] (Variation 1) Next, a first modification of the first embodiment will be described. The following description will focus on the differences from the first embodiment. The configuration of the image forming apparatus 100 of this modified example is the same as that of the image forming apparatus 100 of the first embodiment.

[0038] In the image forming process of this modified example, the control unit 101 controls the image forming unit 150 to form an image of the job, an image of the toner consumption patch P1, an image of the gradation patch P2, an image of the registration patch P3, and an eye mark MK on the recording medium PM. The eye mark MK is a mark that indicates the image forming position of the job image. FIG. 8 is a diagram showing an example of a recording medium PM on which a job image, a toner consumption patch P1, gradation patches P2a and P2b, registration patches P3a to P3d, and an eye mark MK are formed. 8, area A is the job image forming area where the job image is formed. Area B is outside the job image forming area on one side in the main scanning direction from the job image forming area, and is the area where the toner consumption patch P1, gradation patch P2, and registration patch P3 are image-formed. Area C is outside the job image forming area on the opposite side in the main scanning direction from area B, and is the area where the eye mark MK is image-formed. In the example shown in FIG. 8, the same processing as the image forming processing in the first embodiment can be performed to perform the registration correction.

[0039] (Variation 2) Next, a second modification of the first embodiment will be described. The following description will focus on the differences from Modification 1 of the first embodiment. The configuration of image forming apparatus 100 of this modification is the same as that of image forming apparatus 100 of the first embodiment.

[0040] In the image forming process of this modified example, the control unit 101 controls the image forming unit 150 to form an image of the job, an image of the toner consumption patch P1, an image of the gradation patch P2, an image of the resist patch P3, and an image of the resist patch P3m that replaces the eye mark on the recording medium PM. FIG. 9 is a diagram showing an example of a recording medium PM on which an image of a job, a toner consumption patch P1, a gradation patch P2a, registration patches P3a and P3b, and a registration patch P3m substituting an eye mark are formed. 9, area A is the job image forming area where the job image is formed. Area B is outside the job image forming area on one side in the main scanning direction from the job image forming area, and is the area where the toner consumption patch P1, gradation patch P2, and registration patches P3a and P3b are formed. Area C is outside the job image forming area on the opposite side in the main scanning direction from area B, and is the area where the registration patch P3m that replaces the eye mark is formed. 9, the same process as the image forming process of the first embodiment can be performed to carry out the registration correction. In this case, the registration correction process may be carried out using the registration patch P3m. In this way, by forming the resist patch P3m as an image in place of the eye mark, it is possible to reduce the area for forming the images of various patches and effectively utilize the paper width of the recording medium PM. Also, here, only the resist patch P3m is formed as an image in place of the eye mark, but for example, the gradation patch P2 may be formed as an image at the same interval as the eye mark and used as an image in place of the eye mark.

[0041] (Variation 3) Next, a third modification of the first embodiment will be described. The following description will focus on the differences from the first embodiment. The configuration of the image forming apparatus 100 of this modified example is the same as that of the image forming apparatus 100 of the first embodiment.

[0042] In order to perform resist correction when the color of the recording medium PM is white, if a white patch of S (special color) is image-formed on the recording medium PM as the resist patch P3, a white patch will be image-formed on the white recording medium PM, and since it is difficult to read the area in the read image where the white patch is image-formed, resist correction with white toner is difficult. Therefore, in the registration correction process of this modified example, the control unit 101 calculates the deviation amount (correction value) from the pre-job registration reference value for a color material such as white toner that has lower detectability than a predetermined standard, from the deviation amount from the pre-job registration reference value for toners of other colors. The predetermined standard is the degree to which a patch can be read in the scanned image. As in the first embodiment described above, the registration correction value in the registration correction process from the second time onwards after the start of image formation is calculated by adding together the deviation amount from the pre-job registration reference value and the deviation amount from the in-job registration reference value. Specifically, the control unit 101 calculates the deviation amounts from the pre-job registration reference values ​​(or in-job registration reference values) for Y, M, and C, and calculates a regression equation D as shown in FIG. 10 based on these values. In the example shown in FIG. 10, the horizontal axis represents the distance between the image forming unit 151 for the reference color K and the image forming unit 151 for each measurement target color, and the vertical axis represents the deviation amount from the pre-job registration reference value (or in-job registration reference value). The control unit 101 then calculates the deviation amount from the pre-job registration reference value (or in-job registration reference value) for white toner from the regression equation D as Sa shown in FIG. 10. This is because color misregistration during image formation occurs mainly due to expansion and contraction of rotating bodies such as the roller 152 caused by temperature changes, and therefore the deviation amount from the pre-job registration reference value (or in-job registration reference value) is proportional to the distance between the image forming unit 151 for the reference color and the image forming unit 151 for the measurement target color. In addition, in an image forming device having toner of more colors (e.g., six colors), the resist patch P3 may be composed of, for example, four colors of YMCK, and the amount of deviation for the other colors (e.g., two of the six colors) may be calculated based on the mutual distance between the image forming units 151 of the other colors and the four colors of YMCK.

[0043] Second Embodiment Fig. 11 shows the image forming section 150 provided in the image forming apparatus 100 of this embodiment. In the image forming unit 151a of this embodiment provided in the image forming section 150, the order in which toner images are formed on the intermediate transfer belt 153 is S (white), Y (yellow), M (magenta), C (cyan), and K (black), as shown in Fig. 11. In other words, the toner images are formed on the recording medium PM in the order of S, Y, M, C, and K from the top. The other configurations are the same as those of the first embodiment.

[0044] In the image forming process of this embodiment, the control unit 101 forms an image of the resist patch P3e shown in Fig. 12. As shown in Fig. 12, the control unit 101 forms the image so that a patch P3es of a color material with lower detectability than a predetermined standard, such as white toner, is included within patches of other colors to be measured. The predetermined standard is the degree to which the patch can be read in the scanned image. By configuring the registration patch P3e in this way, even if the recording medium PM is white, the area of ​​the white toner patch can be easily read in the read image, and the registration correction value for the white toner can be calculated.

[0045] As described above, the image forming apparatus 100 is equipped with a plurality of image forming units 151 that form images using color materials based on image data, and forms a color image on a recording medium PM by superimposing images of each color formed by each image forming unit 151. The image forming apparatus 100 is equipped with an acquisition unit (control unit 101) that acquires a read image by reading the image forming surface of the recording medium PM on which the color image has been formed, the control unit 101 that causes a resist patch P3 to be image-formed outside the job image forming area of ​​the recording medium PM, and a correction unit (control unit 101) that corrects the image formation position in the plurality of image forming units 151 based on the read image including the resist patch P3 acquired by the acquisition unit. The resist patch P3 has a reference color patch P31 formed using a color material of a reference color and at least one measurement target color patch formed using a color material of each measurement target color, and the reference color patch P31 and the measurement target color patch do not overlap each other at least in the main scanning direction, and the correction unit makes the correction based on the relative positions of the reference color patch and the measurement target color patch. Therefore, the occurrence of color misregistration is less noticeable, and color misregistration can be corrected by forming an image of a patch for correcting color misregistration on a sheet of paper.

[0046] The image forming apparatus 100 also includes an intermediate transfer body (intermediate transfer belt 153) that forms a color image by superimposing images of each color formed by each image forming unit 151, a transfer section (roller 152 and secondary transfer roller 154) that transfers the color image formed on the intermediate transfer body onto a recording medium PM, and a detection section (second image scanner 160) that detects a resist patch P3 that has been imaged on the intermediate transfer body.The control section 101 has a setting section (control section 101) that forms an image of the resist patch P3 on the intermediate transfer body before forming an image related to a job, and sets a reference value (pre-job resist reference value) for the image formation position in the multiple image forming units 151 based on the detection result by the detection section.The correction section calculates a correction value (resist correction value) based on the reference value and the read image. Therefore, color misregistration can be corrected based on the reference value set before the image formation of the job and the read image acquired during the image formation of the job.

[0047] Furthermore, in the image forming apparatus 100, the measurement target color patches each have a different shape, and the positions of their ends are different from each other in the sub-scanning direction. Therefore, even if color shift occurs in the resist patch P3, it is not noticeable and the user is unlikely to notice the occurrence of color shift. Therefore, even if color shift at a non-defective level occurs, the user can be prevented from noticing the occurrence of color shift.

[0048] In the image forming apparatus 100, the color patches to be measured each have a minimum line width of 10 pixels or more at 600 dpi. Therefore, even if the image forming characteristics of the image forming unit 150 change due to a change in the environment or the like, the first image scanner 180 can accurately read the outlines of the reference color patch P31 and the measurement target color patch P33.

[0049] In addition, in the image forming apparatus 100, the control unit 101 forms an image of a gradation patch P2 adjacent to the resist patch P3 on the recording medium PM, and includes an identification unit (control unit 101) that identifies the type of gradation patch P2 based on the shape of each of the color patches to be measured. Therefore, the gradation patch P2 can be identified based on the shape of the measurement target color patch.

[0050] Furthermore, in the image forming apparatus 100, the reference color patch also serves as the detection mark (boundary line P21 or P23) in the gradation patch P2. Therefore, the area in which the gradation patch P2 and the resist patch P3 are image-formed can be made smaller.

[0051] Furthermore, in the image forming apparatus 100, the correction unit calculates a correction value (resist correction value) for a color material whose detectability on the recording medium PM is lower than a predetermined standard, based on the correction values ​​for the other color materials. Therefore, even if the recording medium PM is white, the registration correction value for white toner can be calculated.

[0052] In addition, in the image forming apparatus 100, the control unit 101 forms an image on the recording medium PM of a measurement target color patch relating to a color material whose detectability is lower than a predetermined standard so that the measurement target color patch relating to another color material is included in the image. Therefore, even if the recording medium PM is white, the registration correction value for white toner can be calculated.

[0053] In the image forming apparatus 100, the recording medium PM is a continuous medium. Therefore, color misregistration can be corrected even during image formation on a continuous medium.

[0054] Furthermore, in the image forming apparatus 100, the control unit 101 causes the toner consumption patch P1 to be image-formed on the recording medium PM at the same position in the main scanning direction as the registration patch P3. Therefore, a wider job image forming area can be secured on the recording medium PM.

[0055] Furthermore, in the image forming apparatus 100, the control unit 101 causes a resist patch P3 to be formed on the recording medium PM as an image mark indicating the image formation position. Therefore, it is possible to reduce the area for forming images of various patches and effectively utilize the paper width of the recording medium PM.

[0056] In the image forming apparatus 100, the distance between the ends of the measurement target color patches of the same color is at least a distance that is not an integer multiple of the reading resolution in the sub-scanning direction of the reading unit that reads the read image. Therefore, even if the reading resolution of the first image scanner 180 is not sufficient to read the registration patch P3, the interpolation resolution can be improved to accurately read the registration patch P3.

[0057] The description of the above embodiment is a preferred example of the image forming apparatus according to the present invention, and the present invention is not limited to this.

[0058] For example, in the above embodiment and modified example, the image forming apparatus 100 forms images on the recording medium PM, which is a rollable continuous medium, but this is not limited to this. The recording medium PM may also be a sheet of paper or other medium that is not continuous. By applying the present invention to an image forming apparatus that forms images on sheets of paper or other medium, color misregistration correction in response to environmental changes such as temperature during continuous printing can be performed without temporarily interrupting printing, which can contribute to cost reduction by improving the efficiency of printing work and reducing downtime.

[0059] In the above embodiment and modified examples, the reference color is K (black), but other colors may be used as the reference color. However, because the K patch is displayed at a high density in all of the R, G, and B separated image data, it is preferable to use K as the reference color.

[0060] Furthermore, in the above embodiment and modified examples, the first image scanner 180, which is the reading unit, is located inside the image forming apparatus, but the reading unit may also be provided outside the image forming apparatus.

[0061] Furthermore, in the image forming process of the above embodiment and modified example, the in-job registration reference value is set in the first registration correction process after the start of image formation, but this is not limited to this. The in-job registration reference value may be the average value of measurement results in registration correction processes a predetermined number of times (for example, about 2 to 10 times depending on the print volume of the entire job) after the start of image formation. The measurement result is the relative position of the centers of gravity of two patches of the same color with respect to the center of gravity of the reference color patch P31 calculated in step S45 of the registration correction process. Furthermore, after step S15 of the pre-job reference value setting process is performed, the registration patch P3 may be image-formed on the recording medium PM, and the in-job registration reference value may be set based on the read image of the registration patch P3 formed by the first image scanner 180. In this case, in the first registration correction after the start of image formation in the image forming process, the difference between the pre-job registration reference value and the value calculated in step S45 and the difference between the in-job registration reference value and the value calculated in step S45 are added together to calculate the registration correction value. Furthermore, in the same image forming apparatus as the image forming apparatus 100 of the above embodiment, the job registration reference value may be acquired in advance in a state where no color misregistration occurs.

[0062] In the above description, examples have been disclosed in which a nonvolatile semiconductor memory or a hard disk is used as a computer-readable medium storing a program for executing each process, but this is not limiting. Other computer-readable media may also be portable recording media such as CD-ROMs. Furthermore, a carrier wave may also be used as a medium for providing program data via a communication line.

[0063] In addition, the detailed configuration and detailed operation of each part of the image inspection device can be modified as appropriate without departing from the spirit of the present invention. [Explanation of symbols]

[0064] 100 Image forming device 101 control unit (acquisition unit, correction unit, setting unit, identification unit, computer) 102 Communications Department 103 Operation display section 104 Storage section 105 Paper feed section 105a Paper feed roll 105b Paper feed roller 106 Conveyor 107 Winding section 107a Winding roll 107b Winding roller 150 Image forming unit 151 Image forming unit 152 Roller (transfer section) 153 Intermediate transfer belt (intermediate transfer body) 154 Secondary transfer roller (transfer section) 160 Second image scanner (detection unit) 170 Fixing unit 180 First image scanner (reading unit) N Transfer nip

Claims

1. An image forming apparatus comprising a plurality of image forming units that form an image using colorants based on image data, and which forms a color image on a recording medium by superimposing the images of each color formed by each of the image forming units, An acquisition unit that acquires a read image obtained by reading the image-forming surface of the recording medium on which the color image is formed, A control unit that causes a resist patch to be image-formed outside the job image formation area of ​​the recording medium, A correction unit corrects the image formation position in a plurality of image forming units based on the read image including the resist patch acquired by the acquisition unit, Equipped with, The acquisition unit acquires a read image obtained by reading the image-forming surface of the recording medium on which the color image is formed by the reading unit. The resist patch comprises a reference color patch formed from a colorant of a reference color and at least one measurement target color patch formed from a colorant of each measurement target color, wherein the edges of the reference color patch and the measurement target color patch do not overlap each other at least in the main scanning direction. The aforementioned reference color patch has a step formed at its end in the main scanning direction of the reading unit. The correction unit is an image forming apparatus that corrects based on the relative position between the reference color patch and the color patch to be measured.

2. The image forming apparatus according to claim 1, wherein the step is formed based on the reading resolution of the reading unit.

3. The image forming apparatus according to claim 2, wherein the step is smaller than the reading resolution of the reading unit.

4. The image forming apparatus according to any one of claims 1 to 3, wherein each of the color patches to be measured has a different shape, and the position of each end is different from that of the others in the sub-scanning direction.

5. The image forming apparatus according to any one of claims 1 to 4, wherein each of the color patches to be measured has a minimum line width of 10 pixels or more at 600 dpi.

6. The control unit causes the recording medium to form a grayscale patch adjacent to the resist patch as an image, The image forming apparatus according to any one of claims 1 to 5, further comprising an identification unit that identifies the type of the grayscale patch based on the form of each of the color patches to be measured.

7. The image forming apparatus according to claim 6, wherein the reference color patch also serves as a detection mark in the gradation patch.

8. The image forming apparatus according to any one of claims 1 to 7, wherein the control unit causes the measurement target color patch relating to a color material with lower detectability than a predetermined standard on the recording medium to be included in the measurement target color patch relating to other color materials.

9. The image forming apparatus according to any one of claims 1 to 8, wherein the recording medium is a continuous medium.

10. The image forming apparatus according to any one of claims 1 to 9, wherein the control unit causes the toner consumption patch to be image-formed on the recording medium at the same position as the resist patch in the main scanning direction.

11. The image forming apparatus according to any one of claims 1 to 10, wherein the control unit causes the resist patch to be image-formed on the recording medium as an eye mark indicating an image formation position.

12. The image forming apparatus according to any one of claims 1 to 11, wherein the distance between the ends of the measurement target color patches of the same color is not an integer multiple of the reading resolution in the sub-scanning direction of the reading unit that reads the read image.

13. A computer for an image forming apparatus comprising a plurality of image forming units that form an image using colorants based on image data, and which forms a color image on a recording medium by superimposing the images of each color formed by each of the image forming units, An acquisition unit that acquires a read image obtained by reading the image-forming surface of the recording medium on which the color image is formed. A control unit that causes a resist patch to be image-formed outside the job image formation area of ​​the recording medium. A correction unit corrects the image formation position in a plurality of image forming units based on the read image including the resist patch acquired by the acquisition unit. To make it function as, The acquisition unit acquires a read image obtained by reading the image-forming surface of the recording medium on which the color image is formed by the reading unit. The resist patch comprises a reference color patch formed from a colorant of a reference color and at least one measurement target color patch formed from a colorant of each measurement target color, wherein the edges of the reference color patch and the measurement target color patch do not overlap each other at least in the main scanning direction. The aforementioned reference color patch has a step formed at its end in the main scanning direction of the reading unit. The correction unit is a program that performs correction based on the relative position between the reference color patch and the color patch to be measured.

Images