Image forming apparatus, image forming method, and program

Abstract

To improve the accuracy of the position of a grounding image formed on a sheet with irregularities.SOLUTION: An image forming apparatus comprises: a conveying unit that conveys a sheet; an image forming unit that forms an image on the sheet; a first sheet reading unit that is provided on the upstream side of the image forming unit; and a second sheet reading unit that is provided on the downstream side of the image forming unit. The image forming apparatus causes the first sheet reading unit to read a sheet for correction and create a first read image, generates image data of a grounding image for correction on the basis of irregularity information on the surface of the sheet for correction acquired from the first read image, and controls the image forming unit to form the grounding image for correction on the sheet for correction on the basis of the image data of the grounding image for correction. The image forming apparatus causes the second sheet reading unit to read the sheet for correction on which the grounding image for correction is formed and create a second read image, determines a correction value related to an image forming position in the image forming unit from the second read image, and corrects the image forming position in the image forming unit on the basis of the correction value.SELECTED DRAWING: Figure 8B

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, an image forming method, and a program.

Background Art

[0002] Conventionally, embossed paper has been used as one type of printing paper. The embossed paper has uneven processing on the surface of the paper. The read image obtained by reading the embossed paper includes uneven information.

[0003] For example, when a one-dimensional or two-dimensional code image is formed on embossed paper, the image is interrupted or distorted due to the step difference of the unevenness on the paper surface. Therefore, it is difficult to accurately reproduce the code image on the embossed paper. As a result, an abnormality may occur in the reading by the code reader, and there is a possibility that correct code information cannot be obtained.

[0004] Also, when a patch image for automatic density or color adjustment is formed on embossed paper, density unevenness occurs due to the step difference of the unevenness on the paper surface, and the density of the patch image is not accurately reproduced. This is a factor that reduces the accuracy of automatic adjustment. Similarly, when an inspection image is formed on embossed paper, automatic inspection may not be possible in some cases. As described above, it is necessary to improve the image quality of code images, patch images, etc. formed on embossed paper and improve the printing accuracy.

[0005] Patent Document 1 describes a technique for improving the image quality of a code image formed thereon by forming an underlayer image on the surface of embossed paper with transparent toner or white toner and reducing the step difference of the unevenness. Further, in the technique described in Patent Document 1, the underlayer image is formed only in the area of the code image to suppress toner consumption.

[0006] In addition, in an image forming apparatus, it is conceivable to obtain unevenness information including the pattern of embossed paper and form a base image so as to flatten the uneven steps of the embossed paper. Specifically, the image forming apparatus forms a base image such that more coloring material (such as toner) is placed on parts of the embossed paper with a larger amount of indentation.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, when attempting to form a base image that matches the uneven pattern of embossed paper in an image forming apparatus, the position of the base image may shift with respect to the pattern of the embossed paper. In this case, it has been difficult for the image forming apparatus to achieve a paper surface without unevenness in a state including the base image.

[0009] Conventionally, a registration mark image has been used for alignment of an image with respect to paper. For example, an image forming apparatus forms a registration mark image on the paper and corrects the position of the image by measuring the misalignment from the coordinates of the registration mark image obtained by reading the paper. However, there has also been a problem that it is difficult to accurately read the registration mark image even when the registration mark image is formed on the paper with a coloring material (such as white or transparent) suitable for the base image.

[0010] The present invention has been made in view of the problems in the above prior art, and an object thereof is to improve the positional accuracy of a base image formed on paper with unevenness.

Means for Solving the Problems

[0011] In order to solve the above problems, the invention according to claim 1 is an image forming apparatus including a conveyance unit that conveys a sheet, an image forming unit that forms an image on the sheet, a first sheet reading unit provided upstream of the image forming unit in the sheet conveyance direction, and a control unit that causes the first sheet reading unit to read the sheet, generate a read image, generate image data of a base image based on unevenness information on the surface of the sheet obtained from the read image, control the image forming unit, and form the base image on the sheet based on the image data of the base image. The image forming apparatus further includes a second sheet reading unit provided downstream of the image forming unit in the sheet conveyance direction. The control unit causes the first sheet reading unit to read a correction sheet, generate a first read image, generate image data of a correction base image based on unevenness information on the surface of the correction sheet obtained from the first read image, control the image forming unit, and form the correction base image on the correction sheet based on the image data of the correction base image. The control unit causes the second sheet reading unit to read the correction sheet on which the correction base image is formed, generate a second read image, obtain a correction value regarding an image forming position in the image forming unit from the second read image, and correct the image forming position in the image forming unit based on the correction value.

[0012] The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the control unit calculates a positional deviation amount of the correction base image with respect to the correction sheet from the second read image, and obtains the correction value from the positional deviation amount.

[0013] The invention according to claim 3 is the image forming apparatus according to claim 1, wherein the control unit controls the image forming unit to change conditions regarding an image forming position in the image forming unit, form a plurality of the correction base images on the correction sheet, detect regions corresponding to the plurality of the correction base images from the second read image, and select, as a condition for obtaining the correction value, a condition corresponding to a region having the smallest density difference among the detected regions.

[0014] The invention according to claim 4 is the image forming apparatus according to claim 1, wherein the control unit controls the image forming unit to change conditions related to the image forming position in the image forming unit, and on the correction base paper, a plurality of the correction base images and the code image are formed such that a layer of a code image having information in a one-dimensional or two-dimensional direction is placed on the side opposite to the correction paper of the correction base image, a region corresponding to the plurality of correction base images is detected from the second read image, and a condition corresponding to the region having the lowest misreading rate of the code image among the detected regions is selected as a condition for obtaining the correction value.

[0015] The invention according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein the control unit forms the base image on a partial region of the paper.

[0016] The invention according to claim 6 is the image forming apparatus according to claim 5, wherein the partial region is a region where a code image having information in a one-dimensional or two-dimensional direction, an inspection image, a test pattern image, or a registration mark image is formed.

[0017] The invention according to claim 7 is the image forming apparatus according to any one of claims 1 to 4, wherein the image forming unit has a plurality of image forming units that form images of mutually different colors, and the control unit forms the base image in a color different from the image in the image forming job.

[0018] The invention according to claim 8 is the image forming apparatus according to claim 7, wherein the control unit forms the base image by the image forming units corresponding to two or more colors among the plurality of image forming units.

[0019] The invention according to claim 9 is the image forming apparatus according to claim 7, wherein the control unit controls the color or the number of colors of the base image according to the density corresponding to the recess on the surface of the paper in the read image.

[0020] The invention according to claim 10 is an image forming apparatus according to any one of claims 1 to 4, further comprising a reversing unit that reverses a sheet conveyed downstream of the image forming unit in the sheet conveyance direction and supplies the reversed sheet to the image forming unit again. The control unit sends out the sheet to the reversing unit without forming an image on the sheet in the image forming unit, and forms the base image in the image forming unit on the sheet that has been reversed by the reversing unit and supplied again.

[0021] The invention according to claim 11 is an image forming apparatus according to any one of claims 1 to 4. When the unevenness information on the surface of each of a plurality of sheets is common, the control unit controls the image forming unit to form the base image formed on the first sheet among the plurality of sheets also on the second and subsequent sheets.

[0022] The invention according to claim 12 is an image forming method in an image forming apparatus including a conveyance unit that conveys a sheet, an image forming unit that forms an image on the sheet, a first sheet reading unit provided upstream of the image forming unit in the sheet conveyance direction, and a second sheet reading unit provided downstream of the image forming unit in the sheet conveyance direction. The method includes causing the first sheet reading unit to read the sheet and generate a read image; generating image data of a base image based on unevenness information on the surface of the sheet obtained from the read image; controlling the image forming unit to form the base image on the sheet based on the image data of the base image; causing the first sheet reading unit to read a correction sheet and generate a first read image; generating image data of a correction base image based on unevenness information on the surface of the correction sheet obtained from the first read image; controlling the image forming unit to form the correction base image on the correction sheet based on the image data of the correction base image; causing the second sheet reading unit to read the correction sheet on which the correction base image is formed and generate a second read image; obtaining a correction value regarding an image forming position in the image forming unit from the second read image; and correcting the image forming position in the image forming unit based on the correction value.

[0023] The invention according to claim 13 is a program for causing a control unit of an image forming apparatus including a conveyance unit that conveys a sheet, an image forming unit that forms an image on the sheet, a first sheet reading unit provided upstream of the image forming unit in the sheet conveyance direction, and a second sheet reading unit provided downstream of the image forming unit in the sheet conveyance direction to execute a step of causing the first sheet reading unit to read the sheet and generate a read image, a step of generating image data of a base image based on unevenness information on the surface of the sheet obtained from the read image, and a step of controlling the image forming unit to form the base image on the sheet based on the image data of the base image, wherein the control unit is caused to execute a step of causing the first sheet reading unit to read a correction sheet and generate a first read image, a step of generating image data of a correction base image based on unevenness information on the surface of the correction sheet obtained from the first read image, a step of controlling the image forming unit to form the correction base image on the correction sheet based on the image data of the correction base image, a step of causing the second sheet reading unit to read the correction sheet on which the correction base image is formed and generate a second read image, a step of obtaining a correction value regarding an image forming position in the image forming unit from the second read image, and a step of correcting the image forming position in the image forming unit based on the correction value.

Effect of the Invention

[0024] According to the present invention, it is possible to improve the positional accuracy of a base image formed on a sheet having unevenness.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

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Figure 3B

Figure 3C

Figure 3D

Figure 4

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Figure 5B

Figure 5C

Figure 6

Figure 7A

Figure 7B

Figure 8A

Figure 8B

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0026] Hereinafter, with reference to the drawings, embodiments of an image forming apparatus, an image forming method, and a program according to the present invention will be described. The features and technical effects of the embodiments will be understood from the following detailed description and drawings. However, the scope of the present invention is not limited to the examples of the embodiments or drawings disclosed below.

[0027] [First Embodiment] First, a first embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of an image forming apparatus 10 in the first embodiment. The image forming apparatus 10 forms a color image on a sheet by an electrophotographic method based on image data. The image data may be image data obtained by reading an image from a document or image data received from an external device. The image forming apparatus 10 includes an operation unit 13, a display unit 14, a document reading unit 15, a paper feeding unit 20, a first sheet reading unit 30, an image forming unit 40, an inversion unit 171, a second sheet reading unit 50, a post-processing unit 60, and the like.

[0028] The operation unit 13 includes various operation buttons and a touch screen. The operation unit 13 outputs an operation signal based on a user's operation to a control unit 11 (see FIG. 2). The various operation buttons include numeric buttons, a start button, and the like. The touch screen is provided so as to cover the display screen of the display unit 14.

[0029] The display unit 14 is configured by an LCD (Liquid Crystal Display). The display unit 14 displays various screens according to an instruction of a display signal input from the control unit 11.

[0030] The original document reading unit 15 includes an ADF (Automatic Document Feeder), a scanner, etc. The original document reading unit 15 outputs the image data obtained by reading the image of the original document to the control unit 11.

[0031] The paper feeding unit 20 includes paper feeding trays 21, 22, and 23, and supplies paper to the image forming unit 40. In each of the paper feeding trays 21, 22, and 23, papers of a predetermined paper type and size are stored for each paper feeding tray.

[0032] The first paper reading unit 30 is provided on the downstream side of the paper feeding unit 20 and the upstream side of the image forming unit 40 in the paper conveyance direction. The first paper reading unit 30 reads the paper and generates a read image. The first paper reading unit 30 receives the light emitted from the light source and reflected by the surface of the paper with a light receiving element, and outputs a signal according to the intensity of the light. The first paper reading unit 30 is a line sensor in which a plurality of light receiving elements are arranged at a predetermined interval in a direction orthogonal to the paper conveyance direction. The first paper reading unit 30 includes a reading sensor 31 that reads the first surface (the upper surface in FIG. 1) of the paper and a reading sensor 32 that reads the second surface (the lower surface in FIG. 1) of the paper. The first paper reading unit 30 can simultaneously read both sides of the paper when the paper is conveyed through the first paper reading unit 30 by the reading sensors 31 and 32. Here, a CIS (Contact Image Sensor) is used as the reading sensors 31 and 32. Note that the first paper reading unit 30 may be a CCD (Charge Coupled Device) image sensor. Also, the first paper reading unit 30 may be an area sensor, not limited to a line sensor. Further, the first paper reading unit 30 reads a correction paper and generates a first read image. The correction paper is a paper used for correcting (adjusting) the image forming position. Conventionally, the first paper reading unit 30 has been used for measuring the size of the paper and aligning the positions of the images formed on the front and back of the paper based on the result.

[0033] The image forming unit 40 forms an image on the paper supplied from the paper feeding unit 20. The image forming unit 40 includes image forming units 41Y, 41M, 41C, 41K, and 41W corresponding to each color of yellow (Y), magenta (M), cyan (C), black (K), and white (W). The image forming unit 40 also includes an intermediate transfer belt 47, a secondary transfer roller 48, a fixing unit 49, etc. The image forming units 41Y, 41M, 41C, 41K, and 41W are arranged in series (tandem) along the belt surface of the intermediate transfer belt 47.

[0034] The image forming unit 41Y includes a photosensitive drum 42Y, a charging unit 43Y, an exposure unit 44Y, a developing unit 45Y, and a primary transfer unit 46Y. The image forming unit 41Y forms a yellow-colored image on the intermediate transfer belt 47. The charging unit 43Y uniformly charges the surface of the photosensitive drum 42Y. The exposure unit 44Y scans and exposes the charged photosensitive drum 42Y with a laser beam based on yellow-colored image data to form an electrostatic latent image. The developing unit 45Y attaches and develops yellow-colored toner to the electrostatic latent image on the photosensitive drum 42Y. The primary transfer unit 46Y transfers the yellow-colored toner image formed on the photosensitive drum 42Y onto the rotating intermediate transfer belt 47 (primary transfer).

[0035] The image forming units 41M, 41C, 41K, and 41W are the same as the image forming unit 41Y except that the colors they handle are different, so the description is omitted. The image forming unit 41W is an image forming unit for forming an underlying image (white image).

[0036] On the intermediate transfer belt 47, a color toner image in which toner images of up to five colors are superimposed is formed. On the intermediate transfer belt 47, toner images are formed in the order of yellow, magenta, cyan, black, and white. The secondary transfer roller 48 transfers the color toner image on the intermediate transfer belt 47 onto the paper all at once (secondary transfer).

[0037] The fixing unit 49 includes a heating roller and a pressure roller. The fixing unit 49 fixes the color toner image to the paper by heating and pressurizing.

[0038] When forming images on both sides of the paper, the reversing unit 171 reverses the paper. The reversing unit 171 reverses the paper that has been conveyed downstream of the image forming unit 40 in the paper conveyance direction, and supplies the reversed paper to the image forming unit 40 again.

[0039] The second paper reading unit 50 is provided downstream of the image forming unit 40 and upstream of the post-processing unit 60 in the paper conveyance direction. The second paper reading unit 50 reads the paper (correction paper) on which the correction base image is formed, and generates a second read image. The correction base image is an image used for correcting (adjusting) the image formation position. Since the second paper reading unit 50 is the same line sensor as the first paper reading unit 30, detailed description thereof is omitted. The second paper reading unit 50 includes a reading sensor 51 that reads the first surface (the upper surface in FIG. 1) of the paper, and a reading sensor 52 that reads the second surface (the lower surface in FIG. 1) of the paper. The second paper reading unit 50 can simultaneously read both sides of the paper when the paper is conveyed through the second paper reading unit 50 by the reading sensors 51 and 52. Here, a CIS is used as the reading sensors 51 and 52. Note that the second paper reading unit 50 may be a CCD image sensor. Also, the second paper reading unit 50 is not limited to a line sensor, and may be an area sensor. Conventionally, the second paper reading unit 50 has been used for inspecting the image formation state, optimizing the settings of the image forming unit 40 based on the result, detecting jammed paper, and the like.

[0040] The post-processing unit 60 performs post-processing on the paper conveyed from the image forming unit 40 as necessary. The post-processing includes staple processing, cutting processing, perforating processing, folding processing, sorting processing, and the like. The post-processing unit 60 includes paper discharge trays 61 and 62.

[0041] FIG. 2 is a block diagram showing the functional configuration of the image forming apparatus 10. As shown in FIG. 2, the image forming apparatus 10 includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, a document reading unit 15, a communication unit 16, a conveyance unit 17, a paper feeding unit 20, a first paper reading unit 30, an image forming unit 40, a second paper reading unit 50, a post-processing unit 60, etc. Note that the description of the functional units already described will be omitted.

[0042] The control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The CPU reads out various processing programs stored in the ROM according to an operation signal input from the operation unit 13 or an instruction signal received by the communication unit 16. The CPU expands the read program in the RAM and controls the operations of each part of the image forming apparatus 10 according to the program.

[0043] The storage unit 12 is composed of a storage device such as a hard disk and a flash memory. The storage unit 12 stores various data.

[0044] The communication unit 16 performs data transmission and reception with an external device connected to a communication network such as a LAN (Local Area Network).

[0045] The conveyance unit 17 includes conveyance rollers. The conveyance unit 17 conveys paper in the image forming apparatus 10. For example, the conveyance unit 17 supplies the paper stored in the paper feed trays 21, 22, 23 of the paper feeding unit 20 to the image forming unit 40 via the first paper reading unit 30. The conveyance unit 17 conveys the paper after image formation to the post-processing unit 60 via the second paper reading unit 50 and discharges it to the paper discharge trays 61, 62. The conveyance unit 17 includes a reversing unit 171.

[0046] The control unit 11 acquires the unevenness information on the surface of the sheet from the read image generated by the first sheet reading unit 30. The unevenness information is information indicating the unevenness on the surface of the sheet. The unevenness information includes information indicating at least whether the surface of the sheet protrudes or is recessed from the reference position. Further, the unevenness information includes information indicating the degree of unevenness. For example, the control unit 11 acquires unevenness information indicating that the higher the density (lower the brightness) of each pixel in the read image, the more recessed it is. That is, in the read image, a region with a relatively high density corresponds to a recessed portion of the embossed paper, and a region with a relatively low density corresponds to a protruding portion of the embossed paper. Also, it is estimated that the higher the density region, the deeper the recessed portion in the embossed paper corresponds to. Note that the method for acquiring the unevenness information does not have to be as fine as the shading of the read image. A level obtained by dividing the degree of unevenness into a plurality of levels may be used as the unevenness information.

[0047] Based on the unevenness information acquired from the read image, the control unit 11 generates the image data of the base image. Specifically, the control unit 11 generates the image data of the base image so as to fill the recessed portions (grooves) on the surface of the sheet with a coloring material (toner). For example, the control unit 11 generates the image data of the base image so that the toner for the base image is placed only on the recessed portions of the sheet. Alternatively, the control unit 11 generates the image data of the base image so that more toner for the base image is placed on the recessed portions than on the protruding portions of the sheet.

[0048] The control unit 11 controls the image forming unit 40 to form a base image on the sheet based on the image data of the base image. The control unit 11 forms the base image so as to be closer to the sheet side than the image (main image) in the image forming job. The image forming job includes a print job, a copy job, etc.

[0049] The control unit 11 forms a base image on a part of the area on the sheet. The "part of the area" is an area where a code image, an inspection image, a test pattern image, or a bar code image having information in a one-dimensional or two-dimensional direction is formed.

[0050] A code image having information in a one-dimensional direction (one-dimensional code image) is, for example, a barcode. A code image having information in a two-dimensional direction (two-dimensional code image) is, for example, a QR code (registered trademark). The code image can provide code information by being read by a code reader.

[0051] An inspection image is an image for inspecting whether it deviates from a predetermined standard in the quality to be inspected. As the inspection image, for example, a patch image of a predetermined color or density, a thin line image, etc. are used. When the inspection image formed on the paper does not satisfy the predetermined quality, the paper is discharged as defective paper to a discharge tray different from a normal paper tray.

[0052] A test pattern image is an image for adjusting color, density, etc. For example, when a test pattern image for adjusting density is formed on the paper, the control unit 11 feeds back the measurement result of the density of the test pattern image to the density adjustment value.

[0053] A dragonfly image is an image used as a reference for alignment, image magnification, cutting process, folding process, etc.

[0054] The control unit 11 forms a background image in a color different from the image (this image) in the image forming job. Note that the color of the background image does not necessarily need to be different from all the colors used for the entire paper in the image forming job among YMCK. The color of the background image only needs to be different from the color used for the main image (such as a code image) formed in at least the area where the background image is formed. For example, for barcodes and QR codes, since they are usually formed in black, it is desirable that the color of the background image in the area where the code image is formed be a color other than black.

[0055] Fig. 3A shows an example of the embossed paper P to be an image forming target. The code image forming area 71 of the embossed paper P is an area where the code image is formed.

[0056] Fig. 3B shows an example of a read image 80 corresponding to the code image formation area 71 of the embossed paper P. In the read image 80, the black part (the part with high density) is the groove part (concave part) of the embossed paper P. The control unit 11 generates image data of the base image so that a thicker base image is formed on the part with high density of the read image 80. The control unit 11 may use the density (gray level value) of each pixel of the read image 80 as the white component of the base image as it is.

[0057] Fig. 3C shows an example of a code image 81 (QR code). Fig. 3D shows a state where a base image 82 (white image) and a code image 81 are formed in the code image formation area 71 of the embossed paper P. The code image 81 is formed on the embossed paper P so as to be above the layer of the base image 82.

[0058] If the base image formed on the paper is displaced with respect to the pattern of the embossed paper, the image forming apparatus 10 cannot achieve the original purpose of accurately forming a code image or the like. Therefore, the control unit 11 needs to correct the image forming position.

[0059] The control unit 11 causes the first paper reading unit 30 to read a correction paper and generate a first read image. The control unit 11 acquires the unevenness information on the surface of the correction paper from the first read image generated by the first paper reading unit 30. Since the method for acquiring the unevenness information has already been described, a detailed description thereof is omitted.

[0060] The control unit 11 generates image data of the correction base image based on the unevenness information acquired from the first read image. The method for generating the image data of the correction base image is the same as the method for generating the image data of the base image described above. The target area (the position to aim at) when the correction base image is formed is predetermined.

[0061] The control unit 11 controls the image forming unit 40 to form a correction base image on the correction paper based on the image data of the correction base image.

[0062] The control unit 11 causes the second sheet reading unit 50 to read a correction sheet on which a correction base image is formed, and generate a second read image.

[0063] The control unit 11 obtains a correction value regarding the image formation position in the image forming unit 40 from the second read image generated by the second sheet reading unit 50. Specifically, the control unit 11 calculates the amount of positional deviation of the correction base image with respect to the correction sheet from the second read image, and obtains a correction value from the amount of positional deviation. The control unit 11 corrects the image formation position in the image forming unit 40 based on the correction value.

[0064] Next, the operation of the image forming apparatus 10 will be described. FIG. 4 is a flowchart showing an image forming process executed in the image forming apparatus 10. The image forming process is a process of forming an image including a code image on embossed paper. This process is realized by software processing in cooperation with a program stored in the CPU and ROM of the control unit 11.

[0065] First, the control unit 11 acquires manuscript image data (step S1). In the case of a print job, the control unit 11 acquires the manuscript image data received from an external device via the communication unit 16. In the case of a copy job, the control unit 11 acquires the image data of the manuscript read by the manuscript reading unit 15.

[0066] Next, the control unit 11 detects a code area from the manuscript image data (step S2). The control unit 11 compares the manuscript image data with a predetermined pattern for recognizing a code image, and recognizes the code image from the manuscript image data. Then, the control unit 11 detects a rectangular area surrounding the code image from the manuscript image data as the code area. The control unit 11 stores information indicating the position of the code area in the storage unit 12. As the information indicating the position of the code area, for example, the coordinates of the four corners of the code area (rectangular area) in the manuscript image data are used.

[0067] Next, the control unit 11 controls the conveyance unit 17 to convey the paper (embossed paper) from the designated paper feed trays 21, 22, 23 of the paper feed unit 20 toward the first paper reading unit 30. The control unit 11 controls the first paper reading unit 30 to read the surface of the paper and generate a read image (step S3). In the case of single-sided printing, the control unit 11 causes the reading sensor 31 to read the upper surface of the embossed paper. In the case of double-sided printing, the control unit 11 causes the reading sensors 31, 32 to read the upper and lower surfaces of the embossed paper. The control unit 11 acquires the read image from the first paper reading unit 30. The control unit 11 may cause the first paper reading unit 30 to read the surface of the paper, limited to the code image formation area of the paper.

[0068] Next, the control unit 11 acquires the concavo-convex information of the code image formation area from the read image (step S4). Prior to step S4, the control unit 11 specifies the code image formation area of the read image based on the information indicating the position of the code area stored in the storage unit 12.

[0069] The control unit 11 generates the image data of the base image based on the concavo-convex information of the code image formation area (step S5). The image data of the base image is composed of the shading (tone value) corresponding to the concavo-convex of the embossed paper. Specifically, the control unit 11 generates the image data of the base image such that the toner amount of the image formed by the white toner increases as the density of the read image is higher. That is, for the concave portion of the embossed paper, the deeper the groove, the more white toner is placed. The control unit 11 adjusts the finished image quality by performing image processing such as tone correction or spatial filter processing on the base image (white image).

[0070] The control unit 11 synthesizes the image data of the base image with the original image data (step S6). When the original image data includes a white component, the control unit 11 synthesizes the image data of the base image with the white component of the original image data. The control unit 11 controls the image forming unit 40 to form the original image (this image) and the base image based on the synthesized image data (step S7).

[0071] Specifically, based on the manuscript image data, the control unit 11 causes the image forming units 41Y, 41M, 41C, and 41K to form toner images of respective colors on the photoreceptor drums 42Y, 42M, 42C, and 42K. The control unit 11 sequentially transfers the toner images of respective colors formed on the photoreceptor drums 42Y, 42M, 42C, and 42K onto the intermediate transfer belt 47. The manuscript image includes a code image.

[0072] Also, based on the image data of the background image, the control unit 11 causes the image forming unit 41W to form a white toner image (background image) on the photoreceptor drum 42W. The control unit 11 transfers the white toner image formed on the photoreceptor drum 42W onto the intermediate transfer belt 47. Here, in the region where the code image is formed on the intermediate transfer belt 47, the white toner image is formed in the outermost state.

[0073] The control unit 11 uses the secondary transfer roller 48 to collectively transfer the manuscript image and the background image formed on the intermediate transfer belt 47 onto the paper. The control unit 11 uses the fixing unit 49 to fix the paper onto which the manuscript image and the background image are transferred. Thus, the image forming process ends.

[0074] (Background Image Example 1) FIG. 5A is an enlarged view showing a cross section of the embossed paper P when a background image is formed in the recess Pb of the code image forming region 71 of the embossed paper P. The embossed paper P has a convex portion Pa and a recess Pb. A white toner layer Tw is formed as a background image in the recess Pb within the code image forming region 71 of the embossed paper P. On the other hand, even within the code image forming region 71, the background image is not formed on the convex portion Pa. A black toner layer Tk is formed in the black region 72 where the black image is formed within the code image forming region 71. In this way, the step difference between the convex portion Pa and the recess Pb can be reduced in the code image forming region 71 of the embossed paper P.

[0075] (Background Image Example 2) FIG. 5B is an enlarged view showing a cross-section of the embossed paper P when a base image is formed in the code image formation region 71 of the embossed paper P. A white toner layer Tw is formed as a base image on both the convex portion Pa and the concave portion Pb with respect to the code image formation region 71 of the embossed paper P. However, the thickness of the white toner layer Tw is different between the convex portion Pa and the concave portion Pb. As shown in FIG. 5B, the white toner layer Tw formed in the concave portion Pb is thicker than the white toner layer Tw formed in the convex portion Pa. A black toner layer Tk is formed in the black region 72 of the code image formation region 71. In this way, the step difference between the convex portion Pa and the concave portion Pb can be reduced in the code image formation region 71 of the embossed paper P.

[0076] (Comparative Example) FIG. 5C shows, as a comparative example, a cross-section of the embossed paper P when a base image is formed with a uniform thickness with respect to the code image formation region 71 of the embossed paper P. A white toner layer Tw is formed as a base image on both the convex portion Pa and the concave portion Pb with respect to the code image formation region 71 of the embossed paper P at a constant density (thickness). A black toner layer Tk is formed in the black region 72 of the code image formation region 71. In the comparative example shown in FIG. 5C, a step difference remains between the convex portion Pa and the concave portion Pb in the code image formation region 71 of the embossed paper P.

[0077] Generally, the pattern of the embossed paper is not regular. Therefore, the pattern of the region on the embossed paper where the code image is formed is not uniform and is different for each sheet. The first sheet reading unit 30 reads the pattern of the embossed paper supplied to the image forming unit 40 for each sheet. The control unit 11 generates image data of the base image according to the pattern (concavo-convex information) of the embossed paper and controls the image forming unit 40 to form the base image. The control unit 11 can form a base image that matches the concavo-convex of the paper. Thereby, the control unit 11 can fill the concave portions of the embossed paper with the base image and flatten the concavo-convex on the surface of the paper. For this reason, the control unit 11 can improve the step difference of the code image even if there are differences in the embossing pattern for each sheet.

[0078] The above has mainly been described by taking the case of forming a code image as an example, but the same applies to the cases of forming an inspection image, a test pattern image, a bar code image, etc.

[0079] FIG. 6 is a flowchart showing a first image formation position correction process executed in the image forming apparatus 10. The first image formation position correction process is a process of forming a correction base image (patch image) on the embossed paper and calculating a correction value regarding the image formation position. This process is realized by a software process in cooperation with the CPU of the control unit 11 and a program stored in the ROM.

[0080] First, the control unit 11 controls the conveyance unit 17 to convey a correction sheet (embossed paper) from the designated paper feed trays 21, 22, 23 of the paper feed unit 20 toward the first sheet reading unit 30. The control unit 11 controls the first sheet reading unit 30 to read the surface of the correction sheet and generate a first read image (step S11). The method of reading the correction sheet is the same as that in step S3 of the image formation process (see FIG. 4). The control unit 11 may cause the first sheet reading unit 30 to read the surface of the correction sheet, limited to the area where the correction base image is to be formed (correction base image formation area).

[0081] Next, the control unit 11 acquires the uneven information of the correction base image formation area from the first read image (step S12). The position of the correction base image formation area is predetermined.

[0082] Next, the control unit 11 generates the image data of the correction base image based on the uneven information of the correction base image formation area (step S13). The method of generating the image data of the correction base image is the same as that in step S5 of the image formation process (see FIG. 4).

[0083] Next, the control unit 11 controls the image forming unit 40 to form a correction base image on the correction paper based on the image data of the correction base image (step S14). Specifically, the control unit 11 causes the image forming unit 41W to form a white toner image (correction base image) on the photosensitive drum 42W based on the image data of the correction base image. The control unit 11 transfers the white toner image formed on the photosensitive drum 42W onto the intermediate transfer belt 47. The control unit 11 transfers the correction base image formed on the intermediate transfer belt 47 onto the correction paper by the secondary transfer roller 48. The control unit 11 fixes the correction paper onto which the correction base image has been transferred by the fixing unit 49.

[0084] Next, the control unit 11 controls the transport unit 17 to transport the correction paper after image formation toward the second paper reading unit 50. The control unit 11 controls the second paper reading unit 50 to read the surface of the correction paper on which the correction base image is formed and generate a second read image (step S15). In the case of single-sided printing, the control unit 11 causes the reading sensor 51 to read the upper surface of the embossed paper. In the case of double-sided printing, the control unit 11 causes the reading sensors 51 and 52 to read the upper and lower surfaces of the embossed paper. The control unit 11 acquires the second read image from the second paper reading unit 50. The control unit 11 may cause the second paper reading unit 50 to read the surface of the correction paper, limited to the correction base image formation area and its peripheral area.

[0085] Next, the control unit 11 performs binarization processing on an area wider than the correction base image formation area of the image data of the second read image (step S16). Here, the control unit 11 may change the image processing parameters so that the sharpness of the correction base image formation area of the image data of the second read image is higher than that of the surrounding area (so as to emphasize the edge).

[0086] Next, the control unit 11 calculates the amount of positional deviation of the correction base image with respect to the correction sheet from the binarized second read image (binarized image) (step S17). Specifically, the control unit 11 performs pattern matching on the binarized image using the first read image generated by the first sheet reading unit 30 as a reference image to calculate the amount of positional deviation of the correction base image. Here, the control unit 11 may set, as a processing target, a region wider than the "region where it is presumed that the correction base image is formed" with respect to the binarized image. For example, the result of multiplying the size of the QR code image by an arbitrary magnification (a value greater than 1) is used as the matching region. Regarding the first read image as the reference image, a binarized image may also be used.

[0087] FIG. 7A shows an example of an embossed sheet P1 (correction sheet) on which a correction base image 91 is formed. In FIG. 7A, the direction indicated by arrow X is the main scanning direction, and the direction indicated by arrow Y is the sub-scanning direction. FIG. 7A is an example in the case where the correction base image 91 is not shifted with respect to the embossed sheet P1.

[0088] FIG. 7B shows an example of a binarized image Q1 obtained by binarizing the second read image obtained by reading the embossed sheet P1 with the second sheet reading unit 50. The control unit 11 performs pattern matching on the binarized image Q1 using the first read image as a reference image. In the binarized image Q1, the concavo-convex pattern (groove) is continuous inside and outside the region 101 corresponding to the correction base image. That is, the binarized image Q1 substantially coincides with the reference image (first read image). Therefore, the control unit 11 estimates that there is no positional deviation between the embossed pattern of the embossed sheet P1 and the correction base image 91.

[0089] FIG. 8A shows another example of the embossing paper P2 (correction paper) on which the correction base image 92 is formed. In FIG. 8A, the correction base image 92 is formed at a position deviated from the target area 93 on the embossing paper P2. The target area 93 is an area targeted as the area where the correction base image should be formed, and is the area where the concavo-convex information was acquired when generating the image data of the correction base image. FIG. 8A is an example in the case where the correction base image 92 is deviated with respect to the target area 93 of the embossing paper P2. Specifically, it is deviated by Δx in the main scanning direction X and by Δy in the sub-scanning direction Y.

[0090] FIG. 8B shows an example of the binarized image Q2 obtained by reading the embossing paper P2 with the second paper reading unit 50. The control unit 11 performs pattern matching on the binarized image Q2 with the first read image as a reference image, and calculates the amount of positional deviation between the embossing pattern of the embossing paper P2 and the correction base image 92. The control unit 11 extracts, from the binarized image Q2, an area that does not match the reference image (first read image) as an area 102 corresponding to the correction base image. Further, the control unit 11 identifies an area 103 corresponding to the target area from the binarized image Q2. In the binarized image Q2, it was ideal for the correction base image to be formed in the area 103 corresponding to the target area, but in reality, the correction base image is formed in the area 102 corresponding to the correction base image. As a result, in the binarized image Q2, the concavo-convex pattern (groove) is shifted inside and outside the area 102 corresponding to the correction base image.

[0091] The control unit 11 calculates the amount of positional deviation Δx in the main scanning direction X and the amount of positional deviation Δy in the sub-scanning direction Y. In the binarized image Q2, let the upper left vertex of the area 103 (rectangular area) corresponding to the target area have coordinates (x1, y1), and the upper left vertex of the area 102 (rectangular area) corresponding to the correction base image have coordinates (x2, y2). The amount of positional deviation Δx, Δy is obtained by the following formula. Δx = x2 - x1 Δy = y2 - y1

[0092] When the similarity between the binarized image Q2 and the reference image (first read image) is less than a preset value as a result of the pattern matching process, the control unit 11 determines that the positional deviation is too large to calculate a correction value, and may re-form the correction base image on another correction sheet.

[0093] Next, the control unit 11 obtains a correction value for the image formation position in the image forming unit 40 from the amount of positional deviation (step S18).

[0094] Next, the control unit 11 corrects the image formation position in the image forming unit 40 based on the correction value (step S19). Thereafter, when the control unit 11 controls the image forming unit 40 to form an image on the sheet, the image formation position is corrected using this correction value. Thus, the first image formation position correction process ends.

[0095] According to the first embodiment, the control unit 11 of the image forming apparatus 10 generates the image data of the correction base image based on the unevenness information on the surface of the correction sheet acquired from the first read image generated by the first sheet reading unit 30. The control unit 11 controls the image forming unit 40 to form the correction base image on the correction sheet based on the image data of the correction base image. The control unit 11 causes the second sheet reading unit 50 to read the correction sheet on which the correction base image is formed and generate a second read image. The control unit 11 obtains a correction value for the image formation position in the image forming unit 40 from the second read image, and corrects the image formation position in the image forming unit 40 based on the correction value. Therefore, the control unit 11 can improve the positional accuracy of the base image formed on the uneven sheet. Further, the control unit 11 can adjust the image formation position without forming the registration marks.

[0096] For example, the control unit 11 calculates the amount of positional deviation of the correction base image with respect to the correction sheet from the second read image by pattern matching or the like, and obtains a correction value from the amount of positional deviation. Thereby, the control unit 11 can easily improve the positional accuracy of the base image.

[0097] The control unit 11 acquires the concavo-convex information on the surface of the sheet from the read image generated by the first sheet reading unit 30. The control unit 11 generates the image data of the base image based on the concavo-convex information acquired from the read image. For example, the control unit 11 generates the image data of the base image according to the density distribution corresponding to the concavo-convex on the surface of the sheet in the read image. The control unit 11 controls the image forming unit 40 to form the base image on the sheet based on the image data of the base image. By flattening the concavo-convex on the surface of the sheet with the base image, the control unit 11 can improve the reproducibility of the image formed on the concavo-convex sheet.

[0098] The control unit 11 forms the base image on a partial area on the sheet. For example, the control unit 11 forms the base image on the area where the code image, inspection image, test pattern image or registration mark image is formed on the sheet. The control unit 11 forms the base image only on the area where an image that may have its function impaired due to the concavo-convex on the surface of the sheet is formed. Thereby, the control unit 11 can suppress the consumption of the coloring material for the base image.

[0099] For example, since the control unit 11 forms the base image on the area where the code image is formed on the sheet, the code image can be accurately formed. Thereby, the misreading rate when reading the sheet on which the code image is formed with a code reader can be reduced. Also, since the control unit 11 forms the base image on the areas where the inspection image, test pattern image, and registration mark image are formed, each image can be accurately formed. Thereby, the control unit 11 can accurately perform inspections, adjustments, processes, etc. performed using each image.

[0100] Also, the control unit 11 forms the base image in a color different from that of the image in the image forming job. Thereby, the control unit 11 can flatten the concavo-convex on the surface of the sheet without disturbing the formation of the image in the image forming job.

[0101] In the first embodiment, the calculation of the amount of displacement by pattern matching processing has been described. Instead of this, the control unit 11 may detect the position of the correction base image by detecting a white patch image or the like from the second read image generated by reading the correction paper on which the correction base image is formed. Specifically, the control unit 11 can detect the correction base image by detecting the difference in density between the embossed paper and the correction base image, or by detecting the edge of the correction base image. Then, the control unit 11 calculates the difference between the position where the correction base image should be formed on the correction paper and the position where the correction base image is actually formed as the amount of displacement.

[0102] [Second Embodiment] Next, a second embodiment to which the present invention is applied will be described. Since the image forming apparatus in the second embodiment has the same configuration as the image forming apparatus 10 shown in the first embodiment, FIGS. 1 and 2 are incorporated, and the description of the same components will be omitted. Hereinafter, the characteristic configuration and processing in the second embodiment will be described. In the second embodiment, the control unit 11 of the image forming apparatus 10 obtains the optimum conditions for the image forming position by forming a plurality of correction base images on the correction paper.

[0103] The control unit 11 controls the image forming unit 40 to change the conditions related to the image forming position in the image forming unit 40, and form a plurality of correction base images on the correction paper.

[0104] The control unit 11 causes the second paper reading unit 50 to read the correction paper on which a plurality of correction base images are formed, and generate a second read image. The control unit 11 detects the regions corresponding to the plurality of correction base images from the second read image, and selects the conditions corresponding to the region with the smallest density difference among the detected regions as the conditions for obtaining the correction value. That is, the control unit 11 determines that the position of the correction base image with the smallest density difference among the plurality of correction base images is the correct coordinates.

[0105] Next, the operation of the image forming apparatus 10 according to the second embodiment will be described. FIG. 9 is a flowchart showing a second image forming position correction process executed in the image forming apparatus 10. The second image forming position correction process is a process of forming a plurality of correction base images on the embossed paper and obtaining a correction value regarding the image forming position based on the density difference in each correction base image. This process is realized by software processing in cooperation with the CPU of the control unit 11 and the program stored in the ROM.

[0106] The process of step S21 is the same as the process of step S11 in the first image forming position correction process (see FIG. 6), and thus the description thereof is omitted.

[0107] Next, the control unit 11 acquires the unevenness information of a plurality of correction base image forming regions from the first read image (step S22). The reference position of each correction base image forming region is determined in advance.

[0108] Next, based on the unevenness information of each region, the control unit 11 changes the position condition for each region (correction base image forming region) and generates the image data of the correction base image (step S23).

[0109] Next, the control unit 11 controls the image forming unit 40 to form a plurality of correction base images on the correction paper based on the image data of the correction base image (step S24).

[0110] FIG. 10 shows an example of the embossed paper P11 on which a plurality of correction base images 111 to 119 are formed. The control unit 11 shifts each of the correction base images 111 to 119 from the reference position by a predetermined value in each of the main scanning direction X and the sub-scanning direction Y with respect to the embossed paper P11, assigns position conditions, and forms the correction base images 111 to 119. For example, in FIG. 10, the control unit 11 changes the positions of the correction base images 111 to 119 in the main scanning direction X to -x, 0, and +x with the reference position as the center. The control unit 11 changes the positions of the correction base images 111 to 119 in the sub-scanning direction Y to -y, 0, and +y with the reference position as the center.

[0111] Next, the control unit 11 controls the second sheet reading unit 50 to read the surface of the correction sheet on which a plurality of correction base images are formed, and generates a second read image (step S25). The control unit 11 acquires the second read image from the second sheet reading unit 50. The control unit 11 may cause the second sheet reading unit 50 to read the surface of the correction sheet limited to the correction base image formation region.

[0112] Next, the control unit 11 detects a region corresponding to each correction base image from the second read image (step S26).

[0113] Next, the control unit 11 calculates the density difference in each region (step S27). For example, the control unit 11 calculates the difference between the maximum value and the minimum value of the density in the region to be processed as the density difference.

[0114] Next, the control unit 11 selects the position condition corresponding to the region with the smallest density difference among the plurality of regions (step S28).

[0115] Next, the control unit 11 obtains a correction value regarding the image formation position in the image forming unit 40 from the selected position condition (step S29).

[0116] Next, the control unit 11 corrects the image formation position in the image forming unit 40 based on the correction value (step S30). That is, the control unit 11 sets the correction value (various setting values) corresponding to this position condition as the condition at the time of image formation, with the position condition selected in step S28 as the optimal condition. Thus, the second image formation position correction process ends.

[0117] According to the second embodiment, the control unit 11 of the image forming apparatus 10 can improve the positional accuracy of the base image formed on the paper with unevenness. In the second embodiment, the control unit 11 changes the conditions related to the image formation position to form a plurality of correction base images. The control unit 11 detects a region corresponding to a plurality of correction base images from the second read image generated by the second paper reading unit 50, and selects the condition corresponding to the region with the smallest density difference among the detected regions as the condition for obtaining the correction value. Since the control unit 11 uses the small density difference as the criterion for determining that the positional accuracy of the correction base image is high, the image formation position can be easily corrected. In addition, the control unit 11 can adjust the image formation position without forming the jump image.

[0118] In FIG. 10, an example in which nine correction base images 111 to 119 are formed on the embossed paper P11 is illustrated, but the number of correction base images formed on the correction paper is not limited to this example. By increasing the number of correction base images, there are more options when selecting the conditions for obtaining the correction value, and the correction value related to the image formation position can be efficiently found.

[0119] Also, in the second embodiment, the case where a plurality of correction base images are formed on one sheet of paper has been described. Instead of this, the control unit 11 may form a plurality of correction base images with changed conditions related to the image formation position on two or more sheets of paper.

[0120] [Third Embodiment] Next, a third embodiment to which the present invention is applied will be described. Since the image forming apparatus according to the third embodiment has the same configuration as the image forming apparatus 10 shown in the first embodiment, FIGS. 1 and 2 are incorporated by reference, and the description of the same components is omitted. Hereinafter, the characteristic configuration and processing of the third embodiment will be described. In the third embodiment, the position accuracy of image formation is evaluated based on the formation state of the code image.

[0121] The control unit 11 of the image forming apparatus 10 controls the image forming unit 40 to change the conditions related to the image forming position in the image forming unit 40, and forms a plurality of correction base images and code images on the correction paper. Here, the control unit 11 forms a plurality of correction base images and code images so that the layer of the code image is placed on the side opposite to the correction paper of the correction base image. The code image is a code image having information in one-dimensional or two-dimensional directions.

[0122] The control unit 11 causes the second sheet reading unit 50 to read the correction paper on which a plurality of correction base images and code images are formed, and generates a second read image. The control unit 11 detects the regions corresponding to the plurality of correction base images from the second read image, and selects the conditions corresponding to the region with the lowest misreading rate of the code image among the detected regions as the conditions for obtaining the correction value.

[0123] Next, the operation of the image forming apparatus 10 according to the third embodiment will be described. FIG. 11 is a flowchart showing a third image forming position correction process executed in the image forming apparatus 10. The third image forming position correction process is a process of forming a plurality of correction base images and code images on the embossed paper and obtaining a correction value based on the misreading rate of each code image. This process is realized by software processing in cooperation with the CPU of the control unit 11 and the program stored in the ROM.

[0124] Since the processes in steps S31 to S33 are the same as the processes in steps S21 to S23 in the second image forming position correction process (see FIG. 9), the description thereof is omitted.

[0125] Next, the control unit 11 synthesizes the code image data in each area (correction base image formation area) of the image data of the correction base image (step S34). In order to enable comparison of the misreading rates of the code images in each area, the code images added to each area are the same.

[0126] Next, the control unit 11 controls the image forming unit 40 to form a plurality of correction base images and code images (barcodes, QR codes, etc.) on the correction paper based on the synthesized image data (step S35). For example, the control unit 11 forms a black toner image (code image) on the photosensitive drum 42K in the image forming unit 41K based on the code image data. The control unit 11 transfers the black toner image formed on the photosensitive drum 42K onto the intermediate transfer belt 47. The control unit 11 forms a white toner image (correction base image) on the photosensitive drum 42W in the image forming unit 41W based on the image data of the correction base image. The control unit 11 transfers the white toner image formed on the photosensitive drum 42W onto the intermediate transfer belt 47. Here, on the intermediate transfer belt 47, a state is formed where the white toner image is formed outside the area where the code image is formed. The control unit 11 collectively transfers the code image and the correction base image formed on the intermediate transfer belt 47 onto the correction paper by the secondary transfer roller 48. The control unit 11 fixes the correction paper onto which the code image and the correction base image are transferred by the fixing unit 49.

[0127] FIG. 12 shows an example of an embossed paper P21 on which a plurality of correction base images 121 to 129 and code images 131 to 139 are formed. The control unit 11 shifts each of the correction base images 121 to 129 and the code images 131 to 139 from the reference position by predetermined values in the main scanning direction X and the sub-scanning direction Y with respect to the embossed paper P21. In this way, the control unit 11 sets position conditions to form the correction base images 121 to 129 and the code images 131 to 139. For example, in FIG. 12, the control unit 11 changes the positions of the correction base images 121 to 129 and the code images 131 to 139 in the main scanning direction X to -x, 0, and +x with the reference position as the center. The control unit 11 changes the positions of the correction base images 121 to 129 and the code images 131 to 139 in the sub-scanning direction Y to -y, 0, and +y with the reference position as the center.

[0128] Next, the control unit 11 controls the second sheet reading unit 50 to read the surface of the correction sheet on which a plurality of correction base images and code images are formed, and generates a second read image (step S36). The control unit 11 acquires the second read image from the second sheet reading unit 50. The control unit 11 may cause the second sheet reading unit 50 to read the surface of the correction sheet limited to the correction base image formation area.

[0129] Next, the control unit 11 detects the areas corresponding to the respective correction base images from the second read image (step S37). Code images are also formed in each area.

[0130] Next, the control unit 11 acquires code information from the code images in each area (step S38). The control unit 11 acquires the information indicated by the code image by means of the decoding algorithm of the code image.

[0131] Next, the control unit 11 compares the code information acquired from the code images in each area with the correct answer, and calculates the misreading rate of the code images in each area (step S39). The misreading rate is the ratio of the number of misreads to the number of readings of the code image.

[0132] Next, the control unit 11 selects the position condition corresponding to the area with the lowest misreading rate among the plurality of areas (step S40).

[0133] Next, the control unit 11 obtains a correction value regarding the image formation position in the image forming unit 40 from the selected position condition (step S41).

[0134] Next, the control unit 11 corrects the image formation position in the image forming unit 40 based on the correction value (step S42). That is, the control unit 11 sets the correction value (various setting values) corresponding to this position condition as the condition at the time of image formation, with the position condition selected in step S40 as the optimal condition. Thus, the third image formation position correction process ends.

[0135] According to the third embodiment, the control unit 11 of the image forming apparatus 10 can improve the positional accuracy of the base image formed on the paper with unevenness. In the third embodiment, the control unit 11 changes the conditions regarding the image formation position to form a plurality of correction base images and code images. The control unit 11 detects regions corresponding to the plurality of correction base images from the second read image generated by the second paper reading unit 50, and selects the condition corresponding to the region with the smallest misreading rate of the code image among the detected regions as the condition for obtaining the correction value. Since the control unit 11 uses the small misreading rate as the criterion for determining that the positional accuracy of the correction base image is high, the image formation position can be easily corrected. In addition, the control unit 11 can adjust the image formation position without forming the jump image.

[0136] In FIG. 12, an example in which nine correction base images 121 to 129 and code images 131 to 139 are formed on the embossed paper P21 is illustrated, but the number of correction base images and code images formed on the correction paper is not limited to this example. By increasing the number of correction base images and code images, there are more options when selecting the condition for obtaining the correction value, and the correction value regarding the image formation position can be efficiently found.

[0137] In addition, in the third embodiment, the case where a plurality of correction base images and code images are formed on a single sheet of paper was described. Instead of this, the control unit 11 may form a plurality of correction base images and code images with changed conditions regarding the image formation position on two or more sheets of paper.

[0138] In each of the above embodiments, the case where a base image (including the correction base image) is formed with white toner has been described. However, in the third embodiment, the base image may be formed with transparent toner. Also, in each embodiment, the image forming apparatus 10 may form the base image with toner of a color other than white and transparent. In this case, the image forming unit 40 only needs to include an image forming unit corresponding to the color for forming the base image instead of the image forming unit 41W. Also, the image forming apparatus 10 may form the base image with toner of the same color as the paper. For example, when the paper is white, the image forming apparatus 10 forms the base image with white toner.

[0139] [Modification Example 1] Next, regarding Modification Example 1, the parts different from the above embodiments will be mainly described. In Modification Example 1, the control unit 11 of the image forming apparatus 10 may form the base image with image forming units corresponding to two or more colors among the plurality of image forming units 41Y, 41M, 41C, 41K, 41W. The control unit 11 controls the color or the number of colors of the base image according to the density corresponding to the concave portions on the surface of the paper in the read image generated by the first sheet reading unit 30 (read sensors 31, 32). The higher the density in the read image, the deeper the depth of the concave portion on the paper corresponds. The control unit 11 recognizes the density of a region with a higher density compared to the surroundings in the read image as the "density corresponding to the concave portions on the surface of the paper".

[0140] For each color toner used in image formation, there may be restrictions such as an upper limit on the amount that can be placed on the paper. When the density corresponding to the concave portion on the surface of the paper is less than a predetermined threshold, the control unit 11 determines the number of colors of the base image to be "1". On the other hand, when the density corresponding to the concave portion on the surface of the paper is equal to or greater than the predetermined threshold, the control unit 11 determines the number of colors of the base image to be "2". Note that a plurality of thresholds used for density comparison may be provided, and the base image may be formed with three or more colors.

[0141] Also, when the density corresponding to the concave portion on the surface of the paper is less than a predetermined threshold, the control unit 11 determines the color of the base image to be "white" or "transparent". On the other hand, when the density corresponding to the concave portion on the surface of the paper is equal to or greater than the predetermined threshold, the control unit 11 determines the colors of the base image to be "white" and "yellow".

[0142] FIG. 13 is an enlarged view showing a cross-section of the embossed paper P when a base image is formed in the code image formation area 71 of the embossed paper P and two-color toner is used for the base image of the concave portion Pb of the embossed paper P. A white toner layer Tw is formed as the base image on the convex portion Pa of the code image formation area 71. A yellow toner layer Ty and a white toner layer Tw are formed as the base image in the concave portion Pb of the code image formation area 71. Specifically, a yellow toner layer Ty is formed on the bottom side of the concave portion Pb, and a white toner layer Tw is formed on the upper side of the concave portion Pb. A black toner layer Tk is formed in the black area 72 of the code image formation area 71. In the code image formation area 71, by forming the base image of the concave portion Pb with yellow and white colors, it is possible to deal with an embossed pattern with a large indentation.

[0143] When forming the base image in two colors, an operator or the like sets in advance the arrangement order of the image forming units 41Y, 41M, 41C, 41K, and 41W in the image forming unit 40 according to the formation order of the toner images. Specifically, among the image forming units corresponding to the two colors for forming the base image, the image forming unit corresponding to the color on the bottom side of the concave portion is arranged so as to be primarily transferred onto the intermediate transfer belt 47 later than the image forming unit corresponding to the color on the upper side of the concave portion. Further, the image forming unit corresponding to the color on the upper side of the concave portion is arranged so as to be primarily transferred onto the intermediate transfer belt 47 later than the image forming unit corresponding to the color of the code image. For example, along the intermediate transfer belt 47 shown in FIG. 1, the black image forming unit 41K, the white image forming unit 41W, and the yellow image forming unit 41Y are arranged in this order from the top.

[0144] According to Modification 1, the control unit 11 of the image forming apparatus 10 forms a base image in one or two colors according to the density corresponding to the concave portion on the surface of the paper in the read image. The control unit 11 can form a thicker base image by overlapping two colors of toner, and it becomes possible to fill deeper recesses.

[0145] Further, the control unit 11 can control the color of the base image according to the density corresponding to the concave portion on the surface of the paper in the read image. For example, the control unit 11 makes the color of the base image white or transparent, making it less likely to affect the main image. Also, the control unit 11 can form a thicker base image by using yellow in addition to white as the color of the base image. Also, yellow has less influence on the main image compared to magenta and cyan.

[0146] [Modification 2] Next, regarding Modification 2, the description will focus on the parts different from the above-described embodiments. When forming the background image, in the first sheet reading unit 30, the sheet is read, and before the leading edge of the sheet reaches the position of the secondary transfer roller 48, toner images of respective colors need to be formed on the intermediate transfer belt 47. However, there may be a case where the image data of the background image is generated from the read image, and the timing when the background image formed on the intermediate transfer belt 47 reaches the position of the secondary transfer roller 48 is later than the timing when the leading edge of the sheet reaches the position of the secondary transfer roller 48. In this case, the control unit 11 of the image forming apparatus 10 once circulates the sheet through the conveyance path for double-sided printing to form an image from the second side of the sheet. The second side is the side that was the lower surface when the sheet passed through the first sheet reading unit 30. Specifically, the control unit 11 sends the sheet to the reversing unit 171 without forming an image on the sheet in the image forming unit 40. Then, the control unit 11 forms a background image in the image forming unit 40 on the sheet that has been reversed by the reversing unit 171 and supplied again.

[0147] FIG. 14 is an enlarged view showing the vicinity of the reversing unit 171. The embossed paper P fed out from the paper feeding unit 20 passes through the conveyance path R1 and is read by the first sheet reading unit 30. Then, the embossed paper P is conveyed to the fixing unit 49 through the conveyance path R2 without the toner image being transferred to the first side from the intermediate transfer belt 47. The embossed paper P that has passed through the fixing unit 49 is conveyed again to in front of the secondary transfer roller 48 by the reversing unit 171 through the conveyance paths R3, R4, and R5. In FIG. 14, for the sake of clarity of the front and back of the embossed paper P, the figure is such that unevenness is provided only on the second side of the embossed paper P. In this way, the embossed paper P that has been conveyed again to the secondary transfer roller 48 through the reversing unit 171 is conveyed so that the second side faces the intermediate transfer belt 47. Therefore, the control unit 11 forms an image (background image and original image) from the second side first. Before forming the image on the second side, the control unit 11 generates the image data of the background image for the second side from the read image obtained by the reading sensor 32. After the control unit 11 causes the image forming unit 40 to form an image on the second side of the embossed paper P, the control unit 11 sends the paper out to the reversing unit 171 again and returns it in front of the secondary transfer roller 48. Then, after the control unit 11 causes the image forming unit 40 to form an image on the first side, the control unit 11 discharges the paper to the paper discharge tray 61 or the paper discharge tray 62.

[0148] According to Modification 2, the control unit 11 of the image forming apparatus 10 causes a base image to be formed on the paper that has been reversed by the reversing unit 171 and supplied again. Thereby, the control unit 11 can secure the processing time for acquiring the concavo-convex information from the read image and generating the image data of the base image.

[0149] When there is a distinction between the front and back of the paper, the control unit 11 may cause the base image and the original image to be formed on the first side of the paper by passing the paper through the reversing unit 171 twice (idle feed).

[0150] [Modification 3] Next, regarding Modification 3, the description will focus on the parts different from the above-described embodiments. When the concavo-convex information on the surface of each of a plurality of sheets of paper is common, the control unit 11 of the image forming apparatus 10 controls the image forming unit 40 to cause the base image formed on the first sheet of the plurality of sheets of paper to be formed on the subsequent sheets as well. The case where the concavo-convex information is common includes cases where there is regularity in the pattern of the embossed paper.

[0151] For example, when the control unit 11 forms a code image or the like in the same area within the paper on a plurality of sheets of paper embossed with the same pattern, the control unit 11 uses the image data of the base image generated for the first sheet of paper. Further, the control unit 11 may store the image data of the base image in the storage unit 12 and use the image data of the base image stored in the storage unit 12 when forming a code image or the like in the same area of the paper having the same pattern later.

[0152] When the concavo-convex information is common to each of the plurality of sheets, it is not necessary to read each sheet. According to Modification 3, the control unit 11 of the image forming apparatus 10 can also reuse the base image formed on the first sheet for forming the subsequent sheets. For example, even when it takes time to generate the image data of the base image as in Modification 2, for the subsequent sheets, the processing can be performed without inverting the sheet by the inversion unit 171. Thereby, the control unit 11 can improve the productivity.

[0153] Note that the descriptions in the above embodiments and modifications are examples of the image forming apparatus, image forming method, and program according to the present invention, and are not limited thereto. The detailed configuration and detailed operation of each part constituting the apparatus can also be appropriately changed without departing from the spirit of the present invention.

[0154] For example, in the image forming apparatus, it may be possible to select whether or not to form a base image on the sheet. Further, in the image forming apparatus, it may be possible to select whether to form a base image according to the concavo-convex of the surface of the sheet or to form a base image with a uniform density.

[0155] In the above embodiments and modifications, in the image forming apparatus of the intermediate transfer system, the case where the toner image is simultaneously transferred from the intermediate transfer belt 47 onto the sheet in a state where the present image (document image including the code image etc.) and the base image are overlapped on the intermediate transfer belt 47 has been described. Instead of this, in the image forming apparatus of the direct transfer system, after transferring the base image onto the sheet, the present image may be transferred onto the sheet, and the base image and the present image may be simultaneously fixed. Further, in the image forming apparatus, after forming the base image on the sheet, the sheet may be conveyed again to the image forming unit, and the present image may be formed overlying the base image.

[0156] Further, the present invention is not limited to an electrophotographic image forming apparatus, and may be applied to an inkjet image forming apparatus. In an inkjet image forming apparatus, first, ink for forming an underimage is ejected onto a sheet of paper, and then ink for forming the main image is ejected onto the sheet of paper.

[0157] In the above description, an example in which a ROM is used as a computer-readable medium storing a program for executing each process has been disclosed, but the present invention is not limited to this example. As other computer-readable media, non-volatile memories such as flash memories, portable recording media such as CD-ROMs may be applied. Further, a carrier wave may be applied as a medium for providing program data via a communication line.

Explanation of Signs

[0158] 10 Image forming apparatus 11 Control unit 12 Storage unit 13 Operation unit 14 Display unit 15 Document reading unit 16 Communication unit 17 Conveying unit 20 Paper feeding unit 30 First paper reading unit 31, 32 Reading sensors 40 Image forming unit 41Y, 41M, 41C, 41K, 41W Image forming parts 47 Intermediate transfer belt 48 Secondary transfer roller 49 Fixing unit 50 Second paper reading unit 51, 52 Reading sensors 60 Post-processing unit 171 Reversing unit P Embossed paper Pa Protruding part Pb Concave part

Claims

1. A conveying unit that conveys a sheet; An image forming unit that forms an image on the sheet; A first sheet reading unit provided upstream of the image forming unit in the sheet conveyance direction; The first sheet reading unit reads the sheet to generate a read image, generates image data of a base image based on the unevenness information on the surface of the sheet obtained from the read image, and controls the image forming unit to form the base image on the sheet based on the image data of the base image; a control unit; A second sheet reading unit provided downstream of the image forming unit in the sheet conveyance direction; An image forming apparatus comprising: The control unit: Causes the first sheet reading unit to read a correction sheet and generate a first read image; Generates image data of a correction base image based on the unevenness information on the surface of the correction sheet obtained from the first read image; Controls the image forming unit to form the correction base image on the correction sheet based on the image data of the correction base image; Causes the second sheet reading unit to read the correction sheet on which the correction base image is formed and generate a second read image; Obtains a correction value regarding the image forming position in the image forming unit from the second read image; An image forming apparatus that corrects the image forming position in the image forming unit based on the correction value.

2. The image forming apparatus according to claim 1, wherein the control unit calculates a misregistration amount of the correction base image with respect to the correction sheet from the second read image, and obtains the correction value from the misregistration amount.

3. The control unit: Controls the image forming unit to change conditions regarding the image forming position in the image forming unit, and forms a plurality of the correction base images on the correction sheet; Detects regions corresponding to the plurality of correction base images from the second read image, and selects the conditions corresponding to the region having the smallest density difference among the detected regions as the conditions for obtaining the correction value. The image forming apparatus according to claim 1.

4. The control unit: Controls the image forming unit to change conditions regarding the image forming position in the image forming unit, and forms a plurality of the correction base images and the code image on the correction sheet so that a layer of the code image having information in a one-dimensional or two-dimensional direction is placed on the side opposite to the correction sheet of the correction base image. An image forming apparatus according to claim 1, wherein a region corresponding to a plurality of the correction base images is detected from the second read image, and a condition corresponding to a region having the smallest misreading rate of the code image among the detected regions is selected as a condition for obtaining the correction value.

5. The image forming apparatus according to any one of claims 1 to 4, wherein the control unit forms the base image on a partial region of the paper.

6. The image forming apparatus according to claim 5, wherein the partial region is a region where a code image, an inspection image, a test pattern image, or a trombone image having information in a one-dimensional or two-dimensional direction is formed.

7. The image forming unit includes a plurality of image forming units that form images of mutually different colors. The image forming apparatus according to any one of claims 1 to 4, wherein the control unit forms the base image in a color different from the image in the image forming job.

8. The image forming apparatus according to claim 7, wherein the control unit forms the base image by image forming units corresponding to two or more colors among the plurality of image forming units.

9. The image forming apparatus according to claim 7, wherein the control unit controls the color or the number of colors of the base image according to the density corresponding to a recess on the surface of the paper in the read image.

10. An inversion unit that inverts the paper conveyed downstream of the image forming unit in the paper conveyance direction and supplies the inverted paper to the image forming unit again. The image forming apparatus according to any one of claims 1 to 4, wherein the control unit sends out the paper to the inversion unit without forming an image on the paper in the image forming unit, and forms the base image in the image forming unit on the paper inverted by the inversion unit and supplied again.

11. When the unevenness information on the surface of each of a plurality of sheets of paper is common, the control unit controls the image forming unit to form the base image formed on the first sheet of paper among the plurality of sheets of paper also on the second and subsequent sheets of paper. The image forming apparatus according to any one of claims 1 to 4.

12. An image forming method in an image forming apparatus including a conveyance unit that conveys paper, an image forming unit that forms an image on the paper, a first paper reading unit provided upstream of the image forming unit in the paper conveyance direction, and a second paper reading unit provided downstream of the image forming unit in the paper conveyance direction, comprising: A step of causing the first sheet reading unit to read the sheet and generate a read image; A step of generating image data of a base image based on the unevenness information on the surface of the sheet obtained from the read image; A step of controlling the image forming unit to form the base image on the sheet based on the image data of the base image; including; A step of causing the first sheet reading unit to read a correction sheet and generate a first read image; A step of generating image data of a correction base image based on the unevenness information on the surface of the correction sheet obtained from the first read image; A step of controlling the image forming unit to form the correction base image on the correction sheet based on the image data of the correction base image; A step of causing the second sheet reading unit to read the correction sheet on which the correction base image is formed and generate a second read image; A step of obtaining a correction value regarding the image forming position in the image forming unit from the second read image; A step of correcting the image forming position in the image forming unit based on the correction value; An image forming method including.

13. In a control unit of an image forming apparatus including a conveyance unit that conveys a sheet, an image forming unit that forms an image on the sheet, a first sheet reading unit provided upstream of the image forming unit in the sheet conveyance direction, and a second sheet reading unit provided downstream of the image forming unit in the sheet conveyance direction, A step of causing the first sheet reading unit to read the sheet and generate a read image; A step of generating image data of a base image based on the unevenness information on the surface of the sheet obtained from the read image; A step of controlling the image forming unit to form the base image on the sheet based on the image data of the base image; A program for causing execution, In the control unit, A step of causing the first sheet reading unit to read a correction sheet and generate a first read image; A step of generating image data of a correction base image based on the unevenness information on the surface of the correction sheet obtained from the first read image; A step of controlling the image forming unit to form the correction base image on the correction sheet based on the image data of the correction base image; A step of causing the second sheet reading unit to read the correction sheet on which the correction base image is formed and generate a second read image; A step of obtaining a correction value regarding the image forming position in the image forming unit from the second read image; A step of correcting an image formation position in the image forming unit based on the correction value; A program for causing the above to be executed.

Images