Image inspection apparatus, image forming apparatus, image inspection method, and computer program product

Abstract

This invention provides an image inspection apparatus, an image forming apparatus, an image inspection method, and a computer program product that can detect positional offsets in the image forming position even without using a position detection image. The image forming apparatus (image inspection apparatus) includes a control unit that detects positional offsets in the image forming position within a recording medium after an image is formed by the image forming unit. The control unit has a first detection mode and a second detection mode. In the first detection mode (first positional offset detection process, step S3), the positional offset is detected based on the formation position of a guideline (position detection image) formed by the image forming unit at a predetermined position on the recording medium. In the second detection mode (second positional offset detection process, step S4), the positional offset is detected without the image forming unit forming a guideline.

Description

Technical Field

[0001] This invention relates to an image inspection apparatus, an image forming apparatus, an image inspection method, and a computer program product. Background Technology

[0002] In image forming apparatus (printing press), the process of adjusting the medium so that an image can be formed at a predetermined position on the recording medium is called registration. In registration, crosshairs (register marks) are used as registration marks, so registration is also called register line alignment. Registration requires the formation of register lines at predetermined positions on the recording medium, and the offset of the actual position where the register lines are formed is measured. Besides register lines, quadrilaterals, circles, etc., are also used as registration marks.

[0003] Patent Document 1 discloses a technique that detects positional offsets between a watermark pattern and a printed pattern by reading the positions of the registration marks on the watermark pattern and the registration marks on the printed pattern. According to this technique, it is unnecessary for a person to visually confirm the correctness of the printed pattern's position. Furthermore, the detected offset is used to automatically control the position of the printed pattern, eliminating the need for manual adjustments.

[0004] Existing technical documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2001-270086 Summary of the Invention

[0006] However, in the aforementioned prior art, the formation of alignment marks (position detection images) is a prerequisite for detecting positional shifts. Therefore, positional shifts cannot be detected for operations where alignment marks cannot be formed. Furthermore, attaching alignment marks to the image is time-consuming. Additionally, the alignment marks used in positional shift detection eventually need to be cropped and removed, resulting in waste of recording media. Moreover, there is a problem that registration and alignment cannot be performed on recording media with uncropped blank areas.

[0007] The present invention was made in view of the problems in the prior art described above. The objective is to detect the positional offset of the image formation position even without using an image for position detection.

[0008] To address the aforementioned issues, the invention described in technical solution 1 is an image inspection apparatus comprising a control unit that detects positional offset of an image formation position in a recording medium after an image is formed by an image forming unit. The control unit has: a first detection mode in which the positional offset is detected based on the formation position of a position detection image formed by the image forming unit at a predetermined position on the recording medium; and a second detection mode in which the positional offset is detected without the image forming unit forming the position detection image.

[0009] The invention described in technical solution 2, in the image inspection apparatus described in technical solution 1, further includes an image acquisition unit that acquires a readout image generated by reading a recording medium after the image is formed by a reading unit. In the first detection mode, the control unit controls the image forming unit to form the position detection image at the predetermined position on the recording medium, and detects the position offset based on the predetermined position and the position of the position detection image in the readout image.

[0010] The invention described in technical solution 3, in the image inspection apparatus described in technical solution 1, further includes an image acquisition unit that acquires a readout image generated by reading a recording medium after the image is formed by a reading unit, and the control unit detects the position offset in the second detection mode based on a reference image stored in a storage unit and the readout image.

[0011] In the image inspection apparatus described in technical solution 3, the control unit detects the position offset in the second detection mode based on alignment performed by using image matching of an image contained in the reference image and an image contained in the read image.

[0012] In the image inspection apparatus described in technical solution 4, the control unit detects the position offset based on the edge of the recording medium detected from the read image after the alignment.

[0013] In the image inspection apparatus described in technical solution 3, the control unit further checks whether there are any abnormalities in the read image based on the reference image and the read image.

[0014] The invention described in technical solution 7 is an image inspection apparatus comprising: an image acquisition unit that acquires a readout image generated by reading an image formed by an image forming unit from a recording medium by a readout unit; and a control unit that checks for any abnormalities in the readout image based on a reference image stored in a storage unit and the readout image, wherein the control unit acquires information related to the positional offset of an image formed on the recording medium based on the reference image and the readout image, and controls the image forming position in the image forming unit based on the acquired information related to the positional offset of the image.

[0015] The invention described in technical solution 8 is an image forming apparatus comprising: an image inspection device described in any one of technical solutions 1 to 7; the image forming unit; and a reading unit that reads a recording medium after the image is formed to generate a read image.

[0016] The invention described in technical solution 9 is an image inspection method for detecting positional offset of an image formation position in a recording medium after an image is formed by an image forming unit. The image inspection method includes: a first detection mode in which the positional offset is detected based on the formation position of a position detection image formed by the image forming unit at a predetermined position in the recording medium; and a second detection mode in which the positional offset is detected without the image forming unit forming the position detection image.

[0017] The invention described in technical solution 10, in the image inspection method described in technical solution 9, further includes an image acquisition step. In this image acquisition step, a readout image generated by reading the recording medium after the image is formed by the reading unit is acquired. In the first detection mode, the image forming unit is controlled to form the position detection image at the predetermined position on the recording medium, and the position offset is detected based on the predetermined position and the position of the position detection image in the readout image.

[0018] The invention described in technical solution 11, in the image inspection method described in technical solution 9, further includes an image acquisition step, in which a readout image generated by reading the recording medium after the image is formed by the readout unit is acquired, and in the second detection mode, the position offset is detected based on the reference image stored in the storage unit and the readout image.

[0019] In the image inspection method described in technical solution 11, the invention described in technical solution 12 detects the positional offset in the second detection mode based on alignment performed by using image matching of an image contained in the reference image and an image contained in the read image.

[0020] In the image inspection method described in technical solution 12, after the alignment, the position offset is detected based on the edge of the recording medium detected from the read image.

[0021] The invention described in technical solution 14, in the image inspection method described in technical solution 11, further includes an inspection step in which an abnormality is checked in the read image based on the reference image and the read image.

[0022] The invention described in technical solution 15 is an image inspection method, comprising: an image acquisition step, acquiring a readout image generated by reading an image formed by an image forming unit from a recording medium by a readout unit; an inspection step, checking for any abnormalities in the readout image based on a reference image stored in a storage unit and the readout image; and a control step, acquiring information related to the positional offset of an image formed on the recording medium based on the reference image and the readout image, and controlling the image formation position in the image forming unit based on the acquired information related to the positional offset of the image.

[0023] The invention described in technical solution 16 is a computer program product for enabling a computer to function as a control unit for detecting positional offset of an image formation position in a recording medium after an image is formed by an image forming unit. The control unit has: a first detection mode in which the positional offset is detected based on the formation position of a position detection image formed by the image forming unit at a predetermined position on the recording medium; and a second detection mode in which the positional offset is detected without the image forming unit forming the position detection image.

[0024] In the computer program product described in technical solution 16, the invention described in technical solution 17 enables the computer to also function as an image acquisition unit that acquires a readout image generated by reading the recording medium after the image is formed by the reading unit. In the first detection mode, the control unit controls the image forming unit to form the position detection image at the predetermined position on the recording medium, and detects the position offset based on the predetermined position and the position of the position detection image in the readout image.

[0025] In the computer program product described in technical solution 16, the invention described in technical solution 18 enables the computer to also function as an image acquisition unit that acquires a readout image generated by reading the recording medium after the image is formed by the reading unit, and the control unit detects the position offset in the second detection mode based on the reference image stored in the storage unit and the readout image.

[0026] In the computer program product described in technical solution 18, the control unit in the second detection mode detects the position offset based on alignment performed by image matching of an image contained in the reference image and an image contained in the read image.

[0027] In the computer program product described in technical solution 19, the control unit, after the alignment, detects the position offset based on the edge of the recording medium detected from the read image.

[0028] In the computer program product described in technical solution 18, the control unit further checks whether there is any abnormality in the read image based on the reference image and the read image.

[0029] The invention described in technical solution 22 is a computer program product for causing a computer to perform: an image acquisition step, acquiring a readout image generated by reading an image formed by an image forming unit from a recording medium by a readout unit; an inspection step, inspecting the readout image for any abnormalities based on a reference image stored in a storage unit and the readout image; and a control step, acquiring information related to the positional offset of an image formed on the recording medium based on the reference image and the readout image, and controlling the image formation position in the image forming unit based on the acquired information related to the positional offset of the image.

[0030] According to the present invention, positional offset of image formation location can be detected even without using an image for position detection. Attached Figure Description

[0031] Figure 1 This is a schematic structural diagram of the image forming apparatus according to an embodiment of the present invention.

[0032] Figure 2 This is a block diagram showing the functional structure of the image forming apparatus.

[0033] Figure 3 This is a flowchart illustrating the image inspection process performed in the image forming apparatus.

[0034] Figure 4 This is a flowchart illustrating the first position offset detection process.

[0035] Figure 5 This is a diagram showing an example of a recording medium with regular lines.

[0036] Figure 6 This is a diagram showing a specific example of the formation location of the guide lines on the recording medium.

[0037] Figure 7This is a diagram used to illustrate the detection of positional offset using guide lines.

[0038] Figure 8 It is a diagram showing a comparison between the positions of the predetermined guide lines and the positions of the guide lines obtained from the read image.

[0039] Figure 9 This is a flowchart illustrating the second position offset detection process.

[0040] Figure 10 This is a flowchart illustrating the second position offset detection process.

[0041] Figure 11 It is a diagram used to illustrate the reference image and to read the image location that serves as the reference for image matching.

[0042] Figure 12 This diagram illustrates a method for detecting the four corners of a recording medium from a aligned reference image and by reading the image.

[0043] Figure 13 It is a diagram showing the points at the four corners of the recording medium in the reference image after comparison and the points at the four corners of the recording medium in the read image. Detailed Implementation

[0044] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The advantages and features provided by these embodiments will be understood from the following detailed description and the accompanying drawings. However, the scope of the present invention is not limited to the embodiments disclosed below or the examples in the drawings.

[0045] Figure 1 This is a schematic structural diagram of the image inspection apparatus and the image forming apparatus 100, which is an image forming apparatus, according to this embodiment. The image forming apparatus 100 forms a color image onto a recording medium such as paper using an electrophotographic method. The image forming apparatus 100 forms an image based on image data obtained from reading an image from an original document or image data received from an external device. The image forming apparatus 100 includes an operation unit 10, a display unit 20, an original document reading unit 30, an image forming unit 40, a supply unit 50, a post-processing unit 60, and an image reading unit 70, etc.

[0046] Operation unit 10 outputs operation signals based on user operations to control unit 81 (see reference). Figure 2 The operation unit 10 is equipped with various operation keys and a touch screen. The operation keys accept various user commands. The touch screen is formed to cover the display screen of the display unit 20. The touch screen accepts touch operations on the display screen and detects the touch location.

[0047] The display unit 20 is composed of an LCD (Liquid Crystal Display). The display unit 20 displays various images according to the display signals input from the control unit 81.

[0048] The original document reading unit 30 includes an ADF (Automatic Document Feeder), a scanner, etc. The original document reading unit 30 outputs the image data obtained by reading the image of the original document to the control unit 81.

[0049] The image forming unit 40 forms an image from the recording medium supplied from the supply unit 50. The image forming unit 40 includes photosensitive drums 41Y, 41M, 41C, and 41K corresponding to yellow, magenta, cyan, and black colors, respectively. The image forming unit 40 also includes an intermediate transfer belt 42, a secondary transfer roller 43, a fixing unit 44, and a flipping mechanism 45.

[0050] After uniformly charging the photosensitive drum 41Y, the image forming unit 40 scans and exposes the image data using a laser beam to form an electrostatic latent image. Next, the image forming unit 40 attaches yellow toner to the electrostatic latent image on the photosensitive drum 41Y and develops the electrostatic latent image.

[0051] The photosensitive drums 41M, 41C, and 41K are the same as the photosensitive drum 41Y, except for the different colors they process, so descriptions are omitted.

[0052] The image forming unit 40 sequentially transfers the toner images of each color formed on the photosensitive drums 41Y, 41M, 41C, and 41K onto the rotating intermediate transfer belt 42 (first transfer). That is, a color toner image formed by overlapping the four toner images is formed on the intermediate transfer belt 42. The image forming unit 40 then transfers the color toner image on the intermediate transfer belt 42 onto the recording medium via the secondary transfer roller 43 (secondary transfer).

[0053] The fixing unit 44 fixes the color toner image onto the recording medium by heating and pressurizing.

[0054] The flipping mechanism 45 flips the surface of the recording medium when images are formed on both sides of the recording medium.

[0055] The supply unit 50 has supply trays 51-53 for supplying recording media to the image forming unit 40. Each supply tray 51-53 contains recording media of a predetermined paper type and size.

[0056] The post-processing unit 60 performs post-processing on the recording medium after the image is formed by the image forming unit 40, as needed. For example, post-processing includes cutting, sorting, binding, punching, folding, and stapled processing. The post-processing unit 60 discharges the recording medium after image formation to discharge trays 61 and 62. Alternatively, the post-processing unit 60 stores the recording medium after image formation in a high-capacity stacker 63.

[0057] Image reading unit 70 (reading unit) in the transport direction of the recording medium ( Figure 1 The image reading unit 70 is positioned downstream of the image forming unit 40 in the Y-direction (as shown). The image reading unit 70 reads the transported recording medium and generates a read image (image data). The image reading unit 70 outputs the generated read image to the control unit 81. The image reading unit 70 is a color sensor that uses a light-receiving element to receive light emitted from a light source and reflected from the surface of the recording medium, and outputs a signal corresponding to the intensity of the light. The image reading unit 70 is positioned in a direction orthogonal to the transport direction (Y-direction) of the recording medium (as shown). Figure 1 It is a line sensor composed of multiple light-receiving elements arranged at predetermined intervals in the X direction (as shown). For example, the image reading unit 70 reads the image formed by the image forming unit 40 on the recording medium and is used when checking the position, color, stains, etc. of the image.

[0058] Figure 2 This is a block diagram showing the functional structure of the image forming apparatus 100. For example... Figure 2 As shown, the image forming apparatus 100 includes an operation unit 10, a display unit 20, a document reading unit 30, an image forming unit 40, a supply unit 50, a post-processing unit 60, an image reading unit 70, a control unit 81, a storage unit 82, a communication unit 83, and a transport unit 84. Furthermore, descriptions of the already explained functional units are omitted.

[0059] The control unit 81 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU reads various processing programs stored in the ROM based on operation signals input from the operation unit 10 or instruction signals received from the communication unit 83, and expands the read programs into the RAM. The CPU centrally controls the operation of each part of the image forming apparatus 100 according to the expanded programs.

[0060] The storage unit 82 is composed of non-volatile storage devices such as hard disks and flash memory, and stores various types of data. For example, a reference value V is pre-stored in the storage unit 82.

[0061] The communication unit 83 transmits and receives data with external devices connected to communication networks such as LANs (Local Area Networks).

[0062] The conveying unit 84 is equipped with conveying rollers for conveying recording media. The conveying unit 84 conveys recording media within the image forming apparatus 100. For example, the conveying unit 84 conveys recording media stored in supply trays 51-53 of the supply unit 50 to the image forming unit 40. The conveying unit 84 conveys recording media from which images are formed by the image forming unit 40. The conveying unit 84 conveys recording media from which images are read by the image reading unit 70. The conveying unit 84 conveys the image-formed recording media to discharge trays 61, 62 or a high-capacity stacker 63.

[0063] The control unit 81 detects the positional offset of the image forming position in the recording medium after the image is formed by the image forming unit 40. Positional offsets include offsets from the position where the image should be formed in the recording medium, offsets on both sides during double-sided printing, color offsets, etc.

[0064] The control unit 81 detects the positional offset of the image formation location, and has a first detection mode and a second detection mode.

[0065] The first detection mode is as follows: based on the formation position of the position detection image formed by the image forming unit 40 at a predetermined position on the recording medium, position offset is detected. The predetermined position is stored in the storage unit 82. The position detection image is an image used for registration and alignment during image forming, and is also called an alignment mark. As the position detection image, a guideline (cross-shaped mark), a quadrilateral, a circle, etc., are used.

[0066] The second detection mode is a mode that detects position shifts without using the image forming unit 40 to form a position detection image.

[0067] The control unit 81 (image acquisition unit) acquires the read image generated by reading the recording medium after the image is formed by the image forming unit 40 using the image reading unit 70 (reading unit).

[0068] In the first detection mode, the control unit 81 controls the image forming unit 40 to form a position detection image at a predetermined position on the recording medium. In the first detection mode, the control unit 81 detects position offset based on the predetermined position and the position of the position detection image in the read image.

[0069] In the second detection mode, the control unit 81 detects positional offset based on the reference image stored in the storage unit 82 and the read image. The reference image is pre-registered in the storage unit 82. The reference image can be either a RIP image (RIP data) or an image generated by reading an image formed on a recording medium (an image without positional offset or abnormality).

[0070] In the second detection mode, the control unit 81 detects position offset based on alignment implemented by using image matching of an image contained in a reference image and an image contained in a read image.

[0071] After alignment, the control unit 81 detects positional offset based on the edges of the recording medium detected from the read image. For example, the control unit 81 detects the boundary lines (edges) between the recording medium area and the background area from the read image. The recording medium area is the region within the image corresponding to the recording medium. The background area is the region within the image corresponding to the outer edge of the recording medium. Specifically, the control unit 81 determines a threshold that separates the brightness values ​​corresponding to the recording medium area and the brightness values ​​corresponding to the background area from the distribution (histogram, etc.) of brightness values ​​in the read image. The control unit 81 uses this threshold to detect the edges of the recording medium in the read image. Typically, the recording medium is rectangular, so the control unit 81 detects four straight lines from the read image as the edges of the recording medium. The control unit 81 obtains the positions of four points as the intersections of the four straight lines and sets these four points as the positions of the four corners of the recording medium.

[0072] The control unit 81 checks for any abnormalities in the read image based on the reference image and the read image. For example, the control unit 81 checks whether the color of the image contained in the read image matches the color of the image contained in the reference image at corresponding positions. Additionally, the control unit 81 checks for any dirt or smudges in the read image.

[0073] The control unit 81 acquires information related to the positional offset of the image formed on the recording medium based on the reference image and the read image. This information related to the positional offset of the image includes, for example, the X direction (refer to...). Figure 1 , Figure 12 Position offset on (etc.), Y direction (refer to) Figure 1 , Figure 12 The control unit 81 controls the image formation position in the image forming unit 40 based on the acquired information related to the image's positional offset. In other words, the control unit 81 has a registration and alignment function.

[0074] The control unit 81 calculates the offset from the target position for the image formed on the recording medium, thereby determining whether there is a positional shift in the image forming position of the image forming unit 40. For example, the control unit 81 detects the positional shift of the back side during double-sided printing based on the offset.

[0075] The control unit 81 feeds back the offset to an adjustment value used to correct the position offset.

[0076] The control unit 81 controls the conveying unit 84 to discharge the recording medium that has been detected to a positional deviation to a discharge tray that is different from the discharge tray for the usual recording medium.

[0077] Next, the operation of the image forming apparatus 100 will be explained.

[0078] Figure 3 This is a flowchart illustrating the image inspection process performed in the image forming apparatus 100. This process is implemented through software processing based on the cooperation of the CPU of the control unit 81 and a program stored in ROM.

[0079] First, the control unit 81 selects a detection mode for positional offset detection based on the image formation content related to the printing operation (step S1). The control unit 81 selects either a first detection mode or a second detection mode based on factors such as the size of the recording medium, the presence or absence of cropping, and the image being formed. Alternatively, the control unit 81 can select a user-specified detection mode based on a specification given by the user from the operation unit 10.

[0080] Next, the control unit 81 determines whether the detection mode selected in step S1 is the first detection mode (step S2).

[0081] If the selected detection mode is the first detection mode (step S2; "Yes"), the control unit 81 performs the first position offset detection process (step S3). The first position offset detection process is the position offset detection process in the first detection mode.

[0082] In step S2, if the selected detection mode is not the first detection mode (step S2; "No"), that is, if the selected detection mode is the second detection mode, the control unit 81 performs the second position offset detection process (step S4). The second position offset detection process is the position offset detection process in the second detection mode.

[0083] After step S3 or step S4, the control unit 81 controls the image formation position in the image forming unit 40 based on the detected offset (step S5). Specifically, the control unit 81 corrects the image formation position in the image forming unit 40 in a manner that eliminates positional offset in the image forming unit 40.

[0084] The image inspection and processing are now complete.

[0085] Reference Figure 4The first position offset detection process (step S3) is explained. In the first position offset detection process (first detection mode), guide lines are used as the image for position detection. In the first position offset detection process, the following premise is established: when forming the image, guide lines are formed at predetermined positions near the four corners of the recording medium.

[0086] Figure 5 An example of a recording medium 90 having alignment lines T1 to T4 is shown. Alignment lines T1 to T4 are a type of alignment mark, consisting of two mutually orthogonal line segments. Each alignment line T1 to T4 is positioned near one of the four corners of the recording medium 90. The positions of the alignment lines T1 to T4 are determined by their distance from the end of the recording medium 90.

[0087] also, Figure 5 The X direction shown is orthogonal to the transport direction of the recording medium (main scan direction). Figure 5 The Y direction shown is the transport direction of the recording medium (sub-scan direction). The same applies to the X and Y directions shown in the other figures.

[0088] Figure 6 A specific example of the formation position of the guideline T1 on the recording medium 90 is shown. The guideline T1 is formed by a toner of the color that is the object of positional offset detection. Multiple colors of toner can also be overlapped to form the guideline T1 and detect color offset. Furthermore, the periphery of the guideline T1 is designated as a blank area 91 to make the guideline T1 more prominent. The blank area 91 is an area where no toner of any color is applied.

[0089] First, the control unit 81 controls the image forming unit 40 to form guide lines T1 to T4 at predetermined positions C1 to C4 on the recording medium, in addition to the image formed as a printed material (step S11). Figure 7 The left figure shows examples of positions C1 to C4 on the recording medium 90 where the guide lines T1 to T4 should be formed. The control unit 81 controls the image forming unit 40 to form the guide lines T1 to T4 in such a way that the intersection of the crosshairs in the guide lines T1 to T4 coincides with each position C1 to C4 on the recording medium 90.

[0090] Next, the control unit 81 controls the image reading unit 70 to read the recording medium on which the guide lines T1 to T4 have been formed by the image forming unit 40, generating a readout image. The control unit 81 controls the transport unit 84 to transport the recording medium while simultaneously causing the image reading unit 70 to read the recording medium. The control unit 81 obtains the readout image 110 generated by reading the recording medium on which the guide lines T1 to T4 are formed from the image reading unit 70 (step S12). Figure 7The right image shows an example of a readout image 110. The readout image 110 includes a recording medium area 111 and a background area 112. The recording medium area 111 includes guide lines T1 to T4.

[0091] Next, the control unit 81 obtains the positions E1 to E4 (coordinates) of the guide lines T1 to T4 in the read image 110 (step S13). Specifically, the control unit 81 detects the guide lines T1 to T4 from the read image 110 and calculates the positions E1 to E4 of the intersection points of the crosses in each guide line T1 to T4.

[0092] Next, the control unit 81 compares the predetermined positions C1~C4 with the positions E1~E4 obtained in step S13, and calculates the offsets D1~D4 of the guide lines T1~T4 (step S14). The control unit 81 calculates the offsets D1~D4 based on the differences between the positions C1~C4 and E1~E4 in each of the X and Y directions.

[0093] Figure 8 The image shows a comparison between the predetermined position C1 of the guideline T1 and the position E1 of the guideline T1 obtained from the read image 110. The distance between position C1 and position E1 is called the offset D1.

[0094] Here, the control unit 81 determines whether at least one of the offsets D1 to D4 is greater than or equal to a preset reference value V (step S15). If all offsets D1 to D4 are less than the reference value V (step S15; "No"), the control unit 81 determines that there is no positional offset (step S16).

[0095] In step S15, if at least one of the offsets D1 to D4 is greater than or equal to the reference value V (step S15; "Yes"), the control unit 81 determines that there is a positional offset (step S17). The control unit 81 controls the conveying unit 84 to discharge the recording medium with the positional offset to a discharge tray different from the discharge tray of the normally discharged recording medium (step S18).

[0096] After step S16 or step S18, the first position offset detection process ends.

[0097] Reference Figure 9 as well as Figure 10 The second position offset detection process (step S4) is described below. In the second position offset detection process (second detection mode), the position offset is detected by comparing it with a reference image, without using a position detection image (ruler line).

[0098] exist Figure 11The left figure shows an example of a reference image A1. The reference image A1 includes a recording medium area 121 and a background area 122. Furthermore, even when the reference image A1 is a RIP image, a background area 122 corresponding to the outer edge of the recording medium area 121 is virtually appended to the reference image A1.

[0099] First, the control unit 81 searches for image formation positions in the reference image A1 and obtains image positions O1 to O4 as reference (model points) for image matching (step S21). Simultaneously, the control unit 81 obtains images surrounding image positions O1 to O4 as template images. The image formation position is the area where an image is actually formed (printed area). Image positions O1 to O4 are preferably positions within the printed area that are close to the four corners of the recording medium. When image positions O1 to O4 are close to the four corners of the recording medium, the detection accuracy of positional offset increases. Furthermore, the template image is preferably an image suitable for template matching.

[0100] Next, the control unit 81 controls the image forming unit 40 to form an image of the object to be inspected onto the recording medium (step S22). The image of the object to be inspected is an image corresponding to the reference image A1, and is an image inspected based on the reference image A1.

[0101] Next, the control unit 81 controls the image reading unit 70 to read the recording medium on which the image of the object to be inspected has been formed by the image forming unit 40, generating a readout image B1. The control unit 81 controls the transport unit 84 to transport the recording medium while simultaneously causing the image reading unit 70 to read the recording medium. The control unit 81 obtains the readout image B1 generated by reading the recording medium on which the image of the object to be inspected is formed from the image reading unit 70 (step S23). Figure 11 The right figure shows an example of reading image B1. Reading image B1 includes a recording medium area 131 and a background area 132.

[0102] Next, the control unit 81 performs template matching on the read image B1, using image positions O1-O4 as a reference, to obtain image positions P1-P4 of the read image B1 (step S24). Specifically, the control unit 81 uses the template image obtained from the reference image A1 and image positions O1-O4 to find the part of the read image B1 that has the highest similarity to the template image. The control unit 81 sets the points corresponding to image positions O1-O4 of the parts found in the read image B1 as image positions P1-P4.

[0103] Next, the control unit 81 aligns the reference image A1 with the read image B1 based on the image positions O1-O4 and P1-P4 (step S25). Specifically, the control unit 81 rotates and moves the reference image A1 in parallel, including the edges of the recording medium, by overlapping each of the image positions O1-O4 in the reference image A1 with the image positions P1-P4 in the read image B1. Figure 12 The left image shows the aligned reference image A2.

[0104] Next, control unit 81, as Figure 12 As shown in the left figure, based on the aligned reference image A2, the coordinates of points Q1 to Q4 at the four corners of the recording medium (recording medium area 121) are determined (step S26). Specifically, the control unit 81 detects four straight lines from the aligned reference image A2, which serves as the edge of the recording medium area 121. The control unit 81 obtains the positions of the four points as the intersection of the four straight lines and sets these four positions as the positions of the four corners of the recording medium area 121 (points Q1 to Q4).

[0105] Next, control unit 81, as Figure 12 As shown in the right figure, the coordinates of points R1 to R4 at the four corners of the recording medium (recording medium area 131) are determined based on the read image B1 (step S27). Specifically, the control unit 81 detects four straight lines from the read image B1, which serve as the edges of the recording medium area 131. The control unit 81 obtains the positions of the four points as the intersections of the four straight lines and sets these four positions as the positions of the four corners of the recording medium area 131 (points R1 to R4).

[0106] Next, the control unit 81 calculates the distance between points Q1~Q4 in the aligned reference image A2 and points R1~R4 in the read image B1 as offsets D1~D4 (step S28). The control unit 81 calculates the offsets D1~D4 based on the differences between points Q1~Q4 and points R1~R4 in the X and Y directions respectively.

[0107] Figure 13 The images of points Q1 and R1 are shown for comparison. The distance between point Q1 and point R1 is called the offset D1.

[0108] Transferred to Figure 10 The control unit 81 determines whether at least one of the offsets D1 to D4 is greater than or equal to a preset reference value V (step S29). Furthermore, the reference value V used in step S29 can also be the same as that used in the first position offset detection process (see reference). Figure 4The reference value V used in step S15 is different. If the offsets D1 to D4 are all less than the reference value V (step S29; "No"), the control unit 81 determines that there is no position offset (step S30).

[0109] In step S29, if at least one of the offsets D1 to D4 is greater than or equal to the reference value V (step S29; "Yes"), the control unit 81 determines that there is a positional offset (step S31). The control unit 81 controls the conveying unit 84 to discharge the recording medium with the positional offset to a discharge tray different from the discharge tray of the normally discharged recording medium (step S32).

[0110] After step S30 or S32, the process proceeds to step S33. In step S33, the control unit 81 checks for any abnormalities in the read image B1 based on the aligned reference image A2 and the read image B1. Here, the control unit 81 checks for abnormalities other than positional offsets. Abnormalities in the read image B1 include color variations, smudges, etc. For example, the control unit 81 generates a difference image between the aligned reference image A2 and the read image B1. The control unit 81 calculates the difference in pixel values ​​(brightness values, RGB values, etc.) of each pixel in the two images to generate the difference image. The control unit 81 checks for any abnormalities in the read image B1 based on whether each pixel in the difference image exceeds a predetermined threshold.

[0111] Next, the control unit 81 determines whether there is any abnormality other than positional offset in the read image B1 (step S34). If there is an abnormality other than positional offset in the read image B1 (step S34; "Yes"), the control unit 81 controls the transport unit 84 to discharge the abnormal recording medium to a discharge tray different from the discharge tray for normally discharged recording media (step S35).

[0112] After step S35, or if there are no abnormalities other than positional offset in the read image B1 in step S34 (step S34; "No"), the second positional offset detection process ends.

[0113] Furthermore, in image inspection processing (refer to...) Figure 3In step S1, either the first detection mode or the second detection mode is selected. Alternatively, the control unit 81 can select either the first detection mode or the second detection mode to perform both the first position offset detection processing and the second position offset detection processing. Furthermore, regarding the image formation performed by the image forming unit 40 and the image reading performed by the image reading unit 70 within the processes included in the first and second position offset detection processing, the same recording medium can be used as the processing object. If the control unit 81 determines that there is a position offset in either the first or second position offset detection processing, it adopts the determination result of the position offset detection processing in which the position offset was determined to have a position offset. Alternatively, if the control unit 81 determines that there is a position offset in either the first or second position offset detection processing, it adopts the determination results of both. Furthermore, the control unit 81 outputs a result for each detected position offset in a manner that indicates which position offset detection processing obtained the determination result.

[0114] As explained above, according to this embodiment, the control unit 81 of the image forming apparatus 100 has a first detection mode and a second detection mode for detecting positional offset of the image forming position. In the second detection mode, the control unit 81 detects positional offset without using the image forming unit 40 to form a position detection image (alignment marks such as guide lines). Therefore, the control unit 81 can detect positional offset of the image forming position even without using the position detection image.

[0115] By using the second detection mode, the control unit 81 can save the time of forming a position detection image on or cutting a position detection image from the recording medium. Furthermore, since the second detection mode does not require the recording medium to be cut, the control unit 81 can detect position shifts not only on non-standard paper but also on standard paper.

[0116] In the first detection mode, the control unit 81 detects the positional offset of the image formation position based on a predetermined position and the position of the position detection image in the read image. In the first detection mode, the control unit 81 can detect the positional offset with high precision by using the position detection image.

[0117] In the second detection mode, the control unit 81 detects the positional shift of the image formation position based on the reference image and the read image of the object being inspected. Therefore, the control unit 81 can detect the positional shift of the image formation position even without using the position detection image.

[0118] Specifically, in the second detection mode, the control unit 81 detects positional shifts based on alignment performed by matching images contained in a reference image and images contained in a read image. The control unit 81 is able to align the reference image and the read image using information about the regions where the images actually exist.

[0119] After alignment, the control unit 81 detects positional shifts based on the edges of the recording medium detected from the read image. Therefore, the control unit 81 can detect positional shifts based on information about the recording medium area, which is the largest usable area. Furthermore, the control unit 81 can accurately acquire the recording medium area even when the four corners of the recording medium are not included in the read image due to angles or other reasons.

[0120] The control unit 81 checks for any abnormalities in the read image based on the reference image and the read image. Therefore, the control unit 81 can perform routine product inspection operations while simultaneously detecting positional offsets.

[0121] The control unit 81 acquires information related to the positional offset of the image formed on the recording medium based on the reference image and the read image, and controls the image formation position in the image forming unit 40 based on the acquired information related to the image positional offset. Thus, the control unit 81 is able to correct the positional offset of the image in the image forming unit 40.

[0122] Furthermore, the embodiments described above are examples of image inspection apparatus, image forming apparatus, image inspection method, and computer program products related to the present invention, and are not intended to limit the scope thereof. The detailed structure and operation of each component of the apparatus can be appropriately modified without departing from the spirit of the present invention.

[0123] For example, in the above embodiment, the image forming apparatus 100 (image inspection apparatus) is described as including an image forming unit 40 and an image reading unit 70. Alternatively, the image inspection apparatus may acquire a readout image generated by reading an image formed by an external image forming unit (image forming apparatus) from a recording medium by an external image reading unit (image reading device), and use this image as the inspection object. Furthermore, in the above embodiment, the various processes performed by the image forming apparatus 100 may be performed collaboratively by multiple devices.

[0124] Additionally, the offset detection process at position 2 (see...) Figure 9 as well as Figure 10In this configuration, even when the reference image is a RIP image, a background area corresponding to the outer edge of the recording medium area is virtually added to the reference image. Alternatively, when the reference image is a RIP image, the background area may not be added to the reference image. In this case, the control unit 81 can treat the end of the image data of the reference image as a position corresponding to the edge of the recording medium.

[0125] The computer-readable medium for storing programs used to execute various processes is not limited to the examples mentioned above. Additionally, a carrier wave can also be used as a medium for providing program data via a communication line.

[0126] The embodiments disclosed above are for illustrative and exemplary purposes only, and are not intended to be limiting. The scope of the present invention should be interpreted through the description in the claims.

[0127] [Explanation of Symbols]

[0128] 40: Image forming unit; 50: Supply unit; 60: Post-processing unit; 61, 62: Discharge tray; 70: Image reading unit; 81: Control unit; 82: Storage unit; 84: Conveying unit; 100: Image forming apparatus.

Claims

1. An image inspection apparatus comprising a control unit that detects positional offset of an image forming position in a recording medium after an image is formed by an image forming unit, wherein, The control unit has: In the first detection mode, the position offset is detected based on the formation position of the position detection image formed by the image forming unit at a predetermined position on the recording medium. as well as In the second detection mode, the position shift is detected without the image forming unit forming the position detection image.

2. The image inspection apparatus according to claim 1, wherein, The image inspection apparatus further includes an image acquisition unit that acquires a readout image generated by reading the recording medium after the image is formed by the reading unit. In the first detection mode, the control unit controls the image forming unit to form the position detection image at the predetermined position on the recording medium, and detects the position offset based on the predetermined position and the position of the position detection image in the read image.

3. The image inspection apparatus according to claim 1, wherein, The image inspection apparatus further includes an image acquisition unit that acquires a readout image generated by reading the recording medium after the image is formed by the reading unit. In the second detection mode, the control unit detects the position offset based on the reference image stored in the storage unit and the read image.

4. The image inspection apparatus according to claim 3, wherein, In the second detection mode, the control unit detects the positional offset based on alignment performed by using image matching of the image contained in the reference image and the image contained in the read image.

5. The image inspection apparatus according to claim 4, wherein, After the alignment, the control unit detects the position offset based on the edge of the recording medium detected from the read image.

6. The image inspection apparatus according to claim 3, wherein, The control unit also checks for any abnormalities in the read image based on the reference image and the read image.

7. An image inspection apparatus, comprising: The image acquisition unit acquires a readout image generated by the reading unit reading the image formed by the image forming unit from the recording medium; and The control unit checks for any abnormalities in the read image based on the reference image stored in the storage unit and the read image. The control unit obtains information related to the positional offset of the image formed on the recording medium based on the reference image and the read image, and controls the image formation position in the image forming unit based on the obtained information related to the positional offset of the image.

8. An image forming apparatus comprising: The image inspection apparatus according to any one of claims 1 to 7; The image forming unit; and The reading unit reads the recording medium after the image is formed and generates a read image.

9. An image inspection method for detecting positional offset of an image formation position in a recording medium after an image is formed by an image forming unit, wherein, The image inspection method has the following characteristics: In the first detection mode, the position offset is detected based on the formation position of the position detection image formed by the image forming unit at a predetermined position on the recording medium. as well as In the second detection mode, the position shift is detected without the image forming unit forming the position detection image.

10. The image inspection method according to claim 9, wherein, The image inspection method further includes an image acquisition step, in which a readout image is acquired by reading a recording medium after the image has been formed by a readout unit. In the first detection mode, the image forming unit is controlled to form the position detection image at the predetermined position on the recording medium, and the position offset is detected based on the predetermined position and the position of the position detection image in the read image.

11. The image inspection method according to claim 9, wherein, The image inspection method further includes an image acquisition step, in which a readout image is acquired by reading a recording medium after the image has been formed by a readout unit. In the second detection mode, the position offset is detected based on the reference image stored in the storage unit and the read image.

12. The image inspection method according to claim 11, wherein, In the second detection mode, the positional offset is detected based on alignment performed by using image matching of the image contained in the reference image and the image contained in the read image.

13. The image inspection method according to claim 12, wherein, After the alignment, the positional offset is detected based on the edge of the recording medium detected from the read image.

14. The image inspection method according to claim 11, wherein, The image inspection method further includes an inspection step in which, based on the reference image and the read image, an inspection is conducted to check for any abnormalities in the read image.

15. An image inspection method, comprising: The image acquisition process acquires a read image generated by reading an image formed by an image forming unit from a recording medium by a read unit. The inspection process involves checking for any abnormalities in the read image based on the reference image stored in the storage unit and the read image. as well as The control process obtains information related to the positional offset of the image formed on the recording medium based on the reference image and the read image, and controls the image formation position in the image forming unit based on the obtained information related to the image positional offset.

16. A computer program product for enabling a computer that detects positional offset of an image forming position in a recording medium after an image is formed by an image forming unit to function as a control unit, wherein, The control unit has: In the first detection mode, the position offset is detected based on the formation position of the position detection image formed by the image forming unit at a predetermined position on the recording medium. as well as In the second detection mode, the position shift is detected without the image forming unit forming the position detection image.

17. The computer program product according to claim 16, wherein, The computer program product enables the computer to also function as an image acquisition unit that acquires an image generated by reading the recording medium after the image is formed by the reading unit. In the first detection mode, the control unit controls the image forming unit to form the position detection image at the predetermined position on the recording medium, and detects the position offset based on the predetermined position and the position of the position detection image in the read image.

18. The computer program product according to claim 16, wherein, The computer program product enables the computer to also function as an image acquisition unit that acquires an image generated by reading the recording medium after the image is formed by the reading unit. In the second detection mode, the control unit detects the position offset based on the reference image stored in the storage unit and the read image.

19. The computer program product according to claim 18, wherein, In the second detection mode, the control unit detects the positional offset based on alignment performed by using image matching of the image contained in the reference image and the image contained in the read image.

20. The computer program product according to claim 19, wherein, After the alignment, the control unit detects the position offset based on the edge of the recording medium detected from the read image.

21. The computer program product according to claim 18, wherein, The control unit also checks for any abnormalities in the read image based on the reference image and the read image.

22. A computer program product for causing a computer to execute: The image acquisition process acquires a read image generated by reading an image formed by an image forming unit from a recording medium by a read unit. The inspection process involves checking for any abnormalities in the read image based on the reference image stored in the storage unit and the read image; and The control process obtains information related to the positional offset of the image formed on the recording medium based on the reference image and the read image, and controls the image formation position in the image forming unit based on the obtained information related to the image positional offset.

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