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

Abstract

This enables the detection of positional shifts in the image formation position without the need for position detection images. [Solution] The image forming apparatus (image inspection apparatus) includes a control unit that detects positional misalignment of the image formation position on a recording medium on which an image has been formed by an image forming unit. The control unit has a first detection mode and a second detection mode. In the first detection mode (first positional misalignment detection process, step S3), the positional misalignment is detected based on the formation position of registration marks (position detection images) formed at predetermined positions on the recording medium by the image forming unit. In the second detection mode (second positional misalignment detection process, step S4), the positional misalignment is detected without registration marks being formed by the image forming unit.

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus (printer), adjusting so as to be able to form an image at a predetermined position on a recording medium is called alignment. Since a cross-shaped mark (a flea) is used as a registration mark for alignment, alignment is also called flea alignment. In alignment, it is required to form a flea at a predetermined position on the recording medium and measure the amount of deviation of the position where the flea is actually formed. As registration marks, in addition to fleas, quadrilaterals, circles, etc. are used.

[0003] Patent Document 1 discloses a technique for detecting the positional deviation between a cut-in pattern and a printed pattern by reading the positions of the alignment marks for the cut-in pattern and the alignment marks for the printed pattern. According to this technique, it is no longer necessary for a person to visually confirm whether the position of the printed pattern is correct. Furthermore, by performing automatic control on the position of the printed pattern using the detected deviation amount, manual adjustment work becomes unnecessary.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the conventional technology described above relies on the formation of a register mark (position detection image) in order to detect misalignment. Therefore, misalignment could not be detected for jobs where a register mark could not be formed. Furthermore, adding a register mark to an image is time-consuming. In addition, the register mark used for detecting misalignment must ultimately be cut off and removed, resulting in waste of recording media. Moreover, there was a problem in that registration could not be performed for recording media that did not have a margin for cutting.

[0006] The present invention has been made in view of the problems of the prior art described above, and aims to enable the detection of positional displacement of the image formation position without using a position detection image. [Means for solving the problem]

[0007] To solve the above problems, the invention described in claim 1 is an image inspection apparatus comprising a control unit for detecting a positional shift of the image formation position on a recording medium on which an image has been formed by an image forming unit, wherein the control unit has a first detection mode for detecting the positional shift 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 for detecting the positional shift without the position detection image being formed by the image forming unit.

[0008] The invention described in claim 2 is an image inspection apparatus according to claim 1, further comprising an image acquisition unit that acquires a read image generated by reading a recording medium on which the image is formed by a reading unit, wherein the control unit controls the image forming unit to form the position detection image at a predetermined position on the recording medium in the first detection mode, and detects the position misalignment based on the predetermined position and the position of the position detection image in the read image.

[0009] The invention described in claim 3 is an image inspection apparatus according to claim 1, further comprising an image acquisition unit that acquires a read image generated by reading a recording medium on which the image is formed by a reading unit, wherein the control unit detects the positional misalignment in the second detection mode based on a reference image stored in a storage unit and the read image.

[0010] The invention described in claim 4 is an image inspection apparatus according to claim 3, wherein the control unit detects the positional misalignment in the second detection mode based on alignment by image matching using the image included in the reference image and the image included in the read image.

[0011] The invention described in claim 5 is an image inspection apparatus according to claim 4, wherein the control unit detects the misalignment after the alignment, based on the edge of the recording medium detected from the read image.

[0012] The invention described in claim 6 is an image inspection apparatus according to claim 3, wherein the control unit further inspects whether there is an abnormality in the read image based on the reference image and the read image.

[0013] The invention described in claim 7 is an image inspection device comprising: an image acquisition unit that acquires a read image generated by reading a recording medium on which an image has been formed by an image forming unit using a reading unit; and a control unit that inspects whether or not there is an abnormality in the read image based on a reference image stored in a storage unit and the read image, wherein the control unit acquires information regarding the positional misalignment 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 acquired information regarding the positional misalignment of the image.

[0014] The invention described in claim 8 is an image forming apparatus comprising: an image inspection apparatus according to any one of claims 1 to 7; an image forming unit; and a reading unit that reads a recording medium on which the image is formed and generates a read image.

[0015] The invention described in claim 9 is an image inspection method for detecting a misalignment of the image formation position on a recording medium on which an image has been formed by an image forming unit, comprising: a first detection mode for detecting the misalignment 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 for detecting the misalignment without the position detection image being formed by the image forming unit.

[0016] The invention described in claim 10 is an image inspection method comprising: an image acquisition step of acquiring a read image generated by reading a recording medium on which an image has been formed by an image forming unit using a reading unit; an inspection step of checking for abnormalities in the read image based on a reference image stored in a storage unit and the read image; and a control step of acquiring information regarding the positional misalignment of the image formed on the recording medium based on the reference image and the read image, and controlling the image formation position in the image forming unit based on the acquired information regarding the positional misalignment of the image.

[0017] The invention described in claim 11 is a program for causing a computer that detects a positional shift in the image formation position on a recording medium on which an image has been formed by an image forming unit to function as a control unit having a first detection mode for detecting the positional shift based on the formation position of a position detection image formed at a predetermined position on the recording medium by the image forming unit, and a second detection mode for detecting the positional shift without the position detection image being formed by the image forming unit.

[0018] The invention according to claim 12 is a program for causing a computer to execute an image acquisition step of acquiring a read image generated by reading a recording medium on which an image is formed by an image forming unit with a reading unit, an inspection step of inspecting whether there is an abnormality in the read image based on a reference image stored in a storage unit and the read image, and a control step of acquiring information regarding misalignment of an image formed on the recording medium based on the reference image and the read image, and controlling a formation position of an image in the image forming unit based on the acquired information regarding misalignment of the image.

Advantages of the Invention

[0019] According to the present invention, it is possible to detect misalignment of an image formation position without using a position detection image.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic configuration diagram of an image forming apparatus in an embodiment of the present invention. [Figure 2] It is a block diagram showing a functional configuration of an image forming apparatus. [Figure 3] It is a flowchart showing an image inspection process executed in an image forming apparatus. [Figure 4] It is a flowchart showing a first misalignment detection process. [Figure 5] It is a diagram showing an example of a recording medium on which a bar code is formed. [Figure 6] It is a diagram showing a specific example of a formation position of a bar code on a recording medium. [Figure 7] It is a diagram for explaining detection of misalignment using a bar code. [Figure 8] It is a diagram showing an image for comparing a predetermined position of a bar code with a position of a bar code acquired from a read image. [Figure 9] It is a flowchart showing a second misalignment detection process. [Figure 10] It is a flowchart showing a second misalignment detection process. [Figure 11] This diagram illustrates the image position that serves as the reference for image matching in the reference image and the read image. [Figure 12] This diagram illustrates a method for detecting the four corners of a recording medium from a reference image and a read image after alignment. [Figure 13] This diagram shows an image comparing the points at the four corners of the recording medium in the reference image after alignment with the points at the four corners of the recording medium in the read image. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described below with reference to the drawings. The advantages and features provided by the embodiments will be understood from the following detailed description and drawings. However, the scope of the present invention is not limited to the embodiments or illustrations disclosed below.

[0022] Figure 1 is a schematic diagram of the image forming apparatus 100 as an image inspection apparatus and image forming apparatus in this embodiment. The image forming apparatus 100 forms a color image on a recording medium such as paper using an electrophotographic method. The image forming apparatus 100 forms an image based on image data obtained by reading an image from a document, or image data received from an external device. 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, and the like.

[0023] The operation unit 10 outputs operation signals based on user operations to the control unit 81 (see Figure 2). The operation unit 10 is equipped with various operation keys and a touchscreen. The various operation keys receive various instruction operations from the user. The touchscreen is formed to cover the display screen of the display unit 20. The touchscreen receives touch operations on the display screen and detects the touch position.

[0024] The display unit 20 is composed of an LCD (Liquid Crystal Display). The display unit 20 displays various screens according to the instructions of the display signals input from the control unit 81.

[0025] The document scanning unit 30 includes an ADF (Automatic Document Feeder), a scanner, etc. The document scanning unit 30 reads the image of the document and outputs the resulting image data to the control unit 81.

[0026] The image forming unit 40 forms an image on the recording medium supplied from the supply unit 50. The image forming unit 40 is equipped with photosensitive drums 41Y, 41M, 41C, and 41K corresponding to yellow, magenta, cyan, and black, respectively. The image forming unit 40 further includes an intermediate transfer belt 42, a secondary transfer roller 43, a fixing unit 44, an inversion mechanism 45, and the like.

[0027] The image forming unit 40 uniformly charges the photoreceptor drum 41Y, then scans and exposes it with a laser beam based on yellow image data to form an electrostatic latent image. Next, the image forming unit 40 deposits yellow toner onto the electrostatic latent image on the photoreceptor drum 41Y, thereby developing the electrostatic latent image. The photoconductor drums 41M, 41C, and 41K are the same as the photoconductor drum 41Y, except for the different colors they handle, so we will omit their explanation.

[0028] The image forming unit 40 sequentially transfers the toner images of each color formed on the photoreceptor drums 41Y, 41M, 41C, and 41K onto the rotating intermediate transfer belt 42 (primary transfer). That is, a color toner image is formed on the intermediate transfer belt 42 by superimposing the toner images of the four colors. The image forming unit 40 then transfers the color toner image on the intermediate transfer belt 42 onto the recording medium all at once using the secondary transfer roller 43 (secondary transfer). The fixing unit 44 fixes the color toner image onto the recording medium by heating and pressurizing. The inversion mechanism 45 inverts the surface of the recording medium when forming images on both sides of the recording medium.

[0029] The supply unit 50 is equipped with supply trays 51 to 53 and supplies recording media to the image forming unit 40. Each supply tray 51 to 53 contains a predetermined type and size of recording media.

[0030] The post-processing unit 60 performs post-processing on the recording medium on which the image has been formed by the image forming unit 40, as needed. For example, post-processing may include cutting, sorting, stapling, punching, folding, and binding. The post-processing unit 60 discharges the recording medium on which the image has been formed into the discharge trays 61 and 62. Alternatively, the post-processing unit 60 stores the recording medium on which the image has been formed in the large-capacity stacker 63.

[0031] The image reading unit 70 (reading unit) is located downstream of the image forming unit 40 in the transport direction of the recording medium (Y direction shown in Figure 1). 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 receives light emitted from a light source and reflected from the surface of the recording medium with a photodetector and outputs a signal according to the intensity of the light. The image reading unit 70 is composed of a line sensor in which multiple photodetectors are arranged at predetermined intervals in a direction perpendicular to the transport direction of the recording medium (Y direction) (X direction shown in Figure 1). For example, the image reading unit 70 is used to read an image formed on the recording medium by the image forming unit 40 and to inspect the position of the image, the color of the image, dirt, etc.

[0032] Figure 2 is a block diagram showing the functional configuration of the image forming apparatus 100. As shown in Figure 2, 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, a transport unit 84, and the like. Note that the functional units already described will not be explained further.

[0033] The control unit 81 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The CPU reads various processing programs stored in the ROM in response to operation signals input from the operation unit 10 or instruction signals received by the communication unit 83, and loads the read programs into the RAM. The CPU centrally controls the operation of each part of the image forming apparatus 100 according to the loaded programs.

[0034] 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.

[0035] The communication unit 83 transmits and receives data to and from external devices connected to a communication network such as a LAN (Local Area Network).

[0036] The transport unit 84 is equipped with transport rollers for transporting recording media. The transport unit 84 transports recording media within the image forming apparatus 100. For example, the transport unit 84 transports recording media stored in the supply trays 51-53 of the supply unit 50 to the image forming unit 40. The transport unit 84 transports recording media on which images are formed by the image forming unit 40. The transport unit 84 transports recording media on which images are read by the image reading unit 70. The transport unit 84 transports the recording media after image formation to the discharge trays 61, 62 or the large-capacity stacker 63.

[0037] The control unit 81 detects positional misalignment of the image formation position on the recording medium where the image has been formed by the image forming unit 40. Positional misalignment includes misalignment from the position where the image should be formed on the recording medium, front-to-back positional misalignment during double-sided printing, color misalignment, etc.

[0038] The control unit 81 has a first detection mode and a second detection mode for detecting positional displacement of the image formation position. The first detection mode is a mode in which a positional misalignment is detected based on the formation position of a positional detection image formed by the image forming unit 40 at a predetermined position on the recording medium. The predetermined position is stored in the storage unit 82. The positional detection image is an image used for registration in image formation and is also called a register mark. Crop marks (cross-shaped marks), squares, circles, etc., can be used as positional detection images. The second detection mode is a mode in which a positional shift is detected without a positional detection image being formed by the image forming unit 40.

[0039] The control unit 81 (image acquisition unit) acquires a read image generated by reading the recording medium on which an image has been formed by the image forming unit 40 using the image reading unit 70 (reading unit).

[0040] 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 a positional misalignment based on the predetermined position and the position of the position detection image in the read image.

[0041] In the second detection mode, the control unit 81 detects the positional misalignment 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 may be a RIP image (RIP data), or an image generated by reading an image formed on a recording medium (an image without positional misalignment or abnormalities).

[0042] In the second detection mode, the control unit 81 detects positional misalignment based on alignment achieved through image matching using the image included in the reference image and the image included in the read image.

[0043] After alignment, the control unit 81 detects misalignment based on the edges of the recording medium detected from the read image. For example, the control unit 81 detects the boundary line (edge) between the recording medium area and the background area from the read image. The recording medium area is the area in the image corresponding to the recording medium. The background area is the area outside the recording medium in the image. Specifically, the control unit 81 determines a threshold that separates the luminance values ​​corresponding to the recording medium area from the luminance values ​​corresponding to the background area, based on the distribution of luminance values ​​(histogram, etc.) in the read image. The control unit 81 uses this threshold to detect the edges of the recording medium in the read image. Since the recording medium is usually rectangular, 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 these four points are taken as the positions of the four corners of the recording medium.

[0044] The control unit 81 checks for abnormalities in the read image based on the reference image and the read image. For example, the control unit 81 checks whether the colors of the images in the read image match the colors of the images in the reference image at corresponding positions. The control unit 81 also checks whether there is any dirt in the read image.

[0045] The control unit 81 acquires information regarding the misalignment of the image formed on the recording medium based on the reference image and the read image. This information includes, for example, the misalignment in the X direction (see Figures 1 and 12, etc.), the misalignment in the Y direction (see Figures 1 and 12, etc.), and the amount of misalignment. Based on the acquired information regarding the misalignment of the image, the control unit 81 controls the image formation position in the image forming unit 40. In other words, the control unit 81 has a registration function.

[0046] The control unit 81 determines whether or not there is a positional misalignment of the image formed by the image forming unit 40 by determining the amount of deviation from the target position of the image formed on the recording medium. For example, the control unit 81 detects the front-to-back positional misalignment during double-sided printing based on the amount of deviation. The control unit 81 feeds back the amount of displacement into an adjustment value for correcting the positional misalignment. The control unit 81 controls the transport unit 84 to discharge the recording medium in which misalignment has been detected to a different discharge tray from the discharge tray where normal recording media are discharged.

[0047] Next, the operation of the image forming apparatus 100 will be described. Figure 3 is a flowchart showing the image inspection process performed in the image forming apparatus 100. This process is realized through software processing involving the cooperation of the CPU of the control unit 81 and the program stored in ROM.

[0048] First, the control unit 81 selects a detection mode for detecting misalignment according to the image formation content related to the print job (step S1). The control unit 81 selects either the first detection mode or the second detection mode according to the size of the recording medium, whether or not cutting is performed, the image to be formed, etc. Alternatively, the control unit 81 may accept a specification from the user via the operation unit 10 and select a detection mode specified by the user.

[0049] Next, the control unit 81 determines whether the detection mode selected in step S1 is the first detection mode (step S2). If the selected detection mode is the first detection mode (step S2; YES), the control unit 81 executes the first positional misalignment detection process (step S3). The first positional misalignment detection process is the positional misalignment detection process in the first detection mode.

[0050] 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 executes the second positional misalignment detection process (step S4). The second positional misalignment detection process is the positional misalignment detection process in the second detection mode.

[0051] 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 displacement (step S5). Specifically, the control unit 81 corrects the image formation position in the image forming unit 40 to eliminate the positional displacement in the image forming unit 40. This completes the image inspection process.

[0052] Referring to Figure 4, the first positional misalignment detection process (step S3) will be described. In the first positional misalignment detection process (first detection mode), registration marks are used as the image for position detection. The first positional misalignment detection process assumes that, during image formation, registration marks are formed at predetermined positions near the four corners of the recording medium.

[0053] Figure 5 shows an example of a recording medium 90 on which registration marks T1 to T4 are formed. Registration marks T1 to T4 are a type of registration mark and consist of two mutually orthogonal line segments. Each registration mark T1 to T4 is placed near one of the four corners of the recording medium 90. The position of registration marks T1 to T4 is determined by the distance from the edge of the recording medium 90. Note that the X direction shown in Figure 5 is the direction perpendicular to the transport direction of the recording medium (main scanning direction). The Y direction shown in Figure 5 is the transport direction of the recording medium (sub-scanning direction). The same applies to the X and Y directions shown in other drawings.

[0054] Figure 6 shows a specific example of the formation position of registration marks T1 on the recording medium 90. Registration marks T1 are formed by toner of the color to be used for detecting misalignment. Multiple toner colors may be layered to form registration marks T1 and color misalignment may be detected. The area around the registration marks T1 is designated as a white-out area 91 so that the registration marks T1 are conspicuous. The white-out area 91 is an area where no toner of any color is applied.

[0055] First, the control unit 81 controls the image forming unit 40 to form registration marks 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). The left diagram of Figure 7 shows an example of positions C1 to C4 on the recording medium 90 where registration marks T1 to T4 should be formed. The control unit 81 controls the image forming unit 40 to form registration marks T1 to T4 such that the intersections of the crosses in the registration marks T1 to T4 coincide with the respective positions C1 to C4 on the recording medium 90.

[0056] Next, the control unit 81 controls the image reading unit 70 to read the recording medium on which registration marks T1 to T4 have been formed by the image forming unit 40, and to generate a read image. The control unit 81 controls the transport unit 84 to transport the recording medium and cause the image reading unit 70 to read the recording medium. The control unit 81 obtains the read image 110 generated by reading the recording medium on which registration marks T1 to T4 have been formed from the image reading unit 70 (step S12). An example of the read image 110 is shown in the right-hand figure of Figure 7. The read image 110 includes a recording medium area 111 and a background area 112. The recording medium area 111 includes registration marks T1 to T4.

[0057] Next, the control unit 81 obtains the positions E1 to E4 (coordinates) of the registration marks T1 to T4 in the read image 110 (step S13). Specifically, the control unit 81 detects the registration marks T1 to T4 from the read image 110 and determines the positions E1 to E4 of the cross intersections at each registration mark T1 to T4.

[0058] Next, the control unit 81 compares the predetermined positions C1 to C4 with the positions E1 to E4 acquired in step S13 to calculate the displacement amounts D1 to D4 of the dragonfly marks T1 to T4 (step S14). The control unit 81 calculates the displacement amounts D1 to D4 from the difference between positions C1 to C4 and positions E1 to E4 in the X and Y directions, respectively. Figure 8 shows an image comparing the predetermined position C1 of the registration mark T1 with the position E1 of the registration mark T1 obtained from the read image 110. The distance between position C1 and position E1 is the displacement amount D1.

[0059] Here, the control unit 81 determines whether at least one of the displacement amounts D1 to D4 is greater than or equal to a preset reference value V (step S15). If all of the displacement amounts D1 to D4 are less than the reference value V (step S15; NO), the control unit 81 determines that there is no positional displacement (step S16).

[0060] In step S15, if at least one of the displacement amounts 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 misalignment (step S17). The control unit 81 controls the transport unit 84 to discharge the misaligned recording medium to a different discharge tray from the discharge tray where normal recording media are discharged (step S18). After step S16 or step S18, the first positional misalignment detection process is completed.

[0061] Referring to Figures 9 and 10, the second positional misalignment detection process (step S4) will be described. In the second positional misalignment detection process (second detection mode), the positional misalignment is detected by comparing it with a reference image without using a position detection image (registration marks).

[0062] The left panel of Figure 11 shows an example of a reference image A1. Reference image A1 includes a recording medium area 121 and a background area 122. Note that even when reference image A1 is a RIP image, a background area 122 corresponding to the area outside the recording medium area 121 is added to reference image A1.

[0063] First, the control unit 81 searches for image formation locations within the reference image A1 and obtains image positions O1 to O4, which will serve as reference points (model points) for image matching (step S21). At the same time, the control unit 81 obtains an image of the area surrounding image positions O1 to O4 as a template image. The image formation locations are the areas where images are actually formed (printing areas). It is desirable that image positions O1 to O4 be located close to each of the four corners of the recording medium within the printing area. The closer image positions O1 to O4 are to the four corners of the recording medium, the higher the accuracy of detecting positional misalignment. It is also desirable that the template image be an image suitable for template matching.

[0064] Next, the control unit 81 controls the image forming unit 40 to form the image to be inspected on the recording medium (step S22). The image to be inspected is an image corresponding to the reference image A1, and is an image that is inspected with reference image A1 as the reference.

[0065] Next, the control unit 81 controls the image reading unit 70 to read the recording medium on which the image to be inspected has been formed by the image forming unit 40, and generates a read image B1. The control unit 81 controls the transport unit 84 to transport the recording medium and cause the image reading unit 70 to read the recording medium. The control unit 81 obtains the read image B1 generated by reading the recording medium on which the image to be inspected has been formed from the image reading unit 70 (step S23). An example of the read image B1 is shown in the right-hand figure of Figure 11. The read image B1 includes a recording medium area 131 and a background area 132.

[0066] Next, the control unit 81 performs template matching on the read image B1 based on image positions O1 to O4 to obtain image positions P1 to 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 to 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 in the read image B1 that correspond to image positions O1 to O4 as image positions P1 to P4.

[0067] Next, the control unit 81 aligns the reference image A1 with respect to the read image B1 based on the information of image positions O1 to O4 and image positions P1 to P4 (step S25). Specifically, the control unit 81 rotates, translates, etc., the reference image A1, including the edges of the recording medium, so that each of the image positions O1 to O4 in the reference image A1 overlaps with each of the image positions P1 to P4 in the read image B1. The left figure of Figure 12 shows the reference image A2 after alignment.

[0068] Next, as shown in the left diagram of Figure 12, the control unit 81 determines the four corner points Q1 to Q4 (coordinates) of the recording medium (recording medium area 121) from the reference image A2 after alignment (step S26). Specifically, the control unit 81 detects four straight lines as edges of the recording medium area 121 from the reference image A2 after alignment. The control unit 81 obtains the positions of four points as the intersections of the four straight lines, and these four points are designated as the positions of the four corners (points Q1 to Q4) of the recording medium area 121.

[0069] Next, as shown in the right-hand diagram of Figure 12, the control unit 81 determines the four corner points R1 to R4 (coordinates) of the recording medium (recording medium area 131) from the read image B1 (step S27). Specifically, the control unit 81 detects four straight lines as edges of the recording medium area 131 from the read image B1. The control unit 81 obtains the positions of four points as the intersections of the four straight lines, and these four positions are designated as the positions of the four corners (points R1 to R4) of the recording medium area 131.

[0070] Next, the control unit 81 calculates the distance between points Q1 to Q4 in the reference image A2 after alignment and points R1 to R4 in the read image B1 as the displacement amounts D1 to D4 (step S28). The control unit 81 calculates the displacement amounts D1 to D4 from the difference between points Q1 to Q4 and points R1 to R4 in the X and Y directions, respectively. Figure 13 shows an image comparing point Q1 and point R1. The distance between point Q1 and point R1 is the displacement amount D1.

[0071] Moving to Figure 10, the control unit 81 determines whether at least one of the displacement amounts D1 to D4 is greater than or equal to a preset reference value V (step S29). Note that the reference value V used in step S29 may be a different value from the reference value V used in step S15 of the first positional displacement detection process (see Figure 4). If all of the displacement amounts D1 to D4 are less than the reference value V (step S29; NO), the control unit 81 determines that there is no positional displacement (step S30).

[0072] In step S29, if at least one of the displacement amounts 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 misalignment (step S31). The control unit 81 controls the transport unit 84 to discharge the misaligned recording medium to a different discharge tray from the discharge tray where normal recording media are discharged (step S32).

[0073] After step S30 or step S32, the process moves to step S33. In step S33, the control unit 81 checks for abnormalities in the read image B1 based on the reference image A2 after alignment and the read image B1. Here, the control unit 81 checks for abnormalities other than misalignment. Abnormalities in the read image B1 include image color, dirt, etc. For example, the control unit 81 generates a difference image between the reference image A2 after alignment and the read image B1. The control unit 81 generates a difference image by calculating the difference in the pixel values ​​(luminance value, RGB value, etc.) of each pixel in both images. The control unit 81 checks for abnormalities in the read image B1 by determining whether each pixel in the difference image exceeds a predetermined threshold.

[0074] Next, the control unit 81 determines whether there is any abnormality other than misalignment in the read image B1 (step S34). If there is an abnormality other than misalignment 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 different discharge tray from the discharge tray where normal recording media are discharged (step S35).

[0075] If, after step S35, or in step S34, there are no abnormalities other than positional misalignment in the read image B1 (step S34; NO), the second positional misalignment detection process is terminated.

[0076] In the image inspection process (see Figure 3), step S1 involves selecting either the first detection mode or the second detection mode. Alternatively, the control unit 81 may select both the first and second detection modes and execute both the first and second positional misalignment detection processes. Of the processes included in the first and second positional misalignment detection processes, the image formation by the image forming unit 40 and the image reading by the image reading unit 70 may be processed using the same recording medium. If the control unit 81 determines that a misalignment exists in either the first or second positional misalignment detection process, it adopts the determination result of the misalignment detection process that determined the misalignment exists. Furthermore, if the control unit 81 determines that a misalignment exists in both the first and second positional misalignment detection processes, it adopts both determination results. Finally, the control unit 81 outputs the results in a way that indicates which positional misalignment detection process determined the result for each detected misalignment.

[0077] As described 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 deviations of the image forming position. In the second detection mode, the control unit 81 detects the positional deviation without the image forming unit 40 forming a position detection image (such as a registration mark or registration mark). Therefore, the control unit 81 can detect positional deviations of the image forming position without using a position detection image. By using the second detection mode, the control unit 81 can eliminate the need to form a position detection image on the recording medium or to cut the position detection image from the recording medium. Furthermore, since the second detection mode does not require cutting the recording medium, the control unit 81 can detect positional misalignment not only on irregularly shaped paper but also on standard-shaped paper.

[0078] In the first detection mode, the control unit 81 detects the positional shift 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 shift with high accuracy by using the position detection image.

[0079] 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 image to be inspected. This allows the control unit 81 to detect the positional shift of the image formation position without using a position detection image.

[0080] Specifically, in the second detection mode, the control unit 81 detects positional misalignment based on alignment achieved through image matching using the image included in the reference image and the image included in the read image. The control unit 81 can align the reference image and the read image using information about the region where the image actually exists.

[0081] After alignment, the control unit 81 detects misalignment based on the edges of the recording medium detected from the read image. This allows the control unit 81 to detect misalignment based on information about the recording medium area, which is the largest available 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 corner bending or the like.

[0082] The control unit 81 inspects the read image for any abnormalities based on the reference image and the read image. This allows the control unit 81 to perform normal inspection operations in addition to detecting positional misalignment.

[0083] The control unit 81 acquires information regarding the misalignment 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 regarding the misalignment of the image. This allows the control unit 81 to correct the misalignment of the image in the image forming unit 40.

[0084] The above-described embodiments are examples of the image inspection apparatus, image forming apparatus, image inspection method, and program according to the present invention, and are not limited thereto. The detailed configuration and operation of each part constituting the apparatus can also be modified as appropriate without departing from the spirit of the present invention.

[0085] For example, the above embodiment described a case in which the image forming apparatus 100 (image inspection apparatus) comprises an image forming unit 40 and an image reading unit 70. Alternatively, the image inspection apparatus may acquire a read image generated by reading a recording medium on which an image has been formed by an external image forming unit (image forming apparatus) using an external image reading unit (image reading apparatus), and use that as the object of inspection. Furthermore, in the above embodiment, each process performed by the image forming apparatus 100 may be performed in cooperation with multiple devices.

[0086] Furthermore, in the second positional misalignment detection process (see Figures 9 and 10), even when the reference image is a RIP image, a background region corresponding to the area outside the recording medium is assumed to be added to the reference image. Alternatively, when the reference image is a RIP image, a background region does not need to be added to the reference image. In this case, the control unit 81 can treat the edge of the image data of the reference image as a position corresponding to the edge of the recording medium.

[0087] The computer-readable medium used to store the programs for executing each process is not limited to the examples above. Furthermore, a carrier wave may be used as the medium for providing program data via a communication line.

[0088] The embodiments disclosed herein are for illustrative purposes only and not intended to limit the scope of the invention. The scope of the invention should be interpreted as described in the claims. [Explanation of symbols]

[0089] 40 Image forming unit 50 Supply section 60 Post-processing 61, 62 Discharge trays 70 Image reading unit 81 Control Unit 82 Memory section 84 Conveying section 100 Image forming apparatus

Claims

1. An image inspection apparatus comprising a control unit for detecting positional misalignment of the image formation position on a recording medium on which an image has been formed by an image forming unit, The control unit, A first detection mode for detecting the positional misalignment based on the position of the positional detection image formed by the image forming unit at a predetermined position on the recording medium, A second detection mode in which the positional displacement is detected without the positional detection image being formed by the image forming unit, An image inspection device having the following features.

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

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

4. In the second detection mode, the control unit detects the positional misalignment based on alignment achieved by image matching using the image included in the reference image and the image included in the read image. The image inspection apparatus according to claim 3.

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

6. The control unit further inspects whether there are any abnormalities in the read image based on the reference image and the read image. The image inspection apparatus according to claim 3.

7. An image acquisition unit acquires a read image generated by reading a recording medium on which an image has been formed by an image forming unit, using a reading unit. The system includes a control unit that inspects whether there are any abnormalities in the read image based on a reference image stored in a memory unit and the read image, The control unit acquires information regarding the positional misalignment of an 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 acquired information regarding the positional misalignment of the image.

8. An image inspection apparatus according to any one of claims 1 to 7, The image forming unit and, A reading unit reads a recording medium on which the aforementioned image is formed and generates a read image, An image forming apparatus equipped with the following features.

9. An image inspection method for detecting positional misalignment of the image formation position in a recording medium on which an image has been formed by an image forming unit, A first detection mode for detecting the positional misalignment based on the position of the positional detection image formed by the image forming unit at a predetermined position on the recording medium, A second detection mode in which the positional displacement is detected without the positional detection image being formed by the image forming unit, An image inspection method having the following characteristics.

10. An image acquisition step involves acquiring a read image generated by reading a recording medium on which an image has been formed by an image forming unit using a reading unit, and An inspection step of checking for abnormalities in the read image based on a reference image stored in the memory unit and the read image, A control step which involves acquiring information regarding the positional misalignment of the image formed on the recording medium based on the reference image and the read image, and controlling the image formation position in the image forming unit based on the acquired information regarding the positional misalignment of the image, Image inspection methods including

11. A computer that detects positional misalignment of the image formation position on a recording medium in which an image has been formed by an image forming unit, A first detection mode for detecting the positional misalignment based on the position of the positional detection image formed by the image forming unit at a predetermined position on the recording medium, A second detection mode in which the positional displacement is detected without the positional detection image being formed by the image forming unit, A program to cause a control unit to function as such.

12. On the computer, An image acquisition step involves acquiring a read image generated by reading a recording medium on which an image has been formed by an image forming unit using a reading unit, and An inspection step of checking for abnormalities in the read image based on a reference image stored in the memory unit and the read image, A control step which involves acquiring information regarding the positional misalignment of the image formed on the recording medium based on the reference image and the read image, and controlling the image formation position in the image forming unit based on the acquired information regarding the positional misalignment of the image, A program to execute.

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