Image inspection device, image inspection method, and image inspection program

Abstract

To accurately position a front image and a back image.SOLUTION: An image inspection device includes a first reading unit 11 that reads a first image on one side of a medium (7), a second reading unit 21 that reads a second image on the other side of the medium, and an acquisition signal generation unit 50a that generates a second image acquisition signal that causes the second reading unit to read the second image after a predetermined time has elapsed from a first image acquisition start signal that causes the first reading unit to read the first image.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image inspection apparatus, an image inspection method, and an image inspection program, and more particularly, to a motor control apparatus used when replacing a motor disposed in an image forming apparatus.

Background Art

[0002] There is an image forming apparatus that uses a white toner as the fifth color toner in addition to YMCK toners. Also, there is black paper as a paper for bringing out the effect of the white toner. As a result, the added value of printed materials is enhanced. In general, the background member of the imaging unit (image sensor) is black so that white paper can be easily read. By the way, in such an image forming apparatus, small registration marks (images for position measurement) that do not affect the image content are printed at the four corners of the paper, and the distance between the paper edge and the registration marks is measured. Thereby, the alignment of the image with respect to the paper at the time of printing is performed.

[0003] Here, consider a case where a registration mark is printed on black paper with white toner in an image forming apparatus and the registration mark is read. For example, in the case of a job with a mixture of white and black papers, the black paper is read against a black background member. Since the color of the paper and the color of the background member are similar, it has been difficult to detect the paper edge. Since the paper edge cannot be detected, the distance from the paper edge to the registration mark cannot be measured.

[0004] In order to solve such problems, the image inspection apparatus of Patent Document 1 reads the front and back images, and estimates one of the paper contour information (information on the paper edge) of the acquired read images based on the other paper contour information. By this estimation, the image inspection apparatus of Patent Document 1 acquires the correction amount for alignment.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the technology of Patent Document 1, in order to read the front and back images, both a first reading unit for reading the front surface image and a second reading unit for reading the back surface image are provided. Along with this, in the technology of Patent Document 1, a photosensor for detecting the paper edge is provided individually. That is, the first reading unit reads the front surface image after the first photosensor detects the paper edge, and the second reading unit reads the back surface image after the second photosensor detects the paper edge.

[0007] Also, each photosensor detects the paper edge by polling processing by the CPU (Central Processing Unit). Therefore, time variation occurs in the determination timing of edge detection. In particular, when the CPU is under pressure, the time variation becomes large. As a result, in the technology of Patent Document 1, the positioning between the first image (front surface image) read by the first reading unit on one side of the medium and the second image (back surface image) read by the second reading unit on the other side is inaccurate.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide an image inspection apparatus, an image inspection method, and an image inspection program capable of accurately positioning a first image and a second image.

Means for Solving the Problems

[0009] The above problems of the present invention are solved by the following means.

[0010] An image inspection apparatus including: a first reading unit configured to read a first image on one surface of a medium; a second reading unit configured to read a second image on the other surface of the medium; and an acquisition signal generation unit configured to generate a second image acquisition signal for causing the second reading unit to read the second image after a predetermined time has elapsed from a first image acquisition start signal for causing the first reading unit to read the first image.

[0011] (2) The image inspection apparatus according to (1) above, wherein the first image acquisition start signal is a signal having time variation, and the second image acquisition signal has less time variation than the first image acquisition start signal.

[0012] (3) The image inspection apparatus according to (1) above, wherein the first acquisition start signal is a signal generated by a CPU executing a program by a polling signal, and the second acquisition start signal is a signal generated by a hardware clock or a real-time OS.

[0013] (4) The image inspection apparatus according to (1) above, wherein when a process with high priority is executed and the resources of the CPU are limited, the acquisition signal generation unit generates the second acquisition start signal using a hardware clock.

[0014] (5) The image inspection apparatus according to (1) above, further including a medium color acquisition unit configured to acquire a medium color based on medium information, wherein the acquisition signal generation unit generates the second acquisition start signal based on an acquisition result of the medium color acquisition unit.

[0015] (6) The image inspection apparatus according to (5) above, further including: a first background member provided behind the medium to be read by the first reading unit; and a second background member provided behind the medium to be read by the second reading unit, wherein the first background member and the second background member are black with a reflectance of 20% or less, and the acquisition signal generation unit generates the second acquisition start signal when the medium acquired by the medium color acquisition unit is black with a reflectance of 20% or less.

[0016] (7) The acquisition signal generation unit includes a counter signal generation unit that starts counting from the first image acquisition start signal, a counter value holding unit that holds a predetermined count value, and a comparator unit that compares the count value of the counter signal generation unit with the value of the counter value holding unit. The comparator unit outputs a second image acquisition signal of the second image when the comparison result is reversed. The second reading unit is the image inspection apparatus according to (1) above that scans according to the second image acquisition signal.

[0017] (8) The counter value holding unit acquires the distance between the first reading unit and the second reading unit and the conveyance speed of the medium from the first reading unit to the second reading unit. The count value is determined based on the distance and the conveyance speed. The image inspection apparatus according to (7) above.

[0018] (9) A first background member provided at a position behind the medium read by the first reading unit, A second background member provided at a position behind the medium read by the second reading unit, A paper feeding unit that feeds the medium, An image forming unit that forms an image on the medium, and a medium color acquisition unit that is provided between the paper feeding unit and the image forming unit in the medium conveyance path and detects the color of the medium. The first reading unit reads the first image and its background image, and the second reading unit reads the second image and its background image. When the color of the first background member or the second background member and the color of the medium detected by the medium color acquisition unit are black with a reflectance of 20% or less, the second reading image is acquired according to the second acquisition start signal. The image inspection apparatus according to (1) above.

[0019] (10) The predetermined count value of the counter value holding unit can be varied according to the distance between the first reading unit and the second reading unit, the conveyance speed of the medium conveyed between the first reading unit and the second reading unit, the medium size, the basis weight of the medium, the thickness of the medium, the surface property of the medium, the moisture content of the medium, the resistance of the medium, the stiffness of the medium, the type of the medium, the thickness of the medium, the outside air temperature, and the outside humidity. The image inspection apparatus according to (7) above.

[0020] (11) An image inspection method executed by a control unit of an image inspection apparatus including a first reading unit that reads a first image on one side of a medium and a second reading unit that reads a second image on the other side of the medium, the method comprising: generating a second image acquisition signal for causing the second reading unit to read the second image after a predetermined time has elapsed from a first image acquisition start signal for causing the first reading unit to read the first image.

[0021] (12) An image inspection program for causing a control unit of an image inspection apparatus including a first reading unit that reads a first image on one side of a medium and a second reading unit that reads a second image on the other side of the medium to execute, the program comprising: causing the control unit to generate a second image acquisition signal for causing the second reading unit to read the second image after a predetermined time has elapsed from a first image acquisition start signal for causing the first reading unit to read the first image.

Effect of the Invention

[0022] According to the present invention, the positioning between the first image and the second image can be made accurate.

Brief Description of the Drawings

[0023]

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Mode for Carrying Out the Invention

[0024] The following description is an embodiment of the present invention, and reference is made to the drawings. Note that each figure only schematically shows the present invention to such an extent that it can be sufficiently understood. Therefore, the present invention is not limited to only the illustrated examples. Also, in each figure, common components and similar components are denoted by the same reference numerals, and redundant descriptions thereof are omitted.

[0025] The image inspection apparatus of the present invention includes a first reading unit (11) that reads a first image (for example, a surface image) on one surface of a medium (7), and a second reading unit (21) that reads a second image (for example, a back surface image) on the other surface of the medium. Further, the image inspection apparatus of the present invention has an acquisition signal generation unit (50a) that generates a second image acquisition signal (for example, an image acquisition interrupt signal) for causing the second reading unit to read the second image after a predetermined time has elapsed from a first image acquisition start signal (for example, an acquisition start interrupt signal) for causing the first reading unit to read the first image. At this time, a first background member (13) that is the background of the first image and a second background member (23) that is the background of the second image are provided. The first background member and the second background member have different colors, and are preferably complementary colors (for example, black and white when the medium is a combination of a black medium or a medium with a mixture of white and black papers). Also, the color of one of the background members preferably matches the color of the medium. The first reading unit and the second reading unit are close enough that positional deviation due to conveyance can be ignored.

[0026] (First Embodiment) First, with reference to FIGS. 1 and 2, the configuration of the image inspection apparatus according to the first embodiment of the present invention will be described. When a medium 7 such as a sheet of paper having images (for example, images including dragonflies 81 and 82 (FIG. 2)) formed on both surfaces is conveyed through a medium conveyance path 30, the image inspection apparatus 100 inspects the positional deviation in the conveyance direction (Y direction) between the surface image and the back surface image. That is, the image inspection apparatus 100 inspects a positional deviation Δy = |Δ1 - Δ2| between a measurement distance Δ1 (FIG. 2) and a measurement distance Δ2 (FIG. 2). Here, the measurement distance Δ1 (FIG. 2) is the distance between the edge 71 of the medium 7 and the reading start position 72 on one surface (front surface). Also, the measurement distance Δ2 (FIG. 2) is the distance between the edge 73 of the medium 7 and the reading start position 74 on the other surface (back surface). Note that the medium 7 may be a set of media in which white paper with a white background color and black paper with a black background color are mixed.

[0027] The image inspection apparatus 100 includes a first photosensor 12, a first reading unit 11, a first background member 13, a second reading unit 21, a second background member 23, and an acquisition signal generation unit 50a. The first reading unit 11 is a line sensor of the CCD type that images one surface (front surface) of the medium 7 and reads a first image (for example, a front surface image) of one surface of the medium 7. The first photosensor 12 detects the arrival of the edges 71 and 73 of the medium 7. Thereby, the imaging timing of the first reading unit 11 is determined by the detection signal of the first photosensor 12. The second reading unit 21 is a line sensor of the CCD type that images the other surface (back surface) of the medium 7 and reads a second image (for example, a back surface image) of the other surface of the medium 7. In the present embodiment, as will be described later, the acquisition signal generation unit 50a determines the imaging timing of the second reading unit 21 based on the detection timing of the first photosensor 12.

[0028] The first background member 13 is a plate material that serves as the background of the first reading unit 11. The first background member 13 is larger than the medium 7 and is disposed behind the medium 7 when viewed from the first reading unit 11. The second background member 23 is a plate material that serves as the background of the second reading unit 21. The first background member 13 and the second background member have different colors, and complementary colors are preferable. For example, the first background member 13 is black and the second background member 23 is white. Conversely, the first background member 13 may be white and the second background member 23 may be black. Thereby, if the background color of the medium 7 is different from the color of the first background member 13, the position of the edge 71 of the medium 7 is detected using the front surface image. On the other hand, if the background color of the medium 7 is similar to the color of the first background member 13, the position of the edge 71 of the medium 7 is estimated (detected) using the back surface image. Therefore, regardless of the background color of the medium 7, the edges 71 and 73 of the medium 7 are detected using either one or both of the front surface image and the back surface image.

[0029] The second background member 23 is larger than the medium 7 and is disposed behind the medium 7 when viewed from the second reading unit 21. Note that the second reading unit 21 and the second background member 23 are disposed on the downstream side in the conveyance direction from the first reading unit 11 and the first background member 13. Also, the first background member 13 and the first reading unit 11, and the second background member 23 and the second reading unit 21 are separated by a reading unit interval Y0 (FIG. 1). This reading unit interval Y0 is short enough to ignore the positional deviation due to conveyance.

[0030] The acquisition signal generation unit 50a controls the first photosensor 12, the first reading unit 11, and the second reading unit 21. The acquisition signal generation unit 50a includes a CPU (central processing unit) which is a control unit (not shown) and a storage unit (not shown). The acquisition signal generation unit 50a executes an OS (Operating System) and an application program stored in the storage unit. Thereby, the functions of each unit (FIG. 3) are realized. Note that the OS of this embodiment is premised on a general-purpose OS such as Windows (registered trademark) or Linux (registered trademark).

[0031] FIG. 3 is a configuration diagram showing the internal configuration of the acquisition signal generation unit 50a used in the first embodiment of the present invention. The acquisition signal generation unit 50a includes functional units such as a first medium conveyance position detection unit 51a, a first image acquisition signal generation unit 53a, a counter signal generation unit 55a, a counter value holding unit 52a, and a comparator unit 54a. The first media conveyance position detection unit 51a outputs a first conveyance position detection signal for driving the first photosensor 12 or receiving a detection signal at a substantially constant period (for example, every 1 mSec). As a result, the first media conveyance position detection unit 51a receives a detection signal (first image acquisition start signal) indicating that the edges 71, 73 (FIG. 1) of the media 7 have been detected from the first photosensor 12. Thereby, the first media conveyance position detection unit 51a recognizes the passage of the edges 71, 73 of the media 7. Since the first conveyance position detection signal for driving the first photosensor 12 is generated by the CPU that executes a program under the management of the OS by polling control, there is time variation. Along with the time variation of the first conveyance position detection signal, there may be a time variation ΔT (FIG. 1) in the first image acquisition start signal. For example, when the time variation of the first conveyance position detection signal is large, the first conveyance position detection signal may not be output when the edges 71, 73 of the media 7 pass the first photosensor 12. At this time, the first conveyance position detection signal is output by the first conveyance position detection signal in the next cycle. That is, the edges 71, 73 of the media 7 by the first photosensor 12 are detected in the next cycle, and the detection is delayed.

[0032] The first image acquisition signal generation unit 53a acquires a surface image of the media 7 and a background image of the first background member 13 using the first reading unit 11 at the acquisition timing of the detection signal (first image acquisition start signal). That is, the first image acquisition start signal is also a signal (first image acquisition signal) for starting the acquisition of the surface image of the media 7 using the first reading unit 11. Note that the first conveyance position detection signal, the first image acquisition signal, etc. are often interrupt signals generated by interrupts.

[0033] The counter signal generation unit 55a internally generates a clock signal with a constant frequency and counts the clock signal from the acquisition timing of the detection signal (first image acquisition start signal). Since the acquisition timing of the first image acquisition start signal is equal to the timing of the first image acquisition signal, the counter signal generation unit 55a counts the clock signal with the first image acquisition signal.

[0034] The counter value holding unit 52a is a storage unit that holds a value (held value) generated inside the counter signal generation unit 55a. This held value is determined by the frequency of the clock signal, the reading unit interval distance Y0 (FIG. 1), the medium conveyance speed, the medium size, the medium basis weight, the medium thickness, the medium surface property, the medium moisture content, the medium resistance, the medium stiffness, the medium type, the medium thickness, the outside air temperature, and the outside humidity. Note that the medium conveyance speed is the conveyance speed of the medium 7 conveyed between the first reading unit 11 and the second reading unit 21. The comparator unit 54a compares the count value (counter signal (FIG. 4)) of the counter signal generation unit 55a with the held value held by the counter value holding unit 52a. Then, when the value comparison result is inverted, the comparator unit 54a outputs a second image acquisition signal to the second reading unit 21. Thereby, the second reading unit 21 acquires the back surface image of the medium 7 and the background image of the second background member 23.

[0035] FIG. 4 is an internal configuration diagram of the counter signal generation unit 55a. The counter signal generation unit 55a includes a clock oscillator 56, a frequency divider 57a, and a counter 57b. The clock oscillator 56 is a functional unit that generates a clock of a constant frequency. Note that the clock oscillator 56 may use a hardware clock that drives the CPU. The frequency divider 57a is a functional unit that divides the output signal of the clock oscillator 56. The counter 57b is a functional unit that counts the output signal of the frequency divider 57a starting from the acquisition timing of the first image acquisition signal. Thereby, the counter signal generation unit 55a generates a counter signal (count value by the counter 57b) using the first image acquisition signal (first image acquisition start signal (FIG. 3)).

[0036] As described above, according to the image inspection apparatus 100 of the present embodiment, when the first photosensor 12 detects the edges 71, 73 of the medium 7, the first reading unit 11 captures a surface image and a background image. Further, after the first photosensor 12 detects the edges 71, 73 of the medium 7, the second reading unit 21 captures a back surface image and a background image after a predetermined time has elapsed. Here, even if a time variation ΔT (FIG. 1) occurs from the passing timing at which the edges 71, 73 of the medium 7 pass through the first photosensor 12 to the detection timing of the edges 71, 73, the time from the reading timing at which the first reading unit 11 reads the surface image to the reading timing at which the second reading unit 21 reads the back surface image is constant. Therefore, the positions of the edges 71, 73 of the back surface image are correctly recognized. That is, the positional deviation between the front and back is obtained.

[0037] Here, when the ground color of the medium 7 is different from the colors of the first background member 13 and the second background member 23, the edges 71, 73 clearly appear in the images (surface image, back surface image) read by the first reading unit 11 and the second reading unit 21. Therefore, the distances between the edges 71, 73 and the pins 81, 82 can be measured using the captured back surface image. However, when the ground color of the medium 7 is similar to the colors of the first background member 13 and the second background member 23, the edges 71, 73 do not appear in the images read by the first reading unit 11 and the second reading unit 21. However, according to the present embodiment, regardless of the ground color of the medium 7, the edges 71, 73 of the medium 7 are detected using at least one of the surface image and the back surface image. Therefore, the distances between the edges 71, 73 and the pins 81, 82 can be measured.

[0038] (Second Embodiment) The acquisition signal generation unit 50a of the first embodiment uses a general-purpose OS, but a real-time operating system (RTOS) can also be used. Thereby, the time from when the first medium conveyance position detection unit 51b detects the first image acquisition start signal (FIG. 3) to when the second reading unit 21 reads the back surface image becomes more accurate.

[0039] FIG. 5 is a configuration diagram showing the internal configuration of the acquisition signal generation unit 50b used in the second embodiment of the present invention. The image inspection apparatus 101 includes a first photosensor 12, a first reading unit 11, a second reading unit 21, and an acquisition signal generation unit 50b. The acquisition signal generation unit 50b includes a first medium conveyance position detection unit 51b, a first image acquisition signal generation unit 53b, a counter signal generation unit 55b, a counter value holding unit 52b, and a comparator unit 54b, as in the above embodiment. However, the acquisition signal generation unit 50b is different in that each functional unit functions under the management of the real-time OS 60. The real-time OS is an OS that focuses on satisfying real-time performance on the order of nanoseconds in response to system requirements. For example, embedded OSs such as ITRON (registered trademark) are representative, and real-time Linux (registered trademark) is also included.

[0040] (Third Embodiment) In the first embodiment, a general-purpose OS is used, and in the second embodiment, a real-time OS is used. However, a part of it may be configured by hardware.

[0041] FIG. 6 is a configuration diagram showing the internal configuration of the acquisition signal generation unit 50c used in the third embodiment of the present invention. The image inspection apparatus 102 includes a first photosensor 12, a first reading unit 11, a second reading unit 21, and an acquisition signal generation unit 50c. The acquisition signal generation unit 50c includes a first image acquisition signal generation unit 61, a first medium conveyance position detection unit 62, a counter signal generation unit 55c, a counter value holding unit 52c, and a comparator unit 54c, similar to the acquisition signal generation units 50a and 50b of the above embodiments. However, the first image acquisition signal generation unit 61 and the first medium conveyance position detection unit 62 are different in that they function under the management of the real-time OS 60. Also, the counter signal generation unit 55c and the comparator unit 54c are different in that they are configured by hardware resources. Note that the counter value holding unit 52c is a storage unit (hardware resource) as in the above embodiments. The hardware resources are configured to have, for example, an oscillation clock with a period on the order of nano-orders and a frequency divider by an FPGA / ASIC.

[0042] According to the acquisition signal generation unit 50c of the present embodiment, the counter signal generation unit 55c and the comparator unit 54c are configured by hardware resources. Therefore, the time from the reading by the first reading unit 11 to the reading by the second reading unit 21 is accurate. Since the start of reading by the first reading unit 11 depends on the first image acquisition start signal by the first photosensor 12, the time variation in the start of reading by the second reading unit 21 depends on the time variation ΔT (FIG. 1) of the first image acquisition start signal.

[0043] (Fourth Embodiment) The acquisition signal generation unit 50b of the second embodiment realized its function under the management of the real-time OS 60. Also, the counter signal generation unit 55c and the comparator unit 54c of the acquisition signal generation unit 50c of the third embodiment were configured by hardware resources. The counter signal generation unit and the comparator unit of the present embodiment are configured by a combination of the real-time OS 60 and hardware resources.

[0044] FIG. 7 is a configuration diagram showing the internal configuration of the acquisition signal generation unit 50d used in the fourth embodiment of the present invention. The image inspection apparatus 103 includes a first photosensor 12, a first reading unit 11, a second reading unit 21, and an acquisition signal generation unit 50d. The acquisition signal generation unit 50d, similar to the above embodiments, realizes the functions of the first image acquisition signal generation unit 61, the first medium conveyance position detection unit 62, the counter signal generation unit 55c, the counter value holding unit 52c, and the comparator unit 54c under the management of the real-time OS 60. However, the acquisition signal generation unit 50d further realizes the functions of the counter signal generation unit 55b and the comparator unit 54b under the management of the real-time OS 60.

[0045] That is, the acquisition signal generation unit 50d includes both hardware resources (counter signal generation unit 55c and comparator unit 54c) and program-implemented functional units (counter signal generation unit 55b and comparator unit 54b).The acquisition signal generation unit 50c also differs in that it includes a task management unit 63 that implements functions under the management of the real-time OS 60, an interrupt signal software / hardware switching unit 64, and a medium color acquisition unit 69.

[0046] The task management unit 63 determines whether processing is congested due to, for example, limited CPU resources or the execution of a high-priority process. The interrupt signal software / hardware switching unit 64 switches between the counter signal generation unit 55c and comparator unit 54c and the counter signal generation unit 55b and comparator unit 54b. The medium color acquisition unit 69 acquires the color (hue, saturation, brightness (density, reflectance)) of the medium 7 based on the medium information. The acquisition signal generation unit 50d determines whether to generate a second image acquisition start signal based on the medium information and the color acquisition results acquired by the medium color acquisition unit 69. For example, the acquisition signal generation unit 50d generates the second image acquisition start signal when the reflectance of the color acquired by the medium color acquisition unit 69 is black and is equal to or less than a predetermined value (30%, 20%, 10%, 5%). Conversely, when the reflectance exceeds the predetermined value, the acquisition signal generation unit 50d does not generate the second image acquisition start signal.

[0047] 8 is a flowchart for explaining the operation of the acquisition signal generator 50c used in the fourth embodiment of the present invention. This flow is started at regular intervals (for example, 1 mSec) when reading of the medium 7 is started. First, the task management unit 63 checks the status of CPU resources and the like (S10).

[0048] FIG. 9 is a flowchart when the task management unit 63 checks the status. The task management unit 63 determines whether the resources of the CPU are in a tight state (S1). If the resources of the CPU are in a tight state (Y in S1), the interrupt signal software / hardware switching unit 64 selects the hardware clock (counter signal generation unit 55c, comparator unit 54c) (S2). On the other hand, if the resources of the CPU are not in a tight state (N in S1), the interrupt signal software / hardware switching unit 64 selects the software clock (counter signal generation unit 55b, comparator unit 54b) (S3).

[0049] After the processing of S2 or S3, the task management unit 63 determines whether the medium color is black (S4). If the medium color is white (N in S4), the process ends. That is, if the background color of the medium 7 is white and the color of the first background member 13 is black, the edges 71, 73 of the medium 7 are clearly shown in the surface image. Therefore, the distances between the edges 71, 73 and the dragonflies 81, 82 are obtained using normal calculations (distance calculations using the surface image and the back surface image). On the other hand, if the medium color is black (Y in S4), the process returns to the original flow (Fig. 8) and executes the process specific to the embodiment.

[0050] In the flow of Fig. 8, the first image acquisition signal generation unit 61 (Fig. 7) transmits the first conveyance position detection signal to the first photosensor 12 (S11). As a result, the first photosensor 12 is driven, and the preparation for detecting the edges 71, 73 is completed. After the processing of S11, the first medium conveyance position detection unit 62 determines whether it has detected the first acquired image start signal from the first photosensor 12 (S12). If it has not detected the first acquired image start signal (N in S12), the determination of S12 is repeated. By detecting the first acquired image start signal (Y in S12), the first image acquisition signal generation unit 61 transmits the first image acquisition signal to the first reading unit 11 (S13) and drives the counter signal generation unit 55b or the counter signal generation unit 55c. At this time, if the resources of the CPU are not in a tight state (N in S1 (Fig. 9)), the counter signal generation unit 55b is driven. Conversely, when the resources of the CPU are in a tight state (Y in S1), the counter signal generation unit 55c is driven.

[0051] After the process of S13, the counter signal generation unit 55b or the counter signal generation unit 55c sets a predetermined count value according to the conveyance speed and the distance from the first reading unit 11 to the second reading unit 21 (S14). After the process of S14, the counter signal generation unit 55b or the counter signal generation unit 55c updates the predetermined count value according to the characteristics of the medium (weight, paper pressure, ···) (S15). After the process of S15, the counter signal generation unit 55b or the counter signal generation unit 55c starts counting (S16) and determines whether the count value has reached the predetermined count value (S17). If the count value does not reach the predetermined count value (N in S17), the counter signal generation unit 55b or the counter signal generation unit 55c repeats the counting. If the count value reaches the predetermined count value (Y in S17), the comparator unit 54b or the comparator unit 54c generates a second image acquisition signal (S18) and ends the process.

[0052] As described above, according to the present embodiment, if the resources of the CPU are strained (Y in S1 (FIG. 9)), the hardware resources (counter signal generation unit 55c, comparator unit 54c) are used, and if the resources of the CPU are not strained (N in S1), the program (counter signal generation unit 55b, comparator unit 54b) is executed.

[0053] FIGS. 10 and 11 are diagrams showing the relationship between the front-back positional deviation and the frequency of the fourth embodiment of the present invention. FIG. 10 shows the positional deviation at the left end (-X direction end), and FIG. 11 shows the positional deviation at the right end (X direction end). The front-back positional deviation Δy [mm] is calculated as Δy = (Δ1 - Δ2). Since the position of the edge E1 on the surface of the medium varies, Δ1 varies, and as a result, Δy varies. The frequency of the positional deviation Δy = 1.6 mm at the left end in FIG. 10 is the highest, the frequency of the positional deviation Δy = 1.8 mm at the right end is the highest, and the frequency of Δy = 2 mm is the next highest.

[0054] (Comparative Example) In each of the above embodiments, the conveyance of the medium 7 is detected using one first photosensor 12, but a plurality of photosensors may be used.

[0055] FIG. 12 is a diagram showing the configuration of the image inspection apparatus of the comparative example of the present invention. The image inspection apparatus 104 is common in that it includes a first photosensor 12, a first reading unit 11, a first background member 13, a second reading unit 21, a second background member 23, and an acquisition signal generation unit 50e, similar to the above-described embodiments. The image inspection apparatus 104 is different in that it further includes a second photosensor 22.

[0056] The second photosensor 22 is disposed on the downstream side in the conveyance direction from the first photosensor 12 and detects the arrival of the edges 71 and 73 of the medium 7. Thereby, the second photosensor 22 determines the imaging timing at which the second reading unit 21 captures the back surface image of the medium 7.

[0057] FIG. 13 is a configuration diagram showing the internal configuration of the acquisition signal generation unit 50a used in the comparative example of the present invention. The acquisition signal generation unit 50e is common in that it includes a first medium conveyance position detection unit 51a and a first image acquisition signal generation unit 53a, similar to the above-described embodiments. The acquisition signal generation unit 50e is different in that it further includes a second medium conveyance position detection unit 58 and a second image acquisition signal generation unit 59. The second medium conveyance position detection unit 58 outputs a second conveyance position detection signal that drives the second photosensor 22 or receives a detection signal at a constant period (for example, every 1 mSec). The second medium conveyance position detection unit 58 further receives a detection signal (second image acquisition start signal) indicating that the second photosensor 22 has detected the edges 71 and 73 (FIG. 12) of the medium 7. Since this second conveyance position detection signal is a polling signal generated by a CPU that executes a program under the management of the OS, there is a time variation ΔT (FIG. 1). The second image acquisition start signal is a signal for starting the acquisition of the back surface image of the medium 7 using the second reading unit 21, and there is also a time variation ΔT in the start of the acquisition of the back surface image.

[0058] FIGS. 14 and 15 are diagrams showing the relationship between the positional deviation and the frequency of the front and back surfaces of the comparative example of the present invention. Similar to FIGS. 11 and 12, FIG. 14 shows the positional deviation at the left end, and FIG. 15 shows the positional deviation at the right end. The large displacement Δy occurs at 0.4 mm, 1.2 mm, 1.4 mm, and 2.4 mm in FIG. 14. Also, in FIG. 15, it occurs at 1.0 mm, 1.8 mm, 2.0 mm, and 3 mm. That is, the large displacement Δy occurs every 0.8 mm to 1.0 mm. In other words, the displacement Δy occurs about 2 mm.

[0059] In contrast, the displacement Δy in each of the above embodiments is Δy = 1.6 mm at the left end (FIG. 10) and Δy = 1.8 mm to 2.0 mm at the right end (FIG. 11), with little variation.

[0060] (Modification example) The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention. For example, there are the following (a) to (c). (a) In each of the above embodiments, the inspection device for inspecting the displacement between the front surface image and the back surface image formed on the medium 7 is used. However, it may be provided with an image forming unit for performing printing (image formation) on the medium 7 and a paper feeding unit for feeding the medium 7. In other words, the image inspection device 100 in each of the above embodiments functions as an image forming device. At this time, the medium color acquisition unit 69 (FIG. 7) is provided between the paper feeding unit and the image forming unit.

[0061] (b) In the fourth embodiment, since the first background member 13 and the second background member 23 were black, when the reflectance of the color acquired by the medium color acquisition unit 69 (FIG. 7) was black with a predetermined value or less, the acquisition signal generation unit 50d generated the second image acquisition start signal. Not limited to this, when the color of the medium 7 matches or approximates the color of either the first background member 13 or the second background member 23, the acquisition signal generation unit 50d may generate the second image acquisition start signal. At this time, the first background member 13 and the second background member 23 preferably have different colors and are complementary colors.

[0062] (c) In each of the above embodiments, the detection was aimed at the positional deviation in the conveyance direction (Y direction) of the medium 7, but the positional deviation in the X direction can also be detected. In this case, the control unit converts the coordinates of each vertex of the sheet contour information obtained from the back surface image to the mirror image positions. Further, the control unit estimates that the contour connecting the converted vertices is the sheet contour information read by the first reading unit 11, which is obtained by shifting the contour based on the difference in the reading positions of the medium 7 by the first reading unit 11 and the second reading unit 21.

Explanation of Reference Numerals

[0063] 11 First reading unit 12 First photosensor 13 First background member 21 Second reading unit 22 Second photosensor 23 Second background member 30 Medium conveyance path 50a, 50b, Acquisition signal generation unit (control unit) 51a, 51b, 62 First medium conveyance position detection unit 52a, 52b, 52c Counter value holding unit 53a, 53b First image acquisition signal generation unit 54a, 54b Comparator unit 55a, 55b, 55c Counter signal generation unit 56 Clock oscillator 57b Counter 58 Second medium conveyance position detection unit 59 Second image acquisition signal generation unit 60 Real-time OS 61 First image acquisition signal generation unit 62 First medium conveyance position detection unit 63 Task management unit 69 Medium color acquisition unit 100, 101, 102, 103, 104 Image inspection device (image forming device) 7 Medium (paper, paper sheets) 71, 73 Edge (medium edge)

Claims

1. A first reading unit that reads a first image on one side of the medium, A second reading unit that reads a second image on the other side of the medium, An acquisition signal generation unit that generates a second image acquisition signal for causing the second reading unit to read the second image after a predetermined time has elapsed from a first image acquisition start signal for causing the first reading unit to read the first image, An image inspection apparatus having the above.

2. The first image acquisition start signal is a signal having time variation, The second image acquisition signal has less time variation than the first image acquisition start signal The image inspection apparatus according to claim 1.

3. The first image acquisition start signal is a signal generated by a CPU that executes a program by polling control, The second image acquisition signal is a signal generated by a hardware clock or a real-time OS The image inspection apparatus according to claim 1.

4. When a process with high priority is executed and the resources of the CPU are limited, the acquisition signal generation unit generates the second image acquisition signal using a hardware clock The image inspection apparatus according to claim 1.

5. Having a medium color acquisition unit that acquires a medium color based on medium information, The acquisition signal generation unit generates the second image acquisition signal based on the acquisition result of the medium color acquisition unit The image inspection apparatus according to claim 1.

6. A first background member provided behind the medium read by the first reading unit, Further comprising a second background member provided behind the medium read by the second reading unit, The first background member and the second background member are black with a reflectance of 20% or less, When the medium acquired by the medium color acquisition unit is black with a reflectance of 20% or less, the acquisition signal generation unit generates the second image acquisition signal The image inspection apparatus according to claim 5.

7. The acquisition signal generation unit, A counter signal generation unit that starts counting from the first image acquisition start signal, A counter value holding unit that holds a predetermined count value, Comprising a comparator unit that compares the count value of the counter signal generation unit with the value of the counter value holding unit, The comparator unit outputs a second image acquisition signal for the second image when the comparison result is inverted, The second reading unit scans according to the second image acquisition signal The image inspection apparatus according to claim 1.

8. The counter value holding unit acquires the distance between the first reading unit and the second reading unit and the conveyance speed of the medium from the first reading unit to the second reading unit, and the count value is determined based on the distance and the conveyance speed. The image inspection apparatus according to claim 7.

9. a first background member provided behind the medium read by the first reading unit, a second background member provided behind the medium read by the second reading unit, a paper feeding unit that feeds the medium, an image forming unit that forms an image on the medium, and further includes a medium color acquisition unit that is provided between the paper feeding unit and the image forming unit in the medium conveyance path and detects the color of the medium. The first reading unit reads the first image and its background image, the second reading unit reads the second image and its background image, when the color of the first background member or the second background member and the color of the medium detected by the medium color acquisition unit are black with a reflectance of 20% or less, the second image is acquired by the second image acquisition signal. The image inspection apparatus according to claim 1.

10. A predetermined count value of the counter value holding unit is determined according to the distance between the first reading unit and the second reading unit, the conveyance speed of the medium conveyed between the first reading unit and the second reading unit, the medium size, the basis weight of the medium, the thickness of the medium, the surface property of the medium, the moisture content of the medium, the resistance of the medium, the stiffness of the medium, the type of the medium, the thickness of the medium, the outside air temperature, and the outside humidity. The image inspection apparatus according to claim 7.

11. An image inspection method executed by a control unit of an image inspection apparatus including a first reading unit that reads a first image on one surface of a medium and a second reading unit that reads a second image on the other surface of the medium, wherein after a predetermined time has elapsed from a first image acquisition start signal for causing the first reading unit to read the first image, a second image acquisition signal for causing the second reading unit to read the second image is generated. Image inspection method.

12. An image inspection program to be executed by a control unit of an image inspection apparatus including a first reading unit that reads a first image on one surface of a medium and a second reading unit that reads a second image on the other surface of the medium, wherein after a predetermined time has elapsed from a first image acquisition start signal for causing the first reading unit to read the first image, the control unit is caused to generate a second image acquisition signal for causing the second reading unit to read the second image. Image inspection program.

Images