Image forming apparatus, image forming method, and program

Abstract

To provide an image forming apparatus, an image forming method, and a program that further reduce the out of register between front and back.SOLUTION: In a line-head type printer including: a paper feed unit 3 that conveys a recording medium such as a sheet; an imaging unit 1 that prints an image on the conveyed recording medium; and an image reading unit 7 that reads a printing position from the printed image, a control section comprises: an image position detection section that detects the amount of change of the printing position read by the image reading unit with respect to a target printing position, and a correction value calculation section functioning as an image position correction section that, on the basis of the change amount, corrects the position of an image to be formed on the next and subsequent recording media. The image position correction section determines the image position on the second surface of the recording medium on the basis of a deviation after printing that is the amount of change of the printing position on the first surface of the recording medium from the target printing position and a deviation during printing from the target printing position on the first surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses an image forming device that reads a position detection mark formed on a first side of a recording medium such as paper and the coordinates of the edge of the recording medium, and adjusts the position of the image formed on the second side based on the read image on the first side before forming the second side of the recording medium, thereby reducing misregistration between the front and back. Summary of the Invention [Problem to be solved by the invention]

[0003] However, while the above-mentioned image position adjustment technology corrects the image position on the second side to match the image position on the first side, there is a problem in that it is not possible to correct misalignment at the time of printing (e.g., magnification, registration misalignment, distortion).

[0004] The present invention has been made in view of the above, and an object of the present invention is to provide an image forming apparatus, an image forming method, and a program that can further reduce misregistration between the front and back sides. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems and achieve the object, the present invention comprises a transport unit that transports a recording medium, a printing unit that forms an image on the transported recording medium, an image reading unit that reads the printing position from the printed image, an image position detection unit that detects the amount of change of the printing position read by the image reading unit from a target printing position, and an image position correction unit that corrects the position of the image to be formed on the recording medium from the next time onwards based on the amount of change, and the image position correction unit determines the image position on the second side of the recording medium based on the amount of change of the printing position on the first side of the recording medium from the target printing position, which is the deviation after printing and the deviation at the time of printing from the target printing position on the first side. Effect of the Invention

[0006] According to the present invention, the effect of further reducing misregistration between the front and back sides is achieved. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a line head type printing machine according to the present embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of the configuration of an image forming unit included in a line head type printer according to the present embodiment. [Figure 3A] FIG. 3A is a diagram showing an example of the configuration of an image reading unit included in a line head type printer according to the present embodiment. [Figure 3B] FIG. 3B is a block diagram showing an example of the functional configuration of a control device, a print engine, and an image position detection device of a line head type printing press according to the present embodiment. [Figure 3C] FIG. 3C is a block diagram showing a hardware configuration of the image position detection device according to the present embodiment. [Figure 4] FIG. 4 is a diagram for explaining an example of ideal coordinates and reading coordinates on the first surface of a recording medium in a line head type printer according to the present embodiment. [Diagram 5] FIG. 5 is a diagram for explaining an example of ideal coordinates and reading coordinates of the first and second surfaces of a recording medium in a line head type printer according to the present embodiment. [Figure 6] FIG. 6 is a diagram for explaining an example of print coordinates on the second surface in the conventional technology and in this embodiment. [Figure 7] FIG. 7 is a diagram for explaining an example of front-back positional deviation caused by detection deviation of image position. [Figure 8] FIG. 8 is a diagram for explaining an example of correction of front-back positional deviation due to detection deviation of image position. [Figure 9]FIG. 9 is a diagram for explaining an example of a side effect caused by correcting the detection shift of the image position and a countermeasure therefor. [Figure 10] FIG. 10 is a diagram for explaining an example of a coordinate formula for dealing with side effects of correcting detection deviation of image position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an image forming apparatus, an image forming method, and a program will be described in detail with reference to the accompanying drawings.

[0009] 1 is a diagram showing an example of the configuration of a line head type printer according to the present embodiment. The line head type printer (an example of an image forming apparatus) according to the present embodiment includes an image forming unit 1, a pre-coating unit 2, a paper feed unit 3, a drying / cooling unit 4, a reversing unit 5, a paper discharge unit 6, an image reading unit 7, etc.

[0010] The paper feed unit 3 is an example of a transport section that feeds and transports recording media such as paper one sheet at a time. The pre-coating unit 2 is a unit that applies a pre-coating liquid to the paper in advance to fix liquid such as ink, which is difficult to fix depending on the paper. The imaging unit 1 is a unit that wraps the paper around a drum and performs printing (printing, image formation) with a line head. In addition, the imaging unit 1 detects a main scanning deviation before wrapping the paper around the drum, and corrects the deviation by shifting the image in the main scanning direction and printing it. In other words, the imaging unit 1 is an example of a printing section that forms an image on the transported paper.

[0011] The drying / cooling unit 4 dries the water content of the ink and fixes it on the paper. The drying / cooling unit 4 also includes a cooling unit because the paper can become very hot when necessary. The reversing unit 5 performs a switchback reversal during automatic back-side printing and transports the paper in the direction of the imaging unit 1.

[0012] The paper discharge unit 6 stacks the paper on which printing has been completed. The image reading unit 7 is a unit that reads the printed image. The image reading unit 7 is disposed on the double-sided conveying path in order to read the image when the paper deformation has sufficiently stabilized after drying and cooling and immediately before printing on the second side of the paper. That is, the image reading unit 7 is an example of an image reading section that reads the printing position from the image printed on the paper. The image reading unit 7 may also have a first image reading section that reads the image immediately after printing, and a second image reading section that reads the image when the paper is sufficiently stable after printing.

[0013] 2 is a diagram showing an example of the configuration of an imaging unit of a line head type printer according to this embodiment. In this embodiment, the imaging unit 1 has a shift roller 11, edge sensors (linear image sensors, etc.) 12a, 12b, a gripper 13, an entrance cylinder 14, an imaging drum 15, a print timing sensor 16, print heads (line heads KCMY) 17a, 17b, 17c, 17d, an exit cylinder 18, etc. In the following description, when there is no need to distinguish between the print heads 17a, 17b, 17c, 17d, they may be referred to as print head 17.

[0014] The imaging unit 1 detects the main scanning positional deviation (and the amount of skew) of a recording medium such as paper that has entered the shift rollers 11 with an edge sensor 12, and corrects the main scanning positional deviation and skew with the shift rollers 11. After that, the imaging unit 1 causes the leading edge of the paper to be gripped by a gripper 13 that is attached to an entrance cylinder 14 and opens and closes mechanically. The entrance cylinder 14, the imaging drum 15, and the exit cylinder 18 are connected by gears, and the paper is transported while being gripped by the attached grippers 13 one after the other.

[0015] The print head 17 is a line head in which inkjet heads (for example, K, C, M, Y colors) are arranged in the X-axis direction (main scanning direction), and ejects ink to form an image when the paper passes under the print head 17. At that time, the imaging unit 1 determines the print timing based on the timing when the paper passes the print timing sensor 16.

[0016] 3A is a diagram showing an example of the configuration of an image reading unit of a line head type printer according to this embodiment. In this embodiment, while conveying a recording medium (e.g., paper) in its conveying direction at a conveying speed V, image reading unit 7 reads the paper edges and detection marks, which are the four corners of the recording medium, with an image sensor (e.g., CIS: Compact Image Sensor) arranged in a direction perpendicular to the conveying direction, and detects the positions of the paper edges and detection marks from the read image.

[0017] The image sensor does not need to be positioned across the entire width in the main scanning direction, but rather it only needs to be positioned so that it can detect the edges of the four corners of the recording medium and the detection mark. If the image sensor has a reading cycle T and resolution S, the main scanning resolution is S and the sub-scanning resolution is V x T. If the transport speed V is not constant, the sub-scanning resolution of the read image will vary, so it is necessary to keep the transport speed V constant as much as possible.

[0018] Alternatively, the positional relationship between the paper edge at the leading end of the recording medium and the detection mark and the positional relationship between the paper edge at the trailing end of the recording medium and the detection mark may be detected by an image sensor, and the length L of the recording medium in the sub-scanning direction (sub-scanning distance) may be detected by detecting the leading and trailing ends of the recording medium with a paper detection sensor and measuring the transport distance of the recording medium with an encoder (ENC) attached to the transport roller shaft.

[0019] This is because the distance between the paper edges and the detection marks at each of the four corners of the recording medium is short, so the effect of the detection error due to the deviation in the transport speed is small, but the effect of the detection error due to the deviation in the transport speed is large between the paper edges in the sub-scanning direction and between the detection marks. In addition to the transport speed, the detection error is also susceptible to the effects of paper skew during transport, etc., for the same reason.

[0020] Fig. 3B is a block diagram showing an example of the functional configuration of a control device, a print engine, and an image position detection device of a line head type printing machine according to this embodiment. As shown in Fig. 3B, the control device 1000 according to this embodiment includes an image processing unit 100 and an engine controller 200. The print engine 300 (imaging unit 1) includes a print processing unit 310. The image position detection device 400 includes a reading unit 401 (e.g., image reading unit 7), a sensor image acquisition unit 410, a correction value calculation unit 420, and a coordinate conversion unit 430.

[0021] The image processing section 100 includes a RIP processing section 110 and a job information processing section 120. The job information processing section 120 executes a correction process for correcting the position of an image formed on a recording medium such as printing paper M.

[0022] The control unit 1000 controls the execution of image formation and output based on print jobs input from the outside via a network and print jobs generated by an operator's operation from image data stored inside the control unit 1000. When executing image formation and output, the RIP processing unit 110 generates bitmap data based on the image data included in the print job and transmits the generated bitmap data to the engine controller 200.

[0023] When generating bitmap data, the RIP processor 110 generates bitmap data for the print engine 300 to execute image formation and output based on image data included in the print job. The bitmap data is information on each pixel constituting an image to be formed and output.

[0024] The print engine 300 according to the present embodiment executes image formation and output based on binary images for each of CMYK (Cyan, Magenta, Yellow, Key plate). In contrast, image data included in a print job is generally a multi-value image in which one pixel is expressed in multiple gradations such as 256 gradations. Therefore, the RIP processing unit 110 converts the image data included in the print job from a multi-value image to a low-value image, and generates binary bitmap data for each of CMYK.

[0025] The data acquisition unit 210 acquires the print job and bitmap data from the image processing unit 100, and operates the engine control unit 220. The engine control unit 220 causes the print engine 300 to execute image formation output based on the print job and bitmap data transferred from the data acquisition unit 210. The engine control unit 220 also causes the reading unit 401 to execute a reading operation based on the print job transferred from the data acquisition unit 210.

[0026] The print processing unit 310 is an image forming unit (printing unit) that acquires bitmap data input from the engine controller 200, executes image forming output on a recording medium such as print paper M, and outputs the print paper M on which the image is printed. The print processing unit 310 according to this embodiment is realized by a general image forming mechanism of an electrophotographic system, but it is also possible to use other image forming mechanisms such as an inkjet system.

[0027] The reading unit 401 is composed of a line sensor or the like arranged on the transport path of the recording medium inside the image position detection device 400, and based on control information such as a print job input from the engine control unit 220, scans the surface of the recording medium transported near the reading unit 401 and reads the detection mark formed on the recording medium.

[0028] The read image is an image generated by the reading unit 401 reading the recording medium on which the detection mark is output, and therefore is an image showing the output result by an image forming apparatus (for example, a line head type printer). The sensor image acquisition unit 410 acquires the read image generated by the reading unit 401 reading the recording medium. The read image acquired by the sensor image acquisition unit 410 is input to the correction value calculation unit 420 and the coordinate conversion unit 430 together with the print job when the reading unit 401 generated the read image.

[0029] The correction value calculation unit 420 calculates a correction amount for correcting the position (image position) of the image formed on the recording medium when forming and outputting the image, based on the central coordinates of the detection mark and the coordinates of the end portion (paper edge) of the recording medium included in the read image acquired from the sensor image acquisition unit 410. The correction value calculation unit 420 stores the calculated correction amount in the memory 420a.

[0030] Specifically, the correction value calculation unit 420 functions as an example of an image position detection unit that detects the amount of change from a target print position (target image) of a print position (for example, a detection mark in a read image) read by the reading unit 401. The correction value calculation unit 420 also functions as an example of an image position correction unit that corrects the position of an image to be formed on a recording medium from the next time onward, based on the detected amount of change.

[0031] At that time, the correction value calculation unit 420 determines the image position on the second side (back side) of the recording medium based on the post-printing deviation including the amount of change in the print position on the first side (front side) of the recording medium from the target print position, and the deviation at the time of printing from the target print position on the first side. The deviation at the time of printing on the first side (deviation at the time of printing) is a fixed deviation that the printing system (line head type printing machine) has, and a similar deviation at the time of printing occurs even when the second side is printed using the same printing system (configuration in which printing is performed by switching back). Therefore, by correcting the image to be printed on the second side in advance taking into account the deviation at the time of printing, the image can be formed at the target print position.

[0032] Furthermore, the correction value calculation unit 420 may correct the misalignment during printing in a direction that cancels it, and then determine the image position of the second side according to the amount of change (misalignment after printing). Here, the misalignment during printing may be a positional misalignment (for example, registration misalignment) with respect to the target printing position of the detection mark closest to the paper edge (one example of an edge) that is the printing origin of the first side read by the reading unit 401. Since the change in the registration misalignment after printing is smaller than that of the magnification or distortion, the registration misalignment can be treated as a misalignment at the time of printing even if the image is detected when the recording medium is sufficiently stable after printing. This makes it possible to correct the misalignment during printing even if the reading unit 401 has only one image reading unit.

[0033] Furthermore, when the reading unit 401 has a first image reading unit that reads an image immediately after printing, and a second image reading unit that reads an image when the recording medium is sufficiently stable after printing, the correction value calculation unit 420 may determine the image position on the second side after breaking down the misalignment into two components, misalignment during printing and misalignment after printing, based on the image reading result by the first image reading unit and the image reading result by the second image reading unit. By having two image reading units, it is possible to correct not only the registration misalignment, but also the magnification misalignment and distortion that are susceptible to changes due to moisture, by breaking down the misalignment into two components, misalignment during printing and misalignment after printing.

[0034] Furthermore, the correction value calculation unit 420 may function as an example of a read result correction unit that corrects the amount of change in the detection shift based on an image after the image position has been corrected. In this case, the correction value calculation unit 420 may determine the image position of the second side based on the reading result of the print position of the first side to which correction has been applied not only to the image position but also to the position of the recording medium. In other words, the correction value calculation unit 420 checks the amount of front-back misalignment (amount of change) from a front-back registration chart (an example of an image after the image position has been corrected) output by the print engine 300, and if it can be applied as the amount of correction for the detection shift, it can apply correction not only to the image position but also to the position of the recording medium, so that correction can be applied to the position of the recording medium without changing the registration misalignment of the first side.

[0035] Furthermore, the correction value calculation unit 420 may correct the detection result of the amount of change based on the input result of the correction amount from an external source. This allows the user to visually check the amount of front-back misalignment from the front-back registration chart output, and manually input the correction value from the operation screen.

[0036] The correction value calculation unit 420 may also correct the read result of the position of the recording medium by the same amount as the correction amount of the positional misalignment of the detection mark with respect to the adjacent paper edge. In other words, the correction value calculation unit 420 corrects the detection misalignment between the adjacent paper edge and the detection mark as being equivalent to the positional misalignment of the recording medium.

[0037] The correction value calculation unit 420 may also correct the reading result of the position of the recording medium by multiplying the correction amount of the positional deviation of the detection mark with respect to the adjacent paper edge by the ratio of the distance from the reading origin between the detection mark and the paper edge. In other words, the correction value calculation unit 420 corrects the detection deviation between the adjacent paper edge and the detection mark as the ratio of the distance from the reading origin.

[0038] The coordinate conversion unit 430 converts the center coordinates of the detection mark detected by reading the detection mark formed on the first surface of the recording medium and the coordinates of the end of the recording medium into a coordinate system on the first surface when performing image formation output on the second surface.

[0039] Here, the hardware configuration constituting the functional blocks of the control device 1000, the print engine 300, and the image position detection device 400 according to this embodiment will be described with reference to Fig. 3C. Fig. 3C is a block diagram showing the hardware configuration of the image position detection device according to this embodiment. Fig. 3C shows the hardware configuration of the image position detection device 400, but the hardware configurations of the control device 1000 and the print engine 300 are also configured in the same way as the image position detection device 400.

[0040] As shown in Fig. 3C, the image position detection device 400 according to this embodiment has the same configuration as an information processing device such as a general PC (Personal Computer) or server. That is, the image position detection device 400 according to this embodiment has a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 20, a ROM (Read Only Memory) 30, a HDD (Hard Disk Drive) 40, and an I / F 50 connected via a bus 90. The I / F 50 may also be configured to have an LCD (Liquid Crystal Display) 60, an operation unit 70, and a dedicated device 80 connected thereto.

[0041] The CPU 10 is a computing means and controls the overall operation of the image position detection device 400. The RAM 20 is a volatile storage medium capable of reading and writing information at high speed, and is used as a working area when the CPU 10 processes information. The ROM 30 is a read-only non-volatile storage medium in which programs such as firmware are stored. The HDD 40 is a non-volatile storage medium in which information can be read and written, and in which an OS (Operating System), various control programs, application programs, etc. are stored.

[0042] The I / F 50 connects and controls the bus 90 with various hardware, networks, etc. The LCD 60 is, for example, a visual user interface that allows a user to check the operating state of the image forming apparatus via the control device 1000. The operation unit 70 is a user interface that allows a user to input information to the control device 1000 using a keyboard, a mouse, etc.

[0043] The dedicated device 80 is hardware for realizing dedicated functions in the control device 1000, the print engine 300 and the image position detection device 400. In the case of the print engine 300, it is a transport mechanism that transports paper on which an image is to be formed and output, and a plotter device that performs image formation and output on the paper surface.

[0044] The control device 1000 and the image position detection device 400 are dedicated arithmetic devices for performing high-speed image processing. Such arithmetic devices are configured as, for example, ASICs (Application Specific Integrated Circuits). They also include reading devices such as sensors for reading images output on paper.

[0045] In such a hardware configuration, a software control unit is configured by reading out programs stored in a recording medium such as ROM 30, HDD 40, or an optical disk into RAM 20, and the CPU 10 performing calculations according to the programs. The combination of the software control unit configured in this way and hardware configures functional blocks that realize the functions of the control device 1000, print engine 300, and image position detection device 400 according to this embodiment.

[0046] FIG. 4 is a diagram for explaining an example of ideal coordinates and read coordinates of the first surface of the recording medium in the line head type printer according to the present embodiment. In this embodiment, the ideal coordinates (a1, b1, c1, d1) and read coordinates (a1', b1', c1', d1') of the detection mark on the first surface, and the ideal coordinates (A1, B1, C1, D1) and read coordinates (A1', B1', C1', D1') of the end (four corners) which is the paper edge of the recording medium (e.g., paper) are assumed to be the following formulas (1) and (2). Here, the ideal coordinates are the ideal coordinates of the detection mark and the paper edge, and may be, for example, the coordinates when the print position read by the reading unit 401 is the target print position. Also, the read coordinates are the coordinates of the detection mark and the paper edge read by the image reading unit 8.

[0047] In this embodiment, the ideal coordinates of the detection mark and the edge of the first side of the recording medium may be coordinates when the upper left edge (A1) of the recording medium such as paper is set as the origin (0,0) as shown in the following formula (1). Here, capital letters of the alphabet represent the coordinates of the paper edge of the recording medium, and lower case letters represent the coordinates of the detection mark. The number "1" represents a coordinate system with the upper left paper edge (A1) in the transport direction of the first side (e.g., the front side) of the recording medium as the reference origin (origin (0,0)), and the number "2" represents a coordinate system with the upper left paper edge (A2) in the transport direction of the second side (e.g., the back side) of the recording medium as the reference origin (origin (0,0)).

number

[0048] Furthermore, in this embodiment, the reading coordinates of the detection mark and paper edge on the first side may be coordinates when the upper left edge (A1') of a recording medium such as paper is set as the origin (0,0), as shown in the following formula (2). Here, the positional deviation (e.g., registration deviation) Δa indicates the registration deviation of the reading coordinates with respect to the ideal coordinates based on the transport direction during printing on the first side. The registration deviation Δa is the amount of deviation of the reading coordinates of the read detection mark a1' with respect to the ideal coordinates of the detection mark a1 close to the origin (0,0), as shown in the following formula (3).

number

number

[0049] FIG. 5 is a diagram for explaining an example of ideal coordinates and read coordinates of the first and second surfaces of a recording medium in a line head type printer according to the present embodiment. The following formulas (4) and (5) are ideal coordinates and read coordinates when the ideal coordinates and read coordinates of the detection mark and the end of the first surface of the recording medium are inverted upside down and converted based on the transport direction during printing on the second surface. Specifically, formula (4) represents the ideal coordinates of the first surface when the upper left end C2 of the paper edge of the recording medium such as paper is set as the origin (0,0). Furthermore, formula (5) represents the read coordinates of the first surface when the upper left end C2' of the paper edge of the recording medium such as paper is set as the origin (0,0).

number

number

[0050] Fig. 6 is a diagram for explaining an example of the printing coordinates of the second surface in the conventional technology and the present embodiment. First, in the conventional technology, as shown in Fig. 6(a), the detection mark on the first surface and the reading coordinates of the end of the recording medium are inverted upside down, and the print image on the second surface is formed at a position that matches the reading coordinates when converted based on the transport direction during printing on the second surface. However, in that case, the printing on the second surface also generates a registration deviation at the time of printing, just like the printing on the first surface, and as a result, the printing coordinates on the second surface will have a registration deviation of +Δa with respect to the printing coordinates on the first surface.

[0051] Therefore, in this embodiment, the correction value calculation unit 420 corrects the image position on the second side, and the print processing unit 310 forms the print image on the second side by shifting it in advance by -Δa as shown in Fig. 6(b), so that after the registration misalignment occurs at the time of printing, the registration misalignment between the print coordinates on the first side and the print coordinates on the second side becomes 0, improving the front and back registration accuracy. Here, the print coordinates may be the coordinates of the position where the image is formed on the recording medium.

[0052] 7 is a diagram for explaining an example of front-back positional deviation due to a detection deviation of the image position. Next, an example of front-back positional deviation due to a detection deviation of the reading system (image reading unit 7) will be explained, assuming that there is a system that can print correctly with respect to ideal coordinates. Here, for the sake of simplicity, it will be explained assuming that there is no deviation due to drying after printing. Here, the front-back positional deviation may be a positional deviation between the printed image on the first side and the printed image on the second side.

[0053] FIG. 7(a) is a diagram showing a case where the ideal coordinates of the first surface and the printing coordinates of the first surface coincide with each other. FIG. 7(b) is a diagram showing the read coordinates of the first surface when the first surface is detected as being shifted from the printing coordinates of the first surface shown in FIG. 7(a). As shown in FIG. 7(b), the detection marks at the four corners of the recording medium are shifted by Δa, Δb, Δc, and Δd at each point. FIG. 7(c) is a diagram showing an example of the printing coordinates of the detection marks on the second surface when the second surface is printed in this state. As shown in FIG. 7(c), the read coordinates shown in FIG. 7(b) are inverted upside down, and the printing coordinates of the second surface are determined so as to coincide with the transport direction of the second surface as a reference, and the surface is printed at the target position, so that a front-back position shift occurs by the amount of the detection shift.

[0054] FIG. 8 is a diagram for explaining an example of correction of front-back position deviation due to detection deviation of image position. As a method for solving the problem described in FIG. 7, there is a method for correcting the detection deviation of the reading system (image reading unit 7). In this correction method (image position detection deviation correction), the correction value calculation unit 420 prints an image in which the deviation amount of the front-back position deviation (front-back position deviation amount) at the four corners of the recording medium is known in advance by the print processing unit 310, calculates the front-back position deviation amount, sets the correction amount for correcting this front-back position deviation amount from a user operation screen or the like, and calculates the corrected reading coordinates by adding this correction amount to the subsequent reading coordinates. If this correction method is used, the printing coordinates of the first surface and the corrected reading coordinates of the first surface match, and as shown in FIG. 8, the printing coordinates of the second surface become a position (coordinates) where there is no front-back position deviation with respect to the printing coordinates of the first surface.

[0055] FIG. 9 is a diagram for explaining an example of side effects of image position detection shift correction and countermeasures. First, the side effects of image position detection shift correction will be explained. Here, for the sake of simplicity, it will be explained assuming that there is no shift due to drying after printing. FIG. 9(a) shows a case where the ideal coordinates of the first surface and the printed coordinates of the first surface match. FIG. 9(b) is a diagram for explaining an example where only the detection mark a is shifted by a position shift Δa. At this time, as explained in FIG. 8, if image position detection shift correction (distortion correction) is applied in advance only to the detection mark a by the position shift Δa, the detection result of the detection mark will be corrected to a correct detection result in subsequent detections.

[0056] Here, when the image reading unit 7 is in the double-sided conveying path as shown in FIG. 1, the conveying direction is reversed by the switchback in the reversing unit 5 when printing the first side and when reading the image of the first side, so the print origin A (origin when printing) and the read origin C (origin when reading) are different. Therefore, it is necessary to consider the coordinates of the paper edge of the recording medium at this time. If the detection result (read coordinates) of the detection mark a is shifted by Δa, it is considered that the detection result (read coordinates) of the print origin A is also shifted by about Δa. This is because, as explained in the configuration of the image reading unit 7 shown in FIG. 3A, the influence of the detection shift is small for the relationship between the paper edges and the detection marks at each of the four corners of the recording medium, but the influence of the detection shift is large between the paper edges in the sub-scanning direction and between the detection marks. If the print origin A is also shifted by Δa like the detection mark a, the registration shift at the time of printing explained in FIG. 4 will be 0.

[0057] However, as shown in Fig. 9(b), by applying image position detection shift correction only to detection mark a, the registration shift between the print origin A and detection mark a at the time of printing is Δa. As a result, when the correction described in Fig. 6 is applied, the print position (printed image) on the second side will be registration shifted by Δa with respect to the print result (printed image) on the first side (see Fig. 9(c)).

[0058] Therefore, as shown in Fig. 9(d), the correction value calculation unit 420 also applies the image position detection deviation correction applied to the detection mark to the coordinates of the paper edge of the recording medium. This makes it possible to make a correction that changes only the relationship between the reading origin C and the detection mark a without changing the relationship between the printing origin A and the detection mark a, so that the front-to-back registration accuracy can be improved even when the correction described in Fig. 6 is applied (see Fig. 9(e)). The correction to the coordinates of the paper edge of the recording medium may be exactly the same as the correction value of the detection mark a, or it may be applied to the printing origin A by multiplying Δa by the ratio of the distance between the printing origin A and the detection mark a to the reading origin C.

[0059] FIG. 10 is a diagram for explaining an example of a coordinate formula for a side effect countermeasure of image position detection shift correction. When conventional image position detection shift correction is applied only to the detection mark, the coordinate formula for the paper edge and detection mark is expressed by the following formula (6) (see FIG. 10(a)). In contrast, when image position detection shift correction is applied to the detection mark and paper edge as a side effect countermeasure, the coordinate formula for the paper edge and detection mark is expressed by the following formula (7) (see FIG. 10(b)). Since the detection shift correction is calculated based on the reading origin C, no correction value is applied to the reading origin C. However, if there is a reading path on the single-sided transport path, the reading origin is point A, so this formula does not apply.

number

number

[0060] In this way, with the line head type printing machine of this embodiment, in addition to correcting the image position on the second side to match the image position on the first side, it is also possible to correct the image position on the second side in a direction that cancels out the registration misalignment at the time of printing, thereby further reducing misregistration between the front and back.

[0061] The program executed by the line head printer of this embodiment is provided in advance in ROM 30 or the like. The program executed by the line head printer of this embodiment may be provided by being recorded in an installable or executable file format on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a digital versatile disk (DVD).

[0062] Furthermore, the program executed by the line head printer of the present embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. Also, the program executed by the line head printer of the present embodiment may be provided or distributed via a network such as the Internet.

[0063] The program executed by the line head type printing machine of this embodiment has a modular configuration including each of the above-mentioned units (sensor image acquisition unit 410, correction value calculation unit 420, image conversion unit 430, etc.), and in terms of actual hardware, an example of a processor such as CPU 10 reads out the program from the above-mentioned ROM 30 and executes it, thereby loading each of the above-mentioned units onto the main memory device, and the sensor image acquisition unit 410, correction value calculation unit 420, image conversion unit 430, etc. are generated on the main memory device.

[0064] In the above embodiment, the image forming apparatus of the present invention is described as being applied to a multifunction peripheral having at least two of the functions of a copy function, a printer function, a scanner function, and a facsimile function. However, the image forming apparatus can be applied to any image forming apparatus such as a copier, a printer, a scanner device, or a facsimile device.

[0065] For example, aspects of the present invention are as follows. <1> A conveying unit that conveys the recording medium; a printing unit that forms an image on the conveyed recording medium; an image reading unit that reads a printing position from the printed image; an image position detection unit that detects an amount of change in the print position read by the image reading unit with respect to a target print position; an image position correction unit that corrects the position of an image to be formed on the recording medium from the next time onward based on the amount of change; Equipped with An image forming apparatus, wherein the image position correction unit determines the image position on the second surface of the recording medium based on the deviation after printing, which is the amount of change in the printing position on the first surface of the recording medium from the target printing position, and the deviation at the time of printing from the target printing position on the first surface. <2> the image position correction unit corrects the misalignment during printing in a direction to cancel it, and then determines the image position on the second surface in accordance with the misalignment after printing. <1> 2. The image forming apparatus according to claim 1 . <3> the deviation during printing includes a positional deviation of a detection mark that is closest to an edge of a printing origin of the first surface read by the image reading unit, with respect to the target printing position; <1> or <2> 2. The image forming apparatus according to claim 1 . <4> the image reading unit includes a first image reading unit that reads the image immediately after printing, and a second image reading unit that reads the image when the recording medium is in a sufficiently stable state after printing, the image position correction unit determines the image position on the second surface after decomposing the misalignment into two components, that is, the misalignment during printing and the misalignment after printing, based on the result of reading the image by the first image reading unit and the result of reading the image by the second image reading unit. <1> from <3> 13. The image forming apparatus according to claim 12, <5> a read result correction unit that corrects a detection deviation of the image position detection unit based on the image after the image position has been corrected; the reading result correction unit determines the image position on the second side based on the reading result of the printing position on the first side to which correction has been applied not only to the image position but also to the position of the recording medium. <3> 2. The image forming apparatus according to claim 1 . <6> the read result correction unit corrects the detection result of the amount of change by the image position detection unit based on an input result of an amount of correction from an external source. <5> 2. The image forming apparatus according to claim 1 . <7> the read result correction unit corrects the read result of the position of the recording medium by the same amount as the correction amount of the positional deviation of the detection mark with respect to the adjacent edge. <5> 2. The image forming apparatus according to claim 1 . <8> the reading result correction unit corrects the reading result of the position of the recording medium by multiplying the positional deviation correction amount of the detection mark with respect to the adjacent edge by a ratio of a distance from a reading origin between the detection mark and the edge; <5> 2. The image forming apparatus according to claim 1 . <9> An image forming method carried out in an image forming apparatus, comprising: detecting an amount of change in a print position read by an image reading unit from an image printed on the conveyed recording medium with respect to a target print position; correcting the position of an image to be formed on the recording medium from the next time onward based on the amount of change; determining the image position on the second surface of the recording medium based on the deviation after printing, which is the amount of change of the print position on the first surface of the recording medium from the target print position, and the deviation during printing from the target print position on the first surface; An image forming method comprising the steps of: <10> Computer, an image position detection unit that detects a change in a print position read by an image reading unit from an image printed on the conveyed recording medium with respect to a target print position; an image position correction unit that corrects the position of an image to be formed on the recording medium from the next time onward based on the amount of change; and make it work. The image position correction unit determines the image position on the second surface of the recording medium based on the deviation after printing, which is the amount of change in the printing position on the first surface of the recording medium from the target printing position, and the deviation at the time of printing from the target printing position on the first surface. [Explanation of symbols]

[0066] 1 Imaging unit 2. First coat unit 3 Paper feed unit 4 Drying and cooling unit 5. Reversing unit 6 Paper ejection unit 7 Image reading unit 10 CPU 20 RAM 30 ROM 40 HDD 100 Image processing unit 110 RIP processing unit 120 Job information processing unit 200 Engine Controller 210 Data Acquisition Section 220 Engine control unit 300 Print Engine 310 Print processing unit 400 Image position detection device 401 Reading unit 410 Sensor image acquisition unit 420 Correction value calculation unit 430 Coordinate conversion unit 1000 Control device [Prior art documents] [Patent documents]

[0067] [Patent Document 1] JP 2019-101326 A

Claims

1. A conveying unit that conveys the recording medium; a printing unit that forms an image on the conveyed recording medium; an image reading unit that reads a printing position from the printed image; an image position detection unit that detects an amount of change in the print position read by the image reading unit with respect to a target print position; an image position correction unit that corrects the position of an image to be formed on the recording medium from the next time onward based on the amount of change; Equipped with An image forming apparatus, wherein the image position correction unit determines the image position on the second surface of the recording medium based on the deviation after printing, which is the amount of change in the printing position on the first surface of the recording medium from the target printing position, and the deviation at the time of printing from the target printing position on the first surface.

2. The image forming apparatus according to claim 1 , wherein the image position correction unit corrects the misalignment during printing in a direction that cancels the misalignment, and then determines the image position on the second surface in accordance with the misalignment after printing.

3. 3 . The image forming apparatus according to claim 1 , wherein the deviation during printing includes a positional deviation of a detection mark closest to an edge of a printing origin of the first surface read by the image reading unit, with respect to the target printing position.

4. the image reading unit includes a first image reading unit that reads the image immediately after printing, and a second image reading unit that reads the image when the recording medium is in a sufficiently stable state after printing, 2. The image forming apparatus according to claim 1, wherein the image position correction unit determines the image position of the second surface by decomposing the misalignment into two components, the misalignment during printing and the misalignment after printing, based on the result of reading the image by the first image reading unit and the result of reading the image by the second image reading unit.

5. a read result correction unit that corrects a detection deviation of the image position detection unit based on the image after the image position has been corrected; 4. The image forming apparatus according to claim 3, wherein the reading result correction unit determines the image position on the second side based on the reading result of the printing position on the first side to which correction has been applied not only to the image position but also to the position of the recording medium.

6. The image forming apparatus according to claim 5 , wherein the read result correction section corrects the detection result of the amount of change by the image position detection section based on an input result of an amount of correction from an outside source.

7. The image forming apparatus according to claim 5 , wherein the read result correction unit corrects the read result of the position of the recording medium by the same amount as the correction amount of the positional deviation of the detection mark with respect to the adjacent edge.

8. 6. The image forming apparatus according to claim 5, wherein the reading result correction unit corrects the reading result of the position of the recording medium by multiplying the correction amount of the positional misalignment of the detection mark relative to the adjacent edge by a ratio of the distance from a reading origin between the detection mark and the edge.

9. An image forming method carried out in an image forming apparatus, comprising: detecting an amount of change in a print position read by an image reading unit from an image printed on the conveyed recording medium with respect to a target print position; correcting the position of an image to be formed on the recording medium from the next time onward based on the amount of change; determining the image position on the second surface of the recording medium based on the post-printing deviation, which is the amount of change in the print position on the first surface of the recording medium from the target print position, and the deviation during printing from the target print position on the first surface; An image forming method comprising the steps of:

10. Computer, an image position detection unit that detects a change in a print position read by an image reading unit from an image printed on the conveyed recording medium with respect to a target print position; an image position correction unit that corrects the position of an image to be formed on the recording medium from the next time onward based on the amount of change; and make it work. The image position correction unit determines the image position on the second surface of the recording medium based on the deviation after printing, which is the amount of change in the printing position on the first surface of the recording medium from the target printing position, and the deviation at the time of printing from the target printing position on the first surface.

Images