JP2019130787A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can suppress disturbance of an image due to deformation of a recording sheet at the two-sided printing.SOLUTION: A control unit 4 acquires the pre-spray state being the state of a second surface P2 before spraying ink to a first surface P1 of a sheet P from a state detection unit S1 and the post-spray state being the state of the second surface P2 after spraying the ink to the first surface P1. The control unit 4 decides the correction value by comparing the pre-spray state with the post-spray state. The control unit 4 generates corrected image data obtained by correcting the image data with the correction value and forms an image on the second surface P2 on the basis of the corrected image data.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  When the image forming apparatus forms an image by spraying ink on the recording paper, the recording paper is stretched by spraying ink on the recording paper. When the ink dries, the extended portion shrinks. When the image forming apparatus forms an image on both sides of the recording paper, if the recording paper is stretched by image formation on one side and the image is formed on the other side, when the ink is dried, the recording paper The image formed on the other surface may be displaced. An image forming apparatus capable of suppressing such a shift in image due to deformation (elongation or contraction) of recording paper during image formation is disclosed in Patent Document 1.

  The image forming apparatus disclosed in Patent Document 1 forms double-sided images in a state where measurement position marks are attached to predetermined positions on both sides of a recording sheet based on image data. Then, the positions of the marks on both sides are detected from the image data obtained by reading the recording sheet on which the image is formed with the marks on both sides of the recording sheet by the image reading means. A misalignment of the marks on both sides is detected, and an adjustment value is calculated based on the misalignment to eliminate misalignment between the front and back sides of the recording paper, thereby forming an image. By doing in this way, the shift | offset | difference of the image of the front and back of a recording paper based on the expansion and contraction by forming an image on a recording paper can be suppressed.

JP 2003-173109 A

  However, the image forming apparatus disclosed in Patent Document 1 has a configuration in which a recording sheet on which images on both sides are formed in a state where a mark is attached to a measurement position is read by an image reading unit, and an adjustment with a mark is performed to calculate an adjustment value. A special test pattern must be printed. Recording paper and ink are consumed to calculate the adjustment value. In addition, since the recording paper on which the test pattern is formed is read by the image reading means, the user must attach the recording paper on which the test pattern is formed to the image reading means, and the calculation of adjustment values is troublesome. Take it.

  An object of the present invention is to provide an image forming apparatus capable of suppressing image disturbance due to deformation of a recording sheet during double-sided printing in view of the above-described problems of the prior art.

  In order to achieve the above object, the image forming apparatus according to claim 1 can form an image on both sides of a sheet. The image forming apparatus includes a transport unit, an image forming unit, a state detection unit, a reversing unit, and a control unit. The transport unit transports paper. The image forming unit forms an image by spraying ink onto a sheet conveyed by the conveying unit based on the image data. The state detection unit detects the deformation state of the paper. The reversing unit reverses the sheet from the image forming unit and sends it to the upstream side in the sheet conveying direction of the conveying unit. When image formation is performed on both sides of the sheet, the control unit applies a state before the spraying, which is a state of the second surface opposite to the first surface before the ink is sprayed from the state detection unit to the first surface, and the first surface. The state after the spraying, which is the state of the second surface after the ink is sprayed, is acquired. And a control part compares the state before spraying, and the state after spraying, and determines a correction value. The control unit generates corrected image data obtained by correcting the image data with the correction value, and forms an image on the second surface based on the corrected image data.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing image disturbance due to deformation of recording paper during double-sided printing.

FIG. 2 is a layout diagram illustrating a schematic configuration of a printer. 2 is a block diagram illustrating an example of a hardware configuration of a printer. FIG. It is a figure which shows the signal output from the surface of the paper detected by a state detection sensor, and a state detection sensor. It is a figure which shows an example of the output signal from a state detection sensor. It is the perspective view which showed the 1st surface of the sheet | seat up. It is the perspective view which showed the 2nd surface of the sheet | seat up. 3 is a flowchart illustrating an example of an operation of a printer. It is a figure which shows the 1st surface side of the paper with which the 1st image was printed on the 1st surface. It is a figure which shows the 2nd surface side of the paper shown in FIG. 10 is a flowchart illustrating another example of the operation of the printer.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking a printer 100 as an example of an image forming apparatus. Each element such as the configuration and arrangement described in the present embodiment does not limit the scope of the invention and is merely an illustrative example.

  Hereinafter, an ink jet printer 100 (corresponding to an image forming apparatus) having a fixed head portion 24 will be described as an example with reference to the drawings. Each element such as the configuration and arrangement described in the present embodiment does not limit the scope of the invention and is merely an illustrative example.

(First embodiment)
An overview of the printer 100 according to the present embodiment will be described. FIG. 1 is a layout diagram illustrating a schematic configuration of a printer. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the printer. In the following description, the description of the top, bottom, left, and right is based on the state shown in FIG. 1 unless otherwise specified.

  As shown in FIGS. 1 and 2, the printer 100 includes a paper feed tray 1, an image forming unit 2 (image forming unit), a transport unit 3, a control unit 4, a storage unit 5, and a communication unit 6. And a state detection sensor S1 (state detection unit).

(Paper Tray 1)
The paper feed tray 1 loads and accommodates paper P. A pair of paper feed rollers 11 is provided at the downstream end of the paper feed tray 1 in the paper transport direction. The pair of paper feed rollers 11 sequentially feed the stored paper P from the uppermost paper P one by one toward the image forming unit 2.

(Image forming unit 2)
The image forming unit 2 is provided on the downstream side (the right side in FIG. 1) of the paper feed roller pair 11 in the paper transport direction. The image forming unit 2 includes a drive roller 21, a driven roller 22, a transport belt 23, a head unit 24, a belt drive motor 25, and a carry-out roller pair 26.

  The drive roller 21 rotates upon receiving the driving force of the belt drive motor 25 (see FIG. 2). The driven roller 22 is provided so that the drive roller 21 and the axis are parallel. The conveyor belt 23 is an endless belt stretched around the driving roller 21 and the driven roller 22. The driving roller 21 receives the driving force of the belt driving motor 25 (see FIG. 2) and rotates. The conveyor belt 23 circulates as the driving roller 21 rotates. Thus, the paper P on the transport belt 23 is transported in the direction of the arrow X in FIG. 1, that is, the direction indicated by the arrow X is the transport direction X of the paper P. Note that the conveyance belt 23 may adsorb the paper P onto the conveyance belt 23 by sucking air, or may adsorb the paper P using static electricity or the like. The transport belt 23 preferably has a function of holding the paper P.

  The carry-out roller pair 26 is provided on the downstream side of the conveyance belt 23 in the sheet conveyance direction. The carry-out roller pair 26 carries out the paper P on which an image is recorded (printed) by the head unit 24 from the image forming unit 2.

  As shown in FIG. 1, the head unit 24 is disposed above the transport belt 23. The head unit 24 includes a head unit 24C that ejects cyan ink from the upstream side in the paper conveyance direction, a head unit 24M that ejects magenta ink, a head unit 24Y that ejects yellow ink, and a head unit 24K that ejects black ink. Are arranged in order. These head portions 24C to 24K are filled with inks of four different colors (cyan, magenta, yellow, and black). Then, each color ink is ejected from each of the head portions 24C to 24K, and a color image is recorded (printed) on the paper P. In this embodiment, an example in which the head portions 24 for four colors are provided will be described. However, head portions 24 of other colors may be provided. The head portions 24C to 24K are the same, and in the following description, the reference numerals (C, M, Y, and K) indicating colors are omitted, and the head portions 24 may be simply referred to below.

  As shown in FIG. 2, each head unit 24 (24 </ b> C to 24 </ b> K) includes a plurality of nozzles 242 and a plurality of drivers 241 that control ejection of ink from each nozzle 242. Depending on the printable paper size in the specifications, for example, about 2500 nozzles 242 (2500 dots) are provided in each head unit 24. The number of nozzles 242 provided in each head unit 24 may be less than 2500, or 2500 or more.

  Each nozzle 242 is formed by making a hole in a metal plate by etching or the like. A piezoelectric element (not shown) is provided for each nozzle 242. The driver 241 applies a voltage to the piezoelectric element that discharges ink in accordance with control data among the piezoelectric elements under its control. For example, the control unit 4 (image processing unit 42) transmits information indicating the operation of each nozzle 242 (information indicating whether ejection is present, information indicating density, control data) to each driver 241 in units of one ejection drive. . Each driver 241 applies a voltage to the piezoelectric element corresponding to the nozzle 242 to which ink should be ejected based on information indicating the operation of each nozzle 242. As a result, the piezoelectric element is deformed by voltage application, and pressure is applied to a flow path (not shown) that supplies ink to the nozzle 242. Then, the pressure with respect to the flow path is propagated, and ink is ejected from the nozzle 242.

  In addition, by changing the voltage applied to each piezoelectric element by each driver 241, it is possible to change the ejection speed and ejection amount of the ink ejected from the nozzle 242. For example, the voltage applied to the piezoelectric element can be made smaller than the reference voltage applied to the piezoelectric element. As a result, the driver 241 can adjust the ink discharge speed and the discharge amount with respect to the reference ink discharge speed and the discharge amount to give a difference in the density of one dot.

  The image forming unit 2 conveys the paper P so that the paper P advances by one dot with respect to the ejection of ink from the nozzle 242 once. An image is formed on the paper P by ejecting ink from the head unit 24 (4C, 4M, 4Y, 4K) onto the paper P conveyed by the image forming unit 2. The paper P on which the image is formed is sent to the transport unit 3 by the carry-out roller pair 26.

(Transport section 3)
The transport unit 3 includes a transport path 30, a paper discharge tray 31, a paper discharge roller pair 32, a reverse roller pair 33, a reverse retreat path 34, and a switching unit 35.

  The conveyance path 30 is a guide for guiding the paper P, and includes a first conveyance path 301, a second conveyance path 302, a reverse conveyance path 303, and a discharge conveyance path 304. Although not shown, the conveyance path 30 includes a pair of guide rollers for each conveyance path. At least one of the guide roller pair is connected to a motor and is rotated by driving of the motor. By rotating the guide roller pair, the paper P is transported along the transport path. One pair or a plurality of pairs of guide rollers provided in each transport path may be used.

  The first conveyance path 301 sends the paper P carried out by the carry-out roller pair 26 to the switching unit 35. The switching unit 35 sets the transport destination of the paper P transported from the transport roller pair 26 to either the discharge transport path 304 (that is, the discharge tray 31 side) or the second transport path 302 (that is, the reversing section 36 side). Switch. The discharge conveyance path 304 sends the paper P to the paper discharge roller pair 32. The paper P sent from the discharge conveyance path 304 to the paper discharge roller pair 32 is discharged to the paper discharge tray 31 by the paper discharge roller pair 32. The paper discharge tray 31 is a tray capable of storing the discharged paper P.

  The second conveyance path 302 sends the paper P to the reverse conveyance path 303. The reverse conveyance path 303, the reverse roller pair 33, and the reverse retreat path 34 constitute a reverse unit 36. The reverse roller pair 33 is a roller pair capable of switching the rotation direction. The reverse conveyance path 303 includes a first reverse conveyance path 305 and a second reverse conveyance path 306. The first reverse conveyance path 305 sends the paper P from the second conveyance path 302 to the reverse roller pair 33. The paper P sent to the reverse roller pair 33 temporarily stores the paper P in the reverse retreat path 34.

  After the paper P is stored in the reverse retreat path 34, the rotation direction of the reverse roller pair 33 is reversed, and the paper P is sent to the second reverse conveyance path 306. The reversing unit 36 temporarily stores the paper P in the reversing retreat path 34 and reverses the transport direction, so-called so-called paper P is switched back and sent to the upstream side of the image forming unit 2 of the transport unit 3. By switching back at the reversing unit 36, the surface of the paper P facing the head unit 24 is reversed. That is, the paper P is reversed by the reversing unit 36 and sent to the image forming unit 2.

  The paper feed roller pair 11, the drive roller 21, the carry-out roller pair 26, the paper discharge roller pair 32, and the reverse roller pair 33 described above are each connected to a motor and are driven to rotate by the motor. Each motor is controlled by the control unit 4. For example, the control unit 4 controls the rotation of the paper discharge roller pair 32 by controlling the rotation of a motor that drives the paper discharge roller pair 32. In the following description, the description of the motor is omitted, and the control unit 4 may be referred to as rotating the roller. In this case, it is synonymous with the drive of the motor connected to the roller being controlled. And

(Control unit 4)
The control unit 4 controls the recording operation (printing operation) of the printer 100. The control unit 4 includes a main control unit that performs overall control and image processing, an engine control unit that controls ON / OFF of a motor that rotates image recording and various rotating bodies, an image processing control unit that performs image processing, and the like. A plurality of types of control units may be provided by being divided according to functions and processing contents.

  The control unit 4 includes a CPU 41 and an image processing unit 42. The CPU 41 is a central processing unit. The control unit 4 is communicably connected to the storage unit 5. For example, the storage unit 5 includes ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), and flash ROM non-volatile and volatile storage devices. The storage unit 5 stores control programs, control data, image data, and the like. The CPU 41 performs a calculation based on a control program and control data stored in the storage unit 5 and issues a control signal to each unit of the printer 100.

  The control unit 4 is connected to the communication unit 6. The communication unit 6 is communicably connected to an external computer 200 (for example, a personal computer or a server) or a scanner 300 that reads an image recorded on the paper P and generates image data through a network or a cable. The communication unit 6 includes various connectors, sockets, a communication control controller, a chip, a memory, and the like. The communication unit 6 receives image data (for example, data including image data and print setting data) for causing the printer 100 to perform printing from the external computer 200 or the scanner 300. When the communication unit 6 receives the image data, the image processing unit 42 of the control unit 4 performs image processing on the image data as necessary, and based on the image processed image data, each head unit 24 and the image forming unit 2. Etc. are operated to perform printing.

  The image processing unit 42 performs various image processes on various image data such as image data received from the computer 200 and image data stored in the storage unit 5. Based on the image data indicating the content to be printed on the paper P, the image processing unit 42 finally converts it into printing image data representing the presence / absence and ejection amount of ink of each pixel (each dot). The image processing unit 42 adjusts the print image data according to the position of the nozzle 242 in the paper conveyance direction for each color, and transmits control data to the driver 241 of each head unit 24. The image processing unit 42 may be configured to include a dedicated circuit in the control unit 4, or may be functionally realized by a program stored in the CPU 41 and the storage unit 5.

  The control unit 4 (image processing unit 42) is connected to each head unit 24 and gives an operation instruction to each head unit 24. Each head unit 24 is provided with a driver 241 that actually controls the ejection of ink from each nozzle 242. Each driver 241 simultaneously ejects ink from each nozzle 242 at a constant period. Each driver 241 adjusts the presence / absence of ink ejected from each nozzle 242 and the amount of ink ejected based on the adjusted dot data, thereby adjusting the gradation (dot area) of dots formed on the recording medium. Control. For example, each driver 241 changes the drive voltage value and drive pulse width applied to each nozzle 242 based on an instruction from the control unit 4 to adjust the presence / absence of ink ejection and the ejection amount.

  As shown in FIG. 2, the control unit 4 is connected to each part of the printer 100 such as the paper feed roller pair 11, the image forming unit 2, the transport unit 3, and the state detection sensor S <b> 1. The control unit 4 controls and instructs the operation of each unit. The control unit 4 causes each part to perform an operation according to the input content.

(Status detection sensor S1)
The state detection sensor S1 detects the state of the paper P fed from the paper feed roller pair 11. As the state detection sensor S1, for example, an optical sensor that reads irregularities on the surface of the paper P using an imaging device or the like, that is, a so-called media sensor can be cited. The state detection sensor S1 is not limited to the media sensor, and a wide range of sensors that can detect the state of the surface of the paper P can be used. The state detection sensor S1 is disposed on the upstream side of the head unit 24 in the sheet conveyance direction, and detects the state of the surface of the sheet P. That is, the state detection sensor S1 detects the state of the surface of the paper P on which ink is sprayed from the head unit 24. Note that the state of the paper P detected by the state detection sensor S1 can include, for example, irregularities on the surface of the paper P.

  FIG. 3 is a diagram illustrating a sheet surface detected by the state detection sensor and a signal output from the state detection sensor. In FIG. 3, a part of the surface of the paper P is enlarged and displayed. The state detection sensor S1 detects a minute portion on the surface of the paper P. When viewed microscopically, the paper P is formed by intricately intertwining fine fibers Fb. And state detection sensor S1 detects the state of the surface of paper P by detecting the unevenness of this fiber Fb. Details of detection of the surface state of the paper P by the state detection sensor S1 will be described below.

  As shown in FIG. 3, the state detection sensor S <b> 1 detects the unevenness of the surface of the portion that falls within the detection area Sr of the paper P. For example, the state detection sensor S1 detects the unevenness of the fibers Fb of the paper P in the detection area Sr. Then, the state detection sensor S1 outputs the result of detecting the surface of the paper P as an output signal Sig. As shown in the lower part of FIG. 3, the output signal Sig is a signal obtained by binarizing the unevenness of the fiber Fb of the paper P in the detection region Sr. That is, in the output signal Sig, the convex portion of the paper P is at the H level and the concave portion is at the L level.

  The state detection sensor S1 detects the surface of the paper P being conveyed. The detection area Sr is provided in a direction orthogonal to the transport direction of the paper P. For this reason, the portions of the paper P that enter the detection area Sr are sequentially replaced. Each time the portion of the paper P that enters the detection area Sr is switched, the surface state of the planar portion of the paper P can be detected by detecting the surface of the paper P with the state detection sensor S1.

  When ink is sprayed on the paper P, the paper P gets wet by the ink. When the paper P gets wet with ink, the surface of the portion to which the paper P is sprayed may be extended. When the paper P is stretched, the unevenness of the surface of the paper P changes. In the printer 100, the surface detection sensor S1 detects irregularities on the surface of the paper P before and after the ink is sprayed. Then, the state detection sensor S1 sends information on the unevenness before and after ink ejection to the control unit 4, and the control unit 4 obtains an enlargement ratio. The control unit 4 corrects image data to be printed based on the enlargement ratio.

  Detection of changes before and after ink spraying will be described with reference to the drawings. FIG. 4 is a diagram illustrating an example of an output signal from the state detection sensor. FIG. 4 shows an output signal Sg1 before ink ejection and an output signal Sg2 after ink ejection. Note that the output signal Sg1 and the output signal Sg2 indicate unevenness of the same part.

  As shown in FIG. 4, in the output signal Sg1 before ink ejection, the width of the convex portion is the width W1. In the output signal Sg2 after ink is sprayed on the paper P, the width of the same convex portion is the width W2 (> W1). Then, the control unit 4 compares the width W1 and the width W2, and calculates a magnification, for example, by calculating a ratio.

  As described above, the printer 100 compares the surface state of the paper P before ink spraying and after ink spraying, and acquires the enlargement rate, in other words, the deformation rate. In this example, the detection region Sr extending in the direction orthogonal to the conveyance direction X of the paper P is set and the unevenness on the surface of the paper P is detected. However, the present invention is not limited to this. For example, the detection area may be set in a direction extending in the transport direction of the paper P. Alternatively, a detection area Sr extending in both the conveyance direction X and the direction orthogonal to the conveyance direction X of the paper P may be set, and the deformation rate may be calculated based on the surface state detected in both detection areas Sr. . By setting in this way, even when the ease of deformation of the paper P is different between the transport direction X and the direction orthogonal to the transport direction X, the accuracy of the deformation rate can be increased.

(Operation of printer 100)
FIG. 5 is a perspective view showing the first side of the sheet facing up. FIG. 6 is a perspective view showing the second side of the sheet facing up. As illustrated in FIG. 5, the printer 100 prints the first image Pt1 on one side (here, the first side P1) of the paper P. Further, the second image Pt2 is printed on the surface opposite to the first surface P1 (here, the second surface P2) of the paper P. Note that the printer 100 first prints the first image Pt1 on the first surface P1, and then prints the second image Pt2 on the second surface P2.

  Double-sided printing by the printer 100 will be described. In the printer 100, the control unit 4 drives the paper feed roller pair 11 to feed the paper P from the paper feed tray 1. The paper P from the paper feed roller pair 11 is transported to the transport belt 23 of the image forming unit 2. At this time, the paper P is held on the transport belt 23. The control unit 4 drives the drive roller 21 to move the transport belt 23 in the transport direction X, and transports the paper P to a position facing the head unit 24.

  The control unit 4 drives the head unit 24 to print on the first surface P1 of the paper P. Thereafter, the control unit 4 drives the carry-out roller pair 26 to convey the paper P to the first conveyance path 301. The paper P is sent to the switching unit 35. The control unit 4 drives the switching unit 35 to send the paper P to the second transport path 302. Then, the paper P is guided to the second conveyance path 302 and sent to the reversing unit 36. The control unit 4 operates each unit of the reversing unit 36 as described above to reverse the front and back of the paper P. As a result, the sheet P is held on the transport belt 23 with the second surface P2 facing the head portion 24.

  The control unit 4 moves the transport belt 23 in the transport direction X, and prints on the second surface P <b> 2 of the paper P by spraying ink from the head unit 24 when the paper P faces the head unit 24. The paper P is sent to the first conveyance path 301 by the carry-out roller pair 26. Then, the control unit 4 switches the switching unit 35 so that the paper P is sent to the discharge conveyance path 304 and is sent to the paper discharge roller pair 32 by the discharge conveyance path 304. The control unit 4 drives the paper discharge roller pair 32 to discharge the paper P to the paper discharge tray 31.

  The printer 100 prints on both sides of the paper P according to the above procedure. In the printer 100, when ink is sprayed on the paper P, the paper P gets wet by the ink. Depending on the paper P, when it gets wet with ink, elongation may occur. Then, when the ink is dried, the stretched paper P shrinks. When performing double-sided printing, the printer 100 sprays ink onto the first surface P1 to print the first image Pt1 (see FIG. 5), and then sprays ink onto the second surface P2 before the ink dries. Two images Pt2 (see FIG. 6) are printed.

  Therefore, when printing on the second surface P2, that is, when ink is sprayed, the second surface P2 may be extended by the ink sprayed on the first surface P1, that is, deformed. Then, when the second image Pt2 is printed by spraying ink on the second surface P2 of the deformed paper P based on the original image data, after the ink is dried, the second image Pt2 on the second surface P2 is distorted or the like. May occur and the print quality may deteriorate.

  Therefore, the control unit 4 performs image processing for deforming (here, expanding and contracting) the image data printed on the second surface P2, and the head unit based on the image data enlarged from the original image data. 24, the ink is sprayed onto the second surface P2 of the paper P. The image is corrected based on the correction value provided in the control unit 4. For example, when the correction value is 1.2, the image data is enlarged by 1.2 times in the vertical and horizontal directions. Although the vertical and horizontal correction values of the image data are the same, the vertical correction value and the horizontal correction value may be set independently. Also, other correction values may be used.

  On the other hand, the rate at which the paper P is stretched due to ink adhesion varies depending on the type and thickness of the paper P. Therefore, the printer 100 includes a state detection sensor S1 that detects the state of the paper P. Then, based on the surface state of the paper P detected by the state detection sensor S1, the control unit 4 updates the correction value for correcting the image data to be printed on the second surface P2. Here, the correction value update operation will be described with reference to a new drawing.

  FIG. 7 is a diagram illustrating a procedure for duplex printing on a sheet. Note that the paper P is stacked on the paper feed tray 1 of the printer 100 so that the second surface P2 faces the head unit 24 when the paper P is supplied to the image forming unit 2 by the paper feed roller pair 11. It shall be.

  First, along with the start of printing (step S <b> 101), the control unit 4 drives the paper feed roller pair 11. As a result, the sheets P stacked on the sheet feeding tray 1 are fed one by one to the conveyance belt 23 of the image forming unit 2. The control unit 4 drives the driving roller 21 of the image forming unit 2 to move the transport belt 23 in the transport direction X. Then, the control unit 4 drives the state detection sensor S <b> 1 to detect the surface state of the second surface P <b> 2 of the upper surface of the paper P held on the transport belt 23. And the control part 4 memorize | stores the information from state detection sensor S1 as a state before spraying (step S102). The control unit 4 acquires the state of the surface of the paper P before being wetted with ink by acquiring information on the state before spraying. In addition, as a surface state, although the uneven | corrugated state of the fiber of the surface of the area | region where the printing of 2nd surface P2 is performed as shown in FIG. The surface state may be the shape and size of the area where the second surface P2 is printed.

  After acquiring the pre-spray state of the paper P, the control unit 4 drives the carry-out roller pair 26 without sending ink from the head unit 24 and sends the paper P to the first transport path 301. And the control part 4 switches the switching part 35, and sends the paper P to the 2nd conveyance path 302 side. Furthermore, the control unit 4 operates the reverse roller pair 33 to reverse the paper P (step S103). That is, the control unit 4 causes the reversing unit 36 to invert the paper P.

  The sheet P that has been turned upside down is sent to the image forming unit 2 and held on the conveyor belt 23. At this time, the sheet P held on the transport belt 23 has the first surface P1 on the upper surface, that is, the surface on the head portion 24 side. Then, the control unit 4 drives the driving roller 21 to convey the conveyance belt 23 in the conveyance direction X. Then, the control unit 4 sends printing data to the head unit 24 (4C, 4M, 4Y, 4K) based on the image data, and sprays ink from the head unit 24 onto the first surface P1 of the paper P. That is, the first image Pt1 is printed on the first surface P1 of the paper P (step S104).

  The control unit 4 drives the carry-out roller pair 26, the switching unit 35, and the reversing roller pair 33, that is, drives the reversing unit 36 to reverse the paper P on which the printing on the first surface P1 has been completed (step S105). . Then, the paper P reversed by the reversing unit 36 is sent to the conveyance belt 23 of the image forming unit 2 and is held by the conveyance belt 23. The control unit 4 drives the drive roller 21 to move the transport belt 23 in the transport direction X. At this time, the upper surface of the paper P held by the transport belt 23, that is, the surface facing the head portion 24 is the second surface P2.

  The controller 4 drives the state detection sensor S1 to detect the surface state of the second surface P2 after printing on the first surface P1, that is, after the ink is sprayed on the first surface P1. The surface state is the same as in step S102. And the control part 4 memorize | stores the information from state detection sensor S1 as a state after spraying (step S106). The control unit 4 compares the state before spraying with the state after spraying, and updates the correction value for correcting the image data to be printed on the second surface P2 (step S107).

  After the ink is sprayed, the second surface P2 of the paper P extends before the ink is sprayed. Therefore, as the correction value, for example, an enlargement ratio (deformation ratio) for enlarging the image data is adopted. That is, in the present embodiment, the control unit 4 expands (extends) the surface of the second surface P2 after ink spraying (the state after spraying) relative to the surface of the second surface P2 before ink spraying (the state before spraying). The magnification, which is a ratio, is adopted as a correction value. However, the present invention is not limited to this, and parameters other than the enlargement ratio may be used, or these parameters may be combined to form a correction value.

  The control unit 4 performs correction processing of the image data printed on the second surface P2, that is, enlargement processing, using the updated correction value, and generates post-correction image data in the image processing unit 42 (step S108). ). Based on the corrected image data, the control unit 4 sends printing data to the head unit 24, sprays ink on the second surface P2 of the paper P, and prints the second image Pt2 (step S109). Then, the control unit 4 sends the paper P after double-sided printing by the carry-out roller pair 26 to the switching unit 35 through the first conveyance path 301. Then, the control unit 4 switches the switching unit 35 to send the paper P to the discharge conveyance path 304. Further, the control unit 4 drives the paper discharge roller pair 32 to discharge the paper P after double-sided printing to the paper discharge tray 31 (step S110).

  The printer 100 performs printing based on the corrected image data obtained by correcting the image data with the correction value on the second surface P2 after the ink is sprayed on the first surface P1. In this way, when the second surface P2 is printed based on the enlarged corrected image data so as to correspond to the second surface P2 of the stretched paper P, the ink is dried and the paper P is shrunk. In addition, the image printed on the second surface P2 is an appropriate image. Thereby, in an ink jet printer, the printing quality at the time of double-sided printing can be improved.

  The controller 4 includes a correction value corresponding to normal printing, assuming that the second surface P2 is deformed (stretched here) before and after printing the first surface P1 during double-sided printing. Then, after correcting the image data with this correction value, ink is sprayed onto the second surface P2 based on the corrected image data.

(Second Embodiment)
As described above, in the printer 100 that is an ink jet printer, the paper P is deformed (mainly stretched) when ink is sprayed, that is, when the paper P gets wet. In the first embodiment, the surface state (elongation state) of the second surface P2 before the ink is sprayed on the first surface P1 and after the ink is sprayed are compared, and the image data to be printed on the second surface P2 is corrected. I do. At this time, the state detection sensor S1 detects the entire surface state of the second surface P2, and the control unit 4 corrects the image data based on the surface state.

  On the other hand, the enlargement ratio of the second surface P2 due to the elongation generated when the paper P gets wet with ink changes depending on the wet state, in other words, the amount of ink sprayed onto the paper P per unit area.

  Such a case where the ink spray amount changes will be described with reference to the drawings. FIG. 8 is a diagram illustrating the first surface side of the paper on which the first image is printed on the first surface. FIG. 9 is a diagram illustrating the second surface side of the sheet illustrated in FIG. 8. As shown in FIGS. 8 and 9, an image printed on the first surface P1 of the paper P is a first image Pt11, and an image printed on the second surface P2 is a second image Pt21.

  For example, when the image data printed on the first surface P1 has many portions that are filled with ink such as symbols and photographs, the enlargement ratio is larger than when there are many blank portions such as character strings and diagrams.

  When the printer 100 actually performs double-sided printing, the amount of ink sprayed on the first surface P1 of the paper P may be uneven. In this case, the surface state of the second surface P2 of the paper P varies depending on the region. For example, when the first surface P1 has a first region with a large amount of ink sprayed, such as a photograph or an image, the region opposite to the first region (here, the second region Ar2 on the second surface P2) is The enlargement ratio is larger than the other areas of the second surface P2.

  For example, as shown in FIG. 8, when the first image Pt11 includes a first region Ar1 that is a region to be partially painted with ink, the second surface P2 is the opposite side of the first region Ar1. The second region Ar2 (see FIG. 9) is largely deformed compared to other regions of the second surface P2. That is, the second region Ar2 has a larger enlargement ratio than other regions. Therefore, the control unit 4 of the printer 100 according to the present embodiment detects the first area Ar1 from the image data of the first image Pt11 and updates the correction value of the image data of the second image Pt21. Hereinafter, a correction value updating method will be described with reference to the drawings.

  FIG. 10 is a flowchart illustrating another example of the operation of the printer. Note that the flowchart shown in FIG. 10 includes a step of determining the first area and the second area before the step of feeding the chart shown in FIG. 7 (S101). Moreover, the step (S102, S106) which acquires the state before spraying and the state after spraying differs. About the point other than this, it has the same structure. Therefore, in the flowchart shown in FIG. 10, detailed description of the substantially same part as the flowchart shown in FIG. 7 is omitted.

  The control unit 4 acquires image data for printing the first image Pt11 (step S201). The image data may be supplied from the computer 200 or may be image data read by the scanner 300. The image data is not particularly limited as long as it is image data to be printed on the paper P.

  The control unit 4 analyzes the acquired image data and confirms whether or not there is an area in which the printing rate is equal to or higher than the threshold value in the image data (step S202). Note that the printing rate is a region where a large amount of ink is sprayed per unit area. When viewed as image data, a blank area or an area with a light color has a low printing rate. In addition, a region that is painted with a dark color or is finely drawn has a high printing rate. The threshold value may be determined in advance or may be changed depending on the ink and paper used. Furthermore, the user may be able to arbitrarily select or set. Moreover, you may make it correct by the weather (temperature, humidity), etc.

  If the image data of the first image Pt11 does not include an area where the printing rate is equal to or greater than the threshold (No in step S202), the control unit 4 starts feeding (proceeds to step S101). Since the operation after paper feeding is the same as that in the first embodiment, the details are omitted.

  As shown in FIG. 8, when the image data of the first image Pt11 includes an area where the printing rate is equal to or greater than the threshold (Yes in step S202), the control unit 4 determines that the printing rate of the first surface P1 of the paper P is A portion where an image having a threshold value or more is printed is determined as the first area Ar1 (step S203). Then, the control unit 4 determines a portion of the second surface P2 of the paper P that is opposite to the first area Ar1 as the second area Ar2 (step S204). In the present embodiment, one each of the first region Ar1 and the second region Ar2 is used, but a plurality of each may be provided.

  The second region Ar2 has the same shape and size as the first region Ar1, or is larger than the first region Ar1. For example, when ink is sprayed on the first surface P1 of the paper P, the boundary of the first area Ar1 is easily deformed due to the influence of the ink sprayed on the first area Ar1. Therefore, by making the second region Ar2 larger than the first region Ar1, it is possible to cope with deformation at the boundary of the first region Ar1.

  Then, after determining the second area Ar2 (after step S204), paper feeding is started (step S101). In the printer 100, a lot of ink is sprayed on the first area Ar1 of the first surface P1 of the paper P. That is, the second region Ar2 of the second surface P2 is largely deformed compared to other regions of the second surface P2. Therefore, after determining the second area Ar2, in the acquisition of the state before spraying (step S102) and the acquisition of the state after spraying (step S106), the control unit 4 divides into the second area Ar2 and other areas and sprays. Get the previous state and the state after spraying. In this way, by specifying the second region Ar2, it is possible to partially change the correction value of the portion with large deformation. Thereby, it is possible to improve the print quality of the second image Pt21 printed on the second surface P2.

  In the present embodiment, when the control unit 4 determines the first region Ar1, the determination is based on the result of analyzing the acquired image data. However, it is not limited to this. For example, even if a reading device capable of reading an image is provided in the middle of the conveyance path 30 and the first image Pt11 is printed, the first area Ar1 is determined based on the image data read by the reading device. Good.

  In the above-described embodiment, an inkjet printer having a fixed head unit 24 is cited as the image forming apparatus, but an inkjet printer having a movable head unit to which the head unit 24 moves may be used.

  An example of the image forming apparatus according to the present invention is capable of forming an image on both sides of the paper P, and sprays ink onto the transport unit 3 that transports the paper P and the paper P that is transported by the transport unit 3 based on the image data. The image forming unit 2 for forming an image, the state detecting unit S1 for detecting the deformation state of the paper P, and the paper P from the image forming unit 2 are reversed to the upstream side in the paper transport direction from the image forming unit 2 The reversing part 36 to send and the control part 4 which controls each part are provided. When image formation is performed on both the first surface P1 of the paper P and the second surface P2 that is the back surface thereof, the control unit 4 performs the second surface P2 before ink is blown from the state detection unit S1 to the first surface P1. The state before spraying is obtained, and the state after spraying which is the state of the second surface P2 after ink is sprayed on the first surface P1, and the pre-spraying state and the state after spraying are compared to obtain a correction value. To decide. Then, the control unit 4 generates corrected image data obtained by correcting the image data with the correction value, and forms an image Pt2 on the second surface P2 based on the corrected image data.

  With this configuration, the state of the second surface P2 before and after the ink is sprayed on the first surface P1 is compared, and the image data to be printed on the second surface P2 is corrected. Then, the image Pt2 is printed on the second surface P2 based on the corrected image data. In this way, even if the second surface P2 is deformed (elongated) due to the ink sprayed onto the first surface P1, the second surface has image data that provides an accurate image after drying the ink. An image Pt2 can be formed on P2. Thereby, in the image forming apparatus, the print quality at the time of duplex printing can be improved.

  In the above configuration, the control unit 4 determines the first area Ar1 in which the printing rate on the first surface P1 is higher than the threshold value. The control unit 4 determines the first region Ar1 and the second region Ar2 of the second surface P2 on the back side, and determines the correction value separately for the second region Ar2 and other regions. In this way, the image Pt21 printed on the second surface P2 can be corrected with partially different correction values. As a result, it is possible to obtain an accurate image after the ink has dried, corresponding to partial deformation of the second surface P2.

  In the above configuration, the control unit 4 may determine the first region Ar1 based on image data formed on the first surface P1. The image reading unit 300 further reads an image formed on the first surface P1, and the control unit 4 acquires the printing rate of the first surface P1 from the image data read by the image reading unit 300, and The first region Ar1 and the second region Ar2 may be determined. Since the first area Ar1 and the second area Ar2 are determined from the image data, the first area Ar1 and the second area Ar2 can be determined with high accuracy.

  In the above configuration, the control unit 4 controls the reversing unit 36 to send the paper P to the transport unit 3 a plurality of times, and controls the image forming unit 2 so that ink is not sprayed onto the paper P at least once. May be.

  In the above configuration, the state detection unit S1 may detect the state of the surface of the paper P that faces the image forming unit 2 upstream of the image forming unit 2 in the transport direction of the paper P.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention can be used for an ink jet image forming apparatus capable of duplex printing.

DESCRIPTION OF SYMBOLS 1 Paper feed tray 2 Image forming unit 3 Conveyance part 4 Control part 5 Memory | storage part 6 Communication part 7 Operation panel 11 Feed roller pair 21 Drive roller 22 Followed roller 23 Conveyance belt 24 Head part 24C Head part 24K Head part 24M Head part 24Y Head unit 25 Belt drive motor 26 Unloading roller pair 30 Conveying path 31 Discharging tray 32 Discharging roller pair 33 Reversing roller pair 34 Reversing retreat path 35 Switching unit 36 Reversing unit 41 CPU
42 Image processing unit 100 Printer 200 Computer 241 Driver 242 Nozzle 300 Scanner 301 First transport path 302 Second transport unit 303 Reverse transport path 304 Discharge transport path 305 First reverse transport path 306 Second reverse transport path Ar1 First area Ar2 First 2 area P paper P1 1st surface P2 2nd surface Pt1 1st image Pt11 1st image Pt2 2nd image Pt21 2nd image S1 State detection sensor

Claims (6)

An image forming apparatus capable of forming an image on both sides of a sheet,
A transport unit for transporting the paper;
An image forming unit that forms an image by spraying ink on the paper transported by the transport unit based on image data;
A state detector for detecting the deformation state of the paper;
A reversing unit that inverts the paper from the image forming unit and sends it to the upstream side in the paper transport direction from the image forming unit;
A control unit for controlling each unit,
In the case where image formation is performed on both the first side of the paper and the second side, which is the back side of the first side, the control unit has the second side before ink is blown from the state detection unit to the first side of the paper. A state before spraying, and a state after spraying that is the state of the second surface after ink is sprayed on the first surface, and comparing the state before spraying and the state after spraying Determine the correction value,
The control unit generates corrected image data obtained by correcting image data with the correction value, and forms an image on the second surface based on the corrected image data. The control unit determines a first region where the printing rate on the first surface is higher than a threshold value,
2. The image formation according to claim 1, wherein the control unit determines a second area of the second surface that is behind the first area, and determines the correction value separately for the second area and another area. apparatus.   The image forming apparatus according to claim 2, wherein the control unit determines the first area based on image data formed on the first surface. An image reading unit that reads an image formed on the first surface;
The image forming apparatus according to claim 3, wherein the control unit acquires image data read by the image reading unit.   2. The control unit controls the image forming unit to control the reversing unit to send the sheet to the transport unit a plurality of times and to not spray ink onto the sheet at least once. The image forming apparatus according to claim 4.   The said state detection part detects the state of the surface facing the said image formation part of the said sheet | seat upstream from the said image formation part in the conveyance direction of the said sheet | seat. Image forming apparatus.

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