Inkjet printing apparatus

Abstract

To provide an inkjet printer capable of reducing deterioration of image reproducibility.SOLUTION: The inkjet head ejects ink onto the print medium 15 while moving in the main scanning direction. The medium height sensor detects unevenness of the surface of the print medium 15. The control unit 5 corrects the image data to be printed so as to reduce the distortion of the print image due to the unevenness of the surface of the print medium 15 detected by the medium height sensor 25, and performs control so as to perform printing by ejecting ink from the inkjet head onto the print medium 15 based on the corrected image data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to inkjet printing devices. [Background technology]

[0002] The surface of the print medium on which an inkjet printing device prints may be uneven. When the surface of the print medium is uneven, the distance to the inkjet head (head gap) varies depending on the position on the print medium. The variation in the head gap can cause the ink to land misaligned.

[0003] In response to this, a technique is known that corrects the ink ejection timing in accordance with the height of the surface of the printing medium, thereby reducing deviation in the landing position of ink (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-32626 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even if the above-mentioned techniques are used to reduce ink landing deviation, the unevenness of the surface of the printing medium can cause distortion in the printed image, which can reduce image reproducibility.

[0006] The present invention has been made in view of the above, and has as its object to provide an inkjet printing apparatus that can reduce the deterioration of image reproducibility. [Means for solving the problem]

[0007] In order to achieve the above object, the inkjet printing device of the present invention is characterized by comprising an inkjet head that ejects ink while moving relative to a printing medium, a detection unit that detects unevenness on the surface of the printing medium, and a control unit that corrects image data of the object to be printed so as to reduce distortion of the printed image caused by the unevenness on the surface of the printing medium detected by the detection unit, and controls the inkjet head to eject ink onto the printing medium and print based on the corrected image data. [Effects of the Invention]

[0008] According to the inkjet printing apparatus of the present invention, the deterioration of image reproducibility can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a schematic configuration of an inkjet printing apparatus according to an embodiment; [Figure 2] FIG. 2 is a perspective view showing a schematic configuration of a shuttle unit in the inkjet printing apparatus shown in FIG. [Figure 3] FIG. 2 is a schematic diagram illustrating the configuration of an inkjet head in the inkjet printing apparatus shown in FIG. [Figure 4] FIG. 2 is a control block diagram of the inkjet printing apparatus shown in FIG. [Figure 5] 2 is a flowchart illustrating a printing operation of the inkjet printing apparatus shown in FIG. [Figure 6] 10A and 10B are diagrams showing an example of a waveform of unevenness data and an example of a waveform of height change rate data; DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings.

[0011] The following embodiments are examples of devices that embody the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the materials, shapes, structures, arrangements, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0012] Fig. 1 is a perspective view showing a schematic configuration of an inkjet printing apparatus according to an embodiment of the present invention. Fig. 2 is a perspective view showing a schematic configuration of a shuttle unit in the inkjet printing apparatus shown in Fig. 1. Fig. 3 is a schematic configuration diagram of an inkjet head in the inkjet printing apparatus shown in Fig. 1. Fig. 4 is a control block diagram of the inkjet printing apparatus shown in Fig. 1. In the following description, the up, down, left, right, front, back, and rear directions indicated by arrows in Fig. 1 are referred to as up, down, left, right, front, and rear directions.

[0013] As shown in FIGS. 1 and 4, an inkjet printing apparatus 1 according to this embodiment includes a shuttle base unit 2, a flatbed unit 3, a shuttle unit 4, and a control unit 5.

[0014] The shuttle base unit 2 supports the shuttle unit 4 and moves the shuttle unit 4 in the front-rear direction (sub-scanning direction). The shuttle base unit 2 includes a base unit 11 and a sub-scanning drive motor 12.

[0015] The base 11 supports the shuttle unit 4. The base 11 is formed in the shape of a rectangular frame. Sub-scanning drive guides 13A and 13B extending in the front-rear direction are formed on the left and right frames of the base 11, respectively. The sub-scanning drive guides 13A and 13B guide the shuttle unit 4 as it moves in the front-rear direction.

[0016] The sub-scanning drive motor 12 moves the shuttle unit 4 in the front-rear direction.

[0017] The flatbed unit 3 holds a print medium 15 made of building materials or the like. The flatbed unit 3 is disposed inside the stand portion 11 of the shuttle base unit 2. The flatbed unit 3 has a medium placement surface 3a, which is a horizontal surface on which the print medium 15 is placed. The flatbed unit 3 can adjust the height of the medium placement surface 3a using an elevation mechanism formed by a hydraulic drive mechanism or the like.

[0018] Shuttle unit 4 prints an image on print medium 15. As shown in FIGS. 1, 2, and 4, shuttle unit 4 includes a housing 21, a main scanning drive unit 22, a main scanning moving table 23, a head unit 24, and a medium height sensor (corresponding to a detection unit) 25.

[0019] The housing 21 holds each part such as the head unit 24. The housing 21 is formed in a gate shape that straddles the flatbed unit 3 in the left-right direction. The housing 21 is supported by the stand part 11 of the shuttle base unit 2, and is configured to be movable along the sub-scanning drive guides 13A and 13B.

[0020] The main scanning drive unit 22 moves the main scanning movement table 23 in the left-right direction (main scanning direction) to move the head unit 24 in the left-right direction. The main scanning drive unit 22 includes a drive belt 31, a pair of pulleys 32A and 32B, a main scanning drive motor 33, and a main scanning drive guide 34.

[0021] The drive belt 31 moves in a circular motion to move the main scanning movement table 23. The drive belt 31 is stretched between pulleys 32A and 32B.

[0022] Pulleys 32A and 32B support drive belt 31 and move drive belt 31 in a circular motion. Pulleys 32A and 32B are spaced apart from each other in the left-right direction and are disposed at the same height. Pulley 32B is connected to the output shaft of main scanning drive motor 33 and transmits the rotational driving force of main scanning drive motor 33 to drive belt 31.

[0023] The main scanning drive motor 33 rotates the pulley 32B, thereby moving the drive belt 31 in a circular motion.

[0024] The main scanning drive guide 34 guides the main scanning moving table 23 to move in the left-right direction. The main scanning drive guide 34 is formed in an elongated shape extending in the left-right direction.

[0025] The main scanning movement table 23 is a table on which the head unit 24 is mounted. The main scanning movement table 23 is fixed to a drive belt 31, and moves in the left-right direction along a main scanning drive guide 34 as the drive belt 31 moves in a circular motion.

[0026] The head unit 24 moves left and right while ejecting ink onto the print medium 15 to print an image. The head unit 24 is mounted on the main scanning moving table 23 and moves left and right together with the main scanning moving table 23. The head unit 24 is equipped with four inkjet heads 41.

[0027] The four inkjet heads 41 are arranged side by side in the left-right direction. Each inkjet head 41 has a plurality of nozzles 42 that open to a nozzle surface 41a, which is its lower surface, and are arranged at a predetermined pitch in the front-rear direction, and ejects ink from the nozzles 42 onto the print medium 15. The four inkjet heads 41 each eject ink of a different color (for example, cyan, black, magenta, and yellow).

[0028] The medium height sensor 25 detects the height at multiple points on the surface of the print medium 15 to detect unevenness on the surface of the print medium 15. The medium height sensor 25 extends in the left-right direction and is formed in an elongated shape that is longer than the width (length in the left-right direction) of the print medium 15. The medium height sensor 25 is, for example, a laser displacement sensor.

[0029] The control unit 5 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 5 is configured with a CPU, RAM, ROM, a hard disk, and the like.

[0030] When printing, the control unit 5 corrects the image data of the object to be printed so as to reduce distortion of the printed image caused by unevenness of the surface of the print medium 15 detected by the medium height sensor 25. Then, the control unit 5 controls each inkjet head 41 to eject ink onto the print medium 15 and perform printing based on the corrected image data.

[0031] Next, the printing operation of the inkjet printing apparatus 1 will be described with reference to the flowchart of FIG.

[0032] In the inkjet printing apparatus 1, in a standby state before the start of a printing operation, the shuttle unit 4 is placed at a standby position. The standby position of the shuttle unit 4 is the position of the shuttle unit 4 shown by the solid line in FIG. 1, and is located at the rear end of the stand portion 11 of the shuttle base unit 2.

[0033] Furthermore, prior to the start of the printing operation, the print medium 15 is placed on the medium placement surface 3a of the flatbed unit 3. Then, the height of the medium placement surface 3a is adjusted according to the thickness of the print medium 15.

[0034] 5, the control unit 5 detects the unevenness of the surface of the print medium 15. Specifically, the control unit 5 moves the shuttle unit 4 from the standby position to a position forward of the front end of the print medium 15, while causing the medium height sensor 25 to detect the height of the entire surface of the print medium 15.

[0035] Then, based on the height of the entire surface of the printing medium 15 detected by the medium height sensor 25, the control unit 5 generates unevenness data that indicates the relationship between the position in the main scanning direction and the height of the surface of the printing medium 15 for each of multiple scanning sections during printing.

[0036] Here, the above-mentioned scanning section is a section (area) that is printed by one scan (one pass) of the head unit 24 in the main scanning direction, and a plurality of scanning sections are lined up in the sub-scanning direction.

[0037] In this embodiment, the surface height of the printing medium 15 corresponding to a position in the main scanning direction in the unevenness data for each scanning section described above is the average value of the surface height within the scanning section in the sub-scanning direction at that position. Note that this is not limited to the average value, and values ​​such as the maximum value, minimum value, and median value may also be used.

[0038] Next, in step S2, the control unit 5 generates height change rate data for each scanning section, which is data obtained by first-order differentiation of the unevenness data for each scanning section with respect to the position in the main scanning direction.

[0039] Specifically, the control unit 5 calculates a first-order differential value dz / dx for the position in the main scanning direction (x direction) of the height z of the surface of the printing medium 15 using the following equation (1).

[0040] dz / dx=(z(n+1)-z(n)) / (x(n+1)-x(n)) …(1) Here, x(n) and x(n+1) respectively represent the positions of one end and the other end of a small interval in the main scanning direction (x direction). Furthermore, z(n) and z(n+1) respectively represent the height of the surface of the printing medium 15 at positions x(n) and x(n+1). The first-order differential value dz / dx represents the rate of change of the height of the surface of the printing medium 15 in the main scanning direction.

[0041] The control unit 5 calculates the first-order differential value dz / dx over the entire width of the printing medium 15 while changing x(n) and x(n+1), thereby generating height change rate data that indicates the relationship between the position in the main scanning direction and the rate of change in height of the surface of the printing medium 15.

[0042] Next, in step S3, the control unit 5 corrects the image data of the object to be printed so as to reduce distortion of the print image due to unevenness of the surface of the print medium 15.

[0043] An example of the waveform of unevenness data is shown in the upper part of Fig. 6. The waveform in the lower part of Fig. 6 shows the waveform of height change rate data obtained by first-order differentiation of the unevenness data in the upper part. In this embodiment, as shown in Fig. 6, the control unit 5 corrects the image of an area to be printed in an area where the magnitude (absolute value) of the rate of change in height of the surface of the printing medium 15 in the main scanning direction is equal to or greater than a predetermined value A in the image data of the printing target.

[0044] Specifically, the control unit 5 corrects areas of the image data to be printed where the rate of change in the height of the surface of the printing medium 15 in the main scanning direction is equal to or greater than a predetermined value A by increasing the pixel spacing in the main scanning direction (reducing the resolution in the main scanning direction) according to the rate of change in the height of the surface. The control unit 5 does not correct areas of the image data to be printed where the rate of change in the height of the surface of the printing medium 15 in the main scanning direction is less than the predetermined value A.

[0045] In areas where the rate of change in the height of the surface of the printing medium 15 in the main scanning direction is greater, the ink dots are formed more densely in the main scanning direction, causing the printed image to become distorted and squashed in the main scanning direction. Therefore, the control unit 5 performs the above-mentioned correction to reduce distortion of the printed image due to surface irregularities for areas in the image data to be printed that are printed in areas where the rate of change in the height of the surface of the printing medium 15 in the main scanning direction is equal to or greater than a predetermined value A.

[0046] Here, the control unit 5 sets the above-mentioned predetermined value A based on the type of ink and the type of print medium 15. Specifically, the control unit 5 sets the predetermined value A according to the tendency of the ink to bleed onto the print medium 15, which is determined by the combination of the ink type and the type of print medium 15. The more the combination of the ink type and the type of print medium 15 results in the ink bleed onto the print medium 15, the smaller the predetermined value A. The more the ink bleeds onto the print medium 15, the more noticeable distortion of the printed image due to the unevenness of the surface of the print medium 15 becomes, so by reducing the predetermined value A, the image data can be corrected over a wider range.

[0047] Returning to FIG. 5, in step S4, the control unit 5 executes printing.

[0048] Specifically, first, the control unit 5 places the shuttle unit 4 at the print process start position. The print process start position of the shuttle unit 4 is a position in the sub-scanning direction of the scanning section where printing of the first pass is performed, and is located at the front end of the stand part 11 of the shuttle base unit 2.

[0049] Next, the control unit 5 performs a printing operation for one pass. Specifically, the control unit 5 moves the head unit 24 in the main scanning direction while causing each inkjet head 41 to eject ink based on the image data corrected in step S3.

[0050] At this time, the control unit 5 controls the ink ejection from each inkjet head 41 in accordance with the unevenness of the surface of the print medium 15 in the scanning section where printing of the first pass is performed.

[0051] Specifically, the control unit 5 controls the ink ejection timing of each inkjet head 41 according to the head gap based on the unevenness data for the scanning section where printing of the first pass is performed. The control unit 5 advances the ink ejection timing as the head gap increases. Here, the head gap is the distance from the inkjet head 41 to the surface of the print medium 15.

[0052] When printing of the first pass is completed, the control unit 5 moves the shuttle unit 4 backward to the position of the next scanning section.

[0053] Next, the control unit 5 moves the head unit 24 in the main scanning direction while causing each inkjet head 41 to eject ink based on the image data corrected in step S3. At this time, the control unit 5 controls the ink ejection of each inkjet head 41 in accordance with the unevenness of the surface of the print medium 15 in the scanning section where printing of the current pass is performed, just as when printing the first pass.

[0054] In the same manner, the control unit 5 performs printing for one pass in each subsequent scanning section until the final scanning section. When printing in the final scanning section is completed, the series of operations ends.

[0055] As described above, in the inkjet printing device 1, the control unit 5 corrects the image data of the object to be printed so as to reduce distortion of the printed image caused by the unevenness of the surface of the printing medium 15. Then, based on the corrected image data, the control unit 5 controls each inkjet head 41 to eject ink onto the printing medium 15 for printing. This reduces distortion of the printed image caused by the unevenness of the surface of the printing medium 15, and reduces degradation of image reproducibility.

[0056] Furthermore, the control unit 5 performs the above-described correction on areas of the image data to be printed where the rate of change in height of the surface of the printing medium 15 in the main scanning direction is equal to or greater than a predetermined value A, but does not perform correction on other areas. This makes it possible to reduce the load of the image data correction process while also reducing degradation in image reproducibility.

[0057] Furthermore, when controlling printing based on the corrected image data, the control unit 5 controls the ink ejection from each inkjet head 41 in accordance with the unevenness of the surface of the print medium 15. This reduces deviations in the ink landing position, making it possible to further reduce degradation of image reproducibility.

[0058] The control unit 5 also sets the predetermined value A based on the type of ink and the type of print medium 15. This makes it possible to appropriately set the area in the image data to be corrected depending on the ink bleeding tendency. As a result, it is possible to further reduce the degradation of image reproducibility while reducing the load of the image data correction process.

[0059] In the above-described embodiment, correction is performed on areas of the image data to be printed where the rate of change in height of the surface of the printing medium 15 in the main scanning direction is equal to or greater than a predetermined value A, and correction is not performed on other areas. However, this is not limiting, and correction may also be performed on areas of the image data to be printed where the rate of change in height of the surface of the printing medium 15 in at least one direction other than the main scanning direction is equal to or greater than a predetermined value A. Alternatively, the predetermined value A may not be set, and the image data to be printed may be corrected according to the rate of change in height across the entire surface of the printing medium 15 so as to reduce distortion of the printed image caused by surface irregularities.

[0060] Furthermore, in the above-described embodiment, the medium height sensor 25 is elongated in the left-right direction and longer than the width of the print medium 15. However, this is not limiting, and the medium height sensor may, for example, extend in the front-to-rear direction and be formed to a length that is capable of detecting the height (unevenness) of the surface of the print medium 15 in one scanning section. When using such a medium height sensor, rather than detecting the height of the entire surface of the print medium 15 before printing begins, the height of the surface of the print medium 15 in the scanning section of the next pass may be detected after each printing pass, and the image data may be corrected.

[0061] In the above-described embodiment, the ink ejection timing is controlled to control the ink ejection in accordance with the unevenness of the surface of the print medium 15. However, the ink ejection speed may also be controlled. When controlling the ink ejection speed, the drive voltage of each inkjet head 41 is controlled so that the ink ejection speed corresponds to the head gap. The ink ejection speed increases as the head gap increases.

[0062] In addition, in the above-described embodiment, the predetermined value A was set based on the type of ink and the type of printing medium 15, but the predetermined value A may also be set based on the type of ink or the type of printing medium 15.

[0063] In the above-described embodiment, the print medium 15 is fixed and the shuttle unit 4 is moved in the sub-scanning direction after each pass of printing, but the print medium may be moved in the sub-scanning direction after each pass of printing, or both the shuttle unit 4 and the print medium may be moved.

[0064] In the above-described embodiment, printing is performed on a fixed print medium 15 while the head unit 24 (inkjet head 41) is moved in the main scanning direction. However, the present invention can also be applied to a configuration in which printing is performed on the print medium by ejecting ink from a fixed inkjet head while the print medium is being transported. Any configuration is possible as long as the inkjet head ejects ink while moving relative to the print medium.

[0065] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments.

[0066] [Note] The present application discloses the following inventions.

[0067] (Appendix 1) an inkjet head that ejects ink while moving relative to the print medium; a detection unit that detects unevenness on the surface of the print medium; a control unit that corrects image data of a print target so as to reduce distortion of the print image caused by unevenness on the surface of the print medium detected by the detection unit, and controls the inkjet head to eject ink onto the print medium based on the corrected image data; and An inkjet printing apparatus comprising:

[0068] (Appendix 2) The inkjet printing device described in Appendix 1 is characterized in that, when controlling the printing, the control unit controls the ink ejection of the inkjet head in accordance with the unevenness of the surface of the printing medium detected by the detection unit.

[0069] (Appendix 3) The inkjet printing device described in Appendix 1 or 2, characterized in that the control unit performs correction on areas of the image data to be printed where the rate of change in height of the surface of the printing medium is equal to or greater than a predetermined value, and does not perform correction on other areas.

[0070] (Appendix 4) 4. The inkjet printing device according to claim 3, wherein the control unit sets the predetermined value based on at least one of the type of ink and the type of printing medium. [Explanation of symbols]

[0071] 1. Inkjet printing device 2 Shuttle Base Unit 3 Flatbed Unit 3a Media placement surface 4 Shuttle Unit 5. Control section 11 Mounting section 12 Sub-scanning drive motor 13A, 13B Sub-scanning drive guide 15 Print media 21. Cabinet 22 Main scanning drive unit 23 Main scanning movement table 24 Head Unit 25 Media height sensor 31 Drive belt 32A, 32B pulleys 33 Main scanning drive motor 34 Main scanning drive guide 41 Inkjet head 41a Nozzle surface 42 nozzles

Claims

1. an inkjet head that ejects ink while moving relative to the print medium; a detection unit that detects unevenness on the surface of the print medium; a control unit that corrects image data of a print target so as to reduce distortion of the print image caused by unevenness on the surface of the print medium detected by the detection unit, and controls the inkjet head to eject ink onto the print medium based on the corrected image data; and An inkjet printing apparatus comprising:

2. The inkjet printing device according to claim 1 , wherein the control unit controls the ink ejection from the inkjet head in accordance with the unevenness of the surface of the printing medium detected by the detection unit when controlling the printing.

3. The inkjet printing device according to claim 1 or 2, characterized in that the control unit performs correction on areas of the image data to be printed where the rate of change in height of the surface of the printing medium is equal to or greater than a predetermined value, and does not perform correction on other areas.

4. 4. The inkjet printing apparatus according to claim 3, wherein the control unit sets the predetermined value based on at least one of the type of ink and the type of printing medium.

Images