Image forming apparatus and image forming method

Abstract

This image forming apparatus comprises: a plurality of print heads that each have a nozzle row configured from a plurality of nozzles, and that form an image on a recording medium by ejecting ink droplets from the nozzle rows; and a control unit that performs control to execute multi-pass printing which forms the image by moving the print heads and the recording medium multiple times relatively along a second direction, which is orthogonal to a first direction in which the plurality of nozzles are arranged. The control unit performs control to execute the multi-pass printing so that image-elements spanning one nozzle pitch of the print head are formed by the nozzle row of a single print head.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus and an image forming method.

Background Art

[0002] Conventionally, an inkjet printing apparatus (image forming apparatus) forms an image by performing, in an alternating manner, a process of ejecting ink from a large number of nozzles formed in a print head while moving the print head in a scanning direction with a recording medium stopped, and a process of moving the recording medium little by little in a direction different from the scanning direction.

[0003] Patent Document 1 discloses an inkjet printer that improves print image quality by appropriately correcting an error in a paper feed amount for moving paper as a recording medium in an interlace recording mode.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Due to quality variations during production of the print head, etc., the ejection amount and ejection direction of ink from the nozzles may not be stable, or ink may not be ejected from a specific nozzle due to clogging of the nozzle, etc., and nozzle defects may occur. When an image is formed using a print head having such defective nozzles, the image quality may deteriorate. As a method for improving such deterioration of image quality, multi-pass printing has become widespread.

[0006] Multipass printing is a printing method in which a nozzle array, composed of multiple nozzles, is divided into multiple sections equal to the number of passes, and ink is sequentially ejected from the multiple printing nozzle arrays in each divided area to form an image in stages. With this method, even if the amount or direction of ink ejection from a particular nozzle is unstable, or if ink is not ejected from a particular nozzle, the ink ejected from nozzles that are not experiencing such problems will be applied on top, resulting in an image with reduced quality degradation.

[0007] However, even with multi-pass printing, it can be difficult to suppress image quality degradation. Due to variations in print head production quality, the distance from one effective nozzle to the other effective nozzle in the nozzle row direction (distance between nozzle ends) may differ for each print head. Effective nozzles refer to nozzles that eject ink, unlike dummy nozzles that do not eject ink. In such cases, if adjacent pixels are printed using print heads with different distances between nozzle ends, the spacing between adjacent pixels may shift from their original positions, resulting in a decrease in image quality. Since this shift occurs in units of areas divided by the number of passes, it is difficult to resolve with the technology disclosed in Patent Document 1.

[0008] The present disclosure aims to provide an image forming apparatus and an image forming method that can prevent deterioration of print quality even when the distance between nozzle ends in the nozzle row of a print head differs for each of the multiple print heads. [Means for solving the problem]

[0009] The image forming apparatus disclosed herein has a nozzle row composed of a plurality of nozzles, a plurality of print heads that form an image on a recording medium by ejecting ink droplets from the nozzle row, and a first direction which is the direction of the nozzle row. Or, an operation to move the print head and the recording medium relative to each other multiple times along the opposite direction, and the first direction The print head and the recording medium are moved relative to each other multiple times along a second direction perpendicular to the first direction. Combine actions and with each other.The system comprises a control unit that performs multi-pass printing to form the image, wherein the control unit performs multi-pass printing using a single ink so that in at least a portion of the image, pixels between one nozzle pitch of the print head are formed by the nozzle row of a single print head, and the ink droplets ejected from the same nozzle form adjacent pixel rows along the first direction. The mark Printing action A third printing operation in which, after moving the print head and the recording medium relative to each other along the first direction, they are moved relative to each other along the opposite direction of the first direction, thereby forming one pixel row in multiple passes using the same nozzle. The multi-pass printing is performed by selecting either a first printing operation in which ink droplets ejected from different nozzles among the nozzle rows of a single print head form adjacent pixel rows along the first direction, or a second printing operation in which ink droplets ejected from different nozzles form adjacent pixel rows along the first direction. cormorant .

[0010] The image forming method disclosed herein involves a plurality of print heads having nozzle rows composed of a plurality of nozzles and a recording medium. The operation involves moving the print head and the recording medium relative to each other multiple times along a first direction which is the direction of the nozzle row or the opposite direction, and moving the print head and the recording medium relative to each other multiple times along a second direction which is perpendicular to the first direction. An image forming method that performs multi-pass printing to form an image, In at least a portion of the aforementioned image, the pixels between one nozzle pitch of the print head are, The nozzle array of the single print head te form The multi-pass printing is performed using a single ink, and the ink droplets ejected from the same nozzle are in the direction of the nozzle row. The aforementioned A series of adjacent pixels are formed along the first direction. The mark Printing action A third printing operation in which, after moving the print head and the recording medium relative to each other along the first direction, they are moved relative to each other along the opposite direction of the first direction, thereby forming one pixel row in multiple passes using the same nozzle. The multi-pass printing is performed by selecting either a first printing operation in which ink droplets ejected from different nozzles among the nozzle rows of a single print head form adjacent pixel rows along the first direction, or a second printing operation in which ink droplets ejected from different nozzles form adjacent pixel rows along the first direction. cormorant. [Effects of the Invention]

[0011] According to this disclosure, even when the distance between nozzle ends in the nozzle row of a print head differs for each print head, it is possible to prevent deterioration of the print quality. [Brief explanation of the drawing]

[0012] [Figure 1] Top view showing the main configuration of the image forming apparatus in an embodiment of the present disclosure [Figure 2] It is a diagram showing an example of the configuration of a print head. [Figure 3] Diagram for explaining the positional relationship of the print head [Figure 4A] Diagram showing an example in which one print head has two rows of nozzle arrays [Figure 4B] Diagram showing an example in which a plurality of head chip modules are arranged in one print head [Figure 4C] Diagram showing an example in which a plurality of head chip modules are arranged in one print head [Figure 5] Diagram for explaining the operation of general multi-pass printing [Figure 6] Diagram for explaining a state in which the intervals between columns of pixels become uneven when there is a variation in the print width for each print head in general multi-pass printing [Figure 7] Diagram for explaining the first printing operation by the image forming apparatus [Figure 8] Diagram for explaining the second printing operation by the image forming apparatus [Figure 9] Diagram for explaining a state in which the image area Ry1 and the image area Ry2 overlap near the ends [Figure 10A] Diagram showing a state in which the ink ejected from each nozzle of the print head is ejected so as to narrow inward [Figure 10B] Diagram showing a state in which the ink ejected from each nozzle of the print head is ejected so as to spread outward [Figure 11] Diagram for explaining the third printing operation by the image forming apparatus

Mode for Carrying Out the Invention

[0013] Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described.

[0014] <Configuration of an image forming apparatus> Figure 1 is a top view showing the main components of an image forming apparatus 1 in an embodiment of the present disclosure. The image forming apparatus 1 comprises a transport table 11, a carriage 12, a print head 13, and a control unit 20. Figure 1 is a schematic diagram, and the size of each component is exaggerated and differs from the actual size. In the following description, the front side of Figure 1 is considered the top, and the back side is considered the bottom.

[0015] The transport table 11 is configured to move the recording medium B, which is the object of image formation in the image forming apparatus 1, along the first direction D1. In this embodiment, the recording medium B is, for example, a substrate used in a printed circuit board (PCB). The recording medium B is preferably made of materials such as copper-clad laminates for high-frequency circuits using paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / nonwoven fabric epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, fluorine / polyethylene / PPO / cyanate ester, etc., and preferably of all grades (FR-4, etc.) of copper-clad laminates, as well as polyimide film, PET film, glass substrate, ceramic substrate, wafer plate, and stainless steel plate.

[0016] The carriage 12 is equipped with multiple print heads 13 and ink tanks corresponding to each print head 13. The carriage 12 is also equipped with a position sensor (not shown) for reading the relative position to the recording medium B. The carriage 12 is positioned above the transport table 11 and the recording medium B (towards the front of the paper in Figure 1) so that the nozzles 30 of the print heads 13 (described later) face the recording medium B.

[0017] Furthermore, the carriage 12 is supported by a support (not shown) so as to be movable along the second direction D2.

[0018] Each print head 13 has multiple nozzles 30 for ejecting ink droplets. In the following description, the ejection of ink droplets by the nozzles 30 may be simply referred to as "ejecting ink." Figure 2 is a diagram showing an example of the configuration of a print head 13. In the example shown in Figure 2, multiple nozzles 30 are arranged in a row to form a nozzle row 31. Figure 2 is a schematic diagram, and the number of nozzles 30 provided on the print head 13 may differ from the actual number.

[0019] In this embodiment, the ink is, for example, an ink containing a coating agent or insulating material for the manufacture of printed circuit boards. Each of the multiple nozzles 30 of the multiple print heads 13 is loaded with a single ink. An example of a single ink is solder resist ink used for circuit formation on a PCB substrate.

[0020] Multiple print heads 13 are mounted on a carriage 12 such that their respective nozzles 30 are aligned along a first direction D1. In this embodiment, as shown in Figure 3, two print heads 13, print heads 13A and 13B, are mounted on the carriage 12.

[0021] Figure 3 is a diagram illustrating the positional relationship between print heads 13A and 13B. Figure 3 is a view of the carriage 12 from below, i.e., from the recording medium B side in Figure 1. In this embodiment, as shown in Figure 3, print head 13A and print head 13B are positioned offset from each other in the second direction D2.

[0022] The control unit 20 forms an image on the surface of the recording medium B by controlling each of the above-described components. Specifically, the control unit 20 moves the print head 13 in a second direction D2 relative to the recording medium B and ejects ink from the print head 13 onto the recording medium B. Then, the control unit 20 moves the transport table 11 a predetermined distance in a first direction D1 and again moves the print head 13 in a second direction D2 relative to the recording medium B and ejects ink from the print head 13 onto the recording medium B. By repeating this process, an image is formed on the recording medium B.

[0023] The main configuration of the image forming apparatus 1 according to the embodiment of this disclosure has been described above. However, the above description is just one example of the configuration of the image forming apparatus 1, and this disclosure is not limited thereto. For example, the transport table 11 may be moved in a second direction D2 relative to the print head 13, ink may be ejected from the print head 13 as the transport table 11 moves, and the print head 13 may be moved in a first direction D1 each time the movement is completed. Alternatively, the print head 13 may be fixed, and the transport table 11 may be moved in a second direction D2 relative to the print head 13, and then moved in a first direction D1 each time the movement is completed. Furthermore, both the print head 13 and the transport table 11 may be moved in a second direction D2, and both the print head 13 and the transport table 11 may be moved in a first direction D1 each time the movement is completed.

[0024] Furthermore, while Figures 2 and 3 show examples where each print head 13 has only one row of nozzles 31, each print head 13 may have, for example, multiple rows of nozzles 31. Figure 4A shows an example where one print head 13 has two rows of nozzles 31. Moreover, as shown in the examples in Figures 4B and 4C, multiple head chip modules 32 may be arranged within one print head 13. A head chip module 32 is a module formed by arranging multiple print chips. The example shown in Figure 4B shows two head chip modules 32 arranged side by side along the second direction D2 to improve resolution. The example shown in Figure 4C shows two head chip modules 32 arranged offset from each other along the first direction D1 to expand the area that the print head 13 can print at once.

[0025] <Printing operation> In the following, the printing operation of the image forming apparatus 1 according to the embodiment of this disclosure will be described in comparison with the operation of general multi-pass printing.

[0026] [Typical multi-pass printing operation] First, let's explain the general operation of multi-pass printing. As an example, we will describe the case where a 4-pass multi-pass printing is performed using a print head with a nozzle density of 360 dpi to create an image with a print resolution of 1440 dpi. Figure 5 is a diagram illustrating the operation of general multi-pass printing.

[0027] The left side of Figure 5 shows a schematic diagram illustrating the positional relationship between two integrated print heads H1 and H2 and image regions R1 to R4 formed on the recording medium in a typical multi-pass printing process, over time. The right side of Figure 5 shows a magnified view of the area enclosed by the dashed lines within the image regions R1 to R4 shown on the left side of Figure 5.

[0028] In the following description, a single print head nozzle row is assumed to consist of 1024 nozzles arranged in a single row. Furthermore, in the following description, the distance between the ends of the nozzles in the direction of the nozzle row is referred to as the print width. In the example shown in Figure 5, the print width of the print head is assumed to be 72.1 ± 0.02 mm. ±0.02 mm represents the variation during print head manufacturing. In the following description, the nozzle at one end of each nozzle row is designated as the 1st nozzle, and the nozzle at the other end as the 1024th nozzle.

[0029] First, the first pass of printing is performed by the 1st to 512th nozzles of the first print head H1. More specifically, with the recording medium stationary, the first and second print heads H1 and H2 move along the second direction D2 while ejecting ink from the 1st to 512th nozzles of the first print head H1. This forms the first image region R1, as shown in Figure 5. At the completion of the first pass of printing, the first image region R1 is formed by rows of 512 pixels with a gap between the nozzles 30 (hereinafter referred to as the nozzle pitch). In the enlarged view on the right side of Figure 5, each row of pixels is indicated as "Head1 Nozzle1," indicating which nozzle of which print head formed it. "Head1 Nozzle1" indicates that the row was formed by the 1st nozzle of the first head H1.

[0030] Next, the second pass of printing is performed. More specifically, after the recording medium has moved a predetermined distance along the first direction D1, and the recording medium is stationary, the first and second print heads H1 and H2 move along the second direction D2 while ink is ejected from the 1st to 1024th nozzles of the first print head H1. As a result, in the second image region R2 at the time the second pass of printing is completed, as shown in Figure 5, a new row of 512 pixels is formed adjacent to the row of pixels formed in the first pass by the 513th to 1024th nozzles of the first print head. Then, adjacent to the second image region R2, a new first image region R1 is formed, containing a row of 512 pixels, by the 1st to 512th nozzles of the first print head.

[0031] The amount of movement required to move the recording medium (hereinafter referred to as the feed amount) is the amount by which the first and second print heads H1 and H2 should be positioned to form the next image. In the example shown in Figure 5, this is the value obtained by adding the nozzle pitch of 512 pixels to the value corresponding to the spacing between pixels along the first direction D1 (hereinafter referred to as the inter-pixel distance). That is, (512 nozzle pitches + 1 inter-pixel distance) is the feed amount. For example, the feed amount is 36.10 mm.

[0032] Next, the third pass of printing is performed. More specifically, after the recording medium has been fed a predetermined amount along the first direction D1, and the recording medium is stationary, the first and second print heads H1 and H2 move along the second direction D2, while ejecting ink from the 1st to 1024th nozzles of the first print head H1 and the 1st to 512th nozzles of the second print head H2.

[0033] As a result, in the third image region R3 at the completion of the third print pass, as shown in Figure 5, a new row of 512 pixels is formed adjacent to the row of pixels formed up to the second pass by the 1st to 512th nozzles of the second print head H2. In the second image region R2 at the completion of the third print pass, although not shown in the illustration, a row of 512 pixels is formed adjacent to the row of pixels formed up to the second pass by the 513th to 1024th nozzles of the first print head. Furthermore, adjacent to the second image region R2, a new first image region R1 is formed, containing a row of 512 pixels, by the 1st to 512th nozzles of the first print head H1.

[0034] The amount of recording medium fed from the second pass to the third pass is the same as the amount fed from the first pass to the second pass, which is 36.15 mm.

[0035] Next, the fourth pass of printing is performed. More specifically, after the recording medium has been fed a predetermined amount along the first direction D1, and the recording medium is stationary, the first and second print heads H1 and H2 move along the second direction D2 while ejecting ink from the 1st to the 1024th nozzles of the first print head H1 and the 1st to the 1024th nozzles of the second print head H2, i.e., all nozzles of the first and second print heads H1 and H2.

[0036] As a result, when the fourth print pass is completed, in the fourth image region R4, as shown in Figure 5, a new row of 512 pixels is formed adjacent to the row of pixels formed up to the third pass by the 513th to 1024th nozzles of the second print head H2. This fills in all the gaps equal to the nozzle pitch when the fourth print pass is completed, and the image in the fourth image region R4 is formed.

[0037] In the third image region R3 at the completion of the fourth print pass (not shown in the illustration), a row of 512 pixels is formed adjacent to the row of pixels formed up to the third pass by the 1st to 512th nozzles of the second print head H2. In the second image region R2 at the completion of the fourth print pass (not shown in the illustration), a row of 512 pixels is formed adjacent to the row of pixels formed up to the third pass by the 513th to 1024th nozzles of the first print head H1. Furthermore, adjacent to the second image region R2, a new first image region R1 is formed, containing a row of 512 pixels, by the 1st to 512th nozzles of the first print head H1.

[0038] The feed amount of recording medium B from the 3rd pass to the 4th pass is the same as the feed amount up to the 3rd pass, which is 36.15 mm.

[0039] From this point onward, although not illustrated, the same operations as in the first to fourth passes described above are repeated until the entire image formed on the recording medium is complete.

[0040] In typical multi-pass printing as described above, variations in print width between print heads can result in uneven spacing between pixel rows. Figure 6 illustrates the state in typical multi-pass printing where variations in print width between print heads lead to uneven spacing between pixel rows. Figure 6 exaggerates the misalignment of the pixel rows.

[0041] For example, suppose the print width of the first print head H1 is 72.08 mm and the print width of the second print head H2 is 72.12 mm. In this case, even if the recording medium is fed by the same amount to print heads H1 and H2, the position of each nozzle of each print head H1 and H2 relative to the recording medium will be off from its original position. As a result, due to the variation in print width between print heads H1 and H2, areas Aw where the spacing between pixel rows is wider and areas An where it is narrower may occur, as shown in Figure 6. When printing wiring portions of a PCB using the image forming apparatus 1, such misalignment of pixel rows can become a serious defect.

[0042] Therefore, in the image forming apparatus 1 according to the embodiment of this disclosure, pixel misalignment can be reduced even if there is variation in the printing width of each print head by the following operation.

[0043] [First printing operation by the image forming apparatus 1] First, the first printing operation by the image forming apparatus 1 will be described in detail. In the following description, we will explain the case in which an image with a print resolution of 1440 dpi is formed by performing 4-pass multi-pass printing using a print head with a nozzle density of 360 dpi, similar to the general multi-pass printing operation described above.

[0044] Figure 7 is a diagram illustrating the first printing operation by the image forming apparatus 1. The left side of Figure 7 shows a schematic diagram illustrating the positional relationship between the two print heads 13A and 13B and the image regions Rx1 and Rx2 formed on the recording medium B in a time series during the first printing operation by the image forming apparatus 1. The right side of Figure 7 shows a magnified view of the area enclosed by the dashed lines of the image regions Rx1 and Rx2 shown on the left side of Figure 7.

[0045] First, the control unit 20 performs the first pass of printing using the 1st to 1024th nozzles of the print head 13A and the 1st to 1024th nozzles of the print head 13B, i.e., all nozzles. More specifically, with the recording medium stationary, the control unit 20 moves the print heads 13A and 13B along the second direction D2 while ejecting ink using all the nozzles 30 of the print heads 13A and 13B. As a result, as shown in Figure 7, an image area Rx1 formed only by the nozzles 30 of the print head 13A and an image area Rx2 formed only by the nozzles 30 of the print head 13B are formed adjacent to each other. Although partially omitted in Figure 7, at the completion of the first pass of printing, the image areas Rx1 and Rx2 are each formed by rows of 1024 pixels spaced apart by the nozzle pitch.

[0046] Next, the control unit 20 performs the second pass of printing. More specifically, after the recording medium B has been fed a predetermined amount along the first direction and the recording medium B is stationary, the control unit 20 moves the print heads 13A and 13B along the second direction while ejecting ink from all nozzles of the print heads 13A and 13B. Although some parts are omitted in Figure 7, in the image regions Rx1 and Rx2 at the time the second pass of printing is completed, a new row of pixels is formed adjacent to the row of pixels formed up to the first pass.

[0047] In the first printing operation, the feed amount of the recording medium B is the distance between pixels (inter-pixel distance) along the first direction formed on the recording medium B. That is, in the first printing operation, the control unit 20 moves the recording medium B along the first direction D1 by the inter-pixel distance. The inter-pixel distance is determined by the nozzle pitch and the number of passes. If the nozzle pitch is 70.4 μm and the number of passes is 4, the feed amount for the first printing operation is 17.6 μm. The feed amount is determined by the control unit 20 before the start of the printing operation or at the start of the printing operation and may be stored in a storage unit or the like (not shown).

[0048] Next, the third and fourth passes of printing are performed sequentially. The printing operations for the third and fourth passes are almost identical to those for the second pass. The fourth pass fills in all the gaps corresponding to the nozzle pitch, completing the formation of images in image regions Rx1 and Rx2, respectively. After that, the control unit 20 moves the recording medium B and the print heads 13A and 13B to the position where the next image should be formed, and then the printing operations for the fifth pass and beyond in the new image region begin.

[0049] The amount of material fed from recording medium B until print heads 13A and 13B reach the position where the next image should be formed is the sum of the combined printing widths of print heads 13A and 13B and the combined nozzle pitch of each print head 13A and 13B. For example, the amount of material fed in the 5th pass is 144.3410 mm. By repeating this printing operation, the entire image to be formed on recording medium B is created.

[0050] The amount of feed for recording medium B until the print heads 13A and 13B reach the position where the next image should be formed is not limited to the above. For example, in order to make the seam between the image formed by the first four print passes and the image formed by the fifth and subsequent print passes less noticeable, the feed amount may be slightly smaller than the value described above (144.3410 mm).

[0051] According to the first printing operation described above, two adjacent image regions Rx1 and Rx2 are formed on the recording medium B, one formed solely by the nozzles 30 of the print head 13A and the other by the nozzles 30 of the print head 13B. Therefore, in each of the image regions Rx1 and Rx2 formed by the first printing operation, pixels formed by the nozzles 30 of the print head 13A and pixels formed by the nozzles 30 of the print head 13B do not coexist. As a result, at least within each of the image regions Rx1 and Rx2, the adverse effects (positional misalignment) caused by the different printing widths of the print heads 13A and 13B can be minimized. Specifically, the positional misalignment caused by the different printing widths of the print heads 13A and 13B can be reduced to about half the difference in the one-nozzle pitch between the print heads 13A and 13B. For example, if the print width of print head 13A is 72.08 mm and the print width of print head 13B is 72.12 mm, according to the first printing operation of this disclosure, the positional misalignment due to the difference in print widths of print heads 13A and 13B can be reduced to approximately 0.02 μm. Therefore, even when the print widths of print heads 13A and 13B are different, the image forming apparatus 1 can form an image with reduced adverse effects due to the difference in print widths.

[0052] This configuration minimizes misalignment of the printed result, even when multiple print heads have different printing widths, for example, when printing solder resist ink for circuit formation on PCB substrates. Therefore, it effectively prevents misalignment of the printed result from causing serious defects during circuit formation on PCB substrates.

[0053] [Second printing operation by image forming apparatus 1] Next, the second printing operation by the image forming apparatus 1 will be described in detail. In the following description, we will explain the case in which an image with a print resolution of 1440 dpi is formed by performing 4-pass multi-pass printing using a print head with a nozzle density of 360 dpi, similar to a general multi-pass printing operation and the first printing operation.

[0054] In the first printing operation described above, the amount of data that the recording medium B was fed between passes was the distance between pixels in the first direction D1, but in the second printing operation described below, the amount of data that was fed is greater than this.

[0055] Figure 8 is a diagram illustrating the second printing operation by the image forming apparatus 1. The left side of Figure 8 shows a schematic diagram illustrating the positional relationship between the two print heads 13A and 13B and the image regions Ry1 and Ry2 formed on the recording medium B in a time series during the second printing operation by the image forming apparatus 1. The right side of Figure 8 shows a magnified view of the area enclosed by the dashed lines of the image regions Ry1 and Ry2 shown on the left side of Figure 8.

[0056] The control unit 20 performs the first pass of printing using the first to 1024th nozzles 30 of print head 13A and the first to 1024th nozzles 30 of print head 13B, i.e., all nozzles 30 of print heads 13A and 13B. More specifically, with the recording medium B stationary, the control unit 20 moves the print heads 13A and 13B along the second direction D2 while ejecting ink using all nozzles 30 of print heads 13A and 13B. As a result, as shown in Figure 8, an image region Ry1 formed only by the nozzles 30 of print head 13A and an image region Ry2 formed only by the nozzles 30 of print head 13B are formed adjacent to each other. Although partially omitted in Figure 8, at the completion of the first pass of printing, the image region Ry1 is formed by rows of 1024 pixels spaced apart by the nozzle pitch. Although not shown in the diagram, the image area Ry2 at the completion of the first print pass is formed by rows of 1024 pixels spaced apart by the nozzle pitch.

[0057] Next, the control unit 20 performs the second pass of printing. More specifically, after the recording medium B has been fed a predetermined amount along the first direction D1 and the recording medium B is stationary, the control unit 20 moves the print heads 13A and 13B along the second direction D2 while ejecting ink using all of the nozzles 30 of the print heads 13A and 13B.

[0058] In the example shown in Figure 8, the feed amount for the recording medium B sent by the control unit 20 is (14 nozzle pitches + 1 inter-pixel distance). In the example shown in Figure 8, the feed amount is 1.004 mm. As a result, as shown in Figure 8, in the second pass, the 15th nozzle 30 of the print head 13A forms a new row of pixels adjacent to the row of pixels formed by the 1st nozzle 30 of the print head 13A in the first pass. Then, in the second pass, the 14th nozzle 30 of the print head 13A forms a row of pixels not adjacent to the row of pixels formed by the 1st nozzle 30 of the print head 13A in the first pass, but at a position (1 nozzle pitch + 1 inter-pixel distance) away from the first direction D1.

[0059] Although not shown in Figure 8, the pixel rows formed by the first to thirteenth nozzles 30 of the print head 13A are formed to the right of the pixel row formed by the fourteenth nozzle 30 shown in Figure 8. The pixel rows formed by the first to thirteenth nozzles 30 of the print head 13A are not adjacent to the pixel row formed in the first pass, but are formed independently.

[0060] The amount of recording medium B to be fed in the second printing operation is determined by the control unit 20 before or at the start of the printing operation and may be stored in a storage unit or the like (not shown).

[0061] In the example shown in Figure 8, the feed rate is set to (14 nozzle pitch + 1 pixel distance). As a result, adjacent pixels along the first direction D1 are formed by nozzles 30 within the same print head 13 that are separated by approximately 14 nozzle pitches.

[0062] However, in the second printing operation, the amount of recording medium B that the control unit 20 sends between passes does not have to be equivalent to 14 nozzle pitches. In the second printing operation, it is sufficient to reduce the influence that the ejection curve from a particular nozzle 30 has on the position of adjacent pixels, so the amount of recording medium B sent can be set appropriately so that nozzles 30 that are a certain distance apart can form adjacent pixels. For example, setting it to 2 to 3 nozzle pitches can fully achieve the effect of this second printing operation. In this case, the control unit 20 should set the send amount to (2 to 3 nozzle pitches + 1 pixel distance).

[0063] Next, the control unit 20 performs the third pass of printing. More specifically, after the recording medium B has been fed along the first direction by the same amount as the feed amount from the first pass to the second pass, and with the recording medium B stationary, the control unit 20 moves the print heads 13A and 13B along the second direction while ejecting ink using all of the nozzles 30 of the print heads 13A and 13B.

[0064] As a result, although partially omitted in Figure 8, in the third pass, new rows of pixels are formed adjacent to the row of pixels formed in the second pass, by the 15th to 1024th nozzles 30 of print head 13A, and by the 1st to 1024th nozzles 30 of print head 13B. The row of pixels formed by the 1st to 14th nozzles 30 of print head 13A is not shown, but is formed independently and is not adjacent to the row of pixels formed in the second pass.

[0065] Furthermore, the control unit 20 performs the fourth pass of printing. More specifically, after the recording medium B has been fed along the first direction by the same amount as the feed amount from the first pass to the second pass, and with the recording medium B stationary, the control unit 20 moves the print heads 13A and 13B along the second direction while ejecting ink using all of the nozzles 30 of the print heads 13A and 13B.

[0066] As a result, in the fourth pass, new rows of pixels are formed adjacent to the row of pixels formed in the third pass, by the 15th to 1024th nozzles 30 of print head 13A, and by the 1st to 1024th nozzles 30 of print head 13B. The row of pixels formed by the 1st to 14th nozzles 30 of print head 13A, although not shown in the figure, is formed independently and is not adjacent to the row of pixels formed in the third pass.

[0067] As described above, in the second printing operation, from the second to the fourth pass, the rows of pixels formed by the first to fourteenth nozzles 30 of the print head 13A are not formed adjacent to the rows of pixels formed in the previous pass. Therefore, when the printing operation up to the fourth pass is completed, there will be gaps in some rows of pixels near the upstream end of the image region Ry1 along the first direction D1. The same is true near the downstream end of the image region Ry2 along the first direction D1.

[0068] This empty space is filled in the fifth and subsequent printing operations in the new image area after the fourth pass is completed, when the control unit 20 moves the recording medium B until the print heads 13A and 13B are in the position to form the next image.

[0069] In other words, in the second printing operation, the upstream edge of image region Ry1 along the first direction D1 up to the fourth pass partially overlaps with the downstream edge of image region Ry2 from the fifth pass onward. Figure 9 illustrates how image region Ry1 and image region Ry2 overlap near their edges. Figure 9 shows how the edges of image region Ry1, formed in passes 1 to 4, and the edges of image region Ry2, formed in passes 5 to 8, overlap. Note that Figure 9 exaggerates the overlapping area and is not scaled as it actually is.

[0070] As a result of this second printing operation, two adjacent image regions, Ry1 and Ry2, are formed on the recording medium B, one formed solely by the nozzles 30 of the print head 13A and the other by the nozzles 30 of the print head 13B. Therefore, in each of the image regions Ry1 and Ry2 formed by the second printing operation (excluding the edges), the pixel rows formed by the nozzles 30 of the print head 13A and the pixel rows formed by the nozzles 30 of the print head 13B do not coexist. Consequently, at least within each of the image regions Ry1 and Ry2, the adverse effects (positional misalignment) caused by the different printing widths of the print heads 13A and 13B can be minimized.

[0071] However, in the second printing operation, the feed rate of recording medium B is greater than in the first printing operation. In other words, in the second printing operation, a row of adjacent pixels along the first direction D1 is formed using nozzles 30 located further apart within the same print head 13 than in the first printing operation. This results in the following effects.

[0072] In the first printing operation, the same nozzle 30 is used to print four passes, so four adjacent pixels along the first direction D1 are formed by the same nozzle 30. If there is an ink ejection abnormality (bent, missing, reduced ejection amount, reduced ejection speed, etc.) in a particular nozzle 30 of the nozzle row 31, then in the first printing operation, the nozzle 30 with the ejection abnormality will form four adjacent pixels. The nozzle 30 with the ejection abnormality causes misalignment of the ink, and this misalignment causes positional displacement of the pixels. Therefore, in the first printing operation, the positional displacement will be concentrated in the four adjacent pixels formed by the nozzle 30 with the ejection abnormality.

[0073] On the other hand, in the second printing operation, even within the same print head 13, four adjacent pixels along the first direction D1 are formed using nozzles located at slightly different positions. That is, four adjacent pixels are formed by different nozzles 30. Therefore, even if an ejection abnormality occurs in one nozzle 30, it is possible to prevent the misalignment from concentrating on the four adjacent pixels.

[0074] However, in the second printing operation, as described above, the image region Ry1 is printed so that it partially overlaps with the edges of the image region Ry2 near both ends along the first direction D1. In this case, adjacent pixels are composed of nozzles at least 14 nozzle pitches apart, and a misalignment of pixels may occur due to the difference between the feed amount of the recording medium B and the nozzle pitch of the print heads 13A and 13B. Specifically, a misalignment of approximately 1.1 μm may occur, which is roughly calculated as (difference in nozzle pitch between print heads 13A and 13B) × (14 + 1 / 4) × 4 ÷ 2.

[0075] [Distinguishing between the first and second printing operations] As explained above, the first printing operation and the second printing operation each have their own unique advantages, and it is desirable to use them appropriately depending on the purpose. The user of the image forming apparatus 1 may pre-set which of the first and second printing operations to perform, but the control unit 20 may also be configured to automatically set which operation to perform depending on the environment in which the image forming apparatus 1 is located, as described below. The difference between the first printing operation and the second printing operation is the amount of recording medium B that is fed; in other words, the control unit 20 should appropriately change the amount of recording medium B that is fed during the printing operation according to various conditions as described below.

[0076] For example, if no ejection bend occurs in either nozzle 30 of print heads 13A or 13B, the first printing operation is adopted (the feed amount is set to the distance between pixels), which can result in a high-quality image overall. If ejection bend occurs in either nozzle of print heads 13A or 13B, the second printing operation is adopted (the feed amount is set to the distance between pixels of n nozzle pitch + 1), which may result in some pixel misalignment in the area where image regions Ry1 and Ry2 overlap, but it prevents the concentration of misalignment due to ejection bend in a specific nozzle in other areas, thus resulting in a relatively high-quality image overall.

[0077] Another example of how to differentiate between the first and second printing operations is as follows: The overall ejection angle of the nozzles 30 may differ depending on the print head 13. Figure 10A shows how the ink ejected from each nozzle 30 of the print head 13 narrows inward. Figure 10B shows how the ink ejected from each nozzle 30 of the print head 13 spreads outward. In Figures 10A and 10B, the dashed lines indicate the direction of the ejected ink.

[0078] As shown in Figures 10A and 10B, when the ink ejected from the nozzle 30 is angled, the landing position of the ink will deviate from the target position depending on the distance between the nozzle 30 and the recording medium B. This deviation increases as the distance between the nozzle 30's ejection port and the recording medium B increases.

[0079] Therefore, the control unit 20 adopts the first printing operation when the angle of ink ejected from the nozzle 30 is greater than a predetermined angle for the print head 13 as a whole, or when the distance between the recording medium B and the nozzle 30's ejection port is greater than a predetermined distance. This is because, in the first printing operation, the same nozzle 30 forms adjacent pixels within the image area formed by the same print head 13, so even if the ink ejection angle from the nozzle 30 is biased, the effect is smaller compared to the second printing operation.

[0080] Furthermore, another example of how to differentiate between the first and second printing operations is as follows: In an image forming apparatus 1 that uses heated print heads 13, the temperatures of multiple print heads 13 may differ. If a temperature difference occurs among the multiple print heads 13, the distance between the nozzles 30 will widen due to thermal expansion, resulting in different print widths for each print head 13.

[0081] In such cases, it is preferable to adopt the first printing operation. This is because, in the first printing operation, the same nozzle 30 forms adjacent pixels within the image area formed by the same print head 13, so the effect of differences in printing width between each print head 13 on the formed image is smaller compared to the second printing operation.

[0082] Therefore, the control unit 20 can, for example, acquire information regarding the temperature of each print head 13 using a temperature sensor provided for each print head 13, and if the temperature difference between the print heads 13 is above a predetermined temperature, it can forcibly adopt the first printing operation.

[0083] [Third printing operation] The following describes a modification of the first printing operation as the third printing operation. Figure 11 is a diagram illustrating the third printing operation by the image forming apparatus 1. Figure 11 shows an enlarged schematic diagram of the pixel rows formed by the first to third nozzles 30 of the print head 13A in the first to eighth passes.

[0084] The third printing operation is similar to the first printing operation in that, in the first to fourth passes, four adjacent pixel rows are formed by the same nozzle 30, but it differs from the first printing operation in that not all pixels included in the pixel row are formed in each pass.

[0085] In the third printing operation, not all pixels of a pixel sequence are formed in the first to fourth passes, and the remaining pixels of each pixel sequence are formed in the fifth to eighth passes. The amount of recording medium B fed up to the fourth pass is the same as in the first printing operation, corresponding to the distance between pixels. From the fourth to the fifth pass, the control unit 20 returns the recording medium B to the same position as the pixel sequence formed by a certain nozzle 30 in the first pass. That is, the control unit 20 returns the recording medium B by the distance between three pixels. The amount of recording medium B fed from the fifth to the eighth pass is the same as in the first four passes, corresponding to the distance between pixels.

[0086] Through this operation, in the third printing operation, the same pixel row is formed twice by the same nozzle 30. Therefore, even if the print width differs between the print heads 13A and 13B, the impact can be minimized, and because the same pixel row is formed at once, the occurrence of streaks between adjacent pixel rows can be reduced. [Industrial applicability]

[0087] According to this disclosure, an image forming apparatus capable of forming high-quality images can be provided. [Explanation of Symbols]

[0088] 1. Image forming apparatus 11. Transport platform 12 Carriage 13, 13A, 13B print heads 20 Control Unit 30 nozzles 31 nozzle rows 32 Head Chip Modules

Claims

1. Multiple print heads, each having a nozzle row composed of multiple nozzles, which form an image on a recording medium by ejecting ink droplets from the nozzle row, A control unit that performs multi-pass printing to form the image by combining the operation of moving the print head and the recording medium relative to each other multiple times along a first direction which is the direction of the nozzle row or the opposite direction, and the operation of moving the print head and the recording medium relative to each other multiple times along a second direction which is perpendicular to the first direction, Equipped with, The control unit, Control is performed to execute the multi-pass printing using a single ink so that in at least a portion of the image, pixels between one nozzle pitch of the print head are formed by the nozzle row of the single print head. A printing operation in which adjacent pixel rows are formed along a first direction by ink droplets ejected from the same nozzle, wherein a third printing operation is performed in which a single pixel row is formed in multiple passes by the same nozzle by moving the print head and the recording medium relative to each other along the first direction and then moving them relative to each other along the opposite direction of the first direction; and a second printing operation is performed in which adjacent pixel rows are formed along a first direction by ink droplets ejected from different nozzles among the nozzle rows of a single print head, by selecting either of these two options to perform the multi-pass printing. Image forming apparatus.

2. The control unit repeatedly performs the following actions in the control: a first movement operation in which ink is ejected from one of the nozzles of the print head while the print head is moved relative to the print head along the second direction; a second movement operation in which the recording medium is moved relative to the print head along the first direction; and a third movement operation in which, after printing of at least a portion of the image is completed, the recording medium is moved relative to the print head along the first direction based on the distance between the nozzle ends of the plurality of print heads. The amount of movement in the second movement operation is changed based on whether the third printing operation or the second printing operation is used. The image forming apparatus according to claim 1.

3. In the second movement operation, the control unit moves the recording medium relative to the print head by a distance of less than or equal to one nozzle pitch of the print head. The image forming apparatus according to claim 2.

4. In the second movement operation, the control unit moves the recording medium relative to the print head by a distance of at least one nozzle pitch of the print head in the first direction. The image forming apparatus according to claim 2.

5. The control unit performs the multi-pass printing using the third printing operation when the temperature difference between the multiple print heads is above a predetermined temperature. The image forming apparatus according to claim 2.

6. The control unit performs the multi-pass printing using the third printing operation when the distance between the nozzle outlet and the recording medium is greater than a predetermined distance. The image forming apparatus according to claim 2.

7. An image forming method for performing multipass printing, which forms an image by combining the operation of moving a plurality of print heads having nozzle rows composed of a plurality of nozzles and a recording medium relative to each other multiple times along a first direction which is the direction of the nozzle row or the opposite direction, and the operation of moving a plurality of print heads relative to each other multiple times along a second direction which is perpendicular to the first direction, In at least a portion of the image, the multi-pass printing is performed using a single ink such that the pixels between one nozzle pitches of the print head are formed by the nozzle row of the single print head. A printing operation in which adjacent pixel rows are formed along a first direction, which is the direction of the nozzle row, by ink droplets ejected from the same nozzle, wherein a third printing operation is performed in which a single pixel row is formed in multiple passes by the same nozzle by moving the print head and the recording medium relative to each other along the first direction and then moving them relative to each other along the opposite direction of the first direction; and a second printing operation is performed in which adjacent pixel rows are formed along the first direction by ink droplets ejected from different nozzles among the nozzle row of a single print head, by selecting either of these two options to perform the multi-pass printing. Image forming method.

Images