Image forming apparatus and image forming method

Abstract

An image forming apparatus of the present application includes a plurality of print heads having nozzle rows formed of a plurality of nozzles, which form an image on a recording medium by discharging ink droplets from the nozzle rows, and a control section which performs control to execute a plurality of passes of printing, in which the image is formed by relatively moving the print heads and the recording medium along a second direction orthogonal to a first direction in which the plurality of nozzles are arranged a plurality of times, and performs control to execute the plurality of passes of printing so that, in at least a portion of the image, a pixel between one nozzle pitch of the print heads is formed by a nozzle row possessed by a single print head.

Description

Technical Field

[0001] This disclosure relates to an image forming apparatus and an image forming method. Background Technology

[0002] Traditionally, inkjet printing apparatuses (image forming apparatuses) form images on a recording medium by alternating and repeating the following steps: forming an image by discharging ink from a plurality of nozzles formed on the print head while the recording medium is stopped and the print head is moved in the scanning direction; and moving the recording medium bit by bit in a direction different from the scanning direction.

[0003] Patent Document 1 discloses an inkjet printer that improves print quality by appropriately correcting errors in the amount of paper fed to move the paper as the recording medium in interlaced recording mode.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2003-011344

[0005] Nozzle defects can exist, such as inconsistent ink flow or direction due to manufacturing defects, or ink failure to flow from specific nozzles due to clogging. Using a printhead with such defective nozzles results in degraded image quality. Multi-pass printing is a method to mitigate this quality degradation.

[0006] Multi-pass printing is a printing method that divides a nozzle array consisting of multiple nozzles into multiple sections according to the number of passes. Ink is sequentially ejected from multiple nozzle arrays for each section to form an image in stages. In this way, even if the ink ejection volume or direction from a particular nozzle is unstable, or ink cannot be ejected from a particular nozzle, the ink ejected from nozzles that have never caused these problems is overlapped, thus suppressing image quality degradation.

[0007] However, even with multiple printing passes, it is difficult to suppress image quality degradation. Due to factors such as quality variations during printhead manufacturing, the distance from the effective nozzle at one end to the effective nozzle at the other end (the distance between the nozzle ends) varies from printhead to printhead. An effective nozzle is distinct from a virtual nozzle that does not expel ink; it refers to the nozzle that expels ink. In such cases, if adjacent pixels are printed using printheads with varying distances between their nozzle ends, the spacing between adjacent pixels deviates from its original position, resulting in reduced image quality. Since this deviation occurs in regions divided according to the number of passes, it is difficult to eliminate in the technology disclosed in Patent Document 1. Summary of the Invention

[0008] The purpose of this disclosure is to provide an image forming apparatus and an image forming method that can prevent the deterioration of the quality of the printed result even when the distance between the nozzle tips in the nozzle array of the printhead is different in each of the multiple printheads.

[0009] The image forming apparatus of this disclosure includes: a plurality of printheads having a nozzle array consisting of a plurality of nozzles, forming an image on a recording medium by discharging ink droplets from the nozzle array; and a control unit that controls the execution of multiple passes of printing, wherein the image is formed by moving the printheads and the recording medium relative to each other multiple times along a second direction orthogonal to a first direction in which the plurality of nozzles are arranged, and the control unit controls the execution of the multiple passes of printing such that at least a portion of the image is formed by pixels between a nozzle pitch of the printheads through a single nozzle array of the printheads.

[0010] The image forming method disclosed herein is an image forming method that performs multiple printing passes. In the multiple printing passes, an image is formed by moving multiple printheads having nozzle arrays consisting of multiple nozzles relative to a recording medium multiple times. In the image forming method, the multiple printing passes are performed such that adjacent pixels constituting the image are formed by the nozzle arrays of a single printhead.

[0011] According to this disclosure, even when the distance between the nozzle tips in the nozzle array of the printhead is different in each of the multiple printheads, it is possible to prevent the deterioration of the print quality. Attached Figure Description

[0012] Figure 1 This is a top view showing the main components of the image forming apparatus in the embodiments of this disclosure.

[0013] Figure 2 This is a diagram illustrating an example of the structure of a printhead.

[0014] Figure 3 It is a diagram used to illustrate the positional relationship of the printheads.

[0015] Figure 4A This is a diagram illustrating an example of a printhead having two rows of nozzles.

[0016] Figure 4B This diagram illustrates an example of multiple head chip modules configured within a single printhead.

[0017] Figure 4C This diagram illustrates an example of multiple head chip modules configured within a single printhead.

[0018] Figure 5It is a diagram used to illustrate the typical actions of multiple printing passes.

[0019] Figure 6 It is a diagram used to illustrate the uneven spacing between columns of pixels in a typical multi-pass printing process, where there is a deviation in the character width of each printhead.

[0020] Figure 7 This is a diagram used to illustrate the first printing action of an image forming apparatus.

[0021] Figure 8 This is a diagram illustrating the second printing action of the image forming apparatus.

[0022] Figure 9 This is a diagram used to illustrate how image regions Ry1 and Ry2 overlap near their ends.

[0023] Figure 10A It is a diagram showing how the ink ejected from each nozzle of the printhead is ejected in a narrowing inward manner.

[0024] Figure 10B It is a diagram showing how the ink ejected from each nozzle of the printhead is ejected in an outward expanding manner.

[0025] Figure 11 This is a diagram used to illustrate the third printing action of the image forming apparatus. Detailed Implementation

[0026] The image forming apparatus according to embodiments of the present disclosure will now be described.

[0027] <Composition of the image forming apparatus>

[0028] Figure 1 This is a top view showing the main configuration of the image forming apparatus 1 according to the embodiments of the present disclosure. The image forming apparatus 1 includes a transport table 11, a carriage 12, a print head 13, and a control unit 20. Figure 1 For illustrative purposes, the sizes of the components differ from their actual dimensions and are exaggerated. In the following explanation, [the following will be used to illustrate this]. Figure 1 The front side of the paper is designated as "top," and the inside side of the paper is designated as "bottom."

[0029] The transport stage 11 is configured to move the recording medium B, which is the object of image formation by 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). Preferably, the recording medium B is, for example, a copper-clad laminate of all grades (FR-4, etc.) made of materials such as paper phenolic resin, paper epoxy resin, glass cloth epoxy resin, glass polyimide, glass cloth / non-woven epoxy resin, glass cloth / paper epoxy resin, synthetic fiber epoxy resin, fluoropolymer-polyethylene-PPO-cyanate ester, etc., for high-frequency circuit copper-clad laminates, other polyimide films, PET films, glass substrates, ceramic substrates, wafers, and stainless steel plates.

[0030] The carriage 12 is equipped with multiple printheads 13 and ink reservoirs corresponding to each printhead 13. Additionally, the carriage 12 is equipped with a position sensor (not shown) for reading the relative position with respect to the recording medium B. The carriage 12 is positioned above the transport stage 11 and the recording medium B. Figure 1 (the paper surface near the front side) so that the nozzle 30 of the print head 13, described later, is positioned opposite the recording medium B.

[0031] In addition, the carriage 12 is supported by a support portion (not shown) so that it can move along the second direction D2.

[0032] Each printhead 13 has a plurality of nozzles 30 for expelling ink droplets. Furthermore, in the following description, the expulsion of ink droplets by the nozzles 30 is sometimes described simply as the expulsion of ink. Figure 2 This is a diagram illustrating an example of the configuration of printhead 13. Figure 2 In the example shown, multiple nozzles 30 are arranged in a row to form a nozzle row 31. Figure 2 For illustrative purposes only, the number of nozzles 30 on the print head 13 is different from the actual number.

[0033] In this embodiment, the ink is, for example, an ink containing a coating agent for printed wiring manufacturing, an insulating material, etc. Each of the multiple nozzles 30 of the multiple printheads 13 is filled with a single type of ink. Examples of a single type of ink include solder resist ink used for circuit formation in a PCB substrate.

[0034] Multiple printheads 13 are mounted on the carriage 12, each having multiple nozzles 30 arranged along a first direction D1. In this embodiment, as... Figure 3 As shown, two printheads 13, 13A and 13B, are installed on the carriage 12.

[0035] Figure 3 This is a diagram used to illustrate the positional relationship between printheads 13A and 13B. Figure 3 From the bottom side, that is... Figure 1 A diagram showing the slide 12 viewed from side B of the recording medium. In this embodiment, as... Figure 3 As shown, printhead 13A and printhead 13B are configured to be offset from each other in the second direction D2.

[0036] The control unit 20 forms an image on the surface of the recording medium B by controlling the aforementioned components. Specifically, the control unit 20 moves the print head 13 relative to the recording medium B along the second direction D2 while simultaneously ejecting ink from the print head 13 onto the recording medium B. Subsequently, the control unit 20 moves the transport stage 11 a predetermined distance along the first direction D1, and again moves the print head 13 relative to the recording medium B along the second direction D2 while simultaneously ejecting ink from the print head 13 onto the recording medium B. By repeating this process, an image is formed on the recording medium B.

[0037] The main configuration of the image forming apparatus 1 according to the embodiments of the present disclosure has been described above. However, the above description is only one example of the configuration of the image forming apparatus 1, and the present disclosure is not limited thereto. For example, the transport table 11 may be moved relative to the print head 13 along the second direction D2, and ink may be discharged from the print head 13 while the transport table 11 is moving, and the print head 13 may be moved along the 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 relative to the print head 13 along the second direction D2, and each time the movement is completed, it may be moved along the first direction D1. Furthermore, both the print head 13 and the transport table 11 may be moved along the second direction D2, and each time the movement is completed, both the print head 13 and the transport table 11 may be moved along the first direction D1.

[0038] In addition, although Figure 2 as well as Figure 3 The image shows an example where each printhead 13 has only one column of nozzles 31, but each printhead 13 may also have multiple columns of nozzles 31. Figure 4A This is a diagram illustrating an example of a printhead 13 having two rows of nozzles 31. And, as... Figure 4B as well as Figure 4C As shown in the example, multiple head chip modules 32 can also be configured within a single printhead 13. The head chip module 32 is obtained by arranging multiple print chips in a modular fashion. Figure 4B In the example shown, two head chip modules 32 are arranged along the second direction D2 to improve resolution. Figure 4C In the example shown, two head chip modules 32 are configured offset from each other along the first direction D1, thereby expanding the area that the print head 13 can print at one time.

[0039] <Printing Action>

[0040] Hereinafter, the printing operation of the image forming apparatus 1 according to the present disclosure will be described in comparison with the operation of a general multi-pass printing.

[0041] [A typical multi-pass printing action]

[0042] First, the general operation of multi-pass printing will be explained. As an example, we will explain the case of forming an image with a print resolution of 1440 dpi by performing four passes using a printhead with a nozzle density of 360 dpi. Figure 5 It is a diagram used to illustrate the typical actions of multiple printing passes.

[0043] exist Figure 5 The left side shows a schematic diagram illustrating the positional relationship between two integrally formed printheads H1 and H2 and the image regions R1 to R4 formed on the recording medium, arranged in time sequence during typical multi-pass printing. Figure 5 The right side shows an enlarged view. Figure 5 The image shown on the left shows the area R1 to R4 surrounded by dashed lines.

[0044] In the following description, it is assumed that 1024 nozzles are configured in a row to form the nozzle array of a printhead. Furthermore, in the following description, the distance between the nozzle tips in the nozzle array direction is described as the character width. Figure 5 In the example shown, the printhead width is 72.1 ± 0.02 mm. ± 0.02 mm is the tolerance during printhead manufacturing. In the following description, the nozzle located at one end of each nozzle row is designated as the first, and the nozzle located at the other end is designated as the 1024th.

[0045] First, a first pass of printing is performed through the first to the 512th nozzles of the first printhead H1. More specifically, with the recording medium stationary, ink is expelled from the first to the 512th nozzles of the first printhead H1, and the first printhead H1 and the second printhead H2 move along the second direction D2. Thus, as... Figure 5 As shown, a first image region R1 is formed. The first image region R1 at the moment the first printing operation is completed is formed by columns of 512 pixels that separate the nozzles 30 from each other (hereinafter referred to as nozzle spacing). Furthermore, in Figure 5 The enlarged view on the right shows, for example, "Head1 Nozzle1", which nozzle of which printhead forms the column of each pixel. "Head1 Nozzle1" indicates the column formed by the first nozzle of the first printhead H1.

[0046] Next, a second printing pass is performed. More specifically, after the recording medium has moved a predetermined amount along the first direction D1, while the recording medium is stationary, ink is discharged from the first to the 1024th nozzles of the first print head H1, while the first print head H1 and the second print head H2 move along the second direction D2. Thus, in the second image area R2 at the moment the second printing pass is completed, as shown... Figure 5 As shown, a new column of 512 columns of pixels is formed adjacent to the column of pixels formed in the first pass through the 513th to 1024th nozzles of the first printhead. Furthermore, a first image region R1 containing a column of 512 columns of pixels is formed adjacent to the second image region R2 through the first to 512th nozzles of the first printhead.

[0047] The amount of movement (hereinafter referred to as feed) that moves the recording medium is the amount by which the first print head H1 and the second print head H2 are positioned so that the next image should be formed. Figure 5 In the example shown, the feed rate is the sum of the 512 nozzle spacings and the value corresponding to the spacing between pixels along the first direction D1 (referred to as pixel distance in the following description). That is, (512 nozzle spacings + one pixel distance) becomes the feed rate. In a specific example, the feed rate is 36.10 mm.

[0048] Next, the third printing is performed. More specifically, after the recording medium has been delivered a predetermined amount along the first direction D1, while the recording medium is stationary, the first print head H1 and the second print head H2 move along the second direction D2 while ink is being discharged from the first to the 1024th nozzle of the first print head H1 and the first to the 512th nozzle of the second print head H2.

[0049] Therefore, in the third image region R3 at the moment when the third printing action is completed, as shown... Figure 5 As shown, 512 new columns of pixels are formed adjacent to the columns of pixels formed up to the second pass through the first to the 512th nozzles of the second printhead H2. In the second image region R2 at the moment the third print operation is completed, although not illustrated, 512 columns of pixels are formed adjacent to the columns of pixels formed up to the second pass through the 513th to the 1024th nozzles of the first printhead. Furthermore, a first image region R1 containing 512 columns of pixels is newly formed adjacent to the second image region R2 through the first to the 512th nozzles of the first printhead H1.

[0050] The feed rate of the recording medium in the second and third passes is the same as that in the first and second passes, which is 36.15 mm.

[0051] Next, the fourth printing pass is performed. More specifically, after the recording medium has been delivered a predetermined amount along the first direction D1, while the recording medium is stationary, ink is discharged from the first to the 1024th nozzles of the first printhead H1 and the first to the 1024th nozzles of the second printhead H2, that is, from all the nozzles of the first printhead H1 and the second printhead H2, while the first printhead H1 and the second printhead H2 move along the second direction D2.

[0052] Therefore, in the fourth image region R4 at the moment when the fourth printing action is completed, as shown... Figure 5 As shown, 512 new columns of pixels are formed adjacent to the columns of pixels formed up to the third pass through the 513th to 1024th nozzles of the second print head H2. Thus, at the moment the fourth print pass is completed, the interval between all nozzles is filled, and the image in the fourth image region R4 is formed.

[0053] In the third image region R3 at the moment the fourth printing operation is completed, although not illustrated, a column of 512 columns of pixels is formed adjacent to the columns of pixels formed up to the third printhead H2 through the first to the 512th nozzles. In the second image region R2 at the moment the fourth printing operation is completed, although not illustrated, a column of 512 columns of pixels is formed adjacent to the columns of pixels formed up to the third printhead H1 through the 513th to the 1024th nozzles. Furthermore, a first image region R1 containing a column of 512 columns of pixels is newly formed adjacent to the second image region R2 through the first to the 512th nozzles of the first printhead H1.

[0054] The feed rate of recording medium B in the third and fourth passes is the same as the feed rate up to the third pass, which is 36.15 mm.

[0055] Afterwards, although the illustrations are omitted, the same actions as the first to fourth times described above are repeated until the entire image formed on the recording medium is completed.

[0056] In typical multi-pass printing as described above, when there is a deviation in the print width of each printhead, there is uneven spacing between the pixel columns. Figure 6 It is a diagram used to illustrate the uneven spacing between columns of pixels in a typical multi-pass printing process, where there is a deviation in the character width of each printhead. Figure 6 The positional offset of the pixel column is exaggerated.

[0057] 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 with the same amount of feed relative to print heads H1 and H2, the position of each nozzle of each print head H1 and H2 relative to the recording medium will deviate from its original position. Therefore, due to the deviation in the print width of each print head H1 and H2, such as... Figure 6 As shown, there may be positions where the spacing between pixel columns widens (Aw) and conversely, positions where the spacing narrows (An). Such pixel column positional misalignment can be a significant defect when using the image forming apparatus 1 to print wiring sections of a PCB.

[0058] Therefore, in the image forming apparatus 1 of the present disclosure, the positional offset of pixels can be reduced even if there is a deviation in the printing width of each print head by the following operation.

[0059] [First printing action of image forming apparatus 1]

[0060] First, the first printing operation of the image forming apparatus 1 will be described in detail. In the following description, the case in which an image with a print resolution of 1440 dpi is formed by performing four passes of printing using a print head with a nozzle density of 360 dpi, which is the same as the general multi-pass printing operation described above.

[0061] Figure 7 This is a diagram illustrating the first printing action of the image forming apparatus 1. Figure 7 The left side shows a schematic diagram illustrating the positional relationship between the two printheads 13A and 13B and the image regions Rx1 and Rx2 formed on the recording medium B in a time sequence during the first printing operation of the image forming apparatus 1. Figure 7 The right side shows an enlarged view. Figure 7 The image regions Rx1 and Rx2 shown on the left are the areas enclosed by dashed lines.

[0062] First, the control unit 20 uses the first to the 1024th nozzles of printhead 13A and the first to the 1024th nozzles of printhead 13B, that is, all the nozzles, to perform the first pass of printing. More specifically, with the recording medium stationary, the control unit 20 moves printheads 13A and 13B along the second direction D2 while simultaneously using all the nozzles 30 of printheads 13A and 13B to expel ink. Thus, as... Figure 7 As shown, image regions Rx1 and Rx2, formed only by the nozzles 30 of printhead 13A and printhead 13B respectively, are formed adjacent to each other. Figure 7A portion is omitted, but the image regions Rx1 and Rx2 at the moment the first printing action is completed are formed by columns of 1,024 pixels separated by the nozzle spacing.

[0063] Next, the control unit 20 performs a second printing pass. More specifically, after the recording medium B has been delivered a predetermined amount along the first direction, while the recording medium B is stationary, the control unit 20 simultaneously causes the print heads 13A and 13B to move along the second direction while ink is being expelled from all the nozzles of the print heads 13A and 13B. Although in Figure 7 A portion is omitted, but in the image regions Rx1 and Rx2 at the moment the second printing action is completed, new columns of pixels are formed adjacent to the columns of pixels formed up to the first printing action.

[0064] In the first printing operation, the feed amount of the recording medium B is the distance between the pixels formed on the recording medium B along the first direction (inter-pixel distance). That is, in the first printing operation, the control unit 20 moves the recording medium B along the first direction D1 by one inter-pixel distance. The inter-pixel distance is determined based on the nozzle pitch and the number of passes. When 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 can be determined by the control unit 20 before or at the start of the printing operation and stored in a storage unit (not shown) or the like.

[0065] Next, the third and fourth printing passes are performed sequentially. The printing actions for the third and fourth passes are almost identical to those for the second pass. Through the fourth printing pass, the spacing between all nozzles is filled, and the images in image areas Rx1 and Rx2 are formed. Afterward, the control unit 20, after conveying the recording medium B until the print heads 13A and 13B are in the position where the next image should be formed, begins the fifth printing pass and subsequent printing operations in the new image area.

[0066] The feed amount of the recording medium B up to the position where printheads 13A and 13B should form the next image is the sum of the print widths of printheads 13A and 13B and the sum of the pitches of one nozzle of each printhead 13A and 13B. For example, the feed amount for the fifth pass is 144.3410 mm. By repeating this printing action, the entire image that should be formed on the recording medium B is created.

[0067] Furthermore, the feed rate of the recording medium B up to the position where the print heads 13A and 13B should form the next image is not limited to the above. For example, in order to make the seam between the image formed by the printing operation up to the fourth pass and the image formed by the printing operation from the fifth pass onwards less noticeable, the feed rate may be slightly smaller than the value described above (144.3410 mm).

[0068] According to the first printing operation described above, in the recording medium B, an image region Rx1 formed solely by the nozzles 30 of printhead 13A and an image region Rx2 formed solely by the nozzles 30 of printhead 13B are formed adjacent to each other. Therefore, in each image region Rx1 and Rx2 formed by the first printing operation, pixels formed by the nozzles 30 of printhead 13A and pixels formed by the nozzles 30 of printhead 13B will not be mixed up. Therefore, at least within each image region Rx1 and Rx2, the negative impact (positional offset) caused by the difference in the print widths of printheads 13A and 13B can be suppressed to a lesser extent. Specifically, the positional offset caused by the difference in the print widths of printheads 13A and 13B can be suppressed to approximately half the difference in the nozzle spacing between printheads 13A and 13B. For example, when the print width of printhead 13A is 72.08 mm and the print width of printhead 13B is 72.12 mm, according to the first printing operation of this disclosure, the positional offset caused by the difference in print width between printheads 13A and 13B can be approximately 0.02 μm. Therefore, even when the print widths of printheads 13A and 13B are different, the image forming apparatus 1 can form an image that reduces the negative impact of the difference in print width.

[0069] With this configuration, for example in applications such as solder resist ink used for circuit formation on printed PCB substrates, even when the print widths of multiple printheads differ, positional offset of the printed result can be minimized. Therefore, it is possible to effectively prevent positional offset of the printed result from causing significant defects during circuit formation on the PCB substrate.

[0070] [Second printing action of image forming apparatus 1]

[0071] Next, the second printing operation of the image forming apparatus 1 will be described in detail. In the following description, the case in which a multi-pass printing operation is the same as the first printing operation, and an image with a print resolution of 1440 dpi is formed by performing four passes of printing using a print head with a nozzle density of 360 dpi.

[0072] In the first printing operation described above, the feed amount of the recording medium B between passes is the pixel distance in the first direction D1, but in the second printing operation described below, the feed amount is larger than that.

[0073] Figure 8 This is a diagram illustrating the second printing operation of the image forming apparatus 1. Figure 8 The left side shows a schematic diagram illustrating the positional relationship between the two printheads 13A and 13B and the image areas Ry1 and Ry2 formed on the recording medium B in a time sequence during the second printing operation of the image forming apparatus 1. Figure 8 The right side shows an enlarged view. Figure 8 The image regions Ry1 and Ry2 shown on the left are the areas enclosed by dashed lines.

[0074] The control unit 20 uses the first to the 1024th nozzles 30 of printhead 13A and the first to the 1024th nozzles 30 of printhead 13B, that is, all the nozzles 30 of printheads 13A and 13B, to perform the first pass of printing. More specifically, with the recording medium B stationary, the control unit 20 moves printheads 13A and 13B along the second direction D2 while simultaneously using all the nozzles 30 of printheads 13A and 13B to expel ink. Thus, as... Figure 8 As shown, image regions Ry1 and Ry2, formed only by the nozzles 30 of printhead 13A and printhead 13B respectively, are formed adjacent to each other. Figure 8 A portion is omitted, but the image region Ry1 at the moment the first print pass is completed is formed by columns of 1024 pixels spaced apart by the nozzle spacing. Similarly, although the illustration is omitted, the image region Ry2 at the moment the first print pass is completed is also formed by columns of 1024 pixels spaced apart by the nozzle spacing.

[0075] Next, the control unit 20 performs a second printing. More specifically, after the recording medium B has been delivered a predetermined amount along the first direction D1, while the recording medium B is stationary, the control unit 20 moves the print heads 13A and 13B along the second direction D2 while using all the nozzles 30 of the print heads 13A and 13B to discharge ink.

[0076] exist Figure 8 In the example shown, the feed rate of the recording medium B delivered by the control unit 20 is (the distance between fourteen nozzles + the distance between one pixel). Figure 8 In the example shown, the feed rate is 1.004 mm. Therefore, as... Figure 8As shown, in the second pass, the fifteenth nozzle 30 of printhead 13A forms a new pixel column at a position adjacent to the pixel column formed by the first nozzle 30 of printhead 13A in the first pass. Furthermore, in the second pass, the fourteenth nozzle 30 of printhead 13A is not adjacent to the pixel column formed by the first nozzle 30 of printhead 13A in the first pass, but forms a pixel column at a position separated from the first direction D1 by (one nozzle pitch + one pixel distance).

[0077] In addition, although Figure 8 Not shown in the figure, but based on the first to thirteenth nozzles 30 of printhead 13A, the pixel columns are formed in Figure 8 The pixel column formed by the fourteenth nozzle 30 is shown further to the right. The pixel columns from the first to the fourteenth nozzle 30 of the printhead 13A are not adjacent to the pixel columns formed in the first pass, but are formed independently.

[0078] The feed amount of the recording medium B in the second printing operation can be determined by the control unit 20 before or at the start of the printing operation and stored in a storage unit (not shown).

[0079] exist Figure 8 In the example shown, the feed rate is set to (fourteen nozzle pitches + one pixel pitch). Thus, adjacent pixels along the first direction D1 are formed by nozzles 30 within the same printhead 13, which are approximately fourteen nozzle pitches apart.

[0080] However, in the second printing operation, the amount of recording medium B fed by the control unit 20 between passes does not necessarily have to be fourteen nozzle pitches. In the second printing operation, as long as the effect of the discharge curvature from a particular nozzle 30 on the position of adjacent pixels can be reduced, it is sufficient to appropriately set the feed amount of the recording medium B so that adjacent pixels can be formed by the nozzles 30 with a certain degree of separation. As an example, if it is set to 2 to 3 nozzle pitches, the effect of such a second printing operation can be sufficiently obtained. In this case, the control unit 20 can set the feed amount to (2 to 3 nozzle pitches + one pixel distance).

[0081] Next, the control unit 20 performs a third printing pass. More specifically, after feeding the recording medium B along the first direction with the same amount of feed as from the first to the second pass, while the recording medium B is stationary, the control unit 20 uses all the nozzles 30 of the printheads 13A and 13B to discharge ink, while simultaneously moving the printheads 13A and 13B along the second direction.

[0082] Therefore, although in Figure 8While some illustrations are omitted, in the third pass, new columns of pixels based on the fifteenth to the thousand twenty-fourth nozzles 30 of printhead 13A and columns of pixels based on the first to the thousand twenty-fourth nozzles 30 of printhead 13B are formed adjacent to the columns of pixels formed in the second pass. Although not illustrated, the columns of pixels based on the first to the fourteenth nozzles 30 of printhead 13A are formed independently and are not adjacent to the columns of pixels formed in the second pass.

[0083] Then, the control unit 20 performs a fourth print. More specifically, after the recording medium B is fed along the first direction with the same amount of feed as from the first to the second print, while the recording medium B is stationary, the control unit 20 moves the print heads 13A and 13B along the second direction while using all the nozzles 30 of the print heads 13A and 13B to discharge ink.

[0084] Therefore, in the fourth pass, new columns of pixels based on the fifteenth to the thousand twenty-fourth nozzles 30 of printhead 13A and columns of pixels based on the first to the thousand twenty-fourth nozzles 30 of printhead 13B are formed adjacent to the columns of pixels formed in the third pass. Although not shown, the columns of pixels based on the first to the fourteenth nozzles 30 of printhead 13A are formed independently and are not adjacent to the columns of pixels formed in the third pass.

[0085] As described above, in the second printing operation, from the second to the fourth pass, the columns of pixels based on the first to the fourteenth nozzles 30 of the printhead 13A are not formed adjacent to the columns of pixels formed in the previous pass. Therefore, at the moment when the printing operation up to the fourth pass is completed, the area near the upstream end of the image region Ry1 along the first direction D1 becomes an idle state with a portion of the pixel columns. The same applies to the area near the downstream end of the image region Ry2 along the first direction D1.

[0086] After the fourth pass is completed, the recording medium B is transported through the control unit 20 until the print heads 13A and 13B are in the position where the next image should be formed, and then the gap is filled in the fifth pass and subsequent printing operations in the new image area.

[0087] That is, in the second printing action, the area near the upstream end of the image region Ry1 up to the fourth print coincides with the area near the downstream end of the image region Ry2 from the fifth print onwards. Figure 9 This diagram illustrates how image regions Ry1 and Ry2 overlap near their ends. Figure 9 The image shows the end of image region Ry1 formed in the first to fourth passes coinciding with the end of image region Ry2 formed in the fifth to eighth passes. Furthermore, Figure 9 The overlapping positions are exaggerated, and the scale differs from the actual values.

[0088] Through this second printing action, image region Ry1, formed solely by the nozzles 30 of printhead 13A, and image region Ry2, formed solely by the nozzles 30 of printhead 13B, are formed adjacently on the recording medium B. Therefore, in each image region Ry1 and Ry2 formed by the second printing action (except near the ends), the pixel columns formed by the nozzles 30 of printhead 13A and the pixel columns formed by the nozzles 30 of printhead 13B will not mix. Therefore, at least within each image region Ry1 and Ry2, the negative impact (positional offset) caused by the difference in the printing width of printheads 13A and 13B can be minimized.

[0089] However, in the second printing operation, the feed rate of the recording medium B is greater than that in the first printing operation. In other words, in the second printing operation, even within the same print head 13, nozzles 30, positioned separately from those in the first printing operation, are used to form columns of adjacent pixels along the first direction D1. This results in the following effect.

[0090] In the first printing operation, the same nozzle 30 is used for four passes, thus forming four adjacent pixels along the first direction D1 through the same nozzle 30. If it is assumed that a particular nozzle 30 in the nozzle array 31 has an ink discharge abnormality (bending, damage, reduced discharge volume, reduced discharge speed, etc.), then in the first printing operation, the nozzle 30 causing the discharge abnormality forms four adjacent pixels. The nozzle 30 causing the discharge abnormality causes ink landing offset, which in turn causes pixel position offset. Therefore, in the first printing operation, the position offset is concentrated in the four adjacent pixels formed by the nozzle 30 that caused the discharge abnormality.

[0091] On the other hand, in the second printing operation, even within the same printhead 13, four adjacent pixels along the first direction D1 are formed using nozzles at slightly separate positions. That is, the four adjacent pixels are formed using different nozzles 30. Therefore, even if an ejection anomaly occurs in one of the nozzles 30, it is possible to prevent positional shifts from concentrating on the four adjacent pixels.

[0092] However, in the second printing operation, as described above, the area near both ends of image region Ry1 along the first direction D1 is printed to overlap with the area near both ends of image region Ry2. In this case, adjacent pixels are formed by nozzles at least fourteen nozzle pitches apart, and pixel position shifts may occur due to the difference between the feed rate of the recording medium B and the nozzle pitch of printheads 13A and 13B. Specifically, a position shift of approximately 1.1 μm may occur, which is approximately (difference in nozzle pitch between printheads 13A and 13B) × (14 + 1 / 4) × 4 ÷ 2.

[0093] [Separate use of the first and second printing actions]

[0094] As explained above, the first printing action and the second printing action each have inherent advantages, and it is desirable to use them separately as appropriate for the purpose. Although the user of the image forming apparatus 1 may preset which of the first and second printing actions to perform, the control unit 20 may also automatically set which to perform based on the environment in which the image forming apparatus 1 is located, as described below. The difference between the first and second printing actions is the feed rate of the recording medium B; in other words, the control unit 20 can appropriately change the feed rate of the recording medium B during the printing action according to various conditions as described below.

[0095] For example, if no nozzle 30 of printheads 13A and 13B produces discharge bending, a high-quality image can be formed overall by employing the first printing action (setting the feed rate to a distance between one pixel). If any nozzle of printheads 13A and 13B produces discharge bending, by employing the second printing action (setting the feed rate to the distance between n nozzles + a distance between one pixel), although a slight pixel position shift may occur in the area where image regions Ry1 and Ry2 overlap, the concentration of shifts caused by the discharge bending of a specific nozzle can be prevented in other areas. Therefore, a relatively high-quality image can be formed as a whole.

[0096] Other examples of using the first printing action and the second printing action separately include the following: There are cases where the ejection angle of the nozzle 30 varies depending on the print head 13. Figure 10A This diagram shows the ink ejected from each nozzle 30 of the printhead 13 being ejected in an inward and narrowing manner. Figure 10B This diagram illustrates how ink ejected from each nozzle 30 of the printhead 13 is ejected in an outward expanding manner. Figure 10A as well as Figure 10B In the image, the dashed line indicates the direction of the ejected ink.

[0097] like Figure 10A , Figure 10B As shown, when the ink ejected from the nozzle 30 is angled as a whole as the printhead 13, the landing position of the ink deviates from the target position depending on the distance between the nozzle 30 and the recording medium B. The greater the distance between the nozzle 30's outlet and the recording medium B, the greater this deviation.

[0098] Therefore, the control unit 20 performs a first printing operation when the angle of ink ejected from the nozzle 30, as a whole, is larger than a predetermined angle, or when the distance between the recording medium B and the outlet of the nozzle 30 is larger than a predetermined distance. This is because in the first printing operation, within the image area formed by the same print head 13, the same nozzle 30 forms adjacent pixels, so even if the ejection angle of the ink from the nozzle 30 is skewed, its impact is smaller compared to the second printing operation.

[0099] Furthermore, as another example of using the first printing action and the second printing action separately, there are the following examples. In the image forming apparatus 1 that uses heating of the printhead 13, the temperatures of the multiple printheads 13 are each different. As a result, when a temperature difference is generated among the multiple printheads 13, the distance between the nozzles 30 widens due to thermal expansion, thereby resulting in different character widths in each printhead 13.

[0100] In such cases, the first printing action is preferred. This is because in the first printing action, within the image area formed by the same printhead 13, the same nozzles 30 form adjacent pixels, so the difference in the print width of each printhead 13 has a smaller impact on the formed image compared to the second printing action.

[0101] Therefore, the control unit 20 can, for example, obtain information related to the temperature of each printhead 13 by a temperature sensor provided for each printhead 13, and force the first printing action when the temperature difference between the printheads 13 is above a specified temperature.

[0102] [Third printing action]

[0103] The following is a variation of the first printing action, which is described as the third printing action. Figure 11 This diagram illustrates the third printing action of the image forming apparatus 1. Figure 11 The diagram shows an enlarged view of the pixel columns formed by the first to third nozzles 30 of the printhead 13A in the first to eighth passes.

[0104] The third printing action is the same as the first printing action in forming four adjacent pixel columns through the same nozzle 30 in the first to fourth passes, but it differs from the first printing action in that it does not form all the pixels contained in the pixel column in each pass.

[0105] In the third printing operation, not all pixels in a pixel column are formed in the first to fourth passes, but the remaining pixels in each pixel column are formed in the fifth to eighth passes. The feed amount of the recording medium B up to the fourth pass is the same as in the first printing operation, equivalent to a distance of one pixel. From the fourth to the fifth pass, the control unit 20 returns the recording medium B to the same position as the pixel column formed by a certain nozzle 30 in the first pass. That is, the control unit 20 performs an operation to return the recording medium B to a distance of three pixels. The feed amount of the recording medium B in the fifth to eighth passes is the same as the feed amount up to the fourth pass, equivalent to a distance of one pixel.

[0106] Through this action, in the third printing action, the same pixel column is formed twice by the same nozzle 30. Therefore, even if the printed characters in printheads 13A and 13B have different widths, the impact can be minimized, and by forming the same pixel column at once, the occurrence of stripes between adjacent pixel columns can be reduced.

[0107] Industrial availability

[0108] According to this disclosure, an image forming apparatus capable of forming high-quality images can be provided.

[0109] Explanation of reference numerals in the attached drawings: 1…image forming apparatus, 11…transport stage, 12…carriage, 13, 13A, 13B…print head, 20…control unit, 30…nozzle, 31…nozzle array, 32…head chip module.

Claims

1. An image forming apparatus, wherein, Possessing: a plurality of print heads having nozzle rows composed of a plurality of nozzles, an image being formed on a recording medium by discharging ink droplets from the nozzle rows; and a control section performing control to execute a plurality of passes of printing, in which the image is formed by relatively moving the print heads and the recording medium along a second direction orthogonal to a first direction in which the plurality of nozzles are arranged a plurality of times, the control section performing control to execute the plurality of passes of printing using a single ink so that, in at least a portion of the image, pixels between one nozzle pitch of the print heads are formed by nozzle rows possessed by a single print head, the control section selecting either a first printing operation in which pixel columns adjacent to each other along the first direction are formed by the ink droplets discharged from the same nozzle, a second printing operation in which the pixel columns adjacent to each other along the first direction are formed by the ink droplets discharged from different nozzles in the nozzle rows possessed by a single print head, or a third printing operation in which one pixel column is formed in a plurality of passes in the first printing operation, to execute the plurality of passes of printing.

2. The image forming apparatus according to claim 1, wherein the control section repeatedly performs a first operation in which the print heads are relatively moved along the second direction while discharging ink from any one of the nozzles of the print heads, a second operation in which the recording medium is relatively moved along the first direction with respect to the print heads, and a third operation in which, after printing in at least a portion of the image ends, the recording medium is relatively moved along the first direction with respect to the print heads based on a distance between nozzle ends of the plurality of print heads from each other, in the control, the amount of movement in the second operation is changed based on which of the first printing operation and the second printing operation is used.

3. The image forming apparatus according to claim 2, wherein in the second operation, the control section relatively moves the recording medium with respect to the print heads by an amount of movement of one nozzle pitch of the print heads or less.

4. The image forming apparatus according to claim 2, wherein in the second operation, the control section relatively moves the recording medium with respect to the print heads by an amount of movement of one nozzle pitch of the print heads or more in the first direction.

5. The image forming apparatus according to claim 2, wherein the control section executes the plurality of passes of printing using the first printing operation when a temperature difference between the plurality of print heads is a prescribed temperature or more.

6. The image forming apparatus according to claim 2, wherein the control section executes the plurality of passes of printing using the first printing operation when a distance between a discharge port of the nozzle and the recording medium is greater than a prescribed distance.

7. An image forming method which is an image forming method of performing multi-pass printing in which an image is formed by relatively moving a plurality of print heads having nozzle rows composed of a plurality of nozzles and a recording medium along a second direction orthogonal to a first direction in which the plurality of nozzles are arranged a plurality of times, wherein in the image forming method, the multiple passes of printing is performed using a single ink so that adjacent pixels constituting the image are formed by drops ejected from a single nozzle row of the print head, the multiple passes of printing is performed using a single ink so that adjacent pixels constituting the image are formed by drops ejected from a single nozzle row of the print head, 8. The image forming method according to claim 7, wherein in the execution of the multiple passes of printing, a first operation in which the print head is relatively moved in the second direction while ink is being ejected from any one of the nozzle rows of the print head, a second operation in which the recording medium is relatively moved in the first direction with respect to the print head, and a third operation in which, after printing in at least a part of the region within the image is completed, the recording medium is relatively moved in the first direction with respect to the print head based on the distance between the nozzle ends of the plurality of print heads from each other are repeatedly performed, the amount of movement in the second operation is changed based on which one of the first printing operation and the second printing operation is used.

9. The image forming method according to claim 8, wherein in the second operation, the recording medium is relatively moved with respect to the print head by an amount of movement of one nozzle pitch or less of the print head.

10. The image forming method according to claim 8, wherein in the second operation, the recording medium is relatively moved with respect to the print head by an amount of movement of one nozzle pitch or more of the print head in the first direction.

11. The image forming method according to claim 8, wherein in the execution of the multiple passes of printing, the multiple passes of printing is performed using the first printing operation in a case where a temperature difference between the plurality of print heads is a prescribed temperature or more.

12. The image forming method according to claim 8, wherein in the execution of the multiple passes of printing, the multiple passes of printing is performed using the first printing operation in a case where a distance between the nozzle discharge ports and the recording medium is larger than a prescribed distance.

Images