Printing method and printing system

Abstract

The present invention provides a means for suppressing image quality degradation caused by a non-zero overlap between two pixels formed by two droplets ejected from the end nozzles of two adjacent head units. [Solution] Duplication processing is performed so that the leftmost nozzle 42L of head 11B and the rightmost nozzle 42R of head 11A form the same pixel.

Description

Technical Field

[0001] The present invention relates to a printing method and a printing system.

Background Art

[0002] A certain known printing apparatus includes an inkjet head having a plurality of head units and a transport mechanism that transports a recording medium in a transport direction. The plurality of head units are arranged in a staggered pattern. Specifically, the plurality of head units form two rows of head unit rows arranged in the transport direction, and each head unit row extends along a longitudinal direction orthogonal to the transport direction. In two adjacent head units in the longitudinal direction, the end nozzle A of the used nozzles of one head unit and the end nozzle B of the used nozzles of the other head unit are adjacent in the longitudinal direction. Droplets are ejected from the end nozzle A and the end nozzle B, respectively, to form two adjacent dots. In the above-described known printing apparatus, it is assumed that the overlap amount between the dot formed by the droplet ejected from the end nozzle A and the dot formed by the droplet ejected from the end nozzle B is zero. And in the above-described known printing apparatus, the droplets ejected from the end nozzle A and the droplets ejected from the end nozzle B are ejected based on pixel data corresponding to different pixels.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-mentioned known printing apparatus, if the overlap between dots formed by droplets ejected from end nozzle A and dots formed by droplets ejected from end nozzle B is not actually zero, the quality of the printed image deteriorates. Furthermore, according to the inventors' knowledge, it is extremely difficult to adjust the position of the head unit so that the overlap between dots formed by droplets ejected from end nozzle A and dots formed by droplets ejected from end nozzle B is completely zero. In particular, in recent years, the demand for high-speed printing has increased, and the number of head units included in a single inkjet head tends to increase. Therefore, it is becoming increasingly difficult to adjust the position of all head units so that the overlap between dots formed by droplets ejected from end nozzle A and dots formed by droplets ejected from end nozzle B is completely zero.

[0005] The object of the present invention is to provide a means for suppressing the degradation of image quality caused by the overlap amount of two pixels formed by two droplets ejected from the end nozzles of two adjacent head units when printing using a printing apparatus, even when the overlap amount of two pixels is not zero. [Means for solving the problem]

[0006] According to an aspect of the present invention, a printing method using a printing apparatus, The aforementioned printing apparatus, A first head bar having a first head and a second head arranged apart from each other in a first direction, A transport mechanism configured to transport a recording medium from upstream to downstream along the first direction, The first head is located upstream of the second head in the first direction. The first head and the second head each have a nozzle region in which a plurality of nozzles are arranged at a pitch P along a second direction perpendicular to the first direction, and one end of the nozzle region of the first head in the second direction and the other end of the nozzle region of the second head in the second direction overlap in the second direction. The plurality of nozzles used by the first head include a first nozzle located at one end in the second direction and a plurality of first nozzles excluding the first nozzle. The plurality of nozzles used by the second head include a second nozzle located at the other end in the second direction and a plurality of second nozzles excluding the second nozzle. The overlap amount X between the first pixel formed by the droplet discharged from the first nozzle and the second pixel formed by the droplet discharged from the second nozzle is greater than 0 pixels and less than 1 pixel. The aforementioned printing method is Printing is performed by repeatedly transporting the recording medium along the first direction and ejecting droplets from the nozzles used by the first head and the nozzles used by the second head based on the pixel data, A printing method is provided, which includes making the pixel data for forming the first pixel and the pixel data for forming the second pixel the same. [Effects of the Invention]

[0007] In the above configuration, the overlap amount X between the first pixel formed by droplets ejected from the first nozzle and the second pixel formed by droplets ejected from the second nozzle is greater than 0 pixels and less than 1 pixel. This means that the first pixel and the second pixel overlap each other. Furthermore, in the above configuration, by making the pixel data for the first nozzle to form the first pixel and the pixel data for the second nozzle to form the second pixel the same, the first nozzle and the second nozzle cooperate to form one pixel. As a result, compared to the case where the pixel data for the first nozzle to form the first pixel and the pixel data for the second nozzle to form the second pixel are different, and the first and second nozzles form two pixels that are adjacent and overlap each other, the resulting image is less likely to be compressed horizontally, and the degradation of image quality is suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic plan view of the printing apparatus 1. [Figure 2] Figure 2 is a schematic diagram showing the general structure of the printing apparatus 1. [Figure 3] Figure 3 is a schematic diagram illustrating the arrangement of the heads 11 included in the head group 20. [Figure 4] Figure 4 is a schematic diagram illustrating the interior of the flow channel unit 40. [Figure 5] Figure 5 is a schematic diagram illustrating the state in which head 11A and head 11B are ideally aligned. [Figure 6] Figure 6 is a schematic diagram illustrating the state in which head 11A and head 11B are aligned so that the right end of the nozzle area of ​​head 11A and the left end of the nozzle area of ​​head 11B overlap each other in the left-right direction. [Figure 7] Figure 7 is a schematic diagram illustrating the duplication process of this embodiment. [Figure 8]FIG. 8 is a diagram schematically showing how the formed image changes when the overlap of the printing areas of two adjacent heads 11 is 0 px, 0.1 px, and 0.9 px, respectively. [Figure 9] FIG. 9 is a schematic explanatory diagram for explaining the case where 100% amounts of ink are ejected from the right end nozzle 42R and the left end nozzle 42L, respectively, when the overlap of the printing areas is 0.5 px. [Figure 10] FIG. 10 is a schematic explanatory diagram for explaining the case where 75% amounts of ink are ejected from the right end nozzle 42R and the left end nozzle 42L, respectively, when the overlap of the printing areas is 0.5 px. [Figure 11] FIG. 11 is a printing sequence diagram. [Figure 12] FIG. 12 is an explanatory diagram for explaining adjustment using base color matching. [Figure 13] FIG. 13 is an explanatory diagram for explaining adjustment using the maximum-minimum algorithm.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the printing apparatus 1 according to an embodiment of the present invention will be described based on the drawings. In FIG. 1, the conveyance direction of the recording medium 4 corresponds to the front-rear direction of the printing apparatus 1. Also, the width direction of the recording medium 4 corresponds to the left-right direction of the printing apparatus 1. Further, the direction orthogonal to the front-rear direction and the left-right direction, that is, the direction perpendicular to the paper surface in FIG. 1 corresponds to the up-down direction of the printing apparatus 1. The left-right direction is an example of the second direction of the present invention, and the front-rear direction and the conveyance direction are examples of the first direction of the present invention.

[0010] As shown in FIGS. 1 and 2, the printing apparatus 1 includes a platen 3 housed in a housing 2, four head bars 10, two conveyance rollers 5A and 5B, an arch frame 6, a controller 7, four ink reservoirs 8, and the like. In FIGS. 1 and 2, only one of the four ink reservoirs 8 is shown for simplifying the drawing.

[0011] As shown in FIGS. 1 and 2, the recording medium 4 passes over the upper surface of the platen 3. Three head bars 10 are positioned above the platen 3 so as to face the platen 3. Ink is supplied to each head bar 10 from an ink reservoir 8. The structure of the head bar 10 will be described later. Four head bars 10 are fixed to the arch frame 6 in a state of being arranged along the front-rear direction (the conveyance direction of the recording medium 4). As shown in FIG. 2, the arch frame 6 has an arch shape, and the four head bars 10 are inclined with respect to the horizontal plane at different angles.

[0012] As shown in FIGS. 1 and 2, two conveyance rollers 5A and 5B are respectively positioned behind and in front of the platen 3. The two conveyance rollers 5A and 5B are driven by a motor (not shown). As shown in FIG. 2, the recording medium 4 is sent out from a supply roll 4A wound in a roll shape and is wound around a take-up roll 4B. For example, the recording medium 4 is roll paper. Rotating shafts 4C and 4D that rotate by motors (not shown) are respectively fixed to the supply roll 4A and the take-up roll 4B. These two rotating shafts 4C and 4D and the two conveyance rollers 5A and 5B cooperate so that the recording medium 4 is sent out from the supply roll 4A, conveyed downstream (forward) in the conveyance direction so as to pass over the platen 3, and wound around the take-up roll 4B. The two rotating shafts 4C and 4D and the two conveyance rollers 5A and 5B are an example of the conveyance mechanism of the present invention.

[0013] ​As shown in Figure 3, each head bar 10 is equipped with a head group 20 having multiple heads 11 (for example, 12 heads 11). Note that in Figure 1, the number of heads 11 is reduced for the sake of simplicity in the drawing. As shown in Figure 3, the multiple heads 11 form two head rows arranged in the front-to-back direction. Each head row contains six heads 11 arranged in the left-to-right direction. The front-to-back positions of the six heads 11 arranged in the left-to-right direction in one head row are the same. However, in the following explanation, "the same position" does not mean that the positions are exactly the same, but rather that the positions are the same within the range of manufacturing and mounting tolerances. Note that the left-to-right positions of each head 11 included in the two head rows are offset from each other. In other words, the 12 heads 11 of the head group 20 are arranged in a staggered pattern.

[0014] The lower surface of each head 11 is a nozzle surface 41b (see Figure 4) on which multiple nozzles 42 are formed. In the following description, the area of ​​the nozzle surface 41b on which the nozzles 42 are formed will be called the nozzle area. Not all nozzles 42 of the head 11 are used for printing; the nozzles of the head 11 that are used for printing and from which ink is ejected will be called the used nozzles. In this embodiment, as shown in Figure 3, the head 11 has two rows of nozzles, but this is merely an example, and the head 11 may have more than two rows of nozzles. Also, in Figure 3, the number of nozzles 42 in each nozzle row is reduced for the sake of simplicity in the drawing, but the number of nozzles 42 in each nozzle row can be any number. For example, each nozzle row may have 1000 or more nozzles 42. An internal flow path is formed inside the head 11, and the shape of the internal flow path will be described later.

[0015] As described above, the 12 heads 11 of each head bar 10 (head group 20) form two head rows, and each head 11 has two rows of nozzles. The 12 heads 11 of the rearmost (most upstream in the transport direction) head bar 10 are supplied with yellow ink from one of the four ink reservoirs 8. The 12 heads 11 of the second rearmost (second upstream in the transport direction) head bar 10 are supplied with magenta ink from one of the four ink reservoirs 8. The 12 heads 11 of the third rearmost (third upstream in the transport direction) head bar 10 are each supplied with cyan ink from one of the four ink reservoirs 8. The 12 heads 11 of the fourth rearmost (fourth upstream in the transport direction) head bar 10 are each supplied with black ink from one of the four ink reservoirs 8. In this embodiment, light-colored to dark-colored inks are ejected sequentially from upstream to downstream in the transport direction from four head bars 10 arranged in the transport direction. Although the printing apparatus 1 has four head bars 10, it may also have one more head bar 10. Furthermore, white ink may be ejected from the single head bar 10. The white ink, yellow ink, magenta ink, cyan ink, and black ink are, for example, all UV-curable inks.

[0016] Next, referring to Figures 3 and 4, the flow path unit 40 and actuator unit 50 that constitute each head 11 will be described. Note that the structure of the flow path unit 40 and actuator unit 50 is common to all 12 heads 11, so the flow path unit 40 and actuator unit 50 in one head 11 will be described.

[0017] As shown in Figure 4, the flow path unit 40 is formed by a plurality of metal plates and a nozzle plate 41 stacked in the vertical direction. Ink flow paths, including individual flow paths 12 containing pressure chambers 12a, a supply manifold 13a, and a return manifold 13b, are formed on the plurality of metal plates by etching. The nozzle plate 41 is formed from a polymer synthetic resin material such as polyimide and is bonded to the lower surface of the stacked metal plates with an adhesive. The lower surface of the nozzle plate 41 is the nozzle surface 41b described above. The nozzle plate 41 may also be formed from a metal material such as stainless steel.

[0018] As shown in Figure 4, the flow path unit 40 contains individual flow paths 12 that communicate with each nozzle 42, and a supply manifold 13a and a return manifold 13b that communicate with the individual flow paths 12. Although not shown in the figure, the supply manifold 13a and the return manifold 13b extend in the left-right direction (perpendicular to the plane of the paper in Figure 4). The supply manifold 13a is connected to a tank 400 located outside the head 11 via an ink supply port (not shown) formed in the flow path unit 40. The return manifold 13b is connected to a tank 400 (see Figure 2) located outside the head 11 via an ink discharge port (not shown) formed in the flow path unit 40. This creates an ink circulation path where ink that has left the tank 400 returns to the tank 400 through the supply manifold 13a, individual flow paths 12, and return manifold 13b.

[0019] Although not shown in the diagram, as described above, the multiple nozzles 42 are positioned to form two rows of nozzles extending in the left-right direction. In the flow path unit 40, the multiple individual flow paths 12, each corresponding to a nozzle 42, are positioned to form two rows of individual flow paths extending in the left-right direction. The flow path unit 40 also has 12 supply manifolds 13a and 12 return manifolds 13b, and each supply manifold 13a and each return manifold 13b communicates with the multiple individual flow paths 12 that constitute the two rows of individual flow paths. As a result, multiple ink flow paths are formed inside the flow path unit 40, running from the supply manifold 13a through the pressure chambers 12a of the multiple individual flow paths 12 to the nozzles 42 and the return manifolds 13b. The number of supply manifolds 13a and return manifolds 13b formed in the flow path unit 40 is adjusted to match the number of nozzles 42. Furthermore, the number of individual flow paths 12 communicating with each supply manifold 13a and each return manifold 13b is also adjusted to match the number of nozzles 42.

[0020] As shown in Figure 4, a pressure chamber 12a is formed in each individual flow path 12, and an actuator unit 50 is located above the pressure chamber 12a. The actuator unit 50 includes a diaphragm 51 located on the upper surface of the flow path unit 40 so as to cover all the pressure chambers 12a, a plurality of piezoelectric elements 52 located on the upper surface of the diaphragm 51, facing the pressure chambers 12a, and a plurality of individual electrodes 53 located on the upper surfaces of the plurality of piezoelectric elements 52. As will be described later, the diaphragm 51 functions as a common electrode. The diaphragm 51 as a common electrode, the individual electrodes 53, and the piezoelectric elements 52 form a single drive element 55. In other words, the actuator unit 50 includes a plurality of drive elements 55 corresponding to a plurality of nozzles 42.

[0021] The diaphragm 51 is a metal plate that is roughly rectangular in plan view, and is made of, for example, an iron-based alloy such as stainless steel, a copper-based alloy, a nickel-based alloy, or a titanium-based alloy. The upper surface of the conductive diaphragm 51 is located below the piezoelectric element 52. Therefore, the upper surface of the diaphragm 51 can also serve as a common electrode. The diaphragm 51, as a common electrode, is connected to the ground wiring of a driver IC (not shown) that drives the actuator unit 50 and is always maintained at ground potential. Note that the diaphragm 51 does not necessarily have to be a metal plate; for example, it may be formed from the same piezoelectric material as the piezoelectric element 52, and a metal film may be formed on its upper surface to serve as a common electrode.

[0022] The piezoelectric element 52 is formed from a piezoelectric material whose main component is lead zirconate titanate (PZT), a ferroelectric solid solution of lead titanate and lead zirconate. The piezoelectric element 52 is polarized in the thickness direction (vertical direction) at least in the region facing the pressure chamber 12a (the portion sandwiched between the individual electrodes 53 and the diaphragm 51). In this embodiment, there are multiple piezoelectric elements 52 corresponding to multiple pressure chambers 12a, but the piezoelectric element 52 may also be a layer of piezoelectric material (piezoelectric layer) continuously formed on the upper surface of the diaphragm 51, spanning multiple pressure chambers 12a. In this case, the diaphragm 51 as a common electrode, the individual electrodes 53, and the portion of the piezoelectric element 52 sandwiched between the individual electrodes 53 and the diaphragm 51 form a single driving element 55.

[0023] Next, the operation of the drive element 55 of the actuator unit 50 during ink ejection will be explained. When a predetermined drive potential is applied to a certain individual electrode 53 from a driver IC (not shown), a potential difference is created between the individual electrode 53 to which this drive potential is applied and the diaphragm 51, which is a common electrode held at ground potential. As a result, an electric field in the thickness direction acts on the piezoelectric element 52 sandwiched between the individual electrode 53 and the diaphragm 51. The direction of this electric field is parallel to the polarization direction of the piezoelectric element 52. Therefore, the piezoelectric element 52 in the region facing the individual electrode 53 (active region) contracts in a planar direction perpendicular to the thickness direction. Here, the diaphragm 51 below the piezoelectric element 52 is fixed to the flow channel unit 40. Therefore, as the piezoelectric element 52 located on the upper surface of this diaphragm 51 contracts in the planar direction, the portion of the diaphragm 51 that covers the pressure chamber 12a deforms so that it becomes convex toward the pressure chamber 12a (unimorph deformation, see Figure 4). At this time, the volume inside the pressure chamber 12a decreases, causing the ink pressure inside the pressure chamber 12a to increase, and ink is ejected from the nozzle 42 which is in communication with the pressure chamber 12a.

[0024] The controller 7 comprises a main controller 7A that controls all parts of the printing device 1 except for the head bar 10, and a plurality of head controllers 7B that control the head bar 10 (see Figure 2). The main controller 7A is connected to an external device 9 such as a PC (see Figure 1) for data communication and controls all parts of the printing device 1 based on the print data sent from the external device 9. The head controllers 7B are provided corresponding to each head bar 10. The controller 7 (main controller 7A and head controllers 7B) includes an FPGA (Field Programmable Gate Array), EEPROM (Electrically Erasable Programmable Read-Only Memory), RAM (Random Access Memory), etc. The controller 7 may also include a CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), etc.

[0025] The main controller 7A controls the motors that drive the rotating shafts 4C and 4D, and the motors that drive the transport rollers 5A and 5B, causing the two transport rollers 5A and 5B to transport the recording medium 4 in the transport direction. The head controller 7B controls the three head bars 10, causing ink to be ejected from the nozzles 42 toward the recording medium 4. As a result, an image is printed on the recording medium 4.

[0026] <Structure of Headbar 10> As shown in Figure 3, the head bar 10 has multiple heads 11 arranged in a staggered pattern. Hereafter, we will focus on two heads 11 that are adjacent to each other in the left-right direction and offset in the front-back direction, referring to the head 11 on the left as head 11A and the head 11 on the right as head 11B. As shown in Figure 6, the right region located at the right end of the nozzle area of ​​the nozzle surface 41b of head 11A and the left region located at the left end of the nozzle area of ​​the nozzle surface 41b of head 11B overlap each other in the left-right direction. Note that when the resolution of heads 11A and 11B is 1200 dpi, the width of one pixel (1px) is 21.16 μm, and the pitch P of the nozzle 42 is also 21.16 μm.

[0027] As shown in Figure 5, ideally, heads 11A and 11B should be aligned so that the leftmost nozzle 42 of head 11A (indicated by a black circle in Figure 5) and the leftmost nozzle 42 of head 11B (indicated by a white circle in Figure 5) are exactly the same in the left-right direction. If such alignment is achieved, the nozzles used by heads 11A and 11B are determined as follows. Assume that there is no other head 11 to the left of head 11A. In this case, the nozzles used by head 11A are all the nozzles 42 of head 11A. In Figure 5, the nozzles used are the nozzles 42 indicated by the gray circles and the nozzles 42 indicated by the black circles. For head 11B, all nozzles 42 except for the leftmost nozzle 42 are used. In Figure 5, the nozzles used are the nozzles 42 indicated by the gray circles and the nozzles 42 indicated by the black circles. In other words, in the example in Figure 5, the nozzle 42 located at the leftmost end of head 11B (the nozzle indicated by the white circle in Figure 5) is not used, and the other nozzles 42 are used. Thus, the nozzles used by heads 11A and 11B are determined such that the nozzle 42 at the rightmost end of head 11A becomes the rightmost nozzle among the nozzles used by head 11A, and the second nozzle 42 from the left end of head 11B becomes the leftmost nozzle among the nozzles used by head 11B. In this case, the lateral distance between the rightmost nozzle 42 among the nozzles used by head 11A and the leftmost nozzle 42 among the nozzles used by head 11B (the second nozzle 42 from the left end of head 11B) is exactly equal to the pitch P. Therefore, it becomes possible to treat heads 11A and 11B as one long head. However, due to manufacturing tolerances of heads 11A and 11B, as well as mounting tolerances to the head bar 10, it is extremely difficult to perfectly match the left-right position of the nozzle 42 at the right end of head 11A and the nozzle 42 at the left end of head 11B.Even when attempting to perfectly align the rightmost nozzle 42 of head 11A and the leftmost nozzle 42 of head 11B in the left direction, manufacturing tolerances of heads 11A and 11B, as well as mounting tolerances to the head bar 10, can cause the rightmost nozzle 42 of head 11A and the leftmost nozzle 42 of head 11B to be misaligned in the left direction. For example, the left-right distance between the rightmost nozzle 42 of the nozzles used by head 11A and the leftmost nozzle 42 of the nozzles used by head 11B (the second nozzle 42 from the left of head 11B) may be greater than the pitch P. In such cases, the landing positions of ink droplets ejected from the rightmost nozzle 42 of head 11A and the leftmost nozzle 42 of head 11B will be further apart in the left direction compared to when the left-right positions of the rightmost nozzle 42 of head 11A and the leftmost nozzle 42 of head 11B are perfectly aligned. When ink droplets land far apart horizontally, so-called white streaks occur. Users viewing printed materials can easily spot even slight white streaks, so it is essential to completely eliminate their occurrence.

[0028] Therefore, in this embodiment, in order to reliably suppress the occurrence of white streaks, the positions of head 11A and head 11B are adjusted as follows. Note that the following head position adjustment is performed by the manufacturer or user of the printing device 1, for example, after the printing device 1 has been delivered and installed.

[0029] First, as shown in Figure 6, heads 11A and 11B are aligned so that the right end of the nozzle area of ​​the nozzle surface 41b of head 11A and the left end of the nozzle area of ​​the nozzle surface 41b of head 11B overlap each other in the left-right direction. Then, for head 11A, the nozzle to be used is determined so that the rightmost nozzle 42 of head 11A becomes the rightmost nozzle of the nozzles to be used (hereinafter referred to as the rightmost nozzle 42R). In Figure 6, nozzles that are not used are shown as white circles, the rightmost nozzle 42R and the leftmost nozzle 42L among the used nozzles are shown as black circles, and the other used nozzles are shown as gray circles.

[0030] Furthermore, the leftmost nozzle 42L of head 11B is determined such that the overlap amount X1 between the first pixel G1 formed by the ink ejected from the rightmost nozzle 42R of head 11A and the second pixel G2 formed by the ink ejected from the leftmost nozzle of head 11B (hereinafter referred to as the leftmost nozzle 42L) is greater than 0 and less than the width of one pixel (1px) (see Figure 7). In other words, the leftmost nozzle 42L of head 11B is determined such that the lateral distance between the landing position of the ink ejected from the rightmost nozzle 42R of head 11A and the landing position of the ink ejected from the leftmost nozzle 42L of head 11B is less than the width of one pixel (1px). Note that, as shown in Figure 6, the leftmost nozzle 42L of head 11B is not the leftmost nozzle of head 11B, but a nozzle located to the right of the leftmost nozzle. In the following description, the combination of the rightmost nozzle 42R of head 11A and the leftmost nozzle 42L of head 11B is referred to as the nozzle constituting the stitch. The rightmost nozzle 42R is an example of the first nozzle of the present invention, and the leftmost nozzle 42L is an example of the second nozzle of the present invention. In this embodiment, not all nozzles 42 of head 11B that overlap with the nozzle area of ​​head 11A are used for printing; nozzles located to the left of the leftmost nozzle 42L are not used for printing, i.e., they are not used nozzles. If a nozzle 42 that is not used, i.e., a nozzle 42 located to the left of the leftmost nozzle 42L of head 11B, is to be used for printing, then the nozzle 42 of head 11A and the nozzle 42 of head 11B will cooperate to form a single dot (pixel) using a technique called single-ringing. In order to perform such control, the head controller 7B needs to create single-ringing print data for each nozzle 42 located to the left of the leftmost nozzle 42L of head 11B, which complicates the control. In the heads 11A and 11B of this embodiment, the nozzles 42 located to the left of the leftmost nozzle 42L of head 11B are not used for printing, so the head controller 7B does not need to create singling print data for these nozzles.

[0031] As shown in Figure 7, consider the three heads 11A, 11B, and 11C included in the head bar 10. Head 11C is located to the right of head 11B, and is offset from head 11B in the front-to-back direction. Note that heads 11A and 11C are in the same front-to-back position. Also, the right region located at the right end of the nozzle area of ​​the nozzle surface 41b of head 11B and the left region located at the left end of the nozzle area of ​​the nozzle surface 41b of head 11C overlap each other in the left-to-right direction. Note that in Figure 7, the shapes of heads 11A, 11B, and 11C are not directly shown, but the positional relationship of the corresponding heads 11 and nozzles 42 is shown by the positional relationship of the pixels formed by the ink droplets ejected from the nozzles 42. In addition, to simplify the drawing, the number of pixels formed by the ink droplets ejected from the nozzles 42 of heads 11A to 11C has been greatly reduced in the illustration. Assume that the positional relationship of these three heads 11A to 11C is as follows. The overlap amount X1 between the first pixel G1 formed by the rightmost nozzle 42R of head 11A and the second pixel G2 formed by the leftmost nozzle 42L of head 11B is 0.1px. In other words, the difference in the landing positions of ink droplets ejected from the two nozzles constituting the stitch in head 11A and head 11B is 0.9px. In contrast, the overlap amount X2 between the third pixel G3 formed by the rightmost nozzle 42R of head 11B and the fourth pixel G4 formed by the leftmost nozzle 42L of head 11C is 0.9px. In other words, the difference in the landing positions of ink droplets ejected from the two nozzles constituting the stitch (rightmost nozzle 42R and leftmost nozzle 42L) in head 11B and head 11C is 0.1px.

[0032] Figure 8 schematically shows examples of images formed when the overlap of two pixels formed by the two nozzles (right-end nozzle 42R and left-end nozzle 42L) constituting the stitch in two adjacent heads 11 is 0px, 0.1px, and 0.9px, respectively. As shown in Figure 8, as the overlap of the two pixels formed by the two nozzles constituting the stitch increases, the formed image shrinks in the left-right direction, which degrades the image quality. Therefore, in this embodiment, the following adjustments are made to suppress the degradation of image quality as the overlap of the two pixels formed by the two nozzles (right-end nozzle 42R and left-end nozzle 42L) constituting the stitch in the two heads 11 increases.

[0033] The manufacturer or user of the printing device 1 prints a test pattern using the printing device 1 and reads the test pattern with a scanner connected to the printing device 1. Based on the scan results, the main controller 7A measures the landing position of the ink ejected from the rightmost nozzle 42R of the nozzle used by head 11A and the landing position of the ink ejected from the leftmost nozzle 42L of the nozzle used by head 11B. The main controller 7A then detects the overlap amount X1 between the first pixel G1 formed by the rightmost nozzle 42R of head 11A and the second pixel G2 formed by the leftmost nozzle 42L of head 11B, based on the measured landing positions. Similarly, based on the above scan results, the main controller 7A measures the landing position of the ink ejected from the rightmost nozzle 42R of the nozzle used by head 11B and the landing position of the ink ejected from the leftmost nozzle 42L of the nozzle used by head 11C. The main controller 7A then detects the overlap amount X2 between the third pixel G3 formed by the rightmost nozzle 42R of head 11B and the fourth pixel G4 formed by the leftmost nozzle 42L of head 11C, based on the measured impact position. Although the above explanation uses three heads 11 as an example, the main controller 7A performs the same measurement for all heads 11 based on the scan results and detects the overlap amount for adjacent heads 11. Based on the detected overlap amount, the main controller 7A decides which heads 11 should undergo the duplication process described later. Furthermore, based on the detected overlap amount, the main controller 7A sets how to adjust the amount of ink ejected from the rightmost nozzle 42R and leftmost nozzle 42L that constitute the stitch for the heads 11 undergoing duplication. The main controller 7A then stores information regarding the necessity of duplication processing for each head 11, the nozzles used, and the ink amount adjustment information in the EEPROM of the main controller 7A or head controller 7B.

[0034] In the above case, the overlap amount X1 becomes 0.1px and the overlap amount X2 becomes 0.9px. When the overlap amounts X1 and X2 are 0.5px or more, the head controller 7B modifies the pixel data corresponding to the leftmost nozzle 42L and the rightmost nozzle 42R so that the leftmost nozzle 42L and the rightmost nozzle 42R that constitute the stitch work together to form the same pixel. Hereinafter, the modification of the pixel data of the two nozzles by the head controller 7B so that the two nozzles that constitute the stitch work together to form the same pixel will be referred to as duplication processing.

[0035] In the above example, the overlap amount X1 between the first pixel G1 formed by the rightmost nozzle 42R of head 11A and the second pixel G2 formed by the leftmost nozzle 42L of head 11B is 0.1px. Therefore, the head controllers 7B corresponding to heads 11A and 11B do not modify the pixel data of the rightmost nozzle 42R of head 11A and the pixel data of the leftmost nozzle 42L of head 11B. In other words, the head controllers 7B corresponding to heads 11A and 11B do not perform duplication. In contrast, the overlap amount X2 between the third pixel G3 formed by the rightmost nozzle 42R of head 11B and the fourth pixel G4 formed by the leftmost nozzle 42L of head 11C is 0.9px. In this case, the head controllers 7B corresponding to heads 11B and 11C modify the pixel data of the leftmost nozzle 42L of head 11C and the pixel data of the rightmost nozzle 42R of head 11B so that these two nozzles form the same pixels. In other words, the head controllers 7B corresponding to heads 11B and 11C perform duplication on the pixel data of the leftmost nozzle 42L of head 11C and the pixel data of the rightmost nozzle 42R of head 11B. In this case, the head controller 7B corresponding to head 11C also modifies the pixel data of the remaining nozzles used by head 11C (i.e., the nozzles used excluding the leftmost nozzle 42L). As a result, after the duplication process, the pixel data of the nozzles used by head 11C, excluding the leftmost nozzle 42L, is shifted by one pixel towards the right nozzle compared to before the duplication process.

[0036] By performing duplication processing so that the leftmost nozzle 42L of head 11C and the rightmost nozzle 42R of head 11B form the same pixel, the horizontal shrinkage of the formed image, as shown in Figure 8, is suppressed, and the degradation of image quality is suppressed.

[0037] Next, we will explain the adjustment of the ink amount that is performed simultaneously when the duplication process is carried out. First, consider the case where the overlap amount X1 between the first pixel G1 formed by the rightmost nozzle 42R of head 11A and the second pixel G2 formed by the leftmost nozzle 42L of head 11B is 0.5px. Let the amount of ink droplets ejected from the rightmost nozzle 42R when the duplication process is not performed be 100%. If 100% of the amount of ink is ejected from both the rightmost nozzle 42R and the leftmost nozzle 42L, then 200% of the amount of ink will land in an area with a width of 1.5px (see Figure 9). In this case, compared to the case where the overlap amount X1 is 0px and no duplication process is performed, and 100% of the amount of ink droplets is ejected from the rightmost nozzle 42R, the ink density (the amount of ink that lands in an area of ​​unit width) will be higher, and the possibility of color streaks will increase.

[0038] In contrast, consider the case where the overlap amount X1 is 0.5px, and 75% of the ink is ejected from the rightmost nozzle 42R and the leftmost nozzle 42L (see Figure 10). In this case, 150% of the ink will land in an area with a width of 1.5px. In this case, it is possible to achieve an ink density similar to that when the overlap amount X1 is 0px, thus suppressing the occurrence of color streaks.

[0039] Furthermore, consider the case where the overlap amount X1 is 0.85px. If 100% of the ink is ejected from the rightmost nozzle 42R and the leftmost nozzle 42L, 200% of the ink will land in an area with a width of 1.15px, and for the same reasons as above, the likelihood of color streaks occurring increases. To achieve an ink density similar to that when the overlap amount X1 is 0px, it is necessary to land 115% of the ink in an area with a width of 1.15px. Therefore, when the overlap amount X1 is 0.85px, by setting the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L to 57% of the original amount, an ink density similar to that when the overlap amount X1 is 0px can be achieved. Thus, in this embodiment, the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L that constitute the stitch is adjusted according to the overlap amount X1 in order to achieve an ink density similar to that when the overlap amount X1 is 0px.

[0040] Furthermore, for each combination of the two heads 11, the head controller 7B determines the size of the ink droplets ejected from the rightmost nozzle 42R and the leftmost nozzle 42L according to the overlap amount X1, and by ejecting ink droplets of the determined size from the rightmost nozzle 42R and the leftmost nozzle 42L, it is conceivable that the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L will be reduced. For example, as described above, if the overlap amount X1 is 0.5px, the head controller 7B will reduce the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L by approximately 25% each, so that 75% of the amount of ink droplets is ejected, by making the size of the ink droplets ejected from the rightmost nozzle 42R and the leftmost nozzle 42L approximately 25% smaller than the size of the ink droplets ejected from the other nozzles 42. Furthermore, as described above, when the overlap amount X1 is 0.85px, the head controller 7B reduces the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L by approximately 43% each, so that 53% of the amount of ink droplets is ejected. To achieve this, the size of the ink droplets ejected from the rightmost nozzle 42R and the leftmost nozzle 42L is made approximately 43% smaller than the size of the ink droplets ejected from the other nozzles 42. However, normally, the size of the ink droplets ejected from the head 11 is limited to a predetermined number of sizes. For example, the head 11 of this embodiment can eject ink droplets of three sizes: small (DS1), medium (DS2), and large (DS3). For example, for a certain ink among white, yellow, magenta, cyan, and black inks, the large ink droplet is 3.2 pl, the medium ink droplet is 2.8 pl, and the small ink droplet is 2.0 pl. In addition, it is extremely difficult to eject ink droplets of a size corresponding to the overlap amount X1 from the rightmost nozzle 42R and the leftmost nozzle 42L that constitute the stitch. This is because the three sizes of large, medium, and small ink droplets mentioned above are insufficient, and many more ink droplet size settings must be provided in order to eject multiple ink droplets of different sizes according to the overlap amount X1.

[0041] Therefore, in this embodiment, the head controller 7B adjusts the ratio of large, medium, small, and non-ejected dots when forming a dot line formed by multiple dots continuous in the transport direction, according to the overlap amount X1, so as to achieve an ink density similar to that when the overlap amount X1 is 0px. For example, the head controller 7B adjusts where large dots are ejected to eject medium or small dots, and where medium dots are ejected to eject small dots, thereby correcting the amount of ink by making the size of the ink droplets ejected from the rightmost nozzle 42R and the leftmost nozzle 42L smaller than the size of the ink droplets ejected from the other nozzles 42 used.

[0042] Alternatively, the head controller 7B can achieve an ink density equivalent to that when the overlap amount X1 is 0px by alternately spraying ink droplets from the rightmost nozzle 42R and the leftmost nozzle 42L while thinning out the ink droplets sprayed from the rightmost nozzle 42R and the leftmost nozzle 42L. When forming N consecutive pixels in the transport direction, if the number of pixels formed by the rightmost nozzle 42R is N1 (N1>0) and the number of pixels formed by the leftmost nozzle 42L is N2 (N2>0), then ink droplets are alternately sprayed from the rightmost nozzle 42R and the leftmost nozzle 42L such that N1+N2=N. The ratio of N1 to N2 is preferably 0.3≦N1 / (N1+N2)≦0.7, more preferably 0.4≦N1 / (N1+N2)≦0.6, and even more preferably N1 / (N1+N2)=0.5. By setting N1 / (N1+N2)=0.5, the concentration of ink droplets ejected from the rightmost nozzle 42R and the leftmost nozzle 42L can be made the same.

[0043] Next, the printing process will be described. As shown in Figure 11, when a print start command is input to the main controller 7A from the user of the printing device 1 (S301), the main controller 7A sends a print command to each head controller 7B (S302). Upon receiving the print command, the head controller 7B requests the main controller 7A to send the print data (S303) and receives the print data from the main controller 7A (S304). When the head controller 7B receives the print data from the main controller 7A, it corrects the print data based on the information stored in the EEPROM of the main controller 7A or the head controller 7B regarding the necessity of duplication processing for each head 11, the nozzles to be used, and the ink droplet adjustment (S305). Then, it sends the corrected print data to the head 11 (S306). The printing device 1 repeats the process from S302 to S306 until the end of printing.

[0044] <Matching base colors> In the above description, the duplication process performed to suppress the degradation of image quality was explained using the example of multiple heads 11 contained in one head bar 10. Below, as an example of a duplication process that can be suitably applied to two head bars 10 that eject inks of different colors, the inventors of this application will describe an adjustment method which they call base color matching.

[0045] As shown in Figure 12, consider the three heads 11A, 11B, and 11C contained in the head bar 10b that ejects black ink, and the three heads 11D, 11E, and 11F contained in the head bar 10c that ejects cyan ink. Heads 11D, 11E, and 11F are three heads 11 located adjacent to each other in the left-right direction and offset in the front-back direction in the head bar 10c that ejects cyan ink. Of the three heads 11, the leftmost head 11 is head 11D, the head 11 to its right is head 11E, and the head 11 further to its right is head 11F. Similar to heads 11A, 11B, and 11C, the right region located on the right end of the nozzle area of ​​the nozzle surface 41b of head 11D and the left region located on the left end of the nozzle area of ​​the nozzle surface 41b of head 11E overlap with each other in the left-right direction. Similarly, the right region located on the right end of the nozzle area of ​​the nozzle surface 41b of head 11E and the left region located on the left end of the nozzle area of ​​the nozzle surface 41b of head 11F also overlap with each other in the left-right direction. Note that, similar to Figure 7, Figure 12 does not directly show the shape of head 11, but illustrates the positional relationship of the corresponding head 11 and nozzle 42 based on the positional relationship of the pixels formed by the ink droplets ejected from the nozzle 42. Here, the nozzle used by head 11A and the nozzle used by head 11D overlap in the transport direction. Similarly, the nozzle used by head 11B and the nozzle used by head 11E overlap in the transport direction, and the nozzle used by head 11C and the nozzle used by head 11F overlap in the transport direction. Furthermore, the leftmost nozzle 42L of head 11B is determined such that the overlap amount X1 between the first pixel G1 formed by the ink ejected from the rightmost nozzle 42R of head 11A and the second pixel G2 formed by the ink ejected from the leftmost nozzle of the nozzle used by head 11B (hereinafter referred to as the leftmost nozzle 42L) is greater than 0 and less than the width of one pixel (1px) (see Figure 12). The same applies to head 11B and head 11C, head 11D and head 11E, and head 11E and head 11F.In the example shown in Figure 12, the overlap amount X1 between the first pixel G1 formed by ink ejected from the rightmost nozzle 42R of head 11A and the second pixel G2 formed by ink ejected from the leftmost nozzle 42L of head 11B is 0.1px. The overlap amount X2 between the third pixel G3 formed by ink ejected from the rightmost nozzle 42R of head 11B and the fourth pixel G4 formed by ink ejected from the leftmost nozzle 42L of head 11C is 0.1px. In contrast, the overlap amount X3 between the fifth pixel G5 formed by ink ejected from the rightmost nozzle 42R of head 11D and the sixth pixel G6 formed by ink ejected from the leftmost nozzle 42L of head 11E is 0.5px. The overlap amount X4 between the E7th pixel G7, formed by ink ejected from the rightmost nozzle 42R of the head 11E, and the 8th pixel G8, formed by ink ejected from the leftmost nozzle 42L of the head 11C, is 0.5px.

[0046] First, a test pattern is printed for the three heads 11A, 11B, and 11C contained in the head bar 10b that ejects black ink, and the test pattern is scanned. Based on the scan results, the overlap amount of the two pixels formed by the rightmost nozzle 42R and the leftmost nozzle 42L that constitute the stitch is measured, and pairs of heads 11 with an overlap amount of 0.5px or more are identified. Then, the duplication process described above is performed on the pairs of heads 11 with an overlap amount of 0.5px or more.

[0047] In the example shown in Figure 12, the overlap amount X1 between head 11A and head 11B is 0.1px, and the overlap amount X2 between head 11B and head 11C is 0.1px. Therefore, duplication processing is not performed between head 11A and head 11B, or between head 11B and head 11C. If duplication processing is performed in the head bar 10b that ejects black ink, a new test pattern is printed and scanned again.

[0048] Next, based on the scan results of the test pattern, the overlap amount between the pixels formed by the head 11 in the head bar 10b that ejects black ink and the pixels formed by the head 11 in the head bar 10c that ejects cyan ink is measured. For example, in the example shown in Figure 12, the overlap amount Y1 of the pixels formed by the ink droplets ejected from the second nozzle 42 from the left (the seventh pixel from the left in Figure 12) is measured for heads 11B and 11E, and the overlap amount Y2 of the pixels formed by the ink droplets ejected from the second nozzle 42 from the left (the twelfth pixel from the left in Figure 12) is measured for heads 11C and 11F. In the example shown in Figure 12, the overlap amount Y1 is 0.8px and the overlap amount Y2 is 0.2px.

[0049] Ideally, the Nth nozzle from the left of two overlapping heads 11 (for example, head 11A and head 11D) in the transport direction should be in exactly the same position in the left-right direction. In other words, the two pixels formed by the Nth nozzle from the left of two overlapping heads 11 in the transport direction should ideally completely overlap (the overlap amount should be 1px). However, due to mounting errors of the head bar 10, the left-right positions of the Nth nozzle from the left are often not the same, and the overlap amount is often less than 1px. In particular, the closer the overlap amount approaches 0, the further apart the Nth nozzles become. Therefore, if the Nth nozzles are far apart, for example, if the overlap amount between the Nth nozzles is less than 0.5px, duplication processing is performed.

[0050] In the example in Figure 12, when the overlap amounts Y1 and Y2 are less than 0.5px, the head controller 7B of the head bar 10c that ejects cyan ink modifies the pixel data corresponding to the leftmost nozzle 42L and the rightmost nozzle 42R so that the leftmost nozzle 42L and the rightmost nozzle 42R that constitute the stitch work together to form the same pixel. In the above example, the head controller 7B of the head bar 10c performs duplication on the pixel data corresponding to the leftmost nozzle 42L and the rightmost nozzle 42R that constitute the stitch in the pair of heads 11E and 11F. As a result, in the example in Figure 12, the overlap amount Y2 of the 12th pixel from the left was improved from 0.2px to 0.8px.

[0051] As described above, in base color matching, a misalignment is detected between the head 11 in the head bar 10 that sprays the reference base color ink (e.g., black ink) and the head 11 in the head bar 10 that sprays the ink of another color (e.g., cyan ink). If the misalignment is large (for example, if the pixel overlap is less than 0.5px), duplication processing is performed on the rightmost nozzle 42R and leftmost nozzle 42L that constitute the stitch for the head 11 in the head bar 10 that sprays the ink of the other color. This suppresses the degradation of image quality caused by the misalignment between the head 11 in the head bar 10 that sprays the base color ink and the head 11 in the head bar 10 that sprays the ink of the other color.

[0052] <Maximum / Minimum Algorithm> Next, as an example of a duplication process that can be suitably applied to three or more head bars 10 that eject inks of different colors, we will describe an adjustment method which the inventors of this application call the maximum / minimum algorithm.

[0053] As shown in Figure 13, consider the two heads 11A and 11B in the head bar 10b that ejects black ink, the two heads 11D and 11E in the head bar 10c that ejects cyan ink, and the two heads 11G and 11H in the head bar 10m that ejects magenta ink. Heads 11G and 11H are two heads 11 that are adjacent to each other in the left-right direction and offset in the front-back direction. Of the two heads 11, the head 11 located on the left is head 11G, and the head 11 located to its right is head 11H. Similar to heads 11A, 11B and 11D and 11E, the right region located at the right end of the nozzle area of ​​the nozzle surface 41b of head 11G and the left region located at the left end of the nozzle area of ​​the nozzle surface 41b of head 11H overlap each other in the left-right direction. Figure 13, like Figure 7, does not directly show the shape of the head 11, but illustrates the positional relationship between the corresponding head 11 and nozzle 42 based on the positional relationship of the pixels formed by ink droplets ejected from the nozzle 42. Here, the nozzles used by head 11A, head 11D, and head 11G overlap in the transport direction. Similarly, the nozzles used by head 11B, head 11E, and head 11H overlap in the transport direction. Furthermore, the leftmost nozzle 42L of head 11B is determined such that the overlap amount X1 between the first pixel G1 formed by ink ejected from the rightmost nozzle 42R of head 11A and the second pixel G2 formed by ink ejected from the leftmost nozzle (leftmost nozzle 42L) of head 11B is greater than 0 and less than the width of one pixel (1px) (see Figure 13). Similarly, with respect to heads 11D and 11E, the leftmost nozzle 42L of head 11E is determined such that the overlap amount X3 between the fifth pixel G5 formed by the ink ejected from the rightmost nozzle 42R of head 11D and the sixth pixel G6 formed by the ink ejected from the leftmost nozzle (leftmost nozzle 42L) of head 11E is greater than 0 and less than the width of one pixel (1px).For heads 11G and 11H, the leftmost nozzle 42L of head 11H is determined such that the overlap amount X5 between the 9th pixel G9 formed by the ink ejected from the rightmost nozzle 42R of head 11G and the 10th pixel G10 formed by the ink ejected from the leftmost nozzle (leftmost nozzle 42L) of the nozzle used in head 11H is greater than 0 and less than the width of one pixel (1px).

[0054] First, a test pattern is printed, and based on the scan results of the test pattern, the positions of pixels formed by the head 11 in the head bar 10b that ejects black ink, the positions of pixels formed by the head 11 in the head bar 10c that ejects cyan ink, and the positions of pixels formed by the head 11 in the head bar 10m that ejects magenta ink are measured. Then, the distance δ1 between the two furthest apart pixels is measured. For example, in the example shown in Figure 13, the position of the pixel formed by the ink droplet ejected from the second nozzle 42 from the left (the seventh pixel from the left in Figure 13) is measured for heads 11B, 11E, and 11H. Then, the left-right distance δ1 between the leftmost magenta ink pixel and the rightmost black ink pixel among the seventh pixels from the left in Figure 13 is measured.

[0055] Next, duplication is performed on the head bar 10 corresponding to the leftmost pixel. In the example shown in Figure 13, duplication is performed on the heads 11G and 11H included in the head bar 10m that ejects magenta ink. After that, the test pattern is printed again, and based on the scan results of the test pattern, the positions of the pixels formed by the heads 11A and 11B included in the head bar 10b that ejects black ink, the positions of the pixels formed by the heads 11D and 11E included in the head bar 10c that ejects cyan ink, and the positions of the pixels formed by the heads 11G and 11H included in the head bar 10m that ejects magenta ink are measured again. Then, the distance δ2 between the two furthest pixels among these pixels is measured. The previously measured distance δ1 and the newly measured distance δ2 are compared. If δ1 ≤ δ2, it is determined that the previously performed duplication was not effective, and the previously performed duplication is canceled, returning to the original state. If δ1 > δ2, the previously performed duplication is effective. Then, the following procedure is used to determine whether further duplication processing is necessary. First, duplication processing is performed on the head bar 10 corresponding to the leftmost pixel. In the example shown in Figure 13, duplication processing is performed on the heads 11D and 11E included in the head bar 10c that ejects cyan ink. After that, the test pattern is printed again, and the distance between the two furthest pixels is measured based on the scan results of the test pattern. The distance between the two pixels measured previously is then compared with the distance between the two pixels measured this time to determine whether the previous duplication processing was effective. This process is repeated until it is determined that the previous duplication processing was not effective.

[0056] By performing this process, color misalignment between the three or more head bars 10 that eject inks of different colors can be suppressed, thereby preventing a decrease in image quality.

[0057] <Effects of the Embodiment> In the above embodiment, the head bar 10 of the printing apparatus 1 has heads 11A and 11B disposed at positions separated in the conveyance direction. Further, the printing apparatus 1 has conveyance rollers 5A and 5B configured to convey the recording medium 4 from the upstream side to the downstream side along the conveyance direction. The head 11A is located upstream of the head 11B in the conveyance direction. The heads 11A and 11B each have a nozzle region in which a plurality of nozzles 42 arranged at a pitch P along the left-right direction are disposed, and the right end of the nozzle region of the head 11A and the left end of the nozzle region of the head 11B overlap in the left-right direction. The used nozzles of the head 11A include a right end nozzle 42R located at the right end in the left-right direction and a plurality of other nozzles 42. The used nozzles of the head 11B include a left end nozzle 42L located at the left end and a plurality of other nozzles 42. The overlap amount X1 between the first pixel G1 formed by the ink droplets ejected from the right end nozzle 42R and the second pixel G2 formed by the ink droplets ejected from the left end nozzle 42L is less than one pixel (0 px < X1 < 1 px). While conveying the recording medium 4 along the conveyance direction, printing is performed by repeatedly ejecting ink droplets from the used nozzles of the head 11A and the used nozzles of the head 11B based on pixel data. When the pixel data for forming the pixel group formed by the ink droplets ejected from the used nozzles of the head 11A and the pixel data for forming the pixel group formed by the ink droplets ejected from the used nozzles of the head 11B are different, the printing method further includes executing a duplication process of making the pixel data for forming the first pixel G1 and the pixel data for forming the second pixel G2 the same.

[0058] By performing the duplication process so that the left end nozzle 42L of the head 11B and the right end nozzle 42R of the head 11A form the same pixel, it is possible to suppress the image from shrinking in the left-right direction and suppress a decrease in image quality.

[0059] In the above embodiment, when the overlap amount X1 is 0.5 pixels or more and less than 1 pixel (0.5px ≤ X1 < 1px), a process is performed to make the pixel data for forming the first pixel G1 and the pixel data for forming the second pixel G2 the same. When the overlap amount X1 is 0.5 pixels or more and less than 1 pixel, the degradation of image quality is greater compared to when the overlap amount X1 is less than 0.5 pixels. In such cases, the horizontal shrinkage of the formed image is suppressed, and the degradation of image quality is suppressed.

[0060] The embodiments disclosed herein are illustrative in all respects and not restrictive. Not all of the configurations shown in the embodiments above are essential, and configurations can be modified or omitted as needed.

[0061] In the above embodiment, there were three head bars 10. However, the present invention is not limited to such an embodiment, and the number and position of the head bars 10 can be changed as appropriate. Similarly, the number and position of the heads 11 included in one head group 20 can be changed as appropriate. In addition, the number and position of the nozzles 42 included in each head 11 can also be changed as appropriate.

[0062] In the above embodiment, a recording medium wound in a roll (e.g., roll paper) is used as the recording medium 4. However, the present invention is not limited to such embodiments, and a recording medium 4 of an appropriate shape and material can be used as needed. The printing apparatus 1 in the above embodiment is equipped with three head bars 10 and is configured to spray five colors of ink: white ink, cyan ink, magenta ink, yellow ink, and black ink. The present invention is not limited to such embodiments, and the printing apparatus 1 can be configured to spray ink of an appropriate color. In addition, UV-curable ink was used in this embodiment. However, the present invention is not limited to such embodiments, and inks other than UV-curable ink (e.g., water-based ink, pigment ink, etc.) can also be used.

[0063] Furthermore, the present invention is not necessarily limited to head bars including line heads, but can be broadly applied to head bars including multiple heads. Also, the present invention is not limited to inkjet-type printing apparatuses that spray ink. Furthermore, this teaching can be applied to printing apparatuses used for various purposes other than printing images, etc. For example, this teaching can be applied to printing apparatuses that spray a conductive liquid onto a substrate to form a conductive pattern on the substrate surface. The scope of the present invention is intended to include all modifications within the claims and scopes equivalent to the claims. [Explanation of Symbols]

[0064] 1 Printing device 10 Headbar 11 heads 42 nozzles 42L Left end nozzle 42R Rightmost Nozzle

Claims

1. A printing method performed by a printing device, The aforementioned printing apparatus, A first head bar having a first head and a second head arranged apart from each other in a first direction, A transport mechanism configured to transport a recording medium from upstream to downstream along the first direction, The first head is located upstream of the second head in the first direction. The first head and the second head each have a nozzle region in which a plurality of nozzles are arranged at a pitch P along a second direction perpendicular to the first direction, and the end of the nozzle region of the first head in the second direction and the other end of the nozzle region of the second head in the second direction overlap in the second direction. The plurality of nozzles used by the first head include a first nozzle located at one end in the second direction and a plurality of first nozzles excluding the first nozzle. The plurality of nozzles used by the second head include a second nozzle located at the other end in the second direction and a plurality of second nozzles excluding the second nozzle. The overlap amount X between the first pixel formed by the droplet discharged from the first nozzle and the second pixel formed by the droplet discharged from the second nozzle is greater than 0 pixels and less than 1 pixel. The aforementioned printing method is Printing is performed by repeatedly transporting the recording medium along the first direction and ejecting droplets from the nozzles used by the first head and the nozzles used by the second head based on the pixel data, A printing method comprising making the pixel data for forming the first pixel and the pixel data for forming the second pixel the same.

2. The printing method according to claim 1, wherein when the overlap amount X is 0.5 pixels or more and less than 1 pixel, the pixel data for forming the first pixel and the pixel data for forming the second pixel are the same.

3. The printing apparatus further, It has a third head and a fourth head that are spaced apart from each other in the first direction, and comprises a first head bar and a second head bar that is spaced apart in the first direction, The third head is located upstream of the fourth head in the first direction, The third head and the fourth head each have a nozzle region in which a plurality of nozzles are arranged in a pitch P along the second direction, The end of the nozzle region of the third head in the second direction and the other end of the nozzle region of the fourth head in the second direction overlap in the second direction. The nozzle region of the first head and the nozzle region of the third head overlap in the second direction. The nozzle region of the second head and the nozzle region of the fourth head overlap in the second direction. The plurality of nozzles used by the third head include a third nozzle located at one end in the second direction and a plurality of third nozzles excluding the third nozzle. The plurality of nozzles used by the fourth head include the fourth nozzle located at the other end in the second direction and a plurality of fourth nozzles excluding the fourth nozzle. The aforementioned printing method is When the overlap amount Y between a first reference pixel formed by a droplet ejected from one of the second nozzles used and a second reference pixel corresponding to the first reference pixel, formed by a droplet ejected from one of the fourth nozzles used, is greater than 0 pixels and less than 0.5 pixels, The printing method according to claim 1, wherein the pixel data for forming the first pixel and the pixel data for forming the second pixel are the same.

4. The printing apparatus further, It has a third head and a fourth head positioned at a distance from each other in the first direction, and the first head bar and the second head bar positioned at a distance from each other in the first direction, It has a fifth head and a sixth head positioned at a distance from each other in the first direction, and comprises a first head bar and a second head bar and a third head bar positioned at a distance from each other in the first direction, The third head is located upstream of the fourth head in the first direction, and the fifth head is located upstream of the sixth head in the first direction. The third head and the fourth head each have a nozzle region in which a plurality of nozzles are arranged in a pitch P along the second direction, The end of the nozzle region of the third head in the second direction and the other end of the nozzle region of the fourth head in the second direction overlap in the second direction. The fifth head and the sixth head each have a nozzle region in which a plurality of nozzles are arranged in a line with the pitch P along the second direction. The end of the nozzle region of the fifth head in the second direction and the other end of the nozzle region of the sixth head in the second direction overlap in the second direction. The nozzle region of the first head, the nozzle region of the third head, and the nozzle region of the fifth head overlap in the second direction. The nozzle region of the second head, the nozzle region of the fourth head, and the nozzle region of the sixth head overlap in the second direction. The plurality of nozzles used by the third head include a third nozzle located at one end in the second direction and a plurality of third nozzles excluding the third nozzle. The plurality of nozzles used by the fourth head include the fourth nozzle located at the other end in the second direction and a plurality of fourth nozzles excluding the fourth nozzle. The plurality of nozzles used by the fifth head include a plurality of fifth nozzles excluding the fifth nozzle and the third nozzle located at one end in the second direction, The plurality of nozzles used by the sixth head include the sixth nozzle located at the other end in the second direction and a plurality of sixth nozzles excluding the sixth nozzle. The aforementioned printing method is A first reference pixel formed by a droplet ejected from one of the second nozzles used, a second reference pixel corresponding to the first reference pixel formed by a droplet ejected from one of the fourth nozzles used, and a third reference pixel corresponding to the first reference pixel formed by a droplet ejected from one of the sixth nozzles used are arranged in order from the other side to the one side in the second direction. The width of the variation in the second direction of the first reference pixel, the second reference pixel, and the third reference pixel is The printing method according to claim 1, wherein if the pixel data for forming the first pixel and the pixel data for forming the second pixel become shorter when they are made the same, the pixel data for forming the first pixel and the pixel data for forming the second pixel are made the same.

5. The printing method according to claim 1, comprising adjusting the amount of droplets discharged from the first nozzle and the amount of droplets discharged from the second nozzle so that the average density of a plurality of pixels formed by droplets discharged from the first nozzle and the average density of a plurality of pixels formed by droplets discharged from the second nozzle are predetermined values.

6. Adjusting the amount of droplets discharged from the first nozzle and the amount of droplets discharged from the second nozzle is, The size of the droplet discharged from the first nozzle is made smaller than the size of the droplet discharged from each of the plurality of first nozzles used, The printing method according to claim 5, further comprising making the size of the droplet discharged from the second nozzle smaller than the size of the droplet discharged from each of the plurality of second nozzles used.

7. Adjusting the amount of droplets discharged from the first nozzle and the amount of droplets discharged from the second nozzle is, Reducing the number of times droplets are ejected from the first nozzle, The printing method according to claim 5, further comprising reducing the number of times droplets ejected from the second nozzle are ejected.

8. The printing method according to claim 5, comprising adjusting the amount of droplets discharged from the first nozzle and the amount of droplets discharged from the second nozzle such that the average density of a plurality of pixels formed by droplets discharged from the first nozzle and the average density of a plurality of pixels formed by droplets discharged from the second nozzle are the same.

9. The printing method according to claim 1, wherein the first head does not have a nozzle located on one side of the second direction relative to the first nozzle, and the second head has a nozzle located on the other side of the first direction relative to the second nozzle.

10. The printing method according to claim 1, wherein, in the pixel group formed by droplets ejected from the plurality of nozzles used by the first head and the pixel group formed by droplets ejected from the plurality of nozzles used by the second head, only the first pixel and the second pixel have an overlap amount greater than 0.

11. A head bar having a first head and a second head positioned offset from each other in a first direction, A transport mechanism configured to transport a recording medium from the upstream side to the downstream side along the first direction, The system includes a controller that controls the head bar and the transport mechanism, The first head is located upstream of the second head in the first direction. The first head and the second head each have a nozzle region in which a plurality of nozzles are arranged at a pitch P along a second direction perpendicular to the first direction, and the end of the nozzle region of the first head in the second direction and the other end of the nozzle region of the second head in the second direction overlap in the second direction. The plurality of nozzles used by the first head include a first nozzle located at one end in the second direction and a plurality of first nozzles excluding the first nozzle. The plurality of nozzles used by the second head include a second nozzle located at the other end in the second direction and a plurality of second nozzles excluding the second nozzle. The overlap amount X1 between the first pixel formed by the droplet discharged from the first nozzle and the second pixel formed by the droplet discharged from the second nozzle is greater than 0 pixels and less than 1 pixel. The controller controls the head bar and the transport mechanism, The system is configured to perform printing by repeatedly transporting the recording medium along the first direction and ejecting droplets from the nozzles used by the first head and the nozzles used by the second head based on the pixel data, When the pixel data for forming the first pixel group formed by droplets discharged from the plurality of first nozzles of the first head and the pixel data for forming the second pixel group formed by droplets discharged from the plurality of second nozzles of the second head are different, A printing system in which the controller is further configured to make the pixel data for forming the first pixel and the pixel data for forming the second pixel the same.

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