CN113954530B

CN113954530B - Printing apparatus and printing method

Info

Publication number: CN113954530B
Application number: CN202110817869.5A
Authority: CN
Inventors: 村井厚介
Original assignee: Mimaki Engineering Co Ltd
Current assignee: Mimaki Engineering Co Ltd
Priority date: 2020-07-20
Filing date: 2021-07-20
Publication date: 2023-03-28
Anticipated expiration: 2041-07-20
Also published as: JP2022020473A; CN113954530A; JP7350457B2

Abstract

Provided are a printing apparatus and a printing method, which properly reduce the influence of a nozzle at the end of an ink jet head. A printing apparatus (12) includes a plurality of ink jet heads arranged so as to be shifted from each other in position in a sub-scanning direction and having a plurality of nozzles arranged so as to be shifted from each other in position in the sub-scanning direction, and a control unit (110) that sets an end region and a center region for the ejection concentration of each nozzle in each ink jet head, and sets the ejection concentration to be gradually decreased in the end region as the end of the ink jet head approaches and to be constant in the center region, wherein the width of the end region in the sub-scanning direction is narrower than the width of the center region in the sub-scanning direction in each ink jet head.

Description

Printing apparatus and printing method

Technical Field

The present invention relates to a printing apparatus and a printing method.

Background

Conventionally, ink jet printers, which are printing apparatuses that perform printing by an ink jet method, have been widely used. As a configuration of a large-sized inkjet printer or the like, a configuration using a plurality of inkjet heads that eject ink of the same color is known (for example, see patent document 1). In this case, a plurality of inkjet heads for the same color ink are arranged, for example, in a staggered arrangement, to be used as a composite head.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-035160

Disclosure of Invention

Problems to be solved by the invention

When printing is performed by ejecting ink from an inkjet head onto a medium (media) to be printed, an abnormality in ejection characteristics is likely to occur in a nozzle located near an end (the foremost end or the rearmost end) of the inkjet head. As a result, for example, the landing position of the ink ejected from the nozzles near the end and the shape of the formed dots are varied, and unintended streaks occur in the printed matter, which tends to affect the image quality of the printed matter. In addition, in the case of using a plurality of inkjet heads for the same color ink, it is also conceivable that the image quality of the printed matter is affected by the influence of differences in the characteristics of the respective inkjet heads. As a result, even when the ejection characteristics of the end nozzles are normal, for example, unexpected streaks or the like are likely to occur in the printed matter in the vicinity of the position where the ink is ejected from the end nozzles.

Further, in the case of using a plurality of inkjet heads, the number of ends of the inkjet heads is also large in accordance with the number of inkjet heads, and therefore, the influence of nozzles near the ends is liable to occur. Therefore, when printing is performed using a plurality of inkjet heads, it is desirable to further appropriately reduce the influence of the nozzles at the ends of the respective inkjet heads. Accordingly, an object of the present invention is to provide a printing apparatus and a printing method capable of solving the above-described problems.

Means for solving the problems

In order to reduce the influence of the end nozzles in the inkjet head, it is conceivable to reduce the ejection positions from which ink is ejected from the end nozzles, for example. For example, in the case of the configuration disclosed in patent document 1, the influence of the nozzles at the lower end is reduced by setting the nozzles at both ends as half-discharge nozzles in the head unit corresponding to each inkjet head constituting the composite head.

In contrast, as another configuration for reducing the influence of the nozzles at the lower end, the inventors of the present application have conceived to gradually change the ejection density of each nozzle so that the ejection position from which ink is ejected from each nozzle near the end of each inkjet head gradually decreases toward the end. Further, it was confirmed that the influence of the nozzle at the lower end can be appropriately reduced by such a configuration by actually performing various experiments and the like. Therefore, if the structure is such as this, it is possible to appropriately prevent, for example, the occurrence of unexpected streaks or the like due to the influence of the end nozzles. In addition, this can appropriately prevent, for example, the image quality of the printed matter from being degraded by the influence of the end nozzles.

Further, the inventors of the present application have made further intensive studies and have conceived that, in such a configuration, the ejection density is not changed only in a gradual manner, but is fixed in the vicinity of the center of the inkjet head, and then, gradient regions narrower than a region (flat region) in which the ejection density is fixed are set at both ends of the inkjet head, and the ejection density is changed in the gradient regions. With this configuration, for example, the ejection density can be changed appropriately and gradually while suppressing the influence on the relative movement amount of the inkjet head with respect to the ejection target during the sub-scanning operation (the feed amount during the sub-scanning operation). In addition, this can prevent a large drop in printing speed, for example, to print efficiently, and can appropriately prevent the occurrence of unexpected streaks.

The present inventors have further studied and found out features necessary for obtaining the above-described effects, and have completed the present invention. In order to solve the above-described problems, the present invention is a printing apparatus that performs printing by an inkjet method, including: a plurality of ink jet heads that eject ink of the same color; a main scanning drive unit that causes the plurality of inkjet heads to perform a main scanning operation for ejecting ink while relatively moving the plurality of inkjet heads in a preset main scanning direction with respect to an ink ejection target; a sub-scanning drive unit that causes the plurality of ink jet heads to perform a sub-scanning operation in which the plurality of ink jet heads are moved relative to the ejection target in a sub-scanning direction orthogonal to the main scanning direction; and an ejection control unit configured to control the plurality of ink jet heads to eject ink to each position of the ejection target, wherein the main scanning drive unit and the sub scanning drive unit are controlled to perform ink ejection in a multipass printing method, in the multipass printing method, the number of times of the main scanning operation of any one of the ink jet heads passing through a position facing each position of the ejection target is a plurality of times, wherein each of the plurality of ink jet heads is arranged so as to be shifted in position from each other in the sub-scanning direction, and each of the plurality of ink-jet heads has a plurality of nozzles arranged so as to be shifted in position from each other in the sub-scanning direction, when a ratio of the number of ejection positions at which 1 nozzle ejects ink to the number of ejection positions of the ink set in a unit length in the main scanning direction according to a resolution of printing in 1 main scanning operation is defined as an ejection density of the nozzle, the ejection density of each nozzle in each inkjet head is determined, the ejection control unit sets an end region including a plurality of the nozzles on one end side and the other end side of each of the inkjet heads in the sub-scanning direction, a central region including a plurality of the nozzles is set between the end region on the one end side and the end region on the other end side, and is set such that the ejection density gradually becomes lower as approaching the end of the ink jet head in each of the end regions and is fixed in the central region, in each of the ink-jet heads, the width of the end region on each of the one end side and the other end side in the sub-scanning direction is narrower than the width of the central region in the sub-scanning direction.

In the case of such a configuration, for example, by reducing the ejection density of the end nozzles in each inkjet head, the influence of the end nozzles can be appropriately reduced. In this case, the ejection density is changed so that the ejection density gradually decreases as the ejection density approaches the end of the inkjet head, and thus, the ejection density can be changed more smoothly than in the case where the ejection density is changed stepwise, for example. In addition, this can appropriately prevent, for example, the occurrence of unexpected streaks due to a change in the ejection density of the nozzles.

In this case, the width of the end region in the sub-scanning direction is also made narrower than the width of the central region in the sub-scanning direction, whereby the influence of providing the end region can be reduced appropriately, for example. More specifically, for example, it is possible to appropriately prevent the relative movement amount of the inkjet head with respect to the ejection target (the feed amount in the sub-scanning operation) from being excessively reduced in the sub-scanning operation due to the provision of the end region. Therefore, if the above configuration is adopted, for example, the ejection density of the end nozzles can be appropriately changed while suppressing the influence on the ejection amount in the sub-scanning operation. In addition, for example, it is possible to prevent a large drop in printing speed and the like, to print efficiently, and to appropriately prevent the occurrence of unexpected streaks and the like. Further, with this, for example, when printing is performed using a plurality of inkjet heads, the influence of the nozzles at the ends of the respective inkjet heads can be appropriately reduced.

Here, in this configuration, the ejection target of the ink refers to, for example, a medium (media) as a printing target. Regarding the ejection density at the end region, for example, it can be considered that the ejection density gradually decreases as approaching the end of the inkjet head means that the ejection density gradually decreases (decreases) toward the end of the inkjet head, or the like. In addition, for example, it can also be considered that the ejection density at the end region increases from the end portion toward the center portion of the inkjet head.

In each of the ink jet heads, it is preferable that a sum of a width of the end region on the one end side in the sub-scanning direction and a width of the end region on the other end side in the sub-scanning direction is smaller than a width of the central region in the sub-scanning direction. With such a configuration, for example, the printing operation can be executed more efficiently. In each inkjet head, the width of the central region in the sub-scanning direction is preferably, for example, about 55% or more and less than 95% of the width in the sub-scanning direction of the range in which the plurality of nozzles are arranged in the inkjet head. With such a configuration, for example, efficient printing can be performed more appropriately. In this case, for example, the wider the width of the central region is, the more efficient printing can be performed.

In this configuration, for example, the central region may be a flat region or the like in which the ejection density is constant. For example, the end region may be a gradient region in which the ejection density changes gradually. In this case, the relationship between the width of the flat domain and the width of the gradation domain may be considered to be that the width of the gradation domain is made narrower than the width of the flat domain.

In this configuration, for example, it is considered that the ejection density of each nozzle indicates a ratio of ejection positions from which ink is ejected from the nozzle in the 1-time main scanning operation. For example, the ratio may be considered to be a ratio with respect to ejection positions constituting a line including an ejection position at which the nozzle ejects ink in the current main scanning operation, that is, a main scanning direction line. For example, the main scanning direction line may be a line of a plurality of discharge positions aligned in the main scanning direction and aligned at positions in the sub scanning direction among the discharge positions set according to the resolution of printing.

In this case, for example, the ratio of the ejection positions from which ink is ejected from 1 nozzle in the 1-time main scanning operation may be considered to be the ratio of the ejection positions from which ink is ejected from the nozzles when printing is finally performed at a density of 100%. For example, it is considered that printing at a density of 100% is performed by ejecting ink or the like a predetermined number of times (for example, 1 time) to each ejection position set according to the resolution of printing. In addition, when ink is ejected in a multipass printing method (printing is performed in a multipass printing method), for example, it is considered that printing at a density of 100% at the end is performed such that the density at the time point when all the main scanning operations for each position are completed becomes 100%. For example, it is considered that performing printing so that the density becomes 100% means performing so-called solid printing or the like.

In this configuration, for example, it is considered that the ejection density in the end region is set so that the ejection density changes linearly with respect to the distance from the end of the inkjet head in the sub-scanning direction. With such a configuration, for example, the ejection density at the end region can be set more easily.

In addition, the ejection density at the end region may also vary nonlinearly, for example. In this case, the ejection control section sets, for example, the ejection density of each nozzle to a non-linear change in ejection density with respect to a distance from the end of the inkjet head in the sub-scanning direction, with respect to the ejection density at the end region of each inkjet head. With such a configuration, for example, the ejection density in the end region can be set more flexibly. In addition, this enables, for example, more appropriate setting of the ejection density in accordance with the desired print quality or the like. More specifically, in this case, the ejection density in the end region can be changed rapidly and appropriately with a narrow width, for example.

In this configuration, the ejection density in the central region of each ink jet head may be different from one another. More specifically, in this case, the ejection control section sets, for example, the ejection density of the nozzles in the central region of any one of the ink jet heads to be lower than the ejection densities of the nozzles in the central regions of the other ink jet heads. With such a configuration, for example, the ejection density can be set more flexibly. In this case, for example, the ejection density in the central region of each inkjet head can be set in consideration of a desired state of processing of a printed matter, ink to be used, characteristics of an ejection target, and the like.

More specifically, for example, depending on the desired state of the printed matter to be processed, the ink to be used for printing, or the medium to be ejected, it is also conceivable that more ink is ejected in the main scanning operation performed earlier in the plurality of main scanning operations in the multipass printing method, or conversely, less ink is ejected in the main scanning operation performed earlier. In this case, by individually setting the ejection density in the central region of each inkjet head as described above, for example, the amount of ink ejected in each main scanning operation can be appropriately adjusted in accordance with a preferable condition.

For example, a method of setting the ejection density in the central region of each inkjet head according to the state of each inkjet head may be considered. More specifically, when printing is performed using a plurality of inkjet heads, it is conceivable that the state (situation) of some of the inkjet heads is inferior to that of the other inkjet heads. In this case, for example, it is conceivable to reduce the influence of the inkjet head by reducing the ejection density in the central region of the inkjet head in a poor state. With such a configuration, even when the state of some of the ink jet heads is poor, for example, high-quality printing can be performed more appropriately.

More specifically, for example, a method of reducing the ejection density in the central region of the inkjet head that ejects the ink last to each position of the ejection target may be considered. In this case, the ejection control unit sets, for example, the ejection density of the nozzles in the central region of the inkjet head that ejects the ink last toward each position of the ejection target among the plurality of inkjet heads to be lower than the ejection densities of the nozzles in the central regions of the other inkjet heads. With such a configuration, for example, the surface state in the print result can be smoothed.

In this case, for example, the ejection control unit sets the ratio of the ejection density of the nozzles in the central region of the inkjet head that ejects the ink last to each position of the ejection target to the ejection density of the nozzles in the central region of the other inkjet heads to a ratio within a range of 40 to 10. With such a configuration, for example, the above-described effect obtained by reducing the ejection density of the nozzles in the central region of the inkjet head that ejects the ink last to each position can be more appropriately obtained.

In addition, as the configuration of the present invention, a mode using a printing method having the same characteristics as described above, or the like can be considered. In these cases, for example, the same effects as described above can be obtained.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, for example, in the case of performing printing using a plurality of inkjet heads, the influence of the nozzles at the ends of the respective inkjet heads can be appropriately reduced.

Drawings

Fig. 1 is a diagram showing an example of the configuration of a printing system 10 according to an embodiment of the present invention. Fig. 1 (a) shows an example of the configuration of the printing system 10. Fig. 1 (b) shows an example of the configuration of the printing device 12 in the printing system 10. Fig. 1 (c) shows an example of the structure of the head 102 in the printing device 12.

Fig. 2 is a diagram illustrating the structure of the composite head 202. Fig. 2 (a) shows an example of the structure of the composite head 202. Fig. 2 (b) is a diagram illustrating the nozzle row 312 of the composite head 202.

Fig. 3 is a diagram illustrating an operation of a known multipass printing method. Fig. 3 (a) shows an example of the 2-pass operation. Fig. 3 (b) shows an example of the 4-pass operation.

Fig. 4 is a diagram illustrating the operation of the multipass printing method in more detail. Fig. 4 (a) shows an example of a line of dots 402 formed on a medium when printing is performed. Fig. 4 (b) and (c) show an example of an operation of ejecting ink in a plurality of main scanning operations for ejection positions in 1 main scanning direction line.

Fig. 5 is a diagram for explaining the method of setting the ejection density in this example in more detail. Fig. 5 (a) and (b) show an example of a method for setting ejection density to a plurality of nozzles in a plurality of head units 212 constituting the composite head 202.

Fig. 6 is a diagram showing an example of the operation of the multipass printing method performed in this example.

Fig. 7 is a diagram illustrating a modification of the method of setting the ejection density for each head unit 212. Fig. 7 (a) and (b) show a modification of the method for setting the ejection density.

Fig. 8 is a diagram showing an example of the operation of the multipass printing method in the case where the ejection density setting shown in fig. 7 (a) is performed.

Fig. 9 is a diagram illustrating a modification of the structure of the composite head 202.

Fig. 10 is a diagram showing another modification of the structure of the composite head 202.

Description of the reference numerals

10: a printing system; 12: a printing device; 14: controlling the PC;50: a medium; 102: a head portion; 104: a platen; 106: a main scanning drive section; 108: a sub-scanning drive section; 110: a control unit; 200: a carriage; 202: compounding the head; 204: an ultraviolet light source; 212: a head unit; 302: a nozzle; 304: a nozzle row; 312: a nozzle row; 322: a pass-through area; 402: and (4) point.

Detailed Description

Embodiments according to the present invention will be described below with reference to the drawings. Fig. 1 shows an example of the configuration of a printing system 10 according to an embodiment of the present invention. Fig. 1 (a) shows an example of the configuration of the printing system 10. Fig. 1 (b) shows an example of the configuration of the printing device 12 in the printing system 10. Fig. 1 (c) shows an example of the structure of the head 102 in the printing apparatus 12. The configurations of the printing system 10 and the printing system 10 of the present example may be the same as or have the features of the configurations of the known printing systems and the known printing systems, except for the points described below.

In this example, the printing system 10 is a system that performs printing on a medium (media) 50 to be printed by an inkjet method, and includes a printing apparatus 12 and a control PC 14. In this case, the medium 50 is an example of an ejection target of ink. The printing device 12 is an ink jet printer that performs a printing operation for ejecting ink onto the medium 50, and performs the printing operation on the medium 50 under the control of the control PC 14. The control PC 14 is a computer that controls the operation of the printing apparatus 12, and controls the operation of the printing apparatus 12 by supplying print data indicating an image to be printed to the printing apparatus 12. More specifically, the control PC 14 generates print data by performing RIP (Raster Image Processor) processing, for example, and supplies the generated print data to the printing apparatus 12.

As described above, in the present embodiment, the printing system 10 includes the printing apparatus 12 and the control PC 14 as a plurality of apparatuses. In a modification of the configuration of the printing system 10, for example, a mode in which the printing system 10 is configured by 1 apparatus may be considered. In this case, for example, a mode using the printing apparatus 12 having a function of controlling the PC 14 can be considered. In another modification of the configuration of the printing system 10, a mode in which the printing system 10 is configured by 3 or more devices may be considered. In this case, for example, a mode in which the printing system 10 is configured by a plurality of printing apparatuses 12 and the control PC 14 may be considered. Further, for example, a mode in which the printing system 10 is configured by 3 or more devices using another device having a part of the functions of the printing device 12 or the control PC 14 may be considered.

Next, the configuration of the printing apparatus 12 in this example will be described in more detail. In this example, the printing device 12 includes a head 102, a platen 104, a main scanning drive unit 106, a sub-scanning drive unit 108, and a control unit 110. The head 102 is a portion that ejects ink onto the medium 50. In this example, the head 102 includes a carriage 200, a plurality of composite heads 202, and a plurality of ultraviolet light sources 204. The carriage 200 is a holding member that holds other members in the head 102. Each of the plurality of composite heads 202 is configured to eject ink of each color used for printing. In this case, it is conceivable that the plural composite heads 202 eject ink of different colors. More specifically, in this example, each of the plurality of composite heads 202 ejects ink of each color printed by a process color (process color) as a primary color in color printing. As the inks of the respective colors printed by the primary color method, for example, inks of the respective colors of cyan (C), magenta (M), yellow (Y), and black (K) can be used. In this example, each composite head 202 is formed of a plurality of inkjet heads. For example, an inkjet head may be considered to be an ejection head that ejects liquid by an inkjet method. The structure of the composite head 202 will be described in more detail later.

In this example, each of the plurality of composite heads 202 ejects ultraviolet-curable ink (UV ink) that is cured in response to irradiation of ultraviolet light. In this case, for example, a known ultraviolet-curable ink or the like can be preferably used. In this example, the plurality of composite heads 202 are arranged to: the printing device 12 is aligned in a main scanning direction (Y direction in the figure) orthogonal to the sub-scanning direction, with the position thereof being aligned in the preset sub-scanning direction (X direction in the figure). For example, the sub-scanning direction may be a direction parallel to the feeding direction of the medium 50 to the head 102. For example, the main scanning direction may be considered to be a direction parallel to the scanning direction, which is a direction of relative movement of the head 102 in the main scanning operation described below. In a modification of the structure of the head 102, the arrangement of the plurality of composite heads 202 may be different from the above. For example, the position of a part of the composite head 202 in the sub-scanning direction may be different from the other composite heads 202. The composite head 202 may be configured to eject ink of a color other than each of CMYK colors.

The plurality of ultraviolet light sources 204 are light sources that irradiate ultraviolet light for curing the ultraviolet curable ink. For example, a UVLED or the like can be preferably used as the ultraviolet light source 204. In this example, the plurality of ultraviolet light sources 204 are disposed on one side and the other side of the line of the plurality of composite heads 202 in the main scanning direction, respectively. In addition, in this way, the ultraviolet light source 204 irradiates the ink on the medium 50 with ultraviolet light in the main scanning operation described below, for example, to fix the ink to the medium 50.

In this example, the plurality of ultraviolet light sources 204 are an example of the ink fixing means. In a modification of the printing apparatus 12, it is also conceivable to use ink other than the ultraviolet-curable ink. In this case, it is conceivable to adopt a fixing means corresponding to the ink to be used instead of the ultraviolet light source 204. For example, when ink that evaporates a solvent in the ink (evaporation-drying type ink) is used, a heater or the like can be used as the fixing means.

The platen 104 is a table-like member that mounts the medium 50 on the upper surface, and holds the medium 50 in a state of facing the plurality of composite heads 202 in the printing apparatus 12. The main scanning drive unit 106 is a drive unit that causes the head unit 102 to perform a main scanning operation. In this case, for example, it can be considered that causing the head section 102 to perform the main scanning operation means causing the composite head 202 in the head section 102 to perform the main scanning operation or the like. For example, it can be considered that causing the composite head 202 to perform the main scanning operation means causing the plurality of inkjet heads constituting the composite head 202 to perform the main scanning operation or the like. In the main scanning operation in this example, the main scanning drive unit 106 causes the inkjet heads of the plurality of composite heads 202 to eject ink to the ejection positions set according to the printing resolution under the control of the control unit 110. In this example, for example, the main scanning operation may be an operation of ejecting ink while relatively moving in the main scanning direction with respect to the medium 50.

The sub-scanning drive section 108 is a drive section for causing the head section 102 to perform a sub-scanning operation. In this case, for example, it can be considered that causing the head section 102 to perform the sub-scanning operation means causing the composite head 202 in the head section 102 to perform the sub-scanning operation or the like. For example, it is considered that causing the composite head 202 to perform the sub-scanning operation means causing the plurality of inkjet heads constituting the composite head 202 to perform the sub-scanning operation or the like. In this example, for example, the sub-scanning operation may be considered to be an operation of moving relative to the medium 50 in the sub-scanning direction. For example, the sub-scanning operation may be an operation of feeding the medium 50 in the sub-scanning direction intermittently in the main scanning operation.

The control unit 110 is, for example, a part including a CPU and the like in the printing apparatus 12, and controls the operation of each part of the printing apparatus 12. As described above, in the present embodiment, the main scanning drive unit 106 causes the inkjet heads in the head unit 102 to eject ink under the control of the control unit 110. In this case, for example, it can be considered that the control section 110 controls ejection of ink from each inkjet head. In this example, the control unit 110 is an example of an ejection control unit, and controls the plurality of inkjet heads constituting each composite head 202 to eject ink to each position of the medium 50 to be an ink ejection target.

More specifically, in this example, the control unit 110 controls the operations of the main scanning drive unit 106 and the sub-scanning drive unit 108 so that ink is ejected in the multipass printing method. In this case, for example, the operation of ejecting ink in the multipass printing method may be considered to be an operation in which the number of times of main scanning operations of any one of the inkjet heads passing through each position of the medium 50 is plural. In this case, for example, each position of any one of the inkjet head passing media 50 may be considered to be each position of any one of the plurality of inkjet heads constituting each composite head 202 passing media 50. For example, it can be considered that the number of times of the main scanning operation in which any one of the inkjet heads passes through each position of the medium 50 is a plurality of times, and the like, that any one of the plurality of inkjet heads for the same color passes through each position of the medium 50. The operation of the multipass printing method executed in this example will be described in more detail later. According to this example, for example, the printing operation on the medium 50 can be appropriately performed.

Next, the structure of the composite head 202 in the head portion 102 is described in more detail. Fig. 2 is a diagram illustrating the structure of the composite head 202. Fig. 2 (a) is a diagram showing an example of the structure of the composite head 202, and shows an example of the structure of the composite head 202 for 1 color. As described above, in the present embodiment, the composite head 202 is formed of a plurality of inkjet heads. In addition, more specifically, in the case of the structure shown in fig. 2 (a), 1 composite head 202 is constituted by 2 head units 212 which are shown as head 1 and head 2 differently in the drawing. In this case, each head unit 212 is an inkjet head constituting the composite head 202, and each head unit 212 has a nozzle row 304 composed of a plurality of nozzles 302 arranged so as to be shifted in position from each other in the sub-scanning direction, as shown in the drawing, for example. In this example, the plurality of nozzles 302 in each head unit 212 are arranged at regular intervals in the sub-scanning direction.

In the composite head 202, for example, as shown in the drawing, a plurality of head units 212 are arranged so as to be shifted in position from each other in the sub-scanning direction. In this case, for example, it can be considered that the arrangement of the head units 212 so as to be shifted from each other in the sub-scanning direction means that the head units 212 are arranged so that the positions of the nozzle rows 304 in the respective head units 212 are shifted from each other in the sub-scanning direction. More specifically, in this example, the plurality of head units 212 constituting the composite head 202 are arranged so as to be shifted in position from each other in the sub-scanning direction, and the ranges of the nozzle rows 304 do not overlap in the sub-scanning direction.

In the case of such a configuration, for example, as shown in fig. 2 (b), the nozzle row 312 of the composite head 202 can be configured by the nozzle row 304 of each head unit 212. Fig. 2 (b) is a diagram illustrating the nozzle row 312 of the composite head 202. In this case, for example, the nozzle row 312 of the composite head 202 may be considered to be a virtual nozzle row or the like realized by combining the nozzle rows 304 of the plurality of head units 212 constituting the composite head 202. For example, the nozzle row 312 may be considered as a row in which the rows of the nozzles 302 are considered, focusing on the positions of the nozzles 302 in the sub-scanning direction in each head unit 212. For example, the nozzle row 312 may be considered as a row formed by connecting the nozzle rows 304 in the head units 212.

In this example, for example, as shown in the figure, the nozzle length of the nozzle row 312 in the composite head 202 is considered to be a length obtained by summing up the nozzle lengths of the nozzle rows 304 in the head unit 212 constituting the composite head 202. In this case, for example, the nozzle length of the nozzle row 304 in the head unit 212 may be considered to be a width in the sub-scanning direction of a range in which the nozzles 302 are present in the head unit 212. For example, it can be considered that the nozzle length of the nozzle row 312 in the composite head 202 is a length obtained by summing up the nozzle lengths of the nozzle rows 304 in the head unit 212 constituting the composite head 202, and the like are as follows: the nozzle length of the nozzle row 312 in the composite head 202 is substantially equal to the sum of the nozzle lengths of the nozzle rows 304 in the respective head units 212 in the composite head 202. For example, it is considered that the nozzle length of the nozzle row 312 in the composite head 202 and the sum of the nozzle lengths of the nozzle rows 304 in the respective head units 212 are substantially equal to each other in the following cases: the nozzle length of the nozzle row 312 in the composite head 202 is equal to the sum of the nozzle lengths of the nozzle rows 304 in the head units 212, except for an adjustment portion or the like due to a method of using the nozzle rows 304 at the ends in the head units 212.

More specifically, in this example, each of the plurality of head units 212 included in the composite head 202 has a nozzle row 304 having the same nozzle length Lh. In this case, for example, it can be considered that the nozzle length Lh of the head unit 212 is a distance obtained by multiplying the number of nozzles by the period of the nozzles in the sub-scanning direction. In addition, for example, it can be considered that the period of the nozzles in the sub-scanning direction refers to an interval in the sub-scanning direction between the centers of the nozzles 302 adjacent in the sub-scanning direction, or the like. For example, the number of nozzles may be considered to be the number of nozzles 302 for ejecting ink in the nozzle row 304 of 1 head unit 212, or the like. For example, the nozzle 302 for ejecting ink may be a nozzle other than a nozzle intentionally set not to eject ink. In this case, for example, as shown in the figure, the nozzle length Ln of the nozzle row 312 in the composite head 202 can be considered to be a distance obtained by multiplying Lh by the number of head units 212 constituting the composite head 202. For example, the nozzle length Lh of the head unit 212 may be a width in the sub-scanning direction of a range in which the plurality of nozzles are arranged in the head unit 212.

In fig. 2 (a), the head units 212 constituting the composite head 202 are illustrated as being slightly overlapped in the portions of the ends in the sub-scanning direction. However, as can be understood from the arrangement of the nozzles 302 shown in the figure, the above description, and the like, the overlapping portion is a portion of the head unit 212 located outside the nozzle row 304. Therefore, when focusing attention on the effective part of the head unit 212 for ejecting ink, it can be considered that the plurality of head units 212 shown in fig. 2 are disposed so that the positions in the sub-scanning direction do not overlap with each other, for example. In the following drawings, for the sake of simplicity of illustration, only the width of the effective portion of the head unit 212 in the sub-scanning direction is illustrated as necessary. In a modification of the structure of the composite head 202, a different form from the above can be considered, for example, as to the arrangement form of the plurality of head units 212. Such a modification will be described in more detail later.

Next, the operation of the multipass printing method performed by using the composite head 202 will be described in more detail. First, for convenience of explanation, a general multi-pass printing operation performed by a known method using the composite head 202 will be described. Fig. 3 is a diagram illustrating an operation of a known multipass printing method. Fig. 3 (a) shows an example of an operation (2-pass operation) in which the number of passes is 2. Fig. 3 (b) shows an example of an operation (4-pass operation) in which the number of passes is 4. In this case, the number of passes may be, for example, the number of times any head unit 212 (see fig. 2) of 1 composite head 202 performs the main scanning operation that passes through the position facing 1 position of the medium 50.

In the case of performing the printing operation in the multipass printing method, the printing apparatus 12 (see fig. 1) sets the number of passes to a plurality of times by making the feed amount in the sub-scanning operation smaller than the nozzle length Ln of the composite head 202. In this case, for example, the feed amount in the sub-scanning operation may be referred to as a relative movement amount of the head unit 212 with respect to the medium 50 in the sub-scanning operation. More specifically, when the number of passes is 2, for example, as shown in fig. 3 (a), the sub-scanning movement Dx, which is the feed amount in the sub-scanning operation, is 1/2 (Ln/2) of the nozzle length Ln of the composite head 202. When the number of passes is 4, the sub-scanning movement Dx is 1/4 (Ln/4) of the nozzle length Ln of the composite head 202 as shown in fig. 3 b, for example.

In this case, for example, the operation of the control unit 110 (see fig. 1) in the printing apparatus 12 may be considered as follows: a one-pass region 322 for ejecting ink in each main scanning operation corresponding to the number of passes is set for the nozzle row 312 in the composite head 202 and the nozzle row 304 in each head unit 212. More specifically, when the number of passes is 2, for example, as shown in fig. 3 (a), the control unit 110 sets a one-pass area 322 corresponding to each of the 1 st pass and the 2 nd pass for the nozzle row 312 and the nozzle row 304. When the number of passes is 4, for example, as shown in fig. 3 (b), the control unit 110 sets a one-pass region 322 corresponding to each of the 1 st pass to the 4 th pass for the nozzle row 312 and the nozzle row 304. With such a configuration, for example, a printing operation in the multipass printing method can be appropriately performed.

In the case of performing printing in a multipass printing method, for example, as described below with reference to fig. 4, a line in which a plurality of discharge positions are arranged in the main scanning direction (hereinafter, referred to as a main scanning direction line) is formed by a plurality of main scanning operations. For example, the main scanning direction line may be a line of a plurality of discharge positions aligned in the main scanning direction and aligned at positions in the sub scanning direction, among the discharge positions set according to the resolution of printing. For example, the main scanning direction line may be a set of ejection positions where the same position in the sub scanning direction is extracted from among the ejection positions of ink set according to the resolution of printing.

Fig. 4 is a diagram illustrating the operation of the multipass printing method in more detail. Fig. 4 (a) is a diagram showing an example of an array of dots 402 formed on a medium when printing is performed, and shows an example of an array of dots formed on a part of a medium by 1 composite head 202 in the case of performing printing at a density of 100% (printing density). Fig. 4 (b) and (c) show an example of an operation of ejecting ink in a plurality of main scanning operations for ejection positions in 1 main scanning direction line in the printing operation in the multipass printing method.

In this case, for example, it is considered that printing at a density of 100% means that ink or the like is ejected a predetermined number of times to each ejection position set according to the resolution of printing. More specifically, in the above and the following configurations, it is considered that printing at a density of 100% means that ink or the like is ejected 1 time for each ejection position set according to the resolution of printing. In addition, in the case where ink is ejected in a multipass printing method (printing in a multipass printing method), for example, printing at a density of 100% may be considered to be printing such that the final printing density at the time point when all the main scanning operations for each position are completed becomes 100%. Further, for example, it is considered that performing printing so that the density becomes 100% means performing so-called solid printing or the like.

In this case, for example, as shown in the figure, 1 dot 402 is formed at each ejection position set according to the resolution of printing. In this case, when looking at a plurality of ejection positions constituting 1 main scanning direction line, for example, as shown in fig. 4 (b) and (c), dots 402 at some ejection positions are formed in one main scanning operation, and dots 402 at least some other ejection positions are formed in the other main scanning operations. More specifically, in fig. 4 (b), the plural dots 402a and b formed at the ejection positions in 1 main scanning direction line are shown with the same dot hatching pattern formed in the same main scanning operation and with the different dot hatching patterns formed in the different main scanning operations. That is, in the case shown in fig. 4 (b), the printing device 12 forms a plurality of dots 402a shown by the same hatching pattern in any 1-time main scanning operation and forms a plurality of dots 402b shown by the same hatching pattern in any other 1-time main scanning operation, thereby ejecting ink to a plurality of ejection positions constituting 1 main scanning direction line by 2-time main scanning operation.

In this case, the printing device 12 performs at least 1 sub-scanning operation between the 2 main scanning operations. In this case, ink is ejected from any 1 nozzle in the composite head 202 (see fig. 1) to a part of the ejection positions in the 1 main scanning direction line, and ink is ejected from any other 1 nozzle in the composite head 202 to another part of the ejection positions in the main scanning direction line. In fig. 4 (c), the dots 402a and b included in one main scanning direction line are shown at positions shifted from each other by the corresponding nozzles. In this case, as differently shown as the head 1, the head 2, the nozzle a, and the nozzle B in the drawing, it can be considered that a plurality of dots 402a in (B) of fig. 4 are formed by any nozzle (nozzle a) in any head unit 212 (head 1) among the plurality of head units 212 constituting the composite head 202, and a plurality of dots 402B are formed by any nozzle (nozzle B) in the other head unit 212 (head 2) in the composite head 202. In this case, for example, the nozzle B may be considered as an example of a nozzle other than the nozzle a. With this configuration, for example, each main scanning direction line can be formed appropriately by a plurality of main scanning operations. In addition, this enables, for example, a printing operation in the multipass printing method to be appropriately performed.

Here, when printing is performed in the multipass printing method, 1 main scanning direction line is formed by a plurality of main scanning operations as described above. In this case, it can be considered that the ejection position from which the ink is ejected by 1 nozzle in the 1-time main scanning operation is a part of the plurality of ejection positions constituting the main scanning direction line. Therefore, in the following, the ratio of ejection positions from which ink is ejected from the respective nozzles is considered to be the ejection density of the nozzles. For example, the ejection density of the nozzles may be a ratio of ejection positions from which ink is ejected from 1 nozzle in 1 main scanning operation. For example, the ratio may be considered to be a ratio of ejection positions from which ink is ejected from the nozzles when printing is finally performed at a density of 100%. For example, the ratio may be considered to be a ratio with respect to the ejection positions of the main scanning direction lines constituting the ejection positions at which the nozzles eject the ink in the present main scanning operation. As can be understood from the matters described above using fig. 3 and 4, etc., for example, the ejection density may be a ratio of the number of ejection positions at which ink is ejected from 1 nozzle in 1 main scanning operation to the number of ejection positions of ink set in a unit length in the main scanning direction according to the resolution of printing.

In the case of performing printing in the multipass printing method, each nozzle in the nozzle row 312 of the composite head 202 ejects ink at an ejection density set according to the number of passes or the like in each main scanning operation. For example, when the operation of the multipass printing method is performed by the operation described using fig. 3 and the like, the ejection density of each nozzle is set to a fixed ejection density that is inversely proportional to the number of passes. In contrast, in the operation of the multipass printing method in the present example described below, for example, as shown in fig. 5, the ejection density of some of the nozzles in each head unit 212 is different from that of the other nozzles.

Fig. 5 is a diagram for explaining the method of setting the ejection density in this example in more detail. Fig. 5 (a) and (b) show an example of a method for setting ejection density for a plurality of nozzles in a plurality of head units 212 constituting the composite head 202. In fig. 5 (a) and (b), the left diagram shows an example of the arrangement of the plurality of head units 212 constituting the composite head 202. The right diagram shows an example of the ejection density set for each nozzle in each head unit 212.

As described above, in the printing apparatus 12 (see fig. 1) of the present embodiment, the control unit 110 (see fig. 1) controls the operations of the respective units of the printing apparatus 12. As an example of such control, the control unit 110 determines the ejection position at which the ink is ejected from each nozzle 302, for example, based on print data received from the control PC 14 (see fig. 1). In this case, for example, it can be considered that the operation of the control section 110 is to determine the ejection density of each nozzle 302 based on the print data. Therefore, in this example, it can be considered that the operation of the control unit 110 for determining the ejection position at which ink is ejected from each nozzle in each head unit 212 constituting the composite head 202 is, for example, an operation for setting the ejection density of each nozzle.

As can be understood from the matters illustrated in fig. 6 and the like, in the present example, the control unit 110 sets the ejection density for the nozzles near the end in the sub-scanning direction of each head unit 212 to be lower as the ejection density approaches the end. More specifically, in this example, as shown in the drawing, the control section 110 sets a plurality of gradation domains G1, G2 and a planar domain F for each head unit 212 constituting the composite head 202. In this case, each of the plurality of gradation regions G1 and G2 is an example of an end region including a plurality of nozzles, and is set on one end side and the other end side in the sub-scanning direction in the head unit 212. The flat region F is an example of a central region including a plurality of nozzles, and is set between the gradation regions G1 and G2.

In this example, the plane region F is set between the gradation regions G1 and G2 so as not to leave a gap between the gradation regions G1 and G2. Therefore, each nozzle in each head unit 212 is included in any one of the gradation region G1, the gradation region G2, and the plane region F. Then, the control unit 110 sets the ejection density of each nozzle in each head unit 212 to: in the gradation regions G1 and G2, the ejection density gradually decreases as the end (end in the sub-scanning direction) of the head unit 212 approaches, and the ejection density is fixed in the flat region F.

In this case, for example, the flat region F may be a region in which the ejection density is constant. For example, the gradation regions G1 and G2 may be regions in which the ejection density is changed gradually. For example, the setting of the ejection density as described above in this example may be considered to be a setting in which the ejection density of each nozzle is gradually changed so that the ejection position at which ink is ejected from each nozzle in the vicinity of the end of each head unit 212 gradually decreases toward the end. Regarding the ejection density in the gradient regions G1 and G2, for example, it is considered that the ejection density gradually decreases as approaching the end of the head unit 212, that is, the ejection density gradually decreases (decreases) toward the end of the head unit 212. For example, the ejection density in the gradation regions G1 and G2 may be considered to increase from the end portions toward the central portion of the head unit 212.

When the ejection density is set in this manner, for example, the influence of the end nozzles in each head unit 212 can be appropriately reduced by reducing the ejection density of the end nozzles. In this case, the ejection density is changed so that the ejection density gradually decreases as the end of the head unit 212 approaches, and thus, the ejection density can be changed more smoothly than in the case where the ejection density is changed stepwise, for example. With such a configuration, for example, it is possible to appropriately prevent the occurrence of unexpected streaks or the like due to a change in the ejection density by the nozzle. In addition, this can more appropriately prevent, for example, the image quality of the printed matter from being degraded by the influence of the end nozzles.

In this example, the width of the gradation regions G1 and G2 in the sub-scanning direction is made narrower than the width of the flat region F in the sub-scanning direction, instead of changing only the ejection density in a gradual manner. In this case, for example, it can be considered that the respective widths of the gradation field G1 and the gradation field G2 are smaller than the width of the plane field F. More specifically, in this example, in each head unit 212, the sum of the width of the gradation region G1 and the width of the gradation region G2 is smaller than the width of the flat region F.

With this configuration, for example, the influence of providing the gradient regions G1 and G2 can be reduced, and the influence of the end nozzles in each head unit 212 can be appropriately reduced. More specifically, in this case, for example, it is possible to appropriately prevent the feeding amount during the sub-scanning operation from being excessively reduced due to the provision of the gradation regions G1 and G2. Therefore, according to this example, the ejection density can be changed appropriately and gradually while suppressing the influence on the ejection amount in the sub-scanning operation, for example. In addition, this can prevent a large drop in printing speed, for example, to print efficiently, and can appropriately prevent the occurrence of unexpected streaks. The relationship between the widths of the gradation regions G1 and G2 and the feed amount in the sub-scanning operation will be described in more detail later.

In this example, by providing the flat surface region F in the head unit 212, for example, it is possible to prevent the ejection density from becoming excessively high in some of the nozzles. More specifically, for example, when only the gradient regions G1 and G2 are set for the head unit 212 without providing the flat region F, it is conceivable that the ejection density is highest in the center portion of the head unit 212, for example. In this case, for example, when the number of passes is reduced to efficiently perform printing, the ejection density at the center portion is expected to be extremely high. As a result, the number of ejection positions from which ink is ejected from the nozzles in the center portion is extremely large, and problems such as beading are likely to occur. In contrast, according to this example, by setting the planar region F in the head unit 212, for example, it is possible to appropriately prevent the ejection density from being excessively high in some of the nozzles. In this case, for example, high-quality printing can be appropriately performed also in the flat area F.

Here, as described above, fig. 5 (a) and (b) show an example of a method of setting ejection density for each of the plurality of nozzles in the plurality of head units 212 constituting the composite head 202. In both of these examples, the ejection density of the nozzles is set by setting the flat region F and the gradation regions G1 and G2 for each head unit 212. However, as shown in the figure, the specific ejection density value differs between the example shown in fig. 5 (a) and the example shown in fig. 5 (b).

More specifically, in the example shown in fig. 5 (a), the same ejection density is set for all the head units 212 constituting the composite head 202. In contrast, in the example shown in fig. 5 (b), the ejection density at the planar domain F of each head unit 212 is different with respect to the ejection density at the planar domain F of each head unit 212. Accordingly, the ranges of the discharge density changes in the gradation regions G1 and G2 are different for each head unit 212 as well. As for such setting of the ejection density, for example, it is considered that the ejection density of the nozzles in the planar region F of any one head unit 212 among the plurality of head units 212 constituting the composite head 202 is set to be lower than the ejection densities of the nozzles in the planar regions F of the other head units 212. By performing such setting of the ejection density, for example, the ejection density can be set more flexibly. In this case, for example, the ejection density in the planar region F of each head unit 212 may be set in consideration of a desired state of processing of a printed matter, ink to be used, characteristics of an ejection target, and the like.

More specifically, as a method of setting the ejection density in the flat area F of each head unit 212, for example, a method of setting the ejection density in the flat area F of the head unit 212 that ejects the ink last to each position of the medium 50 to be ejected with the ink, to be low, may be considered. In this case, the control unit 110 in the printing device 12 sets the ejection density of the nozzles in the planar region F of the head unit 212 that ejects the ink last to each position of the medium 50 among the plurality of head units 212 constituting the composite head 202 to be lower than the ejection densities of the nozzles in the planar regions F of the other head units 212. With such a configuration, for example, the surface state in the print result can be smoothed. Effects and the like obtained by setting the ejection density at the planar domain F of the head unit 212, which ejects ink last, low will be described in more detail later.

Next, the operation of the multipass printing method performed in this example, the relationship between the widths of the gradation regions G1 and G2 and the feed amount in the sub-scanning operation, and the like will be described in more detail. Fig. 6 is a diagram showing an example of the operation of the multipass printing method performed in this example, and shows an example of the operation of the multipass printing method in the case where the discharge density is set as shown in fig. 5 (b), and shows an example of the positions of the heads 1 and 2 in the sub-scanning direction as the plurality of head units 212 (see fig. 5) constituting the composite head 202 in the continuous 3-times main scanning operation shown as the 1 st scan to the 3 rd scan in the drawing.

In the case where the gradient regions G1 and G2 are set and the ejection density of some of the nozzles is set low as in this example, the portion of the gradient regions G1 and G2 where the ejection density drops in each sub-main scanning operation needs to be compensated for in the other sub-main scanning operation. In this case, it is conceivable to adjust the feed amount Dx in the sub-scanning operation so that the complementary relationship is established. More specifically, in the case where the gradation regions G1 and G2 are set on one end side and the other end side in the sub-scanning direction of each head unit 212 as in this example, it is conceivable that the width of the gradation region G1 (the width in the sub-scanning direction) in 1 head unit 212 is the same as the width of the gradation region G2, and the sub-scanning feed amount Dx is set to be small in accordance with the distance corresponding to the width of the gradation region G1 (or the gradation region G2). For example, in the case of performing the operation of the multipass printing method corresponding to the conventional 2-pass operation shown in fig. 3 (a), if the width of the flat region F in the sub-scanning direction is denoted by F and the width of the gradation region G1 in the sub-scanning direction is denoted by G1, it can be considered that the feed amount Dx in the sub-scanning operation is set to F + G1 as shown in the figure.

In this case, for example, the operation of the multipass printing method corresponding to the conventional 2-pass operation may be considered to be an operation in which the ejection density in the flat area F is set to be the same as that in the case where the conventional 2-pass operation is performed. As described above, in the present example, the widths of the gradient regions G1 and G2 are set to be the same. Therefore, the above-described delivery amount Dx in this example is considered to be equal to F + G2. It is considered that the feed amount Dx is shorter than the feed amount in the conventional 2-pass operation by an amount corresponding to the width of 1 gradation region (gradation region G1 or gradation region G2).

As can be understood from the configuration of the present example described above, the operation of the multipass printing method performed in the present example is not limited to the operation corresponding to the conventional 2-pass operation, and can be performed in accordance with the conventional operation having a larger number of passes. More specifically, for example, it is considered that the operation of the multipass printing method performed in the present example can perform an operation corresponding to a conventional N-pass operation (N is an integer of 2 or more). In this case, for example, the conventional N-pass operation is considered to be an operation of a multipass printing method having N passes, which is performed similarly to the 2-pass and 4-pass operations shown in fig. 3. For example, the operation of the multipass printing method in the present example corresponding to the N-pass operation may be considered to be an operation in which the ejection density in the flat area F is set to be the same as that in the case where the conventional N-pass operation is performed. In this case, for example, it is conceivable that the feed amount Dx in the sub-scanning operation in the present example is shorter than the feed amount in the conventional N-pass operation by a distance corresponding to the width of 1 gradation region.

Therefore, in the case of performing the multipass printing operation in this example, it can be considered that the wider the gradation regions G1 and G2 are, the shorter the feed amount Dx in the sub-scanning operation is. In contrast, in the present example, as described above, the sum of the width of the gradation region G1 and the width of the gradation region G2 is narrower than the plane region F. Therefore, according to this embodiment, for example, as described above, it is possible to appropriately prevent the feed amount Dx during the sub-scanning operation from being excessively reduced by providing the gradation regions G1 and G2. In addition, this makes it possible to change the discharge density appropriately and gradually while suppressing the influence on the discharge amount Dx during the sub-scanning operation, for example.

In this case, considering the comparison between the width of the flat area F and the nozzle length Lh of the head unit 212, it is considered that the width of the flat area F is preferably set to be, for example, 55% or more and less than 95% of the nozzle length Lh in each head unit 212. With such a configuration, for example, the printing operation in the multipass printing method can be efficiently and appropriately performed. In this case, for example, it can be said that the wider the width of the flat area F, the more efficient printing can be performed. The width of the flat area F is preferably about 60% or more, more preferably about 75% or more of the nozzle length Lh.

Next, supplementary explanation and modified example of each of the above-described configurations will be given. First, an example of a method of considering the number of passes in the operation of the multipass printing method performed in this example will be described. As in this example, when the gradation regions G1 and G2 are set in a part of the head unit 212, a difference occurs in the number of times of main scanning operations of any head unit 212 passing through a position facing the region between the region where ink is ejected only from the nozzles in the plane region F of each head unit 212 in the composite head 202 and the region where ink is ejected from the nozzles in at least either one of the gradation region G1 and the gradation region G2. In this case, for example, it is conceivable to define the number of passes based on the relationship between the delivery amount Dx in the sub-scanning operation and the nozzle length Ln of the nozzle row 312 (see fig. 2) of the composite head 202. More specifically, for example, when the nozzle rows 304 (see fig. 2) of the plurality of head units 212 in the composite head 202 are arranged without a gap in the sub-scanning direction as in the configuration of the present example described above, the number of passes N can be considered to be N = Ln/Dx. In this case, the number of passes N may be a value other than an integer.

In this case, taking into account the fact that the widths of the gradation regions G1 and G2 are larger than the plane region F, and focusing on the relationship between the width of the plane region F (hereinafter referred to as F), the width of the gradation region G1 (hereinafter referred to as G1), and the width of the gradation region G2 (hereinafter referred to as G2) and the number of passes N, the width F approaches 0 and the widths G1 and G2 approach F/2 as the number of passes N increases. When the number of passes N is further increased from the condition of F =0, the ejection density in the flat area F and the gradation areas G1 and G2 may be set low, and the width F may be decreased again from a state in which the entire nozzle row 304 in the head unit 212 is the flat area F and the gradation areas G1 and G1 are not set (a state of F = ALL, G1=0, and G2= 0).

In this case, for example, it is considered that the state in which the ejection density in the flat region F is maximized corresponds to the operation of performing 1-pass printing in the conventional configuration. For example, the state in which the ejection density in the flat region F is maximized may be considered as a state in which the ejection density in the flat region F is 100%. In this case, for example, it can be considered that the nozzles of the planar area F are operated to eject ink to all the ejection positions constituting the main scanning direction line by 1 main scanning operation. In this case, when the widths of the gradient regions G1 and G2 are increased, the number of passes N gradually increases until F = 0. In the case where the number of passes N is further increased from this state, for example, the ejection density in the flat region F and the gradation regions G1 and G2 may be set to the half described above. In this case, for example, it can be considered that the operation of the nozzles of the planar area F ejects ink to all the ejection positions constituting the main scanning direction line by 2 times of main scanning operation. Further, by making the ejection density lower in the flat region F and the gradation regions G1 and G2, the printing operation with a larger number of passes N can be performed.

In a case where such a feature is considered more generally, for example, it can be considered that the operation of the nozzles of the planar domain F is to eject ink to all the ejection positions constituting the main scanning direction line by k times (k is an integer of 1 or more) of main scanning operation. In this case, it is conceivable to set the ejection density in the flat region F and the gradation regions G1 and G2 according to the value of k. In this case, it is conceivable that the main scanning direction line is completed by performing k +1 main scanning operations, for example, in the region where the ink is ejected from the nozzles of the gradation regions G1 and G2. More specifically, in this case, as illustrated in fig. 6, for example, in each head unit 212 (each of the heads 1 and 2) in the composite head 202, the rising edge and the falling edge of the ejection density overlap each other by the main scanning operation of different times. With such a configuration, for example, a complementary relationship with respect to the decrease portions of the ejection density in the gradient regions G1 and G2 can be appropriately established.

Next, a setting method for setting the ejection density for the plurality of head units 212 constituting the composite head 202, and the like will be described in more detail. As described above using fig. 5 (b) and the like, the ejection density at the planar area F of each head unit 212 may be different for each head unit 212. In this regard, for example, depending on a desired state of processing a printed matter, ink to be used for printing, a medium to be used, or the like, it is also conceivable that more ink is preferably ejected in a main scanning operation performed earlier in a plurality of main scanning operations in the multipass printing method, or conversely, that less ink is preferably ejected in a main scanning operation performed earlier. In this case, by individually setting the ejection density in the planar region F of each head unit 212 constituting the composite head 202, for example, the amount of ink ejected in each main scanning operation can be appropriately adjusted in accordance with a preferable condition.

More specifically, in the printing apparatus 12 of this embodiment, for example, as shown in fig. 5 (b), by setting the ejection density at the flat surface region F of the head unit 212 from which ink is ejected last to be low, printing can be performed in a state in which the irregularities on the surface are reduced. In addition, this can suitably improve the smoothness of the surface of the printed matter, for example. Further, for example, it is possible to appropriately prevent the occurrence of light streaks which are likely to be a problem when ultraviolet curable ink is used.

Here, the inventors of the present application confirmed by experiments and the like in which printing was actually performed by setting ejection density corresponding to (a) and (b) of fig. 5, respectively, that in a case where the ejection density is set as in (b) of fig. 5, and more ink is ejected in the main scanning operation performed earlier and less ink is ejected in the main scanning operation performed last, the surface of the printed matter has fewer irregularities and is processed more smoothly, compared to a case where the same ejection density is set for each head unit 212 as in (a) of fig. 5. In this case, the unevenness on the surface is small, and it is determined based on the tactile sensation of the hand and the appearance of the printed image. The reason for this is not clear at the current time point, but the following reasons and the like can be conceived: after a large amount of ink is ejected from the head unit 212 (head 1) that ejects ink first to each position of the medium 50, a small amount of ink is ejected from the head unit 212 (head 2) that ejects ink last, and thus, for example, the ink ejected from the head 2 fills up the unevenness of the surface formed by the ink formed by the head 1, and the unevenness of the surface is reduced to be smooth. In this experiment, in contrast to the case shown in fig. 5 (b), printing was also performed with a setting such that the ejection density at the planar area F of the head unit 212 (head 1) that ejects ink first is lower than the ejection density at the planar area F of the head unit 212 (head 2) that ejects ink later. Further, it was confirmed that the unevenness on the surface can be reduced by the setting shown in fig. 5 (b) even in the case of comparing with such a setting.

When the ejection density of the nozzles in the planar region F of the head unit 212 that ejects the ink last to each position of the medium 50 is set to be low, the control unit 110 (see fig. 1) in the printing device 12 sets, for example, the ratio of the ejection density of the nozzles in the planar region F of the head unit 212 that ejects the ink last to each position of the medium 50 to the ejection density of the nozzles in the planar region F of the other head units 212 to a ratio within the range of 40 to 10. With such a configuration, for example, the above-described effect can be obtained by setting the ejection density of the nozzles in the planar region F of the head unit 212 that ejects the ink last to each position to be low as appropriate. Preferably, the ratio is from 40.

As described above, in the printing apparatus 12 of this example, ultraviolet curable ink is used as the ink. In this case, by reducing the unevenness on the surface of the printed matter by setting the ejection density as described above, it is possible to obtain an effect unique to the case of using the ultraviolet curing ink, for example, to prevent striations and the like. However, even in the case of using ink other than ultraviolet-curable ink, an effect obtained by reducing the ejection density of the nozzles at the flat area F of the head unit 212 that ejects ink last to each position of the medium 50 can be obtained. More specifically, for example, in the case of using an evaporation drying type ink, a problem that ink bleeding is likely to occur is conceivable. In particular, for example, when a medium having a property of absorbing ink is used in combination with an evaporation-drying type ink, the ink penetrates into the medium, and a problem of bleeding is likely to occur. In addition, for example, in the case of a medium using cloth, it is also conceivable that moire or the like occurs depending on the relationship between the texture of the cloth and the positions of the dots. In contrast, it is conceivable that an improvement effect can be obtained against such a problem in the case where the ejection density of the nozzles at the planar area F of the head unit 212, which ejects ink lastly to each position, is reduced as described above.

Next, various modifications will be described with respect to a method of setting the ejection density for each head unit 212, the structure of the composite head 202, and the like. Fig. 7 and 8 are diagrams for explaining a modification of the method of setting the ejection density for each head unit 212. Fig. 7 (a) and (b) show a modification of the method for setting the ejection density. Fig. 8 shows an example of the operation of the multipass printing method in the case where the discharge density setting shown in fig. 7 (a) is performed. In addition, except for the points described below, the structure in which the same reference numerals as those in fig. 1 to 6 are given in the drawings described later may have the same or similar features as those in fig. 1 to 6.

In the above description, an example in which the ejection density in the gradation regions G1 and G2 of each head unit 212 is changed linearly (linear) has been mainly described. In this case, for example, it can be considered that linearly changing the ejection density refers to linearly changing the ejection density with respect to the distance from the end of the head unit 212 in the sub-scanning direction, or the like. With such a configuration, for example, the ejection density in the gradation regions G1 and G2 can be set more easily.

In contrast, in a modification of the method of setting the ejection density, for example, the ejection density in the gradation regions G1 and G2 may be changed nonlinearly as shown in fig. 7 (a). In this case, for example, the non-linear change of the ejection density may be a change of the ejection density as follows: the relationship between the distance from the end of the head unit 212 in the sub-scanning direction and the ejection density is a relationship that cannot be expressed by a first order equation. In this case, the control unit 110 (see fig. 1) in the printing apparatus 12 sets the ejection density of each nozzle to be a non-linear variation in ejection density with respect to the distance from the end of the head unit 212 in the sub-scanning direction, for example, with respect to the ejection density in the gradation regions G1 and G2 of each head unit 212. In this case, for example, as shown in the figure, it is conceivable that the ejection density is set to change nonlinearly and the ejection density is lower as it approaches the end of the head unit 212. With such a configuration, for example, the ejection density in the gradation regions G1 and G2 can be set more flexibly. In addition, this enables, for example, more appropriate setting of the ejection density in accordance with the desired print quality or the like.

In this case, for example, the ejection density in the gradation regions G1 and G2 can be changed rapidly and appropriately with a narrower width. In this case, for example, the ejection density rapidly changes, which means that the change in ejection density according to the distance from the end of the head unit 212 is a rapid increase or a rapid decrease. With such a configuration, for example, by reducing the ratio of the tapered regions G1 and G2 to the nozzle length in the head unit 212 and increasing the ratio of the flat region F to the nozzle length in the head unit 212, the influence on the printing speed due to the provision of the tapered regions G1 and G2 can be appropriately reduced. In this case, it is also considered that the change of the ejection density in the gradation regions G1 and G2 can be made to the predetermined ejection density as soon as possible.

Here, when considering that the ejection density is changed with a narrow width, for example, it is conceivable to change the ejection density stepwise so that the ejection density suddenly changes between 2 adjacent nozzles. However, in this case, for example, since the change in the ejection density is too abrupt, unexpected streaks or the like are likely to occur at positions (positions in the printed matter) corresponding to the nozzles that change the ejection density. Therefore, it is preferable that the change in the ejection density in the gradation regions G1 and G2 be nonlinearly changed within a range that does not become a stepwise change. More specifically, in this case, it is conceivable that the ejection density of some of the nozzles included in the gradation regions G1 and G2 is set to be smaller than the ejection density in the flat region F and larger than 0. In this case, it is conceivable that each of the gradation region G1 and the gradation region G2 is a region including 3 or more nozzles. In addition, when it is considered that the ejection density is changed rapidly so as not to change stepwise, for example, the sum of the width of the gradation region G1 and the width of the gradation region G2 may be set to about 1 to 15% of the nozzle length of the head unit 212. The total amount is preferably less than 10% (for example, about 1 to 10%, preferably about 3 to 8%).

As described above, when the gradient regions G1 and G2 are set and the ejection density of some of the nozzles is set low, the portion of the ejection density that drops in each sub-main scanning operation needs to be compensated for in another sub-main scanning operation. In addition, when the ejection density in the gradation regions G1 and G2 is changed nonlinearly as in the present modification, for example, as shown in the drawing, it is conceivable to set the ejection density to: the discharge density at one of the gradation regions G1 and G2 decreases in accordance with the manner of increasing the discharge density at the other region. For example, it is considered that such setting of the ejection density is setting of the ejection density which is symmetrically performed in accordance with a nonlinear change.

In the method of ejecting density shown in fig. 7 (a), for example, it is considered that in each of the head units 212 shown as the head 1 and the head 2 in the figure, the ejecting density of ink is increased nonlinearly at one end portion, and the ejecting density is decreased nonlinearly at the other end portion. In this case, it is conceivable that the discharge density is changed more rapidly by a nonlinear change in discharge density than by a linear change in discharge density. In the case of such a configuration, although the cause and the principle are not determined at the current time, the influence of the light streak can be further reduced as compared with the case where the ejection density is linearly changed (increased/decreased) as shown in fig. 5 (b) and fig. 6, for example.

As the nonlinear change in the ejection density, for example, a logarithmic change can be used. In this case, for example, it is considered that the logarithmic function of the ejection density is a curve showing a relationship between the position of each nozzle and the ejection density as a logarithmic function. For example, it is considered that a curve showing a relationship between the position of the nozzle and the ejection density as a substantially logarithmic function is: in accordance with the accuracy of the ejection density that can be set for each nozzle, a curve or the like indicating the relationship between the position of the nozzle and the ejection density can be shown as a logarithmic function.

In the case where the ejection density is set as shown in fig. 7 a, for example, as shown in fig. 8, it is conceivable to perform an operation (multi-pass scanning) by a multipass printing method. More specifically, fig. 8 shows an example of the operation performed in the multipass printing method in the case where the discharge density is set as shown in fig. 7 (a), in which the positions of the head 1 and the head 2 in the sub-scanning direction in the continuous 3-times main scanning operation shown as the 1 st scan to the 3 rd scan are shown. As can be clearly understood from a comparison between the items illustrated in fig. 5 (b) and 6 for the case of changing the ejection density linearly and the items illustrated in fig. 7 (a) and 8 for the case of changing the ejection density nonlinearly (for example, logarithmically) as described above, when the ejection density is changed nonlinearly as described above, for example, as described above, the ejection density can be appropriately increased to a predetermined ejection density (ejection density in the planar region F) as soon as possible on the one end side of the head 1 and the head 2. Further, the ejection density can be appropriately decreased as soon as possible on the other end sides of the heads 1 and 2 symmetrically to the one end side. As a result, for example, the gradation domains G1 and G2 can be made narrower and the flat domain F can be made wider than in the case where the ejection density is linearly changed. Therefore, if configured in this way, for example, more efficient printing can be appropriately performed. In this case, for example, the smoothness of the surface of the printed matter to which ink is ejected can be appropriately improved as compared with a conventional configuration or the like.

In the above description, the case where the ejection densities in the flat areas F of the head units 212 are different from each other is mainly described as an example of the case where the ejection densities in the flat areas F of the head units 212, which eject ink last to each position of the medium 50, are set to be low. However, it is conceivable that the ejection density in the planar region F of each head unit 212 differs for various reasons. In this case, for example, a method of setting the ejection density in the planar region F of each head unit 212 according to the state of each head unit 212, or the like can be considered.

More specifically, when printing is performed using the composite head 202 including a plurality of head units 212, it is also conceivable that the state (state) of some of the head units 212 is inferior to that of the other head units 212. In this case, for example, it is conceivable to reduce the influence of the head unit 212 by reducing the ejection density in the planar region F of the head unit 212 having a poor state. With such a configuration, even when the state of some of the head units 212 is poor, for example, high-quality printing can be performed more appropriately. The ejection density in the flat area F of each head unit 212 is not limited to the above, and various methods may be adopted depending on the desired state of the printed matter, the ink to be used for printing, the medium to be ejected, and the like. In these cases, for example, as shown in fig. 7 (b), it is also possible to consider setting the ejection density. It can be considered that such setting of the ejection density is a reverse relationship between the ejection density and the head unit 212 to the case shown in fig. 5 (b), for example.

In a modification of the structure of the composite head 202, a method of arranging the plurality of head units 212, etc. different from the above-described structure, etc. can be considered. More specifically, in the above description, the arrangement of the plurality of head units 212 in the composite head 202 is mainly described as a structure in which the plurality of head units 212 are arranged without a gap in the sub-scanning direction. In contrast, in a modified example of the configuration of the head unit 102, for example, as shown in fig. 9, a plurality of head units 212 may be arranged with a gap in the sub-scanning direction.

Fig. 9 shows a modification of the structure of the composite head 202. In the present modification, as shown in the figure, the plurality of head units 212 in the composite head 202 are arranged with a gap S in the sub-scanning direction. Even in the case of such a configuration, the same effects as described above can be obtained by setting the flat area F and the gradation areas G1 and G2 for each head unit 212.

Here, in the case shown in the figure, the ejection densities at the flat region F and the gradation regions G1, G2 of each head unit 212 are set to be the same as the case shown in (b) of fig. 5. In this case, for example, the printing operation can be performed in the same manner as in the case of using the composite head 202 shown in fig. 5 (b) by adjusting the timing of ink ejection of each head unit 212 in accordance with the phase difference corresponding to the gap S.

More specifically, when printing is performed in a multipass printing method using the composite head 202 including the plurality of head units 212 as in the above-described configurations, it is conceivable to select ejection positions from which the respective head units 212 eject ink, in accordance with a mask map. For example, when the ejection density is set as shown in fig. 5 (b), fig. 9, and the like, the head unit 212 shown as the head 1 ejects ink to the ejection positions 60% of the ejection positions of the finished image. In this case, for example, the ejection position at which the image is completed may be considered to be an ejection position of the image at the time point when the printing is completed. Further, for example, the ejection position of the finished image may be an ejection position set according to the resolution of printing performed by the multipass printing method. In this case, for example, it is conceivable to randomly select an ejection position from which ink is ejected by the head 1 according to a mask pattern. For example, it can be considered that selecting the ejection positions at random means selecting the ejection positions so that the corresponding patterns do not occur at the selected ejection positions, in a manner that can be considered as random. In this case, the remaining head units 212 shown as heads 2 eject ink to the remaining 40% of the ejection positions. For example, it is also possible to randomly select the ejection positions from which the heads 2 eject ink, according to a mask pattern.

In this case, as for the method of applying the mask for determining the ejection positions of the heads 1 and 2, the mask can be applied in consideration of adjusting the phase difference according to the difference in the positions of the heads 1 and 2 in the sub-scanning direction. More specifically, for example, when a plurality of head units 212 are arranged as shown in fig. 5 (b), it can be considered that the head 1 and the head 2 are shifted by an amount corresponding to the width of 1 head unit 212 in the sub-scanning direction (an amount corresponding to 1 head). In this case, for example, it is conceivable to match the phases when applying the masks to the heads 1 and 2 by applying the masks with a phase difference corresponding to the amount of 1 head shifted in the sub-scanning direction. In the case where the gap S is left between the head 1 and the head 2 as shown in fig. 9, for example, when the difference in position between the head 1 and the head 2 in the sub-scanning direction is 2 times the amount corresponding to 1 head (the amount corresponding to 2 heads), for example, it is conceivable that the phase adjustment by the amount corresponding to 2 heads is performed similarly. Even when the position of the head 1 and the position of the head 2 in the sub-scanning direction are different by a distance other than the above, it is possible to perform phase adjustment in accordance with the distance. With this configuration, even when a plurality of head units 212 are arranged with the space S left, for example, ink can be appropriately ejected to all the ejection positions using the plurality of head units 212.

In this way, in the present modification, for example, by adjusting the position to which the mask pattern is applied, the plurality of head units 212 can be appropriately separated. Therefore, according to the present modification, for example, the layout of the plurality of head units 212 constituting the composite head 202 can be set very freely. In this regard, for example, when only a specific arrangement such as a staggered arrangement is used, positioning is usually required to adjust the relative position between the head units 212. In this case, for example, manual adjustment by professional skill is required. In contrast, when a plurality of head units 212 are arranged in a free arrangement as in the present modification, adjustment for eliminating the phase difference is performed by software control, for example. In this case, even if the relative position between the head units 212 is slightly shifted, the influence of the shift can be easily and appropriately reduced by the software adjustment. Therefore, according to the present modification, for example, the convenience of the user can be appropriately improved.

In this case, by providing a gap S between the head units 212, it is possible to more easily install each head unit 212 without interference from another head unit 212. In this case, since there is a space for installing the head unit 212, the head unit 212 and the like can be installed more easily even when the size of the head unit 212 is changed by changing the product of the inkjet head used as the head unit 212, for example. In addition, even when the head units 212 are spaced apart by the gap S, it is easy to align the positions of the plurality of head units 212 in the main scanning direction, for example, as shown in the drawing. In addition, this also makes it possible to make the size of the composite head 202 compact in the main scanning direction, for example.

Here, in the above description, the case where the composite head 202 is configured by arranging the plurality of head units 212 without a gap in the sub-scanning direction has been described, where the relationship between the feed amount Dx in the sub-scanning operation, the nozzle length Ln of the composite head 202, and the number of passes N can be considered to be N = Ln/Dx. In contrast, when a plurality of head units 212 are arranged with a gap S in the sub-scanning direction, the width of the composite head 202 in the sub-scanning direction is directly regarded as the nozzle length Ln, and the gap S has an influence. Therefore, in this case, the length corresponding to the sum of the nozzle lengths in the head unit 212 can be regarded as the substantial nozzle length Ln in the composite head 202, except for the amount of the gap S. In this case, even when a plurality of head units 212 are arranged with a gap S in the sub-scanning direction, the number of passes N can be considered to be N = Ln/Dx. In this case, the delivery amount Dx in the sub-scanning operation can be set to: the decrease amount of the ejection density in each of the gradation domains G1 and G2 in each sub main scanning operation is compensated by another sub main scanning operation. More specifically, in this case as well, it is conceivable to set the feed amount Dx to F + G1 when printing is performed in the minimum number of passes. The feed amount Dx when the number of passes is set to be larger can be set in the same manner as described above, considering that the feed amount Dx is appropriately adjusted according to the number of passes and the like.

In the above description, the configuration of the composite head 202 has been mainly described in the case where the composite head 202 includes 2 head units 212. In contrast, in another modification of the configuration of the composite head 202, the composite head 202 may have 3 or more head units 212.

Fig. 10 shows another modification of the structure of the composite head 202. In the present modification, the composite head 202 is constituted by 4 head units 212 which are shown differently as head 1 to head 4 in the drawing. In this case, the same effects as described above can be obtained by setting the flat area F and the gradation areas G1 and G2 for each head unit 212 as described above. More specifically, in this case as well, it is conceivable that the sum of the width of the gradation region G1 and the width of the gradation region G2 is narrower than the width of the flat region F in each head unit 212. In this case, it is conceivable to set the ejection density in the planar region F of each head unit 212 in accordance with the number of head units 212 included in the composite head 202. More specifically, in this case, for example, the ejection density in the planar region F of each head unit 212 can be set in consideration of the relationship between the number of head units 212 constituting the composite head 202 and the number of passes. In this case, the ejection density in the planar region F may be different for each head unit 212.

More specifically, in fig. 10, characters a1 to a4 are used to show the ejection density at the planar region F of each head unit 212. In the example shown in fig. 10, the ejection density in the flat area F of the head unit 212, i.e., the head 4, which ejects the ink last to each position of the medium 50 may be lower than the ejection density in the flat area F of the other head units 212. The ejection density in the planar region F of the head unit 212 that first ejects ink to each position, that is, the head 1, is higher than the ejection density in the planar regions F of the other head units 212. The ejection density of the head unit 212 located in the middle in the sub-scanning direction, that is, the ejection densities of the heads 2 and 3 in the flat region F are set to the same ejection density.

In another modification of the structure of the composite head 202, each head unit 212 may be disposed with a gap in the sub-scanning direction in the composite head 202 having 3 or more head units 212. In addition, in the above, the following example is explained: the width of each of the flat domain F and the gradation domains G1 and G2 of each head unit 212 in the sub-scanning direction is set similarly for all the head units 212 constituting the composite head 202. In contrast, in another modification of the structure of the composite head 202, the planar domain F and the gradation domains G1 and G2 may have different widths in the sub-scanning direction for each head unit 212. In this case as well, it can be considered that the width of the gradation region G1 in the sub-scanning direction set for 1 head unit 212 is the same as the width of the gradation region G2 in the sub-scanning direction.

In the above description, the method of arranging the plurality of head units 212 in the composite head 202 has been mainly described as an example of a configuration in which the nozzle rows in the respective head units 212 do not overlap in the sub-scanning direction. In contrast, in another modification of the structure of the composite head 202, for example, it is conceivable to arrange the head units 212 adjacent in the sub-scanning direction such that a part of the positions of the nozzle rows overlap in the sub-scanning direction. In this case as well, by separately ejecting ink from the portion where the nozzle rows overlap by dividing the plurality of head units 212, a printing operation using the composite head 202 can be performed appropriately. In this case, it is also possible to set some of the nozzles included in the portion where the nozzle rows overlap as nozzles that do not eject ink (non-ejection nozzles), and the like. In this case, it can be considered that the portion other than the non-discharge nozzles is the nozzle row of the head unit 212.

In the above description, the configuration of the ink jet printer that ejects ink onto a medium to draw a two-dimensional image on the medium has been mainly described as the printing apparatus 12 (see fig. 1). In contrast, in a modification of the printing device 12, a 3D printer (3D printing device) or the like that manufactures a three-dimensional shaped object may be used as the printing device 12. In this case, it is considered that the modeling table supporting the object under modeling and the object under modeling are the objects to which the ink is ejected. In this case as well, by setting the print density in the same manner as described above, for example, the influence of the nozzles at the ends of the head units 212 constituting the composite head 202 can be reduced appropriately. For example, the printing device 12 may be considered as an example of a liquid ejecting apparatus. In this case, for example, ink may be considered as an example of liquid ejected by the liquid ejection device.

Industrial applicability

The present invention can be preferably used for a printing apparatus, for example.

Claims

1. A printing apparatus for performing printing by an ink jet method, comprising:

a plurality of ink jet heads that eject ink of the same color;

a main scanning drive unit that causes the plurality of inkjet heads to perform a main scanning operation for ejecting ink while relatively moving the plurality of inkjet heads in a preset main scanning direction with respect to an ink ejection target;

a sub-scanning drive unit that causes the plurality of ink jet heads to perform a sub-scanning operation in which the plurality of ink jet heads are moved relative to the ejection target in a sub-scanning direction orthogonal to the main scanning direction; and

an ejection control unit configured to control the plurality of inkjet heads to eject ink to each position of the ejection target, wherein the operation of the main scanning drive unit and the sub-scanning drive unit is controlled so as to perform ink ejection in a multipass printing method in which the number of times that any one of the inkjet heads passes through the main scanning operation at a position facing each position of the ejection target is a plurality of times,

wherein each of the plurality of ink-jet heads is arranged so as to be shifted in position from each other in the sub-scanning direction, and each of the plurality of ink-jet heads has a plurality of nozzles arranged so as to be shifted in position from each other in the sub-scanning direction,

in a case where a ratio of the number of ejection positions from which ink is ejected from 1 nozzle to the number of ejection positions of the ink set in a unit length in the main scanning direction according to a resolution of printing in 1-time main scanning operation is defined as an ejection density of the nozzles, the ejection control unit sets an end region including a plurality of the nozzles on one end side and the other end side in the sub scanning direction of each inkjet head, respectively, with respect to the ejection density of each nozzle in each inkjet head, sets a central region including a plurality of the nozzles between the end region on the one end side and the end region on the other end side, and sets the ejection density in each end region gradually lower as approaching an end of the inkjet head and the ejection density in the central region to be constant,

in each of the ink-jet heads, the width of the end region on each of the one end side and the other end side in the sub-scanning direction is narrower than the width of the central region in the sub-scanning direction.

2. Printing device according to claim 1,

the ejection control section sets the ejection density of the nozzles at the central region of any one of the inkjet heads to be lower than the ejection densities of the nozzles at the central regions of the other inkjet heads.

3. Printing device according to claim 1 or 2,

the ejection control unit sets the ejection density of the nozzles in the central region of the inkjet head that ejects the ink last to each position of the ejection target, from among the plurality of inkjet heads, to be lower than the ejection densities of the nozzles in the central regions of the other inkjet heads.

4. Printing device according to claim 3,

the ejection control unit sets a ratio of the ejection density of the nozzles at the central region of the inkjet head that ejects the ink last to each position of the ejection target to the ejection density of the nozzles at the central region of the other inkjet heads to a ratio within a range of 40 to 10.

5. Printing device according to claim 1 or 2,

in each of the inkjet heads, a width of the central region in the sub-scanning direction is 55% or more and less than 95% of a width of a range in which the plurality of nozzles are arranged in the sub-scanning direction in the inkjet head.

6. Printing device according to claim 1 or 2,

in each of the ink jet heads, a sum of a width of the end region on the one end side in the sub scanning direction and a width of the end region on the other end side in the sub scanning direction is narrower than a width of the central region in the sub scanning direction.

7. Printing device according to claim 1 or 2,

the ejection control portion sets the ejection density of each of the nozzles in such a manner that the ejection density varies non-linearly with respect to a distance from an end of the inkjet head in the sub-scanning direction, with respect to the ejection density at the end region of each of the inkjet heads.

8. A printing method for printing by an ink jet method,

a plurality of ink jet heads that eject ink of the same color are caused to perform the following operations:

a main scanning operation of ejecting ink while relatively moving in a preset main scanning direction with respect to an ink ejection target; and

a sub-scanning operation of moving the ejection target in a sub-scanning direction orthogonal to the main scanning direction,

and the number of the first and second electrodes,

in the control of causing the plurality of ink-jet heads to eject ink to the respective positions of the ejection target, the plurality of ink-jet heads are caused to perform the main scanning operation and the sub-scanning operation so as to perform ejection of ink in a multipass printing method in which the number of times that any one of the ink-jet heads passes through the main scanning operation at a position facing the respective positions of the ejection target is a plurality of times,

each of the plurality of ink jet heads is arranged so as to be shifted in position from each other in the sub-scanning direction, and each of the plurality of ink jet heads has a plurality of nozzles arranged so as to be shifted in position from each other in the sub-scanning direction,

in the case where a ratio of the number of ejection positions at which 1 nozzle ejects ink to the number of ejection positions of the ink set in a unit length in the main scanning direction according to a resolution of printing in 1 main scanning operation is defined as an ejection density of the nozzle, an end region including a plurality of the nozzles is set on one end side and the other end side of each inkjet head in the sub scanning direction, respectively, with respect to the ejection density of each nozzle in each inkjet head, a central region including a plurality of the nozzles is set between the end region on the one end side and the end region on the other end side, and the ejection density is set to gradually decrease as the end of the inkjet head approaches in each end region and to be constant in the central region,

in each of the ink-jet heads, the width of the end region on each of the one end side and the other end side in the sub-scanning direction is made narrower than the width of the central region in the sub-scanning direction.