Printer

Abstract

To provide a printer capable of suppressing landing position deviation of droplets caused by misalignment of the other discharge head from one discharge head.SOLUTION: Some of a plurality of nozzles in one discharge head and some of a plurality of nozzles in the other discharge head adjacent to the one discharge head seen in an intersecting direction are arranged to overlap in a conveying direction in a prescribed overlapping region. A control unit performs a position changing process for changing the relative positions of the one discharge head and the other discharge head in the intersecting direction by a position adjustment unit, a test pattern forming process for discharging droplets on a printing medium from some nozzles in at least an overlapping region of the other discharge head and some nozzles in an overlapping region of the one discharge head to form test patterns, and a process for determining optimal relative positions on the basis of the concentration of each test pattern obtained through scanning.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to printing devices, such as inkjet printers. [Background technology]

[0002] Conventionally, inkjet recording devices equipped with an ejection head formed by joining a plurality of head modules in a predetermined direction are known (see Patent Document 1). In such inkjet recording devices, misalignment between the head modules can occur due to various factors such as thermal expansion or distortion of the components of the head modules. To address this issue, a measurement chart is test printed on a print medium, the measurement chart on the print medium after printing is read by a scanner, and the amount of misalignment is calculated based on the read data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-105066 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional technology, because the measurement chart on the print medium is read by a scanner, the accuracy of misalignment correction depends on the reading accuracy of the scanner. Generally, to achieve the expected image quality in a printing device, misalignment correction must be performed in units of several microns, but the reading resolution of a typical scanner is often only several tens of microns. Thus, if the reading accuracy of the scanner is low, the accuracy of misalignment correction decreases, which is an issue.

[0005] Therefore, an object of the present disclosure is to provide a printing device that can suppress deviation in the landing position of droplets caused by deviation in the position of one ejection head relative to another ejection head. [Means for solving the problem]

[0006] The printing device of the present disclosure includes a plurality of ejection heads each having a nozzle row made up of a plurality of nozzles that eject droplets onto a print medium, a transport device that transports the print medium in a transport direction, a position adjustment device that adjusts the position of each of the ejection heads in an intersecting direction that intersects the transport direction, and a control device, wherein some of the nozzles in one of the ejection heads and some of the nozzles in another of the ejection heads adjacent to the one of the ejection heads as viewed along the intersecting direction are arranged to overlap in a predetermined overlapping region as viewed along the transport direction, and the control device controls the position adjustment device. Therefore, the system executes a position change process that changes the relative position between the one ejection head and the other ejection head in the intersecting direction, a test pattern formation process that is executed each time the relative position changes and that forms a test pattern by ejecting droplets onto the printing medium from at least some of the nozzles in the overlapping region of the other ejection head and some of the nozzles in the overlapping region of the one ejection head, and a process that determines the optimal relative position between the one ejection head and the other ejection head in the intersecting direction based on the density of each of the test patterns obtained by scanning.

[0007] According to the present disclosure, a test pattern is formed for each relative position in the intersecting direction between one ejection head and the other ejection heads. Then, an optimal relative position in the intersecting direction between one ejection head and the other ejection heads is determined based on the density of each test pattern obtained by scanning. Because the density of each test pattern obtained by scanning is not significantly affected by the reading accuracy of the scan, the optimal relative position determined based on the density is an appropriate relative position. This sufficiently reduces deviations in the landing positions of droplets due to misalignment of the other ejection heads relative to the one ejection head. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a printing device that can suppress deviation in the landing position of droplets caused by deviation in the position of one ejection head relative to another ejection head. [Brief explanation of the drawings]

[0009] [Figure 1] 1 illustrates a printing system including a printing device and a scanner according to an embodiment. [Figure 2] FIG. 2 is a block diagram illustrating example components of the printing device of FIG. 1. [Figure 3] FIG. 2 is a bottom view showing the configuration of the line head of FIG. [Figure 4] FIG. 2 is a diagram showing a nozzle row in the ejection head. [Figure 5] 4 is a partially enlarged detailed view of FIG. 3, showing the nozzle in a predetermined overlap region, from below. [Figure 6] 6A to 6C are diagrams showing the degree of overlap between ink droplets ejected onto a print medium. [Figure 7] FIG. 10 is a diagram showing the relationship between the position of the ejection head in the intersecting direction and the density of the ink droplets. [Figure 8] 10A and 10B are diagrams showing the density difference between large droplets at a certain position in the intersecting direction when different test patterns are formed, and the density difference between small droplets at the same position when different test patterns are formed. DETAILED DESCRIPTION OF THE INVENTION

[0010] A printing device according to an embodiment of the present disclosure will be described below with reference to the drawings. The printing device described below is merely one embodiment of the present disclosure. Therefore, the present disclosure is not limited to the following embodiment, and additions, deletions, and modifications are possible within the scope of the present disclosure.

[0011] FIG. 1 is a diagram showing a printing system 200 including a printing device 100 and a scanner 150 according to one embodiment. The printing device 100 in this embodiment is a line head type. In FIG. 1, directions that are perpendicular to each other are referred to as a first direction Df and a second direction Ds. In this embodiment, the first direction Df corresponds to the transport direction of the print medium W, and the second direction Ds corresponds to the intersecting direction that is perpendicular to the transport direction. Hereinafter, Df will be referred to as the transport direction, and Ds will be referred to as the intersecting direction.

[0012] 1, the printing apparatus 100 includes a line head group 70, a pair of transport rollers 60, a platen 61, a plurality of storage tanks 62, and a plurality of tubes 63. The scanner 150 will be described later.

[0013] The line head group 70 has a plurality of line heads 71, for example, five line heads 71. The line heads 71 ​​are provided corresponding to the ink colors. The line heads 71 ​​are arranged side by side at approximately equal intervals in the transport direction Df. The line heads 71 ​​extend in the intersecting direction Ds. The line heads 71 ​​are provided with a plurality of ejection heads 10 (FIG. 3), which will be described later.

[0014] The platen 61 supports from below the print medium W. For example, the platen 61 has a predetermined thickness and is made of a rectangular plate material with the transport direction Df as its longitudinal direction.

[0015] The pair of transport rollers 60 extend in the cross direction Ds. The dimension of the transport roller 60 in the cross direction Ds is larger than the dimension of the print medium W in the cross direction Ds. One of the pair of transport rollers 60 is connected to a transport motor 33 (FIG. 2) described below, and is arranged on one side (e.g., the front) of the platen 61 in the transport direction Df. The other of the pair of transport rollers 60 is arranged on the other side (e.g., the rear) of the platen 61 in the transport direction Df. When the transport motor 33 is driven, the transport roller 60 rotates, thereby transporting the print medium W on the platen 61 in the transport direction Df. In this embodiment, the print medium W is transported from the front to the rear.

[0016] Ink is stored in the storage tanks 62. A storage tank 62 is provided for each type of ink. For example, five storage tanks 62 are provided, each storing black, yellow, cyan, magenta, and white ink. A color image is printed by ejecting ink droplets of the four colors of black, yellow, cyan, and magenta onto the print medium W. A base is formed by ejecting white ink droplets onto the print medium W.

[0017] The tube 63 is provided corresponding to the storage tank 62. The tube 63 connects the storage tank 62 and the plurality of ejection heads 10 provided in the line head 71.

[0018] Fig. 2 is a block diagram showing an example of components of the printing device 100 of Fig. 1. As shown in Fig. 2, the printing device 100 includes operation keys 4, a display unit 5, a controller unit 19, a reading device 26, a motor driver IC 30, a head driver IC 31, an irradiation device driver IC 32, a conveyance motor 33, a position adjustment driver IC 34, an ultraviolet irradiation device 40, and a position adjustment device 41. The conveyance motor 33 and the conveyance roller 60 correspond to the conveyance device.

[0019] The operation keys 4 accept operation inputs from the user. The display unit 5 is configured, for example, as a touch panel, and displays predetermined information. Part of the display unit 5 also functions as an operation key. The controller unit 19 realizes the printing function based on inputs from the operation keys 4 or external inputs via a communication interface (not shown), and also controls the display of the display unit 5.

[0020] The controller unit 19 has a control device 20 configured by a CPU, storage units (ROM 21, RAM 22, EEPROM 23, HDD 24), and an ASIC 25. The control device 20 is connected to the storage units and controls the driver ICs 30 to 32, 34, the display unit 5, and the reading device 26.

[0021] The control device 20 performs various functions by executing predetermined processing programs stored in the ROM 21. The control device 20 may be implemented as a single processor in the controller unit 19, or may be implemented as multiple processors cooperating with each other. The processing programs are read by the reading device 26 from a computer-readable recording medium KB such as a magneto-optical disk or a USB flash memory, and stored in the ROM 21. The RAM 22 stores image data received from the outside and calculation results of the control device 20. The EEPROM 23 stores various initial setting information input by the user. The HDD 24 stores various information.

[0022] A motor driver IC 30, a head driver IC 31, an irradiation device driver IC 32, and a position adjustment driver IC 34 are connected to the ASIC 25. When the control device 20 receives a print job from a user, it outputs a print command to the ASIC 25 based on a processing program. The ASIC 25 controls the driver ICs 30 to 32, 34 based on the print command. The control device 20 moves the platen 61 in the transport direction Df by driving the transport motor 33 using the motor driver IC 30.

[0023] The control device 20 converts image data acquired from an external device or the like into ejection data for ejecting ink droplets onto the print medium W. Based on the converted ejection data, the control device 20 controls the head driver IC 31 to eject ink droplets from the ejection head 10 onto the print medium W. The control device 20 also controls the irradiation device driver IC 32 to irradiate ultraviolet light from a light-emitting diode chip provided in the ultraviolet irradiation device 40. The ink droplets ejected onto the print medium W are cured by the ultraviolet light emitted by the ultraviolet irradiation device 40. For example, the ultraviolet irradiation device 40 is disposed between one line head 71 and another line head 71 in the transport direction Df. The control device 20 also drives the position adjustment device 41 using the position adjustment driver IC 34 to move the ejection head 10 in the intersecting direction Ds. The position adjustment device 41 includes an electric motor (not shown) and a mechanism such as a ball screw or rack and pinion (not shown) that connects the electric motor to the ejection head 10.

[0024] Fig. 3 is a bottom view showing the configuration of the line head 71. Fig. 4 is a bottom view showing the arrangement of the nozzles Nz in the ejection head 10.

[0025] 3, the line head 71 is provided with ten ejection heads 10 as an example of the plurality of ejection heads 10. As the ejection heads 10, for example, inkjet heads that eject droplets of ultraviolet curable ink, for example, can be used. However, the ejection heads 10 are not limited to those described above.

[0026] Of the ten ejection heads 10, five are arranged upstream in the transport direction Df, and the remaining five are arranged downstream in the transport direction Df. The upstream ejection heads 10 include ejection heads 111, 113, 115, 117, and 119. The downstream ejection heads 10 include ejection heads 112, 114, 116, 118, and 120. The upstream ejection heads 10 are arranged at approximately equal intervals. The downstream ejection heads 10 are arranged at approximately equal intervals and are shifted a predetermined distance in the intersecting direction Ds from the upstream ejection heads 10. That is, the multiple ejection heads 10 in the line head 71 are arranged in a staggered pattern in the intersecting direction Ds.

[0027] As shown in FIG. 4, the ejection head 10 is provided with a plurality of nozzles 121. The nozzles 121 are arranged regularly in the ejection head 10. Specifically, the nozzles 121 are arranged at approximately equal intervals in both the transport direction Df and the intersecting direction Ds. A plurality of nozzles Nz are arranged side by side in the nozzle row direction Dn to form a nozzle row NL. In other words, the nozzle row NL extends in the nozzle row direction Dn. The nozzle row direction Dn is a direction parallel to the transport direction Df. A plurality of nozzle rows NL are provided, and the nozzle rows NL are arranged at approximately equal intervals in the intersecting direction Ds.

[0028] The arrangement of the nozzles Nz in one ejection head 10 adjacent to each other in the transport direction Df and the arrangement of the nozzles Nz in the other ejection head 10 will be described below. Fig. 5 is a partially enlarged detailed view of Fig. 3, showing the nozzles Nz in a predetermined overlap region RL from below. Figs. 6A to 6C are diagrams showing the degree of overlap between ink droplets Id ejected onto the print medium W. Fig. 7 is a diagram showing the relationship between the position of the ejection head 10 in the intersecting direction Ds and the density of the ink droplets.

[0029] In the following, the arrangement of the nozzles Nz in the ejection head 112 as one of the ejection heads 10 and the arrangement of the nozzles Nz in the ejection head 113 as the other of the ejection heads 10 will be described as examples.

[0030] 5, some nozzles Nza of the plurality of nozzles Nz in ejection head 112 as an example of one ejection head 10 and some nozzles Nza of the plurality of nozzles Nz in ejection head 113 as an example of another ejection head 10 adjacent to ejection head 112 as viewed along the intersecting direction Ds are arranged so as to overlap in a predetermined overlapping region RL as viewed along the transport direction Df. That is, one nozzle Nza in ejection head 113 is arranged upstream (forward) in the transport direction Df with respect to one nozzle Nza in ejection head 112. In this case, the position of one nozzle Nza in ejection head 113 (i.e., the position of the region occupied by one nozzle Nza) may partially or completely overlap in the transport direction Df with the position of one nozzle Nza in ejection head 112 (i.e., the position of the region occupied by one nozzle Nza).

[0031] The number of nozzles Nza in the overlapping region RL of ejection head 112, which is an example of one ejection head 10, is four or more. In FIG. 5, the number of nozzles Nza in ejection head 112 is four. The number of nozzles Nza in the overlapping region RL of ejection head 113, which is an example of another ejection head 10, is four or more. In FIG. 5, the number of nozzles Nza in ejection head 113 is four. Note that similar nozzles Nza are provided in the overlapping region RL of ejection heads 10 other than the ejection heads 112 and 113 given as examples.

[0032] In this configuration, the control device 20 executes a position change process to change the relative position in the intersecting direction Ds between one ejection head 10 and another ejection head 10 using the position adjustment device 41. The relative position in the intersecting direction Ds between one ejection head 10 and another ejection head 10 refers to the position of the other ejection head 10 in relation to the one ejection head 10 in the intersecting direction Ds, or the position of the one ejection head 10 in relation to the other ejection head 10 in the intersecting direction Ds. When changing the relative position, the control device 20 moves the ejection head 10, for example, by dividing a distance equivalent to one nozzle in the intersecting direction Ds into multiple steps.

[0033] In this case, the control device 20 may move only one of the ejection heads 10 in the intersecting direction Ds relative to the other ejection heads 10, or may move only the other ejection heads 10 in the intersecting direction Ds relative to the one ejection head 10. Alternatively, the control device 20 may move one of the ejection heads 10 in the intersecting direction Ds relative to the other ejection heads 10, and may also move the other ejection heads 10 in the intersecting direction Ds relative to the one ejection head 10. In this way, the control device 20 changes the relative position of the one ejection head 10 and the other ejection heads 10 in the intersecting direction Ds multiple times.

[0034] The control device 20 executes the test pattern formation process each time the relative positions of one ejection head 10 and another ejection head 10 in the intersecting direction Ds change. In the test pattern formation process, the control device 20 ejects ink droplets onto the print medium W from at least some of the nozzles Nza in the overlapping region RL of the other ejection heads 10 and some of the nozzles Nza in the overlapping region RL of the one ejection head 10, thereby forming a test pattern. In this case, when executing the test pattern formation process, the control device 20 may eject ink droplets from the nozzles Nz of the one ejection head 10 other than the nozzle Nza, or may eject ink droplets from the nozzles Nz of the other ejection heads 10 other than the nozzle Nza. Furthermore, the test pattern in the test pattern formation process may be, for example, a line pattern (band-shaped pattern) extending in the transport direction Df, or may be a pattern other than the line pattern.

[0035] If the ejection head 10 is an ejection head that ejects ultraviolet-curable ink droplets as liquid droplets, the control device 20 hardens the ink droplets ejected onto the print medium W from some of the nozzles Nza of one ejection head 10 during the test pattern formation process with ultraviolet light from the ultraviolet irradiation device 40. Thereafter, the control device 20 ejects ink droplets onto the print medium W from some of the nozzles Nza of another ejection head 10. Then, the control device 20 hardens the ink droplets ejected onto the print medium W from some of the nozzles Nza of another ejection head 10 with ultraviolet light from the ultraviolet irradiation device 40. This makes it difficult for the ink droplets ejected onto the print medium W to spread.

[0036] In this embodiment, the scanner 150 reads the test pattern on the print medium W and generates scan data. In this case, the print medium W on which the test pattern is formed may be carried by the user to the scanner 150. Alternatively, in this embodiment, the scanner 150 in the printing system 200 is separate and independent from the printing device 100, but this is not limited to this. The printing device 100 may also be equipped with a scanner function. In this case, the print medium W on which the test pattern is formed is automatically read by the scanner. In this way, the control device 20 obtains scan data of each test pattern corresponding to each of the above-mentioned relative positions by scanning with the scanner 150.

[0037] Next, the control device 20 executes a process for determining the optimal relative position of one ejection head 10 and another ejection head 10 in the intersecting direction Ds based on the density of each test pattern obtained by scanning with the scanner 150. Here, if the position of one nozzle Nza of one ejection head 10 relative to one nozzle Nza of another ejection head 10 in the intersecting direction Ds is separated, as shown in FIG. 6A, the ink droplets Id ejected onto the print medium W do not overlap. Therefore, the density of the test pattern formed by the ink droplets is relatively low. On the other hand, if the position of one nozzle Nza of one ejection head 10 relative to one nozzle Nza of another ejection head 10 in the intersecting direction Ds is close to each other, the ink droplets Id ejected onto the print medium W overlap as shown in FIGS. 6B and 6C. Therefore, the density of the test pattern formed by the ink droplets is relatively high. In this way, the relative position of one ejection head 10 and another ejection head 10 in the intersecting direction Ds can be determined from the density of the test pattern.

[0038] In this embodiment, the control device 20 determines as the optimal relative position Pb the relative position in the intersecting direction Ds between one ejection head 10 and another ejection head 10 when performing a test pattern formation process corresponding to the test pattern with the lowest density among the test patterns, as shown in Figure 7. This is intended to ensure that the overlap between ink droplets Id is minimized (or no overlap occurs) when the density in the test pattern is at its lowest value. In this case, the control device 20 may calculate the average density of the entire test pattern as the above density in the test pattern.

[0039] FIG. 8 is a diagram showing the density difference between large droplets at a certain position in the cross direction Ds when different test patterns are formed, and the density difference between small droplets at the same position when different test patterns are formed.

[0040] The control device 20 can cause the ejection head 10 to eject any of large droplets, medium droplets, and small droplets as ink droplets in the test pattern formation process. In this embodiment, the control device 20 causes the ejection head 10 to eject large droplets as ink droplets in the test pattern formation process. This is based on the technical viewpoint that, as shown in Fig. 8, the density difference between the density of a test pattern formed by a test pattern formation process corresponding to one of the above relative positions and the density of a test pattern formed by a test pattern formation process corresponding to another of the above relative positions is such that large droplets appear larger than small droplets (or medium droplets) at a certain position P1.

[0041] Here, the control device 20 determines whether the density difference is smaller than a threshold value. If the density difference is smaller than the threshold value, the control device 20 causes the ejection head 10 to eject medium or small ink droplets instead of the large ink droplets as ink droplets in the test pattern formation process executed at a relative position different from the one relative position and the other relative position. In this case, the density difference may become smaller than the threshold value due to overlapping of ink droplets ejected from the nozzles Nza of one ejection head 10 and ink droplets ejected from the nozzles Nza of the other ejection head 10 in two different test pattern formation processes. In such a case, small ink droplets or the like are ejected again as ink droplets at the relative positions in each of the test pattern formation processes. This makes it easier to produce the density difference in cases where ink droplets overlap and the density difference is not significant.

[0042] As described above, according to the printing device 100 of this embodiment, a test pattern is formed for each relative position in the intersecting direction Ds between one ejection head 10 and another ejection head 10. Then, an optimal relative position Pb between one ejection head 10 and another ejection head 10 in the intersecting direction Ds is determined based on the density of each test pattern obtained by scanning. Because the density of each test pattern obtained by scanning is thus not significantly affected by the reading accuracy of the scan, the optimal relative position Pb determined based on the density is an appropriate relative position. This makes it possible to sufficiently suppress deviations in the landing positions of ink droplets caused by deviations in the position of another ejection head 10 relative to the one ejection head 10.

[0043] Furthermore, in this embodiment, the control device 20 determines as the optimal relative position Pb the relative position in the intersecting direction Ds between one ejection head 10 and another ejection head 10 when executing the test pattern formation process corresponding to the test pattern with the lowest density among the test patterns. In this case, the overlap of the ink droplet landing positions is smallest when the test pattern has the lowest density. This increases the reliability of determining the relative position corresponding to the test pattern in such a case as the optimal relative position Pb.

[0044] Furthermore, in this embodiment, if the ejection head 10 is an ejection head that ejects ultraviolet-curable ink droplets as liquid droplets, the control device 20 causes the ultraviolet irradiation device 40 to harden the ink droplets ejected onto the print medium W in the test pattern formation process. By hardening the ink droplets in this way, the ink droplets become less likely to spread (i.e., the landing positions of the ink droplets become less likely to fluctuate), and therefore fluctuations in the density of the test pattern become less likely to occur.

[0045] Furthermore, in this embodiment, the control device 20 causes the ejection head 10 to eject large, medium, or small ink droplets during the test pattern formation process. This broadens the range of ink droplet sizes available, allowing the user to set the ink droplet size to a desired size when forming a test pattern.

[0046] Furthermore, in this embodiment, the control device 20 executes the following process when the density difference between the density of the test pattern formed by the test pattern formation process corresponding to one of the above relative positions and the density of the test pattern formed by the test pattern formation process corresponding to another of the above relative positions is smaller than a threshold value. That is, in the test pattern formation process executed at a relative position different from the one relative position and the other relative position, the control device 20 causes the ejection head 10 to eject medium or small ink droplets instead of large ink droplets. In this way, by using medium or small ink droplets, the density difference is more likely to occur. This increases the reliability of the optimal relative position Pb determined based on the density difference.

[0047] In this embodiment, the number of nozzles Nza in the overlapping region RL of the ejection head 112 is four or more. The number of nozzles Nza in the overlapping region RL of the ejection head 113 is four or more. In this case, the dimension of the test pattern in the cross direction Ds can be increased to increase the area of ​​the test pattern. This makes it easier for a difference in density to occur between the test pattern corresponding to one relative position and the test pattern corresponding to another relative position.

[0048] Furthermore, in this embodiment, the control device 20 may calculate the average density of the entire test pattern as the above-mentioned density of the test pattern. The landing position of ink droplets tends to shift due to manufacturing variations in the ejection head 10, etc. According to the above configuration, by using the average density of the entire test pattern as the density of the test pattern, it is possible to determine an optimal relative position Pb that is less susceptible to the effects of manufacturing variations in the ejection head 10, etc.

[0049] Although several modified examples have been described above, the following modified examples can also be adopted without departing from the gist of the present disclosure.

[0050] In the above embodiment, the control device 20 may alternately set the nozzles Nza in the overlapping region RL of one ejection head 10 that eject ink droplets in the test pattern formation process in the intersecting direction Ds, and may alternately set the nozzles Nza in the overlapping region RL of another ejection head 10 that eject ink droplets in the intersecting direction Ds. In this case, the positions of the alternate nozzles Nza in the overlapping region RL of the other ejection head 10 may or may not overlap with the positions of the alternate nozzles Nza in the overlapping region RL of the first ejection head 10 in the intersecting direction Ds. This configuration reduces the possibility of one dot ejected from one ejection head 10 at the initial relative position overlapping with another dot ejected from another ejection head 10. This makes it easier for a difference (density difference) to occur between the density of the test pattern corresponding to the initial relative position and the density of the test pattern corresponding to the changed relative position. This increases the reliability of the optimal relative position determined based on the density difference.

[0051] Furthermore, in the above embodiment, multiple line heads 71 ​​are provided, but this is not limiting, and there may be only one line head 71. Alternatively, there may be only multiple ejection heads 10, without providing a line head 71 itself. Furthermore, although ten ejection heads 10 are provided, the number of ejection heads 10 may be any number other than ten.

[0052] Furthermore, in the above embodiment, a color image is printed by ejecting ink droplets of four colors, black, yellow, cyan, and magenta, onto the print medium W, and a base is formed by ejecting white ink droplets onto the print medium W, but this is not limited to this. A configuration for ejecting other inks, such as clear ink, onto the print medium W in addition to the above inks may be added to the printing device 100. [Explanation of symbols]

[0053] 10 Discharge head 20 Control device 33 Transport motor 40 Ultraviolet irradiation device 41 Position adjustment device 60 Conveyor roller 100 Printing equipment 150 scanner 200 Printing System Df Conveying direction Ds cross direction NL nozzle row Nz nozzle Pb optimum relative position RL overlap area W Printing medium

Claims

1. a plurality of ejection heads each having a nozzle row made up of a plurality of nozzles that eject droplets onto a print medium; a conveying device that conveys the print medium in a conveying direction; a position adjustment device for adjusting the position of each of the ejection heads in a direction intersecting the transport direction; a control device; some of the nozzles in one of the ejection heads and some of the nozzles in another of the ejection heads adjacent to the one of the ejection heads as viewed along the intersecting direction are arranged to overlap in a predetermined overlapping region as viewed along the transport direction, The control device a position change process in which the position adjustment device changes the relative position of the one ejection head and the other ejection head in the intersecting direction; a test pattern forming process that is executed each time the relative positions are different, and that forms a test pattern by ejecting the liquid droplets onto the print medium from at least some of the nozzles in the overlapping region of the other ejection head and some of the nozzles in the overlapping region of the one ejection head; and determining an optimum relative position between the one ejection head and the other ejection head in the intersecting direction based on the density of each of the test patterns obtained by scanning.

2. The printing device according to claim 1 , wherein the control device determines, as the optimum relative position, the relative position when the test pattern forming process corresponding to the test pattern with the lowest density among the test patterns is executed.

3. the ejection head ejects ultraviolet-curable ink droplets as the droplets, further comprising an ultraviolet irradiation device for curing the ink droplets, 2. The printing device according to claim 1, wherein the control device hardens the ink droplets ejected from the nozzles of one of the ejection heads using the ultraviolet irradiation device during the test pattern formation process, and then ejects the ink droplets from the nozzles of the other ejection head.

4. The printing device according to claim 1 , wherein the control device controls the ejection head to eject one of large droplets, medium droplets, and small droplets as the droplets.

5. The printing device described in claim 4, wherein when a density difference, which is the difference between the density of the test pattern formed by the test pattern formation process corresponding to one of the relative positions and the density of the test pattern formed by the test pattern formation process corresponding to another of the relative positions, is smaller than a threshold value, the control device ejects the medium droplets or the small droplets as the droplets from the ejection head in the test pattern formation process performed at a relative position different from the one relative position and the other relative position.

6. The printing device described in claim 4, wherein, in the test pattern formation process, the control device sets the nozzles that eject the droplets among the portion of the nozzles in the overlapping area of ​​the one ejection head to be alternate in the intersecting direction, and sets the nozzles that eject the droplets among the portion of the nozzles in the overlapping area of ​​the other ejection head to be alternate in the intersecting direction.

7. The printing device according to claim 1 , wherein the number of nozzles in the overlapping region of the one ejection head is four or more, and the number of nozzles in the overlapping region of the other ejection head is four or more.

8. The printing device according to claim 2 , wherein the control device calculates an average density of the entire test pattern as the density of the test pattern.

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