Droplet dispensing control device

Abstract

To provide a droplet discharge control device which can suppress lowering of image property of a joint part between inkjet heads.SOLUTION: A droplet discharge control device includes a line head in which a plurality of inkjet heads 16 where nozzles for discharging droplet to a predetermined discharge object are arranged in a vertical direction are arranged in a vertical direction, and a control part 50 for controlling the discharge of the droplet from the nozzles, wherein the control part 50 controls the inkjet heads 16 adjacent to each other in the vertical direction to reduce a discharge amount of at least the one nozzle of a joint part between the inkjet heads 16 on the upper side in the vertical direction, and to increase a discharge amount of at least the one nozzle of a joint part of the inkjet heads 16 on the lower side in the vertical direction.SELECTED DRAWING: Figure 6

Description

TECHNICAL FIELD

[0001] The present invention relates to a droplet ejection control apparatus that ejects droplets from a plurality of nozzles arranged in a vertical direction. BACKGROUND ART

[0002] Conventionally, inkjet printing apparatuses that perform printing by ejecting ink onto a printing medium have been proposed.

[0003] As inkjet printing apparatuses, not only inkjet printing apparatuses that eject ink from above in the vertical direction onto a printing medium arranged such that the printing surface is horizontal, but also inkjet printing apparatuses that perform printing by ejecting ink from a direction perpendicular to the printing surface onto a printing medium arranged such that the printing surface is in a direction other than horizontal have been proposed.

[0004] For example, Patent Document 1 and Patent Document 2 propose inkjet printing apparatuses that perform printing by ejecting ink in a horizontal direction onto a vertically oriented printing surface.

[0005] In Patent Document 1, it is proposed that a common liquid chamber in one inkjet head is divided in the longitudinal direction, and sub-tanks communicating with each of the divided common liquid chambers are provided, so that the hydraulic head pressure applied to the nozzles in one inkjet head is made substantially uniform to stabilize ejection.

[0006] Further, in Patent Document 2, it is proposed that sub-tanks communicating with each of a plurality of vertically arranged inkjet heads are provided, so that the hydraulic head pressure applied to each inkjet head is made uniform to stabilize ejection. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0007] PATENT DOCUMENT 1 Japanese Unexamined Patent Application Publication No. 2006-240022 [Patent Document 2] Patent No. 3909443 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, Patent Document 1 does not consider the ejection from nozzles at the joints between divided common liquid chambers, and Patent Document 2 does not consider the ejection from nozzles at the joints between inkjet heads. In other words, regardless of whether Patent Document 1 or Patent Document 2 is used, a pressure difference between nozzles due to the difference in water head within a single inkjet head remains. As a result, as shown in Figure 9, the drop distance of ink ejected from the upper vertical nozzle within a single inkjet head will differ from the drop distance of ink ejected from the lower vertical nozzle. This difference in drop distance becomes more pronounced as the distance between the inkjet head and the printing medium (head gap) increases. Note that, as shown in Figure 9, the drop distance tends to decrease as the number of ink drops increases.

[0009] Therefore, in the case of an inkjet printing device in which multiple inkjet heads are arranged vertically, as shown in Figure 10, at the joints between the inkjet heads, the nozzle at the lower end of the upper inkjet head 100 and the nozzle at the upper end of the lower inkjet head 101 are adjacent, and there are places where the difference in pressure between adjacent nozzles is large.

[0010] In such cases, if ink is ejected horizontally from the nozzle at the joint, differences in nozzle pressure will cause differences in the distance the ink travels upon impact with the printing medium. If the pressure difference between adjacent nozzles at the joint is large, white streaks will appear at the joint, leading to a decrease in image quality.

[0011] In view of the above circumstances, the present invention aims to provide a droplet ejection control device that can suppress the deterioration of image quality at the joints between inkjet heads as described above. [Means for solving the problem]

[0012] The first droplet dispensing control device of the present invention comprises a head unit having a plurality of nozzle groups arranged vertically, each having a plurality of nozzles arranged vertically for dispensing droplets onto a predetermined target, and a control unit for controlling the dispensing of droplets from the nozzles. The control unit controls the nozzles to decrease the dispensing amount of at least one nozzle at the joint portion of the vertically adjacent nozzle group and to increase the dispensing amount of at least one nozzle at the joint portion of the vertically lower nozzle group for vertically adjacent nozzle groups.

[0013] The second droplet ejection control device of the present invention comprises a head unit having a plurality of nozzle groups arranged vertically, each having a plurality of nozzles for ejecting droplets arranged vertically, and a control unit that controls the ejection of droplets from the nozzles based on dot data, wherein the control unit shifts the dot data for controlling the vertically adjacent nozzle group from the vertically upper nozzle group to the vertically lower nozzle group, or shifts the dot data for controlling the vertically lower nozzle group to the vertically upper nozzle group. [Effects of the Invention]

[0014] According to the first droplet ejection control device of the present invention, the ejection amount of at least one nozzle at the joint portion of the upper vertical nozzle group is reduced, and the ejection amount of at least one nozzle at the joint portion of the lower vertical nozzle group is increased, thereby suppressing a decrease in image quality at the joint portions between nozzle groups.

[0015] According to the second droplet ejection control device of the present invention, the dot data for controlling the upper nozzle group in the vertical direction is shifted to the dot data side for controlling the lower nozzle group in the vertical direction, or the dot data for controlling the lower nozzle group in the vertical direction is shifted to the dot data side for controlling the upper nozzle group in the vertical direction, thereby suppressing a decrease in image quality at the joints between nozzle groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] [Figure 1] External perspective view showing the schematic configuration of the main body of an inkjet printing apparatus using one embodiment of the droplet discharge control device of the present invention [Figure 2] Diagram showing an example of six inkjet heads included in a line head [Figure 3] Block diagram showing the configuration of the control system of the inkjet printing apparatus shown in Figure 1 [Figure 4] Diagram showing the schematic configuration of the ink circulation unit and the ink supply unit [Figure 5] Diagram for explaining the ink discharge control of nozzles at the joint portion before the ink amount control [Figure 6] Diagram for explaining an example of control of the ink discharge amount discharged from the nozzles at the joint portion [Figure 7] External perspective view showing the schematic configuration of the main body of an inkjet printing apparatus provided with a distance measurement unit [Figure 8] Diagram for explaining the shift of ink dot data of the upper inkjet head [Figure 9] Diagram for explaining the difference in falling distance of ink droplets discharged from the vertically upper nozzles and the vertically lower nozzles in one inkjet head [Figure 10] Diagram for explaining the state where the nozzles at the lower end portion of the upper inkjet head and the nozzles at the upper end portion of the lower inkjet head are adjacent to each other MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, an inkjet printing apparatus using an embodiment of the droplet discharge control device of the present invention will be described in detail with reference to the drawings. Although the inkjet printing apparatus of the present embodiment is characterized by ink discharge control, the overall configuration of the inkjet printing apparatus will first be described. FIG. 1 is an external perspective view showing a schematic configuration of an inkjet printing apparatus main body 1. In the description of the embodiment shown below, the up, down, left, right, front and rear directions indicated by arrows in FIG. 1 are defined as the up, down, left, right, front and rear directions of the inkjet printing apparatus main body 1. Further, the up-down direction of the inkjet printing apparatus main body 1 is the vertical direction.

[0018] As shown in FIG. 1, the inkjet printing apparatus main body 1 includes a head unit 10 and a conveyance unit 2.

[0019] The conveyance unit 2 conveys the print medium P in the direction of the arrow shown in FIG. 1. As the print medium P, for example, a three-dimensional object (for example, a box body such as a corrugated cardboard box) having a printing surface Ps erected in a direction perpendicular to the conveyance surface as shown in FIG. 1 is used. In the present embodiment, the print medium P corresponds to the discharge target of the present invention.

[0020] The conveyance unit 2 includes a support base 3 and a conveyance belt portion 4. The support base 3 is a base that supports the conveyance belt portion 4.

[0021] The conveyance belt portion 4 includes two platen rollers extending in a direction orthogonal to the conveyance direction of the print medium P, a conveyance belt, and the like. The two platen rollers are arranged spaced apart and parallel to each other in the conveyance direction of the print medium P. An endless conveyance belt is stretched between the two platen rollers arranged in parallel. The platen rollers rotate under the control of a control unit 50 to be described later to move the conveyance belt, whereby the print medium P is conveyed.

[0022] The head unit 10 performs printing by discharging ink onto the printing surface Ps of the print medium P conveyed by the conveyance unit 2.

[0023] As shown in Figure 1, the head unit 10 has four line heads 11, 12, 13, and 14. The four line heads 11 to 14 extend vertically and are arranged parallel to the transport direction of the printing medium P. In this embodiment, each of the line heads 11 to 14 corresponds to the head portion of the present invention.

[0024] The four line heads 11-14 eject C (cyan), M (magenta), Y (yellow), and K (black) inks, respectively.

[0025] As shown in Figure 2, line heads 11 to 14 of this embodiment each have six inkjet heads 16a to 16f. The six inkjet heads 16a to 16f are arranged so that their ink ejection surfaces are vertical (perpendicular to the transport surface of the transport unit 2). The ink ejection surface is the surface on which the nozzle ejection openings are located. Hereinafter, any of the six inkjet heads 16a to 16f may simply be referred to as inkjet head 16.

[0026] Furthermore, the six inkjet heads 16a to 16f are arranged in a vertical line. Also, the six inkjet heads 16a to 16f are arranged in a staggered pattern. As shown in Figure 2, in this embodiment, some nozzles of vertically adjacent inkjet heads are arranged to overlap in the transport direction (front-to-back direction). Note that vertically adjacent inkjet heads are those that are closest to each other in the vertical direction, and in this embodiment, these are inkjet head 16a and inkjet head 16b, inkjet head 16b and inkjet head 16c, inkjet head 16c and inkjet head 16d, and inkjet head 16d and inkjet head 16f.

[0027] Each inkjet head 16 ejects ink supplied from the ink circulation unit 20, which will be described later.

[0028] Each inkjet head 16a to 16f has an ink chamber (not shown) for storing ink and a plurality of nozzles (not shown) for ejecting ink. A piezoelectric element (not shown) is placed inside the ink chamber. Ink is ejected from the nozzles by driving the piezoelectric element.

[0029] As described above, a vertically extending straight line is printed by ejecting ink from the six inkjet heads 16a to 16f. The control of ink ejection from each inkjet head 16a to 16f will be described in detail later.

[0030] Figure 3 is a block diagram showing the configuration of the control system of the inkjet printing apparatus according to this embodiment. The control unit 50 includes a CPU (Central Processing Unit) and storage media such as semiconductor memory and a hard disk, and controls the entire inkjet printing apparatus. The control unit 50 controls the operation of each part of the inkjet printing apparatus by executing a control program pre-stored in the storage media such as the semiconductor memory or hard disk, and by operating electrical circuits.

[0031] Furthermore, the control unit 50 generates ink dot data based on the image data to be printed, and controls the inkjet heads 16a to 16f of each line head 11 to 14 based on that ink dot data. Ink dot data is data that defines the number of ink drops ejected from one nozzle to form one dot. In this embodiment, the ink dot data corresponds to the dot data of the present invention.

[0032] Furthermore, the inkjet printing apparatus of this embodiment includes an ink circulation unit 20 connected to each line head 11 to 14, and an ink supply unit 40 connected to the ink circulation unit 20.

[0033] Figure 4 shows the ink circulation unit 20 connected to two inkjet heads 16a and 16b, out of the six inkjet heads 16a to 16f of the line head 11, and the ink supply unit 40 connected to the ink circulation unit 20. Although Figure 4 only shows the inkjet heads 16a and 16b, in this embodiment, an ink circulation unit 20 and an ink supply unit 40 are provided for each pair of inkjet heads 16. That is, an ink circulation unit 20 and an ink supply unit 40 are provided for each pair of inkjet heads 16c and 16d, and for each pair of inkjet heads 16e and 16f. Similarly, for line heads 12 to 14 other than line head 11, an ink circulation unit 20 and an ink supply unit 40 are provided for each pair of inkjet heads 16.

[0034] The ink circulation unit 20 supplies ink to the inkjet heads 16a and 16b while circulating the ink. The ink circulation unit 20 comprises a pressurized tank 21, a distributor 22, a collector 23, a negative pressure tank 24, an ink pump 25, an ink temperature adjustment unit 26, an ink temperature sensor 27, and ink circulation pipes 28 to 30.

[0035] The pressurized tank 21 stores the ink supplied to the inkjet heads 16a and 16b. The ink in the pressurized tank 21 is supplied to the inkjet heads 16a and 16b via the ink circulation pipe 28 and the distributor 22. An air layer 31 is formed above the liquid surface of the ink inside the pressurized tank 21. The air layer 31 in the pressurized tank 21 is connected to the pressure application unit 5, which will be described later, via the pressurized communication pipe 58, which will be described later. The pressurized tank 21 is positioned lower (below) the line heads 11 to 14.

[0036] The distributor 22 distributes the ink supplied from the pressurized tank 21 via the ink circulation pipe 28 to the inkjet heads 16a and 16b.

[0037] The collector 23 collects any ink that was not consumed by the inkjet heads 16a and 16b. The ink collected by the collector 23 flows to the negative pressure tank 24 via the ink circulation pipe 29.

[0038] The negative pressure tank 24 receives and stores ink that was not consumed by the inkjet heads 16a and 16b from the collector 23 via the ink circulation pipe 29. The negative pressure tank 24 also stores ink supplied from the ink cartridge 46 of the ink supply unit 40, which will be described later. An air layer 36 is formed above the liquid surface of the ink inside the negative pressure tank 24. The air layer 36 of the negative pressure tank 24 is connected to the pressure application unit 5 via the negative pressure communication pipe 59, which will be described later. The negative pressure tank 24 is positioned at the same height as the pressurized tank 21.

[0039] The ink pump 25 delivers ink from the negative pressure tank 24 to the pressurized tank 21. The ink pump 25 is located in the middle of the ink circulation pipe 30.

[0040] The ink temperature adjustment unit 26 adjusts the temperature of the ink in the ink circulation unit 20. The ink temperature adjustment unit 26 is located in the middle of the ink circulation pipe 28. The ink temperature adjustment unit 26 includes a heater 41, a heater temperature sensor 42, a heat sink 43, and a cooling fan 44.

[0041] The heater 41 heats the ink in the ink circulation tube 28. The heater temperature sensor 42 detects the temperature of the heater 41. The heat sink 43 cools the ink in the ink circulation tube 28 by dissipating heat. The cooling fan 44 blows cooling air onto the heat sink 43.

[0042] The ink temperature sensor 27 detects the temperature of the ink in the ink circulation section 20. The ink temperature sensor 27 is located in the middle of the ink circulation pipe 28. The ink temperature sensor 27 can be configured, for example, by a power thermistor.

[0043] The ink circulation pipe 28 connects the pressurized tank 21 and the distributor 22. The ink circulation pipe 28 passes through the heat sink 43 and then through the heater 41. Ink flows through the ink circulation pipe 28 from the pressurized tank 21 to the distributor 22. The ink circulation pipe 29 connects the collector 23 and the negative pressure tank 24. Ink flows through the ink circulation pipe 29 from the collector 23 to the negative pressure tank 24.

[0044] The ink circulation pipe 30 connects the negative pressure tank 24 and the pressurized tank 21. Ink flows through the ink circulation pipe 30 from the negative pressure tank 24 to the pressurized tank 21. The ink circulation pipes 28-30, the distributor 22, and the collector 23 form a circulation path that circulates ink between the pressurized tank 21, the line head 11, and the negative pressure tank 24.

[0045] The ink supply unit 40 supplies ink from the ink cartridge 46 to the negative pressure tank 24 of the ink circulation unit 20 via the ink supply pipe 48 while the ink supply valve 47 is open.

[0046] The pressure application unit 5 applies pressure to the air layer 31 of the pressurized tank 21 and the air layer 36 of the negative pressure tank 24 for ink circulation. The pressure application unit 5 can individually isolate or connect the air layer 31 of the pressurized tank 21 and the air layer 36 of the negative pressure tank 24 to the atmosphere.

[0047] Furthermore, the pressure application unit 5 can apply positive pressure to the air layer 31 of the pressurized tank 21 via the pressurized communication pipe 58. In addition, the pressure application unit 5 can apply negative pressure to the air layer 36 of the negative pressure tank 24 via the negative pressure communication pipe 59.

[0048] Then, by adjusting the positive and negative pressure using the pressure application unit 5, a meniscus is formed at the discharge port of each nozzle of the inkjet heads 16a and 16b.

[0049] In this embodiment, in order to keep the nozzle pressure applied to each inkjet head 16a and 16b within a range that allows for stable ejection, the average nozzle pressure of the inkjet head 16a and the average nozzle pressure of the inkjet head 16b are made equal by adjusting the positive and negative pressure using the pressure application unit 5 and by adjusting the diameter of the ink path connected to each inkjet head 16a and 16b to create a difference in flow path resistance.

[0050] However, even if the average nozzle pressure of the inkjet head 16a and the average nozzle pressure of the inkjet head 16b are made equal in this way, as described above, a pressure difference remains between the nozzle at the lower end of the inkjet head 16a on the vertically upper side and the nozzle at the upper end of the inkjet head 16b on the vertically lower side. In particular, when the average nozzle pressure of the inkjet head 16a and the average nozzle pressure of the inkjet head 16b are made equal as described above, the above pressure difference becomes larger compared to before equalization. Note that although the adjustment of the nozzle pressure of the inkjet head 16a and 16b set has been explained here, the same applies to the inkjet head 16c and 16d set and the inkjet head 16e and 16f set.

[0051] Therefore, at the joints between vertically adjacent inkjet heads 16, there is a large difference in nozzle pressure between adjacent nozzles, and the difference in the distance the ink droplets fall causes white streaks due to misalignment of the landing position.

[0052] Therefore, in this embodiment, the amount of ink ejected from the nozzles at the joints of vertically adjacent inkjet heads is controlled. First, the ink ejection control of the nozzles at the joints before this ink amount control will be explained with reference to Figure 5.

[0053] Figure 5 illustrates the ink ejection control at the joint between vertically adjacent inkjet heads 16a and 16b, but the same applies to other vertically adjacent inkjet heads 16.

[0054] The joint between inkjet head 16a and inkjet head 16b shown in Figure 5 is the area enclosed by the dotted rectangle in Figure 5, and the nozzles at the joint are the nozzles indicated by circles within the area enclosed by the dotted rectangle.

[0055] For example, when printing a straight line with uniform density using the line head 11, as shown in Figure 5, of the six nozzles that overlap in the transport direction (front-to-back direction) between the upper inkjet head 16a and the lower inkjet head 16b, the ink ejection amount of the first three nozzles from the bottom of the upper inkjet head 16a is set to "0", and the ink ejection amount of the fourth to sixth nozzles from the bottom is set to "6", corresponding to the density of the straight line. Note that the numerical value of the ink ejection amount represents the number of ink drops ejected from the nozzle to form one dot.

[0056] Furthermore, for the lower inkjet head 16b, the ink ejection volume of the first three nozzles from the top is set to "0," while the ink ejection volume of the fourth to sixth nozzles from the top is set to "6," corresponding to the density of the straight line.

[0057] However, with this ink ejection rate, as shown in Figure 5, the difference in nozzle pressure between the fourth nozzle from the bottom of the inkjet head 16a and the fourth nozzle from the top of the inkjet head 16b results in different fall distances for the ink droplets ejected from these nozzles. As shown in Figure 5, this difference in fall distance increases as the distance between the line head 11 and the printing medium P (head gap) increases.

[0058] Therefore, in this embodiment, the control unit 50 controls the amount of ink ejected from the nozzles so that the difference in fall distance due to the difference in nozzle pressure described above becomes smaller. Specifically, as shown in Figure 6, the amount of ink ejected from the fourth nozzle from the bottom of the inkjet head 16a is reduced to "5". This lowers the nozzle pressure of this nozzle, so that the fall distance of the ink droplets can be increased, as shown in Figure 6. On the other hand, the amount of ink ejected from the fourth nozzle from the top of the inkjet head 16b is increased to "7". This raises the nozzle pressure of this nozzle, so that the fall distance of the ink droplets can be reduced.

[0059] In other words, as shown in Figure 6, by increasing the fall distance of the ink droplets ejected from the upper nozzle at the joint and decreasing the fall distance of the ink droplets ejected from the lower nozzle at the joint, the distance between the landing positions of the ink droplets ejected from these nozzles can be narrowed. This suppresses the occurrence of white streaks caused by the aforementioned misalignment of landing positions, and thus suppresses the deterioration of image quality.

[0060] As explained in Figure 5, the wider the gap between each line head 11-14 and the printing surface Ps of the printing medium P, the longer the distance the ink droplet ejected from the inkjet head 16 travels to land on the printing surface Ps, and the greater the distance the ink droplet parabolic falls. As a result, the difference in the fall distance of ink droplets ejected from the nozzles at the joints becomes larger. In particular, when the printing medium P is a cardboard box, the gap is set wider because collisions between the cardboard box and each line head 11-14 would cause significant damage, resulting in a larger and more pronounced difference in the landing position.

[0061] Therefore, as shown in Figure 7, a distance measuring unit 15 may be provided. The distance measuring unit 15 measures the distance between the printing surface Ps of the printing medium P being transported by the transport unit 2 and the transport unit 2. The distance measuring unit 15 measures the distance using an optical sensor, such as a laser displacement sensor. The distance measuring unit 15 is installed in the same position as the head unit 10 in the direction perpendicular to the transport direction (left and right direction), and effectively measures the gap between each line head 11-14 and the printing surface Ps of the printing medium P.

[0062] Furthermore, the control unit 50 may change the amount of ink ejected from the nozzles at the joint or change the number of nozzles that increase or decrease the ink ejection amount according to the distance measured by the distance measuring unit 15.

[0063] Specifically, in the example shown in Figure 6, the ink ejection amount of the fourth nozzle from the bottom of the inkjet head 16a is set to "5", and the ink ejection amount of the fourth nozzle from the top of the inkjet head 16b is set to "7". However, if the head gap measured by the distance measuring unit 15 widens, the ink ejection amount of the fourth nozzle from the bottom of the inkjet head 16a may be set to "4", and the ink ejection amount of the fourth nozzle from the top of the inkjet head 16b may be set to "8". This makes it possible to suppress the occurrence of white streaks due to misalignment of the impact position, even when the head gap measured by the distance measuring unit 15 widens, and to suppress the deterioration of image quality.

[0064] Furthermore, in the example shown in Figure 6, for example, the ink ejection amount of the fourth nozzle from the bottom of the inkjet head 16a is set to "5", and the ink ejection amount of the fourth nozzle from the top of the inkjet head 16b is set to "7". However, if the head gap measured by the distance measuring unit 15 widens, the ink ejection amounts of the fourth and fifth nozzles from the bottom of the inkjet head 16a may be set to "5", and the ink ejection amounts of the fourth and fifth nozzles from the top of the inkjet head 16b may be set to "7".

[0065] In the above description, the amount of ink ejected from the nozzle at the joint is changed based on the head gap measured by the distance measuring unit 15. However, this is not limited to this method. For example, a pre-set test pattern may be printed, and the offset in the landing position of the ink ejected from the nozzle at the joint may be measured from the print result of the test pattern, and the amount of ink ejected from the nozzle at the joint may be changed based on that offset.

[0066] Alternatively, a table may be pre-set that associates the head gap or impact position deviation with the amount of ink ejected from the nozzle at the joint, and the control unit 50 may refer to the table based on the head gap or impact position deviation measured by the distance measuring unit 15 to determine the amount of ink ejected from the nozzle at the joint.

[0067] Furthermore, as mentioned above, a larger head gap increases the difference in the distance ink droplets fall from the nozzles at the joints. However, as also mentioned above, simply controlling the amount of ink ejected from the nozzles at the joints may not be sufficient to suppress the occurrence of white streaks.

[0068] Therefore, for example, if the head gap measured by the distance measurement unit 15 is greater than or equal to a preset gap threshold, the control unit 50 may shift the ink dot data of the upper inkjet head 16a vertically downward, as shown in Figure 8. The example shown in Figure 8 is an example in which the ink dot data is shifted vertically downward by one dot. This reduces the difference in the fall distance of ink droplets ejected from the nozzles at the joint (the third nozzle from the bottom of the upper inkjet head 16a and the fourth nozzle from the top of the lower inkjet head 16b), thereby suppressing the occurrence of white streaks.

[0069] In this embodiment, the control unit 50 may shift the ink dot data of the upper inkjet head 16a vertically downward, or conversely, shift the ink dot data of the lower inkjet head 16b vertically upward.

[0070] Furthermore, in the above description, the ink dot data of the upper inkjet head 16a is shifted when the head gap measured by the distance measurement unit 15 is greater than or equal to a preset gap threshold. However, the system is not limited to this. For example, a preset test pattern may be printed, and the offset of the ink ejected from the nozzles at the joints may be measured from the print results of the test pattern. If this offset is greater than or equal to a preset offset threshold, the ink dot data of the upper inkjet head 16a may be shifted.

[0071] In the example shown in Figure 8, only the ink dot data is shifted, but the amount of ink ejected from the nozzle at the joint may also be changed as in the embodiment described above.

[0072] Furthermore, the amount of shift of the ink dot data supplied to the upper inkjet head 16a or the lower inkjet head 16b may be changed based on the head gap measured by the distance measuring unit 15 or the actual measured impact position deviation. Specifically, the control unit 50 may increase the amount of shift as the head gap or impact position deviation increases. This makes it possible to suppress the generation of white streaks due to impact position deviation even when the head gap measured by the distance measuring unit 15 widens, thereby suppressing a decrease in image quality.

[0073] Alternatively, a table may be set in advance that associates the head gap or impact position deviation with the shift amount, and the control unit 50 may refer to the table based on the head gap or impact position deviation measured by the distance measuring unit 15 to determine the shift amount of the ink dot data supplied to the upper inkjet head 16a or the lower inkjet head 16b.

[0074] Furthermore, although the above embodiment described ink ejection control of nozzles at the joints between vertically adjacent inkjet heads, it is also possible to perform the same ink ejection control as in the above embodiment for nozzles at the joints between nozzle groups when dividing a plurality of vertically arranged nozzles within a single inkjet head and controlling the nozzle pressure for each divided nozzle group.

[0075] It should be noted that the present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the embodiments described above. For example, all the components shown in the embodiments may be combined as appropriate. It goes without saying that various modifications and applications are possible without departing from the spirit of the invention.

[0076] The following further notes are disclosed regarding the present invention. (Note)

[0077] In the first droplet dispensing control device of the present invention, the control unit can change the amount by which the discharge volume of at least one nozzle at the joint portion of the vertically upper nozzle group is reduced, and the amount by which the discharge volume of at least one nozzle at the joint portion of the vertically lower nozzle group is increased, based on the distance between the discharge medium and the head portion.

[0078] In the first droplet dispensing control device of the present invention, the control unit can shift the dot data for controlling the upper nozzle group in the vertical direction to the dot data for controlling the lower nozzle group in the vertical direction, or shift the dot data for controlling the lower nozzle group in the vertical direction to the dot data for controlling the upper nozzle group in the vertical direction.

[0079] In the second droplet ejection control device of the present invention, the control unit can change the amount of shift of dot data for controlling the nozzle group on the vertically upper side or vertically lower side based on the distance between the ejection target and the head unit. [Explanation of Symbols]

[0080] 1. Inkjet printing device main unit 2 Conveyor Units 3 Support stand 4. Conveyor belt section 5 Pressure application section 10 Head Units 11-14 Line Head 15 Distance measurement unit 16, 16a~16f Inkjet heads 20 Ink circulation unit 21 Pressurized tank 22 Distributor 23 Collector 24. Vacuum Tank 25 Ink Pump 26 Ink temperature adjustment section 27. Ink temperature sensor 28-30 Ink circulation tubes 31 Air layer 36 Air layer 40 Ink supply unit 41 Heater 42 Heater temperature sensor 43 Heatsink 44 Cooling Fans 46 Ink Cartridges 47 Ink supply valve 48 Ink refill tube 50 Control Unit 58 Pressurized connecting pipe 59. Negative pressure communication pipe 100 inkjet heads 101 Inkjet Head P Print media Ps printing side

Claims

1. A head unit having multiple nozzle groups arranged vertically, each containing multiple nozzles that dispense droplets onto a predetermined target, The system includes a control unit that controls the discharge of droplets from the nozzle, A droplet dispensing control device that controls the nozzle group adjacent to the vertically adjacent nozzle group to decrease the discharge amount of at least one nozzle at the joint portion of the vertically lower nozzle group that is continuous with the vertically upper nozzle group, and increase the discharge amount of at least one nozzle at the joint portion of the vertically lower nozzle group.

2. The droplet dispensing control device according to claim 1, wherein the control unit changes, based on the distance between the object to be dispensed and the head portion, the amount by which the discharge amount of at least one nozzle at the joint portion of the vertically upper nozzle group decreases, and the amount by which the discharge amount of at least one nozzle at the joint portion of the vertically lower nozzle group increases.

3. The droplet dispensing control device according to claim 1, wherein the control unit shifts the dot data for controlling the vertically upper nozzle group to the dot data for controlling the vertically lower nozzle group, or shifts the dot data for controlling the vertically lower nozzle group to the dot data for controlling the vertically upper nozzle group.

4. A head portion having a plurality of nozzle groups arranged vertically, each group having a plurality of nozzles arranged vertically for discharging droplets onto a predetermined target, The system includes a control unit that controls the ejection of droplets from the nozzle based on dot data, A droplet discharge control device wherein, when the discharge target is being transported in a transport direction perpendicular to the vertical direction, the control unit shifts the dot data for controlling the upper nozzle group in the vertical direction to the dot data for controlling the lower nozzle group in the vertical direction, or shifts the dot data for controlling the lower nozzle group in the vertical direction to the dot data for controlling the upper nozzle group in the vertical direction, in order to reduce the difference in the landing position of droplets discharged from adjacent nozzle groups in the vertical direction, caused by the nozzle pressure difference between the nozzles of the upper nozzle group in the vertical direction and the nozzles of the lower nozzle group in the vertical direction.

5. The droplet dispensing control device according to claim 4, wherein the control unit changes the amount of shift of dot data for controlling the vertically upper or vertically lower nozzle group based on the distance between the dispensing target and the head unit.

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