Inkjet printing device

Abstract

To suppress ink landing deviation by an easy control in an inkjet printing device.SOLUTION: An inkjet printing device 1 includes: an inkjet head 10 that discharges an ink IK with respect to a medium M; a pressure adjustment part (for example, air pump 42) that adjusts a pressure acting to a liquid surface of the ink IK held in the inkjet head 10; and a control part 71 that controls the pressure adjustment part so as to adjust the pressure on the basis of a gap L between the medium M and the inkjet head 10.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an inkjet printing device equipped with an inkjet head. [Background technology]

[0002] Conventionally, a method has been proposed for adjusting the drive voltage of the inkjet head and the pressure acting on the ink surface in the nozzle in order to increase the amount of ink ejected when recording images at high speed and to reduce the amount of ink ejected when recording images with high resolution (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6422680 Summary of the Invention [Problem to be solved by the invention]

[0004] In an inkjet printing device that uses suction to transport a medium using a belt platen and ejects ink from multiple head modules aligned across the width of the paper to form an image on the medium, various air currents act on the ink droplets ejected from the head modules, including those from transport, paper suction, and ejection wind. High resolution ink droplets are particularly susceptible to the effects of air currents, as many small droplets are used. When the ejected ink droplets are subjected to air currents, the ink landing position becomes misaligned, resulting in degradation of the image.

[0005] On the other hand, if the ejection speed or ejection volume is increased by increasing the drive voltage or changing the drive waveform in order to make the ink droplets less susceptible to the effects of air currents, the control becomes more complicated and there are also problems with increased power consumption and heat generation.

[0006] An object of the present invention is to provide an inkjet printing apparatus capable of suppressing deviation in ink landing position with simple control. [Means for solving the problem]

[0007] In one embodiment, an inkjet printing device includes an inkjet head that ejects ink onto a medium, a pressure adjustment unit that adjusts the pressure acting on a liquid surface of the ink held in the inkjet head, and a control unit that controls the pressure adjustment unit to adjust the pressure based on a gap between the medium and the inkjet head. Effect of the Invention

[0008] According to this aspect, it is possible to suppress deviation in the landing position of ink through simple control. [Brief description of the drawings]

[0009] [Figure 1] 1 is a front view showing an internal structure of an inkjet printing apparatus according to an embodiment; [Diagram 2] 1 is a plan view showing an internal structure of an inkjet printing apparatus according to an embodiment; [Diagram 3] 1 is a configuration diagram showing an ink circulation unit and the like of an inkjet printing apparatus according to an embodiment; [Figure 4] FIG. 2 is a diagram illustrating a control configuration of an inkjet printing apparatus according to an embodiment. [Diagram 5] FIG. 4 is a diagram showing the relationship between nozzle pressure and ejection amount in one embodiment. [Figure 6] FIG. 4 is a diagram illustrating the relationship between nozzle pressure and ejection speed in an embodiment. [Figure 7] 1A to 1C are diagrams showing examples of landing states of (a) one drop, (b) two drops, and (c) three drops in one embodiment. [Figure 8] 4 is a flowchart illustrating an operation of an inkjet printing apparatus according to an embodiment. [Figure 9]FIG. 11 is a diagram illustrating an example of setting values ​​for each gap according to an embodiment. [Figure 10] FIG. 11 is a bottom view illustrating a wraparound air current in one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An inkjet printing apparatus according to an embodiment of the present invention will now be described with reference to the drawings.

[0011] 1 and 2 are a front view and a plan view showing the internal structure of an inkjet printing apparatus 1 according to one embodiment.

[0012] FIG. 3 is a configuration diagram showing an ink circulation unit 30 and the like of the inkjet printing apparatus 1, and FIG.

[0013] Note that the up-down, front-back, and left-right directions shown in Figures 1 and 2, and Figure 10 described later, are examples for the convenience of explanation, and for example, the up-down direction is the vertical direction, and the front-back and left-right directions are the horizontal directions.

[0014] 1 and 2, the inkjet printing apparatus 1 includes an inkjet head 10 and a transport unit 20. The inkjet printing apparatus 1 also includes an ink circulation unit 30 and an ink supply unit 50 shown in Fig. 3, and a control unit 71, a storage unit 72, and an interface unit 73 shown in Fig. 4.

[0015] As shown in FIG. 1 and FIG. 2, the inkjet head 10 has a plurality of head modules 11. Each head module 11 has two nozzle rows in which nozzles 11a (see FIG. 10) that eject ink IK (see FIG. 3) are arranged in a direction perpendicular to the transport direction T of the medium M. Each head module 11 also has an ink chamber (not shown) that stores the ink IK. A negative pressure acts on the liquid surface of the ink IK held in the nozzle 11a, and the ink IK is ejected from the nozzle 11a by driving a piezoelectric element (not shown) that is disposed in the ink chamber. Note that the medium M in this embodiment is, for example, paper, but may also be a sheet-like object made of a material other than paper, or an object having a folded portion such as an envelope.

[0016] 2, the inkjet head 10 has four sets of six head modules 11 arranged in a staggered pattern along a direction (main scanning direction, which is the front-to-back direction) perpendicular to the transport direction T (sub-scanning direction) of the medium M, for a total of 24 head modules 11. That is, one set of six head modules 11 arranged along the main scanning direction are arranged in two rows with their positions in the transport direction T shifted alternately. As an example, the four sets of head modules 11 (11K, 11C, 11M, 11Y) eject black (K), cyan (C), magenta (M), and yellow (Y) inks IK in that order from the set on the upstream side in the transport direction T.

[0017] Each head module 11 may have only a single nozzle row, or may have multiple nozzle rows that eject inks IK of different colors. Also, the inkjet head 10 may have only a single head module 11.

[0018] 1, the transport unit 20 is disposed opposite the inkjet head 10 and transports the medium M. The transport unit 20 has a belt 21 and a pair of pulleys 22, 23 around which the belt 21 is stretched. The belt 21 is provided with a plurality of suction holes (not shown), and air is sucked through the suction holes by a suction unit such as a suction fan, so that the medium M is adsorbed to the belt 21.

[0019] Also, the transport unit 20 may be held in a suspended state by a wire (not shown), for example, and may be arranged so as to be movable up and down using the wire. This allows the gap L between the medium M and the inkjet head 10 shown in FIG. 1 to be adjusted. The gap L between the medium M and the inkjet head 10 may be adjusted by raising and lowering the inkjet head 10. Here, the gap L varies depending on the thickness of the medium M, and therefore can be said to vary even if the inkjet head 10 and the transport unit 20 do not move relative to each other.

[0020] 3, the ink circulation unit 30 includes a pressurized tank 31, a distributor 32, a collector 33, a negative pressure tank 34, an ink pump 41, a pressurized common air chamber 35, a negative pressure common air chamber 36, an air pump 42, a temperature adjustment unit 37, ink circulation pipes 38a, 38b, 38c, a supply tube 39a, and a discharge tube 39b. Note that it is preferable to provide an ink circulation unit 30 for each color of ink IK ejected by the head module 11 of the inkjet head 10. In this case, for example, some components of the ink circulation unit 30, such as the pressurized common air chamber 35, the negative pressure common air chamber 36, and the air pump 42, may be shared by a plurality of ink circulation units 30 having different colors of ink IK.

[0021] The pressurized tank 31, the ink circulation pipe 38a, the distributor 32, the supply tube 39a, the discharge tube 39b, the collector 33, the ink circulation pipe 38b, the negative pressure tank 34, and the ink circulation pipe 38c are an example of an ink flow path that is connected to the inkjet head 10 and flows the ink IK, and more specifically, constitutes a circulation flow path that circulates the ink IK while supplying the ink IK to the inkjet head 10.

[0022] The pressurized tank 31 stores the ink IK to be supplied to the inkjet head 10. The ink IK in the pressurized tank 31 is supplied to the inkjet head 10 via the ink circulation pipe 38a, the distributor 32, and the supply tube 39a. An air layer is formed on the liquid surface of the ink IK inside the pressurized tank 31. The pressurized tank 31 is disposed at a lower position than the inkjet head 10. The pressurized tank 31 is connected to the ink flow path (ink circulation pipes 38a, 38c) and is an example of a tank that stores the ink IK.

[0023] The distributor 32 distributes the ink IK supplied from the pressurized tank 31 via the ink circulation pipe 38 a to each head module 11 of the inkjet head 10 .

[0024] The collector 33 collects the ink IK that has not been consumed by the inkjet head 10 from each head module 11 via a discharge tube 39b. The ink IK collected by the collector 33 flows to the negative pressure tank 34 via an ink circulation pipe 38b.

[0025] The negative pressure tank 34 receives and stores the ink IK that has not been consumed by the inkjet head 10 from the collector 33. The negative pressure tank 34 also stores the ink IK supplied from the ink cartridges 51 of the ink supply unit 50, which will be described later. An air layer is formed above the liquid surface of the ink IK inside the negative pressure tank 34. The negative pressure tank 34 is disposed at the same height as the pressurized tank 31. The negative pressure tank 34, like the pressurized tank 31 described above, is connected to the ink flow path (ink circulation pipes 38b, 38c) and is an example of a tank that stores the ink IK.

[0026] The negative pressure tank 34 is provided with a liquid level detection sensor (not shown) that detects whether the liquid level of the ink IK in the negative pressure tank 34 has reached a reference level.

[0027] The ink pump 41 supplies the ink IK from the negative pressure tank 34 to the pressurized tank 31. The ink pump 41 is provided midway through the ink circulation pipe 38c.

[0028] The pressurized common air chamber 35 is an air chamber for equalizing the pressures of the multiple pressurized tanks 31 corresponding to each color of ink IK. The pressurized common air chamber 35 has an atmosphere release valve 35a and a pressure sensor 35b. The atmosphere release valve 35a switches the pressurized common air chamber 35 between a sealed state (a state cut off from the atmosphere) and an atmosphere open state (a state connected to the atmosphere). The pressure sensor 35b detects the pressure inside the pressurized common air chamber 35.

[0029] The negative pressure common air chamber 36 is an air chamber for equalizing the pressures of the multiple negative pressure tanks 34 corresponding to each color of ink IK. The negative pressure common air chamber 36 has an atmosphere release valve 36a and a pressure sensor 36b. The atmosphere release valve 36a switches the negative pressure common air chamber 36 between a sealed state (a state cut off from the atmosphere) and an atmosphere open state (a state connected to the atmosphere). The pressure sensor 36b detects the pressure inside the negative pressure common air chamber 36.

[0030] The air pump 42 sends air from the negative pressure common air chamber 36 to the pressurized common air chamber 35. When the air pump 42 is driven, the air release valve 35a of the pressurized common air chamber 35 is closed to seal the pressurized common air chamber 35, thereby generating pressure (positive pressure) in the pressurized common air chamber 35. When the air pump 42 is driven, the air release valve 36a of the negative pressure common air chamber 36 is closed to seal the negative pressure common air chamber 36, thereby generating pressure (negative pressure) in the negative pressure common air chamber 36. The air pump 42 functions as an example of a pressure adjustment unit that adjusts the pressure acting on the liquid surface of the ink IK held in the nozzle 11a (inkjet head 10) in order to adjust the pressure of the gas in the tank (pressurized tank 31 and negative pressure tank 34). The control unit 71, which will be described later, adjusts the pressure acting on the liquid surface of the ink IK held in the nozzle 11a by controlling the air pump 42 based on the gap L between the medium M and the inkjet head 10.

[0031] It should be noted that the pressure acting on the liquid surface of the ink IK held in the nozzle 11a can also be adjusted by other methods, such as opening and closing the atmospheric release valves 35a, 36a of the pressurized common air chamber 35 and the negative pressure common air chamber 36, and the pressure adjustment unit is not limited to the air pump 42. In addition, the pressure adjustment unit is not limited to being disposed in the circulation flow path of the ink IK in the ink circulation unit 30, and may be disposed in a supply flow path that is a non-circulation flow path that unilaterally supplies the ink IK to the inkjet head 10. In this case, the pressure can be adjusted by, for example, controlling a supply unit such as a pump that supplies the ink IK, or by controlling the height of a tank that supplies the ink IK.

[0032] The temperature adjustment unit 37 is provided in the middle of the ink circulation pipe 38a. The temperature adjustment unit 37 has, for example, a heat sink, a cooling fan, a heater, etc., and adjusts the temperature of the ink IK flowing through the ink circulation pipe 38a.

[0033] The ink circulation pipe 38a connects the pressurized tank 31 and the distributor 32. Ink IK flows from the pressurized tank 31 toward the distributor 32 in the ink circulation pipe 38a. The ink circulation pipe 38b connects the collector 33 and the negative pressure tank 34. Ink IK flows from the collector 33 toward the negative pressure tank 34 in the ink circulation pipe 38b. The ink circulation pipe 38c connects the negative pressure tank 34 and the pressurized tank 31. Ink IK flows from the negative pressure tank 34 toward the pressurized tank 31 in the ink circulation pipe 38c.

[0034] The supply tube 39a is made of an elastic material, for example, with an outer layer made of polyurethane resin and an inner layer made of fluororesin, and supplies the ink IK from the distributor 32 to the head module 11. The supply tubes 39a are provided in the same number as the head modules 11. The supply tube 39a is an example of a supply flow path that flows the ink IK supplied to the inkjet head 10. Note that the ink circulation pipe 38a and the like can also be called a supply flow path.

[0035] The discharge tube 39b is made of an elastic material, for example, with an outer layer made of polyurethane resin and an inner layer made of fluororesin, and discharges the ink IK from the head module 11 to the collector 33. The number of discharge tubes 39b provided is the same as the number of head modules 11. The discharge tube 39b is an example of a discharge flow path that flows the ink IK discharged from the inkjet head 10. Note that the ink circulation tube 38b and the like can also be called a discharge flow path.

[0036] The ink replenishing unit 50 replenishing (supplies) the ink IK to the negative pressure tank 34 of the ink circulation unit 30. The ink replenishing unit 50 includes an ink cartridge 51, an ink replenishing valve 52, and an ink replenishing tube 53.

[0037] The ink cartridge 51 contains the ink IK used for printing by the inkjet head 10. The ink IK in the ink cartridge 51 is supplied to the negative pressure tank 34 of the ink circulation unit 30 via an ink supply pipe 53.

[0038] The ink supply valve 52 is an electromagnetic valve that opens and closes the flow path of the ink IK in the ink supply pipe 53. When the ink IK is supplied to the negative pressure tank 34, the ink supply valve 52 is opened under the control of the control unit 71, which will be described later.

[0039] The ink supply pipe 53 connects the ink cartridge 51 and the negative pressure tank 34. Ink IK flows through the ink supply pipe 53 from the ink cartridge 51 toward the negative pressure tank 34.

[0040] 4 has a processor (e.g., CPU: Central Processing Unit) that functions as an arithmetic processing device that controls the overall operation of the inkjet printing apparatus 1. The control unit 71 controls each part of the inkjet printing apparatus 1, such as the inkjet head 10, the transport unit 20, the ink circulation unit 30, and the ink supply valve 52. The control unit 71 also has a known image processing unit 71a that processes image data printed by the inkjet head 10. As will be described in more detail later, the image processing unit 71a converts drop data, which is image data for ejecting ink IK from each nozzle 11a, into drop data excluding areas where the number of drops is equal to or less than a specified number.

[0041] The storage unit 72 has memories such as a ROM (Read Only Memory), which is a read-only semiconductor memory in which a specific control program is pre-recorded, and a RAM (Random Access Memory), which is a semiconductor memory that can be written to and read at any time and is used as a working memory area as needed when the processor executes various control programs.

[0042] The interface unit 73 transmits and receives various information to and from external devices such as a print control device, a user terminal, etc. For example, the interface unit 73 receives a print job including image data to be printed.

[0043] In addition, the inkjet printing device 1 may further include a supply section such as a paper feed section that supplies the medium M to the inkjet head 10, an output section such as a paper output section that outputs the medium M printed by the inkjet head 10, a display that displays various information, and an input section that accepts user input.

[0044] FIG. 5 is a diagram showing the relationship between the nozzle pressure and the ejection amount, and FIG. 6 is a diagram showing the relationship between the nozzle pressure and the ejection speed (flying speed).

[0045] 5, the nozzle pressure [kPa] acting on the liquid surface of the ink IK held in the nozzle 11a decreases the ejection amount [pl] as the negative pressure (absolute negative value) increases when the nozzle 11a ejects one drop at a time. On the other hand, when the nozzle 11a ejects five drops at a time, the ejection amount decreases as the negative pressure increases, but the amount of reduction is the same as in the case of one drop. In other words, even if the negative pressure increases, the ejection amount of mainly the first drop decreases, regardless of the number of drops.

[0046] Next, as shown in Fig. 6, the nozzle pressure [kPa] acting on the liquid surface of the ink IK held in the nozzle 11a increases the flight speed [m / s] as the negative pressure increases when the nozzle 11a ejects one drop or two drops at a time. On the other hand, when the nozzle 11a ejects five drops at a time, no significant change in flight speed is observed even if the negative pressure increases. In this way, the flight speed increases as the number of drops decreases (three drops or less), and no significant change in flight speed is observed when the number of drops increases (four drops or more).

[0047] Therefore, when the number of drops is particularly small (for example, 3 drops or less), it can be said to be effective to increase the negative pressure of the nozzle to increase the ejection speed and improve the landing deviation.

[0048] As shown in Figures 7(a) to (c), when the gap L is increased, the fewer the number of drops, the greater the landing deviation, and it can be said that the landing deviation is particularly significant for one drop. And for one drop, increasing the negative pressure of the nozzle pressure as described above can increase the flight speed, but the ejection volume decreases, making it more susceptible to the effects of air currents. For this reason, there are cases where the landing deviation for one drop cannot be eliminated even by increasing the negative pressure. Also, a decrease in the ejection volume can lead to a decrease in image quality.

[0049] Next, the process of this embodiment for suppressing the landing deviation caused by the number of drops, the gap L, and the like will be described with reference to FIGS.

[0050] FIG. 8 is a flowchart for explaining the operation of the inkjet printing apparatus 1.

[0051] FIG. 9 is a diagram showing an example of setting values ​​for each gap L.

[0052] First, the process in Fig. 8 starts when the control unit 71 shown in Fig. 4 acquires drop data to be printed. This drop data may be data that the image processing unit 71a of the control unit 71 has processed image data of a print job acquired from a print control device, a user terminal, or an image reading device, or the control unit 71 may acquire data that has been processed as drop data.

[0053] First, the control unit 71 determines whether the gap L between the medium M and the inkjet head 10 is a relatively large gap L3 (step S1). Here, an example will be described in which the height of the transport unit 20 is adjusted to three levels, that is, the height of the transport unit 20 is raised and lowered to a position where the gap L is the lowest and the gap L3 is the maximum, a position where the gap L is an intermediate height and the gap L2 is smaller than the gap L3, and a position where the gap L is the highest and the gap L1 is the minimum. As described above, since the gap L varies depending on the thickness of the medium M, the control unit 71 may determine the gap L by acquiring information such as the type of the medium M (cardboard, letter paper, envelope) from a print job, an input unit, or a thickness detection sensor, or by acquiring information from a gap detection sensor that directly detects the gap L.

[0054] If the gap L is gap L3 (step S1: YES), the control unit 71 sets the number of influencing drops that are likely to affect landing deviation to a relatively large number D3 (e.g., 3 drops) because landing deviation is likely to be large, and determines whether the usage rate of the number of drops D3 or less in the drop data is equal to or greater than a threshold (step S2). Here, the usage rate may be the usage rate of only the area where the nozzle 11a ejects the ink IK, or may be the usage rate of the entire print area including the area where the nozzle 11a ejects the ink IK and the area where it does not eject. The usage rate may also be the usage rate of an area excluding specific areas such as character areas.

[0055] If the usage rate of the number of drops D3 or less is equal to or greater than the threshold value (step S2: YES), the control unit 71 sets the negative pressure of the nozzle 11a to a relatively high value P3 by the pressure adjusting unit, which is, for example, the air pump 42 (step S3).

[0056] Then, the image processing unit 71a of the control unit 71 converts the drop data including the area D1 (an example of a number equal to or less than a prescribed number) where the number of drops is, for example, one drop, so that the area with one drop is excluded and the number of drops becomes two or more (step S4). Note that the image processing unit 71a may convert the drop data using a known halftone process such as a process of concentrating a plurality of areas with one drop into an area with two drops. Thereafter, the control unit 71 changes the drop data to be used for printing to the converted drop data, and controls the inkjet head 10 using this drop data to perform printing (step S8). Then, the process shown in FIG. 8 ends.

[0057] In the determination process of step S2 described above, if the usage rate of the drop count D3 or less is less than the threshold value (step S2: NO), the control unit 71 omits the negative pressure setting (step S3) and image processing (step S4) described above, and causes the inkjet head 10 to print using unconverted drop data (step S8), and the process shown in Fig. 8 ends. Note that if the negative pressure setting (step S3) is not performed, the negative pressure is set to the initial value P1.

[0058] In the determination process of step S1 described above, if the gap L is not the gap L3 (step S1: NO), the control unit 71 determines whether the gap L is the gap L2 which is smaller than the gap L3 (step S5).

[0059] If gap L is gap L2 (step S5: YES), the control unit 71 sets the number of influencing drops that are likely to affect landing deviation to D2 (e.g., 2 drops) which is less than D3, and determines whether the usage rate of the drop number D2 or less in the drop data is greater than or equal to a threshold value (step S6).

[0060] If the usage rate of the number of drops D2 or less is equal to or greater than the threshold value (step S6: YES), the control unit 71 sets the negative pressure of the nozzle 11a to P2, which is smaller than P3, by the pressure adjusting unit, which is, for example, the air pump 42 (step S7).

[0061] When the control unit 71 sets negative pressure to P2 (step S7) and when the usage rate of the drop number D2 or less is less than the threshold value (step S6: NO), the control unit 71 causes the inkjet head 10 to print using drop data that has not been subjected to the above-mentioned conversion process (step S8), and the process shown in Figure 8 is completed.

[0062] In the judgment process of step S5 described above, if the gap L is not gap L2 (step S5: NO), the control unit 71 can determine that the gap L is the smallest gap L1, and therefore causes the inkjet head 10 to print using drop data that has not been subjected to the above-mentioned conversion process (step S8) while keeping the negative pressure at the initial value P1, and the process shown in Figure 8 ends.

[0063] In the flowchart shown in FIG. 8, when the usage rate of the specified drop numbers D2 and D3 is equal to or higher than the threshold (steps S2 and S6: YES), not only the gap L, but also the negative pressure setting (steps S3 and S7) and image processing (step S4) are performed. However, the process of determining whether the usage rate is equal to or higher than the threshold (steps S2 and S6) may be omitted. In addition, the negative pressure setting (step S3) and the image processing (step S4) may be performed based on different standards. In addition, in the flowchart shown in FIG. 8, the gap L has three stages. However, when detecting the gap L between the actual inkjet head 10 and the medium M, the gap L3 takes more values. Therefore, the negative pressures P1, P2, and P3 and the specified drop numbers D2 and D3 may be divided into more values. In addition, since the volume of the ink IK per drop varies depending on the device configuration and driving voltage of the inkjet head 10, the drop number D1 excluded by the conversion of the drop data is not limited to one drop, and may be a value equal to or lower than any drop number of two or more drops.

[0064] Incidentally, as shown in FIG. 10, when a plurality of nozzle rows of nozzles 11a are arranged in the head module 11, the transport wind is obstructed by the discharge wind generated when the nozzle row on the upstream side in the transport direction T discharges the ink IK. Therefore, a turnaround air current A is generated to avoid the discharge wind. This turnaround air current A is likely to affect the landing of the nozzle row on the downstream side. Therefore, it is preferable to make the negative pressure of the nozzle row on the downstream side larger than that of the nozzle row on the upstream side, and to improve the landing deviation by increasing the discharge speed of the small droplets. That is, it is preferable that the control unit 71 controls a pressure adjustment unit (for example, the air pump 42) so that the negative pressure of the pressure of the nozzle row located downstream in the transport direction T is larger than the negative pressure of the pressure of the nozzle row located upstream in the transport direction T. In order to set the pressure for each nozzle row in this way, in the ink circulation unit 30 shown in FIG. 3 described above, a different ink flow path (circulation flow path) is connected to each nozzle row, and pressure adjustment is performed for each nozzle row by a pressure adjustment unit such as the air pump 42. In addition, the control unit 71 may change the threshold value of the usage rate below the above-mentioned specified drop number D2 or D3, change the specified drop number itself, or change whether or not to execute the above-mentioned image processing (step S4), between the nozzle row located downstream in the transport direction T and the nozzle row located upstream in the transport direction T.

[0065] The above-mentioned wraparound airflow A can also affect the landing of droplets in the downstream head module 11 (for example, head module 11Y) by wrapping around the air discharged from the head module 11 (for example, head module 11K) upstream in the transport direction T. For this reason, the downstream head module 11 may have a greater negative pressure than the upstream head module 11, thereby increasing the ejection speed of droplets and improving landing deviation. In this case as well, it can be said that in different head modules 11, the downstream nozzle row has a greater negative pressure than the upstream nozzle row.

[0066] Furthermore, the control unit 71 may control a pressure adjustment unit (e.g., the air pump 42) to adjust the nozzle pressure (pressure) based on at least one of the resolution of the inkjet head 10, the color of the ink IK, the temperature of the inkjet head 10 or the ink IK, and the drive voltage value of the inkjet head 10 in addition to the gap L. Alternatively, the control unit 71 may change a threshold value of the usage rate equal to or less than the above-mentioned specified number of drops D2 or D3, change the specified number of drops itself, or change whether or not to execute the above-mentioned image processing (step S4), based on these resolution, color, temperature, drive voltage value, etc. The temperature of the ink IK may be measured inside the inkjet head 10, or may be measured in the circulation path of the ink circulation unit 30, or the surrounding environmental temperature may be regarded as the temperature of the ink IK.

[0067] For example, the control unit 71 may control the pressure adjustment unit to increase the negative pressure of the nozzle pressure when the resolution (printing resolution) of the inkjet head 10 is relatively high, when the color of the ink IK is a noticeable color (e.g., black), when the viscosity corresponding to the temperature of the inkjet head 10 or the ink IK satisfies a specified condition, when the drive voltage value of the head module 11 is relatively low, etc. Note that since the drive voltage value of the head module 11 can be adjusted for each head module 11 by, for example, adjusting the concentration between the head modules 11, there are head modules 11 with a relatively low drive voltage value (slow average ejection speed for each head module 11). Therefore, the nozzle pressure may be adjusted for each head module 11 based on the drive voltage value of the head module 11.

[0068] In the present embodiment described above, the inkjet printing device 1 includes an inkjet head 10 that ejects ink IK onto a medium M, a pressure adjustment unit (e.g., an air pump 42) that adjusts the pressure acting on the liquid surface of the ink IK held in the inkjet head 10, and a control unit 71 that controls the pressure adjustment unit to adjust the above pressure based on the gap L between the medium M and the inkjet head 10.

[0069] As a result, even with simple control that does not adjust the drive voltage or drive waveform of the inkjet head 10, the negative pressure acting on the liquid surface of the ink IK held in the nozzle 11a (inkjet head 10) can be increased when the gap L between the medium M and the inkjet head 10 is large. Even if the gap L is large and the ink is easily affected by air currents such as transport wind, medium suction wind, and discharge wind, the negative pressure can be increased to increase the discharge speed of the ink IK and suppress landing deviation. Therefore, according to this embodiment, landing deviation of the ink IK can be suppressed with simple control. This can also prevent image degradation. Furthermore, heat generation and power consumption of the inkjet head 10 can be reduced compared to an embodiment in which the drive voltage is adjusted.

[0070] Furthermore, in this embodiment, the control unit 71 changes image data that includes an area where the number of drops ejected by the inkjet head 10 in one go is less than a specified number (e.g., 1 drop) based on the gap L (gap L3), to image data that excludes this area and is converted so that the number of drops exceeds the specified number, and controls the inkjet head 10 using this changed image data.

[0071] This allows the image data to be changed only in certain situations where the gap L is relatively large (for example, when the gap is L3 and the usage rate of the drop count D3 or less is equal to or greater than a threshold value (steps S1, S2: YES)), making it possible to omit the ejection of small drops (for example, one drop) whose ejection volume decreases as the negative pressure increases. This makes it possible to avoid situations where landing deviation cannot be eliminated or image quality deteriorates due to a decrease in the ejection volume. Furthermore, because the image data is changed only in certain situations, it is also possible to avoid complicating control.

[0072] Furthermore, in this embodiment, the inkjet head 10 has at least one head module 11 having at least one nozzle row in which nozzles 11a that eject the ink IK are arranged in a direction perpendicular to the transport direction T of the medium M. The control unit 71 controls a pressure adjustment unit (e.g., air pump 42) so that the negative pressure of the nozzle row located on the downstream side in the transport direction T is made greater than the negative pressure of the nozzle row located on the upstream side in the transport direction T.

[0073] This makes it possible to increase the negative pressure of the nozzle row on the downstream side and increase the ejection speed. Therefore, even if the ejection airflow from the nozzle row on the upstream side in the transport direction T obstructs the transport airflow, causing a wraparound airflow A (see FIG. 10) that goes around the ejection airflow and affects the landing of droplets on the nozzle row on the downstream side, it is possible to suppress landing deviation.

[0074] In addition, in this embodiment, the control unit 71 controls a pressure adjustment unit (e.g., air pump 42) to adjust the above-mentioned pressure based on at least one of the resolution of the inkjet head 10, the color of the ink IK, the temperature of the inkjet head 10 or the ink IK, and the driving voltage value of the inkjet head 10.

[0075] This makes it possible to increase the negative pressure depending on the situation, such as when the resolution is high and the ejection volume is small, when a relatively noticeable color of ink IK is used, when the viscosity corresponding to the temperature meets the specified conditions, or when the driving voltage value is low and the droplet speed is slow, and thus makes it possible to reduce landing deviation.

[0076] The present invention is not limited to the above-described embodiment as it is, and the components can be modified and embodied without departing from the gist of the invention in the implementation stage. In addition, various inventions can be formed by appropriate combinations of the multiple components disclosed in the above-described embodiment. For example, all the components shown in the embodiment may be appropriately combined. Of course, various modifications and applications are possible without departing from the spirit of the invention. Some of the inventions described in the specification of this application are described below.

[0077] [Appendix 1] An inkjet head that ejects ink onto a medium; a pressure adjusting unit that adjusts a pressure acting on a liquid surface of the ink held in the inkjet head; a control unit that controls the pressure adjustment unit to adjust the pressure based on a gap between the medium and the inkjet head; An inkjet printing apparatus comprising:

[0078] [Appendix 2] The control unit changes image data including an area where the number of drops ejected by the inkjet head at one time is equal to or less than a specified number, based on the gap, to image data converted so that the area is excluded and the number of drops exceeds the specified number, and controls the inkjet head using the changed image data. 2. The inkjet printing apparatus according to claim 1.

[0079] [Appendix 3] the inkjet head includes at least one head module having at least one nozzle row in which nozzles for ejecting ink are arranged in a direction perpendicular to a transport direction of the medium, The control unit controls the pressure adjustment unit so that the negative pressure of the nozzle row located on the downstream side in the transport direction is greater than the negative pressure of the nozzle row located on the upstream side in the transport direction. 3. The inkjet printing apparatus according to claim 1 or 2.

[0080] [Appendix 4] The control unit controls the pressure adjustment unit to adjust the pressure further based on at least one of a resolution of the inkjet head, a color of ink, a temperature of the inkjet head or ink, and a driving voltage value of the inkjet head. 4. The inkjet printing apparatus according to claim 1, [Explanation of symbols]

[0081] 1 Inkjet printing device 10 Inkjet head 11 (11K, 11C, 11M, 11Y) Head module 11a Nozzle 20 Conveyor section 21 Belt 22,23 Pulley 30 Ink Circulation Section 31 Pressurized Tank 32 Distributor 33 Collector 34 Negative Pressure Tank 35 Pressurized common air chamber 35a Atmospheric release valve 35b Pressure sensor 36 Negative pressure common chamber 36a Atmospheric release valve 36b Pressure sensor 37 Temperature adjustment section 38a, 38b, 38c Ink circulation tube 39a Supply tube 39b Discharge tube 41 Ink pump 42 Air Pump 50 Ink supply unit 51 Ink Cartridges 52 Ink supply valve 53 Ink supply pipe 71 Control Unit 71a Image processing unit 72 Memory section 73 Interface section A. Wraparound airflow IK Ink L(L1,L2,L3) Gap M medium T Transport direction

Claims

1. An inkjet head that ejects ink onto a medium; a pressure adjusting unit that adjusts a pressure acting on a liquid surface of the ink held in the inkjet head; a control unit that controls the pressure adjustment unit to adjust the pressure based on a gap between the medium and the inkjet head; An inkjet printing apparatus comprising:

2. The control unit changes image data including an area where the number of drops ejected by the inkjet head at one time is equal to or less than a specified number, to image data converted so that the area is excluded and the number of drops exceeds the specified number, based on the gap, and controls the inkjet head using the changed image data.

2. The inkjet printing apparatus according to claim 1.

3. The inkjet head includes at least one head module having at least one nozzle row in which nozzles for ejecting ink are arranged in a direction perpendicular to a transport direction of the medium, The control unit controls the pressure adjustment unit so that the negative pressure of the nozzle row located on the downstream side in the transport direction is greater than the negative pressure of the nozzle row located on the upstream side in the transport direction.

3. The inkjet printing apparatus according to claim 1, wherein the inkjet printing apparatus is a liquid ejection apparatus.

4. The control unit controls the pressure adjustment unit to adjust the pressure further based on at least one of a resolution of the inkjet head, a color of ink, a temperature of the inkjet head or ink, and a driving voltage value of the inkjet head.

3. The inkjet printing apparatus according to claim 1, wherein the inkjet printing apparatus is a liquid ejection apparatus.

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