Inkjet printing apparatus and inkjet printing method

Abstract

To provide a technique for suppressing lowering of a printing quality even when a plurality of discharge heads are used.SOLUTION: An ink supply part 41 supplies ink to discharge heads 311 and 312. An image data division part 85 divides image data indicating an image formed on a base material 9 into first image data and second image data. The first image data indicates an image formed on the base material 9 by the discharge head 311, and the second image data indicates an image formed on the base material 9 by the discharge head 312. A supply amount control part 87 controls a first flow rate regulating valve 471 on the basis of the first image data, and thereby changes an amount of ink supplied to the discharge head 311 by the ink supply part 41. The supply amount control part 87 controls a second flow rate regulating valve 472 on the basis of the second image data, and thereby changes an amount of ink supplied to the discharge head 312 by the ink supply part 41.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an inkjet printing apparatus and an inkjet printing method. [Background technology]

[0002] In an inkjet printing device that prints using the inkjet method, an image is formed on the surface of a long strip-shaped substrate by transporting the substrate and ejecting ink droplets (hereinafter referred to as "ink droplets") from multiple ejection heads onto the surface of the substrate.

[0003] In such inkjet printing devices, if ink runs out during printing, the desired printed matter cannot be obtained, resulting in a large amount of waste of ink and substrate. For this reason, the ink consumption is estimated as described in Patent Document 1 (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-155748 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the amount of ink discharged from the multiple discharge heads may vary from one discharge head to the next depending on the density of the image to be printed. Therefore, if ink is supplied to each discharge head in the same manner, there may be cases where the amount of ink supplied is excessive or insufficient for each discharge head, and the shape of the ink meniscus at each discharge port of each discharge head may become unstable. If the shape of the ink meniscus becomes unstable, the ink droplet discharge speed or ink landing accuracy may decrease, or ink droplet discharge failure (nozzle chipping) may occur, which may result in a decrease in print quality.

[0006] An object of the present invention is to provide a technique for preventing a decrease in print quality when multiple ejection heads are used. [Means for solving the problem]

[0007] In order to solve the above problem, a first aspect is an inkjet printing device comprising: a substrate transport unit that transports a substrate in a predetermined transport direction; a first ejection head and a second ejection head that eject ink droplets onto a surface of the substrate transported by the substrate transport unit; an ink supply unit that supplies ink to the first ejection head and the second ejection head; an image data division unit that divides image data representing an image to be formed on the substrate into first image data representing an image to be formed on the substrate by the first ejection head and second image data representing an image to be formed on the substrate by the second ejection head; and a supply amount change unit that changes the amount of ink supplied by the ink supply unit to the first ejection head based on the first image data, and changes the amount of ink supplied by the ink supply unit to the second ejection head based on the second image data. The ink supply unit has a supply tank capable of storing ink, and supply piping connecting the supply tank to the first ejection head and the second ejection head, the supply piping having a common pipe, a first branch pipe section having one end connected to the common pipe and the other end connected to the first ejection head, and a second branch pipe section having one end connected to the common pipe and the other end connected to the second ejection head, and the supply amount change unit is electrically connected to a first flow rate adjustment valve inserted in the first branch pipe section, a second flow rate adjustment valve inserted in the second branch pipe section, and the first flow rate adjustment valve and the second flow rate adjustment valve to operate them. and a control unit that transmits a control signal, wherein the control unit calculates the ejection amount of each of the first ejection head and the second ejection head based on the printing rates of the first image data and the second image data, and generates a control signal to control the first flow rate adjustment valve and the second flow rate adjustment valve so that the amount of ink supplied to the first ejection head via the first branch piping portion is greater than the ejection amount calculated for the first ejection head, and the amount of ink supplied to the second ejection head via the second branch piping portion is greater than the ejection amount calculated for the second ejection head.

[0008] A second aspect is the inkjet printing device of the first aspect, wherein the first ejection head and the second ejection head eject ink droplets onto the substrate at different positions in a width direction intersecting with the transport direction.

[0009] A third aspect is the inkjet printing apparatus of the first or second aspect, wherein the first ejection head and the second ejection head eject the same type of ink droplets.

[0011] No. 4 The aspect is 1 Aspects any one of the above to the third aspect The inkjet printing apparatus further comprises an ink recovery unit that recovers ink that has not been discharged from the first discharge head from the first discharge head and returns the ink to the supply tank.

[0013] No. 5 The aspect is 4 condition DearAn inkjet printing device, wherein the ink recovery unit has a recovery tank that recovers and stores ink not ejected from the first ejection head, and a return pipe that connects the recovery tank to the supply tank, and the ink supply unit has a pressure difference forming unit that creates a pressure difference between the supply tank and the recovery tank to send ink from the supply tank to the first ejection head and the second ejection head. A sixth aspect is an inkjet printing device of the fifth aspect, wherein the pressure difference forming unit of the ink supply unit adjusts the pressure difference between the supply tank and the recovery tank at a timing according to a predicted fluctuation in the ink ejection amount of the first ejection head and the second ejection head.

[0014] No. 7 The embodiment is the first to third embodiments. 6 In the inkjet printing device of any one of the aspects, the supply amount change unit changes the amount of ink supplied to the first ejection head according to an average value of the ink ejection amount of the first ejection head over a predetermined period of time. An eighth aspect is the inkjet printing apparatus of any one of the first to seventh aspects, wherein the first flow rate adjustment valve and the second flow rate adjustment valve change the flow rate of the ink passing therethrough in two or more stages greater than zero.

[0015] A ninth aspect is an inkjet printing method, comprising: a) conveying a substrate in a predetermined conveying direction; b) supplying ink to the first and second ejection heads through a supply tank in which ink is stored, a common pipe connected to the supply tank, a first branch pipe section having one end connected to the common pipe and the other end connected to a first ejection head, and a second branch pipe section having one end connected to the common pipe and the other end connected to a second ejection head; and c) ) on the surface of the substrate transported by the step a), The ink supplied in the step b) is The first ejection head and The above Second discharge head Rato Put out Process and, The step b) comprises the steps of: b-1 ) image data representative of an image to be formed on the substrate, The above First image data representing an image to be formed on the substrate by the first ejection head; ,before and second image data representing an image to be formed on the substrate by the second ejection head. b-2 ) The first image data and Based on the second image data , the first ejection head, and The second ejection head Each of Ink Discharge Amount calculation And a process of b-3) generating a control signal based on the calculated ejection rate to control a first flow rate adjustment valve inserted in the first branch pipe section and a second flow rate adjustment valve inserted in the second branch pipe section so that the amount of ink supplied to the first ejection head is greater than the ejection rate and so that the amount of ink supplied to the second ejection head is greater than the ejection rate, thereby controlling the first flow rate adjustment valve and the second flow rate adjustment valve; Includes. Effect of the Invention

[0016] According to the inkjet printing device of the first to eighth aspects, an appropriate amount of ink can be supplied to the first and second ejection heads based on the first and second image data. This makes it possible to prevent the amount of ink supplied to the first and second ejection heads from becoming insufficient or excessive, thereby stabilizing the shape of the ink meniscus at each ejection port of the first and second ejection heads. This makes it possible to prevent a decrease in print quality. Furthermore, ink is supplied to the first and second ejection heads from a common tank. In addition, the ink flow rate is controlled upstream of the first ejection head, which allows the amount of ink supplied to the first ejection head to be controlled more accurately than when the ink flow rate is changed downstream of the first ejection head.

[0017] According to the inkjet printing device of the second aspect, the first and second ejection heads can form images on the substrate at different positions in the width direction.

[0018] According to the inkjet printing apparatus of the third aspect, when the same type of ink droplets are ejected from the first ejection head and the second ejection head, deterioration of print quality can be suppressed.

[0020] No. 4 According to the inkjet printing device of the embodiment, the ink recovery unit returns the ink that was not ejected by the first ejection head to the supply tank, thereby circulating the ink between the supply tank and the first ejection head. This makes it possible to supply the first ejection head with an amount of ink greater than the amount ejected by the first ejection head, thereby preventing the first ejection head from running out of ink.

[0022] No. 5 According to the inkjet printing device of the embodiment, ink can be sent from the supply tank to the first ejection head and the second ejection head by creating a pressure difference.

[0023] No. 7According to the inkjet printing device of the embodiment, the amount of ink supplied to the first ejection head is changed according to the average value of the ink ejection amount of the first ejection head in a predetermined period. Therefore, even if the ejection amount fluctuates relatively greatly, the amount of fluctuation in the supply amount can be relatively small, so that the pressure fluctuation in the pipe through which the ink passes can be reduced. This makes it possible to stabilize the shape of the ink meniscus at the ejection port of the first ejection head.

[0024] According to the inkjet printing method of the ninth aspect, an appropriate amount of ink can be supplied to the first and second ejection heads based on the first and second image data. This makes it possible to prevent the first and second ejection heads from being supplied with insufficient or excessive ink, thereby stabilizing the shape of the ink meniscus at each ejection port of the first and second ejection heads. This makes it possible to prevent a decrease in print quality. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 illustrates an inkjet printing apparatus according to an embodiment. [Diagram 2] FIG. 2 is a top view showing the printing unit shown in FIG. [Diagram 3] 2 is a diagram showing a configuration of an ink supply unit shown in FIG. 1. [Figure 4] 4 is a diagram showing electrical connections between a control unit, a first flow rate adjustment valve, and a second flow rate adjustment valve. FIG. [Diagram 5] 5A and 5B are diagrams showing changes over time in the ejection amount and supply amount of ink ejected from an ejection head. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the components described in the embodiment are merely examples, and are not intended to limit the scope of the present invention. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary for ease of understanding.

[0027] <1. Embodiment> FIG. 1 is a diagram showing an inkjet printing device 1 of an embodiment. The inkjet printing device 1 forms an image on a long strip-shaped substrate 9 by ejecting ink from a plurality of head units 31-34 of a printing section 3 toward the substrate 9 while transporting the substrate 9. The substrate 9 is, for example, a printing paper. However, the substrate 9 may also be a resin film, a metal foil, or a substrate made of glass. As shown in FIG. 1, the inkjet printing device 1 includes a substrate transport section 2, a printing section 3, four ink supply sections 41, and a control section 8.

[0028] The substrate transport section 2 transports the substrate 9 in a predetermined transport direction. The transport direction is parallel to the longitudinal direction of the substrate 9. The substrate transport section 2 has an unwinding roller 21, a plurality of transport rollers 22, and a take-up roller 23. The substrate 9 is unwound from the unwinding roller 21 and transported along a transport path formed by the plurality of transport rollers 22. Each transport roller 22 rotates about a rotation axis extending horizontally, thereby guiding the substrate 9 downstream of the transport path. After transport, the substrate 9 is collected by the take-up roller 23.

[0029] A motor 25 is connected to the rotation shaft of each of the unwinding roller 21 and the take-up roller 23. Each motor 25 is electrically connected to the control unit 8. Each motor 25 rotates the unwinding roller 21 and the take-up roller 23 at a predetermined rotation speed based on a control signal sent by the control unit 8. This causes the substrate 9 to be transported along the transport path at a predetermined transport speed. Note that the motor 25 may be connected to any of the multiple transport rollers 22.

[0030] At least one of the transport rollers 22 is provided with an encoder 26. The encoder 26 detects the amount of rotation of the transport roller 22. More specifically, the encoder 26 outputs a pulse signal to the control unit 8 every time the transport roller 22 rotates a predetermined angle. The control unit 8, which will be described later, determines the timing at which the head units 31 to 34 eject ink based on the pulse signal. The encoder 26 may detect the amount of rotation of a roller other than the transport roller 22.

[0031] The substrate 9 moves below the head units 31 to 34 in a direction substantially parallel to the arrangement direction of the head units 31 to 34. The surface of the substrate 9 faces the head units 31 to 34. The substrate 9 is stretched across the transport rollers 22 under tension. This prevents the substrate 9 from sagging or wrinkling during transport.

[0032] The printing unit 3 ejects ink droplets (hereinafter referred to as "ink droplets") onto the base material 9 transported by the base material transport unit 2. The printing unit 3 in this embodiment has four head units 31 to . The head units 31 to 34 are arranged along the transport path of the base material 9.

[0033] Fig. 2 is a top view showing the printing unit 3 shown in Fig. 1. The head units 31 to 34 of the printing unit 3 each cover the entire width of the substrate 9. As indicated by the dashed lines in Fig. 2, the bottom surface of each of the head units 31 to 34 is provided with a plurality of ejection ports 35 arranged parallel to the width direction of the substrate 9. Each of the head units 31 to 34 ejects ink droplets of each color, K (black), C (cyan), M (magenta), and Y (yellow), which are color components of a multicolor image, from the plurality of ejection ports 35 toward the top surface of the substrate 9.

[0034] The four head units 31 to 34 eject ink droplets to form respective monochrome images on the upper surface of the substrate 9. In addition, a multicolor image is formed on the upper surface of the substrate 9 by overlapping the four monochrome images.

[0035] 2, each of the head units 31 to 34 has two ejection heads 311, 312. The ejection heads 311, 312 are arranged in the width direction. The width direction is a direction perpendicular to the transport direction and parallel to the surface of the substrate 9. Each of the head units 31 to 34 may have three or more ejection heads.

[0036] The ejection heads 311, 312 have an ejection surface facing the surface of the substrate 9 transported by the substrate transport unit 2. The ejection surface is provided with a plurality of ejection ports 35 arranged along the width direction. Each ejection port 35 is connected to an inkjet element such as a piezoelectric or thermal inkjet element. The inkjet element ejects ink from the corresponding ejection port 35 under the control of the control unit 8. The ejection heads 311, 312 eject ink onto the substrate 9 at positions different from each other in the width direction.

[0037] The ejection heads 311, 312 each have an ink chamber 36 for temporarily storing ink. The ink chamber 36 is connected to a plurality of ejection ports 35. The ink in the ink chamber 36 is ejected from each ejection port 35 by the power of each inkjet element. The four ink supply units 41 each supply ink to the head units 31 to 34. More specifically, each ink supply unit 41 supplies ink to the ink chamber 36 of the ejection heads 311, 312.

[0038] Fig. 3 is a diagram showing the configuration of the ink supply unit 41 shown in Fig. 1. The ink supply unit 41 includes a supply tank 42, a recovery tank 43, a supply pipe 44, a recovery pipe 45, a return pipe 46, a pressure difference generating unit 5, and a refill tank 61. The supply tank 42 and the recovery tank 43 are each capable of storing ink.

[0039] The supply pipe 44 is a flow path connecting the supply tank 42 and the ejection heads 311, 312, and constitutes an ink flow path from the supply tank 42 to each of the ejection heads 311, 312. The ink stored in the supply tank 42 is supplied from the supply tank 42 to the ink chambers 36, 36 of the ejection heads 311, 312 through the supply pipe 44. Therefore, for example, the same type of ink is supplied to the ejection heads 311, 312 of the head unit 31, and therefore the ejection heads 311, 312 eject the same type of ink droplets.

[0040] The supply pipe 44 has a common pipe 440, a first branch pipe section 441, and a second branch pipe section 442. One end of the common pipe 440 is connected to the supply tank 42. The other end of the common pipe 440 is connected to one end of the first branch pipe section 441 and the second branch pipe section 442. The other end of the first branch pipe section 441 is connected to the supply port of the ejection head 311, and the other end of the second branch pipe section 442 is connected to the supply port of the ejection head 312.

[0041] A first flow rate adjustment valve 471 is inserted in the first branch pipe section 441. A second flow rate adjustment valve 472 is inserted in the second branch pipe section 442. The first flow rate adjustment valve 471 and the second flow rate adjustment valve 472 change the flow rate of ink passing through the first branch pipe section 441 and the second branch pipe section 442 to two or more stages greater than zero. The first flow rate adjustment valve 471 and the second flow rate adjustment valve 472 are, for example, proportional control solenoid valves. The first flow rate adjustment valve 471 and the second flow rate adjustment valve 472 are electrically connected to the control section 8 and operate based on a control signal transmitted by the control section 8. The supply amount control section 87, the first flow rate adjustment valve 471, and the second flow rate adjustment valve 472 constitute a supply amount change section.

[0042] The first flow rate adjustment valve 471 changes the amount of ink per unit time supplied to the ejection head 311 (hereinafter simply referred to as the "supply amount"). The second flow rate adjustment valve 472 changes the supply amount of ink supplied to the ejection head 312. The control unit 8 and the first flow rate adjustment valve 471 constitute a supply amount change unit that changes the amount of ink supplied to the ejection head 311. In addition, the control unit 8 and the second flow rate adjustment valve 472 constitute a supply amount change unit that changes the amount of ink supplied to the ejection head 312.

[0043] The recovery pipe 45 is a flow path that connects the ejection heads 311, 312 and the recovery tank 43, and constitutes a flow path of ink from the ejection heads 311, 312 to the recovery tank 43. The recovery pipe 45 has a common pipe 450, a first branch pipe section 451, and a second branch pipe section 452. One end of the first branch pipe section 451 is connected to the exhaust port of the ejection head 311, and one end of the second branch pipe section 452 is connected to the exhaust port of the ejection head 312. The other ends of the first branch pipe section 451 and the second branch pipe section 452 are connected to one end of the common pipe 450. The other end of the common pipe 450 is connected to the recovery tank 43.

[0044] The return pipe 46 is a flow path that connects the recovery tank 43 and the supply tank 42, and constitutes an ink flow path from the recovery tank 43 to the supply tank 42. The ink stored in the recovery tank 43 moves to the supply tank 42 through the return pipe 46. A return pump 461 is attached to the return pipe 46. The return pump 461 sends ink from the recovery tank 43 to the supply tank 42. The recovery pipe 45, the return pipe 46, and the return pump 461 constitute an ink recovery unit. Note that the movement of ink from the recovery tank 43 to the supply tank 42 may be performed by utilizing gravity.

[0045] The refill tank 61 stores ink for refilling. The refill tank 61 is connected to the supply tank 42 via a refill pipe 62. A refill pump 621 is inserted in the refill pipe 62. The refill pump 621 pumps the ink from the refill tank 61 to the supply tank 42. For example, when the total amount of ink circulating through the supply tank 42, the head unit 31, and the recovery tank 43 decreases due to printing or the like, the refill pump 621 refills ink from the refill tank 61 to the supply tank 42.

[0046] The pressure difference generating unit 5 generates a pressure difference between the supply tank 42 and the recovery tank 43 by adjusting the pressure in the supply tank 42 and the pressure in the recovery tank 43. Hereinafter, the pressure difference generated by the pressure difference generating unit 5 will be simply referred to as the "pressure difference." By generating the pressure difference by the pressure difference generating unit 5, ink is sent from the supply tank 42 to the recovery tank 43.

[0047] The pressure difference generating unit 5 includes a first pressure adjusting unit 51a and a second pressure adjusting unit 51b. The first pressure adjusting unit 51a adjusts the pressure in the supply tank 42. The second pressure adjusting unit 51b adjusts the pressure in the recovery tank 43.

[0048] The first pressure adjustment unit 51a has a first pressure change unit 52 and a pressurized tank 53. The first pressure change unit 52 changes the pressure in the pressurized tank 53 based on a control signal output by the control unit 8. The first pressure change unit 52 specifically includes an air pressure sensor 521, a pressurized pump 522, a decompression pump 523, and a suction pump 524.

[0049] The air pressure sensor 521 measures the pressure in a pipe communicating with the inside of the pressurized tank 53. The air pressure sensor 521 outputs a measurement signal indicating the measured pressure to the control unit 8.

[0050] The pressurizing pump 522 and the decompression pump 523 are provided on piping connected to the inside of the pressurizing tank 53. The pressurizing pump 522 sends air to the pressurizing tank 53 to increase the pressure inside the pressurizing tank 53. The decompression pump 523 reduces the pressure inside the pressurizing tank 53 by sucking in the air in the pressurizing tank 53.

[0051] Suction pump 524 is provided in the middle of a pipe having one end connected to inside pressure tank 53 and the other end open to the atmosphere. Suction pump 524 generates pressure in the pipe to release air in pressure tank 53 to the atmosphere.

[0052] The pressurized tank 53 is connected to the supply tank 42 by a pipe through which air can flow. By changing the pressure in the pressurized tank 53, the pressure in the supply tank 42 is changed.

[0053] The second pressure adjustment unit 51b has a second pressure change unit 54 and a negative pressure tank 55. The second pressure adjustment unit 51b is connected to the negative pressure tank 55 and adjusts the pressure in the negative pressure tank 55. The second pressure change unit 54 changes the pressure in the negative pressure tank 55 based on a control signal output by the control unit 8. The second pressure change unit 54 has the same configuration as the first pressure change unit 52, so a description thereof will be omitted. The negative pressure tank 55 is in communication with the recovery tank 43. The pressure in the recovery tank 43 is changed by changing the pressure in the negative pressure tank 55.

[0054] The pressure difference generating unit 5 may generate a pressure difference in a state where both the inside of the supply tank 42 and the inside of the recovery tank 43 are under negative pressure. The pressure difference generating unit 5 may also generate a pressure difference in a state where the inside of the supply tank 42 is under positive pressure and the inside of the recovery tank 43 is under negative pressure.

[0055] The control unit 8 has a computer configuration including a processor such as a CPU, a ROM for storing programs, and a RAM for storing various information. The control unit 8 causes each of the head units 31 to 34 to eject ink droplets based on image data and a pulse signal output by the encoder 26. As a result, an image represented by the image data is formed on the surface of the substrate 9.

[0056] 3, the processor of the control unit 8 operates according to a program, causing the control unit 8 to function as a discharge amount prediction unit 81, a pressure control unit 83, an image data division unit 85, a supply amount control unit 87, and a discharge control unit 89. Note that some or all of the functions of the control unit 8 may be realized by a dedicated circuit.

[0057] The discharge amount prediction unit 81 predicts the amount of ink discharged per unit time from the head units 31 to 34 at a time point ahead of the current time based on the image data. The discharge amount prediction unit 81 calculates a printing rate from the image data, for example. The printing rate represents the amount of ink applied per unit area to the substrate 9. The discharge amount prediction unit 81 calculates a predicted discharge amount, which is a predicted value of the discharge amount, based on the printing rate. Note that the discharge amount prediction unit 81 may use the printing rate as the predicted discharge amount.

[0058] The pressure control unit 83 controls the pressure difference generating unit 5 according to the predicted ejection amount predicted by the ejection amount predicting unit 81 , thereby controlling the amount of ink supplied from the supply tank 42 to the recovery tank 43 .

[0059] The pressure control unit 83 performs, for example, feed-forward control. More specifically, the pressure control unit 83 controls the pressure difference forming unit 5 based on the predicted discharge amount and the time lag. The pressure difference is adjusted at a timing according to the fluctuation of the predicted discharge amount by the control of the pressure difference forming unit 5 by the pressure control unit 83. The time lag is a difference (time difference) from the time when the pressure control unit 83 outputs a control signal for changing the pressure difference to the first pressure adjustment unit 51a or the second pressure adjustment unit 51b to the time when the pressure difference is actually changed. The magnitude of the time lag is appropriately determined, for example, according to the pressure difference forming unit 5, the supply pipe 44, and the recovery pipe 45. More specifically, the magnitude of the time lag is appropriately determined, for example, according to the characteristics of the pressure pump 522 and the decompression pump 523 of the first pressure adjustment unit 51a or the second pressure adjustment unit 51b, the size and shape of the pressure tank 53, or the length and cross-sectional size of the supply pipe 44 and the recovery pipe 45. The magnitude of the time lag may also be determined according to the viscosity and temperature of the ink.

[0060] 4 is a diagram showing electrical connections between the control unit 8, the first flow rate adjustment valve 471, and the second flow rate adjustment valve 472. The image data division unit 85 divides the image data to be formed on the substrate 9 by the head unit 31 into first image data formed by the discharge head 311 and second image data formed by the discharge head 312. The image data division unit 85 transmits the generated first image data and second image data to the supply amount control unit 87 and the discharge control unit 89. The image data division unit 85 also divides the image data corresponding to the head units 32 to 34 into first image data and second image data corresponding to each discharge head 311, 312, in the same manner as the image data corresponding to the head unit 31.

[0061] The supply amount control unit 87 controls the first flow rate adjustment valve 471 and the second flow rate adjustment valve 472 based on the first image data and the second image data. Specifically, the supply amount control unit 87 calculates the ink ejection amount of the ejection heads 311, 312 based on the printing rate of the first image data and the second image data. Then, the supply amount control unit 87 controls the first flow rate adjustment valve 471 and the second flow rate adjustment valve 472 so that the ink supply amount to the ejection heads 311, 312 is greater than the calculated ejection amount. This allows the ejection heads 311, 312 to be supplied with an appropriate amount of ink relative to the ink ejection amount actually ejected by the ejection heads 311, 312. Note that the image data division unit 85 may transmit the printing rates indicated by the first image data and the second image data to the supply amount control unit 87 instead of the first image data and the second image data.

[0062] When the ink flow rate is controlled by the first flow rate adjustment valve 471, the amount of ink supplied to the ejection head 311 can be controlled more quickly than when the supply amount is controlled by a pressure difference like the pressure difference forming unit 5. Therefore, the supply amount control unit 87 may control the first flow rate adjustment valve 471 with a time lag shorter than the time lag set by the pressure control unit 83 for the pressure difference forming unit 5 (or with no time lag).

[0063] The ejection control unit 89 ejects ink droplets from each ejection port 35 of the ejection heads 311, 312 based on the received first image data and second image data. As a result, the ejection heads 311, 312 form an image corresponding to the first image data and an image corresponding to the second image data on the substrate 9. Therefore, an image corresponding to the original image data is formed on the substrate 9.

[0064] Fig. 5 is a diagram showing the change over time in the ejection amount and supply amount of ink ejected by the ejection head 311. In Fig. 5, the horizontal axis represents time, and the vertical axis represents the amount of ink. Also in Fig. 5, graph G11 represents the change in the amount of ink ejected, and graph G21 represents the change in the amount of ink supplied. Also, graph G12 represents the moving average of the ejection amount graph G11.

[0065] The supply amount control unit 87 may control the first flow rate adjustment valve 471 so that the amount of ink supplied to the ejection head 311 is changed according to the average value of the amount of ink ejected from the ejection head 311 in a predetermined period. For example, as shown in FIG. 5, when the supply amount control unit 87 calculates the supply amount QS1 at the target time T1, first, the ejection amounts (QD0, QD1, QD2) at the target time T1, time T0 before the target time T1, and time T2 after the target time T1 are calculated from the first image data. Then, the first flow rate adjustment valve 471 calculates the average (average ejection amount) AQD1 of the calculated ejection amounts. Furthermore, the supply amount control unit 87 may set the value obtained by adding a predetermined amount to the calculated average ejection amount AQD1 as the supply amount QS1 at the target time T1.

[0066] The supply amount control unit 87 may determine the supply amount at the target time T1 based on the average value of only the discharge amount during the period after the target time T1 or before the target time T1. The supply amount control unit 87 may also determine the supply amount QS1 at the target time T1 based on the discharge amounts at two times or four or more times.

[0067] The amount of ink supplied to the ejection head 311 is changed according to the average value of the amount of ink ejected from the ejection head 311 over a predetermined period. This makes it possible to make the fluctuation in the amount of ink supplied to the ejection head 311 relatively small compared to the fluctuation in the amount of ink ejected from the ejection head 311. This makes it possible to suppress a sudden fluctuation in the pressure in the flow path through which the ink passes (the first branch pipe section 441, the ink chamber 36 of the ejection head 311, etc.) even if the amount of ink ejected from the ejection head 311 changes suddenly. This makes it possible to stabilize the shape of the meniscus of the ink at the ejection port of the first ejection head.

[0068] Similar to the control of the first flow rate adjustment valve 471, the supply rate control unit 87 may control the second flow rate adjustment valve 472 so that the amount of ink supplied to the ejection head 312 becomes a value according to the average ejection rate.

[0069] According to the inkjet printing device 1, the amount of ink supplied is controlled according to the amount of ink ejected for each of the ejection heads 311 and 312. Therefore, an appropriate amount of ink can be supplied to each of the ejection heads 311 and 312. This makes it possible to prevent ink shortages and excessive supply to both of the ejection heads 311 and 312. This makes it possible to stabilize the shape of the meniscus of the ink at each ejection port 35 of the ejection heads 311 and 312. By stabilizing the shape of the meniscus, ejection defects (nozzle chipping) of ink droplets are suppressed, and the ejection speed and landing accuracy of the ink droplets are stabilized. This makes it possible to suppress a decrease in print quality.

[0070] Moreover, since it is possible to prevent an excessive supply of ink to the ejection heads 311 and 312, it is possible to extend the life of each pump such as the return pump 461. Moreover, since it is possible to prevent an excessive circulation of ink, it is possible to reduce deterioration of the ink.

[0071] <2. Modification> Although the embodiment has been described above, the present invention is not limited to the above, and various modifications are possible.

[0072] In the above embodiment, the pressure difference forming unit 5 adjusts the pressure difference in accordance with the predicted discharge amount of the head unit 31. However, it is not essential that the pressure difference be adjusted in accordance with the predicted discharge amount of the head unit 31. For example, the pressure difference forming unit 5 may form a constant pressure difference regardless of the predicted discharge amount.

[0073] In the above embodiment, one first flow rate adjustment valve 471 is provided in the first branch pipe section 441 of the supply pipe 44, but multiple first flow rate adjustment valves 471 may be provided in the first branch pipe section 441. The supply amount control section 87 may control the multiple first flow rate adjustment valves 471 to change the supply amount of ink to the ejection head 311. By providing multiple first flow rate adjustment valves 471, it becomes easy to change the supply amount of ink to the ejection head 311 in multiple stages. In addition, when the supply amount control section 87 controls the multiple first flow rate adjustment valves 471, the supply amount control section 87 may control each of the first flow rate adjustment valves 471 with a time difference. This can reduce pressure changes in the first branch pipe section 441, and therefore the shape of the meniscus of the ink at each ejection port 35 of the ejection head 311 can be further stabilized.

[0074] In the above embodiment, the first flow rate adjustment valve 471 is provided in the supply pipe 44 located upstream of the ejection head 311. However, the first flow rate adjustment valve 471 may be provided in the recovery pipe 45 located downstream of the ejection head 311. For example, the first flow rate adjustment valve 471 may be provided in the first branch pipe portion 451 of the recovery pipe 45. The second flow rate adjustment valve 472 may also be provided in the second branch pipe portion 452. When the first flow rate adjustment valve 471 is provided upstream of the ejection head 311, the flow rate of ink flowing to the ejection head 311 can be directly controlled. Therefore, the amount of ink supply can be controlled more accurately than when the first flow rate adjustment valve 471 is provided downstream of the ejection head 311.

[0075] A pump capable of adjusting the flow rate may be provided instead of the first flow rate adjustment valve 471 or the second flow rate adjustment valve 472. By controlling the pump, the amount of ink supplied to the ejection heads 311 and 312 may be changed.

[0076] Although the present invention has been described in detail, the above description is merely illustrative in all respects, and the present invention is not limited thereto. It is understood that countless variations not illustrated can be envisioned without departing from the scope of the present invention. The configurations described in the above embodiments and variations can be appropriately combined or omitted as long as they are not mutually contradictory. [Explanation of symbols]

[0077] 1 Inkjet printing device 2. Substrate conveying section 3 Printing Department 5. Pressure difference forming section 8. Control Unit 9 Base material 31~34 Head unit 41 Ink supply unit 42 Supply Tank 43 Recovery Tank 44 Supply piping 45 Recovery piping 46 Return piping 83 Pressure control section 85 Image data division unit 87 Supply volume control unit 311 Discharge head (first discharge head) 312 Discharge head (second discharge head) 461 Return Pump 471 First flow control valve 472 Second flow control valve

Claims

1. 1. An inkjet printing apparatus comprising: A substrate conveying section that conveys the substrate in a predetermined conveying direction; a first ejection head and a second ejection head that eject ink droplets onto a surface of the base material transported by the base material transport unit; an ink supply unit that supplies ink to the first ejection head and the second ejection head; an image data division unit that divides image data representing an image to be formed on the substrate into first image data representing an image to be formed on the substrate by the first ejection head and second image data representing an image to be formed on the substrate by the second ejection head; a supply amount changing unit that changes the amount of ink supplied by the ink supply unit to the first ejection head based on the first image data, and changes the amount of ink supplied by the ink supply unit to the second ejection head based on the second image data; Equipped with The ink supply unit includes: a supply tank capable of storing ink; a supply pipe connecting the supply tank to the first ejection head and the second ejection head; having The supply pipe is Common piping, a first branch pipe portion having one end connected to the common pipe and the other end connected to the first ejection head; a second branch pipe portion having one end connected to the common pipe and the other end connected to the second ejection head; having The supply amount change unit is A first flow rate control valve inserted in the first branch pipe portion; A second flow rate control valve inserted in the second branch pipe portion; a control unit electrically connected to the first flow rate adjustment valve and the second flow rate adjustment valve and configured to transmit control signals to operate the first flow rate adjustment valve and the second flow rate adjustment valve; having an inkjet printing device, wherein the control unit calculates the ejection amount of each of the first ejection head and the second ejection head based on the printing rates of the first image data and the second image data, and generates a control signal to control the first flow rate adjustment valve and the second flow rate adjustment valve so that the amount of ink supplied to the first ejection head via the first branch piping unit is greater than the ejection amount calculated for the first ejection head, and the amount of ink supplied to the second ejection head via the second branch piping unit is greater than the ejection amount calculated for the second ejection head.

2. 2. The inkjet printing apparatus of claim 1, The first ejection head and the second ejection head eject ink droplets onto the substrate at different positions in a width direction intersecting with the transport direction.

3. 3. The inkjet printing apparatus according to claim 1, An inkjet printing apparatus, wherein the first ejection head and the second ejection head eject the same type of ink droplets.

4. 4. The inkjet printing apparatus according to claim 1, an ink recovery unit that recovers ink that has not been discharged from the first discharge head and returns the ink to the supply tank; The inkjet printing apparatus further comprises:

5. 5. The inkjet printing apparatus of claim 4, The ink recovery unit includes: a recovery tank that recovers and stores ink that has not been ejected from the first ejection head; A return pipe connecting the recovery tank and the supply tank; having The ink supply unit includes: a pressure difference generating unit that generates a pressure difference between the supply tank and the recovery tank to send ink from the supply tank to the first ejection head and the second ejection head; 1. An inkjet printing apparatus comprising:

6. The inkjet printing apparatus of claim 5, An inkjet printing device, wherein the pressure difference forming unit of the ink supply unit adjusts the pressure difference between the supply tank and the recovery tank at a timing according to the predicted fluctuations in the ink ejection amount of the first ejection head and the second ejection head.

7. 7. The inkjet printing apparatus according to claim 1, An inkjet printing apparatus, wherein the supply amount change unit changes the amount of ink supplied to the first ejection head in accordance with an average value of the ink ejection amount of the first ejection head during a predetermined period.

8. An inkjet printing apparatus according to any one of claims 1 to 7, In an inkjet printing apparatus, the first flow rate adjustment valve and the second flow rate adjustment valve change the flow rate of ink passing therethrough in two or more stages greater than zero.

9. 1. An inkjet printing method comprising: a) conveying a substrate in a predetermined conveying direction; b) supplying ink to the first and second ejection heads through a supply tank storing ink, a common pipe connected to the supply tank, a first branch pipe section having one end connected to the common pipe and the other end connected to a first ejection head, and a second branch pipe section having one end connected to the common pipe and the other end connected to a second ejection head; c) ejecting the ink supplied in step b) from the first ejection head and the second ejection head onto the surface of the substrate transported in step a); Including, The step b) comprises: b-1) dividing image data representing an image to be formed on the substrate into first image data representing an image to be formed on the substrate by the first ejection head and second image data representing an image to be formed on the substrate by the second ejection head; b-2) calculating an amount of ink ejected from each of the first ejection head and the second ejection head based on the first image data and the second image data; b-3) generating a control signal based on the calculated ejection amount to control a first flow rate adjustment valve inserted in the first branch pipe portion and a second flow rate adjustment valve inserted in the second branch pipe portion so that the amount of ink supplied to the first ejection head is greater than the ejection amount and so that the amount of ink supplied to the second ejection head is greater than the ejection amount, thereby controlling the first flow rate adjustment valve and the second flow rate adjustment valve; An inkjet printing method comprising:

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