JP2022129768A - Inkjet printing device and inkjet printing method - Google Patents

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

The present invention relates to an inkjet printing apparatus and an inkjet printing method.

In an inkjet printing apparatus that performs printing by an inkjet method, droplets of ink (hereinafter referred to as "ink droplets") are ejected from a plurality of ejection heads onto the surface of a substrate while conveying a long strip-shaped substrate. An image is thereby formed on the surface of the substrate.

In such an inkjet printing apparatus, if the ink runs short during printing, the desired printed matter cannot be obtained, resulting in a great deal of wastage of the ink and the substrate. For this reason, the amount of ink consumed is estimated in Patent Document 1 (for example, Patent Document 1).

JP 2019-155748 A

However, the amount of ink ejected from the plurality of ejection heads may vary from one ejection head to another according to the density of the image to be printed. Therefore, when ink is supplied to each ejection head in the same manner, the amount of ink supplied may be excessive or insufficient for each ejection head. In some cases, the shape of the ink meniscus at each ejection port of the ejection head becomes unstable. If the shape of the ink meniscus becomes unstable, the ink droplet ejection speed or ink landing accuracy may decrease, or ink droplet ejection failure (nozzle defect) may occur, which may reduce print quality. there were.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a technique for suppressing deterioration in print quality when using a plurality of ejection heads.

In order to solve the above problems, a first aspect is an inkjet printing apparatus, comprising: a base material conveying unit that conveys a base material in a predetermined conveying direction; a first ejection head and a second ejection head for ejecting ink droplets; an ink supply section for supplying ink to the first ejection head and the second ejection head; and image data representing an image to be formed on the substrate. an image data dividing unit for dividing into first image data representing an image formed on the substrate by the first ejection head and second image data representing an image formed on the substrate by the second ejection head; and changing the amount of ink supplied to the first ejection head by the ink supply unit based on the first image data, and changing the amount of ink supplied to the second ejection head by the ink supply unit based on the second image data. and a supply amount changing unit that changes the amount of ink to be supplied.

A second aspect is the inkjet printing apparatus of the first aspect, wherein the first ejection head and the second ejection head are positioned at different positions with respect to the base material in a width direction that intersects with the conveying direction. Eject ink droplets.

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

A fourth aspect is the inkjet printing apparatus according to any one of the first aspect to the third aspect, wherein the ink supply unit is connected to a supply tank capable of storing ink, and the ink is supplied from the supply tank to the ink supply tank. Ink is supplied to the first ejection head or the second ejection head.

A fifth aspect is the inkjet printing apparatus of the fourth aspect, further comprising an ink recovery unit that recovers from the first ejection head ink that has not been ejected from the first ejection head and returns the ink to the supply tank.

A sixth aspect is the inkjet printing apparatus according to the fifth aspect, wherein the ink supply section has a supply pipe for supplying ink from the supply tank to the first ejection head, and the supply amount changing section includes: changing the flow rate of ink in the supply pipe;

A seventh aspect is the inkjet printing apparatus according to the fifth aspect or the sixth aspect, wherein the ink recovery unit includes a recovery tank for recovering and storing ink that has not been ejected from the first ejection head, and the recovery tank. and a return pipe connecting the supply tank and the ink supply unit, the ink supply unit forms a pressure difference between the supply tank and the recovery tank, thereby discharging the first discharge from the supply tank It has a pressure difference forming part that sends ink toward the head and the second ejection head.

An eighth aspect is the inkjet printing apparatus according to any one of the first aspect to the seventh aspect, wherein the supply amount changing unit adjusts the amount of ink ejected from the first ejection head during a predetermined period. to change the amount of ink supplied to the first ejection head.

A ninth aspect is an inkjet printing method, comprising: a) the step of transporting a substrate in a predetermined transport direction; When ink droplets are ejected from the second ejection head, c) supplying ink to the first ejection head and the second ejection head; ) into first image data representing an image formed on the substrate by the first ejection head and second image data representing an image formed on the substrate by the second ejection head through step b). e) changing the amount of ink supplied to the first ejection head in step c) based on the first image data; changing the amount of ink supplied to the second ejection head.

According to the inkjet printing apparatuses of the first to eighth aspects, it is possible to supply an appropriate amount of ink to the first ejection head and the second ejection head based on the first image data and the second image data. Therefore, it is possible to prevent the amount of ink supplied to the first ejection head and the second ejection head from becoming insufficient or excessive. Shape can be stabilized. Therefore, deterioration in print quality can be suppressed.

According to the inkjet printing apparatus of the second aspect, images can be formed at different positions in the width direction with respect to the substrate by the first ejection head and the second ejection head.

According to the inkjet printing apparatus of the third aspect, it is possible to suppress deterioration of print quality when ejecting the same type of ink droplets from the first ejection head and the second ejection head.

According to the inkjet printing apparatus of the fourth aspect, ink is supplied from a common tank to the first ejection head and the second ejection head.

According to the inkjet printing apparatus of the fifth aspect, the ink recovery unit returns the ink that has not been ejected by the first ejection head to the supply tank, thereby circulating the ink between the supply tank and the first ejection head. can be done. As a result, it is possible to supply the first ejection head with an amount of ink equal to or larger than the amount ejected by the first ejection head, so that it is possible to prevent the first ejection head from running out of ink.

According to the inkjet printing apparatus of the sixth aspect, the flow rate of ink is controlled on the upstream side of the first ejection head. In this case, the amount of ink supplied to the first ejection head can be controlled more accurately than when the flow rate of ink is changed downstream of the first ejection head.

According to the inkjet printing device of the seventh aspect, by forming a pressure difference, ink can be sent from the supply tank to the first ejection head and the second ejection head.

According to the inkjet printing apparatus of the eighth aspect, the amount of ink supplied to the first ejection head is changed according to the average value of the amount of ink ejected from 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 the pressure fluctuation in the pipe through which the ink passes can be reduced. As a result, the shape of the ink meniscus at the ejection port of the first ejection head can be stabilized.

According to the inkjet printing method of the ninth aspect, an appropriate amount of ink can be supplied to the first ejection head and the second ejection head based on the first image data and the second image data. Therefore, it is possible to prevent the amount of ink supplied to the first ejection head and the second ejection head from becoming insufficient or excessive. Shape can be stabilized. Therefore, deterioration in print quality can be suppressed.

It is a figure which shows the inkjet printing apparatus of embodiment. FIG. 2 is a top view showing a printing unit shown in FIG. 1; 2 is a diagram showing the configuration of an ink supply unit shown in FIG. 1; FIG. It is a figure which shows the electrical connection with a control part, a 1st flow control valve, and a 2nd flow control valve. FIG. 5 is a diagram showing temporal changes in the amount of ink ejected by an ejection head and the amount of ink supplied.

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them. In the drawings, for ease of understanding, the dimensions and numbers of each part may be exaggerated or simplified as necessary.

<1. embodiment>
FIG. 1 is a diagram showing an inkjet printer 1 according to an embodiment. The inkjet printing apparatus 1 forms an image on the base material 9 by ejecting ink from the plurality of head units 31 to 34 of the printing unit 3 toward the base material 9 while conveying the base material 9 having a long belt shape. do. The base material 9 is, for example, printing paper. However, the substrate 9 may be a resin film, a metal foil, a glass substrate, or the like. As shown in FIG. 1 , the inkjet printing apparatus 1 includes a substrate conveying section 2 , a printing section 3 , four ink supply sections 41 and a control section 8 .

The base material conveying section 2 conveys the base material 9 in a predetermined conveying direction. The conveying direction is parallel to the longitudinal direction of the substrate 9 . The substrate conveying section 2 has an unwinding roller 21 , a plurality of conveying rollers 22 and a winding roller 23 . The base material 9 is unwound from the unwinding roller 21 and conveyed along a conveying path formed by a plurality of conveying rollers 22 . Each conveying roller 22 guides the base material 9 to the downstream side of the conveying path by rotating around a rotating shaft extending in the horizontal direction. The substrate 9 after transport is collected by the take-up roller 23 .

Motors 25 are connected to the rotation shafts of the feed roller 21 and the take-up roller 23, respectively. Each motor 25 is electrically connected to the controller 8 . Each motor 25 rotates the unwinding roller 21 and the winding roller 23 at a predetermined rotational speed based on the control signal transmitted by the control section 8 . Thereby, the base material 9 is conveyed along the conveying path at a predetermined conveying speed. Note that the motor 25 may be connected to any one of the plurality of conveying rollers 22 .

At least one of the transport rollers 22 is provided with an encoder 26 . The encoder 26 detects the amount of rotation of the conveying roller 22 . More specifically, the encoder 26 outputs a pulse signal to the controller 8 each time the conveying roller 22 rotates by 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. Note that the encoder 26 may detect the amount of rotation of a roller different from the conveying roller 22 .

The substrate 9 moves substantially parallel to the arrangement direction of the plurality of head units 31-34 under the plurality of head units 31-34. The surface of the base material 9 faces the head units 31-34. Further, the base material 9 is stretched over a plurality of conveying rollers 22 while being tensioned. This suppresses slackness and wrinkles of the base material 9 during transportation.

The printing unit 3 ejects droplets of ink (hereinafter referred to as “ink droplets”) onto the substrate 9 conveyed by the substrate conveying unit 2 . The printing section 3 of this embodiment has four head units 31-34. The head units 31 to 34 are arranged along the transport path of the base material 9. As shown in FIG.

FIG. 2 is a top view showing the printing section 3 shown in FIG. The head units 31 to 34 of the printing section 3 each cover the entire width of the substrate 9 . 2, a plurality of ejection ports 35 arranged in parallel with the width direction of the substrate 9 are provided on the lower surface of each of the head units 31-34. Each of the head units 31 to 34 emits K (black), C (cyan), M (magenta), and Y (yellow), which are color components of a multicolor image, from a plurality of ejection ports 35 toward the upper surface of the substrate 9. ink droplets of each color are ejected.

The four head units 31 to 34 each form a monochromatic image on the upper surface of the substrate 9 by ejecting ink droplets. A multicolor image is formed on the upper surface of the substrate 9 by superimposing the four monochromatic images.

As shown in FIG. 2, each of the head units 31 to 34 has two ejection heads 311 and 312 . The ejection heads 311 and 312 are arranged in the width direction. The width direction is a direction perpendicular to the conveying direction and parallel to the surface of the substrate 9 . Note that the head units 31 to 34 may have three or more ejection heads.

The ejection heads 311 and 312 have ejection surfaces facing the surface of the substrate 9 transported by the substrate transport section 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 piezo system or a thermal system. The inkjet elements eject ink from the corresponding ejection ports 35 under the control of the controller 8 . The ejection heads 311 and 312 eject ink to different positions in the width direction on the substrate 9 .

The ejection heads 311 and 312 have ink chambers 36 for temporarily storing ink. The ink chamber 36 communicates with 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 supply ink to the head units 31 to 34, respectively. More specifically, each ink supply unit 41 supplies ink to the ink chambers 36 of the ejection heads 311 and 312 .

FIG. 3 is a diagram showing the configuration of the ink supply section 41 shown in FIG. The ink supply section 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 forming section 5 and a replenishment tank 61 . The supply tank 42 and the recovery tank 43 can each store ink.

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

The supply pipe 44 has a common pipe 440 , a first branch pipe portion 441 and a second branch pipe portion 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 each of the first branch pipe portion 441 and the second branch pipe portion 442 . The other end of the first branch pipe portion 441 is connected to the supply port of the ejection head 311 , and the other end of the second branch pipe portion 442 is connected to the supply port of the ejection head 312 .

A first flow control valve 471 is inserted in the first branch pipe portion 441 . A second flow control valve 472 is inserted in the second branch pipe portion 442 . The first flow rate control valve 471 and the second flow rate control valve 472 change the flow rate of the ink passing through the first branch pipe section 441 and the second branch pipe section 442 to two or more levels greater than zero. The first flow control valve 471 and the second flow control valve 472 are proportional control solenoid valves, for example. The first flow regulating valve 471 and the second flow regulating valve 472 are electrically connected to the controller 8 and operate based on control signals transmitted by the controller 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.

The first flow rate control valve 471 changes the amount of ink supplied to the ejection head 311 per unit time (hereinafter simply referred to as “supply amount”). The second flow control valve 472 changes the amount of ink supplied to the ejection head 312 . The control unit 8 and the first flow control valve 471 constitute a supply amount changing unit that changes the amount of ink supplied to the ejection head 311 . Also, the control unit 8 and the second flow control valve 472 constitute a supply amount changing unit that changes the amount of ink supplied to the ejection head 312 .

The recovery pipe 45 is a channel that connects the ejection heads 311 and 312 and the recovery tank 43 , and constitutes a channel of ink from the ejection heads 311 and 312 to the recovery tank 43 . The recovery pipe 45 has a common pipe 450 , a first branch pipe portion 451 and a second branch pipe portion 452 . One end of the first branch pipe portion 451 is connected to the outlet of the ejection head 311 , and one end of the second branch pipe portion 452 is connected to the outlet of the ejection head 312 . The other ends of the first branch pipe portion 451 and the second branch pipe portion 452 are connected to one end of the common pipe 450 . The other end of the common pipe 450 is connected to the collection tank 43 .

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 . A return pump 461 sends ink from the collection tank 43 to the supply tank 42 . The recovery pipe 45, the return pipe 46, and the return pump 461 constitute an ink recovery section. It should be noted that the movement of the ink from the recovery tank 43 to the supply tank 42 may be performed using gravity.

The replenishment tank 61 stores ink for replenishment. The replenishment tank 61 is connected to the supply tank 42 via a replenishment pipe 62 . A replenishment pump 621 is inserted in the replenishment pipe 62 . The replenishment pump 621 pumps the ink in the replenishment tank 61 to the supply tank 42 . For example, when the total amount of ink circulating in the supply tank 42 , head unit 31 , and recovery tank 43 decreases due to printing or the like, the supply tank 42 is replenished with ink from the replenishment tank 61 by the replenishment pump 621 .

The pressure difference forming part 5 forms a pressure difference between the supply tank 42 and the recovery tank 43 by adjusting the pressure inside the supply tank 42 and the pressure inside the recovery tank 43 . Hereinafter, the pressure difference formed by the pressure difference forming section 5 is simply referred to as "pressure difference". Ink is sent from the supply tank 42 to the recovery tank 43 by forming a pressure difference with the pressure difference forming unit 5 .

The pressure difference forming section 5 includes a first pressure adjusting section 51a and a second pressure adjusting section 51b. The first pressure adjustment section 51 a adjusts the pressure inside the supply tank 42 . The second pressure adjustment section 51 b adjusts the pressure inside the recovery tank 43 .

The first pressure adjusting section 51 a has a first pressure changing section 52 and a pressure tank 53 . The first pressure changer 52 changes the pressure in the pressurized tank 53 based on the control signal output by the controller 8 . Specifically, the first pressure changer 52 includes an air pressure sensor 521 , a pressure pump 522 , a pressure reduction pump 523 and a suction pump 524 .

The air pressure sensor 521 measures the pressure inside the pipe communicating with the pressurized tank 53 . The air pressure sensor 521 outputs a measurement signal indicating the measured pressure to the controller 8 .

The pressurization pump 522 and the decompression pump 523 are provided in a pipe connected inside the pressurization tank 53 . The pressurization pump 522 increases the pressure in the pressurization tank 53 by sending air to the pressurization tank 53 . The decompression pump 523 reduces the pressure in the pressurization tank 53 by sucking air from the pressurization tank 53 .

The suction pump 524 is provided in the middle of a pipe having one end connected to the pressurized tank 53 and the other end open to the atmosphere. The suction pump 524 generates a pressure in the pipe to release the air in the pressurized tank 53 to the atmosphere.

The pressure tank 53 is connected to the supply tank 42 by a pipe through which air can flow. The pressure in the supply tank 42 is changed by changing the pressure in the pressurization tank 53 .

The second pressure adjusting section 51 b has a second pressure changing section 54 and a negative pressure tank 55 . The second pressure adjusting section 51 b is connected to the negative pressure tank 55 and adjusts the pressure inside the negative pressure tank 55 . The second pressure changer 54 changes the pressure inside the negative pressure tank 55 based on the control signal output by the controller 8 . Since the second pressure changer 54 has the same configuration as the first pressure changer 52, the description thereof is omitted. The negative pressure tank 55 communicates with the recovery tank 43 . By changing the pressure in the negative pressure tank 55, the pressure in the recovery tank 43 is changed.

The pressure difference forming unit 5 may form the pressure difference while the supply tank 42 and the recovery tank 43 are both at a negative pressure. Further, the pressure difference forming unit 5 may form a pressure difference in a state where the inside of the supply tank 42 is at positive pressure and the inside of the recovery tank 43 is at a negative pressure.

The control unit 8 has a configuration as a computer, such as a processor such as a CPU, a ROM that stores programs, and a RAM that stores various information. The controller 8 causes the head units 31 to 34 to eject ink droplets based on the image data and the pulse signal output by the encoder 26 . As a result, an image represented by the image data is formed on the surface of the base material 9 .

As shown in FIG. 3, the processor of the control unit 8 operates according to a program, whereby the control unit 8 includes a discharge amount prediction unit 81, a pressure control unit 83, an image data division unit 85, a supply amount control unit 87, and It functions as a discharge control section 89 . Part or all of the functions of the control unit 8 may be implemented by a dedicated circuit.

Based on the image data, the ejection amount prediction unit 81 predicts the amount of ink to be ejected per unit time by the head units 31 to 34 at a time earlier than the current time. The ejection amount prediction unit 81 calculates, for example, the printing rate from the image data. The print rate represents the amount of ink per unit area applied 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 ejection amount prediction unit 81 may use the print rate as the predicted ejection amount.

The pressure control unit 83 controls the amount of ink supplied from the supply tank 42 to the recovery tank 43 by controlling the pressure difference forming unit 5 according to the predicted ejection amount predicted by the ejection amount prediction unit 81 .

The pressure control unit 83 performs feedforward control, for example. More specifically, the pressure control section 83 controls the pressure difference forming section 5 based on the predicted discharge amount and the time lag. By controlling the pressure difference forming part 5 by the pressure control part 83, the pressure difference is adjusted at the timing according to the fluctuation of the predicted discharge amount. The time lag is 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, and the time when the pressure difference is actually changed. is the difference (time difference) to The magnitude of the time lag is appropriately determined according to, for example, the pressure difference forming section 5, the supply pipe 44, and the recovery pipe 45. More specifically, the magnitude of the time lag is, for example, the characteristics of the pressure pump 522 and the pressure reduction 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 of the supply pipe 44 and the recovery pipe 45, the size of the cross section, and the like. Also, the magnitude of the time lag may be determined according to the ink viscosity, temperature, and the like.

FIG. 4 is a diagram showing electrical connections among the control unit 8, the first flow control valve 471, and the second flow control valve 472. As shown in FIG. The image data division unit 85 divides image data to be formed on the base material 9 by the head unit 31 into first image data formed by the ejection head 311 and second image data formed by the ejection 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 ejection control unit 89 . The image data division unit 85 divides the image data corresponding to the head units 32 to 34 into first image data and second image data corresponding to the respective ejection heads 311 and 312 in the same manner as the image data corresponding to the head unit 31. split into

The supply amount control section 87 controls the first flow control valve 471 and the second flow control valve 472 based on the first image data and the second image data. Specifically, the supply amount control unit 87 calculates the ink ejection amounts of the ejection heads 311 and 312 based on the printing rates 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 amount of ink supplied to the ejection heads 311 and 312 becomes a value larger than the calculated ejection amount. . As a result, an appropriate amount of ink can be supplied to the ejection heads 311 and 312 relative to the amount of ink actually ejected by the ejection heads 311 and 312 . Note that the image data division unit 85 may transmit each printing ratio 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.

When the flow rate of ink is controlled by the first flow rate control valve 471 , the amount of ink supplied to the ejection head 311 can be controlled more quickly than in the case of controlling the amount of supply based on the pressure difference as in the pressure difference forming section 5 . Therefore, the supply amount control unit 87 controls the first flow control valve 471 with a time lag shorter than the time lag set for the pressure difference forming unit 5 by the pressure control unit 83 (or without a time lag). good too.

The ejection control unit 89 ejects ink droplets from the ejection openings 35 of the ejection heads 311 and 312 based on the received first image data and second image data. Thereby, the ejection heads 311 and 312 form an image corresponding to the first image data and an image corresponding to the second image data on the substrate 9 . Accordingly, an image corresponding to the original image data is formed on the substrate 9 .

FIG. 5 is a diagram showing temporal changes in the amount of ink ejected by the ejection head 311 and the amount of ink supplied. In FIG. 5, the horizontal axis represents time, and the vertical axis represents the amount of ink. In FIG. 5, a graph G11 indicates changes in the amount of ink discharged, and a graph G21 indicates changes in the amount of ink supplied. A graph G12 is a diagram showing a moving average of the ejection amount graph G11.

The supply amount control unit 87 controls 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. You may For example, as shown in FIG. 5, when the supply amount control unit 87 obtains the supply amount QS1 at the target time T1, first, the target time T1, the time T0 before the target time T1, and the time T0 after the target time T1. from the first image data. Then, the first flow control valve 471 obtains an average of the calculated discharge amounts (average discharge amount) AQD1. Further, the supply amount control unit 87 may add a predetermined amount to the calculated average discharge amount AQD1 as the supply amount QS1 at the target time T1.

Note that the supply amount control unit 87 may determine the supply amount at the target time T1 based on only the average value of the discharge amount after the target time T1 or before the target time T1. Further, the supply amount control unit 87 may obtain the supply amount QS1 at the target time T1 based on the discharge amount at two times or at least four times.

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. Therefore, fluctuations in the amount of ink supplied to the ejection head 311 can be relatively small with respect to fluctuations in the ejection amount of the ejection head 311 . As a result, even if the ejection amount of the ejection head 311 changes suddenly, the pressure in the flow path through which the ink passes (the first branch pipe portion 441, the ink chamber 36 of the ejection head 311, etc.) suddenly fluctuates. can be suppressed. Therefore, the shape of the ink meniscus at the ejection port of the first ejection head can be stabilized.

The supply amount control unit 87 controls the second flow rate adjustment valve 472 so that the amount of ink supplied to the ejection head 312 becomes a value corresponding to the average ejection amount, similarly to the control of the first flow rate adjustment valve 471 . may

According to the inkjet printing apparatus 1, the ink supply amount is controlled according to the ink ejection amount for each of the ejection heads 311 and 312. FIG. Therefore, an appropriate amount of ink can be supplied to each of the ejection heads 311 and 312 . As a result, it is possible to prevent both of the ejection heads 311 and 312 from running out of ink or being supplied with excess ink. Therefore, the shape of the ink meniscus at each ejection port 35 of the ejection heads 311 and 312 can be stabilized. By stabilizing the shape of the meniscus, ink droplet ejection failure (nozzle defect) is suppressed, and the ink droplet ejection speed and impact accuracy are stabilized. Therefore, deterioration in print quality can be suppressed.

Moreover, since it is possible to suppress excessive supply of ink to the ejection heads 311 and 312, the life of each pump such as the return pump 461 can be extended. In addition, since excessive circulation of ink can be suppressed, deterioration of ink can be reduced.

<2. Variation>
Although the embodiments have been described above, the present invention is not limited to the above, and various modifications are possible.

In the above embodiment, the pressure difference forming section 5 adjusts the pressure difference according to the predicted discharge amount of the head unit 31 . However, it is not essential that the pressure difference is adjusted according to the predicted discharge amount of the head unit 31 . For example, the pressure difference forming section 5 may form a constant pressure difference regardless of the predicted discharge amount.

In the above-described embodiment, one first flow control valve 471 is provided in the first branch pipe portion 441 of the supply pipe 44, but a plurality of first flow control valves 471 are provided in the first branch pipe portion 441. good too. The amount of ink supplied to the ejection head 311 may be changed by the supply amount control unit 87 controlling the plurality of first flow rate adjustment valves 471 . By providing the plurality of first flow rate control valves 471, it becomes easy to change the amount of ink supplied to the ejection head 311 in multiple stages. Further, when the supply amount control section 87 controls the plurality of first flow rate adjustment valves 471, the supply amount control section 87 may control each first flow rate adjustment valve 471 with a time lag. As a result, the pressure change in the first branch pipe portion 441 can be reduced, so that the shape of the ink meniscus at each ejection port 35 of the ejection head 311 can be further stabilized.

In the above embodiment, the first flow control valve 471 is provided in the supply pipe 44 positioned upstream from the discharge head 311 . However, the first flow control valve 471 may be provided in the recovery pipe 45 located downstream of the discharge head 311 . For example, the first flow control valve 471 may be provided in the first branch pipe section 451 of the recovery pipe 45 . Also, the second flow control valve 472 may be provided in the second branch pipe section 452 . If the first flow control valve 471 is provided upstream of the ejection head 311, the flow rate of the ink flowing through the ejection head 311 can be directly controlled. Therefore, compared to the case where the first flow control valve 471 is provided downstream of the ejection head 311, the ink supply amount can be controlled with high accuracy.

Instead of the first flow rate adjustment valve 471 or the second flow rate adjustment valve 472, a pump capable of adjusting the flow rate may be provided. The amount of ink supplied to the ejection heads 311 and 312 may be changed by controlling the pumps.

Although the present invention has been described in detail, the above description is, in all aspects, illustrative and not intended to limit the present invention. It is understood that numerous variations not illustrated can be envisioned without departing from the scope of the invention. Each configuration described in each of the above embodiments and modifications can be appropriately combined or omitted as long as they do not contradict each other.

Reference Signs List 1 inkjet printing device 2 substrate conveying unit 3 printing unit 5 pressure difference forming unit 8 control unit 9 substrate 31-34 head unit 41 ink supply unit 42 supply tank 43 recovery tank 44 supply pipe 45 recovery pipe 46 return pipe 83 pressure control Section 85 Image Data Division Section 87 Supply Amount Control Section 311 Ejection Head (First Ejection Head)
312 ejection head (second ejection head)
461 return pump 471 first flow control valve 472 second flow control valve

Claims (9)

An inkjet printing device,
a substrate conveying unit that conveys the substrate in a predetermined conveying direction;
a first ejection head and a second ejection head that eject ink droplets onto the surface of the substrate conveyed by the substrate conveying unit;
an ink supply unit that supplies ink to the first ejection head and the second ejection head;
image data representing an image to be formed on the substrate, first image data representing an image to be formed on the substrate by the first ejection head, and image data to be formed on the substrate by the second ejection head. an image data division unit that divides the image data into the second image data;
The amount of ink supplied by the ink supply unit to the first ejection head is changed based on the first image data, and the ink supply unit supplies the ink to the second ejection head based on the second image data. a supply amount changing unit for changing the amount of ink to be supplied;
An inkjet printing device, comprising: The inkjet printing device according to claim 1, wherein
The inkjet printing apparatus, wherein the first ejection head and the second ejection head eject ink droplets at different positions on the substrate in a width direction that intersects with the transport direction. The inkjet printing device according to claim 1 or 2,
The inkjet printing apparatus, wherein the first ejection head and the second ejection head eject ink droplets of the same type. The inkjet printing device according to any one of claims 1 to 3,
The ink supply unit is connected to a supply tank capable of storing ink, and supplies ink from the supply tank to the first ejection head or the second ejection head. The inkjet printing device according to claim 4,
an ink recovery unit that recovers from the first ejection head the ink that has not been ejected from the first ejection head and returns it to the supply tank;
An inkjet printing device, further comprising: The inkjet printing device according to claim 5,
The ink supply unit
a supply pipe for supplying ink from the supply tank to the first ejection head;
has
The ink jet printing apparatus, wherein the supply amount changing unit changes the flow rate of ink in the supply pipe. The inkjet printing device according to claim 5 or claim 6,
The ink recovery unit
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;
has
The ink supply unit
a pressure difference forming unit for sending ink from the supply tank toward the first ejection head and the second ejection head by forming a pressure difference between the supply tank and the recovery tank;
An inkjet printing device, comprising: The inkjet printing device according to any one of claims 1 to 7,
The ink jet printing apparatus, wherein the supply amount changing 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 in a predetermined period. An inkjet printing method comprising:
a) conveying the substrate in a predetermined conveying direction;
b) when ink droplets are ejected from the first ejection head and the second ejection head onto the surface of the substrate conveyed in step a),
c) supplying ink to the first ejection head and the second ejection head;
d) combining the image data representing the image to be formed on the base material with the first image data representing the image to be formed on the base material by the first ejection head in step b) and the second ejection head in step b); second image data representing an image to be formed on the substrate by a head;
e) changing the amount of ink supplied to the first ejection head in step c) based on the first image data, and performing the second ejection in step c) based on the second image data; changing the amount of ink supplied to the head;
A method of inkjet printing, comprising:

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