Liquid discharge device and liquid circulation control method
Patent Information
- Application Number
- PCT/JP2026/004375
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-02-25
- Filing Date
- 2026-02-06
- Publication Date
- 2026-09-03
Smart Images
Figure JP2026004375_03092026_PF_FP_ABST
Abstract
Description
Liquid ejection apparatus and method for controlling liquid circulation
[0001] The present disclosure relates to a liquid ejection apparatus and a method for controlling liquid circulation.
[0002] Japanese Unexamined Patent Application Publication No. 2011-240628 discloses a printing apparatus comprising: a print head that ejects ink (corresponding to an inkjet head); a first storage tank that stores ink (corresponding to a recovery tank); and a second storage tank that stores ink supplied from the first storage tank and supplies ink to the print head (corresponding to a supply tank), wherein ink not ejected from the print head is recovered into the first storage tank and circulated to the second storage tank. In the printing apparatus of Japanese Unexamined Patent Application Publication No. 2011-240628, a method has been proposed in which driving of a circulation pump provided in a flow path between the first storage tank and the second storage tank is controlled based on an amount of ink stored in the second storage tank. Further, International Publication No. 2015 / 190201 also discloses an inkjet printing apparatus having an ink circulation configuration that is the same as that of Japanese Unexamined Patent Application Publication No. 2011-240628.
[0003] In the inkjet printing apparatuses described in Japanese Unexamined Patent Application Publication No. 2011-240628 and International Publication No. 2015 / 190201, the circulation pump is controlled based on the amount of ink stored in the supply tank, but when the circulation pump is controlled, the ink pressure in the inkjet head may fluctuate. In order to stably eject ink droplets from nozzles of an inkjet head during image formation and form a high-quality image, it is effective to suppress fluctuations in ink pressure within the inkjet head.
[0004] An object of the present disclosure is to provide a liquid ejection apparatus that stabilizes droplets ejected from a liquid ejection head, and a method for controlling liquid circulation that stabilizes droplets ejected from the liquid ejection head.
[0005] The liquid dispensing device of this disclosure includes: a liquid dispensing head equipped with a nozzle for dispensing liquid; a supply tank for storing liquid supplied to the liquid dispensing head; a recovery tank for storing liquid recovered from the liquid dispensing head; a recovery-side liquid level sensor for measuring the liquid level in the recovery tank; a liquid supply path for supplying liquid from the supply tank to the liquid dispensing head; a liquid recovery path for recovering liquid from the liquid dispensing head to the recovery tank; a liquid circulation path equipped with a circulation pump for circulating liquid from the recovery tank to the supply tank; a first control unit for controlling the discharge amount of the circulation pump so that the measurement value of the recovery-side liquid level sensor becomes a target value; a supply-side pressure adjustment unit for adjusting the pressure of the liquid stored in the supply tank by the air pressure inside the supply tank; a recovery-side pressure adjustment unit for adjusting the pressure of the liquid stored in the recovery tank by the air pressure inside the recovery tank; a supply-side pressure sensor for measuring the pressure of the liquid in the liquid supply path; and a recovery-side pressure sensor for measuring the pressure of the liquid in the liquid recovery path. The system includes a second control unit that controls the supply-side pressure adjustment unit and the recovery-side pressure adjustment unit so that the measured values from the supply-side pressure sensor and the recovery-side pressure sensor reach their respective target values.
[0006] The first control unit preferably performs proportional-integral-derivative control over the circulation pump.
[0007] It is preferable that the liquid level sensor on the recovery side is an analog sensor.
[0008] It is preferable that the supply-side pressure adjustment unit and the recovery-side pressure adjustment unit adjust the air pressure in the supply tank and the air pressure in the recovery tank so that the pressure of the liquid in the supply tank is higher than the pressure of the liquid in the recovery tank.
[0009] The liquid discharge device of the present disclosure preferably further comprises a liquid storage section for storing liquid, a liquid replenishment path equipped with a replenishment pump for supplying liquid from the liquid storage section to a liquid circulation path, a supply-side liquid level sensor for measuring the liquid level height of a supply tank, and a third control unit that controls the replenishment pump so that the sum of the values measured by the supply-side liquid level sensor and the recovery-side liquid level sensor approaches a target value.
[0010] Preferably, the liquid dispensing device of this disclosure further includes a temperature control unit for controlling the temperature of the liquid between the junction of the liquid circulation path and the liquid replenishment path and the supply tank.
[0011] It is preferable that the liquid is an ultraviolet-curing ink, and that the circulation pump and replenishment pump are diaphragm pumps.
[0012] The liquid circulation control method of the present disclosure is a liquid discharge device comprising: a liquid discharge head equipped with a nozzle for discharging liquid; a supply tank for storing liquid supplied to the liquid discharge head; a recovery tank for storing liquid recovered from the liquid discharge head; a recovery-side liquid level sensor for measuring the liquid level in the recovery tank; a liquid supply path for supplying liquid from the supply tank to the liquid discharge head; a liquid recovery path for recovering liquid from the liquid discharge head to the recovery tank; a liquid circulation path equipped with a circulation pump for circulating liquid from the recovery tank to the supply tank; a supply-side pressure adjustment unit for adjusting the pressure of the liquid stored in the supply tank by the air pressure inside the supply tank; a recovery-side pressure adjustment unit for adjusting the pressure of the liquid stored in the recovery tank by the air pressure inside the recovery tank; a supply-side pressure sensor for measuring the pressure of the liquid in the liquid supply path; and a recovery-side pressure sensor for measuring the pressure of the liquid in the liquid recovery path. This is a liquid circulation control method that controls the discharge rate of the circulation pump so that the measurement value of the recovery side liquid level sensor reaches a target value, and controls the supply side pressure adjustment unit and the recovery side pressure adjustment unit so that the measurement values of the supply side pressure sensor and the recovery side pressure sensor reach their respective target values.
[0013] The discharge rate of the circulation pump is preferably controlled by proportional-integral-derivative control.
[0014] According to the technology disclosed herein, a liquid dispensing device that stabilizes the droplets discharged from a liquid dispensing head and a method for controlling liquid circulation to stabilize the droplets discharged from a liquid dispensing head can be obtained.
[0015] This is an overall configuration diagram of an inkjet printing apparatus according to an embodiment. This is a perspective view showing the configuration of the print bar. This is a schematic configuration diagram of the ink supply mechanism. This is a diagram showing the change in ink pressure when the liquid level control method of the reference example is implemented. This is a diagram showing the change in ink pressure when the liquid level control method of the embodiment is implemented.
[0016] Hereinafter, an embodiment of the liquid dispensing device and liquid circulation control method of this disclosure will be described with reference to the drawings. Here, an inkjet printing apparatus will be used as an example of an embodiment of the liquid dispensing device. Furthermore, ink will be given as an example of a liquid, and a method for controlling ink circulation to the inkjet head in an inkjet printing apparatus will be described as an embodiment of a liquid circulation control method. In each figure, the same elements are denoted by the same reference numerals.
[0017] "Configuration of Inkjet Printing Apparatus" Figure 1 is an overall configuration diagram of the inkjet printing apparatus 1. The inkjet printing apparatus 1 is an inkjet-type color digital printing apparatus that forms a desired image on a sheet of paper P. The inkjet printing apparatus 1 is a single-sided printing apparatus that forms an image on only one side of the paper P. However, the technology of this disclosure is also applicable to a double-sided printing apparatus that forms an image on both sides of the paper P. Paper P is an example of a recording medium.
[0018] As shown in Figure 1, the inkjet printing apparatus 1 comprises a transport mechanism 10, a paper feeder 20, an image forming unit 40, and an accumulation device 90.
[0019] The transport mechanism 10 transports the paper P with its recording surface (i.e., the paper surface) Pa facing the print bar of the image forming unit 40, which will be described later. In Figure 1, the transport path 12 through which the paper P is transported is shown by a dashed line.
[0020] The transport mechanism 10 includes a plurality of transport members along the transport path 12. The plurality of transport members include a plurality of transport roller pairs 14, a paper feed drum 16 and an output drum 18, and a drawing drum 41, which will be described later. Each transport roller pair 14 includes a drive roller 14a and a pinch roller 14b arranged opposite each other. The transport roller pair 14 grips the paper P between the drive roller 14a and the pinch roller 14b and rotates to feed out the paper P. The transport members may also include a transport drum, a belt conveyor, a chain gripper and a transport guide. The transport mechanism 10 also includes a drive unit such as a motor (not shown) and a motor drive circuit (not shown) as a power source. The paper P is transported along the transport path 12 by these elements constituting the transport mechanism 10.
[0021] The paper feeder 20 is an example of a paper feed section that houses the paper P to be transported toward the image forming unit 40. The paper feeder 20 is equipped with a paper feed tray on which a stack of multiple sheets of paper P is placed. The type of paper P is not particularly limited, but for example, cellulose-based printing paper such as fine paper, coated paper, and art paper can be used. The maximum paper size that can be used in the inkjet printer 1 is, for example, A0 size (841 mm x 1189 mm).
[0022] The paper feeder 20 takes out the stack of paper P set inside, one sheet at a time from the top, and supplies it to the transport path 12.
[0023] The image forming unit 40 performs image formation by ejecting droplets onto the recording surface Pa of the paper P. The image forming unit 40 includes a drawing drum 41 and a head unit 42. The drawing drum 41 receives the paper P from the paper feed drum 16, subjects the received paper P to image formation by the head unit 42, and discharges the paper P from the discharge drum 18. The drawing drum 41 is equipped with a gripper (not shown) on its circumferential surface, and by gripping the leading edge of the paper P with the gripper and rotating it, the paper P is wrapped around the circumferential surface of the drum and transported. The drawing drum 41 is also equipped with a suction mechanism (not shown), which suctions the paper P wrapped around the circumferential surface of the drum and transports it. Negative pressure is used for suction. The drawing drum 41 is equipped with numerous suction holes on its circumferential surface, and by suction from inside the drawing drum 41 through these suction holes, the paper P is suctioned to the circumferential surface of the drawing drum 41.
[0024] The head unit 42 includes print bars 43C, 43M, 43Y, and 43K. In the following, when it is not necessary to distinguish between print bars 43C, 43M, 43Y, and 43K, they will be referred to as print bar 43. The print bar 43 comprises a rectangular parallelepiped housing 44, and inkjet heads 45, a circuit board 46, and a flexible cable 47, each housed within the housing 44. As shown in Figure 2, the inkjet head 45 includes a plurality of head modules 48, which are arranged along the longitudinal direction A. Each head module 48 has a plurality of nozzles for ejecting liquid, and the nozzle surface 48a having the nozzles is positioned to face the recording surface Pa. The inkjet head 45 is an example of a "liquid ejection head" in the technology of this disclosure.
[0025] In the image forming unit 40, the print bar 43 is arranged such that its longitudinal direction A intersects (orthogonal in this example) with the paper transport direction T of the paper P. Also, as shown in Figure 1, the multiple print bars 43C, 43M, 43Y, and 43K are arranged sequentially along the transport direction T.
[0026] Print bar 43C is equipped with an inkjet head 45 that ejects droplets of cyan ink. Print bar 43M is equipped with multiple inkjet heads 45 that eject droplets of magenta ink. Print bar 43Y is equipped with an inkjet head 45 that ejects droplets of yellow ink. Print bar 43K is equipped with multiple inkjet heads 45 that eject droplets of black ink.
[0027] Furthermore, each inkjet head 45 of print bars 43C, 43M, 43Y, and 43K is supplied with ink corresponding to its respective state by an ink supply mechanism 50 (see Figure 3), which is not shown in Figure 1. For example, ultraviolet-curing ink is used as the ink for drawing in the inkjet printing device 1. Other inks such as water-based ink, oil-based ink, and solvent-based ink can also be used for drawing. The ink supply mechanism 50 will be described later.
[0028] In the image forming unit 40, ink droplets are ejected toward the paper P being transported by the drawing drum 41, and an image is formed on the paper P as the ejected droplets adhere to the paper P.
[0029] In this example, a configuration using four CMYK inks is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment. Print bars equipped with inkjet heads that eject light ink, dark ink, spot ink, etc., may be added as needed. Furthermore, there are no particular limitations on the arrangement order of the print bars for each color.
[0030] The stacking device 90 stacks the paper sheets P on which images have been formed. The stacking device 90 receives the paper sheets P discharged from the transport path 12 and stacks the paper sheets P in bundles on a stacking tray (not shown).
[0031] The inkjet printing apparatus 1 is equipped with a processor (not shown). The processor includes a CPU (Central Processing Unit). The processor functions as a processing unit and / or control unit that performs various processes by executing program instructions stored in a memory device. The processor comprehensively controls the transport mechanism 10, the paper feed device 20, the image forming unit 40, and the integrator 90.
[0032] (Configuration of the ink supply mechanism) Next, with reference to Figure 3, the configuration of the ink supply mechanism 50 that supplies ink to the inkjet head 45 will be described. Note that each inkjet head 45 of print bars 43C, 43M, 43Y, and 43K is provided with an ink supply mechanism 50, and they have the same configuration as each other.
[0033] The ink supply mechanism 50 is driven at least during the printing process by the inkjet printer 1. The ink supply mechanism 50 supplies ink to the inkjet head 45, recovers any ink that is not ejected from the inkjet head 45, and returns the ink to the inkjet head 45, thereby realizing ink circulation. More specifically, the ink supply mechanism 50 supplies ink to each of the head modules 48 of the inkjet head 45 and recovers ink from each head module 48. That is, supplying ink to each head module 48 means supplying ink to the inkjet head 45, and recovering ink from each head module 48 means recovering ink from the inkjet head 45. As shown in Figure 3, the ink supply mechanism 50 includes a supply tank 51, a recovery tank 52, a liquid supply passage 56, a liquid recovery passage 57, and a liquid circulation passage 58.
[0034] The supply tank 51 stores the ink supplied to the head module 48. The supply tank 51 is connected to the recovery tank 52 by a liquid circulation path 58.
[0035] The recovery tank 52 stores the ink recovered from the head module 48. The ink recovered from the head module 48 is the ink that was not ejected from the nozzles of the head module 48.
[0036] The liquid supply passage 56 connects the supply tank 51 and the head module 48. The liquid supply passage 56 is the flow path for ink supplied from the supply tank 51 to the head module 48. A supply-side manifold 61 is provided in the middle of the liquid supply passage 56. The liquid supply passage 56 includes an upstream supply passage 56A and a downstream supply passage 56B. One end of the upstream supply passage 56A is connected to the supply tank 51 and the other end is connected to the supply-side manifold 61. The downstream supply passage 56B includes multiple branch passages 56B1, one end of which is connected to the supply-side manifold 61 and the other end of which is connected to each of the multiple head modules 48. In other words, the liquid supply passage 56 branches off into multiple branch passages 56B1 that connect to each of the multiple head modules 48 via the supply-side manifold 61 in the downstream supply passage 56B. Note that in Figure 3, one head module 48 is shown as a representative example. The supply-side manifold 61 temporarily stores the ink that is supplied to each of the multiple head modules 48. The ink is supplied to each head module 48 via the supply-side manifold 61 and each branch 56B1.
[0037] The liquid recovery path 57 is the flow path for ink recovered from the head module 48 to the recovery tank 52. A recovery-side manifold 62 is provided in the middle of the liquid recovery path 57. The liquid recovery path 57 includes an upstream recovery path 57A and a downstream recovery path 57B. The upstream recovery path 57A includes multiple branch paths 57A1, one end of which is connected to each of the multiple head modules 48 and the other end of which is connected to the recovery-side manifold 62. The downstream recovery path 57B is one end of which is connected to the recovery-side manifold 62 and the other end of which is connected to the recovery tank 52. The recovery-side manifold 62 temporarily stores the ink recovered from the multiple head modules 48.
[0038] The liquid circulation path 58 connects the recovery tank 52 and the supply tank 51. The liquid circulation path 58 is the flow path for ink sent from the recovery tank 52 to the supply tank 51. The liquid circulation path 58 is equipped with a circulation pump 59. The ink supply mechanism 50 is equipped with a circulation pump control unit 60 that controls the circulation pump 59. The circulation pump 59, whose drive is controlled by the circulation pump control unit 60, sends the ink in the recovery tank 52 to the supply tank 51. The circulation pump control unit 60 is an example of the "first control unit" of the technology disclosed herein.
[0039] The recovery tank 52 is equipped with a recovery-side liquid level sensor 55. The recovery-side liquid level sensor 55 measures the liquid level of the ink in the recovery tank 52. The measured value detected by the recovery-side liquid level sensor 55 is transmitted to the circulation pump control unit 60. In this example, the recovery-side liquid level sensor 55 is an analog sensor.
[0040] The circulation pump control unit 60 controls the discharge rate of the circulation pump 59 so that the measurement value from the recovery side liquid level sensor 55 (i.e., the liquid level height in the recovery tank 52) reaches the target value. The circulation pump 59 is constantly driven, and feedback control is performed by the circulation pump control unit 60. For feedback control, proportional (P), integral (I), differential (D), or PI control, PD control, PID control, etc., can be used. PID control is particularly preferred because it has the highest error suppression effect. In the following, the control by the circulation pump control unit 60 may be referred to as liquid level control.
[0041] The ink circulation path is comprised of a supply tank 51, a liquid supply path 56, an inkjet head 45 (more specifically, a head module 48), a liquid recovery path 57, a recovery tank 52, and a liquid circulation path 58.
[0042] The supply-side manifold 61 is equipped with a supply-side pressure sensor 63 for measuring ink pressure. Measuring the ink pressure in the supply-side manifold 61 is equivalent to measuring the ink pressure in the liquid supply passage 56.
[0043] The recovery-side manifold 62 is provided with a recovery-side pressure sensor 64 that measures ink pressure. Measuring the ink pressure in the recovery-side manifold 62 is equivalent to measuring the pressure of ink in the liquid recovery path 57.
[0044] The ink supply mechanism 50 further includes a supply-side pressure adjustment unit 66 and a recovery-side pressure adjustment unit 67.
[0045] The supply-side pressure adjustment unit 66 adjusts the pressure of ink stored in the supply tank 51 by means of the air pressure inside the supply tank 51. The supply-side pressure adjustment unit 66 adjusts the inflow of air into the supply tank 51 and the discharge of air from the supply tank 51 so that the air pressure inside the supply tank 51 becomes a preset supply-side target air pressure.
[0046] The supply-side pressure adjustment unit 66 is configured to include, for example, an air pressure adjustment valve, an air pressure supply source, a primary-side air pipe, a secondary-side air pipe, and an air pressure sensor. The air pressure supply source includes, for example, a compressor and a vacuum pump; the compressor is used when pressurizing, and the vacuum pump is used when depressurizing. The primary-side air pipe is a pipe that connects the air pressure supply source and the air pressure adjustment valve. The secondary-side air pipe is a pipe that connects the air pressure adjustment valve and the supply tank 51. The air pressure sensor detects the air pressure in the secondary-side air pipe. The air pressure in the secondary-side air pipe connected to the supply tank 51 is equal to the air pressure inside the supply tank 51. The air pressure adjustment valve acquires the air pressure of the secondary-side air pipe from the air pressure sensor, and controls the air pressure supply source to cause air to flow into the supply tank 51 or discharge air from the supply tank 51 such that this air pressure reaches the supply-side target air pressure. The supply-side target air pressure is determined based on the relationship with a desired ink pressure of the ink stored in the supply tank 51.
[0047] The recovery-side pressure adjustment unit 67 adjusts the pressure of ink stored in the recovery tank 52 by means of the air pressure inside the recovery tank 52. The recovery-side pressure adjustment unit 67 adjusts the inflow of air into the recovery tank 52 and the discharge of air from the recovery tank 52 so that the air pressure inside the recovery tank 52 becomes a preset recovery-side target air pressure.
[0048] The recovery-side pressure adjustment unit 67 has a configuration similar to that of the supply-side pressure adjustment unit 66, and includes, for example, an air pressure adjustment valve, an air pressure supply source, a primary-side air pipe, a secondary-side air pipe, and an air pressure sensor. Here, the secondary-side air pipe is a pipe that connects the air pressure adjustment valve and the recovery tank 52. The air pressure sensor detects the air pressure in the secondary-side air pipe. The air pressure in the secondary-side air pipe connected to the recovery tank 52 is equal to the air pressure in the recovery tank 52. The air pressure adjustment valve acquires the air pressure of the secondary-side air pipe from the air pressure sensor, controls the air pressure supply source to cause air to flow into the recovery tank 52 or discharge air from the recovery tank 52 such that this air pressure becomes the recovery-side target air pressure. The recovery-side target air pressure is determined based on the relationship with the pressure of ink stored in the recovery tank 52.
[0049] It should be noted that the supply-side target air pressure and the recovery-side target air pressure are set such that the pressure of ink stored in the supply tank 51 is higher than the pressure of ink stored in the recovery tank 52. That is, the supply-side pressure adjustment unit 66 and the recovery-side pressure adjustment unit 67 are configured to adjust the air pressure in the supply tank 51 and the air pressure in the recovery tank 52 respectively such that the ink pressure in the supply tank 51 becomes higher than the ink pressure in the recovery tank 52. This is to allow ink to be fed from the supply tank 51 to the recovery tank 52 via the head module 48 in the ink circulation path.
[0050] Further, the ink supply mechanism 50 is further provided with a pressure control unit 70 that controls the supply-side pressure adjustment unit 66 and the recovery-side pressure adjustment unit 67. The pressure control unit 70 acquires a measured value of the supply-side ink pressure from the supply-side pressure sensor 63, and controls the supply-side pressure adjustment unit 66 such that the measured value becomes a predetermined target value (hereinafter referred to as a supply-side target value). The pressure control unit 70 also acquires a measured value of the recovery-side ink pressure from the recovery-side pressure sensor 64, and performs feedback control on the recovery-side pressure adjustment unit 67 such that the measured value becomes a predetermined target value (hereinafter referred to as a recovery-side target value). The pressure control unit 70 is an example of the "second control unit" in the technology of the present disclosure. Note that the control performed by the pressure control unit 70 may be collectively referred to as pressure control in some cases.
[0051] As previously described, the supply-side pressure adjustment unit 66 adjusts the air pressure in the supply tank 51 to the supply-side target air pressure using an internal air pressure adjustment valve, and the recovery-side pressure adjustment unit 67 adjusts the air pressure in the recovery tank 52 to the recovery-side target air pressure using an internal air pressure adjustment valve. Pressure control by the pressure control unit 70 is performed in addition to these air pressure adjustments.
[0052] The ink supply mechanism 50 further includes an ink storage section 71 and a liquid replenishment passage 72. The ink storage section 71 stores the ink supplied to the liquid circulation passage 58. The ink storage section is an example of a "liquid storage section" in the technology of this disclosure. The liquid replenishment passage 72 connects the ink storage section 71 and the liquid circulation passage 58. The liquid replenishment passage 72 is a passage for ink sent from the ink storage section 71 to the liquid circulation passage 58. The liquid replenishment passage 72 is equipped with a replenishment pump 73. The ink supply mechanism 50 also includes a replenishment pump control unit 75 that controls the replenishment pump 73. The replenishment pump control unit 75 is an example of a "third control unit" in the technology of this disclosure.
[0053] The replenishment pump control unit 75 controls the drive of the replenishment pump 73 to replenish ink in the liquid circulation path 58. The supply tank 51 is equipped with a supply-side liquid level sensor 54. The supply-side liquid level sensor 54 measures the liquid level of the ink stored in the supply tank 51. It is preferable that the supply-side liquid level sensor 54 is also an analog sensor. For example, the replenishment pump control unit 75 controls the replenishment pump 73 so that the sum of the values measured by the supply-side liquid level sensor 54 and the recovery-side liquid level sensor 55 approaches a target value.
[0054] Furthermore, the ink supply mechanism 50 is further equipped with a temperature control unit 77. The temperature control unit 77 is located between the junction of the liquid circulation path 58 with the liquid replenishment path 72 and the supply tank 51. The temperature control unit 77 is a temperature control device that adjusts the temperature of the ink supplied to the supply tank 51. By adjusting the temperature of the ink with the temperature control unit 77, for example, if the ink is UV ink, the viscosity is adjusted to be within the recommended viscosity range for the inkjet head 45.
[0055] The temperature control unit 77 adjusts the temperature of the ink being sent from the recovery tank 52 to the supply tank 51 and the ink being supplied from the ink storage unit 71. As a result, temperature-controlled ink is supplied to the supply tank 51. The temperature control unit 77 includes, for example, a heater and a temperature sensor.
[0056] The types of circulation pump 59 and replenishment pump 73 are not particularly limited. However, if the ink is UV-curing ink, it is preferable that the circulation pump 59 and replenishment pump 73 be diaphragm pumps. UV-curing ink has a stronger attack on materials compared to water-based inks, etc. Although tube pumps can also be used as circulation pump 59 or replenishment pump 73, tube pumps operate by crushing the tube with rollers, so the tube is prone to deterioration due to the attack of UV-curing ink. Diaphragm pumps operate by moving the diaphragm up and down or left and right, so compared to tube pumps, the amount of deformation of the materials is less, and they have higher durability against UV-curing ink.
[0057] The circulation pump control unit 60, the pressure control unit 70, and the replenishment pump control unit 75 each include a processor and can be configured by a computer such as a PLA (Programmable Logic Controller). Alternatively, the circulation pump control unit 60, the pressure control unit 70, and the replenishment pump control unit 75 may be configured by a single control unit consisting of a computer including a processor.
[0058] A brief explanation will now be given of the method for controlling ink circulation to keep the ink pressure constant when supplying ink using the ink supply mechanism 50 configured as described above. In the inkjet printing apparatus 1, when supplying ink to the inkjet head 45, pressure control and liquid level control are performed so that the pressure of the ink supplied to the inkjet head 45 remains constant.
[0059] Pressure control by the pressure control unit 70 is performed as follows.
[0060] The supply-side pressure control is performed based on the pressure in the supply-side manifold 61 measured by the supply-side pressure sensor 63, i.e., the ink pressure in the liquid supply passage 56. The pressure control unit 70 acquires the measured value of the ink pressure measured by the supply-side pressure sensor 63. The pressure control unit 70 compares the acquired measured value with the supply-side target value and controls the supply-side pressure adjustment unit 66 so that the measured value becomes the supply-side target value. For example, if the measured value acquired by the supply-side pressure sensor 63 is greater than the supply-side target value, the pressure control unit 70 lowers the supply-side target air pressure set in the supply-side pressure adjustment unit 66. Accordingly, the supply-side pressure adjustment unit 66 lowers the air pressure in the supply tank 51. As a result, the ink pressure in the liquid supply passage 56 can be lowered. Also, for example, if the measured value acquired by the supply-side pressure sensor 63 is smaller than the supply-side target value, the pressure control unit 70 raises the supply-side target air pressure set in the supply-side pressure adjustment unit 66. Accordingly, the supply-side pressure adjustment unit 66 raises the air pressure in the supply tank 51. As a result, the ink pressure in the liquid supply passage 56 can be increased.
[0061] Pressure control on the recovery side is performed based on the pressure in the recovery manifold 62 measured by the recovery side pressure sensor 64, i.e., the ink pressure in the liquid recovery passage 57. The pressure control unit 70 acquires the measured value of the ink pressure measured by the recovery side pressure sensor 64. The pressure control unit 70 controls the recovery side pressure adjustment unit 67 so that the acquired measured value becomes the supply side target value. For example, if the measured value acquired by the recovery side pressure sensor 64 is greater than the recovery side target value, the pressure control unit 70 lowers the recovery side target air pressure set in the recovery side pressure adjustment unit 67. Accordingly, the recovery side pressure adjustment unit 67 lowers the air pressure in the recovery tank 52. As a result, the ink pressure in the liquid recovery passage 57 can be lowered. Also, for example, if the measured value acquired by the recovery side pressure sensor 64 is smaller than the recovery side target value, the pressure control unit 70 raises the recovery side target air pressure set in the recovery side pressure adjustment unit 67. Accordingly, the recovery side pressure adjustment unit 67 raises the air pressure in the recovery tank 52. As a result, the ink pressure in the liquid recovery passage 57 can be increased.
[0062] The feedback control by the pressure control unit 70 can use P control, I control, D control, or PI control, PD control, PID control, etc. PID control is particularly preferred because it has the highest error suppression effect.
[0063] The liquid level in the recovery tank 52 is controlled by the circulation pump control unit 60 as follows.
[0064] As previously described, the circulation pump 59 is constantly driven, and ink is constantly supplied from the recovery tank 52 to the supply tank 51. The recovery-side liquid level sensor 55 constantly measures the liquid level of the ink stored in the recovery tank 52. The measurement value of the liquid level measured by the recovery-side liquid level sensor 55 is output to the circulation pump control unit 60. The circulation pump control unit 60 controls the discharge rate of the circulation pump 59 so that the measurement value obtained from the recovery-side liquid level sensor 55 reaches a predetermined target value (hereinafter referred to as the recovery-side liquid level target value). For example, if the measurement value is lower than the recovery-side liquid level target value, the circulation pump control unit 60 controls the discharge rate of the circulation pump 59 to decrease. This reduces the amount of ink sent from the recovery tank 52 to the supply tank 51. Also, if the measurement value is higher than the recovery-side liquid level target value, the circulation pump control unit 60 controls the discharge rate to increase. This increases the amount of ink sent from the recovery tank 52 to the supply tank 51. When the circulation pump control unit 60 performs feedback control of the circulation pump 59 based on the measurement value of the recovery side liquid level sensor 55, it preferably performs PID control.
[0065] Furthermore, the replenishment pump 73 is controlled by the replenishment pump control unit 75 as follows.
[0066] The replenishment pump control unit 75 obtains a measurement of the liquid level of the ink stored in the supply tank 51 from the supply-side liquid level sensor 54. The replenishment pump control unit 75 also obtains a measurement of the liquid level of the ink stored in the recovery tank 52 from the recovery-side liquid level sensor 55. The replenishment pump control unit 75 provides feedback control to the replenishment pump 73 so that the sum of the liquid levels on the supply side and the recovery side reaches a preset target value. As ink is ejected from the inkjet head 45, the amount of ink in the circulation path gradually decreases. To compensate for this, ink is supplied from the ink storage unit 71 to the liquid circulation path 58. The replenishment pump control unit 75 controls the drive of the replenishment pump 73 so that the amount of ink present in the circulation path, which consists of the supply tank 51, the liquid supply path 56, the inkjet head 45, the liquid recovery path 57, the recovery tank 52, and the liquid circulation path 58, remains approximately constant.
[0067] The circulation pump control unit 60, the pressure control unit 70, and the replenishment pump control unit 75 perform the above control.
[0068] As described above, the inkjet printing apparatus 1 of this embodiment includes a supply-side pressure adjustment unit 66 that adjusts the pressure of the liquid (in this case, ink) stored in the supply tank 51 using the air pressure in the supply tank 51, and a recovery-side pressure adjustment unit 67 that adjusts the pressure of the liquid stored in the recovery tank 52 using the air pressure in the recovery tank 52. In addition to adjusting the liquid pressure, it also controls the circulation pump 59 so that the measured liquid level in the recovery tank 52 is set to a target value. With this configuration, the stability of the liquid pressure supplied to the liquid discharge head (in this case, the inkjet head 45) can be improved, and as a result, high-quality liquid discharge can be achieved.
[0069] Here, the effects of the configuration of the ink supply mechanism 50 in the inkjet printing apparatus 1 will be explained with reference to Figures 4 and 5. First, as a reference example, we will explain the case in which a control (on / off control) is performed to drive and stop a circulation pump with a fixed discharge rate so that the liquid level of the ink stored in the recovery tank falls within predetermined upper and lower limits. Figure 4 shows (A) a graph showing the liquid level of the recovery tank and the driving status of the circulation pump during on / off control, (B) a graph showing the measured value of the supply side pressure sensor, and (C) a graph showing the measured value of the recovery side pressure sensor.
[0070] In Figures 4(A) to 4(C), the horizontal axis is common to all and represents the time from T1 to T2. In Figure 4(A), the left vertical axis represents the measured liquid level height of the recovery tank 52, and the right side represents the ON (driven) and OFF (stopped) states of the circulation pump. In Figure 4(B), the vertical axis represents the supply side ink pressure, and in Figure 4(C), the vertical axis represents the recovery side ink pressure. The supply side ink pressure is detected by the supply side pressure sensor 63, and the recovery side ink pressure is detected by the recovery side pressure sensor 64.
[0071] As a prerequisite, the supply side pressure adjustment mechanism controls the supply side ink pressure to be within a certain allowable range, and the recovery side pressure adjustment mechanism controls the recovery side ink pressure to be within a certain allowable range. As shown in Figure 4(B), the allowable range for the supply side ink pressure is set to the range from the lower limit SPi1 to the upper limit SPi2, indicated by the dashed line. As shown in Figure 4(C), the allowable range for the recovery side ink pressure is set to the range from the lower limit Spo1 to the upper limit Spo2, indicated by the dashed line.
[0072] Then, the circulation pump was controlled to turn on and off so that the ink level in the recovery tank 52 was within the acceptable range, from the lower limit h1 to the upper limit h2 shown by the dashed line in Figure 4(A). Here, the circulation pump was assumed to be driven with a constant output (fixed discharge rate) when in operation. As shown in Figure 4(A), just before time Ta, the liquid level reached the lower limit h1, so the circulation pump was temporarily stopped. Subsequently, due to the reaction of the circulation pump stopping, the liquid level reached the upper limit h2, and the circulation pump 59 was driven again.
[0073] As described above, when the liquid level in the recovery tank is adjusted by controlling the on / off state of the circulation pump, when the circulation pump stops, a rapid fluctuation occurs in the supply side ink pressure and the recovery side ink pressure, as shown in Figures 4(B) and (C), causing them to exceed the upper or lower limits. It is thought that the supply side ink pressure and the recovery side ink pressure change instantaneously, and therefore the adjustments by the supply side pressure adjustment mechanism and the recovery side pressure adjustment mechanism cannot keep up.
[0074] Next, as an embodiment of the ink supply mechanism 50, we will describe the case in which the circulation pump 59 is PID controlled so that the measurement value of the recovery-side liquid level sensor 55 provided in the recovery tank 52 approaches the target value. Figure 5 shows (A) a graph showing the liquid level height of the recovery tank and the circulation pump duty cycle, (B) a graph showing the measurement value of the supply-side pressure sensor, and (C) a graph showing the measurement value of the recovery-side pressure sensor when the discharge amount of the circulation pump 59 is PID controlled so that the measurement value of the recovery-side liquid level sensor approaches the target value. Here, the circulation pump duty cycle is the output ratio to the maximum output of the circulation pump.
[0075] In Figures 5(A) to 5(C), the horizontal axis is common to all and represents time T1 to T2. In Figure 5(A), the left vertical axis represents the measured liquid level height of the recovery tank 52, and the right vertical axis represents the circulation pump duty cycle. In Figure 5(B), the vertical axis represents the supply side ink pressure, and in Figure 5(C), the vertical axis represents the recovery side ink pressure. The supply side ink pressure is a measured value detected by the supply side pressure sensor 63, and the recovery side ink pressure is a measured value detected by the recovery side pressure sensor 64. For comparison, in Figures 4 and 5, one division on the vertical axis of the corresponding graphs has the same numerical interval. For example, if one division in Figure 4(A) is 0.1 mm, then one division in Figure 5(A) is also 0.1 mm.
[0076] As a prerequisite, the supply-side ink pressure is controlled to be within a certain allowable range by the supply-side pressure adjustment mechanism, and the recovery-side ink pressure is controlled to be within a certain allowable range by the recovery-side pressure adjustment mechanism, as in the reference. Here, as shown in Figure 5(B), the allowable range of the supply-side ink pressure is set to the range from the lower limit EPi1 to the upper limit EPi2, indicated by the dashed line. As shown in Figure 5(C), the allowable range of the recovery-side ink pressure is set to the range from the lower limit EPo1 to the upper limit EPo2, indicated by the dashed line. The difference between the upper and lower limits of the allowable pressure range is the same value ΔP [Pa] in Figures 4 and 5.
[0077] Here, the circulation pump 59 was controlled so that the ink level in the recovery tank 52 would reach the target value h, shown by the dashed line in Figure 5(A). The circulation pump 59 is constantly driven, and control is performed to change the discharge amount based on the measurement value from the recovery-side liquid level sensor 55. As shown in Figure 5(A), the liquid level is maintained at approximately the target value h. In this case, as shown in Figures 5(B) and 5(C), no significant fluctuations occurred in the supply-side ink pressure or the recovery-side ink pressure, and they were able to be maintained within the acceptable range.
[0078] Maintaining the supply-side ink pressure and recovery-side ink pressure within acceptable limits means that the ink pressure supplied to the inkjet head 45 (i.e., the head module 48) is maintained within acceptable limits. Stabilizing the ink pressure supplied to the inkjet head 45 enables stable droplet ejection, resulting in highly accurate droplet ejection. When the droplets are ink, high-quality images can be formed.
[0079] As previously described, when PID control is used as the control method for setting the liquid level sensor measurement value by the circulation pump control unit 60 as the target value, the measurement value and the target value can be matched with higher accuracy.
[0080] By using an analog sensor as the recovery-side liquid level sensor 55, changes in the ink liquid level can be detected precisely, thus reducing the error between the actual ink liquid level and the target value.
[0081] Here, "ink" is used as an example of a liquid, but the liquid in the technology of this disclosure is not limited to ink; it may also be a coating solvent or the like.
[0082] The inkjet printing apparatus 1 may include a pretreatment liquid coating unit and a pretreatment liquid drying unit upstream of the image forming unit 40. Alternatively, the inkjet printing apparatus 1 may include a drying unit downstream of the image forming unit 40.
[0083] The term "recording medium" is a general term encompassing various things that are called by different names, such as paper, recording paper, printing paper, printing media, printing medium, printed medium, image-forming medium, image-receiving medium, and ejected medium.
[0084] The embodiments of the Disclosure described above may be modified, added to, or deleted as appropriate, without departing from the spirit of the Disclosure. The Disclosure is not limited to the embodiments described above, and many modifications are possible within the technical concept of the Disclosure by those with ordinary skill in the equivalent related field.
[0085] The processor may consist of one or more hardware components, and the type of hardware is not limited. For example, a processor may consist of programmable logic devices such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), FPGA (Field Programmable Gate Array), dedicated circuits for executing specific processes such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphic Processing Unit), or an NPU (Neural Processing Unit). Furthermore, the hardware components may be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a processor, these components may reside in physically separate devices or in the same device. Furthermore, in any embodiment, the order of the processes performed by the processor is not limited to the order described above and may be changed as appropriate. The hardware components are composed of electrical circuits (circuits) and the like, which are combinations of circuit elements such as semiconductor elements.
[0086] Regarding the above embodiment, the following additional information is disclosed. <Addendum 1> A liquid discharge head equipped with a nozzle for discharging liquid, a supply tank for storing liquid supplied to the liquid discharge head, a recovery tank for storing liquid recovered from the liquid discharge head, a recovery-side liquid level sensor for measuring the liquid level in the recovery tank, a liquid supply path for supplying liquid from the supply tank to the liquid discharge head, a liquid recovery path for recovering liquid from the liquid discharge head to the recovery tank, a liquid circulation path equipped with a circulation pump for circulating liquid from the recovery tank to the supply tank, a first control unit that controls the discharge amount of the circulation pump so that the measurement value of the recovery-side liquid level sensor becomes a target value, a supply-side pressure adjustment unit that adjusts the pressure of the liquid stored in the supply tank by the air pressure inside the supply tank, a recovery-side pressure adjustment unit that adjusts the pressure of the liquid stored in the recovery tank by the air pressure inside the recovery tank, a supply-side pressure sensor for measuring the pressure of the liquid in the liquid supply path, a recovery-side pressure sensor for measuring the pressure of the liquid in the liquid recovery path, A liquid discharge device comprising: a second control unit that controls the supply-side pressure adjustment unit and the recovery-side pressure adjustment unit so that the measured values of the supply-side pressure sensor and the recovery-side pressure sensor reach their respective target values. <Note 2> The liquid discharge device according to Note 1, wherein the first control unit performs proportional-integral-differential control over the circulation pump. <Note 3> The liquid discharge device according to Note 1 or Note 2, wherein the recovery-side liquid level sensor is an analog sensor. <Note 4> The liquid discharge device according to any one of Notes 1 to 3, wherein the supply-side pressure adjustment unit and the recovery-side pressure adjustment unit adjust the air pressure in the supply tank and the air pressure in the recovery tank so that the pressure of the liquid in the supply tank is higher than the pressure of the liquid in the recovery tank. <Note 5> A liquid discharge device according to any one of Notes 1 to 4, further comprising: a liquid storage section for storing liquid; a liquid replenishment section equipped with a replenishment pump for supplying liquid from the liquid storage section to the liquid circulation section; a supply-side liquid level sensor for measuring the liquid level height of the supply tank; and a third control unit for controlling the replenishment pump so that the sum of the values measured by the supply-side liquid level sensor and the recovery-side liquid level sensor approaches a target value. <Note 6> A liquid discharge device according to any one of Notes 1 to 5, further comprising: a temperature control section for controlling the temperature of the liquid between the junction of the liquid circulation section and the liquid replenishment section and the supply tank.<Note 7> A liquid dispensing device according to any one of Notes 1 to 6, wherein the liquid is ultraviolet-curable ink, and the circulation pump and replenishment pump are diaphragm pumps. <Note 8> A liquid dispensing device comprising: a liquid dispensing head equipped with a nozzle for dispensing liquid; a supply tank for storing the liquid supplied to the liquid dispensing head; a recovery tank for storing the liquid recovered from the liquid dispensing head; a recovery-side liquid level sensor for measuring the liquid level in the recovery tank; a liquid supply path for supplying liquid from the supply tank to the liquid dispensing head; a liquid recovery path for recovering liquid from the liquid dispensing head to the recovery tank; a liquid circulation path equipped with a circulation pump for circulating liquid from the recovery tank to the supply tank; a supply-side pressure adjustment unit for adjusting the pressure of the liquid stored in the supply tank by the air pressure inside the supply tank; a recovery-side pressure adjustment unit for adjusting the pressure of the liquid stored in the recovery tank by the air pressure inside the recovery tank; a supply-side pressure sensor for measuring the pressure of the liquid in the liquid supply path; and a recovery-side pressure sensor for measuring the pressure of the liquid in the liquid recovery path. A liquid circulation control method comprising controlling the discharge rate of the circulation pump so that the measurement value of the recovery side liquid level sensor becomes a target value, and controlling the supply side pressure adjustment unit and the recovery side pressure adjustment unit so that the measurement values of the supply side pressure sensor and the recovery side pressure sensor become their respective target values. <Note 9> The liquid circulation control method described in Note 8, wherein the control of the discharge rate of the circulation pump is proportional-integral-differential control.
[0087] The disclosure of Japanese Patent Application No. 2025-028251, filed on 25 February 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.
Claims
1. A liquid discharge head equipped with a nozzle for discharging liquid; a supply tank for storing the liquid supplied to the liquid discharge head; a recovery tank for storing the liquid recovered from the liquid discharge head; a recovery-side liquid level sensor for measuring the liquid level in the recovery tank; a liquid supply path for supplying the liquid from the supply tank to the liquid discharge head; a liquid recovery path for recovering the liquid from the liquid discharge head to the recovery tank; a liquid circulation path equipped with a circulation pump for circulating the liquid from the recovery tank to the supply tank; a first control unit for controlling the discharge amount of the circulation pump so that the measurement value of the recovery-side liquid level sensor becomes a target value; a supply-side pressure adjustment unit for adjusting the pressure of the liquid stored in the supply tank by the air pressure inside the supply tank; a recovery-side pressure adjustment unit for adjusting the pressure of the liquid stored in the recovery tank by the air pressure inside the recovery tank; a supply-side pressure sensor for measuring the pressure of the liquid in the liquid supply path; a recovery-side pressure sensor for measuring the pressure of the liquid in the liquid recovery path. A liquid dispensing device comprising: a supply-side pressure adjustment unit and a second control unit that controls the supply-side pressure adjustment unit and the recovery-side pressure adjustment unit so that the measured values of the supply-side pressure sensor and the measured values of the recovery-side pressure sensor become their respective target values.
2. The liquid discharge device according to claim 1, wherein the first control unit performs proportional-integral-differential control over the circulation pump.
3. The liquid dispensing device according to claim 1 or 2, wherein an analog sensor is used as the liquid level sensor on the recovery side.
4. The liquid discharge device according to claim 1 or 2, wherein the supply-side pressure adjustment unit and the recovery-side pressure adjustment unit adjust the air pressure in the supply tank and the air pressure in the recovery tank so that the pressure of the liquid in the supply tank is higher than the pressure of the liquid in the recovery tank.
5. A liquid discharge device according to claim 1 or 2, further comprising: a liquid storage section for storing the liquid; a liquid replenishment path equipped with a replenishment pump for supplying the liquid from the liquid storage section to the liquid circulation path; a supply-side liquid level sensor for measuring the liquid level height of the supply tank; and a third control unit for controlling the replenishment pump so that the sum of the values measured by the supply-side liquid level sensor and the recovery-side liquid level sensor approaches a target value.
6. The liquid dispensing device according to claim 5, further comprising a temperature control unit for controlling the temperature of the liquid between the junction of the liquid circulation path and the liquid replenishment path and the supply tank.
7. The liquid dispensing device according to claim 5, wherein the liquid is an ultraviolet-curable ink, and the circulation pump and the replenishment pump are diaphragm pumps.
8. A liquid dispensing device comprising: a liquid dispensing head equipped with a nozzle for dispensing liquid; a supply tank for storing the liquid supplied to the liquid dispensing head; a recovery tank for storing the liquid recovered from the liquid dispensing head; a recovery-side liquid level sensor for measuring the liquid level in the recovery tank; a liquid supply path for supplying the liquid from the supply tank to the liquid dispensing head; a liquid recovery path for recovering the liquid from the liquid dispensing head to the recovery tank; a liquid circulation path equipped with a circulation pump for circulating the liquid from the recovery tank to the supply tank; a supply-side pressure adjustment unit for adjusting the pressure of the liquid stored in the supply tank by the air pressure inside the supply tank; a recovery-side pressure adjustment unit for adjusting the pressure of the liquid stored in the recovery tank by the air pressure inside the recovery tank; a supply-side pressure sensor for measuring the pressure of the liquid in the liquid supply path; and a recovery-side pressure sensor for measuring the pressure of the liquid in the liquid recovery path. A liquid circulation control method comprising: controlling the discharge amount of the circulation pump so that the measurement value of the recovery side liquid level sensor becomes a target value; and controlling the supply side pressure adjustment unit and the recovery side pressure adjustment unit so that the measurement values of the supply side pressure sensor and the recovery side pressure sensor become their respective target values.
9. The liquid circulation control method according to claim 8, wherein the discharge amount of the circulation pump is controlled by proportional-integral-differential control.