Cleaning method for inkjet printers and print heads

Abstract

To more effectively clean the print head of an inkjet printer. [Solution] An inkjet device 1 comprising a head 2 including a nozzle 21, a pressure chamber 22 communicating with the nozzle 21, and a piezoelectric element 23 that increases or decreases the volume of the pressure chamber 22 by vibration, a control unit 3 that controls the piezoelectric element 23, and a cleaning tray 41 that stores a cleaning liquid 94 into which the opening 26 of the nozzle 21 is immersed, wherein the control unit 3 performs ejection control by vibrating the piezoelectric element 23 to eject the ink 91 stored in the pressure chamber 22 from the opening 26, and suction control by vibrating the piezoelectric element 23 when the opening 26 is immersed in the cleaning liquid 94 to draw the cleaning liquid 94 into the inside of the nozzle 21 from the opening 26.

Description

Technical Field

[0001] The present invention relates to an inkjet device and a method for cleaning a head.

Background Art

[0002] When ink adheres to and solidifies on the head of an inkjet device, problems such as non-ejection of ink in the head occur. For this reason, a technique for cleaning the ink adhering to the head is known. For example, Patent Document 1 discloses a technique in which a cleaning liquid is stored in a cap portion and the nozzle surface of an inkjet head is immersed in the cleaning liquid.

[0003] In Patent Document 1, in order to introduce the cleaning liquid into the head, a first pump provided in a first flow path connecting a waste liquid tank and the head is operated to suck up the cleaning liquid stored in the cap portion from the nozzle opening into the head.

[0004] Also, in Patent Document 1, an ultrasonic vibrator is disposed on the outer periphery or inside of the cap portion, and ultrasonic vibration is applied to the cleaning liquid stored in the cap portion and the cleaning liquid in the head while the cleaning liquid is introduced into the head.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to the technology described in Patent Document 1, ink adhering to the inside of the print head and the nozzle surface can be removed by a cleaning solution and ultrasonic vibrations applied to the cleaning solution. On the other hand, Patent Document 1 uses negative pressure from a first pump to introduce the cleaning solution into the print head. Specifically, the pressure setting value of the first pump in the nozzle cleaning process is set to between -50 kilopascals and -20 kilopascals, and the operating time of the first pump is set to between 1 minute and 10 minutes.

[0007] This type of negative pressure forcefully introduces a large amount of cleaning fluid into the print head, which can provide a certain level of cleaning effect, but it also carries the risk of damaging the print head with the cleaning fluid. Furthermore, to resume use of the print head after introducing cleaning fluid, the cleaning fluid inside the head must be replaced with ink. Introducing a large amount of cleaning fluid into the print head increases the amount of ink required for replacement, and the replacement process takes a long time.

[0008] Therefore, in view of these problems, the present disclosure aims to provide an inkjet device and a method for cleaning an inkjet device head that can more effectively clean the head of the inkjet device. [Means for solving the problem]

[0009] The inkjet device according to the present invention comprises a head including a nozzle, a pressure chamber communicating with the nozzle, and a piezoelectric element that increases or decreases the volume of the pressure chamber by vibration, a control unit that controls the piezoelectric element, and a cleaning tray that stores a cleaning solution into which the opening of the nozzle is immersed, wherein the control unit performs ejection control by vibrating the piezoelectric element to eject ink stored in the pressure chamber from the opening, and suction control by vibrating the piezoelectric element while the opening is immersed in the cleaning solution to draw the cleaning solution into the inside of the nozzle from the opening. [Effects of the Invention]

[0010] According to the present invention, the print head of an inkjet device can be cleaned more effectively. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram illustrating an inkjet device according to an embodiment. [Figure 2] This is a schematic diagram illustrating the internal configuration of an inkjet printer. [Figure 3] This is a flowchart illustrating the operation of an inkjet printer. [Figure 4] This is a schematic diagram showing the state of the inkjet device during the immersion process. [Figure 5] This is a schematic diagram illustrating how a piezoelectric element is displaced. [Figure 6] This graph illustrates the waveform pattern of a piezoelectric element when performing discharge control. [Figure 7] This graph illustrates the waveform pattern of a piezoelectric element when performing suction control. [Figure 8] This is a schematic diagram showing the inkjet device during the suction process. [Figure 9] This is a schematic diagram showing the state of the inkjet device during the drainage process. [Modes for carrying out the invention]

[0012] <Summary of Embodiments of the Invention> The embodiments of the present invention are outlined below.

[0013] (1) The inkjet device according to the present invention includes a head including a nozzle, a pressure chamber communicating with the nozzle, and a piezoelectric element that increases and decreases the volume of the pressure chamber by vibration, a control unit that controls the piezoelectric element, and a cleaning tray that stores a cleaning liquid in which an opening of the nozzle is immersed. The control unit executes ejection control for ejecting the ink stored in the pressure chamber from the opening by vibrating the piezoelectric element, and suction control for sucking the cleaning liquid from the opening into the nozzle by vibrating the piezoelectric element in a state where the opening is immersed in the cleaning liquid.

[0014] In the inkjet device according to the present invention, since the cleaning liquid is sucked by the vibration of the piezoelectric element, the amount of the cleaning liquid sucked into the head can be suppressed to a small amount. As a result, it is possible to suppress damage to nozzles and the like caused by suction and deterioration inside the head caused by immersion in a large amount of cleaning liquid. Therefore, for example, compared with the technique of Patent Document 1 in which a large amount of cleaning liquid is introduced into the head by negative pressure using a pump, the head of the inkjet device can be more suitably cleaned.

[0015] (2) In the inkjet device of (1) above, the ejection control may include control for vibrating the piezoelectric element in a first waveform pattern, and the suction control may include control for vibrating the piezoelectric element in a second waveform pattern different from the first waveform pattern.

[0016] By vibrating the piezoelectric element in this way, the piezoelectric element operates in a pattern different from the normal ejection waveform, so that the liquid can be sucked from the opening of the nozzle.

[0017] (3) In the inkjet device of (2) above, the suction control may include control for vibrating the piezoelectric element in the first waveform pattern after vibrating the piezoelectric element in the second waveform pattern.

[0018] By vibrating in this way, after the cleaning liquid is sucked into the nozzle, only a small amount of the cleaning liquid is discharged from the nozzle to the cleaning tray, so that the fixed ink near the opening can be easily separated from the head. Further, by repeating the suction and discharge, the cleaning liquid can be sucked into the nozzle while finely adjusting the suction amount, so that the suction amount of the cleaning liquid to the head can be suppressed to a small amount.

[0019] (4) In the inkjet apparatus according to (1) to (3) above, the head includes a common ink chamber communicating with the plurality of pressure chambers, a drain pipe that is connected to the common ink chamber and has a larger flow path cross-sectional area than the nozzle, and after the suction control, a pumping unit that pumps the cleaning liquid sucked into the nozzle from the common ink chamber to the drain pipe. It may further be provided.

[0020] For example, if the cleaning liquid or the like sucked from the opening is also discharged from the opening, the nozzle may be clogged by foreign matter floating in the cleaning liquid or the like due to cleaning. As described above, by discharging most of the cleaning liquid or the like from the drain pipe, foreign matter is also discharged from the drain pipe, so that clogging of the nozzle can be avoided.

[0021] (5) In the inkjet apparatus according to (1) to (3) above, a vibrating unit that applies ultrasonic vibration to the cleaning liquid stored in the cleaning tray may be further provided.

[0022] The vibration of the cleaning liquid applied by the vibrating unit promotes the dissolution of the fixed ink in the cleaning liquid, and the fixed ink can be easily separated from the inner wall of the head and the nozzle surface.

[0023] (6) In the inkjet apparatus according to (5) above, the vibrating unit may apply ultrasonic vibration at a sound pressure weaker than the first sound pressure at which cavitation occurs in the cleaning liquid during the suction control.

[0024] This allows the cleaning solution to be agitated, while suppressing damage to the print head caused by cavitation-induced shocks. This promotes the dissolution of solidified ink in the cleaning solution, allowing it to separate from the inner wall of the print head and the nozzle surface.

[0025] (7) A method for cleaning a head according to the present invention is a method for cleaning a head, comprising a nozzle, a pressure chamber communicating with the nozzle, and a piezoelectric element that increases or decreases the volume of the pressure chamber by vibration, the method comprising a suction step of vibrating the piezoelectric element to draw the cleaning liquid into the inside of the nozzle from the opening of the nozzle, while the opening of the nozzle is immersed in a cleaning liquid stored in a cleaning tray.

[0026] In the head cleaning method according to the present invention, the cleaning solution is drawn in by the vibration of a piezoelectric element, so the amount of cleaning solution drawn into the head can be kept to a minimum. This suppresses damage to nozzles and other parts caused by suction, and deterioration of the inside of the head caused by immersion in a large amount of cleaning solution. For this reason, the head can be cleaned more effectively than, for example, the technology of Patent Document 1, which introduces a large amount of cleaning solution into the head using negative pressure from a pump.

[0027] <Details of Embodiments of the Invention> The following describes the details of embodiments of the present invention.

[0028] [Outline configuration of inkjet device 1] Figure 1 is a schematic diagram illustrating an inkjet apparatus 1 according to an embodiment. Figure 2 is a schematic diagram illustrating the internal configuration of the inkjet device 1.

[0029] The inkjet device 1 comprises a head 2, a control unit 3, a cleaning unit 4, a drainage unit 5, a coating unit 6, a supply unit 7, and a moving mechanism 8. Figures 1 and 2 are schematic diagrams, and the size relationships of each part are exaggerated as appropriate for explanatory purposes and may differ from the actual size relationships. The inkjet device 1 may be, for example, a device for manufacturing color filters used in flat panel displays such as color liquid crystal displays, or a device for drawing characters, photographs, etc., on the surface of paper such as copy paper.

[0030] The head 2 includes a plurality of nozzles 21, a plurality of pressure chambers 22 each communicating with the plurality of nozzles 21, a plurality of piezoelectric elements 23 that increase or decrease the volume of the plurality of pressure chambers 22 by vibration, and a common ink chamber 24 communicating with the plurality of pressure chambers 22. The head 2 is formed, for example, by laminating a plurality of members having grooves or holes with adhesive.

[0031] The nozzle 21 opens at the nozzle surface 25 formed on the lower surface (vertically downward surface) of the head 2. This opening is referred to as the "opening 26". The pressure chamber 22 forms a space with a larger volume than the nozzle 21, and a piezoelectric element 23 is provided on a part of the wall surface of the pressure chamber 22. The piezoelectric element 23 (piezo) is made of a material that deforms when a voltage is applied. The piezoelectric element 23 includes, for example, lead zirconate titanate (PZT). The common ink chamber 24 forms a space with a larger volume than the pressure chamber 22 and is in communication with the supply unit 7 and the drainage unit 5.

[0032] Ink 91 is supplied from the supply unit 7 into the head 2, and with the common ink chamber 24, pressure chamber 22, and nozzle 21 filled with ink 91, the piezoelectric element 23 vibrates appropriately, causing droplets of ink 91 to be ejected from the opening 26 of the nozzle 21.

[0033] The cleaning unit 4 cleans the print head 2. When the print head 2 is used, ink 91 may adhere to the nozzle surface 25 or the inside of the print head 2 (for example, the inner wall of the pressure chamber 22, the inner wall of the common ink chamber 24). This ink adhesion may cause ejection problems such as failure to eject ink 91 or ejection in a curved direction, so "cleaning the print head 2" is necessary to remove the adhered ink 91.

[0034] The cleaning unit 4 includes a cleaning tray 41 for storing cleaning fluid 94, a cleaning fluid tank 42 for supplying cleaning fluid 94 to the cleaning tray 41, cleaning fluid piping 43 connecting the cleaning tray 41 and the cleaning fluid tank 42, a first valve 44 that controls the flow of cleaning fluid piping 43 by switching between an open state and a closed state, a vibration unit 45 that applies ultrasonic vibration to the cleaning fluid 94 stored in the cleaning tray 41, a drainage pipe 46 connecting the cleaning tray 41 and a drainage tank 51 described later, a second valve 47 that controls the flow of drainage pipe 46 by switching between an open state and a closed state, and a pump 48 that pressurizes the liquid from the cleaning tray 41 through the drainage pipe 46 to the drainage tank 51.

[0035] The cleaning solution 94 is a liquid containing the same components as the solvent used in the ink 91. For example, if the ink 91 contains acetone as an organic solvent, then the cleaning solution 94 is acetone. The cleaning tray 41 has a bowl-shaped form that is open at the top and can accommodate the nozzle surface 25 inside.

[0036] The cleaning fluid tank 42 stores unused cleaning fluid 94 before it is stored in the cleaning tray 41. The cleaning fluid tank 42 is located, for example, higher than the cleaning tray 41. By opening the first valve 44, the cleaning fluid 94 is supplied from the cleaning fluid tank 42 to the cleaning tray 41 through the cleaning fluid piping 43 by gravity. When the cleaning fluid 94 in the cleaning tray 41 has reached a predetermined level, the supply of cleaning fluid 94 from the cleaning fluid tank 42 to the cleaning tray 41 is stopped by closing the first valve 44.

[0037] The vibrating unit 45 is an ultrasonic transducer, such as a Langevin-type transducer, which is provided on the outer bottom surface of the cleaning tray 41. As the cleaning solution 94 is a solvent as described above, if the vibrating unit 45 is immersed in the cleaning solution 94, the components constituting the vibrating unit 45 may dissolve, potentially causing deterioration of the vibrating unit 45. By attaching the vibrating unit 45 to the outside (bottom surface, side surface, etc.) of the cleaning tray 41, ultrasonic vibrations can be applied to the cleaning solution 94 while preventing the vibrating unit 45 from being immersed in the cleaning solution 94.

[0038] Furthermore, in order to facilitate the transmission of ultrasonic vibrations from the vibrating unit 45 to the cleaning fluid 94 inside the cleaning tray 41, the wall thickness of the area of ​​the cleaning tray 41 where the vibrating unit 45 is located may be made thinner than other areas, or it may be constructed of a material that is easily flexible, such as a diaphragm.

[0039] The drain tank 51, described later, is located, for example, lower than the cleaning tray 41. By opening the second valve 47, gravity causes the cleaning fluid 94 to be discharged from the cleaning tray 41 through the drain pipe 46 into the drain tank 51. Furthermore, by opening the second valve 47 and driving the pump 48, in addition to gravity, the negative pressure applied to the cleaning tray 41 by the pump 48 actively discharges the cleaning fluid 94 from the cleaning tray 41.

[0040] The drainage unit 5 stores used ink 91 and cleaning fluid 94 sent from the head 2 and cleaning unit 4 as drainage fluid 96. The drainage unit 5 includes a drainage tank 51 for storing the drainage fluid 96, a drainage pipe 52 connecting the common ink chamber 24 and the drainage tank 51, a third valve 53 that controls the flow of the drainage pipe 52 by switching between an open state and a closed state, a drainage tray 55 (Figure 9) for receiving the drainage fluid 96 discharged from the opening 26 of the nozzle 21, a drainage pipe 56 connecting the drainage tray 55 and the drainage tank 51, a fourth valve 57 that controls the flow of the drainage pipe 56 by switching between an open state and a closed state, and a pump 58 that pressurizes the liquid in the drainage tray 55 through the drainage pipe 56 to the drainage tank 51.

[0041] The drain tank 51 is located, for example, lower than the head 2 and the drain tray 55. By opening the third valve 53, gravity causes the liquid in the head 2 (common ink chamber 24) to be discharged from the head 2 (common ink chamber 24) through the drain pipe 52 into the drain tank 51. Also, by opening the fourth valve 57, gravity causes the liquid in the drain tray 55 to be discharged from the drain tray 55 through the drain pipe 56 into the drain tank 51. Furthermore, by opening the fourth valve 57 and driving the pump 58, in addition to gravity, the negative pressure applied to the drain tray 55 by the pump 58 actively discharges the liquid from the drain tray 55.

[0042] The drain pipe 52 has a larger flow path cross-sectional area than the nozzle 21. For example, the nozzle diameter of the nozzle 21 is about 20 to 40 micrometers, and its flow path cross-sectional area is about 300 to 1200 square micrometers. In contrast, the pipe diameter of the drain pipe 52 is set appropriately according to the physical properties of the ink 91, but for example, the inner diameter is about 4 millimeters, and its flow path cross-sectional area is about 13 square millimeters, which is orders of magnitude larger than the flow path cross-sectional area of ​​the nozzle 21.

[0043] The supply unit 7 supplies ink 91 to the print head 2. The supply unit 7 includes an ink tank 71 for storing ink 91 before use, an ink pipe 72 connecting the ink tank 71 to the common ink chamber 24, and a fifth valve 73 that controls the flow of ink through the ink pipe 72 by switching between an open state and a closed state.

[0044] The ink tank 71 is positioned higher than, for example, the common ink chamber 24. By opening the fifth valve 73, gravity supplies ink 91 from the ink tank 71 through the ink piping 72 to the common ink chamber 24. The ink 91 supplied to the common ink chamber 24 fills the pressure chamber 22 and the nozzle 21, and a meniscus of ink 91 is formed at the opening 26 by surface tension.

[0045] The coating unit 6 includes a stage 61. The substrate 62 is held on the stage 61. With the head 2 positioned close to the coating unit 6, ink 91 is dispensed appropriately from the opening 26 of the nozzle 21, thereby coating the substrate 62 with ink 91. The type of substrate 62 is not particularly limited and may be, for example, a glass substrate, a resin substrate, or paper.

[0046] The moving mechanism 8 is an actuator that moves the head 2 to position it relative to the cleaning section 4, the drainage section 5, and the coating section 6. These sections 4, 5, and 6 are arranged, for example, horizontally. The moving mechanism 8 includes a horizontal moving mechanism 81 that moves the head 2 horizontally relative to these sections 4, 5, and 6, and a vertical moving mechanism 82 that moves the head 2 vertically relative to these sections 4, 5, and 6.

[0047] The control unit 3 controls each part of the inkjet device 1 by outputting control signals to each part of the inkjet device 1. The control unit 3 is a computer device that includes, for example, a processor such as a CPU (Central Processing Unit) and memory such as RAM (Random Access Memory), ROM (Read Only Memory), and HDD (hard disk drive). The control unit 3 generates control signals in response to user operations, etc., by having the processor perform calculations and control as appropriate according to the computer program stored in memory, and outputs these control signals to each part of the inkjet device 1.

[0048] Specifically, the control unit 3 vibrates the piezoelectric element 23 by outputting a control signal to the piezoelectric element 23. The control unit 3 vibrates the vibrating unit 45 by outputting a control signal to the vibrating unit 45. The control unit 3 switches the open and closed states of each valve 44, 47, 53, 57, 73 by outputting control signals to each valve 44, 47, 53, 57, 73. The control unit 3 switches the pumping and stopping of liquid by the pumps 48, 58 by outputting control commands to the pumps 48, 58. The control unit 3 moves the head 2 relative to the cleaning unit 4, the drainage unit 5, and the coating unit 6 by outputting a control signal to the moving mechanism 8.

[0049] [Operation of inkjet device 1] Figure 3 is a flowchart illustrating the operation of the inkjet device 1 (the cleaning operation of the head 2). The series of operations described below are realized by the cooperation of each part of the inkjet device 1, with the processor of the control unit 3 performing calculations and controls according to an appropriate computer program. These operations may be started, for example, in response to user input, may be started periodically, or may be started automatically without waiting for user input when non-discharge of ink droplets 91 from the nozzle 21 is detected.

[0050] Inkjet printer 1 may experience various malfunctions due to ink 91 solidifying on the nozzle surface 25 and inside the print head 2 during use. Therefore, conventionally, the nozzle surface 25 was wiped after using the print head 2. However, wiping only the nozzle surface 25 was insufficient to remove the solidified ink inside the print head 2.

[0051] When Patent Document 1 is applied to the inkjet device 1, the nozzle surface 25 is immersed in the cleaning liquid 94 stored in the cleaning tray 41, the third valve 53 is opened, and a pump (not shown) provided in the drainage pipe 52 is driven, thereby introducing the cleaning liquid 94 into the head 2 through the opening 26 due to the negative pressure from the pump. In this state, the vibrating unit 45 is vibrated to clean the inside of the head 2.

[0052] However, this method introduces a large amount of cleaning fluid 94 into the print head 2 with great force, which may damage the print head 2. In particular, fine nozzles 21 and other components may crack due to the flow rate of the cleaning fluid 94, and the adhesive used inside the print head 2 may dissolve due to the large amount of cleaning fluid 94, causing the print head 2 to deteriorate. Furthermore, in order to resume use of the print head 2 after introducing the cleaning fluid 94, it is necessary to replace the cleaning fluid 94 inside the print head 2 with ink 91. Introducing a large amount of cleaning fluid 94 into the print head 2 increases the amount of ink 91 required for replacement, and the replacement process takes a long time.

[0053] Therefore, in order to solve these problems, in this embodiment, instead of using a negative pressure source such as a pump used in the inkjet device 1, a smaller amount of cleaning fluid 94 than in the conventional method is introduced into the head 2 by vibration of a piezoelectric element 23. Here, the negative pressure source includes, for example, a membrane pump such as a diaphragm pump or ejector built into the inkjet device 1, as well as the system negative pressure from the factory where the inkjet device 1 is installed. The method will be described below.

[0054] The cleaning operation of head 2 is achieved by sequentially executing the following steps: an immersion step (step S11) in which the nozzle surface 25 is immersed in the cleaning solution 94; a nozzle surface air removal step (step S12) in which air 95 remaining on the nozzle surface 25 is removed; a suction step (step S13) in which the cleaning solution 94 is introduced into head 2 by vibration of the piezoelectric element 23 from the opening 26; and a drainage step (step S14) in which the cleaning solution 94 and other contents inside head 2 are discarded.

[0055] [Immersion process: Step S11] Figure 4 is a schematic diagram showing the state of the inkjet device 1 during the immersion process. Before cleaning, ink clumps 92 are present on the inner wall surface of the head 2, and ink clumps 93 are also present on the nozzle surface 25. The ink clumps 92 and 93 are fine clumps that have become solid or semi-solid after the solvent components have been removed from the ink 91.

[0056] In the immersion process, first, the cleaning solution 94 is stored in the cleaning tray 41 at an appropriate liquid level by the control of the first valve 44. Next, the head 2 is moved relative to the cleaning solution 94 stored in the cleaning tray 41 by the moving mechanism 8, so that the opening 26 of the nozzle 21 is immersed in the cleaning solution 94 stored in the cleaning tray 41.

[0057] At this time, air 95 remains on the nozzle surface 25. The air 95 is fine bubbles and remains on the nozzle surface 25 due to factors such as the unevenness of the nozzle surface 25 and the interfacial tension between the nozzle surface 25 and the cleaning solution 94.

[0058] [Nozzle surface air removal process: Step S12] In the nozzle surface air removal process, this air 95 is removed from the nozzle surface 25. If air 95 remains on the nozzle surface 25, in the subsequent suction process, the air 95 may enter the head 2 along with the cleaning solution 94 from the opening 26, potentially causing problems such as air lock in the nozzle 21. Therefore, in this embodiment, the air 95 is removed from the nozzle surface 25 before the suction process to avoid the above-mentioned problems.

[0059] First, with the nozzle surface 25 immersed in the cleaning solution 94, the vibrating unit 45 is vibrated. This vibration causes the air 95 to move horizontally along the nozzle surface 25, and the air 95 that has moved to the end of the nozzle surface 25 moves to the surface of the cleaning solution 94 due to buoyancy and disappears. As a result, the air 95 is removed from the nozzle surface 25.

[0060] Here, the vibration of the vibrating unit 45 is set to a relatively small frequency (e.g., "first frequency F1") and a large amplitude (e.g., "first amplitude A1"). As a result, the sound pressure of the ultrasonic vibration is weak, so that the cleaning fluid 94 can be agitated relatively strongly while suppressing the generation of cavitation in the cleaning fluid 94. As a result, the air 95 can be moved while suppressing damage to the head 2 caused by shocks resulting from cavitation.

[0061] Alternatively, while the nozzle surface 25 is immersed in the cleaning solution 94, the head 2 may be moved back and forth in a fine horizontal or vertical manner relative to the cleaning tray 41 by the moving mechanism 8, thereby moving the air 95 on the nozzle surface 25. The nozzle surface air removal process is completed when the air removal operation by at least one of the vibrating unit 45 and the moving mechanism 8 is performed for a predetermined time.

[0062] [Suction process: Step S13] In the suction process, the control unit 3 performs "suction control" by vibrating the piezoelectric element 23 while the opening 26 of the nozzle surface 25 is immersed in the cleaning liquid 94, thereby drawing the cleaning liquid 94 into the nozzle 21 from the opening 26. The control of the piezoelectric element 23 by the control unit 3 will be explained here with reference to Figures 5 to 7 as appropriate.

[0063] Figure 5 is a schematic diagram illustrating the displacement of the piezoelectric element 23. Figure 6 is a graph illustrating the waveform pattern of the piezoelectric element 23 when performing discharge control. Figure 7 is a graph illustrating the waveform pattern of the piezoelectric element 23 when performing suction control.

[0064] As shown in Figure 5(a), when a first voltage V1 is applied to the piezoelectric element 23 based on a control signal from the control unit 3, the piezoelectric element 23 is compressed and displaced to reduce the volume of the pressure chamber 22. For example, if piezoelectric elements 23 are provided on opposite sides of the pressure chamber 22, and the first voltage V1 is applied to these piezoelectric elements 23, these piezoelectric elements 23 are displaced to move closer to each other. The first voltage V1 is, for example, a positive voltage, and its value is not particularly limited, but for example it is +20V. The first voltage V1 is also called the "ON voltage".

[0065] As shown in Figure 5(b), when a second voltage V2 different from the first voltage V1 is applied to the piezoelectric element 23 based on the control signal of the control unit 3, the piezoelectric element 23 is displaced to expand in order to increase the volume of the pressure chamber 22. For example, when the second voltage V2 is applied to each piezoelectric element 23 provided on the side surface of the pressure chamber 22, these piezoelectric elements 23 are displaced to move away from each other. The second voltage V2 is, for example, a negative voltage, and its value is not particularly limited, but for example it is minus 10V. The second voltage V2 is also called the "OFF voltage".

[0066] [Regarding discharge control] When the control unit 3 performs "discharge control" to eject the ink 91 stored in the pressure chamber 22 from the opening 26, it vibrates the piezoelectric element 23 in a first waveform pattern P1 in which the compression displacement precedes, as shown in Figure 6. In the graph of Figure 6, the horizontal axis represents time and the vertical axis represents the voltage value.

[0067] First, a first voltage V1 is applied to the piezoelectric element 23 from time t11 to time t12. This compresses and displaces the piezoelectric element 23, reducing the volume of the pressure chamber 22, and causing ink 91 to be ejected from the opening 26 of the nozzle 21.

[0068] Next, a second voltage V2 is applied to the piezoelectric element 23 from time t12 to time t13. This causes the piezoelectric element 23 to expand and displace, increasing the volume of the pressure chamber 22, and the ink 91 that has been ejected from the opening 26 flies away as droplets. In addition, as the volume of the pressure chamber 22 increases, ink 91 is filled into the pressure chamber 22 from the common ink chamber 24.

[0069] Subsequently, from time t13 to time t14, the piezoelectric element 23 is maintained in a state without voltage application (zero voltage). As a result, the piezoelectric element 23 is in a neutral state without displacement, and the shaking of the ink 91 inside the pressure chamber 22 and nozzle 21 is suppressed, thereby preventing the current ejection from adversely affecting the next ejection of ink 91.

[0070] Thus, during discharge control, a voltage is repeatedly applied to the piezoelectric element 23 in a first waveform pattern P1, in which a first voltage V1 (ON voltage) is applied first, followed by a second voltage V2 (OFF voltage). The first waveform pattern P1 is a series of voltage patterns shown from time t11 to time t14.

[0071] In the first waveform pattern P1, the application times of the ON voltage, OFF voltage, and zero voltage are not particularly limited. For example, the ON voltage time is shortest at 3.5 microseconds, followed by the OFF voltage time at 7.0 microseconds, and the zero voltage time is longest at 14 microseconds.

[0072] Note that the first waveform pattern P1 shown in Figure 6 is just one example, and ejection control may be performed using other waveform patterns. For example, the second voltage V2 (OFF voltage) may be applied first, and after the ink 91 fills the pressure chamber 22 from the common ink chamber 24, the first voltage V1 (ON voltage) may be applied, and then the second voltage V2 may be applied again to eject droplets of ink 91 from the opening 26. In this case, since the second voltage V2 is applied first to increase the volume of the pressure chamber 22 before the first voltage V1 is applied, more ink 91 is more likely to fly as droplets. For this reason, this waveform pattern may be used when it is desired to increase the droplet size.

[0073] [Regarding suction control] When the control unit 3 performs "suction control" to draw in a liquid such as cleaning solution 94 from the opening 26, it vibrates the piezoelectric element 23 in a second waveform pattern P2 in which the expansion displacement precedes, as shown in Figure 7. The second waveform pattern P2 is a different waveform pattern from the first waveform pattern P1. In the graph in Figure 7, the horizontal axis represents time and the vertical axis represents the voltage value.

[0074] Normally, if suction control is performed when the opening 26 is not immersed in liquid (i.e., the nozzle surface 25 is exposed to the air), "air lock" occurs, where air is sucked in from the opening 26. For this reason, such suction control tends to be avoided by technicians handling the inkjet device 1. This embodiment is characterized by using this suction control, which is not normally performed, to suck in the cleaning liquid 94 from the opening 26 by vibration of the piezoelectric element 23.

[0075] Furthermore, when controlling suction, the control unit 3 may open the third valve 53 to pump a small amount of ink 91 from the common ink chamber 24 to the drain tank 51 via the drain pipe 52. This results in the common ink chamber 24 having a lower pressure than the pressure chamber 22.

[0076] In this case, the opening of the third valve 53 may be adjusted to a half-open or less opening, rather than being fully open. This prevents a large amount of cleaning fluid 94 from being introduced from the opening 26 due to the negative pressure caused by the open state of the third valve 53. The open state of the third valve 53 here is done solely to create a slight negative pressure in the common ink chamber 24 and to assist in suction control by vibration of the piezoelectric element 23.

[0077] Furthermore, the method is not limited to the above if the common ink chamber 24 is at a lower pressure than the pressure chamber 22. For example, if the common ink chamber 24 is already maintained at a lower pressure than the pressure chamber 22 by a pressure adjustment mechanism (not shown), the opening control of the third valve 53 described above does not need to be performed.

[0078] Refer to Figure 7. First, a second voltage V2 is applied to the piezoelectric element 23 from time t21 to time t22. As a result, the piezoelectric element 23 expands in displacement, increasing the volume of the pressure chamber 22, and the liquid level (meniscus) of the ink 91 recedes into the interior of the nozzle 21 at the opening 26 of the nozzle 21. At this time, if the opening 26 is immersed in the cleaning liquid 94, the cleaning liquid 94 is drawn into the interior of the nozzle 21 from the opening 26.

[0079] Next, a first voltage V1 is applied to the piezoelectric element 23 from time t22 to time t23. This compresses and displaces the piezoelectric element 23, reducing the volume of the pressure chamber 22, and the liquid in the pressure chamber 22 (e.g., ink 91 and cleaning fluid 94) is sent to the common ink chamber 24, which has a lower pressure.

[0080] Subsequently, from time t23 to time t24, the piezoelectric element 23 is maintained in a state without applied voltage (zero voltage). As a result, the piezoelectric element 23 is in a neutral state without displacement, and the shaking of the ink 91 inside the pressure chamber 22 and nozzle 21 is suppressed, thereby preventing the current suction from adversely affecting the next suction of liquid.

[0081] Thus, during suction control, a second voltage V2 (OFF voltage) is applied first, followed by the first voltage V1 (ON voltage), and a voltage is repeatedly applied to the piezoelectric element 23 in a second waveform pattern P2. As a result, the piezoelectric element 23 acts like a dropper, drawing liquid from the opening 26 of the nozzle 21. The second waveform pattern P2 is a series of voltage patterns shown from time t21 to time t24.

[0082] In the second waveform pattern P2, the application times of the OFF voltage, ON voltage, and zero voltage are not particularly limited. For example, the OFF voltage time is shortest at 3.5 microseconds, followed by the ON voltage time at 7.0 microseconds, and the zero voltage time is longest at 14 microseconds.

[0083] [Scene from the suction process] Figure 8 is a schematic diagram showing the state of the inkjet device 1 during the suction process. During the suction process, the control unit 3 performs the suction control described above. Specifically, while the opening 26 of the nozzle surface 25 is immersed in the cleaning liquid 94, the piezoelectric element 23 is vibrated in the second waveform pattern P2. As a result, the cleaning liquid 94 is drawn from the opening 26 into the inside of the nozzle 21.

[0084] The cleaning liquid 94 fills, for example, the pressure chamber 22, and an amount sufficient to fill a part of the common ink chamber 24 is sucked from the opening 26. Note that the amount of the cleaning liquid 94 sucked is not enough to fill the entire common ink chamber 24, and most of the common ink chamber 24 (for example, 80% or more of the volume) is filled with the ink 91 even after the cleaning liquid 94 is sucked. The amount of the cleaning liquid 94 sucked is less than the volume of the common ink chamber 24 and is, for example, 1 to 5 milliliters.

[0085] In this embodiment, since the cleaning liquid 94 is sucked by the vibration of the piezoelectric element 23, the amount of the cleaning liquid 94 sucked can be suppressed to a small amount. As a result, it is possible to suppress breakage of the nozzle 21 or the like due to suction and deterioration inside the head 2 caused by immersion in a large amount of the cleaning liquid 94 (for example, deterioration such as the adhesive melting out of the cleaning liquid 94 from the wall surface of the common ink chamber 24). Therefore, for example, compared with the technique of Patent Document 1 in which a large amount of the cleaning liquid is introduced into the head by negative pressure of a pump, the head 2 of the inkjet device 1 can be more suitably cleaned.

[0086] During suction control, the control unit 3 may control the vibration unit 45 to ultrasonically vibrate the vibration unit 45. Thereby, ultrasonic vibration is applied to the cleaning liquid 94 introduced into the cleaning tray 41 and the nozzle 21 and the ink 91 in the head 2.

[0087] Here, the vibration of the vibration unit 45 is controlled to a sound pressure weak enough not to generate cavitation. Specifically, the vibration unit 45 applies ultrasonic vibration to the cleaning liquid 94 through the cleaning tray 41 at a sound pressure X2 lower than the first sound pressure X1 at which cavitation occurs in at least one of the cleaning liquid 94 and the ink 91 (X2 < X1). Thereby, while suppressing damage to the head 2 due to the impact caused by cavitation, the cleaning liquid 94 can be shaken, so that the ink masses 92 and 93 can be dissolved in the cleaning liquid 94 and promoted to separate from the inner wall of the head 2 and the nozzle surface 25.

[0088] For example, the control unit 3 vibrates the vibrating unit 45 at the second frequency F2 and the second amplitude A2. Here, the second frequency F2 may be higher than the first frequency F1 of the nozzle surface air removal step (step S12) (F2 > F1), and the second amplitude A2 may be smaller than the first amplitude A1 (A2 < A1). By vibrating the vibrating unit 45 in small increments at a relatively high frequency in this way, the dissolution of the ink masses 92 and 93 in the cleaning liquid 94 and the cracking of the ink masses 92 and 93 into smaller masses can be promoted, making it easier for the ink masses 92 and 93 to separate from the inner wall of the head 2 and the nozzle surface 25.

[0089] Also, during suction control, the control unit 3 may not only vibrate the piezoelectric element 23 in the second waveform pattern P2, but also vibrate the piezoelectric element 23 in the first waveform pattern P1 after vibrating in the second waveform pattern P2 a plurality of times. For example, the piezoelectric element 23 may be vibrated in a pattern where the second waveform pattern P2 is repeated twice, then the first waveform pattern P1 is executed only once, and then the second waveform pattern P2 is repeated again twice.

[0090] By vibrating in this way, after the cleaning liquid 94 is sucked into the nozzle 21, a small amount of the cleaning liquid 94 is discharged from the nozzle 21 to the cleaning tray 41, making it easier for the ink mass 93 near the opening 26 to separate from the head 2. Also, by repeating suction and discharge, the cleaning liquid 94 can be sucked into the nozzle 21 while finely adjusting the suction amount, so the suction amount of the cleaning liquid 94 to the head 2 can be suppressed to a small amount.

[0091] The suction control is executed, for example, only for a few seconds (about 3 to 10 seconds). Since this time is shorter than the cleaning time of 1 minute or more and 10 minutes or less in Patent Document 1, the inside of the head 2 can be cleaned while suppressing damage to the head 2 by the cleaning liquid 94.

[0092] 〔Drainage step: step S14〕 FIG. 9 is a schematic diagram showing the state of the inkjet device 1 during the drainage step. When the drainage process begins, the moving mechanism 8 moves the head 2 from a position covered by the cleaning tray 41 to a position covered by the drainage tray 55. At the same time, the second valve 47 is opened and the pump 48 is driven, causing the cleaning fluid 94 stored in the cleaning tray 41 to be pumped through the drainage pipe 46 to the drainage tank 51.

[0093] At the start of the drainage process, the drainage tray 55 is empty. With the nozzle surface 25 facing the empty drainage tray 55, the third valve 53 and the fifth valve 73 are opened. As a result, new ink 91 is supplied from the ink tank 71 to the common ink chamber 24 through the ink piping 72 by potential energy, and the ink 91 and cleaning fluid 94 are pumped from the common ink chamber 24 to the drainage tank 51 through the drainage piping 52. Thus, in this embodiment, the supply unit 7 and the drainage unit 5 function as the "pumping unit" of the present invention.

[0094] At this time, since the cross-sectional area of ​​the drain pipe 52 is larger than the cross-sectional area of ​​the flow path of the nozzle 21, most of the ink 91 and cleaning fluid 94 present inside the head 2 are discharged from the drain pipe 52 rather than the nozzle 21. As a result, as shown by arrow AR1 in Figure 9, for example, ink clumps 92 that have separated from the wall in the common ink chamber 24 and are floating inside the common ink chamber 24 are discharged from the drain pipe 52 along with the ink 91 and cleaning fluid 94.

[0095] For example, if the cleaning solution 94 is discharged from the nozzle 21 after the suction process, there is a risk that foreign matter will clog the nozzle 21. As described above, by discharging most of the cleaning solution 94 from the drain pipe 52, foreign matter such as ink clumps 92 is also discharged from the drain pipe 52, thus preventing clogging of the nozzle 21.

[0096] Furthermore, when the ink 91 and cleaning fluid 94 are pumped under pressure as described above, the common ink chamber 24 becomes pressurized, and as shown in Figure 9, a small amount of ink 91 and cleaning fluid 94 drips from the opening 26 through the pressure chamber 22 and nozzle 21 into the drain tray 55. However, since the amount of ink 91 and cleaning fluid 94 discharged from the opening 26 is less than the amount of ink 91 and cleaning fluid 94 discharged from the drain pipe 52, the risk of the nozzle 21 becoming clogged with foreign matter can be reduced compared to when the entire amount of cleaning fluid 94, etc., is discharged from the opening 26.

[0097] Finally, the fourth valve 57 is opened and the pump 58 is driven, causing the wastewater 96 accumulated in the wastewater tray 55 to be pumped through the wastewater pipe 56 to the wastewater tank 51. This completes the series of cleaning operations for the head 2.

[0098] In this embodiment, the amount of cleaning fluid 94 introduced into the head 2 by the vibration of the piezoelectric element 23 is kept to a minimum, thus reducing the amount of ink 91 (replacement ink) used to discharge the cleaning fluid 94 from the head 2 during the draining process. For example, the volume of ink 91 used for replacement may be less than the volume of the common ink chamber 24. This reduces the amount of ink 91 used and allows for faster replacement, thus shortening the time required for the draining process.

[0099] [Variation] The following describes modified examples of the embodiments. In the modified examples, components identical to those in the embodiments are denoted by the same reference numerals and their descriptions are omitted.

[0100] [Variations of the suction process] In the above embodiment, the piezoelectric element 23 vibrates in a pattern including the second waveform pattern P2 during the suction process. However, the waveform pattern used when performing suction control is not limited to this, and any pattern that allows the cleaning liquid 94 to be suctioned from the opening 26 is acceptable.

[0101] Furthermore, in the above embodiment, the vibration of the vibrating section 45 in the suction process is controlled to a sound pressure weak enough to prevent cavitation. However, the impact of cavitation may be used to promote the dissolution of ink clumps 92, 93, etc.

[0102] For example, the vibrating unit 45 may apply ultrasonic vibrations to the cleaning solution 94 via the cleaning tray 41 at a sound pressure X3 equal to or greater than the first sound pressure X1 at which cavitation occurs (X3 ≥ X1). In this case, although the foreign matter removal function is improved due to the impact caused by cavitation, there is a risk of damage to the head 2.

[0103] Therefore, in the suction process, after introducing the cleaning solution 94 into the head 2 through the opening 26, the vibrating part 45 may vibrate at a sound pressure X3 for the first few seconds to promote the dissolution of ink clumps 92 and 93 through cavitation, and then vibrate at a sound pressure X2 to promote the dissolution of the remaining ink clumps 92 and 93 with vibrations that do not cause cavitation. By limiting the vibration at sound pressure X3 to a short time in this way, it is possible to achieve both effective utilization of cavitation and suppression of damage to the head 2.

[0104] [Variations of the drainage process] In the drainage process, after pressurizing the ink 91 and cleaning fluid 94 from the common ink chamber 24 to the drainage pipe 52, the ink 91 and cleaning fluid 94 may be actively discharged from the nozzle 21 opening 26 by keeping the fifth valve 73 open and closing the third valve 53. This can suppress air entrapment in the nozzle 21.

[0105] In this case, the third valve 53 may be switched from an open state to a closed state gradually over a period of time, for example, 5 to 10 seconds. This allows the discharge of ink 91 and cleaning fluid 94 from the opening 26 to begin more gradually compared to when the valve is switched to a closed state in a relatively short time, thereby suppressing the sudden application of liquid pressure to the nozzle 21 and thus suppressing deterioration of the nozzle 21.

[0106] By controlling the process in the order described above, the ink 91 and cleaning fluid 94 are primarily discharged through the drain pipe 52. As a result, most foreign matter such as ink clumps 92 are discharged through the drain pipe 52, thereby suppressing clogging of the nozzle 21. Subsequently, the ink 91 and cleaning fluid 94 are secondarily discharged through the opening 26 of the nozzle 21, which suppresses air trapped in the nozzle 21.

[0107] For example, in the nozzle surface air removal process (step S12), there is a risk that air 95 that was not completely removed may enter the nozzle 21 through the opening 26 in the suction process (step S13). In this regard, by actively discharging the ink 91 and cleaning fluid 94 from the opening 26 of the nozzle 21 at the end of the drainage process, the air 95 can be discharged from the opening 26 along with these liquids. This suppresses air entrapment in the nozzle 21 after cleaning and prevents malfunctions of the nozzle 21.

[0108] [Note] The embodiments and modifications disclosed herein are illustrative in all respects and are not restrictive. The technical scope of the present invention is not limited to the embodiments and modifications described herein, and includes all modifications within the scope equivalent to the configuration described in the claims. [Explanation of Symbols]

[0109] 1. Inkjet device 2 heads 21 nozzles 22 Pressure chamber 23 Piezoelectric element 24 Common Ink Room 25 Nozzle surface 26 Opening 3. Control Unit 4. Cleaning section 41 Washing tray 42 Cleaning solution tanks 43 Cleaning fluid piping 44. Valve No. 1 45 Vibration section 46 Drainage piping 47. Second valve 48 pumps 5. Drainage section 51 Drainage tank 52 Drainage piping 53 Third valve 55 Drainage tray 56 Drainage piping 57. Valve No. 4 58 pumps 6. Coating area 61 stages 62 circuit boards 7 Supply section 71 Ink Tanks 72 Ink Piping 73. Valve No. 5 8 Moving mechanism 81 Horizontal movement mechanism 82 Vertical movement mechanism 91 Ink 92 ink blobs 93 Ink Chunks 94 Cleaning solution 95 Air 96 Drainage V1 First voltage (ON voltage) V2 Second voltage (OFF voltage) P1 First waveform pattern P2 Second waveform pattern X1 First Sound Pressure

Claims

1. A head including a nozzle, a pressure chamber communicating with the nozzle, and a piezoelectric element that increases or decreases the volume of the pressure chamber by vibration, A control unit for controlling the piezoelectric element, A cleaning tray that stores a cleaning solution into which the opening of the nozzle is immersed, Equipped with, The control unit, Discharge control involves vibrating the piezoelectric element to eject the ink stored in the pressure chamber from the opening, With the opening immersed in the cleaning liquid, the piezoelectric element is vibrated to draw the cleaning liquid from the opening into the nozzle; Execute Inkjet printer.

2. The discharge control includes a control that vibrates the piezoelectric element in a first waveform pattern, The attraction control includes a control that vibrates the piezoelectric element with a second waveform pattern different from the first waveform pattern. The inkjet apparatus according to claim 1.

3. The attraction control includes a control that vibrates the piezoelectric element with the second waveform pattern, and then vibrates the piezoelectric element with the first waveform pattern. The inkjet apparatus according to claim 2.

4. The head includes a common ink chamber that communicates with a plurality of pressure chambers, A drain pipe is connected to the aforementioned common ink chamber and has a larger flow path cross-sectional area than the nozzle, After the suction control, a pumping unit pumps the cleaning liquid sucked into the nozzle from the common ink chamber to the drainage pipe. Furthermore, An inkjet apparatus according to any one of claims 1 to 3.

5. A vibrating unit that applies ultrasonic vibrations to the cleaning liquid stored in the cleaning tray. Furthermore, An inkjet apparatus according to any one of claims 1 to 3.

6. The vibrating unit applies ultrasonic vibrations at a sound pressure lower than the first sound pressure at which cavitation occurs in the cleaning liquid during suction control. The inkjet apparatus according to claim 5.

7. A method for cleaning a head, comprising a nozzle, a pressure chamber communicating with the nozzle, and a piezoelectric element that increases or decreases the volume of the pressure chamber by vibration, A suction step in which, with the opening of the nozzle immersed in the cleaning liquid stored in the cleaning tray, the piezoelectric element is vibrated to draw the cleaning liquid into the nozzle from the opening. A method for cleaning the head, which includes the following features.

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