Liquid dispensing device

Abstract

To provide means which can suitably stop circulation of liquid according to nozzle pressure.SOLUTION: A printer 10 includes: an ink circulation section 110 which has a negative pressure pump 112 and circulates ink between an ink sub-tank 74 and a nozzle 33 of a head 30; a negative pressure adjustment valve 114 which controls communication between a gas layer of the ink sub-tank 74 and the atmosphere; and a control section 100. The control section 100 acquires nozzle pressure NP, which is pressure in the vicinity of the nozzle 33 of the ink circulation section 110 and opens the negative pressure adjustment valve 114 according to the nozzle pressure NP which is smaller than a negative side first threshold TM1 of a negative value and is equal to or more than a negative side second threshold TM2 which is smaller than the negative side first threshold TM1.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a liquid discharge device that circulates a liquid and discharges it from a nozzle.

Background Art

[0002] Patent Document 1 describes an example of an image recording device having an ink circulation mechanism. This image recording device has a pressure adjustment unit that adjusts the pressure in the ink circulation path on the ink circulation path. The pressure adjustment unit adjusts the pressure change on the side with the larger pressure change amount between the positive pressure side and the negative pressure side of the image recording unit at the start of ink circulation, thereby maintaining the nozzle pressure in the image recording unit within an appropriate range.

[0003] In a liquid discharge device that circulates a liquid and discharges it from a nozzle, when the nozzle pressure increases, liquid may leak from the nozzle, resulting in a deterioration of the image quality of the recorded image. Also, when the nozzle pressure decreases, air may enter the nozzle, preventing normal image recording. Therefore, when the nozzle pressure becomes above or below a predetermined value, it is necessary to stop the circulation of the liquid and then perform maintenance processing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, a configuration in which the circulation of the liquid is stopped and maintenance processing is performed every time the nozzle pressure becomes below a predetermined value has a problem that the image recording time becomes long and the consumption amount of the liquid increases.

[0006] The present invention has been made in view of the above circumstances, and its object is to provide a means for suitably stopping the circulation of liquid in accordance with the nozzle pressure. [Means for solving the problem]

[0007] (1) The liquid discharge device of the present invention comprises a storage section for storing liquid, a head having a nozzle for discharging liquid, a liquid circulation section including at least a negative pressure pump for circulating liquid between the storage section and the nozzle, a negative pressure adjustment valve for controlling communication between the gas layer of the storage section and the atmosphere, and a control unit. The control unit acquires the nozzle pressure, which is the pressure near the nozzle of the liquid circulation section, and opens the negative pressure adjustment valve when the nozzle pressure is less than a first negative threshold and greater than or equal to a second threshold less than the first threshold.

[0008] According to the above liquid discharge device, when the nozzle pressure is lower than the first threshold but higher than the second threshold, the circulation of the liquid is not unconditionally stopped. Instead, the negative pressure adjustment valve is opened to bring the pressure of the gas layer in the storage section closer to atmospheric pressure, thereby increasing the nozzle pressure. Therefore, the circulation of the liquid can be appropriately stopped based on the nozzle pressure without stopping the circulation of the liquid unnecessarily.

[0009] (2) Preferably, the liquid discharge device further comprises a positive pressure sensor for detecting the pressure in the upstream portion of the liquid circulation section and a negative pressure sensor for detecting the pressure in the downstream portion of the liquid circulation section, and the control unit may acquire the nozzle pressure based on the pressure detected by the positive pressure sensor and the pressure detected by the negative pressure sensor.

[0010] (3) Preferably, the control unit updates the count value when the nozzle pressure is less than the first threshold and greater than or equal to the second threshold, and after opening the negative pressure adjustment valve when the count value is greater than or equal to the threshold for that count value, it may stop the operation of the liquid circulation unit according to a predetermined stop sequence.

[0011] (4) Preferably, the control unit may stop the operation of the liquid circulation unit without following the stop sequence if the nozzle pressure is less than the second threshold.

[0012] (5) Preferably, the control unit may stop the operation of the liquid circulation unit without following the stop sequence if the nozzle pressure is greater than a third positive threshold.

[0013] (6) Preferably, the liquid dispensing device further comprises a display unit, and the control unit may display an error message on the display unit after stopping the operation of the liquid circulation unit based on the nozzle pressure.

[0014] (7) Preferably, the stopping sequence may be a sequence that gradually reduces the amount of liquid circulating in the liquid circulation unit to terminate the circulation of the liquid. [Effects of the Invention]

[0015] According to the present invention, the circulation of liquid can be suitably stopped in accordance with the nozzle pressure. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is an external perspective view of a printer 10 according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view showing the section II-II in Figure 1. [Figure 3] Figure 3 is a block diagram of printer 10. [Figure 4] Figure 4(A) is a schematic diagram showing the nozzle surface 31 of the head 30, and Figure 4(B) is a schematic diagram showing the upper surface of the maintenance section 60. [Figure 5] Figure 5(A) shows the state in which the first support part 40 has rotated to an inclined position, and Figure 5(B) shows the state in which the maintenance part 60 has moved onto the first support part 40. [Figure 6]FIG. 6(A) is a diagram showing a state in which the cap 61 covers the discharge portion 32, and FIG. 6(B) is a diagram showing a state in which the wiper of the maintenance unit 60 wipes the discharge portion 32. [Figure 7] FIG. 7 is a diagram showing the configuration of the ink circulation unit 110. [Figure 8] FIG. 8 is a flowchart of error processing based on the nozzle pressure by the control unit 100.

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described. It should be noted that the embodiments described below are merely examples of the present invention, and it is needless to say that the embodiments of the present invention can be appropriately changed without changing the gist of the present invention. In the following description, the progression from the starting point to the ending point of an arrow is expressed as the direction, and the movement back and forth on the line connecting the starting point and the ending point of the arrow is expressed as the orientation. Further, a vertical direction 7 is defined based on a state in which the printer 10 is installed so as to be usable (the state of FIG. 1), a front-rear direction 8 is defined with the surface on which the discharge port 13 of the printer 10 is formed as the front surface, and a left-right direction 9 is defined when the printer 10 is viewed from the front. The vertical direction 7, the front-rear direction 8, and the left-right direction 9 are orthogonal to each other.

[0018] [Overview of Printer 10] The printer 10 according to the present embodiment is an example of a liquid ejection device that ejects ink (an example of a liquid) onto a sheet by an inkjet printing method. The printer 10 is a monochrome printer that ejects black ink onto a sheet.

[0019] As shown in FIG. 1, the printer 10 includes a housing 11 having a generally rectangular parallelepiped shape. The housing 11 has a size that can be placed on a desktop, for example. The printer 10 is used by being placed on a desktop, a floor surface, or a rack.

[0020] The front surface 12 of the housing 11 houses an output port 13, an operation panel 14, and a display unit 15. The output port 13 is a long, slit-shaped opening in the left-right direction 9. Image-recorded sheets S (see Figure 2) are ejected from the output port 13. The operation panel 14 is operated by the user of the printer 10. By operating the operation panel 14, the user inputs various instructions and settings to the printer 10. The display unit 15 displays the status of the printer 10, etc. For example, the display unit 15 may display that an error has occurred in the printer 10.

[0021] [Internal configuration of printer 10] As shown in Figure 2, the housing 11 contains a holder 21, a tensioner 22, a transport roller pair 23, a transport roller pair 24, a support section 25, a wiper cleaning section 26, a cutter 27, a head 30, a first support section 40, a second support section 50, a maintenance section 60, and a mounting case 71. Although not shown in Figure 2, the housing 11 also contains a control unit 100 (see Figure 3), an ink circulation section 110, an ink sub-tank 74 (see Figure 7), etc. Furthermore, the housing 11 also contains a cleaning fluid tank, a cleaning fluid pump, a waste fluid tank (none of which are shown), etc. The ink circulation section 110 is an example of a liquid circulation section. The ink sub-tank 74 is an example of a storage section.

[0022] Within the housing 11, the holder 21 extends in the left-right direction 9. A roll body R, in which a long sheet S is wound around a core tube (not shown), is attached to the holder 21. The holder 21 supports the roll body R so that it can rotate in the circumferential direction of the core tube. The holder 21 rotates when a driving force is transmitted from the transport motor 81 (see Figure 3). As the holder 21 rotates, the roll body R supported by the holder 21 also rotates.

[0023] The sheet S is pulled upward from the rear end of the roll body R and guided to the tensioner 22. In front of the tensioner 22 is a pair of conveyor rollers 23, which includes a conveyor roller 23A and a pinch roller 23B. In front of the pair of conveyor rollers 23 is a pair of conveyor rollers 24, which includes a conveyor roller 24A and a pinch roller 24B.

[0024] The conveyor rollers 23A and 24A rotate by a driving force transmitted from the conveyor motor 81 (see Figure 3). The conveyor roller pair 23 feeds the sheet S forward by rotating it while nipping it as it extends forward from the tensioner 22. The conveyor roller pair 24 feeds the sheet S further forward by rotating it while nipping it as it is fed out by the conveyor roller pair 23. The sheet S fed out by the conveyor roller pair 24 is cut to the desired length by a cutter 27 located near the discharge port 13 and discharged from the discharge port 13. The dashed line in Figure 2 shows the conveyor path 28 of the sheet S.

[0025] The head 30 is located above the transport path 28, downstream of the transport roller pair 23 in the transport direction. The lower surface of the head 30 is called the nozzle surface 31. The nozzle surface 31 has a plurality of nozzles 33 that open downward. Ink is ejected downward from the plurality of nozzles 33 toward the sheet S supported by the transport belt 41 (described later). This records an image on the sheet S.

[0026] The first support section 40 is located below the head 30 and faces the head 30. The first support section 40 includes a conveyor belt 41, a drive roller 42, a driven roller 43, and gears 44 and 45. The conveyor belt 41 supports a sheet S located directly below the head 30, which is conveyed by the conveyor roller pair 23. The conveyor belt 41 conveys the supported sheet S in a forward direction. As will be described later, the first support section 40 can support a maintenance section 60.

[0027] The drive roller 42 and the driven roller 43 are located at a distance of 8 in the front-rear direction. The conveyor belt 41 is an endless belt and is stretched over the drive roller 42 and the driven roller 43. The conveyor belt 41 is positioned within the conveyor path 28 in the left-right direction 9.

[0028] The drive roller 42 rotates when power is transmitted from the conveyor motor 81 (see Figure 3), causing the conveyor belt 41 to rotate. The driven roller 43 rotates in conjunction with the rotation of the conveyor belt 41. The upper portion of the outer surface of the conveyor belt 41 functions as the conveying surface 46 for the sheet S. The conveying surface 46 supports the sheet S being conveyed between the pairs of conveyor rollers 23 and 24 from below, while applying a conveying force to the sheet S. As a result, the sheet S located on the conveying path 28 is conveyed in a forward direction.

[0029] The first support section 40 has a shaft 47 that extends in the left-right direction 9. The shaft 47 is rotatably supported by the housing 11. The shaft 47 is located upstream of the drive roller 42 in the conveying direction and below the conveying roller pair 23. The shaft 47 rotates when driving force is transmitted from the shaft motor 84 (see Figure 3). As the shaft 47 rotates, the first support section 40 rotates around the shaft 47 and moves between a horizontal position parallel to the nozzle surface 31 of the head 30 (see Figure 2) and an inclined position parallel to the upper surface of the second support section 50 (see Figure 5(A)).

[0030] Gears 44 and 45 are rotatably supported by the first support portion 40. Gear 45 rotates when driving force is transmitted from the first motor 85 (see Figure 3), either directly or via other gears.

[0031] The support section 25 is located downstream of the head 30 and the first support section 40 in the transport path 28, and below the transport roller 24A. The lower surface of the support section 25 is parallel to the diagonal direction 6. The diagonal direction 6 is perpendicular to the left-right direction 9 and is a direction that goes downward as it moves forward. The wiper cleaning section 26 is located on the lower surface of the support section 25. Cleaning fluid is supplied to the wiper cleaning section 26 from a cleaning fluid tank by means of a means not shown.

[0032] The second support section 50 is located below and diagonally behind the support section 25. The second support section 50 has gears 51 to 53. The second support section 50 is arranged to extend diagonally in the direction 6 as a whole. The second support section 50 supports the maintenance section 60 while it is in standby mode.

[0033] To move the second support part 50 in a direction perpendicular to the diagonal direction 6 and the left-right direction 9 (hereinafter referred to as the orthogonal direction), the second support part 50 is attached to the nut member of the ball screw 54. The screw shaft of the ball screw 54 is supported by the housing 11 so as to be rotatable around an axis along the orthogonal direction. The screw shaft rotates when driving force is transmitted from the up-down drive motor 83 (see Figure 3). The nut member of the ball screw 54 moves diagonally upward or diagonally downward along the orthogonal direction as a result of the rotation of the screw shaft. As a result, the second support part 50 moves along the orthogonal direction to a position close to the wiper cleaning unit 26 and to a position farther away from the wiper cleaning unit 26. When the second support part 50 is in the former position, the wiper cleaning unit 26 cleans the wiper (described later) of the maintenance unit 60.

[0034] Gears 51-53 are rotatably supported by the second support section 50. Gear 53 meshes with gears 51 and 52. Gear 53 rotates by a driving force supplied from the second motor 86 (see Figure 3), either directly or via other gears. When gear 53 rotates, gears 51 and 52 rotate in the same direction. Gears 51 and 52 can mesh with a rack 64 located on the underside of the maintenance section 60, which is located opposite each other.

[0035] The mounting case 71 is located at the front and lower part of the housing 11 and is a box shape that opens forward. The mounting case 71 has an ink needle 72. An ink cartridge 73 is mounted in the mounting case 71 facing backward. The ink cartridge 73 stores ink containing pigment, etc. When the ink cartridge 73 is mounted in the mounting case 71, the ink needle 72 is inserted into the ink outlet of the ink cartridge 73. The ink needle 72 is connected to the ink circulation unit 110 shown in Figure 7. The ink stored in the ink cartridge 73 mounted in the mounting case 71 is supplied to the ink sub-tank 74 (see Figure 7), and from the ink sub-tank 74, it is supplied to the nozzle 33 of the head 30 via the ink circulation unit 110.

[0036] [Head 30] As shown in Figures 2 and 4(A), the nozzle surface 31 of the head 30 has three discharge sections 32A to 32C. Each of the discharge sections 32A to 32C has multiple nozzles 33 arranged in two dimensions. The discharge sections 32A to 32C are located within the transport path 28 in the left-right direction 9. Discharge sections 32A and 32B are located at the same position in the front-back direction 8 and spaced apart in the left-right direction 9. Discharge section 32C is located in front of discharge sections 32A and 32B and between discharge sections 32A and 32B in the left-right direction 9. The left end of discharge section 32C is located to the left of the right end of discharge section 32A. The right end of discharge section 32C is located to the right of the left end of discharge section 32B. Note that the number of discharge sections 32 on the head 30 is not limited to three, but can be any number.

[0037] To move the head 30 in the vertical direction 7, the head 30 is attached to the nut member of a ball screw 34. The screw shaft of the ball screw 34 is supported by the housing 11 so as to be rotatable around an axis along the vertical direction 7. The screw shaft rotates with driving force transmitted from the head motor 82 (see Figure 3). The nut member of the ball screw 34 moves upward or downward as the screw shaft rotates. As a result, the head 30 moves along the vertical direction 7 to the recording position shown in Figure 2, the capped position shown in Figure 6(A), the wiped position shown by the solid line in Figure 6(B), and the uncapped position shown by the dashed line in Figure 6(B).

[0038] [Maintenance Department 60] The maintenance unit 60 is a component for performing maintenance on the head 30. The maintenance unit 60 is configured to be movable. When the maintenance unit 60 is in standby mode, it is supported by the second support unit 50 (see Figures 2 and 5(A)). When maintenance is performed on the head 30, the maintenance unit 60 is supported by the first support unit 40 and moved directly below the head 30 (see Figures 5(B) and 6).

[0039] As shown in Figures 2 and 4(B), the upper surface of the maintenance section 60 is equipped with three caps 61A to 61C, three sponge wipers 62A to 62C, and three rubber wipers 63A to 63C. The caps 61A to 61C are made of an elastic material such as rubber or silicone and have a box-shaped form with an open top. The caps 61A to 61C are positioned to cover the discharge sections 32A to 32C when the head 30 is in the capped position and the maintenance section 60 is in the maintenance position (described later). Cleaning fluid is supplied to the caps 61A to 61C from a cleaning fluid tank by means of a means not shown.

[0040] The sponge wipers 62A to 62C are made of sponge. The rubber wipers 63A to 63C are made of rubber. The sponge wipers 62A to 62C and the rubber wipers 63A to 63C have a shape that is elongated in the left-right direction 9. The left-right length 9 of the sponge wipers 62A to 62C is longer in the left-right direction 9 than the left-right length 9 of the area where the nozzle 33 is located in the discharge section 32A to 32C. The left-right length 9 of the rubber wipers 63A to 63C is equal to the left-right length 9 of the sponge wipers 62A to 62C. The height of the rubber wipers 63A to 63C is equal to the left-right height 9 of the sponge wipers 62A to 62C. As shown in Figure 4(B), the sponge wipers 62A to 62C are each positioned behind the caps 61A to 61C, parallel to the rear edges of the caps 61A to 61C. The rubber wipers 63A to 63C are positioned behind the sponge wipers 62A to 62C, parallel to them.

[0041] A rack 64 is located on a portion of the lower surface of the maintenance section 60. The gear 44 of the first support section 40 and the gears 51 and 52 of the second support section 50 can mesh with the rack 64. When the gear 53 rotates with the rack 64 and at least one of the gears 51 and 52 meshed, the maintenance section 60 moves along the upper surface of the second support section 50. When the gear 45 rotates with the rack 64 and gear 44 meshed, the maintenance section 60 moves along the upper surface of the first support section 40. Also, when the first support section 40 is in an inclined position, the front end of the first support section 40 is located near the rear end of the second support section 50, and the upper surfaces of the first support section 40 and the second support section 50 are on the same plane (see Figure 5(A)). Therefore, the maintenance unit 60 is movable to the standby position shown in Figures 2 and 5(A), the retraction position shown by the dashed line in Figure 6(B), the maintenance position shown in Figure 6(A), and the wipe position shown by the solid line in Figure 6(B).

[0042] [Maintenance procedure for head 30] The printer 10 performs purging, cap cleaning, and wiping as maintenance processes for the print head 30. The purging and cap cleaning processes are performed when the print head 30 is in the capping position and the maintenance unit 60 is in the maintenance position (as shown in Figure 6(A)). The purging process involves covering the discharge sections 32A to 32C of the print head 30 with the caps 61A to 61C of the maintenance unit 60, and then sucking ink from the nozzles 33 using a suction pump (not shown). The cap cleaning process is performed in the same state, cleaning the nozzle surface 31 of the print head 30 with cleaning fluid supplied to the cap 61. The wiping process is performed when the print head 30 is in the wiping position and the maintenance unit 60 is in the wiping position (as shown in Figure 6(B)). The wiping process involves wiping the nozzle surface 31 of the print head 30 with the sponge wipers 62A to 62C and rubber wipers 63A to 63C of the maintenance unit 60.

[0043] [Control Unit 100] As shown in Figure 3, the control unit 100 includes a CPU 101, ROM 102, RAM 103, EEPROM 104, and ASIC 105. The CPU 101, ROM 102, RAM 103, EEPROM 104, and ASIC 105 are interconnected by an internal bus 106. ROM 102 stores programs and other data for the CPU 101 to execute various processes. RAM 103 is used as a storage area for temporarily recording data and signals used by the CPU 101 when executing programs, or as a work area for data processing. EEPROM 104 stores information that should be retained even after the power is turned off.

[0044] The ASIC105 receives signals from sensors in the printer 10 and controls the motors and valves in the printer 10 according to the control from the CPU 101. The control unit 100 rotates each motor and the components connected to each motor by driving each motor through the ASIC105. The control unit 100 also outputs a drive signal to the drive element (not shown) of the head 30 through the ASIC105, causing ink to be ejected from the nozzles 33 of the head 30. The ASIC105 outputs a drive signal corresponding to the amount of ink to be ejected from the nozzles 33. An operation panel 14 and a display unit 15 are connected to the ASIC105.

[0045] [Ink circulation unit 110] The ink circulation unit 110 of the printer 10 will be described below with reference to Figure 7. The ink circulation unit 110 shown in Figure 7 comprises a positive pressure pump 111, a negative pressure pump 112, a replenishment valve 113, a negative pressure adjustment valve 114, an atmospheric release valve 115, an exhaust valve 116, a purge shut-off valve 117, a purge bypass valve 118, a positive pressure sensor 121, a negative pressure sensor 122, a filter 123, six FE joints 131-136, and several tubes connecting these elements. The ink circulation unit 110 supplies ink stored in the ink cartridge 73 to the ink sub-tank 74 and circulates the ink between the ink sub-tank 74 and the nozzles 33 of the print head 30.

[0046] The ink cartridge 73 has a connection port C11. The ink sub-tank 74 has five connection ports C21 to C25. Connection ports C21 to C24 are located on the top surface of the ink sub-tank 74 and are connected to the air layer (the part containing air) of the ink sub-tank 74. Connection port C25 is located on the side of the ink sub-tank 74 and is connected to the liquid layer (the part containing ink) of the ink sub-tank 74. The FE joints 131 to 136 each have three connection ports C1 to C3, and these connection ports C1 to C3 are connected to each other internally.

[0047] One end of the replenishment valve 113 is connected to the connection port C11 of the ink cartridge 73. The other end of the replenishment valve 113 is connected to the connection port C21 of the ink sub-tank 74. One end of the negative pressure pump 112 is connected to the connection port C22 of the ink sub-tank 74. One end of the negative pressure adjustment valve 114 and one end of the atmospheric release valve 115 are connected to the connection port C23 of the ink sub-tank 74. The other end of the negative pressure pump 112, the other end of the negative pressure adjustment valve 114, and the other end of the atmospheric release valve 115 are open to the atmosphere.

[0048] One end of the positive pressure pump 111 is connected to the connection port C24 of the ink subtank 74. The other end of the positive pressure pump 111 is connected to one end of the purge bypass valve 118 and, via the filter 123, to the connection port C1 of the FE joint 131. The connection port C2 of the FE joint 131 is connected to the connection port C1 of the FE joint 132. The connection port C2 of the FE joint 132 is connected to the connection port C1 of the FE joint 133. The connection port C2 of the FE joint 133 is connected to one end of the exhaust valve 116. The other end of the exhaust valve 116 is connected to the connection port C1 of the FE joint 134.

[0049] The connection port C3 of FE joint 131 is connected to one end of the discharge section 32A of head 30. The other end of the discharge section 32A is connected to the connection port C3 of FE joint 136. The connection port C3 of FE joint 132 is connected to one end of the discharge section 32B of head 30. The other end of the discharge section 32B is connected to the connection port C3 of FE joint 135. The connection port C3 of FE joint 133 is connected to one end of the discharge section 32C of head 30. The other end of the discharge section 32C is connected to the connection port C3 of FE joint 134.

[0050] The connection port C2 of FE joint 134 is connected to the connection port C1 of FE joint 135. The connection port C2 of FE joint 135 is connected to the connection port C1 of FE joint 136. The connection port C2 of FE joint 136 is connected to one end of the purge shut-off valve 117. The other end of the purge shut-off valve 117 is connected to the other end of the purge bypass valve 118 and to the connection port C25 of the ink sub-tank 74.

[0051] The positive pressure pump 111 is located on the ink flow path of the ink circulation unit 110. The positive pressure pump 111 rotates when power is transmitted from the pump motor 87 (see Figure 3). By rotating, the positive pressure pump 111 pushes ink into the ink flow path within the ink circulation unit 110. The negative pressure pump 112 is not located on the ink flow path, but is connected to the air layer of the ink sub-tank 74. The negative pressure pump 112 rotates when power is transmitted from the pump motor 88 (see Figure 3). By rotating and applying negative pressure to the ink sub-tank 74, the negative pressure pump 112 draws ink from the ink flow path within the ink circulation unit 110 through the air.

[0052] This configuration prevents pulsation when both the positive pressure pump 111 and the negative pressure pump 112 are operating. Pulsation occurs in the positive pressure pump 111 but not in the negative pressure pump 112, so the pressure from the negative pressure pump 112 does not interfere with the pressure from the positive pressure pump 111. Therefore, even when both the positive pressure pump 111 and the negative pressure pump 112 are operating, large pulsations do not occur. In addition, by providing a damper film (not shown) in the ink flow path connecting the positive pressure pump 111 and the filter 123, the pressure from the positive pressure pump 111 can be absorbed.

[0053] The negative pressure adjustment valve 114 controls the communication between the gas layer of the ink subtank 74 and the atmosphere. The negative pressure adjustment valve 114 is a normal solenoid valve. A normal solenoid valve has a spring and is closed due to the elastic force of the spring when no current is flowing, and opens when current flows because the force of the electromagnet becomes greater than the elastic force of the spring. A normal solenoid valve has the characteristic of opening and closing quickly. On the other hand, the atmospheric release valve 115 is a keep solenoid valve. A keep solenoid valve has a permanent magnet and is open due to the magnetic force of the permanent magnet when no current is flowing, and closes when current flows because the force of the electromagnet becomes greater than the magnetic force of the permanent magnet. A keep solenoid valve has the characteristic of being able to maintain an open state when the power supply is lost.

[0054] The positive pressure sensor 121 is located immediately before the connection port C1 of the FE joint 131 and detects the pressure in the upstream portion of the ink circulation section 110. The positive pressure sensor 121 outputs a detection signal to the control unit 100 indicating the detected pressure. The negative pressure sensor 122 is located immediately after the connection port C2 of the FE joint 136 and detects the pressure in the downstream portion of the ink circulation section 110. The negative pressure sensor 122 outputs a detection signal to the control unit 100 indicating the detected pressure. The control unit 100 receives the pressure detected by the positive pressure sensor 121 and the pressure detected by the negative pressure sensor 122 (see Figure 3).

[0055] When performing image recording or other operations, the control unit 100 performs front-end circulation, circulating ink through the nozzles 33 of the head 30. At this time, the control unit 100 controls the purge shut-off valve 117 to be open, the replenishment valve 113, negative pressure adjustment valve 114, atmospheric release valve 115, exhaust valve 116, and purge bypass valve 118 to be closed, and drives the positive pressure pump 111. In addition, the control unit 100 drives the negative pressure pump 112 for a predetermined time when the front-end circulation starts.

[0056] When the positive pressure pump 111 operates, ink is pushed into the ink flow path of the ink circulation unit 110. Also, when the front-end circulation starts, the negative pressure pump 112 operates, drawing ink into the ink flow path of the ink circulation unit 110. Therefore, the ink circulates between the ink subtank 74 and the discharge units 32A to 32C. Each of the discharge units 32A to 32C contains multiple nozzles 33. Some of the ink that reaches the discharge units 32A to 32C is discharged from the nozzles 33, and the rest returns to the ink subtank 74. In this way, the ink circulation unit 110 includes the positive pressure pump 111 and circulates ink between the ink subtank 74 and the nozzles 33 of the head 30.

[0057] When performing exhaust circulation, the control unit 100 performs back-end circulation, which circulates the ink without passing through the nozzles 33 of the head 30. At this time, the control unit 100 controls the exhaust valve 116 and the purge shut-off valve 117 to be open, and the replenishment valve 113, negative pressure adjustment valve 114, atmospheric release valve 115, and purge bypass valve 118 to be closed, and drives the positive pressure pump 111. The resistance of the flow path through the exhaust valve 116 is smaller than the resistance of the flow path through the discharge sections 32A to 32C. Therefore, the ink mainly flows through the flow path through the exhaust valve 116, rather than through the flow path through the discharge sections 32A to 32C. Consequently, air that has entered the ink circulation section 110 can be discharged without introducing air from the nozzles 33.

[0058] When the control unit 100 replenishes ink from the ink cartridge 73 to the ink sub-tank 74, it controls the replenishment valve 113 to be in an open state, the negative pressure adjustment valve 114 and the atmosphere release valve 115 to be in a closed state, and drives the negative pressure pump 112. By applying a negative pressure to the air layer of the ink sub-tank 74 by the negative pressure pump 112, ink is replenished from the ink cartridge 73 to the ink sub-tank 74.

[0059] [Error processing based on nozzle pressure] In order to correctly perform image recording in the printer 10, it is necessary to maintain the meniscus of the nozzle 33. The control unit 100 obtains the pressure near the nozzle 33 (hereinafter referred to as the nozzle pressure NP) in the ink circulation unit 110 based on the pressure detected by the positive pressure sensor 121 and the pressure detected by the negative pressure sensor 122 in order to maintain the meniscus of the nozzle 33, and performs error processing based on the obtained nozzle pressure NP. The nozzle pressure NP is, for example, the pressure in an individual flow path that branches from the main flow path connecting one end and the other end and communicates with one nozzle 33 in any of the discharge units 32A to 32C. Note that the nozzle pressure NP is an estimated value of the pressure near the nozzle 33 based on the pressure detected by the positive pressure sensor 121 and the pressure detected by the negative pressure sensor 122, and is not an actual measurement of the pressure near the nozzle 33.

[0060] The control unit 100 has three threshold values (positive threshold value TP, negative first threshold value TM1, and negative second threshold value TM2) with respect to the nozzle pressure NP. The positive threshold value TP is a positive value. The negative first threshold value TM1 and the negative second threshold value TM2 are negative values. The negative second threshold value TM2 is smaller than the negative first threshold value TM1. That is, the magnitude relationship of the three threshold values is TM2 < TM1 < 0 < TP. The negative first threshold value TM1 is an example of the first threshold value. The negative second threshold value TM2 is an example of the second threshold value. The positive threshold value TP is an example of the third threshold value.

[0061] The control unit 100 has a count value CNT that counts the number of times the nozzle pressure NP is less than the negative first threshold TM1 and greater than or equal to the negative second threshold TM2. The count value CNT is initialized to 0 at the start of a cyclic operation (front-end cycle or back-end cycle) and is incremented according to whether the nozzle pressure NP is less than the negative first threshold TM1 and greater than or equal to the negative second threshold TM2. The count value CNT is initialized to 0 at the start of a cyclic operation. The control unit 100 has a count threshold TC related to the count value CNT. The positive threshold TP, the negative first threshold TM1, the negative second threshold TM2, and the count threshold TC may be fixed values ​​pre-set in the printer 10, or they may be values ​​that change according to the operating status of the printer 10.

[0062] The error handling based on nozzle pressure by the control unit 100 will be explained below with reference to Figure 8. First, the control unit 100 initializes the count value CNT to 0 (S1). Next, the control unit 100 causes the ink circulation unit 110 to perform a circulation operation (S2). In S2, the control unit 100 controls the pump and valves in the ink circulation unit 110 to cause the ink circulation unit 110 to perform front-end circulation or back-end circulation. The circulation operation is performed when the printer 10 is powered on and during printing, etc. The circulation operation is also performed after a predetermined time has elapsed since the end of printing in order to prevent the nozzles 33 from drying out. The circulation operation is also performed before purging.

[0063] Next, the control unit 100 determines whether or not it is a pressure detection timing (S3). If the control unit 100 determines that it is not a pressure detection timing (S3: No), it returns to S2 and causes the ink circulation unit 110 to continue the circulation operation. If the control unit 100 determines that it is a pressure detection timing (S3: Yes), it proceeds to S4. The control unit 100 executes S3, for example, at predetermined time intervals.

[0064] In S4, the control unit 100 acquires the pressure P1 detected by the positive pressure sensor 121 and the pressure P2 detected by the negative pressure sensor 122. Next, the control unit 100 acquires the nozzle pressure NP based on the two pressures P1 and P2 acquired in S4 (S5). In S5, the control unit 100 acquires the nozzle pressure NP as the average of the two pressures P1 and P2 acquired in S12, for example, (P1+P2) / 2. The control unit 100 may acquire the nozzle pressure NP based on the two pressures P1 and P2 by a method other than the one described above. For example, the control unit 100 may acquire the nozzle pressure NP by apportioning the two pressures P1 and P2 by the length of the flow path from the positive pressure sensor 121 to the nozzle 33 and the length of the flow path from the nozzle 33 to the negative pressure sensor 122.

[0065] Next, the control unit 100 determines whether the nozzle pressure NP is greater than or equal to the positive threshold TP (S10). If the control unit 100 determines that the nozzle pressure NP is less than or equal to the positive threshold TP (S10: No), it proceeds to S20. In this case, the control unit 100 determines whether the nozzle pressure NP is less than or equal to the negative second threshold TM2 (S20). If the control unit 100 determines that the nozzle pressure NP is greater than or equal to the negative second threshold TM2 (S20: No), it proceeds to S30. In this case, the control unit 100 determines whether the nozzle pressure NP is less than or equal to the negative first threshold TM1 (S30). If the control unit 100 determines that the nozzle pressure NP is greater than or equal to the negative first threshold TM1 (S30: No), it proceeds to S2 and causes the ink circulation unit 110 to continue the circulation operation.

[0066] In response to determining in S10 that the nozzle pressure NP is greater than the positive threshold TP (S10: Yes), the control unit 100 proceeds to S11. In this case, in order to prevent ink leakage from the nozzle 33, it is necessary to quickly stop the circulation of ink in the ink circulation unit 110. Therefore, the control unit 100 forcibly terminates the ink circulation unit 110 and controls the atmospheric release valve 115 to the open state (S11). Here, forced termination means terminating immediately without executing the normal termination sequence (described later). In S11, the control unit 100 immediately stops the positive pressure pump 111.

[0067] Next, the control unit 100 displays an error message on the display unit 15 indicating that "an error has occurred in which the nozzle pressure has exceeded the positive threshold" (indicated as "positive error" in Figure 8) (S12). Next, the control unit 100 records "an error has occurred in which the nozzle pressure has exceeded the positive threshold" in the EEPROM 104 (S13).

[0068] In response to determining in S20 that the nozzle pressure NP is less than the negative second threshold TM2 (S20: Yes), the control unit 100 proceeds to S21. In this case, it is necessary to quickly stop the circulation of ink in the ink circulation unit 110 in order to prevent air from entering from the nozzle 33. Therefore, the control unit 100 forcibly terminates the ink circulation unit 110 and controls the atmospheric release valve 115 to the open state (S21). Note that S21 is the same process as S11.

[0069] Next, the control unit 100 displays an error message on the display unit 15 indicating that "an error has occurred in which the nozzle pressure has exceeded the negative second threshold" (indicated as "Negative Error 2" in Figure 8) (S22). Next, the control unit 100 records "an error has occurred in which the nozzle pressure has exceeded the negative second threshold" in the EEPROM 104 (S23).

[0070] In response to determining in S30 that the nozzle pressure NP is less than the negative first threshold TM1 (S30: Yes), the control unit 100 proceeds to S31. In this case, the control unit 100 opens the negative pressure adjustment valve 114 for a predetermined time (S31). The predetermined time is, for example, 0.1 seconds. When the negative pressure adjustment valve 114 is opened, the pressure of the gas layer in the ink subtank 74 approaches atmospheric pressure, and the nozzle pressure NP increases. Next, the control unit 100 adds 1 to the count value CNT (S32).

[0071] Next, the control unit 100 determines whether the count value CNT is equal to or greater than the count threshold TC (S33). The count threshold TC is, for example, 10 times. If the control unit 100 determines that the count value CNT is less than the count threshold TC (S33: No), it proceeds to S2 and causes the ink circulation unit 110 to continue the circulation operation.

[0072] The control unit 100 determines that the count value CNT is equal to or greater than the count threshold TC (S33: Yes) and proceeds to S34. In this case, the control unit 100 opens the negative pressure adjustment valve 114 until the nozzle pressure reaches a predetermined level (S34). As a result, the pressure in the ink sub-tank 74 approaches atmospheric pressure, and the nozzle pressure NP rises to a predetermined level.

[0073] Next, the control unit 100 stops the circulation operation in the ink circulation unit 110 according to a normal stop sequence (S35). The normal stop sequence is a sequence that gradually reduces the amount of ink circulated in the ink circulation unit 110 to terminate the ink circulation. In order to gradually reduce the amount of ink circulated in the ink circulation unit 110, the control unit 100 gradually reduces the force with which the positive pressure pump 111 pushes ink into the ink flow path in the ink circulation unit 110. At the same time, the control unit 100 may also control the negative pressure adjustment valve 114 to be open for a predetermined time at a predetermined timing. The normal stop sequence is executed when the power of the printer 10 is turned off.

[0074] Next, the control unit 100 displays an error message on the display unit 15 indicating that "an error has occurred in which the nozzle pressure has exceeded the negative first threshold multiple times" (indicated as "Negative Error 1" in Figure 8) (S36). Next, the control unit 100 records "an error has occurred in which the nozzle pressure has exceeded the negative first threshold multiple times" in the EEPROM 104 (S37).

[0075] After executing S13, S23, or S37, the control unit 100 terminates the image recording process. The user then turns off the printer 10. The user or maintenance worker removes the cause of the error by clearing blockages in the filter 123, replacing a malfunctioning motor, etc. When the printer 10 is then turned on, the control unit 100 performs the head 30 maintenance process described above to form the meniscus of the nozzle 33. Furthermore, if the printer 10 is turned on before the cause of the error is removed, the control unit 100 displays an error message on the display unit 15 indicating the type of error based on the type of error recorded in the EEPROM 104.

[0076] If the control unit 100 determines "Yes" in S33, it stops the operation of the ink circulation unit 110 according to the normal stop sequence (S34). If the control unit 100 determines "Yes" in S10 or S20, it stops the operation of the ink circulation unit 110 without following the normal stop sequence (S11, S21). In the latter case, the control unit 100 immediately stops the positive pressure pump 111. Therefore, when stopping without following the normal stop sequence, the time from the start of the stop operation to the complete cessation of the operation of the ink circulation unit 110 is shorter compared to when stopping according to the normal stop sequence.

[0077] [Effects of the Embodiment] As described above, the printer 10 according to this embodiment includes an ink sub-tank 74, a head 30 having nozzles 33, an ink circulation unit 110 including at least a negative pressure pump 112, a negative pressure adjustment valve 114, and a control unit 100. The control unit 100 acquires the nozzle pressure NP, which is the pressure near the nozzles 33 of the ink circulation unit 110, and opens the negative pressure adjustment valve 114 when the nozzle pressure NP is less than a negative first threshold TM1 and greater than or equal to a negative second threshold TM2 which is less than the negative first threshold TM1.

[0078] In this type of printer 10, when the nozzle pressure is less than the negative first threshold TM1 and greater than or equal to the negative second threshold TM2, the ink circulation is not unconditionally stopped. Instead, the negative pressure adjustment valve 114 is opened to bring the pressure of the gas layer in the ink sub-tank 74 closer to atmospheric pressure, thereby increasing the nozzle pressure NP. Therefore, the ink circulation can be appropriately stopped based on the nozzle pressure NP without stopping the ink circulation unnecessarily. In addition, since printing is not stopped frequently, the downtime of the printer 10 can be reduced.

[0079] Furthermore, the printer 10 is equipped with a positive pressure sensor 121 that detects the pressure in the upstream part of the ink circulation unit 110 and a negative pressure sensor 122 that detects the pressure in the downstream part of the ink circulation unit 110. The control unit 100 obtains the nozzle pressure NP based on the pressure detected by the positive pressure sensor 121 and the pressure detected by the negative pressure sensor 122. Therefore, even if a pressure sensor cannot be placed near the nozzle 33, the nozzle pressure NP can be obtained based on the pressure detected by the positive pressure sensor 121 and the pressure detected by the negative pressure sensor 122, and the ink circulation can be suitably stopped based on the nozzle pressure NP.

[0080] Furthermore, the control unit 100 updates the count value CNT when the nozzle pressure NP is less than the negative first threshold TM1 and greater than or equal to the negative second threshold TM2. When the count value CNT is greater than or equal to the count threshold TC, it opens the negative pressure adjustment valve 114 and then stops the operation of the ink circulation unit 110 according to a predetermined stop sequence. By stopping the circulation of ink according to the stop sequence when the state in which the nozzle pressure NP is less than the negative first threshold TM1 and greater than or equal to the negative second threshold TM2 has been reached for more than the count threshold TC, the circulation of ink can be suitably stopped based on the nozzle pressure NP.

[0081] Furthermore, the control unit 100 stops the operation of the ink circulation unit 110 without following a stop sequence when the nozzle pressure NP is less than the negative second threshold TM2. By quickly stopping the circulation of ink when the nozzle pressure NP is less than the negative second threshold TM2, it is possible to prevent air from entering from the nozzle 33.

[0082] Furthermore, the control unit 100 stops the operation of the ink circulation unit 110 without following a stop sequence when the nozzle pressure NP is greater than the positive threshold TP. By quickly stopping the circulation of ink when the nozzle pressure NP is greater than the positive threshold TP, it is possible to prevent a decrease in the image quality of the recorded image due to ink leaking from the nozzle 33.

[0083] The printer 10 also includes a display unit 15. The control unit 100 stops the operation of the ink circulation unit 110 based on the nozzle pressure NP, and then displays an error message on the display unit 15. Thus, the user can be notified of any abnormalities in the nozzle pressure.

[0084] Furthermore, the stopping sequence is a sequence that gradually reduces the amount of ink circulating in the ink circulation unit 110 to terminate the ink circulation. Therefore, the ink circulation can be gradually stopped over a certain period of time.

[0085] [Differentiation] Various modifications can be made to the printer 10 according to the above embodiment. For example, although the printer 10 according to the embodiment is a monochrome printer, the printer according to the modification may be a color printer that ejects multiple types of color ink onto a sheet. In the case of a color printer, the control unit acquires the nozzle pressure for each of the multiple colors, and opens the corresponding negative pressure adjustment valve when a certain nozzle pressure is less than a negative first threshold and greater than or equal to a negative second threshold, and forcibly terminates the circulation operation of all color inks when at least one of the multiple nozzle pressures is greater than a positive threshold, less than a negative second threshold, or less than a negative first threshold and greater than or equal to a negative second threshold for a count threshold number of times or more.

[0086] Furthermore, while the printer 10 uses a maintenance unit 60 having a cap 61, a sponge wiper 62, and a rubber wiper 63 to perform purging, cap cleaning, and wiping as maintenance processes for the head 30, the modified printer may have a maintenance unit with a configuration other than that described above, and may perform other processes in addition to, or instead of, the above three processes as maintenance processes for the head. For example, the maintenance unit may have a sponge wiper but not a rubber wiper.

[0087] Furthermore, while the control unit 100 of the printer 10 acquires the nozzle pressure NP based on the pressure detected by the positive pressure sensor 121 and the pressure detected by the negative pressure sensor 122, the control unit of the modified printer may acquire the nozzle pressure NP by a method other than that described above. For example, the modified printer may be equipped with a pressure sensor near the nozzle, and the control unit of the modified printer may acquire the pressure detected by the pressure sensor as the nozzle pressure NP.

[0088] Furthermore, in the ink circulation unit 110 of the printer 10, the negative pressure pump 112 is connected to the air layer of the ink sub-tank 74 and applies negative pressure to the ink sub-tank 74. However, in the ink circulation unit of the modified printer, the negative pressure pump may be provided on the ink flow path, similar to a positive pressure pump, and draw in ink from within the ink flow path.

[0089] Furthermore, while the control unit 100 of the printer 10 compares the nozzle pressure NP with the positive threshold TP and then compares the nozzle pressure NP with the negative second threshold TM2, the control unit of the modified printer may compare the nozzle pressure NP with the negative second threshold TM2 and then compare the nozzle pressure NP with the positive threshold TP. Also, the control unit of the modified printer may perform other processing when it detects an error based on the nozzle pressure. For example, when the control unit detects an error based on the nozzle pressure, it may notify other devices connected via a communication interface of the occurrence of the error. [Explanation of symbols]

[0090] 10. Printer (liquid ejection device) 15...Display section 30 heads 33... Nozzle 74. Ink sub-tank (storage section) 100... Control Unit 110... Ink circulation unit (liquid circulation unit) 112... Vacuum pump 114...Vacuum regulating valve 121... Positive pressure sensor 122... Negative pressure sensor

Claims

1. A storage section for storing liquid, A head having a nozzle for dispensing liquid, A liquid circulation unit that includes at least a negative pressure pump and circulates the liquid between the storage unit and the nozzle, A negative pressure adjustment valve controls the communication between the gas layer in the above-mentioned storage section and the atmosphere, A positive pressure sensor detects the pressure in the upstream portion of the liquid circulation section, A negative pressure sensor for detecting the pressure in the downstream portion of the liquid circulation section, It includes a control unit, The control unit acquires the nozzle pressure, which is the pressure near the nozzle of the liquid circulation section, based on the pressure detected by the positive pressure sensor and the pressure detected by the negative pressure sensor, and opens the negative pressure adjustment valve when the nozzle pressure is less than a first negative threshold and greater than or equal to a second threshold that is less than the first threshold. The control unit updates the count value when the nozzle pressure is less than the first threshold and greater than or equal to the second threshold, and when the count value is greater than or equal to the threshold for that count value, it opens the negative pressure adjustment valve and then stops the operation of the liquid circulation unit according to a predetermined stop sequence.

2. The liquid dispensing device according to claim 1, wherein the control unit stops the operation of the liquid circulation unit without following the stop sequence in response to the nozzle pressure being less than the second threshold.

3. The liquid discharge device according to claim 1, wherein the control unit stops the operation of the liquid circulation unit without following the stop sequence when the nozzle pressure is greater than a third positive threshold value.

4. It also includes a display unit, The liquid dispensing device according to any one of claims 1 to 3, wherein the control unit stops the operation of the liquid circulation unit based on the nozzle pressure and then displays an error message on the display unit.

5. The liquid dispensing device according to any one of claims 1 to 3, wherein the above-mentioned stopping sequence is a sequence that gradually reduces the amount of liquid circulating in the liquid circulation section to terminate the circulation of the liquid.

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