Liquid circulation device

Abstract

To provide a liquid circulation device capable of efficiently circulating liquid between the liquid circulation device and an ejection part.SOLUTION: In the liquid circulation device 10, a liquid supply pipe 44 in which a liquid supply pump 48 is arranged and a recovery pipe 46 opened to the outside of the liquid in a main tank 30 are provided between the injection head 18 and the main tank 30 having airtightness and storing the liquid 12. A negative pressure pipe 62 in which an air pump 60 is disposed is opened to the outside of the liquid in the main tank 30. As a result, in the liquid circulation device 10, since the liquid 12 can be circulated so as to be drawn in from the injection head 18 by the negative pressure generated by the air pump 60 while the liquid 12 is sent out by the liquid supply pump 48, the liquid 12 can be efficiently circulated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid circulation device. [Background technology]

[0002] Some inkjet recording devices as liquid ejection devices use an ink circulation device that circulates ink as a liquid between a tank and a liquid ejection head (see, for example, Patent Documents 1 and 2).

[0003] In the ink circulation device of Patent Document 1, a first pump supplies ink from a tank to a liquid ejection head, and a second pump supplies ink from the liquid ejection head to the tank. In this case, Patent Document 1 controls the ink pressure in the liquid ejection head by controlling the first pump and the second pump according to the pressure detected by a first pressure sensor on the secondary side of the first pump and the pressure detected by a second pressure sensor on the primary side of the second pump.

[0004] In addition, the ink circulation device in Patent Document 2 has an ink supply chamber and an ink recovery chamber arranged above the inkjet head, each of which is provided with a pressure adjustment pump, and an ink circulation unit arranged between the ink supply chamber and the ink recovery chamber. As a result, the ink circulation device circulates ink from the ink recovery chamber to the ink supply chamber while adjusting the pressure in the ink supply chamber and the ink recovery chamber, thereby supplying ink from the ink supply chamber to the ink pressure chamber and recovering ink from the ink pressure chamber to the ink recovery chamber while maintaining a required pressure in the ink pressure chamber of the inkjet head. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-137004 [Patent Document 2] Japanese Patent Application Publication No. 2019-196015 Summary of the Invention [Problem to be solved by the invention]

[0006] When liquids such as ink stagnate, the components contained in the liquid can precipitate or condense, resulting in poor ejection when the liquid is ejected from the nozzle of the ejection head. However, by circulating the liquid between the tank and the ejection head, it is possible to prevent precipitation and other problems from occurring.

[0007] However, the viscosity of liquids changes due to evaporation and temperature changes. Furthermore, some liquids, such as paint, have higher viscosities than ink. Therefore, there is room for improvement in the liquid circulation device to circulate the liquid so that the required pressure is maintained at the ejection section.

[0008] The present invention has been made in consideration of the above circumstances, and has an object to provide a liquid circulation device that enables efficient circulation of liquid between an ejection portion that ejects the liquid and the ejection portion. [Means for solving the problem]

[0009] In order to achieve the above object, a liquid circulation device of a first aspect of the present invention includes: a tank that stores liquid and is airtight with respect to the surrounding space; an injection section that is supplied with the liquid and can inject a portion of the supplied liquid; a liquid supply pipe that has one end that opens into the liquid stored in the tank and the other end that is connected to the injection section, so that the liquid in the tank can be supplied to the injection section; a liquid supply pump that is disposed in the middle of the liquid supply pipe and that, when activated, supplies the liquid in the tank to the injection section via the liquid supply pipe; a recovery pipe that has one end that opens to the outside of the liquid in the tank and the other end that is connected to the injection section, so that the liquid supplied to the injection section can be recovered into the tank when the liquid supply pump is activated; a negative pressure supply section that reduces the pressure inside the tank and supplies negative pressure to the tank so that the liquid in the injection section can be recovered into the tank; and a control section that controls the operation of the liquid supply pump and the negative pressure supply section to control the circulation of the liquid between the tank and the injection section.

[0010] In the liquid circulation device of the first aspect, the liquid supplied to the injection part and injected from the injection part is stored in the tank, and this liquid is circulated between the tank and the injection part. The tank is airtight with respect to the surrounding space, and the pressure inside is reduced by supplying negative pressure from the negative pressure supply part.

[0011] Furthermore, a liquid supply pipe and a recovery pipe are connected between the tank and the injection part. One end of the liquid supply pipe opens into the liquid stored in the tank and the other end is connected to the injection part, and the liquid supply pipe can supply the liquid in the tank to the injection part. One end of the recovery pipe opens outside the liquid in the tank and the other end is connected to the injection part, and the recovery pipe can recover the liquid in the injection part into the tank.

[0012] The control unit controls the operation of a liquid supply pump disposed in the liquid supply pipe and a negative pressure supply unit that supplies the generated negative pressure to the outside of the liquid in the tank.

[0013] Here, when the liquid supply pump is operated, it supplies the liquid in the tank to the injection unit via the liquid supply pipe. Also, when the negative pressure supply unit is operated, it reduces the pressure inside the tank. This forces the liquid from the tank through the liquid supply pipe to the injection unit, and from the injection unit through the recovery pipe to draw it back into the tank, so that the liquid is efficiently circulated between the tank and the injection unit even if the viscosity changes.

[0014] The liquid circulation device of the second aspect is the liquid circulation device of the first aspect, and includes a first pressure sensor that detects a first pressure as the pressure of the liquid flowing through the liquid supply pipe toward the injection section, and a second pressure sensor that detects a second pressure as the pressure of the liquid flowing through the recovery pipe toward the tank, and the control unit controls the operation of the liquid supply pump so that the first pressure becomes a predetermined first set pressure, and controls the operation of the negative pressure supply unit so that the second pressure becomes a predetermined second set pressure.

[0015] The second aspect of the liquid circulation device is provided with a first pressure sensor that detects a first pressure as the pressure of the liquid flowing through the liquid supply pipe toward the injection section, and a second pressure sensor that detects a second pressure as the pressure of the liquid flowing through the recovery pipe toward the tank.

[0016] The control unit controls the operation of the liquid supply pump so that the first pressure becomes the first set pressure, and controls the operation of the negative pressure supply unit so that the second pressure becomes the second set pressure. This allows the pressure of the liquid in the injection unit to be the difference between the first set pressure and the second set pressure, making it possible to appropriately control the circulation of the liquid between the tank and the injection unit.

[0017] The liquid circulation device of the third aspect is the first or second aspect, and further includes a second pipe in the liquid supply pipe, one end of which is connected to an intermediate portion of a first pipe between the tank and the liquid supply pump, and the other end of which is open into the liquid in the tank, and the inner diameter of which is smaller than the inner diameter of the first pipe.

[0018] In the liquid circulation device of the third aspect, a second pipe is provided in the liquid supply pipe, one end of which is connected to an intermediate portion of the first pipe between the tank and the liquid supply pump and the other end of which is open to the liquid in the tank, and the inner diameter of the second pipe is smaller than that of the first pipe, thereby allowing the liquid supply pump to operate continuously to circulate the liquid.

[0019] A fourth aspect of the liquid circulation device is any one of the first to third aspects, wherein the negative pressure supply unit includes a negative pressure pump whose operation is controlled to generate negative pressure, a negative pressure pipe whose one end is connected to the negative pressure pump and whose other end is open to the outside of the liquid in the tank, and a throttle valve whose one side is connected to the middle of the negative pressure pipe and whose other side is open to control the negative pressure in the negative pressure pipe.

[0020] In the liquid circulation device of the fourth aspect, the negative pressure supply unit includes a negative pressure pump that generates negative pressure, and a negative pressure pipe that is connected to the negative pressure pump at one end and opens to the outside of the liquid inside the tank at the other end. A throttle valve that controls the negative pressure inside the negative pressure pipe is disposed in the middle of the negative pressure pipe. This allows the throttle valve to control the negative pressure inside the tank and the negative pressure pump to operate continuously, thereby suppressing pressure changes inside the tank caused by the operation / stop of the negative pressure pump.

[0021] A fifth aspect of the liquid circulation device is any one of the first to fourth aspects, and further includes a heating unit that heats the liquid in the tank and a temperature detection unit that detects the temperature of the liquid in the liquid supply pipe, and the control unit controls the operation of the heating unit so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

[0022] In a fifth aspect of the liquid circulation device, a heating unit heats the liquid in the tank, and a temperature detection unit detects the temperature of the liquid in the liquid supply pipe. A control unit controls the operation of the heating unit so that the temperature detected by the temperature detection unit becomes a predetermined target temperature. This allows the temperature of the liquid to be set to the target temperature and the viscosity of the liquid to be adjusted to a value corresponding to the target temperature, enabling more efficient circulation of the liquid. [Effects of the Invention]

[0023] According to this aspect of the present invention, the liquid supply pump supplies the liquid in the tank to the injection section via the liquid supply piping, and the negative pressure supply section reduces the pressure inside the tank, thereby enabling efficient circulation of the liquid between the tank and the injection section even if the viscosity of the liquid changes. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a piping diagram showing a schematic configuration of a liquid circulation device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of a control unit provided in the liquid circulation device. [Figure 3] (A) and (B) are schematic diagrams showing the main parts of the head unit, where (A) shows the state when appropriate positive and negative pressures are applied, and (B) shows the state when the positive pressure is higher than the negative pressure. [Figure 4] 10 is a flowchart showing an example of heater control. [Figure 5] 10 is a flow chart showing an example of control of a liquid supply pump in accordance with a positive pressure measurement value. [Figure 6] 10 is a flowchart showing an example of control of an air pump according to a negative pressure measurement value. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A liquid circulation system 10 according to this embodiment is applied to the circulation of a liquid 12. Fig. 1 shows a piping diagram (piping system diagram) illustrating the general configuration of the liquid circulation system 10 according to this embodiment. Fig. 2 shows a block diagram illustrating the general configuration of a control unit 14 that controls the circulation of the liquid 12 in the liquid circulation system 10.

[0026] The liquid circulation device 10 according to this embodiment is connected to an injection head 18 as an injection unit in an injection device 16 for injecting the liquid 12, thereby forming a circulation path for circulating the liquid 12 between the injection head 18. The liquid circulation device 10 constitutes a liquid injection device (liquid injection system) that circulates the liquid 12 between the injection head 18 and the liquid circulation device 10, and ejects droplets of the circulating liquid 12 from the injection head 18 at required timing.

[0027] In the liquid circulation device 10, it is possible to use ink used for printing, etc., or paint with a higher viscosity than ink as the liquid 12, and in this embodiment, as an example, the liquid 12 will be described as being paint with a higher viscosity than ink.

[0028] As shown in FIG. 1, the liquid circulation device 10 includes a circulation circuit 20 for the liquid 12, a negative pressure circuit 22 as a negative pressure supply unit for supplying the negative pressure used to circulate the liquid 12 to the circulation circuit 20, and a resupply circuit 24 as a resupply unit for replenishing (replenishing) the liquid 12 to the circulation circuit 20.

[0029] 2, the control unit 14 is provided with a controller 26, and various electrical functional devices are connected to the controller 26. The controller 26 includes a microcomputer in which a CPU 28A, a ROM 28B, a RAM 28C, a non-volatile memory 28D, an input / output interface (not shown), and the like are connected via a bus 28E so that data can be transmitted between them. In the controller 26, the CPU 28A reads out programs stored in the ROM 28B and the memory 28D and executes them while expanding them into the RAM 28C, thereby realizing a function according to the executed program.

[0030] The controller 26 controls the supply of the liquid 12, the temperature of the liquid 12, and the circulation of the liquid 12 in the liquid circulation device 10. Note that in the control unit 14, an input / output device (not shown) such as a display or an operation panel may be connected to the controller 26, allowing various settings and operations to be performed.

[0031] 1, the liquid circulation system 10 includes a main tank 30 as a tank (storage container) for storing the liquid 12 to be circulated, and a supply tank 32 for storing the liquid 12 to be replenished to the main tank 30. The main tank 30 disposed in the liquid circulation system 10 is airtight, and the interior of the main tank 30 is sealed from the surrounding space (air).

[0032] The refill circuit 24 includes a refill pipe 34 that connects the main tank 30 and the refill tank 32 and enables the liquid 12 in the refill tank 32 to be refilled into the main tank 30, and a refill pump 36 installed in the middle of the refill pipe 34, and a diaphragm pump or the like can be used as the refill pump 36. The main tank 30 is also equipped with a refill valve 42 that uses a two-way solenoid valve or the like, and one port of the refill valve 42 is connected to the refill pipe 34 and the other port is connected to the inside of the main tank 30.

[0033] In addition, a float switch 38 is disposed in the main tank 30 as a liquid level sensor for detecting the liquid level of the liquid 12 stored in the main tank 30, and a float switch 40 is disposed in the supply tank 32 as a liquid level sensor for detecting the liquid level of the liquid 12 in the supply tank 32.

[0034] 2, in the control unit 14, the supply pump 36 (a driving motor not shown), float switches 38 and 40, and supply valve 42 are each electrically connected to the controller 26. The controller 26 operates the supply pump 36 and the supply valve 42 in accordance with the liquid level of the liquid 12 in the main tank 30 detected by the float switch 38, and supplies the liquid 12 in the supply tank 32 to the main tank 30 to maintain the liquid level of the liquid 12 in the main tank 30 within a predetermined range. When the controller 26 detects that the liquid level of the liquid 12 in the supply tank 32 detected by the float switch 40 has dropped to a predetermined level, it notifies the user that the remaining amount of liquid 12 in the supply tank 32 is low.

[0035] 1, the circulation circuit 20 includes a liquid supply pipe 44, a recovery pipe 46, a liquid supply pump 48, a head-in valve 50, a head-out valve 52, a positive pressure sensor 54 as a first pressure sensor, and a negative pressure sensor 56 as a second pressure sensor. In this circulation circuit 20, two-way solenoid valves or the like are used as the head-in valve 50 and the head-out valve 52.

[0036] One end of the liquid supply pipe 44 opens into the liquid 12 in the main tank 30, and the other end is connected to the IN side (the input side of the liquid 12) of the injection head 18. A liquid supply pump 48 is disposed in the middle of the liquid supply pipe 44, and a head-in valve 50 and a positive pressure sensor 54 are disposed on the injection head 18 side of the liquid supply pump 48.

[0037] The liquid supply pipe 44 has a pipe 44A serving as a first pipe between the main tank 30 and the liquid supply pump 48. A bypass pipe 58 serving as a second pipe is disposed in the circulation circuit 20 between the main tank 30 and the pipe 44A. One end of the bypass pipe 58 is connected to the pipe 44A, and the interior of the bypass pipe 58 is in communication with the interior of the pipe 44A. The other end of the bypass pipe 58 is open into the liquid 12 at the bottom of the main tank 30.

[0038] Moreover, the bypass pipe 58 is thinner than the pipe 44A, and the inside diameter of the bypass pipe 58 is smaller than the inside diameter of the pipe 44A (the opening cross-sectional area is narrower). For example, in the liquid circulation device 10, the inside diameter of the pipe 44A is 3 mm, while the inside diameter of the bypass pipe 58 is 1.5 mm.

[0039] One end of the recovery pipe 46 opens to the outside of the liquid above the liquid level of the liquid 12 in the main tank 30, and the other end is connected to the OUT side of the injection head 18. A head-out valve 52 is disposed in the middle of the recovery pipe 46, and a negative pressure sensor 56 is disposed on the injection head 18 side of the head-out valve 52. Note that for the liquid supply pipe 44 and the recovery pipe 46, hoses (not shown) can be used between the liquid circulation device 10 and the injection head 18.

[0040] As shown in FIG. 2, in the control unit 14, the liquid supply pump 48 (drive motor not shown), head-in valve 50, head-out valve 52, positive pressure sensor 54, and negative pressure sensor 56 are each electrically connected to the controller 26.

[0041] 1, the negative pressure circuit 22 includes an air pump (suction pump) 60 as a negative pressure generating unit and a negative pressure generating source, a negative pressure pipe 62 having one end connected to the air pump 60 and the other end opening into the main tank 30, a negative pressure valve 64, and a throttle valve 66. A two-way electromagnetic valve or the like is used for the negative pressure valve 64, and the negative pressure valve 64 is disposed in the negative pressure pipe 62 between the air pump 60 and the main tank 30.

[0042] One side of the throttle valve 66 is open to the negative pressure pipe 62 between the air pump 60 and the negative pressure valve 64, and the other side is open. In the negative pressure circuit 22, the throttle valve 66 is installed so that air can be constantly discharged, and in the negative pressure circuit 22, the air pump 60 can continue to operate (can operate constantly) so that the rotation speed does not fall below the minimum speed.

[0043] Furthermore, a vent cylinder 68 is disposed on the upper surface of the main tank 30, and the vent cylinder 68 is cylindrical with one longitudinal end closed and the other longitudinal end opening to the interior at the top of the main tank 30 and communicating with the outside of the liquid in the main tank 30. In the negative pressure circuit 22, the main tank 30 side end of the negative pressure pipe 62 is connected to the top of the vent cylinder 68 and opens into the vent cylinder 68. As a result, in the negative pressure circuit 22, the opening of the negative pressure pipe 62 is separated from the liquid surface in the main tank 30, preventing the liquid 12 in the main tank 30 from being sucked into the negative pressure pipe 62.

[0044] As shown in FIG. 2, in the control unit 14, an air pump 60 (a driving motor not shown) and a negative pressure valve 64 are electrically connected to the controller 26.

[0045] The controller 26 operates the liquid supply pump 48, the head-in valve 50, and the head-out valve 52 at the required timing. As a result, in the circulation circuit 20, the liquid 12 in the main tank 30 is pushed out toward the injection head 18 via the liquid supply piping 44. The controller 26 also operates the air pump 60 and the negative pressure valve 64 to suck air from the main tank 30 (supply negative pressure) via the negative pressure piping 62 and the vent tube 68, thereby reducing the pressure in the main tank 30. As a result, in the liquid circulation device 10, the liquid 12 is circulated between the main tank 30 and the injection head 18.

[0046] Furthermore, in the controller 26, the pressure of the liquid 12 in the liquid supply pipe 44 is detected as a push-in pressure (positive pressure Pp) by a positive pressure sensor 54, and the pressure of the liquid 12 in the recovery pipe 46 is detected as a pull-in pressure (negative pressure Pn) by a negative pressure sensor 56. The controller 26 controls the rotation speed of the liquid supply pump 48 and the rotation speed of the air pump 60 in accordance with the positive pressure (also referred to as a measured positive pressure) Pp in the liquid supply pipe 44 detected by the positive pressure sensor 54 and the negative pressure (also referred to as a measured negative pressure) Pn in the recovery pipe 46 detected by the negative pressure sensor 56. This enables the liquid circulation device 10 to properly circulate the liquid 12 between the main tank 30 and the injection head 18.

[0047] 1, the liquid circulation device 10 is provided with a temperature adjustment unit that adjusts the temperature of the circulated liquid 12 by adjusting the temperature of the liquid 12 in the main tank 30. The temperature adjustment unit includes a heater 70 as a heating unit and a temperature sensor 72 as a temperature detection unit. The heater 70 is disposed in the liquid 12 in the main tank 30. The temperature sensor 72 is disposed in a portion of the pipe 44A of the liquid supply pipe 44 that is parallel to the bypass pipe 58, and the temperature sensor 72 detects the temperature of the liquid 12 being extruded toward the injection head 18.

[0048] 2, in the control unit 14, the heater 70 and the temperature sensor 72 are each electrically connected to the controller 26. The controller 26 has a reference temperature as a preset target temperature set as a temperature target value Tt, and controls the operation of the heater 70 so that the temperature (measured temperature value) T detected by the temperature sensor 72 becomes the temperature target value Tt. When controlling the operation of the heater 70, the controller 26 performs, for example, duty control to control the on time per unit time.

[0049] Next, as an operation of this embodiment, we will explain the control of the circulation of the liquid 12 in the liquid circulation device 10. Figures 3(A) and 3(B) are schematic diagrams showing the main parts of an injection head 18 that can be used with the liquid circulation device 10.

[0050] 3(A) and 3(B), a cylindrical (for example, circular cylinder) liquid chamber 80 is disposed in the injection head 18. In the injection head 18, the liquid 12 is circulated between the main tank 30 and the liquid chamber 80 (see FIG. 1), thereby filling the liquid chamber 80 with the liquid 12. A nozzle hole 82 is formed through a wall surface 80A of the liquid chamber 80 on the side in the injection direction of the liquid 12, and the liquid chamber 80 is airtight with respect to the surrounding space except for the nozzle hole 82.

[0051] In the injection device 16, droplets of the liquid 12 are injected (discharged) from the nozzle holes 82 by applying an impact or the like to the liquid 12 in the liquid chamber 80 by movement of the piezoelectric element or the liquid chamber 80 in the injection head 18. Note that the injection head 18 is, as an example, moved within the range allowed by the hose between it and the liquid circulation device 10, and the wall surface 80A of the liquid chamber 80 is oriented downward or horizontally (sideways), and is used so that the liquid 12 is injected downward or horizontally from the nozzle holes 82.

[0052] In the nozzle hole 82, a meniscus 84, which is a curved surface of the liquid 12, is formed due to capillary action (surface tension of the liquid 12). As shown in Figure 3(B), when a meniscus 84B protruding from the wall surface 80A is formed in the injection head 18, dripping of the liquid 12 from the nozzle hole 82 occurs, and the droplets of the liquid 12 ejected from the nozzle hole 82 become non-uniform.

[0053] In contrast to this, as shown in FIG. 3(A), by forming a concave meniscus 84A, dripping of the liquid 12 and the like does not occur, and it becomes possible to eject uniform droplets of the liquid 12.

[0054] The meniscus 84 formed in the nozzle hole 82 affects the pressure of the liquid 12 passing through the liquid chamber 80 as it is circulated, and an appropriate meniscus 84A can be formed by achieving an optimal balance between the pressure of the liquid 12 supplied from the main tank 30 to the liquid chamber 80 and the pressure of the liquid 12 drawn back from the liquid chamber 80 to the main tank 30.

[0055] If the pressure of the liquid 12 supplied to the liquid chamber 80 is a positive pressure Pp [kPa] and the pressure of the liquid 12 drawn back from the liquid chamber 80 is a negative pressure Pn [kPa], the pressure of the liquid 12 in the liquid chamber 80 is expressed as a differential value d [kPa] between the positive pressure Pp and the negative pressure Pn (Pp-Pn=d). The inventors have confirmed through measurement tests and the like that by setting the differential value d to an appropriate value, it is possible to determine the positive pressure Pp and negative pressure Pn that can form an optimal meniscus 84A. In this case, the optimal differential value d varies depending on the viscosity of the liquid 12 and the mechanical and physical configuration (structure) of the injection head 18. Furthermore, the viscosity of the liquid 12 varies depending on the temperature of the liquid 12.

[0056] That is, the meniscus 84 in the injection head 18 is affected by the structure of the injection head 18. In addition, the meniscus 84 in the injection head 18 is affected by the viscosity of the liquid 12, the viscosity relative to temperature (temperature change of viscosity) and other characteristics (type of paint used as the liquid 12), the positive and negative pressures of the liquid 12 in the liquid chamber 80 that affect the flow rate of the liquid 12, and the environmental temperature (ambient temperature).

[0057] The controller 26 of the control unit 14 sets a target temperature value Tt for the liquid 12 for the injection head 18, taking into consideration the viscosity of the liquid 12, the positions of the temperature sensor 72, the positive pressure sensor 54, the negative pressure sensor 56, the structure of the injection head 18, the hose length, etc. The controller 26 also sets the above-mentioned difference value d for the liquid 12, and sets a target positive pressure value Ptp and a target negative pressure value Ptn as optimal values ​​for the positive pressure Pp and the negative pressure Pn.

[0058] The negative pressure target value Ptn is set based on the positive pressure target value Ptp through actual measurement tests or the like so that an optimal meniscus 84A is formed in the nozzle hole 82 of the injection head 18. If the positive pressure target value Ptp (positive pressure Pp) is too low, air bubbles and the like are likely to become mixed in with the droplets of the liquid 12 ejected from the injection head 18 (nozzle hole 82). If the positive pressure target value Ptp is too high, the liquid 12 is likely to leak from the injection head 18 (nozzle hole 82) before ejection, and the droplets of the liquid 12 ejected from the injection head 18 are likely to disperse (they are likely to scatter as multiple small droplets).

[0059] In the controller 26, a range of the target positive pressure value Ptp is set according to the target temperature value Tt of the liquid 12, and a target negative pressure value Ptn is set corresponding to the target positive pressure value Ptp within that range. In this case, the lower limit pressure is set to a pressure at which no air bubbles are mixed into the droplets of the liquid 12 to be ejected, and the upper limit pressure is set to a pressure at which no leakage of the liquid 12 occurs during circulation or no scattering of the ejected liquid 12 occurs, and the target positive pressure value Ptp is set to be equal to or greater than the lower limit pressure and equal to or less than the upper limit pressure.

[0060] The liquid supply pump 48 and the air pump 60 vary in the amount of liquid 12 discharged and the amount of air suctioned depending on the rotation speed of the motors that drive them. The controller 26 uses control values ​​to control the operation (rotation speed) of the liquid supply pump 48 and the air pump 60. The controller 26 controls the amount of liquid 12 discharged (positive pressure Pp) by changing the control value (hereinafter referred to as the DACp value) of the liquid supply pump 48, and controls the negative pressure Pn by changing the control value (hereinafter referred to as the DACn value) of the air pump 60.

[0061] The controller 26 also has set therein a DACpl value as the lower limit of the DACp value of the liquid supply pump 48, and a DACnl value as the lower limit of the DACn value of the air pump 60. The controller 26 uses a DACp value that exceeds the DACpl value and a DACn value that exceeds the DACnl value, so that the liquid supply pump 48 and the air pump 60 operate continuously (always operate).

[0062] Furthermore, the controller 26 sets a target value for the positive pressure Pp (positive pressure target value Ptp) and a target value for the negative pressure Pn (negative pressure target value Ptn) in accordance with the viscosity of the liquid 12 and the structure of the injection head 18 so that an optimal meniscus 84A is generated in the nozzle hole 82 of the injection head 18. The controller 26 adjusts the DACp value so that the positive pressure (positive pressure measurement value) Pp detected by the positive pressure sensor 54 becomes the positive pressure target value Ptp, and adjusts the DACn value so that the negative pressure (negative pressure measurement value) Pn detected by the negative pressure sensor 56 becomes the negative pressure target value Ptn.

[0063] Next, an example of temperature control and circulation control of the liquid 12 in the liquid circulation device 10 (controller 26) will be described.

[0064] The liquid circulation device 10 (controller 26) controls the operation of the heater 70 to adjust the temperature of the liquid 12, thereby suppressing changes in viscosity of the liquid 12. The controller 26 also controls the operation of the liquid supply pump 48 and the air pump 60 to control the circulation of the liquid 12 between the main tank 30 and the liquid chamber 80 of the injection head 18. At this time, the controller 26 controls the positive pressure measurement value Pp detected by the positive pressure sensor 54 to match the positive pressure target value Ptp (positive pressure control), and also controls the negative pressure measurement value Pn detected by the negative pressure sensor 56 to match the negative pressure target value Ptn (negative pressure control).

[0065] Furthermore, the controller 26 sets a target temperature value Tt [°C] for the liquid 12 based on the characteristics of the liquid 12, including changes in viscosity relative to temperature, the target positive pressure value Ptp, and the target negative pressure value Ptn. The controller 26 performs temperature control (heater control) using the heater 70 so that the temperature T of the liquid 12 becomes the target temperature value Tt. In other words, the controller 26 controls the temperature T of the liquid 12 detected by the temperature sensor 72 to become the target temperature value Tt, while performing positive pressure control and negative pressure control so that the positive pressure Pp and the negative pressure Pn become the target positive pressure value Ptp and the target negative pressure value Ptn, respectively.

[0066] Fig. 4 is a flow chart showing an outline of temperature control (heater control) of the liquid 12 using the heater 70. Fig. 5 is a flow chart showing an outline of positive pressure control (liquid supply pump control), and Fig. 6 is a flow chart showing an outline of negative pressure control (air pump control).

[0067] The flowchart shown in FIG. 4 is repeatedly executed at preset time intervals when the circulation of the liquid 12 is started. In the first step 100, the controller 26 measures the temperature of the liquid 12 flowing from the main tank 30 to the liquid supply pipe 44 (pipe 44A). Specifically, the controller 26 acquires the temperature measurement value T [° C] measured (detected) by the temperature sensor 72.

[0068] In the next step 102, the controller 26 compares the temperature measurement value T with the temperature target value Tt [° C], and determines whether the temperature measurement value T is equal to or higher than the temperature target value Tt. At this time, if the temperature measurement value T is equal to or higher than the temperature target value Tt (T≥Tt), the controller 26 makes an affirmative determination in step 102 and proceeds to step 104. In this step 104, the heater 70 is set to off (the duty ratio is set to 0).

[0069] On the other hand, if the temperature measurement value T is less than the temperature target value Tt (T < Tt), the controller 26 makes a negative determination in step 102 and proceeds to step 106. In this step 106, the heater 70 is set to on.

[0070] When the controller 26 sets the heater 70 to on, it proceeds to step 108, and compares the difference value td [° C] between the temperature measurement value T and the temperature target value Tt (td = Tt - T) with a preset temperature reference value ts [° C], and determines whether the temperature difference value td is less than the temperature reference value ts. The temperature reference value ts is used as a criterion for determining whether to suppress the heating of the liquid 12 by the heater 70. As this temperature reference value ts, for example, a value in the range of 1.0 ° C ≤ ts ≤ 5.0 ° C can be applied.

[0071] If the temperature difference value td is equal to or greater than the temperature reference value ts (ts≦td), the controller 26 makes an affirmative determination in step 108 and proceeds to step 110, where it sets the duty ratio (on-duty) of the heater 70 to a reference duty ratio (for example, 50%). If the temperature difference value td is lower than the temperature reference value ts (ts>td), the controller 26 makes a negative determination in step 108 and proceeds to step 112, where it reduces the duty ratio of the heater 70 (to lower it than the reference value).

[0072] Once the on / off and on duty ratio of the heater 70 have been set in this way, in step 114, the heater 70 is put into a standby state for a predetermined time wt [sec] while the duty of the heater 70 is controlled based on the settings (the operation of the heater 70 is controlled in the set state). Note that the time wt can be the time at which the heating (or heating stop) of the liquid 12 in the main tank 30 by the heater 70 appears in the temperature measurement value T of the temperature sensor 72, and the time wt can be, for example, a time in the range of 0.1 [sec]≦wt≦10 [sec].

[0073] As a result, in the liquid circulation apparatus 10, heating of the liquid 12 is stopped when the temperature T of the liquid 12 is equal to or higher than the temperature target value Tt. Also, in the liquid circulation apparatus 10, when the temperature T of the liquid 12 is lower than the temperature target value Tt and the temperature difference exceeds the temperature reference value ts, the liquid 12 is heated by the heater 70 operated at the standard duty ratio. Furthermore, in the liquid circulation apparatus 10, when the temperature T of the liquid 12 is lower than the temperature target value Tt and the temperature difference is within (small than) the temperature reference value ts, the duty ratio is lowered to suppress the heating power of the heater 70 for the liquid 12. Note that the duty ratio may be lowered in stages.

[0074] On the other hand, in the liquid circulation device 10, when circulating the liquid 12, the air pump 60 is operated and the negative pressure valve 64 is opened. At the same time, after the liquid supply pump 48 is operated, the head-in valve 50 is opened and the head-out valve 52 is opened.

[0075] In the liquid circulation system 10, the negative pressure valve 64 is opened to supply negative pressure to the inside of the main tank 30 (outside the liquid), which creates a negative pressure at the opening of the recovery pipe 46 on the main tank 30 side, allowing the liquid 12 in the recovery pipe 46 to be drawn back into the main tank 30. In addition, in the liquid circulation system 10, the liquid supply pump 48 is operated to open the head-in valve 50 and the head-out valve 52, which sends the liquid 12 in the main tank 30 to the injection head 18 (liquid chamber 80) and supplies it to the injection head 18. At this time, in the liquid circulation system 10, negative pressure is created inside the main tank 30, so the liquid 12 in the injection head 18 is drawn back (recovered) into the main tank 30, and the liquid 12 is circulated between the main tank 30 and the injection head 18.

[0076] When the circulation of the liquid 12 is started, the controller 26 executes the positive pressure control of FIG. 5 and the negative pressure control of FIG. 6 in parallel at predetermined time intervals.

[0077] 5, in step 120, the controller 26 acquires a positive pressure measurement value (positive pressure) Pp measured by the positive pressure sensor 54. Next, in step 122, the controller 26 compares the positive pressure measurement value Pp with the positive pressure target value Ptp. As a result, if the positive pressure measurement value Pp is the same as the positive pressure target value Ptp (Pp=Ptp), the controller 26 proceeds from step 122 to step 124.

[0078] On the other hand, if the positive pressure measurement value Pp exceeds the positive pressure target value Ptp, the controller 26 proceeds from step 122 to step 126. In step 126, the controller 26 calculates a positive pressure difference value Ppd [kPa] and compares the positive pressure difference value Ppd with preset positive pressure reference values ​​Pph [kPa] and Ppl [kPa].

[0079] The positive pressure difference value Ppd is set to Ppd = Pp - Ptp. The positive pressure reference values ​​Pph and Ppl are each set to a threshold value, and the positive pressure reference values ​​Pph and Ppl are set to Pph > Ppl. The positive pressure reference value Ppl can be set to a pressure within a range that does not exceed the lower limit of the positive pressure difference value Ppd (the lowest positive pressure (measured positive pressure) Pp relative to the target positive pressure value Ptp) that can form an optimal meniscus 84A in the nozzle hole 82 in the injection head 18. For example, the positive pressure reference value Ppl can be set to a pressure within a range of 0.1 kPa ≦ Ppl ≦ 0.5 kPa.

[0080] Furthermore, the positive pressure reference value Pph can be a pressure within a range that does not exceed the upper limit (the highest positive pressure (measured positive pressure) Pp relative to the target positive pressure value Ptp) of the positive pressure difference value Ppd that can form an optimal meniscus 84A in the nozzle hole 82 in the injection head 18. For example, the positive pressure reference value Pph can be a pressure within the range of 0.5 [kPa]≦Pph≦0.9 [kPa].

[0081] If the positive pressure difference value Ppd is equal to or less than the positive pressure reference value Ppl (Ppd≦Ppl), the controller 26 proceeds from step 126 to step 124.

[0082] On the other hand, if the positive pressure difference value Ppd exceeds the positive pressure reference value Ppl (Ppd>Ppl), the controller 26 updates the DACp value so as to reduce the rotation speed of the liquid supply pump 48. At this time, if the positive pressure difference value Ppd exceeds the positive pressure reference value Ppl but is equal to or less than the positive pressure reference value Pph (Pph≧Ppd>Ppl), the controller 26 proceeds from step 126 to step 128.

[0083] In step 128, the controller 26 updates the DACp value by subtracting a preset correction value cp from the DACp value used to control the rotation speed of the liquid supply pump 48, thereby decreasing the DACp value. After this, the controller 26 proceeds from step 128 to step 124.

[0084] Also, when the positive pressure differential value Ppd exceeds the positive pressure reference value Pph (Ppd > Pph), the controller 26 shifts from step 126 to step 130. In step 130, the controller 26 significantly decreases the DACp value by subtracting the preset correction value 2cp from the DACp value used for controlling the rotational speed of the liquid supply pump 48, and updates the DACp value. After that, the controller 26 shifts from step 130 to step 124.

[0085] On the other hand, in step 122, when the positive pressure measurement value Pp is less than the positive pressure target value Ptp (Pp < Ptp), the controller 26 shifts from step 122 to step 132. In this step 132, the controller 26 calculates the positive pressure differential value Ppd and compares the positive pressure differential value Ppd with the positive pressure reference value -Pph.

[0086] That is, since the positive pressure differential value Ppd is a negative value in step 132, when the positive pressure differential value Ppd is greater than or equal to the positive pressure reference value -Pph (Ppd ≧ -Pph), the controller 26 shifts from step 132 to step 124. Also, when the positive pressure differential value Ppd is less than the positive pressure reference value Pph (Ppd < -Pph), the controller 26 shifts from step 132 to step 134.

[0087] When the positive pressure differential value Ppd exceeds the positive pressure reference value -Pph (Ppd > -Pph) in step 134, the controller 26 updates the DACp value so that the rotational speed of the liquid supply pump 48 increases. At this time, the controller 26 increases the DACp value by adding the preset correction value 2cp to the DACp value used for controlling the rotational speed of the liquid supply pump 48. After that, the controller 26 shifts from step 134 to step 124.

[0088] The controller 26 has a DACpl value set in advance as the lower limit value of the DACp value. When the controller 26 determines (positive determination) in step 124 that the DACp value is greater than or equal to the DACpl value (DACp value ≥ DACpl value), it proceeds from step 124 to step 136.

[0089] On the other hand, when the DACp value has become less than the DACpl value (DACp value < DACpl value), the controller 26 makes a negative determination in step 124 and proceeds to step 138.

[0090] In step 138, the controller 26 sets the DACpl value to the DACp value. That is, when the DACp value becomes lower than DACpl, by setting the DACpl value to the DACp value, it suppresses the rotational speed of the liquid supply pump 48 from decreasing more than necessary.

[0091] After that, in step 136, the controller 26 enters a processing standby state for a predetermined time wp [sec] while operating the liquid supply pump 48 according to the DACp value. At this time, if the DACp value has been updated, the controller 26 operates the liquid supply pump 48 with the updated DACp value. As the time wp, for example, a time such as when the change in the rotational speed of the liquid supply pump 48 is reflected in the pressure (positive pressure measurement value) Pp detected by the positive pressure sensor 54 can be applied, and as the time wp, a range of 0.1 [sec] ≤ wp ≤ 10 [sec] can be applied, for example.

[0092] On the other hand, in the flowchart shown in FIG. 6, in step 140, the controller 26 acquires the negative pressure measurement value (negative pressure) Pn measured by the negative pressure sensor 56. Next, in step 142, the controller 26 compares the negative pressure measurement value Pn with the negative pressure target value Ptn. As a result, when the negative pressure measurement value Pn is the same as the negative pressure target value Ptn (Pn = Ptn), the controller 26 proceeds from step 142 to step 144. Note that the negative pressure measurement value Pn is a negative value (Pn ≤ 0), and the negative pressure target value Ptn [kPa] is also a negative value (Ptn ≤ 0).

[0093] On the other hand, when the negative pressure measurement value Pn is lower than the negative pressure target value Ptn (Pn < Ptn), the controller 26 shifts from step 142 to step 146. In this step 146, the controller 26 calculates the negative pressure difference value Pnd [kPa], and compares the negative pressure difference value Pnd with the preset negative pressure reference values Pnh [kPa] and Pnl [kPa].

[0094] Note that the negative pressure difference value Pnd is set as Pnd = Ptn - Pn. Also, the negative pressure reference values Pnh and Pnl are regarded as threshold values respectively, and Pnh > Pnl. The negative pressure reference value Pnl can apply a pressure within a range that does not exceed the lower limit value of the negative pressure difference value Pnd (the lowest negative pressure (negative pressure measurement value) Pn with respect to the negative pressure target value Ptn) that can form an optimal meniscus 84A in the nozzle hole 82 in the injection head 18. For example, a pressure within the range of 0.1 [kPa] ≦ Pnl ≦ 0.5 [kPa] can be applied to the negative pressure reference value Pnl.

[0095] Also, the negative pressure reference value Pnh can apply a pressure within a range that does not exceed the upper limit value of the negative pressure difference value Pnd (the highest negative pressure (negative pressure measurement value) Pn with respect to the negative pressure target value Ptn) that can form an optimal meniscus 84A in the nozzle hole 82 in the injection head 18. For example, a range of 0.5 [kPa] ≦ Pnh ≦ 0.9 [kPa] can be applied to the negative pressure reference value Pnh.

[0096] When the negative pressure difference value Pnd is less than or equal to the negative pressure reference value -Pnl (Pnd ≦ -Pnl), the controller 26 shifts from step 146 to step 144.

[0097] On the other hand, when the negative pressure difference value Pnd is greater than the negative pressure reference value -Pnl (Pnd > -Pnl), the controller 26 updates the DACn value so that the rotation speed of the air pump 60 decreases. At this time, when the negative pressure difference value Pnd is greater than the negative pressure reference value -Pnl (Pnd > -Pnl), the controller 26 shifts from step 146 to step 148.

[0098] In step 148, the controller 26 decreases the DACn value by subtracting the correction value cn set in advance from the DACn value used for controlling the rotation speed of the air pump 60, and updates the DACn value. After that, the controller 26 proceeds to step 144.

[0099] Also, when the negative pressure difference value Pnd is greater than the negative pressure reference value -Pnh (Pnd > -Pnh), the controller 26 proceeds from step 146 to step 150. In step 150, the controller 26 significantly decreases the DACn value by subtracting the correction value 2cn set in advance from the DACn value used for controlling the rotation speed of the air pump 60, and updates the DACn value. After that, the controller 26 proceeds from step 150 to step 144.

[0100] On the other hand, in step 142, when the negative pressure measured value Pn is greater than the negative pressure target value Ptn (Pn > Ptn), the controller 26 proceeds from step 142 to step 152. In this step 152, the controller 26 calculates the negative pressure difference value Pnd and compares the negative pressure difference value Pnd with the negative pressure reference values Pnh and Pnl. Note that in step 152, due to the negative pressure measured value Pn being greater than the negative pressure target value Ptn, the negative pressure difference value Pnd is a positive value (Pnd > 0).

[0101] In step 152, when the negative pressure difference value Pnd is greater than or equal to the negative pressure reference value Pnl (Pnd ≥ Pnh), the controller 26 proceeds from step 152 to step 144.

[0102] Also, when the negative pressure difference value Pnd is less than the negative pressure reference value Pnl (Pnd < Pnl), the controller 26 proceeds from step 152 to step 154.

[0103] The controller 26 updates the DACn value so that the rotation speed of the air pump 60 increases in step 154. At this time, the controller 26 increases the DACn value by adding a correction value cn set in advance to the DACn value used for controlling the rotation speed of the air pump 60. After that, the controller 26 proceeds to step 144.

[0104] Also, when the negative pressure difference value Pnd is smaller than the negative pressure reference value Pnh (Pnd < Pnh), the controller 26 proceeds from step 152 to step 156.

[0105] The controller 26 updates the DACn value so that the rotation speed of the air pump 60 increases in step 156. At this time, the controller 26 increases the DACn value by adding a correction value 2cn set in advance to the DACn value used for controlling the rotation speed of the air pump 60. After that, the controller 26 proceeds to step 144.

[0106] A DACnl value as the lower limit value of the DACn value is set in the controller 26 in advance. When the controller 26 determines (positive determination) in step 144 that the DACn value is greater than or equal to the DACpl value (DACp value ≧ DACpl value), the controller 26 proceeds from step 144 to step 158.

[0107] On the contrary, when the DACp value becomes less than the DACpl value (DACn value < DACnl value), the controller 26 makes a negative determination in step 144 and proceeds to step 160.

[0108] In step 160, the controller 26 sets the DACnl value to the DACn value. That is, when the DACn value becomes lower than DACnl, setting the DACnl value to the DACn value suppresses the air pump 60 from decreasing more than necessary to rotate.

[0109] Thereafter, in step 158, the controller 26 puts the air pump 60 into a standby state for a predetermined time wn [sec] while operating the air pump 60 in accordance with the DACn value. At this time, if the DACn value has been updated, the controller 26 operates the air pump 60 with the updated DACn value. Note that the time wn can be in the range of 0.1 [sec]≦wn≦10 [sec].

[0110] In this way, in the liquid circulation device 10, the operation of the liquid supply pump 48 is controlled so that the positive pressure Pp measured by the positive pressure sensor 54 becomes the positive pressure target value Ptp, and the operation of the liquid supply pump 48 is controlled so that the negative pressure Pn measured by the negative pressure sensor 56 becomes the negative pressure target value Ptn. Therefore, the temperature T of the liquid 12 is controlled to become the temperature target value Tt, and the positive pressure Pp and the negative pressure Pn are controlled to become the positive pressure target value Ptp and the negative pressure target value Ptn, respectively.

[0111] As a result, the controller 26 suppresses changes in the viscosity of the liquid 12 in the injection head 18, and controls the pressure of the liquid 12 so that an appropriate meniscus 84A is formed in the nozzle hole 82. Therefore, the injection device 16 connected to the liquid circulation device 10 can eject high-quality droplets of the liquid 12 from the injection head 18.

[0112] At this time, the controller 26 increases the changes in the DACp and DACn values ​​as the positive pressure Pp and negative pressure Pn move away from the target positive pressure value Ptp and negative pressure value Ptn, respectively, and reduces the changes in the DACp and DACn values ​​as they approach the target positive pressure value Ptp and negative pressure value Ptn. As a result, in the liquid circulation device 10, changes in the positive pressure Pp and negative pressure Pn are smoothly controlled without overshooting, and the balance between the positive pressure Pp and negative pressure Pn is not lost in the injection head 18, enabling high-quality droplets to be ejected from the injection head 18.

[0113] Furthermore, the liquid circulation device 10 uses a liquid supply pump 48 to send (extrude) the liquid 12 from the main tank 30 to the injection head 18, and uses negative pressure generated by an air pump 60 to pull the liquid 12 back from the injection head 18 to the main tank 30. As a result, the liquid circulation device 10 can effectively circulate the liquid 12 with a simple configuration, preventing precipitation and deposition in the liquid 12 and enabling the injection of high-quality droplets.

[0114] Furthermore, when negative pressure is supplied to the main tank 30 through the negative pressure pipe 62 that opens into the main tank 30 and the liquid 12 is drawn in through the recovery pipe 46 that also opens in the main tank 30, the liquid 12 that has foamed in the main tank 30 may be sucked into the negative pressure pipe 62. In this case, in the liquid circulation device 10, a vent tube 68 is disposed in the main tank 30, and the negative pressure pipe 62 opens into this vent tube 68. This allows the opening of the negative pressure pipe 62 to be separated from the liquid surface of the liquid 12 in the main tank 30, so that the liquid 12 in the main tank 30 can be prevented from being sucked into the negative pressure pipe 62.

[0115] Furthermore, in the liquid circulation system 10, a bypass pipe 58 that is thinner than the pipe 44A is arranged in parallel with the pipe 44A between the main tank 30 and the liquid supply pump 48. This allows the liquid supply pump 48 to be in a continuous (always) operating state, so that precipitation and deposition can be reliably suppressed even for the highly viscous liquid 12.

[0116] The above-described liquid circulation device 10 does not limit the configuration of the present invention. The present invention is not limited to ink or paint, and can be applied to liquid circulation devices that circulate various types of liquid. [Explanation of symbols]

[0117] 10 Liquid circulation device 12 liquid 14 Control Unit 18 Injection head (injection part) 20 Circulation circuit 22 Negative pressure circuit (negative pressure supply section) 26 Controller (control unit) 30 Main Tank (Tank) 44 Liquid supply piping 46 Recovery piping 48 Liquid supply pump 54 Positive pressure sensor 56 Negative pressure sensor 58 Bypass piping 60 Air Pump 62 Negative pressure piping 66 Throttle valve 68 Ventilator 70 Heater (heating part) 72 Temperature sensor (temperature detection part)

Claims

1. a tank in which a liquid is stored and which is airtight with respect to the surrounding space; an ejection section to which the liquid is supplied so that a portion of the supplied liquid can be ejected; a liquid supply pipe having one end that opens into the liquid stored in the tank and the other end that is connected to the injection unit, so that the liquid in the tank can be supplied to the injection unit; a liquid supply pump that is disposed in an intermediate portion of the liquid supply pipe and that, when actuated, supplies the liquid in the tank to the injection portion via the liquid supply pipe; a recovery pipe having one end that opens to the outside of the liquid in the tank and the other end that is connected to the injection unit, so that the liquid supplied into the injection unit can be recovered into the tank when the liquid supply pump is operated; a negative pressure supply unit that reduces the pressure inside the tank and supplies a negative pressure to the tank so that the liquid inside the ejection unit is recovered into the tank; a control unit that controls the operation of the liquid supply pump and the negative pressure supply unit to control the circulation of the liquid between the tank and the injection unit; A liquid circulation device comprising:

2. a first pressure sensor that detects a first pressure as a pressure of the liquid flowing through the liquid supply pipe toward the injection part; a second pressure sensor that detects a second pressure as the pressure of the liquid flowing through the recovery pipe toward the tank; Including, 2. The liquid circulation device according to claim 1, wherein the control unit controls the operation of the liquid supply pump so that the first pressure becomes a predetermined first set pressure, and controls the operation of the negative pressure supply unit so that the second pressure becomes a predetermined second set pressure.

3. 2. The liquid circulation system according to claim 1, wherein the liquid supply piping further comprises a second pipe having one end connected to an intermediate portion of the first pipe between the tank and the liquid supply pump and the other end opening near the bottom of the tank, the second pipe having an inner diameter smaller than that of the first pipe.

4. The negative pressure supply unit is a negative pressure pump whose operation is controlled to generate negative pressure; a negative pressure pipe having one end connected to the negative pressure pump and the other end open to the outside of the liquid in the tank; a throttle valve having one side connected to the middle portion of the negative pressure pipe and the other side open, for controlling the negative pressure in the negative pressure pipe; 2. The liquid circulation system of claim 1, comprising:

5. a heating unit that heats the liquid in the tank; a temperature detection unit that detects the temperature of the liquid in the liquid supply pipe; Further comprising: The liquid circulation device according to claim 1 , wherein the control unit controls the operation of the heating unit so that the temperature detected by the temperature detection unit becomes a preset target temperature.

Images