JP2014172324A - Liquid discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circulation type liquid discharge device which prevents liquid leakage from a nozzle when circulation of a liquid is stopped.SOLUTION: A liquid discharge device includes: a tank for accumulating a liquid; a head for discharging the liquid from a nozzle; a flow passage having a supply passage for supplying the liquid from the tank to the head and a reflux passage for returning the liquid from the head to the tank; a circulation device; a pressure adjusting device; and a controller. The circulation device circulates the liquid in the flow passage. The pressure adjusting device adjusts a pressure of the liquid in the flow passage. The controller controls the circulation device and the pressure adjusting device. In addition, the controller first reduces the pressure of the liquid in the flow passage by the pressure adjusting device, and then stops the circulation device when circulation of the liquid in the flow passage is stopped.

Description

  Embodiments described herein relate generally to a liquid ejection apparatus that ejects liquid from a nozzle.

  2. Description of the Related Art Conventionally, there is a circulation type liquid ejection device that circulates liquid by a circulation device such as a pump in an annular flow path including a head that ejects liquid from a nozzle and a tank that stores the liquid. By circulating the liquid, bubbles generated in the nozzles of the head and foreign matters mixed in the nozzles can be removed from the nozzles. As a result, good ejection performance of the head can be obtained.

JP 2005-125670 A

  When the circulation device is stopped in a state where the liquid circulates in the flow path, a sudden pressure increase occurs in the flow path as the kinetic energy of the liquid decreases. Due to this pressure increase, liquid may leak from the nozzle of the head.

  The problem to be solved by the present invention is to prevent liquid leakage from the nozzle when the circulation of the liquid is stopped in the circulation type liquid ejection device.

  A liquid ejection apparatus according to an embodiment includes a tank, a head, a supply path, a reflux path, a circulation device, a pressure adjustment device, and a controller. The tank stores a liquid. The head discharges liquid from the nozzle. The supply path supplies liquid from the tank to the head. The reflux path returns liquid from the head to the tank. The circulation device circulates a liquid in a closed system flow path including the tank, the head, the supply path, and the reflux path. The pressure adjusting device adjusts the pressure of the liquid in the flow path. The controller controls the circulation device and the pressure adjusting device. Further, when stopping the circulation of the liquid in the flow path, the controller first lowers the pressure of the liquid in the flow path by the pressure adjusting device, and then stops the circulation apparatus.

1 is a schematic diagram illustrating an ink circulation mechanism of an ink jet printer according to an embodiment. FIG. FIG. 2 is a schematic diagram illustrating a schematic structure of an inkjet head of the printer. FIG. 2 is a block diagram schematically showing a control circuit of the printer. 6 is a flowchart showing the operation of the system controller of the printer. The time chart regarding the solenoid valve, circulation pump, and adjustment pump of the printer. 6 is a graph showing ink pressure fluctuations in a conventional configuration. 6 is a graph showing ink pressure fluctuations in the configuration of the present embodiment. 9 is a flowchart showing the operation of a system controller in the second embodiment.

Several embodiments will be described with reference to the drawings.
(First embodiment)
In the present embodiment, as an example of a liquid ejecting apparatus, an ink jet printer that forms an image by ejecting liquid ink onto a recording medium is disclosed.

  FIG. 1 is a schematic diagram illustrating a main configuration of an ink circulation mechanism 1 provided in an ink jet printer. The ink circulation mechanism 1 includes an ink jet head 2, an ink tank 3, an ink supply path 4, an ink reflux path 5, a circulation pump 6 (circulation device), a filter 7, an atmosphere communication path 8, an electromagnetic valve 9, a pressure sensor 10, and The adjustment pump 11 is provided. The electromagnetic valve 9 and the adjusting pump 11 constitute the pressure adjusting device 12 in the present embodiment in a closed system.

  The inkjet head 2 includes an inlet 20 that connects the ink supply path 4, and an outlet 21 that connects the ink reflux path 5.

  The ink tank 3 is disposed below the inkjet head 2 in the direction of gravity. The ink tank 3 includes an ink layer 30 and an air layer 31 inside. The end portions of the ink supply path 4 and the ink reflux path 5 that are not connected to the inkjet head 2 are both located in the ink layer 30. For example, even when bubbles are mixed into the ink from the inkjet head 2, the bubbles are absorbed by the air layer 31 in the ink tank 3.

  The ink supply path 4 and the ink reflux path 5 are, for example, flexible resin tubes or metal pipes such as stainless steel.

  The circulation pump 6 is provided in the ink reflux path 5. The circulation pump 6 circulates ink in a circulation direction indicated by an arrow A in a closed system flow path including the inkjet head 2, the ink tank 3, the ink supply path 4, and the ink reflux path 5. As the circulation pump 6, for example, a tube pump, a diaphragm pump, a piston pump, or the like can be used.

  The filter 7 is provided downstream of the circulation pump 6 in the circulation direction in the ink return path 5. The filter 7 removes foreign matters mixed in the ink flowing through the ink return path 5. As the filter 7, for example, a mesh filter such as polypropylene, nylon, polyphenylene sulfide, or stainless steel can be used.

  One end of the atmosphere communication path 8 is located in the air layer 31 of the ink tank 3, and the other end is located outside the ink tank 3, that is, in the atmosphere. The electromagnetic valve 9 opens and closes the atmosphere communication path 8.

  The pressure sensor 10 detects the pressure value in the air layer 31 of the ink tank 3. For example, a semiconductor piezoresistive pressure sensor can be used as the pressure sensor 10. The semiconductor piezoresistive pressure sensor includes a diaphragm that receives pressure from the outside and a semiconductor strain gauge formed on the surface of the diaphragm, and an electric due to the piezoresistive effect generated in the strain gauge as the diaphragm is deformed by the pressure from the outside. The pressure is detected based on the change in resistance.

  The adjustment pump 11 adjusts the pressure in the flow path. In particular, in this embodiment, the adjustment pump 11 increases the pressure in the flow path by sending air into the air layer 31 of the ink tank 3, and the pressure in the flow path by sucking air from the air layer 31. Lower. The adjustment pump 11 includes, for example, a flexible tube that communicates the air layer 31 and the atmosphere, and one or more pressing members that press the tube, and moves the pressing member to the atmosphere from the air layer 31. It is possible to use a tube pump that performs exhaust to the air and intake from the atmosphere to the air layer 31. The adjustment pump 11 may be another type of pump such as a bellows pump.

  FIG. 2 is a schematic diagram showing a schematic structure of the inkjet head 2. The inkjet head 2 includes a head main body 22, a nozzle plate 23, and a number of actuators 24. A space between the head main body 22 and the nozzle plate 23 is an ink chamber 25 connected to the inflow port 20 and the outflow port 21. The nozzle plate 23 includes the same number of nozzles 26 as the actuators 24. The head main body 22 includes a large number of protrusions 27 provided at positions facing the nozzles 26. At the position where the protrusion 27 is provided, the ink flow path width in the ink chamber 25 is narrower than the other positions. Each actuator 24 is provided on the top surface of each protrusion 27. As the actuator 24, for example, a piezoelectric element such as a piezoelectric element can be used. In FIG. 2, only one set of the actuator 24, the nozzle 26, and the protrusion 27 is shown.

  When the actuator 24 operates, pressure fluctuations occur in the ink in the vicinity of the actuator 24, and ink droplets are ejected from the nozzles 26 corresponding to the actuator 24. In FIG. 2, the configuration in which the energy for ejecting the ink droplets is supplied by the actuator 24 is shown. However, the configuration in which the ink droplets are ejected by changing the ink pressure using the thermal energy generated by the heater or the like. It may be adopted.

  FIG. 3 is a block diagram schematically showing a control circuit of the ink jet printer. The control circuit includes a system controller 100, a memory 101, an interface (I / F) 102, a control panel 103, a head driving circuit 104, a circulation pump driving circuit 105, a valve driving circuit 106, an A / D converter 107, and a regulating pump driving circuit. 108, an inkjet head 2, a circulation pump 6, a solenoid valve 9, a pressure sensor 10, and an adjustment pump 11.

  The system controller 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The system controller 100 executes various processes including processes related to ink circulation in the flow path of the ink circulation mechanism 1. These processes are realized, for example, by executing a computer program stored in a ROM or the like by the CPU.

  The memory 101 stores image data to be printed. This image data may be data received from a host device connected to the ink jet printer, or may be data read by a scanner provided in the ink jet printer.

  The interface 102 is, for example, an I / O port, and relays data transmission / reception performed between the control panel 103 and the system controller 100. The control panel 103 includes various operation buttons, a touch panel, and a display such as an LCD (Liquid Crystal Display).

  The head drive circuit 104 drives the inkjet head 2 in response to a command from the system controller 100. For example, when the command is an instruction to print an image, the head drive circuit 104 selectively drives each actuator 24 according to the image data stored in the memory 101 to form an image on a recording medium such as paper. To do.

  Circulation pump drive circuit 105 drives circulation pump 6 in response to a command from system controller 100.

  The valve drive circuit 106 opens and closes the electromagnetic valve 9 in response to a command from the system controller 100.

  The A / D converter 107 A / D converts an analog signal output from the pressure sensor 10 and outputs a digital signal generated by this conversion to the system controller 100. Hereinafter, the pressure value indicated by the digital signal is referred to as a sensor value P.

  The adjustment pump drive circuit 108 drives the adjustment pump 11 in response to a command from the system controller 100.

  Next, the operation of the ink jet printer related to the circulation of ink in the flow path of the ink circulation mechanism 1 will be described.

  FIG. 4 is a flowchart showing the operation of the system controller 100 regarding ink circulation. The system controller 100 starts the operation shown in the flowchart when, for example, the ink jet printer is turned on or when the ink jet printer returns from the operation in the power saving mode.

  First, the system controller 100 commands the valve drive circuit 106 to close the electromagnetic valve 9 (ACT 101). When receiving this command, the valve drive circuit 106 closes the electromagnetic valve 9.

  After ACT 101, the system controller 100 commands the circulation pump drive circuit 105 to drive the circulation pump 6 (ACT 102). When this command is received, the circulation pump drive circuit 105 starts to drive the circulation pump 6. Thereby, the ink circulates in the flow path of the ink circulation mechanism 1.

  After ACT 102, the system controller 100 determines whether the sensor value P indicated by the digital signal output from the A / D converter 107 is equal to or greater than a predetermined first threshold value Pt1 and less than a predetermined second threshold value Pt2. Is determined (ACT 103). The first threshold value Pt1 is a lower limit value of a pressure range in which the inkjet head 2 can exhibit good ink ejection performance during ink circulation. The second threshold value Pt2 is an upper limit value of the pressure range. The first threshold value Pt1 and the second threshold value Pt2 may be determined experimentally, theoretically from the Bernoulli's theorem, or empirically based on the nozzle size and flow rate.

  When it is determined that the sensor value P is not less than the first threshold value Pt1 and less than the second threshold value Pt2 (ACT 103: No), the system controller 100 commands the adjustment pump drive circuit 108 to drive the adjustment pump 11 (ACT 104). . When receiving this command, the adjustment pump drive circuit 108 drives the adjustment pump 11 to adjust the pressure in the ink tank 3. For example, if the sensor value P is less than the first threshold value Pt1, the adjustment pump drive circuit 108 drives the adjustment pump 11 so that the pressure in the ink tank 3 increases by a predetermined amount. On the other hand, if the sensor value P is equal to or greater than the second threshold value Pt2, the adjustment pump drive circuit 108 drives the adjustment pump 11 so that the pressure in the ink tank 3 decreases by a predetermined amount. After ACT 104, the operation of the system controller 100 returns to ACT 103.

  On the other hand, when it is determined that the sensor value P is greater than or equal to the first threshold value Pt1 and less than the second threshold value Pt2 (ACT 103: Yes), the system controller 100 determines whether to stop the circulation of the ink (ACT 105). ). For example, the system controller 100 determines to stop the ink circulation when the control panel 103 instructs to stop the ink circulation, and determines not to stop the ink circulation otherwise.

  When it is determined not to stop the circulation of ink (No in ACT 105), the operation of the system controller 100 returns to ACT 103.

  On the other hand, when it is determined to stop the circulation of ink (ACT 105: Yes), the system controller 100 instructs the valve drive circuit 106 to open the electromagnetic valve 9 (ACT 106). When receiving this command, the valve drive circuit 106 opens the electromagnetic valve 9.

  After the electromagnetic valve 9 is opened, the system controller 100 commands the circulation pump drive circuit 105 to stop driving the circulation pump 6 (ACT 107). When receiving this command, the circulation pump drive circuit 105 stops driving the circulation pump 6. Thereby, the circulation of the ink in the flow path of the ink circulation mechanism 1 is stopped. With ACT 107, the system controller 100 ends the operation shown in the flowchart.

  FIG. 5 is a time chart showing control of the solenoid valve 9, the circulation pump 6, and the adjusting pump 11 when the operation shown in the flowchart of FIG. 4 is executed.

  When the start of circulation is instructed from the control panel 103, the electromagnetic valve 9 is closed (ACT 101). Further, the circulation pump 6 is activated (ACT 102).

  The adjustment pump 11 pressurizes the inside of the ink tank 3 when the sensor value P becomes less than the first threshold value Pt1 (ACT 104). Further, the adjustment pump 11 depressurizes the inside of the ink tank 3 when the sensor value P becomes equal to or greater than the second threshold value Pt2 (ACT 104).

  When the stop of circulation is instructed from the control panel 103, the electromagnetic valve 9 is opened (ACT 106). Furthermore, after a period T has elapsed since the electromagnetic valve 9 was opened, the circulation pump 6 is stopped (ACT 107). The period T is set to a period sufficient for stabilizing the pressure fluctuation generated in the ink tank 3 when the electromagnetic valve 9 is opened, for example.

The operation of this embodiment will be described.
FIGS. 6 and 7 are graphs showing the pressure fluctuations of the ink in the inkjet head 2 before and after stopping the circulation of the ink. FIG. 7 corresponds to the case where the ink circulation is stopped by the procedure described with reference to FIGS. 4 and 5. On the other hand, FIG. 6 corresponds to the conventional procedure, that is, the case where the circulation of ink is stopped without opening the electromagnetic valve 9.

  While the ink is circulated, the pressure of the ink in the ink jet head 2 is stabilized at a negative pressure in both FIG. 6 and FIG.

  When the circulation pump 6 is stopped, in the example of FIG. 6, the pressure of the ink in the ink jet head 2 rapidly increases as the kinetic energy of the ink decreases. If this pressure exceeds atmospheric pressure, ink may leak from the nozzle 26. The pressure of the ink in the inkjet head 2 is attenuated as time passes, and eventually converges to a negative pressure corresponding to the water head difference between the inkjet head 2 and the ink tank 3.

  On the other hand, in the example of FIG. 7, since the electromagnetic valve 9 is opened before the circulation pump 6 is stopped, the pressure in the ink tank 3 hardly increases. Therefore, the pressure of the ink in the ink jet head 2 converges to a negative pressure corresponding to the water head difference without substantially increasing. In this case, there is no fear of ink leaking from the nozzle 26.

  As described above, the ink jet printer according to the present embodiment can stop the circulation of ink without causing ink leakage from the nozzle 26.

  Furthermore, since the ink jet printer according to the present embodiment adjusts the pressure in the flow path by the adjustment pump 11, the pressure in the ink jet head 2 can be maintained at an appropriate value. Thereby, the ink leakage from the nozzle 26 can be prevented more reliably.

(Second Embodiment)
A second embodiment will be described.
This embodiment is different from the first embodiment in the procedure for stopping the circulation of ink. The configuration described with reference to FIGS. 1, 2 and 3 is the same as that of the first embodiment.

  FIG. 8 is a flowchart showing the operation of the system controller 100 regarding ink circulation. Since the operations in ACT 201 to ACT 205 are the same as the operations in ACT 101 to ACT 105, description thereof will be omitted.

  If the system controller 100 determines in ACT 205 to stop the circulation of ink (Yes in ACT 205), the system controller 100 determines whether the sensor value P is equal to or greater than a predetermined third threshold value Pt3 (ACT 206).

  When it is determined that the sensor value P is greater than or equal to the third threshold value Pt3 (ACT 206: Yes), the system controller 100 instructs the adjustment pump drive circuit 108 to drive the adjustment pump 11 (ACT 207). When receiving this command, the adjustment pump drive circuit 108 drives the adjustment pump 11 to reduce the pressure of the ink tank 3 by an amount corresponding to the difference between the sensor value P and the third threshold value Pt3, for example.

  After ACT 207 or when it is determined that the sensor value P is not equal to or greater than the third threshold value Pt3 (No in ACT 206), the system controller 100 instructs the circulation pump drive circuit 105 to reduce the rotational speed of the circulation pump 6 (ACT 208). ). When this command is received, the circulation pump drive circuit 105 reduces the rotational speed of the circulation pump 6 so that the flow rate of the ink circulating in the flow path of the ink circulation mechanism 1 is reduced by N (ml / min).

  When the flow rate of ink circulating through the flow path of the ink circulation mechanism 1 during the execution of ACT203 to ACT205 is F (ml / min), for example, the flow rate N is a value obtained by dividing the flow rate F by the division number X (N = F / X). For example, the third threshold value Pt3 is sufficiently smaller than a value obtained by subtracting, from the atmospheric pressure, the width of the pressure increase that occurs in the inkjet head 2 when the flow rate of the ink circulating through the flow path of the ink circulation mechanism 1 is reduced by N. Set to value. If the third threshold value Pt3 is set in this way, there is no fear of ink leaking from the nozzles 26 due to a pressure increase that occurs when the flow rate is reduced by N.

  After ACT 208, the system controller 100 determines whether or not the circulation pump 6 is completely stopped (ACT 209). For example, the system controller 100 determines that the circulation pump 6 is not completely stopped when the number of times of executing the ACT 208 is less than the division number X after the circulation stop is instructed. If it is equivalent to the above, it is determined that the circulation pump 6 is stopped.

  When it is determined that the circulation pump 6 has not completely stopped (No in ACT 209), the operation of the system controller 100 returns to ACT 206. That is, the system controller 100 reduces the flow rate of the ink circulating through the flow path of the ink circulation mechanism 1 stepwise until the circulation pump 6 is completely stopped.

  When it is determined that the circulation pump 6 is completely stopped (ACT209: Yes), the system controller 100 ends the operation shown in the flowchart.

  As described above, in the ink jet printer according to this embodiment, the pressure of the ink in the flow path of the ink circulation mechanism 1 is lowered by the adjustment pump 11 before the circulation pump 6 is stopped. Even in this case, ink leakage from the nozzles 26 can be prevented as in the first embodiment.

  Furthermore, the ink jet printer according to the present embodiment stops the ink circulation by decreasing the flow rate stepwise. In this way, the peak of the ink pressure rise in the ink jet head 2 can be suppressed lower than when the ink circulation is stopped instantaneously. Accordingly, ink leakage from the nozzle 26 is less likely to occur.

(Modification)
In each embodiment, an ink jet printer is disclosed as an example of a liquid ejection apparatus. However, the liquid ejection device may be another type of device having a mechanism for ejecting liquid. For example, the configuration disclosed in each embodiment may be applied to a facsimile machine or a copying machine that forms an image by an inkjet method.

  The configuration disclosed in each embodiment can also be applied to a liquid ejection apparatus that ejects liquid other than ink. As such a liquid ejecting apparatus, for example, there is an apparatus that ejects a liquid containing conductive particles for forming a wiring pattern of a printed wiring board.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Ink circulation mechanism, 2 ... Inkjet head, 3 ... Ink tank, 4 ... Ink supply path, 5 ... Ink return path, 6 ... Circulation pump (circulation device), 7 ... Filter, 8 ... Atmospheric communication path, 9 ... Electromagnetic Valves, 10 ... pressure sensor, 11 ... regulating pump, 12 ... pressure regulating device, 20 ... inlet, 21 ... outlet, 26 ... nozzle, 30 ... ink layer, 31 ... air layer, 100 ... system controller.

Claims (3)

A tank for storing liquid;
A head for discharging liquid from the nozzle;
A supply path for supplying liquid from the tank to the head;
A reflux path for returning liquid from the head to the tank;
A circulation device that circulates a liquid in a closed flow path including the tank, the head, the supply path, and the reflux path;
A pressure adjusting device for adjusting the pressure of the liquid in the flow path;
A controller for first reducing the pressure of the liquid in the flow path by the pressure adjusting device and then stopping the circulation device when stopping the circulation of the liquid in the flow path. apparatus.   The controller, when stopping the circulation of the liquid in the flow path, lowers the pressure of the liquid in the flow path by the pressure adjusting device and stops the flow of the liquid circulated by the circulation apparatus in a stepwise manner. The liquid ejection apparatus according to claim 1, wherein The tank includes an air layer inside,
The liquid discharge apparatus according to claim 1, wherein the pressure adjusting device lowers the pressure of the liquid in the flow path by discharging air from the air layer of the tank to the outside.

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