Droplet discharge device and maintenance method

Abstract

To suppress a discharge failure caused by an article staying in a droplet discharge head.SOLUTION: The droplet discharge device comprises: a droplet discharge head; a feed unit; and a control unit. The droplet discharge head discharges droplets of a coloring liquid. The feed unit feeds the coloring liquid to the droplet discharge head. The control unit controls each unit. The control unit controls, during at least a part of a maintenance period after a discharge period of discharging the droplets of the coloring liquid from the droplet discharge head, the feed unit to feed a coloring liquid lower in viscosity than the viscosity during the discharge period.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The disclosed embodiments relate to a droplet ejection device and a maintenance method. [Background technology]

[0002] 2. Description of the Related Art Known printing devices include inkjet printers and inkjet plotters that use an inkjet recording method. These inkjet printing devices are equipped with a droplet ejection head for ejecting liquid.

[0003] Furthermore, in inkjet printing devices, a technique has been proposed in which a cleaning liquid is supplied to the droplet ejection head to prevent clogging of the droplet ejection head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3629926 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned conventional techniques have room for further improvement in terms of suppressing ejection defects caused by accumulated matter inside the droplet ejection head.

[0006] One aspect of the embodiment has been made in consideration of the above, and aims to provide a droplet ejection device and a maintenance method that can suppress ejection defects caused by residue inside the droplet ejection head. [Means for solving the problem]

[0007] A droplet ejection device according to one aspect of the embodiment includes a droplet ejection head, a supply unit, and a control unit. The droplet ejection head ejects droplets of colored liquid. The supply unit supplies the colored liquid to the droplet ejection head. The control unit controls each unit. Furthermore, during at least a portion of a maintenance period following an ejection period in which droplets of colored liquid are ejected from the droplet ejection head, the control unit controls the supply unit to supply the droplet ejection head with colored liquid having a lower viscosity than the colored liquid during the ejection period. [Effects of the Invention]

[0008] According to one aspect of the embodiment, ejection defects caused by accumulated matter inside the droplet ejection head can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of the configuration of a droplet ejection device according to an embodiment. [Figure 2] FIG. 2 is a perspective view that schematically shows the external configuration of the droplet ejection head according to the embodiment. [Figure 3] FIG. 3 is a plan view of the droplet ejection head according to the embodiment. [Figure 4] FIG. 4 is a diagram schematically showing a flow path inside the droplet ejection head according to the embodiment. [Figure 5] FIG. 5 is a diagram schematically illustrating an example of the configuration of a discharge unit according to an embodiment. [Figure 6] FIG. 6 is a diagram schematically showing a circulation mechanism according to an embodiment. [Figure 7] FIG. 7 is a flowchart showing the procedure of a process executed by the droplet ejection device according to the embodiment. [Figure 8] FIG. 8 is an explanatory diagram for explaining the manner in which the circulation flow rate is adjusted according to the embodiment. [Figure 9] FIG. 9 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the first modification of the embodiment. [Figure 10] FIG. 10 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the second modification of the embodiment. [Figure 11] FIG. 11 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the third modification of the embodiment. [Figure 12] FIG. 12 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the fourth modification of the embodiment. [Figure 13] FIG. 13 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the fifth modification of the embodiment. [Figure 14] FIG. 14 is a diagram schematically showing an example of the attitude of a droplet ejection head according to the fifth modification of the embodiment. [Figure 15] FIG. 15 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the sixth modification of the embodiment. [Figure 16] FIG. 16 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to the seventh modification of the embodiment. [Figure 17] FIG. 17 is a diagram showing how a pressure wave propagates according to the seventh modification of the embodiment. [Figure 18] FIG. 18 is an explanatory diagram for explaining the internal structure of a droplet ejection head according to Modification 8 of the embodiment and the circulation mode of colored liquid. [Figure 19] FIG. 19 is an explanatory diagram for explaining the internal structure of a droplet ejection head according to Modification 8 of the embodiment and the circulation mode of colored liquid. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the droplet ejection device and maintenance method disclosed herein will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to the embodiments described below. It should be noted that the drawings are schematic, and the dimensional relationships and ratios of elements may differ from reality. Furthermore, the dimensional relationships and ratios may differ between the drawings.

[0011] Furthermore, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision, installation precision, etc.

[0012] Furthermore, the embodiments can be combined as appropriate within the scope of not causing any contradiction in the processing content. Furthermore, the same components in the following embodiments are denoted by the same reference numerals, and redundant explanations will be omitted.

[0013] The droplet ejection device disclosed in the present application can be applied to various devices that eject droplets by the inkjet method, in addition to inkjet printers and inkjet plotters that use the inkjet recording method.

[0014] <Example of external configuration of droplet ejection device> The configuration of a droplet ejection device according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram schematically showing an example of the configuration of a droplet ejection device according to an embodiment.

[0015] As shown in FIG. 1, the droplet discharge device 1 includes a robot arm 100, a circulation mechanism 200, a droplet discharge head 300, and a control device 2.

[0016] The robot arm 100 is mounted on a base 10 placed on a horizontal floor surface, for example, indoors or outdoors. The robot arm 100 has an arm unit 110. The arm unit 110 is composed of multiple parts assembled so that they can bend, stretch, and rotate freely. The arm unit 110 can move a droplet discharge head 300 mounted on the tip of the arm unit 110 and change the position, posture, and angle of the droplet discharge head 300 in accordance with commands from a control unit 21, which will be described later. The arm unit 110 illustrated in FIG. 1 is not particularly limited to the configuration shown in FIG. 1, as long as it has the degree of freedom to move and change the position, posture, angle, etc. required for the droplet discharge head 300.

[0017] The robot arm 100 can move the circulation mechanism 200 and the droplet discharge head 300 mounted on the tip of the arm unit 110 in the vertical direction (Z-axis direction) by, for example, moving them along a predetermined rotation axis using the arm unit 110. As a result, the circulation mechanism 200 and the droplet discharge head 300 can be oriented such that the liquid discharge surface 30SF of the droplet discharge head 300 faces parallel to the spray surface 50SF of the target object 50, as shown in FIG. 1 . The robot arm 100 can also rotate the circulation mechanism 200 and the droplet discharge head 300 mounted on the tip of the arm unit 110 around a predetermined rotation axis using the arm unit 110. As a result, the circulation mechanism 200 and the droplet discharge head 300 can be swapped between their longitudinal and lateral positions, or their upside-down positions can be reversed, for example.

[0018] The circulation mechanism 200 is installed at the tip of the arm unit 110 of the robot arm 100. The circulation mechanism 200 supplies the colored liquid to the droplet discharge head 300 while controlling the circulation flow rate of the colored liquid circulating between the droplet discharge head 300 and the circulation mechanism 200. The circulation mechanism 200 functions as a supply unit that supplies the colored liquid to the droplet discharge head 300.

[0019] The droplet discharge head 300 is attached to a circulation mechanism 200 installed at the tip of the arm unit 110 of the robot arm 100. The droplet discharge head 300 functions as a droplet discharge unit that discharges droplets of colored liquid onto the target object 50. The colored liquid is a liquid that can be applied to the target object 50 to color it. In addition, the colored liquid will be described using an example in which it is a pseudoplastic fluid whose viscosity decreases as the shear rate increases, but it does not have to be a pseudoplastic fluid. For example, ink, paint, etc. can be used as the colored liquid.

[0020] The control device 2 is, for example, a computer, and includes a control unit 21 such as a processor and a storage unit 22 such as a memory. The storage unit 22 stores programs that control various processes executed in the droplet ejection device 1. The control unit 21 controls the operation of the droplet ejection device 1 by reading and executing the programs stored in the storage unit 22.

[0021] Such a program may be recorded on a computer-readable storage medium and installed from that storage medium into the storage unit 22 of the control device 2. Examples of computer-readable storage media include hard disks (HDs), flexible disks (FDs), compact disks (CDs), magnetic optical disks (MOs), and memory cards.

[0022] However, various kinds of retained matter may remain inside the droplet ejection head 300 after ejecting droplets of colored liquid. Examples of retained matter include solidified colored liquid and air bubbles. If retained matter remains inside the droplet ejection head 300, the flow of colored liquid is hindered, which may cause ejection defects of the droplet ejection head 300. In view of this, the present application proposes a droplet ejection device 1 that can suppress ejection defects caused by retained matter remaining inside the droplet ejection head 300.

[0023] <Configuration example of droplet ejection head> A droplet ejection head 300 according to an embodiment will be described with reference to Figures 2 to 4. Figure 2 is a perspective view schematically showing the external configuration of the droplet ejection head according to an embodiment. Figure 3 is a plan view of the droplet ejection head according to an embodiment. Figure 4 is a view schematically showing a flow path inside the droplet ejection head according to an embodiment.

[0024] 2, the droplet discharge head 300 has a housing including a box-shaped member 310 and a substantially flat plate-shaped member 320. The housing of the droplet discharge head 300 is provided with a supply port 321 for supplying colored liquid to the inside of the droplet discharge head 300, and a recovery port 322 for recovering colored liquid from the inside of the droplet discharge head 300. A first flow path RT1 for supplying colored liquid from the circulation mechanism 200 to the inside of the head is connected to the supply port 321. A second flow path RT2 for returning colored liquid recovered inside the head to the circulation mechanism 200 is connected to the recovery port 322.

[0025] As shown in FIG. 3, the droplet ejection head 300 includes a supply reservoir 301 , a supply manifold 302 , a recovery manifold 303 , a recovery reservoir 304 , and an ejection unit 305 .

[0026] The supply reservoir 301 has an elongated shape extending in the longitudinal direction (Y-axis direction) of the droplet ejection head 300, and is connected to a supply manifold 302. The supply reservoir 301 has a flow path therein. As shown in FIG. 4 , the colored liquid is supplied to the supply reservoir 301 through a first flow path RT1 and a supply port 321, and the colored liquid stored in the flow path of the supply reservoir 301 is sent to the supply manifold 302.

[0027] The supply manifold 302 has an elongated shape that extends in the short direction (X-axis direction) of the droplet ejection head 300 up to just before the recovery reservoir 304. The supply manifold 302 has therein a flow path that communicates with the flow path of the supply reservoir 301 and the ejection unit 305. As shown in FIG. 4 , the colored liquid that has been sent from the supply reservoir 301 to the supply manifold 302 is sent from the supply manifold 302 to the ejection unit 305.

[0028] The collection manifold 303 has an elongated shape that extends in the short direction (X-axis direction) of the droplet ejection head 300 up to just before the supply reservoir 301. The collection manifold 303 has an internal flow path that communicates with the flow path of the collection reservoir 304 and the ejection unit 305. As shown in FIG. 4 , colored liquid that is not ejected from the ejection unit 305 to the outside is sent to the collection manifold 303.

[0029] The recovery reservoir 304 has an elongated shape that extends in the longitudinal direction (Y-axis direction) of the droplet ejection head 300, and is connected to the recovery manifold 303. The recovery reservoir 304 has a flow path therein. As shown in Figure 4, the colored liquid that is sent from the recovery manifold 303 to the recovery reservoir 304 and stored in the flow path of the recovery reservoir 304 is sent back to the tank 201 (see Figure 6) through the recovery port 322 and the second flow path RT2.

[0030] Fig. 5 is a diagram schematically illustrating an example of the configuration of a discharge unit according to an embodiment. As shown in Fig. 5, the discharge unit 305 has a nozzle 351, a pressure chamber 352, and a displacement element 353. The nozzle 351 is a discharge hole that opens in the discharge surface 30SF (see Fig. 1) of the droplet discharge head 300.

[0031] The pressurizing chamber 352 is connected to the nozzle 351. The pressurizing chamber 352 has a main body 361 to which pressure is applied by a displacement element 353, and a descender 362 which is a flow path connecting the main body 361 and the nozzle 351. The pressurizing chamber 352 and the supply manifold 302 are connected via individual supply flow paths 354. The colored liquid sent from the supply manifold 302 to the discharge unit 305 is supplied to the pressurizing chamber 352 through the individual supply flow paths 354. In addition, the pressurizing chamber 352 and the recovery manifold 303 are connected via individual recovery flow paths 355. The colored liquid that is not discharged from the nozzle 351 to the outside is recovered from the pressurizing chamber 352 to the recovery manifold 303.

[0032] The displacement element 353 is located on the surface of the main body 361 of the pressure chamber 352 opposite to the descender 362. The displacement element 353 is an element that deforms in response to a predetermined drive signal. The displacement element 353 functions as a pressure unit that applies pressure to the pressure chamber 352 to eject droplets of colored liquid from the nozzle 351. In other words, as the displacement element 353 deforms, pressure (positive pressure and negative pressure) is applied to the pressure chamber 352, and droplets of colored liquid are ejected from the nozzle 351. The displacement element 353 is electrically connected to and controlled by the control device 2.

[0033] The discharge unit 305 having such a configuration sucks colored liquid from the supply manifold 302 by negative pressure applied to the pressure chamber 352, and then ejects the sucked colored liquid from the nozzle 351 toward the target object 50 by positive pressure applied to the pressure chamber 352.

[0034] <Example of circulation mechanism configuration> Next, a configuration example of the circulation mechanism 200 according to the embodiment will be described. Fig. 6 is a diagram schematically showing the circulation mechanism according to the embodiment.

[0035] 6, the circulation mechanism 200 includes a tank 201, a discharge pump 202, a suction pump 203, a first proportional valve 204, a second proportional valve 205, and a heater 206. The circulation mechanism 200 also includes a first pressure sensor 208, a second pressure sensor 209, a third pressure sensor 210, a fourth pressure sensor 211, and a flow meter 212.

[0036] The circulation mechanism 200 also includes a first flow path RT1 and a second flow path RT2. The first flow path RT1 connects the tank 201 and the droplet discharge head 300, and is a flow path for allowing the colored liquid stored in the tank 201 to flow into the droplet discharge head 300. The second flow path RT2 connects the tank 201 and the droplet discharge head 300, and is a flow path for returning the colored liquid that has flowed into the droplet discharge head 300 to the tank 201. The colored liquid that is collected within the droplet discharge head 300 without being discharged from the droplet discharge head 300 to the outside is sent back to the tank 201 via the second flow path RT2. The first flow path RT1 and the second flow path RT2 can be implemented, for example, by piping made of a predetermined material that does not interact with the components of the colored liquid. The circulation mechanism 200 having these components controls the circulation flow rate of the colored liquid circulating clockwise between the tank 201 and the droplet discharge head 300, for example, as shown in FIG. 6, under the control of the control unit 21.

[0037] The tank 201 stores the colored liquid to be supplied to the droplet discharge head 300. The tank 201 functions as a storage unit that stores the colored liquid to be supplied to the droplet discharge head 300.

[0038] The discharge pump 202 supplies the colored liquid stored in the tank 201 to the droplet discharge head 300 through the first flow path RT1. The discharge pump 202 generates a positive pressure for sending the colored liquid stored in the tank 201 to the droplet discharge head 300. The discharge pump 202 can send the colored liquid stored in the tank 201 to the droplet discharge head 300 at, for example, a preset constant supply pressure.

[0039] The suction pump 203 supplies the colored liquid collected in the droplet discharge head 300 to the tank 201 through the second flow path RT2. The suction pump 203 generates negative pressure to suck the colored liquid collected in the droplet discharge head 300 and return it to the tank 201. The suction pump 203 can send the colored liquid sucked from the droplet discharge head 300 to the tank 201 at, for example, a preset constant recovery pressure.

[0040] The discharge pump 202 and the suction pump 203 can be implemented by a rotary pump such as a gear pump or a positive displacement pump such as a diaphragm pump.

[0041] The first proportional valve 204 is interposed in the first flow path RT1 between the tank 201 and the droplet ejection head 300, and proportionally controls the flow rate of the colored liquid supplied to the droplet ejection head 300. The first proportional valve 204 can continuously change the flow path cross-sectional area of ​​the colored liquid between 0 and 100%, and controls the flow rate of the colored liquid to a desired flow rate. For example, the first proportional valve 204 can reduce the supply flow rate of the colored liquid when supplied to the droplet ejection head 300 by reducing the flow path cross-sectional area of ​​the colored liquid. On the other hand, the first proportional valve 204 can increase the supply flow rate of the liquid when supplied to the droplet ejection head 300 by increasing the flow path cross-sectional area of ​​the liquid.

[0042] The second proportional valve 205 is inserted in the second flow path RT2 between the tank 201 and the droplet discharging head 300, and proportionally controls the flow rate of the colored liquid delivered from the droplet discharging head 300 to the tank 201. Similar to the first proportional valve 204, the second proportional valve 205 can continuously change the cross-sectional area of ​​the liquid flow path between 0 and 100%, and controls the flow rate of the colored liquid to a desired flow rate. For example, the second proportional valve 205 can reduce the recovery flow rate of the colored liquid when it is recovered from the droplet discharging head 300 by reducing the cross-sectional area of ​​the colored liquid flow path. On the other hand, the second proportional valve 205 can increase the recovery flow rate of the colored liquid when it is recovered from the droplet discharging head 300 by increasing the cross-sectional area of ​​the colored liquid flow path.

[0043] The first proportional valve 204 and the second proportional valve 205 can be implemented by an electromagnetic proportional switching valve or a pneumatic proportional switching valve.

[0044] The heater 206 is provided in the first flow path RT1 or adjacent to the first flow path RT1, and heats the coloring liquid flowing through the first flow path RT1.

[0045] The first pressure sensor 208 measures the pressure of the colored liquid fed from the tank 201 to the droplet discharge head 300 by the discharge pump 202. The first pressure sensor 208 measures the pressure downstream of the discharge pump 202 in the circulation direction of the colored liquid in the circulation mechanism 200. The first pressure sensor 208 sends the measurement result to the control unit 21.

[0046] The second pressure sensor 209 measures the pressure of the colored liquid sucked from the droplet discharge head 300 by the suction pump 203 and delivered to the tank 201. The second pressure sensor 209 measures the pressure upstream of the suction pump 203 in the circulation direction of the colored liquid in the circulation mechanism 200. The second pressure sensor 209 sends the measurement result to the control unit 21.

[0047] The third pressure sensor 210 functions as a first pressure measurement unit that measures, as a supply pressure, the pressure of the colored liquid flowing through the first flow path RT1 between the first proportional valve 204 and the droplet discharge head 300. The third pressure sensor 210 sends the measurement result to the control unit 21.

[0048] The fourth pressure sensor 211 functions as a second pressure measurement unit that measures, as a recovery pressure, the pressure of the colored liquid flowing through the second flow path RT2 between the second proportional valve 205 and the droplet discharging head 300. The fourth pressure sensor 211 sends the measurement result to the control unit 21.

[0049] The flow meter 212 measures the flow rate of the colored liquid supplied to the droplet ejection head 300. The flow meter 212 sends the measurement result to the control unit 21.

[0050] (Pump control) The control unit 21 adjusts the positive pressure applied to the colored liquid when the discharge pump 202 discharges the colored liquid so as to maintain a constant value, based on the measurement results of the first pressure sensor 208 and the third pressure sensor 210. For example, the control unit 21 adjusts the positive pressure of the discharge pump 202 so as to maintain the pressure of the colored liquid obtained from the measurement results of the first pressure sensor 208 at a pressure that is approximately 1.2 to 3 times greater than the pressure of the colored liquid obtained from the measurement results of the third pressure sensor 210.

[0051] Furthermore, the control unit 21 adjusts the negative pressure applied to the coloring liquid when the suction pump 203 sucks the coloring liquid so as to be kept constant, based on the measurement results of the second pressure sensor 209 and the fourth pressure sensor 211. For example, the control unit 21 adjusts the negative pressure of the suction pump 203 so that the pressure of the coloring liquid obtained from the measurement results of the second pressure sensor 209 is kept approximately 1.2 to 3 times lower than the pressure of the coloring liquid obtained from the measurement results of the fourth pressure sensor 211.

[0052] The control unit 21 circulates the coloring liquid between the tank 201 and the droplet ejection head 300 by adjusting the pressure difference between the positive pressure applied to the coloring liquid by the ejection pump 202 and the negative pressure applied to the coloring liquid by the suction pump 203 to maintain a constant pressure.

[0053] <Specific Operation of the Droplet Discharge Device> Next, a specific operation of the droplet ejection device according to the embodiment will be described with reference to Fig. 7. Fig. 7 is a flowchart showing the procedure of processing executed by the droplet ejection device according to the embodiment. Note that each processing shown in Fig. 7 is executed under the control of the control unit 21.

[0054] 7, in the droplet discharge device 1, first, a discharge process is performed in which droplets of colored liquid are discharged from the droplet discharge head 300 (step S101). In the discharge process, the control unit 21 controls the displacement element 353 provided in the droplet discharge head 300 to apply pressure to the pressure chamber 352, thereby discharging the colored liquid from the nozzle 351 toward the target object 50. Hereinafter, the cumulative processing period during which the discharge process is performed will be referred to as the "discharge period."

[0055] Before starting the discharge process, the control unit 21 controls the discharge pump 202 and the suction pump 203 to start circulating the colored liquid between the tank 201 and the droplet discharge head 300 .

[0056] Next, the droplet discharge device 1 determines whether or not a maintenance period for performing maintenance processing on the droplet discharge head 300 has arrived (step S102). The determination in step S102 is made, for example, based on whether or not the discharge period has exceeded a predetermined period. If the maintenance period has not arrived yet (step S102; No), the process returns to step S101, and the discharge processing continues.

[0057] On the other hand, if the maintenance period has arrived (Step S102; Yes), a maintenance process is performed on the droplet ejection head 300 (Step S103). In the maintenance process, the control unit 21 controls the circulation mechanism 200 to adjust the circulation flow rate of the colored liquid circulating between the circulation mechanism 200 and the droplet ejection head 300. The manner in which the circulation flow rate of the colored liquid circulating between the circulation mechanism 200 and the droplet ejection head 300 is adjusted will be described later. When the maintenance process is completed, the control unit 21 ends the series of processes in the droplet ejection device 1.

[0058] <Circulation flow rate adjustment mode> Hereinafter, a description will be given of an adjustment mode of the circulation flow rate of the colored liquid circulating between the circulation mechanism 200 and the droplet discharge head 300 with reference to Fig. 8. Fig. 8 is an explanatory diagram for explaining an adjustment mode of the circulation flow rate according to the embodiment.

[0059] 8 shows the changes over time in "circulation flow rate" and "viscosity" during the discharge period and the maintenance period. "Circulation flow rate" refers to the circulation flow rate of the colored liquid circulating between the circulation mechanism 200 and the droplet discharge head 300, and "viscosity" refers to the viscosity of the colored liquid supplied from the circulation mechanism 200 to the droplet discharge head 300.

[0060] As shown in FIG. 8, during the maintenance period after the ejection period, the control unit 21 controls the circulation mechanism 200 to increase the circulation flow rate of the coloring liquid to be higher than the circulation flow rate of the coloring liquid during the ejection period. Here, as described above, the coloring liquid is a pseudoplastic fluid whose viscosity decreases as the shear rate increases. Along with the increase in the circulation flow rate of the coloring liquid, the shear rate with respect to the circulation direction of the coloring liquid increases, and the viscosity of the coloring liquid decreases. Therefore, the control unit 21 can supply the droplet ejection head 300 with a coloring liquid having a lower viscosity than the coloring liquid during the ejection period by increasing the circulation flow rate of the coloring liquid during the maintenance period.

[0061] For example, the control unit 21 changes the cross-sectional areas of the flow paths of the first proportional valve 204 and the second proportional valve 205 in the circulation mechanism 200 to change the supply flow rate and the recovery flow rate of the coloring liquid, thereby increasing the circulation flow rate from the circulation flow rate F1 of the coloring liquid during the ejection period to the circulation flow rate F2 (>F1). Thereby, the control unit 21 can reduce the viscosity of the coloring liquid supplied to the droplet ejection head 300 from the viscosity V1 of the coloring liquid during the ejection period to the viscosity V2 (<V1) during the maintenance period.

[0062] Thus, by increasing the circulation flow rate of the coloring liquid during the maintenance period after the ejection period to be higher than the circulation flow rate of the coloring liquid during the ejection period, the viscosity of the coloring liquid can be reduced compared to the viscosity of the coloring liquid during the ejection period.

[0063] According to the droplet ejection device 1 according to the embodiment, even when deposits such as solidified products and bubbles of the coloring liquid remain in the droplet ejection head 300, by reducing the viscosity of the coloring liquid, it is possible to easily peel off the deposits from the inner wall of the flow path in the droplet ejection head 300. As a result, since the deposits are smoothly discharged to the outside of the droplet ejection head 300, it is possible to suppress the deposits from obstructing the flow of the coloring liquid in the flow path in the droplet ejection head 300. As a result, it is possible to suppress ejection failures caused by deposits remaining in the droplet ejection head 300.

[0064] In the example shown in FIG. 8, an example in which the circulation flow rate of the coloring liquid is increased during all periods of the maintenance period compared to the circulation flow rate of the coloring liquid during the discharge period was shown. However, the circulation flow rate of the coloring liquid may be increased during some periods of the maintenance period. In short, the control unit 21 may control the circulation mechanism 200 during at least some periods of the maintenance period to increase the circulation flow rate of the coloring liquid compared to the circulation flow rate of the coloring liquid during the discharge period.

[0065] <Various Modification Examples of the Adjustment Mode of the Circulation Flow Rate> Next, various modification examples of the adjustment mode of the circulation flow rate according to the embodiment will be described with reference to FIGS. 9 to 17.

[0066] FIG. 9 is an explanatory diagram for explaining the adjustment mode of the circulation flow rate according to Modification Example 1 of the embodiment.

[0067] As shown in FIG. 9, the control unit 21 controls the circulation mechanism 200 to change the circulation flow rate of the coloring liquid between the first period and the second period following the first period, which are included in the maintenance period. Thereby, the control unit 21 can change the viscosity of the coloring liquid between the first period and the second period following the first period, which are included in the maintenance period.

[0068] For example, the control unit 21 changes the cross-sectional areas of the flow paths of the first proportional valve 204 and the second proportional valve 205 in the circulation mechanism 200 to change the supply flow rate and the recovery flow rate of the coloring liquid, thereby setting the circulation flow rate to the circulation flow rate F2 in the first period and setting the circulation flow rate to the circulation flow rate F3 (<F2) in the second period. Thereby, the control unit 21 can set the viscosity of the coloring liquid supplied to the droplet discharge head 300 to the viscosity V2 in the first period and set the viscosity to the viscosity V3 (>V2) in the second period.

[0069] Thus, in Modified Example 1, by changing the circulation flow rate of the coloring liquid, a relatively low-viscosity coloring liquid and a relatively high-viscosity coloring liquid can be supplied to the droplet discharge head 300. Thereby, in Modified Example 1, the residue can be peeled off from the inner wall of the flow path in the droplet discharge head 300 by the relatively low-viscosity coloring liquid, and the residue remaining in the droplet discharge head 300 can be flushed away by the relatively high-viscosity coloring liquid.

[0070] Also, in Modified Example 1, the circulation flow rate of the coloring liquid is changed from a relatively high flow rate (for example, circulation flow rate F2) to a relatively low flow rate (for example, circulation flow rate F3). Thereby, in Modified Example 1, after supplying the relatively low-viscosity coloring liquid to the droplet discharge head 300, the relatively high-viscosity coloring liquid can be supplied to the droplet discharge head 300. That is, after peeling off the residue from the inner wall of the flow path in the droplet discharge head 300 by the relatively low-viscosity coloring liquid, the residue remaining in the droplet discharge head 300 can be flushed away by the relatively high-viscosity coloring liquid. As a result, according to Modified Example 1, the residue can be discharged more smoothly to the outside of the droplet discharge head 300.

[0071] FIG. 10 is an explanatory diagram for explaining the adjustment mode of the circulation flow rate according to Modified Example 2 of the embodiment. In Modified Example 1, the circulation flow rate of the coloring liquid is changed from a relatively high flow rate to a relatively low flow rate, but in Modified Example 2, the circulation flow rate of the coloring liquid is changed from a relatively low flow rate to a relatively high flow rate.

[0072] As shown in FIG. 10, the control unit 21 controls the circulation mechanism 200 to set the circulation flow rate to the circulation flow rate F2 in the first period and to the circulation flow rate F3 (>F2) in the second period. Thereby, the control unit 21 can set the viscosity of the coloring liquid supplied to the droplet discharge head 300 to the viscosity V2 in the first period and to the viscosity V3 (<V2) in the second period.

[0073] In this way, in Modification 2, the circulation flow rate of the colored liquid is changed from a relatively low flow rate (for example, circulation flow rate F2) to a relatively high flow rate (for example, circulation flow rate F3). As a result, in Modification 1, a relatively high-viscosity colored liquid can be supplied to the droplet discharge head 300, and then a relatively low-viscosity colored liquid can be supplied to the droplet discharge head 300. In other words, the relatively high-viscosity colored liquid can wash away any remaining material inside the droplet discharge head 300, and then the relatively low-viscosity colored liquid can transport the remaining material to the downstream side of the flow path inside the droplet discharge head 300 at high speed. As a result, Modification 1 makes it possible to more smoothly discharge the remaining material outside the droplet discharge head 300.

[0074] Although the examples of the first and second modifications show that the circulation flow rate of the coloring liquid is changed once during a first period and a second period following the first period, the disclosed technology is not limited to this. For example, the control unit 21 may control the circulation mechanism 200 to repeatedly change the circulation flow rate of the coloring liquid multiple times during the maintenance period.

[0075] 11 is an explanatory diagram for explaining an adjustment mode of the circulation flow rate according to Modification 3 of the embodiment. Solidified colored liquid (hereinafter referred to as "solidified material") remains as retained matter inside the droplet discharge head 300. In contrast, in Modification 3, the colored liquid contains a soluble component that can dissolve the solidified colored liquid, and the solidified material remaining inside the droplet discharge head 300 is dissolved by the soluble component.

[0076] As shown in FIG. 11, during the maintenance period, the control unit 21 controls the circulation mechanism 200 to stop the circulation of the coloring liquid for a predetermined time period for the solidified matter remaining in the droplet ejection head 300 to dissolve into the soluble component, and then increases the circulation flow rate of the coloring liquid.

[0077] For example, the control unit 21 sets the circulation flow rate to 0 by changing the flow path cross-sectional areas of the first proportional valve 204 and the second proportional valve 205 in the circulation mechanism 200 to 0 and stopping the circulation of the colored liquid for a predetermined time. After the predetermined time has passed, the control unit 21 increases the flow path cross-sectional areas of the first proportional valve 204 and the second proportional valve 205 in the circulation mechanism 200 to a value greater than 0, thereby increasing the circulation flow rate to a circulation flow rate F2 that is higher than the circulation flow rate F1 of the colored liquid during the discharge period. In this way, after the predetermined time has passed, the control unit 21 can reduce the viscosity of the colored liquid supplied to the droplet discharge head 300 to a viscosity V2 that is lower than the viscosity V1 of the colored liquid during the discharge period.

[0078] In this way, in Modification 3, the circulation of the coloring liquid is stopped for a predetermined time before the circulation flow rate of the coloring liquid is increased. As a result, in Modification 3, solidified matter remaining inside the droplet discharge head 300 can be dissolved by the soluble components contained in the coloring liquid, and the dissolved solidified matter can be transported at high speed by the coloring liquid to the downstream side of the flow path inside the droplet discharge head 300. As a result, Modification 3 makes it possible to more smoothly discharge the solidified matter of the coloring liquid outside the droplet discharge head 300.

[0079] Fig. 12 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to Modification 4 of the embodiment. Fig. 12 shows the change over time in "head posture" during the ejection period and the maintenance period. "Head posture" refers to the posture of the droplet ejection head 300 mounted on the robot arm 100.

[0080] As shown in FIG. 12, during the maintenance period following the ejection period, the control unit 21 controls the circulation mechanism 200 to increase the circulation flow rate of the colored liquid, and controls the robot arm 100 to change the posture of the droplet ejection head 300.

[0081] For example, the control unit 21 changes the flow path cross-sectional areas of the first proportional valve 204 and the second proportional valve 205 in the circulation mechanism 200 to change the supply flow rate and the recovery flow rate of the coloring liquid, thereby increasing the circulation flow rate from the circulation flow rate F1 of the coloring liquid during the discharge period to the circulation flow rate F2 (>F1). As a result, the control unit 21 can reduce the viscosity of the coloring liquid supplied to the droplet discharge head 300 during the maintenance period from the viscosity V1 of the coloring liquid during the discharge period to the viscosity V2 (<V1).

[0082] Also, for example, the control unit 21 maintains the posture of the droplet discharge head 300 at a constant posture P1 during the discharge period, and operates the arm portion 110 of the robot arm 100 during the maintenance period to sequentially change the posture of the droplet discharge head 300 to a plurality of arbitrary postures.

[0083] Thus, in the fourth modification, by changing the posture of the droplet discharge head 300 during the maintenance period after the discharge period, the inclination of the droplet discharge head 300 with respect to the direction of gravity can be changed. The solidified matter of the coloring liquid staying in the droplet discharge head 300 tends to move in the direction of gravity under the influence of gravity. The bubbles staying in the droplet discharge head 300 tend to move in the direction opposite to the direction of gravity under the influence of buoyancy. Therefore, in the fourth modification, by changing the posture of the droplet discharge head 300, the staying matter such as the solidified matter and bubbles of the coloring liquid staying in the droplet discharge head 300 can be efficiently moved in the direction of gravity and the direction opposite to the direction of gravity. As a result, in the fourth modification, since the movement of the staying matter in the direction of gravity and the direction opposite to the direction of gravity can be promoted, the staying matter can be smoothly discharged to the outside of the droplet discharge head 300.

[0084] Furthermore, in Modification 4, the attitude of the droplet ejection head 300 is changed at the same time as the circulating flow rate of the colored liquid is increased. In other words, in Modification 4, the timing at which the attitude change of the droplet ejection head 300 starts is matched with the timing at which the circulating flow rate of the colored liquid is increased. As a result, in Modification 4, the movement of retained matter in the direction of gravity and in the direction opposite to the direction of gravity can be further promoted, and therefore the retained matter can be more smoothly discharged outside the droplet ejection head 300.

[0085] 12 shows an example in which the attitude of the droplet ejection head 300 is changed during the entire maintenance period, but the attitude of the droplet ejection head 300 may be changed during part of the maintenance period. In short, the control unit 21 may control the circulation mechanism 200 to increase the circulating flow rate of the colored liquid and may control the robot arm 100 to change the attitude of the droplet ejection head 300 during at least part of the maintenance period.

[0086] Fig. 13 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to Modification 5 of the embodiment. Fig. 14 is a diagram schematically showing an example of the attitude of the droplet ejection head according to Modification 5 of the embodiment. Modification 5 relates to a variation of the attitude change of the droplet ejection head 300 in Modification 4.

[0087] As shown in Figures 13 and 14, during the maintenance period after the discharge period, the control unit 21 controls the robot arm 100 to change the attitude of the droplet discharge head 300 to attitude P2 in which the recovery port 322 is higher than the supply port 321.

[0088] In this way, in Modification 5, by changing the attitude of the droplet discharge head 300 so that the recovery port 322 is higher than the supply port 321, it is possible to efficiently move air bubbles remaining inside the droplet discharge head 300 in the direction opposite to the direction of gravity. As a result, in Modification 5, it is possible to promote the movement of air bubbles in the direction from the supply port 321 to the recovery port 322, and therefore it is possible to smoothly discharge air bubbles from the recovery port 322 to the outside of the droplet discharge head 300.

[0089] 13 and 14 show an example in which the attitude of the droplet discharge head 300 is changed so that the recovery port 322 is higher than the supply port 321, but the height positions of the supply port 321 and the recovery port 322 may be reversed. That is, the control unit 21 may change the attitude of the droplet discharge head 300 so that the supply port 321 is higher than the recovery port 322. In this case, it is possible to efficiently move the solidified colored liquid remaining inside the droplet discharge head 300 in the direction of gravity. This promotes the movement of the solidified colored liquid in the direction from the supply port 321 to the recovery port 322, and therefore it is possible to smoothly discharge the solidified colored liquid from the recovery port 322 to the outside of the droplet discharge head 300.

[0090] 15 is an explanatory diagram for explaining the adjustment of the circulation flow rate according to Modification 6 of the embodiment. Modification 6 relates to a variation of the change in the attitude of the droplet ejection head 300 in Modification 5.

[0091] As shown in Figure 15, during the maintenance period after the ejection period, the control unit 21 changes the posture of the droplet ejection head 300 between posture P2 in which the recovery port 322 is higher than the supply port 321 and posture P3 in which the supply port 321 is higher than the recovery port 322.

[0092] Thus, by changing the posture of the droplet discharge head 300 between a posture in which the recovery port 322 is relatively high and a posture in which the supply port 321 is relatively high, the movement of the solidified matter and bubbles of the coloring liquid between the supply port 321 and the recovery port 322 can be promoted. As a result, according to the modified example 6, the solidified matter and bubbles of the coloring liquid can be smoothly discharged from the recovery port 322 to the outside of the droplet discharge head 300.

[0093] FIG. 16 is an explanatory diagram for explaining an adjustment mode of the circulation flow rate according to a modified example 7 of the embodiment. FIG. 16 shows the time change of the "applied pressure" during the discharge period and the maintenance period. The "applied pressure" refers to the pressure applied from the displacement element 353 to the pressure chamber 352 in the droplet discharge head 300.

[0094] As shown in FIG. 16, during the maintenance period after the discharge period, the control unit 21 controls the circulation mechanism 200 to increase the circulation flow rate of the coloring liquid while applying pressure to the pressure chamber 352 by the displacement element 353.

[0095] For example, during the discharge period, the control unit 21 applies a pressure C1 to the pressure chamber 352 by the displacement element 353, and during the maintenance period, while increasing the circulation flow rate to a circulation flow rate F2 (>F1), the control unit 21 maintains the application of pressure from the displacement element 353 to the pressure chamber 352. Thereby, during the maintenance period, the control unit 21 can reduce the viscosity of the coloring liquid supplied to the droplet discharge head 300 from the viscosity V1 of the coloring liquid during the discharge period to a viscosity V2 (<V1).

[0096] Thus, during the maintenance period after the discharge period, by increasing the circulation flow rate of the coloring liquid while applying pressure to the pressure chamber 352, it is possible to generate a pressure wave in the pressure chamber 352 while reducing the viscosity of the coloring liquid supplied to the droplet discharge head 300.

[0097] According to the seventh modification, by reducing the viscosity of the colored liquid, it is possible to reduce the difference in viscosity between the colored liquid flowing through the pressure chamber 352 and the colored liquid flowing through the supply manifold 302 and the collection manifold 303 (hereinafter collectively referred to as "manifolds") connected to the pressure chamber 352. By reducing the difference in viscosity between the colored liquid flowing through the pressure chamber 352 and the colored liquid flowing through the manifolds, as shown in FIG. 17, the pressure wave PW generated in the pressure chamber 352 is more likely to propagate not only through the pressure chamber 352 but also through the manifold. FIG. 17 is a diagram showing the propagation of a pressure wave according to the seventh modification of the embodiment. In this way, the pressure wave PW generated in the pressure chamber 352 propagates to the manifold, allowing the pressure wave PW to intensively remove material remaining in the manifold.

[0098] 16, the pressure applied to the pressurizing chamber 352 during the ejection period and the pressure applied to the pressurizing chamber 352 during the maintenance period are both pressure C1. However, the present invention is not limited to this, and the pressure applied to the pressurizing chamber 352 during the maintenance period may be lower than the pressure applied to the pressurizing chamber 352 during the ejection period (i.e., the pressure for ejecting the colored liquid from the nozzle 351).

[0099] <Modification of Coloring Liquid Circulation Mode> Next, a modified example of the circulation mode of the coloring liquid according to the embodiment will be described with reference to FIGS.

[0100] 18 and 19 are explanatory diagrams for explaining the internal structure of a droplet ejection head 300 according to Modification 8 of the embodiment and the circulation mode of colored liquid.

[0101] 18 and 19, the flow path resistance of the individual recovery flow path 355 connecting the pressure chamber 352 of the discharge unit 305 and the recovery manifold 303 is smaller than the flow path resistance of the individual supply flow path 354 connecting the pressure chamber 352 and the supply manifold 302. For example, by making the flow path width of the individual recovery flow path 355 larger than the flow path width of the individual supply flow path 354, the flow path resistance of the individual recovery flow path 355 can be made smaller than the flow path resistance of the individual supply flow path 354.

[0102] During a maintenance period following the discharge period, the control unit 21 controls the circulation mechanism 200 to circulate the colored liquid from the recovery port 322 toward the supply port 321. For example, during a first period included in the maintenance period, the control unit 21 controls the circulation mechanism 200 to circulate the colored liquid from the supply port 321 toward the recovery port 322, as shown in FIG. 18 . Then, during a second period following the first period and included in the maintenance period, the control unit 21 controls the circulation mechanism 200 to reverse the flow direction of the colored liquid and circulate the colored liquid from the recovery port 322 toward the supply port 321, as shown in FIG. 19 .

[0103] In Modification 8, the circulation direction (flow direction) of the colored liquid is changed from the direction from the supply port 321 to the recovery port 322 to the direction from the recovery port 322 to the supply port 321. As a result, in Modification 8, the colored liquid flows through the recovery reservoir 304, the recovery manifold 303, the individual recovery flow path 355, the discharge unit 305, the individual supply flow path 354, the supply manifold 302, and the supply reservoir 301 in this order. Here, the flow path resistance of the individual recovery flow path 355 is smaller than the flow path resistance of the individual supply flow path 354. For this reason, the shear rate of the colored liquid increases in the individual recovery flow path 355, reducing the viscosity of the colored liquid. The colored liquid with reduced viscosity flows into the supply manifold 302 via the discharge unit 305 and the individual supply flow path 354, and reaches the tip portion 302a of the supply manifold 302. As a result, according to the eighth modification, the relatively high viscosity colored liquid that remains in the tip portion 302a of the supply manifold 302 can be replaced with the relatively low viscosity colored liquid.

[0104] (Other variations) In the embodiment, the circulation mechanism 200 supplies the colored liquid to the droplet discharge head 300. However, the supply unit that supplies the colored liquid to the droplet discharge head 300 is not limited to the circulation mechanism 200. For example, the supply unit may be a liquid supply mechanism including multiple liquid supply sources that respectively supply multiple colored liquids with different viscosities, supply flow paths connecting the multiple liquid supply sources to the droplet discharge head 300, and on-off valves provided in the supply flow paths for each liquid supply source. When the supply unit is such a liquid supply mechanism, the control unit 21 may control the on-off valves of the liquid supply mechanism during at least a portion of a maintenance period following a discharge period to supply the droplet discharge head 300 with a colored liquid having a lower viscosity than the colored liquid used during the discharge period. In such a case, the colored liquid does not have to be a pseudoplastic fluid. In such a case, the droplet discharge head 300 may at least include a nozzle 351, a pressure chamber 352 connected to the nozzle 351, and an actuator (displacement element 353) that applies pressure to the pressure chamber 352.

[0105] As described above, a droplet ejection device according to an embodiment (for example, the droplet ejection device 1) includes a droplet ejection head (for example, the droplet ejection head 300), a supply unit (for example, the circulation mechanism 200), and a control unit (for example, the control unit 21). The droplet ejection head ejects droplets of colored liquid. The supply unit supplies the colored liquid to the droplet ejection head. The control unit controls each unit. Furthermore, during at least a portion of a maintenance period following an ejection period in which droplets of colored liquid are ejected from the droplet ejection head, the control unit controls the supply unit to supply the droplet ejection head with colored liquid having a lower viscosity than the colored liquid during the ejection period. As a result, the droplet ejection device according to an embodiment can suppress ejection defects caused by retained matter in the droplet ejection head.

[0106] The colored liquid may be a pseudoplastic fluid whose viscosity decreases as the shear rate increases. The supply unit may be a circulation mechanism (e.g., circulation mechanism 200) that supplies the colored liquid to the droplet ejection head while controlling the circulation flow rate of the colored liquid circulating between the droplet ejection head and the supply unit. The control unit may also control the circulation mechanism during at least a portion of the maintenance period to increase the circulation flow rate of the colored liquid relative to the circulation flow rate of the colored liquid during the ejection period. In this way, by increasing the circulation flow rate of the colored liquid during the maintenance period following the ejection period relative to the circulation flow rate of the colored liquid during the ejection period, the viscosity of the colored liquid can be reduced compared to the viscosity of the colored liquid during the ejection period. This allows the droplet ejection device according to the embodiment to easily remove accumulated matter from the inner walls of the flow paths in the droplet ejection head.

[0107] The control unit may control the circulation mechanism to change the circulation flow rate of the colored liquid between a first period included in the maintenance period and a second period following the first period. By changing the circulation flow rate of the colored liquid in this way, a relatively low-viscosity colored liquid and a relatively high-viscosity colored liquid can be supplied to the droplet ejection head. As a result, according to the droplet ejection device of the embodiment, the relatively low-viscosity colored liquid can peel off any accumulated material from the inner walls of the flow paths in the droplet ejection head, and the relatively high-viscosity colored liquid can wash away any accumulated material remaining in the droplet ejection head.

[0108] The control unit may control the circulation mechanism to set the circulation flow rate of the colored liquid to a first flow rate during the first period, and to a second flow rate during the second period that is lower than the first flow rate. As a result, according to the droplet discharge device of the embodiment, the relatively low-viscosity colored liquid can peel off any accumulated material from the inner walls of the flow paths in the droplet discharge head, and then the relatively high-viscosity colored liquid can wash away any accumulated material remaining in the droplet discharge head.

[0109] The control unit may control the circulation mechanism to set the circulation flow rate of the colored liquid to a first flow rate during the first period, and to a second flow rate during the second period that is higher than the first flow rate. As a result, according to the droplet discharge device of the embodiment, the relatively high-viscosity colored liquid can flush out any remaining material inside the droplet discharge head, and then the relatively low-viscosity colored liquid can transport the remaining material to the downstream side of the flow path inside the droplet discharge head at high speed.

[0110] During a maintenance period, the control unit may control the circulation mechanism to stop the circulation of the coloring liquid for a predetermined time and then increase the circulating flow rate of the coloring liquid. As a result, according to the droplet ejection device of the embodiment, when the coloring liquid contains a soluble component capable of dissolving solidified coloring liquid, the solidified coloring liquid remaining in the droplet ejection head can be dissolved by the soluble component contained in the coloring liquid, and the dissolved solidified coloring liquid can be transported by the coloring liquid to the downstream side of the flow path in the droplet ejection head at high speed. The predetermined time may be, for example, the time required for the solidified coloring liquid remaining in the droplet ejection head to dissolve in the soluble component, but it may be shorter or longer.

[0111] The droplet ejection device according to the embodiment may further include a robot arm (for example, robot arm 100). The robot arm mounts the droplet ejection head so that its posture can be changed. The control unit may also control the circulation mechanism to increase the circulating flow rate of the colored liquid during at least a portion of the maintenance period, and may also control the robot arm to change the posture of the droplet ejection head. As a result, the droplet ejection device according to the embodiment can promote the movement of retained matter in the direction of gravity and in the direction opposite to the direction of gravity, thereby enabling the retained matter to be smoothly discharged outside the droplet ejection head.

[0112] The control unit may change the attitude of the droplet ejection head at the timing when the circulation flow rate of the colored liquid is increased. As a result, the droplet ejection device according to the embodiment can further promote the movement of the retained matter in the direction of gravity and in the direction opposite to the direction of gravity, and therefore can more smoothly discharge the retained matter to the outside of the droplet ejection head.

[0113] The droplet discharge head may have a supply port (e.g., supply port 321) for supplying colored liquid to the interior of the droplet discharge head, and a recovery port (e.g., recovery port 322) for recovering colored liquid from the interior of the droplet discharge head. The control unit may also change the attitude of the droplet discharge head so that one of the supply port and the recovery port is higher than the other. This allows the droplet discharge device according to the embodiment to smoothly discharge solidified colored liquid or air bubbles from the recovery port to the outside of the droplet discharge head.

[0114] The control unit may change the attitude of the droplet discharge head between an attitude in which one of the supply port and the recovery port is higher than the other, and an attitude in which the other of the supply port and the recovery port is higher than the other. As a result, according to the droplet discharge device of the embodiment, solidified colored liquid and air bubbles can be smoothly discharged from the recovery port to the outside of the droplet discharge head.

[0115] The droplet ejection head may have an ejection unit (e.g., ejection unit 305), a supply manifold (e.g., supply manifold 302), and a collection manifold (e.g., collection manifold 303). The ejection unit may include a nozzle (e.g., nozzle 351), a pressure chamber (e.g., pressure chamber 352), and a pressure unit (e.g., displacement element 353). The pressure chamber is connected to the nozzle. The pressure unit applies pressure to the pressure chamber to eject droplets of the colored liquid from the nozzle. The supply manifold is connected to the pressure chamber and supplies the colored liquid to the pressure chamber. The collection manifold is connected to the pressure chamber and collects the colored liquid from the pressure chamber. Furthermore, the control unit may control the circulation mechanism during at least a portion of the maintenance period to increase the circulating flow rate of the colored liquid while applying pressure to the pressure chamber using the pressure unit. This reduces the difference in viscosity between the colored liquid flowing through the pressure chamber and the colored liquid flowing through the manifold connected to the pressure chamber, making it easier for the pressure wave generated in the pressure chamber to propagate not only to the pressure chamber but also to the manifold. As a result, the droplet ejection device according to the embodiment can use the pressure wave to intensively remove material remaining in the manifold.

[0116] The droplet ejection head may have an ejection unit (e.g., ejection unit 305), a supply manifold (e.g., supply manifold 302), and a recovery manifold (e.g., recovery manifold 303). The ejection unit may include a nozzle (e.g., nozzle 351), a pressure chamber (e.g., pressure chamber 352), and a pressure unit (e.g., displacement element 353). The pressure chamber is connected to the nozzle. The pressure unit applies pressure to the pressure chamber to eject droplets of colored liquid from the nozzle. The supply manifold is connected to the pressure chamber and supplies the colored liquid, which is supplied from a supply port (e.g., supply port 321) of the droplet ejection head, to the pressure chamber. The recovery manifold is connected to the pressure chamber and recovers the colored liquid from the pressure chamber and delivers it to a recovery port (e.g., recovery port 322) of the droplet ejection head. The pressure chamber and the supply manifold may be connected via an individual supply channel (e.g., individual supply channel 354). The pressure chamber and the recovery manifold may be connected via an individual recovery flow path (e.g., individual recovery flow path 355). The flow path resistance of the individual recovery flow path may be smaller than the flow path resistance of the individual supply flow path. Furthermore, the control unit may control the circulation mechanism to circulate the colored liquid from the recovery port toward the supply port during at least a portion of the maintenance period. In this way, according to the droplet discharge device of the embodiment, the relatively high-viscosity colored liquid that accumulates at the tip portion of the supply manifold (e.g., tip portion 302a) can be replaced with a relatively low-viscosity colored liquid.

[0117] Further advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. [Explanation of symbols]

[0118] 1 Droplet discharge device 2. Control device 10 Foundations 21 Control Unit 22 Memory section 50 Objects 100 Robot Arm 110 Arm section 200 Circulation mechanism 201 Tank 202 Discharge pump 203 Suction Pump 204 First proportional valve 205 Second proportional valve 206 Heater 208 First pressure sensor 209 Second pressure sensor 210 Third pressure sensor 211 4th pressure sensor 212 Flowmeter 300 droplet ejection head 301 Supply Reservoir 302 Supply Manifold 303 Recovery Manifold 304 Recovery Reservoir 305 Discharge Unit 321 Supply Inlet 322 Collection port 351 Nozzle 352 Pressure Chamber 353 Displacement element 354 Individual supply channel 355 Individual collection channel 361 Main body 362 Descendants

Claims

1. a droplet ejection head that ejects droplets of colored liquid; a supply unit that supplies the coloring liquid to the droplet ejection head; a control unit that controls each unit; a robot arm that mounts the droplet discharge head in a position changeable manner; Equipped with the supply unit is a circulation mechanism that supplies the colored liquid to the droplet discharge head while controlling a circulation flow rate of the colored liquid circulating between the droplet discharge head and the supply unit; The control unit controlling the robot arm to change the attitude of the droplet discharge head during at least a part of a maintenance period following a discharge period in which droplets of the colored liquid are discharged from the droplet discharge head; The control unit During at least a part of the maintenance period, the circulation mechanism is controlled to increase the circulation flow rate of the colored liquid to be higher than the circulation flow rate of the colored liquid during the ejection period; The control unit The droplet ejection device changes the attitude of the droplet ejection head at the timing when the circulation flow rate of the colored liquid is increased.

2. The droplet ejection head includes: a supply port for supplying the coloring liquid into the droplet ejection head; a recovery port for recovering the colored liquid from inside the droplet discharge head; and The control unit The droplet ejection device according to claim 1 , wherein the attitude of the droplet ejection head is changed to an attitude in which one of the supply port and the recovery port is higher than the other during at least a part of the maintenance period.

3. The control unit The droplet ejection device according to claim 2, wherein during at least a portion of the maintenance period, the attitude of the droplet ejection head is changed between an attitude in which one of the supply port and the recovery port is higher than the other and an attitude in which the other of the supply port and the recovery port is higher than the one.

4. The control unit The droplet ejection device according to claim 2 , wherein the attitude of the droplet ejection head is changed to an attitude in which the recovery port is higher than the supply port during at least a part of the maintenance period.

5. The control unit The droplet ejection device according to claim 2 , wherein the attitude of the droplet ejection head is changed to an attitude in which the supply port is higher than the recovery port during at least a part of the maintenance period.

6. The control unit The droplet ejection device according to claim 1 , wherein the supply unit is controlled to supply, to the droplet ejection head, a colored liquid having a lower viscosity than the colored liquid during the ejection period, during at least a part of the maintenance period.

7. 2. The droplet ejection device according to claim 1, wherein the colored liquid is a pseudoplastic fluid whose viscosity decreases as the shear rate increases.

8. The control unit 2. The droplet ejection device according to claim 1, wherein the circulation mechanism is controlled to change the circulation flow rate of the colored liquid between a first period included in the maintenance period and a second period following the first period.

9. The control unit 9. The droplet ejection device according to claim 8, wherein the circulation mechanism is controlled to set the circulation flow rate of the colored liquid to a first flow rate during the first period, and to a second flow rate lower than the first flow rate during the second period.

10. The control unit 9. The droplet ejection device according to claim 8, wherein the circulation mechanism is controlled to set the circulation flow rate of the colored liquid to a first flow rate during the first period, and to a second flow rate higher than the first flow rate during the second period.

11. a droplet ejection head that ejects droplets of colored liquid; a supply unit that supplies the coloring liquid to the droplet ejection head; a control unit that controls each unit; a robot arm that mounts the droplet discharge head in a position changeable manner; Equipped with the supply unit is a circulation mechanism that supplies the colored liquid to the droplet discharge head while controlling a circulation flow rate of the colored liquid circulating between the droplet discharge head and the supply unit; The control unit controlling the robot arm to change the attitude of the droplet discharge head during at least a part of a maintenance period following a discharge period in which droplets of the colored liquid are discharged from the droplet discharge head; The control unit During at least a part of the maintenance period, the circulation mechanism is controlled to increase the circulation flow rate of the colored liquid to be higher than the circulation flow rate of the colored liquid during the ejection period; The control unit The droplet ejection device controls the circulation mechanism during the maintenance period to stop the circulation of the colored liquid for a predetermined time, and then increases the circulation flow rate of the colored liquid.

12. The droplet ejection head includes: a discharge unit including a nozzle, a pressure chamber connected to the nozzle, and a pressure unit that applies pressure to the pressure chamber to discharge droplets of the colored liquid from the nozzle; a supply manifold connected to the pressure chamber and supplying the coloring liquid to the pressure chamber; a recovery manifold connected to the pressure chamber and configured to recover the coloring liquid from the pressure chamber; and The control unit The droplet ejection device according to claim 1 , wherein the circulation mechanism is controlled to increase the circulation flow rate of the colored liquid during at least a portion of the maintenance period, while the pressurizing unit applies pressure to the pressurizing chamber.

13. a droplet ejection head that ejects droplets of colored liquid; a supply unit that supplies the coloring liquid to the droplet ejection head; a control unit that controls each unit; a robot arm that mounts the droplet discharge head in a position changeable manner; Equipped with the supply unit is a circulation mechanism that supplies the colored liquid to the droplet discharge head while controlling a circulation flow rate of the colored liquid circulating between the droplet discharge head and the supply unit; The droplet ejection head includes: a discharge unit including a nozzle, a pressure chamber connected to the nozzle, and a pressure unit that applies pressure to the pressure chamber to discharge droplets of the colored liquid from the nozzle; a supply manifold connected to the pressure chamber and configured to supply the colored liquid supplied from a supply port side of the droplet ejection head to the pressure chamber; a recovery manifold connected to the pressure chamber, which recovers the colored liquid from the pressure chamber and sends it to a recovery port side of the droplet discharge head; and the pressure chamber and the supply manifold are connected via individual supply passages, the pressure chamber and the recovery manifold are connected via individual recovery flow paths, a flow resistance of the individual recovery flow path is smaller than a flow resistance of the individual supply flow path, The control unit controlling the robot arm to change the attitude of the droplet discharge head during at least a part of a maintenance period following a discharge period in which droplets of the colored liquid are discharged from the droplet discharge head; The control unit The droplet ejection device controls the circulation mechanism to circulate the colored liquid from the recovery port toward the supply port during at least a part of the maintenance period.

14. a droplet ejection head that ejects droplets of colored liquid; a supply unit that supplies the coloring liquid to the droplet ejection head; a robot arm that mounts the droplet discharge head in a position changeable manner; A maintenance method for a droplet ejection device comprising: the supply unit is a circulation mechanism that supplies the colored liquid to the droplet discharge head while controlling a circulation flow rate of the colored liquid circulating between the droplet discharge head and the supply unit; controlling the robot arm to change the attitude of the droplet discharge head during at least a part of a maintenance period following a discharge period in which droplets of the colored liquid are discharged from the droplet discharge head; During at least a part of the maintenance period, the circulation mechanism is controlled to increase the circulation flow rate of the colored liquid to be higher than the circulation flow rate of the colored liquid during the ejection period; The maintenance method includes changing the attitude of the droplet ejection head at the timing when the circulation flow rate of the colored liquid is increased.

15. a droplet ejection head that ejects droplets of colored liquid; a supply unit that supplies the coloring liquid to the droplet ejection head; a robot arm that mounts the droplet discharge head in a position changeable manner; A maintenance method for a droplet ejection device comprising: the supply unit is a circulation mechanism that supplies the colored liquid to the droplet discharge head while controlling a circulation flow rate of the colored liquid circulating between the droplet discharge head and the supply unit; controlling the robot arm to change the attitude of the droplet discharge head during at least a part of a maintenance period following a discharge period in which droplets of the colored liquid are discharged from the droplet discharge head; During at least a part of the maintenance period, the circulation mechanism is controlled to increase the circulation flow rate of the colored liquid to be higher than the circulation flow rate of the colored liquid during the ejection period; a maintenance method in which, during the maintenance period, the circulation mechanism is controlled to stop the circulation of the coloring liquid for a predetermined time, and then the circulation flow rate of the coloring liquid is increased.

16. a droplet ejection head that ejects droplets of colored liquid; a supply unit that supplies the coloring liquid to the droplet ejection head; a robot arm that mounts the droplet discharge head in a position changeable manner; A maintenance method for a droplet ejection device comprising: the supply unit is a circulation mechanism that supplies the colored liquid to the droplet discharge head while controlling a circulation flow rate of the colored liquid circulating between the droplet discharge head and the supply unit; The droplet ejection head includes: a discharge unit including a nozzle, a pressure chamber connected to the nozzle, and a pressure unit that applies pressure to the pressure chamber to discharge droplets of the colored liquid from the nozzle; a supply manifold connected to the pressure chamber and configured to supply the colored liquid supplied from a supply port side of the droplet ejection head to the pressure chamber; a recovery manifold connected to the pressure chamber, which recovers the colored liquid from the pressure chamber and sends it to a recovery port side of the droplet discharge head; and the pressure chamber and the supply manifold are connected via individual supply passages, the pressure chamber and the recovery manifold are connected via individual recovery flow paths, a flow resistance of the individual recovery flow path is smaller than a flow resistance of the individual supply flow path, controlling the robot arm to change the attitude of the droplet discharge head during at least a part of a maintenance period following a discharge period in which droplets of the colored liquid are discharged from the droplet discharge head; A maintenance method comprising controlling the circulation mechanism to circulate the coloring liquid from the recovery port toward the supply port during at least a portion of the maintenance period.

17. The droplet ejection head includes: the supply port for supplying the coloring liquid to the inside of the droplet ejection head; a recovery port for recovering the colored liquid from inside the droplet discharge head; and The maintenance method according to claim 16 , wherein the attitude of the droplet ejection head is changed to an attitude in which one of the supply port and the recovery port is higher than the other during at least a part of the maintenance period.

18. The process of changing the attitude of the droplet ejection head includes: The maintenance method described in claim 17, wherein during at least a portion of the maintenance period, the attitude of the droplet ejection head is changed between an attitude in which one of the supply port and the recovery port is higher than the other and an attitude in which the other of the supply port and the recovery port is higher than the one.

19. The process of changing the attitude of the droplet ejection head includes: The maintenance method according to claim 17 , wherein the attitude of the droplet ejection head is changed to an attitude in which the recovery port is higher than the supply port during at least a part of the maintenance period.

20. The process of changing the attitude of the droplet ejection head includes: The maintenance method according to claim 17 , wherein the attitude of the droplet ejection head is changed to an attitude in which the supply port is higher than the recovery port during at least a part of the maintenance period.

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