Patent Description:
Inkjet printers and inkjet plotters that utilize an inkjet recording method are known as printing apparatuses. A liquid discharge head for discharging liquid is mounted in printing apparatuses using such an inkjet method.

In addition, in a device that discharges liquid, such as an inkjet printing apparatus, a technique for controlling discharge of liquid, a technique for preventing waste of liquid being discharged, a technique for efficiently replacing liquid, and the like have been proposed.

Moreover, <CIT> discloses a liquid supply mechanism including: a supply pathway that supplies liquid to a plurality of ejection sections each ejecting the liquid from nozzles; a branching path that is branched off from the supply pathway and through which the liquid circulates; a buffer unit that is disposed in the branching path and that lessens pressure fluctuations occurred in the liquid in the branching path; and a changing unit that changes a pathway to the buffer unit so that the changing unit shuts the pathway to the buffer unit during maintenance for discharging the liquid from the nozzles of the ejection sections.

The present invention provides a circulation device according to claim <NUM>. Preferred embodiments are described in the dependent claims.

Embodiments of a circulation device disclosed in the present application will be described in detail below with reference to the accompanying drawings. Note that the invention according to the present application is not limited to the embodiments that will be described below.

The circulation device disclosed in the present application can be applied to inkjet printers and inkjet plotters that each utilize an inkjet recording method as well as devices that each discharge liquid droplets in an inkjet method.

A configuration of a circulation device according to an embodiment will be described using <FIG> and <FIG>. <FIG> is a diagram schematically illustrating a configuration example of a circulation device according to an embodiment. <FIG> is a diagram schematically illustrating a configuration example of a circulation mechanism of a circulation device according to an embodiment.

As illustrated in <FIG> or <FIG>, a circulation device <NUM> includes a base <NUM>, a tank <NUM>, a discharge pump <NUM>, a suction pump <NUM>, a first proportional valve <NUM>, a second proportional valve <NUM>, and a heater <NUM>. As illustrated in <FIG> or <FIG>, the circulation device <NUM> also includes a first pressure sensor <NUM>, a second pressure sensor <NUM>, a third pressure sensor <NUM>, a fourth pressure sensor <NUM>, a liquid droplet discharge head <NUM>, and a robotic portion <NUM>. As illustrated in <FIG>, the circulation device <NUM> having such a configuration controls circulation of the liquid fed from the tank <NUM> to the liquid droplet discharge head <NUM>.

The base <NUM> is placed, for example, on a horizontal floor surface indoors or outdoors. The base <NUM> is provided with the tank <NUM> that stores liquid. This can prevent rocking of the surface of the liquid stored in the tank <NUM>.

The robotic portion <NUM> assembled on the base <NUM> includes an arm portion <NUM>. The arm portion <NUM> is formed of a plurality of parts that are bent and stretched, and rotatably assembled. In accordance with a predetermined command, the arm portion <NUM> can, for example, move the liquid droplet discharge head <NUM> mounted on a tip of the arm portion <NUM> and change the position, posture, and angle of the liquid droplet discharge head <NUM>. The arm portion <NUM> illustrated in <FIG> is not particularly limited to the configuration illustrated in <FIG> as long as the arm portion <NUM> is provided with a degree of freedom with which the liquid droplet discharge head <NUM> can change the movement, position, posture, angle, and the like as necessary.

The discharge pump <NUM> and the suction pump <NUM> are provided on a root side of the arm portion <NUM> including the robotic portion <NUM> assembled on the base <NUM>. In the circulation device <NUM>, pulsation is likely to be caused by the discharge pump <NUM> and the suction pump <NUM>. The circulation device <NUM> according to an embodiment includes the first proportional valve <NUM> and the second proportional valve <NUM>, which are described below, and thereby absorbs the pulsation by the discharge pump <NUM> and the suction pump <NUM>.

The first proportional valve <NUM>, as illustrated in <FIG>, is interposed in a first channel RT<NUM> between the discharge pump <NUM> and the liquid droplet discharge head <NUM>, and as illustrated in <FIG>, is provided on a tip side of the arm portion <NUM> including the liquid droplet discharge head <NUM> assembled on the robotic portion <NUM>. The second proportional valve <NUM>, as illustrated in <FIG>, is interposed in a second channel RT<NUM> between the suction pump <NUM> and the liquid droplet discharge head <NUM>, and as illustrated in <FIG>, is provided on the tip side of the arm portion <NUM> including the liquid droplet discharge head <NUM> assembled on the robotic portion <NUM>. The first proportional valve <NUM> and the second proportional valve <NUM> can be mounted on the arm portion <NUM> by being disposed in a frame member (not illustrated) provided at the tip of the arm portion <NUM>. This strengthens the fixing of the first proportional valve <NUM> and the second proportional valve <NUM>.

Additionally, the first proportional valve <NUM> and the second proportional valve <NUM> are mounted on the tip side of the arm portion <NUM> including the liquid droplet discharge head <NUM> assembled thereupon, thereby providing a degree of distance between the discharge pump <NUM> and the suction pump <NUM>, and the liquid droplet discharge head <NUM>. Thus, the circulation device <NUM> is less likely to transmit pulsation by the discharge pump <NUM> and the suction pump <NUM> to the liquid droplet discharge head <NUM>. Furthermore, the circulation device <NUM> can suppress as much as possible the pulsation that reaches the liquid droplet discharge head <NUM> by the first proportional valve <NUM> and the second proportional valve <NUM>.

The heater <NUM> is provided, for example, inside the tank <NUM> and inside the liquid droplet discharge head <NUM>. Note that the heater <NUM> may be provided adjacent to the tank <NUM> instead of inside the tank <NUM> as long as the heat of the heater <NUM> is transmitted to the tank <NUM>. Likewise, the heater <NUM> may be provided adjacent to the liquid droplet discharge head <NUM> instead of inside the liquid droplet discharge head <NUM> as long as the heat of the heater <NUM> is transmitted to the liquid droplet discharge head <NUM>. Furthermore, the heater <NUM> may be provided in either one of the tank <NUM> and the liquid droplet discharge head <NUM>.

<FIG> illustrates an example in which the discharge pump <NUM> and the suction pump <NUM> are mounted on the root side of the arm portion <NUM> including the robotic portion <NUM> assembled on the base <NUM>, but the configuration may not be particularly limited to this example. A modified example of the mounting positions of the discharge pump <NUM> and the suction pump <NUM> will be described using <FIG> is a diagram schematically illustrating a configuration example of a circulation device according to a modified example.

For example, as illustrated in <FIG>, the circulation device <NUM> may be provided with the discharge pump <NUM> and the suction pump <NUM> at an intermediate position in the vicinity of a midpoint between the tip of the arm portion <NUM> and the root thereof. As illustrated in <FIG>, the discharge pump <NUM> and the suction pump <NUM> may be provided at an intermediate position of the arm portion <NUM>, thereby increasing the output efficiency of the pumps compared to a case, as illustrated in <FIG>, where the pumps are provided on the root side of the arm portion <NUM>. Note that at least one of the discharge pump <NUM> and the suction pump <NUM> may be provided at an intermediate position in the vicinity of a midpoint between the tip of the arm portion <NUM> and the root thereof.

<FIG> explains an example in which the first proportional valve <NUM> is interposed in the first channel RT<NUM> between discharge pump <NUM> and the liquid droplet discharge head <NUM> and the second proportional valve <NUM> is interposed in the second channel RT<NUM> between the suction pump <NUM> and the liquid droplet discharge head <NUM>. However, the configuration may not be particularly limited to this example. A modified example of the mounting positions of the first proportional valve <NUM> and the second proportional valve <NUM> will be described below using <FIG> is a diagram schematically illustrating a configuration example of a circulation mechanism of a circulation device according to a modified example.

As illustrated in <FIG>, the first proportional valve <NUM> and the second proportional valve <NUM> may be housed inside the liquid droplet discharge head <NUM>. As illustrated in <FIG>, the first proportional valve <NUM> and the second proportional valve <NUM> may be closer to the liquid droplet discharge head <NUM> than in the example illustrated in <FIG>, thereby improving response to pulsation by the pumps. Note that at least one of the first proportional valve <NUM> and the second proportional valve <NUM> may be housed inside the liquid droplet discharge head <NUM>.

Additionally, the first proportional valve <NUM> and the second proportional valve <NUM> are each preferably provided, as illustrated in <FIG>, on the tip side of the arm portion <NUM>, but as long as the first proportional valve <NUM> and the second proportional valve <NUM> are interposed in the first channel RT<NUM> and the second channel RT<NUM>, respectively, an effect of suppressing the transmission of the pulsation to the liquid droplet discharge head <NUM> can be expected. Note that at least one of the first proportional valve <NUM> and the second proportional valve <NUM> may be provided on the tip side of the arm portion <NUM>.

Furthermore, the circulation device <NUM> may include a single pump that integrates the discharge pump <NUM> and the suction pump <NUM> as a mechanism for circulating liquid. Also, a proportional valve for controlling the flow rate of the liquid is disposed on a discharge side of the liquid between the discharge pump <NUM> and the liquid droplet discharge head <NUM>. Alternatively, a proportional valve for controlling the flow rate of the liquid is disposed on a recovery side of the liquid between the discharge pump <NUM> and the liquid droplet discharge head <NUM>. Thus, even in a configuration including the pump that integrates the discharge pump <NUM> and the suction pump <NUM>, the pulsation caused by the pump is less likely to be transferred to the liquid droplet discharge head <NUM>.

Also, the tank <NUM> and the liquid droplet discharge head <NUM> may be configured to be heat-resistant. Such a configuration is less susceptible to fluctuations in the outside temperature, and the thermal efficiency of the heater <NUM> can be expected to improve.

An example of a functional configuration of the circulation device <NUM> according to an embodiment will be described using <FIG> is a diagram illustrating an example of a functional configuration of a circulation device according to an embodiment.

Note that <FIG> illustrates an example of a functional configuration of the circulation device <NUM> according to an embodiment, and the functional configuration of the circulation device <NUM> should not be particularly limited to the example illustrated in <FIG>, provided that the functions of the circulation device <NUM> according to the embodiment can be realized. In addition, <FIG> illustrates, in functional blocks, components provided in the circulation device <NUM> according to the embodiment and omits a description of other components in general. Moreover, the components of the circulation device <NUM> illustrated in <FIG> are functional concepts and are not limited to the example illustrated in <FIG>, and are not necessarily physically configured as illustrated. For example, the specific form of distribution and integration of each of the functional blocks is not limited to that illustrated, and all or a portion thereof can be functionally or physically distributed and integrated in any unit, depending on various loads, usage conditions, and the like.

As illustrated in <FIG>, the circulation device <NUM> includes a tank <NUM>, a discharge pump <NUM>, a suction pump <NUM>, a first proportional valve <NUM>, a second proportional valve <NUM>, and a heater <NUM>. The circulation device <NUM> also includes an input/output interface <NUM>, the first pressure sensor <NUM>, the second pressure sensor <NUM>, the third pressure sensor <NUM>, the fourth pressure sensor <NUM>, a flowmeter <NUM>, and the liquid droplet discharge head <NUM>. The circulation device <NUM> further includes a storage <NUM>, a processor <NUM>, and the robotic portion <NUM>.

The circulation device <NUM> illustrated in <FIG> includes the first channel RT<NUM> and the second channel RT<NUM> (see <FIG>). The first channel RT<NUM> is a channel that allows the liquid stored in the tank <NUM> to flow into the liquid droplet discharge head <NUM>. The second channel RT<NUM> is a channel communicating the tank <NUM> and the liquid droplet discharge head <NUM> with each other to allow the liquid that has flowed into the liquid droplet discharge head <NUM> to return to the tank <NUM>. The liquid recovered in the liquid droplet discharge head <NUM> without being discharged from the liquid droplet discharge head <NUM> to the outside is sent back through the second channel RT<NUM> to the tank <NUM>. The first channel RT<NUM> and the second channel RT<NUM> can be implemented, for example, by a pipe formed of a predetermined material that does not interact with constituents of the liquid. The circulation device <NUM> having such components controls the circulation of the liquid fed from the tank <NUM> to the liquid droplet discharge head <NUM>.

The tank <NUM> stores the liquid supplied to the liquid droplet discharge head <NUM>. The tank <NUM> functions as a storage unit for storing the liquid supplied to the liquid droplet discharge head <NUM>.

The discharge pump <NUM> functions as a first pressure portion that feeds the liquid stored in the tank <NUM> to the liquid droplet discharge head <NUM> through the first channel RT<NUM>. The discharge pump <NUM> generates positive pressure for feeding the liquid stored in the tank <NUM> to the liquid droplet discharge head <NUM>. The discharge pump <NUM> feeds the liquid from the tank <NUM> to the liquid droplet discharge head <NUM> at a predetermined constant pressure.

The suction pump <NUM> functions as a second pressure portion that feeds the liquid recovered in the liquid droplet discharge head <NUM> to the tank <NUM> through the second channel RT<NUM>. The suction pump <NUM> generates negative pressure for sucking the liquid from the liquid droplet discharge head <NUM> and sending the liquid back to the tank <NUM>. The suction pump <NUM> sends the liquid back to the tank <NUM> from the liquid droplet discharge head <NUM> at a predetermined constant pressure.

The discharge pump <NUM> and the suction pump <NUM> can be implemented by a rotary pump such as a gear pump or a positive displacement pump such as a diaphragm pump.

The first proportional valve <NUM> functions as a first valve portion interposed in the first channel RT<NUM> between the tank <NUM> and the liquid droplet discharge head <NUM>. The first proportional valve <NUM> proportionally controls the flow rate of the liquid fed from the tank <NUM> to the liquid droplet discharge head <NUM>. The first proportional valve <NUM> can continuously modify the channel cross-sectional area for the liquid between <NUM> to <NUM>%, and controls the flow rate of the liquid to a desired flow rate. For example, the first proportional valve <NUM> can reduce the channel cross-sectional area of the liquid and thereby suppress the pulsation generated in the liquid by the discharge pump <NUM>.

The second proportional valve <NUM> functions as a second valve portion interposed in the second channel RT<NUM> between the tank <NUM> and the liquid droplet discharge head <NUM>. The second proportional valve <NUM> proportionally controls the flow rate of the liquid fed from the liquid droplet discharge head <NUM> to the tank <NUM>. The second proportional valve <NUM> can continuously modify the channel cross-sectional area for the liquid between <NUM> to <NUM>%, and controls the flow rate of the liquid to a desired flow rate. For example, the second proportional valve <NUM> can reduce the channel cross-sectional area of the liquid and thereby reduce the pulsation generated in the liquid by the suction pump <NUM>.

The first proportional valve <NUM> and the second proportional valve <NUM> can be implemented by a proportional selector valve of an electromagnetic type or a proportional selector valve of a pneumatic type.

The heater <NUM> heats the liquid stored in the tank <NUM> and the liquid circulating through the liquid droplet discharge head <NUM>.

The input/output interface <NUM> exchanges various types of information with the robotic portion <NUM>. The input/output interface <NUM> can transmit a control signal for causing the robotic portion <NUM> to perform a predetermined operation.

The first pressure sensor <NUM> measures, by the discharge pump <NUM>, the fluid pressure of the liquid fed from the tank <NUM> to the liquid droplet discharge head <NUM>. The first pressure sensor <NUM> measures the pressure downstream of the discharge pump <NUM> in a circulation direction of the liquid in the circulation device <NUM>. The first pressure sensor <NUM> sends the measurement results to the processor <NUM>.

The second pressure sensor <NUM> measures the fluid pressure of the liquid that is sucked from the liquid droplet discharge head <NUM> by the suction pump <NUM> and fed to the tank <NUM>. The second pressure sensor <NUM> measures the pressure upstream of the suction pump <NUM> in the circulation direction of the liquid in the circulation device <NUM>. The second pressure sensor <NUM> sends the measurement results to the processor <NUM>.

The third pressure sensor <NUM> measures, through the first channel RT<NUM>, the fluid pressure of the liquid flowing between the first proportional valve <NUM> and the liquid droplet discharge head <NUM>. The third pressure sensor <NUM> measures the fluid pressure of the liquid immediately before the liquid flows into the liquid droplet discharge head <NUM> after passing through the first proportional valve <NUM>. That is, the third pressure sensor <NUM> measures the fluid pressure downstream of the first proportional valve <NUM> in the circulation direction of the liquid in the circulation device <NUM>. The third pressure sensor <NUM> sends the measurement results to the processor <NUM>.

The fourth pressure sensor <NUM> measures, through the second channel RT<NUM>, the fluid pressure of the liquid flowing between the second proportional valve <NUM> and the liquid droplet discharge head <NUM>. The fourth pressure sensor <NUM> measures the fluid pressure of the liquid immediately after being fed from the liquid droplet discharge head <NUM> toward the tank <NUM> and before passing through the second proportional valve <NUM>. That is, the fourth pressure sensor <NUM> measures the pressure upstream of the second proportional valve <NUM> in the circulation direction of the liquid in the circulation device <NUM>. The fourth pressure sensor <NUM> sends the measurement results to the processor <NUM>.

The flowmeter <NUM> measures the flow rate of the liquid fed to the liquid droplet discharge head <NUM>. The flowmeter <NUM> sends the measurement results to the processor <NUM>.

The liquid droplet discharge head <NUM> discharges the liquid fed from the tank <NUM> toward the object <NUM> illustrated in <FIG>. The liquid droplet discharge head <NUM> recovers the liquid that is not discharged and feeds the liquid thus recovered to the tank <NUM>.

The storage <NUM> stores programs and data necessary for various processes of the circulation device <NUM>. The storage <NUM> includes, for example, a robot control data storage unit <NUM>, a pump control data storage unit <NUM>, and a flow rate control data storage unit <NUM>.

The robot control data storage unit <NUM> stores control programs, data, and the like for controlling the operation of the arm portion <NUM> included in the robotic portion <NUM>. The data stored in the robot control data storage unit <NUM> stores, for example, data such as an operation procedure for the liquid droplet discharge head <NUM> and a movement direction, position, posture, and angle during the operation thereof (liquid discharge).

The pump control data storage unit <NUM> stores data, set in advance, for pump control. The data for pump control includes, for example, a set value of pressure (positive pressure) applied to the liquid that the discharge pump <NUM> feeds, a set value of pressure (negative pressure) applied to the liquid that the suction pump <NUM> sucks, and the like. When considering the discharge of liquid from the liquid droplet discharge head <NUM>, the positive pressure of the discharge pump <NUM> is preset to, for example, a value approximately <NUM> to <NUM> times higher than the pressure at which the liquid is supplied to the liquid droplet discharge head <NUM>. In contrast, the negative pressure of the suction pump <NUM> is preset to a value approximately <NUM> to <NUM> times lower than the pressure at which the liquid is supplied to the liquid droplet discharge head <NUM>.

The flow rate control data storage unit <NUM> stores flow rate control data for controlling the flow rate of the liquid circulating between the tank <NUM> and the liquid droplet discharge head <NUM>. <FIG> is a diagram illustrating an overview of flow rate control data according to an embodiment.

As illustrated in <FIG>, the flow rate control data stored in the flow rate control data storage unit <NUM> includes an item of a control target and an item of a target value, and these items are associated with each other. In the item of a control target, either the first proportional valve <NUM> or the second proportional valve <NUM>, which is a control target, is registered. A target value in controlling the flow rate of the liquid is registered as the target value. Note that the target value corresponding to each of the first proportional valve <NUM> and the second proportional valve <NUM> may be the same or different. For example, a target value of an average flow rate in a certain time period may be set for each of the first proportional valve <NUM> and the second proportional valve <NUM>. Further, for example, a target value of <NUM>% of the maximum flow rate may be set with respect to the first proportional valve <NUM>, and a target value of an average flow rate in a certain time period may be set with respect to a target value of the second proportional valve <NUM>.

The processor <NUM> executes various processes in the circulation device <NUM> in accordance with programs, data, and the like that are stored in the storage <NUM>. The processor <NUM> implements various functions for controlling the components of the circulation device <NUM> by reading out and executing the computer program stored in the storage <NUM>.

The processor <NUM> controls the operation of the arm portion <NUM> included in the robotic portion <NUM> in accordance with control programs, data, or the like that are stored in the robot control data storage unit <NUM>. The processor <NUM> causes the arm portion <NUM> to execute a desired operation by outputting a command to control the operation of the arm portion <NUM> to an actuator or the like that drives the arm portion <NUM>.

The processor <NUM> makes an adjustment to keep constant the positive pressure applied to the liquid that the discharge pump <NUM> feeds in accordance with the measurement results of the first pressure sensor <NUM> and the measurement results of the third pressure sensor <NUM>. For example, the processor <NUM> adjusts the positive pressure of the discharge pump <NUM> such that the pressure of the liquid obtained from the measurement results of the first pressure sensor <NUM> remains approximately <NUM> to <NUM> times larger than the pressure of the liquid obtained from the measurement results of the measurement results of the third pressure sensor <NUM>.

The processor <NUM> also makes an adjustment to keep constant the negative pressure applied to the liquid that the suction pump <NUM> sucks in accordance with the measurement results of the second pressure sensor <NUM> and the third pressure sensor <NUM>. For example, the processor <NUM> adjusts the negative pressure of the suction pump <NUM> such that the pressure of the liquid obtained from the measurement results of the second pressure sensor <NUM> remains approximately <NUM> to <NUM> times lower than the pressure of the liquid obtained from the measurement results of the measurement results of the third pressure sensor <NUM>.

The processor <NUM> circulates the liquid between the tank <NUM> and the liquid droplet discharge head <NUM> by adjusting and keeping constant the differential pressure between the positive pressure that the discharge pump <NUM> applies to the liquid and the negative pressure that the suction pump <NUM> applies to the liquid.

The processor <NUM> controls the flow rate of the liquid passing through the first proportional valve <NUM> and the second proportional valve <NUM> in accordance with flow rate control data stored in the flow rate control data storage unit <NUM>. An example of a method for controlling the flow rate by the processor <NUM> will be described below using <FIG> is a diagram schematically illustrating an example of a relationship between a flow rate of a liquid and time according to an embodiment.

<FIG> schematically illustrates an example of a relationship between: an instantaneous flow rate of the liquid circulating between the tank <NUM> and the liquid droplet discharge head <NUM>; and time. As illustrated in <FIG>, in the liquid circulating between the tank <NUM> and the liquid droplet discharge head <NUM>, a pulse is generated by liquid supply by the discharge pump <NUM> and by liquid recovery by the suction pump <NUM>.

Suppose, for example, that in the flow rate control data, a target value MV1 has been set for the third pressure sensor <NUM>, the target value MV1 being that a maximum flow rate "Qmax" be changed to an average flow rate per time period "Qave". The processor <NUM>, while referring to the measurement results of the third pressure sensor <NUM>, adjusts the flow rate of the liquid passing through the first proportional valve <NUM> by narrowing the channel cross-sectional area of the first proportional valve <NUM> so as to approximate the target value MV1. This allows the processor <NUM> to control the flow rate of the liquid passing through the first proportional valve <NUM> and the second proportional valve <NUM>. The processor <NUM> can, by such a control, reduce the pressure of the liquid supplied to the liquid droplet discharge head <NUM> and suppress pulsation.

The first proportional valve <NUM> is interposed in the first channel RT<NUM> between the discharge pump <NUM> and the liquid droplet discharge head <NUM> and disposed, for example, on the tip side of the arm portion <NUM> including the liquid droplet discharge head <NUM> assembled on the robotic portion <NUM>. The second proportional valve <NUM> is interposed in the second channel RT<NUM> between the suction pump <NUM> and the liquid droplet discharge head <NUM> and disposed, for example, on the tip side of the arm portion <NUM> including the liquid droplet discharge head <NUM> assembled on the robotic portion <NUM>. The processor <NUM> also controls the flow rate of the first proportional valve <NUM> and the second proportional valve <NUM> in accordance with the flow rate control data. Thus, the circulation device <NUM> according to the embodiment can suppress the transmission, to the liquid droplet discharge head <NUM>, of the pulsation caused by the discharge pump <NUM> and the suction pump <NUM>, and can suppress the pulsation by the discharge pump <NUM> and the suction pump <NUM>.

In addition, the applicant of the present application has discovered a phenomenon in which, in a printing operation using the above-described circulation device <NUM>, correct printing is not performed due to non-discharge of liquid (ink) or leakage of liquid occurs from the liquid droplet discharge head <NUM> after solid printing in which liquid is continuously discharged. <FIG> is a diagram illustrating measurement results of circulation pressure of a liquid during printing according to an embodiment. The vertical axis on the left side of <FIG> indicates the supply pressure, and the vertical axis on the right side of <FIG> indicates the recovery pressure. The horizontal axis in <FIG> indicates time, and time flows to the right side of <FIG>. The upper line in the graph region of <FIG> indicates a time-series change in the supply pressure, and the lower line in the graph region of <FIG> indicates a time-series change in the recovery pressure.

As illustrated in <FIG>, the supply pressure and the recovery pressure during circulation of the liquid before the liquid is discharged have a substantially constant value. Then, the supply pressure and the recovery pressure of the liquid are reduced together from the start to the completion of continuous liquid discharge that occurs in solid printing. After the completion of the discharge, the supply pressure and the recovery pressure of the liquid begin to increase gradually. The phenomenon of non-discharge of liquid or the like occurs when the discharge of liquid resumes with the supply pressure and the recovery pressure being still not fully recovered.

The applicant of the present application infers a mechanism that causes the phenomenon of non-discharge of liquid as follows. Even after the completion of discharge, the liquid continues to flow from the supply side toward the recovery side, but when the recovery pressure is reduced, the second proportional valve <NUM> is configured to be closed. The applicant of the present application infers that this causes water-hammering action (water hammer) by the liquid that is not discharged and has lost an outlet, resulting in leakage of the liquid from the nozzle and the non-discharge thereof. Thus, the applicant of the present application solves the above-described problem by causing the processor <NUM> of the circulation device <NUM> to execute a control method as described below.

As illustrated in <FIG>, the applicant of the present application has gained the insight that when a time tx has elapsed after the completion of liquid discharge, the recovery pressure recovers to a set value in a steady state (e. , liquid circulation). In the example illustrated in <FIG>, approximately <NUM> [msec (milliseconds)] after the completion of discharge, the recovery pressure recovers to approximately -<NUM> kPa (kilopascals), which is an initial value at the time of liquid discharge. Thus, the processor <NUM> is configured to execute control on the basis of this insight. Specifically, after the completion of liquid discharge, the processor <NUM> performs control to tighten the first proportional valve <NUM> on the supply side of the liquid, and to tighten the second proportional valve <NUM> after a predetermined amount of time elapses. Thus, the second proportional valve <NUM> on the recovery side of the liquid is left open at least until the predetermined amount of time elapses, and the liquid can flow to the recovery side. This can prevent the non-discharge of liquid due to the water-hammering action or the leakage of liquid.

In addition, upon the completion of the discharge of liquid from the liquid droplet discharge head <NUM>, the processor <NUM> may control the pressure on the recovery side recovering the liquid such that the pressure is lower than the set value in the steady state. Thus, the force pulling the liquid from the recovery side of the liquid can be increased, and the liquid flows efficiently to the recovery side. This can prevent the non-discharge of liquid due to the water-hammering action or the leakage of liquid.

Additionally, upon the completion of the discharge of the liquid from the liquid droplet discharge head <NUM>, the processor <NUM> may control the pressure on the recovery side recovering the liquid such that the pressure is lower by the amount of the pressure drop due to the discharge of the liquid. In the example illustrated in <FIG>, the pressure drop on the recovery side is approximately <NUM> [kPa (kilopascals)], and it is only required that the processor <NUM> control the pressure on the recovery side recovering the liquid after the completion of the liquid discharge such that the pressure is lower by <NUM> [kPa (kilopascals)], which is generated by the discharge of the liquid. This can prevent the non-discharge of liquid due to the water-hammering action and the leakage of liquid in the same manner as the control to tighten the second proportional valve <NUM>.

Note that the tank <NUM> may or may not be provided in the base <NUM>, or may be provided at a location other than in the robotic portion <NUM>. Also, the discharge pump <NUM> and the suction pump <NUM> may be provided in the base <NUM>.

Claim 1:
A circulation device (<NUM>) for controlling liquid circulation, the circulation device (<NUM>) comprising:
a storage unit (<NUM>) configured to store a liquid;
a liquid droplet discharge unit configured to discharge the liquid;
a robotic portion (<NUM>) mounted with the liquid droplet discharge unit;
a first pressure portion (<NUM>) configured to feed the liquid stored in the storage unit (<NUM>) to the liquid droplet discharge unit through a first channel;
a second pressure portion (<NUM>) configured to feed the liquid recovered in the liquid droplet discharge unit to the storage unit (<NUM>) through a second channel;
a first proportional valve (<NUM>) interposed between the first pressure portion (<NUM>) and the liquid droplet discharge unit;
a second proportional valve (<NUM>) interposed between the second pressure portion (<NUM>) and the liquid droplet discharge unit; and
a processor (<NUM>) configured to control a flow rate of the first proportional valve (<NUM>) and the second proportional valve (<NUM>) in accordance with flow rate control data, wherein the first proportional valve (<NUM>) and the second proportional valve (<NUM>) continuously modify the respective channel cross-sectional area for the liquid between <NUM> to <NUM>% and control a flow rate of the liquid to a desired flow rate.