Patent Description:
A liquid coating apparatus is known in which a liquid supplied from a liquid storage unit is discharged to a material to be coated. Such a liquid coating apparatus changes the volume of a liquid chamber to discharge a liquid in the liquid chamber. <CIT> discloses an example of the liquid coating apparatus, in which the volume of a liquid chamber containing a liquid is changed using a flexible plate that is deformed by driving a piezoelectric element, thereby discharging the liquid through a nozzle. CITATIONS LIST PATENT LITERATURE.

<CIT> discloses a liquid coating apparatus according to the preamble of claim <NUM>. Documents <CIT>; <CIT>; <CIT> and <CIT> disclose further relevant background art.

In the case of a configuration in which a piezoelectric element is driven to deform a flexible body, as in the configuration disclosed in Patent Literature 1it is conceivable to input a rectangular signal to the piezoelectric element to operate the piezoelectric element at a high speed in order to enhance responsiveness of liquid discharge.

Unfortunately, when a drive element including the piezoelectric element is operated at a high speed, the drive element may excessively expand and contract, and then an excessive load may be applied to the drive element. This may affect the life of the drive element.

It is an object of the present invention to provide a liquid coating apparatus capable of preventing an excessive load at a level affecting the life of a drive element from being applied to the drive element, even when the drive element is operated at a high speed.

A liquid coating apparatus according to an embodiment of the present invention includes: a liquid chamber that stores a liquid; an inflow path that is connected to the liquid chamber to allow the liquid to be supplied into the liquid chamber; a diaphragm that constitutes a part of a wall portion defining the liquid chamber and is deformed to change a volume of the liquid chamber; a drive element that expands and contracts in at least one direction to deform the diaphragm in a thickness direction; a first support portion that is located between the drive element and the diaphragm in the one direction to support the drive element on a diaphragm side; a second support portion that supports an end of the drive element on an opposite side to the diaphragm in the one direction; a transmission member that extends in the one direction between the drive element and the diaphragm and passes through the first support portion to transmit expansion and contraction of the drive element to the diaphragm; and a compressive force applying unit that is located between the drive element and the first support portion and supported by the first support portion to apply a compressive force to the drive element in the one direction.

The liquid coating apparatus according to one embodiment of the present invention enables preventing an excessive load at a level affecting the life of a drive element from being applied to the drive element even when the drive element is operated at a high speed.

The same or corresponding parts in the drawings are designated by the same reference numerals, and description thereof will not be duplicated. Each of the drawings shows dimensions of components that do not faithfully represent actual dimensions of the components and dimensional ratios of the respective components.

<FIG> is a diagram schematically illustrating a schematic configuration of a liquid coating apparatus <NUM> according to an embodiment of the present invention. <FIG> is a flowchart illustrating operation of the liquid coating apparatus <NUM>.

The liquid coating apparatus <NUM> is an ink-jet liquid coating apparatus that discharges a liquid in the form of droplets to the outside. Examples of the liquid include solder, thermosetting resin, ink, and a coating liquid for forming a functional thin film such as an alignment film, a resist, a color filter, and organic electroluminescence.

The liquid coating apparatus <NUM> includes a liquid storage unit <NUM>, a pressure adjusting unit <NUM>, a discharge unit <NUM>, and a control unit <NUM>.

The liquid storage unit <NUM> is a container for storing a liquid inside. The liquid storage unit <NUM> supplies the stored liquid to the discharge unit <NUM>. That is, the liquid storage unit <NUM> includes an outlet 10a for supplying the stored liquid to the discharge unit <NUM>. Pressure in the liquid storage unit <NUM> is adjusted by the pressure adjusting unit <NUM>. The liquid storage unit <NUM> includes a supply port (not illustrated) through which a liquid is supplied thereto.

The pressure adjusting unit <NUM> adjusts the pressure in the liquid storage unit <NUM> to any one of positive pressure higher than an atmospheric pressure, negative pressure lower than the atmospheric pressure, and the atmospheric pressure. When the pressure in the liquid storage unit <NUM> is adjusted in this way, as described later, a liquid can be stably discharged from a discharge port 32a of the discharge unit <NUM>, and the liquid can be prevented from leaking from the discharge port 32a.

Specifically, the pressure adjusting unit <NUM> includes a positive pressure generator <NUM>, a negative pressure generator <NUM>, a first switching valve <NUM>, a second switching valve <NUM>, an atmospheric opening unit <NUM>, and a pressure sensor <NUM>.

The positive pressure generator <NUM> generates positive pressure higher than the atmospheric pressure. The positive pressure generator <NUM> includes a positive pressure pump 21a as a positive pressure generation unit. The positive pressure pump 21a generates positive pressure.

The negative pressure generator <NUM> generates negative pressure lower than the atmospheric pressure. The negative pressure generator <NUM> includes a negative pressure pump 22a as a negative pressure generation unit, and a negative pressure adjusting container 22b.

The negative pressure pump 22a generates negative pressure. Pressure inside the negative pressure adjusting container 22b becomes the negative pressure generated by the negative pressure pump 22a. The negative pressure adjusting container 22b is located between the negative pressure pump 22a and a second switching valve <NUM>. When the negative pressure generator <NUM> includes the negative pressure adjusting container 22b, the negative pressure generated by the negative pressure pump 22a is uniformed.

This enables, not only reducing pulsation of the negative pressure generated by the negative pressure pump 22a, but also acquiring a stable negative pressure in the negative pressure generator <NUM>. As described later, even when output of the negative pressure pump 22a changes in accordance with a detection result of pressure in the liquid storage unit <NUM> acquired by the pressure sensor <NUM>, the negative pressure adjusting container 22b reduces pulsation of negative pressure generated by the negative pressure pump 22a, and uniform pressure can be acquired under the negative pressure having changed. Thus, when the negative pressure generator <NUM> is connected to the liquid storage unit <NUM> as described later, pressure in the liquid storage unit <NUM> can be quickly set to negative pressure.

The first switching valve <NUM> and the second switching valve <NUM> are each a three-way valve. That is, the first switching valve <NUM> and the second switching valve <NUM> each have three ports. The first switching valve <NUM> includes the three ports that are each connected to the corresponding one of the liquid storage unit <NUM>, the positive pressure generator <NUM>, and the second switching valve <NUM>. The second switching valve <NUM> includes the three ports that are each connected to the corresponding one of the negative pressure generator <NUM>, the atmospheric opening unit <NUM>, and the first switching valve <NUM>.

The first switching valve <NUM> and the second switching valve <NUM> each allow two ports of the corresponding three ports to be internally connected to each other. In the present embodiment, the first switching valve <NUM> allows the port connected to the liquid storage unit <NUM> to be connected to the port connected to the positive pressure generator <NUM> or the port connected to the second switching valve <NUM>. That is, the first switching valve <NUM> switches between a line connected to the positive pressure generator <NUM> and a line connected to the second switching valve <NUM> to connect the switched line to the liquid storage unit <NUM>. The second switching valve <NUM> allows the port connected to the first switching valve <NUM> to be connected to the port connected to the negative pressure generator <NUM> or the port connected to the atmospheric opening unit <NUM>. That is, the second switching valve <NUM> switches between a line connected to the negative pressure generator <NUM> and a line connected to the atmospheric opening unit <NUM> to connect the switched line to the first switching valve <NUM>.

The first switching valve <NUM> and the second switching valve <NUM> each switch connection between the corresponding ports in response to an open-close signal output from the control unit <NUM>. The open-close signal includes a first control signal, a second control signal, a third control signal, and a fourth control signal, which are described later.

The pressure sensor <NUM> detects pressure in the liquid storage unit <NUM>. The pressure sensor <NUM> outputs the detected pressure in the liquid storage unit <NUM> as a pressure signal to the control unit <NUM>. Negative pressure to be detected by the pressure sensor <NUM> changes in accordance with a remaining amount of liquid in the liquid storage unit <NUM>. That is, when the remaining amount of liquid in the liquid storage unit <NUM> decreases, the negative pressure detected by the pressure sensor <NUM> increases more than when a large amount of liquid remains. The increase in negative pressure means, for example, a state in which the negative pressure has changed from -<NUM> kPa to -<NUM> kPa.

The control unit <NUM> described later controls the drive of the negative pressure pump 22a in response to a pressure signal output from the pressure sensor <NUM>. When decrease in the remaining amount of liquid in the liquid storage unit <NUM> is detected by the pressure sensor <NUM> as high negative pressure in the liquid storage unit <NUM>, the control unit <NUM> sets a negative pressure target value lower to bring negative pressure generated by the negative pressure pump 22a close to the atmospheric pressure.

The above configuration causes the pressure adjusting unit <NUM> to switch the first switching valve <NUM> to connect the positive pressure generator <NUM> to the liquid storage unit <NUM> when pressure in the liquid storage unit <NUM> is made positive, i.e., when the pressure in the liquid storage unit <NUM> is pressurized to positive pressure. This enables a liquid to be pushed out from the liquid storage unit <NUM> to the discharge unit <NUM>. Thus, the liquid can be stably supplied to the discharge unit <NUM>.

When the pressure in the liquid storage unit <NUM> is made negative, the pressure adjusting unit <NUM> switches not only the second switching valve <NUM> to connect the negative pressure generator <NUM> to the first switching valve <NUM>, but also the first switching valve <NUM> to connect the second switching valve <NUM> to the liquid storage unit <NUM>. This enables the liquid to be prevented from leaking from the discharge port 32a of the discharge unit <NUM> by setting the pressure in the liquid storage unit <NUM> to negative pressure.

When the pressure in the liquid storage unit <NUM> is set to the atmospheric pressure, the pressure adjusting unit <NUM> switches the second switching valve <NUM> to connect the atmospheric opening unit <NUM> to the first switching valve <NUM>. At this time, the first switching valve <NUM> is in a state in which the second switching valve <NUM> is connected to the liquid storage unit <NUM>. This enables the pressure in the liquid storage unit <NUM> to be set to the atmospheric pressure.

The discharge unit <NUM> discharges the liquid supplied from the liquid storage unit <NUM> to the outside in the form of droplets. <FIG> is an enlarged view illustrating the structure of the discharge unit <NUM>. Hereinafter, the structure of the discharge unit <NUM> will be described with reference to <FIG>.

The discharge unit <NUM> includes a liquid supply unit <NUM>, a diaphragm <NUM>, and a drive unit <NUM>.

The liquid supply unit <NUM> includes a base member <NUM> provided inside with a liquid chamber <NUM> and an inflow path <NUM>, and a heating unit <NUM>. The liquid storage unit <NUM> is located on the base member <NUM>. The inflow path <NUM> of the base member <NUM> is connected to an outlet 10a of the liquid storage unit <NUM>. The inflow path <NUM> is connected to the liquid chamber <NUM>. That is, the inflow path <NUM> is connected to the liquid chamber <NUM> and allows the liquid to be supplied from the liquid storage unit <NUM> into the liquid chamber <NUM>. The liquid chamber <NUM> stores the liquid.

The base member <NUM> includes the discharge port 32a connected to the liquid chamber <NUM>. The discharge port 32a is an opening for discharging the liquid supplied into the liquid chamber <NUM> to the outside. In the present embodiment, the discharge port 32a opens downward, so that the liquid supplied into the inflow path <NUM> and the liquid chamber <NUM> has a liquid level protruding downward caused by a meniscus in the discharge port 32a.

The heating unit <NUM> is located near the inflow path <NUM> in the base member <NUM>. The heating unit <NUM> heats the liquid in the inflow path <NUM>. Although not particularly illustrated, the heating unit <NUM> includes, for example, a plate-shaped heater and a heat transfer block. The heating unit <NUM> may include another component such as a rod-shaped heater or a Peltier element as long as it can heat the liquid in the inflow path.

Heating the fluid in the inflow path <NUM> with the heating unit <NUM> enables temperature of the liquid to be maintained at a constant temperature higher than room temperature. This enables preventing physical characteristics of the liquid from changing with temperature.

Although not particularly illustrated, the liquid coating apparatus <NUM> may include a temperature sensor for controlling heating of the heating unit <NUM>, being located near the heating unit <NUM> or near the discharge port 32a. The heating unit <NUM> may be located on the base member <NUM> as long as the fluid in the inflow path <NUM> can be heated.

The diaphragm <NUM> constitutes a part of a wall portion defining the liquid chamber <NUM>. The diaphragm <NUM> is located on an opposite side to the discharge port 32a across the liquid chamber <NUM>. The diaphragm <NUM> is supported by the base member <NUM> in a deformable manner in its thickness direction. The diaphragm <NUM> constitutes the part of the wall portion defining the liquid chamber <NUM>, and is deformed to change the volume of the liquid chamber <NUM>. When the diaphragm <NUM> is deformed in the thickness direction to change the volume of the liquid chamber <NUM>, the liquid in the liquid chamber <NUM> is discharged to the outside through the discharge port 32a.

The drive unit <NUM> deforms the diaphragm <NUM> in the thickness direction. Specifically, the drive unit <NUM> includes a piezoelectric element <NUM>, a first base <NUM>, a second base <NUM>, a plunger <NUM>, a coil spring <NUM>, and a casing <NUM>.

The piezoelectric element <NUM> extends in one direction by receiving predetermined voltage. That is, the piezoelectric element <NUM> is stretchable in the one direction. The piezoelectric element <NUM> deforms the diaphragm <NUM> in the thickness direction by expanding and contracting in the one direction. That is, the piezoelectric element <NUM> is a driving element that generates a driving force that deforms the diaphragm <NUM> in the thickness direction. The driving force for deforming the diaphragm <NUM> in the thickness direction may be generated by another driving element such as a magnetostrictive element.

The piezoelectric element <NUM> of the present embodiment has a rectangular parallelepiped shape that is long in the one direction. Although not particularly illustrated, the piezoelectric element <NUM> of the present embodiment is formed by electrically connecting multiple piezoelectric bodies 41a made of piezoelectric ceramics such as lead zirconate titanate (PZT), being laminated in the one direction. That is, the piezoelectric element <NUM> includes the multiple piezoelectric bodies 41a laminated in the one direction. This enables increasing the amount of expansion and contraction of the piezoelectric element <NUM> in the one direction as compared with the piezoelectric element <NUM> including one piezoelectric body. The shape of a piezoelectric element is not limited to a rectangular parallelepiped shape, and another shape such as a columnar shape may be used.

The multiple piezoelectric bodies 41a are electrically connected by side electrodes (not illustrated) located opposite to each other in a direction intersecting the one direction. Thus, the piezoelectric element <NUM> extends in the one direction when the side electrodes receive predetermined voltage. The predetermined voltage applied to the piezoelectric element <NUM> is a drive signal received from the control unit <NUM> described later.

The structure of the piezoelectric element <NUM> is similar to that of a conventional piezoelectric element, so that detailed description thereof will be eliminated. The piezoelectric element <NUM> may have only one piezoelectric body.

The plunger <NUM> is a rod-shaped member. The plunger <NUM> has one end in its axial direction, being in contact with the diaphragm <NUM>. The plunger <NUM> has the other end in the axial direction, being in contact with the first base <NUM> described later, the first base <NUM> covering an end of the piezoelectric element <NUM> in the one direction. That is, the one direction of the piezoelectric element <NUM> aligns with the axial direction of the plunger <NUM>. The plunger <NUM> is located between the piezoelectric element <NUM> and the diaphragm <NUM>. This allows expansion and contraction of the piezoelectric element <NUM> to be transmitted to the diaphragm <NUM> via the plunger <NUM>. The plunger <NUM> is a rod-shaped transmission member.

The other end of the plunger <NUM> is in a hemispherical shape. That is, the plunger <NUM> is in a rod shape, and has a leading end close to the piezoelectric element <NUM>, being in a hemispherical shape. This enables the expansion and contraction of the piezoelectric element <NUM> to be reliably transmitted by the diaphragm <NUM> via the plunger <NUM>.

The piezoelectric element <NUM> has an end close to the diaphragm <NUM> in the one direction, the end being covered with the first base <NUM>. The first base <NUM> is in contact with the plunger <NUM>. The piezoelectric element <NUM> has an end on an opposite side to the diaphragm <NUM> in the one direction, the end being covered with the second base <NUM>. The second base <NUM> is supported by a fixed casing bottom-wall portion 47a of a fixed casing <NUM> described later.

The first base <NUM> and the second base <NUM> include bottom portions 42a and 43a, and vertical wall portions 42b and 43b located on their outer peripheral sides, respectively. The bottom portions 42a and 43a each have a size covering corresponding one of end surfaces of the piezoelectric element <NUM> in the one direction. The vertical wall portions 42b and 43b are each located covering a part of a side surface of the piezoelectric element <NUM>.

The first base <NUM> and the second base <NUM> are each made of a wear-resistant material. At least one of the first base <NUM> and the second base <NUM> may be made of a sintered material in order to improve wear resistance. The first base <NUM> and the second base <NUM> may be different in hardness from each other.

The piezoelectric element <NUM> is housed in the casing <NUM>. The casing <NUM> includes the fixed casing <NUM> and a pressurized casing <NUM>. The pressurized casing <NUM> is housed in the fixed casing <NUM>. The piezoelectric element <NUM> is housed in the pressurized casing <NUM>. The fixed casing <NUM> and the pressurized casing <NUM> are fixed with bolts or the like (not illustrated).

The fixed casing <NUM> has a box shape opening toward the diaphragm <NUM>. Specifically, the fixed casing <NUM> includes a fixed casing bottom-wall portion 47a and a fixed casing side-wall portion 47b.

The fixed casing bottom-wall portion 47a is located on the opposite side to the diaphragm <NUM> across the piezoelectric element <NUM>. The fixed casing bottom-wall portion 47a includes a hemispherical protrusion 47c that supports one of the ends of the piezoelectric element <NUM> in the one direction. That is, the liquid coating apparatus <NUM> includes the hemispherical protrusion 47c protruding from the fixed casing bottom-wall portion 47a toward the piezoelectric element <NUM> in the one direction and supporting the end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM>. This enables the end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM> to be supported by the protrusion 47c of the fixed casing bottom-wall portion 47a without partial contact. Thus, the end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM> can be more reliably supported by the fixed casing bottom-wall portion 47a. The fixed casing bottom-wall portion 47a is a second support portion that supports the end of the piezoelectric element <NUM> on the side opposite to the diaphragm <NUM> in the one direction.

The second base <NUM> is located between the piezoelectric element <NUM> and the protrusion 47c. That is, the liquid coating apparatus <NUM> includes the second base <NUM> between the piezoelectric element <NUM> and the protrusion 47c. This enables the end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM> to be reliably supported by the protrusion 47c with the second base <NUM> interposed therebetween while the end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM> is held by the second base <NUM>.

The pressurized casing <NUM> has a box shape opening toward the opposite side to the diaphragm <NUM> across the piezoelectric element <NUM>. Thus, in a state where the pressurized casing <NUM> is housed in the fixed casing <NUM>, a part of the fixed casing bottom-wall portion 47a is exposed in the casing <NUM>. The protrusion 47c described above is located in the exposed part of the fixed casing bottom-wall portion 47a.

The pressurized casing <NUM> includes a pressurized casing bottom-wall portion 48a and a pressurized casing side-wall portion 48b.

The pressurized casing bottom-wall portion 48a is located close to the diaphragm <NUM>. The pressurized casing bottom-wall portion 48a includes a through-hole allowing the plunger <NUM> to pass therethrough. Thus, the plunger <NUM> extends in the one direction between the piezoelectric element <NUM> and the diaphragm <NUM>, and passes through the pressurized casing bottom-wall portion 48a, thereby transmitting expansion and contraction of the piezoelectric element <NUM> to the diaphragm <NUM>.

The pressurized casing bottom-wall portion 48a is supported on an upper surface of the base member <NUM>. This does not allow force generated by the coil spring <NUM> described later and sandwiched between the pressurized casing bottom-wall portion 48a and the first base <NUM> to act on the diaphragm <NUM> supported by the base member <NUM>, or allows the force even to act on the diaphragm <NUM> slightly.

The coil spring <NUM> described later is held between the pressurized casing bottom-wall portion 48a and the first base <NUM>. The pressurized casing bottom-wall portion 48a is a first support portion that is located between the piezoelectric element <NUM> and the diaphragm <NUM> in the one direction and supports the piezoelectric element <NUM> from a side close to the diaphragm <NUM>.

The pressurized casing side-wall portion 48b has an outer surface in contact with an inner surface of the fixed casing side-wall portion 47b, and the pressurized casing side-wall portion 48b has an inner surface in contact with the vertical wall portions 42b and 43b of the first base <NUM> and second base <NUM>, respectively. This enables the first base <NUM> and the second base <NUM> to be held by the pressurized casing side-wall portion 48b. Thus, even when predetermined voltage is applied to the piezoelectric element <NUM>, deformation of the piezoelectric element <NUM> in a direction orthogonal to the one direction is reduced.

The above structure allows the piezoelectric element <NUM> to be sandwiched between the plunger <NUM> and the protrusion 47c of the fixed casing bottom-wall portion 47a in the one direction. This enables expansion and contraction of the piezoelectric element <NUM> to be transmitted to the diaphragm <NUM> with the plunger <NUM> when the piezoelectric element <NUM> expands and contracts in the one direction. Thus, the diaphragm <NUM> can be deformed in its thickness direction by the expansion and contraction of the piezoelectric element <NUM>. <FIG> illustrates movement of the plunger <NUM> due to the expansion and contraction of the piezoelectric element <NUM> in the one direction with a solid arrow.

The coil spring <NUM> is a spring member that spirally extends along the axis in the one direction. The coil spring <NUM> is sandwiched in the one direction between the first base <NUM> and the pressurized casing bottom-wall portion 48a. The plunger <NUM> in a rod-like shape passes through inside the coil spring <NUM> in the axial direction. That is, the first base <NUM> is located between the piezoelectric element <NUM> and the plunger <NUM> together with the coil spring <NUM>. The coil spring <NUM> extends along the axis of the plunger <NUM> between the piezoelectric element <NUM> and the pressurized casing bottom-wall portion 48a.

This allows the coil spring <NUM> to apply force to compress the piezoelectric element <NUM> in the one direction via the first base <NUM>. <FIG> illustrates compressive force of the coil spring <NUM> with a white arrow. The coil spring <NUM> is a compressive force applying unit that is located between the piezoelectric element <NUM> and the pressurized casing bottom-wall portion 48a and supported by the pressurized casing bottom-wall portion 48a to apply a compressive force to the piezoelectric element <NUM> in the one direction. The compressive force generated by the coil spring <NUM> preferably allows the first base <NUM> to be located in contact with the plunger <NUM> in a state where no voltage is applied to the piezoelectric element <NUM>. For example, the compressive force is preferably <NUM>% to <NUM>% of force generated in the piezoelectric element <NUM> when rated voltage is applied to the piezoelectric element <NUM>.

When the first base <NUM> is located between the piezoelectric element <NUM> and the plunger <NUM> together with the coil spring <NUM>, the expansion and contraction of the piezoelectric element <NUM> can be stably transmitted to the plunger <NUM> via the first base <NUM>. At the same time, the compressive force of the coil spring <NUM> can be stably transmitted to the piezoelectric element <NUM> via the first base <NUM>.

Here, when the liquid has a high viscosity, the piezoelectric element <NUM> is required to operate at high speed. Thus, it is conceivable to improve responsiveness of the piezoelectric element <NUM> by inputting a drive signal with a rectangular wave to the piezoelectric element <NUM>. In this case, when the piezoelectric element <NUM> expands and contracts at high speed, the piezoelectric element <NUM> may expand and contract excessively, causing internal damage such as peeling. In particular, when the piezoelectric element <NUM> has multiple piezoelectric bodies 41a laminated in an expansion-contraction direction, high-speed operation of the piezoelectric element <NUM> tends to cause damage such as peeling inside the piezoelectric element <NUM>. The excessive expansion and contraction of the piezoelectric element <NUM> means that the amount of expansion and contraction of the piezoelectric element <NUM> is larger than the maximum amount of expansion and contraction when the rated voltage is applied to the piezoelectric element <NUM>.

In contrast, when the piezoelectric element <NUM> is compressed in the one direction by the coil spring <NUM> as in the present embodiment, damage such as peeling due to expansion and contraction of the piezoelectric element <NUM> can be prevented from occurring inside the piezoelectric element <NUM>, even when the piezoelectric element <NUM> receives a drive signal with a rectangular wave. That is, the coil spring <NUM> can suppress excessive expansion and contraction of the piezoelectric element <NUM>, and can prevent occurrence of internal damage of the piezoelectric element <NUM> due to its expansion and contraction. This enables improving durability of the piezoelectric element <NUM>.

When the coil spring <NUM> is located between the piezoelectric element <NUM> and the pressurized casing bottom-wall portion 48a as described above, the pressurized casing bottom-wall portion 48a can receive elastic restoring force of the coil spring <NUM>. Thus, the diaphragm <NUM> can be prevented from being deformed by the elastic restoring force of the coil spring <NUM>. This enables preventing a liquid from leaking from the discharge port 32a and liquid discharge performance from being deteriorated.

When the plunger <NUM> passes through inside the coil spring <NUM> spirally extending along the axis in the axial direction, the plunger <NUM> and the coil spring <NUM> can be compactly disposed. This enables the liquid coating apparatus <NUM> to be miniaturized.

Next, a configuration of the control unit <NUM> will be described below.

The control unit <NUM> controls drive of the liquid coating apparatus <NUM>. That is, the control unit <NUM> controls drive of each of the pressure adjusting unit <NUM> and the drive unit <NUM>.

The control unit <NUM> includes a pressure adjustment control unit <NUM> and a drive control unit <NUM>.

The pressure adjustment control unit <NUM> outputs a control signal to the first switching valve <NUM> and the second switching valve <NUM> of the pressure adjusting unit <NUM>. The pressure adjustment control unit <NUM> also outputs a positive pressure pump drive signal to the positive pressure pump 21a. The pressure adjustment control unit <NUM> further outputs a negative pressure pump drive signal to the negative pressure pump 22a. The pressure adjustment control unit <NUM> outputs the control signal to the first switching valve <NUM> and the second switching valve <NUM> to control pressure in the liquid storage unit <NUM>.

For example, when positive pressure is applied to the liquid storage unit <NUM>, the pressure adjustment control unit <NUM> outputs a first control signal for connecting the positive pressure generator <NUM> to the liquid storage unit <NUM> to the first switching valve <NUM>. When negative pressure is applied to the liquid storage unit <NUM>, the pressure adjustment control unit <NUM> outputs a second control signal for connecting the second switching valve <NUM> to the liquid storage unit <NUM> to the first switching valve <NUM>, and outputs a third control signal for connecting the negative pressure generator <NUM> to the first switching valve <NUM> to the second switching valve <NUM>. When pressure inside the liquid storage unit <NUM> is set to the atmospheric pressure, the pressure adjustment control unit <NUM> outputs the second control signal for connecting the second switching valve <NUM> to the liquid storage unit <NUM> to the first switching valve <NUM>, and outputs a fourth control signal for connecting the atmospheric opening unit <NUM> to the first switching valve <NUM> to the second switching valve <NUM>.

The pressure adjustment control unit <NUM> controls drive of the negative pressure pump 22a in response to a pressure signal output from the pressure sensor <NUM>. That is, when driving the negative pressure pump 22a does not allow pressure detected by the pressure sensor <NUM> to reach the negative pressure target value, the pressure adjustment control unit <NUM> sets the negative pressure target value lower and causes the negative pressure pump 22a to be driven in accordance with a new negative pressure target value. In this way, when a decrease in the remaining amount of liquid in the liquid storage unit <NUM> is detected by the pressure sensor <NUM> as high negative pressure in the liquid storage unit <NUM>, the pressure adjustment control unit <NUM> sets the negative pressure target value lower to bring negative pressure generated by the negative pressure pump 22a close to the atmospheric pressure.

The pressure adjustment control unit <NUM> also controls drive of the positive pressure pump 21a. The drive of the positive pressure pump 21a is similar to that of a conventional configuration, so that detailed description thereof will be eliminated.

The drive control unit <NUM> controls drive of the piezoelectric element <NUM>. That is, the drive control unit <NUM> outputs a drive signal to the piezoelectric element <NUM>. This drive signal includes a discharge signal.

The discharge signal allows the piezoelectric element <NUM> to expand and contract to vibrate the diaphragm <NUM> as described later, thereby discharging the liquid in the liquid chamber <NUM> to the outside through the discharge port 32a.

The control unit <NUM> controls timing of allowing the drive control unit <NUM> to output the discharge signal to the piezoelectric element <NUM> and timing of outputting the control signals to the pressure adjusting unit <NUM>.

<FIG> is a flowchart illustrating an example of an operation of discharging a liquid with the discharge unit <NUM> and adjusting pressure in the liquid storage unit <NUM> with the pressure adjusting unit <NUM>. The control of the timing of allowing the drive control unit <NUM> to output the discharge signal to the piezoelectric element <NUM> and the timing of outputting the control signals to the pressure adjusting unit <NUM>, the control being performed by the control unit <NUM>, will be described.

As illustrated in <FIG>, the control unit <NUM> first determines whether an external signal instructing discharge is received (step S1). This external signal is received by the control unit <NUM> from a controller or the like higher than the control unit <NUM>.

When the control unit <NUM> receives an external signal (YES in step S1), in step S2, the pressure adjustment control unit <NUM> of the control unit <NUM> generates the first control signal for connecting the positive pressure generator <NUM> to the liquid storage unit <NUM> in the first switching valve <NUM> of the pressure adjusting unit <NUM> and outputs it to the first switching valve <NUM>. The first switching valve <NUM> is driven in response to the first control signal. This causes the inside of the liquid storage unit <NUM> to be pressurized to positive pressure. In contrast, when the control unit <NUM> receives no external signal (NO in step S1), the determination in step S1 is repeated until the control unit <NUM> receives an external signal.

After step S2, the drive control unit <NUM> of the control unit <NUM> outputs a discharge signal to the piezoelectric element <NUM> to discharge the liquid to the discharge unit <NUM> through the discharge port 32a (step S3).

After the drive control unit <NUM> outputs the discharge signal to the piezoelectric element <NUM>, the pressure adjustment control unit <NUM> may output the first control signal to the first switching valve <NUM>. That is, discharge of the discharge unit <NUM> may be performed before pressurization of positive pressure in the liquid storage unit <NUM>.

After that, the pressure adjustment control unit <NUM> generates the second control signal for connecting the second switching valve <NUM> to the liquid storage unit <NUM> in the first switching valve <NUM> of the pressure adjusting unit <NUM>, and outputs it to the first switching valve <NUM>. The pressure adjustment control unit <NUM> also generates the third control signal for connecting the atmospheric opening unit <NUM> to the first switching valve <NUM> in the second switching valve <NUM>, and outputs it to the second switching valve <NUM> (step S4). The first switching valve <NUM> is driven in response to the second control signal. The second switching valve <NUM> is driven in response to the third control signal. This causes the pressure in the liquid storage unit <NUM> to be the atmospheric pressure.

Subsequently, the pressure adjustment control unit <NUM> generates the fourth control signal for connecting the negative pressure generator <NUM> to the first switching valve <NUM> in the second switching valve <NUM>, and outputs it to the second switching valve <NUM> (step S5). The second switching valve <NUM> is driven in response to the fourth control signal. This causes the pressure in the liquid storage unit <NUM> to be negative pressure. Thus, the liquid can be prevented from leaking through the discharge port 32a of the discharge unit <NUM>. Then, this flow is ended (END). The control unit <NUM> repeatedly performs the above-mentioned flow as necessary.

When the pressure in the liquid storage unit <NUM> is controlled as described above, the liquid can be stably discharged through the discharge port 32a at appropriate timing without leakage of the liquid through the discharge port 32a of the discharge unit <NUM>.

The drive control unit <NUM> may repolarize the piezoelectric element <NUM>. The piezoelectric element <NUM> includes multiple piezoelectric bodies 41a that are made of a polarized sintered material and are electrically connected. Thus, the piezoelectric element <NUM> has characteristics in which when the piezoelectric element <NUM> is left for a long time without being used or when the piezoelectric element <NUM> is at a high temperature. For example, an electric field is generated inside the piezoelectric element <NUM> and the amount of displacement of the piezoelectric element when voltage is applied gradually decreases. When displacement characteristics of the piezoelectric element <NUM> deteriorate as described above, the piezoelectric element <NUM> needs to be repolarized to recover the displacement characteristics of the piezoelectric element <NUM>.

When the piezoelectric element <NUM> is repolarized, the drive control unit <NUM> outputs a drive signal for applying rated voltage to the piezoelectric element <NUM> for a certain period of time, and then turns off the drive signal for a predetermined period of time. In this case, the drive control unit <NUM> generates, as the drive signal, a drive signal capable of preventing a steep rise and fall of the rated voltage applied to the piezoelectric element <NUM>. The rated voltage is predetermined voltage. The voltage applied to the piezoelectric element <NUM> by the drive control unit <NUM> when the piezoelectric element <NUM> is repolarized may be voltage other than the rated voltage of the piezoelectric element <NUM> as long as the voltage enables repolarization of the piezoelectric element <NUM>.

As described above, the liquid coating apparatus <NUM> may include the control unit <NUM> that performs drive control of the piezoelectric element <NUM> and performs a repolarization process of applying the rated voltage to the piezoelectric element <NUM> for a certain period of time and then setting voltage to be applied to zero.

This enables the displacement characteristics of the piezoelectric element <NUM> to be recovered without using a dedicated circuit when the control unit <NUM> repolarizes the piezoelectric element <NUM>.

The piezoelectric element <NUM> may be repolarized at any timing other than a timing at which a liquid is discharged, such as when the liquid coating apparatus <NUM> is started or when the liquid coating apparatus <NUM> receives an external signal instructing liquid discharge.

The liquid coating apparatus <NUM> according to the present embodiment includes the liquid chamber <NUM> that stores a liquid, the inflow path <NUM> that is connected to the liquid chamber <NUM> and allows the liquid to be supplied from the liquid storage unit <NUM> into the liquid chamber <NUM>, the diaphragm <NUM> that constitutes a part of a wall portion defining the liquid chamber <NUM> and is deformed in a thickness direction to change a volume of the liquid chamber <NUM>, the piezoelectric element <NUM> that expands and contracts in at least one direction to deform the diaphragm <NUM> in the thickness direction, the pressurized casing bottom-wall portion 48a that is located between the piezoelectric element <NUM> and the diaphragm <NUM> in the one direction to support the piezoelectric element <NUM> from a diaphragm <NUM> side, the fixed casing bottom-wall portion 47a that supports an end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM> in the one direction, the plunger <NUM> that extends in the one direction between the piezoelectric element <NUM> and the diaphragm <NUM> and passes through the pressurized casing bottom-wall portion 48a to transmit expansion and contraction of the piezoelectric element <NUM> to the diaphragm <NUM>, and the coil spring <NUM> that is located between the piezoelectric element <NUM> and the pressurized casing bottom-wall portion 48a and is supported by the pressurized casing bottom-wall portion 48a to apply a compressive force to the piezoelectric element <NUM> in the one direction.

This enables the piezoelectric element <NUM> to be compressed in one direction in which the piezoelectric element <NUM> expands and contracts by the coil spring <NUM>. Thus, even when the piezoelectric element <NUM> is operated with a high response, the piezoelectric element <NUM> is prevented from excessively expanding and contracting, and thus an excessive load at a level affecting the life of the piezoelectric element <NUM> can be prevented from being applied to the inside of the piezoelectric element <NUM>. Additionally, the coil spring <NUM> is supported by the pressurized casing bottom-wall portion 48a, so that a force generated by the coil spring <NUM> is not transmitted to the diaphragm <NUM>. This enables the diaphragm <NUM> to be prevented from being deformed by the force generated by the coil spring <NUM>.

In particular, the piezoelectric element <NUM> includes the multiple piezoelectric bodies 41a laminated in the one direction. This enables increasing a length of expansion and contraction of the piezoelectric element <NUM> in the one direction as compared with the piezoelectric element <NUM> including one piezoelectric body 41a. Unfortunately, the multiple piezoelectric bodies 41a laminated in the one direction as described above, cause an excessive load to likely be applied to the inside of the piezoelectric element <NUM> when the piezoelectric element <NUM> is operated with a high response to cause the piezoelectric element <NUM> to be excessively expanded and contracted. In contrast, when the coil spring <NUM> compresses the piezoelectric element <NUM> in the one direction as described above, an excessive load at a level affecting the life of the piezoelectric element <NUM> can be prevented from being applied to the inside of the piezoelectric element <NUM>. That is, the above-described structure is particularly effective in a structure in which the piezoelectric element <NUM> includes the multiple piezoelectric bodies 41a laminated in the one direction.

In the present embodiment, the plunger <NUM> has a rod shape extending along the axis. The coil spring <NUM> extends along the axis of the plunger <NUM> between the piezoelectric element <NUM> and the pressurized casing bottom-wall portion 48a to apply a compressive force to the piezoelectric element <NUM> in the one direction.

This enables a compressive force of the coil spring <NUM> to be applied to the piezoelectric element <NUM> in a direction in which the piezoelectric element <NUM> expands and contracts to apply a force to the plunger <NUM>. Thus, even when the piezoelectric element <NUM> is operated with a high response, the piezoelectric element <NUM> is prevented from excessively expanding and contracting, and thus an excessive load at a level affecting the life of the piezoelectric element <NUM> can be prevented from being applied to the inside of the piezoelectric element <NUM>.

In the present embodiment, the plunger <NUM> is in a rod shape, and has a leading end in a hemispherical shape on a piezoelectric element <NUM> side. The liquid coating apparatus <NUM> includes the protrusion 47c in a hemispherical shape protruding from the fixed casing bottom-wall portion 47a toward the piezoelectric element <NUM> in the one direction and supporting the end of the piezoelectric element <NUM> on the opposite side to the diaphragm <NUM>.

This enables a compression direction by the coil spring <NUM> to be set to the one direction in which the piezoelectric element <NUM> expands and contracts, when the piezoelectric element <NUM> is compressed in the one direction by the coil spring <NUM>. The piezoelectric element <NUM> is likely to be damaged by a compressive force in a direction other than the one direction. Thus, when the compression direction by the coil spring <NUM> is set to the one direction as described above, the piezoelectric element <NUM> can be prevented from being damaged by the compressive force of the coil spring <NUM>. The compression direction by the coil spring <NUM> does not need to completely align with the one direction, and may be a direction in which the compressive force generated by the coil spring <NUM> includes a force of a component in the one direction.

Although the embodiment of the present invention is described above, the above-described embodiment is merely an example for implementing the present invention. Thus, the above-described embodiment can be appropriately modified and implemented within a range without departing from the scope of the appended claims and being limited to the above-described embodiment.

In the embodiment, the coil spring <NUM> compresses the piezoelectric element <NUM> in one direction. However, when the piezoelectric element can be compressed in one direction, the piezoelectric element may be compressed by a configuration other than a coil spring. That is, although in the above embodiment, the coil spring <NUM>, which is a spiral spring member, is described as an example of a compressive force applying unit, besides this, the spiral spring member may be, for example, a so-called coiled wave spring in which a wire rod or a flat plate, having a predetermined length and a wavy shape, is spirally wound. The compressive force applying unit may have a structure other than the spiral shape as long as the piezoelectric element can be compressed in one direction. The compressive force applying unit is preferably disposed preventing interference with the plunger regardless of structure.

In the above embodiment, the plunger <NUM> passes through the coil spring <NUM>, extending spirally along the axis. However, the placement of the coil spring is not particularly limited as long as the coil spring extends parallel to one direction that is a direction of expansion and contraction of the piezoelectric element with respect to the plunger.

In the above embodiment, both ends of the piezoelectric element <NUM> are each covered with the corresponding one of the first base <NUM> and the second base <NUM> in one direction in which the piezoelectric element <NUM> expands and contracts. However, in the one direction, only one of both the ends of the piezoelectric element may be covered with a base. In the one direction, each end of the piezoelectric element may not be covered with a base.

In the above embodiment, the piezoelectric element <NUM> is supported by the protrusion 47c in a hemispherical shape of the fixed casing bottom-wall portion 47a and the leading end in a hemispherical shape of the plunger <NUM> on the piezoelectric element <NUM> side. However, the liquid coating apparatus may not have at least one of the protrusion in a hemispherical shape and the leading end in a hemispherical shape of the plunger as long as the direction of expansion and contraction of the piezoelectric element is parallel to the compression direction of the coil spring. The shape of each of the protrusion and the leading end of the plunger is not limited to the hemispherical shape, and may be any shape as long as the shape can support the piezoelectric element.

In the above embodiment, the casing <NUM> housing the piezoelectric element <NUM> includes the pressurized casing <NUM> housed in the fixed casing <NUM>. However, the casing may not include a pressurized casing. In this case, the piezoelectric element is housed in the fixed casing. The coil spring has an end on a diaphragm side that is supported by the upper surface of the base member. That is, an upper wall portion of the base member functions as the first support portion.

In the above embodiment, the discharge unit <NUM> includes the heating unit <NUM> that heats a liquid in the inflow path <NUM>. However, the discharge unit may not include the heating unit.

In the above embodiment, the pressure adjusting unit <NUM> includes the first switching valve <NUM> that is connected to the liquid storage unit <NUM> by switching between a line connected to the positive pressure generator <NUM> and a line connected to the second switching valve <NUM>, and the second switching valve <NUM> that is connected to the first switching valve <NUM> by switching between a line connected to the negative pressure generator <NUM> and a line connected to the atmospheric opening unit <NUM>.

However, the pressure adjusting unit may include a switching valve that connects each of the positive pressure generator, the negative pressure generator, and the atmospheric opening unit, to the liquid storage unit. The pressure adjusting unit may have any configuration as long as the positive pressure generator, the negative pressure generator, and the atmospheric opening unit can be each connected to the liquid storage unit.

In the above embodiment, the liquid storage unit <NUM> can be connected to the atmospheric opening unit by the pressure adjusting unit <NUM>. However, the pressure adjusting unit may have a configuration in which the atmospheric opening unit cannot be connected to the liquid storage unit.

In the above embodiment, the liquid storage unit <NUM> can be connected to the positive pressure generator <NUM> by the pressure adjusting unit <NUM>. However, the liquid coating apparatus may not include a positive pressure generator. That is, the liquid coating apparatus may control pressure in the liquid storage unit using negative pressure and the atmospheric pressure.

Claim 1:
A liquid coating apparatus (<NUM>) comprising:
a liquid chamber (<NUM>) that stores a liquid;
an inflow path (<NUM>) that is connected to the liquid chamber (<NUM>) to allow the liquid to be supplied into the liquid chamber (<NUM>);
characterized in that the liquid coating apparatus (<NUM>) further comprises:
a diaphragm (<NUM>) that constitutes a part of a wall portion defining the liquid chamber (<NUM>) and is deformed to change a volume of the liquid chamber (<NUM>);
a drive element (<NUM>) that expands and contracts in at least one direction to deform the diaphragm (<NUM>) in a thickness direction;
a first support portion (48a) that is located between the drive element (<NUM>) and the diaphragm (<NUM>) in the one direction to support the drive element (<NUM>) on a diaphragm (<NUM>) side;
a second support portion (47a) that supports an end of the drive element (<NUM>) on an opposite side to the diaphragm (<NUM>) in the one direction;
a transmission member (<NUM>) that extends in the one direction between the drive element (<NUM>) and the diaphragm (<NUM>) and passes through the first support portion to transmit expansion and contraction of the drive element (<NUM>) to the diaphragm (<NUM>); and
a compressive force applying unit (<NUM>) that is located between the drive element (<NUM>) and the first support portion (48a) and supported by the first support portion (48a) to apply a compressive force to the drive element (<NUM>) in the one direction.