JP2009246059A - Piezoelectric actuator and liquid transfer equipment - Google Patents

Abstract

[PROBLEMS] To suppress a decrease in power supply voltage during driving without separately providing a large-capacitance capacitor outside.
In an ink jet head, a vibration plate and piezoelectric layers are laminated on the upper surface of a flow path unit, and electrodes are disposed on each surface. The electrode 46 is always held at the ground potential, the electrodes 45 and 47 are always held at the driving potential, and the piezoelectric actuator is driven by switching the potential of the electrode 48 between the ground potential and the driving potential. The Further, the portions sandwiched between these electrodes of the electrodes 46 and 47 and the piezoelectric layer 43 and the portion sandwiched between these electrodes of the electrodes 45 and 46 and the piezoelectric layer 42 constitute a capacitor, respectively. Electric charges are stored in these capacitors due to the potential difference between the electrode 46 and the electrode 47 and the potential difference between the electrode 45 and the electrode 46.
[Selection] Figure 7

Description

  The present invention relates to a piezoelectric actuator having a piezoelectric layer and a liquid transfer device including the piezoelectric actuator.

  In the ink jet head described in Patent Document 1, a capacitor is provided between a power supply voltage terminal and a ground terminal on an FPC for connecting a drive circuit for driving a plurality of piezoelectric elements (piezoelectric actuators) and a power supply. Is connected to the capacitor, and electric charges are stored in the capacitor due to a potential difference between both ends thereof. In addition, since current flows from this capacitor to the piezoelectric element as well as the power supply, for example, when a large number of piezoelectric elements are driven simultaneously, it is possible to prevent a large current from flowing from the power supply to the piezoelectric element. Is temporarily reduced.

Japanese Patent Laid-Open No. 6-171083

  However, in the ink jet head described in Patent Document 1, in order to sufficiently suppress the decrease in the voltage of the power source as described above, it is necessary to allow a sufficient current to flow from the capacitor to the piezoelectric element. It is necessary to have a capacity. If such a large-capacitance capacitor is provided, the manufacturing cost of the inkjet head increases.

  An object of the present invention is to provide a piezoelectric actuator capable of suppressing a decrease in voltage without providing a separate large-capacity capacitor outside, and a liquid transfer device including such a piezoelectric actuator. .

  According to a first aspect of the present invention, there is provided a piezoelectric actuator including a first electrode, a second electrode, and a third electrode, at least the first electrode and the second electrode, and a piezoelectric material sandwiched between the second electrode and the third electrode. A first potential and a second potential different from the first potential are selectively applied to the first electrode, the first potential is applied to the second electrode, and the third electrode is applied to the third electrode. A piezoelectric actuator driven by a driving device that applies the second potential, wherein the piezoelectric material sandwiched between the first electrode and the second electrode is polarized in a sandwiching direction by these electrodes, and the first electrode The second electrode, the third electrode, and the piezoelectric material sandwiched between the second electrode, the third electrode, and the piezoelectric material between them constitute a capacitor that stores electric charges supplied from the driving device. Characterized by A.

  According to this, since the capacitor is composed of the second electrode and the third electrode for driving the piezoelectric actuator and the portion of the piezoelectric material sandwiched between these electrodes, the current is not only supplied from the driving device but also from this capacitor. When the piezoelectric actuator is driven rapidly, a large current is prevented from flowing from the driving device to the piezoelectric actuator, and the voltage of the driving device is suppressed from decreasing.

  Since such a capacitor is provided inside the piezoelectric actuator, there is no need to separately provide a capacitor on an external substrate connected to the piezoelectric actuator. Alternatively, a capacitor provided separately can have a small capacity.

  In addition, since the capacitor is configured inside the piezoelectric actuator using the second electrode for driving the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  A piezoelectric actuator according to a second invention is the piezoelectric actuator according to the first invention, wherein the piezoelectric material is sandwiched between the first electrode and the third electrode, and is sandwiched between the first electrode and the third electrode. The material is characterized in that it is polarized in the clamping direction by these electrodes and is deformed when the first potential is applied to the first electrode.

  According to this, in addition to the first and second electrodes, when the third electrode is also an electrode for driving the piezoelectric actuator, the second electrode and the third electrode for driving the piezoelectric actuator are used to drive the piezoelectric actuator. Since the capacitor is configured inside, the configuration of the piezoelectric actuator is simplified.

  According to a third aspect of the present invention, there is provided a piezoelectric actuator according to the first aspect, further comprising first and second piezoelectric material layers made of a piezoelectric material and laminated with each other, wherein the first piezoelectric material layer includes the first electrode and the second electrode. And the second piezoelectric material layer is sandwiched between the second electrode and the third electrode, and the second electrode is less than the first electrode and the third electrode in plan view. The area of the first piezoelectric material layer overlaps with the first electrode and the third electrode, and is sandwiched between the first electrode and the second electrode of the first piezoelectric material layer. Is polarized in the clamping direction by these electrodes to constitute a first active portion, and the portion of the first piezoelectric material layer and the second piezoelectric material layer sandwiched between the first electrode and the third electrode is The clamping direction by these electrodes The second active portion is polarized in a direction opposite to the polarization direction of the first active portion, and the second electrode, the third electrode, and the second piezoelectric material layer sandwiched between the second electrode, the capacitor, It is characterized by comprising.

  According to this, in the piezoelectric actuator having such a configuration, in addition to the first and second electrodes, the third electrode is also used for driving the second and third electrodes for driving the piezoelectric actuator. Since the capacitor is configured inside the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  A piezoelectric actuator according to a fourth invention is the piezoelectric actuator according to the third invention, wherein a third piezoelectric material layer is laminated on the opposite side of the second piezoelectric material layer to the first piezoelectric material layer, and the third piezoelectric material layer is laminated. On the surface of the material layer opposite to the second piezoelectric material layer, a dummy electrode is provided at a position sandwiching the third piezoelectric material layer together with the third electrode, and the dummy electrode is connected to the first potential. The capacitor is constituted by the third electrode, the dummy electrode, and the third piezoelectric material layer sandwiched between the third electrode, the dummy electrode, and the second electrode.

  According to this, since the capacitor is also constituted by the third electrode and the dummy electrode and the portion of the third piezoelectric material layer sandwiched between these electrodes, the capacitance of the capacitor formed inside the piezoelectric actuator. The sum of becomes larger. Also, since the third electrode for driving the piezoelectric actuator is used to configure this capacitor, the capacitor is configured by arranging a dedicated electrode different from the dummy electrode instead of the third electrode. Compared with the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  According to a fifth aspect of the present invention, there is provided a piezoelectric actuator according to the second aspect, further comprising first and second piezoelectric material layers made of a piezoelectric material and stacked on each other, wherein the first piezoelectric material layer includes the first electrode and the third piezoelectric material layer. And the second piezoelectric material layer is sandwiched between the third electrode and the second electrode, and the third electrode is more planar than the first electrode and the second electrode in plan view. The area of the first piezoelectric material layer overlaps with the first electrode and the second electrode, and is sandwiched between the first electrode and the third electrode. Is polarized in the clamping direction by these electrodes to form a first active portion, and the portion of the first piezoelectric material layer and the second piezoelectric material layer sandwiched between the first electrode and the second electrode is The clamping direction by these electrodes The second active portion is polarized in a direction opposite to the polarization direction of the first active portion, and the second electrode, the third electrode, and the second piezoelectric material layer sandwiched between the second electrode, the capacitor, It is characterized by comprising.

  According to this, in the piezoelectric actuator having such a configuration, in addition to the first and second electrodes, the third electrode is also used for driving the second and third electrodes for driving the piezoelectric actuator. Since the capacitor is configured inside the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  According to a sixth aspect of the present invention, in the fifth aspect, the third piezoelectric material layer is laminated on the opposite side of the second piezoelectric material layer from the first piezoelectric material layer. A dummy electrode is provided on a surface of the material layer opposite to the second piezoelectric material layer at a position sandwiching the third piezoelectric material layer together with the second electrode, and the dummy electrode has the second potential. The capacitor is constituted by the second electrode, the dummy electrode, and the third piezoelectric material layer sandwiched between the second electrode, the dummy electrode, and the third electrode.

  According to this, since the capacitor is also constituted by the second electrode and the dummy electrode and the portion of the third piezoelectric material layer sandwiched between these electrodes, the capacitance of the capacitor formed inside the piezoelectric actuator. The sum of becomes larger. In addition, since the second electrode for driving the piezoelectric actuator is used to configure this capacitor, the capacitor is configured by arranging a dedicated electrode different from the dummy electrode instead of the second electrode. Compared with the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  A liquid transfer device according to a seventh aspect of the invention includes a flow path unit including a pressure chamber in which a liquid transfer flow path for transferring a liquid is formed, a front first electrode, a second electrode, and a third electrode, A piezoelectric actuator that includes at least the first electrode, the second electrode, and a piezoelectric material sandwiched between the second electrode and the third electrode, and that applies pressure to the liquid in the pressure chamber; and drives the piezoelectric actuator A driving device that selectively applies a first potential to the first electrode and a second potential different from the first potential, and applies the first potential to the second electrode. Then, the second potential is applied to the third electrode, and the piezoelectric actuator is configured such that the piezoelectric material sandwiched between the first electrode and the second electrode is polarized in a sandwiching direction between the first electrode and the first electrode. When the second potential is applied to the electrode Is configured to form, the second electrode, the third electrode and the piezoelectric material sandwiched between these are those characterized in that it constitutes a capacitor for storing charge supplied from the drive unit.

  According to the present invention, the capacitor is constituted by the second electrode and the third electrode for driving the piezoelectric actuator, and the portion sandwiched between these electrodes of the piezoelectric material. However, when the current flows, when the piezoelectric actuator is driven suddenly, a large current is prevented from flowing from the driving device to the piezoelectric actuator, and the voltage of the driving device is suppressed from decreasing.

  Since such a capacitor is provided inside the piezoelectric actuator, there is no need to separately provide a capacitor on an external substrate connected to the piezoelectric actuator. Alternatively, a capacitor provided separately can have a small capacity.

  Further, since the second electrode for driving the piezoelectric actuator is used to form a part of the capacitor inside the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment. As shown in FIG. 1, the printer 1 includes a carriage 2, an ink jet head 3 (droplet discharge device), a transport roller 4, and the like.

  The carriage 2 reciprocates in the scanning direction (left and right direction in FIG. 1). The inkjet head 3 is attached to the lower surface of the carriage 2 and ejects ink from nozzles 15 (see FIG. 4) formed on the lower surface. The transport roller 4 transports the recording paper P in the paper feed direction (front side in FIG. 1). In the printer 1, the ink is ejected from the nozzle 15 of the inkjet head 3 that reciprocates in the scanning direction together with the carriage 2 onto the recording paper P that is transported in the paper feeding direction by the transport roller 4, whereby the recording paper P Printing is performed.

  Next, the inkjet head 3 will be described in detail. FIG. 2 is an exploded perspective view of the inkjet head 3 of FIG. FIG. 3 is a plan view of the inkjet head 3 of FIG. FIG. 4 is a partially enlarged view of FIG. FIG. 5 is a view showing the upper surfaces of a diaphragm 41 and piezoelectric layers 42 to 44, which will be described later, in FIG. 6 is a sectional view taken along line VI-VI in FIG. 7 is a cross-sectional view taken along line VII-VII in FIG.

  In order to make the drawings easier to understand, in FIGS. 3 to 5, illustration of the ink flow path excluding the pressure chamber 10 and the nozzle 15 of the flow path unit 31 described later is omitted, and in FIG. 3, the piezoelectric actuator 32 is described later. Illustration of the electrodes 45 to 47 to be performed is omitted. Further, in FIG. 4, the electrodes 45 and 47 to be shown by dotted lines are shown by two-dot chain lines and one-dot chain lines, respectively. Further, in FIG. 5, electrodes 45 to 48 described later are hatched, respectively. Further, in FIG. 7, illustration of a portion below the pressure chamber 10 is omitted.

  As shown in FIGS. 2 to 7, the inkjet head 3 includes a flow path unit 31 in which an ink flow path such as a pressure chamber 10 described later is formed, and a piezoelectric actuator 32 that applies pressure to the ink in the pressure chamber 10. It has. In the flow path unit 31, a plurality of plates 21 to 27 are stacked on each other, whereby the manifold flow path 11 to which ink is supplied from the ink supply port 9, and the outlet of the manifold flow path 11 through the aperture flow path 12. An ink channel (liquid transfer channel) having a plurality of individual ink channels from the pressure chamber 10 to the nozzle 15 through the descender channel 14 is formed. Here, among the plurality of plates 21 to 27, the six plates 21 to 26 excluding the plate 27 on which the nozzle 15 is formed are made of a metal material such as SUS430 or SUS316, and the plate 27 is a synthetic resin such as polyimide. Made of material. Or the plate 27 may be comprised with the metal material like the other plates 21-26.

  The plurality of pressure chambers 10 have a substantially elliptical planar shape with the scanning direction (left-right direction in FIG. 3) as the longitudinal direction, and are arranged along the paper feed direction (up-down direction in FIG. 3). Two pressure chamber rows 8 are formed. Such pressure chamber rows 8 are arranged in two rows in the scanning direction to constitute one pressure chamber group 7. Further, five such pressure chamber groups 7 are arranged along the scanning direction. Here, the pressure chambers 10 constituting the two pressure chamber rows 8 included in one pressure chamber group 7 are arranged so as to be shifted from each other in the paper feeding direction. The plurality of nozzles 15 are also arranged in the same manner as the plurality of pressure chambers 10.

  Then, among these five pressure chamber groups 7, black ink is ejected from the nozzles 15 corresponding to the pressure chambers 10 constituting the right two in FIG. 3, and the pressure constituting the left three in FIG. From the nozzles 15 corresponding to the chambers 10, yellow, cyan, and magenta inks are ejected in order from the nozzles arranged on the right side of FIG. The configuration of other portions of the ink flow path is the same as that of the conventional one, and therefore detailed description thereof is omitted here.

  The piezoelectric actuator 32 includes a vibration plate 41, piezoelectric layers 42 to 44, and electrodes 45 to 48. The diaphragm 41 is made of a piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate, and is formed on the upper surface of the flow path unit 31 so as to cover the plurality of pressure chambers 10. For example, it is joined to the flow path unit 31 by a thermosetting adhesive or the like. The diaphragm 41 does not necessarily need to be made of a piezoelectric material.

  The piezoelectric layers 42 to 44 are made of the same piezoelectric material as that of the vibration plate 41, and are stacked on each other and disposed on the upper surface of the vibration plate 41, whereby the piezoelectric layer 43 (second piezoelectric material layer) and the piezoelectric layer 44. (The first piezoelectric material layer) are laminated on each other, and the piezoelectric layer 42 (third piezoelectric material layer) is laminated on the lower surface of the piezoelectric layer 43 (on the side opposite to the piezoelectric layer 44). The piezoelectric layers 42 to 44 correspond to the piezoelectric material according to the present invention.

  The electrode 45 (dummy electrode) is disposed between the diaphragm 41 and the piezoelectric layer 42 over substantially the entire region, and has a substantially rectangular planar shape at a portion facing the substantially central portion of the plurality of pressure chambers 10. A punching pattern 45a is formed. The electrode 45 is electrically connected to the electrode 47 through through holes (not shown) formed in the piezoelectric layers 42 and 43.

  The electrode 46 is continuously disposed across the plurality of pressure chambers 10 between the piezoelectric layer 42 and the piezoelectric layer 43. The electrode 46 is connected to a connection terminal 39 formed on the upper surface of the piezoelectric layer 44 through a through hole (not shown) formed in the piezoelectric layers 43 and 44. The connection terminal 39 is connected to a driver IC 51 mounted on the upper surface of the connection terminal 39 by being connected to a COF (Chip On Film) 50 disposed above the piezoelectric actuator 32, and the electrode 46 is always connected to the driver IC 51. It is held at the ground potential (first potential). In the present embodiment, a portion of the electrode 46 that falls within the range in which the pressure chamber 10 is arranged in the scanning direction (left-right direction in FIG. 5) corresponds to the second electrode according to the present invention. To do.

  The electrode 47 is disposed between the piezoelectric layer 43 and the piezoelectric layer 44, and includes a plurality of facing portions 47a (third electrodes) and a plurality of connection portions 47b. The plurality of facing portions 47a have a substantially rectangular planar shape whose longitudinal direction is the scanning direction, and are disposed so as to face the substantially central portions of the plurality of pressure chambers 10 in the paper feeding direction. Accordingly, the electrode 47 has a smaller area than the portion corresponding to the second electrode of the electrode 46 in a plan view (viewed from the stacking direction of the piezoelectric layers 42 to 44), and is completely included in this portion of the electrode 46. To overlap.

  The plurality of connecting portions 47b extend in the paper feeding direction between the adjacent pressure chamber groups 7, and end portions of the plurality of facing portions 47a arranged on both sides in the scanning direction are connected to each other. The plurality of connecting portions 47b are connected to each other at a position not shown. Further, the electrode 47 is connected to a connection terminal 38 disposed adjacent to the connection terminal 39 at both ends of the upper surface of the piezoelectric layer 44 in the scanning direction through a through hole (not shown) formed in the piezoelectric layer 44. . The connection terminal 38 is connected to the driver IC 51 mounted on the upper surface of the connection terminal 38 by being connected to the COF 50, and the electrode 47 is always connected to a predetermined drive potential (for example, about 20 V, the second potential) different from the ground potential by the driver IC 51. ). As a result, the electrode 45 connected to the electrode 47 is also held at a predetermined driving potential.

  A plurality of electrodes 48 (first electrodes) are arranged corresponding to the plurality of pressure chambers 10. The electrode 48 has a substantially rectangular planar shape, and opposes almost the entire region of the plurality of pressure chambers 10. Thus, the electrode 48 is opposed to the facing portion 47a at a substantially central portion in the paper feeding direction, and extends to the outside of the facing portion 47a on both sides in the paper feeding direction. That is, the opposing portion 47 a has a smaller area than the electrode 48 in plan view, and overlaps with the electrode 48 so as to be completely included. Further, the electrode 48 is opposed to the electrode 46 at a portion outside the portion facing the facing portion 47a. One end of the electrode 48 in the scanning direction (the end opposite to the nozzle 15) extends to a portion not facing the pressure chamber 10 in the scanning direction, and the tip of the connection terminal is used to connect the COF 50. 48a. The electrode 48 is selectively given a ground potential or the above-described drive potential by the driver IC 51.

  Here, the connection terminal 50a of the COF 50 is connected to a drive power supply 53 (see FIG. 8) via an external substrate 52 (see FIG. 8), and power is supplied to the electrodes 45 to 48 from the drive power supply 53. The above-described potential is applied by the driver IC 51. That is, in the present embodiment, the combination of the driver IC 51 and the drive power source 53 corresponds to the drive device according to the present invention.

  Further, in the piezoelectric actuator 32, the piezoelectric layers 42 to 44 and the electrodes 45 to 48 are arranged as described above, so that a part of the piezoelectric layer 42 is sandwiched between the electrode 45 and the electrode 46, and A part is sandwiched between the electrode 46 and the electrode 47, a part of the piezoelectric layer 44 is sandwiched between the electrode 47 and the electrode 48, and a part of the piezoelectric layers 43 and 44 is sandwiched between the electrode 46 and the electrode 48. A portion (active portion R1, first active portion) sandwiched between the electrodes 48 and 46 of the piezoelectric layers 43 and 44 is polarized downward in the thickness direction (electrode sandwiching direction), and the piezoelectric layer The portion sandwiched between 44 electrodes 48 and 47 (active portion R2, second active portion) is polarized upward (opposite to the polarization direction of active portion R1) in its thickness direction (electrode clamping direction). The portion of the piezoelectric layer 42 sandwiched between the electrode 45 and the electrode 46 (compression strain relaxation portion R3) is polarized upward in the thickness direction.

  In the piezoelectric actuator 32, a part of the piezoelectric layer 43 is sandwiched between the electrode 46 and the electrode 47, and a part of the piezoelectric layer 42 is sandwiched between the electrode 45 and the electrode 46. Capacitors are respectively constituted by the portions of the piezoelectric layer 43 sandwiched between these electrodes, and the portions of the electrodes 45 and 46 and the piezoelectric layer 42 sandwiched by these electrodes. Charges are stored in these capacitors due to the potential difference between the electrode 46 and the electrode 47 and the potential difference between the electrode 45 and the electrode 46. That is, the electric charges supplied from the driving device are stored in these capacitors.

  Here, the operation of the piezoelectric actuator 32 will be described. First, in the standby state before the piezoelectric actuator 32 performs the operation of discharging ink, as described above, the electrodes 45 and 47 are held at the driving potential, the electrode 46 is held at the ground potential, and the electrode 48 is held. Is previously held at the ground potential. In this state, the electrode 48 is at a lower potential than the electrode 47 and is at the same potential as the electrode 46.

  As a result, a potential difference is generated between the electrode 48 and the electrode 47, and an electric field in the same direction as the polarization direction is generated in the active portion R2. As a result, the active portion R2 contracts (deforms) in the plane direction orthogonal to the electric field. As a result, so-called unimorph deformation occurs, and the piezoelectric layers 42 to 44 and the portion of the diaphragm 41 facing the pressure chamber 10 are deformed so as to be convex toward the pressure chamber 10 as a whole. In this state, the volume of the pressure chamber 10 is smaller than when the piezoelectric layers 42 to 44 and the diaphragm 41 are not deformed.

  When the piezoelectric actuator 32 is driven to eject ink, the potential of the electrode 48 is once switched to the driving potential, and is returned to the ground potential after a predetermined time has elapsed. When the potential of the electrode 48 is switched to the drive potential, the electrode 48 becomes the same potential as the electrode 47 and at a higher potential than the electrode 46. As a result, the contraction of the active part R2 is restored, and at the same time, a potential difference is generated between the electrode 48 and the electrode 46, and an electric field in the same direction as the polarization direction is generated in the active part R1. Shrink (deform) in the surface direction. As a result, the piezoelectric layers 42 to 44 and the diaphragm 41 are deformed so as to be convex on the opposite side of the pressure chamber 10 as a whole, and the volume of the pressure chamber 10 is increased.

  Thereafter, when the potential of the electrode 48 is returned to the ground potential, the portions facing the pressure chambers 10 of the piezoelectric layers 42 to 44 and the diaphragm 41 become convex toward the pressure chamber 10 as a whole, as described above. The volume of the pressure chamber 10 is reduced. As a result, the pressure of the ink in the pressure chamber 10 increases (pressure is applied to the ink in the pressure chamber 10), and the ink is ejected from the nozzle 15 communicating with the pressure chamber 10.

  Further, when the piezoelectric actuator 32 is driven as described above, when the potential of the electrode 48 is switched from the ground potential to the driving potential, the active portion R2 expands from the contracted state to the pre-contracted state, and at the same time, the active portion R1. Therefore, the extension of the active part R2 is partially absorbed by the contraction of the active part R1. On the other hand, when the potential of the electrode 48 is returned from the driving potential to the ground potential, the active part R2 contracts and the active part R1 expands to the state before contraction, and therefore the contraction of the active part R2 is caused by the extension of the active part R1. Some are absorbed.

  As a result, the deformation of the active portions R1 and R2 is transmitted to a portion facing the other pressure chamber 10, and the ink ejection characteristics from the nozzles 15 communicating with the other pressure chamber 10 fluctuate. Talk is suppressed.

In addition, the piezoelectric material constituting the vibration plate 41 and the piezoelectric layers 42 to 44 is bonded to the flow path unit 31 (cavity plate 21) having a larger linear expansion coefficient than itself by a thermosetting adhesive or the like (specifically). Specifically, the linear expansion coefficient of the piezoelectric material is about 5.5 [10 ⁻⁶ / ° C.], whereas the linear expansion coefficients of SUS430 and SUS316 are 10.5 [10 ⁻⁶ / ° C.], respectively. 16.0 [10 ⁻⁶ / ° C.]. Therefore, when the flow path unit 31 and the piezoelectric actuator 32 are joined, if they are heated and then returned to room temperature, the vibration plate 41 and the piezoelectric layers 42 to 44 have their surfaces due to the difference in linear expansion coefficient between them. Compressive strain occurs in the direction. As a result, as described above, the contraction amounts of the active portions R1 and R2 when the piezoelectric actuator 32 is driven are reduced, and there is a possibility that the ink ejection characteristics from the nozzles 15 may fluctuate.

  However, in the present embodiment, the compressive strain relaxation portion R3 is polarized downward in the thickness direction, and the electrode 46 is held at the ground potential and the electrode 45 is held at the drive potential. Is generated between the electrode 45 and the electrode 45, and an electric field in the same direction as the polarization direction is generated in the compressive strain relaxation portion R3. As a result, the compression strain relaxation portion R3 contracts in the surface direction, and due to this contraction, the portion of the diaphragm 41 and the piezoelectric layers 42 to 44 facing the pressure chamber 10 faces the outside of the pressure chamber 10 in the surface direction. By being pulled, the compressive strain of the active portions R1 and R2 is relaxed. As a result, a decrease in the amount of contraction of the active portions R1 and R2 when the piezoelectric actuator 32 is driven is suppressed.

  Next, the electrical configuration of the inkjet head 3 will be described. FIG. 8 is a circuit diagram of an equivalent circuit showing a connection relationship between the piezoelectric actuator 32, the driver IC 51, the external substrate 52 connected to the driver IC 51, and the drive power supply 53.

  In the piezoelectric actuator 32, since the piezoelectric layers 42 to 44 and the electrodes 45 to 48 are arranged as described above, the portions sandwiched between the electrodes 46 and 47 and the piezoelectric layer 43 as described above. The portions of the electrodes 45 and 46 and the piezoelectric layer 42 sandwiched between these electrodes constitute a capacitor, respectively, and the portions of the electrodes 47 and 48 and the piezoelectric layer 44 sandwiched between these electrodes and the electrodes The portions sandwiched between the electrodes 46 and 48 and the piezoelectric layers 43 and 44 also constitute capacitors.

  Furthermore, as described above, the electrodes 45 and 47 are held at the drive potential by the driver IC 51, the electrode 46 is held at the ground potential, and the electrode 48 has either the ground potential or the drive potential. It is given selectively. Therefore, the piezoelectric actuator 32 can be expressed by an equivalent circuit in which capacitors C1 to C3 are connected to each other as shown in FIG.

  Here, each capacitor C1 in FIG. 8 corresponds to a portion sandwiched between the electrodes 47, 48 and the piezoelectric layer 44, and each capacitor C2 includes these electrodes 46, 48 and the piezoelectric layers 43, 44. Corresponding to the portion sandwiched between the electrodes, each capacitor C3 includes electrodes 46, 47 and a portion corresponding to one pressure chamber 10 among the portions sandwiched between these electrodes of the piezoelectric layer 43, electrodes 45, 46, and This corresponds to a combination of the portion of the piezoelectric layer 42 sandwiched between these electrodes and the portion corresponding to one pressure chamber 10.

  Further, in the driver IC 51, a plurality of driving elements 61 that selectively apply a ground potential and a driving potential to one terminal (electrode 48) of the capacitors C1 and C2 corresponding to each pressure chamber 10 are connected in parallel. Each drive element 61 is supplied with drive power from a drive power supply 53 connected via an external substrate 52. Furthermore, a capacitor C0 connected to both terminals of the drive power supply 53 is disposed on the substrate 52.

  As described above, when the piezoelectric actuator 32 is driven, the potential of the common terminal (electrode 48) of the capacitors C1 and C2 is switched by the drive element 61, whereby charging and discharging are performed in the capacitors C1 and C2. Become. On the other hand, charges are stored in the capacitors C0 and C3 due to the potential difference between the two terminals (charges supplied from the driving device are stored).

  Here, if the capacitors C0 and C3 are not provided, the piezoelectric actuator 32 (capacitors C1 and C2) is supplied from the drive power source 53 when the piezoelectric actuator 32 is driven rapidly, such as when ink is simultaneously ejected from a large number of nozzles 15. ) Flows a large current, which may reduce the voltage of the drive power supply 53.

  However, in the present embodiment, in addition to the driving power supply 53, current flows from the capacitors C0 and C3 to the capacitors C1 and C2, so that when the piezoelectric actuator 32 is driven rapidly, the driving power supply 53 changes to the piezoelectric actuator 32. A large current is suppressed from flowing, and a decrease in the voltage of the drive power supply 53 is suppressed. That is, the capacitors C0 and C3 operate as so-called bypass capacitors.

  At this time, in order to sufficiently suppress the voltage drop of the drive power supply 53, it is necessary that a sufficient amount of current flows from the capacitors C0 and C3 to the capacitors C1 and C2. For this purpose, the capacitances of the capacitors C0 and C3 are required. Needs to be large enough. However, unlike the present embodiment, if the capacitor C3 is not configured inside the piezoelectric actuator 32, the capacitor C0 provided outside the piezoelectric actuator 32 needs to have a large capacitance, and the printer 1 The manufacturing cost will be high.

  On the other hand, in the present embodiment, the portions of the electrodes 46 and 47 and the piezoelectric layer 43 sandwiched between these electrodes, and the portions of the electrodes 45 and 46 and the piezoelectric layer 42 sandwiched between these electrodes, Since each of the capacitors constitutes a capacitor C3 inside the piezoelectric actuator 32, the capacitance of the capacitor C0 can be reduced by the amount of the capacitor C3. Furthermore, when a sufficient capacitance can be obtained with the capacitor C3 alone, the capacitor C0 on the substrate 52 outside the piezoelectric actuator 32 is not necessary. Thereby, the manufacturing cost of the printer 1 is reduced.

  Further, the capacitor constituted by the electrodes 46 and 47 and the portion sandwiched between these electrodes of the piezoelectric layer 43, which is a part of the capacitor C3, is formed using the electrodes 46 and 47 for driving the piezoelectric actuator 32. The capacitor constituted by the electrodes 45 and 46 and the portion sandwiched between the electrodes of the piezoelectric layer 42 is constituted by using the electrode 46 for driving the piezoelectric actuator 32. The structure of the piezoelectric actuator 32 is simplified and the manufacturing cost is reduced as compared with the case where a capacitor is configured by separately providing a dedicated electrode in the piezoelectric layer instead of the electrodes 46 and 47.

  According to the embodiment described above, in the piezoelectric actuator 32, the portions sandwiched between the electrodes 46 and 47 and the piezoelectric layer 43 and the electrodes 45 and 46 and the piezoelectric layer 42 are sandwiched between these electrodes. Each of these parts constitutes a capacitor, and charges are stored in these capacitors due to the potential difference between the electrode 46 and the electrode 47 and the potential difference between the electrode 45 and the electrode 46. In addition, when current flows from these capacitors, a large current flows from the driving power supply 53 to the piezoelectric actuator 32 when the piezoelectric actuator 32 is driven rapidly, for example, when ink is simultaneously ejected from a large number of nozzles 15. And the decrease in the voltage of the drive power supply 53 is suppressed. Further, since such a capacitor is provided inside the piezoelectric actuator 32, the capacitance of the capacitor C0 provided on the external substrate 52 can be reduced. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary.

  In addition, since the electrodes 46 and 47 for driving the piezoelectric actuator 32 are used to configure the capacitor inside the piezoelectric actuator 32, a dedicated electrode is provided separately from the electrodes 46 and 47 to provide the capacitor. Compared with the case where it comprises, the structure of the piezoelectric actuator 32 becomes simple.

  Next, modified examples in which various changes are made to the present embodiment will be described. However, components having the same configuration as in the present embodiment are denoted by the same reference numerals, and description thereof is omitted as appropriate.

  In one modification, an electrode 77 is disposed instead of the electrode 47 as shown in FIG. The electrode 77 includes a plurality of facing portions 77a (first electrodes) and a plurality of connection portions 77b. The plurality of facing portions 77a extend in the scanning direction (left-right direction in FIG. 9), and face the substantially central portion of the pressure chamber 10 in the paper feeding direction. The plurality of connecting portions 77b extend in the paper feed direction (up and down direction in FIG. 9) between all the adjacent pressure chamber rows 8, and the plurality of facing portions 77a disposed on both sides in the scanning direction. Are connected to each other (Modification 1).

  Even in this case, it has the same cross-sectional shape as FIG. 7 (having a structure in which the reference numeral 47 in FIG. 7 is changed to a reference numeral 77), and can be driven in the same manner as in the embodiment. Also in this case, a capacitor is constituted by the portions of the electrodes 46 and 77 and the piezoelectric layer 43 sandwiched between these electrodes and the portion of the electrodes 45 and 46 and the piezoelectric layer 42 sandwiched by these electrodes. Therefore, not only the drive power supply 53 (see FIG. 8) but also current flows from these capacitors, so that when the piezoelectric actuator is driven rapidly, a large current flows from the drive power supply 53 to the piezoelectric actuator. Is suppressed, and the voltage of the drive power supply 53 is suppressed from decreasing. Since such a capacitor is provided inside the piezoelectric actuator, the capacitor C0 provided on the external substrate 52 can have a small capacitance as in the embodiment. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary.

  In another modification, as shown in FIG. 10, a piezoelectric layer 81 is further disposed between the vibration plate 41 and the piezoelectric layer 42. The electrode 82 has a shape similar to that of the electrode 45 between the piezoelectric layer 42 and the piezoelectric layer 81, and the electrode 82 that is always held at the driving potential is disposed. Between them, like the electrode 46, it is arranged over almost the whole area, and an electrode 83 always kept at the ground potential is arranged. And the part (compression distortion relaxation part R4) where the electrode 82 and the electrode 83 of the piezoelectric layer 81 are facing is polarized downward in the thickness direction (Modification 2).

  In this case, in addition to the portions of the electrodes 46 and 47 and the piezoelectric layer 43 sandwiched between these electrodes, and the portion of the electrodes 46 and 82 and the piezoelectric layer 42 sandwiched between these electrodes, the electrodes 82, 83 and Since the portion sandwiched between these electrodes of the piezoelectric layer 81 also forms a capacitor, the total capacitance of capacitors formed inside the piezoelectric actuator (capacitance of the capacitor C3 in FIG. 8) increases. . For this reason, the capacity of the capacitor C0 provided on the external substrate 52 can be further reduced. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary.

  Further, in this case, in addition to the fact that the compressive strain relaxation portion R3 is contracted in the plane direction as in the embodiment, the electric field generated in the compression strain relaxation portion R3 due to the potential difference between the electrode 46 and the electrode 82 is added. Thus, due to the electric field generated in the compressive strain relaxation portion R4 due to the potential difference between the electrode 82 and the electrode 83, the compressive strain relaxation portion R4 also contracts in the surface direction. Therefore, the active portions R1 and R2 are stronger than those in the embodiment, and are pulled toward the outside of the pressure chamber 10 in the surface direction, so that the compressive strain of the active portions R1 and R2 is further relieved.

  In Modification 2, one piezoelectric layer 81 is disposed between the piezoelectric layer 42 and the vibration plate 41, and between the piezoelectric layer 42 and the piezoelectric layer 81 and between the piezoelectric layer 81 and the vibration plate 41. The electrodes 82 and 83 are respectively disposed between the piezoelectric layer 42 and the piezoelectric layer 42. However, the present invention is not limited to this, and a plurality of piezoelectric layers are disposed between the piezoelectric layer 42 and the diaphragm 41. The electrodes held at the ground potential and the electrodes held at the drive potential are alternately arranged between the diaphragm 41 and the lowermost one of the plurality of piezoelectric layers. The part sandwiched between the electrodes of each piezoelectric layer may be polarized in the same direction as the electric field generated in that part. In this case, these electrodes and the portion of the piezoelectric layer sandwiched between these electrodes constitute a capacitor, respectively, and these portions of the piezoelectric layer contract in the plane direction to thereby activate the active portion. The compression distortion of R1 and R2 is alleviated.

  In another modification, as shown in FIG. 11, the piezoelectric layer 42 (see FIG. 7) and the electrode 45 (see FIG. 7) are not provided, and the piezoelectric layer 43 is disposed on the upper surface of the vibration plate 41. In addition, an electrode 46 is disposed between the vibration plate 41 and the piezoelectric layer 43 (Modification 3).

  Even in this case, since the capacitor is constituted by the portions sandwiched between the electrodes 46 and 47 and the piezoelectric layer 43, current flows not only from the drive power supply 53 (see FIG. 8) but also from this capacitor. When the piezoelectric actuator is driven rapidly, a large current is prevented from flowing from the drive power supply 53 to the piezoelectric actuator, and the voltage of the drive power supply 53 is suppressed from decreasing. Since such a capacitor is provided inside the piezoelectric actuator, the capacitance of the capacitor C0 provided on the external substrate 52 (see FIG. 8) can be reduced. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary. In Modification 3, the portion corresponding to one pressure chamber 10 among the portions sandwiched between the electrodes 46 and 47 and the piezoelectric layer 43 corresponds to the capacitor C3 in FIG.

  In this case, since only the electrodes 46 and 47 used for driving the piezoelectric actuator are used as the electrodes for constituting the capacitor inside the piezoelectric actuator, the configuration of the piezoelectric actuator is simplified.

  In another modification, as shown in FIG. 12, between the diaphragm 41 and the piezoelectric layer 42, between the piezoelectric layer 42 and the piezoelectric layer 43, between the piezoelectric layer 43 and the piezoelectric layer 44, and the piezoelectric layer. Electrodes 91 to 94 having the same shapes as those of the electrodes 45 to 48 are disposed at the same positions as the electrodes 45 to 48 on the upper surface of 44. The electrode 91 (dummy electrode) and the electrode 93 are always held at the ground potential (first potential). The electrode 92 is always held at the drive potential (second potential). The electrode 94 (first electrode) is selectively given either a ground potential or a drive potential.

  In addition, the portion (active portion R5, first active portion) sandwiched between the electrodes 92 and 94 of the piezoelectric layers 43 and 44 is polarized upward in the thickness direction (electrode sandwiching direction), and the piezoelectric layer 44 (the active portion R6, the second active portion) sandwiched between the electrode 94 and the electrode 93 is polarized downward (opposite to the polarization direction of the active portion R5) in its thickness direction (electrode clamping direction). The portion of the piezoelectric layer 42 sandwiched between the electrode 91 and the electrode 92 (compression strain relaxation portion R7) is polarized downward in the thickness direction (Modification 4).

  In this case, the portion of the electrode 92 corresponding to the second electrode of the above-described electrode 46 (see FIG. 5), that is, within the range where the pressure chamber 10 is arranged in the scanning direction. The portion corresponds to the third electrode according to the present invention, and the portion of the electrode 93 corresponding to the facing portion 47a (see FIG. 5) corresponds to the second electrode according to the present invention. Then, by arranging the electrodes 91 to 94 as described above, the portion corresponding to the second electrode of the electrode 93 in the plan view is more than the portion corresponding to the third electrode of the electrode 92 and the electrode 94. The area is small, and the electrode 92 overlaps with the portion corresponding to the third electrode and the electrode 94 so as to be completely included.

  In this case, in the standby state in which ink is not ejected from the nozzle 15 (see FIG. 6), as described above, the electrodes 92 and 93 are held at the drive potential and the ground potential, respectively, and the electrode 94 is The driving potential is maintained. As a result, a potential difference is generated between the electrode 94 and the electrode 93, and an electric field in the same direction as the polarization direction is generated in the active portion R6. As a result, the active portion R6 contracts (deforms) in the surface direction, and deforms such that the portions facing the pressure chamber 10 of the piezoelectric layers 42 to 44 and the diaphragm 41 are convex toward the pressure chamber 10 as a whole. . At this time, the volume of the pressure chamber 10 is smaller than the state in which the piezoelectric layers 42 to 44 and the diaphragm 41 are not deformed.

  When ink is ejected from the nozzle 15, the potential of the electrode 94 is temporarily changed to the ground potential, and after a predetermined time has elapsed, the potential is returned to the driving potential. When the potential of the electrode 94 is switched to the ground potential, the electrode 94 becomes the same potential as the electrode 93, the deformation of the active portion R6 is restored, and a potential difference is generated between the electrode 94 and the electrode 92. An electric field in the same direction as the polarization direction is generated in the portion R5, and the active portion R5 contracts (deforms) in the surface direction. As a result, the portions of the piezoelectric layers 42 to 44 and the diaphragm 41 facing the pressure chamber 10 are deformed so as to be convex on the opposite side of the pressure chamber 10 as a whole, and the volume of the pressure chamber 10 is increased.

  After that, when the potential of the electrode 94 is returned to the driving potential, as described above, the portions of the piezoelectric layers 42 to 44 and the diaphragm 41 facing the pressure chamber 10 as a whole are convex toward the pressure chamber 10 as a whole. Due to the deformation, the volume of the pressure chamber 10 is reduced. As a result, the pressure of the ink in the pressure chamber 10 rises, and the ink is ejected from the nozzle 15 communicating with the pressure chamber 10.

  Also in this case, when the potential of the electrode 94 is switched from the drive potential to the ground potential, the active portion R6 expands from the contracted state to the state before contraction, and the active portion R5 contracts, so that the active portion R6 expands. Is partially absorbed by the contraction of the active part R5. Further, when the potential of the electrode 94 is switched from the ground potential to the driving potential, the active portion R6 contracts and the active portion R5 expands from the contracted state to the state before contraction. A part of the active part R5 is absorbed. Accordingly, even in this case, crosstalk is prevented as in the embodiment.

  Also in this case, the compressive strain relaxation portion R7 is polarized downward in the thickness direction, and the electrodes 91 and 92 are held at the ground potential and the drive potential, respectively. Since the electric field in the same direction as the polarization direction is generated, the compressive strain relaxation portion R7 is contracted in the surface direction, and the active portions R5 and R6 are directed to the outside of the pressure chamber 10 in the surface direction by the contraction. Pulled. Accordingly, in this case as well, as in the embodiment, the compressive strain of the active portions R5 and R6 caused by the difference in the linear expansion coefficient between the vibration plate 41 and the piezoelectric layers 42 to 44 and the flow path unit 31 can be reduced.

  Further, even in this case, a capacitor is constituted by the portions of the electrodes 92 and 93 and the piezoelectric layer 43 sandwiched between these electrodes and the portions of the electrodes 91 and 92 and the piezoelectric layer 42 sandwiched between these electrodes. Since electric charges are stored in these capacitors due to the potential difference between the electrode 92 and the electrode 93 and the potential difference between the electrode 92 and the electrode 91, current flows not only from the drive power supply 53 but also from these capacitors. Thus, when the piezoelectric actuator is driven rapidly, a large current is prevented from flowing from the drive power supply 53 to the piezoelectric actuator, and the voltage of the drive power supply is suppressed from decreasing. Since such a capacitor is provided inside the piezoelectric actuator, the capacitance of the capacitor C0 provided on the external substrate 52 (see FIG. 8) can be reduced. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary.

  In this case, the portions of the electrodes 93 and 94 and the piezoelectric layer 44 sandwiched between these electrodes correspond to the capacitor C2 in FIG. 8, and the electrodes 92 and 94 and the electrodes of the piezoelectric layers 43 and 44 The sandwiched portion corresponds to the capacitor C1 in FIG. 8, and the portions of the electrodes 92, 93 and the piezoelectric layer 43 that correspond to one pressure chamber 10 among the portions sandwiched between these electrodes, the electrodes 91, 92, and the piezoelectric layer. A combination of the portion of the layer 42 sandwiched between these electrodes and the portion corresponding to one pressure chamber 10 corresponds to the capacitor C3 in FIG.

  Also, in the fourth modification, as in the third modification, as shown in FIG. 13, the piezoelectric layer 42 (see FIG. 7) and the electrode 91 (see FIG. 12) are not provided. The piezoelectric layer 43 may be disposed, and the electrode 92 may be disposed between the vibration plate 41 and the piezoelectric layer 43 (Modification 5).

  Even in this case, as in the third modification, a capacitor is configured by the portions of the electrodes 92 and 93 and the piezoelectric layer 43 sandwiched between these electrodes, and electric charges are stored in this capacitor due to the potential difference between the electrodes 92 and 93. Therefore, not only the drive power supply 53 (see FIG. 8) but also current flows from this capacitor, so that when the piezoelectric actuator is driven rapidly, a large current flows from the drive power supply 53 to the piezoelectric actuator. Is suppressed, and the voltage of the drive power supply 53 is suppressed from decreasing. Since such a capacitor is provided inside the piezoelectric actuator, the capacitance of the capacitor C0 provided on the external substrate 52 can be reduced. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary. In Modification 5, the portion corresponding to one pressure chamber 10 among the portions of the electrodes 92 and 93 and the piezoelectric layer 43 sandwiched between these electrodes corresponds to the capacitor C3 in FIG.

  Also in this case, as in Modification 3, only the electrodes 92 and 93 used for driving the piezoelectric actuator are used as the electrodes for configuring the capacitor inside the piezoelectric actuator. It will be easy.

  Further, in the above description, the piezoelectric actuator has one of the second electrode and the third electrode having a smaller area than the first electrode and the other of the second electrode and the third electrode, and the first electrode in plan view. In addition, the first electrode and the second electrode, the first electrode and the third electrode, and the second electrode and the third electrode are respectively piezoelectric so as to be completely included in the other. Although it was the structure arrange | positioned so that material may be pinched | interposed, it is not restricted to this, A piezoelectric actuator is 1st electrode and 2nd electrode, 1st electrode and 3rd electrode, and 2nd electrode and 3rd electrode However, any other configuration may be used as long as it is arranged so as to sandwich the piezoelectric material.

  Also in this case, the piezoelectric material sandwiched between the first electrode and the second electrode and the piezoelectric material sandwiched between the first electrode and the third electrode are respectively polarized in the sandwiching direction of these electrodes, and the first electrode These portions of the piezoelectric material are deformed by the potential difference between the first electrode and the second electrode, and the potential difference between the first electrode and the third electrode, and the piezoelectric material sandwiched between the second electrode, the third electrode, and these electrodes. A capacitor for suppressing a large current from flowing from the drive power supply 53 (see FIG. 8) to the piezoelectric actuator is formed by the material.

  Furthermore, in the above description, the piezoelectric material is sandwiched between the first electrode according to the present invention and the third electrode according to the present invention. However, the present invention is not limited to this. In another modification, as shown in FIG. 14, the vibration plate 101 and the piezoelectric layer 102 are disposed on the upper surface of the flow path unit 31, and the vibration plate 101 and the piezoelectric layer 102 are almost entirely disposed between the vibration plate 101 and the piezoelectric layer 102. The electrode 103 (second electrode) held at the ground potential (first potential) is disposed over the upper surface of the piezoelectric layer 102 so that the electrode 104 (first electrode) faces the substantially central portion of the pressure chamber 10. Electrode). Either the ground potential or the drive potential (second potential) is selectively applied to the electrode 104. Further, on the upper surface of the piezoelectric layer 102, electrodes 105 (held at a driving potential) on both sides of the electrode 104 in the paper feeding direction (left and right direction in FIG. 14), that is, on the portion facing the space between adjacent pressure chambers 10 A third electrode) is arranged. Further, a portion of the piezoelectric layer 102 sandwiched between the electrode 104 and the electrode 103 (active portion R8) and a portion sandwiched between the electrode 105 and the electrode 103 (compressive strain relaxation portion R9) are both in the thickness direction ( The electrode is polarized downward (in the clamping direction of the electrodes) (Modification 6).

  In this case, the potential of the electrode 104 is previously held at the ground potential, and when the potential of the electrode 104 is switched to the driving potential, the active portion R8 has the same direction as the polarization direction due to the potential difference between the electrode 104 and the electrode 103. An electric field is generated, and the active portion R8 contracts (deforms) in the surface direction. Thereby, the diaphragm 101 and the piezoelectric layer 102 are deformed so as to be convex toward the pressure chamber 10 as a whole. As a result, the volume of the pressure chamber 10 decreases, the ink pressure in the pressure chamber 10 increases, and ink is ejected from the nozzle 15 (see FIG. 6).

  In this case, the portion of the electrodes 103 and 105 and the piezoelectric layer 102 sandwiched between these electrodes constitutes a capacitor, and electric charges are stored in the capacitor due to the potential difference between the electrode 103 and the electrode 105. Yes. Therefore, not only the drive power supply 53 (see FIG. 8) but also the current flows from this capacitor, so that a large current flows from the drive power supply 53 to the piezoelectric actuator when the piezoelectric actuator is driven suddenly. As a result, the voltage of the drive power supply 53 is suppressed from decreasing. Further, since such a capacitor is provided inside the piezoelectric actuator, the capacitance of the capacitor C0 provided on the external substrate 52 (see FIG. 8) can be reduced. Furthermore, if the total capacitance of the capacitors formed inside the piezoelectric actuator is sufficiently large, the capacitor C0 becomes unnecessary.

  In this case, as shown in FIG. 15, the equivalent circuit corresponding to FIG. 8 has a configuration in which the capacitor C1 does not exist in FIG. 8, and in FIG. 15, the electrodes 103 and 104 and the electrodes of the piezoelectric layer 102 The portion sandwiched between these electrodes corresponds to the capacitor C2, and the portion of the electrodes 103 and 105 and the piezoelectric layer 102 that corresponds to one pressure chamber 10 among the portions sandwiched between these electrodes corresponds to the capacitor C3.

  Also in this case, the compressive strain relaxation portion R9 contracts in the surface direction due to the electric field generated in the compressive strain relaxation portion R9 due to the potential difference between the electrode 103 and the electrode 105, and this contraction causes the active portion R8. Is pulled toward the outside of the pressure chamber 10 in the surface direction, and the compressive strain of the active portion R8 is relaxed.

  In the above description, the portions constituting the capacitor of the piezoelectric layer, that is, the compressive strain relaxation portions R3, R7, and R9 are polarized in the thickness direction. However, these portions of the piezoelectric layer are polarized. It does not have to be.

  In the above description, the piezoelectric actuator has a diaphragm, and the volume of the pressure chamber 10 is reduced by unimorph deformation of the portion of the piezoelectric layer that opposes the pressure chamber 10 by deformation of the piezoelectric layer. However, the present invention is not limited to this, and the present invention can also be applied to a piezoelectric actuator that does not include a diaphragm and that directly changes the volume of the pressure chamber by deformation of the piezoelectric layer.

  In the above, an example in which the present invention is applied to an inkjet head that ejects ink from nozzles has been described. However, the present invention is not limited thereto, and the present invention may be applied to a droplet ejection apparatus that ejects liquid other than ink. Is possible. It is also possible to apply the present invention to a liquid transfer device that uses a piezoelectric actuator for transferring liquid. Furthermore, the present invention can also be applied to piezoelectric actuators for driving drive units of various devices other than the droplet discharge device and the liquid transfer device.

1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. It is a disassembled perspective view of the inkjet head of FIG. It is a top view of the inkjet head of FIG. FIG. 4 is a partially enlarged view of FIG. 3. It is a figure which shows the diaphragm of FIG. 4, and the surface of each piezoelectric layer. It is the VI-VI sectional view taken on the line of FIG. It is the VII-VII sectional view taken on the line of FIG. It is a circuit diagram which shows the equivalent circuit of a piezoelectric actuator, driver IC, and an external substrate. FIG. 6 is a diagram corresponding to FIG. FIG. 8 is a diagram corresponding to FIG. FIG. 10 is a diagram corresponding to FIG. FIG. 10 is a diagram corresponding to FIG. FIG. 10 is a diagram corresponding to FIG. FIG. 10 is a diagram corresponding to FIG. FIG. 10 is a diagram corresponding to FIG.

Explanation of symbols

3 Inkjet Head 10 Pressure Chamber 31 Channel Unit 32 Piezoelectric Actuators 42-44 Piezoelectric Layers 45-48 Electrode 51 Driver IC
53 Driving power supply 81 Piezoelectric layer 82, 83 Electrode 91-94 Electrode 102 Piezoelectric layer 103-105 Electrode

Claims (7)

A first electrode, a second electrode, and a third electrode;
At least the first electrode and the second electrode, and the piezoelectric material sandwiched between the second electrode and the third electrode,
A first potential and a second potential different from the first potential are selectively applied to the first electrode, the first potential is applied to the second electrode, and the second potential is applied to the third electrode. A piezoelectric actuator driven by a driving device that comprises:
The piezoelectric material sandwiched between the first electrode and the second electrode is configured to be deformed when the second potential is applied to the first electrode by being polarized in a sandwiching direction by these electrodes,
The piezoelectric actuator characterized in that the second electrode, the third electrode, and the piezoelectric material sandwiched between them constitute a capacitor for storing electric charges supplied from the driving device. The piezoelectric material is sandwiched between the first electrode and the third electrode;
The piezoelectric material sandwiched between the first electrode and the third electrode is configured to be polarized in the sandwiching direction between these electrodes and to be deformed when the first potential is applied to the first electrode. The piezoelectric actuator according to claim 1. Comprising first and second piezoelectric material layers made of piezoelectric material and laminated together;
The first piezoelectric material layer is sandwiched between the first electrode and the second electrode, and the second piezoelectric material layer is sandwiched between the second electrode and the third electrode,
The second electrode has a smaller area than the first electrode and the third electrode in plan view, and overlaps with the first electrode and the third electrode so as to be completely included,
A portion sandwiched between the first electrode and the second electrode of the first piezoelectric material layer is polarized in a sandwiching direction by these electrodes to constitute a first active portion,
The portion of the first piezoelectric material layer and the second piezoelectric material layer sandwiched between the first electrode and the third electrode is sandwiched by these electrodes and is opposite to the polarization direction of the first active portion. Polarized in the direction to form the second active part,
3. The piezoelectric actuator according to claim 2, wherein the second electrode, the third electrode, and the second piezoelectric material layer sandwiched therebetween constitute the capacitor. A third piezoelectric material layer is laminated on the opposite side of the second piezoelectric material layer to the first piezoelectric material layer,
On the surface of the third piezoelectric material layer opposite to the second piezoelectric material layer, a dummy electrode is provided at a position sandwiching the third piezoelectric material layer together with the third electrode,
The dummy electrode can be electrically connected to the second electrode so as to have the first potential, and the capacitor is constituted by the third electrode, the dummy electrode, and the third piezoelectric material layer sandwiched between them. The piezoelectric actuator according to claim 3. Comprising first and second piezoelectric material layers made of piezoelectric material and laminated together;
The first piezoelectric material layer is sandwiched between the first electrode and the third electrode, and the second piezoelectric material layer is sandwiched between the third electrode and the second electrode,
The third electrode has a smaller area than the first electrode and the second electrode in plan view, and overlaps with the first electrode and the second electrode so as to be completely included,
A portion of the first piezoelectric material layer sandwiched between the first electrode and the third electrode is polarized in a sandwiching direction by these electrodes to constitute a first active portion,
The portion of the first piezoelectric material layer and the second piezoelectric material layer sandwiched between the first electrode and the second electrode is the direction sandwiched by these electrodes and opposite to the polarization direction of the first active portion. Polarized in the direction to form the second active part,
3. The piezoelectric actuator according to claim 2, wherein the second electrode, the third electrode, and the second piezoelectric material layer sandwiched therebetween constitute the capacitor. A third piezoelectric material layer is laminated on the opposite side of the second piezoelectric material layer to the first piezoelectric material layer,
On the surface of the third piezoelectric material layer opposite to the second piezoelectric material layer, a dummy electrode is provided at a position sandwiching the third piezoelectric material layer together with the second electrode,
The dummy electrode can be electrically connected to the third electrode so as to have the second potential, and the capacitor is constituted by the second electrode, the dummy electrode, and the third piezoelectric material layer sandwiched between them. The piezoelectric actuator according to claim 5. A flow path unit including a pressure chamber in which a liquid transfer flow path for transferring a liquid is formed;
A pressure chamber, comprising: a front first electrode, a second electrode, and a third electrode; and at least the first electrode and the second electrode; and a piezoelectric material sandwiched between the second electrode and the third electrode. A piezoelectric actuator that applies pressure to the liquid;
It has a drive device that drives the piezoelectric actuator,
The driving device selectively applies a first potential to the first electrode and a second potential different from the first potential, applies the first potential to the second electrode, and applies the first potential to the third electrode. Applying a second potential,
The piezoelectric actuator is
The piezoelectric material sandwiched between the first electrode and the second electrode is configured to be deformed when the second potential is applied to the first electrode by being polarized in the sandwiching direction by these electrodes,
The liquid transfer device according to claim 1, wherein the second electrode, the third electrode, and the piezoelectric material sandwiched between the second electrode and the third electrode constitute a capacitor for storing electric charges supplied from the driving device.

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