JP6232802B2 - Piezoelectric actuator and liquid ejection device - Google Patents

Description

  The present invention relates to a piezoelectric actuator and a liquid ejection device.

  Patent Document 1 discloses an ink jet head that ejects ink from nozzles. The ink jet head of Patent Document 1 includes a flow path unit in which a plurality of nozzles and a plurality of pressure chambers are formed, and a piezoelectric actuator joined to the flow path unit so as to cover the plurality of pressure chambers.

  The piezoelectric actuator disclosed in Patent Document 1 includes a piezoelectric body including three piezoelectric layers, and a plurality of individual electrodes, a first common electrode, and a second common electrode provided on the piezoelectric body. The plurality of individual electrodes are arranged on the uppermost piezoelectric layer. The first common electrode is disposed between the uppermost piezoelectric layer and the intermediate piezoelectric layer. The second common electrode is disposed between the intermediate piezoelectric layer and the lowermost piezoelectric layer. Further, the plurality of individual electrodes respectively face the plurality of pressure chambers of the flow path unit. The first common electrode and the second common electrode are respectively disposed across the plurality of pressure chambers and face the plurality of individual electrodes. The portion of the piezoelectric body sandwiched between the individual electrode and the first common electrode (active portion R1) and the portion sandwiched between the individual electrode and the second common electrode (active portion R2) are respectively in the thickness direction of the piezoelectric body. Polarized.

  Two types of potentials, a predetermined drive potential and a ground potential, are selectively applied to the individual electrodes. The first common electrode and the second common electrode are constant potential electrodes that are always maintained at a predetermined potential. The first common electrode is maintained at the driving potential, and the second common electrode is maintained at the ground potential. When the potential of the individual electrode is the ground potential, a potential difference between the drive potential and the ground potential is applied to the active portion R1, and piezoelectric deformation occurs in the active portion R1. Further, when the potential of the individual electrode is a driving potential, a similar potential difference is applied to the active part R2, and piezoelectric deformation occurs in the active part R2. The piezoelectric actuator imparts ejection energy to the ink in the pressure chamber by causing the piezoelectric body to bend and change the volume of the pressure chamber by the piezoelectric deformation of the two types of active portions R1 and R2.

JP 2011-212865 A

  By the way, in the above piezoelectric actuator, in order to achieve high deformation efficiency, it is desired that each piezoelectric layer is as thin as possible. However, when the piezoelectric layer is thinned, the strength of the electric field acting on the active part increases, and there is a possibility that dielectric breakdown may occur in the active part. In addition, since the thickness of the active part R1 is thinner than that of the active part R2, insulation breakdown in the active part R1 becomes a problem.

  Here, it is possible to keep the electric field strength acting on the active portions R1 and R2 low by simply lowering the drive potential to reduce the potential difference applied to the active portions R1 and R2. However, when the electric field applied to the active portions R1 and R2 is lowered, the piezoelectric deformation in each active portion is reduced, so that the displacement amount of the entire piezoelectric body is also reduced, which is counterproductive in that the deformation efficiency is improved. It becomes.

  An object of the present invention is to provide a piezoelectric actuator capable of suppressing the maximum electric field strength acting on the active portion to a low level without reducing the displacement amount of the piezoelectric body as much as possible.

According to a first aspect of the present invention, there is provided a piezoelectric actuator having a laminated first piezoelectric layer and a second piezoelectric layer, and a drive electrode disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer. A first constant potential electrode disposed between the first piezoelectric layer and the second piezoelectric layer and facing the drive electrode in the thickness direction of the piezoelectric body, and the first piezoelectric layer A second constant potential electrode disposed on a surface opposite to the piezoelectric layer and facing the drive electrode in the thickness direction of the piezoelectric body; the drive electrode; the first constant potential electrode; and the second A driving device for applying a potential to each of the constant potential electrodes,
The piezoelectric body has a first active portion polarized in the thickness direction of the first piezoelectric layer in a portion sandwiched between the drive electrode and the first constant potential electrode of the first piezoelectric layer, A portion of the first piezoelectric layer and the second piezoelectric layer sandwiched between the drive electrode and the second constant potential electrode is polarized in the thickness direction of the first piezoelectric layer and the second piezoelectric layer. 2 active parts,
The driving device switches the potential of the driving electrode between a first potential and a second potential lower than the first potential, and sets the potential of the first constant potential electrode higher than the second potential. In addition, a third potential lower than the first potential is maintained, and a potential of the second constant potential electrode is maintained at a fourth potential lower than the third potential.

  Two types of potentials, a first potential and a second potential, are selectively applied to the drive electrode. The potential of the first constant potential electrode is maintained at a third potential between the first potential and the second potential. When the lower second potential is applied to the drive electrode, a potential difference is generated between the drive electrode and the first constant potential electrode that is always maintained at the third potential. An electric field acts on the first active portion sandwiched between the electrodes in the thickness direction. Here, since the third potential applied to the first constant potential electrode is lower than the first potential, the first potential is lower than the conventional configuration in which the first potential is applied to the first constant potential electrode. The potential difference between the electrodes sandwiching the active part is reduced, and the strength of the electric field acting on the first active part is reduced.

  As described above, when the electric field acting on the first active portion is suppressed to a low level, the piezoelectric deformation of the first active portion is naturally reduced accordingly. In this regard, in the present invention, even when the first potential is applied to the drive electrode, a potential difference is generated between the drive electrode and the first constant potential electrode, and an electric field acts on the first active portion. However, the direction of the electric field at this time is opposite to that when the second potential is applied to the individual electrode. Therefore, the first active portion is deformed in the opposite direction to the previous case, and thereby the piezoelectric body is also displaced in the opposite direction.

  Thus, by applying the present invention, the displacement amount of the piezoelectric body when the second potential is applied to the drive electrode is smaller than that of the conventional configuration, but the decrease in the displacement amount is applied to the drive electrode. When the first potential is applied, the piezoelectric body is compensated by displacement in the reverse direction. Therefore, when viewed from the total displacement amount of the piezoelectric body while the potential of the drive electrode is switched between the first potential and the second potential, a displacement amount necessary to drive the drive target can be obtained. That is, according to the present invention, while ensuring the amount of displacement of the piezoelectric body necessary for driving the drive target, the maximum electric field strength acting on the first active portion is suppressed to a low level, and the dielectric breakdown of the first active portion is reduced. Can be prevented.

  According to a second aspect of the present invention, in the piezoelectric actuator according to the first aspect, the driving device applies a potential equal to the second potential as the fourth potential to the second constant potential electrode. Is.

  According to the present invention, since the potential equal to the second potential is applied to the second constant potential electrode, the types of potentials required to drive the piezoelectric actuator can be reduced to three types. Therefore, the circuit configuration necessary for driving the piezoelectric actuator is simplified.

  A piezoelectric actuator according to a third aspect is characterized in that, in the first aspect, the driving device applies a potential higher than the second potential as the fourth potential to the second constant potential electrode. To do.

  Needless to say, the first constant potential electrode and the second constant potential electrode are opposed to each other, and even if the first constant potential electrode and the second constant potential electrode are not opposed to each other, the second constant potential electrode is formed from the first constant potential electrode to the second piezoelectric layer. The electric field heading toward will act somewhat. According to the present invention, the electric field strength acting on the second piezoelectric layer can be reduced by applying a potential higher than the second potential to the second constant potential electrode. Further, when the first potential is applied to the drive electrode, the potential difference between the drive electrode and the second constant potential electrode is reduced, and the electric field acting on the second active part sandwiched between these two types of electrodes is reduced. Strength decreases. Therefore, the maximum electric field strength can also be lowered for the second active portion.

According to a fourth aspect of the present invention, there is provided a liquid discharge device including a nozzle for discharging a liquid, a flow channel structure including a pressure channel communicating with the nozzle, and a piezoelectric element provided in the flow channel structure. An actuator, and
The piezoelectric actuator is provided in the flow path structure so as to cover the pressure chamber, and has a stacked first piezoelectric layer and second piezoelectric layer, and the second piezoelectric layer. A drive electrode disposed in a region facing the pressure chamber in the thickness direction of the piezoelectric body on a surface opposite to the piezoelectric layer; disposed between the first piezoelectric layer and the second piezoelectric layer; and A first constant potential electrode facing the drive electrode in the thickness direction of the piezoelectric body, and a surface of the second piezoelectric layer opposite to the first piezoelectric layer, and the thickness direction of the piezoelectric body A second constant potential electrode facing the drive electrode, and a drive device for applying a potential to each of the drive electrode, the first constant potential electrode, and the second constant potential electrode,
The piezoelectric body has a first active portion polarized in the thickness direction of the first piezoelectric layer in a portion sandwiched between the drive electrode and the first constant potential electrode of the first piezoelectric layer, A portion of the first piezoelectric layer and the second piezoelectric layer sandwiched between the drive electrode and the second constant potential electrode is polarized in the thickness direction of the first piezoelectric layer and the second piezoelectric layer. 2 active parts,
The driving device switches the potential of the driving electrode between a first potential and a second potential lower than the first potential, and sets the potential of the first constant potential electrode higher than the second potential. The third potential is maintained lower than the first potential, and the potential of the second constant potential electrode is maintained at a fourth potential lower than the third potential.

  According to the present invention, as in the first aspect of the invention, the maximum electric field strength acting on the first active portion can be kept small while securing the amount of displacement of the piezoelectric body necessary for driving the driven object. it can.

  According to a fifth aspect of the present invention, the liquid ejection apparatus according to the fourth aspect further includes a temperature detection unit that detects a temperature of the piezoelectric body, and a control unit that controls the driving device, and the control unit includes: The third potential applied to the first constant potential electrode is changed by controlling the driving device in accordance with the temperature detected by the temperature detection unit.

  In the present invention, the temperature detection unit is not limited to the one that directly contacts the piezoelectric body and directly detects the temperature, and the one that is provided away from the piezoelectric body and detects the ambient temperature around the piezoelectric body. Including. In the present invention, since the third potential of the first constant potential electrode is a potential between the first potential and the second potential applied to the drive electrode, the state in which the first potential is applied to the drive electrode and the second potential are applied. The direction of the electric field acting on the first active part is reversed when the potential is applied. That is, in one state, an electric field in the positive direction that is the same as the polarization direction acts on the first active portion, and in the other state, an electric field in the direction opposite to the polarization direction acts on the first active portion. become.

  By the way, when an electric field of a certain level or more acts on the active part polarized in a predetermined direction in the direction opposite to the polarization direction, the state polarized in the thickness direction is broken. Further, the electric field strength in the reverse direction when the polarization state collapses depends on the temperature. Specifically, when the temperature of the piezoelectric body is high, the polarization state tends to collapse even if the electric field strength acting in the reverse direction is small. Therefore, in the present invention, the third potential applied to the first constant potential electrode is changed according to the temperature detected by the temperature detection unit. Thereby, when the temperature of the piezoelectric body is high, the third potential is changed so as to suppress the electric field strength in the reverse direction to be small, so that the inversion state of the first active portion can be suppressed. Conversely, when the temperature of the piezoelectric body is low, the polarization does not collapse even if the electric field strength in the reverse direction is somewhat large. Therefore, the third potential is changed so as to suppress the electric field strength in the positive direction. 1. Prevent dielectric breakdown of the active part.

  In the present invention, since the third potential applied to the first constant potential electrode is a potential between the first potential and the second potential, a potential equal to the first potential is applied to the first constant potential electrode. As compared with the above, the maximum intensity of the electric field acting on the first active portion is lowered. In addition, by applying the present invention, the displacement of the piezoelectric body when the second potential is applied to the drive electrode is reduced, but the decrease in the displacement is caused when the first potential is applied to the drive electrode. The piezoelectric body is compensated by displacement in the opposite direction. Therefore, according to the present invention, the maximum electric field strength acting on the first active portion can be kept small while securing the amount of displacement of the piezoelectric body necessary for driving the drive target.

1 is a schematic plan view of an ink jet printer according to an embodiment. It is a top view of an inkjet head. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. It is the VV sectional view taken on the line of FIG. FIG. 4 is a top view of each of the three piezoelectric layers of the piezoelectric body, where (a) shows the uppermost piezoelectric layer, (b) shows the intermediate piezoelectric layer, and (c) shows the lowermost piezoelectric layer. It is a figure which shows roughly the electrical structure of the control apparatus, a power supply device, and the piezoelectric actuator of an inkjet head. It is an equivalent circuit diagram of two active parts and a drive part of a piezoelectric actuator. It is operation | movement explanatory drawing of a piezoelectric actuator. It is operation | movement explanatory drawing of the piezoelectric actuator of a change form. FIG. 9 is an equivalent circuit diagram corresponding to FIG. 8 in another modification. FIG. 9 is an equivalent circuit diagram corresponding to FIG. 8 in another modification. FIG. 9 is an equivalent circuit diagram corresponding to FIG. 8 in another modification. It is sectional drawing of the piezoelectric actuator of another modification. FIG. 9 is an equivalent circuit diagram corresponding to FIG. 8 in another modification. It is sectional drawing of the piezoelectric actuator of the form which concerns on a disclosed invention. FIG. 17 is an equivalent circuit diagram of an active part and a drive part of the piezoelectric actuator of FIG. 16.

  Next, an embodiment of the present invention will be described. FIG. 1 is a schematic plan view of the ink jet printer of the present embodiment. First, a schematic configuration of the inkjet printer 1 will be described with reference to FIG. In the following, the front side in FIG. 1 is defined as the upper side, and the other side of the page is defined as the lower side, and the explanation will be made using direction words “up” and “down” as appropriate.

(Schematic configuration of the printer)
As shown in FIG. 1, the inkjet printer 1 includes a platen 2, a carriage 3, an inkjet head 4, a transport mechanism 5, a control device 6, and the like.

  On the upper surface of the platen 2, a recording sheet 100 as a recording medium is placed. The carriage 3 is configured to reciprocate in the scanning direction along the two guide rails 10 and 11 in a region facing the platen 2. An endless belt 14 is connected to the carriage 3, and the endless belt 14 is driven by a carriage drive motor 15, whereby the carriage 3 moves in the scanning direction.

  The inkjet head 4 is attached to the carriage 3 and moves in the scanning direction together with the carriage 3. The inkjet head 4 is connected to ink cartridges 17 of four colors (for example, black, yellow, cyan, and magenta) mounted on the printer 1 by a tube (not shown). A plurality of nozzles 25 are formed on the lower surface of the inkjet head 4 (the surface on the opposite side of the paper surface in FIG. 1). The inkjet head 4 ejects the four colors of ink supplied from the ink cartridge 17 to the recording paper 100 placed on the platen 2 from the plurality of nozzles 25.

  The transport mechanism 5 includes two transport rollers 18 and 19 disposed so as to sandwich the platen 2 in the transport direction. The transport mechanism 5 transports the recording paper 100 placed on the platen 2 in the transport direction by two transport rollers 18 and 19.

  As shown in FIG. 7, which will be described later, the control device 6 includes a CPU (Central Processing Unit) 70, a ROM (Read Only Memory) 71, a RAM (Random Access Memory) 72, and an ASIC including various control circuits. Application Specific Integrated Circuit) 73 and the like (see FIG. 7 described later). The control device 6 is connected to an external device such as a PC (not shown) so that data communication is possible.

  The control device 6 executes a printing process on the recording paper 100 by the CPU 70 and the ASIC 73 in accordance with a program stored in the ROM 71. That is, the control device 6 controls the inkjet head 4, the carriage drive motor 15, and the like based on a print command input from an external device such as a PC, and causes an image or the like to be printed on the recording paper 100. Specifically, an ink discharge operation for discharging ink while moving the inkjet head 4 in the scanning direction together with the carriage 3 and a transport operation for transporting the recording paper 100 in the transport direction by the transport rollers 18 and 19 alternately. To do. In the above description, the control device 6 performs various processing by the CPU 70 and the ASIC 73. However, the present invention is not limited to this, and the control device 6 may be realized by any hardware configuration. Good. For example, the processing may be shared by two or more ICs such as a CPU and an ASIC. Further, only one IC chip may be used to control the operation of the ink jet printer 1 based on the above-described program.

(Detailed configuration of inkjet head)
Next, the inkjet head 4 will be described. FIG. 2 is a plan view of the inkjet head. FIG. 3 is a partially enlarged view of FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3, and FIG. 5 is a cross-sectional view taken along line VV in FIG. 2 and 4, the COF 63 connected to the actuator unit 60 of the piezoelectric actuator 21 is schematically shown by a two-dot chain line. In FIG. 5, the flow path structure below the pressure chamber 26 shown in FIG. 4 is not shown. As shown in FIGS. 2 to 5, the inkjet head 4 includes a flow path unit 20 and a piezoelectric actuator 21.

(Configuration of flow path unit)
As shown in FIG. 4, the flow path unit 20 is formed by laminating seven plates 31 to 37 each having a flow path forming hole. When these seven plates 31 to 37 are stacked, the respective flow path forming holes communicate with each other, whereby the flow path unit 20 is formed with an ink flow path as described below.

  As shown in FIG. 2, four ink supply holes 23 connected to the four ink cartridges 17 (see FIG. 1) are formed on the upper surface of the flow path unit 20. In the flow path unit 20, four manifolds 24 connected to the four ink supply holes 23 are formed. Four inks of four ink cartridges 17 are supplied to the four manifolds 24 through the four ink supply holes 23, respectively. The four manifolds 24 extend in the transport direction.

  The flow path unit 20 includes a plurality of nozzles 25 formed on the lowermost plate 37 and a plurality of pressure chambers 26 formed on the uppermost plate 31. As shown in FIG. 2, a plurality of nozzles 25 are arranged along the transport direction on the lower surface of the flow path unit 20 (the surface on the other side of the paper in FIG. 3), and four rows each corresponding to the four manifolds 24. A nozzle row is configured. Each pressure chamber 26 is a hole having a substantially rectangular planar shape that is long in the scanning direction.

  The plurality of pressure chambers 26 are arranged in a plane along the upper surface of the flow path unit 20. The plurality of pressure chambers 26 are covered from above by the piezoelectric body 40 of the piezoelectric actuator 21 joined to the upper surface of the flow path unit 20. The plurality of pressure chambers 26 are arranged in four rows corresponding to the four manifolds 24 and the four nozzle rows. Each pressure chamber 26 communicates with a corresponding manifold 24 through a throttle channel 27. On the other hand, each pressure chamber 26 communicates with a corresponding nozzle 25 via a communication channel 28. As described above, as shown in FIG. 4, the individual ink flow path branches from the manifold 24 to the flow path unit 20 and reaches the nozzle 25 through the throttle flow path 27, the pressure chamber 26, and the communication flow path 28. A plurality of are formed.

(Configuration of piezoelectric actuator)
The piezoelectric actuator 21 includes an actuator unit 60 and a drive unit 61 that drives the actuator unit 60. The actuator unit 60 is joined to the upper surface of the flow path unit 20 so as to cover the plurality of pressure chambers 26. As shown in FIGS. 2 to 5, the actuator unit 60 includes a piezoelectric body 40 including three piezoelectric layers 41 to 43, a plurality of individual electrodes 44, a first common electrode 45, and a second common electrode 46. It has. FIG. 6 is a top view of each of the three piezoelectric layers of the piezoelectric body, where (a) is the uppermost piezoelectric layer, (b) is the intermediate piezoelectric layer, and (c) is the lowermost piezoelectric layer. Respectively. 6A to 6C, the positional relationship among the nozzle 25 and the pressure chamber 26, the individual electrode 44, the first common electrode 45, and the second common electrode 46 is easily understood. A plurality of nozzles 25 and a plurality of pressure chambers 26 are respectively indicated by broken lines.

  Each of the three piezoelectric layers 41 to 43 constituting the piezoelectric body 40 is made of a piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate. The piezoelectric layers 41 to 43 are planarly arranged on the upper surface of the flow path unit 20 so as to cover the plurality of pressure chambers 26 in a state of being stacked on each other.

  As shown in FIGS. 3 to 6, the plurality of individual electrodes 44 are arranged on the upper surface of the uppermost piezoelectric layer 41. The first common electrode 45 is disposed between the uppermost piezoelectric layer 41 and the intermediate piezoelectric layer 42. The second common electrode 46 is disposed between the intermediate piezoelectric layer 42 and the lowermost piezoelectric layer 43.

  As shown in FIGS. 2 and 3, each individual electrode 44 is disposed on the upper surface of the piezoelectric layer 41 in a region facing almost the entire region of the pressure chamber 26 in the thickness direction of the piezoelectric body 40. As shown in FIGS. 2 and 6A, the plurality of individual electrodes 44 are arranged along the transport direction corresponding to the plurality of pressure chambers 26 to form four individual electrode rows. An individual terminal 49 is drawn out from each individual electrode 44, and a bump 57 made of a conductive material such as gold is provided at the end of the individual terminal 49. As shown in FIG. 4, a COF 63 that is a wiring member is pressed against and bonded to the bump 57. Thereby, the individual terminal 49 is electrically connected to the wiring formed in the COF 63 via the bump 57.

  As shown in FIGS. 4, 5, and 6B, the first common electrode 45 includes a plurality of first constant potential electrode portions 45a respectively corresponding to the plurality of pressure chambers 26, and a plurality of first constant potential electrodes. It has the 1st connection part 45b which conducts the part 45a mutually. Each first constant potential electrode portion 45 a has a rectangular planar shape, and is opposed to the central portion in the transport direction of the corresponding pressure chamber 26 in the thickness direction of the piezoelectric body 40. The plurality of first constant potential electrode portions 45 a are also arranged in four rows corresponding to the plurality of pressure chambers 26, similarly to the plurality of individual electrodes 44.

  As shown in FIGS. 4, 5, and 6 (c), the second common electrode 46 includes a plurality of second constant potential electrode portions 46 a respectively corresponding to the plurality of pressure chambers 26, and a plurality of second constant potential electrodes. It has the 2nd connection part 46b which conducts the part 46a mutually. Each of the second constant potential electrode portions 46 a has a U-shaped planar shape, and is opposed to both end portions in the transport direction of the pressure chamber 26 in the thickness direction of the piezoelectric body 40. The plurality of second constant potential electrode portions 46 a are also arranged in four rows corresponding to the plurality of pressure chambers 26, similarly to the plurality of individual electrodes 44.

  As shown in FIG. 5, the individual electrode 44 covering almost the entire area of the pressure chamber 26 is opposed to the first constant potential electrode portion 45 a at the center in the transport direction. That is, the individual electrode 44 and the first constant potential electrode portion 45 a overlap in the thickness direction of the piezoelectric body 40. A portion of the uppermost piezoelectric layer 41 facing the central portion of the pressure chamber 26 is sandwiched between the individual electrode 44 and the first constant potential electrode portion 45a. Hereinafter, the portion of the piezoelectric layer 41 sandwiched between the individual electrode 44 and the first constant potential electrode portion 45a is referred to as a first active portion 51. As indicated by the white arrow a1 in FIG. 5, the first active part 51 is polarized upward in the thickness direction, that is, in the direction from the first constant potential electrode part 45a toward the individual electrode 44.

  The individual electrodes 44 are opposed to the second constant potential electrode portions 46a at both ends in the transport direction. That is, the individual electrode 44 and the second constant potential electrode portion 46 a overlap in the thickness direction of the piezoelectric body 40. And the part which opposes the conveyance direction both ends of the pressure chamber 26 of two upper piezoelectric layers 41 and 42 is pinched | interposed into the individual electrode 44 and the 2nd constant potential electrode part 46a. Hereinafter, the portion of the piezoelectric layers 41 and 42 sandwiched between the individual electrode 44 and the second constant potential electrode portion 46a is referred to as a second active portion 52. As indicated by a white arrow a2 in FIG. 5, the second active portion 52 is polarized downward in the thickness direction, that is, in a direction from the individual electrode 44 toward the second constant potential electrode portion 46a. As shown in FIG. 6C, the second constant potential electrode portion 46 a has a shape in which the central portion is cut out, and the first constant potential electrode portion 45 a that overlaps the central portion of the pressure chamber 26. Are not overlapping in the thickness direction of the piezoelectric body 40.

  As shown in FIGS. 2 and 6A, on the upper surface of the uppermost piezoelectric layer 41, a first connection terminal 47 for the first common electrode 45 and a second connection terminal 48 for the second common electrode 46 are provided. Is provided. The first connection terminal 47 is electrically connected to the first connection portion 45 b of the first common electrode 45 through a plurality of through holes 50 formed in the piezoelectric layer 41. The second connection terminal 48 is connected to the second connection portion 46 b of the second common electrode 46 through the plurality of through holes 53 formed in the piezoelectric layer 41 and the plurality of through holes 54 formed in the piezoelectric layer 42. Conducted.

  As shown in FIGS. 2 and 6A, the plurality of individual terminals 49, the first connection terminals 47, and the second connection terminals 48 arranged on the upper surface of the uppermost piezoelectric layer 41 include COF 63 and Bumps 57, 58, and 59 are provided for connection.

  Next, the drive unit 61 that applies potentials to the three types of electrodes 44, 45, and 46 of the actuator unit 60 will be described. FIG. 7 is a diagram schematically illustrating an electrical configuration of the control device, the power supply device, and the piezoelectric actuator of the inkjet head. The drive unit 61 includes a head substrate 62, a driver IC 64, and the like. In addition, although illustration is abbreviate | omitted, the head board | substrate 62 of the drive part 61 is connected with the power supply device 55 and the control apparatus 6 by wiring members, such as a flexible flat cable (FFC).

  The drive unit 61 includes a power line 66 a connected to the VDD terminal of the power supply device 55 and a ground line 66 b connected to the GND terminal of the power supply device 55 formed on a wiring member such as FFC. A power supply potential (generally also referred to as a power supply voltage) is always applied to the power supply line 66a. The ground line 66b is maintained at the ground potential (0 V). Further, the head substrate 62 of the drive unit 61 is connected to the control device 6 by a plurality of signal wirings 66c formed on a wiring member such as FFC. The ASIC 73 of the control device 6 generates a control signal for controlling the driver IC 64 based on print data input from an external device such as a PC (not shown). The control signal generated by the ASIC 73 is sent to the head substrate 62 through a plurality of signal wirings 66c.

  The head substrate 62 is connected to the actuator unit 60 by a COF 63 on which a driver IC 64 is mounted. As shown in FIGS. 2 and 4, the COF 63 is disposed so as to cover the piezoelectric body 40 of the actuator unit 60 from above. A plurality of terminals (not shown) are provided on the back surface of the COF 63. The plurality of terminals of the COF 63 are formed on the upper surface of the piezoelectric body 40, the individual terminals 49 of the plurality of individual electrodes 44, the first connection terminal 47 that is electrically connected to the first common electrode 45, and the second common electrode 46. The second connection terminal 48 that is conductive is electrically connected to each other through the bumps 57, 58, and 59.

  Based on the control signal transmitted from the control device 6 via the head substrate 62, the driver IC 64 sets the potential applied to the individual electrode 44 to the first potential V1 equal to the power supply potential and the second potential V2 equal to the ground potential. Switch between and. FIG. 8 is an equivalent circuit diagram of two active parts and a drive part of the piezoelectric actuator. The first active part 51 and the second active part 52 of the actuator part 60, which are formed of a piezoelectric material that is a ferroelectric substance, store electric charges when a potential difference occurs between the electrodes sandwiching the active parts 51 and 52, The stored charge is released when the potential difference is resolved. That is, the first active part 51 and the second active part 52 can be regarded as capacitors C1 and C2 having a certain capacitance, respectively. The driver IC 64 is a kind of switching circuit composed of transistors. Based on the control signal transmitted from the control device 6, by switching ON / OFF of the two switches SW1 and SW2 shown in FIG. 8, the potential at the point A in FIG. Switching between the first potential V1 and the second potential V2.

  As shown in FIG. 7, a potential generation circuit 65 is incorporated in the head substrate 62. The potential generation circuit 65 generates an intermediate third potential V3 that is higher than the second potential V2 and lower than the first potential V1. The circuit configuration of the potential generation circuit 65 is not particularly limited, but an example is shown in FIG. The potential generation circuit 65 of FIG. 8 includes a wiring 68 connecting the power supply line 66a and the ground line 66b, and two resistors R1 and R2 provided on the wiring 67. The potential difference between the first potential V1 of the power supply line 66a and the second potential V2 of the ground line 66b is divided by the two resistors R1 and R2, and a third potential V3 intermediate between them is generated.

  The output of the potential generation circuit 65 is connected to the point B in FIG. In other words, the third potential V3 (point B potential) applied to the first constant potential electrode portion 45a sandwiching the first active portion 51 between the individual electrodes 44 is always generated by the potential generation circuit 65. It is maintained at a potential between the first potential V1 and the second potential V2. A ground line 66b is connected to the point C in FIG. That is, the fourth potential V4 (point C potential) applied to the second constant potential electrode portion 46a sandwiching the second active portion 52 with the individual electrode 44 is always maintained at a potential equal to the second potential V2. Is done.

  The potential application to the three types of electrodes 44, 45a, 46a by the driving unit 61 described above is summarized as follows. The potential of the individual electrode 44 is switched between a first potential V1 that is a power supply potential and a second potential V2 that is a ground potential. The first constant potential electrode portion 45a is maintained at a third potential V3 between the first potential V1 and the second potential V2. The potential of the second constant potential electrode portion 46a is maintained at the fourth potential V4 that is equal to the second potential V2. As will be described later, the third potential V3 is closer to the first potential V1 than the second potential V2. For example, V1 = 28V, V2 (= V4) = 0V, and V3 = 23V.

(Operation of piezoelectric actuator)
Next, the operation of the actuator unit 60 of the piezoelectric actuator 21 when the potential of the individual electrode 44 is switched by the driver IC 64 of the driving unit 61 will be described. FIG. 9 is an explanatory diagram of the operation of the actuator unit. In FIG. 9, thick vertical arrows b1 and b2 indicate the directions of the electric fields acting on the active portions 51 and 52, respectively, and solid horizontal arrows c1 and c2 indicate the surface directions in the active portions 51 and 52, respectively. The deformation direction (elongation or contraction) is shown.

(A) When Second Potential is Applied FIG. 9A shows a state where the second potential V <b> 2 is applied to the individual electrode 44. At this time, a potential difference is generated between the individual electrode 44 and the first constant potential electrode portion 45a, and as indicated by an arrow b1, the first active portion 51 moves from the first constant potential electrode portion 45a toward the individual electrode 44. An upward electric field acts. Further, as indicated by an arrow a1, the polarization direction of the first active portion 51 is also upward. Therefore, since the direction of the electric field acting on the first active portion 51 is the same as the polarization direction, the first active portion 51 contracts in the surface direction as indicated by the arrow c1. When the first active portion 51 facing the central portion of the pressure chamber 26 contracts in the surface direction, the piezoelectric body 40 bends so as to be convex toward the pressure chamber 26 (lower side), and the central portion thereof is downward. Displace. Since the same potential as the second potential V2 is applied to the second constant potential electrode portion 46a, no potential difference is generated between the individual electrode 44 and the second constant potential electrode portion 46a. Therefore, an electric field does not act on the second active part 52, and the second active part 52 is not deformed.

  Here, the third potential V3 applied to the first constant potential electrode portion 45a is a potential between the first potential V1 and the second potential V2. Therefore, compared with the case where the first potential V1 is applied to the first constant potential electrode portion 45a, the potential difference between the individual electrode 44 and the first constant potential electrode portion 45a is reduced and acts on the first active portion 51. The strength of the electric field decreases. For example, if V1 = 28V, V2 = 0V, and V3 = 23V, the potential difference between the individual electrode 44 and the first constant potential electrode portion 45a is changed from V1-V2 (= 28V) to V3-V2 (= 23V). Go down. Thereby, since the strength of the electric field acting on the first active part 51 can be lowered, the dielectric breakdown in the first active part 51 can be prevented. As described above, when the electric field acting on the first active part 51 is reduced, the piezoelectric deformation (shrinkage amount) of the first active part 51 is naturally reduced, and the center of the pressure chamber 26 of the piezoelectric body 40 is reduced accordingly. The downward displacement amount of the part facing the part is also reduced. However, as will be described later, in the piezoelectric actuator 21 of the present embodiment, the decrease in the displacement amount of the piezoelectric body 40 is supplemented when a first potential V1 is applied to the individual electrode 44 described later. .

(B) When First Potential is Applied FIG. 9B shows a state where the first potential V1 is applied to the individual electrode 44. FIG. Even in this case, a potential difference is generated between the individual electrode 44 and the first constant potential electrode portion 45a. However, in this case, the potential of the individual electrode 44 is higher than the potential of the first constant potential electrode 45a. Accordingly, as indicated by the arrow b1, a downward electric field acting from the individual electrode 44 toward the first constant potential electrode portion 45a acts on the first active portion 51, contrary to FIG. 9A. This electric field is in the opposite direction to the polarization direction of the first active part 51 indicated by the arrow a1. Therefore, as indicated by the arrow c1, the first active portion 51 extends in the surface direction.

  Further, when the first potential V1 is applied to the individual electrode 44, a potential difference also occurs between the individual electrode 44 and the second constant potential electrode portion 46a, and the second active portion 52 has a potential as indicated by an arrow b2. A downward electric field from the individual electrode 44 toward the second constant potential electrode portion 46a acts. Further, as indicated by the arrow a2, the polarization direction of the second active portion 52 is also downward. Therefore, the direction of the electric field acting on the second active part 52 becomes the same as the polarization direction, and the second active part 52 contracts in the surface direction.

  Thus, the potential of the individual electrode 44 is switched from the second potential V2 to the first potential V1, and the first active portion 51 is contracted in the plane direction of FIG. ), The second active portion 52 conversely contracts in the surface direction. As a result, the piezoelectric body 40 bends so as to be convex on the opposite side (upper side) of the pressure chamber 26, and its central portion is displaced upward.

  In addition, when the first active portion 51 extends, the second active portion 52 contracts at the same time, so that the amount of contraction in the surface direction is changed over the entire portion of the piezoelectric body 40 covering one pressure chamber 26. Can be kept small. Thereby, a phenomenon in which the deformation of the piezoelectric body 40 in a certain pressure chamber 26 is transmitted to another adjacent pressure chamber 26, so-called crosstalk, is suppressed.

  As described above, when the first potential V1 is applied to the individual electrode 44, the piezoelectric body 40 is deformed in the direction opposite to the previous application of the second potential V2. By applying a third potential V3 lower than the first potential V1 to the first constant potential electrode portion 45a, the piezoelectric body 40 when the second potential V2 is applied to the individual electrode 44 of FIG. 9A. The total displacement amount is reduced, but the decrease in the displacement amount is compensated by the displacement of the piezoelectric body 40 in the reverse direction when the first potential is applied to the individual electrode 44 in FIG. 9B. Therefore, when viewed from the total displacement amount of the piezoelectric body 40 when the potential of the individual electrode 44 is switched between the first potential V1 and the second potential V2, a displacement amount necessary to eject ink is obtained. be able to. Therefore, the maximum electric field strength acting on the first active portion 51 can be suppressed to a low level while ensuring the amount of displacement of the piezoelectric body 40 necessary for ejecting ink.

  However, when a strong electric field acts on the first active portion 51 in the direction opposite to the polarization direction, the polarization state is destroyed. Therefore, the first potential V1 applied to the individual electrode 44 and the first constant potential electrode are not applied to the first active part 51 so that an electric field large enough to destroy the polarization state does not act in the direction opposite to the polarization direction. It is necessary that the potential difference of the third potential V3 applied to the portion 45a is not more than a certain value. Therefore, in the present embodiment, the third potential V3 is closer to the first potential V1 than the second potential V2. For example, if V1 = 28V, V2 = 0V, and V3 = 23V, the potential difference between the first potential V1 and the third potential V3 is 5V.

  Since a potential equal to the second potential V2 is applied to the second constant potential electrode portion 46a, when the first potential is applied to the individual electrode 44, there is no gap between the two electrodes 44 and 46a. A relatively large potential difference (V1-V2) is generated. However, since the second active part 52 is thicker than the first active part 51, even if the same potential difference as the first active part 51 occurs, the strength of the applied electric field is lower than that of the first active part 51. . Therefore, the second active portion 52 does not cause problems such as dielectric breakdown even if the potential difference is slightly larger than that of the first active portion 51.

  In the present embodiment, the first constant potential electrode portion 45a and the second constant potential electrode portion 46a do not face each other and do not overlap in the thickness direction. However, even in such a configuration, as shown in FIG. 5, the piezoelectric layer 42 has a thickness direction of the piezoelectric body 40 from the first constant potential electrode portion 45a toward the second constant potential electrode portion 46a. On the other hand, there is a portion 42a where a strong electric field always acts in a direction inclined outward. The portion 42a is originally a portion that should function as the second active portion 52. However, since the above-described electric field is always acting, the portion 42a hardly expands or contracts even when the potential of the individual electrode 44 is switched. Further, as the potential difference between the first constant potential electrode portion 45a and the second constant potential electrode portion 46a is larger, the stronger electric field spreads in the surface direction, and the portion 42a that does not function as the second active portion 52 becomes larger. Therefore, lowering the potential applied to the first constant potential electrode portion 45a is also effective in suppressing the functional degradation of the second active portion 52.

  As described above, when the potential of the individual electrode 44 is switched between the first potential V <b> 1 and the second potential V <b> 2, the piezoelectric body 40 is displaced up and down in a region facing the pressure chamber 26, and thus the volume of the pressure chamber 26. Changes. Due to this volume change, pressure (discharge energy) is applied to the ink in the pressure chamber 26, and the ink is discharged from the nozzle 25 communicating with the pressure chamber 26.

  In the embodiment described above, the inkjet head 4 corresponds to the “liquid ejecting apparatus” of the invention. The flow path unit 20 corresponds to the “flow path structure” of the present invention. The uppermost piezoelectric layer 41 corresponds to the “first piezoelectric layer” of the present invention. The intermediate piezoelectric layer 42 corresponds to the “second piezoelectric layer” of the present invention. The individual electrode 44 corresponds to the “drive electrode” of the present invention. The first constant potential electrode portion 45a corresponds to the “first constant potential electrode” of the present invention. The second constant potential electrode portion 46a corresponds to the “second constant potential electrode” of the present invention. The drive unit 61 corresponds to the “drive device” of the present invention. The control device 6 corresponds to the “control unit” of the present invention.

  Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configuration as in the above embodiment are given the same reference numerals and description thereof is omitted as appropriate.

1] In the above embodiment, the second constant potential electrode portion 46a is applied with the same potential as the second potential V2 applied to the individual electrode 44 as the fourth potential V4 (see FIG. 9). A potential different from the two potential V2 may be applied. In FIG. 10, the point that the potential of the first constant potential electrode unit 45a is maintained at the third potential V3 is the same as in the above embodiment, but the fourth potential V4 of the second constant potential electrode unit 46a is the individual electrode. 44, which is higher than the second potential V2. That is, the relationship between the four potential levels is V1> V3> V4> V2. As shown in FIG. 11, the fourth potential V4, which is different from the second potential V2, is the first potential V1 and the second potential V2 in the potential generation circuit 65 of the drive unit 61 in the same manner as the third potential V3. Can be easily generated by dividing the voltage difference with the three resistors R1, R2 and R3.

  As shown in FIG. 10A, when the second potential V2 is applied to the individual electrode 44, the first active portion 51 contracts in the plane direction, while the second active portion 52 has a polarization direction The electric field in the reverse direction acts, and the second active part 52 extends in the surface direction. The expansion of the second active portion 52 serves to promote the deformation when the piezoelectric body 40 is deformed to be convex downward due to the contraction of the first active portion 51. In order to avoid the polarization state of the second active part 52 from being destroyed by the reverse electric field acting on the second active part 52, the potential difference (V4− between the individual electrode 44 and the second constant potential electrode part 46a). V2) is preferably made smaller than a certain value. Specifically, the fourth potential V4 is closer to the second potential V2 than the first potential V1. For example, V1 = 28V, V2 = 0V, V3 = 23V, V4 = 5V, and V4-V2 = 5V.

  As shown in FIG. 10B, when the first potential V1 is applied to the individual electrode 44, an electric field in the same direction (positive direction) as the polarization direction acts on the second active portion 52, and the second The active part 52 contracts in the surface direction. Here, since the fourth potential V4 of the second constant potential electrode portion 46a is higher than the second potential V2, a potential equal to the second potential V2 is applied to the second constant potential electrode portion 46a. In comparison, the potential difference between the individual electrode 44 and the second constant potential electrode portion 46a is reduced, and the intensity of the electric field acting on the second active portion 52 is also reduced.

  The piezoelectric actuator of FIG. 9 of the embodiment is compared with the piezoelectric actuator of FIG. 10 of the modified embodiment. In the configuration of FIG. 9, since the potential equal to the second potential V2 is applied to the second constant potential electrode portion 46a, the types of potentials applied to the three types of electrodes 44, 45a, 46a are set to three types. Can do. Accordingly, the configuration of the circuit necessary for driving the piezoelectric actuator of the drive unit 61 is simplified. On the other hand, in the configuration of FIG. 10, although the type of potential is increased by one, the fourth potential V4 higher than the second potential V2 is applied to the second constant potential electrode portion 46a, thereby acting on the piezoelectric layer 42. Thus, the strength of the electric field from the first constant potential electrode portion 45a toward the second constant potential electrode portion 46a can be reduced. Furthermore, not only the first active part 51 but also the second active part 52 is advantageous in that the maximum electric field strength can be lowered.

2] The configuration of the drive unit 61 is not limited to that of the above embodiment. For example, as shown in FIG. 12, in the potential generation circuit 65, the third potential V3 may be generated using a Zener diode D instead of a resistor. Alternatively, as shown in FIG. 13, to drop from the first potential V1 to the third potential V3 between the power supply line 66a to which the first potential V1 is applied and the first constant potential electrode portion 45a of the piezoelectric actuator 21. The resistor Ra may be provided.

  Further, the present invention is not limited to the configuration in which the two potentials (first potential V1 and second potential V2) supplied from the power supply device 55 are divided to generate the third potential V3 and the fourth potential V4. That is, the third potential V3 (fourth potential V4) generated by the power supply device 55 is independent of the first constant potential electrode portion 45a (second constant potential electrode portion 46a) via the FFC 67 and the COF 63. May be supplied.

3] Regarding specific values of the first potential V1 to the fourth potential V4, in addition to those exemplified above, within a range where the relationship of the first potential V1> the third potential V3> the second potential V2 is established, It can be changed as appropriate.

  For example, in the previous example, all the potentials are positive potentials, but some potentials (for example, the second potential V2) may be negative potentials. However, such a negative potential cannot be easily generated by dividing the power supply potential and the ground potential as in the above-described embodiment, and the configuration of the drive unit 61 and the like becomes slightly complicated.

  Further, the fourth potential V4 applied to the second constant potential electrode portion 46a may be lower than the second potential V2. However, when the second potential V2 is the ground potential (0V), the fourth potential V4 is a negative potential. In this case, the configuration for supplying the fourth potential V4 becomes complicated as described above. Further, when the fourth potential V4 is lower than the second potential V2, the first constant potential electrode portion 45a to which the third potential V3 is applied and the second constant potential electrode portion 46a to which the fourth potential V4 is applied. This is also disadvantageous in that the potential difference between them increases, and the strength of the electric field acting on the piezoelectric layer 42 increases.

4] In the above embodiment, the second constant potential electrode portion 46a is patterned in a U shape, and the first constant potential electrode portion 45a and the second constant potential electrode portion 46a do not overlap (FIG. 4). To FIG. 6). On the other hand, as shown in FIG. 14, for example, the second constant potential electrode portion 46a is formed so as to face the entire area of the pressure chamber 26 and overlaps the first constant potential electrode portion 45a. Also good.

  In this case, the electric field due to the potential difference between the third potential V3 and the fourth potential V4 always acts on the portion 42b of the piezoelectric layer 42 sandwiched between the first constant potential electrode portion 45a and the second constant potential electrode portion 46a. To do. In order to keep the intensity of the electric field acting on the portion 42b as small as possible, the third potential V3 is set lower than the first potential V1 and the fourth potential V4 is set lower than the second potential V2, as shown in FIG. It is preferable to reduce the potential difference V4-V3, for example, by increasing the potential.

5] As described above, when an electric field of a certain level or more acts on the first active portion 51 in the direction opposite to the polarization direction, the polarization state of the first active portion 51 is destroyed. Here, the electric field strength in the reverse direction when the polarization state collapses depends on the temperature. Specifically, when the temperature of the piezoelectric body 40 is high, the polarization state is easily broken even if the electric field strength in the reverse direction is small. Therefore, the third potential V3 applied to the first constant potential electrode portion 45a may be changed according to the temperature of the piezoelectric body 40.

  As shown in FIG. 15, a signal from a temperature sensor 75 that detects the ambient temperature (environment temperature) of the inkjet head 4 is input to the control device 6. Using this temperature sensor 75, the approximate temperature of the piezoelectric body 40 is detected (estimated). The temperature sensor 75 may be provided in the piezoelectric body 40 itself, and the temperature of the piezoelectric body 40 may be directly detected.

  As described above, the potential generation circuit 65 of the drive unit 61 divides the potential difference between the first potential V1 and the second potential V2 to generate two resistors R1 and R2 for generating the third potential V3. Have. However, one resistor R1 is a variable resistor. In response to the detection signal of the temperature sensor 75, the control device 6 outputs a signal for controlling the resistance value of the variable resistor R1 to the potential generation circuit 65, and changes the resistance value. Specifically, the higher the temperature detected by the temperature sensor 75, the smaller the resistance value of the variable resistor R1, and the third potential V3 approaches the first potential V1.

  Thereby, when the temperature of the piezoelectric body 40 is high, the inversion state of the first active part 51 is destroyed by bringing the third potential V3 close to the first potential V1 and suppressing the electric field strength in the direction opposite to the polarization direction. This can be suppressed. On the contrary, when the temperature of the piezoelectric body 40 is low, the polarization does not collapse even if the electric field strength in the reverse direction is somewhat large. Therefore, the potential difference between the third potential V3 and the first potential V1 is increased, thereby suppressing the maximum electric field strength in the same positive direction as the polarization direction, thereby preventing the dielectric breakdown of the first active portion 51 more reliably.

  Similarly to the above, the fourth potential applied to the second constant potential electrode portion 46 a may be changed according to the temperature of the piezoelectric body 40.

  In the above-described embodiment and its modifications, the present invention is applied to an inkjet head that prints an image or the like by ejecting ink onto a recording sheet. The present invention can also be applied to a liquid ejection apparatus that is used. For example, the present invention can also be applied to a liquid ejection device that ejects a conductive liquid onto a substrate to form a conductive pattern on the substrate surface. Furthermore, the piezoelectric actuator of the present invention is not limited to those used for liquid ejection applications, and the present invention can be applied to piezoelectric actuators used for other applications.

  Next, disclosed inventions other than the inventions according to claims 1 to 5 described in the claims at the beginning of the application will be described.

A nozzle that discharges the liquid, and a flow channel structure in which a liquid channel including a pressure chamber communicating with the nozzle is formed, and a piezoelectric actuator provided in the flow channel structure,
The piezoelectric actuator is disposed in a region facing the pressure chamber in the thickness direction of the piezoelectric layer on one surface of the piezoelectric layer and a piezoelectric layer provided in the flow path structure so as to cover the pressure chamber. Drive electrode, a constant potential electrode facing the drive electrode in the thickness direction of the piezoelectric layer on the other surface of the piezoelectric layer, and a drive for applying a potential to the drive electrode and the constant potential electrode. An apparatus,
The piezoelectric body has an active portion polarized in the thickness direction of the piezoelectric layer at a portion sandwiched between the drive electrode and the constant potential electrode of the piezoelectric layer,
The driving device switches the potential of the driving electrode between a first potential and a second potential lower than the first potential, and sets the potential of the constant potential electrode higher than the second potential. Maintaining a third potential lower than one potential,
Furthermore, a temperature detection unit that detects the temperature of the piezoelectric body, and a control unit that controls the drive device, the control unit according to the temperature detected by the temperature detection unit, The third potential applied to the first constant potential electrode is changed to control the liquid discharge device according to the invention.

  The above disclosed invention corresponds to claim 5 in the scope of claims at the beginning of the application, but the technical scope of the above disclosed invention includes those not based on the configuration of claim 4. For example, the configuration of the piezoelectric actuator does not assume two types of constant potential electrodes, and includes only a drive electrode and one constant potential electrode.

  Hereinafter, modifications of the embodiment of the disclosed invention will be described. As shown in FIG. 16, the piezoelectric actuator 21A (actuator portion 60A) includes a piezoelectric body 40A composed of two stacked piezoelectric layers 41A and 42A, an individual electrode 44A formed on the upper surface of the piezoelectric layer 41A, and two A common electrode 45 </ b> A formed between the piezoelectric layers 41 and 42. A portion of the piezoelectric layer 41A sandwiched between the individual electrode 44A and the common electrode 45A is an active portion 51A that is polarized downward. The individual electrode 44A corresponds to the drive electrode in the above disclosed invention, and the common electrode 45A corresponds to the constant potential electrode in the above disclosed invention.

  FIG. 17 shows an equivalent circuit diagram of the active part 51A and the drive part 61A. The active part 51A is equivalent to the capacitor C. The driver IC 64A switches the potential (point D potential) of the individual electrode 44A between the first potential V1 and the second potential V2. The potential generation circuit 65A divides the potential difference between the first potential V1 and the second potential V2 by the two resistors R1 and R2, and the third potential is lower than the first potential V1 and higher than the second potential V2. V3 is generated. The potential of the common electrode 45A (point E potential) is maintained at the third potential V3. Further, one resistor R2 of the potential generating circuit 65A is a variable resistor. The control device 6A outputs a signal for controlling the variable resistor R2 to the potential generation circuit 65A according to the detection result of the temperature sensor 75A, and changes the resistance value of the variable resistor R2.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 4 Inkjet head 6 Control apparatus 20 Flow path unit 21 Piezoelectric actuator 25 Nozzle 26 Pressure chamber 40 Piezoelectric body 41 Piezoelectric layer 42 Piezoelectric layer 44 Individual electrode 45a 1st constant potential electrode part 46a 2nd constant potential electrode part 51 1st Active part 52 Second active part 60 Actuator part 61 Drive part 64 Driver IC
75 Temperature sensor

Claims (7)

A piezoelectric body having a laminated first piezoelectric layer and second piezoelectric layer;
A drive electrode disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer;
A first constant potential electrode disposed between the first piezoelectric layer and the second piezoelectric layer and facing the drive electrode in the thickness direction of the piezoelectric body;
A second constant potential electrode disposed on a surface of the second piezoelectric layer opposite to the first piezoelectric layer and facing the drive electrode in the thickness direction of the piezoelectric body;
A driving device for applying a potential to each of the driving electrode, the first constant potential electrode, and the second constant potential electrode;
The piezoelectric body is
A portion of the first piezoelectric layer sandwiched between the drive electrode and the first constant potential electrode has a first active portion polarized in the thickness direction of the first piezoelectric layer;
A portion of the first piezoelectric layer and the second piezoelectric layer sandwiched between the drive electrode and the second constant potential electrode is polarized in the thickness direction of the first piezoelectric layer and the second piezoelectric layer. 2 active parts,
The driving device includes:
Switching the driving electrode potential between a first potential and a second potential lower than the first potential;
Maintaining the potential of the first constant potential electrode at a third potential that is higher than the second potential and lower than the first potential;
The piezoelectric actuator characterized in that the potential of the second constant potential electrode is maintained at a fourth potential lower than the third potential.   2. The piezoelectric actuator according to claim 1, wherein the driving device applies a potential equal to the second potential as the fourth potential to the second constant potential electrode.   2. The piezoelectric actuator according to claim 1, wherein the driving device applies a potential higher than the second potential as the fourth potential to the second constant potential electrode. A flow channel structure in which a liquid flow channel including a nozzle for discharging liquid and a pressure chamber communicating with the nozzle is formed;
A piezoelectric actuator provided in the flow path structure,
The piezoelectric actuator is
A piezoelectric body provided in the flow path structure so as to cover the pressure chamber and having a laminated first piezoelectric layer and second piezoelectric layer;
A drive electrode disposed in a region facing the pressure chamber in the thickness direction of the piezoelectric body on the surface of the first piezoelectric layer opposite to the second piezoelectric layer;
A first constant potential electrode disposed between the first piezoelectric layer and the second piezoelectric layer and facing the drive electrode in the thickness direction of the piezoelectric body;
A second constant potential electrode disposed on a surface of the second piezoelectric layer opposite to the first piezoelectric layer and facing the drive electrode in the thickness direction of the piezoelectric body;
A driving device for applying a potential to each of the driving electrode, the first constant potential electrode, and the second constant potential electrode;
The piezoelectric body is
A portion of the first piezoelectric layer sandwiched between the drive electrode and the first constant potential electrode has a first active portion polarized in the thickness direction of the first piezoelectric layer;
A portion of the first piezoelectric layer and the second piezoelectric layer sandwiched between the drive electrode and the second constant potential electrode is polarized in the thickness direction of the first piezoelectric layer and the second piezoelectric layer. 2 active parts,
The driving device includes:
Switching the driving electrode potential between a first potential and a second potential lower than the first potential;
Maintaining the potential of the first constant potential electrode at a third potential that is higher than the second potential and lower than the first potential;
The liquid ejecting apparatus according to claim 1, wherein the potential of the second constant potential electrode is maintained at a fourth potential lower than the third potential. A temperature detection unit for detecting the temperature of the piezoelectric body; and a control unit for controlling the driving device;
The control unit controls the driving device according to the temperature detected by the temperature detection unit to change the third potential applied to the first constant potential electrode. The liquid discharge apparatus according to 1. The piezoelectric actuator according to claim 1, wherein the third potential is higher than ½ of the first potential. The piezoelectric actuator according to claim 1, wherein a difference between the first potential and the third potential is 5 V or less.

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