Piezoelectric actuator

Abstract

To provide a piezoelectric actuator with a strain gauge capable of compensating the influence of temperature change.SOLUTION: A driving part 111 in which a plurality of piezoelectric ceramic layers 113 and a plurality of internal electrodes 115 and 116 are alternately stacked and which is driven when a voltage is applied to the internal electrodes 115 and 116, and a plurality of second piezoelectric ceramic layers 114 and a plurality of second internal electrodes 117 and 118 which are formed in series in a stacking direction of the driving part 111 and are alternately stacked, A piezoelectric actuator 100 includes a piezoelectric actuator body 105 including a non-driving portion 112 that is not driven even when a voltage is applied, a strain gauge 131 that is connected to a driving portion 111 and detects strain in a displacement direction of the driving portion 111, and a second strain gauge 132 that is connected to the non-driving portion 112 and detects strain in the displacement direction of the non-driving portion 112, in which a second piezoelectric ceramic layer 114 is polarized, and second internal electrodes 117 and 118 are electrically short-circuited.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric actuator that is displaced by application of a voltage. [Background technology]

[0002] Piezoelectric elements exhibit different displacement characteristics (hysteresis) when expanded and contracted, so they are used in precision positioning in semiconductor exposure equipment and other devices by performing feedback control using displacement sensors to improve positioning accuracy. High-precision piezoelectric actuators with feedback control using displacement sensors are also used in the fine-motion mechanisms of precision numerically controlled processing machines, medical manipulators, and precision attitude control mechanisms for aerospace applications. Furthermore, piezoelectric actuators are also used to drive flow control valves that supply various gases to semiconductor manufacturing equipment, and as the precision of controlled flow rates increases, actuators with built-in displacement sensors are now being used.

[0003] Patent Document 1 discloses a piezoelectric actuator in which an electrostrictive element, in which piezoelectric ceramic layers and internal electrode conductors are alternately stacked, is sealed in a metal case, in which a displacement sensor is provided on the side of the electrostrictive element and electrically connected to the electrostrictive element, and this displacement sensor is sealed in the metal case together with the electrostrictive element.

[0004] Cited Document 2 discloses a piezoelectric actuator having a structure including an active part of a laminated structure in which at least ceramic layers exhibiting piezoelectricity and internal electrode layers are alternately stacked, and which generates strain along an axis perpendicular to the ceramic layers and the internal electrode layers in response to an externally applied driving voltage, wherein the structure is made up of a plurality of parts along the vertical axis, and adjacent parts of the plurality of parts are made to differ from each other in at least one of the strain along the vertical axis caused by the driving voltage, the strain along the vertical axis caused by elasticity, and the strain along the vertical axis caused by thermal expansion, and wherein a strain gauge is fixed to each of the plurality of parts to detect the strain along the vertical axis generated by the respective parts. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-206536 [Patent Document 2] Japanese Patent Application Publication No. 6-188471 Summary of the Invention [Problem to be solved by the invention]

[0006] When using a strain gauge as a displacement sensor, the total displacement is estimated from the displacement of a portion of the piezoelectric element, so it is necessary to ensure a high correlation between the strain gauge output and the total displacement. However, with the technology described in Patent Document 1, the strain gauge output is affected by temperature changes. For example, when a piezoelectric actuator is expanded and contracted at high speed, or when the piezoelectric actuator is used to control the flow rate of high-temperature gas, the strain gauge output changes due to heat generation in the element and fluctuations in the environmental temperature around the actuator. This can lead to a problem of a decrease in the correlation coefficient between the strain gauge output and the total displacement, resulting in larger detection errors.

[0007] A common temperature compensation method using strain gauges is to perform temperature compensation by measuring displacement strain in two orthogonal axes. This method requires that the substrate on which the strain gauge is attached has an isotropic thermal expansion coefficient. However, this method cannot be applied to polarized piezoelectric ceramics, as they have different thermal expansion coefficients in the polarization direction and the direction perpendicular to it.

[0008] Furthermore, Patent Document 2 describes that by using a temperature compensation member with a strain gauge attached, it is possible to accurately measure the overall displacement while performing temperature compensation. However, it is necessary to select an appropriate temperature compensation member for each piezoelectric material, and consideration is required each time the material is changed. In addition, the longer the driving part of the piezoelectric element, the longer the temperature compensation member must be, which creates the problem of increasing the size of the entire actuator.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a piezoelectric actuator with strain gauges that can compensate for the effects of temperature changes. [Means for solving the problem]

[0010] (1) In order to achieve the above object, a piezoelectric actuator according to an application example of the present invention employs the following measures: That is, the piezoelectric actuator according to an application example of the present invention includes a piezoelectric actuator body including a drive section in which a plurality of piezoelectric ceramic layers and a plurality of internal electrodes are alternately stacked and which is driven when a voltage is applied to the internal electrodes, and a non-drive section in which a plurality of second piezoelectric ceramic layers and a plurality of second internal electrodes are alternately stacked and which is formed in series in the stacking direction of the drive section and which does not drive even when a voltage is applied, a strain gauge connected to the drive section and which detects strain in the displacement direction of the drive section, and a second strain gauge connected to the non-drive section and which detects strain in the displacement direction of the non-drive section, wherein the second piezoelectric ceramic layers are polarized and the second internal electrodes are electrically short-circuited.

[0011] (2) Furthermore, in the piezoelectric actuator of the application example of (1) above, the driving section has an external electrode electrically connected to the internal electrode, and the external electrode is electrically connected to a voltage supply member at one end side of the driving section in the stacking direction, and the non-driving section is formed in the piezoelectric actuator body at the other end of the driving section in the stacking direction.

[0012] (3) In the piezoelectric actuator according to the application example of (1) or (2) above, the strain gauge and the second strain gauge are each provided in plural.

[0013] (4) Furthermore, in the piezoelectric actuator according to any of the application examples (1) to (3) above, the driving unit has an external electrode electrically connected to the internal electrode, and the external electrode is electrically connected to a voltage supply member at one end side of the driving unit in the stacking direction, and further includes a seat supporting an end portion on the one end side of the piezoelectric actuator body, and a metal cap accommodating the piezoelectric actuator body to which the strain gauge and the second strain gauge are connected. [Effects of the Invention]

[0014] According to the present invention, a piezoelectric actuator with a strain gauge can be provided that is capable of compensating for the effects of temperature changes. [Brief explanation of the drawings]

[0015] [Figure 1] 1A and 1B are a front view and a side view, respectively, showing an example of a piezoelectric actuator according to an embodiment of the present invention. [Figure 2] (a) and (b) are front cross-sectional views of a piezoelectric element. [Figure 3] 1A and 1B are a front cross-sectional view and a side cross-sectional view, respectively, showing an example of a sealed piezoelectric actuator according to an embodiment of the present invention. [Figure 4] 1A and 1B are a front cross-sectional view and a bottom view of a seat, a voltage supply member, and a terminal for a strain gauge, respectively. [Figure 5] FIG. 1 is a schematic diagram of a displacement control system. DETAILED DESCRIPTION OF THE INVENTION

[0016] Next, an embodiment of the present invention will be described with reference to the drawings. To facilitate understanding of the description, the same reference numerals are used to designate the same components in the drawings, and duplicated descriptions will be omitted. Note that in the configuration diagrams, the size of each component is shown conceptually and does not necessarily represent the actual dimensional ratio.

[0017] [Embodiment] (Structure of piezoelectric actuator) 1(a) and 1(b) are a front view and a side view, respectively, showing an example of a piezoelectric actuator 100 according to an embodiment of the present invention. Note that the piezoelectric actuator shown in the reference drawings is just an example, and the present invention is not limited by the number of elements, etc.

[0018] Piezoelectric actuator 100 is composed of piezoelectric actuator body 105, strain gauge 131, second strain gauge 132, voltage supply members (driving terminals) 141 and 142, and strain gauge terminals 143, 144, and 145, and expands and contracts when a voltage is applied. Piezoelectric actuator 100 is used, for example, in a valve opening / closing control section of a mass flow controller or a stage driving section of a precision positioning device, and in that case, displaces a driven body (valve, stage).

[0019] When a voltage is applied to a pair of external electrodes 121, 122 via a pair of lead wires 125, 126, the driving section 111 of the piezoelectric actuator body 105 expands and contracts, displacing the tip of the piezoelectric actuator body 105. Voltage supply members 141, 142 are connected to the lead wires 125, 126 of the piezoelectric actuator body 105, respectively, and transmit the applied voltage to the lead wires 125, 126.

[0020] 1(a) and 1(b), piezoelectric actuator 100 has strain gauge 131 and second strain gauge 132 connected to piezoelectric actuator body 105, and is provided with strain gauge terminals 143, 144, and 145. Thus, piezoelectric actuator 100 equipped with strain gauge 131 and second strain gauge 132 can receive a displacement signal of piezoelectric element 110 via strain gauge terminals 143, 144, and 145. Details of strain gauge 131 and second strain gauge 132 will be described later.

[0021] The GND terminal for driving the voltage supply member of the piezoelectric actuator body 105 and the GND terminal for the strain gauge may be common. This prevents the total number of terminals from increasing, and makes it easier to configure the wiring and the like.

[0022] (Piezoelectric actuator body) The piezoelectric actuator body 105 comprises a driving section 111 in which a plurality of piezoelectric ceramic layers 113 and a plurality of internal electrodes 115, 116 are alternately stacked, and which is driven when a voltage is applied to the internal electrodes 115, 116; and a non-driving section 112 in which a plurality of second piezoelectric ceramic layers 114 and a plurality of second internal electrodes 117, 118 are alternately stacked, and which is formed in series in the stacking direction of the driving section 111. The stacking direction of the driving section 111 refers to the stacking direction of the piezoelectric ceramic layers 113 and the internal electrodes 115, 116. The non-driving section 112 in which a voltage is applied does not drive, meaning that it does not drive even when a voltage is applied to drive the piezoelectric actuator 100.

[0023] The second piezoelectric ceramic layer 114 is polarized. The second internal electrodes 117 and 118 are electrically shorted. The polarization of the second piezoelectric ceramic layer 114 results in different thermal expansion coefficients in the polarization direction and the direction perpendicular to the polarization direction, similar to the piezoelectric ceramic layer 103. The electrical shorting of the second internal electrodes 117 and 118 prevents the polarized second piezoelectric ceramic layer 104 from being charged due to the pyroelectric effect. This allows the second strain gauge 132 to measure displacements caused by factors other than the voltage application of the non-driving portion 112, enabling precise displacement control that compensates for the effects of temperature changes in the piezoelectric actuator 100. Furthermore, because the length of the non-driving portion 112 used for temperature compensation does not need to be changed depending on the length of the driving portion 111, the overall size of the piezoelectric actuator 100 can be reduced even if the driving portion 111 is long. The second piezoelectric ceramic layer 114 is preferably formed from the same type of piezoelectric ceramic as the piezoelectric ceramic layer 103. This allows the influence of temperature changes on the piezoelectric ceramic layer 103 to be compensated for more precisely.

[0024] 1(a) and 1(b), the second internal electrodes 117, 118 are electrically short-circuited by running the short-circuit member 127 around the side surface of the piezoelectric actuator body 105, but the short-circuit member 127 may also be run around the top or bottom surface of the piezoelectric actuator body 105. Also, in Figures 1(a) and 1(b), the second internal electrodes 117, 118 are electrically short-circuited by the short-circuit member 127, but they may be short-circuited by a member or method other than the short-circuit member 127.

[0025] The piezoelectric actuator body 105 may include lead wires 125 and 126 for electrically connecting the drive unit 111 and the voltage supply members 141 and 142. The lead wire 125 connects the voltage supply member 141 and the external electrodes 121 of each piezoelectric element 110. Note that a similar connection is made on the side opposite to the side shown in Figure 1(b). Also, Figure 1(b) does not show the connection of the strain gauge lead wire 135 to the strain gauge terminal.

[0026] As described above, when the driving section 111 has external electrodes 121, 122 electrically connected to the internal electrodes 115, 116, and the external electrodes 121, 122 are electrically connected to the voltage supply members 141, 142 on the side of one end 128 of the driving section 111 in the stacking direction, it is preferable that the non-driving section 112 be formed at the other end 129 of the piezoelectric actuator body 105 in the stacking direction of the driving section 111. This simplifies the configuration of the piezoelectric actuator body 105 and reduces manufacturing costs. The other end 129 of the driving section 111 in the stacking direction is the end opposite one end 128 of the driving section 111 in the stacking direction.

[0027] 1(a) and 1(b), the driving section 111 and the non-driving section 112 of the piezoelectric actuator main body 105 may each be configured with a piezoelectric element 110 as the smallest unit. Configuring the driving section 111 and the non-driving section 112 with piezoelectric elements 110 makes it easy to adjust the maximum displacement amount required for the piezoelectric actuator 100. Furthermore, using the same type of piezoelectric elements 110 reduces costs. Below, a case will be described in which the driving section 111 and the non-driving section 112 are each configured with a piezoelectric element 110 as the smallest unit.

[0028] The driving section 111 may be made up of a plurality of piezoelectric elements 110. A large amount of displacement can be ensured by making the driving section 111 up of a plurality of piezoelectric elements 110. The non-driving section 112 may be made up of a plurality of piezoelectric elements 110, but since the non-driving section 112 is a section that does not contribute to the expansion and contraction of the piezoelectric actuator 100, it is preferable that it be made up of a single piezoelectric element 110 if it is long enough to connect the second strain gauge 132.

[0029] The plurality of piezoelectric elements 110 constituting the driving section 111 or the non-driving section 112 are arranged and connected in series (multiplexed), and their end faces are bonded together with an adhesive. The plurality of piezoelectric elements 110 are composed of piezoelectric element 110a constituting the driving section 111 and piezoelectric element 110b constituting the non-driving section 112.

[0030] (piezoelectric element) 2(a) is a front cross-sectional view of the piezoelectric element 110a. The piezoelectric element 110a has a piezoelectric ceramic layer 113, internal electrodes 115 and 116, and external electrodes 121 and 122. The piezoelectric element 110a has piezoelectric ceramic layers 113 and internal electrodes 115 and 116 alternately stacked one on top of the other. Furthermore, on the side surfaces of the piezoelectric element 110a, the external electrodes 121 and 122 are electrically connected to the internal electrodes 115 and 116, respectively. The piezoelectric element 110a outputs a displacement in response to an applied voltage.

[0031] 2(b) is a front cross-sectional view of the piezoelectric element 110b. The piezoelectric element 110b has a second piezoelectric ceramic layer 114, second internal electrodes 117 and 118, second external electrodes 123 and 124, and a short-circuit member 127. In the piezoelectric element 110b, the second piezoelectric ceramic layers 114 and the second internal electrodes 117 and 118 are alternately stacked. Furthermore, the second external electrodes 123 and 124 are electrically connected to the second internal electrodes 117 and 118 on the side surfaces of the piezoelectric element 110b.

[0032] The piezoelectric ceramic layer 113 and the second piezoelectric ceramic layer 114 can be made of a piezoelectric material such as PZT, barium titanate, alkali niobate perovskite oxide, etc. The electrode material can be Ag—Pd, Pt, Ni, etc.

[0033] The second piezoelectric ceramic layer 114 preferably has the same thickness as the piezoelectric ceramic layer 113. The second internal electrodes 117, 118 are preferably formed of the same type of material as the internal electrodes 115, 116. The second internal electrodes 117, 118 preferably have the same thickness as the internal electrodes 115, 116. The same thickness means that a certain manufacturing error is allowed. The piezoelectric element 110b is preferably of the same type as the piezoelectric element 110a. This allows for more precise compensation for the effects of temperature changes on the piezoelectric element 110a. Furthermore, using the same type of piezoelectric element as the piezoelectric element 110a for the piezoelectric element 110b reduces manufacturing costs.

[0034] (strain gauge) The strain gauge 131 detects strain in the displacement direction of the drive unit 111 of the piezoelectric actuator main body 105. The strain gauge 131 is preferably connected by being directly attached to the drive unit 111. An adhesive or the like can be used for attachment. By connecting the strain gauge 131 to the surface of the drive unit 111, when the piezoelectric actuator 100 expands due to the application of voltage, the strain gauge 131 also expands, and the displacement of the piezoelectric actuator 100 and the displacement of the strain gauge 131 become strains in phase, improving controllability.

[0035] Strain gauge 131 may include strain gauge lead wires 133 and 134. Strain gauge lead wires 133 and 134 are connected to strain gauge terminals 143 and 144, respectively, to transmit a detected displacement signal. This allows the displacement of piezoelectric actuator body 105 to be confirmed and accurately grasped, enabling precise positioning using piezoelectric actuator 100 through feedback control.

[0036] (Second strain gauge) The second strain gauge 132 detects strain in the displacement direction due to temperature changes in the non-driven portion 112 of the piezoelectric actuator body 105. The second strain gauge 132 is preferably connected by being directly attached to the non-driven portion 112. An adhesive or the like can be used for attachment. By connecting the second strain gauge 132 to the surface of the non-driven portion 112, when the non-driven portion 112 expands and contracts due to temperature changes, the second strain gauge 132 also expands and contracts in the same manner, and the displacement of the non-driven portion 112 and the displacement of the strain gauge 131 become strains in phase, improving controllability.

[0037] The second strain gauge 132 may include strain gauge lead wires 135 and 136. The strain gauge lead wires 135 and 136 are connected to strain gauge terminals 143 and 145, respectively, to transmit a detected displacement signal. This makes it possible to accurately grasp the displacement of the piezoelectric actuator body 105 due to temperature changes. As a result, it is possible to compensate for the displacement of the strain gauge 131 due to temperature changes, and precise positioning using the piezoelectric actuator 100 becomes possible even when displacement due to temperature changes occurs.

[0038] The strain gauge 131 and the second strain gauge 132 may be wire strain gauges, foil strain gauges, or the like, and may be any gauge capable of measuring strain in two directions. For example, the strain gauge 131 and the second strain gauge 132 may be a single strain gauge with a pattern printed thereon that allows measurement of strain in two directions at right angles. The connection configuration of the strain gauge lead wires 133, 134, 135, and 136 to the strain gauge terminals 143, 144, and 145 shown in FIGS. 1(a) and 1(b) is merely an example, and other configurations may also be used. Furthermore, strain gauge lead wires and strain gauge terminals (not shown) may be provided depending on the configuration of the bridge circuit.

[0039] It is preferable that the piezoelectric actuator 100 includes a plurality of strain gauges 131 and a plurality of second strain gauges 132. This can increase the output obtained from the strain gauges 131 or the second strain gauges 132 and compensate for the effects of temperature changes on the strain gauge lead wires. When the piezoelectric actuator 100 includes a plurality of strain gauges 131 and a plurality of second strain gauges 132, it is more preferable that the piezoelectric actuator 100 includes two strain gauges 131 and two second strain gauges 132. This makes it possible to easily configure a bridge circuit. When the piezoelectric actuator 100 includes two strain gauges 131 and two second strain gauges 132, for example, the second strain gauge 131 and the second strain gauge 132 may be connected to the surface of the piezoelectric actuator body 105 on the back side of FIG. 1(a).

[0040] (Sealed piezoelectric actuator) Although the piezoelectric actuator body 105 is exposed in FIG. 1, the piezoelectric actuator body 105 may be sealed with a cap and a seat. FIGS. 3(a) and 3(b) are a front cross-sectional view and a side cross-sectional view, respectively, showing an example of a sealed piezoelectric actuator 200 according to an embodiment of the present invention. FIGS. 4(a) and 4(b) are a front cross-sectional view and a bottom view, respectively, of the seat 240, the voltage supply members 141 and 142, and the strain gauge terminals 143, 144, and 145. Only the parts different from FIG. 1 will be described below.

[0041] Piezoelectric actuator 200 is composed of piezoelectric actuator body 105, strain gauge 131, second strain gauge 132, voltage supply members 141, 142, strain gauge terminals 143, 144, 145, seat 240, and cap 260, and expands and contracts when a voltage is applied.

[0042] The seat 240 is adhered to the end of the piezoelectric actuator body 105, fixing the end and supporting the piezoelectric actuator body 105. The projection 230 on the tip side is displaced by expansion and contraction of the piezoelectric actuator body 105, to which the end on the seat 240 side is fixed. In this embodiment, the projection 230 is hemispherical. The end fixed to the seat 240 is preferably one end 128 in the stacking direction of the drive section 111 of the piezoelectric actuator body 105.

[0043] The seat 240 is fixed to the end of the cap 260, thereby sealing the piezoelectric actuator body 105. The piezoelectric actuator body 105, strain gauge 131, and second strain gauge 132, which are vulnerable to humidity and corrosive gases, are hermetically sealed with a low-humidity inert gas, thereby improving reliability and durability. For example, when used in precision machining equipment where the displacement device becomes wet with cutting water, or in piezoelectric valves that control the flow rate of corrosive gases, the positioning accuracy using a piezoelectric actuator with open control may be insufficient, and it is therefore effective to perform positioning using a piezoelectric actuator that can perform feedback control using a displacement sensor.

[0044] In this way, the sealing allows the piezoelectric actuator to operate without problems even in harsh environments such as high humidity, corrosive gases, etc. Because the inside of the cap 260 has a completely airtight structure, it can be used in environments that would otherwise impair the durability of piezoelectric elements and strain gauges, such as humidity and corrosive gases, leading to a wider range of applications.

[0045] Voltage supply members 141, 142 and strain gauge terminals 143, 144, 145 are provided as hermetic terminals, penetrating seat 240. The through holes are filled with glass or resin 245 and sealed. It is preferable that the through holes in seat 240 for the voltage supply members and the strain gauge terminals are arranged around the central axis of piezoelectric actuator 100. This allows easy electrical connection between voltage supply members 141, 142 and strain gauge terminals 143, 144, 145.

[0046] The GND terminal for driving the voltage supply member of the piezoelectric actuator body 105 and the GND terminal for the strain gauge may be common. This prevents the total number of terminals drawn out from the seat from increasing when the strain gauge is housed in a cap, making it easier to achieve a configuration with improved environmental resistance in which the strain gauge is housed in a cap. Note that, instead of using a common terminal, separate terminals may be used, as shown in Figure 4(b).

[0047] The cap 260 is made of metal and has a cylindrical shape with a bottom and an open end. The cap 260 houses the piezoelectric actuator body 105 inside while closely adhering it in the stacking direction, and the open end is joined to the seat 240 to seal the inside of the cap 260. This protects the piezoelectric actuator body 105 and improves the durability of the piezoelectric actuator 200.

[0048] Cap 260 has a diaphragm at the tip of the cap, with protrusion 230 abutting against a dome-shaped portion. The straight pipe portion of cap 260 is formed into a cylinder from the center to the bottom of cap 260. The diaphragm is formed into a dome shape. Cap 260 is preferably made of a material with excellent corrosion resistance and spring properties, such as SUS316 or SUS316L. The base fixes seat 240, and seat 340 supports the end of piezoelectric actuator body 105. When the tip of cap 260 comes into contact with the driven body, displacement is transmitted from piezoelectric actuator 200 to the driven body.

[0049] In addition to piezoelectric actuator body 105, strain gauge 131 and second strain gauge 132 are also housed inside cap 260. Cap 260 can protect piezoelectric actuator body 105, strain gauge 131 and second strain gauge 132 from the surrounding environment.

[0050] Piezoelectric actuator 200 has strain gauge 131 and second strain gauge 132 disposed inside cap 260, and has strain gauge terminals provided on seat 240. As a result, piezoelectric actuator 200 incorporating strain gauge 131 and second strain gauge 132 can receive a displacement signal of piezoelectric element 110 via the strain gauge terminals.

[0051] The piezoelectric actuator body 105 is made up of piezoelectric elements 110a and 110b, lead wires 125 and 126, and a protrusion 230. The protrusion 230 is made of an inorganic material and has a hemispherical shape, and is provided on the tip side of the piezoelectric actuator body 105 where it transmits displacement to the driven body. The protrusion 230 and the piezoelectric actuator body 105 are firmly bonded, and the protrusion 230 contacts the dome-shaped inner part of the cap 260. This allows the displacement of the piezoelectric actuator body 105 to be extracted to the outside of the cap 260.

[0052] (Displacement Control System) The above-described piezoelectric actuator 100 can be used to configure a displacement control system 300. Fig. 5 is a schematic diagram of the displacement control system 300. As shown in Fig. 5, the displacement control system 300 includes the piezoelectric actuator 100 or 200, a feedback control device 310, and a drive power supply 320.

[0053] The strain gauge terminals are connected to a feedback control device 310. The detected displacement signal is input to the feedback control device 310, which converts the detected signal into a displacement of the piezoelectric actuators 100 and 200 and calculates the required drive amount based on the detected displacement. The conversion from the detected signal to displacement is in phase, so that when an extension signal is input from the strain gauge 131, the piezoelectric actuator 100 outputs an extension displacement. At this time, by detecting the displacement signal detected from the strain gauge 131 and the displacement signal detected from the second strain gauge 132 using an appropriate bridge circuit, the drive amount can be calculated as the displacement of the piezoelectric actuators 100 and 200 compensated for the displacement due to temperature change. The feedback control device 310 controls the drive power supply 320 according to the calculated drive amount, and the drive power supply 320 applies a voltage commanded by the feedback control device 310 to the piezoelectric actuator body 105. In this way, a displacement control system 300 can be realized that compensates for the effects of temperature change and reduces errors.

[0054] (Manufacturing method of piezoelectric actuator) Next, an example of a manufacturing method for the piezoelectric actuator 100 configured as shown in FIGS. 1(a) and 1(b) will be briefly described. First, piezoelectric elements 110a and 110b are fabricated, each having piezoelectric ceramic layers and internal electrodes alternately stacked. Specifically, electrode paste such as Pt or Ag-Pd is printed on piezoelectric ceramic green sheets, which are then laminated, pressed, and fired. Next, external electrodes 121 and 122 connected to the internal electrodes 115 and 116 are formed on the side surfaces of the piezoelectric element 110a along the lamination direction. The external electrodes 121 and 122 can be formed by printing electrode paste on the side surfaces of the piezoelectric element 110a and firing the printed paste. The external electrodes 121 and 122 are then connected to a power source to polarize the piezoelectric ceramic layer 113. The piezoelectric element 110b can be fabricated in a similar manner.

[0055] An adhesive such as epoxy is applied to the end faces of the resulting multiple piezoelectric elements 110a, 110b in the stacking direction, and the elements are connected in series. After connecting the elements in this manner, the adhesive is cured. Next, adhesive is applied to the strain gauge 131 or to the strain gauge attachment position of the driving section 111 of the piezoelectric actuator body 105, and the strain gauge 131 is directly attached to the driving section 111 of the piezoelectric actuator body 105. Similarly, adhesive is applied to the second strain gauge 132 or to the second strain gauge attachment position of the non-driving section 112 of the piezoelectric actuator body 105, and the second strain gauge 132 is directly attached to the non-driving section 112 of the piezoelectric actuator body 105.

[0056] Next, metal plate-shaped lead wires 125, 126 are fixed to the external electrodes 121, 122. In addition, a metal short-circuit member 127 is fixed so as to short-circuit the second external electrodes 123, 124. Then, the lead wires 125, 126 are electrically connected to the voltage supply members 141, 142, and the strain gauge lead wires 133, 134, 135, 136 are electrically connected to the strain gauge terminals 143, 144, 145. In this manner, the piezoelectric actuator 100 can be fabricated. Note that the polarization treatment, multi-series connection, attachment of the strain gauge or second strain gauge, fixing of the lead wires, and connection of the short-circuit member may be performed in any order as long as manufacturing is possible.

[0057] (Method of manufacturing a sealed piezoelectric actuator) Next, a method for manufacturing a sealed piezoelectric actuator 200 configured as shown in Figures 3(a) and (b) will be described. The method for manufacturing the sealed piezoelectric actuator 200 is the same as the method for manufacturing the piezoelectric actuator 100 described above, except that the piezoelectric actuator body 105, to which the strain gauge 131 and second strain gauge 132 are attached, is placed on a seat 240, the lead wires 125 and 126 are electrically connected to voltage supply members 141 and 142, and the strain gauge lead wires 133, 134, 135 and 136 are electrically connected to the strain gauge terminals 143, 144 and 145. The product is then sealed by being covered with a cap 260. In this manner, the sealed piezoelectric actuator 200 can be manufactured. [Example]

[0058] (Example) Multiple piezoelectric elements constituting the driving and non-driving portions of the piezoelectric actuator of the example were fabricated. First, a sheet molded product, in which a piezoelectric material was formed into a thin film sheet using a doctor blade molding method, was cut to a printable size. An Ag / Pd electrode paste was screen-printed as the internal electrodes of the laminate, and then multiple sheets were laminated and pressure-bonded to obtain a laminated molded product. The piezoelectric material used was a Navy Type II piezoelectric material, a common lead zirconate titanate (PZT)-based soft material. Next, the laminated molded product was cut to the desired shape and co-fired together with the internal electrodes in an air atmosphere to obtain a fired laminate. Next, Ag external electrodes were formed on the side surfaces of the fired product, and a DC electric field was applied externally to perform a polarization process, obtaining multiple piezoelectric elements.

[0059] Next, four piezoelectric elements were bonded in series to form a multi-series structure. The topmost piezoelectric element was designated as a non-driving section, and its external electrodes were short-circuited. The remaining piezoelectric elements were designated as driving sections, and their lead wires were electrically connected to the external electrodes. A strain gauge was then attached to one of the driving section piezoelectric elements, and a second strain gauge was attached to each of the non-driving section piezoelectric elements, using a resin-based adhesive, to produce the piezoelectric actuator of the example.

[0060] (Comparative Example 1) A piezoelectric actuator of Comparative Example 1 was produced by attaching one strain gauge only to the driving section of a piezoelectric actuator identical to that of the example.

[0061] (Comparative Example 2) A piezoelectric actuator of Comparative Example 2 was produced by attaching two strain gauges only to the driving section of a piezoelectric actuator identical to that of the example, in order to measure displacement in the polarization direction and in a direction perpendicular thereto.

[0062] [Checking the effects of temperature changes] The strain gauges of the piezoelectric actuators of the examples and comparative examples were each appropriately assembled into a bridge circuit, and the environmental temperature was raised from 25°C to 65°C, and the change in resistance was converted into a change in voltage to measure the displacement of the piezoelectric actuator.

[0063] The linearity between the strain gauge output and the overall displacement of the piezoelectric actuator was confirmed for the piezoelectric actuators of the examples and comparative examples. In comparative example 1, the linearity between the piezoelectric actuator's displacement and strain gauge output significantly decreased as the ambient temperature increased. This is thought to be because the piezoelectric actuator of comparative example 1 was unable to compensate for the effects of temperature changes. In comparative example 2, the linearity was maintained higher than in comparative example 1, but the linearity between the piezoelectric actuator's displacement and strain gauge output decreased as the ambient temperature increased. In the piezoelectric actuator of comparative example 2, the effects of temperature changes were compensated for using displacement perpendicular to the polarization direction, ensuring a certain degree of linearity. However, because polarized piezoelectric ceramics have different thermal expansion coefficients in the polarization direction and the direction perpendicular to it, it is thought that this effect increased as the temperature increased. In contrast, the piezoelectric actuators of the examples were able to maintain high linearity even at high temperatures.

[0064] The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and equivalents are included within the spirit and scope of the present invention. Furthermore, the structure, shape, number, position, size, etc. of the components shown in each drawing are for the convenience of explanation and may be changed as appropriate. [Explanation of symbols]

[0065] 100, 300 Piezoelectric actuator 105 Piezoelectric actuator body 110, 110a, 110b piezoelectric elements 111 Drive unit 112 Non-driving part 113 Piezoelectric ceramic layer 114 Second piezoelectric ceramic layer 115, 116 Internal electrode 117, 118 Second internal electrode 121, 122 External electrode 123, 124 second external electrode 125, 126 lead wires 127 Short-circuiting element 128 one end 129 other end 131 Strain gauge 132 Second strain gauge 133, 134, 135, 136 Strain gauge lead wires 141, 142 voltage supply member 143, 144, 145 Strain gauge terminals 230 Protrusion 240 seats 245 Glass, Resin 260 Cap 300 Displacement Control System 310 Feedback Control Device 320 Drive power supply

Claims

1. a piezoelectric actuator body including a driving section in which a plurality of piezoelectric ceramic layers and a plurality of internal electrodes are alternately stacked, and which is driven when a voltage is applied to the internal electrodes; and a non-driving section formed in series in the stacking direction of the driving section, in which a plurality of second piezoelectric ceramic layers and a plurality of second internal electrodes are alternately stacked, and which does not drive even when a voltage is applied; a strain gauge connected to the drive unit and configured to detect strain in the displacement direction of the drive unit; a second strain gauge connected to the non-driven portion and configured to detect strain in the displacement direction of the non-driven portion, The piezoelectric actuator is characterized in that the second piezoelectric ceramic layer is polarized and the second internal electrode is electrically short-circuited.

2. the driving section has an external electrode electrically connected to the internal electrode, the external electrode is electrically connected to a voltage supply member at one end side of the driving unit in the stacking direction, The piezoelectric actuator according to claim 1 , wherein the non-driving portion is formed at the other end of the piezoelectric actuator body in the stacking direction of the driving portion.

3. 3. The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator comprises a plurality of the strain gauges and a plurality of the second strain gauges.

4. the driving section has an external electrode electrically connected to the internal electrode, the external electrode is electrically connected to a voltage supply member at one end side of the driving unit in the stacking direction, a seat for supporting an end portion of the piezoelectric actuator body on the one end side; 3. The piezoelectric actuator according to claim 1, further comprising: a metal cap that houses the piezoelectric actuator body to which the strain gauge and the second strain gauge are connected.

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