Piezoelectric Actuator

Abstract

To provide a piezoelectric actuator capable of improving reliability of connection between a terminal inside a cap and a lead wire.SOLUTION: A piezoelectric actuator 100 that is displaced by applying a voltage includes: a piezoelectric actuator body 105 formed by connecting a plurality of piezoelectric elements 110 in series or formed by one piezoelectric element 110; a seat 150 for supporting one end of the piezoelectric actuator body 105; a cap 160 for accommodating the piezoelectric actuator body 105; a terminal 120 fixed to the seat 150; and a connection member 170 made of a hollow cylindrical metal that has a terminal stop portion 175 midway in the longitudinal direction that is soldered between the end inside the cap 160 of the terminal 120 and a lead wire 130 electrically connected to a member disposed inside the cap 160, respectively, and connects the terminal 120 and the lead wire 130.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, and when voltage is continuously applied, they undergo displacement creep, gradually changing dimensions. Therefore, in precision positioning applications such as semiconductor exposure equipment, feedback control is performed 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 increasingly being used.

[0003] Patent Document 1 describes a piezoelectric actuator that uses a piezoelectric displacement part with hysteresis to control the displacement amount of a piston with high precision, and includes a piezoelectric displacement part that expands and contracts in response to an applied voltage, a piston that receives the expansion and contraction force of one end of the piezoelectric displacement part, and a base that receives the expansion and contraction force of the other end of the piezoelectric displacement part, the piston having an inner cylinder 14 that covers the piezoelectric displacement part, the end of this inner cylinder having a displacement detection part close to the base, and a displacement sensor that detects the distance to the displacement detection part being fixed to the base.

[0004] Patent Document 2 describes a piezoelectric actuator in which a displacement sensor is provided on the side of an electrostrictive effect element sealed in a metal case with an airtight terminal or metal member and electrically connected to the electrostrictive effect element, with the aim of eliminating hysteresis in the voltage-displacement characteristics of a piezoelectric actuator using an electrostrictive effect element and improving the detection accuracy of minute movements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-153909 [Patent Document 2] Japanese Patent Application Publication No. 5-206536 Summary of the Invention [Problem to be solved by the invention]

[0006] Non-contact capacitance sensors and eddy current sensors have often been used as displacement sensors for piezoelectric actuators. However, when a feedback control method using a non-contact sensor, as shown in Patent Document 1, is applied, high-precision positioning becomes possible, but the system becomes complex and expensive, and its applications are limited.

[0007] In response to this, a piezoelectric actuator has been proposed in which a displacement sensor such as a strain gauge is directly attached to part of the side of an electrostrictive element to improve the accuracy of detecting minute amounts of movement, as shown in Patent Document 2. In many cases, the strain gauge is simply attached directly to the piezoelectric element, making it a small and inexpensive displacement meter.

[0008] In a configuration in which the piezoelectric actuator body is sealed in a metal housing for the piezoelectric actuator and a strain gauge is placed inside, as in Patent Document 2, the internal wiring of the piezoelectric actuator is connected to the outside of the housing via terminals that penetrate a base part called a seat. In this case, the connection between the terminals and the lead wires of the strain gauge is also made by direct soldering without using any other parts.

[0009] However, the space inside the seat is narrow, and the strain gauge lead wires are very thin and soft, making it difficult to position them for soldering to the seat terminals. The soldering work requires holding the wires with tweezers while bringing them close to the seat terminals, which requires skilled soldering to ensure reliable electrical wiring and leads to variations in product precision. Strain gauges detect displacement strain by detecting resistance changes at the milliohm level using a Wheatstone bridge. Therefore, if the soldering connection is not secure, the product's initial performance will vary, and if a connection resistance of 1 to 2 ohms occurs, the bridge circuit will not be able to detect displacement, resulting in a defective product.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide a piezoelectric actuator that can improve the reliability of the connection between the terminal inside the cap and the lead wire. [Means for solving the problem]

[0011] (1) In order to achieve the above object, the piezoelectric actuator of the present invention is a piezoelectric actuator that is displaced by the application of a voltage, and is characterized by comprising: a piezoelectric actuator body formed by connecting a plurality of piezoelectric elements in series or formed by a single piezoelectric element; a seat that supports one end of the piezoelectric actuator body; a cap that houses the piezoelectric actuator body; a terminal fixed to the seat; and a hollow, tubular metal connecting member having a terminal stopper portion in the middle in the longitudinal direction, which is soldered between the inner end of the terminal of the cap and a lead wire electrically connected to a member disposed inside the cap, connecting the terminal and the lead wire.

[0012] In this way, the inner end of the terminal cap and the lead wire of the component placed inside the cap are soldered via a connecting member made of metal that is hollow and tubular and has a terminal stop portion in the middle of its length, thereby improving the reliability of the connection between the terminal and the lead wire.

[0013] (2) In the piezoelectric actuator of the present invention, the inside of the connection member is filled with solder.

[0014] In this way, by filling the inside of the connection member with solder, the terminal and the connection member, and the lead wire and the connection member are connected over a wide area inside the connection member, thereby further improving the reliability of the connection between the terminal and the lead wire.

[0015] (3) In the piezoelectric actuator of the present invention, the inner surface of the connecting member is gold-plated.

[0016] In this way, by gold-plating the inner surface of the connection member, the wettability of the solder on the inner surface of the connection member is improved, thereby further improving the reliability of the connection between the terminal and the lead wire.

[0017] (4) In the piezoelectric actuator of the present invention, the difference between the inner diameter of the end of the connection member on the terminal side and the outer diameter of the end of the terminal inside the cap is 0.2 mm or less.

[0018] In this way, by setting the difference between the inner diameter of the terminal-side end of the connecting member and the outer diameter of the inner end of the terminal cap to 0.2 mm or less, when solder is supplied to the lower end of the connecting member, the solder fills up to the upper end of the connecting member due to capillary action, allowing the terminal and lead wire to be connected easily and reliably.

[0019] (5) In the piezoelectric actuator of the present invention, the terminal fastening portion of the connection member is formed by recessing the middle of a pipe that constitutes the connection member.

[0020] In this way, the terminal fastening portion of the connection member is formed by recessing the middle of the pipe that constitutes the connection member, which makes it possible to easily manufacture the connection member and reduce costs.

[0021] (6) Furthermore, the piezoelectric actuator of the present invention is characterized in that it further comprises a strain gauge attached to the side of the piezoelectric actuator body directly or via another member, for detecting strain when the displacement of the piezoelectric actuator body changes, and the lead wire is the lead wire of the strain gauge.

[0022] In this way, by further providing a strain gauge that detects strain when the displacement of the piezoelectric actuator body changes and by using the lead wires of the strain gauge as the lead wires connected to the terminals via the connecting member, it is possible to improve the reliability of the connection between the terminals and the thin and easily broken lead wires of the strain gauge. Also, since there is less variation in resistance values ​​due to imperfections in the connection between the strain gauge lead wires and the terminals, product defects can be reduced and the reliability of the strain gauge output when the piezoelectric actuator is in use can be improved. [Effects of the Invention]

[0023] According to the present invention, it is possible to improve the reliability of the connection between the terminal inside the cap and the lead wire. [Brief explanation of the drawings]

[0024] [Figure 1] 1A and 1B are a front cross-sectional view and a side cross-sectional view, respectively, showing an example of a piezoelectric actuator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a front cross-sectional view showing an example of a piezoelectric element. [Figure 3] FIG. 10 is a front cross-sectional view showing a modified example of the piezoelectric element. [Figure 4] FIG. 1 is a schematic diagram showing an example of a bridge circuit when orthogonal two-axis strain gauges are used. [Figure 5] FIG. 1 is a schematic diagram showing an example of a bridge circuit when a single longitudinal strain gauge is used. [Figure 6] 1A and 1B are a front cross-sectional view and a bottom view, respectively, showing an example of a seat and a terminal of a piezoelectric actuator according to an embodiment of the present invention. [Figure 7] 1(a) to 1(c) are a plan view, a front view, and a side view, respectively, showing an example of a connecting member. [Figure 8] 1A and 1B are a front cross-sectional view and a side cross-sectional view, respectively, showing an example of a connecting member when connected. [Figure 9] 10(a) to 10(c) are a plan view, a front view, and a side view, respectively, showing a modified example of the connecting member. [Figure 10] 10(a) to 10(c) are a plan view, a front view, and a side view, respectively, showing a modified example of the connecting member. [Figure 11] 10(a) to 10(c) are a plan view, a front view, and a side view, respectively, showing a modified example of the connecting member. [Figure 12] 10(a) to 10(d) are a plan view, a front view, a side view, and a cross-sectional side view, respectively, showing a modified example of the connecting member. [Figure 13] FIG. 1 is a schematic diagram of a displacement control system. [Figure 14] FIG. 1(a) is a cross-sectional view showing an example of a piezoelectric element in the process of being manufactured, and (b) to (d) are schematic diagrams showing green sheets used in manufacturing the piezoelectric element of (a). [Figure 15] FIG. 1(a) is a cross-sectional view showing an example of a piezoelectric element in the process of being manufactured, and (b) to (e) are schematic diagrams showing green sheets used in manufacturing the piezoelectric element of (a). DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] [Embodiment] (Basic structure of piezoelectric actuator) 1(a) and 1(b) are a front cross-sectional view and a side cross-sectional view, respectively, showing an example of a piezoelectric actuator 100 according to this embodiment. Note that in FIGS. 1(a) and 1(b), only the cap is shown in cross section. Note that the piezoelectric actuator shown in the reference figures is an example, and the present invention is not limited by the number of elements, etc.

[0027] Piezoelectric actuator 100 is composed of piezoelectric actuator body 105, seat 150, cap 160, terminal 120, and connecting member 170, and expands and contracts when a voltage is applied. Piezoelectric actuator 100 is used, for example, in the valve opening / closing control section of a mass flow controller or the stage driving section of a precision positioning device, in which case it displaces the driven body (valve, stage).

[0028] The connecting member 170 is made of metal and has a hollow cylindrical shape and a terminal stopper 175 in the middle in the longitudinal direction. The connecting member 170 is soldered between the inner end of the cap 160 of the terminal 120 and the lead wire 130 electrically connected to a component disposed inside the cap 160, thereby connecting the terminal 120 and the lead wire 130. In this case, the component disposed inside the cap 160 and electrically connected to the lead wire 130 may be any component that extracts an electrical signal from or transmits an electrical signal to the component inside the cap 160, or that is required to apply a voltage to the component inside the cap 160. The lead wire 130 of the component may be formed as a separate component and connected to the component, or may be formed integrally with the component.

[0029] The member in question may be another member different from the piezoelectric actuator body 105, such as a strain gauge 140 or a thermocouple. Alternatively, the member in question may be the piezoelectric actuator body 105. In the following, an example will be described in which the member in question is a strain gauge 140 and the connecting member 170 connects the output terminals 125, 126, and 127 of the strain gauge with the lead wires 135, 136, and 137 of the strain gauge. However, the present invention is not limited to this example, and even a piezoelectric actuator 100 that does not include a strain gauge 140 falls within the scope of the present invention, provided that the connecting member 170 is used at least at one location between the terminals 120 and the lead wires 130 inside the cap 160.

[0030] (Specific Configuration of Piezoelectric Actuator) Piezoelectric actuator 100 is composed of piezoelectric actuator body 105, terminals 120 (driving terminals 121, 122, sensor terminals 125, 126, 127), strain gauge 140, seat 150, cap (metal casing for piezoelectric actuator) 160, and connecting member 170.

[0031] (Piezoelectric actuator body) The piezoelectric actuator body 105 is composed of a piezoelectric element 110, lead wires 131 and 132 of the piezoelectric actuator body, and a protrusion 108. The multiple piezoelectric elements 110 that make up the piezoelectric actuator body 105 are arranged and connected in series (multiple-series), and their end faces are bonded together with an adhesive. Bonding multiple piezoelectric elements 110 together ensures a large amount of displacement. Note that "series" refers to the expansion / contraction direction, i.e., the stacking direction of the piezoelectric layers and internal electrodes within the piezoelectric element 110. The piezoelectric actuator body 105 used in the piezoelectric actuator 100 of the present invention may be formed from multiple piezoelectric elements 110 or from a single piezoelectric element 110.

[0032] When a voltage is applied to a pair of external electrodes 116, 117 via a pair of lead wires 131, 132 of the piezoelectric actuator body, each piezoelectric element 110 expands and contracts, displacing the tip of the piezoelectric actuator body 105. Driving terminals 121, 122 are connected to the lead wires 131, 132 of the piezoelectric actuator body, and transmit the applied voltage to the lead wires 131, 132.

[0033] Lead wires 131, 132 of the piezoelectric actuator body connect the drive terminals 121, 122 to the external electrodes 116, 117 of each piezoelectric element 110. Note that similar connections are made on the side opposite to the side shown in FIG.

[0034] The protrusion 108 is made of an inorganic material and is provided on the tip side of the piezoelectric actuator body 105, where it transmits displacement to the driven body. The protrusion 108 and the piezoelectric actuator body 105 are firmly bonded together, and the protrusion 108 comes into contact with the dome-shaped inner portion of the cap 160. This allows the displacement of the piezoelectric actuator body 105 to be extracted to the outside of the cap 160. In this embodiment, the protrusion 108 is hemispherical, but it may have any other shape. The piezoelectric actuator body 105 may also be configured without the protrusion 108.

[0035] (piezoelectric element) FIG. 2 is a front cross-sectional view showing an example of a piezoelectric element 110. The piezoelectric element 110 outputs a displacement in response to an applied voltage and has a piezoelectric layer 113, internal electrodes 114 and 115, and external electrodes 116 and 117. The piezoelectric element 110 has the piezoelectric layers 113 and the internal electrodes 114 and 115 alternately stacked. Furthermore, the external electrodes 116 and 117 are connected to the internal electrodes 114 and 115 on the side surfaces of the piezoelectric element 110, respectively. The piezoelectric layer can be made of a piezoelectric material such as PZT or barium titanate. The electrode material can be Ag-Pd, Pt, or the like.

[0036] Fig. 3 is a front cross section showing a modified example of the piezoelectric element 110. In Fig. 3, the internal electrodes 114 and 115 are represented by thin solid lines, the stress relaxation layer 118 is represented by dotted lines, and the voids 119 at the ends of the stress relaxation layer 118 are represented by thick solid lines. As shown in Fig. 3, the piezoelectric element 110 according to this embodiment may be provided with the stress relaxation layer 118.

[0037] Generally, a piezoelectric inactive portion is formed around the internal electrodes inside a multilayer piezoelectric element for insulation and to protect against contamination and moisture from the external environment. In a multilayer piezoelectric element for a piezoelectric actuator, a stress relief layer 118 having slit-like voids 119 may be formed in the piezoelectric inactive portion over the entire layer or at regular intervals in order to prevent the piezoelectric inactive portion from hindering displacement. In other words, the stress relief layer 118 is provided to relieve stress generated inside the element when the piezoelectric element 110 is driven.

[0038] (strain gauge) The strain gauge 140 detects the strain of the piezoelectric actuator body 105. The strain gauge 140 is connected by being attached to the side of the piezoelectric actuator body 105 directly or via another member. The other member may be, for example, a mesh for relieving stress in the piezoelectric actuator body 105. For attachment, an adhesive such as an epoxy adhesive, instant adhesive, phenolic adhesive, or polyimide adhesive can be used. Considering durability and use at high temperatures, it is preferable to use an epoxy adhesive.

[0039] The strain gauge 140 in Figure 1 is an example configured as an orthogonal biaxial type gauge, with a vertical gauge extending in the length direction of the piezoelectric actuator 100 and a horizontal gauge extending in the width direction. The horizontal gauge output is connected to terminal 125 of base 150, the vertical gauge output to terminal 127 of base 150, and the common terminal for the vertical and horizontal gauges is connected to terminal 126 of base 150. Figure 4 is a schematic diagram showing an example of a bridge circuit using an orthogonal biaxial type strain gauge. Because the strain gauge 140 is connected directly to the surface of the piezoelectric actuator body 105 or via another member, when the piezoelectric actuator 100 expands in the length direction of the piezoelectric actuator 100, the vertical gauge of the strain gauge 140 expands and the horizontal gauge contracts. Therefore, the resistance of the vertical gauge slightly increases and the resistance of the horizontal gauge slightly decreases. As shown in Figure 4, connecting an orthogonal biaxial type strain gauge to a bridge circuit increases the output voltage from the strain gauge by approximately 30%, which corresponds to the Poisson's ratio of the piezoelectric element. Furthermore, changes due to thermal expansion of the vertical and horizontal gauges are offset, resulting in temperature compensation and improved measurement accuracy.

[0040] The strain gauge 140 may be a wire strain gauge, a foil strain gauge, or the like. The strain gauge 140 is not limited to an orthogonal two-axis strain gauge, but may also be a single-longitudinal strain gauge. FIG. 5 is a schematic diagram showing an example of a bridge circuit when a single-longitudinal strain gauge is used. Using a single-longitudinal strain gauge 140 reduces the number of terminals by one and simplifies connection, thereby reducing costs. When precise detection of strain is required, it is preferable to use an orthogonal two-axis strain gauge as the strain gauge 140. Note that FIGS. 4 and 5 are merely examples, and the configurations of the strain gauge 140 and the bridge circuit are not limited to these.

[0041] The strain gauge 140 is connected to strain gauge lead wires 135, 136, and 137, which are connected to strain gauge output terminals 125, 126, and 127, respectively, to transmit detected displacement signals. This allows the displacement of the piezoelectric actuator body 105 to be confirmed and accurately grasped, enabling precise positioning using the piezoelectric actuator 100 through feedback control. The strain gauge lead wires 135, 136, and 137 may be formed integrally with the strain gauge 140. The strain gauge lead wires 135, 136, and 137 may be in any shape, such as wire or foil. If there is a risk that the strain gauge lead wires 135, 136, and 137 may come into contact with other electrodes or metal parts, the strain gauge lead wires 135, 136, and 137 may be covered with an insulating coating such as a silicone tube at the necessary locations.

[0042] The seat 150 is adhered to the end of the piezoelectric actuator body 105, fixing one end of the body and supporting the piezoelectric actuator body 105. The projection 108 on the tip side is displaced by expansion and contraction of the piezoelectric actuator body 105, the end of which is fixed on the seat 150 side.

[0043] The seat 150 is fixed to the end of the cap 160, thereby sealing the piezoelectric actuator body 105. Reliability and durability can be improved by hermetically sealing the piezoelectric actuator body 105 and strain gauge 140, which are vulnerable to humidity and corrosive gases, with a low-humidity inert gas. 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 is insufficient, so it is effective to perform positioning, etc. 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 160 has a completely airtight structure, it can be used in environments that would impair the durability of the piezoelectric element 110 and strain gauge 140, such as humidity and corrosive gases, leading to a wider range of applications.

[0045] 6(a) and 6(b) are a front cross-sectional view and a bottom view, respectively, showing an example of the seat 150 and terminals 120 (driving terminals 121 and 122, strain gauge output terminals 125, 126, and 127) of the piezoelectric actuator 100 according to this embodiment. The terminals 120 are fixed to the seat 150. The driving terminals 121 and 122 and the strain gauge output terminals 125, 126, and 127 are preferably provided as hermetic terminals that penetrate the seat 150. In this case, the through holes are filled with glass or resin 155 and sealed.

[0046] When the through-hole is filled with glass, Kovar is used for the terminal 120 to accommodate the thermal expansion of the glass, and the surface of the terminal 120 may be nickel-plated. When the lead wire 130 is directly soldered to such a terminal 120, there is a risk of connection failure because the nickel-plated terminal 120 has poor solder wettability. Even in such cases, the risk of connection failure can be reduced by using the connection member 170 of the present invention for connection.

[0047] On the base 150, it is preferable that the driving terminals 121, 122 and the strain gauge output terminals 125, 126, 127 are clearly arranged for outputting and driving the strain gauges around the central axis of the piezoelectric actuator 100. This allows for easy electrical connection of the driving terminals 121, 122 and the strain gauge output terminals 125, 126, 127.

[0048] The cap 160 is made of metal and has a cylindrical shape with a bottom and an open end. The cap 160 houses the piezoelectric actuator body 105 inside while closely adhering it in the stacking direction, and the open end is joined to the seat 150, sealing the inside of the cap 160. This protects the piezoelectric actuator 100 and improves its durability.

[0049] The straight pipe portion of cap 160 is formed cylindrically from the center to the bottom of cap 160. Cap 160 preferably has a diaphragm at the tip of the cap, with protrusion 108 abutting against the dome-shaped portion. Cap 160 is preferably made of a material with excellent corrosion resistance and spring properties, such as SUS316 or SUS316L. The base fixes seat 150, and seat 150 supports the end of piezoelectric actuator body 105. When the tip of cap 160 comes into contact with the driven body, displacement is transmitted from piezoelectric actuator 100 to the driven body.

[0050] 1(a) and 1(b), in addition to the piezoelectric actuator body 105, the strain gauge 140 is also housed inside the cap 160. The cap 160 can protect the piezoelectric actuator body 105 and the strain gauge 140 from the surrounding environment.

[0051] Piezoelectric actuator 100 has strain gauge 140 disposed inside cap 160, and strain gauge output terminals 125, 126, and 127 provided on seat 150. As a result, piezoelectric actuator 100 with built-in strain gauge 140 can receive strain signals from piezoelectric element 110 via strain gauge output terminals 125, 126, and 127. Since the amount of strain in the piezoelectric element and the change in overall length of the positioner are proportional, the displacement of the piezoelectric actuator can be obtained from the strain signal of the piezoelectric element.

[0052] The inner ends of the caps 160 of the strain gauge output terminals 125, 126, 127 and the strain gauge lead wires 135, 136, 137 are preferably soldered via a hollow cylindrical metal connecting member 170 having a terminal stopper 175 in the middle in the longitudinal direction. This improves the reliability of the connection between the strain gauge output terminals 125, 126, 127 and the strain gauge lead wires 135, 136, 137.

[0053] (connecting member) 7(a) to 7(c) are a plan view, a front view, and a side view, respectively, showing an example of a connection member 170. The connection member 170 is made of metal, has a hollow cylindrical shape, and has a terminal stopper 175 in the middle in the longitudinal direction. The lead wire 130 and the connection member 170, and the terminal 120 and the connection member 170 are soldered inside the hollow cylindrical shape of the connection member 170, respectively, thereby electrically connecting the lead wire 130 and the terminal 120. FIG. 7 shows a connection member 170 in the shape of a hollow cylindrical pipe with a dotted recess on one side in the middle.

[0054] This facilitates connection between the lead wires 130 and the terminals 120, even when thin, easily breakable lead wires 135, 136, and 137 of the strain gauges must be connected to a narrow area of ​​the seat 150. This also improves the reliability of the connection between the strain gauge lead wires 135, 136, and 137 and the strain gauge output terminals 125, 126, and 127. This reduces variations in the resistance value of the strain gauge 140 due to imperfect connections between the strain gauge lead wires 135, 136, and 137 and the strain gauge output terminals 125, 126, and 127, thereby improving the reliability of the output of the strain gauge 140 when the piezoelectric actuator 100 is in use. Furthermore, even when the surface of the terminal 120 has poor solder wettability, the terminal 120 can be easily soldered to the connecting member 170. As a result, the reliability of the connection between the lead wires 130 and the terminals 120 can be improved.

[0055] 8(a) and 8(b) are a front cross-sectional view and a side cross-sectional view, respectively, showing an example of the connection member 170 when connected. As shown in FIGS. 8(a) and 8(b), the interior of the connection member 170 is preferably filled with solder 178. This allows the terminals 120 and the connection member 170, and the lead wires 130 and the connection member 170, to be connected over a wide area within the connection member 170, thereby further improving the reliability of the connection between the terminals 120 and the lead wires 130. "The interior of the connection member 170 is filled with solder 178" means that the solder is present in an area of ​​80% or more of the longitudinal length of the connection member 170.

[0056] It is preferable that the length of connecting member 170 from the end on the terminal 120 side to terminal stopper 175 is longer than the length of terminal 120 that protrudes above the bottom surface of seat 150. This creates a gap between the end of connecting member 170 on the terminal 120 side and the bottom surface of seat 150 when connecting member 170 is inserted into terminal 120, making soldering easier.

[0057] It is preferable that the inner surface of the connection member 170 is gold-plated, which improves the wettability of the solder 178 on the inner surface of the connection member 170, thereby further improving the reliability of the connection between the terminal 120 and the lead wire 130.

[0058] The difference between the inner diameter of the end of connecting member 170 on the terminal 120 side and the outer diameter of the end of terminal 120 on the inside of cap 160 is preferably 0.2 mm or less. This allows for easy soldering by capillary action. The lower limit of this difference may be any value as long as it causes capillary action, but is preferably, for example, 0.05 mm or more.

[0059] The terminal stopper 175 of the connection member 170 preferably has a structure that leaves a hollow portion inside, but prevents the terminal 120 to be connected from passing through. Furthermore, the terminal stopper 175 of the connection member 170 preferably has a shape that prevents the hollow portion from being blocked when the terminal 120 is inserted. For example, such a structure can be achieved by crushing the middle of a hollow cylindrical pipe while leaving a hollow portion inside, or by providing a protrusion facing inward. These structures make it possible to easily solder the lead wire 130 and the connection member 170, and the terminal 120 and the connection member 170, inside the hollow cylindrical interior of the connection member 170 by utilizing capillary action. Details will be described in the manufacturing method.

[0060] 9(a)-9(c), 10(a)-9(c), and 11(a)-9(c) are plan, front, and side views, respectively, of modified connection member 170. FIG. 9 shows connection member 170 in a shape in which the middle of a hollow cylindrical pipe is recessed at two points on each side. FIG. 10 shows connection member 170 in a shape in which the middle of a hollow cylindrical pipe is recessed linearly on one side. FIG. 11 shows connection member 170 in a shape in which the middle of a hollow cylindrical pipe is recessed linearly on each side. As shown in FIGS. 7 and 9-11, terminal fastening portion 175 of connection member 170 is preferably formed by recessing the middle of the pipe constituting connection member 170. This allows connection member 170 to be easily manufactured and reduces costs.

[0061] 12(a) to 12(d) are a plan view, a front view, a side view, and a cross-sectional side view, respectively, showing a modified example of the connecting member 170. As shown in Fig. 12, the connecting member 170 does not have a recess on its exterior, and the terminal fastening portion 175 of the connecting member 170 may be formed by providing a protrusion on the inside of the middle of a pipe constituting the connecting member 170. The diameter of the connecting member 170 on the terminal 120 side may be different from the diameter on the lead wire 130 side. The connecting member 170 may also be a hollow cylinder with an elliptical or polygonal cross section.

[0062] (Displacement Control System) The above-described piezoelectric actuator 100 can be used to configure a displacement control system 200. Fig. 13 is a schematic diagram of the displacement control system 200. As shown in Fig. 13, the displacement control system 200 includes the piezoelectric actuator 100, a feedback control device 180, and a drive power supply 190.

[0063] The strain gauge output terminals 125, 126, and 127 are connected to a feedback control device 180. The detected strain signal is input to the feedback control device 180, which converts the detected signal into a displacement of the piezoelectric actuator 100 and calculates the required drive amount based on the detected displacement. The conversion from the detected signal to the displacement is in phase. For example, if the displacement of the piezoelectric actuator needs to be kept constant, an input signal indicating an increase in strain from the strain gauge 140 represents an extensional displacement of the piezoelectric actuator 100. The feedback control device 180 controls the drive power supply 190 according to the calculated drive amount and applies a voltage to the piezoelectric actuator body 105 such that the strain signal becomes the original strain value. In this way, a displacement control system 200 with reduced error can be realized using a piezoelectric actuator 100 with improved reliability of the connection between the terminals inside the cap and the lead wires.

[0064] (Manufacturing method of piezoelectric actuator) Next, a method for manufacturing the piezoelectric actuator 100 configured as shown in FIG. 1 will be described. First, a piezoelectric element 110 is fabricated in which piezoelectric layers and internal electrodes are alternately stacked. FIG. 14(a) is a cross-sectional view showing an example of a piezoelectric element in the process of fabrication, and FIGS. 14(b) to 14(d) are schematic diagrams showing green sheets used to fabricate the piezoelectric element of FIG. 14(a). FIGS. 14(b) to 14(d) respectively show a green sheet 201 in which electrode paste 214, which will become internal electrode 114 after firing, and piezoelectric ceramic 213, which will become piezoelectric layer 113, are laminated; a green sheet 202 in which electrode paste 215, which will become internal electrode 115 after firing, and piezoelectric ceramic 213, which will become piezoelectric layer 113, are laminated; and a green sheet 203 in which only piezoelectric ceramic 213 is laminated without any electrode paste. These are laminated, pressed, and fired according to the design, thereby fabricating the piezoelectric element 110 shown in FIG. 14(a), in which piezoelectric layers and internal electrodes are alternately stacked.

[0065] For the piezoelectric ceramic green sheets, piezoelectric materials such as PZT and barium titanate can be used. For the electrode paste, Pt or Ag-Pd can be used. Note that one or more green sheets 203 may be laminated on the end faces of the piezoelectric element 110 in the lamination direction to form a protective layer.

[0066] Next, a method for producing a piezoelectric element 110 having a stress relaxation layer 118 will be described. Fig. 15(a) is a cross-sectional view showing an example of a piezoelectric element in the process of being produced, and Figs. 15(b) to 15(e) are schematic diagrams showing green sheets used in producing the piezoelectric element of Fig. 15(a). Figs. 15(b) to 15(e) respectively show a green sheet 201 on which electrode paste 214 that will become internal electrode 114 after firing and piezoelectric ceramic 213 that will become piezoelectric layer 113 are laminated, a green sheet 202 on which electrode paste 215 that will become internal electrode 115 after firing and piezoelectric ceramic 213 that will become piezoelectric layer 113 are laminated, a green sheet 203 on which only piezoelectric ceramic 213 is laminated without electrode paste, and a green sheet 204 on which piezoelectric ceramic 213 that will become piezoelectric layer 113 after firing and hard-to-sinter ceramic paste 218 that will become stress relaxation layer 118 are laminated. These are stacked, pressed, and fired according to the design to produce the piezoelectric element 110 shown in FIG. 15(a), which has piezoelectric layers and internal electrodes stacked alternately and has a stress relaxation layer.

[0067] In this way, the piezoelectric element 110 having the stress relaxation layer 118 is manufactured by stacking at a predetermined interval the green sheets 204 coated with the sintering-resistant ceramic paste 218, which will become the stress relaxation layer 118 after firing, and then firing the green sheets 204. For example, zirconia, lead titanate, or the like can be used as the sintering-resistant ceramic paste 218. Note that the shape and spacing of the stress relaxation layer 118 are not limited to these. Also, the stress relaxation layer 118 may be formed without using the sintering-resistant ceramic paste 218.

[0068] Next, external electrodes 116, 117 connected to internal electrodes 114, 115 are formed on the side surfaces of piezoelectric element 110 along the stacking direction. The external electrodes 116, 117 can be formed by printing electrode paste on the side surfaces of piezoelectric element 110 and baking it. An adhesive such as epoxy is applied to the end surfaces of the resulting multiple piezoelectric elements 110 in the stacking direction, and they are bonded and connected in series. Multiple piezoelectric elements 110 are connected in this manner, and the adhesive is then hardened.

[0069] Next, lead wires 131 and 132 of the metal plate-shaped piezoelectric actuator body are fixed to external electrodes 116 and 117 .

[0070] Next, adhesive is applied to the strain gauge 140 or to the position of the strain gauge 140 on the piezoelectric actuator body 105, and the strain gauge 140 is attached to the piezoelectric actuator body 105. The strain gauge may be attached to the piezoelectric actuator body 105 via another member. The strain gauge 140 may be attached to one piezoelectric element 110, or may be attached to multiple consecutive piezoelectric elements 110.

[0071] Next, piezoelectric actuator body 105 with strain gauge 140 attached is placed on seat 150. Next, lead wires 131 and 132 of the piezoelectric actuator body are connected to drive terminals 121 and 122, respectively. Also, lead wires 135, 136 and 137 of the strain gauge are connected to output terminals 125, 126 and 127 of the strain gauge, respectively.

[0072] The connection between the strain gauge lead wires 135, 136, and 137 and the strain gauge output terminals 125, 126, and 127 is preferably made via a connecting member 170. This improves the reliability of the connection between the strain gauge output terminals 125, 126, and 127 and the strain gauge lead wires 135, 136, and 137. Furthermore, by inserting the strain gauge output terminals 125, 126, and 127 and the strain gauge lead wires 135, 136, and 137 into both ends of the connecting member 170, it is no longer necessary to hold the terminals and lead wires with tweezers or the like, which makes positioning during soldering easier and improves workability. The connection between the lead wires 131 and 132 of the piezoelectric actuator body and the drive terminals 121 and 122 may also be made via the connecting member 170.

[0073] At this time, if the connecting member 170 has a predetermined shape, the connection work can be made easier by doing the following. First, one end of the connecting member 170 is placed over the end of the terminal 120, and the lead wire 130 is inserted into the other end of the connecting member 170. Solder 178 is applied from the terminal 120 side and melted, causing the solder 178 to rise inside the connecting member 170 by capillary action and reach above the terminal fastening portion 175. When the solder 178 solidifies, the strain gauge output terminals 125, 126, and 127 are soldered to the connecting member 170, and the strain gauge lead wires 135, 136, and 137 are soldered to the connecting member 170 in one soldering operation, respectively, and the strain gauge output terminals 125, 126, and 127 are connected to the strain gauge lead wires 135, 136, and 137, respectively.

[0074] That is, the connection member 170 having a predetermined shape means that the inner diameter of the connection member 170 is larger than the outer diameter of the terminal 120, allowing the terminal 120 to be inserted up to the terminal stopper 175, and the gap between the inner surface of the connection member 170 and the terminal 120 and the gap between the terminal stopper 175 are large enough to allow capillary action of the solder 178 to occur. Note that even if the solder 178 reaches above the terminal stopper 175, additional solder 178 may be added from the upper end of the connection member 170. This further improves the reliability of the connection.

[0075] Finally, the assembly is sealed with a cap 160. The driving terminals 121 and 122 are electrically connected to a driving power supply 190, and the output terminals 125, 126 and 127 of the strain gauges are electrically connected to a feedback control device 180.

[0076] In this way, it is possible to manufacture the piezoelectric actuator 100 of the present invention, which has improved reliability of the connection between the terminal 120 inside the cap 160 and the lead wire 130.

[0077] [Example] As an example, a piezoelectric actuator with the shape shown in Figure 1 was fabricated. A foil strain gauge with two orthogonal axes was prepared and attached to the side of the piezoelectric actuator body using epoxy adhesive. The connecting member was a gold-plated phosphor bronze pipe with an inner diameter of 0.53 mm, an outer diameter of 0.76 mm, and a length of 5.0 mm, with a small depression in the middle of one side. The minor axis of the inner surface of the terminal fastening portion of the connecting member was less than 0.4 mm. The terminals were nickel-plated Kovar with a diameter of 0.45 mm. The lead wires of the foil gauge and the terminals were soldered via the connecting member. Visually, the connecting member was filled with solder. Furthermore, when the soldered connecting member was cut vertically, it was confirmed that the seat terminals and the lead wires of the strain gauge were inserted into the metal pipe and that the metal pipe was filled with solder.

[0078] From the above, it was confirmed that the piezoelectric actuator of the present invention can improve the reliability of the connection between the terminal inside the cap and the lead wire.

[0079] The present invention is not limited to the above-described embodiments, and 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]

[0080] 100 Piezoelectric Actuator 105 Piezoelectric actuator body 108 Protrusion 110 Piezoelectric element 113 Piezoelectric layer 114, 115 Internal electrode 116, 117 External electrode 118 Stress relief layer 119 Cavity 120 terminals 121, 122 Drive terminals 125, 126, 127 Strain gauge output terminals 130 lead wire 131, 132 Lead wires of piezoelectric actuator body 135, 136, 137 Strain gauge lead wires 140 Strain Gauge 150 seats 155 Glass, Resin 160 Cap 170 Connecting member 175 Terminal stopper 178 Solder 180 Feedback Control Device 190 Drive power supply 200 Displacement Control System 201, 202, 203, 204 Green Sheets 213 Piezoelectric Ceramics 214, 215 Electrode paste 218 Hard-to-sinter ceramic paste

Claims

1. A piezoelectric actuator that is displaced by application of a voltage, a piezoelectric actuator body formed by connecting a plurality of piezoelectric elements in series or formed by a single piezoelectric element; a seat for supporting one end of the piezoelectric actuator body; a cap that houses the piezoelectric actuator body; a terminal fixed to the seat; a hollow cylindrical metal connection member having a terminal stopper portion in the middle in the longitudinal direction, the connection member being soldered between the inner end of the cap of the terminal and a lead wire electrically connected to a member disposed inside the cap, and connecting the terminal and the lead wire; a strain gauge attached directly or via another member to a side surface of the piezoelectric actuator body that is closer to the seat than the center in the connecting direction of the piezoelectric element, and that detects strain when the displacement of the piezoelectric actuator body changes; The piezoelectric actuator is characterized in that the lead wire is a lead wire of the strain gauge.

2. 2. The piezoelectric actuator according to claim 1, wherein the inside of the connection member is filled with solder.

3. 3. The piezoelectric actuator according to claim 1, wherein the inner surface of the connecting member is gold-plated.

4. 4. The piezoelectric actuator according to claim 1, wherein a difference between an inner diameter of the end of the connection member on the terminal side and an outer diameter of the end of the terminal inside the cap is 0.2 mm or less.

5. 5. The piezoelectric actuator according to claim 1, wherein the terminal fastening portion of the connection member is formed by recessing the middle of a pipe that constitutes the connection member.

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