JP7164847B2 - piezoelectric actuator - Google Patents

Description

The present invention relates to a piezoelectric actuator that is displaced by voltage application.

Since the piezoelectric element exhibits different displacement characteristics (hysteresis) when expanding and contracting, it is used in the precision positioning of semiconductor exposure apparatuses and the like by performing feedback control with a displacement sensor to improve the positioning accuracy. In addition, high-precision piezoelectric actuators that perform feedback control with displacement sensors are also used in fine movement mechanisms of precision numerically controlled processing machines, medical manipulators, and precision attitude control mechanisms for aviation and space. Piezoelectric actuators are also used to drive flow control valves that supply various gases to semiconductor manufacturing equipment. there is

Patent Document 1 uses a piezoelectric displacement portion 2 having hysteresis, and for the purpose of controlling the amount of displacement of a piston 3 with high accuracy, the piezoelectric displacement portion 2 expands and contracts according to an applied voltage, and one end of the piezoelectric displacement portion 2 The piston 3 is provided with a piston 3 that receives the expansion/contraction force, and a base 4 that receives the expansion/contraction force at the other end of the piezoelectric displacement section 2. The piston 3 is provided with an inner cylinder 14 that covers the piezoelectric displacement section 2. A piezoelectric actuator 1 is provided with a displacement detector 15 close to the base 4 and a displacement sensor 7 for detecting the distance to the displacement detector 15 is fixed to the base 4 .

In Patent Document 2, an airtight terminal 3 and a metal A piezoelectric actuator is described in which a displacement sensor 2 is provided on the side surface of an electrostrictive effect element 1 sealed by a member 8 and electrically connected to the electrostrictive effect element.

JP-A-8-153909 JP-A-5-206536

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, highly accurate positioning becomes possible, but the system becomes complicated and expensive, and the application is limited.

On the other hand, as shown in Patent Document 2, a simplified feedback control has been proposed in which a displacement sensor such as a strain gauge is directly attached to a resin-sealed piezoelectric actuator body and a partial displacement signal is used. ing. In many cases, strain gauges are simply affixed directly to the element, making them compact and inexpensive displacement sensors.

Piezoelectric actuators are often used for high-speed expansion and contraction, and displacement sensors are also required to have similar responsiveness and repeated durability. Since valves and the like using piezoelectric actuators are required to have durability against tens of millions of times of opening and closing, strain gauges must also have the same or higher durability. For example, a certain strain gauge has a fatigue life of around 10 million cycles at a strain rate of 1500 ppm. With such a long fatigue life, the durability of the displacement sensor for piezoelectric actuators is insufficient. Therefore, it is necessary to improve the durability by incorporating a sensor that reduces the burden on the gauge section.

However, in the technique described in Patent Document 2, it is not considered to incorporate the strain gauge so as to reduce the load on the gauge portion and to improve the durability.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances. It is an object of the present invention to provide a piezoelectric actuator.

(1) In order to achieve the above objects, the piezoelectric actuator of the present invention is a piezoelectric actuator that is displaced by application of a voltage, comprising: a piezoelectric actuator main body formed by connecting a plurality of piezoelectric elements in series; a strain gauge for detecting a strain rate in a displacement direction of the actuator main body, wherein the plurality of piezoelectric elements include a first piezoelectric element having an adhesive portion to which the strain gauge is attached and a second piezoelectric element to which the strain gauge is not attached. 2 piezoelectric elements, wherein the first piezoelectric element has a maximum distortion rate smaller than that of the second piezoelectric element at least at the bonding portion.

By thus reducing the maximum displacement of at least the bonding portion of the first piezoelectric element to which the strain gauge is bonded, the maximum strain rate of the strain gauge can be decreased and the durability of the strain gauge can be improved. can be done. As a result, the durability of the piezoelectric actuator provided with strain gauges for detecting strain is improved.

(2) Further, in the piezoelectric actuator of the present invention, the interval between the internal electrode layers in the bonding portion of the first piezoelectric element is wider than the interval between the internal electrode layers of the second piezoelectric element. In this manner, by making the interval between the internal electrode layers at the bonding portion of the first piezoelectric element wider than the interval between the internal electrode layers of the second piezoelectric element, the maximum displacement of the bonding portion of the first piezoelectric element is reduced. be able to. As a result, the maximum strain rate of the strain gauge can be reduced, and the durability of the strain gauge can be improved.

(3) Further, in the piezoelectric actuator of the present invention, the first piezoelectric element has a piezoelectric strain constant _d33 of the piezoelectric layer at the bonding portion smaller than the piezoelectric strain constant _d33 of the piezoelectric layer of the second piezoelectric element. It is characterized by _In this way, by making the piezoelectric strain constant d33 of the piezoelectric layer at the bonding portion of the first piezoelectric element smaller than the piezoelectric strain constant _d33 of the piezoelectric layer of the second piezoelectric element, the bonding of the first piezoelectric element The maximum displacement of the part can be reduced. As a result, the maximum strain rate of the strain gauge can be reduced, and the durability of the strain gauge can be improved.

(4) Further, in the piezoelectric actuator of the present invention, the area of the internal electrode in the adhesive portion of the first piezoelectric element is smaller than the area of the internal electrode of the second piezoelectric element. In this way, by making the area of the internal electrode at the bonding portion of the first piezoelectric element smaller than the area of the internal electrode of the second piezoelectric element, the maximum displacement of the bonding portion of the first piezoelectric element can be reduced. can be done. As a result, the maximum strain rate of the strain gauge can be reduced, and the durability of the strain gauge can be improved.

(5) In the piezoelectric actuator of the present invention, the number of stress relaxation layers in the adhesive portion of the first piezoelectric element is smaller than that of the stress relaxation layers of the second piezoelectric element. is characterized by a small In this way, the stress relaxation layers in the bonding portion of the first piezoelectric element are compared with the stress relaxation layers of the second piezoelectric element to reduce the number thereof or to reduce the area of the stress relaxation layers. The maximum displacement of the bonding portion of the piezoelectric element can be reduced. As a result, the maximum strain rate of the strain gauge can be reduced, and the durability of the strain gauge can be improved. It should be noted that the fact that the number of stress relieving layers is small also includes the fact that no stress relieving layers are formed.

(6) Further, in the piezoelectric actuator of the present invention, the maximum strain rate at the bonding portion of the first piezoelectric element is 80% or less of the maximum strain rate of the second piezoelectric element. Thus, the durability of the strain gauge can be improved by setting only the maximum strain rate at the bonding portion of the first piezoelectric element to 80% or less of the maximum strain rate of the second piezoelectric element. As a result, the durability of the piezoelectric actuator provided with strain gauges for detecting strain is improved. For example, if the maximum strain rate at the bonding portion is set to 80% of the maximum strain rate of the second piezoelectric element, the durability of the strain gauge is doubled.

According to the present invention, the maximum strain rate of the strain gauge can be reduced, and the durability of the strain gauge can be improved. As a result, the durability of the piezoelectric actuator provided with strain gauges for detecting strain is improved.

1(a) and 1(b) are a front view and a side view, respectively, showing a piezoelectric actuator of the present invention; FIG. It is a front sectional view of a piezoelectric element. Fig. 3 is a graph representing the respective hysteresis of a piezoelectric element with a given maximum displacement and a piezoelectric element with half that maximum displacement; 4 is a graph showing the relationship between maximum strain rate and durability of a strain gauge. 1 is a schematic diagram of a displacement control system; FIG. 1(a) and 1(b) are a front cross-sectional view and a side cross-sectional view, respectively, showing a closed-type piezoelectric actuator of the present invention. (a) and (b) are a front cross-sectional view and a bottom view of a seat and a terminal, respectively. 3(a) and 3(b) are front cross-sectional views respectively showing a first piezoelectric element and a second piezoelectric element of the first embodiment; FIG. 4A to 4C are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of the first embodiment, respectively; FIG. 8A and 8B are front cross-sectional views showing a first piezoelectric element and a second piezoelectric element of the second embodiment, respectively; FIG. 8A to 8E are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of the second embodiment, respectively; FIG. 8A and 8B are front cross-sectional views respectively showing a first piezoelectric element and a second piezoelectric element of a third embodiment; FIG. 8A to 8E are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of the third embodiment, respectively; FIG. 12(a) and 12(b) are front cross-sectional views respectively showing a first piezoelectric element and a second piezoelectric element of a fourth embodiment; FIG. 10A to 10E are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of the fourth embodiment, respectively; FIG.

Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in each drawing, and overlapping descriptions are omitted. In addition, in the configuration diagram, the size of each component is conceptually represented, and does not necessarily represent the actual size ratio.

[Basic configuration common to each embodiment of the present invention]
(Configuration of Piezoelectric Actuator)
1A and 1B are a front view and a side view of the piezoelectric actuator 100, respectively. It should be noted that the piezoelectric actuator shown in the reference diagram is merely an example, and the present invention is not limited by the number of elements or the like.

The piezoelectric actuator 100 includes a piezoelectric actuator main body 105, driving terminals 126 and 127, a sensor terminal 159, and a strain gauge 155, and expands and contracts upon application of a voltage. The 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, in which case it displaces a driven body (valve, stage).

When a voltage is applied to the pair of external electrodes 116 and 117 via the pair of lead wires 121 and 122, the piezoelectric actuator main body 105 is displaced at the tip by the expansion and contraction of each piezoelectric element 110. FIG. Driving terminals 126 and 127 are connected to lead wires 121 and 122 of the piezoelectric actuator main body 105 and transmit applied voltage to the lead wires 121 and 122 .

The GND terminal for driving the piezoelectric actuator body 105 and the GND terminal for the strain gauge can be shared. As a result, an increase in the total number of terminals can be suppressed, and the configuration of wiring and the like can be made easier. Separate terminals may be used instead of using a common terminal.

On the other hand, as shown in FIGS. 1A and 1B, the piezoelectric actuator 100 has a strain gauge 155 connected to a piezoelectric actuator main body 105 and a terminal 159 for a sensor. As a result, in the piezoelectric actuator 100 having the strain gauge 155, a displacement signal of the piezoelectric element 110 can be received via the strain gauge terminal 159. FIG. Details of the strain gauge 155 will be described later.

(piezoelectric actuator body)
The piezoelectric actuator main body 105 is composed of a piezoelectric element 110 and lead wires 121 and 122 . A plurality of piezoelectric elements 110 constituting the piezoelectric actuator main body 105 are arranged and connected in series (multi-connection), and their end surfaces are adhered to each other with an adhesive. A large amount of displacement can be ensured by bonding the plurality of piezoelectric elements 110 . Note that "in series" means the expansion/contraction direction, that is, the lamination direction of the piezoelectric layers and internal electrodes in the piezoelectric element 110 .

The lead wires 121 and 122 connect driving terminals 126 and 127 to the external electrodes 117 of the piezoelectric elements 110 . The connection is made in the same way on the side opposite to the side shown in FIG. 1(b).

(Piezoelectric element)
FIG. 2 is a front sectional view of the piezoelectric element 110. FIG. The piezoelectric element 110 outputs displacement in response to an applied voltage, and has a piezoelectric layer 113 , internal electrodes 114 and 115 and external electrodes 116 and 117 . In the piezoelectric element 110, piezoelectric layers 113 and internal electrodes 114 and 115 are alternately laminated. Also, the external electrodes 116 and 117 are connected to the internal electrodes 114 and 115 on the side surfaces of the piezoelectric element 110 . The piezoelectric layer can be composed of a piezoelectric material such as PZT, barium titanate, or the like. Ag—Pd, Pt, or the like can be used as the electrode material.

The plurality of piezoelectric elements 110 are composed of a first piezoelectric element 110a having an adhesive portion 111 to which the strain gauge 155 is attached and a second piezoelectric element 110b to which the strain gauge 155 is not attached. In addition, the first piezoelectric element 110a has a maximum distortion rate smaller than that of the second piezoelectric element 110b at least at the bonding portion 111 . In the present invention, by changing the configurations of the first piezoelectric element 110a and the second piezoelectric element 110b, at least the maximum distortion factor of the bonding portion 111 can be made smaller than the maximum distortion factor of the second piezoelectric element 110b. but FIG. 2 does not show it. A difference in configuration between the first piezoelectric element 110a and the second piezoelectric element 110b will be described in each embodiment.

The maximum strain rate is the ratio of the maximum amount of displacement to the length of the piezoelectric expansion/contraction portion at the time of maximum contraction. Further, the maximum strain rate of the bonding portion 111 is the ratio of the maximum amount of displacement of the bonding portion 111 to the length of the piezoelectric expansion/contraction portion of the bonding portion 111 at the time of maximum contraction. Further, the maximum strain rate of the second piezoelectric element 110b is the average value of the maximum strain rate of each of the second piezoelectric elements 110b when a plurality of the second piezoelectric elements 110b are present in one piezoelectric actuator body 105. is.

The maximum strain rate of the bonding portion 111 of the first piezoelectric element 110a is preferably 80% or less, more preferably 50% or less, of the maximum strain rate of the second piezoelectric element 110b. In addition, the lower limit of the maximum distortion rate of the bonding portion 111 of the first piezoelectric element 110a with respect to the maximum distortion rate of the second piezoelectric element 110b differs depending on the accuracy required to be detected by the strain gauge 155, so it is necessary to particularly limit it. However, for example, it is preferably 10% or more, more preferably 20% or more, and even more preferably 25% or more. As for the numerical value of the distortion factor, for example, the upper limit of distortion is preferably 1200 ppm or less, and more preferably 750 ppm or less. In addition, the lower limit is, for example, preferably 150 ppm or more, more preferably 300 ppm or more, and even more preferably 375 ppm or more.

The maximum strain rate of the portion other than the bonding portion of the first piezoelectric element may be the same as or different from the maximum strain rate of the bonding portion. For example, if the entire configuration of the first piezoelectric element is the same as the configuration of the adhesive portion, the maximum distortion factor of the portion other than the adhesive portion of the first piezoelectric element is smaller than the maximum distortion factor of the second piezoelectric element. Although the amount of displacement of the piezoelectric actuator as a whole is reduced, the structure of the first piezoelectric element as a whole is the same, which facilitates the manufacture of the first piezoelectric element. Also, since the entire first piezoelectric element can be said to be the bonding portion, bonding of the strain gauge is facilitated. For example, when the configuration of the portion of the first piezoelectric element other than the bonding portion is the same as the configuration of the second piezoelectric element, the maximum distortion rate of the portion of the first piezoelectric element other than the bonding portion is the same as that of the second piezoelectric element. It becomes the same as the maximum strain rate of the element, and the displacement amount of the entire piezoelectric actuator can be increased.

FIG. 3 is a graph representing the respective hysteresis of a piezoelectric element with a given maximum displacement and a piezoelectric element with half that maximum displacement. A piezoelectric element with a maximum displacement of 10 μm when a maximum voltage of 150 V is applied is defined as a standard displacement element, and a piezoelectric element with a maximum displacement of 5 μm when a maximum voltage of 150 V is applied is defined as a half displacement element. As shown in FIG. 3, the hysteresis of a 1/2 displacement element with a maximum displacement of 1/2 exhibits almost the same behavior as the hysteresis of a standard displacement element, so that the 1/2 displacement element is can also obtain about half the displacement of the standard displacement element. Due to such properties, even if the maximum displacement at the bonding portion of the first piezoelectric element is smaller than the maximum displacement of the second piezoelectric element, if the ratio is known, the distortion rate detected at the bonding portion can be used to determine the overall piezoelectric actuator. displacement can be measured.

When the maximum displacement of the piezoelectric element is reduced, the amount of change in the strain gauge is also reduced, which may pose a problem of lowering the S/N ratio as a displacement sensor. In such a case, strain gauges may be bonded to two surfaces of the element, for example, and connected to opposing portions of a Wheatstone bridge that detects minute resistance value changes of the strain gauges, thereby doubling the rate of change and compensating for it. can be done. By using this two-gauge method together, it is possible to improve the durability without lowering the S/N ratio of the strain gauge.

(strain gauge)
The strain gauge 155 detects strain in the displacement direction of the piezoelectric actuator body 105 . A wire strain gauge, a foil strain gauge, or the like can be used as the strain gauge 155 . The strain gauge 155 is connected by being directly attached to the piezoelectric actuator body 105 . An adhesive or the like can be used for attachment. Since the strain gauge 155 is connected to the surface of the piezoelectric actuator main body 105, when the piezoelectric actuator 100 is extended, the strain gauge 155 is also extended, so that the displacement of the piezoelectric actuator 100 and the displacement of the strain gauge 155 are in the same phase. , the controllability is improved.

The strain gauge 155 is connected to lead wires 157 and 158, and the lead wire 158 is connected to the sensor terminal 159 to transmit the detected displacement signal. As a result, the displacement of the piezoelectric actuator main body 105 can be confirmed and the displacement can be accurately grasped, and precise positioning using the piezoelectric actuator can be performed by feedback control.

Strain gauges are known to increase in durability by approximately one order of magnitude for each halving of the strain rate. Therefore, if the maximum strain rate of the strain gauge can be reduced, the durability of the strain gauge will be improved. In the present invention, since the maximum strain rate of at least the bonding portion 111 of the first piezoelectric element 110a having the bonding portion 111 for bonding the strain gauge 155 is made smaller than the maximum strain rate of the second piezoelectric element 110b, the strain The durability of gauge 155 is improved.

FIG. 4 is a graph showing the relationship between the maximum strain rate and durability of strain gauges. Assuming that the durability when the maximum strain rate of the strain gauge is 1500 ppm is 1, the durability against the maximum strain rate of the strain gauge is expressed numerically. The graph of FIG. 4 conceptually shows how the durability of the strain gauge is improved, and does not necessarily show that such durability is always obtained. As shown in FIG. 4, for example, when the maximum strain rate at the bonding portion of the first piezoelectric element is 80% of the maximum strain rate of the second piezoelectric element, and when the maximum strain rate is not reduced. By comparison, the durability of the strain gauge is approximately doubled. Also, when it is 50%, the durability of the strain gauge is increased by about 10 times.

(Displacement control system)
A displacement control system 190 can be configured using the piezoelectric actuator 100 described above. FIG. 5 is a schematic diagram of displacement control system 190 . As shown in FIG. 5, displacement control system 190 includes piezoelectric actuator 100 , feedback controller 170 and drive power supply 180 .

A sensor terminal 159 of the strain gauge 155 is connected to a feedback controller 170 . A signal of the detected displacement is input to the feedback control device 170, and the feedback control device 170 converts the detected signal into the displacement of the piezoelectric actuator 100 and calculates the necessary driving amount based on the detected displacement. do. Conversion from the detection signal to displacement is in phase, and when an extension signal is input from the strain gauge 155, the extension displacement of the piezoelectric actuator 100 is output. The feedback control device 170 controls the drive power source 180 according to the calculated drive amount, and the drive power source 180 applies the voltage commanded by the feedback control device 170 to the piezoelectric actuator main body 105 . In this way, a displacement control system 190 with reduced errors can be realized.

(sealed piezoelectric actuator)
Although the piezoelectric actuator body 105 is exposed in FIG. 1, the piezoelectric actuator body 105 may be sealed by a cap and seat. 6A and 6B are a front cross-sectional view and a side cross-sectional view, respectively, showing the sealed piezoelectric actuator 300. FIG. 7(a) and 7(b) are front cross-sectional and bottom views of seat 340 and terminals 126, 127, 159, respectively. Only parts different from FIG. 1 will be described below.

The piezoelectric actuator 300 includes a piezoelectric actuator main body 105, driving terminals 126 and 127, a sensor terminal 159, a strain gauge 155, a seat 340, and a cap 360, and expands and contracts upon application of voltage.

The seat 340 is adhered to the end of the piezoelectric actuator body 105 and fixed at one end to support the piezoelectric actuator body 105 . The extension and contraction of the piezoelectric actuator body 105 to which the end on the side of the seat 340 is fixed displaces the projection 330 on the tip side. In addition, in this embodiment, the protrusion 330 is hemispherical.

The seat 340 seals the piezoelectric actuator body 105 by being fixed to the end of the cap 360 . Reliability and durability can be improved by hermetically sealing the piezoelectric actuator body 105 and the strain gauge 155, which are vulnerable to humidity and corrosive gases, with a low-humidity inert gas. For example, when used in a precision machine where the displacement device is wet with cutting water, or in a piezoelectric valve that controls the flow rate of corrosive gas, the positioning accuracy using a piezoelectric actuator is insufficient in open control, and the displacement sensor It is effective to perform positioning and the like by a piezoelectric actuator capable of performing feedback control by .

In this manner, sealing enables the piezoelectric actuator to operate without problems even in harsh environments such as high humidity and corrosive gas. Since the inside of the cap 360 has a completely airtight structure, it can be used in environments such as humidity and corrosive gases that impair the durability of the piezoelectric element and the strain gauge, leading to expansion of applications.

Terminals 126, 127, and 159 are provided through seat 340 as hermetic terminals. The through hole is filled with glass or resin 345 and sealed. On the seat 340, the terminals 126, 127, 159 are preferably arranged around the central axis of the piezoelectric actuator 100 for the strain gauge and for the drive, respectively. As a result, the terminals 126, 127 and 159 can be easily electrically connected.

The GND terminal for driving the piezoelectric actuator main body 105 and the GND terminal for detecting the strain gauge 155 can be shared. As a result, when the strain gauge is accommodated in the cap, the total number of terminals pulled out from the seat is suppressed, and it is easy to adopt a configuration with improved environmental resistance in which the strain gauge is accommodated in the cap. can. Separate terminals may be used instead of using a common terminal.

The cap 360 has a bottomed cylindrical shape with an open end and is made of metal. The cap 360 accommodates the piezoelectric actuator body 105 in close contact with it in the stacking direction, and its open end is joined to the seat 340 to seal the inside of the cap 360 . This protects the piezoelectric actuator 300 and improves durability.

The cap 360 has a diaphragm with a dome-shaped portion with a projection 330 abutting at the tip of the cap. A straight tube portion of the cap 360 is formed in a cylindrical shape from the center of the cap 360 to the bottom. The diaphragm is formed in a dome shape. The cap 360 is desirably made of a material such as SUS316 or SUS316L, which is excellent in corrosion resistance and springiness. A base secures the seat 340 , and the seat 340 supports the end of the piezoelectric actuator body 105 . When the tip of the cap 360 comes into contact with the driven body, displacement is transmitted from the piezoelectric actuator 300 to the driven body.

Inside the cap 360, the strain gauge 155 is accommodated in addition to the piezoelectric actuator main body 105. As shown in FIG. The cap 360 can protect the piezoelectric actuator body 105 and the strain gauge 155 from the surrounding environment.

On the other hand, as shown in FIGS. 6A and 6B, the piezoelectric actuator 300 has the strain gauge 155 arranged inside the cap 360 and the sensor terminal 159 provided on the seat 340 . As a result, in the piezoelectric actuator 300 incorporating the strain gauge 155 , a displacement signal of the piezoelectric element 110 can be received via the sensor terminal 159 .

Piezoelectric actuator main body 105 is composed of piezoelectric element 110 , lead wires 121 and 122 and projection 330 . The protrusion 330 is made of an inorganic material and formed in a hemispherical shape, and is provided on the tip side of the piezoelectric actuator main body 105 that transmits displacement to the driven body. The protrusion 330 and the piezoelectric actuator main body 105 are firmly adhered, and the protrusion 330 contacts the dome-shaped inner portion of the cap 360 . Thereby, the displacement of the piezoelectric actuator main body 105 can be extracted to the outside of the cap 360 .

(Basic manufacturing method of piezoelectric actuator)
Next, a basic manufacturing method of the piezoelectric actuator 100 configured as shown in FIG. 1 will be described. First, a piezoelectric element 110 in which piezoelectric layers and internal electrodes are alternately laminated is manufactured. Specifically, an electrode paste such as Pt or Ag—Pd is printed on green sheets of piezoelectric ceramics, laminated, pressure-bonded, and fired. Next, external electrodes 116 and 117 connected to the internal electrodes are formed along the stacking direction on the side surfaces of the piezoelectric element 110 . The external electrodes 116 and 117 can be formed by printing the electrode paste on the side surface of the piezoelectric element 110 and baking it.

An adhesive such as epoxy is applied to the end surfaces of the plurality of piezoelectric elements 110 obtained in the stacking direction, and the elements are connected in series. In this way, multiple connections are made and the adhesive is cured. Then, an adhesive is applied to the strain gauge 155 or the strain gauge 155 arrangement position of the piezoelectric actuator main body 105 to directly attach the strain gauge 155 to the piezoelectric actuator main body 105 . The strain gauge 155 may be attached to one piezoelectric element 110 or may be attached to a plurality of continuous piezoelectric elements 110 .

Then, the piezoelectric actuator 100 can be manufactured by fixing the metal plate-like lead wires to the external electrodes. The driving terminals 126 and 127 are electrically connected to the driving power source 180 and the sensor terminal 159 is electrically connected to the feedback control device 170 .

(Manufacturing method of sealed piezoelectric actuator)
Also, a method of manufacturing the sealed piezoelectric actuator 300 configured as shown in FIG. 6 will be described. The sealed piezoelectric actuator 300 is manufactured by placing the piezoelectric actuator main body to which the strain gauge is attached on the seat in the method of manufacturing the piezoelectric actuator described above, and sealing it by covering it with a cap. Then, the sealed piezoelectric actuator 300 can be manufactured by fixing the metal plate-shaped lead wires to the external electrodes.

[First embodiment]
Next, the piezoelectric actuator of the first embodiment will be explained. The basic configuration of the piezoelectric actuator of the first embodiment is as described above. Therefore, only the configuration unique to this embodiment will be described.

(Piezoelectric element)
FIGS. 8A and 8B are front cross sections of the first piezoelectric element and the second piezoelectric element of this embodiment, respectively. Note that external electrodes are omitted in FIGS. As shown in FIGS. 8A and 8B, in the first piezoelectric element 110a of the present embodiment, the interval between the internal electrode layers in the bonding portion 111 is equal to the interval between the internal electrode layers of the second piezoelectric element 110b. wider. The interval between internal electrode layers refers to the distance in the stacking direction between adjacent internal electrodes 114 and 115 . When the same voltage is applied, the electric field strength between the internal electrode layers is smaller in the portion where the interval between the internal electrode layers is wider than in the portion where the interval between the internal electrode layers is narrower, so the strain therebetween is smaller. . Therefore, in the portion where the interval between the internal electrode layers is wide, the maximum strain rate when the maximum voltage is applied becomes small, and the durability of the strain gauge 155 adhered there is improved.

The displacement amount (displacement strain) of the laminated piezoelectric element is designed by adjusting the internal electrode spacing according to the piezoelectric strain constant of the piezoelectric ceramics used. For example, it is possible to design a certain type of piezoelectric ceramic so that the maximum distortion factor is 1500 ppm when the maximum voltage is applied by adjusting the internal electrode spacing. Thus, the maximum strain rate can be adjusted by changing the thickness of the green sheets used for manufacturing the laminated piezoelectric element. For example, if a green sheet with twice the thickness is used, the interval between the internal electrodes of the laminated piezoelectric element will also be doubled, so that the electric field strength generated there will be halved when the same voltage is applied. Since the amount of displacement of the piezoelectric element is approximately proportional to the intensity of the electric field, when the same voltage is applied as shown in FIG. 4, the strain generated is also halved.

(Manufacturing method for piezoelectric elements with different configurations)
FIGS. 9A to 9C are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of this embodiment, respectively. 9A to 9C show an electrode paste 214 that will become the internal electrode 114 after firing, a piezoelectric ceramic green sheet 201 that will become the piezoelectric layer 113 after firing, and an electrode paste 215 that will become the internal electrode 115 after firing and the piezoelectric layer 113, respectively. A green sheet 202 of piezoelectric ceramics and a green sheet 203 of piezoelectric ceramics on which no electrode paste is laminated are shown.

The second piezoelectric element 110b is manufactured by alternately laminating green sheets 201 and 202 having a normal thickness and firing them. On the other hand, in the first piezoelectric element 110a, when laminating at least the part that becomes the bonding portion 111, the thickness of the piezoelectric ceramic that becomes the piezoelectric ceramic 113 after firing is increased instead of the green sheets 201 and 202 having the normal thickness. The green sheets are alternately laminated. Alternatively, the thickness of the piezoelectric layer 113 may be increased by appropriately laminating the green sheet 203 on which the electrode paste is not laminated on the green sheets 201 and 202 of normal thickness. In this way, it is possible to manufacture the first piezoelectric element 110a in which the interval between the internal electrode layers in the bonding portion 111 is wider than the interval between the internal electrode layers of the second piezoelectric element 110b. In both the first and second piezoelectric elements, one or more green sheets 203 may be laminated on the end face in the lamination direction to form a protective layer.

In the case of a piezoelectric actuator in which a plurality of piezoelectric elements are connected in series in the displacement direction, for the first piezoelectric element to which the strain gauge is adhered, at least the sheet thickness of the layer to be the adhesion portion is adjusted, so that the first of piezoelectric elements can be manufactured. Further, when the piezoelectric element for the piezoelectric actuator is made of one highly laminated element, it is possible to adopt a structure in which a thick sheet is used only for the portion where the strain gauge is adhered. Since the maximum strain rate of the strain gauge can be adjusted by changing the thickness of the piezoelectric ceramic sheet, it is possible to manufacture a piezoelectric actuator with a built-in strain gauge that has sufficient durability required by the market. Become.

[Second embodiment]
Next, a piezoelectric actuator of a second embodiment will be described. The basic configuration of the piezoelectric actuator of the second embodiment is as described above. Therefore, only the configuration unique to this embodiment will be described.

(Piezoelectric element)
10(a) and 10(b) are front cross sections of the first piezoelectric element and the second piezoelectric element of this embodiment, respectively. 10A and 10B omit external electrodes. As shown in FIGS. 10A and 10B, in the first piezoelectric element 110a of the present embodiment, the piezoelectric strain constant of the piezoelectric layer 113a in the bonding portion 111 is equal to that of the piezoelectric layer 113 of the second piezoelectric element 110b. is smaller than the piezoelectric strain constant of where the piezoelectric strain constant is _d33 .

Piezoelectric ceramics for laminated piezoelectric elements include materials with various properties. Piezoelectric actuators require large displacements, so materials with relatively large piezoelectric strain constants, which are generally called soft materials, are used. On the other hand, it is also known that a hard material suitable for high-speed driving can be obtained by adding a small amount of manganese or the like to the soft material. In general, hard materials reduce the piezoelectric strain constant to less than half that of soft materials. In this way, it is possible to easily prepare materials having similar compositions but greatly different piezoelectric strain constants.

(Manufacturing method for piezoelectric elements with different configurations)
FIGS. 11A to 11E are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of this embodiment, respectively. 11A to 11E show an electrode paste 214 that becomes the internal electrode 114 after firing, a piezoelectric ceramic green sheet 201 that becomes the piezoelectric layer 113 after firing, an electrode paste 215 that becomes the internal electrode 115 after firing, and the piezoelectric layer 113, respectively. an electrode paste 214 that becomes the internal electrode 114 after firing and a piezoelectric ceramic green sheet 204 that becomes the piezoelectric layer 113a after firing; an electrode paste 215 that becomes the internal electrode 115 after firing and a piezoelectric ceramic green sheet 202 that becomes the piezoelectric layer 113a after firing. A green sheet 205 and a green sheet 203 of only piezoelectric ceramics without electrode paste laminated are shown.

The second piezoelectric element 110b is manufactured by alternately stacking piezoelectric ceramic green sheets 201 and 202, which will become the piezoelectric layer 113 after firing, and firing the stacked sheets. On the other hand, in the first piezoelectric element 110a, when laminating at least the part that becomes the bonding portion 111, instead of the usual green sheets 201 and 202, piezoelectric ceramic green sheets 204 and 205 that become the piezoelectric ceramic 113a after firing are alternately stacked. to laminate. Compared with the piezoelectric ceramics 201 and 202, the piezoelectric ceramics 204 and 205 have a smaller piezoelectric strain constant _d33 after firing. _In this way, the first piezoelectric element can be manufactured in which the piezoelectric strain constant d33 of the piezoelectric layer 113a in the bonding portion 111 is smaller than the piezoelectric strain constant _d33 of the piezoelectric layer 113 of the second piezoelectric element 110b. For both the first and second piezoelectric elements, one or more green sheets 203 may be laminated on the end face in the lamination direction to form a protective layer.

In the case of a piezoelectric actuator in which a plurality of piezoelectric elements are connected in series in the displacement direction, it is possible to use a material such as a hard material that suppresses piezoelectric characteristics for at least the layer that will be the bonding portion for the first piezoelectric element to which the strain gauge is attached. , the first piezoelectric element can be manufactured. Further, when the piezoelectric element for the piezoelectric actuator is made of one highly laminated element, it is possible to adopt a structure in which a material such as a hard material that suppresses piezoelectric characteristics is used only for the portion where the strain gauge is adhered. Since the maximum strain rate of the strain gauge can be adjusted by changing the composition of the piezoelectric ceramic sheet, it is possible to manufacture a strain gauge built-in piezoelectric actuator having sufficient durability required in the market. .

[Third Embodiment]
Next, a piezoelectric actuator of a third embodiment will be described. The basic configuration of the piezoelectric actuator of the third embodiment is as described above. Therefore, only the configuration unique to this embodiment will be described.

(Piezoelectric element)
12(a) and 12(b) are front cross sections of the first piezoelectric element and the second piezoelectric element of this embodiment, respectively. 12A and 12B, external electrodes are omitted. As shown in FIGS. 12A and 12B, in the first piezoelectric element 110a of the present embodiment, the area of the internal electrodes 114a and 115a in the bonding portion 111 is the same as the area of the internal electrode 114 of the second piezoelectric element 110b. , 115. Note that the portion that is displaced when a voltage is applied is the piezoelectrically active portion that overlaps when the internal electrodes to which different voltages are applied are projected in the stacking direction. The area may simply be smaller than the area of the internal electrodes 114 or 115 .

Internal electrodes are formed inside the laminated piezoelectric element with an area of 80 to 100% of the cross-sectional area, depending on the cross-sectional area of the element. When a voltage is applied to the laminated piezoelectric element, an electric field is generated in the portion where the internal electrodes are formed, and the piezoelectric ceramic expands and contracts. On the other hand, since no electric field is generated in the periphery of the internal electrodes, they do not expand or contract due to voltage application. This piezoelectric inactive portion suppresses the displacement in the internal electrode portion. Therefore, if the ratio of the area where the internal electrodes are formed is reduced only in the portion where the strain gauge is adhered, the displacement of the laminated piezoelectric element can be reduced to the required level, and the maximum strain rate of the strain gauge can be reduced to the required level. level can be adjusted.

(Manufacturing method for piezoelectric elements with different configurations)
FIGS. 13A to 13E are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of this embodiment, respectively. FIGS. 13A to 13E show an electrode paste 214 that becomes the internal electrode 114 after firing, a piezoelectric ceramic green sheet 201 that becomes the piezoelectric layer 113 after firing, an electrode paste 215 that becomes the internal electrode 115 after firing, and the piezoelectric layer 113, respectively. An electrode paste 214a that becomes the internal electrode 114a after firing and a piezoelectric ceramic green sheet 206 that becomes the piezoelectric layer 113 after firing, an electrode paste 215a that becomes the internal electrode 115a after firing, and a piezoelectric ceramic green sheet 202 that becomes the piezoelectric layer 113 after firing. A green sheet 207 and a green sheet 203 of only piezoelectric ceramics without electrode paste laminated are shown.

The second piezoelectric element 110b is manufactured by alternately stacking and firing green sheets 201 and 202 using electrode pastes 214 and 215 having a normal internal electrode area. On the other hand, the first piezoelectric element 110a does not use the usual green sheets 201 and 202 when laminating at least the part that becomes the bonding portion 111, but the green sheets 206 and 206 laminated with the electrode paste 214a that will become the internal electrodes 114a after firing. And the green sheets 207 laminated with the electrode paste 215a which becomes the internal electrode 115a after firing are alternately laminated. Compared to the electrode pastes 214 and 215, the electrode pastes 214a and 215a have smaller areas of internal electrodes after firing. In this way, it is possible to manufacture the first piezoelectric element in which the area of the internal electrodes 114a and 115a in the bonding portion 111 is smaller than the area of the internal electrodes 114 and 115 of the second piezoelectric element 110b. For both the first and second piezoelectric elements, one or more green sheets 203 may be laminated on the end face in the lamination direction to form a protective layer.

In the case of a piezoelectric actuator in which a plurality of piezoelectric elements are connected in series in the displacement direction, for the first piezoelectric element to which the strain gauge is attached, a green sheet with a reduced area of the internal electrode is used for at least the layer that will be the bonding portion. , the first piezoelectric element can be manufactured. Further, when the piezoelectric element for the piezoelectric actuator is made of one highly laminated element, it is possible to adopt a structure using a green sheet in which the area of the internal electrode is reduced only in the portion where the strain gauge is adhered. In this way, by adjusting the area of the internal electrode of the piezoelectric ceramic sheet, the maximum strain rate of the strain gauge can be adjusted. becomes possible.

[Fourth embodiment]
Next, a piezoelectric actuator according to a fourth embodiment will be described. The basic configuration of the piezoelectric actuator of the fourth embodiment is as described above. Therefore, only the configuration unique to this embodiment will be described.

(Piezoelectric element)
14(a) and 14(b) are front cross sections of the first piezoelectric element and the second piezoelectric element of this embodiment, respectively. 14A and 14B, the internal electrodes 114 and 115 are indicated by dotted lines, and the stress relaxation layer 118 is indicated by solid lines. 14A and 14B omit external electrodes. As shown in FIGS. 14A and 14B, in the first piezoelectric element 110a of the present embodiment, the stress relaxation layer 118 in the bonding portion 111 is different from the stress relaxation layer 118 in the second piezoelectric element 110b. and are few in number or small in area. The number of stress relaxation layers 118 is less than the number of stress relaxation layers 118 in the bonding portion 111 and the number of stress relaxation layers 118 in the same length as the bonding portion 111 in the stacking direction of the second piezoelectric element. By comparison, it means that the number is small, and includes the fact that the stress relaxation layer 118 is not formed in the bonding portion 111 . In addition, when the area of the stress relaxation layer 118 is small, it means that the area of the figure obtained by projecting the stress relaxation layer 118 formed on the bonding portion 111 in the stacking direction is larger than the area of the stress relaxation layer 118 formed on the second piezoelectric element 110b. It is smaller than the area of the figure projected in the stacking direction.

In general, a piezoelectric inactive portion is formed around an internal electrode inside a laminated piezoelectric element for insulation and protection against contamination and moisture from the external environment. In a multilayer piezoelectric element for a piezoelectric actuator, a slit-shaped stress relieving layer is formed in the entire layer or at regular intervals in the piezoelectric inactive portion in order to prevent displacement inhibition by the piezoelectric inactive portion. That is, the stress relieving layer is provided to relieve stress generated inside the piezoelectric element when the element is driven. Therefore, by reducing the number and area of the piezoelectric element stress relaxation layers only in the portion where the strain gauge is adhered, or by not forming the stress relaxation layer, the displacement characteristics can be reduced, and the maximum strain of the strain gauge can be reduced. rate can be reduced. This makes it possible to improve the durability of the strain gauge built-in piezoelectric actuator.

(Manufacturing method for piezoelectric elements with different configurations)
FIGS. 15A to 15E are schematic diagrams showing green sheets used for manufacturing the first and second piezoelectric elements of this embodiment, respectively. 15A to 15E show green sheets in which an electrode paste 214 that becomes an internal electrode 114 after firing, a piezoelectric ceramic 213 that becomes a piezoelectric layer 113, and a hard-to-sinter ceramic paste 218 that becomes a stress relaxation layer 118 are laminated. 208, a green sheet 209 laminated with an electrode paste 215 that will become the internal electrode 115 after firing, a piezoelectric ceramic 213 that will become the piezoelectric layer 113, and a hard-to-sinter ceramic paste 218 that will become the stress relaxation layer 118, and an electrode that will become the internal electrode 114 after firing. A green sheet 201 laminated with a paste 214 and a piezoelectric ceramic 213 forming a piezoelectric layer 113, a green sheet 202 laminated with an electrode paste 215 forming an internal electrode 115 after firing and a piezoelectric ceramic 213 forming a piezoelectric layer 113, and an electrode paste. A green sheet 203 of only piezoelectric ceramics 213 without lamination is shown. As the hard-to-sinter ceramic paste 218, zirconia, lead titanate, or the like is used.

The second piezoelectric element 110b is manufactured by alternately stacking and firing green sheets 208 and 209 coated with a hard-to-sinter ceramic paste 218 that will become a stress relaxation layer 118 after firing. The green sheets 201 and 202 not coated with the hard-to-sinter ceramic paste 218 that will become the stress relaxation layer 118 after firing may be used as appropriate. On the other hand, the first piezoelectric element 110a does not use the green sheets 208 and 209 coated with the hard-to-sinter ceramic paste 218, which will become the stress relaxation layer 118 after firing, when laminating at least the portion that will become the bonding portion 111. Alternatively, the number of sheets used is reduced compared to the case of manufacturing the second piezoelectric element. In this way, the first piezoelectric element 110a having a smaller number or a smaller area of the stress relaxation layers 118 in the bonding portion 111 than the stress relaxation layers 118 of the second piezoelectric element 110b can be manufactured. can be done. For both the first and second piezoelectric elements, one or more green sheets 203 may be laminated on the end face in the lamination direction to form a protective layer.

In the case of a piezoelectric actuator in which a plurality of piezoelectric elements are connected in series in the displacement direction, the first piezoelectric element to which the strain gauge is attached is reduced in the number and area of the stress relaxation layers at least in the bonding portion, Alternatively, the first piezoelectric element can be manufactured by not forming the stress relaxation layer. In addition, when the piezoelectric element for the piezoelectric actuator is made of one highly laminated element, only the portion where the strain gauge is adhered has a smaller number of stress relaxation layers than the other portions, and the area is reduced. Alternatively, a structure in which no stress relaxation layer is formed can be employed. In this way, by adjusting the stress relaxation layer of the piezoelectric ceramic sheet, it is possible to adjust the maximum strain rate of the strain gauge. becomes possible.

Although the first to third embodiments do not refer to the stress relaxation layer, this is for the purpose of clarifying the characteristics of each embodiment. It may or may not exist. Also, the present invention can be realized by combining two or more embodiments.

It goes without saying that the present invention is not limited to the above-described embodiments, but extends to various modifications and equivalents within the spirit and scope of the present invention. Also, the structure, shape, number, position, size, etc. of the constituent elements shown in each drawing are for convenience of explanation, and may be changed as appropriate.

100, 300 Piezoelectric actuator 105 Piezoelectric actuator main body 110, 110a, 110b Piezoelectric element 111 Bonding parts 113, 113a Piezoelectric layers 114, 114a, 115, 115a Internal electrodes 116, 117 External electrode 118 Stress relaxation layers 121, 122, 157, 158 Leads Wires 126, 127, 159 Terminal 155 Strain gauge 170 Feedback controller 180 Drive power source 190 Displacement control system 201-209 Green sheet 218 Hard-to-sinter ceramic paste 214, 214a, 215, 215a Electrode paste 330 Protrusion 340 Seat 345 Glass, resin 360 cap

Claims (6)

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;
a strain gauge that detects strain in the displacement direction of the piezoelectric actuator body,
the plurality of piezoelectric elements are composed of a first piezoelectric element having an adhesive portion to which the strain gauge is attached and a second piezoelectric element to which the strain gauge is not attached;
The first piezoelectric element has a maximum strain rate, which is a ratio of the maximum displacement amount to the length of the piezoelectric expansion/contraction portion at the time of maximum contraction, and the maximum strain rate at least at the bonding portion is higher than the maximum strain rate of the second piezoelectric element. A piezoelectric actuator characterized by being small. 2. The piezoelectric actuator according to claim 1, wherein the interval between the internal electrode layers in the bonding portion of the first piezoelectric element is wider than the interval between the internal electrode layers of the second piezoelectric element. 2. The piezoelectric actuator according to claim 1, wherein the first piezoelectric element has a piezoelectric strain constant _d33 of the piezoelectric layer at the bonding portion smaller than the piezoelectric strain constant _d33 of the piezoelectric layer of the second piezoelectric element. . 2. The piezoelectric actuator according to claim 1, wherein the first piezoelectric element has an area of the internal electrode in the bonding portion smaller than that of the internal electrode of the second piezoelectric element. 2. The first piezoelectric element according to claim 1, wherein the stress relieving layers in the bonding portion are smaller in number or smaller in area than the stress relieving layers of the second piezoelectric element. piezoelectric actuator. 6. The method according to any one of claims 1 to 5, wherein the maximum strain rate at the bonding portion of the first piezoelectric element is 80% or less of the maximum strain rate of the second piezoelectric element. piezoelectric actuator.

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