JPH10127069A - Vibration actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the vibration efficiency of an actually assembled vibration actuator from decreasing below a target driving efficiency being set on design stage by forming an electromechanical conversion element of an elastic body through hydrothermal synthesis. SOLUTION: An ultrasonic actuator 1 comprises an elastic body 2, a titanium layer 3 applied to the surface of the elastic body 2, a piezoelectric film 4 of PZT(plumbum zirconate titanate) deposited on the titanium layer 3 through hydrothermal synthesis, and upper platinum electrodes 5a, 5b formed on the surface of the piezoelectric film 4 by sputtering. In the hydrothermal synthesis, a piezoelectric compositional material, water and the elastic body 2 are placed in an autoclave and a temperature difference on the order of several K is set between them at 100-300 deg.C (pressure is 8.5Mpa at 300 deg.C) thus causing convection. The piezoelectric compositional material is thereby fused through variation of solubility with temperature and the PZT is deposited on the surface of the elastic body 2 and grown.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration actuator having an elastic body and an electromechanical transducer which is joined to the elastic body and generates longitudinal vibration and bending vibration in a harmonic manner.

[0002]

2. Description of the Related Art Conventionally, there has been known a vibration actuator including an elastic body and an electromechanical transducer that is joined to the elastic body to generate longitudinal vibration and bending vibration harmoniously.

As a vibration actuator of this type, for example, an elastic body formed in a rectangular plate shape is provided on one plane.
A piezoelectric body, which is an electromechanical conversion element that converts electric energy into mechanical displacement, is mounted. An elastic body is vibrated by applying a two-phase AC voltage to the piezoelectric body, and a first-order longitudinal vibration and a fourth-order bending vibration are generated harmoniously in the elastic body. Generate.

[0004] Driving force extracting portions are formed at two positions on the other plane of the elastic body where the elliptical motion has occurred, which are antinodes of the fourth bending vibration, and these driving force extracting portions are formed. The tip of the part is periodically displaced in an elliptical shape.

[0005] The tip of the driving force take-out unit is in pressure contact with a relative motion member (moving element), and the generated elliptical displacement is transmitted to the relative motion member, and the displacement between the elastic body and the relative motion member. Relative motion occurs.

[0006] As such a vibration actuator,
In "Piezoelectric Linear Motor for Moving Optical Pickup" (Mr. Yoshiaki Tomikawa et al .: Proceedings of the 5th Dynamic Symposium on Electromagnetic Force, pp. 393-398), the configuration and load characteristics of vibration actuators Is described in detail.

The elastic body is designed such that the natural frequencies of the first-order longitudinal vibration and the fourth-order bending vibration generated in the elastic body of the vibration actuator are very close to each other. Therefore, by applying two phases of an AC voltage having a frequency close to the natural frequency of each of the above-described longitudinal vibration and bending vibration to the piezoelectric body, vibration in which the two vibrations are harmonized with the elastic body is generated.

In this conventional vibration actuator, the piezoelectric body is formed on one plane of an elastic body manufactured in a predetermined shape.
For example, it is attached by being attached with an adhesive such as an epoxy resin.

[0009]

As described above, in this vibration actuator, two kinds of vibrations, that is, a first-order longitudinal vibration and a fourth-order bending vibration, are generated harmoniously in the elastic body so that the surface of the elastic body is generated. A driving force is obtained by generating an elliptical motion. Therefore, the natural frequencies of the longitudinal vibration and the bending vibration generated in the elastic body are designed to be very close values.

As described above, matching the natural frequencies of the longitudinal vibration and the bending vibration is required in the design stage of calculating the elastic modulus and density of the entire vibration actuator including the elastic body and the piezoelectric body, as well as the shape and the like. Can be performed relatively easily.

However, at the actual manufacturing stage, the piezoelectric body is bonded to the surface of the elastic body, so that an adhesive layer is inevitably present. Therefore, according to the thickness of the adhesive layer, the natural frequencies of the longitudinal vibration and the bending vibration, which coincided in the design stage, are shifted, and it is extremely difficult to accurately match the natural frequencies of the respective vibrations. I will. Therefore, there is a problem that the driving efficiency of the actually assembled vibration actuator is lower than the target driving efficiency set at the design stage.

From the viewpoint of improving driving efficiency, it is desirable that the thickness of the piezoelectric body be as small as possible.
If the piezoelectric body is made thinner than a certain limit value, cracking of the piezoelectric body occurs frequently at the time of handling at the time of bonding to the elastic body. Therefore, the piezoelectric body cannot be made thinner than a certain value, and from this point as well, the drive efficiency of the actually assembled vibration actuator is lower than the target drive efficiency set at the design stage.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention does not attach a piezoelectric body formed as a separate component to an elastic body by bonding, but uses a hydrothermal synthesis method on the surface of the elastic body. Is used to form a piezoelectric film.

According to a first aspect of the present invention, there is provided a vibration actuator including an elastic body and an electromechanical transducer that is joined to the elastic body and generates a longitudinal vibration and a bending vibration harmoniously. , Characterized by being formed on the elastic body by a hydrothermal synthesis method.

According to a second aspect of the present invention, in the vibration actuator according to the first aspect, the electrode for inputting a drive signal to the electromechanical transducer is a surface of the electromechanical transducer or the electromechanical transducer. Characterized by being formed on both surfaces.

[0016] The invention of claim 3 is claim 1 or claim 2.
Wherein the electromechanical transducer is a piezoelectric or electrostrictive material made of a lead-based ferroelectric.

The invention of claim 4 is the invention of claim 2 or claim 3.
In the vibration actuator described in the above, the electrode formed between the elastic body and the electromechanical transducer is made of a titanium layer.

The "hydrothermal synthesis method" in the first aspect of the present invention refers to a method of synthesizing and growing a substance in the presence of high-temperature (particularly, high-temperature, high-pressure) water. In the present invention, for example, a piezoelectric material, water, and an elastic material are placed in an autoclave and are heated at about 100 ° C. to 300 ° C. (pressure is 300 ° C.).
By providing a temperature difference of about several K between the two at 8.5 ° C., convection occurs, and at the same time, the piezoelectric constituent material dissolves due to the change in solubility with temperature, and PZT precipitates on the surface of the elastic body. Happen and grow.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, an embodiment of a vibration actuator according to the present invention will be described in detail with reference to the accompanying drawings. In the following description of each embodiment, an example of an ultrasonic actuator using an ultrasonic vibration region will be described as the vibration actuator.

FIG. 1 is a perspective view showing the configuration of the ultrasonic actuator 1 according to the first embodiment. The ultrasonic actuator 1 of this embodiment includes an elastic body 2, a titanium layer 3 provided on the surface of the elastic body 2, and PZT (zircon titanate) formed on the titanium layer 3 by hydrothermal synthesis. A piezoelectric film 4 made of lead oxide) and platinum upper electrodes 5a and 5b formed on the surface of the piezoelectric film 4 by sputtering.

Hereinafter, a procedure for manufacturing the ultrasonic actuator 1 will be described. (1) Formation of Elastic Body 2 In the present embodiment, the elastic body 2 is formed in a rectangular flat plate shape using an elastic material such as metal. The material and dimensions of the elastic body 2
As described above, it is set so that the natural frequencies of the first-order longitudinal vibration and the fourth-order bending vibration generated in the elastic body 2 match each other. In addition, in this embodiment, the thickness of the elastic body was 3 mm.

Driving force take-out portions 2a and 2b are formed on one flat surface of the elastic body 2 at two antinode positions of the generated fourth-order bending vibration. The elastic body 2 is brought into pressure contact with a relative movement member (not shown) by the pressure mechanism (not shown) via the end faces of the driving force extracting portions 2a and 2b.

In the present embodiment, the driving force output unit 2
Although a and 2b are formed in the shape of a protrusion, they may be formed so as to be flush with the plane of the elastic body 2 (in other words, a protrusion having a height of zero).

(2) Deposition of Titanium Layer 3 A hydrothermal synthesis is performed on the piezoelectric body forming plane (the surface on which the driving force output portions 2a and 2b are not formed) of the two planes of the elastic body 2 thus formed. A titanium layer 3 serving as a base for crystal growth is formed.

The formation of the titanium layer 3 may be performed by a usual forming method such as plating, whereby the titanium layer 3 having a thickness of about 1 to 20 μm is formed. In this embodiment, 10 μm
m. In the present embodiment, the titanium layer 3 is used as a lower electrode when a polarization process is performed on the piezoelectric film 4 described later.

That is, lead zirconate titanate (PZ)
When a ferroelectric material containing titanium such as T) or lead titanate (PT) is formed on the elastic body 2 as the piezoelectric film 4 by a hydrothermal synthesis method, these ferroelectric materials are elastic. Body 2
In the process of growing on the surface, the titanium layer or the titanium oxide layer 3
Ideally exists. The titanium layer or the titanium oxide layer 3 also functions as a buffer layer for suppressing the diffusion of lead atoms into the elastic body 2. When the titanium layer or the titanium oxide layer 3 is used, a portion that does not contribute to the reaction can be used as it is as an electrode.

(3) Formation of Piezoelectric Film 4 by Hydrothermal Synthesis The piezoelectric film 4 is formed on the titanium layer 3 thus formed by hydrothermal synthesis.

That is, the elastic body 2 on which the titanium layer 3 is formed is made of potassium hydroxide in which lead nitrate (Pb (NO ₃ ) ₂ ) and zirconium oxychloride octahydrate (ZrOCl ₂ : 8H ₂₀ ) are dissolved. Place in an autoclave containing the aqueous solution.

At the time of hydrothermal synthesis, the elastic body 2 is immersed in an aqueous solution of potassium hydroxide and subjected to, for example, treatment at 140 ° C. for about 48 hours. It is considered that at the time of this treatment, PZT particles are nucleated by the reaction between titanium on the surface of the elastic body 2 and lead and zircon in the aqueous potassium hydroxide solution.

Next, the elastic body 2 is immersed in an aqueous potassium hydroxide solution in which lead nitrate, zirconium oxychloride octahydrate and titanium tetrachloride (TiCl ₄ ) are dissolved, and is placed in an autoclave at 150 ° C. × 48. The piezoelectric film 4 is formed by promoting the crystal growth by performing the process for about a time. The thickness of the piezoelectric film 4 was about 5 to 50 μm, and was 10 μm in the present embodiment.

Here, as the piezoelectric film 4 for efficiently exciting the elastic body 2, it is most preferable to use a piezoelectric material or a magnetostrictive material made of a lead-based ferroelectric material because the displacement amount per applied electric field is large. desirable.

In the present embodiment, the thickness of the formed piezoelectric film 4 is about 10 μm, which is reduced to about 1/50 as compared with a conventional single-piece piezoelectric body. Accordingly, the amount is almost negligible in the entire ultrasonic actuator 1. Further, unlike the related art, since the adhesive layer does not exist between the piezoelectric body and the elastic body, vibration generated in the elastic body is not absorbed by the adhesive layer. Therefore,
In the calculation of the natural frequency, the calculation can be performed excluding the unclear amount, so that the ultrasonic actuator can be designed more strictly.

In this embodiment, the piezoelectric film 4 is formed on the plane of the elastic body. However, it is also possible to perform hydrothermal treatment on a processing surface having a complicated shape such as a curved surface other than the plane. As far as possible, the piezoelectric film 4 can be formed very easily. Therefore, the piezoelectric film 4 of the present embodiment
Can sufficiently cope with the future complexity of the ultrasonic actuator shape.

Further, as an effect of utilizing the hydrothermal synthesis method in this embodiment, a hydrothermal film (piezoelectric film 4) can be formed at all places on the titanium layer 3 at the same time. For example, in the case of a plate-like elastic body 2, it is possible to very easily form the thick electric film 4 on both sides of the elastic body 2 as necessary, and to reduce the force generated for excitation. It can be easily doubled.

(4) Formation of Platinum Upper Electrodes 5a and 5b Further, a platinum layer as an upper electrode is formed on the surface of the piezoelectric film 4 by sputtering to form platinum upper electrodes 5a and 5b. These platinum upper electrodes 5a and 5b are formed into two parts by masking the piezoelectric film 4 during sputtering, as shown in FIG. In the present embodiment, the thickness of the platinum upper electrodes 5a and 5b is 0.1 μm.
m.

Further, by applying a voltage to the platinum upper electrodes 5a and 5b thus formed so that the signs of the platinum upper electrodes 5a and 5b are opposite to each other, the polarization of the piezoelectric film 4 is increased. Processing was performed. The polarization treatment was performed at 150 ° C. × 100 V for 1 hour in the air.

In this embodiment, the titanium plating layer 3 and the platinum upper electrodes 5a and 5b are formed on both surfaces of the piezoelectric film 4. The simplest and easy-to-manufacture configuration of an electrode for extracting the piezoelectric effect of the piezoelectric film 4 is a configuration in which electrodes are formed on both surfaces of the piezoelectric film 4 as in the present embodiment. When the elastic body 2 is used as one electrode, only the platinum upper electrodes 5a and 5b may be used.

With respect to the ultrasonic actuator 1 thus formed, an AC voltage A phase is applied to the platinum upper electrode 5a, and an AC voltage B phase which is 90 degrees out of phase with the AC voltage A phase is applied to the platinum upper electrode 4b. Then, an elliptical motion occurred on the end faces of the protrusions 2a and 2b of the elastic body 2, and a driving force could be obtained.

As described above, in the ultrasonic actuator 1 of the present embodiment, the thickness of the elastic body: 3 mm, the thickness of the titanium plating layer 3: 10 μm, the thickness of the piezoelectric film 4: 10 μm, the platinum upper electrode 5a, 5b thickness: 0.1 μm. For this reason, the adverse effect of the adhesive layer does not occur even in the actual assembling as in the related art, and the target value of the natural frequency of the elastic body obtained by calculation from the elastic modulus, density, dimensions, and the like does not occur.

It has been proposed to form the piezoelectric film 4 by a thin film forming technique such as vapor deposition, sputtering, CVD, and sol-gel. Even with these techniques, since a vibration absorbing layer such as an adhesive layer does not exist at the interface between the piezoelectric film 4 and the elastic body 2, the vibration generated in the piezoelectric film 4 is transmitted to the elastic body 2 very efficiently. be able to. However, in order to form a film having a thickness of several μm or more by these thin film forming techniques, a great cost and man-hour are required, and cracks are easily generated in the formed piezoelectric film 4. Therefore, it is difficult to form the piezoelectric film 4 having sufficient performance, especially when the thickness of the elastic body 2 is large. In contrast, in the film formation by the hydrothermal synthesis method in the present invention,
The piezoelectric film 4 capable of transmitting the generated vibration to the elastic body very efficiently can be easily formed on the order of several tens of μm.
This is a method suitable for the formation of

In addition, if the hydrothermal synthesis method of the present invention is used, the elastic body and the piezoelectric body are conventionally bonded one by one, but a large amount can be processed at once by batch processing. Therefore, both work efficiency and mass productivity are improved at a stretch. For example, on a predetermined surface of a large flat elastic base material,
After the titanium layer 3 is formed, the piezoelectric film 4 is formed by hydrothermal synthesis.
After that, the elastic body 2 may be cut out from the elastic body base material to a predetermined size.

Further, even if the miniaturization of the ultrasonic actuator 1 is promoted in the future, it is possible not only to form the piezoelectric body 4 on a predetermined plane of the elastic body 2 but also to form the elastic body 2 as in the prior art. Therefore, it is possible to sufficiently cope with the miniaturization without fear that the vibration propagation efficiency with respect to is significantly impaired by the miniaturization.

Here, the driving efficiency calculated by dividing the obtained maximum output by the input electric energy is calculated and calculated for the design target value, the actually measured value of the conventional ultrasonic actuator, and the ultrasonic actuator 1 of the present embodiment. The measurement is as follows. The drive efficiency of the design target value is converted as 100.

Design target value: 100 Conventional ultrasonic actuator: 85 Ultrasonic actuator of the present embodiment 1: 92

As described above, according to the present embodiment, the driving efficiency of the ultrasonic actuator 1 actually assembled is
The target drive efficiency set at the design stage can be approached, and the drive efficiency can be improved as compared with the conventional ultrasonic actuator.

(Second Embodiment) FIG. 2 is a perspective view showing an ultrasonic actuator 11 according to a second embodiment. The ultrasonic actuator 11 of the present embodiment includes an elastic body 12 and a titanium layer 13 formed on the surface of the elastic body 12 by plating.
And a PZ film formed on the titanium layer 13 by a hydrothermal synthesis method.
And a platinum upper electrode 15a, 15b formed on the piezoelectric film 14 by sputtering.
And a titanium layer 16 formed by plating between the driving force extracting portions 12a and 12b formed in a protruding shape on the back surface of the elastic body 12, and a PZT film formed on the titanium layer 16 by hydrothermal synthesis. And a platinum upper electrode 18a, 1 formed on the piezoelectric film 17 by sputtering.
8b.

The piezoelectric film 14 is formed on the surface opposite to the driving surface of the elastic body 12, and the piezoelectric film 17 is provided between the driving force output portions 12 a and 12 b formed on the driving surface side of the elastic body 12. A film is formed. Elastic body 12, titanium layers 13 and 16, piezoelectric film 1
4, 17, platinum upper electrodes 15a, 15b, 18a, 18
The method of forming b is the same as in the first embodiment. The poling of the piezoelectric films 14 and 17 was performed in the air at 150 ° C. and 100 V for one hour in the same manner as in the first embodiment.

In the ultrasonic actuator 11 configured as described above, the AC voltage A phase is applied to the electrodes 15a and 18b, and the AC voltage B phase which is 90 degrees different from the A phase is applied to the electrodes 15b and 18a. An elliptical motion was generated at the tips of the driving force take-out portions 12a and 12b of the body 12, and a driving force could be obtained.

In this embodiment, the ultrasonic actuator 11
Also, the same effect as the ultrasonic actuator 1 of the first embodiment could be obtained. Also, in the ultrasonic actuator 11 of the present embodiment, the piezoelectric films 14 and 17 are formed on the two planes of the elastic body 12, so that the vibration actuator 1 in which the piezoelectric film 4 is formed on one surface of the first embodiment. By comparison, it is possible to increase the deformation of the bending vibration generated when the same driving voltage is applied, thereby improving the driving force.

Here, the drive efficiency calculated by dividing the obtained maximum output by the input electric energy is calculated and calculated for the design target value, the actually measured value of the conventional ultrasonic actuator, and the ultrasonic actuator 11 of the present embodiment. The measurement is as follows. The drive efficiency of the design target value is converted as 100.

Design target value: 100 Conventional ultrasonic actuator: 85 Ultrasonic actuator 11 of the present embodiment: 92

As described above, according to the present embodiment, the drive efficiency of the actually assembled ultrasonic actuator 11 can be made closer to the target drive efficiency set in the design stage, and the drive efficiency is higher than that of the conventional ultrasonic actuator. It has become possible to improve the efficiency.

(Third Embodiment) FIG. 3 is a perspective view showing an ultrasonic actuator 21 according to a third embodiment. The ultrasonic actuator 21 of the present embodiment is an application example of a type that operates in a high-temperature environment, and the form of the elastic body 22 is the same as the elastic body 2 of the first embodiment.

For this reason, lead titanate (PT), which has a Curie temperature of 490 ° C. and hardly deteriorates in polarization treatment even in a high temperature environment, was selected as the piezoelectric layer for exciting the elastic body. A piezoelectric layer 24 made of lead titanate (PT) is formed on the surface of the elastic body 22 by a hydrothermal synthesis method with a titanium layer 23 formed by plating interposed therebetween. 25a and 25b are formed by sputtering.

As described above, also in the present embodiment, the first
As in the embodiment, the titanium layer 23 is formed by plating, and the piezoelectric layer 24 is formed by hydrothermal synthesis. A method for forming the piezoelectric layer 24 by the hydrothermal synthesis method will be described below.

On the surface of the elastic body 22 where the piezoelectric layer 24 is to be formed, a titanium layer 23 serving as a base for crystal growth by hydrothermal synthesis is formed by plating. The elastic body 22 that has been subjected to the titanium plating is made of lead nitrate (Pb (NO
_{3) 2),} and in a state of being immersed in an aqueous solution of potassium hydroxide were dissolved titanium oxide (Ti0 _2), are subjected to processing 420 ° C. × 60 hours in an autoclave.

At the time of this treatment, the titanium layer 23 formed on the surface of the elastic body 22 reacts with lead in the aqueous potassium hydroxide solution, and nuclei of PT particles are generated on the surface of the elastic body 22. Further, the lead and titanium in the aqueous solution concentrate around the nuclei of the PT particles thus generated, thereby promoting crystal growth and forming the piezoelectric layer 24 made of PT.

In this ultrasonic actuator 21,
The AC voltage A-phase is applied to the electrode 25a, and the AC voltage B-phase 90 ° out of phase with the A-phase is applied to the electrode 25b.
When 5 V is applied, the driving force extracting portion 22 of the elastic body 22
It was confirmed that an elliptical motion occurred on the end faces of a and 22b, and the end faces were driven.

Here, the drive efficiency calculated by dividing the obtained maximum output by the input electric energy is calculated and calculated for the design target value, the actually measured value of the conventional ultrasonic actuator, and the ultrasonic actuator 21 of the present embodiment. The measurement is as follows. The drive efficiency of the design target value is converted as 100.

Design target value: 100 Conventional ultrasonic actuator: 85 Ultrasonic actuator 21 of the present embodiment: 92

As described above, according to the present embodiment, the drive efficiency of the actually assembled ultrasonic actuator 21 can be made closer to the target drive efficiency set in the design stage, and the drive efficiency is higher than that of the conventional ultrasonic actuator. It has become possible to improve the efficiency.

(Modification) In each of the embodiments, the ultrasonic actuator is used as the vibration actuator. However, the vibration actuator according to the present invention is not limited to such an embodiment, and the vibration actuator using another vibration region is used. The same applies to actuators.

In each of the embodiments, the piezoelectric element is used as the electromechanical conversion element. However, as long as the element can convert electric energy into mechanical displacement, other elements can be equally applied. it can. For example, an electrostrictive element other than the piezoelectric element can be exemplified.

Further, in each of the embodiments, the order of the longitudinal vibration and the bending vibration generated in the elastic body is the first and fourth order. However, the vibration actuator according to the present invention is limited to the order of each vibration. Not something. For example, longitudinal vibration primary,
The same applies to a sixth-order vibration actuator.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a configuration of an ultrasonic actuator according to a first embodiment.

FIG. 2 is a perspective view illustrating an ultrasonic actuator according to a second embodiment.

FIG. 3 is a perspective view showing an ultrasonic actuator according to a third embodiment.

[Explanation of symbols]

1,11,21 Ultrasonic actuator 2,12,22 Elastic body 2a, 2b, 12a, 12b, 22a, 22b Driving force output part 3,13,16,23 Titanium layer 4,14,17,24 Piezoelectric film 5a , 5b, 15a, 15b, 18a, 18b, 25
a, 25b Upper electrode

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 41/24 H01L 41/22 A

Claims (4)

[Claims] 1. A vibration actuator comprising: an elastic body; and an electromechanical transducer that is joined to the elastic body and generates a longitudinal vibration and a bending vibration harmoniously, wherein the electromechanical transducer includes the elastic body. A vibration actuator formed by a hydrothermal synthesis method. 2. The vibration actuator according to claim 1, wherein an electrode for inputting a drive signal is formed on a surface of the electromechanical transducer or on both surfaces of the electromechanical transducer. . 3. The vibration actuator according to claim 1, wherein the electromechanical transducer is a piezoelectric material made of a lead-based ferroelectric material or an electrostrictive material. 4. The vibration actuator according to claim 2, wherein an electrode formed between the elastic body and the electromechanical transducer is made of a titanium layer. .