JPH11112046A - Piezoelectric actuator and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric actuator where the structures of vibration electrodes and piezoelectric porcelain layers are simple, inner stress does not occur in piezoelectric porcelain and a manufacture process is considerably simplified and to provide the manufacture. SOLUTION: A piezoelectric actuator 1 has substantially a cylindrical form. The thickness part is constituted by stacking first piezoelectric porcelain layers 1a, first vibration electrodes 2a, second piezoelectric porcelain layers 1b and second vibration electrodes 2a, which continue in a circumferential direction, and it appears at the end part of a substantially cylindrically formed side. Terminal electrodes 3a and 3b are formed in the first vibration electrode 2a and the second vibration electrode 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator used for a vibration generator, fine positioning, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, piezoelectric actuators generally have a laminated structure. A typical structure is disclosed in
21857 and JP-A-6-296049.

For example, Japanese Patent Application Laid-Open No. Hei 5-21857 discloses a laminated structure using a baked piezoelectric plate, in which a disc-shaped piezoelectric plate made of a piezoelectric material and a metal plate serving as a vibrating electrode are composed of: A plurality of layers are alternately stacked via a conductive paste. Then, by alternately applying voltages having different polarities to the metal plates adjacent to each other in the laminating direction, the piezoelectric ceramic sandwiched between the two metal plates expands and contracts.

Japanese Patent Laid-Open No. 6-296049 has a structure in which a piezoelectric ceramic layer and a vibrating electrode are integrally sintered.

[0005] At least one main surface of a piezoelectric ceramic green sheet serving as a piezoelectric ceramic layer is formed by printing a conductive film serving as a vibrating electrode, and a large number of such piezoelectric ceramic green sheets are laminated to form a predetermined rectangular parallelepiped shape. After cutting, firing is performed, and terminal electrodes are respectively formed on a pair of side surfaces of the fired laminate.
The two vibrating electrodes adjacent to each other in the lamination thickness direction are biased so as to be exposed on different side surfaces of the laminated body. One of the external electrodes is connected to one adjacent vibrating electrode in the stacking thickness direction, and the other external electrode is connected to the other vibrating electrode.

[0006]

The above-mentioned piezoelectric actuator is desirably one which can be driven at a low voltage, can obtain a large displacement, and does not damage the piezoelectric ceramic.

However, in the first prior art, since the piezoelectric ceramics are laminated using fired piezoelectric plates, the thickness of the piezoelectric ceramic is reduced to two.
It is technically very difficult to reduce the thickness to 00 μm or less. Therefore, a very high voltage, for example, several hundred volts, must be supplied to the vibrating electrodes sandwiching the thick piezoelectric ceramic. Also, voltages of different polarities must be applied to the vibrating electrodes adjacent in the thickness direction. Therefore, it is necessary to have a structure for alternately connecting the terminal electrodes to the vibration electrodes.

In the second prior art, the manufacturing process requires
Since the piezoelectric ceramic green sheet is used, the thickness of the piezoelectric ceramic layer can be reduced.

However, as many vibrating electrodes as the number of laminations are arranged in the thickness direction of the laminate. In addition, paying attention to the planar shape of one of the adjacent vibrating electrodes, for example, the vibrating electrode connected to the terminal electrode on one side is formed so as to be biased toward one end side on the piezoelectric ceramic layer, and the other side No vibrating electrode is formed at the end. Similarly, the other vibrating electrode adjacent to the piezoelectric ceramic layer is formed so as to be biased toward an end portion on the other side surface on the piezoelectric ceramic layer, and the vibrating electrode is not formed at an end portion on one side surface side. Therefore, there are a portion where the predetermined potential difference is supplied and a portion where the predetermined potential difference is not supplied, sandwiched between the adjacent vibrating electrodes in the piezoelectric ceramic layer. That is, there is a portion that expands and contracts in the thickness direction of the piezoelectric ceramic and a portion that does not expand and contract, and there is a problem that the piezoelectric ceramic layer is easily damaged by internal stress.

The present invention has been devised in view of the above problems, and has as its object to provide a piezoelectric actuator having a simple structure of a vibrating electrode and a piezoelectric ceramic layer and generating no internal stress in the piezoelectric ceramic. Is to do.

A second object is to provide a method of manufacturing a piezoelectric actuator whose manufacturing method is very simple.

[0012]

According to a first aspect of the present invention, a first piezoelectric ceramic layer and a second piezoelectric ceramic layer wound concentrically and spirally, and the first piezoelectric ceramic layer A first vibrating electrode formed between the first piezoelectric ceramic layer and the second piezoelectric ceramic layer;
And a part of the first and second vibrating electrodes is exposed on a peripheral surface, and a terminal electrode is formed on the exposed portion.

According to a second aspect of the present invention, a first piezoelectric ceramic green sheet and a second ceramic green sheet are laminated via a conductor film serving as a first vibrating electrode, and at least one of the two main surfaces is provided. The present invention is a method for manufacturing a piezoelectric actuator in which a laminated sheet formed with a conductive film serving as a second vibrating electrode is spirally wound, and the conductive film and the piezoelectric ceramic green sheet are integrally fired.

[0014]

According to the first aspect of the present invention, the piezoelectric actuator is formed in a substantially cylindrical shape wound in a spiral shape, which is completely different from the conventional laminated type. That is, the piezoelectric ceramic layer, 1
Each of the pair of vibrating electrodes constitutes a thick portion of a cylindrical portion, and furthermore, has a structure in which it is spirally continuous.

Accordingly, the terminal electrodes for connecting the pair of vibrating electrodes to the external circuit may be connected to the vibrating electrodes at one place, respectively, and the connection structure between the terminal electrodes and the vibrating electrodes is greatly simplified. You.

Further, the vibrating electrode and the piezoelectric ceramic layer have a continuous structure with each other, and a portion of the piezoelectric ceramic layer where the vibrating electrode is not joined can be substantially eliminated. The internal stress generated between a portion where the vibration is generated and a portion where the vibration is not generated can be reduced, and the durability is greatly improved.

According to the second aspect of the present invention, the laminated sheet in which the first and second piezoelectric ceramic green sheets each having the conductor film serving as the vibrating electrode formed on at least one principal surface is spirally wound, and the conductor film and Since the piezoelectric ceramic green sheet is integrally fired, the thickness of the piezoelectric ceramic layer can be substantially reduced to a thickness at which a green sheet can be formed, for example, 10 μm or less. Accordingly, the thickness of the piezoelectric ceramic layer of the formed piezoelectric actuator can be made extremely thin, and the piezoelectric actuator can be driven at a low voltage.

In addition, since the manufacturing method only needs to spirally wind the piezoelectric ceramic green sheet on which the conductor film serving as the vibrating electrode is adhered a predetermined number of turns, the manufacturing method itself is greatly simplified. Will be.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a piezoelectric actuator according to the present invention and a method for manufacturing the same will be described with reference to the drawings.

FIG. 1 is an external perspective view of a piezoelectric actuator according to the present invention. FIG. 2 shows a cross-sectional structure taken along line XX in FIG.

Reference numeral 1 denotes a piezoelectric actuator, 10 denotes a substantially cylindrical actuator main body, 3a and 3b denote terminal electrodes, and 4 denotes an insulating protection portion.

The substantially cylindrical actuator body 10 includes a first piezoelectric ceramic layer 1a continuous in a circumferential direction, a second piezoelectric ceramic layer 1b continuous in a circumferential direction, and first vibrating electrodes 2a, 2a.
b is spirally wound a predetermined number of turns.

For example, in the radial direction of the part wound by two turns, the first piezoelectric ceramic layer 1a on the inner side from the inner side, the first vibrating electrode 2a on the inner side, and the first vibrating electrode 2a on the inner side. 2 piezoelectric ceramic layers 1b, an inner peripheral second vibrating electrode 2b, an outer peripheral first piezoelectric ceramic layer 1a, an outer peripheral first vibrating electrode 2
a, an outer peripheral side second piezoelectric ceramic layer 1b, and an outer peripheral side second vibrating electrode 2b.

For example, the piezoelectric ceramic layers 1a and 1b are made of lead titanate (PT), lead zirconate titanate (PTT) or the like, and are polarized in the thickness direction of the porcelain, and have a thickness of 5 to 20 μm. It has become about. The piezoelectric ceramic layers 1a and 1b have a Poisson's ratio of 2 or more.

The vibrating electrodes 2a and 2b are made of a conductor containing palladium, silver, or the like as a main component. For example, the first vibrating electrode 2a is formed on the outer peripheral main surface of the first piezoelectric ceramic layer 1a and its outer periphery. Is adhered to substantially the entire inner peripheral side main surface of the second piezoelectric ceramic layer 1b surrounding the second piezoelectric ceramic layer 1b.

The second vibrating electrode 2b is in close contact with substantially the entire outer circumferential main surface of the second piezoelectric ceramic layer 1b and the inner circumferential main surface of the first piezoelectric ceramic layer 1a surrounding the outer surface. I have.
Note that the outermost peripheral portion of the second piezoelectric ceramic layer 1b is covered with the insulating protective film 4.

The terminal electrodes 3a and 3b are wound on the side of the cylindrical actuator main body 10 by the first vibrating electrode 2a
And the end of the wound second vibrating electrode 2b. Specifically, the exposed portions of the first and second vibrating electrodes 2a and 2b are attached to substantially the center of the cylindrical actuator body 10 in the longitudinal direction, and are mainly composed of Ag in order to improve solder wettability. Made of conductive resin or the like.

The insulating protective film 4 is made of a flexible resin such as silicone resin, and has at least the terminal electrodes 3a,
3b is exposed to cover the entire surface of the actuator body 10.

The actuator 1 composed of such components has a hollow portion 6 extending in the longitudinal direction inside thereof, and the first piezoelectric ceramic layer 1a having the above-described configuration is provided around the hollow portion 6 and the first piezoelectric ceramic layer 1a. A first vibrating electrode 2a, a second piezoelectric ceramic layer 1b,
The laminated structure of the second vibrating electrode 2b is turned one or more times. The dimensions are such that the inner diameter of the cavity is, for example, 1 mm, the outer diameter of the cylindrical actuator body 10 is about 3 to 5 mm, and the length is about 5 mm.

The terminal electrode 3 of such an actuator 1
When an alternating voltage of several V is applied to the first and second vibrating electrodes 2a and 2b or the second vibrating electrode 2b
And first piezoelectric ceramic layer 1 sandwiched between first vibrating electrode 2a and
a and the second piezoelectric ceramic layer 1b generates a predetermined vibration. This predetermined vibration expands and contracts in the length direction of the cylindrical actuator main body 10. That is, in the conventional laminated piezoelectric actuator, expansion and contraction occurred in the lamination thickness direction. The longitudinal vibration is related to the size of the piezoelectric constant d _33.

Actually, when the thickness of the first and second piezoelectric ceramic layers 1a and 1b made of PZT is 10 μm, the length is 5 mm.
When a voltage of 3 V was supplied between the vibrating electrodes 2a and 2b of the cylindrical actuator main body 10 wound 10 turns, a displacement of 3 μm was obtained in the longitudinal direction of the cylindrical actuator main body 10.

With the above-described structure, the first and second piezoelectric ceramic layers 1a and 1b and the first and second vibrating electrodes 2a and 2b are respectively continuous in the circumferential direction.

For this reason, the terminal electrodes 3a, 3a and 3b are located at one end of the winding end of the first vibration electrode 2a and the second vibration electrode 2b.
By simply forming b, a predetermined voltage can be supplied to the first piezoelectric ceramic layer 1a and the second piezoelectric ceramic layer 1b regardless of the number of turns. That is, the structure of the terminal electrodes 3a and 3b is simplified, and the piezoelectric actuator 1 can operate reliably.

The first vibrating electrode 1a and the second vibrating electrode 2a are joined to substantially the entire inner or outer main surface of the first and second piezoelectric ceramic layers 1a and 1b. And a voltage can be supplied to the whole of the first and second piezoelectric ceramic layers 1a and 1b. Therefore, there may be a part that contributes to vibration and a part that does not contribute to vibration in the same piezoelectric ceramic as in the related art. Therefore, the internal stress during vibration is not concentrated, the durability of the piezoelectric ceramic layers 1a and 1b is improved, and the piezoelectric actuator 1 with high reliability is obtained.

Next, a method of manufacturing a piezoelectric actuator according to the present invention will be described with reference to the process flow chart of FIG.

First, in the first step, a piezoelectric ceramic green sheet to be a piezoelectric ceramic layer is prepared.

Specifically, a slurry is formed by mixing the adjusted powder of the PZT piezoelectric material, a binder, a plasticizer, and the like, and the slurry is formed into a tape by a well-known tape forming method such as a doctor blade method. I do.

In the second step, a conductor film serving as a vibrating electrode is formed on the outer peripheral main surface of the piezoelectric ceramic green sheet. The conductor film is printed on the entire outer peripheral main surface of the piezoelectric ceramic green sheet using a conductive paste containing palladium as a main component, and dried.

In the third step, a green sheet serving as the first piezoelectric ceramic layer 1a and a green sheet serving as the second piezoelectric ceramic layer 1b having the conductor film serving as the vibrating electrode formed in the second step are laminated. I do. Specifically, the first piezoelectric ceramic layer 1
A green sheet to be the second piezoelectric ceramic layer 1b is placed on the outer peripheral side main surface (a) (the surface on which the conductor film to be the vibrating electrode is formed) and pressed and adhered. Thereby, the green sheet serving as the first piezoelectric ceramic layer 1a and the first vibrating electrode 2a
, A green sheet to be the second piezoelectric ceramic layer 1b, and a conductive film to be the second vibrating electrode 2b. At this time, the conductive film serving as the first vibrating electrode is bonded to the green sheet serving as the first piezoelectric ceramic layer 1a and the surface of the green sheet serving as the second piezoelectric ceramic layer 1b on which the vibrating electrode is not formed. To do it.

The above-mentioned tape is cut into a predetermined shape to form a green sheet. The width of the green sheet is a length from which the plurality of piezoelectric actuators 1 are cut out, and the length of the green sheet is a length necessary for winding one piezoelectric actuator 1. Note that the length of the green sheet serving as the first piezoelectric ceramic layer 1a located on the inner peripheral side of the cylindrical actuator body 10 is set to be longer than the length of the green sheet serving as the second piezoelectric ceramic layer 1b. At the last end of the winding, the outer peripheral surface of the terminal end of the first piezoelectric ceramic layer 1a is exposed outside the terminal end of the second piezoelectric ceramic layer 1b, facilitating the formation of the terminal electrode 3a. It is desirable to do so. The fourth step is a step of winding the laminated sheet formed in the third step so as to have a cylindrical shape.
Specifically, a laminated sheet is wound a predetermined number of turns around a shaft having a diameter of about 1 mm, on which a surface such as carbon graphite is applied, so that a conductive film to be the second vibrating electrode 2b becomes an outer peripheral surface. Thereafter, uniform pressure and heating are applied as necessary from the outer peripheral surface side of the laminated sheet that has been wound into a cylindrical shape, so that the conductor film serving as the second vibrating electrode 2b, which is the outer peripheral surface of the laminated sheet, and the laminated sheet The first piezoelectric ceramic layer 1a, which is the inner peripheral surface of the first piezoelectric ceramic layer 1a, is brought into close contact with the green sheet.

Thereafter, the above-mentioned shaft is slid off to remove the unsintered cylindrical actuator body 10.
Is formed.

In the fifth step, the unfired cylindrical actuator body 10 formed in the fourth step is subjected to a firing treatment. Specifically, the baking treatment is performed at about 1200 ° C. in an air atmosphere. As a result, the green sheet is divided into the first and second green sheets.
The conductor film is formed on the piezoelectric ceramic layers 1a and 1b.
b. Then, the first and second vibrating electrodes 2a, 2b
Is used to perform polarization processing on the fired piezoelectric ceramic.

In the sixth step, the long cylindrical actuator is cut into a predetermined length in accordance with the length of the piezoelectric actuator 1. Thereby, the cylindrical actuator main body 10 is completed. In the seventh step, the first vibration electrode 2a and the second vibration electrode 2b exposed at the winding end portion of the laminated sheet of the cylindrical actuator body 10 are made of a terminal by using a conductive resin paste containing Ag or the like. The electrodes 3a and 3b are formed. The terminal electrodes 3a and 3b may be formed over the entire length of the cylindrical piezoelectric actuator body 10 in the longitudinal direction. However, in consideration of the vibration of the cylindrical actuator body 10, the cylinder electrodes 3a and 3b are least affected by expansion and contraction vibration. The actuator body 10 may be formed at the center in the length direction.

In the ninth step, an insulating protective film 4 made of a soft resin such as silicone resin is formed so that the terminal electrodes 3a and 3b of the cylindrical actuator body 10 are exposed. In addition, on both end surfaces of the cylindrical piezoelectric actuator body 10 which is the tip of the vibration of the piezoelectric actuator 1,
Insulation member (not shown) made of a disc-shaped ceramic or the like
Adhesive arrangement.

In the above manufacturing process, the piezoelectric ceramic layers 1a, 1a
b is formed by winding a piezoelectric ceramic green sheet, the magnetic thickness can be controlled by the thickness of the green sheet, and the conductive film can be formed by printing, so that the green sheet can be further wound. Can be made thinner. For example, it may be 10 μm or less.

Accordingly, the thickness of the piezoelectric ceramic layers 1a and 1b of the piezoelectric actuator 1 can be made extremely thin, and the piezoelectric actuator 1 can be sufficiently driven even at a low voltage, for example, 3V or less.

Even if the piezoelectric ceramic layers are in a laminated state, only two green sheets to be the piezoelectric ceramic layers 1a and 1b in a planar state are required to be substantially laminated, and the other laminating processes are substantially not required. Since the winding process is performed using a shaft, the entire lamination process can be greatly simplified. Moreover, since a plurality of piezoelectric actuators can be formed in one process, production efficiency is improved.

In the above-described embodiment, the vibrating electrodes are formed only on the outer peripheral side main surfaces of the green sheets to be the first piezoelectric ceramic layers 1a and 1b, however, as shown in FIG.
The vibrating electrodes 2a, 2b,
The conductive films 21, 22, 23, 24 serving as 2b may be formed. In this case, when the green sheets 10a and 10b to be the first piezoelectric ceramic layers 1a and 1b are stacked, the outer peripheral main surface of the green sheet 10a to be the first piezoelectric ceramic layer 1a (the upper main surface in the figure) 2) is integrated with the conductor film 23 on the inner peripheral side main surface (lower main surface in the figure) of the green sheet 10b to be the second piezoelectric ceramic layer 1b.
And a first vibrating electrode 2a between the inner peripheral main surface of the first piezoelectric ceramic layer 1a and the inner peripheral main surface of the second piezoelectric ceramic layer 1b, as shown in FIG. Conductor film 21 on the inner peripheral side main surface (lower main surface in the figure) of the green sheet 10a to be formed
And the conductor film 24 on the outer peripheral main surface (upper main surface in the figure) of the green sheet that will be the second piezoelectric ceramic layer 1b is integrated with the outer peripheral side of the second piezoelectric ceramic layer 1b shown in FIG. A second vibrating electrode 2a is formed between the main surface and the inner peripheral side main surface of the first piezoelectric ceramic layer 1a.

As shown in FIG. 4, each piezoelectric ceramic layer 1
a, 1b, at the beginning of the winding of the conductive films 21 to 24, which are the vibrating electrodes formed on the main surfaces of the green sheets 10a, 10b, at least the first vibrating electrode 2a is formed when both are wound. In order to prevent a short circuit with the second vibrating electrode 2b, a portion having no electrode (gap g) may be provided. Further, the conductor films 21 to 21 serving as vibration electrodes
Each of the piezoelectric ceramic layers 1 a, 24 b has a terminal end of the winding 24 so that a terminal electrode 3 a connected to the first vibration electrode 2 a and a terminal electrode 3 b connected to the second vibration electrode 2 b can be easily formed.
The lengths of the green sheets 10a and 10b which are 1b are different.

Further, conductor films 21 and 22 are formed on both main surfaces of the green sheet 10a serving as the first piezoelectric ceramic 1a.
On both main surfaces of the green sheet 10a serving as the second piezoelectric ceramic 1b, two green sheets having no conductor film may be laminated and wound.

[0051]

As described above, according to the first aspect of the invention, the piezoelectric actuator, the piezoelectric ceramic layer, the vibrating electrode, and the terminal electrode each have a very simplified configuration, and vibration occurs in the entire piezoelectric ceramic layer. Therefore, breakage of the porcelain due to concentration of internal stress as in the related art can be effectively prevented. Further, since the piezoelectric ceramic layer is formed using the piezoelectric ceramic green sheet, the thickness of the piezoelectric ceramic layer can be reduced, so that the piezoelectric ceramic layer can be easily driven with a low driving voltage.

In the second invention, the laminating step is substantially performed in two steps.
The piezoelectric actuator can be achieved by laminating the single-piece piezoelectric ceramic green sheets and winding the laminated green sheets, which greatly simplifies the assembly and manufacturing process, and at the same time, makes it possible to achieve the piezoelectric ceramic layer thinning very easily. Production method.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a piezoelectric actuator of the present invention.

FIG. 2 is a cross-sectional view showing a cross-sectional structure of the piezoelectric actuator of the present invention.

FIG. 3 is a process flowchart illustrating a method for manufacturing a piezoelectric actuator according to the present invention.

FIG. 4 is a schematic diagram illustrating a piezoelectric ceramic green sheet used for manufacturing the piezoelectric actuator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 10 ... roughly cylindrical actuator main body 1a ... 1st piezoelectric ceramic magnetic layer 1b ... 2nd piezoelectric ceramic magnetic layer 2a ... 1st vibration electrode 2b ... 2 vibrating electrodes 3a, 3b ... terminal electrodes 4 ... insulating protective film

Claims (2)

[Claims] 1. A first piezoelectric ceramic layer and a second piezoelectric ceramic layer wound concentrically in a spiral shape, and between the first piezoelectric ceramic layer and the second piezoelectric ceramic layer. A first vibrating electrode and a second vibrating electrode are formed, and a part of the first vibrating electrode and the second vibrating electrode is exposed on a peripheral surface, and a terminal electrode is formed on the exposed portion. A piezoelectric actuator, characterized in that: 2. A first piezoelectric ceramic green sheet and a second ceramic green sheet are laminated via a conductor film serving as a first vibrating electrode, and a second piezoelectric green sheet is formed on at least one of the two main surfaces. A method for manufacturing a piezoelectric actuator, comprising: laminating a laminated sheet formed with a conductive film to be a vibrating electrode in a spiral shape, and integrally firing the conductive film and the piezoelectric ceramic green sheet.