JPH04246872A - Electrostrictive effect element assembly - Google Patents

Abstract

PURPOSE:To obtain an electrostrictive effect element assembly which is excellent enough in reliability not to be broken down in an early stage when it is repeatedly driven by a method wherein all or a part of a metal member is formed of material whose thermal expansion coefficient is 5-0PPM/ deg.C. CONSTITUTION:Concerning this electrostrictive effect element assembly, the thermal expansion coefficient of an electrostrictive effect element is -6PPM/ deg.C in a temperature range of 0-1OO deg.C. An electrostrictive effect element 1 is implanted upright and fixed to the inner base of a circular lower metal member 2 which is U-shaped and formed of super Invar whose thermal expansion coefficient is 0.8PPM/ deg.C. Another circular upper metal member 6 formed of super Invar whose thermal expansion coefficient is 0.8 PPM/ deg.C is made to cover the upside of the electrostrictive effect element ! and fixed with adhesive agent. In result, an electrostrictive effect element can be protected against breakdown when it is driven, so that, an electrostrictive element assembly can be enhanced in reliability.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an electrostrictive element used in a piezoelectric actuator.

0002

2. Description of the Related Art Recently, piezoelectric actuators have become extremely promising as optical or magnetic disk heads, various optical devices, precision positioning devices for precision machine tools, and other mechanical drive elements.

However, since the mechanical displacement caused by the piezoelectric effect is essentially extremely small, the electrostrictive effect element that serves as the drive source of the actuator is made by stacking piezoelectric ceramic members and internal electrode conductors in multiple layers to achieve the longitudinal effect of piezoelectricity. A structure with a high In other words, this electrostrictive effect element is made by mixing multi-component solid solution ceramic powder with a perovskite crystal structure with an organic binder to form a green sheet, and then coating the green sheet with a silver electrode conductor layer in the form of a paste.
It is made by laminating dozens of layers and sintering them. The ends of the silver electrode conductor layers are fully exposed on the side surfaces of the laminate, and in order to form comb-shaped internal electrodes, the ends of the silver electrode conductor layers are insulated every other layer on one side. On the other side, the end portion of the silver electrode conductor layer on which the insulating layer was not formed is subjected to an insulating treatment. Here, a glass insulating film is formed. Then, two comb-shaped internal electrodes are formed by alternately connecting the silver electrode conductor layers every other layer, and when a DC voltage of about 100 V is applied from the outside, a static displacement of about 8 μm is easily generated.

[0004] Therefore, by using the lever device in combination, the problem of mechanical displacement due to the essentially extremely small inverse piezoelectric effect has been solved to a certain extent.

However, since silver is used as the metal for forming the internal electrodes of the electrostrictive effect element made of this laminate, migration occurs in a humid atmosphere and significantly contaminates the side surfaces of the piezoelectric ceramic member. That is, since the ends of the silver-based electrode conductor layer are all exposed on the side surfaces of the laminate, migration is likely to occur, and the contaminated side surfaces of the piezoelectric ceramic member rapidly deteriorate its insulating properties.

[0006] Therefore, the inventors published Japanese Patent Application Laid-Open No. 63-56356.
As disclosed in No. 1, it is proposed to improve reliability by using a metal case or the like and sealing it to prevent moisture from entering.

FIG. 3 shows a longitudinal sectional view of the electrostrictive element assembly.

Reference numeral 1 denotes the electrostrictive effect element described above, in which a lead wire 4 is connected to an external electrode conductor by soldering, and only the side surfaces are covered with resin.

[0009] The metal member (lower part) 2 made of circular stainless steel has a cross section shaped like this and has two lead terminals 3 made of glass terminals attached thereto. Fix it.

Next, the lead wire 4 of the electrostrictive element 1 and one inner end of the lead terminal 3 attached to the metal member 2 are connected by soldering.

Next, a bellows 5 made of stainless steel and having an inner diameter larger than the outer dimensions of the electrostrictive element 1 and the same as the inner diameter of the metal members 2 and 6 is attached from above so as to wrap around the electrostrictive element 1. Another metal member (upper part) 6 is placed over the upper end of the strain effect element 1 and fixed to the upper end surface of the electrostrictive element 1 with adhesive.

Next, both ends of the bellows 5 are attached to upper and lower metal members 6.
, 2 is welded all around using electric arc welding to complete the sealing.

[0013]

[Problems to be Solved by the Invention] In the conventional electrostrictive element assembly described above, the thermal expansion of the electrostrictive element has a large negative coefficient, whereas the thermal expansion of the metal member is large. Since the end of the strain effect element is compressed, the electrostriction effect element assembly is heated at a frequency of 200Hz voltage from 0V to 150Hz.
When driven 100 times with a sine wave at V, breakage of the electrostrictive element was observed.

[0014] An object of the present invention is to provide an electrostrictive element assembly with improved reliability, which does not break early when the element assembly is repeatedly driven.

[0015]

[Means for Solving the Problems] The electrostrictive effect element assembly of the present invention includes a laminate in which piezoelectric ceramic members and internal electrode conductor layers are alternately laminated, and a laminate at one end of the laminate. A metal member is provided with a pair of lead terminals connected to an external electrode conductor by a lead wire, and only the metal member is fixed to the other end of the metal member, and both ends of a cylindrical bellows are fixed to these metal members. The electrostrictive effect element assembly in which the side surfaces of the laminate are covered is characterized in that the metal member is made of a material having a coefficient of thermal expansion of 5 to 0 PPM/°C.

In other words, while conventional electrostrictive effect element assemblies use ordinary metals for the metal members, the present invention uses metal members whose coefficient of thermal expansion is close to that of the piezoelectric effect element. There are characteristics.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention. As described in the conventional example, the electrostrictive effect element assembly used in the example is made by mixing an organic binder with a multicomponent solid solution ceramic powder having a perovskite crystal structure to form a green sheet, and then placing a silver electrode conductor layer on the paste. After coating, several dozen layers are laminated and sintered. The ends of the silver electrode conductor layers are fully exposed on the side surfaces of the laminate, and in order to form comb-shaped internal electrodes, the ends of the silver electrode conductor layers are insulated every other layer on one side, and the other is insulated. On the side surface, the ends of the silver electrode conductor layer on which the insulating layer was not formed are insulated. Here, a glass insulating film is formed. Two comb-shaped internal electrodes are formed by alternately connecting the silver electrode conductor layers every other layer.

In FIG. 1, reference numeral 1 denotes the above-mentioned electrostrictive effect element, in which a lead wire 4 is connected to an external electrode conductor by soldering, and only the side surfaces are covered with resin.

The thermal expansion coefficient of this electrostrictive element in the range of 0 to 100°C is -6 PPM/°C.

The cross section where two lead terminals 3 made of glass terminals are attached has a circular shape with a coefficient of thermal expansion of 0.
．． The electrostrictive effect element 1 is fixed to the inner bottom surface of a metal member (lower part) 2 made of super inverse material having a temperature of 8 PPM/° C. using an adhesive so as to be erected thereon.

Next, the lead wire 4 of the electrostrictive element 1 and one inner end of the lead terminal 3 attached to the metal member 2 are connected by soldering.

Next, a bellows 5 made of stainless steel and having an inner diameter larger than the outer dimensions of the electrostrictive element 1 and the same as the inner diameter of the metal members 2 and 6 is attached from above so as to wrap around the electrostrictive element 1. Another metal member (upper part) 6 made of super inverse having a thermal expansion coefficient of 0.8 PPM/° C. is placed over the upper end of the strain effect element 1 and fixed to the upper end surface of the electrostrictive element 1 with an adhesive.

Next, both ends of the bellows 5 are attached to the upper and lower metal members 6.
, 2 is welded all around using electric arc welding to complete the sealing.

No breakage of the electrostrictive element was observed even when the electrostrictive element assembly thus manufactured was driven 100 million times with a sine wave of 200 Hz voltage from 0 V to 150 V.

FIG. 2 is a longitudinal sectional view of a second embodiment of the present invention. The difference from Example 1 is that a part of the metal member is made of super inverse material with a coefficient of thermal expansion of 0.8 PPM/°C, and the remaining part is made of stainless steel.

When the electrostrictive element assembly of this example was driven under the same conditions as Example 1, no breakage of the electrostrictive element was observed even after driving 100 million times.

The metal material used in Examples 1 and 2 described above was super inverse, but the thermal expansion coefficient was 4.
．． A similar effect can be obtained by using 42 alloy with 5 PPM/°C.

[0028]

As explained above, the present invention uses a material whose thermal expansion coefficient is close to that of the electrostrictive element for the metal member, thereby preventing the electrostrictive element from breaking during driving. This has the effect of improving the reliability of the assembly.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an electrostrictive element assembly according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an electrostrictive element assembly according to a second embodiment of the present invention.

FIG. 3 is a longitudinal cross-sectional view of an example of a conventional electrostrictive element assembly.

[Explanation of symbols]

1 Electrostrictive effect element 2 Metal parts (lower part) 3 Lead terminal 4 Lead wire 5 Bellows 6 Metal parts (upper part)

Claims (3)

[Claims] 1. A laminate in which piezoelectric ceramic members and internal electrode conductor layers are alternately laminated, and a pair of leads connected to one end of the laminate to an external electrode conductor of the laminate by a lead wire. An electrostrictive element assembly in which a metal member provided with a terminal has only the metal member fixed to the other end thereof, and both ends of a cylindrical bellows are fixed to these metal members to cover the side surface of the laminate. In the three-dimensional structure, some or all of the metal members have a coefficient of thermal expansion of 5 to 0 PPM.
An electrostrictive effect element assembly characterized in that it is made of a material with a temperature of /℃. 2. The electrostrictive effect element assembly according to claim 1, wherein the material having a coefficient of thermal expansion of 5 to 0 PPM/° C. is super inverse or 42 alloy. 3. The electrostrictive effect element assembly according to claim 1, wherein a material having a coefficient of thermal expansion of 5 to 0 PPM/° C. is used only in the recessed portion of the metal member having this shape.