JPH04105374A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To further enhance the reliability upon the repeat life of a piezoelectric actuator by a method wherein the parts in smaller section than that of a laminated piezoelectric element are arranged in the section vertical to the displacement direction of the element near the adhering part of a metallic case of the laminated piezoelectric element. CONSTITUTION:The bonding parts 14a, 14b of a stem 8 and an adaptor 16 are formed in the thin thickness of about 1 or 2mm and small volume to weld together the adaptor 16 and bellows 9. Besides, the outer electrode conductors 5a, 5b of a laminated piezoelectric element 17 are electrically connected respectively to the hermetic seal terminals 10a, 10b so as to make the upper and rear surfaces of the laminated piezoelectric element 17, the adaptor 16 with bellows 9 and the step 8 adhere to one another using thermosetting bonding agents 13a, 13b. Finally, the junction part of the stem 8 and the bellows 9 are welded together to enclose the laminated piezoelectric element 17 in a metallic case. Furthermore, the parts (bonding parts 14a, 14b) in small section of the adaptor 16 and the step 8 to be bonded to the laminated piezoelectric element 17 are formed into a circular cylindrical projection and a conical recession.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric actuator that utilizes the inverse piezoelectric effect.

[Conventional technology]

FIG. 8 shows an example of a conventional piezoelectric actuator. Conventionally,
This type of piezoelectric actuator has a piezoelectric effect in which a thin sheet-shaped piezoelectric ceramic member 2 made of piezoelectric ceramic material and an internal electrode conductor 1 made of silver-balasium or platinum are alternately laminated as shown in FIG. a layer 7, piezoelectrically inactive protective layers 3a and 3b made of a piezoelectric ceramic material on both ends of the piezoelectric effect layer 7, an insulator 4 such as glass for insulating the internal electrode conductor 1 every other layer, and an internal electrode. A laminated piezoelectric device having a pair of external electrode conductors 5a, 5b deposited to alternately electrically connect the conductors 1-, and leait wires 6a, 6b electrically connected to the external electrode conductors 5a, 5b. a metal case that surrounds the element 17 and the laminated piezoelectric element 7, is partially fixed to the laminated piezoelectric element 17, and has a mechanism that expands and contracts in the direction in which displacement of the laminated piezoelectric element 17 occurs, and an external electrode conductor 5a of the laminated piezoelectric element 17; 5b and an airtight terminal for applying voltage. In particular, as shown in Fig. 8, the metal case includes a relatively thick metal member (hereinafter referred to as stem) 8 with screw holes for fixing the piezoelectric actuator, and a means for connecting the piezoelectric actuator and the driven object. 1. Problems to be Solved by the Invention 1. The above-mentioned prior art The piezoelectric actuator of linear expansion (1RI
It has a structure in which a ceramic member with a coefficient of linear expansion of 10 x 10-h or more and a metal member with a coefficient of linear expansion of 10 x 10-h or more are fixed with a thermosetting adhesive.
When the temperature drops to room temperature after the adhesive hardens at temperatures above 00°C, tensile and shear stress constantly acts near the adhesive interface due to the difference in linear expansion coefficient between the ceramic and metal parts. Put it away.

Further, FIG. 3 shows a conceptual diagram of deformation when a voltage is applied to the laminated piezoelectric element 17 that is not enclosed in a metal case. At an electric field strength of about 1.5 kV/mm, the piezoelectric effect layer 7 expands by about 0.1% in the stacking direction due to the longitudinal effect and contracts by about 0.03% in the direction parallel to the internal electrode conductor 1 due to the transverse effect. At this time, since no electric field is applied to the protective layers 3a and 3b, neither expansion nor contraction occurs. As a result, the end face of the element is deformed into a spherical shape, and tensile and shear stresses act on the interface between the piezoelectric effect layer 7 and the protective layers 3a and 3b. Furthermore, this force laminated piezoelectric #'
When f17 is sealed in a metal case to form a piezoelectric actuator, it is necessary to fix the end face of the laminated piezoelectric element to the stem 8 of the metal case, the adapter 16, or both, as shown in FIG. Stem 8. The adapter 16 is a metal member having a modulus of longitudinal elasticity approximately 5 to 6 times that of the ceramic base material and having a sufficient thickness. Therefore, when a voltage is applied to the laminated piezoelectric element 17 while the laminated piezoelectric element 17 is fixed to the stem 8t, the adapter 16, or both, the spherical deformation of the protective layers 3a and 3b occurs as shown in FIG. The protective layer 3a is forcibly restrained in a planar shape.
, 3b and the piezoelectric effect layer 7, the tensile and shear stresses acting on the interface are even greater than in the case of no restraint.

This piezoelectric actuator operates at 150V30Hz at room temperature.
When repeatedly driven with a rectangular wave of 108 times or more, as shown in FIG. 7, it enters the wear-out failure region and reaches the end of its life. This is due to the stress caused by the difference in linear expansion coefficients mentioned at the beginning and the stress caused by voltage application being superimposed on the laminated piezoelectric element 17.
Repeated operation II +-5 Protective layer with the greatest stress and low mechanical strength near the edges 3. This is because a phenomenon occurs in which the interface with the piezoelectric effect layer 7 of q and 3b is repeatedly driven 1.08 times or more and breaks. In other words, whether it is due to this phenomenon or the conventional method, the cycle life of the piezoelectric actuator is limited to about 108 cycles, which is a drawback.

The purpose of the present invention is to reduce the stress that acts on the interface between the protective layer and the piezoelectric effect layer due to the difference in linear expansion coefficients mentioned at the beginning, and the stress that acts on the interface between the protective layer and the piezoelectric effect layer due to the voltage application mentioned in the middle. It is an object of the present invention to provide a piezoelectric actuator that can reduce both the stress acting on the interface between the piezoelectric actuator and the piezoelectric actuator, which can extend the life of repeated driving and improve the reliability.

[Means to solve the problem]

The piezoelectric actuator of the present invention has a piezoelectric effect layer in which piezoelectric ceramic members and internal electrode conductors are alternately laminated, and a piezoelectric inactive protective layer made of a piezoelectric ceramic member and one layer of the internal electrode conductor on both ends of the piezoelectric effect layer. a laminated piezoelectric element having a means for connecting to a pair of external electrode conductors at every other interval, and a stem or an adapter surrounding the 1lfIE element, which is fixed to the laminated piezoelectric element and can be expanded and contracted in the direction of displacement of the laminated piezoelectric element. It consists of a metal case having a bellows and an airtight terminal for applying a voltage to the external electrode conductor of the FF layer piezoelectric element from the outside of the metal case. In a cross section perpendicular to the direction in which piezoelectric element displacement occurs, there is a portion having a smaller cross-sectional area than that of the laminated piezoelectric element. [Example] Next, the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of an embodiment of the present invention. FIG. 2 is a longitudinal cross-sectional view of the laminated piezoelectric element used in the piezoelectric actuator of one embodiment of the present invention shown in FIG.

First, for example, nickel lead niobate Pb (Ni%Nb%)
A small amount of an organic binder is added to a pre-fired powder of a piezoelectric material whose main components are PbTi○3, lead titanate, PbTi○3, etc., and this mixture is dispersed in an organic solvent to form a slurry.
）I
+! A piezoelectric ceramic member 2 having a thickness of approximately 100 μm is formed on one side of the piezoelectric ceramic member 2 having a piezoelectric ceramic member 2 having a thickness of about 100 μm.
The internal electrode conductor 1 is formed by depositing about 10 μm of a mixed powder of silver powder and palladium powder or a conductor paste whose main component is platinum powder by screen printing or the like, and about 150 sheets of this are laminated. The laminate to the north becomes the piezoelectrically active piezoelectric effect layer 7. Furthermore, 20 piezoelectric ceramic members on which no internal electrode conductor 1 is formed are stacked on the upper and lower surfaces of the second laminate to form protective layers 3a and 3b. After laminating as described above, the layered sintered body is fired at approximately 1100°C for 2 hours, and the side r surface is cut to form a prismatic laminated sintered body in which no end face of the internal electrode conductor 1 is exposed to the outside. shall be.

Next, glass powder is applied to the ends of the internal electrode conductors 1 exposed on a pair of opposing sides of the laminated sintered body by electrophoresis, alternately every other layer, and sintered to insulate them. Form layer 4.

Next, in order to electrically connect the internal electrode conductors 1 to every other layer, a conductive paste mainly composed of M powder is applied by printing and fired, thereby forming a pair of external electrode conductors 5a,
Further, lead wires 6a and 6b electrically connected to the external electrode conductors 5a and 5b are installed, thereby completing the laminated piezoelectric element 17 shown in FIG. 2.

Next, let's talk about the metal case. The metal case is the first
As shown in the figure, a stem 8 is a relatively thick metal member provided with screw holes etc. for fixing the piezoelectric actuator, and an adapter 16 is a relatively thick metal member having a means for connecting the piezoelectric actuator to a driven object. , consists of a bellows 9 which is a relatively thin circular metal tube provided with bellows. first,
A disk of a predetermined thickness is cut out from a bar material such as stainless steel, iron steel, copper alloy, aluminum alloy, etc. In the case of the adapter 16, this disk is machined using a lathe or the like into a truncated cone shape with a conical depression on the upper bottom surface, as shown in FIG. A groove of about 5 mm is cut to form a hinge 15a. In the case of stem 8, perform a barmetal seal on this disk by forming a through hole and a drilled hole with a disk, etc., and twisting the 4 edges etc. Also for stem 8, use adapter 16 The same processing as above is performed to form the hinge 15b.

The width of the groove for forming the hinges 1.5a and 15b is 0.
．． As long as it is about 1 mm, there is no practical problem, and the narrower the width, the shorter the overall length of the piezoelectric actuator and the smaller the piezoelectric actuator becomes, which is advantageous. In addition, the adhesive portions 14a and 1 of the stem 8 and the adapter 16
The thickness of the piezoelectric element 4b is suitably about 1 mm to 2 mm, and the cross section of the hinges 15a, 15b is circular or suitable with a diameter of 4 mm or less.7 Next, the enclosing of the laminated piezoelectric element 17 in the metal case will be described. First, the adapter 16 and the bellows 9 are welded into the shape shown in FIG. 1 by a laser beam welding method, an electrobeam welding method, a resistance welding method, a TIG welding method, an arc welding method, or the like. Furthermore, the outer electrode conductor 5a of the laminated piezoelectric element 17,
5b and the hermetic seal terminals 10a and 10b, respectively, and the upper and lower surfaces of the laminated piezoelectric element 17, the adapter 16 with the bellows 9, and the stem 8 are bonded with a thermosetting adhesive around the circumference as shown in FIG. Let me pray, finally, in a vacuum,
1. The joint between the stem 8 and the sheath 9 is completed by welding in an inert atmosphere in the air.

Next, the operation of the piezoelectric actuator of this example will be explained. Is it common to use a thermosetting adhesive to bond the laminated piezoelectric element 17 and the stem 8° adapter 16? .

It is unavoidable that it acts near the interface between the piezoelectric effect layer 3b and the piezoelectric effect layer 7. However, in the case of this embodiment, the thickness of the metal member directly bonded to the laminated piezoelectric element 17 is extremely thin and the volume is small compared to the conventional example, so the stress caused by the difference in linear expansion coefficient can be kept relatively small. I can do it. Furthermore, even when a voltage is applied, since the thickness of the metal member directly bonded to the laminated piezoelectric element 17 is thin, it is difficult to restrain the deformation of the laminated piezoelectric element 17, as shown in FIG.

Due to the above two effects, the piezoelectric actuator of this embodiment has the protective layer 3a of the laminated piezoelectric element 17.

This reduces the stress acting on the interface between the piezoelectric layer 3b and the piezoelectric layer 7, prevents the element from breaking, and improves the reliability and illuminance. The front view is worth 4. First, a laminated piezoelectric element 1'7 is created in exactly the same manner as in the first embodiment.Similar to the first embodiment, a piezoelectric element 1'7 of a predetermined thickness is prepared from bar materials such as steelless steel, @alloy, and aluminum alloy. A circular shape is cut out, and a cylindrical protrusion and a conical recess are processed using a cutting tool, a milling cutter, etc. to form the adapter 16. stem 8
The same process is applied to 6 to provide a through hole and a tapped hole.
As the airtight terminal, a hermetic seal having a terminal made of Kovar or the like is suitable. Adapter 16. The portion of the stem 8 having a small cross-sectional area (bonded portion 14a) that is bonded to the laminated piezoelectric element 17 has a cylindrical shape or an appropriate diameter of 5 mm or less. Further, if the generated displacement of the laminated piezoelectric element 17 is about 15 to 30 μm, it is sufficient that the height of this portion is about 0.1 mm.

Furthermore, the bellows 9 is formed into a bellows on a thin-walled circular tube made of steel, copper alloy, aluminum alloy, etc. using a hydraulic pressing method or the like. Enclosure of the laminated piezoelectric element 17 in the rental case is the same as in the first embodiment. First, connect the adapter 7 and herose (,) to 7W j8, and then laminate the laminated piezoelectric element 17 and barmetallic seal terminals 10a, 10b electrically to each other with thermosetting adhesive 13a, 13b. The piezoelectric element 17, the adapter 7, and the stem 8 are bonded together, and finally, the joint between the stem 8 and the helices 9 is welded in a vacuum, dry air, or inert gas to complete the process.

Next, the operation of the piezoelectric actuator of this example will be explained. When the laminated piezoelectric element 17, the adapter 16, and the stem 8 are bonded together using a thermosetting adhesive, the protective layers 3a, 3b and the piezoelectric effect element 7 may It has been known from stress analysis using the finite element method that the tensile and shearing stresses acting on the interface with the bonding portions 14a and 14b are approximately proportional to the lengths of the bonded portions 14a and 14b. Furthermore, the tensile and shear stress that acts on the interface by restraining the end faces of the laminated piezoelectric element when voltage is applied is also approximately proportional to the length of the bonded parts 14a and 14b. The deformation when a voltage is applied to the actuator is conceptually shown in Figure 6, and the maintenance? The stress acting on the interface between the four pads 3a, 3b and the piezoelectric layer 7 decreases as the area of the bonded portion decreases. Adhesive portion 14a from the viewpoint of stress reduction.

The smaller the area of 14b, the better, or the adhesive parts 14a, 14
If the area b is small, the force generated by the piezoelectric actuator will be impaired, so a diameter of approximately 4 mm seems to be good in practice. Reduces stress acting on the interface with the effect layer 7, prevents breakage of the laminated piezoelectric element 17,
It is possible to improve reliability.

FIG. 7 is a characteristic diagram illustrating the present invention in detail. Cross section 5
Using a laminated piezoelectric element with dimensions of mm x 5 mm, length of 20 mm, and generated displacement of 18 μm, the first. It is assembled with the piezoelectric actuator of the second embodiment, and the material of the metal case is 5U.
In the case of the first embodiment using S304, adhesive part 1=
1], the thickness of 1.4b is 1 mm, and the hinge 15
a, ], 51+ is a cylinder with a diameter of 4 mm. In the case of the second embodiment, the bonded portions 14a and 14b have a diameter of 5 mm.
The shape is cylindrical and the height is Q, 5 mm. This figure shows the results of a repeated life test in which 150V was applied with a 30Hz square wave to each sample LOOP.In this way, this piezoelectric actuator had only 1 failure even after 109 pulses were applied.
The remarkable result is that it has made it possible to extend the lifespan, which has always been the case.

(Effects of the Invention) As explained above, the present invention has the advantage that, in the cross section perpendicular to the direction of displacement, a portion having a smaller cross-sectional area than the laminated piezoelectric element exists near the part where the metal case is fixed to the laminated piezoelectric element. This suppresses the difference in thermal expansion between the ceramic laminated piezoelectric element and the metal case to a relatively low level.Furthermore, it reduces the restraint of deformation at the element end, and reduces the stress acting on the protective layer-piezoelectric effect layer interface. This has the effect of further improving the reliability of the piezoelectric actuator's repeated life.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of a force piezoelectric actuator according to an embodiment of the present invention, and Fig. 2 is a longitudinal sectional view showing the structure of only the laminated piezoelectric element shown in Fig. 1. FIG. 4 is a conceptual diagram showing the deformation of the laminated piezoelectric element when voltage is applied to the piezoelectric actuator of FIG. 1. FIG. FIG. 6 is a conceptual diagram showing the deformation of the laminated piezoelectric element when voltage is applied to the piezoelectric actuator of FIG. 5, and FIG. 7 is a repeated life test of the piezoelectric actuators of this example and the conventional example. Characteristic diagrams showing the results. Figure 8 is a vertical cross-sectional view of a conventional piezoelectric actuator. Figure 9 shows the deformation of the laminated piezoelectric element when deformation of the end of the laminated piezoelectric element is restrained by bonding metal members. FIG. 11 to 1o+1 internal electrode conductor, 2, to 2n...piezoelectric ceramic member, 3a, 3b...protective layer, 4, to, ↓0.
1... Insulating layer, 5a, "ih/external electrode conductor, (-)
a, 61)...Chu 1-wire, 7...Pneumatic electric mixed layer 8
．． Stem, 9...Bellows, 10a, 10b...Hermetic seal terminal, 11a, 11b...Barmetal seal, 12...Mounting screw hole, 13a,
13b...Adhesive, 14a, 14b...Adhesive part,
15a. 15b... Hinge, 16 - Adapter, 17... Laminated piezoelectric element.

Claims (1)

[Claims] 1. A piezoelectric effect layer in which piezoelectric ceramic members and internal electrode conductors are alternately laminated, a piezoelectrically inactive protective layer made of a piezoelectric ceramic member on both ends of the piezoelectric effect layer, and the internal electrode conductor. A laminated piezoelectric element having a means for connecting to a pair of external electrode conductors for every other layer, and a mechanism surrounding the laminated piezoelectric element, a part of which is fixed to the laminated piezoelectric element and capable of expanding and contracting in the direction in which displacement of the laminated piezoelectric element occurs. In a piezoelectric actuator comprising a metal case and an airtight terminal for applying a voltage to an external electrode conductor of the multilayer piezoelectric element from outside the metal case, the A piezoelectric actuator characterized in that, in a cross section perpendicular to a displacement generation direction of the laminated piezoelectric element, there is a portion having a smaller cross-sectional area than the laminated piezoelectric element. 2. The metal case according to claim 1, wherein a portion of the metal case that is directly bonded to the laminated piezoelectric element is formed thinly, and a cross-sectional area of a portion subsequent thereto is smaller than the cross-sectional area of the laminated piezoelectric element. piezoelectric actuator. 3. The piezoelectric actuator according to claim 1, wherein a portion of the metal case fixed to the laminated piezoelectric element is formed in a convex shape having a smaller area than the laminated piezoelectric element.