JP2000277821A - Stacked type piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce stress developed in the boundary between a stacked body of piezoelectric plates and electrodes and an inactive insulator even if the actuator is driven at high voltage and high frequency, by bonding the stacked body and the inactive insulator through the material having a low elastic modulus of a specified value or below. SOLUTION: To an upper and a lower face of a stacked body of piezoelectric plates 2 and electrode plates 3, an inactive insulator 7 is piezoelectrically bonded through the material 6 having a low elastic modulus of 100 GPa or below, Due to this structure, the stress transmitted to the inactive insulator 7 by the displaced stacked body can be effectively reduced by the material 6 of a low elastic modulus, preventing the concentration of the stress in the boundary between the stacked body and the inactive insulator 7, Even if the actuator is driven at high voltage and high frequency, the actuator can be driven for a long time without developing cracks or breakage in the piezoelectric plates 2 or in the inactive insulator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator device, for example, a lamination used for a precision positioning device such as an optical device, a drive element for preventing vibration, a drive element for fuel injection of an automobile engine, and the like. The present invention relates to a piezoelectric actuator.

[0002]

2. Related Background Art Hitherto, a laminated piezoelectric actuator in which piezoelectric plates and electrodes are alternately laminated has been known. Such a laminated piezoelectric actuator extends a piezoelectric plate by several tens of μm by an inverse piezoelectric effect by applying a voltage to the piezoelectric plate through an electrode, and uses the displacement as a driving force source of the piezoelectric actuator. It is. Recently, high-voltage and high-frequency driving has been required for a small stacked piezoelectric element in order to secure a large amount of displacement and perform driving even faster.

On the upper and lower surfaces of a piezoelectrically active laminate composed of a laminate of a piezoelectric plate and an electrode, a piezoelectrically active laminate is provided to support and fix the actuator and to maintain insulation from the metal case. An actuator in which an inert insulator is bonded by glass has been proposed.

[0004]

However, in the above-mentioned conventional actuator, the laminated body of the piezoelectric plate and the electrode and the inert insulator are joined by the conductive adhesive made of metal powder and glass. Both are firmly fixed to each other, and when driving for a long time while applying a high voltage to the actuator at a high frequency, a large stress is generated at the boundary between the stacked body of piezoelectric plates and electrodes and the inert insulator. However, there is a problem that the laminate or the inert insulator is broken.

To solve such a problem, for example, according to Japanese Patent Application Laid-Open No. Hei 7-30165, the overlapping area of the electrodes in the laminate adjacent to the inert insulator formed on the upper and lower surfaces of the laminate is determined. An actuator has been proposed in which the displacement of the end of the laminate is reduced by making the overlap area between the electrodes at the center of the body smaller. Also, Japanese Patent Application Laid-Open
According to -257186, an inert insulator is formed of an insulator having a relative permittivity of less than 1200 and a Young's modulus of 7.0 × 10 ¹⁰ N / cm ² or less, and the stress is absorbed by the inert insulator. It has been proposed to.

According to the above-described method, a certain effect can be obtained in driving at a low voltage or a low frequency, but the stress is particularly large when driving at a high voltage of 400 V or more, 50 Hz or more, or a high frequency for a long time. Therefore, it is difficult to sufficiently reduce the stress concentration generated at the boundary between the stacked body of the piezoelectric plate and the electrode and the inert insulator.

In addition, the method disclosed in Japanese Patent Application Laid-Open No. 7-30165 requires strict control of the electrode formation location in the laminate and the alignment at the time of lamination, and thus lacks mass productivity. In the method of Japanese Patent Application Laid-Open No. 60-257186, it is necessary to form an inert insulator with a special material, and as a result, it becomes difficult to match the thermal expansion characteristics of the laminate with the laminate. There is a problem that a new stress is generated due to a difference in thermal expansion from the active insulator.

Therefore, the present invention effectively alleviates the stress generated at the boundary between the laminated body of the piezoelectric plate and the electrode and the inactive insulator even when driven at a high voltage and a high frequency.
An object of the present invention is to provide an actuator having excellent long-term reliability.

[0009]

Means for Solving the Problems The present inventors have repeatedly studied a method for effectively relieving stress generated at a boundary portion between a stacked body of a piezoelectric plate and an electrode and an inert insulator. As a result, by joining a low elastic body having a low elastic modulus between the laminated body and the inert insulator, the stress generated at the boundary portion is effectively absorbed by the low elastic body, and the actuator has a long life. It has been found that reliability can be improved.

That is, a laminated piezoelectric actuator according to the present invention comprises: a laminated body comprising a plurality of piezoelectric plates, a plurality of positive and negative electrode plates alternately laminated; A piezoelectric actuator comprising: a connecting member for connecting electrode plates for negative electrodes to respective side surfaces of the laminate; and a piezoelectrically inactive insulator joined to upper and lower surfaces of the laminate. In the above, the laminate and the inert insulator are joined via a low elastic body having an elastic modulus of 100 GPa or less.

In the above structure, the low elastic body is made of a metal plate of at least one of Ag, Al, and duralumin or silicon rubber. In the case of the metal plate, the metal plate, the actuator, and the metal plate are used. And the inert insulator are desirably joined by glass. In the case of silicon rubber, it is desirable that the actuator and the inert insulator be joined by the adhesiveness of the silicone rubber.

It is preferable that the inert insulator be made of a material having the same composition as that of the piezoelectric plate.

[0013]

According to the laminated piezoelectric actuator of the present invention, a piezoelectrically active laminate formed by laminating a piezoelectric plate and an electrode and an inert insulator disposed above and below the laminate are provided. The stress transmitted to the inactive insulator by the displaced laminated body is effectively alleviated by the low elastic body by interposing the low elastic body having an application rate of 100 GPa or less. Concentration of stress at the boundary with the substrate can be suppressed. Therefore, even when driven at a high voltage and a high frequency at a high speed, the piezoelectric plate or the inert insulator can be driven for a long time without cracking or breaking, and the reliability of the actuator can be improved.

[0014]

1 to 4 are views for explaining an example of a piezoelectric actuator according to the present invention. FIG. 1 is a schematic side view, FIG. 2 is a plan view of an electrode plate, FIG. FIG. 4 is an enlarged sectional view of a main part. This piezoelectric actuator 1
It has a laminated body in which a plurality of piezoelectric plates 2 and a plurality of electrode plates 3 are alternately stacked, and a conductive layer 4 is formed on both surfaces of the piezoelectric plate 2. They are joined by the conductive layer 4. The conductive layer 4 is formed by applying a conductive paste on the surface of the piezoelectric plate 2 and baking it at about 400 to 600 ° C. The conductive paste is made of a conductive powder such as Ag and a glass component, and is baked on the piezoelectric plate 2 by melting the glass component at a high temperature.
This conductive paste contains 70 to 98% by weight of Ag powder.
And 2 to 30% by weight of a glass component such as lead borosilicate.

The piezoelectric plate 2 is made of a known piezoelectric material such as a piezoelectric ceramic material containing lead zirconate titanate as a main component. It is desirable that the piezoelectric material constituting the piezoelectric plate 2 has a high piezoelectric distortion constant d33 in order to increase the amount of displacement during driving. Also,
The thickness of the piezoelectric plate 2 is desirably 0.2 to 0.6 mm from the viewpoint of miniaturization and application of a high voltage.

In particular, as a piezoelectric material constituting the piezoelectric plate, Pb, Zr, Ti, Zn, Sb, N
i, Te and made from a composite perovskite compound containing at least one of Sr and Ba, the composition formula by molar ratio of these metal _{elements, Pb 1-xy Sr x Ba} y
_{(Zn 1/3 Sb 2/4) a (} Ni 1/2 Te 1/2) b Zr c
When expressed as Ti _1-abc O ₃ , the molar ratios of x, y, a, b, and c are 0 ≦ x ≦ 0.12, 0 ≦ y ≦ 0.12, 0 <
x + y, 0.05 ≦ a ≦ 0.12, 0 ≦ b ≦ 0.01
5, basic component 100 satisfying 0.43 ≦ c ≦ 0.52
PbO and Nb _{2 in} equimolar ratio to parts by weight
A piezoelectric ceramic composition containing 0.2 to 1.2 parts by weight of O ₅ in total is desirable.

As shown in FIG. 2, the electrode plate 3 has
A pair of connecting members 5 are integrally formed, and the electrode plate 3 is divided into a positive electrode plate and a negative electrode plate, and the positive electrode plate 3 and the negative electrode plate 3 are alternately provided between the piezoelectric plates 2. It is laminated. Each connection member 5 of each positive electrode plate 3 is led out in a different direction on the side surface of the laminate.

The connecting member 5 of the positive electrode plate 3 and the connecting member 5 of the negative electrode plate 3 led out in the same direction have a predetermined gap L so as not to contact the piezoelectric actuator 1. The positive electrode connecting member 5 and the negative electrode connecting member 5 are bent along the outer peripheral side surface of the piezoelectric actuator 1, and are connected and fixed to each other by soldering or welding.

When the connecting member 5 is disposed close to the piezoelectric actuator 1, the connecting member hinders dissipation of heat generated from the piezoelectric actuator 1. Therefore, the gap L is desirably 0.2 mm or more. If the gap L is too large, the size of the entire apparatus is increased. Therefore, the gap L is desirably 2.0 mm or less.

Since the connecting member 5 has a function of diffusing the heat generated from the piezoelectric actuator 1, the larger the width W of the connecting member 5 is, the better the heat diffusing property is. Is a disk, the radius r
/ 10 or more is desirable. On the other hand, if the width of the connection member 5 is too large, the distance between the adjacent connection members 5 having different polarities becomes short, and the possibility of discharge between the adjacent connection members 5 increases. Therefore, the width W is equal to or less than r. Desirably.

The electrode plate 3 and the connecting member 5 are preferably made of a conductive metal such as silver, brass, copper, stainless steel or the like. The thickness of the electrode plate 3 should be as thin as possible so as not to affect the amount of displacement, especially 20 to 100.
μm is preferred.

Further, the electrode plate 3 is provided with a piezoelectric actuator 1 for preventing a short circuit or discharge between adjacent electrode plates 3.
It is desirable that it be smaller in size than the piezoelectric plate 2 so as not to be exposed on the outer peripheral side surface of the piezoelectric plate 2.

(Inert Insulator) Further, according to the piezoelectric actuator 1 of the present invention, the upper and lower surfaces of the laminate of the piezoelectric plate 2 and the electrode plate 3 have an elastic modulus of 100 GPa or less, particularly 85 GPa or less. An inert insulator 7 is joined piezoelectrically via a low elastic body 6. The elastic modulus of the low elastic body 6 is limited to 100 GPa or less because the elastic modulus is 100 GPa.
If it is higher than a, when driven at a high voltage and at a high speed, cracks occur at the interface between the inert insulator and the low elastic body, and the cracks are caused to break.

As the low elastic body 6 having an elastic modulus of 100 GPa or less, a metal of at least one of Ag, Al and duralumin, or silicon rubber is desirable.

When the low elastic body 6 is made of a metal, it is desirable that the low elastic body 6 be made of a metal plate having a thickness of 25 to 300 μm. This is because if the thickness is smaller than 25 μm, the effect of stress relaxation is reduced.
If it is larger than μm, the amount of displacement will decrease significantly.

As shown in FIG. 3, in order to join the laminate of the piezoelectric plate 2 and the electrode plate 3 and the inert insulator 7 with the low elastic body 6 made of a metal plate, An insulating adhesive made of a glass paste such as lead borosilicate glass is applied in advance to the bonding surface between the surface of the piezoelectric plate 2 and the stacked body of the inert insulator 7 at 400 to 600 ° C.
After laminating the low elastic body 6 and the inert insulator 7 made of the above metal plate on the upper and lower surfaces of the laminate, the laminate is heated at 400 to 600 ° C. , And the low elastic body 6 and the inert insulator 7 can be joined together by the glass 8 to be integrated.

When the low elastic body 6 is formed of a metal plate, it is desirable that the low elastic body 6 be formed of a laminate of a plurality of metal plates. By forming the low elastic body 6 with a plurality of metal plates in this way, the stress generated during driving is dispersed by the plurality of metal plates, and the stress is further reduced as compared with the case where the low elastic body 6 is formed by a single metal plate. Because you can. In such a case, the total thickness of the plurality of metal plates is 2
What is necessary is just to adjust the thickness of one metal plate so that it may become 5-300 micrometers in thickness. The plurality of metal plates are joined with glass or a conductive paste.

When silicon rubber is used as the low elastic body 6 as shown in FIG. 4, since the silicon rubber itself also has a function as an adhesive, the silicone rubber 9 has an adhesive property, so that the silicone rubber 9 has an adhesive property. It can be bonded to the inert insulator 7. In such a case, the thickness of the silicon rubber is 3
Adjusted to ３００300 μm.

With respect to the joined body of the laminate and the inert insulator 7, the outer peripheral surface of the laminate 1 and the inert insulator 7
Is coated with an insulating resin 10 having a low elastic modulus, such as silicon rubber, and a similar insulating resin is formed between the piezoelectric plates 2 and between the piezoelectric plates 2 and the connecting members 5. Is filled without gaps.

The piezoelectric actuator 1 manufactured in this manner is a piezoelectric actuator device which is loaded in a metal case (not shown) from at least one of silver, copper, aluminum and stainless steel having excellent heat dissipation. Becomes

[0031]

EXAMPLES Example 1 Pb _0.94 Sr _0.04 Ba _0.02 (Zn _1/3 Sb _2/3 ) _0.075
(Ni _1/2 Te _1/2 ) _0.005 Zr _0.47 Ti _0.45 O _{3 Based} on 100 parts by weight of the basic component having the composition, equimolar ratios of PbO and Nb ₂ O ₅ in an equimolar ratio are 0.5 parts by weight in total. PZ prepared by baking the composition containing addition at 1130 ° C
Polishing both sides of T type piezoelectric ceramics, diameter 20m
A disk-shaped piezoelectric plate having a thickness of 0.5 mm and a thickness of 0.5 mm was formed.

A conductive paste of 97% by weight of Ag powder and 3% by weight of glass containing PbO-SiO ₂ -B ₂ O ₃ as a main component was printed on both sides of the piezoelectric plate so as to have a thickness of 10 μm. It was dried at 100 ° C and baked at 520 ° C.

Further, a 25 μm-thick Ag thin plate was
An electrode plate was fabricated by punching out a 19 mm diameter circle having a 3 mm × 2 mm connecting member as shown in FIG.

Then, the electrode plates and the piezoelectric plates were alternately laminated to produce a laminate having a total of 100 piezoelectric plates. The connecting members of the electrode plates were made to protrude in the same direction with an angle difference of 90 degrees between the positive electrode and the negative electrode every other layer.

A cylindrical inert insulator having a diameter of 20 mm and a thickness of 5 mm is formed using a PZT-based sintered body having the same composition as that of the piezoelectric plate. each top and bottom surface PbO-SiO ₂ -
After printing a glass paste containing B ₂ O ₃ as a main component so as to have a thickness of 10 μm, the glass paste is dried at 100 ° C. and dried at 520 ° C.
Bake at ℃.

Then, the inert insulator was displaced on the upper and lower surfaces of the laminate, and various metal plates of 19 mm in diameter of Ag, Al, and duralumin having a thickness of Table 1 were displaced by the number of layers shown in Table 1. And apply light pressure on top of the laminate, and place a weight of about 3 kg on top of
By heating at 0 ° C. for 1 hour, the inert insulator and the laminate were joined via a metal plate.

Next, as shown in FIG. 1, the distal ends of the positive and negative connecting members protruding in the radial direction of the piezoelectric plate are bent in the laminating direction, respectively, and are adjacent to the bent distal ends of the connecting members. And the same polarity connecting member was connected by soldering. When connecting the connection members, the connection members were attached such that the connection members were separated from the side surfaces of the piezoelectric actuator by 0.5 mm from one end to the other end of the piezoelectric actuator. Thereafter, the outer peripheral surfaces of the laminate and the inert insulator were covered with silicon rubber.

Then, a polarization process was performed by applying a DC voltage of 3 kV / mm in silicon oil at 80 ° C. for 30 minutes to produce a laminated piezoelectric actuator.

(Evaluation) The obtained laminated piezoelectric actuator was subjected to 0 to +500 V in a temperature atmosphere of 125 ° C.
Is applied at a frequency of 50 Hz, and the number of times of application is 5
Driving was performed up to × 10 ⁸ times. Then, visually observe the amount of displacement by the piezoelectric actuator during driving and the occurrence of cracks and breaks in the piezoelectric plate or the inert insulator at the boundary between the laminate and the inert insulator, and observe the occurrence of cracks and breaks. The number was measured and the results are shown in Table 1.

Further, at 125 ° C., DC 0 to 500
When driven up to 5 × 10 ⁸ times under the conditions of V and 50 Hz, 50 samples were prepared for each sample, and the number of samples in which cracks occurred between the laminate and the inert insulator is shown in Table 1. Was.

The amount of displacement was measured by fixing the piezoelectric actuator device on a vibration isolating table, attaching an aluminum foil to the upper surface of the sample, and measuring the three portions at the center and the periphery of the element using a laser displacement meter. The average was evaluated.

COMPARATIVE EXAMPLE As a comparison, a piezoelectric actuator in which a laminated body and an inert insulator were joined by glass without inserting a thin Ag plate at the interface between the laminated body and the inert insulator was produced.

Example 2 Adhesive silicon rubber was applied to a predetermined thickness on the upper and lower surfaces of the laminate of the piezoelectric plate and the electrode plate manufactured in Example 1 and on one surface of the inert insulator. An inert insulator was attached to the upper and lower surfaces of the laminate. And Example 1
The same evaluation was performed.

[0044]

[Table 1]

As is clear from the results in Table 1, in the comparative piezoelectric actuator (sample No. 1), 1 × 10 ⁶
Breakage occurred at the boundary between the stacked body and the inert insulator by repeated application, and further driving was impossible.

Sample No. 1 in which a low elastic body having an elastic modulus of 80 GPa or less was interposed between the laminate and the inert insulator.
2 to 7, sample No. 500V for 10-13
Even when the DC electric field was applied at a frequency of 50 Hz or when the driving was performed up to 5 × 10 ⁸ times, the occurrence of cracks and breaks at the boundary between the laminate and the inert insulator could be reduced. In particular, the total thickness of the low elastic body is 25 to
Sample No. 300 μm. In 3, 4, and 5, the displacement amount is 30
Even when driving at a high voltage of 500 V, 50 Hz, and at a high frequency of 5 μm or more, it was possible to drive 5 × 10 ⁸ times or more, and the number of occurrences of cracks was completely eliminated.

[0047]

As described in detail above, in the laminated piezoelectric actuator of the present invention, a laminated body composed of a piezoelectrically active piezoelectric plate and a metal plate, and an inert insulator disposed on the upper and lower surfaces of the laminated body. A low elastic body having an elastic modulus of 80 GPa or less is inserted between the laminated body and the stress transmitted to the inert insulator by the displaced laminate is reduced, and the stress concentration at the boundary between the laminate and the inert insulator is reduced. Can be suppressed, and breakage of the end face of the inert insulator or the laminated body can be prevented. Therefore, high voltage,
Even in the case of high-speed driving at a high frequency, long-time driving can be performed without cracking or breakage.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a laminated piezoelectric actuator of the present invention.

FIG. 2 is a plan view of an electrode plate in the multilayer piezoelectric actuator of the present invention.

FIG. 3 is a cross-sectional view of the multilayer piezoelectric actuator of the present invention.
It is a principal part expanded sectional view at the time of using a metal plate as a low elastic body.

FIG. 4 is a cross-sectional view of the multilayer piezoelectric actuator of the present invention.
It is an important section enlarged sectional view at the time of using silicone rubber as a low elastic body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 2 Piezoelectric plate 3 Electrode plate 4 Conductive layer 5 Connecting member 6 Low elastic body 7 Inactive insulator

Continued on the front page (72) Inventor Tsuyoshi Setoguchi 1-4, Yamashita-cho, Kokubu-shi, Kagoshima Inside the Kyocera Research Institute (72) Inventor Katsuhiko Onitsuka 1-4, Yamashita-cho, Kokubu-shi, Kagoshima Kyocera Corporation In the laboratory

Claims (4)

[Claims] 1. A laminated body in which a plurality of piezoelectric plates and a plurality of positive and negative electrode plates are alternately laminated, and said positive electrode plate and said negative electrode plate are laminated. A connection member for connecting each side of the body, and a piezoelectric actuator comprising a piezoelectrically inactive insulator bonded to upper and lower surfaces of the laminate, wherein the laminate and the inert A laminated piezoelectric actuator comprising an insulator and a low elastic body having an elastic modulus of 100 GPa or less. 2. The method according to claim 1, wherein the low elastic body is made of at least one metal selected from the group consisting of Ag, Al, and duralumin.
2. The multilayer piezoelectric actuator according to claim 1, wherein the multilayered piezoelectric actuator is made of a metal of m, and the low elastic body and the laminate, and the low elastic body and the inert insulator are joined by glass. 3. The multilayer mold according to claim 1, wherein said low elastic body is made of silicon rubber having a thickness of 3 to 300 μm, and said laminate and said inert insulator are joined by adhesiveness of said silicone rubber. Piezo actuator. 4. The laminated piezoelectric actuator according to claim 1, wherein said inert insulator is made of the same material as said piezoelectric plate.