JPH07169998A - Piezo-electric actuator - Google Patents

Abstract

PURPOSE:To make it possible to diminish the reduction of durability due to cracks occurring in insulators without reducing the amount of displacement during driving. CONSTITUTION:In a piezo-electric actuator 1 with a plurality of piezo-electric plates 20 and 22 forming a conductive layer 21 which are stacked to form a laminate 2 on at least one surface of the actuator, the conductive layer 2 positioned on the side of the laminate 2 which is covered by an insulator 3 for every other layer, and an external electrode 4 formed as the insulator 3 is covered so that continuity is made to another conductor layer 21 for every other layer, the insulator 3 comprises an elastic member 30 and a bead 31 of an approximately globular shape mixed with the elastic member 30.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a piezoelectric actuator.

[0002]

2. Description of the Related Art As a conventional piezoelectric actuator, for example, a laminated body formed by laminating a plurality of piezoelectric plates (piezoelectric pellets) having a conductive layer (internal electrode) formed on one surface, and a side surface of the laminated body A piezoelectric actuator comprising an insulating material (insulating layer) that covers the conductive layers located every other layer, and an external electrode that is formed so as to cover the insulating material and conduct to every other conductive layer every other layer. In order to prevent cracks, a piezoelectric actuator is known in which a layer having a large piezoelectric constant is sandwiched between layers having a small piezoelectric constant to form a three-layer structure, and an insulating material is formed on the side surface of the layer having a small piezoelectric constant. (Japanese Patent Laid-Open No. 1-223784).

[0003]

According to the conventional piezoelectric actuator described above, since the insulating material is in contact with a layer having a small displacement amount (elongation) during driving and a small piezoelectric constant, cracks are not generated. It can be prevented. However, on the other hand, the amount of displacement of the piezoelectric actuator decreases because a layer having a small piezoelectric constant is used.

An object of the present invention is to provide a piezoelectric actuator capable of reducing the deterioration of durability due to cracks generated in an insulating material without reducing the displacement amount.

[0005]

In the piezoelectric actuator of the present invention, a plurality of piezoelectric plates each having a conductive layer formed on at least one surface thereof are laminated to form a laminated body, and the conductive body located on the side surface of the laminated body is formed. In a piezoelectric actuator formed by covering every other layer with an insulating material and forming an external electrode so as to cover the insulating material and be electrically connected to another conductive layer every other layer, the insulating material is an elastic member, A piezoelectric actuator comprising substantially spherical beads mixed with the elastic member.

[0006]

According to the piezoelectric actuator of the present invention, when a crack is generated in the elastic member during driving, the tip of the crack advances in the elastic member region toward the nearest bead. Then, the tip of the crack reaching the beads moves along the spherical surface shape of the beads, so that the progress in the elastic member region is temporarily stopped. After that, the tip of the crack changes its direction along the spherical surface of the bead, and the phenomenon of proceeding toward the other beads in the elastic member region is repeated, and it takes time for the tip of the crack to reach the external electrode. Prolong.

[0007]

FIG. 1 shows an embodiment of the piezoelectric actuator of the present invention.
~ It demonstrates based on FIG. FIG. 1 is a perspective view of the entire piezoelectric actuator 1 of the embodiment with its length in the stacking direction shortened. The piezoelectric actuator 1 is a laminated body 2
And an insulating material 3 and an external electrode 4.

The laminated body 2 has a piezoelectric plate 20 having a conductive layer 21 formed on one surface or both surfaces thereof facing downward or upward.
The piezoelectric plates 22 are stacked in eight layers, and the piezoelectric plates 22 each having a conductive layer 21 formed on one surface are stacked one above the other and integrated. The piezoelectric plates 22 adjacent to each other on the upper and lower sides of the laminated body 2 share the conductive layer 21. In addition, the piezoelectric plates 22 arranged at the lowest position or the highest position stacked in
Can share the conductive layer 21 of the piezoelectric plates 20 that are vertically adjacent to each other, so that the conductive layer 21 is not formed on one surface in advance.

The piezoelectric plate 20 is mainly composed of PZT (lead zirconate titanate) and has a diameter of 16 mm and a thickness of 0.5 m.
It is a disk-shaped object of m. The piezoelectric plate 22 is made thicker than the piezoelectric plate 20 by 2 mm in order to insulate the piezoelectric actuator 1 from the outside. The material is the same as that of the piezoelectric plate 20. As the conductive layer 21, one surface or both surfaces of the piezoelectric plate 20 is entirely printed with a silver paste containing glass frit, dried, and then 58 piezoelectric plates 20 are stacked.
Two of them are stacked one above the other with the conductive layer 21 inside and thermocompression bonded in that state.

As shown in FIGS. 1 and 2, the insulating material 3 covers the conductive layer 21 at the side surface positions of the laminated body 2 facing each other 180 degrees apart from the circumference of the laminated body 2 and at every other layer. Is formed. The insulating material 3 is composed of an elastic member 30 made of an insulating elastic epoxy resin paste and round glass beads 31 mixed with the elastic member 30 in a weight ratio of 45% to 55%. The average particle size of the glass beads 31 is
It is 20 μm to 30 μm. The weight ratio and average particle diameter of the glass beads 31 can be changed according to the purpose.

The external electrode 4 is formed by using a conductive paste in which silver powder is mixed in epoxy resin. That is,
In order to form the external electrodes 4, a conductive paste (not shown) is applied to the side surfaces of the laminated body 2 shown in FIGS. It is formed by applying and coating the other conductive layer 21 on which the insulating material 3 is not formed continuously, followed by drying and baking. In addition,
In the laminated body 2, steel shims (not shown) are laminated on the upper end side and the lower end side, and a protective layer (not shown) that covers the outer peripheral surface is formed. The protective layer is formed by coating the outer peripheral surface with a heat-shrinkable tube having a thickness of about 0.5 mm.

Ten piezoelectric actuators 1 manufactured as described above were prepared as test samples, and an operation test was carried out under the following conditions. The operating conditions are
Approximately 30 with rectangular wave drive with load of 5KN and frequency of 100Hz
A voltage of 0 to -150 V was applied and the displacement amount was 20 μm. Then, the number of repetitions until a short circuit occurs due to the occurrence of cracks in the insulating material 3 and the operation of the piezoelectric actuator 1 is stopped was confirmed and shown in FIG.

According to the piezoelectric actuator 1 of the embodiment,
The insulating material 3 is composed of the elastic member 30 and the substantially spherical glass beads 31 mixed with the elastic member 30. Therefore, (1) when the piezoelectric actuator 1 is driven, the elastic member 30
When the crack S occurs in the crack S, the tip of the crack S advances in the region of the elastic member 30 toward the nearest glass bead 31. Then, the tip of the crack S reaching the glass beads 31 moves along the spherical surface shape of the glass beads 31, so that the progress in the region of the elastic member 30 is temporarily stopped. After this, the tip of the crack S is covered with the glass beads 31.
The phenomenon of changing the direction along the surface of the sphere and advancing through the region of the elastic member 30 toward the other glass beads 31 is repeated, prolonging the time until the tip of the crack S reaches the external electrode 4.

Therefore, the piezoelectric actuator 1 of the embodiment
Can increase the number of operations and drive durability until short circuit due to the influence of the crack S generated in the elastic member 30 of the insulating material 3. (2) Further, since the piezoelectric actuator 1 does not have a structure in which the displacement amount of the laminated body 2 is reduced during driving unlike the conventional piezoelectric actuator, the displacement function can be sufficiently exhibited during driving. (3) The elastic member 30 of the insulating material 3 is reinforced by the glass beads 31, so that the degree of bonding with the protective layer (not shown) covering the surface of the insulating member 3 can be increased and peeling can be made difficult. (4) In the elastic member 30 of the insulating material 3, the thermal conductivity increases and the thermal expansion coefficient decreases in accordance with the mixing amount of the glass beads 31, and the temperature distribution (temperature difference) of the entire laminate 2 is improved.

The thermal strain of the entire laminated body 2 is reduced, and the occurrence of cracks in the laminated body 2 is reduced. (Comparative Example) In order to confirm the effect of the piezoelectric actuator 1 of Example 1, as shown in FIG. 5, a piezoelectric actuator 1a of Comparative Example was manufactured, and a rectangular wave drive was performed in the same manner as the piezoelectric actuator 1 of Example. The operation test was carried out under the same conditions as described above.

Incidentally, the piezoelectric actuator 1a of the comparative example.
3 has the same structure as that of the first embodiment except that the insulating material 3a is formed only by the elastic member 30 made of the elastic epoxy resin paste having insulating properties. As a result of the operation test, in the piezoelectric actuator 1 of the comparative example, the rate of not being short-circuited at 1 × 10 ⁷ times was 0%.
Met. That is, in the case of the comparative example, the crack S originating from the conductive layer 21 is generated with a small number of repeated operations.
1 (see FIG. 5) reached the external electrode 4.

On the other hand, in the piezoelectric actuator 1 according to the first embodiment, the rate of not causing short circuit (due to crack) even when operated 1 × 10 ⁹ times was 40%, which was a high value. In the embodiment, the insulating member 3 is made of an elastic member 30 made of an insulating elastic epoxy resin paste,
The case where the elastic member 30 and the glass beads 31 mixed with each other is used has been described, but the elastic member 30 is not limited to this. For example, silicon rubber or the like may be used as the elastic member 30 instead of the glass beads 31. beads,
Silica beads or the like can be used.

[0018]

According to the piezoelectric actuator of the present invention,
The insulating material is composed of an elastic member and substantially spherical beads mixed with the elastic member. Therefore, (1) when a crack is generated in the elastic member during driving of the piezoelectric actuator, the tip of the crack advances in the elastic member region toward the nearest bead. Then, the tip of the crack reaching the beads moves along the spherical surface shape of the beads, so that the progress in the elastic member region is temporarily stopped. After that, the tip of the crack changes its direction along the spherical surface of the bead, and the phenomenon of proceeding toward the other beads in the elastic member region is repeated, and it takes time for the tip of the crack to reach the external electrode. Prolong.

Therefore, the piezoelectric actuator can increase the number of operations and the driving durability until it is short-circuited due to the cracks generated in the elastic member of the insulating material. (2) Further, since the piezoelectric actuator does not have a structure in which the displacement amount of the laminated body is reduced during driving unlike the conventional piezoelectric actuator, the displacement function can be sufficiently exhibited during driving. (3) The elastic member of the insulating material is reinforced by the beads, so that the degree of bonding with the protective layer covering the surface of the elastic member can be increased and peeling can be made difficult. (4) In the elastic member made of an insulating material, the thermal conductivity increases and the thermal expansion coefficient decreases in accordance with the amount of the glass beads mixed, and the temperature distribution (temperature difference) of the entire laminate is improved.

Then, the thermal strain of the entire laminate becomes small,
The occurrence of cracks in the laminate is reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of a piezoelectric actuator according to an embodiment of the present invention with a reduced length in a stacking direction.

FIG. 2 is a sectional view taken along the line AA in FIG.

FIG. 3 is an enlarged sectional view showing a part of FIG. 2 in an enlarged manner.

FIG. 4 is a diagram showing the durability performance of the piezoelectric actuators of Examples and Comparative Examples, in which the horizontal axis represents the number of repeated operations of the piezoelectric actuator, and the vertical axis represents the ratio at which the piezoelectric actuator did not short.

5 shows a piezoelectric actuator of a comparative example, and FIG.
It is an expanded sectional view showing a portion corresponding to.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 2 ... Laminated body 20 ... Piezoelectric plate
21 ... Conductive layer 3 ... Insulating material 30 ... Elastic member
31 ... Glass beads 4 ... External electrode 22 ... Piezoelectric plate

Claims (1)

[Claims] 1. A laminated body is formed by laminating a plurality of piezoelectric plates each having a conductive layer formed on at least one surface thereof, and the conductive layers located on the side surfaces of the laminated body are covered with an insulating material every other layer. A piezoelectric actuator in which external electrodes are formed so as to cover the insulating material and be electrically connected to another conductive layer every other layer, wherein the insulating material is an elastic member and substantially spherical beads mixed with the elastic member. A piezoelectric actuator comprising: