JPH02250678A - Laminated piezoelectric actuator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention A9.Objective of the Invention [Field of Industrial Application] The present invention relates to a piezoelectric element that receives electrical energy and converts it into mechanical energy in the form of displacement or force proportional to the electrical energy. In particular, the present invention relates to a laminated piezoelectric actuator in which piezoelectric elements are laminated.

[Conventional technology]

Conventionally, electromagnetic actuators such as voice coil motors and pulse motors have been used as actuators for precision positioning devices and precision X-Y tables, but in recent years electromagnetic actuators have become more popular in terms of positioning accuracy, response speed, power consumption, etc. Laminated piezoelectric actuators with better characteristics are being used.

A laminated piezoelectric actuator has piezoelectric ceramic plates and internal electrode plates alternately laminated to form a piezoelectric ceramic laminated body.

In the laminated piezoelectric actuator, stress concentration can be eliminated by making the cross-sectional area of the piezoelectric ceramic plate orthogonal to the displacement direction coincide with the cross-sectional area of the internal electrode plate, and Advances in manufacturing technology have made it possible to increase the amount of distortion that occurs.

Figure 3 shows a conventional laminated piezoelectric actuator.
The laminated piezoelectric actuator 3 has a structure in which edges of a pair of internal electrodes 12a and 12b facing each other are exposed on the side surface. In FIG. 3, 13 is a glass insulating part, 14 is an external electrode, and 15 is a lead wire. In this laminated piezoelectric actuator 3, as described above, the internal electrodes 12a and 12b are exposed on the side surface, so in order to ensure electrical insulation between other devices and the internal electrodes, it is necessary to Electrode 14 and internal electrodes 12a, 1
In order to form an electrical insulator on the surface of the end face 2b, it is common practice to cover the side surface with an organic resin (not shown).

[Problem to be solved by the invention]

However, even if the side surfaces of the multilayer piezoelectric actuator are coated with organic resin, it is difficult to prevent moisture from entering or passing through, and if the multilayer piezoelectric actuator is used for a long time in a high humidity environment, the internal electrodes 12a and 12 of
The electrical insulation resistance between b and b decreases, which may even lead to an electrical short circuit.

An object of the present invention is to provide a laminated piezoelectric actuator that prevents the intrusion and permeation of moisture and does not cause a decrease in electrical insulation resistance between internal electrodes even after being used for a long time in a high humidity environment. be.

Structure of the Invention [Means for Solving the Problems] The present invention provides a piezoelectric ceramic having high electrical insulation properties even when used for a long time in a high humidity environment. In a laminated piezoelectric actuator having at least a pair of internal electrodes arranged in parallel to each other, electrical insulation is ensured at a portion of the pair of internal electrodes forming an edge exposed to the outside from a side surface of the laminated piezoelectric actuator. Therefore, the laminated piezoelectric actuator is characterized in that a layer of silicone oil is formed on the side surface of the laminated piezoelectric actuator, and further includes a flexible case that seals the layer of silicone oil.

That is, the present invention.

1. A piezoelectric ceramic and at least a pair of internal electrodes arranged alternately in parallel between the piezoelectric ceramic;
The pair of internal electrodes is a laminated piezoelectric actuator in which an external electrode is formed by exposing the side surface of the piezoelectric ceramic, and silicone oil is provided to surround the external electrode and the internal electrode, and the silicone oil is sealed around the outer periphery of the piezoelectric actuator. A laminated piezoelectric actuator characterized by having a flexible case.

2. The laminated piezoelectric actuator according to claim 1, wherein the flexible case for sealing the silicone oil has a structure sealed with a metal case that encloses the entire laminated piezoelectric actuator.

3. The laminated piezoelectric actuator according to claim 1, wherein the flexible case for sealing the silicone oil has a structure in which the piezoelectric ceramic is sealed with a resin case except for both ends thereof.

[Effect]

In a conventional laminated piezoelectric actuator, when the piezoelectric actuator is continuously used in a high humidity environment, the reason for the decrease in electrical insulation resistance between a pair of internal electrodes is that moisture 4 permeates through the organic resin layer. It is presumed that this is because silver adheres to the internal electrode and promotes ionization of silver contained within the internal electrode.

On the positive side of the internal electrode exposed to the surface, Ag = Ag
On the negative electrode side of the internal electrode exposed to the surface at +10e, the reaction expressed as Jg"10e-+ Jg progresses, and silver forms dendrites in the positive electrode direction on the surface of the internal electrode exposed at the negative electrode side. It is observed that the silicone oil layer of the layered piezoelectric actuator according to the present invention prevents moisture from reaching the inner electrode. It has the effect of preventing the adhesion of silver and ionization of silver.

In addition, by sealing the silicone oil with a flexible case that encloses the silicone oil layer, it prevents moisture from entering in high-temperature environments and maintains the electrical insulation properties of the electrode even after long-term use. A laminated piezoelectric actuator that does not deteriorate can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a laminated piezoelectric actuator according to the present invention. In the laminated piezoelectric actuator 1.2, the piezoelectric ceramic 11 is made of lead, nickel, niobium, etc.
Oxide consisting of titanium and zirconium (Pb((Ni-
This is a laminated piezoelectric actuator formed using Nb)Ti-Zr)03) as a starting material by a thick film lamination method to have a cross section of 5 mm x 5 H1 and a length of 18 mm.

The material of the internal electrodes is a silver-palladium alloy, the interval between the internal electrodes 12a and 12b is 115 μm, and the number of internal electrode layers is 150. The external electrode 14 is formed by baking silver paste. Next, an example will be shown in which the four sides of this laminated piezoelectric actuator are sealed with a layer of silicone oil 26, with a metal case 27 in FIG. 1 and a resin case in FIG. 2.

Figure 1 shows a cylindrical metal case 27 made of aluminum.
This figure shows the entire encapsulated shape of the stacked piezoelectric actuator.

The inner surface of the metal case and the top and bottom surfaces of the piezoelectric ceramic are completely in close contact with each other, and the amount of displacement associated with voltage application to the laminated piezoelectric actuator is designed to be within the elastic deformation of the aluminum case in the length direction. The top and bottom surfaces of the piezoelectric ceramics are tightened by threaded portions 28 for case connection, resulting in a laminated piezoelectric actuator with no performance deterioration.

FIG. 2 shows a laminated piezoelectric actuator in which only the four circumferential surfaces of piezoelectric ceramics are sealed with a resin case 29.
For the resin case, apply epoxy adhesive 30 to the ceramic parts near the top and bottom surfaces of the piezoelectric ceramic that do not include the internal electrodes.
It is glued together. The silicone oil sealed inside the metal case or resin case is phenylmethyl silicone oil or dimethyl silicone oil, and is dehydrated by degassing in a vacuum or heated to about 100℃ before use. Also, when wrapping the laminated piezoelectric actuator with silicone oil, the silicone oil is vacuum impregnated.

In order to investigate the reliability of the laminated piezoelectric actuator shown in Figs. 1 and 2 in a high humidity environment, the positive and negative electrodes of the laminated piezoelectric actuator were tested in an atmosphere at a temperature of 50°C and a relative humidity of 95%. Aging was performed by continuously applying a DC voltage of 100 V during this period. For comparison, a stacked piezoelectric actuator with a conventional structure shown in FIG. 3 was also aged at the same time. The number of samples subjected to aging was as per Example 5.
0, and the case where the insulation resistance between the external electrodes 14 of each example decreased by one digit or more was considered to be defective. Results first
Shown in the table.

As is clear from Table 1 below, in the laminated piezoelectric actuator of the conventional structure, the electrical insulation resistance between the external electrodes 14 decreases due to moisture intrusion as the aging time progresses, and
However, in the laminated piezoelectric actuator shown in FIGS. 1 and 2 according to the embodiment of the present invention, electrical insulation defects did not occur even after 2000 hours. It can be seen that the laminated piezoelectric actuator has much better moisture resistance than the laminated piezoelectric actuator with the conventional structure.

Effects of the Invention [Effects of the Invention] As explained above, the outer electrode part of the laminated piezoelectric ceramic with the positive and negative electrodes formed between them is wrapped in a metal case or a resin case around the outer periphery using dehydrated silicone oil. Since this is a multilayer piezoelectric actuator, it is possible to provide a highly reliable multilayer piezoelectric actuator that does not cause a decrease in electrical insulation resistance between internal electrodes even when used for a long time in a high humidity environment.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a laminated piezoelectric actuator according to the present invention, in which piezoelectric ceramics, the entire electrode, and silicone oil are sealed in a metal case. FIG. 2 is a cross-sectional view of the multilayer piezoelectric actuator according to the present invention, in which the entire multilayer actuator excluding the top and bottom surfaces of piezoelectric ceramics and silicone oil are sealed in a resin case. FIG. 3 is a perspective view showing a conventional laminated piezoelectric actuator. 1.2...Laminated piezoelectric actuator of the present invention, di-
・・Conventional laminated piezoelectric actuator, 11 ・Piezoelectric ceramics, 12a, 12b ・Internal electrode, 13
... Glass insulation part, 14 ... External electrode, 15 ...
Lead wire, 26...Silicone oil, 27...Metal case, 28...Threaded portion, 29...Resin case,
30...Epoxy adhesive. Patent applicant Tokin Co., Ltd. 1rya Figure 3 Figure 2

Claims (3)

[Claims] 1. a piezoelectric ceramic and at least one pair of internal electrodes arranged alternately in parallel between the piezoelectric ceramic;
The pair of internal electrodes is a laminated piezoelectric actuator in which an external electrode is formed by exposing the side surface of the piezoelectric ceramic, and silicone oil is provided to surround the external electrode and the internal electrode, and the silicone oil is sealed around the outer periphery of the piezoelectric actuator. A laminated piezoelectric actuator characterized by having a flexible case. 2. 2. The laminated piezoelectric actuator according to claim 1, wherein the flexible case for sealing the silicone oil has a structure sealed with a metal case that encloses the entire laminated piezoelectric actuator. 3. 2. The laminated piezoelectric actuator according to claim 1, wherein the flexible case for sealing the silicone oil has a structure in which the piezoelectric ceramic is sealed with a resin case except for both ends thereof.