JPH04369277A - Multilayer piezoelectric actuator - Google Patents

Abstract

PURPOSE:To provide a multilayer piezoelectric actuator of a structure in which, even if a DC voltage is supplied in a high humidity environment for use in a long time, the insulating resistances between inner electrodes are not decreased. CONSTITUTION:Lead zircotitanate-based piezoelectric ceramics 11 layers and inner electrodes 12 of silver-palladium alloy of positive and negative electrodes are alternately formed. In a multilayer piezoelectric actuator in which opposed end faces of the electrodes are electrically insulated by glass insulating layers 15 and the electrodes are connected to stripelike outer electrodes 13, inner electrodes 12a in which a positive voltage is applied, are formed with a recessed part by removing it by 10 to 200 microns from the ceramic surface by etching, and a polymer organic insulator is filled into the retracted part.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator that converts electrical energy into mechanical energy such as displacement or force, and more particularly to a laminated piezoelectric actuator in which a plurality of internal electrodes and ceramics are integrally sintered.

0002

[Prior Art] 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 such as voice coil motors and pulse motors have Piezoelectric actuators, which are superior to the electromagnetic actuators, are being used. There are two types of piezoelectric actuators: the laminated type and the bimorph type.The laminated type has the characteristics of high displacement accuracy and large generated force, and the bimorph type has the characteristics of a small generated force value but a large amount of displacement.
Laminated type actuators are often used for precision positioning devices and precision X-Y tables. A laminated piezoelectric actuator has a ceramic laminate formed by alternately laminating piezoelectric ceramic plates and internal electrode plates. The amount of displacement of a laminated piezoelectric actuator is proportional to the number of layers of piezoelectric ceramic plates and internal electrode plates, and the value of the applied voltage. Development is underway to enable low-voltage operation. In addition, by creating a structure in which the cross-sectional area of the piezoelectric ceramic plate perpendicular to the displacement direction of the laminated piezoelectric actuator matches the cross-sectional area of the internal electrode plate, it is possible to eliminate internal concentrated stress and generate a large amount of force. can be obtained. FIG. 2 shows a cross-sectional view of the laminated piezoelectric actuator, and the structure of the laminated piezoelectric actuator will be explained with reference to the figure. A plurality of internal electrodes 22 facing each other in every other layer
The edges of the electrodes a and 22b are exposed, and the end faces of the opposing electrodes are electrically insulated from the external electrodes 24 by glass insulating parts 23, and the outer peripheries of the external electrodes are covered with an organic exterior resin 25. , a lead wire 26 is connected to the external electrode.

0003

[Problems to be Solved by the Invention] However, even if the side surfaces of the multilayer piezoelectric actuator are coated with an organic exterior resin, it is difficult to prevent moisture from entering or permeating the multilayer piezoelectric actuator. When a multilayer piezoelectric actuator is used for a long time with a DC voltage applied in a high humidity environment, there is a problem in that the insulation resistance between opposing internal electrodes decreases, and even short circuits occur. The reason for the decrease in insulation resistance of multilayer piezoelectric actuators when DC voltage is applied and used for long periods of time in a high humidity environment is thought to be due to the adhesion of ionic substances and dirt to the exposed surface of the internal electrodes. However, it is also presumed that migration occurs in which moisture permeates through the organic exterior resin layer and adheres to the exposed surface portion of the internal electrode, ionizing the silver contained as a component of the internal electrode. At this time, in the positive and negative electrodes, the surface-exposed internal electrode positive electrode: Ag → Ag+ + e- The surface-exposed internal electrode negative electrode: Ag+ + e- → Ag In other words, the above reaction proceeds in the electrode part, Silver grows in a dendritic manner on the surface-exposed electrode portion on the negative side, and the substantial distance between the positive and negative electrodes of the surface-exposed internal electrode becomes short, and the insulation resistance between the internal electrodes decreases. Therefore, the technical problem of the present invention is to provide a laminated piezoelectric actuator that has a structure that does not cause a decrease in insulation resistance between internal electrodes even when a DC voltage is applied and used for a long time in a high humidity environment. It is.

0004

[Means for Solving the Problems] The present invention provides a piezoelectric ceramic sintered body having a plurality of internal electrode layers having a shape equal to the cross-sectional shape. a stripe which is covered with a glass insulating part in every other layer on two different internal electrodes, and further electrically connected to the exposed internal electrode and every other internal electrode not covered with the glass insulating part on the glass insulating part; In a laminated piezoelectric actuator with a structure in which a shaped external electrode is formed, a positive voltage is applied through the external electrode on the peripheral surface where the glass insulation part and the end of the internal electrode where the external electrode is not formed are exposed to the surface. A multilayer piezoelectric actuator characterized in that an internal electrode portion is set back from the surface of the ceramic by at least 10 to 200 microns into the ceramic, and the set back portion is filled with a polymeric organic insulating material. .

[0005]

[Operation] In a laminated piezoelectric actuator, the structure of the portion where a plurality of opposing internal electrodes are exposed on the surface has an important influence on performance in a high humidity environment. The laminated piezoelectric actuator having the structure of the present invention focuses on the fact that the migration reaction starts from ionization of the electrode material to which a positive voltage is applied, and that the internal electrode exposed to the ceramic side surface is connected to the electrode material to which a positive voltage is applied. Electrochemically etching only the electrodes to be etched to create a structure that is recessed by at least 10 microns or more and about 200 microns from the ceramic surface, increasing the creepage distance between the opposing internal electrodes exposed on the surface, and then recessing. The resulting voids are filled with polymeric insulating material to prevent moisture from entering and ensure mechanical strength. In multilayer piezoelectric actuators, especially those in which the internal electrodes and ceramics are integrally sintered, the gap between the internal electrodes exposed on the side of the ceramic is narrow, about 100 microns, so the organic exterior resin can be penetrated through the ceramic surface. The moisture that reaches the surface causes the migration, which causes a decrease in the insulation resistance of the laminated piezoelectric actuator.However, by adopting the structure of the present invention, the creepage distance between the opposing internal electrodes exposed on the surface is increased. This is a multilayer type that improves the effectiveness of preventing migration, and does not cause a drop in insulation resistance between internal electrodes even when used for long periods of time with DC voltage applied in a high humidity environment. It becomes possible to provide a piezoelectric actuator. Note that if the distance the positive electrode is retreated from the ceramic surface is 10 microns or more, it will have a great effect in preventing migration, but if the distance it is retreated is 200 microns or more, the resin will not be filled sufficiently, and the ceramic part may crack. Therefore, the distance to remove the positive electrode from the ceramic surface is preferably 10 to 200 microns.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a laminated piezoelectric actuator according to the present invention. It has a structure in which piezoelectric ceramics 11 based on lead zirconate titanate and internal electrodes 12 made of a silver-palladium alloy are alternately laminated, and the end surfaces of the internal electrodes are electrically connected to the external electrodes 13, which are opposite electrodes, by means of glass insulating parts 15 alternately. is insulated. The dimensions of the laminated piezoelectric actuator used in the examples were 5 mm x 5 mm in cross section and 18 mm in length.
The internal electrode interval is 115 μm, and the number of internal electrode layers is 150. The internal electrode 12a to which a positive voltage is applied is
After forming an external electrode for connecting a positive potential on the surface of the ceramic, electrochemical etching is performed between the external electrode for connecting a positive potential and a separately provided electrode in an electrolytic solution such as silver nitrate. In the sample of the present invention, the depth of recess into the ceramic is 10 microns, and the recessed portion is filled with a polymeric organic insulating material 17 such as epoxy resin by reducing pressure or the like and solidified. After that, the lead wires were soldered and covered with epoxy paint to form a laminated piezoelectric actuator.

In order to confirm the effects of the present invention, the prepared samples were subjected to long-term aging in a constant temperature and high humidity test chamber by applying a DC voltage of 100 volts. The environmental conditions are temperature 4
The conditions were 0°C and 90% relative humidity. The test results are shown in Table 1. For comparison, samples manufactured using conventional manufacturing methods were also tested at the same time. The number of samples was 100 each.

[Table 1] From the results in Table 1, it is clear that by using the laminated piezoelectric actuator according to the present invention, the failure rate is extremely low compared to the conventional example during long-term aging in a constant temperature and high humidity environment. Indicates that longevity has been achieved.

[0008]

As explained above, the present invention has a structure in which the positive side electrode end face is removed by approximately 20 to 200 microns from the ceramic surface, the positive side electrode end face is not exposed, and the removed portion is filled with resin. By using the laminated piezoelectric actuator as described above, it is possible to provide a long-life laminated piezoelectric actuator in which electrical insulation resistance does not decrease even when a DC voltage is applied and used for a long time in a high humidity environment.

[Brief explanation of the drawing]

FIG. 1 is an external perspective view of a laminated piezoelectric actuator according to the present invention.

FIG. 2 is a cross-sectional view showing the structure of a conventional laminated piezoelectric actuator.

[Explanation of symbols]

11 Zircon lead titanate piezoelectric ceramic 12 Silver-palladium alloy internal electrode 12a Internal electrode 13 to which a positive voltage is applied External electrode 14 Exterior epoxy resin 15, 23 Glass insulation part 16 Lead wire 17 Polymer organic insulating material 21 Piezoelectric ceramics 22a, 22b Internal electrode 24 External electrode 25 Exterior resin 26 Lead wire

Claims (1)

[Claims] 1. A piezoelectric ceramic sintered body having a plurality of internal electrode layers having the same shape as the cross-sectional shape, wherein two opposing surfaces of the peripheral surfaces where the ends of the internal electrodes are exposed have different internal electrodes. Striped external electrodes were formed on the exposed internal electrodes and electrically connected to the internal electrodes in every other layer not covered by the glass insulating parts on the exposed internal electrodes and the glass insulating parts. In the laminated piezoelectric actuator structure, the internal electrode part to which a positive voltage is applied through the external electrode is made of ceramic on the peripheral surface where the end of the internal electrode where the glass insulation part and the external electrode are not formed is exposed. A laminated piezoelectric actuator characterized by having a structure in which the ceramic is recessed from the surface by at least 10 to 200 microns, and the retracted portion is filled with a polymeric organic insulating material.