PIEZOELECTRIC/ELECTROSTRICTIVE ACTUATOR

Abstract

A piezoelectric/electrostrictive actuator includes a piezoelectric body, a plurality of internal electrode layers, side-surface electrodes, and a plurality of electrode lead portions. The internal electrode layers formed only at a central portion of the piezoelectric body. Thus, an active portion is formed at the central portion of the piezoelectric body, and an inactive portion in which no voltage is applied to the piezoelectric body and the piezoelectric body neither expands nor contracts is formed to surround the central portion. The internal electrode layers are formed such that the width of the inactive portion is at least a single layer thickness of the piezoelectric body, which is the distance between a pair of internal electrode layers facing each other, and in a cross section in which each internal electrode layer is formed, the inactive portion has an area not greater than 50% the area of the entire cross section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiments when considered in connection with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a piezoelectric/electrostrictive actuator according to a first embodiment of the present invention;

FIG. 2 is a schematic perspective view of one layer (portion sandwiched between a pair of opposed internal electrode layers) of the piezoelectric body of the piezoelectric/electrostrictive actuator shown in FIG. 1;

FIG. 3 is a vertical cross-sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 1;

FIG. 4 is a cross sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 5 is a conceptual diagram showing the connection between the internal electrode layers and side-surface electrodes of the piezoelectric/electrostrictive actuator shown in FIG. 1;

FIGS. 6A and 6B are conceptual diagrams showing internal stresses generated in an activate portion and an inactive portion of the piezoelectric body;

FIG. 7 is a graph showing the relation between active portion occupancy ratio and expansion/contraction amount of the piezoelectric body for the piezoelectric/electrostrictive actuator according to the embodiment and a conventional piezoelectric/electrostrictive actuator;

FIG. 8 is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator;

FIG. 9 is a graph showing the relation between the active portion occupancy ratio of the piezoelectric body and the maximum stress generated in the piezoelectric body for the piezoelectric/electrostrictive actuator according to the embodiment and the conventional piezoelectric/electrostrictive actuator;

FIG. 10 is a cross sectional view of one modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 11 is a cross sectional view of another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 12A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 12B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 12A;

FIG. 13A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 13B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 13A;

FIG. 14A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 14B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 14A;

FIG. 15A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 15B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 15A;

FIG. 16A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 16B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 16A;

FIG. 17A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 17B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 17A;

FIG. 18A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator shown in FIG. 1, taken along a plane extending along an internal electrode layer;

FIG. 18B is a graph showing changes in expansion/contraction amount of the piezoelectric body with the number of drive cycles of the piezoelectric/electrostrictive actuator shown in FIG. 18A;

FIGS. 19A, 19B, and 19C are cross sectional views of still other modifications of the piezoelectric/electrostrictive actuator shown in FIG. 1, each taken along a plane extending along an internal electrode layer;

FIGS. 20A, 20B, 20C, and 20D are cross sectional views of still other modifications of the piezoelectric/electrostrictive actuator shown in FIG. 1, each taken along a plane extending along an internal electrode layer;

FIGS. 21A, 21B, and 21C are cross sectional views of still other modifications of the piezoelectric/electrostrictive actuator shown in FIG. 1, each taken along a plane extending along an internal electrode layer;

FIG. 22 is a vertical cross-sectional view of a piezoelectric/electrostrictive actuator according to a second embodiment of the present invention;

FIG. 23 is a cross sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 22, taken along line 23-23 of FIG. 22;

FIG. 24 is a cross sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 22, taken along line 24-24 of FIG. 22;

FIG. 25A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator, taken along a plane extending along an internal electrode layer;

FIG. 25B is a vertical cross-sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 25A;

FIG. 26A is a cross sectional view of still another modification of the piezoelectric/electrostrictive actuator, taken along a plane extending along an internal electrode layer;

FIG. 26B is a vertical cross-sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 26A;

FIG. 27 is a figure for describing an individual-punching and laminating method;

FIG. 28 is an enlarged cross-sectional view of a sheet having a through hole formed by the individual-punching and laminating method;

FIG. 29 is an enlarged sectional view of a hollow cylindrical section formed by the individual-punching and laminating method;

FIG. 30 is a figure showing one process for forming a through hole by a simultaneous punching-laminating method;

FIG. 31 is a figure showing another process for forming through holes by the simultaneous punching-laminating method;

FIG. 32 is a figure showing still another process for forming through holes by the simultaneous punching-laminating method;

FIG. 33 is a figure showing still another process for forming through holes by the simultaneous punching-laminating method;

FIG. 34 is a figure showing still another process for forming through holes by the simultaneous punching-laminating method;

FIG. 35 is a partial enlarged cross-sectional view of the piezoelectric/electrostrictive actuator shown in FIGS. 26A and 26B;

FIG. 36A is a schematic perspective view of a piezoelectric/electrostrictive actuator easily manufactured by the simultaneous punching-laminating method;

FIG. 36B is a schematic perspective view of another piezoelectric/electrostrictive actuator easily manufactured by the simultaneous punching-laminating method;

FIG. 36C is a schematic perspective view of still another piezoelectric/electrostrictive actuator easily manufactured by the simultaneous punching-laminating method;

FIG. 37 is a vertical cross-sectional view of a conventional piezoelectric/electrostrictive actuator;

FIG. 38 is a cross sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 37, taken along a plane extending along an internal electrode layer; and

FIG. 39 is a conceptual diagram showing the connection between the internal electrode layers and side-surface electrodes of the piezoelectric/electrostrictive actuator shown in FIG. 37.

Claims

1. A piezoelectric/electrostrictive actuator comprising a piezoelectric body and a plurality of internal electrode layers formed in parallel within the piezoelectric body, in which a predetermined voltage is applied to the internal electrode layers so as to expand and contract the piezoelectric body, wherein the internal electrode layers are disposed at a central portion of the piezoelectric body such that an active portion and an inactive portion are formed in the piezoelectric body, the active portion being the central portion of the piezoelectric body to which a voltage is applied so as to expand and contract the piezoelectric body, and the inactive portion being a peripheral portion of the piezoelectric body which surrounds the central portion of the piezoelectric body and in which no voltage is applied to the piezoelectric body and the piezoelectric body neither expands nor contracts, andwherein the internal electrode layers are formed such that the width of the inactive portion, which is the distance between the outer edge of the piezoelectric body and the active portion, is at least a single layer thickness of the piezoelectric body, which is the distance between a pair of internal electrode layers facing each other, and, in a cross section in which each internal electrode layer is formed, the inactive portion has an area equal to or less than 50% the area of the entire cross section.

2. A piezoelectric/electrostrictive actuator comprising a piezoelectric body and a plurality of internal electrode layers formed in parallel within the piezoelectric body, in which a predetermined voltage is applied to the internal electrode layers so as to expand and contract the piezoelectric body, wherein the internal electrode layers are disposed at a central portion of the piezoelectric body such that an active portion and an inactive portion are formed in the piezoelectric body, the active portion being the central portion of the piezoelectric body to which a voltage is applied so as to expand and contract the piezoelectric body, and the inactive portion being a peripheral portion of the piezoelectric body which surrounds the central portion of the piezoelectric body and in which no voltage is applied to the piezoelectric body and the piezoelectric body neither expands nor contracts, andwherein the piezoelectric/electrostrictive actuator further comprises:electrode lead portions each generally assuming the form of a strip and extending from the internal electrode layers to side surfaces of the piezoelectric body, the width of the strip being equal to or less than 30% the diameter of a circle which can be drawn in an internal electrode layer without extending outside the outer edge of the internal electrode layer, and the circle having the maximum area among all such circles; andside-surface electrodes formed on the side surfaces of the piezoelectric body so as to connect together end portions of the corresponding electrode lead portions exposed to the side surfaces of the piezoelectric body.

3. A piezoelectric/electrostrictive actuator according to claim 2, wherein the shape of each internal electrode layer is a shape having n-fold symmetry, where n is an integer not less than 2, a rectangular shape, or an elliptical shape, or an oval shape.