JP2013157439A - Piezoelectric element and piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element and a piezoelectric actuator capable of preventing breakage of local concentration of a stress, and easily connecting electrodes.SOLUTION: A piezoelectric element 110 used so that it is laminated in a telescopic direction for a piezoelectric actuator comprises: an annularly-formed element body 111 having a piezoelectric layer and first and second internal electrodes alternately laminated via the piezoelectric layer; first external electrodes 115a-115c exposed to both main faces of the element body 111 and connected to the first internal electrode; and second external electrodes 116a-116c exposed to both main faces of the element body 111 and connected to the second internal electrode. Both main face portions of the first external electrodes 115a, 115c are provided nearer a hole 117 than both main face portions of the second external electrodes 116a, 116c.

Description

  The present invention relates to a piezoelectric element and a piezoelectric actuator that are used while being stacked in an expansion / contraction direction.

  2. Description of the Related Art Conventionally, a piezoelectric actuator in which rectangular parallelepiped piezoelectric elements are stacked to form a main body is known. 7A to 7C are a perspective view of a conventional piezoelectric actuator body 500, a perspective view of a piezoelectric element 510, and a cross-sectional view of the piezoelectric element 510, respectively. The piezoelectric actuator body 500 is formed by stacking integrally fired laminated piezoelectric elements 510, and each external electrode 515 is connected by a lead wire 520. The piezoelectric element 510 is formed by laminating a piezoelectric layer and internal electrodes. When a voltage is applied, the piezoelectric layer between the electrodes is deformed as an active region, but the other inactive regions are not deformed. Therefore, stress is likely to be generated near the boundary between these regions, and stress is particularly concentrated at the corner portion C of the internal electrode 512, and breakage is likely to occur.

  On the other hand, a piezoelectric actuator has been developed that can relieve stress by providing a stress absorbing layer made of powder containing lead titanate as a main component so that the piezoelectric layer is discontinuous in the piezoelectric element (for example, Patent Document 1). However, it is still a shape in which stress is easily generated at the corners of the internal electrode. On the other hand, a piezoelectric element has also been developed in which internal electrodes are provided on the entire laminated surface and stress concentration is prevented by eliminating an inactive region on the side surface (see, for example, Patent Document 2).

JP 2006-286774 A JP 05-003351 A

  However, in the piezoelectric element described in Patent Document 2, since the internal electrode is uniformly exposed on the side surface, the exposed portion of the internal electrode that should not be connected to the external electrode needs to be covered with an insulating material, which requires a complicated manufacturing process. To do.

  On the other hand, it is also conceivable to prevent the local stress from being concentrated between the active region and the inactive region by making the piezoelectric element into a disc shape. 8A to 8C are a perspective view of a piezoelectric actuator main body 600 formed by stacking disk-shaped piezoelectric elements 610, a perspective view of the piezoelectric element 610, and a cross-sectional view of the piezoelectric element 610, respectively. As shown in FIG. 8C, in this case, since the corner portion does not exist in the internal electrode 612, stress concentration can be prevented.

  However, as shown in FIG. 8A, it is difficult to arrange the piezoelectric elements 610 so that external electrodes between the plurality of piezoelectric elements can be connected by lead wires 620, and to be stacked in multiple stages. In order to avoid this, a method of chamfering the piezoelectric element 610 to facilitate positioning is conceivable. However, processing the piezoelectric element 610 according to the connection portion between the internal electrode and the external electrode is troublesome and practical. is not.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a piezoelectric element and a piezoelectric actuator that can prevent breakage due to local concentration of stress and can easily connect electrodes.

  (1) In order to achieve the above object, the piezoelectric element of the present invention is a piezoelectric element that is used by being stacked in an expansion / contraction direction for a piezoelectric actuator, and is alternately stacked via a piezoelectric layer and the piezoelectric layer. An element main body having first and second internal electrodes and formed in an annular shape; a first external electrode exposed to both main surfaces of the element main body and connected to the first internal electrode; A second external electrode exposed to both main surfaces of the element body and connected to the second internal electrode, wherein both main surface portions of the first external electrode are formed on both of the second external electrodes. It is provided on the hole side from the main surface portion.

  As described above, since the piezoelectric element of the present invention is formed in an annular shape, stress is not concentrated locally, and it is difficult for destruction to occur. Further, the external electrode can be easily formed, and since both main surface portions of the first and second external electrodes are separated into the hole side and the outer peripheral side, it is easy to connect when stacked.

  (2) In the piezoelectric element of the present invention, even if both main surface portions of the first or second external electrode are rotationally moved with respect to the central axis of the element body, projections in the stacking direction overlap each other. It is characterized by that. Thereby, when a plurality of piezoelectric elements are stacked, the external electrodes can be easily connected to each other. Further, the connection can be ensured even if the positions of the piezoelectric elements adjacent to each other are shifted around the central axis.

  (3) Moreover, the piezoelectric actuator of the present invention is characterized by including a piezoelectric actuator body formed by stacking a plurality of the above-described piezoelectric elements in a telescopic direction on substantially the same central axis. Thereby, the first and second external electrodes can be connected to each other to constitute a piezoelectric actuator and obtain a large displacement.

  (4) Further, the piezoelectric actuator of the present invention is characterized in that a shaft fixing shaft is inserted into a central hole of the plurality of stacked piezoelectric elements. Thereby, even when the elements are not bonded to each other, for example, the elements can be electrically connected to each other while preventing the displacement of the positions on the laminated surface of the plurality of piezoelectric elements.

  (5) The piezoelectric actuator according to the present invention further includes insulating plates provided at both ends of the piezoelectric actuator body, and one of the insulating plates on the displacement end side or the fixed end side of the piezoelectric actuator body is In the central portion, both main surfaces are electrically connected. Thereby, it is possible to connect the external electrode and the drive power supply while ensuring necessary insulation.

  According to the present invention, stress is not concentrated locally, and it is difficult for breakage to occur. Further, the external electrodes can be easily formed, and the electrodes can be easily connected when stacked.

It is a perspective view of the piezoelectric actuator main body of this invention. (A)-(c) It is a perspective view, a top view, and a bottom view of a piezoelectric element, respectively. (A)-(c) is a sectional side view of a piezoelectric element, and a different plane sectional view, respectively. It is sectional drawing which shows one form of a piezoelectric actuator. (A)-(c) It is a top view, a bottom view, and a side sectional view, respectively, of the insulating plate on the displacement end side. (A)-(c) It is a top view, a bottom view, and a side sectional view, respectively, of an insulating plate on the fixed end side. (A)-(c) is the perspective view of the conventional piezoelectric actuator main body, the perspective view of a piezoelectric element, and sectional drawing of a piezoelectric element, respectively. 1A to 1C are a perspective view of a piezoelectric actuator body formed by stacking disc-shaped piezoelectric elements, a perspective view of the piezoelectric element, and a sectional view of the piezoelectric element.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Piezoelectric actuator body)
FIG. 1 is a perspective view of the piezoelectric actuator body 100. As shown in FIG. 1, the piezoelectric actuator main body 100 has a cylindrical shape, and is formed by stacking a plurality of piezoelectric elements 110 on substantially the same central axis in the expansion / contraction direction. Thereby, a piezoelectric actuator can be comprised and a big displacement can be obtained. Details of the piezoelectric element 110 will be described below.

(Piezoelectric element)
2A to 2C are a perspective view, a plan view, and a bottom view of the piezoelectric element 110, respectively. The piezoelectric element 110 is used by being stacked in a telescopic direction for a piezoelectric actuator. As shown in FIGS. 2A to 2C, the piezoelectric element 110 includes an element body 111 and external electrodes 115a to 116c. Since the element main body 111 is formed in an annular shape, stress is not concentrated locally, and the element main body 111 is not easily broken. The shape of the element body 111 is most preferably an annular shape, but may be a polygonal ring such as an octagon or a dodecagon, or an elliptical ring.

  The external electrodes 115 a to 115 c (first external electrodes) are integrally provided on the inner surface of the hole 117 in the center of the element body 111 and the edge portions on the hole 117 side of both main surfaces. The external electrodes 116 a to 116 c (second external electrodes) are integrally provided on the outer side surface of the element body 111 and the outer peripheral edge portions of both main surfaces. Thus, both main surface portions 115a and 115c of the external electrode are provided closer to the hole 117 than both main surface portions 116a and 116c of the external electrode. By dividing the ring-shaped outer periphery and the hole 117, the side external electrodes can be easily formed. Further, since both main surface portions of the external electrodes 115a to 116c are separated into the hole 117 side and the outer peripheral side, it is easy to connect them when stacked.

  Although both main surface portions 115a and 115c of the external electrode are exposed on both main surfaces of the element body 111, the connection portion with the internal electrode 113 is not necessarily a side surface like the external electrode 115b on the above inner surface. It is not necessary to be exposed to the hole, and it can be formed by a via hole. Similarly, both main surface portions 116a and 116c of the external electrode are exposed on both main surfaces of the element body 111, but the connection portion with the internal electrode 114 is not necessarily the external electrode 116b on the inner surface. Thus, it is not necessary to be exposed to the side surface, and it can be formed by a via hole.

  Even if both main surface portions 115 a, 115 c, 116 a, and 116 c of each external electrode are rotated with respect to the central axis of the element body 111, projections in the stacking direction preferably overlap each other. Thus, when the plurality of piezoelectric elements 110 are stacked, the ranges of the external electrodes overlap, and the main surface portion 115a of one piezoelectric element 110 is connected to the main surface portion 115c of the other piezoelectric element 110. Similarly, the main surface portion 116 a of one piezoelectric element 110 is connected to the main surface portion 116 c of the other piezoelectric element 110. As a result, the piezoelectric actuator can be configured by easily connecting the external electrodes to each other. In addition, it is preferable from the point of reliable connection and simplification of a manufacturing process that the both main surface portions 115a, 115c, 116a, and 116c of each external electrode are provided in an axial symmetry.

  3A to 3C are a side sectional view and a different plan sectional view of the piezoelectric element 110, respectively. 3A is a cross-sectional view taken along the cross-section 3a in FIG. 2B, and FIGS. 3B and 3C are cross-sectional views taken along the cross-sections 3b and 3c in FIG. 3A, respectively. . The element body 111 includes internal layers 113 (first internal electrodes) and internal electrodes 114 (second internal electrodes) that are alternately stacked via the piezoelectric layers 112 and the piezoelectric layers 112.

  The external electrodes 115 a to 115 c are connected to the internal electrode 113, and the external electrodes 116 a to 116 c are connected to the internal electrode 114. Thereby, a driving voltage can be applied to each piezoelectric layer 112 of the piezoelectric element 110.

(Piezoelectric element manufacturing method)
A method for manufacturing the piezoelectric element 110 configured as described above will be described. First, as the piezoelectric element 110, an annular integrally fired element having a predetermined shape is manufactured. The piezoelectric layer 112 and the internal electrode 113 are laminated, and a layer in which the internal electrode 113 is not provided at both ends of the main surface is produced. The outer shape of the piezoelectric element 110 is processed, for example, the surface is ground, the outer diameter is cylindrical, and the inner diameter is milled to form a predetermined ring shape. The external electrode 116b on the outer surface and the external electrodes 115a, 115c, 116a, 116c on both main surfaces are applied with an electrode paste by screen printing and baked. The external electrode 115b on the inner side is formed by sucking holes from the opposite side of the printing surface during screen printing of both main surfaces so that the electrode paste adheres to the inner side of the holes and baking it.

  Insulating plates 220 and 230 with lead wires soldered on the electrodes are arranged at both ends of the piezoelectric actuator main body 100 in which a plurality of piezoelectric elements 110 manufactured in this way are stacked, and the shaft 215 is passed through the hole to position the piezoelectric actuator body 100. Do not slip. Further, pressure is applied from above the insulating plate by an elastic portion 250 such as a coil spring to ensure contact of the external electrodes 115a, 115c, 116a, and 116c on both main surfaces of the stacked piezoelectric elements 110. In this way, the piezoelectric actuator body 100 can be manufactured.

(One form of piezoelectric actuator)
FIG. 4 is a cross-sectional view showing one embodiment of the piezoelectric actuator. As shown in FIG. 4, the piezoelectric actuator 200 includes a piezoelectric actuator main body 100, a fixing part 210, a shaft 215, insulating plates 220 and 230, a displacement transmission part 240, an elastic part 250, and a case 260. The piezoelectric actuator 200 is used for a positioning device, for example.

  The fixing portion 210 fixes one end of the piezoelectric actuator main body 100 and serves as a reference for displacement. Further, the fixing portion 210 is coupled to the shaft 215 and fixes the position of the shaft 215.

  The shaft 215 is inserted into the central hole 117 of the plurality of stacked piezoelectric elements 110 and fixes the axis of the piezoelectric actuator main body 100. Thereby, the position shift on the lamination surface of the plurality of piezoelectric elements 110 can be prevented. The shaft 215 is formed to have such a length that a gap 217 is generated between the shaft 215 and the displacement transmitting portion 240 when inserted into the hole 117.

  The insulating plates 220 and 230 are provided at both ends of the piezoelectric actuator main body 100, respectively, and insulate the fixing portion 210 and the case 260 from the drive circuit. The insulating plates 220 and 230 may be insulating plates, but are preferably made of a hard material such as an alumina plate in order to ensure the characteristics of the piezoelectric actuator. The other end of the lead wire 315 having one end connected to the driving power source is connected to the displacement transmitting portion 240 side of the insulating plate 220 on the displacement end side. In addition, the other end of the lead wire 316 whose one end is connected to the driving power source is connected to the piezoelectric actuator main body 100 side of the insulating plate 230 on the fixed end side.

  5A to 5C are a plan view, a bottom view, and a side sectional view of the insulating plate 220 on the displacement end side, respectively. FIG.5 (c) is sectional drawing of the cross section 5c in Fig.5 (a) and FIG.5 (b). As shown in FIGS. 5A to 5C, a hole 227 having the same diameter as the piezoelectric element 110 is formed in the insulating plate 220. The main surface on the piezoelectric actuator main body 100 side is closer to the displacement transmission unit 240 side. The electrode 225 is integrally provided through the hole 227 to the main surface. Thus, in the insulating plate 220, both main surfaces are electrically connected at the center.

  6A to 6C are a plan view, a bottom view, and a side sectional view of the insulating plate 230 on the fixed end side, respectively. FIG.6 (c) is sectional drawing of the cross section 6c in Fig.6 (a) and FIG.6 (b). As shown in FIGS. 6A to 6C, a hole 237 having the same diameter as the piezoelectric element 110 is formed in the insulating plate 230, and the edge of the hole 237 is formed on the main surface on the piezoelectric actuator main body 100 side. An electrode 236 is provided on the outer peripheral side so as not to overlap the portion. Thereby, it is possible to connect the external electrode 116c and the drive power supply while ensuring insulation from the fixing portion 210.

  In the above example, the insulating plate 220 on the displacement end side and the insulating plate 230 on the fixed end side are respectively connected to the drive power source. However, the insulating plate on the displacement end side is simply an insulating plate, and the insulation on the fixed end side is insulated. You may connect with a drive power supply only by a board. In that case, in the insulating plate on the fixed end side, the hole side electrode and the outer peripheral side electrode are separately provided on the main surface on the piezoelectric actuator main body 100 side, and only the hole side electrode is connected to the back main surface. Then, it is connected to the case 260, and the outer peripheral side electrode is extended outside the diameter of the piezoelectric actuator main body 100 to be lead-wired. As described above, either one of the displacement end side and the fixed end side insulating plate of the piezoelectric actuator main body 100 is electrically connected to each other at the central portion. Thereby, it is possible to connect the external electrode and the drive power supply while ensuring necessary insulation.

  The displacement transmission part 240 includes a flange part 241 and a columnar part 242, is formed in an axially symmetric shape with a T-shaped cross section, and the displacement is transmitted to the outside by the tip 245 of the columnar part 242. The elastic part 250 is, for example, a spring, and presses the piezoelectric actuator main body 100 together with the displacement transmitting part 240 and the insulating plates 220 and 230 toward the fixed part 210 along the displacement direction with an elastic force. Accordingly, the external electrodes 115a, 115c, 116a, and 116c can be reliably brought into contact with each other in a continuous portion of the plurality of piezoelectric elements 110 constituting the piezoelectric actuator main body 100. The case 260 is made of metal, for example, and covers the piezoelectric actuator main body 100 and the like.

(Example)
The piezoelectric actuators of Examples and Comparative Examples were manufactured, and the breakdown voltage was measured after the characteristics were confirmed. As an example, a piezoelectric actuator having a form as shown in FIG. 1 was produced. First, as a piezoelectric element, an annular integrally fired element having an outer diameter of 6 mm, an inner diameter of 2 mm, and a thickness of 3 mm was produced. 50 layers each having a thickness of 50 μm were laminated, and 0.25 mm layers each having no internal electrode were provided at the ends on both main surfaces. The thickness was surface ground, the outer diameter was cylindrically processed, and the inner diameter was milled. The external electrode on the outer surface and the external electrode on the upper and lower surfaces were baked by applying an electrode paste by screen printing. The outer electrode on the inner surface was formed by sucking holes from the opposite side of the printing surface during screen printing of both main surfaces so that the electrode paste adhered to the inner surface of the holes, and baking this.

  An alumina plate (insulating plate) with lead wires soldered on the electrodes is placed on both ends of the piezoelectric actuator body in which the 20 piezoelectric elements fabricated in this way are stacked, and the metal shaft is passed through the hole to shift the position. I tried not to. Furthermore, pressure was applied from above the alumina plate with a coil spring to ensure contact between the upper and lower external electrodes. The displacement of the piezoelectric actuator thus fabricated was about 76 μm at 150V.

  On the other hand, as a comparative example, a piezoelectric actuator having a form as shown in FIG. 7 was produced. First, as a piezoelectric element, a rectangular parallelepiped piezoelectric element having a length and width of 6 mm and a height of 10 mm was manufactured. 170 layers each having a thickness of 50 μm were laminated, and 0.75 mm layers each having no internal electrode were provided at the ends on both main surfaces. The entire surface was ground and the electrode paste was applied as an external electrode by screen printing and baked. Six of these were stacked using an adhesive to produce a piezoelectric actuator. The displacement of the piezoelectric actuator thus fabricated was about 76 μm at 150V.

  Thirty piezoelectric actuators of Examples and Comparative Examples as described above were prepared, and overvoltage was applied to check the breakdown voltage. The comparative example was destroyed by applying a voltage of about 350 V on average. The position where the breakdown occurred was at the corner of the internal electrode. In the example, the device was broken by applying a voltage of 480 V on average. The position where the breakdown occurred was the outer edge of the internal electrode. From the above measurement results, it was proved that destruction was difficult to occur in the examples.

DESCRIPTION OF SYMBOLS 100 Piezoelectric actuator main body 110 Piezoelectric element 111 Element main body 112 Piezoelectric layer 113, 114 Internal electrode 115a-115c External electrode (1st external electrode)
116a-116c External electrode (second external electrode)
117 hole 200 piezoelectric actuator 210 fixed portion 215 shaft 217 gap 220 displacement end side insulating plate 225 electrode 227 hole 230 fixed end side insulating plate 236 electrode 237 hole 240 displacement transmission portion 245 tip portion 250 elastic portion 260 case 315, 316 lead line

Claims (5)

Piezoelectric elements that are used in a stacking direction for piezoelectric actuators,
An element body having a piezoelectric layer and first and second internal electrodes alternately stacked via the piezoelectric layer and formed in an annular shape;
A first external electrode exposed on both main surfaces of the element body and connected to the first internal electrode;
A second external electrode exposed on both main surfaces of the element body and connected to the second internal electrode;
The piezoelectric element according to claim 1, wherein both main surface portions of the first external electrode are provided closer to the hole than both main surface portions of the second external electrode.   2. The piezoelectric element according to claim 1, wherein both main surface portions of the first or second external electrode are projected in the stacking direction even if they are rotated with respect to the central axis of the element body. .   A piezoelectric actuator comprising a piezoelectric actuator body formed by stacking a plurality of the piezoelectric elements according to claim 1 or 2 on substantially the same central axis in a telescopic direction.   The piezoelectric actuator according to claim 3, wherein a shaft fixing shaft is inserted into a central hole of the plurality of stacked piezoelectric elements. Insulating plates provided at both ends of the piezoelectric actuator body, respectively,
5. The piezoelectric actuator according to claim 3, wherein the insulating plate on either the displacement end side or the fixed end side of the piezoelectric actuator main body is electrically connected to both main surfaces at the center portion. .

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