JP6135123B2 - Piezoelectric element unit and piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric element unit and a piezoelectric actuator that expand and contract by application of a voltage.

  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. 5A to 5C 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.

  In contrast, a plurality of annular piezoelectric elements are stacked in a telescopic direction on substantially the same central axis to form a piezoelectric actuator body, and a shaft fixing shaft is inserted into the central hole of the stacked piezoelectric elements. It is conceivable to construct a piezoelectric actuator. FIG. 6 is a cross-sectional view showing a comparative piezoelectric actuator 600 formed by inserting a shaft 615 through a hole of an annular piezoelectric element 610.

  In the example illustrated in FIG. 6, a spring 650 is disposed between the cap 660 and the piezoelectric element 610 that are covered with the piezoelectric actuator 600, and preload is applied to the piezoelectric element 610. In such a configuration, the spring 650 for applying the internal preload needs to be suppressed by the cap 660, and the state of the series of piezoelectric elements cannot be confirmed without the cap 660.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a piezoelectric element unit and a piezoelectric actuator that can be easily assembled and can easily check the state of the piezoelectric element.

  (1) In order to achieve the above object, a piezoelectric element unit of the present invention is a piezoelectric element unit that expands and contracts by application of a voltage, and is formed in a ring shape, and a series of piezoelectric elements stacked in an expansion and contraction direction, and a protrusion At one end, inserted into the communication hole of the series of piezoelectric elements, the shaft having the projections hung on the first end face of the series of piezoelectric elements, and the second end face of the series of piezoelectric elements. It is characterized by comprising: an elastic body that applies pressure; and a support that is fixed to the other end of the shaft and supports the elastic body.

  Thus, the piezoelectric element unit of the present invention can apply a preload to a series of piezoelectric elements with a simple structure of a shaft, an elastic body, and a support. Thereby, the assembly of the piezoelectric actuator is facilitated, and the state of the piezoelectric element can be easily confirmed. In addition, since the piezoelectric element is formed in an annular shape, stress is not concentrated locally, and it is difficult for destruction to occur.

  (2) Further, in the piezoelectric element unit of the present invention, the support is fixed by a function of allowing the slide in one direction with respect to the shaft and restraining the slide in the other direction. Yes. Accordingly, the piezoelectric element unit can be formed by easily applying a preload to the series of piezoelectric elements by sliding the support.

  (3) Further, in the piezoelectric element unit of the present invention, the protrusion is formed in a hemispherical shape, and is hung on the first end face of the series of piezoelectric elements on the base side of the hemisphere, It is characterized by transmitting the displacement of the series of piezoelectric elements. Thereby, a preload mechanism and a displacement transmission mechanism can be realized with a simple structure, and the piezoelectric element unit can be made compact.

  (4) Moreover, the piezoelectric actuator of this invention accommodates said piezoelectric element unit, the said support tool, and an elastic body inside, and has a countersink hole which fixes the 2nd end surface of a series of said piezoelectric element. And a cap that covers the piezoelectric element unit and is sealed in the seat. Thereby, a part of a preload mechanism can be accommodated in the seat which fixes the end surface of a series of piezoelectric elements, and a piezoelectric actuator can be made compact.

  (5) Moreover, the piezoelectric actuator of the present invention is characterized in that the seat has a terminal insertion hole which is inserted with a terminal and sealed with glass. Thereby, the countersink hole is provided by utilizing the height of the seat provided with the terminal insertion hole, and the structure of the seat can be effectively used.

  According to the present invention, the piezoelectric actuator can be easily assembled and the state of the piezoelectric element can be easily confirmed. In addition, since the piezoelectric element is formed in an annular shape, stress is not concentrated locally, and it is difficult for destruction to occur.

It is sectional drawing which shows the piezoelectric element unit of this invention. (A)-(c) is a perspective view of a piezoelectric element, and a different plane sectional view, respectively. It is sectional drawing which shows the piezoelectric actuator of this invention. It is a side view which shows each component of a piezoelectric actuator. (A)-(c) is the perspective view of the conventional actuator main body, the perspective view of a piezoelectric element, and sectional drawing of a piezoelectric element, respectively. It is sectional drawing which shows the piezoelectric actuator of a comparative example.

  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 element unit)
FIG. 1 is a cross-sectional view showing the piezoelectric element unit 100. The piezoelectric element unit 100 is a component constituting a piezoelectric actuator, and expands and contracts when a voltage is applied. As shown in FIG. 1, the piezoelectric element unit 100 includes a series of piezoelectric elements 110, a washer 120, a shaft 130, a disc spring 140 (elastic body), and a push nut 150 (support).

  The piezoelectric elements 110 are formed in an annular shape and are stacked in the expansion / contraction direction. Since a plurality of piezoelectric elements are stacked on substantially the same central axis, a large displacement can be obtained. Details of the piezoelectric element 110 will be described later.

  The washer 120 is formed as a plate smaller than the diameter of the piezoelectric element 110, and is provided with a hole equal to or larger than the hole of the piezoelectric element 110. Two washers 120 are provided on both end faces of the series of piezoelectric elements 110. The washer 120 is made of alumina, for example. The washer 120 is not necessarily provided, but is preferably provided for fixing the piezoelectric element unit 100 and for electrical insulation.

  The shaft 130 has a protrusion 132 at one end, and is inserted through the communication holes of the series of piezoelectric elements 110. The shaft 130 has a protrusion 132 hung on an end surface 112 (first end surface) of the series of piezoelectric elements 110. The protrusion 132 is formed in a hemispherical shape, is hung on the end face 112 of the series of piezoelectric elements 110 on the base side of the hemisphere, and transmits the displacement of the series of piezoelectric elements 110 on the top side of the hemisphere.

  Thereby, a preload mechanism and a displacement transmission mechanism can be realized with a simple structure, and the piezoelectric element unit 100 can be made compact. Note that “the protrusion 132 is hung on the end face of the piezoelectric element 110” is not only the case where it is hung directly on the end face of the piezoelectric element 110 but also the case where it is hung indirectly via the washer 120. Including.

  The disc spring 140 (elastic body) applies a pressing force to the end surface 114 (second end surface) of the series of piezoelectric elements 110 via the washer 120. Instead of this, the disc spring 140 may be a wave washer, for example.

  The push nut 150 (support) is fixed to the other end of the shaft 130 and supports the disc spring 140. The push nut 150 allows the shaft 130 to slide in one direction and restrains the slide in the other direction. It is fixed to the shaft 130 by such a function. When assembling the piezoelectric actuator, the push nut 150 can be slid with respect to the shaft 130 and the disc spring 140 can be pushed toward the piezoelectric element 110 to easily apply a preload to the series of piezoelectric elements 110. The push nut 150 may be a screw or a retaining ring instead of the push nut 150 as long as it can be easily fixed to the shaft 130.

  The piezoelectric element unit 100 can apply a preload to the series of piezoelectric elements 110 with a simple structure using these components. As a result, the assembly of the piezoelectric actuator is facilitated, and the state of the piezoelectric element 110 can be easily confirmed when the piezoelectric element unit 100 is assembled.

(Piezoelectric element)
2A to 2C are a perspective view and a different plan sectional 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 an external electrode 115.

  The element body 111 is formed in an annular shape. As a result, the stress is not concentrated locally, and it is difficult for destruction to occur. The shape of the element body 111 is most preferably an annular shape, but may be a polygonal ring such as an octagon or an elliptical ring. The element body 111 includes internal electrodes 113a and internal electrodes 113b that are alternately stacked via piezoelectric layers and piezoelectric layers.

  The external electrode 115 is integrally provided on the outer surface of the element body 111. The external electrode 115 is connected to the internal electrode 113a via the connection portion 114a, and the other external electrode is connected to the internal electrode 113b via the connection portion 114b. Thereby, a driving voltage can be applied to each piezoelectric layer of the piezoelectric element 110 via the external electrode 115. The piezoelectric element 110 includes a protective layer 117 that is provided on the end face side and does not expand and contract, and an electrode layer 118 that is provided on the center side and expands and contracts when a voltage is applied.

(Piezoelectric actuator)
FIG. 3 is a cross-sectional view showing the piezoelectric actuator. The piezoelectric actuator 200 includes the piezoelectric element unit 100, a seat 210, and a cap 220.

  The seat 210 has a counterbore hole 213. The counterbore hole 213 accommodates the disc spring 140 and the push nut 150 inside, and fixes the end surface 114 (second end surface) of a series of piezoelectric elements. The seat 210 has a terminal insertion hole 215 that is inserted through the terminals 219a and 219b and sealed with glass 216. Thereby, the counterbore hole 213 is provided by utilizing the height of the seat 210 provided with the terminal insertion hole 215, and the structure of the seat 210 can be effectively used.

  The cap 220 covers the piezoelectric element unit 100 and is sealed to the seat 210 by welding. Thereby, a part of the preload mechanism can be accommodated in the seat 210, and the piezoelectric actuator 200 can be made compact.

(Method for manufacturing piezoelectric actuator)
A method for manufacturing the piezoelectric actuator 200 configured as described above will be described. FIG. 4 is a schematic view showing each part of the piezoelectric actuator 200.

  First, the annular piezoelectric element 110 onto which the external electrodes 115 and 116 are baked is manufactured. On the other hand, a shaft 130 with a hemispherical protrusion is prepared, and a washer 120, a series of piezoelectric elements 110, a washer 120, a disc spring 140, and a push nut 150 are passed through the shaft 130 in this order, and the push nut 150 is lightly pushed and temporarily fixed. . Thereafter, after adjusting the position of the external electrode, the push nut 150 is further pushed in so as to apply a predetermined pressure to form a unit.

  Next, a countersink 214 having a diameter of the washer 120 is provided on the seat 210, a countersink 214 larger than the diameter of the washer 120 is provided, and a countersink hole 213 is provided. An adhesive is applied to the counterbore 214 to bond the piezoelectric element unit 100. Then, the lead wires 171 and 172 connected to the terminals 219 a and 219 b of the seat 210 are connected to the external electrodes 115 and 116. Then, the cap 220 is put on the piezoelectric element unit 100 to seal the cap 220 and the seat 210.

(Example)
The piezoelectric actuator 200 of the example was manufactured and the operation was confirmed. First, an integrally fired piezoelectric 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 layers having no internal electrode were provided on the top and bottom each by 0.25 mm. Thickness was surface ground and outer diameter was cylindrical. The inner diameter was drilled before firing and not processed after firing. The internal electrodes were exposed at different portions of the side surface every other layer, and the external electrodes were baked.

  A shaft with a diameter of φ1.95mm with a φ3.2mm hemisphere (protrusion) was prepared. Pass the washers, 20 piezoelectric elements, washers, two disc springs, and a retaining ring in this order to lighten the retaining ring. The indentation was temporarily fixed. A CA retaining ring manufactured by Taiyo Stainless Spring Co., Ltd. was used as the retaining ring. Thereafter, after adjusting the position of the external electrode, the retaining ring was further pushed in so as to apply a predetermined pressure to form a unit.

  Although the washer may not be provided, since the area fixed to the seat is not the entire surface, it is preferably hard to suppress deformation of the piezoelectric element, and an insulator is preferable to ensure insulation between the seat and the external electrode. In order to satisfy these requirements, the washer was made of alumina.

  The seat was provided with a countersink with a washer diameter, and further a countersink hole with a countersink larger than the washer diameter. And the adhesive agent was apply | coated to the countersink part of a washer diameter, and the piezoelectric element unit was adhere | attached.

  Then, the lead wire was soldered to the external electrode together with the seat lead wire. The unit manufactured in this way is not yet lowered in reliability even if it is energized because it is pre-loaded before the metal cap is sealed. In the case of a defective product, it can be removed before sealing the metal cap.

  A comparative piezoelectric actuator 600 was also produced (see FIG. 6). In the piezoelectric actuator 600, the length of the spring is added to the element length. Compared with the piezoelectric actuator 600 as described above, the piezoelectric actuator 200 of the example can store the spring portion in the seat, so that the total length can be shortened by about 3 mm.

DESCRIPTION OF SYMBOLS 100 Piezoelectric element unit 110 Piezoelectric element 111 Element main body 112 End surface 113a, 113b Internal electrode 114a, 114b Connection part 115 External electrode 117 Protective layer 118 Electrode layer 120 Washer 130 Shaft 132 Projection 140 Disc spring 150 Push nut 200 Piezoelectric actuator 210 Seat 213 Seat Counterbore 220 cap

Claims (4)

A piezoelectric element unit that expands and contracts by application of a voltage, and has a series of piezoelectric elements formed in an annular shape and stacked in an expansion and contraction direction, and a protrusion at one end, and is inserted into a communication hole of the series of piezoelectric elements, A shaft in which the protrusion is hung on a first end face of a series of piezoelectric elements; an elastic body that applies a pressing force to a second end face of the series of piezoelectric elements; and the elastic body fixed to the other end of the shaft. A piezoelectric element unit comprising: a support that supports the body ;
A seat having a counterbore hole for accommodating the support and the elastic body therein and fixing the second end face of the series of piezoelectric elements;
A piezoelectric actuator comprising: a cap that covers the piezoelectric element unit and is sealed in the seat. The piezoelectric actuator according to claim 1, wherein the support is fixed by a function of permitting sliding in one direction relative to the shaft and restraining sliding in the other direction. The protrusion is formed in a hemispherical shape, is hung on the first end face of the series of piezoelectric elements on the base side of the hemisphere, and transmits the displacement of the series of piezoelectric elements on the top side of the hemisphere. The piezoelectric actuator according to claim 1 or 2. The piezoelectric actuator according to any one of claims 1 to 3, wherein the seat has a terminal insertion hole which is inserted with a terminal and sealed with glass.

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