JP2015070093A - Piezoelectric actuator and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric actuator in which the insulation resistance can be enhanced, by preventing migration of Ag of the internal electrode, without increasing the number of members, and to provide a manufacturing method therefor.SOLUTION: A piezoelectric actuator 10 driving under high temperature environment includes a piezoelectric actuator body 100 where a plurality of piezoelectric elements are stacked in series, and a metal case 260 for housing the piezoelectric actuator body 100. Surface of a metallic member exposed into the case 260 is covered with an anode oxide film. Since moisture in the case 260 is absorbed by the absorption effect of the anode oxide film, migration of Ag of the internal electrode is prevented even in the driving under high temperature environment, and thereby the insulation resistance can be enhanced. Furthermore, a hygroscopic material is not required in the case 260, and complication of assembling due to increase in the number of members is prevented, thus reducing the number of steps.

Description

  The present invention relates to a piezoelectric actuator that is driven in a high-temperature environment and a method for manufacturing the same.

  As a piezoelectric actuator, there is known a piezoelectric actuator configured by covering a case with a piezoelectric actuator body in which a plurality of piezoelectric elements are connected. For example, in the piezoelectric actuator described in Patent Document 1, a shaft for shaft fixation is inserted into a piezoelectric actuator main body formed by stacking a plurality of piezoelectric elements in a telescopic direction on substantially the same central axis, and is covered with a metal case. It is configured. Such a piezoelectric actuator may be used under high humidity.

In general, when a piezoelectric actuator is driven under high humidity, Ag of the internal electrode embedded in the piezoelectric element undergoes migration, and the insulation resistance decreases. Therefore, for example, measures have been taken to increase the insulation resistance by filling and sealing an inert gas (N ₂ ) in a metal case. However, in a general sealing method, about 1 to 5% of humidity remains in the metal case. Even at this level of humidity, Ag migration tends to occur when the piezoelectric actuator is driven in a high temperature environment. On the other hand, an expensive apparatus can be introduced to further reduce the humidity inside the metal case, but the cost increases. Therefore, in the piezoelectric actuator described in Patent Document 1, the insulation resistance is improved by using a hygroscopic material in the metal case.

JP 2013-157439 A JP 2010-258025 A

  However, in the method using a hygroscopic material in the metal case as described above, the number of members increases. And when manufacturing a piezoelectric actuator, an assembly becomes complicated and the number of processes will increase.

  The present invention has been made in view of such circumstances, and provides a piezoelectric actuator capable of preventing the migration of Ag of the internal electrode and increasing the insulation resistance without increasing the number of members, and a method for manufacturing the same. Objective.

  (1) In order to achieve the above object, a piezoelectric actuator of the present invention is a piezoelectric actuator that is driven in a high-temperature environment, and includes a piezoelectric actuator body in which a plurality of piezoelectric elements are stacked in series, and the piezoelectric actuator body. A metal case to be housed, and the surface of the metal member exposed in the case is covered with an anodized film.

  As described above, in the piezoelectric actuator of the present invention, the surface of the metal member exposed in the case is covered with the anodic oxide film. Even under driving, the migration of Ag in the internal electrode can be prevented, and the insulation resistance can be improved. Further, it is not necessary to use a hygroscopic material in the case, so that the assembly is prevented from being complicated due to an increase in the number of members, and the number of steps can be reduced.

  (2) Further, the piezoelectric actuator of the present invention is provided at a fixed portion for fixing the piezoelectric actuator body at one end and at the other end of the piezoelectric actuator body, and transmits the displacement of the piezoelectric actuator body. A displacement transmitting portion; and an elastic portion that applies a compressive force to the piezoelectric actuator main body, and surfaces of the fixing portion, the displacement transmitting portion, and the elastic portion that are exposed inside the case are covered with an anodized film. It is characterized by that. Thereby, conduction to the exposed surface of the fixed portion, the displacement transmitting portion, and the elastic portion can be prevented.

  (3) Moreover, the piezoelectric actuator of the present invention is characterized in that the piezoelectric element includes an element body formed in an annular shape and an external electrode formed on a surface of the element body. In the case of using an annular piezoelectric element, the number of metal members in the case increases, so that it is effective to improve the insulation by the anodic oxide film.

  (4) Moreover, the manufacturing method of the piezoelectric actuator of the present invention is the manufacturing method of the piezoelectric actuator described above, and a step of anodizing the surface inside the case of the fixed portion, the displacement transmitting portion, and the elastic portion; Sealing the piezoelectric actuator main body, the fixed portion, the displacement transmitting portion, and the elastic portion in the case. Since the surface of the member exposed in the case is covered with the anodic oxide film in this way, the moisture in the case is absorbed by the moisture absorption effect of the anodic oxide film, so that the Ag of the internal electrode can be driven even in a high temperature environment. Migration can be prevented and the insulation resistance can be improved.

  According to the present invention, the moisture in the case is absorbed by the moisture absorption effect of the anodic oxide film, so that Ag migration of the internal electrode can be prevented and the insulation resistance can be improved even when driven in a high temperature environment. Further, it is not necessary to use a hygroscopic material in the metal case, so that the assembly is not complicated due to the increase in the number of members, and the number of processes can be reduced.

It is sectional drawing which shows one form of the piezoelectric actuator which concerns on 1st Embodiment. It is a perspective view of the piezoelectric actuator main body which concerns on 1st Embodiment. (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. (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. It is sectional drawing which shows the piezoelectric actuator which concerns on 2nd Embodiment. It is a graph which shows the result of an endurance test.

  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.

[First Embodiment]
(Piezoelectric actuator)
FIG. 1 is a cross-sectional view showing one embodiment of a piezoelectric actuator. As shown in FIG. 1, the piezoelectric actuator 10 includes a piezoelectric actuator main body 100, a fixing part 210, insulating plates 220 and 230, a displacement transmission part 240, an elastic part 250, and a case 260. The piezoelectric actuator 10 is used in a high temperature environment of 120 ° C. or higher. In the piezoelectric actuator 10, since the surface of the metal member exposed in the case 260 is covered with the anodic oxide film, Ag migration of the internal electrode is prevented by the moisture absorption effect of the anodic oxide film, and the insulation resistance is improved. Can do. Each part will be described below.

(Piezoelectric actuator body)
FIG. 2 is a perspective view of the piezoelectric actuator body 100. As shown in FIG. 2, 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 a telescopic direction.

(Piezoelectric element)
3A to 3C 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. The piezoelectric element 110 includes an element body 111 and external electrodes 115a to 116c. The shape of the element body 111 may be a polygonal ring such as an octagon or a dodecagon, or an elliptical ring. When the annular piezoelectric element 110 is used, since the number of metal members in the case 260 increases, it is effective to improve the insulation by the anodic oxide film.

  The external electrodes 115a to 115c (first external electrodes) are provided on the surface of the element main body 111. Specifically, the inner surface of the hole 117 at the center of the element main body 111 and the edge on the hole 117 side of both main surfaces. It is provided integrally with the part. 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. In addition, the connection part of both the main surface parts of an external electrode and an internal electrode can also 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. In addition, it is preferable that both main surface portions 115a, 115c, 116a, and 116c of each external electrode are provided symmetrically about the axis.

  4A to 4C are a side sectional view and a different plan sectional view of the piezoelectric element 110, respectively. 4A is a cross-sectional view taken along a cross section 4a in FIG. 3B, and FIGS. 4B and 4C are cross-sectional views taken along cross sections 4b and 4c in FIG. 4A, 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.

(Other parts)
Referring to FIG. 1, the fixing portion 210 fixes the piezoelectric actuator main body 100 at one end with a fixing plate and serves as a reference for displacement. Further, the fixing plate is coupled to the shaft 215 to fix the position of the shaft 215, and these are collectively referred to as the fixing portion 210.

  The shaft 215 is inserted into the central hole 117 of the plurality of piezoelectric elements 110 stacked in series, and fixes the axis of the piezoelectric actuator main body 100. 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 formed of a hard material such as an alumina plate. 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.

  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.

  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 compresses the piezoelectric actuator main body 100 by pressing 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. Giving power.

  The case 260 is made of metal and accommodates the piezoelectric actuator main body 100, the displacement transmission unit 240, and the fixing unit 210. The surfaces exposed to the inside of the case 260 of the fixing part 210, the displacement transmission part 240, and the elastic part 250 are covered with an anodic oxide film. The anodic oxide film has a high hygroscopic property, and absorbs moisture in the gas contained in the inert gas and moisture generated from other members such as elements when the case 260 is sealed. Thereby, conduction to the exposed surfaces of the fixed portion 210, the displacement transmitting portion 240 and the elastic portion 250 can be prevented.

  In particular, it is effective when the piezoelectric actuator 10 is used in a high temperature environment of 120 ° C. or higher, and more effective in an environment of 160 ° C. or higher. The thickness of the anodic oxide film is preferably 3 to 40 μm. When the thickness is less than 3 μm, the reliability and durability of the hygroscopic property are lowered and the amount of absorbed moisture is significantly reduced. On the other hand, when it is thicker than 40 μm, the mechanical strength of the metal member is significantly reduced.

  Further, it is not necessary to use a hygroscopic material in the case 260, so that the assembly is not complicated due to an increase in the number of members, and the number of steps can be reduced. In addition, as the metal member exposed in the case 260, specifically, an anodized metal (aluminum, titanium, zirconium, etc.) can be used.

(Method for manufacturing piezoelectric actuator)
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.

  On the other hand, members constituting other than the piezoelectric actuator main body 100 are prepared. That is, the anodizing process is performed on the surfaces inside the case 260 of the fixed portion 210, the displacement transmitting portion 240 and the elastic portion 250.

  Next, insulating plates 220 and 230 with soldered lead wires on the electrodes are arranged at both ends of the piezoelectric actuator body 100 in which the plurality of produced piezoelectric elements 110 are stacked, and the shaft 215 is passed through the hole so that the position is shifted. Do not be. 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.

  Then, the piezoelectric actuator main body 100, the fixing portion 210, the displacement transmitting portion 240, and the elastic portion 250 are sealed in the case 260. In this way, the piezoelectric actuator body 100 can be manufactured. In this way, the surface of the member exposed in the case 260 is covered with the anodic oxide film, so that moisture in the case is absorbed by the moisture absorption effect of the anodic oxide film, so that the internal electrode can be driven even in a high temperature environment. Ag migration can be prevented and the insulation resistance can be improved.

[Second Embodiment]
(Piezoelectric actuator structure)
In the above embodiment, an annular piezoelectric element is used, but a rectangular piezoelectric element may be used. FIG. 7 is a cross-sectional view showing the piezoelectric actuator 20. The piezoelectric actuator 20 includes a piezoelectric actuator main body 405, a seat 440 (fixed portion), and a case 460, and is displaced when a voltage is applied. Also in the piezoelectric actuator 20, the surface of the metal member exposed in the case 460 is covered with an anodic oxide film.

  The piezoelectric actuator body 405 includes a plurality of piezoelectric elements 410, a lead member 420, and a hemisphere 430 (displacement transmission unit). The plurality of piezoelectric elements 410 are connected to each other in series (stretching direction by voltage application) by bonding the piezoelectric elements 410 to each other at the end faces. The piezoelectric actuator body 405 has a hemisphere 430 at one end, and the other end is bonded to the seat 440 as a bottom, and expands and contracts when a voltage is applied to the multiple piezoelectric elements 410.

  The lead member 420 is made of metal and has a plate shape, and is bonded to external electrodes 415 formed on both side surfaces of the piezoelectric element 410. The pair of lead members 420 are connected to the pair of terminals 450 at the seat 440.

  In the piezoelectric actuator main body 405, a voltage is applied to the external electrode 415 through the lead member 420. The seat 440 supports the other end of the piezoelectric actuator body 405, and the hemisphere 430 is displaced by the expansion and contraction of the piezoelectric actuator body 405.

  The piezoelectric element 410 is formed in a rectangular body by alternately stacking piezoelectric layers and internal electrodes. In addition, an external electrode 415 connected to the internal electrode is provided on the side surface of the piezoelectric element 410. The piezoelectric layer is made of a piezoelectric material such as PZT. The internal electrode is made of Ag-Pd or the like.

  The case 460 covers the piezoelectric actuator main body 405 and is sealed in a seat, and has a diaphragm 465 (elastic portion) with which the hemisphere 430 comes into contact with a dome-shaped portion. The straight pipe portion of the case 460 is formed in a cylindrical shape from the center to the bottom of the case 460. A diaphragm 465 having a dome shape is formed at the tip of the case. The case 460 is made of metal and is preferably made of a material such as SUS. The seat 440 is formed in a substantially disc shape and supports the other end of the piezoelectric actuator body 405. The inside of the case 460 including the hemisphere 430, the seat 440, and the diaphragm 465 is exposed inside the case 460, and the surfaces of these members are covered with an anodized film. By absorbing moisture in the case 460 by the moisture absorption effect of the anodic oxide film, Ag migration of the internal electrode can be prevented even in driving in a high temperature environment, and the insulation resistance can be improved.

(Method for manufacturing piezoelectric actuator)
First, a piezoelectric element 410 in which piezoelectric layers and internal electrodes are alternately stacked is manufactured. Specifically, an electrode paste such as Ag or Ag-Pd is printed on a green sheet of piezoelectric ceramic, laminated, pressure-bonded, and fired. Next, the external electrode 415 connected to the internal electrode is formed on the side surface of the piezoelectric element 410 along the stacking direction. The external electrode 415 can be formed by printing and baking an electrode paste on the side surface of the piezoelectric element 410.

  An end face in the stacking direction of the obtained plurality of piezoelectric elements 410 is coated and bonded with an adhesive such as epoxy and connected in series. In this way, multiple linking is performed and the adhesive is cured. Finally, the plate-like lead member 420 made of metal is fixed to the external electrode 415, so that the piezoelectric actuator main body 405 can be manufactured.

  On the other hand, members constituting other than the piezoelectric actuator main body 405 are prepared. That is, an anodizing process is performed on the inner surface of case 460 including hemisphere 430, seat 440 and diaphragm 465. Then, the hemisphere 430 is bonded to the tip of the piezoelectric actuator body 405.

  On the other hand, the piezoelectric actuator main body 405 is installed on the seat 440, and the case 460 is covered and sealed. At this time, the lead member 420 is electrically connected to the outside through a terminal 450 inserted through the seat 440. In this way, the piezoelectric actuator 20 can be manufactured.

[Example]
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 on which the three piezoelectric elements fabricated in this way are stacked, and the metal shaft passes through the hole and the position is shifted. 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. This was sealed in a case of aluminum (alumite) anodized in an inert gas flow by welding to obtain a piezoelectric actuator of an example. On the other hand, a SUS316 metal case was sealed by welding to obtain a comparative piezoelectric actuator.

  Durability tests were performed on these piezoelectric actuators under conditions of a temperature of 120 ° C. and a DC of 150V. The criterion for defects was set to 1.0 MΩ or less. FIG. 8 is a graph showing the results of the durability test. As shown in FIG. 8, the insulation resistance of the piezoelectric actuator of the comparative example rapidly deteriorated after 750 h, and became 1.0 MΩ or less at 1000 h. On the other hand, in the piezoelectric actuator of the example using the anodized aluminum case, the tendency for the insulating property to deteriorate rapidly was not observed even after 1000 hours. As described above, it was proved that the insulating property of the piezoelectric actuator can be improved without increasing the number of members and the number of steps in the example.

DESCRIPTION OF SYMBOLS 10 Piezoelectric actuator 100 Piezoelectric actuator main body 110 Piezoelectric element 111 Element main body 112 Piezoelectric layer 113, 114 Internal electrode 115a-115c, 116a-116c External electrode 117 Hole 210 Fixing part 215 Shaft 217 Gap 220 Insulating plate 225 Electrode 227 Hole 230 Insulating plate 236 Electrode 237 Hole 240 Displacement transmission part 241 Flange part 242 Columnar part 245 Tip 250 Elastic part 260 Case 315, 316 Lead wire 405 Piezoelectric actuator body 410 Piezoelectric element 415 External electrode 420 Lead member 430 Hemisphere (displacement transmission part)
440 seat (fixed part)
450 Terminal 460 Case 465 Diaphragm (elastic part)

Claims (4)

A piezoelectric actuator that is driven in a high temperature environment,
A piezoelectric actuator body in which a plurality of piezoelectric elements are stacked in series;
A metal case for housing the piezoelectric actuator body,
The surface of the metal member exposed in the case is covered with an anodic oxide film. A fixing portion for fixing the piezoelectric actuator body at one end;
A displacement transmitting portion that is provided at the other end of the piezoelectric actuator body and transmits the displacement of the piezoelectric actuator body;
An elastic portion for applying a compressive force to the piezoelectric actuator body,
2. The piezoelectric actuator according to claim 1, wherein surfaces of the fixed portion, the displacement transmitting portion, and the elastic portion exposed inside the case are covered with an anodized film.   The piezoelectric actuator according to claim 2, wherein the piezoelectric element includes an element body formed in an annular shape and an external electrode formed on a surface of the element body. A method of manufacturing a piezoelectric actuator according to claim 2 or claim 3,
A step of anodizing the surface inside the case of the fixed portion, the displacement transmitting portion and the elastic portion;
Sealing the piezoelectric actuator main body, the fixed portion, the displacement transmitting portion, and the elastic portion in the case.

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