JP6249698B2 - Piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric actuator that is displaced by application of a voltage.

  A piezoelectric actuator is manufactured by covering a piezoelectric actuator body with multiple stacked piezoelectric elements with a metal cap and sealing the tube. In such a piezoelectric actuator, a diaphragm is formed at the tip of the cap. A hemisphere is provided at the end of the piezoelectric actuator main body so as to contact the inner surface of the diaphragm, thereby displacing the diaphragm. The hemisphere is bonded to a ceramic shim plate at the end of the piezoelectric actuator body, and the shim plate is bonded to the piezoelectric element.

  When these piezoelectric actuators are continuously driven, the diaphragm may crack, and the sealed tube may not be maintained. On the other hand, in the piezoelectric actuator described in Patent Document 1, fatigue failure is prevented by using a cap provided with an expansion / contraction part on the side surface and relaxing the stress generated in the diaphragm by the expansion / contraction part.

Japanese Patent Laid-Open No. 3-175683

  However, the expansion / contraction part is like a groove shape with the side wall inserted inward, and in order to provide it, the piezoelectric actuator body to be accommodated and the expansion / contraction part of the cap do not contact each other. It is necessary to ensure sufficient clearance during the period. And if it is going to ensure such a clearance, a piezoelectric actuator will become a large diameter shape.

  The present invention has been made in view of such circumstances, and is a piezoelectric actuator that can reduce the stress generated in the cap and prevent the cap from being damaged even when continuously driven by a compact design without increasing the diameter. The purpose is to provide.

  (1) In order to achieve the above object, a piezoelectric actuator of the present invention is a piezoelectric actuator that is displaced by application of a voltage, a plurality of piezoelectric elements connected in series, and one end fixed, A metal that is provided at an end of the piezoelectric actuator body on the displacement side and that transmits the displacement of the piezoelectric actuator body, and a bellows part that can be expanded and contracted on a side surface, and that accommodates the piezoelectric actuator body and the transmission body A cap made of metal, wherein the transmission body is accommodated in contact with the closed end side of the cap and has a small diameter portion at a position facing the bellows portion of the cap.

  Thereby, it is possible to prevent the cap from being damaged even when continuously driven by relaxing the stress generated in the cap at the bellows portion with a compact design without increasing the diameter. As a result, the tensile stress generated at the tip of the cap is relaxed and sufficient durability is obtained.

(2) Further, the piezoelectric actuator of the present invention is characterized in that a space of 1 mm or more is provided between the small diameter portion and the bellows portion. As a result, a sufficient clearance can be secured between the cap and the piezoelectric actuator body without increasing the maximum diameter of the piezoelectric actuator, and the piezoelectric actuator can be made compact. The closed end side of the cap is formed as a diaphragm that is displaced in accordance with the displacement of the transmission body. Thereby, the tensile stress which generate | occur | produces in a cap front-end | tip is relieve | moderated and sufficient durability is acquired.

  According to the present invention, it is possible to prevent the cap from being damaged even when continuously driven by relaxing the stress generated in the cap with a compact design without increasing the diameter.

It is sectional drawing which shows the piezoelectric actuator of this invention. 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.

[Piezoelectric actuator structure]
FIG. 1 is a cross-sectional view showing the piezoelectric actuator 100. The piezoelectric actuator 100 includes a piezoelectric actuator main body 105, a transmission body 130, a seat 140, and a cap 160, and is displaced when a voltage is applied.

  The piezoelectric actuator main body 105 includes a plurality of piezoelectric elements 110 and lead members 120. The plurality of piezoelectric elements 110 are connected to each other in series (stretching direction due to voltage application) by bonding the piezoelectric elements 110 to each other at the end faces. The piezoelectric actuator main body 105 has a transmission body 130 at one end, and the other end is bonded to the seat 140 as a bottom, and expands and contracts when a voltage is applied to the multiple piezoelectric elements 110.

  The lead member 120 is made of metal and formed in a plate shape, and is bonded to the external electrodes 115 formed on both side surfaces of the piezoelectric element 110. The pair of lead members 120 are connected to the pair of terminals 150 at the seat 140.

  In the piezoelectric actuator main body 105, a voltage is applied to the external electrode 115 via the lead member 120. The seat 140 fixes and supports one end of the piezoelectric actuator body 105, and the transmission body 130 is displaced by the expansion and contraction of the piezoelectric actuator body 105.

  In the piezoelectric element 110, piezoelectric layers and internal electrodes are alternately stacked. An external electrode 115 connected to the internal electrode is provided on the side surface of the piezoelectric element 110. The piezoelectric layer is made of a piezoelectric material such as PZT. The internal electrode is made of Ag-Pd or the like.

  The transmission body 130 is provided at the end of the piezoelectric actuator main body 105 on the displacement side, is accommodated in contact with the closed end of the cap 160, and transmits the displacement of the piezoelectric actuator main body 105 to the tip of the cap 160. The transmission body 130 includes a shim plate 131, a small diameter portion 132, and a hemisphere 133.

  The shim plate 131 is formed as a plate having a shape that matches the shape of the end surface of the piezoelectric actuator main body 105, and is bonded to the end of the piezoelectric actuator main body 105 on the displacement side. The shim plate 131 is preferably formed of ceramics such as alumina.

  The small diameter portion 132 is formed to have a smaller diameter than the piezoelectric actuator body 105 and is provided on the shim plate 131 at a position facing the bellows portion 162 of the cap 160. Thereby, since the stress which generate | occur | produces in the cap 160 can be relieve | moderated by the bellows part 162 by a compact design without enlarging a diameter, even if it drives continuously, the damage of the cap 160 can be prevented. The small diameter portion 132 may be a columnar shape or a rectangular body. The small-diameter portion 132 is preferably formed of a highly rigid metal such as SUS.

  It is preferable that the space between the small diameter portion 132 and the bellows portion 162 is 1 mm or more. Thus, a sufficient clearance can be secured between the cap 160 and the piezoelectric actuator body 105 without increasing the maximum diameter of the piezoelectric actuator 100, and the piezoelectric actuator 100 can be made compact.

  In addition, if the small diameter part 132 is lengthened, the part with a large clearance can also be taken long, and the bellows part 162 can be provided longer. A bellows part 162 can be added to the cap 160 provided with the diaphragm 161 as an expansion / contraction mechanism without changing the radial dimension. As a result, the tensile stress generated in the diaphragm 161 can be relaxed.

  For example, it is effective to provide the bellows part 162 so as to relieve 25 to 30% of the tensile stress generated in the diaphragm 161 with respect to the cap in which the diaphragm is damaged when the diameter is 7 to 10 mm and 5 to 7 million times. It is. In that case, the diaphragm 161 can obtain sufficient durability so that fatigue failure does not occur even if the fatigue limit exceeds 10 million times.

  Further, in the above configuration, since the piezoelectric element 110 receives preload through the small diameter portion 132 having a larger contact area than the hemisphere 133, there is also an effect that the compressive stress caused by the preload generated in the piezoelectric element 110 is widely dispersed. .

  The hemisphere 133 is made of, for example, metal and is bonded onto the small diameter portion 132. The hemisphere 133 is in contact with the inner surface of the dome-shaped portion on the closed end side of the cap 160, and transmits the displacement of the piezoelectric actuator main body 105 to the distal end portion of the cap 160.

  The cap 160 is made of metal, covers the transmission body 130 and the piezoelectric actuator main body 105, and is sealed to the seat 140 in a state in which these are accommodated. A diaphragm 161 having a dome shape is formed at the distal end portion (closed end side) of the cap 160.

  The hemisphere 133 is in contact with the dome-shaped portion of the diaphragm 161 and is displaced according to the displacement of the transmission body. Thereby, the tensile stress which generate | occur | produces at the front-end | tip of the cap 160 is relieved, and sufficient durability is acquired. The straight pipe portion on the side surface of the cap 160 is formed in a cylindrical shape, and has a bellows portion 162 that can be expanded and contracted. The cap 160 is preferably formed of a material such as SUS.

  The seat 140 is formed in a substantially disc shape and supports the other end of the piezoelectric actuator main body 105. The seat 140 is joined to the open end of the cap 160. A terminal 150 is inserted into the seat 140 from the outside, and the lead member 120 is connected to the terminal 150 at the seat 140.

[Method of manufacturing piezoelectric actuator]
First, the piezoelectric element 110 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 115 connected to the internal electrode is formed on the side surface of the piezoelectric element 110 along the stacking direction. The external electrode 115 can be formed by printing and baking an electrode paste on the side surface of the piezoelectric element 110.

  An end face in the stacking direction of the obtained plurality of piezoelectric elements 110 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. Then, the plate-like lead member 120 made of metal is fixed to the external electrode 115, so that the piezoelectric actuator main body 105 can be manufactured in a multiple connection.

  On the other hand, the transmission body 130 is produced. A metal small diameter portion 132 is bonded onto a shim plate 131 having a predetermined thickness. The diameter of the small diameter portion 132 is designed and processed in advance in consideration of the clearance with the cap 160. Further, the hemisphere 133 is bonded onto the metal small diameter portion 132. The shim plate 131 side of the transmission body 130 thus obtained is bonded to one end of the piezoelectric actuator main body 105.

  The other end side of the piezoelectric actuator main body 105 is installed on the seat 140, and the cap 160 is put on the transmission body 130 and the piezoelectric actuator main body 105 and sealed. The lead member 120 is electrically connected to the outside through a terminal 150 inserted through the seat 140. In this way, the piezoelectric actuator 100 can be manufactured.

[Examples and Comparative Examples]
Next, a piezoelectric actuator was designed and simulated. As an example, the piezoelectric actuator 100 shown in FIG. 1 was used. Further, as a comparative example, a piezoelectric actuator 200 shown in FIG. 2 was used as follows.

  FIG. 2 is a cross-sectional view showing a piezoelectric actuator 200 of a comparative example. The piezoelectric actuator 200 includes a piezoelectric actuator body 205, a transmission body 230, a seat 240, and a cap 260.

  The piezoelectric actuator body 205 is composed of a plurality of piezoelectric elements 210 and lead members 220 connected in series with each other. The piezoelectric actuator main body 205 has a transmission body 230 at one end, and the other end is bonded to the seat 240 as a bottom. In the piezoelectric element 210, piezoelectric layers and internal electrodes are alternately stacked, and external electrodes 215 are provided on the side surfaces. The lead member 220 is bonded to the external electrode 215 and connected to the pair of terminals 250 at the seat 240.

  The transmission body 230 has a shim plate 231 and a hemisphere 233, and the hemisphere 233 is bonded onto the shim plate 231. Thus, the transmission body 230 does not have a small diameter part. The cap 260 is made of metal, covers the transmission body 130 and the piezoelectric actuator main body 205, and is sealed by the seat 240 in a state in which these are accommodated. A diaphragm 261 having a dome shape is formed at the tip portion (closed end side) of the cap.

The following table shows conditions common to both the examples and the comparative examples.

  In the example, the depth d1 of each valley of the bellows portion was 1.0 mm, and in the comparative example, the depth d2 of each valley of the bellows portion was 0.2 mm, and the same displacement was given. As a result, in the comparative example, the tensile stress of the diaphragm was 630 MPa, whereas in the example, the tensile stress of the diaphragm was 470 MPa. Thus, it has been demonstrated that the piezoelectric actuator 100 can reduce the tensile stress generated in the diaphragm.

  Next, caps of these shapes were actually manufactured and subjected to a continuous driving test. As a result, the caps of the comparative examples were broken at an average of about 5 million times, whereas the caps of the examples were 10 million times. No breakage was observed even after exceeding.

DESCRIPTION OF SYMBOLS 100 Piezoelectric actuator 105 Piezoelectric actuator main body 110 Piezoelectric element 115 External electrode 120 Lead member 130 Transmission body 131 Shim plate 132 Small diameter part 133 Hemisphere 140 Seat 150 Terminal 160 Cap 161 Diaphragm 162 Bellows part 200 Piezoelectric actuator 205 Piezoelectric actuator main body 210 Piezoelectric element 215 External Electrode 220 Lead member 230 Transmitter 231 Shim plate 233 Hemisphere 240 Seat 250 Terminal 260 Cap 261 Diaphragm

Claims (3)

A piezoelectric actuator that is displaced by application of a voltage,
A piezoelectric actuator body in which a plurality of piezoelectric elements are connected in series and one end is fixed;
A transmission body provided at an end portion on a displacement side of the piezoelectric actuator body, and transmitting the displacement of the piezoelectric actuator body;
A bellows part that can be expanded and contracted on a side surface; and a metal cap that houses the piezoelectric actuator body and the transmission body,
The transmission body includes a hemispherical portion abutting the closed end side of the cap, is provided at a position opposite to the bellows part of the cap, have a, and a small diameter portion which is bonded to the hemispherical portion, the piezoelectric actuator A piezoelectric actuator characterized in that a cross-sectional area of the small-diameter portion by a plane perpendicular to a displacement direction of the main body is larger than a cross-sectional area of the hemispherical portion and smaller than a cross-sectional area of the piezoelectric actuator main body .   The piezoelectric actuator according to claim 1, wherein a space of 1 mm or more is provided between the small diameter portion and the bellows portion.   3. The piezoelectric actuator according to claim 1, wherein a closed end side of the cap is formed as a diaphragm that is displaced in accordance with the displacement of the transmission body.

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