JP3535111B2 - Piezo actuator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator used in, for example, a precision positioning device, a switching element or the like.

[0002]

2. Description of the Related Art Conventionally, as a form of a piezoelectric actuator, as shown in FIG.
The electrodes 92a and 92b are formed on both main surfaces of the piezoelectric plate 91.
There is known a monomorph element 90 in which a piezoelectric element 93 that is polarized in the thickness direction is attached to one of the main surfaces of a thin metal plate 94 having a predetermined thickness called a shim material. One end of the monomorph element 90 in the longitudinal direction is fixed at a predetermined position by using fixing means 96.

The monomorph element 90 is, for example, a piezoelectric plate 9
When an electric field is applied in the same direction as the polarization direction of No. 1, the piezoelectric plate 91 becomes thick due to thickness-longitudinal displacement, and conversely, the longitudinal length of the piezoelectric plate 91 becomes short due to thickness-lateral displacement. Such displacement occurs. At this time, since the piezoelectric element 93 is attached to the metal plate 94, bending displacement occurs so as to be inside the arc on the piezoelectric element 93 side (FIG. 6B). Further, when an electric field is applied in a direction opposite to the polarization direction of the piezoelectric plate 91, displacement occurs such that the thickness of the piezoelectric plate 91 becomes thin and the longitudinal length of the piezoelectric plate 91 extends. In this case, bending displacement occurs such that the piezoelectric element 93 side is outside the arc (FIG. 6C).

The amount of displacement of the tip of the monomorph element 90 can be controlled by the voltage applied to the piezoelectric element 93, and thus the monomorph element 90 is used as a positioning device or a switching element. In the case of a so-called bimorph element having a structure in which piezoelectric elements are attached to both main surfaces of a shim material, when the longitudinal length of one piezoelectric element is extended, the longitudinal length of the other piezoelectric element is By bonding the piezoelectric element to the shim material so that the length becomes shorter, it becomes possible to obtain a larger displacement.

[0005]

In the conventional monomorph element and the like, it has been generally accepted that a metal plate is used as the shim material. However, the metal plate made of a single material has a problem in that it is likely to generate a resonance vibration peculiar to the metal plate and has a poor vibration damping property. If the vibration damping property of the monomorph element or the like is poor, it causes various problems that the response speed is slow and the positioning accuracy is lowered.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a piezoelectric actuator having improved vibration damping property.

[0007]

That is, according to the present invention, there is provided a piezoelectric actuator in which a flat plate-shaped piezoelectric element is bonded to a reinforcing plate, wherein the reinforcing plate is a sheet or a material made of materials having different elastic moduli. There is provided a piezoelectric actuator having a structure in which foils are laminated in a thickness direction.

In such a piezoelectric actuator, the reinforcing plates are made of materials having different elastic moduli such as metal and resin.
It is preferable that. Further, as the reinforcing plate, it is preferable to use a printed wiring board in which a conductor, preferably a metal plate such as a metal foil is provided on at least one of the main surfaces of the sheet-shaped resin. A liquid crystal polymer resin is preferably used as this resin. By using the reinforcing plate made of such materials having different elastic moduli, it is difficult for the inherent resonance vibration to occur, and the vibration damping property at the time of driving the piezoelectric actuator is enhanced. The piezoelectric actuator of the present invention is preferably used as a bimorph structure in which piezoelectric elements are bonded to both main surfaces of such a reinforcing plate.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a sectional view showing the structure of a bimorph element 10 which is an embodiment of a piezoelectric actuator of the present invention, FIG. 2 is an explanatory view showing the displacement of the form when driving the bimorph element 10 by the DC voltage, Figure 3 is an explanatory view showing the displacement of the form in the case of driving by the AC voltage bimorph element 10.

The bimorph element 10 is constructed by bonding piezoelectric elements 12a and 12b to both main surfaces of a reinforcing plate 11, and the reinforcing plate 11 has metal foils (metal plates) 14a to both main surfaces of a resin sheet 13. It has a laminated structure in which 14b is laminated. Further, the piezoelectric element 12a has electrodes 16a.1 on both main surfaces of a flat plate-shaped piezoelectric body 15a having a predetermined thickness.
6a ′ is formed, and similarly, the piezoelectric element 12
b has a structure in which electrodes 16b and 16b 'are formed on both main surfaces of a plate-shaped piezoelectric body 15b having a predetermined thickness.

Examples of the material of the resin sheet 13 include a liquid crystal polymer resin. When the liquid crystal polymer resin is used, it is possible to bond the metal foils 14a and 14b by heat fusion. Then, the resin sheet 13 and the metal foil 14a-1
It is difficult to separate from 4b, and the reliability is improved.

Copper foil is preferably used as the metal foils 14a and 14b, but aluminum foil or the like may be used. Since a laminate sheet obtained by laminating a copper foil on a liquid crystal polymer resin sheet is easily available as a so-called printed wiring board, it is possible to reduce production cost and improve productivity by using such a laminate sheet. be able to.

In the present invention, by using the reinforcing plate 11 having a structure in which materials having different elastic moduli are laminated in the thickness direction, generation of resonance vibration is suppressed and vibration damping property is enhanced.
It is possible to improve the responsiveness when the bimorph element 10 is driven.

A fixing jig 19 is attached to one end of the reinforcing plate 11 in the longitudinal direction. When the bimorph element 10 is driven by applying a predetermined voltage to the piezoelectric elements 12a and 12b, the fixing jig 19 is attached. The other end that is not attached is displaced.

As the piezoelectric bodies 15a and 15b, lead zirconate titanate-based piezoelectric ceramics having high piezoelectric characteristics are preferably used. Electrodes 16a, 16a ', 16b
16b ′ can be formed by printing an electrode paste such as a silver paste using a screen printing method or the like on both main surfaces of a plate-shaped piezoelectric ceramic, and then firing it. Electrode 1
When the screen printing method is used, the thickness of 6a, 16a ', 16b, and 16b' is generally 2 to 8 m.

Usually, the piezoelectric elements 12a and 12b have substantially the same shape, and either an insulating adhesive or a conductive adhesive is used to bond the piezoelectric elements 12a and 12b to the reinforcing plate 11. When an insulating adhesive is used, the electrode 16a 'of the piezoelectric element 12a and the metal foil 14a of the reinforcing plate 11 are used.
The thickness of the adhesive layer is thinned so that part of the adhesive layer contacts with the electrode 16b ′ of the piezoelectric element 12b and part of the metal foil 14b of the reinforcing plate 11. The adhesive layer is not shown in FIGS. 1 to 3.

By short-circuiting the metal foils 14a and 14b and the electrode 16a in the piezoelectric element 12a and the electrode 16b in the piezoelectric element 12b and connecting these terminals to a power source, the piezoelectric elements 12a and 12b are connected. It can be driven at the same time. At this time, electric fields in opposite directions are applied to the piezoelectric bodies 15a and 15b with the reinforcing plate 11 sandwiched therebetween, so that the piezoelectric elements 12a and 12b have the same polarization directions of the piezoelectric bodies 15a and 15b. To do.

Thus, for example, as shown in FIG. 2, when a DC voltage is applied to the piezoelectric elements 12a and 12b,
In the piezoelectric element 12a, the direction of polarization in the piezoelectric body 15a and the direction of the electric field match each other.
If a contracts in the longitudinal direction due to the thickness-transverse effect, the piezoelectric element 12b has a polarization direction and an electric field direction opposite to each other in the piezoelectric element 12b. As a result, the bimorph element 10 is warped and deformed so that the tip of the reinforcing plate 11 moves toward the piezoelectric element 12a.

Further, as shown in FIG. 3, the piezoelectric element 12a
When the AC voltage is applied to 12b, the piezoelectric element 12
When one of the a and 12b expands in the longitudinal direction, the other contracts in the longitudinal direction, so that the tip of the reinforcing plate 11 is located at the piezoelectric element 1.
The entire bimorph element 10 is bent and displaced depending on the frequency of the AC voltage so as to be alternately moved to the 2a side and the piezoelectric element 12b side. The reinforcing plate 1 for the piezoelectric elements 12a and 12b
Adhesion to No. 1 is performed in consideration of the polarization direction after polarization of the piezoelectric bodies 15a and 15b in the piezoelectric elements 12a and 12b.

Next, FIG. 4 shows a characteristic comparison between the above-described bimorph element 10 according to the present invention and a conventional bimorph element. FIG. 4A is an explanatory diagram showing the driving characteristics of the bimorph element 10 having the above-described structure, and FIG.
(B) shows the piezoelectric element 12a as shown in the cross-sectional view of FIG.
FIG. 11 is an explanatory diagram showing the driving characteristics of a conventional bimorph element 80 using the piezoelectric elements 82a and 82b having the same structure as the above, using a metal plate 81 as a shim material, both of which are applied with a predetermined DC voltage. -It shows the operating characteristics from the state where the bending displacement is caused to 80 to the time when the voltage application is stopped and the apparatus stands still.

The bimorph element 10 has a length of 50.
mm, Width 8 mm, Thickness 180 μm Piezoelectric element 12a ・ 1
2b is bonded to a reinforcing plate 11 having a length of 55 mm, a width of 8 mm and a thickness of 200 μm. The reinforcing plate 11 has a thickness of 5 μm on both main surfaces of a liquid crystal polymer resin sheet having a thickness of 100 μm.
It is a printed wiring board in which copper foil of 0 μm is bonded.
On the other hand, the bimorph element 80 has a length of 50 mm and a width of 8 m.
The piezoelectric element 12a, 12b having a thickness of m and a thickness of 180 μm is bonded to a 42 alloy plate having a length of 55 mm, a width of 8 mm and a thickness of 50 μm.

From FIGS. 4 (a) and 4 (b), it takes about 60 milliseconds (ms) to stop the vibration in the conventional bimorph element 80, but in the bimorph element 10 according to the present invention, it is about 16 mm. It can be seen that the vibration stops in seconds (ms) and that it has excellent vibration damping properties. Due to such vibration damping property, the bimorph element 10 according to the present invention is said to have a short time to settle to a predetermined displacement amount even when the bimorph element 10 is driven by a predetermined DC voltage or AC voltage. Shows good responsiveness. Therefore, for example, when precision positioning is performed by the bimorph element 10, the positioning accuracy is improved, and the bimorph element 10 is also improved.
When is used as a switching element, the reliability of switching on / off is enhanced.

Although the embodiment of the piezoelectric actuator of the present invention has been described above by taking the bimorph element as an example, the present invention is not limited to the above-mentioned embodiment, and it goes without saying that the monomorph element shown in FIG. 6 is used. Can also be applied to. Also, instead of the metal foils 14a and 14b,
It is also possible to use a reinforcing plate in which another conductor, for example, a carbon sheet or a conductive resin sheet is attached to a resin sheet 13 such as a liquid crystal polymer resin, and the resin sheet 13 has a laminated structure composed of a plurality of resin sheets. It is also possible.

Furthermore, as long as it is possible to drive the piezoelectric elements 12a and 12b, a conductor is not necessarily required on the surface of the reinforcing plate 11. That is, a reinforcing plate having a laminated structure in which a metal foil or a metal plate is sandwiched between resin sheets may be used, and the reinforcing plate 11 does not necessarily include a conductor. As long as it is a laminated body of materials having different elastic moduli, the material forming each layer may be a composite material formed by mixing a plurality of types of materials.

[0025]

As described above, according to the piezoelectric actuator of the present invention, resonance vibration is less likely to occur by using a reinforcing plate in which materials having different elastic moduli are laminated in the thickness direction, so that the vibration damping property is improved. , Responsiveness is improved. Thus, when the piezoelectric actuator of the present invention is used as a positioning device, highly accurate positioning can be performed in a short time, and when it is used as a switching element, the reliability of on / off switching operation is improved. The remarkable effect that the property is enhanced is exhibited.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a piezoelectric actuator of the present invention.

FIG. 2 is an explanatory view showing a displacement form of the piezoelectric actuator shown in FIG.

FIG. 3 is another explanatory view showing a displacement form of the piezoelectric actuator shown in FIG.

FIG. 4 is an explanatory diagram comparing the damping characteristics of a bimorph element according to the present invention and a conventional bimorph element.

FIG. 5 is a cross-sectional view showing the structure of a conventional bimorph element.

FIG. 6 is a sectional view showing a structure of a conventional monomorph element.

[Explanation of symbols] 10; Bimorph element 11; Reinforcing plate 12a and 12b; piezoelectric element 13; Resin sheet 14a and 14b; metal foil 15a and 15b; piezoelectric body 16a, 16a ', 16b, 16b'; electrodes 19; Fixing jig 80; Bimorph element 81; Metal plate 82a / 82b; piezoelectric element 90; Monomorph element 91; Piezoelectric plate 92a / 92b; electrodes 93; Piezoelectric element 94; Metal plate 96; fixing means

Claims (5)

(57) [Claims] 1. A piezoelectric actuator in which a flat plate-shaped piezoelectric element is bonded to a reinforcing plate, wherein the reinforcing plate is a sheet or a sheet made of materials having different elastic moduli.
Is a piezoelectric actuator having a structure in which foils are laminated in the thickness direction. 2. A material having a different elastic modulus that constitutes the reinforcing plate.
The piezoelectric actuator according to claim 1, wherein the material is a resin and a metal . 3. The piezoelectric actuator according to claim 1, wherein the reinforcing plate is a printed wiring board in which a conductor is provided on at least one main surface of a sheet-shaped resin. 4. A piezoelectric actuator according to claim 2 or claim 3 wherein the resin is characterized in that it is a liquid crystal polymer resin. 5. The piezoelectric actuator according to any one of claims 1 to 4, characterized in that it comprises a bimorph structure in which the bonding the piezoelectric element on both main surfaces of the reinforcing plate.