JPH05226719A - Laminated piezoelectric actuator - Google Patents

Abstract

PURPOSE:To get a piezoelectric actuator large in displacement without bonding it by putting the direction of the displacement of an actuator in parallel with or a right angle to a band-shaped electrode. CONSTITUTION:A band-shaped electrode 11 is made as a first band-shaped electrode on one side of a piezoelectric ceramic sheet 1. A full-face electrode 12 is made at the end of the piezoelectric ceramic sheet 1, and a first electrode layer is made together with the first band-shaped electrode. A band-shaped electrode 13 is made as a second band-shaped electrode on one side of a piezoelectric ceramic sheet 2. A full-face electrode 14 is made in the position opposite to the full-face electrode 12 of the first electrode layer, thus a second electrode layer is made together with the second band-shaped electrode. These piezoelectric ceramic sheets 1 and piezoelectric ceramic sheets 2 are stacked in plural numbers alternately so that the other band-shaped electrode may be positioned in nearly center position of the other band-shaped electrode. The band-shaped electrodes 11 and 13 and the full-face electrodes 12 and 14 are connected, respectively, in parallel to external electrodes.

Description

Detailed Description of the Invention

[0001]

The present invention utilizes the inverse piezoelectric effect,
The present invention relates to a laminated piezoelectric actuator that converts electrical input energy into mechanical energy such as displacement and force.

[0002]

2. Description of the Related Art FIG. 5 is a schematic view of the structure of a conventional laminated piezoelectric actuator. Referring to FIG. 5, the conventional piezoelectric actuator has an actuator portion in which a plurality of piezoelectric ceramic layers 21 and internal electrode layers 22 made of silver palladium are alternately laminated, a piezoelectric ceramic layer 21 ′ formed near one end and an internal portion. It is composed of a displacement amount detecting portion in which electrode layers 22 'are alternately laminated and ceramic portions 23, 24 having no piezoelectric characteristics joined to the upper and lower ends.

The internal electrode layer 22 formed on the actuator portion and the internal electrode layer 2 formed on the displacement amount detecting portion
2'is alternately laminated so as to form a counter electrode consisting of a positive electrode and a negative electrode every other layer. The electrode ends of the positive electrode and the negative electrode are exposed on different side faces facing each other, and one of the electrode ends of the positive electrode and the negative electrode is electrically insulated by the electric insulating portion 25 made of glass on the different side faces. The exposed portions of the internal electrode layers that are not electrically insulated in the actuator portion and the displacement amount detecting portion are connected to the external electrodes 26, 27 and 26 ', 27' made of a silver thin film containing glass frit, and the external electrodes are further Are connected to external leads 28, 29 and 28 ', 29'.

In such a structure, the external lead wire 2
When a desired voltage is applied to 8 and 29, this voltage is applied to each of the plurality of laminated piezoelectrically active piezoelectric ceramic layers 21. As a result, expansion / contraction strains in the thickness direction are generated in the respective piezoelectric ceramic layers 21 due to the inverse piezoelectric effect, and all of these are added to obtain expansion / contraction displacement in the stacking direction of the piezoelectric actuator. At this time, if a load is connected to the piezoelectric actuator, a compressive force or a tensile force acts on the displacement amount detecting portion, and the piezoelectric effect produces an output that is substantially proportional to the stress from the external lead wires 28 ', 29' for displacement detection. The voltage can be obtained.

[0005]

In the conventional laminated piezoelectric actuator, the thickness of each piezoelectric ceramic layer 21 can be reduced to about 0.1 mm.
It has the feature that a large displacement can be obtained with a low drive voltage. On the other hand, if the number of laminated layers is increased in order to increase the length in the displacement direction, the characteristics of the surface and the inside change during sintering. Therefore, when the total laminated thickness is limited to about 20 mm and a laminated piezoelectric actuator having a length longer than that is required, it is necessary to bond a plurality of these.

Further, as described above, in order to make the adjacent electrode layers have electrodes of different polarities, the electrodes exposed on the opposite side surfaces are covered with glass layers every other layer for insulation, and thereafter the external electrodes 26, 27 are formed. Since it is formed, it is difficult to reduce the thickness of the piezoelectric ceramics layer 21 to 0.1 mm or less, and the process is complicated and the working time is long.

Moreover, since it is almost impossible to completely shut off water molecules with a resin made of a general organic material, it is difficult to secure high insulation in a high humidity condition.

Further, when an attempt is made to increase the capacitance of the displacement amount detecting portion in order to improve the low frequency response of the displacement amount detecting portion, the thickness of the piezoelectric ceramic layer 21 is 0.1.
Since it is limited to about mm, it is necessary to increase the number of laminated layers of the displacement amount detecting portion, and accordingly, the number of laminated layers used as an actuator is reduced.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional laminated piezoelectric actuator and to obtain a laminated piezoelectric actuator having a long length in the displacement direction without adhering.

It is another object of the present invention to obtain a piezoelectric actuator excellent in humidity resistance by making the electrodes exposed on the same end face or side face have the same polarity so that insulation by a glass layer is unnecessary.

A further object of the present invention is to increase the value of the electrostatic capacitance about twice as large as the conventional value when the sizes of the displacement amount detecting portions are the same.

[0012]

According to the present invention, there is provided a laminated piezoelectric actuator which utilizes expansion and contraction displacement in the length direction of a prismatic piezoelectric ceramic laminate in which piezoelectric ceramic sheets and electrode layers are alternately laminated. , Including a first piezoelectric ceramic sheet having a first electrode layer formed on one surface and a second piezoelectric ceramic sheet having a second electrode layer formed on one surface, the first electrode layer, A first strip-shaped electrode portion formed of a plurality of strip-shaped electrodes that are perpendicular or parallel to the length direction of the prism, and a first full-surface electrode portion formed near one end portion in the length direction of the prism. Then, the second electrode layer is formed at a position facing the second strip-shaped electrode portion formed of a plurality of strip-shaped electrodes in the same direction as the first strip-shaped electrode portion and the first overall electrode portion. Two full-surface electrode parts, and The second piezoelectric ceramic sheet,
A plurality of strip-shaped electrodes of the first strip-shaped electrode portion and the strip-shaped electrode of the second strip-shaped electrode portion are alternately laminated so that the other strip-shaped electrode is located at a substantially central position of one strip-shaped electrode, The plurality of first strip-shaped electrode portions are connected in parallel by a common external electrode on one side surface of the piezoelectric ceramic laminate, and the plurality of second strip-shaped electrode portions are the other side surface of the piezoelectric ceramic laminate. In parallel connection by a common external electrode, the plurality of first and second whole surface electrode portions are also respectively connected in parallel by a common external electrode on the one side surface and the other side surface, A laminated piezoelectric actuator is obtained.

[0013]

1 and 2 are schematic views showing the structure of a laminated piezoelectric actuator according to an embodiment of the present invention. Figure 1
In (a), a plurality of strip-shaped electrodes 11 are formed as first strip-shaped electrode portions on one surface of a rectangular plate-shaped piezoelectric ceramic sheet 1 in a direction perpendicular to the length direction of the piezoelectric ceramic sheet 1. There is. One end of each strip electrode 11 is pulled out to one side edge of the piezoelectric ceramic sheet 1, and a full-surface electrode portion (first full-surface electrode portion) 12 is provided in the vicinity of the end portion in the length direction of the piezoelectric ceramic sheet 1. Are formed to form a first electrode layer together with the first strip electrode portion. In FIG. 1B, a plurality of strip-shaped electrodes 13 are formed as second strip-shaped electrode portions on one surface of the piezoelectric ceramic sheet 2 in a direction perpendicular to the length direction thereof.
One end of each strip-shaped electrode 13 is led out to the side edge of the first electrode layer opposite to the side edge where the strip-shaped electrode 11 is pulled out, and to the whole surface electrode portion 12 of the first electrode layer. A full-face electrode portion 14 (second full-face electrode portion) is formed at a position facing each other to form a second electrode layer together with the second strip-shaped electrode portion.

As shown in FIG. 2, the piezoelectric ceramic sheet 1 on which the first electrode layer is formed and the piezoelectric ceramic sheet 2 on which the second electrode layer is formed are strip-shaped electrodes of one electrode layer. A plurality of sheets are alternately laminated so that the strip-shaped electrodes of the other electrode layer are located at a substantially central position.

In the laminated piezoelectric actuator shown in FIG. 2, the end portion of the strip electrode 11 and the end portion of the entire surface electrode portion 12 of the first electrode layer are drawn out on one side surface, and the second side portion is formed on the other side surface. The end portion of the strip electrode 13 and the end portion of the entire surface electrode portion 14 of the electrode layer are drawn out. For this reason,
As shown in FIG. 3, when the external electrodes 15 and 16 are formed at the positions corresponding to the actuator portions on the respective side surfaces, the strip electrodes of the first electrode layer are connected in parallel to the external electrodes 15 and the second electrode is formed. The strip electrodes of the electrode layer are connected to the external electrodes 16 in parallel. Therefore, the external electrodes 15, 16
A laminated piezoelectric actuator can be obtained by applying a direct current high voltage to the substrate and performing polarization treatment. Further, by forming the external electrodes 15'16 'on the respective side surfaces at positions corresponding to the whole electrode portions 12 and 14, the whole electrode portions 12 of the first electrode layer are connected to the outer electrodes 15'. The entire surface electrode portion 14 of the second electrode layer is the external electrode 1
6'are respectively connected in parallel. Therefore, when stress is applied to the entire surface electrode region, a voltage substantially proportional to the stress is generated between the electrodes due to the piezoelectric effect.

FIG. 4 is an explanatory view of the operating principle of the laminated piezoelectric actuator of the present invention. FIG. 4 shows only one layer of each of the piezoelectric ceramic sheet 1 and the piezoelectric ceramic sheet 2 in the cross-sectional view in the direction perpendicular to the strip electrodes in FIG. In FIG. 4, the broken line indicates the direction of polarization when the band-shaped electrode 11 is a positive pole and the band-shaped electrode 13 is a negative pole and polarization processing is performed.

FIG. 4 shows the direction of the electric field when a voltage having the same polarity as that at the time of polarization is applied to each strip electrode and the state of strain generated at that time. In this case, since the direction of polarization and the direction of the applied electric field are the same, elongation strain occurs along the direction of polarization, and when a voltage of the opposite polarity to that at the time of polarization is applied, in contrast to the case of FIG. Since the direction of the electric field is opposite to the direction of the applied electric field, shrinkage strain occurs along the direction of polarization. When the electrode pitch of the strip-shaped electrodes is sufficiently larger than the thickness of the piezoelectric ceramic sheets 1 and 2 and the width of the strip-shaped electrodes is smaller than the pitch, the piezoelectric ceramic sheets 1 and 2 are lengthwise due to the piezoelectric longitudinal effect. The expansion and contraction displacement becomes large, and it is possible to obtain a piezoelectric actuator that utilizes displacement in the length direction.

As described above, the principle of operation of the laminated piezoelectric actuator of the present invention is that each of the piezoelectric ceramic sheets 1 and 2 is one.
Although the case of the layer has been described, it may be considered that the present invention is configured by laminating a plurality of piezoelectric ceramic sheets having such an electrode layer, and each operates in the same manner.

When a plurality of piezoelectric ceramic sheets having electrode layers as described above are laminated, the displacement amount when the applied voltage is the same is the same as the case of each one, but the generated force is almost proportional to the number of laminated layers. To increase.

The above description has been made on the case of utilizing the so-called piezoelectric vertical effect in which a plurality of strip electrodes are formed in a direction perpendicular to the expansion / contraction direction of the piezoelectric actuator as shown in FIG. The same can be applied to a case where a so-called piezoelectric lateral effect is used in which each strip-shaped electrode is formed in parallel with the expansion / contraction direction of the piezoelectric actuator.

As a method of forming the electrode layer as shown in FIG. 1 on the piezoelectric ceramic sheet, a method of printing a metal paste on the piezoelectric ceramic sheet after sintering by screen printing and then baking, or a method of plating or vapor deposition to form a piezoelectric film. There is a method of forming a pattern by photoetching after forming an electrode on the entire surface of the ceramic sheet.

As a method of laminating the piezoelectric ceramic sheets having the electrode layers as shown in FIG. 2, there is a method of laminating and adhering using an adhesive. However, in the present invention, a metal paste (for example, silver palladium paste) is printed on one surface of the piezoelectric ceramic green sheet before sintering to form the electrode layer, and the piezoelectric ceramic green sheets are aligned to form a plurality of sheets. The sheets are laminated and integrated, and then sintered. Further, a metal paste is applied to both side surfaces of the laminated body after sintering so as to be connected to the strip-shaped electrodes 11 and 13 to form an external common electrode, and then the external common electrode is baked.

Before sintering the laminated body, after applying an external common electrode by applying a metal paste to both side surfaces of the laminated body so as to connect to the strip electrodes 11 and 13, the laminated body is formed. The body and the external common electrode may be sintered at the same time.

[0024]

As described above, according to the present invention,
The displacement direction of the stacked actuators is parallel to or perpendicular to the strip electrodes, the direction of the surface of the piezoelectric ceramic sheet,
That is, since it is in the plane perpendicular to the stacking direction, a piezoelectric actuator with large displacement can be obtained without bonding.

The first strip-shaped electrode portion and the first whole surface electrode portion, and the second strip-shaped electrode portion and the second whole surface electrode portion are electrically connected to each other on the piezoelectric ceramic sheet or on the side surface of the laminated body, respectively, and are the same. Since it has a potential, there is no concern about dielectric breakdown in the same plane.

Further, according to the present invention, since the electrodes of different polarities of the laminate are drawn out to different side surfaces,
The humidity resistance is greatly improved. Furthermore, the fact that the electrodes of different polarities are drawn to different sides means that
No need for insulation treatment on the same surface.

In addition, according to the present invention, the thickness of the piezoelectric ceramic sheet can be reduced to, for example, 0.05 mm, which is a half of the conventional thickness, and as a result, the entire surface electrode portion used for the displacement detection can be detected. The value of capacitance can be made more than twice as large as the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic view of a piezoelectric ceramic sheet used in the present invention.

FIG. 2 is a sectional view of a piezoelectric actuator according to the present invention.

FIG. 3 is an external view for explaining an external electrode of a piezoelectric actuator according to the present invention.

FIG. 4 is a diagram for explaining the operation principle of the laminated piezoelectric actuator of the present invention.

FIG. 5 is a schematic structural view of a conventional laminated piezoelectric actuator.

[Explanation of symbols]

 1, 2 Piezoelectric ceramics sheets 11, 13 Strip electrodes 12, 14 Full surface electrode parts 15, 15 ', 16, 16' External electrodes 21, 21 'Piezoelectric ceramic layers 22, 22' Silver palladium inner electrode layers 23, 24 Piezoelectric Non-characteristic ceramic part 25 Electrical insulating part 26, 26 ', 27, 27' External electrode 28, 28 ', 29, 29' External lead wire

Claims (1)

[Claims] 1. A laminated piezoelectric actuator utilizing expansion and contraction displacement in the length direction of a prismatic piezoelectric ceramics laminated body in which piezoelectric ceramics sheets and electrode layers are alternately laminated, wherein a first electrode layer is provided on one surface. And a second piezoelectric ceramic sheet having a second electrode layer formed on one surface thereof, the first electrode layer being perpendicular or parallel to the length direction of the prism. A plurality of first strip-shaped electrode portion by a strip-shaped electrode, and a first whole surface electrode portion formed in the vicinity of one end in the length direction of the prism, the second electrode layer, A second strip-shaped electrode portion having a plurality of strip-shaped electrodes in the same direction as the first strip-shaped electrode portion, and a second full-surface electrode portion formed at a position facing the first full-scale electrode portion, The first and second piezoelectric ceramic sheets are The plurality of strip-shaped electrodes of the first strip-shaped electrode portion and the strip-shaped electrode of the second strip-shaped electrode portion are alternately laminated so that the other strip-shaped electrode is located substantially at the center of one strip-shaped electrode. , The plurality of first strip-shaped electrode portions are connected in parallel by a common external electrode on one side surface of the piezoelectric ceramics laminated body, and the plurality of second strip-shaped electrode portions are connected to the other side of the piezoelectric ceramics laminated body. The side surfaces are connected in parallel by a common external electrode, and the plurality of first and second whole surface electrode portions are also connected in parallel by a common external electrode on the one side surface and the other side surface, respectively. And a laminated piezoelectric actuator.