JPH08242025A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE: To provide a piezoelectric actuator in which piezoelectric elements are interconnected with electrodes by simple means without using solder. CONSTITUTION: A plurality of piezoelectric element plates are formed with an internal electrode on a surface of a piezoelectric seat and stacked, and a piezoelectric element having an electrode lead of the internal electrode on a side surface is formed, and a plurality of piezoelectric elements are connected to form a piezoelectric element pillar, and a piezoelectric element coupling electrode 46 having a thin plate form is made of a conductive material having elasticity and is adhered along a surface of the electrode lead of this piezoelectric element pillar with conductive adhesives 50. Thus, as coupling electrodes can be connected without using solder, it is possible to prevent silver easing or heat shock element damages caused by solder heat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator used in a positioning mechanism for an XY stage, an ultrasonic motor, a mass flow controller and the like.

[0002]

2. Description of the Related Art Generally, a piezoelectric element formed by alternately laminating a piezoelectric ceramic material and a thin film electrode is known as a minute displacement element used as an actuator for an XY stage positioning mechanism, an ultrasonic motor, a mass flow controller and the like. The piezoelectric ceramic material is used as an actuator for a portion requiring a large load with a small stroke by utilizing the effect that the piezoelectric ceramic material expands and contracts due to an electric field. Since this element is incorporated into the main parts of the manufacturing line, long-term reliability is required, and thus high mechanical strength and high humidity resistance are required.

The structure of a conventional piezoelectric element of this type will be described with reference to FIG. FIG. 14 is a perspective view of a conventional piezoelectric actuator of a full-surface electrode type. This piezoelectric actuator includes a piezoelectric sheet 2 made of a ceramic material such as titanate / lead zirconate (PZT) and a thin film of platinum or silver-palladium. The internal electrodes 4 are alternately laminated in a large number, for example, about 100 layers. The end of the internal electrode 4 is exposed to the outside over the entire circumference.
Since it is necessary to alternately apply voltages having different polarities, insulating layers 6 and 8 are applied to two orthogonal side surfaces of the block-shaped piezoelectric element to form the application electrode, and one of the electrodes is applied. In the insulating layer 6, every other layer of the internal electrode 4
The edges of the internal electrodes are exposed again by shaving with the dicer along the edges of the internal electrodes 4, and the edges of the other internal electrodes 4 in the other insulating layer 8 different from the above are similarly shaving with the dicer. Re-expose the ends of the internal electrodes.

Then, external electrodes 10 and 12 made of silver paste or the like are formed by coating on the insulating layers 6 and 8, and the exposed internal electrodes 4 are electrically connected every other layer. Therefore, one external electrode 10 is commonly connected to internal electrodes every other layer, and the other external electrode 12 is commonly connected to internal electrodes every other layer different from the above. It is possible to apply an electric field to each piezoelectric sheet 2 by applying a DC voltage between the first and second electrodes 12, thereby producing an electrostrictive effect.

As other full-surface electrode type piezoelectric actuators, those disclosed in, for example, Japanese Patent Laid-Open Nos. 63-155684 and 4-256381 are known. In the former actuator, Metal protrusions are provided on the side portions of every other piezoelectric plate, and side electrodes are connected so as to bridge the metal protrusions to provide external electrodes. In the latter actuator, an external electrode is formed on the side surface of the actuator through an insulating layer, and the external electrode is connected to the internal electrodes of every other layer by a wire bonder with a gold wire to form an internal electrode of every other layer. The electrodes are commonly connected.

The alternating electrode type piezoelectric actuator is
Unlike the above-described full-electrode-type piezoelectric element actuator in which internal electrodes are formed on the entire surface of the piezoelectric sheet, the electrode lead-out portion 14 reaching the end side of the piezoelectric sheet 2 is formed only on a part of the surface of the piezoelectric sheet 2. No internal electrode is formed on the peripheral portion, and the internal electrode 4 is formed at a slight distance from the edge of the sheet. Then, as shown in FIGS. 15 and 16, the piezoelectric sheets 2 thus formed are laminated so that the electrode lead-out portions 14 of the internal electrodes are alternately arranged in opposite directions as shown in FIG. 15 and FIG. Since the end portions are exposed to the outside, by forming the external electrodes 10 and 12 here, the internal electrodes of every other layer are electrically connected to each other.

[0007]

In a conventional ordinary actuator, first, about 23 thin ceramic layers having internal electrodes formed on the surface thereof are laminated to form a subunit 25 as shown in FIG. , The external electrode 3 on its surface
1 and then as many sub-units 2 as required to obtain the required telescopic stroke as shown in FIG.
Piezoelectric element columns 29 are formed by connecting 5 with an adhesive 27.
Then, silver paste or the like is evenly applied to the external electrodes and baked to connect the external electrodes 31.
The external connection lead wires 33 of the book will be soldered.

In this case, however, the thin external electrode 31 may be cracked and broken due to the expansion and contraction drive of the actuator, resulting in electrical non-conduction. Such breaks are especially caused by subunit 25
It tended to occur at the part that connects the two. Therefore,
As shown in FIG. 19, the external electrode 31 of each subunit 25
Each time, a lead wire 35 was connected in a bridge shape with solder 37 to make an electrical connection.

However, in this case, the silver contained in the material forming the external electrode 31 causes so-called electrode silver erosion due to heat at the time of soldering, and not only the lead wire 35 is easily peeled off, but also The piezoelectric element itself may be thermally damaged due to heat shock during soldering. Further, since it is necessary to solder each sub-unit, particularly when the number of units is large, a lot of time is required for the soldering work, which causes a high cost.

The present invention focuses on the above problems,
It was created to solve this effectively. An object of the present invention is to provide a piezoelectric actuator in which a piezoelectric element connecting electrode for connecting piezoelectric elements can be easily attached without using solder.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention laminates a plurality of piezoelectric element plates each having an internal electrode formed on the surface of a piezoelectric sheet, and takes out the electrode of the internal electrode. Forming a piezoelectric element having a portion on its side surface, forming a piezoelectric element column by joining a plurality of the piezoelectric elements, and a piezoelectric element made of a conductive material having elasticity along the surface of the electrode lead-out portion of the piezoelectric element column. The connection electrode is formed by adhering it with a conductive adhesive.

[0012]

Since the present invention is configured as described above, when the piezoelectric element connecting electrode is formed on the surface of the electrode lead-out portion of the piezoelectric element column by using a conductive adhesive, it is necessary in the prior art. Therefore, it is possible to eliminate various problems caused by solder heat, that is, damage to the element due to electrode silver erosion and heat shock, and to simplify the paste operation. You can Further, since the connecting electrode itself has elasticity, it is not restrained when the actuator is extended. In this case, an external electrode for connecting the internal electrodes to every other layer is formed on the surface of the electrode lead-out portion of each piezoelectric element before the piezoelectric element connecting electrode is attached, and the piezoelectric element is formed on the external electrode via a conductive adhesive. By forming the element connection electrode, the internal electrodes in each piezoelectric element can be reliably electrically connected to each other, and the reliability of the actuator can be improved.

Further, the thin plate-shaped piezoelectric element connecting electrode itself is provided with cut portions which are alternately cut from different directions so as to have a hinge function, so that when the piezoelectric actuator is driven, it extends. Since this extension can be allowed, not only the extension of the actuator itself is not restricted, but also the breakage of the connecting electrode itself can be prevented. Further, if the pitch between the cut portions is set to be substantially the same as the thickness of the piezoelectric element, the hinge function can be more effectively exhibited.

[0014]

EXAMPLE An example of the piezoelectric actuator according to the present invention will be described in detail below. 1 to 6 are views showing a manufacturing process of a piezoelectric element column used in the piezoelectric actuator of the present invention, and FIG. 1 is a plan view showing a piezoelectric element plate in which internal electrodes and contraction rate matching thin films are provided on a piezoelectric sheet, FIG. 1 is an enlarged view showing a portion of the contraction rate matching thin film of the piezoelectric element plate shown in FIG. 1, FIG. 3 is a view showing a laminated state of the piezoelectric element plates shown in FIG. 1, and FIG. 4 is a piezoelectric formed by laminating piezoelectric element plates. FIG. 5 is a perspective view showing the element.
4 is a side view of the piezoelectric element plate shown in FIG. 4, and FIG. 6 is a perspective view showing a piezoelectric element column formed by stacking and connecting piezoelectric elements.

FIG. 7 is a view showing a state when the piezoelectric element connecting electrode is attached to the piezoelectric element column, FIG. 8 is a plan view showing the piezoelectric element connecting electrode, and FIG. 9 is a perspective view showing the piezoelectric actuator according to the present invention. 10 and 11 are sectional views of the piezoelectric actuator shown in FIG. The same parts as those of the conventional device described above are designated by the same reference numerals. An important point of the present invention is that a thin plate-shaped piezoelectric element connecting electrode is attached to the side surface of the piezoelectric element via a conductive pillar adhesive as an electrode structure for applying a voltage to the internal electrodes as shown in FIG. The point is that the use of solder is eliminated.

First, steps required to form a piezoelectric element column as shown in FIG. 6 will be described. As shown in FIG. 1 (A), P
A very thin interior made of, for example, silver-palladium or the like on the surface of a thin piezoelectric sheet 2 having a thickness of about 100 μm and a length of 25 mm, which is made of a ceramic material such as ZT, at a predetermined distance D from its edge 2A. Forming the electrode 4,
The electrode lead-out portion 14 is formed by partially extending the thin-film metal of the internal electrode 4 only on a part of the edge 2B and exposing it from the edge 2B to the outside. As a result, the piezoelectric element plate 21 is formed. The thin plate of the piezoelectric sheet is formed by, for example, the doctor blade method, and the internal electrodes 4 are formed by screen printing or the like.

In this case, an electric field is applied to a region formed in a U-shape so as to surround the internal electrode 4 other than the electrode lead-out portion 14, that is, a region on the piezoelectric sheet where the internal electrode 4 is not formed, as described later. Since the region is not applied and does not contribute to the piezoelectric effect, the piezoelectric inactive region 24 is formed.
On the other hand, the region where the internal electrode 4 is formed becomes the piezoelectric active region 26.

Then, a contraction rate matching thin film 28, which is a feature of the present invention, is formed in the substantially U-shaped piezoelectric inactive region 24 by using screen printing or the like like the internal electrodes. in this case,
The matching thin film 28 is formed of a thin metal thin film that is as thin as the internal electrode 4, and is positioned slightly inside each of the side edges 2A and 2B of the piezoelectric sheet 2, and at the same time, is slightly separated from the internal electrode 4. It is formed so that it is electrically floated when laminated as described later. The width D of the piezoelectric inactive region is about 1.0 mm, while the width of the matching thin film 28 is set to about 0.5 mm.

In FIG. 1 (A), the electrode lead-out portion 14 is located at the center of the end side 2B. However, the present invention is not limited to this, and the electrode lead-out portion 14 is provided as shown in FIG. 1 (B). The take-out portion 14 may be provided so as to be located at one of the end portions 2B, or the shrinkage factor matching thin film 28 that surrounds the take-out portion 14 may be provided while being partially divided. May be. In addition, the matching thin film 28
The reason for providing is to prevent the generation of stress during firing of the piezoelectric element, as will be described later in detail.

The matching thin film 28 may be formed as a solid metal thin film on the entire surface, but in consideration of the adhesion between the piezoelectric sheets at the time of stacking, for example, a fine circular shape as shown in the enlarged view of FIG. It is preferable to form the matching thin films 28 so as to be densely arranged and scattered in, for example, a polka dot pattern. This is because the strength after firing between the piezoelectric sheets and the electrodes is weaker than the strength after firing between the piezoelectric sheets, and considering the strength of the entire piezoelectric element, it is necessary to increase the adhesion between the piezoelectric sheets as much as possible. is there. In FIG. 2, the distance between the circular matching thin films 28 is shown large for ease of description, but is actually very small, for example, 0.06 to
It is set to about 0.15 mm.

When the matching thin films are provided in a scattered manner, each shape is not limited to a circular shape, and may be any shape such as an elliptical shape, a rectangular shape, and a triangular shape. The matching thin film 24 may be made of the same material as the internal electrodes, for example, silver-palladium. In that case, the matching thin film 28 can be formed at the same time when the internal electrodes are formed by screen printing or the like. There is no need to increase the number of steps. However, the material may not be the same as that of the internal electrode as long as the same effect for achieving the contraction rate can be obtained.

In this way, the internal electrodes 4 are formed on the piezoelectric sheet 2.
When the piezoelectric element plate 21 is completed by forming the matching thin film 28 and the piezoelectric element plate 21, a plurality of similarly formed piezoelectric element plates 21 are laminated, for example, 25 sheets as shown in FIG. Hydrostatic method (CIP: Cold Isostatic Pre)
While pressing with ss), a pressure bonding process is performed at a temperature of about 120 ° C., and this is sintered at a high temperature of about 1075 ° C. to form a single piezoelectric element 22 as shown in FIG. The piezoelectric element 22 corresponds to the subunit 25 shown in FIG.

When the piezoelectric element plates 21 are laminated, the piezoelectric element plates 21 that are adjacently joined in the vertical direction are laminated so that the positions of the electrode lead-out portions 14 are opposite to each other. Therefore, the electrode lead-out portions 14 are arranged in the same direction in every other layer of the piezoelectric sheet 2. As a result, the end portions of the electrode lead-out portions 14 are exposed to the outside every other layer on the side wall of the piezoelectric element after sintering, as shown in FIG. As shown in FIG. 4, when the piezoelectric element is sintered, irregularities are formed on the surface of the piezoelectric element, though very slight. Therefore, the upper and lower surfaces of the piezoelectric element are ground to secure flatness before stacking them. Good to do. In this case, in order to prevent the internal electrodes from being exposed by the surface polishing, as shown in FIG. 5, the upper and lower surfaces of the piezoelectric element 22 have a thickness (about 300 μm) corresponding to about three layers of the piezoelectric sheet,
It is preferable that only the piezoelectric sheets on which the internal electrodes and the matching thin film are not formed are stacked as a dummy. By this surface polishing, for example, the piezoelectric element, which had a height of about 2.7 mm at the time of sintering, was ground and set to about 2.5 mm.

The reason why the piezoelectric element 22 is formed by laminating about 25 piezoelectric element plates as described above is that the number of layers is 30 or less in the material and size of the piezoelectric sheet as described above. This is because, when the number is preferably about 25, the internal stress can be reduced without reducing the number of layers too much. This will be described based on the simulation result shown in FIG. FIG. 13 is a graph showing a simulation result of the relationship between the distance from the center of the piezoelectric element and the stress in the stacking direction when the number of laminated piezoelectric sheets is variously changed, and the corresponding portion of the piezoelectric element is shown above the graph. .

The thickness of one PZT piezoelectric sheet was set to 0.09 mm, the length of the piezoelectric inactive portion (piezoelectric inactive region) was set to 0.6 mm, and a DC voltage of 150 V was applied. The result of time is shown. In the figure, the origin of the horizontal axis indicates the center of the element, and the maximum value of 2.5 mm indicates the surface of the element. As is clear from the graph, as the number of laminated sheets increases, the stress at the interface between the piezoelectric inactive portion and the piezoelectric active portion increases, and in particular, the tensile stress, which is the largest cause of cracking, depends on the number of laminated sheets. To increase. Therefore, the tensile stress can be reduced by reducing the number of laminated layers, but unfortunately the tensile stress is always generated at the interface between the piezoelectric active portion and the piezoelectric inactive portion. However, when considering improvement of the moisture resistance of the element, it is desirable to prevent cracks on the surface of the element, considering that the main purpose is to cut off the moisture invasion route, and to minimize the occurrence of cracks in that part. It can be said that it should be suppressed to the limit. This simulation result revealed that the stress on the surface of the device acts on the compression side when the number of laminated layers is 30 or less.

Therefore, by setting the number of laminated layers to about 25, it becomes possible to form a piezoelectric subunit in which cracks are less likely to occur on the element surface. If the number of laminated layers is too small, the production efficiency will decrease, which is not preferable. Here, the results of this simulation use, as a model, an ideal sintered body in which the state of close contact between the piezoelectric sheet and the internal electrode is good and there is no residual stress inside. Therefore, as described above, when the thin film for achieving the contraction rate matching during sintering is not formed, the adhesion strength in the element is reduced, and for example, due to the tensile stress generated in the vicinity of the piezoelectric active portion and the piezoelectric inactive portion, A fatal crack that reaches the side surface of the device is generated. In this way, the internal electrode 4
When a piezoelectric element is formed by laminating a large number of piezoelectric sheets 2 (the number of which is based on the result of this simulation) with the contraction rate matching thin film 28 in the piezoelectric inactive region 24 in which no element is formed, It is possible to provide an element in which the contraction rates of the ceramic materials in the piezoelectric inactive region 24 and the piezoelectric active region 26 are substantially the same, no residual stress is generated, the adhesion strength is high, and cracks are less likely to occur. Become.

In this case, by forming the matching thin films in the form of polka dots, for example, as described above, the adhesion strength between the sheets is less deteriorated, and cracks can be further prevented. Further, as described above, by setting the maximum number of laminated piezoelectric sheets to about 25, it is possible to obtain a piezoelectric actuator having a high strength against cracks without increasing the number of stacked elements at the time of manufacturing the piezoelectric actuator. Then, the first and second external electrodes 30 and 32 are formed by applying silver-paste or the like along the two side surfaces where the electrode lead-out portion 14 of the piezoelectric element is exposed and baking the same at about 700 ° C. . Then, by applying a DC voltage to the external electrodes 30 and 32, the ceramic material of the piezoelectric sheet is polarized to complete the piezoelectric element.

As described above, the expansion / contraction stroke of the piezoelectric element is generally very small. For example, the expansion / contraction amount obtained by applying a DC voltage of about 150 V to a piezoelectric sheet having a thickness of about 0.1 mm is about 0.1 μm. Therefore, in order to obtain the amount of expansion and contraction corresponding to the required stroke, a plurality of these piezoelectric elements are connected in series. Therefore, a plurality of piezoelectric elements 22 after polarization, which are formed as shown in FIG. 4, are stacked as shown in FIG. 6, four in the illustrated example, and they are bonded by an elastic adhesive 23 to complete a piezoelectric element column 44. The dimensions of the piezoelectric element columns 44 are, for example, 5.5 mm in length and width,
The total length is about 2 by stacking eight piezoelectric elements 22 with a thickness of about 2.5 mm in series in the thickness direction and connecting them.
It becomes 0 mm.

In the state of the piezoelectric element column 44, the external electrodes 30 or 32 formed on each piezoelectric element 22 are not electrically connected to each other. The reason is that since the adhesive 23 is interposed when the piezoelectric elements 22 are bonded to each other, a very small gap is generated between the external electrodes of the adjacent piezoelectric elements. In order to electrically connect these external electrodes to each other, as described above, in the past, the lead wires and the like were joined by soldering so as to connect the external electrodes. There was an inconvenience due to heat. Therefore, in the present invention, the electrodes are formed without using solder by attaching and fixing the piezoelectric element connecting electrodes with a conductive adhesive. That is, as shown in FIGS. 7 and 8, the piezoelectric element connecting electrode 46 made of a thin plate-like conductive member is attached to the surface of the electrode extraction portion, that is, the conductive adhesive 50 (see FIG. 10) along the external electrodes 30 and 32. Join using. The external electrode is
Since there are two series of positive side and negative side, in this case, one is formed on each of the pair of opposing electrode surfaces of the piezoelectric element column 44.

The piezoelectric element connecting electrode 46 is set to have a length that covers substantially the entire external electrode array, that is, substantially the same length as the piezoelectric element column 44, and is provided at a substantially central portion in the length direction. Has a land portion 48 protruding toward the center side of the joint side surface, so that a lead wire for applying a voltage from the outside, that is, an external connection lead wire 50 (see FIG. 9) can be connected thereto. Has become. As the material of the piezoelectric element connection electrode 46, a flexible conductive material is used. Examples of this material include a metal material having elasticity or elasticity such as phosphor bronze, beryllium copper, nickel silver, etc., carbon,
Alternatively, a flexible conductive resin or the like can be used.

As shown in FIG. 8, the thickness of the piezoelectric element connecting electrode 46 is made as thin as possible, for example, about 0.1 to 0.2 mm, and the length L1 is the piezoelectric element column to which this is attached as described above. And the width W1 is set to be substantially the same as the width of the external electrode, for example, about 1 mm.
The width W2 of the land portion 48 is also set to about 1 mm. To form the shape of the connecting electrode 46, the material plate can be punched with a press, or in the case of a metal plate, it can be formed with high dimensional accuracy by etching. In the case of punching with a press, warpage, bending, burrs, and the like are likely to occur, but in the case of etching, they do not occur, and the molding is preferably performed by etching.

The conductive adhesive 50 may be applied to the entire surface of the external electrode array, or may be applied to the entire attachment surface side of the piezoelectric element connecting electrode 46.
The conductive adhesive 50 may be any conductive adhesive, such as powdered gold,
Dautite (trade name) obtained by mixing silver, copper, nickel, carbon or the like with a synthetic resin such as an acrylic resin, an epoxy resin, a phenol resin, or a polyester resin can be used. In this way, if the piezoelectric element connecting electrode 46 is attached and fixed without using solder, the external connection lead wire 50 is soldered to the land portion 48 as shown in FIG.
Then, the piezoelectric actuators are completed by bonding the two. This cross-sectional view is shown in FIG. 7, 8 and 1
The structure shown in 0 or the like shows the structure in the case where the piezoelectric element plates having the electrode lead-out portion 14 provided at the end portion instead of the center of the end side 2B are laminated as shown in FIG.

When a DC voltage is applied to each internal electrode of the piezoelectric actuator constructed as described above via the lead wire 50 to drive the piezoelectric actuator, the entire actuator is proportional to the applied voltage in the longitudinal direction due to the electrostrictive effect. Will be extended. In this case, since the material forming the connecting electrode 46 is a conductive material having elasticity, the connecting electrode 46 itself also slightly expands in the lengthwise direction when the actuator is expanded, so that the expanding operation of the actuator can be restricted. Since it does not exist, a large amount of generated displacement can be obtained.

Further, since the piezoelectric element connecting electrode 46 is bonded to the external electrode array of the piezoelectric element column 29 by using the conductive adhesive 50, it is not necessary to use solder for bonding, and therefore, It is possible to prevent various problems caused by the heat of solder, for example, the external electrodes being eroded by silver due to the heat of solder, and the piezoelectric element being damaged by heat shock. Furthermore, since it is not necessary to perform complicated soldering on each piezoelectric element, and the connecting electrode 46 can be easily joined by a sticking operation, the workability becomes correspondingly easier and the manufacturing cost is reduced. It becomes possible to do.

By solder-plating the surface of the land portion 48 in advance, the connection operation can be easily performed when the external connection lead wire 50 is connected. In addition, as shown in FIG.
If the lead wire 50 is provided not at the center but at the end, the connection point of the lead wire 50 is located at the center of the width direction of the actuator, and the lead wire mounting operability is improved. Further, in the above-described embodiment, the structure in which the external electrodes 30 and 32 are provided by firing in advance at the exposed end portion of the electrode lead-out portion of the piezoelectric element has been described, but the present invention is not limited to this and the external electrode is not formed. Then, a predetermined number of piezoelectric elements without external electrodes are vertically connected as shown in FIG. 6, and a conductive adhesive is directly applied along the exposed end of the electrode lead-out portion. The element connection electrode may be attached.

Further, in the above-mentioned embodiment, the piezoelectric element connecting electrode 46 is formed so as to have a long and substantially rectangular shape as shown in FIG. 8, but the present invention is not limited to this, and as shown in FIG. A connection electrode structure may be provided in which a large number of cut portions 54 formed along the width direction are provided at a predetermined pitch along the length direction. In this case, the cutting directions of the cut portions 54 are set so that the adjacent cut portions 54 are opposite to each other. As a result, the connecting electrode 46 can be bent slightly in the vertical direction in the drawing at the cut portions 54 to have a hinge function, and the restraining force when the actuator itself is extended can be further reduced. ,
The amount of generated displacement can be further increased.

The connecting electrode 56 shown in FIG. 11A has a structure in which the notch 54 is simply formed in the long rectangular connecting electrode 48 shown in FIG. In the case of the connecting electrode 58 shown in (B), the entire shape of the connecting electrode 58 is a zigzag shape that bends at a slight angle, and the cut portion 54 is formed in the bent portion, and at the same time, a circular cut hole is formed in the cut deep portion. 60 is formed to further enhance the hinge function and reduce the restraining force at the time of extension. In the structure shown in FIGS. 11A and 11B, the pitch L2 between the adjacent notches 54 is preferably set to be substantially the same as the thickness L3 of the piezoelectric element 22 as shown in FIG. And this connecting electrode 5
When bonding 6, 58 to the external electrodes 30, 32 of the piezoelectric element 22, instead of applying a conductive adhesive over the entire surface of the external electrode array as described in FIGS. 7 and 8,
The conductive adhesive 50 is applied to each of the external electrodes in a pinpoint manner, and the connecting electrodes are attached so that the positions of the piezoelectric element joints and the connecting electrode notches 54 substantially coincide with each other. Fix it. Then, the position of the remaining portion of the cut portion 54 and the position of the pinpoint adhesive 50 are slightly shifted in the external electrode width direction.

With this structure, the joint area between the connecting electrode and the external electrode is reduced, so that the cut portion 5 is formed.
The hinge function in 4 can be further increased, and therefore, the restraining force when the actuator is extended can be further reduced, and the generated displacement amount can be further increased. still,
In the above embodiment, the case where four piezoelectric elements are connected has been described, but it goes without saying that this element plate may be increased or decreased as necessary. The alternate electrode type piezoelectric actuator having a structure in which the shrinkage factor matching thin film is provided on the piezoelectric element plate has been described as an example, but it is needless to say that the present invention can be applied to an alternate electrode type piezoelectric actuator that does not use this matching thin film.

[0039]

As described above, according to the piezoelectric actuator of the present invention, the following excellent operational effects can be exhibited. Since a thin plate-shaped piezoelectric element connecting electrode made of a conductive material having elasticity is attached and fixed to the side surface of the piezoelectric element column using a conductive adhesive, the generated displacement amount is hardly reduced, and The connection electrode can be provided without using the conventionally used solder. Therefore, it is possible to eliminate the occurrence of silver erosion and element heat shock damage due to solder heat,
The durability and reliability can be improved. When the piezoelectric element connecting electrode is formed with a cut portion to have a hinge function, a restraining force when the actuator is extended is hardly generated, so that the generated displacement amount can be increased.

[Brief description of drawings]

FIG. 1 is a plan view showing a piezoelectric element plate in which internal electrodes and a shrinkage ratio matching thin film are provided on a piezoelectric sheet.

FIG. 2 is an enlarged view showing a portion of a shrinkage factor matching thin film of the piezoelectric element plate shown in FIG.

FIG. 3 is a diagram showing a laminated state of the piezoelectric element plates shown in FIG.

FIG. 4 is a perspective view showing a piezoelectric element formed by stacking piezoelectric element plates.

5 is a side view of the piezoelectric element shown in FIG.

FIG. 6 is a perspective view showing a piezoelectric element column formed by stacking and connecting piezoelectric elements.

FIG. 7 is a diagram showing a state in which a piezoelectric element connecting electrode is attached to a piezoelectric element column.

FIG. 8 is a plan view showing a piezoelectric element connecting electrode.

FIG. 9 is a perspective view showing a piezoelectric actuator according to the present invention.

10 is a cross-sectional view of the piezoelectric actuator shown in FIG.

FIG. 11 is a diagram showing a modification of the piezoelectric element connecting electrode.

FIG. 12 is an enlarged view showing a state when the connecting electrodes shown in FIG. 11 are joined.

FIG. 13 is a graph showing simulation results showing the relationship between the distance from the center of the piezoelectric element and the stress in the stacking direction when the number of stacked piezoelectric sheets is variously changed.

FIG. 14 is a perspective view showing a conventional full-surface electrode type piezoelectric actuator.

FIG. 15 is a perspective view showing a conventional alternating electrode type piezoelectric actuator.

16 is an explanatory diagram for explaining a laminated state of piezoelectric sheets of the actuator shown in FIG.

FIG. 17 is a diagram showing a subunit of a conventional piezoelectric actuator.

FIG. 18 is a diagram showing a state when the subunits shown in FIG. 17 are stacked and joined.

19 is a diagram showing a state in which lead wires are joined to the external electrodes of the stacking unit shown in FIG.

[Explanation of symbols]

 2 Piezoelectric sheet 4 Internal electrode 14 Electrode extraction part 16 Piezoelectric active part 18 Piezoelectric inactive part 21 Piezoelectric element plate 22 Piezoelectric element 28 Shrinkage ratio matching thin film 30 First external electrode 32 Second external electrode 44 Piezoelectric element pillar 46 Piezoelectric element Connecting electrode 48 Land portion 50 Conductive adhesive 54 Notch portion 56, 58 Piezoelectric element connecting electrode

Claims (7)

[Claims] 1. A plurality of piezoelectric element plates each having an internal electrode formed on the surface of a piezoelectric sheet are laminated to form a piezoelectric element having an electrode lead-out portion of the internal electrode on its side surface. A piezoelectric element column is formed by bonding, and a piezoelectric element connecting electrode made of a conductive material having elasticity is attached along a surface of the electrode lead-out portion of the piezoelectric element column with a conductive adhesive to form the piezoelectric element columnar electrode. A piezoelectric actuator characterized in that 2. The piezoelectric actuator according to claim 1, wherein the piezoelectric element connecting electrode is made of a thin plate-shaped conductive material having elasticity. 3. An external electrode for connecting each internal electrode to each other is formed on the surface of the electrode lead-out portion of the piezoelectric element, and the piezoelectric element connecting electrode is provided on the surface of the external electrode. The piezoelectric actuator according to claim 1 or 2, wherein the piezoelectric actuator is bonded to the piezoelectric actuator. 4. The piezoelectric element connecting electrode is provided with a plurality of notches formed along the width direction thereof along the length direction of the piezoelectric element connecting electrode, and the piezoelectric elements are connected by the notches. 4. A hinge function that allows extension of the element connecting electrode is provided.
The piezoelectric actuator according to any one of 1. 5. The pitch between the adjacent notches is
The piezoelectric actuator according to claim 4, wherein the thickness is substantially the same as the thickness of the piezoelectric element. 6. The piezoelectric actuator according to claim 1, wherein the piezoelectric element connection electrode is pinpoint-connected for each of the piezoelectric elements. 7. The piezoelectric actuator according to claim 1, wherein the piezoelectric element connecting electrode has a land portion for connecting an external connection lead wire.