JPH10284763A - Piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate miniaturization at a low cost, and obtain high reliability capable of preventing breakdown of an element by constituting an elastic member which is bonded, in a previously stretched state, to outer electrodes formed on the side surface of a multilayer piezoelectric element. SOLUTION: A piezoelectric element 2 is to be an alternate electrode type element, wherein inner electrodes are exposed on one side surface and the other side surface of a laminate, every one layer interposing piezoelectric ceramics. Outer electrodes 3 are formed by printing conductive paste on the side surface of the laminate and baking the paste, and connected with the inner electrodes exposed on the side surface. An elastic member 4 is bonded to the outer electrodes 3 of the element 2 by using solder or the like. At least the upper ends and the lower ends of the outer electrodes 3 are necessary to be bonded. The elastic member 4 is bonded to the outer electrodes 3, in a previously stretched state. After the elastic member 4 is connected with the outer electrodes 3 by using solder or the like, polarization treatment is performed, and the element is stretched. At the same time, the elastic member 4 is also stretched, and a restoring force acts and applies a compressive force to the lamination direction of the piezoelectric element 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed ultra-precision fine movement device which is mounted on an XY stage such as an optical fiber bonding device, a magnetic head processing dicing device, a semiconductor exposure device, and the like, and moves a minute distance. .

[0002]

2. Description of the Related Art In recent years, with the advancement of optical communication, an optical fiber having a small loss even when transmitted over a long distance is required. However, in order to make such an optical fiber, the cores of the optical fibers are joined together. Sometimes, positioning accuracy in the submicron region (1 μm or less) is required.

In order to satisfy this demand, the following precision positioning device has been used. That is, a piezoelectric element is housed in a bottomed cylinder, an output member is fixed to the tip of the piezoelectric element, and the output shaft is slidably protruded from a cap placed on the tip of the cylinder. A precision positioning device having a coil spring interposed between the locking portion (see JP-A-4-165683)

In the conventional positioning device, since the output member of the piezoelectric element has a structure penetrating the cap, the sealing of the shaft sliding portion is not complete, and the penetration of water vapor in the air in a long-time high-humidity environment is prevented. I cannot shut it off. For this reason, the piezoelectric element may be destroyed due to a short circuit caused by migration between the external electrodes on the side surfaces of the piezoelectric element.

Therefore, a piezoelectric actuator is used in which a piezoelectric element is sealed by a metal case, a metal member, and a glass terminal and receives a preload from a metal case expansion / contraction portion (see Japanese Patent Application Laid-Open No. 2-196479). )

[0006]

The conventional piezoelectric actuator has three functions in the metal case, namely, a function of expanding and contracting in the direction of the output shaft, a function of blocking water vapor in the air, and a function of applying a preload to the piezoelectric element. Are required. Therefore, the conventional metal case has a problem that it has a complicated structure and is expensive, and has a larger shape than the piezoelectric element main body, so that it cannot be downsized.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention does not complicate the structure of the metal case, and is therefore low in cost, easy to miniaturize, and even when a tensile force is applied to the piezoelectric element during manufacturing and operation. It is an object to realize a highly reliable piezoelectric actuator capable of preventing the destruction of the piezoelectric actuator.

[0008]

Means for Solving the Problems A multilayer piezoelectric element; an external electrode formed on a side surface of the multilayer piezoelectric element in a laminating direction; and joined on the external electrode in a state of being extended along the external electrode in advance. It is made of an elastic member. (Claim 1)

According to this means, the elastic member joined to the external electrode of the piezoelectric element is stretched by stretching the laminated piezoelectric element (hereinafter, simply referred to as a piezoelectric element) by a certain dimension,
The force to return to the elastic member is always applied in the stacking direction of the piezoelectric element, and a compressive force acts on the piezoelectric element. To extend the piezoelectric element by a certain dimension means to extend the piezoelectric element by a polarization process. However, the elastic member may be joined to an external electrode in a stretched state. When the piezoelectric element itself is given a compressive force in this way, even if a tensile force is applied to the piezoelectric element during manufacturing and operation, it is possible to prevent the piezoelectric element from being broken, and it is necessary to provide the metal case with a preload. The metal case only needs to have a function of expanding and contracting in the direction of the output shaft and a function of blocking water vapor in the air, so that the metal case has a simple structure.

In the present invention, it is preferable that the elastic member is "made of a conductive metal material" (claim 2). When the elastic member has conductivity, it also serves as a lead wire, applies a compressive force to the piezoelectric elements, and electrically connects the external electrodes of each piezoelectric element. Further, since the elastic member is joined to the external electrode by a low melting point alloy such as solder, a metal material which can be easily joined to solder or the like is preferable.

In the present invention, it is preferable that the elastic member is "joined at least at the upper and lower ends of the external electrode". In order to apply a compressive force in the laminating direction of the piezoelectric elements, it is necessary that the elastic members are joined to at least the upper and lower ends of the external electrodes. Since the external electrode is formed over substantially the entire length of the piezoelectric element in the laminating direction, a compressive force can be applied to almost the entire length of the piezoelectric element in the laminating direction by joining the elastic members to at least upper and lower ends of the external electrode. .

In the present invention, the elastic member is preferably "joined to the external electrode over substantially the entire length" (claim 4). When joined in this manner, cracks are less likely to occur in the external electrode due to repeated expansion and contraction of the piezoelectric element, and the connection between the internal electrode and the external electrode can be prevented from being partially cut. Also, even if the external electrode cracks due to the repeated expansion and contraction of the piezoelectric element, the internal electrode and the external electrode do not break, the electrical connection is maintained, and no voltage is applied to the internal electrode. It can be prevented that the amount of expansion and contraction cannot be obtained.

[0013] In the present invention, the elastic member has a plate-like, rod-like, linear, or net-like shape.
Is preferred. Basically, the shape of the elastic body may be any shape, but if it has a simple shape of a plate, a bar, a line, or a net, by simply changing its dimensions,
Any elasticity can be provided, the elastic force can be set freely, and the target elastic force can be obtained with high accuracy. Further, since this elastic body has a simple shape, it can be manufactured at low cost.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the piezoelectric actuator of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the piezoelectric actuator of the present invention. In FIG. 1, a piezoelectric actuator 1 includes a piezoelectric element 2, an external electrode 3 formed on a side surface of the piezoelectric element 2 in a stacking direction, and an elastic member bonded on the external electrode 3 along the external electrode 3. 4 mainly.

The piezoelectric element 2 refers to an element such as piezoelectric, electrostrictive, or magnetostrictive. A phenomenon in which distortion occurs when an electric field is applied to a certain kind of crystal is called an electrostrictive effect or a piezoelectric effect. Is an element that converts electrical energy into mechanical energy using The piezoelectric element 2 includes, for example, one or a plurality of piezoelectric elements formed in a quadrangular prism shape, and the number is appropriately selected as needed. As the piezoelectric element 2, for example, a laminated body obtained by alternately laminating PZT-based piezoelectric ceramics having high piezoelectricity and high rigidity as materials exhibiting an electrostrictive effect and internal electrodes and firing them is used. The piezoelectric element 2 is a so-called alternating electrode type in which the internal electrodes are exposed on one side and the other side of the laminate every other layer via piezoelectric ceramics, and the internal electrodes are laminated such that the internal electrodes are exposed on both side faces of the laminate. However, any one of a so-called full-electrode type laminated piezoelectric element in which an exposed portion is covered with an insulating material and connected to an external electrode every other layer may be used. Here, description will be made using an alternate electrode type.

The external electrodes 3 are formed by printing and firing a conductive paste on the side surfaces of the laminate, and are connected to the internal electrodes exposed on the side surfaces. The internal electrodes are not shown. Further, the external electrode 3 is formed at a predetermined width over substantially the entire length of the laminate in the laminating direction. The thickness of these external electrodes 3 is generally several microns. One of the pair of external electrodes 3 is a positive electrode, and the other is a negative electrode. By applying a voltage to the external electrode 3, an electric field is generated between the internal electrodes, and the piezoelectric ceramic can be expanded and contracted.

The elastic material 4 is preferably a conductive metal material. Examples of such a metal material include brass, nickel silver, phosphor bronze, beryllium copper, and the like, but are not limited thereto, and any material having conductivity and elasticity may be used. The shape of the elastic member 4 may be, for example, plate-like, rod-like, linear, or net-like, but is not particularly limited. The elastic force of the elastic member 4 can be freely designed depending on the material of the metal material and the shape of the elastic member 4. For example, the thickness of the elastic member 4 and the thickness of the elastic member 4 are set so that a compressive force of 5 to 100 kgf is applied to the piezoelectric element. By changing the width, the elastic force can be easily obtained as designed. Such an elastic member 4 is joined to the external electrode 3 of the piezoelectric element 2 by soldering or the like. At this time, at least the upper and lower ends of the external electrode 3 need to be joined. If the upper and lower ends of the external electrodes 3 are connected, a compressive force can be applied over substantially the entire length of the piezoelectric element 2 in the laminating direction. Also, if the elastic member 4 is soldered over substantially the entire length of the external electrode 3 as shown in FIG.
The cracks are less likely to occur in the external electrodes due to expansion and contraction. Even if the external electrodes 4 are cracked, the electrical connection between the internal electrodes and the external electrodes 3 is maintained, and the voltage is applied to all the internal electrodes. The amount of displacement of the piezoelectric element 2 does not change. The elastic member 4 is joined to the external electrode 3 in a state where it is stretched in advance. The state in which the elastic member 4 is stretched in advance can be, for example, a state in which the elastic member 4 is stretched to a certain size by joining the elastic member 4 to the piezoelectric element 2 and then polarizing the piezoelectric element 2. 4 may be joined to the external electrode 3 while being stretched.

Next, the operation of the elastic member 4 will be described. The piezoelectric element 2 usually needs to be polarized at a high voltage, for example, 3 kv / mm in order to make the direction of expansion and contraction uniform. When the elastic member 4 is connected to the external electrode 3 by soldering or the like, the polarization is performed. By processing, the element elongates about 0.01 mm,
At the same time, the elastic member 4 joined to the external electrode is also extended. When the elastic member 4 is stretched, a force for returning the elastic member 4 to the original position acts, and always applies a compressive force in the stacking direction of the piezoelectric elements 2.
Since the amount of expansion of the element due to polarization is constant, the compression force applied to the piezoelectric element 2 is determined by selecting the elasticity of the elastic member 4 to an appropriate value. This compressive force is a force that does not suppress the displacement of the element due to the electric field.
Designed to kg. When the piezoelectric element 2 itself is given a compressive force in this way, the piezoelectric element 2 is protected by the compressive force even when a tensile force is applied to the piezoelectric element 2 from the outside during the manufacture and operation of the piezoelectric actuator 1.

[0019]

EXAMPLES The piezoelectric actuator of the present invention will be further described based on examples. FIG. 3 shows a piezoelectric actuator 1 hermetically sealed with a metal case 6 used for a precision fine movement device or the like. This will be described in detail with reference to FIG. The piezoelectric actuator 1 is joined to a piezoelectric element 2 fixed to a base 7, an external electrode 3 formed on a side surface of the piezoelectric element 2 in a laminating direction, and soldered in a state of being extended on the external electrode 3 in advance. And a metal case 6 that is fixed to the base 7 and seals the piezoelectric element 2.

The base 7 is made of a metal member, and is provided with a lead wire introduction hole 10 for introducing a lead wire 9 for applying a voltage from an external power supply (not shown) to the external electrode 3 of the piezoelectric element 2. After connection to the external electrode 3, the lead wire introduction hole 10 is filled with glass, glass is fused, completely shut off from the outside air, and the piezoelectric element 2 is sealed.

The metal case 6 has a wave-shaped spring portion 6 a at its tip, and expands and contracts in the output axis direction A following expansion and contraction of the piezoelectric element 2. Further, by welding the metal case 6 and the base 7, the piezoelectric element 2 is sealed, and the piezoelectric element 2 is prevented from being broken by humidity in the air.

The piezoelectric element 2 uses an alternating electrode type element, and an external electrode 3 having a constant width in the laminating direction is formed on the side surface of the piezoelectric element 2 by printing and firing a conductive paste. A hemispherical body 8 is provided at the tip of the piezoelectric element 2, and the hemispherical body 8 is fitted on a spring portion 6 a of the metal case 6 to form a ball joint 11.

The elastic member 4 is made of a metal material having a plate-like or rod-like conductivity and is joined to the external electrode 3 of the piezoelectric element 2. The shape of the elastic member 4 is not particularly limited, and may be linear or net-like, or may be plate-like and perforated. In the case of a plate having holes, the solder is easy to flow around, and the bonding with the external electrode 3 becomes stronger.

For example, the elastic force of the elastic member 4 is easily changed by changing the thickness, the width, etc. of a plate-like member.
The elastic force can be designed so that a compressive force of f is given. Further, since the elastic member 4 has a simple shape, it can be easily manufactured, and an error in elastic force is small.

Next, the operation of the elastic member 4 will be described. Normally, the piezoelectric element 2 has a high DC voltage, for example, 3 k
It is necessary to perform polarization processing at V / mm, and by performing this polarization processing after connecting the elastic member 4, the elastic member 4 expands by a certain dimension, and its contraction force is applied as a compressive force in the laminating direction of the piezoelectric elements 2. . Since the amount of expansion of the piezoelectric element 2 during polarization is determined, the compressive force applied to the piezoelectric element 2 is determined by selecting the elastic coefficient of the elastic member 4 to an appropriate value.

Next, the operation of this embodiment will be described. When a predetermined voltage, for example, 140 V, is applied to the piezoelectric element 2, the piezoelectric element 2 expands in the direction of arrow A while overcoming the compressive force of the elastic member 4. The elongation at this time is, for example, 40 μm. The extension of the piezoelectric element 2 causes the metal case 6 to move in the direction of arrow A, thereby causing a moving object (not shown) to slightly move in the same direction. Since the spring portion 6a is set to have a spring constant softer than the elastic member 5, the spring portion 6a does not have such a large resistance as to hinder the displacement of the piezoelectric element 2.

When the voltage applied to the piezoelectric element 2 is reduced to zero, the piezoelectric element 2 returns to its original length. At this time, since the piezoelectric element 2 receives the compressive force from the elastic member 4, even if a tensile force smaller than the compressive force is applied to the ball joint 11, the piezoelectric element 2 is not affected by the tensile force.

When the tensile force applied to the ball joint 11 is larger than the compressive force, the spring 6a formed on the metal case 6 and the hemispherical body 8 fixed to the piezoelectric element 2 separate. Therefore, no tensile force is applied to the piezoelectric element 2.

When an external force is applied to the ball joint 11 in a direction different from the displacement direction A of the piezoelectric element 2, for example, in the direction of arrow B, this force deforms the metal case 6, but the hemispherical body 8 of the ball joint 11 and the metal Spring part 6 of case 6
Therefore, the piezoelectric element 2 is not transmitted to the piezoelectric element 2 because it is absorbed by a and is prevented from being broken by an external force.

One of the features of the piezoelectric actuator 1 is that the piezoelectric actuator 1 has a sealed structure as described above and completely blocks water vapor, dust and the like in the air.

【The invention's effect】

Since the present invention is configured as described above, it is possible to easily apply a compressive force to the piezoelectric element simply by joining the elastic member to the external electrode of the piezoelectric element. Also, since an elastic member having a desired elastic force can be easily manufactured,
The designed compression force can be applied to the piezoelectric element. When the element itself is given a compressive force as described above, the element can be protected from destruction even when a tensile force is applied to the piezoelectric element during manufacturing or operation. In addition, compared to a method of applying a preload with a metal case, a metal case having a complicated shape is not required, and miniaturization is easy.

[Brief description of the drawings]

FIG. 1 is a perspective view of a piezoelectric actuator.

FIG. 2 is an embodiment showing another joining method of the elastic member.

FIG. 3 is a sectional view of an embodiment sealed with a metal case.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric actuator 2 piezoelectric element 3 external electrode 4 elastic member

Claims (5)

[Claims] 1. A laminated piezoelectric element; an external electrode formed on a side surface of the laminated piezoelectric element in a laminating direction; and an elastic member which is joined to the external electrode in a state of being stretched in advance along the external electrode. A piezoelectric actuator comprising a member. 2. The piezoelectric actuator according to claim 1, wherein the elastic member is made of a conductive metal material. 3. The device according to claim 1, wherein the elastic member is joined to at least upper and lower ends of the external electrode.
Or the piezoelectric actuator according to 2. 4. The piezoelectric actuator according to claim 1, wherein the elastic member is joined to an external electrode of the multilayer piezoelectric element over substantially the entire length thereof. 5. The piezoelectric actuator according to claim 1, wherein the shape of the elastic member is plate-like, rod-like, linear, or net-like.