JPH0846260A - Piezoelectric actuator and its assembling method - Google Patents

Abstract

PURPOSE:To reduce the probability of breakdown of a piezoelectric element which is caused by tensile stress, by applying preliminary pressure to the element without applying tortional stress to the element. CONSTITUTION:A piezoelectric element 2 is accommodated in a case 4, and fixed on a pedestal 3 of the case bottom. An elastic member, e.g. a coned disc spring 7 is arranged between a lid 5 and a piston 6. Preliminary pressure is applied to the element 2 by an assembling method, in the state that tortional stress is not applied by adjasting the position of the lid 5. Strain gauges 8, 9 for detecting strain of the element 2 are fixed on the outer peripheral surface of the element 2, for the inputting to a preliminary pressure adjusting equipment. The outputs of the strain gauges 8, 9 are inputted in bridge circuits 20 and 21, respectively, which have a source power supply VSO. Hence the preliminary pressure is applied to the piezoelectric element 2 without applying tortional stress, and maintained. Thereby the probability that the piezoelectric element 2 is broken down by tensile stress can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator capable of applying a preload required for high-accuracy positioning in a microscope, a measuring instrument or the like, and a preload without applying a torsional stress to the piezoelectric actuator. Relates to an assembling method for adjusting.

[0002]

2. Description of the Related Art Piezoelectric actuators have the characteristic that when an electric field is applied to a piezoelectric element, distortion occurs inside the piezoelectric element, which expands and contracts itself to obtain a large displacement at low voltage. The characteristics are that a small displacement can be obtained on the order of submicron, excellent responsiveness, and large generated stress. For this reason, a piezoelectric actuator has been conventionally used as a highly accurate positioning device.

Recently, a piezoelectric actuator enclosed in a metal case is commercially available, and a fine movement actuator of an electron microscope or a laser scanning microscope (L
(SM) focusing unit actuator.

FIG. 6 is a diagram showing an example of a displacement magnifying device used in a conventional microscope.
Is fixed vertically to the fixed surface, one end of the lever 14 is horizontally fixed to the upper part of the actuator 1, the stage support structure 23 is vertically fixed to the other end of the lever 14, and the upper part of the stage support structure 23 is fixed. The stage 15 is fixed horizontally.

FIG. 7 is a sectional view showing the structure of the piezoelectric actuator 1 shown in FIG. 6, in which a later-described actuator body is enclosed in a metal case 13. The actuator body includes a piezoelectric element 2, a pedestal 3 to which the lower end of the piezoelectric element 2 is fixed, and a piston 6 fixed to the upper end of the piezoelectric element 2.

[0006]

When a downward inertial force F of the stage 15 shown in FIG. 6 is applied to the lever 14, the piezoelectric actuator 1 is pulled by the lever 14 and tensile stress is applied to the piezoelectric element. .

In the piezoelectric actuator 1 enclosed in the metal case 13 as shown in FIG. 7, the piezoelectric element 2 is not preloaded, and the piezoelectric element 2 is subjected to tensile stress.
Has the drawback of being easily damaged.

Further, even when a preload is applied, torsional stress may be applied to the piezoelectric element 2 due to mechanical error or friction between parts, and the piezoelectric element 2 may be damaged. The present invention has been made to eliminate the above-mentioned problems, and an object of the present invention is to provide a piezoelectric actuator that can reduce the risk of damage due to tensile stress, and can reduce damage to the piezoelectric element during assembly. An object is to provide a method for assembling a piezoelectric actuator.

[0009]

In order to achieve the above-mentioned object, the invention corresponding to claim 1 has a bottomed cylindrical case,
A piezoelectric element that is housed inside this case and fixed to the bottom of the case, and expands and contracts itself when an electric field is applied,
Provided on the opposite side of the piezoelectric element inside the case,
A piston that moves with the expansion and contraction of the piezoelectric element, a fixing member that is movable in the expansion and contraction direction of the piezoelectric element and can be fixed at a predetermined position on the opening end side of the case, and the fixing member and the piston. A piezoelectric actuator comprising: an elastic body provided between the elastic elements and applying a preload to the piezoelectric element.

In order to achieve the above object, the invention according to claim 3 has a bottomed cylindrical case, which is housed inside the case and fixed to the bottom surface of the case, and expands and contracts itself when an electric field is applied. A piezoelectric element, a piston provided inside the case on the side opposite to the fixed side of the piezoelectric element, and a piston that moves as the piezoelectric element expands and contracts, and an opening end side of the case that is movable back and forth in the expansion and contraction direction of the piezoelectric element. A piezoelectric actuator comprising: a fixing member that can be fixed at a predetermined position; and an elastic body that is provided between the fixing member and the piston and applies a preload to the piezoelectric element. A piezoelectric actuator, characterized in that after applying a preload to the elastic body from the outside, the fixing member is positioned at a predetermined position, and then the preload by the preload member is released. Which is the assembly method.

[0011]

According to the invention corresponding to claim 1, since the piezoelectric element is preloaded in advance, the risk of damage due to tensile stress can be reduced. According to the method of the invention corresponding to the third aspect, it is possible to reduce the damage of the piezoelectric element during assembly by applying the preload while monitoring the torsional strain so as not to be applied to the piezoelectric element.

[0012]

Embodiments of the piezoelectric actuator according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment according to the present invention. The cylindrical metal case 4 and the pedestal 3 fixed to the lower end of the metal case 4 constitute a bottomed cylindrical case. Inside the case 4, the piezoelectric element 2
Then, the piezoelectric element 2 is fixed to the pedestal 3 on the bottom surface of the case. When an electric field is applied, the piezoelectric element 2 in this case is internally distorted and expands and contracts itself.
Inside the case 4, a piston 6 having a convex cross-section that moves as the piezoelectric element 2 expands and contracts is fixed to the opposite side (upper end) of the piezoelectric element 2 that is not fixed. A female screw portion (not shown) is formed on the inner peripheral side of the upper end portion of the case 1, and the female screw portion has a screw-in lid 5 having a hole 5a for guiding the tip portion of the piston 6 to the outside at the central position. Screw together. An elastic body such as a disc spring 7 is provided between the lid 5 and the piston 6 inside the case 1,
A preload is applied to the piezoelectric element 2 by adjusting the position of the lid 5 by a later-described assembling method without applying a torsional stress. Strain gauges 8 and 9 for detecting the strain of the piezoelectric element 2 are attached to the outer peripheral surface of the piezoelectric element 2 for inputting to a preload adjusting device described later.
The outputs of the strain gauges 8 and 9 are configured to be input to the bridge circuits 20 and 21 having the source power source VSO, respectively.

According to the above-described embodiment, the preload is applied to the piezoelectric element 2 so that the torsional stress is not applied, and the preload is maintained, whereby the probability of damage of the piezoelectric element 2 due to the tensile stress can be reduced. it can.

Further, since the disc spring 7 is used as the elastic body, a relatively large preload can be obtained in a limited space. The spring constant k of the disc spring 7 is not linear, and the spring constant k is determined by the amount of deformation of the spring. Therefore, if the preload is set so that the region in which the spring constant k is close to zero can be used, even if the spring is compressed by the expansion of the piezoelectric element 2, the spring constant k is zero, so that the spring hanging on the piezoelectric element 2 is generated. The force becomes constant and fluctuations in preload can be suppressed.

Here, in the embodiment of FIG. 1, the region where the spring constant k is close to zero is very limited, and if the region cannot be used, even if the piezoelectric element 2 is slightly stretched, The generated force is increased, and the generated amount of the piezoelectric element 2 is reduced accordingly. However, in the case piston 6 and lid 5
A coil spring can be used when there is enough space in between. Since the coil spring generally has a small spring constant k, the fluctuation of the preload can be suppressed to a small level. As a result, even if the displacement of the piezoelectric element 2 changes, the change in the generated force of the piezoelectric element 2 decreases.

Next, the above-mentioned preload adjusting device will be described with reference to FIGS. As shown in FIG. 4, the bottomed cylindrical preload bar 12 is inserted into the hole 5a formed in the lid 5 and is also inserted into the convex portion of the piston 6, and is brought into contact with the disc spring 7 so that the disc spring 7 Is to add power to. Specifically, this is a jig 2 such as a vise as shown in FIG.
Do in 2.

In this case, preferably, even if the preload bar 12 rotates, the lower end portion of the preload bar 12 contacting the disc spring 7 is made of a material having a low friction coefficient so that the rotation is not transmitted to the disc spring. You can leave it as it is.

The strain gauges 8 and 9 for detecting the strain of the above-mentioned piezoelectric element 2 are bridge circuits 2 constructed independently of each other.
Bridge circuit 20, electrically connected to one side of 0, 21
The monitors 16 and 17 are connected to the output side of the monitor 21,
An arithmetic unit 18 is connected to the output side of 6, 7 and the output of the arithmetic unit 18 is input to a monitor 19 equipped with a warning device.

In the bridge circuits 20 and 21, fixed resistors are connected to the three sides of the rhombus, and strain gauges 8 and 9 are electrically connected to the remaining one side of the rhombus, whereby the piezoelectric element 2 is formed.
Detect the distortion of.

When the strain gauge 8 detects strain in the Z-axis direction of the piezoelectric element 2, the bridge circuit 20 changes the resistance value, so that a potential difference proportional to the change in the resistance value is output. Similarly, when the strain gauge 9 detects a strain of the piezoelectric element 2 in the X-axis direction, the bridge circuit 21 changes the resistance value. Therefore, a potential difference proportional to the resistance value change is output. Monitor 1
Reference numerals 6 and 17 display the outputs of the bridge circuits 20 and 21 and output them to the arithmetic unit 18. The computing unit 18 computes the torsional strain (torsional stress) ε _TX by the following equation (1).

Now, let the strain detected by the strain gauge 8 be ε
_Z , strain detected by strain gauge 9 is ε _X , piezoelectric element 2
The Poisson's ratio [nu, the compressive strain epsilon _C, when the torsional strain ε _TX, ε _Z and epsilon _X is expressed by the following _{equation, ε Z = ε C ε X} = ε TX + νε C torsional strain epsilon _TX is the following Separated by formula.

Ε _X −νε _Z = (ε _TX + νε _C ) −ν (ε _C ) = ε _TX (1) ε _Z and ε _X are displayed on the monitors 16 and 17, and at the same time, their signals are calculated by the arithmetic unit 18. Then, the formula (1) is calculated, the result is displayed on the monitor 19, and a warning is issued.
The preload bar 12 is adjusted so that the torsional strain ε _TX becomes zero, ε _Z is monitored, and a preload slightly larger than the target preload is applied. Therefore, the lid 5 is completely closed. At this time, a preload larger than the target preload of the disc spring 7 is applied and greatly distorted so that the disc spring 7 does not come into contact with the lid 5. Therefore, no torsional stress is applied to the piezoelectric element 2. After the lid 5 is completely closed, the preload bar 12 is removed, and the disc spring 7 extends due to the release of the force, but the disc spring 7 hits the bottom of the lid 5 and the extension is blocked, so that the target preload can be maintained. .

FIG. 5 is a sectional view showing a second embodiment of the piezoelectric actuator of the present invention. The difference from the embodiment of FIG. 1 is that a top lid 11 is newly added. Specifically, the piston insertion hole 11a is formed at the center position of the upper lid 11, and the piston insertion hole 11a is slightly larger than the outer diameter of the convex portion of the piston 6 so that the force perpendicular to the Z axis is Even when it is applied to the piston 6, it is possible to reduce the possibility that the piston 6 hits the upper lid 11 and a force perpendicular to the Z axis is applied to the piezoelectric element 2 by 100%, and the risk of damage to the piezoelectric element 2 due to bending stress is reduced. Further, in the case having a cylindrical shape with a bottom, the pedestal 3 may be detachable in order to facilitate the fixation of the piezoelectric element 3.

[0024]

According to the present invention, there is provided a piezoelectric actuator and a method of assembling the piezoelectric actuator, which can apply a preload to the piezoelectric element without applying a torsional stress to the piezoelectric element and reduce the probability of damage of the piezoelectric element due to tensile stress. Can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a piezoelectric actuator according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a preload adjusting device for a piezoelectric actuator used in the method of the present invention.

FIG. 3 is a circuit diagram showing an example of a preload adjusting device for the piezoelectric actuator of FIG.

FIG. 4 is a diagram for explaining a state before a preload is applied to the piezoelectric actuator according to the present invention.

FIG. 5 is a sectional view showing a second embodiment of the piezoelectric actuator according to the present invention.

FIG. 6 is a diagram showing an example of a displacement magnifying device incorporating a conventional piezoelectric actuator.

7 is a cross-sectional view showing the piezoelectric actuator of FIG.

[Explanation of symbols]

1 ... Piezoelectric actuator, 2 ... Piezoelectric element, 3 ... Pedestal, 4
... Case, 5 ... Lid, 6 ... Piston, 7 ... Disc spring, 8, 9
... Strain gauge, 11 ... Top lid, 16, 17, 19 ... Monitor, 18 ... Arithmetic unit, 20, 21 ... Bridge circuit.

Claims (3)

[Claims] 1. A case having a bottomed cylindrical shape, a piezoelectric element that is housed inside the case and fixed to the bottom surface of the case, and expands and contracts itself when an electric field is applied, and an anti-fixation of the piezoelectric element inside the case. Provided on the side,
A piston that moves with the expansion and contraction of the piezoelectric element, a fixing member that is movable toward and away from the opening end side of the case in the expansion and contraction direction of the piezoelectric element and can be fixed at a predetermined position, and the fixing member and the piston. A piezoelectric actuator comprising: an elastic body that is provided between the elastic elements and applies a preload to the piezoelectric element. 2. The piezoelectric actuator according to claim 1, wherein the elastic body is either a disc spring or a coil spring. 3. A bottomed cylindrical case, a piezoelectric element which is housed inside the case and fixed to the bottom surface of the case, and which expands and contracts itself when an electric field is applied, and an anti-fixation of the piezoelectric element inside the case. Provided on the side,
A piston that moves with the expansion and contraction of the piezoelectric element, a fixing member that is movable toward and away from the opening end side of the case in the expansion and contraction direction of the piezoelectric element and can be fixed at a predetermined position, and the fixing member and the piston. A piezoelectric actuator comprising: an elastic body that is provided between the elastic body and applies a preload to the piezoelectric element, wherein the elastic member is preloaded from the outside by a preloading member, and then the fixing member is fixed to a predetermined position. To the position of
After that, the preload by the preload member is released, and a method of assembling a piezoelectric actuator.