JP3400578B2 - Piezoelectric actuator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element actuator used for providing fine movement required for highly accurate positioning in, for example, a microscope or measuring instrument, and more particularly to measuring the fine movement amount. The present invention relates to a piezoelectric element actuator having a strain gauge for working.

[0002]

2. Description of the Related Art Conventionally, for example, PZT (lead zircon titanate) has an electrostrictive effect of about 10 ⁻⁴ per 200 V, but a displacement actuator that can be electrically controlled up to about 100 μm by laminating these thin plates has been proposed. It is known to be obtained.

As a displacement detecting sensor for detecting the displacement amount of such a piezoelectric element actuator, an inexpensive and easy-to-handle strain gauge which can detect displacements of the order of microns and submicrons is generally used. is there.

However, in the strain gauge, a measurement error occurs due to a temperature change. As a device for reducing the measurement error due to this temperature change, for example, Japanese Patent Laid-Open No. 3-2350
There is one disclosed in Japanese Patent Laid-Open No. 01. This is a piezoelectric element with a strain gauge for temperature compensation using a dummy gauge, and as shown in FIG. 4A, displacement measurement is performed on the surface of the piezoelectric element actuator 100 at a position where expansion / contraction in the displacement direction to be measured is detected. Along with the active gauge 102 for temperature, a dummy gauge 104 for temperature compensation is attached to a position other than the position for detecting expansion and contraction of the displacement position to be measured,
As shown in (B) of the figure, the active gauge 102,
The dummy gauge 104 and the fixed resistors 106 and 108 form a bridge circuit. Here, for example, the strain measured by the bridge circuit when a temperature change occurs is ε 0, the strain detected by the active gauge 102 is ε A, the strain detected by the dummy gauge 104 is ε D, the piezoelectric element and the piezoelectric inverse effect. If the strain is εP and the strain due to temperature change is εt, then ε0 = εA-εD = (εP + εt)-(εt) = εP (1).

Therefore, the distortion due to the temperature change is canceled and the output of the bridge circuit is simply the distortion ε P due to the piezoelectric inverse effect of the piezoelectric element, so that no measurement error occurs.
Further, in Japanese Patent Laid-Open No. 63-283180, as shown in FIG. 5A, a piezoelectric element 110 is housed in a container 112, and four strain gauges 11 are provided on one side surface of the container 112.
A piezoelectric actuator is disclosed which forms 4, 116, 118 and 120 and measures the displacement amount regardless of the influence of the adhesive.

[0006]

However, there is a problem that the strain gauge is susceptible to disturbance depending on the number of sheets and the place where the strain gauge is bonded. For example, Japanese Patent Laid-Open No. 3-2
In the piezoelectric element actuator disclosed in Japanese Patent No. 35001, as shown in FIG. 4A, when a bending force FY is applied to the piezoelectric element actuator 100, the piezoelectric element actuator 100 bends and the strain gauges 102 and 104 bend. It also detects distortion in the direction,
That is detected as a part of the distortion in the expansion / contraction direction.

That is, in the equation (1), when the bending strain is εBY, ε0 = εA -εD = (εP + εt + εBY)-(-νεBY + εt) = εP + εBY (1 + ν), and the output VST of the bridge circuit is bent. The distortion εBY is included and cannot be distinguished, resulting in a measurement error.

Therefore, the inventor of the present invention has
In order to reduce the measurement error due to the moment when a bending force FY from the direction is applied to the piezoelectric element actuator, we proposed a 4-gauge active dummy method that uses four strain gauges.
I am applying for No. 4.

That is, as shown in FIG. 5B, a similar strain gauge 1 is formed on the surface which faces the surface of the piezoelectric element actuator 100 to which the strain gauges 102 and 104 are attached.
02 'and 104' are attached, and these strain gauges 102, 104, 102 ', 10 are attached as shown in FIG.
4'constitutes a bridge circuit.

Here, the strain gauges 102, 104, 10
The strains detected at 2'and 104 'are represented by ε 102, ε 104, ε
102 ′, ε104 ′, and the bending strain due to bending force FY is εBY, ε0 = ε102 −ε104 + ε102′−ε104 ′ = (εP + εBY) − (− νεP −νεBY) + (εP −ε
BY)-(-νεP + νεBY) = 2εP (1 + ν), and the bending strain is canceled.

As described above, in the piezoelectric element actuator of Japanese Patent Application No. 6-112864, it is possible to reduce the measurement error due to the moment when the bending force FY from one direction is applied. As shown in B), the countermeasure against the case where the bending force FX in the direction orthogonal to the bending force FY is added is still insufficient.

That is, the bending strain when the bending force FX is applied to the piezoelectric element actuator 100 is ε.
If BX, then ε0 = ε102 -ε104 + ε102'-ε104 '= (εP)-(νεP -εBX) + (εP)-(-νεP
−εBX) = 2εP (1 + ν) + 2εBX, and the bending strain εBX is not canceled and is detected as a part of the strain in the expansion / contraction direction, resulting in a measurement error.

Similarly, in the piezoelectric element actuator disclosed in Japanese Patent Laid-Open No. 63-283180, strain gauges 114, 1
The strains measured at 16, 118 and 120 are ε 11
4, ε116, ε118 and ε120, and bending strains due to bending forces FX and FY are εBX and εBY, then ε0 = ε114 -ε116 + ε118 -ε120 = (εP + εBX)-(-εBY) + (εP + εBX)-(-
εBY) = 2 (εP + εBX + εBY), and since the output of the bridge circuit includes εBX and εBY and cannot be distinguished, a measurement error occurs.

The present invention has been made in view of the above points, and cancels bending strain due to bending force in the two X-axis and Y-axis directions to eliminate a measurement error, thereby extending and contracting directions of the piezoelectric element actuator. It is an object of the present invention to provide a piezoelectric element actuator that can detect only the displacement amount of 1 and measure uniaxial displacement with high accuracy.

[0015]

In order to achieve the above object, a piezoelectric element actuator according to the present invention comprises a piezoelectric element having a plurality of surfaces each parallel to a stretching direction, and a plurality of surfaces of the piezoelectric element. A plurality of strain gauges, which are bonded to each of the four surfaces having a right angle relationship with each other, for measuring the displacement in the expansion and contraction direction, and the piezoelectric including bending strains of the plurality of strain gauges. A plurality of bridge circuits for detecting a value corresponding to the amount of expansion and contraction of the element in the direction of expansion and contraction, and arithmetic processing of the outputs of the plurality of bridge circuits so as to cancel bending strain in directions other than the direction of expansion and contraction of the piezoelectric element. And a calculation means for performing the calculation.

[0016]

That is, according to the piezoelectric element actuator of the present invention, at least one sheet is arranged on each of the four surfaces of the piezoelectric element, which have a perpendicular relationship to each other, to measure the displacement in the expansion / contraction direction. A plurality of strain gauges are adhered to each other, and a bridge circuit detects a value corresponding to the expansion / contraction amount in the expansion / contraction direction of the piezoelectric element including the bending strain of each of the plurality of strain gauges. Then, in the calculating means, so as to cancel the bending strain in a direction other than the expansion and contraction direction of the piezoelectric element,
The outputs of the plurality of bridge circuits are arithmetically processed to calculate the expansion / contraction amount of the piezoelectric element.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. In the piezoelectric element actuator of the present embodiment, as shown in FIGS. 1A and 1B, the strain gauges 12, 14, 16, 18 are respectively provided on the four side surfaces of the quadrangular prism-shaped piezoelectric element actuator 10. Sheet by sheet, ie 9
It is glued 0 ° apart. The strain gauges 12, 14, 16 and 18 are connected to the corresponding bridge circuits 20, 22, 24 and 26 as shown in FIG. These bridge circuits 20, 22, 24,
As shown in FIG. 2A, the inside of 26 is composed of one strain gauge 12, 14, 16, or 18 and three fixed resistors R1, R2, R3. Then, the output Vst of each bridge circuit 20, 22, 24, 26
Is connected to the calculation unit 28, and is calculated by the calculation unit 28 so as to cancel the bending strain, and the result is displayed on the output monitor 30.

The type piezoelectric element actuator 10 having such a configuration is used by being incorporated in an inverted microscope 32 as shown in FIG. 2B, for example. That is, the piezoelectric element actuator 10 is connected to one end of the lever 34, and the other end of the lever 34 is connected to the movable portion 36.
The movable unit 36 is connected to the focusing unit 38. Here, by measuring the displacement amount of the piezoelectric element, the displacement amount of the focusing portion 38 can be known. For example, when this is used in a laser scanning microscope, the displacement amount of the quasi-focal part can be accurately known, so that the three-dimensional construction image of the slice image becomes clearer. Here, in order to cope with the fact that the piezoelectric element generally has a small amount of displacement, a lever 34 is used as an enlarging mechanism, as shown in FIG.

Next, the operation of this embodiment will be described. That is,
When the laminated piezoelectric element actuator 10 having the above structure is used, the amount of fine movement can be increased by the magnifying mechanism using the lever 34 as shown in FIG. Occurs, and a bending force is applied to the piezoelectric element actuator 10.

FIG. 3B shows the bending force F.
4 shows how the piezoelectric element actuator 10 is deformed when X and FY are applied to the piezoelectric element actuator 10. That is, due to the bending force FX, tension is applied to the strain gauge 14 and compression is applied to the strain gauge 18. Further, due to the bending force FY, tension is applied to the strain gauge 16 and compression is applied to the strain gauge 12.

In such a case, the respective distortions are detected by the bridge circuit as shown in FIG.
8, the strain gauge 14 tension is strain gauge 18
At the same time it is canceled by the compression of
The tension of the strain gauge 16 is calculated so as to be canceled by the compression of the strain gauge 12.
That is, when bending strain due to bending force occurs, strain detected by strain gauges 12, 14, 16, 18 is ε 12, ε 14, ε 16, ε 18, strain due to piezoelectric element and piezoelectric inverse effect is ε P, and bending force FY is caused. If the bending strain is εBY and the bending strain due to the bending force FX is εBX, then ε12 = εp + εBX ε14 = εp + εBY ε16 = εp −εBX ε18 = εp −εBY. Perform processing.

Ε0 = ε12 + ε14 + ε16 + ε18 = (εp + εBX) + (εp + εBY) + (εp−εBX) +
(Εp−εBY) = 4εP, the bending strain is canceled, the output of the bridge circuit is only strain due to the piezoelectric inverse effect, and the measurement error is eliminated. Further, there is also an effect that the output becomes four times as large as the output when one strain gauge is used.

According to the above construction, even if bending strain occurs due to bending force in the X and Y biaxial directions, the displacement amount measurement in the expansion / contraction direction is not affected, and the displacement measurement of the piezoelectric element actuator is highly accurate. Therefore, it is possible to perform uniaxial positioning by the piezoelectric element actuator with high accuracy.

Of course, the present invention is not limited to the above embodiment. For example, in FIG.
The piezoelectric element actuator may have a cross section other than a quadrangle, such as an octagon as shown in FIG.

Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications and applications are possible within the scope of the present invention. Here, the summary of the present invention is summarized as follows.

(1) At least 1 is provided for each of the piezoelectric element having a plurality of surfaces parallel to the expansion and contraction direction and each of the four surfaces having a right angle relationship among the plurality of surfaces of the piezoelectric element.
Detecting a plurality of strain gauges, which are bonded one by one, for measuring the displacement in the expansion / contraction direction, and a value corresponding to the expansion / contraction amount in the expansion / contraction direction of the piezoelectric element including the bending strain of each of the plurality of strain gauges. A plurality of bridge circuits, and a computing means for computing the outputs of the plurality of bridge circuits so as to cancel the bending strain in a direction other than the expansion / contraction direction of the piezoelectric element. Element actuator.

That is, even if bending strain due to bending force from the two X- and Y-axis directions occurs, the displacement in the expansion / contraction direction is calculated by canceling the bending strain in directions other than the expansion / contraction direction of the piezoelectric element. Since the quantity measurement is not affected and the displacement of the piezoelectric element actuator can be measured with high accuracy, it is possible to perform positioning of one axis by the piezoelectric element actuator with high accuracy.

(2) A piezoelectric element in which at least one strain gauge is arranged on each of the four sides separated by 90 ° and a strain gauge for measuring the displacement in the expansion / contraction direction is provided for each strain gauge. A piezoelectric element actuator comprising: a bridge circuit composed of a fixed resistor and three fixed resistors, and an arithmetic means for arithmetically processing each output of the bridge circuit.

That is, even if bending strain due to bending force from the two X- and Y-axis directions occurs, the displacement in the expansion / contraction direction is calculated by canceling the bending strain in directions other than the expansion / contraction direction of the piezoelectric element. Since the quantity measurement is not affected and the displacement of the piezoelectric element actuator can be measured with high accuracy, it is possible to perform positioning of one axis by the piezoelectric element actuator with high accuracy.

(3) The piezoelectric element actuator according to (1) or (2), wherein the arithmetic means adds the outputs of the plurality of bridge circuits. That is, it can be canceled by adding bending strains in opposite directions.

(4) A piezoelectric element which expands and contracts in response to an applied voltage and a tension is applied when the piezoelectric element is displaced by an external pressure applied in a first direction perpendicular to the expansion and contraction direction of the piezoelectric element. A first strain gauge and a second strain gauge arranged to apply compression when the piezoelectric element is displaced by an external pressure applied in the first direction.
And a third strain gauge arranged to apply tension when the piezoelectric element is displaced by an external pressure applied in a second direction perpendicular to the expansion and contraction direction of the piezoelectric element and perpendicular to the first direction. Strain gauge, a fourth strain gauge arranged to apply compression when the piezoelectric element is displaced by an external pressure applied in the second direction, and tensions of the first to fourth strain gauges. And first to fourth bridge circuits for detecting a value corresponding to the amount of expansion / contraction in the expansion / contraction direction of the piezoelectric element, including bending distortion due to compression, and the bending distortion of the piezoelectric element in directions other than the expansion / contraction direction. like,
A piezoelectric element actuator comprising: an arithmetic unit that performs addition arithmetic processing on the outputs of the first to fourth bridge circuits.

That is, even if bending strain due to bending force from the X and Y biaxial directions occurs, the displacement in the expansion / contraction direction is calculated by canceling the bending strain in directions other than the expansion / contraction direction of the piezoelectric element. Since the quantity measurement is not affected and the displacement of the piezoelectric element actuator can be measured with high accuracy, it is possible to perform positioning of one axis by the piezoelectric element actuator with high accuracy.

[0033]

As described in detail above, according to the present invention,
By canceling bending strain due to bending force from the X and Y biaxial directions and eliminating measurement errors, it is possible to detect only the displacement amount of the piezoelectric element actuator in the expansion and contraction direction and perform highly accurate uniaxial displacement measurement. The piezoelectric element actuator can be provided.

[Brief description of drawings]

1A to 1C are a perspective view, a plan view, and a block configuration diagram for explaining a configuration of a piezoelectric element actuator of an embodiment.

2A is a diagram showing a circuit configuration of each bridge circuit in FIG. 1C, and FIG. 2B is a front view of an inverted microscope using the piezoelectric element actuator of the embodiment.

3A is a diagram showing an enlarging mechanism, FIG. 3B is a diagram showing bending of a piezoelectric element, and FIG. 3C is a plan view of a piezoelectric element actuator of another embodiment.

4A and 4B are a perspective view showing a configuration of a conventional piezoelectric element actuator and a circuit configuration diagram of a displacement amount measuring bridge circuit.

5A is a perspective view showing another example of a conventional piezoelectric element actuator, and FIGS. 5B and 5C are perspective views and displacements showing yet another example of a conventional piezoelectric element actuator. It is a circuit block diagram of a bridge circuit for quantity measurement.

[Explanation of symbols]

10 ... Piezoelectric actuator 12, 14, 16, 18 ... Strain gauge 20, 22, 24, 26 ... Bridge circuit 28 ... Operation unit 30 ... Output monitor 32 ... Inverted microscope 34 ... 36 ... Movable part 38 ... Semi-focus section

Claims (3)

(57) [Claims] 1. A piezoelectric element having a plurality of surfaces each parallel to a direction of expansion and contraction, and at least one sheet bonded to each of four surfaces of the plurality of surfaces of the piezoelectric element having a mutually orthogonal relationship, A plurality of strain gauges for measuring the displacement in the expansion / contraction direction, and a plurality of bridge circuits for detecting a value corresponding to the expansion / contraction amount in the expansion / contraction direction of the piezoelectric element including the bending strain of each of the plurality of strain gauges. A piezoelectric element actuator comprising: arithmetic means for arithmetically processing the outputs of the plurality of bridge circuits so as to cancel bending strain in a direction other than the expansion / contraction direction of the piezoelectric element. 2. At least one on each of four sides separated by 90 °
Piezoelectric elements in which strain gauges for measuring displacement in the expansion and contraction direction are arranged one by one, a bridge circuit that is provided for each of the strain gauges and that is composed of the strain gauge and three fixed resistors, and the bridge circuit. A piezoelectric element actuator comprising: an arithmetic unit that arithmetically processes each output. 3. The piezoelectric element actuator according to claim 1, wherein the arithmetic means adds outputs of the plurality of bridge circuits.