JPH0979920A - Force detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a force detecting device which is improved in temperature characteristic, sensitivity, and resolution. SOLUTION: One ends of two parallel piezoelectric substrates 2 and 4 having piezoelectric properties are fixed with a weight member 1 while the other ends of the substrates 2 and 4 are held on a fixed base 6. Two resonators which utilize surface acoustic waves are provided on the external side faces of the substrates 2 and 4 opposite to the internal side faces facing each other in conductive patterns. Each resonator is provided with a plurality of reflecting elements 5 which are separated from each other in the propagating direction of the surface acoustic waves and a pair of comb-shaped electrodes 3 which are positioned between the reflecting elements and convert the surface acoustic waves into electric signals. Input-output terminals 7 are connected to the electrodes 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a force detection device for detecting the magnitude of an external force, and more particularly to a device for detecting vibration or acceleration of an automobile or the like, a device for detecting camera shake, or a magnitude of gravity. TECHNICAL FIELD The present invention relates to a force detection device suitable for a device for detecting a tilt angle to obtain an inclination angle.

[0002]

2. Description of the Related Art Conventionally, there are a force detecting device using a strain gauge resistor made of a metal resistor and a device utilizing the piezoresistive effect of a semiconductor. An example thereof is shown in FIG.

In the force detecting device shown in FIG. 4, a weight member 8 is fixed to the other end of an elastic plate 9 whose one end side is fixedly held on a fixed base 11. A strain gauge resistor 10 is provided between both ends of the elastic plate 9. Reference numeral 12 is an input / output terminal.

According to this force detecting device, the force applied to the elastic plate 9 is detected by the resistance change of the strain gauge resistor 10.
That is, the resistance change of the strain gauge resistor 10 is taken out through the input / output terminal 12.

[0005]

However, although the strain gauge resistance is suitable for mass production, it has the problems of poor temperature characteristics and low sensitivity.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide a force detection device that improves temperature characteristics, sensitivity, and resolution.

[0007]

According to the present invention, two elastic plates having piezoelectricity and parallel to each other, holding means for holding one end of the two elastic plates, and the two elastic plates. There is provided a force detecting device characterized by including fixing means for fixing the other ends of the two elastic plates to each other and two resonators respectively provided on the two elastic plates and utilizing surface acoustic waves of the elastic plates.

Further, according to the present invention, the surface acoustic waves are electrically coupled to each other on a plurality of reflecting elements which are parallel to each other and which have piezoelectricity, and which are located between a plurality of reflecting elements separated in the propagation direction of the surface acoustic waves. A resonator composed of a pair of comb-shaped electrodes for converting into a signal is formed of a thin film, and the reflection element is formed with a plurality of conductor patterns extending in a direction perpendicular to the propagation direction in parallel to each other and The two ends of the pattern are electrically connected, and the two elastic plates are partially held by holding the fixing base so that the surfaces on which the resonators are arranged are opposite to each other. A weight member for holding an inertial force is held at the tip on the side opposite to the fixed base, and the output from each of the resonators is input to a subtraction circuit to determine the difference between the resonance frequencies of the two resonators. Force test characterized by having been obtained Device is obtained.

[0009]

When the two elastic plates are subjected to an external force, they are distorted accordingly. As a result of this distortion, one of the two resonators has a high resonance frequency and the other has a low resonance frequency. Therefore, the magnitude of the strain, that is, the force applied to the elastic plate can be detected by the difference between these resonance frequencies.

By making the elastic plates identical, the temperature characteristics of the resonance frequencies of the two resonators can be made the same. Therefore, in this case, even if the resonance frequency changes due to the change in ambient temperature, the difference in resonance frequency does not change depending on the temperature.

[0011]

1 shows a force detection device according to an embodiment of the present invention. This force detecting device has piezoelectric substrates (hereinafter referred to as elastic plates) 2 and 4 made of a piezoelectric material as two elastic plates having piezoelectricity and parallel to each other, and one end of each of these elastic plates 2 and 4. Fixed table 6 as holding means for holding
And a weight member 1 for obtaining an inertial force that also serves as a fixing means that fixes the other ends of the two elastic plates 2 and 4, and the surface elasticity of the elastic plates provided on the two elastic plates 2 and 4, respectively. Use the waves 2
It includes two resonators. Each of the resonators is composed of a conductor pattern formed on the outer surface of the two elastic plates 2 and 4 that is opposite to the inner surface of the elastic plates 2 and 4, which face each other. It has one reflective element 5 and a pair of comb-shaped electrodes 3 which are located between these reflective elements 5 and convert surface acoustic waves into electric signals. An input / output terminal 7 is connected to these comb electrodes 3.

The conductor pattern forming each resonator may be formed on the inner surface of the two elastic plates 2 and 4. Further, each elastic plate may be one in which a piezoelectric thin film is formed on the surface of a plate member having elasticity.

This will be described in more detail. In each reflecting element 5, the conductor pattern 5 is formed of a thin film of aluminum or the like by means such as sputtering or vapor deposition, and a large number of them are arranged in parallel so as to extend in the direction orthogonal to the propagation direction of the surface acoustic wave. And both ends of each conductor pattern are electrically connected to each other. Since the two reflecting elements 5 are spaced apart from each other, a resonant cavity is formed between them, and a standing wave of a surface acoustic wave stands in this resonant cavity. A pair of comb-shaped electrodes 3 for converting surface acoustic waves into electric signals are arranged in the center between the two reflecting elements 5 so as to strongly couple with the standing waves. In the thus-configured resonator, when the wavelength of the signal excited by the comb-shaped electrode 5 is λ, the conductor pattern forming the reflective element 5 and the pattern width forming the comb-shaped electrode 3 are each λ / 4, and Interval is λ
/ 2.

Further, from each of the pair of comb-shaped electrodes 3,
The pattern extends near the fixed base 1 for fixing the elastic plates 2 and 4 in parallel with the propagation direction of the surface acoustic wave, and an input / output terminal 7 for extracting a signal from the resonator is provided at the tip of the pattern. There is.

Referring to FIG. 2 in addition to FIG. 1, each resonator 21, 22 is connected to a subtracting circuit 23. Specifically, the comb-shaped electrode 3 is connected to the subtraction circuit 23 via the input / output terminal 7.

The above-described structure has the same structure with the two elastic plates 2 and 4, and therefore the subtraction circuit 23 outputs a signal representing the difference between the resonance frequencies of the resonators 21 and 22.
The output signal of the subtraction circuit 23 is frequency / voltage converted, and converted into a voltage signal by a so-called FV conversion circuit 24 and output. This output and the external force applied to the elastic plates 2 and 4 have a proportional relationship, as is clear from FIG. 3 showing the mutual relationship between them. Therefore, it is possible to detect the external force applied to the elastic plates 2 and 4.

The output from the subtraction circuit 23 may be input to a frequency counter or the like to read the frequency. Also by this, the external force applied to the elastic plates 2 and 4 can be detected.

[0018]

As described above, in the force detecting device according to the present invention, one of the two elastic plates has a high resonance frequency due to the surface acoustic wave formed on each of the elastic plates. Since the other becomes low, the high sensitivity and resolution can be realized by detecting the external force by the difference in the resonance frequency.

Further, since the two elastic plates are exactly the same, there is no difference in the resonance frequencies of the two resonators even if the ambient temperature changes, so that stable force detection is possible even if the ambient temperature changes. A device can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view showing a force detection device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a part of the force detection device of FIG.

FIG. 3 is a graph showing the relationship between external force and output by the force detection device of FIG.

FIG. 4 is a perspective view showing an example of a conventional force detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Weight member 2,4 Piezoelectric substrate (elastic plate) 3 Comb-shaped electrode 5 Reflective element 6 Fixing stand 7 Input / output terminal 8 Weighting member 9 Elastic plate 10 Strain gauge resistance 11 Fixing stand 12 Input / output terminal 21,22 Resonator 23 Subtraction Circuit 24 F-V conversion circuit

Claims (8)

[Claims] 1. Two elastic plates having piezoelectricity and parallel to each other, holding means for holding one ends of the two elastic plates, and fixing means for fixing the other ends of the two elastic plates. , The above 2
A force detecting device comprising: two resonators, each of which is provided on each of the elastic plates and uses surface acoustic waves of the elastic plates. 2. Each of the resonators is composed of a conductor pattern formed on one of an inner surface of the two elastic plates facing each other and an outer surface of the two elastic plates opposite to each other. Item 1. The force detection device according to item 1. 3. Each of the resonators has a plurality of reflecting elements that are separated from each other in the propagation direction of the surface acoustic wave, and an electrode that is located between the plurality of reflecting elements and that converts the surface acoustic wave into an electric signal. The force detection device according to 1 or 2. 4. The force detection device according to claim 1, wherein the fixing means has a weight member for obtaining an inertial force. 5. The force detection device according to claim 1, further comprising a subtraction circuit for obtaining a difference between resonance frequencies of the two resonators. 6. The force detection device according to claim 1, wherein each elastic plate is made of a piezoelectric material. 7. The force detection device according to claim 1, wherein each of the elastic plates is a plate member on which a piezoelectric thin film is formed. 8. A plurality of reflective elements, which are parallel to each other and have piezoelectricity, are provided between a plurality of reflecting elements separated in the propagation direction of the surface acoustic wave, and the surface acoustic wave is converted into an electric signal. A resonator consisting of a pair of comb-shaped electrodes is formed in a thin film, the reflecting element forms a plurality of conductor patterns extending in a direction perpendicular to the propagation direction in parallel with each other, and both ends of these conductor patterns are electrically connected. The two elastic plates are partly fixed and held by sandwiching the fixing base so that the surfaces on which the resonators are arranged are opposite to each other. A weight member for obtaining an inertial force is held at the tip on the opposite side to the output of each of the resonators is input to a subtraction circuit to obtain the difference between the resonance frequencies of the two resonators. Force detection device characterized by.