JP2001082909A - Capacity type distortion sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion sensor easy to be corrected by forming a distortion sensor portion comprising a pair of cross finger electrodes on a surface of a substrate having a film with a dielectric constant varying with distortion, and a reference capacitor portion comprising cross finger electrodes with the same shape. SOLUTION: A dielectric layer 4 comprising a material with dielectric constant varying with distortion is formed on a surface of a ceramics substrate 3 having regions with different thicknesses. A pair of cross finger electrodes are formed on a deformed surface 11 to provide a capacity type distortion sensor portion 1, and electrodes with the same shape as the capacity type distortion sensor portion 1 are formed on a deformed surface 12 to provide a reference capacitor portion 2 for correcting temperature, and this capacity type distortion sensor 20 is constructed. A temperature characteristic of the reference capacitor portion 2 is the same as the capacity type distortion sensor portion 1, a change amount of the capacity of the capacity type distortion sensor portion 1 in relation to peripheral temperature change is corrected with a change amount of the capacity of the reference capacitor portion 2, and a change amount of the capacity in relation to the change of distortion due to an external pressure is determined. This allows the temperature correction in a simple structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type strain sensor utilizing the effect of changing the capacitance due to distortion, and more particularly, to a capacitance correction capacitor for correcting the capacitance of the capacitance type strain sensor. The present invention relates to a capacitance-type strain sensor that performs correction using capacitance.

[0002]

2. Description of the Related Art Conventionally, a strain gauge whose resistance value changes due to strain has been used for a strain sensor. These strain gauges can be roughly classified into those using a metal and those using a semiconductor. The latter strain gauge using a semiconductor has a sensitivity several tens of times higher than the former strain gauge using a metal due to a piezoresistance effect, and thus is convenient as a strain sensor.

However, a strain gauge using a semiconductor has a drawback that a resistance change due to a temperature is large and a strain sensitivity changes according to a strain amount. Therefore, when a minute strain is measured, the configuration becomes complicated. There was a problem.

Therefore, a capacitance type strain sensor has been developed which utilizes the fact that the capacitance changes due to the change in dielectric constant due to strain. The capacitance type strain sensor has a simple structure and can constitute an LC oscillation circuit or an RC oscillation circuit, and is very effective even when measuring a minute strain.

[0005]

However, the capacitance of the capacitance type strain sensor varies not only with the change in the amount of strain but also with the change in the ambient temperature. Therefore, a correction circuit for correcting the characteristic change is required, and there is a problem that this configuration is complicated and expensive.

Accordingly, the present invention is to provide a capacitance type strain sensor which eliminates the drawbacks of the capacitance type strain sensor, has a simple structure, and can easily perform correction.

[0007]

According to the present invention, in a capacitance type strain sensor utilizing an effect of changing a dielectric constant by strain, the same material as a capacitance type strain sensor portion is used.
And a capacitor having substantially the same capacitance as a reference capacitor portion, wherein a change in capacitance of the capacitance type strain sensor due to temperature or the like is corrected by the capacitance of the reference capacitor portion. A type strain sensor is obtained.

According to the present invention, a thick film or a thin film layer made of a material whose dielectric constant changes due to strain is formed on a deformable surface of a structure in which a surface deformed by external stress and a surface not deformed are integrally formed. To form a capacitive strain sensor by forming at least a pair of interdigital electrodes on the surface thereof, and form the capacitive strain sensor on the same thick film or thin film that is not deformed. In addition, a capacitance type strain sensor having a reference capacitor portion having substantially the same capacitance is obtained.

Further, according to the present invention, the temperature distortion is corrected by utilizing the impedance of the capacitance of the capacitance type strain sensor unit and using the impedance of the reference capacitor unit. A sensor is obtained.

Further, according to the present invention, an LC or RC oscillating circuit including the capacitance of the capacitance type strain sensor unit is constituted, and the oscillating circuit including the reference capacitor unit similarly configured for the oscillating frequency. The capacitance type strain sensor is characterized in that the temperature is corrected using the oscillation frequency.

That is, the present invention provides a capacitance type strain sensor unit comprising at least a pair of interdigital electrodes and a pair of said pair of electrodes on a surface of a ceramic substrate on which a film layer made of a material whose dielectric constant changes due to strain is formed. This is a capacitance-type strain sensor in which a reference capacitor section including the interdigital electrode having the same shape as the interdigital electrode is formed.

Further, the present invention is the above-mentioned capacitance type strain sensor, wherein the ceramic substrate comprises a thin portion and a thick portion.

Further, the present invention is the above-mentioned capacitive strain sensor, wherein the capacitive strain sensor section is formed on the thin portion and the reference capacitor is formed on the thick portion.

Further, the present invention is the above-mentioned capacitive strain sensor, wherein the capacitance-dependent change in the capacitance of the capacitive strain sensor is corrected by the capacitance of the reference capacitor.

Further, the present invention is the above-mentioned capacitive strain sensor which performs temperature correction using the impedance of the capacitive strain sensor section and the impedance of the reference capacitor section.

Further, the present invention provides an oscillation circuit comprising LC or RC including the capacitance of the capacitance type strain sensor unit and LC or R including the capacitance of the reference capacitor unit.
The capacitance type strain sensor performs temperature correction using an oscillation frequency of an oscillation circuit including C.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a capacitive strain sensor according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory diagram of a capacitance type strain sensor according to the present invention. In FIG. 1, a dielectric layer 4 made of a material whose dielectric constant changes due to strain is formed on a plane of a ceramic substrate 3 having regions having different thicknesses. Here, the ceramic substrate 3 deforms the surface of the thin plate region which receives a large strain due to the external pressure by the deformation surface 11 due to the strain,
A surface having a large thickness that does not deform when subjected to external pressure is defined as a deformed surface 12 due to distortion.

The capacitive strain sensor 20 includes a pair of interdigital electrodes formed on a deformed surface 11 to form a capacitive strain sensor unit 1.
Is formed, and an electrode having the same shape as the capacitance type strain sensor unit 1 is formed on the deformed surface 12 to constitute a reference capacitor unit 2 for temperature correction.

Here, the change in the capacitance of the capacitance type strain sensor unit 1 will be described with reference to FIG.

FIG. 2 shows a basic structure of the interdigital electrode 13 of the capacitive strain sensor 1. In FIG. 2, every other linear electrode 14 is connected to a common electrode 15 on a dielectric layer 4 formed on a ceramic substrate 3, and the interdigital electrodes 13 are adjacent to each other. 14
And two terminals having a pair of terminals 16 so as to have a capacitance between them.

Next, the relationship between the pressing force and the capacitance of the capacitance type strain sensor unit 1 shown in FIG. 1 will be described with reference to FIG.

FIG. 3 shows a rectangular zirconia porcelain plate having excellent flexibility as a ceramic substrate, on which a lead-based high dielectric constant thick film used for a ceramic capacitor or the like is formed. On this, the interdigital electrode in which the direction of the linear electrode 14 of the interdigital electrode 13 shown in FIG. 2 was parallel to the short side of the zirconia porcelain plate was formed.

The relationship between the pressing force and the capacitance when the central portion parallel to the short side of the rectangular zirconia porcelain plate is pressed by a knife-edge-shaped pressing plate is shown. In FIG. 3, the line marked with □ indicates the case where the back surface of the interdigital electrode surface is pressurized, and the line indicated with △ indicates the measured value obtained when the interdigital electrode surface is pressurized.

As can be seen from FIG. 3, in the case of the seal, the rate of change of the capacitance increases as the pressing force increases, despite the deformation in which the distance between the linear electrodes increases. Conversely, in the case of the mark △, the distance between the linear electrodes is reduced, and when strain is applied to the dielectric layer, the rate of change in capacitance decreases as the applied pressure increases, and the dielectric constant in that direction decreases. So-called "positive strain-dielectric constant characteristics"
Has been shown.

When a material having a large "strain-permittivity characteristic" is used as the material of the dielectric layer, the change in the capacitance between the terminals is smaller than the change in the capacitance simply due to the change in the electrode interval. growing.

The capacitance type strain sensor using a material having a large "strain-permittivity characteristic" has a simple structure and can easily constitute an LC oscillation circuit or an RC oscillation circuit.
Although very effective in practical use, the capacitance also changes due to a change in ambient temperature, so it is necessary to correct the change in capacitance due to temperature.

The temperature characteristic of the reference capacitor unit 2 shown in FIG. 1 is the same as the temperature characteristic of the capacitance type strain sensor unit 1, and the capacitance characteristic of the capacitance type strain sensor unit 1 with respect to a change in ambient temperature. By correcting the amount of change in capacitance with the amount of change in capacitance of the reference capacitor unit 2, the amount of change in capacitance with respect to the change in distortion due to external pressure can be obtained.

Hereinafter, two specific examples of the correction method will be described.

First, a first correction example will be described with reference to FIG.

FIG. 4 is a circuit diagram for performing temperature correction using the impedance of the reference capacitor using the impedance of the capacitance of the capacitance type strain sensor.
In FIG. 4, the capacitor 17 and the resistor 5 represent the capacitance and the internal resistance of the capacitive strain sensor unit, and the capacitor 18 and the resistor 6 represent the capacitance and the internal resistance of the reference capacitor unit. Temperature characteristics and internal resistance of the capacitance of the capacitance type strain sensor unit and the reference capacitor unit are
Since they are almost equal, each impedance is taken out from the output terminal as a voltage value, and the difference is calculated by the comparator 7.
The temperature is corrected by using the above equation.

Next, a second correction example will be described with reference to FIG.

FIG. 5 shows an LC or RC oscillating circuit including the capacitance of the capacitance type strain sensor unit, and the oscillation frequency of the oscillating circuit including the reference capacitor unit which is similarly configured with respect to the oscillating frequency. FIG. 3 is a configuration diagram for performing temperature correction using the configuration. In FIG. 5, the oscillation circuits 8 and 9
Is an LC or RC oscillation circuit configured using a capacitance type strain sensor unit and a reference capacitor unit, respectively. The output of each of them is f−f because the output frequency changes when the capacitance changes. The voltage is converted by the v-converter 19 and the difference is obtained using the comparator 10 to perform temperature correction.

In the above description, the dielectric layer is a high dielectric constant thick film used for a ceramic capacitor or the like. However, as a capacitor for the reference capacitor portion, a dielectric material, a film thickness and a cross finger are used. When the electrode dimensions are substantially equal to those of the capacitor for the capacitive strain sensor, they need not necessarily be formed on the same surface, and the capacitor 17 for the capacitive strain sensor and the capacitor for the reference capacitor are not required. If the temperature environment of the capacitor 18 is considered to be the same, these may be separately arranged. Further, in the case of a dielectric, the influence of the temperature is large, so only the temperature correction has been described. However, for example, other environmental factors such as humidity are also corrected.

[0035]

As described above, according to the present invention, it is possible to obtain a capacitance type strain sensor having a simple structure and capable of easily performing temperature correction.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a capacitance type strain sensor of the present invention.

FIG. 2 is a plan view showing the structure of a capacitive strain sensor unit of the capacitive strain sensor of the present invention.

FIG. 3 is a diagram showing a pressing force-capacitance characteristic of an interdigital electrode type capacitor formed on a dielectric layer on a zirconia ceramic plate in the capacitance type strain sensor of the present invention.

FIG. 4 is a circuit configuration diagram of a capacitance type strain sensor that performs a temperature correction using impedance, showing a first correction example according to the present invention.

FIG. 5 is a circuit configuration diagram of a capacitance type strain sensor that performs a temperature correction using an LC and RC oscillation circuit, showing a second correction example according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Capacitance type strain sensor part 2 Reference capacitor part 3 Ceramics substrate 4 Dielectric layer 5 Resistance (inside a capacitance type strain sensor) 6 Resistance (inside a reference capacitor) 7 Comparator (for impedance comparison) 8 ( LC or RC including capacitive strain sensor)
Oscillation circuit 9 (LC or RC including reference capacitor) Oscillation circuit 10 Comparator (for comparing oscillation frequencies) 11 Deformed surface 12 Deformed surface 13 Interdigital electrode 14 Linear electrode 15 Common electrode 16 Terminal 17 Capacitor 18 Capacitor 19 f− V converter 20 Capacitive strain sensor

Claims (6)

[Claims] 1. A capacitive strain sensor comprising at least a pair of interdigital electrodes and a pair of interdigital electrodes on a surface of a ceramic substrate on which a film layer made of a material whose dielectric constant changes due to strain is formed. An electrostatic capacitance type strain sensor comprising a reference capacitor portion formed of interdigital electrodes of the same shape. 2. The capacitance type strain sensor according to claim 1, wherein the thickness of the ceramic substrate comprises a thin portion and a thick portion. 3. The capacitance type strain sensor according to claim 2, wherein said capacitance type strain sensor portion is formed in said thin portion and said reference capacitor is formed in said thick portion. 4. The electrostatic capacitance according to claim 1, wherein a change in the capacitance of the capacitance type strain sensor is corrected by the capacitance of the reference capacitor. Capacitive strain sensor. 5. The capacitive strain sensor according to claim 1, wherein the correction is performed using the impedance of the capacitive strain sensor and the impedance of the reference capacitor. . 6. Oscillation of an oscillation circuit composed of LC or RC including capacitance of the capacitance type strain sensor unit and an oscillation circuit composed of LC or RC including capacitance of the reference capacitor unit. The capacitance type strain sensor according to claim 1, wherein the correction is performed using a frequency.