JPH1030971A - Strain detecting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain detecting apparatus which is hardly subjected to the influence of a disturbance noise or the like and whose circuit configuration is simple. SOLUTION: This apparatus is constituted of a strain detection part 1 wherein a strain sensor 11 composed of a resistor and of a capacitor and an oscillator 12 whose oscillation frequency is decided by the electric resistance value of the resistor and by the capacitance value of the capacitor are formed on the same substrate, of a frequency detection part 2 which detects the oscillation frequency of the oscillator 12 and of a conversion part 3 in which the value of the detected frequency is converted into a strain value. Thereby, the strain value can be read out directly from a stress which is applied to the strain sensor 11. Alternatively, this apparatus is constituted in such a way that a plurality of strain detection parts 1 are installed and that a computing part which computes the position of a stress on the basis of information on installation positions of strain sensors 11 in the plurality of strain detection parts 1 and on the basis of oscillation frequencies of the oscillators in the respective strain detection parts 1 provided. Thereby, the position of the stress can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a strain detecting device. To detect strain, a strain sensor is usually attached to a subject, and a change in the resistance value is detected to convert the strain into strain.

[0002] In general, since the amount of change in resistance value due to strain is small, the electric signal obtained from the change in resistance value is also small. For this reason, an amplifier (amplifier) that amplifies electric signals
In addition to reducing internal noise, it is necessary to devise a detection method (such as using a bridge circuit) to suppress disturbance noise.

[0003]

2. Description of the Related Art The outline of three typical examples of conventional strain detecting devices will be described. In the first conventional example shown in FIG. 8, a change in the resistance value of the strain sensor is detected as a change in the balanced voltage of the bridge. Rg in the figure is a strain sensor (resistance)
It constitutes one side of the resistance bridge together with the wiring (one-way resistance value rl / 2), and if it is balanced in a state without distortion, when the distortion is applied, it is proportional to the magnitude of the distortion. , The output increases. In this case, either direct current (DC) or alternating current (AC) is used as the bridge drive power supply, but in the case of an AC power supply, the frequency is fixed.

In a second conventional example shown in FIG. 9, a vibrator of an oscillating circuit is used as a strain sensor, and a change in the oscillating frequency is detected to detect a strain. This is to convert a change in resistance value of the strain sensor into a change in frequency that is less susceptible to disturbance noise than a change in voltage.
Incidentally, an invention based on this principle is disclosed in Japanese Unexamined Patent Publication No. 5-157647.
Published in the issue.

In the third conventional example shown in FIG. 10, a change in the resistance value of the strain sensor is converted into a change in the balanced voltage of the bridge in the same manner as in the first example. The distortion is detected by detecting a change in the oscillation frequency when applied to a circuit. This is characterized in that it is hardly affected by noise and has high sensitivity. Incidentally, an invention based on this principle is disclosed in Japanese Patent Application Laid-Open No. 60-122336.

[0006]

However, the above-described conventional strain detectors have the following problems.

In the first conventional example, since a change in resistance is detected as a change in voltage using a bridge circuit, disturbance noise tends to be applied to a minute voltage, and the bridge circuit requires external parts with adjusted resistance. It is.

In the second conventional example, a complicated circuit configuration such as an AGC circuit is required. In the third conventional example, many constituent members are required. An object of the present invention is to provide a distortion detecting apparatus which is hardly affected by disturbance noise and the like and has a simple circuit configuration.

[0009]

According to the present invention, as shown in FIG. 1, an oscillation frequency is determined by a strain sensor 11 consisting of a resistor and a capacitor, and the value of the electric resistance of the resistor and the value of the capacitance of the capacitor. A distortion detecting section 1 in which an oscillator 12 is determined on the same substrate, a frequency detecting section 2 for detecting an oscillation frequency of the oscillator 12, and a converting section 3 for converting the value of the detected frequency to a distortion value. With this configuration, the value of the strain can be directly read from the stress applied to the sensor 11. Note that the resistor and the capacitor of the sensor form part of circuit elements of an oscillator, and an oscillator is formed including these elements. In the following description, the resistor and the capacitor of the sensor are used for convenience of explanation. The electronic circuit excluding the above may be called an oscillator.

[0010] By arranging two resistors and one capacitor on the same substrate, it is possible to use a Wien bridge oscillator. The two capacitors of the strain sensor are connected in parallel to each other, and the two capacitors are each formed of a comb-shaped electrode, and the lines indicating the comb directions of the comb-shaped electrodes of the two capacitors are orthogonal to each other. Thereby, the present invention can be mainly applied to an application utilizing a change in resistance value.

By disposing a plurality of the strain detecting units on the same substrate and making the oscillation frequencies of the oscillators of the respective strain detecting units different from each other, it becomes possible to know the distribution of the strain.

The frequency detecting section is configured to receive the electromagnetic wave induced from the oscillator, thereby increasing the degree of freedom in selecting the mounting position of the sensor. In addition, by providing an operation unit that calculates a stress position from information on the installation positions of the strain sensors of the plurality of strain detection units and the oscillation frequency of the oscillator of each of the strain detection units, the stress position can be known. become.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 2 shows a first embodiment of the present invention, in which a Wien bridge oscillator is used as an oscillator.

As is well known, assuming that the value of the electric resistance of the resistor in FIG. 2 and the value of the capacitance of the capacitor are R and C, respectively, the oscillation frequency f is given by the following equation. f = 1 / 2πRC It is assumed that the value R of the electric resistance of the resistor and the value C of the capacitance of the capacitor in the above equation change as follows according to the strain.

R = R ₀ (1 ± αε) C = C ₀ (1 ± βε) where R ₀ is the value of the electric resistance of the resistor before the occurrence of strain, C
₀ is the value of the capacitance of the capacitor before strain is generated, α is the rate of change in resistance due to strain, β is the rate of change in capacity due to strain, and ε is the strain (the change in length caused by the application of external force before the external force is applied). Divided by the total length of

Therefore, the oscillation frequency f is given by the following equation. f = 1 / 2πR ₀ (1 ± αε) C ₀ (1 ± βε) When the conditions of α ² << 1 and β ² << 1 are satisfied, the oscillation frequency f is given by the following equation ( order).

[0017]

(Equation 1)

That is, the change in the oscillation frequency due to the strain is proportional to the change in the value of the electrical resistance of the resistor and the change in the value of the capacitance of the capacitor, which change with the strain ε. Therefore, compared to the method using only the change in the electric resistance value of the resistor, the change in the frequency using the method using also the change in the capacitance value of the capacitor becomes larger, and the detection sensitivity of the distortion is increased. You can see that it rises.

In the case of this configuration, if the resistor and the capacitor are formed on the same substrate (for example, a polyimide substrate),
An oscillation circuit can be easily formed simply by adding an amplifier, and distortion can be detected as a frequency change.

In the above description, both the change in the value of the electric resistance of the resistor of the strain sensor and the change in the value of the capacitance of the capacitor are used, but only the value of the electric resistance of the resistor is changed. It is also possible to adopt a configuration in which these are performed.

FIG. 3 is an explanatory diagram of the deflection detection. The test object is a Si (Si) substrate in which a strain sensor comprising a resistor and a capacitor is attached to a silicon (Si) substrate, and is configured to generate a flexure in the plate by applying pressure from above the plate as shown in the figure. The figure shows the change Δf in the amount of deflection v and the oscillation frequency f of the oscillator.
An example of the relationship with is shown. As shown in the figure, the oscillation frequency decreases almost linearly with the amount of deflection. Therefore, by using an appropriate conversion means, it is possible to directly read the deflection amount from the change amount of the oscillation frequency.

FIG. 4 is a diagram showing a first configuration example of a strain sensor. FIG. 4A shows a pattern forming a strain sensor (resistor and capacitor) formed on a substrate, and FIG. An equivalent circuit is shown. For example, a polyimide film or a silicon substrate is used for the substrate, and the pattern is made of a metal thin film material (C
u Ni or the like is formed by a photolithography process.

In FIG. 4, the value of the electric resistance of the resistor and the value of the capacitance of the capacitor change with respect to the strain in the direction indicated by the arrow. FIG. 5 is a diagram illustrating a second configuration example of the strain sensor, and illustrates an example of the arrangement of the capacitors in a configuration in which only the value of the electrical resistance of the resistor is changed. That is, the strain sensor is configured by connecting two capacitors in parallel to each other, the two capacitors are both formed of comb electrodes, and the lines indicating the comb directions of the comb electrodes of the two capacitors are orthogonal to each other. By doing so, the value of the capacitance of the battery is made hard to depend on the distortion. That is, assuming that a tensile force is applied in the direction of strain in the figure, the upper capacitor has a reduced capacitance due to the effect of increasing the electrode spacing, and the lower capacitor has a static effect due to the effect of increasing the electrode area. It is considered that the electric capacity increases. In this case, if the Poisson's ratio of the substrate material constituting the capacitor is sufficiently small, the effect of reducing the distance between the electrodes of the lower capacitor can be neglected.
C ₁ ) and the amount of decrease (ΔC ₂ ) have substantially the same value, and a capacitor independent of distortion can be configured as shown in the equalizing circuit in the figure.

FIG. 6 shows a second embodiment of the present invention, in which a plurality of strain sensors are arranged on a substrate, and an oscillator is added to each of them to change the oscillation frequency (in the example of FIG. 6, f ₀ ~f _3). Oscillation frequency f _i in response to strain applied by each strain sensor _(i = 1 to 3, the same applies hereinafter) is changed by changing the amount of delta _i.

If the oscillation frequency is high, a wireless detection system in which the electromagnetic wave induced or emitted from the oscillator is detected by the frequency detection unit becomes possible. In this case, the degree of freedom of the installation location of the strain sensor increases.

FIG. 7 shows a third embodiment of the present invention, in which a stress position is calculated from the information on the installation positions of the strain sensors of the plurality of strain detecting units and the oscillation frequency of the oscillator of each of the strain detecting units. The configuration is such that an arithmetic unit is provided. In this embodiment,
Which position the operation unit to know the amount of change delta _i of frequency is large, that it is possible to identify the stress applying coordinates.

[0027]

According to the present invention, strain can be detected as a frequency change with a simple configuration, and a position where a stress has occurred can be wirelessly detected by disposing a plurality of strain detectors on a substrate. Becomes

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention,

FIG. 2 is a diagram showing a first embodiment of the present invention;

FIG. 3 is an explanatory diagram of deflection detection,

FIG. 4 is a diagram showing a first configuration example of a strain sensor;

FIG. 5 is a diagram showing a second configuration example of the strain sensor;

FIG. 6 is a diagram showing a second embodiment of the present invention;

FIG. 7 is a diagram showing a third embodiment of the present invention;

FIG. 8 is a diagram showing a first conventional example;

FIG. 9 is a diagram showing a second conventional example;

FIG. 10 is a diagram showing a third conventional example.

[Explanation of symbols]

1 is a strain detecting unit, 2 is a frequency detecting unit, 3 is a converting unit,
Is an operation unit, 11 is a strain sensor, and 12 is an oscillator.

Claims (6)

[Claims] 1. A strain sensor comprising a resistor and a capacitor, and a strain detector comprising an oscillator whose oscillation frequency is determined by the value of the electric resistance of the resistor and the value of the capacitance of the capacitor formed on the same substrate. A frequency detecting unit for detecting an oscillation frequency of the oscillator; and a converting unit for converting a value of the detected frequency into a value of distortion. 2. The strain detecting apparatus according to claim 1, wherein said oscillator is a Wien bridge oscillator in which each of said resistor and said capacitor is formed on the same substrate. 3. The strain sensor comprises two capacitors connected in parallel to each other, the two capacitors both comprising comb-shaped electrodes, and the combs of the comb-shaped electrodes of the two capacitors. 3. The strain detecting device according to claim 1, wherein the lines indicating the directions are orthogonal to each other. 4. The strain detecting section according to claim 1, wherein a plurality of strain detecting sections are formed on the same substrate, and the oscillators of the respective strain detecting sections have different oscillation frequencies when no strain is applied. 2. The strain detection device according to 2. 5. The distortion detection device according to claim 4, wherein the frequency detection unit receives an electromagnetic wave induced from the oscillator. 6. A position where a stress is applied based on position information of a strain sensor of the strain detecting unit and an oscillation frequency of the oscillator corresponding to each of the strain sensors. The strain detecting apparatus according to claim 4, wherein the distortion detecting apparatus calculates the following.