JPH08184404A - Displacement sensor, acceleration sensor and clinometer - Google Patents

Abstract

PURPOSE: To enhance the sensitivity and reliability while extending the linearity by arranging a weight in the center, suspending the weight with a shape-memory alloy wire having electric resistance variable due to strain in a plurality of directions, and detecting the electric resistance of the suspension wire. CONSTITUTION: Wires 2a, 2b are made of a shape-memory alloy exhibiting superelasticity and suspends a weight 1. The wires 2a, 2b are connected, at the opposite ends thereof, with electric conductors 6 which are connected, at the other ends thereof, with detection circuits 3a, 3b. Terminals 7 are provided between the weight 1 and the wires 2a, 2b. The circuits 3a, 3b are resistance bridge circuits and deliver detection signals (A), (B), respectively, to a measurement control circuit. When the weight 1 is displaced in the direction shown by an arrow by an external force, tensile force is applied to the wires 2a, 2b and the variation of resistance caused by corresponding strain is measured. When the relationship between the strain caused by tensile force and the variation of resistance is previously determined and an initial value is set, the strain can be determined based on the variation of resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a wire rod made of a shape memory alloy as a sensitive resistance element and utilizes the rate of change in electrical resistance due to strain change to detect a displacement amount and an acceleration sensor for detecting acceleration. , And an inclinometer for detecting an inclination angle.

[0002]

2. Description of the Related Art A large number of mechanical quantity measuring instruments for measuring the amount of elastic deformation due to tension by changing the electrical resistivity are used in the fields of civil engineering, construction, machinery and the like. For example, there are strain gages of both-supported beam type, load sensors, displacement sensors, and the like.
Alternatively, there is a cantilever type acceleration sensor having one end as a support portion and the other end as a free end, a displacement sensor, and the like. As the sensitive resistance element of the above-mentioned conventional sensor, Cu-Ni-based, Ni-
A metal resistor such as a Cr-based material, or a semiconductor resistance strain gauge is used.

Generally, in strain measurement due to a change in resistance value, it is important that the relationship of ΔR / R = Kε is established in the sensitive resistance element. Where R is the resistance of the metal resistor, ε
If the strain amount (deformation amount) and the gauge factor K are constant, the strain amount can be known from the resistance value change without performing non-linearity correction. That is, in accurate measurement,
It is necessary that the elastic limit range of the metal resistor material is wide and the gauge factor K is large and constant. This resistance change rate Δ
R / R was 0.5% or less in the above-mentioned conventional Cu-Ni, Ni-Cr-based metal resistor.

Further, an acceleration system using a cantilever type semiconductor resistance strain gauge has a high sensitivity and is small in size and is used in various fields, but it cannot cope with a large strain amount.

On the other hand, it is well known that shape memory alloys such as Ti-Ni type alloys and Cu-Zn type alloys exhibit a remarkable shape memory effect accompanying the reverse transformation of martensitic transformation. At the same time, it is well known that it exhibits good superelasticity. Here, the shape memory effect means that the strain received by the external force in the martensite phase is eliminated by heating, while the superelasticity eliminates the strain received by the external force without releasing the external force and without heating. It is a phenomenon. These strains that can be eliminated exceed the elastic limit strain and reach up to about 8%. Also in the shape memory effect, the strain that can be eliminated without heating is 1.5 to 2.
0%, which is larger than that of ordinary steel wire.

[0006]

In the conventional metal resistor, the resistance change rate ΔR / R within the elastic limit is Cu-Ni,
In the Ni-Cr based metal resistor, it was small at 0.5% or less.

Therefore, the first technical problem of the present invention is to provide a sensor member using a sensitive resistance element of a metal resistor capable of measuring strain over a wide range with high sensitivity and accuracy, a displacement sensor using the same, and an acceleration. It is to provide a sensor and an inclinometer.

Further, an accelerometer using a semiconductor resistance strain gauge has high sensitivity and is small in size, and is used in various fields, but it cannot cope with a large amount of strain.

Therefore, a second technical object of the present invention is to provide a highly reliable sensor member which can cope with a large amount of strain and a displacement sensor and an acceleration sensor using the same.

[0010]

In order to solve the above technical problems, in the sensor member of the present invention, a weight is arranged at the center, and the electric resistance is changed in two or more directions by a strain change. It is characterized in that it is suspended by a changing wire rod, and the other end portion on the opposite side of the weight is fixed so that tension strain is applied to the wire rod.

Here, in the sensor member of the present invention, the two or more wire rods on which the weight is suspended have the same properties and the same cross-sectional dimensions, thereby canceling the electric resistance fluctuation due to the environmental conditions of the detected wire rod portion. It is preferable.

Further, in the sensor member of the present invention, a current is caused to flow through each of the two or more wire rods on which the weight is suspended, so that the detected wire rod portion cancels the electric resistance fluctuation caused by the heat generation by the current. preferable.

Further, in the sensor member of the present invention, the wire rod for suspending the weight has a round wire, a deformed wire or a ribbon wire, and the wire rod has an outer shape of a linear helical coil or a zigzag coil. Preferably there is.

Further, in the sensor member of the present invention, the strain applied to the suspended wire rod is preferably any one of tensile strain, bending strain, shear strain, and compressive strain.

Further, in the sensor member of the present invention, it is preferable that the wire for suspending the weight is made of a shape memory alloy.

Furthermore, in the present invention, it is preferable that the wire member be made of a Ni-Ti type shape memory alloy having a superelastic effect to form a sensor member.

Further, according to the present invention, a displacement sensor, an acceleration sensor, and an inclinometer can be constructed by using the wire.

[0018]

In the present invention, the weight is suspended on the wire having the superelastic effect in which the electric resistance changes according to the elastic deformation amount, and the change in the electric resistance due to the strain applied to the wire is detected.
It is possible to configure a low cost sensor member that has a wide range of elastic deformation amount and less deterioration due to metal fatigue, and a displacement sensor, an acceleration sensor, and an inclinometer using the sensor member.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a conceptual diagram for explaining an embodiment of the present invention. Weight 1 as shown in FIG.
Are suspended by the wire rod 2a and the wire rod 2b. Fixed end 4
a, the fixed end 4b is fixed and does not move. The wire rods 2a and 2b are made of a shape memory alloy exhibiting superelasticity. Although the wire rods 2a and 2b are formed in a spiral shape, the absolute value of the resistance value is small, but they may be straight lines. It can also be formed in a zigzag zigzag shape.

Electrical conductors 6 are connected to both ends of the wire rods 2a and 2b, and the detection circuit 3a and the detection circuit 3 are connected.
connected to b. A terminal 7 is formed between the weight 1 and the wires 2a and 2b. The detection circuits 3a and 3b are resistance bridge circuits. The wires 2a and 2b may be elements on opposite sides of one resistance bridge circuit. In this case, it is possible to correct the resistance change due to the temperature change of the wire.

The wire rods 2a and 2b are preferably made of wire rods having the same properties and the same cross-sectional shape in order to cancel fluctuations in electrical resistance due to environmental conditions.

Signals of the detection value (A) and the detection value (B) are transmitted from the detection circuit 3a and the detection circuit 3b to a measurement control circuit (not shown).

In FIG. 1, the weight 1 is displaced by an external force, for example, in the direction of the arrow in FIG. 1, so that tension is applied to the wire rods 2A and 2B, and the resistance value change Δ due to the corresponding strain Δ
R is measured. If the relationship between the strain amount (deformation rate) ε due to the tension and the resistance change rate ΔR is obtained in advance and the initial value is set, the strain amount (change rate) ε can be obtained from the change in the resistance value.

In the first embodiment of the present invention, the shape memory alloy wire rod having the superelastic effect for suspending the weight is N
This is a Ti-Ni based alloy in which i is 50.7 at% and the balance is Ti. The manufacturing method will be described below. First, the raw materials were melted using an arc melting furnace in a non-oxidizing atmosphere. The molten alloy ingot was hot-rolled and then cold-worked to a target shape of wire diameter φ40 μm. The wire rod 4
After heat treatment was performed at 00 ° C. for 5 minutes, the resistance change (resistance temperature coefficient) depending on the ambient temperature was investigated. The result is shown by line 3 in FIG. The alloy of the present invention showed negative characteristics within the measurement temperature range, and had characteristics of a specific resistance of 137 μΩ · cm and a temperature coefficient of resistance (TCR) of about -120 ppm / ° C.
The result of obtaining the relationship between the tensile strain amount and the resistance value change at room temperature for this wire is shown by the line 32 in FIG. As shown in FIG. 3, it was found that this wire has a very good linearity, no hysteresis, and a wide elastic limit in the relationship between the amount of strain and the change in resistance value. As described above, in the first embodiment, the wire member is used to form the sensor member.

The cross-sectional shape of the wire rod is generally a circular cross-section, but it may be a modified wire having a polygonal cross-section including a square shape, which is determined by the hole shape of the drawing die.

(Second Embodiment) FIG. 4 is a conceptual diagram showing a second embodiment according to the present invention. As shown in FIG. 4, the weight 11
On a horizontal plane (fixed ends 14a, 14b, 14c are horizontal planes)
From the three directions of A, B, and C, wire rod 1 similar to that of the first embodiment
It is suspended by 2a, 12b and 12c. A,
If the three directions of B and C are at an angle of 120 degrees, the amount of strain (deformation rate) due to the weight 11 will be equal, and the detected value (A), detected value (B), and detected value (C) will be equal. . However, when the positional relationship between the fixed ends 14a, 14b, 14c is inclined, a difference occurs in the strain amount applied to the wire rods 12a, 12b, 12c, and the detected values (A), (B), (C) also differ. appear.

If the tilt angle between the fixed ends and the detected value are obtained in advance, it can be used as a tilt sensor or a displacement sensor.

Further, when acceleration is applied to the weight 11, the tension corresponding to the acceleration is applied to each of the wire rods 12a, 12b, 12c.
Therefore, the resistance value of the wire changes. If the relationship between the magnitude and direction of the acceleration applied to the weight 11 and the resistance change rate ΔR of each wire is obtained in advance, it can be used as an acceleration sensor.

(Third Embodiment) FIG. 5 shows a third embodiment according to the present invention.
It is the schematic which showed. As shown in FIG. 5, the weight 21
Is vertically suspended by a wire rod 22z similar to those in the first and second embodiments. And downward from the wire 22z, angle 1
A, B, C divided into angles of 20 degrees and 120 degrees around
From the three directions of the wire rods 22a, 22b, 22c to the weight 21
It is a suspended structure. With this configuration, the weight 21 is in a suspended state, and it is possible to detect acceleration in all directions applied to the weight 21.

Further, in the configuration of FIG. 5, when the correlation positional relationship between the fixed ends 24z, 24a, 24b, and 24c changes from the initial setting positional relationship, the resistance value of each wire rod changes according to the positional relationship. Since it is detected, it can be used as an omnidirectional displacement sensor.

In the first to third embodiments of the present invention described above,
Although only an example using a Ti-Ni alloy exhibiting superelasticity is shown, a TiN alloy exhibiting a shape memory effect can be sufficiently used as an elastic material if the strain amount is 1.5 to 2.0% or less. It is obvious that the present invention can be applied to the shape memory alloy containing the Cu-Zn system.

[0033]

As described above, according to the present invention, a wire for suspending a weight of a sensor member is made of a shape memory alloy exhibiting superelastic characteristics, and displacement or acceleration is measured from a change in its resistance value. Therefore, it is possible to provide a displacement sensor, an acceleration sensor, and an inclinometer which have high sensitivity, wide linearity, and high reliability.

[Brief description of drawings]

FIG. 1 is a conceptual diagram for explaining a first embodiment of the present invention.

FIG. 2 is a graph of the resistance change rate with respect to temperature of the shape memory alloy used in Example 1 of the present invention.

FIG. 3 is a graph of resistance change rate with respect to strain amount (deformation rate) of the shape memory alloy used in Example 1 of the present invention.

FIG. 4 is a configuration diagram of a sensor member according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a sensor member according to a third embodiment of the present invention.

[Explanation of symbols]

1,11,21 Weights 2a, 2b, 12a, 12b, 12c, 22a, 22
b, 22c, 22z wire rods 3a, 3b, 13a, 13b, 13c, 23a, 23
b, 23c, 23z detection circuit 4a, 4b, 14a, 14b, 14c, 24a, 24
b, 24c, 24z Fixed end 6 Electric wire 7 Terminal

Claims (10)

[Claims] 1. A weight is arranged in the center, the weight is suspended by a wire rod whose electric resistance changes in at least two directions, and the change in the electric resistance of the wire rod caused by the movement of the weight is detected. A sensor member characterized by. 2. The sensor member according to claim 1, wherein the two or more wire rods on which the weight is suspended have the same property and the same cross-sectional dimension, thereby canceling the electric resistance fluctuation due to the environmental conditions of the detected wire rod portion. A sensor member characterized by being. 3. The sensor member according to claim 1, wherein an electric current is applied to each of the two or more wire rods on which the weight is suspended, so that the detected wire rod portion cancels the electric resistance fluctuation caused by the heat generation by the electric current. A sensor member characterized by the above. 4. The sensor member according to claim 1, wherein the wire rod for suspending the weight has a round wire, an irregular wire, a ribbon wire, or a thin film, and the wire rod has an outer shape of a straight line or a helical coil. Or a sensor member having a zigzag coil shape. 5. The sensor member according to claim 1, wherein the strain applied to the suspended wire rod is one of tensile strain, bending strain, shear strain, and compressive strain. Element. 6. The sensor member according to claim 1, wherein the wire for suspending the weight is made of a shape memory alloy. 7. The sensor member according to claim 1, wherein the wire is made of a Ni—Ti-based shape memory alloy that exhibits superelasticity at a normal temperature. 8. A displacement sensor using the sensor member according to claim 1 to obtain a displacement amount based on a relationship between a predetermined resistance value and displacement amount. . 9. Using the sensor member according to any one of claims 1 to 7, to obtain the acceleration based on the magnitude of the acceleration applied to the weight, the direction, and the resistance value of each wire. Acceleration sensor characterized by. 10. Using the sensor member according to any one of claims 1 to 7, to obtain an inclination angle based on a relationship between a predetermined inclination angle between the fixed ends and a resistance value. Inclinometer characterized by.