JPH0961143A - Displacement detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement detection apparatus whose resolution is high and whose accuracy is high. SOLUTION: Current pulses are made to flow from the side of the starting end part of a magnetostrictive wire 1 to its axial-line direction. Torsional elastic waves are generated in the part of the magnetostrictive wire 1 to which a permanent magnet 12 movable along the magnetostrictive wire 1 is brought close. The torsional elastic waves are received by a receiver 10 which is arranged on the side of the starting end part of the magnetostrictive wire 1. Thereby, a mechanical displacement which is given to the permanent magnet 12 is detected. A reflection member 9 which reflects the torsional elastic waves is installed in a specific position on the side of the termination part of the magnetostrictive wire 1. The receiver 10 receives first torsional elastic waves which are generated by the permanent magnet 12 so as to reach the receiver 10 as they are and second torsional elastic waves which are generated by the permanent magnet 12 and which are reflected by the reflection member 9 so as to reach the receiver 10. A detection circuit 14 detects the mechanical displacement, given to the permanent magnet 12, on the basis of the difference in the arrival time between the first torsional elastic waves and the second torsional elastic waves.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement detecting device for detecting a mechanical displacement of an object or a displacement of a liquid surface by using a magnetostriction phenomenon.

[0002]

2. Description of the Related Art Conventionally, as a displacement detection device, as shown in FIG. 1, a permanent magnet 52 movable along a magnetostrictive line 50 is brought close to a magnetostrictive line 50 by passing a current pulse from a pulse generating circuit 51. A receiver 5 provided on the starting end side of the magnetostrictive line 50 by generating a torsional elastic wave (ultrasonic wave) at the site of the magnetostrictive line.
By measuring the propagation time of the torsional elastic wave up to 3,
A device that detects a mechanical displacement applied to the permanent magnet 52 is known (Japanese Patent Laid-Open No. 61-112923). Both ends of the magnetostrictive wire 50 are held by damping materials 54 and 55 such as rubber that suppress reflection of torsional elastic waves.

FIG. 2 is a waveform diagram showing a method for detecting displacement. A is a current pulse, B is a waveform received by the receiver 4, and C is a waveform obtained by shaping the waveform B. If the time t from the supply of the current pulse A to the arrival of the waveform C is measured, the displacement x given to the permanent magnet 52 can be measured by the following equation. x = v · t Note that v is the propagation velocity of the torsional elastic wave.

There are various methods for measuring the time t. For example, as shown in D of FIG. 2, a clock that starts by supplying a current pulse A from a crystal oscillator is generated, and a clock is set when the waveform C arrives. Then, the time t can be detected as a digital signal.

[0005]

As is well known, the propagation velocity of a torsional elastic wave is about 2.75 mm / μsec, although it varies somewhat depending on the material of the magnetostrictive wire. Here, when the propagation time until the torsional elastic wave generated in the permanent magnet 52 reaches the receiver 53 is measured by a 50 MHz crystal oscillator, one clock is 1 / (50 × 10 ⁶ ) = 0.02 μsec. Therefore, the resolution that can be detected in one clock is 2.75 mm / μsec × 0.02 μsec = 0.05.
It is 5 mm, which is not sufficient for highly accurate displacement detection. To increase this resolution, there is a method to raise the frequency of the crystal oscillator, but this causes technical and economic difficulties.

Further, when the displacement detecting device as described above is used for measuring the liquid level of gasoline, the detecting device needs to have an explosion-proof structure (for example, an intrinsically safe explosion-proof structure is optimal). For that purpose, it is necessary to reduce the current consumption of the electric circuit of the detection device, and it is desired to lower the oscillation frequency of the crystal oscillator as much as possible. However, the lower the oscillation frequency of the crystal oscillator, the lower the resolution, and therefore the oscillation frequency cannot be lowered.

Therefore, an object of the present invention is to provide a displacement detecting device capable of remarkably increasing the resolution without changing the structure, as compared with the conventional displacement detecting device. Another object of the present invention is to provide a displacement detection device capable of increasing the resolution without increasing the oscillation frequency and reducing the current consumption when measuring the propagation time using an oscillator. Still another object is to provide a displacement detection device suitable for liquid level detection, in which the liquid level and the measurement result can correspond one-to-one and the measurement circuit can be simplified.

[0008]

In order to achieve the above object, the present invention provides a current pulse in the axial direction from the starting end side of a magnetostrictive wire to bring a permanent magnet movable along the magnetostrictive wire into proximity. A device for detecting a mechanical displacement applied to a permanent magnet by generating a torsional elastic wave at a site of a magnetostrictive line and receiving the torsional elastic wave by a receiver arranged on the starting end side of the magnetostrictive line, A reflecting member that reflects a torsional elastic wave is provided at a specific position on the terminal end side of the receiver, and the receiver generates the first torsional elastic wave generated by the permanent magnet and reaches the receiver as it is, and the permanent magnet generates the permanent elastic magnet. The second torsional elastic wave that has reached the receiver after being reflected by the reflecting member is received, and the mechanical displacement given to the permanent magnet is obtained from the arrival time difference between the first torsional elastic wave and the second torsional elastic wave. Is provided with a detection circuit for detecting. In the above displacement detecting device, it is desirable to use, as the permanent magnet, an axially magnetized magnet having opposite poles magnetized on both side surfaces in the axial direction. Moreover, you may provide the some permanent magnet which can be moved individually along a magnetostriction line.

The torsional elastic wave (ultrasonic wave) generated in the portion of the magnetostrictive wire near the permanent magnet propagates to the receiver side (start end side) and at the same time to the opposite side (end side). The ultrasonic wave propagating to the starting end side is received by the receiver, and the ultrasonic wave propagating to the terminal end side is reflected by the reflecting member, then propagates the magnetostrictive line to the starting end side and is received by the receiver. The arrival time difference between these two torsional elastic waves is proportional to twice the distance between the permanent magnet and the reflecting member. Therefore, if this time difference is detected, the resolution is halved and the detection accuracy is remarkably improved, as compared with the case where the arrival time of only the first torsion elastic wave is detected as in the conventional case.

In the conventional case, since the distance from the receiver arranged on the starting end side of the magnetostrictive line to the permanent magnet is measured, if the terminal end side of the displacement detecting device is immersed in the liquid, when the liquid surface is high. The liquid level and the measurement result are reversed, such as measuring a short time and measuring a long time when the liquid level is low, and an extra circuit such as subtraction processing is required. On the other hand, in the case of the present invention, twice the distance from the reflecting member arranged on the terminal side of the magnetostrictive line to the permanent magnet is detected, so that when the liquid level is high, a long time is measured and the liquid level is low. Sometimes it will be a short time. That is, the liquid level and the measurement result have a one-to-one correspondence, and a subtraction processing circuit or the like is unnecessary, and the circuit is simplified.

When an axially magnetized magnet is used as the permanent magnet, the first torsional elastic wave propagated from the permanent magnet portion to the beginning side of the magnetostrictive line and the second torsional elastic wave propagated to the terminal side. Have mutually reversed phases, but when the second torsional elastic wave is reflected by the reflecting member, the phases are reversed again, so that the two waveforms detected by the receiver have the same phase. Therefore, each waveform is easily triggered, and the risk of false detection is reduced.

When detecting the liquid level of gasoline in the tank, water may be accumulated at the bottom of the tank. In order to accurately detect the liquid level of gasoline, it is necessary to detect both the liquid level of water and the liquid level of gasoline. In such a case,
If a plurality of permanent magnets that can be individually moved along the magnetostrictive line are provided, it is possible to detect the water surface with one of them and the gasoline surface with the other.

As the reflecting member, for example, a metal material is preferably fixed to the magnetostrictive line in order to totally reflect the torsional elastic wave propagating through the magnetostrictive line. As a fixing method,
Any method such as crimping, soldering, brazing, welding, and screwing can be used. When solder is used as the reflection member, it is easy to totally reflect the torsional elastic wave, the distortion is not generated in the magnetostrictive wire, and unnecessary ultrasonic waves are not easily generated. The solder melting temperature (about 190 ° C) is Since the temperature is lower than the crystal temperature, there is an advantage that the magnetostriction effect is not deteriorated.

After the ultrasonic signal generated at the permanent magnet portion is received by the receiver and then reflected at the beginning of the magnetostrictive line and received again by the receiver, it is confused with the ultrasonic signal reflected by the reflecting member. There is a risk of For this reason, it is desirable to provide a damping material such as rubber on the starting end side of the magnetostrictive wire, especially behind the receiver to absorb unnecessary waveforms.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows an example of a magnetostrictive displacement detecting device according to the present invention, and FIG. 4 shows a waveform received by a receiver. The starting end of the magnetostrictive wire 1 is pressure-bonded between the pressing plate 3 fixed on the base 2 and the support plate 4 via damping materials 5 and 6 such as silicone rubber. Damping material 5,
Reference numeral 6 absorbs ultrasonic waves (torsional elastic waves) and suppresses reflection of ultrasonic waves from the start end. Further, if the damping materials 5 and 6 are made of an insulating material, the current pulse supplied to the starting end side of the magnetostrictive wire 1 can be prevented from flowing to other parts, and all the current can be effectively passed through the magnetostrictive wire 1. be able to. The end of the magnetostrictive wire 1 is supported by the end fixture 8 via the spring 7, and a constant tension is always applied to the magnetostrictive wire 1. A reflecting member 9 that reflects ultrasonic waves is fixed immediately before the spring 7, that is, at the portion of the magnetostrictive wire 1 that is closer to the starting end than the spring 7. The fixing method may be any method such as soldering, clamping, and welding. The ultrasonic waves propagated through the magnetostrictive line 1 to the terminal side are almost totally reflected by the reflecting member 9, so that the ultrasonic waves hardly propagate to the spring 7 side.

The starting end of the magnetostrictive wire 1, especially the damping material 5,
A receiver 10 is arranged in the vicinity of the end portion side of 6 and a magnetostrictive wire 1 penetrates the central portion of a coil 10a incorporated in the receiver 10 in a non-contact manner. The coil 10a detects the arrival of ultrasonic waves propagating through the magnetostrictive line 1 by utilizing the inverse magnetostrictive effect. The negative electrode of the coil 10a is grounded, and the positive electrode is the amplifier 11
Connected to. The receiver 10 is the coil 10
It is not limited to “a”, but for example, a piezoelectric element or a coil attached to the end portion of the contactor by contacting the contactor substantially perpendicular to the magnetostrictive line to convert the torsional elastic wave into an axial force of the contactor Alternatively, the arrival of the torsional elastic wave may be detected.

An annular permanent magnet 1 is provided in the middle of the magnetostrictive wire 1.
2 is inserted movably in the axial direction. In this embodiment, axially magnetized magnets having N and S poles magnetized on both sides of the permanent magnet 12 are used.

Magnetostrictive wire 1 protruding from the damping materials 5 and 6
A current pulse is supplied from the pulse generation circuit 13 to the start end of the magnetoresistive wire 1, and the end of the magnetostrictive wire 1 is grounded. In particular,
The current pulse is transmitted through the spring 7 to the pulse generation circuit 13
Returned to the ground side of. When a current pulse is supplied, an ultrasonic wave (torsional elastic wave) is generated at a portion of the magnetostrictive line 1 in the vicinity of the permanent magnet 12 due to the Biedemann effect, and the ultrasonic wave is simultaneously generated on the start end side and the end side of the magnetostrictive line 1. Propagate. The first ultrasonic wave propagating to the start side is received by the receiver 10, and the ultrasonic wave propagating to the end side is reflected by the reflecting member 9 and then the permanent magnet 1
It passes through two adjacent parts and is received by the receiver 10.
When an axially magnetized magnet is used as the permanent magnet 12, the phases of the first ultrasonic wave propagating from the part of the permanent magnet 12 to the starting end side of the magnetostrictive wire 1 and the second ultrasonic wave propagating to the terminal end side are mutually reversed. However, since the phase is inverted again when the second ultrasonic wave is reflected by the reflecting member 9, the two waveforms detected by the receiver 10 have the same phase as shown in FIG. Therefore, it becomes very easy to trigger each waveform.

In FIG. 4, a waveform p is a current pulse, a waveform n is electromagnetic noise when a current pulse is applied, a waveform a is a first ultrasonic signal generated by the permanent magnet 12, and b is a second ultrasonic signal reflected by the reflecting member 9. It is an ultrasonic signal. Propagation time T of signals a and b
_Although the measurement points of _a and T _b are triggered by the predetermined potential V in FIG. 4, they may be measured at the zero cross point of the waveform or the apex of the waveform. In any case, the arrival of the waveform may be detected at the fixed point of each waveform, and the times T _a and T _b can be measured by _a known method.

The output of the amplifier 11 is input to the detection circuit 14, which detects the propagation time difference ΔT (= T _b −T _a ) while waveform-shaping the input signal, and applies it to the permanent magnet 12. The dynamic displacement x is detected. Further, the detection circuit 14 may have a function of driving the pulse generation circuit 13 so as to generate a current pulse at regular time intervals.

Next, a method for obtaining the mechanical displacement x given to the permanent magnet 12 will be described. First, the distance between the reflecting member 9 and the permanent magnet 12 is x, the distance between the receiver 10 and the reflecting member 9 is L (constant), and the first ultrasonic wave a generated by the permanent magnet 12 is generated.
Arrival time of T _{a is} the second ultrasonic wave b reflected by the reflecting member 9.
Of the arrival time T _b, when the propagation speed of the ultrasonic v, the arrival time T _a, T _b is given by the following equation. T _a = (L−x) / v T _b = (L + x) / v When the difference between the arrival times T _b and T _a is calculated, ΔT = T _b −T _a = 2x / v. Propagation velocity v of the ultrasonic wave because it is known, as _{x = v (T b -T a} ) / 2, it is possible to obtain the displacement x.

By the way, when the permanent magnet 12 is slightly moved to the starting end side, the detected waveform becomes as shown by the broken line in FIG. That is, the arrival time T _a of the first ultrasound a is shortened by Delta] t, the arrival time T _b of second ultrasound b is longer by Delta] t. Therefore, if the arrival time difference ΔT is measured, 2 × Δt
Will be a time difference and can be measured. Therefore,
Even if a crystal oscillator having the same oscillation frequency as before is used, the resolution becomes 1/2, that is, 0.0275 mm, and the displacement can be detected with high accuracy.

FIG. 5 shows a second embodiment of the present invention. Reference numeral 20 denotes a magnetostrictive wire made of, for example, a constant elastic metal, which is inserted through the center portion of a middle cylinder 21 made of a non-magnetic and conductive metal pipe such as copper, brass or aluminum, and a reflecting member at the right end of the middle cylinder 21. It is fixed by a terminal fixing tool 22. The terminal fixture 22 may be any device that totally reflects ultrasonic waves (torsional elastic waves). The starting end of the magnetostrictive wire 20 penetrates through the center of the detection coil 23 that is a receiver, and the detection coil 23 detects the arrival of ultrasonic waves propagating through the magnetostrictive wire 20 by utilizing the inverse magnetostrictive effect. A starting end portion of the magnetostrictive wire 20 penetrating the detection coil 23 is connected to a starting end fixture 25 that also serves as a spring receiver via a damping material 24 such as silicone rubber. Ultrasonic waves are absorbed by the damping material 24,
The reflection of ultrasonic waves from the starting end fixture 25 is suppressed. A spring 26 is provided between the detection coil 23 and the starting end fixture 25.
Are arranged to absorb expansion and contraction of the magnetostrictive wire 20 due to changes in ambient temperature. A support member 27 made of rubber or the like is provided at an intermediate portion of the magnetostrictive wire 20 at an appropriate interval in the axial direction to prevent the magnetostrictive wire 20 and the inner wall of the middle cylinder 21 from coming into contact with each other due to mechanical vibration.

The outer cylinder 30 is made of a metal pipe made of a non-magnetic material, and surrounds the outer circumference of the middle cylinder 21 in a non-contact state. The end side of the outer cylinder 30 is closed, and the head housing 31 is integrally provided on the start end side. Components such as the detection coil 23, the damping material 24, the starting end fixture 25, and the spring 26 are housed in the head housing 31.

In the annular space between the middle cylinder 21 and the outer cylinder 30,
An insulating tube 32 that holds the middle cylinder 21 at the center of the outer cylinder 30 and electrically insulates the inner cylinder 21 and the outer cylinder 30 from each other is arranged.

First and second permanent magnets 33 and 34 are individually inserted through the outer periphery of the outer cylinder 30 so as to be movable in the axial direction. The permanent magnets 33, 34 of this embodiment are also annular magnets that are magnetized in the axial direction and have N and S poles magnetized on both sides.

The current pulse P is supplied from the pulse generating circuit 35 to the magnetostrictive wire 20 via the starting end fixture 25. The output signal of the detection coil 23 is sent to the amplifier 36,
Output signal B is waveform-shaped by a waveform-shaping circuit 37 such as a comparator to become a final output signal C. Note that in FIG. 5, in order to facilitate understanding, the pulse generation circuit 35 and the amplifier 3
Although the circuits such as 6 and the waveform shaping circuit 37 are arranged outside, they may be housed inside the head housing 31.

When the current pulse P is supplied to the magnetostrictive wire 20, the end of the magnetostrictive wire 20 is terminated by the end fixture 2 as described above.
Since it is fixed at 2, the end fixing tool 22 is
A circuit for returning the current pulse P supplied to the magnetostrictive wire 20 to the pulse generating circuit 35 is configured by electrically connecting the terminal end of 1 and connecting the starting end side of the middle cylinder 21 to the pulse generating circuit 35. Although the middle cylinder 21 is a metal pipe in this embodiment, it may be made of a non-metal material such as plastic or ceramic. In this case, the lead wire for returning the current pulse supplied to the magnetostrictive wire 20 may be arranged parallel to the magnetostrictive wire 20.

FIG. 6 is a detection waveform diagram of the displacement detecting device shown in FIG. Waveform n is the electromagnetic noise when a current pulse is applied,
The waveform c is the first ultrasonic signal generated by the first permanent magnet 33,
d is the second ultrasonic wave signal generated by the second permanent magnet 34, and e is the second ultrasonic wave signal generated by the second permanent magnet 34.
The signal detected by the detection coil 23 after being reflected by the first ultrasonic wave generated by the first permanent magnet 33 is f.
It is a signal detected by the detection coil 23 after being reflected by.

The propagation times of the signals _c to _f are represented by T _c , T _d , and T
_{Assuming e} and T _f , the propagation time difference ΔT ₁ between the signals c and f is proportional to twice the distance x ₁ between the first permanent magnet 33 and the reflecting member 22. The propagation time difference ΔT ₂ between the signals d and e is proportional to twice the distance x ₂ between the second permanent magnet 34 and the reflecting member 22. This can be expressed as follows. ΔT ₁ = T _f −T _c = 2x ₁ / v ΔT ₂ = T _e −T _d = 2x ₂ / v Since the ultrasonic propagation velocity v is known, x ₁ = v (T _f −T _c ) / The displacements x ₁ and x ₂ can be obtained as in 2 x ₂ = v (T _e −T _d ) / 2.
Also in the case of this embodiment, as in the first embodiment (see FIGS. 3 and 4), twice the amount of movement of each of the first permanent magnet 33 and the second permanent magnet 34 can be detected as a time difference, so The resolution is halved as compared with the displacement detection.

FIG. 7 shows an example in which the displacement detecting device of FIG. 5 is used to detect the liquid level in a gasoline tank. 40 is a tank, 41
Is a first float, 42 is a second float, and these floats 4
The first and second permanent magnets 33 and 34 are incorporated in the reference numerals 1 and 42, respectively. The floats 41 and 42 are set to have a specific gravity so that the liquid level of the gasoline 43 and the liquid level of the water 44 can be detected. The outer cylinder 30 is vertically inserted into the liquid so that the end side thereof faces downward, and the float 41,
The displacement of 42 is detected.

In order to detect the liquid level of an ignitable liquid such as gasoline, the detection device must have an explosion-proof structure and its current consumption must be reduced. Therefore, the oscillation frequency of the crystal oscillator cannot be increased, and the detection resolution is low. On the other hand, according to the present invention, since the resolution can be increased without increasing the oscillation frequency of the crystal oscillator, it is possible to obtain a displacement detection device with low power consumption, an explosion-proof structure, and high accuracy.

When a conventional displacement detecting device that does not utilize reflection is used for liquid level detection, the propagation time (measurement time) of ultrasonic waves becomes longer when the liquid level drops, and the position of the liquid level and the measurement time are The correspondence was reversed, and an extra circuit such as subtraction processing was required. On the other hand, in the present invention, since the distance between the reflecting member 22 and the permanent magnets 33 and 34 is measured, the propagation time becomes shorter when the liquid surface drops, and the liquid surface and the measurement time correspond one-to-one. No extra circuit is needed.

Although water may collect at the bottom of the gasoline tank, a plurality of permanent magnets 33, 34 are used as in the second embodiment.
It is also possible to detect the liquid level of gasoline and water at the same time with one displacement detection device by individually detecting the displacements of. The number of permanent magnets is not limited to two, and the number of permanent magnets is not limited as long as it is possible to prevent interference due to the proximity of adjacent permanent magnets.

The above embodiment is merely an example of the present invention, and can be modified within the scope of the present invention.
In the above embodiment, the case where the arrival time of the torsional elastic wave is measured by a digital signal using a clock pulse of a crystal oscillator or the like has been described, but the invention is not limited to this. For example, if a triangular wave voltage rising by the supply of a current pulse is started and the voltage value is sampled and held by the arrival of the torsional elastic wave, it can be detected as an analog signal. Alternatively, any method may be used for detection. In the above embodiment, a current pulse is passed through the magnetostrictive wire,
The torsional elastic wave propagating through the magnetostrictive line is detected. However, as described in JP-A-59-162412,
The magnetostrictive wire may be formed in a tube shape, and a conducting wire for flowing a current pulse may be separately inserted in the center of the magnetostrictive wire so that the medium through which the current pulse flows and the medium through which the torsional elastic wave propagates may be different. In the above embodiment, the axial magnetized magnets having the N and S poles magnetized on both sides of the permanent magnet are used, but the magnetized in the radial direction with the N and S poles magnetized on the inner peripheral surface and the outer peripheral surface, respectively. A magnet may be used. However, in the case of radial magnetization, unlike the axial magnetization, the waveforms of ultrasonic waves propagating from the permanent magnet to the start side and the end side of the magnetostrictive line are in phase, so the waveform when reflected by the reflecting member Is reversed, and eventually the waveforms of the first ultrasonic wave and the second ultrasonic wave detected by the receiver have opposite phases. Further, the shape of the permanent magnet is not limited to the annular shape, and may be any shape such as a rectangular parallelepiped shape and a U shape.

[0036]

As is apparent from the above description, according to the present invention, a reflecting member that reflects a torsional elastic wave is provided at a specific position on the terminal end side of the magnetostrictive wire, and a portion of the magnetostrictive wire adjacent to the permanent magnet is provided. The mechanical displacement of the permanent magnet is determined by the difference between the arrival time of the first torsional elastic wave that has arrived at the receiver after being generated in step 1 and the arrival time of the second torsional elastic wave that has reached the receiver after being reflected by the reflecting member. Since the arrival time difference is proportional to twice the distance between the permanent magnet and the reflecting member, the resolution is higher than that in the case of detecting only the arrival time of the first torsion elastic wave as in the conventional case. Is 1/2 times, and the detection accuracy is significantly improved. Further, when measuring the propagation time using a crystal oscillator or the like, the resolution can be improved without increasing the oscillation frequency, so that the cost is low and the current consumption can be reduced. Further, in the present invention, since the distance between the permanent magnet and the reflecting member is measured, when used for liquid level detection, the liquid level and the measurement result can correspond one-to-one, and the subtraction processing circuit becomes unnecessary, simplifying the measurement circuit. it can.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a general displacement detection device.

FIG. 2 is a received waveform diagram in the displacement detection device of FIG.

FIG. 3 is a schematic configuration diagram of a first embodiment of a displacement detection device according to the present invention.

FIG. 4 is a received waveform diagram in the displacement detection device of FIG.

FIG. 5 is a structural diagram of a second embodiment of the displacement detecting device according to the present invention.

6 is a received waveform diagram in the displacement detection device of FIG.

FIG. 7 is a layout diagram of an example in which the displacement detection device of FIG. 5 is used for liquid level detection.

[Explanation of symbols]

 1 Magnetostrictive Line 9 Reflecting Member 10 Receiver 12 Permanent Magnet 13 Pulse Generation Circuit 14 Detection Circuit

Claims (3)

[Claims] 1. A starting point of a magnetostrictive line is generated by causing a current pulse to flow from the starting end side of the magnetostrictive line in the axial direction thereof to generate a torsional elastic wave at a portion of the magnetostrictive line adjacent to a permanent magnet movable along the magnetostrictive line. In a device for detecting a mechanical displacement applied to a permanent magnet by receiving a torsional elastic wave by a receiver arranged on the side of the magnetostrictive line, a reflection member for reflecting the torsional elastic wave to a specific position on the terminal end side of the magnetostrictive wire. In the receiver, the first torsional elastic wave generated by the permanent magnet and reaching the receiver as it is and the second torsional elastic wave generated by the permanent magnet and reflected by the reflecting member and then reaching the receiver are provided. A displacement detection device, which is provided with a detection circuit that receives an elastic wave and detects a mechanical displacement applied to the permanent magnet based on a difference in arrival time between the first torsion elastic wave and the second torsion elastic wave. . 2. The displacement detecting device according to claim 1, wherein the permanent magnet is an axially magnetized magnet having opposite poles magnetized on both side surfaces in the axial direction. 3. The displacement detecting device according to claim 1 or 2, wherein a plurality of permanent magnets that are individually movable along the magnetostrictive line are provided.