JPH08145651A - Displacement detector - Google Patents

Abstract

PURPOSE: To obtain a highly reliable displacement detector in which easy setting and fine adjustment can be made without increasing the number of components. CONSTITUTION: A current pulse is fed on an magnetostrictive wire 1 to generate a torsional elastic wave at a part of the magnetostrictive wire 1 proximate to a magnet 2 movable along the wire 1. Propagation time of the elastic wave up to a receiver 3 disposed at a specified part of the wire 1 is then measured and mechanical displacement of the magnet 2 is detected. At this time, the torsional elastic waves, generated at the rising and falling of the current pulse, are amplified while being superposed on each other and received by the receiver 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the propagation time of a torsional elastic wave generated in a portion of a magnetostrictive line which is close to a magnet movable along the magnetostrictive line by passing a current pulse through the magnetostrictive line. Then, the present invention relates to an improvement of the displacement detection device that detects the mechanical displacement applied to the magnet.

[0002]

2. Description of the Related Art By passing a current pulse through a magnetostrictive wire,
The displacement detection device that detects the mechanical displacement given to the magnet by measuring the propagation time of the torsional elastic wave generated in the portion of the magnetostrictive line that is close to the magnet that can move along the magnetostrictive line And, in order to improve reliability, it is necessary to obtain a large torsional elastic wave with less noise. As a method of obtaining a large torsional elastic wave with less noise, see Japanese Patent Laid-Open No. 5-17.
No. 2555 ”and“ JP-A-5-187855 ”have already been proposed.

FIG. 7 is a block diagram showing a configuration of a displacement detecting device (magnetostrictive displacement detecting device) proposed in Japanese Patent Laid-Open No. 5-172555. This displacement detecting device is provided with a clamp jig 16 in which the starting end of the magnetostrictive wire 17 is fixed on the base 14.
Is clamped by the clamp jig 5, and the end thereof is supported by the clamp jig 5 via the spring 8 for always applying a constant tension to the magnetostrictive wire 17. The end portion of the magnetostrictive wire 17 is
A damping material 23 such as silicon rubber is applied to suppress the influence of the reflected wave from the spring 8 or the clamp jig 5.

The receivers 19 and 21 are arranged in the vicinity of the clamp jig 16 and have coils 18 and
The magnetostrictive wire 17 penetrates the central portion of 20 without contact. The coils 18 and 20 have the same characteristics, are arranged at a distance L in the axial direction of the magnetostrictive wire 17, and detect the torsional elastic wave propagating in the magnetostrictive wire 17 by utilizing the inverse magnetostrictive effect. The negative electrodes of the coils 18 and 20 are grounded, and the positive electrodes are connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 24, respectively, so that the coils 18 and 20 are connected in opposite phases. An annular permanent magnet 22 is inserted into the magnetostrictive wire 17 so as to be movable in the axial direction of the magnetostrictive wire 17, and both ends of the permanent magnet 22 in the axial direction of the magnetostrictive wire 17 are magnetized to N and S poles, respectively. The magnetization direction of the permanent magnet 22 is
The inner circumference / outer circumference may be the N / S pole or the S / N pole.

The operation of the displacement detecting device having such a configuration will be described below. A current pulse is supplied from a pulse generator (not shown) to the start end of the magnetostrictive wire 17 protruding from the clamp jig 16, and is returned to the ground of the pulse generator via the spring 8 at the end of the magnetostrictive wire 17. for that reason,
Due to the interaction between the magnetic field of the permanent magnet 22 and the magnetic field generated by the current pulse flowing through the magnetostrictive line 17, the permanent magnet 22
The torsional elastic waves generated in the nearby magnetostrictive line 17 and propagating through the magnetostrictive line 17 are detected by the receivers 19 and 21.

In general, the detected waveform has a shape as shown in FIG. 8 in the receiver. That is, a valley I1 appears at the start of the waveform, a peak I2 appears thereafter, and then a valley I3 appears. Two receivers 19 and 2 of opposite polarities
In No. 1, the shape is as shown in FIG. That is, after the waveform I4 having the peak I4a and the valley I4b is received by the receiver 21, the waveform having the peak I5b and the valley I5a is received by the receiver 19 after the delay time Td due to the distance L between the receivers 19 and 21. I5 (inverted waveform of waveform I4) is received. Here, when the distance L is gradually reduced, the delay time Td between the waveform I5 and the waveform I4 is gradually reduced as shown in FIG. When the distance L is further reduced, as shown in FIG. 11, the peak I4a of the waveform I4 and the peak I5b of the waveform I5 overlap each other, and the valley I4b of the waveform I4 and the valley I5 of the waveform I5.
5a and 5a overlap each other, and a very large waveform can be obtained.

Therefore, the distance L between the receivers 19 and 21 is
By setting the distance at which the two waveforms overlap as described above, even if the strength of the current pulse and the magnetic force of the permanent magnet 22 are the same as in the conventional case, and even if the gain of the differential amplifier 24 is not particularly increased, the difference is increased. A very large waveform can be obtained as the output of the dynamic amplifier 24. By measuring the time t from the supply of the current pulse to the arrival of the torsional elastic wave at the receiver 21, the displacement X of the permanent magnet 22 can be easily obtained by the following equation. X = v · t (v is the propagation velocity of the torsional elastic wave of the magnetostrictive line 17)

FIG. 12 shows "JP-A-5-187855".
3 is a block diagram showing the configuration of a displacement detection device (magnetostrictive displacement detection device) proposed in FIG. This displacement detection device is shown in FIG.
As shown in FIG. 3, two permanent magnets 25a and 25b are inserted into the magnetostrictive wire 17 so as to be movable in the axial direction of the magnetostrictive wire 17, and the permanent magnets 25a and 25b are made of a non-magnetic cylindrical holder 25. Are held at a constant interval M. The magnetizing directions of the permanent magnets 25a and 25b are N / S poles on the inner circumference / outer circumference. The other configuration is the same as the configuration of the displacement detecting device of the above-mentioned "Japanese Patent Application Laid-Open No. 5-172555", and thus the description thereof is omitted.

The operation of the displacement detecting device having such a configuration will be described below. A current pulse is supplied from a pulse generator (not shown) to the start end of the magnetostrictive wire 17 protruding from the clamp jig 16, and is returned to the ground of the pulse generator via the spring 8 at the end of the magnetostrictive wire 17. for that reason,
Magnetic fields of the permanent magnets 25a and 25b and the magnetostrictive line 1
By the interaction with the magnetic field generated by the current pulse flowing through 7, the respective torsional elastic waves generated in the magnetostrictive line 17 near the permanent magnets 25a and 25b and propagated through the magnetostrictive line 17 are It is detected by the receivers 19 and 21. Here, the distance L between the receivers 19 and 21 is set to the distance at which the peak of the front waveform received by the receiver 21 and the first peak of the rear waveform received by the receiver 19 exactly overlap. It is set. Therefore, the output of the differential amplifier 24 is
Larger waveforms can be obtained than can be obtained with a single receiver. Other operations are described in the above-mentioned "Japanese Patent Application Laid-Open No. 5-1725".
Since it is the same as the operation of the displacement detecting device of "No. 55", its explanation is omitted.

[0010]

In the above-mentioned two proposed examples, two detectors or permanent magnets are required, the number of parts increases, space cannot be used effectively, and the interval adjustment of parts is required. There is a problem that once it is mechanically fixed, it cannot be changed, etc. The present invention has been made in view of the above circumstances, and in the first invention, means for setting the respective torsional elastic waves generated by the rising and falling of the current pulse to be overlapped and amplified is provided. Accordingly, it is an object of the present invention to provide a highly reliable displacement detection device that can be easily set, can be finely adjusted without increasing the number of parts. According to the second aspect of the present invention, by providing a pulse width adjusting circuit for adjusting the width of the current pulse, it is possible to easily perform the setting without increasing the number of parts, and to perform the fine adjustment and provide a highly reliable displacement detecting device. The purpose is to do.

[0011]

A displacement detecting device according to a first aspect of the present invention applies a current pulse to a magnetostrictive wire to twist a magnetostrictive wire to a portion of the magnetostrictive wire adjacent to a magnet movable along the magnetostrictive wire. A displacement detection device that detects a mechanical displacement applied to a magnet by generating a torsion elastic wave and measuring a propagation time of the torsional elastic wave to a receiver provided at a specific portion of the magnetostrictive line, It is characterized in that the respective torsional elastic waves generated by the rising and falling of the current pulse are overlapped and amplified, and are received by the receiver.

A displacement detecting device according to a second aspect of the invention is characterized by comprising a pulse width adjusting circuit for adjusting the width of the current pulse.

[0013]

In the displacement detecting device, the inventor of the present invention, when the influence of the current pulse on the detected waveform is experimented and the width of the current pulse is made sufficiently large as shown in FIG. 3, the current pulse shown in FIG. Of the magnetic field ma of the magnetostrictive line 1 due to the rising a and the magnetic field mb of the magnetostrictive line 1 due to the falling b and the magnetic field due to the permanent magnet 2.
It has been discovered that torsional elastic waves Pa and Pb having the same waveform with inverted polarities are generated. As a result, in FIG. 3, the two waveforms Pa and Pb are brought close to each other, and the width of the current pulse is set so that the amplitude of the waveform resulting from the sum of the two waveforms is maximized. , A highly reliable displacement detection device that can be set easily, can be finely adjusted, and was realized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments. FIG. 1 is a block diagram showing a configuration of a displacement detection device according to the first and second inventions. In this displacement detecting device, one end of the magnetostrictive wire 1 is clamped by a clamp jig 4 fixed on a base 14. An elastic body 6 is inserted into the clamp jig 4, and the elastic body 6 is pressed by tightening a screw 10 to sandwich the magnetostrictive wire 1 and fix one end of the magnetostrictive wire 1. Prevents the reflection of torsional elastic waves. On the other hand, the other end of the magnetostrictive wire 1 is pressed by the elastic body 7 and the screw 9 similarly to the one end, and is supported by the clamp jig 5 via the spring 8 for always applying a constant tension to the magnetostrictive wire 1. ing.

The receiver 3 is arranged near the clamp jig 4, and the magnetostrictive wire 1 penetrates the built-in coil without contact. The coil of the receiver 3 utilizes the inverse magnetostriction effect to detect the torsional elastic wave propagating in the magnetostrictive wire 1. One end of the coil of the receiver 3 is grounded and the other end is the differential amplifier 11
Is connected to the non-inverting input terminal of the differential amplifier 11 and a predetermined positive voltage V1 is applied to the inverting input terminal of the differential amplifier 11. The detected waveform input from the receiver 3 to the differential amplifier 11 is subjected to resonance processing in order to determine that it is a single noise generated after this output, and is input to the waveform processing circuit 13. A permanent magnet 2 is attached to the magnetostrictive wire 1 so as to be movable in the axial direction of the magnetostrictive wire 1, and the end of the permanent magnet 2 on the magnetostrictive wire 1 side is magnetized to an N pole. The end of the permanent magnet 2 on the magnetostrictive line 1 side may be the S pole. Further, the permanent magnet 2 may have a ring shape surrounding the magnetostrictive wire 1.

One end of the magnetostrictive wire 1 has a current pulse generator 1
2 is connected to the output terminal. Current pulse generator 1
Reference numeral 2 is composed of a monostable multivibrator circuit, a grounded-emitter amplification circuit for amplifying its output, and a grounded-emitter amplification circuit by a Darlington circuit connected to this grounded-emitter amplification circuit through a speed-up capacitor C4. .

In the steady state of the monostable multivibrator circuit, the NPN transistor Q2 is turned on by the base current flowing through the variable resistor R3 (trimmer) and the diode D2, and the NPN transistor Q1 has the collector of the NPN transistor Q2 at 0V. Therefore, the base becomes 0 V and is turned off through the resistors R5 and R4. Here, the speed-up capacitor C3 is charged substantially equal to the power supply voltage Vcc. When a negative trigger pulse is input to the capacitor C1, it passes through the diode D1 and NP
The collector voltage of the N transistor Q1 decreases, the voltage of the capacitor C2 is applied to the base of the NPN transistor Q2 in the negative direction through the diode D2, and the NPN transistor Q2 is turned off. The NPN transistor Q1 is
When the collector voltage of the NPN transistor Q2 rises, a base current flows and it is turned on, and the NPN transistor Q2 is completely turned off.

After that, the capacitor C2 changes the variable resistor R3.
It starts discharging to the power supply through
The potential of C3 changes from 0V to NPN transistors Q1 and Q2.
V _BE+ V_F(V_F: Forward voltage of diode D2)
From the moment when the NPN transistor Q2 turns on,
The transistor Q1 returns to the original off state. Capacitor C
2 starts to discharge and then the NPN transistor Q2
The time until it turns on is
The operating time t of the path (width of the current pulse), t = K · C
2. Determined by R3 (K: constant). Therefore, of the current pulse
The width is easily adjusted by the variable resistor R3 (trimmer)
be able to.

In the grounded-emitter amplifier circuit, the collector voltage of the NPN transistor Q2 is applied to the base of the NPN transistor Q3, and the emitter of the NPN transistor Q3 is grounded via the resistor R7, and the output of the monostable multivibrator circuit is amplified. To do. The grounded-emitter amplifier circuit by the Darlington circuit has a speed-up capacitor C4 and a resistor R8 at the emitter of the NPN transistor Q3.
NPN transistor Q4, which is connected to the base via a parallel circuit and has its emitter grounded via a resistor R9,
N, whose base is connected to the emitter of the PN transistor Q4
It is a Darlington circuit with the PN transistor Q5, and amplifies the output of the grounded-emitter amplifier circuit so that no time delay occurs.

The operation of the displacement detecting device having such a configuration will be described below. A current pulse is supplied from one of the current pulse generators 12 to one end of the magnetostrictive wire 1, and is returned to the ground of the pulse generator through the spring 8 at the other end of the magnetostrictive wire 1. At this time, if the width of the current pulse is made sufficiently large as shown in FIG. 3, the circumferential magnetic field ma of the magnetostrictive line 1 due to the rising a of the current pulse and the magnetostrictive line due to the falling b as shown in FIG. 1 circumferential magnetic field mb is generated,
The outer edge of the magnetostrictive wire 1 is moved in the axial direction together with the current pulse (the moving speed is the current speed, so the moving time can be ignored).

When the magnetic fields ma and mb pass in the vicinity of the permanent magnet 2, due to the interaction between the magnetic fields ma and mb and the magnetic field of the permanent magnet 2, the torsional elasticity of the magnetostrictive line 1 is opposite to each other. Waves are generated. The elastic waveforms Pa and Pb processed by the waveform processing circuit 13 when the torsional elastic waves generated by the magnetic fields ma and mb are received by the receiver 3 are as shown in FIG. 3, and the torsional elastic waves are magnetostrictive lines. The time from propagating 1 to reaching the receiver 3 is the delay time for the current pulse. The position of the permanent magnet 2 can be obtained from this delay time and the propagation speed of the magnetostrictive line 1 of the torsional elastic wave.

Here, the elastic waveforms Pa and Pb are assumed as in the following equations. eu = Asin (2πt / T) [V] (1) ed = -Asin {2π (t + Tw) / T} [V] (2) (A: amplitude [V], T: elastic wave period, t: time [ s],
Tw: current pulse width [s], eu: wave generated at rising edge, ed: wave generated at falling edge (1), (2)
The combined waveform is obtained by adding the equations and is represented by the following equation. e = Asin (2πt / T) -Asin {2π (t + Tw) / T} = 2Asin (-Tw / T) π · cos {2πt / T + (Tw / T) π} [∵sinx-siny = 2sin {(x -Y) / 2} · cos {(x + y) / 2}]

When the elastic wave period T = 8 [μs], the current pulse width Tw = 4, 12, 20, 28 ... [μ]
[s], the waveforms overlap and the amplitude increases. The current pulse width Tw can be easily set by the variable resistor R3 of the current pulse generator 12. FIG. 4 is a waveform diagram showing elastic waveforms Pa and Pb when the current pulse width Tw is set to 16 [μs]. Elastic waveform P
a and the elastic waveform Pb do not overlap, and the amplitudes of both waveforms are small. FIG. 5 is a waveform diagram showing elastic waveforms Pa and Pb when the current pulse width Tw is set to 20 [μs]. The elastic waveform Pa and the elastic waveform Pb overlap with each other, and the amplitude of the overlapped waveform increases.

Therefore, by setting the current pulse width Tw to the width at which the two waveforms overlap as described above, even if the strength of the current pulse and the magnetic force of the permanent magnet 2 are the same as in the conventional case, the differential amplifier 11 is also used. It becomes possible to obtain a very large waveform as the output of the differential amplifier 11 without particularly increasing the gain of. The displacement X of the permanent magnet 2 can be easily obtained by the following equation by measuring the time t from the supply of the current pulse to the arrival of the torsional elastic wave at the receiver 3. X = v · t (v is the propagation velocity of the torsional elastic wave of the magnetostrictive wire 1.) In this embodiment, a coil is used as the receiver 3, but as shown in FIG. The same effect can be obtained also by a method in which an AE sensor 15 (AE: Acoustic Emission) using an element is brought into contact with the magnetostrictive wire 1 to detect a torsional elastic wave.

[0025]

According to the displacement detecting device of the first and second aspects of the present invention, an output waveform having a larger amplitude than before can be obtained without increasing the number of detectors and permanent magnets, and detection accuracy and reliability are improved. improves. Moreover, since the number of detectors and permanent magnets does not increase, the structure is simplified and the space can be effectively used. Further, since the detection waveform and the permanent magnet are combined at a predetermined interval in order to synthesize the detected waveforms, there is no need for high-precision processing, and it is only necessary to adjust the variable resistance (trimmer) of the circuit. Adjustment and installation costs can be reduced. Also, even if the elastic wave propagation velocity of the magnetostrictive wire changes due to temperature change, etc., and the time until the elastic wave reaches the receiver changes, and there is a deviation in the combined waveform, it is easy to Since the degree of overlap can be finely adjusted, reliability is increased.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a displacement detection device according to first and second aspects of the invention.

FIG. 2 is a schematic diagram showing a circumferential magnetic field and a torsional elastic wave of a magnetostrictive line due to rising and falling of a current pulse.

FIG. 3 is a waveform diagram showing a waveform of a current pulse and a torsional elastic wave generated by rising and falling of the current pulse.

FIG. 4 is a waveform diagram showing a composite waveform of a torsional elastic wave generated by rising and falling of a current pulse.

FIG. 5 is a waveform diagram showing a combined waveform of torsional elastic waves generated by rising and falling of a current pulse.

FIG. 6 is a perspective view showing a method of detecting a torsional elastic wave by an AE sensor.

FIG. 7 is a block diagram showing a configuration example of a conventional displacement detection device.

FIG. 8 is a waveform diagram showing a waveform of a torsional elastic wave in a conventional displacement detection device.

FIG. 9 is a waveform diagram showing a combined waveform of torsional elastic waves in a conventional displacement detection device.

FIG. 10 is a waveform diagram showing a combined waveform of torsional elastic waves in a conventional displacement detection device.

FIG. 11 is a waveform diagram showing a combined waveform of torsional elastic waves in a conventional displacement detection device.

FIG. 12 is a block diagram showing a configuration example of a conventional displacement detection device.

13 is a front view showing the configuration of two permanent magnets used in the displacement detection device shown in FIG.

[Explanation of symbols]

 1 Magnetostrictive wire 2 Magnet (permanent magnet) 3 Receiver 4,5 Clamping jig 6,7 Elastic body 8 Spring 11 Differential amplifier 12 Current pulse generator 13 Waveform processing circuit 14 Base

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[Procedure amendment]

[Submission date] January 18, 1995

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Front page continuation (72) Inventor Murata, 4-1796 Tsurumi, Tsurumi-ku, Osaka-shi, Osaka Prefecture Tsubakimoto Chain Co., Ltd. (72) Akihiko Utaki 4--1796, Tsurumi, Tsurumi-ku, Osaka, Osaka Tsubakimoto Chain Co., Ltd.

Claims (2)

[Claims] 1. By applying a current pulse to the magnetostrictive wire,
A torsional elastic wave is generated at a portion of the magnetostrictive wire that is close to a magnet that can move along the magnetostrictive line, and the propagation time of the torsional elastic wave to a receiver provided at a specific portion of the magnetostrictive line is measured. With the displacement detecting device for detecting the mechanical displacement applied to the magnet, the respective torsional elastic waves generated by the rising and falling of the current pulse are overlapped and amplified,
A displacement detecting device, which is received by the receiver. 2. The displacement detecting device according to claim 1, further comprising a pulse width adjusting circuit for adjusting the width of the current pulse.