JP2899787B2 - Displacement detector - Google Patents

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 at a portion of a magnetostrictive wire close to a magnet movable along the magnetostrictive wire by flowing a current pulse through the magnetostrictive wire. Further, the present invention relates to an improvement of a displacement detecting device for detecting a mechanical displacement applied to a magnet.

[0002]

2. Description of the Related Art By applying a current pulse to a magnetostrictive wire,
The displacement detection device measures the propagation time of the torsional elastic wave generated at the part of the magnetostrictive wire near the magnet that can move along the magnetostrictive line, and detects the mechanical displacement applied to the magnet. It is necessary to obtain a large torsional elastic wave with little noise in order to improve the reliability. As a method for obtaining a large torsional elastic wave with little noise, a method disclosed in Japanese Patent Laid-Open Publication No.
No. 2,555 and Japanese Patent Laid-Open No. 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 includes a clamp jig 16 in which the starting end of a magnetostrictive wire 17 is
The end is supported by a clamp jig 5 via a spring 8 for always applying a constant tension to the magnetostrictive wire 17. The end of the magnetostrictive wire 17 is
A damping material 23 such as silicon rubber is applied to suppress the influence of a reflected wave from the spring 8 or the clamp jig 5.

[0004] The receivers 19 and 21 are arranged near the clamp jig 16 and have built-in coils 18 and 21 respectively.
The magnetostrictive wire 17 penetrates the center of the reference numeral 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 a torsional elastic wave propagating through the magnetostrictive wire 17 using the inverse magnetostrictive effect. The negative poles of the coils 18 and 20 are grounded, the positive poles are connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 24, respectively, and the coils 18 and 20 are connected in opposite phases. An annular permanent magnet 22 is movably inserted in the magnetostrictive wire 17 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
May be N / S poles or S / N poles.

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 returned to the ground of the pulse generator via the spring 8 at the end of the magnetostrictive wire 17. for that reason,
The interaction between the magnetic field of the permanent magnet 22 and the magnetic field generated by the current pulse flowing through the magnetostrictive wire 17 causes the permanent magnet 22
The torsional elastic waves generated in the nearby magnetostrictive wire 17 and propagated through the magnetostrictive wire 17 are detected by the receivers 19 and 21.

In general, a detection waveform of a receiver has a shape as shown in FIG. That is, at the start of the waveform, a valley I1 appears, followed by a peak I2, which is a peak, and then a valley I3. Two receivers 19, 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, after the delay time Td caused by the distance L between the receivers 19 and 21, the waveform having the peak I5b and the valley I5a is received by the receiver 19. I5 (an inverted waveform of the waveform I4) is received. Here, as the distance L is gradually reduced, as shown in FIG. 10, the delay time Td of the waveform I5 with respect to the waveform I4 is gradually reduced. When the distance L is further reduced, as shown in FIG. 11, the peak I4a of the waveform I4 overlaps the peak I5b of the waveform I5, and the valley I4b of the waveform I4 and the valley I4b of the waveform I5.
5a overlap, 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, the difference can be obtained even if the intensity of the current pulse and the magnetic force of the permanent magnet 22 are the same as before and the gain of the differential amplifier 24 is not particularly increased. An extremely 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 speed of the torsional elastic wave of the magnetostrictive wire 17)

FIG. 12 is disclosed in Japanese Patent Application Laid-Open No. 5-187855.
1 is a block diagram showing a configuration of a displacement detection device (magnetostrictive displacement detection device) proposed in FIG. This displacement detecting device is shown in FIG.
As shown in FIG. 3, two permanent magnets 25a and 25b are inserted through 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 cylindrical holder 25 made of a non-magnetic material. Is held at a constant interval M. Regarding the magnetization direction of the permanent magnets 25a and 25b, the inner and outer circumferences are N / S poles. The other configuration is the same as the configuration of the displacement detection device described in Japanese Patent Application Laid-Open No. 5-172555, and 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 returned to the ground of the pulse generator via the spring 8 at the end of the magnetostrictive wire 17. for that reason,
The magnetic field of each of the permanent magnets 25a and 25b and the magnetostriction line 1
7, the torsional elastic waves generated in the magnetostrictive wires 17 near the permanent magnets 25a and 25b and propagated through the magnetostrictive wires 17 are generated by the interaction with the magnetic field generated by the current pulse flowing through the magnetostrictive wires. Detected by the receivers 19 and 21. Here, the distance L between the receivers 19 and 21 is set to a distance where the peak of the front waveform received by the receiver 21 and the first peak of the rear waveform received by the receiver 19 just overlap. It has been set. Therefore, the output of the differential amplifier 24 includes
Larger waveforms than can be obtained with a single receiver can be obtained. Other operations are described in the above-mentioned “Japanese Patent Laid-Open No. 5-1725.
The operation is the same as that of the displacement detecting device of No. 55, and the description is omitted.

[0010]

In the two proposals described above, two detectors or two permanent magnets are required, so that the number of parts is increased, the space cannot be used effectively, and the spacing between the parts is adjusted. It takes time, and once it is mechanically fixed, it cannot be changed. The present invention has been made in view of the above circumstances, and in the first invention, the width of the current pulse is adjusted so that the respective torsional elastic waves generated by the rise and fall of the current pulse overlap and are amplified. Pulse width adjustment for adjustment
By providing the circuit, without increasing the number of parts, setting easy, shall be the object of providing a fine adjustment can be highly reliable displacement detection device.

[0011]

Displacement detecting device according to the present onset bright SUMMARY OF THE INVENTION, by passing a current pulse to the magnetostrictive wire, twisting the site of the magnetostrictive wire in proximity to the magnet which can be moved along the magnetostrictive wire A displacement detecting device that generates a torsional elastic wave and measures a mechanical displacement applied to the magnet by measuring a propagation time of the torsional elastic wave to one receiver provided at a specific portion of the magnetostrictive wire. , The respective torsional elastic waves generated by the rise and fall of the current pulse
In order to adjust the width of the current pulse to the match I Heavy
And a pulse width adjusting circuit .

[0012]

[0013]

The inventor of the present invention has studied the effect of the current pulse on the detected waveform in the displacement detection device, as shown in FIG. 3, when the width of the current pulse was sufficiently increased during the experiment, as shown in FIG. Of the circumferential magnetic field ma of the magnetostrictive wire 1 due to the rising a and the circumferential magnetic field mb of the magnetostrictive wire 1 due to the falling b, and the magnetic field of the permanent magnet 2,
It has been discovered that torsional elastic waves Pa and Pb of the same waveform with inverted polarity are generated. Thereby, in FIG. 3, the two waveforms Pa and Pb are brought closer to each other, and the width of the current pulse is set so that the amplitude of the waveform by the sum of the two waveforms is maximized. A highly reliable displacement detection device that can be easily set, finely adjusted, and realized.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing embodiments thereof. FIG. 1 is a block diagram showing the configuration of the displacement detection device according to the first and second inventions. In this displacement detection 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. The elastic body 6 is pressed by tightening a screw 10, sandwiches the magnetostrictive wire 1, and fixes one end of the magnetostrictive wire 1. Prevents 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 like the one end, and is supported by the clamp jig 5 via a 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 a built-in coil without contact. The coil of the receiver 3 detects the torsional elastic wave propagating through the magnetostrictive wire 1 using the inverse magnetostriction effect. One end of a coil of the receiver 3 is grounded, and the other end is a 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 it as a single-shot noise occurring after the 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 an 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 wire 1 side may be an S pole. Further, the permanent magnet 2 may be in a ring shape surrounding the magnetostrictive wire 1.

One end of the magnetostrictive wire 1 is connected to the current pulse generator 1
2 output terminal. Current pulse generator 1
Reference numeral 2 denotes a monostable multivibrator circuit, a common emitter amplifier circuit for amplifying its output, and a common emitter amplifier circuit of a Darlington circuit connected to the common emitter amplifier circuit via a speed-up capacitor C4. .

In the monostable multivibrator circuit, in a steady state, the base current flows through the variable resistor R3 (trimmer) and the diode D2 to turn on the NPN transistor Q2, and the collector of the NPN transistor Q2 is 0 V in the NPN transistor Q1. Therefore, the base becomes 0 V through the resistors R5 and R4, and the base is turned off. 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, 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 to turn on the NPN transistor Q2, thereby completely turning off the NPN transistor Q2.

Thereafter, the capacitor C2 connects the variable resistor R3.
Discharge to the power supply through the
When the potential of C3 is changed from 0V to NPN transistors Q1, Q2
V _BE+ V_F(V_F: Forward voltage of diode D2)
NPN transistor Q2 is turned on and NPN
The transistor Q1 returns to the off state. Capacitor C
2 starts discharging, and the NPN transistor Q2 restarts.
Time to turn on and turn on the monostable multivibrator
Road operating time t (width of current pulse), t = K · C
It is determined by 2.R3 (K: constant). Therefore, the current pulse
The width is easily adjusted by the variable resistor R3 (trimmer)
be able to.

In the common 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 amplifies the output of the monostable multivibrator circuit. I do. A Darlington circuit-grounded emitter amplifier circuit includes a speed-up capacitor C4 and a resistor R8 connected to the emitter of an NPN transistor Q3.
An NPN transistor Q4, which is connected to the base via a parallel circuit, and whose emitter is grounded via a resistor R9;
N connected to the base of the emitter of PN transistor Q4
This is a Darlington circuit with the PN transistor Q5, and amplifies the output of the common-emitter amplifier circuit so that no time delay occurs.

The operation of the displacement detecting device having such a configuration will be described below. One end of the magnetostrictive wire 1 is supplied with a current pulse from the current pulse generator 12, and is returned to the ground of the pulse generator via the spring 8 at the other end of the magnetostrictive wire 1. At this time, as shown in FIG. 3, when the width of the current pulse is made sufficiently large, 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. And a circumferential magnetic field mb of 1
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, the interaction between the magnetic fields ma and mb and the magnetic field generated by the permanent magnet 2 causes the magnetostrictive wire 1 to have a torsional elasticity in which the directions of torsion are opposite to each other. Waves are generated. The torsional elastic waves generated by the magnetic fields ma and mb are received by the receiver 3, and the elastic waveforms Pa and Pb processed by the waveform processing circuit 13 are as shown in FIG. The time from the propagation of 1 to the arrival at the receiver 3 is the delay time for the current pulse. From the delay time and the propagation speed of the magnetostrictive wire 1 of the torsional elastic wave, the position of the permanent magnet 2 is obtained.

Here, the elastic waveforms Pa and Pb are assumed as follows. 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, ed: wave generated at falling) (1), (2)
A combined waveform is obtained by adding the expressions, and is represented by the following expression. 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｝]

Here, when the elastic wave period T is 8 [μs], the current pulse width Tw = 4, 12, 20, 28.
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 the elastic waveforms Pa and Pb when the current pulse width Tw is set to 16 [μs]. Elastic waveform P
a does not overlap with the elastic waveform Pb, and the amplitudes of both waveforms are small. FIG. 5 is a waveform diagram showing the 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, and the amplitude of the overlapped waveform increases.

Therefore, by setting the current pulse width Tw to a width at which the two waveforms overlap as described above, even if the intensity of the current pulse and the magnetic force of the permanent magnet 2 are the same as those in the related art, Thus, a very large waveform can be obtained as the output of the differential amplifier 11 without increasing the gain of the differential amplifier 11 in particular. By measuring the time t from when the current pulse is supplied to when the torsional elastic wave reaches the receiver 3, the displacement X of the permanent magnet 2 can be easily obtained by the following equation. X = v · t (v is the propagation speed 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. A similar effect can be obtained 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 present invention, it is possible to obtain an output waveform having a larger amplitude than before, without increasing the number of detectors and permanent magnets, thereby improving the detection accuracy and reliability. Further, since the number of detectors and permanent magnets does not increase, only one receiver is required , so that the configuration is simplified and the space can be used effectively. Also, since the detection waveform is synthesized, high-precision processing for arranging the detector and the permanent magnet at a predetermined interval is not required, and only the variable resistance (trimmer) of the circuit needs to be adjusted. Adjustment
Installation costs can be reduced. Also, for example, when the propagation speed of the elastic wave of the magnetostrictive wire changes due to a temperature change or the like, the time required for the elastic wave to reach the receiver changes, and even when a deviation occurs in the composite waveform, the pulse width adjusting circuit Current pulse
By adjusting the width, the degree of overlap of the synthesized waveforms can be easily finely adjusted, so that the reliability is improved.

[Brief description of the drawings]

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

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 waveforms of a current pulse and a torsional elastic wave generated by its rise and fall.

FIG. 4 is a waveform diagram showing a composite waveform of a torsional elastic wave generated by the rise and fall of a current pulse.

FIG. 5 is a waveform diagram showing a composite waveform of a torsional elastic wave generated by the rise and fall 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 illustrating 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 illustrating a configuration example of a conventional displacement detection device.

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Akihiko Utaki 4-17-96, Tsurumi-ku, Tsurumi-ku, Osaka-shi, Osaka Inside Tsubakimoto Chain Co., Ltd. (56) References JP-A-5-172555 (JP, A) JP-A-63-217224 (JP, A) JP-A-55-67702 (JP, A) JP-A-61-112923 (JP, A) JP-A-59-162412 (JP, A) JP-B-57-32761 (JP, A) JP, B2) Jikken Hei 3-55860 (JP, Y2) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 17/00 G01D 5/48

Claims (1)

(57) [Claims] 1. By flowing a current pulse through a magnetostrictive wire,
A torsional elastic wave is generated at a portion of the magnetostrictive wire close to the magnet that can move along the magnetostrictive wire, and the torsional elastic wave is transmitted to one receiver provided at a specific portion of the magnetostrictive wire. by measuring the propagation time, the displacement detecting device for detecting a mechanical displacement imparted to the magnet, the current pulse to align it heavy respective torsion elastic wave generated by the rise and fall of the current pulse Adjust width
A displacement detecting device comprising a pulse width adjusting circuit for performing the operation .