JPH02183117A - Displacement detector - Google Patents

Abstract

PURPOSE:To enable elimination of measuring errors due to a temperature change in a circuit section by measuring a relative displacement of two permanent magnets based on a difference in arrival time of ultrasonic wave signals. CONSTITUTION:A circular permanent magnetic 2 is movable along a magnetostrictive line 1 and polarized along the axis of the magnetostrictive line 1. A pulse generator 3 supplies a current pulse to an initial end of the magnetostrictive line 1. A distortion detector 4 is provided on the initial end side of the magnetostrictive line 1 and a circular fixed permanent magnet 5 is fixed at a specified part of the magnetostrictive line 1 and has the same characteristic as that of the permanent magnet 2. Moreover, a pulse forming circuit 6 converts a detection signal of a detector 4 to a pulse-like signal. Then, a propagation time difference from the permanent magnets 2 and 5 will not change free from a change in a threshold of the circuit 6 as well as in the sensitivity of the detector 4. Thus, it is possible to determine a relative distance l between the permanent magnet 2 and the permanent magnet 5 precisely without being affected by a temperature change by determining the propagation time difference.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a displacement detection device that detects mechanical displacement of an object, displacement of a liquid surface, etc. using a magnetostrictive phenomenon.

[Conventional technology]

Conventionally, as an M1 distortion type displacement detection device, US Patent No. 317
As described in Japanese Patent Application No. 3131, a magnetostrictive wire, a permanent magnet movable along the magnetostrictive wire, a transmitting means for supplying a current pulse to the magnetostrictive wire, and a transmitting means provided at a specific part of the magnetostrictive wire, and a permanent magnet movable along the magnetostrictive wire. A device is known that is equipped with a receiving means for receiving an ultrasonic signal generated at a site of a magnetostrictive wire in the vicinity.

When a current pulse is supplied to the magnetostrictive wire by the receiving means, a circumferential magnetic field is formed in the magnetostrictive wire, and the axial direction of the magnetostrictive wire is caused by the permanent magnet only in the part of the magnetostrictive wire that is close to the permanent magnet. A magnetic field is formed, and torsional strain is generated in the relevant part of the magnetostrictive wire due to the so-called Beepmann effect. This torsional strain is intense, causing torsional vibration (super sound waves) propagate. If this ultrasonic wave is detected by the receiving means, the distance*2 from the position of the receiving means of the magnetostrictive line to the permanent magnet can be determined as a function of time using the following equation.

j! In the above equation, ■ is the propagation velocity of the ultrasonic wave, which is given by G being the transverse elastic modulus of the magnetostrictive line and ρ being the density of the M1 strain line.

However, when Ni, which is a common magnetostrictive material, is used as the magnetostrictive wire, the transverse elastic modulus G and density ρ have characteristics that change depending on temperature, so the propagation velocity V changes depending on temperature, making measurement difficult. This will cause an error in the distance l.

In order to solve this problem, the applicant fixed a permanent magnet at a specific part of the magnetostrictive cotton in addition to a permanent magnet that can move along the magnetostrictive line, and the arrival time of the ultrasonic signal propagated from the movable permanent magnet We proposed a displacement detection device that can measure distances without being affected by temperature changes by determining the ratio of the arrival time of ultrasonic signals propagated from a fixed permanent magnet.
(Japanese Patent Application Laid-Open No. 61-226615).

[Problem to be solved by the invention]

However, in the case of the above displacement detection device, although measurement errors due to temperature changes in the propagation velocity of ultrasonic waves can be eliminated,
It is not possible to eliminate measurement errors due to temperature changes in the circuit section of the receiving means. In other words, when the ambient temperature changes, the sensitivity of the strain detection device that detects ultrasonic signals changes, and the comparison point (called the dark value) of the comparator that shapes the detected wave of the strain detection device into a pulse shape changes. It is.

FIG. 5 is a waveform diagram when the sensitivity of the strain detection device changes. Waveform A is the current pulse supplied from the transmitting means, waveform B is the detection waveform of the ultrasonic signal detected by the strain detection device, and waveform C. is an output waveform obtained by shaping the detected waveform B with a comparator. Among these, when the sensitivity of the strain detection device changes due to temperature, the detected waveform B changes as shown by the broken line in Figure 5, and the output waveform C of the comparator also changes as shown by the broken line, causing the original measurement time to change. shifts to Lo, measurement error ΔL
produce.

FIG. 6 is a waveform diagram when the darkness value of the comparator changes, and when the original threshold (I!!h changes to ho due to temperature change), a measurement error ΔL occurs.

There is a temperature compensation circuit to eliminate measurement errors in the circuit section as described above, but this increases cost due to the use of a large number of electronic components such as temperature sensors, and also increases the cost due to variations in each component. It was difficult to expect adequate temperature compensation.

Therefore, an object of the present invention is to
An object of the present invention is to provide a displacement detection device that can eliminate measurement errors caused by temperature changes in a circuit section.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a linear or tubular magnetostrictive material, a first permanent magnet and a first permanent magnet arranged near the magnetostrictive material at an arbitrary interval. 2 permanent magnets, a transmitting means for supplying a current pulse in the axial direction of the magnetostrictive material, and a transmitting means provided at a specific part of the magnetostrictive material, and transmitting an ultrasonic signal generated at a part of the magnetostrictive material adjacent to the 1st and 2nd permanent magnets. Due to the difference between the propagation time of the ultrasonic signal from the first permanent magnet to the receiving means and the propagation time of the ultrasonic signal from the second permanent magnet to the receiving means, It is equipped with calculation means for determining the amount of relative displacement with respect to the magnet.

That is, if the ultrasonic signal waveform from one permanent magnet changes due to a temperature change in the circuit section, the ultrasonic signal waveform from the other permanent magnet changes in exactly the same way.
By determining the difference in the arrival times of these waveforms, the influence of temperature changes can be eliminated. Therefore, in the present invention, by determining the arrival time difference of the ultrasonic signals from both permanent foundation stones, accurate displacement detection can be performed without using any temperature compensation circuit or the like.

In the present invention, the propagation speed of ultrasonic waves does not change with temperature, but this can be solved by using a constant elastic metal such as N15panC (trade name) as the magnetostrictive material. The temperature change rate of the ultrasonic propagation velocity of constant-modulus metals can be changed from O to 20 ppm/'' by heat treatment, etc.
It can be reduced to about C. On the other hand, the measurement variation due to the temperature of the circuit section is generally 200 to 500 ppm/
Since the temperature is approximately 100°C, the temperature change in the ultrasonic propagation velocity of the constant elastic gold 1 can be practically ignored.

〔Example〕

FIG. 1 shows an example of the basic configuration of the displacement detection device according to the present invention, in which 1 is a magnetostrictive wire made of a constant elastic metal such as N15panC (trade name), and 2 is a magnetostrictive wire that surrounds the magnetostrictive wire 1 and extends along the magnetostrictive wire 1. The permanent magnet 2 is an annular permanent magnet that can be moved by the magnetostrictive wire 1. The permanent magnet 2 is polarized in the axial direction of the magnetostrictive wire 1. 3 is a pulse generator which is an example of a transmitting means for supplying a current pulse to the starting end of the magnetostrictive wire 1; 4 is a strain detecting device which is an example of a receiving means provided on the starting end side of the magnetostrictive wire l; 5 is a magnetostrictive wire l An annular fixed permanent magnet is fixed at a specific location and has characteristics similar to those of the movable permanent magnet 2, and 6 is a pulse shaping circuit such as a comparator that converts the detection signal of the strain detection device 4 into a pulsed signal.

Figure 2 shows the waveforms of each part of the displacement detection device with the above configuration,
A is the current pulse supplied to the magnetostrictive wire 1 by the pulse generator 3, B is the signal waveform detected by the strain detection device 4, of which 7 is the ultrasonic signal waveform generated by the fixed permanent magnet 5, and 8 is the waveform of the ultrasonic signal generated by the fixed permanent magnet 5. This is an ultrasonic signal waveform generated by the movable permanent magnet 2. Further, C is a pulse forming port-path 6 which converts the above waveform 7°8 into a pulsed waveform 9. It is converted to lO.

The distance between the movable permanent magnet 2 and the strain detection device 4 is 11, the distance between the fixed permanent magnet 5 and the strain detection device 4 is 28, and the movable permanent magnet is in.
The time it takes for the ultrasonic waves generated by the stone 2 to propagate to the strain detection device 4 is Ll, the time it takes for the ultrasonic waves generated by the fixed permanent magnet 5 to propagate to the strain detection device 4 to reach the strain detection device 4 is 1, [If the propagation speed of the sound wave is V] ,42, =v-t, ...(1)
! □=V −jl ... is given by (2).

Now, as shown by the broken line in FIG. 2, when the dark value of the pulse shaping circuit 6 changes from h to ho due to temperature change, the second
As shown in Figure C', the ultrasonic propagation time of the movable permanent magnet 2 is 1+
is t1+ΔL, ultrasonic propagation time t2 of fixed permanent magnet 2
The beam changes to +Δt, respectively. Therefore, (1)
The equation and equation (2) are as follows.

j! , =v (t, +Δt)...
(3) Il, -v (tt +Δt)
-(4) Here! When calculating the ratio between , and l, the error ΔL in the circuit cannot be eliminated, so equation (1) and (
2) Calculating the relative distance 2 between the movable permanent magnet 2 and the fixed permanent magnet 5 using the difference from the formula, 1 = l Il z = v (t + tg) (6),
The error ΔL in the circuit section can be eliminated. In other words, even if the dark value of the pulse shaping circuit 6 changes or the sensitivity of the strain detection device 't4 changes, the propagation time difference tc from both permanent magnets 2.5
=t+ L does not change. Therefore, by determining the propagation time difference t, it is possible to accurately determine the relative distance 2 between the movable permanent magnet 2 and the fixed permanent magnet 5 without being affected by temperature changes. Incidentally, by using a constant-elasticity metal as the magnetostrictive wire 1, errors in the propagation velocity V due to temperature changes can be practically ignored.

The above-mentioned propagation time difference can be easily converted into an electrical signal using conventional technology. Then it can be detected as an analog signal, and waveform 9 can be detected as shown in Figure 2E.
If the clock is started at , and the clock is set at the time of waveform lO, it can be detected as a digital signal.

Another embodiment - In the above embodiment, one of the two permanent magnets is replaced with the movable permanent magnet 2.
．． Although the other one is the fixed permanent magnet 5, it is also possible to use movable permanent magnets for both of them instead and measure the relative distance between the two permanent magnets.

In addition, the permanent magnet is not limited to an annular magnet with different poles magnetized on both sides, but for example, as shown in Figure 3, two or It may be constructed with the above permanent magnets 11 and 12, or it may be constructed with only one permanent magnet shown in FIG.

In addition, it is not limited to the case where a magnetostrictive wire is used as the magnetostrictive material and a current pulse is directly supplied to the magnetostrictive wire, and a cylindrical magnetostrictive tube 13 is used as shown in FIG. A configuration may be adopted in which a conductive wire 14 for flowing the water is inserted. In this case, the ultrasonic waves propagating through the distortion tube 13 may be detected by the receiving means.

Further, as the receiving means, a contact receiving means such as a strain detection device may be used, but a non-contact receiving means such as a coil may also be used.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, the relative displacement of the two permanent magnets is measured based on the arrival time difference of the ultrasonic signals from the two permanent magnets. Displacement can be detected accurately without being affected by temperature changes. Moreover, since there is no need to use a complicated temperature compensation circuit or the like, it can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of an example of a displacement detection device according to the present invention, FIG. 2 is a waveform diagram showing an example of a detection method, FIG. 3 is a perspective view of another embodiment of a permanent magnet, and FIG. A perspective view of another embodiment of the magnetostrictive material, FIG. 5 is a waveform diagram when the sensitivity of the strain detection device changes, and FIG. 6 is a waveform diagram when the comparator threshold changes. l... Magnetostrictive wire, 2... Movable permanent magnet, 3... Pulse generator (transmission means), 4... Strain detection device (receiving means), 5... Fixed permanent magnet, 6...・Pulse forming path. Patent applicant Sankyo Boeki Co., Ltd. Representative Hidetaka Tsutsui Figure 1 Figure 3 Figure 4 Figure 5 Figure 6 Δt

Claims (1)

[Claims] A linear or tubular magnetostrictive material, a first permanent magnet and a second permanent magnet arranged near the magnetostrictive material at an arbitrary interval, a transmitting means for supplying a current pulse in the axial direction of the magnetostrictive material, and a magnetostrictive material. a receiving means that is provided at a specific part of the material and receives an ultrasonic signal generated at a part of the magnetostrictive material adjacent to the first and second permanent magnets; and a propagation time of the ultrasonic signal from the first permanent magnet to the receiving means. and calculation means for calculating the amount of relative displacement between the first permanent magnet and the second permanent magnet based on the difference between the propagation time of the ultrasonic signal from the second permanent magnet to the receiving means. Device.