JPS6285819A - Displacement detector - Google Patents

Abstract

PURPOSE:To detect displacement in a state that there are no restrictions in the approaching distance between two magnets without being influenced by transmission speed of ultrasonic waves by detecting separately ultrasonic signals of the fixed and movable permanent magnets by supply signals of two transmission means. CONSTITUTION:The movable permanent magnet 2 movable along a magnetostrictive line 1 and the fixed permanent magnet 3 fixed on a prescribed part of the magnetostrictive line 1 are provided. Then, the 1st pulse generator 4 impresses a starting end of the magnetostrictive line 1 with an electric current pulse A1 and the 2nd pulse generator 5 impresses just behind the magnet 3 of the magnetostrictive line 1 with an electric current pulse A2. Further, a distortion detector 6 is provided at the starting end side of the magnetostrictive line 1 and receives the ultrasonic signal transmitting through the magnetostrictive line 1. Then, a signal in connection with transmission time until the detector 6 of an ultrasonic signal produced or reflected on a part of the magnetostrictive line 1 where the magnets 2 and 3 approach is introduced into an arithmetic circuit and the mechanical displacement given to the magnet 3 is calculated. Accordingly, there is no possibility being influenced by the transmission speed of the ultrasonic waves. Further, since a reception means may be provided at only one place, the displacement can be detected without being restricted by an object to be measured.

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, liquid level, etc. using magnetostriction phenomena.

Prior art and its problems Conventionally, as a displacement detection device that detects mechanical displacement of an object or liquid surface using magnetostriction phenomenon, for example, U.S. Pat. No. 317313
As described in Publication No. 1, a current pulse is passed through one end of a magnetostrictive wire, and a so-called Wiedema effect (Wiedema
There is a known device that detects mechanical displacement given to a permanent magnet by generating ultrasonic waves (torsional strain) using magnetostrictive lines and measuring the propagation time of the ultrasonic waves to a specific part of the magnetostrictive line. However, in the case of this type of displacement detection device, there is a problem in that if the propagation speed of the ultrasonic wave changes due to, for example, a temperature change, an error occurs in the measured distance.

In order to eliminate measurement errors caused by such variations in propagation velocity, first and second receiving means are provided at both ends of the magnetostrictive wire, as described in, for example, Japanese Patent Laid-Open No. 55-66710,
A displacement detection device is provided that can determine the position of a permanent magnet regardless of the propagation speed by detecting the propagation time of each ultrasonic wave from the permanent magnet to these receiving means. However, in the case of the above-mentioned displacement detection device, it is necessary to provide receiving means at both ends, so if one end of the device is buried inside the object to be measured, for example, when detecting the liquid level, etc. When used, since one of the receiving means is located in the liquid, a lead wire must be wired in the liquid, making measurement difficult and having the disadvantage of being expensive since two receiving means are required.

Therefore, in order to eliminate the above-mentioned drawbacks, the present applicant provided a permanent magnet fixed at a specific part of the magnetostrictive line in addition to a permanent magnet movable along the magnetostrictive line, and the applicant proposed that the fixed permanent magnet and the movable permanent magnet We proposed a displacement detection device that detects the mechanical displacement given to a movable permanent magnet based on the propagation time of both ultrasonic signals (Japanese Patent Application No. 67716/1982).
.

In this case, as shown in FIG. 7, ultrasonic signals 31 and 32 are simultaneously generated in both the fixed permanent magnet and the movable permanent magnet based on the current pulse 30 from the transmitting means, and these signals are detected by the receiving means. However, especially when the movable permanent magnet approaches the fixed permanent magnet within a certain distance, the ultrasonic signal 32 from the movable permanent magnet is superimposed on the reverberation wave of the ultrasonic signal 31 from the fixed permanent magnet, and at measurement time t. There is a risk of errors. To explain this according to Figure 8,
In the figure, the broken line wave 32a is the original wave generated by the movable permanent magnet, which is not affected by the aftereffect wave, and the solid line wave 32b is the wave when superimposed on the aftereffect wave.Originally, time t would be measured. But, there's more! The wave 32a is pushed downward by the influence of L, and the measurement time becomes t', resulting in an error of Δt. The only way to avoid such errors is to limit the approach distance between the two permanent magnets, which has the disadvantage that the measurable range is limited by the distance (travel) compared to the total length of the magnetostrictive wire.

Purpose of the Invention The present invention has been made in view of such conventional problems.
The purpose is to provide a displacement detection device that can detect displacement without being affected by the propagation speed of ultrasonic waves and eliminates the limitation on the approach distance between two permanent magnets.

Structure of the Invention In order to achieve the above object, the displacement detection device of the present invention has the following features:
A magnetostrictive wire, a movable permanent magnet movable along the magnetostrictive wire, a fixed permanent magnet fixed to a specific part of the magnetostrictive wire, and a first transmitting means for supplying a current pulse or an ultrasonic signal to one end of the magnetostrictive wire. a second transmitting means that supplies a current pulse or an ultrasonic signal to a portion between the movable permanent magnet and the fixed permanent magnet on the magnetostrictive line and in the vicinity of the fixed permanent magnet at a different time from that of the first transmitting means; Receiving means for receiving ultrasonic signals generated or reflected at adjacent magnetostrictive wire portions of a permanent magnet and a fixed permanent magnet; and ultrasonic signals generated or reflected at adjacent magnetostrictive wire portions of a movable permanent magnet and a fixed permanent magnet. and calculation means for determining the mechanical displacement given to the movable permanent magnet by a signal related to the propagation time to the receiving means.

That is, the ultrasonic signals of the fixed and movable permanent magnets are detected separately based on the supply signal of the first transmitting means and the supply signal of the second transmitting means, thereby eliminating detection errors in propagation time due to superimposition of waveforms. It is something.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an example of the basic configuration of a displacement detection device according to the present invention, in which 1 is a magnetostrictive wire made of a magnetostrictive material such as Ni, 2 is a magnetostrictive wire made of a magnetostrictive material such as Ni,
3 is a cylindrical movable permanent magnet with N and S poles magnetized on both end faces and movable along the magnetostrictive line I; 4 is a first pulse generator which is an example of a transmitting means for applying a current pulse A1 to the starting end of the magnetostrictive wire 1; 5 is a first pulse generator that applies a current pulse A2 to the magnetostrictive wire 1 immediately after the fixed permanent magnet 3; A second pulse generator 6 is provided on the starting end side of the magnetostrictive wire 1 and is an example of a receiving means for receiving an ultrasonic signal propagating through the magnetostrictive wire 1; This is a pulse shaping circuit that shapes the ultrasonic signal B into a pulsed signal B'.

The current pulse A of the first pulse generator 4 is input to the S terminal of the S-R type flimp flop circuit 8, and the current pulse A2 of the second pulse generator 5 is input to the R terminal. The output Q of the flip-flop circuit 8 is input to the AND circuit 9.
and the output signal B of the pulse shaping circuit 7 are input, and AN
The output of the flip-flop circuit 8, that is, the output signal B' of the pulse shaping circuit 7 is input to the D circuit 10.

Figure 2 shows the voltage waveforms of each part of the circuit shown in Figure 1.
1 is an ultrasonic signal waveform generated at the fixed permanent magnet 3 by the current pulse A, 12 is an ultrasonic signal waveform generated at the movable permanent magnet 2 by the current pulse A1, and 13 is an ultrasonic signal waveform generated at the movable permanent magnet 2 by the current pulse A2. This is the ultrasonic signal waveform generated at part 2. That is, since the current pulse A1 flows throughout the entire magnetostrictive wire 1, the ultrasonic signals 11 and 12 generated by both permanent magnets 2 and 3 are detected, but the current pulse A2 flows from immediately after the fixed permanent magnet 3 to the end. Since only the ultrasonic signal 13 generated by the movable permanent magnet 2 is detected. These waveforms 11, 12, 13 are converted into pulsed signals 14, 15, 16 by the pulse shaping circuit 7. Since the output Q of the flip-flop circuit 8 is ON from the time when the current pulse A1 is applied until the time when the current pulse A2 is applied, the output C7 of the AND circuit 9 becomes only the pulse signal 14.15, while the flip-flop circuit The output of 8 is ON from the time the current pulse A2 is applied until the next current pulse A1 is applied, so
The output C2 of the AND circuit 10 is only the pulse signal 16.

The distance between the movable permanent magnet 2 and the strain detection device 6! , t is the propagation time of the ultrasonic wave 13 generated by the movable permanent magnet 2,
The distance between the fixed permanent magnet 3 and the strain detection device 6 is 7! . , t is the propagation time of the ultrasonic wave 11 generated by the fixed permanent magnet 3.

, let S be the propagation speed of ultrasonic waves, then β = s-t...(111
2o=s·to...(2). In this way, by using two permanent magnets 2.3, two types of signals 1 and 1o are obtained, and when the ratio of 1.1o is calculated using +11 and equation (2), t/1o - IlZIlo
...(3). (In Equation 32, the propagation speed S is eliminated and !!o is known, so if we calculate the ratio of the two types of signals 1.1o, we can calculate the ratio of the position l of the movable permanent magnet 2 to a constant distance l. This enables distance measurements that are not affected by propagation speed.

Furthermore, since the propagation time of the ultrasonic wave 12 generated in the movable permanent magnet 2 by the current pulse A is between - and the propagation time t of the ultrasonic wave 13 generated in the movable permanent magnet 2 by the current pulse A2, the ultrasonic wave 12 It is also possible to measure the propagation time of Ultrasonic wave 1 of magnet 2
2, which may cause a detection error in the measurement time t. Therefore, in the present invention, the ultrasonic wave 12 is ignored and only the propagation time t of the ultrasonic wave 13, which does not include any error, is measured.

As a method for determining the ratio of the above signal 1.1o, for example, 1
, 1o, and calculate these two voltage signals with a divider made of a semiconductor integrated circuit, we get (
3) Equations can be calculated. In addition, as another method 1,
If 1o is detected as a digital signal by a counter, the microprocessor can calculate equation (3). Both methods can be calculated using existing technology, but the disadvantages are that the components are expensive and the adjustment is complicated.
An arithmetic circuit, which is an inexpensive and highly stable arithmetic means, will be described below.

Fig. 3 shows an example of an arithmetic circuit, and Fig. 4 shows voltage waveforms at various parts of the circuit.
, C2 are the same as in FIG.

In FIG. 3, 17 is a triangular wave generating circuit, and 18 is a sample and hold circuit. occurs. The sample and hold circuit 18 is operated by the pulse 14 of FIG. 4 C7, which is a pulse of the waveform 11 generated by the fixed permanent magnet 3, and the voltage V of the triangular wave at that time. hold.

Now, assuming that the propagation speed of the ultrasonic wave has become faster,
The waveform 11 arrives as fast as 11”, and the voltage of the triangular wave held by the pulse 14° becomes voo, and V
It becomes smaller than Q. Conversely, when the propagation speed becomes slower, waveform 1
1 arrives late like 11'', and the voltage of the triangular wave held by the pulse 14 becomes V.°, which is larger than V.°.

Expressing this in a formula, vo is time. Since it is proportional to , if its proportionality constant (slope) is a, then VO=a Lg
-...(4) Substituting equation (2) into this, v (1wa l1t3 - -(
It will be 51.

As already mentioned, the propagation speed S of the ultrasonic waves propagating on the magnetostrictive wire changes depending on the temperature, but the rate of change is not so large in the practical temperature range. Therefore, the propagation speed at room temperature is S. If the change in propagation velocity due to temperature change at room temperature is expressed as ΔS, and equation (5) is expanded by Taylor, and if the second order or higher order of ΔS is ignored, it can be approximated by a linear equation as shown below.

The operational amplifier 1 shown in Figure 3 specifically calculates equation (6).
9, and V calculated by the operational amplifier 19.

is applied to the positive input of amplifier 20. Amplifier 20, PN
PN upper type resistor 21. The resistor 22 (resistance value R) and the capacitor 23 (capacitance value C) constitute an integrating circuit, and the NP
N-type transistor 24 is turned on by current pulse A2. Therefore, the voltage charged in the capacitor 23 is grounded through the transistor 24 by the current pulse A2 and becomes zero, and the voltage of the capacitor 23 changes in a triangular waveform that starts at the same time as the current pulse A2, as shown in FIG. 4E. . Amplifier 20 operates such that the voltages at its positive and negative inputs are the same, so transistor 2
1, the emitter voltage becomes v(1), and the current i flowing through the resistor 22 to which a constant voltage V is supplied is controlled by the relationship , and flows into the capacitor 23 via the transistor 21. When the voltage of the capacitor 23 is set to 0, the voltage V of the capacitor 23 becomes, and by substituting the equation (7) into this and integrating the equation (8), v = -(V - VO) t...
(9)C, and changes as shown in Figure 4E.

As in the case of the fixed permanent magnet 3, the waveform of the ultrasonic wave 13 generated by the movable permanent magnet 2 has a waveform of 13° in FIG. If the slope of the triangular wave is constant as shown by the solid line in FIG. 4E, the output voltage 2 held by the sample and hold circuit 25 will change depending on the arrival time. At this time, the voltage V at the positive input of the amplifier 20. If we change the slope of the triangular wave as shown by the broken line in Figure 4E, the output voltage y will remain the same even if the propagation speed changes.
(You will get it.

The arrival time of the waveform 13 emitted from the movable permanent magnet 2 is t= □...
・Since it is expressed as 00S, if we perform Taylor expansion in the same way as equation (6), we get: Therefore, by substituting equation (61, (11) into equation (9) and rearranging it, we get SQ 5QSQ.If we set the voltage ■ so that O in equation (12), equation (12) becomes the following It becomes like this.

RCSo s6 S.

In equation (14), the only variables are the distance l of the movable permanent magnet 2 and the change in propagation speed ΔS. In addition, the second term in parentheses in equation (14) is quadratic and can be ignored in many cases as described above, so it can actually be approximated as follows.

RCSo S.

As described above, a stable temperature compensation circuit can be constructed using inexpensive components as shown in Figure 3, and even if the propagation speed of the ultrasonic wave propagating on the magnetostrictive wire varies depending on the temperature, the variation can be compensated for. , it becomes possible to make the displacement detection device using the magnetostriction phenomenon, which is originally capable of highly accurate detection, even more stable.

5 and 6 show another embodiment of the present invention, in which a fixed permanent magnet 3 is fixed to the terminal end side of the magnetostrictive wire l, and a movable permanent magnet 2 is placed between the strain detection device 6 and the fixed permanent magnet 3. It was designed to be moved. In this case, the second pulse generator 5
Since the current pulse A2 is supplied just before the fixed permanent magnet 3, only the ultrasonic wave 11 generated by the fixed permanent magnet 3 by the current pulse A2 can be detected as shown in FIG. Note that another ultrasonic wave 11° generated by the fixed permanent magnet 3 due to the current pulse A may be affected by the aftereffect wave of the ultrasonic wave 13 generated by the movable permanent magnet 2, so it can be ignored.

For example, when the displacement detection device shown in FIG. Temperature compensation is more accurate than in Figure 1,
Highly accurate liquid level detection becomes possible. Furthermore, when the circuit shown in Fig. 3 is used as the calculation means of this displacement detection device,
current pulse A, to transistor 24, current pulse A2
It is sufficient to input the output C2 to the triangular wave generation circuit 17, the output C2 to the sample hold circuit 25, and the output C2 to the sample hold circuit 18. As a result, the triangular wave in Figure 4 is started by the current pulse A2, and the triangular wave in Figure 4E is started by the current pulse A1.

Note that the displacement detection device of the present invention is not limited to the above embodiments, and can be modified in various ways. For example, in order to extract two types of signals C7 and C2 from the current pulses A, A2 of the pulse generator 4.5 and the detection signal B of the distortion detector 6,
Flip-flop circuit 8 and AND circuit 9. Although an example in which IO is provided is shown, this is just an example, and it is possible to replace it with an existing circuit. Furthermore, although two pulse generating bags W4 and 5 are provided as receiving means, it is possible to configure one pulse generating device to supply current pulses A, A2 at different times and to separate locations. is also possible.

In addition to the method in which a current pulse is passed through a magnetostrictive wire to generate an ultrasonic wave at a portion adjacent to a permanent magnet, the present invention also relates to a method in which an ultrasonic wave is caused to flow through a magnetostrictive wire as described in, for example, Japanese Unexamined Patent Publication No. 55-23420. , it can also be used to reflect part of the ultrasonic waves at a part close to a permanent magnet. In this case, an excitation device such as a coil or a piezoelectric element may be used instead of the pulse generator as the transmitting means.

Furthermore, the permanent magnet used in the present invention is not limited to a cylindrical magnet with N and S poles magnetized on both end faces as in the embodiment, but also a regular bar-shaped magnet or a magnetostrictive wire as described in the above publication. A U-shaped magnet with a magnetic field that intersects may be used.

Effects of the Invention As is clear from the above explanation, according to the present invention, the mechanical displacement given to the movable permanent magnet is detected based on the propagation time of the ultrasonic signals from both the fixed permanent magnet and the movable permanent magnet. Since there is no risk of being affected by the propagation velocity of ultrasonic waves, and the receiving means only needs to be provided at one location, there is no restriction on the object to be measured, and the structure can be constructed at low cost.

Furthermore, since the ultrasonic signals of the fixed and movable permanent magnets are detected separately based on the supply signal of the first transmitting means and the supply signal of the second transmitting means, detection errors in propagation time due to superimposition of both waveforms are eliminated. can. Therefore, there is no need to limit the approach distance between the movable permanent magnet and the fixed permanent magnet, and the measurable range for the entire length of the magnetostrictive wire can be expanded compared to the conventional method.

[Brief explanation of drawings]

Fig. 1 is a basic structural 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 configuration diagram of an arithmetic circuit, and Fig. 4 is a diagram of each part of the arithmetic circuit. Voltage waveform diagram; Figure 5 is a basic configuration diagram of another example of the present invention; Figure 6 is a waveform diagram showing its detection method; Figures 7 and 8 are waveform diagrams showing a conventional detection method. . DESCRIPTION OF SYMBOLS 1... Magnetostrictive wire, 2... Movable permanent magnet, 3... Fixed permanent magnet, 4... First pulse generator (first transmitting means), 5... Second pulse generator (first transmitting means),... 2 transmission means), 6
...Distortion detection device (receiving means). Applicant Sankyo Boeki Co., Ltd. Agent Patent attorney Outside Hidetaka Figure 7 Figure 8

Claims (2)

[Claims] (1) A magnetostrictive wire, a movable permanent magnet movable along the magnetostrictive wire, a fixed permanent magnet fixed to a specific part of the magnetostrictive wire, and a magnet that supplies a current pulse or an ultrasonic signal to one end of the magnetostrictive wire. a second transmitting means for supplying a current pulse or an ultrasonic signal at a time different from that of the first transmitting means between the movable permanent magnet and the fixed permanent magnet on the magnetostrictive wire and to a region near the fixed permanent magnet; and a receiving means for receiving an ultrasonic wave signal generated or reflected by the magnetostrictive wires adjacent to the movable permanent magnet and the fixed permanent magnet; 1. A displacement detection device comprising: calculation means for determining the mechanical displacement given to the movable permanent magnet by a signal related to the propagation time of the ultrasonic signal to the reception means. (2) The calculation means generates a triangular wave-like voltage having a constant slope that starts when a current pulse is applied to the magnetostrictive wire from one of the first and second transmitting means, and generates a superfluous voltage generated at a portion of the fixed permanent magnet. The voltage is held when the sound wave signal reaches the receiving means, and the gradient of another triangular wave voltage is adjusted by the voltage, which starts when a current pulse is applied to the magnetostrictive wire from the other of the first and second transmitting means. , the triangular wave voltage is maintained when the ultrasonic signal generated at the moving permanent magnet reaches the receiving means.
Displacement detection device described in section.