JPH0678899B2 - Displacement detection device - Google Patents

Description

The present invention relates to a displacement detecting device that detects a mechanical displacement of an object, a displacement of a liquid surface, and the like by using a magnetostriction phenomenon.

[Conventional technology]

Conventionally, as a magnetostrictive displacement detection device, US Pat.
As described in the publication, a magnetostrictive line, a permanent magnet movable along the magnetostrictive line, a transmission means for supplying a current pulse to the magnetostrictive line, and a proximity portion of the permanent magnet provided at a specific portion of the magnetostrictive line. There is known a device including a receiving means for receiving an ultrasonic signal generated at the site of the magnetostrictive line.

When a current pulse is supplied to the magnetostrictive wire by the receiving means, a magnetic field in the circumferential direction is formed on the magnetostrictive wire,
The magnetic field in the axial direction of the magnetostrictive line is formed by the permanent magnet only in the part of the magnetostrictive line where the permanent magnet is in close proximity, and the so-called Wiedemann effect causes torsional distortion in that part of the magnetostrictive line. Occurs suddenly, so that the torsional vibration (ultrasonic wave) propagates toward both ends of the magnetostrictive wire. If this ultrasonic wave is detected by the receiving means, the distance 1 from the position of the receiving means of the magnetostrictive line to the permanent magnet can be obtained as a function of time t by the following equation.

l = v · t In the above equation, v is the propagation velocity of the ultrasonic wave, where G is the transverse elastic coefficient of the magnetostrictive line and ρ is the density of the magnetostrictive line. Given in.

However, when Ni, which is a general magnetostrictive material, is used as the magnetostrictive wire, since the transverse elastic modulus G and the density ρ have characteristics that change with temperature, the propagation velocity v changes with temperature and This will cause an error in the distance l.

In order to solve this problem, the present applicant fixed a permanent magnet to a specific portion of the magnetostrictive line in addition to the permanent magnet movable along the magnetostrictive line, and the arrival time of the ultrasonic signal propagated from the movable permanent magnet. A displacement detection device capable of performing distance measurement without the influence of temperature change has been proposed by obtaining the ratio between the arrival time of the ultrasonic signal propagated from the fixed permanent magnet and the arrival time of the ultrasonic signal (Japanese Patent Laid-Open No. 61-226615). ).

[Problems to be Solved by the Invention]

However, in the case of the displacement detection device, although the measurement error due to the temperature change of the propagation velocity of the ultrasonic wave can be eliminated,
It is not possible to eliminate the measurement error due to the temperature change of the circuit section of the receiving means. That is, when the ambient temperature changes, the sensitivity of the strain detection device that detects the ultrasonic signal changes, or the comparison point (called a threshold value) of the comparator that shapes the detection wave of the strain detection device into a pulse shape changes. is there.

FIG. 5 is a waveform diagram in the case where the sensitivity of the strain detecting device is changed. A waveform A is a current pulse supplied from the transmitting means, a waveform B is a detected waveform of an ultrasonic signal detected by the strain detecting device, and a waveform C. Is an output waveform obtained by shaping the detected waveform B by a comparator. Of these, when the sensitivity of the strain detection device changes with temperature, the detection waveform B changes as shown by the broken line in FIG.
As a result, the output waveform C of the comparator also changes as shown by the broken line, the original measurement time t deviates to t ', and a measurement error Δt occurs.

FIG. 6 is a waveform diagram when the threshold value of the comparator changes, and when the original threshold value h changes to h ′ due to temperature change, a measurement error Δt occurs.

There is a temperature compensation circuit to eliminate the measurement error of the circuit section as described above, but this increases the cost due to the use of many electronic components such as temperature sensors, and is good because of variations in each component. It was difficult to expect accurate temperature compensation.

Therefore, an object of the present invention is to use a temperature compensation circuit,
It is an object of the present invention to provide a displacement detection device capable of eliminating a measurement error due to a temperature change in a circuit section.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a solid or hollow magnetostrictive wire, a fixed permanent magnet fixed at a fixed position of the magnetostrictive wire, a movable permanent magnet movable along the magnetostrictive wire, and a magnetostrictive wire. A transmitting means for supplying a current pulse in the axial direction of, a receiving means provided at a specific portion of the magnetostrictive line, and receiving an ultrasonic signal generated at a portion of the magnetostrictive line adjacent to the fixed permanent magnet and the movable permanent magnet, In a displacement detection device comprising: an ultrasonic wave signal propagating from the fixed permanent magnet to the receiving means and an ultrasonic wave signal propagating from the movable permanent magnet to the receiving means; and a calculating means for calculating a mechanical displacement given to the movable permanent magnet,
The magnetostrictive wire is made of a constant elastic metal, the arithmetic means,
Triangular voltage with a constant gradient is started by the ultrasonic signal generated at the part of the magnetostriction line near one of the permanent magnets near the supply end of the current pulse, and generated at the part of the magnetostriction line near the other permanent magnet. The above-mentioned triangular wave voltage is held by the generated ultrasonic signal, and the mechanical displacement of the movable permanent magnet is obtained by this voltage.

That is, when the ultrasonic signal waveform from one permanent magnet changes due to the temperature change of the circuit part, the ultrasonic signal waveform from the other permanent magnet also changes in exactly the same way. If the time difference is obtained, the effect of temperature change can be eliminated. Therefore, in the present invention, by obtaining the arrival time difference of the ultrasonic signals from both permanent magnets,
Accurate displacement detection can be performed without using a temperature compensation circuit or the like.

In the present invention, it is premised that the propagation velocity of ultrasonic waves does not change with temperature, but this can be solved by using a constant elastic metal such as NiSpanC (trade name) as the magnetostrictive material. The temperature change rate of the ultrasonic wave propagation velocity of a constant elastic metal can be reduced to about 0 to 20 ppm / ° C by heat treatment or the like. On the other hand, since the measurement variation due to the temperature of the circuit portion is generally 200 to 500 ppm / ° C, the temperature change of the ultrasonic propagation velocity of the constant elastic metal can be practically ignored.

〔Example〕

FIG. 1 shows an example of the basic configuration of a displacement detecting device according to the present invention, where 1 is a solid magnetostrictive wire made of a constant elastic metal such as NiSpanC (trade name), and 2 is a magnetostrictive wire that surrounds the magnetostrictive wire 1. 1 is a ring-shaped permanent magnet movable along 1, and the permanent magnet 2 is polarized in the axial direction of the magnetostrictive line 1. Reference numeral 3 is a pulse generator that is an example of a transmitting unit that supplies a current pulse to the starting end of the magnetostrictive line 1, 5 is a strain detecting device that is an example of receiving unit that is provided on the starting end side of the magnetostrictive line 1, and 5 is a magnetostrictive line 1 An annular fixed permanent magnet having a characteristic similar to that of the movable permanent magnet 2 and fixed to a specific part of the reference numeral 6 is a pulse shaping circuit such as a comparator for converting the detection signal of the strain detecting device 4 into a pulse signal.

FIG. 2 shows the waveform of each part of the displacement detecting device having the above-mentioned configuration,
A is a current pulse supplied to the magnetostrictive wire 1 by the pulse generator 3, B is a signal waveform detected by the strain detector 4, 7 of which is an ultrasonic signal waveform generated by the fixed permanent magnet 5, and 8 is It is an ultrasonic signal waveform generated by the movable permanent magnet 2. Further, C is a waveform obtained by converting the above waveforms 7 and 8 into pulsed waveforms 9 and 10 by the pulse shaping circuit 6.

The distance between the movable permanent magnet 2 and the strain detecting device 4 is l ₁ , the distance between the fixed permanent magnet 5 and the strain detecting device 4 is l ₂ , and the time when the ultrasonic wave generated by the movable permanent magnet 2 propagates to the strain detecting device 4. T ₁ ,
Assuming that the time for the ultrasonic wave generated by the fixed permanent magnet 5 to propagate to the strain detecting device 4 is t ₂ and the propagation speed of the ultrasonic wave is v, l ₁ = v · t ₁ (1) l ₂ = v · t ₂ … Given in (2).

Now, as shown by the broken line in FIG. 2, when the threshold value of the pulse shaping circuit 6 changes from h to h ′ due to temperature change, the second
As shown in FIG. C ′, the ultrasonic wave propagation time t ₁ of the movable permanent magnet 2 is t ₁
+ Δt, the ultrasonic wave propagation time t ₂ of the fixed permanent magnet ₂ is t ₂ + Δ
It changes to t respectively. Therefore, equations (1) and (2) are as follows.

l ₁ = v (t ₁ + Δt) (3) l ₂ = v (t ₂ + Δt) (4) Here, when the ratio of l ₁ and l ₂ is calculated, Therefore, even if the influence of the propagation velocity v is eliminated, the error Δt of the circuit portion cannot be eliminated. Therefore, equation (1) and (2)
When the relative distance l between the movable permanent magnet 2 and the fixed permanent magnet 5 is calculated from the difference from the equation, l = l ₁ −l ₂ = v (t ₁ −t ₂ ) ... (6), and the error Δt of the circuit part Can be resolved. That is, even if the threshold value of the pulse shaping circuit 6 changes or the sensitivity of the strain detection device 4 changes, the propagation time difference t from both permanent magnets 2 and 5 is increased.
(= T ₁ −t ₂ ) does not change. Therefore, the propagation time difference t
By determining, the movable permanent magnet 2 and the fixed permanent magnet 5
It is possible to accurately determine the relative distance l between the and. By using a constant elastic metal as the magnetostrictive line 1, the propagation velocity v can be practically neglected by an error due to temperature change.

The propagation time difference t can be easily converted into an electric signal. For example, as shown in FIG. 2D, a voltage that changes in a triangular waveform with a waveform 9 is started, and the voltage value of the triangular waveform at that moment is sampled and held by the waveform 10 to be detected as an analog signal. In this case, it is possible to detect as a digital signal by starting the clock with the waveform 9 and setting the clock at the time of the waveform 10 as shown in FIG. 2E. The circuit is much simpler to detect as a signal and can be constructed at a lower cost-Other Embodiments-In the above embodiment, the permanent magnet is not limited to the annular magnet having opposite poles magnetized on both sides, for example, the third magnet. As shown in the figure, it may consist of two or more permanent magnets 11 and 12 with the same pole (N pole in the figure) facing each other with the magnetostrictive line 1 in between, or one of the three in FIG. You may comprise only the permanent magnet of this.

Further, the magnetostrictive wire is not limited to one that directly supplies a current pulse to this magnetostrictive wire, but a magnetostrictive wire 13 made of a hollow constant elastic metal is used as shown in FIG. A configuration may be adopted in which a conductor wire 14 for passing a current pulse is inserted therein. In this case, the receiving means may detect the ultrasonic wave propagating through the magnetostrictive line 13.

Further, as the receiving means, a contact type receiving means such as a strain detecting device may be used, or a non-contact type receiving means such as a coil may be used.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the relative displacement of both permanent magnets is measured by the arrival time difference of the ultrasonic signals from the two permanent magnets. The displacement can be detected accurately without being affected. In addition, since it is not necessary to use a complicated temperature compensation circuit or the like, the cost can be reduced.

In addition, the triangular wave-shaped voltage having a constant gradient is started by the ultrasonic signal generated in the part of the magnetostrictive line adjacent to one of the permanent magnets near the supply end of the current pulse, and the part of the magnetostrictive line adjacent to the other permanent magnet is started. The triangular wave-shaped voltage is held by the ultrasonic signal generated in 1., and the mechanical displacement of the movable permanent magnet is obtained by this voltage. Therefore, the displacement can be detected by a simple analog circuit and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an example of a displacement detecting device according to the present invention, FIG. 2 is a waveform diagram showing an example of a detecting method, FIG. 3 is a perspective view of another embodiment of a permanent magnet, and FIG. FIG. 5 is 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 threshold value of the comparator changes. 1 ... Magnetostrictive wire, 2 ... Movable permanent magnet, 3 ... Pulse generator (transmitter), 4 ... Strain detector (receiver), 5
...... Fixed permanent magnet, 6 ...... Pulse shaping circuit.

Claims (1)

[Claims] 1. A solid or hollow magnetostrictive wire, a fixed permanent magnet fixed at a fixed position of the magnetostrictive wire, a movable permanent magnet movable along the magnetostrictive wire, and a current pulse in the axial direction of the magnetostrictive wire. It is provided in a specific part of the magnetostrictive wire and the transmitting means for supplying,
Receiving means for receiving the ultrasonic signal generated at the portion of the magnetostrictive line where the fixed permanent magnet and the movable permanent magnet are close to each other, and an ultrasonic signal propagating from the fixed permanent magnet to the receiving means and propagating from the movable permanent magnet to the receiving means. In a displacement detecting device comprising an arithmetic means for obtaining a mechanical displacement given to a movable permanent magnet by an ultrasonic signal, the magnetostrictive wire is made of a constant elastic metal, and the arithmetic means is provided at a current pulse supply end. The triangular wave voltage having a constant gradient is started by the ultrasonic signal generated at the portion of the magnetostrictive line adjacent to one of the permanent magnets close to each other, and the above mentioned by the ultrasonic signal generated at the portion of the magnetostrictive line adjacent to the other permanent magnet. A displacement detection device, which holds a triangular wave voltage and obtains a mechanical displacement of a movable permanent magnet by this voltage.