JPS63150612A - Absolute displacement sensor using magnetostrictive delay line - Google Patents

Abstract

PURPOSE:To improve measurement accuracy by providing transmitters to both terminals of a delay line, and multiplying the ratio of the propagation time of a signal between each transmitter and a receiver and the propagation time of a signal between both transmitters by the distance between both terminals and thus finding the distances between the transmitters and receiver. CONSTITUTION:An absolute displacement sensor consists of the transmitters 2 and 3 provided on both terminals of the magnetostrictive delay line 1, the receiver 3, and magnets 5-7 which apply bias magnetic fields to the respective transmitters and receiver. Equations I hold, where (l) and T1 are the distance and propagation time between the transmitter 2 and receiver 3, l0 and T2 are the distance and propaga tion time between the transmitter 4 and receiver 3, and L and V are the distance distance between the transmitters 2 and 4 and the propagation speed. An equation II is therefore obtained, and then this is expressed by the distance (l) to obtain an equation III. Here, if the propagation speed varies by alpha.V (0<alpha<1) owing to tempera ture variation, the propagation times T1 and T2 are shown by equations IV, but the distance l'' is not affected by the temperature variation in equations V, so that the measurement accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an absolute displacement sensor using a magnetostrictive delay line.

(Prior Art) FIG. 3 is a diagram showing the structural principle of a magnetostrictive delay line. magnet 6
When a current pulse is passed through the coil of the transmitter 2 which is biased by an external magnetic field, an ultrasonic wave is generated due to the magnetostriction phenomenon. This ultrasonic wave propagates on the magnetostrictive delay line 1. receiver 3
A bias magnetic field is applied by an external magnet 5, and when an ultrasonic wave is received, the circulating magnetic flux changes and the voltage changes, so that the ultrasonic wave can be detected. Then, the distance between the two (transmitter 2 and receiver 3) can be measured from the propagation time during this time.

By making the transmitter 2 or the receiver 3 movable, it can be used as a displacement sensor.

FIG. 4 is a diagram showing the structural principle of a torsional wave mode magnetostrictive delay line. When a pulse current is passed through the cylindrical magnetostrictive tube 8 from the transmitter 9, when this pulse reaches the position of the external magnet 10,
The circulating magnetic flux caused by the pulsed current causes changes in the magnetic flux, and the magnetostriction phenomenon generates torsional mode ultrasound. Since the time during this period is proportional to the distance between the external magnet 10 and the receiver 11, it can be used as a displacement sensor.

[Problem that the invention seeks to solve]

In sensors that use such magnetostrictive phenomena, the delay time changes due to temperature fluctuations in the elastic modulus of the material, so it is necessary to select materials with excellent temperature characteristics, but there is a problem that the error is small. .

Now, assuming that the propagation speed of the ultrasonic wave is V, the relationship between the distance ra2 between the transmitter 2 and the receiver 3 and the propagation time T is It=v-T. Here, if the propagation velocity changes by α·V (0<α × 1) due to temperature fluctuation, the velocity V' after the change is v'=(1+α). If the propagation time at this time is T', then the distance @fl
is unchanged, so V'·T' =v-T=1 holds true.

Therefore, the propagation time T' is T’ = (1/1+α))・T becomes.

By the way, with this device, by measuring only the propagation time T, the distance 2 from a constant propagation velocity V can be calculated as ff1=v
-T, or even if the propagation velocity becomes V' due to temperature fluctuations, it is not corrected inside the device, so R,' = v-T' despite the actual distance l. = (1/ (1+a))
・It will be incorrectly measured as 1.

An object of the present invention is to provide an absolute displacement sensor that eliminates errors due to temperature fluctuations and improves accuracy.

Means for Solving Problem C] In the absolute displacement sensor using the magnetostrictive delay line of the present invention, transmitters are provided at both ends of the delay line, and the propagation time of a signal between each transmitter and receiver is determined. , the distance between the transmitter and the receiver is determined by multiplying the ratio of the signal propagation time between the transmitter and the receiver and the sum of both propagation times by the distance between the transmitters.

[For production]

When the propagation speed changes due to temperature fluctuation, each propagation time also changes, but the rate of change is the same for both propagation times, so (propagation time of the signal between the transmitter and receiver/both propagation times) The value of (additional value) does not change. Therefore, even if the propagation velocity changes due to temperature fluctuations, no errors occur in the measured values.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of an absolute displacement sensor of the present invention, and FIG. 2 is a diagram showing the distance relationship thereof.

This embodiment has a configuration in which a transmitter 4 and a magnet 7 are added to the conventional example shown in FIG.

Here, the distance and propagation time between transmitter 2 and receiver 3 are 2 and T2, respectively, and the distance and propagation time between transmitter 4 and receiver 3 are fio and T2, respectively. Letting the distance between the transmitters 2 and 4 be V, and the propagation speed as V, then the following holds true: 1=v−T1 2°=■·T2 2+c=L. Therefore, (TI + 72) = L v = (1/ (TI + 72)) ・L, and when the distance Hx is expressed by this, it becomes R-= (TI / (TI + 72)) ・S. Here, the propagation velocity is α・v(0
If 〈α〈1) changes, the propagation time T,
, T2 are respectively T+'=(1/(1+α))・T.

T2'=(1/(1+α))・T2, but the distance U'' is 2"=(T+'/ (Tl'+72"))・S" (
TI/(TI+T2)) L=l, it is not affected by temperature fluctuations and it is possible to improve measurement accuracy.

In this embodiment, it is assumed that the actual distance R does not change with temperature.

(Effects of the Invention) As explained above, the present invention provides transmitters at both ends of a delay line, determines the signal propagation time between each transmitter and receiver,
Temperature fluctuations can be calculated by multiplying the ratio of the signal propagation time between the transmitter and the receiver by the distance between the transmitters and the receiver. This has the effect of improving accuracy by eliminating errors caused by

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an embodiment of the absolute displacement sensor of the present invention, Fig. 2 is a diagram showing its dimensional relationship, Fig. 3 is a diagram showing the structural principle of the magnetostrictive delay line, and Fig. 4 is a torsional wave mode. FIG. 3 is a diagram showing the structural principle of a magnetostrictive delay line. l...Magnetostrictive delay line, 2.4...Transmitter, 3...Receiver, 5,6.7...
magnet.

Claims (1)

[Claims] In an absolute displacement sensor using a magnetostrictive delay line, in which the absolute position of a transmitter and a receiver on a delay line is determined based on the signal propagation time between the two, the transmitter is provided at both ends of the delay line, and the transmitter and receiver are connected to each other. Find the signal propagation time between the transmitter and receiver, and multiply the ratio of the signal propagation time between the transmitter and receiver by the sum of both propagation times by the distance between the transmitter and receiver. An absolute displacement sensor that uses magnetostrictive delay lines to find the distance between