JPH0545149A - Straight line position sensor - Google Patents

Abstract

PURPOSE:To obtain a straight line position sensor which can detect a position of a movable body over a wide range accurately in a simple configuration while utilizing advantages of a magnetic acoustic wave propagation system. CONSTITUTION:A plurality of excitation coils 4a and 4b for generating a magnetic acoustic wave whose phase is inverted for a magnetic body 1 with a specified spacing are provided along the magnetic body 1 magnetostriction and continuous length. Detection coils 3a and 3b which detect a magnetic acoustic wave which is generated by the excitation coils 4a and 4b are provided at a same position as that of the excitation coils 4a and 4b. A magnet 5 is provided at a movable body 6 which is provided along the longitudinal direction of the magnetic body 1. The magnet 5 which is provided at the movable body 6 gives a bias magnetic field to the magnetic body 1, thus enabling the acoustic wave to be shut off or attenuated at that position, balance of the acoustic wave which is propagated from both sides to the detection portion to be lost, and then a voltage to be induced at the detection coils 3a and 3b, thus obtaining a position of the movable body 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear position sensor for magnetically detecting the moving position of a movable body in NC equipment and the like.

[0002]

2. Description of the Related Art As a linear position sensor of this type, a digital type includes a magnescale, and an analog type includes a magnetoelastic wave propagation system. Of these, the latter type of magneto-elastic wave propagation method is often used when quick response, operability, and simplicity are generally required rather than accuracy. For example, the configuration shown in FIG. There is.
That is, the elongated magnetic body 1 having magnetostriction is arranged on the movable body 6 in parallel with the moving direction thereof.
The exciting coil 4 is provided at one end of the movable body 6 and the detection coil 3 is provided on the movable body 6. Excitation coil 4
When an alternating current is applied to, a magnetic elastic wave is generated in the magnetic body 1,
This propagates to the other end of the magnetic body 1. In this case, since the magnetoelastic wave propagates in the magnetic body 1 at 4 to 5 km / s,
The phase delay and the amplitude attenuation increase as the distance from the exciting coil 4 increases. That is, the magnetoelastic wave observed at the unspecified position of the magnetic body 1 has different amplitude and phase depending on the observation position. On the other hand, a voltage is induced in the detection coil 3 by the magnetoelastic wave propagating in the magnetic body 1.
Therefore, for example, in FIG. 4, the detected voltages at both positions (a) corresponding to the same position as the exciting coil and (b) corresponding to a position separated along the magnetic body 2 by about half of the whole are compared. Then, it becomes as shown corresponding to FIGS. 5A and 5B, respectively. That is, the detected voltage in (b) at a position away from the exciting coil 4 has an amplitude of A compared to (a).
From A to A ′, a delay time τ required for propagation occurs, and the position shifts. Based on the occurrence of such a relationship,
By comparing the voltage induced in the detection coil 3 with the voltage applied to the exciting coil 4, the position of the movable body 6 can be detected.

[0003]

However, in the conventional structure as described above, the magnetoelastic wave decays exponentially as the propagation distance increases, so long-distance propagation cannot be expected and the detection range is small. Therefore, there is a problem in that the detection cannot be performed in a wide range, and therefore, accurate detection cannot be performed in a wide range as described above. This is because the magnetic body 1 has a material limit, and even if the exciting current is increased, the magnetic body 1 causes a saturation phenomenon and the magnetization does not increase proportionally. It means that the propagation distance, that is, the detection distance cannot be increased in proportion to the increase of the input to the. Further, since the detection coil 3 is provided on the movable body 6 which is a movable portion, there is a problem that the processing of the detection signal becomes complicated.

The present invention has been made in view of the above circumstances, and an object thereof is to accurately detect the position of a movable body over a wide range with a simple structure while taking advantage of the magnetoelastic wave propagation method. It is to provide a linear position sensor capable of

[0005]

A linear position sensor of the present invention is arranged with a long distance between a magnetic body having magnetostriction and a long shape, and a phase is inverted with respect to each of the magnetic bodies. A plurality of exciting means for generating a magnetoelastic wave, a detecting means arranged at the same position as these exciting means for detecting the magnetoelastic wave generated by the exciting means, and moving along the longitudinal direction of the magnetic body. It is characterized in that it is configured so as to include a movable body that is disposed so as to be possible and is provided with a magnet so as to face the magnetic body.

[0006]

According to the linear position sensor of the present invention, when an exciting current is applied to a plurality of exciting means, a magnetic elastic wave is generated in the magnetic body, and a magnetic elastic wave generated between adjacent exciting means is generated. Since the phases are opposite to each other, they interfere with each other under certain conditions. For example, if the amplitudes of both are the same, the amplitude will be zero at the center, and will be the peak at the position where the excitation means is provided. Such a distribution state is obtained. The detecting means provided at the same position as the exciting means detects the elastic waves propagating from the exciting means and converts them into a voltage, but in the above-mentioned state, the elastic waves cancel each other out, so that the voltage is not induced. However, since the magnet attached to the movable body applies a bias magnetic field to the magnetic body, the elastic wave is blocked or attenuated at that position, the balance of the elastic wave propagating from both sides to the detection section is lost, and a voltage is induced in the detection means. To be done. Since this voltage has a one-to-one correspondence with the position of the movable body, the position of the movable body can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of the linear position sensor. A magnet 5 is attached to a movable body 6 that is movably arranged, and a permanent magnet (or an electromagnet may be used) is used as the magnet. The elongated magnetic body 1 having magnetostriction is arranged in a non-contact manner corresponding to the moving position of the movable body 6. The magnetic body 1 is made of a material such as Fe-based amorphous ribbon. Exciting coils 4a and 4b serving as exciting means are arranged at both ends of the magnetic body 1, and these are connected in series in reverse connection so as to invert the phase of the magnetoelastic wave generated in the magnetic body 1. AC power supply 7 which becomes the excitation source
Is connected between both terminals.

Further, detection coils 3a and 3b as detection means are arranged at the same positions as the excitation coils 4a and 4b, and these are connected in series and terminals c-d are drawn out. The detection coils 3a and 3b are excitation coils 4a and 4b.
It may be arranged coaxially with and molded. Next, the operation of this embodiment will be described.

When a current having an excitation frequency f is applied from the AC power supply 7 to the excitation coils 4a and 4b, magnetoelastic waves of the same frequency are generated in the magnetic body 1. Since the phases of the magnetoelastic waves are opposite to each other, the voltages induced when the magnetoelastic waves pass through the detection coils 3a and 3b are also opposite to each other. Therefore, between the terminals cd of the detection coils 3a and 3b connected in series, only the induced voltage component due to the difference in the amplitude of the elastic wave appears. Exciting coils 4a, 4b
When the number of coil turns is equal, the generated elastic waves also have the same amplitude, so the induced voltages are also equal and the detection coil terminal c
No voltage is induced between −d. However, when the movable body 6 exists within the movable range (between the exciting coils 4a and 4b) in the figure, the magnetic body 1 is locally biased by the DC magnetic field generated by the magnet 5 attached to the movable body 6. The elastic wave is blocked or attenuated at that portion. Due to this effect, the respective detection coils 3a and 3b
A difference occurs in the amplitude of the voltage generated at the detection coil terminal c-
A voltage is induced between d. The phase and amplitude of this voltage is
It changes depending on the position where the magnet 5 is biased, that is, the position of the movable body 6, and shows a one-to-one correspondence with the position.

Here, the results obtained experimentally by the inventors will be described. When the ratio of the magnitude of the output voltage to the input voltage is expressed using the distance L between the exciting coils 4a and 4b as a parameter, the result shown in FIG. 2 is obtained. That is,
In this case, the distance L is 5 cm, 8 cm and 16 cm, the excitation frequency is 5 KHz, the number of turns of the excitation coils 4a and 4b is 3, and the number of turns of the detection coils 3a and 3b is 20. As is apparent from FIG. 2, the input / output voltage ratio R
(%) Is the movable body 6 at the midpoint of the distance L in each case.
When the movable body 6 is located at the same position as the exciting coils 4a and 4b, the phases are mutually inverted and the maximum amplitude is obtained. With respect to the distance L, the shorter the distance L is, the larger the peak value is and the better the resolution is.
When it was 16 cm, it was difficult to detect the change in voltage. On the other hand, according to the present embodiment, sufficient resolution is obtained even when the distance L is 16 cm, and the detection distance is increased. You can see that

Therefore, according to the present embodiment, the position of the movable body 6 can be accurately detected in a non-contact manner over a wide range. Further, according to the present embodiment, since the detection coils 3a and 3b are not provided on the movable body 6 which is a movable portion, the processing of the detection signal becomes easy. Moreover, since the detection coils 3a and 3b are fixedly provided, the amplifier can be connected, and even if the leads of the detection coils 3a and 3b are long, the influence of noise is lessened and the deterioration of accuracy can be prevented. ..

As shown in FIG. 2, there is a one-to-one correspondence between the position of the movable body 6 and the detected voltage, but since this relationship is generally linear, it is corrected to a linear relationship. It is better to do it. The detection voltage is EXPONENT with respect to the position.
Since it changes like a (power exponent), it can be corrected to a linear relationship with a considerable accuracy (0.01 mm in the experiment) by logarithmically converting the detected voltage. However, if the accuracy of a certain degree (one digit lower than the logarithmic conversion) is sufficient, the 1/2 power conversion is also sufficient.
This depends on the cost relationship, and the latter is considerably cheaper. FIG. 1 shows a case where a 1/2 power conversion circuit is connected as the correction circuit 9 to the detection coil terminals cd to correct the relationship between the detected voltage and the position of the movable body 6 into a linear relationship.

In the above embodiment, the detection coil 3
Instead of a, 3b and exciting coils 4a, 4b, a magnetic head 8 as shown in FIG. 3 may be used. The magnetic head 8 is formed by winding a coil 8b around a magnetic yoke 8a having a gap G, and a magnetic detection element such as a Hall element can be used for excitation and detection of magnetoelastic waves.

[0014]

As described above, according to the linear position sensor of the present invention, the detecting means in the magnetoelastic wave propagation method is fixedly provided at the same position as the exciting means, so that the linear position sensor has a simple structure and a wide range. Therefore, it is possible to detect the position of the movable body with high accuracy, and there is no need for a configuration for taking out a signal from the movable body, so that there is an excellent effect that the signal processing is simplified.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing the results of experimentally determining the input / output voltage ratio.

FIG. 3 is a schematic view of a main part showing another embodiment of the present invention.

FIG. 4 is a view corresponding to FIG. 1 showing a conventional example.

FIG. 5 is a diagram showing a detection signal waveform of a conventional example.

[Explanation of symbols]

1 is a magnetic body, 3a and 3b are detection coils, 4a and 4b are excitation coils, 5 is a magnet, 6 is a movable body, 7 is an AC power supply, and 8a
Is a magnetic yoke, 8b is a coil, and 9 is a correction circuit.

Claims (1)

[Claims] 1. An elongated magnetic body having magnetostriction, and a plurality of exciting means arranged at a predetermined interval to generate magnetoelastic waves whose phases are inverted with respect to the magnetic body. ,
Detecting means arranged at the same position as these exciting means, for detecting the magnetoelastic wave generated by the exciting means, and movably arranged along the longitudinal direction of the magnetic body, so as to face the magnetic body. A linear position sensor comprising a movable body provided with a magnet.