JPH0412224A - Straight line position sensor - Google Patents

Abstract

PURPOSE:To detect the movable body with high accuracy in a wide range by placing an exciting means at a prescribed interval against a magnetic material, and also, providing plural pieces so that each adjacent one generates a magnetic elastic wave whose phase is inverted to the magnetic material, respectively. CONSTITUTION:When a movable body 11 moves along a magnetic material 13 in a state that a magnetic elastic wave occurs in the magnetic material 13, a magnetic field by a permanent magnet 12 works on the magnetic material 13, and a voltage is induced in a detection coil 17. That is, since the magnetic elastic wave allowed to occur by an excited coil 14 or 15 of the side in which the magnet 12 is positioned is attenuated, it is offset by a magnetic elastic wave allowed to occur by the other coil 15 or 14 in a position of the coil 17. Also, an amplitude value and a phase of an induced voltage are varied in accordance with a position at the time when the magnet 12 works on the magnetic substance 13, therefore, by comparing the induced voltage obtained from the coil 17 with an exciting current, a position of movable body 11 can be detected. In such a way, a moving position of the movable body can be detected with high accuracy in a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a linear position sensor that magnetically detects the moving position of a movable body in an NC device or the like.

(Prior technology) This type of magnetic linear position sensor has been in demand in the mechatronics, medical, and other fields in recent years due to its high reliability, environmental resistance, and ease of handling. is expanding. In principle, there are two types: digital type and analog type.For example, digital type includes magnetic recording type Magnescale, and analog type includes type using magnetoelastic wave propagation type. Among these, the former magnetic recording method is used when detection accuracy is particularly required, whereas the latter magnetoelastic wave propagation method generally improves coordination and operability rather than accuracy. It is often used when simplicity is required.

The detection principle of such a magnetoelastic wave propagation type linear position sensor will be described below.

That is, FIG. 4 shows the principle configuration of a linear position sensor, in which an elongated magnetic body 2 having magnetostriction is arranged parallel to the direction of movement of the movable body 1. An excitation coil 3 is disposed at one end of the movable body 1, and a detection coil 4 is disposed on the movable body 1. When a pulse current is applied to the excitation coil 3, the portion of the magnetic body 2 facing the excitation coil 3 locally expands and contracts, producing elastic waves.
This propagates to the other end of the magnetic body 2. In this case, since the magnetoelastic wave propagates within the magnetic body 2 at 4 to 51 an/s, the phase delay and amplitude attenuation increase as the distance from the exciting coil 3 increases. In other words, the magnetoelastic waves observed at an unspecified position of the magnetic body 2 have different amplitudes and phases depending on the observation position. On the other hand, the detection coil 4 has
A voltage pulse is generated by a change in magnetization caused by a magnetoelastic wave propagating within the magnetic body 2. Therefore, for example, in FIG. 4, the detection coil is located at both positions (a), which corresponds to the same position as the excitation coil 3, and (b), which corresponds to a position that is approximately half the distance along the magnetic body 2. Comparing the detected voltages of 4, the results are shown in FIGS. 5(a) and 5(b), respectively. That is, the detected voltage in (b) at a position far from the excitation coil 3 has an amplitude from A to A' compared to (a).
The delay time τ required for propagation occurs and the phase shifts.

Based on the existence of such a relationship, the position of the movable body 1 can be detected by comparing the voltage induced in the detection coil 4 with the voltage applied to the excitation coil 3.

(Problem to be Solved by the Invention) However, with the conventional configuration as described above, magnetoelastic waves decay exponentially as the propagation distance increases, so long-distance propagation cannot be expected and the detection range is limited. Therefore, as mentioned above, there was a problem that accurate detection could not be performed over a wide range. This means that even if the input to the excitation coil 3 is simply increased, the propagation distance, that is, the lateral distance, cannot be increased proportionally, and furthermore, the magnetic material 2 has a limited advantage. Therefore, even if the excitation current is increased, the magnetic body 2 undergoes a saturation phenomenon and the magnetization does not increase proportionally.

In addition, in the conventional configuration, since the detection coil 4 is disposed on the movable body 1, there is a drawback that the configuration for performing signal processing such as extracting the detection signal from the detection coil 4 becomes complicated. Ta.

The present invention has been made in view of the above circumstances, part 1.
The aim is to make use of the advantages of detection using the magnetoelastic wave propagation method, to be able to accurately detect the position of a movable object over a wide range with a simple configuration, and to be able to locate the detection part in a fixed manner. The object of the present invention is to provide a linear position sensor in which the signal processing structure can be integrated into a cylinder.

[Structure of the Invention (Means for Solving the Problems)] The linear position sensor of the present invention includes a long magnetic body having magnetostriction, and adjacent pieces arranged at a predetermined interval, each of which has the above-mentioned shape. a plurality of excitation means for generating magnetoelastic waves whose phases are reversed with respect to the magnetic body; a detection means arranged between adjacent excitation means for detecting the magnetoelastic waves propagating through the magnetic body; It is characterized in that it includes a movable body disposed so as to be movable along the longitudinal direction of the body, and a magnet provided on the movable body to apply a magnetic field to the magnetic body.

(Function) According to the linear position sensor of the present invention, when an excitation current is applied to a plurality of excitation means, magnetoelastic waves are generated in the magnetic body, and the magnetoelastic waves generated between adjacent excitation means are Since their phases are inverted, they will interfere with each other under certain conditions, so for example, if the amplitudes of both are the same, the amplitude will be zero exactly at the center, and will peak at the position where the excitation means is installed. A distribution state can be obtained. In other words, the distribution state is such that the magnitude of the amplitude changes not exponentially but approximately proportionally to the distance. In this state, a constant voltage according to the above-mentioned distribution is induced in the detection means, but at this time, the magnetic field of the magnet acts on the magnetic body depending on the position of the movable body, and attenuates the magnetoelastic wave at that position. work like that. Thereby, the amplitude and phase of the voltage induced in the above-mentioned detection means can obtain different values depending on the moving position of the movable body. Therefore, the position of the movable body is detected by comparing this induced voltage with the excitation current.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 schematically shows the overall configuration, in which a movable body 11 that is movably arranged is provided with a permanent magnet 12, and the length of the movable body 11 is adjusted according to the movement position of the movable body 11. A magnetic material having magnetostriction] 3 is arranged. The magnetic material 13 is made of a material such as an Fe-based amorphous ribbon. Excitation coils 14 and 15, which serve as excitation means, are disposed at both ends of the magnetic body 13, respectively, and these are connected in reverse so as to reverse the phase of the magnetoelastic waves generated in the magnetic body 13. AC power supply 1 which is connected in series and serves as an excitation source.
It is connected between both terminals of 6. Also, the length L/2 from each of the approximately central part of the magnetic body] 3 (excitation coil) 4 and 15
A detection coil 17, which is a detection means, is disposed at a portion (separated by a distance of They are set so that they cancel each other out at the position of the coil 17 and the amplitude becomes zero.

Next, the operation of this embodiment will be explained with reference to FIG. 2.

First, for convenience of explanation, it is assumed that the movable body 11 is not present, that is, the magnetic field from the permanent magnet 12 does not act on the magnetic body 13. In this state, when a current with an excitation frequency f is applied from the AC power supply 16 to the excitation coils 14 and 15, magnetoelastic waves are generated inside the magnetic body 12 in response to the pulsed excitation current. The phases of these magnetoelastic waves are inverted (1800 degrees out of phase).
Therefore, the vibration state of the magnetic body 12 obtained as a combination of these magnetoelastic waves exhibits a positive or negative peak value at the positions of the excitation coils 14 and 15, and decreases as it approaches the center, that is, the position of the detection coil 17. Its amplitude approaches zero and becomes zero at the position of the detection coil 17. this is,
This is because the magnetoelastic waves generated from the positions of the excitation coils 14 and 15 interfere with each other as they advance.
It becomes exactly zero at position 7. In other words, since the amplitude is forced to zero at the position of the detection coil 17 due to interference between the magnetoelastic waves of the magnetic body 13, the amplitude distribution along the longitudinal direction of the magnetic body 13 is not the same as in the conventional case. It does not decay exponentially, but rather changes in a relationship close to direct proportion.

Here, to briefly describe the results obtained experimentally by the inventors, the ratio (percentage) of the magnitude of the output voltage to the input voltage is expressed using the distance between the excitation coil 14 and ]5 as a parameter. The results shown in FIG. 3 were obtained. That is, in this case, the distances are 5 cm, 8 cm, and 1.
6 cm, the excitation frequency was 5 kllz, the number of turns of the excitation coil was 3, and the number of turns of the detection coil was 20. In this case, as the magnetic body 13, a 10 mm wide amorphous ribbon METGLAS2605S2 material manufactured by Allied Co., Ltd. is used. In this FIG. 3, the input/output voltage ratio R (%) becomes zero at the midpoint of the distance in each case, and reaches the maximum amplitude at the part of the magnetic body 11 corresponding to each exciting coil 14 and 15. You can get results like this. As for the distance, the shorter the interval, the larger the peak value, which indicates that the resolution is better.

Next, when the movable body 11 moves along the magnetic body 13 while magnetoelastic waves are being generated in the magnetic body 13 as described above, the magnetic field by the permanent magnet 12 acts on the magnetic body 13 and is detected. A voltage is induced in the coil 17.

That is, when the DC magnetic field of the permanent magnet 12 acts on the magnetic material,
Excitation coil 14 or 15 on the side where permanent magnet 12 is located
Since the magnetoelastic waves generated by the magnetoelastic waves are attenuated, they are canceled out by the magnetoelastic waves generated by the other excitation coil 15 or 14 at the position of the detection coil 17. That is, at the position of the detection coil 17, one attenuated magnetoelastic wave and the other normal magnetoelastic wave interfere, and a voltage is induced in the detection coil 17 due to the difference in amplitude and phase. It becomes. The amplitude value and phase of this induced voltage change depending on the position when the permanent magnet 12 acts on the magnetic body 13, so by comparing the induced voltage obtained from the detection coil 17 with the exciting current, 1
1 movement position can be detected.

According to this embodiment, it is possible to increase the change in the amplitude of the magnetoelastic wave over the entire length of the magnetic body 13, and therefore, the voltage that changes greatly in the detection coil 12 with respect to a change in the detection distance can be increased. can be induced, and the position of the movable body 11 can be detected more accurately over a wide range.

Further, according to this embodiment, the detection coil 17 is connected to the movable body 11.
Since there is no need to provide a detection voltage, signal processing of the detection voltage becomes easy.

According to the above embodiment, the excitation coils 14 and 15
The smaller the interval, the larger the change in the detection voltage can be, and thereby the detection accuracy can be further improved.

In the above embodiment, a case was described in which an Fe-based amorphous material was used as the magnetic material, but the material is not limited to this, and any magnetic material that has magnetostriction and generates magnetoelastic waves may be used.

In addition, in the above embodiment, the magnet is a permanent magnet]2
However, a configuration using an electromagnet may also be used.

Furthermore, a magnetic detection element such as a Hall element may be used to detect magnetoelastic waves.

In the above embodiment, a configuration is described in which two excitation coils ] 4 and ] 5 are used as excitation means, but the configuration is not limited to this, and a configuration in which three or more excitation coils are provided as excitation means may also be used. . That is, in this case, the detection area is divided into a plurality of parts to detect the moving position of the movable body, and the characteristics of the detection voltage shown in FIG. 2 are reversed in adjacent detection areas. By storing these in advance in association with each area, the moving position of the movable body can be detected over a wider range than in the case described above.

[Effects of the Invention] As explained above, according to the linear position sensor of the present invention, the excitation means are arranged at a predetermined interval with respect to the magnetic body, and adjacent ones are arranged in phase with respect to the magnetic body. Since we installed multiple units to generate magnetoelastic waves in which the
The amplitude of the detection voltage can be largely changed with respect to the movement of the movable body over a wide range over the entire area of the magnetic body, and the moving position of the movable body can be detected accurately over a wide range with a simple configuration. Further, since the detection means is arranged in a fixed manner, there is no need for a structure for extracting a signal from a movable part, resulting in an excellent effect of simplifying signal processing.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention.
2 is a diagram showing the distribution characteristics of the detected voltage, and FIG. 3 is a diagram showing the results of the input/output voltage ratio determined by experiment. 4 and 5 show a conventional example, where FIG. 4 is a diagram corresponding to FIG. 1, and FIG. 5 is a waveform diagram of a detected voltage. In the drawing, 11 is a movable body, 12 is a permanent magnet (magnet), 13 is a magnetic body, 14 and 15 are excitation coils (excitation means), and 17
is a detection coil (detection means). <Delivery U Tazawa (Me) % 11th edition

Claims (1)

[Claims] 1. An elongated magnetic body having magnetostriction, and a plurality of excitation means arranged at a predetermined interval and adjacent to each other, each of which generates a magnetoelastic wave whose phase is reversed with respect to the magnetic body. , a detection means arranged between the adjacent excitation means to detect magnetoelastic waves propagating in the magnetic body, and a movable body disposed so as to be movable along the longitudinal direction of the magnetic body.
A linear position sensor comprising a magnet provided on the movable body and applying a magnetic field to the magnetic body.