JPH06221940A - Magnetostrictive torque sensor - Google Patents

Abstract

PURPOSE:To achieve a smaller size and a less thickness of a magnetorstrictive torque sensor. CONSTITUTION:A coil so arranged to laminate a 8-shaped exciting coil 1 and a detection coil 2 concentrically is arranged as opposed near a shaft 3 having a magnetostrictive effect. The magnetic permeability of a surface portion of the axis changes differentially in the direction of + or -45 deg. by an applied torque. Therefore, two cases appear depending on the direction of torque. In one case, a magnetic flux turns to (c) to (b) with the rising of an excitation current and in the other, it turns from (d) to (a). (the direction may be opposite to that in this combination) An axial circumference component of a magnetic flux proportional to the torque interlinks with the detection coil to generate an induced voltage and the phase thereof depends on the polarity of the torque. The induced voltage is rectified in synchronization to obtain an output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive torque sensor.

[0002]

2. Description of the Related Art Magnetostrictive torque sensors include a so-called solenoid coil type in which an amorphous magnetostrictive ribbon is fixed to a torque transmission shaft with an adhesive and a change in permeability due to the stress is utilized, and a magnetostrictive effect of a steel shaft. There is a so-called magnetic head type that is used directly. The former is suitable for high-precision torque sensors with high sensitivity, but has problems in terms of ease of mounting and durability, while the latter directly depends on the magnetic characteristics of the shaft, which causes accuracy problems and the U-shaped or U-shaped magnetic head. There was a problem in terms of structure and size because it required a V-shaped iron core. In order to solve the problem of the latter magnetic head type torque sensor, a torque sensor using a coil formed by stacking a pair of 8-shaped coils in a perpendicular arrangement has been announced. (Sasada, Koga, Harada: "Magnetic head type torque sensor without magnetic core", Proc. Of the 16th Annual Meeting of the Japan Society for Applied Magnetics, 7
pD-9, p75, 1992) This is because the self-inductance of a pair of coils arranged near each other in the vicinity of the axis so that the straight part of the figure 8 coil is approximately ± 45 ° with respect to the axial direction of the steel axis is the torque. The voltage output is obtained by the bridge circuit by utilizing the increase on the one hand and the decrease on the other hand by the application. Although it has made great progress in terms of downsizing and thinning, excitation and detection are performed by the same coil in order to see changes in self-inductance, and the excitation side circuit with a relatively large voltage and current level and operation at a voltage of about 5V In order to facilitate electrical signal processing such as synchronous rectification by taking electrical insulation between the detection side circuits, it is necessary to further separate the bridge output with a transformer. Further, since a high frequency exciting current of about 60 kHz is simultaneously applied to both of the pair of coils which are overlapped with each other,
There is a problem that copper loss increases due to the skin effect and the proximity effect.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to solve the problems of the magnetic head type torque sensor described above, and excites a torque sensor using a coil formed by arranging a pair of 8-shaped coils orthogonally and overlapping each other. The present invention aims to provide a torque sensor that can electrically isolate the detection side circuit from the detection side circuit and can reduce the excitation power to half.

[0004]

In the magnetostrictive torque sensor of the present invention, a coil formed by stacking a pair of 8-shaped coils at right angles and overlapping each other is disposed so as to face each other near the shaft surface having a magnetostrictive effect. Is an exciting coil for alternating-current magnetizing the shaft, and the other is ± 45 ° at the shaft surface part caused by the torque.
It is characterized in that it is used as a detection coil for detecting a magnetic flux corresponding to a magnetic permeability difference in a direction as an induced voltage.

[0005]

The function of the present invention is ± 45 ° of the shaft surface portion due to the torque.
Since the magnetic permeability difference in the direction is detected through the alternating magnetic flux that is commonly linked to both the exciting coil and the detecting coil, the exciting coil,
It is not necessary to electrically connect the detection coils, and insulation can be provided. In addition, since the exciting current flows through only one of the figure-eight coils, the exciting current flows through both of the pair of figure-eight coils to detect the difference in the self-inductance. Good with current. Therefore, the exciting power is halved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (A) is a diagram showing the construction of the main part of a torque sensor of the present invention, and FIG.
FIG. 1C is a diagram showing the excitation and detection coils separated by parallel movement when it is assumed to be a turn, FIG. FIG. 3 is a diagram for explaining the operation principle of the embodiment, FIG. 3 is a diagram showing a result of an experiment on the dependency of sensitivity on an excitation current with an excitation frequency as a parameter, and FIG. 4 is an experiment result of an input / output characteristic of a torque sensor. It is a figure. In the figure, 1 is an excitation coil 2, 2 is a detection coil, 3 is a torque transmission shaft (steel shaft) having a magnetostrictive characteristic, and 4 is an excitation power supply.

First, the structure of the torque sensor of the present invention will be described. For simplification, FIG. 1 (A) shows a case where an eight-shaped coil having one turn is used. How to stack two 8
The C-shaped coils are arranged to be substantially concentric, and one coil is arranged so as to be rotated approximately 90 ° with respect to the other coil. Where (a,
b) and (c, d) belong to the same coil area of the 8-shaped excitation coil, and (a, c) and (b, d) belong to the same coil area of the 8-shaped detection coil. FIG. 1B shows the two coils laterally displaced in parallel. As shown in FIG. 1 (A), the straight portions of the 8-shaped coil used as the exciting coil are arranged so as to face each other so as to be substantially parallel to the axial circumferential direction. Alternatively, conversely, the straight portions may be positioned so as to be substantially parallel to the axial direction. In this case, the straight portion of the figure-eight coil used as the detection coil naturally becomes the axial direction.

Next, the operating principle will be described. When torque T is applied to the torque transmission shaft in the direction as shown in FIG. 2A, stress is generated in the directions of ± 45 ° with respect to the shaft as shown in FIG. Assuming that the magnetostriction constant of the shaft is positive, the alternating magnetic flux is distributed with an inclination in the tension direction. This is indicated by arrows e and f. On the contrary, when the torque direction is reversed, the inclination is reversed as shown in g and h of FIG. Now, ignoring the axial direction component of the magnetic flux and considering only the axial direction component, it can be seen that e is downward and g is upward. Here, e and g are nothing but the directions of the magnetic flux with respect to the same phase of the excitation voltage in FIG. Therefore, if the figure-eight coil of FIG. 1 (B) 2 is concentrically overlapped with FIG. 2 (A) or (B) and is used as the detection coil, the axial component of the magnetic flux does not interlink and only the axial circumferential component is present. Because of the interlinkage, the output voltage becomes in-phase or anti-phase with the excitation voltage depending on the torque direction, as shown in FIG. 2 (C). At this time, the amplitude of the output voltage is proportional to the applied torque T. Therefore, if the output voltage is synchronously rectified with reference to the phase of the excitation voltage, the magnitude and direction of the torque can be detected. The same result can be obtained by using the figure 8 coil of FIG. 1B as the exciting coil and the figure 8 coil 1 as the detecting coil.

Generally, the steel shaft is often hardened, and when the coercive force of the shaft is high and the magnetizing force is insufficient, 8
It is possible to increase the number of turns of the C-shaped coil. FIG. 1C shows an example of how the exciting coil and the detecting coil are stacked in this case. If necessary, in order to increase the exciting magnetomotive force applied to the shaft, the coils 1 and 2 of FIG.
A magnetic yoke made of a soft magnetic plate can be covered from above.

Next, the results obtained by constructing a torque sensor by this method and examining the characteristics by experiments are shown in FIGS. The shaft used as the torque transmission shaft is an SCM415 (Vickers hardness 310) material having a diameter of 25 mm and subjected to tempering.
The pair of 8-shaped coils were manufactured by the method shown in FIG. The outer diameter was 20 mm and the number of windings was 25 turns each. Also, in these experiments, Metg manufactured by Allied Signal
A yoke in which a plurality of las2705M amorphous ribbons were stacked was used. FIG. 3 shows the dependence of the sensitivity on the exciting current with the exciting frequency as a parameter. From this, it can be seen that the higher the excitation frequency, the higher the sensitivity. When the excitation frequency is increased, the excitation magnetic flux passes only through the extremely shallow surface portion of the shaft, and the stress generated by the torque coincides with the maximum portion, so that the sensitivity is also increased. However, in reality, due to the skin effect, proximity effect of the conductor, eddy current loss in the shaft, etc., there is a limit to the high frequency, and it cannot be inevitably increased. FIG. 4 shows exciting currents of 0, 4 A, and 0, 8
It is an input / output characteristic at the time of A. There is some hysteresis when the applied torque rises and falls slightly, but the linearity is good. The exciting power was about 1 W when the exciting current was 0.8 A.

[0011]

As described above, according to the present invention, a magnetic head type torque sensor can be realized with a small and thin excitation detection coil, and the excitation circuit side and the signal processing circuit side can be electrically insulated. Therefore, the circuit structure becomes simple and the exciting power can be reduced to half compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a main part of a torque sensor according to an embodiment, a letter-shaped excitation of multiple windings 8, and a configuration method of a detection coil.

FIG. 2 is a diagram for explaining the operation principle of the embodiment.

FIG. 3 is a diagram showing a result of an experiment on the excitation current dependency of the torque sensor sensitivity of the embodiment in which the excitation frequency is a parameter.

FIG. 4 is a diagram showing a result of an experiment of input / output characteristics of the torque sensor of the example.

[Explanation of symbols]

1 ... 8 shaped excitation coil, 2 ... 8 shaped detection coil, 3 ... torque transmission shaft (steel shaft), 4 ... AC excitation power supply.

Claims (1)

[Claims] 1. A magnetostrictive torque sensor using a coil in which a pair of 8-shaped coils are arranged substantially orthogonal to each other and stacked, wherein one of the pair of 8-shaped coils is used as an exciting coil and the other is used as a detection coil. A magnetostrictive torque sensor characterized by being configured as follows.