JPH02154130A - Strain detector - Google Patents

Abstract

PURPOSE:To facilitate a winding operation and to prevent the mutual interference of magnetic yokes by providing the magnetic yokes made of high magnetic permeability soft magnetic materials at the outer peripheries of detection coils at an interval. CONSTITUTION:When torque is applied to a driven shaft 1 from outside, magnetostrictive element piece groups 7 and 8 are strained to vary in magnetic permeability corresponding to the strain. The detection coils 4 and 5 detect the magnetic permeability variation as variation in magnetic impedance and a detecting circuit 19 which inputs the detection outputs generates their differential output as a strain detection output V. The magnetic yokes 12 and 13 decreases magnetic impedance viewed from the detection coils 4 and 5 to increase the sensitivity. The detection coils 4 and 5 can be driven with a low current, so the heat generation of the detection coils 4 and 5 is suppressed to reduce power-on drift. A shield 16 is formed of nonmagnetic metal and the skin depth of magnetic flux is reduced by skin effect during high-frequency driving to prevent the infiltration of an external magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a strain detector that detects distortion caused by shaft torque of a passive shaft such as a rotating shaft.

[Conventional technology]

FIG. 2 shows a conventional strain detector shown in, for example, Japanese Unexamined Patent Publication No. 57-211030, in which 1 is a passive shaft receiving torque, 2.3 is fixed to the passive shaft 1 in a chevron shape, and the passive shaft 1 is It is a group of magnetostrictive elements whose magnetic permeability changes according to the amount of strain generated by the torque applied to the
, -45''. 4.5 is the magnetostrictive element group 2
．． This is a detection coil that is wound around 3 and detects the change in magnetic permeability of each.

Next, the operation will be explained. When torque is applied to the passive shaft 1 from the outside, it acts on one of the magnetostrictive element groups 2.3 as a tensile force and acts on the other as a compressive force. In general, when stress is applied to a magnetic material, its magnetic properties change, resulting in a change in magnetic permeability. This phenomenon is used in magnetostrictive transducers to convert mechanical energy into electrical energy, and when the magnetic material is deformed, Vil whose magnetic permeability changes depending on the amount of deformation
This corresponds to the lari effect. Additionally, when the magnetostriction constant, which quantitatively represents the magnitude of magnetostriction, is positive, the magnetic permeability increases due to tensile force and decreases due to compressive force, and the opposite result occurs when the magnetostrictive constant is negative. It is also known that Therefore, the magnetic permeability of the magnetostrictive element group 2.3 changes due to deformation according to the amount of torque applied from the outside, and the detection coil 4.5 detects this change in magnetic permeability as a change in magnetic impedance.

Further, Japanese Patent Application Laid-Open No. 60-260821 discloses a torque sensor in which a magnetic yoke made of a Co--Ni amorphous magnetic alloy is disposed outside a detection coil to prevent magnetic flux leakage.

(Problems to be Solved by the Invention) However, the above-mentioned conventional device was not provided with a shield and did not have sufficient protection from disturbance magnetic fields.
The supporting structure of the magnetic yoke was not clear, and thermal stress was applied to the magnetic yoke from other members, causing changes in magnetic properties.

This invention was made to solve the above-mentioned problems, and provides sufficient protection from disturbance magnetic fields and prevents stress from other members from being applied to the magnetic yoke. (The purpose is to obtain a distortion detector that can perform accurate distortion detection.

In addition to the above object, a second object of the invention is to facilitate winding work and to prevent mutual interference of magnetic yokes.

[Means for Solving the Problems j] The strain detector according to the first aspect of the present invention includes a magnetic yoke provided at intervals around the outer periphery of the detection coil, and a magnetic yoke provided at intervals at the outer periphery of the magnetic yoke. A shield made of non-magnetic metal is also provided.

Further, the strain detector according to the second invention includes an integral coil bobbin provided on the outer periphery of the pair of magnetostrictive element groups, and a pair of detection sensors wound around the coil bobbin in correspondence with each magnetostrictive element group. The sensor includes a coil, a pair of magnetic yokes spaced apart from each other around the outer periphery of each detection coil, and a shield spaced apart from each other around the outer periphery of each magnetic yoke.

[Function] The shield in the present invention blocks disturbance magnetic fields. Further, the magnetic yoke is provided with a space between the detection coil and the shield, so that it is not subjected to stress from other members.

Further, the pair of detection coils in the second invention are wound around an integral coil bobbin, and the pair of magnetic yokes are provided on the outer periphery of each detection coil.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure shows the configuration according to the first embodiment of the present invention, where 6 is the central axis of the passive shaft 1, and 7 and 8 are a pair of magnetostrictive element groups formed in the same shape as the conventional magnetostrictive element group 2.3. It is made of a commercially available H-rate soft magnetic material with a large magnetostriction constant, such as permalloy, amorphous magnetic alloy, etc. 9.10 is the bearing of passive shaft 1,
11 is a bearing 9, which surrounds the outer periphery of each magnetostrictive element group 7, 8.
An integrated coil bobbin 10 is supported, and 4.5 is a detection coil wound around the coil bobbin 11 in correspondence with the magnetostrictive element groups 7 and 8. 12. ．． 13 is Fe Ni system, F
The magnetic yoke 12.13 is made of a high permeability soft magnetic material such as e-Co amorphous or PC permalloy and has a magnetostriction constant of about 1 to 3. The magnetic yoke 12.13 has a gap 14.15 on the outer periphery of the detection coil 4.5. The coil bobbin 11 has both ends fixedly supported by an adhesive tape or the like. A shield 16 is provided around the outer periphery of the magnetic yoke 12.13, and is supported at both ends and the center by a coil bobbin, and a gap 1718 is formed between it and the magnetic yoke 12.13. Further, the shield 16 is made of a non-magnetic metal material such as Cu or A/. 19 is the detection coil 4, 5
This is a detection circuit connected to the output side of the

Next, the operation of the distortion detector having the above configuration will be explained. When torque is applied to the passive shaft 1 from the outside, each magnetostrictive element group 7
, 8 causes distortion, and a change in transmittance 6n occurs in accordance with this distortion. The detection coils 4 and 5 detect this change in magnetic permeability as a change in magnetic impedance, and the detection circuit 19 to which each detection force is input outputs its differential output as a strain detection force V. The magnetic yoke 12.13 has the function of passing the magnetic flux generated from the detection coil 4.5, lowering the magnetic impedance seen from the detection coil 4.5, increasing sensitivity and efficiency, and increasing the detection efficiency. Since the coil 4.5 can be driven with a low current, heat generation in the detection coil 4.5 can be suppressed and power-on drift can be reduced. The shield 16 is made of non-magnetic metal,
As shown in FIG. 3, during high-frequency driving, the skin depth of the magnetic flux becomes small due to the skin effect, making it possible to prevent penetration of external magnetic fields.

In the above embodiment, by providing the shield 16, it is possible to prevent the disturbance magnetic field from entering, and the magnetic yoke 12.
13 is provided with a gap 14□ 15, 17.18 between the detection coil 4.5 and the shield 16, and can prevent the generation and propagation of thermal stress due to the difference in linear expansion coefficient with these members. It is possible to improve the accuracy of distortion detection. Further, by employing the body-shaped coil pobbin 11, the winding process is simplified and the dimensional precision of the winding can be improved.

Further, since the magnetic yokes 12 and 13 are not integrated but have a divided structure, mutual interference of magnetic impedance can be prevented. Furthermore, since the magnetic yokes 12 and 13 are made of a material with a brush strain constant close to that of the atmosphere, generation of magnetostrictive sound during audio frequency drive is prevented, and the sensitivity of magnetic impedance to excessive stress disturbances can be lowered. can.

FIG. 4 shows a second embodiment of the present invention. In this embodiment, the magnetic yokes 12 and 13 have a multilayer structure of 5 to 20 turns, making it possible to prevent heat generation during high frequency driving.

FIG. 5 shows a third embodiment of the present invention. In this embodiment, a shield 20 also made of non-magnetic metal is provided around the outer periphery of the shield 16, so that the shielding effect can be further enhanced. Since the shield 16 is strong, the winding of the shield 20 can function as a bobbin.

【Effect of the invention〕

As described above, according to the first aspect of the present invention, since the shield is provided on the outer periphery of the magnetic yoke, it is possible to prevent the penetration of a disturbance magnetic field, and there is no gap between the magnetic yoke, the detection coil, and the shield. Since the magnetic shield is provided, the magnetic shield is not subjected to thermal stress, and strain detection accuracy can be improved.

Further, in the second invention, in addition to the above effects, the coil bobbin for the pair of detection coils is integrally formed,
Winding work can be facilitated and dimensional accuracy can be improved. Moreover, by making the IF-type yoke have a divided structure, mutual interference of magnetic impedance can be prevented, and detection accuracy can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a strain detector according to a first embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional strain detector, FIG. 3 is a characteristic diagram of magnetic flux skin depth, and FIGS. FIG. 5 is a sectional view of strain detectors according to second and third embodiments of the present invention. 1... Passive axis, 4.5... Detection coil, 7, 8...
・Magnetostrictive element group, 11... Coil bobbin, 12.13.
...Magnetic yoke, 14.15.17.18...Gap, 16.20...Shield. Incidentally, the V intermediate symbol indicates the same or equivalent part. Agent Yudai Masu Oiwa! figure

Claims (2)

[Claims] (1) A passive shaft to which stress is applied, a group of magnetostrictive elements made of a high magnetic permeability soft magnetic material and fixed on the passive shaft, whose permeability changes according to strain, and a group of magnetostrictive elements. a detection coil that is wound around the magnetostrictive element group and detects changes in magnetic permeability of the group of magnetostrictive elements; a magnetic yoke that is provided at intervals around the outer circumference of the detection coil and is formed from a high permeability soft magnetic material;
A strain detector characterized by comprising a shield provided at intervals around the outer circumference of a magnetic yoke. (2) A passive shaft to which stress is applied, a pair of magnetostrictive element groups made of a high magnetic permeability soft magnetic material and fixed on the passive shaft and whose magnetic permeability changes according to strain, and each magnetostrictive element. an integral coil bobbin provided on the outer periphery of the piece group; a pair of detection coils wound around the coil bobbin in correspondence with each magnetostrictive element group; and a pair of detection coils for detecting changes in magnetic permeability of each magnetostrictive element group; A pair of magnetic yokes formed from a high magnetic permeability soft magnetic material are provided at intervals on the outer circumference of the coil, and a shield is provided at intervals on the outer circumference of each magnetic yoke. Distortion detector.