JPH06313741A - Magnetostriction type torque sensor - Google Patents

Abstract

PURPOSE:To reduce hysteresis and to measure torque accurately by setting the diameter of a crystal particle at least on the surface of a metal material with a magnetic anisotropy constituting a rotary shaft to a specific value or less. CONSTITUTION:An excitation coil 12 and a detection coil 13 are laid out coaxially around a torque transmission shaft 11 (rotary shaft). Permeability change due to tensile and compression stress generated at rhombic groove machining parts 14 and 15 provided at the shaft 11 is detected. A shield yoke 16 is provided outside the coils 12 and 13 to prevent external leakage of magnetic field and to increase detection sensitivity. A metal material which has magnetic anisotropy and where the diameter of a crystal particle of the ferrite phase at least on the surface part is micronized to 50mum or less is used for the shaft 11, thus suppressing the magnetic directionality of the shaft material to be small and suppressing the hysteresis of the detection output to a level without any problem and hence improving a solenoid coil type magnetostriction type torque sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting a transmission torque of a rotary shaft, and more particularly to a non-contact type magnetostrictive torque sensor.

[0002]

2. Description of the Related Art As a sensor for contactlessly detecting torque applied to a torque transmission shaft of a rotary drive system in an industrial machine such as an electric motor and a machine tool, an automobile, etc., an alternating magnetic field is applied to the shaft surface so that the torque is applied to the rotary shaft. A magnetostrictive torque sensor has been widely used, which detects a change in magnetic permeability caused on the shaft surface by being applied as an electric quantity.

In the magnetostrictive torque sensor, a winding (magnetic head) having a U-shaped core, which is an open magnetic circuit core, is installed near the shaft as an excitation / detection means, and the main stress generated on the shaft surface by the torque application. That detects the change in magnetic permeability in the direction (± 45 ° to the axial direction), or imparts magnetic anisotropy to the surface of the rotating shaft with the easy axis of magnetization as the direction inclined with respect to the axial direction. Next, an exciting solenoid coil (exciting winding) and a solenoid coil (detecting winding) that detects a change in magnetic permeability are arranged adjacent to this, and the change in magnetic permeability in the axial direction caused by torque application is detected. It is known that such a thing.

A method of introducing magnetic anisotropy on the surface of a rotary shaft in a solenoid coil type magnetostrictive torque sensor is, for example, a laser hardening method in which a plurality of strips are hardened parallel to each other in a direction inclined with respect to the axial direction. Part to form residual stress, and as a stress effect, magnetic anisotropy is given to the shaft surface, or a plurality of parallel spiral grooves are formed on the shaft surface by a rolling method or the like. As a shape effect, a method of giving magnetic anisotropy to the shaft surface is known (Japanese Patent Laid-Open No. 252487/1988, Japanese Patent No. 169326, etc.).

[0005]

Among the above-described magnetostrictive torque sensors, the solenoid coil type magnetostrictive torque sensor has a torque measuring time, as shown in FIG. At, a difference (hysteresis) occurs in the detection output. Therefore, it is suitable for measurement of a part where the torque change is relatively small, but when measuring a torque that constantly fluctuates in a complicated manner such as a torque transmission shaft of a rotary drive system of an industrial machine or an automobile, a hysteresis Is larger, there is a problem that the detection accuracy is significantly deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to reduce the hysteresis and to enable a highly accurate torque measurement even in a region where fluctuations are large. A type magnetostrictive torque sensor is provided.

[0007]

In a solenoid coil type magnetostrictive torque sensor, a rotating shaft for transmitting torque is magnetized by an exciting solenoid coil, and a change in permeability obtained by applying torque is measured by a detecting solenoid coil. To do. Conventionally, attention has been paid to the mechanical properties such as strength of the material used as the rotary shaft, but the present inventors have a relationship between the magnetic characteristics of the material and the magnitude of hysteresis. As a result of the investigation, the following findings were obtained.

Generally, a metal material such as carbon steel or manganese steel used as a shaft material is generally polycrystalline, and the orientation of each crystal grain is random. The magnetic characteristics of each crystal grain depend on its orientation, but when the crystal grains are sufficiently fine, the variations in orientation are averaged, and the magnetic directivity of the entire shaft material is reduced. However, when the crystal grains become large, variations in orientation are not averaged, and magnetic anisotropy becomes large.

The inventors of the present invention have conducted experiments to investigate the magnetic characteristics that change depending on the size of the crystal grains of the shaft material and the magnitude of the hysteresis. As a result, among the crystal grains of the shaft material, the crystal grains of the surface portion are particularly fine. It has been found that the hysteresis of the detection output is remarkably reduced and the torque measurement accuracy is greatly improved.

The magnetostrictive torque sensor of the present invention obtained by the above-mentioned examination has a rotation axis provided with magnetic anisotropy on the surface of which an axis of easy magnetization is an axis of easy magnetization, and a rotation axis adjacent to the rotation axis. In the solenoid coil type magnetostrictive torque sensor, in which the exciting solenoid coil and the detecting solenoid coil are arranged, the transmitted torque is measured by detecting the change in the magnetic permeability in the axial direction caused by the torque application, the magnetic anisotropic It is characterized in that the crystal grain size of at least the surface portion of the metal material imparted with the property is 50 μm or less.

[0011]

In the magnetostrictive torque sensor of the present invention, by using the shaft material in which the crystal grain size of the ferrite phase of at least the surface portion is made finer to 50 μm or less, the magnetic directivity of the shaft material is suppressed to be small. The hysteresis of the detection output can be suppressed to a level that does not interfere with the torque measurement, and the accuracy of the solenoid coil type magnetostrictive torque sensor is significantly improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In this embodiment, the solenoid coil type magnetostrictive torque sensor is targeted, and the surface layer of the torque transmission shaft (500 μm from the surface is used).
An experiment was conducted to measure the relationship between the size of the ferrite crystal grains (within m) and the size of the hysteresis of the torque detection output curve. As shown in FIG. 3, the solenoid coil type torque sensor used in the experiment has the excitation coil 12 and the detection coil 13 arranged coaxially around the torque transmission shaft 11 (coaxial with the torque transmission shaft 11). Transmission shaft 1
The change in magnetic permeability due to the tensile (+ σ) and compressive (−σ) stresses generated in the oblique groove processed portions 14 and 15 provided in No. 1 is detected. The excitation coil 12 and the detection coil 1
A shield yoke 16 is provided on the outer side of 3 to prevent the magnetic field from leaking to the outside and to increase the detection sensitivity.

Using the torque sensor, the relationship between the ferrite crystal grain size of the torque transmission shaft 11 and the size of hysteresis was investigated as follows.

Carbon steel S25C and manganese steel SMn40 having a diameter of 26 mm were used as materials, and various heat treatments were applied to the grains to change the crystal grain size. These materials were machined into a shaft having a diameter of 25 mm, and further grooved portions 14 and 15 were manufactured by machining to manufacture the torque transmission shaft 11 of the solenoid coil type magnetostrictive torque sensor shown in FIG. Then, the excitation coil 12 and the detection coil 13 are coaxially arranged on the outer circumference of the torque transmission shaft 11.

A solenoid coil type magnetostrictive torque sensor having the above-described structure is used, and -50 Nm to 50 N
The relationship between the applied torque and the output voltage when rotating while applying a torque in the range of m was measured. An example of the measured output curve is shown in FIG. The results of plotting the relationship between the size of the hysteresis [= (a ₁ -a ₂ ) / (A ₁ -A ₂ )] obtained from this output curve and the size of the ferrite crystal grains of the shaft material are shown in FIG. The ferrite crystal grain size is obtained by cutting a part of the surface of the machined torque transmission shaft 11 and measuring the surface layer portion of the grooved portions 14 and 15 that is 500 μm or less from the surface.

As shown in FIG. 2, the crystal grain size is 50 μm.
When m is exceeded, the hysteresis of the output curve exceeds 10%, and it can be seen that stable output cannot be obtained. Further, as is clear from this result, the hysteresis can be reduced as the crystal grains of the shaft material are made finer,
Desirably, the crystal grain size is adjusted to 10 μm or less. By suppressing the crystal grain size to 10 μm or less, the hysteresis can be reduced to 5% or less, and a highly accurate solenoid coil type magnetostrictive torque sensor can be provided.

[0017]

According to the magnetostrictive torque sensor of the present invention,
The ferrite crystal grain size of the torque transmission shaft is set to 50 μm or less to suppress the hysteresis of the torque detection characteristic to a small value. Therefore, a stable output can be obtained, and precise shaft transmission torque can be detected and measured.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the relationship between applied torque and detection output.

FIG. 2 is a graph showing a change in hysteresis when a size of a crystal grain of a material of a torque transmission shaft is changed in a solenoid coil type magnetostrictive torque sensor.

FIG. 3 is a diagram showing a configuration of a solenoid coil type magnetostrictive torque sensor.

[Explanation of symbols]

 11 Torque Transmission Shaft 12 Excitation Coil 13 Detection Coil 14 and 15 Groove Processing Section 16 Shield Yoke

Claims (1)

[Claims] 1. A rotary shaft provided with magnetic anisotropy on the surface of which a direction inclined with respect to the axial direction is defined as an easy axis of magnetization, and an exciting solenoid coil and a detecting solenoid coil are arranged adjacent to the rotary shaft. In a solenoid coil type magnetostrictive torque sensor that measures the transmission torque by detecting the change in the magnetic permeability in the axial direction caused by the application, the crystal grain size of at least the surface part of the metal material with the magnetic anisotropy that constitutes the rotating shaft Is 50 μm or less, a magnetostrictive torque sensor.