JP2002107241A - Torque transmission shaft and torque sensor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a shape of a torque transmission shaft and durability and strength of a magnetostrictive layer in a magnetostrictive detection body. SOLUTION: In this torque transmission shaft, the surface part of a core material is formed of a material transformed from a non-magnetic or feebly magnetic one into a ferromagnetic one when it is cooled after heated. A ferromagnetic part provided in the torque transmission shaft is formed when the surface part is locally heated and then cooled down.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque transmission shaft whose surface magnetic properties change according to an applied torque. Further, the present invention relates to a torque sensor that detects torque in a non-contact manner by utilizing a change in magnetic characteristics of a magnetic film due to a torque applied to a torque transmission shaft, and particularly relates to a rotating shaft of an automobile, a machine tool, a robot, or the like. The present invention relates to a torque sensor suitable for detecting torque.

[0002]

2. Description of the Related Art Accurate detection of torque applied to a rotating shaft is required particularly in the technology of automobiles, machine tools, robots and the like. In this case, a non-contact method in which the detection object does not contact is suitable. Non-contact type torque sensors are roughly classified into the following two types. That is, the encoder system detects the angle of twist from the phase difference between the outputs of a pair of rotary encoders provided at both ends of the torsion bar, and the reverse magnetostriction effect detects changes in magnetic characteristics induced by strain on the surface of the rotating shaft. This is a magnetostrictive system. Since the encoder system detects the torsional angle of the torsion bar, a part of the shaft is usually thinned to increase the distortion. Therefore, the stress limit is easily exceeded and the reliability is poor.
On the other hand, the magnetostrictive method generally has a magnetic part with a magnetostrictive effect on the surface of the torque transmission shaft and a solenoid coil disposed on the outer periphery. Is that the rotation does not affect the characteristics. In addition, since it can be configured without using a torsion bar, the allowable detection range of torque is wide.

[0003] A magnetostrictive torque sensor is disclosed in Japanese Patent No. 169326.
There is a method in which a 45 ° spiral groove is dug in two opposite directions on the rotating shaft surface of a ferromagnetic material having a magnetostrictive effect in a direction opposite to each other, and a differential structure is provided by the shape effect as proposed in the above publication. . With such a differential structure, the positive and negative directions and the magnitude of the rotational torque can be detected.

[0004] Although many proposals have been made so far derived from this known technique, there remains a problem with the reliability and durability of the sensor because it is determined by the state of the rotating shaft having the magnetostrictive portion. . In this regard, in the above-described proposal, in the case of an application in which a repeated stress is applied, the torque transmission shaft is likely to be subjected to stress rupture due to a shape notch effect of the groove.
As an example of a torque sensor that does not form a groove, for example, as proposed in Japanese Patent No. 2512552, while applying a torsional torque to a shaft and generating tensile strain, the surface of this shaft is further pulled by shot peening. A proposal has been made in which a strain is caused to increase the total tensile strain in the direction of the main tensile stress based on the torsional torque to be greater than the strain at the time of the tensile yield of the material of the shaft, thereby increasing the fatigue strength. However, there is a problem that it is extremely low in productivity to perform shot peening while generating tensile strain.

[0005]

Conventionally, a torque generated by detecting an apparent magnetic permeability due to a change in electric resistance of a strain gauge or deformation of a thin ribbon of an amorphous foil having a high magnetic permeability is used to measure a strain generated by torsion of a rigid body. Sensors have been used, but there is a need for a torque sensor that is structurally poor in reliability and has a long life and high reliability. As described above, the conventionally proposed magnetostrictive detector has problems in the shape of the torque transmission shaft and the durability and strength of the magnetostrictive layer, and improvement thereof has been desired. An object of the present invention is to provide a torque transmission shaft that exhibits stable output characteristics without the magnetostrictive portion being peeled off from the torque transmission shaft even with repeated stress, and a torque sensor using the torque transmission shaft.

[0006]

Accordingly, a first aspect of the present invention is to form a surface portion of a core material from a material which transforms from non-magnetic or weak magnetic to ferromagnetic by cooling after heating,
An object of the present invention is to provide a torque transmission shaft having a ferromagnetic portion formed by locally heating and then cooling the surface portion. The torque transmission shaft has a structure in which the surface portion is formed on a core material, and the core material is preferably made of a non-magnetic material. The non-magnetic or weak magnetic part and the ferromagnetic part are about 4
It is preferable that the angle is 5 degrees and that the pattern is formed in a stripe pattern in the circumferential direction.

A second invention provides a torque sensor having the torque transmission shaft and magnetic change detecting means for detecting a magnetic change of the surface portion.

The torque transmission shaft according to the first aspect of the present invention is characterized in that at least a part of a surface that is twisted when a torque is applied is electroless.
It was formed by Ni-P plating. The crystal structure of the electroless Ni-P plating changes from amorphous to crystalline by cooling after heating,
Changes from non-magnetic or weak magnetic to ferromagnetic. This makes it possible to obtain a torque sensor with excellent durability because the surface is smooth and there are no stress concentration points.

Electroless Ni-P plating is used as the plating which changes from non-magnetic to ferromagnetic by heat treatment. Ni-P plating deposited from a general acidic bath is amorphous, and shows little magnetism when the P content exceeds 8%. But 250 ° C
As described above, preferably, when the heat treatment is performed at 400 ° C. or more, the structure changes from an amorphous state to a crystalline form, and exhibits a precipitation hardening phenomenon. At this time, it becomes a ferromagnetic material.

The surface of the ferromagnetic material of the present invention is partially weakly magnetic.
The heating means for forming the conductive part is a heatable energy beam.
It is not particularly limited as long as it is a program. For example, a YAG laser
CO ₂Laser beams such as lasers and infrared beams
No. When irradiating the energy beam,
Scanning the spot continuously to make the heat treatment part linear
Alternatively, scanning may be performed discontinuously to form dots. Also that sport
The unit scans at a predetermined interval along a predetermined direction.
However, regarding the angle, the torque transmission shaft
The direction of tension or compression of stress strain generated on the surface +
45 degrees or the same or at right angles to the -45 degrees direction
Is desirable.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof. FIG. 1 is a schematic view showing an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a torque transmitting shaft, which is made of non-magnetic SUS303 having a diameter of 20 mm and has a thickness on the surface.
Electroless Ni-P plating of 10 μm was applied. The YAG laser beam having a beam diameter of 50 μm and having a beam diameter of 50 μm is applied to two surfaces 11 and 12 of the surface-plated portion of the torque transmission shaft over the entire circumference with a width of 10 mm.
Irradiation is repeatedly performed at 1 mm pitch in the degree direction. The energy intensity of the laser beam is appropriately adjusted so that the Ni-P plating part is at least 250 ° C, preferably at least 400 ° C, that is, the heat-treated portion becomes ferromagnetic, and the non-heated portion remains nonmagnetic. Select the irradiation intensity.
By this irradiation, ferromagnetic and non-magnetic are alternately arranged in a chevron shape, and a structure having a shape with magnetic anisotropy is provided.

The outer circumference of the shaft 1 is provided with cylindrical solenoid coils 21 and 22 for detection in portions 11 and 12 in a non-contact state. The number of turns of the coil is 10
0 times. Further, a solenoid coil 23 for exciting both 21 and 22 at the same time is provided, and the number of turns is 300.

FIG. 2 is a block diagram showing a circuit configuration of a magnetic change detecting means for detecting a magnetic change on the surface of the torque transmitting shaft 1. As shown in FIG. In FIG.
A sine wave exciting current of 0 KHz is generated and applied to the exciting coil 23. As a result, the chevron-like heat treatment places 11,
12, an alternating magnetic field is applied. When a torsional torque is applied to the torque transmission shaft, tensile and compressive strains are applied to the ferromagnetic portions 11 and 12 in the chevron-shaped heat-treated portions, so that the magnetic permeability changes and the magnetic flux is induced by the solenoid coils 21 and 22 for detection. Voltage shows different values. Then, the obtained detection signal is rectified by the synchronous detector 34 via the amplifiers 31 and 32 and the differential amplifier 33, and a DC torque signal corresponding to the torque change is obtained. Repeated application of a torque ± 10 kg · m in different directions to the torque transmission shaft was continued, but the plating layer did not peel off from the torque transmission shaft. No abnormalities such as cracks were observed on the torque transmission shaft.

[0014]

According to the present invention, the surface of the torque transmitting shaft is formed by electroless Ni-P plating which has a magnetostrictive effect and can form a ferromagnetic portion by heating and cooling. There is no need to perform groove processing for providing a dynamic structure. In addition, since electroless Ni-P plating provides extremely high adhesion to the substrate, the torque transmission shaft that shows stable output characteristics without the plating layer peeling off from the torque transmission shaft against repeated stress on the torque transmission shaft and A torque sensor using this torque transmission shaft can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment.

FIG. 2 is a block diagram showing a circuit configuration of a magnetic change detecting unit of the torque sensor according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Torque transmission shaft, 11, 12 ... Striped pattern consisting of ferromagnetic part and weak magnetic part 21, 22, 23 ... Solenoid coil

Claims (5)

[Claims] 1. A surface portion of a core material is formed of a material that changes from nonmagnetic or weak magnetic to ferromagnetic by cooling after heating, and a ferromagnetic portion formed by locally heating and cooling the surface portion is formed. A torque transmission shaft having: 2. The torque transmission shaft according to claim 1, wherein the material which changes from non-magnetic or weak magnetic to ferromagnetic by cooling after heating is electroless Ni-P plating. 3. The torque transmission shaft according to claim 1, wherein the core material is made of a non-magnetic material. 4. The method according to claim 1, wherein the non-magnetic portion or the weak magnetic portion and the ferromagnetic portion are at an angle of about 45 degrees with respect to the torque transmission axis and are patterned in a circumferential direction in stripes. The torque transmission shaft according to claim 1. 5. A torque sensor comprising: the torque transmission shaft; and a magnetic change detecting unit for detecting a magnetic change of the surface portion.