JPH05231966A - Magnetostrictive torque sensor - Google Patents

Abstract

PURPOSE:To obtain a torque sensor which eliminates need of matching magnetic characteristics like a magnetic film, improves magnetic characteristics of carbon steel for a mechanical structure by a non-magnetic film, stabilizes the characteristics, largely improves an output and is resistant to noise. CONSTITUTION:A magnetostrictive sensor comprises a non-magnetic material film 3 of copper, copper allay and aluminum alloy whose thermal expansion coefficient is larger than that of a material of a rotating shaft 1 and which has tensile strength of 20kg/mm<2> or more coated by thickness of 0.1 to 30mum at a predetermined surface position of the rotation shaft 1 made of carbon steel for a mechanical structure at a temperature of 250 to 550 deg.C by means of vacuum technology such as sputtering, ion plating or laser evaporation to constitute a rotation shaft structure. In addition, a pattern shape of the film 3 is chevron-shaped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type torque sensor utilizing the inverse magnetostrictive effect of a magnetic material, and more particularly to a torque sensor for detecting the torque of a motor used in robots, machine tools and the like.

[0002]

2. Description of the Related Art A non-contact and small torque sensor is required for controlling a robot having a rotary drive system, a manipulator, and a machine tool. There are various types of torque sensors, but a magnetostrictive torque sensor is a non-contact type that is advantageous for size reduction. This is to detect torque by utilizing the inverse magnetostriction effect that the magnetic permeability of the magnetic body changes when a force is applied to the magnetic body. A change in magnetic permeability of the rotating shaft made of a magnetic material is detected as an impedance change of a coil wound around the rotating shaft 1 with a constant gap or a magnetic head (not shown) wound with the coil. Inexpensive carbon steel for mechanical structure is desirable as the material of the magnetic body rotating shaft, but it is difficult to extract it as an output because this carbon steel has a small change in magnetic characteristics with respect to torque. Therefore, there is a method in which a magnetic amorphous foil or a magnetic film is formed on the circumference of the rotating shaft by adhesion, sputtering, or the like, and a change in the magnetic characteristics of the foil or film is detected.

[0003]

However, there is a problem of reliability of the adhesive in the method of adhering the amorphous foil on the circumference of the carbon steel for machine structure, and in the method of forming the magnetic film by sputtering, However, there is a problem in that it is difficult to obtain stable magnetic characteristics due to poor properties. The present invention has improved these problems, and an object of the present invention is to provide a magnetostrictive torque sensor that increases the output characteristics of the carbon steel for machine structure with respect to torque and is stable against noise and capable of stable measurement.

[0004]

For this reason, the present invention uses a vacuum technique such as a sputtering method, an ion plating method, or a laser vapor deposition method at a temperature of 250 ° C. to 550 ° C. to form a rotating shaft made of carbon steel for machine structural use. Has a coefficient of thermal expansion greater than that of the material of the rotating shaft and a tensile strength of 20 kg / m.
The magnetostrictive torque sensor has a rotating shaft structure in which any one film of copper, copper alloy and aluminum alloy made of a non-magnetic material of m ² or more is coated to a thickness of 0.1 to 30 μm. Further, the film pattern is formed in a chevron shape.

[0005]

[Operation] The effect of the extreme surface condition of carbon steel for mechanical structure on the magnetic properties is not clear, but from various experimental results,
At present, it can be considered as follows. When a film made of a material having a thermal expansion coefficient higher than that of the carbon steel for mechanical structure is coated at a high temperature, a compressive stress is applied to the carbon steel for mechanical structure during cooling due to the difference in the thermal expansion coefficient, causing a change in magnetic properties. If the strength of the film is low, this change will be insufficient. Similarly, if the film thickness is too thin, it becomes insufficient. On the contrary, if the film thickness is too thick, the magnetic field does not flow through the carbon steel for machine structure during measurement due to the skin effect, and the output becomes small. Regarding the film formation temperature, the higher the temperature, the higher the high-temperature strength of the carbon steel for machine structural use, so the effect is great. However, at a temperature of 550 ° C. or higher, the effect is lost because diffusion occurs with the film. Further, by making the pattern shape of the film chevron-like, the compressive stress on the surface of the rotating shaft can be further increased, and the output characteristics can be further improved.

[0006]

EXAMPLES The present invention will be described in detail below based on examples. FIG. 1 is a block diagram of a magnetostrictive torque sensor showing a first embodiment used in the present invention.
Forming a film. FIG. 2 is a view showing a second embodiment of the present invention, in which a film is formed on the rotary shaft which is grooved. In the figure, 1 is a rotation axis, 2 is a coil for detecting application of a magnetic field and changes in magnetic permeability, 3 is a film, and 4 is a groove. The rotating shaft 1 is S35C and S45C of carbon steel for machine structure
(Coefficient of thermal expansion is 10 to 11 × 10 ⁻⁶ / ° C.),
The material of the film 3 is non-magnetic Ti alloy, Cr, Al-Cu, C
u, Cu-Al, and duralumin. Table 1 shows the coefficient of thermal expansion and tensile strength of the film material.

[0007]

[Table 1]

The membrane 3 was prepared by ultrasonically cleaning the rotary shaft 1 in the order of trichlene, pure water and alcohol, and then setting it in various vacuum chambers (sputtering, ion plating, laser). After evacuation to 5 × 10 ⁻⁶ Torr or less, the rotary shaft 1 was heated to various constant temperatures between 200 and 600 ° C., and then various films were formed to have various thicknesses.
Next, Table 2 to Table 4 show the results of measuring the torque output characteristics.
Shown in. The output without a film is 2 mV.

[0009]

[Table 2]

[0010]

[Table 3]

As can be seen from Tables 2 and 3, the rotary shaft 1 has a larger coefficient of thermal expansion and a tensile strength of 20 kg.
The film of Cu, Cu-Al, and duralumin of 1 mm2 / mm ² or more has a film thickness of 0.1 to 30 µm and a forming temperature of 300 to 550 ° C
It can be seen that the torque output becomes larger than that of the conventional method in the range of. On the other hand, a film having a small thermal expansion coefficient or a small tensile strength, such as Al-Cu, Ti alloy, or Cr, had a small output and no effect (Table 4). FIG. 3 is a diagram showing a third embodiment of the present invention in which a film pattern is formed in a chevron shape. Duralumin is used as the material of the film, and the film is formed by changing the number of patterns with a film thickness of 10 μm. The results of measuring the torque output characteristics are shown in FIG. It can be seen that the output is better than that of the continuous film. Although only the chevron shape is shown in this example, it is clear that similar results can be obtained even when the film is discontinuous. Although the present embodiment has been described with respect to the rotation axis, it is clear that the same effect can be obtained with a sensor that detects strain on a plane.

[0012]

As described above, according to the present invention, it is not necessary to make the magnetic properties uniform as in the magnetic film, and the magnetic properties of the carbon steel for machine structural use are improved by the non-magnetic film. Since it is stable and the output can be greatly improved, a torque sensor that is strong against noise can be configured.

[Brief description of drawings]

FIG. 1 is a sectional view of a magnetostrictive torque sensor showing a first embodiment using the present invention.

FIG. 2 is a sectional view of a magnetostrictive torque sensor showing a second embodiment using the present invention.

FIG. 3 is a sectional view of a magnetostrictive torque sensor showing a third embodiment using the present invention.

FIG. 4 is a diagram showing torque output characteristics of a third embodiment using the present invention.

[Explanation of symbols]

 1 rotating shaft 2 coil 3 film 4 groove

[Table 4]

Claims (2)

[Claims] 1. A rotating shaft of a ferromagnetic body whose magnetic permeability changes in response to applied torque, magnetic field applying means applied to detect a change in magnetic permeability of the rotating shaft of this ferromagnetic body, and a magnetic field applying means. In a magnetostrictive torque sensor consisting of a magnetic permeability detection means for detecting a change in magnetic susceptibility in a non-contact manner, the ferromagnetic body is made of carbon steel for mechanical structure, and its surface has a coefficient of thermal expansion larger than that of the carbon steel for mechanical structure. A film of any one of copper, a copper alloy and an aluminum alloy, which is a non-magnetic material having a tensile strength of 20 kg / mm ² or more, using a vacuum technique at a temperature of 250 ° C. to 550 ° C. and a thickness of 0.1 μm. A magnetostrictive torque sensor having a thickness of 30 μm. 2. A rotating shaft of a ferromagnetic body whose magnetic permeability changes in response to applied torque, magnetic field applying means applied to detect a change in magnetic permeability of the rotating shaft of this ferromagnetic body, and In a magnetostrictive torque sensor consisting of a magnetic permeability detection means for detecting a change in magnetic susceptibility in a non-contact manner, the ferromagnetic body is made of carbon steel for mechanical structure, and its surface has a coefficient of thermal expansion larger than that of the carbon steel for mechanical structure. A film of any one of copper, a copper alloy and an aluminum alloy, which is a non-magnetic material having a tensile strength of 20 kg / mm ² or more, and a thickness of 0.1 μm at a temperature of 250 ° C. to 550 ° C. by using a vacuum technique. A magnetostrictive torque sensor having a chevron shape with a thickness of 30 μm.