JPH08145820A - Magnetostrictive strain sensor - Google Patents

Abstract

PURPOSE: To obtain a magnetostrictive strain sensor in which an irregularity in the characteristic of a strain output is reduced by a method wherein the direction of the finishing operation of the surface of a force transmission member is set to be the same direction as, or the right-angled direction of, the direction of a maximum strain and the face roughness of the surface and the film thickness of a magnetostrictive film are eliminated. CONSTITUTION: The surface, on which a magnetostrictive film 3 is formed, of a force transmission shaft 1 is ground by using a grinding machine in such a way that the surface becomes the direction of the maximum strain of a torque, i.e., the direction of 45 deg. with reference to the shaft. An Ni-Fe alloy film 3 is formed, by a sputtering method, on the part in a width L of the shaft 1. The film 3 by the sputtering method is formed in such a way that an ultrasonic cleaning operation is executed to the shaft 1 according to a prescribed sequence, that the shaft is set inside a vacuum tank, that the tank is evacuated, that the shaft is heated and that the Ni-Fe alloy film is formed. Then, a coil 2 for excitation and detection is formed around the film 3 in a concentric circle shape, and a torque sensor is manufactured. As the output of the torque sensor, a detectable output signal is obtained when its average face roughness is in a range which is 0.8 times or higher the film thickness of the film and the film thickness is 1μm or higher, and the direction of a load can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive strain sensor for non-contact detection of motor torque of robots, machine tools, tension of overhead wires and the like.

[0002]

2. Description of the Related Art Conventionally, for the purpose of miniaturization and high reliability as a magnetostrictive strain sensor, a sensor for measuring torque of a robot having a rotary drive system, a manipulator and a machine tool,
Sensors for measuring the tension of overhead wires have been proposed.
This method attaches a magnetostrictive film, which is a magnetic material having magnetostriction, to the surface of a force transmission shaft such as a rotating shaft or a tension transmission shaft, and changes the strain that occurs when torque or tension is applied to the force transmission shaft. The change in magnetic characteristics of the magnetostrictive film due to is detected as a change in impedance by a detection coil or a magnetic head. This magnetostrictive film is formed on the surface of the force transmission shaft by a method such as a sputtering method, a wet plating method or a vacuum deposition method. However, when a strain sensor is formed by forming a magnetostrictive film by a method such as a sputtering method, a vacuum deposition method, or a wet plating method, there are the following problems. First, in the case of a torque sensor having a belt-shaped magnetostrictive film 3 provided on the entire circumference of the surface of the force transmission shaft 1 as shown in FIG. 3, when torque is applied to the force transmission shaft 1, the reverse magnetostriction of the magnetostrictive film 3 is applied. Due to the effect, the magnetic permeability changes and the impedance of the detection coil 2 changes, so that a torque output signal can be obtained. However, in the magnetostrictive film 3 having such a structure, since the magnetic anisotropy affecting the inverse magnetostrictive effect is in the direction shown by the arrow D ′ in FIG. 3, the torque in either the left or right direction is applied to the axis. Even if the magnitudes are the same at all times, the amount of change in magnetic permeability due to the inverse magnetostriction effect is also the same, so that there is a drawback that the direction of torque cannot be detected. Therefore, as shown in FIG.
Must be striped, and the (magnetic anisotropy) strain detection direction must be aligned with the maximum strain application direction of the magnetostrictive film. For example, when torque is applied by rotating to the right, tensile stress is applied in the longitudinal direction of the strip, that is, the direction of magnetic anisotropy, and when torque is applied by rotating to the left, the compressive stress is applied unless torque is applied. The direction of application cannot be detected (Japanese Patent Publication No. 3-26339). In such a case, a method of forming a strip-shaped pattern is used, and a mask is used for forming the strip-shaped pattern.

[0003]

However, when the magnetostrictive film of the torque sensor is formed by using a mask, there is a problem that the mask application pattern cannot be detected because the mask shift pattern is disturbed. Further, in the case of the tension sensor, although the pattern is not formed, there is a problem that the strain output characteristics vary widely. The cause of this tension sensor was also considered to be the anisotropy of the magnetostrictive film. When examined by the Bitter method, as shown in FIG. 5, the anisotropy of the magnetostrictive film 3 is mainly in the circumferential direction of the axis (the direction of the solid line arrow), but there is a disturbance deviated from that direction (the direction of the broken line arrow). I understand. Due to the variation in the direction of the magnetic anisotropy, the output also varies. Therefore, it is an object of the present invention to provide a magnetostrictive strain sensor using a magnetostrictive film, which has a stable output characteristic with less variation in strain output characteristic.

[0004]

In order to solve the above problems, the present invention forms a band-shaped magnetostrictive film on the surface of a force transmission shaft,
A solenoid coil for excitation and detection is arranged in the vicinity of the magnetostrictive film, and a change in the magnetostrictive film based on a strain generated on the surface of the force transmission shaft is detected as an impedance change of the detection coil, and the surface of the force transmission shaft is detected. In the magnetostrictive strain sensor for detecting the generated strain, the final processing direction of the surface of the range where the magnetostrictive film of the force transmission shaft is attached is the main direction that senses the maximum strain or a direction perpendicular to the main direction that senses the maximum strain. It is configured to match. The film thickness t of the magnetostrictive film
Is at least 1 μm, and the average surface roughness of the final processed surface is at least 0.8 t.

[0005]

By aligning the direction of the machining flaw with the force transmission direction by the above means, in the case of the torque sensor, the sign of the change in the magnetic permeability of the magnetostrictive film also changes due to the change of the strain direction (sign). The direction of rotation can be detected. On the other hand, in the case of the tension sensor, since the directions of magnetic anisotropy of the magnetostrictive film are aligned in one direction, output characteristics without variations can be obtained, and stable output sensitivity characteristics can be obtained.

[0006]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram of a torque sensor showing a first embodiment of the present invention. In the figure, 1 is a rotating shaft which is a force transmitting shaft, 2 is a coil for excitation and detection, and 3 is a strip-shaped magnetostrictive film.
The rotating shaft 1 is made of SUS304 having a diameter of 20 mm, and the surface on which the magnetostrictive film 3 is formed is grinded by using a grinder so that the direction of the maximum strain of torque, that is, the direction of 45 ° with respect to the shaft (arrow C). went. The surface roughness is 0.8 μm,
There are five types, 4 μm, 8 μm, 16 μm, and 40 μm.
Ni-F is sputtered on the portion of the rotary shaft 1 having a width L.
An e-alloy magnetostrictive film 3 was formed. The formation of the magnetostrictive film by the sputtering method uses a SUS304 tension transmission shaft with a neutral detergent, pure water,
After ultrasonic cleaning in the order of alcohol, set in a vacuum tank, evacuate to 5 × 10 ^-4 Pa or less, and heat to 4
A Ni-Fe alloy film was formed at 00 ° C. The sputtering conditions were a target voltage of 325V and a target current of 1A. Film thickness is 0.5, 1.0, 5, 10, 20, 50 μm
There are 6 types. Next, the excitation / detection coil 2 was concentrically provided around the magnetostrictive film 3 to fabricate a torque sensor, and the output when a load was applied and the detection feasibility of the direction were examined. The results of the output characteristics are shown in Table 1. In addition, as a conventional example, the one in which the direction of the grinding streak on the rotating shaft is perpendicular to the shaft (direction of FIG. 3D ′) and the surface roughness of the surface is 0.4 μm is added.

[0007]

[Table 1]

As can be seen from Table 1, the output of the torque sensor of the present invention can be detected when the average surface roughness is 0.8 times or more the thickness of the magnetostrictive film and the film thickness is 1 μm or more. A signal was obtained and it was possible to detect the direction of the load. In contrast, the conventional example has an average surface roughness of 0.4 μm and a film thickness of 1 to 50 μm, and cannot detect the direction of the load.
Thus, even if the strip-shaped magnetostrictive film is used without forming the strip-shaped pattern, anisotropy can be provided depending on the direction of the grinding stripe (arrow C). FIG. 2 is a diagram of a tension sensor showing a second embodiment of the present invention. The tension sensor is made by SU
The tension transmission shaft 1 made of S304 and having a diameter of 20 mm was processed using a grinder so that grinding streaks were formed in the circumferential direction of the shaft. A band-shaped magnetostrictive film 3 made of a Ni—Fe alloy was formed by a sputtering method in the portion having the width L of the tension transmission shaft thus processed. An excitation / detection coil 2 was provided around the magnetostrictive film 3 in the same manner as in the first embodiment to fabricate a tension sensor, and the output and its variation when a load was applied were examined.
The results are shown in Table 2. Incidentally, as a conventional example, the one in which the direction of the grinding streak on the rotating shaft was disturbed by polishing was added (FIG. 5).

[0009]

[Table 2]

As can be seen from Table 2, the output of the tension sensor of the present invention can be detected if the average surface roughness is 0.8 times or more the thickness of the magnetostrictive film 3 and the film thickness is 1 μm or more. An output signal was obtained, and the variation was within 2%. The evaluation of good variation was within 2%. On the other hand, the variation in the output of the conventional example is as large as 4% or more than that of the present invention. That is, the tension sensor of the present invention is superior to the conventional one. In this embodiment, the method of forming the magnetostrictive film 3 is described by the sputtering method, but similar results were obtained by the vacuum evaporation method and the wet plating method.

[0011]

As described above, according to the present invention, the direction of finishing of the surface of the force transmission member is aligned with the direction of maximum strain or the direction at right angles, and the surface roughness of the surface and the film of the magnetostrictive film are aligned. Since the thickness is limited, it is possible to provide a torque sensor that can detect the direction of torque without forming a strip pattern and a stable tension sensor with less variation in output characteristics.

[Brief description of drawings]

FIG. 1 is a partial plan view showing a torque sensor of the present invention.

FIG. 2 is a partial plan view showing a tension sensor of the present invention.

FIG. 3 is an explanatory diagram showing directions of magnetic anisotropy of a conventional torque sensor.

FIG. 4 is a partial plan view showing the shape of a magnetostrictive film of a conventional torque sensor.

FIG. 5 is an explanatory diagram showing directions of magnetic anisotropy of a conventional tension sensor.

[Explanation of symbols]

 1 Force transmission shaft 2 Coil 3 Magnetostrictive film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuaki Ikeda No. 2 Kurosaki Shiroishi, Yawatanishi-ku, Kitakyushu, Fukuoka Prefecture Yasukawa Electric Co., Ltd.

Claims (4)

[Claims] 1. A magnetostrictive film having a strip shape is formed on the surface of the force transmission shaft, and a solenoid coil for exciting and detecting is arranged in the vicinity of the magnetostrictive film, and the magnetostriction based on the strain generated on the surface of the force transmission shaft. By grasping the change of the film as the impedance change of the detection coil, in the magnetostrictive strain sensor for detecting the strain generated on the surface of the force transmission shaft, the final processing direction of the surface of the range of the force transmission shaft to which the magnetostrictive film is attached is A magnetostrictive strain sensor, characterized in that a main direction for sensing maximum strain or a direction perpendicular to the main direction for sensing maximum strain is made to coincide. 2. The thickness t of the magnetostrictive film is at least 1 μm.
And the average surface roughness of the final processed surface is at least 0.8 t. 3. The magnetostrictive strain sensor according to claim 1, wherein the force transmission shaft is a rotating shaft that detects torque. 4. The magnetostrictive strain sensor according to claim 1, wherein the force transmission shaft is a tension transmission shaft that detects tension.