JPH11118629A - Magnetostrictive strain sensor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent a sensor characteristic from changing with time when a temperature change of a use environment is large. A magnetic film having an inverse magnetostriction effect is formed on an outer peripheral surface of a predetermined position of a shaft, and an exciting coil and a detection coil are arranged close to the magnetic film. In a magnetostrictive strain sensor that detects a distortion by measuring a change in impedance of a coil that changes a strain generated on the surface in accordance with a change in the magnetic permeability of the magnetic film 2, the true stress of the magnetic film 2 is +3 kgf / mm ² to −3 kgf. The magnetic film 2 adjusted to a value of / mm ² was used. Therefore, it is possible to obtain a magnetic film having the reverse magnetostriction effect that does not change with time.

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 utilizing a reverse magnetostriction effect of a magnetic material, for example, a motor torque,
The present invention relates to a magnetostrictive strain sensor for measuring pressure of a liquid or tension of an electric wire.

[0002]

2. Description of the Related Art Non-contact small torque sensors are required for controlling robots, manipulators, and machine tools having a rotary drive system. Such a torque sensor has the same configuration as that of FIG. 1 of the configuration of the present invention. As the rotating shaft 1, maraging steel, stainless steel, or the like is used. When the rotating shaft 1 is made of a non-magnetic material such as SUS304 stainless steel, a magnetic film 2 (Ni-Fe permalloy film) or the like is formed on its surface by a sputtering method or the like. When a maraging steel is used to form a high-sensitivity sensor, a permalloy film or the like is formed on the surface thereof before use. When a torque is applied to the rotating shaft 1, strain is applied to the magnetic film 2 formed on the surface of the rotating shaft 1, and the magnetic characteristics change. The change in the magnetic characteristics is detected by the detection coil 4 as an impedance change by the exciting coil 3 wound around the rotating shaft 1 and converted into torque. Various magnetic materials can be used for the magnetic film 2 formed on the shaft 1. Permalloy having a composition having a low coercive force, a large film strength and a large magnetostriction constant is desirable. Specifically, 50% to 75% N
i-Fe permalloy or 85% to 95% permalloy. Further, as the manufacturing method, a sputtering method having good reproducibility of the composition and the film thickness is preferable. Attempts are being made to measure the tension of transmission lines and train lines. For example, when a power transmission line is supposed to be snowy and the weight increases, the power line cannot withstand the load, leading to disconnection. Therefore, attempts have been made to monitor the tension of the electric wires to prevent an accident. FIG. 2 shows a configuration example of the tension sensor. A Ni-Fe alloy film 5 is formed on the outer periphery of a shaft 1 made of non-magnetic stainless steel. The change in the synthetic film 5 based on the change in the tension is regarded as a change in the magnetic characteristics by the detection coil 4 by the impedance change due to the exciting coil 3 and is converted into a tension.

[0003]

However, it has been found that when a permalloy film produced by a sputtering method is used as a strain sensor, if the temperature of the operating environment changes greatly, the sensor characteristics change over time. When the strain sensor is used in an environment where the temperature changes drastically, the magnetic film 2 is distorted due to a difference in thermal expansion coefficient between the magnetic film 2 and the shaft 1. If the true stress remains in the magnetic film 2, the true stress changes due to the stress applied to the magnetic film 2. True stress is particularly apparent in the magnetic film 2 produced by a film forming method using a vacuum technique such as a sputtering method.
Gas taken in the film when forming a sputtered film, magnetic film 2
Due to slight disturbance of the crystal of the crystal. Therefore, over a long period of time, a slight change is caused by external factors such as repeated thermal stress. If this true stress is reduced, the change over time of the strain sensor is reduced. Therefore, the present invention
It is an object of the present invention to obtain a strain sensor made of a magnetic film having a reverse magnetostriction effect that does not change with time.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention forms a magnetic film having an inverse magnetostrictive effect on an outer peripheral surface of a predetermined position of a shaft, and brings an exciting coil and a detection coil close to the magnetic film. A magnetostrictive strain sensor for arranging a coil and measuring a change in impedance of the coil, which changes a strain generated on a shaft surface by a strain transmitted to the shaft in accordance with a change in magnetic permeability of the magnetic film, and detects the strain, A magnetic film whose true stress is adjusted to a value of +3 kgf / mm ² to −3 kgf / mm ² is used.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a magnetostrictive torque sensor. FIG. 2 is a configuration diagram of the magnetostrictive tension sensor. In the figure, reference numeral 1 denotes a shaft having a diameter of 30 mm. The shaft is made of Ti or SUS304 stainless steel.
-Fe film on Ti shaft, 90% Ni-Fe film on S shaft
Coated on US304 shaft. The axis temperature during film formation was 400 ° C. On the other hand, soda-lime glass (5 × 10 mm,
SUS304 thin plate (5 mm thick, 1 m thick) having the same coefficient of thermal expansion as SUS304 shaft
m) The magnetic film 2 or the synthetic film 5 having the same thickness was formed on the upper surface. After heat-treating this sample at 500 ° C. for various time conditions, the true stress remaining in the film was measured by a bending measurement method (for example, Kobayashi and Hosokawa: Introduction to Thin Film Technology, p149, Sogo Denshi Publishing Co., Ltd.). Next, with reference to this bending measurement method, a sample was prepared by performing a heat treatment on the shaft samples of both materials under the condition that various true stresses remain. Subsequently, the relationship between the tension and the output was measured 50 times after the sample was subjected to a heat cycle of −15 to + 50 ° C. and the output change rate was examined. The characteristics were measured by placing a 200-turn excitation coil 3 and a 400-turn detection coil 4 around the magnetic film 2 or the synthetic film 5 of the sample. As can be seen from the results in the following table, when the true stress is small, the change with time is small. True stress is +3 kgf / mm ² to -3 kgf / mm ²
It has been found that when the value exceeds the range, the change with time increases. In the example, the heat treatment was used for removing the true stress.
There are a method of removing by applying ultrasonic waves and a method of performing simultaneous heat treatment during sputtering. Although only Permalloy is taken up as the magnetic film 2 or the composite film 5 in the embodiment, it is apparent that the same result is obtained in other magnetic films 2 or the composite film 5 because the true stress is caused. Further, the output may be detected by a magnetic head.

[0006]

[Table 1]

[0007]

As described above, since the magnetostrictive strain sensor according to the present invention does not change with time even when used for a long time, a highly reliable strain sensor can be constructed. This can contribute to the advancement of equipment that requires measurement of torque, tension, and the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a magnetostrictive torque sensor of the present invention.

FIG. 2 is a configuration diagram of a magnetostrictive tension sensor of the present invention.

[Explanation of symbols]

1 axis, 2 magnetic film, 3 excitation coil, 4 detection coil, 5 synthetic film

Claims (5)

[Claims] A magnetic film having an inverse magnetostriction effect is formed on an outer peripheral surface of a shaft, and an exciting coil and a detection coil are arranged close to the magnetic film. In a magnetostrictive strain sensor for detecting distortion by measuring an impedance change of the coil corresponding to a change in magnetic permeability of the magnetic film, a true stress of the magnetic film is +3 kgf / mm ² to −3 kgf.
The magnetostrictive strain sensor is adjusted to a value of / mm ² . 2. The magnetostrictive strain sensor according to claim 1, wherein said shaft is made of SUS304 stainless steel. 3. The magnetostrictive strain sensor according to claim 1, wherein said magnetic film is made of permalloy. 4. The apparatus according to claim 1, wherein the detection of the impedance change is performed by a magnetic head.
A magnetostrictive strain sensor according to claim 1. 5. The apparatus according to claim 1, wherein the detection of the impedance change is performed by an excitation coil and a detection coil arranged concentrically around the outer periphery of the magnetic film.
A magnetostrictive strain sensor according to claim 1.