JP3307465B2 - Magnetostrictive strain sensor - Google Patents

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 the inverse magnetostriction effect of a magnetic material, and more particularly to a strain sensor for measuring the pressure of a liquid or detecting the tensile force of a wire.

[0002]

2. Description of the Related Art Conventionally, in a pressure sensor, the performance of a die cast machine, an actuator, and the like using a hydraulic pressure has been improved. For example, by precisely controlling the hydraulic pressure, the defect rate of the die-cast material can be reduced in the die-cast machine, and the operation of the actuator can be accurately controlled. In this sense, pressure sensors are being developed, and pressure sensors utilizing the piezo effect of semiconductors and pressure sensors utilizing magnetostriction have been developed. Among them, the latter is excellent in heat resistance and therefore advantageous for high temperature use. FIG. 10 shows the structure. An amorphous magnetic material 14 is provided around a titanium pipe 12 comprising a pressure receiving portion 1 and an atmospheric pressure portion 2 which are two hollow portions,
Excitation coils 16 and 17 and detection coil 1
8 and 9 are arranged. One of the cavities is connected to the piping and receives hydraulic pressure directly, while the other receives no hydraulic pressure. When the oil pressure changes, the magnetic material 14 on the pressure receiving portion is distorted, and the magnetic characteristics change. Accompanying this, detection coil 1
Since the impedance of 9 changes but the detection coil 18 does not change, this difference is detected and measured as a change in hydraulic pressure. Further, in a tension sensor, an attempt to measure the tension of a transmission line or a train line has been advanced. For example, in the case of a power transmission line, snow accumulates on the electric wire, and when the weight increases, the electric wire cannot withstand the load, leading to disconnection. Therefore, it is necessary to constantly monitor the tension of the electric wire. In the case of a trolley wire used for a train line, if the tension is not maintained at a constant level, not only will the current collection from the pantograph be hindered, but also the trolley wire will be abnormally worn due to the occurrence of an arc and will cause radio interference. There are various types of tension sensors for measuring these tensions, and a magnetostrictive tension sensor capable of obtaining a large output is excellent. Its structure is the same as the detection method of FIG. 10 except that the transmission member is solid.
When the tension is applied, the force transmitting member is distorted, and the magnetic characteristics of the magnetic film change, and as a result, the impedance of the detection coil changes. The tension is measured from this change.

[0003]

However, since only strain in the same direction acts as in a pressure sensor or a tension sensor, in a conventional structure, a difference from a compressive force used in a torque sensor is obtained. Measures such as increasing the output could not be taken. That is, in the case of the torque sensor, there is a portion where a tensile force and a compressive force are applied by the addition of the torque, and signals having opposite signs are output to the coils arranged at the respective positions. Therefore, taking the differential not only doubles the output but also cancels noise. However, when distortion in the same direction acts, if two sets of coils are provided and their outputs are summed, the output will be doubled, but the noise will also be doubled, meaningless and the output cannot be improved. As described above, since the conventional pressure sensor and tension sensor have small outputs, there has been a problem that the practical use is hindered, such as an increase in cost due to measures against noise. Further, the change in the output of such a magnetostrictive strain sensor with respect to the strain has a large hysteresis of about 1%, so that the measurement accuracy is poor, and further higher accuracy has been desired.
This hysteresis is caused by the fact that the magnetic domain structure of the magnetic material is an in-plane magnetized film (FIG. 9) and involves domain wall motion. Therefore, a first object of the present invention is to provide a magnetostrictive strain sensor having a large output and being resistant to noise, and a second object is to provide a magnetostrictive strain sensor having a small hysteresis.

[0004]

In order to solve the above problems, the present invention forms a magnetic film having a reverse magnetostrictive effect on the surface of a force transmitting member, and an exciting coil and a detecting coil are wound near the magnetic film. Magnetostrictive strain sensor that arranges a pair of coils and detects the change in the magnetic permeability of the magnetic film based on the strain generated on the surface of the force transmitting member as a change in the impedance of the detection coil, and detects the strain generated on the surface of the force transmitting member. Coil pair is composed of at least two sets, one set is disposed near the magnetic film, the other set is disposed in the non-formed portion of the magnetic film, and
The configuration is such that two excitation coils are connected in series.
In addition, the force transmitting member has a columnar or cylindrical shape, and in one, a magnetic film is formed all around the partial surface of the force transmitting member, and a coil pair is concentrically wound therearound. The other is a solenoid coil in which a magnetic film is formed on a part of the force transmitting member on the same circumference and a coil pair is provided with a magnetic head wound around a yoke having a gap. Furthermore, four coil pairs are provided, two coil pairs are provided on the force transmitting member and the other two coil pairs are provided on the non-force transmitting member,
One set is arranged around the magnetic film, and the other set is arranged at a portion where the magnetic film is not formed. The magnetic film has a magnetic domain structure composed of stripe magnetic domains.

[0005]

According to the above-mentioned means, when two pairs of coil pairs each comprising an excitation coil and a detection coil are arranged in a portion where a magnetic film is provided and a portion where no magnetic film is provided, and a tensile force is applied to a force transmitting member, Since the magnetic characteristics change and the impedance increases, the output of the detection coil arranged at the portion where the magnetic film is formed changes. On the other hand, since the exciting current decreases as the impedance increases, the current flowing through the coil without the magnetic film also decreases. As a result, the output of the detection coil in the portion without the film decreases due to the decrease in the mutual inductance. That is, since the output change is opposite in both coils, a double output can be obtained by taking the differential. Further, by forming the magnetic domain structure of the magnetic film into a stripe shape (FIG. 8), the mechanism of the magnetic characteristic which changes by the addition of the strain changes from the conventional one due to the domain wall motion of the in-plane magnetized film to the one due to the rotation of the magnetization. Therefore, the hysteresis is reduced.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. First Embodiment FIG. 1 is a sectional view of a magnetostrictive pressure sensor using a solenoid coil according to a first embodiment of the present invention. In the figure, 1
Is a force transmitting member, a pipe made of Ti alloy and SUS3
It consists of 16 stainless steel pipes. Reference numeral 11 denotes a pressure receiving portion, 7 denotes an excitation coil provided in a portion where a magnetic film is not formed, 8 denotes an excitation coil provided in a portion where a magnetic film 13 is formed, 3 denotes a detection coil provided concentrically outside the excitation coil 7, and 4 denotes a detection coil. This is a detection coil provided concentrically outside the excitation coil 8. Magnetic film 1
Reference numeral 3 denotes a 30% Ni—Co film formed on the outer peripheral surface of the force transmitting member 1 by an ion plating method and N formed by an electroplating method.
It is formed by covering with i-plating. The coil specifications are as follows: the excitation coils 7 and 8 each have 200 turns, the detection coil 3
4 for 400 turns each. As shown in an equivalent circuit of the electric circuit in FIG. 2, the exciting coils 7 and 8 are connected in series. 20 is an AC power supply, 21 is a DC conversion circuit for converting an AC voltage into a DC voltage, and 22 is a differential amplifier. As a result of connecting the pressure receiving portion 11 to a high-pressure oil pipe and changing the pressure to 200 atm and examining the output, the output of the pressure sensor of the present invention is twice as large as that of the conventional type regardless of the material of the magnetic film.
A three-fold improvement in S / N ratio was observed. Further, under the condition that the output was measured with the excitation coil connected in parallel in the configuration of FIG. 1, the output was doubled as compared with the conventional method, but the S / N ratio was also doubled, and the effect was seen. I couldn't. In the case of the parallel connection, it is considered that since each coil is independent, the characteristic change of the magnetic film affects only one side. It can be seen that the effects of increasing the output and improving the S / N ratio are obtained only when the coils are connected in series and the coils are arranged at the place where the magnetic film is present and where the coil is not present. It is apparent that the coil disposed in the area where the magnetic film is not provided is not a force transmitting member but may be another part, for example, an air-core coil.

Second Embodiment FIG. 3 is a sectional view of a magnetostrictive pressure sensor using a solenoid coil according to a second embodiment of the present invention. This configuration is the first
In the configuration of the embodiment, two pairs of coil pairs 15 are further added to the outer peripheral portion of the non-force transmitting member 2. That is, the magnetic film 1
3 is extended to the non-force transmitting member 2, and one set of coil pairs 15 is provided on the outer peripheral portion, and another set of coil pairs 15 is provided on the non-formed portion of the magnetic film. FIG. 4 shows an equivalent circuit thereof. The excitation circuits 9 and 10 of the two pairs of coils provided on the outer periphery of the non-force transmitting member 2 are also connected in series, and have exactly the same circuit as in FIG. The final output is a differential between the differential output on the pressure receiving section 11 side and the differential output on the atmospheric pressure section 12 side. As a result of examining the differential output in the same manner as in the first embodiment, the output of the pressure sensor of the present invention was 3.5 times and the S / N ratio was irrespective of the material of the magnetic film.
A five-fold improvement was seen. Third Embodiment FIG. 5 is a partial sectional view of a magnetostrictive tension sensor using a solenoid coil according to a third embodiment of the present invention. In the figure, reference numeral 1 denotes a force transmitting member made of a titanium alloy rod. Magnetic film 1
Reference numeral 3 is formed in the same manner as in the first embodiment, and one set of coil pairs is formed on the outer periphery of the magnetic film 13 and another is formed on the portion where the magnetic film is not formed.
This is a configuration in which a set of coil pairs is provided. Coil specifications are first
This is the same as the embodiment. Now, a tensile force is applied to both ends of the force transmitting member 1 to measure a tensile force-output characteristic. As a result, it was found that the output was doubled and the S / N ratio was doubled as compared with the conventional method. In the embodiment of the present invention, only the plating method and the ion plating method are used for forming the magnetic film. However, the same applies when other magnetic film forming methods such as a sputtering method and a method of bonding an amorphous magnetic material are used. It is clear that the effect is obtained. In addition, although an example in which only a tensile force is applied has been described, it is apparent that a similar effect is obtained when only a compressive force is applied.

FIG. 6 is a partial sectional view of a magnetostrictive tension sensor using a magnetic head according to a fourth embodiment of the present invention. In the figure, reference numeral 1 denotes a tension transmitting shaft (shaft) as a force transmitting member, 13 denotes a magnetic film, and 23 and 27 denote magnetic heads. Shaft 1 is SU
This was composed of S304, which was subjected to ultrasonic cleaning in the order of trichlene, pure water, and alcohol, and then set in a sputtering apparatus. After evacuating to 5 × 10 ⁻⁶ Torr or less, the shaft was heated to 400 ° C., and a 90% Ni—Fe magnetic film was formed on a part of the shaft to a thickness of 5 μm almost halfway. The magnetic head 23 was arranged on the outer periphery of the portion of the tension transmitting shaft (shaft) 1 where the magnetic film 13 was formed, and the magnetic head 27 was arranged on the outer periphery of the portion where the magnetic film 13 was not formed. The excitation coil 25,
29 is 200 turns, and the detection coils 26 and 30 are 600 turns, and two sets of excitation coils are connected in series for wiring. Now, a tensile force is applied to both ends of the tension transmitting shaft (shaft) 1 to measure a tensile force-output characteristic. As a result, as in Example 1, it was found that the output was doubled and the S / N ratio was doubled as compared with the conventional method. Fifth Embodiment FIG. 7 is a partial sectional view of a magnetostrictive pressure sensor using a magnetic head according to a fifth embodiment of the present invention. In the figure, 1 is a force transmitting member, 11 is a pressure receiving portion, 13 is a magnetic film, and 31 and 35 are magnetic heads. One of the force transmitting members 1 is made of a titanium alloy pipe, a part of the surface of which is coated with a 30% Ni-Co film by an ion plating method, and the other is S
A portion of the surface of the US316 stainless steel pipe was coated with Ni plating by electroplating. In the pressure sensor, magnetic heads 31 and 35 were arranged with a certain gap in the vicinity of a portion where the magnetic film 13 was formed and a portion where the magnetic film 13 was not formed. The specifications of the excitation coils 33 and 37 and the detection coils 34 and 38 of the magnetic head are the same as in the fourth embodiment, and the two excitation coils 33 and 37 are connected in series. Now, the pressure receiving section 11 was connected to a high-pressure oil pipe, pressure was applied to 200 atm, and pressure-output characteristics were measured. As a result, the output is doubled and the S / N ratio is 2
It was found to improve twice.

Sixth Embodiment A sixth embodiment of the present invention comprises a magnetostrictive tension sensor similar to the third embodiment shown in FIG. In the figure, reference numeral 1 denotes a shaft whose force transmitting member is made of SUS304, and 13 denotes a magnetic film having a magnetic domain structure of stripe magnetic domains. The shaft 1 is subjected to ultrasonic cleaning in the order of trichlene, pure water, and alcohol, then set in a sputtering apparatus, evacuated to 5 × 10 ⁻⁶ Torr or less, heated to 400 ° C., and partially heated. A 90% Ni—Fe magnetic film was formed to a thickness of 5 μm. At the time of film formation, samples with various film formation rates were prepared, and magnetic domains of the film were observed using the Kerr effect and the Bitter method. The detection coil 11 arranged around the shaft 1 has 600 turns, and the excitation coil 12 has 200 turns. Next, using these samples,
Hysteresis was measured by applying a tension up to kg / mm ² . Table 1 shows the results.

[0010]

[Table 1]

From these results, it can be seen that when the film forming speed is high, stripe-shaped magnetic domains are formed and the hysteresis is small. What is described as in-plane magnetization in Table 1 is a conventional example, and the hysteresis is large. Seventh Embodiment A seventh embodiment of the present invention constitutes a magnetostrictive pressure sensor similar to the first embodiment of FIG. In the figure, reference numeral 1 denotes a shaft whose force transmitting member is made of a Ti alloy, and 13 denotes a magnetic film having a magnetic domain structure of stripe magnetic domains. Shaft made of Ti alloy 1
Was performed in the same manner as in the sixth embodiment, and the magnetic film 13 was formed by coating a 30% Ni—Co film under various argon partial pressures by a sputtering method. The winding specifications and magnetic domain observation method were the same as in the sixth embodiment. Next, using these samples, various pressures up to 200 atm were applied and the results of examining the hysteresis are shown in Table 2.

[0012]

[Table 2]

It can be seen that the hysteresis is reduced when the magnetic domains are stripes as in the sixth embodiment. It is considered that there are various conditions under which the magnetic domains of the magnetic material become stripe magnetic domains. In the embodiment of the present invention, the stripe-shaped magnetic domains are formed as the film formation rate is increased and the argon partial pressure is decreased. However, it is considered that stripe magnetic domains can be produced by a method other than the sputtering method.

[0014]

As described above, according to the present invention, two exciting coils of a solenoid coil or a magnetic head provided respectively in the vicinity of the magnetic film of the force transmitting member and in the portion without the magnetic film are connected in series. With this configuration, it is possible to obtain a magnetostrictive strain sensor capable of obtaining a large output with respect to distortion, having a large S / N ratio, and being resistant to noise. Further, since the magnetic domain structure of the magnetic film is formed in a stripe shape, a high-precision magnetostrictive strain sensor with small hysteresis can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetostrictive pressure sensor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of the first embodiment of the present invention.

FIG. 3 is a sectional view of a magnetostrictive pressure sensor according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an equivalent circuit according to a second embodiment of the present invention.

FIG. 5 is a partial sectional view of a magnetostrictive tension sensor showing a third embodiment of the present invention.

FIG. 6 is a partial sectional view of a tension sensor showing a fourth embodiment of the present invention.

FIG. 7 is a partial sectional view showing a pressure sensor according to a fifth embodiment of the present invention.

FIG. 8 is a schematic diagram showing stripe magnetic domains of a magnetic film used in the magnetostrictive strain sensor of the present invention.

FIG. 9 is a schematic diagram showing a magnetic domain structure of an in-plane magnetized film of a magnetic film used in a conventional magnetostrictive strain sensor.

FIG. 10 is a sectional view showing a conventional pressure sensor.

[Explanation of symbols]

1 Force transmission member 2 Non-force transmission member 3, 4, 5, 6, 18, 19, 26, 29, 34, 38
Detection coil 7, 8, 9, 10, 16, 17, 25, 30, 33, 3
7 Excitation coil 11 Pressure receiving part 12 Atmospheric pressure part 13, 14 Magnetic film 15 Coil pair 20 AC power supply 21 DC conversion circuit 22 Differential amplifier 23, 27, 31, 35 Magnetic head 24, 28, 32, 36 Yoke

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hidenori Hasegawa 2-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City, Fukuoka Prefecture (72) Inventor Masao Matino 2 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City, Fukuoka Prefecture No. 1 Examiner, Yaskawa Electric Co., Ltd. Shinichi Nagai (56) References JP-A-3-131733 (JP, A) JP-A-3-10138 (JP, A) JP-A-3-10137 (JP, A) JP-A-2-128131 (JP, A) JP-A-4-145334 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01L 9/16 G01L 1/12 G01L 5/10 G01L 3/10 G01R 33/18 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. A magnetic film having an inverse magnetostriction effect is formed on a surface of a force transmitting member, and a coil pair in which an exciting coil and a detecting coil are wound is disposed near the magnetic film, and the magnetic film is generated on the surface of the force transmitting member. In a strain sensor that detects a change in magnetic permeability of the magnetic film based on strain as a change in impedance of a detection coil and detects strain generated on the surface of the force transmitting member, the coil pair includes at least two pairs, Magnetostrictive strain sensors characterized in that one set is located near the magnetic film and the other set is located at the non-formed portion of the magnetic film, and two exciting coils are connected in series. . 2. The force transmitting member has a columnar or cylindrical shape, the magnetic film is formed on the entire periphery of a partial surface of the force transmitting member, and the coil pair is concentrically wound therearound. 2. The magnetostrictive strain sensor according to claim 1, wherein the magnetostrictive strain sensor is a turned solenoid coil. 3. The force transmitting member has a cylindrical or cylindrical shape, the magnetic film is formed on a part of the force transmitting member on the same circumference, and the coil pair is wound around a yoke having a gap. 2. The magnetostrictive strain sensor according to claim 1, wherein the magnetostrictive strain sensor is a turned magnetic head. 4. The magnetostrictive strain sensor according to claim 2, wherein the non-formed portion of the magnetic film is a non-force transmitting member. 5. The apparatus according to claim 1, wherein the coil pairs are four sets, two coil pairs are provided on the force transmitting member, and the other two coil pairs are provided on the non-force transmitting member. 4. The magnetostrictive strain sensor according to claim 2, wherein one set is arranged in a portion where no magnetic film is formed. 6. The magnetostrictive strain sensor according to claim 1, wherein the magnetic domain structure of the magnetic film is a stripe magnetic domain. 7. The magnetostrictive strain sensor according to claim 6, wherein the directions of the stripes of the stripe magnetic domains are aligned in the magnetic film.