JPH09229797A - Magnetostrictive strain sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetostrictive strain sensor in which a measuring error is not generated by making the temperature of a detection coil follow the temperature of a magnetic film. SOLUTION: The magnetostrictive strain sensor is provided with a cylindrical force transmission member 1 which has a reverse magnetostrictive effect on its surface, a force transmission part 2 which is formed at the force transmission member 1, a force nontransmission part 3 which is formed at the force transmission member 1 so as to be adjancent to the force transmission part 2, and two coil groups 5A, 5B which are composed of exciting coils 51A, 51B and detection coils 52A, 52B which are installed respectively at the force transmission part 2 and the force nontransmission part 3 so as to be faced via gaps. In the magnetostrictive strain sensor, a nonmagnetic viscous fluid 8 whose thermal conductivity is at 10<-3> cal/cm.sec. deg.C or higher is filled into a space between the force transmission member 1 and the coil grouops 5A, 5B.

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 which utilizes the inverse magnetostrictive effect of a magnetic material to detect the pressure of a fluid such as hydraulic fluid of a hydraulic device whose temperature changes drastically and the tension of an overhead wire.

[0002]

2. Description of the Related Art Recently, the performance of die cast machines and actuators utilizing hydraulic pressure has been improved. For example, in a die-casting machine, the defective rate of the die-cast material is reduced by accurately controlling the hydraulic pressure of the hydraulic device. Also, by accurately controlling the hydraulic pressure of the actuator, it is possible to perform an accurate positioning operation. Therefore, a pressure sensor of a hydraulic system needs stable characteristics, but a magnetostrictive strain sensor having excellent heat resistance has been developed to meet such requirements (for example, issued by Industrial Research Board). : M
& E, September 1989 issue, p. 124). FIG. 3 is a cross-sectional view showing an example thereof, in which a partition wall 11 is provided inside the force transmission member 1 made of a titanium pipe, and two cavity portions 12,
13 is formed, one side is used as the force detection unit 2 and the other side is used as the non-force detection unit 3, the cavity 12 of the force detection unit 2 is connected to the hydraulic oil pipe, and the hydraulic pressure is directly received. A magnetic film 4 made of an amorphous magnetic material is provided on the outer peripheral surfaces of both the force detecting unit 2 and the non-force detecting unit 3, and the exciting coil 51A and the detecting coil 52A and the exciting coil 51B and the detecting coil 52B are concentrically formed. The two coil groups 5A and 5B arranged in the above are opposed to the magnetic film 4 with a gap. Reference numeral 6 is a yoke provided on the outer circumference of the coil groups 5A and 5B. In such a pressure sensor, when the hydraulic pressure in the cavity 12 changes, the magnetic film 4 is distorted via the force detection unit 2 to change the magnetic characteristics, and the detection coil 52A accordingly.
Impedance changes. Since there is no change in impedance of the detection coil 52B arranged around the non-force detection unit 3, the difference between the detection coils 52A and 52B is detected and measured as a change in hydraulic pressure.

[0003]

However, in the above-mentioned prior art, since the force transmission member 1 is formed of a titanium pipe having a high thermal conductivity when the temperature of the hydraulic oil of the hydraulic device changes, The force detector 2 into which the hydraulic oil enters immediately becomes the same temperature as the hydraulic oil, and the temperature of the magnetic film 4 itself provided on the outer periphery of the force detector 2 immediately follows the temperature of the hydraulic oil. However, the detection coils 52A and 52B are not
Since the heat is detected through the air, which is placed in a non-contact manner with low thermal conductivity, it cannot immediately follow the temperature change of the hydraulic oil. The temperature characteristic as the pressure sensor is obtained from the data when the temperatures of the magnetic film 4 and the detection coils 52A and 52B are the same. Therefore, when the temperatures of the magnetic film 4 and the detection coils 52A and 52B are different, different measurement results from the actual results. Therefore, there is a problem that a measurement error occurs. An object of the present invention is to provide a magnetostrictive strain sensor in which a measurement error does not occur by allowing the temperature of a detection coil to follow the temperature of a force transmission member or a magnetic film provided on the force transmission member. .

[0004]

In order to solve the above problems, the present invention provides a cylindrical or cylindrical force transmitting member having at least a surface having an inverse magnetostrictive effect, and facing the force transmitting member with a gap. In a magnetostrictive strain sensor including a coil group including an exciting coil and a detection coil provided as
A space between the force transmission member and the coil group is filled with a nonmagnetic viscous fluid having a thermal conductivity of 10 ⁻³ cal / cm · sec · ° C. or more. Further, O-ring members that prevent the viscous fluid from flowing out from the space are provided at both ends of the coil group. Further, the force transmission member,
The pressure of the fluid is measured by a cylindrical body having a cavity into which the fluid can be introduced. Further, the transmission member is made of a cylindrical shape and measures the force in the axial direction.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 is a front sectional view showing a first embodiment of the present invention. In the figure, 1 is a force transmission member made of a non-magnetic material such as a hollow cylindrical titanium pipe, 11 is a partition wall provided inside the force transmission member 1, and two cavities 12 and 13 are formed on both sides thereof. There is. With the partition wall 11 as a boundary, one cavity 12 side is used as the force detection unit 2 and the other cavity 13 side is used as the non-force detection unit 3, and the cavity 12 of the force detection unit 2 is connected to a hydraulic oil pipe to operate. Oil is introduced into the hollow portion 12 to directly receive hydraulic pressure. 4 is a force detector 2 and a non-force detector 3
A magnetostrictive material made of an amorphous magnetic material having an inverse magnetostrictive effect on the surface of the force transmitting member 1 over both outer peripheral surfaces of the force transmitting member 1, and is a magnetic film provided by a vacuum deposition method or a sputtering method. 5A and 5B are an exciting coil 51A and a detecting coil 52A, and an exciting coil 51B and a detecting coil 52, respectively.
Two coil groups in which B is arranged concentrically,
The magnetic film 4 is opposed to the magnetic film 4 via a gap. 6 is a yoke provided outside the detection coils 52A and 52B, and 7 is a yoke 6
Is an O-ring provided in a portion facing the force transmission member 1, and 8 is a non-magnetic viscous fluid filled in a space S surrounded by the force transmission member 1, the coil group 5A, the coil group 5B and the O ring 7. The O-ring 7 prevents the viscous fluid 8 from flowing out of the space S.

The viscous fluid 8 may be grease such as Al ₂
The thermal conductivity is increased by mixing non-magnetic oxide particles such as O ₃ , Zr ₂ O ₃ and BeO and changing the mixing amount. Here, the viscous fluid 8 having different thermal conductivity is prepared by changing the mixing amount of the particles of the non-magnetic oxide, the viscous fluid 8 is filled in the space S, and the temperature of the hydraulic oil is changed from 50 ° C. to 70 ° C. ℃
When the temperature of the coil groups 5A and 5B is changed to 70
The following Table 1 shows the results of investigating the time required to reach the temperature of about 0 ° C. and examining the ability of the coil groups 5A and 5B to follow the temperature change of the hydraulic oil. The condition in which the space S is filled is a state in which the viscous fluid 8 is not filled, that is, air (heat conductivity is 0.06 × 10 ⁻³ c
Al / cm · sec · ° C.) and the viscous fluid 8 has a thermal conductivity of 0.5 × 10 ⁻³ cal / cm · sec.
Measurement was carried out in 4 steps from-° C to 2 x 10 ^-3 cal / cm-sec- ° C. The temperature was measured with a copper-constantan thermocouple.

[0007]

[Table 1]

From these results, the coil group 5 was heated within 10 seconds from the time when the temperature of the hydraulic oil was changed from 50 ° C to 70 ° C.
The temperatures of A and 5B followed when the thermal conductivity of the viscous fluid 8 was 10 ⁻³ cal / cm · sec · ° C. or higher. This follows that when the viscous fluid 8 is not filled, the follow-up time is significantly faster than when the follow-up time takes 50 seconds, and it is within the allowable delay time of 10 seconds in measurement. I understand. With such a configuration, even if the temperature of the hydraulic oil changes, the temperatures of both detection coils follow each other, so that a measurement error does not occur.

FIG. 2 is a front sectional view showing a second embodiment of the present invention. In the above-described first embodiment, the case where the hollow portion is provided in the cylindrical force transmission member to apply pressure has been described, but in this case, the force transmission member is formed in a solid columnar shape,
This is applied to a tension sensor that detects the tension applied in a state where heat with temperature change is detected in a non-contact manner. That is, the force transmitting member 1 is a non-magnetic columnar member such as an electric wire or a rotating shaft, and a magnetostrictive material made of an amorphous magnetic substance having an inverse magnetostrictive effect on the surface of the force detecting portion 2 ′ which is a part of the force transmitting member 1. Then, the magnetic film 4 is provided by the vacuum deposition method, the sputtering method, or the like. The portion without the magnetic film 4 is the non-force detecting portion 3 '. The coil groups 5A and 5B include an exciting coil 51A, a detecting coil 52A, and an exciting coil 51B, respectively.
And a detection coil 52B, each of which has a force detection unit 2 '.
And are arranged concentrically on the outer periphery of the non-force detection portion 3'through a gap. A yoke 6 is provided outside the detection coils 52A and 52B, and O is provided in a portion of the yoke 6 facing the force transmission member 1.
A ring 7 is provided. Space S surrounded by force transmission member 1 and coil group 5A and coil group 5B and O-ring 7
Is filled with a non-magnetic viscous fluid, and the viscous fluid 8 is prevented from flowing out of the space S by the O-ring 7. With such a configuration, the tension or pressure applied to the force transmission member 1 in the axial direction can be detected by taking the difference between the detection coils 52A and 52B. Moreover, since the viscous fluid 8 is filled in the space S surrounded by the force transmission member 1, the magnetic film 4, the coil group 5A, and the coil group 5B, the temperature of the coil group 5A and the coil group 5B from the force transmission member 1 is increased. The ability to follow changes is several times faster than when the viscous fluid 8 is not filled. Therefore, even if the temperature of the force transmitting member 1 changes, the temperatures of both the detection coils 52A and 52B follow, so that a measurement error does not occur.

[0010]

As described above, according to the present invention, a viscous fluid having high thermal conductivity is filled between the force transmitting member and the coil group to prevent the temperature of the coil group from changing with respect to the temperature change of the force detecting portion. Since the followability is improved, there is an effect that a high-precision magnetostrictive strain sensor can be provided without a decrease in measurement accuracy due to a temperature change of the force detection unit due to hydraulic oil.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a first embodiment of the present invention.

FIG. 2 is a front sectional view showing a second embodiment of the present invention.

FIG. 3 is a front sectional view showing a conventional example.

[Explanation of symbols]

1: force transmission member, 11: partition wall, 12, 13: hollow portion,
2, 2 ': force detector, 21: female screw, 31: male screw,
3, 3 ': Non-force detection part, 4: Magnetic film, 5A, 5B: Coil group, 51A, 51B: Excitation coil, 52A, 52B:
Detection coil, 6: Yoke, 7: O-ring, 8: Viscous fluid

Claims (4)

[Claims] 1. A cylindrical or cylindrical force transmitting member having an inverse magnetostrictive effect on at least a surface thereof, and a coil group including an exciting coil and a detecting coil, which are opposed to the force transmitting member via a gap. In a magnetostrictive strain sensor,
A magnetostrictive strain sensor characterized in that a space between the force transmitting member and the coil group is filled with a non-magnetic viscous fluid having a thermal conductivity of 10 ⁻³ cal / cm · sec · ° C. or more. 2. An O-ring member for preventing the viscous fluid from flowing out from the space is provided at both ends of the coil group.
The magnetostrictive strain sensor described. 3. The magnetostrictive strain sensor according to claim 1, wherein the force transmission member is a cylindrical member having a hollow portion into which a fluid can be introduced, and measures the pressure of the fluid. 4. The magnetostrictive strain sensor according to claim 1, wherein the force transmission member is formed of a cylindrical shape and measures the force in the axial direction.