JP2000266621A - Pressure sensor using magnetostrictive element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the stability of temperature characteristics and output characteristics satisfactorily by improving the impression of a bias field and an internal structure and suppressing the amount of change in inductance which occurs due to changes in temperature. SOLUTION: In the pressure sensor, an ultra magnetostrictive element 3, at least one coil 6 arranged around the ultra magnetostrictive element 3, and permanent magnets 7 and 8 to impress bias fields approximately parallelly with the direction of the exertion of weight on the magnetostrictive element 3 are housed in a casing 1 to detect changes in the magnetic permeability of the magnetostrictive element 3 due to the exertion of weight as changes in the inductance of the coil 6. The ultra magnetostrictive element 3 is formed in a column shape out of a magnetic body including a lanthanoid element system and an iron family element system. In addition, a pre-load is exerted on the ultra magnetostrictive element 3, and a pre-load mechanism to absorb expansion and contraction is provided in the casing 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor using a magnetostrictive element used for measuring pressure, torque, and the like, and particularly to a magnetostrictive element which stabilizes temperature characteristics and has a small measurement error due to temperature. It relates to a pressure sensor.

[0002]

2. Description of the Related Art In general, a pressure sensor using a magnetostrictive element detects a pressure by measuring a change in magnetic permeability due to an external stress of the magnetostrictive element as a change in an induced voltage generated in a coil. As a conventional example similar to the present invention in the technical field, there is JP-A-8-320337, for example.

[0003]

By the way, Japanese Patent Application Laid-Open No. Hei 8-
The pressure sensor using the magnetostrictive element disclosed in Japanese Patent No.
The main purpose is to suppress eddy currents, and no particular consideration is given to the improvement of temperature characteristics, which is a major factor that deteriorates measurement accuracy in a conventional pressure sensor using a magnetostrictive element.

[0004] In view of the above, the present invention provides a pressure sensor using a magnetostrictive element in which the temperature change of the inductance of a coil using the magnetostrictive element is reduced and the fluctuation of the detected pressure value due to the temperature change is suppressed. The purpose is to do. More specifically, the present invention can suppress the amount of inductance change caused by a temperature change by applying a bias magnetic field to the magnetostrictive element and improving the internal structure, has a good temperature characteristic, and has a stable output characteristic. It is an object of the present invention to provide a pressure sensor using a magnetostrictive element having an increased number.

[0005] Other objects and novel features of the present invention will be clarified in embodiments described later.

[0006]

In order to achieve the above object, a pressure sensor using a magnetostrictive element according to the present invention comprises: a magnetostrictive element; at least one coil disposed around the magnetostrictive element; And a permanent magnet that applies a bias magnetic field substantially parallel to the load direction is housed in a casing, and a change in the magnetic permeability of the magnetostrictive element due to the load is detected as a change in the inductance of the coil.

In the pressure sensor using the magnetostrictive element, it is preferable that the magnetostrictive element is a giant magnetostrictive element formed of a magnetic material containing a lanthanoid element system and an iron group element system in a columnar shape.

It is preferable that a preload mechanism that applies a preload to the magnetostrictive element and absorbs expansion and contraction is provided in the casing.

In a configuration in which a spherical or hemispherical member is brought into contact with each of the weight receiving members on both ends of the magnetostrictive element so that the load direction coincides with the center axis direction of the magnetostrictive element, a load is applied. Good to do.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pressure sensor using a magnetostrictive element according to the present invention will be described below with reference to the drawings.

1 to 3, a cylindrical magnetic yoke 2 made of iron or the like is provided in a non-magnetic casing 1 made of a non-magnetic metal or the like.
A giant magnetostrictive element 3, at least one coil 6 in which a non-magnetic bobbin 4 surrounding the outer periphery is wound with a coil 5, and permanent magnets 7 and 8 provided in contact with upper and lower end surfaces of the giant magnetostrictive element 3.
A pressing force is applied to the disc-shaped receiving plate 9 in contact with the lower surface of one of the permanent magnets 7, the disc-shaped receiving plate 10 in contact with the upper surface of the other permanent magnet 8, and the giant magnetostrictive element 3. A disc spring 11, which is a main component of the preload mechanism for applying the pressure, and a disc-shaped receiving plate 12 for receiving the disc spring 11 are provided. The receiving plate 9,
Reference numerals 10 and 12 are formed using a stainless steel plate or the like, and disc springs 11 as elastic members are formed by brushing special steel or the like.

The giant magnetostrictive element 3 is an element having an extremely large magnetostriction formed of a lanthanoid element-based and iron group element-based magnetic material in a columnar shape. Giant magnetostrictive element 3, coil 6 on its outer periphery, permanent magnets 7, 8 at both ends of giant magnetostrictive element, lower receiving plate 9, disc spring 11, receiving plate 12, and upper receiving plate 10.
Is a magnetic circuit configuration which is disposed in the cylindrical yoke 2 and applies a bias magnetic field substantially parallel to the axial direction of the giant magnetostrictive element 3 by the permanent magnets 7 and 8 whose upper and lower surfaces are magnetic poles. In other words, the arrangement is such that the N pole of one permanent magnet faces one end face of the giant magnetostrictive element 3 and the S pole of the other permanent magnet faces the other end face.

Further, in the casing 1, an upper sphere as a spherical member is provided on both upper and lower ends of the giant magnetostrictive element 3 so that a weight due to an external pressure acts on the central axis of the giant magnetostrictive element 3. 13, a lower sphere 14 is disposed, and a support member 16 holding a preload adjusting screw member 15 such as stainless steel for applying a load to the upper sphere 13 is fixed to the screw member 19 by a fixing member 18 (a lid for the casing 1). And is fixed to the casing 1. Here, the lower sphere 14 is in line contact with the conical concave surface 1a formed on the inner bottom surface of the casing 1 and is in point contact with the lower surface of the receiving plate 12 as a weight receiving member. The upper sphere 13 is in line contact with the conical concave surface 10a formed on the upper surface of the receiving plate 10 as a weight receiving member, and is in point contact with the tip surface of the preload adjusting screw member 15.

An O-ring 17 is fitted into the supporting member 16 so as to improve the adhesion between the supporting member 16 and the fixing member 18 for waterproofing and dustproofing.

As described above, the pressure sensor using the magnetostrictive element according to the present embodiment is covered with the casing 1, the fixing member 18 and the like, is sealed, and is connected to the winding 5 of the coil 6 as shown in FIG. A signal output conductor 20 is led out.

The support member 16 is slidably supported in the axial direction of the giant magnetostrictive element 3 with respect to the fixed member 18, and applies an external pressure to be measured between the bottom surface of the casing 1 and the support member 16. By doing so, the pressure is transmitted in the axial direction of the giant magnetostrictive element 3.

The preload is applied to the giant magnetostrictive element 3 in the intermediate portion even when no external pressure is applied by the disc spring 11 made of special steel or the like interposed between the receiving plate 9 and the receiving plate 12. A preload mechanism for applying the pressure is configured.
The preload mechanism also has a function of absorbing the thermal contraction of the giant magnetostrictive element 3 and each member (such as a receiving plate) in series with the giant magnetostrictive element 3 by the elastic displacement of the disc spring 11. Further, by rotating the screw member 15, the amount of protrusion of the distal end surface from the support member 16 is changed, play of both ends of the giant magnetostrictive element 3 is eliminated, and preload applied to both ends of the giant magnetostrictive element can be adjusted. It forms an adjustment mechanism.

In the pressure sensor using the giant magnetostrictive element according to this embodiment, the bottom surface of the casing 1 and the supporting member 16
If a pressure to be measured is applied from the outside during the
A change in the magnetic permeability of the giant magnetostrictive element due to a stress applied to the giant magnetostrictive element 3 due to the application of pressure in the axial direction can be detected by the coil 6 as a change in inductance.

As each of the permanent magnets 7 and 8, a ferrite magnet which is a general magnetic material can be used.
However, a rare-earth magnet made of a material having a strong magnetic field, such as a rare-earth metal, is more suitable for reducing the temperature change of the inductance caused by the change in the magnetic permeability of the giant magnetostrictive element 3. These permanent magnets 7 and 8 are applied with a magnetic field in series (substantially parallel) with respect to the direction of the pressure application axis of the giant magnetostrictive element 3 in order to suppress a change in inductance value due to a temperature change of the giant magnetostrictive element 3. It is provided as a bias magnet sandwiching the giant magnetostrictive element 3.

The characteristics of the pressure sensor using the magnetostrictive element according to the embodiment of the present invention will be described with reference to FIG. 4 and Tables 1, 5 and 2. However, FIG. 4 and Table 1 are comparative examples and temperature characteristics when no magnetic field is applied, and FIGS. 5 and 2 show temperature characteristics when the bias magnetic field is applied in the embodiment.

First, the temperature change of the inductance value without the bias magnetic field shown in FIG. 4 and Table 1 will be considered. In FIG. 4, the horizontal axis represents the ambient temperature of the sensor, and the vertical axis represents the inductance value (μH). The loads applied to the giant magnetostrictive element were 0 kgf, 50 kgf, 100 kgf, 150 kgf,
At 200 kgf, the measurement results and temperature coefficient for each were the results shown in Table 1 below. Characteristic curves A to E in FIG. 4 show the results of Table 1.

[Table 1]

Referring to FIG. 5 and Table 2, the outer diameter is 5.6 mm,
A giant magnetostrictive element 3 having a height of 15.2 mm was used. The magnet was a neodymium magnet having a residual magnetic flux density of 1,240 (millitesla), an outer diameter of 12 mm, and a height of 2 mm. The gap magnetic flux density at the center between the applied bias magnets was 64.6 (millitesla).

Each of the loads applied to the giant magnetostrictive elements is 0 k
gf, 50kgf, 100kgf, 150kgf, 20
0 kgf, and the measurement results and temperature coefficients for each were as shown in Table 2 below. The characteristic curves a to e in FIG. 5 are obtained by plotting the results in Table 2.

[Table 2]

A comparison of the amount of change in inductance with respect to temperature between the present embodiment and a comparative example having no bias magnetic field shows that the temperature coefficient is uniform at each load with and without the bias magnet. It can be seen that the temperature characteristics have been significantly improved. As a result, the accuracy of the measured pressure can be improved, and the processing of an electric signal for performing processing such as converting an inductance value to a voltage value becomes easier (for example, temperature compensation becomes easier).

According to this embodiment, the following effects can be obtained.

(1) The giant magnetostrictive element 3, at least one coil 6 disposed around the giant magnetostrictive element 3, and permanent magnets 7, 8 for applying a bias magnetic field substantially parallel to the weighting direction of the giant magnetostrictive element 3 And the change in the magnetic permeability of the giant magnetostrictive element 3 due to the load is detected as a change in the inductance of the coil 6. By applying a bias magnetic field substantially parallel to the load direction of the giant magnetostrictive element 3, the ambient temperature change Accordingly, a change in inductance of the coil 6 due to this is reduced, so that measurement accuracy can be improved, and temperature compensation of a subsequent electric circuit can be facilitated.

(2) The magnetostrictive element is a giant magnetostrictive element formed of a magnetic material containing a lanthanoid element system and an iron group element system in a columnar shape, and enables highly sensitive pressure detection.

(3) A preload mechanism for applying a preload to the giant magnetostrictive element 3 and absorbing expansion and contraction is provided in the casing 1, and in this respect, reliability against temperature changes can be ensured.

(4) A receiving plate 10 having concave portions on both ends of the giant magnetostrictive element 3 and a spherical body with respect to the inner bottom surface of the casing 1 so that the load direction and the central axis direction of the giant magnetostrictive element 3 coincide with each other. In this configuration, the load is applied by bringing the members 13 and 14 into contact with each other, and an accident in which the shear force is applied to the giant magnetostrictive element 3 to damage it can be prevented.

The receiving plates 10 on both sides of the giant magnetostrictive element 3
Although the spheres 13 and 14 are used as a pair of spherical members abutting to apply an external load to 12, a semispherical member contacting a concave surface such as a conical shape on the other side may be used.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and various modifications and changes can be made within the scope of the claims. There will be.

[0032]

As described above, according to the pressure sensor using the magnetostrictive element according to the present invention, the magnetostrictive element, at least one coil disposed around the magnetostrictive element, and the weighting direction of the magnetostrictive element. And a permanent magnet that applies a bias magnetic field substantially in parallel to the casing, and a change in the magnetic permeability of the magnetostrictive element due to the load is detected as a change in the inductance of the coil, so that the bias magnetic field is applied to the magnetostrictive element. , The temperature characteristic is improved, and the detected value of the measured load amount using the magnetostrictive element having the increased stability of the output characteristic can be obtained.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an embodiment of a pressure sensor using a magnetostrictive element of the present invention.

FIG. 2 is a side view showing the appearance of the embodiment.

FIG. 3 is a plan view of the same.

FIG. 4 is a temperature characteristic diagram in a comparative example in which no bias magnetic field is applied.

FIG. 5 is a temperature characteristic diagram in the case of an embodiment in which a bias magnetic field is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casing 2 Yoke 3 Giant magnetostrictive element 4 Bobbin 5 Winding 6 Coil 7,8 Permanent magnet 9,10,12 Receiving plate 11 Disc spring 13 Upper sphere 14 Lower sphere 15,19 Screw member 16 Support member 17 O-ring 18 Fixing member 20 conductors

Continued on the front page F term (reference) 2F055 AA40 BB20 CC11 DD01 EE21 EE29 FF01 5E041 AA11 AA14 AA17 AA19 BD00 CA10

Claims (4)

[Claims] 1. A magnetostrictive element, at least one coil disposed around the magnetostrictive element, and a permanent magnet for applying a bias magnetic field substantially parallel to a weighting direction of the magnetostrictive element are housed in a casing. A pressure sensor using a magnetostrictive element, wherein a change in magnetic permeability of the magnetostrictive element is detected as a change in inductance of the coil. 2. A pressure sensor using a magnetostrictive element according to claim 1, wherein said magnetostrictive element is a giant magnetostrictive element formed in a columnar shape from a magnetic material containing a lanthanoid element system and an iron group element system. 3. A pressure sensor using a magnetostrictive element according to claim 1, wherein a preload mechanism for applying a preload to the magnetostrictive element and absorbing expansion and contraction is provided in the casing. 4. A load is applied by bringing a spherical or hemispherical member into contact with weight receiving members on both sides of the magnetostrictive element, respectively, such that the load direction coincides with the center axis direction of the magnetostrictive element. Item 7. A pressure sensor using the magnetostrictive element according to Item 1, 2, or 3.