JP2001264187A - Magnetostrictive detection type force sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetostrictive detection type force sensor which can detect external stress with high sensitivity by improving the use efficiently of a magnetostrictive element. SOLUTION: The magnetostrictive detection type force sensor is equipped with a coil 5 for detection which has cylindrical winding, a magnetostrictive element 6 which is shorter than the winding width of the winding of the coil 5, and positioning member 7 and 8 which position the magnetostrictive element almost in the center in the winding width direction of the coil 5 and the positioning members 7 and 8 are made of ferromagnetic bodies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive detection type force sensor for measuring external stress acting on a magnetostrictive element by detecting a change in magnetic permeability of the magnetostrictive element with a detecting coil.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional magnetostriction detection type sensor 10 includes a cylindrical case 20 having a bottom.
The detection coil 50 wound around the bobbin 40 is inserted and arranged, the columnar magnetostrictive element 60 is housed inside the bobbin, and the lid 30 that is in contact with the upper end face of the magnetostrictive element 60 is attached. .

When a compressive stress is applied to the magnetostrictive detection type force sensor 10, the compressive stress is transmitted to the magnetostrictive element 60 via the lid 30, and the magnetic permeability of the magnetostrictive element 60 changes. This change in the magnetic permeability is detected by the detection coil 50.

[0004]

However, in the conventional magnetostriction detection type force sensor 10, the bottom surface inside the case 20 is formed flat, so that the lower end surface of the bobbin 40 around which the detection coil 50 is wound. Not only is the lower end surface of the magnetostrictive element 50 aligned, but also the lower surface of the lid 30 is formed flat, so that the bobbin 40 around which the detection coil 50 is wound.
Is aligned with the upper end surface of the magnetostrictive element 60, and the magnetostrictive element 60 becomes equal to or longer than the winding width of the detection coil 50.

As a result, near the two end faces of the magnetostrictive element 60, a large amount of leakage magnetic flux is generated because the magnetic permeability of the magnetostrictive element 60 is low. Therefore, the magnetostrictive element 60
However, there is a problem that the utilization efficiency of the magnetic field decreases, that is, the amount of magnetic flux per unit volume passing through the magnetostrictive element 60 decreases.

Therefore, the present invention provides a magnetostrictive detection type force sensor capable of reducing the leakage magnetic flux near the end face of the magnetostrictive element, improving the use efficiency of the magnetostrictive element, and detecting a highly sensitive external stress. The purpose is to do.

[0007]

According to the present invention, there is provided a magnetostrictive detection type force sensor comprising: a detecting coil having a cylindrical winding; a columnar magnetostrictive element having a winding width shorter than the winding width of the detecting coil; And a positioning member for positioning the magnetostrictive element substantially at the center in the winding width direction of the detection coil, wherein the positioning portion is made of a magnetic material. Thereby, the magnetostrictive element is arranged substantially at the center in the winding width direction of the detection coil.

Further, the positioning member includes a first member abutting on one end of the magnetostrictive element and a second member abutting on the other end, wherein the first and second members are made of a magnetic material. Things. Thereby, the first and second magnetostrictive elements are formed.
Is positioned in a state of being sandwiched between the members. At this time, since the first and second members are made of a magnetic material, most of the magnetic flux passing through the magnetostrictive element passes through the first and second members having high magnetic permeability without leaking to the detection coil side. Will be.

Further, in the magnetostrictive detection type force sensor of the present invention, a concave portion into which the magnetostrictive element fits is formed in the center of at least one end face of the first and second positioning members. Since the magnetostrictive element is usually slightly deformed in the radial direction of the magnetostrictive element by applying a compressive stress, when the magnetostrictive element is arranged in contact with a detection coil, a bobbin, or the like, The deformation is hindered, and the change in the magnetic flux is smaller than in the case where it is not. For this reason, by positioning the magnetostrictive element substantially at the center in the radial direction, the variation of the magnetic flux change in the magnetostrictive element is eliminated, and a highly reliable sensor is configured.

[0010] The bottom surface of the concave portion may be a flat surface which is equal to or larger than the end surface of the magnetostrictive element.
The side surface of the concave portion is formed of a tapered surface inclined toward the bottom surface. Thus, the end surface of the magnetostrictive element is guided to the bottom surface along the side surface of the concave portion, and the end surface of the magnetostrictive element comes into surface contact with the bottom surface of the concave portion of the positioning member.

Further, the magnetostrictive element, the detecting coil,
A frame surrounding the positioning member is provided, and the frame is made of a magnetic material. Thereby, a magnetic path is formed around the magnetostrictive element, the detection coil, and the pre-determining member.

Further, among the first and second members,
At least one is fixed to the frame. Thereby, the detection coil and the magnetostrictive element are arranged based on the member fixed to the frame.

[0013]

Embodiments of the present invention will be described below.

FIGS. 1 and 2 show a schematic configuration of a magnetostrictive detection type force sensor according to the first embodiment.

As shown in FIG. 1, a magnetostrictive detection type force sensor 1 according to the present embodiment includes a U-shaped first frame 2 made of a ferromagnetic material such as ferrite or iron, and a first frame 2 made of the same. And a flat plate-shaped second frame 3 fixed at both ends of the bobbin 4, a bobbin 4, a detection coil 5, a magnetostrictive element 6, a first positioning member 7, The second positioning member 8 and the like are arranged.

The first positioning member 7 is a columnar member made of a ferrite-based magnetic material and having a height T1. The first positioning member 7 is attached and fixed to the substantially center of the bottom surface of the first frame 2 using an adhesive or the like. Have been.

The second positioning member 8 is a columnar member made of a ferrite-based magnetic material and having a height T1. Is protruding. The protrusion 81 has a spherical end, and the spherical end penetrates the circular opening 31 provided at the center of the second frame 3 to abut on the object 9 to be measured. I have.

The upper end face of the first positioning member 7 contacts one end via a Teflon (registered trademark) sheet 61, and the other end contacts the lower face of the second positioning member 8 via a Teflon sheet 62. A columnar magnetostrictive element 6 having a height T0 is arranged so as to be in contact therewith.

The magnetostrictive element 6 is made of a magnetostrictive material containing a rare earth metal element and iron, that is, a material that generates a displacement when a magnetic field is applied, or a material that has reverse magnetostriction (Villary effect) in which a magnetic field is generated by applying a displacement. And made of, for example, a Ni—Fe magnetostrictive material, an RFe magnetostrictive material, or the like. In particular, it is desirable to use an RFe-based magnetostrictive material having an extremely large magnetostriction and called a giant magnetostrictive material. In this case, a very large change in magnetoresistance, a large output voltage,
A sensor having stable temperature characteristics and the like can be obtained.

The detection coil 5 has a thickness S1 at both ends.
Is formed by winding a normal enamel-coated copper wire of an appropriate thickness on a cylindrical bobbin 4 having a flange portion 41, and a first and a second portion at a substantially central portion of the bottom surface of the first frame 2. The positioning members 7 and 8 and the magnetostrictive element 6 are arranged so as to surround them. Further, the winding width S of the detection coil 5
0 is a dimension longer than the length T0 of the magnetostrictive element 6. That is, the length T0 of the magnetostrictive element 6 and the detection coil 5
Is configured to satisfy Expression 1 below.

[0021]

(Equation 1)

In the magnetostrictive detection type force sensor 1 having such a configuration, when a compressive stress acts on the projection 81 from the object 9 to be measured, the compressive stress is transmitted via the second positioning member 8 and the Teflon sheet 62 to the magnetostrictive element. 6 is transmitted. Thereby, a strain displacement occurs in the magnetostrictive element 6, and the magnetic permeability of the magnetostrictive element 6 changes. For this reason, the magnetic flux density of the magnetostrictive element 6 changes, the magnetic flux linked to the detection coil 5 changes, and the inductance of the detection coil 5 changes. Then, from the change in the inductance, the magnitude of the stress applied to the magnetostrictive element 6 can be detected. The detection coil 5
Various methods can be considered as a method of detecting the change in inductance of, for example, connecting an oscillation circuit to the detection coil 5 and detecting the oscillation frequency.

As described above, according to the magnetostrictive detection type force sensor 1 of the present embodiment, the position of the magnetostrictive element 6 in the winding width direction of the detecting coil 5 is determined by the first and second ferromagnetic materials. 2 is positioned near the center of the detection coil 5 by the positioning members 7 and 8 of the magnetostrictive element 6.
, The leakage flux near both end faces decreases. Thereby, the utilization efficiency of the magnetostrictive element 6 is improved, that is, the magnetostrictive element 6
Can increase the amount of magnetic flux per unit volume passing through. For this reason, when the magnetostrictive element 6 having the same shape as the magnetostrictive element 60 described in the related art is used, a change in magnetic flux appears more remarkably than in the related art, and the sensitivity as a sensor can be improved.

Further, according to the magnetostrictive detection type force sensor 1 of the present embodiment, the magnetostrictive element 6, the detecting coil 5, the first
Since the magnetic path is formed by surrounding the second positioning members 7 and 8 with the first and second frames 2 and 3 made of a ferromagnetic material, detection with higher sensitivity can be performed. Preferably, a frame that surrounds all of the magnetostrictive element 6, the detection coil 5, and the first and second positioning members 7, 8 may be used.

Further, according to the magnetostrictive detection type force sensor 1 of the present embodiment, since the first positioning member 7 is fixed to substantially the center of the bottom surface of the first frame 2, the position is used as a reference. The bobbin 4 around which the magnetostrictive element 6, the second positioning member 8, and the detection coil 5 are wound can be arranged, and assembly is facilitated.

FIG. 3 shows a schematic configuration of a magnetostriction detection type force sensor according to a second embodiment of the present invention. In addition, about the structure similar to 1st Embodiment, the same figure number is attached | subjected and the description is abbreviate | omitted.

As shown in the figure, the magnetostriction detecting type force sensor 1 according to the present embodiment has a first concave portion 72 substantially at the center of the upper end surface of the first positioning member 7 according to the first embodiment. The second positioning member 8 is provided with a second concave portion 82 at a substantially central portion on the lower surface thereof.

The first concave portion 72 has a bottom surface 72a formed of a circular flat surface having substantially the same shape as the lower end surface of the magnetostrictive element 6, and a side surface 72b formed with a tapered surface inclined toward the bottom surface 72a over the entire circumference. It is composed of

Further, the second recess 82 is provided with the first recess 72.
Similarly to the above, it is composed of a bottom surface 82a formed of a circular flat surface having substantially the same shape as the upper end surface of the magnetostrictive element 6, and a side surface 82b having a tapered surface inclined from the periphery toward the bottom surface 82a over the entire circumference. .

The magnetostrictive element 6 is arranged such that the lower end face is in contact with the upper end face of the first positioning member 7 via the Teflon sheet 61, and the upper end face is the second end face.
Is arranged so as to contact the lower surface of the positioning member 8 via the Teflon sheet 62.

At this time, the concave portion 7 of the first positioning member 7
2, the side surface 72b is formed in a tapered shape,
Along the side surface 72b, the lower end surface of the magnetostrictive element 6 is
It is guided to a position where it makes surface contact with the bottom surface 72a of the second. Similarly, the concave portion 82b of the second positioning member 8 is
Is formed in a tapered shape, so that the upper end surface of the magnetostrictive element 6 is guided along the side surface 82b to a position where the upper end surface comes into surface contact with the bottom surface 82a of the concave portion 82.

As described above, according to the present embodiment, the magnetostrictive element 6 is guided substantially at the center in the radial direction of the bobbin 4 around which the detection coil 5 is wound. Positioning can be easily performed. Thereby, the magnetostrictive element 6 can be arranged so that its side surface does not contact the inner peripheral surface of the bobbin 4, and a measurement error due to a change in the relative position between the magnetostrictive element 6 and the bobbin 4 in the radial direction, and the magnetostrictive element 6 There is no variation in measured values due to contact between the bobbin 4 and the side surface of the bobbin 4, and highly reliable measurement can be performed.

Although the present embodiment has been described with reference to the case where the concave portions are provided in both the first and second positioning members, the concave portions are provided in only one of the first and second positioning members. You may. In this case, the position in the radial direction of the magnetostrictive element is determined by the positioning member on the side where the concave portion is provided.

In this embodiment, the case where the side surface of the concave portion is formed in a tapered shape inclined with respect to the bottom surface has been described, but the side surface of the concave portion may be set at an arbitrary angle with respect to the bottom surface. Good. In this case, positioning of the magnetostrictive element in the radial direction is performed by fitting the magnetostrictive element into a concave portion of the positioning member.

In this embodiment, the case where the bottom surfaces of the concave portions of the first and second positioning members are formed to have substantially the same shape as the end surface of the magnetostrictive element has been described. It may be configured as long as it has a shape and size capable of making surface contact with the entire end face of the magnetostrictive element.

In each of the above-described embodiments,
Although the columnar member is used as the first and second positioning members, any member having a contact surface larger than the end surface of the magnetostrictive element may be used. For example, a prismatic or frustoconical member can be used.

As an application example of the magnetostrictive detection type force sensor 1 according to the present invention, for example, it is used as a pedaling torque sensor in an electric assisted bicycle (assisted electric bicycle) equipped with an electric motor and a battery serving as a power source thereof. In this case, the sensor is attached to a pedal portion of the bicycle to detect a pedaling torque, and if necessary, adds an auxiliary power from an electric motor to facilitate traveling on a slope or the like. Further, as another application example, it is used as a weight sensor for detecting the weight of laundry in a fully automatic washing machine using a microcomputer. In this case, the washing time and the like are automatically set according to the weight of the laundry detected by the sensor.

[0038]

According to the present invention, the position of the magnetostrictive element in the direction of the winding width of the detecting coil is positioned near the center of the detecting coil by the positioning member made of a ferromagnetic material. , The leakage magnetic flux near the end face decreases. Thereby, the utilization efficiency of the magnetostrictive element can be improved, that is, the amount of magnetic flux per unit volume passing through the magnetostrictive element can be increased, and the sensitivity as a sensor can be improved.

[Brief description of the drawings]

FIG. 1 is a top view illustrating a schematic configuration of a magnetostriction detection type force sensor according to a first embodiment of the present invention.

FIG. 2 is a partially cutaway side view showing a schematic configuration of the magnetostrictive detection type force sensor of FIG.

FIG. 3 is a partially cutaway side view illustrating a schematic configuration of a magnetostriction detection type force sensor according to a second embodiment of the present invention.

FIG. 4 is a partially broken side view showing a schematic configuration of a conventional magnetostriction detection type force sensor.

[Explanation of symbols]

 1: Magnetostrictive detection type force sensor 2: First frame 3: Second frame 4: Bobbin 5: Detection coil 6: Magnetostrictive element 7: First positioning member 8: Second positioning member 9: Measurement object

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) (72) Inventor Hideaki Aoki 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. ( 72) Inventor Minoru Nakanishi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Bungo Kondo 2-5-2-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. In company

Claims (6)

[Claims] 1. A detection coil having a cylindrical winding,
A magnetostrictive detection type force sensor including a columnar magnetostrictive element shorter than the winding width of the winding of the detection coil, and a positioning member that positions the magnetostrictive element substantially at the center in the winding width direction of the detection coil, A magnetostrictive detection type force sensor, wherein the positioning portion is made of a magnetic material. 2. The positioning member includes a first member in contact with one end of the magnetostrictive element and a second member in contact with the other end, and the first and second members are made of a magnetic material. 2. The magnetostrictive detection type force sensor according to claim 1, wherein: 3. A magnetostrictive detection type force sensor according to claim 2, wherein a concave portion in which said magnetostrictive element is fitted is recessed at a central portion of at least one end face of said first and second positioning members. 4. A bottom surface of the concave portion is formed of a plane equal to or larger than an end surface of the magnetostrictive element, and a side surface of the concave portion is formed of a tapered surface inclined toward the bottom surface. 3. The magnetostrictive detection type force sensor according to 3. 5. The magnetostrictive detection type force sensor according to claim 1, further comprising a frame surrounding the magnetostrictive element, the detection coil, and the positioning member, wherein the frame is made of a magnetic material. 6. The magnetostrictive detection type force sensor according to claim 4, wherein at least one of the first and second members is fixed to the frame.