JP2003194639A - Force sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a force sensor capable of accurately measuring applied pressure. <P>SOLUTION: This force sensor is provided with an iron core 16 of which a part of the circumferential wall of a cylindrical body formed of a magnetic material is opened throughout the total length in its axial direction; a magnetostrictive member 11 housed in the iron core 16, having two mutually opposed surfaces 11b and 11c fixed to the inside surface of the iron core 16 and having a magnetic permeability varying corresponding to the applied pressure; an excitation coil 13 for generating magnetic flux in the iron core 16; and a sensing coil 15 for sensing the magnetic flux passing the iron core 16. Gaps 18 formed in the iron core 16 change in response to the pressure applied to the iron core 16. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a force sensor for measuring the amount of stress, load, weight, etc. applied to industrial machinery, consumer machinery, etc. by detecting changes in magnetic flux.

[0002]

2. Description of the Related Art Conventionally, in industrial machines, consumer machines and the like, as a measuring device for a load applied to mechanical components thereof, there are a strain gauge and a differential transformer. In these methods, when the strain gauge or differential transformer undergoes physical movement such as bending, stretching, or compression, the strain gauge or differential transformer outputs a signal corresponding to the movement and is applied from that signal. The load is measured.

For example, in a measuring device using a strain gauge, a strain gauge is attached to a load cell which is a mechanical component, and the magnitude of the load applied to the load cell is measured.
When a load is applied to the load cell, the strain gauge provided in the load cell is stretched or compressed, whereby the resistance value of the strain gauge changes and the voltage value across the strain gauge changes. The load applied to the load cell is calculated from this voltage value.

Further, in the measuring device using the differential transformer, the differential transformer has a hollow cylindrical pipe around which one primary coil and two secondary coils are wound, and A cylindrical metal core is movably formed in the center of the pipe, and the metal core is attached to the load cell and the pipe is attached to a fixed part of the machine to perform measurement. When a load is applied to the load cell, it corresponds to the displacement of the load cell,
The metal core moves in the pipe. As the metal core moves in the pipe, a difference in voltage is induced in the two secondary coils, so the amount of displacement of the metal core is detected from the voltage difference and the load applied to the load cell is calculated. is doing.

However, in such a method, the strain gauge,
A sensor such as a differential transformer has low durability against mechanical interference, and since the location where the sensor is provided is a movable part of a mechanical component, in order to accurately measure the applied load, Recalibration should be performed after the sensor is installed.

As a solution to this problem, Japanese Unexamined Patent Publication No.
There is a load detection device of 1-241955. This one uses a magnetic material whose inductance changes when pressure is applied, and by detecting the output voltage of the exciting coil that changes in response to this change in inductance,
The magnitude of the applied pressure is calculated.

[0007]

However, in this case, since the inductance of the magnetic body changes only in response to the applied pressure, the accuracy of the pressure value that can be measured by the load detecting device is the inductance with respect to the pressure. Will depend on the rate of change. That is, when a small pressure is applied to the extent that the inductance does not change, it may be impossible to detect the change in the pressure.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a force sensor capable of accurately measuring an applied pressure.

[0009]

In order to achieve the above object, the force sensor of the present invention has the following configuration. That is, according to the first aspect of the invention, the core body is provided with an opening portion that is opened over the entire axial length of a part of the peripheral wall of the cylindrical body made of a magnetic material, and is fixed to the inner peripheral surface of the core body. A magnetostrictive member that has two curved surfaces and is housed in the core body, and whose magnetic permeability changes according to the pressure applied to the two surfaces, and a magnetic flux can be generated in the core body or the magnetostrictive member. Magnetic flux generating means formed in, and a magnetic flux detecting means formed to be able to detect the magnetic flux passing through the core body or the magnetostrictive member, the open gap of the open portion and the magnetic permeability of the magnetostrictive member, It is characterized in that it changes according to the pressure applied to the core body.

According to a second aspect of the present invention, in the first aspect of the invention, the magnetic flux detecting means has a Hall element.

According to a third aspect of the invention, in the first or second aspect of the invention, the magnetic flux generating means has a permanent magnet.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, at least one of the two surfaces of the magnetostrictive member has a core of the core body with a magnetic rubber interposed therebetween. It is characterized in that it is fixed to the inner peripheral surface.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the invention, the core body has at least one of the inner peripheral surfaces at which the two surfaces of the magnetostrictive member are fixed to each other. In addition, it is characterized in that it has a protrusion having a substantially convex cross section.

According to a sixth aspect of the invention, in any one of the first to fifth aspects of the invention, the magnetostrictive member is provided with a stress concentration portion for stress concentration of applied pressure.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of a force sensor according to the present invention will be described below. As shown in FIG. 1, the force sensor according to the present embodiment is made of a magnetically permeable iron core 16 having two iron core halves 17 having a substantially U-shaped cross section, and a magnetic material sandwiched and fixed to the iron core halves 17. The amount of magnetic flux that is wound around the cylindrical magnetostrictive member 11, the exciting coil 13 as magnetic flux generating means for generating magnetic flux in the iron core 16, and the iron core leg portion 17a as the peripheral wall of the iron core 16, and passes through the iron core 16. And a detection coil 15 as a magnetic flux detection means for detecting FIG. 1A is a view of the iron core 16 seen from the axial direction, and FIG. 1B is a side view of the iron core 16.

As shown in FIG. 1A, the iron core half body 17
Is formed in a substantially U-shaped cross section, and the concave portion of one iron core half body 17 and the concave portion of the other iron core half body 17 are opposed to each other so that the respective iron core leg portions 17a are aligned and the iron core 16 A closed magnetic circuit type iron core 16 is formed by combining parts of the peripheral walls so as to form a gap 18 as an open portion that is open over the entire length in the axial direction. When the iron core 16 as the core body is considered as one, FIG.
As shown in (b), the iron core 16 has an opening formed by cutting out a part of its peripheral wall over the entire length in the axial direction.

The exciting coil 13 is wound around the iron core legs 17a of the two iron core halves 17, and the detection coil 15 is also wound around the iron core legs 17a of the two iron core halves 17 in the same manner.

The magnetostrictive member 11 has a magnetostriction of several tens of ppm.
The material which shows-several thousands ppm is used. Magnetostriction is tens of pp
Examples of materials showing m include ferrite to which Ni or Zn is added, pure Ni, Fe—Ni based alloys, Fe—Co based alloys, and the like. Further, alloys such as Tb, Dy, and Fe that have a magnetostriction of several thousands ppm may be used. One surface 11b of the magnetostrictive member 11 is fixed to the bottom surface of the recess of the one iron core half body 17, and the other surface 1
1c is fixed to the bottom surface of the recess of the other core half 17 and is sandwiched and fixed by combining and joining two core halves 17. That is, the two facing surfaces 11 b and 11 c of the magnetostrictive member 11 are provided so as to be inscribed in the inner peripheral surface of the iron core 16.

Next, the operation of the force sensor according to this embodiment will be described. When an alternating current is passed through the exciting coil 13, magnetic flux is generated in the iron core 16 and the magnetostrictive member 11. M2 represents the magnetic path of the magnetic flux passing through the iron core leg 17a-gap 18-iron core leg 17a, and M3 is the magnetic path of the magnetic flux passing through the iron core half body 17-magnetostrictive member 11-iron core half body 17. Is shown. A voltage is induced in the detection coil 15 wound around the iron core leg 17a by the magnetic flux passing through the iron core leg 17a.
If the amount of magnetic flux generated from the exciting coil 13 is constant, the voltage induced in the detecting coil 15 is constant.

When a compressive load P is applied to the iron core 16 as a pressure to push it down in the axial direction of the magnetostrictive member 11, the compressive load P is transmitted to the magnetostrictive member 11 via the iron core 16, and the magnetostrictive member 11 is transmitted. 11 is compressed. The magnetic resistance of the compressed magnetostrictive member 11 increases, so that the magnetic permeability decreases. At the same time, the gap 18 between the iron core leg portions 17a is
, The magnetic resistance of the magnetic path M2 is reduced. This reduces the amount of magnetic flux passing through the magnetic path M3 and increases the amount of magnetic flux passing through the magnetic path M2.

That is, when the compressive load P is applied to the magnetostrictive member 11, the magnetic path M is corresponding to the increase of the compressive load P.
Since the magnetic resistance of the magnetic path M2 decreases while the magnetic resistance of the magnetic path 3 increases, the amount of magnetic flux passing through the magnetic path M2 increases. Therefore, the amount of magnetic flux detected by the detection coil 15 increases, and the induced voltage also increases. The compressive load P applied to the iron core 16 is calculated from the voltage value.

Further, as another embodiment of the magnetostrictive member 11,
If formed as shown in FIG. 2, the compressive load P applied to the magnetostrictive member 11 concentrates on the stress-concentrated portion of the magnetostrictive member that has been processed, and the change in magnetic permeability can be increased.
Since the voltage can be induced more accurately with respect to the load change, it is possible to measure the load change in more detail.

FIG. 2A shows a hole 11 as a stress concentrating portion in a direction crossing the direction in which the load of the magnetostrictive member 11 is applied.
d is provided, and stress concentrates on the peripheral wall of the hole 11d. Further, in FIG. 2B, since the diameter of the central portion 11e is smaller than the diameter of the two surfaces 11b and 11c of the magnetostrictive member 11 fixed to the inner peripheral surface of the iron core 16, the central portion 11e is made smaller. Stress can be concentrated on. Also, FIG.
In (c), the magnetostrictive member 11 is provided with the cutout portion 11f in a direction intersecting with the direction in which the load is applied, and the stress can be concentrated on the peripheral wall provided with the cutout portion 11f.

Further, as another embodiment of the core body, the iron core 38 may be provided with a projection portion in which the portions fixed to the two surfaces 11b and 11c of the magnetostrictive member 11 are formed in a substantially convex cross section. In the embodiment shown in FIG. 3, the fixed portion is a tapered portion 39a formed in a tapered shape. Iron core 38
Is formed by combining two iron core halves 39 each having a tapered portion 39a and having a substantially U-shaped cross section. By forming in this way, the compressive load P transmitted through the iron core 38 can be concentrated and applied to the magnetostrictive member 11.

As yet another embodiment of the core body,
As shown in FIG. 4, two iron core halves 4 each having a substantially U-shaped cross section are provided.
3 is formed by forming a portion of the iron core 40 having the No. 1 fixed to the magnetostrictive member 11 into a hemispherical portion 41a having a semicircular cross section.
It is possible to obtain the same effect as the embodiment shown in FIG.
In the embodiment shown in FIGS. 3 and 4, the core body is provided with the protrusion, but the protrusion is formed separately from the iron core and is inserted between the iron core and the magnetostrictive member to form the force sensor. Even if it is formed, the same effect can be obtained.

As described above, according to the force sensor of the present invention, the magnetoresistive member 11 whose magnetic resistance changes by receiving pressure is provided, and the iron core half body 17 is formed so that the size of the air gap changes when receiving pressure. As a result, when the pressure is applied, the change in the voltage induced in the detection coil 15 can be made large, and the pressure can be accurately measured.

(Second Embodiment) A second embodiment of the force sensor according to the present invention will be described below. As shown in FIG. 5, in the present embodiment, an iron core 16 including two iron core halves 17, an exciting coil 13, a magnetostrictive member 11, and a Hall element 19 as magnetic flux detecting means are provided. is doing. The same components as those in the first embodiment are designated by the same reference numerals.

The Hall element 19 is made of silicon and is inserted into a gap formed when the iron core halves 17 are combined to receive the magnetic flux emitted from the end face of the iron core leg 17a. ing. In addition to silicon, indium antimony,
Alternatively, gallium, arsenic, or the like can be used.

As described above, since the Hall element 19 is used as the magnetic flux detecting means, the magnetic flux detecting means can be downsized and the force sensor as a whole can be downsized.

(Third Embodiment) A third embodiment of the force sensor according to the present invention will be described below. As shown in FIG. 6, in the present embodiment, the core member is an iron core 20 including two iron core halves 22 each having a substantially L-shaped cross section, and the magnetic flux generating means is a permanent magnet 21. The same parts as those in the first or second embodiment are designated by the same reference numerals.

When the two iron core halves 22 are assembled, the permanent magnet 21 is fixed so as to be sandwiched from both end faces. Further, since the generated magnetic field is always a constant DC magnetic field, the detection coil 15 can detect only the temporal change of the magnetic resistance of the magnetostrictive member 11, so that the differential value of the load can be detected.

As another embodiment, as shown in FIG. 7, a hall element 19 may be provided in the gap between the iron core leg portions 22a of the iron core half body 22 instead of the detection coil 15. In this case, Makes it possible to further reduce the size and cost.

As described above, since the permanent magnet 21 is used as the magnetic flux generating means, a power source for generating the magnetic flux in the iron core half body 22 is not required, and it is possible to further reduce the size and cost. .

(Fourth Embodiment) A fourth embodiment of the force sensor according to the present invention will be described below. As shown in FIG. 8, in the present embodiment, the core member is an iron core 23, and the iron core 23 is an iron core half body 24 formed so that a cutout portion is provided in a part of a side having a substantially rectangular cross section. When,
An iron core half 25 having a substantially convex cross section, and a coil spring 27 and a coil 29 as a magnetic flux generating means and a magnetic flux detecting means are provided, and the iron core half 24 and the iron core half 25 are provided. A gap 26 is provided between the and. The same components as those described in the first to third embodiments are designated by the same reference numerals. FIG. 8A shows
FIG. 8B is a view of the iron core 23 seen from its axial direction, and FIG. 8B is a view of the iron core 23 seen from its upper surface.

The iron core half body 25 is housed inside the iron core half body 24, and the apex portion 25a of the iron core half body 25 is combined so that it can project from the inside of the iron core half body 24 to the outside. Inner surface of 24 and collar 25 of iron core half 25
A coil spring 27 is provided between it and b. The coil spring 27 may be any one as long as it has elasticity and restoring force, and for example, a leaf spring or rubber can be used.

The magnetostrictive member 11 is provided between the inner side surface of the iron core half body 24 and the bottom surface of the flange portion 25b of the iron core half body 25, and a constant pressure is always applied by the coil spring 27.

The coil 29 is wound around the magnetostrictive member 11 to generate a magnetic flux in the magnetostrictive member 11 and detect the magnetic flux passing through the magnetostrictive member 11.
The magnetic flux generated in the magnetostrictive member 11 passes through the magnetic path M4 of the magnetostrictive member 11-iron core half 24-gap 26-iron core half 25.

Next, the operation of the force sensor according to this embodiment will be described. In the present embodiment, the magnetostrictive member 11
There is a case where the pressure applied to is a compressive load and a case where it is a tensile load.

First, the case where the applied pressure is a compressive load will be described. When the compressive load P is not applied to the apex 25a of the iron core half 25, the force exerted on the magnetostrictive member 11 is only the pressure from the coil spring 27, and the pressure is always constant. The induced voltage is also constant. Here, when a compressive load is applied to the apex 25a of the iron core half 25, the pressure applied to the magnetostrictive member 11 increases, and the magnetic resistance of the magnetostrictive member 11 increases,
Since the distance between the iron core half body 24 and the iron core half body 25 increases, the magnetic resistance of the entire magnetic path M4 increases and the magnetic flux flowing through the magnetostrictive member 11 decreases. As a result, the coil 29
The voltage induced by is reduced. The magnitude of the applied compressive load is calculated by using the voltage induced at this time and the induced voltage when the compressive load is not applied.

On the contrary, when the applied pressure is a tensile load, it is the same as when the compressive load P is applied until the pressure is applied to the apex portion 25a of the core half 25. Here, when the tensile load T is applied so that the iron core half body 25 is pulled, the force applied to the magnetostrictive member 11 decreases, so that the magnetic resistance becomes smaller and the iron core half body 24 and the iron core half body 25 become smaller. 25, the magnetic resistance of the entire magnetic path M4 also decreases, and the magnetic flux flowing through the magnetostrictive member 11 increases. As a result, the voltage induced in the coil 29 increases. The magnitude of the applied tensile load T is calculated by using the voltage induced at this time and the induced voltage when the tensile load T is not applied.

As another embodiment, FIG. 9 shows that the magnetic flux generating means for generating magnetic flux is the exciting coil 31 and the magnetic flux detecting means is the hall element 19. In this case, the Hall element 19 is connected to the collar portion 25 of the iron core half 25.
It is provided between the bottom surface of b and the one surface 11b of the magnetostrictive member 11 to detect the amount of magnetic flux passing from the iron core half 25 to the magnetostrictive member 11 or in the opposite direction. By doing so, the magnetic flux detecting means can be downsized, and the force sensor as a whole can be downsized.

As another embodiment, as shown in FIG. 10, the exciting coil 13 and the detecting coil 15 may be separately wound around the magnetostrictive member 11. In this case, when an alternating current is passed through the exciting coil 13, the voltage induced in the detecting coil 15 is detected as it is as a change in inductance, so that the applied load can be measured more accurately. .

As described above, since the magnetostrictive member 11 is provided with the coil spring 27 that constantly applies a constant pressure, not only the compressive load P but also the tensile load T can be measured. Is possible.

(Fifth Embodiment) The fifth embodiment of the force sensor of the present invention.
Embodiments of will be described below. As shown in FIG. 11, in the present embodiment, the core member is the core 34.
The iron core 34 has an iron core half body 35 and an iron core half body 37. The same parts as those in the first to fourth embodiments are designated by the same reference numerals.

The iron core half body 35 has a substantially rectangular cross section having a notch on one side of its side wall, and the end face of the notch is tapered. Further, the iron core half body 37 is formed such that a part thereof from the apex portion 37a to the brim portion 37b is tapered. By doing so, the facing surfaces of the iron core half body 35 and the iron core half body 37 are closer to each other when a tensile load is applied, and are separated from each other when a compressive load P is applied, so that the load is reduced. The amount of change in magnetoresistance when applied is larger.

In this embodiment, as in the fourth embodiment, the coil spring 27 is provided between the iron core halves 35 and 37, and the load applied to the magnetostrictive member 11 is the tensile load T. Alternatively, the applied load can be measured in either case of the compressive load P.

As described above, the iron core half body 35 and the iron core half body 3 are
By making a part of the shape of 7 a taper shape, the amount of change in magnetoresistance when a load is applied can be made larger, so the amount of change in the induced voltage also becomes larger and the applied load is It is possible to measure in more detail.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this embodiment and can be implemented in various forms.

[0049]

As described above, according to the present invention, a core body provided with an opening portion that is opened over the entire axial length of a part of the peripheral wall of a cylindrical body made of a magnetic material, and a core body Generates magnetic flux in the core body or magnetostrictive member, and the magnetostrictive member that has two surfaces fixed to the inner peripheral surface and is housed in the core body and whose permeability changes according to the pressure applied to the two surfaces. A magnetic flux generating means freely formed and a magnetic flux detecting means freely formed so as to detect the magnetic flux passing through the core body or the magnetostrictive member, and the open interval of the open portion and the magnetic permeability of the magnetostrictive member are the core body. Since it changes according to the pressure applied to, it is possible to increase the change in the magnetic permeability of the magnetostrictive member with respect to the change in the applied load value, and it is possible to measure the load value accurately. Play.

Further, if the magnetic flux detecting means is provided with a Hall element, there is an effect that the size can be reduced.

If the magnetic flux generating means is provided with a magnet, a power source for generating the magnetic flux becomes unnecessary,
It is possible to achieve further downsizing and cost reduction.

If at least one of the two surfaces of the magnetostrictive member is fixed to the inner peripheral surface of the core body via the magnetic rubber, the elasticity of the magnetic rubber causes the sidewall of the core body to receive an external force. Since the displacement amount of a part of the open space becomes larger, the change amount of the magnetic flux detected by the magnetic flux detecting means can be made larger than the applied external force, and the magnitude of the applied external force can be increased. It is possible to measure the height more accurately.

If the core body is formed to have a protrusion having a substantially convex cross section at at least one of the positions where the two surfaces of the magnetostrictive member are fixed to each other on the inner peripheral surface, the stress acting on the magnetostrictive member is reduced. It is possible to concentrate more and to increase the amount of change in the magnetic flux detected by the magnetic flux detecting means with respect to the applied external force, so that the magnitude of the applied external force can be measured more accurately. It has the effect of being able to.

Further, by providing the magnetostrictive member with a stress concentrating portion for concentrating the stress applied thereto, the stress acting on the magnetostrictive member can be further concentrated, and the external force applied is
Since the amount of change in the magnetic flux detected by the magnetic flux detecting means can be further increased, it is possible to more accurately measure the magnitude of the applied external force.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a force sensor according to the present invention.

FIG. 2 is a diagram showing another embodiment of the force sensor.

FIG. 3 is a diagram showing another embodiment of the force sensor.

FIG. 4 is a diagram showing another embodiment of the force sensor.

FIG. 5 is a diagram showing a second embodiment of a force sensor according to the present invention.

FIG. 6 is a diagram showing a third embodiment of a force sensor according to the present invention.

FIG. 7 is a diagram showing another embodiment of the force sensor.

FIG. 8 is a diagram showing a fourth embodiment of a force sensor according to the present invention.

FIG. 9 is a diagram showing another embodiment of the force sensor.

FIG. 10 is a diagram showing another embodiment of the force sensor.

FIG. 11 is a diagram showing a fifth embodiment of a force sensor according to the present invention.

[Explanation of symbols]

11 Magnetostrictive member 13 Excitation coil 15 Detection coil 16 iron core 18 Gap 19 Hall element 21 Permanent magnet 23 iron core 26 Gap 31 Excitation coil 34 iron core 38 iron core 39a taper part 40 iron core 41a hemisphere

Continued front page    (72) Inventor Shigeki Fujiwara             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.             Inside the company (72) Inventor Koichi Mitani             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.             Inside the company

Claims (6)

[Claims] 1. A core body having a cylindrical body made of a magnetic material, and an opening portion provided on a part of a peripheral wall of the cylinder body so as to be opened over its entire length in the axial direction, and two core bodies fixed to an inner peripheral surface of the core body. A magnetostrictive member having a surface and housed in the core body, the magnetic permeability of which changes in response to pressure applied to the two surfaces, and a magnetic flux which is freely generated in the core body or the magnetostrictive member. A magnetic flux generating means, and a magnetic flux detecting means formed to be able to detect the magnetic flux passing through the core body or the magnetostrictive member,
A force sensor, wherein an opening interval of the opening portion and a magnetic permeability of the magnetostrictive member change according to a pressure applied to the core body. 2. The force sensor according to claim 1, wherein the magnetic flux detecting means has a Hall element. 3. The force sensor according to claim 1, wherein the magnetic flux generating means has a permanent magnet. 4. The at least one surface of the two surfaces of the magnetostrictive member is fixed to the inner peripheral surface of the core body via a magnetic rubber. Item 5. The force sensor according to any one of Items 3. 5. The core body has a protrusion having a substantially convex cross section at least at one of the positions on the inner peripheral surface where the two surfaces of the magnetostrictive member are fixed to each other. The force sensor according to claim 4. 6. The force sensor according to claim 1, wherein the magnetostrictive member is provided with a stress concentrating portion in which stress is concentrated by applied pressure.