JP2004184189A - Magnetostriction torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensitive, accurate and inexpensive magnetostriction torque sensor easily processed so as to have magnetic anisotropy in a torque sensing part. <P>SOLUTION: In the magnetostriction torque sensor having a wound coil for applying a magnetic field around a rotational shaft and sensing the torque based on a coil impedance change due to distortion on the rotational shaft by the torque externally applied, first and second sensing parts having a wound linear magnetostriction material are provided on a surface of the rotational shaft. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetostrictive torque sensor that winds a coil for applying a magnetic field around a rotating shaft and detects the torque based on a change in impedance of the coil caused by distortion of the rotating shaft due to externally applied torque.
[0002]
[Prior art]
A non-contact type magnetostrictive torque sensor using the magnetostrictive effect is a coil wound around the rotating shaft made of a ferromagnetic material due to a change in magnetic permeability of the rotating shaft itself according to the distortion when torque is applied to the rotating shaft. A change in impedance of the AC resistance including the change occurs, and the torque is detected from the change in impedance.
[0003]
Conventionally, such a magnetostrictive torque sensor has a magnetic anisotropy in a direction inclined with respect to the center axis of the rotating shaft on which the torque acts in order to accurately detect the torque and improve the temperature characteristics. Attempts have been made to arrange the sets of magnetostrictive materials at an angle so as to be directed in opposite directions.
[0004]
For example, in Patent Document 1 shown below, a technique is disclosed in which a spiral groove is formed in a magnetostrictive material forming a torque sensing portion, and the magnetostrictive material is joined by sandwiching the magnetostrictive material with general steel to exhibit magnetic anisotropy. Disclosure has been made.
[0005]
In addition, a technology has been proposed in which a film of a magnetostrictive material is formed on a torque sensing portion and heat treatment is performed while applying a torsional stress to a rotating shaft to thereby exhibit magnetic anisotropy (for example, Patent Document 1). 2).
[0006]
[Patent Document 1]
JP 2001-330524 A
[Patent Document 2]
JP-A-2002-82000
[Problems to be solved by the invention]
Of the above-mentioned conventional techniques, in the case of the technique disclosed in Patent Literature 1, it is troublesome to perform processing for forming a groove, which is troublesome, and of course, there is a possibility that the torque detection characteristics may vary, It was inefficient and expensive.
[0009]
Further, in the case of the technology disclosed in Patent Document 2, heat treatment is performed in a state where a torsional stress is applied, so that the size of the film formation chamber is limited and the number of steps before the heat treatment is increased. There was a point to be improved in terms of cost.
[0010]
The present invention has been made in view of the above, and an object thereof is to provide easy processing for imparting magnetic anisotropy to a torque sensing portion, high sensitivity and high accuracy, and further reduction in cost. An object of the present invention is to provide a magnetostrictive torque sensor that can be achieved.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention according to claim 1 winds a coil for applying a magnetic field around a rotating shaft, and changes impedance of the coil due to distortion of the rotating shaft due to externally applied torque. In the magnetostrictive torque sensor for detecting the torque based on the above, the gist of the present invention is to provide a first and a second sensing portion formed by winding a linear magnetostrictive material on the surface of the rotating shaft.
[0012]
According to the first aspect of the present invention, by providing a magnetostrictive torque sensor provided with first and second sensing portions in which a linear magnetostrictive material is wound around the surface of a rotating shaft, the torque is increased. Processing for imparting magnetic anisotropy to the sensing part is easy, high sensitivity and high accuracy, and further cost reduction can be realized.
[0013]
According to a second aspect of the present invention, in the first aspect, the magnetostrictive material is an iron-based alloy having soft magnetism.
[0014]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the first and second sensing portions are arranged such that any one of axes perpendicular to a longitudinal central axis of the rotation axis is a symmetric axis. The gist of the present invention is to have magnetic anisotropy pointing in mutually symmetric directions.
[0015]
According to the third aspect of the present invention, two portions for sensing the torque on the rotating shaft are provided, and the magnetic anisotropy of each sensing portion has a magnetic anisotropy in a direction perpendicular to the longitudinal direction of the rotating shaft. By arranging the two sensing portions so as to be symmetrical, it is possible to provide a magnetostrictive torque sensor that can improve the temperature characteristics with higher accuracy.
[0016]
According to a fourth aspect of the present invention, in the first aspect of the present invention, the linear magnetostrictive material is fixed to the rotating shaft by applying a tensile or compressive stress. Make a summary.
[0017]
According to a fifth aspect of the present invention, in the first aspect of the present invention, the linear magnetostrictive material is an elastic body having an end fixed on the rotating shaft. And
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings.
[0019]
FIG. 1 is a partial cross-sectional view illustrating a configuration of a magnetostrictive torque sensor according to an embodiment of the present invention. The magnetostrictive torque sensor 1 shown in FIG. 1 includes a rotating shaft 11 that rotates by an external torque, and sensing units 13A and 13B (first and second sensing units) that directly sense the torque on the rotating shaft 11. And coils 15A and 15B wound around the sensing parts 13A and 13B, respectively, and a yoke 17 for accommodating the above-mentioned parts.
[0020]
The rotating shaft 11 is rotatably supported with respect to the main body of the magnetostrictive torque sensor 1 via bearings 19A and 19B. The rotating shaft 11 may be a non-magnetic material or a ferromagnetic material depending on the state of the magnetic flux passing therethrough. In FIG. 1, both ends of the rotating shaft 11 have different shapes. This assumes that the bearing 19A is connected to the motor while the bearing 19B is connected to the brake, and the rotating shaft 11 is rotated by the motor, and the torque generated when the brake is applied is applied to the rotating shaft 11. However, the configuration at both ends is not limited to this, and the following description does not change even when both ends have other shapes.
[0021]
The yoke 17 is made of a magnetic material, and recirculates a magnetic flux generated by a current flowing through the coil together with the rotating shaft 11 to form a magnetic path of the magnetic flux.
[0022]
The sensing portions 13A and 13B have magnetic anisotropy in a direction forming a predetermined inclination angle that is greater than 0 degree and smaller than 90 degrees with respect to the central axis in the longitudinal direction of the rotating shaft 11. Magnetic anisotropy is a tendency of macroscopic magnetization to be directed in a certain direction of a magnetic material. The direction in which magnetization is stabilized in the absence of an external magnetic field, that is, the internal energy (or magnetic anisotropic energy) is The direction of stabilization is called the easy axis.
[0023]
In order to impart such magnetic anisotropy, a portion of the rotating shaft 11 around which the coil 15A or 15B is wound is a linear member made of a magnetostrictive material such as an iron-based alloy having soft magnetism. 31A and 31B are densely wound so as to exhibit magnetic anisotropy in a plurality of directions described above. That is, the inclination directions of the linear members 31A and 31B with respect to the longitudinal center axis of the rotating shaft 11 coincide with the direction in which the easy axis of magnetization is directed due to the magnetic anisotropy. The linear members 31A and 31B may be wound around portions of the rotary shaft 11 where the coils 15A and 15B are wound around the outer periphery, but may be wound slightly longer than the portions in some cases. And may be wound slightly shorter.
[0024]
It is theoretically preferable that the inclination angles of the linear members 31A and 31B with respect to the rotation axis 11 form an angle of 45 degrees with respect to the central axis in the longitudinal direction of the rotation axis 11. Since it is technically difficult to form an angle of 45 degrees when winding the wire around the winding 11, besides that, besides being parallel to the longitudinal central axis of the rotating shaft 11, Thus, it is sufficient that the inclination angle is at least larger than 0 degrees and smaller than 90 degrees.
[0025]
Although not shown, a secondary coil may be further wound around each coil, and a torque may be detected by utilizing mutual induction between the coils and the coils 15A and 15B.
[0026]
FIG. 1 shows only the configuration of the main part of the magnetostrictive torque sensor 1, and some parts of the drawing are simplified. For example, a member such as a screw for fixing the magnetostrictive torque sensor 1 to an application target is not described.
[0027]
In the case shown in FIG. 1, it is assumed that the linear members 31 </ b> A and 31 </ b> B are wound around the surface of the rotating shaft 11 in a single line, but the angle of the rotating shaft 11 with respect to the central axis in the longitudinal direction is set as close to 45 degrees as possible. In that sense, it is preferable to form a multi-roll. However, in general, it is technically difficult to wind the multi-turn winding as the number of turns increases, so that the torque range required for sensing by the magnetostrictive torque sensor 1, the shaft diameter of the rotating shaft 11, etc. The number of lines is appropriately changed depending on various conditions.
[0028]
FIG. 2 is a side view of the magnetostrictive torque sensor 1 shown in FIG. As shown in the figure, the magnetostrictive torque sensor 1 preferably has a cylindrical side surface.
[0029]
FIG. 3 is an explanatory diagram schematically showing an action applied to the sensing units 13A and 13B when a torque is applied from the outside.
[0030]
In FIG. 3A, a torque is applied to rotate the sensing unit 13A in the P direction (counterclockwise when viewed from the left side of the sensing unit 13 in the figure). When such a torque is applied, a tensile strain is generated in the linear member 31A, and the magnetic permeability increases. As a result, the magnetic flux penetrating through the sensing section 13A also increases.
[0031]
On the other hand, in FIG. 3B, a torque for rotating the sensing unit 13B in the P direction is applied as in FIG. 3A. In this case, since the linear member 31B is oriented in a symmetrical direction with the vertical direction as the axis of symmetry in FIG. 3A, the direction of the strain is opposite to that in FIG. A compressive strain occurs in 31A, and the magnetic permeability of the sensing portion 13B decreases. As a result, the magnetic flux penetrating through the sensing portion 13B also decreases.
[0032]
As described above, by providing two sensing portions 13A and 13B having different directions of the axis of easy magnetization on the rotation shaft 11 by winding the linear members 31A and 31B, two sensing portions 13A and 13B for sensing the torque are provided. Since the difference between the changes in the self-inductance of the coils 15A and 15B increases according to the magnitude of the torque, a sensor output signal corresponding to the torque can be obtained by differentially amplifying the difference. The magnitude and direction of the torque can be detected from the magnitude of the sensor signal and the sign of the output value. Further, if the two sensing units 13A and 13B are used, in addition to the improvement of the sensitivity described above, the improvement of the temperature characteristic can be realized.
[0033]
In addition, it is of course possible to configure the magnetostrictive torque sensor according to the present embodiment by reversing the inclination directions of the linear members 31A and 31B provided in the two sensing units.
[0034]
In the case where magnetic anisotropy is developed by providing a groove or the like on the surface of the sensing portion as in the related art, an advanced technique for performing cutting or forging is required. On the other hand, the magnetostrictive torque sensor 1 of the present embodiment merely winds the linear members 31A and 31B around the rotating shaft 11, so that the winding of those linear members and the winding of the linear members Only processing for fixing 31A and 31B on the rotating shaft 11 is required. Of these, the winding can be easily carried out with existing equipment, and at that time, a sufficient tension or compression load may be applied and fixed. As a method of fixing the end of each linear member to the rotating shaft 11, for example, brazing of the entire linear member can be assumed. In addition, the diameter of the portion where the linear members 31A and 31B are wound around the rotating shaft 11 is slightly smaller than the outer diameter of the portion to provide a step, so that the ends of the linear members 31A and 31B are May be fixed.
[0035]
As described above, according to the magnetostrictive torque sensor 1 according to the present embodiment, it is possible to significantly reduce processing time and cost.
[0036]
Note that, as described above, the diameter and number of the linear members and the number of turns at the time of winding vary as appropriate according to the shaft diameter of the rotating shaft 11, the desired sensitivity according to the application object, and the like.
[0037]
According to the embodiment of the present invention described above, it is not necessary to perform difficult cutting such as digging a groove in a shaft or providing a slit in a sleeve, and there is no waste in a magnetostrictive material such as thermal spraying. In addition, material costs can be reduced.
[0038]
Further, since the linear member generally has high strength, it is possible to increase the strength of the sensing portion by winding the linear member.
[0039]
Further, since processing such as magnetic annealing is not required, the strength of the rotating shaft does not decrease due to the heat treatment.
[0040]
By the way, as the linear member, an elastic member which is an elastic body such as a spring made of a magnetostrictive material can be used. At this time, a method in which a load is applied to the elastic member by tension or compression to fix the end to a fixing hole provided in the rotating shaft 11 is also conceivable.
[0041]
FIG. 4 is an explanatory diagram in the case where one elastic member 41A and 41B are wound around the surface of the rotating shaft 11, respectively.
[0042]
FIG. 5 is an explanatory view showing the configuration of the sensing portions 13A and 13B which are also received on the rotating shaft 11 when the two elastic members 51A and 53A and 51B and 53B are wound respectively.
[0043]
Further, as shown in FIG. 6, the rectangular wire elastic members 61A and 61B can be wound around the rotating shaft 11. In this case, the cross-sectional area of the sensing portion is smaller than that of the above-described circular elastic member, but the inclination angle of the rotating shaft 11 with respect to the central axis in the longitudinal direction is easily approached to 45 degrees, so that the sensitivity of the sensor is improved. In addition to the above, it is also effective in further downsizing the sensor.
[0044]
As shown in FIG. 7, the sensitivity of the sensor can be improved by further winding the elastic members 71A and 71B around the outer periphery of the elastic members 73A and 73B.
[0045]
When each of the elastic members described above is fixed on the rotating shaft 11, the inner diameter of the elastic member to be applied is smaller than the diameter of the rotating shaft 11, and after lightly press-fitting, the end portion is fixed. It is also possible to braze the elastic member.
[0046]
According to the embodiment of the present invention described above, it is not necessary to perform difficult cutting such as digging a groove in a shaft or providing a slit in a sleeve, and there is no waste in a magnetostrictive material such as thermal spraying. In addition, material costs can be reduced.
[0047]
The magnetostrictive torque sensor described above is, for example, an electrically assisted bicycle or an electric wheelchair, or the like, in a small electric vehicle that uses an electric motor as an auxiliary driving force in addition to human power, when detecting externally applied torque by human power, or It is suitable to be provided on a steering shaft of a motorcycle such as a motorcycle, a four-wheel buggy, a water beagle or the like to detect a rotational torque at the time of operating a steering wheel. The size of the magnetostrictive torque sensor, the diameter of the rotating shaft, the absolute value of the torque to be detected, and the required accuracy differ for each of these applications. However, the basic configuration is none other than the above.
[0048]
By the way, the present invention is not limited to the above-described embodiment. Various design changes and the like can be made within a range in which the same effects as those of the above-described embodiment can be obtained. Of course, various application examples other than those described above can be assumed. In a sense, the present invention can include various embodiments and the like having the same effects as the above embodiments.
[0049]
【The invention's effect】
As is clear from the above description, according to the present invention, the processing for imparting magnetic anisotropy to the torque sensing portion is easy, the sensitivity is high, the accuracy is high, and the cost is reduced. And a magnetostrictive torque sensor that can perform the method.
[0050]
Further, according to the present invention, the strength of the linear member wound around the rotation axis is generally high, so that the strength of the entire sensing section can be increased.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view illustrating a configuration of a magnetostrictive torque sensor according to an embodiment of the present invention.
FIG. 2 is a side view in the direction of arrow A in FIG.
FIG. 3 is an explanatory view schematically showing a case where a torque is applied from the outside and a magnetic permeability changes in a sensing portion.
FIG. 4 is an explanatory diagram of a case where a sensing unit is formed by winding a single elastic member around a rotation shaft.
FIG. 5 is an explanatory diagram in a case where a sensing section is formed by winding two elastic members around a rotation shaft.
FIG. 6 is an explanatory diagram of a case where a sensing unit is formed by winding a rectangular wire elastic member around a rotation shaft.
FIG. 7 is an explanatory diagram of a case where a sensing unit is formed by superposing two elastic members and winding the same around a rotation shaft.
[Explanation of symbols]
1 Magnetostrictive torque sensor 11, 21 Rotating shaft 13, 13A, 13B, 23, 23A, 23B Sensing part 15A, 15B, 25A, 25B Coil 17, 27 Yoke 19A, 19B, 29A, 29B Bearing 31A, 31B Linear member 41A, 41B, 51A, 51B, 53A, 53B, 63A, 63B, 71A, 71B, 73A, 73B Elastic member 61A, 61B Rectangular wire elastic member

Claims (5)

A magnetostrictive torque sensor that winds a coil for applying a magnetic field around a rotation axis and detects the torque based on an impedance change of the coil caused by distortion of the rotation axis due to externally applied torque,
A magnetostrictive torque sensor, comprising: a first and a second sensing portion formed by winding a linear magnetostrictive material on a surface of the rotating shaft. The magnetostrictive torque sensor according to claim 1, wherein the magnetostrictive material is an iron-based alloy having soft magnetism. The first and second sensing units each have a magnetic anisotropy that is directed in mutually symmetric directions with one of axes orthogonal to a central axis in the longitudinal direction of the rotation axis as a symmetry axis. The magnetostrictive torque sensor according to claim 1 or 2, wherein: The magnetostrictive torque sensor according to any one of claims 1 to 3, wherein the linear magnetostrictive material is fixed to the rotating shaft by applying tensile or compressive stress. The magnetostrictive torque sensor according to any one of claims 1 to 3, wherein the linear magnetostrictive material is an elastic body having an end fixed on the rotating shaft.

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