JP2008145165A - Magnetoelastic torque sensor and hysteresis elimination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the hysteresis in a torque transducer element. <P>SOLUTION: A coil is excited with alternative current and generates magnetism for saturating the torque transducer element. The magnetic saturation of the torque transducer element is imparted by the alternative frequency exceeding the coercive force of the material. By slowly reducing the alternative current, undesired magnetism is essentially made to reduce. The coil assembly is excited by the amplitude and frequency only serving to eliminate the undesired components of the magnetism. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetoelastic torque sensor and a method of eliminating hysteresis in such a sensor, and more particularly to a method of erasing residual magnetism from a required magnetic flux path.

  A magnetoelastic torque sensor utilizes one or more magnetoelastic bands supported on a substrate. The magnetoelastic band has a circumferential remanence due to the magnetocrystalline anisotropy of the material. When torque is applied to the base material, spiral stress is generated in the magnetoelastic material, which shifts the magnetic flux path from the circumferential direction to the spiral direction. A magnetic measuring device is used to measure the axial component of magnetism, and this is used to determine the torque.

  However, there is a problem that even if the torque acting on the substrate is released, a part of the magnetism remains. The axial residual magnetism in the magnetoelastic band causes a zero point shift of the torque sensor. Such a zero value shift is called hysteresis. As a known method of erasing the magnetism in the magnetic body, there is a method of arranging a structure in an alternating magnetic field having a peak amplitude exceeding the coercive force of the magnetoelastic material. However, such a method requires another device that cannot be used during operation, and erases all the magnetic components contained in the required circumferential magnetism.

  Therefore, it is desired to develop a method and apparatus for selectively erasing only the axial residual magnetism that produces hysteresis while maintaining the required circumferential residual magnetism.

Summary of the Invention

  One embodiment of the method according to the present invention allows the elimination of hysteresis by applying an alternating magnetic field from the coil to the torque transducer element to eliminate residual magnetism along the axis of the torque transducer shaft.

  In the method of the present invention, the coil is supported axially around the torque transducer. The coil is excited by an alternating current with sufficient amplitude to generate an alternating magnetic field with an amplitude comparable to the coercivity of the material making up the torque transducer. Excitation of the residual magnetism in the axial direction is possible by exciting the torque transducer. By properly aligning the coil with the magneto-elastic band of the torque transducer, axial residual magnetism can be eliminated without disrupting the required circumferential magnetism present in the transducer's magneto-elastic band.

  Accordingly, the torque sensor of the present invention includes a coil assembly that is magnetized by alternating current to generate magnetism that reduces or eliminates undesirable residual magnetism without disturbing the required magnetic components in the torque transducer.

  These and other features of the present invention will be described in detail below with reference to the accompanying drawings.

  FIG. 1 schematically illustrates a portion of the torque transducer sensor assembly 10. The torque sensor 10 includes a torque transducer element 15 comprising a substrate or shaft 12 that supports a magnetoelastic ring 16. When the torque 26 acts on the shaft 12, the magnetoelastic ring 16 transmits this to the magnetoelastic ring 16.

  Circumferential magnetism 18 exists in the magnetoelastic ring material 16. The circumferential direction of the magnetism 18 is a state in which the torque transducer element 15 is neutral, that is, no torque is applied. While the torque 26 is acting, a part of the magnetism 18 appears as an axial component and deviates from the circumferential direction. An axial component of the magnetism 18 is indicated by an arrow 20. This axial component 20 of the magnet 18 is measured by a magnetometer 22. The magnetometer 22 is arranged with respect to the transducer element 15 so as to detect the axial component 20 of the magnetism 18. However, even if the torque acting on the shaft 12 is released, a part of the axial component 20 of the magnetism 18 remains. The residual axial component 20 of the magnet 18 distorts the zero position of the torque transducer element 15, resulting in undesirable hysteresis.

  Thus, the torque transducer assembly 10 of the present invention includes a magnetometer coil 22 comprising a plurality of magnet wires 24 wound coaxially with the torque transducer element 15. The coil 22 is connected to a power source 28 that supplies an alternating current 25. The alternating current 25 excites the coil 22 and generates an alternating magnetic field. The amplitude and frequency of the alternating current 25 are selected to remove the hysteresis-induced magnetic component 20 while keeping the circumferential component 18 intact.

  The alternating magnetic field 25 is selected to have an amplitude and frequency based on the particular material utilized for the torque transducer element 15. In the embodiment of the torque transducer element 15 made of 9310 steel alloy, a frequency of 60 Hertz with a peak field of 50 Oersted is utilized. Such a large alternating current eliminates the axial component 20 of the magnet 18 by exciting the transducer element 15. By eliminating the axial component 20 of the magnetic 18 that induces hysteresis, the zero point shift can be greatly reduced.

  When the torque is released and the axial component of the magnetism 20 that induces hysteresis is eliminated, the torque sensor operates with little or no hysteresis, allowing higher accuracy.

  As is well known, the excitation of the coil 22 by a large alternating current may interfere with the detection of the magnetism 18 by the magnetometer or magnetometer. However, the method of the present invention provides a magnetic detection function by alternating the amplitude and frequency of alternating current, and also provides a function of eliminating magnetism that induces hysteresis.

  Another embodiment 60 of the torque transducer shown in FIG. 3 includes a coil assembly 65 that operates solely for the degaussing function to selectively erase the hysteresis induced axial component of the magnet 68. A known magnet vector detection device 62 is embedded in the coil assembly 65. These magnet vector detection devices transmit magnetic measurements to a known control device 64. The coil assembly 65 operates to selectively erase the magnetic axial component 66. The coil assembly 65 of the torque sensor embodiment 60 is supplied with an alternating current 70 to excite the coil 65, and a period of amplitude and frequency set so as to eliminate an undesirable hysteresis component of magnetism generated under the influence of the torque 26. To generate dynamic excitation.

  FIG. 4 is a flowchart showing a method 80 for partially erasing magnetism in order of steps. The method begins with the first torque acting on the substrate shaft 12 (82). Torsion or torque acting on the shaft 12 causes torsion not only in the shaft 12 but also in the magnetoelastic band 16. The twist of the magnetoelastic band 16 is detected by a magnetic detection device (84). When the torque is released (86), part of the magnetism generated by the torque remains. The axial component of the magnetic hysteresis causes a shift in the magnetism read by the torque transducer element 15. By eliminating this shift caused by the magnetic axial component that induces hysteresis, the accuracy of the torque transducer assembly can be increased. The coil surrounding the torque transducer element 15 is excited with alternating current (88). It is set to provide the amplitude and frequency necessary to generate a peak amplitude alternating field that exceeds a substantial portion of the coercivity of the material. The amplitude of the magnetism generated by the coil is sufficient to saturate the core material of the fluxgate device 62. The saturation of the fluxgate devices can be determined by a coil that directly surrounds these fluxgate devices in a known manner. The asymmetry of the voltage waveform in the fluxgate coil suggests that magnetism exists in the transducer element.

  Thus, the method and apparatus of the present invention increases the accuracy of the torque sensor by eliminating the magnetic axial component that causes the zero shift in torque measurement.

  While the preferred embodiment of the present invention has been described above, various modifications will occur to those skilled in the art within the scope of the present invention. Accordingly, the following claims should be studied to determine the true scope and content of this invention.

It is a perspective view which shows the Example of the torque transducer of this invention in a partial cross section. FIG. 6 is a perspective view, partly in cross section, of another embodiment of the torque transducer of the present invention. FIG. 6 is a perspective view, partly in section, showing still another embodiment of the torque transducer of the present invention. It is a flowchart which shows the method of this invention in order of a step.

Claims (17)

In a method of removing magnetism that induces hysteresis from a magnetoelastic torque transducer,
a) supporting the coil concentrically with the magnetoelastic portion of the torque transducer;
b) selectively erasing residual magnetism that induces hysteresis by exciting the coil with alternating current of desired frequency and amplitude.   The method of claim 1, wherein step b) is a step of removing only the axial component of remanence.   The method of claim 1, wherein step b) is a step that does not affect a circumferential component of the magnetic polarization of the torque transducer.   The method of claim 1, wherein the frequency and amplitude are selected to include a magnetic peak amplitude that exceeds a substantial portion of the coercivity of the material comprising the torque transducer.   The method of claim 1, including a magnetometer supported about a torque transducer and including eliminating axial magnetism that induces hysteresis by alternately operating the magnetometer and the coil. .   The coil includes a magnetometer and is alternately excited with a detection AC frequency and amplitude that detects distortion in the magnetism of the torque transducer, and an AC frequency and amplitude for cancellation that selectively eliminates unwanted hysteresis-induced magnetic components. 6. The method of claim 5, wherein:   7. The method of claim 6, further comprising the step of generating a distortion signal based on a superposition of excitation air and magnetism generated by the torque transducer by periodically saturating the magnetic core.   The method of claim 1 including detecting magnetism in a torque transducer with a magnetic sensor disposed in the coil. In the torque sensor,
A substrate subjected to a torque load;
A belt-like magnetoelastic material that is supported by the substrate and generates magnetism that reflects the torque load in response to the torque load acting on the substrate;
A magnetic sensor for measuring magnetism;
The torque sensor comprising a coil that is arranged around the band-shaped magnetoelastic material and generates an alternating magnetic field that erases at least a part of the magnetism remaining in the band-shaped magnetoelastic material.   10. The assembly according to claim 9, wherein when the coil is excited, a magnetism is generated that erases an axial portion of the magnetism remaining in the belt-like magnetoelastic material.   11. An assembly according to claim 10, wherein the axial portion of the magnetism is erased when the torque acting on the substrate is released.   The assembly of claim 10, wherein the coil is disposed in a coaxial relationship about the substrate.   The assembly according to claim 10, wherein the coil has an axial length longer than or equal to an axial length of the belt-like magnetoelastic material.   The assembly of claim 10 including a power source for supplying alternating current to a coil that generates an alternating magnetic field.   15. The method of claim 14, wherein the power supply provides a first alternating current that generates a periodic magnetic saturation in the torque sensor and a second alternating current that selectively eliminates unwanted portions of remanence.   The method according to claim 15, wherein the coil is excited by selectively supplying the first alternating current and the second alternating current.   The method according to claim 9, wherein the coil includes a first coil and a second coil for detecting magnetism in the belt-like magnetoelastic material.

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