Compensating magnetic interference for electronic magnetometer sensors

• US 9,506,755 B2
• Filed: 06/18/2014
• Issued: 11/29/2016
• Est. Priority Date: 06/20/2013
• Status: Active Grant

• Current Assignee: STMicroelectronics China Investment Co Ltd (STMicroelectronics NV)
• Original Assignee: STMicroelectronics China Investment Co Ltd (STMicroelectronics NV)
• Inventors: Tu, Travis, Fang, Shu
• Primary Examiner(s): FULTON, CHRISTOPHER W
• Application Number:
  US14/308,076
• Publication Number:
  US 20150000145A1
• Time in Patent Office: 895 Days
• Field of Search: 333/57, 333/56
• US Class Current: 1/1
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01R 33/007 Environmental aspects, e.g. temperature variations, radiation, stray fields G01R33/025 takes precedence
• CPC Class Codes: G01R 33/0082 Compensation, e.g. compensating for temperature changes

Abstract

Apparatus and methods to compensate hard iron and soft iron magnetic interference in magnetic sensing devices are described. Hard and soft iron interference may be modeled using an ellipsoidal surface generated by a plurality of magnetic field measurements. A displacement of the ellipsoid from a reference frame origin corresponds to hard iron or permanent magnetic field interference. A shape and orientation of the ellipsoid corresponds to soft iron magnetic field interference. The ellipsoidal surface may be analyzed to obtain magnetic field compensation values for cancelling hard iron and soft iron interference.

Claims

1. An electronic device configured to sense a magnetic field and compensate at least one measured value, the electronic device comprising:

a magnetometer configured to measure at least one value of an external magnetic field along at least one axis; and

at least one processor configured to receive magnetic field data from the magnetometer and to calculate radii r₁, r₂ and r₃ of an ellipsoid, wherein the magnetic field data is representative of the ellipsoid,

wherein the at least one processor is configured to calculate eigenvalues λ

₁, λ

₂, and λ

₃ of a matrix of coefficients relating to an equation that is descriptive of the ellipsoid and to calculate the radii r₁, r₂, and r₃ of the ellipsoid as

r₁=1/√

{square root over (λ

₁)}, r₂=1/√

{square root over (λ

₂)}, r₃=1/√

{square root over (λ

₃)},

and wherein the at least one processor is further configured to compensate, based on the calculated radii, at least one measured value of the external magnetic field.

2. The device of claim 1, further comprising a visual display wherein the at least one processor is further configured to cause display of a navigational aid on the visual display to a user of the device.

3. The device of claim 2, wherein the navigational aid is representative of a compass heading.

4. The device of claim 1, wherein the at least one processor comprises a field programmable gate array.

5. The device of claim 1, wherein the at least one processor is further configured to calculate a location of the center of the ellipsoid with respect to an origin of a spatial frame of reference.

6. The device of claim 5, wherein the spatial reference frame is aligned to the device.

7. The device of claim 5, wherein the at least one processor is further configured to determine an offset calibration parameter to compensate for a displacement of the location of the center of the ellipsoid from the origin of the spatial frame of reference.

8. The device of claim 7, wherein the at least one processor is further configured to apply the offset calibration parameter to measured magnetic field data received from the magnetometer.

9. The device of claim 1, wherein the at least one processor is further configured to determine recovery calibration parameters to compensate for differences of the radii of the ellipsoid from a spherical surface.

10. The device of claim 9, wherein the at least one processor is further configured to apply the recovery calibration parameters to measured magnetic field data received from the magnetometer.

11. The device of claim 9, wherein the at least one processor is further configured to calculate spatial orientations of the radii.

12. The device of claim 9, wherein the at least one processor is configured to determine recovery calibration parameters by calculating eigenvalues of a matrix of coefficients, wherein the coefficients relate to an equation that is descriptive of the ellipsoid.

13. A method for compensating a sensed magnetic field wherein the magnetic field is sensed by a device having at least one processor and a magnetic sensor, the method comprising:

measuring, with a magnetic sensor, at least one value of an external magnetic field along at least one axis;

receiving, by the at least one processor, magnetic field data from the magnetometer;

calculating, by the at least one processor, a center and radii of an ellipsoid, wherein the magnetic field data is representative of the ellipsoid; and

compensating, by the at least one processor, at least one measured value of the external magnetic field based on the calculated center and the calculated radii.

14. The method of claim 13, further comprising:

displaying, on a visual display of the device, a navigational aid to a user of the device.

15. The method of claim 14, wherein the navigational aid is representative of a compass heading.

16. The method of claim 13, wherein the at least one processor comprises a field programmable gate array.

17. The method of claim 13, wherein a location of the center of the ellipsoid is calculated with respect to an origin of a spatial frame of reference that is aligned to the device.

18. The method of claim 17, further comprising determining, by the at least one processor, an offset calibration parameter to compensate for a displacement of the location of the center of the ellipsoid from the origin of the spatial frame of reference.

19. The method of claim 18, further comprising applying, by the at least one processor, the offset calibration parameter to measured magnetic field data received from the magnetometer.

20. The method of claim 13, further comprising:

calculating eigenvalues λ

₁, λ

₂, and λ

₃ of a matrix of coefficients, wherein the coefficients relate to an equation that is descriptive of the ellipsoid,

wherein the radii of the ellipsoid are r₁, r₂, and r₃ and calculating the radii of the ellipsoid includes calculating;

r₁=1/√

{square root over (λ

₁)}, r₂=1/√

{square root over (λ

₂)}, r₃=1/√

{square root over (λ

₃)}.

21. The method of claim 20, further comprising determining, by the at least one processor, recovery calibration parameters to compensate for differences of the radii of the ellipsoid from a spherical surface.

22. The method of claim 21, further comprising applying, by the at least one processor, the recovery calibration parameters to measured magnetic field data received from the magnetometer.

23. The method of claim 21, wherein the at least one additional parameter further includes spatial orientations of the radii.

24. The method of claim 21, wherein the determining recovery calibration parameters comprises calculating, by the at least one processor, eigenvalues of a matrix of coefficients, wherein the coefficients relate to an equation that is descriptive of the ellipsoid.