METHOD AND APPARATUS FOR FAST MAGNETOMETER CALIBRATION

• US 20150354980A1
• Filed: 03/05/2014
• Published: 12/10/2015
• Est. Priority Date: 03/05/2013
• Status: Active Grant

• Current Assignee: Trusted Positioning Inc. (TDK Corporation)
• Original Assignee: Trusted Positioning Inc. (TDK Corporation)
• Inventors: Georgy, Jacques, Abdelfatah, Walid, Noureldin, Aboelmagd, Wahdan, Ahmed
• Granted Patent: US 10,337,884 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 17/02 Magnetic compasses
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A method and apparatus for fast magnetometer calibration with little space coverage is described herein. The present method and apparatus is capable of performing both 2-dimensional (2D) and 3-dimensional (3D) calibration for a magnetometer (magnetic sensor) and calculating calibration parameters. The present method and apparatus does not need the user to be involved in the calibration process and there are no required specific movements that the user should perform. The present method and apparatus performs magnetometer calibration in 2D or 3D depending on the natural device movements whatever the application that the magnetometer is used in.

Claims

1. A method for fast magnetometer calibration from natural motion with little space coverage, the method comprising the steps of:

a) obtaining earth magnetic field information in a region where the magnetometer is located, the magnetic field information to be used as reference values;

b) collecting magnetometer readings;

c) determining sufficient space coverage; and

d) performing magnetometer calibration to calculate calibration parameters when the sufficient space coverage is available.

2. The method of claim 1, wherein the method is for performing 2-dimensional magnetometer calibration, wherein the earth magnetic field information is horizontal earth magnetic field information;

wherein the method further comprises obtaining heading information from a source different from the magnetometer, the heading information to be used as a second reference;

wherein determining sufficient space coverage uses the heading information; and

wherein the 2-dimensional calibration uses a relationship between the horizontal earth magnetic field information, the magnetometer readings, the heading information, and the calibration parameters.

3. The method of claim 1, wherein the method is for performing 3-dimensional magnetometer calibration utilizing 2-dimensional calibration and different sectors covering pitch and roll angles, wherein the earth magnetic field information is horizontal earth magnetic field information;

wherein the method further comprises obtaining heading information from a source different from the magnetometer, the heading information to be used as a second reference;

wherein the method further comprises obtaining pitch and roll angles;

wherein the method further comprises using the pitch and roll angles to level the magnetometer readings;

wherein the method further comprises using the pitch and roll angles to determine a current sector;

wherein determining sufficient space coverage for the current sector uses the heading information; and

wherein the 2-dimensional calibration for the current sector uses a relationship between the horizontal earth magnetic field information, the levelled magnetometer readings, the heading information, and the calibration parameters.

4. The method of claim 1, wherein the method is for performing 3-dimensional magnetometer calibration utilizing heading information from a source different from the magnetometer, wherein the method further comprises obtaining heading information to be used as a second reference;

wherein the method further comprises obtaining pitch and roll angles;

wherein determining sufficient space coverage uses the heading information and one or both of the pitch and roll angles; and

wherein the 3-dimensional calibration uses a relationship between the earth magnetic field information, the magnetometer readings, the pitch and roll angles, the heading information, and the calibration parameters.

5. The method of claim 1, wherein the method is for performing 3-dimensional magnetometer calibration utilizing gravity acceleration, wherein the method further comprises obtaining gravity acceleration;

wherein the method further comprises obtaining pitch and roll angles;

wherein determining sufficient space coverage uses the pitch and roll angles; and

wherein the 3-dimensional calibration uses a relationship between the earth magnetic field information, the magnetometer readings, the pitch and roll angles, the gravity acceleration, and the calibration parameters.

6. The method of claim 1, wherein the method is for performing 3-dimensional magnetometer calibration;

and wherein the method utilizes any one or any combination of the following;

(i) 2-dimensional calibration and use of different sectors covering pitch and roll angles;

(ii) 3-dimensional calibration using heading information from a source different from the magnetometer;

or (iii) 3-dimensional calibration using gravity acceleration.

7. The method of any one of claim 1, 2, 3, 4, 5, or 6, wherein the method further comprises quality checks to determine if the calibration parameters are valid.

8. The method of any one of claim 1, 2, 3, 4, 5, 6, or 7, wherein the method further comprises conducting a post-calibration quality check to determine if the calibration parameters are valid.

9. The method of any one of claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the method further comprises conducting a periodic quality check that is called periodically starting after the calibration is done to check whether the calibration parameters are valid.

10. The method of any one of claim 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein the method further comprises storing the calibration parameters.

11. The method of any one of claim 7, 8, or 9, wherein the method further comprises shelving the calibration parameters for future use.

12. The method of claim 11, wherein the shelving of the calibration parameters happens even if quality checks determine that the calibration parameters are not valid.

13. A device comprising:

a. a magnetometer;

b. a processor, coupled to receive readings from the magnetometer, and operative to perform magnetometer calibration from natural motion with little space coverage, wherein the processor is operative to;

i) obtain earth magnetic field information in a region where the magnetometer is located, the magnetic field information to be used as reference values;

ii) collect magnetometer readings;

iii) determine sufficient space coverage; and

iv) perform magnetometer calibration to calculate calibration parameters when the sufficient space coverage is available.

14. The device of claim 13, wherein the processor is operative to perform 2-dimensional magnetometer calibration;

wherein the earth magnetic field information is horizontal earth magnetic field information;

wherein the processor is further operative to obtain heading information from a source different from the magnetometer to be used as a second reference;

wherein the determination of sufficient space coverage uses the heading information, and wherein the 2-dimensional calibration uses a relationship between the horizontal earth magnetic field information, the magnetometer readings, the heading information, and the calibration parameters.

15. The device of claim 13, wherein the processor is operative to perform 3-dimensional magnetometer calibration utilizing 2-dimensional calibration and different sectors covering pitch and roll angles;

wherein the earth magnetic field information is horizontal earth magnetic field information;

wherein the processor is further operative to obtain heading information from a source different from the magnetometer to be used as a second reference;

wherein the processor is further operative to obtain pitch and roll angles;

wherein the processor is further operative to use the pitch and roll angles to level the magnetometer readings;

wherein the processor is further operative to use the pitch and roll angles to determine the current sector;

wherein the determination of sufficient space coverage for the current sector uses the heading information, and wherein the 2-dimensional calibration for the current sector uses a relationship between the horizontal earth magnetic field information, the levelled magnetometer readings, the heading information, and the calibration parameters.

16. The device of claim 13, wherein the processor is operative to perform 3-dimensional magnetometer calibration utilizing heading information from a source different from the magnetometer;

wherein the processor is further operative to obtain heading information to be used as a second reference;

wherein the processor is further operative to obtain pitch and roll angles;

wherein the determination of sufficient space coverage uses the heading information and one or both of the pitch and roll angles, and wherein the 3-dimensional calibration uses a relationship between the earth magnetic field information, the magnetometer readings, the pitch and roll angles, the heading information, and the calibration parameters.

17. The device of claim 13, wherein the processor is operative to perform 3-dimensional magnetometer calibration utilizing gravity acceleration;

wherein the processor is further operative obtain gravity acceleration;

wherein the processor is further operative to obtain pitch and roll angles;

wherein the determination of sufficient space coverage uses the pitch and roll angles, and wherein the 3-dimensional calibration uses a relationship between the earth magnetic field information, the magnetometer readings, the pitch and roll angles, the gravity acceleration, and the calibration parameters.

18. The device of claim 13, wherein the processor is operative to perform 3-dimensional magnetometer calibration;

and wherein the processor is operative to utilize any one or any combination of the following;

(i) 2-dimensional calibration use of different sectors covering pitch and roll angles;

(ii) 3-dimensional calibration using heading information from a source different from the magnetometer;

or (iii) 3-dimensional calibration using gravity acceleration.

19. The device of any one of claim 13 or 14, wherein the magnetometer is a two-axial magnetometer.

20. The device of any one of claim 13, 14, 15, 16, 17 or 18, wherein the magnetometer is a tri-axial magnetometer.

21. The device of any one of claim 13, 14, 15, 16, 17, 18, 19, or 20, wherein the magnetometer is part of a plurality of sensors.

22. The device of any one of claim 13, 14, 15, 16, 17, 18, 19, 20, or 21, wherein the device further comprises a receiver for receiving absolute navigational information about the device from an external source.