System and Method for Calibrating an Accelerometer

• US 20120203486A1
• Filed: 02/08/2011
• Published: 08/09/2012
• Est. Priority Date: 02/08/2011
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Snow, Christopher Harris, Almalki, Nazih
• Granted Patent: US 8,676,528 B2
• Time in Patent Office: Days
• US Class Current: 702/96
• 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: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A method and system are provided for obtaining data for calibrating an accelerometer. The method and system operate by using at least one magnetometer reading to detect that a first orientation is being maintained; obtaining a plurality of accelerometer readings at the first orientation; using at least one magnetometer reading to detect that a plurality of additional orientations are being maintained and, for each orientation, obtaining a plurality of accelerometer readings at that orientation; determining calibration parameters comprising, for each axis of the accelerometer, at least one of a gain value and an offset value, using the plurality of accelerometer readings at the first and plurality of additional orientations; and applying the calibration parameters to subsequent accelerometer readings.

Claims

1. A method of calibrating an accelerometer, the method comprising:

using at least one magnetometer reading to detect that a first orientation is being maintained;

obtaining a plurality of accelerometer readings at the first orientation;

using at least one magnetometer reading to detect that a plurality of additional orientations are being maintained and, for each orientation, obtaining a plurality of accelerometer readings at that orientation;

determining calibration parameters comprising, for each axis of the accelerometer, at least one of a gain value and an offset value, using the plurality of accelerometer readings at the first and plurality of additional orientations; and

applying the calibration parameters to subsequent accelerometer readings.

2. The method according to claim 1, wherein detecting that the first and plurality of additional orientations are being maintained comprises determining that one or more values are being maintained substantially constant.

3. The method according to claim 2, wherein the one or more values are a function of both the at least one magnetometer reading and at least one accelerometer reading.

4. The method according to claim 3, wherein the one or more values are vectors obtained by combining a magnetometer vector with an accelerometer vector.

5. The method according to claim 4, wherein a first vector is obtained by determining a cross product of the magnetometer vector and the accelerometer vector and a second vector is obtained by determining a cross product of the accelerometer vector and the first vector.

6. The method according to claim 1, further comprising determining if the magnetometer readings are of a sufficient quality before determining whether or not the first orientation is being maintained.

7. The method according to claim 1, further comprising checking whether or not the accelerometer readings are of sufficient quality prior to the determining and applying operations.

8. The method according to claim 7, wherein the checking comprises determining whether or not at least some of the accelerometer readings lie within a predetermined sphere.

9. The method according to claim 1, wherein the gain and offset values are determined by applying a least squares estimation using the plurality of accelerometer readings at the first and plurality of additional orientations.

10. A computer readable storage medium comprising computer executable instructions for obtaining data for calibrating an accelerometer, the computer executable instructions comprising instructions for:

using at least one magnetometer reading to detect that a first orientation is being maintained;

obtaining a plurality of accelerometer readings at the first orientation;

using at least one magnetometer reading to detect that a plurality of additional orientations are being maintained and, for each orientation, obtaining a plurality of accelerometer readings at that orientation;

determining calibration parameters comprising, for each axis of the accelerometer, at least one of a gain value and an offset value, using the plurality of accelerometer readings at the first and plurality of additional orientations; and

applying the calibration parameters to subsequent accelerometer readings.

11. The computer readable medium according to claim 10, wherein detecting that the first and plurality of additional orientations are being maintained comprises determining that one or more values are being maintained substantially constant.

12. The computer readable medium according to claim 11, wherein the one or more values are a function of both the at least one magnetometer reading and at least one accelerometer reading.

13. The computer readable medium according to claim 12, wherein the one or more values are vectors obtained by combining a magnetometer vector with an accelerometer vector.

14. The computer readable medium according to claim 13, wherein a first vector is obtained by determining a cross product of the magnetometer vector and the accelerometer vector and a second vector is obtained by determining a cross product of the accelerometer vector and the first vector.

15. The computer readable medium according to claim 10, further comprising instructions for determining if the magnetometer readings are of a sufficient quality before determining whether or not the first orientation is being maintained.

16. The computer readable medium according to claim 10, further comprising instructions for checking whether or not the accelerometer readings are of sufficient quality prior to the determining and applying operations.

17. The computer readable medium according to claim 16, wherein the checking comprises determining whether or not at least some of the accelerometer readings lie within a predetermined sphere.

18. The computer readable medium according to claim 10, wherein the gain and offset values are determined by applying a least squares estimation using the plurality of accelerometer readings at the first and plurality of additional orientations.

19. An electronic device comprising a processor, memory, an accelerometer, and a magnetometer, the memory comprising computer executable instructions for obtaining data for calibrating the accelerometer, the computer executable instructions comprising instructions for:

using at least one magnetometer reading to detect that a first orientation is being maintained;

obtaining a plurality of accelerometer readings at the first orientation;

using at least one magnetometer reading to detect that a plurality of additional orientations are being maintained and, for each orientation, obtaining a plurality of accelerometer readings at that orientation;

determining calibration parameters comprising, for each axis of the accelerometer, at least one of a gain value and an offset value, using the plurality of accelerometer readings at the first and plurality of additional orientations; and

applying the calibration parameters to subsequent accelerometer readings.

20. The electronic device according to claim 19, wherein detecting that the first and plurality of additional orientations are being maintained comprises determining that one or more values are being maintained substantially constant.

21. The electronic device according to claim 20, wherein the one or more values are a function of both the at least one magnetometer reading and at least one accelerometer reading.

22. The electronic device according to claim 21, wherein the one or more values are vectors obtained by combining a magnetometer vector with an accelerometer vector.

23. The electronic device according to claim 22, wherein a first vector is obtained by determining a cross product of the magnetometer vector and the accelerometer vector and a second vector is obtained by determining a cross product of the accelerometer vector and the first vector.

24. The electronic device according to claim 19, further comprising instructions for determining if the magnetometer readings are of a sufficient quality before determining whether or not the first orientation is being maintained.

25. The electronic device according to claim 19, further comprising instructions for checking whether or not the accelerometer readings are of sufficient quality prior to the determining and applying operations.

26. The electronic device according to claim 25, wherein the checking comprises determining whether or not at least some of the accelerometer readings lie within a predetermined sphere.

27. The electronic device according to claim 19, wherein the gain and offset values are determined by applying a least squares estimation using the plurality of accelerometer readings at the first and plurality of additional orientations.