Auto-calibration of orientation sensing systems

• US 8,374,817 B2
• Filed: 03/27/2008
• Issued: 02/12/2013
• Est. Priority Date: 04/04/2007
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Boeve, Hans Marc Bert, Ikkink, Teunis Jan, Duric, Haris
• Primary Examiner(s): Moffat, Jonathan C. Teixeira
• Assistant Examiner(s): SUN, XIUQIN
• Application Number:
  US12/594,244
• Publication Number:
  US 20100121599A1
• Time in Patent Office: 1,783 Days
• Field of Search: 702/93, 333/56
• US Class Current: 702/93
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

An electronic device has an orientation sensing system for determining an orientation of the device. The system includes a magnetometer and an accelerometer. The system further has a calibration device configured to calibrate the sensing system for operational use. The accelerometer supplies measurements used to constrain a range of possible directions of the external magnetic field to be determined. The calibration device numerically solves a set of equations and is equally usable for a 2D or 3D magnetometer in combination with a 2D or 3D accelerometer.

Claims

1. An electronic device with an orientation sensing system for determining an orientation of the electronic device in operational use of the electronic device, the orientation sensing system comprising:

a first sensor comprising a 2D magnetometer or a 3D magnetometer configured to supply first vectors representative of earth-magnetic field vectors;

a second sensor comprising a 2D accelerometer or a 3D accelerometer configured to supply second vectors representative of gravity field vectors; and

a calibration device coupled to the first and second sensors configured to calibrate the orientation sensing system for operational use, wherein the calibration device is configured to use the second vectors to constrain a range of possible directions of corresponding earth-magnetic field vectors to be determined per corresponding orientations of the electronic device and numerically solve a set of equations involving first quantities representative of the first vectors and second quantities representative of the second vectors, wherein the set includes, for each of the first quantities, a corresponding equation that comprises a term that is equivalent to a matrix multiplication of a parameter matrix with the corresponding earth-magnetic field vector, second equations specifying a magnitude of the earth-magnetic field vector for the multiple orientations, third equations specifying a value of a dot product of the earth-magnetic field vector with the gravity field vector for the multiple orientations, and a minimum number of the multiple orientations is no more than ten.

2. The electronic device of claim 1, wherein at least each of the first quantities is an average of multiple first vectors supplied by the first sensor.

3. The electronic device of claim 1, wherein the calibration device is configured to exclude a specific one of the first vectors and a specific one of the second vectors from being taken into account for creating a particular one of the first quantities as a first average of particular ones of the first vectors, and configured to create a corresponding particular one of the second quantities as a second average of particular ones of the second vectors.

4. The electronic device of claim 3, wherein the calibration device is configured to discontinue the creating of the particular first quantity and the creating of the corresponding particular second quantity if the specific first vector deviates from a running version of the first average of the particular first vectors by a vector distance that exceeds a first threshold.

5. The electronic device of claim 3, wherein the calibration device is configured to discontinue the creating of the particular first quantity and the creating of the corresponding particular second quantity if the specific second vector deviates from a running version of the second average of the particular second vectors by a vector distance that exceeds a second threshold.

6. The electronic device of claim 1, wherein a current sample is excluded from the set of equations to be solved if a magnitude of the current sample deviates from a running average by more than a further threshold.

7. The electronic device of claim 1, wherein an averaged sensor data vector is excluded from the set of equations to be solved if a measure of dissimilarity between the averaged sensor data vector and previously collected averaged vectors is smaller than a distance threshold.

8. The electronic device of claim 1, wherein the calibration device is configured to operate in a background process during operational use of the electronic device.

9. The electronic device of claim 1, wherein at least each of the second quantities is an average of multiple second vectors supplied by the second sensor.

10. A method of calibrating an orientation sensing system configured to determine an orientation of the orientation sensing system, wherein the orientation sensing system, comprises a first sensor comprising a 2D magnetometer or a 3D magnetometer configured to supply first vectors representative of earth-magnetic field vectors;

and a second sensor comprising a 2D accelerometer or a 3D accelerometer configured to supply second vectors representative of gravity field vectors, wherein the method comprises;

using the second vectors to constrain a range of possible directions of corresponding earth-magnetic field vectors to be determined per corresponding orientations of the system; and

numerically solving, by a microprocessor, a set of equations involving first quantities representative of the first vectors and second quantities representative of the second vectors, wherein the set includes, for each of the first quantities, a corresponding equation that comprises a term that is equivalent to a matrix multiplication of a parameter matrix with the corresponding earth-magnetic field vector, second equations specifying a magnitude of the earth-magnetic field vector for the multiple orientations, and third equations specifying a value of the dot product of the earth-magnetic field vector with the gravity field vector for the multiple orientations, and a minimum number of the multiple orientations is no more than ten.

11. The method of claim 10, further comprising:

averaging multiple ones of the first vectors to form the first quantities.

12. The method of claim 10, further comprising:

excluding a specific one of the first vectors and a specific one of the second vectors from being taken into account for creating a particular one of the first quantities as a first average of particular ones of the first vectors; and

creating a corresponding particular one of the second quantities as a second average of particular ones of the second vectors.

13. The method of claim 12, further comprising:

discontinuing the creating of the particular first quantity and the creating of the corresponding particular second quantity if the specific first vector deviates from a running version of the first average of the particular first vectors by a vector distance that exceeds a first threshold.

14. The method of claim 12, further comprising:

discontinuing the creating of the particular first quantity and the creating of the corresponding particular second quantity if the specific second vector deviates from a running version of the second average of the particular second vectors by a vector distance that exceeds a second threshold.

15. The method of claim 10, further comprising:

excluding a current sample from the set of equations to be solved if the current sample has a magnitude that deviates from a running average by more than a further threshold.

16. The method of claim 10, further comprising:

excluding an averaged sensor data vector from the set of equations to be solve if a measure of dissimilarity between the averaged sensor data vector and previously collected averaged vectors is smaller than a distance threshold.

17. The method of claim 10, wherein the method is performed as a background process during operational use of the orientation sensing system.

18. A non-transitory medium comprising instructions for implementing the method of claim 10.

19. The method of claim 10, further comprising:

averaging multiple ones of the second vectors to form the second quantities.