AUTO-CALIBRATION OF ORIENTATION SENSING SYSTEMS

• US 20100121599A1
• Filed: 03/27/2008
• Published: 05/13/2010
• 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
• Granted Patent: US 8,374,817 B2
• Time in Patent Office: Days
• 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 comprises a magnetometer and an accelero meter. The system further has calibration means 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 means numerically solves a set of equations and is equally well useable 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 device in operational use of the device

the orientation sensing system comprising:

a first sensor comprising a 2D magnetometer or a 3D magnetometer for supplying first vectors representative of sensed magnetic field vectors that include earth-magnetic field vectors;

a second sensor comprising a 2D accelerometer or a 3D accelerometer for supplying second vectors representative of sensed acceleration vectors that include the gravity field vectors; and

calibration means coupled to the first and second sensors for calibrating the sensing system for operational use, wherein the calibration means is operable to;

use the second vectors to constrain a range of possible directions of corresponding ones of the earth-magnetic field vectors to be determined per corresponding ones of multiple orientations of the 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 and wherein the set further comprises second equations specifying the magnitude of the earth magnetic field vector per corresponding one of the multiple orientations, and third equations specifying the value of the dot product of the earth magnetic field vector with the gravity field vector per corresponding one of the multiple orientations.

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

3. The device of claim 1, wherein the calibration means is operable to exclude a specific one of the first vectors and an in time corresponding 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 for creating a corresponding particular one of the second quantities as a second average of particular ones of the second vectors, and 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;

or

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.

4. The device of claim 1, wherein a special one of the first quantities and an, in time corresponding, special one of the second quantities are excluded from the set of equations to be solved if the special second quantity has a magnitude that deviates from a further pre-determined value by more than a further threshold.

5. The device of claim 1, wherein an individual one of the first quantities and an, in time corresponding, individual one of the second quantities are excluded from the set of equations to be solved, if a measure of dissimilarity between the individual first quantity or the individual second quantity, on the one hand, and other ones of the first or second quantities included in the set of equations, on the other hand, is smaller than still a further threshold.

6. The device of claim 1, wherein the calibration means is operable in a background process during operational use of the device.

7. (canceled)

8. A method of calibrating an orientation sensing system operable to determine an orientation of the system, wherein the system, comprises:

a first sensor comprising a 2D magnetometer or a 3D magnetometer for supplying first vectors representative of sensed magnetic field vectors that include the earth-magnetic field vectors; and

a second sensor comprising a 2D accelerometer or a 3D accelerometer for supplying second vectors representative of sensed acceleration vectors that include the gravity field vectors;

wherein the method comprises;

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

numerically solving 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, and wherein the set further comprises second equations specifying the magnitude of the earth-magnetic field vector per corresponding one of the multiple orientations, and third equations specifying the value of the dot product of the earth-magnetic field vector with the gravity field vector per corresponding one of the multiple orientations.

9. The method of claim 8, comprising at least averaging multiple ones of the first vectors to form the first quantities, or averaging multiple ones of the second vectors to form the second quantities.

10. The method of claim 8, comprising excluding a specific one of the first vectors and an in time corresponding 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 for creating a corresponding particular one of the second quantities as a second average of particular ones of the second vectors, and 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;

or

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.

11. The method of claim 8, comprising excluding a special one of the first quantities and an, in time corresponding, special one of the second quantities from the set of equations to be solved if the special second quantity has a magnitude that deviates from a further pre-determined value by more than a further threshold.

12. The method of claim 8, comprising excluding an individual one of the first quantities and an, in time corresponding, individual one of the second quantities from the set of equations to be solved, if a measure of dissimilarity between the individual first quantity or the individual second quantity, on the one hand, and other ones of the first or second quantities included in the set of equations, on the other hand, is smaller than still a further threshold.

13. The method of claim 8, performed as a background process during operational use of the system.

14. Software for comprising instructions for implementing the method of claim 8.

15-19. -19. (canceled)