Systems and methods for detecting and handling a magnetic anomaly

Patent metadata

Field	Value
Publication number	US-10072956-B2
Application number	US-201414329531-A
Country	US
Kind code	B2
Filing date	Jul 11, 2014
Priority date	Jul 11, 2014
Publication date	Sep 11, 2018
Grant date	Sep 11, 2018

Abstract

Systems and methods are disclosed for detecting when a magnetic anomaly may impact the quality of data being output by a magnetometer. A plurality of detection algorithms may be performed in parallel on the sensor data. Further, indication of a anomaly from one or a combination of the detection algorithms may cause the magnetometer data to have a reduced contribution in any sensor fusion operation or may be omitted from a sensor fusion operation as desired.

First claim

What is claimed is:

1. A method for detecting a magnetic disturbance affecting sensor data comprising:
providing a portable device having a magnetometer;
obtaining magnetometer sensor data from the device;
performing a plurality of magnetic disturbance detection algorithms in parallel on the sensor data;
performing a disturbance handling routine for the sensor data when at least one magnetic disturbance detection algorithm indicates an anomaly; and
determining an orientation of the portable device based at least in part on the disturbance handling routine.

2. The method of claim 1 , wherein the disturbance handling routine comprises discarding the magnetometer sensor data.

3. The method of claim 1 , wherein the disturbance handling routine comprises assigning a reduced confidence index to the sensor data.

4. The method of claim 1 , wherein the disturbance handling routine comprises performing a calibration procedure.

5. The method of claim 1 , wherein one of the magnetic disturbance detection algorithms comprises:
determining a magnitude of a magnetic field using the magnetometer sensor data;
comparing the determined magnitude to a reference magnitude; and
detecting a disturbance in the magnetometer sensor data when a difference between the determined magnitude and the reference magnitude exceeds a threshold.

6. The method of claim 5 , wherein the reference magnitude is derived from a calibration routine.

7. The method of claim 5 , wherein the reference magnitude is derived from low pass filtering a plurality of samples of the magnetometer sensor data.

8. The method of claim 5 , wherein the reference magnitude is derived from location information regarding a geographical position of the device.

9. The method of claim 1 , wherein one of the magnetic disturbance detection algorithms comprises:
determining a three dimensional vector using the magnetometer sensor data;
determining a dip angle corresponding to an angle formed by the determined three dimensional vector and a gravity vector;
comparing the determined dip angle to a reference dip angle; and
detecting a disturbance in the magnetometer sensor data when a difference between the determined dip angle and the reference dip angle exceeds a threshold.

10. The method of claim 9 , wherein the reference dip angle is derived from a calibration routine.

11. The method of claim 9 , wherein the reference dip angle is derived from low pass filtering a plurality of samples of the magnetometer sensor data and accelerometer data during a motionlessness state.

12. The method of claim 9 , wherein the reference dip angle is derived from location information regarding a geographical position of the device.

13. The method of claim 1 , wherein one of the magnetic disturbance detection algorithms comprises:
determining an orientation of the device;
determining a three dimensional vector using the magnetometer sensor data;
rotating the determined three dimensional vector to a stationary frame using the determined orientation;
determining a two dimensional yaw angle from the rotated three dimensional vector;
comparing the determined yaw angle to a reference yaw angle; and
detecting a disturbance in the magnetometer sensor data when a difference between the determined yaw angle and the reference yaw angle exceeds a threshold.

14. The method of claim 13 , wherein the reference yaw angle is derived from a calibration routine.

15. The method of claim 13 , wherein the orientation of the device is determined using motion sensor data and not the magnetometer sensor data.

16. The method of claim 1 , wherein one of the magnetic disturbance detection algorithms comprises:
determining an orientation of the device using sensor fusion without the magnetometer sensor data;
determining an orientation of the device using sensor fusion with the magnetometer sensor data;
comparing the orientation determined with magnetometer sensor data to the orientation determined without magnetometer sensor data; and
detecting a disturbance in the magnetometer sensor data when a difference between the orientation determined with magnetometer sensor data and the orientation determined without magnetometer sensor data exceeds a threshold.

17. The method of claim 16 , further comprising identifying a change in pattern in the difference between the orientation determined with magnetometer sensor data and the orientation determined without magnetometer sensor data at a plurality of times.

18. The method of claim 16 , wherein the orientation determined with magnetometer sensor data comprises a 9-axis sensor fusion and the orientation determined without magnetometer sensor data comprises a 6-axis sensor fusion.

19. The method of claim 1 , wherein performing a plurality of magnetic disturbance detection algorithms on the sensor data comprises performing four magnetic disturbance detection algorithms.

20. A system for detecting a magnetic disturbance affecting sensor data comprising:
a portable device;
a magnetometer integrated with the portable device and configured to output a plurality of samples of sensor data, and
a detection module configured to:
perform a plurality of magnetic disturbance detection algorithms in parallel on the sensor data;
perform a disturbance handling routine for the sensor data when at least one magnetic disturbance detection algorithm indicates an anomaly; and
determine an orientation of the portable device based at least in part on the disturbance handling routine.

21. The system of claim 20 , wherein the disturbance handling routine comprises discarding the magnetometer sensor data.

22. The system of claim 20 , wherein the disturbance handling routine comprises assigning a reduced confidence index to the sensor data.

23. The system of claim 20 , wherein the disturbance handling routine comprises performing a calibration procedure.

24. The system of claim 20 , wherein the detection module is configured to perform one of the magnetic disturbance detection algorithms by:
determining a magnitude of a magnetic field using the magnetometer sensor data;
comparing the determined magnitude to a reference magnitude; and
detecting a disturbance in the magnetometer sensor data when a difference between the determined magnitude and the reference magnitude exceeds a threshold.

25. The system of claim 24 , wherein the detection module is configured to derive the reference magnitude is derived from a calibration routine.

26. The system of claim 24 , wherein the detection module is configured to derive the reference magnitude by low pass filtering a plurality of samples of the magnetometer sensor data.

27. The system of claim 24 , wherein the detection module is configured to derive the reference magnitude from location information regarding a geographical position of the magnetometer system.

28. The system of claim 20 , wherein the detection module is configured to perform one of the magnetic disturbance detection algorithms by:
determining a three dimensional vector using the magnetometer sensor data;
determining a dip angle corresponding to an angle formed by the determined three dimensional vector and a gravity vector;
comparing the determined dip angle to a reference dip angle; and
detecting a disturbance in the magnetometer sensor data when a difference between the determined dip angle and the

Assignees

• Invensense Incorporated
• Invensense Inc

Inventors

• Zheng Yuan
• Lin Shang-Hung
• Keal William Kerry

Classifications

• G01C17/38

  Testing, calibrating, or compensating of compasses · CPC title

• G01R33/00

  Arrangements or instruments for measuring magnetic variables · CPC title

• G01D18/00 Primary

  Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00 · CPC title

• G01R33/0035 Primary

  Calibration of single magnetic sensors, e.g. integrated calibration · CPC title