Restoring and Storing Magnetometer Calibration Data

• US 20100312513A1
• Filed: 06/05/2009
• Published: 12/09/2010
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Piemonte, Patrick, Mayor, Robert, Huang, Ronald Keryuan
• Granted Patent: US 8,437,970 B2
• Time in Patent Office: Days
• US Class Current: 702/104
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration

Abstract

Responsive to a recalibration trigger event, magnetometer data output by a magnetometer can be compared to historical magnetometer data previously output by the magnetometer. If a match is determined, a confidence of the match can be determined using theoretically constant data related to Earth'"'"'s magnetic field. The constant data can be calculated from the historical magnetometer data. If the confidence of the match exceeds a confidence threshold level, historical calibration data can be used to calibrate the magnetometer. If the confidence of the match does not exceed the confidence threshold level, a calibration procedure can be performed to generate new calibration data, and the new calibration data can be used to calibrate the magnetometer.

Claims

1. A computer-implemented method, comprising:

receiving a reading from a magnetometer of a mobile device;

comparing the reading to historical data;

determining a confidence of a match between the reading and historical data, where the confidence is determined at least in part on historical data associated with Earth'"'"'s magnetic field; and

if the confidence of the match exceeds a threshold confidence level, calibrating the magnetometer with historical calibration data.

2. The method of claim 1, where if the reading does not match historical data, further comprising:

performing a calibration procedure to determine new calibration data.

3. The method of claim 2, further comprising:

calibrating the magnetometer using the new calibration data.

4. The method of claim 1, where the confidence is determined based on Earth'"'"'s total magnetic field intensity.

5. The method of claim 1, where the confidence is determined based on an angle between Earth'"'"'s magnetic field vector and Earth'"'"'s gravitational acceleration vector.

6. The method of claim 1, where comparing the reading to historical magnetometer data comprises:

searching a look up table of historical magnetometer data that was stored on the mobile device during a previous calibration procedure.

7. The method of claim 6, where match datum for the searching is a parameter used to dynamically adjust sensor readings output by the magnetometer.

8. The method of claim 1, where determining a confidence of the match using historical data associated with Earth'"'"'s magnetic field further comprises:

determining a confidence of the match using historical offsets stored during an earlier calibration procedure.

9. An apparatus, comprising:

a magnetometer;

memory storing historical magnetometer data; and

a processor coupled to the magnetometer and the memory, the processor configured for;

receiving a reading from the magnetometer;

comparing the reading to historical magnetometer data;

if the reading matches the historical magnetometer data,

determining a confidence of the match using historical data associated with Earth'"'"'s magnetic field;

if the confidence of the match exceeds a threshold confidence level,

calibrating the magnetometer with historical calibration data; and

if the confidence of the match does not exceed the threshold confidence level,

performing a calibration procedure to determine new calibration data.

10. The apparatus of claim 9, where the processor is further configured for calibrating the magnetometer using the new calibration data.

11. The apparatus of claim 9, where the processor is further configured for performing a calibration procedure to determine new calibration data if the reading does not match the historical data.

12. The apparatus of claim 9, where the confidence is determined using at least in part Earth'"'"'s total magnetic field intensity.

13. The apparatus of claim 9, where the confidence is determined using at least in part an angle between Earth'"'"'s magnetic field vector and Earth'"'"'s gravitational acceleration vector.

14. The apparatus of claim 9, where comparing the reading to historical magnetometer data comprises:

searching a look up table of historical magnetometer data that was stored on the mobile device during a previous calibration procedure.

15. The apparatus of claim 14, where match datum for the searching is a parameter used to dynamically adjust sensor readings output by the magnetometer.

16. The apparatus of claim 9, where determining a confidence of the match using at least in part historical data associated with Earth'"'"'s magnetic field, further comprises:

determining a confidence of the match using historical offsets stored during an earlier calibration procedure.

17. A computer-readable medium having instructions stored thereon, which, when executed by at least one processor, causes the processor to perform operations comprising:

receiving a reading from an magnetometer of a mobile device;

comparing the reading to historical magnetometer data;

if the reading matches the historical magnetometer data, determining a confidence of the match using historical data associated with Earth'"'"'s magnetic field;

if the confidence of the match exceeds a threshold confidence level, calibrating the magnetometer with historical calibration data; and

if the confidence of the match does not exceed the threshold confidence level, performing a calibration procedure to determine new calibration data.

18. The computer-readable medium of claim 17, where if the reading does not match the historical data, further comprising:

performing a calibration procedure to determine new calibration data.

19. The computer-readable medium of claim 17, where the confidence is determined based on Earth'"'"'s total magnetic field intensity.

20. The computer-readable medium of claim 17, where the confidence is determined based on an angle between Earth'"'"'s magnetic field vector and Earth'"'"'s gravitational acceleration vector.