DYNAMIC COMPASS CALIBRATION IN A PORTABLE DEVICE

• US 20100312510A1
• 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: Mayor, Robert, Piemonte, Patrick S., Shrivastav, Madhu, Mishra, Puntee, Huang, Ronald K.
• Granted Patent: US 8,239,153 B2
• Time in Patent Office: Days
• US Class Current: 702/93
• 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

Abstract

The magnitude of a sensed, raw magnetic field in a portable device is monitored over a given time interval. The monitored magnitude is compared with predetermined criteria. Based on the comparison, recalibration of a compass function is signed. Other embodiments are also described and claimed.

Claims

1. A machine-implemented method for dynamic calibration of a compass in a portable device, comprising:

monitoring the magnitude of a sensed magnetic field in the device as detected by the compass, over a given time interval;

monitoring one of position, orientation and movement (POM) data about the device using a position, orientation or movement (POM) sensor in the device;

comparing the monitored magnitude and POM data with predetermined criteria; and

signaling a recalibration of the compass based on the comparison.

2. The method of claim 1 wherein the monitoring the magnitude comprises:

maintaining a running average of the magnitude.

3. The method of claim 1 further comprising;

computing a geomagnetic field based on the sensed magnetic field;

monitoring inclination of the computed geomagnetic field over the given time interval; and

comparing the inclination with predetermined criteria,

wherein signaling the recalibration is further based on the comparison involving the inclination.

4. The method of claim 3 wherein the monitoring the inclination comprises:

maintaining a running average of the inclination.

5. A portable device comprising:

a portable device housing having integrated therein

a position, orientation or movement (POM) sensor to provide one of position, orientation and movement data (POM data) concerning the portable device,

a magnetic sensor to provide a sensed, magnetic field,

a compass calibrator coupled to the magnetic sensor, and

an indicator module to monitor the magnitude of the sensed magnetic field and the POM data over a given time interval, compare the monitored magnitude and POM data with predetermined criteria, and, based on the comparison, signal the calibrator to recalibrate.

6. The portable device of claim 5 wherein the indicator module is to monitor the magnitude so as to maintain a running average of the magnitude.

7. The portable device of claim 5 wherein the indicator module is to monitor inclination of a geomagnetic field computed by the compass calibrator, over the given time interval, compare the inclination with predetermined criteria, and signal the recalibration further based on the inclination comparison.

8. The portable device of claim 7 wherein the indicator module is to monitor inclination so as to maintain a running average of the inclination

9. An article of manufacture comprising:

a machine-readable medium having stored thereon instructions that program a processor in a portable device to monitor the magnitude of a sensed magnetic field from a compass in the device over a given time interval, monitor one of position, orientation and movement data (POM data) from one of a position, orientation and movement sensor (POM sensor) in the device over the given time interval, compare the monitored magnitude with predetermined criteria, and signal a recalibration of a compass based on the comparison.

10. The article of manufacture of claim 9 wherein the machine-readable medium contains further instructions that program the processor to monitor the magnitude so as to maintain a running average of the magnitude.

11. The article of manufacture of claim 9 wherein the machine-readable medium contains further instructions that program the processor to monitor inclination of a geomagnetic field computed by the compass, over the given time interval, compare the inclination with predetermined criteria, and signal the recalibration further based on the inclination comparison.

12. The article of manufacture of claim 11 wherein the machine-readable medium contains further instructions that program the processor to monitor inclination so as to maintain a running average of the inclination.

13. A machine-implemented method for dynamic calibration of a compass in a portable device, comprising:

monitoring a magnetic field surrounding the device during a given time interval;

monitoring one or more of position, orientation, and movement (POM) of the device during the given time interval;

comparing a change in the monitored magnetic field with a change in the monitored POM; and

signaling a recalibration of the compass when the change in the monitored magnetic field is large relative to the change in the monitored POM.

14. The method of claim 13 wherein the monitoring a magnetic field comprises maintaining a running average of the magnetic field, and wherein the monitoring one or more of POM of the device comprises maintaining a running average of acceleration of the device.

15. The method of claim 13 wherein the monitoring a magnetic field comprises maintaining a running average of the magnetic field, and wherein the monitoring one or more of POM of the device comprises maintaining a running average of acceleration of the device.