Dynamic compass calibration in a portable device

• US 8,239,153 B2
• Filed: 06/05/2009
• Issued: 08/07/2012
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Piemonte, Patrick S., Mishra, Puneet, Mayor, Robert, Huang, Ronald K., Patel, Parin, Shrivastav, Madhu
• Primary Examiner(s): Barbee, Manuel L
• Application Number:
  US12/479,203
• Publication Number:
  US 20100312510A1
• Time in Patent Office: 1,159 Days
• Field of Search: 702 92- 94, 702/141, 702/151, 702/153, 702/154, 333/24, 333/26, 333/56, 333/57
• US Class Current: 702/92
• 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:

detecting a sensed magnetic field in the device using the compass, over a given time interval;

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

computing a geomagnetic field based on the sensed magnetic field;

computing inclination of the geomagnetic field over the given time interval to maintain a running average;

comparing the sensed magnetic field and the position, orientation or movement data with predetermined criteria; and

signaling a recalibration of the compass based on the comparison.

2. The method of claim 1 wherein the detecting the sensed magnetic field comprises:

maintaining a running average of a magnitude of the sensed magnetic field.

3. The method of claim 1 further comprising;

comparing the inclination with predetermined criteria,

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

4. 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 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 sensed magnetic field and the position orientation or movement data over a given time interval, compare the monitored sensed magnetic field and the position, orientation or movement data with predetermined criteria, and, based on the comparison, signal the calibrator to recalibrate, wherein the indicator module is to monitor inclination of a geomagnetic field so as to maintain a running average of the inclination, over the given time interval.

5. The portable device of claim 4 wherein the indicator module is to monitor a magnitude of the sensed magnetic field so as to maintain a running average of the magnitude.

6. The portable device of claim 4 wherein the indicator module is to compare the inclination with predetermined criteria and signal the recalibration further based on the inclination comparison.

7. An article of manufacture comprising:

a non-transitory machine-readable medium having stored thereon instructions that program a processor in a portable device to detect a sensed magnetic field in the device over a given time interval, monitor one of position, orientation and movement data from a position, orientation or movement sensor (POM sensor) in the device over the given time interval, compute inclination of a computed geomagnetic field so as to maintain a running average of the inclination, compare the sensed magnetic field with predetermined criteria, and signal a recalibration of a compass based on the comparison.

8. The article of manufacture of claim 7 wherein the non-transitory machine-readable medium contains further instructions that program the processor to monitor a magnitude of the sensed magnetic field so as to maintain a running average of the magnitude.

9. The article of manufacture of claim 7 wherein the non-transitory machine-readable medium contains further instructions that program the processor to compare the inclination with predetermined criteria and signal the recalibration further based on the inclination comparison.

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

monitoring, by an indicator module, a magnetic field surrounding the device during a given time interval;

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

computing a geomagnetic field based on the magnetic field;

computing inclination of the geomagnetic field during the given time interval to maintain a running average;

comparing a change in the monitored magnetic field with a change in the monitored position, orientation, or movement; and

signaling a recalibration of the compass when the change in the monitored magnetic field is large relative to the change in the monitored position, orientation or movement.

11. The method of claim 10 wherein the monitoring one or more of position, orientation and movement of the device comprises maintaining a running average of acceleration of the device.