Calibration techniques for an electronic compass in portable device

• US 8,370,097 B2
• Filed: 06/05/2009
• Issued: 02/05/2013
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Patel, Parin, Huang, Ronald K., Piemonte, Patrick S., Mayor, Robert
• Primary Examiner(s): Barbee, Manuel L
• Application Number:
  US12/479,182
• Publication Number:
  US 20100312509A1
• Time in Patent Office: 1,341 Days
• Field of Search: 702 92- 94, 702/151, 702/153, 702/154, 333/56, 333/57, 333/24, 333/26
• US Class Current: 702/92
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

Measurement data is collected from a magnetic sensor in a portable device, while the device is being carried by its end user and without requiring the end user to deliberately rotate or position the device while the output data is being collected. For example, the device may be held in the user'"'"'s hand while walking or standing, or it may be fixed to the dashboard of an automobile or boat. Measurement data may also be collected from one or more positing, orientation or movement sensors. The collected measurement data from one or both of the magnetic sensor and the position, orientation or movement sensor is processed. In response, either a 2D compass calibration process or a 3D process is signaled to be performed. Other embodiments are also described and claimed.

Claims

1. A portable device comprising:

a three axis magnetic sensor;

a first compass calibrator to compute a first offset field based on a set of magnetic field measurements by the sensor that define a generally spherical surface, and to use the first offset field to compute a first geomagnetic direction;

a second compass calibrator to compute a second offset field based on a set of magnetic field measurements by the sensor that define a generally circular path, and to use the second offset field to compute a second geomagnetic direction; and

a compass direction output module that selects one of the first and second geomagnetic fields to be its direction output, based on data from a position, orientation or motion (POM) sensor, wherein the POM sensor is a different component than the three axis magnetic sensor.

2. The portable device of claim 1 further comprising:

a user context detector to detect how the portable device is being carried by its user, wherein the compass direction output module is to select from amongst the first and second geomagnetic fields responsive to the user context detector.

3. The portable device of claim 2 wherein the user context detector, responsive to the POM sensor, is to indicate that the device has remained level for a period of time.

4. The portable device of claim 2 wherein the detector indicates automobile mode when the device is fixed to a car that is being driven,

the compass direction output module to select the second geomagnetic field as its direction output and not the first geomagnetic field, when in automobile mode.

5. The portable device of claim 4 wherein the detector indicates pedestrian mode when the device is being held in the user'"'"'s hand and the user is walking,

the compass direction output module to select the first geomagnetic field and not the second, when in pedestrian mode.

6. The portable device of claim 2 wherein the detector indicates pedestrian mode when the device is being held in the user'"'"'s hand and the user is walking,

the compass direction output module to select the first geomagnetic field and not the second, when in pedestrian mode.

7. The portable device of claim 2 wherein the user context detector detects, responsive to the POM sensor, how the portable device is being carried by its user, and wherein the POM sensor is one of a GPS and an accelerometer.

8. The portable device of claim 7 wherein the POM sensor is an accelerometer, wherein the user context detector detects, responsive to the POM sensor and responsive to the three axis magnetic sensor, that the portable device is being carried by its user in an automobile mode or in a pedestrian mode, and wherein the second compass calibrator uses a 2D calibration to calibrate the magnetic sensor using the set of magnetic field measurements measured by the sensor that define a generally circular path and using the data from the POM sensor.

9. The portable device of claim 8 wherein the detection of how the portable device is being carried by its user, responsive to the three axis magnetic sensor, is validated by the user context detector, responsive to the POM sensor.

10. The portable device of claim 1, wherein the first compass calibrator is deactivated when the second compass calibrator computes the second offset field, and wherein the second compass calibrator is deactivated when the first compass calibrator computes the first offset field.

11. An article of manufacture, comprising:

data storage having stored therein data that programs a processor to perform a calibration routine on an electronic compass that has a 3-axis magnetic sensor, to compute an interference field for the compass,

wherein the calibration routine is to determine that the magnetic sensor has remained essentially level, in that it has not rotated about a horizontal plane, for at least a predetermined time interval while moving along the horizontal plane, based on data from a position, orientation or motion (POM) sensor, and in response select a 2D calibration process to be performed on the sensor for computing the interference field,

and wherein the calibration routine is to determine that the sensor is sufficiently tilting or rotating about the horizontal plane, based on data from the position, orientation or motion (POM) sensor, and in response select a 3D calibration process to be performed on the sensor for computing the interference field, wherein the POM sensor is a different component than the three axis magnetic sensor.

12. The article of manufacture of claim 11 wherein the 2D calibration process accepts more than one solution for the interference field, wherein the acceptable solutions lie on and are spaced apart along the center axis of a geomagnetic measurement sphere, so long as the magnetic sensor is essentially staying in the horizontal plane while moving.

13. The article of manufacture of claim 12 wherein the 3D calibration process is to find a solution for the interference field that lies at the center of the geomagnetic measurement sphere.

14. The article of manufacture of claim 11, wherein the 2D calibration process is deactivated while the 3D calibration process is being performed, and the 3D calibration process is deactivated when the 2D calibration process is being performed.

15. A machine-implemented method for operating a portable device having a three-axis magnetic sensor to provide a compass function, the method comprising:

collecting measurement data from the magnetic sensor in the portable device, while the device is being carried by its end user and without requiring the end user to deliberately rotate or position the device while the data is being collected;

collecting measurement data from one or more position, orientation or movement (POM) sensors in the portable device, while the device is being carried by its end user and without requiring the end user to deliberately rotate or position the device while the data is being collected; and

processing collected measurement data from both of the magnetic sensor and the POM sensor and in response signaling that one of a 2D compass calibration process and a 3D compass calibration process be performed upon the magnetic sensor, wherein the POM sensor is a different component than the three axis magnetic sensor.

16. The method of claim 15 further comprising:

performing the 2D compass calibration process by solving for an unknown offset magnetic field vector based on the collected measurement data from the magnetic sensor,

wherein the collected measurement data from the magnetic sensor define a generally circular path, not a sphere, and

wherein the 2D calibration process allows for a solution of the unknown offset vector that can point to locations along a perpendicular center axis of the generally circular path that need not be at the center of the path.

17. The method of claim 15 further comprising:

performing the 3D compass calibration process by solving for the unknown offset magnetic field vector based on the collected measurement data from the magnetic sensor,

wherein the collected measurement data from the magnetic sensor define a generally spherical surface and

wherein the 3D calibration process requires a solution of the unknown offset vector that points to the center of the generally spherical surface.

18. The method of claim 15 wherein said processing collected measurement data comprises:

performing statistical analysis of the collected measurement data from the POM sensor to determine whether or not the device has remained essentially level, wherein the 2D calibration process, and not the 3D process, is signaled in response to having so determined.

19. The method of claim 15 wherein said processing collected measurement data comprises:

performing statistical analysis of the collected measurement data from the POM sensor to determine whether or not the device is undergoing sufficient rotation or tilting about a horizontal plane, wherein the 3D calibration process, and not the 2D process, is signaled in response to having so determined.

20. The method of claim 15 wherein the POM sensor is an accelerometer;

and further comprising;

calibrating the magnetic sensor using a 2D calibration that uses data from both of the magnetic sensor and the POM sensor.

21. The method of claim 15, wherein the 2D calibration process is deactivated while the 3D calibration process is being performed, and the 3D calibration process is deactivated when the 2D calibration process is being performed.

22. A portable device comprising:

a three axis magnetic sensor;

a first compass calibrator to compute a first offset field based on a set of magnetic field measurements by the sensor that define a generally spherical surface, and to use the first offset field to compute a first geomagnetic direction;

a second compass calibrator to compute a second offset field based on a set of magnetic field measurements by the sensor that define a generally circular path, and to use the second offset field to compute a second geomagnetic direction;

a compass direction output module that selects one of the first and second geomagnetic fields to be its direction output; and

a user context detector to detect, responsive to a position, orientation or motion (POM) sensor, how the portable device is being carried by its user, wherein the compass direction output module is to select from amongst the first and second geomagnetic fields responsive to the user context detector, wherein the POM sensor is a different sensor than the three axis magnetic sensor.

23. The portable device of claim 22 wherein the POM sensor is an accelerometer chip that is installed on the same circuit board as the three axis magnetic sensor, and wherein the user context detector detects, responsive to the POM sensor and responsive to the three axis magnetic sensor, that the portable device is being carried by its user in an automobile mode or in a pedestrian mode, and wherein the second compass calibrator uses a 2D calibration to calibrate the magnetic sensor using the set of magnetic field measurements measured by the sensor that define a generally circular path and using the data from the POM sensor.