Using magnetometer data to calculate angular rate measurement bias

• US 9,285,225 B2
• Filed: 09/11/2012
• Issued: 03/15/2016
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Pham, Hung A., Zhang, Hengliang
• Primary Examiner(s): Desta, Elias
• Application Number:
  US13/610,719
• Publication Number:
  US 20140074424A1
• Time in Patent Office: 1,281 Days
• US Class Current: 1/1
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

Implementations are disclosed for using magnetometer measurements to estimate bias for angular rate measurements provided by an angular rate sensor (e.g., a gyro sensor). In some implementations, a bias estimator running on a device is configured to determine if the device is rotating based on the magnetometer measurements. If the device is not rotating, a dynamic bias is calculated and added to a temperature compensated static bias to provide a total angular rate measurement bias. The total angular rate measurement bias can be provided to an attitude estimation system where it is used to update an attitude (orientation) of the device. In some implementations, the angular rate measurements are used to determine if the device is oscillating according to a threshold value. If the device is not rotating and the device is oscillating according to a threshold value, the static bias is updated in a calibration table.

Claims

1. A method comprising:

receiving magnetometer measurements from a magnetometer of a mobile device;

determining that the device is not rotating based on the magnetometer measurements;

responsive to the determining, estimating a dynamic bias;

estimating an angular rate measurement bias based on the dynamic bias and a temperature compensated static bias; and

calibrating an angular rate measurement using the estimated angular rate measurement bias.

2. The method of claim 1, where determining that the device is not rotating based on the magnetometer measurements, further comprises:

filtering the magnetometer measurements with a variance filter;

comparing the filtered magnetometer measurements with a threshold value; and

determining that the device is not rotating based on results of the comparing.

3. The method of claim 1, further comprising:

receiving angular rate measurements from an angular rate sensor of the mobile device;

determining that the mobile device is oscillating according to a threshold value based on the angular rate measurements; and

updating the static bias based on previous angular rate and temperature measurements.

4. The method of claim 3, where determining that the mobile device is oscillating according to a threshold value further comprises:

filtering the angular rate measurements with a variance filter; and

comparing the filtered angular rate measurements with the threshold value.

5. The method of claim 3, further comprising:

synchronizing the magnetometer and angular rate measurements; and

estimating the angular rate measurement bias based on the synchronized magnetometer and angular rate measurements.

6. The method of claim 1, further comprising:

filtering the magnetometer measurements with a first filter to suppress sample noise or high frequency magnetic field interference.

7. The method of claim 6, further comprising:

filtering the magnetometer measurements with a second filter to reject a constant bias in the magnetometer measurements while maintaining sensitivity to device motion.

8. The method of claim 3, where synchronizing the magnetometer and angular rate measurements, further comprises:

applying a zero-order-hold to a number of angular rate measurements.

9. The method of claim 8, where the number of angular rate measurements held by the zero order hold is based on an accumulated estimated phase distortion resulting from filters applied to the magnetometer and angular rate measurements.

10. The method of claim 1, where the angular rate sensor is a gyroscopic sensor.

11. A mobile device comprising:

a magnetometer;

an angular rate sensor;

one or more processors;

memory coupled to the one or more processors and configured to store instructions, which, when executed by the one or more processors, causes the one or more processors to perform operations comprising;

receiving magnetometer measurements from the magnetometer of the mobile device;

determining that the mobile device is not rotating based on the magnetometer measurements;

responsive to the determining, estimating a dynamic bias;

estimating an angular rate measurement bias based on the dynamic bias and a temperature compensated static bias; and

calibrating an angular rate measurement provided by the angular rate sensor using the estimated angular rate measurement bias.

12. The mobile device of claim 11, where determining that the device is not rotating based on the magnetometer measurements, further comprises:

filtering the magnetometer measurements with a variance filter;

comparing the filtered magnetometer measurements with a threshold value; and

determining that the device is not rotating based on results of the comparing.

13. The mobile device of claim 11, where the instructions, when executed by the one or more processors, causes the one or more processors to perform operations comprising:

determining that the mobile device is oscillating according to a threshold value; and

updating the static bias based on previous angular rate and temperature measurements.

14. The mobile device of claim 13, where determining that the mobile device is oscillating according to a threshold value comprises:

filtering the angular rate measurements with a variance filter; and

comparing the filtered angular rate measurements with the threshold value.

15. The mobile device of claim 13, where the instructions, when executed by the one or more processors, causes the one or more processors to perform operations comprising:

synchronizing the magnetometer and angular rate measurements; and

estimating the angular rate measurement bias based on the synchronized magnetometer and angular rate measurements.

16. The mobile device of claim 11, where the instructions, when executed by the one or more processors, causes the one or more processors to perform operations comprising:

filtering the magnetometer measurements with a first filter to suppress sample noise or high frequency magnetic field interference.

17. The mobile device of claim 16, where the instructions, when executed by the one or more processors, causes the one or more processors to perform operations comprising:

filtering the magnetometer measurements with a second filter to reject a constant bias in the magnetometer measurements while maintaining sensitivity to mobile device motion.

18. The mobile device of claim 13, where synchronizing the magnetometer and angular rate measurements, further comprises:

applying a zero-order-hold to a number of angular rate measurements.

19. The mobile device of claim 18, where the number of angular rate measurements held by the zero order hold is based on an accumulated estimated phase distortion resulting from filters applied to the magnetometer and angular rate measurements.

20. The mobile device of claim 11, where the angular rate sensor is a gyroscopic sensor.