Angular velocity estimation using a magnetometer and accelerometer

• US 9,465,044 B2
• Filed: 01/07/2013
• Issued: 10/11/2016
• Est. Priority Date: 01/07/2013
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: Kionix Incorporated (ROHM Co., Ltd.)
• Inventors: Anderson, Erik
• Primary Examiner(s): LAU, TUNG S
• Application Number:
  US13/735,815
• Publication Number:
  US 20140195185A1
• Time in Patent Office: 1,373 Days
• Field of Search: 702/88
• US Class Current: 1/1
• CPC Class Codes: G01P 3/44 for measuring angular speed G01P3/56 takes precedence
• CPC Class Codes: G06F 17/00 Digital computing or data processing equipment or methods, specially adapted for specific functions information retrieval, database structures or file system structures therefor G06F16/00

Abstract

A system and method for estimating angular velocity are provided. The system and method use an accelerometer and magnetometer to estimate an angular velocity in place of a gyroscope in 9-axis sensor fusion to estimate angular orientation. The final angular velocity estimate is constructed from two partially independent angular velocity estimates, one using only magnetometer measurements and the other using only accelerometer measurements. The unobservable portion of each partial angular velocity estimate is provided by a projection from a third complete estimate that uses both accelerometer and magnetometer data.

Claims

1. A system comprising:

an angular velocity processor stored in memory, executing on a processor, and causing the processor to;

determine a first angular velocity component from magnetic vector measurements provided by a magnetometer;

determine a second angular velocity component from gravitational vector measurements provided by an accelerometer;

determine a third angular velocity component from a combination of measurements provided by the magnetometer and accelerometer, wherein the third angular velocity component compensates for measurements that are not observed by the magnetic vector and the gravitational vector and are not included in determining the first angular velocity component and determining the second angular velocity component;

compensate the first angular velocity component with a projection of the third angular velocity component around a first unobservable axis;

compensate the second angular velocity component with a projection of the third angular velocity component around a second unobservable axis; and

generate an angular velocity estimate using the compensated first angular velocity component and the compensated second angular velocity component and without using a measurement from a gyroscope.

2. The system of claim 1, wherein the angular velocity processor further causes the processor to generate the angular velocity estimate using a first weight associated with the first angular velocity component and a second weight associated with the second angular velocity component.

3. The system of claim 2, wherein the first and second weights are based on a fusion angle noise.

4. The system of claim 2, wherein the first weight is based on calibration associated with the magnetometer.

5. The system of claim 1, wherein the angular velocity processor further causes the processor to determine the first angular velocity component using a cross product between the magnetic vector measurements of the magnetometer, wherein the magnetic vector measurements are normalized to unit length.

6. The system of claim 1, wherein the angular velocity processor further causes the processor to determine the second angular velocity component using a cross product between the gravitational vector measurements of the accelerometer, wherein the gravitational vector measurements are normalized to unit length.

7. The system of claim 1, wherein the angular velocity processor further causes the processor to determine the third angular velocity component using a rotation matrix comprising the magnetic vector measurements of the magnetometer and the gravitational vector measurements of the accelerometer.

8. The system of claim 1, wherein the angular velocity processor further causes the processor to calculate the projection of the third angular velocity component around the first unobservable axis using a dot product between the third angular velocity component and the magnetic vector measurements of the magnetometer normalized to unit length.

9. The system of claim 8, wherein the first unobservable axis is an axis in the direction of the magnetic field vector.

10. The system of claim 1, wherein the angular velocity processor further causes the processor to calculate the projection of the third angular velocity component around the second unobservable axis using a dot product between the third angular velocity component and the gravitational vector measurements of the accelerometer normalized to unit length.

11. The system of claim 10, wherein the second unobservable axis is in the direction of the gravitation field vector.

12. The system of claim 1, wherein the angular velocity processor causes the processor to determine the first and second angular velocity components using filtered magnetic vector and gravitational vector measurements.

13. The system of claim 12, further comprising a filter stored in the memory and wherein the filter causes the processor to filter the magnetic vector measurements provided by the magnetometer based on a function associated with the estimated angular velocity.

14. The system of claim 12, further comprising a filter stored in the memory and wherein the filter causes the processor to filter the gravitational vector measurements provided by the accelerometer based on a function associated with the estimated angular velocity.

15. The system of claim 12, further comprising a filter stored in the memory and wherein the filter causes the processor to filter the magnetic vector measurements provided by the magnetometer based on a function associated with an estimated angular acceleration.

16. The system of claim 12, further comprising a filter stored in the memory and wherein the filter causes the processor to filter the gravitational vector measurements provided by the accelerometer based on a function associated with an estimated angular acceleration.

17. The system of claim 1, further comprising a gyroscope calibration module stored in the memory and executing on the processor and causing the processor to:

determine sensitivity of a bias-calibrated gyroscope using the angular velocity estimate and an angular velocity generated using the calibrated gyroscope.

18. The system of claim 1, further comprising a gyroscope calibration module stored in the memory and executing on the processor and causing the processor to:

determine sensitivity and a bias offset of a non-calibrated gyroscope using the angular velocity estimate and an angular velocity generated using the non-calibrated gyroscope and linear regression.