Joint angle tracking with inertial sensors

• US 20090204031A1
• Filed: 02/12/2009
• Published: 08/13/2009
• Est. Priority Date: 02/12/2008
• Status: Active Grant

• Current Assignee: Wearables IP Holdings LLC
• Original Assignee: Portland State University (Oregon University System)
• Inventors: McNames, James Nathan, Pearson, Sean Christopher, El-Gohary, Mahmoud
• Granted Patent: US 9,597,015 B2
• Time in Patent Office: Days
• US Class Current: 600/595
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/1071 measuring angles, e.g. using goniometers A61B5/1123 takes precedence
• CPC Class Codes: A61B 5/1121 Determining geometric values, e.g. centre of rotation or angular range of movement
• CPC Class Codes: A61B 5/1126 using a particular sensing technique
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence

Abstract

A method for estimating joint angles of a multi-segment limb from inertial sensor data accurately estimates and tracks the orientations of multiple segments of the limb as a function of time using data from a single inertial measurement unit worn at the distal end of the limb. Estimated joint angles are computed from measured inertial data as a function of time in a single step using a nonlinear state space estimator. The estimator preferably includes a tracking filter such as an unscented Kalman filter or particle filter. The nonlinear state space estimator incorporates state space evolution equations based on a kinematic model of the multi-segment limb.

Claims

1. A method for estimating and tracking joint angles of a multi-segment linkage, the method comprising:

a) measuring inertial data as a function of time using a single inertial measurement unit positioned at a distal end of the multi-segment linkage;

b) computing from the measured inertial data estimated joint angles of the multi-segment linkage as a function of time using a nonlinear state space estimator.

2. The method of claim 1 wherein the single measurement unit includes multiple sensors, wherein each of the multiple sensors is selected from the group consisting of a gyroscope, an accelerometer, and a magnetometer.

3. The method of claim 1 wherein the single inertial measurement unit includes a triaxial gyroscope and triaxial accelerometer.

4. The method of claim 1 wherein the nonlinear state space estimator comprises a tracking filter selected from the group consisting of an unscented Kalman filter and a particle filter.

5. The method of claim 1 wherein the nonlinear state space estimator comprises state space evolution equations based on a kinematic model of the multi-segment linkage.

6. The method of claim 1 wherein the nonlinear state space estimator comprises state space evolution equations that incorporate physical limitations of the joint angles.

7. The method of claim 1 wherein the nonlinear state space estimator comprises observation equations that incorporate sensor measurement noise.

8. The method of claim 1 wherein the nonlinear state space estimator computes an estimate of uncertainty of the estimated joint angles.

9. The method of claim 1 wherein the nonlinear state space estimator computes predicted estimates of the joint angles.

10. The method of claim 1 wherein the nonlinear state space estimator computes smoothed estimates of the joint angles.

11. The method of claim 1 wherein the multi-segment linkage is a human limb.

12. A system for estimating joint angles of a multi-segment linkage, the system comprising:

a) a single inertial measurement unit for measuring inertial data as a function of time from a distal segment of the multi-segment linkage;

b) a memory for storing the measured inertial data; and

c) a nonlinear state-space estimator implemented in a computer for estimating from the measured inertial data the joint angles of the multi-segment linkage as a function of time.

13. The system of claim 12, wherein the single measurement unit includes multiple sensors, wherein each of the multiple sensors is selected from the group consisting of a gyroscope, an accelerometer, and a magnetometer.

14. The system of claim 12 wherein the single inertial measurement unit includes a triaxial gyroscope and triaxial accelerometer.

15. The system of claim 12 wherein the nonlinear state space estimator comprises a tracking filter selected from the group consisting of an unscented Kalman filter and a particle filter.

16. The system of claim 12 wherein the nonlinear state space estimator comprises state space evolution equations based on a kinematic model of the multi-segment linkage.

17. The system of claim 12 wherein the multi-segment linkage is a human limb.