Human motion analysis using inertial sensing

C. Baten

Roessingh Research and Development, Enschede, The Netherlands

Introduction

Recent developments have delivered new technology for ambulatory assessment of 3D kinematics of miniature motion sensors. These sensors combine signals from 3 accelerometers, 3 rate gyroscopes, 3 magnetometers and a temperature sensor, all inside one module, through optimal Kalman filtering technology into accurate estimates of 3D orientation, angular velocity and several components of 3D acceleration. Orientations are derived as the orientation of the sensor casing axes relative to a global inertial ‘world’ coordinate system and velocities and accelerations are derived relative to the sensor casing axes. To perform human motion analysis with this type of sensor technology human body segment kinematics have to be derived from the sensor kinematics. For this the relationship between the casing axes frame and the axes frame of the body segment on which the sensor is mounted has to be known.

Methods

Because mounting the sensor such that both body segment and sensor axes frame are in parallel is not a practically viable option, the sensors are mounted as stable as possible after which the relative 3D orientation of the sensor axes frame and the body axes frame are determined in a short calibration procedure. In this procedure sensor data is recorded during a few recordings in which a: the body segment is rotated purely around one of its defined segment frame axes or b: one of the body segment frame axes is kept parallel with one of its defined frame axes.

Results

This ‘helical axes’-calibration was tested and validated in normals for accuracy and robustness for 3 parts of the trunk, for shank and thigh and for upper and lower arm.

Discussion

The quality of this calibration determines the quality of the clinical motion assessment. It depends in part on the ability of the subject to consistently perform the required motions. Therefore research is started to develop derived methods for use with patients in several areas of motion analysis and test accuracy, robustness of variations of this methods and protocols.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

© 2005 Noldus Information Technology bv