IMU-based Joint Angle Measurement Made Practical

This contribution is concerned with hinge joint angle calculation based on inertial measurement data in the context of human motion analysis. Unlike most robotic devices, the human body lacks even surfaces and right angles. Therefore, we focus on methods that avoid to assume a certain mounting orientation, i.e. certain orientations in which the sensor should be mounted with respect to the body segment or to a global coordinate system. After a review of available methods that may cope with this challenge, we present two new methods which use recent results on joint axis and position estimation based on the exploitation of kinematic constraints. Results from an experiment with a transfemoral amputee are provided in which we compare the IMU-based methods to an optical 3d motion capture system. RMS errors are found to be less than 0.6◦on the prosthesis and below 4◦on the contralateral leg.