Dynamics Assessment and Minimal Model of an Orthosis-Assisted Knee Motion

Assisting a human motion with an orthosis requires the modeling of the human-orthosis system to estimate online human joint torque. The current paper proposes an assessment framework for: (i) the analysis of the sources of inaccuracies in joint torque estimation and (ii) the selection of the minimal dynamic model required to estimate joint torque. The proposed framework was validated with eight-healthy subjects wearing a knee joint orthosis and performing standardized sitting knee flexion/extension motions. As a result, the misalignment between the orthosis and wearer knee joint axis was quantified, as well as the influence of the kinematic and dynamic measurements in the knee joint torque estimation. Based on these results, a minimal dynamic model, of only two parameters, estimating 97.5% of the reference knee joint torque was selected.