A method for estimating the instantaneous axis of rotation of rigid-body motion /

This thesis develops, validates and applies the Least-Squares Axis of Rotation (LSAR) method, a new method for estimating the position and orientation of a moving axis of rotation (AOR) of a three dimensional joint motion. The LSAR estimation method, which is more accurate and robust than previous methods, minimizes the sensitivity to measurement noise by using rigid-body motion constraints, multiple data samples per estimate and sound numerical methods. Results of simulations and in vitro experiments demonstrate that the LSAR method provides better results than the popular Reuleaux and helical axis methods. Furthermore, the parameters obtained with the LSAR method accurately predict the trajectory of arbitrary points of the rigid-body, given their initial position and orientation. An in vivo experiment studying the location of the AOR of the human ankle joint using the LSAR method is presented. The results show that the LSAR method estimates are compatible with published experimental data