Design framework for a simple robotic ankle evaluation and rehabilitation device

This paper juxtaposes simple yet sufficiently general robotic mechanisms for ankle function evaluation, measurement and physiotherapy. For the choice, design and operation of the mechanism, a kinematics model of foot is adopted from biomechanics, based on the hypothesis that foot kinematics are similar to a 2R serial robot. We undertake experiments, using a 3D scanner and an inertial sensor in order to fully specify the design framework by studying a larger sample of healthy subjects. Our experimental analysis confirms and enhances the 2R foot model, and leads us to the choice of the specific mechanism. We compute the required workspace and thus address the issues required for a complete and efficient design. The robot must be capable to perform several multi-axis motions and sustain a significant range of forces and torques. We compare mechanisms based on serial and parallel robots, and choose a parallel tripod with an extra rotation axis for its simplicity, accuracy and generality.