A parallel robot for ankle rehabilitation-evaluation and its design specifications

This paper investigates several robotic mechanisms for ankle function evaluation, measurement and physiotherapy. For the choice, design and operation of the mechanism the kinematics of the foot is described. This is based on a kinematics model of foot adopted from biomechanics literature, under the hypothesis that foot kinematics is similar to that of a 2R serial robot. A 3D scanner and an inertial sensor were used 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. 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. The robot must be capable to perform several multi-axis motions and sustain a significant range of forces and torques. The kinematic analysis of the robot confirms that it can follow all the range of foot movements.