Design, modeling and control of an ankle rehabilitation robot

A robotic device has been designed to carry out the range of motion and muscle strengthening exercises required for ankle rehabilitation. This chapter presents the design, modeling and control of this robotic device. Analysis on the ankle anatomy and required rehabilitation procedures resulted in the use of a parallel robot. Based on singularity and workspace analysis, suitable robot kinematic parameters were selected for the redundantly actuated parallel robot. Modeling of the manipulator and the human ankle was carried out to facilitate controller design. The manipulator was modeled through application of Lagrange's equations while ankle kinematics and dynamics was assumed to be based on the biaxial joint ankle model. A computed torque impedance controller has been developed to regulate the relationship between the applied moments at the ankle and the ankle rotary motion. To ensure accurate estimation of state variables, a kinematic self calibration routine has also been developed for the parallel robot using redundant sensing. To allow for further development of the controller, the recursive least squares algorithm has been applied to estimate the ankle stiffness and damping parameters. This information will be used in future work for stability analysis and controller parameter adaptation. Finally, results on the simulation of the system were presented to show the performance of the developed controller.