Hybrid Modeling and Fractional Control of a SCKAFO Orthosis for Gait Assistance

SCKAFO, stance-control knee-ankle-foot orthosis, is a type of orthosis that permits free knee motion during swing while resisting knee flexion during stance, supporting thereby the limb during weight bearing. This orthosis specially assists patients who have incomplete spinal cord injury and allows them to walk with the aid of canes or crutches, maintaining a proper gait. In this paper, based on the human walking biomechanics, the SCKAFO hybrid modeling is proposed, which consists of eight different stages whose evolution is given by means of four planar sensors on each foot. In the model, it is considered that the patients can move their hip but not their knee that will be controlled using a DC motor. Two fractional order controllers are designed, following decision based control techniques, to control the knee angle. Simulation results are given in order to demonstrate the efficiency of the system performance.