Controller Design for a Stance-control Knee-ankle-foot Orthosis based on Optimization Techniques

Design of active orthosis is a challenging problem from both the dynamic simulation and control points of view. The redundancy problem of the simultaneous human-orthosis actuation is an interesting exercise to solve concerning the analytical and computational cost effectiveness. The physiological static optimization approach tries to solve the actuation sharing problem. Its objective is to quantify the contributions of muscles and active orthosis to the net joint torques in order to select the proper actuator for the joint. Depending on the disability of each patient, different controllers can be designed. As a matter of fact, the duration of the gait cycle for each patient should be different. In this paper, a PI controller is designed whose parameters are tuned by optimizing a cost function which takes into account the patients muscle power and the error of the knee angle with the reference value. Moreover, the final time is obtained by minimizing the mean of integral squared errors. The performance of the method is shown by designing the controller for three types of patients, ordered from low to high disability. The objective of this work is to use optimal control techniques based on physiological static optimization approach to the design of active orthosis and its control.