Fractional Order Based Controllers For Lower Limb Exoskeleton In Contact Environments

In this paper , a three degrees of freedom lower limb exoskeleton is modeled in case of contacting with ground . The dynamic equations for lower limb exoskeleton in reduced order form are derived based on augmented Lagrange equations which include Lagrange multiplier and Jacobian vectors. The controller is constructed using fractional order calculus theory combined with the sliding mode surface to ensure that the control system has strong robust characteristics and fast convergence. A comparative study between a conventional Fractional Order proportional derivative controller (FOPD) and Fractional order sliding mode (FOSMC) has been established. Simulation results have performed by comparing both controllers in the same conditions. The results of simulation indicate that FOSMC has a good tracking performance and an excellent robustness against system uncertainties and external disturbances as compared with Fractional order PD Controller FOPD.