From PD to Fractional Order PD controller used for gait rehabilitation

Lower limb exoskeleton has become the most known solution for gait rehabilitation. It helps children with cerebral palsy disease to overcome their walking disability by gait training. The fundamental part is to control the lower limb exoskeleton using the performing and the adequate controller. Several control systems have been developed. In this paper, two approaches based on Proportional-Derivative (PD) controller are proposed in order to control two degrees of freedom (2-DOF) lower limb exoskeleton. Both controllers employed a filtered action on their derivative terms. A comparative study is established to prove the performance of the fractional order PD (FOPD) regards the filtered PD by means of the integral absolute error criteria and the initial torque values.