Composite position control based on finite time observer and super-twisting algorithm for flexible lower exoskeleton

To improve the control accuracy of flexible exoskeleton of lower limb under external disturbance and parameter uncertainty, a compound position control method is designed. Firstly, the Lagrange function is used to establish the model of exoskeleton robot . Secondly, two finite time state observers (FTSO) are utilized to observe disturbances that will be compensated, because the system is impacted by both matched and unmatched disturbances. In the controller, the super twisting algorithm is used and to guarantee that the knee joint's trajectory tracking error will converge. Finally, the Lyapunov function is set up to show that the controller is stable. It can be seen from the experiment that the suggested control method is better than the conventional SMC because it has a more precise trajectory tracking effect and is more stable.