Practical finite-time adaptive sliding mode control for 5-link biped robot in the presence of uncertainty

In this paper, novel practical finite-time robust adaptive controllers are investigated for a 5-link single support phase (SSP) lower limb biped robot subjected to unknown physical and dynamical parameters, disturbances, and unknown input saturation. The developed adaptive approaches are based on a terminal sliding surface and a finite-time stability analysis to design controller and adaptation laws. The adaptive mechanisms deal with estimating unknown terms, the upper bound of the unknown term vector, or estimating the unknown limits of input saturation. Consequently, the proposed approach is applicable when the physical and dynamical parameters of the robot and the saturation input parameters are not known. In addition, the Lyapunov stability approach warranties that the tracking errors are robust finite-time uniformly ultimately bounded and provides the practical finite-time stability of the closed-loop system. Finally, numerical simulations are provided to show the feasibility, effectiveness, and performance enhancement of the proposed methods over state-of-the-art methods.