This paper investigates robust stabilization of underactuated two-link manipulators. The well-known benchmark robotic mechanisms of the Acrobot and the Pendubot are taken as case studies. These systems belong to a broader class of underactuated mechanical systems which find many important practical applications. To achieve desired control performance and robustness, we propose a unified control design framework based on the application of a smooth second-order sliding mode (SSOSM) control. Furthermore, we design swingup control laws and use the SSOSM control as balancing control to achieve global stabilization. Simulation results verify the effectiveness of the proposed control design approach. The proposed control design framework can be applied to nonlinear systems other than the two-link manipulators.
two-link manipulator, second-order sliding mode, Acrobot, Pendubot, underactuated systems