Increasing the robustness of Acrobot walking control using compliant mechanisms

Application of the compliance to increase the robustness of the bipedal walker locomotion is the main target of this paper. The control of bipedal robots with point feet is one of the most challenging problems in the domain of hybrid dynamical systems. In order to make an exponentially stable periodic walking for an Acrobot as a planar biped with only one degree of freedom, a controller is designed based on the hybrid zero dynamics analysis. Then, through appropriate alterations in robot structure, the controller complexities are reduced which result in fewer parameters for tuning. Improvement of the robot structure via compliance insertion not only compensates the lower degree of freedom of the control design process, but also expands the domain of stability of the closed-loop system. In this regard, a nonlinear damper is inserted between two legs of Acrobot to enable it to walk on a wider range of slopes. The main controller is designed for walking on a flat terrain and the compliance of the damper empowers it to make stable walking on slopes up to 17°. The simulation results confirmed the efficiency of the proposed approach.