Feedback control for compass-like biped robot with underactuated ankles using transverse coordinate transformation

This paper deals with the walking control problem of a compass-like biped robot with underactuated ankles in the framework of hybrid control systems. The compass-like biped robot is equipped with a constraint mechanism to lock the hip angle when the swing leg retracts. First, based on the Poincare return map, a limit cycle gait is obtained, and the stability of the gait is also checked. Then, a method based on transverse coordinate transformation is introduced to transform the problem of tracking a desired limit cycle into the stabilization problem of a linear time-invariant impulsive system. A feedback control design for stabilizing the walking gait is then presented. Finally, comparisons to several existing approaches for the similar model are provided to demonstrate the advantages of our proposed approach.