Limit cycle based walk of a powered 7DOF 3D biped with flat feet

Our ultimate goal is introducing energy-efficient walking patterns to actual humanoid robots. It is known that limit cycle based walking methods, e.g. Passive Dynamic Walking, have such a desired property. Unfortunately, the application of the methods has been limited to simple planar biped models. In this paper, we propose a way of extending limit cycle based walking pattern generation toward a 7DOF 3D biped with ankles, knees, an upper body and with flat feet. This is achieved via first decoupling roll and pitch motions in the frontal/sagittal planes, and then, by designing a limit cycle based walking pattern in the sagittal plane for a planar 5DOF model with ankles, knees and torso. Robustness of the motion is ensured via a feedback control method based on mechanical energy. Then, the planar motion pattern is projected back into 3D space by incorporating dynamic components for gravity compensation and designing a proper trajectory for ankle roll motion. The performances of the walking pattern generator and the controller are confirmed via numerical simulations. The results are presented also as animated motion of a 7DOF 3D biped in the accompanying video.