Effects of compliant ankles on bipedal locomotion

The influence of ankle compliance on bipedal robot locomotion is investigated in this paper. The focus is on reduction of energy consumption. The concept of hybrid zero dynamics is adapted to design walking gaits with three phases: underactuated heel roll, full actuation and underactuated toe roll. Ankle springs work in parallel with the ankle actuators. Stiffness and offset of the linear torsional springs at the ankle and gait parameters are optimized simultaneously. It is shown that simultaneous optimization of spring properties and gait is superior to optimizing the spring after the gait. Optimal spring stiffness and offset lead to a major reduction in energy consumption. Furthermore, a more human-like gait is observed for simultaneous optimization of gait and spring parameters compared to gait optimization with zero stiffness.