Hip vertical motion effects on walking gait for biped robots

Abstract In biped robot walking, hip height is often assumed to be constant. However, during human walking, the hip oscillates in the vertical direction. Whether a gait with human-like hip vertical motion (HVM) is more energy efficient than the one with fixed hip height (FHH) has not been thoroughly investigated. We propose two classes of gaits to study the effects of HVM on the modeled mechanical energy consumption of biped robots. The gait parameters are determined by optimization. The optimization criterion for the periodic gaits parameters minimizes the modeled mechanical energy consumption of the joint actuators per unit distance. The optimal gait performances of HVM and FHH were compared for different step lengths and gait periods. Based simulation results, it was observed that: (1) HVM achieves approximately 14% lower modeled mechanical energy consumption per unit distance compared with FHH in simulation; (2) in HVM, the overall hip height decreases and the magnitude of hip oscillation increases as step length increases, and the overall hip height increases as the gait period increases; and (3) the main factor contributing to energy-saving in HVM compared with FHH is the reduction in modeled mechanical energy consumption of the stance knee.