Proximal Joint Compliance as a Passive Method for Ground Reaction Force Redirection during Legged Locomotion

Abstract Ground reaction forces (GRFs) are a critical component of legged locomotion, and controlling their direction leads to more stable, efficient, and robust performance. The novelty of this work is to studying passive proximal joint (hips/shoulders) compliance for the purpose of redirecting the GRF passively. Previous works have redirected the GRF actively or studied passive proximal joint compliance for purposes such as swing phase efficiency, but passive methods of stance-phase GRF redirection are under-developed. This paper analyzes the relationship between hip compliance and the GRF direction analytically and with simulations of a trotting quadruped. The results show increased GRF redirection, on average, with increased joint stiffness, for a range of cases. An example method of utilizing this relationship to improve locomotion performance is presented by simulating online compliance adaptation. By adapting the compliance parameter during locomotion, the cost of locomotion was reduced toward the known minimum within the parameter space explored. These results support the conclusion that adjusting the hip compliance provides a passive way of redirecting the GRF, which leads to improved locomotion performance. Other systems can utilize this knowledge to passively improve their own performance.