Posture Control of Legged Locomotion Based on Virtual Pivot Point Concept

This paper presents a novel control approach for achieving robust posture control in legged locomotion, specifically for SLIP-like bipedal running and quadrupedal bounding with trunk stabilization. The approach is based on the virtual pendulum concept observed in human and animal locomotion experiments, which redirects ground reaction forces to a virtual support point called the Virtual Pivot Point (VPP) during the stance phase. Using the hybrid averaging theorem, we prove the upright posture stability of bipedal running with a fixed VPP position and propose a VPP angle feedback controller for online VPP adjustment to improve performance and convergence speed. Additionally, we present the first application of the VPP concept to quadrupedal posture control and design a VPP position feedback control law to enhance robustness in quadrupedal bounding. We evaluate the effectiveness of the proposed VPP-based controllers through various simulations, demonstrating their effectiveness in posture control of both bipedal running and quadrupedal bounding. The performance of the VPP-based control approach is further validated through experimental validation on a quadruped robot, SCIT Dog, for stable bounding motion generation at different forward speeds.