Full-degree-of-freedom impact mitigation for dynamic quadruped robots via nonlinear active compliance control

Effective impact mitigation is a critical aspect of ensuring the stable motion of legged robots, especially in challenging environments. This work introduces a leg motion control system integrating nonlinear active compliance and impedance control with a balance controller. Designed for high-speed dynamic locomotion, the proposed system achieves superior impact absorption and precise leg position tracking without relying on passive spring mechanisms. The proposed nonlinear control, featuring state-dependent adaptive laws for stiffness and damping, outperforms linear alternatives in vibration suppression while maintaining tracking accuracy. A nonlinear PD parameter tuning method and optimized footstep locations are utilized for the balance controller to ensure quick recovery from external disturbances. Experimental validation on the SCIT Dog platform demonstrates exceptional cushioning capability during high-speed maneuvers and effective full-degree-of-freedom impact mitigation, including lateral disturbances. Crucially, this work advances beyond prior research by demonstrating active springless leg compliance/impedance control with formal stability guarantees and represents a fundamental locomotion layer that is essential for enabling future autonomous navigation capabilities in quadruped robots operating in unstructured environments.