A Hybrid Force/Impedance Motion Controller for Robust Quadruped Locomotion on Sandy, Slippery, and Collapsing Terrains

Slippery, sandy, or collapsing terrains still represent a challenging scenario for quadruped locomotion. Mainly in situations where not a single robot failure is admissible. In this paper, we propose a new control structure that combines well-known optimization-based strategies applied to legged motion control, i.e. whole-body controllers (WBC), with indirect force control strategies, i.e. impedance control, to increase quadruped locomotion robustness when navigating on such terrains. The proposed strategy is mainly designed for gaits that allow for statically stable locomotion and its core aspect lies in the maintenance of the locomotion support polygon. We introduce a new assessment metric and extensively evaluate the controller performance through simulation and experimental trials using a Unitree’s Aliengo quadruped robot.