Locomotion Control of Three Dimensional Passive-Foot Biped Robot Based on Whole Body Operational Space Framework

This study presents a whole body operational space (WBOS) framework for controlling three dimensional passive-foot biped robot. Stability of WBOS controller is analyzed, and a foot placement planner is proposed. In many cases, the WBOS controller generates torque commands to execute the trajectories planned by high-level planners at every control loop. The planners design trajectories by sensing the locomotion behaviors over a long horizon. Instead, our planner updates a step location every control loop by estimating the center-of-mass (CoM) state to achieve robust balancing. The robustness is enhanced because contact events vary the stance leg switching time from a given nominal step frequency. Via this new foot placement planner, the locomotion robustness to unknown terrains is improved. Dynamically stable walking are tested on flat and unknown terrains, and under push recovery by using a real-time dynamic simulation.