Balance Gait Controller for a Bipedal Robotic Walker With Foot Slip

Low-friction ground conditions present a navigation challenge for bipedal robotic locomotion. While robots might traverse slippery surfaces by carefully planning trajectories, balance recovery from unexpected slip remains a challenge. We present a motion and gait control design for bipedal robotic walkers under foot slip. Slipping dynamics are explicitly considered as a part of the walker's dynamic model. A two-mass inverted pendulum model is presented to capture the ankle actuation effect and used to determine the gait recovery stepping location. A whole-body balance controller is then applied to realize the stepping task. The integration of the abstracted inverted pendulum model and the multi-link model helps to build a whole-body operational space design to compute the controlled joint torques. We design a five-link planar walking robot and implement the control system on the platform. A comprehensive set of walking experiments are presented, demonstrating the performance of the controller for walking on both high-, low-, and extremely low-friction ground surfaces. The experimental results confirm that explicit consideration of foot slip improves the performance and yields a stable gait on a low-friction ground surface.