3-D Underactuated Bipedal Walking via H-LIP Based Gait Synthesis and Stepping Stabilization

In this article, we holistically present a hybrid-linear inverted pendulum (H-LIP) based approach for synthesizing and stabilizing 3-D foot-underactuated bipedal walking, with an emphasis on thorough hardware realization. The H-LIP is proposed to capture the essential components of the underactuated and actuated part of the robotic walking. The robot walking gait is then directly synthesized based on the H-LIP. We comprehensively characterize the periodic orbits of the H-LIP and provably derive the stepping stabilization via its step-to-step (S2S) dynamics, which is then utilized to approximate the S2S dynamics of the horizontal state of the center of mass of the robotic walking. The approximation facilities a H-LIP based stepping controller to provide desired step sizes to stabilize the robotic walking. By realizing the desired step sizes, the robot achieves dynamic and stable walking. The approach is fully evaluated in both simulation and experiment on the 3-D underactuated bipedal robot Cassie, which demonstrates dynamic walking behaviors with both high versatility and robustness.

Automated summary

This article presents a hybrid-linear inverted pendulum (H-LIP) based approach for synthesizing and stabilizing 3-D foot-underactuated bipedal walking. The H-LIP captures the essential components of the underactuated and actuated part of the robotic walking, and the robot walking gait is directly synthesized based on it. By approximating the step-to-step dynamics, a H-LIP based stepping controller provides desired step sizes to stabilize the robotic walking, resulting in dynamic and stable walking. The approach is evaluated on the 3-D underactuated bipedal robot Cassie, demonstrating versatile and robust dynamic walking behaviors.