Dynamic Walking on Highly Underactuated Point Foot Humanoids: Closing the Loop between HZD and HLIP

TL;DR

This paper presents a novel control framework combining Hybrid Zero Dynamics and Hybrid Linear Inverted Pendulum methods to enable the first successful dynamic walking of a point foot humanoid robot, ADAM, demonstrating robustness and adaptability.

Contribution

It introduces a new hybrid control approach that integrates HZD and HLIP for stable, dynamic walking on highly underactuated point foot humanoids, validated through simulations and real-world experiments.

Findings

First humanoid point foot walking achieved

Robustness to pushes and uneven terrain demonstrated

Successful speed tracking and stability confirmed

Abstract

Realizing bipedal locomotion on humanoid robots with point feet is especially challenging due to their highly underactuated nature, high degrees of freedom, and hybrid dynamics resulting from impacts. With the goal of addressing this challenging problem, this paper develops a control framework for realizing dynamic locomotion and implements it on a novel point foot humanoid: ADAM. To this end, we close the loop between Hybrid Zero Dynamics (HZD) and Hybrid linear inverted pendulum (HLIP) based step length regulation. To leverage the full-order hybrid dynamics of the robot, walking gaits are first generated offline by utilizing HZD. These trajectories are stabilized online through the use of a HLIP based regulator. Finally, the planned trajectories are mapped into the full-order system using a task space controller incorporating inverse kinematics. The proposed method is verified through numerical simulations and hardware experiments on the humanoid robot ADAM marking the first humanoid point foot walking. Moreover, we experimentally demonstrate the robustness of the realized walking via the ability to track a desired reference speed, robustness to pushes, and locomotion on uneven terrain.