Experimental Comparison of Whole-Body Control Formulations for Humanoid Robots in Task Acceleration and Task Force Spaces

TL;DR

The paper experimentally compares inverse-dynamics WBC (ID-WBC) and passivity-based WBC (PB-WBC) on a humanoid platform, highlighting their fundamental differences in task acceleration versus task force spaces and their robustness to disturbances. Four experiments—swing-foot control, squats, squats with unmodeled weight, and jumping—reveal that PB-WBC is typically easier to tune and yields more uniform disturbance rejection across tasks, while ID-WBC requires high, inertia-aware gains for low-inertia tasks. The authors provide theoretical analyses of how disturbances appear in each formulation and validate them with hardware experiments, including implications for landing and impact robustness. Overall, the study informs controller selection by trade-offing tuning simplicity, formulation constraints, and robustness to contact transitions in humanoid WBC applications.

Abstract

This paper studies the experimental comparison of two different whole-body control formulations for humanoid robots: inverse dynamics whole-body control (ID-WBC) and passivity-based whole-body control (PB-WBC). The two controllers fundamentally differ from each other as the first is formulated in task acceleration space and the latter is in task force space with passivity considerations. Even though both control methods predict stability under ideal conditions in closed-loop dynamics, their robustness against joint friction, sensor noise, unmodeled external disturbances, and non-perfect contact conditions is not evident. Therefore, we analyze and experimentally compare the two controllers on a humanoid robot platform through swing foot position and orientation control, squatting with and without unmodeled additional weights, and jumping. We also relate the observed performance and characteristic differences with the controller formulations and highlight each controller's advantages and disadvantages.

Figures (9)

• Figure 1: Snapshots of experiments covered in this paper: jumping (top), disturbed and undisturbed squatting (bottom left), and foot position and orientation control (bottom right). Supplemental video collects all experiments.
• Figure 2: Snapshots of Kangaroo following the desired foot position and orientation trajectories while hanging from a crane.
• Figure 3: The response of ID-WBC and PB-WBC to the foot position and orientation control tasks. The feet are commanded to move back and forward at a constant height and orientation w.r.t. the inertial frame. The desired trajectory is a peak-to-peak $30cm$ sinusoidal signal with $0.2 Hz$ frequency.
• Figure 4: Snapshots of Kangaroo doing $20cm$ squats.
• Figure 5: The response of ID-WBC and PB-WBC to squatting. The desired trajectory is a peak-to-peak $20cm$ sinusoidal signal with $0.4 Hz$ frequency.