Feedback Regularization and Geometric PID Control for Robust Stabilization of a Planar Three-link Hybrid Bipedal Walking Model

TL;DR

This paper introduces a novel control approach combining feedback regularization and geometric PID control to achieve robust stabilization of a planar three-link bipedal robot, effectively handling underactuation and environmental variations.

Contribution

It develops a feedback regularization technique to restore mechanical structure, enabling geometric PID control for underactuated bipedal walking stabilization.

Findings

The method tolerates large inclination variations.

It achieves robust asymptotic regulation of virtual constraints.

The approach enhances stability compared to traditional methods.

Abstract

This paper applies a recently developed geometric PID controller to stabilize a three-link planar bipedal hybrid dynamic walking model. The three links represent the robot torso and two kneeless legs, with an independent control torque available at each hip joint. The geometric PID controller is derived for fully actuated mechanical systems, however in the swing phase the three-link biped robot has three degrees of freedom and only two controls. Following the bipedal walking literature, underactuation is addressed by choosing two "virtual constraints" to enforce, and verifying the stability of the resulting two-dimensional zero dynamics. The resulting controlled dynamics do not have the structure of a mechanical system, however this structure is restored using "feedback regularization," following which geometric PID control is used to provide robust asymptotic regulation of the virtual constraints. The proposed method can tolerate significantly greater variations in inclination, showing the value of the geometric methods, and the benefit of integral action.