An Analysis of the Effect of Gravity Compensation on Compliant Biped Walking Controllers

\This paper presents and compares three distinct control schemes aimed at the endowment of compliant humanoid robots, with locomotion capabilities. It is demonstrated that the aforementioned control methods share a common foundation composed of linear state feedback elements, although they distinguish themselves from one another through their utilization of different forms of gravity compensation terms. The controller analysed herein exploits the direct motor position feedback, while the benchmarking schemes revolve around the use of link position feedback and desired link position gravity compensation. Additionally, it is demonstrated that the application of the motor position-based gravity compensation schemes on the various dynamical models, leads to asymptotically stable closed-loop systems for regulation, whilst delineating the extension to trajectory tracking. The practical results generated from a series of experiments involving the COmpliant huMANoid (COMAN), corroborate the controllers' abilities to permit the successful execution of walking trajectories. Furthermore, they reveal the superior efficacy of the two feedback-dependent gravity compensation control techniques in terms of tracking walking trajectories, in comparison to the feedforward controller.