Extended State Observer-Based Robust Capture Point Tracking Controller of NAO Humanoid

Abstract In this work, a robust control design for balance and walking control of humanoid biped robot in the presence of external disturbances is proposed. The controller combines capture point (CP) tracking controller with extended state observer (ESO) in order to achieve robustness against unknown disturbances, parametric uncertainties, as well as unmodeled dynamics denoted as a composite disturbance. The effect of the composite disturbance is estimated by ESO as an extended state of the system, and the estimate is used to augment the CP tracking controller in order to achieve robustness. Closed-loop stability analysis under the proposed control is carried out. The efficacy of the design is first verified for a simplified linear inverted pendulum model (LIPM) and subsequently, through NAO multibody simulations. It is shown that the proposed design achieves robust balance and walking control for biped humanoid robot in the presence of unknown composite disturbances.