Stabilizing humanoids on slopes using terrain inclination estimation

This paper presents an integrated control framework for balancing humanoids on uneven terrains combining stabilization control and terrain inclination estimation. The stabilization is realized by passivity based admittance control that utilizes the force/torque feedback in feet to actively regulate the compliance. The logic-based terrain estimation algorithm exploits feet to probe the terrain inclination and deals with underactuation when feet tilt on the contact surface. The equilibrium position in the admittance control is thereby adapted for recovering balance on the slope. Both the theoretical work and experimental validation are presented. The method is implemented and validated on the real humanoid by demonstrating the capability of estimating terrain inclination, balancing on the slope with varying gradient, and maintaining upright posture in the meantime. Experimental data such as inclination estimation in the comparison study, center of pressure measurement, and body attitude compensation are presented and analyzed.