Integration of Hip Strategy and Ankle Strategy by Optimal Regulator on Humanoid Balance Control

Abstract

This paper proposes an integration of two balancing controllers; so called, Hip Strategy and Ankle Strategy for humanoid model. The former achieves the balance equilibrium utilizing the reaction moment from the high-speed upper body motion. The latter also achieves the balancing, but does so in the way that won't interrupt the hip strategy. The controller integration is done by computing the optimal inputs; the horizontal ground reaction force and ankle torque, by linear quadratic regulator, then transformed to the joint torques. We also utilize a special structure of the system having the relative degree of three, first found by Stojic, to stabilize the upright posture. Simulation results shows that the humanoid model robustly achieves dynamic upright balance from the initial posture far from static equilibria, while simultaneously avoiding the negative vertical ground reaction force that often happens with Hip Strategy alone.