Consistent biped step control with COM-ZMP oscillation based on successive phase estimation in dynamics morphing

A self-consistent autonomous foot stepping control is proposed. It works on a self-excited oscillator of COM (center of mass) developed by the author, in which the stabilizability is maximized through a nonlinear feedback to the ZMP (zero-moment point) manipulation. Different from the conventional artificial CPGs (central pattern generators), its dynamics seamlessly morphs from/to that of a standing controller and enables an easy tuning of controller parameters for the desired oscillation amplitude and period. Based on a novel motion index defined by a complex number, the phase and spatial information about the COM-ZMP movement is abstracted. By a successive estimation of the foot-liftable phase, the up-down of feet is controlled so that it automatically synchronizes to the COM-ZMP oscillation with the unilaterality constraint on the reaction forces explicitly taken into account.