Reflexive step-out control superposed on standing stabilization of biped robots

A novel step-out controller which is superposed on the stationary standing controller and enables an automatic transition to such a reflexive behavior in emergency cases is proposed in the framework of the dynamics morphing. The step-out motion has a distinctive property in spite of the simpleness of the motion itself, which requires temporarily inconsistent escapement from an equilibrium point on purpose and transition to another stable equilibrium point produced by the enlargement of the supporting region. It is largely different from steady motions such as standing and periodic stepping, which keep stability around a fixed point. In our scheme, the position of ZMP is determined based on a linear state feedback in the stationary phase, while it is forced to be positioned in the pivot sole to emerge instantaneous step-out motion in the emergency phase. Immediately after the landing, it returns to be manipulated to stabilize the robot again. As the result, two requirements which tend to conflict with each other, namely, the stabilization of COM and the dynamically feasible manipulation of reaction forces, are concurrently achieved. Our scheme is based on the maximally stable COM-ZMP regulator, which enables one to judge if the step-out is necessary for fall-prevention, so that a complete controller on which the stabilization and the emergent disequilibrating maneuver are compatible was implemented.