Behaviour Synthesis of the Erect Stance for a Biped Control

Abstract

In this paper we use free fall approach to develop a high level control/command strategy for a bipedal robot called ‘BIPMAN’, based on a multi-chain mechanical model with a general control architecture. The strategy is composed of three levels: the ‘Legs and arms’ level, the ‘Coordinator’ level and the ‘Supervisor’ level. The ‘Coordinator’ level is devoted to controlling leg movements and to ensure the stability of the whole biped. Actually perturbation effects threaten the equilibrium of the ‘human’ robot and can only be compensated using a dynamic control strategy. This one is based on dynamic stability studies with a ‘center of mass acceleration control’ and a force distribution on each leg and arm. Free fall in the gravity field is assumed to be deeply involved in the human locomotor control. According to studies of this specific motion through a direct dynamic model, the notion of ‘equilibrium classes’ is introduced. They allow one to define time intervals in which the biped is able to maintain its posture. This notion is used for the definition of a ‘reconfigurable’ high level control of the robot.