Robust pseudo virtual passive dynamic walking with control of swing-leg retraction

This paper proposes a simplified method of underactuated virtual passive dynamic walking without having any singularities in the control input, which is termed as the pseudo virtual passive dynamic walking (PVPDW), and analyzes the gait properties considering quasiconstraint on the impact posture. First, we introduce a planar underactuated biped model that added an upper body by means of a bisecting hip mechanism and formulate the method of PVPDW based on the concept of pseudo center of mass. Second, we introduce a control law for inhibiting swing-leg retraction and analyze the effect on the gait stability. The simulation results show that falling down as a 1-DOF rigid body dramatically increases the stable domain even though the hip angle at impact is not precisely kept constant. Finally, we discuss the mechanism from the energy-loss coefficient point of view.