Humanoid Gait Synthesis with Moving Single Support Zmp Trajecories

The control of a biped humanoid is a difficult task due to the hard-to-stabilize dynamics. Walking reference trajectory generation is a key problem. Reference generation techniques with the so-called Linear Inverted Pendulum Model (LIPM) are reported. Improved versions of the LIPM based reference generation are obtained by applying the Zero Moment Point (ZMP) Criterion, widely employed in the stability analysis of biped robot walk. Typically, the ZMP reference during a stepping motion is kept fixed in the middle of the supporting foot sole. This kind of reference generation lacks naturalness, in that, the ZMP in the human walk does not stay fixed, but it moves under the supporting foot. This paper proposes a reference generation algorithm based on single support foot ZMP references which move in directions parallel and perpendicular to the walking direction. A simple inverse kinematics based independent joint position controller is used in the full dynamics 3-D simulations with the model of a 12 Degrees of Freedom (DOF) biped robot. Simulation studies indicate that the moving ZMP references result in a more successful walk.