What Is the Real Frictional Constraint in Biped Walking? - Discussion on Frictional Slip with Rotation

In this paper, a new considering approach for frictional constraint is proposed. It is pointed out that the conventional method only considering translational friction is not appropriate for biped walking, and the frictional rotation constraint should be taken into account. It is stressed that the translational motion and rotational motion will occur simultaneously when slip starts in biped walking, and the frictional rotation constraint plays a more important role than the frictional translation constraint. Furthermore, a method to calculate the slipping frictional force and torque, to predict the most possible slipping direction of a support foot in single support phase is developed. With this method, the quantitative compensation for the yaw-axis moment gets possible. Finally, a new frictional constraint rule applicable for any frictional motions is suggested