Angular momentum primitives for human turning: Control implications for biped robots

Human locomotion involves a number of different complex activities. Humanoid robots, if they are expected to work in a human environment, should be expected to navigate obstacles and transients as well as, or better than a human being. Turning is one aspect of human walking that is poorly understood from the perspective of biomechanics and robotics. It is an important task comprising a large percentage of daily activities through most human environments. During turning the body is subjected to torques that the leave the body unstable. By understanding the contributions of the spin angular momentum about the center of mass we can gain insight on how to design better controllers for bipedal robots. There are several different types of turning; using alternate legs as the stance leg to accomplish the turn and then recover and also, turning can be a steady-state phenomena as well as a more transient behavior depending on speed. The contributions of spin angular momentum to the center of mass is considered in the case of a spin-turn where the inside foot pivots and the opposite foot the direction of the turn returns the body to level ground walking. Motivations for control of human walking bipeds are discussed. Further, a theory is developed that turning is dominated by contributions from the swing leg producing angular momentum about the body during the turn.