M. Popovic, A. Hofmann, and H. Herr. Zero spin angular momentum control: Definition and applicability, 4th IEEE/RAS International Conference on Humanoid Robots, vol. 1, pp. 478–493, 2004.

Abstract

In this paper, we seek control strategies for legged robots that produce resulting kinetics and kinematics that are both stable and biologically realistic. Recent biomechanical investigations have found that spin angular momentum is highly regulated in human standing, walking and running. Motivated by these biomechanical findings, we argue that hiomimetic control schemes should explicitly control spin angular momentum, minimizing spin and CM torque contributions not only local in time but throughout movement tasks. Assuming a constant and zero spin angular momentum. we define the Zero Spin Center of Pressure [ZSCP) point. For human standing contrd, we show experimentally and by way of numerical simutation that as the ZSCP point moves across the edge of the foot support polygon, spin angular momentum control changes from regulation to non-regulation. However, even when the ZSCP moves beyond the foot support polygon, stability can be achieved through he generation of restoring CM forces that reestablish the CM position over the foot support polygon. These results are interesting because they suggest that different control strategies are utilized depending on the location of the ZSCP point relative to he foot support polygon.