Study of Toe Joints to Enhance Locomotion of Humanoid Robots

Most humanoid robots still walk with bent knees and flat feet which is considered highly unnatural, i.e. not biologically inspired, and also energy inefficient. The paradigm and benefits of walking with non-bent knees and with an active toe joint are explored in this study. Non-bent knee walking trajectories are created using an instantaneous capture point (ICP) planner within a momentum based quadratic program (QP) whole body control framework. The toe joint trajectories are obtained as an emergent behavior of the QP determined by under-constraining the objective function and modeling movement of the toe joint as a torsional spring. A comparison between similar systems with and without toe joints reveal a stronger thrust vector during toe-off, reduced knee joint angles and a more human like gait. Experiments in simulation are conducted on the Atlas humanoid robot.