Muscle-reflex control of robust swing leg placement

Swing leg placement is vital to dynamic stability in legged robots and animals. The most common approaches to generating swing leg motions in robotics use either position or impedance tracking of defined joint trajectories. While these approaches suffice in humanoids, they severely limit swing leg placement under large disturbances in prosthetic limbs, for which stabilizing reactions cannot be planned centrally. We previously identified a control for a conceptual double-pendulum swing leg that does not require predefined trajectories to robustly place the leg into target points on the ground in the presence of large disturbances. We here develop a more detailed neuromuscular model of the human swing leg and interpret the identified control with local muscle reflexes. The resulting reflex control robustly places the swing leg into a wide range of landing points observed in human walking and running, and it generates similar patterns of joint torques and muscle activations. While we plan to take advantage of the comparison between the neuromuscular model and humans to further improve robust swing leg placement, the current results suggest an alternative to existing swing leg controls in humanoid and rehabilitation robotics which does not require central processing.