Design and experimental implementation of a compliant hybrid zero dynamics controller for walking on MABEL

This paper extends the method of virtual constraints and hybrid zero dynamics, developed for rigid robots with a single degree of underactuation, to MABEL, a planar biped with a novel compliant transmission. A time-invariant feedback controller is designed for realizing exponentially stable waking gaits in such a way that the closed-loop system preserves the natural compliance of the system, and therefore the energetic benefits of springs. This is accomplished by incorporating the compliance into the hybrid zero dynamics. The compliant-hybrid-zero-dynamics-based controller is implemented experimentally and shown to realize stable walking gaits which make use of the compliance to store and return energy to the gait.