Event-based PI Control of an Underactuated Biped Walker

This paper addresses the control of a planar, biped robot with one degree of underactuation. Previous work has designed controllers that induce provably, exponentially stable, periodic walking motions at fixed, pre-determined walking rates. These controllers operate in continuous-time during the single support phase of the robot. The present paper shows how to design an event-based PI controller that provides an additional control feature: the ability to regulate the average walking rate to a continuum of values. The PI-controller is active only in the (instantaneous) double support phase and achieves regulation by adjusting key parameters of the in-stride controller.