A Planar Stable Walking Model based on Ankle Actuation and the Virtual Pendulum Concept

Abstract

In this paper, we propose a novel planar biped model which achieves asymptotically stable walking, based on ankle actuation and the virtual pendulum concept. Simple models for walking have provided useful insights in understanding fundamental principles of human locomotion as well as developing controllers for biped robots. Existing simplest walking models include a point mass with either rigid legs or compliant legs. Both models are able to describe different gaits such as walking and running, but are not able to address posture stabilization, which is another important issue in bipedalism. Recently, the virtual pendulum (VP) concept was proposed as an intuitive posture stabilization strategy and successfully demonstrated on the compliant leg scheme. However, the model does not address inherent peripheral mechanics of walking, i.e., ankle actuation and collisional energy loss from foot-ground interaction. The model proposed in this paper consists of a rigid trunk, rigid legs and ankle actuation. The energy dissipation due to collision and compensation by ankle actuation play an essential role for asymptotically stable walking, while the trunk posture is stabilized based on the VP concept. Nonlinear dynamic simulation verifies that the model constructs a stable limit cycle with a small angular oscillation of trunk.