title: Stable bipedal walking with a swing-leg protraction strategy.
abstract: In bipedal locomotion, swing-leg protraction and retraction refer to the forward and backward motion, respectively, of the swing-leg before touchdown. Past studies have shown that swing-leg retraction strategy can lead to stable walking. We show that swing-leg protraction can also lead to stable walking. We use a simple 2D model of passive dynamic walking but with the addition of an actuator between the legs. We use the actuator to do full correction of the disturbance in a single step (a one-step dead-beat control). Specifically, for a given limit cycle we perturb the velocity at mid-stance. Then, we determine the foot placement strategy that allows the walker to return to the limit cycle in a single step. For a given limit cycle, we find that there is swing-leg protraction at shallow slopes and swing-leg retraction at steep slopes. As the limit cycle speed increases, the swing-leg protraction region increases. On close examination, we observe that the choice of swing-leg strategy is based on two opposing effects that determine the time from mid-stance to touchdown: the walker speed at mid-stance and the adjustment in the step length for one-step dead-beat control. When the walker speed dominates, the swing-leg retracts but when the step length dominates, the swing-leg protracts. This result suggests that swing-leg strategy for stable walking depends on the model parameters, the terrain, and the stability measure used for control. This novel finding has a clear implication in the development of controllers for robots, exoskeletons, and prosthetics and to understand stability in human gaits.
authors.affiliation: Department of Mechanical Engineering, University of Texas San Antonio, One UTSA Circle, San Antonio, TX 78249, USA. Electronic address: pranav.bhounsule@utsa.edu.
authors.forename: Pranav A
authors.initials: PA
authors.lastname: Bhounsule
authors.affiliation: Department of Mechanical Engineering, University of Texas San Antonio, One UTSA Circle, San Antonio, TX 78249, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Zamani
mesh_terms: D001696:Biomechanical Phenomena; D005528:Foot / Q000502:physiology; D006801:Humans; D007866:Leg / Q000502:physiology*; D008954:Models, Biological; D016138:Walking / Q000502:physiology*
keywords: Dead-beat control; Locomotion; Poincaré map; Swing-leg retraction; Walking stability