Stability of Planar Compass Gait Walking with Series Elastic Ankle Actuation

Passive dynamic walking models capture the natural dynamics of stable human-like walking. The passive compass gait (PCG) model, consisting of a point mass and two rigid legs, is among the simplest of such models. The fully passive nature of these models, however, necessitates a sloped ground to recover the energy lost during the ground collisions [1]. A variety of methods have been proposed to eliminate this requirement through different actuation methods. Among these are impulsive energy injection after foot collision, torque actuation on the hip, active ankle joints or tunable compliance in the leg [2, 3]. In this study, we propose a simple model to investigate how series elastic actuation (SEA) at the ankle can be used to achieve stable walking on level ground. The structure we propose is designed to behave in a similar fashion to how humans utilize toe push-off prior to leg liftoff, and is intended for eventual use within a lower-body robotic orthosis.