Stability of a Compass Gait Walking Model with Series Elastic Ankle Actuation

Kerimoglu, Deniz
Morgul, Omer
Saranlı, Uluç
Passive dynamic walkers exhibit stable human-like walking on inclined planes. The simplest model of this behavior is the well known passive compass gait (PCG) model, which consists of a point mass at the hip and two stick legs. Due to their passive nature, these systems rely on a sloped ground to recover energy lost to ground collisions. A variety of methods have been proposed to eliminate this requirement by using different actuation methods. In this study, we propose a simple model to investigate how series elastic actuation 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 to be used for controlling the ankle joint in a lower-body robotic orthosis. We present the derivation of the hybrid equations of motion for this model, resulting in a numerically computed return map for a single stride. We then numerically identify fixed points of this system and investigate their stability. We show that asymptotically stable walking on flat ground is possible with this model and identify the dependence of limit cycles and their stability on system parameters.


Stability and control of planar compass gait walking with series-elastic ankle actuation
KERIMOGLU, Deniz; MORGUL, Omer; Saranlı, Uluç (2017-03-01)
Passive dynamic walking models are capable of capturing basic properties of walking behaviours and can generate stable human-like walking without any actuation on inclined surfaces. The passive compass gait model is among the simplest of such models, consisting of a planar point mass and two stick legs. A number of different actuation methods have been proposed both for this model and its more complex extensions to eliminate the need for a sloped ground, balancing collision losses using gravitational potent...
Stability of Planar Compass Gait Walking with Series Elastic Ankle Actuation
Kerimoğlu, Deniz; Morgül, Ömer; Saranlı, Uluç (null; 2015-07-24)
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 fo...
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Citation Formats
D. Kerimoglu, O. Morgul, and U. Saranlı, “Stability of a Compass Gait Walking Model with Series Elastic Ankle Actuation,” 2015, Accessed: 00, 2020. [Online]. Available: