Do Non-linearities Enhance Stability of Bipedal Locomotion?

This contribution deals with the question if and how non- linearities can improve the stability of bipedal locomotion. In order to investigate this issue, three nonlinear modifications of a planar point- mass model are investigated: the classical spring-mass model, a model with nonlinear leg kinematics and a model with a sophisticated nonlin- ear muscle model. Already the simple spring-mass model is nonlinear due to its variable stucture: this basic model will serve as a benchmark. Augmented with leg-kinematics the passive two segmented leg model in- corporates geometric non-linearities. By substituting the passive spring element by muscle-dynamics, the model is extended with physical non- linearities. The orbital stability of the periodic motion is analysed using Poincare-maps at touch down. A parameter study is carried out in order to reveal differences in performance and stability of periodic motion of the three models. The influence of the different types of non-linearities is demonstrated and discussed in detail.