Biomechanical Models and Stability Analysis of Bipedal Running = Biomechanische Modelle und Stabilitätsanalyse des zweibeinigen Rennens
Humans and birds both walk and run bipedally on compliant legs. However, differences in leg architecture may result in species-specific leg control strategies as indicated by the observed gait patterns. In this work, control strategies for stable running are derived based on a conceptual model and compared with experimental data on running humans and pheasants (Phasianus colchicus). From a model perspective, running with compliant legs can be represented by the planar spring mass model. However, to compare experimental data to simulated spring mass running, an effective leg stiffness has to be defined. In chapter 2, different methods of estimating a leg stiffness during running are compared to running patterns predicted by the spring mass model, and a new method only relying on temporal parameters is proposed and used in the further course of this work. It has been shown that spring mass running is self-stabilizing for sufficiently high running speeds. However, to provide stability over a broader range of running, control strategies can be applied and swing leg control is one elegant approach to stabilize the running pattern, while maintaining the system energy conservative. Here, linear adaptations of the swing leg parameters, leg angle, leg length and leg stiffness, are assumed. Experimentally observed kinematic control parameters (leg rotation and leg length change) of running humans (chapter 3 and 4) and pheasants (chapter 4) are compared, and interpreted within the context of this model, with specific focus on stability and robustness characteristics.