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Stable Running with Segmented LegsLauflabor Locomotion Laboratory, University of Jena, Domburger Strasse 23, 07743 Jena, Germany, juergen.rummel{at}uni-jena.de
Lauflabor Locomotion Laboratory, University of Jena, Domburger Strasse 23, 07743 Jena, Germany, andre.seyfarth{at}uni-jena.de
Spring-like leg behavior is found in both humans and animals when running. In a spring-mass model, running proves to be self-stable in terms of external perturbations or variations in leg properties (for example, landing angle). However, biological limbs are not made of springs, rather, they consist of segments where spring-like behavior can be localized at the joint level. Here, we use a two-segment leg model to investigate the effects of leg compliance originating from the joint level on running stability. Owing to leg geometry a non-linear relationship between leg force and leg compression is found. In contrast to the linear leg spring, the segmented leg is capable of reducing the minimum speed for self-stable running from 3.5 m s-1 in the spring-mass model to 1.5 m s-1 for almost straight joint configurations, which is below the preferred transition speed from human walking to running (
Key Words: self-stability • running • two-segment leg • spring-mass model • SLIP • knee joint stiffness • nonlinear stiffness
The International Journal of Robotics Research, Vol. 27, No. 8,
919-934 (2008) |
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2 m s-1). At moderate speeds the tolerated range of landing angle is largely increased (17° at 5 m s-1) compare with the linear leg spring model (2°). However, for fast running an increase in joint stiffness is required to compensate for the mechanical disadvantage of larger leg compression. This could be achieved through the use of non-linear springs to enhance joint stiffness in fast running.