Concepts of Softness for Legged Locomotion and their Assessment

In human and animal locomotion, compliant structures play an essential role in the body and actuator design. Recently, researchers have started to exploit these compliant mechanisms in robotic systems with the goal to achieve the yet superior motions and performances of the biological counterpart. For instance, compliant actuators such as series elastic actuators (SEA) can help to improve the energy efficiency and the required peak power in powered prostheses and exoskeletons. However, muscle function is also associated with damping-like characteristics complementing the elastic function of the tendons operating in series to the muscle fibers. Carefully designed conceptual as well as detailed motion dynamics models are key to understanding the purposes of softness, i.e. elasticity and damping, in human and animal locomotion and to transfer these insights to the design and control of novel legged robots. Results for the design of compliant legged systems based on a series of conceptual biomechanical models are summarized. We discuss how these models compare to experimental observations of human locomotion and how these models could be used to guide the design of legged robots and also how to systematically evaluate and compare natural and robotic legged motions. Biomechanics of Legged Locomotion Computer simulation models can be very powerful tools for analyzing and describing human and animal locomotion. In the last years sophisticated human motion simulation environments have become widely accessible to the research community both for forward dynamics (e.g. OpenSim [5]) as well as for inverse dynamic calculations (e.g. AnyBody [4]). These software tools can be used to describe human (or animal) motion dynamics as the result of the interaction between