Trajectory optimization for walking robots with series elastic actuators

Series elastic actuators are a promising feature for future walking robots. Utilizing the natural oscillation of the elastic actuation can lead to efficient locomotion. However finding a matching combination of joint stiffness and actuator input is challenging as these robots share the properties of underactuated and hybrid dynamic systems. In this paper an optimization problem for cyclic walking of a robot with series elastic actuators is formulated and a flatness based solution method is presented. The method efficiently generates trajectories which exploit the actuator capabilities while respecting all limitations of the system. Additionally the relevant aspects of the trajectories for the design of a flexible robot are discussed.