Simulation and Control of Running Models

Kurzfassung

This work focuses on the locomotion of one-legged robots, with focus on approaches that stabilize passive limit cycles. Locomotion based on the socalled passive gaits promises to greatly reduce the actuation effort required for legged robots to move. In this work, the passive gaits of robots of varying complexity are characterized and stabilizing controllers are reviewed from the literature and newly formulated. The robots are modelled as hybrid dynamical systems and numerically simulated, thereby allowing to validate the proposed control strategies. Firstly, the vertical control through energy regulation of a one-dimensional hopper is considered. Secondly, the SLIP model is reviewed and then extended to the “pitchingSLIP”, with the aim of characterizing its passive gaits with somersaults. Two controllers based on energy and angular momentum regulation are then formulated to stabilize passive gaits with somersaults, making the control effort converge to zero. A further extension of the SLIP template, denominated “bodySLIP”, is then used to test the control approach on a more realistic model. The controllers shall be later extended to more complex cases, in which the somersaults are not necessarily present in the passive gaits. Thirdly, the locomotion of a one-legged robot with a body link is studied. Raibert’s control approach based on the foot placement algorithm is reviewed and compared to the non-dissipative touchdown controller of Hyon and Emura. The latter is then extended to be used with continuous torque profiles and to perform velocity tracking. Moreover, damping is added to the joints in order to study its effect on the controller, which was then modified to achieve stable running even in such conditions. The results obtained shall lay the foundations for a later test on hardware on DLR’s quadruped Bert.