Utilizing the Natural Dynamics of Elastic Legged Robots for Periodic Motions

Abstract

The progress in mobile computing, electronics and battery technology allowed the creation of very agile mobile robots. Having no cables attached, these robots can move freely in their environment but rely on the power supply by the battery. In addition to a lightweight construction, agile locomotion requires energy efficient motions in order to cope with the limited power and energy. This work focuses on the energy efficient control of a planar bipedal robot by using elastic elements in the joints for short-term energy storage. The considered biped Compliant Runner (C-Runner) exhibits three degrees of freedom per leg and each joint is equipped with a series-elastic actuator(SEA). A controller is developed to enable point foot hopping based on the spring loaded inverted pendulum (SLIP) template. The control design was split into a high-level controller for the rigid-body dynamics and a lower-level control of the elastic dynamics. In particular, the high-level control is, as the gait itself, hybrid and utilizes different strategies on the ground and in the air. The control design is validated for hopping motions by numerical simulations. It is shown, that the underactuated elastic system can outperform the corresponding rigid counterpart with regard to energy efficiency in stance phase. The increased efficiency was achieved by exploiting the elastic nature of the springs to temporarily store and release energy in a beneficial way. By this, over 50% of the energy required for hopping in place could be saved during stance phase.