Dynamic Trajectory Generation for Serial Elastic Actuated Robots

Robotic systems can benefit from the introduction of properly chosen joint elasticity. Besides their robustness against rigid impact, the energy saving capabilities may increase the system dynamics. In this paper, a method applicable for robots with serial elastic joints is presented, which embodies a desired oscillatory behavior into the hardware and thereby leads to improved performance. This is achieved by shaping the flexible joint robot as a linear onemode system and embodying the natural frequency of the real intrinsic behavior. An algorithm is presented for shaping the one-mode property and exciting the system via a negative definite damping term in a decoupled coordinate space. The output of the approach is a dynamic trajectory resulting in a coordinated link motion and synchronized transfer of kinetic and potential energy. Furthermore, the dynamic trajectory is commanded to the real robot via a motor PD controller, where asymptotic stability for both subsystems—i.e. the trajectory generator and the controlled robot—is proven. The method is validated on a two-link serial elastic actuated robot. Both, simulation and experiment confirm the eigenmode embodiment, energy efficiency by velocity enlargement between motor and link side motion, and synchronized joint motion.