Modeling and benchmarking energy efficiency of Variable Stiffness Actuators on the example of the DLR FSJ

Abstract

Robots with Variable Stiffness Actuators (VSA) are intrinsically flexible in the joints. The built-in mechanical spring has the advantage of a higher peak performance, in some extend increased safety for humans interacting physically with the robot, and promises a more energy efficient robot for certain trajectories. This paper shows the modeling process of a VSA including energy losses on the example of the DLR Floating Spring Joint (FSJ). The model includes the full actuator dynamics with losses in electromechanical transformation of the motors. Furthermore, it models bearing and gear friction with stiction, Coulomb friction, viscous friction, and load dependent effects. With the obtained model the energy losses of benchmark trajectories are investigated and compared with a comparable stiff joint actuator.