On the Stiffness Selection for Torque-Controlled Series-Elastic Actuators

Abstract

Series-elastic actuators are quickly becoming the core component of robots operating in real-world environments, allowing for robust, safe, torque-controlled robots. This letter investigates the influence of the selected stiffness and control parameters. By consolidating several analyses, it is shown two opposing criteria exist for the choice of stiffness: lowering stiffness increases actuator transparency, while increasing stiffness increases torque tracking bandwidth. This fact is used in the context of impedance rendering to propose an optimal stiffness selection criterion that maximizes the renderable impedance frequency. This provides a concrete method for choosing stiffness based on the application of the joint. Extensive simulation and experimental results are presented that validate the analyses.