Series elastic actuators (SEA) are widely used for impact protection and compliant behavior, but they typically fall short in tasks calling for accurate position control. In this paper, we propose a simple and effective heuristic for tuning series elastic actuator controllers to a high impedance position control behavior, which compares favorably with previous publications. Our approach considers two models, an ideal model and a nonideal model with time delays and filtering lag. The ideal model is used to design cascaded proportional-derivative (PD)-type outer impedance and inner force loops as a function of critically damped closed-loop poles for the force and impedance loops. The nonideal model provides an estimate of the phase margin of the position controller for each candidate controller design. A simple optimization algorithm finds the best high-impedance behavior for which the nonideal model meets a desired phase margin requirement. In this way, the approach automates the trade-off between force and impedance bandwidth. The effect of important system parameters on the impedance bandwidth is also analyzed and the proposed method verified with a physical actuator.

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