Robust Elastic Structure Preserving Control for High Impedance Rendering of Series Elastic Actuator

In this letter, a new robust approach is proposed to address the limitation of impedance rendering for Series Elastic Actuators (SEA). The concept of Elastic Structure Preserving (ESP) control allows for the attachment of desired load-side dynamics to the SEA while maintaining a passivity condition, regardless of the parameters for the attached dynamics. The characteristics of ESP control are revisited and translated in the frequency domain, which grants a new perspective to identify its advantages compared to conventional impedance control in terms of passivity. Additionally, we analyze the degradation of performance due to unwanted disturbance and uncertainties in spring stiffness and motor inertia, and a new form of the robust ESP method is proposed by endowing disturbance rejection capability and robustness against uncertainty.