Effect of Low-Pass Filtering on Passivity and Rendering Performance of Series Elastic Actuation.

We study the effect of low-pass filtering on the passivity and performance of series elastic actuation (SEA) under velocity-sourced impedance control (VSIC) while rendering virtual linear springs and the null impedance. We analytically derive the necessary and sufficient conditions for the passivity of SEA under VSIC with filters in the loop. We demonstrate that low-pass filtered velocity feedback of the inner motion controller amplifies the noise at the outer force loop, necessitating the force controller also be equipped with low-pass filtering.