Selection of Positive Position Feedback Controllers for Damping and Precision Positioning Applications

Positive Position Feedback (PPF) is a widely used control technique for damping the lightly damped resonant modes of various dynamic systems. Though PPF controller is easy to implement any rigorous mathematical optimization is not possible due to the controller structure. Therefore, almost all PPF designs reported in literature use a trial-and-error approach to push the closed-loop system poles adequately into the left-half plane to achieve adequate damping. In this paper, a full parametric study of the PPF controller based on the closed-loop DC gain vs achievable damping relationship is carried out. It is shown that the PPF controller best suited to only damp the resonance is not the best if both damping and tracking control is required (as is the case in most precision positioning systems). This leads to a more systematic and goal-oriented selection of appropriate PPF controller for specific applications, hitherto unreported in literature. Experiments performed on a piezoelectric-stack actuated nanopositioning platform are presented to support this conclusion.