H∞ control for piezo-actuated nanopositioning stages with time delays

Many piezo-driven nanopositioning systems employ ultra high resolution capacitive sensors for displacement feedback, which results in significant time delays induced by AD conversion. The infinite dimensionality of such systems poses new challenges for nanopositioning control, where traditional control methods can not be applied directly. In this paper, a model with time delay on a nanopositioning stage is discussed, and a parameter identification method is further deployed using experiments to determine the time delay and other model parameters. A robust H∞ control design approach is also developed by using Pade expansion to approximate the time delay block. Real time experiments with the proposed control design are conducted on a piezo-actuated nanopositioning stage, where high precision motions, robustness against model uncertainties, as well as hysteresis compensation capability, are demonstrated, which significantly outperforms traditional PI control approach.