A Discrete-Time Single-Parameter Combined Feedforward/Feedback Adaptive-Delay Algorithm With Applications to Piezo-Based Raster Tracking

We evaluate the performance of a combined feedforward/feedback control architecture applied to the raster scan of a piezo-based positioning system. Proper design of feedforward filters for minimum and nonminimum-phase plants is discussed. Further, empirical work suggests that a nontraditional variation upon the feedforward plant-injection architecture allows our system to track a raster pattern at a greater performance level than previously achieved in our research. This variation is manifested as additional delay inserted in the feedforward control system rather than a unity-gain filter constructed from plant parameters. An online adaptive technique is used to determine the required amount of additional delay. The key benefit of the algorithm is an adaptation calculation that does not require knowledge of plant parameters. This method can be applied to piezo-based positioning systems including atomic force microscopes, other scanning probe microscopes, probe-based data storage systems or other systems in which raster tracking is a critical control objective.