Exploiting iterative learning control for input shaping, with application to a wafer stage

The objective of an input design technique is to design an input to the system that results in an optimal tracking performance given some knowledge of the system response. Many such techniques focus on eliminating excitation of certain dominant system poles from the trajectory thus reducing any vibrations caused by these system poles. A downside to these methods is that they result in an elongation of the original trajectory. For a point-to-point control setting this means that there will be a trade-off between the elongation of the trajectory and the reduction of the settling time. In this paper will be shown that iterative learning control (ILC) can be used to design the input signal (trajectory) for a point-to-point motion in a way that eliminates all vibrations in the system without any elongation of the trajectory. This result is exactly the objective of classic input shaping techniques. The technique is illustrated with an application to a high precision wafer-stage.