Standard and lifted approaches of iterative and learning control applied on a motion system

Iterative Learning Control (ILC) is a technique for improving the performance ofsystems or processes that operate repetitively over a fixed time interval. The basic idea of ILCis that it exploits every possibility to incorporate past repetitive control information, such astracking errors and control input signals into the construction of the present control action.Past control information is stored and then used in the control action in order to ensure thatthe system meets the control specifications such as convergence. The goal of the researchpresented in this paper is to liken two different ILC techniques applied to the wafer stage ofa wafer scanner motion system. Namely, we consider briefly the concepts of standard andlifted ILC and we evaluate the ILC performance in terms of tracking errors.