A compliance feedforward scheme for a class of LTV motion systems

The implementation of lightweight high-performance motion systems in lithography applications imposes among others lower requirements on actuators, amplifiers, and cooling. However, the decreased stiffness of lightweight designs brings the effect of structural flexibilities to the fore especially when the so-called point of interest is not at a fixed location. This is for example the case when exposing a silicon wafer. To deal with structural flexibilities, a feedforward controller is proposed that combines two concepts: (a) continuous compliance compensation control and (b) snap feedforward control. Expanded to a subclass of LTV motion systems, the resulting controller compensates for the position-dependent and time-varying compliance of a flexible structure. The compliance function used will be derived using partial differential equations (PDE). The method is validated by simulation results.