Distributed parameter flexible systems face increasingly tighter specifications and performance requirements, which are typically handled by improving and developing novel feedforward control design methods. In the control synthesis of these systems, taking into account flexible dynamics play an increasingly important role. This work proposes an LTV feedforward control scheme which is based on the feasible and stable inversion of a minimum-phase fourth-order LTV approximation of the plant. This approximation takes into account resonant dynamics and (as a result) provides improved phase tracking. The results are validated through measurement results obtained through a rotational two-mass-spring-damper system.
Abstract-The implementation of lightweight highperformance 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.
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