Suppressing non-collocated disturbances in inferential motion control:With application to a wafer stage

Structural deformations are a key obstruction to achieve the ever-increasing performance demands in high-precision positioning systems. This applies especially to systems in which the performance variables are not directly measured and the disturbance inputs do not coincide with the actuated inputs. The aim of this paper is to establish a robust observer-based inferential motion control framework, wherein non-collocation of both the performance variables with the measured variables, and the disturbance variables with the actuated variables is addressed explicitly. Experimental results from an industrial wafer stage setup confirm that the developed techniques lead to a significant performance improvement compared to classical approaches.