Attenuation of disturbances introduced by dynamic links in precision motion systems using model-based observers

This paper presents an extension to the Unknown Input Disturbance Observer (UIDO) and the Disturbance Estimation Filter (DEF). This extension enables the inclusion of the mechanics of dynamic links to the observer model, in order to attenuate the specific disturbances introduced by those dynamic links. A design method of the state space feedback gain based on the dynamics, and an observer gain based on basic Kalman filter theory is given. It is shown how the observer is designed for a practical example; the cable schlepp within the wafer stage of a lithography machine. Using a simple model of the cable schlepp the disturbance observer design has been validated with an experiment on an actual machine.