Development of an adaptive observer algorithm using RMS signal

Because of recent progress of nano positioning technology, the feature of low vibration in controlling a stage has received great attention. In lithography process, the stage hunting directly affects the performance of the manufactured product. The stage perturbation results from various noise sources, and actually the statistical characteristics of the noises easily changes. This paper focused on the design of a novel state observer which filters out the random noises that cause stage vibration, and simultaneously maintains fast detection against external disturbances. The proposed algorithm was designed to use the RMS signal in the feedback loop of the position controller, and it continually measures the level of noises and adjusts the statistical parameters in the digital Kalman filter. The RMS signal is measured by a RMS convertor chip for fast filter performance, and an air levitated precision stage with linear voice coil motor (LVCM) was used for the experiment. The results show that the performance of the system is effectively improved by the proposed observer algorithm with a conventional PID controller.