Ultra-precision positioning control based on the frequency response analysis

In some industrial fields such as optical part mold making or fabrication of the nano structure by ultra-precision machinery, an ultra-precision positioning system is widely used. In this paper, an experimental ultra-precision positioning system is designed and fabricated, consisted of an ultra-precision stage supported by flexure hinges, a piezoelectric actuator and an ultra-precision linear encoder. In order to obtain the system transfer function of the ultra-precision positioning system, the frequency response for the sinusoidal input was analyzed. From the bode diagram, the system was modeled in 4^th order system. Also, in order to have robustness for the system uncertainty; modeling error and external disturbances, some weighting functions were selected and H_infin controller was designed. A series of experiments was conducted using the designed H_infin controller and it was found that this ultra-precision positioning system could be controlled in 5 nm resolution.