Design and Testing of a Nanometer Positioning System

This paper presents the design and implementation of a positioning system with a dc servomotor and ball-screw mechanism used to realize high-precision positioning over a wide travel range with nanometer level positioning error and near zero overshoot. Instead of the popular dual-model control strategy and friction compensation, a high-gain proportional-integral-derivative controller is used to realize a single-step point-to-point positioning. The controller parameters are obtained by placing closed-loop poles according to the macrodynamics of a ball-screw mechanism only to avoid identification of microdynamics and friction modeling. In order to suppress the overshoot caused by actuator saturation in long-stroke positioning, a trajectory planning method is applied to calculate the input of the closed-loop system. Experimental and simulation results demonstrate that single-step precision positioning responses to different size commands are achieved without producing any large overshoot. In point-to-point positioning from 100 mm down to 10 nm, the positioning error is within 2 nm and the response dynamics is satisfactory.