Long-stroke nanometer positioning of frictional table system by conventional controller

For a DC-motor and ball-screw-drive table system, the nonlinearities such as friction, saturation and high frequency resonance are the major obstacles to the achievement of high-precision and long-stroke point-to-point (PTP) positioning without overshoot. Based on the transfer function obtained according to rigid body dynamics of the ball screw mechanism, a high gain PID controller and an input filter was designed to realize long-range nanometer positioning. Parameters of the closed-loop control system were calculated by multi-poles placement so that neither friction compensation nor dual-mode control strategy was necessary. The input signal of the closed-loop system was designed based on digital low-pass filter to avoid large overshoot due to the actuator saturation. Experimental and simulated results demonstrate that the proposed system can achieve long-stroke nanometer positioning without producing any large overshoot, with the steady-state error within ±5 nm in PTP positioning from 100 mm down to 10 nm.