Precision positioning of a DC-motor-driven aerostatic slide system

This paper deals with precision positioning in the presence of friction. The object studied is an aerostatic slide system driven by a DC motor with brushes that introduce friction to the system. For such systems, models that do not account for friction can only be used to describe the macrodynamic behavior. The microdynamic behavior is significantly different. Instead of designing two controllers for the different dynamics, a single-step precision positioning using a high-gain controller designed according to the macrodynamics alone is proposed. A proportional-integral-derivative (PID) controller with finite-gain derivative and a modified anti-windup integral reset is designed. Controller parameters are obtained by pole placement rather than manual tuning or other rules of thumb. Identification of the microdynamics is avoided. Single-step precision positioning and uniform response to different sizes of step input are achieved. This method is particularly effective when the friction has uncertainty. Experimental and simulated results indicate that the PID controller can provide a sufficiently high loop gain. In point-to-point positioning for step inputs from millimeter size down to submicrometer size, the positioning error is within ±2 nm and the response dynamics is satisfactory.