Precise Positioning of an Air Bearing Lead Screw Stage by Semi-Closed Loop Control
An air bearing lead screw, whose nuts are levitated from the screw threads, has a great advantage of accurately transforming rotational motion to linear motion due to no friction, no backlash and no hysteresis. Therefor precise linear motion can be provided by precise rotational motion which can be obtained by a precise rotary encoder and a motor controller. We developed a positioning controller with servo sampling rate of 10 kHz that employed FPGA (Field Programmable Gate Array) and applied it to positioning of an air bearing stage. The stage consists of an air bearing lead screw and an air bearing linear guide. A rotary encoder, whose resolution has 225000 pulses per rotation, was directly mounted on an axis of the lead screw. This paper describes the positioning performance of the stage by the use of this semi-closed loop control, such as the resolution of less than 10 nm, the linearity over the long stroke.
Tojiro Aoyama, Hideki Aoyama, Atsushi Matsubara, Hayato Yoshioka and Libo Zhou
M. Fukuda and Y. Niwase, "Precise Positioning of an Air Bearing Lead Screw Stage by Semi-Closed Loop Control", Key Engineering Materials, Vols. 523-524, pp. 538-543, 2012