A linear air bearing stage with active magnetic preloads for ultraprecise straight motion

• Published in: Precision engineering Vol. 34; no. 1; pp. 186 - 194
• Main Authors: Ro, Seung-Kook, Kim, Soohyun, Kwak, Yoonkeun, Park, Chun Hong
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 2010; Elsevier
• Subjects: Active magnetic preload; Air bearing stage; Applied sciences; Bearings, bushings, rolling bearings; Drives; Exact sciences and technology; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Magnetic circuit model; Mechanical engineering. Machine design; Motion error compensation; Physics; Porous air bearing; Precision engineering, watch making; Transducers; Porous air bearing; Motion error compensation; Magnetic circuit model; Active magnetic preload; Air bearing stage; Positioning; Precision engineering; Magnetic circuit; XY stage; Ball screw; Magnetic force; Mechanical clearance; Modeling; Static load; Linear guide; Load capacity; Active system; Linear motor; Capacitive transducer; Porous bearing; Gas bearing; Laser interferometer; Magnetic bearing; Error correction; System with three degrees of freedom; Permanent magnet; Motion control; Magnetic device
• ISSN: 0141-6359; 1873-2372
• DOI: 10.1016/j.precisioneng.2009.06.010

In this paper, we propose a linear motion stage designed with magnetically preloaded air bearings. The magnetic actuators for preloading air bearings were combined with permanent magnets and coils to adjust the air bearing clearance by actively controlling the magnetic force. The system was designed to achieve a simplified configuration of air bearing stage while providing ultraprecise straight motion by actively compensating for the motion errors. The porous aerostatic bearings and magnetic preload actuators were designed and analyzed numerically for a single-axis prototype linear stage driven by a coreless linear motor. A magnetic circuit model was derived for the magnetic actuators. The static stiffness and load capacity of the air bearing stage in the vertical (magnetically preloaded) direction were experimentally measured and compared with the results from the numerical analysis. Motion control laws for three degrees of freedom (
i.e., vertical, pitch, and roll motions) were obtained with a high linearity and independence for each axis. The active compensation of three motion errors, the vertical, pitch and roll motion errors were performed through curve-fitting the three errors measured with combination of capacitive gap sensors and a laser interferometer. The errors were reduced from 1.09 to 0.11
μm for the vertical straightness error, from 9.42 to 0.18
arcsec for the pitch motion, and from 2.42 to 0.18
arcsec for the roll motion as level of measured repeatability.