Finite Element and Experimental Analysis on Micro-Vibration of Ultra Precision Air Bearing Linear Motion Stage and Methods of Its Elimination

Air bearing linear motion stages with high speed and ultra high positioning performances are always used in steppers or scanners which are the most important equipments in microlithography process. Excellent air bearing design is one of the keys to archive those performances. Good load capacity and stiffness are always the main design objective for designers. But experiment shows that air bearing stage with high stiffness and load capacity may suffer from micro vibration. The micro vibration is not the “pneumatic hammer” which usually happens to air bearing due to poor restrictor design. Its amplitude ranges from tens to hundreds of nanometers and frequency from tens to thousands of Hz. For an ultra precision linear motion stage which positioning accuracy level is about ten nanometers, the vibration amplitude is obviously unacceptable. Further more, the micro-vibration seriously lower system’s dynamic characteristics. To find the reason of micro-vibration, finite element method is used to analyze the air flow in the air channel of air bearing. The result shows that the turbulence flow in the air channel will induce the micro-vibration. So the laminar flow in the air channel is the key way to eliminate the micro-vibration of air bearing stage. To turn the turbulence flow into laminar flow, the designer must consider the radius of the air channel, the number of air inlet and mass flow rate of air bearing comprehensively.