AN AIR LAYER MODELING APPROACH FOR AIR AND AIR VACUUM BEARINGS/

Air layer supported bearing pads, or ''air bearings'' as they are comm only called, are popular because of their high load capacity and low i n-plane coefficient of friction, making them well suited for supportin g moving, high accuracy manufacturing stages. Air/vacuum bearings enha nce these capabilities by giving the bearing pad load resistance capac ity in both the upward and downward directions. Consequently, it is de sirable to know how to model the air layer between the bearing pad and the bearing surface. In this paper, a simple finite element modeling approach is presented for investigating the vibrational characteristic s of an air layer supported bearing. It was as found that by modeling the air layer as a bed of uniform springs who's stiffness is determine d by load-displacement tests of the bearing, a reasonable representati on of the response can be obtained. For a bearing supported by air wit hout vacuum, the dynamic response was very similar to that of a freely supported bearing. The addition of vacuum to an air bearing was found to significantly lower its fundamental frequency which could lead to unwanted resonance problems.