Vacuum preloaded bearings

• Do not require opposed bearing action from two bearings and so only need a single flat guide surface. Sometimes magnetic preload is applied as an alternative.
• By adjusting the vacuum and pressure, the optimal stiffness and flying height can be tuned.
• Adjustability of the film thickness can be used for ultra precision vertical positioning.
• Even accurate angular adjustment is possible when applied with a flexure mount. Mechanically preloaded bearings with ball pivots may suffer from friction in the pivot point.

Bearing principle: The pressurized part of the bearing can be considered as a collar bearing. This collar bearing is loaded internally by the action of vacuum acting on the inner part of the bearing. The groove connected to ambient pressure is applied to reduce the flow through the vacuum system.

It's obviously clear that the flying height (film thickness) in aerostatic bearings increases with decreasing bearing load. Or visa versa, the load capacity decreases with increased flying height. The "tensile" force in vacuum preloaded bearings is approximately independent of the flying height. It follows that equilibrium between the tensile force and the pressure force can be established for a specific flying height. With decreased flying height the pressure force increases resulting in load capacity whereas with increased flying height the pressure force decreases resulting in a net pulling action.