TourTourvacuum preloaded air bearing
fed through a porous ring
 Diameter 2R0 (outer diameter bearing)   10-3 m
 Diameter 2R1 (outer diameter porous ring)   10-3 m
 Diameter 2R2 (inner diameter porous ring)   10-3 m
 Diameter 2R3 (inner diameter collar bearing)   10-3 m
 Diameter 2R4 (outer diameter vacuum preload)   10-3 m
 Diameter 2R5 (inner diameter vacuum preload)   10-3 m
 Film thickness h0   10-6 m
 Ambient pressure pA   106 Pa
 Vacuum level pV   106 Pa
 Supply pressure pS   106 Pa
 Restrictor pressure pR   106 Pa
 Flow through porous surface Mb   10-6 kg/s
 Flow through porous surface Qb   10-3 liter/min
 Flow through vacuum system Mv   10-6 kg/s
 Flow through vacuum system Qv   10-3 liter/min
 Load capacity collar bearing Fb   N
 Tensile force vacuum preload Fv   N
 External load vacuum preloaded bearing F   N
 Axial bearing stiffness S=-dF/dh   106 N/m

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.

The pressure in the center part of the bearing where vacuum is drawn is constant, independent of the flying height, resulting in a constant preload. With increased flying height the pressure force in the collar bearing decreases resulting in a net pulling action. It follows that equilibrium between the preload and the pressure force in the bearing can be established for a specific flying height.