vacuum
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 
10^{6}
Pa 
Vacuum level pV 
10^{6}
Pa 
Supply pressure pS 
10^{6}
Pa 
Restrictor pressure pR 
10^{6}
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 
10^{6}
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. 


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