Of the more important advantages which are offered by gas lubrication, the low viscosity of gases as compared with liquids can be exploited to special benefit. The extremely low static friction which externally pressurized bearings can offer, finds its uses in torque measuring equipment, dynamic balancing machinery, semiconductor positioning systems, micro or zero gravity trajectory simulators and other instruments requiring near-static conditions.
This type of bearing shares many of the advantages of the aerodynamic bearing. In addition, it supports all of its designed load at zero speed. This effect results from its principal disadvantage: it requires an external pressure source to create the air film..
All air bearings ride on a thin film of gas which provides lubrication. In the case of aerodynamic or self-acting bearings, the air film is created by the relative motion of two mating surfaces separated by small distance. From rest, as the speed increases, a velocity induced pressure gradient is formed across the clearance..
Quality air bearings and diamond turned parts can only be produced where there exists a means to accurately inspect and measure the critical features. In all cases, the standards to which measurement takes place is generally much higher than typically found in conventional quality inspection. To that end, it is often necessary to employ stringent standards and methods..
It is often advantageous to obtain rough order magnitude performance information when determining the feasibility of a particular air bearing in an application..
Definitions of varibles used in describing off-axis parabolas
Areas such as the time required for alignment and collimation of the optical elements in their final subassembly or assembly is greatly reduced by use of integral precision reference surfaces that defines the optical axis and a face normal to the optical axis that can be built into the unit.
A further advantage of precision machined or diamond turned optical surfaces is that they can be incorporated as a part of the primary structure that would normally be used to support the optics in use.