Modular Air Bearings for Motion Control

Bigger Role for Radial Air Bearings As speed and economy become more important in motion applications, air-bearing technologies are getting another look. Founder, Chairman, and Chief Technology Officer • Air bearings are candidates for tasks where high speed, low friction, and low noise are paramount. • Radial air bearings are now standard items. applied for a patent that employed air bearings to support a steam turbine. Today, air bearings' high precision make them candidates for applications such as coordinate-measuring and lithography machines. They are also frequently used for circuit-board drilling and waferdicing spindles because of their capability for working at high speeds. Recently a type of air bearing called a modular-radial air bearing has become more widely available. These devices were once generally created only for custom orders. Today, they are standard products available from several suppliers. Radial air-bearing modules do not constrain rotary motion using a 360° housing as is the case with rolling-element bearings. Instead they are positioned in combinations of three or four segments to support a rotor over just a small percentage of its circumference. Radial-bearing modules can be constructed with either of the two basic approaches for air bearings. One uses a surface comprised of numerous small orifices which feed air from a reservoir to the bearing surface. This produces a film of air which supports the bearing load. The second approach uses a porous media (usually carbon but sometimes ceramic for clean rooms or superhard surfaces). This media distributes clean dry air evenly through millions of submicron-sized holes across the surface of each bearing. These holes are much smaller than the orifices found in the more conventional approach. When it comes to radial air-bearing modules, the porous-media approach tends to be most widely used. Porous-media air bearings are robust compared with orifice-based devices and can withstand repeated crashes (loss of air pressure) even at high speeds. It is possible to lap them in place by reducing air pressure until the bearing is dragging intentionally and then repeatedly flushing with alcohol. The porous carbon is a sintered material and will not "pick up or spall," even on a soft material like aluminum. And porous-media bearings can support a rotor with extremely high precision. It is interesting to