Many motion control applications use mechanical guiding systems, such as crossed-roller bearings. However, when parameters such as angular repeatability, precision or runout and straightness are a concern, air bearings are an excellent option.

Air bearings use a thin film of pressurized air or gas to support a load. Fluid film bearings have no solid-to-solid contact under typical running conditions; instead, a pressurized fluid forms a layer between the solid machine elements and serves to transfer loads. The most common means of creating the film is with an orifice. Other designs deliver the gas through a porous medium to ensure uniform pressure across the entire bearing area. Although the gas constantly dissipates from the bearing site, the continual flow of pressurized air through the bearing is sufficient to support the working loads.

Since air bearing surfaces are non-contact, they avoid the traditional bearing problems of friction, tribological wear and relubrication. Air bearings offer distinct advantages in precision positioning and high-speed applications.

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1. High precision, frictionless motion

In linear applications, a moving carriage can be precisely positioned within nanometers using a direct-drive motor and high-resolution encoder supported by an air bearing. For rotational applications, the range changes from nanometer to tenths of arc-seconds.

For many inspections and manufacturing uses, air bearings are ideal due to minimum hysteresis effect or reversal error from minimum mechanical contact and friction. It is possible to reduce in-position hunting and improve resolution capabilities by virtually eliminating friction. Flexure guided piezo stages achieve similar precisions, but typically for smaller travel ranges.

2. High speeds and constant velocity

High speed velocity is easily accommodated by the fluid film. In fact, many air bearings operate more efficiently at high speeds, as it provides a self-pressurizing effect. Continuous motion at highly controlled speeds is required in many processes and experiments, such as tomography, wafer scanning and inertial sensor testing. Air bearing systems are the best for providing this required continuous motion at highly controlled speeds, and will typically provide a longer lifespan than mechanical bearings.

3. Highly linear travel

The high accuracy of an air bearing is due to the high quality manufacturing of the components. Linear air bearing stages contain extremely straight and flat travel. In the case of roll, pitch and yaw, there is a chance of error about 1 arc-sec per 100 mm travel.

For manufacturing and measuring, there is high repeatability of the same procedure and good ability to compensate for deviations of the ideal trajectory. Current semiconductors often have tolerances near single-digit nanometers. In the latest automotive engines, some components are even required to surpass the submicron precision. For many applications ranging from precision machining to optics inspection, repeatable part quality and measurement reliability is ensured.

4. Longer-range than flexure stages

Many high-precision positioning applications can use flexure guided piezo stages and actuators, but piezo designs have travel limitations, sometimes of just a few millimeters. For travel of 25 mm or more, an air bearing linear stage is optimal. Some linear air bearings are manufactured with the travels up to a meter, and can be engineered for even greater travels.

5. Wobble-free rotary motion

Rotary air bearings can be used to deliver precise rotary motion as they are extraordinarily stiff. Wobble or tilt error occurs in the range of 0.1 to 1 arc-second in case if rotary stages. Errors generated by wobble, axial and radial motions are much smaller than that generated by the most mechanical bearing solutions.

6. Minimal maintenance

As there is little or no mechanical contact between parts, there is no need for periodic inspection or relubrication. This also eliminates considerations for bearing seals, a common challenge for traditional bearing types. Air bearings typically require little recalibration, and the only wear items are external cables or hoses for the pressurization system.

7. For linear amplifiers

Linear amplifiers filter out line noise and have no switching noise, which prevents interference for a more accurate power output. Air bearings are better able to match the precision of a linear amplifier, for highly accurate positioning.