Why Engineers Must Invest in Air Bearings for Motion Control

Why Engineers Must Invest in Air Bearings for Motion Control

Manufacturing Technology Insights | Friday, October 01, 2021

Mechanical guiding systems, such as crossed-roller bearings, are used in a wide variety of motion control applications.

FREMONT, CA: Air bearings sustain weight by using a thin pressurized air or gas coating. Under normal operating conditions, fluid film bearings have no solid-to-solid contact; instead, a pressurized fluid forms a layer between the solid machine elements and serves to transfer loads. The most frequently used method of producing the film is through an orifice. Other systems distribute the gas uniformly across the bearing surface by passing it via a porous material. While the gas continuously dissipates from the bearing site, the steady airflow supports the operating loads.

Due to the non-contact nature of air bearing surfaces, they avoid the difficulties associated with traditional bearings, such as friction, tribological wear, and relubrication. Precision positioning and high-speed applications benefit significantly from air bearings.

Exact, frictionless movements: A moving carriage may be precisely positioned within nanometers in linear applications with a direct-drive motor and a high-resolution encoder supported by an air bearing. The range changes from nanometer to tenths of arc-seconds for rotational applications.

Air bearings are helpful for various inspection and manufacturing applications due to their low hysteresis effect or reversal error caused by minimal mechanical contact and friction. By essentially removing friction, it is possible to reduce in-position searching and improve resolution capabilities. Similar precision is achieved with flexure-guided piezo stages, although often over a narrower travel range.

Rapid acceleration and consistent velocity: The fluid film easily accommodates high velocity. Indeed, many air bearings perform better at high speeds due to the self-pressurizing effect. Numerous operations and tests, such as tomography, wafer scanning, and inertial sensor testing, require continuous motion at extremely regulated rates. Air bearing systems are the most efficient way to achieve this required constant motion at remarkably steady rates, and often have a longer lifespan than mechanical bearings.

The range is greater than that of flexure stages: Numerous high-precision positioning applications can benefit from flexure-guided piezo stages and actuators; however, piezo designs have limited motion, often as little as a few millimeters. A linear stage with air bearings is best for travels of 25 mm or greater. Specific linear air bearings are manufactured with travels up to one meter and can be developed to have even longer journeys.

Rotary motion with no wobble: Rotary air bearings can deliver precise rotating motion due to their extreme stiffness. In the case of rotating stages, wobble or tilt error occurs in the range of 0.1 to 1 arc-second. The errors caused by wobbling, axial, and radial motions are far less than those caused by most mechanical bearing systems.

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