Reasons to consider air bearings

 

Air bearings are easy to miss. In most cases, mechanical bearings work well enough for motion applications. Most, but not all. Sub-micron bearing noise not an option? Are geometric performance and angular repeatability paramount? Here are some tips to make the spec process easier.

Air bearings offer several advantages in precision positioning, including no backlash or traction. It is also suitable for most high-speed applications. However, some conditions do not help with the use of air bearings. Knowing the parameters of an air bearing can be key to applying a truly optimized bearing system.

Friction is less

Friction-free bearing and drive technology is a prerequisite for vibration-free precision movement with nano-scale resolution, repeatability and induction precision. There are several ways to achieve frictionless movement. Piezo drive and flex guide are suitable for short strokes. Other principle is based on magnetic bearings.  These motion systems are more exotic, but their movement is not restricted and are often designed for multi-axis motion applications. Another solution for long run consists of air bearings driven by linear and torque electromagnetic motors.

An air carrier stage is a rotary or linear positioner floating on an air cushion, utilizing one of several preload mechanisms to virtually eliminate mechanical contact, eliminating the effects of wear, friction and hysteresis. Especially, it provides high performance and precision for multi-axis movement.

Motion control application benefits.

Some common factors supporting to the use of air bearing stages for motion control applications.

1.Precise and frictionless positioning

Direct drive motors and high-resolution encoders can place moving carriages supported by air bearings within nanometers in linear applications or in 1/10 seconds in rotary applications. The absence of friction and mechanical contact minimizes hysteresis or reversal errors, making it highly repeatable and suitable for many inspection and manufacturing operations. Friction is virtually eliminated, improving resolution and reducing “shake” in position (limit cycle). Position repeatability can be achieved with even a few encoder counts. Similar precision can be achieved with the piezoelectric bending guide step, but with a much smaller range of travel. Magnetic levitation is another option.

2. Scanning and speed stability

The absence of mechanical support elements means that there is nothing to interfere with the smooth, controlled speed (stability is more than 0.01%). When experiments and processes such as inertial sensor testing, tomography, wafer scanning and surface profiling require continuous movement at tightly controlled speeds, air systems are most useful.

3. Low error shift due to surface averaging effect

The linear air stage has a straight and flat path. Pitch, roll and yaw errors can be measured in tens of a second. A rotating step can have a pitch (shake) error of less than 1 second. Also, the angular performance of air bearings is repeated. This feature ensures component quality and measurement reliability in applications such as optical and mirror inspection, semiconductor inspection, and medical device manufacturing.

4. Long-distance travel requirements

Bending stages and piezo actuators can satisfy many high-precision positioning applications. However, these designs are usually limited to a few millimeters of travel. Linear stages with air bearings can be used for movements of 25 mm or more. Manufacturers can provide linear air bearings with travel distances of up to 1 m or more in custom designs.

5. Rotating movement without vibration or high speed

The rotary air bearing is very sturdy and can provide high precision rotary motion. The radial, axial and vibrating error motion is much smaller than what most mechanical bearing systems can provide, and since there are no roller elements, the rotational motion is very smooth. Rotary positioning stages can usually reach speeds of up to 600 rpm, while air bearing spindles are used for high speed applications. The rotating bearing design can be mounted in the plane of the table in a horizontal direction or vertically.

6. Minimal maintenance

There are no mating parts to wear out, and regular maintenance procedures such as lubrication should not be performed. Air bearing stages are essentially maintenance free. Also, the system is very stable. As there is no wear, the performance characteristics should not change over the life of the system. Little recalibration is required. Moving cables and hoses are often the only wear items in an air system.

7. Cleaning

Air bearings are wear-free and therefore virtually no airborne particles. This feature is an option for clean room applications such as optical inspection, wafer inspection, biopharmaceutical research and flat panel inspection. For very clean applications, it is recommended that air bearings operate with 99.9% pure nitrogen.

8. Accurate force detection and control

Because air bearings are frictionless, they work well in micro and nano-Newtonian force control applications when combined with direct drive motors or voice coils. These applications may include delicate item selection and placement, material testing, and coordinated measurement applications.

 

 

Precision application

Linear, planar, spherical and rotating stages with air bearings are optimal motion control components for industry and research.

Air bearings ensure friction-free movement, making them the preferred choice for zero gravity simulations. The guide accuracy (straightness and flatness of movement) is less than 1µm for long driving. This precision ensures optimum component quality and measurement reliability in applications such as flat panel inspection, optical inspection, semiconductor inspection and medical device manufacturing.

Environment not suitable for air bearing

Due to their design nature, air bearings are not suitable for all operating environments.

1. Vacuum environment

Operating air bearings in a vacuum is not impossible, but challenging. In general, vacuum application should be avoided. Instead, stages based on mechanical bearings, magnetic levitation, or flex guide systems should be used.

2. Dirty and dusty applications

Air bearings are generally used in clean environments. In general, applications with large amounts of dust, dirt, debris and liquids should be avoided.

3. No pressurized air or nitrogen available

Air bearings must be continuously supplied with clean compressed air or nitrogen. Air bearings cannot be used unless the application allows such a supply.