WHITE PAPER – Air Bearings: When to Use and When to Avoid in Your Motion Application– Matt Reck –Air Bearings: When to Use and When to Avoid
in Your Motion Application
All Positioning Stages are not Created Equal

PI (Physik Instrumente) LP, 16 Albert St, Auburn, MA 01501, USA
Phone +1 508 832 3456, Fax +1 508 832 0506, Email info@pi-usa.us, www.pi.wsw w w. p i . w s

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WHITE PAPER – Air Bearings: When to Use and When to Avoid in Your Motion Application– Matt Reck –Introduction
Most motion applications are perfectly well-served by mechanical bearing guidance; but there are many cases whereprecision, angular repeatability, and geometric performancemust be optimal or where submicron bearing rumble is problematic. An air bearing stage can help in these situations. An
air-bearing stage is a rotary or linear positioner that floats ona cushion of air, using one of several preload mechanisms,
nearly eliminating mechanical contact and thus wear, friction,and hysteresis effects. These are the most common indicatorsthat an air bearing stage might be the right choice for yourapplication (s. Fig. 1).

1

Frictionless High-Precision Positioning

A direct drive motor and high-resolution encoder canposition a moving carriage supported by an air bearing towithin nanometers in a linear application or within tenthsof arcseconds in rotational applications. The lack of friction
and mechanical contact means there is minimal hysteresis orreversal error, making it highly repeatable and ideal for many
inspection and manufacturing operations. Stiction is virtuallyeliminated, improving resolution capabilities and reducing inposition “hunting” (limit cycling) and position repeatability canbe obtained within a few fundamental encoder counts.

Similar precision can be obtained by piezo flexure guided
stages, however over much smaller travel ranges. Magneticlevitation is another option.

2Velocity Stability and Scanning

The lack of mechanical bearing elements means there is nothing to get in the way of smooth, controlled velocity (stabilityto better than 0.01%). Experiments and processes like inertial
sensor testing, tomography, wafer scanning, and surface proﬁling require continuous motion at a tightly controlled speeds
are best served by air bearing systems.

3Very Low Error Motions

Linear air bearing stages have incredibly straight and flat travels,and pitch, roll, and yaw errors can be measured in tenths ofarcseconds. Rotary stages can have tilt (wobble) errors lessthan 1 arcsecond.
Additionally, the angular performance of an air bearing isremarkably repeatable. This guarantees optimal part quality
and measurement reliability for applications like mirror andoptics inspection, semiconductor inspection, and medicaldevice manufacturing.

Fig. 1 Three motor planar XY air bearing stage with active yaw control(Image: PI)

PI (Physik Instrumente) LP, 16 Albert St, Auburn, MA 01501, USA
Phone +1 508 832 3456, Fax +1 508 832 0506, Email info@pi-usa.us, www.pi.ws

MOTION | POSITIONING

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WHITE PAPER – Air Bearings: When to Use and When to Avoid in Your Motion Application– Matt Reck –4

Travel Requirements are Greater
Than a Flexure Stage Can Provide

6

Piezo-driven flexure stages and actuators can satisfy manyhigh-precision positioning applications. However, these designs
are usually limited to a few millimeters of travel. Use an air
bearing linear stage for travels of 25 mm or more (s. Fig. 2).
PI manufactures linear air bearings with travels up to a meter,and even greater with a custom design.

There are no contacting parts to undergo wear and tear, andno regular maintenance procedures to be performed likelubrication. An air bearing stage is essentially maintenancefree. Further, the system is highly stable, since there is no wear;
the performance characteristics should not change over thelife of the system. There is little need for recalibration. Moving
cables and hoses are often the only items subject to wear in an
air bearing system.

7Cleanliness

Because air bearings are wear free, they generate virtuallyno particulates that can become airborne. This makes them
ideal for cleanroom applications like optics inspection, wafer
inspection, bio-pharma research, and flat-panel display inspection. For extremely clean applications, it is recommended thatthe air bearing operate using 99.9 % pure nitrogen.

Fig. 2 Miniature air bearing linear stage (Image: PI)

5

Minimal Maintenance

Wobble-Free or High-Speed
Rotary Motion is Needed8Rotary air bearings (s. Fig. 3) are exceptionally stiff and candeliver highly precise rotary motion. Radial, axial, and wobble
error motions are much smaller than most mechanical bearing
solutions can provide, and the rotary motion is very smooth,since there are no roller elements. Rotary positioning stages
generally can achieve speeds up to 600 RPM, while air bearing
spindles are used in higher speed applications. Rotary bearing
designs can be mounted with the plane of the table in either
the horizontal (i.e. turntable) or vertical orientations.

Precise Force Control and Sensing

Air bearings are virtually frictionless, which means when they
are coupled with a direct drive motor or voice coil, they areideal for micro and nanonewton force control applications(s. Fig. 4). Such applications can include pick-and-place ofdelicate items, materials testing, and coordinate measuring
applications.

Fig. 4 Spherical air bearings can be used to simulate zero gravity(Image: Nelson Air)

Fig. 3 Rotary air bearing (Image: Nelson Air)

PI (Physik Instrumente) LP, 16 Albert St, Auburn, MA 01501, USA
Phone +1 508 832 3456, Fax +1 508 832 0506, Email info@pi-usa.us, www.pi.ws

MOTION | POSITIONING

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WHITE PAPER – Air Bearings: When to Use and When to Avoid in Your Motion Application– Matt Reck –9	When Would You Avoid an Air Bearing
for Your Motion Control Application?
9.1 Vacuum Environments

9.3 Pressurized Air or Nitrogen is not Available

While it is not impossible to operate an air bearing in a vacuum,
it is challenging. Vacuum applications should generally beavoided and instead use mechanical bearing, maglev, or flexuresystems (s. Fig. 5).

Air bearings require a continuous supply of clean compressed
air or nitrogen. If the application does not allow for such asupply to be present, an air bearing cannot be used.

AuthorMatt Reck is Air Bearing Product Line Manager at PI (PhysikInstrumente) LP in Auburn, MA. He has many years ofexperience in the design of air bearing stages and project
management of complex motion systems.

Experience with Air Bearing Technology

9.2 Very Dirty Applications
Air bearings are generally used in clean environments.
Applications where heavy amounts of dust, dirt, debris, andfluids are present should generally be avoided.

PI is building on over 200 man-years of in-house air bearing
experience and offers comprehensive precision air bearing
motion control and positioning products and systems. With
4 decades of experience in piezo nanopositioning systems
design and motorized precision positioning equipment, the
new air bearing systems capabilities are a natural and logicalextension of PI’s precision motion offerings.

Physik Instrumente (PI) GmbH & Co. KG
Auf der Roemerstrasse 176228 Karlsruhe
Germany

PI (Physik Instrumente) L.P.
USA and Canada (East)
16 Albert St.
Auburn, MA 01501
USA

Phone +49 721 4846-0
Fax +49 721 4846-1019
info@pi.ws
www.pi.ws

Phone +1 508 832 3456
Fax +1 508 832 0506
info@pi-usa.us
www.pi-usa.us

PI (Physik Instrumente) LP, 16 Albert St, Auburn, MA 01501, USA
Phone +1 508 832 3456, Fax +1 508 832 0506, Email info@pi-usa.us, www.pi.ws

w w w. p i . w s

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WP4003 Air Bearings 09/2015.0,250 Subject to changes. © Physik Instrumente (PI) GmbH & Co. KG 2015

Fig. 5	A flexure-guided, UHV-compatible XYZ piezo nanopositioning stage(Image: PI)