ADVERTORIAL TECHNOLOGY IN ACTION
If friction is your enemy, can Air Bearings be your Batman?
Physik Instrumente (PI’s) air bearing product line manager Matt Reck outlines when design engineers should consider air bearings, over conventional mechanical bearings
ost motion applications are perfectly well- served by mechanical bearing guidance; but there are many cases where precision, angular repeatability, and geometric performance must 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 on a cushion of air nearly eliminating mechanical contact and thus wear, friction, and hysteresis effects. Frictionless drive and bearing technology is a prerequisite for vibration-free precision motion with nano-scale resolution, repeatability and guiding accuracy. There are several ways to achieve frictionless motion. Piezo drives and flexure guidance are well established for short travel ranges.
M
Another principle is based on magnetic levitation (magnetic bearings). These motion systems are more exotic, but not travel limited and are often designed for multi-axis motion applications. Another solution for long travel ranges consists of air bearings driven by electromagnetic linear and torque motors. Air bearings ensure frictionless motion, a fact that makes them the preferred choice for zero- gravity simulations. Their guiding accuracy (straightness and flatness of motion) is well below 1µm over long travel ranges. This precision guarantees optimal part quality and measurement reliability for applications such as flat panel inspection, optics inspection, semiconductor inspection and medical device manufacturing.
Benefits for motion-control
Here are some of the most common factors supporting the use of air-bearing stages for motion-control applications:
1. Frictionless, accurate positioning A direct-drive motor and high-resolution encoder can position a moving carriage supported by an air bearing to within nanometers in a linear application, or within tenths of arc-seconds in rotational applications. The lack of friction and mechanical contact means there is minimal hysteresis or reversal error, making it highly repeatable and suitable for many inspection and manufacturing operations. Stiction is virtually eliminated, improving resolution capabilities and reducing in-position “hunting”. Position repeatability can also be obtained within a few encoder counts. Similar precision can be obtained by piezo flexure guided stages, however over much smaller travel ranges.
2. Velocity stability and scanning The lack of mechanical bearing elements means there is nothing to get in the way of smooth, controlled velocity (stability to better than 0.01%). Experiments and processes, like inertial sensor testing, tomography, wafer scanning and surface profiling - which require continuous motion at tightly controlled speeds -are best served by air- bearing systems.
46 SEPTEMBER 2016 | DESIGN SOLUTIONS
Surface Averaging effect of the air bearing. The result is elimination of high-frequency bearing rumble and much better straightness and flatness of motion compared to mechanical bearings. Image courtesy of PI.
Carriage lifts and is free to move. Preload is provided by opposing forces between a pressurised air film and a vacuum area.
3. Low error motions due to surface averaging effect
Linear air-bearing stages have straight and flat travels; pitch, roll and yaw errors can be measured in tenths of arc-seconds. Rotary stages can have tilt (wobble) errors less than 1 arc-second. Additionally, the angular performance of an air bearing is repeatable.
4. Long travel requirements
Piezo-driven flexure stages and actuators can satisfy many high-precision positioning applications. However, these designs are usually limited to a few millimeters of travel. Air-bearing linear stages can be used for travels of 25mm or more. Manufacturers can provide linear air bearings with travels up to 1m or more with custom design.
5. Wobble-free or high-speed rotary motion
Rotary air bearings are exceptionally stiff and can deliver highly precise rotary motion. Radial, axial and wobble error motions are much smaller than most mechanical bearing systems can provide, and the rotary motion is exceptionally smooth since there are no roller elements.
7. Cleanliness
Because air bearings are wear-free, they generate virtually no particulates that can become airborne. This feature makes them an option for cleanroom applications like optics inspection, wafer inspection, bio-pharma research and flat-panel display inspection.
8. Precise force control and sensing Air bearings are frictionless, which means when they are coupled with a direct-drive motor or voice coil, they work well in micro- and nano-Newton force control applications. Such applications can include pick-and-place of delicate items, materials testing and coordinate measuring applications.
Physik Instrumente u 01234 756 360 u
www.physikinstrumente.co.uk
/ DESIGNSOLUTIONS
6. Minimal maintenance There are no contacting parts to undergo wear and tear and no regular maintenance procedures to be performed, like lubrication. An air-bearing stage is essentially maintenance-free. Further, the system is highly stable; because there is no wear, the performance characteristics should not change over the life of the system. There is little need for recalibration.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
