Flat Air Bearing Design and Installation Guide
Flat air bearings are typically configured with a preload as described below. Mounting components are used to position and assemble the bearings.
Preload: Flat bearings can be preloaded in 4 different ways.
1) Opposite bearing: The most common way is to preload with a bearing on the opposite end. This requires more space and adds more weight, but it provides for more stiffness and load capacity. To achieve the highest stiffness and balance, it is recommended to make sure the two bearings are placed opposite of one another, and that both surfaces are parallel to each other.
When preloading with other air bearings, the preload force needs to be considered in order to determine the appropriate size bearing.
Preloading with other air bearings is typically utilized to provide a load capacity in both directions, as well as for increasing the stiffness.
2) Weights: Flat bearings can also be preloaded if there is a constant force pushing down on them. This type of preload is typically used when moving large objects. It is recommended to use a minimum of 3 bearings for this configuration.
3) Magnets. Magnets are a good option if low mass is desired. Typically there will be one magnet on the bearing and one along the entire length of the guide.
4) Vacuum: Vacuum Preloaded Air bearings use a vacuum to preload. The vacuum gives more control over the air film thickness and in turn maintains optimal stiffness and performance while reducing the overall weight and size of the system.
Other considerations: It is best to keep the resulting force of the load distribution in the center of the bearing. In order to determine the proper size of the bearing, it is best to ask the following questions:
-Where is the resulting load located on the bearing?
-What is the surface roughness of the guide?
-What is the maximum load being applied to the bearing?
Keep in mind that the load capacities for each bearing are based on the maximum load being applied to the center of the bearing. Smoother surface finishes will always result in a better performance. However, if a smooth surface finish is not possible, you will need a bigger bearing and high input pressure, because it will be crucial to maintain a higher fly height and to improve on the damping capabilities.
When supporting a load on a flat surface, it is most reliable to use 3 bearings (rather than 4). Assuming that the location of the load is maintained between the three bearings, this will add the most stability. 3 bearings are especially best when the guide surface is not perfectly flat because the bearings will always maintain their approximate fly height. If 4 bearings are used on an uneven surface, there will always be one or two bearings suspended too high until the weight shifts, or the surface changes.