Besides cleanliness, it is of utmost important to foresee a reliable source of air at constant pressure. An oversized compressor system delivers pressurized air, which is regulated down to a supply pressure for which the air bearing system is designed. When the pressurized air supply fails and a lower pressure is realized, the load carrying capacity of the bearing is reduced which results in lower bearing performance and can ultimately result in a bearing seizure. Costly downtime of the machine and a replacement of the bearing components might be required after such an event. Therefore, in many applications, a pressure guard is foreseen, which monitors the correct air pressure, and triggers the motion control unit not to activate the motion of the system, or to slow down the system to a standstill in order to protect the air bearings. A storage tank in combination with a pressure sensor can help to maintain a safe operating pressure during failure of the air compressor and to allow for a safe deceleration of the system before the supply pressure drops below a safe threshold, making sure that the air supply is reliable at any time during motion.

A clean and dry environment

Aerostatic air bearings exhibit a good resistance to a dusty environment, since the air bearing has the capability to keep the dust out of the bearing gap and clean the raceway. Attention has to be paid to avoid dust build-up in confined areas where the dust cannot be blown or wiped away. Moreover, sticky dust due to moisture or other substances with high affinity to the surfaces, is even more problematic.

Oil or water contamination on the guideways of the air bearing is absolutely to be avoided, since the moisture will creep into the bearing gap when the supply pressure is switched off, creating friction and interruption of the air film.

Overload and temperature load

Typically, air bearings have a lower overload resistance as compared to mechanical bearings. In some applications, this drawback is resolved by using crash-resistant coatings or full porous graphite surfaces which are known for the resistance against seizure.

An overload situation can occur due to mechanical overload (e.g., a spindle crash in a CNC machine tool). Another often overlooked aspect is a proper mounting of an air bearing system. In order to realize the full performance of an air bearing, a low distortion mounting is required. Whether it is an air bearing bushing or a rotation stage, it is required that the interfaces of the air bearing with the environment (e.g., mounting sleeve for a bushing, a machine bed for a rotation stage, or a wafer chuck for a linear stage) distort the air bearing components as little as possible. The precision of the system and its load carrying capacity can only be guaranteed when the mounting instructions are carefully followed. Flatness and cleanliness of the mating surfaces before installation is important, as well as respecting the tightening torques as specified by the manufacturer.

Thermal overload due to temperature gradients in the machine and differential thermal expansion of materials used in the construction1 also result in distortions within the air bearing components and, as a result a lower performance. A good thermal management of both the room in which the machine is located2, as well as internal heat sources within the machine, such as direct drive linear motors or heat originating from the process (e.g. laser welding) is mandatory.