Nowadays, the requirements of precision motion system in precision and speed are higher and higher. The requirement of static index is no longer the only standard to check the motion system. The frequency characteristics, vibration error, high acceleration and other indicators have become the key factors to evaluate a precision motion system.

The design and manufacture of a precision motion system with excellent dynamic and static characteristics is affected by various factors, and the first problem for designers is the selection and use of bearings.

Traditional sliding and rolling bearings inevitably produce friction between moving parts and stationary parts, so the size error and surface roughness of bearing system have great influence on transmission error, and these effects become more significant with the increase of frequency.

Technology development and customer demand promote the development of non-contact special bearings. The biggest feature of these special bearings is that there is no direct mechanical contact between the moving parts and the static parts. The error spectrum can be optimized from the perspective of dynamic design, so that the motion error appears periodically in the frequency range that does not affect the performance of the system, or the control system adopts special-purpose The filtering technology optimizes the system characteristics.

Another decisive factor that makes these special bearings get attention and application is that the motion error will decrease with the decrease of the air film gap on the working plane, the gas film stiffness will increase rapidly, the system error will decrease rapidly, and the system has better high precision characteristics. This characteristic can be illustrated by the change of air film clearance with air pressure for a typical air bearing.

Characteristic curve of relationship between air film clearance and rigidity of air bearing

Characteristic curve of relationship between air film clearance and rigidity of air bearing

It can be seen from the figure that when the rigidity of the air bearing is 30um, the bearing capacity and rigidity are low, and the performance of the air bearing is good when the air film is below 5um.

Therefore, when there are high requirements for the precision and stability of the motion system, it is a more wise choice to use the non-contact special bearing air bearing. The common non-contact bearings include elastic support, hydraulic bearing, air bearing and magnetic bearing.