Design Of The Performance Testing Device For Aerostatic Bearing Used In Vacuum Condition

Operated with small friction, high accuracy, excellent thermal stability and long service life, aerostatic bearings have been widely employed in manufacturing, measuring and detection field, e.g. micro-electronics fabrication facility, ultra-precision CNC machine tool, coordinate measuring machine and precise turntable. But some applications, such as extreme ultraviolet exposure, electron beam exposure, film thickness measurement and line width measurement, not only require accurate movement and positioning, but also need to be operated in a vacuum or super clean environment. However, compared with atmospheric application, the performance of aerostatic bearing working in a vacuum changes significantly and the gas influences the level of a vacuum chamber due to the inevitable leakage. The performance testing device for aerostatic bearing used in ambient condition is no longer applicable. Therefore, a performance testing device for aerostatic bearing used in vacuum condition is designed in this paper. And the main work is as follows:1)The performance testing device for aerostatic bearing used in vacuum condition is designed for the measurement of load capacity, film thickness, gas pressure distribution in the film and gas leakage. By the device, static and dynamic characteristics of aerostatic bearing under different bearing parameters(restrictor modes, geometric parameters of restrictor) and exhaust system parameters(the position, width, depth, and number of exhaust grooves) can be obtained. The way of loading and the measuring methods of load, film thickness and gas pressure in the film are presented, as well as the structures of these units. Forces of key parts are analyzed. Calculations and selections of vacuum-compatible parts are offered in the paper.2) Based on the construction principles of a vacuum system, the exhaust system for vacuum chamber and the vacuum pumping system for aerostatic bearing are established. The exhaust system for vacuum chamber can build a vacuum environment for the performance detection of aerostatic bearing, and the vacuum pumping system for aerostatic bearing guarantees the reliability of bearing. The working principles and structures of the exhaust systems are described. Calculations and selections of primary pumps in the systems are explained in the paper.3)Aerostatic bearing works with external compressed gas. A simple air supply system is established to provide compressed air to aerostatic bearing.4) In order to measure the performance of aerostatic bearing working in a vacuum, a rectangular vacuum chamber with a volume of 0.4m3 is built. The design methods and mounting positions of the doors of the vacuum chamber, the tubes of the exhaust systems, the tube of the air supply system for aerostatic bearing, viewports and electrical elements are reported. Then, the exact structure of the vacuum chamber can be determined. Furthermore, a reliability analysis of the vacuum chamber is carried out.5) The number of the components in the exhaust systems is large. Thus, an electric control cabinet based on relay control logic is designed to ensure the exhaust systems reliable. The electric control principles of vacuum pumps and valves, depending on relay contacts, are presented in the paper. Meanwhile, alarm circuits are set to protect molecular pumps and gate valves, when water and air pressure are insufficient.6) According to the exact structures and mounting methods of the performance testing device, exhaust system for vacuum chamber, exhaust system for aerostatic bearing, air supply system for aerostatic bearing and vacuum chamber, the overall structure of the device is given. The experimental methods for performance testing of aerostatic bearing and gas leakage measurement are offered, being prepared for experimental study when the assembly is finished.By the study on the subject, it’s hoped that the influence rules of the bearing parameters and exhaust system parameters on load capacity, stiffness, gas pressure distribution in the film and gas leakage of aerostatic bearing can be achieved by the research based on the device. It’s expected to provide some reference for the optimal design of aerostatic bearing used in vacuum condition and offer some technical support to aerostatic bearing’s further development.