Fundamentals of low-transmissibility aerostatic pads

Abstract

Air bearings are known for their low friction losses, constant viscosity and cleanliness, making them favourable in numerous high-tech applications. The relatively low aerostatic bearing stiffness is the major topic in state-of-the-art research and some recently proposed concepts are able to create infinite stiffness. This results in a strong coupling between the base and flying mass, enabling unwanted propagation of base vibrations. Why not integrate the vibration-isolation and bearing function? To reduce the out of plane vibrations of a flying mass. A previous study shows the possibility of creating a zero-stiffness bearing with the use of multiple aerostatic pads. However, the effect of the dynamic- thin-film stiffness and damping on the transmission of base vibrations is still unknown. The aim of this research is to optimise and validate the zero-stiffness concept and to study the effect of the static and dynamic pad characteristics on the transmissibility function. It is shown that both the stiffness and damping need to be minimised at equal operating fly height to create a stable system. A stable design is found with the use of a parametric optimisation procedure. The design shows a lower transmissibility when compared to a standard aerostatic bearing, although there are some challenges regarding high design sensitivities and displacement non-linearity. Different manufacturing methods are investigated to build a prototype to validate the concept. The measurements prove the validity of the model, although a clear low-stiffness operating point is not found, due to a combination of manufacturing difficulties and high design sensitivities.