On the modelling of the dynamic characteristics of aerostatic bearing films: From stability analysis to active compensation

Determination of the static characteristics of air bearings constitutes the necessary first phase in a design problem, which determines general feasibility. In order to realize a successful application, a good knowledge and assessment of the dynamic behaviour is needed to complement the previous step. In a conventional, passive bearing application, dynamically stable behaviour should be ensured by overcoming the occurrence of self-excited vibrations; the so-called "pneumatic hammering". In active bearing applications, on the other hand, the dynamic bearing force, induced by actuation of the gap geometry or supply pressure, provides for a means of enhancing bearing static and dynamic performance, when integrated in a mechatronics system context. This paper presents on the one hand an overview of the methods used to model the dynamic characteristics of aerostatic films, deducing that the method of harmonic perturbation is often sufficient in providing a good estimate of the dynamic stiffness. This is confirmed by comparing theoretical results with dynamic response experiments. On the other hand, the general problem of active dynamic compensation is outlined and an application example is provided to show the high levels of performance achievable by employing this method. (C) 2008 Elsevier Inc. All rights reserved.