Dynamic stiffness compensation with active aerostatic thrust bearings

Aerostatic thrust bearings are used in linear guideways as an alternative to contact bearings. The absence of friction in the motion makes aerostatic guideways most suitable for high precision and high speed machines. The low stiffness and damping of the aerostatic support, however, limits their application in machining processes. Active compensation, applied to the bearing films, is proposed as a solution to overcome this limitation and to achieve further performance improvements in terms of stiffness and damping, adding positioning capabilities. Previous research shows that gap shape control is the most promising activation method. However the need for a flexible bearing surface increases the complexity of the design. A simulation model that considers the coupling between the structural, fluid dynamics and piezoelectric aspects has been developed in order to aid in the design of active air bearings. The simulation results show the validity of the coupling strategy and the relevant influence of the flexibility of the bearing plate on the bearing performance. However, the simplified models used, in order to keep short simulation times, and the influence of some phenomena, such as surface roughness, which are not modeled, require that the model accuracy be validated by experimental investigation. For this purpose, a test setup capable of identifying the bearing performance with high bandwidth and resolution has been built. Experimental results show that high dynamic stiffness can be obtained by active compensation. The final performance is highly dependent on the bearing design and the working conditions, and thus the need of a coupled simulation model is confirmed.