Air gap pressure distribution measurement device

Aerostatic bearing operating principle is based on a thin air film between the bearing and the opposing surface. Air film thickness varies commonly in the range of 1 to 10 μm. Pressure and the pressure distribution in the airgap are important factors when estimating the performance of aerostatic bearings. The pressure distribution influences the stiffness and the overall load capacity of the aerostatic bearing. The pressure distribution in the air gap varies due to the type and geometry of the bearing. This study investigates an automated test device for the measurement of the pressure distribution in the air gap. The measuring setup consists of a measurement rig to load the aerostatic bearing and to measure the air gap height. The load for the bearing is applied with lowfriction pneumatic cylinder and the force conducted to the sample is measured with a load cell. The investigated bearing is supported with a four-bar linkage where all joints are flexure hinges. Parallel alignment of the bearing against its counter surface is ensured with a separate two axial flexure joint. The height of the air gap is measured with three linear gauges. The pressure distribution in the air gap was measured using a moveable bearing counter surface where a 0.10 mm diameter hole was located. The moving countersurface was used to position the hole at various radial locations in the air gap of the aerostatic bearing. The counter surface had two parallel spring guides in series to provide guiding for linear displacement with minimal parasitic error motions. The results show that the pressure in the air gap varies in relation to the distance from the bearing edge. Furthermore, it is shown that increasing the bearing load increases the pressure in the air gap until overload of the bearing is reached. Overloading brings the bearing close to or in contact with the guiding surface and significantly restricts air flow, thus decreasing pressure in the air gap. The results of the present study give corroborative evidence on the feasibility of the pressure measurement method and usefulness of the automated test device.