Porous aerostatic bearing with integrated air gap height measurement

Porous gas bearings are frictionless motion components commonly used in precision engineering applications. These bearings form a high-pressure gas film between bearing and guide surfaces, which allows for near frictionless motion. The height of the air gap provides information on operational characteristics of the bearing, such as stability and stiffness. External sensors have been used in conjunction with the bearing to measure the air gap height. The present research proposes a novel method and design to measure the air gap by using the bearing as a capacitive displacement sensor. The restrictor of the investigated aerostatic bearing was split into two electrodes - an annular guard electrode and a disk-shaped sensing electrode. This geometry isolated the electric field of the sensing electrode from environment and minimized its fringe fields. A capacitive bearing and measurement electronics were designed, manufactured and experimentally verified to determine the viability of the proposed method. The experiments included non-pressurized and pressurized experiments to determine the capacitance of the bearing at varying gap heights. The results confirm the validity of the concept. • Porous type aerostatic bearing acts as a capacitive displacement sensor to measure air gap height. • Cost efficient electronics design for converting the capacitance to voltage. • Analysis and experimental verification of bearing performance.