Effect of an out-of-sphericity error on the radial stiffness of an air dynamic bearing

Out-of-sphericity error is degree of deformation of an air bearing sphere deviated from a perfect sphere. This paper investigates numerically the effect of out of sphericity error on the radial stiffness of an air bearing. Three types of out-of sphericity modes are considered. In this study, the stiffness is calculated from pressure distribution at the bearing surface, which is obtained by solving the Reynolds equation. In some cases, large out-of-sphericity errors are found to improve the stiffness of an air bearing. This implies that an air bearing of perfect hemispheres is not necessarily of the best performance. Thus, much labor and cost in manufacturing air bearings can be saved. In addition, the radial stiffness depends greatly on the force applying direction for bearings of radially deformed stator hemisphere.