This paper presents theoretical and experimental characteristics of a self-acting step-groove gas bearing. This bearing has some axial grooves on its surface. However, its configuration is much simpler than the conventional spiral groove, so it is applicable to use in many precision apparatus, like a laser beam scanner. When a rotor in the bearing rotates, compressibility number Λ: 6μω/ Pα(R/ C)2 increases and hydrodynamic pressure is generated on the groove parts. Here, μ : coefficient of gas viscosity, ω; rotor angular velocity, Pα ; atmosphere pressure, R; rotor radius, C; bearing clearance. The configuration and number of grooves affect hydrodynamic pressure, bearing load carrying capacity and stability. When eccentricity ε and Λ are given, an appropriate groove configuration is determined. Generally, in small Λ and ε, the bearing with small groove depth gives much higher load carrying capacity and stability. However, in large Λ and ε, large groove depth gives higher stability than small groove depth. The laser beam scanner, which uses this bearing and the newly designed thrust magnetic bearing can rotate less than 1.0 μm run out and 0.003% revolution fluctuation at 12000 rpm.
