Optimization of Groove Dimensions in Spiral-Grooved Journal Bearings for Spindles of Precision Equipments

Spiral-grooved bearings have lately attracted considerable attentions as better substitutions for current ball bearings, especially in motor spindles of precision equipments such as hard disk drive systems. Their high stiffnesses and high damping abilities can realize good run-out characteristics even for such small-sized equipments. Regarding the groove dimensions of the spiral-grooved journal bearings, it seems that we usually design them according blindly to a traditional standard aiming for maximizing the direct bearing stiffness. It is also the fact that the bearings designed according to this standard can realize comparatively good bearing performances. On the other hand, there have been considerably few discussions on optimum designs of the groove dimensions specialized for a reduction of amplitude of the operating run-out, which is a major characteristic for applications to precision equipments. The optimization of groove dimensions of the spiral-grooved journal bearings is, then, discussed in this paper. The subjects for optimizations are: 1) reduction of rotor displacement against a static load, 2) reduction of amplitude of the operating repeatable run-out (RRO) due to an unbalanced rotor mass, and 3) reduction of amplitude of the operating non-repeatable run-out (NRRO) against an external impulse load.