Evaluation of fluid dynamic bearing spindle by vibration base

At present, ball bearings (BBs) are generally used in spindles of hard disk drives, but it has been known that BBs generate high-frequency vibration and acoustic noise. Hence, other types of spindles using fluid dynamic bearings (FDBs) that have high rotational accuracy and less vibration characteristics have been developed and put into practical use. FDB spindles have become common in use; nevertheless, a conventional characteristics evaluation method based on rotational accuracy, such as repeatable runout and nonrepeatable runout, is still used for FDB spindles. Since the FDB mechanism is different from BBs, we think that not only rotational accuracy, but also the shaft stiffness and the damping effect of spindle, are important in evaluating the spindle. In this study, we propose a new evaluation method for damping characteristics and frequency characteristics of FDB bearing spindles using a high-frequency vibration base. The presented method in this study is not a precious evaluation of bearing characteristics, but an evaluation method for basic mechanical comprehensive design considering tracking servo and the vibration of the disk and base in use for hard disk drives.