Identifying damping of a gyroscopic system through the half-power method and its applications to rotating disk/spindle systems

This paper applies the half-power method to identify damping of a gyroscopi c system. As first, the underlying principle of the half-power method for d amped, gyroscopic systems is explained. Then the method is demonstrated on a rotating disk/spindle system often used in computer hard disk drives. The disk/spindle system consists of multiple elastic disks mounted on a rigid spindle supported by ball bearings. The flexibility of the bearings allows the spindle to undergo rigid-body translation and rocking. Calibrated exper iments were conducted in vacuum to obtain frequency response functions at d ifferent rotational speed. Application of the half-power method shows that the disk and bearing dampings are independent of rotational speed and can b e modeled adequately as viscous damping. Moreover, the damping of the ball bearings is two orders of magnitude smaller than that of a fluid-film beari ng of similar size.