Free vibration of a rotating disk pack and spindle motor system with a rotating-shaft design

This paper studies the free vibration of a rotating disk-spindle system wit h a rotating-shaft design. This design is more desirable for disk-drive man ufacturing because it has fewer components and a better prevention of lubri cant leakage than the rotating-hub design. The disk-spindle system consists of multiple circular disks clamped to a rigid hub, which spins at constant speed and allows infinitesimal rigid-body translation and rocking. In addi tion, the hub is press-fit onto a flexible shaft, which is mounted on spind le housing through ball or hydrodynamic bearings. Equations of motion are d erived through Lagrangian equations and discretized in terms of hub rocking , hub translation, disk eigenmodes, and shaft eigenmodes. In addition, the equations of motion are valid for spindles with either ball bearings or hyd rodynamic bearings. Experimental results and finite-element simulations of stationary disk packs indicate that spindles with a rotating-shaft design d iffer from those with rotating-hub design in two ways. First, the shaft can not be modeled as an Euler-Bernoulli beam because of its aspect ratio. Shea r deformation of the shaft has to be considered. Second, the hub undergoes significant elastic deformation at the hub-shaft interface, because a consi derable inertia load is transmitted. Finally, natural frequencies of rotati ng-shaft spindles with ball or hydrodynamic bearings are measured at differ ent spin speeds to validate the mathematical model.