Vibration of rotating-shaft HDD spindle motors with flexible stationary parts

Demonstrates an accurate mathematical model predicting forced vibration of rotating-shaft hard disk drive spindle motors with flexible stationary parts. The mathematical model consists of three parts: a rotating part, a stationary part, and bearings. The rotating part includes a flexible hub, a flexible shaft press-fit into the hub, and N elastic disks mounted on the hub. The stationary part can include motor bracket (stator), base casting, and a top cover. The bearings under consideration can be ball bearings or fluid-dynamic bearings (FDB). The rotating disks are modeled through the classical plate theory. The rotating part (except the disks) and the stationary part are modeled through finite-element analyses (FEA). With mode shapes and natural frequencies obtained from FEA, the kinetic and potential energies of the rotating and stationary parts are formulated and discretized to compensate for the gyroscopic effects from rotation. Finally, use of the Lagrange equation results in the equations of motion. To verify the mathematical model, frequency response functions are measured experimentally for an FDB spindle carrying two identical disks at motor and drive levels.