Vibration Characteristics of Optical/Magnetic Disk Drive Subjected to Base Excitation

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The purpose of this study is to obtain the principles of mechanical design for disk drives which are secure against external vibrations. Vibration characteristics of disk drives in operation subjected to base excitation are theoretically analyzed. In the analytical model of disk-spindle system, a disk is treated as an uniform thin elastic annular plate in rotation, a hub of a spindle motor is treated as a rotating rigid body, and bearings of a spindle motor are treated as elastic and damping components. Formulation of the deflections of the rotating disk to base excitation is derived as an eigenfunction series where the eigenfunctions are given in the form of rotating waves. The expressions of the response of the rotating disk-spindle system for an axial translation, a forward whirl motion of tilting, and a backward whirl motion of tilting are obtained separately. The graphical method for the natural frequencies of the rotating disk-spindle system is proposed. Moreover, the radial displacements are added to the degrees of freedom of the analytical model, and inplane motion of the disk are also considered. On the basis of the analytical consideration and numerical results, the effects of hub inertia, bearing flexibility, and spindle configuration both on the natural frequencies and on the steady-state response are discussed. The effects of the damping and the gyroscopic effects are also discussed. The experiments were carried out for a bare optical disk and a spindle motor, and the experimental results have varified the validity of the present analysis.