A numerical study on rotating-shaft spindles with nonlinear fluid-dynamic bearings

The purpose of this paper is to present a numerical model predicting the shock response of a rotating-shaft spindle motor with nonlinear fluid-dynamic bearings (FDBs). The paper consists of three parts. The first part is to modify an existing linear spindle vibration model to include arbitrary FDB nonlinearity. The model consists of a rotating part, a stationary part, and nonlinear FDB. Equations of motion are derived and numerically integrated to predict nonlinear shock response of the spindle. The second part summarizes requirements on global coordinates and operating points in formulating nonlinear FDB-load characteristics to be used in the nonlinear spindle model. If bearing stiffness and damping appear as nonlinear functions of bearing eccentricity in local coordinates, the global-bearing stiffness and damping matrices can be obtained through coordinate transformation. The third part of this paper is to apply the mathematical model to various hard disk drive designs. When FDB nonlinearity appears as stiffening springs and dampers, the nonlinear spindle model predicts a slight increase in resonance frequencies and a slight decrease of resonance amplitude for the half-speed whirls. Also, peak amplitude of shock response from the nonlinear analysis is much less than that obtained from the linear analysis.