Dynamic characteristics of a HDD spindle system due to imperfect roundness of shaft

This research proposes a modified Reynolds equation for the coupled journal and thrust FDBs to include the variable film thickness due to the imperfect roundness of a rotating shaft. Finite element method is used to solve the Reynolds equation to determine pressure, reaction force and friction torque. The dynamic behavior of a HDD spindle system is determined by solving the equations of a motion in six degrees of freedom with the Runge-Kutta method. This research shows that the imperfect roundness of the shaft increases the nonlinearity of FDBs. It generates the harmonics of the bearing reaction force and the displacement of the HDD spindle system which correspond to groove number ±1 even in the case of stationary grooved FDB.