This paper investigates the whirling, tilting and axial motions of a hard disk drive (HDD) spindle system due to manufacturing errors of fluid dynamic bearings (FDBs). HDD spindle whirls around the sleeve with tilting angle due to the centrifugal force of unbalanced mass and the gyroscopic moment of rotating spindle in addition to axial motion. The whirling, tilting and axial motions may be increased by the manufacturing errors of FDBs such as imperfect cylindricity of sleeve bore, or imperfect perpendicularity between shaft and thrust plate. They increase the disk run-out to limit memory capacity and they may result in the instability of the HDD spindle system. This paper proposes the modified Reynolds equations for the coupled journal and thrust FDBs to include the variable film thickness due to the cylindricity of sleeve bore and the perpendicularity between shaft and thrust plate. Finite element method is used to solve the modified Reynolds equation to calculate the pressure distribution. Reaction forces and friction torque are obtained by integrating the pressure and shear stress, respectively. The whirling, tilting and axial motions of the HDD spindle system are determined by solving the equations of a motion of a HDD spindle system in six degrees of freedom with the RungeKutta method. It shows that the imperfect cylindricity and perpendicularity increase the whirl radius, axial runout and tilting angle of the HDD spindle system. However, the degradation of dynamic performance due to the imperfect perpendicularity between shaft and thrust plate can be improved by allowing the other manufacturing error of the cylindricity of sleeve bore in such a way to compensate the bad effect of the imperfect perpendicularity.

No abstract

This paper proposes a modified Reynolds equation for the coupled journal and thrust fluid dynamic bearings (FDBs) to include variable film thickness due to imperfect roundness of a rotating shaft. A finite element method is used to solve the modified Reynolds equation to calculate the pressure. Reaction force, moment, and friction torque of FDBs are calculated by integrating the pressure and shear stress along the fluid film. The dynamic behavior of a hard disk drive (HDD) spindle system is investigated by solving the equations of motion with six degrees of freedom using the Runge-Kutta method. This research shows that the imperfect roundness of the shaft increases the nonlinearity of FDBs. Imperfect roundness of the shaft generates harmonics of the groove number 1 in the bearing reaction force and the displacement of the HDD spindle system even in the case of stationary grooved FDBs.

No abstract

This research proposes a modifiedReynolds 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 ±l even in the case of stationary grooved FDB.