Design Optimization of FDBs to Minimize Friction Torque

We proposed a design method to optimize the design variables of fluid dynamic bearings (FDBs) in a hard disk drive (HDD) in such a way as to minimize the friction torque while satisfying the constraints of robust dynamic performance of a rotating disk-spindle system. The objective function was defined as the friction torque of the FDBs and was calculated by integrating the shear stress determined from the Reynolds equation using the finite element method (FEM). Two kinds of constraints were used to satisfy the robust dynamic performance of a rotating disk-spindle system. For under-damped vibration modes of a rotating disk-spindle system, the critical mass was set to be greater than that of the conventional disk-spindle system; for over-damped vibration modes, the related direct stiffness and damping coefficients were set to be greater than those of conventional FDBs. A micro-genetic algorithm was applied to solve the proposed optimal design problem of the FDBs in a 3.5-in HDD, and it showed that the friction torque of the FDBs decreased by 9.5% with the better dynamic performances of the rotating disk-spindle system.