Inphase Design of the Lowest Two Natural Modes of Vibrations of Swing-Arm for High Frequency Band Head Positioner

Abstract

This paper describes an inphase design method of the lowest two natural modes of vibrations of swing-arm supported by pivot bearing for a high frequency band head positioner of 3.5 inch hard disk drive. From modal analysis of swing-arm mechanism with isotropic bearing stiffness, it is found that the inphase mode condition can be realized if the position of arm's mass center is designed at more than 5.6 mm distance from the pivot and if arm is bent slightly. If the pivot bearing stiffness can be made anisotropic, a marginal mass center region for inphase mode condition can also be secured even in a straight arm. Based on a classical control design with a lead filter and a notch filter, it is shown that the control frequency band of inphase mode swing-arm of having additional 10 kHz bending mode can be increased twice higher than the conventional swing arm whose mass center is located at pivot.