Taming disk/spindle vibrations through aerodynamic bearings and acoustically tuned-mass dampers

This paper studies the feasibility of suppressing the vibration of a spinning disk/spindle system by creating an aerodynamic bearing between the spinning disks and adjacent stationary flat surfaces. An automated impact hammer was first developed and instrumented to obtain repeatable and consistent frequency response functions (FRF). Through this device, frequency response functions of a 5-platter disk/spindle system were measured in the air and in the vacuum up to 7200 rpm with and without an air bearing, which consists of a flat surface 0.635 mm (25 mils) away from the top spinning disk. Compared with the experimental results in vacuum, the presence of the air (without the air bearing) causes the resonance frequencies of the disk/spindle system to split resulting in smaller resonance amplitudes. Nevertheless, the splitting does not increase the modal dampings of the disk/spindle system. When the air bearing is present, the air bearing does not further reduce the resonance amplitudes, but it does increase the modal dampings by 100-200%. Moreover, the presence of the air bearing lowers the resonance frequencies by 3%, because the air in the bearing behaves like incompressible fluid adding considerable inertia to the disk/spindle system. Also, the increase in damping and shift in natural frequencies are independent of the rotational speed. Finally, combination of the air bearing and a tuned-mass damper can significantly reduce the resonance amplitudes by 50-75%.