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

This paper studies the feasibility of suppressing the vibration of a spinni ng disk/spindle system by creating an aerodynamic bearing between the spinn ing disks and adjacent stationary Rat surfaces. An automated impact hammer was first developed and instrumented to obtain repeatable and consistent fr equency response functions (FRF). Through this device, frequency response f unctions of a 5-platter disk/spindle system were measured in the air and in the vacuum up to 7,200 rpm with and without an air bearing, which consists of a flat surface 0.635 mm (25 mils) away from the top spinning disk. Comp ared with the experimental results in vacuum, the presence of the air (with out the air bearing) causes the resonance frequencies of the disk/spindle s ystem 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 t he resonance amplitudes, but it does increase the modal dampings by 100-200 %. Moreover, the presence of the air bearing lowers the resonance frequenci es 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 rotation al speed. Finally, combination of the air bearing and a tuned-mass damper c an significantly reduce the resonance amplitudes by 50-75%.