Effect of airflow on the vibration of head gimbal assembly and disk flutter in a hard disk drive

The hard disk drive is the most commonly used information storage device in the computer industry today. Due to constant demand for higher performance, new generations of hard disk drives are required to pack higher data densities and to transfer data at higher rates. More precise motion control of the dynamic components in hard disk drives is the key to improved performance of hard disk drives. Extensive research on the dynamics of the head suspension assembly and the disk, including the excitation from the surrounding air flow at high disk rotation speeds, is necessary. The present study investigates experimentally the air flow excitation of vibration of the slider and head suspension assembly, and it also investigates aeroelastic disk flutter.; The contributions of the present study are threefold. First, air flow induced vibration of the slider was investigated experimentally. Flow fluctuations were measured upstream and downstream of the slider with a single, constant temperature hot wire anemometer. Displacement of the slider was measured with a laser Doppler displacement meter. Two unsteady flow phenomena that can affect slider vibration in the plane of the disk were studied: the vortex shedding from the slider and periodic flow fluctuations caused by disk geometry. Vortex shedding of relatively low frequency from the slider is shown to occur in a range of the disk speeds and slider positions but its effect on the slider vibration is observed to be negligible. The periodic pressure fluctuation, caused by air flow over a particular geometry of disk hub, was found and its excitation of the slider vibration is significant near the disk hub. The amplitude of slider vibration was reduced substantially by use of a hub with a flat surface.; Second, turbulence induced vibration of the head gimbal assembly in a disk drive was investigated experimentally. Mean and fluctuating components of the air velocity upstream of the head gimbal assembly were measured using the hot wire anemometer to permit estimation of the fluid loading of the head gimbal assembly. The dependence of fluid loading on the cover geometry and disk speed were studied. The hot wire measurements were compared to the radial slider vibration with a focus on the first torsional mode of head gimbal assembly. It was found that the product of the mean and fluctuating components of velocity near the load beam correlates strongly to the radial slider vibration. Changes to the cover geometry reduced the slider vibration in the first torsional mode of head gimbal assembly, especially at higher disk speeds where turbulent excitation is more significant.; Third, an experimental technique, predicting the onset of aeroelastic flutter in a hard disk drive, was presented. The aerodynamic force was modeled by the sum of dissipative and circulatory linear operators which subsumes, as a special case, the pressure generated in a thin hydrodynamic film between the disk and a wall. The aeroelastic parameters for an acoustically excited single disk at different enclosure gaps were derived for the speed range 6,000--19,800 rpm. The flutter speed predicted is strongly influenced by the enclosure gap width. Flutter speeds in these drives as low as 35,000 rpm are predicted. The technique can also be extended to predict the flutter speeds in other systems including DVD and CDROM drives.