Improved servo performance of hard disk drives with a passive vibration damper

primary trend in hard disk drives is that the track density and storage capacity are increasing very rapidly. This is projected to place extreme requirements on the precision with which the head actuator rapidly moves the read/write heads across the disk surfaces and maintains them over the specific data tracks for reading and writing information. It is therefore required to further improve the read/write head positioning servo performance for future high track density hard disk drives. However, the servo bandwidth is limited mainly by the inherent mechanical resonance of the head actuator. Also, the further decreasing of the data access time is hampered by residual vibrations caused by the flexibility of the head actuator. As a result, the improvement of the head actuator dynamics is needed for future high-performance hard disk drives.;A thorough understanding of the head actuator dynamics under the normal operation is essential to control the vibration and optimize drive performance. In this dissertation, the experimental method of measuring the head actuator dynamics under the actual operating condition is developed based on a scanning laser vibrometer. The representative tracking dynamics of the head actuator are identified from the measurements of commercially available hard disk drives. Finite element modeling is also used to obtain further insights on the dynamics of the entire head actuator. The effect of the head actuator dynamics on the servo performance is further investigated in both the frequency domain and the time domain. An experimental track seeking and settling servo system is developed based on a laser vibrometer and a servo selection controller. It is shown that the system mode and the actuator mode of the head actuator are the predominant factors that limit the servo bandwidth and generate the residual vibration during the track settling operation. The sway mode and other suspension modes are not as important as the system and actuator modes.;Passive damping has the potential to improve the head actuator dynamics. In this dissertation, a practical passive damper is developed for effectively damping the critical mechanical resonance of the head actuator. The tracking dynamics of the head actuator are therefore greatly improved. The measured data shows that the settling time can be reduced from 7 ms to 1.5 ms for 0.1...