Experimental and analytical study of head-disk impact and dynamics of negative-pressure sliders in the unloading process

摘要

This paper presents an experimental and theoretical study of the head-disk impact and dynamics of negative-pressure sliders in the unloading process. The dimple impacts, which reflect the close of the separated dimple from the slider in the unloading process, are observed by using acoustic emission measurements. The head-disk impact is observed by using electrical resistance measurements. When laser Doppler vibrometer and AE measurements are used, the dimple impact frequencies are characterized from the response of the unloaded head gimbal assembly to an impulse excitation. A finite-element analysis shows that the head gimbal assembly with a separated dimple has two cantilever mode frequencies, which are correlated with the measured dimple impact frequencies. A theoretical model is developed for unloading process dynamics, which takes into account the loadbeam's dynamic effect. A simulation shows that the vibration of the loadbeam is likely one of the major factors in causing head-disk impact in the unloading process. Based on the model, a theoretical approximation of the unloading time is derived. The result shows that the unloading time is proportional to the preload force, maximum negative force, and limiter gap, and is inversely proportional to the effective/loadbeam compression stiffness, gimbal/limiter stiffness, and unloading velocity.