The studies of wall profile effect on taper-less air bearing in magnetic hard disk drive

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The studies of wall profile effect on taper-less air bearing in magnetic hard disk drive


Author: Pang, Chi-chung
Title: The studies of wall profile effect on taper-less air bearing in magnetic hard disk drive
Year: 1998
Subject: Magnetic disks
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Mechanical Engineering
Pages: xiii, 109 leaves : ill. ; 30 cm
Language: English
Abstract: Information processed by computers is often stored on magnetic disks for later retrieval. One of the critical areas of this storage process, referred to as the slider-disk interaction, is the dynamics of suspending a magnetic recording head over a rotating disk while maintaining a finite clearance between the disk and the slider carrying the head. In magnetic disk drives, the areal density of stored information continues to increase from year to year. This goal is primarily accomplished by lowering the slider and disk spacing, and maintaining a controlled clearance and profile across the disk. In general, miniaturizing sliders make it possible to lower flying height and follow disk surface more accurately. However, the reduction of air bearing stiffness causes the flying height sensitive to manufacturing tolerance, such as taper length and its angle. In order to minimize the influence of manufacturing tolerance, it is essential to implement a taper-less slider design. In such case, wall profile of air bearing surface becomes a critical factor which influence the dynamic performance of slider motions under flying condition. The main objective of the dissertation is to analyze the dynamic flying response of taper-less slider by the influence of wall profile effect. Several groups of samples with same air bearing but different wall profile contours are developed by adjusting the incidence angle of ion beam etching (20, 45, 60 and 70 degree) and named as group A, B, C and D respectively. The larger of milling angle, the longer and flatter of wall profile is resulted. By using of dynamic flying height tester (DFHT), the flying responses for each group of samples have been tested under same condition to provide fair comparison. Skew sensitivities, take-off velocity and head seeking tests are used for studying the flying characteristic by the influence of wall effect. Long wall profile sample provides comparative higher flying height profile and pitch in result. Fast take-off and less seek sensitivity are the advantage of long wall profile head, however, it sensitive to the inlet angle of air flow and suffer serious problem of slider rolling. Therefore, wall profile optimization becomes an important issue to make balance from each side. Numerical flying simulator, CML, are utilized to simulate the head flying response under consideration of wall effect by a additional stepped rail around the leading edge. The modeling result shows have a good agreement with practical finding and depend strongly on the wall effect. Sub-ambient pressure are generated at air bearing recess region which induce of suction force towards the disk media, and hence improve the stability of flying. In general speaking, wall profile effect is considered as an important factor which affect the dynamic flying response of magnetic head. The change of wall angle and it's length shows to have significant affect of flying height. And this factor have to take into account by simulation.

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