Modal analysis of a computer disk drive

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Title: Modal analysis of a computer disk drive
Author: Thurston, Michael G.
Abstract: The normal (real) modes of a Winchester type hard disk drive were determined in the frequency range 0-2200hz. Two methods of analysis were used in order to allow cross-correlation of the results. Experimental modal analysis was performed using Structural Measurement Systems' (SMS) Modal 3.0 analysis system and the requisite experimental hardware. A finite element analysis was also performed using MSC/NASTRAN; the NASTRAN model was created using the PATRAN pre-processing program. In order to alleviate the complications associated with matching the structural mounting conditions, a free-free analysis was performed using NASTRAN, and a light string was used to free mount the test specimen for the experimental work. The two analyses showed a one-to-one correspondence of modes; both showed 15 modes in the frequency range. Deviations of the NASTRAN natural frequencies from the experimentally determined natural frequencies ranged from -22 percent to +11.7 percent. Of the 15 modes, 10 showed deviation magnitudes of 10 percent or less, and 6 of the 15 were below 5 percent. Mode shape correlation was performed solely by observation. Errant DOFs in the experimental mode shapes made correlation difficult for several of the modes. In particular, the modes which showed higher frequency deviation (in excess of 10 percent) did not yield exact mode shape correlation although the primary deflection patterns were similar.
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Date: 1988-01

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