10 December 2001 CD-ROM optics for flying height measurement in hard disk drives
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Abstract
One of the most critical and effective parameters in increasing areal density is the flying height or spacing between the read-write head and the recording disk medium. As the flying height reduces to near contact, the head flies around 5 nm about the disk surface. To date, optical interferometry has been the major means for the characterization of this parameter. However, it is difficult to use it directly to measure the flying height on a sealed drive. To circumvent this limitation, a system based upon CD-ROM optics has been designed. The results from the system are correlated to measurements of suspension arm movement and disk flutter using poly-vinylidine-flouride (PVdF) strain sensors. A CD-ROM drive utilizes a laser with photodiodes to read data from the disk. The photo detector output responds linearly to changes in the lens-disk separation. In our system two CD-ROM heads are located within a rig that allows independent positioning in all three planes. The optics are configured to reflect off of a typical hard disk drive disk and the slider. To validate its performance a thin (110 micron) sheet of poly vinylidine flouride (PVdF) piezoelectric material is bonded to the suspension arm to measure the average induced strain. A further PVdF sensor was used to measure the edge displacement of the disk due to disk bending. The sensor used was in a cantilever configuration, with one end rigidly bonded to the drive chassis in a manner that pre-tensions the cantilever against the disk. Any movement of the disk would change the strain induced in the cantilever.
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Glen Tunstall, Glen Tunstall, David F. L. Jenkins, David F. L. Jenkins, Warwick W. Clegg, Warwick W. Clegg, Amei Li, Amei Li, Paul Davey, Paul Davey, } "CD-ROM optics for flying height measurement in hard disk drives", Proc. SPIE 4442, Novel Optical Systems Design and Optimization IV, (10 December 2001); doi: 10.1117/12.449966; https://doi.org/10.1117/12.449966
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