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Optical Servo Technique using Moire Fringes

IP.com Disclosure Number: IPCOM000080843D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Hart, DM: AUTHOR

Abstract

Fig. 1 shows an optical servo scheme making use of moire patter s, to provide a simple optical "magnification" of the relative motion between a disk and a read/write head mounted on slider 1. This moire pattern is formed when two gratings of equal pitch are skewed in respect to each other, or when one grating has a pitch slightly different from the other.

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Optical Servo Technique using Moire Fringes

Fig. 1 shows an optical servo scheme making use of moire patter s, to provide a simple optical "magnification" of the relative motion between a disk and a read/write head mounted on slider 1. This moire pattern is formed when two gratings of equal pitch are skewed in respect to each other, or when one grating has a pitch slightly different from the other.

A moire pattern suitable for servo applications in a disk file may be formed, by fabricating opaque or nonreflecting concentric circles 5 with equal spaces on the storage disk, and by fabricating parallel lines of the same dimensions on a transparent section 3 of the runner of a flying slider 1. If the slider 1 is skewed by a few degrees in respect to the disk, moire patterns will be formed. The lines may be greater than, equal to, or less than the width of the magnetic track. The lines may be formed on each surface by thin-film technology and photolithography techniques.

The slider section 3 is more clearly shown in Fig. 2. The light-emitting diode (LED) light source 4 and photodiode detectors 2 are mounted on transparent Section 3. LED's 4 are mounted on the leading edge and cause light to be transmitted through section 3, as indicated by the arrow. The photodiode detectors 2 are mounted on the upper rear portion of section 3. Lines 6 are formed on the bottom surface of section 3.

The moire pattern produces a sinusoidal optical density variation which can be detected...