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Externally Sensed Grating Track Sensing Arrangement

IP.com Disclosure Number: IPCOM000042661D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Whitefield, RJ: AUTHOR

Abstract

An optical arrangement is described which uses a reflecting grating to determine position. The grating has a relief profile which allows the grating to act as a beam divider, and as a metrological scale. The arrangement has advantage in that for sufficiently angled relief profiles the required imaging numerical aperture is minimized and the detection of the position signal is performed on a non-imaged basis. The detection of the position signals on a non-imaged basis provides cost reduction. The relief grating arrangement is of particular advantage when the location of equally spaced positions, such as the centers of magnetic recording tracks, is desired with high accuracy. An example of the arrangement is shown in Fig 1.

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Externally Sensed Grating Track Sensing Arrangement

An optical arrangement is described which uses a reflecting grating to determine position. The grating has a relief profile which allows the grating to act as a beam divider, and as a metrological scale. The arrangement has advantage in that for sufficiently angled relief profiles the required imaging numerical aperture is minimized and the detection of the position signal is performed on a non-imaged basis. The detection of the position signals on a non-imaged basis provides cost reduction. The relief grating arrangement is of particular advantage when the location of equally spaced positions, such as the centers of magnetic recording tracks, is desired with high accuracy. An example of the arrangement is shown in Fig 1. A lens images a slit-like object (or an array of such objects) onto a grating which has a profiled contour. When the image is centered on an apex of a triangularly profiled grating element, the action of the grating is to divide the reflected beam into two components which are propagated at an angle with respect to the grating normal. If the slope of the profiled grating element is appropriately chosen, the divided reflected components need not pass back through the imaging lens, but may be directed so as to be detected in a non-imaged configuration by two photodetectors. The signals from these photodetectors may be used to determine when the image is centered on the apex of the grating element (i.e., when the signals are equal). For the case where the width of the slit image is equal t...