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Precise Optical Position Indication

IP.com Disclosure Number: IPCOM000083605D
Original Publication Date: 1975-Jun-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Barnard, CP: AUTHOR [+2]

Abstract

Precise registration of a moving object 1 with a fixed reference mask 2 is indicated, by providing both the mask 2 and a grating on the object 1 with identical patterns of slots 3 and 3; respectively. (Fig. 2). A photosensor 4 detects light from light source 5 through all the slots simultaneously when the grating and mask are in registry.

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Precise Optical Position Indication

Precise registration of a moving object 1 with a fixed reference mask 2 is indicated, by providing both the mask 2 and a grating on the object 1 with identical patterns of slots 3 and 3; respectively. (Fig. 2). A photosensor 4 detects light from light source 5 through all the slots simultaneously when the grating and mask are in registry.

The spacing of the slots is so arranged that, as the grating slot pattern overlaps the mask slot pattern, no more than one pair of slots at a time passes light until, upon precise registration, all eleven pairs of slots transmit light simultaneously. The photosensor 4 thus produces an output signal (Fig. 3) in which a sharp position indicating signal is evident. This signal has ten times the amplitude of the adjacent signals resulting from the coincidence of single pairs of slots.

The use of multiple slots gives a signal of greater signal-to-noise ratio than a single narrow slot would give, and allows greater tolerances on the positioning of the individual slots than could be allowed on the position of a single narrow slot. The use of multiple slots also gives an output signal of much faster rise time, than would be obtainable from a single wide slot of overall width equal to the combined width of the multiple slots.

This technique of optical position indication, finds application in a system for writing permanent position and timing information on magnetic disks. In such a system, an optical...