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Lateral Position Detector for Moving Web

IP.com Disclosure Number: IPCOM000075794D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Everett, LH: AUTHOR

Abstract

In the system shown, the lateral position of the tape loop 10 is detected by monitoring light picked up by photodetectors 12 and 14. Tape 10 carries triangular-shaped perforations 16 along each edge. Light from light sources 18 and 20 direct light onto the tape 10 near each edge of the tape. As the tape moves past the light sources, perforations 16 will pass light through the tape to photodetector 12 or 14. The duration of the light shining on each photodetector will depend upon that portion of the triangular perforation that crosses the light path between light source and photodetector. If the path of light on the tape moves across the base of the triangle as the tape moves, the length of time that the light illuminates the photodetector will be longer than if the light moves across the top of the triangular perforation.

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Lateral Position Detector for Moving Web

In the system shown, the lateral position of the tape loop 10 is detected by monitoring light picked up by photodetectors 12 and 14. Tape 10 carries triangular-shaped perforations 16 along each edge. Light from light sources 18 and 20 direct light onto the tape 10 near each edge of the tape. As the tape moves past the light sources, perforations 16 will pass light through the tape to photodetector 12 or 14. The duration of the light shining on each photodetector will depend upon that portion of the triangular perforation that crosses the light path between light source and photodetector. If the path of light on the tape moves across the base of the triangle as the tape moves, the length of time that the light illuminates the photodetector will be longer than if the light moves across the top of the triangular perforation. Thus, the length of time that each photodetector is illuminated, is an indication of the lateral position of the tape 10.

To eliminate the necessity of having light sources of equal brightness and/or photodetectors of equal sensitivity, the pulses produced by the photodetectors are clipped and fed into a differential amplifier. When the pulses from each photodetector at each edge of the web are different in duration, the output from the differential amplifier is a pulse whose length is equal to the difference in the pulse lengths from each photodetector. This pulse from the differential amplifier is a dir...