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Document Hole Reader

IP.com Disclosure Number: IPCOM000092769D
Original Publication Date: 1967-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Von Feldt, JL: AUTHOR

Abstract

High-speed hole reading or document detection is made possible by sensing changes in voltage across thermistors 15 as air from supply 12 is permitted and prevented from impinging upon 15 under control of document 10. Air supply 12 can be placed on either side of the document 10 path. It is preferred to have air supply 12 on the same side of the document 10 path as thermistors 15 when the device is used as a document detector in an optical character reader. The arrangement shown is suitable for reading holes.

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Document Hole Reader

High-speed hole reading or document detection is made possible by sensing changes in voltage across thermistors 15 as air from supply 12 is permitted and prevented from impinging upon 15 under control of document 10. Air supply 12 can be placed on either side of the document 10 path. It is preferred to have air supply 12 on the same side of the document 10 path as thermistors 15 when the device is used as a document detector in an optical character reader.

The arrangement shown is suitable for reading holes.

Impinging air cools 15 and its resistance increases. Thus, when document 10 is not between 12 and 15, the voltage at point A is at an up level. Transistors T1, T2, and T3 are conducting. When 10 blocks air from 15, its resistance decreases due to heating. Therefore, the voltage at point A drops. This change of voltage is AC-coupled into the base of T1 driving it toward cut off. The collector voltage of T1 rises and this causes T2 to conduct more heavily. T3 is already saturated and therefore no voltage change appears at its collector. Then as hole 11 passes by, 15 is cooled and the voltage at point A stops decreasing.

This instantaneous change is detected at the base of T1 and it starts conducting more heavily. Consequently, its collector voltage drops and this change in voltage appears at the emitter of T2 to turn T3 off. The collector voltage of T3 rises to give a positive going output signal at terminal 16. After hole 11 passes by, 15...