Browse Prior Art Database

Document Detection

IP.com Disclosure Number: IPCOM000081772D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Eckholm, DG: AUTHOR [+2]

Abstract

A document detector 10 is positioned adjacent lens 11 to collect reflected scanning light 12 for control of an erase lamp 13. Light detector 10 provides a baffle forming housing 14 having a funnel-shaped light entrance portion 15, that permits entry of only scanning light to the exclusion of stray light.

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Document Detection

A document detector 10 is positioned adjacent lens 11 to collect reflected scanning light 12 for control of an erase lamp 13. Light detector 10 provides a baffle forming housing 14 having a funnel-shaped light entrance portion 15, that permits entry of only scanning light to the exclusion of stray light.

An infrared filter 16 passes only visible light to a phototransistor mounted on a circuit board 17 under a lens element 18. Filter 16 thus assists in removal of stray light from illumination source 19 which has a high-infrared output, which output does not necessarily follow the same path as the visible light.

The printed circuit on card 17 is provided with a positive power supply input 20, a negative power supply input 21, and a ground input 22. Comparative voltages derived on lines 23 and 24 are input to an operational amplifier 25 connected as a Schmitt trigger to generate a precise fast output on line 26.

A voltage level is derived on line 23 that is a function of the light-level intensity applied to phototransistor 27 and a particular setting of threshold adjustment potentiometer tap 28. Line 24 receives a voltage that varies with ambient temperature in a manner that is similar to the temperature variation voltage drop across phototransistor 27, thereby negating effects of ambient temperature.

In operation, output line 26 normally presents a positive potential, so long as the light received by phototransistor 27 is below the threshold set...