Browse Prior Art Database

Reflective Mark/Document Sensor

IP.com Disclosure Number: IPCOM000075853D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Anderson, TH: AUTHOR

Abstract

This sensing system uses a solid state electronic device such as GaAs light emitting diode (LED) as a light source, and a phototransistor as a receiver. The components are positioned very close together and in close proximity to the document from which marks are to be read. This construction results in a very efficient, low-cost system and does not require elaborate lenses or fiber optics as are frequently used in mark sensing and document detection.

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Reflective Mark/Document Sensor

This sensing system uses a solid state electronic device such as GaAs light emitting diode (LED) as a light source, and a phototransistor as a receiver. The components are positioned very close together and in close proximity to the document from which marks are to be read. This construction results in a very efficient, low-cost system and does not require elaborate lenses or fiber optics as are frequently used in mark sensing and document detection.

An opaque barrier 1 is placed between light source 2 and phototransistor 3 to prevent unwanted cross talk between the source and detector. Light emits from the source and illuminates the document 4. The cone of light rays is limited by mask 5 on the window 7 to prevent specular reflection from striking photodetector
3. Window thickness and spacing between the light source and photodetector are such that when a mark is in the read position, only diffused light will strike the photodetector. A low quality lens 6 is molded in window 7 to increase the light efficiency. The sensor is constructed in a multichannel module on a substrate 8 having contact pins 9, and modules may be assembled into a linear array for mark-read applications.

When used in the mark-read mode of operation, the LEDs are pulsed with a series of pulses. The recognition of a mark requires detection of m out of n pulses by photodetector 3. This decreases the possibility of detecting erasures, extraneous marks or smudges o...