Browse Prior Art Database

Improved Light/Dark Ratio for Reflective Sensor

IP.com Disclosure Number: IPCOM000036764D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 20K

Publishing Venue

IBM

Related People

Nard, ME: AUTHOR [+3]

Abstract

There are many applications involving the detection of an area or edge of a moving mechanical member where an optical reflective sensor would integrate perfectly. However, implementation of reflective sensor systems is sometimes difficult, particularly in a direct couple mode because of the sensor's wide parameter range and the difficulty of obtaining a large signal-to-noise ratio.

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Improved Light/Dark Ratio for Reflective Sensor

There are many applications involving the detection of an area or edge of a moving mechanical member where an optical reflective sensor would integrate perfectly. However, implementation of reflective sensor systems is sometimes difficult, particularly in a direct couple mode because of the sensor's wide parameter range and the difficulty of obtaining a large signal-to-noise ratio.

The desirable electronics used with an optical reflective sensor is a fixed current source to energize the transmitter (LED) and a comparator with a fixed threshold connected to the receiver (phototransistor) to generate a logic level output signal. Because of the large variation of sensor assembly parameters (30:1 phototransistor current with a fixed LED current and a fixed reflective surface), the comparator usually has a low threshold level and a small amount of hysteresis. A direct coupled system with this type of electronics will only function properly if there is sufficient light current in the phototransistor during 'Light', and near zero current in the phototransistor during 'Dark.' Light refers to the mechanical arrangement where it is desirable to have reflected light energize the receiver in the optical reflective assembly. Dark is just the opposite in that the mechanical arrangement dictates that very little light energizes the receiver.

The figure is a diagram of a mechanical assembly which attains the desired 'Light' and 'Da...