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Differential Paper-Skew Detector Independent of X or Y Velocity

IP.com Disclosure Number: IPCOM000046308D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Barteck, JC: AUTHOR [+2]

Abstract

Paper-feed misalignment can be accurately detected by reading the difference in signals from two photodiodes that are arranged geometrically transverse to the paper path. A typical geometric arrangement is illustrated in Fig. l.

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Differential Paper-Skew Detector Independent of X or Y Velocity

Paper-feed misalignment can be accurately detected by reading the difference in signals from two photodiodes that are arranged geometrically transverse to the paper path. A typical geometric arrangement is illustrated in Fig. l.

If the paper moves across the diodes with no skew, the difference in signals will be zero. However, any misalignment would produce a diode output difference that is proportional to the degree of feed error and easily correlated to various measurement schemes. When paper moves across the sensor misaligned, the difference signal will be as shown in Fig. 2.

The A interval represents paper moving across only diode 1, and the B interval represents paper moving across both diodes. During interval C, diode 1 is totally covered by paper and paper is still moving across diode 2. In D, a proportional difference exists between paper covering diode 1 and diode 2. In E, both diodes are totally covered.

It should be noted that even though the voltage is shown going in a positive direction, it could have been in a negative direction if diode 2 had started to cover first. Thus, the same detector circuit can additionally be used as a trailing-edge detector.

A specific circuit for evaluating the photodiode outputs is shown in Fig. 3, where R1 is a current-limiting resistor, LEDs 1 and 2 are the light emitting diodes associated with photodiodes 1 and 2, and P1 is a gain adjusting balance potent...