Method of detecting the improper separation of documents being fed through a document counter or the like

Claim 1

A method of detecting if a double document feed occurs past a reference point as documetns, such as paper currency or the like, are being fed successively past the reference point at a high speed comprising the steps of: (1) making a plurality of measurements of the opacity of a plurality of parts of each document as it is fed past said reference point, each of said opacity measurements including the steps of (a) controlling a light emitting diode to emit successive discrete brightness emissions of varying brightness, said brightness emissions being directed across the document feed path at said reference point, (b) sensing each of said brightness emissions and providing an electrical output whose voltage corresponds to the brightness sensed, (c) directing said voltage output to one input of a voltage comparator, (d) directing a constant voltage to a second input of the voltage comparator in opposition to said one input, said voltage comparator providing an output signal indicating whether or not said voltage supplied to said one input thereof is greater than said constant voltage applied to said second input thereof, and (e) determining which of said successive discrete brightness emissions of varying brightness produces a voltage output from the sensor to said one input of said voltage comparator that most closely approximates said constant opposing voltage input thereto to provide a measure of the opacity of that part of the document being fed past said reference point, (2) integrating said plurality of opacity measurements, and (3) comparing the integrated value to a threshold value to determine if there is a double document feed past the reference point.

Claim 2

A method of detecting if a double document feed occurs past a reference point as documetns, such as paper currency or the like, are being fed successively past the reference point at a high speed comprising the steps of: (1) making a plurality of measurements of the opacity of a plurality of parts of each document as it is fed past said reference point, each of said opacity measurements including the steps of (a) controlling a light emitting diode to emit successive discrete brightness emissions of varying brightness, said brightness emissions being directed across the document feed path at said reference point, (b) sensing each of said brightness emissions and providing an electrical output whose voltage corresponds to the brightness sensed, (c) directing said voltage output to one input of a voltage comparator, (d) directing a constant voltage to a second input of the voltage comparator in opposition to said one input, said voltage comparator providing an output signal indicating whether or not said voltage supplied to said one input thereof is greater than said constant voltage applied to said second input thereof, and (e) determining which of said successive discrete brightness emissions of varying brightness produces a voltage output from the sensor to said one input of said voltage comparator that most closely approximates said constant opposing voltage input thereto to provide a measure of the opacity of that part of the document being fed past said reference point, (2) integrating said plurality of opacity measurements, and (3) comparing the integrated value to a threshold value to determine if there is a double document feed past the reference point.