Discriminating paper sensor
AssigneeXerox Corporation
InventorsAlan Walters, Simon M. Derricutt
Life of this patent
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Abstract
A paper sensor uses two sample and hold circuits which are fired by the phase and antiphase of an oscillator that also drives an infrared light emitting diode (LED). These circuits sample the output from a phototransistor. If the outputs from the phototransistor are different when the LED is lit and unlit, then a comparator will give an output, thus synchronously filtering out unwanted infrared light that may cause a false paper reading.
Claims13
A system for sensing the presence or absence of an object at a sensing station, comprising:
- an infrared light emitting diode positioned at said sensing station and adapted to project an infrared beam onto an object positioned at said sensing station;
- a phototransistor adapted to receive light from said light emitting diode and transmit a signal;
- an oscillator, said oscillator being adapted to activate said light emitting diode;
- first and second sample and hold circuits adapted to be driven by phase and antiphase from said oscillator to sample said signal from said phototransistor and wherein said oscillator is adapted to provide an input current to each of said first and second sample and hold circuits;
- and
- a comparator for comparing outputs from said first and second sample and hold circuits, and wherein if said sampling frequencies coincide with said oscillator frequency said comparator gives off an output indicating the presence of an object at the sensing station.
A sensor device for sensing the presence of an object at a sensing station, comprising:
- an infrared light emitting diode positioned at said sensing station and adapted to project an infrared beam onto an object positioned at said sensing station;
- a phototransistor adapted to receive light from said light emitting diode and transmit a signal;
- an oscillator;
- first and second sample and hold circuits adapted to be driven by phase and antiphase from said oscillator to sample said signal from said phototransistor and;
- a comparator for comparing outputs from said first and second sample and hold circuits to thereby indicate the presence of an object at the sensing station.
A discriminating substrate sensor, comprising:
- an opto-emitter adapted to transmit infrared light toward a substrate;
- an opto-detector adapted to receive light from said opto-emitter and transmit an output;
- an oscillator;
- a pair of sample and hold circuits, said sample and hold circuits being fired by the phase and antiphase of said oscillator to sample said output from said opto-detector;
- and
- a comparator, and wherein if outputs from said opto-detector are different when said opto-emitter is lit and unlit, then said comparator will give an output, thus indicating the presence of a substrate while simultaneously synchronously filtering out unwanted infrared light that may cause a false substrate reading.
Dependencies are inferred from the claim text.