Threshold voltage determination system

Claim 2

In a multi-channel character recognition system, a threshold voltage determination system comprising: scanning means having a plurality of individually and parallelly arranged scanning members each member scanning a predetermined channel of a preselected portion of indicia on a document as said document moves relative to said scanning means, a plurality of transducing means operatively coupled respectively to each of said scanning members for generating an electrical signal in response to the predetermined channel of the portion of indicia scanned thereby, said electrical signal having a voltage range between a first voltage characterizing the document background and an extreme voltage characterizing the indicia, a plurality of diodes electrically connected at one end to each of said plurality of transducing means and collectively electrically connected together at the other end, the voltage at said collectively connected end being equal to the extreme voltage level generated by said plurality of transducing means for providing an extreme voltage level characterizing the indicia, voltage divider means electrically connected at one end to a reference voltage level characterizing a minimum threshold voltage level and at the other end to said collectively connected end of said diodes, said divider means providing a threshold voltage level intermediate the reference voltage level and the extreme voltage level as generated by said plurality of transducer means, and capacitive means electrically connected at one end to said collectively connected end of said diodes and at said other end to said reference voltage, said capacitive means being of a fast charge time constant to immediately charge to said threshold voltage level provided by said divider means in response to the extreme voltage level generated by said plurality of transducer means and being of a slow discharge time constant to maintain said threshold voltage level for a predetermined time in the absence of continuous indicia in said preselected portion of indicia.

Claim 3

In a multi-channel optical character recognition system, a threshold voltage determination system comprising: a document having a plurality of light absorptive characters printed thereof, said characters alignEd in a spaced apart pattern longitudinally positioned on said document, means for singly transporting said document along a predetermined path of travel, a source of radiant energy adjacent to the path of travel, radiant energy transmitting means positioned substantially orthogonal to said document and operable for transmitting the radiant energy from said source to the characters on said document, data scanning means for each channel responsive to the reflected radiant energy from said document and from the characters printed thereon, a transducer operatively coupled to each of said data scanning means for generating a first electrical signal in response to the radiant energy reflected from said document and for generating a second electrical signal in response to the radiant energy reflected from the characters on said document, a differential amplifier for each channel operatively coupled respectively to each of said transducers at one input thereof and each electrically connected at the other input thereof to a reference voltage signal representing the amount of reflected energy from a standard document background, said amplifiers responsive to said first and second electrical signal for generating a third electrical signal representing the voltage magnitude between either said first or second electrical signal applied to said one input and the reference voltage signal applied to said other input, a plurality of diodes electrically connected at one end to the output of each of said differential amplifiers respectively and electrically connected at the other end to a common terminal, said diodes forming a logical OR gate for coupling the magnitude of the largest third signal to said common terminal for maintaining the voltage at said common terminal substantially equal to said largest voltage magnitude, a voltage divider electrically connected between said common terminal and said reference voltage for generating at its output a threshold voltage signal proportional to the difference between said reference voltage and the largest third signal voltage magnitude, an R-C circuit electrically connected in parallel to said voltage divider and having a fast charge time constant to immediately charge to said threshold voltage signal and a slow discharge time constant to maintain said threshold voltage signal for a predetermined period of time during interruptions in the character printed in said spaced apart pattern on said document, and comparator means for each channel operatively connected respectively at one input thereof for receiving said third electrical signal from said differential amplifier and electrically and commonly connected at another input thereof to said output of said voltage divider for generating a binary one voltage signal when the magnitude of said third electrical signal is greater than the magnitude of said threshold voltage signal and for generating a binary zero signal when the magnitude of said third electrical signal is less than the magnitude of said threshold voltage signal.

Claim 4

In a multi-channel optical character recognition system, a threshold voltage determination system comprising: a document having a plurality of light absorptive characters printed thereof, said characters alignEd in a spaced apart pattern longitudinally positioned on said document, means for singly transporting said document along a predetermined path of travel, a source of radiant energy adjacent to the path of travel, radiant energy transmitting means positioned substantially orthogonal to said document and operable for transmitting the radiant energy from said source to the characters on said document, data scanning means for each channel responsive to the reflected radiant energy from said document and from the characters printed thereon, a transducer operatively coupled to each of said data scanning means for generating a first electrical signal in response to the radiant energy reflected from said document and for generating a second electrical signal in response to the radiant energy reflected from the characters on said document, a differential amplifier for each channel operatively coupled respectively to each of said transducers at one input thereof and each electrically connected at the other input thereof to a reference voltage signal representing the amount of reflected energy from a standard document background, said amplifiers responsive to said first and second electrical signal for generating a third electrical signal representing the voltage magnitude between either said first or second electrical signal applied to said one input and the reference voltage signal applied to said other input, a plurality of diodes electrically connected at one end to the output of each of said differential amplifiers respectively and electrically connected at the other end to a common terminal, said diodes forming a logical OR gate for coupling the magnitude of the largest third signal to said common terminal for maintaining the voltage at said common terminal substantially equal to said largest voltage magnitude, a voltage divider electrically connected between said common terminal and said reference voltage for generating at its output a threshold voltage signal proportional to the difference between said reference voltage and the largest third signal voltage magnitude, an R-C circuit electrically connected in parallel to said voltage divider and having a fast charge time constant to immediately charge to said threshold voltage signal and a slow discharge time constant to maintain said threshold voltage signal for a predetermined period of time during interruptions in the character printed in said spaced apart pattern on said document, and comparator means for each channel operatively connected respectively at one input thereof for receiving said third electrical signal from said differential amplifier and electrically and commonly connected at another input thereof to said output of said voltage divider for generating a binary one voltage signal when the magnitude of said third electrical signal is greater than the magnitude of said threshold voltage signal and for generating a binary zero signal when the magnitude of said third electrical signal is less than the magnitude of said threshold voltage signal.