Character recognition system employing extraneous and required peak detection with variable threshold controlled timing

• US 3,987,411 A
• Filed: 08/11/1975
• Issued: 10/19/1976
• Est. Priority Date: 08/11/1975
• Status: Expired due to Term

• Current Assignee: Unisys Corporation
• Original Assignee: Burroughs Incorporated (Terreno Realty Corp.)
• Inventors: Kruklitis, Karlis, Hickman, Steven C., Ratkowski, Christopher J.
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US05/603,592
• Time in Patent Office: 435 Days
• Field of Search: 340/146.3 C, 340/146.3 MA, 340/146.3 Z, 340/146.3 R, 340/146.3 Q, 340/146.3 AQ
• US Class Current: 382/208
• CPC Class Codes: G06V 10/10 Image acquisition document image scanning and transmission H04N1/00; control of digital cameras H04N23/60
• CPC Class Codes: G06V 30/144 using a slot moved over the image; using discrete sensing elements at predetermined points; using automatic curve following means
• CPC Class Codes: G06V 30/192 using simultaneous comparisons or correlations of the image signals with a plurality of references
• CPC Class Codes: G06V 30/2253 Recognition of characters printed with magnetic ink G06V30/2247 takes precedence

Abstract

A character recognition system utilizing precisely designed correlation network to match the voltage waveform of a character being read with the closest ideal waveform in a standard character font along with an extraneous peak detector that determines whether extraneous peaks are present in the voltage waveform and a required peak detector that determines whether a predetermined pattern of required peaks are missing from the voltage waveform for that voltage waveform to have been induced by the printed character with which it was preliminarily identified, under the control of a variable threshold controlled timing circuit for an extended dynamic range of voltage waveforms.

Claims

1. In a symbol recognition system having means for inducing an analog voltage waveform having spaced apart voltage peaks of varying amplitude corresponding to the configuration of a symbol being recognized, a correlation system including a plurality of outputs each uniquely corresponding to an ideal voltage waveform associated with a symbol in a standard symbol font, the correlation system responsive to the induced voltage peaks for providing a greater correlation output signal on one of said plurality of correlation system outputs relative the remaining correlation system outputs for preliminarily identifying the standard symbol most nearly correlated with the induced analog voltage waveform, and output means responsive to said correlation system plurality of outputs for providing a coded representation of the preliminarily identified standard symbol;

wherein the improvement comprises;

means responsive to said inducing means for detecting the absence of a predetermined required peak from said induced analog voltage waveform;

means for comparing said detected absence of a predetermined required peak with a required peak pattern uniquely associated with the ideal voltage waveform for the preliminarily identified standard symbol; and

means responsive to said comparing means for disabling said output means and for indicating a reject upon the detected absence of a required peak for the ideal standard voltage waveform associated with the symbol identified by the correlation system.

2. The improvement of claim 1 wherein said required peak absence detecting means comprises:

a dual polarity balanced delay line for receiving said induced analog voltage waveform, said delay line including a plurality of sample tap pairs spacially separated in accordance with the spacing of said spaced apart voltage peaks of said induced analog voltage waveform;

a plurality of absolute value peak detector means individually coupled to said sample tap pairs for providing an absolute value peak signal of said voltage peaks received at predetermined significant ones of said sample tap pairs;

threshold responsive comparator means individually coupled to associated ones of said plurality of absolute value peak detector means for providing a binary valued digital signal for each of said associated absolute value peak signals exceeding a predetermined first voltage threshold level;

required peak error detection logic means individually associated with predetermined ones of said ideal voltage waveforms and responsive to said binary valued digital signals from said comparator means for providing a binary valued peak error signal at a first logic state for each of said predetermined ones of said ideal waveforms upon the coincidence of at least one of said binary valued digital signals provided by said comparator means with its associated ideal waveform.

3. A character recognition system for preventing the misreading of a voltage waveform induced by a magnetically encoded character that may have a predetermined distortion causing the voltage waveform induced therefrom upon relative movement across an electromagnetic transducer reading head to be more nearly correlated with a voltage waveform associated with a standard character of a standard character font other than the voltage waveform associated with a corresponding but non-distorted character, comprising:

analog storage means having an input for receiving the induced voltage waveform from the electromagnetic transducer reading head and a plurality of sample tap outputs corresponding to spacially separated sample points along said induced voltage waveform;

correlation system means including a plurality of input means individually coupled to said plurality of sample taps for determining the closest correlation between the induced voltage waveform and an ideal voltage waveform of a standard font of ideal waveforms corresponding to said standard character font, the correlation system means including a plurality of correlation system output means, an individual correlation system output means associated with each waveform in said standard waveform font, the individual output associated with said closest correlated ideal voltage waveform providing a greater output signal than the other of said correlation system individual outputs;

amplifier means for degeneratively feeding back said greater output signal to said correlation system input means for maximizing said greater output signal relative said other correlative system outputs;

means responsive to said degenerative amplifier feedback means for dynamically establishing two different threshold voltage levels;

extraneous peak detection means responsive to the induced voltage signal at said plurality of sample taps for detecting the presence of an induced voltage signal peak at each of said sample taps exceeding one of said two dynamically established threshold voltage levels;

required peak detection means responsive to the induced voltage signal at said plurality of sample taps for detecting at predetermined ones of said sample taps the absence of an induced voltage signal peak exceeding the other of said two dynamically established threshold voltage levels;

peak error detection logic means responsive to both said extraneous peak detection means and said required peak detection means for providing a plurality of peak error signals individually associated with certain of said standard ideal waveforms having a predetermined statistically significant tendency to be misread, at least one of said plurality of peak error signals providing a possible peak error indication upon either the detection of the presence of an extraneous induced voltage peak by said extraneous peak detection means or the detection of the absence of a required voltage peak by said required peak detection means for said certain individually associated standard ideal waveforms;

pre-character recognition logic means responsive to said plurality of correlation system means outputs for providing a binary coded output identifying said induced voltage waveform preliminarily recognized as corresponding to a particular one ideal waveform of said standard waveform font;

peak error gating logic means for comparing said plurality of peak error signals with said binary coded pre-character recognition logic means output to determine the occurrence of a peak error signal for the particular ideal waveform preliminarily recognized; and

means responsive to said comparing means for providing an electrical signal representative of the occurrence of a misread upon the determined occurrence of a peak error signal for the particular ideal waveform preliminarily recognized.

4. The character recognition system of claim 3 wherein said correlation system means further includes a plurality of unique resistive adding network coupled between said correlation system input means and said correlation system output means, each of said plurality of unique resistive adding networks including a plurality of interconnected resistors, each of said resistors having an ohmic value selected in accordance with the actual voltage at predetermined significant ones of said plurality of sample tap outputs.

5. A system for identifying each of a plurality of different waveforms comprising:

analog storage means for serially receiving at least one of said plurality of different waveforms, said analog storage means including a plurality of spaced sample taps for providing a pattern of waveform peak signals as a leading portion of said serially received waveform travels toward a final one of said plurality of sample taps;

correlation means including a plurality of correlation inputs and outputs, said correlation means responsive to said pattern of waveform peak signals for generating a correlation output signal at a unique one of said plurality of correlation outputs for identifying said different waveforms;

feedback means responsive to said correlation outputs for providing a feedback signal to said correlation inputs for maximizing said correlation output signal at said unique one correlation output relative the remaining correlation outputs;

variable threshold responsive first comparator means for comparing said waveform leading portion at one of said sample taps preceding said final sample tap to a predetermined initial variable threshold level;

coarse timing means responsive to said first comparator means for providing a coarse timing signal upon said waveform leading edge at said one sample tap exceeding said predetermined initial threshold;

timing peak detector means responsive to said coarse timing signal for detecting a waveform peak at said one sample tap;

second comparator means for comparing said coarse timing signal with a portion of said waveform arriving at said final sample tap;

first logic means responsive to said first and second comparator means for producing a limited duration sample timing interval upon a detected waveform peak at said one sample tap in coincidence with said portion of said waveform at said final sample tap exceeding said coarse timing signal;

means for detecting a peak on said feedback signal;

means responsive to said detected feedback signal peak for outputting a fine timing pulse only during said limited duration sample timing interval; and

means responsive to both said plurality of correlation outputs and said fine timing pulse for providing an output code representative of the waveform identified by said correlation means.

6. The system of claim 5 further comprising:

means coupled to said feedback means for dividing said feedback signal into first and second variable threshold signals;

extraneous peak detection means responsive to the pattern of waveform peak signals at said plurality of spaced sample taps for detecting the presence of an extraneous peak signal at each of said sample taps exceeding said first variable threshold signal;

required peak detection means responsive to said pattern of waveform peak signals at predetermined significant ones of said plurality of sample taps for detecting the absence of a required peak exceeding said second variable threshold;

peak error logic means responsive to both said extraneous peak detection means and said required peak detection means for providing a peak error code representative of the existence of a peak error for various ones of said different waveforms;

preliminary waveform identifying logic means for assigning a preliminary identification code to said waveform identified by said correlation means; and

gating means responsive to both said peak error logic means and said preliminary waveform identifying logic means for comparing said peak error code with said preliminary identification code to determine the coincidence of a peak error for the waveform preliminarily identified.

7. The system of claim 6 wherein said first variable threshold signal is greater than said second variable threshold.

8. The system of claim 7 further comprising means responsive to said gating means for disabling said output code providing means upon coincidence of a peak error for the waveform preliminarily identified.

9. The system of claim 5 wherein said timing peak detector means comprises means responsive to said detected waveform peak at said one sample tap for thereafter disabling said first comparator means.