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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a magnetic character recognition system and, more
particularly, to a document reader system in which a single gap magnetic
read head is used for reading magnetized characters embodied in the form
of E-13B character font printed on a document.
In single-gap magnetic character reading systems, a single analog input
waveform is obtained by passing the characters to be sensed, normally
printed on a document, beneath a magnetic read head at least as wide as
the height of the characters and having a single flux gap. The signal
generated by the read head is a derivative waveform representing the rate
of change of magnetic flux traversing the head as the characters are
scanned. Since the distribution of ink, and thus flux, associated with
each different character is unique, the waveform derived for each
different character uniquely identifies that character.
To simplify the timing of the waveform analysis process, the characters are
provided with stylized geometric features which impart anticipatable
timing characteristics to the derived waveforms. Thus, in accordance with
this scheme for reader identification, each character of the E-13B font is
divided into a predetermined number of vertical segments corresponding to
the location of bar portions of the character. The characters are designed
such that the distribution of ink undergoes significant change only at the
boundaries between each segment. Hence, peak fluctuations in the derived
waveform caused by these variations in ink distribution can occur at only
predetermined times during the character scan.
Prior character recognition systems have utilized the amplitudes of each of
the peaks of the generated waveform for correlating with known peak
amplitude characteristics of each of the E-13B characters to identify the
character read. An example of this type of recognition system may be found
in U.S. Pat. No. 3,851,309. Critical to this type of recognition system is
the timing of the sampling of the waveform for detecting the occurrence of
each of the peaks in the waveform. It is well known that in the actual
printing of the magnetic character on the document, variations in width of
the bar portion of the characters are obtained which affect the peak
amplitude of the waveform. Other errors found in the reading of the
magnetic characters can be traced to variations in the speed of the
document past the read head thereby displacing the peak position of the
waveform with respect to the vertical segment in which the peak amplitudes
of the reference characters are measured and used in recognizing the
unknown character. Prior art recognition systems have been eveloped to
compensate for these variations. In U.S. Pat. No. 3,528,058, issued to
Bond, each peak in the waveform of the unknown character is sensed for
controlling the generation of the next window during which time the next
peak of the waveform is to be sensed. In U.S. Pat. No. 3,629,829, issued
to Ordower, each peak in the unknown character is integrated over a
predetermined time span for generating a value which is used in
recognizing the unknown character, which value is not affected by
registration or gross distortion of the input waveform. Difficulties arise
using these systems in those cases where the peak curve in the waveform of
the unknown character are skewed or unsymmetrical. Using the prior art
peak detection systems, the timing of windows generated in response to the
sensing of the prior peak amplitude fail to completely cover the peak
curve resulting in the generation of a value not representing the total
area of the peak. In those cases where the distortion of the waveform
results in a multi-peak waveform, complex timing circuits are required to
select which peak is the required peak for use by the system in generating
a peak amplitude value.
It is therefore an object of this invention to provide a character
recognition system which generates a high degree of successful recognition
operations under present-day operating conditions. It is a further object
of this invention to provide a character recognition system which
functions independently of the speed of the characters past the read head.
It is another object of this invention to provide a character recognition
system which minimizes the effects of variation in ink intensity found in
the characters that are to be read. It is a still further object of this
invention to provide a character recognition system which consists of a
smplified system and circuitry which can be installed at a relatively low
cost.
SUMMARY OF THE INVENTION
These and other objects are fulfilled by providing a magnetic character
reader system in which the ink intensity of the printed magnetic character
is normalized by rectifying and integrating the analog waveform generated
by the magnetic head passing over a printed magnetic character to produce
a value which is used as the gain of a programmable analog amplifier to
output a normalized waveform. To compensate for variation in the speed of
the transport, the center of gravity of the area of each peak is generated
for use in controlling the start of a plurality of windows for orientating
each peak of the waveform within its required window. The area under each
peak in the waveform is then digitized and compared with corresponding
values of a plurality of reference characters for generating a value
representing the difference between the values. The character represented
by the minimum value of the differences is selected as that character read
by the read head.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and various other objects, advantages, and meritorious
features of the present invention will be apparent from the following
detailed description and appended claims when read in conjunction with the
drawing, wherein like numerals identified corresponding elements.
FIGS. 1A and 1B taken together disclose a block diagram of the character
recognition system in accordance with the present invention.
FIG. 2 is a schematic representation of an idealized analog waveform
generated by a magnetic read head;
FIG. 2A is a schematic representation of the idealized windows which are
used by the system for sensing the peaks in the waveform showing the
location of the windows with respect to analog waveforms of FIG. 2.
FIG. 3 is a schematic representation of the analog waveform of FIG. 2 which
has been distorted due to variation in speed of the document past the
magnetic read head;
FIG. 3A is a schematic representation of the windows generated in
accordance with the present invention showing the location of the windows
with respect to the analog waveform of FIG. 3.
FIG. 4 is a diagram illustrating the actual analog waveform of a character
read by the read head together with the various waveforms generated during
the operation of the reader system.
FIG. 4A is a diagram of the various pulses generated during the operation
of the reader system.
FIG. 5 is a logic diagram of the Analog Divider network of FIG. 1A.
FIG. 6 is a logic diagram of the Priority Timing network of FIG. 1B.
FIG. 7 is a logic diagram of the Subtractor network of FIG. 1B.
FIG. 8 is a logic diagram of the Accumulator network of FIG. 1B.
FIG. 9 is a logic diagram of the Minimum Selection network of FIG. 1B.
FIG. 10 is a table showing an example of the absolute values of the unknown
normalized character read by the magnetic read head.
FIG. 11 is a table showing an example of the absolute values of the
normalized reference characters stored in the ROM unit and which are
subtracted from the absolute values of the unknown normalized character
for use by the minimum selection network of FIG. 9 to select the character
corresponding to the unknown character.
FIG. 12 is a logic diagram of the Window Timing Generator of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIGS. 1A and 1B, there is shown a block diagram of the
character recognition system embodying the present invention. The system
is divided into four sections, the section designated by the numeral 20
containing that portion of the system which generates and amplifies the
analog waveform representing the unknown character, section 22 which
modifies the analog waveform to compensate for variations in the ink
intensity of the unknown character by rectifying and integrating the
amplitude of the analog waveform and normalizing the waveform in
accordance with the integrated value, section 24 which controls the
generation of the windows so as to compensate for variation in speed of
the character past the read head, and section 26 which is directed to the
recognition of the unknown character by correlating values representing
the unknown character with known values of a plurality of reference
characters.
The present system includes a single gap magnetic read head 28 (FIG. 1A) of
well-known construction, which is positioned adjacent the path of movement
of a document having characters such as the character 30 printed thereon
in magnetic ink. While the characters 30 are printed in the form of the
E-13B character font which has been adopted by the American Bankers
Association for use in banking checks in this country, it is obvious that
the recognition system of the present invention can be used with any
character font which results in a unique analog waveform when scanned by
the magnetic read head 28. Movement of the character 30 past the magnetic
read head 28 results in the generation of an analog electrical signal
corresponding to the time derivative of the change in flux of the
magnetized ink, such signal being represented by the analog waveform 32 in
FIG. 4. The analog waveform 32 is transmitted from the read head 28 to a
pre-amplifier 34 for transmission to a plurality of logic modules which
includes a Delay module 36, a Character Start module 38, a Peak Detector
module 40 and a Rectifier module 42.
The Delay module 36 (FIG. 1A) is of well-known construction and stores the
analog waveform 32 (FIG. 4) for one character time T. The Character Start
module 38 detects the positive going edge of the analog waveform 32 after
applying a threshold value to the waveform 32 (FIG. 4). An example of a
circuit which may be utilized in the present embodiment is disclosed in
the co-pending application of Robert Nally, entitled "Character
Recognition Apparatus", Ser. No. 846,877 filed on the same day as this
application and assigned to the present assignee. If the voltage level of
the waveform is greater than the threshold level applied by the Character
Start module 38, a digital pulse 44 (FIG. 4) will be outputted to an AND
logic gate 46 whose other input is connected to the output of the Peak
Detector module 40. The Peak Detector module 40 is of well-known
construction and functions to detect the time of occurrence of each peak
in the waveform 32 (FIG. 4). Upon detecting the first peak in the waveform
32, the Peak Detector module 40 will output a pulse 48 (FIG. 4) to the AND
logic gate 46 enabling the gate to output a pulse to a Character Window
Generator module 50 which opens a window 52 shown in FIG. 4 extending over
the length of time T the character waveform 32 is generated by the read
head 28. An example of a Character Window Generator module that may be
used can be found in FIG. 3 of the previously-cited Nally co-pending
application.
The output of the Character Window Generator module 50 is connected to an
Integrator module 54 which integrates the rectified waveform 56 (FIG. 4)
outputted by the Rectifier module 42. The Rectifier module 42 rectifies
the analog waveform 32 received from the pre-amplifier 34 to produce a
plurality of positive amplitude portions 56 (FIG. 4), which amplitude
portions are integrated by the Integrator module 54 for the time period T
of the character window 52 (FIG. 4) generated by the Character Window
Generator module 50. The Integrator module 54 outputs a voltage signal
which is transmitted to a Programmable Gain Analog Amplifier module 58.
The Amplifier module 58 is programmed to reduce the amplitude of the
analog waveform 32 (FIG. 4) received from the Delay module 36 if the
voltage signal received from the Integrator module 54 is high, and to
increase the voltage amplitude of the analog waveform 32 if the voltage
signal from the Integrator module is low. Thus, the function of the
Amplifier module 58 is similar to an analog divider wherein the voltage of
the waveform is divided by the voltage gain from the Integrator module 54.
The resulting analog waveform 60 (FIG. 4) outputted from the Amplifier 58
represents the analog waveform of a character having an ink intensity
level of 100% for every character 30 (FIG. 1A) that is read by the read
head 28. Thus, section 22 of the present character recognition embodiment
will equalize the voltage of the waveform with respect to the ink
intensity of the character read such that if the ink intensity is low due
to printing conditions, the output of the Amplifier module 58 will be the
same as in the case where the ink intensity is high due to a very heavy
printing condition. An example of a commercially-available Programmable
Gain Analog Amplifier module that may be used in this embodiment is the
Burr-Brown Amplifier module 3602 while Evans Associates Company Integrator
module 4130 is an example of an integrator module that may be used for the
Integrator module 54.
The analog waveform 60 (FIG. 4) outputted from the Programmable Gain Analog
Amplifier module 58 (FIG. 1A) is transmitted over conductor 62 to an
Integrator module 64 (FIG. 1A) which includes an integrating capacitor 65
and to an Analog Multiplier module 66 for controlling the timing of the
start of the windows which are used by the system for detecting
characteristics of the peaks in the waveform 32 (FIG. 4) in order to carry
out the character recognition operation.
As shown in FIG. 2, an ideal analog waveform 68 representing each character
of the E-13B font will have a plurality of clearly defined peak portions
70. Each E-13B character is designed to provide up to eight peaks in the
waveform, wherein peak occurs at a discreet time with respect to the start
of the generation of the waveform. Each discreet time is represented in a
manner well-known in the art by a window 72 (FIG. 2A) within which each
peak is centrally located. As shown in FIG. 2A, each of the windows 72 is
generated to include the start of each of the peak curves where the
voltage is at 0 volts, with the identifying characteristics of the E-13B
reference characters being based on such occurrence. The numerical values
disclosed hereafter utilized in identifying each of the reference
characters represent the area under each peak in the analog waveform
located within a specified window. Since these values are determined based
on the peak being centrally located within its associated window, any
deviation in the location of the peak within the window will reduce the
area of the peak sensed and therefore reduce the accuracy of the
correlation. FIG. 3 shows the same analog waveform 68 distorted with
respect to the window 72 due to a decrease in speed of the printed
magnetic character 30 past the magnetic read head 28 (FIGS. 1A). If the
system utilized the windows 72 (FIG. 2A) to sense the peak 74 of the
waveform 75 shown in FIG. 3, it is obvious that the start of each of the
windows 72 would not coincide with the start of each peak 74 with the
result that the correlation between the unknown character using data based
on that portion of the peak 74 within the window 72 and the reference
characters would not produce the accuracy of recognition that is desired.
In order to overcome this problem, the present invention contemplates
generating the windows 76 (FIG. 3A) associated with each peak 74 in the
waveform 75 of FIG. 3 based on the location of the center of gravity CG
(FIG. 3) of the area of the previous peak in order to vary the timing
width of the windows to include the total peak curve of the waveform. The
location of the center of gravity CG of each peak 74 (FIG. 3) can be
determined in accordance with the following general equation;
##EQU1##
Referring to FIG. 2A, it will be seen that the center of gravity CG of each
idealized peak 70 (FIG. 2) is located at a point equal to 1/2T where T is
the time zone of the window 72. To allow for the start of the next window
72, a reset portion R of the window 72 is provided, R being equal to the
term (1-K)T where K is an arbitrary portion of T. In the present
embodiment, K is selected to be equal to 7/8T. As further shown in FIG.
3A, to compensate for the distortion of the waveform 68 of FIG. 2 due to
variation in speed of the transport, the start of the generation of each
window 76 is based on the determination of an incremental center of
gravity CG represented by T.sub.1 in FIG. 3A which is equal to the
difference between the location of the center of gravity CG.sub.1 of the
distorted peak 74 of FIG. 3 to the location of the center of gravity CG of
the normal peak 70 of FIG. 2. Using the value of T and CG.sub.1, the time
T.sub.1 (FIG. 3A) which starts the generation of the next window 76 is
found in accordance with the following equations:
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(2) T.sub.1 = KT + R.sub.1
where K = 7/8
(3) R.sub.1 = (1-K) T + .DELTA. T.sub.1
= 1/8 T + .DELTA. T.sub.1
If .DELTA. T.sub.1 = CG.sub.1 -1/2 T, then equation (3) becomes
R.sub.1 = 1/8 T + CG.sub.1 -1/2 T
(4) = CG.sub.1 -3/8 T, then equation (2) becomes
(5) T.sub.1 = 7/8 T + CG.sub.1 -3/8 T or
(6) T.sub.1 = 1/2 T + CG.sub.1
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Thus, the start of the next window is a function of the center of gravity
CG.sub.1 of the area under the previous peak curve. The present embodiment
discloses circuitry for generating the value of T.sub.1 in accordance with
equation (5).
As described previously with respect to FIG. 1A, the analog waveform output
60 (FIG. 4) of the Analog Amplifier 58 representing the unknown character
30 is transmitted to the integrator module 64 and the Analog Multiplier
66. The integrator module 64 comprises timing control circuits for
controlling the operation of the integrating capacitor 65 for integrating
the waveform 75 (FIG. 3) for the time of K which in the present embodiment
is equal to 7/8 T. The output of the Integrator module 64 will represent
the term (B) of Equation 1 while the output of the Analog Multiplier
module 66 over conductor 67 will represent the product of the analog
values of the input waveform 60 and the time T of the latch windows 72
(FIG. 2) which in the present embodiment is 125 micro-seconds representing
a speed of 104 in/sec.. The value of time T is generated in a Ramp
Generator module 80. The output of the Analog Multiplier module 66 is
transmitted over conductor 67 to an Integrator module 82 (FIG. 1B) which
includes an integrating capacitor 83 whose output over conductor 90 will
represent the term (A) of Equation 1. The outputs of Integrator module 82
and Integrator module 64 are transmitted to an Analog Divider network 84
(FIG. 1B) which will produce an output representing the center of gravity
CG.sub.1 (FIG. 3A) of the areas under each of the peaks 74 (FIG. 3A) of
the analog waveform 75 as defined by equation (1).
A circuit for the Analog Divider module 84 which may be utilized in the
present embodiment is shown in FIG. 5 and includes an Analog Multiplier 86
for receiving over the conductor 88 the output of the Integrator module 64
representing the term (B) of equation (1) and the output of an Operational
Amplifier 92 over conductor 94. The output of the Multiplier 86
transmitted over conductor 96 is subtracted from the output of the
Integrator network 82 representing the term (A) of equation (1) and
received over conductor 90, which difference is inputted into the
Operational Amplifier 92 whose output over conductor 100 is the center of
gravity CG.sub.1 of the areas of the peak 74 in the waveform. An example
of a commercially-available Analog Multiplier that may be used includes a
Motorola multiplier MC1594L, while the Operational Amplifier 92 may be a
Motorola amplifier MC1741G. The circuit shown in FIG. 5 is more fully
disclosed on page 9-37 of the Integrated Circuit Data Book, Supp. 2,
published April, 1969 by Motorola Semiconductor Products Inc.
The output of the Divider network 84 representing the center of gravity
CG.sub.1 (FIG. 3A) of the peak 74 (FIG. 2) is transmitted over conductor
100 to a Priority Timing module 102 (FIG. 1B). The function of the
Priority Timing module 102 is to generate a series of timing signals
T.sub.1 (FIG. 3A) for transmission to the latch 78 (FIG. 1A) over
conductor 103 for controlling the start of each of the windows 76 (FIG.
3A) in accordance with equation (5) utilizing the center of gravity of the
previous peak 74 in the waveform 75 (FIG. 3). The Priority Timing module
102 is shown in FIG. 6 and includes an Analog/Digital Converter Module 104
which receives over the conductor 100 from the Divider module 84 (FIG. 1A)
the analog value representing the center of gravity CG.sub.1 of the peak
76 (FIG. 3A) and a Subtractor module 106 which subtracts a digital value
representing three-eighths (3/8) of the time T from a digital value
representing the center of gravity to produce the term R.sub.1 in
accordance with equation (4). The output of the Subtractor 106
representing the term R.sub.1 (FIG. 3A) is then transmitted over conductor
113 to a Window Generator module 116 which adds to the output of the
Subtractor 106 the value seven-eighths (7/8) of the time T representing
the term K (FIG. 3A) in accordance with equation (5) to produce the timing
signal T.sub.1 (FIG. 3A), which signal sets the latch 78 for sampling the
next peak portion 74 of the waveform 75. The clock pulses used in
generating 7/8 T are transmitted from a timing network which includes a 1
Mhz Oscillator 108 (FIG. 1A) outputting clock pulses 109 (FIG. 4A) and a
Signal Converter module 110 (FIG. 1A) for outputting a plurality of timing
signals over conductor 112 to the Priority Timing module 102 and to an
Addressing and Timing module 114 which outputs timing signals over
conductors 161 for controlling the operation of the modules in the
character recognition system in a manner well-known in the art. The
digital value equal to 3/8 T may be transmitted over conductor 105 from a
ROM storage unit 122 (FIG. 1B) or from ground and the power supply (not
shown) to the Subtractor 106 (FIG. 6) while the clock pulses 109 (FIG. 4A)
are transmitted over conductor 112 to the Window Generator module 116.
Referring now to FIG. 12 there is shown a logic diagram of the Window
Generator module 116 which includes a 4 bit 74193 Binary Up/Down Counter
119, and two 4 bit 7493 Binary Counters 121, 123. The clock pulses 109
(FIG. 4A) received over conductor 112 from the Converter module 110 (FIG.
1A) are transmitted to AND gates 115 and 141. At time T.sub.0 (FIG. 4),
AND gate 115 is enabled to output clock pulses 107 (FIG. 4A) to the Binary
Counter 121 while AND gate 141 is disabled. Since the time zone T (FIG.
2A) of the window 72 has been selected at 125 us, seven-eighths (7/8) T
will be 108 us. The clock pulses 107 (FIG. 4A) will count counters 121 and
123 up producing the output pulses 111A-111F (FIG. 4A) which are
transmitted to AND gate 125 (FIG. 12) whose output is fed to an inverter
127 the output of which is the timing pulse 159 (FIG. 4A) transmitted over
conductor 103 to the latch 78 (FIG. 1B) which opens the window 76 (FIG.
3A). During the time the counters 121, 123 are counting up to 108 pulses,
the AND gate 125 will be disabled thereby resulting in the inverter 127
outputting the pulse 159 (FIG. 4A) which constitute the time K (FIG. 3A).
Upon outputting the 108th clock pulse, the output of the counters 121, 123
through the inverters 129, 131, will enable the AND gate 125 whose output
pulse 133 (FIG. 4A) will go high thereby turning off the pulse 159
resulting in the disabling of AND gate 115 and the enabling of AND gates
141, 137 over conductor 135 (FIG. 12).
The enabling of AND gate 137 will output a single pulse 145 (FIG. 4A) prior
to the disabling of AND gate 115 whose clock output is inputted to AND
gate 137 over conductor 147. The output pulse 145 is inverted when applied
to the Up/Down counter 119 thereby loading the 4-bit preset value of
R.sub.1 into the counter 119 over conductors 113 as received from the
Subtractor module 106 (FIG. 6). Enabling of AND gate 141 will output the
clock pulses 149 (FIG. 4A) which counts down the counter 119 for the time
of the preset value R.sub.1 after which a pulse 151 (FIG. 4A) is outputted
from the inverter 155 derived from a pulse received from the counter 119
over conductor 153. The pulse 151 is transmitted over conductor 157 for
resetting the counters 121, 123 wherein the output of AND gate 125 will be
low and the output of Inverter 127 goes high thereby enabling AND gate 115
to clock the counters 121 and 123 for the generation of the next window 76
(FIG. 3A). If equation (6) is utilized to generate the timing signals
T.sub.1, the digital value of 1/2 T will be added to the digital value of
CG.sub.1 to provide the timing signals T.sub.1 for the generation of the
next window 76.
The output of the Integrator module 64 (FIG. 1A) representing the area
under the peak 74 (FIG. 3) is transmitted over conductor 117 to an
Analog/Digital Converter module 118 which digitizes the integrated value
for transmission to the latch 78 which senses that portion of the digital
output representing the peak curve 74 in accordance with the timing
signals transmitted over conductor 103 from Timing module 102 (FIG. 1B).
The digital value stored in the latch 78 is outputted in the form of eight
bit parallel data to the eight bit Shift Register 119 (FIG. 1B) for
storage therein. The digital values stored in the Shift Register 119
represent the area under each of the peak curves 74 (FIG. 3) sensed during
the opening of its associated window 76. This data | | |
