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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates in general to control systems for activating
machines and in particular to a ticket acceptor and validation apparatus
for use with a card, tape or the like encoded with magnetic signals.
Most vending machines, laundry and dry cleaning machines and the like which
are provided for public use are coin-operated. Many of these machines are
made available 24 hours a day and consequently are unattended or are
supervised only at great cost. Because of the presence of coins in these
machines, the machines have been and are, with increasing frequency in
recent years, subject to a great deal of vandalism. The economic losses
which have resulted have not been limited to a loss of the coins, but have
included additional expenses necessitated by repairs to the damaged
control units and coin boxes and the losses associated with machines being
operable for long periods of time while the repairs are being made.
There is also associated with a great many coin-operated mechanisms the
problem of a lack of adjustability to accept coins of different
denominations. Typically, whenever a change is made in the number or type
of coins required to operate such mechanisms, the entire mechanism must be
replaced. There are mechanisms which accept various combinations of coins
and provide change; however, they are generally quite expensive and are
typically limited to accepting nickels, dimes and quarters.
In certain foreign countries, paper currency is widely used in
denominations corresponding closely to the cost of obtaining goods and
services from a machine. Like the more expensive coin-operated mechanisms,
a mechanism operable with paper currency is undesirably expensive.
Heretofore, a number of proposals have been made for using a ticket or a
card in lieu of coins for activating machines. In one such proposal, a
ticket of thermoplastic material is employed as a substrate. On the
substrate, there is provided a printed circuit. An apparatus detects the
presence of the printed circuit and, if the ticket is valid, activates a
machine and destroys the ticket. This is an excellent solution to the
problem of vandalism of machines and machine coin boxes, but,
unfortunately, each use requires a separate ticket and such tickets tend
to be easily duplicated.
Cards bearing magnetic signals, on the other hand, may be used repeatedly
for activating a machine by means of an apparatus which records on the
card appropriate signals each time the card is used and returning the card
to the user. The number of times the card may be used is readily
controllable.
Presently, such cards are used repeatedly in locking mechanisms for gaining
access to secured areas. Cards of this type are also used for gaining
access through turnstiles, as in a subway system. Typically, in the latter
case, computers are employed to read an amount encoded on the card. The
amount is reduced according to predetermined criteria and a lesser amount
recorded on the card in place of the previously encoded amount. While
appropriate for large installations, and providing relatively security
against fraudulent duplication of cards, the cost and complexity of such
computer-augmented control systems mitigate their use in apparatus for
controlling the activation of individual vending machines, laundry and dry
cleaning machines and the like. Consequently, it is desirable to not only
have a relatively inexpensive means for using magnetic cards for operating
machines but to have a means by which such cards can be used with a
reasonable degree of security against fraudulently produced cards.
SUMMARY OF THE INVENTION
In view of the foregoing, a principal object of the invention is a
relatively inexpensive but reliable and secure control apparatus for
activating a machine using a magnetic card, tape or the like bearing
magnetic signals.
Another object of the invention is an apparatus of the type described above
including means for modifying the signals on the card such that the same
card may be used repeatedly for activating a machine.
A further object of the invention is a control apparatus of the type
described above which uses a card bearing magnetic signals for activating
venting machines, laundry and dry cleaning machines and the like which is
relatively difficult to fraudulently duplicate.
A principal feature of the present invention is the use of a card bearing
pulse-width-modulated magnetic signals. The coded signal on the card
corresponds to the number of times the card is intended to be used for
activating a machine. Each time a machine is activated, the coded number
on the card is reduced by one. Along with the data or "credit" signals, as
these last described signals are conveniently called, there are provided
additional signals called identification signals. The identification
signals are employed to validate the card. Means are also provided to
visually display a number which shows the remaining number of times the
card may be used each time the card is inserted in the apparatus.
In addition to being pulse-width-modulated, the magnetic signals may also
be sawtooth-modulated. Sawtooth-modulated signals provide a degree of
security against fraudulent duplication in that they tend to be more
difficult to analyze and duplicate using known techniques.
DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present
invention will become apparent from the following detailed description in
which
FIG. 1 is a top plan view of a typical card used in accordance with the
present invention.
FIG. 2 is an exploded perspective view showing a portion of the reader used
to read the card.
FIG. 3 is a perspective view showing the reader assembled and a card about
to be inserted.
FIG. 4 is a vertical sectional view, somewhat schematic, through the reader
taken substantially along the line 4--4 of FIG. 3.
FIG. 5 is a horizontal sectional view taken substantially along the line
5--5 of FIG. 4.
FIG. 6 is a vertical sectional view taken substantially along the line 6--6
of FIG. 5.
FIGS. 7 and 8 are fragmentary sectional views taken substantially along the
lines 7--7 and 8--8 respectively of FIG. 5.
FIG. 9 is a perspective view of an encoder used in accordance with the
invention.
FIG. 10 is a horizontal sectional view taken substantially along the line
10--10 of FIG. 9.
FIG. 11 is a vertical sectional view taken substantially along the line
11--11 of FIG. 10.
FIG. 12 is a block diagram of the apparatus of FIG. 2.
FIGS. 13a-f are pulse diagrams representing the operation of the apparatus
of FIG. 2.
FIG. 14 is a schematic of a first embodiment of the apparatus of FIG. 2.
FIG. 15 is a partial schematic of a second embodiment of the apparatus of
FIG. 2.
FIG. 16 is a diagram representing pulses and signals in the apparatus of
FIG. 15.
FIG. 17 is an enlarged view of a portion of the diagram within the lines
17--17 of FIG. 16.
FIG. 18 is a schematic view of the apparatus of FIG. 14 as modified by the
apparatus of FIG. 15.
FIG. 19 is a diagram of skewed and non-skewed magnetic dipoles on a
magnetic recording medium.
FIG. 20 is a diagram of the output of a reproduction head versus an angle B
between the head and the axis of magnetic dipoles detected by the head.
FIG. 21 is a diagram of a skewed head and magnetic dipoles having an axis
describing an angle B relative to the head.
FIG. 22 is a diagram showing the relationship between a skewed head
according to the present invention and a fraudulently fabricated magnetic
card.
DETAILED DESCRIPTION
Referring to FIG. 2, the control system of the present invention is housed
typically in a coin box 21. Coin box or housing 21 is shown as a
rectangular box, which may be mounted on a vending machine, a laundry or
dry cleaning machine or the like in the same manner as the housings of
conventional coin mechanisms are presently mounted. Housing 21 shown in
FIGS. 2 and 3 is a rectangular metallic box of a type commonly used with
coin acceptors in automatic laundry equipment. A pair of vertically spaced
apart openings 22 is formed in the front panel 23 thereof. A feature of
the present invention is the fact that it is adapted to fit into such a
housing 21 without modification, it being understood that other boxes may
be substituted. Indeed, the apparatus of the present invention may be
placed in such conventional housings and thereby effect a substantial
savings in costs of manufacturing. Alternatively, the apparatus may be
mounted in the interior of a machine in any suitable manner so long as an
access thereto is provided for the insertion and removal of a card as
hereinafter described.
Considering the housing 21 of FIG. 2, there is provided in housing 21, a
front panel 27. In panel 27 there is provided a card-receiving slot 28.
Slot 28 is provided for receiving a card 31 on which is encoded a
plurality of magnetic signals 33 and, typically, a sufficient amount of
identifiable indicia for identifying the nature of the card and the manner
in which it is used as described more fully with respect to FIG. 1. In
applications other than those involving vending machines and the like, the
card 31 may take the form of a tape or other equivalent structure.
Referring to FIG. 1, there is provided on card 31 a strip 32. Strip 32
comprises any suitable material on which magnetic signals may be encoded.
As presently conceived for use in laundromats, the magnetic signals
encoded on strip 32 correspond to a first number, identified as a data or
credit number 16 and an identification number 17 preceded and followed by
a series of zero's 18 and 19. In addition to the strip 32, there is
provided on the face of card 31, a visual indicator 34, such as an arrow,
for showing the direction in which the card 31 is properly inserted in the
slot 28.
The numbers 16 and 17 encoded on strip 32 of card 31 serve to identify the
card as a valid and usable card. More specifically, the number 16
corresponds to the number of times the card 31 may be used to activate a
machine. The number 17 corresponds to a predetermined number which serves
to identify a valid card. For example, similar cards may be employed for
activating different types of machines having different operating prices.
In those cases, the number 16 will prevent inadvertent use of the wrong
card in a machine. The zero's 18 and 19 may be replaced by other signals
if, for example, an expansion of the fields for the numbers 16 and 17
becomes necessary.
Referring to FIG. 12, immediately interiorly of slot 28, there are provided
motor-driven rollers 54 and 72. There is also provided a magnetic head 69
for "reading" the magnetic signals on the card 31. The head 69 is also
used for recording signals. Positioned in a location to be contacted by
the card 31, there are provided a forward switch 61 and a limit or
reversing switch 66. Coupled to the head 69 and switches 61 and 66 there
is provided a control circuit 20, which will be described herein after in
more detail, for controlling a machine 24.
Fitting into the box 21 is a reader 26 having a front panel 27 compatible
with panel 23 and formed with a slot 28 for reception of a card 31. Also
formed in panel 27 is a display window 29 through which the patron may
observe the number of credits (i.e., the number of times which a washing
machine may be energized in accordance with the amount paid in the
purchase of the card) at the beginning and at the completion of each use
of the card.
Reader 26 comprises a top casing 36 horizontally disposed and having its
forward end attached to panel 27 and a bottom casing 37 there-below and
held parallel and spaced apart by one or more shims 38 so that a gap 39
exists between the casings 36 and 37 which is in registry with the slot 28
and is dimensioned to accommodate passage of a card 31. Screws 40 spaced
along the longitudinal edges of casings 36 and 37 pass through holes in
shims 38 and hold casings 36 and 37 assembled. The spacing between shims
38 is equal to the width of card 31. The forward edges of shims 38 curve
outwardly to facilitate insertion of cards into gap 39.
Top casing 36 has a base 41, upstanding sides 42 and is preferably closed
with a cover 43. Mounted extending transversely by means of a clamp 45
fastened to base 41 is a miniature motor and reduction gear combination 46
which is preferably D.C. operated and reversible. Pinion 47 is mounted on
the outer end of the final shaft of motor and reduction gear 46 and pinion
47 drives a train of gears 48 which are affixed to one of the sides 42 by
means of a series of pins 49. The final gear 51 of the train of gears is
rotatably mounted on the forward end of top casing 36 and fits through a
slot 52 in the base 41 to engage a similar gear 51 in bottom casing 37 as
hereinafter explained. Gear 51 also turns horizontal transverse shaft 53
on which is mounted a rubberized roller 54 which fits into gap 39 through
a slot 55 cut in base 41. Shaft 53 is flexibly mounted by means of two
mounting brackets 56 shown in detail in FIG. 7. Each bracket 56 has a
spring 57 held down by member 58 and formed with a reverse bend 59 into
which the shaft 53 fits. Screw 60 (FIG. 7) adjusts the roller spring to
set the pressure between the top and bottom rollers 54, 72. The mounting
56 permits the roller 54 to be moved slightly upward when a card 31 passes
through the gap 39. It exerts sufficient downward force on roller 54,
however, so that the card 31 is driven into the gap 39.
Also mounted in top casing 36 is a microswitch 61 having a switch arm 62
which extends down through a hole 63 in base 41 into the gap 39. When a
card 31 is inserted through the slot 39 and into the gap 39, it engages
arm 62 so that switch 61 starts motor 46 in forward direction. Spaced
rearwardly on base 41 is a second microswitch 66 having a switch arm 67
extending into gap 39 through hole 68. When the card 31 is driven
rearwardly through gap 39 until it contacts arms 67, switch 66 reverses
motor 46 and causes the roller 54 which still engages the card to reverse
the direction of movement thereof and discharge the card through slot 28.
Lower casing 37 has a base 71 in which is rotatably mounted bottom roller
72 which is similar to roller 54 and which projects through a slot 73
formed in base 71 and rotates on a shaft 74 which carries the gear 51
mating with the gear 51 of casing 36. Shaft 74 may be mounted by means of
mountings 76 which resemble the mountings 56 of casing 36.
Likewise mounted on panel 27 is a bracket 78 for a plurality of electronic
components 79 including the power supply and one or more printed circuit
boards (not shown) located in bracket 37.
Mounted on base 41 is transducer (head) 69 which is located over the path
of movement of strip 32. The electronic system used with the head 69 is
explained in detail hereinafter in this specification.
In operation, a card 31 is inserted through the slot 28 and contacts the
switch 61. The switch 61 generates a start signal on a line 176. The start
signal generates a motor control signal on line 177 causing the rollers 54
and 72 to be driven in a forward direction, transporting the card 31 past
the head 69 until the card 31 contacts the limit switch 66. When the card
31 contacts the limit switch 66, a reverse signal is generated on a line
178 generating a second signal on the line 177 causing the rollers 54 and
72 to be driven in a reverse direction expelling the card 31 from slot 28.
If the capacity of the card 31 to activate a machine has been exhausted,
the reverse signal, in that instance, could be used to cause the card to
be driven into a refuse container by any suitable means (not shown).
As the card is driven in the forward direction, the signals on the card 31
are "read" by the control circuit 20 on a line 179. If the card is valid
and usable in the specific machine in which it is inserted and its
capacity to activate the machine has not been exhausted, a start signal is
generated on a line 180 for activating the machine 24.
Referring to FIGS. 13a-f, the magnetic signals encoded on the strip 32 of
card 31 are pulse-width-modulated and are best illustrated by
representations of pulses of varying widths. As used herein, each magnetic
signal corresponds to a binary bit or number (e.g., a "one" or a "zero").
For simplicity, each bit is considered as occupying a bit cell or field of
predetermined length. A one is chosen to be represented by a pulse
occupying one-fourth or 25% of a cell and a zero is chosen to be
represented by a pulse occupying three-fourths or 75% of a cell, as shown
in FIG. 13a. Clock pulses, which are generated from the leading edge of
the one and zero pulses, as will be described in detail below, are chosen
to occupy one-half or 50% of a cell, as shown in FIG. 13e.
As one and zero magnetic signals are transported past head 69, positive and
negative pulses corresponding, respectively, to the leading and trailing
edges of the magnetic signals are generated on the line 179 as shown in
FIG. 13b. From the pulses of FIG. 13b there are generated by means
described below, corresponding positive and negative pulses, as shown in
FIGS. 13c and 13d. It will be noted that the negative pulses trail the
positive pulses with which they are associated to a greater or lesser
extent depending on whether the corresponding magnetic pulses are a one or
a zero. As will become apparent, the control circuit 20 distinguishes
between the one's and the zero's by the correspondence which exists or
fails to exist between the negative pulses of FIG. 13d and the clock
pulses of FIG. 13e, as shown in FIG. 13f.
Referring to FIG. 14, there is provided, coupled in parallel to head 69, a
pair of voltage comparators 130 and 131. Comparators 130 and 131 respond,
respectively, to the positive and negative pulses appearing on line 179.
Coupled in series to comparators 130 and 131 is a pair of one shots 132
and 133.
One shot 132 is provided to output a clock pulse, as shown in FIG. 13e, for
each of the positive pulses of FIG. 13b detected by comparator 130. One
shot 133 is provided to output a pulse, as shown in FIG. 13d,
corresponding to each of the negative pulses, as shown in FIG. 13b,
detected by comparator 131. The outputs of one shots 132 and 133 are
coupled to the inputs of a flip-flop 134. The output of one shot 132 is
also coupled to the clock or shift input of a serial-to-parallel shift
register 135. The data input of register 135 is coupled to the output of
the flip-flop 134.
Coupled in parallel to the register 135 is a subtractone circuit 136, and
an identification circuit 137. Circuit 136 is coupled to that portion of
the register 135 which contains the data or "credit" number 16 for
providing an output corresponding to that number reduced by a
predetermined amount, such as one. The circuit 137 is coupled to the
register 135 for both validating the number 17, which is located in an
adjacent portion of the register and to determine whether the number 16 in
the register is such as to allow an activation of the machine 24. If the
numbers 16 and 17 in register 135 are suitable, an enable signal is
generated on a line 138 on the output of circuit 137. In a typical
application, the enable signal thus generated is applied to a start
flip-flop or a corresponding start circuit 139 to activate a machine.
In some applications, it is desirable to visually display the initial and
remaining number of times a machine can be activated with the same card.
Accordingly, there is provided a gate 180 having one input coupled to the
register 135 and a second input coupled to the output of circuit 136, a
display driver 140 and a visual display device 141, such as a conventional
seven-segment display. The display is provided for selectively displaying
the number 6 in the register 135 or the output of the circuit 136 under
the control of a gate enable signal on a line 181 generated from a card
reverse signal. While the display device 141 may be positioned in any
suitable location, it is preferably located for viewing through a window
29 in the front panel 27 of reader 26 as seen in FIG. 2.
Thus, in operation, the initial number 16 is displayed and thereafter when
the reverse signal is generated, the initial number less one is displayed
under the control of the gate 180.
In order that the card 31 may be used repeatedly, the magnetic signals on
the card corresponding to the number 16 are changed (i.e., reduced) each
time the card is used.
To change the number 16 on the card 31, there is provided a
parallel-to-serial shift register 150. The input to register 150 is
provided via two sets of parallel lines 151 and 152 coupled, respectively,
to the output of that portion of register 135 containing the
identification number 17 and the output of the subtract-one circuit 136.
To shift the data in register 150 for modification of the number 16 on the
card 31 after each use, there is provided an input circuit 161 for
receiving a "card-reverse" signal from the card reverse switch 66. Circuit
161 is provided to output a signal for starting an internal clock 162 and
enabling a gate 163 and a head driver 164. This signal, as previously
described also switches the gate 180 for changing the number displayed in
the device 141 from the initial number 16 to the number at the output of
the subtract-one circuit. The output of clock 162 is coupled to a
pulse-width modulator 165 and also to the gate 163 via a divide-by-four
circuit 166 for shifting the data in register 150 serially through the
modulator 165. The output of modulator 165 is coupled to the head driver
164 either directly or through a sawtooth modulator 167 as shown. If
included, the sawtooth modulation of the output of modulator 165 will
shape the pulse width modulated magnetic signals recorded on the card 31
in a manner which, it is believed, will tend to make much more difficult
the analysis of the signals on the card using conventional magnetic
transducers and, consequently, will provide a greater degree of security
against the fraudulent duplication of the cards 31 by known forgery
techniques.
Referring to FIG. 15, there is provided for use in place of the one shots
132, 133 and 134 of the circuit of FIG. 14 an alternative decoding circuit
170. In circuit 170 there is provided a flip-flop 171 having a set input S
for coupling to the output of voltage comparator 130 and a reset input R
for coupling to the output of voltage comparator 131. To the output of
flip-flop 171, there is coupled in series to ground a resistor R.sub.1 and
a capacitor C. Coupled in parallel with capacitor C is a grounded emitter
transistor Q having a base resistor R.sub.2 and an operational amplifier
172. Coupled to the base of transistor Q is the output of a one short 173.
The input to one shot 173 is coupled to the output of voltage comparator
130 via a line 174. The output of voltage comparator 130 is also coupled
via the line 174 to the clock/shift input of the register 135. The data
input of register 135 is coupled to the output of amplifier 172.
In operation, the output of amplifier 172 and, hence, the data input to
register 135 is a function of the potential on capacitor C at the time of
occurrence of each clock pulse.
Referring to FIGS. 16 and 17, there is provided a representation of an
output from head 69 wherein the positive-going pulses are equidistantly
spaced and the negative-going pulses are displaced from their associated
leading positive-going pulse by an amount corresponding to the binary
number 101 as described above with respect to FIG. 13.
Referring to the wave form of FIG. 16, upon the occurrence of each
positive-going pulse, flip-flop 171 is set and capacitor C begins charging
positively as shown by the positive-going portions, A, B, and C of the
wave form. Upon the occurrence of each negative-going pulse, flip-flop 171
is reset and capacitor C begins charging with an opposite polarity, as
shown by the negative-going portions, D, E and F of the wave form.
Capacitor C continues to charge negatively until the occurrence of the
next succeeding clock pulse at which time capacitor C is discharged
through transistor Q and is returned to a reference potential, such as
ground, as represented by the vertical lines G and H and the horizontal
line of the wave form.
The amount that capacitor C charges positively and negatively depends on
the relative locations of the positive and negative-going pulses shown in
FIG. 16. When a pulse represents a one the period of positive-going
potential on capacitor C is considerably less than the same period when
the pulse represents a zero. Conversely, the periods of negative-going
potential under the same conditions are reversed. Consequently, it will be
noted that the charge on capacitor C becomes negative (ie.e, below a
reference potential, such as ground) as shown by the horizontal line, when
the magnetic signal corresponds to a one, but remains poistive (i.e.,
above the reference potential) when the magnetic signal corresponds to a
zero.
The output of amplifier 172,, which tracks the change in potential on
capacitor C, provides, as previously described, the data input to register
135 under the control of the clock pulses. The clock pulses also "reset"
the capacitor C (that is, discharge it to a reference potential). The
discharging of capacitor C is, however, not instantaneous. As shown in
FIG. 17, there is actually a brief period t during which the output of
amplifier 172 does not change significantly with the occurrence of a clock
pulse and, accordingly, the values of resistors R.sub.1 and R.sub.2,
capacitor C and the characteristics of transistor Q and amplifier 172 are
chosen to insure sufficient time to clock the data into register 135.
Referring to FIG. 18, there is provided a schematic of the circuit of FIG.
14 as modified by the circuit of FIG. 15. In FIG. 18, the principal
circuit components shown in block form comprise conventional integrated
circuit components which are commercially available under the device type
designation provided from a number of sources as follows:
______________________________________
Device Type Source
______________________________________
3302 Fairchild
9002 "
74164 "
T1-T6 211 3904 "
9374 "
T7-T10 2N3906 "
9302 "
96L02 "
741 "
9301 "
9322
2240 EXAR
7403 Fairchild
9312 "
9004 "
9004 "
555 Signetics
FND 507 Fairchild
FCD 810 "
______________________________________
While each of the principal features of the circuits of FIGS. 14 and 15 are
identified in FIG. 18 for convenience by corresponding numerical
designators, it will be helpful to note that the functions of the clock
162, divider 166, pulse width modulator 165, gate 163 and register 150 of
FIG. 14 are incorporated in and performed by the integrated circuits and
associated circuitry designated 162, 163 and 150 in FIG. 18. The
consolidation of their functions as described is a result of the use of
integrated circuits. It is, of course, understood that other circuit
arrangements may be employed to perform the same function.
Encoder 86 (FIGS. 9-11) is used to encode cards 31. Such encoder is located
at a central point where suitable security exists. Top casing 87 is closed
with a top cover 88 and mounted above bottom casing 89 with a gap 91
dimensioned for card 31. Bottom casing 89 has a front panel 92 formed with
an indicator window 93 surrounded by a bezel and also having extending
therethrough the perimeter of a wheel 94 which may be manually adjusted
for a given number of credits to be encoded onto the card 31. Within
casing 89 is a motor 96 having a shaft 97 here shown as projecting out one
side of casing 86 and carrying a drive pulley 98 which, through belt 99,
drives a plurality of speed reduction idler pulleys 101 mounted on the
outside of casing 86 through belts 102. The final shaft 103 extends into
the casing 89 and carries on its inner end a gear 106 which mates with a
gear 118 on front bottom transverse horizontal shaft 118 on which is
mounted bottom roller 119. Shaft 118 carries a gear (not shown) which
meshes with gear 107 on top front transverse horizontal shaft 108,
appropriate holes being formed in the casing so that the gears can mesh.
Front top roller 109 is fixed to shaft 108. Shaft 108 also carries one of
a pair of pulleys 111 which are connected together by belt 112, the
rearward pulley 111 being fixed on rear top shaft 113 which also carries a
rear top roller 114. Rollers 109 and 114 extend down through slots in the
bottom of casing 87 into the gap 91 through which card 31 passes. Top
shafts 108 and 113 are mounted on casing 87 by means of supports 116 which
resemble the support 56 shown in FIG. 7. In bottom casing 89 are similar
supports 117 for bottom front shaft 118 which carries bottom front roller
119 which mates with roller 109. Bottom rear shaft 122 is driven from
shaft 108. Shaft 122 carries a roller 123 which mates with roller 114.
Mounted in casing 87 is a magnetic record head (transducer) 126 which is
positioned to magnetically act upon the strip 32 of card 31. A photocell
127 and exciter lamp mounted in casings 87 and 89 has an upper element
which views through a hole 128 in casing 87. Motor 96 drives rollers 109,
114, 119, 123 continuously while the encoder is operating. The photocell
and lamp 127 operating together indicate when card 31 is in proper
position with respect to head 126 gap and at such time the electrical
components hereinafter described generate the appropriate binary number
(determined by the manual setting of selector switch 94) to be recorded on
card 31.
When the recording machine is turned on, the rollers 109, 119, 114, 123,
which draw card 31 into the encoder 86 and push it out are continuously
turning so that any time a card 31 is inserted, it is immediately pulled
through the machine. When the leading edge of card 31 reaches photocell
127, it interrupts light from the exciter lamp and, in turn, activates the
rest of the circuitry.
The specific circuitry for encoding pulse-width-modulated signals on card
31 in response to the output of photocell 127 comprises essentially the
same components as are employed in the signal recording portions of the
decoder circuitry described above with respect to FIGS. 14 and 18. The
minor differences which may be noted include the use of a digital switch
or the like for setting the desired numbers in an input register
corresponding to the decoder register 150 and the fact that the encoder
does not include the "signal reading" structure employed in the decoder
for decoding the signals. It should be understood, however, that other
means well known to those skilled in the art may be employed for encoding
the card 31 with the necessary pulse-width-modulated signals.
When pulse-width modulated signals and other forms of signals are encoded
on a magnetic recording medium, it is convenient, when considering the
signals on the medium, such as card 31, to consider them as comprising a
plurality of magnetic dipoles having an axis parallel to the axis of the
recording head used for recording them. In the embodiments of the present
invention described above, the axis of the recording head is perpendicular
to the direction of travel of the card in the apparatus. Consequently, the
axis of the dipoles encoded on the card is also perpendicular to the
travel of the card. This orientation of the magnetic recording and
reproduction heads and the magnetic dipoles encoded on the card with
respect to the travel of the card is relatively conventional. However, it
it known that certain advantages can be obtained by skewing the magnetic
recording and reproduction heads relative to the direction of travel of
the recording medium.
One of the principal advantages in skewing a head is an improvement in
signal discrimination. This is because the output of a reproduction head
varies as a function of the wave length of the recorded signal and the
angle by which the head is skewed from the axis of the magnetic dipoles
forming the signal. Therefore, the signal level generated from a dipole
having an axis which is not parallel to the head will be low.
Referring to FIG. 19, there is shown a length of magnetic tape 200. Tape
200 corresponds to the magnetic strip 32 on the card 31. The tape 200 is
given an assumed direction of travel in the direction of the arrow 201.
Orientated at an angle perpendicular to this assumed direction is a head
269. Head 269 corresponds to the head 69 of FIGS. 14 and 18 and to a head
similarly orientated which is in the encoder.
In response to the moving strip, the head 269 will decode magnetic dipoles
on the strip 200. Those dipoles with an orientation parallel to the axis
of the head, such as, for example, the dipoles designated 202 and 203 will
provide a maximum output from the head. However, other signals in the form
of dipoles, such as dipoles 204, 205 may also be on the strip. These
dipoles, for example, may have an orientation with respect to the head 269
which describes an angle B. Such signals may result, for example, from
noise in the recording circuitry.
Referring to FIG. 20, there is shown a diagram of the output signal of the
head 269 versus the angle B. From the diagram it can be noted that the
output signal from the head is maximum when the angle B is zero and falls
off sharply with an increasing angle B in either a positive or negative
direction. It follows from the diagram that for a sufficiently large angle
B between a recorded dipole, such as the dipoles 204 and 205, and the
head, that the output of the head will be very low, if not zero. It
further follows from the foregoing that if the head 269 is skewed
initially in the recording or encoding of signals on the card 31, as shown
in FIG. 21, the output of a reading head not similarly skewed will be very
low, if not zero, for signals such as dipoles 202 and 203 which are
recorded with the conventional perpendicular orientation. Consequently, by
skewing the head 269, signals not having the preferred orientation will be
discriminated against.
In addition to discriminating against extraneous magnetic signals having an
orientation other than parallel to the axis of the reading head, the
skewing of the reading head to read intentionally skewed recorded signals
has the further advantage of reducing the usability of fraudulently
duplicated cards in the apparatus of the present invention. This advantage
arises from the nature of the techniques most commonly employed for that
purpose. The techniques referred to typically employ a transfer process in
which the signals on one medium are transferred to a second medium. During
the transfer process, the signals resulting on the second medium are the
mirror image of the signals on the first medium with a corresponding
reversal in the polarity of the signals.
Referring to FIG. 22, there is shown a duplicated card fabricated according
to the techniques described in which the orientation and polarity of the
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