U.S. patent number 3,704,890 [Application Number 05/102,005] was granted by the patent office on 1972-12-05 for device for displaying symbols in a pseudo-random sequence.
This patent grant is currently assigned to Pitney-Bowes, Inc.. Invention is credited to Joseph Kaswer, Jr., Thomas S. Wilczynski, Fredric E. Zucker.
United States Patent |
3,704,890 |
Zucker , et al. |
December 5, 1972 |
DEVICE FOR DISPLAYING SYMBOLS IN A PSEUDO-RANDOM SEQUENCE
Abstract
A device for displaying numbers of a pseudo-random sequence. For
each change in the number to be displayed, a mutilated gear is
rotated by a suitable mechanism through a predetermined angular
displacement. For each such rotation, a variable number of teeth of
the mutilated gear drive a number wheel through a variable number
of numeral display positions. Two different locking elements
prevent rotation between actuations. One of the locking elements
carries a window shutter which in combination with a second window
blocks observation of the number wheel during actuation and reveals
the wheel when indexed.
Inventors: |
Zucker; Fredric E. (Stamford,
CT), Kaswer, Jr.; Joseph (Stamford, CT), Wilczynski;
Thomas S. (Trumbell, CT) |
Assignee: |
Pitney-Bowes, Inc. (Stamford,
CT)
|
Family
ID: |
22287615 |
Appl.
No.: |
05/102,005 |
Filed: |
December 28, 1970 |
Current U.S.
Class: |
273/143R;
340/5.86 |
Current CPC
Class: |
G07C
15/00 (20130101); G07F 7/1016 (20130101) |
Current International
Class: |
G07F
7/10 (20060101); G07C 15/00 (20060101); A63f
005/04 () |
Field of
Search: |
;340/149A,147 ;235/61.9
;35/3,4,2 ;273/138R,138A,143R,143A,143B,143C,143D,143E ;74/435 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Oechsle; Anton O.
Assistant Examiner: Kramer; Arnold W.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A device for displaying symbols in pseudo-random sequence:
comprising
a frame;
a main drive shaft rotatably mounted in said frame;
wheel display means rotatably mounted on said frame;
gearing means including at least one mutilated gear for
interconnecting said drive shaft and said wheel display means so
that said display means may be rotated through varying angles
dependent upon the mutilated pattern of said gear;
a first locking means movable into and out of positive locking
condition with respect to a first portion of said gearing
means;
a second locking means movable into and out of positive locking
condition with respect to a second portion of said gearing means;
and
cam means driven by said main drive shaft for moving both of said
locking means out of their respective locking conditions when said
drive shaft is to rotatably index said wheel display means.
2. Apparatus as defined by claim 1 wherein said wheel display means
includes two display wheels, and said gearing means includes two
separate gear trains functionally arranged in parallel relation and
each driven directly from said main drive shaft to rotate a
respective display wheel.
3. Apparatus as defined by claim 1: additionally comprising shutter
means mounted on said frame for movement into and out of view
blocking position with respect to said display wheel means; and
said cam means including actuating means operated in timed relation
to the rotation of said main drive shaft for moving said shutter
means into and out of said view blocking position.
Description
FIELD OF THE INVENTION
This invention relates to a device for displaying symbols in a
pseudo-random sequence, and to the use of such a device in a credit
card verification system.
BACKGROUND OF THE INVENTION
A purely probabilistic device which selects numbers or other
symbols in a sequence completely devoid of any predictable pattern,
such as a roulette wheel, is a true random number generator. Other
random number generating devices, using sophisticated electronic
circuitry, are utilized in various statistical analysis problems
and for transmitting coded messages; but they are relatively
expensive and thus not suitable for applications where cost is a
prime consideration.
A device which generates a predetermined but unpatterned sequence
of numbers may appear to an observer to be a random number
generator, if the predetermined sequence is unknown to him. Such a
sequence is necessarily of finite length, however, and must
eventually repeat. Therefore, if the observer realizes that the
sequence is starting over, he can distinguish it from a random
sequence and predict the numbers in the second occurrence of the
sequence, based upon his observations of the first occurrence. But
this generally will not be possible if the sequence is so lengthy
that the observer finds it impractical to detect the eventual
repetition. Devices for generating such sequences, which may be
referred to as pseudo-random generators, offer a less expensive
alternative to random devices in some applications where the
appearance of randomness will suffice. In an inexpensive game of
chance, for example, a pseudo-random display device might be an
acceptable substitute for a roulette wheel, slot machine, or other
truly probabilistic device.
Another application for an inexpensive pseudo-random number
generator arises in credit card verification systems of the type in
which a central computer is connected by telephone or other
communication lines to service a plurality of credit card readers
located at remote sales stations. Such systems can be defeated by
credit card cheats who are able to obtain the collusion of the
sales clerk, unless special measures are taken. One such measure is
to lay down a trail for subsequent audit, by providing a separate
identifying number for each sales transaction, and requiring the
sales clerk to record these transaction numbers on the charge
slips. But if the transaction numbers must be generated by the
central computer and transmitted over long distance phone lines to
the sales station for display by the credit card reader, the
additional transmission time required, and the extra data reception
equipment which must be provided at each of the point-of-sale
stations, make the cost excessive.
The cost can be significantly reduced, however, if only a binary
accept-reject response is provided by the central computer, and the
transaction number is generated right at the sales station. But in
order for such a system to operate effectively, the transaction
number sequence generated at the sales station must be either
random or pseudo-random, so that the collusive sales clerk cannot
detect any pattern; otherwise he could correctly predict the next
number, and such predictability would enable him to defeat the
system by entering the correct transaction number without
consulting the computer and registering the rejection of a
fraudulent credit card in its memory. The transaction number
generator must also be tamper-proof; and since it will be
duplicated at each remote terminal, it should be compact, simple,
reliable and inexpensive.
THE INVENTION
This invention concerns a simple, reliable and relatively
inexpensive mechanical device which acts as a pseudo-random number
generator. The device is suitable for use in a credit card
verification system, as well as in simulated games of chance, and
is tamper-proof. It includes a display wheel about which the
numbers, or other symbols to be displayed, are distributed in a
predetermined order. A mutilated gear or gears are provided which
are advanced by suitable drive means through a predetermined number
of gear tooth positions for each change in the symbol to be
displayed. The mutilated gear is then effective to increment the
display wheel a pseudo-random variable number of symbol
positions.
Another aspect of the invention concerns the use of this or any
other type of unpredictable numerical display device to generate a
transaction number at a credit card verification station.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram giving an overall view of a credit
card verification system according to the teachings of this
invention.
FIG. 2 is a partially exploded perspective view of a pseudo-random
sequence generating device embodying another aspect of the
invention.
FIG. 3 is a top plan view of a portion of the device shown in FIG.
2.
And FIG. 4 is a side elevational view of the same portion of the
same device.
The same reference characters refer to the same elements throughout
the several views of the drawing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, the credit card verification system
includes a central processing unit (CPU) 10 and a plurality of
remote credit card verification stations having respective credit
card reader terminals 12.1 through 12.N. Each card reader 12
accepts a credit card 18 having machine-readable numerical
subscriber identification information thereon. The particular
credit card reading technology utilized may be conventional, and
does not form any part of the present invention. The subscriber
identification number read from the card is transmitted over an
associated one of transmission lines 20.1 through 20.n, which may,
for example, be standard telephone lines. The information is
received by CPU 10, which determines whether the card is acceptable
and may also determine whether the proposed credit transaction is
permissible. If the CPU determines that credit should not be
granted, it transmits a negative response over the appropriate line
20 to the interrogating station, which causes a light 26 to be
turned on in the associated card reader 12 (see reader 12.n, for
example). The CPU may handle simultaneous inquiries on a
time-sharing or a queuing basis, as desired, using conventional
computer programming techniques.
If the credit card sale is acceptable, the card reader illuminates
a transaction number, e.g., the number "32" in the example
represented by reader 12.1. The transaction number is preferable in
the range from 00 to 99, the tens and units digits being displayed
on opposite sides of a window 28. The mere presence of this number
does not represent a positive response from CPU 10; but its
illumination by a lamp 90, seen in FIGS. 2 through 4, does
represent a positive response. The transaction number itself is to
be copied onto the charge slip by the sales clerk, in order to
identify the particular sales transaction for subsequent audit
purposes.
This number can be generated in several different ways. If cost
were no object, the CPU could generate the transaction number,
record it in the computer memory for subsequent audit purposes, and
transmit it to the remote terminal 12 for display to the sales
clerk. With such a system, the numbering sequence does not matter,
because the transaction number which the sales clerk enters on the
charge slip can always be compared to the contents of the computer
memory, and any lack of correspondence between the two would be
evidence of misbehavior. The problem with that system, however, is
cost.
A basic insight of the present invention is that it is cheaper to
generate the transaction number within the card reader 12 than to
receive it from the CPU 10. Not only does this approach avoid the
need for additional transmission time, but it also permits the
transaction number display device to do double duty by both
generating the number and displaying it. In addition, data-decoding
and display-driving circuitry are eliminated entirely from the
remote terminal 12.
On the theory that the mere appearance of traceability may be
sufficient to discourage wrongdoers, the internally generated
transaction number may be a fake; i.e., it may not represent an
actually traceable audit trail, provided the dishonest sales clerk
does not know that.
One way to generate a fake sequence of transaction numbers is to
incorporate a true random number generator within the card reader
12. But this requires sophisticated electronic circuitry at each
sales station, and is therefore expensive. Moreover, a true random
number system, or any other system which is completely untraceable,
relies entirely on the prior deterrent effect of fear of detection.
If the fake nature of the system ever became known, the dishonest
sales clerk would no longer be deterred by fear of detection, and
there would be no way to perform a subsequent audit.
If the internally generated transaction number is not truly random,
however, some way must be devised to make sure that it cannot be
predicted by the sales clerk; because if he fabricates a false
transaction number to make a fraudulent sale look authentic, the
CPU will not have a stored check-list of transaction numbers usable
to discover the subterfuge.
In accordance with the preferred embodiment of this invention, each
card reader 12 displays an internally generated pseudo-random
sequence of transaction numbers which, for all practical purposes,
is just as difficult to predict as a truly random one. It
accomplished this, preferably, by employing a compact simple,
reliable, low cost mechanical sequence-generating device of the
type illustrated in FIGS. 2 through 4. The tens and units digits to
be display at window 28 are carried on two number display wheels
36A and 36B respectively, located on opposite sides of the device.
These wheels are mounted for rotation, independently of each other,
about a common shaft 38. The drive mechanisms for the wheels 36A
and 36B are substantially identical, so that in the discussion to
follow only general reference numerals need be utilized, it being
understood that the indicated element may be that for either the A
or B side of the device.
In the discussion which follows, there are references to the
"effective" number of teeth on various driving gear members. This
term is intended to designate the actual number of tooth increments
of angular displacement imparted to driven gears by driving members
having discontinuous gear tracks, such as gear sectors or mutilated
gear tracks. When two full-track gears are in mesh for 360.degree.,
the effective number of teeth is equal to the actual number; but
when the driving gear track is discontinuous, special effects may
occur upon engagement and disengagement, which cause N teeth on the
driving gear member to impart less than N tooth increments of
angular displacement to the driven gear member. Such effects depend
upon the geometry of the gear teeth, specifically their "contact
ratio;" see "Standard Handbook for Electrical and Mechanical
Engineers" by Marks.
Each of the wheels 36 has a plurality of numerals uniformly spaced
about its periphery. In order to enhance the apparent randomness of
the number display sequence, the digits 0 through 9 are in random
rather than numerical order on each of the wheels 36; and, in a
preferred embodiment of the invention, some of the digits appear
more than once on each wheel so that there is not an equal
probability of occurrence.
A final drive pinion 40, having a number of teeth N.sub.40 equal to
the number of digits distributed about the corresponding wheel 36,
is attached to each of the wheels 36 so that rotation of a pinion
40 about shaft 38 drives the associated wheel 36. Each pinion 40 is
driven by a mutilated gear track 42, i.e. one with a number of
teeth missing, formed on one side of an intermediate drive gear 44.
The directions of rotation of pinion 40 and all other elements are
indicated by the arrows in FIG. 4. In the particular embodiment
illustrated N.sub.40 is 12.
The other side of the gear 44 is full-toothed gear track 43, the
number of teeth N.sub.43 on which is preferably a relatively large
prime number. For the particular embodiment of the invention
illustrated here, N.sub.43 =73. The exact value of N.sub.43 is not
critical, but a prime number of teeth should be utilized, and it
should be relatively large, since the magnitude of this number and
its "primeness" are factors which determine the number of times the
display can be operated before the number sequence repeats. Both
gears 44 are mounted for rotation on a shaft 46, and may either be
free to rotate independently thereon as shown in the drawings, or
keyed to the shaft to rotate together.
The mutilation of gear track 42 is achieved by removing some teeth,
and not removing others, in a random, non-repetitive, unpredictable
sequence. In operation the gear 44 is advanced (by means discussed
in detail subsequently) through a predetermined number of tooth
increments N.sub.56 (in the range from 2 through N.sub.43 -1) each
time that the numerical display is to be changed. In the specific
example illustrated, N.sub.56 is 7; but the exact number is not
critical so long as it remains in the range indicated, which in
this case is from 2 through 72.
Each time gear 44 rotates through seven teeth positions, some
random effective number of teeth of its mutilated track 42 engage
with the associated pinion 40. This number will depend on how many
teeth happen to be missing from the particular sector of track 42
which is currently in position to drive pinion 40. Thus, for each
cycle of operation each of the pinions 40 will be advanced by a
number of tooth positions which varies from cycle to cycle in a
pseudo-random fashion. Since each tooth of pinion 40 corresponds to
one numeral position of the associated number wheel 36, the number
wheel will advance a number of numeral positions equal to the
number of tooth positions by which its pinion 40 is advanced. Thus
the number of numeral positions by which each display wheel
advances also changes pseudo-randomly from cycle to cycle.
Because the number of teeth N.sub.43 in the unmutilated track 43 of
gear 44 is a prime number (73), starting from any initial position
the gear 44 must be advanced through N.sub.43 =73 consecutive
operating cycles of seven tooth increments each (or N.sub.56 =7
revolutions) before it comes to rest again at that same position,
and the cycle starts over. Since gear 44 goes through N.sub.43 =73
different operating cycles, and the pinion 40 driven thereby has
N.sub.40 =12 teeth, the pinion and its number wheel 36 go through
N.sub.43 .times. N.sub.40 = 73 .times. 12 = 876 different cycles
before repeating; provided N.sub.42 (i.e., the effective number of
unmutilated teeth) in the mutilated gear track 42 times the number
of revolutions which gear 44 goes through before repeating (in this
case seven) equals a quantity which has no factors in common with
(i.e., is "prime" relative to) N.sub.40. Thus, if the mutilated
track 42 is designed to observe this requirement, there is an 876
cycle interval before repetition. A non-repetitive sequence of that
length is so time-consuming to observe, and so difficult to keep in
mind, that most people will have enormous difficulty in detecting
and using the repetition of the sequence to predict the next digits
to be displayed by the wheels 36.
The reader's attention is directed next to the mechanism for
incrementing gear 44 by N.sub.56 =7 teeth for each operating cycle.
Each of the gears 44 is driven by an intermediate pinion 48 which,
as best seen in FIG. 3, has a full-toothed track 50 of any
convenient number of teeth on one side for driving the full-toothed
track 42 of gear 44. thus a seven-tooth advance of pinion 48 will
produce the desired seven-tooth advance of the associated gear
44.
The remainder of the drive mechanism constitutes a means to produce
a seven-tooth advance of pinions 48 during each operating cycle,
while confining that advance to a fraction of the cycle time.
Pinions 48 are mounted for rotation on a common shaft 49. One side
of each pinion 48 comprises a gear track 52 with one tooth missing.
The tooth gap in each track 52 first receives the high lobe of a
Geneva cam 54, to lock the gear train 48, 44 against rotation
during the first phase of each operating cycle, i.e. until the
toothed sector of a driving gear 56 is in position to engage the
full-toothed track 50 of the pinion 48. Then a low dwell of the
Geneva cam 54 rotates into position adjacent the pinion track 52,
unlocking the pinion 48 to permit rotation of the gear train. The
desired seven-tooth advance of pinion 48 during this phase of the
operating cycle is achieved by providing the driving gear 56 with
an effective number of teeth N.sub.56 =7, all of which are grouped
together along a limited sector of its circumference. If desired,
the effective number of teeth N.sub.56A and N.sub.56B in gears 56A
and 56B could be different, which would make the number sequence
even more difficult to detect.
Geneva cam 54 and drive gear 56 are both keyed to drive shaft 58
which, as may be seen in FIG. 3, is connected to a one-revolution
drive mechanism 60. When the CPU 10 of FIG. 1 approves a credit
sale, a signal is applied to an electrical line 62, indicating that
the number displayed in window 28 is to be changed, and causing
mechanism 60 to rotate the drive shaft 58 one revolution. The
particular construction of mechanism 60 does not form part of the
present invention, and any conventional means for performing this
function may be utilized. The CPU at this time also initiates a
signal on an electrical line 92, to light lamp 90, indicating the
approval of the credit sale.
One reason for confining the rotation of pinion 48 and the
remainder of the number wheel drive train to a fraction of the
cycle time of drive shaft 58, is to permit that shaft to be used
also as the main timing shaft of the entire credit card reader
device 12 (FIG. 1), which drives other rotary equipment during each
operating cycle before and/or after changing the transaction number
display. Another reason is to allow a certain amount of coasting
tolerance for the drive mechanism 60, while still assuring that it
will drive the transaction number display device of this invention
through the same angular increment of seven teeth each time it is
operated. A third reason, relating to shutter 78, is discussed
below.
In addition to the Geneva cam 54 and drive gear 56, shaft 58 also
has keyed thereto a cam 64 for each of the display wheels. The rear
end of each pawl arm 66, which is pivotably mounted on shaft 46, is
biased upwardly by a tension spring 68 to bear against the
associated cam 64. The upper ends of springs 68 are anchored to a
shaft 72. When the arm 66 is against a low dwell of cam 64 (as seen
in FIG. 2), the forward end of the arm is so positioned that a pawl
tooth 69 formed thereon engages the teeth of the associated pinion
40, to lock the pinion and the associated number wheel 36 against
rotation. This situation occurs when the transaction number display
is not in the process of being changed. When it is being changed,
as seen in FIG. 4, a high lobe of cam 64 comes into contact with
arm 66, raising the pawl 69 out of engagement to permit rotation of
the pinion 40 and number wheel 36. This feature helps to prevent
tampering with the number display generator, by preventing any
unauthorized rotation of the number wheels.
Shafts 38, 46, 49, 58 and 72 are all supported between the walls of
a metal frame 70. If the various gears are keyed to, but slidable
on, the shafts 46, 49 and 58, respective spacers 73, 75 and 77 are
provided.
In order to prevent the sales clerk from detecting the sequence in
which the numerals appear on wheel 36 as it is moving, which might
give him a somewhat greater probability of prediction, shutter 78
is attached to forward extension 80 of both pawl arms 66. The
shutter is formed with an aperture 82, and the window 28 and
aperture 82 are so proportioned that only one of the numerals on
each wheel can be seen at one time. The aperture is aligned with
window 28 (see FIG. 2) only when the number display is not
changing. While the display is changing, shutter 78 is raised to
block window 28 (FIG. 4), preventing the operator from seeing the
rotation of the wheel. After each display has been completed, arms
66 are permitted to drop down again, realigning the shutter
aperture 82 with window 28 to permit viewing of the number display,
provided the lamp 90 is lit by a signal from the CPU 10. Thus the
Geneva mechanisms 54, 52 discussed above cooperate with the cams 64
to divide each cycle of drive shaft 58 into separate time intervals
for changing and revealing the display, respectively.
Alternatively, the lamp 90 could be lit at all times when the card
reader 12 is in operation, and the shutter 78, instead of being
actuated by the drive cams 64, could be raised or lowered by a
conventional solenoid mechanism (not shown) responsive to signals
from CPU 10. In that case, mere visibility of the transaction
number display would constitute the computer-generated approval
signal for each credit sale.
An additional feature which improves the security of the device
relates to the prevention of reverse number wheel rotation.
Anti-reverse pawls 74, bent from resilient sheet metal and secured
to the floor of frame 70 by fasteners 76, engage each pinion 40.
The pawls are self-biased into engagement with the pinions, and
angled upwardly so as to lock when an attempt is made to turn the
pinions counter-clockwise as viewed in FIG. 4. The pawls yield
resiliently, however to ratchet over the pinions 40 and permit easy
rotation in the clockwise direction.
It is not necessary that the mutilation pattern on the two gears 44
be completely different. Instead, in order to reduce the cost of
manufacturing this device, the gears 44A and 44B are preferably
identical but flipped-over relative to each other, so that their
mutilation patterns progress in opposite sequence, in effect
providing two entirely different mutilation sequences. Furthermore,
while separate drive trains have been shown for each of the
mutilated gears 44, if the gears 44 are both keyed to shaft 46 only
a single drive train 50, 56 and a single Geneva mechanism 52, 54
may be required.
While two digit positions (units and tens) are employed in this
embodiment, a lesser or greater number of digit positions could be
provided as required. It should be noted, however, that the more
digit positions there are in the transaction number, the lower is
the probability that a prospective wrongdoer will be able to guess
the entire number, because all the digits proceed independently
through their respective pseudo-random sequences.
Finally, it should be noted that a pseudo-random device of this
kind has an additional very important advantage for use in a credit
card verification system. The actual transaction number sequence,
however long it may be, and however many digit positions are
employed, is still actually predetermined and predictable, if only
the observer had the time and capacity to perform the necessary
observations and calculations. Modern computers, which are able to
compress time through their great calculating speeds, and also have
the memory capacity to handle a great deal of data, can do it. The
CPU 10 of FIG. 1, therefore, when properly programmed and provided
with information as to the sequence of numerals on display wheels
36, the number of teeth on each gear and pinion in the drive train,
and the exact mutilation pattern and angular directions of gear
tracks 43, can actually calculate the entire 876 member sequence of
two-digit transaction numbers, and thus provide a true basis for
subsequent audit if one should be necessary.
Alternatively, a true audit can be provided without the need for as
much computer software, if the display output shafts 38 drive
conventional commutating switches (which can be plated on the sides
of number wheels 36, if desired) to provide digitally encoded
feedback indicating to the CPU 10 which numbers were displayed.
It will now be appreciated that the present invention provides
pseudo-random number generation, which is especially useful for
both generating and displaying transaction numbers at the remote
terminals of a credit card verification system, avoiding the need
for deriving such numbers from the central computer station, and
which also is able to lay down a true audit trail.
Since the foregoing description and drawings are merely
illustrative, the scope of protection of the invention has been
more broadly stated in the following claims; and these should be
liberally interpreted so as to obtain the benefit of all
equivalents to which the invention is fairly entitled.
* * * * *