Money validation system using acceptance criteria
US005931277A
Ulllted States Patent [19]
[11] Patent Number:
Allan et al.
[45]
[54]
[75]
5,355,989
10/1994 Best ...................................... .. 194/317
5,371,681
12/1994 Juds et a1. ............................. .. 364/479
Inventors: Richard Douglas Allan, Reading;
5,392,364
2/1995 Yokoyama et a1. .
5,404,987
4/1995 Allan et al. ........................... .. 194/317
FOREIGN PATENT DOCUMENTS
Sher?eld-on-Loddon, all of United
[73] Assignee: Mars, Incorporated, McLean, Va. [21] Appl. No.:
08/952,240
[22] PCT Filed:
May 9, 1995
[86]
PCT No.:
PCT/GB96/01109
§ 371 Date:
Feb. 2, 1998
PCT Pub. No.: WO96/36022 PCT Pub. Date: Nov. 14, 1996
Foreign Application Priority Data
May 9, 1995
[GB]
0 0 0 0 0 0
155 367 480 505 520 560
126 921 736 609 230 023
A2 9/1985 A2 5/1990 A2 4/1992 A2 9/1992 A1 12/1992 A1 9/1993 2059129 4/1981
2238152 5/1991 002250848 6/1992 2250848 6/1992 2251111 6/1992 2272319 5/1994 2287341 9/1995 2288266 10/1995 WO 92/18951 10/1992
§ 102(e) Date: Feb. 2, 1998
[51]
Aug. 3, 1999
MONEY VALIDATION SYSTEM USING
Kingdom; Frank Mars, McLean, Va.
[30]
Date of Patent:
ACCEPTANCE CRITERIA
Derek Hutchinson, Wokingham; Bernard Joseph Campbell,
[87]
5,931,277
United Kingdom ................. .. 9509387
Int. Cl.6 ..................................................... .. G07D 5/08
European Pat. Off. European Pat. Off. European Pat. Off. European Pat. Off. European Pat. Off. European Pat. Off. United Kingdom . United Kingdom .
. . . . . .
United Kingdom ................. .. 194/317
United United United United United
Kingdom Kingdom Kingdom Kingdom Kingdom
. . . . .
WIPO .
Primary Examiner—F. J. Bartuska Assistant Examiner—Bryan J. Jaketic Attorney, Agent, or Firm—Fish & Richardson PC.
[57]
ABSTRACT
[52]
US. Cl. ............................................................ .. 194/317
A method of testing coins comprising at least taking tWo
[58]
Field of Search ................................... .. 194/206, 317,
measurements of an unknown coin: and accepting said unknown coin as corresponding to a ?rst coin type if the
194/318, 319
point de?ned by the measurements lies, in the space de?ned
[56]
References Cited
by the axes of the measurements, on a ?rst side of a discriminant surface at Which the Mahalanobis distances of the centers of the distribution of said ?rst coin type and a
U.S. PATENT DOCUMENTS 4,417,450 4,463,607
11/1983 Morgan, Jr. et al. ................... .. 62/126 8/1984 Hilton .
4,864,238 9/1989 SeitZ. 4,967,156 10/1990 SeitZ. 5,104,006 4/1991 SeitZ. 5,167,313 5,217,224
12/1992 Dobbins et al. . 6/1993
second coin type are in a predetermined relationship, char
acterized in that said relationship corresponds (at least approximately) to equality of the sums of the respective Mahalanobis distances With respective predetermined con
194/317
stants at least one of Which is non-Zero.
Sincock ................................. .. 273/138
5,351,798 10/1994 Hayes.
50 Claims, 14 Drawing Sheets
U.S. Patent
Aug.3, 1999
Sheet 1 0f 14
5,931,277
7
2b 28
FIG. 1
(PRIOR ART)
2
5;
E
16 &
AL — 10
\'—
14E 72\ '
524 FIG.Z
(PRIOR ART)
U.S. Patent
Aug.3, 1999
Sheet 3 0f 14
5,931,277
1.0 5
08f 0.6
0.4
FIG. 4B
510
515
520
525
530
U.S. Patent
I
Aug. 3, 1999
BEGIN
5,931,277
Sheet 5 0f 14
)
7
106\
INPUT SENSOR OUTPUTS X
/102
ACCESS STORE I0
/104
CALCULATE DISTANCE
ALL COIN TYPES
AD] V
FIND MINIMUM
ADI‘ AND CLASSJ
OUTPUT VALIDITY AND DENOIVIINATION SIGNALS
/112
4I FIG. 6
RETURN
FIG. 11
U.S. Patent
Aug. 3, 1999
100
FIG. 8
Sheet 6 0f 14
5,931,277
U.S. Patent
Aug. 3, 1999
I
BEGIN
Sheet 7 0f 14
5,931,277
’
V
102\
INPUT SENSOR OUTPUTS X NEXT TYPE
/176
ACCESS
104\
STORE
105
I06\
CALCULATE DISTANCE
ADj FIND MINIMUM
ADIAND CLASSJ OUTPUT VALIDITY AND DENOMINATION SIGNALS
__:— FIG. 9
LAST VALID COIN TYPE ?
114
REJECTED
/178
U.S. Patent
Aug.3, 1999
Sheet 8 0f 14
FIG. 10
210-\
INCREASE P FOR SLUG |:__.
FIG. 12
5,931,277
U.S. Patent
Aug. 3, 1999
5,931,277
Sheet 9 0f 14
500
-
FIG. 13A
530
_
530
FIG. 13B
U.S. Patent
Aug.3, 1999
Sheet 10 0f 14
5,931,277
FRED.
Q4-3-2-10123456789
MEASUREMENT M1—> FIG. 14
N0
306
YES USE com
T0 RESTRICT /310 WINDOW
RESTORE WINDOW
@ FIG. 15
/314
U.S. Patent
Aug.3, 1999
Sheet 12 0f 14
5,931,277
(208)
l 276
MEASURE TIME T
\
278
SINCE LAST SLUG CALCULATE
\
A P=K1/T
A
FIG. 20
V_ _
U.S. Patent
Aug.3, 1999
Sheet 13 0f 14
406\
/ 404
RESTRICT ACCEPTANCE
414\
5,931,277
WIDEN ACCEPTANCE
RESTRICTION ?
REDUCE
/478
TH2 (
RETURN FIG. 19
)
/410
U.S. Patent
Aug.3, 1999
Sheet 14 0f 14
5,931,277
4
M2
W1
>
M1 FIG. 21
w l
26
t A
25\
27
Ir2261
81
/28, 30
A
/26
lr2217 l—l
218
FIG. 22
£24
95
23
5,931,277 1
2
MONEY VALIDATION SYSTEM USING ACCEPTANCE CRITERIA
only in dependence upon the distribution of measurements from coins of that type but also in dependence on the relative frequency of occurrence of coins of that type, relative to
FIELD OF THE INVENTION
other types.
This invention relates to a validation apparatus and
method for articles of value; particularly, but not exclusively, coins and banknotes. BACKGROUND OF THE INVENTION 10
Such validators generally comprise a sensing system for generating tWo or more measurement signals, and a pro
cessing system for determining acceptability based on the signals and on stored data de?ning acceptability criteria corresponding to a valid type of article. The acceptability criteria generally de?ne an area or
non Zero.
15
sponding to the measurement signals) determined by, and encompassing, the statistical distribution of measurements from a population of knoWn genuine articles. The distributions of genuine articles may overlap With
accuracy in discriminating particular knoWn slug types by taking into account their probability of occurrence. Where a
those of others, or With those of forgeries, counterfeits or
particular knoWn slug type is distributed Widely throughout
slugs. tance region With a curved boundary.
25
space from the center of the distributions of the coin of the slug, but instead is shifted further toWards the center of distribution of the slug, because Where a given received item of money falls into the area of measurement space in Which
5,351,798 disclose coin validators in Which a coin is clas si?ed as one of several types in dependence upon the
the distribution ranges of the coin of the slug overlap (so that
Mahalanobis distance (ie the square of the Euclidean distance in a space in Which the measurements are each 35
EP-A-0560023 discloses a banknote validator in Which a
it could be either a coin or a slug) the fact that slugs of that type are knoWn to be extremely rare is used to bias the decision toWards deciding that the article is a coin.
Conversely, Where a particular type of slug is common, the decision boundary in measurement space may lie closer (as
de?ned by the respective Mahalanobis distances) to the
banknote is accepted as genuine if its measurements de?ne a point Within a predetermined Mahalanobis distance from
center of the coin distribution than the slug distribution, so as to Weight the decision toWards deciding that the article is a slug.
the center of a valid banknote distribution.
An acceptance region boundary de?ned by a ?xed Mahal anobis distance corresponds to an ellipsoidal boundary, and also de?nes a contour of equal probability (assuming the distribution of genuine coins is unimodal and Normal (Gaussian)) that measurements of a genuine coin are likely to fall Within the boundary.
the space represented by the measurements but occurs extremely infrequently over time, and its distribution over laps With a genuine coin, the decision boundary is not positioned so as to bisect the distances in the measurement
EP-A-0367921, EP-A-0505609, US. Pat. No. 5,351,798 and WO-A-92/ 18951 disclose coin validators using accep tance regions having an ellipsoidal or circular boundary. WO-A-92/18951, GB-A-2251111 and US. Pat. No.
normalised by the variance) from the coin measurement to the center of the distribution of each type.
The invention may be practised by calculating Mahalano bis distances for the ?rst and second coin distributions and then adjusting one or both of the distances, but this is not essential. Thus, this aspect of the invention enables an increased
volume (in a measurement space de?ned by axes corre
GB-A-2272319 discloses a coin validator using an accep
Preferably, this leads to an acceptance boundary at a point Where the relative measurement distribution probabilities of the coin being of ?rst or second types are in a predetermined, non unity, ratio. This therefore equates to the Mahalanobis distances to the center of the distributions of tWo coin types (for example a valid coin and a slug) being in a relationship corresponding to equal sums of the respective Mahalanobis distances With respective predetermined constants at least one of Which is
The frequency With Which different slugs and/or coin types are found to occur depends not only upon the total 45
number of such slugs or coin types in circulation but also, under some circumstances, upon the geographical location of the validator and/or upon the time of day, the day of the Week or the season of the year. In embodiments of the present invention, account is taken of one or more of these factors in decided Whether a given coin is valid or not. In EP-A-0480736, an example of an anti-cheat criterion
The above-described systems may represent an advance
in many areas of validation. Their operation is, hoWever,
predicated on the unspoken assumption that the probability of given measurements being associated With a particular item type (the a posteriori probability) is Well correlated With the probability of an item of that type exhibiting those
given is the use of a WindoW just outside the normal coin acceptance WindoW so that slugs Which are close to being
measurements.
stances this assumption is inaccurate. The present invention,
same idea is employed, and the anti-cheat criterion used is a WindoW Within the acceptance region. In another aspect of the present invention, an attempt is made to detect knoWn slugs using an anti-cheat criterion corresponding to a slug acceptance area in measurement
in one aspect, is concerned With validation Which takes into account factors relevant to the a priori probability to calcu
by altering acceptance criteria.
SUMMARY OF THE INVENTION
acceptable fall Within this WindoW. In EP-A-0520230, the 55
We have realised, hoWever, that under some circum
space, and subsequent acceptance of similar slugs is reduced
late the a posteriori probability rather than relying solely on measurement distributions.
In one aspect, the present invention takes into account the relative frequencies of the occurrence of different types of coins and counterfeit coins or slugs in determining the
acceptance region boundary. Thus, in accordance With the invention, a coin is identi?ed as being of a particular type not
65
In a ?rst method of achieving this, the principles of the ?rst aspect of the invention are employed, and the relative frequency of occurrence of the knoWn slug is increased depending upon actual validation results. The effect of increasing the relative frequency of occurrence term is to increase the volume in measurement space Within Which further slugs of the same type Will be identi?ed as slugs, and
5,931,277 3
4
therefore to decrease the volume in measurement space
FIG. 4b is a scatter diagram shoWing the distribution of the coin and slug measurements of FIG. 4a on the tWo
Within Which they Will be accepted as genuine coins.
measurement axes;
In an alternative method, a linear discriminant is used to
determine Whether a given coin is a slug, and both the slope
FIG. 5a is a notional vieW shoWing a discriminant plane betWeen tWo exactly equal coin distributions, on tWo sensor
and the position of the discriminant are altered on detection
of a slug (for example, by selecting a different discriminant Which reduces subsequent acceptance of similar slugs).
measurement axes; and
In a yet further method according to this aspect of the invention, detection of a slug by using one measurement is
utilised to restrict acceptance of the slug in future by
10
adjusting acceptance criteria on another measurement. In a yet further method according to this aspect of the invention, on one or more measurement axes, a “de?nite
slug” acceptance WindoW is positioned, spaced apart from the coin acceptance WindoW, so as to encompass the mea
15
surement values most likely to correspond to a slug. It is knoWn to provide coin or banknote validators in Which the acceptance criteria are continually self adjusted or self tuned, to track changes in the sensor responses or in the characteristics of the coin or banknote population; such systems are disclosed in GB-A-2059129, EP-A-0155126, or
ERA-0480736 for example. In another embodiment, the present invention provides alternative methods of effecting such self tuning.
FIG. 5b is a corresponding plot for tWo unequal coin distributions shoWing a curved discriminant therebetWeen; FIG. 6 is a How diagram illustrating the operation of the control circuit of FIG. 2 in the ?rst embodiment; FIG. 7 is a plot shoWing an acceptance region in a second embodiment of the invention and corresponding to FIG. 5b; and FIG. 8 shoWs an alternative acceptance region to that of FIG. 7 in the second embodiment; FIG. 9 is a How diagram shoWing the operation of the control circuit of FIG. 2 in the second embodiment; FIG. 10 is a schematic block diagram illustrating the electrical components of a coin validation apparatus of a
25
third embodiment of the invention; FIG. 11 is a How diagram modifying the operation of FIG. 6 in the third embodiment; FIG. 12 is a How diagram shoWing the operation of the
In one aspect, rather than employing only measurements from Within an inner range Within the acceptance region to
control circuit of FIG. 10 in a fourth embodiment of the
perform self tuning (as described in the above referenced ERA-0480736) measurements from throughout the accep
FIG. 13a is a scatter diagram corresponding to FIG. 4b and shoWing a curved discriminant C; and FIG. 13b is a scatter diagram corresponding to FIG. 13a
invention;
tance region are used, but account is taken of the probability
that they represent valid coins.
and shoWing ?rst and second pieceWise linear approximate
Thus, account can be taken even of outlying valid coins
discriminants used in a ?fth embodiment of the invention;
Within the population, although only relative sloWly, so that sharp changes to the coin population can nonetheless can be tracked. In another aspect, Where acceptance ranges are provided for several different measurements (or, combinations of measurements), and such acceptance ranges are of different Widths for each different measurement, the acceptance ranges may be adjusted in accordance With the measure
FIG. 14 is a plot of frequency (on a vertical axis) against one coin sensor measurement (on a horiZontal axis) for 35
FIG. 15 is a How diagram illustrating the operation of the
sixth embodiment; FIG. 16 is a plot on tWo sensor measurement axes
shoWing coin and slug distributions Which may be discrimi
ments of accepted articles scaled by unequal Weighting
nated in a seventh embodiment;
factors, Which may depend upon the Width of the acceptance
FIG. 17 is a plot on tWo sensor measurement axes
ranges on the different measurement axes. This arrangement
may under some circumstances enable more rapid tracking
of changes in the coin population. Corresponding apparatus is also provided. Other aspects and preferred embodiments of the invention
45
shoWing coin and slug distributions Which may be discrimi nated in an eighth embodiment; FIG. 18 is a How diagram illustrating the modi?cation to FIG. 12 in a ninth embodiment;
FIG. 19 is a How diagram shoWing the operation of the
are as disclosed in the accompanying description and claims, With advantages that Will be apparent hereafter.
control circuit in a tenth embodiment;
FIG. 20 is a diagram shoWing a rectangular acceptance
BRIEF DESCRIPTION OF THE DRAWINGS
region on tWo measurement axes utilised in a ?rst arrange
The invention Will noW be illustrated, by Way of example only, With reference to the accompanying draWings in Which: FIG. 1 is an illustrative sectional front elevation of the
overlapping coin and slug classes and illustrates acceptance WindoWs used in a sixth embodiment;
55
ment according to a tWelfth embodiment of the invention; FIG. 21 corresponds to FIG. 20 and illustrates an accep tance region used in a second arrangement according to the
tWelfth embodiment; and
mechanical components of a coin validator utilised in a ?rst
FIG. 22 is an illustrative diagram shoWing the compo
embodiment of the invention, but knoWn in itself;
nents of a banknote validator utilised in a thirteenth embodi
FIG. 2 is a schematic block diagram of the electrical components of the coin validator of FIG. 1;
ment of the invention (but knoWn of itself). DETAILED DESCRIPTION
FIG. 3 is a diagram illustrating the contents of a memory of the validator of FIG. 2 in the ?rst embodiment; FIG. 4a is a three dimensional plot of the distribution over tWo horiZontal measurement axes of sensor measurements
from coins knoWn to correspond to overlapping coin and
slug populations, frequency or probability being illustrated on the vertical axis; and
65
First Embodiment Referring to FIG. 1, a coin to be validated in this embodi ment enters through an inlet 1 and rolls past a sensing system 2 comprising, for example, tWo inductive coil sensors 2a, 2b (eg a sensor 2a primarily responsive to coin thickness and a sensor 2b primarily responsive to coin-diameter). In
5,931,277 5
6
dependence upon the sensor outputs, an accept gate 3 is
system 2; in this case k=3) indicating, Er the type of coin
controlled to either direct the coin on an accept path 4 or a
concerned, the vector of mean values M for each of the k measurements Which are exhibited by a knoWn coin popu lation of that type. Thus, the mean vector de?nes the
reject path 5. Where multiple denominations can be recognised, further gates (not shoWn) are provided to selectively route an
position, in the measurement space de?ned by the measurements, of the center of the population of coins of that type. Also comprised Within each coin type record is the (k>
Ulllted States Patent [19]
[11] Patent Number:
Allan et al.
[45]
[54]
[75]
5,355,989
10/1994 Best ...................................... .. 194/317
5,371,681
12/1994 Juds et a1. ............................. .. 364/479
Inventors: Richard Douglas Allan, Reading;
5,392,364
2/1995 Yokoyama et a1. .
5,404,987
4/1995 Allan et al. ........................... .. 194/317
FOREIGN PATENT DOCUMENTS
Sher?eld-on-Loddon, all of United
[73] Assignee: Mars, Incorporated, McLean, Va. [21] Appl. No.:
08/952,240
[22] PCT Filed:
May 9, 1995
[86]
PCT No.:
PCT/GB96/01109
§ 371 Date:
Feb. 2, 1998
PCT Pub. No.: WO96/36022 PCT Pub. Date: Nov. 14, 1996
Foreign Application Priority Data
May 9, 1995
[GB]
0 0 0 0 0 0
155 367 480 505 520 560
126 921 736 609 230 023
A2 9/1985 A2 5/1990 A2 4/1992 A2 9/1992 A1 12/1992 A1 9/1993 2059129 4/1981
2238152 5/1991 002250848 6/1992 2250848 6/1992 2251111 6/1992 2272319 5/1994 2287341 9/1995 2288266 10/1995 WO 92/18951 10/1992
§ 102(e) Date: Feb. 2, 1998
[51]
Aug. 3, 1999
MONEY VALIDATION SYSTEM USING
Kingdom; Frank Mars, McLean, Va.
[30]
Date of Patent:
ACCEPTANCE CRITERIA
Derek Hutchinson, Wokingham; Bernard Joseph Campbell,
[87]
5,931,277
United Kingdom ................. .. 9509387
Int. Cl.6 ..................................................... .. G07D 5/08
European Pat. Off. European Pat. Off. European Pat. Off. European Pat. Off. European Pat. Off. European Pat. Off. United Kingdom . United Kingdom .
. . . . . .
United Kingdom ................. .. 194/317
United United United United United
Kingdom Kingdom Kingdom Kingdom Kingdom
. . . . .
WIPO .
Primary Examiner—F. J. Bartuska Assistant Examiner—Bryan J. Jaketic Attorney, Agent, or Firm—Fish & Richardson PC.
[57]
ABSTRACT
[52]
US. Cl. ............................................................ .. 194/317
A method of testing coins comprising at least taking tWo
[58]
Field of Search ................................... .. 194/206, 317,
measurements of an unknown coin: and accepting said unknown coin as corresponding to a ?rst coin type if the
194/318, 319
point de?ned by the measurements lies, in the space de?ned
[56]
References Cited
by the axes of the measurements, on a ?rst side of a discriminant surface at Which the Mahalanobis distances of the centers of the distribution of said ?rst coin type and a
U.S. PATENT DOCUMENTS 4,417,450 4,463,607
11/1983 Morgan, Jr. et al. ................... .. 62/126 8/1984 Hilton .
4,864,238 9/1989 SeitZ. 4,967,156 10/1990 SeitZ. 5,104,006 4/1991 SeitZ. 5,167,313 5,217,224
12/1992 Dobbins et al. . 6/1993
second coin type are in a predetermined relationship, char
acterized in that said relationship corresponds (at least approximately) to equality of the sums of the respective Mahalanobis distances With respective predetermined con
194/317
stants at least one of Which is non-Zero.
Sincock ................................. .. 273/138
5,351,798 10/1994 Hayes.
50 Claims, 14 Drawing Sheets
U.S. Patent
Aug.3, 1999
Sheet 1 0f 14
5,931,277
7
2b 28
FIG. 1
(PRIOR ART)
2
5;
E
16 &
AL — 10
\'—
14E 72\ '
524 FIG.Z
(PRIOR ART)
U.S. Patent
Aug.3, 1999
Sheet 3 0f 14
5,931,277
1.0 5
08f 0.6
0.4
FIG. 4B
510
515
520
525
530
U.S. Patent
I
Aug. 3, 1999
BEGIN
5,931,277
Sheet 5 0f 14
)
7
106\
INPUT SENSOR OUTPUTS X
/102
ACCESS STORE I0
/104
CALCULATE DISTANCE
ALL COIN TYPES
AD] V
FIND MINIMUM
ADI‘ AND CLASSJ
OUTPUT VALIDITY AND DENOIVIINATION SIGNALS
/112
4I FIG. 6
RETURN
FIG. 11
U.S. Patent
Aug. 3, 1999
100
FIG. 8
Sheet 6 0f 14
5,931,277
U.S. Patent
Aug. 3, 1999
I
BEGIN
Sheet 7 0f 14
5,931,277
’
V
102\
INPUT SENSOR OUTPUTS X NEXT TYPE
/176
ACCESS
104\
STORE
105
I06\
CALCULATE DISTANCE
ADj FIND MINIMUM
ADIAND CLASSJ OUTPUT VALIDITY AND DENOMINATION SIGNALS
__:— FIG. 9
LAST VALID COIN TYPE ?
114
REJECTED
/178
U.S. Patent
Aug.3, 1999
Sheet 8 0f 14
FIG. 10
210-\
INCREASE P FOR SLUG |:__.
FIG. 12
5,931,277
U.S. Patent
Aug. 3, 1999
5,931,277
Sheet 9 0f 14
500
-
FIG. 13A
530
_
530
FIG. 13B
U.S. Patent
Aug.3, 1999
Sheet 10 0f 14
5,931,277
FRED.
Q4-3-2-10123456789
MEASUREMENT M1—> FIG. 14
N0
306
YES USE com
T0 RESTRICT /310 WINDOW
RESTORE WINDOW
@ FIG. 15
/314
U.S. Patent
Aug.3, 1999
Sheet 12 0f 14
5,931,277
(208)
l 276
MEASURE TIME T
\
278
SINCE LAST SLUG CALCULATE
\
A P=K1/T
A
FIG. 20
V_ _
U.S. Patent
Aug.3, 1999
Sheet 13 0f 14
406\
/ 404
RESTRICT ACCEPTANCE
414\
5,931,277
WIDEN ACCEPTANCE
RESTRICTION ?
REDUCE
/478
TH2 (
RETURN FIG. 19
)
/410
U.S. Patent
Aug.3, 1999
Sheet 14 0f 14
5,931,277
4
M2
W1
>
M1 FIG. 21
w l
26
t A
25\
27
Ir2261
81
/28, 30
A
/26
lr2217 l—l
218
FIG. 22
£24
95
23
5,931,277 1
2
MONEY VALIDATION SYSTEM USING ACCEPTANCE CRITERIA
only in dependence upon the distribution of measurements from coins of that type but also in dependence on the relative frequency of occurrence of coins of that type, relative to
FIELD OF THE INVENTION
other types.
This invention relates to a validation apparatus and
method for articles of value; particularly, but not exclusively, coins and banknotes. BACKGROUND OF THE INVENTION 10
Such validators generally comprise a sensing system for generating tWo or more measurement signals, and a pro
cessing system for determining acceptability based on the signals and on stored data de?ning acceptability criteria corresponding to a valid type of article. The acceptability criteria generally de?ne an area or
non Zero.
15
sponding to the measurement signals) determined by, and encompassing, the statistical distribution of measurements from a population of knoWn genuine articles. The distributions of genuine articles may overlap With
accuracy in discriminating particular knoWn slug types by taking into account their probability of occurrence. Where a
those of others, or With those of forgeries, counterfeits or
particular knoWn slug type is distributed Widely throughout
slugs. tance region With a curved boundary.
25
space from the center of the distributions of the coin of the slug, but instead is shifted further toWards the center of distribution of the slug, because Where a given received item of money falls into the area of measurement space in Which
5,351,798 disclose coin validators in Which a coin is clas si?ed as one of several types in dependence upon the
the distribution ranges of the coin of the slug overlap (so that
Mahalanobis distance (ie the square of the Euclidean distance in a space in Which the measurements are each 35
EP-A-0560023 discloses a banknote validator in Which a
it could be either a coin or a slug) the fact that slugs of that type are knoWn to be extremely rare is used to bias the decision toWards deciding that the article is a coin.
Conversely, Where a particular type of slug is common, the decision boundary in measurement space may lie closer (as
de?ned by the respective Mahalanobis distances) to the
banknote is accepted as genuine if its measurements de?ne a point Within a predetermined Mahalanobis distance from
center of the coin distribution than the slug distribution, so as to Weight the decision toWards deciding that the article is a slug.
the center of a valid banknote distribution.
An acceptance region boundary de?ned by a ?xed Mahal anobis distance corresponds to an ellipsoidal boundary, and also de?nes a contour of equal probability (assuming the distribution of genuine coins is unimodal and Normal (Gaussian)) that measurements of a genuine coin are likely to fall Within the boundary.
the space represented by the measurements but occurs extremely infrequently over time, and its distribution over laps With a genuine coin, the decision boundary is not positioned so as to bisect the distances in the measurement
EP-A-0367921, EP-A-0505609, US. Pat. No. 5,351,798 and WO-A-92/ 18951 disclose coin validators using accep tance regions having an ellipsoidal or circular boundary. WO-A-92/18951, GB-A-2251111 and US. Pat. No.
normalised by the variance) from the coin measurement to the center of the distribution of each type.
The invention may be practised by calculating Mahalano bis distances for the ?rst and second coin distributions and then adjusting one or both of the distances, but this is not essential. Thus, this aspect of the invention enables an increased
volume (in a measurement space de?ned by axes corre
GB-A-2272319 discloses a coin validator using an accep
Preferably, this leads to an acceptance boundary at a point Where the relative measurement distribution probabilities of the coin being of ?rst or second types are in a predetermined, non unity, ratio. This therefore equates to the Mahalanobis distances to the center of the distributions of tWo coin types (for example a valid coin and a slug) being in a relationship corresponding to equal sums of the respective Mahalanobis distances With respective predetermined constants at least one of Which is
The frequency With Which different slugs and/or coin types are found to occur depends not only upon the total 45
number of such slugs or coin types in circulation but also, under some circumstances, upon the geographical location of the validator and/or upon the time of day, the day of the Week or the season of the year. In embodiments of the present invention, account is taken of one or more of these factors in decided Whether a given coin is valid or not. In EP-A-0480736, an example of an anti-cheat criterion
The above-described systems may represent an advance
in many areas of validation. Their operation is, hoWever,
predicated on the unspoken assumption that the probability of given measurements being associated With a particular item type (the a posteriori probability) is Well correlated With the probability of an item of that type exhibiting those
given is the use of a WindoW just outside the normal coin acceptance WindoW so that slugs Which are close to being
measurements.
stances this assumption is inaccurate. The present invention,
same idea is employed, and the anti-cheat criterion used is a WindoW Within the acceptance region. In another aspect of the present invention, an attempt is made to detect knoWn slugs using an anti-cheat criterion corresponding to a slug acceptance area in measurement
in one aspect, is concerned With validation Which takes into account factors relevant to the a priori probability to calcu
by altering acceptance criteria.
SUMMARY OF THE INVENTION
acceptable fall Within this WindoW. In EP-A-0520230, the 55
We have realised, hoWever, that under some circum
space, and subsequent acceptance of similar slugs is reduced
late the a posteriori probability rather than relying solely on measurement distributions.
In one aspect, the present invention takes into account the relative frequencies of the occurrence of different types of coins and counterfeit coins or slugs in determining the
acceptance region boundary. Thus, in accordance With the invention, a coin is identi?ed as being of a particular type not
65
In a ?rst method of achieving this, the principles of the ?rst aspect of the invention are employed, and the relative frequency of occurrence of the knoWn slug is increased depending upon actual validation results. The effect of increasing the relative frequency of occurrence term is to increase the volume in measurement space Within Which further slugs of the same type Will be identi?ed as slugs, and
5,931,277 3
4
therefore to decrease the volume in measurement space
FIG. 4b is a scatter diagram shoWing the distribution of the coin and slug measurements of FIG. 4a on the tWo
Within Which they Will be accepted as genuine coins.
measurement axes;
In an alternative method, a linear discriminant is used to
determine Whether a given coin is a slug, and both the slope
FIG. 5a is a notional vieW shoWing a discriminant plane betWeen tWo exactly equal coin distributions, on tWo sensor
and the position of the discriminant are altered on detection
of a slug (for example, by selecting a different discriminant Which reduces subsequent acceptance of similar slugs).
measurement axes; and
In a yet further method according to this aspect of the invention, detection of a slug by using one measurement is
utilised to restrict acceptance of the slug in future by
10
adjusting acceptance criteria on another measurement. In a yet further method according to this aspect of the invention, on one or more measurement axes, a “de?nite
slug” acceptance WindoW is positioned, spaced apart from the coin acceptance WindoW, so as to encompass the mea
15
surement values most likely to correspond to a slug. It is knoWn to provide coin or banknote validators in Which the acceptance criteria are continually self adjusted or self tuned, to track changes in the sensor responses or in the characteristics of the coin or banknote population; such systems are disclosed in GB-A-2059129, EP-A-0155126, or
ERA-0480736 for example. In another embodiment, the present invention provides alternative methods of effecting such self tuning.
FIG. 5b is a corresponding plot for tWo unequal coin distributions shoWing a curved discriminant therebetWeen; FIG. 6 is a How diagram illustrating the operation of the control circuit of FIG. 2 in the ?rst embodiment; FIG. 7 is a plot shoWing an acceptance region in a second embodiment of the invention and corresponding to FIG. 5b; and FIG. 8 shoWs an alternative acceptance region to that of FIG. 7 in the second embodiment; FIG. 9 is a How diagram shoWing the operation of the control circuit of FIG. 2 in the second embodiment; FIG. 10 is a schematic block diagram illustrating the electrical components of a coin validation apparatus of a
25
third embodiment of the invention; FIG. 11 is a How diagram modifying the operation of FIG. 6 in the third embodiment; FIG. 12 is a How diagram shoWing the operation of the
In one aspect, rather than employing only measurements from Within an inner range Within the acceptance region to
control circuit of FIG. 10 in a fourth embodiment of the
perform self tuning (as described in the above referenced ERA-0480736) measurements from throughout the accep
FIG. 13a is a scatter diagram corresponding to FIG. 4b and shoWing a curved discriminant C; and FIG. 13b is a scatter diagram corresponding to FIG. 13a
invention;
tance region are used, but account is taken of the probability
that they represent valid coins.
and shoWing ?rst and second pieceWise linear approximate
Thus, account can be taken even of outlying valid coins
discriminants used in a ?fth embodiment of the invention;
Within the population, although only relative sloWly, so that sharp changes to the coin population can nonetheless can be tracked. In another aspect, Where acceptance ranges are provided for several different measurements (or, combinations of measurements), and such acceptance ranges are of different Widths for each different measurement, the acceptance ranges may be adjusted in accordance With the measure
FIG. 14 is a plot of frequency (on a vertical axis) against one coin sensor measurement (on a horiZontal axis) for 35
FIG. 15 is a How diagram illustrating the operation of the
sixth embodiment; FIG. 16 is a plot on tWo sensor measurement axes
shoWing coin and slug distributions Which may be discrimi
ments of accepted articles scaled by unequal Weighting
nated in a seventh embodiment;
factors, Which may depend upon the Width of the acceptance
FIG. 17 is a plot on tWo sensor measurement axes
ranges on the different measurement axes. This arrangement
may under some circumstances enable more rapid tracking
of changes in the coin population. Corresponding apparatus is also provided. Other aspects and preferred embodiments of the invention
45
shoWing coin and slug distributions Which may be discrimi nated in an eighth embodiment; FIG. 18 is a How diagram illustrating the modi?cation to FIG. 12 in a ninth embodiment;
FIG. 19 is a How diagram shoWing the operation of the
are as disclosed in the accompanying description and claims, With advantages that Will be apparent hereafter.
control circuit in a tenth embodiment;
FIG. 20 is a diagram shoWing a rectangular acceptance
BRIEF DESCRIPTION OF THE DRAWINGS
region on tWo measurement axes utilised in a ?rst arrange
The invention Will noW be illustrated, by Way of example only, With reference to the accompanying draWings in Which: FIG. 1 is an illustrative sectional front elevation of the
overlapping coin and slug classes and illustrates acceptance WindoWs used in a sixth embodiment;
55
ment according to a tWelfth embodiment of the invention; FIG. 21 corresponds to FIG. 20 and illustrates an accep tance region used in a second arrangement according to the
tWelfth embodiment; and
mechanical components of a coin validator utilised in a ?rst
FIG. 22 is an illustrative diagram shoWing the compo
embodiment of the invention, but knoWn in itself;
nents of a banknote validator utilised in a thirteenth embodi
FIG. 2 is a schematic block diagram of the electrical components of the coin validator of FIG. 1;
ment of the invention (but knoWn of itself). DETAILED DESCRIPTION
FIG. 3 is a diagram illustrating the contents of a memory of the validator of FIG. 2 in the ?rst embodiment; FIG. 4a is a three dimensional plot of the distribution over tWo horiZontal measurement axes of sensor measurements
from coins knoWn to correspond to overlapping coin and
slug populations, frequency or probability being illustrated on the vertical axis; and
65
First Embodiment Referring to FIG. 1, a coin to be validated in this embodi ment enters through an inlet 1 and rolls past a sensing system 2 comprising, for example, tWo inductive coil sensors 2a, 2b (eg a sensor 2a primarily responsive to coin thickness and a sensor 2b primarily responsive to coin-diameter). In
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6
dependence upon the sensor outputs, an accept gate 3 is
system 2; in this case k=3) indicating, Er the type of coin
controlled to either direct the coin on an accept path 4 or a
concerned, the vector of mean values M for each of the k measurements Which are exhibited by a knoWn coin popu lation of that type. Thus, the mean vector de?nes the
reject path 5. Where multiple denominations can be recognised, further gates (not shoWn) are provided to selectively route an
position, in the measurement space de?ned by the measurements, of the center of the population of coins of that type. Also comprised Within each coin type record is the (k>
