Note: Descriptions are shown in the official language in which they were submitted.
CA 02288297 1999-10-25
DESCRIPTION
METHOD OF AND APPARATUS FOR DETERMINING
AUTHENTICITY OF COINS
Technical Field
The present invention relates to a method of and apparatus for
determining authenticity of coins by discriminating them, and more
particularly to a method of and apparatus for determining authenticity of
coins used in automatic vending machines, game machines, etc.
Background Art
1o Coin discrimination apparatus prevailing in recent years is an
electronic type using induction coils. This type of coin discrimination
apparatus generally utilizes the falling of coins due to their own weight
and is provided with a passage for guiding a coin inserted from a coin
slot. A plurality of sets of induction coils are arranged along the passage
15 to produce electromagnetic fields excited by respective different
frequencies.
Inspection of coins is performed by detecting an amount of
electrical change (change in frequency, voltage or phase) derived. due to
the interaction between the electromagnetic field and a coin when the
2o coin passes through the electromagnetic field, to thereby inspect the
authenticity of the coin.
Since in many cases features of coins appear in relation to
frequency-dependent parameters, conventional coin inspection apparatus
employs techniques of inspecting materials, outside diameters,
2s thicknesses, etc. of coins by means of a plurality of frequencies, as
CA 02288297 1999-10-25
2
disclosed in U.S. Patent No. 3,870,137.
In recent so-called borderless societies in which coins can be
easily brought from one country to another, an increasing number of
such unacceptable coins tend to be used erroneously or deceitfully.
Some of the coins used in various countries resemble each other in
material, outside diameter, thickness, etc., and a typical example is S-
cent coin used in the U.S.A. and 5-centesimo coin used in Panama. Such
coins differ from each other only in surface design (surface irregularity
pattern) and are substantially identical with each other in material,
outside diameter and thickness. With the conventional arrangement
using induction coils, however, the surface irregularity patterns of coins
show too subtle a change to be detected by simply using a plurality of
frequencies, with the result that resembling coins like those mentioned
above cannot be discriminated from each other.
Is Also, a 500-yen coin used in Japan and a S00-won coin used in
South Korea are almost identical with each other in material and outside
diameter, and differ from each other in that a 500-won coin has a slightly
greater thickness. Thus, if a 500-won coin is machined and is used as a
S00-yen coin, it is difficult to discriminate the two from each other with
2o the conventional method in which the thickness, outside diameter and
material of coins are inspected to determine the authenticity thereof.
Attempts have also conventionally been made to adopt an optical
process such as image processing as a means of discriminating
resembling coins like those mentioned above. However, optical
25 apparatus has a problem that the authenticity determination of coins can
CA 02288297 2003-02-03
3
be adversely affected by adhesion of dust or the like, and is also large in
size and expensive because of its complicated structure.
Disclosure of Invention
The object of the present invention is to provide a method and
s apparatus for determining authenticity of coins whereby coins can be
discriminated from each other with high accuracy.
A coin authenticity determining method of the present invention
comprises the steps of arranging an exciting coil and a receiving coil in
the vicinity of a coin passage so that the exciting coil and the receiving
1o coil are electromagnetically connected with each other; exciting the
exciting coil to produce an electromagnetic field with such a frequency
that an influence of a reactive magnetic field caused by eddy current
induced on a surface of the coin when the coin passes the
electromagnetic field is detected by the receiving coil, and detecting the
15 electromagnetic field influenced by the reactive magnetic field as an
electromotive force signal by the receiving coil; and discriminating the
coin based on the electromotive force signal detected by the receiving
coil.
The surface of the coin passing through the coin passage and the
2o receiving coil should preferably be close to each other, and therefore the
coin passage is formed such that the coin is inclined to one side of the
coin passage where the exciting coil and the receiving coil are arranged.
Also, the degree of penetration of electromagnetic field into a coin varies
depending on the material of the coin and excitation frequency. Thus, an
25 excitation frequency with which a difference in surface irregularity
CA 02288297 1999-10-25
4
pattern of coins appears well as a difference of the signal from the
receiving coil varies depending on the material of coins to be
discriminated. Accordingly, the frequency at which the exciting coil is
to be excited is selected in accordance with material of coins to be
discriminated.
Specifically, authenticity of coins is determined by using an
exciting coil arranged in the vicinity of one side of a coin passage
inclining at a predetermined angle so that magnetic poles of the exciting
coil faces the coin passage, two receiving coils having substantially
1o identical characteristics and arranged in the vicinity of the coin passage
so that the receiving coils are electromagnetically connected with the
exciting coil, exciting means for exciting the exciting coil at a
predetermined frequency to produce an electromagnetic field, bridge
circuit means including the receiving coils, differential amplifier means
15 connected to the bridge circuit means, detector means connected to the
differential amplifier means, and determining means connected to the
detector means, for comparing a signal obtained when a coin passes the
electromagnetic field with a feature of a predetermined denomination
stored in advance and determining that the coin is authentic if the signal
2o is within a predetermined allowable range with respect to the feature.
Brief Description of Drawings
FIGS. la and 1b are a front view and a sectional view,
respectively, showing a detection coil arrangement for detecting a
surface irregularity pattern of a coin according to a first embodiment of
25 the present invention;
CA 02288297 1999-10-25
FIG. 2 is a block diagram showing a circuit arrangement according
to the embodiment of the present invention;
FIG. 3 is a diagram showing details of circuits according to the
embodiment;
s FIG. 4 is a front view of an apparatus for inspecting authenticity of
coins according to an embodiment of the present invention;
FIGS. 5a and Sb are a front view and a sectional view,
respectively, showing details of the coil arrangement according to the
embodiment of the present invention;
1 o FIG. 6 is a characteristic diagram showing the characteristics of
representative coins according to the embodiment of the present
invention;
FIG. 7 is a diagram showing comparison of data of the
representative coins according to the embodiment of the present
1 s invention;
FIG. 8 is a flowchart showing an operation according to the
embodiment of the present invention;
FIGS. 9a and 9b are a front view and a sectional view,
respectively, showing a detection coil arrangement for detecting a
2o surface irregularity pattern according to a second embodiment of the
present invention;
FIGS. 10a and lOb are a front view and a sectional view,
respectively, showing another detection coil arrangement for detecting a
surface irregularity pattern according to a third embodiment of the
25 present invention;
CA 02288297 1999-10-25
6
FIGS. l la and l 1b are a front view and a sectional view,
respectively, showing still another detection coil arrangement for
detecting a surface irregularity pattern according to a fourth embodiment
of the present invention; and
s FIG. 12 is a view illustrating an example of structure in which a
portion of a coin passage wall where receiving coils are arranged in the
individual embodiments of the present invention is made of a material
with high magnetic permeability.
Best Mode of Carrying out the Invention
1o Referring first to FIGS. la, 1b and 2, one embodiment of the
present invention will be described.
As shown in FIGS. la and 1b, a detector for discriminating a coin
3 comprises one exciting coil 1 and two receiving coils 2a and 2b, and is
arranged in contact with one side wall 7a of a coin passage 6. The coin
1 s passage 6 is sloped at a predetermined angle to allow the coin 3 to roll
down while being guided thereby and comprises a coin rail 4 arranged at
the bottom thereof and a pair of passage walls 7a and 7b. The passage
walls 7a and 7b are, as shown in FIG. 1b, inclined with respect to the
vertical direction so that the coin 3 may roll down while being inclined
2o toward the passage wall 7a. Also, the surface of the coin rail 4, on which
the coin is guided, is inclined in the direction in which the passage walls
7a and 7b are inclined so that the coin 3 passing thereon may be inclined
toward the passage wall 7a.
Each of the two receiving coils 2a and 2b comprises, as shown in
2s FIG. 5b, a drum type core 43 and a coil 44 wound around the core 43.
CA 02288297 1999-10-25
7
As shown in FIG. 1 a, the receiving coils 2a and 2b are arranged above
the coin rail 4 at a predetermined distance from each other such that a
line Sa connecting the centers of the coils 2a and 2b is substantially
parallel with the coin rail 4.
The exciting coil 1 comprises, as shown in FIG. 5a, a ~-shaped
core 40 made of a magnetic material and a coil 41 wound around the core
40. As shown in FIG. 1 a, the exciting coil 1 is arranged above the
receiving coils 2a and 2b such that the center C3 of the core 40 thereof is
located on a line Sc which is perpendicular to the line Sa connecting the
to centers C1 and C2 of the receiving coils 2a and 2b and which passes
through the middle point M of the line segment C 1 C2 and also that a line
Sb connecting the centers of two pole faces 40a thereof is substantially
parallel with the coin rail 4. Further, as shown in FIG. 1b, the core 40 is
arranged such that the pole faces 40a thereof are parallel with the face of
the coin 3 passing thereby. In FIGS. 5a and Sb, reference numerals 42
and 45 each denote a lead wire.
The exciting coil 1 and the receiving coils 2a and 2b arranged as
described above are electromagnetically coupled by means of an
electromagnetic field produced by excitation of the exciting coil 1.
2o In FIG. 2, an oscillation circuit 11 outputs to an output terminal
thereof a rectangular wave signal of predetermined frequency generated
by an MPU (microprocessor unit) or the like, for example. The output of
the oscillation circuit 11 is connected to an excitation driver circuit 12,
the output of which is in turn connected to the exciting coil 1 to excite
same. Consequently, in accordance with the output signal of the
CA 02288297 2003-02-03
excitation driver circuit 12, the exciting coil 1 produces an
electromagnetic field in the vicinity thereof.
In the two receiving coils 2a and 2b, on the other hand, an
electromotive force corresponding to the strength of the electromagnetic
field produced by the exciting coil 1 is generated. The exciting coil 1
and the receiving coils 2a and 2b are preferably arranged for inspection
so as to be close to the face of the coin 3, as mentioned above.
When the coin 3 is acted upon by the electromagnetic fteld, eddy
current is induced in the vicinity of the surface of the coin 3 excited by
to the exciting coil 1, and with increase in excitation frequency, the eddy
current produces an intenser reactive magnetic field in the vicinity of the
outer periphery of the coin due to skin effect. Demagnetizing current
induced in the vicinity of the surface region at the outer periphery of the
coin due to this phenomenon interacts with the receiving coils 2a and 2b,
accompanying a change corresponding to a subtle contour feature of the
coin surface. Thus, in each of the receiving coils 2a and 2b is produced
an electromotive force corresponding to such change of the
demagnetizing current caused by change of the contour feature of the
coin 3. A signal generated by the electromotive force is hereinafter
2o referred to as the "detection signal."
Further, since the magnetic poles of the exciting coil 1 are
arranged in the vicinity of the receiving coils 2a and 2b, a change of the
demagnetizing current induced when the coin 3 is acted upon by the
electromagnetic field produced by these magnetic poles can be acquired
at a location near the magnetic poles.
CA 02288297 1999-10-25
9
The demagnetizing current induced due to the skin effect is
noticeably observed near the outer periphery of the coin, but in cases
where coins have large surface irregularity, the region of coins where a
change of the demagnetizing current can be detected is not particularly
s limited to the outer peripheral region alone. Based on the detection
signal of the receiving coils 2a and 2b, a corresponding alternating
voltage signal is generated in a bridge circuit 13 including the receiving
coils 2a and 2b, and is output to a differential amplifier 14. The
differential amplifier 14 amplifies the alternating voltage signal
1 o generated by the bridge circuit 13 and outputs the thus-amplified signal
to a detector circuit 15. The detector circuit 1 S, which is supplied with
the alternating voltage signal amplified by the differential amplifier 14,
generates a direct voltage signal corresponding to the detection signal
and outputs same to a determination circuit 16. The direct voltage signal
1 s is supplied to an AD converter 17 in the determination circuit 16, in
which the sigaal is converted to a digital signal of corresponding
voltage, which signal is then output to a signal inspection circuit 18 in
the determination circuit 16. The signal inspection circuit 18 determines
whether or not the coin 3 has a given feature, and outputs the result of
2o determination to an output terminal 19. The output of the signal
inspection circuit 18 is used to drive a deflector solenoid, described
later, or a coin counter or the like, not shown.
FIG. 3 shows details of the circuits appearing in the block diagram
of FIG. 2. FIG. 4 is a front view of a coin inspection apparatus using the
2s detection coil for detecting surface irregularity patterns, and FIGS. 5a
CA 02288297 1999-10-25
and Sb are a front view and a sectional view, respectively, showing
details of the coil arrangement.
Referring to FIG. 3, the arrangement of the individual circuits
shown in the block diagram of FIG. 2 will be described in detail. The
s oscillation circuit 11 is constructed with the use of frequency divider
means or the like which is connected to an MPU 20 for dividing a
reference clock signal generated therein. The exciting coil 1 is
connected in parallel with a capacitor C1 to form an LC parallel
resonance circuit so that resonance thereof may occur in the vicinity of
1o the predetermined frequency output from the oscillation circuit 11.
The excitation driver circuit 12 comprises a transistor TR1 and
resistors R3 and R4 connected to one another to perform switching
operation; an integrating circuit made up of a resistor R5, a capacitor C4
and a resistor R6 for converting the rectangular wave output from the
1 s oscillation circuit 11 into a waveform approximate to a triangular wave;
and a driver circuit including a transistor TR2 connected to the exciting
coil 1 constituting the LC parallel resonance circuit, and a resistor R7.
The bridge circuit 13 comprises a capacitor C2 connected in
parallel with the receiving coil 2a, a capacitor C3 connected in parallel
2o with the receiving coil 2b, and resistors R1 and R2.
The differential amplifier 14 comprises capacitors CS and C6
connected to the output of the bridge circuit 13 in an AC coupling
fashion, an operational amplifier Al, and resistors R8, R10 and R9, R11
connected so as to determine the gain of the operational amplifier.
2s The detector circuit 15 comprises a rectifier circuit (voltage
CA 02288297 2003-02-03
11
multiplying rectifier circuit) including diodes D1 and D2 connected to a
coupling capacitor C7 connected to the output of the differential
amplifier 14, and an integrating circuit including a resistor R 12 and a
capacitor C8.
The AD converter 17 and the signal inspection circuit 18 of the
determination circuit 16 are constituted by using the MPU 20
(microprocessor unit).
The oscillation circuit 11 outputs a rectangular wave signal with a
predetermined frequency, and to detect a difference of the surface
t o irregularity pattern of the coin 3 with high sensitivity, the frequency of
the signal is preferably selected such that the electromagnetic field
penetrates into the surface region of the irregularity pattern of the coin,
but not up to the central region thereof, and that the influence of the
reactive ma,~etic field caused by eddy current is noticeable. The frequency
1 s to be employed varies depending on the material of coins to be
discriminated, and in the case of discrimination between 5-cent coin of
the U.S.A. and 5-centesimo coin of Panama; both made of cupronickel,
the excitation frequency of the exciting coil 1 is preferably 70 kHz to 90
kHz. An experiment according to this invention, described later, was
2o conducted with the frequency set at 90 kHz.
The frequency at which the exciting coil 1 is to be excited is
selected in accordance with the material of coins to be detected.
Specifically, using coins having an identical outside diameter but
different thicknesses, the voltage detected by the receiving coils 2a and
25 2b is measured with the excitation frequency successively varied, and
CA 02288297 1999-10-25
12
that frequency with which a large change of the detected voltage is
caused by the difference in thickness of coins is selected as the
excitation frequency.
In the case of cupronickel, for example, it was confirmed by
s experiment that, with the excitation frequency set at about 70 kHz to 90
kHz, the detected voltage showed the largest change in response to the
difference in thickness. With frequencies higher than or lower than a
frequency band of 70 kHz to 90 kHz, change of the detected voltage in
response to the difference in thickness of coins gradually lessens as the
1 o frequency becomes remoter from the frequency band. To discriminate
coins by difference in thickness, that is, by difference in surface
irregularity pattern of coins, the above excitation frequency of 70 kHz to
90 kHz is preferred for cupronickel coins.
Where the material of coins to be discriminated is brass, for
1 s example, an excitation frequency of about 7 kHz to 10 kHz causes the
output voltage to greatly vary in response to the difference in thickness
of coins. Accordingly, in the case of discriminating coins made of brass
by their surface irregularity pattern, the discrimination can be efficiently
carried out by using the excitation frequency of 7 kHz to 10 kHz.
2o In the excitation driver circuit 12, the rectangular wave signal
output from the oscillation circuit 11 is integrated to be converted into a
waveform approximate to a triangular wave by the integrating circuit
composed of the resistor R5, the capacitor C4 and the resistor R6, so that
the exciting coil 1 is excited by the approximated triangular wave signal.
2s The LC resonance circuit constituted by the exciting coil l and the
CA 02288297 1999-10-25
13
capacitor C1 resonates with the aforementioned frequency, and as a
result, the exciting coil 1 is driven at both ends by a sinusoidal wave.
The bridge circuit 13 with the above-described arrangement
constitutes an AC bridge circuit, and this AC bridge circuit is balanced
s when the condition
Z1~Z4 = Z2~Z3
is fulfilled, where Z1 is the impedance caused by the receiving coil 2a
and the capacitor C2 connected in parallel with each other, Z2 is the
impedance caused by the receiving coil 2b and the capacitor C3
1o connected in parallel with each other, Z3 is the impedance of the resistor
R1, and Z4 is the impedance of the resistor R2.
The output of the bridge circuit 13 is a signal appearing between
the junction point between the receiving coils 2a and 2b and the junction
point between the resistors R1 and R2, as shown in FIG. 3; therefore,
15 provided the voltage across the receiving coil 2a is V1, the current
flowing to the impedance Zl is i1, the voltage across the receiving coil
2b is V2, and the current flowing to the impedance Z2 is i2, a voltage
Vdef of the signal appearing between the above two junction points is
given as follows (it is assumed that the impedance Z3 of the resistor Rl
2o is equal to the impedance Z4 of the resistor R2):
V1 = Zl~il
V2 = Z2~i2
Vdef = V 1 - V2
Vdef = Zl~il - Z2~i2
25 In this embodiment, the resonance frequency of the LC resonance
CA 02288297 1999-10-25
14
circuit constituted by the receiving coil 2a and the capacitor C2 and the
resonance frequency of the LC resonance circuit constituted by the
receiving coil 2b and the capacitor C3 are set so as to be substantially
equal to the oscillation frequency output from the oscillation circuit 11.
s Accordingly, the impedances Z1 and Z2 are substantially equal to each
other, and the signal appearing between the aforementioned two junction
points is a voltage signal induced by the difference between the currents
i l and i2 .
The differential amplifier 14 amplifies the alternating voltage
to signal input thereto from the bridge circuit 13 to obtain a desired
alternating voltage signal, which is then output to the detector circuit 15.
The detector circuit 1 S, which is supplied with the alternating
voltage signal output from the differential amplifier 14, performs
detection and rectification of the signal by means of the diode Dl, and
15 then converts the signal to a direct voltage signal corresponding to the
output of the bridge circuit 13 by means of the integrating circuit
constituted by the resistor R12 and the capacitor C8.
The AD converter 17 is implemented by an AD converter of
successive approximation and conversion type built in the MPU 20 and
2o having a resolution of, for example, 8 bits. The AD converter 17
samples the analog direct voltage signal from the detector circuit 15 at
predetermined intervals of time and converts same to a digital signal
corresponding to the output of the bridge circuit 13, the resulting digital
signal train being output to the signal inspection circuit 18.
2s The signal inspection circuit 18, which is thus supplied with the
CA 02288297 1999-10-25
digital signal train on an amplitude axis from the AD converter 17,
temporarily stores the signal train in a memory such as RAM, obtains a
statistic based on the digital signal train temporarily stored in the RAM
and data train of a corresponding denomination stored beforehand in the
s memory 21, then compares the obtained statistic with a predetermined
value stored in advance in the memory 21 to determine whether or not
the coin in question has a given feature, and outputs the result of
inspection to the output terminal 19.
As a specific method of obtaining the above statistic, the following
1o equation may be used to derive a correlation coefficient:
N
(Xi - Xa) (Yi - Ya)
r = i=1 .....(1)
N N
(Xi - Xa)2 ~ (Yi - Ya)2
In equation (1) above, N represents the number of samples,
variable Xi is a sampling value, that is, a value of the aforementioned
digital signal train obtained through measurement of a coin to be
1 s detected, and variable Yi is a statistical value obtained through
sampling/measurement of coins of acceptable denomination with the use
of an apparatus according to this invention. Xa and Ya are average
values of the respective variables.
Taking the processing speed of the MPU into consideration, the
2o deviation (Yi - Ya) between the sampling value Yi of acceptable
denomination and its average value Ya in the sum of deviation cross
products in the numerator of equation (1) and the square root of the sum
of squares of the deviation between the sampling value Yi and its
CA 02288297 1999-10-25
16
average value Ya in the denominator of equation ( 1 ) may be calculated in
advance and stored in the memory 21, in which case the speed of
execution of the subsequent process can be greatly increased.
The absolute value of the correlation coefficient r obtained by
equation (1) falls within a range of 0 s ~ r~ s 1, as is conventionally
known, and therefore, whether a coin to be detected has a given feature
or not can be determined by comparing the correlation coefficient r with
a predetermined value stored beforehand. If the coefficient r is infinitely
close to "1", then the coin in question can be judged to be a genuine coin
of acceptable denomination. On the other hand, if, as a result of the
inspection, the coefficient is found to be infinitely close to zero, the coin
in question can be judged false. Thus, the above predetermined value for
authenticity judgment is set to a value smaller than and close to "1" for
coins to be discriminated, and when a correlation coefficient r greater
than the set value is derived, the coin in question is judged to be a
genuine coin.
Referring now to FIGS. 6 and 7, characteristics of representative
coins measured using the apparatus of this invention will be described.
FIG. 6 shows the characteristics of the representative coins and FIG. 7
2o shows comparison of data of the coins. As shown in FIG. 7, 5-cent coin
of the U.S.A. and 5-centesimo coin of Panama, as representative coins,
are very alike in material (cupronickel), diameter, and thickness: The
two coins, when observed visually, are different from each other only in
their surface design.
2s FIG. 6 is a characteristic diagram showing the results of
CA 02288297 2003-02-03
17
measurement of these coins by means of the apparatus of this invention
wherein the exciting coil 1 was excited at an excitation frequency of 90
kHz. In FIG. 6, reference numeral 50 (thick line) represents the
characteristic curve of 5-cent coin of the U.S.A., and 51 represents the
characteristic curve of 5-centesimo coin of Panama. As shown in FIG. 6,
difference in characteristics between these two coins appears in the first
and last peaks. This peak difference arose presumably because a
reactive magnetic field characterized by the irnegularity of surface pattern
of the coin was produced by eddy current induced on the coin surface
1o and was detected as a subtle difference in electromotive force generated
in the aforementioned two receiving coils. The above difference could
not be detected by conventional techniques.
Referring now to FIGS. 4 and 2, the operation of an apparatus 30
for inspecting authenticity of coins will be described in detail.
In the authenticity inspection apparatus 30 for coins shown in FIG.
4, a coin 3 inserted from a coin slot 31 falls naturally due to its own
weight onto the coin rail 4 arranged under the coin slot 31. The coin 3
thus dropped on the coin rail 4 rolls down through the coin passage 6
(FIG. 1b) in a downstream direction away from the coin slot 31. While
2o moving through the coin passage 6, the coin 3 passes by an outside
diameter detection coil 32, a material detection coil 33, and a surface
irregularity pattern detection coil including the exciting coil 1 and the
receiving coils 2a and 2b. The apparatus 30 inspects the authenticity of
the coin 3 while the coin 3 passes the individual detection coils. If, as a
result of the inspection, the coin 3 is judged to be genuine, a deflector
CA 02288297 1999-10-25
18
solenoid 35 is driven in accordance with the signal output to the output
terminal 19, to actuate a gate 34 such that the coin 3 is guided to a
genuine-coin passage, not shown. On the other hand, if as a result of the
inspection the coin 3 is judged to be a false coin, the gate 34 is not
actuated, so that the coin 3 is guided to a false-coin passage, not shown,
to be let out from an outlet, not shown.
When the coin 3 is genuine and thus introduced to the genuine-
coin passage, it continues to fall naturally and drops onto a coin rail 36.
The coin 3 which has dropped onto the coin rail 36 is then sorted by
to conventionally known sorting means, not shown, according to
denomination, and let out from a corresponding one of outlets A, B, C
and D provided for respective denominations.
For the outside diameter detection coil 32 and the material
detection coil 33 mentioned above, conventional inspection techniques
may be used.
Referring now to the flowchart of FIG. 8, the operation of the
apparatus 30 for inspecting the authenticity of coins by means of the
detection coil for detecting surface irregularity pattern will be described
in detail. In FIG. 8, when the power supply to the apparatus is switched
on, initial settings such as input/output settings in the MPU 20 are
carried out in Step 100. After execution of Step 100, a process for
determining whether or not a coin has been inserted in the apparatus is
executed in Step 101 by using the signal from the detection coil. If it is
judged in Step 101 that a coin has been inserted, the program proceeds to
an AD conversion process in Step 102. On the other hand, if it is judged
CA 02288297 1999-10-25
19
in Step 101 that a coin has not been inserted yet, a standby process is
repeated until arrival of a coin.
When it is judged in Step 101 that a coin has been inserted, the AD
conversion process is executed in Step 102, as mentioned above. On
reception of the signal indicative of arrival of a coin at the detection coil,
the AD conversion process of Step 102 starts to sample the output signal
of the detector circuit 15, which is the signal from the receiving coils 2a
and 2b of the detection coil for detecting surface irregularity pattern.
The result of sampling is temporarily stored in memory such as RAM in
1o the MPU 20 and the program proceeds to a computation process in Step
103.
In the computation process of Step 103, a correlation coefficient r
is obtained using the value of the digital signal train temporarily stored
in the memory and the statistic of acceptable coin stored beforehand in
the memory 21, in accordance with the aforementioned equation (1), and
the program proceeds to an authenticity judgment process in Step 105.
In the authenticity judgment process of Step 105, the correlation
coefficient obtained in the computation process of Step 103 is compared
with the predetermined value of acceptable coin stored in advance, and if
2o the relationship, correlation coefficient r > predetermined value, is
fulfilled, the coin in question is judged to be genuine, and the program
proceeds to a genuine-coin process in Step 106. If, on the other hand, it
is judged that the relationship, correlation coefficient r < predetermined
value, is fulfilled, the coin in question is judged to be false; in which
case the program executes a false-coin process in Step 104 and returns to
CA 02288297 1999-10-25
the standby loop.
When the coin in question is judged to be genuine in the
authenticity judgment process of Step 105, the genuine-coin process is
executed in Step 106, as mentioned above. In the genuine-coin process
s of Step 106, a process of outputting a genuine-coin signal, a
denomination signal, etc. is executed in accordance with the result of
authenticity judgment, whereupon the program returns to the standby
loop.
FIGS. 9a and 9b show the arrangement of a detector for detecting
1o surface irregularity pattern according to a second embodiment of the
present invention. The second embodiment differs from the first
embodiment described above only in that the exciting coil 1 and the
receiving coils 2a and 2b are arranged such that the line Sb connecting
the centers of the pole faces 40a at the longitudinally opposite end
1s portions of the ~-shaped core 40 of the exciting coil 1 is perpendicular to
the line Sa connecting the centers of the receiving coils 2a and 2b and
passes through the middle point M between the centers C 1 and C2 of the
receiving coils 2a and 2b. The operation and effects of the second
embodiment are identical with those of the first embodiment, and
2o therefore, description thereof is omitted.
FIGS. 10a and lOb show the arrangement of another detector for
detecting surface irregularity pattern according to a third embodiment of
the present invention. The third embodiment differs from the above-
described first embodiment only in that the line Sa connecting the
centers of the receiving coils 2a and 2b is shifted in the vertical direction
CA 02288297 1999-10-25
21
with respect to the coin rail 4 on which the coin 3 rolls down, so as to
pass the central portion of the coin 3 to be detected. In the third
embodiment, the receiving coils 2a and 2b are arranged at a location
corresponding to the central portion of the coin 3 to be detected, and
s accordingly, the detection value varies in accordance with difference in
surface irregularity pattern of the central portion of the coin 3, so that the
arrangement is suited for judging authenticity of coins by determining
whether or not the coin has a hole in the center thereof.
FIGS. l la and l 1b show the arrangement of still another detector
1 o for detecting surface irregularity pattern according to a fourth
embodiment of the present invention. The fourth embodiment differs
from the above-described first embodiment in that the side-by-side
arrangement of the receiving coils is rotated by 90 degrees so that the
line Sa connecting the centers of the receiving coils 2a and 2b may be
15 perpendicular to the line Sb connecting the centers of the pole faces of
the core of the exciting coil 1 and pass through the center of the exciting
coil 1. Also in the fourth embodiment, the receiving coils 2a and 2b are
arranged at a location corresponding to the central portion of the coin to
be detected, and therefore, the arrangement of the fourth embodiment is
2o suited for judging authenticity of coins by discriminating between
presence and absence of change in the surface irregularity pattern of the
central portion thereof.
As described above, the position where the receiving coils 2a and
2b are arranged (the position where the exciting coil is arranged in
25 relation to the position of the receiving coils) may be changed in
CA 02288297 2003-02-03
22
accordance with difference in surface irregularity pattern of coins whose
authenticity is to be determined (depending on whether the difference in
surface irregularity pattern exists in the central portion, e.g.
presence/absence of a hole, or in the peripheral portion of the coin).
Also, according to the present invention, the exciting coil 1 is
excited at a frequency such that the electromagnetic field produced
penetrates only into the surface region of the coin but not up to the
centr al region of same, and the influence of a reactive magnetic field caused
by eddy current induced in the vicinity of the surface of the coin is
1o measured. Accordingly, the surfaces of the receiving coils 2a and 2b
facing the coin should desirably be as close to the coin surface as
possible.
As shown in FIG. 12, therefore, a portion of the passage wall 7a
where the receiving coils 2a and 2b are arranged, that is, a portion of the
passage wall 7a extending along the line Sa connecting the centers of the
receiving coils 2a and 2b as shown in FIG. 1 a, may be made of a material
200 having high magnetic permeability, so that the receiving coils 2a and
2b may be virtually located closer to the surface of the coin.
In the individual embodiments described above, the exciting coil I
2o having a ~-shaped core is used, but cores of any other suitable shape
such as a U-shaped core may be used without departing from the spirit
and scope of this invention.
According to the present invention, since the surface irregularity
patterns of coins can be detected, it is possible to provide at low cost a
small-sized, high-performance coin inspection apparatus capable of
Image
