U.S. patent number 3,749,220 [Application Number 05/186,964] was granted by the patent office on 1973-07-31 for coin discriminating apparatus.
This patent grant is currently assigned to Anritsu Electric Company, Ltd., Nippon Telegraph and Telephone Public Corporation. Invention is credited to Toshimitsu Kataoka, Takao Saito, Yukio Tabiichi, Yuichi Yamazaki.
United States Patent |
3,749,220 |
Tabiichi , et al. |
July 31, 1973 |
COIN DISCRIMINATING APPARATUS
Abstract
The coin discriminating apparatus comprising a bridge circuit
including an electromagnetic detection coil, a reference element, a
bandpass filter connected to the output of the bridge circuit, an
amplifier responsive to the output of the bandpass filter and a
feedback circuit for positively feeding back the output of the
amplifier to the bridge circuit. The reference element includes a
reference metal piece which compensates for the variation of the
characteristic of the electromagnetic detector coil caused by the
variation in the ambient temperature.
Inventors: |
Tabiichi; Yukio (Tokyo,
JA), Yamazaki; Yuichi (Tokyo, JA), Saito;
Takao (Kawasaki, JA), Kataoka; Toshimitsu (Tokyo,
JA) |
Assignee: |
Nippon Telegraph and Telephone
Public Corporation (Tokyo, JA)
Anritsu Electric Company, Ltd. (Tokyo, JA)
|
Family
ID: |
22687028 |
Appl.
No.: |
05/186,964 |
Filed: |
October 6, 1971 |
Current U.S.
Class: |
194/319 |
Current CPC
Class: |
G07D
5/00 (20130101); G07D 5/08 (20130101) |
Current International
Class: |
G07f 003/02 () |
Field of
Search: |
;194/1R,1A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Coleman; SAmuel F.
Claims
What is claimed is:
1. Coin discriminating apparatus comprising a bridge circuit
including an electromagnetic detection coil, a reference element
and a pair of proportionality arm elements; a bandpass filter
connected to the output of said bridge circuit; an amplifier for
amplifying the output of said bandpass filter; a discriminator
connected to the output of said amplifier; and a feedback loop for
positively feeding back the output of said amplifier to said bridge
circuit to measure the attenuation characteristics of coins
subjected to the action of the electromagnetic detection coil, the
feed back loop being constructed such that upon a given coin to be
discriminated favorably being subjected to the magnetic field
created by said electromagnetic detection coil the feedback loop is
maintained in one operating condition, and upon coins to be
discriminated against being subjected to the electromagnetic coil,
the feedback loop converts to a different operating condition, said
discriminator being responsive to the operating condition of the
feed back loop.
2. The coin discriminating apparatus according to claim 1 wherein
said bridge circuit comprises an electromagnetic detection coil for
discriminating coins, a reference element connected to one end of
said electromagnetic detection coil, said reference element
manifesting an impedance equivalent to the impedance manifested by
said electromagnetic detection coil when a given coin to be
discriminated favorably is brought into the magnetic field created
by said electromagnetic detection coil, a first proportionality arm
element connected to the other end of said electromagnetic
detection coil and a second proportionality arm element connected
between the other end of said reference element and the other end
of said first proportionality arm element, said bridge circuit
being constructed to assume a balanced condition only when a given
coin to be discriminated favorably is brought to said
electromagnetic detection coil to thereby maintain the feedback
loop in a non-oscillatory condition, and said bridge circuit
assumes an unbalanced condition upon a coin to be discriminated
against being brought to said electromagnetic detection coil
whereby the feed back loop is maintained in an oscillatory
condition.
3. The coin discriminating apparatus according to claim 2 wherein
said discriminator comprises means for smoothing an AC signal from
said amplifier for producing a DC voltage, means responsive to said
DC voltage for determining a permissible balanced voltage level
which is used to detect the balanced condition of said bridge
circuit, and signal generating means responsive to the operation of
said D.C. voltage responsive means for determining the permissible
balanced voltage level for generating a coin discriminating
signal.
4. The coin discriminating apparatus according to claim 2 wherein
said reference element comprises a coil having the same rating as
said electromagnetic detection coil and a reference metal piece
having the same characteristic as said given coin to be
discriminated favorably, said reference metal piece being
positioned in the magnetic field of the coil of said reference
element.
5. The coin discriminating apparatus according to claim 3 wherein
said means for determining the permissible balanced voltage
comprises a Zener diode.
6. The coin discriminating apparatus according to claim 4 wherein
said reference element comprises a coil divided into two sections
and having the same capacity as said electromagnetic detection
coil, a pair of spaced apart magnetic cores, said two sections
being wound upon said cores respectively to produce magnetic fields
in the same direction, a reference metal piece manifesting the same
impedance as the center value of the impedance distribution
manifested by said electromagnetic detection coil when a given coin
to be discriminated favorably is brought thereto, said reference
metal piece being mounted close to the flux generating surface of
one of said cores, a base for supporting one of said cores and a
slide plate slidably mounted on said base and supporting the other
of said cores.
7. Coin discriminating apparatus comprising a bridge circuit
including an electromagnetic detection coil included in the first
arm, of said bridge circuit, proportionality arm elements
respectively included in the second and third arms, and a plurality
of reference elements adapted to be selectively connected in the
fourth arm of said bridge circuit; a bandpass filter connected to
the output of said bridge circuit; an amplifier for amplifying the
output of said bandpass filter; a discriminator connected to the
output of said amplifier; a feed back loop for positively feeding
back the output of said amplifier to said bridge circuit; and a
change over device for selectively connecting one of said reference
elements in said fourth arm when said discriminator detects the
unbalanced condition of said bridge circuit upon a coin being
brought to said electromagnetic detection coil.
8. The coin discriminating apparatus according to claim 7 wherein
each one of said reference elements manifests an impedance
equivalent to the impedance manifested by said electromagnetic
detection coil upon a predetermined coin to be discriminated
favorably being inserted in the magnetic field produced by said
electromagnetic detection coil.
9. The coin discriminating apparatus according to claim 7 which
further includes means for producing discriminating signals
indicating whether the inserted coins correspond to predetermined
types or not.
10. The coin discriminating apparatus according to claim 8 wherein
each one of said reference elements comprises a coil having the
same rating as said electromagnetic detection coil and a reference
metal piece cooperating with said first mentioned coil and having
the same characteristic as a particular coin to be discriminated
favorably thereby.
11. The coin discriminating apparatus according to claim 10 wherein
each one of said reference elements comprises a coil divided into
two sections, a pair of spaced apart magnetic cores, said coil
sections being wound upon said magnetic cores respectively to
produce magnetic flux in the same direction, a reference metal
piece manifesting the same impedance as the center value of the
impedance distribution manifested by the coins of a predetermined
type to be discriminated favorably by said one reference element,
said reference metal piece being mounted on the flux generating
surface of one of said cores and a base for supporting one of said
cores, a slide plate slidably mounted on said base for supporting
the other of said cores.
12. A coin discriminating apparatus comprising an electromagnetic
detection coil divided into two sections, each section being
supported within magnetically permeable, insulating housings
secured on respective sides of a coin receptacle, a pair of spaced
apart magnetic cores each mounted in a respective one of the
housings with said two sections of said coil being wound upon said
cores respectively to produce magnetic fields in the same direction
such that upon a coin being deposited in the coin receptable, it is
disposed in the flux path between the two cores and causes a
characteristic impedance value to be manifested by said
electromagnetic detection coil.
13. A coin discriminating apparatus comprising a reference element
for inclusion in a measuring bridge with an electromagnetic
detection coil, said reference element including a coil divided
into two sections, a pair of spaced apart magnetic cores, said coil
sections being wound upon said magnetic cores respectively to
produce magnetic flux in the same direction, a reference metal
piece manifesting the same impedance as the center value of the
impedance distribution manifested by the electromagnetic detection
coil in the presence of coins of a predetermined type to be
discriminated favorably by said reference element, said reference
metal piece being mounted on the flux generating surface of one of
said cores, a base for supporting one of said cores and a slide
plate slidably mounted on said base for supporting the other of
said cores.
Description
BACKGROUND OF THE INVENTION
This invention relates to coin discriminating or sorting apparatus
for use in coin telephone sets or slot machines and more
particularly to coin discriminating apparatus utilizing the
variation in the impedance of an electromagnetic detection coil
which occurs when a coin is inserted in the magnetic field created
by the electromagnetic detection coil.
In the well known coin discriminating apparatus, an electromagnetic
detection coil is connected in one arm of a bridge circuit so as to
detect the variation in the impedance of the detection coil caused
by the insertion of the coin in the magnetic field created thereby
thus discriminating the type of the coin. However, this type of the
well known coin discriminating apparatus not only requires to use
an AC oscillator having a stabilized output level as the source for
the bridge circuit but also to use an amplifier of a large gain in
order to stabilize the operation of the discriminating circuit.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a new and
improved coin discriminating apparatus of the type employing a
bridge circuit containing an electromagnetic coil in one arm
thereof but does not require to use an AC oscillator as has been
the prior practice.
A further object of this invention is to provide an improved coin
discriminating apparatus capable of discriminating genuine and
counterfeit coins without the necessity of using an AC
oscillator.
Still further object of this invention is to provide an improved
coin discriminating apparatus capable of discriminating not only
the type of the coin but also whether it is a genuine coin or a
counterfeit coin.
Another object of this invention is to provide a coin
discriminating apparatus capable of discriminating the coins at
high accuracies without being affected by the variation in the
characteristic of the electromagnetic detection coil caused by the
temperature rise thereof.
Still another object of this invention is to provide a reference
element of novel construction to be incorporated in the bridge
circuit of the coin discriminating apparatus of the type referred
to above.
Further objects and advantages of the invention will become
apparent as the description proceeds.
According to one feature of this invention, there is provided coin
discriminating apparatus comprising a bridge circuit including an
electromagnetic detection coil for detecting a coin, a reference
element and two proportionability elements, a bandpass filter
connected across the output terminals of the bridge circuit, an
amplifier connected to the output of the bandpass filter, and means
to feed back the output of the amplifier to the bridge circuit.
With this construction the AC oscillator can be eliminated.
Further, in accordance with this invention, the reference element
of the bridge circuit is comprised by a plurality reference
elements which are selectively connected into the bridge circuit
through a transfer switch and there is provided a change-over
device driven by the output from the discriminating means so as to
actuate the transfer switch. This arrangement permits
discrimination of a plurality of the types of the coins. Further, a
reference metal piece having the same characteristic as the genuine
coin is included in the reference element so as to accurately
determine the type of the coin irrespective of the variation in the
characteristic of the electromagnetic detection coil caused by the
rise in temperature.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing;
FIG. 1 is a simplified block diagram of the coin discriminating
apparatus embodying the invention;
FIG. 2 shows a detailed connection of the block diagram shown in
FIG. 1;
FIG. 3 shows a portion of the coin passage;
FIG. 4 shows a sectional view taken along a line shown in FIG.
3;
FIG. 5 shows a simplified block diagram of a modified embodiment of
this invention capable of discriminating two types of the
coins;
FIG. 6 shows a connection diagram showing the relationship between
the discriminating means, the change-over device and the bridge
circuit and is utilized to explain the operation of the embodiment
shown in FIG. 1;
FIG. 7 shows a connection diagram of the discriminating means the
change-over device and the bridge circuit of another embodiment
capable of discriminating three types of coins;
FIG. 8 is a plot showing the impedance distribution of the coins
manifested by the electromagnetic detection coil when three types
of the coins are subjected to the magnetic field produced by the
detection coil;
FIG. 9 is a graph showing temperature-impedance characteristics of
respective electromagnetic detection coils used to discriminate
three types of coins, a temperature-impedance characteristic curve
of a reference element used to detect one type of coin and the
threshold value region of the discriminating means;
FIGS. 10 and 11 are graphs to explain the probability of
miss-discrimination of the coin caused by temperature rise;
FIG. 12 is a perspective view of the reference element of the
bridge circuit utilized in this invention;
FIG. 13 shows a cross-section taken along a line XIII -- XIII shown
in FIG. 12 and
FIG. 14 is a graph to explain how the miss-discrimination of the
coin can be prevented by the use of the novel reference
element.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the coin discriminating apparatus
illustrated in FIG. 1 comprises a bridge circuit 1 including an
electromagnetic detection coil 11 for discriminating the coin, a
reference element 12 which exhibits an impedance equivalent to the
impedance exhibited by the detection coil 11 when a given coin to
be discriminated is subjected to the magnetic field produced
thereby, and a pair of proportionality arm elements 13 and 14. The
electromagnetic detection coil 11 and the reference element 12 are
connected in adjacent arms of the bridge circuit, and the
proportionality arm elements 13 and 14 and connected in the two
remaining adjacent arms. The juncture 15 between electromagnetic
detection coil 11 and the proportionality arm element 13 and the
juncture 16 between reference element 12 and proportionality arm
element 14, are connected to a bandpass filter 2 and the output of
filter 2 is connected to a discriminator 4 through an amplifier 3.
A portion of the output from amplifier 3 is fed back to juncture 17
between proportionality arm elements 13 and 14 via a feedback
conductor 5. The bridge circuit is adjusted such that it becomes
balanced when a given coin 6 to be discriminated is brought to the
position of electromagnetic detection coil 11 as will be described
later. Under the balanced state, the bridge circuit 1 produces a
small output whereas when a coin other than the given coin is
brought to the electromagnetic detection coil the bridge circuit
becomes unbalanced to produce a large output. The bandpass filter 2
may be a well known bandpass filter that produces a small
attenuation in a predetermined frequency band and wherein the phase
angle of the frequencies at both ends of the band varies more than
360.degree.. The amplifier 3 is designed to have a gain which is
smaller than the absolute value of the sum of the attenuation of
the bridge circuit when detecting the given coin and the
attenuation of the bandpass filter. Consequently, the attenuation
of the bridge circuit is increased when the given coin 6 is brought
to the electromagnetic detection coil 11 so that the voltage fed
back to the bridge circuit through conductor 5 is decreased whereby
the feedback system does not oscillate. On the other hand, when a
counterfeit coin is brought to the electromagnetic detection coil
the attenuation of the bridge circuit will be decreased thus
causing the feedback system to oscillate. Thus, it is possible to
determine whether the coin is a genuine coin or a counterfeit coin
by discriminating the oscillation and non-oscillation conditions
described above.
FIG. 2 shows a detailed connection diagram of the embodiment shown
in FIG. 1 in which junctures 15 and 16 of bridge circuit 1 are
connected across the primary winding of a transformer 7 so as to be
coupled with bandpass filter 2. The bandpass filter 2 is of the
known type comprising capacitors 21 to 24 and inductors 25 to 27
connected as shown. Amplifier means 3 is comprised by an IC
amplifier circuit 31 and a plurality of resistors 32 through 37.
The purpose of variable resistor 34 is to set the gain of amplifier
circuit 31. As above described, the gain of the amplifier means 3
is set to be smaller than the absolute value of the sum of the
attenuation of the bridge circuit and that of the bandpass filter
when the given coin is inserted. The output from amplifier means 3
is fed to feedback conductor 5 through a coupling capacitor 38 as
well as to discriminator 4 which comprises an input capacitor 41, a
smoothing circuit 42, a Zener diode 43, transistors 44 and 45 and
resistors 46 and 47. The Zener diode 43 functions to determine the
threshold value of the discriminator 4. Numeral 8 represents a
source of supply and 48 an output terminal. When the given coin is
brought to face electromagnetic detection coil 11 amplifier 31 will
not produce an output because of the large attenuation in the
bridge circuit as above described so that the loop circuit
comprising bridge circuit 1, bandpass filter 2, amplifier 3 and
feedback conductor 5 does not oscillate. Accordingly, transistor 45
is rendered ON to produce a zero potential at the output terminal
48. On the other hand when a coin different from the given coin is
brought to face the electromagnetic detection coil, the attenuation
in bridge circuit 1 is decreased whereby amplifier circuit produces
an output which is positively fed back through conductor 5 to cause
oscillation. This oscillation output is converted into a DC current
by means of a rectifier 42 and is then applied to a Zener diode 43.
When this applied voltage exceeds a predetermined threshold voltage
of the diode Zener 43, transistor 44 is turned ON and results in
transistor 45 being turned OFF to supply the source voltage to
output terminal 48. As above described with the circuit shown in
FIG. 2, it is possible to determine whether the coin is the given
coin or not by observing the voltage appearing at output terminal
48.
Turning now to FIGS. 3 and 4 which show the relationship between a
coin path and an electromagnetic detection coil associated
therewith, the coin path 64 is defined by a pair of parallel side
walls 60 and 61 which are spaced apart by upper and lower spacers
62 and 63. Side walls 60 and 61 are provided with circular openings
65 and 66 respectively. Two sections of the coil 11 are disposed in
these openings to oppose each other on the opposite sides of the
passage 64. Sections of the coil are wound on pot shaped ferrite
cores 67 and 68, respectively, to produce magnetic flux in the same
direction. Respective sets of the coil sections and cores are
enclosed by insulative casings made from polyacital resin 69 and 70
which fit in openings 65 and 66 respectively. Inner faces of the
casings 69 and 70 which are exposed to the passage 64 are flush
with the inner surfaces of the side walls 60 and 61. The sections
of coil 11 are connected in series between terminals 15 and 18 also
shown in FIG. 1. The mechanism for holding the coin 6 in passage 64
between the sections of coil 11 is not shown because it is well
known in the art.
The modified embodiment shown in FIG. 5 which is used to
discriminate two types of coins are identical to that shown in FIG.
1 except that reference element 12 shown in FIG. 1 is replaced by a
pair of reference elements 121 and 122 which are selectively
connected in one arm of bridge circuit 1 by a transfer switch 19
under control of a change-over device 9 connected to the output of
discriminator 4. Reference element 121 is designed to have an
impedance equivalent to that of detection coil 11 when one type of
the coin is broght to the detection coil whereas the other
reference element 122 is designed to have an impedance equivalent
to that of the detection coil when the other type of the coin is
brought to the detection coil.
FIG. 6 shows the detail of the change-over device 9 connected to
the discriminator 4 for operating transfer switch 19 shown in FIG.
5. Where the invention is applied to a coin telephone set, a switch
SW shown in FIG. 6 represents the hook switch of the telephone set,
whereas a source switch in the case of a coin exchanger or a slot
machine. Relay G may also be included in the collector circuit of
transistor 45 shown in FIG. 2 and connected between source 8 and
discriminator 4 to be energized when the inserted coin is of the
predetermined type. Change-over device 9 comprises a control relay
T, a relay TRS for switching the reference elements and contacts of
these relays. Contacts C1 and C2 are operated when a coin is
inserted and relays G, T and TRS are provided with contacts g1, g2
and g3; t1; and trs1, trs2, trs3 and trs4, respectively.
It is now supposed that reference elements 121 and 122 are adapted
to determine 10 yen and 100 yen Japanese coins respectively.
Accordingly, reference element 121 is designed to have an impedance
equal to that of detection coil 11 when a 10 yen coin is brought
thereto whereas reference element 122 has an impedance equal to
that of the detection coil 11 and when a 100 yen coin is brought
thereto. During operation, switch SW is closed as above described.
Then relays TRS and T are operated successively to throw contact
trs1 (which corresponds to transfer switch 19 shown in FIG. 5)
toward reference element 121. Under these conditions when a coin is
inserted, contacts C1 and C2 open and close, respectively, due to
the insertion of the coin. Contact C1 opens the circuit of relay
TRS to release it with a time delay. However, when the inserted
coin is a 10 yen coin, the bridge circuit 1 with element 121
connected through switch trs1 becomes balanced. Under this balanced
state, the attenuation of the bridge circuit is increased as above
described, so that the loop circuit including feed back conductor 5
does not oscillate. Accordingly, relay G connected to discriminator
4 will operate to close its contact g1 before release of relay TRS
so as to continue the energization of relay TRS. Thus, contact trs1
remains continuously connected to reference element 121. At this
time, contacts C2, g3 and trs4 are all closed to produce an output
signal at terminal T121 indicating the coin that has been inserted
is the given coin, that is a 10 yen coin.
In the event the, coin inserted is not a 10 yen coin, the bridge
circuit 1 with element 121 connected becomes unbalanced to cause
the loop circuit to oscillate. Under these conditions, relay G will
not be energized so that relay TRS will release with the time
delay. Consequently, transfer contact trs1 is switched from
reference element 121 to reference element 122. Opening of contact
trs3 commerces the time delay release of relay T. Where the
inserted coin is a 100 yen coin, the bridge circuit now including
reference element 122 becomes balanced to terminate the oscillation
of the loop circuit. Consequently, relay G is energized by the
output of discriminator 4 to close contact g2 to continue the
energization of relay T. Under these conditions, contacts C2 and g
3 are closed to provide a 100 yen coin discriminating signal at
output terminal T122. If the coin inserted were a coin different
from 10 or 100 yen coin or a counterfeit coin the bridge circuit 1
would not be balanced with either reference element 121 or 122 so
that relay G will not be energized to prevent release of either
relays TRS or T with time delays. Under these conditions, a signal
is produced at output terminal NO indicating that the coin due to
the release of relay T and return of contact t.sub.1 to its
normally closed position is not either 10 or 100 yen coin. In this
embodiment, by the operation of relays TRS, T and G, it is possible
to discriminate 10 yen, 100 yen and another coins as well as
counterfeit coins, and signals discriminating these coins are
produced at output terminals, T121, T122 and NO.
FIG. 7 shows another embodiment of this invention capable of
discriminating three types of coins. In this embodiment, a third
reference element 123 is added to the bridge circuit 1 and a relay
TRS2 for switching the reference elements is added to change-over
device 9. Relay TRS shown in FIG. 6 is designated by a reference
character TRS1 in FIG. 7. Since the embodiment shown in FIG. 7
operates in the same manner as that shown in FIG. 6, detailed
description thereof will not be made. Where it is desired to
discriminate more than four types of coins it is only necessary to
add the required number of reference elements and relays for
switching them for the desired number of types of coins to be
discriminated.
Current coins have more or less different electromagnetic
characteristics so that the impedance of the detection coil
responsive to the insertion of the coins varies over a range for
the same type of the coin. FIG. 8 shows the impedance distribution
of the electromagnetic detection coil where each type of 5 yen, 10
yen and 100 yen coins are inserted in the magnetic field produced
by the detection coil at a temperature of 20.degree.C. In this
figure, regions D10, D100 and D5 represent impedance distributions
of the detection coil for 10 yen, 100 yen and 5 yen coins,
respectively. Symbols X in respective regions show the center
impedance manifested by respective types of the coins. As can be
noted from FIG. 4 since an air gap is included in the passage of
the magnetic flux passing through the coin 6, the impedance of the
electromagnetic detection coil varies greatly when the temperature
in the casing of a coin telephone set or a slot machine embodying
the invention varies. FIG. 9 is a graph showing the impedance
variations of respective types of the cons at various temperatures.
Impedance variations of the detection coil for 5 yen, 10 yen and
100 yen coins are plotted for temperatures of -20.degree.C (plotted
by small white, circles), 0.degree.C (black circles), +20.degree. C
(symbols X), +40.degree.C (white triangles), +60.degree.C (black
triangles) and +80.degree.C (white squares), respectively. Thus,
dotted lines L10 show the impedance variation characteristic of the
detection coil at respective temperatures, solid line L100 and dot
and dash lines L5 show corresponding impedance variation
characteristics. Region D100 (+20) in FIG. 9 represents the
impedance distribution region of the electromagnetic detection coil
for 100 yen coins at +20.degree.C, while regions D100 (-20) and
D100 (+80) represent the impedance distribution regions of the
electromagnetic detection coil for 100 yen coins at -20.degree.C
and +80.degree.C, respectively.
Of course the impedance of reference element comprising one arm of
the bridge circuit varies with the ambient temperature. The
impedance variation characteristic of the reference element is
shown by a thick line S in FIG. 9. Thick line S shows the impedance
variation characteristic of a reference element for 100 yen coins
and crosses the characteristic for 100 yen coins (measured at
20.degree.C) at the center impedance thereof (shown by a symbol
X).
For the sake of description, discrimination of 100 yen coins is
assumed. In a temperature range of from -20.degree.C to
+80.degree.C, the impedance viz. temperature characteristic of the
electromagnetic detection coil is shown by L100 and that of the
reference element by S. From this it will be evident that these
characteristics differ greatly. For this reason, in order to
correctly determine the coin inserted at 80.degree.C as a genuine
one it is necessary to set a permissible range of the unbalanced
voltage of the bridge circuit. Such permissible unbalanced voltage
corresponds to the value at which the discriminator shown in FIG. 2
does not operate, that is the threshold voltage of the Zener 43. In
FIG. 9, this permissible unbalanced voltage is shown by the area of
a circle P1 containing the distribution region D100 (+80) of the
electromagnetic detection coil for 100 yen coins at a point
corresponding to +80.degree.C (shown by a square) on line L100 when
the reference element is maintained at +80.degree.C. Also in the
case of -20.degree.C, it is necessary to set a permissible range of
the unbalanced voltage covered by a circle P2 having center at a
point indicated by a small circle on line S, said circle P2
covering the distribution region D100 (-20) for 100 yen coins
indicated by a small circle on line D100. However, since P1>P2,
the permissible unbalanced voltage necessary and sufficient to
discriminate genuine 100 yen coins in the entire range of
-20.degree.C to +80.degree.C is represented by P1. Consequently,
the permissible unbalanced voltage at -20.degree.C is represented
in FIG. 9 by a circle P3 which is equal to circle P1.
In this manner, it is possible to determine the inserted coin as
the genuine 100 yen coin in a temperature range of from
-20.degree.C to +80.degree.C by setting the permissible unbalanced
voltage at a value determined by circle P1(=P3). However, where the
permissible unbalanced voltage which is set as above described is
made to be equal to the threshold value of discriminator 4, the
discriminating apparatus operates to determine coins other than 100
yen coins as 100 yen coins.
More particularly, as shown in FIG. 10, the impedance distribution
region of the electromagnetic coil for 5 yen coins at -20.degree.C
is represented by a dotted line region D5 (-20) which is partially
included in the region of the permissible unbalanced voltage for
100 yen coins at -20.degree.C, that is the region P3 of the
threshold value of the discrimination 4. The portion of the region
D5 (-20) included in the area of circle P3 is shown as shaded and
amounts to 20 percent of region D5 (-20). This means that 20
percent of the 5 yen coins are determined as 100 yen coins.
Turning now to FIG. 11, the impedance distribution region of the
detection coil for 10 yen coins at +80.degree.C is represented by a
dotted line region D10 (+80), the shading portion thereof being
included in circle P1 representing the threshold value of
discriminator 4 for 100 yen coins maintained at +80.degree.C. This
shaded portion occupies about 60 percent of region D10 (+80) which
means that 60 percent of the 10 yen coins inserted at +80.degree.C
is determined as 100 yen coins.
In order to prevent such a miss-discrimination, it is necessary to
design the reference element to have the same temperature
characteristic as the electromagnetic detection coil. This can be
accomplished by so constructing the reference element as to
comprise a given coin and two sections of a coil of the same
construction as the detection coil and disposed on the opposite
sides of the coin. As shown in FIG. 8, even for given coins since
the impedance characeteristic of the detection coil varies in a
region of some area, the reference element should have an impedance
at the center of this region. For this reason, for positioning a
given coin in the reference element it is necessary to select a
coin manifesting the center impedance out of a plurality of such
given coins. Accordingly, where the novel discriminating apparatus
is incorporated into a coin telephone set or a slot machine which
are ordinarily manufactured on a mass production scale, it is
advantageous to use a reference metal piece which manifests the
same impedance value as the center value of the impedance
distribution of the detection coil for the given coin instead of
utilizing the same. The metal piece utilized in the reference
element should have smaller impedance distribution region than the
given coin, low cost, and should have such dimension and
configuration that do not permit insertion of the metal piece into
the coin telephone set or a slot machine instead of the given coin.
The result of experiment shows that when a reference metal piece to
be utilized in the reference element for discriminating 100 yen
coins is made to have a diameter of 18mm and a thickness of 1.8mm
from an alloy consisting of 64.0 to 68.0 parts of copper, less than
0.15 part of lead, less than 0.15 part of iron and the balance of
zinc it is possible to cause the reference metal piece to have an
impedance equal to the center value of the impedance distribution
for 100 yen coins maintained at 20.degree.C.
FIGS. 12 and 13 show one example of the reference element embodying
the invention. As shown in these figures, two sections 121 of a
coil of the reference element are wound on pot shaped ferrite cores
83 and 84 and respective sets of the coil segment and the ferrite
core are contained in casings 81 and 82, respectively, of
polyacetal resin. Two sections of the coil are wound cummulatively
and are connected in series between terminals 85 and 86. Casings 81
and 82 are formed with lateral flanges 87 and 88 projecting in the
opposite directions. The reference element is mounted on a base 89
having vertical wall 90 at its left hand end as viewed in FIG. 12
which is used to fixedly secure the flange 87 of casing 81. A
reference metal piece 91 is secured on the inner surface of casing
81. A ring 92 of polyacetal resin is secured to flange 87 by means
of screws 93 to hold in position the reference metal piece 91. The
right hand end of the base 89 as viewed in FIG. 12, is formed into
a channel to form vertical guide walls 94 for the purpose to be
described later. A slide plate 95 is mounted upon base 89 between
guide walls 94. A vertical wall 96 is formed at the left hand end
of slide plate 95 which is secured to flange 88 of casing 82 to
support the same. A pair of guide slots 97 are formed through slide
plate 95 to receive set screws 98 threaded into base 89. The mutual
inductive coefficient of the coil sections contained in casings 81
and 82 can be varied by moving slide plate 95 in the direction
indicated by an arrow A after loosening screws 98 thus enabling
fine adjustment of the impedance of the reference element.
FIG. 14 is a graph showing temperature viz. impedance variation
characteristics of a reference element including the reference
metal piece described above, in which straight lines L10, L100 and
L5 represent the temperature viz. impedance characteristics of the
electromagnetic detection coil when 10 yen, 100 yen and 5 yen coins
are inserted in the field of the detection coil, and a straight
line S1 represents the temperature viz. impedance characteristic of
a reference element for 100 yen coins containing a reference metal
piece manifesting an impedance equal to the center impedance of the
detection coil when it receives a 100 yen coin at 20.degree.C.
Comparing two characteristics L100 and S for 100 yen coins,
different from the case shown in FIG. 9 curve S1 is located closer
to curve L100. For this reason, in a temperature range from
+20.degree.C to 80.degree.C, the permissible unbalanced voltage of
the bridge circuit sufficient to determine the inserted 100 yen
coins as the genuine 100 yen coins, or the threshold value of the
discriminator 4 may be set in an area bounded by a circle P4 shown
in FIG. 14, thus permitting decrease in the permissible unbalance
voltage. By setting the permissible unbalance voltage in circle P4
in this manner, the possibility of misdiscriminating 5 yen coins at
-20.degree.C as 100 yen coins as has been described in connection
with FIG. 10 and 10 yen coins at +80.degree.C as 100 yen coins as
has been described in connection with FIG. 11, can be efficiently
obviated. While above description has been made in terms of 100 yen
coins it will be understood that coins other than 100 yen coins can
also be discriminated by utilizing reference metal pieces made of
metals having the same impedance characteristics as those of the
coins to be discriminated.
While the invention has been shown and described in terms of
preferred embodiments thereof it should be understood that many
changes and modifications will be ovious to one skilled in the art
within the true spirit and scope of the invention as defined in the
appended claims.
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