EP1123537B1 - Bimetallic coin discriminating device and method - Google Patents

Abstract

A coin discriminating device has first and second coils (10, 20) positioned to induce and detect eddy currents in an outer ring (40) and an inner disk (50), respectively, of a bimetallic coin (30). A storage device is adapted to store coin reference data, and a logic device is adapted to determine an identity of the coin by comparing the coin reference data to data obtained from the detected eddy currents and related to the conductivity of the coin. A magnetic sensor (60) is coupled to the logic device and is positioned to detect a magnetic field generated by at least one of the first and second coils (10, 20), when the coin (30) is positioned betwwen the first and second coils and the magnetic sensor. The logic device uses data obtained by the magnetic sensor and related to the permeability of the coin when determining the identity of the coin (30).

Description

Technical Field

The present invention relates to a coin discriminatingdevice of the type having first and second coilspositioned to induce and detect eddy currents in an outerring and an inner disk, respectively, of a bimetallic coin,where a storage device is adapted to store coin referencedata and a logic device is adapted to determine an identityof the coin by comparing the coin reference data to dataobtained from the detected eddy currents and related to theconductivity of the coin.

The present invention also relates to a method ofidentifying a bimetallic coin, and to a coin processingmachine including a coin discriminating device of the abovetype.

Description of the Prior Art

Coin discriminators, which are arranged to measurethe electric characteristics, e.g. the resistance or conductivity,of a coin by exposing it to a magnetic pulse anddetecting the decay of eddy currents induced in the coin,are generally known in the technical field. Such coin discriminatorsare used in a variety of coin processing machines,such as coin counting machines, coin sorting machines,coin validators for vending and gaming machines, etc.Previously known coin processing machines are for instancedisclosed in WO 97/07485 and WO 87/07742.

The way in which such coin discriminators operate isdescribed in e.g. EP-B-0 119 000, in which a coin testingarrangement comprises a transmitter coil, which is pulsedwith a rectangular voltage pulse so as to generate a magneticpulse, which is induced in a coin when being movedpast the transmitter coil along a coin rail. The eddy currentsthus generated in the coin give rise to a magnetic field, which is monitored or detected by a receiver coil.The receiver coil may be a separate coil or may alternativelybe constituted by the transmitter coil having twooperating modes. By monitoring the decay of the eddy currentsinduced in the coin, a value or reading representativeof the coin conductivity may be obtained, since therate of decay is a function thereof.

One embodiment of EP-B-0 119 000 uses two transmittercoils with different effective cross-sectional areas. Thelarge coil is larger than the largest acceptable coin,whereas the small coil is smaller than the smallest coin.The position of the small coil is such that the effectivecross-sectional area thereof is covered by the smallestcoin when passing along the coin rail.

The purpose of the small coil is to solve a problemthat can occur if only a large coil was used. The readingsfrom the large coil are a function of the conductivity anddiameter of the coin. A large diameter and a highconductivity both produce large coin readings. Hence, thereis a problem in that coins of different diameter andconductivity can produce identical readings. For example, aBritish 2p copper coin and an aluminium token of 2 mmsmaller diameter produce identical readings from the largecoil. The small coil produces a signal that depends on theconductivity, but is independent of diameter. Thus,aluminium and copper may be differentiated by the smallcoil. The small coil cannot be used alone, because coins ofthe same material but different diameter give the samereadings.

Another prior art coin discriminator is disclosed inEP-B-0 300 781.

While the above coin discriminators often aresufficient for traditional, homogeneous coins made of asingle metal or metal alloy, the above prior artdiscriminators are less useful for successfully discriminating also among bimetallic coins, as will bebriefly addressed below.

In recent years, bimetallic coins have been issued onthe market in different countries. Well known examples ofbimetallic coins are the French 10F, the British £2, theCanadian $2 and the 1 and 2 Euro coins.

Bimetallic coins are made as follows. Outer rings andcentral disks are punched from sheets (also known asblanks) of the two metal or metal alloys, of which the bimetalliccoin is to be made. The disk is then fitted intothe ring, and the coin is minted. Minting consists of pressingthe coin between two hardened dies. The dies stamp thehead and tail pattern onto the coin and also force the diskand ring together. The joint between the disk and ring iscalled a bond.

When identifying a bimetallic coin, there are threeconductivities to be considered: the inner disk, the outerring and the bond between them. The conductivities of theinner disk and outer ring depend on the metals used and donot change. The conductivity of the bond between the twometals, however, may vary to a large extent. The bond maybe a perfect conductor, if freshly cut metal surfaces arepushed hard together (molecular welding). However, if theinner disk and outer ring are covered in an oxide layerbefore they are joined together, the bond will conduct lesswell. In extreme cases, with a thick oxide layer, the bondwill not conduct at all. In addition, bond conductivity iseven more complex, since it also depends on the voltage ofthe eddy currents induced for the measurement. A largemeasurement voltage will "punch through" the oxide layerand indicate a higher conductivity than a low voltage. Incoin discriminators, the voltages across the bond are smalland these non-linear effects are significant.

As a result, the poorly defined bond conductivity inbimetallic coins causes problems for many existing coin discriminators. With bimetallic coins, the variability ofthe bond causes different readings from coins of the sametype, thereby making a positive identification of the coinall the more difficult. For instance, in the dual transmittercoil arrangement of aforesaid EP-B-0 119 000, thesmall coil is located close to the coin rail (so as tocover also very small monometallic coins), thereby generatingeddy currents in a bimetallic coin, which will crossthe bond and cause great uncertainty as regards theconductivity reading.

GB-A-2 323 200 discloses a coin validator forbimetallic coins. An oval-shaped sensor 16 induces eddycurrents, which are confined to the outer ring of thebimetallic coin. These eddy currents are detected and usedfor measuring the electric conductivity of the outer ring.A separate, smaller coil 14 is used for measuring theconductivity of the central disk of the bimetallic coin.

US-A-5 119 916 discloses a magnetic field sensor fordetecting tokens. A magnetic sensor is used to provide ameasurement of magnetically responsive characteristics,when the token is exposed to a magnetic field generated bya permanent magnet.

Summary of the Invention

It is an object of the present invention to providean improved coin discriminator for identifying bimetalliccoins. Moreover, an object of the invention is to allow thecoin discriminator to be implemented by means of a smallnumber of components.

The above objects are achieved by a coin discriminatingdevice, and a method of identifying a bimetalliccoin according to theattached independent patent claims.

Other objects, features and advantages of the presentinvention are the subject of dependent claims.

Brief Description of the Drawings

The invention will now be described in more detail,reference being made to the accompanying drawing, in which:

Fig. 1 is a schematic perspective view of a coindiscriminator according to one embodiment of the invention,

Fig. 2 is a schematic lateral view of the arrangementin Fig. 1, and

Fig. 3 is a schematic block diagram of a coinprocessing machine according to one aspect of the presentinvention.

Detailed Description

As shown in Figs 1 and 2 the coin discriminatorcomprises alarge coil 10 and asmall coil 20, both ofwhich are mounted to asupport member 80. Thecoils 10, 20are connected to an electrical device (not shown) forsupplying voltage pulses thereto.

Thebimetallic coin 30 comprises aring 40 of a firstmetal or alloy and a disk 50 of a second metal or alloy. Abond between the disk and the ring is labeled 90.

Thecoils 10, 20 act as transmitter coils for exposingthebimetallic coin 30, which is moved past the coindiscriminator along acoin rail 70, to a respectivemagnetic pulse giving rise to eddy currents in theouterring 40 and the inner disk 50 of thecoin 30. Furthermore,thecoils 10, 20 act as receiver coils for detecting themagnetic field variations generated by the eddy currents intheouter ring 40 and inner disk 50 and converting theminto corresponding voltage signals. The voltage signals aresupplied to a detector (not shown), which is arranged tomeasure the decay of the signals and in response determinea respective value of the conductivity of theouter ring 40and inner disk 50. The determined conductivity values aresubsequently used for identifying thecoin 30.

The coin discriminator is arranged to carry out theconductivity measurements when the center of thecoin 30 isaligned with the center of thecoils 10, 20, i.e. when thecoin is located as in Fig. 2. As shown in Fig 2, thesmall coil 20 is mounted relatively high above thecoin rail 70,thereby assuring that the induced eddy currents will flowessentially exclusively in the disk 50 without crossing thebond 90. Conversely, the eddy currents induced by thelargecoil 10 will flow essentially exclusively in thering 40,again without crossing thebond 90. Hence, the eddy currentsinduced within the coin flow in concentric circlesaround the center of the coin, and none of the eddy currentscrosses thebond 90 in the bimetallic coin. Thus, theconductivity measured is independent of the bond.

The duration and waveform of the voltage pulsessupplied by the electrical device to thecoils 10, 20 maybe chosen in accordance with the actual application, as isreadily realized by the skilled person.

For further improved accuracy, the inventive coindiscriminator is provided with amagnetic sensor element60, preferably a Hall element. TheHall element 60 isarranged to measure the magnetic permeability of theouterring 40 and inner disk 50 of thecoin 30. In this way coinswith identical electric properties (e.g. conductivity) butdifferent magnetic properties (e.g. permeability) may bedifferentiated.

Thecoils 10, 20 are driven to generate a respectivemagnetic field, to which theouter ring 40 and inner disk50 are exposed. Depending on the magnetic properties of thering 40 and disk 50, the magnetic fields will be influencedto different extents. The Hall element measures the amplitudeof the magnetic fields produced by the coils. Theamplitude of the magnetic field from thelarge coil 10indicates the permeability of theouter ring 40 of thebimetallic coin 30. Similarly, thesmall coil 20 measuresthe permeability of the inner disk 50. In the preferredembodiment, because two measurements are obtained from theHall element, some form of multiplexing must be used, either frequency division multiplexing or time divisionmultiplexing.

In frequency division multiplexing the large andsmall coils are driven by sine waves of different frequencies.For typical coins, frequencies of 9 kHz and 7 kHzwould be suitable. The output from the Hall element is awaveform containing both frequencies. Using appropriateelectronics, e.g. synchronous detection, the amplitudes ofthe two frequencies can be measured.

In time division multiplexing only one coil is drivenat a time. For example, thesmall coil 20 can first bedriven and the Hall element output measured. Then thelargecoil 10 is driven and the second measurement from the Hallelement is made. Whichever method of multiplexing is used,the results are equivalent.

For the permeability measurement it is not requiredthat the coin is exactly concentric with the coils.

In some applications it may be sufficient to measurethe permeability of only one of the outer ring and thecentral disk of the bimetallic coin.

Referring now to Fig. 3, acoin processing machine100 according to one aspect of the present invention isillustrated. In an exemplifying but not limiting sense, thecoin processing machine 100 of Fig. 3 is selected to be acoin sorter. The mass of coins to be sorted by themachine100 are deposited into acoin inlet 110. The coins are fedby acoin feeder 120, such as a hopper and/or an endlessbelt, to thecoin discriminator 130, which has beendescribed above with reference to Figs. 1 and 2. Thecoindiscriminator 130 is operatively connected to alogicdevice 132 in the form of a CPU, which is operativelyconnected to amemory 134, such as a RAM, ROM, EEPROM orflash memory. Thememory 134 stores a set of coin referencedata, which is used by thelogic device 132 to discriminateamong the coins received through thecoin inlet 110. More specifically, the coin reference data relates to typicalvalues of conductivity and permeability for all differenttypes of coins, that thecoin processing machine 100 iscapable of processing.

Thelogic device 132 is programmed to receivemeasurement data obtained by thecoils 10, 20 and themagnetic sensor element 60, said data relating to theconductivity of theouter ring 40 and the inner disk 50,respectively, as well as the permeability of at least oneof the outer ring and inner disk. Once these measurementdata have been received for acoin 30, thelogic device 132will read the coin reference data stored in thememory 134and search for any matches. If both the conductivity andthe permeability measured by thecoin discriminator 130correspond to one specific coin type defined by the coinreference data, then the type ofcoin 130 has beenpositively identified. Otherwise, thecoin 30 is of anunknown type, which is handled by acoin reject device 140,which preferably will deliver the coin through an externalopening in themachine 100, so that the coin may be removedby a user.

The coin types defined by the coin reference data inthememory 134 may preferably relate to the denomination ofeach different coin type, which is to be handled by thecoin processing machine 100.

Once the type or identity of thecoin 30 has beendetermined by thecoin discriminator 130 and thelogicdevice 132, thecoin 30 is passed to acoin sorter 150,which uses the identified coin type to sort thecoin 30into one specific coin box, etc., in acoin storage 160.The coin boxes, etc., in thecoin storage 160 arepreferably externally accessible for the user of themachine 100.

The invention has been described above with referenceto a few embodiment examples. However, embodiments other than the ones described above are possible within the scopeof the invention, as defined by the appended independentpatent claims.

Claims (12)

1. A coin discriminating device, comprising: firstand second coils (10, 20) positioned to induceeddy currents in an outer ring (40) and an inner disk (50),respectively, of a bimetallic coin (30); a storage device(134) adapted to store coin reference data; and a logicdevice (132) adapted to determine an identity of the coinby comparing said coin reference data to data obtained fromdetected eddy currents and related to the conductivityof the coin,characterized in that
      said first and second coils (10, 20) are positioned todetect said eddy currents in said outer ring (40) and innerdisk (50), respectively, and
      a magnetic sensor (60) is coupled to the logic device(132) and positioned to detect a magnetic field generatedby at least one of the first and second coils (10, 20),when the coin (30) is positioned between the first andsecond coils and the magnetic sensor, wherein the logicdevice (132) is adapted to use data obtained by themagnetic sensor and related to the permeability of the coinwhen determining the identity of the coin (30).
2. A coin discriminating device according to claim 1,wherein the magnetic sensor (60) is a Hall element.
3. A coin discriminating device according to anypreceding claim, wherein the magnetic sensor (60) ispositioned to detect a respective magnetic field generatedby the first coil (10) as well as the second coil (20).
4. A coin discriminating device according to anypreceding claim, wherein the second coil (20) is positionedinside the first coil (10).
5. A method of identifying a bimetallic coin (30)having an outer ring (40) and an inner disk (50) by generatingeddy currents, by means of first and second coils(10, 20), essentially exclusively in the outer ring and theinner disk, respectively, measuring the eddy currents thusinduced so as to determine the electric conductivity of theouter ring and the inner disk, respectively, and using theelectric conductivity of the outer ring and the inner disk,respectively, for identifying the coin (30),characterizedby the further steps of
      exposing the coin (30) to a magnetic field generatedby at least one of said first and second coils (10, 20)when the coin (30) is positioned between said first andsecond coils and a magnetic sensor (60),
      using said magnetic field to measure thepermeability of at least one of the outer ring (40) andinner disk (50), and
      using the permeability when identifying the coin(30).
6. A method according to claim 5, wherein the outerring (40) is exposed to a first magnetic field and theinner disk (50) is exposed to a second magnetic field.
7. A method according to claim 6, wherein eachmagnetic field varies periodically in amplitude.
8. A method according to claim 7, wherein eachmagnetic field varies as a sinewave.
9. A method according to any of claims 7-8, whereinthe steps of exposing, measuring and using are executed ata first frequency of the first magnetic field for the outerring (40) and at a second frequency of the second magneticfield for the inner disk (50).
10. A method according to claim 9, wherein said firstfrequency is 9 kHz.
11. A method according to claim 9 or 10, wherein saidsecond frequency is 7 kHz.
12. A coin processing machine comprising a coin inlet(110), a coin feeder (120), a coin discriminator (130)according to any of claims 1-4 and a coin processor (150),the coin discriminator being coupled to the coin processorand being adapted to determine a type, identity ordenomination of respective coins (30) received from thecoin feeder, and being adapted to supply the determinedtype, identity or denomination to the coin processor.

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