BIMETALLIC COIN DISCRIMINATING DEVICE AND METHOD

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: BIMETALLIC COIN DISCRIMINATING DEVICE AND METHOD Technical Field The present invention relates to a coin discriminating device of the type having first and second coils positioned to induce and detect eddy currents in an outer ring and an inner disk, respectively, of a bimetallic coin, where 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. The present invention also relates to a method of identifying a bimetallic coin, and to a coin processing machine including a coin discriminating device of the above type. Description of the Prior Art Coin discriminators, which are arranged to measure the electric characteristics, e.g. the resistance or conductivity, of a coin by exposing it to a magnetic pulse and detecting the decay of eddy currents induced in the coin, are generally known in the technical field. Such coin dis- criminators are 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 instance disclosed in WO 97/07485 and WO 87/07742. The way in which such coin discriminators operate is described in e.g. EP-B-0 119 000, in which a coin testing arrangement comprises a transmitter coil, which is pulsed with a rectangular voltage pulse so as to generate a magnetic pulse, which is induced in a coin when being moved past the transmitter coil along a coin rail. The eddy currents thus 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 alternatively be constituted by the transmitter coil having two operating modes. By monitoring the decay of the eddy cur- rents induced in the coin, a value or reading representative of the coin conductivity may be obtained, since the rate of decay is a function thereof. One embodiment of EP-B-0 119 000 uses two transmitter coils with different effective cross-sectional areas. The large 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 effective cross-sectional area thereof is covered by the smallest coin when passing along the coin rail. The purpose of the small coil is to solve a problem that can occur if only a large coil was used. The readings from the large coil are a function of the conductivity and diameter of the coin. A large diameter and a high conductivity both produce large coin readings. Hence, there is a problem in that coins of different diameter and conductivity can produce identical readings. For example, a British 2p copper coin and an aluminium token of 2 mm smaller diameter produce identical readings from the large coil. The small coil produces a signal that depends on the conductivity, but is independent of diameter. Thus, aluminium and copper may be differentiated by the small coil. The small coil cannot be used alone, because coins of the same material but different diameter give the same readings . Another prior art coin discriminator is disclosed in EP-B-0 300 781. While the above coin discriminators often are sufficient for traditional, homogeneous coins made of a single metal or metal alloy, the above prior art discriminators are less useful for successfully discriminating also among bimetallic coins, as will be briefly addressed below. In recent years, bimetallic coins have been issued on the market in different countries. Well known examples of bimetallic coins are the French 10F, the British £2, the Canadian $2 and the 1 and 2 Euro coins. Bimetallic coins are made as follows. Outer rings and central disks are punched from sheets (also known as blanks) of the two metal or metal alloys, of which the bi- metallic coin is to be made. The disk is then fitted into the ring, and the coin is minted. Minting consists of pressing the coin between two hardened dies. The dies stamp the head and tail pattern onto the coin and also force the disk and ring together. The joint between the disk and ring is called a bond. When identifying a bimetallic coin, there are three conductivities to be considered: the inner disk, the outer ring and the bond between them. The conductivities of the inner disk and outer ring depend on the metals used and do not change. The conductivity of the bond between the two metals, however, may vary to a large extent. The bond may be a perfect conductor, if freshly cut metal surfaces are pushed hard together (molecular welding) . However, if the inner disk and outer ring are covered in an oxide layer before they are joined together, the bond will conduct less well. In extreme cases, with a thick oxide layer, the bond will not conduct at all. In addition, bond conductivity is even more complex, since it also depends on the voltage of the eddy currents induced for the measurement. A large measurement voltage will "punch through" the oxide layer and indicate a higher conductivity than a low voltage. In coin discriminators, the voltages across the bond are small and these non-linear effects are significant. As a result, the poorly defined bond conductivity in bimetallic coins causes problems for many existing coin discriminators. With bimetallic coins, the variability of the bond causes different readings from coins of the same type, thereby making a positive identification of the coin all the more difficult. For instance, in the dual trans- mitter coil arrangement of aforesaid EP-B-0 119 000, the small coil is located close to the coin rail (so as to cover also very small monometallic coins) , thereby generating eddy currents in a bimetallic coin, which will cross the bond and cause great uncertainty as regards the conductivity reading. GB-A-2 323 200 discloses a coin validator for bimetallic coins. An oval-shaped sensor 16 induces eddy currents, which are confined to the outer ring of the bimetallic coin. These eddy currents are detected and used for measuring the electric conductivity of the outer ring. A separate, smaller coil 14 is used for measuring the conductivity of the central disk of the bimetallic coin. Summary of the Invention It is an object of the present invention to provide an improved coin discriminator for identifying bimetallic coins. Moreover, an object of the invention is to allow the coin discriminator to be implemented by means of a small number of components. The above objects are achieved by a coin discriminating device, a method of identifying a bimetallic coin and a coin processing machine according to the attached independent patent claims . Other objects, features and advantages of the present invention 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 coin discriminator according to one embodiment of the invention, Fig. 2 is a schematic lateral view of the arrangement in Fig. 1, and Fig. 3 is a schematic block diagram of a coin processing machine according to one aspect of the present invention. Detailed Description As shown in Figs 1 and 2 the coin discriminator comprises a large coil 10 and a small coil 20, both of which are mounted to a support member 80. The coils 10, 20 are connected to an electrical device (not shown) for supplying voltage pulses thereto. The bimetallic coin 30 comprises a ring 40 of a first metal or alloy and a disk 50 of a second metal or alloy. A bond between the disk and the ring is labeled 90. The coils 10, 20 act as transmitter coils for exposing the bimetallic coin 30, which is moved past the coin discriminator along a coin rail 70, to a respective magnetic pulse giving rise to eddy currents in the outer ring 40 and the inner disk 50 of the coin 30. Furthermore, the coils 10, 20 act as receiver coils for detecting the magnetic field variations generated by the eddy currents in the outer ring 40 and inner disk 50 and converting them into corresponding voltage signals. The voltage signals are supplied to a detector (not shown) , which is arranged to measure the decay of the signals and in response determine a respective value of the conductivity of the outer ring 40 and inner disk 50. The determined conductivity values are subsequently used for identifying the coin 30. The coin discriminator is arranged to carry out the conductivity measurements when the center of the coin 30 is aligned with the center of the coils 10, 20, i.e. when the coin is located as in Fig. 2. As shown in Fig 2, the small coil 20 is mounted relatively high above the coin rail 70, thereby assuring that the induced eddy currents will flow essentially exclusively in the disk 50 without crossing the bond 90. Conversely, the eddy currents induced by the large coil 10 will flow essentially exclusively in the ring 40, again without crossing the bond 90. Hence, the eddy currents induced within the coin flow in concentric circles around the center of the coin, and none of the eddy currents crosses the bond 90 in the bimetallic coin. Thus, the conductivity measured is independent of the bond. The duration and waveform of the voltage pulses supplied by the electrical device to the coils 10, 20 may be chosen in accordance with the actual application, as is readily realized by the skilled person. For further improved accuracy, the inventive coin discriminator is provided with a magnetic sensor element 60, preferably a Hall element. The Hall element 60 is arranged to measure the magnetic permeability of the outer ring 40 and inner disk 50 of the coin 30. In this way coins with identical electric properties (e.g. conductivity) but different magnetic properties (e.g. permeability) may be differentiated . The coils 10, 20 are driven to generate a respective magnetic field, to which the outer ring 40 and inner disk 50 are exposed. Depending on the magnetic properties of the ring 40 and disk 50, the magnetic fields will be influenced to different extents. The Hall element measures the amplitude of the magnetic fields produced by the coils. The amplitude of the magnetic field from the large coil 10 indicates the permeability of the outer ring 40 of the bimetallic coin 30. Similarly, the small coil 20 measures the permeability of the inner disk 50. In the preferred embodiment, because two measurements are obtained from the Hall element, some form of multiplexing must be used, either frequency division multiplexing or time division multiplexing . In frequency division multiplexing the large and small coils are driven by sine waves of different frequen- cies. For typical coins, frequencies of 9 kHz and 7 kHz would be suitable. The output from the Hall element is a waveform containing both frequencies . Using appropriate electronics, e.g. synchronous detection, the amplitudes of the two frequencies can be measured. In time division multiplexing only one coil is driven at a time. For example, the small coil 20 can first be driven and the Hall element output measured. Then the large coil 10 is driven and the second measurement from the Hall element is made. Whichever method of multiplexing is used, the results are equivalent. For the permeability measurement it is not required that the coin is exactly concentric with the coils. In some applications it may be sufficient to measure the permeability of only one of the outer ring and the central disk of the bimetallic coin. Referring now to Fig. 3, a coin processing machine 100 according to one aspect of the present invention is illustrated. In an exemplifying but not limiting sense, the coin processing machine 100 of Fig. 3 is selected to be a coin sorter. The mass of coins to be sorted by the machine 100 are deposited into a coin inlet 110. The coins are fed by a coin feeder 120, such as a hopper and/or an endless belt, to the coin discriminator 130, which has been described above with reference to Figs. 1 and 2. The coin discriminator 130 is operatively connected to a logic device 132 in the form of a CPU, which is operatively connected to a memory 134, such as a RAM, ROM, EEPROM or flash memory. The memory 134 stores a set of coin reference data, which is used by the logic device 132 to discriminate among the coins received through the coin inlet 110. More specifically, the coin reference data relates to typical values of conductivity and permeability for all different types of coins, that the coin processing machine 100 is capable of processing. The logic device 132 is programmed to receive measurement data obtained by the coils 10, 20 and the magnetic sensor element 60, said data relating to the conductivity of the outer ring 40 and the inner disk 50, respectively, as well as the permeability of at least one of the outer ring and inner disk. Once these measurement data have been received for a coin 30, the logic device 132 will read the coin reference data stored in the memory 134 and search for any matches. If both the conductivity and the permeability measured by the coin discriminator 130 correspond to one specific coin type defined by the coin reference data, then the type of coin 130 has been positively identified. Otherwise, the coin 30 is of an unknown type, which is handled by a coin reject device 140, which preferably will deliver the coin through an external opening in the machine 100, so that the coin may be removed by a user. The coin types defined by the coin reference data in the memory 134 may preferably relate to the denomination of each different coin type, which is to be handled by the coin processing machine 100. Once the type or identity of the coin 30 has been determined by the coin discriminator 130 and the logic device 132, the coin 30 is passed to a coin sorter 150, which uses the identified coin type to sort the coin 30 into one specific coin box, etc., in a coin storage 160. The coin boxes, etc., in the coin storage 160 are preferably externally accessible for the user of the machine 100. The invention has been described above with reference to a few embodiment examples. However, embodiments other than the ones described above are possible within the scope of the invention, as defined by the appended independent patent claims.

Claims: CLAIMS 1. A coin discriminating device, comprising: 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 (134) adapted to store coin reference data; and a logic device (132) adapted to determine an identity of the coin by comparing said coin reference data to data obtained from the detected eddy currents and related to the conductivity of the coin, characterized by a magnetic sensor (60) coupled to the logic device (132) and 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 between the first and second coils and the magnetic sensor, wherein the logic device (132) is adapted to use data obtained by the magnetic sensor and related to the permeability of the coin when 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 any preceding claim, wherein the magnetic sensor (60) is positioned to detect a respective magnetic field generated by the first coil (10) as well as the second coil (20) . 4. A coin discriminating device according to any preceding claim, wherein the second coil (20) is positioned inside the first coil (10) . 5. A method of identifying a bimetallic coin (30) having an outer ring (40) and an inner disk (50) by gene- rating eddy currents essentially exclusively in the outer ring and the inner disk, respectively, measuring the eddy currents thus induced so as to determine the electric conductivity of the outer ring and the inner risk, respectively, and using the electric conductivity of the outer ring and the inner disk, respectively, for identifying the coin (30) , characterized by the further steps of exposing the coin (30) to a magnetic field, measuring the permeability of at least one of the outer ring (40) and inner disk (50) , and using the permeability when identifying the coin (30) . 6. A method according to claim 5, wherein the outer ring (40) is exposed to a first magnetic field and the inner disk (50) is exposed to a second magnetic field. 7. A method according to claim 5 or 6 , wherein the or each magnetic field varies in amplitude. 8. A method according to any of claims 5-7, wherein the or each magnetic field varies as a sinewave. 9. A method according to any of claims 7-8, wherein the steps of exposing, measuring and using are executed at a first frequency of the first magnetic field for the outer ring (40) and at a second frequency of the second magnetic field for the inner disk (50) . 10. A method according to claim 9, wherein said first frequency is about 9 kHz. 11. A method according to claim 9 or 10, wherein said second frequency is about 7 kHz. 12. A coin processing machine comprising a coin inlet (110) , a coin feeder (120) , a coin discriminator (130) and a coin processor (150) , the coin discriminator being coupled to the coin processor and being adapted to deter- mine a type, identity or denomination of respective coins (30) received from the coin feeder, and being adapted to supply the determined type, identity or denomination to the coin processor, characterized in that the coin discriminator (130) comprises: 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 magnetic sensor (60) 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 between the first and second coils and the magnetic sensor; a storage device (134) adapted to store coin reference data; and a logic device (132) adapted to determine an identity of the coin by comparing said coin reference data to data obtained from the detected eddy currents and related to the conductivity of the coin, as well as data obtained by the magnetic sensor and related to the permeability of the coin.

Inventors: HOWELLS GEOFFREY, HOWELLS, GEOFFREY
Applicants: HOWELLS GEOFFREY, SCAN COIN IND AB, HOWELLS, GEOFFREY, SCAN COIN INDUSTRIES AB
Application year: 1999
Main classification: G07D5
IPC codes: G07D5, G07D9