Discriminator for bimetallic coins

(54)

PATENT HOLDER Scan Coin Industries AB, Jägershillgatan 26 213 75 Malmö SE

INVENTOR'S OFFICE

NAME

Geoffrey Howells, Near Salisbury GB Ström & Gulliksson AB (56) (57)

Apparatus and method for authentication of bimetallic coins

CALLED PUBLICATIONS: - - SUMMARY:

A coin discriminator has a coin path (3) along which a coin (5) consisting of a first and a second portion (13a, 13b) of various metals and / or metal alloys is arranged to pass; a coil means (1a, 1b) located near the coin path; an electrical means (7) for supplying time-varying drive signals to the coil means; and a detecting means (9) for detecting eddy currents induced in the coin by the coil means. The coil means (1a, 1b) are arranged to induce in the coin (5) an eddy current loop (27) which crosses in a predetermined area (25) of the coin a transition (11) between the first and second parts (13a, 13b) of the coin .

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The numbers in brackets indicate international identification code, INID code. Letter Within the pinch indicates international document code.

512 200

Technical area

The present invention relates to a coin discriminator, comprising: a coin path along which a coin may pass containing a first and a second portion consisting of various metals and / or metal alloys; coil means located near the coin path; electrical means for delivering varying drive signals to the coil means over time; and detecting means for detecting eddy currents induced in the coin by the coil means. The present invention further relates to a method of measuring conductivity in a transition between the first and second portions of such a coin.

The prior art

Coin discriminators, which are designed to measure for a coin its electrical properties, such as resistance and conductivity, by subjecting the coin to a magnetic pulse and detecting the decay of eddy currents induced in the coin are well known in the art. Such coin discriminators are used in many different coin handling machines, such as coin counting machines, coin sorting machines, devices for checking the authenticity of coins in vending and gaming machines, etc. Prior art coin handling devices are disclosed, for example, in WO 97/07485 and WO 87/07742.

The manner in which such coin discriminators operate is described in, for example, GB-A-2 135 095, wherein a coin test arrangement comprises a transmitter coil driven by a rectangular voltage pulse to generate a magnetic pulse induced in a passing coin. 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 can be its own coil or

512 200 may alternatively comprise the transmitter coil, if it has two working modes. By monitoring the decay of the eddy currents induced in the coin, a value representing the conductivity of the coin can be obtained, since the decay rate is a function of the conductivity.

Previously known coin discriminators often utilize a small coil having a diameter smaller than the coin diameter. The coil induces and detects eddy currents at any point on the coin (the part of the coin, which is in fact subjected to the conductivity measurement described above, will vary depending on the coin's orientation, velocity, angle, etc. relative to the coil). This methodology is sufficient for a normally homogeneous coin consisting of a single metal or metal alloy.

Recently, however, bimetallic coins have been introduced on the market in different countries. A well-known example of a bimetallic coin is the French 10-franc coin. Furthermore, some of the euro coins, which are planned to be issued in the European Community in the near future, are planned to be bimetallic.

Bimetallic coins are manufactured as follows. Outer rings and central discs are punched out from sheets (also known as raw materials) consisting of the two metals or metal alloys from which the bimetal coin is to be made. The disc is then placed inside the ring, and the coin is embossed. Embossing means that the coin is pressed between two hardened coins. The embossing creates the front and back pattern of the coin and also forces the disc together with the ring. The connection between the disc and the ring is called a transition.

If the wafer and ring are clean and oxide free, the transition between the metals will exhibit near zero electrical resistance. Ideally, the resistance of the metals or alloys is much greater than the resistance over the transition. However, if the ring or disc is covered by an oxide layer prior to embossing, the resistance of

512 200 transition to be greater than the resistance of the metals or alloys. Thus, by controlling the handling and storage conditions of the plates between punching and embossing, it is possible to control the transition resistance (or alternatively the conductivity, which is substantially equal to the inverse of the resistance) of the finished bimetallic coin.

In this way, being able to control the resistance of the transition can be particularly desirable as a counterfeit preventive measure. During production, coins with too low or high resistance will not be issued. Making such controlled production practically feasible would require a method for repeated measurement of the transient resistance of large coin volumes.

The previously described coin discriminators described above are unable to achieve a sufficiently accurate determination of the transition resistance or conductivity, since the measurement results would vary widely depending on the actual measurement point of the coin. In other words, if the conductivity of a particular coin were to be measured at a point on the ring, the measurement results would differ from such results as would have been obtained if the measurement had taken place on the plate. If the measurement point were to comprise part of the transition between the ring and the disc, a different measurement result would be obtained. A coin discriminator according to the prior art is stated in the preamble of claim 1.

Summary of the Invention

It is therefore an object of the present invention to allow repeated and accurate determination of the transition conductivity or resistance of a coin comprising a first and a second portion consisting of various metals or metal alloys, such as, for example, a bimetallic coin.

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This object is achieved for a coin discriminator, comprising: a coin path along which a coin is arranged to pass; flushing means located near the coin path; electrical means for supplying time-varying drive signals to the coil means; and detecting means for detecting eddy currents induced in the coin by the coil means by arranging the coil means so that a eddy current loop is induced in the coin in such a way that the loop crosses the transition between the first and second portions of the coin.

The above object is further achieved by a method for measuring the conductivity at the transition between the first and second parts of the coin, the coin being exposed to a magnetic field of coil means outside the coin and wherein in the coin 15 induced currents are detected by detection means outside the coin, where the magnetic field is applied. means that a eddy current loop crosses the transition in a predetermined area of ​​the coin.

The solutions described above are defined by the appended independent claims. Preferred embodiments of the invention are subject to subclaims.

Brief description of the drawings

The invention will now be described in more detail with reference to the accompanying drawings, in which:

Fig. 1 is a schematic sectional view of a coin discriminator according to a preferred embodiment of the invention;

FIG. 2 is a schematic top view of the arrangement of FIG

FIG. 1 as well

FIG. 3 is a schematic illustration of a bimetallic coin and eddy currents generated therefrom by the coin discriminator of FIGS. 1 and 2.

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Detailed description

As can be seen in FIG. 1, the coin discriminator comprises a coil means in the form of two coil portions 1a and 1b which are connected to an electrical means 7 for supplying voltage pulses thereto. The coin discriminator further comprises a detecting means 9 for detecting eddy currents induced in the coin by the magnetic pulses generated by the coil means upon receiving the voltage pulses from the electrical means 7. The coil means 1a, 1b act as a transmitter coil to expose a bimetallic coin 5 which is moved past the coin discriminator along a 1 mm thick ceramic plate 3 in an arrow-indicated direction, for a magnetic pulse which produces eddy currents in the coin 5, and in addition For example, the coil means acts as a receiver coil for detecting the magnetic field variations generated by the eddy currents in the coin and converting them to a corresponding voltage signal.

As shown in FIG. 3, the coin 5 comprises a ring 13a of a first metal or alloy and a disc 13b of a second metal or alloy. A transition between the disc 13b and the ring 13a is indicated by 11. The detecting means 9 is arranged to measure the decay of these eddy currents and, as a result, to produce a value of the transition conductivity or resistance. As will be described below, the coin discriminator is arranged to conduct the conductivity measurements when the center of the coin 5 coincides with a center plane 21 of the coin discriminator.

As shown in FIG. 2, the coil member 1a, 1b comprises a first and a second coil frame 17a, 17b, which are provided with a first and second winding 15a, 15b, respectively. The coil frames 17a, 17b are essentially semi-circular in cross-sectional shape and are symmetrically arranged on either side of the coil.

512 200 center plane 21. The distance between the coil frames 17a and 17b is about 5-10 mm, and the radius of each semicircular part is about 10-20 mm. An electrical conductor is wound on the coil with equal number of turns on each coil frame 17a, 17b.

For example, a polyurethane-coated copper wire with an inner diameter of 0.2 mm and an outer diameter of about 0.25 mm can be used for the electrical conductor forming the windings 15a, 15b of the coil frames 17a, 17b. Each winding preferably contains 10-100 turns, and further 10 one of the windings 15a is wound clockwise, while the other winding 15b is wound counterclockwise, for the reasons set forth below.

The adjacent portions 19a and 19b of the two halves 1a, 1b of the coil contain wire windings which run substantially parallel to each other and are symmetrically arranged with respect to the coil plane 21. Since the coils 15a, 15b are formed by a single continuous conductor, common electric current to flow through the entire windings 15a, 15b as they are supplied by a voltage pulse from the electrical means 7.

As a result, a pulsed magnetic field will be generated around the windings 15a, 15b. In the central part of the coil, i.e. around the adjacent portions 19a, 19b and the center plane 21, the current will flow in the same direction in both windings 15a, 15b and will therefore cooperate in the generation of a magnetic field.

The transition conductivity is measured when the coin is in the center of the coil, as shown in FIG. 1, i.e. when the diameter 23 (see FIG. 3) of the coin 5 coincides with the center plane 21 of the coil 1a, 1b. The duration of the voltage pulses supplied from the electrical means 7 to the coil 1a, 1b can be selected according to current application; however, a duration of 10-100 microseconds seems appropriate for most situations.

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Thanks to the above arrangement, an eddy current loop 27 in the coin 5 is generated along a path approximately similar to the wire pattern of the two coils 15a, 15b (i.e., the symmetrical, double semicircular shape), which is schematically illustrated in FIG. 3. The exact appearance of one in a coin generated eddy current loop is a complex issue, which is difficult to model mathematically. However, experiments have indicated that the eddy current loop has a flow which is approximately consistent with that described below.

The coil shown in FIGS. 1 and 2 is intended to be used for coins with a diameter less than the diameter of coil 1a, 1b. As a result, the eddy current loop 27 produced in the coin 5 will have the shape shown in FIG. In the central portion 25 of the coin 5, i.e. in a region adjacent to the diameter 23 of the coin, the eddy current loop 27 (or, in fact, the two eddy current loops 27) will run parallel to the diameter 23 from a point on one side of the coin to a point of opposite side of the coin. When the eddy current loop 27 reaches the circumference of the coin 5, the eddy current is forced to flow around the coin surface and finally return to the first side of the coin. As a result, the eddy current loop 27 will cross the junction 11 between the ring 13a and the disc 13b of the coin 5 twice on its way from the first side of the coin to the opposite side, i.e. along the diameter 23 of the coin 5, since the measurements take place when the coin 5 is opposite the coil 1a, 1b, the detection of the eddy current loop 27 must therefore comprise the transition 11, unlike previously known methods, which are unsuccessful in this regard.

By using a coin discriminator according to the present invention, it is possible to reduce the risk of fraud, since the coin discriminator can be used in the manufacture of coins to sort out such coins, the transition of which appears to have a resistance or

512 200 conductivity, which falls outside predetermined limits.

The coin discriminator is preferably operatively connected to storage means not shown in the drawing with the task of storing predetermined maximum and minimum values ​​for the transition conductivity or resistance of the current coin type. After measuring the conductivity or resistance of the coin, the output of the detection means 9 is compared to the predetermined limits to determine whether the transient conductivity or resistance is within an acceptable range, the coin being allowed to be issued, or whether the measured value is not within the acceptable range. the area, preventing the coin from being issued.

In an alternative embodiment, the above-described coin discriminator can be used to determine the authenticity of bimetallic coins already on the market by determining their transition conductivity or resistance and comparing a detected value with predetermined limits.

The invention has been described above with reference to a few embodiments. However, embodiments other than those described above are possible within the scope of the invention, as defined by the appended independent claims. For example, the coil means may be driven by electrical signals other than voltage pulses, such as sine waves or square waves. In order to generate desired eddy currents in the coin, variable electrical drive signals of more or less arbitrary type can be used over time, as will be readily apparent to those skilled in the art.

The coil means may further comprise more than two coil frames and windings. For example, the coil means may be formed of four frames and windings, which are advantageously arranged symmetrically around some / some coil center planes.

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