EP2040227A2 - Method for inspecting coins - Google Patents

Abstract

The method involves generating a periodic transmitting signal, which contains harmonics. The amplitude of the attenuation function is determined from the receiving signals of a receiving coil at three different measuring points recurring segments of the transmitting signal during a given measuring signal. Four measuring cycles chronologically pass through. The measuring value or attenuation function is composed from one of the measuring cycles which are in relation to each other and are compared to given reference values.

Description

The invention relates to a method for testing coins according to claim 1.

More particularly, the invention relates to a method of testing coins by the inductive measuring method. Generally, this method relies on directing a magnetic signal from a transmitting coil onto a coin running along a track and receiving a receiving coil receiving the resulting signal. Depending on the material composition of the coin, a more or less pronounced attenuation of the transmission signal takes place. It is also well known to arrange the receiving coil both on the same side as the transmitting coil ( DE 10 2004 013 286 B4 ) as well as on the opposite side ( DE 689 21 608 T2 ). Out DE 10 2004 013 286 B4 It is also known to arrange a single receiving coil on a single ferrite core and the receiving coil in a coaxial annular recess of the ferrite core to be arranged on the coin track facing end face, the design of the transmitting and receiving coil is selected so that the receiving coil is flooded by a substantially homogeneous magnetic field of the transmitting coil. By means of such an arrangement, coins of sufficiently high resolution can be tested across the thickness of the coin without the spacing variations of the coin being particularly detrimental.

For a last-described arrangement is off DE 198 36 490 C2 known to provide a secondary coil in addition to the transmitting coil, which is coupled to the transmitting coil. The signal of the secondary coil is applied to the second input of a differential amplifier, to which the transmission signal passes. The signal of the secondary coil is switched so that the signal of the secondary coil coincides with the transmission signal. The induced in the secondary coil voltage acts as a negative feedback signal and causes the voltage induced in the primary coil is equal to the voltage with which the primary coil is driven (transmission signal). At idle, therefore, the receiving coil is penetrated by the same magnetic flux as the primary coil, whereby also in this coil, the induced voltage has the same waveform as in the transmitting coil. However, such a circuit arrangement is also suitable for an inductive measuring arrangement, are arranged in the transmitting and receiving coil on different sides of the coin path. In this case, one speaks of a transmissive measurement, while the measurement is referred to only on one side of the coin path as a reflective measurement.

The generation of a suitable transmission signal, as in DE 198 36 490 C2 is above all important for a so-called multi-frequency measurement, as in EP 0 886 247 B1 is described. In this measuring method, a periodically recurring portion of the transmission signal in a Number of switching steps divided. From the values of the received signal of the receiving coil, envelopes are formed at the respective switching steps repeating the frequency of the transmission signal. An evaluation device forms from the number of concurrently generated envelopes at least one criterion for generating the acceptance or return signal. In this measurement method, it is assumed that attenuation curves which generate a coin during the passage of the measuring device are significantly frequency-dependent. At low frequencies, the penetration depth is much greater than at high frequencies. At very high frequencies, a so-called skin effect is known to be produced in which the penetration depth is close to zero. In the known measuring method, one makes use of the property of, for example, a square wave signal consisting of a plurality of harmonics. In the section of the rectangular signal near its rising edge, the signal shape of the receiving coil is essentially determined by the high frequency components.

As the number of switching steps increases, predominantly the lower frequency components determine the signal shape.

From the above-mentioned DE 689 21 608 T2 It is also known to choose on both sides of a coil arrangement in which two coils are arranged on a common core on each side. A first transmit coil generates a signal received by the receive coils on both sides of the coin path. Subsequently, the second transmitter coil on the other side of the coin path generates a signal which in turn is received by both receiver coils.

The invention has for its object to provide a method for checking coins, which allows a particularly good discrimination of different coin designs of counterfeit coins.

This object is solved by the features of patent claim 1.

The inventive method is based on a specific Meßspulenanordnung. On each side of the track a transmitting and a receiving coil is arranged on a ferrite core. The diameter of the receiving coil, which is closer to the track than the transmitting coil, is smaller than that of the transmitting coil, for example in the ratio of 1 to 2. The diameter of the transmitting coil is smaller than the diameter of the smallest coin to be accepted. On the ferrite core, coupled to the transmitting coil, a secondary coil is arranged, whose signal is fed back as a negative feedback signal to the transmitting coil. This is to ensure that a constant transmission signal can be given to the transmission coil. This method is, as already explained above, from the DE 198 36 490 C2 known. This document is expressly incorporated by reference. The arrangement of transmitting and receiving coil can be provided, for example, in the manner as in the already mentioned DE 10 2004 013 286 B4 is described.

The generation of transmission and processing of received signals is similar as in EP 0 886 247 B1 described. A transmit signal containing harmonics is generated periodically. This is for example a rectangle or triangle signal. During a predetermined measuring interval of periodically recurring sections of the transmission signal, the amplitudes of the damping function are determined from the input signals of the respective receiver coil at at least three chronologically different measuring times.

In chronological succession, at least four measuring cycles are run through. On each side of the track, a reflection measurement is carried out in each case with the transmitting and receiving coil. In this case, the transmission coils are controlled on each side, and the reception signals of the receiving coils are evaluated on each side. In addition, two transmission measurements are carried out, wherein the transmitting coil of the respective opposite receiving coil is evaluated with their signals. The peculiarity is that in one case the receiving coil is formed by a transmitting coil. The order of the reflection and transmission measurements can be chosen arbitrarily. The measured values from the four measuring cycles are related to each other and / or compared with predetermined reference values.

In the method according to the invention, since the receiving coils (with the exception of the case in which a transmitting coil is used as the receiving coil) have clearly different diameters compared to the transmitting coils, it is possible, for example. Evaluate at the same time and independently determined waveforms in the ring-shaped Bicolor coins as distinguishing criterion. The waveforms vary according to the differences in the electrical and magnetic properties of the ring and core materials.

In the event that a transmitting coil is used as a receiving coil, at the maximum attenuation compared to the otherwise used receiving coils, a waveform is obtained which is better suited for determining the centric position of the coin in the coil assembly.

The method according to the invention is not only suitable for distinguishing counterfeit coins from genuine ones, but also for classifying the inserted coin values.

According to a preferred embodiment of the invention, the coins are moved into abutment against a wall of the track, and in the transmission measurement, the coil arrangement associated with the wall forms the receiving side.

According to a further embodiment of the invention, a normalization of the measured values of the four cycles is carried out before the evaluation of the measurement results. A normalization can take place, for example, by shifting a quiescent level of the received signals to a standard level (one-point standardization). The quiescent level is known to be the state where no coin is in the measuring arrangement. The standard level is an arbitrary level.

Another standardization can be carried out by shifting a first measured value of the respective cycle to a zero point. After determining the facing measured values or measured value curves, a better evaluation can take place in that the standardized measured values or measured value functions are spread.

It is known, for example, to provide for the diameter measurement two further offset in the path of the coins probes, which determine from the entry and exit signals for a coin and their speed the diameter of the coins. According to the invention, a sensor arranged in front of the inductive measuring arrangement can initiate the starting signal for the inductive measurement. With the help of this and / or another sensor is also possible to determine the relative position of a coin to the inductive measuring device, for example, to be able to better measure edge regions of a coin. With pronounced extreme values of the damping curves, it can also be readily ascertained that when a coin is centered to the measuring device. This serves, for example, to test the core material of a bicoloured coin.

Fig. 1

zeigt schematisch eine Spulenanordnung zur Durchführung des erfindungsgemäßen Verfahrens.

Fig. 2

zeigt schematisch eine der beiden Spulenanordnungen nach Fig. 1.

Fig. 3

zeigt die Schaltungsanordnung der Spulenanordnung nach Fig. 2.

Fig. 4

zeigt die Anordnung einer induktiven Meßanordnung zur Durchführung des erfindungsgemäßen Verfahrens und drei weitere Meßsonden bzw. Sensoren.

Fig. 5

zeigt eine konstruktiv detailliertere induktive Meßanordnung nach Fig. 1.

Fig. 6

zeigt jeweils drei Dämpfungskurven von drei Meßzyklen einer induktiven Meßanordnung nach Fig. 1 bzw. 5.

Fig. 7

zeigt verschiedene Tabellen und Kurven für eine Einpunkt-Normierung der Meßergebnisse.

Fig. 8

zeigt verschiedene Tabellen und Kurven für eine Zweipunkt-Normierung der Meßergebnisse des erfindungsgemäßen Verfahrens.

The invention will be explained in more detail with reference to drawings.

Fig. 1

schematically shows a coil assembly for carrying out the method according to the invention.

Fig. 2

schematically shows one of the two coil arrangements after Fig. 1 ,

Fig. 3

shows the circuit arrangement of the coil assembly after Fig. 2 ,

Fig. 4

shows the arrangement of an inductive measuring arrangement for carrying out the method according to the invention and three further measuring probes or sensors.

Fig. 5

shows a structurally more detailed inductive measuring device after Fig. 1 ,

Fig. 6

shows in each case three attenuation curves of three measuring cycles of an inductive measuring arrangement Fig. 1 or 5.

Fig. 7

shows different tables and curves for a one-point normalization of the measurement results.

Fig. 8

shows various tables and curves for a two-point normalization of the measurement results of the method according to the invention.

In FIG. 1 a coin channel 10 is shown with a first wall 12 and a second wall 14. An inclined bottom 16 of the coin channel 10 ensures that a coin 18 is guided along the wall 12. On the coin-engaging wall 12 of the coin channel 10, a first inductive measuring arrangement 20 and on the opposite side a second inductive measuring arrangement 22 is provided. The measuring arrangement 20 consists of a receiving coil A, a transmitting coil C and a secondary coil E. The measuring arrangement 22 has a receiving coil B, a transmitting coil D and a secondary coil F. The construction of the coil arrangement or measuring arrangement 20, 22 results from FIG. 2 ,

On a relatively long ferrite core 24, on the outside of the transmitting coil C and the secondary coil E are arranged. Preferably, the coils E and C are bifilar wound. The receiving coil A is seated with a significantly smaller diameter, for example, half the diameter of the transmitting coil C, in a recess of the ferrite core 24. As is clear from FIG. 1 results, the receiving coils A and B are located directly on the coin channel 10th

An electrical connection of the measuring arrangement 20 goes out FIG. 3 out. A square-wave signal 26 reaches an input of a differential amplifier 28, which feeds the transmitting coil C. The transmitting coil C is inductively coupled to the secondary coil E and its output goes to a second input of the differential amplifier 28. The signal of the secondary coil E is given as a negative feedback signal to the differential amplifier 28 such that the signal of the secondary coil E coincides with the transmission signal.

The structural design of the arrangement according to FIG. 1 comes from FIG. 5 out. With FIG. 1 the same parts are provided with the same reference numerals. In FIG. 5 is structurally the measuring arrangement according to FIG. 1 shown. The coin 18 is a bi-color coin with a rim 18a and a core 18b. It moves along the wall 12 of the main plate, in which the first coil arrangement 20 is arranged, wherein the transmitting coil A is located very close to the wall 12.

With the in FIG. 1 or 5 measuring arrangement shown are repeated in the coin check four cycles consecutively. The period of a measuring signal, for example a square-wave signal, is for example 300 μs, where one pulse has a duration of 50 μs and the pause lasts 250 μs. Therefore, four cycles of 300 μs are required to complete four cycles. The measuring points of the measurements of the four cycles therefore have a distance of 1.2 milliseconds. With a typical throughput time of a coin through the measuring arrangement of about 70 to 80 milliseconds, therefore, four measured values in the four cycles represent an immediate consequence and thus a measurement of material properties of the coin almost in the same place.

Below is an example of four cycles with the measuring arrangement according to FIG. 1 or 5: cycle 1 2 3 4 description RA RB TC TA transmitting coil C D D D receiving coil A B C A

As shown in the table, the transmitting coil C is activated in the first cycle while the transmitting coil D is activated in the other three cycles. In cycles 1 and 4, it is receiver coil A which generates the measurements, while in cycle 2 receiver coil B generates the measurement signal and in cycle 3 C is the receiver coil.

The respective transmitting coil is subjected to the multi-frequency principle with a square wave, as in connection with EP 0 886 247 B1 already described. This document is expressly incorporated by reference.

It can be seen that in the first two cycles 1 and 2 after the reflective and in the cycles 3 and 4 according to the transmission principle is used.

Each cycle can generate any number of measured values, for example 10, by means of a corresponding division of the transmitted pulse.

Wherein the first measured value is not determined at the time t = o of the transmission pulse, but only after a predetermined time offset so that a stable state of the amplifier is ensured.

With preferably 4 cycles, 4 × 10 measured values are thus generated, which can be used for classification and evaluation.

However, it is sufficient to select measured values only at certain sampling times, for example at sampling instants 1, 3 and 9 or 1, 2 and 9 or the like. Because the immediately adjacent sampling times result in some cases redundant measured values, so that the number of reference values to be stored can be reduced in this way.

In FIG. 6 For the cycles RA, TC and TA three attenuation curves are plotted. For the cycle RA these are the damping curves for the switching steps 1, 2 and 9. For the damping curves TC this applies to the switching steps 1, 3 and 9. For the cycle TA are for the switching steps 1, 2 and 9, the damping curves applied. In addition, the times in the diagram are entered by the vertical arrows LS1, LS2 and LS3, at which a coin reaches or leaves one of the sensors LS1, LS2 and LS3. Reaching shows an up arrow and leaving indicates a down arrow. The sensors LS1 to LS3 are, for example, optical light barriers, transmitters and receivers being arranged on the same side as the main plate of the coin validator, while a reflection element is arranged on the carrier plate, which reflects the light of the light transmitter onto the receiver. With the light barrier or the sensor LS1 is the starting point for the measurement with the measuring device after the FIGS. 1 and 3 given. After starting the measurement, a quiescent level prevails until the damping starts. It can be seen that for the cycle RA, the minima are cup-shaped and thus very much flattened, so that it is relatively difficult to determine the time at which the coin is located centrally in the measuring arrangement. The minimum for the cycle TC is much more pronounced. The reason for this is that in this case a transmitting coil is used as a receiving coil. As mentioned several times, the transmitting coil has a significantly larger diameter than the receiving coils of the measuring arrangement.

The distance of the sensor LS1 from the measuring arrangement is chosen so that the ring section of the 2 € Bicolor coin is positioned approximately centrally in front of the receiving coils.

The arrow LS1 down indicates leaving the coin in front of the sensor LS 1.

Consequently, the property of the edge can be measured at the time at which the coin edge substantially affects the measuring arrangement. As is known, the edge of a bicolour coin has different material properties than the core. The core of the coin can be effectively determined by taking a measurement of that Time takes place in which the damping curve has its minimum. The minimum can be determined, for example, in the cycle TA.

When leaving the coin of the sensor area, the sensor LS3 generates a signal which can end the measuring process. By means of the sensors shown, the speed of the coin can also be measured, e.g. to determine a minimum. In addition, a diameter measurement can take place, as it is known per se with the aid of such sensors.

In FIG. 7 is an example of the evaluation of the measured values from the four cycles described reproduced. In the example, five measured values for the different switching steps 1 to 5 for the cycle RA are plotted. These are eg the minima of the curves RA1 to RA5 (not all drawn in). The course of such a curve, as shown in the uppermost diagram, corresponds to the deformation of a rectangular signal with which, for example, the transmitting coil C was fed. The diagram also contains the quiescent level R and a standard level.

In the first standardization step, the quiescent level is shifted to the standard level, which leads to a raising of the curve (middle diagram). In the second step, the distance between measured value 1 and quiescent level is set to approximately 100. This results in a spread of the curve, as shown in the bottom diagram. With one-point normalization after Fig. 7 is shown that the distance of a specific measured value of the cycle RA, for example, RA1 is normalized to the quiescent value.

With the help of normalization, the influence of the air gap field is eliminated, which arises for example by the fact that the coin does not run smoothly along a track wall, but at a distance to this, the distance is also oscillating can change, depending on the movement of the coin on the track.

In FIG. 8 is another example of a standardization of measured values shown, a so-called two-point normalization. By two-point normalization is meant that the distance of two specific measured values of the cycle RA is standardized, for example, from RA 1 to RA3. Again, for example, for five switching steps of a measuring cycle RA, the measured values are plotted in a diagram with resting and standard levels (see top diagram). In the first normalization step, the measured value is pulled to the zero point. In the second step, the distance between measured value 1 and measured value 2 is set to 100. In this way, there is an elimination of the influence of the air gap field and thus a disturbance on the determination of measurement results.

The circuitry with which the individual cycles RA, RB, TC and TA are controlled is not shown. It is easily realizable. The electronic circuit for generating the transmission and processing of the received signals is also not shown. It is also understood that in addition to the cycles described also other measuring cycles can be performed in which, for example, the transmitting coil D receiving coil, while the coil C is activated as a transmitting coil.

Claims (10)

A method of inspecting coins moving along a track using a coil arrangement comprising on each side of the track a transmitting coil C, D and receiving coil A, B on a common ferrite core (transmit coil C and receive coil A on one Side and transmitting coil D and receiving coil B on the other side of the track), wherein the smaller diameter receiving coil is closer to the track than the transmitting coil and the diameter of the transmitting coil is smaller than the diameter of the smallest coin to be accepted and wherein on the ferrite core with a the transmission coil coupled secondary coil is arranged, whose signal is connected as a negative feedback signal to the input of a differential amplifier so that the signal of the transmitting coil coincides with the signal given to the other input of the differential amplifier transmission signal, comprising the following steps: a periodic signal is generated which contains harmonics, - During a predetermined measuring interval of periodically recurring sections of the transmission signal, the amplitudes of the attenuation function from the received signals of a respective receiving coil are determined at least three different measuring times, - There are successively at least four measuring cycles through, - In which each carried out on each side of the track with transmitting and receiving coil a reflection measurement and two transmission measurements are performed, wherein in one of the two transmission measurements the opposite transmitting coil is switched as a receiving coil, the measured values or damping functions from at least one of the measuring cycles are set in relation to each other and / or compared with predetermined reference values. A method according to claim 1, characterized in that the coins are moved into contact with a wall of the track and in the transmission measurement, the wall facing the transmitting and receiving coils form the receiver side. A method according to claim 1, characterized in that the coins are moved into contact with a wall of the track and in the transmission measurement the transmitting and receiving coils facing away from the wall form the receiver side. Method according to Claim 1, characterized in that, prior to comparison with reference values, the measured values of the measuring cycles are normalized. Method according to Claim 4, characterized in that the normalization is carried out by shifting a quiescent level of the received signals to a standard level. Method according to Claim 4, characterized in that the normalization is carried out by shifting a first measured value to a zero point. Method according to Claim 5 or 6, characterized in that the standardized measured values or measured value functions are spread. Method according to one of claims 1 to 7, characterized in that a presence signal is generated by at least one measuring probe in the direction of movement in front of the coil arrangement, with which a relationship between measured values and the actual position of the coin with respect to the coil arrangement is produced. A method according to claim 8, characterized in that the first measuring cycle is started with the signal of a measuring probe. Method according to one of claims 1 to 9, characterized by the application to a secondary coil which is bifilar with the transmitting coil (C or D) wound on the ferrite core.

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