LV11505B

LV11505B - Device for testing the authenticity of coins, tokens or other flat metallic objects

Info

Publication number: LV11505B
Application number: LVP-95-290A
Authority: LV
Inventors: Thomas Seitz; Jacob De Vries; Manuel Vasconcelos
Original assignee: Landis & Gyr Tech Innovat
Priority date: 1994-09-21
Filing date: 1995-09-21
Publication date: 1996-12-20
Also published as: ATE160639T1; ES2109795T3; RU2155381C2; CZ243795A3; FI954442A; CN1134000A; TR199501151A2; EP0704825B1; RO115994B1; EP0704825A1; DK0704825T3; EE03103B1; GR3025581T3; NO308719B1; PL177877B1; LV11505A; PL310542A1; NO953707D0; FI954442A0; DE59501034D1

Abstract

The coin testing system has the coins (M) introduced into a channel section that is inclined such that the coins roll past a pair of inductive sensors. The channel is of a rectangular cross section and is tilted such that the coins move against one side wall that is ridged to facilitate motion. The inductive sensors have coils (9, 10) set into one side wall and metallic discs (11, 12) set in the other wall such that the coins pass in between. The sensors provide inputs to an electronic circuit (14) that measures the time response of the resistance of each one and determine maximum values. The circuit uses the values to determine the coin thickness.

Description

LV 11505

Device for testing the authenticity of coins. tokens or other flat metallic objects

The invention relates to a device for testing the authenticity of coins, tokens or other flat metallic objects of the type mentioned in the precharacterizing clause of Claim 1.

Such devices are suitable, for example, as collection stations in public telephone stations, vending machines, meters for measuring electricity, etc. A device for testing the authenticity of coins of the type mentioned in the precharacterizing clause of Claim 1 is known from EP304 535B1. The device has three inductive sensors, operating independently of one another, for determining the thickness, the alloy composition and the diameter of the coin to be tested. These inductive sensors are constructed as double coils which are arranged on both sides of the coin channel and are connected electrically in parallel or in series, so that measurement scatter as a result of bouncing or jumping of the coin in the coin channel can be partially compensated for, bouncing and springing meaning a lifting off from the bottom of the coin channel or a change in the position with respect to the side walls of the coin channel. The use of double coils, hovvever, is associated with the disadvantage that the alloy composition and the thickness of the coin cannot be determined independently of each other. Each of the inductive sensors are part of a parallel resonant Circuit in vvhich the shift of the resonant frequency, brought about by the coin, and the changed quality are measured. The measured changes in these parameters serve as decision criteria for the acceptance or rejection of the coin. It is also envisaged to construct an inductive sensor serving for the determination of the a!loy composition as a simple coil vvhich is fitted to only one side of the coin channel. A coin detector with inductive sensors, vvhich is operated at frequencies from 3 kHz to 1 MHz, is knovvn from GB 1 397 083. The inductive sensors are arranged in resonant circuits and in bridge circuits. The resonant frequency in the presence of the coin serves to characterise the coin.

The use of energy-absorbing elements, in order to achieve rolling of the coin without bouncing or jumping in the region of the sensors, is knovvn from GB 2 266 804 and also from German Utility Modei G 90 13 836.8. Such energy-absorbing elements are preferably platelets made of ceramie vvhich are arranged in the coin channel in such a way that each coin inserted into the coin inlet opening impacts thereon.

It is knovvn from DE 30 07 484 to construct the lovver side wall of a coin channel vvhich is inclined by a predetermined angle with respect to the vertical with ribs designated as guide rails along the running direction of the coin.

The invention is based on the object of providing a device for testing the authenticity of coins in vvhich the alloy composition and the thickness of the coin may be determined independently of each other, in which bouncing or jumping of the coin is firstly 2 excluded as far as possible and secondly any remaining bouncing or jumping leads to a measurement scatter which is as small as possible.

The said object is achieved according to the invention by means of the features of Claims 1,2 and 8.

Exemplary embodiments of the invention are explained in more detail belovv using the drawing, the reference to the coin M in the following also being understood to refer to tokens or other flat metallic objects.

Fig. 1 shows a coin channel of a testing device,

Fig. 2 shovvs the coin channel in cross-section,

Figs. 3, 4 show measured value diagrams,

Fig. 5 shovvs a sensor signal and Fig. 6 shovvs an electronic Circuit.

Fig. 1 shovvs a device for testing the authenticity of coins, tokens or other metallic objects, having a coin channel 1 vvhich is preferably constructed as a recess in a body 2 consisting of two plastic parts. The coin channel 1 is confined by the bottom 3, a lovver and an upper side wall 4 and 5 and a cover 6. The lovver side vvall 4 is provided with integrally moulded ribs 7 vvhich are running parallel to the bottom 3 in the travel direction of the coin M. The coin channel 1 is inclined in the running direction of a coin M to be tested and the tvvo side vvalls 4 and 5 are inclined by an acute angle of typically 10° with respect to the vertical V, so that the coin M to be tested rolls or slīdes on the bottom 3 down along the coin channel 1 and, vvhile one face of the coin M is laying flat on the ribs 7 of the lovver side vvall 4, ideally. Both side vvalls 4 and 5 have, on their side facing away from the coin channel 1, recesses to accommodate coils 9 and 10 vvhich are arranged in an off-axis displacement and, optionally, metallic platelets 11, 12. The coil 9 and the platelet 12 are located on the lovver side vvall 4, for vvhich reason they are shovvn by dashed lines. The recesses are shovvn only in Fig. 2 on grounds of clarity. The platelets 11 and 12 are fitted opposite the coils 9 and 10, respectively. They are preferably round or rectangular but can also have any other desired geometric form. In each case one coil 9 or 10 and, if appropriate, the metallic platelet 11 or 12 arranged in the opposite side vvall 5 or 4 form an inductive sensor. The tvvo coils 9 and 10 have tvvo connections, one each of vvhich is led to a common electric ground connection m, the other to a svvitch 13, so that they can be~connected to an electronic Circuit 14 for electrical operation independent of one another. The device further contains a control and evaluation unit 15, for example in the form of a microprocessor, for evaluating the output signal supplied by the electronic Circuit 14 and for controlling the device. The Circuit 14 and the microprocessor 15 are constructed to the effect that they derive, from the signāls measured vvith the coils 9 and 10, discrete values vvhich are a measure of the alloy and the thickness d of the coin M. The coin M is only considered to be authentic and is accepted by 3 LV 11505 the testing device if these values agree with predetermined values vvithin prescribed limits, otherwise the coin M is rejected.

Fig. 2 shovvs the coin channel 1 in cross-section at the Ievel of the coil 10. The ribs 7 are arranged at a mutual distance a vvhich is preferably a = 7.25 mm. The shape of their surface facing the coin channel 1 is cylindrical, their radius of curvature R is of comparable size to the spacing a: R = a. A somevvhat larger value of R = 8 mm is preferred.

The ribs 7 are naturally separated by depressions 16 vvhose depth is about 0.5 mm. The depressions 16 have a flat area 17 in the region of the greatest depth between the ribs 7, so that the side wall 4 has a minimum wall thickness in the region of the recesses 8, the wall thickness is chosen based only on the material properties of the body 2 and on the mechanical stresses to be expected as a result of the coins M, but irrespective of the radius of curvature R and the spacing a. Preferably, a minimum wall thickness of 0.6 mm is provided, so that the coil 9 fitted in the recess 8 in the lower side wall 4 has a fixed spacing of 1.1 mm from a coin M rolling past in an ideal manner. The ribs 7 are also there in order to prevent undesired sticking or even jamming of a wet coin.

The construction of the ribs 7 having a cylindrical surface with a comparatively large radius of curvature R results in a greater contact area betvveen the lovver side wall 4 and the coin M than is the case in ribs according to the prior art. This leads to the fact that an impact, directed against the lovver side wall 4, of a coin M vvhich does not rest in an ideally flat manner, is connected with a relatively high damping, so that bouncing and jumping of the coin M in the region of the coils 9 and 10 rarely will occur, even if the coin has damages such as scratches or indentations. The extent to vvhich the bouncing and jumping of the coin M can also be suppressed with ribs 7 vvhose radius of curvature R is smaller than the spacing a and, for exampie, is only a/2, is easy to determine by means of trials. Also, the shape of the ribs 7 does not have to be exactly that of a cylinder.

The high damping of the coin M impacting against the lovver side wall 4 also results in significantly lovver noise emissions compared to a conventional construction of the ribs 7.

Another embodiment of the invention comprises instead of the ribs 7 in the lovver side wall 4 in the region of the coils 9 and 10, a thin plate vvhich is loosely fastened parallel to the side vvall 4. The plate has a comparatively low mass, compared vvith the masses of the coins M to be tested, and consists, for example, of mētai or of ceramie. It serves for the purpose of absorbing the energy of the jumping coin M, if necessary in the event of an impact of the coin M on the plate, and as a result to damp the jumping of the coin M.

According to a further embodiment of the invention, apart from the mechanical precautions to prevent the bouncing and/or jumping of the coin M, improvements in terms of measurement are also provided vvhich further reduce the influence of any possible remaining 4 bouncing or jumping on the measurement of the important characteristics of alloy composition and thickness of the coin M.

Insofar as the considerations apply to both, the coil 9 and the coil 10, the reference symbol S is used belovv on grounds of simplicity instead of the reference number 9 or 10. Thus, a coil S means one of the coils 9 or 10. The coil S is electrically characterised by its inductance Lg and its ohmic internai resistance Rg. It represents an inductive sensor. The above mentioned combination of the coil S with one of the platelets 11 or 12 represents another inductive sensor. During the passage of the coin M past the coil S, the values Lg and Rg change briefly because of physical interactions betvveen the coil S and the coin M. The internai resistance Rg comprises a stātie component Rs,DC ar|d a dynamic component RgļAC(cū) which is a funetion of the angular frequency ω of the current flowing through the coil S, of the physical properties of the coin M, of the geometry of the coil S and, in particular, of the spacing betvveen the coil S and the coin M. As soon as the coin M, while rolling along the coin channel 1, passes into the measurement region of the coil S, its internai resistance Rg inereases. The typical variation with time of the internai resistance Rg is shovvn in Fig. 5. In order to avoid any influence of the diameter of the coin M on the measurements of the thickness d and of the alloy composition, the diameter of the coil S is selected to be smaller than the diameter of the smallest coin M to be measured and the coil S is arranged on the side wall 4 or 5 of the coin channel 1 at a corresponding Ievel, so that the smallest coin M to be tested completely covers the coil S during the passage for a short time. The diameter of the coil S is, for example, 14 mm. The resistance of the feed vvires is comparatively small. Wire-wound coils with a ferrite core are particularly suitable as coils 9 and 10. The implementation of the coils 9 and 10 as single coils arranged in each case on only one side of the coin channel 1, and their complete electrical separation, avoids the loss of sensitivity associated with double coils.

The electronic Circuit 14 operates the coil S in a series resonant Circuit and supplies at its output an analogue signal which is proportional to the internai resistance Rg of the coil S. During the passage of a coin M through the measurement region of the coil S, the variation with time of this output signal is acquired by the microprocessor 15 by means of an analogue/digital converter as a series f1 of digital values vvhich are stored. Subsequently, the microprocessor 15 carries out a detailed analysis vvhich is explained belovv, vvhose result are two values, for example the values K-| and K2 deseribed belovv, vvhich are used to decide about the acceptance or rejection of the coin M.

The coil 9 is located on the lovver side vvall 4 along vvhich the coin M moves in contact, so that the spacing betvveen the coil 9 and the nearest face of the coin M is fixed, for example, at 1.1 mm. The coin M is made either from a single alloy or from a composition of a plurality of alloys. The internai resistance Rg of the coil 9, measured in the presence of the coin M, is a approximate funetion of the material of the coin M, exclusively, if the 5 LV 11505 frequency ω of the current flovving through the coil 9 is selected property. Fig. 3 shovvs the internai resistance Rg as a function of the thickness d of the coin M for coins produced from various alloys L1, L2 and L3, the coin M being located during the measurement in a symmetrical position resting in front of the coil 9. It can be seen from this that the internai resistance Rg is practically independent of the thickness d. Hence, using the coil 9, an important first characteristic variable of the coin M, vvhich is almost exclusively a function of its alloy or its alloy composition, can be determined in a simple way.

The spacing betvveen the coil 10 and the coin M is a function of its thickness d. In the case of the coil 10, the internai resistance R-ļg is thus a function not only of the material of the coin M but also of its thickness d. As Fig. 4 shovvs, the dependence on the thickness d in the range of interest is approximately linear for ali the alloys L1, L2 and L3 shovvn. If the alloy of the coin M is knovvn, the thickness d of the coin M can be determined unambiguously.

In contrast to the use of so-called double coils vvhich are arranged on both sides of the coin channel 1 and are connected electrically in parallel or in series, the use of the two single coils 9 and 10 vvith or vvithout platelets 11 and 12, vvhich are arranged on only one side vvall 4 and 5, respectively, allovvs the mutually completely independent determination of the tvvo parameters of the coin M vvhich characterise the coin M on the basis of its alloy or alloy composition and thickness.

Fig. 5 shovvs the variation vvith time of the output signal of the electronic Circuit 14 for three coins of the same type. The coins come into the measurement region of the first coil 9 at time tļ, and leave it again approximately at time At time t3 they come into the measurement region of the second coil 10, vvhich they leave again approximately at time t4. The output signal from the coil 9 has tvvo maxima M1 and M2 having values U1 and U2, the output signal from the coil 10 tvvo maxima m1 and m2 having values v1 and v2. The continuous line represents the output signal of a coin M vvhich rolls dovvn the coin channel 1 (Fig. 1) vvithout bouncing or jumping and, in so doing, lies flat on the ribs 7. In this case, the measured values U1 and U2 and also the values v1 and v2 are equal: U1=U2, v1=v2. The dash-dotted line shovvs the output signal of a coin M vvhich bounced or jumped in the measurement region of the first coil 9: the values U1 and U2 are different. The dashed line shovvs the output signal from a coin M vvhich bounced or jumped in the measurement range of the second coil 10: the values v1 and v2 are different. Trials have shovvn that at least one of the values U1 or U2 and v1 or v2 is relatively stable, that is to say it has a lovv scatter, vvhereas the minimum lying betvveen the corresponding maxima is subject to a greater scattering. In the case of the first coil 9, the value of the greater of the tvvo maxima corresponds to the smallest spacing betvveen the coil 9 and the coin M, since then the damping of the coil 9 is at its strongest. In the case of the example shovvn in Fig. 5, this is for both lines the second maximum M2 having the value U2, vvhich is also the more stable of the 6 two maxima. The microprocessor 15 is therefore programmēti to the effect that it determinēs the greatest value of the output signal in the first coil 9 and stores it as the value K-ļ. The damping of the second coil 10 is smaller, the larger the spacing is betvveen the coil 10 and the coin M. The microprocessor 15 is therefore programmed to the effect that it determinēs the values v1 and v2 of the two maxima m1 and m2 in the second coil 10 and stores the smaller of the two values v1 and v2 as the value K2: K2=min(v1, v2). In the example in Fig. 5, the maximum m2 corresponds to this case. in a manner known per se the microprocessor 15 carries out this described analysis of the output signāls. In order to balance out noise effects and to reduce the scatter of the values K-ļ and K2 to be determined, it is advantageous to convert the sequence f1 into a sequence f2, each value of the sequence f2 being the running average determined over, for example, ten successive values of the sequence f1. The determination of the greatest value of the output signal from the first coil 9 can be carried out by means of numeric comparisons, the determination of the maxima m1 and m2 can be carried out by calculating the first and second derivatives of the sequence f2.

In order to exclude the influences of other physical factors such as temperature, humidity, etc. on the measured results to the greatest extent possible, it is advantageous for the microprocessor 15 to form relative values P-ļ = r-ļ/K-ļ and P2 = the variables r-ļ and Γ2 representing reference resistances which are equal to the internai resistance Rg of coil 9 and R-ļo of coil 10 in the absence of the coin M. The reference resistances r-ļ and Γ2 are advantageously determined each time directly before or after the passage of the coin M.

As is known, each coin M has two faces which are embossed differently and vvhich, in common English usage, are designated “head" and "tail". This asymmetrical embossing of the coin M leads to the fact that the characteristic variables K-ļ and K2 determined in the case of the coin M depend on vvhich side of the coin M rests on the side wall 4. The scatter in the variables K-ļ and K2 vvhich is present in the case of a specific type of coin is additionally increased by this effect. Hovvever, the range of scatter of the variable K-j remains sufficiently small in order to be able to determine the alloy of the coin M unambiguously. On the other hand, the measurement of the thickness d is disturbed by this effect to such an extent that the assessment of the authenticity of the coin M and/or the determination of its value is made more difficult since coins of different value produced from the same alloys often differ very little in their thickness. Using a further measure, vvhich vvill novv be described, the influence of this effect on the determination of the thickness d can be reduced. In the case of a coin M without embossing, the measurements from the coils 9 and 10 yield, for example, a value K-ļ and a value K2· lf the coin M has an asymmetrical embossing, and if the head side faces the coil 9, the measurements yield slightly changed values K-ļ + 6r-| and K2 - δ^. An increase in the variable K-ļ leads to a decrease in the variable K2, since a reduction in the spacing betvveen the coil 9 and the coin M leads to a 7 LV 11505 consequent increase in the spacing between the coin M and the coil 10. Because of the linearity of the variables Kļ and K2 as a function of the spacing of the coin M from the corresponding coil, it is tnje in the case of using identical coils 9 and 10 and using the same frequency ω to excite the coils 9 and 10 that: 5rļ = 6r2 = 6r. In the case of the same coin M, if the tail side faces the coil 10, the measurements yield values Kļ - 5r and K2 + 6r instead. Hence, the sum Hļ = Kļ + K2 or the sum I2 = Pļ + P2 thus advantageously serves as a measure of the thickness d of the coin M and thus as a decision criterion for the acceptance or rejection of the coin M. The sums H2 and I2 are independent of how the coin M faces the side wall 4, since the values - δ r and + δ r cancel each other out.

Fig. 3 shovvs that the measurement values Kļ are distinctly different for different alloys. The alloy of the coin M can thus be determined comparatively easily, that is to say the tolerance limits which specify whether the coin M is accepted or rejected on the basis of its measured alloy can be set to be relatively wide. The closer the tolerance limits for the variables K2 or P2 or H2 or I2 are set, the more coins M can be reliably distinguished on the basis of their thickness d. The prevention of the bouncing or jumping of the coins in the region of the inductive sensors by means of the newly constructed ribs 7 in combination with the detailed signal analysis described now makes possible the setting of very close tolerance values for the variables K2 or P2 or H2 or I2.

Fig. 6 shovvs an advantageous electronic Circuit 14 having a series resonant Circuit RLC for the separate acquisition of the change of the ohmic resistance Rg and the inductance Lg of a coil S. The starting point is the knovvledge that the series resonant Circuit RLC formed from the coil S and a capacitive element C represents in the case of resonance a purely ohmic impedance Zg vvhich is equal to the resistance Rg of the coil S. In contrast to this, in the case of resonance, a parallel resonant Circuit in vvhich the coil S and the capacitive element C are connected in parallel behaves like an impedance vvhich is a function of the ratio of the resistance Rg to the inductance Lg of the coil S (j designates the imaginary unit). The resonant frequency ^(Lg) of the series resonant Circuit RLC is given by

The electronic Circuit 14 has a differential amplifier 18 vvith an inverting input 19 and a non*inverting input 20, a resistor 21, a tvvo-stage amplifier Circuit 22 and an amplitude detector 23. The series resonant Circuit RLC consists of the coil S and a capacitive element C vvhich are connected in series, and is connected to ground m vvith one 8 connection and to the inverting input 19 of the differential amplifier 18 with the other connection. The output of the differential amplifier 18 is fed back via the resistor 21 to the inverting input 19 and via the amplifier Circuit 22 to the non-inverting input 20.

The amplifier Circuit 22 has the objects, firstly, of bringing the series resonant Circuit RLC into oscillation when the Circuit 14 is svvitched on and, secondly, to make available an amplitude-stabilised voltage U3(t) for exciting the series resonant Circuit RLC. This object is realised by means of two inverters 24 and 25, connected in series, and a dovvnstream-connected voltage divider 26. A capacitor 27 and 28 is in each connected upstream of the input of the inverters 24 and 25, and the output of the inverters 24 and 25 is fed back to the input in each case via a resistor 29 and 30. The capacitors 27 and 28 serve for direct current DC decoupling. The resistors 29 and 30 determine the DC operating point of the inverters 24 and 25. On switching on the Circuit 14, the amplifier Circuit 22 behaves like a linear AC amplifier so that, because of the positive feedback of the output voltage Uļ(t) of the differential amplifier 18 to its input 20, the series resonant Circuit RLC begins to oscillate. The amplification of the input signal Uļ (t) is seiected to be so high that the second inverter 25 is then always brought into saturation, so that a square wave voltage U2(t) is present on its output, the two voltage Ievels of said voltage corresponding to the positive and the negative voltage Ievel with vvhich the entire electronic Circuit 14 is fed in a bipolar fashion with reference to ground m in a manner known per se. With the aid of the ohmic voltage divider 26 connected to ground m, the Ievel of the voltage U2O) is reduced. A square wave voltage U3(t) is thus present at the output of the amplifier Circuit 22 and hence at the input 20 of the differential amplifier 18, said voltage being in phase with the voltage U-ļ(t), but its amplitude being independent of the amplitude of the voltage Uļ(t). The voltage divider 26 has two resistors 31 and 32, the resistor 31 being of the order of magnitude of the resistance Rg of the coil S. The resistor 32 is to be dimensioned such that the Ievel of the voltage U3(t) is a few tens to one hundred millivolt. The amplitude detector 23 serves to measure the amplitude of the voltage U-ļ(t) and to transmit it to the microprocessor 15 in a suitable form.

During the passage of the coin M past the coil S, the resonant frequency a>o(Ls) changes, as appropriate with the change of the inductance Lg. The Circuit 14 described operates such that the series resonant Circuit RLC oscillates at a frequency ω vvhich is always equal to the resonant frequency cūq(Ls). During the passage of the coin M past the coii S, the resistance Rg of the latter also changes. Since the series resonant Circuit RLC has the ohmic impedance Zq = Rs at resonance, and since the voltage U3(t) vvhich serves to excite the series resonant Circuit RLC is a periodic voltage of constant amplitude, the current i(t) flovving through the series resonant Circuit RLC and hence the amplitude of the voltage U-j(t) at the output of the differential amplifier 18 is directly a measure for the resistance R§ of the coil S. The evaluation of the signal U-ļ(t) is now carried out by means of the microprocessor 15 as previously described. 9 LV 11505

The frequency ω of the rectangular voltage U2(t) present at the output of the second inverter 25 can be determined in a simple manner, not shown, for example using a counter modulē which is enabled to count by the microprocessor 15 in accordance with the variation with time of the amplitude of the voltage U -j (t). vvhile the coin M covers the coil S. The frequencies ωι and determined in this manner in the coil 9 or in the coil 10 correspond to the resonant frequencies during the passage of the coin M and represent a third and fourth characteristic variable K3 and K4, vvhich can serve as further decision criteria for the acceptance or rejection of the coin M.

Using the device described, the variables Kļ and K2 and hence the alloy composition and the thickness d of the coin M can be determined with an accuracy vvhich is sufficient to be able to distinguish a multiplicity of coins M. In order to exclude the possibility of deceit, whereby a coin M2 of a specific alloy and greater thickness d can be faked by using a coin M1 of smaller thickness d or with a thin metallic platelet, in that the spacing of the coin M1 or of the metallic platelet from the coil 9 is intentionally increased, for example by inserting a non-metallic layer betvveen the coin M1 and the coil 9, it is sufficient to establish vvhether the resonant frequency coo(Ls) of the coil 9 during the passage of the coin M is greater or smaller than in the absence of a coin. The sign of the change in resonant frequency cūo(Ls) of the coil 9 thus advantageously serves as a further decision criterion for the acceptance or rejection of the coin M. An exact determination of the resonant frequency £ūo(Ls) in the presence of the coin M is not necessary.

The arrangement of the coil 9 or 10 in the series resonant Circuit RLC offers the advantage that a variabie characterising the alloy composition or a variable characterising the thickness d may be determined with a Circuit vvhich is of simple construction and vvhich measures the damping of the series resonant Circuit RLC in the presence of the coin M. The series resonant Circuit RLC consequently represents a particularly suitable means for measuring the resistance change induced in the coii S. Hence, coins can also be detected vvhich yield no signal change or an insufficient signal change vvhen using a parallel resonant Circuit, if the changes in the inductance Lg and in the resistance Rg mutually compensate each other.

The inductance Lg of the coil S and the value of the capacitive element C are selected such that the resonant frequency cuo(Ls) of the tuned Circuit RLC is located in the range from 50 to 200 kHz, a typical value being 90 kHz. At these frequencies, the penetration depth of the magnetic field generated by the coil S into the coin M is sufficiently large, vvith the result that the composition in terms of materiāls of the coin M may be detected sufficiently selectively.

Fluctuations in the Ievel of the voltage U3(t) exciting the resonant Circuit RLC, which are brought about, for example, by fluctuations in the operating voltage vvhich serves 10 as the povver supply of the Circuit 14, have no influence on the variables Pļ and P2, since these represent a ratio of two directly successive resistance measurements.

The inverters 24 and 25 can, for example, be inverters of the knovvn type 4007. In a special embodiment of the Circuit 14, at least one of the inverters 24 or 25 is substituted by a NAND or a NOR component with an additional input, the additional input being connected to an output of the microprocessor 15. The Circuit 14 can be svvitched on and off in a simple manner via the logic potential at this output of the microprocessor 15. The Circuit 14 can thus be svvitched on briefly as required, only just for the testing of a coin M. The substitution of both inverters 24 and 25 by a NAND or a NOR component offers the advantage that the Circuit 14 needs exceptionally little povver in the switched-off condition.

Fig. 6 shovvs only one example of an electronic Circuit 14 vvhich is suitable to detect the change in resistance Rg of the coil S by means of a series resonant Circuit RLC. Numerous further examples of electric circuitry of the series resonant Circuit RLC, vvhich excite the series resonant Circuit RLC vvith a voltage or a current, can be found in the technical literature. 11 LV 11505

PATENT CLAIMS 1. Device for testing the authenticity of coins (M), tokens or other flat metallic objects, having a coin channel (1) with a lovver (4) and an upper (5) side wall, the coin channel (1) being inclined by a predetermined angle with respect to the vertical (V) and the coin (M), in the ideal case, moving along the lower side wall (4) in contact, having two inductive sensors arranged along the coin channel (1), an electronic Circuit (14) and having a control and evaluation unit (15), characterised in that the first inductive sensor is a coil (9) fitted to the lovver side wall (4), in that the second inductive sensor is a coil (10) fitted to the upper side wall (5) in that means (13, 14) are provided to operate the two coils (9, 10) electrically independently, in that the electronic Circuit (14) is equipped to measure the variation with time of the ohmic resistance Rg(t) and Rļo(t) ofthe two coils (9. 1°) during the passage of a coin (M), in that the control and evaluation unit (15) determinēs the greatest value of the resistance Rg(t) of the first coil (9) as the value K-ļ, in that the control and evaluation unit (15) determinēs the local maxima (m1, m2) of the resistance R-io(l) assumed by the second coil (10) and determinēs the greater of the two values (v1, v2) of the two maxima (m1, m2) as the value K2, and in that the values Kļ and K2 or the values Kļ and H2 = Kļ + K2 serve to decide about the acceptance or rejection of the coin (M). 2. Device for testing the authenticity of coins (M), tokens or other flat metallic objects, having a coin channel (1) with a lovver (4) and an upper (5) side wall, the coin channel (1) being inclined by a predetermined angle with respect to the vertical (V) and the coin (M), in the ideal case, moving along the lovver side wall (4) in contact, having two inductive sensors arranged along the coin channel (1), an electronic Circuit (14) and having a control and evaluation unit (15), characterised in that the first inductive sensor is a coil (9) fitted to the lovver side wall (4), in that the second inductive sensor is a coil (10) fitted to the upper side wall (5) in that means (13, 14) are provided to operate the two coils (9, 10) electrically independently, in that the electronic Circuit (14) is equipped to measure the variation vvith time of the ohmic resistance Rg(t) and Rļo(t) of the two coils (9, 10) during the passage of a coin (M), in that the control and evaluation unit (15) determinēs the greatest value of the resistance Rg(t) of the first coil (9) as the value K-ļ, in that the control and evaluation unit (15) determinēs the local maxima (m1, m2) of the resistance Rļo(t) assumed by the second coil (10) and determinēs the greater of the tvvo values (v1, v2) of the two maxima (m1, m2) as the value K2, in that the control and evaluation unit (15) determinēs the internai resistance r-ļ of the first coil (9) and the internai resistance Γ2 of the second coil (10) directly before or after the passage of the coin (M), and in that the values Pļ = r-ļ/K-ļ and P2 = Γ2/Κ2 or the values Pļ and I2 = P1 -‘-P2 serve to decide about the acceptance or rejection of the coin (M). 3. Device according to Claim 1 or 2, characterised in that the coils (9, 10) are arranged to measure the resistance in a series resonant Circuit (RLC). 12 4. Device according to Claim 3, characterised in that the electronic Circuit (14) comprises a differential amplifier (18) and an amplifier Circuit (22), the output of the differential amplifier (18) being fed back via a resistor (21) to the inverting input (19) and via the amplifier Circuit (22) to the non-inverting input (20), and the amplifier Circuit (22), firstly, on svvitching on the electronic Circuit (14), brings the series resonant Circuit (RLC) into oscillation and, secondly, makes available an amplitude-stabilised voltage (U3(t)) for exciting the series resonant Circuit (RLC). 5. Device according to Claim 4, characterised in that the amplifier Circuit (22) has two inverters (24, 25) connected in series or NAND or NOR components. 6. Device according to one of Claims 3 to 5, characterised in that means are provided in order, during the passage of the coin (M), to determine the sign of the change in the resonant frequency (coo(Ls)) in the first coil (9), and in that this sign serves as a further decision criterion for the acceptance or rejection of the coin (M). 7. Device according to one of Claims 1 to 6, characterised in that a metallic plateiet (11, 12) is fitted in each case on that side wall (5, 4) lying opposite the coils (9, 10). 8. Device for testing the authenticity of coins (M), tokens or other flat metallic objects, having a coin channel (1) vvith a lower (4) and an upper (5) side wall, the lovver side wall (4) being provided vvith ribs (7) in the running direction of the coin, the coin channel (1) being inclined by a predetermined angle vvith respect to the vertical (V) and the coin (M), in the ideal case, moving along the ribs (7) of the lovver side wall (4) in contact, characterised in that the radius of curvature (R) of the ribs (7) is at least half as large as the spacing (a) of adjacent ribs (7). 9. Device according to Claim 8, characterised in that the radius of curvature (R) of the ribs (7) is approximately comparable to the spacing (a) of adjacent ribs (7). LV 11505

ABSTRACT A device for testing the authenticity of coins (M), tokens or other flat metallic objects contains a coin channel (1) having a lower (4) and an upper (5) side wall. A coin (M) moves along the coin channel (1) on the lower side wall (4) in contact, past a first and a second inductive sensor (9, 10). The two inductive sensors are either a coil (9,10) or a coil and a metallic platelet (9, 11; 10, 12), the first coil (9) being fitted to the lovver side wall (4) and the second coil (10) to the upper side wall (5). The two coils (9, 10) can be operated electrically independently. The coils (9, 10) are advantageously arranged electrically in a series resonant Circuit (RLC). During the passage of the coin (M), the variation of the resistance change induced in each coil (9, 10) is measured and analysed and the alloy composition and the thickness d of the coin (M) are determined therefrom. (Fig. 1)

Claims

A device for verifying the authenticity of coins (M), tokens or other flat metal objects comprising: a coin channel (1) with a lower (4) and an upper (5) side wall, wherein the coin channel (1) placed on a certain slope with respect to the vertical (V), and ideally the coin (M) moves along the lower side wall (4), in contact with it, 10 two inductive sensors, embedded in the coin channel (1), electronic circuits (14) and control and an evaluation unit (15), characterized in that: the first inductive sensor is a coil (9) mounted at the lower side wall (4), the second inductive sensor being a coil (10) mounted at the top side wall (5); ), the blocks (13, 14) are designed to work with both coils (9, 10) electrically independently, the electronic circuit (14) is designed to measure the intrinsic resistance R (t) of both coils (9, 10), and R10 (t) Change Coin (M) Direction during control, the control and evaluation unit (15) determines the maximum value control and evaluation unit (15) of the output resistor R (t) of the first coil (9) determines the maximum resistance (m1, m2) of the output 25 of the second coil (10) and determine the maximum value (v1, v2) of the peak (m1, m2) denoted by K, the values K1 and K2 or K1 and H sK ^ K are used to decide whether the coin (M) is valid or rejected.

A coin (M), token or other flat metal object authentication device comprising: a coin channel (1) with a lower (4) and a top (5) side wall, wherein the coin channel (1) is positioned at a certain slope with respect to vertically (V), and the coin (M) ideally moves along the lower side wall 35 of the lower side (4), in contact with it, two inductive sensors, embedded in the coin channel (1), electronic circuit (14) and control and evaluation unit (15) 2, characterized in that: the first inductive sensor is a coil (9) mounted at the lower side wall (4), the second inductive sensor being a coil (10) mounted at the top side wall (5), blocks (13) 14) designed to work with both coils (9, 10) electrically independent, the electronic circuit (14) is designed to measure the variation of the resistances R (t) and R (t) of both spoils (9,10). coin (M) while driving, management and appreciate The control unit (15) determines the maximum value K of the resistance R9 (t) of the first coil (9), the control and evaluation unit (15) determines the maximum (m1, m2) and the maximum (m1, m2) of the resistance R10 (t) of the second coil (10). ) the highest value (v1, v2), denoted by K2, the control and evaluation unit (15) determines the internal resistance of the first coil (9) to the internal resistance r and the second coil (10) of the coil (9) just before or after the coin (M) passes the coils. , the values P = r / K and P = r / K or P and l = P + P "are used to make a decision on the acceptance or rejection of the coin (M).

Device according to claim 1 or 2, characterized in that the coils (9, 10) are adapted to measure the resistance of the string resonance circuit (RLC).

Device according to claim 3, characterized in that the electronic circuit (14) comprises a differential amplifier (18) and an amplifier circuit (22), wherein the output voltage of the differential amplifier (18) through the resistor (21) is feeds to the inverse input '(19) and through the amplifier circuit (22) to the non-inverting input (20), wherein the amplifier circuit (22) at the on-board electronic circuit (14), firstly, deflects the string resonance circuit (RLC), secondly, to produce a stable amplitude voltage (U3 (t)) for a series resonance circuit (RLC). 3 3 EN 11505

Device according to claim 4, characterized in that the amplifier circuit (22) comprises two inverters (24, 25) which are either NAND or NOR elements connected in series.

Device according to one of claims 3 to 5, characterized in that means are provided for determining the variation of the oscillation frequency (coo (Ls) in the first coil (9) during the movement of the coin (M) and that these changes are used as a criterion for deciding whether a coin (M) is valid or rejected.

Device according to one of Claims 1 to 6, characterized in that in each case the metal plate (11, 12) is attached to the opposite side wall (5, 4) of the coils (9, 10).

8. A coin (M), token and other flat metal object authentication device having a coin channel (1) with lower (4) and upper (5) side walls, the lower (4) side wall being provided with ribs ( 7) in the direction of the coin movement, the coin channel (1) is positioned at a certain angle to the vertical (V), and the coin (M) ideally moves along the ribs (7) of the lower side wall (4) when in contact with it, that the radius of curvature (R) of the ribs (7) is at least half the distance (a) between adjacent ribs (7).

Device according to claim 8, characterized in that the radius of curvature (R) of the ribs (7) is approximately comparable to the distance (a) between the adjacent ribs (7).