GB2046974A - Method and apparatus for the identification of coins and equivalent - Google Patents

Abstract

A method and an apparatus for testing and identifying electrically conductive coins and similar. According to the method, the effect of each coin 1 to be tested and identified on a magnetic field, generated by means of coils 101, 201, is measured and compared with a reference value such that a coin is accepted if the measured value is close enough to the reference value. This reference value is determined on the basis of the effect produced by a preselected reference coin 2 on a reference magnetic field generated by coils 102, 201 having the same magnitude as the measurement magnetic field. <IMAGE>

Description

SPECIFICATION Method and apparatus for the identification of coins and equivalent The present invention concerns a method for testing and identifying electrically conductive coins on equivalent, according to which method - a first magnetic field is generated by means of a first transmitter coil, - each coin to be tested and identified is placed into the first magnetic field, thus influencing said first magnetic field, - a measurement signal is generated as a function of the first magnetic field as influenced by the coin to be tested and identified, - a second magnetic field, preferably similar to the first magnetic field, is generated by means of a second transmitter coil, - a preselected reference coin is kept in the second magnetic field, thus influencing said second magnetic field, - a reference signal is generated as a function of a second magnetic field as influenced by the reference coin in a manner similar to the measurement signal, -the measurement signal obtained is compared to the reference signal, and -the coin is accepted if the measurement signal is similar enough to the reference signal.

The invention also concerns an apparatus for carrying out this method, said apparatus comprising - first means for generating a magnetic field of measurement, - second means for guiding the coins to be examined into the range of influence of the magnetic field of measurement, - third means for generating a reference magnetic field, -fourth means for the comparison of the magnetic field of measurement with the reference magnetic field.

In known methods for distinguishing coins from each other on the basis of their electro-magnetic properties (erg., U.K. Patent 1,397,083 and U.S.

Patent 3,952,851) the changes in frequency and/or amplitude of a freely oscillating oscillator are usually utilized when a coin moves in the proximity of a coil connected to the oscillator. In these methods reference values permanently stored in the circuitry of the apparatus are used, with which reference values the measurement results obtained from the oscillator by means of various measurement methods are compared. Thus, the measurements must be highly stable in respect of changes in time and temperature, for which reason it has been necessary to attach various temperature and other compensation couplings to the circuitry of several apparatuses.In known methods, one or two measurement signals of the sine form are commonly used, and the examination of the changes in these signals is often started by means of a particular sensing unit or similar when the coin arrives in the proximity of the measurement coil or coils.

Drawbacks of the prior art methods are the complicated circuits required for compensating for the creepage of the measurement results and, on the whole, the required precision of the measurement circuits. Moreover, the reference values stored in the apparatuses make the circuitry more complicated, and it is often difficult to change these values. The oscillation of a freely oscillating oscillator is almost sine-formed as examined across the coil associated with the oscillation circuit, so that the frequency spectrum of the magnetic field examining the coin is relatively free from harmonics, owing to which the coin is, properly speaking, examined only with one frequency per oscillation circuit.In several prior art methods it is also necessary to initialize the measurement when the coin arrives, which requires further circuitry technology as well as some sensing means. This may cause disturbance of operation when several coins in contact with each other are subsequently fed into the apparatus.

It is an object of the present invention to eliminate the above drawbacks and to provide a more reliable identification method and identification apparatus.

The invention is based on the idea that a reference coin fitted into the apparatus is used as an aid, with which reference coin the coin to be examined and passing in a coin channel is compared. The comparison can be performed, e.g., by using a magnetic bridge coupling consisting of three coils, in which bridge coupling the magnetic coupling between two transmitter coils and one receiver coil is changed by means of the reference coin and the coin to be examined. This coupling is affected essentially by the materials and dimensions of the coins.

More specifically, the method in accordance with the invention is mainly characterized in that - the first magnetic field and the second magnetic field are generated by passing one and a same, or a similar, current signal through the first and the second transmitter coil so as to generate at least substantially similar magnetic fields such that the measurement signal and the reference signal are generated simultaneously and - the comparison of the measurement signal with the reference signal is carried out by forming their difference signal.

The apparatus in accordance with the invention is characterized in that - said reference magnetic field is preferably of the same magnitude as compared with the magnetic field of measurement, and - a preselected reference coin is arranged into the reference magnetic field, which reference coin is preferably identical with the coins to be identified (accepted).

An advantage of the method in accordance with the invention is the remarkable simplicity of the circuitry, which results from the fact that in the method no reference memory or reference couplings are used, but the reference values are obtained from the reference coin and the comparison takes place in the coil arrangement during the measurements. The circuitry is also simplified by the circumstance that the requirements imposed on the measurement signal required in the method and on the measurement system permit the use of simple couplings, because lack of precision in the measure ment signal or in the measurement couplings does not affect the operability of the method, for this lack of precision is compensated for in the magnetic bridge coupling. Moreover, owing to the constant measurement, the method to be used does not require initilization of the measurements.The method also permits identification of coins when they pass one after the other in contact with each other. Since it is possible to use any arbitrary wave form in the measurement signal, its frequency spectrum can be selected as desired, whereby in the identification of a coin consideration can be given to its magnetic properties at several differentfrequen- cies. Since the information on the properties of an acceptable coin is received from the reference coin to be used, the same apparatus can be made to accept any coin whatsover by positioning a coin of the corresponding type as the reference coin.

The invention will be examined below in more detail, reference being made to the exemplifying embodiments in accordance with the attached drawings.

Figure 1 is a schematical presentation of one apparatus that may be used in the method in accordance with the invention.

Figure 2 shows a bridge coupling used in the apparatus shown in Figure 1.

Figure 3 shows a bridge coupling in accordance with a second embodiment.

Figure 4 shows a coin channel arrangement used in an apparatus in accordance with the invention.

Figure 5 shows a coil arrangement in accordance with a third embodiment.

In the following description the expression "coin" has been used as meaning metal coins, counters, tokens, or any other objects that may be used or whose use may be attempted in coin-operated apparatuses.

The apparatus in accordance with the invention operates, for example, by using a magnetic bridge coupling shown in Figure 3, consisting of three coils, and the mechanics and circuitry in accordance with Figures 1 and 4. The coin 1 to be examined is dropped into the apparatus through the mouth piece 7 into the coin channel 5. The coin channel 5 is so designed that its depth is somewhat larger than the thickness of the thickest coin to be examined. The coin channel 5 is covered by a cover plate 8. The coin channel 5 passes through a group of coils so that the coin 1 to be examined rolls along an inclined plane 6 between a first transmitter coil 101 and a receiver coil 201.Between the second receiver coil 201 and the transmitter coil 102, the reference coin 2 is positioned, whereby the coin 1 to be measured, when rolling, comes into a position symmetrical with the reference coin 2 in respect of the symmetry axis a-a passing through the coils 101, 201, 102 (Figure 2).

A rectangular-wave oscillator 11 feeds a signal through both transmitter coils 101, 102 so that the coils produce opposite magnetic fields at the receiver coil 201 unless there are coins in the system. Now, if there is no coin in the coin channel 5 or if the coin in the channel does not have electro-magnetic properties similar to those of the reference coin 2 placed in position, the receiver coil 201 yields a signal induced by the magnetic field acting upon same.However, if there is a'coin 1 to be measured passing in the coin channel 5 and having electromagnetic properties identical with those of the reference coin 2 to be used, the bridge coupling formed by the magnetic couplings of the coils 101, 201, 102 is momentarily in equilibrium when the coin 1 passes between the coils 101 and 201 Then the signal received from the receiver coil 201 is momentarily totally repressed.

The signal received from the receiver coil 201 is observed by means of an amplifier 21, a rectifier 22, an integrator 23, and a level indicator 24 so that, when the signal is sufficiently repressed for a sufficiently long period of time, the level indicator 24, as an indication of this, gives an impulse to a monostable multivibrator 25, which controls the solenoid 26 (Figure 1). The time constant of the monostable multivibrator 25 has been selected so that the guide flap 3 operated by the solenoid 26 guides the coin passing in the coin channel 5 into the channel 4 of accepted coins (Figure 4). Thus only such coins 1 end up in the channel 4 of accepted coins whose magnetic properties, i.e. material and dimensions, are, with the desired precision, identical with those of the reference coin 2.

The coil arrangement used in the embodiment described above may also be substituted for by such a coil arrangement in which a transmitter coil and a receiver coil constitute an identification unit 40 another similar pair of coils constitutes a reference unit 50 (Figure 3). By increasing the number of reference units 50a, it is possible to make the coin selector identify several different coins.

The coil elements described above may also be substituted for by such coil units 41,51 (Figure 5) in which one coil 301,302 operates both as transmitter as receiver.

The apparatus may also be constructed so that, when the magnetic bridge is out of balance, its measurement current is reduced and, when the state of unbalance changes towards the state of balance, the measurement current increases to its normal value.

Claims (11)

1. A method for testing and identifying electrically conductive coins and similar, according to which method - a first magnetic field is generated by means of a first transmitter coil; - each coin to be tested and identified is placed into the first magnetic field, thus influencing said first magnetic field; - a measurement signal is generated as a function of the first magnetic field as influenced by the coin to be tested and identified; - a second magnetic field, preferably similar to the first magnetic field, is generated by means of a second transmitter coil; - a preselected reference coin is kept in the second magnetic field, thus influencing said second magnetic field; - a reference signal is generated as a function of the second magnetic field as influenced by the reference coin in a manner similarto the measurement signal;; - the measurement signal obtained is compared to the reference signal; and - the coin is accepted if the measurement signal is similar enough to the reference signal, wherein - the first magnetic field and the second magnetic field are generated by passing a similar, preferably one and the same, current signal (I) through the first and the second transmitter coil so as to generate at least substantially similar magnetic fields such that the measurement signal and the reference signal are generated simultaneously; and - the comparison of the measurement signal with the reference signal is carried out by forming a difference signal of same.

2. A method as claimed in Claim 2, wherein the coin to be tested and identified is placed into the measurement magnetic field in such a way that its influence on the measurement signal to be generated is at least substantially similar to the influence of the reference coin on the reference signal.

3. A method as claimed in Claim 1, wherein the effect of the reference coin on the magnetic field is measured constantly.

4. A method as claimed in Claim 1, wherein the effects produced by the coin to be examined and by the reference coin on their respective magnetic fields are compared with each other by means of a magnetic bridge coupling known per se.

5. An apparatus used for carrying out the method in accordance with Claim 1 fortesting and identifying electrically conductive coins or equivalent, said apparatus comprising: - first means for generating a magnetic field of measurement; - second means for guiding the coins to be examined into the range of influence of the magnetic weld of measurement; - third means for generating a reference magnetic field preferably of the same magnitude as compared with the magnetic field of measurement; - fourth means for the comparison of the magnetic field of measurement with the reference magnetic field, and - a preselected reference coin arranged into the reference magnetic field, which reference coin is preferably identical with the coins to be identified.

6. An apparatus as claimed in Claim 5, wherein '1e means generating the magnetic field are coils and one transmitter coil generating the magnetic field of measurement and one transmitter coil generating the reference magnetic field, on one hand, and one receiver coil, on the other hand, are connected into a magnetic bridge coupling for the purpose of performing the comparison (Figures 1 and 2).

7. An apparatus as claimed in Claim 6, wherein both transmitter coils are connected in series.

8. An apparatus as claimed in Claim 6, wherein both transmitter coils are at least approximately identical.

9. An < pparatus as claimed in Claim 5, wherein the means generating the magnetic field are coils, and at each particular time one pair of coils consisting of a transmitter coil and a receiver coil, respectively, forms an identification unit and at least one other similar pair of coils forms a reference unit.

10. An apparatus as claimed in Claim 9, wherein the number of reference coins is at least two and each reference coin has a transmitter and a receiver coil of its own as well as a receiver circuit and the coin to be examined has one transmitter and one receiver coil and both types of coins have one common transmitter circuit.

11. An apparatus as claimed in Claim 5, wherein the transmitter coil and the receiver coil are combined in one and the same coil (Figure 5).