The present invention relates to a method and apparatus for coin discrimination, and in particular to a method and apparatus for determining the denomination of a coin, and/or for determining whether a coin is legal tender or a foreign coin or token.

A coin discrimination method and apparatus is known from UK patent application No. 2135095 in which a rectangular voltage pulse of predetermined length is applied to a coil when a coin is adjacent to the coil. As a result of the voltage pulse in the coil, decaying eddy currents are induced in the coin which, as a result of magnetic flux linkage between the coin and the coil, induce a voltage in the coil which can then be measured in order to determine the identity of the coin. The induced eddy current decay characteristic is dependent upon the type of coin, and so the identity of the coin can be determined by measuring the characteristic. The measurement is carried out by taking a value of the voltage induced in the coil by the eddy currents in the coin at a selected time after the initial voltage pulse is completed. By taking a series of such values for different voltage pulse widths and at different selected times, the characteristic can be evaluated and the coin identified. One drawback of this known coin discriminating apparatus is that although the coil is pulsed for each discrimination with a predetermined voltage pulse, because of changes in the resistance and inductance of the coil as a result of, among other things, temperature changes, the level of eddy current actually induced in the coin can vary and so the measured induced voltage in the coin can vary. Problems can consequently arise as a result of the variation of the decaying eddy currents in the coin.

Another drawback of this known apparatus is that the inductance of the coil is of the order of 500mH, so that the initial characteristic derives from the coil with the voltage induced by the magnetic flux of the eddy current in the coin being swamped. As a result, there is typically a

SUBSTITUTE SHEET

delay of up to 20 to 25s before useful information can be derived from the characteristic regarding the coin. The series of values for a coin is typically obtained by applying six voltage pulses of varying width to the coil and taking a value of the induced voltage produced from each pulse. If an attempt is made to increase the throughput of coins by using more than one measuring apparatus, care must be taken not to locate two or more measuring apparatus too close to each other because of magnetic interference between the apparatus. Also, as a consequence of the time needed by the apparatus to discriminate each coin, that is to say coins move a large distance relative to the apparatus in the time needed to complete a discrimination operation, coin throughput is limited.

In accordance with one aspect of the present invention, a coin discrimination method comprises applying to a coil an electrical current pulse which increases from zero to a predetermined, absolute value, whereby an eddy current is induced in a coin adjacent the coil; and monitoring the decay of the induced eddy current.

In accordance with a second aspect of the present invention, coin discrimination apparatus comprises an electrical coil for generating an electrical current pulse which increases from zero to a predetermined, absolute value so as to induce an eddy current in a coin adjacent the coil; and monitoring means for monitoring the decay of the induced eddy current.

The invention has general application to coin discriminating apparatus because of the advantage that since the current pulse is applied to the means to the maximum, absolute current level, so the eddy current inducing magnetic flux produced by the coil is substantially the same for repeated pulses, regardless of changes in the temperature or inductance of the coil, and so the monitoring of the decay of the eddy current induced in a coin is improved in a simple and effective manner.

Typically, the current pulse will rise logarithmically to a programmably set limit (for example 2 amps) before being turned off. This injects an accurate amount of energy into the coil thereby achieving greater consistency between the samples.

Preferably, the inductance of the coil is of the order of two millihenries. This is a significant reduction which enables the decay curve to be monitored much earlier than has previously been possible. Furthermore, the use of a steep decay curve which can now be achieved allows multiple coils to be operated in a time multiplexed manner without interfering with one another or sampling at a rate too slow to accurately plot the decay characteristic. Typically, these multiple coils will be arranged in line with adjacent coin transport paths so as to increase throughput. In one embodiment, there are four coin pathways but in other embodiments there may be other numbers of pathways, for example six.

The coils could be fabricated in a variety of ways but preferably are constructed within a printed circuit board (PCB) which greatly improves the reproducibility of electrical and mechanical characteristics. In general, the coils will be operated from the surface of the PCB by a single insulation layer of about 0.125 mm. This allows coins to run much closer to the coils than has been achieved hitherto.

In a very simple application, the monitored decays could simply be stored for future reference. Preferably, however, the method further comprises outputting a signal indicative of a coin under test. Again, in a simple case, this signal could simply actuate a light or other indicator to show the passage of a particular type of coin. However, in a preferred arrangement the output signal comprises a control signal for controlling subsequent passage of the coin. Thus, the control signal could cause actuation of a divert mechanism which diverts the coin to a particular destination for coins of that type. This

clearly has particular application to coin sorting apparatus.

The decay of the induced eddy current can be monitored in a variety of ways. Preferably, however, the decay is monitored at at least three points and preferably at least sixteen points. These points may be determined relative to the point at vhich the electrical current pulse ceases or is switched off. Alternatively, the decaying induced eddy current could be monitored and the periods which pass corresponding to selected amplitudes (for example at least three, preferably at least sixteen) could be monitored.

The method could comprise applying a single electrical current pulse to the coil during the passage of the coin. Preferably, however, the method comprises repeating at least once the application of the electrical pulse and the monitoring of the decay of the resultant, induced, eddy current, determining the maximum value of the eddy current at corresponding sample points of the decay in each application; and comparing the determined maximum values with corresponding reference values. The monitoring of the decay of the induced eddy current could be carried out by specific detection means, but is preferably performed by the coil to vhich the electrical current pulse has been applied earlier. As explained earlier, preferably, a number of sets of apparatus according to the second aspect of the invention are provided, the coils of the apparatus being positioned in line with adjacent coin pathways to enable a plurality of coins to be discriminated. In this case, preferably means are provided for cyclically actuating the coil.

This gives the advantage that a coin discrimination operation is carried out for one of the coin transport paths in a time during which the coins located on the other transport paths have moved only a relatively small distance relative to the apparatus, so that successive coin discrimination operations can be carried out in relation to the other coin transport paths. Furthermore, the speed of

completion of each coin discriminating operation avoids interference between different coils used together because each coil has finished operating before the next apparatus is actuated. This enables the rate of throughput of coins through the apparatus to be greatly increased in comparison with the prior art apparatus.

In a preferred embodiment of the invention, a peak detector is provided for detecting a peak of the decaying signal in the detecting means for each point in order to determine the optimum location of the coin relative to the corresponding coil for identifying a coin. This provides values for comparison with a reference and gives the advantage that for each type of coin to be discriminated, the strongest possible output signal is obtained by the apparatus during the discrimination operation.

A memory is preferably provided in association with the peak detector.

In a preferred embodiment of the invention, the apparatus is provided with coin identifying means for determining the identity of a coin from values obtained by monitoring the induced current in the coin.

An example of a coin sorting apparatus in accordance with the present invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a side view of one example of the transporting apparatus;

Figure 2 is a plan of the support plate of the conveying system shown in Figure 1;

Figure 3 is a side elevation, partly cut away, of the plate shown in Figure 2;

Figure 4 is a plan of of the leading end of the conveyor system shown in Figure 1;

Figure 5 is a schematic block diagram of the control system; Figure 6 illustrates the control system in more detail in block diagram form;

Figure 7A shows the variation during the course of one current pulse of the excitation current coil of the apparatus shown in Figure 6;

Figure 7B shows the variation of the amplifier output of the coil referred to with reference to Figure 7A; and, Figure 8A illustrates the coils in more detail, and Figure 8B is a section on the line X-X.

The apparatus shown in Figures l to 5 comprises an endless belt 1 entrained around three rollers 2-4, one of which, 4, is driven, and an idler drum 5. Coins are supplied to the drum 5 along a supply plate 6 from a hopper 7 and slide towards the drum. As will be described below, the coins are picked up by the conveyor belt 1 and transported along a transport path 8 extending from the drum 5 to the drive roller 4 past a number of coin sorting paths 9 into which the coins are selectively urged. The belt then returns via the idler pulley 3 to pick up further coins.

A portion of the belt 1 is shown in Figure 4 as it passes under the drum 5. As can be seen in Figure 4, the drum 5 comprises five laterally spaced discs 10-14 mounted on an axle 15. The drum is frictionally rotated in a clockwise direction as shown in Figure 1.

The belt 1 is divided into four subsidiary transport paths 16-19 spaced laterally across its width. Each subsidiary transport path 16-19 has sets of mechanical locators 20 spaced substantially equally along its length, the mechanial locators each comprising a pair of flanges 20A, 20B positioned to define a "V" coin location position. At each coin location position the belt also has an elongate aperture 21. It will be noted that the coin location positions 20 of adjacent subsidiary transport paths 16-19 are offset in the direction of movement of the belt. As the belt 1 is driven past the drum 5 it passes over a plate 22 forming one surface of a suction chamber 23. The plate 22 has a generally rectangular form with a set of

four elongate grooves 24-27 (Figure 2) extending along it, the grooves being aligned with respective sets of apertures 21 in the subsidiary transport paths 16-19 defined by the belt 1. Each groove 24-27 has a set of spaced apertures 28, two being indicated in Figure 2, through which vacuum is communicated from the suction chamber 23. The suction chamber 23 itself is evacuated by a vacuum pump (not shown) . As the belt 1 passes over the plate 22 therefore it is sucked towards the plate along the grooves 24-27. Underneath the plate 22 and within the chamber 23 are positioned 44 solenoids 29 each having a plunger 30 aligned with a respective aperture 28. Each plunger 30 has a small compression spring 30\' at its tip.

Upstream of the solenoids 29 are positioned a set of four coin discriminators 31-34 laterally spaced apart across the plate 22 in alignment with respective subsidiary transport paths 16-19.

Each solenoid 29 is aligned with a respective coin sorting path 9. The paths 9 shown in Figure 1 correspond to the 11 solenoids cooperating with the groove 24 and subsidiary transport paths 16. There will be further coin sorting paths provided which are not shown in Figure 1. The coin sorting paths are connected by conventional slideways (not shown) to respective collection bags. Operation of the solenoids 29 is controlled by a microprocessor 35 (Figure 5) which has 44 output lines 36 one connected to each of the solenoids 29. In addition, the control processor 35 receives coin discrimination information from the coin discriminating circuits 31-34. Operation of the control processor 35 will be described below.

In a typical operation, a group of unknown coins is tipped into the hopper 7, the coins passing through the outlet of the hopper onto the inclined plate 6. The drum 5 is rotated in a clockwise direction and the coins are gradually sorted to pass between respective pairs of the discs 10-14. Each coin is then picked up by a pair of

mechanical locators 20A, 2OB and is carried around the lower periphery of the drum 5 into the transport path 8. The coin will cover the associated aperture 21 so that as soon as the coin reaches the upstream end of the vacuum chamber 23, it will begin to experience suction through the appropriate groove 24-27. This suction in combination with the mechanical locators 20A, 20B will hold the coin in position on the belt as the coin is transported upwardly but at an acute angle α to the horizontal. This acute angle is typically in the range 80-90°.

The coin then passes over the appropriate coin discriminating circuit 31-34 which carries out a discriminating process to be described below to determine the denomination of the coin. This information is then fed to the control processor 35. The control processor 35 knowing the speed of movement of the belt l, and the position of the solenoid 29 corresponding to the appropriate ejection point for that denomination of coin, actuates the solenoid at a time at which the coin is passing the correct coin sorting path 9. This actuation causes the plunger 30 to be moved outwardly through the appropriate apertures 21, 28 where it will push the coin off the belt and into the coin sorting path 9. The coin then rolls down into the collection hopper or bag. In some circumstances, it is possible that more than one coin will be picked up by the mechanical locators 20A, 20B as they pass under the drum 5. Only coins held in the locators and subject to suction will be carried upwards. The residue, when reaching the vertical or near vertical attitude will fall back to be reprocessed. Any two (or more) coins overlapping in the locations will have the outermost coin fall back, the removal being assisted by brushes or fingers. For example, two coins could be picked up in a locator, one coin above the other. In these circumstances, the two (or more) coins would be carried around the lower periphery of the drum 5. Due to the slope of the transport path 8, the poorly located coin less

influenced by the vacuum will fairly quickly drop off the belt 1 back towards the drive 4, when they can be reprocessed. Brushes 40 will then assist the removal of any remaining mislocated coins. In all cases, this will occur before the coins reach the discriminating circuits 31-34.

The control processor 35 also monitors the number of coins which have been sorted to a particular location. It does this by recording in a memory the number of times it has actuated each plunger 30. This facility can also be used to enable other functions such as coin batching to be achieved where the processor is told that only a predetermined number of coins should be sorted to a particular location. It will be appreciated that a number of variations of the coin transporting apparatus and coin validation apparatus are possible. For example, the belt 1 is not limited to having four subsidiary transport paths but may have any number. In addition, the apparatus need not use solenoid-controlled plungers 30 for ejecting coins but may use other suitable means, e.g. a high pressure compressed air source. Also, the plungers 30 could act on the belt rather than pass through apertures 21. Other variations are described in our copending International Application of even date and entitled "Coin Transporting Apparatus and Coin Validation Apparatus Employing Same". (Agents Ref: 30/3941/03) .

A coin discrimination method will now be described in more detail. Referring now to Figure 6, each coin discriminator 31-34 has a coil 52, comprising a spiral-shaped track (60, Figure 8A) on a printed circuit board (PCB) 61 and having an inductance of the order of 2mH. The track 60 is secured to the board 81 by adhesive 62 (Figures 8B 8C) and covered by a top layer 63 having a thickness of about 0.125mm. Each coil 52 is connected to a respective pulse circuits 53 and a respective comparator 54. Each

comparator output is supplied to the microprocessor 35. Each of the coils 52 is also connected through a switch 56 to an amplifier 57, which is in turn connected through an analogue-to-digital converter 58 to the microprocessor 35. When the discriminating apparatus is actuated, the conveying means causes coins located on the four coin transport paths to pass the coils 52 at a rate of approximately lm/s. At the same time, the microprocessor 35 is informed that coins are approaching the coils 52 by an index sensor (not shown) . Then, at time t=0, the microprocessor 35 actuates one coil pulse circuit 53 corresponding to a coil 52, which then applies an electric current pulse to the selected coil 52 and the associated comparator 54. The current in that coil 52 then increases as shown in Figure 7A until, at time to the comparator 54 detects a predetermined maximum current level, which is of the order of 2A and is preset by a current preset circuit 59 which is connected to the microprocessor 35. The time between t=0 and t=t ₀ is variable because of variations in the temperature of the coil, but is typically approximately 25/is. When the pre-set maximum current level is reached, the corresponding comparator 54 switches to input a signal to the microprocessor 35 which as a result switches the coil pulse circuit 53 off. The switching off of the coil pulse circuit 3 causes a rapid charge of current in the coil 52, which in turn produces a large magnetic pulse. The magnetie pulse induces a decaying eddy current to flow in a coin located adjacent to the coil 52, and this current in the coin decays at a rate which depends on various physieal parameters of the coin.

Because of the magnetic flux linkage between the coin and the corresponding coil 52, the decaying eddy current in the coin induces a voltage in the coil 52. The switch 56 is actuated to connect the coil 52 to the buffer amplifier 57 to amplify the output voltage of the coil 52 and which forms a critically damped circuit. This allows the back

e f to decay without ringing. The output of the amplifier 57 passes into the analogue-to-digital converter 58, which is in turn monitored at 16 times during a single decay pulse of the voltage in the coil 52, and this produces a series of values unique to each type of coin discriminated. The first monitoring point t ₁ occurs at about Sμs after the cut off time to and the remaining monitoring points t ₂ to t ₁₆ occur approximately at 25μs intervals thereafter, although these time intervals can be varied. This situation is illustrated in Figure 7B. Thus, the time taken to produce values for discriminating a coin is of the order of 500 s, in which time the coin has moved approximately 0.5mm, which is not a significant amount of movement.

It can therefore be seen that the coin discrimination operation ean be easily carried out in relation to an individual coin in a small time interval compared with the time required for the coin to move a significant amount through the apparatus 1 relative to the corresponding coil 52. Furthermore, it can also be seen that only one pulse is required in order obtain the necessary monitoring values for identifying a coin.

The decay curve corresponding to an individual coin varies with the position of the coin relative to the corresponding coil 52. A position of the coin relative to the coil 52 exists such that the voltage induced in the coil 52 as a result of the decaying eddy current in the coin is a maximum, and this position is the optimum and most reliable position for identifying a coin. Each of the 16 monitoring points for the discriminating process is associated with a memory register so that in order to determine the optimum position for a particular coin, the coil 52 is repeatedly pulsed and on each new sample the microprocessor 35 carries out a peak detecting process such that it overwrites the stored value in the memory , if the measured value is greater than the value already stored. The stored values are used by the microprocessor 35 for comparison with a table of values (upper and lower values

for each sample point) for known coin types, in order to determine the denomination of that coin. Thus if all samples fall within the ranges for a particular coin, the coin is identified. The values stored in the memory are cleared before that coil 52 repeats the measuring operation on another coin.

The reference upper and lower values are set during a calibration run when sets of coins of known denominatin are processed and the extremes at each sample point recorded in the table.

When a pulse has been applied to one coil 52 and the measurements made on the decay characteristic, the microprocessor 35 applies a current pulse to the coil 52 corresponding to the adjacent coin transport path and connects the coil output to the microprocessor 35 via the switch 56. This operation is then repeatedly cycled through all of the four coils 52, so that by switching between different coils 52, coin discrimination can be carried out in relation to coins located on all four coin transporting paths, each having a throughput rate of about lm/s.

It can thus be seen that the coins on each respective one of all four transport paths can be discriminated at the same transport rate as the known discriminating apparatus discriminates coins located on a single transport path having the same transport rate. Thus the apparatus of the present embodiment has a throughput rate of four times that of the known apparatus without increasing the rate of feeding of coins on an individual transport path through the apparatus.

It will be appreciated that various modifications of the apparatus are possible without departing from the scope of the invention. In particular, the apparatus is not limited to having four coils with associated transport paths, and the number of coils is limited only by the requirement that all coin discriminating operations can be carried out before the coins located on the transport paths

have moved a significant distance relative to the apparatus Also, the coils 52 are not limited to being in the form of printed circuit board tracks, but may be in any form having suitable resistance and inductance values. In addition, the values of the current pulse and time point positions and spacings can be varied. Moreover, the apparatus is not limited to the arrangement in which each coil 52 has a separate coil p lse circuit 53 and comparator 54 corresponding thereto, and by the provision of suitable switching means, a single coil pulse circuit 53 and comparator 54 may be used. The apparatus is also not limited to the embodiment in which the induced current in the coin is monitcred by the coil 52 to which the electric pulse is applied, and a coil separate from the excitation coil may be provided to monitor the induced current.