COIN DISCRIMINATION APPARATUS WITH OPTICAL SENSOR

Abstract: Coin discrimination apparatus such as a coin validator includes a coin rundown path (2) with an optical sensing station (6) and an inductive sensing station (7) which both provide coin validation data to a microprocessor (8) that operates an accept gate (3) when a coin is determined to be of an acceptable denomination. The optical sensing station (6) includes an array of emitters (16) and detectors (18) disposed transversely of the coin rundown path (2) to define rays of light which intersect the coin at different chordal positions. The duration of pulses produced by detectors (18) are processed in terms of a ratio of their durations so as to determine coin diameter independently of coin velocity along the path. Compensation for coin acceleration is also described together with a technique to determine coin thickness.

Description: COIN DISCRIMINATION APPARATUS WITH OPTICAL SENSOR DESCRIPTION FIELD OF THE INVENTION This invention relates to coin discrimination apparatus such as a coin validator. BACKGROUND TO THE INVENTION Conventional coin validators utilise mechanical or electrically inductive techniques to discriminate between true and false coins and also to provide an indication of coin denomination. Some systems utilise a light beam which is interrupted by the passage of the coin along the path so as to provide an approximate indication of coin diameter. The present invention provides an improved optical discrimination apparatus for coins. By optical is meant apparatus which operates both with visible and non-visible radiation e.g. infra-red. SUMMARY OF THE INVENTION In accordance with the invention, it has been appreciated that by measuring the coin at first and second chordal positions optically, and utilising the duration of both of the measurements, it is possible to provide an output signal as a function of a dimensional parameter of the coin in which the velocity of the coin along the path does not significantly affect the output signal. More particularly, in accordance with the present invention there is provided coin discrimination apparatus comprising means defining a path for a coin under test, first and second optical sensors including means for directing first and second light rays transversely across the path to be intersected by the coin during its passage along the path at first and second different chordal positions thereof, and detector means for providing first and second detector signals as a function of duration of intersection of the first and second rays by the coin, and control means responsive to both of said first and second detector signals to produce an output signal as a function of a dimensional parameter of the coin wherein a compensation is effected for different coin velocities along the path. Preferably, the control means is operative to compute said output signal as a function of the ratio of the durations of the first and second detector signals whereby said output signal is a function of coin diameter and is compensated for coin velocity. The control means may also compute the output signal as a function of the relative commencement and finishing times of the first and second detector signals in such a manner as to compensate for acceleration (or deceleration) of the coin along the path. It is also possible according to the invention to provide an output signal as a function of coin thickness. One of the light rays may be directed across the path at a different angle to the other and said control means may thereby be rendered operative to provide an output signal as a function of coin thickness. The first and second detector signals may also be processed to compensate for coin bounce along the path. It is also possible to compensate for coin wobble i.e. wobble of the coin from side to side along the path. The optical discrimination apparatus according to the invention may be used in combination with an inductive sensor in order to determine whether the coin has a metallic content corresponding to a true coin. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully understood an embodiment thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic block diagram of a coin validator incorporating coin discrimination apparatus according to the invention; Figure 2 is a schematic perspective view, partially broken away, of the coin rundown path shown in Figure i; Figure 3 shows in more detail the configuration of optical emitters and detectors for use in coin diameter measurement; Figure 4 illustrates waveforms produced by the detectors of Figure 3 when the coin moves with a constant velocity along the coin rundown path; Figure 4a illustrates waveforms corresponding to those of Figure 4 when the coin is subject to deceleration along the path; Figure 5 is a schematic view of the coin rundown path from above showing a coin subject to wobble (to the right) as it passes the optical detectors; and Figure 6 illustrates the waveforms produced by the detectors of Figure 5. DESCRIPTION OF EMBODIMENT Referring to Figure 1, the coin validator consists of a coin entrance slot 1 through which coins are inserted into a coin rundown path 2. True coins are directed by a solenoid operated accept gate 3 into an accept chute 4 whereas unacceptable coins pass directly to a reject chute 5. The coin rundown path passes two detection stations 6, 7 for the coins, which provide electrical signals to a microprocessor 8 that controls the solenoid operated accept gate 3. The sensing station 6 comprises an optical detecting station whereas the station 7 utilises an inductive sensor which operates for example as described in our specification GB-A-2 169429. Whilst the detecting stations 6, 7 are shown to be at separate locations in Figure 1, they may in fact overlie one another. Broadly, the optical detecting station 6 consists of a plurality of light emitting devices (not shown in Figure 1 but described in more detail hereinafter) driven by electrical drive circuit 9, which produce a plurality of light beams that extend transversely across the coin rundown path 2 to be interrupted by the passage of a coin along the path. The beams are detected by a plurality of detectors (not shown in Figure 1) which feed electrical signals to interface circuitry 10 that processes the detector outputs for application to the microprocessor 8. Similarly, the inductive sensor for the station 7 is driven by circuitry 11 and produces electrical signals to interface circuitry 12 for application to the microprocessor 8. The circuits 11 and 12 may operate in the manner described in our specification aforesaid. Referring now to Figure 2, the configuration of the sensing stations 6, 7 is shown in more detail. A coin 14 is shown on the coin rundown path 2 moving in the direction of arrow 15. In order to achieve diameter measurement, the optical sensing station 6 includes in this example four optical emitters 16A, B, C, D typically in the form of light emitting diodes or solid state laser devices, which are configured to produce respective beams of light that pass through apertures 17 in the wall of the coin rundown path so as to be detected by corresponding detectors 18A, B, C, D. The beams are conveniently parallel, but could be converging or diverging. The emitters 16 however each produce rays which pass transversely across the path 2, to be received by the respective detectors 18. The aperture 17A is shown in Figure 2 but apertures 17B - D are not shown, since the wall of the rundown path 2 has been shown broken away for purposes of clarity. The emitters 16 and detectors 18 are each arranged in a respective straight line running perpendicular to the length of the coin rundown path 2. The emitters 16 produce respective light beams 19A, 19B, 19C, 19D shown in dotted outline which are disposed at right angles to the plane of the side wall of the coin rundown path 2. As the coin rolls down the path 2 through the optical station 6, the beams of light 19 are interrupted. The duration of the interruptions for the individual beams depend upon the diameter of the coin 14 and its velocity along the path 2. Each of the beams 19 impinges upon the coin 14 at a different chordal position and as shown in Figure 3, the various chordal lengths over which the beams 19 pass are shown schematically by dotted lines 20A, 20B, 20C, 20D. The electrical outputs of the detectors 18A - 18D are fed to the interface circuitry 10 (Figure 1) so as to produce the waveforms shown in Figure 4, for the detectors 18A, B, C, D respectively. It will be seen that the duration of the pulse derived from each detector 19 is dependent upon the chordal length of the coin that intersects the relevant light beaut 19A - D. Thus considering the pulse lengths from the detectors 18C, 18D, the corresponding pulse lengths t., t 2 can be processed to provide an output indicative of coin diameter. The ratio ^/t j^ relates directly to the coin's diameter and is independent of the velocity of the coin along the coin rundown path (assuming no coin acceleration). It will be appreciated that if the coin travels at a increased velocity both t- and t, will become of shorter duration but the ratio thereof remains substantially independent of velocity. Thus, the microprocessor 8 is configured to compute the ratio to P rovide an output signal indicative of coin diameter. This signal is then compared with preprogrammed values thereof corresponding to true coins and if the coin is determined to be a true coin, the accept gate 3 (Figure 1) is operated to direct the coin to the accept chute 4. Otherwise, the coin is rejected and passes to chute 5. Further verifying checks of coin diameter can be carried out by comparing ratios of the pulse length developed by detectors 18A, 18B in various combinations. Certain smaller sized coins will not necessarily produce an interruption for the uppermost detectors 18C, 18D and such information can be preprogrammed into the microprocessor in order to provide reference information for acceptable coins. Thus, in use the microprocessor 8 analyses the output signals from the uppermost two detectors 18A - D, which are blocked by the passage of the coin, and computes the ratio t-/t 1 for these signals. The microprocessor also identifies which of the signals from detectors 18A - D constitutes the uppermost signed. blocked by the coin. For example a coin X may block detectors 18A and 18B during its passage along the rundown path 2, so that the microprocessor will compute e.g. an - wil1 note that the top detector 18 blocked is referenced B, thus giving a signal 1.032 B. Similarly a different larger diameter coin Y, which blocks all four detectors 18A - D may give a result 1.032 D. These results can be compared with preprogrammed values in the microprocessor. Thus, even though the ratio -JZ- Λ -- or ( -θLτιs X and Y may spuriously be the same, the coding suffix A to D gives an unambiguous coding for the coin diameter. Although the system just described is able to compensate for coins passing the optical sensor station at differing velocities, compensation is required for an accelerating or decelerating coin which would otherwise introduce some error into the results. Figure 4a shows the outputs of the detectors 18A - D in the event of deceleration of a coin. It will be seen that the waveforms assume an assymetrical pattern and the relative times of commencement and cessation of the pulses is changed as a result of the acceleration or deceleration. By reference to Figure 4, it will be seen that in conditions of no acceleration, the pulse from detector 18D is disposed symmetrically in relation to the pulse of detector 18C such that the duration between the start times for the pulses t_ is substantially the same as the duration between the pulse cessation times t β . However, as shown in Figure 4a, in the event of deceleration, the time periods t- and tg become different; the difference is a function of the deceleration (or acceleration). Thus, the microprocessor 8 is arranged to compute the time periods t,. and t g and thereby provide an indication of acceleration. Such indication of acceleration can then be used in a predetermined algorithm to modify the values of the pulse lengths derived for the various detectors 18A - D (Figure 4a), so as to make a correction for acceleration. The diameter measurement can then be carried out as previously described. Referring again to Figure 2, in order to provide a signal indicative of thickness of the coin, the optical sensing station 6 includes an optical emitter 16E which produces a beam 19E which is disposed obliquely to the plane of the side wall of the coin rundown path 2. The beam 19E passes through an aperture 17E to a detector. This configuration is shown in more detail in Figure 5 wherein certain details have been omitted for the purposes of clarity. It will be seen that the beam 19E from the emitter 16E is disposed obliquely to the longitudinal direction of the coin rundown path 2. The source detector pair 16A, 18A is shown configured at 90 degrees to the coin rundown path. Additionally, the source detector pair 16F, 18F may be included in order to correct for coin wobble as will be described hereinafter. The outputs derived from the various detectors 18A - F by the interface circuitry 10 (Figure 1) are shown in detail in Figure 6. An indication of coin thickness can be derived from the outputs of detectors 18A, 18E. From Figure 2, it will be seen that the beams 19A, 19E intercept the coin at substantially the same chordal position. However, since the beam 19E is disposed obliquely relative to the beam 19A, the pulse derived from detector 18E is of a longer duration than the pulse derived from detector 18A. The relative length of the pulses depends upon coin thickness. This is shown in detail in Figure 6a, 6b. As shown in Figure 6b, for a thin coin there is a relatively small pulse length difference between the outputs of detectors 18A, 18E whereas from Figure 6b it can be seen that for a thicker coin, the pulse length difference is substantially greater. In accordance % with the invention, the microprocessor 8 (Figure 1) is programmed to compare the pulse length durations and determine coin thickness. Whilst the computation is preferably performed on the basis of comparison of the outputs of 18A, 18E (which xelate to the same chordal position of the coin) a computation could be performed on the basis of the outputs of detectors 18E, 18B or some other appropriate reference detector. The resulting thickness computation can then be compared by the microprocessor 8 with appropriate reference values stored in its memory, preferably in combination with the previously described diameter measurements to provide an indication of a true coin. If for some reason the coin has a side-to-side instability or wobble this may affect the thickness computation causing an apparent increase in thickness. Referring to Figure 5, the emitter/detector pair 16F, 18F provides additional signals to compensate for coin wobble. Referring to Figure 6c, in the event that the coin wobbles in a direction away from the detectors 18 (i.e. towards the sources 16) the output of detector 18E will be of a shorter duration than if no wobble were to occur. However, the output of detector 18F is commensurately increased and therefore the microprocessor can utilise an algorithm responsive to the outputs derived from detectors 18E, 18F in order to correct for wobble. The relative increase and decrease of the pulse durations from detectors 18E, 18F are shown as X, Y in Figure 6c. In order to minimise coin wobble, the geometry of the coin rundown path may be configured so that there is a slight inclination of the side wall of the path 2 towards the detector 18. Another problem that may arise is coin bounce. Thus, as a coin rolls down the path 2, it may bounce vertically upwardly. A compensation for coin bounce is achieved by monitoring the time period t. (Figure 4) derived from the lowermost detector 18A. In the event of coin bounce, the time period t. will be of a shorter duration than would be otherwise expected and this can be utilised to normalise the values of t., t 2 used for computing coin diameter thereby compensating for coin bounce. Referring again to Figure 2, the inductive sensor station 7 includes an inductive sensor coil 21 which is utilised to form an inductive coupling with the coin as it passes along the coin rundown path. As explained in specification GB-A-2169429 the inductive coupling provides an indication of the coin size and its metallic content. The inductive coupling is a function of the coil size and geometry, and its orientation with respect to the coin, and such factors will produce different emphasis for coin diameter, thickness, metallic content etc. in the inductive coupling. The inductive coupling between the coil and the coin can be utilised to produce a frequency and/or amplitude shift in the output from the coil, which can be digitised and utilised as a signature signal indicative of coin denomination. The signature signal can be compared by the microprocessor 8 with preprogrammed values to determine whether the coin is of an acceptable denomination. The provision of the inductive sensor coil has the advantage of permitting the system to discriminate between plastic and metallic items under test and also to determine whether a particular coin under test has the correct metallic composition. As previously mentioned, the light emitters 16 are conveniently infra-red diodes or laser emitting devices. The use of infra-red radiation has the advantage that it penetrates contaminants such as particulate dirt, grease and the like, and permits discrimination from ambient light. In practice, a lens system may be applied over the emitters or detectors. The lens system may constitute a focussing lens or a protective transparent window. Appropriate apertures in the walls of the coin rundown path may be utilised to collimate the various light beams and to limit cross-talk. The light emitting sources may be operated under a pulse system e.g. the clock frequency of the microprocessor or a time divided signal derived therefrom in order to provide discrimination from ambient light. The sensitivity of the apparatus for any given coin diameter depends in part upon the spacing of the source/detector pairs and the number utilised. In use, the microprocessor 8, in response to an initial review of the outputs of the detectors 18, determines which outputs are to be utilised for coin diameter and/or thickness measurement and which (if any) are to be utilised to -compensate __or_-bounce and acceleration compensation. Such decisions are based upon the relative pulse lengths from the various detectors. Thus, the invention provides an improved optical means of discriminating between true and fraudulent coins and discrimination between different coin denominations. As used herein, the term coin includes a token or like item of credit. The advantage of the optical system described herein is that is provides an accurate actual measurement of the dimensional parameters of the coin i.e. diameter and/or thickness. In contrast, conventional inductive systems provide an output which is a complex function of dimension, electrical resistance/inductance, rim characteristics and surface pattern. By means of the optical techniques used in the invention, the diameter readings will be of high resolution typically less than .02 mm. Also, if required, the system can be used to identify the dimensions of plastic tokens and coins. Additionally, the apparatus according to the invention can be used for low current applications wherein a detector is utilised to detect a coin entry and "wake up" the remainder of the circuit. Additionally, one of more of the optical emitter/detectors could be used for the detection of unauthorised or fraudulent insertion of non-metallic objects, in a manner that cannot be achieved with a conventional inductive system. The optical detection station 6 is comparatively immune from metal proximity problems that can be encountered with conventional inductive systems. Also, problems associated with "hand capacitance" i.e. the capacitance presented by a user upon insertion of a coin into the validator and EMI radiation are less of a problem than with conventional inductive validator systems. Objects containing holes such as washers can be more readily identified or ejected and if necessary, the hole size can be computed. The optical detecting station 6 described herein can be very compact and occupy of the order of 5 mm of the length of the coin rundown path 2. unlike inductive sensors, the optical sources and detectors can be placed close to each other and can even be combined physically within the body of a conventional inductive sensor.

Claims: CLAIMS 1. Coin discrimination apparatus comprising: means defining a path for a coin under test; first and second sensors including means for directing first and second light rays transversely through the path to be intersected by the coin at first and second different chordal positions thereof and detector means for providing first and second detection signals having durations as a function of the duration of intersection of the first and second rays by the coin respectively, and control means responsive to the duration of both of said first and second detection signals to provide an output signal as a function of a dimensional parameter of the coin wherein compensation is effected for different coin velocities. 2. Coin discrimination apparatus according to claim 1 wherein the control means is operative to compute said output signal as a function of the ratio of the durations of said first and second signals whereby said output signal is a function of coin diameter and is compensated for coin velocity. 3. Coin discrimination apparatus according to claim 1 or 2 wherein the control means is operative to compute said output signal as a function of the relative starting and cessation times of the first and second signals in such a manner as to compensate for acceleration of the coin along the path. 4. Coin discrimination apparatus according to any preceding claim wherein one of said light rays is directed across said path at a different angle to the other and said control means is operative to provide an output signal as a function of coin thickness. 5. Coin discrimination apparatus according to any preceding claim including a third optical sensor including means for directing a third light ray obliquely of said coin path and at a different angle to said first and second rays whereby to provide a third detector signal to compensate for coin wobble. 6. Coin discrimination apparatus according to any preceding claim including further optical sensors including means for directing further light rays transversely of the path to provide further detector signals. 7. Coin discrimination apparatus according to claim 6 including means for determiningτriιich of said rays are not intersected by the passing coin. 8. Coin discrimination apparatus accroding to claim 6 or 7 including means responsive to said first, second and further detector signals for determining if the coin is subject to coin bounce. 9. Coin discrimination apparatus according to any preceding claim including inductive sensor means for forming an inductive coupling with said coin to provide an output signal indicative of the metallic content of the coin. 10. Coin discrimination apparatus according to any preceding claim including means for comparing the or each said output signal with reference values thereof to determine coin validity and/or demonination. 11. Coin discrimination apparatus comprising: means defining a path for coins under test; first and second sensors including means for directing first and second light rays transversely through the path at different angles thereto to be intersected by the coin, and detector means for providing first and second detection signal having durations as a function of the duration of intersection of the first and second rays by the coin respectively; and control means responsive to both said first and second detection signals to provide an output signal as a function of the thickness of the coin.

Inventors: WOOD DENNIS, WOOD, DENNIS
Applicants: COIN CONTROLS, COIN CONTROLS LIMITED
Application year: 1991
Main classification: G07D5
IPC codes: B65H7, G07D5