GB2325076A - Coin validator - Google Patents

Abstract

A coin validator (1) includes coils (12) for sensing properties of coins passing along a passageway (2a). Magnets (13a, 13b), or some other means of producing a time-invariant magnetic field, are associated with at least one of the coils (12) so as to add a time-invariant magnetic field to the alternating magnetic field produced by the coils. The addition of the time-invariant magnetic field enables magnetic coins to be distinguished from non-magnetic coins which otherwise appear substantially identical when inductively sensed. The coin diameter is determined from the times the coin interrupts optical beams U, D1 and D2 extending across the passageway 2a.

Description

Coin Validator with Time-invariant Magnetic Field Component Description The present invention relates to a coin validation apparatus.

In many known forms of coin validator, an oscillating current signal is applied to one or more coils which produce an oscillating magnetic field in a coin path. As a coin passes through this field, it absorbs energy from it resulting in a decrease in the voltage across the coil or coils. This decrease in voltage is used to determine the identity of the coin under test. Situations arise where a non-magnetic coin cannot be reliably distinguished from a similar coin formed from magnetic material.

It has been proposed that this problem be solved by positioning a magnet near a coin path. Coins of magnetic material will be slowed by passing through the magnet's field and can then be distinguished on the basis of their speed after passing through the magnet's field. However, this technique is only applicable if coins reach the magnet's field with the same speed. This condition cannot always be met, particularly in the case of validators in which coins are sensed while in free fall in a vertical coin path. The speed of a coin when it reaches the magnet's field will vary in dependence on the distance through which it has been accelerated by gravity.

The present inventor has discovered that adding a time-invariant field to a timevarying field enables magnetic and non-magnetic coins to be distinguished and that, surprisingly, the effect is not dependent on coin speed.

According to the present invention, there is provided a coin validation apparatus comprising a coin path, a sensor coil for inductively sensing a coin in the coin path and means for adding a time-invariant magnetic field component to a time-varying magnetic field generated by the sensor coil. The time-varying magnetic field will usually be produced by applying a sinewave current to the coil. A processor for analysing sensor signals is a standard feature of a coin validator and may be included in the apparatus to which the present invention is directed. The processor typically analyses amplitude and/or frequency changes in the sensor signal.

The present invention has been found to be particularly advantageous where the sensor coil is configured such that the time-varying magnetic field has a major component parallel to the coin path. Such a field configuration may be produced by winding the sensor coil on an elongate former, the former having first and second elongate pole faces each extending across the coin path to be parallel to the faces of a coin therein and being spaced along the coin path in the direction of coin travel. This configuration has the added advantage of providing a magnetic field which is constant across the width of the coin path.

Preferably, the means for adding a time-invariant magnetic field is configured to produce a magnetic field substantially free of a component parallel to the coin path.

Preferably, the time-invariant magnetic field is stronger than the peak strength of the time-varying magnetic field. Indeed, the stronger the time-invariant magnetic field the better the results obtained. However, this field should not be so strong that magnetic coins are held by it against a wall of the coin path.

It is not believed that the success of the present invention is due to the time-invariant magnetic field pulling magnetic coins towards the sensor coil because similar effects were not achieved for non-magnetic coins by tilting the coin path so that they ran hard against a sensor coil.

Conveniently, the means for adding a time-invariant magnetic field comprises one or more permanent magnets. These magnets are preferably mounted with a pole in contact with a magnetic former on which a sensor coil is wound. If more than one magnet is used, they are preferably arranged such that they assist each other in the generation of the time-invariant magnetic field. In the preferred embodiment, described below, the magnets both have their north poles in contact with the coil former, although they could both have their south poles in contact with the coil former.

The time-invariant magnetic field may also be produced by an electromagnet, by applying a dc bias current to the sensor coil, or by winding the coil on a magnetised former.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a validator according to the present invention with its front cover removed; Figure 2 is a sectional view along AA of the validator of Figure 1; Figure 3 shows the arrangement of the sensor coils and magnets of the validator of Figure 1 Figure 4 is a block diagram of the electronic circuit of the validator of Figure 1; Figures 5a to 5d illustrate the passage of a small coin past the optical sensor stations of the validator of Figure 1; and Figures 6a to 6e illustrate the passage of a large coin past the optical sensor stations of the validator of Figure 1.

Referring to Figures 1 and 2, a coin validator body 1 defines a rectangular crosssection coin passageway 2. The passageway 2 comprises a straight, vertical upper portion 2a, where various sensor stations 3 are located, and a wider lower portion 2b.

An accept gate 4 is arranged for diverting coins along either of two routes A, B. The accept gate 4 normally blocks route A but is opened if the signals from the sensor stations 3 indicate that a valid coin has been inserted into the validator. The upper portion 2a of the passageway 2 has a width w greater than the diameter of the largest coin 5 of interest and a depth b greater than the thickness of the thickest coin of interest. The entry to the upper portion 2a of the passageway is flared so as to simplify alignment of the validator with a coin insertion slot (not shown).

Considering the sensor stations 3 in more detail, an upstream optical sensor station comprises a lensed light emitting diode (LED) 6 mounted in the validator body 1, so as to shine a beam U of light across the width w of the passageway 2 through a slit 7 opening into the passageway 2. The slit 7 extends across the full depth b of the upper portion 2a of the passageway. A lensed photosensor 8 aligned to receive the beam from the LED 6 completes the upstream optical sensor station. A downstream optical sensor is similarly constructed from a lensed LED 9, a slit 10 and a lensed photosensor 11 to shine a beam D1 across the passageway 2, and is located a short distance below the upstream sensor. A further downstream optical sensor station, comprising a LED 30 for producing a beam D2, a slit 31 and a photosensor 32, is provided.

Two elongate sense coils 12 are located between the upstream and the downstream optical sensor stations. The sense coils 12 are press fitted longitudinally into respective slots extending transversely across the width w of the upper portion 2a of the passageway. First and second magnets 13a, 13b are affixed to the former of one of the sense coils 12. The sense coils 12 will be described in more detail below.

Reflective strips 100 are provided on the walls of the passageway 2 between each of the LEDs 6,9,30 and the corresponding photosensors 8,11,32. The reflective strips 100 increase the light intensity at the photosensors 8,11,32 in the absence of a coin by reducing the amount of light absorbed by the walls of the passageway. As a result, the reduction in light intensity at the photosensors 8,11,32, due to the passage of a coin, is more profound than would be the case without the reflective strips 100. This makes it easier to detect accurately the edges of passing coins.

The reflective strips 100 also solve the problem of the LEDs 6,9,30 not directing light directly across the coin passageway, making the apparatus much less sensitive to the orientation of the LEDs 6,9,30 and the direction in which light is actually emitted therefrom. In the absence of the reflective strips 100, misaligned LEDs result in regions of the passageway 2 which are not illuminated. If a coin passes through one of these regions, it will not affect the light intensity at the relevant photosensor 8,11,32.

The reflective strips 100 may be, for example, painted onto the walls of the passageway 2 with metallic paint or formed from metal foil stuck to the walls of the passageway 2.

Referring to Figure 3, each coil 12 comprises an elongate, I-section former 42 about which the winding 43 is wound. The former 42 is formed from a high permeability material such as sintered ferrite or iron bonded in a polymer, for example 91% oxidised iron bonded in a polymer. Thus, the former 42, if it is non-conducting, can serve both as a core and as a bobbin onto which the winding 43 is wound directly.

An electromagnetic shield 44 comprises an elongate member having a flange extending perpendicularly at each end. The shield 44 is arranged to be attached to the coil 12 such that the winding 43 is wholly covered along one long side of the former 42 by the elongate member and at least partially covered at the ends of the former 42.

The purpose of the shield 44 is to increase the Q of the coil 12 but also reduces both the susceptibility of the coil 40,41 to electromagnetic interference (EMI) and the electromagnetic energy emanating from the coil, other than into the coin passageway 2 (Figure 1) of the validator.

The first magnet 13a is glued to an end face of one of the coils 12 and the second magnet 13b is glued to the underside of the coil 12 towards the other end thereof. In both cases, it is the north pole of the magnet 13a, 13b that is glued to the coil. The positioning of the magnets 13a, 13b is dictated in this case by the need to incorporate them in a particular validator design. Other arrangements of magnets may be used.

For instance, the north pole of a single magnet could be glued to the closed, rear face of the coil 12.

In use, the coils 12 generate magnetic fields whose lines of flux link the top and bottom cross-pieces of their I-section formers 42 via the passageway 2a.

Consequently, the fields have major components parallel to the direction of coin travel in the passageway 2a.

Referring to Figure 4, the LEDs 6,9,30 are driven by LED driver circuitry 15 in order to produce the upstream and downstream beams U,D1,D2. The LEDs 6,9,30 typically produce optical radiation in the infra-red range although visible radiation can also be used. It will thus be appreciated that as used herein, the term optical radiation includes both visible and non-visible optical radiation.

The photosensors 8,11,32 are connected to interface circuitry 16 which produces digital signals xi, x2, x3 in response to interruptions of the upstream and downstream beams U,D1,D2 as a coin falls along the passageway 2 past the sensor stations 3. The coin signals x" X2, x3 are fed to a microprocessor 17. As explained in our United Kingdom patent application no. 2 169 429, the inductive coupling between the coils 12 and a passing coin 5 gives rise to apparent impedance changes for the coil which are dependent on the type of coin under test. The apparent impedance changes are processed by coil interface circuitry 18 to provide a coin parameter signals X3, X4 which are a function of the apparent impedance changes.

The microprocessor 17 carries out a validation process on the basis of the signals x" x2, X3, X4, X5 under the control of a program, stored in an EEPROM 19. If, as a result of the validation processes performed by the microprocessor 17, the coin is determined to be a true coin, a signal is applied to a gate driver circuit 20 in order to operate the accept gate 4 (Figure 1) so as to allow the coin to follow the accept path A. Also, the microprocessor 17 provides an output on line 21, comprising a credit code indicating the denomination of the coin.

Referring to Figure 5a, a coin 25, entering the passageway 2 (Figure 1), first intercepts the upstream beam U. When the incursion is detected, the state of signal x, changes.

This change in state is not important for coin diameter determination but may conveniently be used as a wake up signal for the microprocessor 17.

Referring to Figure 5b, as the coin 25 continues to fall down the passageway 2, it continues to block the upstream beam U, at least partially, and the state of signal x, is maintained until the coin 25 leaves the upstream beam U, when signal x, returns to its original value. This change of state is noted by the microprocessor 17 which stores a value tl representing the timing of the event. Shortly thereafter, the coin intercepts the first downstream beam D1, causing a change in state of signal x2. This change of state is also noted by the microprocessor 17 which stores a value t2 representing the timing of the event.

Referring to Figure 5c, as the coin continues to fall down the passageway 2, it continues to block the first downstream beam D1, at least partially, and the state of signal x2 is maintained. Next, the coin 25 intercepts the second downstream beam D2, causing a change in state of signal x5. This change of state is noted by the microprocessor 17 which stores a value t3 representing the timing of the event.

Finally, referring to Figure 5d, as the coin 25 leaves each of the downstream beams D1,D2, the corresponding signals X2, x5 return to their original states.

Correction for coin speed is based upon the time taken for the leading edge of the coin to travel the distance s5, between the downstream beams D1,D2: Sso - d = ssl x (t2 - tl) or Sso + ss- d = SsJ x (t3 - tl) ((3 - t2) (t3 - t2) where 5sO is the distance between the upstream beam U and the first downstream beam D1.

Thus, since 5sO and 5s1 are constants, a coin can be characterised on the basis of its diameter by evaluating: (t2 fl) or (t3 (t3 - t2) - (t3 - t2) Referring to Figures 6a to 6h, it can be seen that t2 occurs before t,. If the first form of the above equation is used a negative result will be obtained. However, the negative sign does not effect the validity of the characterisation of the coin by its diameter.

While the optical coin diameter determination is being carried out, one or more of the coils 12 are energized as set out in our European patent application publication no. 0 599 844. The effects of the coin 25 interacting with the magnetic fields, produced by the coils 12 and the magnets 13a,13b are detected by the coil interface circuitry 18 which outputs signals X3, x4 to the microprocessor 17.

Generally, as a coin 25 passes through the combined magnetic field, it absorbs energy and causes drops in the voltages across the coils 12. The time-invariant component of the field results in magnetic coins producing a significantly larger voltage drop than similar non-magnetic coins. For instance, in the absence of the magnets 13a,13b, a South African 1 Rand coin produces virtually the same voltage drop as a South African 1 cent coin. However, with the magnets 13a,13b, the 1 Rand coin, which is made of nickel, i.e. magnetic, produces a voltage drop in the order of 20% larger than in the absence of magnets.

The microprocessor 17 then determines whether the coin under test is valid on the basis of the signals xl, X2, x5 generated by the optical sensing process and the signals x3, x4 generated by the inductive sensing process. If the coin is valid the microprocessor 17 sends a signal to the gate driver 20 to cause the accept gate 4 to open.

It is to be noted that although the optical coin diameter determination is corrected for coin speed, no such correction is necessary for the results of the inductive sensing.

In the foregoing description, only one coil has magnets associated with it. It will be appreciated that means for producing a time-invariant magnetic field may be associated with any or each coil in a coin validator.

Claims (7)

Claims

1. A coin validation apparatus comprising a coin path, a sensor coil for inductively sensing a coin in the coin path and means for adding a time-invariant magnetic field component to a time-varying magnetic field generated by the sensor coil.

2. An apparatus according to claim 1, wherein the sensor coil is configured such that the time-varying magnetic field has a major component parallel to the coin path.

3. An apparatus according to claim 1 or 2, wherein the means for adding a timeinvariant magnetic field is configured to produce a magnetic field substantially free of a component parallel to the coin path.

4. An apparatus according to claim 1, 2 or 3, wherein the time-invariant magnetic field is stronger than the peak strength of the time-varying magnetic field.

5. An apparatus according to any preceding claim, wherein the means for adding a time-invariant magnetic field comprises a permanent magnet.

6. An apparatus according to any preceding claim, wherein the sensor coil is wound on an elongate former, the former having first and second elongate pole faces each extending across the coin path to be parallel to the faces of a coin therein and being spaced along the coin path in the direction of coin travel.

7. A coin validation apparatus substantially as hereinbefore described with reference to the accompanying drawings.