GB2296122A

GB2296122A - Bank-note checking

Info

Publication number: GB2296122A
Application number: GB9512611A
Authority: GB
Inventors: Nicholas Quill; Neil Shakespeare; John Armstrong
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-16
Filing date: 1995-06-21
Publication date: 1996-06-19
Anticipated expiration: 2015-06-21
Also published as: GB9512611D0; GB2296122B

Abstract

Apparatus for detecting the presence of a metallic strip in a bank-note has a detector head in which are formed a pair of insulated conductive plates 20 and 21, arranged end-to-end. A bank-note having a metallic strip is guided to pass through the detector head with the strip aligned with the length of the plates 20 and 21. A high frequency signal is applied to one plate and in the rest state, there is very little capacitive coupling of that signal to the other plate. When the metallic strip overlies both plates, there is significant capacitive coupling and the presence of the signal on the other plate can be detected. An infra-red beam may be directed through the bank-note, in alignment with the conductive plates. A valid bank-note signal will be given only when the metallic strip blocks transmission of the infra-red, simultaneously with the capacitive coupling of the signal by the metallic strip. <IMAGE>

Description

BANK-NOTE CHECKING This invention relates to apparatus for and methods of detecting the presence (or otherwise) in a bank-note of a metallic thread, strand or strip (all of which will hereinafter for convenience be referred to simply as a stripS. The term "bank-note" as used herein is intended to refer to any document printed on paper or a paper-like sheet material such as a spunbonded plastics sheet, which additionally includes a metallic strip extending thereacross in a pre-defined manner. Thus, in addition to true bank-notes (that is, so-called paper currency), the term bank-note may extend to, but is not limited by, paper or paper-like sheets having an apparent value such as gift vouchers, stock certificates, tickets, passes and so on.

Most bank-notes are printed on fluorescence-free paper, but carry one or more patterns, designs or the like printed with fluorescing inks so that an inspection of the bank-note under ultraviolet light will reveal that pattern, design or the like. The paper used for most bank-notes includes a water-mark and many bank-notes further include a metallic strip introduced into the paper during the papermanufacturing process. In many bank-notes, such a strip is woven into the paper so that along the length of the strip, the strip alternately appears to lie on one surface and then the other of the paper.

All of the above devices increase the difficulties for a forger of bank-notes. Fluorescence-free paper is not commercially available and is supplied by the manufacturers thereof only to security printers.

Equally, the paper manufacturers will not supply watermarked paper nor paper including metallic strips to printers other than those authorised to print banknotes. Consequently, forgers have to resort to other means, in order to emulate authentic bank-notes. For example, it is possible to "print" both water-marks and metallic strips on paper using special inks, so that to a casual glance, a bank-note appears authentic, though such printed features do not withstand close scrutiny.

Bank-note checking apparatus comprising a UV source under which a bank-note is placed to check that the paper is non-fluorescing but that the note includes a design printed in fluorescing inks have become widely used. However, forgers are now able to produce forged bank-notes which will pass a simple UV test and it has become desirable to provide an alternative checking device in order to eliminate some of the better forgeries.

There have been proposals for metallic strip detectors, such as those disclosed for example in GB-A2017996 and GB-A-2271642. The detector of GB-A-2017996 generally relies on the presence of the metallic strip altering the frequency of resonance of a resonant circuit, but such a device is subject to extraneous fields and other metallic items. It is difficult adequately to shield the apparatus to render it immune from external influences, and yet to make the apparatus easily usable, by - for example - a cashier in a busy shop. The detector of GB-A-2271642 impresses a high frequency signal across a capacitor, and the change in the voltage across the capacitor, consequent upon the presence of a bank-note metallic strip changing the capacity, is detected. The change in voltage, at a high frequency, is relatively small and can be difficult to detect in a reliable manner.Temperature variations and other factors can cause drift of the high frequency signal and of the detector, leading to uncertainty in detection.

A principal object of the present invention is to provide apparatus for, and a method of, detecting the presence of a metallic strip in a bank-note, which apparatus is easy and rapid to use, is largely immune to external influences, and is reliable in operation.

According to the present invention, there is provided apparatus for detecting the presence of a metallic strip in a bank-note, comprising a detector head having guide means to constrain a bank-note passed through the detector head to lie substantially in a predetermined plane with the metallic strip extending in a defined direction, the detector head also having first and second conductive elongate plates arranged end-to-end along said defined direction in a substantially non-overlapping manner with both plates lying closely adjacent said predetermined plane, the apparatus further comprising an oscillator arranged to supply a signal to the first plate, and a detector circuit connected to the second plate and arranged to detect the capacitive coupling of said signal from the first plate to the second plate by the presence of the metallic strip in a bank-note passed through the detector head.

It will be appreciated that in the present invention, only when a metallic strip of a bank-note is aligned with the first and second plates will there be capacitive coupling between the first and second plates; at all other times the capacity between the two plates will be so small that there will be only insignificant signal transfer from the first plate to the second. A stable oscillator may provide a signal to the first plate, and that signal will be transferred to the second plate when a bank-note having a metallic strip is passed through the detector head; the signal obtained from the second plate may be appropriately amplified and filtered to eliminate signals other than that transferred to ensure that any detected signal truly originates from the oscillator.In this way, a high order of discrimination against external noise or influences may be obtained, leading to high reliability in the checking operation.

Preferably, the first and second plates lie in substantially the same plane, extending to one side of the predetermined plane, though it would be possible to construct the apparatus with one plate on one side, and the other plate on the other side, of said predetermined plane. Moreover, said defined direction advantageously lies at right angles to the direction in which a bank-note is passed through the apparatus in said predetermined plane, though the apparatus may be arranged so that the bank-note is passed through the detector head in the same direction as extends the metallic strip. It is of course important that the length of the first and second plates extends in the direction of the metallic strip, at the point at which the check for the presence of the strip is made.

In order to prevent a false check being made for example by a conductive ink printed on a bank-note, it is preferred for the surfaces of the first and second plates facing said predetermined plane to be electrically insulated. This may be achieved by means of a thin film of a plastics material, coated on or otherwise laid over those surfaces of the first and second plates.

The apparatus may include optical means to check for the presence of the metallic strip, in addition to the capacitative coupling described above. Such optical means advantageously comprises a light source on one side of the predetermined plane and a detector for light from the source on the other side of the plane. Provided the source has a sufficient intensity of an appropriate wavelength, and both the source and the detector co-operate to detect over a sufficiently small area of a bank-note passed therebetween, the paper of a bank-note will not obstruct all light from the source reaching the detector, though the metallic strip will mask the detector from that light. The apparatus may then be configured to give a "valid" output only if the metallic strip gives sufficient capacitative coupling and the optical means also indicates the bank-note has a portion wholly opaque to the light. Preferably, the optical means employs light in the infra-red part of the spectrum.

It is important that the guide means is arranged to ensure a bank-note passed through the detecting head lies closely adjacent the first and second elongate plates. To that end, the guide means may include an elongate brush generally aligned with said direction and disposed to wipe against a bank-note passed through the detector head, in direct opposition to the first and second elongate plates.

The detector circuit may include an alarm which is triggered whenever the detected capacitive coupling of said signal exceeds a predetermined threshold level.

Such an alarm may comprise at least one of, though preferably both of, a visual indicator and a sounder, which are respectively illuminated and energised when the alarm is triggered.

According to a second aspect of the present invention, there is provided a method of detecting the presence of a metallic strip in a bank-note, comprising passing the bank-note through a detector head having guide means to constrain the bank-note to lie in a predetermined plane with the metallic strip extending in a defined direction, the detector head also having first and second conductive elongate plates arranged end-to-end along said defined direction in a substantially non-overlapping manner with both plates lying closely adjacent said predetermined plane, supplying a signal to the first plate, and detecting on the second plate the presence of a capacitively-coupled signal from the first plate by the presence of a metallic strip of a bank-note as the bank-note is passed through the detector head.

The signal provided by the oscillator may comprise a sine-wave alternating signal, typically in the range of 100kHz to 1MHz but preferably of the order of 500kHz.

The detector circuit may include a tuned receiver adjusted to the frequency of the oscillator, together with one or more amplifying stages, before or after the receiver. The output of the receiver may be rectified and supplied to a voltage level detection circuit.

When the detected voltage level exceeds a predetermined threshold, a mono-stable device may be triggered to energise the alarm. Conveniently, the alarm is selfcancelling after some predetermined period - such as 1 or 2 seconds. The voltage level detection circuit may include an upper threshold as well, the alarm being triggered only if the detected voltage level lies between the two threshold values.

The method of this invention may further include the step of optically detecting, for example with infra-red light, the relative opacities of the metallic strip and the paper of a bank-note, and to provide a "valid" output only when a sufficient capacitivelycoupled signal is detected and sufficient relative opacity of the metallic strip is detected.

By way of example only, one specific embodiment of bank-note metallic strip detecting apparatus and a modification thereof, constructed and arranged in accordance with the present invention will now be described in detail, reference being made to the accompanying drawings, in which: Figures 1 to 3 show three stages of a detecting process using the apparatus in association with a bank note including a metallic strip; Figure 4 is an exploded view of the detector head of the apparatus; Figure 5 is a block diagram of the electronic circuitry employed in the detecting apparatus; Figure 6 is a plan view on the detecting region of a modified form of the apparatus of Figure 4; and Figure 7 is a perspective view of part of the modified apparatus of Figure 6.

Referring initially to Figures 1 to 4, there is shown the embodiment of bank-note metallic strip detecting apparatus of this invention, which comprises a main body 10 upstanding from a platform 11, which also supports a guide block 12. The main body 10 has an elongate generally planar surface 13 and the guide block 12 has a shorter planar surface 14 which, with the block mounted as shown in Figures 1 to 3, is parallel to but closely spaced from the planar surface 13 of the main body 10. Thus, a narrow slot is defined by the opposed planar surfaces 13 and 14, through which a bank-note 15 may be passed, as shown in Figures 1 to 3.

The end regions of the planar surface 13 are rounded, as are the end regions of the planar surface 14; this facilitates the entry of a bank-note 15 into the slot between the planar surfaces so that the banknote may be passed easily and smoothly through the slot, with the lower edge 16 of the bank-note 15 resting on the platform 11.

The bank-note shown in Figures 1 to 3 includes a metallic strip 17 woven into the paper of the bank-note during the production thereof. Such a strip typically is of aluminium or an aluminium alloy and forms an integral part of the bank-note. That strip extends perpendicularly to the lower edge 16 of the bank-note, so that on passing the bank-note through the slot between planar surfaces 13 and 14, the strip 17 is advanced transversely to the length of the slot.

The planar surface 13 carries a pair of conductive plates 20 and 21 (Figure 4), mounted in the region thereof opposed to the planar surface 14 of the guide block 12. Each of the plates 20 and 21 is of truncated isosceles triangular form with a relatively narrow included angle, the two plates being co-planar and aligned end-to-end with their truncated apices adjacent one another but with a slot therebetween, as shown in Figure 4. The common axis of the two plates is coincident with the line of the metallic strip 17 of a bank-note, when that strip is disposed between the planar surfaces 13 and 14 on being passed through the detecting apparatus. The exposed surfaces of the plates 20 and 21 are covered with a plastic film to insulate those plates from direct metallic contact.

The main body 10 houses the required electronic circuitry, for the operation of the detecting apparatus. A block diagram of that circuitry is shown in Figure 5. The circuitry consists of a stable sinewave oscillator 30, operating at about 500kHz, which supplies a signal to plate 20. Any signal coupled capacitively to plate 21 is fed to block 31, where the signal is amplified, and filtered through circuits arranged to reject signals at frequencies other than that of oscillator 30, the resultant signal then being rectified. The rectified signal is provided to a voltage threshold detector 32 and provided the detected voltage lies between lower and upper predetermined threshold values, then a mono-stable vibrator is triggered, both to illuminate a LED 33 and to energise a sounder 34. Both the LED and the sounder are energised for a pre-set period of time (and typically 2 seconds) before the apparatus resets itself, ready for the next detecting operation.

The circuit is driven by a power supply 36. This may be integral within the body 10, or may be a separate unit for example directly plugged into a mains outlet socket, and supplying low voltage d.c. to the components of the circuit.

In operation, the presence of a metallic strip is detected by the principle of capacitive coupling, to transfer a waveform through a capacitor. The capacitor is defined by the two plates 20 and 21 together with the metallic strip of the bank-note. When no metallic strip is present in the region of the plates 20 and 21, virtually no waveform appears on plate 21 since the mutual capacitance between the two plates is too low to allow any significant signal transfer. When the metallic strip 17 bridges the two plates, the mutual capacitance rises so that the waveform transfers on to plate 21. The magnitude of the transferred waveform is proportional to the capacitance and thus to the area of the metallic strip in contact with the plates 20 and 21.Provided that the DC voltage resulting from the detection of the waveform falls between the lower and upper limits for a valid bank-note, the alarm is sounded so that an operator is made aware that the bank-note may be regarded as valid.

Figure 6 shows a modified form of the apparatus using additional infra-red sensing for the metallic strip of a bank-note and also a brush to ensure close contact of a bank-note with the conductive plates 20 and 21. The brush 40 is in the form of an elongate strip of soft relatively short bristles arranged with the length of the brush aligned with the conductive plates 20 and 21. On passing a bank-note through the detector head, the bristles will wipe against the surface of the bank-note facing away from the plates 20 and 21 and so will ensure the metallic strip (if present) in the bank-note will couple the signal from one plate to the other.

Also shown in Figures 6 and 7 is an infra-red transmitter 41 and an infra-red receiver 42, arranged to cooperate with each other but on opposite sides of a bank-note passed through the apparatus. The transmitter and receiver are arranged in alignment with the conductive plates 20 and 21 and an aperture 43 is formed through the detector head, between the plates 20 and 21, such that infra-red radiation from the transmitter may fall on the receiver. The metallic strip in a bank-note is substantially opaque to infrared radiation, but the paper of the bank-note is substantially transparent to such radiation.

Consequently, the receiver will detect infra-red radiation from the transmitter when a bank-note is passed through the apparatus, except for the moment when the metallic strip is aligned with the conductive plates 20 and 21.

This modified form of the apparatus works essentially as described with reference to Figure 5, except that an alarm is given (to indicate a valid bank-note) only if the capacitive coupling of the signal from one conductive plate to the other occurs substantially simultaneously with a drop in output from the infra-red receiver. Unless both events occur essentially simultaneously, no valid output is given.

Claims

1. Apparatus for detecting the presence of a metallic strip in a bank-note, comprising a detector head having guide means to constrain a bank-note passed through the detector head to lie substantially in a predetermined plane with the metallic strip extending in a defined direction, the detector head also having first and second conductive elongate plates arranged end-to-end along said defined direction in a substantially non-overlapping manner with both plates lying closely adjacent said predetermined plane, the apparatus further comprising an oscillator arranged to supply a signal to the first plate, and a detector circuit connected to the second plate and arranged to detect the capacitive coupling of said signal from the first plate to the second plate by the presence of the metallic strip in a bank-note passed through the detector head.

2. Apparatus as claimed in claim 1, wherein the first and second plates lie in substantially the same plane, extending to one side of said predetermined plane.

3. Apparatus as claimed in claim 1 or claim 2, wherein said defined direction lies at right angles to the direction in which a bank-note is passed through the apparatus in said predetermined plane.

4. Apparatus as claimed in any of the preceding claims, wherein the surfaces of the first and second plates facing said predetermined plane are electrically insulated.

6. Apparatus as claimed in any of the preceding claims, wherein the detector circuit includes an alarm which is triggered whenever the capacitive coupling of said signal exceeds a pre-set threshold level.

7. Apparatus as claimed in claim 6, wherein the alarm comprises at least one of a visual indicator which is illuminated when the alarm is triggered, or a sounder which is energised when the alarm is triggered.

8. Apparatus as claimed in any of the preceding claims, wherein the guide means comprises a pair of members having opposed surfaces arranged in a spacedapart manner so as to define a slot therebetween, through which a bank-note may be passed.

9. Apparatus as claimed in claim 8, wherein an elongate brush is provided on one member within said slot, to cause a bank-note passed through the slot to bear on the other member.

10. Apparatus as claimed in any of the preceding claims, wherein there is provided optical means to check for the presence of a metallic strip in a banknote being processed.

11. Apparatus as claimed in claim 10, wherein the optical means comprises a light source on one side of the predetermined plane and a detector for light from the source on the other side of the plane.

12. Apparatus as claimed in claim 10 or claim 11, wherein the detector circuit gives a valid note output only when capacitative coupling is detected substantially simultaneously with an output from the optical means indicating the presence of a metallic strip in a bank-note.

13. Apparatus as claimed in any of claims 10 to 12, wherein the optical means employs infra-red radiation.

14. Apparatus as claimed in claim 1 and substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

15. A method of detecting the presence of a metallic strip in a bank-note, comprising passing the bank-note through a detector head having guide means to constrain the bank-note to lie in a predetermined plane with the metallic strip extending in a defined direction, the detector head also having first and second conductive elongate plates arranged end-to-end along said defined direction in a substantially non-overlapping manner with both plates lying closely adjacent said predetermined plane, supplying a signal to the first plate, and detecting on the second plate the presence of a capacitively-coupled signal from the first plate by the presence of a metallic strip of a bank-note as the bank-note is passed through the detector head.

16. A method as claimed in claim 15, wherein the signal from the second plate is amplified, filtered and rectified, and is then supplied to a voltage level detector.

17. A method as claimed in claim 16, wherein an alarm is triggered only if the detected voltage level falls between lower and upper threshold values.

18. A method as claimed in any of claims 15 to 17, wherein the signal comprises a sine-wave alternating signal.

19. A method as claimed in any of claims 15 to 18, wherein the signal is at a frequency in the range of 100kHz to 1MHz.

20. A method as claimed in any of claims 15 to 19, wherein the presence of the metallic strip in a banknote is additionally checked on an optical basis.

21. A method as claimed in claim 20, wherein the optical check utilises infra-red radiation.

22. A method as claimed in claim 20 or claim 21, wherein a valid note output is given only when the metallic strip is detected both by capacitative coupling and by the optical check.

23. A method as claimed in any of claims 15 to 22, wherein the detection of the presence of a metallic strip in a bank-note passed through the detector head causes at least one of an alarm to sound and a light to be illuminated.

24. A method as claimed in claim 15 and substantially as hereinbefore described with reference to the accompanying drawings.