GB2291705A - Detection of counterfeit bank notes - Google Patents

Abstract

Detecting counterfeit bank notes is achieved by directing ultraviolet light at a sample from a source (104) and measuring the level of ultraviolet light reflected from the sample using a first photocell (105) and the amount of fluorescent light generated by the sample using a second photocell (106). The detected levels are compared with reference levels and only if both reflective and fluorescent criteria are satisfied is the note declared genuine. The sample, during test, is supported on a glass plate (102). The apparatus uses the value of the intensity of light reflected from the glass plate (in the absence of a sample) as a basis for producing at least one reference level against which a subsequent comparison can be made. <IMAGE>

Description

DETECTION OF COUNTERFEIT BANKNOTES This invention relates to the detection of counterfeit objects. In particular, it relates to the detection of counterfeit banknotes by detecting unauthorised material of which the banknote is made.

The production of counterfeit bank notes is continually increasing as a result of continuing improvements in printing technology, particularly colour printing. Counterfeit notes are now being made which appear, to the unaided eye, virtually indistinguishable from a genuine note.

Genuine monetary notes are now generally made to a specific formulation such as security or unbleached paper. Counterfeit notes, on the other hand, are generally but not always made from bleached paper. It is known to differentiate bleached from unbleached paper by viewing the paper under a source of ultraviolet radiation, such as an ultraviolet (W) lamp which emits light having a wavelength which peaks in band of from 300 to 400 nm.

Bleached paper includes chemical components which fluoresce when exposed to ultraviolet radiation, that is, the molecules in the composItion of the paper are excited and emit light at a longer wavelength which peaks in the band of from 400 to 500 nm. Because wavelengths of 300 to 400 nm generally lie outside the spectral region of the human eye and because wavelengths of from 400 to 500 nm lie within the spectral region, the phenomena of fluorescence allows some counterfeits to be detected with the human eye.

This process can be automated with the use of electronics by providing a sensor and a comparator which compares the intensity of the fluorescent light sensed with a reference level so as to provide an indication as to whether the paper is a likely counterfeit or not. Such an apparatus is disclosed in US Patent No. 4,558,224. However, some genuine money notes if washed acquire a deposit of chemicals which fluoresce and some counterfeit notes are made with paper containing little or no fluorescent materials and so the fluorescing phenomenon is not always an infallible way of deciding whether a note is counterfeit or not.

It is an object of this invention to provide an improved method and apparatus of detecting counterfeit objects.

According to one aspect of the present invention there is provided apparatus for detecting counterfeit objects comprising means for illuminating the object with light within a first wavelength band, a detector for detecting light from said object having a first wavelength within said first wavelength band and a second wavelength within a second wavelength band different from said first wavelength band and said second wavelength band including wavelengths at which counterfeit objects may fluoresce when exposed to light in said first wavelength band, comparison means for comparing the output of the detector with at least one reference level and decision means for deciding, based on said comparison whether said object is counterfeit or not and providing an appropriate indication.

According to another aspect of the present invention there is provided apparatus for detecting counterfeit objects comprising a detector for providing a first signal indicative of the reflectivity of an object within a first wavelength band and a second indicative of the fluorescence of the object within a second wavelength band different from said first wavelength band and decision means for deciding, based on said first and second signals, whether said object is a genuine banknote and for providing an appropriate indication.

It has been discovered that genuine and counterfeit bank notes often have different reflectivities particularly when exposed to ultraviolet radiation in the band of from 300 to 400 nm. It has also been discovered, somewhat surprisingly, that when the reflectivities of genuine and counterfeit notes are similar, the fluorescence exhibited by the notes is usually dissimilar, and vice versa. Thus by applying two tests to sense both the fluorescent light and the reflected light from a bank note exposed to ultraviolet radiation, a bank note can be declared genuine or counterfeit with great certainty.

The use of these techniques provides a surprisingly quick and effective way of detecting counterfeits. It has been found that no other measurements are needed, and consequently it is preferred that the indication of genuineness is given in response to measurements related only to reflectivity and fluorescence. However, the invention is applicable to other arrangements also; for example the technique may be used to supplement the measurements made in an otherwise-conventional banknote validator.

Although reference is made herein to reflectivity measurements, it is believed that transmissivity could be measured instead or in addition thereto.

The techniques enable the construction of a simple counterfeit detector which is easy to use, e.g.

beside a cash till. Preferred aspects of the invention are directed to enhancing the usability of the apparatus. Although these will be described in the context of an apparatus which employs the techniques mentioned above, they are considered independently inventive and could be applied to apparatus which does not employ such techniques.

According to a further aspect of the invention, apparatus for detecting counterfeit banknotes comprises a housing having a first part containing a radiation source and provided with a window enabling a sheet to be illuminated by the source, sensor means (preferably within said first part) responsive to radiation from the illuminated sheet for enabling a test to be performed to determine whether the sheet is a genuine banknote, and a shield overlying the window for reducing the amount of ambient light received by the sensor means.

The shield is preferably arranged so that a sheet can be held by the user of the apparatus, inserted between the shield and the window and then withdrawn therefrom without being released. If used by a shop assistant at the cash till, this would give greater confidence to the customer as the note is always seen to be visible and held while the testing operation is carried out. The gap between the window and the shield is therefore preferably open on at least two adjacent sides, and preferably on three adjacent sides so that the user can swipe the banknote into the gap via one side and out of the gap via the opposite side.

The gap between the shield and the window is preferably narrow (e.g. from 2 to 25 mm and preferably from 2 to 10 mm) to reduce the effect of ambient light, and preferably widens at least along one side of the shield to facilitate insertion. The widened opening may be for example at least 10, or possibly at least 60 mm.

Preferably, the arrival of the note is automatically sensed so as to actuate the decision means. This automatic sensing could be achieved using one or more of the sensor or sensors used for the testing operation, or alternatively a separate arrival sensor could be provided.

Preferably, the machine is operable to give a first positive indication if the note is tested and found to be genuine, and a different positive indication if the note is tested and found to be counterfeit, so that the user knows when the test is finished. There is preferably also a third indication, which is given when the apparatus is ready to receive and test a further note.

Use of these techniques enables the construction of a counterfeit detection apparatus which is simple, easy to use and relatively rapid in operation, enabling quick insertion of successive banknotes after each testing operation, which is reliable and which can be used while maintaining customer confidence.

Counterfeit detection apparatus embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a plan view of a first embodiment of the invention; Figure 2 is a section taken on line 2-2 of Figure 1; Figure 3 is a section taken on line 3-3 of Figure 1; Figure 4 is a perspective view of a second embodiment; Figure 5 is a side view of the Figure 4 embodiment; and Figure 6 is a block diagram of circuitry which can be used in the apparatus of Figure 1 or that of Figure 4.

Figure 1 shows apparatus for irradiating a bank note with light and then measuring the amount of fluorescent light and reflected light.

As shown the apparatus includes a generally rectangular container 100 having a window 102 against which a bank note to be sensed can be placed. Within the container 100 there is provided an elongate light source 104 for producing light in the 365 nm region and directing it through the window 102. Also within the container are two photo diodes 105 and 106 spaced apart from one another but angularly inclined so that their optical axes intersect generally at the outer surface of the window 102. Each photo-diode 105 and 106 is mounted on the floor of a respective tubular opaque housing 108 and 110. The inner walls of the housing are lined with reflective material to increase the sensitivity of the photo-diodes. A 365 nm band pass optical filter 112 covers the housing 108 and a 450 nm band pass optical filter covers the housing 110.

The lamp 104 is surrounded on three sides by reflective material 116 for example aluminium foil which reflects light generally in the direction of the window 102 to concentrate the light at the window.

Preferably the reflective material is so positioned around the light source that the optical plane o the light directed at the window, makes the same angle with the window as do the optical axes of the photo detectors in a manner to ensure that the photo-detectors receive the maximum fluorescent and maximum reflected light from any bank note placed on the window iG2. Although it is preferred that at least the photosensor for the reflected light receive light from the source which has been specularly reflected, this is not essential.

The window 102 is provided by a glass plate which reflects some of the light received from the source 104 back to the photo-diode 105. The light is principally reflected back from the glass-air boundary of the plate and typically is around 8 of the light directed at the glass plate.

When a genuine bank note is placed on the window the amount of reflected light at 365 nm is usually fairly small and so typically the amount of reflected light will increase from 8W to a value in the range of from 12 to 18W. Thus it will be seen that the light reflected from the plate when no bank note is present can be used as a reference level to compare the degree of reflection with when a bank note is present.

Thus any diminution in light output from the lamp due to ageing or any other defect is automatically compensated. Other errors are also eliminated because the light paths and components used to determine the reference level are the same as the light paths and components used to effect a measurement.

In the case of fluorescence the amount of fluorescent light emitted by a counterfeit bank note is generally several orders higher than the amount of light emitted by a genuine bank note and so any degradation of the light source 104 makes little or no difference to the detection of fluorescent light.

An electronic processor (not shown but which will be described in more detail hereinafter) monitors the light received by both photocells with the lamp 104 switched on. In the absence of a bank note on a window the photocell 105 will provide a steady state output. As soon as a bank note is placed on the window the output from the photocell 105 will rise and a trigger signal is then generated to activate two measurement circuits for measuring the outputs of the two photocells 105 and 106.

The measurement circuits provide readings which can be displayed by a display device 126, and a decision circuit will, in response to the readings, activate one of two optical indicators 122 and 124 respectively indicating that the bank note is genuine or counterfeit.

A printer (not shown) may be provided to record the values displayed by the display device 126.

It will thus be seen that the apparatus is automatically activated by the placement of a bank note on the window to determine whether the bank note is genuine or counte-.ei.

Figures 4 and 5 show another embodiment, wherein like reference numbers indicate like elements. It is to be noted that any features describes with reference to the first embodiment may be applied to this second embodiment and vice versa.

The embodiment of Figures 4 and 5 has a shield 400 located over the window 102 formed in the housing 100 which represents a base part of the structure.

The shield 400 is spaced from the window 102 by a small distance d of, e.g. 2 to 10 mm. As can be seen from Figure 5, the left, right and front sides of the shield 400 are open so that a user gripping a banknote can swipe it through the space between the shield 400 and window 102 from the left to the right side of the shield 400 without letting go. The left edge 402 of the shield 400 is curved upwardly to provide a widened entrance to the gap to facilitate insertion. The entrance gap D is preferable at least several times greater than the gap d, and may for example be 10 to 60 mm.

The housing 100 has a receptacle part 404 adjacent the right side of the shield 400 for receiving banknotes after they have been swiped past the window 102. There is a third indicator 406 which is illuminated when the apparatus is ready to receive and tst a banknote. The indicators 122, 124 and 406 thus form an indication means having four indication states, and the apparatus may be operated as follows.

When a shop assistant is handed a stack of bills, she passes them one by one through the gap between the shield and the window, each time waiting for the indicator 406 to be illuminated (indication state A).

The indicator 406 ceases to be illuminated (state B) when the bill is detected. The indicator 122 is illuminated (state C) after successful testing and the bill withdrawn and placed in the receptacle 404. The next bill is then tested. If any bill is counterfeit, the indicator 124 is instead illuminated (state D).

The block diagram of Figure 6 shows the processor in more detail. Each photocell 105 and 106 feeds a respective trigger circuit 130 and 132 for detecting a rapid change in signal for example as a result of a banknote being placed on the window. Either or both trigger circuits 130 and 132 feed a signal to a gate 134 which, via actuator 140, actuates two measurement circuits 136 and 138 (for example by supplying power to them or deactivating Inhibitors which inhibit their operation) and deactuates the indicator 406. A delay circuit in the actuator 140 deactuates the measurement circuits 135 and 138 after a snort measurement period.

A flrst comparator 142 compares the output of the thotocell 1C5 with a refrec values stored in a store le and an output dependen- on sn relationship between the detected value and the reference value is generated and is fed simultaneously to logic circuits 146 and 148. The signal stored in the store 144 is derived from the photocell 105 during the quiescent state of the apparatus. The output of the photocell 105 is amplified by an amplifier 150 by a factor of between 25% and 50% and stored in the store 144.As soon as the actuator 140 is triggered, the amplifier 150 is inhibited so that the store 144 only stores the quiescent value of reflected light. (In practice a delay circuit or similar may be provided so the quiescent value in the store 144 is not influenced by the increased output which triggers actuator 140.) A comparator 152 compares the output of the measurement circuit 138 with a reference value 154 and generates an output signal dependent on the relationship therebetween which is fed to the two logic circuits 146 and 148.

The logic gates 146 and 148 are enabled by the actuator 140 (via a delay circuit 156 to allow time for the measurements to stabilise). The logic circuit 146 responds when a genuine note is detected to energise the indicator 122. Similarly the logic circuit 148 responds to energise the indicator 124 when a counterfeit note is detected. Relative to the dynamic ranges of the sensor circuits, it is expected that a genuine banknote will produce relatively low responses from both photosensors. Accordingly, if the comparators 142 and 152 compare their inputs with a simple threshold, the logic gate 146 may be arranged to produce an output only if each input indicates that the respective threshold has not been exceeded, and the logic gate 148 can produce an output in other circumstances.

Preferably, however, one or both of the comparators 142 and 152 is/are arranged to compare its input with upper and lower thresholds defining a window around a reference level and to produce one output if the input is between the thresholds and a different output otherwise. Thus, the apparatus may be arranged to determine a banknote to be genuine only if a (probably relatively low) level of fluorescence is detected and only if a (relatively low) reflectivity is detected.

The actual values at the outputs of the two measured circuits 136 and 138 are fed to the display 125 for display thereby.

If it is required to make more precise measurement of the fluorescence signal then it can be normalised to the reference level in the same way as the reflectance signal. The associated reference level may thus be dependent on the detected quiescent fluorescence or on the detected quiescent W radiation.

After the indicator 122 or 124 has been illuminated, and the trigger circuits sense that the note has been withdrawn, the actuator 140 causes the indicator 406 to be illuminated again.

It will be appreciated that the value of the reference signals stored in the stores 144 and 154 can be adjusted as required. This could be done at manufacture during a calibration stage, or means may be provided for user-adjustment. Switch means may be provided for altering the reference values to correspond with pre-stored references suitable for currencies of respective countries. If desired, the apparatus could be made self-calibrating by automatically adjusting one or more of the reference values so that they at least approximately track the actual measured values of notes determined to be genuine.

To reduce further the effect of ambient light the light source can be modulated at a selected frequency and the outputs of the photo diodes demodulated at the same frequency to eliminate the effects of ambient light.

The circuit of Figure 6 can be used either with the first-described embodiment, in which case the indicator 406 is not required, or the second described embodiment, in which case the display 126 is not required.

To a near approximation the following relationship applies: r= (Ps/Pr) *rg/ 2 where Ps is the reflected portion of the irradiating signal from the specimen, Pr is similarly that portion returned from the glass plate to be used as a reference, and rS and rg are the coefficients of reflectance from the specimen and the glass plate. It will be noted that the effect of variation in rg is negligible if small and significant if rg is allowed to become large. Also that the relationship is inherently non linear and has been simplified to a first approximation. More precise normalisation could be carried out if required.

It has been observed that W reflection from a bank note varies with the degree of soiling. It may be possible to measure the degree of soiling (e.g. by using an infra-red source and measuring the amount of radiation transmitted through the note) and to compensate by adJusting the reference values stored accordingly. Preferably at least most of the infrared light path is the same as that of the UV radiation so tat the response is also sensitive to soiling in other areas, e.g. on the glass plate. There could be a manual switch which is operated when the user sees that a note is soiled to alter one or both reference values.

The size of the area of banknote from which radiation is received by the sensors 105 and 106 (which corresponds substantially with the window size) is preferably large, e.g. at least 6 cm2 and preferably at lest 30 cm2. Sensing a large area of the banknote makes the measurements less dependent on positioning and alignment.

The signal indicating a counterfeit note could be applied to a timer which produces a pulse of, for example, approximately one second which actuates an audible and/or a visual alarm. The output pulse from the timer may also or alternatively be applied to a line driver which is adapted to provide a suitable signal for application to a management system. This management system may be used to provide a warning to a remote control position, such as a manager's or security office in a shop for example, that a counterfeit note has been identified. Thus, as an alternative or in addition to the warnings at the point of sale (ie the till) management or security is discretely informed. The line driver may, in one example, provide TTL signals.

It may be useful to be able to monitor the output of the lamp directly so that lamp degradation can be noted and thus the lamp replaced in good time. This may be achieved by applying the output from the sensor 105 (or another sensor receiving radiation from the source 104 irrespective of the presence of a banknote) to an input of a comparator. Another input of the comparator would receive a suitable threshold value.

If the signal from the sensor becomes less than this threshold value then a signal is output from comparator to a warning means (e.g. audible and/or visual) to warn the operator to replace the lamp or one of its components.

Instead of making only one measurement of fluorescence it would be possible to make a plurality of measurements at different wavelengths using, e.g.

different optical filters, and to base the determination of genuineness on the relative distributions.

In the above embodiments the measurements of reflectivity and fluorescence are separately processed to determine whether each is appropriate for a genuine banknote. Instead, the measurements could be combined (e.g. by multiplication or divisionj, preferably after pre-processing at least one of them, and the result then tested to determine wnetner it is appropriate for a genuine note. For example, the difference between each measurement and a mean obtained by measuring a plurality of genuine notes may be squared, and the squares summed to obtain an overall measurement of the note.

Although it is preferred that the measured fluorescence be generated by the same W source as is used for measuring reflectivity, a different source may alternatively be used.

It would be possible to modify the abovedescribed embodiments so that only one sensor is used, e.g. by making the measurements in succession and switching filters.

The apparatus of the present invention may be embodied in a banknote counting machine for automatically counting notes in a stack and providing an alarm indication if a counterfeit note is detected.

The apparatus may also be embodied in a safe box system provided with means for conveying notes to a safe, and testing each note before deposit.

Alternatively, the apparatus could be attached to the side of a cash till.

Claims (24)

CLAIMS:

1. Apparatus for detecting counterfeit banknotes comprising a detector for providing a first signal indicative of the reflectivity of an object within a first wavelength band and a second signal indicative of the fluorescence of the object within a second wavelength band different from said first wavelength band, and decision means for deciding, based cn said first and second signals, whether said object is a genuine banknote and providing an appropriate indication.

2. Apparatus according to Claim 1 wherein said first wavelength band is the ultraviolet light wavelength band and said second wavelength band is 400 to 500 nm.

3. Apparatus according to Claim 1 or Claim 2 including a transparent plate for supporting a said object on one side thereof with the detector being located on the other side thereof and directed at the object through said plate.

4. Apparatus according to any preceding claim wherein said detector comprises first and second photocells each positioned to receive light from a said object and respectively arranged to be sensitive to light only in saLd first wave e-gXh band and light only in said second wavelength band.

5. Apparatus according to Claim 4 as dependant upon Claim 3 including reference means for storing a first reference level which is a function of the light reflected by the plate in the absence of an object thereon and received by the first photocell, the decision means using the reference level in deciding whether the said object is a genuine banknote.

6. Apparatus according to Claim 4 or Claim 5 as dependant upon Claim 3 including means for illuminating a said object, wherein the optical axes of the photocells and the illuminating means converge upon that surface of the plate which is arranged to support a said object.

7. Apparatus according to any preceding claim including shielding means for shielding said detector from ambient light.

8. Apparatus according to any preceding claim including sensor means for detecting the presence of a said object to actuate said decision means.

9. Apparatus according to claim 8, wherein the sensor means comprises said detector.

10. Apparatus according to any preceding claim including measurement means responsive to the detector to provide a record of the magnitude of the received signals having wavelengths in said first and second bands.

11. Apparatus according to any preceding claim wherein said decision means comprises indication means for providing a first indication when the object is a counterfeit banknote and a second indication when the object is a genuine banknote.

12. Apparatus according to claim 11, wherein said indication means is operable to provide a third indication when the apparatus is ready to receive and test a said object.

13. Apparatus for detecting counterfeit banknotes, the apparatus comprising a housing having a base, a window in an upper surface of the base, a radiation source within the base for illuminating a sheet placed over the window and sensor means responsive to radiation received from the sheet so that a test can be carried out to determine whether the sheet is a genuine banknote, and a shield overlying the window in such a way as to allow the sheet to be inserted between the window and the shield, to reduce the amount of ambient light received by the sensor means.

14. Apparatus for detecting counterfeit banknotes, the apparatus comprising a housing having a first part containing a radiation source and provided with a window for enabling a sheet to be illuminated by the source, sensor means responsive to radiation from the illuminated sheet for enabling a test to be performed to determine whether the sheet is a genuine banknote and a shield overlying the window for reducing the amount of ambient light received by the sensor means, the shield being separated from the window by a narrow gap sufficient to allow insert ion of the sheet therebetween, the narrow gap having a relatively wide opening at at least one side of the shield to facilitate such insertion.

15. Apparatus for detecting counterfeit banknotes, the apparatus comprising a housing having a first part containing a radiation source and provided with a window for enabling a sheet to be illuminated by the source, sensor means responsive to radiation from the illuminated sheet for enabling a test to be performed to determine whether the sheet is a genuine banknote and indication means having at least three states, a first state being adopted prior to the results of the test being indicated, a second state indicating that the sheet is a genuine banknote and a third state indicating that the sheet is a counterfeit banknote.

16. Apparatus as claimed in Claim 15, wherein the indication means has a fourth state, means being provided to determine whether the apparatus is ready to test a sheet and, depending upon said determination, to select whether the indication means adopts said fourth state or said first state.

17. Apparatus claimed in Claim 13 or Claim 14, wherein the gap between the shield and the window is open on at least two adjacent sides, so that the sheet can be inserted from one side and withdrawn from another.

18. Apparatus claimed in Claim 17, wherein the gap is open on two opposed sides of the shield so that a note can be held by user while it is drawn across the window from one of the opposed sides to the other opposed side.

19. Apparatus claimed in Claim 18, wherein the housing includes a receptacle for receiving tested notes, the receptacle being located adjacent said other opposed side.

20. Apparatus for detecting counterfeit banknotes, the apparatus comprising a housing containing a radiation source and a radiation sensor means, the arrangement being such that a user holding a sheet can transport the sheet along a path in proximity to the housing so that the sheet is illumInated by the source and so that the sensor means receives radiation from the sheet, the sensor means being responsive to radiation from the illuminated sheet in at least two discrete wavebands for enabling a test to be performed to determine whether the sheet is a genuine banknote.

21. Apparatus for detecting counterfeit banknotes, the apparatus comprising a housing containing a radiation source and a radiation sensor means, the arrangement being such that a user holding a sheet can transport the sheet along a path in proximity to the housing so that the sheet is illuminated by the source and so that the sensor means receives radiation from the sheet, the sensor means being responsive to radiation from the illuminated sheet for enabling a test to be performed to determine whether the sheet is a genuine banknote, the apparatus comprising means for automatically sensing the presence of the sheet and in response thereto for using the output of the sensor means in said test.

22. Apparatus for validating banknotes, comprising means for detecting the degree of soiling of a banknote, means for performing a test to determine whether the banknote is genuine by sensing radiation from the banknote, and means for modifying the test in dependence on the output of the detecting means.

23. Apparatus claimed in any one of Claims 13 to 22, wherein the sensor means is operable to detect radiation from an illuminated area of the sheet of at least 6 cm2.

24. Counterfeit detection apparatus substantially as hereinbefore described with reference to Figures 1 to 3 and 5, or Figures 4 to 6, of the accompanying drawings.