Title:
DOCUMENT RECOGNITION SYSTEMS
United States Patent 3782543


Abstract:
A bank note recognition system includes an optical analyser for scrutinising the watermark, selected areas of print on the surface of the bank note, the wire band in the bank note and the density of the paper of the bank note. The analyser in its simplest form includes a lamp for illuminating a discrete area of the bank note and two photo electric elements on opposite side of the bank note for respectively sensing the transparency and reflectivity of the discrete area of the bank note. The analysis will provide indication whether the bank note is genuine and will accept the bank note only if considered to be genuine.



Inventors:
Martelli, Mario (Compiobbi, IT)
Martelli, Mario (Firenze, IT)
Application Number:
05/296853
Publication Date:
01/01/1974
Filing Date:
10/12/1972
Assignee:
MARTELLI M,IT
MARTELLI M,IT
Primary Class:
Other Classes:
209/534, 209/587, 209/588, 250/556
International Classes:
G07D7/12; G07D7/20; (IPC1-7): B07C5/342
Field of Search:
209/75,111
View Patent Images:



Primary Examiner:
Knowles, Allen N.
Attorney, Agent or Firm:
Nichol, Sandoe Et Al M.
Claims:
We claim

1. In a document recognition device, an optical analyser comprising

2. A device according to claim 1, in which the light source means comprises a single light source.

3. A device according to claim 1, in which the light source and the first photosensitive member lie along a common axis which extends through and is inclined to the plane of the document, and in which the second photosensitive member lies on the same side of the document as the light source and extends along an axis that intersects the said common axis in the plane of the document and makes the same angle with the said plane as the said common axis.

4. A device according to claim 1, including another optical analyser similar to the first mentioned analyser, the light source means of the two analysers being located on opposite sides of the document and directed at the same predetermined area.

5. A device according to claim 1 wherein the two optical analysers are spaced apart in the direction of the plane of the document for sequementially analysing the said predetermined area.

6. A bank note recognition system, comprising

7. A system according to claim 6, wherein the first path upstream of the analysing means follows a bend.

8. A device according to claim 6 including sensing means located in the first guide path upstream of the analyser and responsive to the passage of a bank note there past to activate the analysing means for analysis of the bank note.

9. A device according to claim 6, wherein said first guide means includes

10. A device according to claim 6, wherein said diverter comprises an electromagnetically operated guide member.

11. wherein the analyser means includes

12. A device according to claim 7, including further sensing means located in the first guide path down stream of the analyser and responsive to the passage of the trailing edge of the bank note there past to deactivate the analysing means in readiness for the analysis of a subsequent bank note.

13. A device according to claim 6 including

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to document recognition systems for recognising documents such as bank notes.

2. Description of the Prior Art

Previously proposed bank note Examination systems have involved a search of the bank note surface by photo electric means for recognisable patterns and contours in conjunction with detecting other characteristics of the bank note. Such as the detection of luminous or magnetic inks such systems have not proved to be sufficiently reliable or sufficiently flexible.

It is an object of the invention to provide an improved system for recognising documents.

SUMMARY OF THE INVENTION

The invention provides a document recognition device, an optical analyser comprising support means for supporting a document to be analysed, light source means mounted to direct light at a predetermined area of the document, a first photo sensitive member mounted to receive from the light source means, light which has passed through the predetermined area of the document and providing an output indicative of the light received, a second photo sensitive member mounted to receive light from the light source that has been reflected from the predetermined area and providing an input indicative of the light received, reference means for establishing reference ranges for the transparency and reflectivity of valid documents, and comparison means connected to receive the output signals from the first and second photo sensitive members and connected to the reference means to compare the output signals with the reference ranges to determine the validity of the document in dependence upon the result of the comparison.

In the specification and claims, the phrase "banknote" includes (except where the context indicates otherwise) a counterfeit as well as a genuine banknote.

BRIEF DESCRIPTION OF THE DRAWINGS

Banknote recognition systems embodying the invention will now be described by way of example, with reference to the accompanying diagrammatic drawings in which:

FIG. 1 is a cross section through an optical analyser of the systems;

FIG. 2 is a cross section through one of the systems, for analysing a bank note in motion;

FIG. 3 is another of the systems, for analysing a bank note in motion;

FIG. 4 is a circuit diagram of a reversing mechanism for the system of FIG. 3;

FIG. 5 is a circuit diagram of a gated control circuit for the systems of FIG. 2 and 3;

FIG. 6 is a part cross-sectional view of an adjustable optical analyser for use in the systems;

FIG. 7 is an under plan view of the analyser of FIG. 6;

FIG. 8 is a part cross-sectional view of another analyser for use in the systems and having a plurality of sensing head apertures;

FIG. 9 is an underneath view of the analyser of FIG. 8;

FIG. 10 is a block diagram of the control circuit for a comprehensive optical analyser for use in the systems; and

FIG. 11 is a block diagram of part of the control circuit of FIG. 10 in more detail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an optical analyser for determining the transparency and reflectivity of a document, for example a bank note. The analyser includes a light source 1 providing light of a desired wavelength. The light source can be a microlamp having a built-in or an external lens, and be provided with a selection of chromatic filters. The analyser also includes two photosensitive elements 3 and 5 (for example photo resistors or photo diodes). The element 3 is located on the opposite side of the bank note 7 to the light source 1 and provides an indication of the transparency of the note. The element 5 lies on the same side of the bank note as the light source 1. The bank note 7 is arranged to be driven through the analyser along guide 8.

In order to make the two measurements of transparency and reflectivity simultaneously at a selected point on the bank note the element 3 is located on the same axis as the optical axis of the light source, which optical axis is inclined with respect to the plane of the bank note 7 under test, and the element 5 is located in a position in which it is substantially symmetrically positioned with respect to the element 3 but on the opposite side of the bank note. The source 1 is rotatable about its own axis by means of a lamp holder 9 so as to orientate the image of the filament on the bank note in any desired manner, as will be described in more detail hereinafter. The data derived from the simultaneous transparency and reflection measurements enables the note to be speedily recognised.

A scrutiny of the paper on which the bank note is printed is performed by making a plurality of transparency measurements at discrete points on the bank note. Discrete points are located by using an edge of the bank note or a detail of the print on the bank note as a reference location. The value of the transparency measurement must lie within upper and lower limits if the bank note is to be considered genuine. The upper and lower limits are determined by the type of paper employed in the manufacture of legal bank notes.

The presence of a watermark in a particular zone of the bank note can be detected as a variation in the transparency of the bank note. In the case of an authentic watermark, variations in transparency but not in the reflection may be noted as the bank note is scanned. Appreciable reflection variations can be observed where the watermark is counterfeit and made by means of oil stains or paraffin, for example. Therefore, comparison of the transparency and reflectivity of the watermark of the bank note enables it to be recognised. The above criteria can be built into electronic circuits which can then be used to distinguish counterfeit from real bank notes.

Some bank notes have a built-in metallic strip. An optical analysis of this strip can also be used in determining whether or not the bank note is genuine.

In the case of a forged bank note the wire may have been applied to the outer surface of the bank note or have been simulated as a mark on the outer surface. In either case the result will be a change in the reflectivity of the surface.

In order to distinguish a genuine wire from such forgeries, a transparency measurement must be taken at the location of the wire and in addition reflection measurements must be made from opposite sides of the bank note at the same point in the bank note. The reflection measurements may be taken at separate instants but should preferably be made simultaneously.

It will be appreciated that if a genuine bank note becomes marked during use and the mark is somewhat similar to that of a wire then the resultant measurements can cause the bank note to be rejected even though the bank note is genuine. It is, however, preferable to reject a genuine bank note rather than to accept a counterfeit one.

When scrutinising the bank note wire, the sensitivity of the analyser is preferably increased. Sensitivity can be increased by placing a mask in front of the lamp or the photo electric element. The mask has a slot extending in the direction of the wire so that only a narrow area of the bank note is scrutinised.

Instead, sensitivity can be improved by orientating the sleeve 9 which holds the illumination source so that the filament of the lamp is in alignment with the bank note wire.

In order to make the counterfeiting of a bank note more expensive and more complex, some portions of the drawing of the bank note are made by a relief printing method. Relief print provides a much lower reflection than print made by conventional methods and inks. By using a diaphragm in conjunction with the lamp, (the diameter of the hole, of the diaphragm advantageously being of the order of 0.3 mm) a reflection analysis can be made of a sufficiently small point that very small detail of the banknote surface can be observed. In order to locate a selected point on the banknote, the scanning of the banknote is only initiated when a reference point on the banknote, for example an edge of the banknote or a major detail of the subject printed on the banknote reaches a predetermined position. Once the detail is located the scanning will determine whether or not the reflection from the detail lies within the prescribed limits for a genuine banknote.

The above method of examining a selected detail of the bank note can be extended to examining another selected detail so that the mutual position of the two details can be checked against that of a genuine bank note.

By activating and de-activating the transparency and/or reflection photo sensitive elements of a single analyser in accordance with a predetermined programme as the bank note passes through the analyser at a constant velocity, measurements cna be made of discrete areas of the banknote. The resultant measurements are then compared with upper and lower limits and if all the measurements be found to be within these upper and lower limits, the banknote will be accepted as genuine.

Instead of using a single analyser to examine each selected point of the bank note in turn a plurality of analysers can be used to make simultaneous measurements of all the selected points. The measurements may be obtained when the banknote is in motion or with a system in which the bank note is held in a fixed position; the analyser being appropriately positioned with respect to the bank note. It is also possible to use a system in which the banknote is temporarily halted in a predetermined position, for a predetermined time (however short) sufficient to effect the simultaneous measurements.

It will be appreciated that with the system described in which transparency and reflection measurements are made at the same point and at the same time, it is very difficult for a counterfeit note to escape detection, as in practice, a forger must simultaneously re-create the same transparency and reflection conditions at the same point as those in a conventional bank note.

The head of FIG. 1 performs both transparency and reflection measurements using only one light source. If a separate lamp were used for each measurement then the turning off of the transparency measurement lamp would lead to the acceptance of banknotes without a wire and without surface marks in a selected zone. Thus for example a photo copy of the bank note would be accepted.

The analysers described can be made more sensitive by using a colour filter with the light source appropriate to the colour of the bank note to be examined and by making the photo electric elements specially sensitive to that selected colour.

FIG. 2 illustrates a bank note recognition system for analysing a bank note in motion. The system includes an ingress switch 11 (formed by a micro switch or a photo electric relay, for example) which is arranged to be triggered by the leading edge of the bank note to energise the electric circuits of the system. When the switch 11 is triggered, rollers 17A are energised to feed the bank note along a guide track 13 through an optical analyser 15. The optical analyser 15 can take the form shown in FIG. 1.

The analyser 15 scrutinises selected discrete points of the bank note and determines whether or not it considers the bank note to be genuine. As the bank note emerges from the analyser it is fed by rollers 17B further along the path 13 until its leading edge triggers a reset switch 19 (a micro switch or a photo electric relay for example) whereupon the analyser 15 and the rollers 17A are de-energised in readiness to receive the next bank note. This enables the system to start processing the next bank note before the processing of the previous bank note has been completed.

The guide track 13 includes a plurality of stretching rollers (not shown) to maintain the bank note flat.

After the bank note has triggered the switch 19 it is fed towards an electromechanical switch 21 which is controlled by the analyser 15 to direct the bank note along one or other of two paths 23 and 25 in dependence on whether or not the bank note is considered genuine. If the note is not considered to be genuine it passes along the path 25 while if it is considered to be genuine it is diverted along the path 23. An outlet switch 27 (a micro switch or photo electric relay, for example) is triggered by the bank note to return the switch 21 into its initial position each time a bank note is accepted as genuine.

It is advantageous that the distance between the switches 11 and 9 is smaller than the length of the bank note. The distance between the switches 19 and 27 should also be smaller than the length of the bank note.

FIG. 3 shows another bank note recognition system in which parts similar to those in FIG. 2 are similarly referenced. In operation the bank note is fed into an inlet 29 and along guide 31 having a portion 31a passing through the optical analyser 15. The portion 31a of the guide 31 is inclined at an angle α with respect to the initial portion of the guide 31. An electro magnetic switch 33 is operable to direct the bank note along the path 35 or along the path 37 in dependence on whether the bank note has been rejected or accepted. A rejected bank note is directed along the path 35 and eventually emerges from the outlet 39. The bend in the guide path 31 as it passes into the analyser 15 is advantageous in reducing the possibility of damage to the analyser, for example by a person attempting to tamper with the system by introducing a small screwdriver or the like into the inlet 29.

In order to reduce errors whilst scrutinising the bank notes that result from the presence of folds, wrinkles or the like in the bank note (which would particularly affect the reflection measurements) the bank note is stretched while it is being scrutinised. To achieve this, the two pairs of rollers 17A and 17B on opposite sides of the analyser are arranged so that the second pair of rollers 17B drives the bank note at a greater speed than the first pair.

In order to avoid the acceptance obtained by a genuine bank note from being used to provide acceptance for a subsequent forged bank note that closely follows the genuine bank note, a system is provided which automatically separates subsequently introduced bank notes from the first bank note. The system comprises a pair of initial rollers 41 which are driven independently of the rollers 17A and 17B. The rollers 41 are triggered by a normally open contact of the switch 11 and a normally closed contact of switch 19. Because the distance between the switches 11 and 19 along the guide path 31 is arranged to be shorter than the length of the bank note, the trailing edge of the bank note will still lie between the rollers 41 when switch 19 is triggered by the leading edge of the bank note. The actuation of the switch 19 will lock the rollers 41, but the bank note will continue to be driven along the path by the combined action of the pairs of rollers 17A and 17B and any subsequently introduced bank note will not be advanced.

An excessive thickness of the bank note caused for example by the superimposition of foreign elements (gummed paper, adhesive paper or the like) on the bank note or in the case of a forgery where the natural thickness of the bank note is greater than that of a genuine bank note, can be detected by means of a mechanical feeler (a micro switch for example). When this thickness is sensed, the direction of drive of the rollers 41 is reversed to return the bank note back to the inlet 21. By this means the bank note is prevented from entering the analyser and other parts of the system where it could cause the system to lock or seize up. The period for which the rollers 41 are driven in reverse must last for a sufficient time to ensure the return of the bank note. This can be achieved by using electric and electronic timing circuits, for example as shown in FIG. 4.

In FIG. 4 the timing circuit includes a motor 45 for driving the rollers 41, a feeler 47 which may form part of the switch 11, and a delay circuit 51 having a switch operated by the feeler 47. The delay circuit 51 controls an electromagnetic switch 53 for reversing the power supply to the motor 45.

The analyser 15 as it scrutinises the various selected discrete areas of the bank note passes the information derived to gate and bistable circuits or to electromagnetic relays to be memorised.

FIG. 5 shows a circuit having two relays 55 and 57 (only the contacts being shown). The relay 57 stores information given concerning the watermark while the relay 55 stores information concerning the bank note wire. The contacts of the two relays are connected in series with the electromagnetic switch circuit 21 or 33 (see FIGS. 2 and 3). Only when the wire and the watermark have been accepted as genuine will the electromagnetic switch 21, 33 be operated to be followed by the collection of the bank note in an appropriate container and the start of a merchandise dispensing function for which the bank note was inserted.

It will be seen that every step in the analysis of the bank note must be accompanied by a positive response before the bank note is accepted as genuine. Thus any malfunction of the analyser in failing to provide a positive response even though a bank note is genuine will result in the return of the bank note rather than its retention and acceptance.

The analyser need not be limited to scrutinising the same predetermined area of the bank note but can be readily adjusted to scrutinise a different area. FIGS. 6 and 7 show an adjustable analyser in which a support head 61 houses a first assembly 63 carrying a source and a photo electric sensor and a second assembly 63A carrying a second photo electric sensor, the light source and photo-electric sensors being positioned as in the arrangement of FIG. 1. The head 61 has a pair of stop pins 65, 67 which can engage a selected one of a plurality of discrete pairs of holes 69 in a base member 71, thereby enabling the head to be accurately located in a plurality of discrete positions on the base 71. By this means the head can be arranged to scrutinise different areas of the bank note as desired.

A similar result can be obtained with the modification shown in FIGS. 8 and 9 in which parts similar to those in FIGS. 6 and 7 are similarly referenced. In FIGS. 8 and 9 the head 61 is rigidly secured to the base and has a plurality of pairs of apertures 83a for receiving the assemblies 63 and 63A. By locating the assemblies 63 and 63A in different pairs of apertures, different zones 75, 77 and 79 of the bank note can be scrutinised as it travels along the guide 81. Associated with each of the zones 75, 77 and 79 are upper and lower limit criteria for the output of the analyser. Thus if the output of the analyser falls between the two limits the bank note under consideration will be accepted as genuine.

It will be appreciated that if the system has two analysers (each analyser determining the transparency and the reflection of the bank note at a different point) and each analyser is capable of occupying up to ten different positions in the head, the program for any particular analysis can be selected from one hundred different programs. This will make it difficult for a potential forger to be sure that his bank note will be accepted by the analyser unless he copies the whole bank note and not just one or two particular zones thereof.

FIG. 10 and 11 show a block diagram of a control system for a bank note detection system in which the following features of the bank note are examined:

a. the watermark;

b. the reflection from a printed surface of the bank note at two different areas;

c. the wire;

d. the type of paper used;

e. the bank note thickness; and

f. the length of the bank note.

The examination of features (a) and (b) of the bank note is carried out by using an analyser such as that shown in FIG. 1. Such an analyser has a transparency photosensitive element 103 T1 and a reflection photosensitive element 105 R1 corresponding to those denoted by 3 and 5 in FIG. 1. The output of each photosensitive element 103 T1 and 105 R1 is fed to a respective ipper limit threshold circuit 109 and 111 and also to a respective lower limit threshold circuit 110 and 112. The output of the four threshold circuits are fed to an AND gate 114.

The examination of features (c) and (d) of the bank note is carried out by using two analysers each similar to that shown in FIG. 1. One analyser has a transparency photosensitive element 203 T2 and a reflection photosensitive element 205 R2 while the other analyser has a transparency photosensitive element 303 T3 and a reflection photosensitive element 305 R3. The output of elements 203 T2 and 303 T3 are fed to respective circuits 209 and 309. The outputs of the photosensitive elements 205 R2 and 305 R3 are fed to a respective upper limit threshold circuit 211 and 311, and also to a respective lower limit threshold circuit 212 and 312. The circuits 311 and 312 are connected to an AND gate 314. The outputs from the four circuits 209, 309, 214 and 314 all feed another AND gate 216 to provide an output indicative of the presence of a genuine wire incorporated in the bank note.

The same photosensitive elements 105 R1 and 203 T2, although shown separately, are also used to examine the print of the bank note at two points A and B. During examination of the print at point A, the output of element 105 R1 is fed to upper and lower limit threshold circuits 116 and 118 and the outputs of threshold circuits 116 and 118 are fed to an AND gate 120. During the examination of the print at point B of the bank note, the output of the element 105 R1 is fed to upper and lower limit threshold circuits 122 and 124. The outputs of the threshold circuits 122 and 124 are fed to an AND gate 126.

The photosensitive element 203 T3 (although shown separately) is also used to examine the kind of paper on which the bank note is printed. The output of the element 203 T3 is fed to both upper and lower limit threshold circuits 218 and 220. The outputs of the threshold circuits 218 and 220 are fed to an AND gate 222.

The AND gates 114, 216 and 120 are connected to a switching circuit 401 which is shown in more detail in FIG. 11. All the AND gates 114, 216, 120, 126 and 222 are connected to a final AND circuit 501 which when triggered feeds an output signal to a switching circuit 503. The switching circuit 503 has a switch which is operable to connect the power supply 505 to an acceptance unit 511. The power supply 505 also feeds an ingress unit 507, a reset unit 509, and a thickness feeler 515 for controlling the direction of the rotation of the rollers 17A and 41 in the system of FIG. 3.

The output of the ingress unit 507 and also one output of the reset unit 509 are connected to a line 517 that powers the analyser so that current from the power source 505 to the analyser can be fed either via the ingress unit 507 or the reset line 509.

The acceptance unit 511 has three outputs, one output is connected to a line 519 that controls the clearing and sorting of accepted and rejected bank notes, another output is connected to a line 512 controlling the dispensing of merchandise for which the bank note was inserted, and the third output is connected to a reset member of the means for clearing and sorting bank notes.

The switching unit 401 shown in FIG. 10 will now be described in more detail with reference to FIG. 11. The three signals which arrive at the switching unit from the circuits 114, 120 and 216 control the energisation of respective coils 114B, 120B and 216b. Each coil controls the operation of a switch. At the completion of the watermark analysis, the switch 114C of coil 114B disconnects the element 105 R1 from line 403 (that connects the element to the threshold circuits 111 and 112) and instead connects the element to line 405. The switch 120C of the coil 120B when energised disconnects the line 405 from the line 407 and instead connects it with the line 409 to thereby couple the element 105 R1 to the threshold circuits 112 and 124 in readiness for scrutinising point B of the bank note. The contacts 216c1 of the switch when operated by the coil 216B, decouple the element 203 T2 from the line 411 that connects the element 203 T2 to the unit 209, and instead couples the element 203 T2 to the line 413 which connects the element 203 T2 to the threshold circuits 218 and 220. At the same time the contacts 216C2 of the same switch close to connect the line 407 with the line 415 and thereby complete the circuit from the element 105 R1 to the threshold elements 116 and 118 thus enabling analysis of point A on the bank note to be made.

The elements 203 T2, 305 R2, 303 T3 and 305 R3 are all arranged to lie in a common plane which extends parallel to the edge of a bank note, the elements 203 D2 and 305 R3 being arranged to lie on one side of the bank note and the elements 303 D3 and 205 R2 being arranged to lie on the other side of the bank note.

In operation as soon as the bank note is introduced into the bank note recognition system, it energises the ingress unit 507 which supplies current from the source 505 to the line 517 and, through a normally closed contact set of the reset unit 509, to the thickness feeler 515 to drive the rollers 17A or 41. If the bank note thickness is greater than a predetermined thickness the sense of rotation of the rollers 17A or 41 (see FIG. 4) is reversed, and the bank note is returned. If the detected thickness lies within the prescribed limits for a particular bank note, the bank note continues its motion in the same direction and passes into the optical analyser. As the leading edge of the bank note approaches the analyser, it triggers the reset unit 509 to de-energise the rollers 41. The normally open contact of the reset unit 509 is now closed and so continues to supply current to the analysers. The normally closed contacts of the unit 509 is open to discontinue the supply of current driving the first pair of rollers to prevent insertion of a fresh bank note. From this instant, forward motion of the bank note is continued by pairs of subsequent rollers while the ingress of further bank notes is prevented until the trailing edge of the present bank note emerges from the unit 509. As the distance along the bank note path between the units 507 and 509 is smaller than the length of the bank note the leading edge of the bank note reaches the unit 509 before its trailing edge has left the unit 507. This insures an uninterrupted supply of current to the line 517.

If all the inputs to the AND gate 501 are present, indicating that the bank note analysed is considered to be genuine, the switch circuit 503 connects the acceptance unit 511 to the power supply 505. Energisation of the acceptance unit 511 triggers the merchandise dispensing means (not shown), the means controlling acceptance or rejection of bank notes, and a resetting device of the latter means.

As the bank note continues its motion through the system, the leading edge triggers the outlet unit 513 to close the switch thereof. As the length of the bank note is greater than the distance along the bank note path between the units 509 and 513 the means controlling acceptance or rejection of the bank note is released to return to its initial rejection position. When the trailing edge of the bank note has passed the unit 509 the supply of current to the line 517 is discontinued and the system is de-energised.

The pairs of threshold circuits for each photosensitive element are binary devices. Taking for example the circuits 109 and 110, the circuit 109 which determines the upper limit provides a binary output of "1" until the input signal exceeds the preset threshold level whereupon the output will change into a binary "0". In the case of the circuit 110 which determines the lower level, the output will be a binary "0" until the input signal reaches the lower threshold limit when it would change to a binary "1".

Thus the outputs of the two threshold circuits will vary as follows for the various input conditions:

"0" and "1" when the input signal is lower than threshold level of both circuits;

"1" and "1" when the input signal exceeds the threshold of the lower limit threshold circuit but does not exceed the threshold of the upper limit threshold circuit; and

"1" and "0" when the input signal is greater than that of the threshold levels of both circuits.

Once the input signal to a threshold circuit has exceeded the threshold level the output will remain at binary "1" until the circuit is reset, for example by the de-energisation followed by re-energisation of the circuit. The outputs of the different threshold circuits are applied to their respective AND gates 114, 216, 120, 126 and 222 which will only be triggered if all the signals applied thereto are binary "1's". It will be appreciated that since the outputs of the threshold circuits are memorised, the input signals to the AND gates will be maintained until the threshold circuits are reset.

Considering for example the case of the four threshold circuits 109 to 112, if all the threshold circuits provide a binary "1" indicating that the watermark of the bank note is considered to be genuine, then the AND gate 114 will be triggered to provide a binary "1" output in turn. This binary "1" is applied to the final AND gate 501 and to a switch unit 401. The switching unit will thereupon react and through switches 114B and 114C connect the photosensitive element 105 R1 to the threshold circuits 116 and 118 in readiness to analyse the print at point A on the bank note. Point A, however, cannot be analysed until the analyser has analysed the metal wire in the bank note and accepted it as genuine. If the metal wire is considered genuine then a binary "1" from the AND gate 216 will operate the switches 216B and 216C2. When these latter switches are operated, the output of the photosensitive element 203 D2 is connected to the threshold circuits 218 and 220.

Where, during an analysis of point A of the bank note, the signals derived from the element 105 R1 cause both threshold circuits 116 and 118 to provide a binary "1", both outputs of the circuits 116 and 118 are fed to the AND gate 120 which itself then provides a binary "1" that is fed to the final AND gate 501. The binary "1" is simultaneously applied to the switching unit 401 causing the switch 120C to connect the elements 105 R1 to the line 409 and causing the element 105 to be connected to the threshold circuits 122 and 124 for analysing the point B on the bank notes.

If the outputs of the threshold circuits 112 and 124 are binary "1's" then the AND gate 126 will also generate a binary "1". With all the AND gates 114, 120, 126, 222 now providing a binary "1" the final AND gate 501 now also generates a binary "1" which will trigger the consent circuit 503 to connect the acceptance unit 511 with the power supply 505 thus initiating the collection of the accepted bank note in the corresponding container and the execution of the dispensing of merchandise.

As soon as the rear edge of the bank note has left the reset unit 509, the power supply is disconnected from all the analysers and the threshold circuits, which consequently return to their initial conditions upon re-energisation. The system is thus ready to take another bank note.

It will be appreciated that even if only one of the selected features of the scanned bank note is not acknowledged as genuine then the final AND gate will not energise the consent circuit so that the bank note is returned to the operator and no further operation is authorised.

It will be appreciated that the analysers described need not be limited to analysing moving bank notes, they can be used to check bank notes located in a fixed frame.

Many modifications may be made to the invention as will be apparant to those skilled in the art and it is intended to encompass any such modifications as fall within the spirit and scope of the invention.