The counting of the banknotes is a costly and repetitive action that occurs many times throughout the lifetime of a banknote. During the manufacture of banknotes, each note is counted ten times on average, both in the form of a sheet consisting of several banknotes, and in the form of the note itself. The number of times the note is counted by a central bank owner, commercial banks and the remainder of the private sector is significantly influenced by the denomination of that note. Some denominations of circulating banknotes may be counted up to thirty times by the central bank over a three year life of the note. In the private sector, some notes may be counted up to ninety times over a three year note life.

Currently, the counting of banknotes is mainly performed by mechanical means which produce considerable wear on the banknotes, and are often inaccurate.

Optical techniques of counting banknotes are also known. According to one such technique, a region of the edge of a stack of banknotes is illuminated and light reflected from the edge of the stack is directed onto a detector which produces an output corresponding to amount of light collected when scanning the edge of the stack in direction generally perpendicular to the plane of the stacked sheets. The output signal in such a system shows the change in reflectivity at the edge of the sheets and may be used to estimate the number of sheets in the stack. Such techniques, however, have been found to be inherently inaccurate due to irregularities in the disposition of the banknotes within the stack, variation in the reflectivity of the edges of these banknotes and interaction of the light reflected from the edges of the banknotes.

It is an object of the invention to provide a method of counting security documents, such as banknotes, which ameliorates or overcomes one or more disadvantages of known security document counting methods.

It is a further object of the invention to provide a method of counting security documents which improves upon the accuracy of known security document counting methods.

The present invention provides a method of counting sheets of plastics material, including security documents, such as banknotes, having a sheet like substrate of plastics material, the method comprising the steps of: (a) projecting radiation from a radiation source onto the substrate of each sheet for propagation therein, (b) detecting a radiation Emission from the substrate of each sheet, the radiation Emission resulting from the propagated radiation, and (c) counting the number of radiation Emissions detected in step (b).

The present invention takes advantage of a hitherto unsuspected light-guide effect (total internal reflection) of sheets of plastics, such as polymer banknotes and other security documents including a sheet like substrate of plastics material.

Security documents that have such layered construction have been observed to act as a light guide within which incident light or other radiation can propagate. Light projecting from the banknote can conveniently be detected as it exits in order to accurately count a given number of banknotes.

The projected radiation in step (a) may be projected onto an edge of the sheets or substrate.

Similarly, the radiation emission may be detected in step (b) from an edge of the sheet or substrate.

In one embodiment, an opacifying layer may be applied to opposing faces of the sheet or substrate of the security document, the opacifying layers acting to further guide the projected radiation within the substrate. The opacifying layers may only partially cover at least one of the faces of the substrate to leave an uncovered zone on that face, the projected radiation in step (a) being projected onto the uncovered zone. It will be appreciated from the above that the or each opacifying layers are not required to achieve the desired effect.

Although the invention is applicable to methods in which each security document is supported individually during counting, in one embodiment, the

security documents may be supported in a stack prior to step (a), and radiation projected in step (a) onto the substrate of each security document in the stack. The radiation in (a) may be projected simultaneously onto the substrate of each security document in the stack.

The radiation may be projected onto a side wall of the stack in step (a).

Alternatively, in applications where each face of the security document includes an uncovered zone, the uncovered zones of each security document in the stack may be superposed to enable the projected radiation to be transmitted through the superposed zones and onto the substrate of each security document in the stack.

An optical reading head may act in step (b) to scan a side wall of the stack and thus detect the radiation emissions.

The substrate may include material which acts to assist in the propagation of the radiation in the substrate. Such material may include fluorescent, phosphorescent, anti-stokes, pearlescent or like inks.

One or more of the opacifying layers may be formed from ink.

Alternatively, one or more of the opacifying layers may be formed from paper.

The radiation used in the method of counting security documents according to the invention may include visible light, ultraviolet light, radio waves or infrared light. Visible and non-visible radiation may be used in accordance with the present invention.

Preferably, the projected radiation is projected onto the substrate of each security document in step (a) at a central location. Similarly, the radiation emission detected in step (b) may be detected from a central location of the substrate.

In embodiments of the invention in which the security documents are supported in a stack prior to step (a), the stack of security documents may be counted two or more times. Radiation may be projected onto the substrate of each security document in the stack in step (a) and the radiation emissions exiting the stack of banknotes in step (b) at two or more different locations of the substrates, including on the same side of the stack as that by which the radiation entered in step (a).

The number of radiation emissions counted at each location may be compared to verify the accuracy of the count.

Several embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is perspective view of a banknote to be counted according to the method of counting security documents of the present invention; Figure 2 is a perspective view of the banknote of Figure 1 as counted according to a first variation of the method of counting security documents of the present invention; Figure 3 is a perspective view of the banknote of Figure 1 which is counted according to a second variation of the method of counting security documents of the present invention; Figure 4 is a schematic side view of a stack of banknotes to be counted according to the present invention; and Figure 5 is a side view of an apparatus for use in performing the method of counting security documents according to the present invention.

Referring now to Figure 1, there is shown a banknote 1 which is substantially rectangular in shape having substantially parallel sides 6 and 7 and substantially parallel ends 8 and 9. The banknote 1 includes a sheet like substrate 2 of transparent plastics material. The substrate 2 is covered over most of its upper and lower surfaces by opacifying layers 3 and 4.

Preferably, the sheet like substrate 2 is made of flexible material, but in security documents other than banknotes, this need not necessarily be the case.

Similarly, whilst the use of a transparent plastics material in the banknote 1 so that the substrate has a transparent appearance, the term"transparent"is to be understood in the context of the present specification as enabling the transmission of light or other form of radiation therethrough.

As shown in Figure 1, the opacifying layers need not be applied over the entire surfaces of the sheet like substrate 2 and thus leave a transparent portion 5 of the substrate which is at least partially not covered by the opacifying layers. This

transparent portion 5 constitutes a"window"in the banknote through which light or other radiation may be transmitted.

The substrate 2 of transparent plastics material preferably is formed from a transparent polymeric material which may be made up of at least one biaxially oriented polymeric film. The substrate may comprise a single layer film of polymeric material. Alternatively, the substrate may comprise a laminate of two or more layers of transparent biaxially colour oriented polymeric film.

The opacifying layers 3 and 4 may comprise anyone or more of a variety of opacifying inks which can be used in the printing of banknotes or other security documents. For example, the layers of opacifying ink may comprise pigmented coatings comprising a pigment, such as titanium dioxide, dispersed within a suitable binder or carrier of heat activated cross-linkable polymeric material. Alternatively, a substrate of transparent plastics material 2 may be sandwiched between opacifying layers of paper to which indicia is printed or otherwise applied.

The opacifying layers 3 and 4 form a outer shell which act as a light guide to direct light or other radiation incident on an uncovered portion of the banknote 1 through the inner substrate 2 of the banknote 1 to exit at another uncovered portion of the banknote.

It has been found, however, that the present invention is also applicable to the counting of security documents including non-opacified substrates. As seen in Figure 1, incident radiation 10 may be projected from a light source onto a first, uncovered end 9 of the banknote 1. The incident light 10 is caused to propagate within the substrate 2 assisted by the light-guiding effect of the opacifying layers 3 and 4, and thus produce a radiation emission 11 at the opposite end 8 of the banknote 1. Counting of the number of radiation emissions from each banknote provides an accurate means of establishing the number of banknotes in a given quantity to be counted.

The substrate may include material which acts to assist in the propagation of radiation, such as fluorescent, phosphorescent, anti-stokes; pearlescent of like materials. This material may change the nature of the radiation emitted from the substrate by the wavelength.

Incident radiation may also be projected onto a side edge of the banknote 1.

As seen in Figure 2, incident radiation 10 is projected onto the uncovered side 6 of the substrate 2 and caused to propagate across the width of the banknote in the substrate 2 by the opacifying coatings 3 and 4 applied to the upper and lower surfaces of the substrate 2. A radiation emission exits the substrate 2 at the opposite side 7.

Incident radiation may also be projected onto the clear plastic window 5, or other uncovered zone on one of the faces of the security document 1. As seen in Figure 3, the use of the clear window 5 in this manner can provide for an easier point of entrance for incident radiation 10 to be projected onto the substrate 2 and then propagate therewithin. The light will then be reflected along the length and width of the banknote 1 and will exit the banknote through the sides 6,7 and ends 8, 9, resulting in a detectable radiation emission 11.

One application in which the present invention has been found to be particularly effective is in the counting of banknotes in a stack. Typically, many banknotes are produced together in the form of a sheet, from which the individual banknotes are cut. A predetermined number of banknotes are bundled together into a stack, and bands are then placed around the stack to facilitate its manipulation.

Figure 4 schematically depicts one such stack 20 of banknotes bound together by bands 21 and 22.

Rather than breaking the bands 21 and 22, and mechanically counting the banknotes in the stack 20, a light or other radiation source 23 may be used to project incident light or radiation 24 onto one wall of the stack, in this case the wall being formed from the ends of the banknotes in the stack. The incident radiation 24 is caused to propagate through the length of the banknotes in the stack 20 by the opacifying coatings on the surfaces of each banknote. Radiation emissions 25 are accordingly caused to exit the opposing end of each banknote in the stack 20.

Counting of the number of radiation emissions 25 enables the number of banknotes in the stack 20 to be accurately determined.

When the present invention is used to count used banknotes, folded corners and edge tears may ordinarily inhibit the entering and exiting of the light or other radiation into and from the plastics substrate 2. Accordingly, it is desirable to position the light source 23 and radiation emission detector towards the centre of the banknote within the stack 20.

Moreover, when some used notes are placed in a stack, it is possible for one or more of the notes to be folded in half, as is the case with the banknote referenced 25 in Figure 4. In this case, projecting light or other radiation onto an uncovered end of the banknote 25 may not result in a corresponding radiation emission from an opposing end of the banknote. Counting the number of radiation emissions 25 exiting each of the banknotes in the stack at the opposite end to which incident radiation is received from the radiation source 23 will therefore provide an inaccurate result. In order to address this problem, it is therefore preferable that the method of counting security documents according to the present invention be repeated second or further times by detecting radiation exiting the substrate 2 of the banknotes in the stack 20 at different locations on the same or on different sides or ends of the stack. The results of the two counts may then be compared, and if a difference is detected, the stack 20 of banknotes manually counted.

It is also possible to introduce projected radiation onto the substrate of each security document including a clear window such as that illustrated in Figure 3, by firstly arranging each of the banknotes in the stack 20 so that the clear windows of all banknotes are superposed, and then projecting incident radiation from the radiation source 23 through the superposed uncovered zones and onto the substrates of each security document in the stack.

Figure 5 illustrates one embodiment of an apparatus which may be used to perform the method of counting security documents according to the present invention. The banknote counting apparatus 30 shown in this figure includes a base 31 carrying a support surface 32 upon which is placed a stack 33 of banknotes or other security documents to be counted. One edge of the stack of banknotes is placed in contact with a vertically extending reference member 34. The support

member includes apertures through which radiation may be projected from a radiation source 35, such as a fluorescent light tube.

A support plate 36, movable in the direction indicated by the arrows 37 and 38, carries an optical reading head 39. Movement of the support plate 36 is produced by a suitable actuator such as a rotatable screw 40 driven by a motor 41 driven by a control unit 42. Electrical signals from the optical reading head 39 are applied to the control unit 42 by means of electrical connections 43. The control unit 42 acts to drive the rotatable screw 40 and thus cause the optical reading head to be moved across an edge of the stack 33 which is remote from the edge abutting the vertically extending member 34. The optical reading head is operative to produce an electrical signal as it moves across the edge of the stack 33 corresponding to the incident radiation thereupon. The control unit 42 acts to digitise the signals received from the optical reading head 39 and to the count the peaks of the signals received, so as to determine the number of banknotes in the stack 33.

In other embodiments, the optical reading head 39 may be displaceable so as to scan the stack of banknotes at two or more locations and the number of radiation emissions accounted each time compared in order to verify the accuracy of the count.

Many other variations may be made to the above described components and arrangements without departing from the spirit or ambit of the invention. For example, whilst the present invention has been described in relation to the counting of banknotes in a stack, the invention is also applicable to the counting of other security documents and sheet-like articles.