De La Rue Systems Ltd.

Barry J Curl

Graham H Hilton

Victor B Chapman

Apparatus is disclosed for scanning a banknote (33). A lengthwise strip of the banknote (33) is illuminated with white light, and the banknote is moved parallel to its width. Light reflected from all regions of the lengthwise strip is conveyed through an optical fibre fishtail array to a single photodetector, or to a spectroscope and then to several photodetectors for color scanning. The waveform produced by the or each photodetector is then characteristic of the surface of the banknote, and is used in an analyzing circuit for banknote pattern recognition, or to sense the condition of the banknote with regard to its age or degree of soiling. The analyzing circuit includes means for compressing or expanding the length of the waveform to give it a standard length for subsequent comparison with one or more stored characteristic waveforms in a memory (16). The apparatus also determines the mean level of intensity of the waveform in an integrator (9), and includes a circuit (24 to 28) for obtaining the standard deviation of selected points of the waveform from the mean value, a low standard deviation indicating a badly soiled or worn banknote.

Apparatus for scanning a sheet

Apparatus for scanning a document includes an array of light emitting diodes, or optical fibers, arranged across the width of the document and extending further than its edges, a corresponding array of photo-diodes, or fiber optics connected to photo-diodes, for providing analog intensity signals indicative of the degree of transmission of light to each sensor, and an analyzing circuit responsive to each of the intensity signals to determine the condition of the document, and especially to determine the position of the edges of the document, and the size of any pin-holes or tears in the document. According to the invention, the analyzing circuit derives digital signals indicative of the relative intensity value of each analog signal with regard to three or more predetermined threshold values of intensity, each threshold level corresponding to a different degree of obscuration of a sensor by the corresponding area of the document. If a threshold value T3 is exceeded, but a higher threshold value T4 is not exceeded, then the circuit assumes that the corresponding sensor indicates 1/4 obscuration, and that for example the edge of the document lies at a distance from the neighboring sensor equal to 1/4 of the separation between adjacent sensors.

Apparatus for determining with high resolution the position of edges of

In an optical detection system for detecting a feature located at a predetermined lateral position on a banknote, for example, the banknote is moved along a flow path and a series of light receivers are arranged transversely across that portion of the flow path which the feature is expected to occupy, so that different ones of the light receivers will respond to the feature in the banknote depending on the lateral offset of the banknote at that portion of the flow path. The margins of the note are utilized in the detection system to gate the said light receivers so that for any position of lateral offset of the banknote only that light receiver which responds to the said feature of the banknote will produce an effective output signal. In the embodiment of FIG. 1, two sets of fibre optics are used to effect this gating, one set having its first ends (S1 to S5) opposite a light source at one margin of the sheet and its other ends (F1 to F5) adjacent the above mentioned light receivers (F1' to F5'). The said light receivers are constituted by first ends of the second set of fibre optics, the other ends (D1 to D5) of which provide light output for a detector at the other margins of the notes. An electronic gating system is also disclosed (FIG. 2).

Optical detection system for features on a sheet or web

Apparatus for detecting missing areas or folded corners in sheets, for example banknotes (14), is disclosed. FIG. 1 shows a banknote (14) being scanned in a strip along one edge of the banknote. A strip light source 12 and a strip sensor 16 are disposed on opposite faces of the banknote which is caused to move perpendicularly to the light path between the source and sensor, and perpendicularly to the plane of the drawing. A photometer (18) responds to the total amount of light transmitted through the edge strip of the banknote (14) as the banknote is scanned. A filter (20) may be interposed in the light path to improve the sensitivity of the apparatus. The total amount of transmitted light detected by the photometer (18) is integrated over a period of the scan during which the intensity differs substantially from the mean level for an unflawed portion of the banknote. Integration is thus performed only over missing or folded areas of the banknote. It may also be limited to only the leading and trailing portions of the edge strip of the banknote, corresponding to the corners of the note. In order to compensate for the passage of a skewed banknote passing through the apparatus, integration is inhibited over the said period whenever the intensity waveform from the photometer (18) is steeper than a predetermined gradient.

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Southampton, United Kingdom

Barry J Curl