Apparatus for scanning a sheet

Abstract

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.

Dependencies are inferred from the claim text.