Optics: measuring and testing – Document pattern analysis or verification
Patent
1999-01-05
2000-03-21
Font, Frank G.
Optics: measuring and testing
Document pattern analysis or verification
G06K 974
Patent
active
060409010
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an apparatus for optical detection of sheet material such as bank notes or papers of value.
DE 195 17 194 A1 discloses an apparatus with a stationary detection device for detecting the light of an area of the sheet material incident from the direction of a detector axis and emitted in the direction of an optical sheet material axis. For optical detection the sheet material is transported past the stationary detection device along a transport direction. The area detected by the detection device comprises the total width of the sheet material perpendicular to the transport direction so that the total surface of the sheet material is detected when it is transported past.
In addition, an illumination device is provided for illuminating the sheet material during detection. The illumination device has components for illuminating the sheet material from both sides so that the detection device can detect both reflected and transmitted light.
The resolution of the apparatus is about 50 dpi. For certain applications, such as the detection of a bank note number on a bank note by means of optical character recognition (OCR) software, this resolution is deficient. Increasing the resolution to about 250 dpi, e.g. for detecting a bank note number, leads to very high data rates which are about a factor of 25 higher than the data rates of the known apparatus. The problem here is that such data rates can only be processed with high effort, if at all.
SUMMARY OF THE INVENTION
Starting out from this, the invention is based on the problem of proposing an apparatus for optical detection of sheet material which permits high resolution during detection at a data rate requiring little effort to process.
The basic idea of the invention is essentially that only an area of the sheet material which is preferably smaller than the total width of the sheet material is detected with high resolution. The area is selected on the sheet material so that the areas on the sheet material necessary for the intended application are detected with high resolution. For this purpose a reflection device with a plurality of reflectors is provided for deflecting the light emitted by the area of the sheet material in the direction of the sheet material axis in the direction of the detector axis. An adjusting device can be used to change the position of at least two reflectors for fixing the position of the area on the sheet material relative to the detection device. The reflectors are disposed so that the length of the optical path of the emitted light from the sheet material to the detection device is independent of the position of the area on the sheet material.
An advantage of the apparatus is that the areas relevant for intended applications can be detected with high resolution. Due to the preferably stationary detection device a particular adjustment is retained. The constant length of the optical path during detection ensures that once an imaging system is adjusted it need not be changed when the position of the area on the sheet material is fixed. Since the adjusting device only changes the position of the relatively lightweight reflectors and there is thus no motion of relatively large masses, the relevant area on the sheet material can be adjusted very precisely with simple means.
In a first preferred embodiment, the detector axis and the sheet axis are disposed parallel. A first reflector forms with the detector axis a first angle of reflection of 45.degree., and a second detector with the sheet material axis a second reflector angle of 45.degree.. For fixing the position of the area on the sheet material the reflectors are shifted by the adjusting device parallel in a direction perpendicular to the detector axis or the sheet material axis.
In a second preferred embodiment, the detector axis and the sheet material axis form a fixed axis angle. A first reflector forms with the detector axis a first reflector angle, and a second reflector forms with the sheet material axis a second reflecto
REFERENCES:
patent: 5847859 (1998-12-01), Murata
Fiedler Michael
Stapfer Michael
Font Frank G.
Giesecke & Devrient GmbH
Stafira Michael P.
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