Device and process for checking sheet articles such as bank note

Details Device and process for checking sheet articles such as bank note Device and process for checking sheet articles such as bank note

1997-11-10

2000-05-09

Hantis, K P

Optics: measuring and testing

Document pattern analysis or verification

250271, G06K 974

Patent

active

060611219

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of Invention
This invention relates to an apparatus and method for testing sheet material such as bank notes or papers of value.
2. Description of Related Art
EP-A 0 537 513 shows such an apparatus wherein the authenticity of bank notes is tested. For this purpose the bank note is first illuminated with light-emitting diodes in the colors, red and green, and in the infrared spectral region. The light-emitting diodes are pulsed sequentially so that the bank note is only illuminated with one color or in the infrared spectral region at a time. The diodes are disposed on both sides of the bank note. The light transmitted or reflected by the bank note is detected by means of a single linear CCD array and converted into electric signals which are then further processed accordingly.
By using a linear CCD array one can achieve a relatively high local resolution on the bank note. However, a disadvantage is the high equipment expense necessary for illuminating the bank note in different colors or in the infrared spectral region. A special problem is mutually balancing the illumination levels in the different colors or in the infrared spectral region.
DE-OS 38 15 375 shows a further apparatus for testing the authenticity of sheet material. It is constructed from a plurality of like modules. Each module has its own illumination device with white light and a linear photodiode array. Further, before each module is a filter which transmits for example the colors, red, green or blue, or in the infrared spectral region.
For testing the sheet material, the light emitted by the illumination device passes through the filter of the corresponding module and illuminates the sheet material. The light diffusely reflected by the sheet material then passes through the filter of the module and is detected by the linear photodiode array. The latter converts the impinging light into corresponding signals which are then further processed.


SUMMARY OF THE INVENTION

By using like modules for the individual colors or the infrared spectral region one can ensure high ease of repair for the apparatus, on the one hand. On the other hand, however, this requires relatively high equipment expense. The use of a photodiode array permits the sheet material to be scanned virtually in its total width. However, the resolutions achieved are comparatively low.
The invention is directed to the problem of proposing an apparatus for testing sheet material which tests the sheet material with high resolution and in a plurality of spectral regions and requires comparatively low equipment expense.
This problem is solved by the features of the main claim.
The basic idea of the invention is substantially that the apparatus has an illumination device which illuminates the sheet material continually and in the total spectral region to be tested. For detecting the light diffusely reflected or transmitted by the sheet material one uses a receiving device having at least two linear parallel CCD arrays. A filter transmitting a certain spectral region is mounted on each CCD array. The individual filters are selected such that at least one transmits in the visible spectral region and one in the invisible spectral region. The individual CCD arrays produce from the received light electric signals which are then processed in an evaluation device and compared with reference data for testing the sheet material.
The advantage of the invention is that both the illumination device and the receiving device require low equipment expense. The individual CCD arrays and corresponding filters can be disposed compactly on a carrier and are relatively cost-effective to produce. The use of a plurality of CCD arrays permits a plurality of different spectral regions to be detected simultaneously with high resolution and over the total width of the sheet material.
In a preferred embodiment the receiving device has four parallel CCD arrays with filters, the filters each transmitting a spectral region in the color range, red, green, blue, and in the inf

REFERENCES:
patent: 4542829 (1985-09-01), Emery et al.
patent: 4710963 (1987-12-01), Chapman et al.
patent: 4943159 (1990-07-01), Oetliker et al.
patent: 5026159 (1991-06-01), Allen et al.
patent: 5471281 (1995-11-01), Hayashi et al.
patent: 5724437 (1998-03-01), Bucher

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