Device and method for verifying the authenticity of banknotes

• US 20030039359A1
• Filed: 08/20/2002
• Published: 02/27/2003
• Est. Priority Date: 12/03/1999
• Status: Active Grant

• Current Assignee: Giesecke & Devrient (Giesecke & Devrient GmbH)
• Original Assignee: Giesecke & Devrient GmbH
• Inventors: Thierauf, Klaus
• Granted Patent: US 6,918,482 B2
• Time in Patent Office: Days
• US Class Current: 380/54
• CPC Class Codes: G01N 21/645 Specially adapted constructive features of fluorimeters
• CPC Class Codes: G01N 2201/0624 Compensating variation in output of LED source
• CPC Class Codes: G07D 7/1205 Testing spectral properties
• CPC Class Codes: G07D 7/121 Apparatus characterised by sensor details

Abstract

An apparatus and method for testing the authenticity of bank notes are proposed.

The apparatus includes a light source for emitting light suitable for exciting fluorescent light in a bank note to be checked, and a fluorescence detector for detecting the fluorescent light emitted by the bank note to be checked. According to the invention it is provided that the light source is a light-emitting diode and the light-emitting diode is formed to emit light containing ultraviolet light at least in a partial spectral region. This makes it possible in particular to obtain a compact structure of the apparatus.

The method involves exciting and detecting fluorescent light in the bank note to be checked and comparing the detected fluorescent light with a predefined threshold value. According to the invention it is provided that the detected fluorescent light is reduced by the ambient light detected with the light source switched off. This permits the elimination of measuring inaccuracies at the same time as simple operation.

Claims

1. An apparatus for testing the authenticity of bank notes having

at least one light source for emitting light suitable for exciting fluorescent light in a bank note to be checked (1 1), and

at least one fluorescence detector (12) for detecting the fluorescent light emitted by the bank note to be checked (11), characterized in that

the light source is a light-emitting diode (10), and

the light-emitting diode (10) is formed to emit light containing ultraviolet light at least in a partial spectral region.

2. An apparatus according to claim 1, characterized in that the light-emitting diode (10) has an emission spectrum with a peak in the ultraviolet spectral region.

3. An apparatus according to either of the above claims, characterized in that

the light-emitting diode (10) is formed to emit light suitable for exciting fluorescent light in an extended partial area of the bank note to be checked (11), and

the fluorescence detector (12) is formed for integral detection of the fluorescent light emitted by the bank note (11).

4. An apparatus according to any of the above claims, characterized in that a first filter (15) is provided for filtering the light emitted by the light-emitting diode (10), the filter (15) being permeable to a partial spectral region of the light emitted by the light-emitting diode (10) and suitable for exciting fluorescent light in the bank note to be checked (11).

5. An apparatus according to any of the above claims, characterized in that a second filter (16) is provided for filtering the fluorescent light emitted by the bank note to be checked (11) and to be detected by the fluorescence detector (12).

6. An apparatus according to any of the above claims, characterized in that a transport plate (20) is provided which is disposed between light-emitting diode (10) and fluorescence detector (12), on the one hand, and the bank note to be checked (11), on the other hand, and

has at least one three-dimensional partial area (21) which is permeable at least to a partial spectral region of the light emitted by the light-emitting diode (10) and at least to a partial spectral region of the fluorescent light emitted by the bank note to be checked (11).

7. An apparatus according to any of the above claims, characterized in that a monitor detector (25) is provided for detecting at least part of the light emitted by the light-emitting diode (10).

8. An apparatus according to claims 6 and 7, characterized in that light-emitting diode (10), monitor detector (25) and transport plate (20) or first filter (15) are disposed such that light emitted by the light-emitting diode (10) is partly reflected on the transport plate (20) or the first filter (1 5) and reaches the monitor detector (25).

9. An apparatus according to either of claims 7 and 8, characterized in that a third filter (17) is provided for filtering the light emitted by the light-emitting diode (10) and partly reflected on the transport plate (20) and to be detected by the monitor detector (25).

10. An apparatus according to any of the above claims, characterized in that a first screen (22) is provided for collimating the fluorescent light emitted by the bank note to be checked (11) onto the fluorescence detector (12).

11. An apparatus according to any of the above claims, characterized in that a system (18) of optical lenses is provided for collimating the fluorescent light emitted by the bank note to be checked ( 11) onto the fluorescence detector (12).

12. An apparatus according to either of claims 7 and 8, characterized in that a second screen (23) is provided for collimating the light emitted by the light-emitting di-diode (10) and partly reflected on the transport plate (20) onto the monitor detector (25).

13. An apparatus according to any of the above claims, characterized in that a voltage source for generating a voltage with periodic time behavior is provided for supplying power to the light-emitting diode (10).

14. An apparatus according to any of the above claims, characterized in that at least one amplifying device is provided for amplifying output signals from the fluorescence detector (12) and/or the monitor detector (25), the amplifying device being formed as a lock-in amplifier.

24. Use of the apparatus for testing the authenticity of bank notes according to any of claims 1 to 14, characterized by the steps of

measuring fluorescent light emitted by the bank note (11) with the fluorescence detector (12) with the light-emitting diode (10) switched on,

measuring phosphorescent light emitted by the bank note (10) with the fluorescence detector (12) with the light-emitting diode (10) switched off, and

using the measured fluorescent and phosphorescent light of the bank note (11) for authenticity testing.

15. A method for testing the authenticity of bank notes comprising the steps of illuminating a bank note to be checked (11) with ultraviolet light from a light source, measuring visible fluorescent light emitted by the bank note to be checked (11) with a fluorescence detector (12), and comparing the measured fluorescent light with a predefined threshold value, characterized by the following steps:

a) illuminating at least a partial area of the bank note to be checked (11) with light emitted by a light-emitting diode (10) and suitable for exciting fluorescent light in the bank note to be checked (11), measuring with a fluorescence detector (12) and generating a first measured value,

b) measuring with the fluorescence detector (12) with the illumination switched off and generating a second measured value,

c) correcting the first measured value generated with the illumination switched on with the second measured value generated with the illumination switched off, and

d) comparing the corrected measured value with a predefined threshold value.

16. A method according to claim 15, characterized in that the light-emitting diode (10) is switched on and off periodically.

17. A method according to either of claims 15 and 16, characterized in that the first measured value generated with the illumination switched on is corrected with the second measured value generated with the illumination switched off by subtracting the second measured value from the first measured value.

18. A method according to either of claims 15 and 16, characterized in that the first measured value generated with the illumination switched on is corrected with the second measured value generated with the illumination switched off by lock-in amplification of an output signal generated by the fluorescence detector (12).

19. A method according to any of claims 15 to 18, characterized in that the corrected measured value or the threshold value is corrected with correction value K which takes account of the change of intensity in the light emitted by the light-emitting diode in the course of the operating lifetime of the light-emitting diode (10).

20. A method according to claim 19, characterized by the steps of

measuring at least part of the light emitted by the light-emitting diode (10) with a monitor detector (25) at a first and a later second time with the light-emitting diode (10) switched on and without a bank note ( 11) in each case, thereby generating first and second monitor values associated with the measurements at the first and second times in each case, and

determining correction value K from the first and second monitor values.

21. A method according to any of claims 15 to 20, characterized in that the method is performed at several places on the bank note to be checked (11).

22. A method according to claim 21, characterized in that the measured values measured at several places on the bank note (11) and corrected are averaged, thereby generating a mean value that is compared with the threshold value.

23. A method according to any of claims 15 to 22, characterized by the steps of

measuring fluorescent light emitted by the bank note (11) with the light-emitting diode (10) switched on,

measuring phosphorescent light emitted by the bank note (10) with the light-emitting diode (10) switched off, and

using the measured fluorescent and phosphorescent light of the bank note (11) for authenticity testing.