Methods and devices for testing the colour fastness of imprinted objects

• US 20030123049A1
• Filed: 11/07/2002
• Published: 07/03/2003
• Est. Priority Date: 02/21/2000
• Status: Active Grant

• Current Assignee: Giesecke & Devrient (Giesecke & Devrient GmbH)
• Original Assignee: Giesecke & Devrient GmbH
• Inventors: Thierauf, Klaus, Gerz, Christoph
• Granted Patent: US 6,937,322 B2
• Time in Patent Office: Days
• US Class Current: 356/71
• CPC Class Codes: G07D 7/1205 Testing spectral properties
• CPC Class Codes: G07D 7/121 Apparatus characterised by sensor details

Abstract

The invention relates to methods and apparatuses for testing the authenticity of objects printed with security ink, for example bank notes, security documents, identification documents or documents of value, by measuring light emanating from, in particular reflected or transmitted by, an object to be checked.

To guarantee especially reliable authenticity testing it is provided that light emanating from the object to be checked is detected in spectral regions outside the visible spectral region.

To obtain easily operated and safe authenticity testing in addition, it is provided that light emanating from the object is detected at a plurality of places on the object in at least two selected spectral regions, a test series being produced for each spectral region, two test series adapted to each other, and authenticity testing then performed by comparing the adapted two test series.

An especially compact, easily operated and easily adjusted apparatus is characterized in that at least one diaphragm is provided between object and detector for adjusting the size of an area to be examined on the object.

Claims

1. A method for testing the authenticity of printed objects by measuring light emanating from an object (10) to be checked in at least two defined spectral regions, wherein

the object (10) to be checked is irradiated with light having a spectrum with components in the defined spectral regions,

light emanating from at least one place on the object (10) to be checked is detected in the defined spectral regions, and

authenticity testing is effected on the basis of the light detected in a first spectral region and the light detected in a second spectral region,

characterized in that the spectral regions where light emanating from at least one place on the object (10) to be checked is detected are outside the visible spectral region.

2. A method according to claim 1, characterized in that

detection of light emanating from the object (10) is effected at a plurality of places on the object (10) so that a test series (I₁, I₂) is produced from individual measured values for each defined spectral region, and

authenticity testing is effected using the test series (I₁, I₂).

3. A method according to claim 2, characterized in that

a first (I₁) and a second (I₂) test series are adapted to each other by determining from the measured values of the first test series (I₁) values of an adapted series (I′

₁) that deviate only slightly from the values of the second test series (I₂) in areas (B) where the two test series (I₁, I₂) have substantially an identical qualitative course, and

authenticity testing is effected by comparing the adapted test series (I′

₁, I₂).

23. An apparatus according to any of claims 1 to 3, characterized in that authenticity testing is effected on the basis of light detected in at least two invisible spectral regions and in at least one visible spectral region.

4. A method for testing the authenticity of printed objects by measuring light emanating from an object (10) to be checked in at least two defined spectral regions, wherein

the object (10) to be checked is irradiated with light having a spectrum with components in the defined spectral regions,

light emanating from the object (10) to be checked is detected in the defined spectral regions, and

authenticity testing is effected on the basis of the light detected in the defined spectral regions,

characterized in that

detection of light emanating from the object (10) is effected at a plurality of places on the object (10) so that a test series (I₁, I₂) is produced from individual measured values for each defined spectral region,

a first (I₁) and second (I₂) test series are adapted to each other by determining from the measured values of the first test series (I₁) values of an adapted series (I′

₁) that deviate only slightly from the values of the second test series (I₂) in at least one area (B) where the two test series (I₁, I₂) have substantially an identical qualitative course, and

authenticity testing is effected by comparing the adapted test series (I′

₁, I₂).

5. A method according to claim 4, characterized in that

conversion of the measured values of the first test series (I₁) into the values of the adapted series (I′

₁) is effected by a linear transformation, and

the linear transformation is performed by multiplying the measured values of the first test series (I₁) by a first parameter (a₁) and then adding a second parameter (a₂).

6. A method according to claim 5, characterized in that the two parameters (a₁, a₂) are determined from the measured values of the two test series (I₁, I₂) at the places of a local minimum (I_1j, I_2j) and a local maximum (I_1k, I_2k) in the defined areas.

7. A method according to claim 5, characterized in that those parameters (a₁, a₂) are determined for which the sum of the square of the differences of the values of the adapted test series (I′

₁, I₂) is minimized.

8. A method according to claim 7, characterized in that determination of the two parameters (a₁, a₂) is effected in two runs, wherein

in a first run, adaptation of the test series (I₁, I₂) is effected by determining the two parameters (a₁, a₂) from all measured values of the two test series (I₁, I₂),

the adapted series (I′

₁, I₂) are then compared with each other to determine a measured value area (A) where the adapted series (I′

₁, I₂) deviate from each other, and

in a second run, another adaptation of the test series (I₁, I₂) is effected by redetermining the two parameters (a₁, a₂), the two parameters (a₁, a₂) being determined only from values of the two test series (I₁, I₂) outside the certain measured value area (A).

9. A method according to any of claims 4 to 8, characterized in that comparison of the adapted series (I′

₁, I₂) is effected by subtracting the two series (I′

₁, I₂) from each other.

10. An apparatus for testing the authenticity of printed objects by measuring light emanating from a object (10) to be checked in at least two defined spectral regions having

at least one light source (12) for irradiating the object (10) with light having components in the defined spectral regions, and

at least one detector (13) for detecting light emanating from the object (10), the detector (13) having detection units (14) each sensitive in one of the defined spectral regions,

characterized in that the defined spectral regions in which the detection units (14) are sensitive are outside the visible spectral region.

11. An apparatus according to claim 10, characterized in that the light source (12) has a broad-band spectrum at least partly including the defined spectral regions.

12. An apparatus according to either of claims 10 and 11, characterized in that at least one optical device is disposed between object (10) and detector (13) for fo-focusing light emanating from the object (10) and to be detected by the detector (13).

13. An apparatus according to claim 12, characterized in that the optical device contains a self-focusing lens (16).

14. An apparatus according to any of claims 10 to 13, characterized in that at least one diaphragm (15) is provided between object (10) and detector (13) for adjusting the size of an area to be measured on the object (10) from which light emanating from the object (10) is detected by the detector (10).

15. An apparatus according to any of claims 10 to 14, characterized in that the detection units (14) of the detector (13) have side-by-side photosensitive elements.

16. An apparatus according to any of claims 10 to 14, characterized in that the detection units (14) of the detector (13) have tandem mounted photosensitive elements, each photosensitive element being permeable to the light to be detected with the particular photosensitive elements therebehind.

17. An apparatus according to either of claims 15 and 16, characterized in that at least one optical filter (17) is provided before at least one of the photosensitive elements of the detection units (14).

18. An apparatus for testing the authenticity of printed objects by measuring light emanating from an object (10) to be checked in at least two defined spectral regions having

at least one light source (12) for irradiating the object (10) with light having components in the defined spectral regions, and

at least one detector (13) for detecting light emanating from the object (10),

characterized in that at least one diaphragm (15) is provided between object (10) and detector (13) for adjusting the size of an area to be measured on the object (10) from which light emanating from the object (10) is detected by the detector (13).

19. An apparatus according to claim 18, characterized in that the diaphragm (15) has a round diaphragm opening.

20. An apparatus according to claim 18, characterized in that the diaphragm (15) has a rectangular, in particular slit-shaped, diaphragm opening.

21. An apparatus according to any of claims 18 to 20, characterized in that at least one imaging optic is additionally provided between object (10) and detector (13) for focusing light emanating from the object (10) and to be detected by the detector (13).

22. An apparatus according to claim 21, characterized in that the imaging optic includes at least one self-focusing lens (16).