US 6,365,907 B1Granted

Device for recognizing diffraction optical markings

AssigneeOVD Kinegram AG

InventorsRené Staub, Wayne Robert Tompkin

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Abstract

The invention relates to a device for the simultaneous machine recognition of Q diffraction optical markings (11) of a security element (4), which devices comprises a light source (1) for projecting parallel light (10) onto a document (3) provided with said security element (4), an optical collector element (2), photodetectors (5; 6) for converting the light (15; 16) diffracted on the markings (11) or the rays reflected on the substrate (3) into electrical signals, as well as an evaluation unit for evaluating said signals. The photodetectors (5; 6) are positioned in the focal plane (8′) of the optical collector element (2). In each case two photodetectors (5; 6) form a photodetector pair. The electrical signals of each pair are analysed and the results of all photodetector pairs are compared with corresponding reference values in the evaluation unit. All the optical markings (11) are read simultaneously and form a code for identifying the security element (4).

Claims18

Dependent claims

Apparatus for simultaneous machine recognition of optical-diffraction markings (11) of a security element (4) on a substrate (3;

24) arranged in a reading plane (25) having a light source (1) for irradiating light (10) of at least a predetermined wavelength λ onto the reading plane (25), at least three pairs of photodetectors (A-A′;
a-a′, B-B′;
b-b′;
C-C′;
c-c′;
D-D′;
d-d′) each comprising two photodetectors (5;
5′;
6;
6′) which are arranged symmetrically with respect to the optical axis (7) and which establish a diffraction plane (100;
101;
102;
103) and which are adapted to convert the radiation (15;
16;
16′) diffracted at the markings (11) or reflected at the substrate (3;
24) respectively into electrical signals S1, S2 of the pair from the photodetectors (5;
5′;
6;
6′), and an evaluation unit (17) for evaluation of the signals S1, S2, characterised in that
an exit pupil (33) of the light source (1) is in a focal surface (8′) remote from the reading plane (25), of a convergent element (2 and 53) with a large aperture, which is arranged between the light source (1) and the reading plane (25) and which serves to produce a parallel ray beam (10) illuminating the reading plane (25), from a beam cone (9) issuing from the exit pupil (33),
between the markings (11) and the photodetectors (5;
5′;
6;
6′) is the convergent element (2) which is adapted to focus the parallel radiation (15;
16;
16′) diffracted at the markings (11) and reflected at the substrate (3;
24) respectively onto the operative surface (12;
12′) of the photodetectors (5;
6 and 5′, 6′), which operative surface is arranged in the focal surface (8′ and 45 and 46) of the convergent element (2),
the photodetectors (5;
5′;
6;
6′) are adapted to produce electrical signals S1 and S2 respectively proportional to the intensity of the diffracted light (15 and 16) incident on the operative surface (12 and 12′), and
the evaluation unit (17) is adapted to form the output signals X, Y from each pair of the electrical signals S1, S2 and at least to calculate relative differences RD=(X−Y):(X+Y) from the output signals X, Y of each of the pairs of photodetectors (A-A′;
a-a′, B-B′;
b-b′;
C-C′;
c-c′;
D-D′;
d-d′) and to identify the security element (4) by means of the calculated relative differences RD.

37 more elements

Apparatus for simultaneous machine recognition of optical-diffraction markings (11) of a security element (4) on a substrate (3;

24) arranged in a reading plane (25) having a light source (1) for irradiating light (10) of at least a predetermined wavelength λ onto the reading plane (25), photodetectors (5;
5′;
6;
6′;
50) for converting the radiation (15;
16;
16′) diffracted at the markings (11) and reflected at the substrate (3;
24) respectively into electrical signals S1, S2 proportionally to the intensity of the reflected radiation (15;
16;
16′), and an evaluation unit (17) for evaluation of the signals S1, S2, characterised in that
an exit pupil (33) of the light source (1) is disposed in a focal surface (8′) remote from the reading plane (25) of a convergent element (2 and 53) with a large aperture, which is arranged between the light source (1) and the reading plane (25) and which serves to produce a parallel ray beam (10) illuminating the reading plane (25) from a beam cone (9) issuing from the exit pupil (33),
between the markings (11) and the photodetectors (5;
5′;
6;
6′;
50) is the convergent element (2) which is adapted to focus the parallel radiation (15;
16;
16′) which is diffracted at the markings (11) and reflected at the substrate (3;
24) respectively onto the operative surface (12;
12′) of the photodetectors (5;
6;
5′, 6′;
50), which operative surface is arranged in the focal surface (8′ and 45 and 46) of the convergent element (2),
the evaluation unit (17) is adapted to read the electrical signals S1, S2 of the photodetectors (5;
5′;
6;
6′;
50) and to recognise the light pattern which occurs upon illumination of the optical markings (11) in the focal surface (8′ and 45 and 46), wherein evaluation is effected in the steps:
a) by a comparison of a light pattern registered by the photodetectors (5;
5′;
6;
6′;
50) with reference patterns stored in the memory (22) with at least three pairs of points of concentration of intensity symmetrically with respect to the optical axis (7 and 43) of the convergent element (2),
b) by association of the pairs of output signals X and Y of the corresponding photodetectors (5;
5′;
6;
6′;
50) with the pairs of the points of concentration of intensity in the reference pattern, wherein the output signals X and Y correspond to the signals S1, S2 in the corresponding points of concentration of intensity in the light pattern of the diffracted radiation (15;
16;
16′) and wherein each pair of the output signals X and Y is produced by one of the optical markings 11 with predetermined grating parameters, and
c) by calculation of relative differences RD=(X−Y):(X+Y) from the output signals X, Y of each of the pairs of signals (A-A′;
a-a′, B-B′;
b-b′;
C-C′;
c-c′;
D-D′;
d-d′), and
the evaluation unit (17) is adapted to identify the security element (4) by means of the calculated relative differences RD.

45 more elements

Dependencies are inferred from the claim text.