Patent ID: 6365907
Filing Date: 2002-04-02
Classification: G06K

Abstract:
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 &lgr; onto the reading plane (25), at least three pairs of photodetectors (A-Aâ€²; a-aâ€², B-Bâ€²; b-bâ€²; C-Câ€²; c-câ€²; D-Dâ€²; d-dâ€²) each comprising two photodetectors (5; 5â€²; 6; 6â€²) 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; 16â€²) 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; 5â€²; 6; 6â€²), and an evaluation unit (17) for evaluation of the signals S1, S2, characterised in thatan exit pupil (33) of the light source (1) is in a focal surface (8â€²) 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; 5â€²; 6; 6â€²) is the convergent element (2) which is adapted to focus the parallel radiation (15; 16; 16â€²) diffracted at the markings (11) and reflected at the substrate (3; 24) respectively onto the operative surface (12; 12â€²) of the photodetectors (5; 6 and 5â€², 6â€²), which operative surface is arranged in the focal surface (8â€² and 45 and 46) of the convergent element (2), the photodetectors (5; 5â€²; 6; 6â€²) 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 12â€²), 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=(Xâˆ’Y):(X+Y) from the output signals X, Y of each of the pairs of photodetectors (A-Aâ€²; a-aâ€², B-Bâ€²; b-bâ€²; C-Câ€²; c-câ€²; D-Dâ€²; d-dâ€²) and to identify the security element (4) by means of the calculated relative differences RD.