METHOD AND APPARATUS FOR INSPECTION OF SECURITY ARTICLES INCORPORATING A DIFFRACTIVE OPTICAL PROJECTION ELEMENT

摘要

A method and apparatus for inspection of a security article (10) is provided in which a substantially collimated light beam (15) from a point light source (14) is directed onto a diffractive optical projection element (DOE) (11). The light beam is transformed by the DOE (11) into a patterned beam (17) which is reconstructed to form a projected image at a particular position in space remote from the surface of the security article 910). An optical detection device 916) is located at which the patterned beam (17) is reconstructed to detect the projected image. The inspection method and apparatus may be used in equipment for handling, sorting, counting or otherwise processing security articles, in particular security documents such as banknotes. The apparatus may include a processor for generating a signal when the absence or poor quality of a DOE is detected and which is used to isolate or mark the security article.