Method and apparatus for inspection of security articles incorporating a diffractive optical projection element

Abstract

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.

1 - 41 . (canceled) 
   
   
       42 . An apparatus for inspection of at least one security article incorporating a diffractive optical projection element as a security device, the diffractive optical projection element being provided in a substantially transparent or translucent portion or window in the security document, wherein the apparatus comprises:
 a light source for directing a beam of light onto said diffractive optical projection element in said transparent or translucent portion or window, wherein the diffractive optical projection element transforms the beam into a patterned beam of light that is reconstructed at a particular position in space to form a projected image; and   at least one optical detection device located at the position at which the patterned beam of light is reconstructed to form the projected image.   
   
   
       43 . An apparatus according to  claim 42  wherein the light source is arranged to direct a substantially collimated beam of light onto the diffractive optical projection element. 
   
   
       44 . An apparatus according to  claim 42  wherein the light source is a point light source. 
   
   
       45 . An apparatus according to  claim 44  wherein the light source is any one of:
 a light emitting diode (LED); or   a halogen light source; or   a laser.   
   
   
       46 . An apparatus according to  claim 42  wherein the optical detection device is arranged to detect the amplitude of different parts of the patterned light beam forming the projected image. 
   
   
       47 . An apparatus according to  claim 46  wherein the optical detection device comprises one or more photodiodes. 
   
   
       48 . An apparatus according to  claim 46  wherein the optical detection device comprises a charge coupled device (CCD). 
   
   
       49 . An apparatus according to  claim 42  wherein the diffractive optical projection element is provided in a substantially transparent or translucent portion or window in the security article, the light source is positioned on one side of a security article and the detection means is positioned on the opposite side of the security article such that the light passes through the diffractive optical projection element so that the incident beam is transformed into the patterned beam on the opposite side of the document and projected onto the optical detection device. 
   
   
       50 . An apparatus according to  claim 42  wherein the diffractive optical projection element is provided on an underlying reflective surface, and the light source and optical detection device are positioned on the same side of the security article such that the optical detection device detects a reflected beam transformed by the diffractive optical projection element into the patterned beam and projected onto the optical detection device. 
   
   
       51 . An apparatus according to  claim 42  wherein the apparatus includes a plurality of optical detection devices. 
   
   
       52 . An apparatus according to  claim 42  wherein the apparatus includes a plurality of light sources for illuminating at least one diffractive optical projection element. 
   
   
       53 . An apparatus according to  claim 52  wherein each of the light sources causes a patterned beam to be diffracted at a slightly different point on the optical detection device, creating multiple signals at the optical detection device. 
   
   
       54 . An apparatus according to  claim 42  wherein the light source is a moving light source which produces an incident light beam that scans across the diffractive optical projection element to create multiple signals at the optical detector. 
   
   
       55 . An apparatus according to  claim 42 , further including a processor for processing signals from the optical detection device, and wherein the processor analyses multiple signals to differentiate constructive diffraction produced by the diffractive optical element from a random or diffuse scattering of light. 
   
   
       56 . A method for inspection of at least one security article, wherein the security article incorporates a diffractive optical projection element as a security device, the diffractive optical projection element being provided in a substantially transparent or translucent portion or window in the security document, and wherein the method comprises the steps of:
 directing a beam of light from a light source onto said diffractive optical projection element, the diffractive optical projection element provided in a substantially transparent or translucent portion or window in the security document transforms the beam into a patterned beam of light that is reconstructed at a particular position in space to form a projected image; and   detecting the projected image with an optical detection device located at the position at which the patterned beam of light is reconstructed to form the projected image.   
   
   
       57 . A method of processing or handling security articles comprising a method for inspection in accordance with  claim 56 , wherein a signal is generated when the absence or poor quality of a diffractive optical projection element is detected in a security article. 
   
   
       58 . A method of processing or handling security articles as claimed in  claim 57  wherein the security article is isolated or marked when the signal is generated by the optical device.