Holograms for security markings

• US 5,623,347 A
• Filed: 06/02/1994
• Issued: 04/22/1997
• Est. Priority Date: 06/21/1991
• Status: Expired due to Fees

• Current Assignee: Light Impressions International Limited (OpSec Security Group Ltd.)
• Original Assignee: Light Impressions Europe PLC
• Inventors: Pizzanelli, David J.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Schuberg, Darren E.
• Application Number:
  US08/167,997
• Time in Patent Office: 1,055 Days
• Field of Search: 359/2, 359/3, 359/9, 359/24, 359/32, 359/33, 359/572, 380/54, 283/86
• US Class Current: 359/2
• CPC Class Codes: B42D 25/328 Diffraction gratings; Holograms
• CPC Class Codes: G03H 1/0011 for security or authentication holograms on information-bearing cards B42D25/328; testing papers with holograms G07D7/0032
• CPC Class Codes: G03H 1/18 Particular processing of hologram record carriers, e.g. for obtaining blazed holograms photographic processing in general G03C, G03D
• CPC Class Codes: G03H 1/22 Processes or apparatus for obtaining an optical image from holograms G03H1/26 - G03H1/34 take precedence

Abstract

A hologram for security markings is provided by a laser transmission hologram (1-4) formed as a surface relief pattern and a coating of a thin metallic layer (5) on the surface relief pattern whereby the hologram is capable of reflecting light from a laser (10). The metallic layer is, preferably, about 500 angstroms thick and the hologram may be mounted on a substrate (7) of an item required to bear the security marking defined by the hologram. In a feature of the invention an apparatus is provided for reading light reflected from the hologram comprising a laser (10) for projecting a beam (9) onto the hologram to be read and a detector (31) and associated logic devices for recognizing a real image of the hologram. The apparatus has the advantage that the laser (10) and detector (31) are both located on the same side of the hologram to be read.

Claims

1. An apparatus for reading light reflected from a hologram and a hologram for security markings comprising a laser transmission hologram known per se formed as a surface relief pattern embossed into an embossable material, said laser transmission hologram being formed by sequential layers of a carrier layer, an embossable thermo-plastic lacquer into which the hologram is formed, and a layer for adhesively bonding the hologram to a substrate, a thin metallic layer coated onto said thermo-plastic lacquer whereby the laser transmission characteristics of the hologram are transformed into laser reflection characteristics capable of reflecting light from a laser, said apparatus comprising a laser light source for projecting a laser light beam onto the hologram to be read, and means located on the same side as the laser light source for recognising a real image of the hologram, said hologram having an information image and a triggering image, said information image being a series of light reflective portions and light non-reflective portions, together forming a binary code, said triggering image being formed to indicate the presence of an information image area and so as to reflect the laser light beam at a different angle to that reflected by said information image, and a light detector provided for receiving said information image and a further light detector provided for receiving said triggering image, whereby said light detector is activated only when triggered by a signal from said further light detector indicating the presence of a light reflective portion.

2. An apparatus as claimed in claim 1 wherein the metallic layer is about 500 angstroms thick.

3. An apparatus as claimed in claim 1 wherein the hologram is mounted on a substrate of an item required to bear the security marking defined by the hologram.

4. An apparatus as claimed in claim 1 wherein means are provided for moving the hologram with respect to the laser light beam and for activating said laser.

5. An apparatus as claimed in claim 1 wherein a plurality of triggering images are overlaid onto respective information images, the spacing between the triggering images being at least equal to the diameter of the laser beam.

6. An apparatus as claimed in claim 1 wherein the light detector may be a CCD arrangement to provide output to a frame grabber, and logic means are provided to analyse the output of the frame grabber for determining the presence of a valid binary code.

7. A method of reading light reflected from a laser reflection hologram including the steps of projecting a laser light beam onto the hologram to be read and positioning a light detector on the same side of the hologram as the laser light source for recognising a real image of the hologram and for discriminating said image from a non-valid image, said image being a bar code formed of a series of light reflective portions and light non-reflective portions, and wherein a triggering image is formed to indicate the presence of an information image area and to reflect the laser light beam at a different angle to that reflected by an information image formed to indicate the presence of said non-reflective portions, said information image being detected by a light detector which is activated only when triggered by a signal from a further light detector positioned to indicate the presence of the light reflective portion derived from the triggering image.

8. An apparatus for reading light reflected from a hologram in combination with a hologram for security markings comprising a laser transmission hologram known per se formed as a surface relief pattern embossed into an embossable material, said laser transmission hologram being formed by sequential layers of a carrier layer, an embossable thermo-plastic lacquer into which the hologram is formed, and a layer for adhesively bonding the hologram to a substrate, a thin metallic layer coated onto said thermo-plastic lacquer whereby the laser transmission characteristics of the hologram are transformed into laser reflection characteristics capable of reflecting light from a laser, and wherein said hologram comprises an information image and a triggering image, said apparatus comprising a laser light source for projecting a laser light beam onto the hologram to be read, light detector means including means for receiving laser light reflected from the information image and means for receiving laser light reflected from the triggering image, said information image light receiving means being in communication with said triggering image receiving means so as to be activated only when triggered from a signal from said triggering image receiving means, said information image light receiving means being connected to a logic means for detecting the presence of a valid reflected signal.

9. An apparatus as claimed in claim 8 wherein said information image receiving means is adapted to be at a different angular position with respect to the plane of the hologram images from the triggering image receiving means.