Spurious signal removal in optical processor fingerprint identification apparatus

• US 3,968,476 A
• Filed: 07/17/1974
• Issued: 07/06/1976
• Est. Priority Date: 07/17/1974
• Status: Expired due to Term

• Current Assignee: Sperry Rand Corporation
• Original Assignee: Sperry Rand Corporation
• Inventors: McMahon, Donald H.
• Primary Examiner(s): Thesz, Joseph M.
• Application Number:
  US05/489,212
• Time in Patent Office: 720 Days
• Field of Search: 340/146.3 E, 340/146.3 F, 340/146.3 P, 356/71, 250/567, 250/233, 250/237 G
• US Class Current: 382/127
• CPC Class Codes: A61B 5/1172 using fingerprinting
• CPC Class Codes: G02B 26/0808 by means of one or more diffracting elements
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence
• CPC Class Codes: G07C 9/37 using biometric data, e.g. fingerprints, iris scans or voice recognition

Abstract

An improved incoherent optical processor fingerprint identification apparatus employs a rotatable grating for inspecting the ridge orientations in a plurality of preselected finite sample areas of a fingerprint. A detector array including a plurality of detectors each related to a discrete sampled area is disposed to receive an image of the fingerprint filtered by the rotating grating. An incoherent light source and a lens and retroreflective prism assembly function in cooperation with the grating to produce an image thereof superposed on the grating itself such that minimum light is propagated to the detector array in the absence of an input fingerprint pattern whereas, in the presence of a fingerprint pattern, light is diffracted thereby to be filtered by the grating for supply to the detectors. Maximum light may occur at each detector under a condition of spatial alignment of the grating lines with the ridge lines of the related sampled area whereby the time interval between a reference orientation of the grating and the instant of maximum light at each detector may be converted to equivalent electrical signals uniquely representative of a particular fingerprint pattern. The signal to noise factor of the optical system is significantly improved by the use of a novel grating element having plural reflecting and transmitting stripes, with optically absorbing stripes interposed between them.

Claims

1. In pattern recognition apparatus:

rotatable support means having a regular array of alternating parallel elongate spaced light transmitting and reflecting elements,

light source means for illuminating said regular array,

retroreflective means including focusing means for forming an image of said regular array in substantial but imperfect alignment with said regular array,

elongate light absorbing elements disposed between each of said alternate parallel elongate light transmitting and reflecting elements for substantially eliminating light misdirected because of said imperfect alignment,

said retroreflective means including surface means for supporting an input pattern to be recognized in the light received by said retroreflective means from said regular array of elongate elements,

said input pattern being characterized by light transmissive or reflective lines of varying orientation over the area of said input pattern and having the effect, when present at said input pattern supporting surface means and when said rotatable means is rotating, of variably diffracting light from said image of said regular array onto said regular array, and

signal processing means responsive to the position of said rotatable support means and to said variably diffracted light directed by said regular array for determining the angular orientation of said rotatable support means with respect to a reference position thereof at the instants of extremum values of light intensity of said variably diffracted light.

2. Apparatus as described in claim 1 further including:

motive means for rotating said rotatable support means,

said signal processor means including sensor means responsive to indicia disposed on said rotatable support means for generating signals representative of the angular orientation of said rotatable means with respect to a reference position thereof.

3. Apparatus as described in claim 2 wherein said signal processing means further includes a light detector array disposed for receiving said variably diffracted light directed thereto by said regular array.

4. Apparatus as described in claim 3 wherein:

said light source is disposed on a first side of the plane of said rotatable support means,

said retroreflective means is disposed on a second side of said plane, and

said variably diffracted light is reflected by said regular array into said light detector array,

said light detector array being disposed on the second side of said plane.

5. Apparatus as described in claim 3 wherein:

said light source is disposed on a first side of the plane of said rotatable support means,

said retroreflective means is disposed on said first side, and

said variably diffracted light is transmitted by said regular array into said light detector array,

said light detector array being disposed on a second side of said array.