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Optical fingerprint imaging device

  • US 4,925,300 A
  • Filed: 08/02/1988
  • Issued: 05/15/1990
  • Est. Priority Date: 08/02/1988
  • Status: Expired due to Fees
First Claim
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1. Apparatus for acquiring the image of a fingerprint comprising:

  • a stationary conical lens formed of a solid transparent substrate and having a front surface in the shape of a partial cone tapering in a forward direction for allowing light rays interior to the conical lens to be refracted in said forward direction, and into which lens is formed a well, coaxial with said front surface along a central axis, into which well a finger to be imaged is placed, and which lens additionally possesses a side surface through which interrogating light rays may pass, the front surface and well together possessing the property that only light rays which arise off the surface of the well at an angle to its normal which is greater than the critical angle of light refracted through the air-substrate interface, emerge from said front surface and are refracted in said forward direction substantially, parallel to said central axis;

    a stationary polychromatic light source for interrogating the object to be scanned such that light rays are directed through the substrate of the conical lens onto the internal surface of the well;

    an imaging lens positioned such that it is coaxial with a central axis of the front conical surface and such that it creates a focused image surface of the well surface of the conical lens;

    a photodetector array for converting light signals focused by the imaging lens into electrical signals corresponding to the image of papillary ridges and valleys of a finqer positioned in the well of the conical lens;

    a means for positioning the photodetector array such that it is tangential to the image surface of the well and such that a line through the endpoints of the array intersects the central axis;

    a means for rotating the photodetector array such that the aforementioned relationship to the central axis is preserved, and such that it sweeps out in steps a surface of revolution corresponding to the image surface of the well in the conical lens;

    a means for acquiring the electrical data generated by the photodetector array and processing the data in such a way as to create a complete fingerprint image for subsequent display and storage.

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