Apparatus for imaging fingerprint or topographic relief pattern on the surface of an object

• US 5,448,649 A
• Filed: 05/24/1994
• Issued: 09/05/1995
• Est. Priority Date: 05/24/1994
• Status: Expired due to Fees

• Current Assignee: Chen-Lung Kuo, Wang S. Chen
• Original Assignee: Chen-Lung Kuo, Wang S. Chen
• Inventors: Kuo, Chen-Lung, Chen, Wang S.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US08/248,310
• Time in Patent Office: 469 Days
• Field of Search: 382/4, 382/5, 356/71, 359/831
• US Class Current: 382/126
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence

Abstract

An apparatus for imaging a fingerprint or a topographic relief pattern (i.e., ridges) on the surface of an object comprising: (a) a transparent platen having a top layer of microprisms in a matrix form and a bottom layer of a platen substrate, the top of the layer of microprisms being the surface against which the object is pressed and the bottom surface of the platen substrate being provided for receiving light to illuminate the object surface, both layers of materials having equal or nearly equal refractive indices; (b) a light source with a focusing lens for providing substantially uniform and parallel light rays; (c) a beam splitter for splitting incident light emitted by the light source into tow parts, one part passing through and the other part being reflected by 90 degrees, the beam splitter being positioned at an angle to the object contact surface of the platen so that the reflected beams of the split light enter the platen bottom surface perpendicularly; (d) a 2-D photo electric image sensor with an imaging lens for receiving light reflected from portions of the platen surface not in contact with the object ridges so as to produce an object surface image, the image sensor having a focal plane which is positioned in such a manner such that the focal plane is parallel to portions of the platen surface in contact with the object. The microprisms has sufficient elasticity so that they become deformed when pressed by the object, and return to their original shape when the object impression is released. A fraction of light emitted by the light source enters the platen substrate perpendicularly by means of the beam splitter and travels forward toward faces of the microprisms, the light rays reverse their traveling directions if the microprism faces impinged by the light rays are not in contact with the object ridges and the reversed light rays are then received by the image sensor to give rise of bright regions on the dark background in the object surface image, the dark background is associated with the microprism surfaces which are in contact with the object ridges and is due to sweat on the object ridges or the deformation of the microprism faces.

Claims

1. An apparatus for imaging a fingerprint or a topographic relief pattern on a surface of an object, said object having a plurality of ridges as a result of said fingerprint or said topographic relief patterns provided thereon, and said apparatus comprising:

(a) a transparent platen having a top layer of microprisms in a matrix form and a bottom layer of a platen substrate, the top of said top layer of microprisms being the surface against which said object is pressed and the bottom surface of said platen substrate being provided for receiving light to illuminate said object surface, both layers of materials having equal or nearly equal refractive indices;

(b) a light source with a focusing lens for providing substantially uniform and parallel light rays;

(c) a beam splitter for splitting incident light emitted by said light source into tow parts, one part passing through and the other part being reflected by 90 degrees, said beam splitter being positioned at an angle to the object contact surface of said platen so that said reflected beams of the split light enter said platen bottom surface perpendicularly;

(d) a 2-D photo electric image sensor with an imaging lens for receiving light reflected from portions of said platen surface not in contact with said object ridges so as to produce an object surface image, said image sensor having a focal plane which is positioned in such a manner such that said focal plane is parallel to portions of said platen surface in contact with said object;

(e) further wherein said microprisms being of sufficient elasticity so that said microprisms become deformed when pressed by said object and return to the original shape when object impression is released;

whereby a fraction of light emitted by said light source enters said platen substrate perpendicularly by means of said beam splitter and travels forward toward faces of said microprisms, said light rays reverse their traveling directions if said microprism faces impinged by said light rays are not in contact with said object ridges and said reversed light rays are then received by said image sensor to create a bright region on the dark background in said object surface image, said dark background is associated with said microprism surfaces which are in contact with said object ridges and is due to sweat on said object ridges or the deformation of said microprism faces.

2. The apparatus of claim 1 wherein said microprism matrix has a pitch which is sufficiently smaller than a width of an object ridge placed against said platen.

3. The apparatus of claim 1 wherein said microprisms have four triangular faces, three being right-angled and isosceles and one being equilateral, said equilateral triangle being the microprism face resting on a flat surface of said platen substrate.

4. The apparatus of claim 1 wherein said microprisms have a strip structure with a cross section which is a right-angled and isosceles triangle.

9. The apparatus of claim 1 wherein said apparatus is provided for imaging a fingerprint and said pitch of said microprism matrix is 50 micrometers or less.

5. An apparatus for imaging a fingerprint or a topographic relief pattern on a surface of an object, said object having a plurality of ridges as a result of said fingerprint or said topographic relief patterns provided thereon, and said apparatus comprising:

(a) a transparent platen having a top layer of microprisms in a matrix form and a bottom layer of a platen substrate, the top of said top layer of microprisms being the surface against which said object is pressed and the bottom surface of said platen substrate being provided for receiving light to illuminate said object surface, both layers of materials having equal or nearly equal refractive indices;

(b) two light sources for emitting substantially uniform and parallel light, said two light sources being so positioned that said emitted light is incident on said platen back surface at an oblique incident angle to the surface normal;

(c) a 2-D photo electric image sensor with an imaging lens for receiving light reflected from portions of said platen surface not in contact with said object ridges so as to produce an object surface image, said image sensor having a focal plane which is positioned in such a manner that said focal plane is parallel to portions of of said platen surface in contact with said object;

(d) wherein said microprism matrix having a pitch which is sufficiently smaller than a width of an object ridge placed against said platen; and

(e) further wherein said microprisms being of sufficient elasticity so that said microprisms become deformed when pressed by said object and return to its original shape when the object impression is released;

(f) whereby light entering said platen surface at an inclined angle is reflected back to said platen surface perpendicularly, if a finger valley is present at boundary faces of the microprism.

6. The apparatus of claim 5 wherein said microprisms have a strip structure whose cross section is a triangle.

7. Apparatus for imaging a fingerprint or a topographic relief pattern on a surface of an object, said object having a plurality of ridges as a result of said fingerprint or said topographic relief patters provided thereon, and said apparatus comprising:

(a) a transparent platen having a bottom layer of microprisms in a matrix form and a top layer of flat substrate, the top surface of said platen substrate being the surface against which said object is pressed and the bottom surface of said platen microprism for receiving light to illuminate said object surface, both layers of materials having equal or nearly equal refractive indices;

(b) a mobile carriage housing a 1-D light array with a rod lens array for emitting substantially uniform and parallel light, and a 1-D image sensor;

(c) a motor and motor control device for controlling the movement of said carriage;

(d) a track on which said carriage is to move under the control of said motor control device;

(e) wherein said microprism have a strip structure with a triangular cross section;

whereby said 1-D light array and said 1-D image sensor are so arranged that light rays incident at an angle to said platen microprism surface will be reflected back to said 1-D image sensor to produce a one-line image of said object surface, said carriage moving at a speed in synchronization with the sensing rate of 1-D image sensor to produce a 2-D image of said object surface pattern.

8. The apparatus of claim 7 wherein said platen and said track take the form of partial cylindrical surfaces so as to obtain a roll fingerprint image.