Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-10-09
2001-07-10
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C356S071000, C382S126000
Reexamination Certificate
active
06259108
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of creating electronic images of a finger or other object with ridges and the like, and a compact optical apparatus to project high contrast image slices of a fingerprint onto sensors.
BACKGROUND
The prior art for contact image sensors is exemplified by U.S. Pat. No. 5,214,273 (“the '273 patent”) which issued May 25, 1993 for an invention called “Contact Image Sensor.” A second example of prior art is U.S. Pat. No. 5,331,146 (“the '146 patent”) which issued Jul. 19, 1994 for an invention called “Contact-type Image Sensor for Generating Electric Signals Corresponding to an Image Formed on a Document.” Unlike the present invention, the '273 patent and the '146 patent do not employ frustrated total internal reflection (FTIR) to view a high contrast fingerprint.
The prior art for fingerprint sensors is exemplified by U.S. Pat. No. 4,784,484 (“the '484 patent”) which issued Dec. 4, 1986 for an invention called “Method and Apparatus for Automatic Scanning of Fingerprints.” Unlike the present invention, the '484 patent uses a separate sensing means to measure the speed of finger motion. Also, unlike the present invention, the '484 patent does not teach the use of FTIR to view a high contrast image of the fingerprint. Finally, unlike the present invention, the '484 patent does not employ a gradient index rod lens array or an array of relay lens pairs.
The prior art for fingerprint sensors is also exemplified by U.S. Pat. No. 5,619,586 (“the '586 patent”) which issued May 3, 1995 for an invention called “Method and Apparatus for Producing a Directly Viewable Image of a Fingerprint.” The '586 patent shows prior art employing FTIR to obtain a high contrast fingerprint image. However, unlike the present invention, the '586 patent shows imaging of the entire fingerprint at once as an area image, instead of a narrow strip image projected onto a linear array sensor. Also, unlike the present invention, the '586 patent does not show the use of gradient index rod lenses or relay lenses to image the fingerprint.
The prior art for fingerprint sensors is also exemplified by U.S. Pat. No. 5,096,290 (“the '290 patent”) which issued Mar. 17, 1990 for an “Apparatus for Imaging Fingerprint Using Transparent Optical Means Having Elastic Material Layer.” Unlike the present invention, the '200 patent covers an elastic layer for the entire area of the fingerprint, rather than a narrow strip of the fingerprint.
SUMMARY OF INVENTION
The invention provides a fingerprint image optical input apparatus in the form of a contact image sensor (CIS) which projects high contrast image slices onto a linear array sensor. Novel optics is employed to provide a high contrast image by means of FTIR of the fingerprint which is projected by a GRIN (GRadient INdex of refraction) lens array onto a linear array sensor.
The generally preferred embodiment is a miniaturized CIS sensor arranged to view the width of the moving fingerprint as it is wiped over the optically transparent platen of the sensor. To view the fingerprint, light must be introduced inside the platen. Light from the light source may be introduced inside the transparent platen through a flat or curved surface, which acts as a lens to help collimate the light so that it forms a flat sheet of light the width of the linear array sensor. Once introduced, the light may be directed inside the platen by using total internal reflection (TIR) or reflections from a mirror-like surface or surfaces. The use of reflections to direct the light inside the platen allows the light source to be located anywhere convenient, such as on a printed circuit board; the location of the light source can alter the form of the platen, or allow the platen to be made more compactly. The reflective surfaces or TIR surfaces of the platen can be slightly rough, not perfectly flat, to partially diffuse the light beam and thus cause more even lighting of the fingerprint.
A high contrast image may be obtained by viewing the fingerprint through the transparent platen at an oblique angle; the fingerprint image is then focused by a GRIN lens array onto a linear sensor array. Alternatively, the GRIN lens or other focusing means can be arranged to view reflected images of the fingerprint, and to project reflected images onto the linear array sensor. To provide a high contrast image of the fingerprint, light is directed at an angle to the top interior surface of the platen (typically 45 degrees or more to a line normal to the surface of the platen, depending on the index of refraction of the platen, which is advantageously greater than 1.5), where it is reflected by TIR if no fingerprint is present. Where the fingerprint ridges touch the top surface of the platen, light is not reflected, due to FTIR at the surface of the platen causing absorption of light, resulting in a dark pattern for the fingerprint ridges and bright light at the fingerprint valleys, which are reflected by TIR from the interior of the platen. Foreshortening effects can be accommodated by image processing.
The total internal reflection surface of the platen can be raised strip to increase the pressure of the finger on the imaging surface, thereby giving better contact for total internal reflection. The platen surface or raised portion can also be constructed of silicone or some other material with optical wetting or low friction properties to improve imaging or finger movement respectively. A liquid reservoir can be integrated into the platen or an adjacent surface to allowing wetting of the finger with oil or other liquid to improve the total FTIR imaging, as well as lubricating the finger for smooth motion. The platen itself can be part of the protective housing of the sensing elements. Surfaces of the platen can be coated in a light absorbing material to absorb stray light, thus reducing the noise at the sensor element
The high contrast fingerprint image is viewed by a GRIN lens array, or alternatively a relay lens pair array, or any other functionally equivalent means that creates a series of coherent overlapping images. The GRIN lens array looks at an oblique angle opposite to the incoming light; the narrow fingerprint strip image is focused by the GRIN lens array onto the width of a linear array sensor, which may have one linear array of light sensing pixels or two or more parallel linear arrays of light sensing pixels. The advantages of this arrangement are that a very compact optical system can be achieved which provides fingerprint images which have low distortion, high resolution and large format size.
The CIS sensor for fingerprint imaging can be arranged in several novel configurations, which can be optimized for different applications and manufacturing techniques. For those skilled in the art of design of optical components, the different features of various configurations may be utilized or combined, and other materials, components or technologies may used or combined to achieve substantially similar fingerprint imaging systems.
REFERENCES:
patent: 4784484 (1988-11-01), Jensen
patent: 4832485 (1989-05-01), Bowles
patent: 5448649 (1995-09-01), Chen et al.
patent: 5619586 (1997-04-01), Sibbald
patent: 5942761 (1999-08-01), Tuli
patent: 6011860 (2000-01-01), Fujieda et al.
patent: 0098607 (1983-07-01), None
patent: 96/13742 (1995-10-01), None
Antonelli Keith
Immega Guy
Vanderkooy Geoffrey
Vlaar Timothy
Allen Stephone B.
Kinetic Sciences Inc.
Smith Randolph A.
Yang Mark M.
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