Optics: measuring and testing – Document pattern analysis or verification
Reexamination Certificate
2001-02-05
2002-06-18
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Document pattern analysis or verification
Reexamination Certificate
active
06407804
ABSTRACT:
BACKGROUND OF THE INVENTION
a). Field of the Invention
The invention is directed to an arrangement for detecting the surface structures of fingers, palms or other parts of the skin placed on an image scanning surface, wherein the image scanning surface is formed at a scanning prism, an illumination beam path is directed to the image scanning surface in the interior of the scanning prism, and the light reflected from the image scanning surface impinges on a reception surface of an optoelectronic detection device.
b). Description of the Related Art
As with other precision optical equipment in which image information is acquired by scanning, arrangements of this type must be monitored and calibrated by technical apparatus to ensure operability and accuracy requirements.
For example, in a line image scanner outfitted with an image scanning surface, a sensor line and a mechanical drive for displacing the sensor line, it is provided in Patent DE 41 03 646 C1 to carry out the geometric calibration with the aid of reference marks which are applied to an edge of the image scanning surface running vertical to the sensor line and to image them on the sensor line during the image scanning. The images of reference marks which are obtained in the course of a scan are used to monitor and, if necessary, correct the displacement speeds and, in this way, to compensate for distortions caused by a displacement speed diverging from the reference value. However, this suggestion is not suited to calibration of devices with a stationary surface image scanner.
In devices having a stationary surface image scanner, for example, an array of individual sensors, it was formerly common for reference structures which are used over and over again in the course of operation as a basis for comparison with the results obtained by the same arrangement to be included with delivery to the user. The user or service can ascertain from time to time on the basis of these reference structures whether the quality parameters have been maintained or have resulted in deviations due to influences of some kind, e.g., aging or wear of subassemblies, which must be corrected. It is also often necessary to check the functioning of the equipment after assembly, e.g., for cleaning purposes.
The reference structures in the form of test structures are arranged on a carrier, e.g., a sheet or foil, which is placed on the image scanning surface for checking the equipment function. The test structures are recorded by the device and the results of the recording are subsequently compared with the test structure. Based on this comparison, it is possible to ascertain whether the arrangement still corresponds to quality requirements or whether changes have taken place. The foil with the test structures is then removed from the image scanning surface which is now available again for detection of surface structures of fingers and palms.
In this regard, the same areas of the image scanning surface are utilized for equipment testing and for the detection of the surface structures of the fingers and palms. In order to preclude falsification of test results, it is necessary to thoroughly clean the image scanning surface before placing the foil. Further, the foil must be carefully stored and handled so that it is not damaged, and it must also be carefully placed so that there is optical contact with the image scanning surface. In this connection, it is often recommended that an optical coupling medium, such as oil or water, is introduced between the image scanning surface and the foil. However, even when this is done, there is also a danger of falsified results, namely, when the layer thicknesses between the image scanning surface and the foil are too great or too varied.
The above-described procedure for calibration is stipulated, for example, by the Federal Bureau of Investigation (FBI) in the USA for automatic fingerprint identification systems which are used for official detection purposes to ensure that these systems meet the required technical parameters over their entire period of use.
OBJECT AND SUMMARY OF THE INVENTION
Based on this prior art, it is the primary object of the invention to reduce the sources of error and the possibilities of error when checking arrangements for detecting the surface structures of fingers and palms supported on an image scanning surface.
According to the invention, in arrangements of the type described above, a part of the illumination beam path or a separate illumination beam path is directed to reference structures and, from the latter, to the reception surface of the optoelectronic detection device, wherein separate partial areas of the reception surface are reserved for the detection of surface structures and for the detection of reference structures.
By means of the arrangement according to the invention, it is possible at desired times before, during or after the recording of fingerprint images or palm print images to obtain images of the reference structures, to base a check of the quality parameters on the results, and to draw conclusions from these results about the optical and electronic characteristics of the arrangement.
In a preferred construction of the invention, it is provided that the reference structures are arranged on the image scanning surface so that they cannot change position, wherein separate partial areas of the image scanning surface which do not intersect are reserved for the reference structures and for the support of the fingers or palms and a common illumination beam path is provided for these partial areas. The areas of the image scanning surface which are provided for placement of the fingers or palms are accordingly no longer required for carrying out the equipment test.
A substantial advantage consists in that the detection of fingerprints and hand prints and the recording of images of the reference structures are no longer mutually exclusive and, therefore, can be carried out simultaneously and not only consecutively. Further, a falsification of the test results due to contamination caused by contact with the fingers or palms, at least for the areas of the image scanning surface reserved for the reference structures, and the occurrence of errors resulting from the arrangement of optical intermediate layers (oil, water) between the image scanning surface and a movable carrier provided with the reference structures is ruled out. The disadvantages of the prior art are overcome in this way.
In the latter constructional variant, the reference structures are applied directly to the image scanning surface, i.e., they are arranged in the object plane. In contrast, in a further development of the invention, the reference structures, although they are likewise unchangeable with respect to position, are positioned outside of the object plane, for example, at the entrance face for the illumination beam path and/or at the exit face for the beam reflected by the image scanning surface. Accordingly, the reference structures are placed out of contact with the fingers or palms to be imaged in a highly dependable manner.
Further, the optoelectronic detection device is combined with an evaluating circuit in which the images which are obtained from the reference structures and which characterize the actual state of the arrangement are subjected to a comparison with electronically stored data giving the reference state, and conclusions are drawn concerning whether or not the quality parameters specific to the equipment are being adhered to. Automatic monitoring is possible in this way.
In this regard, it lies within the scope of the invention to provide a control circuit by which, for example, whenever the apparatus is put into operation and/or after expiration of a predetermined operating period, the reference structures are recorded and the recorded images are compared with the stored data. When this comparison has negative results, the erroneous detection of fingerprints or hand prints is prevented when minimum requirements are not met by triggering an alarm, an error message on the device d
Hillmann Juergen
Richter Uwe
Font Frank G.
Heimann Biometric Systems GmbH
Reed Smith LLP
Stafira Michael P.
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