The present invention relates to a fingerprint detection apparatus for detecting the fingerprint of a person required to be identified as a two-dimensional image signal.
In recent years, a personal identification apparatus has attracted attention, which determines whether or not a person required to be identified is a person who has been registered to perform identification in order to control entrance and exit to and from an important institution. A portion of personal identification apparatuses of the foregoing type has been adapted to a method of detecting the fingerprint in order to identify a person. Among a variety of suggested methods adaptable to the fingerprint detection apparatus, a major portion of the methods has a structure such that the fingerprint is detected as a two-dimensional image by an optical method. The optical fingerprint detection methods include three typical methods below.
A first method has a structure such that the finger of a person required to be identified is brought into contact with the surface of a transparent member, for example, a prism, and light emitted from a light source is made incident upon another surface of the transparent member to converge light totally reflected by the surface touched by the finger by using an image forming lens to form the image on an image pickup device so that a fingerprint image is read. The foregoing method is called a total reflection method.
A second method has a structure having a similar optical system and arranged such that only light scattered by the convex portions of the fingerprint is converged by an image forming lens to form an image on an image pickup device so as to obtain a fingerprint image. The foregoing method is called an optical-path separation (scattering) method.
A third method has the steps of converging light emitted from a light source by a condenser lens, bending the optical passage by a mirror to irradiate a surface of contact between the surface of a transparent member and the finger of a person required to be identified with a small light beam spot, moving the mirror in a plane which is in parallel to the transparent member to scan the surface of the finger with a light beam spot and making scattered light reflected by the surface of the finger incident upon an optical sensor through a mirror to photoelectrically convert light so as to obtain a two-dimensional fingerprint image. The foregoing method is called a scanning method.
However, the fingerprint detection apparatuses respectively adapted to the foregoing three methods involve the size of the optical system comprising the light source, the prisms, the lenses and so forth being enlarged excessively. Thus, there arises a problem in that the size of the fingerprint detection apparatus cannot be reduced. In particular, the scanning method must be further provided with an optical system for forming light into a small light beam spot and a scanning mechanism using the light beam spot. Since each of the foregoing additional units has an optically or mechanically complicated structure and requires a significant accuracy, the overall size and the cost of the fingerprint detection apparatus cannot be reduced.