Keyless holographic lock - Patent Review 5138468

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FIELD OF THE INVENTION

This invention relates in general to keyless locking devices and in particular to an automatic and keyless holographic locking device which utilizes known coherent pattern recognition techniques.

BACKGROUND OF THE INVENTION

Pattern recognition systems have been proposed in which stored reference images are correlated with input images.

For example, U.S. Pat. No. 3,716,301, issued Feb. 13, 1973, to Caulfield, et al., describes a fingerprint identification apparatus in which a user presses a finger against an input prism (prism 14), and a laser beam is reflected from the input prism's surface to generate an input image representing the Fourier transform of the finger image. The input image is then correlated with a reference image having been recorded in an already prepared hologram of the said transform. At column 5, lines 57-62, Caulfield, et al. teach use of a mechanically rotating dove prism to compensate for misalignment of the user's finger with respect to the input prism. At column 7, lines 28-66, Caulfield, et al. also teach use of a prerecorded Fourier transform hologram representing two or more reference images (each having a different rotational orientation) and presentation by the user of two different input images (each having a different orientation).

U.S. Pat. No. 4,227,805, issued Oct. 14, 1980, to Schiller, describes another pattern recognition system. In the system of U.S. Pat. No. 4,227,805, the user's finger rests in a linearly translatable carriage (carriage 20), and is scanned by a laser beam as the carriage translates linearly. The laser beam is reflected from a surface of the carriage, and the reflected beam is passed through a lens to generate an input image representing the Fourier transform of the finger image. The input image is then correlated with a reference image as it propagates through a prerecorded Fourier transform hologram (hologram 34).

However, the use of mechanically moving components in conventional correlation systems (such as the rotating Dove prism of U.S. Pat. No. 3,716,301, and the translating carriage of U.S. Pat. No. 4,227,805) undesirably causes noise due to vibration of the moving components. Furthermore, the mechanical motion is undesirably slow, so that scanning time required for producing a single correlation signal is undesirably long.

It has been proposed that pattern recognition systems of the correlation type be employed in lock devices. For example, U.S. Pat. No. 2,936,607, issued May 17, 1960, discloses a lock apparatus in which a user's fingerprint is electronically correlated with a stored reference fingerprint image.

However, it has not been known until the present invention how to design or operate a holographic locking device in which an input image is correlated in real time with an already prepared Fourier transform hologram (representing a single reference image), without employing mechanically moving components. Nor has it been known how to implement a two-stage holographic locking device in which correlation between two input images and two prerecorded reference images is performed rapidly and accurately in order to open a lock, and which does not employ moving mechanical parts.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a locking device with an input element that utilizes a real-time angular-invariant unique identification of an authorized user, such as a fingerprint or other unique identification, to open the lock.

A further object of the invention is to provide a holographic lock which utilizes a particular fingerprint of an authorized user stored in the form of a hologram that is optically continuously compared to a presented rotating fingerprint and which authorizes unlocking of the device only when the presented fingerprint correlates with the stored fingerprint.

A further object of the invention is to provide an automatic and keyless holographic locking device in which the stored fingerprint of the authorized user may be readily changed by the user.

A further object of the invention is to provide, in one embodiment, double authentication, such as a first level requiring the fingerprint of the authorized user and a second level requiring the signature of the authorized user, before the locking device will be activated.

Further objects and advantages of the invention will become apparent from the following description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a locking system according to the present invention;

FIG. 2 is a schematic representation of another embodiment of the inventive locking system showing how the complex spatial Fourier transform of a fingerprint of an authorized user is registered by the user himself on a storage medium within the locking system; and

FIG. 3 illustrates schematically another embodiment of the inventive locking system which employs double authentication features.

FIG. 4 is a schematic representation of yet another embodiment of the inventive locking system.

FIG. 5 is a side view of an embodiment of the inventive transparent window and mirrored rectangular lid.

DETAILED DESCRIPTION

The locking device shown in FIG. 1 may include any sort of mechanical, electronic or pneumatic lock control 15 which operates in response to a command signal from photoelectric element 7. The system includes a source of coherent light, such as for example a laser 1. In a low cost implementation, the source of coherent light for the authentication step may be a source of partially coherent light such as a neon lamp. (During the step of storing a reference fingerprint holographically, a laser light-source should always be used.) Thus the phrase "coherent light-source" is used here to denote both sources of completely coherent light and sources of partially coherent light. Use of a laser provides a very small probability of error at a significant cost compared to a neon lamp but is justified in many applications of the invention by the said probability of error.

The usage of Fourier transforms (and not the images themselves) is fully justified and not discussed here, as the practice is already approved and widely realized in the numerous applications of pattern recognition techniques. Among the advantages of use of Fourier transforms is the invariance of the in-plane filter's orientation. Also, when using the Fourier transform of such an informative object as a fingerprint, only about 1% of the initial fingerprint is needed for assured recognition.

Procedures under discussion are utilized in coherent pattern recognition techniques, but in all the applications of the latter, the main problem is that the accuracy is dependent on the placement of the matched filter (or on the relative orientation of the input object and corresponding matched filter).

The recognition system (lock) of the invention is very sensitive to the relative angular orientation of the matched filter and the object under recognition, i.e., the fingerprint of the user.

This produces the main and biggest problem to the real-time automatic recognition of all the existing optical pattern recognition systems. In the claimed system (lock) the inventor deals with the named problem in the most simple and efficient way.

To realize this procedure in the simplest way the inventive system includes an input element in the form of a transparent window 4. This element makes it possible to overcome the main disadvantages of prior similar systems by providing a means for the real-time angular orientation that makes the system functional in real-time. Against this element 4 the user places the tip of a particular finger 6 for identification purposes and, optionally, to activate the light source 1.

The light from the source 1 illuminates fingertip 6, and the light reflected from the fingertip passes as an encoded beam 2 through the spherical lens 5 which projects said beam upon the matched filter 3, located at its shadow plane. Matched filter 3 represents the complex spatial Fourier transform of the image of a reference (authorized) fingerprint, having been produced with coherent light on any suitable recording medium such as photographic, thermoplastic or photothermoplastic media.

In use, the user rotates the fingertip 6 in order to align the Fourier-transform of the introduced fingerprint with the stored holographic representation of the authorized fingerprint in matched filter 3, and in that way to eliminate the main, mentioned disadvantage of prior art systems.

As the user rotates fingertip 6 correlation procedures are realized continuously in time until the images are angularly matched and a correlation signal is present.

The Fourier-spectrum comparison provides invariance to in-plane displacements (i.e., displacements in the plane of window 4's surface) of the introduced image and invariance to in-plane scale differences. The chosen procedure provides automatically the formation of the correlation signal inside of the wavefront, the procedure being absolutely real-time, as a result of the implementation of the two-dimensional spatial comparison.

Two additional sources of displacement errors are treated as follows.

The correlation signal is greatly dependent on in-focal orientation of the matched filter 3. This problem is avoided by fitting the filter exactly in the back focal plane of lens 5 in the lock. That can be easily achieved by different methods. Two of them are as follows:

(a) The pre-prepared filter is fitted into the lock, and the entire device is afterwards produced like solid state optics (being, for instance, melted with transparent plastic);

(b) The system being optically reversible, the lock of the invention itself is used for filter preparation.

The linear shifts (misplacements) of the matched filter in the back focal plane of the lens 5 absolutely do not affect the recognition procedure.

In the shadow plane of the matched filter 3 a photosensitive element 7 is located. Its output command signal is connected to lock control 15 (mechanical, electronic or pneumatic) which unlocks the device.

For further functional improvement the device of the invention may additionally include a second spherical lens (not shown) which is situated in such a way that the matched filter is in the front focal plane and the photodetector is in the rear focal plane of said lens correspondingly. The function of said lens is to focus the signal of correlation, if any, on the surface of photodetector 7.

The correlation signal's orientation in the plane of photodetector 7 is unambiguously defined by the angular orientation of the reference beam (to be discussed below with reference to FIG. 3) during the stage of matched-filter preparation. The correlation optical signal, if any, appears in the exact geometrical point of the plane of photodetector 7. This can additionally serve as a protective measure, keeping the angle of reference wave orientation secure. Thus the photoelement 7 can be located in the fixed position, and the optical part of the lock easily realized in solid-optics form.

Photoelement 7 serves the purpose of registering the formed correlation signal and generates an electrical output command signal when the correlation signal between the stored and introduced fingerprint is present. As the correlation signal in a single stage version of the inventive lock will always be a bright spot (plane reconstructed wave, or the Delta-function after additional focusing), it can be registered by simple photosensitive means.

In a recognition mode of operation, laser 1 is activated by pressing the user's finger against the transparent window 4. The reflected light beam 2, being modulated in amplitude by the user's fingerprint 6, passes through the spherical lens 5, which forms its complex Fourier spectrum in the plane of the matched optical filter 3. The user rotates his finger against transparent window 4, until the spectra coincide angularly. If the spectra additionally match, and only then, the correlation signal in the form of a bright spot appears on the surface of photodetector 7. The position of the named spot, if any, is unambiguously predetermined.

The process can be further refined by focusing the correlation signal. To achieve this a second focusing lens is added (not shown). It is situated in such a way that matched filter 3 is in its forward focal plane and photosensor 7 is in its rear focal plane. The said photosensitive element 7 then generates the command electrical signal as previously described.

By utilizing the user's fingerprint as the source of authentication, the probability of error is of the order of 1 in 10,000,000. The inventive device will still be functional even if only a small part of the fingerprint is presented.

The recognition procedure is a real-time one and can be realized with the speed of 10-.sup.8 second.

The present invention eliminates the main problem of similar prior devices, that is the extreme sensitivity of the system to the input fingerprint/filter relative angular orientation. This problem is solved by the chosen input element--a transparent window 4 against which the user rotates his finger. This causes the rotation of the corresponding spectrum in the plane of matched filter 3 until the position of angular coincidence is achieved. Then and only then may the correlation peak be formed.

Rotation of the input fingerprint can be formally represented as a sequence of separate recognition steps, each one being realized with practically unlimited speed. In other words, the user can rotate his finger with any speed he likes.

It should be noted that using self-developing registering media for the matched filter, the user himself, fully automatically, can prepare the needed filter using the claimed lock (as will be described below with reference to FIG. 2).

Such filter preparation procedures are discussed in detail in the theory of optical matched filtering. The thing to be emphasized is that the claimed lock can be produced in a user-modifiable form, the memory for matched filters being long-time, changeable and realized on reversible media optically.

Structurally this changeability can be realized by adding an optical switch which activates a reference beam during filter preparation. Such a switch can be connected to a knob on the outside of the lock's housing, with an instructional indication such as "prepare", for