Barooptical Verification Apparatus

This invention pertains to personal identification verifier apparatus and more particularly to such apparatus which utilizes signature pressure patterns and stylus movements in the identification process.

In many fields and particularly in personal identification fields such as access control, charge account, banking and credit card operations it is desirable to convert person's signature to electrical signals which are then used in a verification and/or identification process. It has been found that when a person writes his signature he not only generates a unique visual pattern on a record medium, but he also generates a unique pressure pattern. The uniqueness of the pressure pattern has been exploited to build verification systems. Typical systems are disclosed in U.S. Pat. Nos. 3,480,911, 3,563,097 and 3,618,019, for example.

Some of these systems use pens with strain gauge transducers therein while other systems employ pressure sensitive writing surfaces. The transducer pens generally are very expensive and delicate and suffer low gauge factor/sensitivity and significant hysteresis. In fact, most of such pens break down when subjected to a high impact shock which occurs from the forceful dotting of an "i." In addition, the pen and associated wire are difficult to shield electromagnetically and are subject to data interception. Finally, the pen which dangles from the end of a cable is subject to theft and vandalism.

On the other hand, pressure sensitive tablets, while not being subjected to the same set of problems, create their own set. In particular, the major problem is associated with the nonlinearity of the generated signals because of the extended writing surface. In order to linearize the signal, complex and delicate systems using springs, strain gauges and the like are employed. Even with these expensive solutions, such devices still suffer from relatively high hysteresis and marginal natural frequency.

In a previous attempt to solve these problems I invented an improved transducer system which is the subject matter of my U.S. Pat. No. 4,035,768, issued July 12, 1977. While that system performed with high accuracy it created a demand for even higher accuracies by measuring more variables.

It is a general object of the invention to provide improved personal identification verifier apparatus.

It is another object of the invention to provide such apparatus which is more reliable than presently available apparatus.

It is a further object of the invention to provide such apparatus which is extremely linear over its entire operating range while instantaneously measuring the three coordinates required for personal identification.

These and other objects of the invention are satisfied by apparatus which includes first and second opposed planar conductor means. There is also provided a stylus adapted to be gripped by the person whose identification is to be verified for writing on the upper surface of one of the planar conductor means. A utilization means sensitive to changes in the electrical capacitance resulting from the change in separation of the planar conductor means in response to the pressure exerted by the stylus is connected to the conductor elements. In addition optical means simultaneously senses the planar position of the stylus on the planar conductor means to give position indicating signals to the utilization device whereby a combined three dimensional indication of the movement can be obtained.

Other objects, the features and advantages of the invention will be apparent from the following detailed description of the invention when read with the accompanying drawing which shows by way of example, and not limitation, several embodiments of the invention. In the drawing:

FIG. 1 is a perspective view of the pressure sensitive verifier apparatus according to the invention;

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1 according to one embodiment of the invention;

FIG. 3 is a schematic top view with the escutcheon removed to show the optical system in more detail; and

FIG. 4 shows the details of an optical receiver.

In FIG. 1 there is shown a verifier system including personal verifier apparatus having a housing 10 supporting a pressure sensitive writing tablet 12 and a stylus 14. When a user writes his signature on the writing surface of tablet 12, signals are generated which are fed via cable 16 to utilization device 18.

More particularly, according to the embodiment of FIG. 2 the apparatus comprises the housing with escutcheon 10 having a writing window 20. Extending across writing window 20 is a record medium such as paper or Mylar tape 22 which is moved by means (not shown) connected to reels 24 and 26. Tape 22 is a record medium upon which a user will write his signature to provide a visual record when stylus 14 is a ball point pen or the like. Below tape 22 within the region of window 20 the writing tablet 12 comprises a sheet or lamina writing pad 27 in the form of a moderately yieldable elastomeric material to provide a resilient writing surface which performs a further function hereinafter more fully described. A support structure (not shown) supports a base plate 30 preferably of fused quartz. The support structure is rigidly connected to the escutcheon of housing 10 so that the escutcheon and base plate float together. On the top surface of base plate 30 is fixed a layer 36 of electrically conductive material such as a vaporized layer of gold. A connector is fixed to the gold layer for connection to cable 16 of FIG. 1. On top of layer 36 there is a sheet 38 of dielectric material such as Mylar film. At one end of base plate 30 is rigidly fixed a spacer 37 and fixed to the other end thereof is foot rest point edge 39. A metallic plate 28 has one end rigidly fixed to spacer 37 and has its other end freely resting on edge 39. Thus a parellel plate capacitor is obtained from layer 36 and plate 28. The role of sheet 38 is to increase the capacitance between the layer 36 and plate 28 while still providing a workable spacing. It should be noted that in spite of sheet 38 there is still an air gap between the layer 36 and plate 28. When pressure is exerted on pad 27 the spacing between plate 28 and layer 36 changes, thus changing the capacitance.

It should be noted that the plate 28 can be considered as a beam having one clamped end and a remote floating end. The use of one clamped end and one floating end is a definite improvement over the transducer disclosed in my above-cited U.S. Pat. No. 4,035,768 in that temperature coefficients and hysteresis phenomenon approach zero. Lower stresses and greater deflection sensitivity for a given plate thickness are obtained. In addition the dynamic capacitance range is increased. Up until now the pressure portion of the transducer has been described. The optical part will now be discussed.

In FIG. 3 there is shown a schematic top view of the signature area or writing window 20. The window is framed underneath the escutcheon 10 by the ends of ribbons of optical fibers. In FIG. 3 light transmitting ends 52a of one ribbon are positioned along one edge of the window 20 while light receiving ends 60a of another ribbon are positioned along an opposite edge of the window 20. Similarly light transmitting ends 52b of a ribbon are positioned along a further edge orthogonal to said one edge; and light receiving ends 60b of another ribbon are positioned along the edge opposite to said further edge. In operation the optical fibres having ends 52a are sequentially illuminated in the direction from A to B and then the optical fibres having ends 52b are sequentially energized in the direction from B to C. By means of focusing techniques hereinafter more fully described herein can be assumed the light travels across the area with minimum diffusion. Thus whenever the stylus is at a point in the area, there will be two optical fibres one in each of the receiving ribbons which will receive less light. Thus by knowing which bundles don't receive a given amount of light one can tell the X-Y position of the stylus.

A means for illuminating the ribbons and for actually sensing for the light is shown in FIG. 2. A cathode ray tube system CRT with a fibre optics face plate FP is controlled to generate a straight line trace. A suitable cathode-ray tube system is a Thomas Electronics 6M.136PMFO series cathode ray tube system. Optically connected to the face plate FP by means of glued butting is a ribbon 50 of optical fibers such as Crofon ribbon manufactured by DUPONT. The ribbon is partially bifurcated with one branch 50a having the ends 52a in FIG. 3 and the other branch 50b having the ends 52b in FIG. 3.

Similarly, there is a linear array of photodiodes 54 connected by optical gain means 56 hereinafter described to ends of the ribbon of optical fibres 58 which can be bifurcated with one branch 58a connected to ends 60a in FIG. 3 and another branch 58b connected to ends 60b in FIG. 3. A suitable photodiode array is a set of a number of Fairchild FPT diodes fixed in a line.

In FIG. 4 there is shown the details of the connection of the fibres of ribbon 58 to the diode array 54. In general the end of an optical fiber OF is glued to the cylindrical surface of semi-cylindrical lens LENS. Preferably the fiber is positioned radial to the lens surface. At the center of curvature of the lens there is positioned one of the photodiode PD of the linear array of similar photodiode. It should be noted that there is one elongated cylindrical lens for all optical fibers, but a different photodiode is associated with and aimed at the end of each receiving optical fiber. With such a lens 10x magnification can be obtained. Furthermore, difusion is minimized by setting back the ends of the transmitting optical fibers a fraction of an inch from the edge of the escutcheon as seen in FIG. 3. This technique creates an Aires summation lens which in effect focuses the beams.

While only one embodiment of the invention has been shown and described in detail there will now be obvious to those skilled in the art many modifications and variations satisfying many or all other objects of the invention but which does not depart from the point thereof as defined by the appended claims. An alternate approach to the fiber-optic CRT array shown is the CCD (capacitor charge device) shift/pulsed LED source.