A TRANSDUCER FOR USE IN SIGNATURE VERIFICATION AND IN HANDWRITING RECOGNITION

Abstract: A transducer for generating data concerning pen movement on paper, such transducer based on electrode patterns metalized on piezoelectric films made of polyvinylidine fluoride and such data used for signature verification and handwriting recognition.

Description: 2 3 4 5 A TRANSDUCER FOR USE IN SIGNATURE VERIFICATION AND IN 6 HANDWRITING RECOGNITION 7 8 FIELD OF THE INVENTION 9 10 Signature verification is required in various 11 financial and legal matters. Recognition of 12 handwriting is useful in computer entries as a 13 substitute to keyboard. 14 15 16 BACKGROUND OF THE INVENTION 17 18 Writing is as old as civilization. The 19 stylus, brush, pencil and pen are some of the various 20 mechanical means used to create graphic patterns of 21 letters, words and names, mostly on a flat surface, be 22 it clay, stone, metal or paper. Images of script are 23 stored in the brain and are transformed into the 24 physically visible pattern through learned sensory- 25 motor schemes which are embedded in the human brain. 26 Such learned schemes of action which are formed by 27 training, are not only language specific, but include 28 also specific traits of the individual's script. 2 The personalized signature is the ultimate 30 example of the "individualistic" quality that is 31 manifested in human handwriting. Graphology, the art * 32 of analysis and evaluation of writing, relies also on ' 1 33 individual and general traits that are manifested in 3 handwriting. 35 The sensory mo tor action of wri ting should 36 no t be measured and analyzed only by the " end product " 37 ~ the two dimensional pattern appearing on paper . 38 There i s much more date in handwri ting and in s i gning than what appears to the eye; the dynamics of signing and writing which are manifested by movement direction, speed of movement, and applied pressure. Such attributes are part of the sensory-motor action scheme. after all, we learn how to write by learning how to move a pen across the paper, direct it, rotate it, or emphasize part of the script by pressing harder with it. The analysis of such attributes of handwriting and signing can be of great value for both the identification of the individual who wrote, and for deciphering what he wrote. These attributes of the writing act can be considered in part, at least, also as manifestations of the way a specific person writes, therefore displaying an individual motor "signature". While the number of alphabet letters is rather small, handwriting and signing are not absolutely fixed, and can vary from time to time. Thus the end result appearing on the paper is not constant. Therefore, relying only on the actual writing pattern makes recognition and identification difficult. The sensory-motor program itself, like any other learned motor behavior, has its own characteristics. If such characteristics are captured and identified, they can contribute to the recognition and identification of writing in addition to recognition of the visual pattern. Currently, most processes and devices which are used for OCR (Optical Character Recognition) of handwriting are based on analysis of the written image per se, i.e., on analysis of the two dimensional patterns resulting from writing. These patterns are mostly being captured by varieties of "writing tablets" - Some (Microtouch; Bradley) are made of glass coated by conductive material; others (Argyll) are rade of plastic. Writing on them is by metal stylus. By measuring resistance (or capacitance) at the fcur corners of the tablets, it is possible to calculate and pinpoint at any fraction of a second the X-Y position of the stylus, and to do it with great accuracy (several hundreds of points per inch) . The rasterized image is then subjected to pattern analysis by computer and is matched with prestored patterns for recognition or identification. As far as the current state of the art goes, the above method is successful only for recognition of carefully drawn block letters, and not for recognition of cursive handwriting. This is due to the rather wide variation of writing by different individuals, as well as to certain variability of writing by the same individual. Another negative aspect of the available process is that it requires the writing to be executed not on the most common and familiar substrate, paper, but on glass or plastic. Such writing is not a "natural" one. SUMMARY OF THE INVENTION The present invention is designed to enhance handwriting recognition and signature verification by a device that will subject for computer analysis not only the two dimensional image of writing and signature, but also their dynamic attributes such as pressure, direction and speed. The device will allow the collection of the direction and speed of movement as well as pressure data and make it available for comparison with other data generated during writing by the same individual, thus securing better recognition * and verification. Furthermore, the device, a transducer in the form of a tablet, allows the writing to be performed on paper and yet permits all the parameters to be captured in real time from the transducer. BRIEF DESCRIPTI ON OF THE DRAWINGS The present invention will be unders tood and appreciated more fully from the following detailed description , taken in conj unction with the drawings , in which: Fig. 1 is an illustration of a pattern of interdigitated electrodes useful in a transducer for generating data relating to pen movement in accordance with a preferred embodiment of the present invention; Figs. 2 and 3 are signal diagrams illustrating electrical signals generated by the application of force across the pattern of Fig. 1 in respective first and second mutually perpendicular directions; Fig. 4 is an illustration of a pair of overlapping patterns of interdigitated electrodes of the type illustrated in Fig. 1, mutually rotated by 90 degrees, useful in a transducer for generating data relating to pen movement in accordance with a preferred embodiment of the present invention; Fig. is an illustration of a pattern of interdigitated electrodes arranged along a diagonal, useful in a transducer for generating data relating to pen movement in accordance with a preferred embodiment of the present invention; Fig. 6 is an illustration of a pattern of interdigitated electrodes of width narrower than that of .the electrodes shown in Figs. 1 - 5. useful in a transducer for generating data relating to pen movement in accordance with a preferred embodiment of the present invention ; Fig . 7 is an illustration of a pair of overlapping patterns of interdigi tated electrodes of the type illus trated in Fig . 1 and 6 respectively , use ful in a transducer fo r generating data relating to pen movement in accordance wi th a preferred embodiment of the presen t inven tion ; Figs. 8 and 9 are signal diagrams illustrating electrical signals generated by the ap p lication of force across the pattern of Fig. 7 in respective first and second mutually perpendicular directions; DETAI LED DESCRIPTI ON OF A PREFERRED EMBODI MENT The transducer is a small tablet made from piezoelectric film, polyvinylidene fluoride (PVDF) . It is made as a polymorph by laminating several layers of PVDF. PVDF is a commercially available piezoelectric thin film (for example, PVDF manufactured by Atochem, U.S.A., under the trade name Kynar). The outer surface of the laminate is coated with a protective coating, thus avoiding damage from scratching. When the PVDF material is formed, its molecules are poled when it is exposed to a strong electrical field. The polling process endows PVDF with piezoelectric qualities and when strained or pressured mechanically, polled PVDF will generate voltage. The direction of the electrical field detercines the axis of piezoelectric response. This can be either along or across the film, or in its thickness axis (Z-axis). In the present invention, we tend to prefer the last type (Z) of polling, but do not exclude other axes. Each PVDF layer is plated with a particular electrode pattern. The patterns are described below. Voltage is achieved between the electrodes , thus only areas which are plated on both sides yield a measureable electric response. PVDF film can generate up to 1G volts when it is under pressure or strain. PVDF film comes in various thicknesses, from a few micrometers up to hundreds of micrometers. The thicker the material, the stronger is the voltage generated by the same pressure. Since the transducer of the present invention utilizes several layers of PVDF laminated together, it is desirable to use thin films, so that the response of the bottom layers will not be dampened too much. At the same time, the thickness of each layer should be sufficient to create enough voltage that would be easy to sense by common electronic components such as voltage level detectors or A/D converting integrated circuits. For example, if five film layers, each of 50 microns thickness, are used, the total thickness will be less than 0.25 mm, which is rather a thin laminate (two times the thickness of standard bond paper). Yet such thickness allows measureable voltage, even when using standard components. The laminate is glued firmly to a hard flat substance, a metal or a plastic plate. When paper is placed on top of the transducer, the pressure of the pen is transmitted through the paper to the piezoelectric layers of the PVDF. Whenever pressure is applied directly above an electrode, voltage will be generated on this electrode and sent to an analog to digital converter or to a voltage level detector. Each layer has a minimum two outputs , each connected to one electrode. Each layer has a specific alternative pattern of the parts of the two electrodes. It is also possible to use a separate layer for each electrode within a pair. This can be achieved by die cutting. Since the parts of the two electrodes do not overlap, die cutting will not result in increased thickness, nor in the use of more material. The only added cost will be in the process of lamination, which will be more complicated. A basic pattern is depicted in Fig. 1, with one set of electrodes la and another set of electrodes lb. Each electrode in this pattern is arranged as a basis from which columns are protruding. If pressure is applied in the direction of the arrow 11, across the longitudinal axis of the electrode columns, a series of pulses will be measured at la and lb in an alternating sequence which is shown in Fig. 2. When measured by rate (pulses over time) , these pulses reflect the speed of the movement across the electrodes. If, on the other hand, pressure is applied in the direction of arrow 21, along the longitudinal axis of the electrode, only a single, long pulse will be detected as shown in Figure 3 • By utilizing two PVDF layers with the same pattern, but placed at 90° shift to each other, it is possible to detect movement and rate along orthogonal axes at the same time. This arrangement is shown in Fig. 4, which depicts vertical columns (3) and horizontal rows (4). Such an arrangement makes it possible to compute quite accurately the X-Y direction of movement by the relative rate of pulses obtained in each. By adding two more layers with diagonally directed electrodes 3& and 3 as shown in Fig. ι further refinement can be obtained and so on. In order to determine not only the X-Y direction of the pen movement, but also the right-left or up-down direction of the same movement of the pen (and thus also be able to derive clock-wise and anti- clock-wise directions, which are important for handwriting recognition) , each of the linear electrode sets of la and lb described above is complemented by another set 2a and 2b which are laid out in the same way, except that the electrode patterns of 2a and 2b are less than half the width of electrodes la and lb. These electrodes are shown in Fig. 6. The superimposition of a layer with electrodes 2a and 2b on a layers with electrodes la and lb is depicted in Fig. 7. When a pen is pressed, and moves in the direction of arrow 31. voltage will be generated in first electrode lb. During that period, voltage will be generated on 2a and 2b as shorter pulses, each less than half the period of pulse on lb. The sequence of the short pulses will be 2a-- 2b. Continuation of the movement will generate pulse on la and then 2a and 2b within the period of la pulse. This is shown in Fig. 8. If, however, the movement is in the direction of arrow 4l, the sequence of the short pulses pair will be reversed within each pulse period la and lb, thus the sequence will be 2b and 2a and not 2a and 2b. This is shown in Fig. 9- From this data it is very simple to deduce right to left and left to right motion; similarly, just using one more layer of the same kind, but at 90° rotation, up-down and down-up movements can also be detected. For finding the movement of the pen, it is not necessary to measure the exact voltage, but sufficient to use a voltage level detector (which is a simple circuit such as one designed by Atochem) while setting the voltage detection level at a desired value. For measuring the pressure itself, an additional layer, which is etalized completely on both sides, is used. This layer is placed on top of the others in order to ensure reliable, direct detection of pressure. The voltage of this layer is fed into an A/D circuit which can generate accurate measurement. It is appreciated that the proposed arrangement is only one of many possibilities of electrode patterns and their combinations, that can allow measurement of the direction, speed and pressure of the pen during writing and signing on paper. It is appreciated that the detailed description herein has been limited only to a basic arrangement, with a small number of electrodes, thus keeping the electronic circuits small in number to reduce cost. This does not preclude other, more detailed arrangements , the ultimate being a totally rasterized pattern allowing measurement of pressure in discrete points, and allowing computation of movement and speed across such points. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow:

Claims: C A I M S 1 . A transducer for generating data concerning pen movement on paper , s aid transducer comprising a plurality of overlapping layers of force transducers , each layer bearing a di fferent electrode pattern . 2 . A transducer for generating data concerning pen movement on paper , such transducer based on electrode patterns metalized on piezoelectric films made of polyvinylidine fluoride and such data used for signature verification and handwri ting recognition . 3- The transducer of claim 2 where one or more layers of PVDF film are used, and if there is more than one layer it is superimposed on others, all layers being laminated together. 4. The transducer of claims 1 or 2 where each electrode is composed of parallel columns that are joined together. 5- The transducer and electrodes of claim 4, where two electrodes are used on each layer of PVDF film, with their columns alternating without the electrodes touching each other. 6. The transducer of any of claims 1-5, where an additional layer with the same electrode patterns is used, but where the width of the columns is less than half the width of the columns in the other layer; the columns of both layers are placed in the same direction and two narrow columns at least superimposed directly over the wider columns . 7- The transducer of any of claims 1-6, where another layer of PVDF film is superimposed on top of all other film layers, with this top layer metalized completely on both sides. 8. The transducer of any of claims 1-7 and where the electrodes are connected to either a voltage level detection circuit, or to the inputs of an analog to digital converter.

Inventors: CARMON AMIRAM, CARMON, AMIRAM
Applicants: TELEMOND HK LTD, TELEMOND (H.K.) LTD.
Application year: 1992
Main classification: G06K11
IPC codes: G06F3, G06K9