Signature verification apparatus and method utilizing relative angle measurements
First Claim
1. A pressure sensitive data input stylus particularly configured for use with an electronic signature verification system wherein indicators of the angle of the stylus in relation to a writing surface, and variations in said indicators, are used as the identifying discriminate, the device comprising:
- (a) a stylus housing with an elongated body, substantially cylindrical, and having a longitudinal axis;
(b) a stylus cartridge mounted within said stylus housing along the longitudinal axis thereof, the stylus cartridge terminating at one end in a writing tip, and terminating at the other in a bearing surface in contiguous relation with a first transducer means sensing axial pressure from said writing tip produced while writing with the stylus on said writing surface, the axial pressure hereafter being known as a direct pressure;
(c) a second transducer means surrounding said stylus cartridge near the writing tip, secured to interior of said stylus housing, having sufficient clearance to allow axial movement of said stylus cartridge, while sensing pressure transmitted through the stylus cartridge transverse to said direct pressure, the transverse pressure hereafter being known as a lateral pressure;
(d) said first transducer means mounted axially within said stylus housing so as to produce a direct pressure signal that increases in proportion the transverse pressure as the stylus angle becomes more nearly perpendicular to said writing surface when stylus tip is in contact with said writing surface while writing;
(e) said first transducer means producing a direct pressure signal that decreases in proportion to the transverse pressure as the stylus angle becomes more nearly parallel to said writing surface when stylus tip is in contact with said writing surface while writing;
(f) said second transducer means mounted within said stylus housing around the stylus cartridge so as to produce a lateral pressure signal that increases in proportion to the transverse pressure as the stylus angle becomes more nearly parallel to said writing surface when stylus tip is in contact with said writing surface while writing;
(g) said second transducer means producing a lateral pressure signal that decreases in proportion to the direct pressure signal as the stylus angle becomes more nearly perpendicular to said writing surface when stylus tip is in contact with said writing surface while writing;
(h) said first transducer means and said second transducer means positioned in said stylus housing so that they produce inversely correlated signal strengths as the angle of the stylus changes relative to said writing surface during writing;
(i) a first signal transmission means for conveying a first signal train produced by said first transducer means from stylus to a signal processing means, and a second signal transmission means for conveying a second signal train produced by said second transducer means from stylus to said signal processing means.
1 Assignment
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Accused Products
Abstract
A signature verification system consisting of a durable pressure sensitive data input stylus, signal processing, and computer algorithms for enrollment of signatures and verification. The stylus contains two transducers placed so that axial force and lateral force are measured simultaneously. Combining the two signals at digitized sample points yields a ratio of pressures indicative of the angle of the stylus to the writing surface at that moment, controlling for variations in actual force. The ratio, called a relative angle, is calculated for the entire signal train of a signature and for various simple divisions, or segments. Segments are equal divisions of the signal train by various divisions. While the relative angle of the whole signature may vary unpredictably between signings, the unique variations around the average relative angle form unique signature discriminates. Variations are measured by comparing relative angle measurements of segments, one to another, in all mathematical combinations. The combinations are called measurement points and each measurement point has a value based on the comparison. Some measurement point values, out of many sampled by computer, are uniquely consistent for particular signers. These unique measurement points and their limited ranges of variation are determined during enrollment and become the signature discriminates. These signature discriminate measurement points and values electronically distinguish an enrolled signer. Verification is simplified by comparing only chosen reference measurements to determine if the incoming values fall within the acceptable range of values. An easily adjustable score determines rejection or acceptance of a signature to be verified.
63 Citations
27 Claims
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1. A pressure sensitive data input stylus particularly configured for use with an electronic signature verification system wherein indicators of the angle of the stylus in relation to a writing surface, and variations in said indicators, are used as the identifying discriminate, the device comprising:
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(a) a stylus housing with an elongated body, substantially cylindrical, and having a longitudinal axis; (b) a stylus cartridge mounted within said stylus housing along the longitudinal axis thereof, the stylus cartridge terminating at one end in a writing tip, and terminating at the other in a bearing surface in contiguous relation with a first transducer means sensing axial pressure from said writing tip produced while writing with the stylus on said writing surface, the axial pressure hereafter being known as a direct pressure; (c) a second transducer means surrounding said stylus cartridge near the writing tip, secured to interior of said stylus housing, having sufficient clearance to allow axial movement of said stylus cartridge, while sensing pressure transmitted through the stylus cartridge transverse to said direct pressure, the transverse pressure hereafter being known as a lateral pressure; (d) said first transducer means mounted axially within said stylus housing so as to produce a direct pressure signal that increases in proportion the transverse pressure as the stylus angle becomes more nearly perpendicular to said writing surface when stylus tip is in contact with said writing surface while writing; (e) said first transducer means producing a direct pressure signal that decreases in proportion to the transverse pressure as the stylus angle becomes more nearly parallel to said writing surface when stylus tip is in contact with said writing surface while writing; (f) said second transducer means mounted within said stylus housing around the stylus cartridge so as to produce a lateral pressure signal that increases in proportion to the transverse pressure as the stylus angle becomes more nearly parallel to said writing surface when stylus tip is in contact with said writing surface while writing; (g) said second transducer means producing a lateral pressure signal that decreases in proportion to the direct pressure signal as the stylus angle becomes more nearly perpendicular to said writing surface when stylus tip is in contact with said writing surface while writing; (h) said first transducer means and said second transducer means positioned in said stylus housing so that they produce inversely correlated signal strengths as the angle of the stylus changes relative to said writing surface during writing; (i) a first signal transmission means for conveying a first signal train produced by said first transducer means from stylus to a signal processing means, and a second signal transmission means for conveying a second signal train produced by said second transducer means from stylus to said signal processing means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 27)
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14. In a signature verification system, a method for enrolling the reference signatures of individuals comprising the following steps:
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(a) measuring incoming digitized electronic signal trains through a signal processing means, said signal trains originating in a pressure sensitive data input stylus with a first transducer means capable of sensing axial pressure, hereafter known as a direct pressure, and a second transducer means capable of measuring pressure transverse to the direct pressure, hereafter known as a lateral pressure said first transducer means producing a first signal train representative of variations in direct pressures on the stylus while signing a signature said second transducer means producing a second signal train representative of variations in pressures lateral to the axis of the stylus when signing a signature, said first transducer means positioned axially within the stylus and the second transducer positioned about the axis of the stylus, the first and second transducers producing inversely correlated signal strengths as the angle of the stylus to a writing surface varies while signing a signature, indicators of said variations forming the verification discriminate; (b) recording the direct pressure values and the lateral pressure values at each digitized sample point in said signal trains; (c) calculating the ratio of the direct pressure to the lateral pressure at each sample point, whereby the resulting measurement is a relative measure independent of actual amounts of direct or lateral force representing the physical orientation of the stylus, said ratio hereafter being known as a relative angle ratio; (d) dividing the incoming signal train into segments of equal length representing the relative angle ratio of the stylus for portions of the signal trains, and repeating this process several times, each segmentation yielding a different number of segments of varying lengths, whereby segments can be compared in order to yield variation measurements, said segments hereafter being known as defined segments; (e) computing the overall ratio of the direct pressure signals and the lateral pressure signals, being known as the relative angle ratio, for the whole signal and all said defined segments; (f) comparing the relative angle ratio measurement of said defined segments to each other, and to the relative angle of the whole signal train, in different segment combinations, each resulting comparison hereafter being known as a measurement point; (g) characterizing angular relationships in the individuals signature by calculating the difference in relative angle measures between the two compared segments at each measurement point, the resulting value hereafter being known as the measurement point value; (h) repeating the enrollment steps above for a plurality of reference signatures generated by enrolle using said data input stylus; (i) listing the measurement point values from multiple enrollment signature signal trains at each measurement point; (j) determining variations in the physical orientation of the individual signature by calculating the range of values obtained from said reference signatures at each measurement point to establish a range of acceptable values for each measurement point, said range hereafter being known as an acceptable range of values, whereby the corresponding measurement value from a putative signature is counted as either a scored point falling inside the range of acceptable values, or a missed point, falling outside the range of acceptable values during a later verification measurement; (k) selecting a reduced number of least range measurement points, said measurement points comprising the consistent measurement points and range of acceptable variation for each forming the signature identification discriminate; (l) selecting measurement points for a tentative stringency score, being the number of matched measurement point values required for verification of a putative signature; (m) testing actual signatures of true signer and adjusting said stringency measure and said range of acceptable values at measurement points in order to maximally balance probability of false rejections and false acceptances; (n) assigning the final signature identification discriminates to individual enrolle.
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19. A method for verifying a signature comprising the following steps:
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(a) receiving incoming digitized electronic signals from a sample signature produced by a putative signer, through a signal processing means, and originating in a pressure sensitive data input stylus, containing a first transducer means capable of sensing axial pressure, hereafter known as a direct pressure, and producing a first signal train representative of variations in said direct pressure, and a second transducer means capable of measuring pressure transverse to the direct pressure, hereafter known as a lateral pressure, and producing a second signal train representative of variations in pressures lateral to the axis of the stylus while signing, said first transducer means axially positioned inside said stylus and said second transducer means positioned transversely around the axis of said stylus, the first and second transducers producing inversely correlated electronic signal values as the angle of the stylus to a writing surface varies while signing a signature; indicating said electronic variations in the form of a verification discriminate; (b) identifying from said first and second electronic signal trains specific reference measurement points and their reference measurement point values for different locations in the signal trains said reference measurement points and the reference measurement point values determined during enrollment of reference signatures by the putative signer, the value of each reference measurement point being a difference between two segments, each segment representing the relative angle of the stylus for a portion of the electronic signal train; (c) comparing incoming measurement point values for sample signatures with the reference measurement point values from the verification discriminate; (d) tracking the total number of incoming measurement point values falling within a predetermined allowable range of acceptable values of said reference measurement point values; (e) sending an accept message if a preselected number of said incoming measurement point values are within the predetermined range of the reference measurement point values; and (f) sending a reject message if a predetermined number of said incoming measurement point values are not within the predetermined range of the reference measurement point values. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26)
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Specification