Apparatus for signature verification

Claim 1

Apparatus for comparing a working signature of an individual to verify the working signature, comprising: a transducer responsive to the pressure of a pointed writing instrument when the individual writes on a sheet of paper that overlies the transducer, which transducer generates digital electronic signals in real time representing the position of the tip of the writing instrument in terms of X and Y coordinates relative to a predetermined origin of coordinates, means arranged to sample at a rapid rate the X and Y coordinates and therefrom to determine the changes from one sample of each coordinate to the next, program memory means in which is stored algorithms for identifying significant features of the signature including upper and lower turning points of loops, points at which the writing instrument is applied to and lifted from the paper, and lengths of segments of the signature, and digital electronic processor means arranged to operate according to said stored algorithms to: a. compute from said changes in X and Y coordinates, from one sample of each coordinate to the next, mathematical parameters representing said significant features of said working and sample signatures, b. derive from several specimen signatures for said individual means values and spread indicators of said mathematical parameters and to store said mean values and spread indicators for said individual in data memory means, c. respond to a working signature of the individual by calculating the differences between said parameters of said working signature and said mean values of said parameters for said individual retrieved from said data memory means, d. calculate for each parameter according to said spread indicator a first difference limit and a second larger difference limit and to calculate a first score for said parameter that corresponds to less than the calculated difference if the difference is less than the first limit, to calculate a second score that corresponds to the calculated difference if the difference is between the first and second limits, and to calculate a third score that is substantially larger than the calculated difference if said calculated difference is greater than the second limit, and e. adds the scores for the several parameters and rejects the working signature if the total score exceeds a threshold, said substantially larger third score being such that said threshold will be exceeded if the calculated difference of any parameter exceeds the second limit.