Apparatus and method for digitizing and segmenting a handwriting movement based on curvilinear and angular velocities

Apparatus for digitizing and segmenting a handwriting movement, comprising:

• an electrical transducer for generating three electrical digital position signals characterizing a trajectory of said handwriting movement, said transducer including a pencil provided with a point and an analog-to-digital tablet, said three signals being D.sub.x (t), D.sub.y (t) and D.sub.z (t), where D.sub.x (t) and D.sub.y (t) are respectively position signals according to X and Y axes of a cartesian reference with respect to time, and D.sub.z (t) is a discrete signal indicating whether or not said point is contacting said tablet, said electrical transducer having substantially a sampling frequency of 100 Hz, said electrical transducer having substantially a resolution of 393.7 l/cm;
• means for low-pass filtering said D.sub.x (t) and D.sub.y (t) electrical signals, said means for low-pass filtering being a low-pass filter having a bandwidth of 20 to 50 Hz, said low-pass filter having a predetermined time function F.sub.2 (t.sub.i) where:
• ##EQU26## said low-pass filter having a predetermined transfer function H.sub.2 (.omega.) where:
• ##EQU27## means for taking the derivative of said D.sub.x (t) and D.sub.y (t) electrical signals by predetermined time and transfer functions for generating V.sub.x and V.sub.y electrical components which represent respectively speeds of said point according to X and Y axes of a cartesian reference, said means for deriving being a filter having a predetermined time function F.sub.5 '(t.sub.i) where:
• ##EQU28## said means for deriving having a predetermined transfer function H.sub.5 (.omega.) where:
• ##EQU29## where:
• F.sub.c is a cutoff frequency of 20 Hz, and
• F.sub.s is a sampling frequency of 100 Hz;
• means for calculating V.sub..sigma. and V.sub..theta. values from V.sub.x and V.sub.y components where:
• ##EQU30## where V.sub..theta. has a sign determined by:
• ##EQU31## means for calculating handwritten components and handwritten strings, where each of said handwritten components is delimited by two successive liftings of said point along said trajectory, and each of said handwritten strings is delimited by two successive portions of said trajectory where said V.sub..theta. value is higher than a predetermined angular speed value, said V.sub..sigma. value is lower than a predetermined curvilinear speed value, said predetermined angular speed is 50 rad/s., said predetermined curvilinear speed is V.sub..sigma. /2 cm/s., where V.sub..sigma. is an average curvilinear speed of said point during said trajectory, said lifting of the pen has a minimal period of time of 0.03 s., and each of said handwritten strings has a minimal period of time of 0.05 s;
• means for calculating, by means of said D.sub.z (t), a first simple dynamic parameter consisting of a period of time of said trajectory during which said point of said pencil is contacting said tablet;
• means for calculating, by means of D.sub.z (t), a second simple dynamic parameter consisting of a percentage representative of a period of time of said trajectory during which said point is lifted;
• means for calculating, by means of said D.sub.x (t), D.sub.y (t) and D.sub.z (t), a third simple dynamic parameter consisting of a percentage representative of a period of time of said trajectory during which said point is stopped;
• means for calculating, by means of said V.sub..theta. value, a fourth simple dynamic parameter consisting of a percentage representative of a period of time of said trajectory during which said V.sub..theta. value is positive;
• calculating means for applying respectively a first predetermined rotating operator and a second predetermined rotating operator to said D.sub.x (t) and D.sub.y (t) signals for correcting inclination of said trajectory and aligning a base line of said trajectory with a horizontal base line;
• and
• calculating means for scaling said D.sub.x (t) signal according to said X cartesian axis with values varying from 0 to 10,000, and for scaling said D.sub.y (t) according to said Y cartesian axis with a value of 0 when said D.sub.y (t) signal crosses said base line of said trajectory.

Method for digitizing and segmenting a handwriting movement, comprising steps of:

• generating three electrical digital position signals characterizing a trajectory of said handwriting movement, by means of a transducer including a pencil provided with a point and an analog-to-digital tablet, said three signals being D.sub.x (t), D.sub.y (t) and D.sub.z (t), where D.sub.x (t) and D.sub.y (t) are respectively position signals according to X and Y axes of a cartesian reference with respect to time, and D.sub.z (t) is a discrete signal indicating whether or not said point is contacting said tablet;
• filtering said D.sub.x (t) and D.sub.y (t) electrical signals;
• taking the derivative of said D.sub.x (t) and D.sub.y (t) electrical signals by predetermined time and transfer functions for generating V.sub.x and V.sub.y electrical components which represent respectively speeds of said point according to X and Y axes of a cartesian reference;
• calculating V.sub..sigma. and V.sub..theta. values from said V.sub.x and V.sub.y components where:
• ##EQU32## where V.sub..theta. has a sign determined by:
• ##EQU33## calculating handwritten components and handwritten strings, where each of said handwritten components is delimited by two successive liftings of said point along said trajectory, and each of said handwritten strings is delimited by two successive portions of said trajectory where said V.sub..theta. value is higher than a predetermined angular speed value and said V.sub..sigma. value is lower than a predetermined curvilinear speed value.