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Analysis of handwritten personal signatures for identity verification Omoruto, Francis Emmanuel Emauke 1980

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ANALYSIS OF HANDWRITTEN PERSONAL SIGNATURES FOR IDENTITY VERIFICATION by FRANCIS EMMANUEL EMAUKE OMORUTO B.Sc. (Eng.) (Hons,>, Makerere U n i v e r s i t y , 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF • THE REQUIREMENTS FOR THE DEGREE OF THE FACULTY OF GRADUATE STUDIES Department of E l e c t r i c a l E n g i n e e r i n g We accept t h i s t h e s i s as co n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA 1980 December c Y F r a n c i s Emmanuel Emauke Omoruto, 1980 MASTER OF APPLIED SCIENCE i n In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Depar tmen t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l no t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tmen t n f E l e c t r i c a l E n g i n e e r i n g The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5 Date 1 9 8 0 D e c e m b e r 2 2 — D E - 6 B P 75-51 1 E ABSTRACT I t i s becoming i n c r e a s i n g l y n e c e s s a r y t o be a b l e t o v e r i f y p e r s o n n e l i d e n t i t i e s q u i c k l y and a c c u r a t e l y . The d e s i g n o f automated methods o f p e r f o r m i n g t h i s t a s k i s t h e r e f o r e o f prime concern . Ba s i n g such an automated i d e n t i t y v e r i f i e r on a g e n e r a l l y accepted means o f i d e n t i t y a u t h e n t i c a t i o n such as the h a n d w r i t t e n p e r s o n a l s i g n a t u r e would make i t q u i t e w i d e l y a c c e p t a b l e i n the community. P r e v i o u s work i n automated i d e n t i t y a u t h e n t i c a t i o n by s i g n a t u r e v e r i f i c a t i o n has shown t h a t i t i s f e a s i b l e to a c h i e v e a degree o f a c c u r a c y q u i t e s u p e r i o r t o the average performance o f human v e r i f i e r s i n a s i m i l a r e nvironment. In t h i s t h e s i s , the i m p l e m e n t a t i o n o f b a s i c t o o l s f o r the a c q u i s i t i o n and a n a l y s i s o f c e r t a i n s i g n a t u r e v a r i a b l e s f o r i d e n t i t y v e r i f i c a t i o n i s r e p o r t e d . The l a r g e r s et o f p o s s i b l e m e t r i c s f o r a s i g n a t u r e are d e s c r i b e d t o g e t h e r w i t h some o f the c r i t e r i a f o r the s e l e c t i o n o f the subset examined. The r e s u l t s o f a p i l o t s t u d y u t i l i z i n g these t o o l s i n d i c a t e the p o t e n t i a l f o r a v i a b l e commercial a p p l i c a t i o n o f the t e c h n i q u e . TABLE OF CONTENTS. ABSTRACT i i TABLE OF CONTENTS. i i i LIST OF TABLES. v i i LIST OF FIGURES v i i i ACKNOWLEDGEMENT. i x 0. INTRODUCTION : The V e r i f i c a t i o n of I d e n t i t y . 1 0.0.1 Human i n t e r p r e t a t i o n . 4 0.0.2 P r a c t i c a l c o n s i d e r a t i o n s . 5 0.1 Automated I d e n t i t y V e r i f i c a t i o n . 7 0.1.1 Systems f o r Automated I d e n t i t y V e r i f i c a t i o n . 7 0.1.2 Automated s i g n a t u r e v e r i f i c a t i o n . 8 0.1.2.1 H a n d w r i t t e n s i g n a t u r e dynamics. 9 0.2 P r e v i o u s Research i n H a n d w r i t i n g Dynamics. 10 0.2.1 I d e n t i t y v e r i f i c a t i o n u s i n g h a n d w r i t i n g dynamics. 10 0.3 M o t i v a t i o n f o r t h i s s t u d y . 13 0.4 The O b j e c t i v e s of T h i s Work. 16 0.5 The Scope o f T h i s T h e s i s . 17 1. THE ACQUISITION OF HANDWRITING DATA. 19 1.1 H a n d w r i t i n g V a r i a b l e s . 20 1.1.1 V a r i a b l e s used i n b a s i c h a n d w r i t i n g r e s e a r c h . 20 1.1.2 Waveform parameters used f o r s i g n a t u r e v e r i f i c a t i o n . 2 2 1.2 Tra n s d u c e r s f o r H a n d w r i t i n g Measurement. 24 1.2.1 Tran d u c e r s f o r b a s i c h a n d w r i t i n g r e s e a r c h . 24 1.2.2 T r a n s d u c e r s used f o r measuring s i g n a t u r e v a r i a b l e s . 2 6 1.3 Parameters of H a n d w r i t i n g . 28 1.4 S e l e c t i o n of the V a r i a b l e s Used i n t h i s Work. 33 - i i i -2. LABORATORY EVALUATION OF THE TRANSDUCER SYSTEM. 35 2.1 L a b o r a t o r y s e t u p f o r the e v a l u a t i o n . 37 2.2 E v a l u a t i o n of the t r a n s d u c e r system, 38 2.2.1 E x p e r i m e n t a l p r o c e d u r e . 40 2.2.1.1 L i n e a r i t y . 41 2.2.1.2 R e l a t i v e independence between o u t p u t s . 42 2.2.1.3 Dynamic range. 42 2.2.1.4 S i g n a l - t o - n o i s e r a t i o . 43 2.2.2 Q u a l i t a t i v e assessment. 43 2.2.3 E x p e r i m e n t a l R e s u l t s . 44 2.2.3.1 P o s i t i o n l i n e a r i t y , . 50 2.2.3.2 Force l i n e a r i t y . 50 2.2.3*3 R e l a t i v e independence of o u t p u t s . 51 2.2.3.4 Dynamic range o f p o s i t i o n s e n s i n g . 52 2.2.3.5 Dynamic range o f f o r c e t r a n s d u c t i o n . 5 3 2.2.3«6 S i g n a l - t o - n o i s e r a t i o and u n c e r t a i n t y i n p o s i t i o n . 5 3 2.2.3-7 S i g n a l t o n o i s e r a t i o and u n c e r t a i n t y i n f o r c e . 5 3 2.3 The adequacy of the d e v i c e . 59 2.3.1 L i n e a r i t y o f p o s i t i o n c a l c u l a t i o n . 59 2.3.2 L i n e a r i t y of f o r c e t r a n s d u c t i o n . 59 2.3-3 R e l a t i v e independence of o u t p u t s . 59 2.3.4 W r i t i n g window s i z e and l o c a t i o n . 60 2.3.5 Ruggedness of the t r a n s d u c e r w i t h r e s p e c t t o a p p l i e d f o r c e . 60 2.3.6 S i g n a l - t o - n o i s e r a t i o . 60 2.4 Comparison With Other Systems. 62 - i v -3. IDENTITY VERIFICATION EXPERIMENT. 64 3.1 P r e v i o u s Work i n H a n d w r i t t e n S i g n a t u r e V e r i f i c a t i o n . 66 3.1.1 C l a s s i f i c a t i o n o f Systems. 66 3.1.1.1 S t a t i c systems. 66 3.1.1 . 2 Dynamic systems. 67 3.1 . 2 S i g n a t u r e F e a t u r e s Used I n V e r i f i c a t i o n . 68 3.1 . 2.1 F e a t u r e s f o r s t a t i c systems. 69 3 . 1 . 2 . 2 F e a t u r e s used i n dynamic systems. 70 3 . 2 C h a r a c t e r i s a t i o n s of the H a n d w r i t t e n S i g n a t u r e , 73 3 . 2.1 P r o c e s s i n g T e c h n i q u e s . 74 3 . 2.1.1 S i m i l a r i t y measures. 7^ 3 . 2 . 1 . 2 Waveform parameters. 7 6 3 . 2.1.3 Comparison o f t h e two approaches. 77 3 . 2 . 2 C o n s i d e r a t i o n s f o r Parameters. 78 3 . 2 . 2 . 1 Parameters c h a r a c t e r i s t i c o f the s i g n a t u r e . 7 8 3 . 2 . 2 . 2 Parameters c h a r a c t e r i s i n g both s i g n e r and s i g n a t u r e , 79 3 . 2 . 2 . 3 Parameters c h a r a c t e r i s t i c o f the s i g n e r . 79 3 . 2.3 F e a t u r e s to be e v a l u a t e d . 80 3.3 The S i g n a t u r e A n a l y s i s and V e r i f i c a t i o n Experiment. 8 3 3-3.1 E x p e r i m e n t a l D e s i g n . 8 3 3 . 3 . 2 Survey P r o t o c o l . 86 3 . 3 . 3 L a b o r a t o r y p r o c e d u r e . 86 3 . 4 Data P r o c e s s i n g . 88 3.4.1 Parameter c a l c u l a t i o n . 88 3.4 . 2 D i s t a n c e Measurement and Sample C l a s s i f i c a t i o n . 89 3.4.3 T h r e s h o l d s e l e c t i o n . 90 - v -3-4.4 E x p e r i m e n t a l r e s u l t s . 91 3 . 5 D i s c u s s i o n of R e s u l t s , 105 3.5.1 Parameter dependencies. 105 3.5.2 F a l s e r e j e c t i o n r a t e . 106 3 . 5 . 3 F a l s e acceptance r a t e , 107 3.5.4 Random f o r g e r y acceptance r a t e . 107 3.5.5 Data Compression. 108 3.6 Sources of E r r o r . 109 3 . 7 Performance Comparison. 110 4. CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK. 113 4.1 C o n t r i b u t i o n s Of T h i s Research. 113 4.2 S u g g e s t i o n s F o r F u r t h e r Work. 115 5. REFERENCES. 118 APPENDIX A. 121 A1. D e t a i l e d R e s u l t s . 122 A2. Programme c o n t r o l f l o w c h a r t s . 138 APPENDIX "B. 144 The P o s i t i o n and F o r c e T r a n s d u c e r . 144 - v i -LIST OF TABLES. Table l a : P o s i t i o n T r a n s d u c t i o n Data. 46 Table l b : Force T r a n s d u c t i o n Data. 48 Table I I : D e c i s i o n t h r e s h o l d v a l u e s . 91 Table I I I : The parameter s t a t i s t i c s . 94 Table IVa: Performance o f the f i r s t - d a y f o r g e r y s e t . 96 Table IVb : Performance o f the f i n a l - d a y f o r g e r y s e t . 98 Table V: Performance o f the genuine samples. 101 Table VI: Random F o r g e r y - S u b j e c t 00. 102 Table V I I : T h r e s h o l d v a l u e s f o r parameter c o r r e l a t i o n s . 106 Table V i l l a : Parameters F1 - F8 computed from f i r s t samples. 124 Table V H I b : R e l a t i v e d u r a t i o n s o f pen-down segments. 126 - v i i -LIST OF FIGURES. F i g . 1 : Event sequence i n fo r m a l i d e n t i f i c a t i o n and i d e n t i t y v e r i f i c a t i o n . 2 F i g . 2 : Some o f the a c t i v e f o r c e s i n h a n d w r i t i n g . 3 0 F i g . 3: R e a c t i o n s i n the w r i t i n g plane to the i n p u t s of F i g . 2 . 31 F i g . 4: L a b o r a t o r y s e t u p f o r d e v i c e e v a l u a t i o n and d a t a a c q u i s i t i o n . 36 F i g . 5: Method of a p p l y i n g p o i n t l o a d s . 39 F i g . 6: Load a p p l i c a t i o n g r i d . 39 F i g . 7: Output vs. i n p u t 'x' v a l u e s . 55 F i g . 8 : Output vs. i n p u t 'y' v a l u e s . 56 F i g . 9 : Output vs. i n p u t 'p' v a l u e s . 57 F i g . 10: Worst case u n c e r t a i n t y i n p o s i t i o n measurement vs. a p p l i e d l o a d . 58 F i g . 11: Sample o f the name f o r g e d by the v o l u n t e e r s . 85 F i g . 1 2 : Survey c i r c u l a r . 85 F i g . 1 3 : Sample p l o t s of d e v i c e o u t p u t s . 1 2 3 F i g . 14: T h r e e - p o i n t support' system f o r f o r c e and p o s i t i o n t r a n s d u c t i o n . 145 F i g . 15: Force and p o s i t i o n t r a n s d u c t i o n system - o v e r v i e w . 147 F i g . 16: Force and p o s i t i o n t r a n s d u c t i o n system -a l t e r n a t i v e p r o c e s s i n g methods. 148 - v i i i -ACKNOWLEDGEMENT. I s h o u l d l i k e t o thank the Department of E l e c t r i c a l E n g i n e e r i n g f o r p r o v i d i n g computing and o t h e r f a c i l i t i e s . The work of members o f the Deparment of Computer S c i e n c e i n p r o v i d i n g the e d i t i n g and t e x t - p r o c e s s i n g programmes used f o r p r o d u c i n g t h i s t h e s i s i s g r a t e f u l l y acknowledged. The support of Makerere U n i v e r s i t y , Uganda, i n the form of a S t a f f Development F e l l o w s h i p (1978-1980), and The U n i v e r s i t y of B r i t i s h Columbia i n the form of Teaching A s s i s t a n t s h i p s (1979-1980), b u r s a r i e s (1979-1980) and a M e i l i c k e Award (1979) i s h i g h l y a p p r e c i a t e d . I would l i k e t o f u r t h e r e x p r e s s my g r a t i t u d e t o a l l my f r i e n d s e s p e c i a l l y J e a n e t t e McDougall, Stephen Omule and my o f f i c e - m a t e s , w i t h o u t whose c o n s t a n t encouragement and s u p p o r t , moral and m a t e r i a l , I c o u l d not have completed t h i s work. My t h e s i s s u p e r v i s o r and a d v i s o r , Dr. P e t e r Lawrence, d e s e r v e s s p e c i a l mention f o r h i s f a i t h and guidance. I a l s o thank Dr. Grant Anderson who f i r s t suggested the p r o j e c t t o me. - i x -0. INTRODUCTION : The V e r i f i c a t i o n o f I d e n t i t y . When a person i s f i r s t i n t r o d u c e d i n t o a s o c i e t y o r community, ( s ) h e a c q u i r e s a means of i d e n t i f i c a t i o n , u s u a l l y d i s t i n c t from t h a t o f any o t h e r member of the same s o c i e t y . T h i s i d e n t i f i c a t i o n may be of the person's own c h o o s i n g , or one s i m p l y a s s i g n e d t o him/her. I t i s m a i n t a i n e d by a s s o c i a t i n g w i t h i t o b s e r v a b l e c h a r a c t e r i s t i c s of the person i t has been a s s i g n e d t o . T h i s means of i d e n t i f i c a t i o n i s c l e a r l y not a permanent p a r t o f the perso n . Because o f t h i s , another person a l t o g e t h e r c o u l d f r a u d u l e n t l y c l a i m i t as h i s / h e r own. Hence, the need a r i s e s t o s u b s t a n t i a t e c l a i m s t o g i v e n i d e n t i f i c a t i o n s . The v e r i f i c a t i o n o f i d e n t i t y i s t h e r e f o r e m a n i f e s t as the problem of d e c i d i n g whether or not the person u s i n g an i d e n t i f i c a t i o n at any i n s t a n c e i s indeed the person t h a t i d e n t i f i c a t i o n was a s s i g n e d t o i n the f i r s t p l a c e . T h i s i s done by o b s e r v i n g c h a r a c t e r i s t i c s of the person u s i n g the i d e n t i f i c a t i o n at t h a t t i m e , and comparing w i t h the c o r r e s p o n d i n g r e c o r d e d c h a r a c t e r i s t i c s a s s o c i a t e d w i t h the id e n t i f i c a t i o n . F i g . 1 i l l u s t r a t e s t h e g e n e r a l p r o c e s s o f i d e n t i f i c a t i o n and subsequent i d e n t i t y v e r i f i c a t i o n . A new member to a community can be any of the f o l l o w i n g . - 1 -COPER ATE "J ("IDENTIFY) Ass ign an identification to the individual Await service request ( V E R I F Y ) Obtain the individual 's identification (if any) Observe the features of the individual ^rnembzi IDENTIFY) X ^ C V E R I F Y ) Observe and record the characteristics of the individual's features (OPERATE)  ^ Retrieve the stored feature characteristics Determine the closeness of the observed features to the stored (expected) ones. ' 1 Reject or accept the claim to the identification COPERATE^ Fig. 1: Event sequence in formal identification and identity verification. - 2 -0 (1) A c h i l d b e i n g born. (2) A person a c q u i r i n g a c c e s s to a ( l a r g e t i m e - s h a r e d ) computing f a c i l i t y . ( 3 ) A pers o n opening an account i n a commercial bank, (4) An employee j u s t e n t e r i n g s e r v i c e i n a s e c u r i t y i n s t a l l a t i o n . The i d e n t i f i c a t i o n p r o v i d e d would then be: (1) A name f o r the newborn. (2) A computing "ID". ( 3 ) The person's ( p r e f e r r e d ) name. (4) The employee's p r e f e r r e d name. The numbering on t h i s l i s t i s i n d i r e c t correspondence w i t h the one b e f o r e . The v e r i f i c a t i o n r e q u e s t would then be ge n e r a t e d when t h e f o l l o w i n g o c c u r : (1) The (grown up) c h i l d goes t o v i s i t r e l a t i v e s who haven't seen him/her, but know some of h i s / h e r c h a r a c t e r i s t i c f e a t u r e s , and l a y s c l a i m t o the i d e n t i t y ( s ) h e r e c e i v e d a t b i r t h . (2) The user wishes t o a c c e s s the computing f a c i l i t y . ( 3 ) A banking t r a n s a c t i o n i s i n i t i a t e d by the customer. - 3 -(4) The employee r e p o r t s f o r duty. The procedures f o l l o w e d by humans p e r f o r m i n g the v a r i o u s f u n c t i o n s i n d i c a t e d i n F i g . 1 are d e t a i l e d i n the next s e c t i o n . T h i s r e p r e s e n t s an i d e a l i z e d l i n e a r i z a t i o n o f the u s u a l i d e n t i f i c a t i o n and i d e n t i t y v e r i f i c a t i o n p r o c e s s . I t , however r e p r e s e n t s the case of f o r m a l i z e d i d e n t i f i c a t i o n and i d e n t i t y v e r i f i c a t i o n . 0.0.1 Human i n t e r p r e t a t i o n . I n t h e case o f human s o c i e t i e s i d e n t i f y i n g human i n d i v i d u a l s , the c h a r a c t e r i s t i c s used f o r i d e n t i f i c a t i o n i n c l u d e f a c i a l and o t h e r p h y s i c a l f e a t u r e s such as gender, h e i g h t and b u i l d , v o c a l f e a t u r e s and/or speech h a b i t s . In b r i e f , the f e a t u r e s used are those f o r which n a t u r a l means of o b s e r v a t i o n -the senses - e x i s t . Community members who have d i s a b i l i t i e s i n e i t h e r s i g h t or h e a r i n g , as r e q u i r e d f o r o b s e r v i n g the above f e a t u r e s , might a l s o use t h e i r t a c t i l e sense to observe the pe r s o n . With t h i s arrangement, e v e r y member of the community r e c o r d s h i s / h e r own o b s e r v a t i o n s o f the i n d i v i d u a l , which r e q u i r e s p e r s o n a l a c q u a i n t a n c e . For cases where i t may not be f e a s i b l e f o r some or a l l members of the community to observe these ' n a t u r a l ' c h a r a c t e r i s t i c s , o t h e r c o n t r i v a n c e s have t o be used to f a c i l i t a t e the v e r i f i c a t i o n o f i d e n t i t i e s . One method i s to g i v e the person an a r t i f i c i a l c h a r a c t e r i s t i c , such as a password, which ( s ) h e must then commit t o memory and reproduce on demand. - 4 -A s l i g h t l y more n a t u r a l c h a r a c t e r i s t i c has been used i n l i t e r a t e communities, where i t has been observed t h a t h a n d w r i t i n g i s q u i t e d i s t i n c t i v e i n most i n d i v i d u a l s . In p a r t i c u l a r , most people have a c q u i r e d the h a b i t of c o n s i s t e n t l y w r i t i n g t h e i r u s u a l i d e n t i f i c a t i o n , t h e i r name, i n a manner p e c u l i a r to t h e m s e l v e s . T h i s p a r t i c u l a r v e r s i o n o f t h e i r h a n d w r i t t e n name, t h e i r s i g n a t u r e , has t h e r e f o r e been used to v e r i f y t h e i r i d e n t i t i e s . F u r t h e r , the almost n e g l i g i b l e e f f o r t of remembrance r e q u i r e d to r e p r o d u c e a s i g n a t u r e has made t h i s one o f the i d e n t i t y v e r i f i c a t i o n means most a c c e p t e d , even e x p e c t e d , by such communities. 0.0.2 P r a c t i c a l c o n s i d e r a t i o n s . Now, i t i s r a r e t h a t people v e r i f y the i d e n t i t i e s of o t h e r s f o r t h emselves any more. U s u a l l y , the v e r i f i e r i s employed to p e r f o r m the f u n c t i o n f o r an o r g a n i s a t i o n or i n s t i t u t i o n . The use o f a human to p r o v i d e t h i s f u n c t i o n , as has been the p r a c t i c e h i t h e r t o , i s r a t h e r s e v e r e l y l i m i t e d by v a r i o u s c o n s i d e r a t i o n s as i n d i c a t e d h e r e a f t e r . - The pace o f most a c t i v i t i e s which g i v e r i s e t o the requirement f o r i d e n t i t y v e r i f i c a t i o n has become v e r y h i g h i n most communities. - The a c c u r a c y r e q u i r e d f o r the volume o f work i n v o l v e d i s g e n e r a l l y u n a t t a i n a b l e t h r o u g h human e f f o r t . - The tedium o f p e r f o r m i n g r e p e t i t i v e t a s k s i s one t h a t most people a v o i d nowadays. - 5 -Thus, the automation o f the e x e r c i s e o f i d e n t i t y -v e r i f i c a t i o n i s q u i t e d e s i r a b l e and even n e c e s s a r y . The next s e c t i o n d e s c r i b e s what i s i n v o l v e d i n the i m p l e m e n t a t i o n o f an automated i d e n t i t y v e r i f i c a t i o n scheme. I t a l s o g i v e s a b r i e f r e v i e w o f some p r e v i o u s work done towards r e a l i z i n g such scheme s. - 6 -0.1 Automated I d e n t i t y V e r i f i c a t i o n . The c o n s i d e r a t i o n s i n the p r e v i o u s s e c t i o n and v a r i o u s modern developments, s u r v e y e d i n a l a t e r s e c t i o n , have made i t i n c r e a s i n g l y n e c e s s a r y t o be a b l e t o v e r i f y i d e n t i t i e s q u i c k l y and a c c u r a t e l y [SYKE78]. An e f f i c i e n t way to i n c r e a s e both speed and a c c u r a c y r e l a t i v e l y i n d e p e n d e n t l y of each o t h e r i s by r e l e g a t i n g the t a s k o f o b s e r v i n g the s u b j e c t s , d e t e r m i n i n g s i m i l a r i t i e s and making r e j e c t i o n or acceptance d e c i s i o n s t o a machine. T h i s , t h e n , i s automated i d e n t i t y v e r i f i c a t i o n . The v a r i o u s p o s s i b l e means of a c h i e v i n g automated i d e n t i t y v e r i f i c a t i o n are d i s c u s s e d i n the next s e c t i o n . 0.1.1 Systems f o r Automated I d e n t i t y V e r i f i c a t i o n . An automated system may be designed t o u t i l i s e one or more o f the c h a r a c t e r i s t i c s l i s t e d above f o r human v e r i f i e r s . For example, a system which a n a l y s e s f a c e s c o u l d be c o n s t r u c t e d . However, s i n c e p e o p l e ' s f a c e s g e n e r a l l y do not s t a y e x a c t l y the same f o r any g r e a t l e n g t h of t i m e , the ke e p i n g of up - t o - d a t e r e f e r e n c e f e a t u r e s would be q u i t e d i f f i c u l t . V o i c e - r e c o g n i t i o n f o r i d e n t i t y v e r i f i c a t i o n i s an approach c u r r e n t l y under i n v e s t i g a t i o n [SYKE78], For the h i g h - s e c u r i t y a p p l i c a t i o n s , Sykes [SYKE78] mentions the use o f hand geometry f o r i d e n t i f i c a t i o n . However, t h i s and o t h e r r e l a t e d schemes, such as f i n g e r p r i n t i n g , run the r i s k of not being g e n e r a l l y a c c e p t a b l e . The use o f h a n d w r i t t e n s i g n a t u r e s f o r automated i d e n t i t y v e r i f i c a t i o n i s another a l t e r n a t i v e mentioned i n [SYKE78], That - 7 -t h i s approach i s f e a s i b l e was demonstrated by Mauceri [MAUC65] and Dyche [DYCH??] among o t h e r s . The added o b s e r v a t i o n t h a t most peopl e have come t o accept [STER75], [HERB77], t h e use of t h e i r p e r s o n a l s i g n a t u r e f o r i d e n t i t y v e r i f i c a t i o n makes t h i s a v e r y a t t r a c t i v e o p t i o n . T h i s r e s e a r c h was t h e r e f o r e d i r e c t e d towards the development of an automated s i g n a t u r e v e r i f i c a t i o n system. 0.1.2 Automated s i g n a t u r e v e r i f i c a t i o n . Due to the observed c o n s i s t e n c y i n s i g n a t u r e s mentioned above, the problem of i d e n t i t y v e r i f i c a t i o n can be reduced, i n most c a s e s , t o the problem of v e r i f y i n g the h a n d w r i t t e n p e r s o n a l s i g n a t u r e . As w i t h the g e n e r a l i d e n t i t y v e r i f i c a t i o n problem, t h i s c o n s i s t s of f i r s t p r o v i d i n g the person w i t h a means of i d e n t i f i c a t i o n . The person i s then asked t o g i v e h i s / h e r s i g n a t u r e s e v e r a l t i m e s , and these sample s i g n a t u r e s are kept on r e c o r d as a r e f e r e n c e s e t . On subsequent o c c a s i o n s when the perso n g i v e s h i s / h e r i d e n t i f i c a t i o n , ( s ) h e i s asked t o g i v e a s i g n a t u r e to j u s t i f y t h e i r c l a i m t o the i d e n t i t y . T h i s i s then compared w i t h the p r e v i o u s l y r e c o r d e d samples and the c l a i m i s c o n s i d e r e d v a l i d i f the new sample i s s i m i l a r enough t o the r e f e r e n c e s e t . The • s i m i l a r i t y i s de c i d e d on the b a s i s of o b s e r v a b l e f e a t u r e s of the s i g n a t u r e which are s e l e c t e d t o r e p r e s e n t i t . The o b s e r v a b l e f e a t u r e s o f a h a n d w r i t t e n s i g n a t u r e can be s e p a r a t e d i n t o two groups. These are the f e a t u r e s of : ( i ) the s t a t i c s p a t i a l p a t t e r n t h a t i s l e f t on the paper when the s i g n i n g i s o v e r ; and - 8 -( i i ) the dynamics of the p a t t e r n g e n e r a t i o n . The ease w i t h which some i n d i v i d u a l s can reproduce s p a t i a l p a t t e r n s makes i t more a t t r a c t i v e to i n v e s t i g a t e the use o f dynamic f e a t u r e s f o r our purpose o f i d e n t i t y v e r i f i c a t i o n . These are h a r d e r to observe w i t h o u t , a t l e a s t , the a c t i v e p a r t i c i p a t i o n o f the a u t h e n t i c s i g n e r . The f o l l o w i n g s u b s e c t i o n i s t h e r e f o r e used t o i n t r o d u c e these dynamic f e a t u r e s i n g r e a t e r d e t a i l . 0.1.2.1 H a n d w r i t t e n s i g n a t u r e dynamics. The dynamic a s p e c t s of the h a n d w r i t t e n s i g n a t u r e which have been used t o r e p r e s e n t the s i g n a t u r e have i n c l u d e d : ( i ) Speed of w r i t i n g a l o n g the t r a c e . ( i i ) A c c e l e r a t i o n p a t t e r n a l o n g the t r a c e . ( i i i ) O rthogonal components of the speed and a c c e l e r a t i o n d u r i n g w r i t i n g . ( i v ) The f o r c e e x e r t e d on the w r i t i n g s u r f a c e as w r i t i n g i s i n p r o g r e s s . The measurement of many of these h a n d w r i t i n g c h a r a c t e r i s t i c s has been the s u b j e c t o f most b a s i c h a n d w r i t i n g r e s e a r c h [ H A R V 3 4 ] , [ M E L 0 3 4 ] , [ T R I P 5 7 ] . The work done by t h e s e r e s e a r c h e r s i s reviewed n e x t . - 9 -0.2 P r e v i o u s Research i n H a n d w r i t i n g Dynamics. H a n d w r i t i n g dynamics have been e x t e n s i v e l y i n v e s t i g a t e d and a p p l i e d to v a r i o u s problems. These a p p l i c a t i o n a r e a s have i n c l u d e d : ( i ) B a s i c p h y s i o l o g i c a l m o d e l l i n g of the h a n d w r i t i n g system [DENI65], [MACD66], [MCD070], [VRED71], [ YASU7 1 ] • ( i i ) M o d e l l i n g o f h a n d w r i t t e n s c r i p t f o r c h a r a c t e r r e c o g n i t i o n a p p l i c a t i o n s [EDEN61], [EDEN62]. An e x t e n s i v e r e v i e w of t h i s aspect of the r e s e a r c h appears i n [LIND65]. ( i i i ) I d e n t i t y v e r i f i c a t i o n , u s u a l l y from the p e r s o n a l s i g n a t u r e [MAUC65], [ L I U . 7 9 ] , [HERB77], [STER75], [CRAN7 8 ] , [DYCH??], [SAKA??]. 0.2 .1 I d e n t i t y v e r i f i c a t i o n u s i n g h a n d w r i t i n g dynamics. The use o f h a n d w r i t i n g dynamics f o r i d e n t i t y v e r i f i c a t i o n has been r e p o r t e d from v a r i o u s i n s t i t u t i o n s as d e s c r i b e d below. The U n i t e d S t a t e s A i r F o r c e General Design Company c a r r i e d out an i n v e s t i g a t i o n i n t o the use o f a c c e l e r a t i o n i n f o r m a t i o n f o r t h i s purpose [MAUC65]. They a l s o i n v e s t i g a t e d the f e a s i b i l i t y of i d e n t i f y i n g p e r s o n n e l by a n a l y s i n g samples of t h e i r h a n d w r i t i n g . These samples i n c l u d e d t h e i r a t t e m p t s at f o r g i n g o t h e r s u b j e c t s ' s i g n a t u r e s . They managed t o c o r r e c t l y c l a s s i f y 226 out of 250 s i g n a t u r e s on a f e a t u r e space of d i m e n s i o n a l i t y 1 9 . From t h a t they c o n c l u d e d t h a t the i d e n t i f i c a t i o n / v e r i f i c a t i o n t e c h n i q u e was f e a s i b l e . At S y l v a n i a E l e c t r o n i c Systems, the use o f s e c o n d - o r d e r - 10 -s e l f - and cross-moments of h a n d w r i t t e n s i g n a t u r e v a r i a b l e s f o r i d e n t i t y v e r i f i c a t i o n was r e s e a r c h e d [DYCH??]. The v a r i a b l e s i n v o l v e d i n the a n a l y s i s were the o r t h o g o n a l components o f the p o s i t i o n , v e l o c i t y and a c c e l e r a t i o n o f the pe n - p o i n t on the paper. With t h a t arrangement, a z e r o - e r r o r c l a s s s e p a r a t i o n on a d a t a s e t of 333 genuine s i g n a t u r e s and 167 f o r g e r i e s - a l l o f the same name - was r e a l i z e d u s i n g 40 measures and a B a y e s i a n d e c i s i o n r u l e . They c o n c l u d e d , however, t h a t a l t h o u g h the use o f down t o f i f t e e n measures c o u l d s t i l l ensure a complete s e p a r a t i o n i n t h e i r d a t a s e t , t h a t p a r t i c u l a r s e t of measures c o u l d not be guaranteed t o work i n g e n e r a l . I.B.M. r e s e a r c h e r s i n v e s t i g a t e d the f e a s i b i l i t y o f u s i n g o r t h o g o n a l components of the p e n - p o i n t a c c e l e r a t i o n waveform f o r s i g n a t u r e v e r i f i c a t i o n [HERB77]. They used a two- d i m e n s i o n a l c o r r e l a t i o n measure between the samples and the r e f e r e n c e s t o make t h e i r d e c i s i o n . (They used the d u r a t i o n of the s i g n a t u r e f o r p r e - s c r e e n i n g the s i g n a t u r e s . Any samples w i t h d u r a t i o n s t h a t d i f f e r e d from the mean v a l u e by more than 20% were r e j e c t e d o u t r i g h t . ) T h e i r achievements f o r 70 s u b j e c t s over a four-week p e r i o d were : 2.9% of v a l i d s i g n a t u r e s r e j e c t e d and 2.1% of f o r g e r i e s a c c e p t e d . The random f o r g e r y acceptance r a t e was 0.16?. They concluded t h a t i t was f e a s i b l e to use s i g n a t u r e s f o r p e r s o n a l i d e n t i f i c a t i o n and t h a t most of the f a i l u r e s of t h e i r system c o u l d be a s c r i b e d t o the i n s t r u m e n t a t i o n , r a t h e r than the p r i n c i p l e o f the t e c h n i q u e . L a t e r , the same workers added a t h i r d o b s e r v a t i o n to t h e i r system - the w r i t i n g "pressure"' [ L I U . 7 9 ] . T h i s was c o r r e l a t e d - 1 1 -i n d e p e n d e n t l y of the a c c e l e r a t i o n s , t h e r e b y p r o v i d i n g another measure to be used i n the d e c i s i o n . T h e i r new performance was : a f a l s e r e j e c t i o n r a t e o f 1.7%, a f o r g e r y acceptance r a t e of 0.4% and a random f o r g e r y acceptance of 0.02% w i t h 248 s u b j e c t s o v e r a six-month p e r i o d . At V e r i p e n I n c . , the dynamics of the w r i t i n g f o r c e - the " p r e s s u r e p r i n t " - were used i n a s i g n a t u r e v e r i f i c a t i o n experiment [STER75]. The r e s u l t s of a t e s t i n v o l v i n g some one hundred s u b j e c t s i n d i c a t e d a f a l s e r e j e c t i o n r a t e of about 0.7%. The acceptance of d e l i b e r a t e f o r g e r i e s by f i f t y s u b j e c t s was a p p r o x i m a t e l y 1.8%, w h i l e the acceptance of random f o r g e r i e s was a l s o about 1.8%. S t a n f o r d Research I n s t i t u t e workers [CRAN78], used the t h r e e - d i m e n s i o n a l dynamic drag f o r c e s on the t i p of the w r i t i n g i n s t r u m e n t i n t h e i r s i g n a t u r e v e r i f i c a t i o n scheme. They o b t a i n e d equal f a l s e r e j e c t i o n and f a l s e a cceptance e r r o r r a t e s of about 1.7% u s i n g a d i s t a n c e - b a s e d c l a s s i f i e r . They a l s o c o n s i d e r e d t h a t t h e i r r e s u l t s were c o n s e r v a t i v e and c o u l d be improved upon. From these e a r l y s u c c e s s e s , i t can be concluded t h a t the d e s i g n and c o n s t r u c t i o n o f a system f o r automated i d e n t i t y v e r i f i c a t i o n u s i n g the dynamics of h a n d w r i t t e n p e r s o n a l s i g n a t u r e s i s indeed f e a s i b l e . - 12 -0 . 3 M o t i v a t i o n f o r t h i s s t u d y . As i n d i c a t e d above, t h e r e i s a v e r y e v i d e n t need f o r automated i d e n t i t y v e r i f i c a t i o n systems. The f o l l o w i n g examples ser v e t o f u r t h e r i l l u s t r a t e t h i s . H i g h - q u a l i t y l o n g - d i s t a n c e t r a n s p o r t and communication f a c i l i t i e s have become r e a d i l y a v a i l a b l e . T h i s has l e d t o more people t r a n s a c t i n g b u s i n e s s w i t h a s s e t s t h a t are f a r removed from each o t h e r . Q u i t e o f t e n , a person t r a v e l l i n g away from h i s / h e r home town needs to use f a c i l i t i e s at home f o r a t r a n s a c t i o n . W ith the development o f comp u t e r i s e d banking systems, many banks now o f f e r t h e i r customers the a b i l i t y to a c c e s s t h e i r funds from branches o t h e r than t h e i r own. Thus, the t r a n s a c t i o n can be completed through a l o c a l branch of the buyer's bank. I t i s then n e c e s s a r y f o r the l o c a l bank to be a b l e to a c c u r a t e l y v e r i f y the i d e n t i t y of the t r a v e l l e r . Because of the d i s t a n c e s which might be i n v o l v e d , a human-based system would be i m p r a c t i c a l . With the c u r r e n t employment of humans, the s e c u r i t y of banked a s s e t s depends on the c o n s i s t e n c y of the h a n d w r i t t e n s i g n a t u r e as i n t e r p r e t e d by another human. The h i g h e s t s e c u r i t y i s a c h i e v e d through p e r s o n a l a c q u a i n t a n c e between i n t e r p r e t e r and s u b j e c t . T h i s i s because the i n t e r p r e t e r begins to use c h a r a c t e r i s t i c s o t h e r than j u s t the s i g n a t u r e to v e r i f y the person's i d e n t i t y . T h i s c l e a r l y f a v o u r s l o n g - e s t a b l i s h e d customers over r e l a t i v e l y new ones such as the l o n g - d i s t a n c e t r a v e l l e r away from home. The p r o v i s i o n of a r e a s o n a b l y u n i f o r m l e v e l o f s e c u r i t y to a l l customers, both l o c a l and o u t - o f - t o w n , - 13 -i s q u i t e a d e s i r a b l e goal i n t h i s i n s t a n c e . Another development i s the use o f funds t h a t are not i m m e d i a t e l y a v a i l a b l e , by the e x t e n s i o n o f c r e d i t f a c i l i t i e s t o people t h a t r e q u e s t and q u a l i f y f o r them. The goodness of c r e d i t i s then i n d i c a t e d by a c a r d the person c a r r i e s and uses on a l i m i t e d " c a r t e b l a n c h e " b a s i s . These c a r d s , which o f t e n double as means of i d e n t i t y a u t h e n t i c a t i o n , can e a s i l y be l o s t o r s t o l e n . T h i s emphasises the i n s e c u r i t y common to means of i d e n t i f i c a t i o n t h a t are not a permanent p a r t of the pers o n . In another c o n s i d e r a t i o n , v e r y s o p h i s t i c a t e d h i g h - t e c h n o l o g y systems f o r defence and o f f e n c e have been developed. In o r d e r to m a i n t a i n t h e i r i n t e g r i t y , h i g h l y r e l i a b l e schemes f o r v e r i f y i n g the i d e n t i t y o f p e r s o n n e l employed i n the development and maintenance o f such systems are mandatory. With human v e r i f i e r s , a g a i n the h i g h e s t l e v e l o f s e c u r i t y i s a c h i e v e d when the v e r i f i e r s are p e r s o n a l l y a c q u a i n t e d w i t h the p e r s o n n e l . However, i n h i g h - r i s k s i t u a t i o n s l i k e t h e s e , t h i s alone i s u s u a l l y not enough, s i n c e a human v e r i f i e r can l i e and undermine the s e c u r i t y o f the system. Hence, a scheme w i t h p r e d i c t a b l e and c o n t r o l l a b l e r e l i a b i l i t y i s to be f a v o u r e d . The developments i n d i c a t e d above, and the r e s e a r c h b r i e f l y r e v i e w e d b e f o r e c o n f i r m t h a t t h e r e i s a d e f i n i t e need f o r a c o m m e r c i a l l y v i a b l e product' f o r automated i d e n t i t y v e r i f i c a t i o n . The d e s i g n o f such a system has t o be c o m p e t i t i v e i n terms of the s e r v i c e i t b r i n g s t o r e p l a c e the human v e r i f i c a t i o n f u n c t i o n . I t s main t a r g e t s h o u l d be the p o t e n t i a l f o r widespr e a d a p p l i c a t i o n . I t s h o u l d be p o s s i b l e t o adapt i t f o r - 14 -use i n e v e r y s i t u a t i o n where a human v e r i f i e r would be used. The c o s t of i n s t a l l a t i o n , use, and maintenance s h o u l d make i t a more a t t r a c t i v e i n v e s t m e n t than the employment of a human v e r i f i e r . A f t e r s t u d y i n g the systems r e p o r t e d i n [MAUC65], [STER75], [HERB77], [CRAN78], [ L I U . 7 9 ] , i t was c l e a r t h a t t h e y would not meet th e above o b j e c t i v e s . Many of the systems have been d e s i g n e d and implemented on l a r g e mainframe computers. The one t h a t has been implemented on a s m a l l machine [STER75], uses much l e s s i n f o r m a t i o n than i s a c t u a l l y a v a i l a b l e . T h i s r e n d e r s i t prone to h i g h e r e r r o r s than n e c e s s a r y . F u r t h e r m o r e , the i n t e r f a c e s i n most cases have been more c o m p l i c a t e d and cumbersome than c o u l d have been r e a l i s e d . T h e i r a c c e p t a b i l i t y as l o g i c a l s u b s t i t u t e s f o r human v e r i f i e r s i s t h e r e f o r e q u i t e 1 i m i t e d . The above c o n s i d e r a t i o n s f u r t h e r prompted the i n i t i a t i o n o f the p r e s e n t r e s e a r c h , w i t h the o b j e c t i v e s d i s c u s s e d below. - 15 -0.4 The O b j e c t i v e s of T h i s Work. The u l t i m a t e o b j e c t i v e o f the r e s e a r c h r e p o r t e d here i s the development of a compact and r o b u s t r e a l - t i m e s i g n a t u r e v e r i f i c a t i o n system f o r i d e n t i t y a u t h e n t i c a t i o n . The system/user i n t e r f a c e i s r e q u i r e d to be v e r y s i m p l e , as i s the r e g i s t r a t i o n and subsequent v e r i f i c a t i o n p r o t o c o l . The above g o a l s r e q u i r e the i n v e s t i g a t i o n of s e v e r a l areas : ( i ) The s e l e c t i o n o f f e a t u r e s to be observed. ( i i ) The a c q u i s i t i o n of a s u i t a b l e h a n d w r i t i n g t r a n s d u c e r to f a c i l i t a t e the the d e t e r m i n a t i o n of the s e l e c t e d f e a t u r e s . ( i i i ) The d e s i g n of the r e f e r e n c e s to be used i n v e r i f i c a t i o n . ( i v ) The p r i n c i p l e and d e s i g n o f the comparison a l g o r i t h m which d e t e r m i n e s the degree o f s i m i l a r i t y between h a n d w r i t i n g samples and/or t h e i r r e p r e s e n t a t i o n s and the c o r r e s p o n d i n g r e f e r e n c e s ( i i i ) . The e x t e n t t o which the work done f o r t h i s t h e s i s addressed the above i s s u e s i s summarised i n s e c t i o n 0.5, which comes ne x t . - 16 -0.5 The Scope o f T h i s T h e s i s . For t h i s t h e s i s , methods of data a c q u i s i t i o n , f e a t u r e s of the data a c q u i r e d and methods of e x t r a c t i n g these f e a t u r e s from the d a t a were i n v e s t i g a t e d . The breakdown o f the r e p o r t by c h a p t e r i s d e s c r i b e d i n the f o l l o w i n g p a ragraphs. Chapter 1 d e s c r i b e s the data a c q u i s i t i o n as performed by p r e v i o u s workers i n the f i e l d . I t co n c l u d e s w i t h a statement of the s i g n a t u r e v a r i a b l e s s e l e c t e d f o r measurement i n t h i s s t u d y . Chapter 2 i s concerned w i t h the p h y s i c a l r e a l i s a t i o n 'of the da t a a c q u i s i t i o n f u n c t i o n . I t c o n t a i n s as i t s major p a r t the performance e v a l u a t i o n o f the t r a n s d u c e r used i n t h i s r e s e a r c h . I t a l s o g i v e s a b r i e f c o n s i d e r a t i o n o f the adequacy of the t r a n s d u c e r f o r the a p p l i c a t i o n . In Chapter 3, t h e use of h a n d w r i t t e n s i g n a t u r e dynamics f o r i d e n t i t y v e r i f i c a t i o n i s d e t a i l e d . An i d e n t i t y v e r i f i c a t i o n experiment which was performed f o r t h i s work i s a l s o d e s c r i b e d and the r e s u l t s t h e r e o f are p r e s e n t e d . The l a s t c h a p t e r , Chapter 4, c o n t a i n s a summary of the c o n t r i b u t i o n s of t h i s s t u d y , and the work t h a t remains to be done i n o r d e r to r e a l i s e the u l t i m a t e g o a l s of the s i g n a t u r e a n a l y s i s p r o j e c t . Appendix A c o n t a i n s d e t a i l e d r e s u l t s and a d e s c r i p t i o n o f the programmes used i n the data a c q u i s i t i o n and p r o c e s s i n g r o u t i n e s . Appendix B c o n t a i n s a d e s c r i p t i o n o f the p r i n c i p l e o f o p e r a t i o n o f the t r a n s d u c e r developed by the a u t h o r f o r t h i s r e s e a r c h . I t a l s o c o n t a i n s a d e s c r i p t i o n of the i m p l e m e n t a t i o n - 17 -a c t u a l l y used i n the e x p e r i m e n t s . - 18 -1 . THE ACQUISITION OF HANDWRITING DATA. In o r d e r t o observe i d e n t i f y i n g c h a r a c t e r i s t i c s of a person or o b j e c t , one must choose the c h a r a c t e r i s t i c s b eforehand. I f some o f them are not d i r e c t l y o b s e r v a b l e , i t i s a l s o n e c e s s a r y to determine the o b s e r v a b l e f e a t u r e s of the person or o b j e c t from which the r e q u i r e d c h a r a c t e r i s t i c s can be det e r m i n e d . I t w i l l be noted t h a t human v e r i f i e r s do not have the freedom of s p e c i f y i n g the c h a r a c t e r i s t i c s which t h e y use. The ones they can observe are p r e - s p e c i f i e d by the o b s e r v a t i o n t o o l s a v a i l a b l e to them, t h a t i s , t h e i r s e nses. For t h e automated systems i n which there i s . a c h o i c e , once the c h o i c e has been made, the r e q u i s i t e means of o b s e r v a t i o n or measurement have t o be developed and/or c o n s t r u c t e d . The c h a r a c t e r i s t i c s which v a r i o u s r e s e a r c h e r s have used f o r s t u d y i n g h a n d w r i t i n g dynamics are summarised i n the f o l l o w i n g . A s e t of p o s s i b l e measures f o r the h a n d w r i t t e n s i g n a t u r e i s g i v e n , t o g e t h e r w i t h the subset s e l e c t e d f o r t h i s s t u d y . In a d d i t i o n , a s u r v e y o f the t r a n s d u c e r s used i n the v a r i o u s s t u d i e s i s p r e s e n t e d . - 19 -1.1 H a n d w r i t i n g V a r i a b l e s . R e s e a r c h e r s o b s e r v i n g h a n d w r i t i n g dynamics both f o r the b a s i c a n a l y s i s of h a n d w r i t i n g and f o r s i g n a t u r e v e r i f i c a t i o n have i n v e s t i g a t e d v a r i o u s c o m b i n a t i o n s of the measurable h a n d w r i t i n g v a r i a b l e s . These are c o n s i d e r e d i n the next two s e c t i o n s . The t r a n s d u c e r s developed f o r measuring them are reviewed i n s e c t i o n 1.2. 1.1.1 V a r i a b l e s used i n b a s i c h a n d w r i t i n g r e s e a r c h . T r i p p et a l . [TRIP57] f i r s t performed some i n v e s t i g a t i o n o f the v a r i o u s f o r c e - s i g n a l s a p p l i e d t o the h a n d w r i t i n g system ( i n s t r u m e n t and s u r f a c e ) . A f t e r t h i s , they s e t t l e d on m o n i t o r i n g the f o r c e a p p l i e d p e r p e n d i c u l a r to the s h a f t of the w r i t i n g i n s t r u m e n t , i n a plane a p p r o x i m a t e l y normal t o the w r i t i n g s u r f a c e . D e n i e r van der Gon and T h u r i n g [DENI65] r e c o r d e d the w r i t t e n t r a c e on paper, i n a form which made p o s s i b l e the c a l c u l a t i o n of the r a t e o f motion o f the w r i t i n g i n s t r u m e n t a l o n g i t . The computed v a r i a b l e s i n c l u d e d the speed and a c c e l e r a t i o n o f the p e n - p o i n t a l o n g the t r a c k of the w r i t i n g . One o f the r e s u l t s t h e y r e p o r t e d was t h a t t h e r e was evidence t o r e s o l v e t h e w r i t i n g movement i n t o two n e a r l y o r t h o g o n a l d i r e c t i o n s . T h i s i d e a has s i n c e c a r r i e d o v er to most o t h e r h a n d w r i t i n g r e s e a r c h . F o l l o w i n g D e n i e r van der Gon and Th u r i n g [DENI65] above, MacDonald [MACD66] b u i l t b o th a h a n d w r i t i n g a n a l y s e r and an e l e c t r o n i c s i m u l a t o r f o r g e n e r a t i n g a r t i f i c i a l s c r i p t i n o r d e r to t e s t the v a l i d i t y of the model o f D e n i e r van der Gon e t a l . - 20 -[DENI62], The system measured the x and y components of the d i s p l a c e m e n t of the w r i t i n g i n s t r u m e n t from the c e n t r e . Each of these components was then p r o c e s s e d t o determine the c o r r e s p o n d i n g a c c e l e r a t i o n and v e l o c i t y u s i n g l o w - f r e q u e n c y (up t o 100 Hz) d i f f e r e n t i a t o r s and f i l t e r s . The r e s u l t s t h e r e o f were reco r d e d f o r f u r t h e r p r o c e s s i n g and a n a l y s i s . L a t e r , McDonald [MCD070] extended the above work [MACD66], by d e s i g n i n g a more r e f i n e d mechanical model and a l s o s i m u l a t i n g i t e l e c t r o n i c a l l y . In t h i s work, comparison o f the model responses t o known p h y s i o l o g i c a l phenomena was a l s o c a r r i e d out. The a n a l y s e r used i n [MCD070] was e s s e n t i a l l y the same as t h a t used i n [MACD66]. A system i n which d i s p l a c e m e n t s i n o n l y one d i r e c t i o n -p e r p e n d i c u l a r to the o v e r a l l d i r e c t i o n of motion - were r e c o r d e d was implemented by Vredenbregt and K o s t e r [VRED71]. These s i g n a l s were used i n the v a l i d a t i o n o f t h e i r model of h a n d w r i t i n g as a r e s u l t of the i n t e r a c t i o n o f ' a g o n i s t ' and ' a n t a g o n i s t ' muscle- p a i r s . An e l e c t r o m e c h a n i c a l analogue o f the model was c o n s t r u c t e d t o s y n t h e s i z e s c r i p t . The model used e l e c t r i c motors t o s i m u l a t e muscle a c t i o n . I t was t h e r e f o r e found n e c e s s a r y t o d e t e r m i n e the n a t u r e of the e x c i t a t i o n s i g n a l t o be used i n d r i v i n g them. F o r t h i s purpose, electromyogram (EMG) r e c o r d i n g s of the human ( e x t e n s o r and f l e x o r [DENI65]) muscle a c t i v i t y d u r i n g w r i t i n g were made. The use o f EMGs to m o n i t o r muscular a c t i v i t y d u r i n g w r i t i n g was a l s o r e p o r t e d by Yasuhara [YASU7 1]. I n h i s work, an even g r e a t e r v a r i e t y o f measurements were made than i n p r e v i o u s - 21 -i-esearch. The (x - y) p o s i t i o n c o - o r d i n a t e s and the downward w r i t i n g f o r c e ("pressure") were measured. 1.1.2 Waveform parameters used f o r s i g n a t u r e v e r i f i c a t i o n . I n [MAUC65], the a c c e l e r a t i o n o f the hand/pen mass system p a r a l l e l t o the o v e r a l l d i r e c t i o n of w r i t i n g was measured. In a d d i t i o n , a pen-paper c o n t a c t s i g n a l was recorded as a b i n a r y (ON/OFF) waveform. At S y l v a n i a E l e c t r o n i c Systems [DYCH??], a "data t a b l e t " was used t o r e c o r d p o s i t i o n i n o r t h o g o n a l c o - o r d i n a t e s . The o t h e r v a r i a b l e s were: the d u r a t i o n of the s i g n a t u r e and the d u r a t i o n s o f the pen-up and pen-down i n t e r v a l s . I n the V e r i p e n , Inc. SIGNAC system [STER75], o n l y " p r e s s u r e " i n f o r m a t i o n was used. The a x i a l f o r c e on the w r i t i n g i n s t r u m e n t was the one chosen. I t i s i n t e r e s t i n g t o note t h a t i n e a r l i e r r e s e a r c h , T r i p p e t . a l . [ T R I P 5 7 ] , had deemed t h i s p a r t i c u l a r s i g n a l l e s s i n f o r m a t i v e than the f o r c e p e r p e n d i c u l a r to the s h a f t of the p e n ( c i l ) i n a plane normal to the w r i t i n g s u r f a c e as used i n t h e i r system. They a l s o c o n s i d e r e d i t not as i n t e r e s t i n g as the f o r c e normal to the w r i t i n g s u r f a c e - as measured, f o r example, i n [ YASU71 ] - when used as the s o l e data sour ce . IBM r e s e a r c h e r s m o n i t o r e d a c c e l e r a t i o n i n two o r t h o g o n a l d i r e c t i o n s [HERB77]• They a l s o r e c o r d e d the " p e n - l i f t p a t t e r n " ( c f . [MAUC65] , [DYCH??]). L a t e r , a mechanism f o r measuring the a x i a l w r i t i n g f o r c e was added [ L I U . 7 9 ] , S t a n f o r d Research I n s t i t u t e workers [CRAN78] measured drag f o r c e s i n v a r i o u s d i r e c t i o n s at the pen t i p . These f o r c e s were - 22 -r e s o l v e d i n t o t h r e e o r t h o g o n a l components: 'x' and 'y' c o n t r i b u t i n g t o motion i n the plane o f the paper, and ' z ' t o the net f o r c e normal to the w r i t i n g p l a n e . The above r e s e a r c h e r s were a l l concerned w i t h measures f o r machine-based d e c i s i o n a l g o r i t h m s f o r a u t o m a t i c s i g n a t u r e v e r i f i c a t i o n . However, t h a t i s not a l l t h a t has been done. Another experiment i n which the measurements were made by machine f o r a human v e r i f i e r t o use i n a v i s u a l comparison has been r e p o r t e d i n [SAKA??]. The system measured the p o s i t i o n of the w r i t i n g i n s t r u m e n t on, and t o a c e r t a i n e x t e n t , o f f the w r i t i n g s u r f a c e . - 2 3 -1.2 T r a n s d u c e r s f o r H a n d w r i t i n g Measurement. The d e t e r m i n a t i o n of the v a r i a b l e s mentioned above depended upon the a v a i l a b i l i t y of a s u i t a b l e t r a n s d u c e r , o r the f e a s i b i l i t y of i t s c o n s t r u c t i o n . The d e v i c e s developed and used by the above mentioned r e s e a r c h e r s are d e t a i l e d below. 1.2.1 Tranducers f o r b a s i c h a n d w r i t i n g r e s e a r c h . In t h e [TRIP57] system, a mechanical p e n c i l was m o d i f i e d by the a d d i t i o n o f a s u p p o r t i n g b r a c k e t at the t i p . S t r a i n gauges mounted on the b r a c k e t were used t o measure the a p p l i e d s t r e s s from the f l e x u r e which t h e b r a c k e t underwent d u r i n g w r i t i n g . The i n s t r u m e n t a t i o n i n [DENI65] c o n s i s t e d o f an i r o n t a b l e c o v e r e d w i t h T e l e d e l t h o s paper, an i r o n pen and a p u l s e s i g n a l g e n e r a t o r . The T e l e d e l t h o s paper had the p r o p e r t y o f changing c o l o u r at a p o i n t where c u r r e n t f l o w e d through i t . The pen and t a b l e were w i r e d t o g e t h e r i n t o a c i r c u i t e x c i t e d by the s i g n a l g e n e r a t o r . The pen a l s o had a w i r e wound around i t so t h a t i t c o u l d be made p a r t of an e l e c t r o - m a g n e t i c c i r c u i t i n o r d e r to study the e f f e c t of i n c r e a s e d f r i c t i o n on n a t u r a l w r i t i n g . By u s i n g the p u l s e - t r a i n e x c i t a t i o n f o r the p e n - t a b l e c i r c u i t , the path of the w r i t i n g i n s t r u m e n t a c r o s s the paper would be t r a c e d out i n d o t s . From the r e s u l t i n g t r a c e and the known p u l s e f r e q u e n c y , i t was p o s s i b l e to compute the v e l o c i t i e s and a c c e l e r a t i o n s a l o n g the l i n e o f s c r i p t by s i m p l y measuring the d i s t a n c e s between d o t s . The r e s e a r c h e r s a l s o mention the c o n s t r u c t i o n o f a h a n d w r i t i n g s i m u l a t o r embodying r e s u l t s o f t h e i r i n v e s t i g a t i o n . T h i s s i m u l a t o r was the s t a r t i n g p o i n t of - 24 -[ M A C D 6 6 ] . The a n a l y s e r i n [ M A C D 6 6 ] comprised a d i s p l a c e m e n t t r a n s d u c e r and a system of f i l t e r s and d i f f e r e n t i a t o r s t o d e r i v e v e l o c i t y and a c c e l e r a t i o n s i g n a l s . There were a l s o f a c i l i t i e s f o r v i s u a l m o n i t o r i n g and r e c o r d i n g of the v a r i o u s s i g n a l s . The p o s i t i o n t r a n s d u c e r o p e r a t e d on the c u r r e n t - d i v i d e r p r i n c i p l e , u s i n g an e l e c t r o l y t i c tank w i t h f o u r e l e c t r o d e s f o r m i n g the s i d e w a l l s . The w r i t i n g p e n c i l was made of c o n d u c t i v e m a t e r i a l and was c o nnected t o a c u r r e n t s o u r c e . D i s p l a c e m e n t s from the c e n t r e i n two o r t h o g o n a l d i r e c t i o n s (as d e f i n e d by the w a l l s of the tank) c o u l d then be o b t a i n e d by s i m p l y s u b t r a c t i n g the c u r r e n t s r e a c h i n g o p p o s i n g p a i r s of e l e c t r o d e s . Thus, any motion of the w r i t i n g i n s t r u m e n t would i m m e d i a t e l y be r e s o l v e d i n t o o r t h o g o n a l (x - y) components. In the system of Vredenbregt and K o s t e r [VRED71], a l i g h t p i s t o n had i t s ' s m a l l end' a t t a c h e d to the w r i t i n g i n s t r u m e n t and i t s ' b i g end' s u p p o r t e d by a p a i r o f ( l i g h t ) l e a f s p r i n g s . These s p r i n g s would d e f l e c t to a g r e a t e r or l e s s e r e x t e n t , depending on the d i s p l a c e m e n t of the p i s t o n a l o n g i t s a x i s . S t r a i n gauges mounted on the s p r i n g s p r o v i d e d the means f o r o b t a i n i n g e l e c t r i c a l analogues of the motion. I n [YASU7 1 ] , t h e x - y p o s i t i o n o f the s t y l u s was d etermined u s i n g the v o l t a g e - d i v i d e r p r i n c i p l e . T h e t r a n s d u c e r s u r f a c e c o n s i s t e d o f a u n i f o r m , square p l a t e of r e s i s t i v e m a t e r i a l w i t h c o n t a c t s a l o n g a l l f o u r s i d e s . The c o n d u c t i v e w r i t i n g s t y l u s a c t e d as the s l i d e r on a v a r i a b l e p o t e n t i o m e t e r . T h i s enabled the d e t e c t i o n o f t h e p o s i t i o n from the p o t e n t i a l at the s t y l u s . - 25 -The c i r c u i t s e t - u p was such t h a t c u r r e n t c o u l d f l o w i n o n l y one o f two p e r p e n d i c u l a r d i r e c t i o n s at a t i m e . By a l t e r n a t e l y s w i t c h i n g the c u r r e n t f l o w from a l o n g the 'X' a x i s t o a l o n g the 'Y' a x i s , b oth c o - o r d i n a t e s were determined i n a m u l t i p l e x e d f a s h i o n . The "pressure'' was o b t a i n e d from f o u r p r e s s u r e t r a n s d u c e r s mounted i n the s u p p o r t s on the c o r n e r s of the w r i t i n g p l a t e . These f o u r s i g n a l s were " c o r r e l a t e d " t o determine the a c t u a l f o r c e s i g n a l . 1.2.2 T r a n s d u c e r s used f o r measuring s i g n a t u r e v a r i a b l e s . The t r a n s d u c e r s developed f o r s i g n a t u r e a n a l y s i s r e s e a r c h have been v a r i e d i n n a t u r e , and o f t e n q u i t e d i f f e r e n t from those developed f o r b a s i c h a n d w r i t i n g r e s e a r c h . B r i e f s k e t c h e s of some o f the t r a n s d u c e r s r e p o r t e d i n the l i t e r a t u r e f o l l o w now. Mauceri [MAUC65], used an a c c e l e r o m e t e r a t t a c h e d t o the body of the pen to measure the a c c e l e r a t i o n . The pen-paper c o n t a c t s i g n a l was o b t a i n e d by w r i t i n g on c o n d u c t i v e T e l e d e l t h o s paper and u s i n g the metal core of the pen as p a r t of a c i r c u i t . The c o n t a c t between the paper and the pen c o r e completed the c i r c u i t , g i v i n g the r e q u i r e d s i g n a l . In [DYCH??], a t a b l e t w i t h a w i r e g r i d i n i t was used. The pen used w i t h i t had a c o i l o f w i r e i n i t so t h a t v a r y i n g c u r r e n t s through i t c o u l d be e l e c t r o m a g n e t i c a l 1 y coupled t o the t a b l e t i f they were c l o s e enough. T h i s a l l o w e d the d e t e r m i n a t i o n o f the pen p o s i t i o n by p u l s i n g c u r r e n t through s u c c e s s i v e g r i d elements to determine the c r o s s e d p a i r y i e l d i n g the l a r g e s t o u t p u t from the pen. T h i s p a i r then c o n s t i t u t e d the c o - o r d i n a t e s of the p o i n t . The r e s t of the parameters were - 26 -c a l c u l a t e d from t h i s p o s i t i o n i n f o r m a t i o n . S t e r n b e r g [STER75], b u i l t a p r e s s u r e t r a n s d u c e r i n t o an e s s e n t i a l l y o r d i n a r y b a l l - p o i n t pen i n such a way t h a t the r e f i l l was i n c o n t a c t w i t h i t . Any f o r c e a p p l i e d t o the pen t i p would then be t r a n s m i t t e d through the r e f i l l t o the t r a n s d u c e r and a p r o p o r t i o n a t e s i g n a l o b t a i n e d . The pen developed i n [HERB77] had two a c c e l e r o m e t e r s mounted i n i t f o r the d e t e r m i n a t i o n o f o r t h o g o n a l components o f the o v e r a l l pen a c c e l e r a t i o n . A p r e s s u r e a c t i v a t e d s w i t c h was used to g e n e rate the pen-paper c o n t a c t s i g n a l which they a l s o measured. T h i s s w i t c h was c l o s e d by the a p p l i c a t i o n o f a f o r c e g r e a t e r than 3 0 grammes t o the pen t i p . 'When th e y l a t e r i n c o r p o r a t e d a f o r c e s e n s o r i n t h e i r pen [USP7 8b],, [ L I U . 7 9 ] , i t c o n s i s t e d of adding a h i n g e - l i k e s u p p o r t f o r the r e f i l l so t h a t any f o r c e e x e r t e d on the pen t i p would s t r e s s t h i s hinge and a c t i v a t e the s t r a i n gauges mounted on i t . The " p r e s s u r e " s i g n a l was then o b t a i n e d from the s t r a i n gauges. The SRI pen [CRAN78], [USP78c], had an a r r a y of s t r a i n gauges mounted a t the t i p . T h i s a l l o w e d the measurement of the dr a g f o r c e s i n v a r i o u s d i r e c t i o n s . The g r a p h i c t a b l e t used by S a k a i e t . a l . [SAKA??] was s i m i l a r to the one used by Dyche [DYCH??]. However, the pen l o c a t i o n was mon i t o r e d u s i n g s o n i c p u l s e s . These a l l o w e d the p o s i t i o n o f the pen to be f o l l o w e d even when the pen was o f f the page. Thus, i t had the p o t e n t i a l o f r e c o r d i n g t h r e e - d i m e n s i o n a l space motion. - 27 -1.3 Parameters of H a n d w r i t i n g . I n o r d e r t o det e r m i n e the parameters of the h a n d w r i t i n g system t h a t are o b s e r v a b l e , i t i s n e c e s s a r y t o c o n s i d e r the p h y s i c a l a s p e c t s of h a n d w r i t i n g . Through t h i s , v a r i o u s p h y s i c a l / p h y s i o l o g i c a l models can a l s o be reviewed f o r the i n f o r m a t i o n t hey can p r o v i d e . F i g . 2 i s a s k e t c h of a t y p i c a l hand/pen w r i t i n g s e t u p . Some o f the f o r c e s which are generated by the body and t r a n s m i t t e d through the hand are a l s o i n d i c a t e d . F o r c e s F1 through F3 are the g r i p f o r c e s which ensure t h a t p r e s s u r e from the w r i s t can be e x e r t e d onto the w r i t i n g s u r f a c e v i a the p e n ( c i l ) . M i s the w r i s t moment which r e s u l t s i n a f o r c e being e x e r t e d through the w r i t i n g i n s t r u m e n t onto the w r i t i n g s u r f a c e . T h i s f o r c e i s g e n e r a l l y e s s e n t i a l to the p r o d u c t i o n of a v i s i b l e w r i t t e n t r a c e . Rk i s the k n u c k l e r e a c t i o n r e q u i r e d t o bal a n c e out t h e ( s t a t i c ) r e s u l t a n t of the non-coplanar f o r c e s F1 through F3. In F i g . 3, t h e r e a c t i o n s i n the w r i t i n g plane t o the f o r c e s F1 through F3 and the moment M are i n d i c a t e d . The i n d i c a t e d d i r e c t i o n o f the r e a c t i o n s assumes t h a t the pen i s moving i n the p o s i t i v e 'x' and 'y' d i r e c t i o n s . The f r i c t i o n f o r c e s f x and f^ are l i n e a r l y r e l a t e d t o the normal r e a c t i o n F s . The r e a c t i o n F z , t o g e t h e r w i t h the v e r t i c a l a c c e l e r a t i o n r e a c t i o n mz, are due t o M. (The component mz i s v i r t u a l l y zero as l o n g as the pen i s on the paper.) The (dynamic) v e r t i c a l component of the m o d u l a t i o n s on F 1 , F2 and F3 d u r i n g w r i t i n g f u r t h e r c o n t r i b u t e s t o these r e a c t i o n s . The m o d u l a t i o n s mentioned here are the v a r i a t i o n s i n - 28 -F 1 , F2 and F3 t h a t are a c t u a l l y used f o r g e n e r a t i n g the w r i t t e n t r a c e . Thus, the a c c e l e r a t i o n r e a c t i o n s rax and ray ( o r j u s t ms al o n g the d i r e c t i o n o f motion) c o n s t i t u t e the r e a c t i o n s t o the h o r i z o n t a l component of the dynamic r e s u l t a n t of F1, F2 and F3, l e s s the f r i c t i o n a l l o s s e s . (Rk b a l a n c e s out the s t a t i c r e s u l t a n t as mentioned b e f o r e . ) I f t h ey were e a s i l y a c c e s s i b l e , f o r c e s F1 - F3 and moment M would be measured t o p r o v i d e a r e a s o n a b l y complete d e s c r i p t i o n o f the w r i t i n g p r o c e s s . I t i s , however, q u i t e d i f f i c u l t t o t r a n s d u c e them w i t h a s i m p l e i n s t r u m e n t . I n s t e a d , we l o o k at the r e a c t i o n s of t h e hand-pen-paper system t o the s e i n p u t s as shown i n F i g . 3- The r e a c t i o n s here account f o r the motion of the w r i t i n g system and the a t t e n d a n t f o r c e on the w r i t i n g s u r f a c e . I n t h i s , t h e y p r o v i d e us w i t h most of the measurable i n f o r m a t i o n a v a i l a b l e . The m i s s i n g r e a c t i o n i s Rk, the support f o r c e on the hand a t the j u n c t i o n o f the thumb and f o r e f i n g e r . However t h a t would be d i f f i c u l t t o measure i n d e e d . The measurement of the a c t u a l p o s i t i o n a l i n f o r m a t i o n i s d e s i r a b l e so t h a t c h a r a c t e r i s t i c s of the si g n e d word can a l s o p l a y a r o l e i n d e c i s i o n making. Thus, a l i s t o f the b a s i c v a r i a b l e s t o be measured can be made up as f o l l o w s : - 29 -a : - Side view. b :- View from X, along pencil axis . Fig. 2: Some of the active forces in handwriting. - 30 -y f y + my fx • mx F, • mz Fig. 3: Reactions in the writing plane to the inputs of . Fig. 2. - 31 -- P o s i t i o n a l i n f o r m a t i o n i n , say, o r t h o g o n a l c o - o r d i n a t e s . - W r i t i n g f o r c e i n f o r m a t i o n . - G r i p p i n g f o r c e i n f o r m a t i o n . - I n s t a n t a n e o u s speed and a c c e l e r a t i o n . The subset of these v a r i a b l e s which were s e l e c t e d f o r measurement i n t h i s r e s e a r c h i s d e t a i l e d i n the f o l l o w i n g s e c t i o n . - 3 2 -1.4 S e l e c t i o n o f the V a r i a b l e s Used i n t h i s Work. The measurement of a l l the b a s i c v a r i a b l e s mentioned above would be d e s i r a b l e , s i n c e we would t h e r e b y use almost a l l the a v a i l a b l e and measurable i n f o r m a t i o n . However, f o r v a r i o u s r e a s o n s , i t i s not f e a s i b l e to measure a l l those v a r i a b l e s . The g r i p p i n g f o r c e i s d i f f i c u l t t o measure w i t h o u t r e c o u r s e to a s p e c i a l pen w i t h r a t h e r severe c o n s t r a i n t s on i t s h a n d l i n g . We d e c i d e d t o do w i t h o u t i t f o r reasons of p r a c t i c a l i t y w i t h i n the d e s i g n g o a l s of a s i m p l e i n t e r f a c e . The i n s t a n t a n e o u s speed and a c c e l e r a t i o n would a l s o r e q u i r e r a t h e r e l a b o r a t e i n s t r u m e n t a t i o n i f measured d i r e c t l y . However, they can be computed from the p o s i t i o n i n f o r m a t i o n . T h i s c o u l d be done by r e a l - t i m e s o f t w a r e . With those c o n s i d e r a t i o n s , the f o l l o w i n g v a r i a b l e s were s e l e c t e d f o r measurement : ( i ) The p o s i t i o n o f the p e n - p o i n t i n o r t h o g o n a l c o - o r d i n a t e s . ( i i ) The normal f o r c e e x e r t e d on the w r i t i n g s u r f a c e . In a d d i t i o n to measuring the named v a r i a b l e s , the d a t a a c q u i s i t i o n system s h o u l d p r e s e n t as s i m p l e an i n t e r f a c e to the u s e r as p o s s i b l e . I d e a l l y , t h e r e s h o u l d be no d i f f e r e n c e between the w r i t i n g c o n d i t i o n s f o r t h i s d a t a a c q u i s i t i o n and the u s u a l c o n d i t i o n s f o r w r i t i n g a s i g n a t u r e . Because of the l i m i t a t i o n s i n the s e n s i t i v i t y o f p r a c t i c a l d e v i c e s , however, a s m a l l number of r e a s o n a b l e c o n s t r a i n t s may be imposed on the u s e r . W i t h i n the framework of the above c o n s i d e r a t i o n s , a d a t a a c q u i s i t i o n - 3 3 -system was o b t a i n e d f o r the s i g n a t u r e v e r i f i c a t i o n setup s t u d i e d i n t h i s t h e s i s . I n i t i a l l y , a c o m m e r c i a l l y a v a i l a b l e g r a p h i c s t a b l e t (Computek GT50/10) was s e l e c t e d f o r the measurement of the 'x' and 'y'. The pen f o r i t was m o d i f i e d w i t h a f o r c e t r a n s d u c e r f o r measuring the f o r c e . Because of the l i m i t a t i o n s of the pen, and the d i f f i c u l t i e s i n t r a n s d u c i n g normal f o r c e , the system was r e j e c t e d . I n s t e a d , a new approach was t a k e n i n measuring 'x', 'y' and f o r c e ('p'). The development of t h i s new t r a n s d u c e r system, a l t h o u g h p a r t of the o v e r a l l r e a s e a r c h p r o j e c t , i s not c l a i m e d as p a r t of t h i s t h e s i s r e s e a r c h . (A p a t e n t f o r the d e v i c e i s c u r r e n t l y being sought.) The d e v i c e was however e v a l u a t e d i n terms of both i t s p r a c t i c a l and a e s t h e t i c adequacy f o r the p r o j e c t , and t h i s e v a l u a t i o n appears i n the next c h a p t e r . - 34 -2. LABORATORY EVALUATION OF THE TRANSDUCER SYSTEM. The h a n d w r i t i n g d a t a a c q u i s i t i o n a pparatus as des i g n e d and c o n s t r u c t e d f o r t h i s s t u d y p r o v i d e d s i g n a l s i n d i c a t i n g the 'x' and 'y' c o - o r d i n a t e s of p o s i t i o n o f a p o i n t l o a d ( t h e t i p of the w r i t i n g i n s t r u m e n t ) a p p l i e d t o the w r i t i n g s u r f a c e . In a d d i t i o n , the a p p a r a t u s p r o v i d e d the magnitude of the downward f o r c e a p p l i ed. O p e r a t i o n a l l y , the a p p a r a t u s had the f o l l o w i n g f e a t u r e s : ( i ) The i n t e r f a c e w i t h the user was j u s t an o r d i n a r y w r i t i n g s u r f a c e on which paper c o u l d be p l a c e d i n o r d e r to o b t a i n a r e c o r d o f what was w r i t t e n . T h i s paper was, however, not e s s e n t i a l t o i t s o p e r a t i o n . ( i i ) There was no requirement f o r a s p e c i a l pen. An o r d i n a r y b a l l - p o i n t pen or p e n c i l c o u l d be used. In a d d i t i o n , a n y t h i n g w i t h a r e a s o n a b l y s m a l l t i p through which a f o r c e o f up to 1 Kg. c o u l d be a p p l i e d was u s a b l e . The d e v i c e was e v a l u a t e d b o t h q u a l i t a t i v e l y and q u a n t i t a t i v e l y . The proce d u r e f o r the q u a n t i t a t i v e assessment i s g i v e n the next two s e c t i o n s . The q u a l i t a t i v e assessment and the r e s u l t s o f the q u a n t i t a t i v e e v a l u a t i o n are p r e s e n t e d t h e r e a f t e r . - 35 -2 . 1 L a b o r a t o r y s e t u p f o r the e v a l u a t i o n . The s e t u p i n the l a b o r a t o r y i s i n d i c a t e d i n F i g . 4. The components were: 1. Data General NOVA 840 minicomputer w i t h V e r s i o n 6.2 RDOS ( R e a l - t i m e D i s k O p e r a t i n g System). 2. A n a l o g u e - t o - d i g i t a l (A/D), d i g i t a l - t o - a n a l o g u e (D/A) c o n v e r s i o n subsystem. The A/D f u n c t i o n was r e a l i z e d from an A n a l o g i c MP6912 16-channel Data A c q u i s i t i o n System. The D/A c o n v e r t e r s were a l s o A n a l o g i c components. 3 . T r a n s d u c e r f r o n t end i n containment box w i t h a w r i t i n g window. 4. Transducer A m p l i f i e r s . 5. T e k t r o n i x 4010-1 g r a p h i c s t e r m i n a l p r o v i d i n g a c o n t r o l keyboard and an a l p h a n u m e r i c / g r a p h i c CRT m o n i t o r . The t r a n s d u c e r was connected t o the computer through the a n a l o g u e - t o - d i g i t a l c o n v e r t e r . T h i s c o n v e r t e r sampled and co n v e r t e d the t r a n s d u c e r o u t p u t s on command from the computer. The c o n v e r t e d v a l u e s were then read i n t o the computer memory and e v e n t u a l l y s t o r e d i n a d i s k f i l e which was l a t e r used by the dat a p r o c e s s i n g programmes. The a c t u a l e x p e r i m e n t a l procedure i s d e s c r i b e d i n s e c t i o n 2.2 and i t s s u b s e c t i o n s . The e x p e r i m e n t a l r e s u l t s are a l s o i n c l u d e d t h e r e i n . - 37 -2.2 E v a l u a t i o n of the t r a n s d u c e r system. The performance of t h e p r o t o t y p e a p p a r a t u s was e v a l u a t e d i n terms of l i n e a r i t y , dynamic range and s i g n a l - t o - n o i s e r a t i o . The procedures f o l l o w e d i n d e t e r m i n i n g these performance c r i t e r i a are d e s c r i b e d i n the next s u b s e c t i o n . These e v a l u a t i o n s were performed on each of the d e v i c e o u t p u t s , t h a t i s , the two p o s i t i o n c o - o r d i n a t e s and the a p p l i e d f o r c e . The r e l a t i v e o r t h o g o n a l i t y of each d e v i c e output w i t h r e s p e c t t o the o t h e r two was a l s o p a r t i a l l y checked. - 38.-Method of applying point loads. 6: Load application grid. The points are spaced 5mm. apar t . - 39 -2.2.1 E x p e r i m e n t a l p r o c e d u r e . The arrangement d e p i c t e d i n F i g . 5 was used i n a l l o f the data c o l l e c t i o n f o r t h i s e x periment. The v a r i o u s components a r e : (1) Weights. (2) S u p p o r t i n g f l a n g e t o h o l d the w e i g h t s above. (3) P o i n t e d s t e e l s h a f t f o r c o n c e n t r a t i n g the l o a d onto a p o i n t . (4) Clamp to h o l d the s h a f t (3) and the s l e e v e (5) i n a v e r t i c a l p o s i t i o n . (5) B r a s s s l e e v e to m a i n t a i n the s h a f t i n p o s i t i o n w i t h o u t h i n d e r i n g l o a d t r a n s m i s s i o n . B r a s s , being a b e a r i n g m a t e r i a l , p r o v i d e s the l o w - f r i c t i o n support r e q u i r e d t o a c h i e v e t h i s . (6) W r i t i n g s u r f a c e ( g l a s s ) exposed through window i n h o u s i n g . For the e v a l u a t i o n , mi 1 l i m e t r i c a l 1 y squared paper was taped onto the w r i t i n g s u r f a c e and r e f e r e n c e axes were marked out on i t ( F i g . 6 ) . The p o i n t s at which r e a d i n g s were to be taken were a l s o marked o u t . These were s e l e c t e d i n such a way t h a t most o f the u s a b l e area was covered i n the e v a l u a t i o n . F i g . 6 a l s o shows the l o c a t i o n of the w r i t i n g window w i t h r e s p e c t t o the r e f e r e n c e axes and the g r i d o f e v a l u a t i o n p o i n t s . Only the g r i d p o i n t s f a l l i n g w i t h i n the w r i t i n g window were used. The a p p l i e d l o a d s were w e i g h t s o f known v a l u e (50 - 200 gm. den o m i n a t i o n s ) . The o b t a i n e d v a l u e s were used to c a r r y out a s t a t i s t i c a l f i t t o the p o l y n o m i a l v = a + bu + c u 2 + du 3 - 40 -f o r each output v w i t h r e s p e c t t o the c o r r e s p o n d i n g i n p u t u. 2.2.1.1 L i n e a r i t y . L i n e a r i t y i s a c t u a l l y determined i n terms of n o n - 1 i n e a r i t y , which i s taken as the d e p a r t u r e of the d e v i c e response from the form v = a + bu where v i s the output c o r r e s p o n d i n g t o the i n p u t u (a and b are c o n s t a n t s ) . The data used f o r t e s t i n g the l i n e a r i t y of the a p p a r a t u s i n t r a n s d u c i n g p o s i t i o n i n f o r m a t i o n was g a t h e r e d by a p p l y i n g a f i x e d l o a d a t each of the g r i d p o i n t s a l o n g a f i x e d 'y' v a l u e . S e v e r a l r e a d i n g s were t a k e n at each p o i n t . These numbered 10, w i t h a p p r o x i m a t e l y one second s p a c i n g between s u c c e s s i v e r e a d i n g s . (Each r e a d i n g was i n i t i a t e d by s t r i k i n g the RETURN key on the c o n t r o l t e r m i n a l keyboard, hence the approximate time s p a c i n g between them.) The l o a d v a l u e and the 'y' v a l u e were then changed s i m u l t a n e o u s l y i n o r d e r to a l s o g a t h e r i n f o r m a t i o n about any in t e r - d e p e n d e n c e between the d e v i c e r e s p o n s e s . In o r d e r to determine the l i n e a r i t y w i t h r e s p e c t t o w r i t i n g f o r c e t r a n s d u c t i o n , a few of the g r i d p o i n t s (shown c i r c l e d i n F i g . 6) were used f o r o b t a i n i n g a second d a t a s e t f o r the d e v i c e . The l o a d was i n c r e a s e d from z e r o , i n s t e p s of 50 gm., t o 400 gm. which was the maximum o f the i m m e d i a t e l y a v a i l a b l e w e i g h t s . For t h i s second s e t of r e s u l t s , a g a i n s e v e r a l r e a d i n g s per l o a d v a l u e were t a k e n . The r e s u l t s of f i t t i n g the p o l y n o m i a l above t o the two s e t s - 41 -o f d a t a were used f o r d e t e r m i n i n g q u a d r a t i c and c u b i c n o n l i n e a r i t i e s . These n o n l i n e a r i t i e s were c h a r a c t e r i s e d by the r a t i o o f the c o e f f i c i e n t s c and d t o the c o e f f i c i e n t b ( e x p e c t e d t o be u n i t y ) , r e s p e c t i v e l y . 2.2.1.2 R e l a t i v e independence between o u t p u t s . By v i r t u e o f the f a c t t h a t the r e a d i n g s were taken at d i s p e r s e d p o i n t s on the g r i d , the r e p e a t a b i l i t y o f the o b s e r v a t i o n s over the area can be determined. The dependence can be d e s c r i b e d by the b e h a v i o u r o f the c o e f f i c i e n t a ( t h e i n t e r c e p t ) i n t h e p o l y n o m i a l f i t mentioned above. The p o l y n o m i a l f i t was t h e r e f o r e performed i n s e v e r a l s t a g e s . F i r s t , the t o t a l d a t a s e t was used i n o r d e r to o b t a i n an o v e r a l l performance r a t i n g as i n d i c a t e d above i n the l i n e a r i t y t e s t s . The data was then regrouped i n o r d e r t o t e s t the b e h a v i o u r o f t h e d e v i c e at s p e c i f i c p o i n t s o r areas on the w r i t i n g s u r f a c e . T h i s then a l l o w e d the d e t e r m i n a t i o n o f the r e l a t i v e independence o f a p a r t i c u l a r output response from the v a l u e s of o t h e r two i n p u t s by s t u d y i n g the i n t e r c e p t s (a) obt a i n e d . 2.2.1.3 Dynamic range. T h i s i s the range o f i n p u t v a l u e s over which an a c c e p t a b l y l i n e a r response can be a c h i e v e d . The dynamic ranges would be determined from F i g s . 7, 8 and 9 as the ranges w i t h i n which the responses of the system ( t h e t r a n s f e r c h a r a c t e r i s t i c s ) a r e most l i n e a r . However, the p o l y n o m i a l f i t t i n g mentioned above a l s o i d e n t i f i e s t h i s . By - 42 -e v a l u a t i n g the response over s h o r t ranges of the i n p u t v a r i a b l e and s t u d y i n g the b e h a v i o u r o f the q u a d r a t i c and h i g h e r c o e f f i c i e n t s , the l i n e a r r e g i o n s o f o p e r a t i o n can be e s t a b l i s h e d . The ranges of i n p u t over which these c o e f f i c i e n t s become n o t i c e a b l y l a r g e can be t a k e n to i n d i c a t e the b e g i n n i n g o f n o n l i n e a r o p e r a t i o n , and the l i m i t s o f the dynamic range. 2.2.1.4 S i g n a l - t o - n o i s e r a t i o . N o i s e i s taken as the l a c k of s h o r t - t e r m time i n v a r i a n c e o f the response. The time i n t e r v a l chosen was a p p r o x i m a t e l y one second. The r a t i o o f s i g n a l power to n o i s e power ( s i g n a l - t o - n o i s e r a t i o (SNR)), can be o b t a i n e d by c o n s i d e r i n g the average n o i s e power i n each of the 'x', 'y' and 'p' c h a n n e l s , and the c o r r e s p o n d i n g average s i g n a l power. The use o f r e p e a t e d r e a d i n g s a t each t e s t v a l u e a l l o w e d the use of s t a t i s t i c a l methods f o r the c a l c u l a t i o n of the s i g n a l t o n o i s e r a t i o s . The mean v a l u e o f the r e a d i n g s gave the s i g n a l v a l u e w h i l e t h e i r v a r i a n c e r e p r e s e n t e d the n o i s e power. 2.2.2 Q u a l i t a t i v e assessment. The q u a l i t a t i v e assessment of the t r a n s d u c e r system i n d i c a t e d the f o l l o w i n g major drawbacks : ( i ) A r a t h e r s m a l l w r i t i n g a r e a . The t r a p e z o i d a l w r i t i n g window was 24 mm wide on one s i d e and 64 mm wide on the o t h e r . The h e i g h t was about 17 mm. - 43 -( i i ) The w r i t i n g f o r c e r e q u i r e d f o r a c l e a r output was s l i g h t l y i n e x c e s s o f t h a t n o r m a l l y a p p l i e d by most p e o p l e . ( i i i ) Lack of a means of c o n v e n i e n t l y clamping the paper w h i l e w r i t i n g was i n p r o g r e s s . Most of these drawbacks c o u l d be e a s i l y overcome, and the temporary s o l u t i o n s adopted d u r i n g the h a n d w r i t i n g d a t a a c q u i s i t i o n d i d not appear to unduly i n c o n v e n i e n c e the u s e r s . S p e c i f i c a l l y , ( i ) The w r i t i n g area proved q u i t e adequate f o r most of the samples c o l l e c t e d . T h i s can be i n f e r r e d from a comparison of the t r a n s d u c e r w r i t i n g area w i t h the s i z e o f the s i g n a t u r e area on, f o r example, a s o c i a l i n s u r a n c e number c a r d , which i s a p p r o x i m a t e l y 10 mm h i g h by 60 mm wide. The e q u i v a l e n t area a v a i l a b l e on the t r a n s d u c t i o n d e v i c e used i s 10 mm by 40 mm, which compares f a v o u r a b l y w i t h the above. ( i i ) I t d i d not take l o n g t o get a d j u s t e d t o w r i t i n g s l i g h t l y h a r d e r than normal. ( i i i ) The temporary remedy of a s k i n g the u s e r s t o h o l d the paper down u s i n g t h e i r f r e e hand was q u i t e a c c e p t a b l e . 2.2.3 E x p e r i m e n t a l R e s u l t s . The r e s u l t s of the v a r i o u s phases of the experiment are d e t a i l e d here. The r e s u l t s of the procedure d e s c r i b e d a t the b e g i n n i n g o f s e c t i o n 2.2.1.1 are g i v e n i n Table I . The f i r s t p a r t c o n t a i n s the r e s u l t s of the t e s t s d i r e c t e d a t d e t e r m i n i n g - 44 -the p o s i t i o n response c h a r a c t e r i s t i c s and the second p a r t c o n t a i n s the r e s u l t s of the f o r c e t r a n s d u c t i o n t e s t s . The v a l u e s of the c h a r a c t e r i s t i c s l i s t e d at the b e g i n n i n g of s e c t i o n 2.2 above, and determined as d e s c r i b e d i n the l a t t e r p a r t of s e c t i o n 2.2.1.1 are g i v e n a f t e r Table I . In the t a b l e s , the headings have the f o l l o w i n g meanings: Load i s the a p p l i e d l o a d v a l u e . P-av i s the average o f the computed f o r c e a t each l o a d p o i n t . o~p i s the s t a n d a r d d e v i a t i o n of the computed f o r c e v l u e s at the l o a d p o i n t . S/Np i s the SNR i n t h e f o r c e t r a n s d u c t i o n at the l o a d p o i n t . T h i s was t a k e n to be the r a t i o o f P-av t o Op. X-av i s the average computed 'x' c o o r d i n a t e , ox i s the s t a n d a r d d e v i a t i o n of the computed 'x' v a l u e s . Y-av i s the average computed 'y' c o o r d i n a t e . ay i s the s t a n d a r d d e v i a t i o n o f the computed 'y' v a l u e s . and E r r . r i s the ' e r r o r r a d i u s ' o f p o s i t i o n measurement. T h i s was taken as the square r o o t o f the sum o f the 'x' and 'y' v a r i a n c e s . - 45 -Table l a : P o s i t i o n T r a n s d u c t i o n Data. >ad P-av crp S/Np X- av ox Y-av o-y E r r '. r ;ra gra gm dB mm mm ram mm mm 50 240 . 19 0 . 125 65.67 -14 .94 0 .011 8 • 99 0 .012 0. 017 50 236. 37 0 • 738 50. 1 1 -10 .37 0 .032 8 .49 0 .043 0. 054 50 242 . 22 0 .164 63.41 -4 .34 0 .003 8 .26 0 ,008 0. 009 50 228. 23 0 .726 49 .95 1 .58 0 .130 7 .95 0 .060 0. 143 50 251 . 13 1 .529 44.31 5 .75 0 .219 7 .81 0 .077 0. 232 50 251 • 13 1 .876 42.54 10 .89 0 ,146 7 .81 0 , 1 12 0. 184 50 242 . 48 1 • 319 45.29 16 .29 0 .201 7 .46 0 . 071 0. 213 100 288. 81 0 .702 52.29 15 . 7 2 0 .067 3 .94 0 .036 0. 076 100 301. 51 0 .694 52.75 10 . 12 0 . 126 3 .99 0 .036 0. 132 100 289. 80 1 . 094 48.46 6 .95 0 . 025 3 .2-7 0 .069 0, 074 100 317. 28 2 .035 43.86 1 .62 0 .099 3 .23 0 . 091 0. 134 100 287- 51 0 .916 49 .93 -3 • 35 0 .012 3 .60 0 . 061 0. 062 100 281 . 15 0 .707 51.99 -9 .03 0 . 024 3 .66 0 . 048 0. 054 100 279. 37 0 • 987 49 .04 -13 .78 0 .295 3 • 97 0 .051 0. 299 150 352. 14 0 . 354 59 .97 -14 .42 0 . 000 -0 .90 0 . 001 0. 001 150 372. 24 0 .655 55. 10 -9 .43 0 . 102 -1 .46 0 .019 0. 104 150 350. 61 0 .911 51 .70 -4 • 74 0 .013 -1 .20 0 .063 0 . 065 150 358. 25 0 .189 65. 56 0 .73 0 .000 -1 .08 0 .000 0. 000 150 375. 55 1 .558 47.6 4 5 .13 0 . 126 -0 .64 0 .043 0 . 133 150 356. 47 0 .750 53.54 10 .34 0 .066 -1 .03 0 . 021 0. 069 150 380. 89 0 .756 54 .05 14 .74 0 . 054 -1 • 3 2 0 .018 0. 057 200 408. 23 1 .414 49.21 14 . 10 0 .087 -5 • 3 2 0 . 022 0. 090 20 0 405 . 83 1 .069 51 .59 9 • 97 0 .082 -5 .60 0 . 054 0. 099 - 46 -200 419-31 0.378 200 399.47 1.414 200 407-35 0.845 200 411.43 1-309 200 409.14 0.000 60.90 5.64 0.011 49.02 0.93 0.104 53.66 -3.65 0.007 49.94 -9.20 0.076 D -13.05 0.018 -5.80 0.010 0.015 -5.62 0.078 0.130 -5.62 0.050 0.050 -5.39 0.048 0.090 -5-50 0.000 0.018 - 47 -Table l b : Force T r a n s d u c t i o n Data. >ad P-av crp S/Np X-av Ox Y- av oy E r r . r ;m gm gm dB mm mm mm mm mm 0 193- 37 0 .177 60.78 -14. 48 0 .011 4 * • 70 0 .005 0 .012 50 248. 78 0 .931 48 .54 -15. 05 0 .209 4 .46 0 .057 0 .216 100 302. 61 1 .038 49 .29 -14. 27 0 . 193 4 .61 0 . 054 0 .201 150 375. 66 1 .458 48 .22 -13. 98 •0 .129 4 .63 0 .063 0 . 144 20 0 424. 06 1 .458 49 .27 -14. 22 0 .098 4 .75 0 .054 0 .111 250 483. 77 1 . 1 18 52.72 -14. 35 0 . 121 4 .76 0 .034 0 . 126 300 533. 98 0 .935 55.13 -14. 64 0 .054 4 .54 0 .030 0 .062 350 582. 15 0 .707 58.31 -14. 58 0 .012 4 .18 0 . 006 0 .014 400 640. 96 1 . 118 55. 17 - 15. 02 0 .022 4 .03 0 .020 0 .030 0 199. 48 1 .000 46 .00 15 . 02 0 . 209 4 .56 0 .081 0 .224 50 251 . 50 1 .807 42.87 15 • 43 0 .224 4 .47 0 . 090 0 .242 100 333. 37 1 .725 45 .72 14. 3 0 0 .206 4 .42 0 . 051 0 .212 150 381 . 77 1 .061 51.12 14. 21 0 .041 4 .47 0 .051 0 .065 20 0 429 • 94 0 .707 55.68 14. 86 0 .030 4 . 7 3 0 . 0 3 7 0 .048 250 490 . 10 1 .061 53-29 14. 31 0 .082 4 .54 0 .035 0 .089 300 521. 09 0 .354 6 3 . 3 7 14. 1 1 0 .008 4 .54 0 .005 0 . 009 350 569 . 49 1 . 8 3 7 49 .83 13- 88 0 .081 4 .52 0 .047 0 .094 400 622. 18 1 • 369 53.15 13. 46 0 . 050 3 • 96 0 .025 0 . 056 0 181 . 84 1 • 772 40 .22 1. 61 0 . 251 -1 .08 0 . 107 0 .273 50 2 3 7 . 93 0 • 707 50.54 1. 47 0 . 004 -1 .74 0 .069 0 .069 100 293- 11 0 .234 61.96 1 . 19 0 .000 -1 .40 0 .000 0 .000 150 360. 28 1 .803 46 .01 0. 46 0 .146 -1 • 3 2 0 .048 0 .154 20 0 414. 34 1 . 061 51 .84 0. 94 0 .114 -1 .29 0 .026 0 . 117 - 48 -250 476. 53 0 .612 57 .82 0. 71 0. 062 -1 .15 0. 014 0 . 064 30 0 539- 41 0 .000 D 0. 49 0 . 000 -1 .05 0. 000 0. 000 350 573- 56 1 .581 51 .19 0. 17 0. 051 -1 .10 0. 040 0. 065 400 649. 3 2 2 .062 49 .97 -0 . 46 0. 069 -1 .34 0. 028 0. 075 0 180. 48 1 .027 44 . 9 0 -14. 06 0. 081 -6 .00 0. 161 0. 180 50 256. 9 3 0 . 9 1 0 49 .02 -13. 70 0. 1 0 3 -5 • 33 0 . 0 2 3 0. 105 100 289. 72 1 .479 45 .84 -13. 63 0, 099 -6 .22 0. 026 0. 102 150 356. 44 0 .707 54 .05 -13. 75 0. 026 -5 .60 0. 054 0 . 060 20 0 412. 9 8 1 . 118 51 • 35 -13. 28 0 . 103 -5 .55 0. 017 0 . 104 250 472. 69 0 .935 54 .07 -13. 70 0. 0 2 8 -5 .65 0. 054 0 . 061 300 527. 42 0 .9 35 55 .02 -13. 77 0 . 014 -5 .72 0, 037 0. 039 350 597. 9 8 1 . 118 54 .56 -13. 76 0. 025 -5 .49 0. 042 0. 049 400 6 7 8 . 05 0 .791 58 .67 - 1 3 . 81 0. 022 -5 • 3 2 0. 0 2 9 0. 0 3 7 0 1 8 7 . 49 0 .679 48 .82 1 6 . 75 0. 215 -6 . 0 8 0 . 0 1 8 0. 2 1 6 50 1 8 9 . 75 0 .910 46 • 3 8 15. 6 8 0 . 076 -6 .42 0 . 136 0. 156 1 0 0 316. 18 1 • 750 45 .14 14. 92 0 . 214 -5 • 39 0. 0 8 3 0 . 229 150 352. 59 1 • 732 46 .17 15. 28 0. 199 -5 .60 0. 065 0. 210 20 0 392. 62 0 .707 54 .89 14. 47 0. 051 -5 .26 0. 011 0. 052 250 446. 91 1 .732 48 . 2 3 13. 21 0 . 173 -5 .25 0. 044 0 . 179 300 506 . 84 0 • 354 63 • 13 12. 6 1 0. 015 -5 .25 0. 008 0. 016 350 56 4. 51 1 .061 54 .52 12. 51 0. 101 -5 .37 0. 011 0. 1 02 400 628. 97 0 .707 58 .98 12. 3 8 0. 011 -4 .66 0. 009 0. 014 - 49 -2.2.3-1 P o s i t i o n l i n e a r i t y . The c o e f f i c i e n t s of the p o l y n o m i a l f i t t o the 'x' p o s i t i o n c o o r d i n a t e response gave the v a l u e s below. R e g r e s s i o n c o e f f i c i e n t s f o r : XALL 8 0 - 1 1 - 1 7 a = 9-390E -1 b = 9.990E -1 c = 2.180E - 3 d = 1.030E -4 T h i s g i v e s us t h a t the 'x' t r a n s d u c t i o n has a g a i n e r r o r of about 0.1?. T h i s however i s easy to c o r r e c t f o r i f n e c e s s a r y . The q u a d r a t i c n o n l i n e a r i t y i s a l i t t l e over 0.2? and the c u b i c n o n l i n e a r i t y i s about 100 ppm. The t a b l e o f c o e f f i c i e n t s f o r 'y' i s as f o l l o w s . R e g r e s s i o n c o e f f i c i e n t s f o r : YALL 8 0 - 1 1 - 1 7 a = 3 . 6 O O E 0 b = 9 . 0 1 0 E - 1 c = 1 . 5 6 O E - 3 d = 2 . 3 9 0 E - 7 S i m i l a r l y , F i g , 8 and the t a b l e above g i v e the g a i n e r r o r i n 'Y' as a p p r o x i m a t e l y 1 0 ? , which a g a i n i s e a s i l y c o r r e c t a b l e by a d j u s t i n g the ( s o f t w a r e or hardware) g a i n . The q u a d r a t i c n o n l i n e a r i t y i s l e s s than 0 . 2 ? , w i t h the c u b i c n o n l i n e a r i t y b e i n g l e s s than 0 . 3 ppm. - 50 -2.2 . 3-2 Force l i n e a r i t y . F i g . 9 g i v e s the r e l a t i o n between the measured f o r c e and the a p p l i e d f o r c e . The f o l l o w i n g t a b l e g i v e s the c o r r e s p o n d i n g r e g r e s s i o n c o e f f i c i e n t s f o r the p o l y n o m i a l f i t d i s c u s s e d b e f o r e , when a p p l i e d t o the data i n Table l b . R e g r e s s i o n c o e f f i c i e n t s f o r : PRESSURE 80-11-17 a = 1 .880E 2 b = 1.140E 0 c = 3.540E -5 d = 7.620E-15 The o v e r a l l l i n e a r i t y e r r o r here i s such t h a t b =' 1.14, r a t h e r than u n i t y , the q u a d r a t i c e r r o r i s around 35 ppm and the c u b i c e r r o r i s v i r t u a l l y n o n e x i s t e n t . 2 . 2 - 3 - 3 R e l a t i v e independence o f o u t p u t s . The o f f s e t s c a l c u l a t e d f o r the 'x' response f o r d i f f e r e n t 'y' and 'p' v a l u e s are p r e s e n t e d below. a (y,p) 8.750E -1 ( 5, 50) 1.540E 0 ( 0,100) 4.540E -1 ( -5,150) 8.890E -1 (-10,200) Thus, the 'x ' o f f s e t v a r i e s by about 1 mm as 'y' and 'p' change by 15 mm. and 150 gm. r e s p e c t i v e l y . - 51 -The 'y' p o l y n o m i a l f i t gave the f o l l o w i n g v a l u e s of the o f f s e t at d i f f e r e n t v a l u e s of the 'x' c o o r d i n a t e . (The 'p' v a l u e changed w i t h 'y'.) 4.0 20E 0 3.580E 0 3-560E 0 3-350E 0 3.460E 0 3-6 30E 0 3.420E 0 -15) -10) -5) 0) 5) 10) 15) The change i n o f f s e t here works out at a p p r o x i m a t e l y 0.7 mm. T h i s , s i m i l a r l y the p r e v i o u s v a l u e f o r 'x', i s taken as the d i f f e r e n c e between the minimum and the maximum o f f s e t s . The f o r c e o f f s e t s at v a r i o u s p o i n t s were found t o be 1.900E 2 2.010E 2 1.790E 2 1.950E 2 1.780E 2 (x,y) -15, 5) 15, 5) 0, 0) -15,-5) 15,-5) Thus, the change i s a p p r o x i m a t e l y 201 - 178 (= 23) gm. s i n c e these two v a l u e s a r e , r e s p e c t i v e l y , the maximum and the minimum of f s e t s . - 52 -2.2.3-4 Dynamic range o f p o s i t i o n s e n s i n g . The range over which the d e v i c e was t e s t e d d i d not i n c l u d e any r e g i o n where the 'x' and 'y' n o n l i n e a r i t i e s became g r e a t e r t h a n , say, 5%. Thus, i t was not p o s s i b l e t o e s t i m a t e the dynamic range o f p o s i t i o n s e n s i n g . The maximum v a l u e o f the 'x' n o n l i n e a r i t y was 0.36%, f o r y = 0 mm. The maximum f o r 'y' was 0.022%, o c c u r r i n g a t x = -10mm. 2.2.3-5 Dynamic range o f f o r c e t r a n s d u c t i o n . The p o i n t beyond which t h e f o r c e response becomes n o n - l i n e a r i s not covered by the range o f weigh t s used f o r the e v a l u a t i o n . T h i s means t h a t the f o r c e response i s l i n e a r at l e a s t up to the maximum o u t p u t r e c o r d e d . 2.2.3-6 S i g n a l - t o - n o i s e r a t i o and u n c e r t a i n t y i n p o s i t i o n . The graph i n F i g . 10 g i v e s the v a l u e s of p o s i t i o n u n c e r t a i n t y , a c t u a l l y the r o o t mean square (RMS) p o s i t i o n e r r o r , g i v e n by: E r r . r = V(dx.dx + dy.dy) as a f u n c t i o n o f the a p p l i e d l o a d . I n the above e x p r e s s i o n , dx i s the 'x' RMS e r r o r and dy i s the 'y' RMS e r r o r . The v a l u e s shown are the worst case RMS e r r o r s f o r each l o a d v a l u e , as l i s t e d i n Table l b . The maximum RMS e r r o r i s l e s s than 0.3 mm, i m p l y i n g a worst case measurement u n c e r t a i n t y of about +1 mm. - 53 -2.2.3-7 S i g n a l t o n o i s e r a t i o and u n c e r t a i n t y i n f o r c e . Table l b g i v e s the v a l u e s of the s i g n a l - t o - n o i s e r a t i o s f o r v a r i o u s v a l u e s of a p p l i e d f o r c e . The u n c e r t a i n t y i n the f o r c e (o"p) was used i n computing these v a l u e s . The maximum u n c e r t a i n t y was about 2.1 gm. and the l o w e s t s i g n a l - t o - n o i s e r a t i o (SNR) was around 40 dB. - 54 -20 10 - 1 0 10 -10 h -20 Fig. 7: Output vs. input 'x' values. (mm/mm) - 55 -15 10 X 1 5 i 0 * i -10 -j5 5 10 i - 5 --10 --15 -Fig. 8: Output vs. input 'y' va lues . (mm /mm) - 56 -700r 600h 500r AOCf-300f-200J-i c n l . 1 I 1 I I I I "T) 100 200 300 A00 Fig. 9: Output vs. input 'p' values. (gm/gm) - 57 -0-2h O-lh - • i i l i I i I 100 200 300 400 Fig. 10: Worst case uncertainty in position measurement vs . applied load, ( m m / g m ) -. 58 -2.3 The adequacy of the d e v i c e . The above r e s u l t s were compared t o what were c o n s i d e r e d a c c e p t a b l e v a l u e s and the f o l l o w i n g assessment was o b t a i n e d . 2.3'1 L i n e a r i t y of p o s i t i o n c a l c u l a t i o n . The g a i n e r r o r s are not c r i t i c a l , s i n c e these can e a s i l y be compensated f o r . The q u a d r a t i c n o n l i n e a r i t y of 0.2% i n each of 'x' and 'y' o b t a i n e d over the whole working area i s w e l l below \% . T h i s l a t t e r i s a v a l u e which i s g e n e r a l l y a c c e p t e d as r e a s o n a b l y p r e c i s e f o r measurement. 2.3.2 L i n e a r i t y of f o r c e t r a n s d u c t i o n . The l i n e a r i t y e r r o r of a 35 ppm q u a d r a t i c and a n e g l i g i b l e c u b i c component q u a l i f i e s the f o r c e response as e x c e l l e n t w i t h i n the range o f the t e s t l o a d s . 2 . 3 . 3 R e l a t i v e independence of o u t p u t s . The s e n s i t i v i t y o f the 'x' response to v a r i a t i o n s i n 'y' and 'p' amounting t o 1 mm i s r a t h e r h i g h . T h i s i s one aspect of the t r a n s d u c e r which w i l l c l e a r l y need improvement b e f o r e a w o r k i n g system can be implemented. A l s o , the 'y' s e n s i s t i v i t y of 0.7 mm needs t o be improved upon. However, as l o n g as the p o s i t i o n a l i n f o r m a t i o n i s not used i n i t s raw form i n o r d e r to make d e c i s i o n s about the i n p u t p a t t e r n , a s e n s i t i v i t y of 1 mm o r l e s s s h o u l d not pose to o g r e a t a problem. The observed change i n f o r c e o f f s e t o f about 25 gm. i n d i c a t e s t h a t the f o r c e t r a n s d u c t i o n can be c o n s i d e r e d r e l a t i v e l y decoupled from the p o s i t i o n c o o r d i n a t e s . Thus i t i s - 59 -q u i t e a c c e p t a b l e p r o v i d e d a g a i n t h a t the magnitude of the a p p l i e d f o r c e i s not used d i r e c t l y i n the d e c i s i o n making p r o c e s s . The r e d u c t i o n of t h i s dependence i s n e v e r t h e l e s s a w o r t h w h i l e t a r g e t f o r r e d e s i g n . 2 . 3.4 W r i t i n g window s i z e and l o c a t i o n . S i n c e t h e r e was no e x c e s s i v e n o n l i n e a r i t y i n measuring the p o s i t i o n over the e n t i r e area o f the w r i t i n g window, i t s l o c a t i o n was a c c e p t a b l e . As noted above, i t s s i z e was not a source o f g r e a t concern e i t h e r . I t would be d e s i r a b l e to have i t r e c t a n g u l a r , p r o v i d i n g an area perhaps t w i c e t h a t o f f e r e d on c a r d s such as the s o c i a l i n s u r a n c e number card c i t e d above. ( T h i s i s m a i n l y an a e s t h e t i c improvement.) 2 . 3-5 Ruggedness of the t r a n s d u c e r w i t h r e s p e c t t o a p p l i e d f o rc e . O b s e r v a t i o n s made d u r i n g the t e s t i n g i n d i c a t e d t h a t what c o u l d be c o n s i d e r e d 'heavy' w r i t i n g from most s u b j e c t s averaged about 500 gm. The a c t u a l f o r c e used w h i l e w r i t i n g was not q u i t e as g r e a t . A l t h o u g h the w e i g h t s used i n the d e v i c e e v a l u a t i o n d i d not go beyond 400 gm., the combined e f f e c t of the s h a f t and r e s t of the arrangement d e p i c t e d i n F i g . 5 was to add another 200 gm. or so. Thus, the d e v i c e i s u s a b l e up to 600 gm. a t l e a s t , making i t adequate f o r the p r e s e n t purpose. 2 . 3 . 6 S i g n a l - t o - n o i s e r a t i o . From the v a l u e s of the u n c e r t a i n t i e s i n p o s i t i o n and f o r c e , we see t h a t , p r o v i d e d the a p p l i e d f o r c e i s i n excess of 200 gm., c o r r e s p o n d i n g t o the z e r o - i n p u t l e v e l i n F i g . 10, we s h o u l d be - 60 -a b l e to c a l c u l a t e the p o s i t i o n to w i t h i n one m i l l i m e t r e . T h i s i s q u i t e a c c e p t a b l e f o r the c a l c u l a t i o n o f the r e q u i r e d p o s i t i o n a l p arameters, p r o v i d e d a g a i n t h a t they are not used ' r aw'. The maximum f o r c e u n c e r t a i n t y o f l e s s than 3 gm. and the minimum SNR of 40 dB a r e q u i t e a c c e p t a b l e f o r the purposes of the experiment d e s c r i b e d i n the next c h a p t e r . An example o f the d e v i c e o u t p u t s p l o t t e d as y ( x ) , x ( t ) , y ( t ) and p ( t ) appears as F i g . 13 i n the appendix. - 61 -2.4 Comparison With Other Systems. The a p p a r a t u s chosen determined the 'x', 'y' and 'p' c o - o r d i n a t e s of t h e samples. Not a l l o t h e r p u b l i s h e d approaches to dynamic s i g n a t u r e a n a l y s i s have used t h i s . For example, i n [HERB77], the a c c e l e r a t i o n s x and y were used, w i t h the l a t e r [LIU.79] a d d i t i o n of the a x i a l f o r c e on the w r i t i n g i n s t r u m e n t . In [CRAN78], the f o r c e s a p p l i e d t o the w r i t i n g i n s t r u m e n t i n the 'x', 'y' and ' z ' d i r e c t i o n s were used. T h i s i s e s s e n t i a l l y e q u i v a l e n t t o measuring the ( o r t h o g o n a l ) a c c e l e r a t i o n s p l u s the normal f o r c e . In u s i n g a p o s i t i o n - t r a n s d u c e r system, we have a means of v i s u a l v a l i d a t i o n o f a c q u i r e d d a t a , to ensure t h a t the da t a i s t r u l y r e p r e s e n t a t i v e o f the w r i t t e n sample. The v i s u a l comparison can be a c h i e v e d by r e p r o d u c i n g the re c o r d e d p o s i t i o n i n f o r m a t i o n on some g r a p h i c o u t p u t d e v i c e and comparing w i t h the o r i g i n a l as re c o r d e d on paper. In a d d i t i o n , s e v e r a l d e r i v a t i v e s can be computed w i t h o u t r e c o u r s e t o cumbersome i n t e g r a t i o n . T h i s would be r e q u i r e d i f speed i n f o r m a t i o n was needed and the t r a n s d u c e r o n l y measured a c c e l e r a t i o n s , f o r example. The above l e v e l o f performance from the data a c q u i s i t i o n subsystem was found s a t i s f a c t o r y and the a u t h o r proceeded w i t h the data a c q u i s i t i o n and a n a l y s i s . The s e l e c t i o n o f measures computed from the a c q u i r e d d a t a appears i n the next c h a p t e r , t o g e t h e r w i t h the e x p e r i m e n t a l procedure f o l l o w e d i n the data a c q u i s i t i o n . The c h a p t e r a l s o c o n t a i n s a d e s c r i p t i o n o f the a n a l y s i s performed on the d a t a , and the r e s u l t s of a p p l y i n g t h i s a n a l y s i s to a sample c o l l e c t i o n o f genuine s i g n a t u r e s and - 62 -amateur f o r g e r i e s . 3. IDENTITY VERIFICATION EXPERIMENT. In u s i n g the v e r i f i c a t i o n o f h a n d w r i t t e n s i g n a t u r e s as a means of i d e n t i t y v e r i f i c a t i o n , s u c c e s s f u l automated o p e r a t i o n can be r e a l i z e d i f i t i s p o s s i b l e to determine a s e t of measurable and/or computable parameters of the s i g n a t u r e w i t h the f o l l o w i n g c h a r a c t e r i s t i c s : ( i ) The parameters v a r y r e l a t i v e l y l i t t l e between d i f f e r e n t genuine samples of one i n d i v i d u a l ' s s i g n a t u r e . T h i s a s s u r e s us o f a c o n s i s t e n c y s i m i l a r to t h a t o f the i n d i v i d u a l ' s own i d e n t i t y . ( i i ) There i s a measurable d i f f e r e n c e - between mean parameter v a l u e c o m b i n a t i o n s f o r d i f f e r e n t i n d i v i d u a l s . s i g n i n g t h e i r own s i g n a t u r e s . T h i s makes i t p o s s i b l e t o use the parameters f o r d i s c r i m i n a t i n g between the d i f f e r e n t i n d i v i d u a l s . ( i i i ) At l e a s t some of the parameters w i t h the above p r o p e r t i e s depend more on who i s w r i t i n g than on what i s b e i n g w r i t t e n . T h i s would enhance t h e i r u t i l i t y i n d i f f e r e n t i a t i n g • between genuine s i g n a t u r e samples and h i g h -q u a l i t y f o r g e r i e s . In a d d i t i o n , i t s h o u l d be p o s s i b l e t o perform the r e q u i s i t e measurements and computations e c o n o m i c a l l y and w i t h a h i g h degree of a c c u r a c y . I f d i g i t a l computing elements are used, i t s h o u l d a l s o be p o s s i b l e t o do t h i s i n ' r e a l t i m e ' , t h a t i s , w i t h a minimum o f d e l a y between d a t a i n p u t and system r e s p o n s e . - 64 -In t h i s c h a p t e r , an experiment t o v e r i f y i d e n t i t i e s through the a n a l y s i s o f s i g n a t u r e parameters i s - d e s c r i b e d . The work done by p r e v i o u s workers i n the f i e l d i s d i s c u s s e d f i r s t , w i t h a view to i s o l a t i n g the b a s i c p r i n c i p l e s i n v o l v e d . A f t e r t h a t , a g e n e r a l s e t o f c h a r a c t e r i s a t i o n s o f the s i g n a t u r e which can be c o n s i d e r e d t o s a t i s f y the above r e q u i r e m e n t s i s g i v e n , and the approach, taken f o r t h i s s t u d y i s d e t a i l e d . - 65 -3 - 1 P r e v i o u s Work i n H a n d w r i t t e n S i g n a t u r e V e r i f i c a t i o n . As mentioned above, t h e r e are two a s p e c t s t o a h a n d w r i t t e n s i g n a t u r e : the s t a t i c s p a t i a l p a t t e r n t h a t i s l e f t on the w r i t i n g s u r f a c e and the dynamics o f the g e n e r a t i o n o f t h i s p a t t e r n . The p u b l i s h e d approaches to s i g n a t u r e a n a l y s i s f o r i d e n t i t y v e r i f i c a t i o n have i n v e s t i g a t e d the use o f both a s p e c t s , a l t h o u g h no one system has used both at once. Thus, the r e p o r t e d approaches to s i g n a t u r e v e r i f i c a t i o n can be b r o a d l y c l a s s i f i e d on the b a s i s o f the d a t a used. The u s u a l d a t a c o l l e c t i o n t e c h n i q u e s f o r each c l a s s are g i v e n as w e l l . 3 . 1.-1 C l a s s i f i c a t i o n o f Systems. The c l a s s e s i n t o which s i g n a t u r e a n a l y s i s systems, may be s e p a r a t e d are as - f o l l o w s : ( i ) ' S t a t i c ( d a t a ) ' systems - i n which the s i g n a t u r e samples are f i r s t w r i t t e n out on paper and then p r e s e n t e d t o the system f o r c o n v e r s i o n i n t o the system's i n t e r n a l r e p r e s e n t a t i o n and subsequent a n a l y s i s . T h i s i s e q u i v a l e n t to the way most c u r r e n t (human-based) systems o p e r a t e . ( i i ) 'Dynamic ( d a t a ) ' systems - where the sample d a t a i s c o l l e c t e d ' o n - l i n e ' as the samples are be i n g w r i t t e n . T h i s i s u s u a l l y a c h i e v e d by the use o f e l e c t r o m e c h a n i c a l or e l e c t r o m a g n e t i c t r a n s d u c e r s mounted i n s p e c i a l s t y l i and/or w r i t i n g s u r f a c e s . A b r i e f d e s c r i p t i o n o f the s a l i e n t - f e a t u r e s of v a r i o u s systems examined i s g i v e n below f o r purposes o f comparing the two c l a s s e s . - 66 -3.1.1.1 S t a t i c systems [NAGE73],[NEMC74]. These systems r e q u i r e f a c i l i t i e s t o t r a n s l a t e o p t i c a l i n f o r m a t i o n ( w r i t i n g on paper) i n t o the k i n d o f d a t a s i g n a l s t h a t can be handled by d i g i t a l p r o c e s s i n g elements. T h e r e f o r e , the use o f such d e v i c e s as o p t i c a l c h a r a c t e r r e c o g n i t i o n (OCR) d e v i c e s , has been 'necessary. A r e s u l t a n t r e s t r i c t i o n i s t h a t these systems cannot n o r m a l l y o b t a i n i n f o r m a t i o n 'on l i n e ' , s i n c e the w r i t e r s ' hands and w r i t i n g i n s t r u m e n t s would be i n the way. A major r e s e a r c h problem i s i s o l a t i n g the s i g n a t u r e from i t s background, and encoding i t i n a form s u i t a b l e f o r a n a l y s i s . The i n h e r e n t advantage of t h i s approach i s t h a t u s e r s need no.t i n t e r a c t d i r e c t l y w i t h complex d a t a - a c q u i s i t i o n hardware. T h i s d e s i r a b l e s i n c e such an i n t e r a c t i o n might unduly a f f e c t the form o f s i g n a t u r e i n v a r i o u s ways. The u s e r s need never p e r c e i v e the system as b e i n g any d i f f e r e n t from t h a t which they encounter when they p r e s e n t a cheque at t h e i r bank. A n o t a b l e d i s a d v a n t a g e o f these systems i s t h a t good f o r g e r i e s would be v e r y hard t o d e t e c t , more so i f the f o r g e r c o u l d take h i s / h e r time p r e p a r i n g the sample. For example, a f o r g e r who t r a c e s from a copy o f the v a l i d s i g n a t u r e c o u l d pass e a s i l y , e s p e c i a l l y i f t h e r e was o p p o r t u n i t y t o prepare the sample w i t h o u t s u p e r v i s i o n . T h i s i s i n d i s t i n c t c o n t r a s t to the dynamic systems i n which t r a c i n g would be a v e r y poor f o r g e r y s t r a t e g y indeed [CRAN78]. 3.1.1.2 Dynamic systems. In these [MAUC65], [DYCH??], [STER75], [HERB77], [CRAN78], [ L I U . 7 9 ] , s p e c i a l w r i t i n g i n s t r u m e n t s and/or s u r f a c e s are used - 67 -to m o n i t o r p o s i t i o n , v e l o c i t y , a c c e l e r a t i o n and/or " p r e s s u r e " i n v a r i o u s d i r e c t i o n s . T h i s i s done as the s i g n a t u r e i s b e i n g w r i t t e n , so t h a t t i m i n g i n f o r m a t i o n i s a l s o p r e s e r v e d . I t i s the i n c l u s i o n o f t h i s t i m i n g i n f o r m a t i o n t h a t l e a d s to these t e c h n i q u e s b e i n g termed 'dynamic'. C l e a r l y , i f a f o r g e r attempts to take h i s / h e r time making the v i s u a l product n e a r - p e r f e c t , or i f an attempt i s made to t r a c e a p r e v i o u s l y - o b t a i n e d sample, the r e s u l t i n g time waveforms w i l l be q u i t e d i f f e r e n t from those o f the a u t h e n t i c s i g n e r . The most n o t i c e a b l e d i f f e r e n c e s w i l l be i n the smoothness of s t r o k e , t h a t i s the y ( x ) waveform, and l o c a t i o n o f pauses t h a t are not v i s i b l e i n the f i n i s h e d p r o d u c t . In a d d i t i o n , t r a c i n g would produce s i g n a l s s i m i l a r to those from e i t h e r u n p r a c t i s e d or u n n a t u r a l h a n d w r i t i n g , m a i n l y due to the use o f heavy v i s u a l feedback c o n t r o l . The n a t u r a l 1 y - s i g n e d sample, on the o t h e r hand, i s an example of p r a c t i s e d motion i n which i n s t a n t a n e u o s f e e d b a c k - c o n t r o l cannot p l a y a r o l e due to i t s r a p i d i t y [DENI65], [MCD070]. 3.1.2 S i g n a t u r e F e a t u r e s Used In Ver-if i c a t i o n . In o r d e r to implement a d e c i s i o n a l g o r i t h m on the machine t o be used i n the s i g n a t u r e v e r i f i c a t i o n scheme, a s e t o f m e t r i c s has to be- d e f i n e d and r e f e r e n c e v a l u e s o b t a i n e d f o r each p r o s p e c t i v e c a n d i d a t e f o r s c r e e n i n g . T h i s s e t o f m e t r i c s w i l l c o n s t i t u t e a ' f e a t u r e v e c t o r ' and i t s elements are s t r o n g l y dependent on the a p p a r a t u s used. The c o n s i d e r a t i o n o f some model o f the h a n d w r i t i n g p r o c e s s would be a c o n t r i b u t i n g f a c t o r t o the c h o i c e o f the f e a t u r e s and, hence, the i n s t r u m e n t a t i o n . A b r i e f - 68 -d i s c u s s i o n of the f e a t u r e s used i n the p u b l i s h e d t e c h n i q u e s examined i s g i v e n . 3.1.2.1 F e a t u r e s f o r s t a t i c systems. I t i s here t h a t models o f c u r s i v e s c r i p t , r a t h e r than the p h y s i c a l h a n d w r i t i n g system, have been a p p l i e d . The f e a t u r e s sought . i n c l u d e d cusps [NEMC74] and parameters of the p a r t i c u l a r model of s c r i p t [EDEN61], [EDEN62] bei n g used. These and o t h e r r e l a t i o n s h i p s [HARV34], [MEL034] - such * as t h a t between the h e i g h t s o f t a l l and s h o r t l e t t e r s [NAGE73] - are used t o c h a r a c t e r i s e the s i g n e r . Below are l i s t e d the s p a t i a l , m e a s u r e s mentioned i n two o f the papers surveyed [YASU77] and [NAGE73]• - C a p i t a l . 1 e t t e r s - Upper and lower zone l e t t e r s - R a t i o o f t a l l l e t t e r s to s m a l l l e t t e r s - S pacing between t a l l l e t t e r s - R e l a t i v e h e i g h t s o f t a l l l e t t e r s - G e n e r a l i z e d shape o f c a p i t a l and t a l l l e t t e r s - Width or h e i g h t o f h a n d w r i t i n g . I n c o n s i s t e n c i e s i n the above, and the q u a l i t y o f s t r o k e s i n l o n g rounded are a s (such as are found i n c a p i t a l , upper or lower zone l e t t e r s ) were used t o d e t e c t f o r g e r i e s [NAGE73], - 69 -Other measures mentioned were: - Forms o f l e t t e r s . - B e g i n n i n g and ending s t r o k e s o f l e t t e r s . - S p a c i n g between l e t t e r s . - S i z e r e l a t i o n s h i p between t a l l and s h o r t l e t t e r s . - S i z e r e l a t i o n s h i p s between o v e r a l l h e i g h t s o f l e t t e r s l i k e h, b and d compared w i t h the lower p a r t o f each. - R e l a t i v e p r e s s u r e h a b i t s as r e v e a l e d i n the s t r o k e s -of the w r i t i n g . - C o n n e c t i n g s t r o k e s between the l e t t e r s . - S p e c i a l marks such as i dot s and t - c r o s s i n g s . - B a s e l i n e o f the., h a n d w r i t i n g . 3.1.2.2 F e a t u r e s used i n dynamic systems. . . In these systems, as the c l a s s i f i c a t i o n i m p l i e s , the dynamic a s p e c t s o f the w r i t i n g sample r a t h e r than the f i n a l ( s t a t i c ) g r a p h i c p r o d u c t , are used i n the d e t e r m i n a t i o n o f the f e a t u r e s e t . In [MAUC65], a c c e l e r a t i o n s i g n a l s of the hand/pen mass system were measured v i a a pen f i t t e d w i t h an a c c e l e r o m e t e r . In a d d i t i o n , a pen-paper c o n t a c t s i g n a l was r e c o r d e d as a b i n a r y (ON/OFF) waveform. In p r o c e s s i n g the a c c e l e r a t i o n d a t a , power s p e c t r a l d e n s i t i e s i n v a r i o u s f r e q u e n c y bands were c a l c u l a t e d - 70 -and a l s o used i n the s p e c i f i c a t i o n o f the f e a t u r e v e c t o r s . At S y l v a n i a E l e c t r o n i c Systems Dyche [DYCH??], r e c o r d e d p o s i t i o n i n o r t h o g o n a l c o - o r d i n a t e s . The s i g n a l s thus o b t a i n e d were used t o d e r i v e v e l o c i t y and a c c e l e r a t i o n s i g n a l s i n the 'x' and 'y' d i r e c t i o n s . Other parameters measured were: the l e n g t h o f the s i g n a t u r e and the l e n g t h s o f the pen-up and pen-down i n t e r v a l s . The l a t t e r were n o r m a l i s e d a c c o r d i n g to the s i g n a t u r e l e n g t h p r i o r t o the g e n e r a t i o n o f a f e a t u r e v e c t o r . In the V e r i p e n , I n c . SIGNAC system [STER75 ] , o n l y ' p r e s s u r e ' i n f o r m a t i o n was used. The a x i a l f o r c e on the w r i t i n g i n s t r u m e n t was the one chosen, Herbst and L i u [HERB77] monitored a c c e l e r a t i o n i n two o r t h o g o n a l d i r e c t i o n s . The ' p e n - l i f t p a t t e r n ' was a l s o r e c o r d e d ( c f . [MAUC65], [DYCH??]). These measurements gave a b a s i s f o r the ' f e a t u r e space' used i n the v e r i f i c a t i o n , i n which c o r r e l a t i o n was employed to d e r i v e some of the c o o r d i n a t e s . A f t e r f u r t h e r work [ L I U . 7 9 ] , a .mechanism f o r m o n i t o r i n g the ( a x i a l ) w r i t i n g f o r c e was added. The use o f t h i s l e d t o a much-improved system performance. The SRI workers [CRAN78], measured drag f o r c e s as mentioned above. Among the parameters computed from these measurements were average energy and angle o f i n c l i n a t i o n o f the pen w h i l e w r i t i n g ( p r o v i d i n g some f a c i l i t y f o r d i f f e r e n t i a t i n g between l e f t - and r i g h t - h a n d e d w r i t e r s ) . These were used i n d e t e r m i n i n g the c h a r a c t e r i s t i c ( f e a t u r e ) v e c t o r o f the s i g n e r . S a k a i et a l . [SAKA??] u t i l i s e d a g r a p h i c pen and t a b l e t system which- a l l o w e d the m o n i t o r i n g o f t h r e e - d i m e n s i o n a l motion - 71 -o f the pen. T h i s f e a t u r e c o u l d prove u s e f u l f o r s u b j e c t s who may-be c o n s i d e r e d t o have a t r u l y t h r e e - d i m e n s i o n a l space s i g n a t u r e . Such people -move t h e i r w r i t i n g i n s t r u m e n t s i n 'a c h a r a c t e r i s t i c f a s h i o n d u r i n g the (pen-up) pauses in-between w r i t t e n segments. These are the k i n d o f motions a f o r g e r would be h a r d - p r e s s e d t o mimic. The f e a t u r e s computed i n t h a t system i n c l u d e d : the o r d e r - o f - s t r o k e s ( i t was t e s t e d on s u b j e c t s w r i t i n g Chinese c h a r a c t e r s ) and number o f s t r o k e s . These were d i s p l a y e d , w i t h c o l o u r c o d i n g , on a c o l o u r TV mo n i t o r w i t h expected and pr e s e n t e d f e a t u r e s d i s p l a y e d s i m u l t a n e o u s l y f o r ease o f comparison. - 72 -3.2 C h a r a c t e r i s a t i o n s o f the H a n d w r i t t e n S i g n a t u r e . The v a r i a b i l i t y of human motor response i s a well-known phenomenon and h a n d w r i t i n g i s a l s o s u b j e c t to t h i s v a r i a b i l i t y . T h i s v a r i a b i l i t y w i l l appear, f o r example, i n d i f f e r e n t l e t t e r s i z e s and d i f f e r e n t shapes of i n d i v i d u a l c h a r a c t e r s or c h a r a c t e r - segments of the w r i t t e n sample. In the dynamic a s p e c t s o f h a n d w r i t i n g , the l o c a t i o n , i n t i m e , o f c e r t a i n d i s t i n c t i v e (but g r o s s ) waveform f e a t u r e s w i l l - v a r y , as w i l l the f i n e d e t a i l of the waveform. When c o n s i d e r i n g w r i t i n g - f o r c e l e v e l s i n p a r t i c u l a r , v a r i a t i o n w i t h the w r i t i n g i n s t r u m e n t used and w i t h the s i g n e r ' s (mental and p h y s i c a l ) s t a t e wil-1 o c c u r . One c o u l d attempt to use s e v e r a l samples of a person's s i g n a t u r e to g e n e r a t e a mean s i g n a t u r e which would then be used as a r e f e r e n c e . T h i s c o u l d be c o n s i d e r e d to approach the t a r g e t s i g n a t u r e o f the s i g n e r as the number of l e a r n i n g samples i n c r e a s e s . The g e n e r a t i o n o f the mean would be a c h i e v e d by s t a t i s t i c a l a v e r a g i n g over the s i g n a t u r e s , e i t h e r i n whole u n i t s or- i n segments. T h i s would be e a s i e s t t o a c h i e v e i f each sample or segment c o u l d be e x p r e s s e d i n terms of some ' c o - o r d i n a t e s ' , or f e a t u r e s from which the sample i s u n i q u e l y r e c o v e r a b l e . However, t h i s can become a r a t h e r d i f f i c u l t problem [ H E R B 7 7 ] . For dynamic measurements, the a p p l i c a t i o n o f the work of some i n v e s t i g a t o r s i n t o the c h a r a c t e r i s a t i o n o f g e n e r a l f a m i l i e s o f waveforms would be of v a l u e . S u g g e s t i o n s f o r t h i s have i n c l u d e d F o u r i e r e x p a n s i o n s , Karhunen-Loeve exp a n s i o n s [CHRI79], [ODEL79] and a system f o r '...waveform p a r s i n g . . . ' [STOC73]. T h i s l a s t i n v o l v e s the use of l i n g u i s t i c ( s y n t a c t i c ) a n a l y s i s o f the - 73 -waveform i n terms of some waveform p r i m i t i v e s such as peaks, t r o u g h s and p o s i t i v e and n e g a t i v e s l o p e s . 3.2.1 P r o c e s s i n g T echniques. The t e c h n i q u e s f o r p r o c e s s i n g s i g n a t u r e waveforms can a l l be c o n s i d e r e d to be f e a t u r e e x t r a c t i o n t e c h n i q u e s . T h e i r d i f f e r e n c e l i e s i n the . n a t u r e o f the e x t r a c t e d f e a t u r e s . These f e a t u r e g r o u p i n g s are : ( i ) S i m i l a r i t y measures, f o r which reference-waveforms have t o be s t o r e d f o r comparison w i t h o t h e r waveforms; and ( i i ) Waveform parameters. For t h e s e , the -waveforms are compressed i n t o " v e c t o r s " o f c o - o r d i n a t e s i n some f e a t u r e space. The methods used i n e x t r a c t i n g these v a r i o u s f e a t u r e s are a l s o u s u a l l y c h a r a c t e r i s i t i c o f the g r o u p i n g . A b r i e f summary o f them i s g i v e n below. 3.2.1.1 S i m i l a r i t y measures. The t e c h n i q u e g e n e r a l l y used i n d e t e r m i n i n g s i m i l a r i t y measures between waveforms i s c r o s s - c o r r e l a t i o n . The d e c i s i o n s tage then compares the v a l u e o f the c o r r e l a t o r output to a p r e v i o u s l y e s t a b l i s h e d t h r e s h o l d and makes the a p p r o p r i a t e d e c i s i o n . C l e a r l y , the c o r r e l a t i o n can be c o m p u t a t i o n a l l y i n t e n s e . For example, i f a t e s t sample of M p o i n t s i s to be c o r r e l a t e d _ 74 -w i t h -an N-point t e m p l a t e , M+N-1 m u l t i p l i e s and adds have to be done. T h i s i s because i t . i s the maximum v a l u e o f the c o r r e l a t i o n c o e f f i c i e n t t h a t i s sought [USP77a]. Sometimes, i t might even be n e c e s s a r y to a d j u s t the time l e n g t h o f the t e s t sample to t h a t o f the r e f e r e n c e . F u r t h e r m o r e , i n the case of h a n d w r i t t e n s i g n a t u r e s , i t i s not o n l y the d u r a t i o n t h a t w i l l v a r y from sample to sample. The l o c a l t i m i n g s o f the waveform segments w i l l a l s o v a r y , r e q u i r i n g the use o f " r u b b e r y " [CRAN78] or " r e g i o n a l " [HERB77] c o r r e l a t i o n . In o r d e r to c o r r e c t these " j i t t e r " phenomena, n o n l i n e a r , time a l i g n m e n t [YASU77], i n v o l v i n g dynamic programming has been sug g e s t e d . The b e s t sample t o use f o r d e t e r m i n i n g s i m i l a r i t y measures would be what the a u t h o r of the s i g n a t u r e s c o n s i d e r s t o be h i s / h e r ' t a r g e t ' or i d e a l s i g n a t u r e . The normal way to o b t a i n t h i s would be by s t a t i s t i c a l a v e r a g i n g over a- number o f genuine samples. However, t h i s i s q u i t e a d i f f i c u l t problem as mentioned i n s e c t i o n 3-2 and, t h e r e f o r e , s e v e r a l c o p i e s of the genuine s i g n a t u r e w i l l have to be kept at hand i n s t e a d . The t e s t sample i s then c o r r e l a t e d w i t h a number o f them i n o r d e r to a v o i d b i a s [USP77a], [USP77b], [USP77c], Thus, the c o m p u t a t i o n a l and s t o r a g e space r e q u i r e m e n t s can be q u i t e L a r g e . The major advantage o f t h i s approach i s t h a t , u s u a l l y , o n l y one c o m p u t a t i o n a l " s t e p " - the c o r r e l a t i o n - i s r e q u i r e d i n o r d e r to determine the v e r i f i c a t i o n measure. In a d d i t i o n , the r e f e r e n c e s e t can s t a r t out w i t h o n l y a few genuine samples, b u i l d i n g up i t s ' i n v e n t o r y ' w i t h subsequent c o r r e c t l y c l a s s i f i e d samples [HERB77]. Thus one can get p e r i o d s d u r i n g which some of - 75 -the s u b j e c t s are c o n s i d e r e d " p r o v i s i o n a l " [HERB77], whereas the system i s o p e r a t i o n a l . T h i s would reduce the apparent r e g i s t r a t i o n time q u i t e markedly. 3.2.1.2 Waveform parameters. The parameters approach i n v o l v e s the - c a l c u l a t i o n o f the v a l u e s o f p r e d e t e r m i n e d - f e a t u r e s of the waveforms, thus r e q u i r i n g the use of the t e s t sample a l o n e . The - d e c i s i o n stage then uses the computed v a l u e s to determine the d i s t a n c e o f the t e s t sample from the r e f e r e n c e . The s t o r a g e r e q u i r e d i s then o n l y a r e l a t i v e l y s m a l l m a t r i x c o n s i s t i n g o f the e x p e c ted v e c t o r t and one or more v e c t o r s r e p r e s e n t i n g the v a r i a t i o n c h a r a c t e r i s t i c s o f the elements. U s u a l l y o n l y [_t | a-] i s r e q u i r e d , where G i s the v a r i a n c e v e c t o r . Because of t h i s , the v e r i f i c a t i o n s tage can be implemented on a s m a l l - s c a l e machine, w i t h r e g i s t r a t i o n and r e c o r d keeping b e i n g handled by a l a r g e r f a c i l i t y . In a d d i t i o n , the approach can be termed i n h e r e n t l y r e a l - t i m e , s i n c e d e l a y e d c o p i e s o f the i n p u t s i g n a l are g e n e r a l l y not r e q u i r e d f o r computing the f e a t u r e v e c t o r . I f the machine i s f a s t enough, most of the r e q u i r e d p r o c e s s i n g i s then i n t e r l a c e d w i t h the ( u n i f o r m ) sampling o f the i n p u t . The major drawbacks i n the parameters approach a r e : ( i ) One needs s e v e r a l samples to s t a r t w i t h . For a s t a t i s t i c a l l y s i g n i f i c a n t e s t i m a t e o f the mean v a l u e s , a r a t h e r l a r g e number, _> 25, o f samples may a c t u a l l y be needed. (25 i s u s u a l l y c o n s i d e r e d the minimum sample s i z e f o r u s i n g the normal - 76 .-p p r o x i m a t i o n to a b i n o m i a l d i s t r i b u t i o n , f o r example [MEND73]•) I f the chosen parameters are r e a s o n a b l y c o n s i s t e n t , however, t h i s number need not be too l a r g e . ( i i ) The parameters to be e v a l u a t e d have t o be s p e c i f i e d i n advance. A poor c h o i c e o f parameters can l e a d t o an extended r e g i s t r a t i o n p e r i o d ( l a r g e number o f t r a i n i n g samples r e q u i r e d ) and a v e r y poor system performance. T h i s u s u a l l y n e c e s s i t a t e s the i n i t i a l s p e c i f i c a t i o n o f a v e r y l a r g e number o f parameters, o f which a minimal subset p o s s e s s i n g a c c e p t a b l e d i s c r i m i n a t o r y c h a r a c t e r i s i t i c s i s then sought. T h i s would a g a i n i m p l y a r a t h e r e x p e n s i v e r e g i s t r a t i o n p e r i o d . 3 . 2 . 1 . 3 Comparison o f the two approaches. We note t h a t w i t h the d i f f e r e n c e i n s t o r e d v a r i a b l e s , the two approaches o f f e r d i f f e r e n t l e v e l s o f s e c u r i t y from u n s c r u p u l o u s v e r i f i c a t i o n p e r s o n n e l . The c o r r e l a t i o n methods keep s e v e r a l c o p i e s o f the a u t h e n t i c signa-tures around, p o t e n t i a l l y a l l o w i n g such people to st u d y any s i g n a t u r e i n the database at l e i s u r e . The parameters methods, on the o t h e r hand, needn't keep any c o p i e s o f the sample around and t h e r e b y a v o i d t h i s p o t e n t i a l problem. Some might argue t h a t i t i s n e c e s s a r y to be a b l e t o reproduce the expected s i g n a t u r e i n o r d e r to v a l i d a t e a r e j e c t i o n , f o r example. T h i s would be a p p r o p r i a t e i f a t r u e mean s i g n a t u r e c o u l d be g e n e r a t e d . T h i s would then t r u l y be an "e x p e c t e d " s i g n a t u r e ( i n the s t a t i s t i c a l s e n s e ) . S i n c e , as noted above, t h i s i s not p r a c t i c a b l e , the use o f parameters i s p r e f e r r e d . The c o m p u t a t i o n a l i n t e n s i t y o f the s i m i l a r i t y - 77 -approach makes the parameters method more a t t r a c t i v e . I t was t h e r e f o r e s e l e c t e d as the t e c h n i q u e f o r t h i s s t u d y . However, t h i s c h o i c e b r i n g s a l o n g the problem o f parameter p r e - s p e c i f i c a t i o n . T h i s i s addressed i n the r e m a i n i n g s e c t i o n s . 3.2.2 C o n s i d e r a t i o n s f o r Parameters. The o b s e r v a t i o n t h a t people s i g n t h e i r names i n a u n i q u e l y c o n s i s t e n t manner i n d i c a t e s t h a t i t s h o u l d be p o s s i b l e t o d e f i n e two, not n e c e s s a r i l y d i s j o i n t , s e t s o f s i g n a t u r e waveform par a m e t e r s . These would be: ( i ) Parameters t h a t are c h a r a c t e r i s t i c o f the s i g n a t u r e ; and ( i i ) Parameters t h a t are c h a r a c t e r i s t i c o f the s i g n e r . In u s i n g h a n d w r i t t e n s i g n a t u r e s f o r i d e n t i t y v e r i f i c a t i o n , i t i s the l a t t e r s e t o f parameters t h a t would be more i m p o r t a n t . Some c a n d i d a t e parameters f o r the two c l a s s e s are o u t l i n e d below. 3.2.2.1 Parameters c h a r a c t e r i s t i c o f the s i g n a t u r e . These i n c l u d e : ( i ) x t r e n d x ( t ) ( i i ) z e r o - c r o s s i n g s o f x ( t ) = x ( t ) - x ( t ) ( i i i ) y t r e n d y ( t ) ( i v ) z e r o - c r o s s i n g s o f y ( t ) = y ( t ) - y ( t ) (v) l e n g t h o f t r a c e $ - 78 -( v i ) magnitude o f peaks/troughs o f x ( t ) ( v i i ) magnitude o f peaks/troughs of y ( t ) ( v i i i ) z e r o - c r o s s i n g d e n s i t y o f x ( t ) ( i x ) z e r o - c r o s s i n g d e n s i t y o f y ( t ) (x) e n e r g i e s i n x and y n o r m a l i s e d a c c o r d i n g t o $. Parameters ( v i ) and ( v i i ) a l s o have t o be n o r m a l i s e d a c c o r d i n g t o the t r a c e l e n g t h $. 3-2.2.2 Parameters c h a r a c t e r i s i n g both s i g n e r and s i g n a t u r e . ( i ) Time l e n g t h o f the s i g n a t u r e . ( i i ) A m p l i t u d e sequence of p o s i t i v e peaks o f x ( t ) ( i i i ) " » " y ( t ) ( i v ) A m p l i t u d e sequence o f n e g a t i v e peaks o f X ( t ) (v) " " " y ( t ) ( v i ) Number o f pen-down segments. 3.2.2.3 Parameters c h a r a c t e r i s t i c o f the s i g n e r . Some p o s s i b l e parameters which are dependent o n l y on the s i g n e r and not p a r t i c u l a r l y on what ( s ) h e i s s i g n i n g are : ( i ) S i z e o f the h a n d w r i t i n g (arm-hand-pen) system. T h i s c o u l d be e s t i m a t e d through the r a t e o f change o f momentum i n the r e g i o n s o f the w r i t t e n s t r o k e s j u s t b e f o r e pen l i f t - o f f . MacDonald [MACD66] a l s o c o n s i d e r e d the r i s e t imes o f t r a p e z o i d a l a p p r o x i m a t i o n s t o the a c c e l e r a t i o n s x and y i n d i c a t i v e o f t h i s . ( i i ) Average v a l u e s o f speed and a c c e l e r a t i o n - a l o n g the - 79 -t r a c e (s and s) when these are n o r m a l i s e d a c c o r d i n g t o the l e n g t h of the t r a c e , on a per-segment b a s i s . ( i i i ) S p e c t r a l d e n s i t i e s o f the speed and a c c e l e r a t i o n a l o n g the t r a c e ; n o r m a l i s e d by m u l t i p l y i n g the f r e q u e n c y a x i s by the time l e n g t h o f the s i g n a t u r e . An e s t i m a t e o f the above can be o b t a i n e d from the number o f z e r o - c r o s s i n g s o f the speed and a c c e l e r a t i o n waveforms. ( i v ) The c u r v a t u r e o f the y ( x ) t r e n d c u r v e . T h i s i n d i c a t e s the e f f e c t i v e l e n g t h of the w r i t i n g member i f e v a l u a t e d w i t h i n - each pen-down segment and averaged over a l l segments. (v) Downward average w r i t i n g f o r c e ( " p r e s s u r e " ) . ( v i ) Energy i n the ' h i g h - f r e q u e n c y ' p o r t i o n o f the p r e s s u r e waveform. T h i s - - c o u l d be n o r m a l i s e d a c c o r d i n g t o the 'l o w - f r e q u e n c y ' energy. ( v i i ) Rate of f a l l o f the . p r e s s u r e waveform between segments. T h i s s h o u l d be i n d i c a t i v e o f the . degree o f feedback c o n t r o l b e i n g used i n the w r i t i n g . 3.2.3 F e a t u r e s to be e v a l u a t e d . A c r o s s - s e c t i o n o f the parameters l i s t e d above and the measures used by e a r l i e r workers were s e l e c t e d f o r e v a l u a t i o n i n the i d e n t i t y v e r i f i c a t i o n experiment d e s c r i b e d l a t e r . The ones s e l e c t e d were: F1 : The time l e n g t h o f the s i g n a t u r e . { A c t u a l l y , , i t i s the t o t a l pen-down time ( i n no. o f samples) s i n c e our - 80 -system does not save any d a t a w h i l e the pen i s o f f the paper}. T h i s was used i n [ M A U C 6 5 J , [ H E R B 7 7 ] , [ U S P 7 7 a ] and [DYCH??]. F2 : Number o f zero c r o s s i n g s o f the a c c e l e r a t i o n a l o n g the t r a c e . T h i s i s r e l a t e d t o the average f r e q u e n c y o f the waveform m u l t i p l i e d by the time l e n g t h o f the sample. T h i s is- because z e r o - ( o r average-) c r o s s i n g r a t e s are good e s t i m a t e s o f the f r e q u e n c y c o n t e n t . F3 : Number of times the p r e s s u r e waveform c r o s s e s i t s average v a l u e . T h i s i s a g r o s s e s t i m a t e at the number o f s t r o k e s ( c h a r a c t e r segments) i n the sample. A b e t t e r measure would be the number o f peaks i n the waveform. F4 : Number of zero c r o s s i n g s of r a t e o f change o f a p p l i e d f o r c e ( " p r e s s u r e " ) . T h i s i s r e l a t e d t o the 'smoothness' o f the s t r o k e s . J e r k y motion i s expected t o l e a d t o v e r y r a p i d changes i n the a p p l i e d . f o r c e , g i v i n g a l a r g e v a l u e i n t h i s parameter. F 5 : Number o f pen-down segments i n the- s i g n a t u r e . T h i s i s the number o f p o r t i o n s the s u b j e c t breaks the s i g n a t u r e i n t o . A f o r g e r who has not seen the genuine s i g n e r produce h i s / h e r s i g n a t u r e i s not l i k e l y t o know t h i s . T h i s measure was a l s o used i n [ M A U C 6 5 ] , [ H E R B 7 7 ] , [ U S P 7 7 a ] and [DYCH??]. F6 : Second c e n t r a l moment of the speed alon g the t r a c e . ( T h i s i s n o r m a l i s e d a c c o r d i n g t o e i t h e r the average speed a l o n g the t r a c e or the l e n g t h o f the t r a c e . ) T h i s i s a - 81 -c o m b i n a t i o n o f two o f the moments used by Dyche [DYCH??]. F7 : Average speed a l o n g the t r a c e . T h i s may be expected t o be r e a s o n a b l y c o n s t a n t f o r someone w r i t i n g something as f a m i l i a r and unambiguous as h i s / h e r p e r s o n a l s i g n a t u r e . F8 : Second c e n t r a l moment of the r a t e o f change of p r e s s u r e n o r m a l i s e d a c c o r d i n g t o the v a r i a n c e o f p r e s s u r e . The p ercentage d u r a t i o n s o f the segments i n the s i g n a t u r e were a l s o determined but have not yet been used i n the v e r i f i c a t i o n p a r t o f the experiment d e t a i l e d i n the subsequent s e c t i o n s . These measures would be used to show up where the person breaks up the s i g n a t u r e r e g a r d l e s s o f how f a s t or s l o w l y ( s ) h e i s w r i t i n g . T h i s f e a t u r e c o u l d prove d i f f i c u l t f o r f o r g e r s t o d e c i p h e r from samples they have o b t a i n e d f o r s t u d y . - 82 -3 - 3 -The S i g n a t u r e A n a l y s i s and V e r i f i c a t i o n Experiment. The p r o t o t y p e system was used to e v a l u a t e some of the f e a t u r e s which were c o n s i d e r e d c h a r a c t e r i s t i c o f s i g n e r s and t h e i r s i g n a t u r e s as mentioned above. The r e s u l t s were then used i n another phase of the experiment to determine the performance o f the s e l e c t e d f e a t u r e s i n i d e n t i t y v e r i f i c a t i o n . 3 - 3 « 1 E x p e r i m e n t a l D e s i g n . F i f t e e n v o l u n t e e r s were asked to g i v e samples of t h e i r s i g n a t u r e s , and a l s o f o r g e one o t h e r . Each s u b j e c t was asked to g i v e f i v e samples of h i s own s i g n a t u r e at a s i t t i n g , over f i v e s e s s i o n s . The f o r g e r y attempts c o n s i s t e d o f f i v e samples at each s e s s i o n , w i t h o n l y the f o r g e r y samples from the f i r s t and l a s t s e s s i o n s b e i n g used i n the a n a l y s i s . The unused samples were s i m p l y c o l l e c t e d t o g i v e the f o r g e r adequate p r a c t i c e , s i m u l a t i n g the case of a. c h a i n o f . s u c c e s s f u l f o r g e r i e s . The reason f o r u s i n g f i v e samples per s e s s i o n was the. r e s u l t o f a p i l o t t e s t on one v o l u n t e e r and the a u t h o r . The parameters computed from the f i v e samples (a c o n v e n i e n t number) g i v e n by the s u b j e c t at one s i t t i n g i n d i c a t e d t h a t , i n o r d e r t o e s t i m a t e the mean parameter v a l u e s to a r e a s o n a b l e degree of a c c u r a c y , on the average s i x samples per s e s s i o n would be r e q u i r e d . The a n a l y s i s o f the a u t h o r ' s samples as averaged over a l o n g e r p e r i o d o f time i n d i c a t e d the need f o r a t l e a s t s i x t e e n samples i n t o t a l . Thus, a r o u n d i n g up o f the f i g u r e s gave the t o t a l number of samples as t w e n t y - f i v e and the number per s e s s i o n as f i v e . An a d d i t i o n a l - c o n s i d e r a t i o n was m a i n t a i n i n g the g o o d w i l l - 8 3 -o f the s u b j e c t s ; " In o r d e r t o s i m u l a t e the c o n d i t i o n s o f e x p e r t f o r g e r y , the " s i g n a t u r e " the s u b j e c t s were asked to f o r g e was a v e r y l e g i b l e word - the a u t h o r ' s name ( F i g . 11). The use o f a l e g i b l e word makes every t e s t s u b j e c t a p o t e n t i a l l y good f o r g e r and a l s o s i m u l a t e s the case o f e a s i l y - f o r g e d s i g n a t u r e s . These c o n s t i t u t e the worst cases an o p e r a t i o n a l system would have to contend w i t h . The a u t h o r p r o v i d e d a copy of h i s name i n h i s own h a n d w r i t i n g f o r the f o r g e r s t o s t u d y , w i t h more c o p i e s i n p u t t o the system database f o r the a n a l y s i s phase. - 84 -F i g . 11: Sample o f the name f o r g e d by the v o l u n t e e r s . To: A l l i n t e r e s t e d From: F r a n c i s Omoruto. Experiment f o r the A n a l y s i s of H a n d w r i t t e n S i g n a t u r e s . T h i s i s an experiment to c a r r y out dynamic a n a l y s i s of h a n d u r i t t e n s i g n a t u r e s . The d e v i c e b e i n g used to measure the s i g n a t u r e v a r i a b l e s c a l c u l a t e s the p o s i t i o n of the p e n - p o i n t and a l s o how h a r d i t i s b e i n g p r e s s e d down. I t i s hoped to use these s i g n a l s to d e t e r m i n e c h a r a c t e r i s t i c f e a t u r e s f o r t h - pu r p o s e of s c r e e n i n g s i g n a t u r e s i n o r d e r to d e t e c t f o r g e r i e s . I f you v o l u n t e e r to take p a r t i n the experiment* you w i l l be osked to g i v e f i v e s c a p l e s of your s i g n a t u r e at each of f i v e s e s s i o n s to 'on a r r a n g e d with" you. You w i l l a l s o be asked to f o r g e one o l h o r person'?; s i g n a t u r e on each o c c a s i o n . (Everybody u i l l be f o r g i n g the s i g n a t u r e - the e x p e r i m e n t e r ' s name - so p l e a s e do not be alc-rr-v-ri. ) _ . Procedure'* • . The r e w i l l be a s h o r t t r a i n i n g p e r i o d at the f i r s t s e s s i o n t o fami 1 i a r i s e you w i t h the equipment. You w i l l then be asked to g i v e the agreed number of samples of yo u r own s i g n a t u r e p l u s the f o r g e r y . ft time f o r the next s e s s i o n w i l l a l s o be a r r a n g e d . I t i s e x p e c t e d that the f i r s t s e s s i o n w i l l l a s t about 10 m i n u t e s pe r p e r s o n . The subsequent s e s s i o n s s h o u l d take about f i v e m i n u t e s e a c h . * F r e e c o f f e e u i l l be a v a i l a b l e f o r p a r t i c i p a n t s at e a c h s e s s i o n . * R e c o r d i n g Tir>=S: Morning r e c o r d i n g times w i l l be between 09hS9 end l l h 8 9 , end a f t e r n o o n times w i l l be between KhQO and 16h83 <2 - 4 p. m. > e v e r y da-; s t a r t i n g from Monday the S t h September 1930. The d a t a c o l l e c t i o n and a n a l y s i s w i l l be c a r r i e d out i n Room 343 of t h e IE. E. b u i l d i n g - the h y b r i d computer l a b o r a t o r y . Ccrnmunicat i o n ; Please" f i l l out the form below and r e t u r n i t to me. Ue u i l l t h e n a r r a n g e a time f o r . y o u r f i r s t s e s s i o n . Thanks f o r your c o - o p e r a t i o n and I hope to hear from you soon. L o c o t i o n : F r a n c i s E. E. Omoruto. I agree to take p a r t i n t h i s i n v e s t i g a t i o n . $ i gnci t ure Room Ho. F i g . 12: Survey C i r c u l a r . - 85 -To: A l l i n t e r e s t e d From: F r a n c i s Omoruto. Re: Experiment f o r the A n a l y s i s of H a n d w r i t t e n S i g n a t u r e s . T h i s i s an experiment t o c a r r y out dynamic a n a l y s i s of h a n d w r i t t e n s i g n a t u r e s . The d e v i c e being used to measure the s i g n a t u r e v a r i a b l e s c a l c u l a t e s the p o s i t i o n o f the p e n - p o i n t and a l s o how hard i t i s b e i n g p r e s s e d down. I t i s hoped t o use these s i g n a l s t o determine c h a r a c t e r i s t i c f e a t u r e s f o r the purpose of s c r e e n i n g s i g n a t u r e s i n o r d e r t o d e t e c t f o r g e r i e s . I f you v o l u n t e e r t o take p a r t i n the exp e r i m e n t , you w i l l be asked t o g i v e f i v e samples of your s i g n a t u r e at each of f i v e s e s s i o n s t o be arranged w i t h you. You w i l l a l s o be asked to f o r g e one o t h e r person's s i g n a t u r e on each o c c a s i o n . (Everybody w i l l be f o r g i n g the same s i g n a t u r e - the e x p e r i m e n t e r ' s name - so p l e a s e do not be alarmed.) P r o c e d u r e : There w i l l be a s h o r t t r a i n i n g p e r i o d a t the f i r s t s e s s i o n t o f a m i l i a r i s e you w i t h the equipment. You w i l l then be asked t o g i v e t h e agreed number of samples of your own s i g n a t u r e p l u s t h e f o r g e r y . A time f o r the next s e s s i o n w i l l a l s o be a r r a n g e d . I t i s expected t h a t the f i r s t s e s s i o n w i l l l a s t about 10 minutes p e r perso n . The subsequent s e s s i o n s s h o u l d take about f i v e minutes each. * Free c o f f e e w i l l be a v a i l a b l e f o r p a r t i c i p a n t s a t each s e s s i o n . * Re c o r d i n g Times: Morning r e c o r d i n g t i m e s w i l l be between 09h00 and 11h00, and a f t e r n o o n t i m e s w i l l be between I4h00 and I6h00 ( 2 - 4 p.m.) every day s t a r t i n g from Monday the 8 t h September 1980. L o c a t i o n : The data c o l l e c t i o n and a n a l y s i s w i l l be c a r r i e d out i n Room 348 o f the E.E. b u i l d i n g - the h y b r i d computer l a b o r a t o r y . Communication: P l e a s e f i l l out the form below and r e t u r n i t t o me. We w i l l t h en arrange a time f o r your f i r s t s e s s i o n . Thanks f o r your c o - o p e r a t i o n and I hope t o hear from you soon. F r a n c i s E. E. Omoruto. * . I agree to take p a r t i n t h i s i n v e s t i g a t i o n . S i g n a t u r e Room No. - 85 A 3.3-2 Survey P r o t o c o l . A c i r c u l a r ( F i g . 12) was sent to s e l e c t e d i n d i v i d u a l s i n o r d e r t o s o l i c i t v o l u n t e e r s f o r the experiment. They were s e l e c t e d o n l y on the b a s i s o f t h e i r e xpected a v a i l a b i l i t y over the p e r i o d o f the e x p e r i m e n t . The i n d i v i d u a l s who v o l u n t e e r e d were then i n v i t e d one at a time to g i v e t h e i r s i g n a t u r e s and a l s o p r a c t i s e f o r g i n g the a u t h o r ' s name. They then gave sample f o r g e r i e s as w e l l . 3-3-3 L a b o r a t o r y p r o c e d u r e . The a c q u i s i t i o n s o f t w a r e comprised a r o u t i n e to c a l c u l a t e the p o s i t i o n and f o r c e i n f o r m a t i o n and- d i s p l a y the p o s i t i o n , modulated by a f o r c e - l e v e l - t h r e s h o l d , on a g r a p h i c s t e r m i n a l . A u d i b l e a l a r m prompts were i n c l u d e d i n the d a t a a c q u i s i t i o n s o f t w a r e t o i n d i c a t e when the system was-ready to accept-, d a t a . T h i s was n e c e s s a r y because o f the d e l a y i n h e r e n t i n s e t t i n g up o p e r a t i n g system f i l e s f o r s t o r i n g the d a t a . In o r d e r t o g i v e the s u b j e c t s the " f e e l " o f the d a t a a c q u i s i t i o n system, the d e f a u l t mode of o p e r a t i o n was d i s p l a y - o n l y w i t h o u t s a v i n g . When the s u b j e c t s were c o n f i d e n t enough, the d i s p l a y - a n d - s a v e mode was i n v o k e d . In t h i s mode, the p o s i t i o n and f o r c e i n f o r m a t i o n was determined and d i s p l a y e d as b e f o r e . In a d d i t i o n , however, a b u f f e r was s e t up to h o l d t h i s i n f o r m a t i o n , and another b u f f e r s e t up to s t o r e i t s time d e r i v a t i v e s as computed by a p a r t of the programme a c t i v a t e d i n t h i s mode. These b u f f e r s were ••transferred i n t o system d i s k f i l e s whenever they became f u l l or an o p e r a t o r i n t e r r u p t w a s - r e c e i v e d . These i n t e r r u p t s were used t o i n s t i t u t e changes i n the programme - 86 -f l o w t h rough s h o r t commands. The p r o c e s s i n g t h a t was c a r r i e d out a f t e r the d a t a a c q u i s i t i o n i s d e s c r i b e d i n the next s e c t i o n . The r e s u l t s o f the a n a l y s e s performed are g i v e n t h e r e a f t e r . - 87 -3 . 4 Data P r o c e s s i n g . The p r o c e s s i n g o f the d a t a i n v o l v e d e x t r a c t i n g the f e a t u r e s s e l e c t e d above f o r each sample; u s i n g a subset o f the samples t o o b t a i n mean v a l u e s and s t a n d a r d d e v i a t i o n s o f these t r a i n i n g samples about t h e i r mean; c a l c u l a t i n g the d i s t a n c e s o f t e s t samples from the mean and s e l e c t i n g a s u i t a b l e t h r e s h o l d d i s t a n c e f o r c l a s s i f y i n g the t e s t samples as genuine or f o r g e d . 3.4.1 Parameter c a l c u l a t i o n . The parameters F1 - F8 l i s t e d i n s e c t i o n 3 . 2 . 3 above were c a l c u l a t e d as shown below. F1 : D u r a t i o n ( i n number of samples) - was o b t a i n e d by g e t t i n g i n f o r m a t i o n from the o p e r a t i n g system about the s i z e o f the f i l e i n b y t e s and d i v i d i n g by 6, the number of b y t e s per r e c o r d . T h i s i s because t h e r e were t h r e e elements per r e c o r d ( r e l a t e d to x, y and p) and each r e c o r d was a two-byte i n t e g e r . F2 : Number of a c c e l e r a t i o n z e r o - c r o s s i n g s . T h i s was determined as where s ( k ) i s the sampled v e r s i o n o f s ( t ) and sgn(.) i s the s i g n e x t r a c t i o n f u n c t i o n . F3 : the zero c r o s s i n g s o f the . f o r c e waveform ( p ( t ) ) was d e t e r m i n e d u s i n g the same f o r m u l a as f o r s ( t ) above.. I n s t e a d o f 1/2 >[1 - s g n ( s ( k ) ) . s g n ( s ( k - 1 ) ) ] k s( .) , [ p ( . ) - p _ a v ( . ) ] was used. S i m i l a r l y , F4, the number o f - 88 -zero c r o s s i n g s of p ( t ) was o b t a i n e d by s i m p l y s u b s t i t u t i n g p(.) f o r s ( . ) i n the F2 f o r m u l a . F5 : The number of segments was taken as the number of times the p ( t ) waveform c r o s s e d a g i v e n t h r e s h o l d w h i l e i n c r e a s i n g . The t h r e s h o l d was the minimum v a l u e o f p ( t ) p l u s a s m a l l o f f s e t . The o f f s e t was n e c e s s a r y f o r the comparison t o a v o i d s p u r i o u s f l u c t u a t i o n s of s h o r t d u r a t i o n t h a t would s t i l l c o n t r i b u t e t o the number sought, F6 : Second moment of speed ( n o r m a l i s e d u s i n g the average speed). T h i s was determined as: 2 2 2 L ^  ( s ( k ) ) /Nrec - (Avg_spd) ] / (Avg_spd) ~k F7 : The average speed was computed as s ( k ) / Nrec k F8 : The n o r m a l i s e d second c e n t r a l moment of the r a t e o f change o f a p p l i e d f o r c e p ( t ) . The n o r m a l i s a t i o n f a c t o r used here was the second c e n t r a l moment of the a p p l i e d f o r c e i t s e l f . (v fl ( p ( k ) ) /Nrec - > p ( k ) / N r e c J >/ PMOM I k ^ k PMOM was c a l c u l a t e d by the same f o r m u l a , s u b s t i t u t i n g p(.) f o r p(.) and 1 f o r PMOM. - 89 -3.4,2 D i s t a n c e Measurement and Sample C l a s s i f i c a t i o n . In o r d e r to t e s t the d i s c r i m i n a t i o n of the s e t as a whole, a d i s t a n c e based c l a s s i f i e r was implemented. The d i s t a n c e measure used was : where D ( t , r ) V ~ ( t ( i ) - r ( i ) ) 2 ) < > Z_( <y(i) ) i = 1 1/2 t i s the t e s t v e c t o r of parameters; r i s the r e f e r e n c e v e c t o r of parameters; G i s the v e c t o r of s t a n d a r d d e v i a t i o n s of the r e f e r e n c e p arameters; x ( i ) i s the v a l u e o f the i - t h element of v e c t o r x; and n i s the d i m e n s i o n a l i t y of the f e a t u r e space. 3.4.3 T h r e s h o l d s e l e c t i o n . I f the parameters are assumed n o r m a l l y d i s t r i b u t e d about t h e i r means f o r genuine samples, then the n o r m a l i s e d e r r o r terms d ( i ) t ( i ) - r ( i ) o-(i) s h o u l d have s t a n d a r d normal, t h a t i s , zero-mean and u n i t v a r i a n c e , s t a t i s t i c a l d i s t r i b u t i o n s . I f they are f u r t h e r assumed to be s t a t i s t i c a l l y i n d e pendent, the q u a n t i t y - 90 -D ( t , r ) = 2^ d ( i ) i= 1 s h o u l d have a c h i - s q u a r e d ( 'fy d i s t r i b u t i o n w i t h n degrees of freedom. The number n i s the d i m e n s i o n a l i t y o f the f e a t u r e space i n which the samples are b e i n g compared. T h i s i s p r e c i s e l y the square o f the d i s t a n c e m e t r i c mentioned above. For t h i s k i n d o f d i s t r i b u t i o n , a t h r e s h o l d can be s e l e c t e d which i s independent o f the s u b j e c t i n q u e s t i o n . T h i s t h r e s h o l d can be determined on the b a s i s o f the r e q u i r e d Type I ( f a l s e r e j e c t i o n ) e r r o r r a t e . The c r i t i c a l v a l u e s o f the c h i - s q u a r e d i s t r i b u t i o n f o r a few v a l u e s o f the Type I e r r o r (06) are g i v e n below. These v a l u e s are from Table 5 i n Appendix I I I o f [-MEND73 ] • Table I I : D e c i s i o n t h r e s h o l d v a l u e s . 06 ! Xl i T h r e s h o l d t 1 1 i 0 . 0 5 0 ! 1 5 . 5 0 7 3 ! 3.94 0.025 ! 17.5346 ! 4.19 0.010 ! 20.0902 ! 4 . 5 1 0.005 ! 21.9550 ! 4.69 3 . 4 . 4 E x p e r i m e n t a l r e s u l t s . The v a l u e s o f the f i r s t - d a y parameters f o r the ten s u b j e c t s who appeared then are g i v e n i n the appendix, s e c t i o n A1, Table V I I I . Table I I I p r e s e n t s the parameter s t a t i s t i c s f o r two s u b j e c t s . The d a t a i n Table I I I a l s o r e p r e s e n t s the r e f e r e n c e v a l u e s used i n c l a s s i f y i n g subsequent samples from the two s u b j e c t s . I t can be seen t h a t t h e r e are d i f f e r e n c e s between the - 91 -mean parameter v a l u e s f o r the two s u b j e c t s . However, some o f the d i f f e r e n c e s are not s i g n i f i c a n t , so t h a t we d e f i n i t e l y need t o use m u l t i p l e measures i n r e p r e s e n t i n g the samples. A l s o shown are the c o r r e l a t i o n m a t r i c e s between the parameters f o r each s u b j e c t . I t i s q u i t e apparent t h a t most of the measures are not s i g n i f i c a n t l y c o r r e l a t e d ( r < 0.6 - see s e c t i o n 3-5.1). Subsets of the genuine samples from each p a r t i c i p a n t were used as t r a i n i n g s e t s f o r g e n e r a t i n g the r e f e r e n c e s such as those i n Table I I I , shown f o r two s u b j e c t s . The t r a i n i n g s e t was composed of a l l f i v e samples from each o f the f i r s t , t h i r d and f i f t h s e s s i o n s the s u b j e c t a t t e n d e d . In o r d e r to determine the performance o f the system w i t h r e s p e c t t o f o r g e r y d e t e c t i o n , the f o r g e r y samples from the s u b j e c t s who f o r g e d the a u t h o r ' s name on two o c c a s i o n s were p r o c e s s e d . As can be seen from the r e s u l t s i n Table IV, the s u b j e c t s ' f o r g i n g a b i l i t y improved w i t h e x p e r i e n c e . (The m i s s i n g l a b e l s i n the d a t a sequence i d e n t i f i e r s p e r t a i n t o d a t a t h a t was s p o i l e d due to bad c u e i n g , i nadequate p r e s s u r e on the p a r t o f the s u b j e c t s and some d e s t r u c t i v e system command e r r o r s among o t h e r .things . ) The t e s t s f o r genuine . ( i . e . non-forged) sample a c c e p t a n c e / r e j e c t i o n were performed on samples from the author and the ten s u b j e c t s who managed to a t t e n d f i v e s e s s i o n s . The samples which were not i n c l u d e d i n the t r a i n i n g s e t c o n s t i t u t e d a t e s t s e t f o r the - c o r r e s p o n d i n g r e f e r e n c e . The performance o f each s e t was determined and the r e s u l t s are i n Table V. - 92 -The random f o r g e r y t e s t s c o n s i s t e d o f u s i n g genuine samples from one s i g n e r and t r y i n g t o pass them o f f as samples from a d i f f e r e n t genuine s i g n e r . The r e s u l t s o f these appear i n Table V I . In a l l the t e s t s , the d e c i s i o n t h r e s h o l d was s e t at the v a l u e c o r r e s p o n d i n g to an expected f a l s e r e j e c t i o n r a t e o f 2.5$. T h i s t h r e s h o l d v a l u e was 4 . 1 9 . - 9 3 -T a b l e I I I : The parameter s t a t i s t i c s . Parameter S t a t i s t i c s f o r : PDLR 80-12- 3 Dur. Za Zp Zp #Seg CM2(s) Avg. Spd. CM2(p) Mean 215 51 20 39 4 1.040E 0 3.110E 1 1.970E 0 Stdv 15.86 5.72 4 . 5 1 2 . 9 5 0.50 1.620E -1 3.070E 0 5.180E -1 C o r r e l a t i o n c o e f f i c i e n t s . 1.000 0.519 -0.280 0.324 - 0 . 3 1 9 -0.087 - 0 . 3 6 1 -0.578 0 . 5 1 9 1.000 0.293 0.267 -0.375 -0.452 0.199 -0.095 -0.280 0.293 1.000 0.240 -0.252 - 0 . 3 2 3 0.744 0.602 0.324 0.267 0.240 1.000 -0.426 -0.147 -0.074 0.189 -O . 3 I 9 -0.375 -0.252 -0.426 1.000 -0.203 -0.170 0.005 -0.087 -0.452 -0.323 -0.147 -0.203 1.000 -0.521 -0.315 -0.361 0.199 0.744 -0.074 -0.170 -0.521 1.000 0.420 -0.578 -0.095 0.602 0 . 1 8 9 0.005 -0.315 0.420 1.000 - 94 -Table I I I c o n t d . Parameter S t a t i s t i c s f o r : LMAR 80-12- 3 Dur. Za Zp Zp #Seg CM2(s) Avg . Spd. CM2(p) Mean 172 36 27 36 9 1.430E 0 4.120E 1 3.390E 0 Stdv 10.53 1-97 3-68 1.95 1.25 1.830E -1 5.520E 0 3.920E -1 C o r r e l a t i o n c o e f f i c i e n t s 1.000 0.045 0.258 0.130 0.401 0 . 2 3 4 -0.691 -0.290 0.045 1.000 -6.370 0.149 -0.221 -0.782 -0.037 - 0.1 17 0.258 -0.370 1.000 -0.073 -0.124 0.127 -0.041 0.359 0.130 0.149 -0.073 1.000 0.039 0.055 0.324 -0.610 0.401 -0.221 -0.124 0.039 1.000 0 . 1 9 7 -0.401 -0.334 0 . 2 3 4 - 0 . 7 8 2 0 . 1 2 7 0.055 0 . 1 9 7 1.000 - 0 . 2 2 1 -0.194 -0.691 -0.037 -0.041 0.324 -0.401 -0.221 1.000 0.039 - 0 . 2 9 0 - 0 . 1 1 7 0 . 3 5 9 - 0 . 6 1 0 - 0 . 3 3 4 - 0 . 1 9 4 0 . 0 3 9 1 . 0 0 0 - 9 5 -Table IVa: Performance of the f i r s t - d a y f o r g e r y s e t . V e r i f i c a t i o n measures. R e f e r e n c e : OMOR 8 0 - 1 2 - 6 DELIBERATE FORGERIES - FIRST SESSIONS. SAMPLE DISTANCE DECISION SAF1 8. 73 F SAF2 12. 52 F SAF3 1 1 . 00 F SAF4 10. 34 F SCF1 27. 46 F SCF2 5 6 . 56 F SCF4 21 . 07 F SCF5 18. 12 F SCF6 22. 66 F SLF1 26. 71 F SLF2 100. 66 F SLF3 700. 02 F SLF4 15. 83 F SEF1 400. 20 F SEF2 400. 14 F SEF3 400. 57 F SEF4 500. 1 1 ' F SEF5 700. 01 F SFF01 201 . 09 F SFF02 1 3 - 5 3 F SFF03 201 . 30 F SFF04 1 3 - 5 3 F (PASS/FAIL) - 96 -SFF05 9.08 F SHF1 31 -82 F SHF2 2 0 . 7 3 F SHF3 11.12 F SHF4 3-11 P SGF1 35.60 F SGF2 34.20 F SGF3 15 . 6 3 F SGF4 18.55 F SGF5 27. 30 F SJF 1 14. 45 F SJF2 18.41 F SJF3 16.26 F SJF4 19.66 F SJF5 13 - 5 1 F SKF1 200.94 F SKF2 7.45 F SKF3 - 5.07 F SKF4 6 . 3 3 F SKF5 100.20 F Test s t a t i s t i c s : T h r e s h o l d = 4.19;No. Maximum = 700. 02; Minimum = 3 . 1 1 Average = 106. 47; S t d . dev. = 184.144 Success r a t e = 2 . 3 8 ? - 97 -Table IVb: Performance o f the f i n a l - d a y f o r g e r y s e t . V e r i f i c a t i o n measures. Reference : OMOR DELIBERATE FORGERIES - LAST SESSIONS. SAMPLE DISTANCE DECISION AKF41 6. 44 F AKF42 4. 13 P A K F 4 3 5. 80 F AKF44 3- 9 6 P AKF45 3- 90 P DDF 41 3 4 . 64 F DDF42 1 6 . 54 F DDF 4 3 16. 86 F DDF 4 4 1 3 - 62 F DDF45 10. 87 F JMF 1 1 7- 11 F JMF12 100. 11 F JMF 13 500. 03 F JMF 14 700. 00 F JMF 15 41 . 75 F LMF41 300. 0 3 F LMF42 100. 16 F LMF43 300. 01 F LMF44 200. 14 F LMF45 500. 01 F MIF11 14. 52 F MIF12 19. 78 F (PASS/FAIL) - 98 -MIF13 22. 40 F MIF14 15.15 F MIF15 14.36 F PDF51 100.30 F PDF52 100.25 F PDF53 3.87 P PDF54 4 . 9 3 F PDF55 4. 20 F PLF41 24. 16 F PLF42 23-06 F PLF43 23-98 F PLF44 1 7 . 8 3 F PLF45 21.65 F RCF41 14.84 F RCF42 11.04 F RCF43 16.22 F RCF44 17.54 F RCF45 25.59 F RCF46 23-98 F TSF51 9.10 F TSF52 • 4.38 F TSF53 9.67 F TSF54 7.00 F TSF55 6.40 F Test s t a t i s t i c s : T h r e s h o l d = 4.19;No. sampl - 99 -Maximum = 700.00; Minimum = 3-87 Average = 74.40; Std . dev. - 149-529 Success r a t e = 8.70% - 100 -Table V: Performance o f the genuine samples. SUBJECT CORRECT RECOGNITION RATE. AA 8 1 . 8 2 % BB 1 0 0 . 0 0 % CC 1 0 0 . 0 0 % DD 1 0 0 . 0 0 % EE 8 1 . 8 2 % FF 7 0 . 0 0 % GG 1 0 0 . 0 0 % HH 1 0 0 . 0 0 % J J 9 0 . 0 0 % KK 9 0 . 9 1 % AVERAGE 9 1 . 4 5 5 % - 101 -Table V I : Random F o r g e r y - S u b j e c t 00. V e r i f i c a t i o n measures. R e f e r e n c e : 0M0R 80-12- 7 RANDOM FORGERY ON SUBJECT 00. AKI3 100.28 F AKI13 400.07 F AKI23 300.21 F AKI33 400.15 F AKI43 300.14 F AYA3 600.05 F AYA13 1000. F AYA23 600.04 F AYA33 500.03 F AYA43 800.03 F DDE03 300.09 F DDE 13 400.09 F DDE23 100.25 F DDE33 100.35 F DDE43 200.15 F DST3 300.29 F DST13 500.14 F DST23 500.22 F DST33 400.24 F DST43 400.26 F LMA3 800.06 F LMA13 900.03 F - 102 -LMA23 900.05 F LMA33 800 . 0 6 F LMA43 900 . 0 2 F M I M 0 3 300.32 F MIM13 300.24 F MIM23 300 . 2 1 F MIM33 300.24 F MIM53 400.14 F PDL3 2 0 0 . 3 1 F PDL23 300 . 0 9 F PDL33 2 0 0 . 0 8 F PDL43 2 0 0.15 F PFD3 1 0 0 . 2 1 F PFD13 100.07 F PFD33 5 - 7 2 F PFD43 1 0 0 . 1 0 F P F D 5 3 3.17 P RDC3 100.05 F RDC23 100.04 F RDC33 1 0 0 . 0 6 F RDC43 1 0 0 . 1 5 F T S A 3 400 . 1 1 F T S A 1 3 500.08 F T S A 2 3 500.05 F T S A 3 3 500.07 F T S A 5 3 500.04 F - 103 -Test s t a t i s t i c s : T h r e s h o l d = 4.19;No. sampl Maximum = 1000.03; Minimum 3-17 Average = 377-40; S t d . dev. = 260.003 Success r a t e = 2.08% - 104 -3.5 D i s c u s s i o n of R e s u l t s . The r e s u l t s of the v a r i o u s t e s t s are here d i s c u s s e d from s e v e r a l p o i n t s o f view. The assumption o f independent parameters f o r c o m p u t a t i o n a l ease i s reviewed f i r s t . A f t e r t h a t , the acceptance and r e j e c t i o n r a t e s are examined. 3.5.1 Parameter dependencies. From the above, we can see t h a t q u i t e a few of the parameters have non-zero o f f - d i a g o n a l c o r r e l a t i o n c o e f f i c i e n t s f o r most s u b j e c t s . However, f o r the number of samples used to g e n e r a t e the r e f e r e n c e , we can see t h a t some of them can be c o n s i d e r e d i n d e p e n d e n t , at a g i v e n l e v e l o f c o n f i d e n c e . Mendenhall and S c h e a f f e r [MEND73] g i v e a s t a n d a r d normal t e s t s t a t i s t i c f o r use i n t e s t i n g hypotheses about the c o r r e l a t i o n (p) u s i n g the sample c o r r e l a t i o n r . In o r d e r to t e s t the h y p o t h e s i s t h a t the p o p u l a t i o n c o r r e l a t i o n p= 0, the s t a t i s t i c i s : (1 + r ) Z = ( 1 / 2 ) l n < > • 7 ( n - 3 ) (1 - r ) At the ot l e v e l o f s i g n i f i c a n c e , we can d e c l a r e t h a t two parameters are u n c o r r r e l a t e d i f the v a l u e 'z| _< z(<*/2). The v a l u e o f z(o(./2) i s o b t a i n e d from the s t a n d a r d normal t a b l e . E q u i v a l e n t l y , t h i s v a l u e of \z\ can be used to determine the t h r e s h o l d v a l u e o f the sample c o r r e l a t i o n | r ( o 6 ) | . From the t a b l e s , z(0.025) = 1.960 - 105 -z(0.005) = 2.575 Using these v a l u e s , and d i f f e r e n t v a l u e s o f n r e f e r e n c e or t r a i n i n g sample s i z e - we o b t a i n the |r(c6)! i n Table V I I . Table V I I : T h r e s h o l d v a l u e s f o r parameter c o r r e l a t i o n s . n : 5 10 15 2 0 25 ! r ( 0 . 05)! : 0 . 8 8 2 0 . 5 8 8 0 . 5 1 2 0 . 4 4 3 0 . 3 8 7 ! r ( 0 . 0 1)1 : 0 . 9 4 9 0.750 0 . 6 1 3 0 . 5 5 4 0 . 4 9 1 Thus, a t the ci= 0.05 l e v e l o f s i g n i f i c a n c e , a sample s i z e o f 16 would s e t the t h r e s h o l d o f the sample c o r r e l a t i o n at a p p r o x i m a t e l y 0.5- The c o r r e s p o n d i n g v a l u e f o r ot = 0.01 i s 25. Look i n g a t the da t a i n Table IV we see t h a t the s i g n i f i c a n t parameter dependencies d i f f e r from s u b j e c t t o s u b j e c t . I t i s a l s o apparent t h a t o n l y a few of the parameters can be c o n s i d e r e d s i g n i f i c a n t l y c o r r e l a t e d . T h i s means t h a t we can o p e r a t e r e a s o n a b l y w e l l w i t h the assumption t h a t the c o - o r d i n a t e system o f parameters i s o r t h o g o n a l . T h i s s i m p l i f i e s the com p u t a t i o n s r e q u i r e d t o determine the d i s t a n c e o f a g i v e n sample from the mean of the p o p u l a t i o n i t i s p u r p o r t e d t o belong t o . 3-5.2 F a l s e r e j e c t i o n r a t e . The f a l s e r e j e c t i o n r a t e of n e a r l y 10? i s r a t h e r d i s c o u r a g i n g . We n o t e , however, t h a t i n t h i s work, o n l y e i g h t parameters were used. In [MAUC65], f o r example, 19 parameters - 106 -- the v a l u e s were used and a f a l s e r e j e c t i o n r a t e o f 10% was a l s o o b t a i n e d . Thus, i t may be n e c e s s a r y to i n c r e a s e the number of parameters, or s u b s t i t u t e those e x h i b i t i n g h i g h v a r i a b i l i t y w i t h o t h e r s o f l o wer v a r i a n c e ( h i g h e r p r e c i s i o n ) to improve the performance beyond t h i s l e v e l . A r e v i s i o n o f the measures used and the method of r e f e r e n c e g e n e r a t i o n employed i s q u i t e c l e a r l y c a l l e d f o r and s h o u l d be one o f the major t a r g e t s i n f u r t h e r development of the system. 3 . 5 . 3 F a l s e a c c e ptance r a t e . The f a l s e acceptance r a t e o f under 3% f o r f i r s t - d a y f o r g e r i e s was q u i t e r e a s o n a b l e . T h i s i n d i c a t e s the l e v e l o f s u c c e s s to be expected from . ' o c c a s i o n a l ' f o r g e r s . The h i g h e r v a l u e (9%) o f f i n a l - d a y f a l s e a c c e p t a n c e s i n d i c a t e s t h a t as some l e a r n i n g o f the s p a t i a l c h a r a c t e r i s t i c s i s a c q u i r e d by the f o r g e r s , t h e i r s u c c e s s becomes more a s s u r e d . The r e s u l t i s q u i t e e n c o u r a g i n g and f u r t h e r work on r e d u c i n g the f a l s e r e j e c t i o n r a t e s h o u l d a l s o c o n s i d e r r e d u c i n g t h i s p a r t i c u l a r e r r o r . 3 . 5 . 4 Random f o r g e r y acceptance r a t e . The random f o r g e r y r a t e f o r the examples p r o c e s s e d was 2.08%. However, i t must be noted t h a t the database on which t h i s e r r o r was e v a l u a t e d c o n s i s t e d o f a r a t h e r s m a l l number of p e o p l e . The r e - e v a l u a t i o n o f t h i s parameter on a much l a r g e r database would g i v e a more s i g n i f i c a n t e s t i m a t e . - 107 -1 3.5.5 Data Compression. C o n s i d e r i n g t h a t we are u s i n g o n l y 8 measures i n the v e r i f i c a t i o n , the above are v e r y e n c o u r a g i n g r e s u l t s . The r e q u i r e d s t o r a g e o f the measures, i n the p r i n t a b l e form shown i n Table I I I , t a k e s up o n l y 830 b y t e s per pers o n . T h i s i s q u i t e r e a s o n a b l e s i n c e the e l i m i n a t i o n of unused d a t a and t e x t w i l l reduce t h i s c o n s i d e r a b l y . T h i s w i l l make i t f e a s i b l e t o encode the d a t a on a p o r t a b l e medium such as a " m a g s t r i p e " c a r d . - 108 -3.6 Sources o f E r r o r . F o r g e r y e r r o r s a r i s e from a l a c k o f s e p a r a t i o n o f parameter v a l u e s f o r d i f f e r e n t s u b j e c t s . F a l s e r e j e c t i o n e r r o r s , on the o t h e r hand, a r i s e from too d i v e r s e a s c a t t e r i n g o f parameter v a l u e s from one s u b j e c t . Both t y p e s o f e r r o r are dependent on the parameters chosen. However, a v e r y l a r g e f r a c t i o n o f the e r r o r can a l s o a r i s e by assuming p e r f e c t measurements from the t r a n s d u c e r s . The parameters used here which are most i n s e n s i s t i v e to l i n e a r i t y and h y s t e r e s i s i n the measuring d e v i c e s a r e : ( i ) The d u r a t i o n o f the s i g n a t u r e . and ( i i ) The z e r o - and a v e r a g e - c r o s s i n g measurements. S i n c e t h e s e m e a s u r e m e n t s - c o n s t i t u t e o n l y h a l f the parameter s e t , improvements i n the t r a n s d u c t i o n s h o u l d have a s i g n i f i c a n t b e n e f i c i a l i n f l u e n c e on the performance. - 109 -3«7 Performance Comparison. In comparing t h i s approach t o i d e n t i t y v e r i f i c a t i o n by o t h e r means we can observe the f o l l o w i n g . The r e l a t i v e m e r i t of automated s i g n a t u r e v e r i f i c a t i o n over human s i g n a t u r e i n t e r p r e t a t i o n i n the commercial s e t t i n g i s q u i t e h i g h . A l t h o u g h no f i g u r e s are i m m e d i a t e l y a v a i l a b l e , i t i s h e l d t h a t bank t e l l e r s and cash r e g i s t e r o p e r a t o r s accept v i r t u a l l y 100? o f the f o r g e d s i g n a t u r e s they are p r e s e n t e d w i t h [SYKE78]. F i n g e r p r i n t s have l o n g been used to p o s i t i v e l y i d e n t i f y p e o p l e , e s p e c i a l l y those w i t h r a t h e r f l u i d i d e n t i t i e s , t h a t i s : v a r y i n g names and appearances. As a r e s u l t , f i n g e r p r i n t i n g has tended t o be a s s o c i a t e d w i t h the appr e h e n s i o n o f c r i m i n a l s . Thus, the g e n e r a l a c c e p t a b i l i t y o f f i n g e r p r i n t i n g i s lower than t h a t of s i g n a t u r e v e r i f i c a t i o n . However, even i f t h i s s t i g m a were to be e r a s e d , the s t a t i c n a t u r e o f the f i n g e r p r i n t makes i t s u s c e p t i b l e to f a l s i f i c a t i o n , say by making a rubber r e p l i c a o f the genuine p r i n t and p l a c i n g t h i s over the i m p o s t o r ' s own d i g i t . The e s s e n t i a l l y 0? f a l s e r e j e c t i o n would t h e r e b y be o f f s e t by a p o t e n t i a l 100? f a l s e a c c e p t a n c e . T h i s i s f u r t h e r enhanced by the f a c t t h a t a commercial u n i t can not perform the e l a b o r a t e comparisons done by d e t e c t i v e s [SYKE78], and w i l l t h e r e f o r e use a c o a r s e r r e p r e s e n t a t i o n o f the f i n g e r p r i n t . The use o f a f a c e p i c t u r e i s s u b j e c t t o the same k i n d o f e r r o r s mentioned above. Due t o i t s s t a t i c n a t u r e , a f a c e mask o f the genuine s u b j e c t c o u l d be made and used f o r f r a u d u l e n t a c c e s s . The i n t r o d u c t i o n o f dynamic measures, such as the sequence o f changes the person's f a c e goes through when - 1 10 -b e g i n n i n g t o s m i l e , would h e l p but i t i s d i f f i c u l t t o s m i l e i n the same f a s h i o n under d i f f e r e n t c o n d i t i o n s . P r o t e c t i o n u s i n g passwords i s q u i t e w i d e s p r e a d , f o r example i n computing communities. The i n i t i a l password i s ge n e r a t e d by the system and r e v e a l e d t o the u s e r . S u b s e q u e n t l y , t h i s may be changed by e i t h e r the user or the system ( i n m i l i t a r y encampents, f o r example) w i t h the knowledge o f the o t h e r . Now, i t _is p o s s i b l e t o f i n d out passwords e i t h e r from the system database or by c l o s e l y w atching a genuine u s e r when ( s ) h e uses the f a c i l i t y , and t h e r e b y g a i n a c c e s s t o the o t h e r person's a s s e t s . Changing the passwords f r e q u e n t l y w i l 1 i n c r e a s e the s e c u r i t y , but i t w i l l a l s o put the u s e r s under g r e a t e r s t r e s s , w i t h the p o s s i b l e consequence o f a h i g h e r f a l s e r e j e c t i o n r a t e due- t o the people f o r g e t t i n g t h e i r c u r r e n t passwords. The use o f v o i c e r e c o g n i t i o n methods i s q u i t e s i m i l a r t o the use of s i g n a t u r e v e r i f i c a t i o n . However, the use o f a tape r e c o r d i n g o f the s u b j e c t ' s v o i c e can not be d i s c o u n t e d . The method used to c o u n t e r a c t t h i s p a r t i c u l a r s t y l e o f ' f o r g e r y ' i s to randomise the words the person i s asked to pronounce. However, t h i s b r i n g s up a major f a c t o r i n a l l o f these a l t e r n a t i v e systems - the c o s t of the i n p u t and ou t p u t t r a n s d u c e r s t o g e t h e r w i t h t h e i r c o n t r o l l e r s i s v e r y h i g h . The t r a n s d u c e r used i n the p r e s e n t work i s v e r y easy t o manufacture and can be packaged v e r y c o m p a c t l y . Thus, the mass p r o d u c t i o n o f t h i s u n i t i s c o m m e r c i a l l y v i a b l e . The major r e s t r i c t i o n on the use o f the d e v i c e here i s the i m p l i c i t r e q u i r e m e n t f o r a secure s i g n a l path from the - 1 1 1 -tran-sducer t o the p r o c e s s i n g and comparison system. T h i s system would o n l y have l i m i t e d s e c u r i t y , as would most o t h e r s , i n a p p l i c a t i o n s where t h e r e i s room f o r a ' t r a c i n g ' ( r e c o r d i n g ) o f the s i g n a l s from the genuine s i g n e r t o be made. These s i g n a l s c o u l d c o n c e i v a b l y be l a t e r i n j e c t e d by an i m p o s t o r i n t o the communication channel f o r t r a n s m i s s i o n t o the p r o c e s s i n g system. Such a s i t u a t i o n c o u l d be e n v i s a g e d i n a "bank-at-home" environment. The next and f i n a l c h a p t e r summarises c o n t r i b u t i o n s o f the work done f o r t h i s t h e s i s and g i v e s some s u g g e s t i o n s f o r the f u r t h e r work r e q u i r e d t o f i n a l i s e the i d e n t i t y v e r i f i c a t i o n p r o j e c t . - 112 -4. CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK. Th i s c h a p t e r i s a summary of the c o n t r i b u t i o n s made i n t h i s work. I t a l s o o u t l i n e s a r e a s where more work needs t o be done i n o r d e r to r e a l i s e the u l t i m a t e g o a l s o f the p r o j e c t as s t a t e d a t the o u t s e t . 4.1 C o n t r i b u t i o n s Of T h i s Research. The main c o n t i b u t i o n o f t h i s work i s the i n v e s t i g a t i o n o f the use o f p o s i t i o n ( x , y and h i g h e r d e r i v a t i v e s ) and normal f o r c e (p and h i g h e r d e r i v a t i v e s ) to develop a parameter based s i g n a t u r e v e r i f i c a t i o n system. T h i s system thus i n c o r p o r a t e s i n f o r m a t i o n c h a r a c t e r i s t i c o f both the s i g n e r and the s i g n a t u r e . The i n f o r m a t i o n c h a r a c t e r i s t i c o f the s i g n a t u r e c o r r e s p o n d s to t h a t used i n t r a d i t i o n a l s i g n a t u r e v e r i f i c a t i o n by humans, whereas the i n f o r m a t i o n c h a r a c t e r i s t i c o f the s i g n e r ( h i s / h e r dynamic w r i t i n g h a b i t s ) i s t y p i c a l o f the-more modern approach o f machine-based v e r i f i c a t i o n . The system developed here a l l o w s the use o f a combined approach i n c o r p o r a t i n g both t y p e s of i n f o r m a t i o n i n a non-'ad hoc' manner. The advantages o f t h i s approach a r e : 1. The v a r i a b l e s t r a n s d u c e d a l l o w the d i s p l a y i n g o f the a c q u i r e d s i g n a t u r e w h i l e s i m u l t a n e o u s l y computing the w r i t i n g dynamics. T h i s i s a l s o a c h i e v e d w i t h minimal i n t e r f e r e n c e w i t h the w r i t i n g p r o c e s s . 2. The parameters method of d a t a r e p r e s e n t a t i o n l e a d s to a - 113 -r e l a t i v e l y s m a l l d a t a s t o r a g e r e q u i r e m e n t , low run-time c o m p u t a t i o n a l c o m p l e x i t y and h i g h s e c u r i t y , e s p e c i a l l y from ' i n s i d e ' f o r g e r s . In c o n c l u s i o n , the f o l l o w i n g can be s a i d about the system t e s t e d i n t h i s work. 1. The t r a n s d u c e r system used here has a n o t i c e a b l e amount o f h y s t e r e s i s and n o i s e . Both o f these would a d v e r s e l y a f f e c t the performance o f the o v e r a l l system, 2. The e r r o r r a t e s due to f a l s e a c c e p tance (10% maximum) and f a l s e r e j e c t i o n (9%) are u n a c c e p t a b l y h i g h , a l t h o u g h the number o f parameters used was q u i t e s m a l l ( 8 ) . 3. The parameters chosen f o r the study were found to be r e l a t i v e l y u n c o r r e l a t e d . Assuming t h a t they c o l l e c t i v e l y f o l l o w a m u l t i v a r i a t e normal d i s t r i b u t i o n , they can be c o n s i d e r e d independent [MEND73]• When t h i s i s the c a s e , the paramaters form an o r t h o g o n a l s e t of c o o r d i n a t e s i n the f e a t u r e space, which makes the d e t e r m i n a t i o n of d i s t a n c e s between p o i n t s r e l a t i v e l y easy. - 1 1 4 -4.2 S u g g e s t i o n s For F u r t h e r Work. The r e s u l t s of the v e r i f i c a t i o n experiment suggest t h a t i t i s n e c e s s a r y to r e v i s e the parameter s e t used. In a d d i t i o n , the setup f o r o n - l i n e v e r i f i c a t i o n s h o u l d be r e a l i z e d . T h i s o n l y r e q u i r e s changing the p r e s e n t r o u t i n e s so t h a t the end o f the d a t a a c q u i s i t i o n s t a r t s o f f the c h a i n o f program e x e c u t i o n s c u r r e n t l y b e i n g done manu a l l y . Some more work needs to be done on the system/user i n t e r f a c e , to improve i t s convenience as shown -below. ( i ) The s e n s i t i v i t y o f the d e v i c e s h o u l d be improved so t h a t t h e r e i s no need f o r people to p r e s s h a r d e r than they u s u a l l y do, f o r the system to o b t a i n good p o s i t i o n a l r e s o l u t i o n . T h i s w i l l enhance the usage of parameters d i r e c t l y dependent on the magnitude o f the w r i t i n g f o r c e and the a c t u a l p o s i t i o n a l c o o r d i n a t e s . For example, persons who n o r m a l l y w r i t e h e a v i l y w i l l be e a s i l y d i s t i n g u i s h a b l e from those who n o r m a l l y w r i t e r a t h e r l i g h t l y , ( i i ) F a c i l i t i e s f o r e a s i l y c lamping the paper w h i l e w r i t i n g , and changing i t a f t e r w r i t i n g so t h a t no c o p i e s o f s i g n a t u r e s are l e f t l y i n g around, s h o u l d be d e v e l o p e d . In o r d e r to improve the performance o f the d a t a a c q u i s i t i o n system, the f o l l o w i n g s h o u l d be c o n s i d e r e d . ( i ) R e d u c t i o n o f h y s t e r e s i s and n o i s e i n the system. ( i i ) D i g i t a l f i l t e r i n g o f the a c q u i r e d s i g n a l s b e f o r e the parameter e x t r a c t i o n i s performed. T h i s would f u r t h e r reduce the e f f e c t s o f n o i s e on the o v e r a l l system performance. - 1 1 5 -Another a r e a which needs to be addressed i s the i m p l e m e n t a t i o n o f the system on a s m a l l machine, such as a microcomputer. T h i s would open up the p o s s i b i l i t y o f i n c o r p o r a t i n g the s i g n a t u r e a n a l y s i s f u n c t i o n i n t o the t e r m i n a l s c u r r e n t l y b e i n g used f o r o t h e r purposes o n l y . C a n d i d a t e s f o r t h i s m o d i f i c a t i o n would i n c l u d e p o i n t - o f - s a l e t e r m i n a l s i n s t o r e s , t e l l e r s ' t e r m i n a l s i n banks and au t o m a t i c banking t e r m i n a l s among o t h e r s . T h i s s t e p r e q u i r e s o b t a i n i n g or d e v e l o p i n g a d a t a a c q u i s i t i o n f r o n t end which i s l a r g e l y s e l f - c o n t a i n e d so t h a t the t e r m i n a l p r o c e s s o r i s not o v e r l o a d e d . In a d d i t i o n , the d e t e r m i n a t i o n o f a s m a l l number o f c h a r a c t e r i s t i c s , s u i t a b l e f o r encoding on a ca r d the user c a r r i e s would be v e r y advantageous. The advantage would be even g r e a t e r i f the da t a c o u l d be encoded on a 'read o n l y ' k i n d o f medium f o r h i g h e r s e c u r i t y . With t h i s f a c i l i t y , p o i n t - o f - s a l e t e r m i n a l s c o u l d then be used f o r v a l i d a t i n g t r a n s a c t i o n s based on a s p e c i a l l y coded c r e d i t c a r d . The use o f a c a r d w i t h the v e r i f i c a t i o n c h a r a c t e r i s t i c s encoded on i t would a l s o enable the v a l i d a t i o n o f s i g n a t u r e s on p e r s o n a l cheques r i g h t at the p o i n t where they are i s s u e d . I t would t h e r e f o r e o b v i a t e the need f o r c a r d s w i t h v i s i b l e s i g n a t u r e s , s i n c e the machine coded c a r d s c o u l d then be used e x c l u s i v e l y . M o d i f y i n g the t e l l e r s ' t e r m i n a l s would b r i n g g r e a t e r a c c u r a c y t o the u s u a l f u n c t i o n of v a l i d a t i n g banking t r a n s a c t i o n s by h a n d w r i t t e n s i g n a t u r e . The use o f s i g n a t u r e s a n a l y s e d ' o n - l i n e ' i n a u t o m a t i c banking t e r m i n a l s would g r e a t l y - 1 1 6 -enhance t h e i r s e c u r i t y and p o s s i b l y i n c r e a s e t h e i r usage. T h i s l a s t e f f e c t c o u l d g r e a t l y reduce c o n g e s t i o n i n s i d e banks. The c o m p i l a t i o n and maintenance o f r e f e r e n c e parameter r e c o r d s would be handled by a l a r g e r , c e n t r a l i s e d computing f a c i l i t y . The c e n t r a l i s e d f a c i l i t y would a l s o be used to p r o v i d e the customers w i t h t h e i r s i g n a t u r e - e n c o d e d c a r d s . The i m p l e m e n t a t i o n and f i e l d t e s t i n g o f at l e a s t one s p e c i f i c a p p l i c a t i o n of the t e c h n i q u e , embodying the f u r t h e r developments i n d i c a t e d above s h o u l d be a major t a r g e t f o r f u t u r e work on t h i s p r o j e c t . - 1 1 7 -5- REFERENCES. 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[ N E M C 7 4 ] Nemcek, W.F. and L i n , W.C.: " E x p e r i m e n t a l i n v e s t i g a t i o n o f a u t o m a t i c s i g n a t u r e v e r i f i c a t i o n " , IEEE T r a n s a c t i o n s on Systems, Man and C y b e r n e t i c s , 1 9 7 4 , SMC-4 ( 1 ) , pp. 1 2 1 - 1 2 6 . [ O D E L 7 9 ] O d e l l , P.L.: "A model f o r dimension r e d u c t i o n i n p a t t e r n r e c o g n i t i o n u s i n g - c o n t i n u o u s d a t a " , P a t t e r n R e c o g n i t i o n , 1 9 7 9 , 11 ( 1 ) , PP- 51-54. [SAKA??] S a k a i , T., Kanade , T. and A r i k i , Y.: " M u l t i - f e a t u r e d i s p l a y o f o n - l i n e s i g n a t u r e by c o l o u r TV", anon., pp. 303-304. [STER75] S t e r n b e r g , J . : "Automated s i g n a t u r e v e r i f i c a t i o n u s i n g h a n d w r i t i n g p r e s s u r e " , Wescon T e c h n i c a l P a p e r s , 1975, 19, Paper no. 3 1/4. [ S T O C 7 3 ] Stockman, G.C., Kanal , L. and K y l e , M.C.: "Design o f a waveform p a r s i n g system", P r o c e e d i n g s o f the F i r s t I n t e r n a t i o n a l J o i n t Conference on P a t t e r n R e c o g n i t i o n , 1 9 7 3 , pp. 2 3 6-243-[ S Y K E 7 8 ] Sykes, D.J.: " P o s i t i v e p e r s o n a l i d e n t i f i c a t i o n " , D atamation, 1 9 7 8 , 24 (Nov. 1 ) , pp. 1 7 9 - 1 8 6 . - 1 1 9 -[ T R I P 5 7 ] T r i p p , C.A., F l u c k i g e r , F.A., and Weinberg, G.H.: "Measurement of h a n d w r i t i n g v a r i a b l e s " , P e r c e p t u a l and Motor S k i l l s , 1 9 5 7 , 2, pp. 2 7 9-294. [USP77a] U.S. P a t e n t No. 4 040 010, 1 9 7 7 Feb. 08 (Crane, Wolf and Ostrem). [USP77b] U.S. Pa-tent No. 4 040 01 1, 1 9 7 7 Feb. 08 (Crane and J o n e s ) . [ U S P 7 7 c ] U.S. P a t e n t No. 4 040 0 1 2 , 1 9 7 7 Feb. 08 (Crane, Wolf and L i n d e n b e r g ) . [USP78a] U.S. P a t e n t No. 4 086 567, 1978 Apr. 25 (Crane and Wolf) . [USP78b] U.S. P a t e n t No. 4 128 829, 1978 May 12 ( H e r b s t and L i u ) . [USP78c] U.S. P a t e n t No. Re. 29 765, 1978 Sep. 19 (Crane, Taenzer and Andeen). [VRED71] V r e d e n b r e g t , J . and K o s t e r , W.G.: " A n a l y s i s and s y n t h e s i s o f h a n d w r i t i n g " , P h i l i p s T e c h n i c a l Review, 1971, 3 2 ( 3/4) , pp. 73-78. [ Y A S U 7 1 ] Yasuhara, M.: "Steps toward h a n d w r i t i n g a n a l y s i s and r e c o g n i t i o n " , V i s i b l e Language, 1 9 7 1 , 5. ( 3 ) , pp. 229-248. [YASU77] Yasuhara, M. and Oka, M.: " S i g n a t u r e v e r i f i c a t i o n e xperiment based on n o n - l i n e a r time a l i g n m e n t : a f e a s i b i l i t y s t u d y " , IEEE T r a n s a c t i o n s on Systems, Man and C y b e r n e t i c s , 1 9 7 7 , SMC-7 ( 3 ) , PP. 212-216. - 120 -APPENDIX A. In t h i s appendix, c o l l e c t i o n s o f i n f o r m a t i o n t h a t would have c l u t t e r e d up the main p r e s e n t a t i o n are p r e s e n t e d . A1 c o n t a i n s the d e t a i l e d e x p e r i m e n t a l r e s u l t s and A2 g i v e s the programme d e s c r i p t i o n s . 121 -A1. D e t a i l e d R e s u l t s . The d e t a i l e d r e s u l t s t a b l e s from the experiment are p r e s e n t e d h e r e , t o g e t h e r w i t h some o t h e r i n f o r m a t i o n t h a t c o u l d not be put i n the main body o f the t h e s i s . Table V I I I c o n t a i n s the parameters computed from the samples a c q u i r e d on the f i r s t day o f the i n v e s t i g a t i o n . In t h a t t a b l e , the f i r s t p a r t c o n t a i n s the e i g h t parameters used i n the i d e n t i t y v e r i f i c a t i o n e x p e r i m e n t , l i s t e d i n the same o r d e r t h a t they are d e s c r i b e d i n s e c t i o n s 3 . 2 . 3 and 3 . 4 . 1 . Table IX c o n t a i n s the d e t a i l s o f the performance o f i n d i v i d u a l samples i n the t e s t s t o determine the average c o r r e c t r e c o g n i t i o n . F i g . 13 i s a sample p l o t of the t r a n s d u c e d v a r i a b l e s . - 122 -Table V i l l a : Parameters F1 - F8 computed from f i r s t samples. PRELIMINARY DATA ANALYSIS: Parameter Values • 80-11- 17 Source Dur . Za Zp ZP #Seg CM2(s) Av g. spd. CM2(p>) SAA1 113 33 21 27 4 1 .210E 0 5. 900E 1 3 .040E 0 SAA2 1 7 3 37 31 31 6 1 . 220E 0 5. 010E 1 3 . 340E 0 SAA3 146 31 21 31 2 1 .560E 0 4. 520E 1 3 . 350E 0 SAA4 145 35 22 31 4 1 . 610E 0 4. 470E 1 3 . 010E 0 SAA5 1 3 5 33 22 25 5 1 .640E 0 4. 620E 1 2 .800E 0 SBB1 179 37 31 33 6 1 . 190E 0 3- 140E 1 3 . 430E 0 SBB2 156 33 27 31 7 1 .060E 0 3- 150E 1 3 . 360E 0 SBB3 194 43 33 37 7 1 . 190E 0 2. 700E 1 2 .780E 0 SBB4 1 9 3 43 29 37 6 1 .240E 0 2. 920E 1 3 . 100E 0 SBB5 182 33 27 35 6 1 .260E 0 2. 7 1 0 E 1 3 . 580E 0 SDD1 207 43 31 45 5 1 . 220E 0 2. 900E 1 2 .970E 0 SDD2 218 49 32 43 5 1 . 300E 0 2. 970E 1 2 . 200E 0 SDD3 208 47 31 47 4 1 . 120E 0 2. 850E 1 3 .030E 0 SDD4 2 1 9 45 31 49 5 1 . 150E 0 3 . 080E 1 2 . 550E 0 SDD5 212 47 34 47 6 1 . 140E 0 3 . 190E 1 2 . 470E 0 SMM1 243 51 7 33 1 2 .250E 0 2. 270E 1 5 .870E -1 SMM2 210 47 13 33 1 1 . 440E 0 2. 560E 1 1 . 330E 0 SMM3 108 21 17 23 3 2 . 200E 0 6. 600E 1 2 . 400E 0 SMM4 1 1 1 21 11 23 2 2 . 470E 0 5. 500E 1 2 . 700E 0 SMM5 1 1 5 27 12 21 2 2 . 1 10E 0 5. 700E 1 2 . 190E 0 SLL1 227 51 37 45 10 1 . 180E 0 6. 450E 1 1 . 860E 0 SLL2 2 3 1 5 3 43 43 12- 1 .060E 0 5. 950E 1 2 • 570E 0 SLL3 238 55 39 43 12 1 .220E 0 5. 990E 1 2 . 3 1 0 E 0 SLL4 2 3 5 49 44 45 12 1 .080E 0 5. 410E 1 2 • 350E 0 - 124 -SLL5 238 49 41 45 13 1 . 430E 0 6 .270E 1 2 . 580E 0 SNN1 305 63 33 47 4 1 . 480E 0 2 . 120E 1 2 . 9 1 0 E 0 SNN2 306 67 33 47 4 1 .820E 0 2 .010E 1 2 .660E 0 SNN3 308 53 27 43 5 1 .830E 0 2 .210E 1 1 . 620E 0 SNN4 308 57 37 47 4 1 . 800E 0 2 230E 1 3 . 120E 0 SNN-5 281 61 37 43 4 1 . 590E 0 2 200E 1 3 .010E 0 SGG1 219 53 17 39 4 1 • 060E 0 3 030E 1 1 520E 0 SGG2 185 51 23 35 4 1 .050E 0 3 480E 1 1 810E" 0 SGG3 214 51 21 45 3 1 . 080E 0 3 060E 1 2 030E 0 SGG4 218 49 19 41 3 1 250E 0 3 100E 1 1 370E 0 SGG5 252 55 19 39 3 1 300E 0 2 720E 1 9 640E -1 SHH1 90 31 15 13 1 4 .850E -1 3 500E 1 2 490E 0 SHH2 101 33 15 19 1 6 . 190E -1 2 970E 1 1 9 10E 0 SHH3 130 35 23 23 2 1 030E 0 2 690E 1 3 210E 0 SHH4 138 33 17 23 1 7 510E -1 2. 350E 1 1 920E 0 SHH5 129 29 19 19 3 2 760E 0 3- 050E 1 2 000E 0 SJJ1 169 35 21 29 3 1 160E 0 2. 980E 1 2 420E 0 SJJ2 170 37 21 27 3 1 180E 0 3< 220E 1 3- 030E 0 SJJ3 162 41 14 29 2 1 030E 0 3- 510E 1 2. 050E 0 SJJ4 160 39 15 27 2 1 060E 0 3- 300E 1 2. 050E 0 SJJ5 163 33 23 27 3 1 220E 0 3- 240E 1 3- 220E 0 SKK1 137 31 17 29 8 1 530E 0 5. 360E 1 2 , 270E 0 SKK2 160 39 27 33 5 1 . 090E 0 3- 400E 1 4 . 030E 0 SKK3 170 45 29 37 5 9- 720E -1 2, 980E 1 4 . OOOE 0 SKK4 173 43 26 33 6 9- 950E -1 3- 180E 1 4 . 230E 0 SKK5 179 43 29 35 6 1. 020E 0 3 . 050E 1 4 . 420E 0 / - 125 -Table V H I b : R e l a t i v e d u r a t i o n s o f pen-down segments. PRELIMINARY DATA ANALYSIS: Parameter 1 V a l u e s . 80--11-•17 Source #Seg pD( D pD(2) PD ( 3 ) pD(4) pD(5) pD(6) PD(7) PD(8) SAA1 4 20. 35 1. 77 6 3 . 72 10. 62 0. 00 0. 00 0. 00 0. 00 SAA2 6 1 9 . 65 4. 05 10. 98 16 . 76 9. 83 3 4 . 68 0. 00 0. 00 SAA3 2 1 9 . 86 7 8 . 08 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 SAA4 4 19 . 31 4. 83 7 1 . 03 1. 38 . o . 00 0. 00 0. 00 0. 00 SAA5 5 17. 78 1. 48 4. 44 1 1. 85 60. 74 0. 00 0. 00 0. 00 SBB1 6 13- 97 5. 03 16. 20 5. 59 28. 49 27. 37 0. 00 0. 00 SBB2 7 19- 23 6. 41 16 . 03 4. 49 25. 64 5. 13 17. 95 0. 00 SBB3 7 14. 95 6. 19 14. 95 3- 61 24. 23 12. 89 1 9 . 07 0. 00 SBB4 6 14. 51 4. 15 12. 95 3- 63 24. 87 3 6 . 79 0. 00 0. 00 SBB5 6 14. 29 4. 95 14. 29 3- 30 24. 73 35. 16 0. 00 0. 00 SDD1 5 11. 59 30. 92 15. 94 35. 27 3- 86 0. 00 0. 00 0. 00 SDD2 5 12. 84 28. 90 0. 92 54. 13 0. 92 0. 00 0. 00 0. 00 SDD3 4 43. 27 15. 87 3 7 . 50 1. 44 0. .00 0. 00 0. 00 0. 00 SDD4 5 11 . 87 28. 77 17. 35 0. 91 3 8 . 36 0. 00 0. 00 0. 00 SDD5 6 12. 26 28. 77 0. 94 16. 04 3 6 . 32 2. 83 0. 00 0. 00 SMM1 1 99. 59 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 SMM2 1 99. 52 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 SMM3 3 18. 52 1. 85 75. 93 0. 00 0. 00 0. 00 0. 00 0. 00 SMM4 2 18. 02 80. 18 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 SMM5 2 17. 39 80. 87 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 SLL1 10 14. 98 14. 10 6. 17 3. 52 3- 08 4. 41 4. 41 8. 81 SLL2 12 12. 12 14. 72 6. 49 4. 76 9 . 52 0. 87 13- 85 15. 15 SLL3 12 11. 34 14. 71 7. 14 4. 20 10. 92 1 3 . 45 15. 55 6. 72 SLL4 12 10. 64 22. 98 5. 11 8 . 94 1. 28 14. 89 15. 74-• 4. 68 - 126 -SLL5 13 13 • 03 21 .85 4 .20 8 .82 0 . 8 4 4 .62 7 . 9 8 13 . 8 7 SNN1 4 20 . 3 3 14, . 10 2 • 30 61 • 97 0 .00 0 .00 o. .00 o. .00 SNN2 4 21 • 90 9 .80 1 • 96 64 • 71 0. .00 0, .00 o. .00 o. .00 SNN3 5 22 . 0 8 10, • 39 1, • 95 37 .01 26 , • 95 o, .00 0. .00 o. .00 SNN4 4 20, .13 16, . 2 3 32, .47 29 .87 o, .00 0. .00 0. . 00 o. .00 SNN5 4 33 • .81 4, .27 32. • 38 28 , . 11 0. .00 0. .00 0. . 00 0. .00 SGG1 4 15. .53 2 3 . . 74 1. . 8 3 57 , .08 0. .00 0. .00 0. .00 0. .00 SGG2 4 13. .51 22. .16 2. . 16 60. .00 0. .00 0. . 00 0. ,00 0. .00 SGG3 3 13. .55 2 4 . . 30 6 0 . • 75 0. .00 0. .00 0. .00 0. ,00 0. ,00 SGG4 3 13-. 30 22. .02 6 3 . . 30 0. .00 0. .00 0. .00 0. ,00 0. ,00 SGG5 3 11. .51 21 . -43 65. , 48 0. .00 0, ,00 0. , 00 0. ,00 0' ,00 SHH1 1 98. .89 0. ,00 0, ,00 0. .00 0. ,00 0. ,00 0. ,00 0. ,00 SHH2 1 99. .01 0. , 00 0. ,00 0. , 00 0. ,00 0. ,00 0. ,00 0. , 00 SHH3 2 44. . 62 53-,85 0. ,00 0. .00 0. ,00 0. ,00 0. , 00 0. ,00 SHH4 1 99-,28 0. , 00 0. ,00 0. ,00 0. ,00 0. ,00 0. , 00 0. ,00 SHH5 3 0. ,78 53- 49 44. , 19 0. , 00 0. ,00 0. ,00 0. ,00 0. ,00 SJJ1 3 19-• 53 1. 78 7 6 . • 92 0. ,00 0. ,00 0. ,00 0. . 00 0. ,00 SJJ2 3 17. ,06 2. 35 78. ,82 0. ,00 0. 00 0. ,00 0. 00 0. 00 SJJ3 2 23. ,46 7 5 . 31 0. 00 0. , 00 0. 00 0. 00 0. 00 0. 00 SJJ4 2 19. 38 7 9 . 38 0. 00 0. ,00 0. 00 0. 00 0. 00 0. 00 SJJ5 3 17 . 79 2. 45 77. •91 0. 00 0. 00 0. 00 0. 00 0. 00 SKK1 8 14 . 60 31. 39 16. 79 1 3 . 87 5. 11 5. 84 1. 46 2. 19 SKK2 5 10. 63 23. 13 13. •13 1 1. 88 3 7 . 50 0. 00 0. 00 0. 00 SKK3 5 11. 76 2 4 . 12 12. 94 45. 88 1. 76 0. 00 0. 00 0. 00 SKK4 6 12. 14 2 3 - 70 13- 87 11. 56 31. 79 3- 47 0. 00 0. 00 SKK5 6 12. 85 22. 35 12. 85 12. 29 31- 84 4. 47 0. 00 0. 00 - 127 -Table IX: D e t a i l s o f genuine sample t e s t s . V e r i f i c a t i o n measures. R e f e r e n c e : AKIR 80-12- 3 GENUINE SAMPLES -- SUBJECT AA. AKI2. 5.04 F AKI4. 2. 26 P AKI12. 7.14 F AKI14. 3.28 P AKI22. 3.13 P AKI24. - 2.56 P AKI26. 2.47 P AKI32. 2.54 P AKI34. 3-75 P AKI42. 3.53 P AKI45- 1.32 P Test s t a t i s t i c s : T h r e s h o l d = 4.19;No. samples = 11. Maximum = 7.14; Minimum = 1.32 Average = 3-37; S t d . dev. = 1.575 Success r a t e = 81.82? - 128 -- T a b l e I X • c o n t i n u e d . V e r i f i c a t i o n measures. R e f e r e n c e : AYAR 80-12- 4 GENUINE SAMPLES -- SUBJECT BB AYA2. 1.81 P AYA4. 1 .89 P AYA12. 2. 32 P AYA14. 2.05 P AYA22. 2. 69 P AYA24. 1.81 P AYA26. 2.97 P AYA32. 2.43 P AYA34. 1 .27 P AYA42. - 1.69 P AYA44. 1.98 P Test s t a t i s t i c s : T h r e s h o l d = 4.19;No. samples = 11. Maximum = 2.97; Minimum = 1.27 Average = 2.08; S t d . dev. = 0.485 Success r a t e = 100.00% - 129 -T a b l e - I X c o n t i n u e d . V e r i f i c a t i o n measures. R e f e r e n c e : DDER 80-12- 5 GENUINE SAMPLES - SUBJECT CC. DDE02. 1.53 P DDE04. 2.21 P DDE 12. 2.31 P DDE 14. 2.67 P DDE22. 1 . 40 P DDE24. 3.31 P DDE32. 2.69 P DDE34. 1.72 P DDE42. 2.31 P DDE44. 1.92 P Test s t a t i s t i c s : T h r e s h o l d = 4.19 ;No . Maximum = 3- 31 ; Minimum = 1. 40 Average = 2. 21; S t d . dev. = 0. 589 Success r a t e = 100.00% - 130 -Table IX c o n t i n u e d . V e r i f i c a t i o n measures. R e f e r e n c e : DSTR 8.0-12- 4 GENUINE SAMPLES - SUBJECT DD. DST2. 3-16 P DST4. 2.02 P DST12. 2.60 P DST14. 3-34 P DST22. 2. 30 P DST24. 2.87 P DST32. 2.11 P DST34. 3.60 P DST42. 1 . 42 P DST44. 2.07 P Test s t a t i s t ! c s : -Threshold = 4. 19 ;No . Maximum = 3- 60; Minimum = 1. 42 Average = 2. 55; S t d . dev. = 0 .687 Success r a t e = 100.00% - 131 -Table IX c o n t i n u e d . V e r i f i c a t i o n measures. R e f e r e n c e : LMAR 80-12- 3 GENUINE SAMPLES -. SUBJECT EE. LMA2. 2.14 P LMA4. 4.40 F LMA12. 3-87 P LMA14. 3-82 P LMA22. 3-96 P LMA24. 4.26 F L M A 3 2 . 3-56 P L M A 3 4 . 3-84 P L M A 3 6 . 1 . 32 P LMA42. 2. 32 P LMA44. 3. 15 P Test s t a t i s t i c s : •Threshold = 4.19;No. Maximum = 4. 40; Minimum = 1 . 32 Average = 3 . 3 3 ; S t d . dev. = 0.989 Success r a t e = • 81.82% - 132 -T-able IX c o n t i n u e d . V e r i f i c a t i o n measures. Ref e r e n c e : MIMR 80-12- 5 GENUINE SAMPLES - SUBJECT FF. MIM02. 1 7 - 7 6 F MIM04. 4.64 F MIM12. 3-59 P MIM14. 2 . 9 4 P MIM22. 2.48 P MIM24. 2.12 P M I M 3 2 . 2.82 P MIM34. 4.12 P MIM52. 2 . 3 9 P MIM54. 4.25 F Test s t a t i s t i c s : T h r e s h o l d = 4.19 ;No. Maximum i 1 7 - 7 6 ; Minimum = 2. 12 Average = 4 . 71; S t d . dev. = 4.664 Success r a t e = 70.00? - 1 3 3 -T a b l e IX c o n t i n u e d V e r i f i c a t i o n measures. R e f e r e n c e : PDLR 80-12- 3 GENUINE SAMPLES. PDL2. PDL4. PDL7. PDL9. PDL22. PDL24. PDL32. PDL34. PDL42. PDL44. 2.72 2.77 3-55 3.27 3. 18 2.12 3-34 3- 24 3-97 2.74 P P P P P P P P P P Test s t a t i s t i c s : T h r e s h o l d 4.19;No. samples 10 Maximum = 3>97; Minimum Average = 3.09;- S t d . dev 2.12 0.517 Success r a t e = 100.00% - 134 -Table IX c o n t i n u e d . V e r i f i c a t i o n measures. Re f e r e n c e : PFDR 80-12- 5 GENUINE SAMPLES - SUBJECT HH. PFD2. 2.96 P PFD4. 1.64 P PFD14. 3.61 P PFD32. 2. 10 P PFD34. 2. 47 P PFD42. 1.23 P PFD44. 2.70 P PFD46. 1.56 P PFD52. 2. 15 P PFD54. 1.98 P Test s t a t i s t i c s : T h r e s h o l d = 4. 19 ; N o . Maximum = 3- 6 1 ; Minimum = 1.23 Average = 2. 24; S t d . dev. = 0 • 715 Success r a t e = 100.00% - 135 -Table IX c o n t i n u e d V e r i f i c a t i o n measures. R e f e r e n c e : RDCR- 80-12- 3 GENUINE SAMPLES, RDC2. RDC4. RDC7. RDC9 . RDC22. RDC24. RDC32. RDC34. RDC42. RDC44. 2.20 2. 47 5.56 2. 17 2.72 1.21 3-39 1.96 2.10 2.81 P P F P P P P P P P Test s t a t i s t i c s : T h r e s h o l d 4.19;No . saraples 10, Maximum = 5.56; Minimum = 1.21 Average = 2.66;- S t d . dev. = 1.173 Success r a t e 90.00% - 136 -Table IX c o n t i n u e d . V e r i f i c a t i o n measures. R e f e r e n c e : TSAR 80-12- 4 GENUINE SAMPLES -- SUBJECT KK. TSA2. 2.06 P TSA4. 1.39 P TSA12. 3-04 P TSA14. 1 .62 P TSA22. 1 .66 P TSA24. - 1.06 P TSA32. • 1.89 P TSA34. 1.92 P TSA52. 1.84 P TSA54. 7.17 F TSA56. 1.59 P Test s t a t i s t i c s : T h r e s h o l d = 4.19;No. samples = 11. Maximum = 7.17; Minimum = 1.06 Average = 2.29; S t d . dev. = 1.690 Success r a t e = 90.91% - 137 -A2. Programme c o n t r o l f l o w c h a r t s . In t h i s appendix, the c o n t r o l s t r u c t u r e s o f the d a t a a c q u i s i t i o n and d a t a p r o c e s s i n g r o u t i n e s are d e s c r i b e d i n the form o f p r o g r a m - f l o w c h a r t s . The r o u t i n e s d e s c r i b e d are the f o l l o w i n g : READY (REA l - t i m e D i s p l a Y ) The major d a t a a c q u i s i t i o n r o u t i n e . T h i s was the r o u t i n e t h a t was ru n n i n g i n or d e r t o g i v e the " v o l u n t e e r s p r a c t i c e on the system b e f o r e a c q u i r i n g d a t a from them. The command AQNAME would r e s u l t i n the c r e a t i o n or r e v i s i o n of two f i l e s : NAME and NAME.D i n which the x, y, p and x, y, p d a t a would be saved, r e s p e c t i v e l y . SPX (SPeed e x t r a c t i o n ) For speed and a c c e l e r a t i o n d a t a . The o u t p u t o f t h i s r o u t i n e was a f i l e c o t a i n i n g the i n s t a n t a n e o u s speed and a c c e l e r a t i o n o f the ppen p o i n t a l o n g the d i r e c t i o n o f motio n . I t used the NAME.D f i l e s produced by READY. The f o l l o w i n g r o u t i n e s have a c o n t r o l s t r u c t u r e q u i t e s i m i l a r to t h a t o f SPX and t h e r e f o r e - have not b e e n - d e s c r i b e d . T h e i r p r i n c i p l e s o f o p e r a t i o n -have, however, been covered i n s e c t i o n 3.4 and i t s s u b s e c t i o n s . PROC (PROCessing) F e a t u r e e x t r a c t i o n . T h i s r o u t i n e used the da t a from c o r r e s p o n d i n g NAME and NAME.S f i l e s as produced by SPX. VERI ( V E R I f i c a t i o n ) Sample c l a s s i f i c a t i o n . T h i s used the ( t e x t i n c l u s i v e ) d a t a f i l e s produced by PROC to - 138 -c l a s s i f y the p r o c e s s e d samples on a ' P a s s ' / ' F a i l ' b a s i s . The c o n t e n t s o f Table IX are the o u t p u t s o f t h i s programme. - 139 -(READY) Set up c o n s t a n t s ; Set up m u l t i t a s k i n g ; C l e a r s c r e e n ; Prompt o p e r a t o r f o r s c a l e and f o r c e t h r e s h o l d f o r the d i s p l a y . Set c u r r e n t t a s k p r i o r i t y t o 2; A c t i v a t e keyboard m o n i t o r a t a h i g h e r p r i o r i t y (1) CI e a r - s c r e e n ; C a l l - t a b l e t d r i v e r f o r i n i t i a l f o r c e o f f s e t v e c t o r (FOV) Ring b e l 1 .  /Assumes no w r i t i n g i s t a k i n g p l a c e •(ACCEPT COMMAND) JL C a l l f o r c u r r e n t f o r c e v e c t o r (CFV); Set CFV = CFV - FOV; Compute a p p l i e d f o r c e p from CFV. D i s p l a y the p o i n t (x,y) on the s c r e e n . (£) - 140 -® Coraput e x, y» P Increment a r r a y i n d i c e s IEXT and IDEXT Save x, y P § IEXT; Save x, y, p § IDEXT. 0 Save x, y, p a r r a y on d i s k ; • r e s e t IEXT. Save x, y; p a r r a y on d i s k ; r e s e t IDEXT. ACCEPT COMMAND .Save? N C l e a r i n t e r r u p t f l a g ; Type prompt c h a r a c t e r ; -Read the command -1 i n e : "CCAAA...A" INTERPRET COMMAND Save x _y, p and x, y, p a r r a y s on d i s k . - 141 -INTERPRET COMMAND { E x i t ) Set up system| command f i l e t o execute "AAA...A"; E x i t t o system. K i l l keyboard m o n i t o r Make a copy o f the s c r e e n c o n t e n t s on [+(5) the hardcopy u n i t H5 Set Save?=TRUE; Empty or c r e a t e the f i l e s : AAA...A and AAA...A.D; Open these f i l e s f o r s a v i n g the x, y, p and x, y, p d a t a ; I n i t i a l i z e IEXT and IDEXT; R e a c t i v a t e suspended Keyboard m o n i t o r . - 142 -( s i x ) d> O b t a i n the name o f the p r o c e s s i n g command f i l e from the o p e r a t o r ; Open the f i l e f o r i n p u t . Read the command l i n e CONN...N Open f i l e "NN...N.D" on d a t a - i n p u t channel ; Cr e a t e or empty f i l e "NN...N.S" and open i t on the output channel Read x, y, p from d a t a f i l e ; [Rewind o/p f i l e Compute s from x and y; Save s, NULL, p i n the output f i l e ; • ( E x i t ) • ( E x i t ) <D Read s, NULL and p from p r e v i o u s output f i l e ; END? N Compute s from s; O v e r w r i t e the c o r r e s p o n d i n g r e c o r d i n the output- f i l e w i t h s, s, p. ( 3 ) - 143 -APPENDIX B. T h i s appendix c o n t a i n s a d e s c r i p t i o n o f the p r i n c i p l e o f o p e r a t i o n o f the t r a n s d u c e r developed f o r t h i s work. The P o s i t i o n -and Force T r a n s d u c e r . The t r a n s d u c e r developed f o r t h i s r e s e a r c h i s based on the s u p p o r t r e a c t i o n s o f a si-rapl y -supported p l a t e . In o r d e r t o ensure t h a t - a l l the s u p p o r t s are a c t i v e , a t h r e e - p o i n t s u p p o r t system was chosen. T h i s s e l f - l e v e l l i n g arrangement was found t o be unique among h a n d w r i t i n g t r a n s d u c e r s and a p a t e n t a p p l i c a t i o n was i n i t i a t e d . The e q u a t i o n s which a p p l y i n the system d e p i c t e d i n F i g . 14 are g i v e n below. I t i s assumed t h a t a p o i n t l o a d o f weight F has been a p p l i e d at the p o i n t of which the - c o - o r d i n a t e s are ( x , y ) . The h e i g h t o f the i s o s c e l e s t r i a n g l e which has the f o r c e s e n s i n g elements at i t s v e r t i c e s i s h- and i t s base l e n g t h i s b. 0 i s the c e n t r o i d o f the t r i a n g l e and a l s o the c o - o r d i n a t e o r i g i n . The r e a c t i o n s at the s u p p o r t s l a b e l l e d 1, 2 and 3 are i n d i c a t e d as f^ , fz and f 3 , r e s p e c t i v e l y . The e q u a t i o n s a r e : f 1 + fz + f 3 = F ( h / 3 ) ( 2 f 1 - f 2 - f 5 ) = Fy ( b / 2 ) ( f 3 - fz) = Fx That i s , 1 1 1 ! : f i ! I i ! o -1 1 ! . ! ?z I = = ! 2 x / b ! F 2 -1- -1 ! i _ f 3 _ : !_3y/h_! - 144 -Fig. 14: T h r e e - p o i n t support sys tem f o r force a n d pos i t ion t r a n s d u c t i o n . The above i m p l i e s t h a t a means o f computing the c u r r e n t v a l u e of F b e f o r e we can c a l c u l a t e the p o s i t i o n c o - o r d i n a t e s i s r e q u i r e d . For d i g i t a l computing el e m e n t s , t h i s can be a c h i e v e d by p e r f o r m i n g a two-stage c a l c u l a t i o n as d e s c r i b e d by the two s e t s of equations-.below. I . _ I = _ I ?z and ! x ! !_y_! o -b/2 b/2 !_2h/3 -h/-3 -h/3_ f i fz _ f 3 . (1/F) An o v e r v i e w o f a system - u t i l i s i n g the t r a n s d u c e r i s g i v e n i n - 145 -F i g . 15 which a l s o incl-udes t r a c i n g s o f an i n p u t sample and the r e s u l t i n g d i s p l a y on a g r a p h i c s t e r m i n a l . F i g . 16 i n d i c a t e s two p o s s i b l e means of p e r f o r m i n g the computations f o r d e t e r m i n i n g the f o r c e and the c o - o r d i n a t e s . The method i n d i c a t e d as A was chosen f o r t h i s work, u s i n g the two-stage c a l c u l a t i o n d e s c r i b e d above. ( F i g s . 15 and 16 are s l i g h t l y m o d i f i e d v e r s i o n s o f diagrams s u b m i t t e d f o r the p a t e n t a p p l i c a t i o n . ) - 146 -1 i QT2 h T 1 QT3 PROCESSING x= ( f 3 - f 2 ) l h \ J y ^ - f j -f 3)7F 3 1 = 1 F= If: UL1  T1-T3: Force transducing elements. A1-A3: Signal conditioning elements. /OUTPUT/ Fig. 15: Force and posit ion transduction system - overview. - 147 -*1 Analogue h Mul t i -plexor f3 Digital processing e.g. by computer programme. A/D conv. - n> F = f-j +f2 *f3 x=( fo- f z ) IF y = ( 2 l r 1 2 - f 3 "DTA~> D/A > =>1 10 appro-^ priate s torage a n d / o r d i s p l a y J devices. B Analogue processing. xjto stor-l [age and/i or disp-J lay, 'devices I via J convert-| ers as | i required.) l I Fig. 16: Force a n d . posit ion t ransduct ion system -a l t e r n a t i v e p r o c e s s i n g methods. - 148 -

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