Tactile Sensation for Robots

In t h i s paper we p r o v i d e a b r i e f d i s c u s s i o n o f t he r e l a t i o n s h i p o f t a c t i l e sensa t i on t o o the r sensory m o d a l i t i e s c u r r e n t l y showing prominence i n i n d u s t r i a l r o b o t s . A t a c t i l e sensor i s p resented which p r o v i d e s a m a t r i x o f t he f o r c e s e x i s t i n g between i t and the o b j e c t w i t h which i t i s i n c o n t a c t . The p o s s i b l e uses o f t h i s i n f o r m a t i o n i n the c o n t r o l o f t he m a n i p u l a t i o n o f o b j e c t s by a r o b o t arm/hand system are c o n s i d e r e d . Examples o f the da ta r e t r i e v e d from the sensor are g i v e n and p o s s i b l e i n i t i a l p rocess ing s teps are d i s c u s s e d . A . I n t r o d u c t i o n To d a t e , t h e dominant area in r o b o t sens ing resea rch has been v i s i o n . Notab le e x c e p t i o n s i n c l u d e the f o r c e feedback o r a c t i v e accommodation work done in connec t i on w i t h t he t a s k o f peg i n s e r t i o n , e . g . [ 6 ] and [ 1 1 ] , and the use o f v i s i o n and f o r c e sens ing i n assembly [ 1 ] , [ 1 1 ] , [ 1 2 ] , [ 1 8 ] and [43 ( p a s s i v e accommodat ion) . Other areas o f sensor resea rch i n c l u d e range f i n d i n g t e c h n i q u e s , [ 1 4 ] [ 1 5 3 , p r o x i m i t y sens ing and some l i m i t e d i n v e s t i g a t i o n s i n t o the use o f t a c t i l e f o r c e sensor a r r a y s i n m a n i p u l a t i o n (see b e l o w ) . For a comprehensive rev iew o f the c u r r e n t s t a t e o f r o b o t sensor t echno logy t h e reader i s r e f e r r e d t o [ 1 3 3 . An area r e c e i v i n g l i m i t e d a t t e n t i o n in t he l i t e r a t u r e , bu t compr i s i ng an i m p o r t a n t area in and o f i t s e l f i s t h a t o f t he use o f t a c t i l e sensory da ta i n t he c o n t r o l o f r o b o t sys tems. Research i n t h i s area has been in p r o g r e s s , and f o r f u r t h e r d i s c u s s i o n s , t h e reader i s r e f e r r e d t o [17] and recen t work by Dixon [ 3 3 . Research in the use of t a c t i l e da ta by r o b o t m a n i p u l a t o r s has been g e n e r a l l y l i m i t e d t o g ross f o r c e sens ing i n the w r i s t , and in some cases the f i n g e r s , f o r two gene ra l r e a s o n s . F i r s t , u n t i l r e c e n t l y , t h e r e has been a l a c k o f h i g h r e s o l u t i o n sens ing a r r a y s which c o u l d be u t i l i z e d in t he end e f f e c t o r s o f a m a n i p u l a t o r . Second, and p robab ly more i m p o r t a n t , peop le a re f a r l e s s consc ious o f the r o l e t h a t the "sense o f t ouch ' ' p l ays i n everyday a c t i v i t y , a s compared t o v i s i o n . Whi le v i s i o n may c o n t i n u e t o • T h i s work was suppor ted in p a r t by NIH Grant NS 14971-03 (Michae l A . A r b i b , P r i n c i p a l I n v e s t i g a t o r ) and D i g i t a l Equipment C o r p o r a t i o n . • • I n t e r n a t i o n a l Business Machines Graduate Fe l l ow d u r i n g the 1980-81 academic yea r . Thomas W i l l i a m s Corpora te Research Group D i g i t a l Equipment C o r p o r a t i o n Maynard, Massachuset ts b e the p r ima ry sense u t i l i z e d i n r o b o t s , t a c t i l e sens ing f i l l s a n i m p o r t a n t r o l e , no t o n l y when v i s i o n i s i n a p p l i c a b l e due t o i n h e r e n t a m b i g u i t i e s , bu t i n t he ve r y f i n e c o n t r o l o f d e l i c a t e m a n i p u l a t i o n . T a c t i l e sensors can be d i v i d e d i n t o t h r e e genera l c a t e g o r i e s depending upon the type o f i n f o r m a t i o n they p r o v i d e . Contact sensors compose the f i r s t c l a s s and y i e l d i n f o r m a t i o n i n d i c a t i n g e i t h e r the presence o r absence o f p h y s i c a l s t i m u l i . A r o b o t hand w i t h c o n t a c t sens ing on s e v e r a l s i d e s was developed by Goto [7 3 to handle b l o c k s p laced on a t a b l e . In l a t t e r work , G a r r i s o n and Wang [ 5 ] c o n s t r u c t e d a hand c o n t a i n i n g an a r r a y o f c o n t a c t senso rs . Recent sensor a r r a y s have u t i l i z e d woven g r a p h i t e f i b e r s as the p h y s i c a l t r ansduce r [ 1 0 3 . The Labo ra to r y f o r Automat ion and Systems A n a l y s i s at CNRS in Tou louse , F rance , has deve loped an " a r t i f i c i a l s k i n " t a c t i l e sensor s u i t a b l e f o r g ross o b j e c t r e c o g n i t i o n [ 2 3 . A h i g h s p a t i a l r e s o l u t i o n c o n d u c t i v e rubber c o n t a c t sens ing a r r a y has been developed a t the A r t i f i c i a l I n t e l l i g e n c e L a b o r a t o r y at M . I . T . and has been s u c c e s s f u l l y used to i d e n t i f y a b o l t f rom i t s c o n t a c t p a t t e r n [ 9 3 . The second c a t e g o r y c o n t a i n s the sensors which p r o v i d e i n f o r m a t i o n r e g a r d i n g the magni tude o f t h e f o r c e at each sens ing p o i n t . A hand c o n s t r u c t e d by H i l l and Sword [83 employed analog f o r c e sens ing a r r a y s . Severa l o f the c o n t a c t sens ing a r r a y s ment ioned above can and are be ing extended to p r o v i d e ana log f o r c e images. Depending upon the compl iance o f t he m a t e r i a l s u p p o r t i n g such s e n s o r s , t he f o r c e i n f o r m a t i o n can be r e l a t e d to t h e amount o f d e f l e c t i o n o f the senso r , t h u s p r o v i d i n g i n f o r m a t i o n d e s c r i b i n g the t h r e e d imens iona l shape o f the o b j e c t be ing sensed. The f i n a l c l a s s o f t a c t i l e sensors p r o v i d e s t h i s i n f o r m a t i o n d i r e c t l y . Th i s g roup c o n s i s t s o f sensors which are des igned to t r ansduce t h e t h r e e d imens iona l shape of an o b j e c t . Page and Pugh [163 presented a sensor which b u i l d s a con tou r map of the o b j e c t be ing sensed as t he sensor i s lowered onto the o b j e c t . Takeda c o n s t r u c t e d a hand w i t h a r r a y s o f f r e e f l o a t i n g need les as s e n s o r s . The need les would conform to the shape o f t he s u r f a c e be ing t o u c h e d , t h e r e b y p r o v i d i n g i d e n t i f i c a t i o n i n f o r m a t i o n [ 1 7 3 .