elastic_materials_for_robots flexible human like hand
TRANSCRIPT
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E L S E V I E R
R o b o t i c s a n d A u t o n o m o u s S y s t e m s 1 8 ( 1 9 96 ) 1 3 5 - 1 4 0
Robotics nd
utonomous
Systems
lastic m aterials prod ucing com pliant robots
K o i c h i S u z u m o r i
Toshiba Corporation 4-1 Ukishima-cho Kawasaki-ku Kawasaki 210 Japan
Abstract
A lot of research has been conducted on producing c om plian t robots by apply ing software algorithms such as force controls
and com plian ce controls while l it t le research has been done in app lying soft materials to robo t mechanical designs. The
author believe s that the use of soft materials h as grea t potential for producing com pliant robots which are chea p and reliable.
This pap er reports on a new pneumatic rubb er actuator and its applications to robot mechanisms. This actuator is made of
silicone r ubb er and is called a flexible microactuator an FMA . It has goo d com plianc e properties resulting fr om the elasticity
of the materials and the com pressibili ty of air.
Keywords:
A ctua to r ; M ic roac tua to r ; R obo t ; R ubbe r
I I n t r o d u c t i o n
Co n v e n t i o n a l d e s i g n s o f i n d u s t r i a l r o b o t s h a v e
f o c u s e d o n p o s i t i o n i n g a c c u r a c y s p e e d a n d l o a d
c a p a c i t y . I n o r d e r t o a c h i e v e t h is i t i s i mp o r t a n t
f o r d e s i g n e r s t o ma k e r o b o t s t r u c t u r e s me c h a n i c a l l y
r i g i d t o d e c r e a s e t h e d e f l e c t i o n a n d v i b r a t i o n s o f t h e
r o b o t a r ms . Be c a u s e o f t h is s o f t ma t e r i a l s h a v e b e e n
s e l d o m u s e d i n i n d u s t r ia l r o b o t d e s i g n s .
O n t h e o t h e r h a n d p o s i t i o n i n g a c c u r a c y a n d s p e e d
a r e n o t v e r y i mp o r t a n t f o r h u ma n - f r i e n d l y r o b o t s b u t
s a f e ty l g e n t l e mo t i o n s a n d a s o f t t o u c h a r e i mp o r t a n t .
T o a c h i e v e c o m p l i a n t r o b o t s t h e r e a r e g e n e r a l l y t w o
c a t e g o r ie s o f a p p ro a c h : n a m e l y c o n t ro l a p p r o a c h e s
a n d m a t e r i a l a p p ro a c h e s . C o n t r o l a p p r o a c h m e a n s a p -
p l y i n g s o f t w a r e c o n t r o l s u c h a s f o r c e c o n t r o l s a n d
c o mp l i a n c e c o n t r o l s t o c o n v e n t i o n a l r o b o t s w i t h r i g i d
l i n k s . I t s a d v a n t a g e i s t h e c o mp l i a n c e c o n t r o l l a b i l i t y
a c h i e v e d ju s t b y t u n i n g c o n t r o l p a r a m e t e r s . O n t h e
o t h e r h a n d m a t e r i a l a p p r o a c h m e a n s u s i n g s o f t m a t e -
r i a ls s u c h a s r u b b e r s a n d e l a s t o m e r s f o r r o b o t d e s i g n s .
T h e a d v a n t a g e h e r e i s t h e s i mp l i c i t y o f t h e me c h a -
0921-8890 /96 / 15 . 00 © 1996 E l sev i e r S c i ence B . V . A l l r i gh t s
SSDI
0 9 2 1 - 8 8 9 0 ( 9 5 ) 0 0 0 7 8 - X
n i s m w h i c h r e s u l t s in r e li a b i li t y a n d c h e a p n e s s . S o f t
ma t e r i a l s a ls o e n a b l e c o n t i n u o u s d e f o r ma t i o n f o r e x -
a m p l e c o m p l i a n t f in g e r s w h i c h c a n d e f o r m t o fi t t h e
s h a p e s o f d i f f e r e n t o b j e c t s .
T h e r e h a s b e e n m u c h a p p l i e d r e s e a r c h o n c o n t r o l
a p p r o a c h e s b u t li tt le r e s e a r c h h a s b e e n c o n d u c t e d i n
t h e ma t e r i a l f ie l d s e x c e p t s o me r e s e a r c h o n a n a r t if i -
c i a l r u b b e r m u s c l e [ 1 . T h e a u t h o r b e l i e v e s t h a t t h e r e i s
g r e a t p o t e n t i a l i n th e ma t e r i a l a p p r o a c h e s . T h e f l e x ib l e
mi c r o a c t u a t o r d e s c r i b e d i n t h i s p a p e r w a s d e v e l o p e d
f r o m t h i s p o i n t o f v i e w [ 2 - 5 ] .
2 F M A m e c h a n i s m a n d i ts m o t i o n s
Fi g . 1 s h o w s a n FM A s t ru c t u r e . I t i s ma d e o f
s i l i c o n e r u b b e r r e i n f o r c e d w i t h n y l o n f i b e r i n t h e
c i r c u m f e r e n t i a l d i r e c ti o n . T h e f i b e r g i v e s t h e r u b b e r
an an i so t rop ic e l as t i c i ty i . e . t he rub ber i s eas i ly de-
f o r me d i n t h e a x i a l d i r e c t i o n b u t r e s i s t s d e f o r ma t i o n
i n th e r a d i a l d ir e c t io n . Fo r th i s r e a s o n w h e n t h e p r e s -
s u r e is i n c r e a s e d i n o n e c h a mb e r t h e FM A b e n d s i n
r e se rved
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136
K. Suzumo ri/Robotics and Autonom ous Systems 18 199 6) 135-140
Z
x l O 3
C e n t e r a x i s
~- ~ '
~
3 0
' ,
C h a m ~ i..__e
• •
~ ] A R C M o d e l O r . ~ 0 . 1 9 6 1 N 1
| 0 • E x p e r i m e n t =
0 0 . 1 0 . 2 0 3 ~ M P a G )
Fig. 3. FM A compliance.
C h a rn b e r l C h a m b e r
~ ~
' x
Fig. 1. FMA structure.
10
S
A ,
•
0 1
0 2 P iE v
Fig. 2. Bending characteristics of FMAs of various sizes.
t h e d i r e c t i o n o p p o s i t e t o t h e p r e s s u r i z e d c h a m b e r . I t
c a n b e b e n t i n a n y d i r e c ti o n t h r o u g h a p p r o p r i a t e p r e s -
s u r e c o n t r o l i n e a c h c h a m b e r , a n d c a n b e s t r e t c h e d i n
t h e a x i a l d i r e c t i o n w h e n t h e p r e s s u r e i s i n c r e a s e d i n
a l l t h r e e c h a m b e r s .
I t i s a s s u m e d t h a t t h e F M A d e f o r m a t i o n i s s m a l l
a n d t h a t it t a k e s t h e f o r m o f a n a r c a s s h o w n i n F i g . 1 .
T h e n , t h e d e f o r m a t i o n c a n b e d e s c r i b e d u s i n g t he t h r e e
p a r a m e t e r s 0 , R , a n d Z : 0 r e p r e s e n t s t h e b e n d i n g d i -
r e c t i o n a n g l e , w h i c h i s d e f i n e d a s t h e a n g l e b e t w e e n
t h e x - a x i s a n d t h e t - a x i s , t h e p r o j e c t i o n o f t h e c e n -
t e r a x is o n t o t h e x y - p l a n e ; R i s t he c u r v a t u r e o f t h e
c e n t e r a x i s ; Z i s t h e a n g l e b e t w e e n t h e z - a x i s a n d t h e
t i p d i r e c t i o n o f t h e F M A . B y a p p l y i n g t h e i n f i n i t e s i -
m a l d e f o r m a t i o n t h e o r y , 0 , R , a n d ,~ c a n b e d e r i v e d a s
f o l l o w s :
2P j - P2 - P3
t a n
0 = I )
~ P 2 - - P3)
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R = , (2)
a p 6 ) - ~ = I
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3
L - - A p L o Z P i + L o ,
(3 )
3 A o E t i + I
Z = L / R ,
(4 )
w h e r e
P i
d e s c r i b e s t h e i n t e r n a l p r e s s u r e i n t h e i t h
c h a m b e r ( i = 1 , 2 , 3 ), E t i s Y o u n g s m o d u l u s f o r th e
f i b e r - r e i n f o r c e d r u b b e r i n t h e t r a n s v e r s e d i r e c t i o n , L 0
i s t h e n o r m a l F M A l e n g t h , a n d L i s t h e c u r r e n t F M A
l e n g th . 1 is th e m o m e n t o f i n e r t i a f o r th e F M A c r o s s -
s e c t i o n a r e a , A p i s t h e p r e s s u r i z e d a r e a , A 0 i s t h e a r e a
o f t h e r u b b e r , a n d ,~ i s t h e d i s t a n c e b e t w e e n t h e F M A
c e n t e r a n d t h e c e n t e r o f e a c h f a n - s h a p e d a r e a .
F i g . 2 s h o w s s t a t i c c h a r a c t e r i s t i c s o f v a r i o u s F M A s
w i t h d i f f e r e n t s i z e s . F i g . 3 s h o w s c o m p l i a n c e a t t he t i p
o f an F M A w h i c h i s 1 2 m m i n d i a m e t e r a n d 5 0 m m
in l eng th .
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K. Suzumori/Robotics and Autonomous Systems 18 1996) 135-140 137
3 A p p l i c a t io n s t o c o m p l i a n t r o b o t m e c h a n i s m s
3.1. Robot arm
B y c o n n e c t i n g F M A s s e r i a l l y , a n a r m i s o b t a i n e d
w i t h m a n y d e g r e e s o f fr e e d o m a n d s n a k e - li k e m o v e -
m e n t s . F i g. 4 s h o w s a p r o t o t y p e m a d e o f t w o F M A s
a n d a m i n i - g r ip p e r , w h i c h i s a l s o m a d e o f f i b e r r e -
i n f o r c e d r u b b e r [ 4 ] . It h a s s e v e n d e g r e e s o f f r e e d o m
i n c l u d i n g t h e g r i p p e r m o t i o n . P n e u m a t i c t u b e s c o n -
n e c t e d t o t h e u p p e r F M A a n d t h e g r i p p e r p a s s t h r o u g h
t h e c h a m b e r s i n t h e l o w e r F M A .
F i g . 5 s h o w s t h e e x p e r i m e n t a l c o m p l i a n c e c o n t r o l
r e su l ts . T h e a r m m o v e m e n t i s d e t e c t e d o p t i c a l l y u s i n g
a n L E D a t t a c h e d t o th e t ip o f t h e a r m a n d a p o s i t i o n
s e n s i n g d e v i c e . M e a s u r e d d a t a r e g a r d i n g t h e L E D p o -
s i t i o n s a r e f e d t o a c o m p u t e r , a n d a c l o s e d l o o p w i t h
p r o p o r t i o n a l c o n t r o l i s c o n s t r u c t e d . I t i n d i c a t e s t h a t t h e
F M A a r m c o m p l i a n c e c a n b e c o n t r o l l e d b y a d j u s t i n g
f e e d b a c k g a i n K f . I n th i s e x p e r im e n t , r e f e r e n c e i n p u t s
w e r e k e p t c o n s t a n t . T h e s a m p l i n g p e r i o d f o r t h e c o n -
t r o l s y s t e m w a s 5 0 m s .
I t i n d i c a t e d t h a t c o m p l i a n c e c o n t r o l c o u l d b e
a c h i e v e d a l s o w i t h r o b o t s m a d e o f s o f t m a t er i al s .
W h i l e t h e c o m p l i a n c e c o n t ro l o f a co n v e n t i o n a l r o b o t
m a d e o f ri g i d l in k s i s u s ed t o i n c r e a s e c o m p l i a n c e , t h e
c o m p l i a n c e c o n t r o l o f a r o b o t m a d e o f s o f t m a t e r i a l s
i s u s e d t o i n c r e a s e s t i f f n e s s .
3.2. Mult i-finger ed robot hand
Fig. 4. Robot arm, 4 mm in diameter.
5
0 5
1 5 C a l c u l a t i o n
T h e h a n d , s h o w n i n F i g . 6 , c o n s i st s o f f o u r F M A s ,
e a c h 1 6 m m i n d i a m e t e r . I t s l o a d c a p a c i t y i s a b o u t
5 0 0 g f . I n c o m p a r i n g t h e F M A h a n d s t o c o n v e n t i o n a l
r o b o t h a n d s c o n s i s t i n g o f r i g i d l in k s , t w o o b s e r v a t i o n s
c a n b e m a d e : 1 ) F M A h a n d s c a n h a n d l e fr a g i l e o b j e c t s
Fig. 5. Com pliance control of robot arm. Fig. 6. Robot hand.
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38
K. Suzumori /Rob otic s and Autonomous Systems 18 1996) 135-140
1
2
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/
9 9
/
~ o / 0
/ /
o o z~
~ / 0 I
\ 0 1 0 2
\ o
/
\ o ~ /
\ o I
/
I
o ,~/o n0n-sl ip imi l
I A Slabi l i ty imff
t~ / 2 r = 3 1 . 5 m m
Fig. 8. H uman-like hand grasping grape.
Fig. 7. W eight holding capacity and stable region of the hand
shown in F ig. 6.
s u c h a s th o s e m a d e o f g l a s s , o r e v e n a n e g g , w i t h m o r e
c a r e t h a n p e r h a p s a r o b o t c o n s i s t i n g o f r i g i d l in k s . ( 2 )
E a c h f i n g e r c a n a l s o d e f o r m t o s u i t th e s h a p e o f th e
o b j e c t s h a n d l e d .
F i g . 7 s h o w s a r e g i o n o f h o l d i n g s t a b i l it y o f th i s
h a n d , w h e r e t h e c r it i c a l f o r c e , Q z f o r s t a b i li t y a n d t h e
w e i g h t h a n d l i n g c a p a c i t y a re s h o w n f o r e a c h p r es s u r e
P I . W h e n t h e w o r k i n g f l u id p re s s u re r e a c h e s s o m e
l im i t, a n u n s t a b le p h e n o m e n o n o c c u r s w h e r e t h e o b j e c t
a n d F M A s t u r n u n s t a b l y a r o u n d t h e c e n t e r a x i s o f
t h e h a n d . T h i s i s j u s t l i k e th e p h e n o m e n o n w h i c h i s
o f t e n e x p e r i e n c e d w h e n g r a s p i n g a s m a l l b e a n w i t h
c h o p s t ic k s . I t c o m e s f r o m t h e f a c t th a t F M A s h a v e
c o m p l i a n c e n o t o n l y i n t h e g r a s p i n g d i r e c t i o n b u t a l s o
i n t h e l a t e r a l d i r e c t i o n .
F i g . 8 sh o w s a h u m a n - l i k e h a n d f o r re s e a r c h p u r -
p o s e s , m i m i c k i n g h u m a n h a n d m o t i o n s o b s e r v e d i n
e v e r y d a y l i f e, s u c h a s g r a s p i n g a g l a s s c u p , u s i n g s c is -
s o r s , c o u n t i n g , e t c .
3.3. W alking robots
A n F M A c a n e a s il y s i m u l a te a l e g m o t i o n w h i c h i s
a c h i e v e d b y a s e ri a l m o t i o n c o n t r o l o f k i c k a n d r e t u r n
a c t i o n .
Fig. 9. M iniature walking robot w ith straight legs.
F i g s . 9 a n d 1 0 s h o w t w o t y p e s o f w a l k i n g r o b o t s .
O n e is a s t r a i g h t l e g r o b o t w h i c h k e e p s i ts f e e t u n d e r
t h e b o d y li k e m a m m a l s , a n d th e o t h e r i s a n o v e r h a n g
l e g r o b o t w h i c h k e e p s i t s f e e t w e l l o u t t o t h e si d e o f
t h e b o d y l i k e r e p t i l e s . T h e r o b o t s h o w n i n F i g . 9 i s
a b o u t 1 g i n w e i g h t a n d 1 5 m m i n le n g t h . T h e r o b o t
s h o w n i n F ig . 1 0 i s 1 0 k g i n w e i g h t a n d 7 0 0 m m i n
l e n g th . A i r is s u p p l i e d t h r o u g h 1 8 p n e u m a t i c t u b e s . I t
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K . S u z u m o r i / R o b o t i c s a n d A u to n o m o u s S y s t e m s 1 8 1 9 9 6 ) 1 3 5 - 1 4 0
139
Fig. 10. W alking robot w ith overhang legs.
Fig. 11. Pipeline mobile robot designed for 2 in. pipe.
i s n o t n e c e s s a r y t o d r i v e t h e s i x FMA s i n d e p e n d e n t l y
a n d o n l y 1 2 t u b e s a r e s u f f i c i e n t f o r o mn i - d i r e c t i o n a l
w a l k i n g .
T h e a l t e r n a t i n g t r ip o d a l g o r i t h m h a s b e e n a p p l i e d t o
t h e r o b o t s . T h e s t r a i g h t l e g r o b o t a c c o mp l i s h e s o mn i -
d i r e c t i o n a l w a l k i n g a n d t u rn i n g w h i l e th e o v e r h a n g
l e g r o b o t a c c o m p l i s h e s f o r w a r d / b a c k w a r d w a l k i n g
a n d t u r n i n g . T h e w a l k i n g s p e e d i s a b o u t 2 0 c m / m i n
a n d t h e l o a d c a p a c i t y i s a b o u t 3 0 0 mg f f o r t h e r o b o t
shown in F ig . 9 .
A n a d v a n t a g e o f th e FM A w a l k i n g r o b o t s i s s a f e ty
b e c a u s e o f t h e ir l ig h t n e s s a n d c o m p l i a n c e . E v e n i f th e
r o b o t f a l l s d o w n s t a i r s t h e r e w i ll b e l e s s d a n g e r t o t h e
r o b o t a n d t o t he s u r r o u n d i n g s .
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140 K . S u z u m o r i / R o b o t i c s a n d A u to n o m o u s S y s t e m s 1 8 1 9 9 6 ) 1 3 5 - 1 4 0
3 4 Pipe l ine in ter ior robo t
T h e n e e d f o r i n s p e c t i o n s i n s i d e s ma l l p i p e l i n e s h a s
g r o w n i n t h e f ie l d o f p l a n t ma i n t e n a n c e e s p e c i a l l y i n
n u c l e a r p l a n t s a n d c h e mi c a l p l a n t s .
F i g . 1 1 sh o w s a p r o t o t y p e d e s i g n e d f o r a 2 in .
p i p e l i n e . I t i s d r i v e n f o r w a r d o r b a c k w a r d b y w h e e l e d
u n i ts a n d a n FM A i s u s e d to s t e e r t h r o u g h p i p e l i n e
b r a n c h e s a n d e l b o w s .
T h e c o m p l i a n c e o f t h e F M A g i v e s t h e r o b o t t w o
a d v a n t a g e s . O n e i s a d a p t a b i l i t y f o r c h a n g e s i n t h e i n -
t e r n a l d i a me t e r o f t h e p i p e . E v e n i f t h e r e i s p l e n t y o f
e n c r u s t a t i o n a n d r u s t o n t h e p i p e w a ll t h e r o b o t c a n
p a s s o v e r t h e m b e c a u s e o f t h e f l e x i b il i ty o f th e FM A .
T h e o t h e r a d v a n t a g e i s t h a t r o u g h c o n t r o l o f t h e FMA
i s a d e q u a t e f o r s t e e r in g b e c a u s e th e FM A c a n b e b e n t
p a s s i v e l y t o f o l l o w t h e p i p e l i n e c u r v e s .
4 . Conclus ions
A m a j o r p r o b l e m i n a p p l y i n g c o n v e n t i o n a l r o b o t s
t o h u ma n - f r i e n d l y t a s k s i s t h a t t h e y h a v e r i g i d a n d
h e a v y b o d i e s . T h e y a r e a l so s o m e t i m e s d a n g e r o u s a n d
w i t h o u t v e r y r e l i a b l e c o n t r o l s .
M o s t o f t h e r e s e a r c h e r s i n t h e r o b o t i c s f ie l d s e e m t o
b e i n t e r e s t e d i n u s i n g c o n t r o l s t o a c h i e v e c o mp l i a n c e
w h i l e o n l y a f e w r e s e a r c h e r s h a v e b e e n i n t e r e s t e d i n
t h e u s e o f s o f t ma t e r i a l s . T h e a u t h o r b e l i e v e s t h a t m o r e
r e s e a r c h o n s o f t ma t e r i a l s f o r h u ma n - f r i e n d l y r o b o t s
s h o u l d b e e n c o u r a g e d b e c a u s e th e r e i s g r e a t p o t e n t i a l
f o r d e v e l o p i n g c o mp l i a n t r o b o t s w h i c h a r e c h e a p a n d
re l i ab le .
cknowledgements
T h e a u t h o r w o u l d l i k e t o t h a n k P r o f . H i r o h i s a
T a n a k a o f Y o k o h a ma N a t i o n a l U n i v e r s i t y f o r h i s u s e -
f u l a d v i c e a n d e n c o u r a g e m e n t . T h e a u t h o r a l s o t h a n k s
M r . S a d a o S e k ig u c h i a n d M s . F u m i k a K o n d o b o t h
o f T o s h i b a Co r p o r a t i o n f o r t h e ir a s s is t a n c e i n t h e
d e v i c e f a b r i c a t i o n a n d e x p e r i me n t s .
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