Development of a Fully Automated Tensile and Flexure Test System

Chapter 5 Development

of a Fully Automated Tensile a n d Flexure Test System Richard L. Scott and James K. Rieke

Downloaded by EAST CAROLINA UNIV on April 10, 2018 | https://pubs.acs.org Publication Date: August 29, 1989 | doi: 10.1021/bk-1989-0404.ch005

Central Research, The Dow Chemical Company, 1776 Building, Midland, MI 48674 The l a b o r - i n t e n s i v e nature of polymer t e n s i l e and flexure t e s t s makes them l o g i c a l candidates for automation. We have developed a f u l l y automated instrument for performing these t e s t s on rigid m a t e r i a l s . The instrument i s comprised of an Instron u n i v e r s a l t e s t e r , a Zymark laboratory robot, a D i g i t a l Equipment Corporation minicomputer, and custom-made accessories to manipulate the specimens and measure t h e i r dimensions a u t o m a t i c a l l y . Our system allows us to determine the t e n s i l e or f l e x u r a l properties of over one hundred specimens without human i n t e r v e n t i o n , and it has s i g n i f i c a n t l y improved the p r o d u c t i v i t y of our laboratory. This paper describes the s t r u c t u r e and performance of our system, and it compares the r e l a t i v e costs of manual versus automated testing. ASTM t e n s i l e p r o p e r t i e s t e s t D638 a n d f l e x u r a l p r o p e r t i e s t e s t D7 90 a r e u s e d t h r o u g h o u t t h e p o l y m e r i n d u s t r y t o c h a r a c t e r i z e b o t h r e s e a r c h a n d q u a l i t y c o n t r o l samples (1,2). These t e s t s d e t e r m i n e t h e s t r e s s o f a m a t e r i a l i n t e n s i o n o r f l e x u r e as a f u n c t i o n o f s t r a i n u n d e r a d e f i n e d s e t o f t e s t c o n d i t i o n s , and f r o m t h i s r e l a t i o n s h i p t h e modulus o f e l a s t i c i t y , s t r e n g t h a t y i e l d , and s t r e n g t h a t b r e a k c a n be c a l c u l a t e d . The l a b o r - i n t e n s i v e n a t u r e o f t h e s e t e s t s makes them l o g i c a l c a n d i d a t e s f o r a u t o m a t i o n . At The Dow C h e m i c a l Company we have d e v e l o p e d a f u l l y a u t o m a t e d i n s t r u m e n t f o r p e r f o r m i n g t e n s i l e and f l e x u r e t e s t s on r i g i d p o l y m e r i c m a t e r i a l s Q ) . The i n s t r u m e n t c o n s i s t s o f an I n s t r o n u n i v e r s a l t e s t e r , a Zymark l a b o r a t o r y r o b o t , a D i g i t a l Equipment C o r p o r a t i o n m i n i c o m p u t e r , and custom-made a c c e s s o r i e s t o m a n i p u l a t e t h e s p e c i m e n s and t o measure t h e i r d i m e n s i o n s automatically. Our s y s t e m a l l o w s us t o d e t e r m i n e t h e 0097-6156/89/0404-0045$06.00/0 o 1989 American Chemical Society

Provder; Computer Applications in Applied Polymer Science II ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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t e n s i l e o r f l e x u r a l p r o p e r t i e s o f o v e r one h u n d r e d specimens w i t h o u t human i n t e r v e n t i o n , and i t has s i g n i f i c a n t l y improved t h e p r o d u c t i v i t y o f o u r l a b o r a t o r y . T h i s p a p e r d e s c r i b e s t h e s t r u c t u r e and p e r f o r m a n c e o f t h i s automated system, i n c l u d i n g d e s c r i p t i o n s o f t h e t e n s i l e and f l e x u r e equipment, t h e automated specimen h a n d l i n g a p p a r a t u s , t h e specimen m e a s u r i n g d e v i c e , and t h e computer hardware and s o f t w a r e which c o n t r o l t h e s y s t e m . Also i n c l u d e d i s a c o m p a r i s o n o f t h e r e l a t i v e c o s t s o f manual v e r s u s automated t e s t i n g .


D e s c r i p t i o n of the System Hardware The system, as c o n f i g u r e d f o r p e r f o r m i n g t e n s i l e t e s t s , i s i l l u s t r a t e d i n F i g u r e s 1 and 2. Key components o f t h e s y s t e m a r e an I n s t r o n 1125 u n i v e r s a l t e s t e r w h i c h p e r f o r m s t h e t e n s i l e and f l e x u r e t e s t s , a Zymark l a b o r a t o r y r o b o t w h i c h p e r f o r m s he specimen h a n d l i n g , a Dow-designed s p e c i m e n b a r magazine (U.S. P a t e n t 4,606,230) w h i c h s t o r e s t h e t e s t b a r s and makes them a c c e s s i b l e t o t h e r o b o t , a Dow-designed d e v i c e t o measure t h e w i d t h and t h i c k n e s s o f t h e t e s t b a r s , and a D i g i t a l Equipment C o r p o r a t i o n PDP11/44 m i n i c o m p u t e r which p r o v i d e s o v e r a l l c o n t r o l and a c q u i r e s , s t o r e s , and a n a l y z e s t h e e x p e r i m e n t a l d a t a . F o r t e n s i l e t e s t s t h e I n s t r o n 1125 t e s t e r i s f i t t e d w i t h p n e u m a t i c - h y d r a u l i c g r i p s w h i c h can be opened and c l o s e d by remote c o n t r o l . We have i n s t a l l e d m i c r o s w i t c h e s t o i n d i c a t e when a specimen i s i n p l a c e , and p n e u m a t i c a c t u a t o r s t o e j e c t t h e specimens f r o m t h e g r i p s a f t e r e a c h test. For flexure t e s t s e i t h e r a three or a four-point compression-cell f l e x u r e f i x t u r e i s s u b s t i t u t e d f o r the grips. We have a t t a c h e d a i r j e t s t o t h e l o w e r s u p p o r t s t o e j e c t the specimens. Sample h a n d l i n g i s p e r f o r m e d by a Zymark l a b o r a t o r y r o b o t c o n s i s t i n g o f a r o b o t i c arm, a m i c r o c o m p u t e r c o n t r o l l e r , a power and e v e n t module, and an RS-232 s e r i a l interface. The r o b o t i s programmed t o move specimen b a r s between t h e magazine, m e a s u r i n g s t a t i o n , and g r i p s upon r e c e i p t o f commands from t h e PDP-11/44. The power and e v e n t module o p e r a t e s t h e t e n s i l e g r i p s , t h e specimen m e a s u r i n g d e v i c e , and t h e specimen e j e c t o r s . The RS-232 i n t e r f a c e a l l o w s t h e r o b o t i c arm's c o n t r o l l e r t o communicate w i t h t h e h o s t PDP-11/44. The Zymark equipment has n o t been m o d i f i e d f o r t h i s a p p l i c a t i o n , however, t h e g e n e r a l - p u r p o s e hand has been e q u i p p e d w i t h Dow-designed f i x t u r e s , one f o r t e n s i l e b a r s and a n o t h e r f o r f l e x u r e bars, t o f a c i l i t a t e the h a n d l i n g o f the specimens. A p a t e n t e d Dow-designed specimen b a r magazine w i t h a c a p a c i t y o f 125 b a r s makes t h e specimens a v a i l a b l e t o t h e r o b o t i c arm. Specimens a r e s t a c k e d v e r t i c a l l y , w i t h t h e i r end t a b s c o n s t r a i n e d by two c h a n n e l s so t h a t o n l y v e r t i c a l motion i s p o s s i b l e . A s l o t i n t h e base o f e a c h c h a n n e l a l l o w s t h e r o b o t t o p u l l specimens, one a t a t i m e , f r o m the bottom o f the s t a c k . Once removed f r o m t h e c h a n n e l s , t h e b a r s a r e d r o p p e d down a p a i r o f c i r c u l a r s l i d e s which



F i g u r e 1. O v e r a l l instrument l a y o u t showing: (A) I n s t r o n 1125 u n i v e r s a l t e s t e r , (B) Zymark l a b o r a t o r y robot, (C) Specimen b a r magazine, (D) Specimen b a r m e a s u r i n g d e v i c e .



F i g u r e 2. Closeup view of t e n s i l e t e s t apparatus showing: (A) R o b o t i c arm w i t h s p e c i a l f i n g e r s attached, (B) I n s t r o n p n e u m a t i c - h y d r a u l i c g r i p s , (C) Specimen b a r , (D) A i r c y l i n d e r s u s e d t o d i s l o d g e tested specimens.



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49

r o t a t e them n i n e t y d e g r e e s , e n a b l i n g them t o be g r i p p e d a l o n g t h e i r narrow edges by t h e r o b o t ' s f i n g e r s t o be moved t o t h e m e a s u r i n g s t a t i o n . The w i d t h and t h i c k n e s s o f t h e b a r s a r e measured w i t h a Dow-designed d e v i c e c o n s i s t i n g o f two M i t u t o y o MC-100-2 d i g i t a l i n d i c a t o r s mounted a t r i g h t a n g l e s t o one a n o t h e r . The i n d i c a t o r s have s p r i n g - l o a d e d p r o b e s w h i c h measure t h e d i s t a n c e between t h e t i p o f t h e p r o b e and a f i x e d r e f e r e n c e p o i n t . To advance and r e t r a c t t h e p r o b e s , t h e i n d i c a t o r s have been f i t t e d w i t h d o u b l e - a c t i n g a i r cylinders. The r o b o t p o s i t i o n s t h e b a r s i n t h e m e a s u r i n g d e v i c e so t h a t b o t h t h e wide and narrow f a c e s o f t h e b a r are a g a i n s t metal stops. Then t h e a i r c y l i n d e r s advance t h e p r o b e s t o measure t h e w i d t h and t h i c k n e s s . The p r o b e s t r a n s m i t t h e d i m e n s i o n s t o t h e PDP-11/44 t h r o u g h an RS-232 interface.

D e s c r i p t i o n of the System Software O v e r a l l c o n t r o l i s p r o v i d e d by t h e PDP-11/44, r u n n i n g DEC's RSX-11M o p e r a t i n g s y s t e m . RSX-11M i s a m u l t i - u s e r m u l t i - t a s k o p e r a t i n g system, and a number o f o t h e r a n a l y t i c a l i n s t r u m e n t s a r e i n t e r f a c e d t o t h i s computer s y s t e m and a r e r u n n i n g c o n c u r r e n t l y . The automated I n s t r o n s o f t w a r e i s m e n u - d r i v e n b e c a u s e o u r e x p e r i e n c e has shown t h a t m e n u - d r i v e n s o f t w a r e i s p a r t i c u l a r l y e f f e c t i v e for a p p l i c a t i o n s of t h i s type. To p e r f o r m e i t h e r t e s t t h e u s e r a c c e s s e s a main menu from w h i c h s e p a r a t e menus f o r i n s t r u m e n t c a l i b r a t i o n , t e n s i l e t e s t s , and f l e x u r e t e s t s can be r e a c h e d . The t e n s i l e and f l e x u r e menus have e q u i v a l e n t o p t i o n s ; t h e c h o i c e s p e r t a i n i n g t o automated t e s t i n g a r e as f o l l o w s : S e t u p an Automated T e s t S e r i e s . B e f o r e t e s t i n g can b e g i n t h e u s e r must i d e n t i f y t h e specimen b a r s i n t h e magazine and s p e c i f y t h e t e s t c o n d i t i o n s . T h i s i s a c c o m p l i s h e d w i t h s e t u p r o u t i n e s w h i c h prompt t h e u s e r t o d e f i n e t h e test series. At v a r i o u s p o i n t s the user i s g i v e n t h e o p p o r t u n i t y t o go back and c o r r e c t e r r o n e o u s e n t r i e s . The i n f o r m a t i o n p r o v i d e d by t h e u s e r i s s t o r e d i n a queue f i l e t o be a c c e s s e d l a t e r by t h e d a t a a c q u i s i t i o n s o f t w a r e . P e r f o r m an Automated T e s t S e r i e s . The d a t a a c q u i s i t i o n t a s k s p e r f o r m t h e t e s t s e r i e s d e f i n e d by t h e s e t u p t a s k s , and, once t h e command t o p e r f o r m a t e s t s e r i e s i s g i v e n , no manual i n t e r v e n t i o n i s r e q u i r e d u n t i l t h e t e s t s a r e complete. When p e r f o r m i n g t e n s i l e t e s t s , t h e PDP-11/44 i s s u e s a command t o i n s e r t a specimen, a n d t h e r o b o t removes t h e b o t t o m b a r from t h e magazine and p l a c e s i t on the measuring d e v i c e . The PDP-11/44 o b t a i n s t h e specimen d i m e n s i o n s from t h e m e a s u r i n g d e v i c e t h r o u g h a d e d i c a t e d RS-232 l i n e , t h e n i t commands t h e r o b o t t o move t h e specimen t o t h e g r i p s . A f t e r the robot's microcomputer acknowledges t h a t t h e b a r has been l o a d e d s u c c e s s f u l l y t h e PDP-11/44 s t a r t s t h e c r o s s h e a d . W h i l e t e s t s a r e underway



50

COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE II

i d e n t i f i c a t i o n o f t h e c u r r e n t specimen, t e s t c o n d i t i o n s , and i n s t r u m e n t s t a t u s a r e d i s p l a y e d on t h e s c r e e n . The e l a p s e d t i m e , l o a d c e l l f o r c e , s t r e s s , and s t r a i n v a l u e s a r e p r e s e n t e d and u p d a t e d once p e r s e c o n d . The t e s t c o n t i n u e s u n t i l t h e s p e c i m e n b r e a k s , t h e l o a d c e l l maximum f o r c e i s r e a c h e d , o r a s p e c i f i e d maximum s t r a i n v a l u e i s reached. When one o f t h e s e c o n d i t i o n s o c c u r s t h e c r o s s h e a d i s s t o p p e d , t h e specimen i s e j e c t e d from t h e g r i p s , and t h e c r o s s h e a d i s r e t u r n e d t o i t s i n i t i a l position. T h i s p r o c e s s i s r e p e a t e d f o r each specimen u n t i l t h e t e s t s e r i e s i s complete. The d a t a a c q u i s i t i o n t a s k c r e a t e s f i l e s c o n t a i n i n g t h e f o r c e v e r s u s time data, w i t h h e a d e r r e c o r d s t o i d e n t i f y t h e m a t e r i a l and t h e t e s t conditions. Automated f l e x u r e t e s t s a r e s i m i l a r . The r o b o t moves t h e b o t t o m b a r from t h e magazine t o t h e m e a s u r i n g d e v i c e where i t s w i d t h and t h i c k n e s s a r e d e t e r m i n e d , t h e n i t p l a c e s t h e b a r on t h e f l e x u r e t e s t f i x t u r e . The PDP-11/44 b e g i n s t h e t e s t by p u t t i n g t h e c r o s s h e a d i n m o t i o n . Data c o l l e c t i o n b e g i n s when t h e f i r s t l o a d i s d e t e c t e d , and t h e t e s t c o n t i n u e s u n t i l t h e specimen b a r breaks, t h e l o a d c e l l maximum f o r c e i s r e a c h e d , o r a s p e c i f i e d maximum s t r a i n value i s reached. Then t h e c r o s s h e a d i s s t o p p e d , t h e s p e c i m e n i s e j e c t e d from t h e f i x t u r e , and t h e crosshead i s returned t o i t s i n i t i a l p o s i t i o n . This p r o c e s s i s repeated u n t i l t h e t e s t s e r i e s i s complete. A n a l y z e Test Data. This option allows the user t o analyze previously acquired t e s t data. Our p h i l o s o p h y h a s been t o s e p a r a t e t h e d a t a a c q u i s i t i o n and d a t a a n a l y s i s o p e r a t i o n s , and t o s t o r e o n l y t h e o r i g i n a l t e s t d a t a . D a t a a n a l y s i s r o u t i n e s may change w i t h t i m e , and i t i s d e s i r a b l e t o be a b l e t o r e a n a l y z e o l d d a t a w i t h new a n a l y s i s software. Our t e n s i l e t e s t a n a l y s i s s o f t w a r e c r e a t e s p l o t s o f e n g i n e e r i n g s t r e s s as a f u n c t i o n o f e n g i n e e r i n g s t r a i n , as i l l u s t r a t e d i n F i g u r e 3. Our f l e x u r e t e s t s o f t w a r e p l o t s maximum f i b e r s t r e s s a s a f u n c t i o n o f maximum f i b e r s t r a i n , w i t h t h e o p t i o n o f i n c l u d i n g Poisson's r a t i o i n the c a l c u l a t i o n s . Both r o u t i n e s generate p r i n t e d r e p o r t s which p r e s e n t t h e t e s t r e s u l t s i n t a b u l a r form, a s i l l u s t r a t e d i n F i g u r e 4. D i s p l a y t h e H e l p F i l e f o r T h i s Menu. One o f o u r g o a l s was t o make t h i s s o f t w a r e as s e l f - e x p l a n a t o r y as p o s s i b l e . E a c h menu h a s a h e l p f i l e a s s o c i a t e d w i t h i t t o e x p l a i n the v a r i o u s s e l e c t i o n s . Discussion T h i s p r o j e c t came i n t o b e i n g b e c a u s e o u r l a b o r a t o r y h a s been a s k e d t o p e r f o r m an e v e r - i n c r e a s i n g number o f t e s t s w i t h a f i x e d number o f t e c h n o l o g i s t s , making i t n e c e s s a r y f o r us t o improve o u r p r o d u c t i v i t y by a u t o m a t i n g as much o f o u r o p e r a t i o n as p o s s i b l e . Because our automated I n s t r o n t e s t e r c a n r u n u n a t t e n d e d a t a l l h o u r s , we c a n




5. SCOTT & RIEKE


51


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0.1273

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5.07E+03

5.09E+03

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8.11E-»03

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6.91E+00

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SCOTT &RIEKE

53

p r o c e s s a t l e a s t two t o t h r e e t i m e s as many s p e c i m e n s p e r 24 h o u r day w i t h t h i s s y s t e m as we c o u l d w i t h t h e same t e s t e r b e i n g r u n m a n u a l l y e i g h t h o u r s p e r d a y . The i n v e s t m e n t o f a p p r o x i m a t e l y $25,000 i n r o b o t i c s equipment and $20,000 i n development c o s t s f o r t h e f u l l y automated t e n s i l e a n d f l e x u r e t e s t s h a s more t h a n d o u b l e d t h e t h r o u g h p u t o f t e s t i n g equipment c o s t i n g $ 1 0 0 , 0 0 0 . These a r e 1984 p r i c e s , b u t t h e r e l a t i v e c o s t s w o u l d be s i m i l a r today. Probably o f g r e a t e r importance i s t h e decrease i n l a b o r expenses and t h e c o n s t a n t q u a l i t y o f d a t a o b t a i n e d . I f one compares o u r system w i t h a m a n u a l l y o p e r a t e d t e s t e r w i t h manual t r e a t m e n t o f d a t a t h e n t h e improvement i n p r o d u c t i v i t y i s even g r e a t e r . We c a n p r o c e s s f o u r t o f i v e t i m e s a s many s p e c i m e n s p e r day w i t h o u r a u t o m a t e d s y s t e m as c o u l d be h a n d l e d b y a t e c h n o l o g i s t on a c o m p l e t e l y manual t e s t e r d u r i n g an e i g h t h o u r p e r i o d . The d a t a f i l e s c r e a t e d by t h i s s y s t e m a r e s t o r e d p e r m a n e n t l y a n d w i l l s e r v e a s a v a l u a b l e d a t a b a s e i n t h e y e a r s t o come. Literature 1.

Cited

Standard Test Method for T e n s i l e P r o p e r t i e s of Plastics D638-84, American Society for T e s t i n g and Materials: P h i l a d e l p h i a , 1985, V o l 8.01, p 227. Standard Test Method for F l e x u r a l P r o p e r t i e s of Unreinforced and Reinforced P l a s t i c s and E l e c t r i c a l I n s u l a t i n g M a t e r i a l s , D790-84a, American S o c i e t y for T e s t i n g and M a t e r i a l s : P h i l a d e l p h i a , 1985, V o l 8.01, p 397. S c o t t , R. L.; Rieke, J . K. In Advances i n Laboratory Robotics 1984, Hawk, G. L.; S t r i m a t i s , J . R . , E d s . ; Zymark C o r p o r a t i o n : Hopkinton, MA, 1984, p 151. f

2.

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RECEIVED February14,1989


Development of a Fully Automated Tensile and Flexure Test System

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