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The Use of Expert Systems in Process-Planning
The Use of Expert ystems in Process-Planning B. J. Davies ( 1 ) and I . L. Darbyshire, UMIST/England
Summary With t h e r a p i d l y d i m i n i s h i n g number of e x p e r t p r o c e s s - p l a n n e r s i n i n d u s t r y , t h e r e i s an i n c r e a s i n g l y u r g e n t need t o automate t h e process-planning f u n c t i o n , and t o emulate a s f a r a s p o s s i b l e on a computer, t h e e x p e r t i s e of t h e p l a n n e r . P r o c e s s - p l a n n i n g i s n o t o r i o u s l y d i f f i c u l t t o perform u s i n g normal a l g o r i t h m i c t e c h n i q u e s , and s o Expert Systems a r e proposed a s a method of c a p t u r i n g human planning knowledge, and making d e d u c t i o n s l e a d i n g t o s e n s i b l e p l a n n i n g sequences. EXCAP, an Expert Computer-Aided Process-Planning System i s d e s c r i b e d . Although o n l y a t a development s t a g e a t p r e s e n t , s u f f i c i e n t work h a s been done t o d e m o n s t r a t e t h e f e a s i b i l i t y of an Expert Systems' approach t o t h e p l a n n i n g problem. The d i a l o g u e of a simple i n t e r a c t i v e FXCAP s e s s i o n i s g i v e n , and n e c e s s a r y f u t u r e developments proposed.
Introduction There i s a t p r e s e n t c o n s i d e r a b l e i n t e r e s t i n computer-aided process-planning s y s t e m s , and a r e c o g n i t i o n t h a t t r a d i t i o n a 1 , a l g o r i t h m i c methods of s o l u t i o n a r e i n a d e q u a t e . P r o c e s s - p l a n n i n g , t h e s y n t h e s i s of a sequence of i n s t r u c t i o n s f o r t h e manufacture o f a component, i.: t r a d i t i o n a l l y performed by a s k i l l e d p l a n n e r on t h e b a s i s of y e a r s of accumulated experience.With t h e ever-diminishing number of such p l a n n e r s , t h e need f o r an automated process-planning system becomes more u r g e n t . Some s u c c e s s i n automating t h e p l a n n e r ' s r o l e h a s been a c h i e v e d u s i n g t h e " v a r i a n t " method of p r o c e s s - p l a n n i n g , by which a p l a n f o r a new component i.: adapted To some e x t e n t , from t h e e x i s t i n g plan f o r a s i m i l a r component. However, hc i s a l s o t h i s i s what t h e s k i l l e d p l a n n e r does. c a p a b l e of f o r m u l a t i n g p l a n s f o r completely new components f o r which t h e r e i s no e x i s t i n g v a r i a n t . A " g e n e r a t i v e " processplanning system must be c a p a b l e of emulating t h e p l a n n e r ' s logic. T h i s l o g i c i s found t o be so complex t h a t s o l u t i o n by a l g o r i t h m i c methods i s t o o cumbersome, n a i v e and i n f l e x i b l e . Expert Systems provide a method of s o l u t i o n which can overcome t h e s e problems.
A t y p i c a l c o n v e n t i o n a l r u l e h a s t h e form
IF THEN < a c t i o n > A f u z z y l o g i c r u l e i n t r o d u c e s an element of u n c e r t a i n t y , and h a s t h e form IF < t o a c e r t a i n extent) THEK < t o some degree> We can t h i n k of < c o n d i t i o n > a s being e v i d e n c e f o r an hypothesis. A fuzzy r u l e d e f i n e s n o t o n l y t h e n e c e s s a r y evidence and t h e h y p o t h e s i s , but a l s o t h e e x t e n t t o which t h e h y p o t h e s i s i s j u s t i f i e d when t h e c e r t a i n t y i n t h e e v i d e n c e i s known. C e r t a i n t y i n both evidence and h y p o t h e s i s i s measured i n log-odds u n i t s a s a p r o b a b i l i t y of each being TRUE. If the normal l i n e a r p r o b a b i l i t y of evidence E i s p [ E ] , t h e n t h e odds OLE] a r e c a l c u l a t e d by
and t h e log-odds
l o [ E ] by
Expert Systems The term "Expert System" i s one coined by r e s e a r c h e r s i n t o A r t i f i c i a l I n t e l l i e n c e and b r o a d l y speaking r e f e r s t o a system which s e e k s t o emufate t h e r e a s o n i n g c a p a c i t y of an e x p e r t i n a p a r t i c u l a r f i e l d of e x p e r t i s e . Expert Systems d i f f e r from a l g o r i t h m i c systems i n t h a t t h e y a r e r u l e - d r i v e n r a t h e r t h a n code and d a t a - d r i v e n . The r u l e s which d e s c r i b e t h e d e c i s i o n l o g i c of a problem a r e e x t e r n a l t o t h e main system, which i s e s s e n t i a l l y an " i n f e r e n c e e n g i n e " , c a p a b l e of i n t e r p r e t i n g t h e r u l e s and i n f e r r i n g d e c i s i o n s from them ( s e e F i g u r e 1 ) . S i n c e t h e r u l e s a r e e x t e r n a l , t h e y can be w r i t t e n i n a s p e c i a l language which b e s t e x p r e s s e s t h e knowledge of t h e expert. They a r e e a s y t o modify, s o t h a t t h e system can be It i s even a d a p t e d t o a v a r i e t y of o p e r a t i n g environments. p o s s i b l e f o r t h e system t o improve i t s own r u l e s i n t h e l i g h t of e x p e r i e n c e , so t h a t i t becomes " c l e v e r e r " w i t h time. It i s a simple m a t t e r t o program t h e i n f e r e n c e e n g i n e t o l i s t i t s " c h a i n of r e a s o n i n g " , s o t h a t i t can e x p l a i n any d e c i s i o n i t makes. The r u l e s can employ t h e concept of "fuzzy l o g i c " which i n t r o d u c e s an element of u n c e r t a i n t y i n t o d e c i s i o n s , more c l o s e l y emulating thought p r o c e s s e s i n r e a l l i f e , and which i s e x t r e m e l y d i f f i c u l t t o program u s i n g a l g o r i t h m i c methods. The r u l e s , by p r o v i d i n g a s t a n d a r d i s e d medium f o r t h e e x p r e s s i o n of a n e x p e r t ' s knowledge, a l l o w c o n t r i b u t i o n s by more t h a n one e x p e r t , s o t h a t t h e system n o t o n l y o u t l a s t s , but may a l s o outperform, any one of t h e e x p e r t s alone. Expert intelligent l o g i c which planning i s
l o [ E ] = 10 x l o g l O ( o [ E ] ) ( -100 <= l o [ E ] <= +lo0 Evidence can j u s t i f y s e v e r a l d i f f e r e n t h y p o t h e s e s ; a s i n g l e h y p o t h e s i s may need more than one p i e c e of evidence. A g r a p h i c a l r e p r e s e n t a t i o n , o f t e n c a l l e d an i n f e r e n c e network, i s t h e b e s t way of v i s u a l i s i n g a complex i n t e r a c t i o n of r u l e s ( s e e Figure 2 ) . I n d i v i d u a l nodes of t h e i n f e r e n c e network a r e c a l l e d "spaces". Spaces which do n o t provide evidence f o r a n y t h i n g e l s e a r e " g o a l " h y p o t h e s e s , which t h e system s e e k s t o u l t i m a t e l y prove or d i s p r o v e . These g o a l hypotheses a r e j u s t i f i e d by a c h a i n of r e a s o n i n g which e v e n t u a l l y t e r m i n a t e s a t s p a c e s which do n o t have any evidence of t h e i r own. These can be c a l l e d " a s k a b l e " s p a c e s , s i n c e t h e system must o b t a i n a v a l u e f o r t h e i r c e r t a i n t y from somewhere, and t h i s i s u s u a l l y by a s k i n g t h e u s e r t o respond w i t h an e s t i m a t e . T h i s v a l u e can t h e n be f i l t e r e d back through t h e i n f e r e n c e network t o p a r t i a l l y prove or disprove t h e current goal hypothesis. Spaces can be l i n k e d i n s e v e r a l ways.
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By a f u z z y (Bayesian) l i n k . A rule defines a positive weight pw, and a n e g a t i v e weight nw, f o r t h e l i n k . If the evidence s p a c e i s found t o have a c e r t a i n t y of +100 (TRUE), t h e n pw i s added t o t h e c e r t a i n t y of t h e h y p o t h e s i s . If the e v i d e n c e i s FALSE, t h e n nw i s added t o t h e h y p o t h e s i s certainty. For a v a l u e of evidence c e r t a i n t y between -100 and +loo, a l i n e a r i n t e r p o l a t i o n i s performed between nw and pw t o f i n d t h e v a l u e t o be added t o t h e h y p o t h e s i s certainty.
2)
By a l o g i c a l AND. The h y p o t h e s i s c e r t a i n t y i s c a l c u l a t e d a s t h e maximum of t h e evidence c e r t a i n t i e s .
3)
By a l o g i c a l OR. The h y p o t h e s i s c e r t a i n t y i s c a l c u l a t e d a s t h e minimum of t h e evidence c e r t a i n t i e s .
4)
By a l o g i c a l NOT. The h y p o t h e s i s c e r t a i n t y i s c a l c u l a t e d a s t h e n e g a t i v e of t h e ( s i n g l e ) evidence c e r t a i n t y .
Systems t h e r e f o r e p r o v i d e a u s e r - f r i e n d l y , f l e x i b l e , s o l u t i o n t o t h e kind of problems i n v o l v i n g complex occur f r e q u e n t l y i n e n g i n e e r i n g , of which processa good example.
Fuzzy Logic I n f e r e n c e s The f u z z y l o g i c i n f e r e n c e mechanism d e s c r i b e d h e r e i s a s used by t h e commercially a v a i l a b l e AL/X system, but i s f a i r l y r e p r e s e n t a t i v e of a range of well-known Expert Systems. AL/X was o r i g i n a l l y commissioned by B r i t i s h Petroleum Ltd t o h e l p i n a n a l y s i n g o i l - r i g monitor d a t a i n t h e event of a r i g shut-down. I t h a s s i n c e been developed a s a g e n e r a l i s e d Expert System i . e . i t p r o v i d e s t h e i n f e r e n c e engine f o r which t h e u s e r AL/X i s s u p p l i e s t h e r u l e s t o a d a p t i t t o a p a r t i c u l a r problem. marketed by I n t e l l i g e n t Terminals Ltd of Oxford, England.
The f u z z y l o g i c a l o p e r a t i o n s AND, OR and NOT can be s e e n t o be e q u i v a l e n t t o normal Boolean o p e r a t i o n s i f t h e c e r t a i n t y v a l u e s a r e r e s t r i c t e d t o +lo0 (TRUE) and -100 (FALSE). An Expert System w i l l i n v e s t i g a t e a l l t h e g o a l h y p o t h e s e s i n t h e i n f e r e n c e network, b a c k t r a c k i n g through t h e e v i d e n c e t o f i n d an a s k a b l e space. When a l l evidence h a s been i n v e s t i g a t e d , a h y p o t h e s i s w i l l have been proved e i t h e r more TRUE or more FALSE.
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EXCAP AUTOCAP [ I ] and ICAPP [ 2 ] a r e two systems p r e v i o u s l y developed a t UMIST f o r t h e planning of r o t a t i o n a l and p r i s m a t i c p a r t s respectively. AUTOCAP could not plan g e n e r a t i v e l v a t a l l , w h i l e even t h e most automated, g e n e r a t i v e ICAPP mode of o p e r a t i o n was over s i m p l i f i e d . EXCAP (an Expert Computer-Aided Process-planning system) i s an a t t e m p t t o r e s o l v e t h e s e inadequacies.
f a c i l i t y can be used t o d i s p l a y t h e o p e r a t i o n s a v a i l a b l e , and can o b t a i n c e r t a i n t y v a l u e s f o r each space i n t h e i n f e r e n c e networkfor a p a r t i c u l a r o p e r a t i o n . This f a c i l i t y a l l o w s t h e u s e r t o e f f e c t i v e l y a s k MCAP why i t has chosen one o p e r a t i o n i n preference t o another. The u s e r can impose l i m i t s on t h e development of t h e sequence t r e e . Branch L i m i t . The maximum number of branches which a r e allowed t o develop from a node. This can be expressed as an a b s o l u t e v a l u e , or as a p e r c e n t a g e of t h e t o t a l number of branches from t h e node. The branch l i m i t parameter has a d e f a u l t v a l u e of 1, so a l l o w i n g t h e g e n e r a t i o n of o n l y one sequence.
EXCAP i s w r i t t e n i n PASCAL, and runs on a VAX 1 1 / 7 5 0 under t h e VMS o p e r a t i n g system. Each module of t h e system i s run s e p a r a t e l y under t h e c o n t r o l of a c e n t r a l command module. G r a p h i c s f a c i l i t i e s a r e provided by a s e p a r a t e module run c o n c u r r e n t l y a s a sub-process. The code of t h e l a r g e s t module o c c u p i e s about 150K i n main memory, but most d a t a s t o r a g e i s dynamically a l l o c a t e d a t run-time, so t h e amount used depends on t h e complexity of t h e planning problem. The VM has about 1.5 Mb of heap s t o r a g e a v a i l a b l e f o r dynamically a l l o c a t e d variables.
Confidence Cut-off. The cut-off v a l u e of confidence f o r a branch below which i t w i l l n o t be allowed t o develop further. The confidence cut-off parameter h a s a d e f a u l t v a l u e of -100, imposing no r e s t r i c t i o n on t r e e development. Maximum Sequence L i m i t . The maximum number of sequences t h a t can be g e n e r a t e d . The u s e r can also t e r m i n a t e sequence g e n e r a t i o n using CTRL/C. The maximum sequence l i m i t parameter h a s a d e f a u l t v a l u e of 50.
U n t i l r e c e n t l y , t h e emphasis has been on t h e d e s i g n of t h e i n f e r e n c e mechanism, and t h e language i n which p l a n n i n g knowledge can be expressed. T h i s p r o v i d e s t h e framework f o r which it i s hoped t h a t adequate r u l e s can be found f o r an e f f e c t i v e s o l u t i o n of t h e problem.
F u t u r e Developments t o MCAP EXCAP i s designed t o p l a n r o t a t i o n a l components, but t h i s l i m i t a t i o n i s a r e s u l t of t h e way i n which t h e component geometry i s d e s c r i b e d , not i n t h e way t h e r u l e s a r e d e f i n e d . It s h o u l d be p o s s i b l e t o u s e a n almost i d e n t i c a l t e c h n i q u e f o r p r i s m a t i c p a r t s , and perhaps f o r o t h e r sequencing problems t h a n process-planning.
I t i s envisaged t h a t t h e c u r r e n t planning f u n c t i o n of EXCAP w i l l form t h e c e n t r a l module of a complete planning system i n t e r f a c i n g w i t h CAD and KC part-program g e n e r a t i o n . There a r e s e v e r a l a r e a s where t h e a p p l i c a t i o n of an Expert System would be beneficial.
The component and blank a r e d e f i n e d i n terms of an ordered sequence of dimensioned f e a t u r e s , such a s FACE, CYLINDER o r TAPER ( s e e F i g u r e 3 ) .
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S e l e c t i o n of t o o l s .
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S e l e c t i o n of machines.
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S e l e c t i o n of clamping/workpiece
EXCAP uses much t h e same i n f e r e n c e mechanism a s t h a t p r e v i o u s l y d e s c r i b e d f o r AL/X. AL/X was o b t a i n e d a t an e a r l y s t a g e i n t h e development of MCAP, and was used t o e v a l u a t e t h e p o t e n t i a l a p p l i c a b i l i t y of an Expert System t o processplanning. The A L / X r u l e language p o s s e s s e s no a r i t h m e t i c c a p a b i l i t y , so only l i m i t e d process-planning knowledge can be expressed. MCAP uses a more powerful language which does i n c l u d e a r i t h m e t i c , but which i s n e v e r t h e l e s s r e c o g n i s a b l y a d e r i v a t i v e of t h e AL/X language. A fragment of t b e EXCAP r u l e base i s shown i n F i g u r e 4 .
set-up.
The most immediately urgent development i s t h e improvement of t h e r u l e base. This w i l l i n v o l v e t h e co-operation of process-planning e x p e r t s , and t h e d e s i g n of an i n t e r a c t i v e r u l e g e n e r a t i o n and maintainance module. A t present, the rules a r e extremely simple and do n o t n e c e s s a r i l y g e n e r a t e a t r u l y optimum sequence. Changes t o t h e r u l e s a r e made u s i n g t h e normal VAX t e x t e d i t o r , and a r e n o t under t h e c o n t r o l of t h e EXCAP system. Improvement of t h e r u l e s w i l l have two main e f f e c t s .
The r u l e s perform two d i s t i n c t f u n c t i o n s .
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The d e f i n i t i o n of t h e a v a i l a b l e machining o p e r a t i o n s i n terms of a) t h e f e a t u r e s on which they can be used, and b) t h e e f f e c t t h a t t h e o p e r a t i o n ha.; oil t h e workpiece, The s e l e c t i o n of a p a r t i c u l a r o p e r a t i o n from among t h o s e which have been found t o he a p p l i c s h l e .
EXCAP s p l i t s t h e planning proces.; i n t o two d i s t i n c t phases. The f i r s t , MACRO phase p l a n s t h e o r d e r i n which hulk m e t a l removal o p e r a t i o n s must be performed t o a c h i e v e t h e d e s i r e d component c o n f i g u r a t i o n . The second, MICRO phase p l a n s t h e f e e d s , speeds and d e p t h s of c u t f o r each of t h e preTriously planned MACRO o p e r a t i o n s . I n t h e manner of Lewis e t a 1 [3! and Matsushima e t a 1 [ & I , EXCAP l o o s e l y d e f i n e s planning as t h e i n v e r s e of machining, a n d s o works backwards from t h e f i n i s h e d component towards t h e blank. This makes t h e o p e r a t i o n a p p l i c a t i o n r u l e s much s i m p l i r ,
Each of t h e a v a i l a b l e o p e r a t i o n s i s a g o a l h y p o t h e s i s i n t h e EXCAP i n f e r e n c e network, and FXCAP s e e k s t o prove o r d i s p r o v e them. "Askable" evidence i s j u s t i f i e d not by a s k i n g t h e u s e r t o s u p p l y a v a l u e , hut by c a l c u l a t i o n s on t h e c u r r e n t workpiece d a t a b a s e . A disproved o p e r a t i o n h y p o t h e s i s i s rejected. For proved o p e r a t i o q s , EXCAP determines t h e l e s s worked workpiece which r e s u l t s from t h e i r use. T h i s new workpiece can be used i n t h e next Level of p l a n n i n g . Thus EXCAP forms a " t r e e " of p o s s i b l e o p e r a t i o n sequences. Nodes i n t h e t r e e r e p r e s e n t v a r i o u s i n t e r m e d i a t e workpiece c o n f i g u r a t i o n s ; t h e r o o t node r e p r e s e n t s t h e f i n i s h e d component,and t h e t e r m i n a l nodes r e p r e s e n t t h e blank. Branches between nodes r e p r e s e n t t h e o p e r a t i o n s used. For each o p e r a t i o n branch, f u r t h e r r u l e s s e t a c e r t a i n t y v a l u e f o r t h e hypothesis t h a t the operation it represents i s s u i t a b l e f o r u s e a t t h a t p o i n t i n t h e sequence. This c e r t a i n t y v a l u e p r o v i d e s a measure of comparison between branches l e a v i n g a p a r t i c u l a r node, and s o i n d i c a t e s t h e b e s t o v e r a l l p a t h through t h e t r e e . This p a t h r e p r e s e n t s t h e optimum planned sequence a c c o r d i n g t o t h e r u l e s used. Reading t h e sequence i n r e v e r s e p r o v i d e s t h e e q u i v a l e n t optimum machining sequence. EXCAP i s c a p a b l e of producing j u s t one ( t h e optimum) o r a l l p o s s i b l e s e q u e n c e s , provided s u f f i c i e n t memory i s a v a i l a b l e . Tt can a l s o be d r i v e n i n a step-by-step mode i n which t h e u s e r i s a d v i s e d a s t o t h e o p e r a t i o n s EXCAP t h i n k s a r e most s u i t a b l e , but can o v e r - r i d e t h e s e i f he wishes. A t each s t e p , t h e g r a p h i c s
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B e t t e r d e c i s i o n making, y i e l d i n g a more t r u l y optimum sequence.
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G r e a t e r range of a v a i l a b l e o p e r a t i o n s , a l l o w i n g t h e planning of more complex components.
A s t h e number of f e a t u r e s which can be machined i n c r e a s e s , s o t h e complexity of t h e r u l e s governing o p e r a t i o n a p p l i c a b i l i t y i n c r e a s e s , and t h e y r a p i d l y become extremely d i f f i c u l t t o code By p r o v i d i n g f a i r l y u s i n g normal a l g o r i t h m i c t e c h n i q u e s . powerful pattern-matching f a c i l i t i e s w i t h i n t h e r u l e language, t h e r u l e s (ispd b y FXCAP can remain comprehensjhle and e a s y t o e x t end.
I t may be found d e s i r a b l e t o r e - w r i t e t h e r u l e base and i n f e r e n c e e n g i n e u s i n g PROLOG o r POPLOG. The f e a s i b i l i t y o f t h i s will be i n v e s t i g a t e d i n t h e n e a r f u t u r e . However, t h e r e a r e d e f i n i t e advantages i n w r i t i n g t h e r u l e s i n a d e d i c a t e d language.
I f EXCAP i s t o be used i n an i n d u s t r i a l environment, t h e n a f a i r amoclnt of t h e i n t e r a c t i v e d i a l o g u e w i l l need t o be changed. FXCAP a t p r e s e n t d i s p l a y s much i n f o r m a t i o n which would be meaningless t o t h e normal u s e r of t h e system. It should be s t r e s s e d a g a i n t h a t MCAP i s s t i l l a t a development s t a g e , and i r , c o n s t a n t l y being improved a n d e x t e i d e d .
Example I n t e r a c t i v e S e s s i o n IJsing EXCAP _ l _ l _ _
I t i s d i f f i c u l t t o a d e q u a t e l y convey t h e degree of i n t e r a c t i o n p o s s i b l e when u s i n g EXCAP, and much u s e i s made of c o l o u r g r a p h i c s which cannot be reproduced h e r e . The f o l l o w i n g d i a l o g u e a t t e m p t s t o demonstrate t h e s i m p l i c i t y w i t h which a ( p r e - d e f i n e d ) component can be planned u s i n g MCAP i n i t s most a u t o m a t i c mode. The component i s as shown i n F i g u r e 3. A l l commands throughout t h e FXCAP system u s e a common language which i n c l u d e s f u l l HELP f a c i l i t i e s . These a r e used t o comment t h e d i a l o g u e . User i n p u t s a r e shown ____underlined f o r clarity.
x
c c c
x u
x
?.
x
x x
E EEEEE
X
23-FEE-84
c
A hMAA A A
C
C
A
A
CCC
X
P
A A
A
c
X X
PPPP
A
CCC
A d d i t i o n a l i n f o r m a t i o n a v a i l a b l e :-
_-
___---
x
EFEEF II E EEE E
A A
STEP
ATTO?lATT C
r'
I' 1' PPPP
SEO> h e l p plan a u t o m a t i c
P P P
PLA?; AI'TOMATIC Sequence g e n e r a t i o n proceeds a u t o m a t i c a l l y , a l l o w i n g more than one sequence t o be g e n e r a t e d i f t h e branch l i m i t and c o n f i d e n c e cut-off a r e s e t a c c o r d i n g l y . G e n e r a t i o n may be t e r m i n a t e d n r e m a t u r e l y u s i n g CTQL/C.
10 :$3 :54
Enter ? € 0 1 summary o f EXCAP commancls HELP f o r more d e t a i l e d i n f o r m a t i o n
SEO> ~ plan a u t_ o m_ a t i_ c _ _
_
Sequence g e n e r a t i o n complete EXCAP commands avaj l a b l e a r e :
SET
SEO> h e l p show siimmarl ____-
GEOMETRY SFOIJENCF, NC HELP
SHOW
RESOCkCES
RULFS
DFTAIL PRINTROVIX OIJTT
PT,AW 7
SHOW SLMMARY D i s p l a v s v a r i o u s s t a t i s t i c s of t h e l a s t sequepce planning a t t e m p t i n i t i a t e d by t h e PLAN command. SFO> show summary
EXCAP> h e l p sequence
Workpiece c o n f i g u r a t i o n s developed : Sequences g e n e r a t e d :
SEOUENCE
10 1 1
Confidence 8.57
mins 7.70
1
8.57
7.70
Xo
Tnvokes t h e SFOUFNCF module t o plan YACRO o p e r a t i o n sequences f o r one o r more romponents.
Best sequence r a t i n g s
EXCAP> sequence Best sequence p r o d u c t i o n t i m e s
1 2 3 4 5
: : : :
1 2 3 4 5
: : : :
:
:
SEO> h e l p show sequence
SHOW SEOUENCE=Sequence number P a r t s e t t o LEYl
D i s p l a y s t h e planned sequence w i t h t h e s p e c i f i e d number.
1
SEO>
Oualif i e r
SEO commands a v a i l a b l e a r e : GEOMETRY-FILE
PART
SFOW
DRAW SAVF EXCAP
SET
PLAK HELP
7
The number of t h e r e q u i r e d sequence. Append 'R' o r I F ' t o s p e c i f y t h e sequence w i t h a p a r t i c u l a r c o n f i d e n c e r a t i n g p o s i t i o n o r p r o d u c t i o n time r a t i n g p o s i t i o n r e s p e c t i v e l y . D e f a u l t =1
OiJIT A d d i t i o n a l i n f o r m a t i o n a v a i l a b l e :-
SEO> h e l p show p a r t
FULL
ABBREVIATED
SHOW PART
SEO> show sequence D i s p l a y s t h e c o n f i g u r a t i o n of t h e c u r r e n t component, a s d e f i n e d by t h e PART command.
SEO> show p a r t PART NUMBER: PLANNER : DATE :
LEYl
21-FEB-84 Feature
PART NAME: LEYLAFD FXAMPLF DRAWING KUMBER: YATERIAL CODE: AA l h Diam
r h Diam
0.000 4 2 .000 42.000
42.000
0 .000 40 .000 40 .000 34.000 20 .000 20 .000 24 .000 24.000 16 .000 10 .000 10 .000 14 .000 14 .O00 10 -000
40 .000
Length
SF
_____--_-_--------- ------- ------- --BLAhK
FACE CYL FACE
122.000
n.m
. s
COMPONENT
FACE CYL TAPER FACE CYL FACE CYL TAPER FACE CY L FACE CY L TAPER FACE
AAO 0 RAOO CAOO DAOO FA00 FA00 GAOO HA0 0 1.400 JAOO KAO 0 LA0 0 MA0 0 NAO 0
34.000 20 .000
Sequence g e n e r a t i o n number : Confidence r a t i n g p o s i t i o n : Prod. time r a t i n g p o s i t i o n : Oper'n Old
->
New
Length
R.FACE R.TURR R.TURN R.TURN R.TURN R.TURN ETAPER
-> -> -> -> -> -> -> -> ->
NA04 BA02 GA03 LA02 JA00
2 .000 120 .000 77 .000 27 .000 2 .000 3 .000 2 .000 23 .000 3 .000
------ -_ -BA03 BA02 GA03 LA02 GA02 LA01 ETAPER GAOl ETAPER RAOl
1 1 1 Diam 1
Diam 2
Time
-_-- -_-_-_ --_---- -_____-
EA00 MA00 IIA00 CAOO
0 .000 40 .000 24 .000 14 -000 10.000 20 .000 10 .000 16.000 34 .000
42.000 42.000 40.000 24.000 14.000 24.000 14.000 24.000 40.000
_---( ( ( ( ( ( ( ( (
40 .000 3.000 3 .000
SEO>
Conf
------
0.39, 0.81, 1.49, 0.68, 0.30, 0.31, 0.45, 0.50, 0.46,
18.00) 16.00) 17.90) 17.90) 8.57) 10.32) 24.41) 21.33) 20.00)
5.52
8.57
-_---- -------
quit
24 .000 16 .0O0 10 .000
2/r.000 23 .000
EXCAP t e r m i n a t e d 23-FEB-84 Returning t o DCL
...
10:54:12
2 .000 14.000 10.000
23 .000 2.000
0 .000
SEO> h e l p p l a n PLAN I n i t i a t e s a DlanninE sequence a t t e m p t . w i t h t h e branch l i m i t and c o n f i d e n c e cut-off parameters a s d e f i n e d by t h e SET BRANCH and SET CUTOFF commands, € o r t h e component d e f i n e d by t h e PART command. A sequence t r e e i s g e n e r a t e d which m y be examined by t h e v a r i o u s o p t i o n s of t h e SHOW and DRAW command 4.
References El-Midany,T.T. " I n t e r a c t i v e Computer-Assisted System f o r Turned P a r t s " Ph.D. t h e s i s , UMTST, October 1979 Ssemakula, M.E. " E v a l u a t i o n of an I n t e r a c t i v e P r o c e s s P l a n n i n g System (ICAPP) f o r Eon-Rotational P a r t s . " M.Sc D i s s e r t a t i o n LWIST October 1981. Lewis J r , W . C . , Bartlet,Elizabeth, Finter,I.I. Rarash,M.M. "Tool-Oriented Process-Planning" Proc. 23rd MTDR Conf, UMIST, September 1982
and
305
[ 4 ] M a t s u s h i m a , K . , Okada,N. and S a t a , T . "The I n t e g r a t i o n of CAD and CAEI by A p p l i c a t i o n of A r t i f i c i a l I n t e 11i g e n c e T e c h n i q u e s " A n n a l s of CIRP V o l . 3 1 / 1 / 1 9 8 2 .
[ 5 ] E s k c i o g l u , H. a n d D a v i e s , R . J .
,
n
"An I n t e r a c t i v e P r o c e s s P l a n n i n g System f o r P r i s m a t i c P a r t s (ICAPP) A n n a l s of CIRP Vol. 3 2 / 1 / 1 9 8 3 .
."
)m-p
/1
Display R e s u l t s
IF IF IF IF
Supplu Data
1
ELSE
El E2 H1 H?
AND AND AND AND
E2 AND E3 THEN E3 THEN E2 AND H2 THEN E4 THEN
E l E? E3 E4 H1 H2 H3 H4
"Askable" evidence
Sub-hypotheses Goal hqpotheses
H1 H2 H3 H4
I
FIG 2 A
Simple Inference Network
FIG l ( a ' Structure o i Typical Conventional Prograf BAOO
1-1-7
._
Se 1f -Lear n i nq
feedback
FACE
AAOO
CYL
BAOO
TAPER FACE CYL FACE CYL TAPER FACE CYL FACE CYL TAPER FACE
CAOO
DAOO EAOO FA00 GAOO HA00
I A00 JAOO KAOO LAO0 MA00 NAOO
00 40 0
40 0
40 0 34 0 20 0 20 0 24 0 24 0 16 0 10 0 10 0 14 0 140
340 20 0
100
00
40 0 3 0
3 0 24 0 16 0 10 0
24 0 23 0 20
14 0 100
23 0 20
FIG 3
A
Sinple EXCAP Component
OPERATION R TURN
"basic rough-turning operation''
Inquire Ansuer
AIlD
Interface Engine
(
ROO1 ROO2 ROO3 ROO4 LOO1 LO03 LO05 1
ACTION 1-R TURN "the current
cylinder feature has a greater diameter than
those on either side" AND ( R501 R502 )
u
RELATION ROO3
# Kt11
Name
FACE
Opera t ion5u 1tab 1 e "an operation is suitable" " 1 e reflects overall confidence that operation, will ultimately lead to a good sequence" 2 -20 BAY ( Economical Finishing 10 0
SELECTION
port FIG l ( b )
Structure o f T y p i c a l Expert System
Special
11
If
chosen,
01
FIG 4 Fragment of EXCAP Rules Base
306
Summary With t h e r a p i d l y d i m i n i s h i n g number of e x p e r t p r o c e s s - p l a n n e r s i n i n d u s t r y , t h e r e i s an i n c r e a s i n g l y u r g e n t need t o automate t h e process-planning f u n c t i o n , and t o emulate a s f a r a s p o s s i b l e on a computer, t h e e x p e r t i s e of t h e p l a n n e r . P r o c e s s - p l a n n i n g i s n o t o r i o u s l y d i f f i c u l t t o perform u s i n g normal a l g o r i t h m i c t e c h n i q u e s , and s o Expert Systems a r e proposed a s a method of c a p t u r i n g human planning knowledge, and making d e d u c t i o n s l e a d i n g t o s e n s i b l e p l a n n i n g sequences. EXCAP, an Expert Computer-Aided Process-Planning System i s d e s c r i b e d . Although o n l y a t a development s t a g e a t p r e s e n t , s u f f i c i e n t work h a s been done t o d e m o n s t r a t e t h e f e a s i b i l i t y of an Expert Systems' approach t o t h e p l a n n i n g problem. The d i a l o g u e of a simple i n t e r a c t i v e FXCAP s e s s i o n i s g i v e n , and n e c e s s a r y f u t u r e developments proposed.
Introduction There i s a t p r e s e n t c o n s i d e r a b l e i n t e r e s t i n computer-aided process-planning s y s t e m s , and a r e c o g n i t i o n t h a t t r a d i t i o n a 1 , a l g o r i t h m i c methods of s o l u t i o n a r e i n a d e q u a t e . P r o c e s s - p l a n n i n g , t h e s y n t h e s i s of a sequence of i n s t r u c t i o n s f o r t h e manufacture o f a component, i.: t r a d i t i o n a l l y performed by a s k i l l e d p l a n n e r on t h e b a s i s of y e a r s of accumulated experience.With t h e ever-diminishing number of such p l a n n e r s , t h e need f o r an automated process-planning system becomes more u r g e n t . Some s u c c e s s i n automating t h e p l a n n e r ' s r o l e h a s been a c h i e v e d u s i n g t h e " v a r i a n t " method of p r o c e s s - p l a n n i n g , by which a p l a n f o r a new component i.: adapted To some e x t e n t , from t h e e x i s t i n g plan f o r a s i m i l a r component. However, hc i s a l s o t h i s i s what t h e s k i l l e d p l a n n e r does. c a p a b l e of f o r m u l a t i n g p l a n s f o r completely new components f o r which t h e r e i s no e x i s t i n g v a r i a n t . A " g e n e r a t i v e " processplanning system must be c a p a b l e of emulating t h e p l a n n e r ' s logic. T h i s l o g i c i s found t o be so complex t h a t s o l u t i o n by a l g o r i t h m i c methods i s t o o cumbersome, n a i v e and i n f l e x i b l e . Expert Systems provide a method of s o l u t i o n which can overcome t h e s e problems.
A t y p i c a l c o n v e n t i o n a l r u l e h a s t h e form
IF
and t h e log-odds
l o [ E ] by
Expert Systems The term "Expert System" i s one coined by r e s e a r c h e r s i n t o A r t i f i c i a l I n t e l l i e n c e and b r o a d l y speaking r e f e r s t o a system which s e e k s t o emufate t h e r e a s o n i n g c a p a c i t y of an e x p e r t i n a p a r t i c u l a r f i e l d of e x p e r t i s e . Expert Systems d i f f e r from a l g o r i t h m i c systems i n t h a t t h e y a r e r u l e - d r i v e n r a t h e r t h a n code and d a t a - d r i v e n . The r u l e s which d e s c r i b e t h e d e c i s i o n l o g i c of a problem a r e e x t e r n a l t o t h e main system, which i s e s s e n t i a l l y an " i n f e r e n c e e n g i n e " , c a p a b l e of i n t e r p r e t i n g t h e r u l e s and i n f e r r i n g d e c i s i o n s from them ( s e e F i g u r e 1 ) . S i n c e t h e r u l e s a r e e x t e r n a l , t h e y can be w r i t t e n i n a s p e c i a l language which b e s t e x p r e s s e s t h e knowledge of t h e expert. They a r e e a s y t o modify, s o t h a t t h e system can be It i s even a d a p t e d t o a v a r i e t y of o p e r a t i n g environments. p o s s i b l e f o r t h e system t o improve i t s own r u l e s i n t h e l i g h t of e x p e r i e n c e , so t h a t i t becomes " c l e v e r e r " w i t h time. It i s a simple m a t t e r t o program t h e i n f e r e n c e e n g i n e t o l i s t i t s " c h a i n of r e a s o n i n g " , s o t h a t i t can e x p l a i n any d e c i s i o n i t makes. The r u l e s can employ t h e concept of "fuzzy l o g i c " which i n t r o d u c e s an element of u n c e r t a i n t y i n t o d e c i s i o n s , more c l o s e l y emulating thought p r o c e s s e s i n r e a l l i f e , and which i s e x t r e m e l y d i f f i c u l t t o program u s i n g a l g o r i t h m i c methods. The r u l e s , by p r o v i d i n g a s t a n d a r d i s e d medium f o r t h e e x p r e s s i o n of a n e x p e r t ' s knowledge, a l l o w c o n t r i b u t i o n s by more t h a n one e x p e r t , s o t h a t t h e system n o t o n l y o u t l a s t s , but may a l s o outperform, any one of t h e e x p e r t s alone. Expert intelligent l o g i c which planning i s
l o [ E ] = 10 x l o g l O ( o [ E ] ) ( -100 <= l o [ E ] <= +lo0 Evidence can j u s t i f y s e v e r a l d i f f e r e n t h y p o t h e s e s ; a s i n g l e h y p o t h e s i s may need more than one p i e c e of evidence. A g r a p h i c a l r e p r e s e n t a t i o n , o f t e n c a l l e d an i n f e r e n c e network, i s t h e b e s t way of v i s u a l i s i n g a complex i n t e r a c t i o n of r u l e s ( s e e Figure 2 ) . I n d i v i d u a l nodes of t h e i n f e r e n c e network a r e c a l l e d "spaces". Spaces which do n o t provide evidence f o r a n y t h i n g e l s e a r e " g o a l " h y p o t h e s e s , which t h e system s e e k s t o u l t i m a t e l y prove or d i s p r o v e . These g o a l hypotheses a r e j u s t i f i e d by a c h a i n of r e a s o n i n g which e v e n t u a l l y t e r m i n a t e s a t s p a c e s which do n o t have any evidence of t h e i r own. These can be c a l l e d " a s k a b l e " s p a c e s , s i n c e t h e system must o b t a i n a v a l u e f o r t h e i r c e r t a i n t y from somewhere, and t h i s i s u s u a l l y by a s k i n g t h e u s e r t o respond w i t h an e s t i m a t e . T h i s v a l u e can t h e n be f i l t e r e d back through t h e i n f e r e n c e network t o p a r t i a l l y prove or disprove t h e current goal hypothesis. Spaces can be l i n k e d i n s e v e r a l ways.
1)
By a f u z z y (Bayesian) l i n k . A rule defines a positive weight pw, and a n e g a t i v e weight nw, f o r t h e l i n k . If the evidence s p a c e i s found t o have a c e r t a i n t y of +100 (TRUE), t h e n pw i s added t o t h e c e r t a i n t y of t h e h y p o t h e s i s . If the e v i d e n c e i s FALSE, t h e n nw i s added t o t h e h y p o t h e s i s certainty. For a v a l u e of evidence c e r t a i n t y between -100 and +loo, a l i n e a r i n t e r p o l a t i o n i s performed between nw and pw t o f i n d t h e v a l u e t o be added t o t h e h y p o t h e s i s certainty.
2)
By a l o g i c a l AND. The h y p o t h e s i s c e r t a i n t y i s c a l c u l a t e d a s t h e maximum of t h e evidence c e r t a i n t i e s .
3)
By a l o g i c a l OR. The h y p o t h e s i s c e r t a i n t y i s c a l c u l a t e d a s t h e minimum of t h e evidence c e r t a i n t i e s .
4)
By a l o g i c a l NOT. The h y p o t h e s i s c e r t a i n t y i s c a l c u l a t e d a s t h e n e g a t i v e of t h e ( s i n g l e ) evidence c e r t a i n t y .
Systems t h e r e f o r e p r o v i d e a u s e r - f r i e n d l y , f l e x i b l e , s o l u t i o n t o t h e kind of problems i n v o l v i n g complex occur f r e q u e n t l y i n e n g i n e e r i n g , of which processa good example.
Fuzzy Logic I n f e r e n c e s The f u z z y l o g i c i n f e r e n c e mechanism d e s c r i b e d h e r e i s a s used by t h e commercially a v a i l a b l e AL/X system, but i s f a i r l y r e p r e s e n t a t i v e of a range of well-known Expert Systems. AL/X was o r i g i n a l l y commissioned by B r i t i s h Petroleum Ltd t o h e l p i n a n a l y s i n g o i l - r i g monitor d a t a i n t h e event of a r i g shut-down. I t h a s s i n c e been developed a s a g e n e r a l i s e d Expert System i . e . i t p r o v i d e s t h e i n f e r e n c e engine f o r which t h e u s e r AL/X i s s u p p l i e s t h e r u l e s t o a d a p t i t t o a p a r t i c u l a r problem. marketed by I n t e l l i g e n t Terminals Ltd of Oxford, England.
The f u z z y l o g i c a l o p e r a t i o n s AND, OR and NOT can be s e e n t o be e q u i v a l e n t t o normal Boolean o p e r a t i o n s i f t h e c e r t a i n t y v a l u e s a r e r e s t r i c t e d t o +lo0 (TRUE) and -100 (FALSE). An Expert System w i l l i n v e s t i g a t e a l l t h e g o a l h y p o t h e s e s i n t h e i n f e r e n c e network, b a c k t r a c k i n g through t h e e v i d e n c e t o f i n d an a s k a b l e space. When a l l evidence h a s been i n v e s t i g a t e d , a h y p o t h e s i s w i l l have been proved e i t h e r more TRUE or more FALSE.
Annals of the ClRP Vol. 33/1/1984
303
EXCAP AUTOCAP [ I ] and ICAPP [ 2 ] a r e two systems p r e v i o u s l y developed a t UMIST f o r t h e planning of r o t a t i o n a l and p r i s m a t i c p a r t s respectively. AUTOCAP could not plan g e n e r a t i v e l v a t a l l , w h i l e even t h e most automated, g e n e r a t i v e ICAPP mode of o p e r a t i o n was over s i m p l i f i e d . EXCAP (an Expert Computer-Aided Process-planning system) i s an a t t e m p t t o r e s o l v e t h e s e inadequacies.
f a c i l i t y can be used t o d i s p l a y t h e o p e r a t i o n s a v a i l a b l e , and can o b t a i n c e r t a i n t y v a l u e s f o r each space i n t h e i n f e r e n c e networkfor a p a r t i c u l a r o p e r a t i o n . This f a c i l i t y a l l o w s t h e u s e r t o e f f e c t i v e l y a s k MCAP why i t has chosen one o p e r a t i o n i n preference t o another. The u s e r can impose l i m i t s on t h e development of t h e sequence t r e e . Branch L i m i t . The maximum number of branches which a r e allowed t o develop from a node. This can be expressed as an a b s o l u t e v a l u e , or as a p e r c e n t a g e of t h e t o t a l number of branches from t h e node. The branch l i m i t parameter has a d e f a u l t v a l u e of 1, so a l l o w i n g t h e g e n e r a t i o n of o n l y one sequence.
EXCAP i s w r i t t e n i n PASCAL, and runs on a VAX 1 1 / 7 5 0 under t h e VMS o p e r a t i n g system. Each module of t h e system i s run s e p a r a t e l y under t h e c o n t r o l of a c e n t r a l command module. G r a p h i c s f a c i l i t i e s a r e provided by a s e p a r a t e module run c o n c u r r e n t l y a s a sub-process. The code of t h e l a r g e s t module o c c u p i e s about 150K i n main memory, but most d a t a s t o r a g e i s dynamically a l l o c a t e d a t run-time, so t h e amount used depends on t h e complexity of t h e planning problem. The VM has about 1.5 Mb of heap s t o r a g e a v a i l a b l e f o r dynamically a l l o c a t e d variables.
Confidence Cut-off. The cut-off v a l u e of confidence f o r a branch below which i t w i l l n o t be allowed t o develop further. The confidence cut-off parameter h a s a d e f a u l t v a l u e of -100, imposing no r e s t r i c t i o n on t r e e development. Maximum Sequence L i m i t . The maximum number of sequences t h a t can be g e n e r a t e d . The u s e r can also t e r m i n a t e sequence g e n e r a t i o n using CTRL/C. The maximum sequence l i m i t parameter h a s a d e f a u l t v a l u e of 50.
U n t i l r e c e n t l y , t h e emphasis has been on t h e d e s i g n of t h e i n f e r e n c e mechanism, and t h e language i n which p l a n n i n g knowledge can be expressed. T h i s p r o v i d e s t h e framework f o r which it i s hoped t h a t adequate r u l e s can be found f o r an e f f e c t i v e s o l u t i o n of t h e problem.
F u t u r e Developments t o MCAP EXCAP i s designed t o p l a n r o t a t i o n a l components, but t h i s l i m i t a t i o n i s a r e s u l t of t h e way i n which t h e component geometry i s d e s c r i b e d , not i n t h e way t h e r u l e s a r e d e f i n e d . It s h o u l d be p o s s i b l e t o u s e a n almost i d e n t i c a l t e c h n i q u e f o r p r i s m a t i c p a r t s , and perhaps f o r o t h e r sequencing problems t h a n process-planning.
I t i s envisaged t h a t t h e c u r r e n t planning f u n c t i o n of EXCAP w i l l form t h e c e n t r a l module of a complete planning system i n t e r f a c i n g w i t h CAD and KC part-program g e n e r a t i o n . There a r e s e v e r a l a r e a s where t h e a p p l i c a t i o n of an Expert System would be beneficial.
The component and blank a r e d e f i n e d i n terms of an ordered sequence of dimensioned f e a t u r e s , such a s FACE, CYLINDER o r TAPER ( s e e F i g u r e 3 ) .
1)
S e l e c t i o n of t o o l s .
2)
S e l e c t i o n of machines.
3)
S e l e c t i o n of clamping/workpiece
EXCAP uses much t h e same i n f e r e n c e mechanism a s t h a t p r e v i o u s l y d e s c r i b e d f o r AL/X. AL/X was o b t a i n e d a t an e a r l y s t a g e i n t h e development of MCAP, and was used t o e v a l u a t e t h e p o t e n t i a l a p p l i c a b i l i t y of an Expert System t o processplanning. The A L / X r u l e language p o s s e s s e s no a r i t h m e t i c c a p a b i l i t y , so only l i m i t e d process-planning knowledge can be expressed. MCAP uses a more powerful language which does i n c l u d e a r i t h m e t i c , but which i s n e v e r t h e l e s s r e c o g n i s a b l y a d e r i v a t i v e of t h e AL/X language. A fragment of t b e EXCAP r u l e base i s shown i n F i g u r e 4 .
set-up.
The most immediately urgent development i s t h e improvement of t h e r u l e base. This w i l l i n v o l v e t h e co-operation of process-planning e x p e r t s , and t h e d e s i g n of an i n t e r a c t i v e r u l e g e n e r a t i o n and maintainance module. A t present, the rules a r e extremely simple and do n o t n e c e s s a r i l y g e n e r a t e a t r u l y optimum sequence. Changes t o t h e r u l e s a r e made u s i n g t h e normal VAX t e x t e d i t o r , and a r e n o t under t h e c o n t r o l of t h e EXCAP system. Improvement of t h e r u l e s w i l l have two main e f f e c t s .
The r u l e s perform two d i s t i n c t f u n c t i o n s .
1)
2)
The d e f i n i t i o n of t h e a v a i l a b l e machining o p e r a t i o n s i n terms of a) t h e f e a t u r e s on which they can be used, and b) t h e e f f e c t t h a t t h e o p e r a t i o n ha.; oil t h e workpiece, The s e l e c t i o n of a p a r t i c u l a r o p e r a t i o n from among t h o s e which have been found t o he a p p l i c s h l e .
EXCAP s p l i t s t h e planning proces.; i n t o two d i s t i n c t phases. The f i r s t , MACRO phase p l a n s t h e o r d e r i n which hulk m e t a l removal o p e r a t i o n s must be performed t o a c h i e v e t h e d e s i r e d component c o n f i g u r a t i o n . The second, MICRO phase p l a n s t h e f e e d s , speeds and d e p t h s of c u t f o r each of t h e preTriously planned MACRO o p e r a t i o n s . I n t h e manner of Lewis e t a 1 [3! and Matsushima e t a 1 [ & I , EXCAP l o o s e l y d e f i n e s planning as t h e i n v e r s e of machining, a n d s o works backwards from t h e f i n i s h e d component towards t h e blank. This makes t h e o p e r a t i o n a p p l i c a t i o n r u l e s much s i m p l i r ,
Each of t h e a v a i l a b l e o p e r a t i o n s i s a g o a l h y p o t h e s i s i n t h e EXCAP i n f e r e n c e network, and FXCAP s e e k s t o prove o r d i s p r o v e them. "Askable" evidence i s j u s t i f i e d not by a s k i n g t h e u s e r t o s u p p l y a v a l u e , hut by c a l c u l a t i o n s on t h e c u r r e n t workpiece d a t a b a s e . A disproved o p e r a t i o n h y p o t h e s i s i s rejected. For proved o p e r a t i o q s , EXCAP determines t h e l e s s worked workpiece which r e s u l t s from t h e i r use. T h i s new workpiece can be used i n t h e next Level of p l a n n i n g . Thus EXCAP forms a " t r e e " of p o s s i b l e o p e r a t i o n sequences. Nodes i n t h e t r e e r e p r e s e n t v a r i o u s i n t e r m e d i a t e workpiece c o n f i g u r a t i o n s ; t h e r o o t node r e p r e s e n t s t h e f i n i s h e d component,and t h e t e r m i n a l nodes r e p r e s e n t t h e blank. Branches between nodes r e p r e s e n t t h e o p e r a t i o n s used. For each o p e r a t i o n branch, f u r t h e r r u l e s s e t a c e r t a i n t y v a l u e f o r t h e hypothesis t h a t the operation it represents i s s u i t a b l e f o r u s e a t t h a t p o i n t i n t h e sequence. This c e r t a i n t y v a l u e p r o v i d e s a measure of comparison between branches l e a v i n g a p a r t i c u l a r node, and s o i n d i c a t e s t h e b e s t o v e r a l l p a t h through t h e t r e e . This p a t h r e p r e s e n t s t h e optimum planned sequence a c c o r d i n g t o t h e r u l e s used. Reading t h e sequence i n r e v e r s e p r o v i d e s t h e e q u i v a l e n t optimum machining sequence. EXCAP i s c a p a b l e of producing j u s t one ( t h e optimum) o r a l l p o s s i b l e s e q u e n c e s , provided s u f f i c i e n t memory i s a v a i l a b l e . Tt can a l s o be d r i v e n i n a step-by-step mode i n which t h e u s e r i s a d v i s e d a s t o t h e o p e r a t i o n s EXCAP t h i n k s a r e most s u i t a b l e , but can o v e r - r i d e t h e s e i f he wishes. A t each s t e p , t h e g r a p h i c s
304
1)
B e t t e r d e c i s i o n making, y i e l d i n g a more t r u l y optimum sequence.
2)
G r e a t e r range of a v a i l a b l e o p e r a t i o n s , a l l o w i n g t h e planning of more complex components.
A s t h e number of f e a t u r e s which can be machined i n c r e a s e s , s o t h e complexity of t h e r u l e s governing o p e r a t i o n a p p l i c a b i l i t y i n c r e a s e s , and t h e y r a p i d l y become extremely d i f f i c u l t t o code By p r o v i d i n g f a i r l y u s i n g normal a l g o r i t h m i c t e c h n i q u e s . powerful pattern-matching f a c i l i t i e s w i t h i n t h e r u l e language, t h e r u l e s (ispd b y FXCAP can remain comprehensjhle and e a s y t o e x t end.
I t may be found d e s i r a b l e t o r e - w r i t e t h e r u l e base and i n f e r e n c e e n g i n e u s i n g PROLOG o r POPLOG. The f e a s i b i l i t y o f t h i s will be i n v e s t i g a t e d i n t h e n e a r f u t u r e . However, t h e r e a r e d e f i n i t e advantages i n w r i t i n g t h e r u l e s i n a d e d i c a t e d language.
I f EXCAP i s t o be used i n an i n d u s t r i a l environment, t h e n a f a i r amoclnt of t h e i n t e r a c t i v e d i a l o g u e w i l l need t o be changed. FXCAP a t p r e s e n t d i s p l a y s much i n f o r m a t i o n which would be meaningless t o t h e normal u s e r of t h e system. It should be s t r e s s e d a g a i n t h a t MCAP i s s t i l l a t a development s t a g e , and i r , c o n s t a n t l y being improved a n d e x t e i d e d .
Example I n t e r a c t i v e S e s s i o n IJsing EXCAP _ l _ l _ _
I t i s d i f f i c u l t t o a d e q u a t e l y convey t h e degree of i n t e r a c t i o n p o s s i b l e when u s i n g EXCAP, and much u s e i s made of c o l o u r g r a p h i c s which cannot be reproduced h e r e . The f o l l o w i n g d i a l o g u e a t t e m p t s t o demonstrate t h e s i m p l i c i t y w i t h which a ( p r e - d e f i n e d ) component can be planned u s i n g MCAP i n i t s most a u t o m a t i c mode. The component i s as shown i n F i g u r e 3. A l l commands throughout t h e FXCAP system u s e a common language which i n c l u d e s f u l l HELP f a c i l i t i e s . These a r e used t o comment t h e d i a l o g u e . User i n p u t s a r e shown ____underlined f o r clarity.
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A
c
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A d d i t i o n a l i n f o r m a t i o n a v a i l a b l e :-
_-
___---
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PLA?; AI'TOMATIC Sequence g e n e r a t i o n proceeds a u t o m a t i c a l l y , a l l o w i n g more than one sequence t o be g e n e r a t e d i f t h e branch l i m i t and c o n f i d e n c e cut-off a r e s e t a c c o r d i n g l y . G e n e r a t i o n may be t e r m i n a t e d n r e m a t u r e l y u s i n g CTQL/C.
10 :$3 :54
Enter ? € 0 1 summary o f EXCAP commancls HELP f o r more d e t a i l e d i n f o r m a t i o n
SEO> ~ plan a u t_ o m_ a t i_ c _ _
_
Sequence g e n e r a t i o n complete EXCAP commands avaj l a b l e a r e :
SET
SEO> h e l p show siimmarl ____-
GEOMETRY SFOIJENCF, NC HELP
SHOW
RESOCkCES
RULFS
DFTAIL PRINTROVIX OIJTT
PT,AW 7
SHOW SLMMARY D i s p l a v s v a r i o u s s t a t i s t i c s of t h e l a s t sequepce planning a t t e m p t i n i t i a t e d by t h e PLAN command. SFO> show summary
EXCAP> h e l p sequence
Workpiece c o n f i g u r a t i o n s developed : Sequences g e n e r a t e d :
SEOUENCE
10 1 1
Confidence 8.57
mins 7.70
1
8.57
7.70
Xo
Tnvokes t h e SFOUFNCF module t o plan YACRO o p e r a t i o n sequences f o r one o r more romponents.
Best sequence r a t i n g s
EXCAP> sequence Best sequence p r o d u c t i o n t i m e s
1 2 3 4 5
: : : :
1 2 3 4 5
: : : :
:
:
SEO> h e l p show sequence
SHOW SEOUENCE=Sequence number P a r t s e t t o LEYl
D i s p l a y s t h e planned sequence w i t h t h e s p e c i f i e d number.
1
SEO>
Oualif i e r
SEO commands a v a i l a b l e a r e : GEOMETRY-FILE
PART
SFOW
DRAW SAVF EXCAP
SET
PLAK HELP
7
The number of t h e r e q u i r e d sequence. Append 'R' o r I F ' t o s p e c i f y t h e sequence w i t h a p a r t i c u l a r c o n f i d e n c e r a t i n g p o s i t i o n o r p r o d u c t i o n time r a t i n g p o s i t i o n r e s p e c t i v e l y . D e f a u l t =1
OiJIT A d d i t i o n a l i n f o r m a t i o n a v a i l a b l e :-
SEO> h e l p show p a r t
FULL
ABBREVIATED
SHOW PART
SEO> show sequence D i s p l a y s t h e c o n f i g u r a t i o n of t h e c u r r e n t component, a s d e f i n e d by t h e PART command.
SEO> show p a r t PART NUMBER: PLANNER : DATE :
LEYl
21-FEB-84 Feature
PART NAME: LEYLAFD FXAMPLF DRAWING KUMBER: YATERIAL CODE: AA l h Diam
r h Diam
0.000 4 2 .000 42.000
42.000
0 .000 40 .000 40 .000 34.000 20 .000 20 .000 24 .000 24.000 16 .000 10 .000 10 .000 14 .000 14 .O00 10 -000
40 .000
Length
SF
_____--_-_--------- ------- ------- --BLAhK
FACE CYL FACE
122.000
n.m
. s
COMPONENT
FACE CYL TAPER FACE CYL FACE CYL TAPER FACE CY L FACE CY L TAPER FACE
AAO 0 RAOO CAOO DAOO FA00 FA00 GAOO HA0 0 1.400 JAOO KAO 0 LA0 0 MA0 0 NAO 0
34.000 20 .000
Sequence g e n e r a t i o n number : Confidence r a t i n g p o s i t i o n : Prod. time r a t i n g p o s i t i o n : Oper'n Old
->
New
Length
R.FACE R.TURR R.TURN R.TURN R.TURN R.TURN ETAPER
-> -> -> -> -> -> -> -> ->
NA04 BA02 GA03 LA02 JA00
2 .000 120 .000 77 .000 27 .000 2 .000 3 .000 2 .000 23 .000 3 .000
------ -_ -BA03 BA02 GA03 LA02 GA02 LA01 ETAPER GAOl ETAPER RAOl
1 1 1 Diam 1
Diam 2
Time
-_-- -_-_-_ --_---- -_____-
EA00 MA00 IIA00 CAOO
0 .000 40 .000 24 .000 14 -000 10.000 20 .000 10 .000 16.000 34 .000
42.000 42.000 40.000 24.000 14.000 24.000 14.000 24.000 40.000
_---( ( ( ( ( ( ( ( (
40 .000 3.000 3 .000
SEO>
Conf
------
0.39, 0.81, 1.49, 0.68, 0.30, 0.31, 0.45, 0.50, 0.46,
18.00) 16.00) 17.90) 17.90) 8.57) 10.32) 24.41) 21.33) 20.00)
5.52
8.57
-_---- -------
quit
24 .000 16 .0O0 10 .000
2/r.000 23 .000
EXCAP t e r m i n a t e d 23-FEB-84 Returning t o DCL
...
10:54:12
2 .000 14.000 10.000
23 .000 2.000
0 .000
SEO> h e l p p l a n PLAN I n i t i a t e s a DlanninE sequence a t t e m p t . w i t h t h e branch l i m i t and c o n f i d e n c e cut-off parameters a s d e f i n e d by t h e SET BRANCH and SET CUTOFF commands, € o r t h e component d e f i n e d by t h e PART command. A sequence t r e e i s g e n e r a t e d which m y be examined by t h e v a r i o u s o p t i o n s of t h e SHOW and DRAW command 4.
References El-Midany,T.T. " I n t e r a c t i v e Computer-Assisted System f o r Turned P a r t s " Ph.D. t h e s i s , UMTST, October 1979 Ssemakula, M.E. " E v a l u a t i o n of an I n t e r a c t i v e P r o c e s s P l a n n i n g System (ICAPP) f o r Eon-Rotational P a r t s . " M.Sc D i s s e r t a t i o n LWIST October 1981. Lewis J r , W . C . , Bartlet,Elizabeth, Finter,I.I. Rarash,M.M. "Tool-Oriented Process-Planning" Proc. 23rd MTDR Conf, UMIST, September 1982
and
305
[ 4 ] M a t s u s h i m a , K . , Okada,N. and S a t a , T . "The I n t e g r a t i o n of CAD and CAEI by A p p l i c a t i o n of A r t i f i c i a l I n t e 11i g e n c e T e c h n i q u e s " A n n a l s of CIRP V o l . 3 1 / 1 / 1 9 8 2 .
[ 5 ] E s k c i o g l u , H. a n d D a v i e s , R . J .
,
n
"An I n t e r a c t i v e P r o c e s s P l a n n i n g System f o r P r i s m a t i c P a r t s (ICAPP) A n n a l s of CIRP Vol. 3 2 / 1 / 1 9 8 3 .
."
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/1
Display R e s u l t s
IF IF IF IF
Supplu Data
1
ELSE
El E2 H1 H?
AND AND AND AND
E2 AND E3 THEN E3 THEN E2 AND H2 THEN E4 THEN
E l E? E3 E4 H1 H2 H3 H4
"Askable" evidence
Sub-hypotheses Goal hqpotheses
H1 H2 H3 H4
I
FIG 2 A
Simple Inference Network
FIG l ( a ' Structure o i Typical Conventional Prograf BAOO
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._
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FACE
AAOO
CYL
BAOO
TAPER FACE CYL FACE CYL TAPER FACE CYL FACE CYL TAPER FACE
CAOO
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I A00 JAOO KAOO LAO0 MA00 NAOO
00 40 0
40 0
40 0 34 0 20 0 20 0 24 0 24 0 16 0 10 0 10 0 14 0 140
340 20 0
100
00
40 0 3 0
3 0 24 0 16 0 10 0
24 0 23 0 20
14 0 100
23 0 20
FIG 3
A
Sinple EXCAP Component
OPERATION R TURN
"basic rough-turning operation''
Inquire Ansuer
AIlD
Interface Engine
(
ROO1 ROO2 ROO3 ROO4 LOO1 LO03 LO05 1
ACTION 1-R TURN "the current
cylinder feature has a greater diameter than
those on either side" AND ( R501 R502 )
u
RELATION ROO3
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Name
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Opera t ion5u 1tab 1 e "an operation is suitable" " 1 e reflects overall confidence that operation, will ultimately lead to a good sequence" 2 -20 BAY ( Economical Finishing 10 0
SELECTION
port FIG l ( b )
Structure o f T y p i c a l Expert System
Special
11
If
chosen,
01
FIG 4 Fragment of EXCAP Rules Base
306