10.01.2013 Views

ComputerAided_Design_Engineering_amp_Manufactur.pdf

ComputerAided_Design_Engineering_amp_Manufactur.pdf

ComputerAided_Design_Engineering_amp_Manufactur.pdf

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

TABLE 8.1 Summary of the Rules<br />

Conditions of Generations PP Rule TT Rule<br />

A. cycles created — TT.2<br />

B. no cycles created — —<br />

B.1 only one of ng and nj in a cycle from PP.1<br />

— TT.0<br />

B.2 exclusive PP.2 TT.0<br />

B.3 concurrent PP.0 —<br />

B.3.1 neither ng nor nj in<br />

a cycle from PP.1<br />

— TT.4<br />

B.3.2 both ng and nj in<br />

a cycle from PP.1<br />

— TT.3<br />

B.4 sequential or cyclic PP.1 (PG)<br />

TT.1 (PG)<br />

PP.2 (IG)<br />

TT.4 (IG)<br />

(0) PP.0 If pg pj , then signal “forbidden, delete the � ” and return.<br />

(1) PP.1 if<br />

(2) PP.2<br />

, signal “a pure PP generation;” otherwise signal “an interactive PP generation.”<br />

(a) PP.2.1 Generate a TP-path from a transition of NP to a place of each in .<br />

(b) PP.2.2 Generate a virtual PSP, a PT-path, from a place of each in to the transition<br />

of NP.<br />

w<br />

�g � �j tk pj �j Cjg pg �g Cgj n˙ g<br />

Note that some generations may require the application of more than one rule. For instance, a backward<br />

IG may need both Rules TT.2 and TT.4. Note also the partial dual relationship between the TT and PP<br />

rules. Replacing transitions with places (and vice versa) reversing each arc in Rule TT.4, we obtain Rule<br />

PP.2. The rules are summarized in Table 8.1.<br />

Section 8.6 demonstrates the application of these rules to an automated manufacturing system. Note<br />

that during each application of a rule, more than one new PSP may be generated; we call such a generation<br />

a macro generation. Otherwise, it is a singular generation.<br />

In the remainder of this chapter, all nets mentioned refer to nets synthesized using the rules presented<br />

above.<br />

Below, we explain the rules starting with the rules that forbid generations. Forbidden TT and PP<br />

generations come from synchronic and concurrency mismatches, respectively, which cause uncoordinated<br />

actions. For a TT generation, a single parameter, the synchronic distance between tg and tj , can unify<br />

all cases of the structural relationships between and .<br />

n g<br />

Definition: Synchronic Mismatch: A TT generation causes a synchronic mismatch of , where<br />

1 w<br />

( dgj)<br />

denotes the synchronic distance between tg and tj and N (NP).<br />

1<br />

d gj<br />

Definition: Concurrency Mismatch: A PP generation causes a concurrency mismatch if ( pg � pj ) and �<br />

a p � P, p � pg , and ¬ (p � pj ).<br />

There are three possible synchronic distances: 1, �, and the integers in between. A TT generation<br />

should not alter the synchronic distance between tg and tj . But a TT-path implies a synchronic distance<br />

of 1 between tg and tj . Thus, if the synchronic distance between tg and tj is 1 prior to the generation,<br />

the TT generation will not alter the reachable markings of N . If ( ) can fire infinitely often without<br />

firing , then the NP will get unbounded tokens (become nonlive due to deficiency of tokens).<br />

In terms of structural relationship, �� for the following cases: (1) � , (2) and/or is in a cycle<br />

generated earlier using the PP rule, (3) ↔ or � , such that , and/or , and , and<br />

(4) tg and are in two separate PNs. For cases (1) and part of (2) where only one of and is in a<br />

cycle, the generation is chosen to be forbidden to make Rule TT.0. The rest of the cases need additional<br />

generations to make Rules TT.3 and TT.4.<br />

1<br />

tg tj tj ( tg) dgj tg tj tg tj tg tj tg tj �tx tg tx tj tx tg tj tg tj n j<br />

1 w<br />

dgj � dgj

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!