Controllability of Strongly and Weakly Dependent Siphons under Disturbanceless Control

Chao, Daniel Yuh; Wu, Kuo-Chiang; Chen, Jiun-Ting; Lee, Mike Y. J.

doi:10.4236/ica.2011.24036

Cited by 3 publications

(1 citation statement)

References 22 publications

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“…Monitors are added to prevent deadlocks from occurring (Ezpeleta, Colom, and Martinez 1995;Chu and Xie 1997;Uzam 2002;Li and Zhou 2004;Zhou 2006a, b, 2008a, b;Chao 2007aChao , b, 2008aLi, Zhou, and Jeng 2008;Piroddi, Cordone, and Fumagalli 2009;Li and Hu 2009;Li, Zhu, and Zhou 2009;Li, Yan, and Zhou 2010;Zhao and Li 2010;Shih and Chao 2010;Chen, Li, Khalgui, and Moshabi 2011;Chao, Wu, Chen, and Lee 2011). This affects the original model in particular losing live states.…”

Section: Introductionmentioning

confidence: 99%

Controllability of control and mixture weakly dependent siphons in S³PR

Hong

Chao

2013

International Journal of Systems Science

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Deadlocks in a flexible manufacturing system modelled by Petri nets arise from insufficiently marked siphons. Monitors are added to control these siphons to avoid deadlocks rendering the system too complicated since the total number of monitors grows exponentially. Li and Zhou propose to add monitors only to elementary siphons while controlling the other (strongly or weakly) dependent siphons by adjusting control depth variables. To avoid generating new siphons, the control arcs are ended at source transitions of process nets. This disturbs the original model more and hence loses more live states. Negative terms in the controllability make the control policy for weakly dependent siphons rather conservative. We studied earlier on the controllability of strongly dependent siphons and proposed to add monitors in the order of basic, compound, control, partial mixture and full mixture (strongly dependent) siphons to reduce the number of mixed integer programming iterations and redundant monitors. This article further investigates the controllability of siphons derived from weakly 2-compound siphons. We discover that the controllability for weakly and strongly compound siphons is similar. It no longer holds for control and mixture siphons. Some control and mixture siphons, derived from strongly 2-compound siphons are not redundant -no longer so for those derived from weakly 2-compound siphons; that is all control and mixture siphons are redundant. They do not need to be the conservative one as proposed by Li and Zhou. Thus, we can adopt the maximally permissive control policy even though new siphons are generated.

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