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Mingming Yan1, Zhiwu Li1,2, Na Wei1 and Mi Zhao1
1School of Electro-Mechanical Engineering
Xidian University
Xi'an, 710071 P. R. China
E-mail: zhwli@xidian.edu.cn
2Laboratory of CAD and Lifecycle Engineering
Department of Mechanical Engineering
Technion - Israel Institute of Technology
Haifa, 32000 Israel
E-mail: zhwli@technion.ac.il
This paper focuses on the problem of deadlocks in automated flexible manufacturing
systems (FMS) where deadlocks are caused by unmarked siphons in their Petri net
models. A deadlock prevention policy is proposed for a subclass of Petri nets, S3PMR
that can well model a large class of FMS. We distinguish siphons in such a net model by
elementary and dependent ones. For each elementary siphon, a monitor is added to the
plant model such that it is invariant-controlled. The monitor addition way guarantees that
no emptiable control-induced siphon is generated due to the presence of monitors in the
resultant net. This novel deadlock prevention policy can usually lead to a more permissive
supervisor by adding a small number of monitors and arcs than the existing methods
for the design of liveness-enforcing Petri net supervisors. Experimental study indicates
that the proposed policy appears to be more permissive than closely related approaches
in the literature.
Received March 28, 2007; revised June 11, 2007; accepted August 3, 2007.
Communicated by Chin-Laung Lei.
* This work was partially supported by the National Nature Science Foundation of China under grant No.
60474018, and the Laboratory Foundation for the Returned Overseas Chinese Scholars, State Education
Ministry of China, under grant No. 030401.