Computationally Improved Optimal Control Methodology for Linear Programming Problems of Flexible Manufacturing Systems

Deadlock prevention policies are used to solve the deadlock problems of FMSs. It is well known that the theory of regions is the efficient method for obtaining optimal (i.e., maximally permissive) controllers. All legal and live maximal behaviors of Petri net models can be preserved by using marking/transition-separation instances (MTSIs) or event-state-separation-problem (ESSP) methods. However, they encountered great difficulties in solving all sets of inequalities that is an extremely time consuming problem. Moreover, the number of linear programming problems (LPPs) of legal markings is also exponential with net size when a plant net grows exponentially. This paper proposes a novel methodology to reduce the number of MTSIs/ESSPs and LPPs. In this paper, we used the well-known reduction approach Murata (1989) to simply the construct of system such that the problem of LPPs can then be reduced. Additionally, critical ones of crucial marking/transition-separation instances (COCMTSI) are developed and used in our deadlock prevention policy that allows designers to employ few MTSIs to deal with deadlocks. Experimental results indicate that the computational cost can be reduced. To our knowledge, this deadlock prevention policy is the most efficient policy to obtain maximal permissive behavior of Petri net models than past approaches

Discrete event system techniques for CIM: guest editorial

International audienc

Modeling and Analysis of Semiconductor Manufacturing Systen with Degraded Behavior Using Petri Nets and Siphons” submitted to IEEE Trans. Robotics Automat.,

Abstr act Degraded behavior, such as reworks, failures, and maintenance, of a semiconductor manufacturing system (SMS) is not negligible in practice. When modeled by Petri nets, degraded behavior may be represented as initially-unmarked elementary circuits, interpreted as local processing cycles. Most existing "well-behaved" net classes for manufacturing have problems of describing such cycles and thus may have difficulties in modeling SMSs. In this paper, we extend the class of nets i

Siphon-based deadlock prevention policy for flexible manufacturing systems

International audienceA siphon-based algorithm for deadlock prevention of a type of Petri nets called (SPMR)-P-3, which is a subclass of S(3)PGR(2), is presented in this correspondence. The proposed method is an iterative approach by adding two kinds of control places called ordinary control (OC) places and, weighted control (WC) places to the original model to prevent siphons from being unmarked. An OC place with ordinary arcs, which optimally prevent a siphon from becoming unmarked, is employed whenever it is possible, and otherwise, the WC places that adopt a conservative policy of controlling the release of parts into the system are used. Furthermore, this algorithm is not only for the subclass Petri nets but also for (SPR)-P-3, (ESPR)-P-3, (SLSPR)-L-2, and S(3)PGR(2) nets. The authors prove the liveness and reversibility of the controlled net, and hence establish the correctness of the deadlock prevention policy. Finally, numerical experiments indicate that the proposed policy appears to be more permissive than closely related approaches in the literature