A simple Suboptimal siphon‐based control model of a well‐known S 3 PR

This paper develops an approach to the design of an optimal Petri net supervisor that enforces liveness to flexible manufacturing systems. The supervisor contains a set of observer places with weighted inhibitor arcs. An observer place with a weighted inhibitor arc is used to forbid a net from yielding an illegal marking by inhibiting the firing of a transition at a marking while ensuring that all legal markings are preserved. A marking reduction technique is presented to decrease the number of considered markings, which can dramatically lower the computational burden of the proposed approach. An integer linear program is presented to simplify the supervisory structure by minimizing the number of observer places. Finally, several examples are used to shed light on the proposed approach which can lead to an optimal supervisor for the net models that cannot be optimally controlled via pure Petri net supervisors.

Section: Introductionmentioning

confidence: 99%

Design of Optimal Petri Net Supervisors for Flexible Manufacturing Systems via Weighted Inhibitor Arcs

Cong

Uzam

et al. 2017

“…The existing deadlock control policies in the framework of Petri nets mainly focus on structural analysis. As a structural object, siphons are widely used to characterize and analyze deadlock situations in an FMS that is modeled by PN [12,13]. Researchers have developed a large number of deadlock control policies based on siphon control, among which the representative works are given in [10,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

New Controllability Condition for Siphons in Ws³PR Nets

Guan

Wang

2014

Existing policies for deadlock control are mainly based on siphons due to their ability to indicate deadlocks, and can be used as a powerful tool to deal with deadlock situations in flexible manufacturing systems. In order to avoid deadlocks, researchers often add monitors to control siphons. This may result in redundant monitors, unnecessary cost, and restriction of the behavior permissiveness. For example, for a system of sequential systems with shared resources (S4R), the existing deadlock control policies based on max, max′ or max′′‐controlled siphons tend to overly restrict the behavior of a controlled system. To ensure maximal permissive behavior of controlled systems, a new concept of siphon controllability named W‐control is defined and then a sufficient and necessary condition under which a WS3PR is live if all its siphons are W‐controlled. Examples are given to demonstrate them.

“…Deadlock prevention is considered to be a well-defined problem in an FMS [54], which is usually achieved either by designing an effective system or using an off-line computational mechanism to control the request for resources to ensure that deadlocks never occur. In the Petri net framework, monitors (control places) and related arcs are added to a plant net model to realize the off-line computational mechanism [6][7][8]18,27,29,30,36,38,40,[43][44][45].…”

Section: Introductionmentioning

confidence: 99%

Deadlock Control for a Class of Generalized Petri Nets Based on Proper Resource Allocation

Hou¹,

Zhao²,

Liu³

2014

This article develops a deadlock prevention policy for a class of generalized Petri nets, namely G‐systems, which can model flexible manufacturing systems with machining, assembly, and disassembly operations. In this research, a polynomial complexity control policy for non‐blocking supervisors is established by properly adjusting resource allocation. First, a set of linear inequality constraints is derived with respect to different resource requirements such that the allocation of the system resources to various requesting processes can be appropriately restricted, that is, the resulting system has no deadlock state by imposing monitors on operation places. Moreover, an algorithm is proposed to identify the redundant constraints such that structurally simple liveness‐enforcing net supervisors can be obtained. Compared with existing polices, the proposed method can usually lead to a suboptimal supervisor with high computational efficiency. Finally, a flexible manufacturing system example is utilized to demonstrate the proposed method.