Designing supervisory policies that avoid livelocks in Manufacturing- and service-systems modeled using general Petri Nets: A tutorial using an illustrative example

Roshanak Khalegi, Arun Raman, Ramavarapu S Sreenivas

Research output: Contribution to journalConference article

Abstract

When a Manufacturing- or Service-System gets into a deadlocked state none of the activities can proceed towards completion. When the same system is in a livelocked state, some activity of the system enters a state of suspended animation and is never completed, while other activities proceed to completion without hindrance. A livelock-free system does not experience deadlocks; but a deadlock-free system can experience livelocks. This tutorial is about the synthesis of livelock avoidance policies for Manufacturing- and Service-Systems that are modeled by Petri Nets (PNs). After characterizing livelock-freedom, we introduce the paradigm of liveness enforcing supervisory policies (LESPs). An LESP is said to be minimally restrictive, if the fact that it prevents the occurrence of an event at a given state is reason enough to infer that all livelock-avoidance policies would do the same. If there is an LESP for a system, there is a unique minimally restrictive LESP. We restrict attention to LESPs that can be implemented using a Disjunctive Normal Form (DNF) expression on the state of the PN modeling the system. We describe the process of synthesizing the minimally restrictive LESPs using an illustrative example using a software-product developed by the authors.

Original languageEnglish (US)
Pages (from-to)895-902
Number of pages8
JournalProceedings of the International Conference on Industrial Engineering and Operations Management
Volume2019
Issue numberMAR
StatePublished - Jan 1 2019
Event9th International Conference on Industrial Engineering and Operations Management, IEOM 2019 - Bangkok, Thailand
Duration: Mar 5 2019Mar 7 2019

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Petri nets
Animation
Service system
Tutorial
Manufacturing systems

Keywords

  • Livelock avoidance
  • Manufacturing systems
  • Service systems
  • Supervisory control

ASJC Scopus subject areas

  • Strategy and Management
  • Management Science and Operations Research
  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering

Cite this

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AB - When a Manufacturing- or Service-System gets into a deadlocked state none of the activities can proceed towards completion. When the same system is in a livelocked state, some activity of the system enters a state of suspended animation and is never completed, while other activities proceed to completion without hindrance. A livelock-free system does not experience deadlocks; but a deadlock-free system can experience livelocks. This tutorial is about the synthesis of livelock avoidance policies for Manufacturing- and Service-Systems that are modeled by Petri Nets (PNs). After characterizing livelock-freedom, we introduce the paradigm of liveness enforcing supervisory policies (LESPs). An LESP is said to be minimally restrictive, if the fact that it prevents the occurrence of an event at a given state is reason enough to infer that all livelock-avoidance policies would do the same. If there is an LESP for a system, there is a unique minimally restrictive LESP. We restrict attention to LESPs that can be implemented using a Disjunctive Normal Form (DNF) expression on the state of the PN modeling the system. We describe the process of synthesizing the minimally restrictive LESPs using an illustrative example using a software-product developed by the authors.

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