Robust Deadlock Control For Automated Manufacturing Systems Based On Generalized Petri Nets

There have been a variety of deadlock control policies proposed for automated manufac-turing systems(AMSs)based on Petri nets.However,a majority of them presume that all the resources are reliable in an AMS.In a real-world production process,in addition to deadlocks,machine malfunction problems may also arise to make a system collapse.This thesis develops new policies for deadlock control for the generalized system of simple se-quential process with resources(GS~3PR),where a class of unreliable GS~3PR(UGS~3PR)is considered.In order to resolve the problem,Petri nets are used to model the unreliable re-source failure and recovery process in this work.Recovery subnets are used to simulate the unreliable resource failure and recovery process in a Petri net model.Siphons are very important in the analysis and control of deadlocks in a Petri net.In this the-sis,an approach based on max controllability of siphons is developed to control a UGS~3PR.First,we compute all the strict minimal siphons(SMSs)in a UGS~3PR net.Second,based on max controllability of siphons,a control place is added corresponding to each SMS.However,a unit of resource failure is presented by the decrease of the count of tokens re-moved from the resource place,making an original controlled system possibly insufficient.Therefore,the net loses liveness when unreliable resources are taken into consideration with recovery nets being added to their operation places.Then we borrow the concept of con-straint set to design a robust control policy to keep the corresponding siphon to be never insufficient even if some resources break down.In order to optimize the above robust method,this thesis provides a robust control policy based on elementary siphons theory to reduce the structural complexity.And we employ the concept of max-controlled siphons for more permissive.First,we compute the elementary and dependent SMSs in a UGS~3PR.Then based on the concept of max-controllability of siphons,we can decide if an elementary SMS is a self-max-controlled siphon or not.Af-terwards,the concept of constraint set for a siphon is introduced,and a controller is added to each non-max-controlled elementary SMS.And then the supervisor is adjoined to the uncontrolled dependent SMS.A robust deadlock control algorithm is developed to control each SMS to keep max-controlled,even if there exist unreliable resources.Finally,some examples are given to illustrate the developed approach,showing that the robust control approach can maintain the original GS~3PR live whenever a single type or multiple types of unreliable resources break down.