Operational Control Of A Class Of Petri Net Models With Variation In Resource Counts

In the Flexible Manufacturing Systems(FMS),improper resource allocation may lead to a deadlock due to unreasonable or imperfect control functions,and system deadlock may some-times lead to severe consequences.Petri nets can better model the discrete behavior of exist-ing manufacturing systems and accurately describe the relationship between system events and states,so it has been widely used in the modeling,analysis,and control of FMS in the past two decades.When modeling the manufacturing process,some tokens in the Petri net represent resources.When the Petri net was used to formally model and analyze the Resource Allocation System(RAS)in the past,it was usually considered that resources(i.e.,the number of tokens in the P_Rin the model)were constant,but in reality,the opposite is true:machine tools wear out with usage,and the information resource in the manufacturing resource keeps increasing.The change of resources in the system will directly or indirectly affect the system’s behav-ior and may also cause new deadlocks and other problems.Therefore,this thesis takes the resource-varying Petri net as the research object and designs the controller to make the sys-tem run smoothly.The control strategy based on the reachability graph can generally obtain the optimal controller to ensure the maximum permissive behavior of the system.This thesis focuses on the Petri net model with increasing resources.The main work is as follows:1.A class of Petri net models with varying resource quantity is defined,and the reachabil-ity graph of this kind of net model is compared with the reachability graph of the resource conservation net model.Focus on network models with incremental resources,combine a subclass of such network models with data inhibitor arcs according to control requirements,and limit the number of resource increases through the execution rules of the inhibitor arcs.2.Using the properties of data inhibitor arcs and the coverage relationship between the reachable states of Petri nets,a control strategy based on data inhibitor arcs is improved.Through the analysis of the reachability graph,it is necessary to ensure that all legal mark-ings in the original network are reachable to satisfy the maximum permissibility of the con-trolled system.Then,the number of constraints is reduced by the covering relationship be-tween the markings,and the computational complexity is reduced.When the Petri net is at a t-dangerous marking,the token number in the control place is within an integer set of the data inhibitor arc.Then the critical transition is disabled,i.e.,MTSIs are prevented.Con-versely,when the network model is at the t-enabled good marking,the token number of the control place does not belong to the integer set of the data inhibitor arc,the critical transition t is enabled.3.Based on the ILPP,two control policies based on data inhibitor arc are obtained.According to these two control policies,the optimal supervisor can be designed and then applied to the Petri net models with increasing resources,adjusted according to the characteristics of its resource increase,and finally give several examples to demonstrate the supervisory control policies with data inhibitor arc.