On Model Control Based On Colored Resource-Oriented Petri Nets

Petri nets are one of the basic theories that describe the concepts of concurrency,uncertainty,synchronization,conflict,and resource sharing.They are widely used in the modeling,anal-ysis,simulation and control of flexible manufacturing systems(FMSs).With the continuous improvement of Petri nets,process-oriented Petri nets(POPNs)and resource-oriented Petri nets(ROPNs)have become the main modeling frameworks of FMSs.When simulating the production process of a system,colors are introduced to ROPN,and all operation places are omitted.Since an ROPN is more compact compared with POPNs,it makes up for the deficiency of a POPN to model a practical large and complex system model.Therefore,in terms of model complexity,ROPNs are a better choice.In an FMS,the occurrence of deadlocks often degrades the use of resources and may lead to catastrophic consequences for the systems that are critical to security.Therefore,it is very important to study the deadlock control problem.In this thesis,a class of colored resource-oriented Petri nets(CROPNs)is taken as the research object to analyze the control strategy of the system deadlock prevention.The main tasks completed are as follows:1.Based on the POPN model of a kind of resource allocation systems with a single resource in each operation,their corresponding system of resource-oriented sequences(SRSs)models are established.The SRSs are a class of CROPNs.The establishment of this kind of models makes the formal models of this kind of resource allocation systems more compact.Then,the simulation model of the SRS is obtained by using CPN Tools,and the analysis of the model properties is realized.2.Based on the intrinsically live structures,namely the relationship between resource capac-ity and weights,the concept of resource usage ratios is proposed to describe the possession of resources.And a design method of liveness and ratio-enforcing controller is further elab-orated according to the structure.First,given an SRS model,the topology of a controller is determined based on the connection form of a resource place.Then,the intrinsically live structures are analyzed from the perspective of resource usage ratios.Finally,the parameters of the capacity and weights of the controller are obtained by solving integer linear program-ming problems,and the design of a liveness and ratio-enforcing controller is realized.3.Based on a class of SRSs,the notion of ?-resource is introduced.And an optimal control method of a liveness-enforcing controller is proposed.It is found that the existence of a maximal perfect resource-transitions circuit in the model is the cause of deadlocks when it is saturated at a reachable state.If there does not exist any ?-resource in the model,the max-imum permissible behavior can be achieved,and it's proved that there are only two kinds of reachable markings:safe markings and unsafe markings.Given an SRS model,we first find all of the maximal perfect resource-transitions circuits.Then,add a controller for each circuit.Every controller is connected with all the input and output transitions in the circuit,and the liveness control of the model can be realized by restricting the number of tokens in the circuit.