Design And Implementation Of A Petri Net Model Controller With Variable Resources

The automatic manufacturing system(AMS)is a manufacturing process that is completely unmanned or requires less human intervention.The system is prone to deadlocks due to ir-rational resource allocation.In some cases,deadlocks can cause significant economic losses and even catastrophic consequences.Therefore,it is particularly important to deal with the deadlock problem in the system.Petri net is a graphical mathematical tool suitable for an-alyzing asynchronous concurrent systems and is widely used in the modeling of automated manufacturing systems.The deadlock control methods based on Petri nets can be divided into two types:reachable graph analysis and structure analysis.The former can usually get the optimal controller but has to face the problem of state explosion,while the latter will lose some legal states,but the design is simpler.In previous studies,especially when using the Petri net to formalize the resource allocation system(RAS),the number of resources in the RAS is mostly fixed,which is reflected in its Petri net model as there are a number of conserved tokens in the repository.This kind of modeling method that regards the amount of resources in the system as constant is an ideal,phased,and simplified modeling method.In practice,the resources in any system are constantly changing,or decreasing(such as continuous wear of machine tools,coolant consumption,fuel required by engines),or increasing(such as neutrons in nuclear fission reactions,messages source in social networks).Changes in system resources will affect the behavior of its Petri net model,which may cause new deadlocks and other problems.However,previous studies have paid less attention to resource changes,so it is necessary to study the existence of a variable resource Petri net model.This thesis focuses on a class of Petri net models with increasing resources.First,such Petri net subclasses with increasing resources is defined.Then,reachable graph and structure-based strategies are used to control such net models.Finally,the PLC is used to implements the designed controller.The main work completed in this thesis is as follows:1.A kind of Petri net model with variable resources is defined and its state space is analyzed.Focus on the research of the network model with increasing resources,and add appropriate restrictions to this type of network model according to control requirements.2.The P-invariant design controller controls this type of network model.Firstly,the prob-lems of state overlap and deadlock recurrence caused by designing the controller for the inner increasable net within bounds using the original method are analyzed,and correspond-ing solutions are proposed.Then analyze from the perspective of linear programming,and expand li to the whole integer to solve the problem of unsolved part of the network model Then,the general strategy of the inner increasable net within bounds based on P-invariant design controller is given,and the correctness of the algorithm is verified through sever-al examples.Then,the control of the outer increasable net is transformed into the control problem of the resource conservation network model.Finally,the limitations of the inner increasable net within bounds control based on the reachable graph are pointed out3.The controller of this kind of network model is designed based on the structure.When the original Liveness and Ratio-enforcing Supervisor was transplanted to the inner increasable net within bounds,the excessive reachable state was restricted,and the control effect was average.Since the outer increasable net can be converted to a resource conservation network model for control,the control effect is better.At this time,an adaptive controller is designed to the inner increasable net within bounds.Unlike traditional controllers,the parameters of such controllers can change dynamically with the system.A recoverable transition controller is also designed,this controller can make all the marks reachable and the control effect is the best.Finally,based on the structure,the control problem of the unbounded network model is studied.4.The programmable logic controller(PLC)is used for industrial implementation of the designed controller.Because PLC has the advantages of strong functions,simple and con-venient use,strong anti-interference ability,high reliability,etc.,this paper chooses PLC to implement the designed controllers initially,and converts the controllers from the theoretical form into specific control codes.