| Cyber Physical System(CPS)is a networked,intelligent and integrated system based on the perception of the physical environment and the deep integration of computing,commu-nication and control.In recent years,with the rapid development of CPS with their related technologies,it has promoted the upgrading of key technologies in various industrial fields and information fields,including automated manufacturing systems(AMSs),logistics management systems and intelligent transportation systems.As an important product of advanced manu-facturing industries,AMSs can significantly reduce manufacturing costs,increase productivity,and improve product quality.Once the resources are not properly allocated or some resources failed,deadlock or blocking states will occur,which greatly affect the productivity of systems.In order to solve the deadlock problems,research scholars have done a lot of researches,but most methods assume that the resources in the system can not fail.In practice,the resource failure is uncontrollable.In this thesis,resource failures are considered to solve the deadlock problems in AMSs.Since Petri nets have rich structural features and strict mathematical descriptions,they can well describe the concurrency and resource share of systems.Petri nets are used to model and analyze AMSs.In order to avoid enumerating exponential levels of reachable states and siphons with system scales,this thesis takes an algebraic approach to achieve deadlock detection and design deadlock controllers by iteratively solving integer linear programming,and then proposes an adaptive deadlock control strategy to achieve robust deadlock-free control which can improve system’s performance.The main works in this thesis are:1.Resolving deadlock problems with faulty resources in the typical class of systems.For Systems of Simple Sequential Processes With Resources(S~3PRs),resource failure recovery subnets are designed and added.The deadlock state of the system is detected by solving the integer linear programming and analyzed to find a critical transition resource circuit,deadlock controllers are designed based on the above process.Further considering the problem of resource failures,by analyzing the relationship between the deadlock and resource failures,an adaptive controller is designed and added such that the system can dynamically switch between normal working mode and robust working mode to ensure the robust deadlock-free operations of the system.Finally,illustrate example is performed to verify the correctness of the proposed method.2.Further extending the generality of the method and propose an improved adaptive dead-lock control strategy to solve the deadlock problems in the AMSs which have the function of sharing resources.Recovery subnets are designed and added for a class of Systems of Sequen-tial Systems With Shared Resources(S~4Rs),by using integer linear programming method,a deadlock states is detected.At the deadlock state,by analyzing the relationship among critical transitions,critical resources and critical places,a deadlock controller is developed.Further considering the problem of resource failures,an adaptive controller is designed and added to ensure that the system maintains planned production without reducing systems’performance.In this way,even if unreliable resources fail,the system can still work normally.Finally,the correctness of the proposed control strategy is verified by examples.3.Through the analyses of a typical AMS example,the corresponding Petri net model is established.The adaptive deadlock control strategies proposed in this paper are applied to the Petri net model,respectively.By comparative experiments,the advantages and shortages of the methods proposed in this thesis are obtained. |
