Consistency Control Of Critical Path In Dynamic Reconfigurable Manufacturing System Based On NCES

Dynamic reconfigurable manufacturing systems(DRMSs)are a type of manufacturing systems that can dynamically adjust configurations according to the changes in production requirements.A DRMS consists of a reconfiguration controller and multiple configurations,each of which is an autonomous system.With the help of the reconfiguration controller,the dynamic switch of configurations can be realized during the running of a DRMS.Different from a traditional reconfigurable manufacturing system,a DRMS emphasizes on-line reconfigurations.Specifically,such a system can smoothly adjust the current configuration to the target configuration,while keeping normal operations.As a tool of reconfiguration study,DRMSs can abstract the processing procedures of an actual manufacturing system as a series of paths of firing events in the model.Among them,a critical path is a global control specification of system.Although it is possible to design a local control specification that abides a critical path with some particular initial states for each configuration,the critical path cannot be guaranteed by the entire system.The reason is that a reconfiguration event may occur at any reachable state of the running configuration and assigns an initial state to the objective configuration.If a system always abides the global control specification after any reconfiguration,that is,the system behavior is consistent with a critical path,then the system is said to satisfy the consistency requirement of the critical path;otherwise,it is said to violate the consistency requirement.This thesis studies the consistency control problem of a critical path in a dynamic reconfigurable manufacturing system from the perspective of discrete event systems.1).Assuming that all transitions are controllable,we design a method of constructing a consistency controller based on net condition/event systems(NCESs).To formalize the consistency problem of a critical path,we partition the states of a DRMS into four categories,i.e.,reconfigurable states,compatible states,acceptable states and unreconfigurable states.The consistency requirement of DRMSs requires that the system should be reconfigured at reconfigurable states only.In order to obtain reconfigurable states,we propose a method of constructing a canonical recognizer that can recognize critical paths.Using the canonical recognizer,we introduce an approach of designing the consistency controller.2).Assuming that some transitions are uncontrollable,we design a method of constructing a partially uncontrollable consistency controller(PUCC)based on supremal controllable sublanguage.First,we propose the actual global control specification of a system,namely the critical path language.Due to the existence of uncontrollable transitions,the behavior of system is not completely controllable.Given the global control specification of a system,we can obtain its supremal controllable behavior,namely,the supremal controllable sublanguage.Then,using a recognizer of the supremal controllable sublanguage,we propose a PUCC design method.