Fault Analysis,Detection,and Recovery Of Automated Manufacturing Systems Based On Petri Nets

An automated manufacturing system(AMS)is a typical automated processing system that produces different kinds of raw parts using limited and shared resources such as machines,robots,and automated guided vehicles.The competition for resources in different production processes may lead to deadlocks.Deadlocks are undesirable situations resulting the whole system or a part of it being blocked,and some production processes become discontinuous.A fault is defined as an interruption of an item’s ability to perform a particular function,and it is in general synonymous with errors,mistakes,disturbances,or failures,leading to undesired or unacceptable equipment behaviour in AMSs.Petri nets are believed to be suitable mathematical tools,especially for modeling,analysis,and control of the behaviors of AMSs.In many previous studies,most strategies for analyzing and recovering deadlocks are based on Petri net models.This thesis addresses the common issue of faults in AMSs and proposes novel methods for early detection and handling to ensure safe,efficient,and reliable operation.The methods are tested and found to outperform existing studies,making significant contributions to the field of AMS fault prevention and control.The main results and contributions made in this particular research are stated as follows:1.Despite significant advances of technology,failures happen from time to time in AMSs,which is difficult to prevent in practice.A fault in AMSs is one of the most common causes of failure to complete operations,and its diagnosis is an important and crucial stage in fault-recovery and repair.A methodology is developed in this study from the viewpoint of discrete event systems with failure-prone resources by investigating faults behavior.We propose a way to make the system continue to perform its duties while addressing the problem of fault-tolerance,and the failed resources are subject to repair and recovery.This work proposes a failure-safe model and a method for fault recovery and repair,which does not disrupt task processing when faults occur in some elements.This work also presents a fault recovery and repair method for a faulty element.Another element,similar to the target element,called a redundant element,is used to replace the target element in the event of the target element failure.A redundant element can accomplish the same work as a target element.Thus,redundant elements are used when faults occur to the target elements.A target element is prone to failure and is an unreliable element.An applied example is used to test the proposed method.Compared with the results from previous research,our results reveal that the proposed technique outperforms the existing studies in terms of performance.2.Failure of resource in AMSs could cause complete system shut down.This paper addresses the issue of unreliable resource failure in manufacturing cells through the use of load-sharing redundant resources(LSRRs).The aim is to use more than one type of a failure-prone resource to share tasks between a failure-prone resource,called the target resource,and reliable ones called the load-sharing redundant resource(LSRRs).Both an unreliable resource and its LSRR perform the same tasks,and there is normally a system that assigns tasks to them.If the target resource fails,all the tasks will be performed by the LSRRs.After the faulty target resource is fixed and restored,its assigned tasks are automatically returned to it.In This way,the system can continue to produce or process parts.Thus,total system shutdown due to unreliable resource failure is eliminated.The proposed method is tested using real examples.The results,compared with those obtained by the studies in the literature,show that the proposed method has an outstanding performance and outperforms some of the existing studies.3.AMSs are susceptible to failures,and one new approach to detecting the faults in AMSs is trust evaluation.For systems with unreliable resources,a two-step robust deadlock control technique is proposed.In the first step,recovery subnets based on Petri nets are included for all system resources that are prone to failure.In order to guarantee that a system operates in a reliable mode,recovery subnets are applied to it.Using colored Petri nets and trust-models combined with hybrid techniques,faults acquired in step one are detected and handled in step two.The proposed approach includes the descriptive features of a modular Petri net integration with the trust method.It provides the combination of three kinds of procedures:management of all resource failures,detection,and treatment of faults in a system.Consequently,the proposed model considers not only resolving resource failures in AMSs,but also their treatment once they are detected.Finally,an example from the literature is used to test the proposed approach.