Control Law And Performance Analysis Of Dual-Process Manufacturing System

In flexible manufacturing systems(FMS),different types of products are typically processed in parallel.The same resource in the production process will be shared by different process-es.If the resources are not properly distributed,the system may lead to deadlocks.While a deadlock occurs,it may cause whole system or part of it halted.Therefore,solving the deadlock problem is a prerequisite for ensuring the normal operation of the FMS.Petri net as a mathematic tool can effectively model,analyze and control deadlocks in FMS.There are many kinds of deadlock prevention strategies based on Petri nets,where computational complexity is a major problem needed to be considered.Based on the Petri net theory and its structural analysis,this paper considers two special subclasses in the S~3PR net:the dual-process S~3PR and the dual-process US~3PR.The re-lationship between the structural characteristics of the net and the deadlocks is analyzed,and then a regular method of adding controllers for these two models is proposed,which computational complexity is reduced.The main tasks completed are as follows:1.For the dual-process S~3PR net,it is found that the saturation of the encountering places will make the system enter the encounter state,so that deadlocks occur by structural analysis.When the initial marking of every resource place equals 1,if the progressive encounter state is not controlled,the system will inevitably enter the encounter state.When the initial marking of every resource place equals 2,the blocked state and encounter state will cause deadlocks.According to the cause of the deadlocks,the controller design method of the dual-process S~3PR net is given respectively while the initial marking of very resource place equals 1 or 2,and it is verified that the controlled system can retain the maximally permissive behavior.Further analysis shows that the encountering places,the progressive encounter places and the blocking places can be directly obtained without complicated calculation,due to they are regularly distributed in the structure,thus we obtain the control law.For the dual-process S~3PR the initial marking of every resource place equals 1,the majority of the control places can be merged to simplify the controller.2.Based on the research of the dual-process S~3PR control law,the net is extended to the dual-process US~3PR net and?-net,and saturated encounter path pair will cause deadlocks.A-invariant consisting of the control places and the controlled places is constructed,so that the system does not enter the encounter state and the progressive encounter state.The system can be proved to live,and the maximum permissible behavior is retained.Further analysis,the mathematical relationship between the number of independent holder-resource circuits and the number of control places is obtained.This mathematical relationship indi-rectly reflects the control law of the dual-process US~3PR net.The?-net is less structurally constrained than the US~3PR net.It was found that the control law of the US~3PR net also applies to the?-net.3.Aiming at the dual-process S~3PR net,when the initial marking of every resource place equals 1,it is analyzed that how to control the production sequence is beneficial to improve the production efficiency of the whole system under the premise of ensuring the liveness of the system.