برنامه ريزي همزمان A,V ها و ماشين الات با استفاده از يكپارچه سازي شبكه هاي پتري و الگوريتم هاي جستجوي ابتكاري در سيستم هاي توليد منعطف

On-Line Scheduling Of AGVs And Machines With Integrating Petri Nets And Heuristic Search Algorithms In Flexible Manufacturing Systems

This paper aims at developing a manufacturing planning methodology for an Automated Guided Vehicle (AGV) based flexible manufacturing system by simultaneously dealing with material processing and transportation functions based on the Petri Nets (PN). As a graphical tool, PN provides visualization of a dynamic system and as a mathematical tool, it checks the properties related to the behavior of the underlying system, by using a set of linear algebraic equations. The integrated model is developed based on three modules: AGV module, Product module and machine module. The AGV module models the movement of AGVs from a current location to a destination. For each part type, the. product module provides information to perform the operations of the products in accordance with the precedence relations. The machine module models the assignment of machines to tasks by using Sequential Petri Net (SPN). Each of these modules can model partial properties of the system and we can get a total picture of system by integrating them. In order to obtain an effective schedule while avoiding the NP-complete computing complexity, scheduling is performed as a heuristic search in the reachability tree, which is guided by heuristic dispatching rules of AGVs and machines. The algorithm combines on-line dispatching rules of AGVs and machines based on the information provided by the PN simulation with the Limited Expansion A Algorithm. Experhiental results for a practical example from IRAN KHODRO HEMMING SHOP indicate the effetttaveness of PN- based heuristic search for FMS scheduling.