اثر استراتژی های دیسپاچینگ دینامیک و استاتیک در FMS به صورت پویا برنامه ریزی شده و برنامه ریزی نشده

Dispatching strategies are crucial in scheduling of flexible manufacturing systems (FMSs), in which each operation of a job may be performed by any of the several machines. This paper presents a study of the effect of dynamic and static dispatching strategies on dynamically planned and unplanned FMS. The proposed simulation model comprised eight machines, storage buffer areas, receiving area, and three robots and pallets. Parts enter and leave the FMS at load/unload stations and transferred between machine centers by available trucks. Based on a number of specific assumptions, 12 different dispatching strategies were considered. A simulation run was made for each strategy, where the design parameters were systematically changed. The analysis of the obtained results showed that an overall improvement could be achieved for dynamic dispatching than that rendered by static dispatching.

Scheduling plays a crucial role in the efficiency of any production system. The emergence of flexible manufacturing system (FMS) has sparked an increased interest and appreciation of real-time planning, scheduling and control. Dispatching strategies (rules) is a key element to an optimized performance of manufacturing systems [1] and [2]. Basically, there are two approaches to solve the problem of switching to proper dispatching rules in manufacturing systems: the look-ahead simulation approach and the rule-based (heuristic) approach. For the look-ahead simulation approach, a dispatching rule is determined for each short period just before the implementation time occurs. For the rule-based approach the scheduling of changing dispatching rules is first acquired, and then this knowledge is incorporated into a rule-based system to guide the manufacturing system to make intelligent decisions in real-time. In the past two decades, many researchers have tried to evaluate the performance of dispatching rules in dynamic flexible manufacturing systems.

This paper presented a study of the effect of dynamic and static dispatching strategies on dynamically planned and unplanned FMS. In this work, the look-ahead approach was applied under the condition that part types and their quantities are dynamically changed over the specified stages of the whole scheduled horizon. The results obtained, for both unplanned and planned cases, pointed out the following conclusions: 1. An overall improvements (throughput, make span) have been achieved for a dynamic dispatching schedule than that obtained in static dispatching schedule. 2. Both machines and resources are not best utilized for the best schedule, but they are close to the best conditions with the evaluated dispatching mechanisms. 3. The overall measuring performance criteria under consideration for planned model are better than those for unplanned case. This leads to the fact that as long as the real life models are dynamic in their changes, the planning should be oriented to these dynamic changes to make it predictable and to achieve the best schedule.