فرایند تعاملی بین برخی مکانیزم های اعزام و مراکز دستگاه های قطع در FMSs

Scheduling in flexible manufacturing systems (FMSs) differs from that conventional job shop because each operation of a job may be performed by any one of several machines. In the current paper, the interactive process between routing flexibility index (single route index up to 192 route index are classified into nine route flexibility indices), different interruption ratios (zero up to 100% are classified into six interruption indices), as well as 16 dispatching polices are studied. The dispatching mechanism that will perform the best with the considered measuring performance criteria for each route flexibility index and model configuration has been determined. Global conclusions and trend of variations have been highlighted.

Product deliverability is becoming more important in today’s competitive markets. While it used to suffice to manufacture products of high quality and low price, today’s manufacturing practices necessitate on-time product deliveries for customer satisfaction. Thus scheduling plays a crucial role not only in the efficiency of operating the system but also in customer satisfaction. The emergency of flexible manufacturing system (FMS) has sparked an increased interest and appreciation of real-time planning, scheduling and control. FMS is defined as a manufacturing system consisting of automatically reprogrammable machines, automated tool deliveries and changes, automated material handling and transport, and coordinated shop floor control. Pertinent areas of interest include job releases, loading sequences, deadlocks, and response to resource disruptions such as machine break downs (interruptions) or tool failure. Drake et al. [1] introduced a flexible simulation technique that facilitates automated experimentation of different scheduling rules. An enhanced version of Arena/SIMAN is used to develop an extremely high fidelity model of the manufacturing system. A procedure for design and scheduling of cellular manufacturing systems for implementation in small-to-large size manufacturing systems has been developed by Logen [2]. This procedure has focused on group scheduling, machine break downs and batch size, increasing flexibility by increasing process plans of part types. The combined interactive process between material handling systems and dispatching mechanisms in FMS has been studied by Shouman and Husien [3]. It has been noticed that the considered interactive process has a great influence on the performance of the system. The rules that perform the best have been determined. The interaction between planning and scheduling stages in a hierarchical production planning system is developed by Hatchuel et al. [4]. The results show that significant lead time performances improvements result from a specific combination between MRP, PERT, and some dynamic priority rules. An extended dispatching rule approach, which applies different dispatching rule combinations in the mechanisms, and a search algorithm to find an appropriate dispatching rule combination has been advised by Ishii and Muraki [5]. The study showed better effectiveness as an on-line scheduling frame work for batch process management. A classification scheme for scheduling problems in FMSs based on an analysis discussion of scheduling decisions in an FMS has been presented by Liu and MacCarthy [6]. The scheme identifies and describes all the major factors that affect the modeling of, and the solution to, FMS scheduling problems. A new shop-based and predictive scheduling heuristic for cellular manufacturing has been developed by Mahmoodi and Martin [7]. This heuristic includes a feature for dynamically assessing variations in a subfamily’s arrival rate, enhancing suitability for realistic transient-state conditions as well as minimizing aggregate times required for major sequence-dependent machine setups at a work center. An effective tabu search (TS) approach to the job shop scheduling is applied on 56 test problems by Barnes and Chambers [8]. The procedure starts from the best solution rendered a set of 14 heuristic dispatching solutions. It makes use of the classical disjunctive network representation of the problem and iteratively moves to another feasible solution reversing the order of two adjacent critical path operations performed by the same machine. A vast majority of production scheduling process involves the determination of schedule over a certain time frame assuming all problem characteristics are known. Such schedules are often produced in advance in order to direct production operations and support other planning activities such as tooling, raw material delivery, and resource allocation. The TS approach gives superior solution in some problems and achieves the optimum in the others. A decision rule for real-time dispatching of parts, each of which may have alternative processing possibilities, has been developed by Chandra and Talavage [9]. For the effective use of the system’s routing flexibility, an intelligent part-selection strategy that takes into account the current state and trends of the system has been designed. This procedure has been found to achieve better shop performance than some of popular dispatching rules. A two level distributed production control system (DPCS) is developed for on-line scheduling in a multi-cell FMS in case of operating in a produce-to-order environment by Arzi [10]. The DPCS allows autonomous and simultaneous operation of each cell-controller, utilizing only local and short-term information as well as heuristic rules. Simulation experiments show that DPCS achieves good results in throughput, tardiness of orders and WIP inventory level and it is robust to machine and handling device failures. Unfortunately, in a dynamic environment such as the job shop, as soon as the schedule is released to the shop, it is immediately subject to random disruptions which may render the initial schedule obsolete. These disruptions or “rescheduling factors” include machine break downs, delays in the arrival of materials, arrival of rush orders, and cancellation of orders. Deadlocks and response to resource disruptions are vital parameters in FMS performance. As a matter of fact, most rescheduling factors can be modeled as machine break downs [11] and since they involve a disruption in the processing of operations on a machine or machines of a period of time. The main objective of the current work is to study the interactive process between some dispatching mechanisms at different interruption ratios and route indices on disrupted machine centers in FMS.

The interactive process between dispatching strategies, route flexibility index and interruption ratio has crucial influence on the performance of FMS. The dispatching strategy that will perform the best for each route index and interruption ratio has been determined. The present study clarified that although the interruption ratio may be relatively high for some model configurations, the best performance is achievable at certain specified route flexibility index. Also one of the main conclusion of the current work is that the increase of performance utilization is achievable at higher route flexibility index. Hence it is recommended to study the interactive process between dispatching strategies along with interruption ratios and route flexibility for FMS under consideration to pick up its configurations under which the performance will be utilized.