A Heuristic Rule-Based Approach for Dynamic Scheduling of Flexible Manufacturing Systems

Abstract

Operations planning and scheduling (OPS) problems in flexible manufacturing systems (FMSs), are composed of a set of interrelated problems, such as part-type batching, machine grouping, part routing, tool loading, part input sequencing, and resource assignment. The performance of an FMS is highly dependent on the efficient allocation of the limited resources to the tasks, and it is strongly affected by the effective choice of scheduling rules. In this study, a heuristic ruled based approach for dynamic scheduling of FMSs, which integrates loading, part inputting, routing, and dispatching issues of the OPS is presented, and the implementation results are compared with several dispatching rules. Scheduling is a decision making process and it concerns the allocation of the limited resources to tasks over time [1]. In a manufacturing system, resources represent machines, operators, robots, tools, buffers etc., and activities are the processing of products on machines, the transportation of products among workstations, or loading/unloading the parts from/to machines by the operators. The scheduling problems in FMSs, relate to the execution of production orders and include raw part input sequencing, machine, material handling device and operator scheduling, part routing, monitoring the system performance and taking the necessary corrective actions [2]. Since FMSs comprise very diverse properties and constraints (e.g. the availability of alternative machines to perform the same operation(s), multi-layer resource sharing, and product varieties), scheduling problems in FMSs are more complex than job-shop or flow-shop problems and often very difficult to be solved by conventional optimization techniques. Prior studies on FMS scheduling problem point out the great impact of scheduling decisions to the system performance [3-5]. Scheduling decisions and the effective choice of dispatching rules are influenced by the performance criterion and existing shop-floor conditions such as process plans, due date requirements, release dates, job priorities, machine setup requirements, and the availability of system resources. Scheduling/dispatching control decisions in an FMS must be capable of handling simultaneously these diverse factors on a real-time basis. Therefore, rather than designing an optimum scheduler, there is a definitive need for a flexible and integrated scheduling in order to handle the dynamic and stochastic nature of real-world problems, and computationally efficient compared to analytical methods. In this study, a heuristic rule-based approach is proposed to solve the resource contention problem in an FMS, and to determine the best route(s) of the parts, which have routing O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m