مدل لجستیک در تولید انعطاف پذیر

An integrated modeling approach that considers the overall production schedule is needed in order to effectively manage different material flows in a flexible manufacturing system (FMS), where large amounts of data intervene in the dynamic control and decision making process. This study focuses on the development of an integrated FMS control model that includes essential features, such as routing of simultaneously processed work orders and batch dispatching, as well as dynamic vehicle path determination and conflict-free routing. A logistics-oriented modeling methodology for FMS distributed control design is proposed that provides the capability for rapid development and evaluation of the control policy.

A high degree of flexibility and quick response times have become essential features of modern manufacturing systems. Flexible manufacturing systems (FMS) allow for more efficient use of resources in terms of increased machine utilization, reduced work-in-progress inventory, increased productivity, a reduced number of machine tools, lower labor costs, shorter lead times and less floor space [1] and [3]. This is obtained, however, at the expense of more complex control of these systems. Some of the most recurring and important control tasks are those related to scheduling and dispatching, because it is commonplace in an FMS environment — where many different types of work orders, in varying batch or lot sizes, are produced simultaneously — to find jobs competing simultaneously for the same resource [14], be it an intersection in an automated guided vehicle system (AGVS), machine tool time or access to an automated materials handling system.

The common features of the class of system consisting of a set of sequential and repetitive processes specified by fixed routing are complexity and the lack of adequate performance evaluation tools. The methodology proposed in this study integrates workpiece flow structure design, buffer capacity assignment, and allocation of the dispatching rules that control the workflows. Conditions for designing the procedures that permit achievement of the required performance of the system while preserving some of its qualitative constraints are given. The main element of the methodology is the distributed control design guaranteeing the qualitative (i.e. starvation- and deadlock-free operation) and quantitative (i.e. satisfying the performance index) requirements for system operation. Sufficient conditions for obtaining a cyclic steady state for a given configuration of FMS are given. The principal advantage of the proposed approach is that the distributed control method allows the system to return to a unique cyclic steady state from any state reached as the result of an accidental disturbance. The presented approach can be easily adapted to the design of distributed control of the material flow of an entire system. It has been used in CRP, a Java-written decision support tool [7] for rapid prototyping of distributed control systems, aimed particularly for modeling and performance evaluation of concurrently interacting processes.