Scheduling of a computer integrated manufacturing system : a simulation study

In recent years Computer Integrated Manufacturing (CIM) systems are increasingly being used in the manufacturing for their advantages of flexibility, quality, reduced labor and inventory cost. CIM systems are consisting of a number of computer-controlled machines and material handling devices integrated with ERP (Enterprise Resource Planning) and supporting systems. Production scheduling problem is one of the main area of research of CIM Systems since with a proper scheduling, the utilization of resources is optimized and orders are produced on time which improves the shop performance and associated cost benefits. In general terms, the scheduling problem is defined as the allocation of resources, machinery or people, to accomplish specific tasks over a certain time-period such that the desired performance of the system is maximized. In many situations, production scheduling is done by the use of dispatching rules due to their effectiveness and ease of use. Dispatching rules are simple algorithms that use various priority attributes and relevant information concerning the availability status of resources in prioritizing the jobs waiting for processing. The target of this study is to research the effect of selected scheduling dispatching rules on the performance of an actual CIM System located in the Mechanical and Industrial Engineering Department using different performance measures and to compare the results with the literature. To achieve this objective, a computer simulation model of the existing CIM system based on the control logic that describes the operation of the system is developed to test the performance of different scheduling rules with respect to mean flow time, Machine Efficiency and Total Run Time as performance measures. The Design of Experiments (D.O.E.) method is used to set up runs for the experimental study of combinations of number of factors in various levels that influence the performance of the selected dispatching rules. Furthermore, ANOVA analysis of the variance was adapted to evaluate and analyze the relative effectiveness of the dispatching rules for each set of experiments based on the performance measures. Based on the assumptions of this study, the experimental work performed suggests that the system performs much better considering the Machine Efficiency when the initial part release is maximum and the buffer size is minimum. Furthermore, considering the Average Flow Time, the system performs much better when the selected dispatching rule is either Earliest Due Date (EDD) or Shortest Process Time (SPT) with buffer size of five and initial part release of eigh