Analyzing the performance of an order accumulation and sortation system using simulation: A design of experiments approach
An Order Accumulation and Sortation (OA/S) system is one of three component systems of a typical distribution center. The three systems in order of material flow are (1) the storage (warehouse) system, (2) the OA/S system, and (3) the shipping system. An efficient distribution center requires a successful link of all three systems. In this study efforts are concentrated on one of the least researched, the OA/S system. In an OA/S system items are delivered to a conveyor where they are sorted into shipping lanes, consolidated and then packed. A simulation model of an OA/S used in automated distribution centers is developed. The OA/S system developed for this study uses non-recirculating conveyors; thus, once an item is introduced into the system, it has to be assigned to a shipping lane. The main concern of the study is to find which factors affect the throughput of the system and at what levels these factors give the best system throughput. Design of experiments (DOE) is a very effective and organized way to perform an experiment and has been commonly used in industry to improve the performance of manufacturing processes. The application of experimental design techniques early in process development can result in improved process yields, reduced variability, closer conformance to nominal or target requirements, reduced development time and reduced overall cost. Emphasis is given to designing quality into the process at the initial stages of research by making it robust (insensitive) to various sources of variability, which may be uncontrollable during the process or during its usage by the customer. A recently introduced approach based on response surface methodology (RSM) showed that the results of an RSM study are easier to interpret and are very efficient with respect to the number of experiments. A RSM tool, the Central Composite Design (CCD) is one of the most effective designs that can be used for robust parameter design. The CCD is basically a two-level factorial or fractional factorial design that has a number of center point and axial point runs. This design is used to analyze the results of the simulation runs and to achieve robustness. The final equation to calculate the throughput rate considering all the independent factors was calculated using design of experiments. It is concluded that the independent factors Lane Length, Items / Lane and Distribution do not affect the throughput rate of the system. Though the noise factors are insignificant in the phase two of experimentation, it is suggested to have longer lane lengths (control factor A) as seen in the screening experiment. The screening experiment shows that the lane length is insignificant. Thus longer the lanes, lesser the variability in the throughput rate is obtained.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:order accumulation system sortation simulation model material flow response surface methodology central composite design experiments approach
Date of Publication:01/01/2001