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Hughes Aircraft Designs Automated Storeroom System Through Simulation Application
Hughes Aircraft Company, Radar Systems Group of El Segundo, California, manufactures airborne radar systems for the F14, F15, and F18 military aircraft. A project to modernize all storeroom operations at the plant was initiated in 1987. The primary objectives of the storerooms are to receive, store, and issue material in an efficient and economical manner which will ensure accurate inventory accountability and parts disbursals. The current system consists of six independently functioning storerooms, each supporting an individual program or process. All are manually operated and employ an alphanumeric storage strategy. Corrugated boxes, tote pans, and closed shelving units are utilized to store approximately 27,000 unique parts.
A new system which combines the six storerooms into one automated facility is currently being implemented. The primary elements of that system are powered conveyor, double stacked horizontal carousels, robotic inserters/extractors, and tote pans. All parts are randomly, stored within the carousels. At the onset of the project, a task team was given the responsibility to integrate those elements and many other components into one operating system capable of achieving a desired throughput rate while upholding all storeroom objectives.
Analyzing potential design concepts became complicated due to the large number of elements within the system. System complexity multiplied significantly as the number of elements and interrelationships increased. When exposed to various stimuli, the synergism of the components was difficult to predict. What impact would conveyor speed have on workstation utilization? How would horizontal carousel speeds influence system throughput? Would changing control logic at a specific conveyor merge point cause bottlenecks at other locations? What effect would the stochastic processes induced by random storage locations have on system response time? Hughes elected to utilize simulation modeling as a tool for providing insight into answering these questions.
Figure 1 depicts a top view of a proposed design concept. A bi-level powered belt conveyor is used throughout the system to transport totes. The upper level conveys totes to workstations while the lower level returns totes to carousels. There are twenty multi-purpose workstations. Each has either a four or five tote queueing conveyor for staging incoming totes. The stations are designed to process any of six different stores transactions: kitting, cycle inventory counts, receipts processing, part replacement requests, backorder processing, and kit verification. Each transaction requires between one and four totes to be sent from the carousels. The system must be capable of delivering eight hundred totes per hour to workstations in order to accommodate peak production demands. Average cycle times for the various transaction types range from twenty-seven seconds to ten minutes. Upon completion of a task at a workstation, an operator places totes used in the operation onto an outgoing queueing conveyor. They are then merged onto the lower level transport conveyor and directed to either of two destinations. The majority return to the …