Order picking oriented storage assignment problem in a vertical lift module system.

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2019
Öz, Bura
Since the advancements in technology paved the way for an increased consumer-manufacturer interaction, companies are forced to adapt a mass customization phi-losophy in their production operations. This philosophy requires a higher variationof raw materials to be stored by the manufacturer to fill the customer orders on time.However, this increased variation in the inventory will also mean increased require-ments for the storage area. Using automated storage and retrieval systems (AS/RS)is one way of using the volume in warehouse buildings more efficiently. By storingtrays into the shelves inside a shuttle, vertical lift modules (VLMs) are among theAS/RSs promising more dense storage. These units can also be combined and usedas a system called "VLM Pod". Although using a VLM helps in using the volumemore efficiently, retrieval of the trays in the VLM units may take some time and causeunwanted waits.This study analyses a design-to-order manufacturing company’s transaction historyand discusses the factors that make the responsiveness of a warehouse important insuch an environment. Then, the throughput related VLM decisions are discussed. With the help of the observations from a time study and the transaction history of thecompany, various combinations of those throughput related decisions are simulated.After these considerations, an integer linear programming model is proposed for as-signing parts to trays and trays to shelves in VLM units. The proposed model andits variants are used in a computational experiment on small data sets sampled fromthe company’s transaction records. The optimal solutions for the small data sets areused in a picking simulation. According to the picking simulation with the small datasets, the proposed model yielded an average of 10% improvement in the completiontime of all pick tasks, while the number of tray retrievals during picking is reducedby approximately 65%, compared to the current system at the analyzed company.

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Citation Formats
B. Öz, “Order picking oriented storage assignment problem in a vertical lift module system.,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Industrial Engineering., Middle East Technical University, 2019.