Sequencing and batching procedures for minimizing earliness and tardiness penalty of order retrievals

Order retrieval is considered one of the most costly activities in automated warehouses. A recent survey, Warehousing Education and Research Council’s 1986 Survey, identified order picking as the highest priority warehousing activity for productivity improvement. The recent implementations of the widely used just-in-time approach to production control, which requires accurate order retrievals such that production delays and inventory accumulation between production stages are minimized, have further emphasized the importance of the order sequencing and batching problems. In this research, the authors investigate the multiple address automated storage/retrieval systems (AS/RS) when orders are assigned due dates. Orders to be retrieved arrive at the AS/R system and each order is defined by a set of products (parts) type, the corresponding quantities to be retrieved and a due date. Orders can be retrieved (processed) individually or grouped in batches and every batch is retrieved in one tour (trip) of the automated storage/retrieval machine. The grouping of orders into batches (batching processes) is performed based on a penalty function which incorporates both the earliness and the tardiness of the orders. The objective is to sequence and group the orders into batches such that the penalty function is minimized. The authors develop efficient procedures for order sequencing and batching such that just-in-time order retrieval can be achieved.