Optimal Storage Assignment in Automatic Warehousing Systems

Abstract

In the past few years, increasing numbers of automatic warehousing systems using computer-controlled stacker cranes have been installed. Our research concerns the scientific scheduling and design of these systems. There are three elements to scheduling: the assignment of multiple items to the same pallet (Pallet Assignment); the assignment of pallet loads to storage locations (Storage Assignment); and rules for sequencing storage and retrieve requests (Interleaving). This paper deals with optimal storage assignment. Results are obtained which compare the operating performance of three storage assignment rules: random assignment, which is similar to the closest-open-location rule used by many currently operating systems; full turnover-based assignment: and class-based turnover assignment. It is shown that significant reductions in crane travel time (and distance) are obtainable from turnover-based rules. These improvements can, under certain circumstances, be directly translated into increased throughput capacity for existing systems, and may be used to alter the design (e.g., size and number of racks, speed of cranes, etc.) of proposed systems in order to achieve a more desirable system balance between throughput and storage capacity.

A survey of literature on automated storage and retrieval systems

“…Hausman et al (1976) prove that a L-shaped configuration with square-in-time boundaries for classes A, B and C is optimal when single command scheduling is applied in square-in-time racks. Graves et al (1977) demonstrate through simulation that this L-shaped configuration is close to optimal for dual command scheduling in square-in-time racks.…”

“…Five often used storage assignment policies for AS/RSs are described here in more detail (see e.g., Hausman et al, 1976or Graves et al,1977. These rules are:…”

“…Hsieh and Tsai (2001) suggest a class-based method for production facilities based on the bill of materials. Thonemann and Brandeau (1998) alter the algorithms of Hausman et al (1976) such that they can be used in an environment with stochastic demand. Several authors (e.g., Hwang and Ha, 1994;Fujimoto, 1996, andLu, 1998 ) examine class-based policies for carousels.…”

Warehouse Layout Design for an Automotive Raw Material Supplier

“…Hausman et al [7] proposed three storage policies: 1) Random Storage Assignment; store a product closest to the I/O without any concern on the turnover. 2) Turnover-Based Assignment; store the highest-turnover pallets closest to the I/O.…”

Robust Storage Assignment in Unit-Load Warehouses

“…Another example of a shared storage policy is the class-based turnover policy proposed by Hausman et al (1976), Graves et al (1977), and Schwarz et al (1978). Under this policy, storage locations are grouped into several classes.…”