A geometrical approach to computing expected cycle times for zone-based storage layouts in automated storage and retrieval systems

An exact, geometry-based analytical model is presented that can be used to compute the expected cycle time for a storage/retrievel (S/R) machine, executing single-commands, dual-commands, or both, in a rack structure that has been laid out in pre-specified storage zones for classes of goods. The rack may be either square-in-time or non-square-in-time. The approach is intuitively appealing and it does not assume any certain layout shape, such as traditional ‘L-shaped’ class layouts. The model has been coded in Turbo Pascal, and be used by designers as a tool for quickly evaluating alternative layout configurations with respect to expected S/R cycle time in an AS/RS, and thereby the throughput of an automated warehouse over time. This model has been successfully applied in a major manufacturing plant in Europe to evaluate reconfigurations of their rack storage layouts over the past five years.