Class-based storage with exact S-shaped traversal routeing in low-level picker-to-part systems

We consider a low level picker-to-parts system in a one-block warehouse with P/D point located at a corner point. We develop new and exact analytical models to estimate travel distance for random, full turnover and class-based storage in which a single picker follows an S-shaped traversal routeing policy. Our analytical results for random, full turnover and class-based storage follow corresponding simulations very closely with an accuracy of within 2% for the range of warehouse parameters considered. We also report the percentage improvement obtained by the optimal 3-class storage strategy over the random storage policy and the potential gain of this 3-class policy as compared to the full turnover policy. Further, we conduct a computational study to determine the optimal layout parameters for a warehouse with a 3-class optimal storage strategy for a given pick size per tour. Sensitivity analysis of pick travel distances with important warehouse parameters is also presented.