A COMPARISON OF DWELL POINT RULES IN AN AUTOMATED STORAGE-RETRIEVAL SYSTEM

In the operation of an automated storage/retrieval system (AS/RS), several policies to strategically position the storage/retrieval (S/R) machine when idle to reduce travel time in warehouse operation have been advocated. In this paper, computer simulation is utilized to examine six dwell point rules under dedicated and randomized storage methods. The results indicate that positioning the S/R machine whenever idle at a location that minimizes the expected travel time (called LP expect rule) dominates all other dwell point rules under two storage methods. The dwell point rule of minimization of the maximum S/R travel time (called LP minmax) dominates the other remaining four rules under dedicated storage method. On these two rules, LP expect and LP minmax, the performance of dedicated storage method is superior to that of randomized storage method. Furthermore, these two rules are very suitable for dynamic control of an AS/RS system.