Crane-operated warehouses : integrating location assignment and crane scheduling.

Abstract

Crane-operated warehouses constitute an essential asset for the many industries which must temporarily store products on their way from manufacturers to consumers. Such warehouses are a practical necessity rather than an explicitly desired service and they introduce significant operational costs which should be minimized. The problem addressed by the current paper, the Crane-operated Warehouse Scheduling Problem (CWSP), concerns the location assignment of input products and the scheduling of cranes for product movement in such warehouses. Several constraints are associated with the problem, for example certain products should not be stored close to each other (due perhaps to a difference in temperature or aroma) and cranes must respect operational safety distances between each other in order to prevent dangerous collisions. The present paper explores a novel methodology which combines these two decisions – location assignment and crane scheduling - instead of solving them sequentially. In addition to mathematical formulations for location assignment and crane scheduling, both an integrated mathematical formulation and a fast heuristic are presented for the CWSP. The quality of the mathematical formulation and the heuristic are compared against the conventional sequential approaches. Experimentation upon an extensive range of instances show significantly improved results are attainable when integrating location assignment and crane scheduling, despite some (expected) increase in computational time.