Integrated scheduling of zone picking and vehicle routing problem with time windows in the front warehouse mode

This paper examines the optimal scheduling of order picking and delivery. We present a mixed-integer model for managing integrated scheduling of zone picking and vehicle routing problem with time windows (ISZPVRPTW) in the FWM and consider the real-world factors impactive in planning order fulfillment process, such as the fulfillment deadline, convey time between the picking zones, setup time and the variable driving speed. The decisions on order batching, picking sequencing, and vehicle routing are made together. A Two-stage Iterated Search (TIS) algorithm is developed to minimize operation costs and overdue penalty costs. With extensive numerical experiments, we demonstrate the effectiveness and efficiency of the proposed approach by comparing the results produced by TIS with that of the Traditional Sequential Scheduling (TSS) approach. The results show that the TIS algorithm outperforms the traditional approach in different evaluation indicators, and the time allocation as well as the caution intensity is significant for the fulfillment expense.