32nd European Conference on Operational Research, Espoo, Finland, 3 - 06 July 2022, pp.215
The material handling systems used in warehouses involve important operations such as the usage of order picker forklifts. The order picker forklifts provide efficient utilization of the storage space by their ability in moving in narrow aisles and picking items from high racks. Routing the order picker forklifts to pick ordered items belongs to operational decision level done in high frequency. Therefore, finding energy-efficient routes for order picker forklifts can yield significant savings in energy consumption in warehouses and the resulting CO2 emission. We introduce and study the energy minimizing order picker forklift routing problem (EMFRP) which aims to find energy-efficient routes for order picker forklifts to pick given list of items. We calculate the forklift’s energy consumption in both horizontal and vertical moves considering the effects of friction forces, the acceleration and deceleration of the forklift, and its load. A mixed integer programming formulation and a dynamic programming approach are developed to solve small size instances of the EMFRP exactly. To solve larger instances, we provide tour construction and tour improvement heuristics and integrate them into a single solution approach. Computational results show that the proposed heuristic approach finds high quality solutions. Moreover, it is observed that significant energy savings can be achieved by solving the EMFRP instead of the classical distance minimization problem.