Dynamic Scheduling of Shuttle Robots in the Warehouse of a Polymer Plant Based on Dynamically Configured Timed Automata Models

Abstract

The increasing demand for customized products and the pressure to produce them on time with low-cost upon customers’ demands not only call for efficient and economical production processes but also require high-performance logistic planning to make the best possible use of the available resources. The elements to be planned besides the production itself include preproduction material handling, such as raw material deliveries and storage, and the postproduction material handling, such as storage and distribution of products. Specialty products are usually stored in warehousing systems where the speed of the removal and the distribution of products can strongly affect the efficiency of the complete system. Hence, optimal scheduling of the distribution operations is required to meet throughput targets and lead to improved efficiency and financial gains. In this contribution, we deal with a bottleneck subsystem of an industrial polymer processing plant, the pallet removal system of a high-rise warehouse. A dynamic scheduling approach that uses optimization to solve the problem on a moving window is proposed. The shuttle management problem is modeled using timed automata and is solved by cost-optimal reachability analysis. The most challenging aspect of the problem is introduced by the a priori unknown arrival times of the pallets and their unknown routes. The proposed dynamic solution approach is compared to an enhanced version of the currently used first-come, first-served dispatching rule. The comparative study shows that the proposed approach leads to makespan reductions of about 30%.