Simulation-based Evaluation of Idle Vehicle Positioning on Logistics Performance in OHT Systems

This paper investigates the idle vehicle positioning problem in Overhead Hoist Transport (OHT) systems, commonly used in the semiconductor manufacturing industry. We present a mathematical model for dynamically reallocating idle vehicles to optimal locations, aiming to reduce expected retrieve distances and improve overall logistics efficiency. Given the computational challenges of solving the model exactly, we propose heuristic approaches based on the k-median problem. These approaches are evaluated through simulation experiments, which demonstrate that median-based idle vehicle positioning can significantly enhance logistics performance. However, frequent reallocations can lead to congestion and reduce system efficiency, particularly in high-demand scenarios.