Dispatching and conflict-free routing based on model predictive control in semiconductor fab

This paper proposes a new scheduling method of dispatching and conflict-free routing for overhead hoist transport (OHT) systems in semiconductor fabrication (Fab). This paper utilizes a model predictive control (MPC) strategy in which the cycle of measurement, prediction, optimization and control is repeated. The first aim of the MPC application is to set a small prediction horizon for the scheduling optimization, which leads to reduce computational complexity. The second aim is to address the dynamic situation such that transport requests are given in real time. This paper introduces a switching type multi-objective cost function and considers how the MPC based method adds new request tasks to the scheduling problem in real-time for the dynamic situation. To verify the validity of the proposed method, some numerical examples are shown.