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It is well known that routing problems are recast as a binary integer linear programming in overhead hoist transport (OHT) vehicle systems. Two kinds of discrete-time state space models of the routing problem are proposed in this paper that simplifies the constraints and binary variables. First, a Petri Net (PN) method is used to simplify the constraints. Second, a Deterministic Finite (DF) Automaton...
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...
This paper proposes a new static simultaneous optimization of dispatching and conflict-free routing for unidirectional Overhead Hoist Transport (OHT) systems. Our objective is to minimize the entire transportation time where the given transportation tasks are finished. A hybrid system modeling is applied for OHT system that is constituted by the OHT vehicles at the lower level and governed by the...
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