Virtual vehicle in the connecting transport automated material-handling system (AMHS)

In the connecting transport system, the time spent waiting for an empty vehicle is eliminated effectively and the work-in-process level can be reduced. Four different fixed vehicle types were used to carry out the wafers moving task. Thus, the automated material-handling system for a 300-mm wafer fab can be one of the three methods above or any mixture of these three connecting transport methods. However, no one method outperformed the others in all operational scenarios. A new concept of the virtual vehicle in the connecting transport automated material-handling system is proposed that can improve the task of moving wafers between bays and within each bay by a single system with interconnected lines. In this virtual vehicle environment, when the moving request is initiated, the wafers are assigned to the appropriate vehicle that can be changed to the vehicle type. Discrete-event simulation models are developed in eM-Plant™ and compared with the virtual vehicle through the fixed vehicle in the connecting transport automated material-handling system. Using the virtual vehicle, the simulation results show that the performance measures such as throughput, transport time, 95% transport time and waiting time can be improved for different flow rates of the environment.