12吋晶圓製造廠自動搬運系統之 最佳化派工與排程
Optimized Dispatching and Scheduling for OHTs in a 300mm Wafer Fab
Date Issued
2006
Date
2006
Author(s)
Chan, Da-Wei
DOI
en-US
Abstract
In this thesis, we use a graphical and mathematical modeling tool- Coloured Timed Petri Net (CTPN) to model the production flow in the wafer fabrication plant. Overhead hoist Transport (OHT) is taken as the transportation vehicle, and we take the priority rules for lot dispatching and OHT dispatching. Moreover, we apply the genetic algorithm to help us obtain the near-optimal solution.
The model in this thesis comprises two parts, including the processing model and transportation model. With this CTPN model, we can simulate the production process and transportation issues, thus the equipment status, OHT status, and the lot conditions can be tracked efficiently and precisely. In addition, different scheduling policies can be evaluated via simulations and a superior policy will then be determined.
In the dispatching phase of lot dispatching, we first present the lot based selection scheme and the equipment based selection scheme. The available equipment will select the fittest lot according to the lots priority if there are multiple waiting lots, and the lot will choose the fittest equipment under multiple pieces of available equipment. In the dispatching phase of OHT dispatching, reassignment of the pair of lot and OHT is applied as the traffic condition of the plant is changing.
Besides, “zone control” is used to ensure that OHTs will not collide, and “push vehicle” is used whenever an idle OHT blocks the zone another OHT is trying to occupy. Moreover, through OHT reassignment the block phenomenon can be eliminated, and the traffic congestion problem is also considered and reduced.
At last in the scheduling phase, we apply the genetic algorithm (GA) based approach to obtain a near-optimal solution to our scheduling problem. From our experiment results, the developed CTPN based genetic algorithm will yield a more efficient solution than other scheduler, so that this GA scheduler can indeed satisfy the need of a rapidly changing environment, such as the wafer fabrication plant.
Subjects
十二吋晶圓廠
排程
派工
裴氏網路
300mm wafer fab
scheduling
dispatching
Petri net
SDGs
Type
thesis