To quickly and efficiently estimate the performance of continuous flow transporters of automated material handling systems with multi-loop conveyors and priority rules of wafer lots in wafer fabrication systems, the M/M/1/K queuing model and non-pre-emptive priority M/G/1 queuing model with multi-class customers were introduced to analyse the queuing features of the continuous flow transporters. An analytical model is presented for a spine layout of continuous flow transporters which are configured with conveyors and crossovers. In the modelling procedure, a spine layout with crossovers and an outer loop was set up to make differentiated routes. Priority rules of wafer lots were implemented by controlling the outer loop, inner loop and crossovers to access. A case of a 300 mm wafer fabrication with 24 intrabays was applied to validate the analytical model. The performance of the analytical model has been compared with that of an Arena simulation model. Experimental results show that in most cases the relative errors can be controlled to be smaller than 5%. It indicates that the model perform well in performance analysis for continuous flow transporters of automated material handling systems.
['Binghai Zhou', 'Jin-Xiang Chen', 'Zhiqiang Lu']
An analytical model for continuous flow transporters of AMHSs with multi-loop conveyors and priority rules