A Dispatching Rule Study of a LED Sorting System

The scheduling problem of LED chip sorting workstation is a multiprocessor open shop scheduling problem. In practice, this problem is usually solved with finding a dispatching rule to achieve certain performance indexes. Experimental design was applied to find a proper rule, and dispatching rule, wafer quantity, wafer mix type, and bottleneck location were chosen as independent variables. Maximum make-span and average queuing time were selected as dependent variables. Five dispatching rules were considered in the dispatching rule factor. Experimental results showed that all independent variables are significant on all dependent variables. While make-span as the performance index, three dispatching rules common in applying LPT in bottleneck machines obtained better results. A dispatching rule with applying SPT in non-bottleneck machines has least average queuing time among those three, and this rule is recommended for practical application.