Optimal one-wafer scheduling of single-arm multi-cluster tools with tree-like topology

摘要

The scheduling problem of a multi-cluster tool with a tree topology whose bottleneck tool is process-bound is investigated. A method for scheduling the multi-cluster tool to thereby generate an optimal one-wafer cyclic schedule for this multi-cluster tool is provided. A Petri net (PN) model is developed for the multi-cluster tool by explicitly modeling robot waiting times such that a schedule is determined by setting the robot waiting times. Based on the PN model, sufficient and necessary conditions under which a one-wafer cyclic schedule exists are derived and it is shown that an optimal one-wafer cyclic schedule can be always found. Then, efficient algorithms are given to find the optimal cycle time and its optimal schedule. Examples are used to demonstrate the scheduling method.