The present invention relates to apparatus and method of collision avoidance in a cluster tool having a plurality of processing stations and at least two robots. In one embodiment of the invention, the system is configured such that each of the processing stations is accessible by only one of the at least two robots. For each of the at least two robots, a set of trajectories is determined so that each robot is capable of transferring substrates among the corresponding processing stations, wherein the envelope formed by the set of trajectories of each robot does not overlap.