Robotic cells with parallel machines and multiple dual gripper robots: a comparative overview

The combination of parallel machines and multiple dual gripper robots has become increasingly prevalent in modern manufacturing with robotic cells. However, there has been no previous study of the design and scheduling challenges faced by managers who employ these complex cells. The benefit of implementing dual grippers in cells with multiple robots over cells with the same number of single gripper robots is quantified in this paper. Configuration decisions are addressed by comparing different implementations of multi-robot cells to show that the method of exchanging parts between robots (shared machines versus transfer stations) has little bearing on the throughput. In contrast, it is demonstrated that the assignment of processing stages to robots can have a significant effect on a cell's potential throughput. A scheme that allows multiple robots to cooperate without colliding or suffering gridlock is described; this is realized with minimal impact on throughput. The optimality is analytically established, under conditions that are very common in practice, for a particular cyclic sequence of robot moves in robotic cells with one or more dual gripper robots, parallel machines and transfer stations.