Scheduling in dual gripper robotic cells for productivity gains
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In many applications, robotic cells are used in repetitive production of identical parts. A robotic cell contains two or more robot-served machines. The robot can have single or dual gripper. The cycle time is the time to produce a part in the cell. We consider single part-type problems. Since all parts produced are identical, it is sufficient to determine the sequence of moves performed by the robot. The processing constraints define the cell to be a flowshop. The objective is the minimization of the steady-state cycle time to produce a part, or equivalently the maximization of the throughput rate. The purpose of this paper is to study the problem of scheduling robot moves in dual gripper robot cells functioning in a bufferless environment. We develop an analytical framework for studying dual gripper robotic cells and examine the cycle time advantage (or productivity advantage) of using a dual gripper rather than a single gripper robot. It is shown that an m-machine dual gripper robot cell can have at m ost double the productivity of its single gripper counterpart. We also propose a practical heuristic algorithm to compare productivity for given cell data. Computational testing of the algorithm on realistic problem instances is also described.