Scheduling in Dual Gripper Robotic Cells for Productivity Gains

Abstract:  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 most 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.