Related Studies

Abstract: In this paper, we study the problem of two-machine, identical parts robotic cell scheduling with operational flexibility. We assume that every part to be processed has a number of tasks to be completed in these two machines and both machines are capable of performing all of the tasks. The decision to be made includes finding the optimal robot move cycle and the optimal allocation of tasks to these two machines corresponding to this robot move cycle that jointly minimize the cycle time. We proved that 1-unit robot move cycles are not necessarily optimal with this definition of the problem any more and that according to given parameters either one of the 1-unit robot move cycles or a 2-unit robot move cycle is optimal. We proposed a new robot move cycle, which is a result of the assumption of operational flexibility. This cycle is not only simple and practical but also dominates all of the common cycles reported in the literature. Finally, we considered the change of layout and showed that the cycle time of the proposed cycle can be further reduced by a change in the layout while the cycle times of all other cycles remain the same.

Abstract: In this study, we deal with the robotic cell scheduling problem with two machines and identical parts. In an ideal FMS, each machine is capable of performing all tasks of all parts by changing tools. However, this assumption may be unrealistic at times since the required tools are stored in the tool magazines which have limited capacity and in many practical instances the required number of tools exceeds this capacity. Consequently, we assume that some tasks can only be processed on the first machine while some others can only be processed on the second machine. Remaining tasks can be processed on both machines. The problem is to find the allocation of the remaining tasks to the machines and the optimal robot move cycle that jointly minimize the cycle time. As a solution of the problem, we prove that the optimal solution is either a 1-unit or a 2-unit robot move cycle and we present the regions of optimality. Finally, a sensitivity analysis on the results is conducted.

Abstract: In this study, we consider a Flexible Manufacturing Cell (FMC) processing identical parts on which the loading and unloading of machines are made by a robot. The machines used in FMCs are predominantly CNC machines and these machines are flexible enough for performing several operations provided that the required tools are stored in their tool magazines. Traditional research in this area considers a flowshop type system. The current study relaxes this flowshop assumption which unnecessarily limits the number of alternatives. We propose a new robot move cycle which is a direct consequence of process and operational flexibility. We prove that this proposed cycle dominates all 2-unit robot move cycles and present the regions where the proposed cycle dominates all 1-unit cycles. We also present a worst case performance bound of using this proposed cycle instead of the optimal robot move cycle.

Abstract: The focus of this study is identical parts robotic cell scheduling problem with m-machines under the assumption of process and operational flexibility. A direct consequence of this assumption is a new robot move cycle which is overlooked in the existing literature. We prove that this new cycle dominates all classical robot move cycles considered in the literature for m=2. We also prove that changing the layout from an in-line robotic cell to a robot centered cell reduces the cycle time of the proposed cycle even further whereas the cycle times of all other robot move cycles remain the same. For the general $m$-machine case we find the regions of optimality for the proposed cycle and present a worst case performance bound for the remaining regions. Considering the number of machines as a decision variable, we also find the optimal number of machines that minimizes the cycle time of the proposed cycle.