Sequencing and scheduling in a three-machine robotic cell

Abstract

Owing to intense global competition, one of the main concerns of the production-scheduling literature is the modelling and the optimisation of the robotic cells. In this type of cell, as in a classical flowshop, each part follows the same processing order on all machines. The objective is the minimisation of the cycle time. To efficiently exploit the potential of such cells, an algorithmic framework to a variety of challenging NP-hard optimisation problems is required. In this paper we consider the problem of scheduling operations in a three-machine robotic cell producing multiple part types. Besides the part sequence, the sequence of robot moves must be optimised as well. The simultaneous optimisation of the sequences of part and of robot activities has rarely been tackled in the literature. In addition, most studies restrict the search of the best MPS cycle to CRM sequences or to the combination of one-unit cycles despite the fact that these restrictions may not lead to the optimality. This paper attempts to fill this gap by providing a constructive heuristic based on specific features of the problem. The reported computational tests provide clear evidence that this new way to tackle the problem is promising.