Workload balancing and loop layout in the design of a flexible manufacturing system

This paper considers combined scheduling and machine layout problems in a flexible manufacturing system. All machines have the capability of performing several different types of operation. However, each operation type is to be assigned to only one of the machines, which are to be positioned around a unidirectional conveyor belt loop. For a known set of products, the primary objective is to maximise the throughput and the secondary objective is to minimise the movement of work between machines. Throughput is maximised by balancing workload, which indicates that the primary objective is equivalent to minimising the bottleneck workload. A three-phase integer programming model is derived. The first phase balances the machine workload by assigning operations to machines. The second phase minimises inter-machine travel, while respecting the workload balance attained in the first phase. In the third phase, machines are assigned to positions in the loop layout so that the total number of circuits made by the products is minimised. It is shown that this phase can be modelled as a linear ordering problem. The three-phase method is applied to a case study.