Comparisons of two-machine line models in throughput analysis

Throughput analysis is important for the design, operation and management of manufacturing systems. Due to the large state space, exact analytical results only exist for two-machine serial lines. To analyse longer lines or more complex systems, the two-machine line model becomes the building block for further development. Therefore, many two-machine line models have been presented in the literature. A thorough understanding of the nature and differences of the various two-machine line models is critical for future analysis and development. In this paper, we study eight different two-machine models, categorized by synchronous and asynchronous lines with both time-dependent and operation-dependent failures, respectively. For each model, we introduce and compare the assumptions, calculation formulae, and their performance in system throughput. The results show that all the models exhibit similar performance with small differences, comparable to (or less than) the accuracy of data collection on the factory floor.