Purpose This paper aims at analyzing different possible assembly systems, including innovative potential configurations such as the fully flexible assembly systems (FAS), by defining a novel analytical model that focuses on the concept of agility and its impact on the whole system performance, also evaluating the economic convenience in terms of the unit direct production cost. Design/methodology/approach The authors propose a comparison model derived by Newton’s second law, introducing a quantitative definition of agility (acceleration), resistance of an assembly system to any change of its operative state (inertia) and unit direct production cost (force). Different types of assembly systems (manual, flexible and fully FAS) are analyzed and compared using the proposed model, investigating agility, system inertia and their impact on the unit direct production cost. Findings The proposed agility definition and the proposed comparison model have been applied considering different sets of parameters as independent variables, such as the number of components to assemble (product model complexity) and the target throughput of the system. The main findings are a series of convenience areas which either, for a given target unit direct production cost (force), defines the most agile system to adopt or, for a given target agility (acceleration), defines the most economical system to adopt, as function of the independent variables. Originality/value The novelty of this work is, first, the analytical definition of agility applied to assembly systems and contextualized by means of the definition of the new comparison model. The comparison between different assembly systems on the basis of agility, and by using different sets of independent variables, is a further element of interest. Finally, the resulting convenience areas represent a desirable tool that could be used to optimally choose the most suitable assembly system according to one or more system parameters.

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