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Systems with fewer design parameters (DPs) than functional requirements (FRs) are coupled or cannot achieve all their FRs simultaneously, as per Axiomatic Design's theorem 1. In that case, production processes have lower productivity and production rate than uncoupled or decoupled designs. This paper reports the upgrading of a salt washing machine concerning its performance, not only on separation of salt from saltwater but also on washed salt production. The machine analysis showed it is a coupled design, with one more functional requirement than the design parameters. A viable enhancement was the addition of one design parameter, which made it possible to control separation and washing independently. This redesign enforced functional independence and allowed increasing the production rate between 20% and 30%. Furthermore, one could perceive increased productivity, quality of the final product, and reduced water and energy consumption.

Most of the Axiomatic Design research work focuses on the design as being a relation between the functional domain and the physical domain. Yet, the outcome of a successful design results from a definition of the functional requirements that accurately reflect the customer needs. The contribution of this paper is to help defining a theoretical framework to describe the customer needs and the related functional requirements, using the 'Theory of Practices' (TP). This theory highlights every human activity in terms of a set of actions called 'practices'. Practices relate to the actions required to fulfill a need through three variables: a material support, a competence to perform the action and a meaning that arises from the action. TP also takes into account the surrounding functions of the practice, defining them according to the milieu of its usage. Thus, TP allows a clear identification of the customer needs to fulfill and facilitates the scrutiny of the related functional requirements.