Designing a Representation to Support Function – Means Based Synthesis of Mechanical Design Solutions

This paper describes the function-means-context (FMC) structure, a set of representations intended to form the basis for a computational design tool, aimed at synthesising solutions to mechanical design problems that can only currently be addressed by unstructured approaches. From an initial functional requirement, a top level context, and a choice of working principle, an FMC structure is developed by the application of a database of stored rules. Alternative complete design schemes are generated from it, each comprising a list of parts and their connections. The representations and proposed synthesis process are illustrated by means of a well known case study: the conceptual design of a one-handed mixer tap as described by Pahl and Beitz [1]. In the original, solution principles were generated by brainstorming. The approach described here utilises functional decomposition and satisfaction rules representing mechanical design synthesis knowledge. The rules store known ways that single functions or function structures, can be performed by single parts or networks of parts and/or functions. In an unusual approach for a traditional mechanical design problem, the functions of the mixer tap are viewed as partly involving signal processing, but performed by mechanical elements. The problem is to decode independent temperature and flow rate demands to give appropriate control signals to two modulated orifices metering the hot and cold supplies. In the representation described here, signal flows may be carried either by the across or the through variable (velocity or force) of any of the 6 degrees of freedom of a mechanical connection.