A Process Approach to Robust Design in Early Engineering Design Phases

Abstract: The activity of robust design of mechanical products and how it can be accomplished in pre-prototype design phases, is discussed in this thesis. It is advocated that to be fully efficient and effective optimization of product robustness should commence already in the conceptual design phase. Moreover, since product optimization is a process, robust design should be perceived and implemented as a process too, and not as an isolated method. A process for robust design engineering is proposed, which is based on a Swedish design methodology devised by prof. Fredy Olsson (systematic design). Further, the concept of robustness is linked to a theory of machine systems. Some traditional methods of robust design are reviewed and the recurring problems of noise identification and insufficient information about the magnitudes of noise sources' variations are discussed. Means to overcome these problems are proposed. A modified use of the error transmission formula is proposed in which analysis of interactions between design variables is facilitated, and it also allows preliminary analysis of systems' robustness properties irrespective of uncertainties regarding the variabilities of primary input and control variables. The requirements set on methods for robust design from the viewpoint of design science are formulated in seven hypotheses. Examples of suitable methods to be used in a robust design methodology are given.