A Bivariate Plot Useful in Selecting a Robust Design

A sound engineering practice for improving quality and productivity is to design quality into products and processes. The ideas of G.Taguchi about parameter design were introduced in the US some ten years ago. Despite some strong controversy about some aspects of it, they play a vital role in the concept of robustness in the design of industrial products and processes. In this paper, we present a new methodology for designing products and processes that are robust to variations in environmental or internal variables. First, a tentative model for the response as a function of the design and noise factors is assumed. This model is then estimated using a single design matrix and the expected value and variance of the response are calculated over the space of the design factors. Finally, the best setting of the parameters values can be located in a newly developed bivariate plot where the distance to the target is plotted against the variance of the response.