The Taguchi approach to robustness

A parameter design is a design where two kinds of independent variables are used. These are the controllable influences and the uncontrollable influences, also called control factors and noise factors. The aim of the parameter design is to find settings of the control factors where the variability due to the noise factors is minimal. 

In order to use a parameter design it is necessary to be able to control the levels of the noise factors during the optimization period. This control of the noise factors is necessary in order to use fixed levels of the noise factors. The responses at the extreme settings of the noise factors determine what variation (noise) in the response values is present. 

In the next section the parameter design is explained for the experiments of this paper. This can be used as a guideline to understand the problem and the method by which the problem is tackled. 

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In chromatographic terms the purpose of this paper is to find a mixture composition which results in a good separation of the solutes, both under standard environmental conditions and for different temperatures and relative humidities. In this section this chromatographic purpose is combined with the Taguchi approach to robustness. This results in mathematical expressions which quantify the separation and the robustness against environmental influences. 

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