Visual Robustness: Effects of Variation on Product Appearance and Perceived Quality

Licentiate thesis, 2009

For consumer products where the product appearance plays an important role in meeting expectations, the visible effects of manufacturing variation can have a negative influence on the product experience. A prerequisite in mass production is that no manufactured units are exactly identical, as a result of variation. However, reducing variation is often associated with increased manufacturing and development costs. The main question addressed in this thesis is therefore how to evaluate the effects of variation on product appearance and perceived quality. The product property controlling these effects is referred to as visual robustness. Visual robustness is the ability of a product to stimulate the same visual experience as the nominal product, despite small variations. It depends only on the product appearance in terms of form and colours of visible parts. A key suggestion is therefore that product appearance should be made robust to deviations in appearance. The visual consequences of variation are thereby dampened instead of eliminated. Particular focus is set on visual robustness to geometrical manufacturing variation, visible in the split-lines between parts. However, a product can be visually robust to different types of deviations from its intended appearance, such as colour deviations occurring during manufacture or to the effects of ageing or wear. As visual robustness controls the effects of deviations on the perceived product quality, special attention is given to this relationship. Different types of aspects that influence the perceived product quality have been identified and categorized. The main result of this thesis is a framework describing visual robustness and perceived quality. To explain what makes products visually robust to geometrical manufacturing variation, the concepts of visual references and amplifying factors are introduced. Two different evaluation methods have also been developed using the suggested framework. The fit complexity evaluation method aims to reduce visual references between different parts in an assembly. The Appearance FMEA is a procedure for enabling detection of different kinds of appearance imperfections, and promotes considerations of visual robustness in early design stages. A study that describes how visual robustness is handled at a Swedish car manufacturer today is also presented.