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Quality... Part III: a listening

© Dimitris Vayenas

...continued from Part II

There are a number of undesirable and uncontrollable factors that can cause deviation from the target values, which are known as external and internal noise factors.

Variations of the operating environment (such as temperature and humidity) are examples of external noise factors. The internal noise factors are:
1. Deterioration i.e. the wearing out of parts caused by friction and the loss of spring resilience
2. Manufacturing process imperfections.

So we come to conclude that the broad purpose of the overall quality system is to produce a product that is robust with respect to all noise factors.

This robustness will ensure the predictable behavior of the product. Those who followed my past editorials will remember the redundancy concept in good engineering and this series of editorials on quality gives me the opportunity to explain better why this is so. I believe that the concept of robustness will ensure the redundancy of the product and its consideration by the user/customer not as the result of exhaustive engineering thought and practice but only as means to an end.

Remember the days the VCR was introduced in the market? At that time most people were "button-illiterate" and the, nowadays, tedious task of programming a recording was considered then to be an achievement as well as the cause of great frustration for the majority of the VCR owning public. At that time the designers of the VCR had not complied well with what I call "redundancy" engineering (nevertheless I guess that at the time they had no feasible and pragmatic alternative to make that process any easier-and it seems that the first video owners were a kind of guinea pigs for the VCR manufacturers that helped them in future efforts in designing their products and not just their VCRs - but allow me not to deviate further from the discussion on quality - in a later editorial the Human Interface in audio visual products these will be discussed in detail).

In order to achieve robustness during the product design and the production engineering phases, the Taguchi theory suggests the three steps that must be followed:
1. System Design: Here the intentioned life cycle of the product is considered. For example, during the research and development phase, system design involves the development of a prototype design and determination of materials parts, components, and assembly systems. In the production engineering phase, the determination of the manufacturing process is involved.
2. Parameter design: In this step the levels (values) of controllable factors are selected in order to minimize the effect of noise factors on the functional characteristics of the product.

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