Supplemental Text Material
The Taguchi Approach to Robust Parameter Design
Throughout this book, we have emphasized the importance of using designed
experiments for product and process improvement.
Today, many engineers and scientists
are exposed to the principles of statistically designed experiments as part of their formal
However, during the 1960-1980 time period, the principles of
experimental design (and statistical methods, in general) were not as widely used as they
In the early 1980s, Genichi Taguchi, a Japanese engineer, introduced his approach to
using experimental design for
Designing products or processes so that they are robust to environmental conditions.
Designing/developing products so that they are robust to component variation.
Minimizing variation around a target value.
Note that these are essentially the same objectives we discussed in Section 11-7.1.
Taguchi has certainly defined meaningful engineering problems and the philosophy that
recommends is sound.
However, as noted in the textbook, he advocated some novel
methods of statistical data analysis and some approaches to the design of experiments
that the process of peer review revealed were unnecessarily complicated, inefficient, and
In this section, we will briefly overview Taguchi's philosophy
regarding quality engineering and experimental design.
We will present some examples
of his approach to parameter design, and we will use these examples to highlight the
problems with his technical methods.
As we saw in Chapter 12 of the textbook, it is
possible to combine his sound engineering concepts with more efficient and effective
experimental design and analysis based on response surface methods.
Taguchi advocates a philosophy of quality engineering that is broadly applicable.
considers three stages in product (or process) development: system design, parameter
design, and tolerance design.
the engineer uses scientific and
engineering principles to determine the basic system configuration.
For example, if we
wish to measure an unknown resistance, we may use our knowledge of electrical circuits
to determine that the basic system should be configured as a Wheatstone bridge.
are designing a process to assemble printed circuit boards, we will determine the need for
specific types of axial insertion machines, surface-mount placement machines, flow
solder machines, and so forth.
stage, the specific values for the system parameters are
This would involve choosing the nominal resistor and power supply values
for the Wheatstone bridge, the number and type of component placement machines for
the printed circuit board assembly process, and so forth.
Usually, the objective is to