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Unformatted text preview: and measurability (e.g., precision and accuracy). Each type of factor
is discussed in detail in following sections. A descrip- PLANNING FOR A DESIGNED INDUSTRIAL EXPERIMENT Figure 4. Jet Engine impeller (side view; z axis is vertical, x axis is horizontal, and y axis is into the page):
2. Diameter of Wheel; 3. Inducer Blade Height; 4. Exducer Blade Height; 5. Z Height of Blade. 1. Height of Wheel; tion of the diagram is as follows: 4.1 1. Control variables are measurable, controllable,
and thought to be (very) influential.
2. Held-constant factors are controlled.
3. Nuisance factors are uncontrolled factors (either
they cannot be controlled, or they are allowed to
vary). There are two reasons it helps to know the allowed
ranges and nominal values of control variables under
current use. First, the degree to which historical process data can be used to gain relevant knowledge
may be revealed. This is discussed in Section 4.2.
Second, the experimenter should select a range large
enough to produce an observable effect and to span
a good proportion of the operating range, yet not
choose so great a range that no empirical model can
be postulated for the region, as discussed in Section
4.3. In some, less mature experimental situations,
there may be no well-defined “current use,” in which
case trial runs before or during experimentation are
they are with response variables. In discussing different variables and factors the
team may choose to reassign variables from one group
to another, and this is part of the ordinary process
for planning a designed experiment. For the CNCmachining problem, the control-variable information
was developed as shown in Table 3; those below the
space are considered to be of secondary importance.
Similar to the response variables sheet, the control
variables sheet solicits information about (a) current
use (col. 2), (b) ability to measure and set (col. 3),
and (c) knowledge sought through experimentation
“held constant” factors nuisance
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- Fall '14
- The Land