A Systematic Approach to Planning for a Designed Industrial

G precision and accuracy each type of factor is

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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 helpful-as 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 (cols. 4-5). “held constant” factors nuisance f...
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