Whole number factors in DOE (MiniTab)

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• #37818

mcleod
Member

We will use the old Stat-a-pult for this example. When setting up a DOE in MiniTab, is there anyway to specify that the factors will stay as whole numbers only. Example, The Stat-a-pult has 4 adjustments. The first adjustment on the Stat-a-pult (A) has 5 settings (1,2,3,4,5). The second (B) has 5. The third (C) has 4. The forth (D) has a value from 10 to 50 degrees. I need MiniTab to see factors A,B & C as whole numbers so that the response optimizer outputs realistic settings ( A=2, B=3, C=4, D=37.7635). As it stands now, I get linear responses (A=2.34, B=3.63, C=2.773, D=37.3453). I realize I can derive the needed settings by using the expression MiniTab provides, but is there and automatic way of doing this?
Thanks.

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#112220

Tim F
Member

Scott,I don’t think there is a really elegant way but here are two options.1) If you are doing a response surface, set the alpha value to “2”. Then you will get 5 evenly spaced values. By default these are -2,-1,0,1,2, but you could change them to anything you want, like 1,2,3,4,5.The downside, is that ALL factors will have five evenly spaced values. So C would be problematic.2) Create a full factorial design with 5 levels for A, 5 for B, 4 for C and, say, 5 for angle (10,20,30,40,50). This will be an unmanageable 5x5x4x5 = 500 runs.
Then create a custom response surface using those four factors.
Finally do “Select Optimal Design” using however many runs you want. Voile! A custom design to match your needs. Downside. It is a few extra steps and doesn’t produce a “standard” design, but it will force integers for the levels and find a relatively optimal solution at the same time.
Tim F

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