June 14, 2009
June 14, 2009
June 17, 2009
14.283.1 - 14.283.7
Black Box Design of Experiments Abstract
The faculty at Grand Valley State University, a primarily undergraduate engineering school, use black boxes to teach basic design of experiments techniques. The black boxes are literally wooden cubes painted black with four knobs projecting from the surface for the adjustable variables. One of the knobs was a dummy and did not affect the response. The measured response is the height of a metal rod projecting from the top of the box. Anecdotal evidence suggests that the black boxes were an effective teaching aid.
Design of Experiments (DOE) is a useful tool for practicing engineers1,2,3. It can be applied to both processes and products. DOE is a very efficient methodology for generating a great deal of useful data with a minimum of expended time and resources. Teaching DOE fits the coupled lecture and lab model for covering material. The lecture portion of a class is useful for conveying the necessary knowledge regarding statistics, orthogonal arrays, variable selection and a variety of other items. Typical labs using DOE range from optimizing injection molding processes to paper airplane flight time. Injection molding is a mature technology and has been the subject of a great deal of research. A design of experiments intended to characterize a new product or machine type can be very efficient. Past experience may be used to make decisions about which interactions and main effects are important. Similarly for the paper airplane example. The students can use their intuition to guide them when selecting variables and levels. These examples address the situation where a great deal is already known about the product or process and fine tuning is required. Situations where very little is known about the variables influencing the process or product variables and their possible interactions. This second area is the focus for using the black boxes for DOE. The black boxes are simple mechanisms to simulate an unknown or unfamiliar process.
Two black boxes were constructed and are shown in Figures 1 and 2. Each box has four color coded knobs for the inputs and the length of the steel rod projecting from the box is the response variable. The blue and green knobs (top left and top right) were connected to the horizontal rubber band. The pink knob (bottom left) was connected to the vertical rubber band. Both rubber bands were connected to the vertical rob to create a response. The yellow knob (bottom right) was a dummy knob and was not connected to the rubber band/metal rod assembly. The boxes were inexpensive and were constructed from plywood, rubber bands and common fasteners.
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