Evaluating_Concepts_Feb15 - [email protected]

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Unformatted text preview: [email protected] 647-883-0149 Evaluating Concepts Assume that you have a well defined problem Assume that you have used a variety of methods to generate some conceptual solutions Question: How do we choose the best conceptual solution? Reminder: Characteristics of the ideal solution Obviously performs F, meets C, maximizes O Generally it is: Simple to implement, not in concept simplicity leads to reliability Feasible Capital cost limitations Parts availability Comprehensive Addresses all DFX concepts Human Factors Safety Manufacturability Durability Maintainability Life Cycle Intellectual Property Aesthetics 1 Techniques for evaluation Dieter Section 5.9 Comparison then Decision - compare -compare to requirements use this to screen solutions to create a subset of feasible solutions Absolute screening --Feasibility - Technological readiness - can solution be implemented using existing technology - Evaluating F,O,C Methods of Relative Screening Client Decides - may not have expertise to make the decision Technical Guru Decides - individual bias? - group evaluation is best Consensus - if there is one winner - risk is that the alternatives are not adequately evaluated Voting - must be structured. 2 Example: Corkscrew design. 6 concepts all meet the functional requirement: Apparatus for removing wine from bottle. Objectives: 1) As safe as possible 2) Minimum Force 3) Minimal instruction intuitive. 4) Inexpensive 5) Reliable, low/no maintenance. Picture Credits: Ashby, M.F., Materials Selection in Mechanical Design, 2nd Ed, ButterworthHeinemann, London, 1999. Wikipedia: Corkscrews, www.HomeDepot.ca Pugh's Concept Selection Method: Relative screening of feasible concepts 1. 2. 3. 4. 5. List the criteria. Simplest implementation is to list the objectives as evaluation criteria. (e.g. ease of use, aesthetics, safety, etc.) Enter criteria as row headings in decision matrix. Discuss and clarify the design concepts. Combine to generate hybrid concepts if needed. Enter the concepts as columns in the matrix. Choose one reference or datum concept, against which others will be compared. Choose one that is likely to be quite good. For each criterion, determine if the concept is better (+), worse (-), or about the same (s) as the datum. Consensus required, but since the decision is precisely defined, consensus is easier to reach. Sum up the ratings qualitatively, and approximately. Numbers are not used to prevent simple summation and rejection of concepts. Eliminate the weak and irredeemable concepts. Establish a new datum and re-run the process. Iterate. 6. 7. 8. Your Job Run a Pugh's selection procedure to choose the optimal solution from those specified. Assume that each criteria (objective) is equally important. Choose the basic corkscrew as the datum point initially. 3 First pass Second Pass Problems with this example We did not weight the objectives properly. Safety is always a priority objective, if not a constraint. Can weight the objectives by pair-wise comparison. 4 Weighted Decision Matrix Compute the relative weight of each objective or criterion used for judging. Numerical score on 5 or 11 point scale for each concept for each criterion. Product of score * weight = rating. Sum of ratings used to evaluate. Finding Weights 0 - inadequate 1- weak 2- satisfactory 3- good 4- excellent Weighted Decision Matrix 5 Conclusions Even if you think that one alternative is obviously better - you must still provide some reasoning in CDS Structured decision making tools can help. 6 ...
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