1. Engineering Design GE121 Finding Answers to the Problem Part V
Lecture 13C

2. Connecting Concepts to Objectives: Selecting the BEST Designs
Can be done by many different approaches
Some Formal and Rigorous
Others are simple – Example: Simply the alternative that the team likes the best!
Use Objectives (and Constraints) to compare
Process usually begins by examining alternatives in terms of Constraints
Alternatives that don’t satisfy ALL constraints can be immediately rejected
Different clients have different Values (weights on objectives)
May end up choosing different designs for same problem

3. Numerical Evaluation Matrices
Following Examples show Numerical Evaluation Matrices for two different clients
Notice that calculated Weights (importance of each objective) are different for each – possibly due to different corporate values
Constraints dictate that two options are eliminated - Glass bottle with twist-off cap, and Aluminum can with pull-tab (don’t meet constraints)
Compare / Contrast for your own benefit

4. Numerical Evaluation Matrices (continued)
Fig. 5.4 p110 (2nd Edition)

5. Numerical Evaluation Matrices (continued)
Fig. 5.5 p111 (2nd Edition)

6. Weighted Checkmark Method
Simpler, Qualitative version of Numerical Evaluation Method
High / Medium / Low Priority
3 Checkmarks for High, 2 for Medium, 1 for Low
Metrics are taken as 1 if greater than 0.5 and 0 if less than 0.5
Binary Method is susceptible to temptation to ‘Cook’ results to achieve desired outcome

7. Weighted Checkmark Method (continued)
Fig. 5.6 p112 (2nd Edition)

8. Best of Class Chart
Rank each alternative for how it meets the objective, with 1 being the best down to 5 for the worst (assuming 5 alternatives)
Ties allowed, but split rankings (two alternatives tied for 1st would each get (1+2)/2 = 1.5)
Lowest score is best, unless used with previous weighting scheme (then use 5 as best and 1 as worst for ranking, and Highest score wins)
Advantages – Ranks alternatives rather than just binary, and is easy
Disadvantages – Opinion-based, may also be tempted to ‘fudge’ results

9. Caution on All 3 Methods
No excuse for accepting results blindly and uncritically
Treat relatively close scores for 2 alternatives as equal
If results were unexpected, check expectations/ metrics/ weights
Check to see if evaluations were really fair
Examine alternatives rejected based on constraints to see if it was really valid

10. Concept Screening
These same processes can be used earlier in the design process (especially weighted checkmark) to do Informal Concept Screening

11. Activity
Continue working on your 4 (or 3 if you’re a group of 3) design concepts (all 4 must meet all constraints)
Make sure that you have Metrics and Weighting factors ready to go for ALL of your Objectives – you will need them next week to make a decision as to which design is best
Continue to work on your Final Report and your Presentation weekly as you cover each step of the process!