Design Evaluation Methods

Transcription

1 Design Evaluation Methods Christopher Saldana, Ph.D. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia USA

2 Learning Objectives Understand the importance of evaluation in the design process Identify criteria for evaluation Utilize three levels of evaluation matrices for product development through concept screening and scoring Strategies for Visual/Descriptive Communication of Designs 2

3 Design Tools Current Progress Problem Understanding House of Quality Specification Sheet Function Tree Place Mass on Target Generate Power Transmit Power Hit Target Brake on Target Move to Target Navigate to Target Concept Generation Morphological Chart Design Alternatives Generate Power Gravity Mouse Traps Transmit Power Brake on Target Move to Target Car Hit by Trap Rip Cord Effect Ramp Catapult Friction String Break Anchor Rubber Stopper Weighted Skid Rolling Sliding Projectile Launch Navigate to Target Equal Size Wheels Larger Front Wheels 3

4 Example: Insulin Pen Redesigning the Insulin Pen Customer Wants 1. Dose metering accuracy 2. Portability 3. Durability 4. Ease of handling 5. Readability of settings 6. Ease of use 7. Ease of manufacture 4

5 Example: Insulin Pen Redesigning the Insulin Pen 5

6 Example: Insulin Pen Redesigning the Insulin Pen 6

7 Structured Evaluation Benefits Customer-focused product, competitive design Better product-process coordination, faster product introduction Effective group decision-making Documentation of design process Challenge Need to make informed decisions despite lack of information Selection requires estimation, analysis, prototyping Identify bad concepts versus picking optimal ones 7

8 Structured Evaluation How do we evaluate each of these designs? What criteria do we use for evaluation? What is the best design? 8

9 Concept Selection Strategies Multi-voting: team members vote independently, work together to resolve differences and/or average results Strengths/Weaknesses: list strengths and weaknesses of design concepts, use this to evaluate based on specific opinions Prototype and Test: build or simulate, use empirical or simulated test data! 9

10 Concept Selection Process 10

11 Stages and Types of Concept Selection Concept screening First-level evaluation matrix Concept scoring Second-level evaluation matrix Third-level evaluation matrix 11

12 First Level Evaluation (Pugh Matrix) 1. Identify the criteria for comparison. 2. Select the alternatives to be compared. Alternatives are developed during concept generation. All concepts should be compared at e same level of abstraction. 3. Generate scores. Use a design concept as datum, with all the other being compared to it Evaluate each alternative as better (+), same (S), or worse (-) relative to datum. 4. Compute the total score Sum the total number of (+) s, (-) s, (S) s Compute overall score with +1 for (+) s, -1 for (-) s, 0 for (S) s 5. Note: other variations on scoring in the first-level evaluation Optional scale: +3 if extremely better than datum +2, +1, 0, -1, -2, -3 12

13 First Level Evaluation (Pugh Matrix) + = better than datum; - = worse than datum; S = same as datum 13

14 First Level Evaluation Matrix (example) + = better than datum; - = worse than datum; S = same as datum 14

15 First-Level Evaluation Matrix Ranking depends on choice of datum Does not factor in how much better a specific alternative is compared to others Some criteria may be more important Consider: (i) no datum, (ii) numerical rating, (iii) criteria weighting Second-level evaluation matrix (i), (ii) Third-level evaluation matrix (i), (ii) and (iii) 15

16 Second Level Evaluation Matrix Common Scale: 4 = very good (ideal) 3 = good 2 = adequate 1 = just tolerable 0 = unsatisfactory Alternate Scale: 10 = ideal solution 9 = solution exceeds requirement 8 = very good solution 7 = good solution 6 = good solution with drawbacks 5 = satisfactory solution 4 = adequate solution 3 = tolerable solution 2 = weak solution 1 = very inadequate solution 0 = useless solution 16

17 Second Level Evaluation Matrix 17

18 Third Level Evaluation Matrix 18

19 Third Level Evaluation Matrix 19

20 Summary - Evaluation Matrix Elements Designs rated relative to customer requirements in HOQ Level 1: sum +/-/S relative to datum Level 2: numerical rating Level 3: weighted sum of num. rating Describing this figure in text Which design performed best? Why? Which performed worst? Why? Use numerical information from figure 20

21 Concept Selection Pitfalls Not doing it Running with the first idea Forgetting the customer Evaluation matrix doesn't correspond to HOQ Letting an "experienced" designer make the choices Going by gut feel Letting a manager decide Not buying into the process as a team Ignoring cost 21

22 Design Tools Complete Process Problem Understanding House of Quality Specification Sheet Function Tree Place Mass on Target Generate Power Transmit Power Hit Target Brake on Target Move to Target Navigate to Target Concept Generation Morphological Chart Design Alts. Concept Selection Evaluation Matrices Final Design Generate Power Gravity Mouse Traps Transmit Power Brake on Target Move to Target Car Hit by Trap Rip Cord Effect Ramp Catapult Friction String Break Anchor Rubber Stopper Weighted Skid Rolling Sliding Projectile Launch Navigate to Target Equal Size Wheels Larger Front Wheels 22

23 23 Detailed Design - Communication General organization Primary systems and subsystems Mechanisms, operation/sequencing, construction and materials Performance relative to specifications Clarity in written descriptions Be clear in describing design features. Match words in the body to label text in figures. Avoid describing things that are not shown with evidence or detail. Don t rely on the reader s imagination. 23

24 24 Detailed Design - CAD Important CAD elements: Labels match text explanations Mechatronics (see ME2110 website) Common COTS components (fasteners, etc.) Detail views Dimensions Formatting (text, resolution, annotations) 24

25 Evaluation Tools Summary Understand the importance of evaluation in the design process Identify criteria for evaluation Utilize three levels of evaluation matrices for product development (First-level, Second-level, Third-level) Strategies for Visual/Descriptive Communication of Designs 25

26 Introductory Project Report Goal: conceptual design of a collection device Design tools: HOQ, specification sheet, function tree, morphological chart, alternative generation Detailed design: labels, triggering, mechanisms, sequencing, materials Similar restrictions as final competition (cost, size, power, etc.) 26

27 Introductory Project Report - Layout Cover Page: See book for example cover page. Abstract: One-paragraph summary with key findings/results. Introduction: Restatement of the problem, goal and inherent design challenges in achieving this goal. Problem Understanding: Important customer needs, engineering specifications to address needs, tradeoffs and synergies, functions and concept generation. Design Overview: Presentation of a single concept alternative, detailed description of design including drawings that shows its parts and how it operates. Conclusions: Summary with key results, potential next steps and final thoughts. Appendix: Figures and Tables 27