concept selection pugh analysis-3

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Ken Youssefi UC Berkeley, ME Dept. 1 Concept Evaluation & Selection

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Ken Youssefi UC Berkeley, ME Dept. 1

Concept Evaluation & Selection

Ken Youssefi UC Berkeley, ME Dept. 2

Concept Selection (Evaluation)

• Minimize the possibility of misrepresenting a solution that may be effective.

Engineer is not familiar with the technology.

• Fully consider the different ramifications of a decision.

For example, not considering the costumer’s need

may lead to the product failing in the marketplace.

Concept selection is one of the most critical decision-making exercises in product development.

To make decisions effectively, one must basically carry out two steps.

Ken Youssefi UC Berkeley, ME Dept. 3

Concept Selection

• Design EvaluationsOccur at all phases of product evaluation, from concept to detailed design phases. Structured decision-making methods are needed.

• Quality of InformationLow quality of information - how well each alternative design would meet criterion cannot be fully understood.

High quality of information - The alternative solutions are well understood.

Ken Youssefi UC Berkeley, ME Dept. 4

Estimation

• Imagine the concept to estimate

• Construct a simple model

• Use the model to provide a comparison with a known quantity

• Judge whether the estimated quantity compares with the known quantity

The estimation process should be used to eliminate concepts that are not technically feasible.

Ken Youssefi UC Berkeley, ME Dept. 5

Example – can crusher

Alternate concept – dropping a weight on the can

Imagine the concept: flow of energy

Simple model: F = (mass)(acceleration) + weight

Known quantity: 200 lb of force needed to crush the can (from a simple crush test)

Choose 30 lb weight, and calculate the height needed to exert 200 lbs to crush the can 5 inches.

V 2 = 2gH, a = V 2/2S, F = WH/S + W = 200, Height = 28.33”

Judge: is the height practical?

Ken Youssefi UC Berkeley, ME Dept. 6

Concept Selection (Evaluation)

• Technology Readiness AssessmentIf a technology is to be used as part of a product design, it must be mature enough that its use is a design issue, not a research issue.

• GO/NO-GO screeningEach concept must be compared to the customer requirements in an absolute fashion. Each customer need must be transformed into a question to be addressed to each concept. The questions should be answerable as either yes or maybe (go), or no (no-go). This evaluation will weed out concepts quickly and will help generate new ideas.

Ken Youssefi UC Berkeley, ME Dept. 7

Concept Selection

• Based on the Decision-Matrix (Pugh’s method)The method is very effective for comparing concepts that are not refined enough for direct comparison with the engineering requirements.

Ken Youssefi UC Berkeley, ME Dept. 8

Concept Selection – Pugh’s Method

• Step 1 – Select the Criteria for ComparisonThe list of criteria must be developed from the customer needs and engineering specifications. All team members should contribute in making the list. The list then should be debated until consensus is reached.

The method is an iterative evaluation that tests the completeness and understanding of requirements, and quickly identifies the strongest concept.

The method is most effective if each member of the design team performs it independently. The results of the comparison will usually lead to repetition of the method, with iteration continued until the team reaches a consensus.

Ken Youssefi UC Berkeley, ME Dept. 9

Concept Selection – Pugh’s Method

• Step 2 – Select the Concepts to be ComparedThese alternatives should be those that proceed from the concept generation. It is important that all the concepts to be compared be at the same level of abstraction.

• Step 3 – Generate the ScoreA favorite concept should be selected as a datum. All other designs are compared to it relative to each customer need. For each comparison, the concept being evaluated is judged to be either better than (“+” score), about the same (“s” score), or worse than the datum (“-” score).

Ken Youssefi UC Berkeley, ME Dept. 10

Concept Selection – Pugh’s Method

• Step 4 – Compute the total scoreThree scores are generated, the number of plus scores, the number of minus scores and the total.

If a concept has a good overall score or a high “+” score, it is important to notice what strengths it exhibits, that is, which criteria it meets better than datum. Same for “-” score.

If most concepts get the same score on a certain criterion, examine that criterion closely. More knowledge may have to be developed in the area of the criterion. Or, it may be ambiguous, is interpreted differently by different members.

Ken Youssefi UC Berkeley, ME Dept. 11

Bike Splashguard Concepts

Ken Youssefi UC Berkeley, ME Dept. 12

Pugh’s Method – Example Bike splashguard

Initial decision matrix

Best overall score, design II (17), should be used as a datum concept for the next step.

Concepts IV and V are rated as next best designs.

Ken Youssefi UC Berkeley, ME Dept. 16

Summary• Estimation is a critical skill to develop and can help in

quickly eliminating weak concepts• The feasibility of the concepts is based on the design

team’s knowledge. It is often necessary to augment this knowledge with research and development of simple models.

• In order for a technology to be used in a product, it must be ready.

• A go/no-go screening based on customer needs helps to eliminate some of the concepts quickly.

• The decision matrix (Pugh’s method) provides means of comparing and evaluating concepts. The method gives insight into strong and weak areas of the concepts.