EML4550 2007 1 EML4550 - Engineering Design Methods Concept Selection Settling on one or more promising ideas to pursue to final design Hyman: Chapter.

EML4550 2007 1

EML4550 - Engineering Design Methods

Concept SelectionSettling on one or more promising ideas to pursue to final design

Hyman: Chapter 9, Sec. 9.1 & 9.2Ulrich and Eppinger: Chapters 5 and 6

Dym and Little: Sections 6.1 – 6.3

EML4550 1-07-2

Concept Development Diagram

IdentifyCustomerNeeds

EstablishTargetSpecs

GenerateProductConcepts

SelectProductConcept

RefineSpecs

AnalyzeCompetitiveProducts

PerformEconomicAnalysis

PlanDesign/DevelopmentProject

MissionStatement

ActionPlan

EML4550 1-07-3

Concept Selection

The ‘Concept Generation’ phase spawned many ideas (good and bad) and potential solutions to the problem at hand

How do we select from all these competing concepts?

A ‘method’ is needed to systematically weed out poor concepts and select the best one to proceed with to Final Design

EML4550 1-07-4

Concept Selection Methods

External decision (customers, consultants, etc.) Product “Champion” (strong personal decision) Intuition (no rational method) Pros and Cons (systematic but subjective) Prototype and test (hardware, expensive and time-

consuming) Decision matrices (match characteristics vs. pre-

specified and weighted criteria)

EML4550 1-07-5

Concept Selection Methods (Cont.)

Although all methods are used in practice, most of the ‘subjective’ methods are very case-specific

Decision matrices represent the most ‘rational’ approach to concept selection

We will focus this section on the Decision Matrix method

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Concept Selection: Why a Structured Approach?

A customer-focused product (use the needs as guidelines) A competitive design (do not overlook competing designs) Better product-process coordination (forces manufacturing

issues into the trade-off) Reduced time to market (accelerated ‘downselect’) Effective group decision-making (minimize ‘arbitrary’

decisions and maximize team exposure) Documentation of decision process (not lost in someone’s

‘memory’)

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Concept Selection: Why a Structured Approach? (Cont.)

Need to balance:

Desire to have an expedient ‘downselect’ Expediency: proceed to design sooner Faster time-to market Less cost of ‘carrying’ many concepts forward

Desire ‘to know more’ before deciding Risk of making a mistake (pick a loser) Risk of avoiding a concept because it is new (potential big

winner) Engineers tend to be conservative

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Decision Matrix Method

Stage 1: Concept Screening Apply an initial ‘filter’ to ‘weed out’ bad concepts and

determine likely ‘winners’. Apply some elements of ‘scoring’ for the purposes of ranking only

Stage 2: Concept Scoring Apply weighted criteria to the concepts and proceed with a

quantitative ‘scoring’ system to pick a winner (or winners)

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Decision Matrix Method (Cont.)

Each Stage has 6 steps:

Prepare the selection matrix Rate the concepts Rank the concepts Combine and improve the concepts Select one or more concepts Reflect on the results of the process

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Concept Screening

Selection Criteria A B CCriterion 1Criterion 2Criterion 3Sum “+”Sum “0”Sum “-“Net ScoreRank

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Screening: Step 1 - Prepare Selection Matrix

Develop a set of criteria Customer needs (condensed into criteria) Corporate needs (cost, manufacturing, liability, image, etc.)

Give equal weight to all criteria

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Screening: Step 2 - Rate the Concepts

Give +, -, or neutral rating to each concept based on criteria

Use general notions (no need to get ‘specific’)

Use team consensus (or majority vote)

Refine or split criteria if team consensus is hard to reach

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Screening: Step 3 - Rank Concepts

Add scores and build a ranking

Identify a “benchmark” concept (from ranking or from external products - competition)

Group the concepts into three categories: “possible winners”, “neutral”, and “losers”

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Screening: Step 4 - Combine and Improve Concepts

Are we throwing away as ‘loser’ a ‘good’ concept because it has one or two negatives? Can they be neutralized?

Can two concepts be combined to preserve ‘better than’ qualities while neutralizing ‘worse than’ items? Can we derive a concept that takes the ‘best of both worlds’?

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Screening: Step 5 - Select one or more concepts

If there is a ‘clear’ winner, then select it and proceed with it MISSION ACCOMPLISHED

However, usually more than one concept will survive the screening

Number of concepts to carry forward will depend on resources and time available

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Screening: Step 6 - Reflect on the Process

Did we achieve consensus? Were all the team members treated equally? No

trampling? Did we avoid personal agendas? Department

politics?

It is very disruptive to team spirit to ‘drop’ a concept that someone was championing.

Grudges linger for a long time within a team

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Concept Screening

Selection Criteria A B CCriterion 1 + 0 +Criterion 2 0 - +Criterion 3 0 + 0Sum “+” 1 1 2Sum “0” 2 1 1Sum “-“ 0 1 0Net Score 1 0 2Rank 2 3 1

An example

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From Screening to Scoring (quantitative)

Selection Criteria A A B B C C% R S R S R S

Criterion 1Criterion 2Criterion 3

Score

Rank

Proceed?

R = Rank, S = Score

EML4550 1-07-19

Scoring: Step 1 - Prepare Selection Matrix

Using the same selection criteria used in screening give relative weight to each (must add to 100%) It is possible to slightly modify the criteria in light of the

surviving concepts Weights to each criterion are given by team consensus or

related to customer needs

An example

EML4550 1-07-20

Scoring: Step 2 - Rate the Concepts

As with screening, give a ‘score’ to each concept based on a ‘quantitative’ (yet still subjective) numbering scale as follows:

Relative Performance1 - Much worse than reference concept2 - Worse than reference concept3 - Same as reference concept4 - Better than reference concept5 - Much better than reference concept

EML4550 1-07-21

Scoring: Step 3 - Rank the Concepts

Compute score for each concept

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criterionofweightw

criteriaofnumbern

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EML4550 1-07-22

From Screening to Scoring

Selection Criteria A A B B C C% R S R S R S

Criterion 1 10 4 .4 2 .2 5 .5Criterion 2 30 2 .6 1 .3 3 .9Criterion 3 60 4 2.4 3 1.8 3 1.8

Score 3.4 2.3 3.2

Rank 1 3 2

Proceed? Y N Y

R = Rank, S = Score

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Scoring: Step 4 - Combine and Improve Concepts

As before, can concepts be combined to arrive at a better solution? Looking at the concepts in the new light of ‘scoring’ can

encourage the team to improve on the initial ideas

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Scoring: Step 5 - Select One or More Concepts

The final selection is never easy

Do ‘parametric’ studies by assigning different weight distributions and see which concepts come on top on each try

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Scoring: Step 6 - Reflect on the Process

Are we ready to proceed with the ‘winning’ concept?

Did the method facilitate the selection?

Can the method be improved?

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Concept Selection: Caveats!

Decomposition of product quality Failure to capture relationship among criteria

Subjective criteria Methodical, but still high content of subjectivity

Where to include cost Derived from customer needs, but how about ‘manufacturing’

the product, not all parameters known

Selecting elements of complex systems Can a complex concept be reduced to a set of simpler concepts?

How about interactions between sub-concepts?

Applying concept selection throughout the development process The same approach can apply to the selection of concepts within

a design effort when developing sub-systems of a larger system

EML4550 1-07-27

Concept Selection: Implications to Project

If many concepts are considered, perform a screening

Record results of screening (and criteria used) Decision matrix for the selection and scores for each

concept Presentation of the ‘winning’ concept