Transcript Design Process-4 (concept selection)

EML4550 - Engineering Design Methods
Concept Selection
Settling on one or more promising ideas to pursue to final
design
Hyman: Chapter 9, Sec. 9.1 & 9.2
Ulrich and Eppinger: Chapters 5 and 6
Dym and Little: Sections 6.1 – 6.3
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Concept Development Diagram
Identify
Customer
Needs
Mission
Statement
Establish
Target
Specs
Analyze
Competitive
Products
Generate
Product
Concepts
Select
Product
Concept
Perform
Economic
Analysis
Refine
Specs
Plan
Design/
Development
Project
Action
Plan
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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
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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 timeconsuming)
 Decision matrices (match characteristics vs. pre-specified
and weighted criteria)
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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:
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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
Criterion 1
Criterion 2
Criterion 3
Sum “+”
Sum “0”
Sum “-“
Net Score
Rank
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A
B
C
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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
Criterion 1
Criterion 2
Criterion 3
Sum “+”
Sum “0”
Sum “-“
Net Score
Rank
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An example
A
+
0
0
1
2
0
1
2
B
0
+
1
1
1
0
3
C
+
+
0
2
1
0
2
1
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From Screening to Scoring (quantitative)
Selection Criteria
A
% R
A
S
B
R
B
S
C
R
C
S
Criterion 1
Criterion 2
Criterion 3
Score
Rank
Proceed?
R = Rank, S = Score
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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
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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 Performance
1 - Much worse than reference concept
2 - Worse than reference concept
3 - Same as reference concept
4 - Better than reference concept
5 - Much better than reference concept
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Scoring: Step 3 - Rank the Concepts
 Compute score for each concept
n
s j   wi rij
i 1
s j  score _ of _ concept_ j
n  num ber_ of _ criteria
wi  weight _ of _ criterion
rij  rating _ of _ concept_ j _ on _ criterion _ i
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From Screening to Scoring
Selection Criteria
Criterion 1
Criterion 2
Criterion 3
Score
Rank
Proceed?
R = Rank, S = Score
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A A B B
% R S R S
10 4 .4 2 .2
30 2 .6 1 .3
60 4 2.4 3 1.8
3.4
2.3
1
3
Y
N
C C
R S
5 .5
3 .9
3 1.8
3.2
2
Y
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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
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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
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