Concept Selection Facts About Concept Selection

Identify
Customer
Needs
Concept Selection
Topic 7
ME EN 4000 – Engineering Design I – Concept Selection 1
Select Concepts in Relation to Concept
Development Activities
Establish
Target
Specifications
Timeline of Concept Development
Generate
Product
Concepts
Select
Product
Concepts
Test
Product
Concepts
Perform Economic Analysis
Benchmark Competitive Products
Build and Test Models and Prototypes
Set
Final
Specifications
Plan
Downstream
Development
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 3
Product Design and Development
Karl T. Ulrich and Steven D. Eppinger
4th edition, Irwin McGraw-Hill, 2008.
Chapter Table of Contents
1. Introduction
2. Development Processes and Organizations
3. Product Planning
4. Identifying Customer Needs
5. Product Specifications
6. Concept Generation
7. Concept Selection
8. Concept Testing
9. Product Architecture
10. Industrial Design
11. Design for Manufacturing
12. Prototyping
13. Product Development Economics
14. Managing Projects
ME EN 4000 – Engineering Design I – Concept Selection 2
Facts About Concept Selection
• Concept selection is a convergent process.
• Concept selection is also an iterative process that does
not always produce the dominant concept immediately.
• Better concepts may be found through recombination of
pre-screened concepts.
• Recombination may temporarily enlarge the number of
available concepts.
• The final concept is chosen after several iterations.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 4

Concept Development Funnel
concept generation
concept screening
concept scoring
concept testing
ME EN 4000 – Engineering Design I – Concept Selection 5
Selection Methods (contd.)
• Multivoting. Each member of the team votes for a set
number of projects.
– Maybe: Depends on how objectively the team members vote..
• Pros and cons. The team lists strengths and
weaknesses of each concept and makes a choice based
upon group opinion.
– Yes: The decision is group based and (presumably) objective.
• Prototype and test. The organization builds and tests
prototypes of each concept, making a selection based
upon test data.
– No: Too costly for hundreds of concepts.
– Yes: Final concept selection.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 7
Selection Methods
• External decision. Concepts are turned over to the
customer or other external entity.
– No: Customer should not be bothered with hundreds of
concepts.
– Maybe: Final concept selection.
• Product champion. An influential member of the
product development team chooses a concept based on
personal preference.
– No: Group consensus is preferable both for confidence and
harmony.
• Intuition. The concept is chosen by its feel. No explicit
criteria are used. The concept simply seems better.
– No: Design decisions need to be objective and justifiable.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 6
Selection Methods (contd.)
• Decision matrices. The team rates each concept
against pre-specified selection criteria, which may be
weighted.
– Yes: Preferred method.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 8

Two Stage Process
1. Concept Screening
– Quick, approximate evaluation aimed at
producing a small number of viable
solutions.
2. Concept Scoring
– Much more careful analysis of a relative
small number of concepts in order to choose
the single best option.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 9
Concept Screening: Steps 4-6
• Step 4 – Combine and Improve Concepts.
– Is there a generally good concept which is degraded by a single
bad feature?
– Are there two concepts which can be combined to preserve the
“better than” qualities while canceling the “worse than” features?
• Step 5 – Select One or More Concepts.
– After the team has gained sufficient understanding of each
concept and its relative quality, a small number of concepts are
chosen for further analysis and refinement (and perhaps testing).
• Step 6 – Reflect on the Results and Process.
– All team members should be comfortable with the outcome.
Differences between team members may indicate missing
criteria or rating errors.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 11
Concept Screening: Steps 1-3
• Step 1 – Prepare the Selection Matrix.
– Enter concepts and criteria into the matrix.
– Select reference concept (industry standard, main competitor,
current product). Its performance is rated using 0’s.
• Step 2 – Rate the Concepts.
– Concepts that perform better than the reference are rated with +’s.
– Concepts that perform similarly compared to the reference are
rated with 0’s.
– Concepts that perform worse than the reference are rated with –’s.
• Step 3 – Rank the Concepts.
– Sum up “better than”, “same as”, and “worse than” and enter the
sum for each category in the lower rows of the matrix.
– The net score is calculated by subtracting the number of “worse
than” from the number of “better than”.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 10
Outpatient Syringe
Concept A – Master Cylinder
Each concept should include a sketch and short description
All concepts should include a similar level of detail
Displaced fluid from master cylinder actuates pusher. Upon release, sealed
fluid cavity is filled with more fluid if necessary.
Dose is set by length of stroke.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 12

Outpatient Syringe
Concept B – Rubber Brake
Pushnut grips shaft when pushed but releases when being pulled (rubber
clutch offers resistance).
Dose is set by length of stroke.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 13
Outpatient Syringe
Concept D – Plunge Stop (Reference)
Stroke length is set by screwing outer sleeve forward, thereby increasing the
spacing between plunger and outer sleeve
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 15
Outpatient Syringe
Concept C - Ratchet
Ratchet engages pusher when plunger is being pushed and disengaged is
plunger is being pulled.
Dose is set by length of stroke.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 14
Outpatient Syringe
Concept F
Stroke length is set through angle of operating lever.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 16

Outpatient Syringe
Concept G – Dial Screw
Set dose by turning knob. This energy is stored in a spring.
Actuate by releasing the lead screw, which will turn according to the
rotational energy supplied by the spring.
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 17
Concept generation
Pair-up with a team mate
In upper right of your page
•Names of students
•Project Name
•TA Name
• List some criteria that you might judge your
designs on
CONCEPT VARIANTS
SELECTION
CRITERIA
A B C D E F G REF.
Ease of Handling 0 0 – 0 0 – – 0
Ease of Use 0 – – 0 0 + 0 0
Number Readability 0 0 + 0 + 0 + 0
Dose Metering + + + + + 0 + 0
Load Handling 0 0 0 0 0 + 0 0
Manufacturing Ease + – – 0 0 – 0 0
Portability + + – – 0 – – 0
PLUSES 3 2 2 1 2 2 2
SAMES 4 3 1 5 5 2 3
MINUSES 0 2 4 1 0 3 2
NET 3 0 –2 0 2 –1 0
RANK 1 3 7 5 2 6 4
CONTINUE? Yes Yes No No Yes No Yes
ME EN 4000 – Engineering Design I – Concept Selection 19
Example: Concept Screening
CONCEPT VARIANTS
SELECTION
CRITERIA
A B C D E F G REF.
Ease of Handling 0 0 – 0 0 – – 0
Ease of Use 0 – – 0 0 + 0 0
Number Readability 0 0 + 0 + 0 + 0
Dose Metering + + + + + 0 + 0
Load Handling 0 0 0 0 0 + 0 0
Manufacturing Ease + – – 0 0 – 0 0
Portability + + – – 0 – – 0
PLUSES 3 2 2 1 2 2 2
SAMES 4 3 1 5 5 2 3
MINUSES 0 2 4 1 0 3 2
NET 3 0 –2 0 2 –1 0
RANK 1 3 7 5 2 6 4
CONTINUE? Yes Yes No No Yes No Yes
ME EN 4000 – Engineering Design I – Concept Selection 18
Outpatient Syringe
Concept DF
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 20

Outpatient Syringe
Concept G+
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 21
Example: Concept Scoring
Concepts
A
(reference)
DF E G+
Master Cylinder Lever Stop Swash Ring Dial Screw+
Weighted
Weighted
Weighted
Weighted
Selection Criteria Weight Rating Score Rating Score Rating Score Rating Score
Ease of Handling 5% 3 0.15 3 0.15 4 0.2 4 0.2
Ease of Use 15% 3 0.45 4 0.6 4 0.6 3 0.45
Readability of Settings 10% 2 0.2 3 0.3 5 0.5 5 0.5
Dose Metering Accuracy 25% 3 0.75 3 0.75 2 0.5 3 0.75
Durability 15% 2 0.3 5 0.75 4 0.6 3 0.45
Ease of Manufacture 20% 3 0.6 3 0.6 2 0.4 2 0.4
Portability 10% 3 0.3 3 0.3 3 0.3 3 0.3
Total Score 2.75
3.45
3.10
3.05
Rank
4
1
2
3
Continue? No Develop No No
ME EN 4000 – Engineering Design I – Concept Selection 23
Concept Scoring
• Similar to concept screening.
• Criteria are weighted according to their importance.
• Suggested rating scale:
Relative Performance
Much worse than reference
Worse than reference
Same as reference
Better than reference
Much better than reference
Rating
ME EN 4000 – Engineering Design I – Concept Selection 22
1
2
3
4
5
Source: Ulrich K, Eppinger S, Product Design and Development
Concept generation
Pair-up with a team mate
• List some areas of your project that you will
want to generate concepts to be evaluated
– e.g., steering linkages, transmission designs…
CONCEPT VARIANTS
SELECTION
CRITERIA
A B C D E F G REF.
Ease of Handling 0 0 – 0 0 – – 0
Ease of Use 0 – – 0 0 + 0 0
Number Readability 0 0 + 0 + 0 + 0
Dose Metering + + + + + 0 + 0
Load Handling 0 0 0 0 0 + 0 0
Manufacturing Ease + – – 0 0 – 0 0
Portability + + – – 0 – – 0
PLUSES 3 2 2 1 2 2 2
SAMES 4 3 1 5 5 2 3
MINUSES 0 2 4 1 0 3 2
NET 3 0 –2 0 2 –1 0
RANK 1 3 7 5 2 6 4
CONTINUE? Yes Yes No No Yes No Yes
ME EN 4000 – Engineering Design I – Concept Selection 24

Concept Scoring Example: Outpatient Syringe
Selection Criteria
Ease of of handling
Ease of use
Readability of of settings
Dose metering accuracy
Durability
Ease of of manufacture
Portability
Continue?
Weight
Total
Rank
A
(Reference)
Master
Cylinder
Rating
Concepts Concepts
DF
G+ E
Lever Stop
Dial Swash Screw+ Ring
Weighted
Rating
Weighted
Rating
Weighted
Score
Score
Score
Source: Ulrich K, Eppinger S, Product Design and Development
ME EN 4000 – Engineering Design I – Concept Selection 25
Caveats
• Decomposition of concept quality. Assumption: the
overall quality equals the sum of the individual qualities.
This may not be the case where relationships between
individual criteria are complex.
• Subjective criteria. Some selection criteria, particularly
those related to aesthetics are highly subjective. Use
external reviewers for such criteria.
• Where to include cost. The overall cost are one of the
dominant factors determining the economic success.
While “ease of manufacturing” is not a customer need, it
brings cost into the equation.
ME EN 4000 – Engineering Design I – Concept Selection 26