Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.1/ INTRODUCTION
How can a
rough conceptual idea evaluated?
Information is often
incomplete, uncertain and evolving
Evaluation involves: Comparison AND Decision
making
To make a
valid comparison concepts must have the same
level of abstraction.
EXAMPLE:
Function: To move some object
Concepts
To use fluid pressure
Linear electric motor.
=> Change “to use fluid pressure” to “hydraulic piston” to
levelize the abstraction.
Absolute comparison:
Concept is
compared to a set of
requirements.
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.2/ Comparison Based on Absolute Criteria
Evaluation based on judgment of feasibility of the design.
Categorize concepts into three groups.
1. Not feasible (Ask “Why is it not feasible?” )
2. Conditional - might work (if something else happens)
3. Looks as if it will work
Evaluation based on assessment of technology readiness.
(a) Can the technology be manufactured with known processes? (b) Are the critical parameters that control the function identified?
(c) Are the safe operating latitude and sensitivity of the parameters known? (d) Have the failure modes been identified?
(e) Does hardware exist that demonstrates positive answers to the above four questions?
Evaluation based on go-no-go screening of the customer requirements.
Each customer requirement should be translated into questions that can be addressed by each concept.
Answers:
Yes (go)
Maybe (go) (work on weak areas)
No (no-go)
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.3/ Pugh Concept Selection Method
Compare each concept to a reference concept.
Determine the criterion to base the comparison.
For each criterion, determine if the concept in question is
better than,
poorer than,
or about the same as the reference concept.
STEP 1:
Choose the criteria by which the concepts will be evaluated.
STEP 2:
Formulate the decision matrix.
STEP 3:
Clarify the design concepts.
STEP 4:
Choose the datum concept.
STEP 5:
Run the matrix.
STEP 6:
Evaluate the ratings.
STEP 7:
Establish a new datum and rerun the matrix.
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.3/ Pugh Concept Selection Method
STEP 8
: Examine the selected concept for improvement opportunities
-Consider each criterion that performed worse than the datum.
- Keep asking questions about the factors detracting from the merits of an
idea.
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.3/ Pugh Concept Selection Method
E XAMPLE 7.9
Four concepts for improving the design of an on/off switch in a right-angle drill are: -Concept A is a modest change to the existing switch, and will be the DATUM. -Concept B adds three buttons for on/off/ and reverse.
- Concept C is a track and slider design,
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.3/ Pugh Concept Selection Method
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.3/ Pugh Concept Selection Method
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.4/ Weighted Decision Matrix
Determining weighting factors
Direct Assignment: The team decides how to assign 100 points between the
different criteria according to their importance. Dividing each criterion’s score by 100 normalizes the weights. This method is followed by design teams where there are many years of experience designing the same product line.
Objective Tree: Weighting factors can be determined by using a hierarchical objective. Better decisions regarding preferences will be made when the comparisons are made at the same level in the hierarchy.
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.4/ Weighted Decision Matrix
EXAMPLE 7.10
A heavy steel crane hook, for use
in supporting ladles filled with
molten steel as they are
transported through the steel mill,
is being designed. Two crane
hooks are needed for each steel
ladle. These large, heavy
components are usually made to
order in the steel mill machine
shop when one is damaged and
needs to be replaced. Three
concepts
(1)built up from flame-cut steel
plates, welded together;
(2)built up from flame-cut steel
plates, riveted together;
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
7.5/ Analytic Hierarchy Process (AHP)
A more structured way of constructing a Weighted Decision Matrix.
Well-suited for problems when design objectives have an
hierarchical structure.
Helps with deciding on weights of each criteria.
Uses pair-wise comparison when finding weighting factors for
evaluation criteria.
Uses pair-wise comparison when finding ratings of concepts against
the design criteria.
AHP Process for Determining Criteria Weights
- Complete criteria comparison matrix [C] using 1–9 ratings described in Table 7.6.
- Normalize the matrix [C] to give [NormC].
- Average row values. This is the weight vector {W}.
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
Chapter 7- Concept Evaluation and Selection
Chapter 7-
Concept Evaluation and Selection
