Embed Size (px)
DESCRIPTION
HSE Teachers’ Workshop Jean Kampe Summer 2011 Delivered by Jonathan Riehl. Design I. Engineering design the process the language . Today’s Focus. What engineers do …. Problem Solution. Design. is a process is modeled in many different ways involves the use of tools - PowerPoint PPT Presentation
Citation preview
HSE Teachers’ Workshop
Jean KampeSummer 2011
Delivered by Jonathan Riehl
Design I
Today’s Focus
Engineering design – the process– the language
What engineers do …
Problem SolutionDesign
Design … in an engineering context
• is a process• is modeled in many different ways• involves the use of tools• has its own language/vocabulary
Engineering Design Process
ProblemDefinition
DetailedDesign
PreliminaryDesign
Conceptual Design
Client’s Need
Documentationof Fabrication Specifications
A Linear Model(Not very realistic)
Ref: Dym, C.L. and Patrick Little, Engineering Design, a Project-Based Introduction, 3 rd Ed., John Wiley & Sons, Inc., 2009, Chapt.2.
Engineering Design Process A Cyclic Model – a much better view
Define Criteria
Develop Alternate Solutions
Gather Information
Revise
Choose a Strategy
Does solution meet requirements?
Test and evaluate
Build a Prototype
Model and Analyze
Documentation of Fabrication Specifications
Yes
No
Start(Define the Problem)
Engineering Design Process A Cyclic Model
Define Criteria
Develop Alternate Solutions
Gather Information
Revise
Choose a Strategy
Does solution meet requirements?
Test and evaluate
Build a Prototype
Model and Analyze
Documentation of Fabrication Specifications
Yes
No
Start(Define the Problem)
Problem Definition
Engineering Design Process A Cyclic Model
Define Criteria
Develop Alternate Solutions
Gather Information
Revise
Choose a Strategy
Does solution meet requirements?
Test and evaluate
Build a Prototype
Model and Analyze
Documentation of Fabrication Specifications
Yes
No
Start(Define the Problem)
Conceptual
Design
Engineering Design Process A Cyclic Model
Define Criteria
Develop Alternate Solutions
Gather Information
Revise
Choose a Strategy
Does solution meet requirements?
Test and evaluate
Build a Prototype
Model and Analyze
Documentation of Fabrication Specifications
Yes
No
Start(Define the Problem)
Preliminary Design
Engineering Design Process A Cyclic Model
Define Criteria
Develop Alternate Solutions
Gather Information
Revise
Choose a Strategy
Does solution meet requirements?
Test and evaluate
Build a Prototype
Model and Analyze
Documentation of Fabrication Specifications
Yes
No
Start(Define the Problem)
Detailed Design
Engineering Design
• Is a cyclic process― real-life design does not happen in a linear sequential way
• Uses tools and procedures― we need to know how to use those tools
• Has its own language ― we need to understand that language
Engineering Design Process A Cyclic Model
Define Criteria
Develop Alternate Solutions
Gather Information
Revise
Choose a Strategy
Does solution meet requirements?
Test and evaluate
Build a Prototype
Model and Analyze
Documentation of Fabrication Specifications
Yes
No
Start(Define the Problem)
Realm of our design focus
Team Activity
Staple Remover Exercise
Design Criteria(a.k.a. Objectives)
Attributes the solution should have(Think in terms of “The design should be ______.”)
• Determined from a manufacturing viewpoint• Weighted by their importance• Used to rate each candidate design
through metrics
Confusing TermsThese two items are very different things in design.
design criterion (a.k.a. “Objective”) n: Designer chosen characteristic of the solution that is related to the problem, such as durability, size, or weight, and used as an evaluation factor. Plural: design criteria
design constraint n: An imposed limit or boundary placed on the design solution by an external source, such as nature, your boss (i.e., company management), a government agency, or other vested stakeholder.
Getting it right …
The “right” constraints, criteria, weights, and metrics are the bases of a good Decision Matrix.
Engineering is diminished and impoverished by a lack of diversity.
At a fundamental level, we all experience the world differently, and those differences in experience are the “gene pool” for creativity.
We will never be able to engineer as well as we could until all stakeholders are adequately represented on engineering design teams.
Paraphrasing William A Wulf (NAE):(Former president of the National Academy of Engineering, 1996-2007)
On the lack of diversity in engineering ...
“There is a real ... cost to that ... it is an opportunity cost ... measured in design options not considered, in needs unsatisfied and hence unfulfilled.* It is measured in ‘might have beens,’ and those kinds of costs are very hard to measure. That doesn’t change the fact that they are very real and very important.”
Quoting Wm. Wulf:
* He’s talking about criteria and constraints that are either not anticipated or not correctly interpreted because the design team does not adequately represent all the stakeholders.
The “right” constraints, criteria, weights, and metrics are the bases of a good Decision Matrix.
Decision Matrix DesignsCriteria
Design A Design B Design C
Criterion 1(weight1)
Ratefor A1
Score for A1
Ratefor B1
Score for B1
Ratefor C1
Score for C1
Criterion 2(weight2)
Ratefor A2
Score for A2
Ratefor B2
Score for B2
Ratefor C2
Score for C2
Criterion 3(weight3)
Ratefor A3
Score for A3
Ratefor B3
Score for B3
Ratefor C3
Score for C3
Criterion 4(weight4)
Ratefor A4
Score for A4
Ratefor B4
Score for B4
Ratefor C4
Score for C4
Score Totals Sum of A scores
Sum ofB scores
Sum ofC scores
Score = Rate x weight Design with highest sum wins!!
Design Tools
• Objective tree• Pair-wise comparison chart• Metrics for Criteria• Decision Matrix
Design Tool Use
• To organize Criteria (a.k.a. Objectives) – Use an Objective Tree
• To assign Weights to Criteria – Use a Pair-wise Comparison Chart
• To Rate Alternate Designs for a given Criterion – Use the metric for the criterion to decide on a
rating
Where does all this get you?
To a Decision Matrix that is generated according to real engineering design procedures instead of guesswork
Tool: The Objective Tree
• Objective Trees help us organize our design objectives (criteria), so that we can use the objectives in other tools.
• Objective trees should be solution independent. – Stop when functions and implementations (which are not objectives)
begin to appear
Safe Ladder
Marketable
Inexpensive Portable Useful Durable
Safe
Stiff Stable
Light in weight Small
Ref: Dym, C.L. and Patrick Little, Engineering Design, a Project-Based Introduction, 3 rd Ed., John Wiley & Sons, Inc., 2009, Chapt.3.
Tool: Pair-wise Comparison Chart
• Compare only objectives emanating from a common node at the same sub-level in the objective tree
• Compare two objectives in a one-on-one fashion: Compare higher-level objectives first
• Know whose perspectives are being assessed.
Results give an approximate subjective judgment of relative value and importance (i.e., weight) rather than a strong meaningful measurement
Safe Ladder
Marketable
Inexpensive Portable Useful Durable
Safe
Stiff Stable
Light in weight Small
Used to help us weight our objectives
Ref: Dym, C.L. and Patrick Little, Engineering Design, a Project-Based Introduction, 3 rd Ed., John Wiley & Sons, Inc., 2009, Chapt.3.
Tool: Pair-wise Comparison Chart
Objectives Cost Portability Usefulness Durability ScoreCost N/A 0 0 1 1
Portability 1 N/A 1 1 3Usefulness 1 0 N/A 1 2Durability 0 0 0 N/A 0
Safe Ladder
Marketable
Inexpensive Portable Useful Durable
Safe
Stiff Stable
Light in weight Small
Example pair-wise Comparison Chart for marketability of the ladder.
Ref: Dym, C.L. and Patrick Little, Engineering Design, a Project-Based Introduction, 3 rd Ed., John Wiley & Sons, Inc., 2009, Chapt.3.
How did we get this? In the cost row, compare cost to portability, then to usefulness, and then to durability.
Enter 1 if cost is more important, 0 if cost is less important , 0.5 if equally important (rare)Add the row entries to get a subjective ranking of criterion importance by “Score.”
Tool: Metrics for the criteria (objectives)Use metrics to measure how well a design alternative
achieves the objective, then rate the designs using those measurements (e.g., use a scale of 1-5 with higher ratings being better).
Good metrics are essential to rate the design alternatives.
To develop metrics– Identify units and scale of something appropriate to
measure about the objective (e.g., $$, kg, or a defendable subjective scale)
– Identify the way to measure the designs in those units (tests, surveys)
– Determine if the measurement is feasible (remember, the designs are only conceptual at this point)
Characteristics of a “good” metric• Measures something directly related to the criterion
in a way that gives you a number or value• Is capable of appropriate level of precision or
tolerance• Is repeatable• Is expressed in understandable units of measure• Promotes clear interpretation
– e.g., criterion = ease of assembly• Possible metrics
Number of partsEstmated time to assemble
Decision Matrix DesignsCriteria
Design A Design B Design C
Criterion 1(weight1)
Ratefor A1
Score for A1
Ratefor B1
Score for B1
Ratefor C1
Score for C1
Criterion 2(weight2)
Ratefor A2
Score for A2
Ratefor B2
Score for B2
Ratefor C2
Score for C2
Criterion 3(weight3)
Ratefor A3
Score for A3
Ratefor B3
Score for B3
Ratefor C3
Score for C3
Criterion 4(weight4)
Ratefor A4
Score for A4
Ratefor B4
Score for B4
Ratefor C4
Score for C4
Score Totals Sum of A scores
Sum ofB scores
Sum ofC scores
Score = Rate x weight Design with highest sum wins!!
Summary
Engineering design:– is a cyclic process– has its own language (criteria/constraints)– uses tools (objective tree, pair-wise
comparison chart, metrics, decision matrix)
