HSE Teachers’ Workshop

Jean KampeSummer 2011

Delivered by Jonathan Riehl

Design II

Today’s Focus

Defining Design Space

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 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)

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 HSE design focus

Design Tools from Design I*(Remember the staple remover exercise)

• Objective tree• Pair-wise comparison chart• Metrics for Criteria• Decision Matrix

* Review slides are available at the end of this presentation.

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

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!!

Getting it right …

The “right” constraints, criteria, weights, and metrics are the bases of a good Decision Matrix.

This is the key piece in explaining the value of diversity to engineering design.

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.

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 Terms

These 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.

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)

Design II focus

Tool: Morphological Charts a.k.a.“Morph charts”

• Help us define our design space – the number and the kinds of alternate solutions that are possible through different approaches.

• Example – Think about designing a new beverage container. – What must the container do (functions)? – How will it do those things (means)?

More design language

More Design Language

• Functions – in very general terms, what the design must do

• Means – in a strategy sense, how the design will accomplish the function

• Implementations – specific ways to meet objectives that end choice-making

Morph Chart

Function Means

Contain liquid can bottle pouch box

Allow drinking access

screw cap straw insert unfolding top pull tab

Display product information

labels container shape

Example morph chart for design of new beverage container

How did we build this morph chart?List the design functions in the left-most column, and put the meansto achieve the functions in the columns to the right.How many alternate designs paths do we get from this chart?Maximum = 4 x 4 x 2 = 32, but some of these are not feasible (e.g., a canwith an unfolding top) and must be excluded. We can expand our designspace by adding more functions or means for the container, and we canshrink our design space by eliminating any means that will not allow thedesign to meet constraints.

Ref: Dym, C.L. and Patrick Little, Engineering Design, a Project-Based Introduction, 3rd Ed., John Wiley & Sons, Inc., 2009, Chapt.5.

Design Space Adjustments …

If our morph chart gives us an overwhelming number of alternatives for our project,

• we can pick a general approach to pursue and not consider other paths – this is called “Choosing a strategy” in our cyclic model.

If our design space is fairly manageable,• we reduce the number of alternatives by

– excluding all incompatible alternatives (e.g., a can with an unfolding top)

– applying design constraints to eliminate means

Example: Toaster

• Functions:

• Means for ______________:

• Implementation for _____________:

Summary

Engineering design:– is a cyclic process– has its own language (criteria/constraints)– uses tools (objective tree, pair-wise

comparison chart, metrics, decision matrix, morph charts)

Extra Slides

The slides that follow are from Design I (or Workshop 2009) and are provided just for convenient review.

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, 3rd 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, 3rd Ed., John Wiley & Sons, Inc., 2009, Chapt.3.

Tool: Pair-wise Comparison Chart

Objectives Cost Portability Usefulness Durability Score

Cost N/A  0 0 1 1

Portability 1  N/A 1 1 3

Usefulness 1 0  N/A 1 2

Durability 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, 3rd 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