HSE Teachers’ Workshop

Design I

Jean Kampe Summer 2011 Delivered by Jonathan Riehl

Today’s Focus

Engineering design – the process – the language

What engineers do …

Solution

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 Linear Model (Not very realistic) Client’s Need Problem Definition Conceptual Design Preliminary Design Documentation of Fabrication Specifications Detailed Design 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 Start (Define the Problem) Gather Information Define Criteria Choose a Strategy Develop Alternate Solutions

No

Revise Does solution meet requirements?

Yes

Documentation of Fabrication Specifications Test and evaluate Model and Analyze Build a Prototype

Engineering Design Process

A Cyclic Model Problem Definition Start (Define the Problem) Gather Information Define Criteria Choose a Strategy Develop Alternate Solutions

No

Revise Does solution meet requirements?

Yes

Documentation of Fabrication Specifications Test and evaluate Model and Analyze Build a Prototype

Engineering Design Process

A Cyclic Model Start (Define the Problem) Gather Information

No

Define Criteria Revise Choose a Strategy Conceptual Design Develop Alternate Solutions Does solution meet requirements?

Yes

Documentation of Fabrication Specifications Test and evaluate Model and Analyze Build a Prototype

Engineering Design Process

A Cyclic Model Start (Define the Problem) Gather Information Define Criteria Choose a Strategy Develop Alternate Solutions

No

Revise

Yes

Does solution meet requirements?

Documentation of Fabrication Specifications Test and evaluate Model and Analyze Build a Prototype Preliminary Design

Engineering Design Process

A Cyclic Model Start (Define the Problem) Gather Information Define Criteria Choose a Strategy Develop Alternate Solutions

No

Revise

Yes

Does solution meet requirements?

Documentation of Fabrication Specifications Model and Analyze Test and evaluate Detailed Design Build a Prototype

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

Realm of our design focus A Cyclic Model Start (Define the Problem) Gather Information Define Criteria Choose a Strategy Develop Alternate Solutions

No

Revise Does solution meet requirements?

Yes

Documentation of Fabrication Specifications Test and evaluate Model and Analyze Build a Prototype

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 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.

Getting it right …

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

Decision Matrix

.

Paraphrasing William A Wulf (NAE):

(Former president of the National Academy of Engineering, 1996-2007)

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.

Quoting Wm. Wulf:

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.

very important.” * 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 * 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

Criteria Designs Criterion 1 (weight1) Criterion 2 (weight2) Criterion 3 (weight3) Criterion 4 (weight4) Score Totals Design A Rate for A1 Rate for A2 Rate for A3 Rate for A4 Score for A1 Score for A2 Score for A3 Score for A4 Sum of A scores Design B Rate for B1 Rate for B2 Rate for B3 Rate for B4 Score for B1 Score for B2 Score for B3 Score for B4 Sum of B scores Design C Rate for C1 Rate for C2 Rate for C3 Rate for C4 Score for C1 Score for C2 Score for C3 Score for C4 Sum of C 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

Criterion Alternate Designs for a given – 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 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

Used to help us weight our objectives • 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 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

Example pair-wise Comparison Chart for marketability of the ladder. Objectives Cost Portability Usefulness Durability Cost N/A 1 1 0 Portability 0 N/A 0 0 Usefulness 0 1 N/A 0 Durability 1 1 1 N/A Score 1 3 2 0 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.” Ref: Dym, C.L. and Patrick Little,

Engineering Design, a Project-Based Introduction, 3 rd Ed

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

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 parts  Estmated time to assemble

Decision Matrix

Criteria Designs Criterion 1 (weight1) Criterion 2 (weight2) Criterion 3 (weight3) Criterion 4 (weight4) Score Totals Design A Rate for A1 Rate for A2 Rate for A3 Rate for A4 Score for A1 Score for A2 Score for A3 Score for A4 Sum of A scores Design B Rate for B1 Rate for B2 Rate for B3 Rate for B4 Score for B1 Score for B2 Score for B3 Score for B4 Sum of B scores Design C Rate for C1 Rate for C2 Rate for C3 Rate for C4 Score for C1 Score for C2 Score for C3 Score for C4 Sum of C 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)