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HSE Teachers’ Workshop Jean Kampe Summer 2011 Delivered by Jonathan Riehl

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HSE Teachers’ WorkshopJean KampeSummer 2011Delivered by Jonathan Riehl

Design I

Engineering design

the process

the language

Problem Solution

Design

is a process

is modeled in many different ways

involves the use of tools

has its own language/vocabulary

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, 3rd Ed., John Wiley & Sons, Inc., 2009, Chapt.2.

Define Criteria

Gather Information

Choose a Strategy

Start

(Define the Problem)

Engineering Design Process

Develop Alternate Solutions

Revise

No

A Cyclic Model – a much better view

Does solution meet requirements?

Build a Prototype

Model and Analyze

Yes

Test and evaluate

Documentation of Fabrication Specifications

Problem Definition

Define Criteria

Gather Information

Choose a Strategy

Start

(Define the Problem)

Engineering Design Process

Develop Alternate Solutions

Revise

No

A Cyclic Model

Does solution meet requirements?

Build a Prototype

Model and Analyze

Yes

Test and evaluate

Documentation of Fabrication Specifications

Define Criteria

Gather Information

Choose a Strategy

Start

(Define the Problem)

Engineering Design Process

Develop Alternate Solutions

Conceptual

Design

Revise

No

A Cyclic Model

Does solution meet requirements?

Build a Prototype

Model and Analyze

Yes

Test and evaluate

Documentation of Fabrication Specifications

Define Criteria

Gather Information

Choose a Strategy

Start

(Define the Problem)

Engineering Design Process

Develop Alternate Solutions

Revise

No

A Cyclic Model

Does solution meet requirements?

Build a Prototype

Model and Analyze

Yes

Preliminary

Design

Test and evaluate

Documentation of Fabrication Specifications

Define Criteria

Gather Information

Choose a Strategy

Start

(Define the Problem)

Engineering Design Process

Develop Alternate Solutions

Revise

No

A Cyclic Model

Does solution meet requirements?

Build a Prototype

Model and Analyze

Yes

Test and evaluate

Documentation of Fabrication Specifications

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

Realm of our design focus

Define Criteria

Gather Information

Choose a Strategy

Start

(Define the Problem)

Engineering Design Process

Develop Alternate Solutions

Revise

No

A Cyclic Model

Does solution meet requirements?

Build a Prototype

Model and Analyze

Yes

Test and evaluate

Documentation of Fabrication Specifications

Staple Remover Exercise

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 constraintn: An imposedlimit 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.

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.

Score = Rate x weight Design with highest sum wins!!

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

- 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

To a Decision Matrix that is generated according to real engineering design procedures instead of guesswork

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

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

Example pair-wise Comparison Chart for marketability of the ladder.

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

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)

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

Score = Rate x weight Design with highest sum wins!!

Engineering design:

- is a cyclic process
- has its own language (criteria/constraints)
- uses tools (objective tree, pair-wise comparison chart, metrics, decision matrix)