chapter 1. mechanical design process - yuan ze...

Copyright 2010. All rights reserved.1

What is Design? Design Starts with a Problem.

In 1946, Bell Telephone Labs (AT&T) asked designer Henry Dreyfuss to improve the

phone used in millions of American homes and offices.

1. Thinking: What needed to be improved ?

Chapter 1. Mechanical Design Process

Receiver easily falls over the

hook

Handset needs to fit better

in cradle

Awkward appearance

and proportions

Easily toppled

Have to use two hands

Can’t cradle handset

between ear and shoulder

Can’t read the number

while dialing

Material easy to break and

chip

Too

heavy

“Candlestick” and “Series 300” telephone

Awkward cord


2. Sketching the idea

Designers used sketches to envision, develop, and evaluate new ideas.

Design Example: Telephone Improvement (I)


3. Making models

Designers created models of wood and clay to give form to their ideas for

the phone’s handset, base, and dial. They also used models and drawings

to share their ideas with the clients, AT&T.

Design Example: Telephone Improvement (II)


4. Evaluation

Based on the models, designers and clients could see how the phone would

fit the user’s hand and ear. They then created prototypes to test the

performance of the whole phone. Together, they determined the final design.

5. Manufacturing

Designers proposed a new kind of plastic for the final product because it’s

more efficient and cost-effective in manufacturing. Also, this plastic was

lightweight but durable and came in many colors. AT&T agreed and mass-

produced 25 million phones from this one design. They called it “Series

500”.

Design Example: Telephone Improvement (III)

Design Ends with a Solution.

Design is a problem solving process.


Knowledge Needed for Mechanical Design

The route from “problem” to “solution” can be along many different paths.

Designer’s knowledge of the process and the problem’s domain determines

the path.

Knowledge used in the design process includes domain knowledge and design

process knowledge, how to effectively integrate the domain knowledge to

generate the solution.

Culvethouse[1993] classified design into 4 types: Repeat order design, variant

design, innovative design, and strategic design.

Design process plays an important role to the success of development of a

product. Design process influences performance, quality, cost, and developing

time of the product.


“T-shaped” People (IDEO CEO Tim Brown)

T-shaped people have two kinds of characteristics, hence the use of the letter

“T” to describe them.

The vertical stroke of the “T” is a depth of skill that allows them to contribute

to the creative process. That can be from any number of different fields: an

industrial designer, an architect, a social scientist, a business specialist or a

mechanical engineer.

The horizontal stroke of the “T” is the disposition for collaboration across

disciplines. It is composed of two things.

First, empathy. It’s important because it allows people to imagine the problem

from another perspective- to stand in somebody else’s shoes.

Second, they tend to get very enthusiastic about other people’s disciplines, to the

point that they may actually start to practice them.

T-shaped people have both depth and breadth in their skills.

Inter-disciplinary Trans-disciplinary


IDEO’s Design Thinking

“Design thinking is an approach that uses the designer’s sensibility and

methods for problem solving to meet people’s needs in a technologically

feasible and commercially viable way. In other words, design thinking is

human-centered innovation.” —Tim Brown


Design Process Models

Most researches in design process try to establish a structured model to describe or

facilitate design.

Design process models are usually categorized into descriptive models,

prescriptive models, and cognitive models [Finger and Dixon, 1989; Cross, 1994].

• According to Cross, descriptive models simply describe the sequences of

activities that typically occur in designing.

• Prescriptive models attempt to prescribe a better or more appropriate pattern of

activities. They usually offer a more algorithmic, systematic procedure for the

whole design team to follow.

Cross[1994] presented a simple descriptive design process model:

Exploration Concept generation Evaluation Communication

Ullman[1992] stated that the life cycle of a product consists of 6 phases, and the

first 3 phases focus on design:

Specification development/planning Conceptual design Product design

Production Service Product retirement


Ullman’s Prescriptive Design Process Model

市場

新科技

子問題

成立設計小組

了解設計問題

計畫安排

產生設計記錄

劃分子系統

階段一：規範建立/規劃

設計回顧

產生設計記錄

更新計畫

建立子系統

概念產生概念評估

中斷計畫

設計回顧

子問題

設計回顧

中斷計畫

階段二：概念設計

產生產品雛形

評估產品產生設計

記錄

中斷計畫子問題

階段四：製造

階段五：服務

階段六：淘汰

階段三：產品設計

建立子裝配


Specification Development/Planning (I)

The Design Process Paradox (Ullman [1992])


1. Identifying the customers

• Those who have certain needs to the products are all customers. Besides consumers

or users, the designer’s own management, manufacturing personnel, sales staff, and

service personnel must also be considered as customers.

2. Determining customer requirements

• Market investigation, questionnaires,observing product in use, and interviewing lead

users

• Types of customer requirements:

Performance: functional performance and spatial constraints

Appearance

Time

Cost: capital and unit

Manufacture/assembly: quantity to be manufactured, company capability

Standards

Safety

Environment issues

Specification Development/Planning (I)


3. Determining relative importance of the requirements

• Some requirements are “musts”, and some requirements are “wants”.

Specify the “musts” and determine the “wants” in a 1-5 scale.

4. Competition Benchmarking

• The competitors include similar products available in the market, as well as

any alternative methods that can achieve the same functions.

5. Transferring customer requirements into measurable engineering requirements

• A product specification includes a “metric” and a “value”.

• There are standard specification items in products such as computers,

automobiles, audios, etc. These items should be considered first.

6. Setting engineering target for the design

• Quality Function Deployment, QFD

Specification Development/Planning (II)


三

、

決

定

顧

客

需

求

之

間

相

對

重

要

性

比

重

二、了解顧客需求

四

、

競

爭

對

手

的

評

估

五、建立設計規格項目

六、設定設計目標

設計

名稱

比

重

尺

寸

裝

配

時

間

重

量

輕

壽

命 …規

格

Ａ

規

格

Ｂ

競

爭

者

1

競

爭

者

2

重量 * ‧ 1 4

需求 A 2 ‧ 1 2

需求 B 4 ‧ 4 2

性

能

需

求需求 C 2 ‧ 1 2

美觀 1 ‧ 3 4外

觀需求 D 2 1 3

易裝配 4 ‧ … 3 2

需求 E * ‧ 3 1

需求 F 1 1 4

製

造

組

裝需求 G 3 3 1

.

.

.

.

.

.

.

.

安全 * ‧ 4 4

成本 3 1 3

單位 m sec kg 年 … # #

目標 6× 6× 7 <60 <45 6 3 2

競爭者 1 5× 8× 7 <130 45 5 3 1

競爭者 2 7× 6× 9 >100 76 3 5 2

Quality Function Deployment, QFD

chapter 1. mechanical design process - yuan ze...

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