Biomechanical
Design(051:083)
Lecturer:
- Tae-Hong Lim, Ph.D.
1420 Seamans Center
335-5810 (office); talim@engineering.uiowa.edu (email)
- David Wilder, PhD and Nicole Grossland, PhD
Office Hours:
M, W, F: 4:00 – 5:00 PM
Appointment
Pre-requisites:
57:007 Statics
57:019 Mechanics of Deformable Bodies
51:050 Biomechanics
1
Text and Grading

Text:
“The Mechanical Design Process, 3rd Edition”
David G. Ullman
McGraw-Hill (ISBN: 0-07-237338-5)

Grading:
15% Homework and Quiz
20% Individual Design Notebook
10% Reverse engineering report
40% Team Project
15% Final Exam
– Final exam will be a short answer exam covering the terminology and concepts studied
throughout this course
2
Individual Design Notebooks


You are to keep a design notebook for use in this course.
This is to be a spiral bound notebook.
–
–


Every page must be numbered at the beginning of the term.
No pages can be removed and each page must be dated and initialed when used.
All work related to this course (homework and design project) will be entered into
this note book.
Each notebook will be collected at the end of the term and graded on the number of
“quality entries” it contains.
–
–
A quality entry is a significant sketch or drawing of some aspect of design; a listing of
functions, ideas or other features; a table such as morphology or decision matrix; or a
page of text.
Unintelligible entries are not quality entries.
3
Team Project

Design Team:
–
–

Design teams will be organized by the instructor.
Team members will determine the leader (CEO).
Team Project:
–
–
Each team will determine a design problem (new invention or modification) related to
biomechanical devices through discussion with the instructor.
The team project will be considered completed by obtaining final product documentation
(drawings, part list with specified materials, and assembly instructions).
• No final product in physical form is required.

Each team should record the whole history of the design in the Product Development
File (PDF).
4
Documents in the PDF
Problem Appraisal Phase
Conceptual Design Phase
Product Design Phase
Understanding the Problem:
1. Description of Customers
2. Customer’s Requirements
3. Weighting of Customer’s
Requirements
4. Competition’s Benchmarks vs.
Customer’s Requirements
5. Engineering Requirements
6. Competition’s Benchmarks vs.
Engineering Requirements
7. Engineering Targets
Concept Generation:
13. Function Decomposition
14. Literature and Patent Search
Process and Results
15. Function-Concept Mapping
16. Sketches of Overall Concepts
Product Generation:
21. Usable off-the-shelf Products
22. Shape Development Driven by
Function
23. Materials Selection
24. Manufacturing Process
Selection
Planning the Project
8. Task Titles
9. Objectives of Each Task
10. Personnel Required for Each
Task
11. Time Required for Each Task
12. Schedule of Tasks
Concept Evaluation and
Assessment of Tech. Readiness:
17. Identification of Failure Modes
18. Identification of Critical
Parameters
Concept Selection:
19. Decision Matrices to Determine
Best Concepts
20. Analsysi, Experiments and
Models Supporting Evaluation
Product Evaluation:
25. Comparison to Engineering
Function
26. Functional Changes Noted
27. Design for Assembly Evaluation
28. Cost Evaluation
29. Analysis, Experiments and
Models Supporting Evaluation
Final Product Documentation:
30. Layout Drawings
31. Detail Drawings of
Manufactured Parts
32. Parts List (Bill of Materials)
33. Assembly Instructions
* The file is to be maintained by the group in a binder. This PDF, when completed, is effectively a
final report. It will be graded on completeness and quality of both the design and the
5
documentation itself.
Biomechanical Design

Design:
–
–
–
–
–

Deliberate purposive planning
A mental project or scheme in which means to an end are laid out
A preliminary sketch or outline showing the main features of something to be executed: DELINEATION
The arrangement of elements or details in a product or work of art
The creative art of executing aesthetic or functional designs
Biomechanical Design:
–
Design something related to biomechanics, such as:
Biomechanical devices
•
•
•
Medical devices: orthopedic implants, scissors, scalpers, staplers, etc.
Exercising devices: treadmill, weight-lifting, helmets, wrist-guards, etc.
Rehabilitation devices: wheel-chairs, canes, etc.
Biomechanical activities
•

Exercises for fitness or strengthening body parts
Biomechanical design includes:
–
–
Development (or invention) of new biomechanical stuffs; and
Modification of existing biomechanical stuffs
6
What will we learn in this class?

Typical design process:
–
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–
–
–
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Techniques helping generate better quality designs in less time:
–
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
Concurrent engineering
Computer aided drawing
Legal and regulation issues:
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
Identification of design problems
Design
Evaluation of the design
Decision making
Final report
Safety and liability
Patent, FDA, CE, and UL
Importance of communication of design data:
–
–
Records of design data, design process, and final report
Oral presentations
7
The Life of A Product
*Process of idea development,
production, use, and end of product
life.
*The whole process must be
considered in the design process.
8
Design Process

What is the design process?
–

Design process is the organization and management of people and the information they develop in the
evolution of the product.
Why study the design process?
–
Design process determines the efficiency of new product development.
•
–
The design process needs to improved consistently and executed for developing better products because:
•
•
–

85% of the problems with new products not working as intended, taking too long to bring to market, or costing
too much are the result of poor design process.
There is a continuous need for new, cost-effective, high-quality products.
Most products require a team of people from diverse areas of expertise to develop an idea into hardware.
We will study the design process to get the tools to develop an efficient design process regardless of the
product being developed.
3 types of knowledge used by designers:
–
Knowledge to generate ideas
•
–
Knowledge to evaluate ideas
•
–
Experience and natural ability
Experience and formal training (focus of most engineering education)
Knowledge to structure the process
•
•
Non-domain-specific knowledge
What we will study in this class
9
History of the Design Process


One person, with sufficient knowledge of the physics, materials and manufacturing
processes to manage all aspects of the design and construction of the project, could
design and manufacture an entire product in the past.
By the middle of the 20th century, products and manufacturing processes had become
too complex for one person to have sufficient knowledge or time to focus on all
aspects of the evolving product.
–

Different groups of people for marketing, design, manufacturing and overall management
One-way communication over the wall:
–
–
What is manufactured is not often what the customer had in mind.
Inefficient, costly, and greater possibility for making poor-quality products
10
History of the Design Process

Simultaneous Engineering (in late 1970s and early 1980s):


Simultaneous development of the manufacturing process with the evolution of the product by assigning
manufacturing representatives to be members of design team
Concurrent Engineering (in late 1980s):




–
Integrated Product and Process Design (IPPD) in the 1990s
A greater refinement in thought about what it takes to efficiently develop a product
Primarily focusing on the integration of teams of people, design tools and techniques, and information about
the product and the processes used to develop and manufacture it.
10 Key Features of Concurrent Engineering
 Focus on the entire product life (chap 1)
 Use and support of design team (chaps 3 and 5)
 Realization that the processes are as important as the product (chaps 4 and 5)
 Attention to planning for information-centered tasks (chap 5)
 Careful product requirements development (chap 6)
 Encouragement of multiple concept generation and evaluation (chaps 7 and 8)
 Awareness of the decision-making process (chap 8)
 Attention to designing in quality during every phase of the design process (throughout)
 Concurrent development of product and manufacturing process (chaps 9-13)
 Emphasis on communication of the right information to the right people at the right time (throughout)
A key point of concurrent engineering is a concern for information.
–
Drawings, plans, concept sketches, meeting notes, etc.
11
Controllable Variables in Concurrent Engineering
12
Overview of the Design Process
13
Design Problems
What size SAE grade 5 bolt should be
used to fasten together two pieces of
1045 sheet steel (4 mm thick and 6 cm
wide) which are lapped over each other
and loaded with 100 N?
Design a joint to fasten together two
pieces of 1045 sheet steel (4 mm thick
and 6 cm wide), which are lapped over
each other and loaded with 100 N?
- Well defined analysis problem finding
the diameter of the bolt
Ill-defined design problem with number
of potential problems
-How to connect the sheets? (Bolted,
glued, welded, etc.?)
-Disassembly required later?
-What working environment?
-etc.
HWK#1: Change a problem from one of your engineering science classes into a design problem by
changing as few words as possible. Do your home work in your design notebook. Due14
is
one week.
Design problems have many satisfactory solutions and no clear
best solution.
Design problems
- are ill-defined;
- have no correct answer;
- have no clear best answer.
Design process knowledge is based
upon the domain knowledge.
Mechanical design problems begin
with an ill-defined need and result in
a piece of machinery that behaves in
a certain way.
PARADOX:
A designer must develop a machine
that has the capabilities to meet
some need that is not fully defined.
15
Basic Actions of Design Problem Solving

ESTABLISH the need or realize that there is a problem to be solved.
–

PLAN how to solve the problem.
–

Evaluation techniques also depend on the design phase; there are differences between the
evaluation techniques used for concepts and those used for products.
DECIDE and acceptable solutions
–
–

Concept Generation vs. Product Generation
EVALUATE the alternatives by comparing them to the design requirements and to
each other.
–

Formal efforts to understand new design problems continue throughout the process. Each
new subproblem requires new understanding.
GENERATE alternative solutions.
–

Planning occurs mainly at the beginning of a project. Plans are always updated because
understanding is improved as the process progresses.
UNDERSTAND the problem by developing requirements and uncovering existing
solutions for similar problems.
–

New needs also can be established throughout the design effort because new design
problems arise as the product evolves. Design of these details poses new subproblems.
Decision making requires a commitment based upon incomplete evaluation.
Decision requires a consensus of team members.
COMMUNICATE the results
–
Communication of the information developed to others on the design team and to
management is an essential part of concurrent design.
16
Basic Terminologies used to describe the Design Process

“Communication” as a one key feature of concurrent engineering
–

Communication depends on a shared understanding of terminology.
Function:
–
–
What a product or a system is supposed to do;
Described using action verbs and a noun describing the object on which the
action occurs:
• Record images; quantify the blood pressure; fix an unstable spine segment; etc.

System:
–
A grouping of objects that perform a specific function;
• Shutter system; timer system; CD-R system; cooling system; etc.
–
–
A system can be decomposed into another subsystems
or further
individual
In general,
during theinto
design
process, the
components (or parts).
function of the system and its
first. a
After
Multiple systems can be assembled into a higher decomposition
level systemare
orconsidered
further into
the function has been decomposed to the
final product.
finest subsystems possible, assemblies and
 Feature: the important form and function aspects
of mechanical
components
are developeddevices
to provide
these functions.
• dimensions, material properties, shapes, or functional
details (speed of opening and
closing for shutter system)
17
Decomposition of design disciplines
Function, Behavior, and Performance

Function:
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
Form:
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–

describes what a device does.
But, function provides no information about how a device accomplishes the function.
The term “form” relates to any aspect of physical shape, geometry, construction, material,
or size.
provides some information on how a device accomplishes the function.
Behavior and Performance in association with Function.
- Function is the desired output from a
system yet to be designed.
- Behavior is the actual output, the response
of the system’s physical properties to the
input energy or control.
- Performance is the measure of function
and behavior – how well the device does
what it is designed to do.
- A clear picture of desired performance
should developed in the beginning of the
design process.
18
Types of Mechanical Design Problems

Selection Design:
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
Configuration Design:
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

How to assemble all the components into the completed product
Parametric Design:
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Finding values for the features that characterize the object being studied or that meet the
requirements
–
Design a cylindrical tank: V = r2l, determine r and l for known V
Original Design:
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
choosing one item (or more) from a list of similar items
choosing a bearing, bolt, motor, etc. from a catalog
Design a process, assembly or component not previously in existence
Redesign:
–
–
Redesign of an existing product
Most design problems are redesign problems since they are based on prior,
similar solutions. Conversely, most design problems are original as they contain
something new that makes prior solutions inadequate.
19
Languages of Mechanical Design
A mechanical object can be described by:
 Semantic language:
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Graphical language:
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
drawing of the object
Sketches, scaled representations of orthogonal drawings, or artistic renderings
Analytical Language:
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–

Verbal or textual representation of the object
“bolt” or “The shear stress is equal to the shear forces on the bolt divided by the
x-sectional area.”
Equation, rules, or procedures representing the form of function of the object
 = F/A
Physical Language:
–
Hardware or physical model of the project
- In most cases, the initial need is expressed in a semantic language as a
written specification or a verbal request by a customer or supervisor, and the
final result of the design process is a physical product.
20
Design, State, Constraints and Decision

Design State:
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
Collection of all the knowledge, drawings, models, analyses and notes thus far
generated
In the beginning, design state is just the problem statement
Design Constraints:
–
Factors limiting the design process
• Examples: size, strength of material, corrosion properties, anatomy, etc.
–
–
In the beginning, the design requirements effectively constrains the possible
solutions to a subset of all possible product designs.
Two sources of constraints added during the design process:
• Designer’s knowledge of mechanical devices and the specific problem being solved
• Result of design decisions

Design Decision:
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Continuous comparison between design state and the goal (requirements for the
product given in the problem statement)
• The difference controls the process.
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
Design is the successive development and application of constraints until only
one unique products remains.
Each design decision changes the design state.
The design progresses in increment punctuated by design decisions.
21
The Value of Information
*The most valuable information is the decisions that are communicated to others.
22
Design as Refinement of Abstract Representations
See Table 2.2 for levels of abstraction in
other languages.
Graphical Refinement
23
Information-processing Model of Human Problem Solving
Information-Processing System used by the human mental system
in solving any type of problem
24
Chunks of Information
25
Information-processing Model of Human Problem Solving
Types of Knowledge that might be in a chunk of information:
–
General knowledge
• Information that most people know and apply without regard to a specific domain
– “red is a color.” “4 is bigger than 3.”
• Gained through everyday experiences and basic schooling
–
Domain Specific Knowledge:
• Information on the form or function of an individual object or a class of objects
– Bolts are used to carry shear or axial stress
– The proof stress of a grade 5 bolt is 85 kpsi.
• Gained from study and experience in the specific domain
– It may take about 10 years to gain enough specific knowledge to be considered an expert in a domain
–
Procedural Knowledge:
• The knowledge of what to do next
– If there is no answer to problem X, then decompose X into two independent subproblems of x1 and x2 that
are easier to solve.
• Gained mostly from experience
• Required for solving mechanical design problems
26
Implications of the Information-processing Model

The size of STM is a major limiting factor in the ability to solve problem.
–
–
–
To accommodate this limitation, breakdown problems into finer and finer subproblems
until we can “get our mind around it”
– in other word, manage the info in our STM
Human designers are quite limited although our expertise about the constraints and
potential solutions increases and our configuration of chunks becomes more efficient as we
solve problems.
These limitations would preclude our ability to solve complex problems.
27
Mental Processes that Occur during Design

Understanding the problem:
–
–

A problem is understood by comparing the requirements on the desired function to information in the
long-term memory.
Every designer’s understanding of the problem is different, we need to develop a method to ensure that
the problem is fully understood with minimal bias from the designer’s own knowledge.
Generating a solution:
–
–
Use the information stored in LTM that meets the design requirements.
If no solution found from LTM, then use a three step approach
•
•
•
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
–
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Evaluation requires comparison between generated ideas and the laws of nature, the capability of
technology and the requirements of the design problem itself.
Evaluation requires modeling the concept to see how it performs.
The ability to model is usually a function of knowledge in the domain.
Deciding:
–

Creative part of this approach is in knowing how to decompose and recombine cognitive chunks
Evaluating the solution:
–

Decompose the problem into subproblems
Try to find partial solutions to the subproblems
Recombine the subsolutions to fashio a total solution
A decision is made at the end of each problem-solving activity to accept the generated and evaluated
idea or to address another topic that is related to the problem.
Controlling the design process:
–
Path from initial problem to solution seemed random.
28
Problem-Solving Behavior


A person’s problem-solving behavior affects how problems are solved individually and has a significant
impact on team effectiveness.
Four Personal-Problem Solving Dimensions (or styles):
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Individual Problem-solving Style:
•
•
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Individual Preference to work with Facts or Possibilities:
•
•
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Facts oriented people:
– literal, practical, and realistic
– 75 % of Americans, 66% of top executives, 34% of all engineering students
Possibility oriented people:
– Like concepts and theories and look for relationship between pieces of information and meaning of the information
Objectivity with which decisions are made:
•
•
–
Introvert:
– Solve problem internally (reflective); a good listener; think and speak; enjoy having time alone for problem solving
Extrovert:
– Sociable; tend to speak and think
– About 75% Americans and 48% of engineering students and executives
Objective:
– Logical, detached and analytical
– Taking objective approach to make decisions
– 51% of Americans, 68% of engineering students, 95% of top executives
Subjective:
– Make decisions based on an interpersonal involvement, circumstances, and the “right thing to do”
Need to Make Decisions:
•
•
Decisive:
– Tend to make decisions with a minimum of stress and like an ordered, scheduled, controlled and deliberate environment
– 50% of Americans, 64 % of engineering students, and 88% of top executives
Flexible:
– People goes with flow is flexible, adaptive, and spontaneous, and finds making and sticking with decisions difficult
29
• Please make sure to read section 3.3.6 carefully for better design team activities.
Characteristics of a Creative Designer

Problem solving involves:
–

Understanding the problem, generating solutions, evaluating the solutions, deciding on the best one, and
determining what to do next
Criteria of Creative Solution:
–
–
It must solve the design problem.
It must be original.
•

Originality and creativity are assessed by society.
Creativity in relation to other Attributes
–
–
Intelligence: no correlation with creativity
Visualization Ability:
•
•
–
Knowledge:
•
•
–
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–
Creative designers have more than one approach to problem solving.
Environment:
•
–
Constructive nonconformists take a stand because they think they are right and might generate a good idea.
Obstructive nonconformists take a stand just to have an opposing view and will slow down the design progress.
Technique:
•
–
A person must have knowledge of existing products to be a creative designer
A firm foundation in bioengineering science is essential to being a creative biomechanical designer.
Partial Solution Manipulation: important attribute
Risk Taking: certainly required
Conformity: Creative people tend to be nonconformists.
•
•
–
Creative engineers have good ability to visualize, to generate and manipulate visual images in their head.
The ability to manipulate complex images can be improved with practice and experience.
Higher creativity when the work environment allows risk taking and nonconformity and encourages new ideas.
Practice:
•
•
Creativity comes with practice.
Practice enhances the number and quality of ideas.
30
Creative Designer

A creative designer is a:
–
–
–

Visualizer;
Hard worker; and
Constructive nonconformist with knowledge about the domain and
ability to dissect things in his or her head
Good News:
–
–
Designers with no strong natural ability can develop creative methods by
using good problem-solving techniques to help decompose the problems
in ways that maximize the potential for understanding it, for generating
good solutions, for evaluating the solutions, for deciding which solution is
best and for deciding what to do next
A design project requires:
• much attention to detail and convention;
• demands strong analytical skills; and thus
• People with a variety of skills.
–
There are many good designers who are not particularly creative
individuals.
31
Engineering Design Team


A team is a group of people working toward a common understanding.
Team vs. Individual Problem Solving
–
–

There are social aspects of team work.
Each team member may have different understanding of the problem, different alternatives for solving
it, and different knowledge for evaluating it. (more solutions but also more confusion)
Team Goals:
–
–
A small number of people with complementary skills who are committed to a common purpose, common
performance goals and a common approach for which team members hold themselves mutually
accountable are required for an effective team.
Team members must:
•
•
•
•

Team Roles:
–

learn how to collaborate with each other, i.e., to get the most out of other team members.
Comprise to reach decisions through consensus rather than by authority.
Establish communications.
Be committed to the good of the team.
Organizer; Creator; Resource-investigator; Motivator; Evaluator; Team worker; Solver; Completer
(finisher or pusher)
Building Team Performance:
–
For developing productive teams;
•
•
•
•
•
•
Keep the team productive
Select team members on the basis of skills in both primary and secondary roles
Establish clear rule of behavior
Set and seize upon a few immediate performance-oriented goals.
Spend time together.
Develop a common understanding
32
Overview of the Design Process
An Ideal Flow Chart of Activities During Design Process
33
What initiates a Design Project?

Need for a New Design:
–
Market:
• About 80% of new product development is market-driven.
• Assessment of the market is most important in understanding the design problem
because there is no way recover the costs of design and manufacture without market
demand.
• Incorporation of the latest technology can improve its perception as a high quality
product.
–
New product idea without market demand
• To use new technologies whose development requires an extensive amount of capital
investment and possibly years of scientific and engineering time
– High financial risk but greater profit due to uniqueness
• Examples of successful products: sticky notes; Walkman

Need for Redesign
–
–
–
–
By market demand for a new model
Desire to include a new technology
Fix a problem with an existing product
Redesign process can be applied to the subproblems that result from the
decomposition of a higher-level system.
34
Overview of the Design Process

Project Planning:
–
–
to allocate the resources of money, people, and equipment to accomplish the design activities:
Planning should precede any commitment of resources although requiring speculations about the
unknowns
•
–

Plans are often updated whenever unknown demands become certain with the progress of design
project
Specifications Definition:
–
Goal is to understand the problem and to lay the foundation for the remainder of the design project.
•
–
To generate and evaluate the concepts for the product
•
•
–
Generate concepts based on the defined specifications for developing a functional model of the product
Evaluate concepts by comparing the concepts generated to the targets for its performance
Design Review
Product Development:
–
–
–
Evaluate the product for performance, cost, and production
Make product decisions
Documentation and Communication
•

formal meeting for progress report and design-decision making
Conceptual Design:
–

Identify the customers: Generate the customer’s requirements: Evaluate the competition: Generate engineering
specifications: Set targets for its performance
Design Review:
•

Easier to plan a project similar to earlier projects than to plan a totally new one
BOM (Bill of Materials), Drawings, etc.
Product Support:
–
Support for vendors, maintenance of engineering change, customer, manufacturing and assembly,35
and
retirement of the product
Why Do We Have to Follow The Design Process Techniques?

Paradox:
–

Techniques in the design process may imply “RIGIDITY” whereas the creativity implies
“FREEDOM.”
Following the techniques in the design process helps the designers develop a quality
product that meets the needs of the customer by several ways:
–
–
Eliminating expensive changes later
Developing creative solutions to design problems systematically
• Creativity does not spring from randomness.
• “Genius is 1 percent inspiration and 99 percent perspiration.”
• The inspiration for creativity can only occur if the perspiration occur early is properly directed
and focused.
• The techniques that make up the the design process are only an attempt to organize the
perspiration.
–
Forcing documentation of the progress of the design (record of the design’s evolution) that
will be useful later in the design process.
36
Design Process Examples
Simple Process
Complex Process
37
Communication during the Design Process

Design Records:
–
Importance of documents in design file:
•
•
•
–
To demonstrate the state-of-the-art design practices
To prove originality in case of patent application
To demonstrate professional design procedures in case of a lawsuit
Design Notebook:
•
A diary of the design tracking the ideas development and the decision made in a design notebook
– Name; Affiliation; Title of the problem; Problem Statement; and all sketches, notes and calculations that concerns the design
•
A design notebook sequentially numbered, signed and dated pages is considered good documentation whereas
random bits of information scrawled on bits of papers are not.
– Good evidences for legal purposes (patent or lawsuit) as well as a reference to the history of the designer’s own work

Documents Communicating with Management:
–
–

Needed for periodic presentations to managers, customers, and other team members for design review
Regardless of its form (oral or written);
• Make it understandable (consider the recipients’ level of knowledge about the design problem)
• Carefully consider the order of presentation (whole – parts – whole: 3-step approach: gradual
introduction of new ideas)
• Be prepared with quality material (good visual and written documentation; following the agenda;
being ready for questions)
Documents Communicating the Final Design:
–
–
Material describing the final design, e.g, Drawings (or data files) of individual components and of
assemblies
Written documentation to guide
• manufacture, assembly, inspection, installation, maintenance, recruitment, and quality control
38
Team Project

Select an original design problem to solve throughout the
remainder of the course.
–
–

The problem should concern biomechanical devices in which some of
the design team members have some knowledge or training.
The final product will be data from analyses and evaluation and final
drawings, not an actual hardware.
Design Team Activity :
–
–
Each student should start gathering the design ideas immediately and
recording the ideas in the design notebook.
Start the team meeting ASAP for:
• Organization of the team
• Planning the design process to finish the project by the end of April.
–
Each team will present their design project in May.
Any discussion about the design project with the instructor is welcome.
39
Project Definition and Planning
• Concurrent engineering encourages involvement
through out the entire product life cycle from the
project definition to product retirement.
• Project definition and planning is the first phase of
the mechanical design process.
40
Project Definition

Why developing new products?
–
To fill some market need
• Mostly driven by the customer
–
To exploit a technological development
• Driven by new technologies and what is learned during the design

Project Definition:
–
–

the challenges of choosing from the many suggestions as to which products to
spend time and money on to develop or refine
“Fuzzy front end” of dealing with vague design ideas
Specific Questions in Project Definition Phase:
–
–
–
–
–
Is there a good potential return on investment (ROI)?
Does the new product or improvement fit the company image?
Does it fit the distribution channels?
Is there sufficient production capacity in-house or with known vendors?
What will the project cost?
41
Project Planning

Planning is like trying to measure the smile of the Cheshire cat; you are
trying to quantify something that isn’t there.

Planning is the process used to develop a scheme for scheduling and
committing the resources of time, money, and people.
–
–
–
–

Producing a map showing how product design process activities are scheduled.
The whole activities of specification definition, conceptual design, and product
development must be scheduled and have resources committed to them
Planning generates a procedure for developing needed information and
distributing it to the correct people at the correct time.
Important information: product requirements, concept sketches, system
functional diagrams, component drawings, assembly drawings, material
selections, and any other representation of decisions made during the
development of the product.
Typical Master Plan (a generic process) of a Company for Specific Products:
–
A blue print for a process:
• product development process; delivery process; new product development plan; or
product realization plan, etc.

We will refer to this generic process as the product development process
(PDP).
42
ISO-9000

A quality management system of the International Standard Organization
–
–

ISO-9000 registration means that the company has a quality system that:
–
–
–
–
–

First issued in 1987 and now adopted by over 150 countries
Over 350,000 companies worldwide and 8500 U.S. companies have the ISO-9000
certification
Standardizes, organizes, and controls operations.
Provides for consistent dissemination of information.
Improves various aspects of the business-based use of statistical data and analysis.
Enhances customer responsiveness to products and services.
Encourage improvement.
To receive certification,
–
One should develop a process that describes how to develop products, handle product
problems, and interact with customers and vendors.
• Required written procedures that:
– Describe how most work in the organization gets carried out (i.g., the design of new products, the
manufacture of products, and the retirement of products).
– Control distribution and reissue of documents.
– Design and implement a corrective and protective action system to prevent problems from recurring.
–
–

Evaluation of the effectiveness of the process by an accreditted external auditor
Certification expires in 3 years and audits at 6-month intervals to maintain the currency of
the certificate.
ISO-9000 requires a company to have a documented development process on which
43
the plan for a particular product can be based.
Background for Developing a Design Project Plan


A plan tells how a project will be initiated, organized, coordinated, and monitored, e.g.,
managerial activities.
Types of Design Projects:
–
–
Variation of existing product:
Improvement of existing product:
• Redesign of some features of an existing product due to:
– Customers request; no longer supply of materials or components from the vendor; needed improvement in
manufacturing; or New technology or new understanding of an existing technology
–

Members of the Design Team:
–
–
–

Development of a new product for a single (or small) run or for mass production
Product design engineer:
Product manager (product marketing engineer):
Manufacturing engineer; Detailer; Drafter; Technician; Materials specialist; QC/QA specialist; Analyst;
Industrial engineer; Assembly manager; Vendor’s or supplier’s representatives
Structure of Design Teams:
–
Functional Organization (13 %):
•
–
Functional Matrix (26 %):
•
–
–
A project manager is assigned to oversee the project and shares the responsibility and authority with functional
managers.
Project Matrix (28 %):
•
–
project manager with limited authority is designated to coordinate the project across different functional areas
Balanced Matrix (16 %):
•
–
Each project is assigned to a relevant functional area, focusing a single discipline
A project manager oversees the whole project and functional managers assign personnel as needed.
Project Team (16 %)
Organize the talent around the project whenever possible.
•
44
Structures focus on the project are more successful than those built around the functional areas in the company.
Planning for Deliverables

Deliverables:
–
–

Models vs. Prototypes:
–
–

All models of the product, such as drawings, prototypes, bills of materials, analysis results, test results,
and other representations of the information generated in the project
Measure of the progress in design project
Models are analytical and/or physical representations of design information.
Prototypes are physical models. Solid models in CAD can replace the physical models these days.
4 Purposes of Prototypes:
–
Proof-of-concept:
•
•
–
Proof-of-product:
•
•
•
–
Refine the components and assemblies
Geometry, materials and manufacturing processes are as important as functions
Rapid prototyping and CAD models have greatly improved the time and cost efficiency in building prototypes.
Proof-of-process:
•
•
–
Developing function of the product to compare with the goals
Learning tool
Verify both the geometry and manufacturing process.
Exact materials and manufacturing processes are used to build sample for functional testing.
Proof-of-production
•
•
Verify the entire production product.
The result of preproduction run.
45
Types of Models
Medium
Analytical
(mainly Function)
Phase
Physical
(Form and Function)
Concept
Proof-of-concept prototype
Back-of-the envelope
analysis
Sketches
Proof-of-product prototype
Engineering science analysis
Layout drawings
Proof-of-process and proofof-production prototype
Finite element analysis;
detailed simulation
Detail and assembly
drawings; solid models
Final Product
Graphical
(mainly Form)
An important decision in planning the project:
-How many models and prototypes should be scheduled in the design process?
Because of cost effectiveness, there is a strong move toward replacing physical prototypes with
computer models. But not always right.
Be sure to set realistic goals for the time required and the information learned.
46
Five Steps in Planning

Step 1: Identify the Tasks
–
–

Tasks in terms of the activities that need to be performed (generate concepts,
producing prototypes, etc.)
Make the tasks as specific as possible.
Step 2: State the Objective for Each Task
–
Each task must be characterized by a clearly stated objective
• The results of the tasks (or activities) should be the stated objectives.
–
Task objectives should be:
• Defined as information to be refined or developed and communicated to others.
– This information should be contained in deliverables
• Easily understood by all in the design team.
• Specific in terms of exactly what information is to be developed. If concepts are
required, then tell how many are sufficient.
• Feasible, given the personnel, equipment, and time available



Step 3: Estimate the Personnel, Time, and Other Resources Needed to meet
the Objectives
Step 4: Develop a sequence for the tasks
47
Step 5: Estimate the Product Development Costs
Step 3: Estimate the Personnel, Time, and Other
Resources Needed to Meet the Objective

Necessary Identification for each Task:
–
–
–

Who on the design team will be responsible for meeting the objectives?
What percentage of their time will be required?
Over what period of time they will be needed?
Time (in hours) = A x PC x D0.85
–
A = a constant based on past projects
• A = 30 for a small company with good communication
• A = 150 for a large company with average communication
–
–
PC = product complexity based on function
PC =  j x Fj (j = the level in the functional diagram; Fj = the number of functions at that level)
D = project difficulty
• D = 1, not too difficult; D = 2, difficult; D = 3, extremely difficult

Time estimation = (o + 4m + p)/6
–

O = optimistic estimate; m = most-likely estimate; p = pessimistic estimate
Time Distribution across the Phases of the Design Process
–
Project Planning (3 –5 %); Specifications Definition (10 – 15%); Conceptual Design (15
48 –
35%); Product Development (50 – 70%); Product Support (5 – 10%)
Step 4: Develop a Sequence for the Tasks

The goal is to have each task accomplished before its result is needed and to make
use of all of the personnel, all of the time.
–
–
For each task, it is essential to identify its precessors and successors.
Tasks are often interdependent – two tasks need decisions from each other in order to be
completed.
• Sequential vs. Parallel (uncoupled and coupled) tasks


Bar Chart (or Gantt Chart) – best way to develop a schedule for a fairly simple
project
Design Structure Matrix (DSM) – for a complex project with coupled tasks
–
–
Showing the relationship (or inter-dependence) among tasks (example: see page 104
Useful tool for to help sequence the tasks (Page 104)
49
Step 5: Estimate the Product Development Cost

The planning document can serve as a basis for estimating the cost of
designing the new product in terms of:
–
–
Personnel cost
Resources (supplies and equipment)
Team Project:
- Planning must be done and written in the PDF.
- Read examples in pages from 105 – 109 for planning.
- Gantt chart or DSM should be good entries.
50
Understanding the Problem and
the Development of Engineering Specifications

Importance of finding the right problem to be solved:
–
–

Unnecessary effort to design a retarder (dampener) determining the final
position of the solar panels in the Mariner IV satellite
Finding the right problem to be solved is often not easy although it may seem a
simple task.
Creeping Specifications:
–
Specifications changing during the design process
• More features can be added as more is learned during the process
• New technologies or competitive products introduced during the design (ignore,
incorporate or start all over?)
• Changes in any spec. affecting the previous decisions depedent upon that spec

Engineering Specifications (requirements) should be:
–
Discriminatory:
• Reveal the difference between alternatives.
–
–
Measurable (most important and major topic of chap 6)
Orthogonal
• Each specification should identify a unique feature of the alternative.
– “Product must give smooth ride over rough road.” vs. “Product should reduce shocks from bumps.”
–
Universal
• Characterizing an important attribute of all the proposed alternatives
–
External
• Only external features are observable.
51
Quality Function Deployment (QFD)

Most popular technique used to generate engineering
specifications in an organized manner
–
Developed in Japan in the mid-1970s and introduced to the US in the late
1980s
• 69% of the US companys use the QFD method recently

Important Points
–
–
–
–
Employ QFD no matter how well the design team thinks it understands a
problem.
QFD takes time to complete, but time spent for QFD saves time later.
QFD can be applied to the entire problem and also any subproblems.
QFD helps overcome our cognitive limitation.
• We tend to try to assimilate the customer’s functional requirement (what is
to be designed) in terms of form (how it will look).
52
Quality Function Deployment (QFD)
House of Quality
53
Example of QFD
Step 1: identify the customers
Step 2: determine the requirements
Step 3: determine the relative
importance of requirements
Step 4: identify and evaluate the
competition
Step 5: generate engineering specification
Step 6: Relate customers’ requirements to
engineering specifications
Step 7: Set engineering targets
Step 8: identify the relationships between
engineering requirements
54
QFD Step 1: Identify the Customers: Who are they?
For general products:
For a spinal implant system:
Who are the customers?
-Consumers
-Designers’ management
-Manufacturing personnel
-Sales staff
-Service personnel
-Standard organizations
-Etc.
Who are the customers?
-Orthopaedic surgeons
-Neurosurgeons
-Nurses
-Hospitals
-Distributors
-Sales Reps
-Patients ?
For many products,
there are 5 or more
classes of customers
whose voices need to be
heard
55
QFD Step 2: Determine the Customer’s Requirements: What
do the customers want
Consumers:
-
works as it should,
lasts long,
is easy to maintain,
looks attractive,
incorporates the latest technology,
and has many features.
Production Customer:
-
is easy to produce (both manufacture and assemble),
uses available resources (human skills, equipment, and raw materials),
uses standard parts and methods,
uses existing facilities,
produces a minimum scraps and rejected parts.
Marketing/Sales Customer:
- easy to package, store, and transport,
- attractive and suitable for display
Types of Requirements:
-Basic features: neutral satisfaction with existence
-basic assumed functions; not included in QFD
- Performance Features: good satisfaction with existence
- verbalized in the form that the better the performance, major part of QFD
- Excitement (or WOW) Features: high satisfaction with existence
56
QFD Step 2: Determine the Customer’s Requirements:
What do the customers want?

How to collect customer’s requirements:
–
–
–
Observation of customers
Surveys: mail, telephone, face-to-face
Focus-group technique
•

A group of surgeons for orthopaedic implants
Steps for developing useful data for requirements:
–
Specify the information needed:
•
–
Determine the type of data-collection method to be used:
•
–
•
Order them to give context
Take data:
•
•
–
Each question should seek unbiased, unambiguous, clear and brief information.
Do not: assume that the customers have more than common knowledge; use jargon; lead the customer toward the answer
you want; tangle two questions together.
Do use complete sentences
Order the questions:
•
–
Write a clear goal for the results expected from each question.
Design the questions:
•
•
–
Depending on the use of data collection methods
Determine the content of individual questions:
•
–
Reduce the problem to a single statement. If impossible, more than one data collecting effort may be warranted.
Any set of questions should be considered a test or verification.
Repeated application is required to generate usable information.
Reduce the data:
•
•
Make a list of customer’s requirements in the customer’s own word (easy; fast; other abstract terms).
The list should be in positive terms, i.e., wanted, not unwanted
57
QFD Step 2: Determine the Customer’s Requirements:
What do the customers want?
Types of Customers’ Requirements:
 Functional Performance
–
–

Human Factors
–
–

Distribution (shipping); Maintainability; Diagnosability; Repairability; Testability; Cleanability; Installability;
Retirement
Resources Concerns
–

Mean time between failures; Safety (hazard assessment)
Life-Cycle-Concerns
–

Available spatial envelope; Physical properties
Reliability
–

Required in any products that is seen, touched, heard, tasted, smelled or controlled by a human
Appearance; Force and motion control; Ease of controlling and sensing state
Physical Requirements
–

Performance about the product’s desired behavior
Flow of energy, information, or materials; Operational steps; operation sequence
Time; Cost; Capital; Unit; Equipment; Standards; Environment
Manufacturing Requirements
–
Materials; Quantity; Company capabilities
**For Spinal Implants:
-
Functional performance (flow of energy, operational steps and operation sequence)
Human Factors
Physical Requirements
Reliability (mechanical failure, corrosion, biocompatibility, and complications due to the failure)
Other requirements are not as critical as for other common products
58
Resource Concerns

Time requirements:
–

Cost Requirements:
–
–
–

Timing to introduce a new product
Capital Cost:
Cost per Unit:
Cost estimation will be covered in Chap 12.
Standards (Codes):
–
Types of Standards:
• Performance: seat-belt strength, helmet durability
– The Product Standards Index lists US standards that apply to various products.
– American National Standards Institute (ANSI) does not write standards but is a clearing house for
standards written by other organizations
• Test Methods:
– American Society for Testing and Materials (ASTM) publishes over 4000 individual standards covering the
properties of materials, specifying equipment test the properties and outlining the procedures for testing.
– Underwriters Laboratories (UL) testing standards.
• Codes of Practice:
– Give parameterized design methods for standard mechanical components, such as pressure vessels, welds,
elevators, piping and heat exchangers
–

Knowledge of which standards apply to the current situation are important to
requirements and must be noted from the beginning of the project
Environment Concerns:
59
QFD Step 3: Determine the Relative Importance of the
Requirements: Who vs. What

Evaluate the importance of each of the customers’ requirements
–
Generate a weighting factor for each requirement considering
• To whom is the requirement important
• How is a measure of importance developed for this diverse group of
requirements
–
How to determine the weight factor
• Customer’s rating from 1 (unimportant) to 10 (important)
• Fixed Sum Method:
– Distribute the importance on all the listed requirements
60
QFD Step 4: Identify and Evaluate the Competition:
How satisfied is the customer now?

Determine how the customer perceives the competition’s ability
to meet each of the requirements.
–
–
–
–
–

The product does not meet the requirement at all.
The product meets the requirement slightly.
The product meets the requirement somewhat.
The product meets the requirement mostly.
The product meets the requirement completely.
Why studying existing products?
–
–

1
2
3
4
5
It creates an awareness of what already exists.
It reveals opportunities to improve on what already exists.
This process is called “Competition Benchmarking.”
61
QFD Step 5: Generate Engineering Specifications:
How will the customers’ requirements be met?

Engineering Specifications:
–
Restatement of the design problems in terms of parameters that can be measured and have target
values.
• Measurable behaviors of the product-to-be
–

If units for an engineering parameter can not be found, the parameter is not measurable and must
be readdressed.
Examples:
–
Easy to attach
• The number of steps; time to attach; number of parts; number of tools used

Every effort must be made to find as many ways as possible to measure customer’s
requirements.

Carefully check each entry to see what nouns are or noun phrases have been used
because each noun refers to an object that is part of the product or its environment
and should be considered to see if new objects are being assumed.
–
“easy to adjust suspension system …” then “an adjustable suspension system” has been
assumed as part of the solution.
62
QFD Step 6: Relate Customers’ Requirements to Engineering
Specifications: How to measure what?
Strong, medium, weak, and no relationship
QFD Step 7: Set Engineering Targets: How much is good
enough?
1. Ascertain how the competition meets the engineering goal.
2. Establish targets for the new product.
Remember:
- Set the target early.
- Too tight target may eliminate new ideas.
- If a target is much different than the values achieved by the competition, it should be
questioned.
QFD Step 8: Identify Relationships between Engineering
Requirements: How are the “HOWS” dependent to each
other?
Strong negative; negative; Positive; Strong positive
63
Example of QFD
Step 1: identify the customers
Step 2: determine the requirements
Step 3: determine the relative
importance of requirements
Step 4: identify and evaluate the
competition
Step 5: generate engineering specification
Step 6: Relate customers’ requirements to
engineering specifications
Step 7: Set engineering targets
Step 8: identify the relationships between
engineering requirements
64
Basic Methods for Idea Generation

Brainstorming:
–
–
–
–

6-3-5 Method (Brainwriting):
–
–
–


Consider needed function and then ask, What else provides this function?
Use of Extremes and Inverses:
–

Brainwriting to force equal participation by all.
6 (optimal number of members); 3 (number of ideas); 5 (minute interval)
No verbal communication allowed until the end.
Use of Analogies in Design:
–

Record all the ideas generated.
Generate as many ideas as possible, then visualize them.
Think wild.
Do not allow evaluation of the ideas
Transform current concepts into others by taking them to extremes or considering
inverses
Finding Ideas in Reference Books and Trade Journals:
Using Experts to Help Generate Concepts:
–
Needed to design in a new domain
65
Guideline for Team Project

Use Brainstorming Method to determine a design item.
–
–

Make sure to write your own ideas in an individual notebook and finalized
team project item in PDF with minutes of brainwriting.
Do not try to make a fancy and complete product. Any improvement in a
small component can be a product for the design team project as long as the
techniques introduced in this class are well executed.
Make sure to follow all the steps suggested in this book and
produce a good design records.
66
Concept Generation

Concept:
–
–
–
An idea that is sufficiently developed to evaluate the
physical principles that govern its behavior.
Goal of concept generation is to confirm that the proposed
product will operate as anticipated and that, with
reasonable further development, it will meet the targets
set.
• Concepts must be refined enough to evaluate the
technologies needed to realize them, to evaluate the
basic architecture (form) of them, and to evaluate the
manufacturability to some extent
• Concepts can be represented in deliverables (sketch,
flow diagram, a set of calculations, prototypes, etc)
Examples of weak methodology:
• Start design with a concept to be developed into a
product.
• There is a tendency for designers to take their first
idea and start to refine it toward a product.
– If you generate one idea, it is probably a poor one. If you
generate twenty ideas, you may have a good one. (or,
alternatively, he who spends too much time developing a single
concept realizes only that concept.

Main goal of this chapter is to learn techniques
for the generation of many concepts.
–
–
Functional decomposition
Concept variant generation
67
Understanding the Function of Existing Devices

Bench marking (review of existing devices) is always a good practice because:
–
–

There is nothing so new that ideas for it can not be borrowed from other devices.
Lots of engineering hours have been spent developing the features of existing products (it is
foolish to ignore it).
Defining Function:
–
Remember that function tells what the product must do, whereas its form conveys how the
product will do it.
• Develop the what and then map the how as we mapped what the customer required into how the
requirements were to be measured in QFD.
–
Function is the logical flow of energy (including static forces), material, or information between
objects or the change of state of an object caused by one or more of the flows.
• Functions required to attach any component to another are GRASP, POSITION, ATTACH. In
undertaking these actions, human provides information and energy in controlling movement and in
applying force to it. (Flow of energy, material, and information)
–
Functions associated with flow of energy:
• Types of energy: mechanical, electrical, fluid and thermal
• Its action: transformed, stored, transferred (conducted), supplied, and dissipated
–
Functions associated with flow of material:
• Through-flow: position, lift, hold, support, move, translate, rotate and guide
• Diverging flow: disassemble, separate
• Converging flow: assembling or joining materials (mix, attach, and position relative to)
–
Functions associated with flow of information:
• In the form of mechanical signals, electrical signals or software
• Generally used as part of automatic control or to interface with a human operator
–
Function associated with the change of state of an object:
• Changes in energy storage, kinetic or potential energy, material properties, form or information content
68
Using Product Decomposition to
understand the Function of Existing Product

Step 1: For the whole device, examine interfaces with other objects.
–

Examine the flows of energy, information and material into and out of the device
Step 2: Remove a component for more detailed study.
–
Carefully note how it was fastened to the rest of the device and also any relationship it
has to other parts that may not contact.
• It may have a clearance with some other parts in order to function.

Step 3: Examine each interface of the component to find the flow of energy
–
Understand:
•
•
•
•
How the functions identified in step 1 are transformed by the component;
How the parts are fastened together;
How forces are transformed and flow from one component to anther; and
The purpose of each feature of component
69
Patents as a Source of Ideas

Patent Literature:
–
–
Good source of ideas although
hard to read
Sources for Patent Searches
• http://www.uspto.gov/patft/index.
html
• http://www.delphion.com/home
• http://gb.espacenet.com - source
for European and other foreign
patents

Types of Patents:
–
Utility Patents:
• Claiming how an idea operates or
is used
–
Design Patents:
• Covering only the look or form of
the idea
70
Technique for Designing with Function

Goal of Functional Modeling:
–
To decompose the problem in terms of flow of energy, material, and
information
• Decomposition forces a detailed understanding of what the product-to-be is to
do.

4 Basic Steps:
–
Find the overall function that needs to be accomplished.
• The goal is to generate a single statement of the overall function on the basis of
the customer requirements.
–
Create subfunction descriptions.
• The goal is to decompose the overall function.
–
–
Order the subfunctions.
Refine subfunctions.
71
Step 1: Find the overall function

Most important functions must be
reduced to a simple clause and put it in
a black box.
–

The BikeE suspension Example:
 Overall function:
–
Inputs into and outputs out of this black
box are all flows of the energy, material
and information.
• To transfer forces between wheel,
chain, and frame and absorb peak
loads between wheel and frame
–
Guidelines:
–
–
–
Energy must be conserved.
Material must be conserved
All interfacing objects and known, fixed
parts of the system must be identified.
• List all the objects (all features,
components, assemblies, humans, etc)
that interact, or interface, with the
system.
–
transfer and absorb

Goal: alter the energy flow
Make sure to state the overall function
of your design in individual design
notebook (personal ideas) and finalized
overall function in the PDF.
Ask how will the customer know if the
system performing?
• Answers to this question will help
identify information flows that are
important.
–
Use action verbs to convey flow.
• Typical mechanical design functions:
– See Table 7.1
72
Step 2: Create subfunction description


Goal is to decompose the overall function into subfunctions.
Reasons for Decomposition:
–
The resulting decomposition controls the search for solution to the design problem.
• Since concepts follow function and products follow concepts, we must fully understand the function
before wasting time generating products that solve the wrong problem.
–
Decomposition into functional detail leads to a better understanding of the problem.
• Most good ideas come from fully understanding the functional needs of the design problem.
• It is useful to begin function decomposition before the QFD and use the functional development to help
determine the engineering specifications.
–

Decomposition may lead to the realization that there are some already existing components that
can provide some of the functionality required.
Guidelines:
–
Consider what needs to happen (the function) not how.
• Detailed, structured-oriented how consideration must be suppressed as they add detail too soon, which
limit the number of possible concepts too early.
–
Use only objects described in the problem specification or overall function.
• Use only “nouns” previously used to describe the material flow or interfacing objects to avoid the new
components creeping into the product.
–
Break the function down as finely as possible.
• Let each function represent a change or transformation in the flow of material, energy, or information.
–
Use standard notation when possible.
• Whenever available, use common notations, such as block diagrams used to represent elec. circuits,
piping system, or transfer functions in systems dynamics and control, although there is no standard
notation for general mechanical product design.
–
Consider all operational sequences.
• Think of each function in terms of its preparation, use, and conclusion.
73
Functional Decomposition for the Space Shuttle aft Field Joint
74
Step 3: Order the Subfunctions

Order the functions found in step 2 to accomplish the overall function in step
1.

Guidelines:
–
The flows must be in logical or temporal order.
• Arrange the subfunctions in independent group (preparation, use, and conclusion).
• In each group, arrange them so that the output of one function is the input of another.
–
Redundant functions must be identified and combined.
• Similar subfunctions must be combined into one.
–
Functions not within the system boundary must be eliminated.
• This step helps the team come to mutual agreement on the exact system boundary; it is
often not as simple as it sounds.
–
Energy and material must be conserved as they flow through the system.
• Inputs to each function must match the outputs of the previous function.
75
Step 4: Refine Subfunctions


Examine each subfunction to see if it can be further divided
into sub-subfunctions.
This step should be continued until:
–
‘atomic’ functions are developed; or
• “atomic” implies that the function can be fulfilled by existing objects.
–

It is a struggle to develop the suggested diagram of function
decompositions.
–
–

new objects are needed for further refinement.
It is a fact that the design can be only as good as the understanding of the
functions required by the problem.
This exercise is both the first step in developing ideas for solutions and
another step in understanding the problem.
The functional decomposition diagrams are intended to be
updated and refined as the design progresses.
76
Concept Generation

Concepts are the means for providing function.
–
–
–

Any form that gives an indication how the function can be achieved.
What to do  Function vs. How to do  Concepts (forms)
Remember that the idea is often not original.
Many methods for concept generation are available, but no
single method is best.
–
A good designer is familiar with these methods and uses them, or a
combination of them, as needed.
77
Basic Methods for Concept Generation
78
Morphological Method

This technique uses the functions identified
to foster ideas.
–
–

Powerful method that can be used formally or
informally as part of everyday thinking
2 step approach
Step 1 - Developing Concepts for Each
Function:
–
Goal is to find as many concepts as possible
that can provide each function identified in the
decomposition.
•
•
–
Situations explaining the lack of more concepts.
•
•
•
–
How to store mechanical energy: springs,
elastomers (rubbers or plastics), etc.
If there is a function with only one conceptual
idea, this function must be re-examined.
The designer has made a fundamental
assumption.
The function is directed at how, not what. - e.g.
“store energy in coil spring” rather than “store
energy”
Domain knowledge is limited.
Keep the concepts as abstract as possible and at
the same level of abstraction for better
comparison of developed concepts.
•
Morphology for BikeE Suspension System
The force required for moving an object can be
provided by a hydraulic piston, a linear electric
motor, the impact of another object, or magnetic
repulsion.
–
Refined mechanical components vs. basic physical
principles.
79
Morphological Method

Step 2 - Combining Concepts:
–
to combine these individual concepts into
overall concepts to meet all the functional
requirements.
• Select one concept for each function and
combine those into a single design.
–
Pitfalls:
• This method may generate too many ideas.
• It erroneously assumes that each function of
the design is independent and that each
function satisfies only one function.
• The results may not make any sense.

Concept generation process is the time
that back-of-the-envelope sketches begin
useful.
–
–
–
We remember functions by their forms
Only way to design an object with any
complexity is to use sketches to extend the
short-term memory.
Sketches made in the design notebook
provide a clear record of the development of
the concept and the product.
Combined Concepts for BikeE Suspension System
80
Logical Methods for Concept Generation

The Theory of Inventive Machines, TRIZ:
–
–
Developed by Genrikh Altshuller (a ME engineer, inventor, and Soviet patent
investigator) in Soviet Union in the 1950s based on patterns found in patented
ideas
Goal of TRIZ:
• Find the major contradiction that is making the problem hard to solve, then
• Use TRIZ’s 40 inventive ideas for overcoming the contraindication
–

With TRIZ, we can systematically innovate; we don’t have to wait for an
inspiration or use the trial and error common to other methods.
Axiomatic Design:
–
–
Evolved in MIT by Prof. Nam Suh in an effort to make the design process
logical.
1st Axiom:
• Maintain the independence.
– Then, a change in a specific design parameter should have an effect only on a single function.
–
2nd Axiom:
• Minimize the information content of the design.
– The simplest design has the highest probability of success and is the best alternative.
81
Concept Evaluation

How to choose the best of the concepts generated for
development into a quality product?
–
–
Goal is to expend the least amount of resources on deciding which concepts
have the highest potential for becoming a quality product.
It is difficult to evaluate concepts, or to choose which concepts to spend time,
particularly when we still have very limited knowledge and data on which to
base this selection.
• Design is learning, and resources are limited.

Techniques for systematic evaluation of rough concepts.
–
Evaluation implies both “comparison” and “decision making.”
• It is the comparisons between alternative concepts and the requirements that they
must meet that gives the information necessary to make decisions.
–
For all design decisions:
• Itemizing the alternatives and the criteria for their evaluation
• Comparing the alternatives to the criteria to each other
–
For comparisons:
• Alternatives and criteria must be in the same language and they must exist at the
same level of abstraction
82
Concept Evaluation Techniques
Be ready during concept
evaluation to abandon your
favorite idea, if you can not
defend it in a rational way.
Abandon if necessary “the
way things have always have
been done around here”.
83
Information Presentation in Concept Evaluation
Design Evaluation Cycles
84
Evaluation based on Feasibility Judgment

Three Immediate Reactions of a Designer as a concept is generated based on
designer’s “gut feel”:
–
–
–

It is not Feasible.
It might work if something else happens.
It is worth considering.
Implications of Each of these Reactions:
–
It Is Not Feasible.
• Before discarding an idea, ask “Why is it not feasible?”
• Make sure not to discard an idea because:
– a concept is similar to ones that are already established, or
– a concept is not invented here (less ego-satisfying).
–
It is Conditional.
• To judge a concept workable if something else happens.
• Factors are the readiness of technology, the possibility of obtaining currently unavailable
information, or the development of some other part of the product.
–
It is Worth Considering.
• The hardest concept to evaluate is one that is not obviously a good idea or a bad one, but
looks worth considering.
• Such a concept requires engineering knowledge and experience. If sufficient knowledge is
not immediately available, it must be developed using models or prototypes that are easily
85
evaluated.
Evaluation based on GO/NO-GO Screening

Measures for deciding to go or no-go:
–
Criteria defined by the customer requirements:
• Absolute evaluation by comparing each alternative concept with the customer
requirements.
• A concept with a few no-go responses may be worth modifying rather than
eliminating
• This type of evaluation not only weeds out designs that should not be considered
further, but also helps generates new ideas.
–
Readiness of the technologies used:
• This technique refines the evaluation by forcing an absolute comparison with
state-of-the-art capabilities.
• 6 Measures for a Technology’s Maturity:
–
–
–
–
–
–
Are the critical parameters that control the function identified?
Are the safe operating latitude and sensitivity of the parameters known?
Have the failure modes been identified?
Can the technology be manufactured with known process?
Does hardware exist that demonstrates positive answers to the preceding four questions?
Is the technology controllable throught the product’s life cycle?
• If these questions are not answered in the positive, a consultant or vendor is
86
added to the team.
Evaluation based on a Basic Decision Matrix

Decision-Matrix Method (or Pugh’s
Method):
–
–

Step 1: Choose the criteria for Comparison.
–
–


Criteria are the functional requirements and
engineering specification determined in QFD.
The concepts must be refined enough to
compare with the engineering targets for
evaluation (mismatch in the level of
abstraction).
Step 3 in QFD should provide the data for
relative importance.
Step 3: Select the Alternatives to be
Compared.
Step 4: Evaluate Alternatives.
–

**This method is most effective if
each member performs it
independently and the individual
results are then compared.
- have BDM in individual notebook.
Step 2: Develop Relative Importance
Weightings.
–

effective comparison of alternative concepts
(basic form Table 8.2)
Iteratively test the completeness and
understanding of requirements, rapidly
identifies the strongest
Relative evaluation among alternatives
Step 5: Compute the Satisfaction.
87
Decision Matrix for Energy Management System
S indicates “Same as datum”
88
Robust Decision Making



Robust decision refers to make decisions that are as insensitive
as possible to the uncertainty, incompleteness, and evolution of
the information that they are based on.
For robust decision making, we need to improve the method
used to evaluate the alternatives (step 4 in decision-matrix
method).
Word Equations used for Robust Decision Making
–
–
Satisfaction = belief that an alternative meets the criteria
Belief = knowledge + confidence
• Belief is the confidence placed on an alternative’s ability to meet a target set by a
criterion, requirement, or specification, based on current knowledge.
• Belief (virtual sum of knowledge and confidence) can be expressed on a “belief
map.”
89
Belief Map
Measure of Confidence:
Belief = p(k) x p(c) + (1 – p(k)) x (1 – p(c))
Knowledge = a measure of the information held by a decision maker about
90
a feature of an alternative defined by a criterion
Belief Map showing the Probabilities
Belief Model:
Belief = p(k) x p(c) + (1 – p(k)) x (1 – p(c))
91
Extreme Cases of Belief Map
p(k) = 1.0
p(c) = 1.0
p(k) = 1.0
p(c) = 0.0
Certainly work
Certainly not
work
p(k) = 0.5
p(c) = 1.0
p(k) = 0.5
p(c) = 0.0
Optimist corner
Pessimist corner
Not clear
No more info. For
evaluation
92
Belief Map Example
Point A: p(k) = 0.8 (informed knowledge) and p(c) = 0.65 (high confidence); belief = 0.59
He/she has a belief of 59% that the concept will meet the functional requirements.
Point B: p(k) = 0.9, p(c)=0.25, Belief = 0.30
93
Arrow shows the evolution (With increasing knowledge, confidence and belief decrease.).
Belief Map to Choose Where to Eat
Criteria:
delighted (p(c) = 1.0) if < $5.00
disgusted (p(c)= 0.0) if > $10.00
fast food = $6.00 (sure)
Family diner = $9 (most likely)
Chinese = $7 (little knowledge)
Fast food should be chosen for the
best probability for satisfaction.
* Choice can be altered with inclusion of other
criteria, such as food quality, taste, nutrition, etc.
94
Advanced Decision Matrix


Steps 1 through 3: same as the Decision Matrix Method
Step 4: Evaluate Alternatives
–
–

Use a belief map for comparison
If little is known or the evaluation result is that the alternative possibly meets the criterion, then belief
= 0.5
Step 5: Compute Satisfaction
–
Satisfaction =  (belief x importance weighting)
•
Max satisfaction = 100 (evaluator is 100% satisfied.)
95
Product Safety and Liability

Safety is best thought of early in the design process.
–

Product safety and liability are often overlooked until late in the project.
Product Safety:
–
–
Design for safety means ensuring that the product will not injury or loss.
2 Safety Issues:
• Who or what is protected from injury or loss?
• How is the protection actually implemented in the product?
–
3 Ways to Institute the Safety:
• Design safety directly into the product
– device poses no inherent danger during normal operation
• Add protective devices to the product (automatic cut-off switch).
• Warning of the dangers inherent in the use of the product.

Products Liability:
–
Special branch of law dealing with alleged personal injury or property or
environmental damage resulting from a defect in a product.
96
Products Liability

3 Different Charges of Negligence against Designers:
–
The product was defectively designed.
• Failure to use state-of-the-art design considerations.
• Improper analyses, use of poor materials
–
–

The design did not include proper safety devices.
The designer did not foresee possible alternative uses of the product.
What to do for protecting ourselves as a designer?
–
–
–
–
Keep good records to show all that was considered during the design process.
Use commonly accepted standards when available.
Use state-of-the-art evaluation techniques for proving the quality of the
design before it goes into production.
Follow a rational design process so that the reasoning behind design
decisions can be defended.
97
Hazard Assessment
When a potential hazard is identified,
1. Estimate the frequency of occurrence
(Table 8.6);
2. Estimate the consequence of occurrence
(Table 8.7);
3. Predict the hazard index using the hazardassessment matrix (Table 8.8);
If the hazard index is low (undesired or
unacceptable), further consideration must
be given on the design.
98
The Product Design Phase
Goal:
- Refine the concepts already generated into
quality products.
- Giving flesh to what was the skeleton of an
idea (hardware design, shape design, or
embodiment design)
Steps:
- Generate Product (chapter 10)
- Evaluate the product (chaps 11, 12)
- Decision Making
*Drawings, Bills of Materials, and other preliminary
records of the product design effort
99
Drawings Produced during Product Design

Layout Drawings:

Detail Drawings:

Assembly Drawings:

Graphical Models produced in CAD Systems:
100
Layout Drawings
- A layout drawing is a working document that supports the development of the
major components and their relationship.
- Characteristics:
- Frequently changed during the design process. Care should be taken not to lose the records of
changes.
- A layout drawing is made to scale.
- Only the important dimensions are shown.
- Tolerances are usually not shown, unless they are critical.
- Notes on the layout drawing are used to explain in a design feature or the function of the
product.
- A layout drawing often becomes obsolete as detail drawings and assembly drawings are
developed.
101
Detail Drawings


The detail of individual
components, developed as the
product evolves on the layout
drawing, are documented on detail
drawings.
Characteristics:
–
–
–
–
All dimensions must be toleranced.
No tolerance indicates the use of
standard tolerances used in a
company.
Materials and manufacturing detail
must be in clear and specific
language.
Drawing standards (ANSI Y 14.5M1994, Dimensions and Tolerancing,
and DOD-STD-100, Engineering
Drawing Practices, or company
standards) should be followed.
Detail drawings are a final
presentation of the design effort and
will be used to communicate the
product to manufacturing. Thus, a
signature block for management
approval is a standard part of a detail
drawing.
102
Assembly Drawings


Assembly drawings are made to
show how the component fit
together.
Characteristics:
–
–
–
–
Each component is identified with a
number or letter keyed to the bill of
materials (BOM).
References can be made to other
drawings and specific assembly
instructions for additional needed
information.
Necessary detailed views are
included to convey information not
clear in the major views.
Assembly drawings require a
signature block.
103
Graphical Models produced in CAD Systems
Positive Aspects:





Rapid representation of concepts and
the ability to see how they assemble
and operate without the need for
hardware.
Improves the design process because
features, dimensions, and tolerances
are developed and recorded only once
(less potential error)
Easy to ensure that mating
components fit together.
Detail and assembly drawings are
produced semi-automatically, reducing
the need to have expert knowledge of
drafting methods and drawing
standards.
Files created are useful for making
prototypes and developing figures for
any other purposes.
Negative Aspects:




There is a tendency to abandon
sketching although sketches are
a rapid way to develop a high
number of ideas. (Longer time
for solid modeling)
Too much time is often spent on
details too soon because solid
model systems require details in
order to even make a rough
drawing.
Often valuable design time is
spent just using the tool.
Many solid modeling systems
require the components and
assemblies to be planned out
ahead of time. These systems
are more like an automated
drafting system than a design
aid.
104
Bills of Materials (Part Lists)

An index to the product
–
–

It is a good practice to generate the BOM as the product evolves on a spreadsheet,
which is easy to update.
To keep lists to a reasonable length, a separate list is made for each assembly.
Minimum Pieces of Information on BOM
–
–
–
–
–
–
The item number or letter
The part number
The quantity needed in the assembly
Name or Description of the Component
Material from which the component is made
Source of the component (if the component is purchased from other companies)
105
Product Data Management

A major undertaking in a company is to manage design
information, a company’s most valuable asset.

Product Data Management Systems (PDMs)
–
–
Database programs used to support the management of documents and files,
product structure and processes for better management of both product and
process information
Records stored in PDMS
•
•
•
•
•
–
–
–
CAD files (all kinds of drawings and solid models)
Text documents (meeting notes, contracts, etc.)
Spread sheets (QFD, decision matrices, and other analysis)
Database reports
Parts libraries, vendor data, engineering change orders
PDMs allow easy search and organization of the data.
PDMs allow management of the way people create and modify data.
PDMs help support the task schedule by the tools to support the development
and maintenance of Gantt charts, worker allocation, and task definitions.
106
Product Generation (Chaps 10, 11, 12)


The goal of product
generation is to
transform the design
concepts into products
that perform the desired
functions.
Such refinement requires
work on all the elements
in the figure.
107
Form Generation

Form development is the evolution of
components, how they are configured
relative to each other and how they are
connected to each other within the
constraints.
–
–
–
–

Understand the spatial constraints:
Configure components:
Develop Connections: Create and refine
interfaces for functions:
Develop Components:
Understand the Spatial Constraints:
–
–
Kyphoplasty: The balloon size is constrained by the
vertebral body size.
Spatial constraints are the walls or
envelope for the product.
Some spatial constraints are for
functionally needed space.
• For medical implants, human body limits
the space significantly.
108
Form Generation

Configure Components:
–
–
–
Configuration is the architecture, structure, or arrangement of the components and
assemblies of components in the product.
Developing the configuration involves decisions that divide the product into
individual components and develop the location and orientation of them.
6 Reasons to decompose a product or assembly into separate components:
components must be separate if:
•
•
•
•
•
•
–
They need to move relative to each other;
They need to be of different materials for functional purposes;
They need to be moved for accessibility;
They need to accommodate material or production limitations;
There are available standard components that can be considered for the product;
Separate components would minimize costs.
Location and Orientation of the Components with each other:
• Location: Measure of relative position in a space (x, y, z)
• Orientation: angular relationship of the components
109
Form Generation

Develop Connections (Create and refine interfaces for functions):
–
A key step when embodying a concept because the connections or interfaces between
components support their function and determine their relative positions and locations.
–
Guidelines to help develop and refine the interfaces between components:
• Interfaces must always reflect force equilibrium and consistent flow of energy, material,
and information.
– These flows are means through which the product will be designed to meet the functional
requirements.
• After developing interfaces with external objects, consider the interfaces that carry the
most critical functions.
– In general, most critical functions are those that seem hardest to achieve or those described as most
important in the customers’ requirements.
• Try to maintain functional independence in the design of an assembly or component.
– This means that the variation in each critical dimension in the assembly or component should
affect only one function.
• Exercise care when separating the product into separate components.
– Complexity arises since one function often occurs across many components or assemblies and
since one component may play a role in many functions.
• Creating and refining interfaces may force decompositions that result in new functions or
may encourage the refinement of the functional breakdown.
110
Form Generation

Develop Connections (Create and refine interfaces for
functions):
–
Types of Connections:
• Fixed, nonadjustable connection
• Adjustable connection
– Should allow at least 1-DOF that can be locked.
• Separable connection
• Locator connection
– The interface determines the location or orientation of one of the components relative to another.
– Care must be taken in these connections to account for errors that can accumulate in joints.
• Hinged or pivoting connection
– Many connections have one or more degrees of freedom.
– The ability to transmit energy and information is usually key to the function of the device
–
Degrees of Freedom (DOF):
• Number of directions required for complete description of location and
orientation of a component moving relative to another.
• Fundamentally, every connection between 2 components has 6 DOF – 3
translations and 3 rotations.
• It is the design of connections that determine how many DOF the final
111
product will have.
Examples of Connections with Varying DOF
A single pin or short wall was inserted into B for positioning A.
The effect will be to only limit the position of A relative to B in
the +x direction.
3 DOF Situation
Most joints need to position parts relative to
each other and transmitted forces. Thus, it is
worthwhile to think in terms of positioning and
then force transmission.
Efforts to fully constrain along the x-axis.
Putting a second support on the x-axis to limit motion in –x
direction can have unintended consequences.
112
Examples of Connections with Varying DOF
Block A restriction in x-direction and z-rotation
Block A is fully constrained under the force F.
Other fully constrained blocks.
113
Form Generation

Develop Components:
–
Determine adequate shape and size of each component.
• Critical dimensions on most components are found in functional interfaces.
• In designing the bodies of components, be aware that stiffness determines the adequate size more
frequently than stress.
–
–
Use force flow visualization to estimate the required stiffness and strength of each component
Use standard shapes when possible.
Major functions are to transfer forces and
clear (not interfere with) other components.
114
Form Generation

Material between interfaces generally serves 3 main purposes.
–
–
–

To carry forces or other forms of energy between interfaces with sufficient
strength and rigidity
To act as an enclosure or guide for other components
To provide appearance surfaces
When the body of a component provides the function (e.g.
needed mass, stiffness, or strength), shape of the component can
be as important as the interface.
–
–
It is best to connect interfaces with strong structural shape.
Size and shape (area an polar moment of inertia) of the component should be
considered.
• Rod to resist tension or compression
• Hollow cylinder to resist torque
• I-beam to carry bending loads in the most efficient way possible
115
Form Generation

Force Flow Visualization
–
–
A good method to visualize how forces are transmitted
through components and assemblies
Method
• Treat forces like a fluid that flows in and out of the interfaces
and through the component.
• The fluid takes the path of least resistance through the
component.
• Sketch multiple flow lines. The direction of each flow line
will represent the maximum principal stress at the location.
• Label the flow lines for the major types of stress occurring at
the location: tension (T), Compression (C), shear (S), or
bending (B).
–
–
B can be decomposed into T and C.
S must occur between T and C on a flow line.
• Remember that force is transmitted at interfaces primarily by
compression. Shear only occurs in adhesive, welded and
friction surfaces.
–
Advantages:
• Force flow helps us visualize the stresses in a component or
assembly.
• It is best if the force paths are short and direct.
–
The more indirect the path, the more potential failure points and stress
concentrations.
116
Form Generation

Refine and Patch
–
–
Refine is to make an object less abstract (or more concrete).
Patching is to change a design without changing its level of abstraction.
• The goal is to make things work and to make them simpler.

Types of Patching
–
Combining is making one component serve multiple functions or replace multiple components.
• strongly encouraged when the product is evaluated for its ease of assembly.
–
Decomposing is breaking a component into multiple components or assemblies.
• It is worthwhile to consider returning to the beginning of the design process.
–
Magnifying means making a component or some feature of it bigger relative to adjacent items.
• Exaggerating the size or number of a feature often increases one’s understanding.
–
Minifying means making a component or some feature of it smaller.
• Eliminating, streamlining, or condensing a feature may improve the design.
–
Rearranging means reconfiguring the components or their features.
• This often leads to new ideas because the reconfigured shapes force to rethinking of how the component
fulfills the functions.
–
–
Reversing means transposing or changing the view of the component or feature.
Substituting means identifying other concepts, components, or features that will work in place of
the current idea.
• Care must be taken because new ideas sometimes carry with them new functions.
117
Example of Patching
118
Materials and Process Selection

Material and production processes selected must evolve as the
shape of the product evolves in concurrent engineering.
–
Constraints in determining the material:
• Mass (weight); Environment (corrosion); Strength and stiffness
• Biocompatibility

Information influencing the embodiment of the product:
–
–
Quantity of the product to be manufactured
Prior-use knowledge
• When studying existing devices, get into the habit of determining what kind of
materials were used for what types of functions.
–
–
Knowledge and experience
Availability of a material
119
Vendor Development

Mechanical designers seldom design basic mechanical components (such as bolts,
nuts, gears, or bearings) for each new product since such components are readily
available.
–

Advantages of using a components available through vendors.
–
–
–

This is not true in designing an orthopaedic implant.
Vendors have history of designing and manufacturing the product, so they already have the
expertise and machinery to produce a quality product.
They already know what can go wrong during design and production.
They specialize in the design and manufacture of the component, so they can make it in
volumes high enough to keep the cost below what can be achieved through an in-house effort.
After using concurrent engineering which involves a small number of vendors in the
design process from the beginning and includes them in the decisions that affect
what they will be supplying, many companies have been able to reduce the number
of vendors.
–
These tight relationships lead to improved product quality.
120
Product Evaluation for Performance and the
Effects of Variation

to compare the performance of the product to the engineering specifications (or
targets) developed earlier in the design project

The process of Product Evaluation
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Monitoring functional change
Goals of performance evaluation
Accuracy, variation, and noise
Modeling for performance evalution
Tolerance analysis
Sensitivity analysis
Robust design
Design for cost (DFC)
Value Engineering
Design for manufacture (DFM)
Design for assembly (DFA)
Design for reliability (DFR)
Design for test and maintenance
Design for the environment
121
Functional Evaluation
In earlier design process:
Design
Problems
Function
models
Potential
Concepts
Product
Generation
Changes in functions and concepts

Benefits in refining the function model as the form is evolving
–
The functions that the product must accomplish can be kept very clear by updating the
functional breakdown.
• Nearly every decision about the form of an object adds something, either desirable or
undesirable to the function of the object.
–
Tracking the evolution of function means continuously updating the flow models of
energy, information, and materials.
• These flows determine the performance of the product.
122
Goals of Performance Evaluation
P-Diagram


To evaluate the product design relative to targets set previously.
Factors must be supported by the evaluation of product performance:
–
Evaluation must result in numerical measures of the product for comparison with the
engineering requirement targets developed during the problem understanding.
• Measurements must be of sufficient accuracy and precision for valid comparison.
–
–
Evaluation should give some indication of which features of the product design to modify;
and by how much in order to bring the performance on target.
Evaluation procedures must include the influence of variations due to manufacturing, aging,
and environmental changes.
• Insensitivity to these “noises” while meeting the targets results in a robust, quality product.

Additional concepts for better design:
–
Optimization; trade studies, accuracy, tolerances, sensitivity analysis and robust design123
How to Evaluate Performance?

Performance can be evaluated using a
model.
–
Graphical model for form evaluation
• Sketches and layout drawings
–
Analytical model for function evaluation
• Back-of-the-envelope analysis,
• engineering science analysis,
• or detailed computer simulation
(optimization, FEM, etc.)
–
Physical model for function and form
evaluation
• Prototypes for proof-of-concept, proof-of
product and proof-of-production

Example: Design of a Tank to hold
liquid:
–
–
–
A customer’s requirement is to design the
“best” tank to hold “exactly” 4 m3 of
liquid.
Assume that conceptual design of the
tank resulted in a cylindrical shape with
an internal radius r and an internal length
l.
Analytical model: V = r2l
1.27 m3 = r2l
*More thoughts required:
1. Other quality measures that may limit the
potential r and l values.
- weight, size targets, manufacturability,
environment, etc.
2. What is meant by the terms “best” and
“exactly”?
- accuracy, variation, and noise
124
Accuracy, Variation, and Noise


The purpose of modeling is to find the easiest method by which to evaluate the product for
comparison with the engineering targets using available resources.
Two types of errors in any model
–
–

Errors due to inaccuracy
Errors due to variation
Accuracy
–
–
–
The correctness or truth of the model’s estimate
In case of distributed results, the best estimate (mean) will be a good predictor of product performance.
The variation in the results obtained from the model refers to statistical variation of the results about the mean
value.
•
–
–

Precision, resolution, range and deviation are also used to refer to the distribution of the evaluation.
The obvious goal in modeling is to develop an accurate model with a small variation.
Accuracy tells “how much” whereas distribution tells “how sure”.
Why concern the variation?
–
Each parameter that defines the product or process has variation and so each may vary greatly from the desired
mean.
125
Examples of Variation

Remember that, during
production, not all samples of the
product:
–
–
–

are exactly the same size;
are made of exactly same material; or
behave in exactly the same way.
We have to consider how such
variations affect the performance
in the design process.
–
–
Deterministic analytic models
Non-deterministic (or stochastic)
analytical models that account for
both the mean and the variation by
using methods from probability and
statistics
126
Effect of Variation on Product Quality


A product is considered to be of high
quality if its quality measures stay on
target regardless of parameter
variation due to manufacturing, aging,
or environment.
Control parameters vs. Noise as a
source of variation
–
Control parameters:
• parameters controllable by the designer,
such as working environment, geometry,
etc.
–
Noise:
• Uncontrollable parameters
• Noises affecting the design parameters
– Manufacturing, or unit-to-unit
variations
– Aging, or deterioration, effects,
including etching, corrosion, wear
and other surface effects
– Environmental, or external,
conditions including all effects of
the operating environment.
127
How to Deal With Noises

Noises that affect the strength are often accounted for by using a “safety factor
(or factor of safety).”
–
–




FS = Sal/ap (Sal = allowable strength; ap = applied stress)
Rule-of-Thumb Factor of Safety (see appendix C)
Keep noises small by tightening manufacturing variations (generally expensive)
Add active controls that compensate for the variations (generally complex and
expensive).
Shield the product from aging and environmental effects (sometimes difficult
and may be impossible).
Make the product insensitive to the noises (robust design).
–
Key Philosophy of Robust Design:
• Determine values for the parameters based on easy-to-manufacture tolerances and default
protection from aging and environmental effects so that the best performance is achieved. The
term, best performance, implies that the engineering targets are met and the product is
insensitive to noise. If noise-insensitivity cannot be met by adjusting the parameters, then
tolerances must be tightened or the product shielded from the effects of aging and environment.
128
Modeling for Performance Evaluation

Steps to give order to the considerations taken into account
during evaluation:
1.
2.
3.
4.
5.
6.
7.
8.
Identify the output responses (i.e., critical or quality parameters) that need
to be measured.
Note how accurate the output needs to be.
Identify the input signal, the control parameters and their limits, and noises.
Understand analytical modeling capabilities.
Understand the physical modeling capabilities
Select the most appropriate modeling method.
Perform the analysis or experiments.
Verify the results.
129
Tolerance Analysis


Theoretically, tolerance is assumed to represent 3% standard deviations about
the mean value, implying that 99.68% of all the samples should fall within the
tolerance.
Focus of tolerance design is the concern about tolerances on dimensions and other
variables (i.e., material properties) that affect the product.
–
It is shown that only a fraction of the tolerances on a typical component actually affect
its function.
130
Effect of Tighter Tolerances
on the Manufacturing Cost
*Specification of tighter tolerances will
increase the manufacturing cost.
- use nominal tolerance whenever possible.
Meaning of the Tolerances Specified on the
Drawings:
1. It communicates information to
manufacturing that is essential in helping to
determine the manufacturing processes that
will be used.
2. Tolerance information is used to establish
quality-control guide-line. (conformance
quality)
131
Additive Tolerance Stack-up

Most common form of tolerance
analysis.
*Example of Air shock-swingarm:
When the joint is assembled,
lg = ls – (lb + 2 x lw)
lg = gap length
ls = distance between fingers
lb = bushing length
lw = washer thickness
Worst-case Analysis:
If lb = 19.97 (min), lw = 1.95 (min), ls = 24.1 (max), then
lg = 0.23 mm.
If lb = 20.03 (max), lw = 2.05 (max), ls = 23.9 (min), then
lg = -0.23 mm (interference).
If you want assembly to be easy, no interference, then
You should specify ls = 24.33  0.1 mm so that the
narrowest possible distance between the fingers will still fit
the widest components.
132
Statistical Stack-Up Analysis

A more accurate estimate of the gap can be found statistically, in a form of statistical analysis.

Consider a stack-up problem composed of n components, each with mean length li and tolerance ti (assumed
symmetric about the mean).
In general, a length of the dependent parameter is,
l = l1  l2  l3  …..  ln
the sign on each term depends on the structure of the device.
The standard deviation is
s = (s12 + s22 + s32 + ….. + sn2)1/2
Since s = t / 3,
t = (t12 + t22 + t32 + ….. + tn2)1/2

For the example,
lg = ls – (lb + 2 x lw), tg = (ts2 + tb2 + 2 x tw2) ½
For ls = 24.00  0.1, lb = 20.00  0.03, lw = 2.00  0.05;
lg = 24 – (20 + 2 x 2) = 0.0
and
tg = (0.102 + 0.032 + 2 x 0.052) 1/2 = 0.126 mm
On the average, there is no gap and the tolerance on it is 0.126 mm.
133
Example of Statistical Stack-Up Analysis

For the example of Air shock-swingarm,
lg = ls – (lb + 2 x lw), tg = (ts2 + tb2 + 2 x tw2) ½
For ls = 24.00  0.1, lb = 20.00  0.03, lw = 2.00  0.05;
lg = 24 – (20 + 2 x 2) = 0.0
and
tg = (0.102 + 0.032 + 2 x 0.052) 1/2 = 0.126 mm
On the average, there is no gap and the tolerance on it is 0.126 mm.
In this problem, let’s make further assumptions:
1)
When bolted, the fingers can flex up to 0.07 mm inward without undo stress on the welds to
compensate for any clearance.
2)
The assembly personnel can get the parts in between the fingers even if there is a 0.03 mm
interference.
Then, what percentage of the assemblies will meet these requirements?
Figure shows that the probability for problems to
occur during assembly is 29% (24 + 5).
How can we readjust the tolerance values?
1) Inspect each part and reworking on the
numbers.
2) Determine which tolerance is most sensitive to
the results using sensitivity analysis and repeat
the tolerance analysis.
134
Sensitivity Analysis

Technique for evaluating the statistical relationship of control
parameters and their tolerances in a design problem.
–

Sensitivity analysis allows the contribution of each parameter to the variation
to be easily found
For 1-dimensional problem (air shock-swingarm):
s = (s12 + s22 + s32 + ….. + sn2)1/2
For Pi = si2 / s2, where Pi is the contribution of the i-th term to the tolerance (or variance) of the dependent
variable
1 = P1 + P2 + ….. + Pn
For air shock-swingarm problem;
Ps = (0.1 x 0.1)/(0.126 x 0.126) = 0.63 = 63%
Pb = (0.03 x 0.03)/(0.126 x 0.126) = 0.05 = 5%
Pw = (0.05 x 0.05)/(0.126 x 0.126) = 0.16 = 16%
0.63 + 0.05 + 2 x 0.16 = 1.00
- The tolerance on the spacing has the greatest effect on the gap. Thus, the tolerance on the spacing is the most
likely candidate for change.
135
Multi-dimensional Sensitivity Analysis
Consider a general function:
F  f ( x1, x2 , x3, ......,xn )
F = a dependent parameter (length, volume, stress or energy) and
xi = the control parameters (usually dimensions and material properties)
For means and standard deviations (si),
F  f ( x1 , x2 , x3 ,.......,xn )
 F
F 2 2 
s  ( ) 2 s12  ...... (
) sn 
x n
 x1

1/ 2
If F/ xi = 1, this SD equation becomes a linear equation
136
Tank Problem
For the independent parameters of r and l,
the mean volume is:
V  3.1416r 2l
The tolerance on these parameters can be
based on what is easy to achieve with
nominal manufacturing processes.
Let tr = 0.03 m (sr = 0.01) and tl = 0.15 m
(sl = 0.05), then SD on this volume is:
 V  2 2  V  2 2 
sv  
 sl  
 sr 
 r  
 l 
where
V
 6.2830rl
r
and
V
 3.1416r 2
l
1/ 2
For point A, V/ r = 6.61 and V/ l = 4.60, so
sv = [6.612 x 0.052 + 4.602 x 0.032]1/2 = 0.239
- 99.68% (3 SD) of all the vessels built will have volumes within 0.717 m3(3 x
0.239) of the target 4 m3.
For point B, V/ r = 16 and V/ l = 0.78, so
sv = [0.782 x 0.052 + 162 x 0.032]1/2 = 0.166
- 99.68% (3 SD) of all the vessels built will have volumes within 0.498 m3of
the target 4 m3.
*Reduction in variation can be achieved not by changing the tolerances on the
parameters but by changing only their nominal values.
*If we can find the values of r and l that give the smallest variance on 137
the
volume, then we are employing the philosophy of robust design.
Robust Design by Analysis


In the previous tank example, the tank with greater length had less sensitivity to
the large tolerance on the length, so the tank volume varies less.
What are the most robust values for the parameters?
–
–
It is impossible to have V = 4 m3, exactly due to random variations in r and l.
The best we can do is to minimize the difference between V and 4 m3.
C  variance   bias
The objective function to be minimized is:
T = target
 F  2
 F
 s12  .... 
C  
 x1 
 xn
 
2
 2
 sn    F  T 


2
2
2
2
For the tank, C  2rl  sr  r sl   (r l  T )
2
2
For known SDs on r and l, and known target T
C
2
 0  2r 2l  sr2  4r 3 2 sl2   2rl r  1.414l  sr 
s 
r
 l
C
2 2
2
1
 0  2l 2r  sr   r
2 3
l
2  s  
l    l  
C
2
 0  r l  4
   sr  

For sr=0.01, sl=0.05;
r = 0.71 m; l = 2.52 m; sv = 0.138 m3
Improvement in volume variation!
*If this SD is not small enough, we need
to tighten the tolerances of r and/or l.
138
Summary: Robust Design

Step 1: Establish the relationship between quality
characteristics and the control parameters. Also
define a target for the quality characteristics.

Step 2: Based on known tolerances (SDs) on the
control variables, generate the equation for the
standard deviation of the quality characteristics.

Step 3: Solve the equation for the minimum SD of
the quality characteristic subject to this variable being
kept on target.
F  f ( x1 , x2 , x3, ......,xn )
 F 2 2
F 2 2 
s  (
) s1  ...... (
) sn 

x

x
1
n


1/ 2
Limitations on this method:
1. It is only good for design problems that can be represented by an equation.
2. The objective function used in the previous example does not allow for the inclusion
of constraints in the problem. For example, if the radius had to be less than 1.0 m
because of space limitations, the previous cost function would need additional terms to
include.
139
Robust Design Through Testing

Used when the quality characteristics cannot be represented in an
equation.
–
–

Drawbacks:
–
–

V = f(r,l), i.e., analytically in-deterministic relationship, as compared with V = r2l,
analytically deterministic relationship
Begin by building a tank with some best-guess dimensions and measure the volume.
Repeat building a tank until we can find the right dimensions.
Repetitive model building is not efficient.
There is no guarantee that the final design will be the most robust.
Steps to overcome such drawbacks.
1.
2.
3.
4.
5.
Identify signals, noise, control, and quality factors (i.e., independent parameters.
For each quality measure (i.e., output response) to be evaluated, recall or determine
its target value and the nature of the quality loss function.
Design the experiment.
Take and reduce data.
Analyze the results, and select new test conditions if needed.
140
Step 1: Identify signals, noise, control, and quality factors
Step 2: For each quality measure (output response), determine its target value and the nature of
the quality loss function.
Quality loss is proportional to the mean square deviation (MSD), average difference between the output
response and the target. This difference is often referred to as signal-to-noise (S/N) ratio.
Quality Loss Function:
smaller-is-better
larger-is-better
Nominal-is-best
MSD
1
2
y
 i
n i 1
1 n  1 
 2 

n i 1  yi 
S/N Ratio
1 n 2
 10 log  yi 
 n i 1 
1 n 1 
2
1 n
 10log  2   10log  yi  y  
141
 n i 1

 n i 1 yi 
n

2

1 n
2


y

y

y

m
 i
n i 1

Step 3: Design the experiment.
–
The experiment should be designed so that the results give a clear understanding of
1) the effects on the output response of changing control parameters; and 2) an
understanding of the effects of noise.
• An ideal experiment will show how to adjust the control parameter to meet the target
and show which one to choose so that the resulting system is insensitive to noise.
–
Goals:
• Control factors can be changed to represent the options available.
• Noises can be controlled over the expected range.
• The output responses can be measured accurately.
142


Step 4: Take and Reduce Data
Step 5: Analyze the Results, and Select New Test Conditions if Needed
Is 4.34 m3 is close enough?
If not, there can be 2 ways for further refinement:
1) r can be estimated to bring the output to 4 because l=5.5 resulted in better S/N. (How
much to change r is not clear from the table)
2) Perform experiments by setting new values for r and l around the values.
143
Product Evaluation for Cost, Manufacture, Assembly, and
Other Measures

Cost Estimating in Design
–
Most difficult and yet important tasks
• A rough estimate should be generated
in the conceptual phase or at the
beginning of the embodiment phase;
and
• Cost estimate is refined as the
product is refined.
–

DFC (Design For Cost): keeping an
evolving cost estimate current as the
product is refined.
Determining the Cost of a Product:
–
Direct Cost
• All costs that can be directly traced
to a specific component, assembly, or
product
–
It is the responsibility of the designer to
know the manufacturing cost of
components designed.
Indirect Cost
144
Cost of Machined Components


Machining is to remove portions of
the material not wanted
7 significant control factors for the
machining cost:
1.
2.
3.
4.
5.
6.
7.
From what material is the component to
be machined?
What type of machine is used to
manufacture the component?
What are the major dimensions of the
component?
How many machined surfaces are there,
and how much material is to be
removed?
How many components are made?
What tolerance and surface finishes are
required?
What is the labor rate for machinists?
145
Cost of Injection-Molded Components


Most popular method for making
high-volume products with less
precision requirements
Factors for Cost:
–
–
All factors for machined component
Cost for manufacturing the mold
• Wall thickness
• component complexity
–
–
Molding time (cooling time)
Number of components
146
Value Engineering

Developed by GE in the 1940s and evolved into the 1980s.

How to determine the value of a function in relation to the
required cost?
–
–

Value = Worth of a feature, component, or assembly / Cost of it
Value = function provided per dollar of cost
The worth of the function to the customer must be well
identified.
147
Design For Manufacture (DFM)


DFM is widely used but poorly defined.
DFM is establishing the shape of components to allow for
efficient, high-quality manufacture.
–
–
–
–

Key concern: Specification of the best manufacturing process
How to hold the components for machining?
How to release from the molds?
How to move components between the processes?
The concurrent engineering philosophy, with manufacturing
engineers as members of the design team, help incorporate the
DFM.
148
Design –for-assembly (DFA) Evaluation

DFA is the best practice used to measure the ease with which a product can be assembled in
terms of efficiency.
–
–
Assembling a product means that a person must 1) retrieve components from storage, 2) handle the
components to orient them relative to each other, and 3) mate them.
A product with high assembly efficiency has a few components that are easy to handle and virtually fall
together during assembly.
149
Guidelines for better DFA

Evaluation of the overall assembly:
1.
2.
3.
4.
5.

Evaluation of component retrieval:
6.
7.

Avoid component characteristics that complicate retrieval.
Design components for a specific type of retrieval handling, and mating.
Evaluation of component handling:
8.
9.
10.

Overall component count should be minimized.
Make minimum use of separate fasteners.
Design the product with a base component for locating other components.
Do not require the base to be repositioned during assembly.
Make the assembly sequence efficient.
Design all components for end-to-end symmetry.
Design all components for symmetry about their axes.
Design components that are not symmetric about their axes of insertion to be clearly
asymmetric.
Evaluation of component mating:
11.
12.
13.
Design components to mate through straight line assembly.
Make use of chamfers, leads and compliance to facilitate insertion and alignment.
Maximize component accessibility.
150
DFA for Orthopaedic Implants

DFA is critical in designing a product for mass production.

For orthopaedic implants:
–
–
–
–
Actual assembly is performed during operation by surgeons.
Easy assembly is one of the major features that surgeons are looking for
from an implant.
Make sure to minimize the number of components, assembling
procedures and instruments for assembly.
It is always better to consider the removal of implants.
151
Design For Reliability (DFA)

Reliability is a measure of how the quality of a product is maintained over
time.
–
Quality = satisfactory performance under a stated set of operating conditions.
•
•
•
–
Failure Modes and Effects Analysis (FMEA):
•

Technique for identifying failure potential used in calculating the reliability of a product.
Failure-Potential Analysis
1.
2.
3.
4.

Unsatisfactory performance = failure
Mechanical failure = any change or error that renders a component, assembly or system
incapable of performing its intended function.
Typical source of mechanical failure: wear, fatigue, yielding, jamming, bonding
weakness, property change, buckling and imbalance
Identify the function affected.
Identify the effect of failure on other parts of the system.
Identify the failure modes affecting the function.
Identify the corrective action.
Reliability (R(t)) = exp(-Lt), L = failure rate or mean time between failures
(MTBF) determined from the experiments
–
–
R(t) is the probability that the component has not failed.
R(8760 hrs) = 0.892 implies that it would be expected that 89.2 out of 100 would
152
still be operating after a year within specifications.

Design for Test and Maintenance (DFTM):
–
–
–

Testability refers to the ease with which the performance of critical functions
is measured.
To design products that are easy to diagnose, disassemble, and repair at any
level of function.
Practice following the design process suggested in this class increases the
testability.
Design for the Environment:
–
–
Green design, environmentally conscious design, life cycle design, or design
for recyclability.
Guidelines:
•
•
•
•
Be aware of the environmental effects of the materials used in products.
Design the product with high separability
Design components that can be reused to be recycled.
Be aware of the environmental effect of the material not reused.
153
Launching and Supporting the Product

Documentation and communication
–
–
–
–
–
–
–

Support
–
–
–


Quality assurance and quality control
Manufacturing instructions
Assembly instructions
Installation instructions
Operating instructions
Maintenance instructions
Retirement instructions
Vendor relationships
Customer relations
Support for manufacturing and assembly
Engineering changes
Patent applications
154