design process v4

7/24/2019 Design Process v4

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Notes on Design Processes and Methodologiesby Dan Frey

1 Design ProcessesDesign has been defined in many, slightly different ways by many different people. Onegood definition is given by the Accreditation Board for Engineering and Technology

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(ABET) which defines design as The process of devising a system, component, orprocess to meet desired needs. This definition is simple yet covers the essentials of

design in all its various forms including mechanical design, software, architecture, andeven less technical fields such as fashion design.

ABET elaborates further describing design as a decision-making process (often

iterative) in which the basic sciences, mathematics, and engineering sciences are appliedto convert resources optimally to meet a stated objective. This elaboration is useful in

the sense that it adds elements important to modern engineering design. But theseadditional statements ought not to be part of the definition of design. For example,

design cannot be called a decision-making process since it must also include generationof alternatives as well as selection among them. It would be more accurate to say design

includesdecision making processes within itas opposed to saying it isa decision makingprocess. This will be discussed more in the section

on Pugh Controlled Convergence. In addition, theapplication of sciences and the explicit use of

optimization may not always be present in everydesign activity. This will be explored further in the

section on historical context.

1.1 Mo t ivat ion

1.1.1 Historical Context

As defined by ABET, design has an extremely long history. The earliest stone tools arebelieved to have been crafted over one million years ago. The shapes of early stone toolsappear to have been devised for very specific purposes some for chopping wood, some

for grinding grains, some for the tips of spears used to hunt animals. It can fairly be saidthat these tools must have been designed. The humanoids who fashioned these earliest

stone tools had brains far smaller than those of modern humans, they did not have

1ABET is the body that accredits MITs engineering degrees and therefore is the same people who require

that you to take design courses like 2.007

ABET defines design as

The process of devising asystem, component, orprocess to meet desiredneeds.


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language (maybe they had a proto-language), and they apparently couldnt draw pictures. The design process used to define the shapes of early stone tools surely wasnt very

sophisticated. Their design probably involved a lot of trial and error over generations ofindividuals who slowly evolved the designs. Over time, shapes that worked well were

passed on. Small changes were made and, for the most part, only changes that led to

improvements were retained.

Consider by contrast the design of a spear thrower depicted in Figure 1 (sometimes called

and atlatl) which apparently dates to 14,000 BCE. Scientists argue that humans at thetime this design first appeared were essentially as intelligent people are today. They

could learn languages and draw pictures. However, there was no civilization at that timeand surely no science as we know it today. Yet looking at the spear thrower, there

appears to be some fairly sophisticated thought required to understand the physicaleffects involved. To throw a spear farther by hand, it helps to move your hand faster.

But physical limits prevent even the most athletic people2from moving their hand morethan about 100 mph (45 m/s). Given that constraint and assuming low drag and an

approximately no lift, a simple ballistics model suggests the range of a spear could be asmuch as 200 meters, but in practice its more like 100 meters3. But extending the point

of contact with the spear and involving the wrist in the throwing motion could extend thetime for applying force and increase the initial velocity of the spear increasing both the

range of the throw and the force with which it penetrates. Studies of this type ofthrowing device suggest the device can roughly double the release speed and that an

atlatl dart can travel as far as 260 meters4.Enabling this kind of performance improvement,

many details had to be worked out. Maintainingcontact between the throwing device and the back of

the spear places some demands on the shape of thecontact point. It is essential to apply force but also

allow the two bodies to freely rotate with respect toone another. Proper release of the spear at the end of

the throwing motion places further requirements onthe shape at the contact area.

Figure 1. A Spear Thrower.

The spear thrower in Figure 1 seemed to require some sophisticated design thinking. We

can be sure no proper model of the multi-body dynamics could have been used in thisdesign process since it didnt exist at the time the thrower was designed . It is possible

that the physical effects were understood by the designers in some intuitive sense. It is

2The fastest clocked baseball pitch in history was 104.8mph. It was thrown by Joel Zumaya of the Detroit

Tigers while playing in the American League Championship in 2006.3The world record in the javelin throw is 98.48 mters set in 1996 by Jan Zelezny of the Czech Republic.4The record distance is 258.64m by Dave Engvall in 1995

www.worldatlatl.org/Articles/Atlatl%20Experiments.pdf

Exercise: Explain, in amanner that a bright highschool student wouldunderstand, why doublingthe initial velocity of a

projectile will quadruple itsrange assuming zero dragand zero lift and fixedinitial launch angle.


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likely that much of the design was worked out by trial and error. In any case, a designemploying some complex physical effects can proceed first, and the underlying science

apparently can be developed later. This pattern also applied to many other developments.Watts steam engine appeared in 1850 and the basic developments of thermodynamics by

Kelvin, Carnot, and others came at least three decades later. This pattern is changing

quickly in the modern engineering context with increasing dependence of design on ascience base.

1.1.2 Modern Context

As the previous section explains, historically, many advances first emerge through design

and later find an explanation in science. However, design in a modern context must relyon the vast base of existing science. To the extent that a science base begins to become

available in any particular area, the best organizations will use that science to advancetheir designs. To be commercially competitive, other firms seek to employ the science

base as effectively or even more so then other companies making similar products.

Design today is carried out by individuals, small firms, large companies, and governmentorganizations. They develop products of mind boggling complexity and staggering levels

of performance and reliability. For example, consider a modern jet engine such as theGE90. It can generate about 75 MW -- as much power as about 6,000 US citizens

consume on average by driving, running appliances, and so on. The GE90 weighs justabout 8 tons, so each ton of engine is producing about 10MW. Thats about 2000 times

an athletic humans power-to-weight ratio. Whole fleets of GE90 engines operate on thewing of a modern aircraft and have so far accumulated 20 million flight-hours with about

one in-flight-shutdown per 4 million hours on average and logging an engine departure

reliability of about 99.96 percent. So this is a machine that accomplishes a stunningtechnical feat with nearly complete regularity under all sorts of demanding conditions.This is just one example to help you appreciate the remarkable capability and

sophistication of engineering design today.

Despite all the knowledge about engineering design that apparently resides in people andorganizations, it is hard to find a single coherent picture of design process that fits the

whole range of activity. Each company typically describes it design process using somediagrams, charts, and text. Pratt and Whiney develops jet engines. It describes its design

process in a carefully defined process of standard work5. A simple description of their

engine design process is shown in Figure 2. The Pratt standard work depicts the design

process as a set of stages of increasing detail and completeness which is sometimesdescribed as a waterfall.

5Sullivan, John P., 1999, The relationship between organizational architecture, product architecture, and

product complexity, Thesis, MIT System Design and Management Program.


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Figure 2. A design process at a major company (in this case, Pratt and Whitney) might

be represented as a waterfallwith a series of phases of increasing detail and

completeness ending in a complete plan for production.

Figure 3. A design process at a major company (in this case, Ford Motor

Company) might be represented as a V with requirements coming in one

end, flowing down to parts at the bottom, and with complete system designs.


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By contrast, Ford Motor Company describes its process as a V (see Fig 3) with

requirements being subdivided from vehicles to subsystems to components on one side.Components are designed in the middle phase represented by the bottom of the V.

Then, on the ascending side of the V, the parts are composed into subsystems and then

subsystems are integrated into vehicles and all along tests are employed to verify thedesign.

Pratt and Ford are just two examples. There is much more variety we could show acrosssuccessful companies. Some software companies describe their design process as a spiral

with requirements at the core leading to simple prototypes which are used to furtherexplicate the requirements in another layer of the spiral. Other companies describe their

design process as a funnel with many design concepts being considered in parallel withrefinement and selection to a smaller number of options over time.

Many of these differences among design process descriptions arise from the different

demands imposed by the nature of the artifact being designed, the rate of technicalchange in the field, or the nature of the customers being served. Other differences have

more to do with the individual style of the people and the companies involved. Forexample, the design processes used by the three largest jet engine manufacturers (General

Electric, Pratt and Whitney, and Rolls Royce) are vastly different even for productswhere all three companies make engines that are performing essentially identical

functions. In some cases, three different engine designs can literally be bolted onto thesame aircraft and offered as different options for the airlines to choose, yet they are all

designed by quite different processes.

To summarize, the modern context of engineering design is characterized by tremendoussophistication and broad variety. It is interesting to consider the implications for your

professional education. To add something valuable to the existing system, you will needlots of knowledge, skill, and creativity. Those capacities can be developed through study

and practice which begins in school. To fit usefully into a broader engineering designeffort in a modern organization, you will need to adapt to a design process we cant teach

you while youre at a University, because we cant predict which process your companywill use. Being a designer in a modern context seems to require life-long learning. Each

design project you undertake will pose challenges -- many becoming familiar as youaccumulate experience, but always some new ones to master. This is something to

celebrate if you enjoy having a variety of life experiences.

1.2 Design Methods

Despite the fact that there is no one design process used uniformly across successfulcompanies, there is value in learning some of the most common design methods and

tools. This section will review the basics of a small sample of tools and methods usedacross the design process, starting with ones typically used early in the process and

progressing chronologically.


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1.2.1 Requirements Definition

Before a design project can begin in earnest, a significant amount of front end workshould be undertaken to prepare the designer or the design team for what lies ahead. One

of the key outcomes of this work is a document alternately called a requirementsdefinition document, product design specification, or design brief. This document must

describe the design opportunity clearly, but without unintentionally locking in designdecisions. Failure to spend adequate time and energy at this stage can doom a project to

poor outcomes.One important piece of advice for designers at this stage is to express the requirements

for the design in solution neutral language. For example, if you plan to create a newproduct to compete with existing snow throwers, rather that stating that you want a

system for throwing snowfrom a driveway, it is preferable to describe the requirementas removing snow. Thisphrasing leaves open many more possibilities such as plowing

the snow, conveying it on a belt, or even melting it. The key point is that, in the earlyphases of a design we want to describe WHAT is to be done without unnecessarily

constraining HOW it can be done.

Another key guideline for this stage is to express the requirements for the design inmeasurable engineering terminology. For example, in defining the requirement forremoving snow, youmay need to constrain the amount of snow to some extent or the

surfaces from which it will be removed. In that case, the requirement might be modifiedto be removing snow of up to one meter depth from asphalt and concrete driveways.

There may also be constraints on the system set by its context or interfaces. For the snowremoval device, that might include noise or power. These should be made specific such

as emitting no more than 20dB of noise in any direction as measured one meter from thedevice or employing either unleaded gasoline or no more than 10 Amps of 120VAC

power at 60Hz.

1.2.2 Concept Generation

After a good description of the requirements is ready, a period of initial conceptgeneration should proceed. There are many techniques that have been proposed forincreasing the creative output of individuals and teams. These include brainstorming, use

of analogies, morphological analysis, Altschullers TRIZ, and deBonos processes forLateral Thinking. Meta-studies suggest there are no silver bullets for concept

generation, but that most any form of training regarding creativity will tend to improveoutputs perhaps just by increasing the awareness of the people involved in the need for or

Exercise: Evaluate the following problem statements and suggestimprovements if possible:Because damp clothing severely impacts back country enjoyment and cancontributeto hypothermia, hikers require a means to dry their clothing.Bicycle riders need a lightweight (


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desirability of creativity. This subsection reviews the essence of just two methods,brainstorming and TRIZ.

Brainstorming is an activity in which a group of people quickly work to develop alarge number of solutions to a design challenge. It takes just about an hour to do, so there

is not much risk in giving it a try on any given project. The approach involves setting up

a room with plenty of paper, writing implements, and other props and inviting a diverseset of people to participate. A typical goal is to develop 100 ideas in an hour. Arecommended group size is 5 to 7 as this provides enough variety of input. Larger groups

would tend to create too much production blocking wherein participants spend toomuch time listening passively to others ideas and not enough time producing ideas of

their own. A key aspect of the method is adherence to the standard five rules of thebrainstorm:

Defer judgment

Build upon the ideas of others

One conversation at a time

Stay focused on the topic

Encourage wild ideas

Another widely known approach to generating ideas is known as the Theory ofInventive Problem Solving, known most often as TRIZ (its acronym in Russian). The

approach was based on study of a large set of patents. Common solutions werecategorized in terms of the ways that inventions had resolved technical contradictions.

Technical contradictions are cases wherein the action to improve some featuresimultaneously appears to reduce some other needed property which sets up a conflict

among the two needs. Writing the conflict in this form provides a means to access adatabase that is supposed to help access patents that are likely to inspire some useful

ideas that might be adapted to the given situation.

An example serves to illustrate the approach. To study the effects of acids on metalalloys, specimens are placed into a hermetically sealed chamber filled with acid. Theacid reacts not only with the specimen but also the walls. The challenge is to invent a

system that avoids the adverse effects of the chamber walls on the testing procedure.First the problem is re-stated as a contradiction, in this case, that the walls must be

present to contain the acid, but in a sense, the walls must be absent to avoid participatingin the reaction. The proposed solution from TRIZ is to make the wall out of the specimen

material itself. This sort of system simplification is frequently a feature of TRIZsolutions as they promote evolution toward ideality.

The actual set of TRIZ methods are complex and the effectiveness of the approach inpractice shows at best mixed results. I would suggest taking away the key idea that

knowledge of lots of inventions is helpful in developing more inventions. Rather thanstudying any specific creativity methodology, I would suggest you invest the same time

in another activity. Specifically, I suggest you find time every week to read some patentsfrom your field of engineering and some very good patents from other fields, this will be

a long term strategy for increasing your inventive capacity.


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1.2.3 Pugh Controlled Convergence

After engaging in a process of concept generation, there will be more ideas available thanone can reasonably pursue. There must be some reasonable process for culling down the

set to a smaller number that can be developed in greater detail.Many design decision making processes have been proposed. Most of them are fairly

complex and rigid. Very few formal methods are used widely in industry. Surveysindicate that practitioners describe their concept selection methods most often as "concept

review meetings", "intuitive selection" or "expert assessment". These labels suggestessentially no structure. The process suggested in this chapter adds just a little formality

because, without that structure, experience shows that individuals and teams tend tofixate on a single design concept too earlya serious misstep that is common in practice,

especially for inexperienced designers. Another key benefit to a modicum of structure isthat it creates a space for team discussion and prompts the more reserved participants to

speak up. In a complete lack of structure, the most brash people on the team tend todominate the decision, even if they dont have all the relevant facts at their disposal.

The process we advocate in this section was developed through field work by a noted

design researcher, Stuart Pugh [1990]. He described an approach aimed at 1) 'controlledconvergence' on a strong concept that has promise of out-competing the current marketleader; and 2) a shared understanding of the reasons for the choice. In this section, we

refer to this as Pugh Controlled Convergence or PuCC.A prominent aspect of PuCC is presentation and discussion of information in the

form of a matrix. The columns of the Pugh matrix are labeled with a description, indrawings and text, of design concepts. The rows of the matrix are labeled with concise

statements of the criteria by which the design concepts can be judged. The methodrequires selection of a datum, preferably a design concept that is both well understood

and known to be generally strong. Often the initial datum concept is currently the leaderin the market. Evaluations are developed and entered into the matrix through a facilitated

discussion among the experts. Each cell in the matrix contains symbols +, -, or Sindicating that the design concept related to that column is clearly better than, clearly

worse than, or roughly the same as the datum concept as judged according to the criterionof that row.


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Textooks and papers on Pughs method usually present neatly formatted tables to

explain the Pugh matrix, such as the one shown in Figure 4. This may contribute to amisunderstanding of what is actually done. In practice, Pugh matrices are messy collages

of drawings and notes (such as the Pugh matrix from a software development team shownin Figure 5). This is a reflection of the nature of early-stage design. The PuCC process is

simple and coarse-grained as it should be for use in early stage design. By contrast,alternatives to Pugh's method often require greater resolution of the scale (suggesting five

or ten levels rather than just three) and often require numerical weighting factors. Pughfound by experience that this sort of precision is not well suited to concept design.

Figure 4. A neatly formatted representation of a Pugh

Concept Selection Matrix intended for use in a textbook.

Figure 5. An actual example of a Pugh Concept Selection Matrix

from industry practice.


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It is common practice to place summary scores along the bottom of the matrix. Thenumber of +, -, or S scores for each concept are counted and presented as a roughmeasure of the characteristics of each alternative. This raises an important potential for

misunderstanding. These scores should NOT be interpreted as a means by which tochoose the single winning design. Although a single run of an evaluation matrix can help

reduce the number of design concepts under consideration, but is not meant to choose asingle alternative. A single matrix run can result in at least four kinds of decisions (not

mutually exclusive) including decisions to: 1) eliminate certain weak concepts fromconsideration, 2) invest in further development of some concepts, 3) invest in information

gathering, and 4) develop additional concepts based on what has been revealed throughthe matrix and the discussions it catalyzed.

Figure 6 illustrates how iterated uses ofPugh matrices can lead to convergence. The

key feature to note is that controlledconvergence generally includes periods of

divergence of the set of concepts.

Experience shows that studying the relativemerits of design concepts is a good way toprepare ones mind for concept generation.

Seeing the ways that one concept attains astrength where another is weak may suggest

a means to bring the positives of one concepton board to another concept. When this

occurs, decision making is greatly facilitatedbecause trade-off is no longer necessary

between the involved criteria.

Figure 6. A graphical depiction of the Pugh

Controlled Convergence process.


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1.2.4 Experimentation in Design

During your process of convergence, it is essential that you advance your design adding

more detail and working out the critical parameters, components, and geometric

proportions. Some of this design work can be carried forward primarily throughComputer Aided Design supported by engineering calculations. However, experiencetells us that almost all designs also require a thoughtful process of experimental work.

Experiments fill in the needed information that analysis and CAD cant provide. Thesegaps can be small (and few in number) for some well-established design concepts or there

can be many, large gaps we need to fill in when executing highly innovative designs.This section presents some advice and methodology for effective experimentation as part

of the electromechanical design process.A careful study of industry design practice led Stephan Thomke

6 to suggest the

following advice for using experiments in design:

Organize for rapid experimentation When it comes to experimentation, some

people and some organizations are much faster than others. Experimentation canbe greatly accelerated by having the right instrumentation, computer tools, andknow-how in place. Some of that preparation falls on the organization of 2.007

itself. Most of it, however, is up to you. Lets work together to make it possiblefor you to do the right experiments quickly. One aspect of rapid experimentation

is statistical planning and analysis of experiments. When experimental error islarge compared to the effects being estimated, these techniques are essential. I

would need an entire chapter on this topic here, but 2.007 experiments can begenerally made with relatively low pure error. For the exceptional cases, there is

an excellent paper by George E. P. Box that is directly relevant to the method andstyle of experimentation for use in refinement of electromechanical designs.

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Fail early and often, but avoid mistakes Design requires a major change in themind-set regarding failure. Most of the time, we work hard to avoid failure andfeel a sense of frustration and even shame when we experience failure. In design,

innovation makes some degree of failure essential as a means to learn what worksand what doesnt. The key is to push the failures up to the early stages of the

design process. Also, since failure is expensive, recognize that some failures canbe avoided by application of good engineering knowledge. The point is not really

to fail a lot, but to use failure to learn those things we cant learn in other ways.

Anticipate and exploit early informationA key to effective experimentation is toget information into the process early. In some cases, the best way to get that

information is through virtual experiments such as in CAD. If you can detect an

interference in a Solidworks Model, that may save a week of re-design and re-building later. If CAD is not convenient for the task at hand, perhaps a foam coremockup will do the job. How to decide which approach is best? IDEO suggests

you think about the three Rs your experiment should be rough, rapid, and

6Thomke, Stephan, 2001, Enlightened Experimentation: The New Imperative for Innovation, Harvard

Business Review, Feb, pg. 67-75.7Box, G. E. P. and P. T. Y. Liu, 1999, Statistics as a Catalyst to Learning by Scientific Method, Journal

of Quality Technology31(1): 1-29.


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right. Dont build a fancy prototype early if a simpler one would answer thequestion.

Combine new and traditional technologies New technologies (well, relativelynew) at your disposal include CAD, 3D printing, and water-jet cutting. Thomkes

advice is that new technologies like this have the biggest payoff when used early

in the design process. This is especially true in 2.007 where some of thesetechnologies become over-tasked late in the term when everyone is clamoring foraccess at the same time.

1.2.5 Robust Design

There is a huge difference between the two following objectives:

Making a machine that can function properly when every possible factor is at its

ideal value, such as when the machine is demonstrated under carefully controlledlaboratory conditions

Making a machine that can function properly under the full range of conditions itis likely to experience in authentic field use

The distinction above is a key to having customers who are delighted by your productand loyal to the brand. The alternative is to have former customers who are frustrated by

the constant breakdowns, recalls, warrantee service, and never-ending calls to tech helplines.

In the context of commercial product development, robustness is not optional. Mostcompanies know that. A select few also have the set of tools and willingness to invest in

the steps needed to follow through on implementing robust design.In the context of 2.007, it is easy to drift into the mindset that the first objective is

sufficient. Many students get some good results in the last weeks of the class. Thesegood outcomes appear when the machine exhibits no wear or distortion, when the battery

is at peak charge, when the radios are in mint condition, and when the opposing player isnot there to create other adverse conditions. Unless there has been adequate attention to

robust design, when any one of several factors drifts off the ideal state, the outcome is

poor.

Implementing robust design is conceptually simple.1) You have to deliberately expose your design to a broad set adverse conditions.2) You must do this early enough that you can repeat the process for multiple design

alternatives so that you can choose the options that perform better.

1.2.6 Failure Modes and Effects Analysis

Failure Mode and Effects Analysis (FMEA) is an engineering technique aimed at identifying

and classifying potential failure modes, their effects on the system, and definingcountermeasures -- actions to avoid the failures previously identified. FMEA may be


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performed at either the system or piece-part level. Ideally, it should begin as early as possible

in design and be used continually throughout the whole product life cycle in order tostructure information flow in the organization. The feature of FMEA is classification of theeffects of potential failure modes by severity, occurrence, and detection. FMEA can also be

used to prioritize the countermeasures. This may be done by calculating the risk prioritynumbers (RPN) for each failure mode.

As an early step in conducting an FMEA, a list of potential failure modes must be compiled.

While it is not possible to anticipate every possible failure mode, it is very important to dothe search as thorough as possible. It is necessary for the FMEA to be conducted by a team ofexperts with various views of the product. The designer of the product is essential, but as he

or she often lacks the necessary critical view of the product, so experts from other fields oreven the customer should be part of the team. Subsequent steps vary among practitioners,but a good baseline process is:

a. Define the ideal function (or functions) of the design.b. Determine all of the potential failure modes associated with each function

c. Write down the effects of these failure modes on each type of customer

d. Determine the failure mechanisms (sometimes called root causes) that can cause thefailure modes to occure. Identify a detection event (e.g. a set of design rules & standards, analytical methods, or

physical testing) that can discover and excite the failure mode via the determinedmechanism.

f. Determine the action that constitutes a countermeasure to the failure mode occurring(either eliminate the cause, or mitigate the effect of the cause with appropriate design

modifications).g. Verify the effectiveness of the failure mode avoidance action in f, and determine if

better detection events and/or more countermeasures might be required.

The output of the analysis is a FMEA Table (such as Table 1 below) which lists all the failuremodes together with possible effects on the system and other issues that may be important indealing with the failure. It is generally important to consider possible detection events. Afailure that cannot be detected clearly and early enough will often prove to have more serious

consequences. There is no universally accepted layout for the FMEA (although certain

standards exist within industries, for example automotive), but loosely they all follow thesequence of information flow listed below, laid out on a landscape document reading

from left to right.

A major concern with FMEA is that it can devolve into a bureaucratic exercise That fillsup paper and takes up time, but doesnt really improve the design. To make FMEA

useful, you need to move beyond analysis, into avoidance of the failure mode through thedeployment of an effective counter measure. Tim Davis has proposed that we rethink

FMEA and rename it Failure Mode Avoidance to emphasize the changed mind-set. Thiswill require some further development to explain how FMEA, when practiced well, can

influence the design process and structure information flow among designers.


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Table 1. Example FMEA Worksheet

FunctionFailure

modeEffects

S

(severity

rating)

Cause(s)

O

(occurrence

rating)

Current

controls

D

(detection

rating)

CRIT (critical

charactertics)

RPN

(risk

priority

number)

Recommended

actions

Responsibility

and target

completion

date

Action

taken

Fill tub

Highlevel

sensornevertrips

Liquidspills oncustomer

floor

8

level sensorfailed

level sensordisconnected

2

Fill

timeoutbased on

time tofill to low

levelsensor

5 N 80

Perform cost

analysis of addingadditional sensorhalfway between

low and high levelsensors

Jane Doe10-Oct-2010


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Summary

Design is a process that has been around a long time. No doubt, our ancestors

survived substantially because of their skill in developing solutions to problemsthey faced with the materials and technology that was available to them. They have

passed this skill onto you and I expect youll find you have natural ability to design.

Your natural ability can be improved by practice and by reflection on what makes

design processes work effectively. Some of the key lessons from scholars who havestudied design carefully include:

Develop many concepts, not just one.

Select concepts based on evaluation against multiple criteria.

Develop your designs using the best available scientific and empirical

knowledge of relevant phenomena.

Expose your design to difficult conditions early in the process. Evolve your design through iterative improvement based on modelling,

simulation, and experimentation.

Document your design process as well as your final design results.

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