A survey of design philosophies, models, methods and systems

301

Review Paper

A survey of design philosophies, models, methods and
systems
....; F 0 Evbuomwan, * BEng, MSc, PhD, DIC, CEng, MIStructE, S Sivaloganathan, BSc, MSc, PhD, CEng, FIMechE, MIEE,
!IE(Sri Lanka) and A Jebb, BSc, PhD, DIC, CEng, MIMechE, MIEE ·
Engineering Design Centre, City University, London

The study of the design process, design theory and methodology has been a preoccupation of engineers, designers and researchers over
1he fast four to jive decades. As the end of this millenium is approached and with the renewed inrerest around the world in engineering
design. it is fitting to examine the state of the art and currenr status of issues relating to design philosophies, theory and methodology.
(Jeer the last 40 years, many approaches to design have been put forward by various researchers, designers and engineers, both in
, 1cademia and industry, on how design ought to and might be carried out. These proposals on design have tended towards what has
, orne to be regarded as design philosophies, design models and design methods. The thesis of !his paper is to discuss various aspects of
,1eneric research in design, within the above classifications in the light of the work that has been done in the last four decades.
Discussions will focus on various definitions of design, design theory and methodology, the nature and variety of design problems, design
classifications, philosophies, models, methods and systems.

f ev words: design philosophies, design theory, design methodology, design models, design methods, design systems, design process,
rrciduct design, computer aided design

1 INTRODUCTION theory and methodology. Further discussions will be on
The design activity, although performed for many cen- the nature and features of the design process, the nature
turies, did not, however, have any structure or organiz- and stages of thought in design, types of design prob-
;.ttion to it. It was only just after the middle of this lems, product design classification and design goals.
century that efforts began to give some formalism to the
way design was done. What is design? Why is it done?
How is it or can it be done? These questions have been 2.1 Definitions of design
the subject of discussions at various conferences on Several designers, engineers and researchers, from
engineering design and design methodology. In these observation and experience, have expressed their views
conferences, which were held in the United Kingdom on the definition of design or what they consider design
il-5), Europe (~10) and North America (11-18), a to be. Some of these viewpoints are expressed below:
number of ideas were put forward on design method-
ology. These ideas were mostly associated with design Feilden (19): 'Engineering Design is the use of scientific
models, philosophies and methods or techniques as well principles, technical information and imagination in
as applications, and they represented several schools of the definition of a mechanical structure, machine or
thought on design and design methodologies. More system to perform prespecified functions with the
recently, other researchers have started to report on maximum economy and efficiency.'
computer-based design systems . Finkelstein and Finkelstein (20): 'Design is the creative
. The main focus of this paper is to give a detailed elu- process which starts from a requirement and defines a
cidatiOn of design philosophies, models, methods and contrivance or system and the methods of its realis-
systems that have been proposed and developed over ation or implementation, so as to satisfy the require-
the years. Discussions will centre on: definitions of ment. It is a primary human activity and is central to
design and design methodologies, the nature and fea- engineering and the applied arts.'
tures of design problems and the design process, as well Luckman (21): 'Design is a man's first step towards the
~s the stages of thought in design and product classi- mastering of his environment . . . The process of
tJcati?n. The nature and control of design goals will also design is the translation of information in the form of
be discussed, including an extensive review of many requirements, constraints, and experience into poten-
design models, methods and systems. This paper focuses tial solutions which are considered by the designer to
on completely general aspects of engineering design meet required performance characteristics ... some
research, and it should be noted that there is a large creativity or originality must enter into the process
amount of other work in this area. for it to be called design.'
Archer (22): ·. . . design involves a prescription or
2 DESIGN, DESIGN THEORY AND DESIGN model, the intention of embodiment as hardware, and
METHODOLOGY the presence of a creative step.'
The discussions in this section focus on definitions of Caldecote (23): '. . . the basic design function ... to
design, as well as definitions and viewpoints on design design a product which will meet the specification, to
design it so that it will last and be both reliable and
; ~e liS was received on 3 June 1995 and was accepted for publication on easy to maintain, to design it so that it can be eco-
· 'nrember /995.
: Prnenr address: Deparrmenr of Civil Engineering, University of Newcastle. nomically manufactured and will be pleasing to the
·' •{ a.stle upon Tyne.
eye.'
Proc Instn Mech Engrs Vol 210

:
302 N F 0 EVBUOMWAN, S SIVALOGANATHAN AND A JEBB

The foregoing definitions of design reflect the various refinements) are proposed to the current design in
viewpoints of the proponents. In general, certain key- order to move to a 'better' design.
words and phrases can be noted which have a strong 3. Design as an exploratory activity (29) involves an
bearing on design. These include: needs, requirements, exploration-based model of design and describes the
solutions, specifications, creativity, constraints, scientific design process as a knowledge-based exploration
principles, technical information, functions, mapping, task.
transformation, manufacture and economics. The word 4. Design as an investigative (research) process involves
'customer', although absent, seemed to be implicitly rep- an enquiry into the client's needs and expectations,
resented by the words 'needs', 'requirements' or available design techniques, previous similar design
'market'. Taking account of these key words, design can solutions, past failures and successes, etc.
be described as: 5. Design as a creative process (art) involves creating a
design solution with the help of know-how, ingenu-
The process of establishing requirements based on human
ity, good memory, pattern recognition abilities,
needs, transforming them into performance specification
and functions, which are then mapped and converted random search in the solution space, lateral thinking,
(subject to constraints) into design solutions (using cre- brainstorming, analogies, etc.
ativity, scientific principles and technical knowledge) that 6. Design as a rational process (logic based) relates to
can be economically manufactured and produced. checking and testing of proposed solutions, involving
logical reasoning, mathematical analysis, computer
simulation, laboratory experiments and field trials,
2.2 Viewpoints on design theory and methodology etc.
The subjects of design theory and design methodology, 7. Design as a decision-making process (value based).
although well discussed by researchers, have not been In the design process, designers usually make a lot of
fully explicated. Some definitions have, however, been value judgements in adopting alternative courses of
given to them by various designers and researchers, and action or choosing between competing design solu-
are reported below. The American Society of Mechani- tions. Such judgements and evaluation are usually
cal Engineers (ASME) (24) defines the field of design based on experience and criteria derived from the
theory and methodology as '. . . an engineering disci- customer's or client's requirements.
pline concerned with process understanding and 8. Design as an iterative process. The iterative activity
organised procedures for creating, restructuring and is the most common process in design. Proposed pre-
optimising artifacts and systems'. Design theory is taken liminary designs are usually analysed with respect to
as a collection of principles that are useful for explain- constraints and, if unsatisfactory, are revised based
ing the design process and provide a foundation for the on experience and the results of the analysis.
basic understanding required to propose useful method- 9. Design as an interactive process. Interactive design
ologies. Design theory is about design; it explains what brings the designer directly into the process by
design is or what is being done when desi~ning. On the forcing him or her to be an integral part of it. This is
other hand, design methodology is a collection of pro- necessitated in situations where: (a) the design
cedures, tools and techniques for designers to use when problem is ill-defined, (b) there are insufficient ana-
designing. Design methodology is prescriptive as it indi- lytical tools developed to enable quantitative analysis
cates how to do design, while design theory is descrip- and (c) there is little or no experience available or
tive as it indicates what design is. Rabins et al. (25) state associated with the design problem.
that' ... design theory refers to systematic statements of The above views on the nature and features of the
principles and experientially verified relationships that design process represent different facets of the overall
explain the design process and provide the fundamental design process. They are dependent on the engineering
understanding necessary to create a useful methodology or design domain from which the particular viewpoint
for design'. is expressed as well as the nature, type, variety and com-
These viewpoints represent the first steps towards plexity of the particular artefact/process or system being
defining what might be regarded as design theory and designed. Most of the viewpoints are, however, comple-
design methodology. The definitions by ASME are par- mentary to each other. A comprehensive design system
ticularly encompassing and are worth noting. must therefore be able to support these various facets of
design involving: (a) a top-down and bottom-up
approach, (b) the evolutionary process of design, (c) the
2.3 The nature and features of the design process
knowledge-based/exploratory aspects of design, (d) the
The design process for any design model usually investigative and search aspects of the design process.
exhibits certain properties and features which represent (e) the creative process in design, (f) the logical reason-
various associated viewpoints and philosophies, activ- ing process involved in design, (g) the iterative as well as
ities and processes that occur during the process. These the interactive process involved in design, (h) the
features as highlighted by several researchers (26-28) are making of decisions based on value judgements and (i)
discussed below: the mathematical analysis and computational simula-
tion processes performed during design.
1. Design as an opportunistic activity represents the
case where both top-down and bottom-up
approaches are used by the designer in an opportun-
2.4 The nature and stages of thought in design
istic manner.
2. Design as an incremental activity involves an evolu- In the process of design, most designers tend to go
tionary process. where changes (improvements or through certain stages, referred to here as stages of
Part B: Journal of Engineering Manufacture © !MechE 1996

A SURVEY OF DESIGN PHILOSOPHIES, MODELS, METHODS AND SYSTEMS 303

thought, as they move from an abstract problem to a tures are introduced, which still bear some resem-
realizable product. These are the divergent, transform- blance to existing variables or features, and the.
ation and convergent stages of design: decomposition of the problem is known. but the
sub-problems and various alternatives to their
1. Divergence. This is the act of extending the boundary
solution must be synthesized. In other situations,
of a design situation in order to have a large enough
alternative recombination of the sub-problems
solution search space. The divergent search approach may yield new designs. It is also considered that
aims to de-structure the original design brief, while
solving the same problem in different ways, or
identifying the features of the design situation that different problems in the same way (by analogy),
will permit a valuable and feasible degree of change.
would fall under this class.
Divergent search is most productive in the initial
(b) Creative designs. In this case new variables or
stages of design.
features are introduced which bear no similarity
2. Transformation. This is the stage of pattern making, to variables or features in the previous prototype
high-level creativity, flashes of insight, changes of set and the resulting design has very little resem-
and inspired guesswork. The objective here is to blance to existing designs. For creative designs
impose upon the results of the divergent search a no design plan is known, a priori, for the problem
pattern that is precise enough to permit convergence under consideration.
to a single design.
3. Convergence. The main objective of the convergent Sriram et al. (32), in the light of the foregoing,
stage is to progressively reduce secondary uncer- describes the creative-routine spectrum of design as
tainties as fast as possible as well as ruling out alter- follows: 'At the creative end of the spectrum, the design
natives. The end result of this stage should be the process might be nebulous (hazy), spontaneous, chaotic,
reduction of the range of options to a single chosen and imaginative, whereas at the routine end, the design
design as quickly and as cheaply as can be managed is precise, predetermined, systematic, and mathematical.'
and without the need for unforeseen retreats or
recursion.
2.6 Product design classification
The end result of any design process is a product or
2.5 The variety of design problems
system. Such products, depending on the engineering
A design is strongly influenced by the lifestyle, training discipline or domain, vary in one way or the other.
and experience of the designer, and the creativity and Product variation also arises depending on the market
effort a designer puts into a design varies, depending on segment, knowledge available, the design process and
the type of design problem (30). Design problems that manufacturing capabilities. In the light of general con-
confront engineers and designers can be classified under straints, products can be classified as either over-
the following types (30-33): constrained or underconstrained, and depending on the
customer demands and competition in the market, some
1. Routine designs. These are considered to be derived products are considered as static or dynamic. These
from common prototypes with the same set of vari- various forms or classifications are discussed below (34,
ables or features and the structure does not change.
35):
Here a design plan exists, with sub-problem decom-
position, alternatives and prototypical solutions 1. Static product designs. Static products are those
known in advance. whose market share is undiminishing and no changes
2. Redesigns. This involves modifying an existing design are being demanded in the product. The design
to satisfy new requirements or improve its per- concept is already known from existing products,
formance under current requirements. The end result and hence such products are considered to be con-
of redesigns may also exhibit some form of creative, ceptually static (also referred to as dominant design).
innovative or routine design content. Redesigns will 2. Dynamic product designs. Dynamic products have a
be discussed under adaptive designs and variant limited life before the next generation supersedes
designs. them. Here, development is focused on the product,
(a) Adaptive, configurative or transitional designs. and the design process involves the development of
These forms of design involve adapting a known new, radical and alternative designs. In discussing the
system (solution principle remaining the same) to dynamic-static spectrum of products, Clausing (34)
a changed task. They also involve improvements highlights the following types of products sand-
on a basic design by a series of 'detail' refine- wiched between the two extremes: (a) genesis
ments. product, (b) radical product, (c) new product, (d)
(b) Variant, extensional or parametric designs. This clean sheet (generational) product, (e) market-
follows an extrapolative or interpolative pro- segment entry (new) product, (f) market-segment
cedure. The design technique involves using a entry (generational) product, (g) associated product,
proven design as a basis for generating further (h) variant product and (i) customized product.
geometrically similar designs of differing capa- 3. Overconstrained product designs. These products
cities. tend to exist in the high-technology markets. Here,
3. Non-routine designs, original or new designs. These the design process evolves around analysing alterna-
forms of design are also known as original designs tive proposals until the <;orrect (or most acceptable)
and are classified into innovative and creative solution is found. Overconstrained products are
designs. usually subjected to several constraints of function,
(a) Innovative designs. Here new variables or fea- materials, manufacturing processes, some of which
:g IMechE 1996 Proc Instn Mech Engrs Vol 210


might be conflicting, and the product undergoes Cross (39), reporting on Lawson's work (40), whi<
severaJ·analysis and trade-off situations. compared the ways in which designers and scientis
4. Underconstrained product designs (ideas centred). In solved the same problem, states that: 'The scientis
the case of underconstrained designs, the design tended to use a strategy of systematically exploring tt
activity is centred around bringing products into the problem, in order to look for underlying rules whic
market to satisfy market demands. There are usually would enable them to generate the correct or optimur
not very many constraints, and the designer has solution. In contrast, the designers tended to suggest
ample room for innovation. The focus here is usually variety of possible solutions until they found one tha
on the product concept, and materials and tech- was good or satisfactory. The evidence from the experi
niques are chosen to satisfy the required function and ments suggested that scientists "problem-solve b;
recognizable market style. Most industrial designs analysis", whereas designers "problem-solve by synthe
fall into this category, and development is on aes- sis". Scientists use "problem-focused" strategies anc
thetics, ergonomics and functionality. designers use "solution-focused" strategies.' Thi5
5. Underconstrained product designs (skill based). This phenomenon was also observed in a creative design
form of design focuses on the manufacturing aspects workshop organized at City University, London (41).
of product development. Efforts are usually concen- Yoshikawa (42), in his paper on design philosophy,
trated on the capabilities and skills available in the also discusses design from some philosophical view-
company. points attributed to various designers who belong to the
semantics, syntactics and past experience schools of
thought. These viewpoints constitute the platform for
2.7 Design goals most of the controversies in the design community.
Some of them, however, complement each other, while
Design goals can be defined as the purposes for design
others are completely contradictory.
actions and decisions taken in each design step. They
guide the choice of what to do at each point during the
design process (36). Design goals represent one or more 3.1 Semantics school
decision points from a problem-solving point of view,
This school of thought is attributed to Rodenacker (43).
and they define some of the dimensions of the design
The central dogma of this school is that any machine, as
space. Design goals do exhibit one kind of interaction
an object of design, is something that transforms three
or the other in the form of: (a) goal conflicts, involving
forms of inputs, viz. substance, energy and information,
non-simultaneous achievement of two goals, (b) goal
into three outputs respective to each input, but having
sharing, achieving a sub-goal helps achieve a goal other
different states from the inputs. The differences between
than its ancestors in the goal tree, and (c) goal prerequi-
sites, where one goal must be achieved before another the inputs and outputs are called functionality. The
goal in a different part of the goal tree. Typical types of initial requirements are usually given in terms of the
design goals include: (a) functionality goals, (b) per- functionality, which has to be analysed into a logical
formance goals, (c) knowledge goals and (d) design structure, which gives connections between sub-
process goals. In the control and management of the functionalities. On decomposing the initial functionality
design process, there is need to explicate strategies for into finer sub-functionalities, these resulting sub-
how to handle interacting design goals. functionalities are substituted with particular physical
phenomena that realize the transformations respec-
tively.
3 DESIGN PHILOSOPHIES
There have been various schools of thought expressed 3.2 Syntax school
by designers and researchers as regards how design is, This school is associated with the effort made to give
might be or should be done. This undoubtedly has some formalism to the design process, and attention is
resulted in controversy. Three schools of thought within paid to the procedural aspects of the design activity
the British design community were expressed by Broad- rather than on the design object itself. Here attempts
bent in the book Design: science: method (37). The first are made to abstract the dynamical or temporary
group believed that the design process should be aspects from the design, neglecting the static aspects of
chaotic and creative, the second group believed that design as emphasized in the semantics school. The
design should be organized and disciplined, while the process of abstraction is considered as the premise for
third group argued that no design process should be improving the universality of design model~ belonging
imposed on a designer (38). Support for the first view to this school, which are usually regarded as prescrip-
point is usually based on the argument that the design tive models. This philosophy, which emphasizes the
function is an art, and hence cannot be taught, which dynamical aspects of design, can be combined with the
seems to imply that designers are born and not made. semantics one, which emphasizes the static aspects of
Archer (22), in support of the second viewpoint, com- design to achieve a more sophisticated design method-
ments that: 'Systematic methods come into their own, ology.
under one or more of three conditions: when the conse-
quences of being wrong are grave; when the probability
of being wrong is high (e.g. due to lack of prior 3.3 Past experience school
experience); and/or when the number of interacting Arguments put forward by those belonging to this
variables is so great that the break-even point of man- school of thought are usually that universality, which is
hour cost versus machine-hour cost is passed.' the target of most design methodologists, is contradic-


tory to practical usefulness and that the creativity of good number of these models emphasize the need to
designers can be hampered and may deteriorate if perform more analytical work, prior to the generation
design methodologies are adopted. In this school of solution concepts (39). Models put forward by pro-
emphasis is placed on the significance of case historie~ ponents of prescriptive models are discussed below.
of design, including all necessary knowledge to be learnt
for improving design ability. This school of thought is 4.1.1 Model by J. C. Jones
closely associated with the view that the design ability
cannot be acquired efficiently in a theoretical manner This model by Jones (1) is principally made up of three
but by experience. ' stages, viz. analysis, synthesis and evaluation. At the
analysis stage, the first activity involves producing a
random list of factors related to the problem to be
3.4 Summary solved and/or to its solution. These factors are then
The above schools of thought, although they stand their classified into workable categories and sub-categories,
ground in arguments, are relevant in one way or the after which the interactions between them are investi-
other with respect to design. In today's world, it is gated. The final step then involves rewriting all the
increas!ngly becoming evident that design approaches design requirements into solution neutral performance
belongmg to the syntax (prescriptive models) school of specifications.
thought are more likely to stand the test of time. In the synthesis stage, creative techniques like brain-
Wallace (44) in his article points out that 'the engineer- storming (45, 46) are used to generate ideas and solu-
ing design process cannot be carried out efficiently if it tions to the performance specifications. Limits are then
is left entirely to chance .. .' and ' ... the aim of a sys- set for each partial solution within a range of dimen-
tematic approach is to make the design process more sions, shape and variations in material properties that
visible and comprehensible so that all those providing will satisfy any performance specifications. The next
inputs to the process can appreciate where their contri- step then involves combining compatible partial solu-
butions fit in'. Furthermore, the need to equip and train tions into combined solutions.
young engineers as well as support collaborative design The last stage of this model is the evaluation stage
teams will necessitate the adoption of a structured and which involves mainly two activities. These are (a)
systematic approach to design. methods of evaluation and (b) evaluation for operation,
manufacture and sales. Under methods of evaluation,
Jones advocates the use of evaluation methods to detect
4 DESIGN MODELS errors at the stage when they can be most cheaply cor-
Design models are the representations of philosophies rected. Such methods include evaluation by per-
or strategies proposed to show how design is and may formance specifications and evaluation by use of precise
be done. Often, they are drawn as flow diagrams, judgements.
showing the iterative nature of the design process by a This model emphasizes the need to establish specifi-
feedback link. cations in a solution neutral form as well as investigat-
In the past, design models that arose from various ing interactions between design factors. The synthesis
philosophical viewpoints have tended to belong to two stage does exhibit a bottom-up approach in developing
main classes, namely prescriptive and descriptive the overall design. The idea of evaluating the designs by
models. The prescriptive models are associated with the the pre-operation, pre-production and pre-sales team is
syntactics school of thought and tend to look at the a late occurrence in this model. These teams in a
design process from a global perspective, covering the modern manufacturing industry should be involved
procedural steps (that is suggesting the best way some- right from the start of the design process. In this model,
thing should be done). The descriptive models, on the they should be involved at the analysis stage.
other hand, are concerned with designers' actions and
activities during the design process (that is what is 4.1.2 Model by Asimow
involved in designing and/or how it is done). More
In representing the design activity, Asimow (47) shows
recently, another group of models known here as com-
the process of design in three phases that bear on the
putational models have started to emanate. These com-
solution of the design project, while the part that deals
putational models place emphasis on the use of
with the solution of subordinate problems is repre-
numerical and qualitative computational techniques,
sented as a sequence of operations as every step of the
artificial intelligence techniques, combined with modern
process proceeds. The three phases of design repre-
computing technologies. Each of these design models,
sented are the feasibility study phase, preliminary design
although discussed under one of the above classes, share
phase and detailed design phase:
some characteristics of the other classes.
1. Feasibility study phase. In the feasibility study phase,
the need for the project is established, after which the
4.1 Prescriptive models based on the design process
design problem is explored and the design param-
These models in general tend to prescribe how the eters, constraints and major criteria identified. Plaus-
design process ought to proceed and in some cases ible solutions are generated and then analysed for
appear to suggest how best to carry out design. They their physical realizability, economic worthwhileness
also attempt to encourage designers to adopt improved and financial feasibility.
ways of working. They usually offer a more algorithmic 2. Preliminary design phase. In the preliminary design
and systematic procedure to follow, and are often phase, the best design concept from among the viable
regarded as providing a particular methodology. A solutions is selected. Mathematical models are then
:Q !~hE 1996 Proc lnstn Mech Engrs Vol 210

306 N F 0 EVBUOMWAN, S SIVALOGANA THAN AND A JEBB

prepared for each of the solutions, upon which sensi- inary layouts and (f) the ·development of definitive
tivity analysis is performed to establish the fineness layouts and final documentation.
of the range within which the design parameters
must be controlled, compatibility analysis is per- 4.1.5 Model by Watts
formed to investigate the tolerances in the character-
istics of major components and stability analysis is Watts (48) in his paper represents the design process by
performed to examine the extent to which pertur- an iconic model of a designer or design team in
bations of environmental or internal forces affect the dynamic relationship with an environment. The design
design. The chosen concept finally goes through an process is described as consisting of three processes of
optimization process, an evaluation process, a pre- analysis, synthesis and evaluation, as also proposed by
diction process as well as an experimental design Jones (1). These processes are performed cyclicly from a
process. The third, fourth and fifth steps in this lower (more abstract) level to a higher (more concrete)
phase, if considered in today's terms, are somewhat level (representing design phases), as represented by the
synonymous to Taguchi's system, parameter and tol- helical path in Fig. 1. In moving from the abstract level
erance design. to the concrete one, the designer or design team during
3. Detailed design phase. In this stage, capital budgets the design process frequently reiterate at one or more
and time schedules are prepared for the design. The levels, and decisions are made along the way as shown
sub-systems, components and parts of the product on the surface of the cylinder. A state function D of the
are then completely designed. Assembly drawings are design is associated with the process path and can be
then prepared for the components and sub-systems, externalized as a set of statements at intersections of the
after which the prototype is constructed and tested path and the decision line. Various states of the design
respectively. Further analysis of the prototype is then thus relate to the different levels. The design states (Dm,
performed, before making minor revisions as con- Dn, etc.) give a vertical structure to the process and
vergence is made towards the final design. proceed through analysis, synthesis of design concepts,
evaluation of feasibility, optimization, revision and
The design process as discussed by Asimow (47) is in communication.
steps of analysis, synthesis, evaluation, decision, optim- The process can be considered complete when the
ization and revision. The important aspect here is that designer releases into E (a particular environment) a
these six steps are repeated at each of the process communication P, being a set of prescriptions for the
phases. embodiment of the design. The end to which P is a
means is an artefact A. This possesses several functional
4.1.3 Model by Pahl and Beitz attributes, some of which fulfil the need implied by N;
others enhance the profits and reputation of the
Pahl and Beitz (33) represent their model of the design
designer and the company while others could have
process in four main phases, which are: (a) clarification
effects that are far reaching into the socioeconomic
of the task, (b) conceptual design, (c) embodiment
design and (d) detail design. The first phase of clari- environment
fication of the task involves the collection of informa-
tion about the requirements in a solution neutral form. 4.1.6 Model by Marples (49)
The second phase, which is the conceptual design phase,
This model represents an attempt to abstract the
involves the establishment of function structures, the
process of design, as a result of design case studies
search for suitable solution principles and their com-
bination into concept variants. At the embodiment
design phase, the designer starting from the concept CONCRETE
determines the layout and forms and develops a techni-
cal product or system in accordance with technical and
economic considerations. At the last phase of the detail
design, the arrangement, form, dimensions and surface
properties of all the individual parts are finally laid DECISION
down, the materials specified, the technical and eco-
nomic feasibility rechecked and all the drawings and
other production documents produced.
(E)
4.1.4 Model by VDI 2221 (39)
This model was produced by Germany's professional
engineers body, Verein Deutscher Ingenieure (VDI), in
their guidelines VDI 2221, 'Systematic approach to the
design of technical systems and products'. The VDI
D
2221 model expresses the design process in seven stages.
These stages involve (a) the clarification and definition
of the design task, (b) the determination of the required
functions, (c) the search for solution principles for all
sub-functions and combination into principal solutions,
N
(d) the division of the solution into realizable modules,
(e) the developmem of key modules into a set of prelim- Fig. 1 The design model by Watts
Part 8: Journal of Engineering Manufacture © !MechE 1996


carried out. These studies were used to illustrate design- 1. Programming: establishment of crucial issues and
ing as a sequence of decisions leading from the original proposal of course of action
statement of the requirements to the specification of the 2. Data collection: collection, classification and storing
details of the 'hardware' to be manufactured. The start- of data
ing point in this model is a statement of the main 3. Analysis: identification of sub-problems, preparation
y problem to be solved. This represents the starting node of design specifications, reappraisal of proposed pro-
~ in the 'Marples tree'. gramme and estimation
1 From this node, sub-problems are derived that must 4. Synthesis: preparation of outline design proposals
f be solved before a solution to the main problem is pos- 5. Development: development of prototype design(s),
sible. This involves a cyclic process of analysis of the preparation and execution of validation studies
problem, theorizing solutions, delineating these solu- 6. Communication: preparation of manufacturing
tions and modifying them (49, 50). Figure 2 shows a documents
general representation of a typical sequence of the
The above six stages were further classified and grouped
design process. In this figure, the final solution is the
into three phases, namely analytic, creative and execu-
sum of the solutions a(21211), a(22211), a(22221) and
tive. In describing his model, Archer comments that:
a(232). If, for example, a(2) is preferred to a(l) or a(3), all
' ... the special features of the process of designing is
the sub-problems p(21), p(22) and p(23) must be solved.
that the analytic phase with which it begins requires
Similarly, if a(222) is accepted as a solution to p(22),
objective observation and inductive reasoning, while the
then sub-sub-problems p(2221) and p(2222) must be
creative phase at the heart of it requires involvement,
solved. In the figure, a vertical line denotes a problem,
subjective judgement, and deductive reasoning. Once
while a slanting line denotes a solution. Eder (50)
the crucial decisions are made, the design process con-
further proposes that all precedent solutions to the
tinues with the execution of working drawings, sched-
main problem, such as competitor's models, should also
ules, etc., again in an objective and descriptive mood.
appear on the design tree. This is analogous to competi-
The design process is thus a creative sandwich. The
tive assessment in quality function deployment (51).
bread of objective and systematic analysis may be thick
The model by Marples involves three principal
or thin, but the creative act is always there in the
phases of synthesis, evaluation and decision. At the syn-
thesis phase, two activities are involved, that is the middle.' Figure 3 shows the stages and phases of the
design process as well as their interrelationships.
search for possible solutions and the examination of
proposed solutions. This phase is then followed by the
evaluation of the viable solutions against certain cri-
teria, before a final decision is made in choosing a par- 4.1.8 Model by Krick
ticular solution. Krick (52) in his model describes the design process in
five stages of problem formulation, problem analysis,
search, decision and specification. The first step of
4.1.7 Model by Archer
problem formulation involves defining clearly the design
Archer (22) defines the nature of design methodology in problem to be solved. The next step involves analysing
his model in six stages, viz.: the design problem and arriving at a detailed definition

0 POINT OF PROBLEM FORMULA noN

a331 a332
a321

p3211 p3311 p3321 I

p2111

i p222221

SOLUnON ACCEPnED

SOLUnON REJECTED

PROPOSED SOLUnON - AN AL nERNA TIVE

A SUB-PROBLEM ARISING FROM ANY AL nERNA TIVE

Fig. 2 The design model by Marples
~ I~1echE 1996 Proc Instn Mech Engrs Vol 210


TRAINING

BRIEF PROGRAMMING PROGRAMMING OBSERVATION
EXPERIENCE MEASUREMENT

j ANALYTICAL
PHASE j INDUCTIVE
REASONING

DATA COillCTION DATA COLLECTION

j j
ANALYSIS ANALYSIS

j CREATIVE
j EVALUATION
JUDGEMENT
DEDUCTIVE
SYNTIHESIS SYNTIHESIS
PHASE REASONING
DECISION

j j
DEVELOPMENT DEVELOPMENT

j j DESCRIP110N
SOLUTION COMMUNICATION EXECUTIVE COMMUNICATION TRANSLATION
TRANSMISSION
PHASE

(c) MOOEL Of THE DESIGN PROCESS (b) MAJN PHASES Of DESIGN

Fig. 3 The design model by Archer

of the specifications, constraints and criteria. In the objective in that stage. In the first stage of clarifying
third step, the search for and generation of alternative objectives, the objectives tree method is used to clarify
solutions is performed through inquiry, invention and design objectives and sub-objectives and the relation-
research. The decision stage, which is the fourth step, ship between them. The function analysis method is
involves the evaluation, comparison and screening of then used to establish the function required and the
alternative solutions until the best solution evolves. system boundary of a new design at the second stage. In
Finally, the fifth step, which is the specification stage, is the third stage involving setting of requirements, an
performed. This involves a detailed documentation of accurate specification of the performance required of a
the chosen design with engineering drawings, reports design solution is done using the performance specifi-
and possibly iconic models being the resulting output. cations method. The morphology chart method is then
used at the fourth stage to generate the complete range
of alternative design solutions for a product. In the fifth
4.1.9 Model by Nigel Cross
stage the design alternatives are evaluated using the
In representing his model, Cross (39) expresses the weighted objectives method to compare the utility
design process in six stages within a symmetrical values of alternative design proposals on the basis of
problem-solution model, as shown in Fig. 4. The six performance against differently weighted objectives. The
stages are clarification of objectives, establishing func- sixth and final stage of improving details involves using
tions, setting requirements, generating alternatives, the value engineering method to increase or maintain
evaluating alternatives and improving details. For each the value of a product to its purchaser while reducing
of the stages, a design method is used to achieve the its cost to its producer.

OVERALL PROBLEM
• OVERALL SOLUTION

(SUB - PROBLEMS ) SUB - SOLUTIONS

Fig. 4 The design model by Cross


4.1.10 Model by Hubka Phase 4. Elaboration
The model by Hubka (53) represents the design process Step 6. Detailing and elaboration
in four phases and six stages or steps. These phases and
steps in a procedural model, as shown in Fig. 5, are:
Phase 1. Elaboration of assigned problem 4.1.11 Model by French
Step 1. Elaborate or clarify assigned specifi- This model, as shown in Fig. 6, is based on the follow-
cation
ing activities of design (54):
Phase 2. Conceptual design
Step 2. Establish functional structures and 1. The analysis of the problem phase involving the
Step 3. Establish concept identification of the need to be satisfied as precisely
Phase 3. Laying out as possible or desirable
Step 4. Establish preliminary layout and 2. The conceptual design phase involving the gener-
Step 5. Establish dimensional layout ation of broad solutions in the form of schemes

"'
a:
wz~
'-' STATE OF MACHINE SYSTEM
tJoe (CIRCLED STATEMENTS)
'-' gs ~
2 8 w ~--------------------------------------------,_--------------------~
~ < 5 ESTABUSHED DESIGN
u.. ...J c.:>
CHARACTERISllCS OF THE DESIGN DOCUMENT
~ §~ MACHINE SYSTEM
"' :::E f-

1. DESIGN SPECIFlCA TlON

2.1 BLACK BOX DIAGRAM

ESTABUSH TE~OI.OGICAL PRINCIPLE
2.2
ESTABUSH SEQUENCE ~ OPERATICN

2.3

2.4 N'PLY liS IN TP AND BOUNDAAJES ~ liS
2.5 E51'ABUSH GROUP1NG ~ FUNCTIONS

5
FUNCTION
2.6 STRUC11JRE Z ( FUNCTlDNAL STRUCTIJRE

SCHEMAllC
2.7 ( OPTIMAL FUNCTlON STRUCTURE
AI~
3.1 INPUTS TO MS. IIOOE ~ ACTION
MORPHOLOGICAL MATRIX
3.2 FAIIIUES ~ FUNCTION-CARRIERS
3.3, 3.4

CDNCEPTIJAL SCHEMA TlC
3.5
CONCEPT SKETCH

4.2 PARTs. ARRANCEIIENT. ROUGH FORM, SOME Dt.£NSIONS
4.3, 4.4 TYPE OF WATER1AL MD MANUFACTURlNG METHODS

4.5

4.6 ( OPTIIr.tAL PREUhiiNARY LAYOUT
AI~
5.2 OEF1N111£ ARRANG04ENT. FORM, ALL DIMENSIONS
5.3, 5.4 MATCR1AL AND MANUFACTURING METHODS,
PARTIAL TOL£RANCES

5.5 DIMENSIONAL DIIIENSIONAL TRUE- TO- SCALE DIMENSIONAL!
LAYOUT 1 LAYOUT 2
LAYOUT
5.6
( OPTIMAL DIIIENSIONAL LAYOUT ) - I
6.1 - MACHINE ELEMENTS
0 RELEASE

I
6.5

5.6. 5.7
~ $§>$ (IdS REPRESENTATION )
DETAIL DRAWING

ASSEMBLY DRAWING
I

Fig. 5 The design model by Hubka
c; l!ect:E 1996 Proc Instn Mech Engrs Vol 210

:JlO N F 0 EVBUOMWAN, S SIVALOGANATHAN AND A JEBB

Proposed schemes are critically examined to see if
they satisfy the needs, can be constructed, and how
economic they are both in first cost and in function
throughout their working life. Preliminary structural
analyses are also carried out to check the broad ade-
quacy of schemes.
4. Decision. After successive operations of conception
and appraisal, it then becomes necessary to decide on
a particular design scheme. Criteria for decision
making may include both simplicity and distinction
of the design, as well as constructability. ·
5. Checking and elaboration. This is the stage where
the designer makes sure of the adequacy of what is
proposed and performs elaboration of necessary
details. Here, models can be built and tested. Power-
ful analytical techniques can also be employed in (a)
defining the actions on the structure such as load,
temperature difference, corrosion, etc., (b) analysing
the effects of these actions and (c) comparing these
SELECTED effects with a criterion of adequacy. The end result of
SCHEMES
the design process is the communication of the
detailed design both in the form of drawings and
text.

4.1.13 Total design activity model by Pugh (56)
Pugh regards total design as the systematic activity
necessary from the identification of the market/user
need, to the selling of the successful product to satisfy
that need-an activity that encompasses product,
process, people and organization. The total des~gn
activity model consists principally of a central design
core, which in turn consists of market (user need),
product design specification, conceptual design, detail
design, manufacture and sales. The design process in
this model proceeds, firstly, by identifying a need which,
Fig. 6 The design model by French when satisfied, fits into an existing or a new market.
From the statement of the need, the product design spe-
cification (PDS), representing the specification of the
3. The embodiment of schemes phase involving the
product to be designed, is then formulated. The estab-
development of generated schemes into greater
lished PDS then acts as a mantle that envelops all the
details subsequent stages in the design core, thus acting as the
4. The detailing phase. where the selected scheme is
control for the total design activity. Within this model,
worked into finer details
the design processes flow from market to sales, is an
iterative one and recourse can be made to any of the
4.1.12 Model by Sir Alan Harris (55) earlier stages, as new ideas and information emerge.
This causes interactions between the different stages of
This model is based on proposals regarding the teach- the design core. This model also recognizes the fact that,
ing of design within the civil engineering discipline. The for effective and efficient design to be carried out, it is
model consists of five stages, viz.: appreciation of the necessary to utilize various design techniques, to enable
task, conception, appraisal of concepts, decision, check-
the designer/design team to operate the core activity.
ing and elaboration:
These design techniques or methods include:
1. Appreciation of the task. This means discovering (a) discipline-independent ones which relate directly to
what is needed and ascertaining what resources are
the design core and can be applied to any product
needed and from where. It involves finding out what
or technology, such as tools for performing analysis,
a client wants-regarded as the 'total function'.
synthesis, decision making, modelling, etc.;
2. Conception. In this stage, based on the full digestion
(b) specific discipline-dependent technique~ and tech~o
of the facts generated from the previous stage, ideas logical knowledge such as stress analysis. hydraulics,
of solutions should begin to emanate. Here the thermal analysis, thermodynamic analysis, elec-
designer is putting together what is known of the tronics, etc.
function of the work with tentative ideas of form,
material and method of construction. This model also takes into account, within the overall
3. Appraisal of concepts. This stage is where the search- product development process. the framework of plan-
ing eye based on experience becomes invaluable. ning and organization. thus gaining insight into the way
Part B: Journal of Engineering :!anufacture ~!MechE 1996

,,

if products should be designed within a business structure. 2221, the other models also contained in a more
JW The total design activity model is shown in Fig. 7. detailed form within each of their design phases/stages,
)n the design activities that characterized a majority of the
·a! 4.1.14 The BS 7000 design model (57) other models. The Watts model showed only the two
e- ends of the design phase, that is abstract and concrete,
This model commences with a feasibility study stage
with the interval between represented by a cyclic
and proceeds through conceptual design, embodiment
(iterative, refining and progressive) process.
design, detail design and design for manufacture stages.
The models that were based on design acttv1ttes
It also shows the output of each design stage in the
included those by Jones, Marples, Archer, Krick, Cross
form of design brief, concept drawings, layout drawings,
and Harris. It can also be observed that in all of the
detailed product definition and manufacturing instruc-
models, three key activities were predominant, that is
tions respectively. The model ends with a post-design
·e analysis, synthesis and evaluation. Analysis was mostly
support stage. It can be observed that this model
IS related to analysing the design problem, requirements
derives from other models by Pahl and Beitz (33) and
y and specifications. Synthesis was concerned with gener-
French (54), with design for manufacture included as an
·- ating ideas, proposing solutions to large or small design
additional stage. This model is shown schematically in
l) problems as well as exploring the design soiution space,
Fig. 8.
i, while evaluation involved the appraisal of design solu-
g tions in order to establish whether they satisfied the
4.2 A critical appraisal of prescriptive models
e requirements and specifications and set corporate cri-
,f An in-depth review of the prescriptive models on the teria. The sequence in general also tended to be analysis
design process shows that a majority of them based the first, followed by synthesis and then evaluation. In the
i procedural steps of their models on what can be re- model by Krick, synthesis was replaced by search and
garded as design activities (that is analysis, synthesis, evaluation by decision. The model by Harris represent-
evaluation, decisions, etc.), while others based their pro- ed analysis, synthesis and evaluation by appraisal of the
cedural steps on what can be regarded as the phases/ task, conception and appraisal of concepts respectively.
stages of design (that is conceptual design, embodiment It is not surprising that the three activities of analysis,
design and detailed design). The models that were based synthesis and evaluation were predominant as they rep-
on the phases of the design process include those of resent the core of the design process. If proper analysis
Asimow, Pahl and Beitz, VDI 2221, Watts, Hubka and of the problem or requirements is not carried out, syn-
French. With the exception of that of French and VDI thesizing solutions will be difficult and inappropriate

Technology Technique

TOTAL ACTIVITY

UD~DHS CT
S:PCClfJCAT!(l'-j

SYNTHESIS I

CONCEPTUAL
DESIGN
Equa.t~s to Spec.

J .~ECi-.ANISMS

I DETAIL DESIGN
Equ.:a.tPS to S:pN:.
I

OPTIMISATION I
<C_______~DA~T~A_H~AN~D~L~IN~Gi
1 Df~~~~L~~~~L~w~,
SPECIFICATION

C::.~GANISED

Fig. 7 The total design activity model by Pugh
i;' 1!echE 1996 Proc lnstn Mech Engrs Vol 210

FEASIBILITY STUDY

DESIGN FOR
MANUFACTURE

POST DESIGN SUPPORT

Fig. 8 The BS 7000 design model

solutions might be the result. Once plausible solutions In the above equation, the matrix [A] represents the
are created, there is then a need to evaluate, test and design relationship. In furthering his principles of
assess their fidelity to the originating requirements and design, Suh defines two axioms, which are:
specifications as well as set criteria.
Besides the three activities, there are, however, other
necessary activities that should be performed during the Axiom 1: the independent axiom
design process, such as optimization, revision, data col- Maintain the independence of functional requirements
lection, documentation, communication, selection, deci- (FRs).
sion making, modelling, etc. Some of these activities Alternative statement 1: an optimal design always
were included in some of the models. maintains the independence of FRs.
Alternative statement 2: in an acceptable design, the
4.3 Prescriptive models based on product attributes DPs and FRs are related in such a way that a specific
DP can be adjusted to satisfy its corresponding FR
A majority of product or systems failures can be attrib- without affecting other functional requirements.
uted to either or a combination of the following: (a)
incorrect or excessive functional requirements, (b) con-
tinuing alterations to functional requirements, (c) wrong Axiom 2: the information axiom
design decisions and (d) the inability to recognize faulty
decisions early enough to rectify them. Thus the exis- Minimize the information content of the design.
tence of unacceptable designs as well as good designs Alternative statement: the best design is a functionally
lends weight to the argument that there should be some uncoupled design that has the minimum information
features or attributes that can distinguish between good content.
and unacceptable designs. The foregoing reasoning Associated with these axioms are eight corollaries
formed the basis of Suh's axiomatic approach to design (having a flavour of design rules) and sixteen theorems
based on attributes of the design produced (58). Taguchi (propositions that follow from the axioms or other
(59) also argues that the total costs at the point of pro- propositions). Suh also classifies designs into three cate-
duction and at the point of consumption should be gories, namely uncoupled, coupled and decoupled
minimum for good designs and this should be the goal designs. An uncoupled design is a design that obeys the
of product development. He introduces a 'loss function' independent axiom and any specific DP can be ~djusted
as an attribute of the product designed which has to be to satisfy a corresponding FR. A coupled design has
minimized to achieve robust designs. some of the FRs dependent on other functions. When
the coupling is due to an insufficient number of DPs
4.3.1 Suh 's axiomatic design model when compared to the number of FRs, they may be
decoupled by adding additional DPs. A decoupled
The basic premise of Suh's (58) axiomatic approach to
design may have more information content. ~n t~e
design is that there are basic principles that govern deci-
axiomatic approach, the design model (process) IS spht
sion making in design, just as the laws of nature govern
into four main aspects of: (a) problem definition, which
the physics and chemistry of nature. He describes the
results in the definition of FRs and constraints, (b) ide-
design process as a mapping process between the func-
ation or creation of ideas, which is the creative process
tional requirements (FRs) in the functional domain and
of conceptualizing and devising a solution, (c) analysis
the design parameters (DPs) in the physical domain.
of the proposed solution, which involve~ the proc~ss of
Mathematically this can be expressed as:
determining whether the proposed solutiOn ts a rat~~nal
{FR} = [A]{DP} solution that is consistent with the problem defirutton,


and (d) checking the fidelity of the final solution to the To achieve robustness, Taguchi suggests the follow-
original needs. ing. sequence of events in .his design model: (a) systenr·
design, (b) par~meter des~gn and (c) tolerance desi~
43.2 Taguchi's quality loss function model System design IS the physical embodiment of the func-
tional requirements of the product, where special engin-
The recent past has witnessed the shift in focus from eering and scientific knowledge is applied. Parameter
on-line quality control to off-line quality. This has led design is the process of identifying the optimal settings
to increasing focus on the integration of quality into the of various parameters under the control of the designer
early design stage of product development Ensuring to limit variation. Tolerance design involves the control
quality by design thus involves the use of structured off- of the variation in critical parameters when everything
line methods to determine the design configurations else has failed to control the variation of performance
that meet the customer's needs and are robust, where within the required limit .
robustness means that product performance character-
istics are insensitive to variation in the manufacturing
and operating environments (60). One of the main pro- 4.4 Descriptive models
ponents of off-line quality control is the renowned
Japanese, Professor Genichi Taguchi, who introduced Descriptive models emanated both from experience of
the concept of 'quality loss' or 'loss to society'. individual designers and from studies carried out on
Taguchi's methodology is based on the precept that the how designs were created, that is what processes, strat-
lowest cost to society represents the product with the egies and problem-solving methods designers used.
highest quality, which is achieved by reducing variation These models usually emphasize the importance of gen-
in product characteristics. This approach is expressed erating one solution concept early in the process, thus
by what is called the 'loss function'. The loss function is reflecting the 'solution focused' nature of design think-
he ing (39). The original solution goes through a process of
of a mathematical way of qualifying cost as a function of
product variation. This loss function allows a determi- analysis, evaluation, refinement (patching and repair)
nation to be made as to whether further reduction in and development (39, 62, 63).
the variation will continue to reduce costs. The loss In their paper, Finger and Dixon (38) discuss descrip-
function includes production costs as well as costs tive models from a different perspective and have identi-
incurred by the customer during use (61). The simplest fied the research work in this area along two main lines:
ItS
form of the loss function is expressed by a quadratic 1. Research based on techniques from artificial intelli-
relationship obtained from a Taylor series expansion, gence such as protocol analysis, involving systematic
ys and can be approximated by: gathering of data on how designers design.
he L(Y) = k(Y- M) 2 2. Research based on modelling the cognitive process.
fie where The aim of this research is to build computer-based
"R L = loss associated with a particular performance cognitive models, which describe, simulate and
characteristic Y emulate the mental processes and skills used by
M = the performance target value designers while creating a design.
k =loss parameter= LJD6
where
4.4.1 Model by March
Lc = average loss to the customer when the per-
ly formance characteristic is not within the limit The model of the design process proposed by March
m Do (64) draws on the work of the American philosopher
D 0 = customer tolerance limit Peirce on the three modes of reasoning, which are
deduction, induction and abduction (production). In
es The loss function L(Y), which is shown graphically in rephrasing Peirce's remarks, rational designing is con-
ns Fig. 9, can thus be defined as the average of the finan- ceived as having three tasks:
er cial loss due to deviations of the product characteristic
e- Y from the target function M over all customer condi- 1. The creation of a novel composition-accomplished
!d tions up to the time required for the product life. by productive reasoning
J.e ?
LCYl = k(Y-M)~
!d
as
!n
:Js
Je
!d
1e
cit
Lm

_'Lc~, l _
"·~
~

~
-i
I
II
I

;h
e-
/1
ss I
is
Ji .~+Do
:li
n. Fig. 9 Taguchi's quality loss function
~ 1le<:hE 1996 Proc lnstn Mech Engrs Vol 210


2. The prediction of performance characteristics- from several viewpoints, (d) thinking with concepts and
accomplished by deductive reasoning (e) thinking with basic elements:
3. The accumulation of habitual notions and estab-
lished values, an evolving typology-accomplished 1. Thinking with outline strategies. The idea here is (a)
by inductive reasoning. to be able to decide in advance what strategy (that is,
a sequence or network of design actions or thoughts)
Summarily, production (abduction) creates, deduction is to be adopted in the design process, (b) to be able
predicts and induction evaluates. In this model the to compare what has been achieved in the design
design process begins with the first phase of productive project with what was planned and (c) to be able to
reasoning, which draws on a preliminary statement of produce strategies for producing strategies.
required characteristics and some presuppositions 2. Thinking in parallel planes. This consists of detached
about a solution, to produce the first design proposal. observation of the thoughts and actions of oneself
From the design suppositions and established theory, and one's colleagues during the design project, and
the first design proposal is then deductively analysed to attention is focused upon the pattern of thought
predict the expected performance characteristics. From while designing.
the predicted performance characteristics, it is then pos- 3. Thinking from several viewpoints. Effort here is
sible to inductively evaluate further design possibilities directed at the solution to the design problem instead
or suppositions. This cycle is then repeated, starting of at the process of finding it.
from a revised statement of characteristics, resulting in 4. Thinking with concepts. This consists of imagining
further refinements and/or changes in the design propo- or drawing of geometric patterns that enable a
sal. The PDI (production/deduction/induction) model designer to relate the fundamental design method
described above is shown in Fig. 10. (FDM) checklists to the pattern of his or her own
memories and thoughts. The main purpose of this is
to provide the designer with a memorable pattern of
4.4.2 Model by Matchett the relationship between the design problem, the
The approach to design as enunciated by Matchett (65, design process and the solution.
66) is also known as the fundamental design method 5. Thinking with basic elements. This thinking pattern
(FDM). The aim of this approach is 'to enable a is the most rational of the five modes of thinking.
designer to perceive and to control the pattern of The use of basic elements is to make the designer
his/her thoughts and to relate this pattern more closely aware of the large number of alternative actions that
to all aspects of a design situation'. The approach are open to him or her at each point of decision.
adopted by Matchett to design is built around five These basic elements are considered under seven
thinking patterns. These are: (a) thinking with outline groups of: (a) decision options, (b) judgement
strategies, (b) thinking in parallel planes, (c) thinking options, (c) strategic options, (d) tactical options, (e)

)
DESIGN

, _________
THEORIES
/

DEDUCTION

Fig. 10 The design model by March
Part B ·Journal of Engmeering ~!anufacture © !MechE 1996

A SURVEY OF DESIGN PHILOSOPHIES, MODELS, METHODS AND SYSTEMS 3I5
md
relational options, (f) obstacle options and (9)
concept options.
(a) lir------F-Bs_ B o .
IS,
The primary roulette is intended to generate a variety
ltS) of design alternatives. The actions here involve estab-
ble lishing how each part of a design can be eliminated,
tgn combined, standardized, transferred, modified or simpli- I - - - F - - Be-- S-- D --P
to fied. The secondary roulette is intended to ensure that
all changes introduced are compatible with each other
ted and with all the needs. In using the fundamental design
;elf method, the following procedure is recommended (66):
nd 1. Study the design situation.
Es Eo.
~ht 2. Then identify provisionally the needs that the design
is to satisfy. Ccir1po.r;son Process
IS 3. Identify the primary functional need (that is the need Tro.nsforr1o. tion Process
ad that if not properly satisfied makes the fulfillment of
all other needs pointless). Fig. 11 The evolutionary design model
ng 4. Explore alternative principles upon which a means of
a satisfying the primary need can be based. Designing in this model is based on the concept of an
od 5. Complete an outline of a design capable of satisfying iterative cyclic process of generation and refinement of
vn both the primary and secondary needs. partial solutions which are evaluated using a model of
IS 6. Review the functional effectiveness of this design. the environment.
of 7. Review the material and work content in producing
he the design as well as the component quality.
4.5 Computational design models
rn Neville (68) considers that computational models of
tg. design play two major roles: firstly, that they are a
er 4.4.3 Model by Gero-evolutionary design model (67) necessary part of the development of more effective
at This model considers the design process as a series of CAD (computer aided design) tools and, secondly, that
•n. transformations from one state of the design to another they play a role of supporting research into design
~n
state, for example transforming function F, structure S theory and methodology. Computational models con-
nt and behaviour B into a design description D. The evo- sidered here focus on mapping function into structure
:e) lutionary model is formulated with due cognizance of and investigate which are intended for computer imple-
the use environment E the resulting product will be mentation. Within these models design is considered to
exposed to as well as the originating designer's intent I. be a process that maps an explicit set of requirements
The resulting model is shown in Fig. 11 along with the into a description of a physically realizable product
activities. The activities in this model are: which would satisfy these requirements plus implicit
requirements imposed by the domain/environment (68).
Formulation or design brief or specification: I-» F Emerging computational models are due to Agogino et
Analysis: F -»Be al. (69), Mostow et al. (70), Dixon (71), Cagan and
Synthesis: Be-» S Agogino (31), Gero (72) and Fitzhorn (73).
Production of design description: S- » D
Manufacture of the product: D-» P 5 DESIGN METHODS
Simulation: S «-»E.
Real world interaction: P «-»E. During the different phases of a design project and
Evaluation: B.«-» Be(F), B.«-» Be(F) through the various stages of the design process, a
Reformulation: B5 - » Be, B.-» Be number of design aids, tools and support systems are
Simulated structure performance: S( «-»E.)-» B. used, in order to arrive at a realizable product and/or
Actual product performance: P( «-»E.)-» B. process. These tools and aids are what are generally
regarded as design methods. Design methods generally
where I = designer's intent, F =function (purpose of help to formalize and systematize activities within the
product), S = structure (configuration of product's design process and externalize design thinking, that is
constituents), D = design description, B. = set of behav- they try to get the designer's thoughts and thinking pro-
iours of structure, Be = set of expected behaviours, cesses out of the head into charts and diagrams (39).
B, = set of actual behaviour of the product, E. = actual Hubka (74) defines a design method as 'any system of
environment, E, =simulated environment, P = actual methodical rules and directives that aim to determine
product. The complete evolutionary design process the designer's manner of proceeding to perform a par-
model then incorporates the cross-over mechanism C, ticular design activity, and regulate the collaboration
which allows for 'cross-breeding' of different structures with available technical means .. .'. Design methods
sn from a population of structures to achieve a satisfac- were also considered to exhibit certain characteristics in
tory design. The mutation mechanism M is also added terms of their usage, such as the goals the methods
and used to mutate any unsatisfactory design structure serve, their general applicability, conditions under
S. Both the cross-over and mutation mechanisms are which they can be used, whether the methods are
not mutually dependent and are not necessarily both intended for single designers or for design teams, their
applied at each step of the evolutionary design process. origins, how they function (modus operandi) and the
~ lleohE 1996 Proc Instn Mech Engrs Vol 2IO

, ,'

time demanded by the methods. Taking into account plants, offshore facilities· and aerospace products (7
the above characteristics, design methods can be classi- Within the design environment, several functionali
fied under the following broad headings: (a) methods and resource components exist, consisting of (a) genet
intended to provide basic improvements in the way functionality, applicable throughout the design proce!
designers work, (b) methods that act on the creative (b) specific functionality, relating to specific tasks in tl
characteristics of the human being, (c) methods that design process, for example solid modelling, (c) to
attempt to describe and master the problem situation resource, which is third party software employed 1
by means of strict logic and mathematics, (d) methods deliver enabling technology for addressing specif
that prescribe methodical rules and regulations, which design tasks, (d) external information resource, such '
can significantly increase the overall probability of company-specific databases, and (e) programming Jar
success, (e) methods based particularly on the know- guage resource, which includes languages lik
ledge of the artifact being designed, (f) methods that FORTRAN, Modula-2, Prolog and Expert syster
encourage the use of technical means and aids, and aim shells. This design environment is being implemented i
towards automation of that part of the design process an integrated system architecture, consisting of fou
and (g) combinations of the above methods appropriate layers based on a networked workstation environmen
to the existing situation. Jones (66) in his book gives a The four layers are: (a) the distributed design protoco
description of 35 design methods. These methods were (b) the design process management, (c) the design func
classified broadly into the following: (a) prefabricated tionality and (d) the design repository.
methods, (b) strategy control methods, (c) methods of
exploring design situations, (d) methods of searching for
6.2 The integrated design framework
ideas, (e) methods of exploring problem structures and
(f) methods of evaluation. The design system under development at the Cambridg(
Other design methods that have emerged within the University Engineering Design Centre is called the inte·
recent past include the following: (a) design axioms, (b) grated design framework (IDF) (76). This system i~
design for manufacture, (c) design for assembly, (d) described as an open and flexible computer environ·
design for disassembly, (e) design for the environment, ment, which is based on framework support modules
(f) design for cost, (g) design for maintenance, (h) design (FSMs). These FSMs are being developed to aid
. for reliability, (i) design for testing, (j) design for service- designers in specifying requirements, synthesizing and
ability, (k) failure mode and effect analysis (FMEA), (1) evaluating solution concepts, performing embodiment
robust engineering design, (m) Taguchi methods, (n) design, optimizing the configuration and manufacturing
manufacturing process design rules, (o) finite element their products.
analysis (FEA), (p) group technology, (q) fault tree
analysis (FT A), (r) computer aided modelling (solid
body modelling), (s) sketching input and (t) design 6.3 The Schemebuilder
retrieval (design databases). 'Schemebuilder', the design system under development
at Lancaster University Engineering Design Centre (77,
6 COMPUTER-BASED DESIGN SYSTEMS
78), is a conceptual design tool aimed at guiding
designers through the vast range of design options
In the recent past, several issues have been raised in the available to them. The aim is to facilitate the explora-
design and research community about the limitations of tion of alternative conceptual schemes with an appro-
currently available geometry-based computer aided priate allocation of function between mechanical,
design (CAD) systems and their failure to accommodate electronic and software elements. Schemebuilder aims to
other aspects of the design life-cycle, ranging from provide for the creation of a model of the system to be
problem definition and specifications down to pro- designed, while giving advice on appropriate means.
duction planning. Preliminary work in this regard The solution approach adopted uses Bond Graphs to
(although limited) has focused on developing more inte- classify individual components, both by their function
grated and robust design systems that can support not and the type of ports they possess. Associated with the
only geometric modelling but can also accommodate Schemebuilder is the Layout module, which supports
various design models, -design methods and techniques the preliminary embodiment phase of design. It is used
as well as providing sufficient flexibility for the designer to quickly generate three-dimensional solid geometries
to innovate and be creative. A major intention of such of selected schemes.
systems is for them to be able to handle varying forms
of design information in addition to geometric data. 6.4 Vehicles knowledge-based design environment
Several of these systems will be discussed including
those being developed in a number of the engineering The vehicles design environment (79), which is being
design centres within the United Kingdom, who are developed by the Aerospace Corporation, Los Angeles,
sponsored by the Engineering and Physical Sciences California, is a knowledge-based system with an inter-
Research Council (EPSRC). active environment built to enhance, assist, simplify and
expedite design activities under the guidance of
designers. It is being developed to support varied styles
6.1 Integrated design environment
of design, handle and evaluate multiple designs, provide
The Engineering Design Centre at the University of meaningful status reports on the results obtained and
Newcastle is concerned with the generic design pro- on the degree of completion of a design, provide a
cesses and their integration, with particular reference to variety of analysis tools and create an open and exten-
large made-to-order (MTO) products, such as power sible architecture in which new models, tools and design


(75). the design object which should exhibit maximum simi-
ality SPV
larity to the designer's own images about them. The
1eric Scenarios
Applico tion architecture of this system and its components is shown
cess,
1 the
DODD in Fig. 12. The supervisor SPY is at the core of IIICAD
and controls all the information flow. It also adds intel-
tool
B
I.DDS
ligence to the system by comparing user actions with
i to CIDDL is the bose
scenarios which describe standard design procedures, as
longuoge)
cific well as performing error handling when necessary. The
lUI API
h as

@
integrated data description schema (IDDS) regiments
Ian-
like
[;] the databases and knowledge-bases and relieves the user
from the burden of specifying where and how· to store
tern and retrieve data.
din The IDDS has a kernel language called the integrated
i'cur data description language (IDDL), which is used by all
ent. Fig. 12 IIICAD architecture the system elements. IDDL is based on logic and the
'col, concepts of knowledge engineering. IIICAD also has a
me- high-level interface called the intelligent user interface
concepts may be added. The kernel of vehicles is written
in Quintus Prolog and C on a Sun workstation. The (lUI), which is driven by scenarios written in IDDL.
user interface is being built using X-windows, C++ The application interface (API) is used to secure the
and the Interviews widget set. It also has links to exist- mapping between the central model descriptions about
ing software tools (in Fortran and C) for graphics and a design object and the individual models used by appli-
dge engineering analysis. cation programs. Such application programs can
1te- include programs for: (a) conceptual designs, (b) geo-
Is metric and product modelling, (c) finite element analysis
on- 6.5 An integrated CAD system (80)
and other engineering analysis activities.
lies This system was developed based on a model for the
aid process of machine design, taking into account the
md requirements of computer aided design (CAD), and con- 6.8 Design fusion project-CMU ED R C (83--85)
ent sists of three main elements, that is product-defining The primary goal of this work is to infuse knowledge of
rng models (PDM), which support modelling of product downstream activities of product development into the
properties, product-defining data (PDD), which adjust upstream design process so that designs can be gener-
the overall, general models to an appropriate size, given ated rapidly and correctly. The design space is hence
the design problem, and operational principles (OP), viewed as a multi-dimensional space in which each
which select the design methods with all the necessary dimension represents a different life-cycle objective such
~nt information about the process. The resulting integrated as fabrication, testing, serviceability and reliability. This
77, and flexible CAD system consists of four main modules, system thus aims to provide an intelligent aid to the
ng which are: (a) the task analysis processor (AAP), (b) the designer which would help in the understanding of the
>llS solution coordination processor (LKP), (c) the design interactions and trade-offs among these different and
ra- management system (KLS) and (d) the database (DB). conflicting requirements of a product or system. This
·o-
computer-based system surrounds the designer with
al, 6.6 The design system MFK (81) expert modules that provide continuous feedback based
to on incremental analysis of the design as it evolves. The
be The primary objective in the development of this system
was, on the basis of a traditional CAD system, to expert modules are called perspectives and can be used
OS.
support the designer/design team through an object- to generate: (a) comments on the design, (b) information
to that becomes part of the design and (c) portions of the
on orientated component description offering an integrated
knowledge-based analysis of the component. The geometry. These perspectives represent a collection of
he modules (fabrication, assembly, etc.) that interact with
cts system consists of an information generating synthesis
part and an information processing analysis part. Also one another and with the designer. It integrates the per-
ed spectives (expert modules) around a dynamic, shared
es included is the component model module, which adjoins
both the synthesis and the analysis parts. Contained representation of the design. The shared representation
within the component model is ·the product defining includes the geometric model of the design as well as
data. Connected to the design system is a CAD system, the features, the constraints and the design record. The
through an interactive/procedural interface. This design design record contains the design decisions that led to
system allows different types of analysis to be per- the creation of a constraint or feature. The system archi-
ng
formed, such as design for production, tolerance tecture for the design fusion system is shown in Fig. 13.
es.
~r- analysis, cost and stress calculations as well as com-
1d ponent search. 7 CONCLUSIONS
of
This paper has examined various design philosophies,
es 6.7 Intelligent integrated interactive CAD system models, methods and systems, developed over the past
de few decades, including definitions of design, features of
The philosophy of the intelligent integrated interactive
1d
CAD (IIICAD) system (82) is that it should support the the design process, types of design and product classi-
a designer/design team in the entire design process using fications. Different approaches to design, representing
n-
unified models with rich functionalities for various various schools of thought in the design community,
;n design activities. The system should also have models of were observed. These approaches, described in the form
l96
:Q !MechE 19% Proc Instn Mech Engrs Vol 210


Perspectives

Constro.ints Fo.brico.tion
Goo.ls
Control Po.nel

D
Tes-ting
E
s
I
G
N
E
R
Fea--ture

Noodles Reclo.no. tion

GeoMetry Pa-nel

Fig. 13 The design fusion system architecture

of design models, were either prescriptive or descriptive. aspects of design, examining ways to support creativity,
Prescriptive models represented the design process in innovation and generation of conceptual design solu-
phases and/or stages, and prescribe how the design tions. It is in this aspect that there will be an
process should be carried out, in an algorithmic and opportunity for design and manufacturing companies to
systematic way. Descriptive models, on the other hand, excel.
were based on the strategies used by designers, and
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