2002 a hybrid systematic and conventional approach for the design and development of a product a...

7/29/2019 2002 a Hybrid Systematic and Conventional Approach for the Design and Development of a Product a Case Study

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Systematic approach to design breaks down the design process into

a sequence of transparent activities1 and each of these activities are

further assisted by design tools which are generally called design

methods. One such systematic approach is Design Function Deployment,

DFD2,3. The underlying structure of DFD is given in Figure 1 where level

1 represents the design model consisting of six stages and level 2 consists

of the design methods.

In a computer implementation level 0 represents the initialisation where

the chosen design methods from level 2 are incorporated with the stages

in level 1 to form the process chain of the design process. This process

chain creates the path followed in the designing of a product, unique and

1 Cross, N Engineering designmethods John Wiley and Sons,

Chichester, 2nd edition (1994)

2 Sivaloganathan, S, Evbu-omwan, N F O, Jebb A andWynn , H P Design function

deploymenta design system

for the future Design StudiesVol

16 No 4 (1995)

3 Sivaloganathan, S, Evbu-omwan, N F O and Jebb, A A

design system for concurrent

engineering Concurrent Engin-

eering Research and Appli-

cations Vol 3 No 4 (1995)

www.elsevier.com/locate/destud

0142-694X/00 $ - see front matter Design Studies 21 (2000) 5974

PII: S0142-694X(99)00004-6 59 2000 Elsevier Science Ltd All rights reserved Printed in Great Britain

A hybrid systematic and conventionalapproach for the design anddevelopment of a product: a case

studyS Sivaloganathan, T M M Shahin, M Cross and M Lawrence,

Engineering Design Group, Department of Manufacturing and

Engineering Systems, Brunel University, Uxbridge, Middlesex UB8

3PH, UK

This paper aims to study the effectiveness of systematic and conventional

approaches to design. A team of students who had been educated on the

systematic approach to design was engaged in the design of a new

producta disposable bicycle made out of paper. The students tried the

systematic approach wherever they could use it and adopted the

conventional approach whenever they encountered difficulties with

systematic design. When they adopted new philosophies or concepts not

proven by either systematic or conventional models, some rework was

needed. The work suggests that a hybrid approach is the most suitable

one when developing new products with limited data available. This

paper describes the different approaches and the approach undertaken

by the students. 2000 Elsevier Science Ltd. All rights reserved

Keywords: product design, systematic design, intuitive design, design

studies, case study


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appropriate in each case. The success of DFD depends on the design

methods that are used in conjunction with its design model shown from

left to right in level 1.

A conventional approach to design on the other hand defines the problem

as a Brief. It then collects as much relevant data to the problem and

solution as possible to develop adequate insight. Conceptual solutions are

then proposed and developed in an iterative fashion until they meet the

specifications. Models of subsystems are then built to prove the designs.

The Engineering Design Group at Brunel University and the Centre for

Design Research at Stanford University put a group of students to work

on the design and development of a cardboard bicycle in order that they

might build the prototype within 15 days. This was carried out as part of

the Stanford postgraduate module Design Project Experience. The stu-

dents had formal education in systematic design (advocated by DFD) and

in design methods. This paper describes the way the product was designed

and developed and identifies the strengths and weaknesses of both system-

atic and conventional approaches to design. It identifies a hybrid approach

as a suitable way for new product development. Section 1 describes the

problem, Section 2 describes the way it should have been handled using

a systematic approach as per DFD, Section 3 describes the way it would

have been handled in a conventional way, Section 4 describes how the

team actually designed and built the product, and Section 5 discusses the

advantages and disadvantages of the three approaches. Finally conclusions

are drawn in Section 6.

60 Design Studies Vol 21 No 1 January 2000

Figure 1 Structure of Design Function Deployment


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4 Akiyama K Function analy-sissystematic improvement of

quality and performance Pro-

ductivity Press, Ohio, USA

(1991)

1 The problemA successful entrepreneur turned cyclist has hypothesised that there is a

market for disposable bicycles. The requirement is to construct a prototype

of a disposable bicycle made out of paper that can be shipped in oversized

shipping cartons. It can involve the words some assembly required to

minimise the shipping volume. The use of non-paper materials is permittedbut at a significant cost, so they should be considered as a precious resource

and used wisely. The bicycle should withstand the travel of four laps

around a predefined course. A design constraint uses a standard inter-

national shipping formula from UPS, FedEx, etc. Determine the dimen-

sional weight in pounds by dividing the cubic size, in inches, of the ship-

ment by 166: dimensional weight = L W H/166. Increase fractions of

a pound to the next full pound. Bicycle cartons with a dimensional weight

of greater than 166 lb or an actual weight of greater than 166 lb will be

returned to the design team for modification. Each team will be assigned

a client team and the clients requirements should also be taken into con-sideration.

2 Designing with the systematic approachThe systematic design within the taxonomy of DFD starts with establishing

the stakeholders and their prioritised requirements. In the case of the dis-

posable bicycle the stakeholders include the shipping companies, end users,

the entrepreneur (to decide on price etc.) and any others who have some

connection with it. Once these requirements and their relative importance

ratings are established the specifications of the product are drawn. Specifi-

cations essentially describe the functions that the product should performin order to satisfy the requirements. Specifications also include the restric-

tions that have to be imposed on the product, which are called the con-

straints. Since the product under consideration is a variant of an existing

product (a bicycle), a list of functions performed by the product can be

easily established by performing a function analysis4 of a normal bicycle

and then adapting it to a disposable bicycle. Once the specifications are

drawn the development of the solution can be started. Here the function

family tree established in function analysis is analysed critically to identify

the essential subsystems and the unnecessary subsystems for the disposable

bicycle. Using these, subsystems can be proposed for the paper bicycle.

A morphological analysis at this stage may reveal useful new conceptual

solutions. These conceptual solutions are then developed as embodiments

by specifying the constituent parts. These parts have to then be tested for

strength and other properties that are necessary for their functioning indi-

vidually and as part of an assembly. Often these tests are done with com-

puter models, which may be verified with a prototype. Since the material

used is to be mainly paper, little material selection is needed. However,

A hybrid systematic and conventional approach for the design of a product 61


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material for non-paper components must be selected and tested at this

stage. Subsequently, manufacturing methods also have to be established.

Thus, the design process for the paper bicycle under the systematic

approach under DFD should be as illustrated in Figure 2.

3 Designing under the conventional approachThe conventional approach often practised by designers, starts with theinterpretation of the design brief. In order to understand the design brief

a technical interpretation of it is written. Often at this stage, enough infor-

mation is collected and a better insight is derived. Then conceptual sol-

utions are proposed and often conceptual models are built. Inferences are

then made about the individual concepts by experimenting with conceptual

models. A set of assessment criteria is then developed to evaluate the vari-

ous concepts. Using these criteria, one solution is selected for further devel-

opment. At this stage a prototype is built and more tests are carried out.

Some of these tests may include building and experimenting with computermodels and relating the results with the results obtained from the prototype.

An evaluation is also carried out at this stage to identify unresolved issues.


Figure 2 Design process

under the systematic

approach


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The next stage in this process is to resolve the issues and improve the

prototype. At the end there will be a working prototype representing the

final design. The design process for the paper bicycle in the Conventional

approach can be described in the form of a flow chart as shown in Figure 3.

4 Design process as carried out by the studentsThe students started with individual brainstorming sessions. The results of

these sessions were not that impressive. They also used spider diagrams

to develop ideas unsuccessfully. Establishing a function tree for the new

design seemed to be a good idea. They triedagain unsuccessfully. At

this stage a parts analysis of an existing BMX bicycle appeared a suitable

option for the starting point of the project. This parts analysis, a design


Figure 3 Design process in

a conventional approach


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method, often used under systematic design to analyse and improve exist-

ing designs, was used to develop the parts tree shown in Figure 4.

Once the parts tree of the BMX was complete, the essential subsystems

needed for the disposable bicycle were proposed using the parts tree as a

basis. This marked the starting point of the design process. A morphologi-

cal analysis was then carried out to consider the alternative subsystems for

the proposed bicycle. Figure 5 shows the morphological chart.

From the morphological analysis, a harmonious and conforming solution

was selected and the components were designed separately. The compo-

nents thus designed were as follows:

(1) Frame with seat and seat bar.

(2) Wheels.

(3) Steering system.

(4) Propulsion.


Figure 4 Partial parts tree of a BMX bicycle


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4.1 Frame with seat and seat post designThe bicycle frame with seat and seat post provides for a number of func-

tions. It gives a rigid platform to support the rider and also houses thedrive mechanism. The frame provides the reactions against the axle, the

total of which is equal to the weight of the rider plus the pedalling force.

The frame also supports the force produced as a result of the front forks

during a steering manoeuvre. The calculations of the dimensions for the

members of the frame proved to be difficult without a finite element analy-

sis, for which structural properties of various materials were required.

Hence, a trial and error method with physical members was used for decid-

ing the right dimensions for the members.

The frame consists of four components shown in Table 1 and Figure 6.The main tube was essentially a tube with two holes cut for the forks and

the seat post. A slot was cut at the rear to house the rear wheel and drive

system. Reinforcement was added to the rear by gluing a section of tube

inside the main tube. The same technique was used to reinforce the seat

post where it housed the drive crank. Gluing a 6-in. diameter tube section

into the tube perpendicular to the main tube reinforced the front of the main


Figure 5 Morphological

analysis of concepts

Table 1 Main frame

Component Made from Length (in.) Diameter (in.) Wall thickness

(mm)

1 Main tube Tube 47 8 62 Seat post Tube 27.3 4.5 53 Seat Laminated N/A N/A N/A

corrugated card4 Bearing surface Tube and 3 6 5

corrugated card


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tube. This, along with the fork-bearing surface, eliminated deformation of

the main tube. The seat post was glued in place and secured with a smaller

cardboard tube through both main tube and seat-post.

4.2 WheelsThe wheels provide a number of functions within the bicycle. Firstly, they

must be sufficiently robust to support the total force exerted on them by

the axles. They must rotate in order to allow motion and propulsion. They

therefore must be circular and have a high friction surface around the per-

iphery to provide traction. They must also provide a cambered surface to

allow the bike to tilt during cornering. The wheels were fabricated from

10 layers of corrugated cardboard laminated with a 72 lay-up. The layers

were secured using wood glue. The layers were angled to give the

maximum possible strength from the grain of the card. A diagram of

this configuration is shown in Figure 7.


Figure 6 Main frame ass-

embly with the drive system


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The wheel diameters were chosen to fit the tyre diameters available from

the local cycle shop. The wheel rims were made from strips of hard board,

which were glued around the perimeter. Three strips each having a different

width were used. This gave the wheel the required camber as shown in

Figure 8. The tyres were then glued on top of the rim. Finally, cardboard

tube bushes were glued into the centre of the wheels. Trials with these

bushes showed heavy friction and PVC tubes were then used as the axles

and bushes.

4.3 Steering systemThe forks and handlebars provide the steering function. The direction con-

trol of the rider is transmitted to the steering column by rotation of the

handlebars, which in turn rotate the column within the main frame. The

forks were built from two sections of cardboard tube as shown in Figure 9.


Figure 7 Cardboard lay-up

procedure for wheels


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The final fork assembly consists of a 6-in. diameter tube joined to a 4.5-

in. diameter tube joined by two smaller diameter tubes glued in place per-

pendicular to the main tube.


Figure 8 Part cross section

of wheel showing reinforc-

ing rims

Figure 9 Fork assembly


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The handlebars made from 2.5-in. diameter cardboard tube, simply fitted

into a hole in the top of the forks. Trials with the system revealed that the

friction at the interface between the fork and the main frame was too high.

Therefore, a circular piece of transparency film was placed between the

mating surfaces to reduce the friction.

4.4 Drive systemThe cogs for the drive system were cut from an MDF sheet of 18-mm

thickness. The rear cog was attached to the wheel using five lengths of

dowel as shown in Figure 10.

They were driven by a knotted rope drive to act like a chain. The knots

were placed at intervals of 50 mm from each other. In order to provide a

free wheel action the tooth profile had a sloping relieve side and sharp

engaging side. As trials with the drive showed slipping, groves to lower

the rope were cut in the teeth to alleviate this problem. The main drivecog was glued to the crankshaft using a keyway and an MDF key. The

cranks were also cut from MDF as shown in Figure 11.

4.5 Full assemblyThe final bike assembly with all the subsystems is presented in Figure 12

5 Advantages and disadvantages of the approachesEvaluating the effectiveness of the three approaches needed a set of criteria.

The following seven characteristics were seen as the requirements for

evaluation.

(1) Clear starting point. Clear starting point is an important aspect

because this avoids the waste of time at the early stages when the


Figure 10 Rear drive cog

assembly


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insight of the problem and solution space is low. This permits the

development of insight while working on the project.

(2) Clear steps. Clear steps provide for the planning of the project. This

is particularly useful when the time allowed for the project is limited.


Figure 11 Crank and pedal assembly

Figure 12 Final bike assembly


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(3) Requirement of market data. This is the data on the shapes, forms,

sizes and prices of different materials available in the market. This

is very important because a design, which may be optimal in several

perspectives, may have to be tailor made and hence become very

expensive.

(4) Requirement of properties. This relates to the data on material proper-ties such as, Youngs Modulus, surface roughness and friction, etc.

The properties required may not be known at the beginning of a pro-

duct and this can aggravate the situation.

(5) Reliance on models and tests. Tests with physical models are carried

out for two reasons: (a) to ensure compliance with the laws of physics

and nature and (b) to estimate the performance characteristic, which

is difficult to do otherwise.

(6) Reliance on computer models. Because physical models are difficult

to make there is now an increasing tendency to use computer models.

It is therefore important to know which model uses this techniquemore.

(7) Knowledge capturing. This is one of the most important aspects of

the design process because the information captured not tells us which

considerations were used but also which considerations were not used

in the various decisions made. This will enable an explanation of the

performance to be made and thus provide ways of improving the

product at later stages in time.

5.1 Systematic approach

The Systematic approach to handle this problem is given in section 3. Ifthe approach is considered according to the above criteria the following

observations can be made:

(1) Clear starting point. The starting point under the systematic approach

is to establish the list of stakeholders and their requirements. These

are collected to establish the specifications of the product together

with their constraints.

(2) Clear steps. In the systematic approach this means the process chain

with computer modelling and analysis.

(3) Requirement of market data. This becomes a standard requirement in

the systematic approach because the computer models and their analy-

sis needs them. Without this data, it is not possible to perform any

analysis. In the case of the paper bicycle the lack of data on paper

and different available forms almost inhibited the use of systematic

methods.

(4) Requirement of properties. This relates to the data on material proper-

ties such as, Youngs Modulus, surface roughness and friction, etc.



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These form the other component of data required for analysis. The

lack of this group of information on materials for the paper bicycle

was another reason preventing the systematic approach for design.

(5) Reliance on models and tests. In systematic design most of the tests

are carried out with computer models and the final confirmation tests

are only carried out with physical models.(6) Reliance on computer models. Most of the tests are carried out with

computer models.

(7) Knowledge capturing. Knowledge capturing is much easier with sys-

tematic design because each stage in the design process has a speci-

fied output.

5.2 Conventional approachThe conventional approach to handle this problem is given in section 3. If

the approach is considered according to the above criteria the following


(1) Clear starting point. The starting point in the conventional approach

is the need statement or brief. It does not have a clear format and

hence understanding the need statement takes quite a lot of time

and effort.

(2) Clear steps. There are no clearly defined steps. The designer is

expected to plan his work.

(3) Requirement of market data. Even though this data is important the

method relies on working around what is available in the market andhence does not create serious problems.

(4) Requirement of properties. Here again the data is important. But the

absence of it is not crucial because estimates can be made from exper-

imentation.

(5) Reliance on models and tests. The conventional design approach

relies heavily on building models and testing them.

(6) Reliance on computer models. Computer models form part of the

testing programme.

(7) Knowledge capturing. Special effort has to be taken to capture

design knowledge.

5.3 Approach by the studentsThe students started with a systematic approach and deviated from it wher-

ever they found it difficult and the conventional approach proved easy. If

the approach is considered according to the above criteria the following




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(1) Clear starting point. The students approach used the parts tree analy-

sis as the starting point for the design. This is somewhat similar to

the function structure advocated by the systematic approach.

(2) Clear steps. The students tried to follow the steps defined by DFD

but found it difficult. The reason being the lack of availability of

market data and the properties of the materials.(3) Requirement of market data. The students tried to collect data, but

managed to procure only the available materials within the two-

week period.

(4) Requirement of properties. The students could find a limited infor-

mation only during the two-week programme.

(5) Reliance on models and tests. The students relied heavily on testing

the physical model and wherever this was insufficient they had prob-

lems.

(6) Reliance on computer models. Very limited computer modelling was

done because of the lack of required data.(7) Knowledge capturing. Special effort had to be taken to capture

design knowledge.

5.4 DiscussionComparison of the three approaches shows that the systematic approach is

easy and comfortable when the problem is clearly defined and the required

data and information are available. This facilitates computer modelling and

analysis and thus eliminates the necessity for extensive physical modelling.

However, the approach becomes difficult with limited data. The conven-

tional approach on the other hand permits the use of limited data and usesphysical modelling and experimentation as the principal tools for

developing the design. In the absence of a lot of information this method

seems to be more efficient. The students used a hybrid systematic and

conventional approach. For instance establishing the parts tree is a system-

atic approach. Using the structured layering and other methods in the fabri-

cation of wheels were systematic methods that worked. When details were

not known, as in the design of the main frame, they brought the materials,

built the models and tested to prove the design. Wherever they did no

testing and had limited knowledge, they encountered failures. Therefore,

it is safe to conclude that the systematic approach is easy only when enough

data is known and the conventional approach is easy when limited data is

known. A hybrid approach is the most suitable when developing a new

product. This permits the benefits offered by both approaches.

6 ConclusionsThe design process adopted by a team of students trained in the systematic

approach to design was engaged into the design of a new product. Their



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approach followed the easy methods in both systematic and conventional

design methods. Analysis revealed that with a lack of the required data,

the systematic design approach had limited success whilst the conventional

approach was effective in these circumstances. It is therefore safe to con-

clude that a hybrid systematic and conventional approach is the easy way

for the development of new products.


2002 a hybrid systematic and conventional approach for the design and development of a product a...

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