module 1 lecture 2 final

7/28/2019 Module 1 Lecture 2 Final

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Module1

Introduction


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Lecture

2Concept Generation and Evaluation


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Instructional objectives

The primary objective of this lecture is to outline the importance of concept generation and

selection in decision making exercises in a product development.

Introduction

Concept generation and the final selection of a concept through proper evaluation are critical

decision making steps in product development. The primary aim of concept generation and

evaluation is to ensure that the product can perform all of the major functions. This may be done

by simple calculations, sketches, circuit diagram, proof-of-concept models, or by a detailed

written description of the concept. The stage of concept generation and evaluation should

minimize the possibility of misrepresenting a solution, which may actually be effective, and

consider different ramification of a final decision. For example, not considering the customers

need during the concept generation and evaluation phase may lead to the failure of the product in

the market. Typical steps involved in concept generation and evaluation is shown below [Figure

1.2.1].

Figure 1.2.1 Various stages involved during concept generation and evaluation


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Creative Thinking

Creative thinking is critical for concept generation for a product development. The process of

creative thinking can be viewed as a step to move from an unstructured idea to a well-structured,

from an implicit to an explicit design. Following steps are considered helpful in encouragingeffective creative thinking in the process of concept generation.

Develop a creative attitude

It is very essential to develop confidence that one can provide a creative solution to a given

problem.

Unlock your imagination

One should always ask questions like what or what if and discuss all possibilities. One

should spend time on understanding the problem given and be able to realize various queries that

may be associated with the problem given.

Be persistent

Most of the problems are never solved in their first or even initial few attempts. One should

rather peruse the solution of a given problem with persistence to find out alternate solutions or

designs.

Develop an open mind

One should always be receptive to ideas from any and all sources for newer concepts.

Suspend your judgment

The concept generation stage should preclude early judgments. Often the creative ideas develop

slowly and require time to proceed in an explicit manner. Thus, the concept generation stage

should not be hampered by critical judgment at the initial level.

Set problem boundaries

This is extremely important for concept generation. It is widely accepted that setting problem

boundaries at the very initial stage does not limit creative design ideas but rather focuses it more.

Conceptual Decomposition

An effective way to solve a complex problem is to decompose it into smaller parts that are easier

to manage and then recombine all the ideas or designs to arrive at the final solution. There are

two main approaches towards conceptual decomposition.


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Decomposition in Physical Domain

In this stage, the product design is decomposed directly into a number of subassemblies and parts

/ components. This is the initial step. It should be possible to describe how these subassemblies

and part/components work together to accomplish the required function of the product. The

function of each of the parts and sub-assemblies, and the way there are connected and interact

with each other should be realized explicitly. Each of these subassemblies may be further

decomposed into smaller subassemblies and component. This continues till we reach the

component level of all the subassemblies. The design information that is available at every level

of decomposition is slightly different from its preceding level. However, the functions of the

components and subassemblies down the line would possibly be quite different from the function

of the final product. Following example [Figure 1.2.2] shows the decomposition of a typical

bicycle in the physical domain for the purpose of product design.

Figure 1.2.2 Decomposition of a bicycle in physical domain for product design purpose

Decomposition in Function Domain

In functional decomposition, the system functions are descried as the transformation between an

initial stage and the desired final state. The approach of concept generation by functional

decompositions was originated in the German schools of design. The input and the output of the

functional devices are usually described in terms of either energy flow, material flow or

information flow. The functions associated with the flow of energy are classified both by the

type of energy and by its action on the system. The types of energy are usually classified as

mechanical, chemical, electrical, fluid and thermal energy. The actions on the system are

envisaged as change, change back, enlarge, reduce, change in direction and so on. The material

flow is classified as through-flowor material-conserving process in which the position or shape


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of the material is changed, diverging flowin which the material is divided in two or more number

of small parts, and converging flow, in which the materials are joined or assembled. The

information flow is basically in the form of mechanical or electrical signal or software

instruction. Hence, the process of functional decomposition describes the design problem in

terms of flow of energy material and information.Table 1.2.1 shows the decomposition of

typical devices in functional domain.

Table 1.2.1 Functional domain decomposition of three common devices

Device Input Function Other effect Output

Gear

Rotating

mechanical

energy

Change speed of rotationChange direction

of rotation

Rotational

mechanical energy

PencilMechanical

energy

Transfers Graphite from

pencil to paper

Graphite deposit on

paper

MotorElectrical

energy

Converts electrical

energy to mechanical

energy

Generate

Thermal energy

Rotational

mechanical energy

Generating Design Concepts

The design concepts are necessary to build the functions of the product. In other words, the

design concepts provide the answer how for the intended function of a product. Usually, a

design team is formed in which every team member spends several hours working individually

on a few subsets of the overall problem for example, how to identify the sub-functions, and so

on, Next, the team members would assemble together to discuss and improve the concepts

developed individually and in turn, a number of small design concepts would be generated.

Morphological Chart

The morphological chart is a method to arrange all the functions and sub-functions in a logical

order. The morphological chart also enlists the possible hows for each sub-functions with an


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aim to realize the combinations of ideas comprising several design concepts. Following is the

typical procedure to develop a morphological chart.

(1)Establish the functions that the design product must perform(2)List the functions, one per row, in a chart.(3)For each function (row), list a wide range of sub-solutions, one per column.(4)Select an acceptable set of sub-solutions, one for each function.

Table 1.2.2 shows an example of a morphological chart for the packing of parts like nuts and

screws, etc. In the chart, some of the alternatives along a row may be combined to give a single

solution, e.g. for picking up the parts, a vacuum arm could be used and for orienting parts, step

feeder can be used. I f every solution on each row is compatible with all the solutions on the other

rows the number of the possible solutions to the system is a multiple of all the ideas on the rows,

the possibilities would be enormous.

Table 1.2.2 Schematic presentation of a morphological chart of packing parts

Functions Option1 Option1 Option1

Picking parts Mechanical Arm Vacuum Arm Pneumatic arm

Orienting parts Step feeder Bowl feeder Centrifugal feederStoring parts Rack system Shelves and Bins Drawer Storage

Transporting partsIndustrial manual

trolleys

Industrial trucks

(powered)

Automatic Guided

vehicles

Combining Concepts

This is the step when many fragmented small design concepts are combined to yield a final

design concept. Number of possible combinations may be many and all should equally beevaluated or checked for viability. The next step is to combine the concepts to arrive at a set of

ultimate design concepts.


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Evaluation Method

Once all the design concepts are more or less selected based on feasibility, these concepts are to

be evaluated before the final finished design. Evaluation of these concepts involves various

comparisons either in an absolute or in a relative manner among several possible designconcepts.

Absolute Comparison of Design Concepts

It consists of comparing the concepts to a series of absolute filters.

[1] Evaluation based on judgment of feasibility of the design: This is the first screening andinvolves an assessment of the feasibility of the design concepts by the experts.

[2]

Evaluation based on assessment of technology readiness: This is the second screening andinvolves an assessment of the readiness of a product manufacturer to produce the designed

product without additional research efforts.

[3] Evaluation based on go-no-go screening of the customers requirements: This step involvesan evaluation whether the design has undertaken the customers requirements or feedbacks.

Each customer requirement should be transformed in to a question and should be

answerable as either yes (go), maybe(go) or no (no-go). This should help to eliminate any

design concept that cannot address an important customer requirement.

Relative Comparison of Design Concepts

Relative comparisons help to work out the importance of a number of options relative to each

other especially when there are no objective data available to set the standard for comparison

relative comparison really helps to remove any sort of ambiguity while selecting the most

appropriate candidate. There are various ways methods for comparing concept designs by

relative comparisons. Some of the most important ones are

Pugh's Concept selection Method Weighted Decision Matrix Analytical hierarchy process.


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Pugh's Concept Selection Method

This is a widely accepted method for comparing concepts that are not refined enough for direct

comparison with the engineering requirements. Following are the steps involved in this method

which are explained with the help of an example.In the example comparison of the effectivenessbetween three different types of hinges that are used in cabinets is being done. The three options

for the hinge are butt hinge, flush hinge and barrel hinge as shown in theFigure 1.2.3.

1. Choose or develop the criteria for comparison: The criteria can be identified by examiningthe customer requirements and generating a corresponding a set of engineering requirements

and targets. In our example the criterias arecost of the part, durability, time to production of

the partandreliability.

2. Select the alternatives to be compared: The alternatives refer to the alternate ideas developedduring concept generation. All concepts should be compared at the same level of

generalization and in similar language. In the following example, thebarrel hinge is taken as

the datum and the other two hinge are compared with this datum level

3. Generate Scores: Designers should pick one of the design concepts that they think is themost appropriate and call it the datum. Now all the other being compared to the datum

concept as measured by each of the customer requirements. For each comparison the product

should be evaluated as being better (+), the same (S), or worse (-).If it is impossible to make

a comparison, more information should be developed. The scores are shown inTable 1.2.3

for our example.

4. Compute the total score: Four scores will be generated, the number of plus scores, minusscores, the overall total and the weighted total. The overall total is the number of plus scores

minus the number of minus scores. The weighted total is the scores times their respective

weighting factors, added up. The totals should not be treated as absolute in the decision

making process but as the guidance only. If the two top scores are very close or very similar,then they should be examined more closely to make a more informed decision. For our

example, we can clearly see that the overall score for theflush hinge is 1 and that for thebutt

hinge is -1.


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Figure 1.2.3 Schematic presentation of three different types of hinges

[Source:http://www.technologystudent.com/joints/hinge1.htm]

Table 1.2.3 Evaluation on the basis of Pugh's Concept Selection Method

Criterion Butt Hinge Flush hinge Barrel hinge

Cost of part - +

D

A

T

U

M

Durability + S

Time to produce S -

Reliability - +

+

-

S

1

2

1

2

1

1

Weighted Decision Matrix

A decision matrix is used to evaluate the competing design concepts by ranking them with

weighting factors and scoring the degree to which each design concept meets the criteria.It is a

simple tool that can be very useful in making complex decisions, especially in cases where there

are many alternatives and many criteria to be considered. Thus it makes as a qualitative tool to

evaluate the alternatives. The procedure for weighted decision matrix is explained below with the

help of the above example [Figure 1.2.3]. The above example considers three different types of

hinges (1) butt hinge, (2) flush hinge, and (3) barrel hinge that are used in a cabinet. These

hinges are required to be produced in bulk. Following is usually the procedure to evaluate the

concept based on a weighted decision matrix.

Butt hinge Flush hinge Barrel hinge
http://www.technologystudent.com/joints/hinge1.htmhttp://www.technologystudent.com/joints/hinge1.htmhttp://www.technologystudent.com/joints/hinge1.htmhttp://www.technologystudent.com/joints/hinge1.htm


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1. Identify the Criteria: The more specific the criteria are, the better will be the results of theevaluation. While it is also desirable to have the criteria that are independent of one another,

it is rarely possible. For our current example the criteria are the cost of the part, the time to

production of the part, and durability and reliability of the parts.

2. Rank and Weigh the Criteria: Some criteria are probably more important than the others.The relative ranking of the criteria will off course affect the evaluation. It is therefore

preferable to find out a a way of assigning weights to the criteria so that their relative

importance (e.g., reliability may be more important than cost of the part) can be quantified.

We can consider the following criteria and the respective weights within parenthesis.

(a) Cost of the part (0.50);(b) Durability (0.30)(c) Time to production of the part(0.10)(d) Reliability (0.10)

3. Choose a Ranking Scale: In order to evaluate each design concept option, we need toconfirm which one is better (with respect to each criterion). An often-used scale for this is a

linear, symmetrical scale as shown below inTable 1.2.4.

Table 1.2.4 Evaluation scale for design objective

11-point scale Description 11-point scale Description

0 Totally useless solution 6 Good solution but a few drawbacks

1 Very inadequate solution 7 Good solution

2 Weak solution 8 Very good solution

3 Poor solution 9 Excellent

4 Tolerable solution 10 Ideal solution

5 Satisfactory solution

4. Calculating the weighting factor for each criterion: This is achieved by multiplying theweightage of the criteria by the score of the criteria for each of the design concept. The

calculation for the above example is shown below [Table 1.2.5].


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Table 1.2.5 Weight decision matrix for selection of a hinge

Design CriteriaWeight

Factor

Butt Hinge Flush hinge Barrel hinge

Score Rating Score Rating Score Rating

Cost of part 0.5 8 4.0 7 3.5 9 4.5

Durability 0.3 7 2.1 6 1.8 9 2.7

Time to produce 0.1 6 0.6 5 0.5 7 0.7

Reliability

Total0.1 6

0.6

7.35

0.5

6.38

0.8

8.7

5. Overall score rating: This is the sum of the weighted factors of all the criteria for aparticular design concept in step 4. For example, the overall rating for the butt hinge is

3.76.06.01.20.4 =+++ .

6. The one with the highest score is the best design concept which is the Barrel Hinge inTable 1.2.2.

Analytical Hierarchy Process

Analytical Hierarchy Process (AHP) is designed to solve multi-criteria decision problems.

Several alternatives are compared in AHP on the basis of the same set of attributes. The typical

steps involved in performing the AHP: (a) make pairwise comparisons, (b) synthesize judgments,

and (c) check for consistency. A typical AHP based evaluation process is explained in detail in

Figure 1.2.4considering the selection of the most suitable hinge as in the previous method.


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Figure 1.2.4 Evaluation of different types of hinges through AHP method

1. Make pairwise comparisons: Pairwise comparison is widely found to be effective with theassignment of relative weights. We compare here each alternative with another in a pairwise

manner for each criterion. Following [Table 1.2.6] is the scale that is used for pairwise

comparison [inTable 1.2.7,Table 1.2.8,Table 1.2.9andTable 1.2.10].

Table 1.2.6 Scale / Rating used for selection of a hinge

Verbal J udgment of Preferences Numerical Rating

Extremely preferred 9

Very strongly to extremely 8

Very strongly preferred 7

Strongly to very strongly 6

Strongly preferred 5

Moderately to strongly 4

Moderately preferred 3

Equally to moderately 2

Equally preferred 1

Criteria

Alternatives

Selecting the best hinge

Cost Durability Time to produce

Butt hinge

Flush hinge

Barrel hinge

Butt hinge

Flush hinge

Barrel hinge

Butt hinge

Flush hinge

Barrel hinge


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Table 1.2.7 Pairwise comparison of cost, durability and time to produce


Cost 1 5 6

Durability 1/5 1 1/3

Time to produce 1/6 3 1

Table 1.2.8 Pairwise comparison of three different hinges for cost


Butt hinge 1 4 1/3

Flush hinge 1 1/7

Barrel hinge 3 7 1

Table 1.2.9 Pairwise comparison of three different hinges for durability


Butt hinge 1 1/6 1

Flush hinge 6 1 6

Barrel hinge 1 1/6 1

Table 1.2.10 Pairwise comparison of three different hinges for time to produce


Butt hinge 1 5 8

Flush hinge 1/5 1 3

Barrel hinge 1/8 1/3 1

2. Synthesis The priority of each criterion in terms of its contribution to the overall goal ofachieving your goal is computed in this step. It involves the following step.[a] Sum values in each column of pairwise comparison matrix[b] Divide each element by its column total (gives normalized pairwise comparison matrix)[c] Compute average in each row (gives estimate of relative priorities of elements being

compared) by dividing each element by the column total [Tables 1.2.11to1.2.16]


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Table 1.2.11 Assign priority rating of each criterion for pairwise comparison of cost


Butt hinge 1 4 1/3

Flush hinge 1/4 1 1/7

Barrel hinge 3 7 1

SUM 17/4 12 31/21

Table 1.2.12 Compute average priority of each criterion for pairwise comparison of cost

Butt hinge Flush hinge Barrel hinge Average

Butt hinge 1 4 1/3 0.266

Flush hinge 1/4 1 1/7 0.080

Barrel hinge 3 7 1 0.654

These relative priority means that with respect to Cost, the barrel hinge will be preferred first

(65%), followed by butt hinge (27%) and flush hinge (8%). We can do similar calculations for

durability and time to produce.

Table 1.2.13 Assign priority rating of each criterion for pairwise comparison of durability


Butt hinge 1 1/6 1

Flush hinge 6 1 6

Barrel hinge 1 1/6 1

SUM 8 8/6 8

Normalized pairwise comparison matrix

Relative

Prior

ity


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Table 1.2.14Compute average priority of each criterion for pairwise comparison of durability


Butt hinge 0.125 0.125 0.125 0.125

Flush hinge 0.75 0.75 0.75 0.75

Barrel hinge 0.125 0.125 0.125 0.125

Table 1.2.15 Assign priority rating of each criterion for pairwise comparison of time to produce


Butt hinge 1 5 8

Flush hinge 1/5 1 3

Barrel hinge 1/8 1/3 1

SUM 53/40 19/3 12

Table 1.2.16 Compute average priority of each criterion for pairwise comparison of time to produce


Butt hinge 0.755 0.790 0.667 0.737

Flush hinge 0.151 0.158 0.25 0.186Barrel hinge 0.094 0.053 0.083 0.077

We will follow the same process for calculating the relative priority for the criteria as follows

[Tables 1.2.17 1.2.18]

Table 1.2.17 Assign rating of each criterion for pairwise comparison of relative priority


Cost 1 5 6

Durability 1/5 1 1/3

Time to produce 1/6 3 1

SUM 41/30 9 22/3


Relative

Pri

ority


Rela

tive

Prio

rity


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Table 1.2.18 Compute average rating for pairwise comparison of relative priority

Cost Durability Time to produce Average

Cost 0.73 0.55 0.81 0.70

Durability 0.14 0.11 0.04 0.10

Time to produce 0.11 0.33 0.13 0.19

To calculate the overall ranking of the alternatives we now multiply the relative priority of each

criteria with each of the attributes o and add them up [Table 1.2.19].

Table 1.2.19 Overall ranking of the three hinge alternatives

Cost (0.7) Durability (0.1) Time to produce (0.2) Final Score

Butt hinge 0.266*0.7=0.18 0.125*0.1=0.012 0.737*0.2=0.14 0.3461

Flush hinge 0.08*0.7=0.056 0.75*0.1=0.075 0.186*0.2=0.037 0.1682

Barrel hinge 0.654*0.7=0.45 0.125*0.1=0.0125 0.077*0.2=0.015 0.4857

So we can see that the barrel hinge depicts as the best option followed by butt hinge and then the

flush hinge

3. Check for Consistency: A key step in the making of several pairwise comparisons isconsidering the consistency of the pairwise judgments. Example: If A compared to B =3

and B compared to C = 2 then A compared to C should be 6 (3 x 2). Otherwise, an

inconsistency will occur.


Relative

Priority


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Exercise

1. Create a functional decomposition of a refrigerator

References

1. G Dieter, Engineering Design - a materials and processing approach, McGraw Hill, NY, 2000.

module 1 lecture 2 final

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