Design Concept Handout

7/28/2019 Design Concept Handout

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EG1020 DESIGN CONCEPT SELECTION EXERCISE

Groups should select a design problems and produce:

1. a specification for the product

2. a range of concepts (labelled sketches) which attempt to meet this specification

3. assess the concepts with respect to a datum (maybe an existing product)

4. make a choice as to the best concept or mix of ideas from concepts.

Design examples :

Nut cracker Automated swimming pool cleaner Multispeed wheelchair Automated brush cleaner Exercise system Solar powered airconditioning Dirt-free bicycle drivetrain Automatic internal house sliding door Automated car window deicer/snow melting system Wind powered irrigation system Automatic dog/cat feeding system Environmentally friendly bicycle warning system Hygienic domestic kitchen bin New razor design Electronic guide dog for the blind Domestic snow clearing system Automated log splitter Solar operated window blind Slab lifting/laying device Fire alarm for the deaf or blind. Foot drive wheel chair Automated soil moisture content controller Automated car parking system Boiled egg cooker/timer device Bottle counting system Electric bicycle Water powered toothbrush Robotic lawn mower or vacuum cleaner


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EG1020 CONCEPTUAL DESIGN AND SELECTION

Traditional design approaches are no longer effective as products have become more sophisticated,

consumer driven and government influenced and an increasing number of concepts are protected by

patenting, precluding their economic usage. Products based on blank sheets of paper ideas are not that

likely to be able to compete with todays global industries unless the originators have raised their

comprehensive competence to such a level that they can undertake design from consideration of the

system to detailed design, marketing and costing.

"technical excellence is not enough without commercial competitiveness" (Hodgson 1986 from Pugh)

Success requires systematic thoroughness and meticulous attention to detail from the beginning to the end

of the design process defined as Total Design (Pugh) made up of the sum of partial design inputs.

The successful product requires:

1. Technical feasibility - Directive of engineers

Will a concept work?

Can you judge from sketch concept something will actually work? - may require brief calculationsor experimental program.

Use of engineering analysis/computer simulation to obtain a qualitative understanding of the problem.

2. Economic feasibility - Directive of sales

Can the product be produced and marketed at a price which will yield good sales and company profit?

Final decision making

The decision making needs to take account of all requirements from the customer and the company.

To choose the best decision is to choose the one alternative from those available that best balances or

optimises the total product value considering all factors and information. This can be undertakensystematically using a decision selection method (DSM).


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Conceptual Design

Much of a designers work is to propose solutions to problems and evaluate their suitability. The ability

to be creative is an essential attribute for a good designer.

It was this demand for creative effort that gave rise to our present day word engineer which is derived

from the French ingenieur meaning ingenious or clever.


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Solution focused - the nature of a designers activity.

Design problems naturally decompose into the design of functionally independent subsystems.

Two basic steps in decomposition:

1. All design problems have one or two most important functions. Find the overall function that needs to

be accomplished.

Generate a single statement of this overall function based on customer requirements.

2. Decompose the function into subfunctions.

Redefine the overall function as much as possible.

Concepts follow functions and products follow concepts.

The division of subfunctions into finer detail leads to a better understanding.

Product Design Specification (PDS)

This document includes the parameters which the designer has to meet in order to satisfy the customer's

requirements.

Typical outline specifications of functionality may include:

Performance

Function(s)

Loadings Environment / noise Service life Size / critical dimensions Weight Ergonomics (human factors) Aesthetics (visual appeal) Safety Cost Maintenance and reliability Legal implications / restrictions / hazards

Manufacturing Processes Materials Packaging Quantity

Each of these outline functions may then broken down into subfunctions.


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Some features of a specificationare usually more important thanothers; called requirements or criteria.

Allocation of weightings gives agreater discrimination to thematrix in choice of the "best"concept.

Weighting are usually applied ona top down basis starting from 1using the PDS as a guide.

Weightings can also be appliedusing a 1-5 or 1-10 scale.

Weightings are applied to eachconcept by multiplying the

weighting factor by the score for each criteria and then totalizedfor each concept.


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Creativity Methods

Definition: to bring into being by force of imagination. Individual or group creativity:

Morphologically - consider all the different methods that can be used to meet the various

functional requirements of a design problem by breaking down a complex problem into sub-

problems. Various concepts can then be derived by linking one method for one function to amethod for a second function and so on.

Group creativity:

Bouncing ideas off colleagues and friends

Brainstorming in which a group comes up with a series of ideas to solve a problem which arerecorded however ridiculous they may appear at first sight. Ideas should trigger other ideas.Criticism following the presentation of an idea should be avoided since it inhibits the productionof other ideas.

Generating ideas comes from stimulation of the imagination which results from an association between

the problem and some past experience.

This is fine for a standard solution yielding a standard solution.

More innovative ideas do not necessarily require experience but still require stimulation which usuallycomes by the techniques above.


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Concepts

Conceptual design should be documented as sketches with a brief indication of the important features.Some examples are presented from Hurst 1999:


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DESIGN SELECTION CHART ( DSC)

A DSC is a method which allows the choice of a design from a range of concepts that best meets thespecification of the customer.

Concepts are often best generated by individuals

Concept selection is best performed in groups.

Experience gained over many projects has lead to the conclusion that matrices are the best way to presentthe process of evaluating concepts in order to identify those that best satisfy the criteria that have beenidentified as being significant for a design.

Matrices here are not mathematical simply a format for expressing and recording ideas and choices. Thecompleted matrix provides a useful document which records the outcome of the decisions reached by adesign team and can be filed as part of the quality control of a project or used as a means of assessment inyour group design.

Each concept "sketch" should be considered in turn.

Concepts are rated in turn against the criteria which have been identified as constraints and objectives for a design to meet the needs of the customer.

The requirements or criteria are laid out in a product design specification (PDS) which is usually agreed by the customer. A vital part of a concept involves the element of technical risk in implementing a particular design feature either from the company point of view or the technology involved. Risk must beconsidered with a negative weighting factor. Another factor to be considered is the cost of developmentand the time involved.

Criteria should include factors that the customer may not specify but would be expected of a design whichare going to appeal to the market in general if the product is to succeed. Factors such as safety(regulations and standards), aesthetics ( appearance), ergonomics ( human interaction) and reliability.

When an existing product is used as a basis for comparison, for say redesign, concepts should be ratedagainst this "datum" design. In the case of a new product the datum concept is that which the groupconsiders, from first thought, to be one of the better ideas.

Ratings are the applied relative to the datum for each criteria using S for same, + for better and - for worse than datum.

Choice is then made by summing the Ss, -s and +s where the scale can be -1>0>1 or if more

discrimination is required -2>-1>0>1>2 ( 5 point scale). The best choices being those with (1) highest +s(2) lowest -s (3) highest Ss.

Weightings are applied to each concept by multiplying the weighting factor by the score for each criteriaand then totalizing these for each concept.

The highest scoring concepts are those that appear to satisfy the criteria best; arrived at by groupconsensus .

If there is no clear winner in the first phase of concept selection then the strongest concepts should bedeveloped in a second phase where the criteria are expanded and weightings adjusted to allow even morediscrimination and hopefully a clear "best" solution.


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A Torque capacity

B11 Axial location

B12 Small number of components

B2 Use of bought out components

B3 Simple machining

C1 Stress raising effect

C2 Tolerance to overload

C31 Ease of gear replacement

C32 Use of prehardened component s

Criteria selection for gear fixing

The data in the criteria table above are derived from the criteria requirement tree which is shown on page5. The tree is produced on a top down basis using the prime requirement and the next level down is theresult of asking the question what does this mean until a stage is reached where there is no further

breakdown in this process and a base requirement is produced.

The number of steps will depend on the number of levels required down the tree and each stage should benumbered.

Each concept is now assessed as to how well it meets these criteria either with resepect to an existing product or relative to one of the concepts which is chosen as a datum ( usually one which is considered to be a good candidate in that it does meet the criteria in most areas.

The process of awarding points has already been outlined under DSC.


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No. Criteria Concepts

1 2 3 4 5 6

A Torque capacity d s - - - +

B11 Axial location a - + + + -

B12 Small number of components t s - + s +

B2 Use of bought out components u - - + - +

B3 Simple machining m - + + + -

C1 Stress raising effect s + + + +

C2 Tolerance to overload s - - - +

C31 Ease of gear replacement + + s + +

C32 Use of prehardened components + + + + +

Datum method of concept evaluation - 1 st run.

Replacing these with a numerical range of -1>0>+1 the matrix becomes:

No. Criteria Concept

1 2 3 4 5 6

A Torque capacity d 0 -1 -1 -1 1

B11 Axial location a -1 1 1 1 -1

B12 Small number of components t 0 -1 1 0 1

B2 Use of bought out components u -1 -1 1 -1 1

B3 Simple machining m -1 1 1 1 -1

C1 Stress raising effect 0 1 1 1 1

C2 Tolerance to overload 0 -1 -1 -1 1

C31 Ease of gear replacement 1 1 0 1 1

C32 Use of prehardened components 1 1 1 1 1

Sum -1 3 4 4 7


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Adding the previously assigned weightings for each specification and concept the matrix now becomes:

No. Criteria Weighting Concept

1 1W 2 2W 3 3W 4 4W 5 5W 6 6W

A Torque capacity 0.4 d 0 0 0 -1 -0.4 -1 -0.4 -1 -0.4 1 0.4B11 Axial location 0.063 a 0 -1 -0.1 1 0.06 1 0.06 1 0.06 -1 -0.1

B12 Small number of components 0.027 t 0 0 0 -1 -0 1 0.03 0 0 1 0.03

B2 Use of bought outcomponents 0.06 u 0 -1 -0.1 -1 -0.1 1 0.06 -1 -0.1 1 0.06

B3 Simple machining 0.15 m 0 -1 -0.2 1 0.15 1 0.15 1 0.15 -1 -0.2

C1 Stress raising effect 0.12 0 0 0 1 0.12 1 0.12 1 0.12 1 0.12

C2 Tolerance to overload 0.09 0 0 0 -1 -0.1 -1 -0.1 -1 -0.1 1 0.09

C31 Ease of gear replacement 0.036 0 1 0.04 1 0.04 0 0 1 0.04 1 0.04

C32 Use of prehardenedcomponents 0.054 0 1 0.05 1 0.05 1 0.05 1 0.05 1 0.05

sum +ives 2 5 6 5 7

sum -ives 3 4 2 3 2

sum sames 4 1 1

sum weighted 0 -0.2 -0.2 0 -0.1 0.57

Selection of the best concept or concepts is made firstly by (1) assessing the highest positive score(s), (2)lowest negative score(s),(3) highest sames score(s) and most significantly the highest weighted score(s)

If there is no outstanding concept then it is necessary to revisit the previous matrix and asign a larger spread of scores (-2>0>+2) or to increase the number of subfunctions of the specification criteria.

References.

Stuart Pugh, Total Design, Addison-Wesley, 1991 620.0042

Clifford Matthews, Case Studies in Engineering Design, Arnold, 1998 620.0042MAT

David Ullman, The Mechanical Design Process, McGrawHill, 1992 621.815ULL

Ian Wright, Design Methods in Engineering and Product Design, McGrawHill, 1998 620.0042

Ken Hurst, Engineering Design Principles, Arnold, 1999


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MARKING SCHEME FOR CONCEPT DESIGN SELECTION EXERCISE

Groups should submit a report containing individually named concepts fromgroup members together with the 4 other sections and the final design choice asa result of weighted marking.

TASK GROUP/INDIVIDUAL MARK

Specifications Group 2

Criteria Group 2

Weightings Group 1

Concepts Individual 2

Concept marking Group 2.5

Final designchoice

Group 0.5

.

Specifications (pds) - Document showing the parameters which define customer requirements.

Criteria the pds needs to be broken down into a list of design constraints andobjectives that need to be addressed.

Weightings define the importance to the design of each of the criteria.

Concepts simple sketched solutions produced by individuals in the grouprepresenting and explaining possible solutions to the criteria. Not all of the criterianeed to be satisfied by each concept.

Concept marking a spreadsheet matrix showing the relative strength of oneconcept relative to a datum device or concept.

Documents

Design Concept Handout