EPT 221

CONCEPTUAL DESIGN

Lecture Objectives

• Define and describe concept design• Describe and apply methods to clarify functional

requirements of a design: activity analysis, component decomposition, functional decomposition

• Understand and apply various methods to analyze design concepts alternatives: Pugh’s Concept Selection Method, weighted-rating method.

• Generate alternative design concepts using various methods

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Info flow during formulation and concept design phases

FormulationFormulationCustomer NeedsCustomer requirementsImportance weightsQFDEng. characteristicsEng. Design Spec’s Concept DesignConcept Design

“Best”AlternativeConcepts

Alternative Concept Design

Physical Principle

• Definition: the means by which some effect is caused, or produced.

Conservation of energy Archimedes’ principle Ohm’s law Conservation of mass Bernoulli’s law Ampere’s law Conservation of momentum Boyle’s law Coulomb’s laws of electricity Diffusion law Gauss’ law Newton’s laws of motion Doppler effect Hall effect Newton’s law of gravitation Joule-Thompson effect Photoelectric effect Pascal’s principle Photovoltaic effect Coriolis effect Siphon effect Piezoelectric effect Coulomb friction Thermal expansion effect Euler’s buckling law Hooke’s law Newton’s law of viscosity Poisson effect/ratio Newton’s law of cooling Heat conduction Heat convection Heat radiation

Abstract Embodiment

• Embodiment: a representation of an abstract idea in concrete terms; giving concrete form to an abstract concept

• Abstract: Considered apart from concrete existence

Design Concept

Example: Disc Brake

A disc brake is a device for slowing/ stopping the rotationof a wheel.

Ref: http://en.wikipedia.org/wiki/Disc_brake

Design Process during Concept Design Phase

Clarifying Functions

• Why do we need to clarify functions?

During the problem formulation stage, we determine the customer and company requirements. But we do not provide sufficient details/ information to achieve these requirements i.e. may lack sufficient details on specific functions and subfunctions.

• How do you clarify functions?

Using the following methods:1. Activity analysis

2. Product decomposition diagram

3. Function decomposition diagram

Activity Analysis Method

• To learn how the customer will use and retire the product.

• Customer activities examine the relationship between customer and product.

Component Decomposition Method• Product decomposition diagram – a block diagram of the parts and

subassemblies that make up the product. • A hierarchical structure of component forms, not functions• Why? To obtain a better overall understanding of how individual

components interact with each other and ultimately contribute to the overall product function.

Function Decomposition Method

• Subdivides the major/ overall product functional requirement into its respective subfunctions and subsubfunctions.

• (Product ) Function Decomposition Diagram –– A hierarchical structure of functions, not forms.– Helps to identify whether functions are connected, and where the

interface connections might be.

Sample functions

Example of a Function Decomposition Diagram for a Coffee Maker

Overall product function

Sub-function

Sub-subfunction

Helps separate what functions need to be performed versus how it gets done (form)

Generating Alternative Concept Designs

Synthesis the process of generating alternatives

• Synthesis @ the process of generating alternatives may include the following activities:– Investigating archives

• design catalogs, reference handbooks, encyclopedias, monographs, periodicals, technical journals, trade magazines, microfilm, etc.

– Talking to people• Co-workers, professors, vendors, representatives from professional societies and

trade organizations, consultants– Connecting to the internet

• Patents, vendor catalogs, professional societies, trade organizations – Using creative methods

• Brainstorming – an iterative group method that takes advantage of team members’ diverse skills, experience and personalities to generate innovative ideas.

• Method 6-3-5 6 people brainstorms. Each person writes down 3 ideas on a piece of paper. The paper is circulated 5 times where each time 3 more ideas is written down.

• Synectics - a method that requires the problem solver to view the problem from 4 perspectives:

i. Analogyii. Fantasyiii. Empathyiv. Inversion

• Checklist

Developing Product Concepts

i.e. generating alternative design concepts • Generate many alternative concepts for each subfunction.• Use morphological matrix

Sketching is encouraged duringthis stage.

Example

• A design team is developing new concepts for a gasoline-powered minibike. They decompose the primary functions into transmit engine power, steer, and brake. They select three concepts for transmitting power: chain drive, belt drive, and gearbox; two concepts for braking: disc and drum; and three concepts for steering: handlebar, airplane control stick, and fly-by-wire.

• Prepare a morphological matrix and systematically develop alternative combinations.

Analysing Design Concepts

Reason to analyse: to screen out, or eliminate design concepts that are not feasible

• Methods: Back-of-the-envelope: do rough calculations that, while not

rigorous, test or support a point. Proof-of-concept: a short and/or incomplete realization of a

certain method or idea(s) to demonstrate its feasibility, or a demonstration in principle, whose purpose is to verify that some concept or theory is probably capable of exploitation in a useful manner. @ a new concept or a particular device or configuration can be shown to work in the manner in which it was designed.

Bench test/ pilot : used when a real plant is expensive.

• Screening criteria: functionality and manufacturability Functionality – customer requirements, operating conditions, etc Manufacturability – existing technology (ready for production or

only for RnD), materials, financial, marketing considerations.

Evaluating Alternative Concepts

• 2 methods commonly used:i. Pugh’s concept selection methodii. Weighted-rating method

Pugh’s Concept Selection Method

• 1. Select criteria, • 2. Establish datum

column, • 3. Rate alternatives

(+, -, S) against datum

• 4. Select best, or better alternatives

Datum = a reference concept+ is for better-is for worse-S is for same as datum

So the weakest concept would be eliminated form further development.

Modified Pugh’s Method

• Includes an importance weight column.• Importance weight gives different importance to different criteria. So,

the calculation for the concepts will factor in the importance weight.

Weighted Rating Method(or weighted sum method @ Pahl and Beitz

method)

Concept Alternatives gears v-belts chain

Criteria Importance Weight (%)

Rating Weighted Rating

Rating Weighted Rating

Rating Weighted Rating

high efficiency 30 4 1.20 2 0.60 3 0.90

high reliability 25 4 1.00 3 0.75 3 0.75

low maintenance 20 4 0.80 3 0.60 2 0.40

low cost 15 2 0.30 4 0.60 3 0.45

light weight 10 2 0.20 4 0.40 3 0.30

100 NA 3.50 NA 2.95 NA 2.80

Rating Value Unsatisfactory 0

Just tolerable e 1 Adequate 2 Good 3 Very Good 4

references

• http://homepages.cae.wisc.edu/~me349/lecture_notes/product_design_spec.pdf