Early Stages of Design

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Early Stages of Design

• CPE x350-01 F07
• Lynne Slivovsky

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Outline

• Overview of design process
• A variety of models
• Requirements Specification
• (Chapter 3 of Ford Coulston)

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Phases of Design

• Engineering Your Future, Great Lakes Press
• Stage 1 Identify the problem/product innovation
• Stage 2 Define the working criteria/goals
• Stage 3 Research and gather data
• Stage 4 Brainstorm/generate creative ideas
• Stage 5 Analyze potential solutions
• Stage 6 Develop and test models
• Stage 7 Make the decision
• Stage 8 Communicate and specify
• Stage 9 Implement and commercialize
• Stage 10 Perform post-implementation review and
  assessment

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IEEE Std 1220-2005
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IEEE Std 1220-2005
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IEEE Std 1220-2005
CPE 350
CPE 450
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Ullmans Mechanical Design Process

• Phase 1 Specification development/planning
• Phase 2 Conceptual design
• Phase 3 Product design
• Phase 4 Production
• Phase 5 Service
• Phase 6 Retirement

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Phases of the Design Cycle
Specification Development
Redesign
Conceptual Design
Retirement
Disposal
Product Design
Service
Production
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Ford Coulston
Image taken from Design for Electrical and
Computer Engineers, Ford and Coulston
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Design Process Models

• MANY formal models for the design process
• IEEE Std 1220-2005 IEEE Standard for Application
  and Management of the Systems Engineering Process
• The Mechanical Design Process, McGraw Hill, 1997,
  2003
• Design for Electrical and Computer Engineers,
  Ford and Coulston, McGraw Hill, 2007
• Take Home Points
• Do not use a hobbyist/hacker approach
• Be explicit with the process model you select
• (e.g., in your documentation)

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Inside or Outside the Box?
How your problem is constrained.....

..determines the variability in its design
Many Possible Designs
Few Specifications
Many Specifications
One Design
Where do specifications comes from?
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Requirements Specification (Ch 3)

• Requirements Setting Process
• Marketing Requirements
• Engineering Requirements
• Taxonomy of Requirements
• Developing Requirement Specifications
• Example
• Criteria

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Requirements Specification

• The requirements specification identifies those
  requirements that the design must satisfy in
  order for it to be successful.

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Requirements Setting Process

• Three stakeholder groups
• Customer
• Gives raw (marketing) requirements
• Gives feedback based on usability, marketing
• Environment
• Imposes constraints and standards
• Technical Community
• Gives feedback based on engineering knowledge

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Requirements Setting Process
Customer
Marketing, Customer Feedback
Customer Representation
Develop System Requirements
Constraints and Standards
Technical Feedback
Technical Representation
Technical Community
Environment
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Marketing Requirements

• Short statements that address a user need
• The system should be small
• The positioning should be accurate
• Not specific enough to complete a design

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Engineering Requirements

• Engineering requirements are short statements
  that address a technical need of the design.
• The system should be able to supply 50W of power

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Engineering Requirements

• Four Properties
• Abstract
• Verifiable
• Unambiguous
• Traceable

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Engineering Requirements

• Abstract
• A requirement should specify what the system
  should do, not how it will be implemented
• Beware of preconceived concepts for solutions
• Example
• In getting more people from Oakland to San
  Francisco, the requirement should not be to
  design a bridge.
• It could be transport people from one side of
  the river to the other.

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Engineering Requirements

• Verifiable
• There should be a way to measure (or demonstrate)
  the requirement is met
• Allows us to continually answer the question
  Are we building the system correctly?
• Example
• One requirement might be the flying robot must
  be able to hide 3.5 meters below the surface.
• A better requirement could be the flying robot
  must be able to determine its ground based
  position with a tolerance of 2cm.

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Engineering Requirements

• Unambiguous
• Each requirements must have a single meaning,
  stated with short complete sentences
• Example
• Not The robot must operate with a battery life
  of 1 hour.
• Maybe The robot must operate for a minimum of 1
  hour.

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Engineering Requirements

• Traceable
• Each requirement should be traceable to marketing
  requirements
• Example
• Engineering requirement
• Must be manufactured for less than 2.00
• Marketing requirement
• Must be affordable

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Engineering Requirements

• Realism
• Realistic
• Justified
• This comes from experience (e.g. technical
  feedback from the technical community).

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Engineering Requirements

• Constraints
• In design, a constraint is a special type of
  requirement
• It is a design decision imposed by the
  environment or a stakeholder that impacts or
  limits the design
• Windows platform must be used
• Note that constraints can violate the
  abstractness property
• Can make a design decision that adheres to the
  constraint
• In choosing between windows and Unix, windows is
  chosen because 99999 out of the 100000 customers
  use windows.

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Engineering Requirements

• Standards
• Established ways of doing things to ensure
  interoperability
• Ensure products work together
• Safety, testing, reliability, communications,
  data formats, documentation, design methods,
  programming languages, connector standards,
  metastandards
• Knowing details of standards is often required at
  the Implementation stage of development

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Taxonomy of Requirements

• Identifying Engineering Requirements
• Structured workshops and brainstorming sessions
• Interviews, surveys, questionnaires
• Observation of processes or devices in use
• Competitive benchmarking and market analysis
• Prototyping and simulations
• Research and technical documentation review

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Taxonomy of Requirements

• Performance
• Functionality
• Economic
• Energy
• Environmental
• Health and Safety
• Legal

• Maintainability
• Manufacturing
• Operational
• Political
• Reliability and Availability
• Social and Cultural
• Usability

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Criteria

• The requirements provide an minimum set of
  objectives that the design must meet.
• What if you have two designs that meet all
  requirements? Which one should you use?

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Criteria

• Criteria provide a method for comparing different
  designs.
• Example robot speed (m/s)
• They should have all the properties of
  engineering requirements.
• They are often confused with requirements. BUT
  THEY ARE DIFFERENT!

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Criteria

• Example
• Requirement
• The dimensions of the prototype should not exceed
  6 x 4 x 1.5
• Criteria
• The dimensions of the prototype (smaller is
  better) in inches