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Class2_1. Introduction to a rational design process Defining the problem Specifying requirements. Reminder…. I hope you have: Downloaded the design report template Read the syllabus carefully Read the design requirements carefully Read the requirements clarifications page

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class2 1
Class2_1
  • Introduction to a rational design process
  • Defining the problem
  • Specifying requirements
reminder
Reminder…

I hope you have:

Downloaded the design report template

Read the syllabus carefully

Read the design requirements carefully

Read the requirements clarifications page

Read the “lessons learned” list on our class website

questions about dp

Questions about DP?

(Remember to check class web page for detailed information about DP requirements)

design work this week

Design work this week

Write your draft problem definition and specifications in your design report template.

What data will you need for your specifications? Start gathering…

Bring your design template file with you to class on Thursday.

Thursday will be a working session to improve your draft.

slide7

Model of the Design Process

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

design process
Design process
  • This is only one of many models of the design process
  • Examples…
design process1
Design process
  • All of these model have two characteristics in common

Design occurs in stages

Design is iterative

why do design in stages
Why do design in stages?
  • Organizes a complex process
  • Less likely to overlook something or make mistakes
  • Helps others collaborate on the design
  • Helps communicate the current status of the design
some effects of iteration in design
Some effects of iteration in design
  • Makes engineering design messy
  • Bane of concurrent engineering
  • Source of expensive changes
  • Basis for claim that “all design is re-design”
  • Tempts management and engineering into being conservative in their design goals
accommodating iteration
Accommodating iteration
  • Good engineering design planning makes the best possible accommodation for the necessity of iteration in design.
  • What does this mean for you in your design project work?
  • Brainstorm with your row mates and make a list…
our design process
Our design process
  • We will follow the process shown on the next slide.
  • Give it a try. Avoid short-circuiting the process (i.e., deciding on a design and then going through the motions of the process)
slide21

Model of the Design Process

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

stage 1 define the problem
Stage 1: Define the problem
  • Seems an obvious first step
  • But often not well done!
  • Elevator example
  • Moral of the story: before you start a design always think carefully about what is really the problem
define the problem
Define the problem
  • Typically the problem statement is one to several paragraphs, giving an overall description of the goals and constraints.
define the problem1
Define the problem
  • What are some things you can do to help you define a design problem?
  • Example: talk to customers
  • Others?
define the problem2
Define the problem
  • I propose there are two basic questions the engineer must answer when trying to define the problem

1. Who is the constituency for my design?

(who are the customers and what are their needs?)

2. What is the context of my design?

(social, regulatory, technical feasibility, cost, time and expertise available, etc.)

slide26

Model of the Design Process

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

stage 2 specify requirements
Stage 2: Specify requirements
  • Product specifications describe what the design should accomplish (but not how it will accomplish it) 
  • These are a further refinement of the problem definition
  • Define the problem in “engineering terms”
specifications
Specifications

At the beginning of the design process, good specifications strive to:

1. Describe what the design must accomplish, but not how.

2. Be as quantitative as possible; be as unambiguous as possible 

slide29
Example of a bad specification:

The mouse trap spring will be easy to set.

Bad because it is not quantitative and presumes how the design will be built rather that what it must do.

slide30
  Example of a good specification:

The mouse trap will be settable by one inexperienced person in less than 30 seconds.

Good because it says what the trap should be able to do, and is quantitative in its description.

specification list example
Specification list example
  • Example of specification list from a previous ME 212 design project

(see Word document “specifications_example_2010.docx”)

purposes of specifications
Purposes of specifications
  • Help define the problem.
  • Become a basis for evaluating design alternatives.
  • Provide a description of the design that can be used internally for manufacturing plans, quality control, cost estimating, etc.
  • Provide a description of the design that can be used externally, for communication to customers, meeting legal obligations, intellectual property definitions, etc.
specifications1
Specifications
  • As the design evolves, the product specifications are also expected to evolve. 
  • Product specifications are typically organized under a variety of headings.
  • It is also quite common to assign priorities to the specifications.
specification headings
Specification headings

Functional requirements

Physical requirements

Marketing

Cost/budget limitations

Service environment

Safety objectives

Legal/regulatory/standards requirements

Manufacturing

specifications headings
Specifications headings

Maintainability

Reliability

Environmental impacts

Ergonomics/aesthetics/human factors

Schedule requirements

Intellectual property protection

Transportation/distribution limitations

Compliance/interface with existing products

Company resource issues/needed expertise/personnel

spec priority schemes
Spec. priority schemes
  • Typical prioritization schemes include: 
  • D (demand), W (wish)
  • R (required), G (goal), P (preferred)
  • 1, 2, 3 (high to low)
more tips and help
More tips and help…

Can be found in the design report template

slide39
That’s all for today.
  • Remember, bring your draft problem statement and specifications on Thursday.