Class2_1 Introduction to a rational design process Defining the problem Specifying requirements

Class2_1

• Introduction to a rational design process• Defining the problem• Specifying requirements

Reminder…

I hope you have:1. Downloaded the design report template2. Read the syllabus carefully3. Read the design requirements carefully4. Read the requirements clarifications page5. Read the “lessons learned” list on our class

website

Questions about DP?

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

requirements)

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.

Monitors off please

How is engineering design done?

Is there a process?

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

Model of the Design Process

Design process

• This is only one of many models of the design process

• Examples…

Design process

• All of these model have two characteristics in common

Design occurs in stages

Design is iterative

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

Why is design iterative?

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

• 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…

What did you come up with?

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)

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

Model of the Design Process

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

• Typically the problem statement is one to several paragraphs, giving an overall description of the goals and constraints.

Define the problem

• What are some things you can do to help you define a design problem?

• Example: talk to customers• Others?

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.)

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

Model of the Design Process

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

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 

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.

  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

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

(see Word document “specifications_example_2010.docx”)

Purposes of specifications

1. Help define the problem. 2. Become a basis for evaluating design

alternatives. 3. Provide a description of the design that can be

used internally for manufacturing plans, quality control, cost estimating, etc.

4. Provide a description of the design that can be used externally, for communication to customers, meeting legal obligations, intellectual property definitions, etc.

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

Functional requirements

Physical requirements

Marketing

Cost/budget limitations

Service environment

Safety objectives

Legal/regulatory/standards requirements

Manufacturing

Specifications headings

MaintainabilityReliabilityEnvironmental impactsErgonomics/aesthetics/human factorsSchedule requirementsIntellectual property protectionTransportation/distribution limitationsCompliance/interface with existing productsCompany resource issues/needed expertise/personnel

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…

Can be found in the design report template

That’s all for today.Remember, bring your draft

problem statement and specifications on Thursday.