ME101 Design Midterm

Needs Analysis

(Have a general understanding)

A process of comprehending and translating the need into a working document (= problem finding and formalizing but NOT problem solving)

Express the need in terms of functions and specified parameters

Generating and maintaining an engineering specification document

Needs analysis can be broken down into...

(see flowchart in lecture 1 slides)

1. Problem definition (Research, Real need identification - which become primary function and constraint)

2. Need Statement

3. Represent problem (functional requirements, constraints, ROM Calculations, Organize Functions)

4. Function structure

5. Communicate problem

6. Design specifications

What is a requirement?

(Know one of the definitions)

Essential attribute or characteristic for a system

Something the product must do or a quality it must have

Where do requirements come from?

(Have examples)

1. Client, customer, user

2. Regulatory bodies (law, standards...)

3. Ethical considerations

4, Material constraints, Budget

5. you, engineer

Functional requirement

(must know definition and differentiate with other requirements)

An action the design MUST perform (What does the design do)

It would be a criteria in ME100

Non-Functional Requirement

(must know definition and differentiate with other requirements)

A quality the design must have (e.g. Easy to use, reliable...)

Would also be a criteria in ME100

Constraint Requirement

(must know definition and differentiate with other requirements)

A boundary condition on the solution space.

Almost always Numbers (e.g. cost < $100, mass < 10 kg...)

Would be a constraint in ME100

Functional Analysis (Know how to do one)

Expresses the problem using non-solution-specific representations

Use verb/noun pairs to describe functions (i.e. transfer torque)

(See useful verbs for describing function in slides if you need)

Example of Brake (good to keep in mind):

What are 2 functional requirements of a brake system?

Dissipate Kinetic energy

Respond to user control

Example of Brake (good to keep in mind):

What are 2 constraints of a brake system?

Safety (ALWAYS)

Cost

Weight

...

Example of Brake (good to keep in mind):

What are 2 non-functional requirements of a brake system?

Easy to use

Reliable

Quiet

Compact

Easy to Repair

Need statement (Know how to do one)

Represents the prime design requirement of the overall function

Consists of the primary Functional requirement and the Primary constraint requirement.

e.g. A need exists to {primary function} while {primary constraint}

Must be concise (1 sentence) and identify a rea need but NOT imply a solution

Example of Brake (good to keep in mind):

Make a Need Statement

A need exists to [ Dissipate kinetic energy](PF) of a vehicle at a rate required to [stop safely](PC)

Engineering Design Specifications (Know what they are and how to fill a table)

Specified design characteristics attributes or parameters

Derived form FR, NFR and CR

e.g. output torque < 250 Nm, Reliability >550 hours MTBF, Cost < $5000

Minimum elements of a requirement specification statement are: (you will likely be asked to fill out a table)

- Requirement number

- Characteristic or attribute

- Value and tolerances

- Relation

- Units of measure

- Verification method ( Analysis or Test)

(can be added a comment column where you write what to use for the test/verification)

Conceptual Design Process Breakdown

(Prob don't have to know that by heart)

1. Concept generation (Enabling context +Generate A LOT OF concepts)

2. Concept devlopement (develop concepts and refine requirements, get to about 3 concepts)

3. Evaluation selection (chose 1 concept)

Conventional methods to generate concepts (know a couple of these)

• Information gathering, trade publications and reference works

• Analysis of natural systems, i.e. burr as inspiration for Velcro

• Analysis of technical systems,patent reviews

• Use of analogies, i.e. productionprocess analogous to flowin a river

• Measurements and prototype model testing

• Trial and error (experimentation)

Intuitive methods to generate concepts (know a couple of these)

• Brainstorming

• Method 635

• Gallery method

• DELPHI method

• Synectics

• Random stimulation

• IDEO method cards

• Combination of methods

6-3-5 method (def given in lectures so likely important to know)

1. 6 people around a table(can be as few as 3 and as many as 8)

2. Each person sketches 3ideas, then passes the paper to their neighbor

3. Each person refines each design, then passes the page to the next

person

4. The paper is passed 5 times- then its returned to the original owner

Logial methods to generate concepts (know a couple of these)

• Systematic study of physical processes

• Systematic search (Morphological analysis)

• TRIZ

• IIDE Techniques

• Use of design catalogues and standards

• Axiomatic design

• Evolutionary computing

Morphological Matrix (know what it looks like and how to fill one out)

Subfunctions on the left and Solutions on top. Then sketch multiple solutions for each subfunction (one solution per box)

Concept Developement (know what it is)

Narrow breadth of concepts to several that employ distinct technological approaches (to about 3 concepts)

Examining feasibility ( ROM calculations and Proof of concept)

Challenge current requirements - identify negotiable constraints and make proposals to relax constraints

Concept Evaluation & Selection (know how to do it well)

• A critical point in the design process

• Should be a team-based decision-making activity

• Five step process:

- Forming consensus on the criteria

- Forming consensus on the alternatives

- Ranking the alternatives

- Evaluating the alternatives

- Attacking the negatives

Decision making matrix (know how it works and how to do it)

Make a list of criteria (important requirements) (e.g. performance, cost, safety, schedule...)

Design 3 different concepts and sketch them with details

Select a concept as datum and fill its column with 0s

For each other concept, put a + 1 in a row if the concept answers the criteria better that datum and a -1 if it does it worse (and a 0 if the have similar performance)

Add up the numbers (datum should be at 0) and take the concept that has the highest grade.

Remember what Sketching is or isn't:

IS:

Simple drawing

Includes key functional elements, shows how the design works

Clear, legible, drawn with care

Minimal words included or required

IS NOT:

3D CAD

Art, what the design looks like

Small, messy, drawn without care

Sentences or paragraphs of description

A good sketch of a conceptual design for a mechanical system includes a clear presentation of

Function (Shows how the design works, shows all the functions and sub functions)

Context (Shows interfaces with surroundings - i.e. user, item, infrastructure, ground... - It isn't floating in the air )

Clarity (Clear, Legible etc...)

Measurement system - from Sensor lecture (Prob know what they are)

Senses measurement (physical quantity) and produces a unique numerical value to describe it

common elements of a measurement system

Measurement is made by sensor (Temperature, position, color...)

It is made visible by a signal modification system which uses an indicator or value transmitted to the software. (many systems use electrical signal to transmit info to computer)

Example of the thermometer (helps visualize/understand different parts of measurement system)

Sensor: thermal expansion/contraction of liquid

Signal measurement system: Small diameter tube connected to reservoir, calibrated

indicator: Scale printed on/near tube

Sensor characteristics (know what to say when asked to describe a sensor)

Information type:

Input (pressure, color...) or output (analog, digital...)

Range (min and max value of input in which sensor is intended or useful) - operating outside the range can lead to inaccurate readings or damage to sensor.

Accuracy:

Measurement error= measured value-true value

determined based on calibration = compare with known standards or measurement systems of known accuracy

Sensor output consists of :

Signal - useful information

Noise - extra unwanted information (often seen as small oscillations on graphs) - see lecture notes with the case of push button

Always need to consider noise, uncertainty, unexpected results when using sensors