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Voice of the Engineer (VOE)

Function Trees

Fall 2012-1

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Functions (VERB NOUN pairs)• Start with ranked groups of needs• Create a list of functions that need to be

accomplished to meet those needs• VERB NOUN pair (support load, apply torque,

store data, etc.) – Does it need:

• Power• Information• User interface• Supports• Enclosures

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Step 1: Formulate – Identify Core Functions

Shopping carts

That leaves us with…

1. Function 1: Handle Products2. Function 2: Transport Products

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Step 2: Assume – Identify the subfunctions which Each Primary function must achieve

Next, identify the further details or subfunctions that the shopping cart needs to provide.

Focus on WHAT the shopping cart needs to do, in order to provide the functionality of each primary function.

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1. Function 1: Handle Productsa) Support Productsb) Contain Productsc) Protect Products

2. Function 2: Transport Products1. Translate products2. Stop moving3. Rotate products

Step 2: Assume – Identify the subfunctions which Each Primary function must achieve

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Step 3: Chart - Function Tree in Graphical FormDescribe HOW you plan to meet your shopper’s need:

Design a device to enable a customer to collect products and easily move them through the store.

Handle Products.

Support Products

Contain Products

Protect Products

Transport the Products

Translate products Stop moving Rotate

products

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Step 4: Execute – Fill in the details of the function tree, and articulate the interface specifications

Design a shopping cart.

Handle Products.

Support Product

s

Mass of product

(kg)

Contain Products

Max volume

of product

(m3)

Min volume

of product

(m3)

Max surface area of product

(m2)

Min surface area of product

(m2)

Protect Product

s

Transport

products

without damage? (Y/N)

Transport the Products

Translate

products

Force to initiate motion

to # speed

(N)

Stop moving

Force to stop

moving from #

speed in # sec (N)

Rotate products

Turning radius (rad)

Force to change

direction (N)

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Constraints

There might be other things that have to be met that are not functions

-cost limits-production methods

These constraints can be listed alongside the functions

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Functions interrelate

• Flow of power (mechanical, electrical)• Flow of information (signals, sensors, actuators)• Flow of material (water, widgets)

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Example

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Functions (focus of brainstorming)

• Brainstorming focuses on ways to achieve the functions

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Brainstorm on

– Shopping cart handle

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Brainstorm on

– Obtain direction information from user

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Specifications

• Objective• Can be measured

– Practical (test costing $10,000 won’t work)– Need to be measured

• Complete - Relate to the customer needs

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Needs vs. Metrics

• Metrics translate needs into objective things that can be measured.

• “I need it to be light”• Product and battery but not charger must have a

mass <= 1.5kg• This allows you to objectively see if a design

meets the customer needs• One metric may meet more than a single need• House of Quality

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Specifications cover all needs

• “House of Quality”• Some needs are covered by more than one

metric• Some metrics cover more than one need

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House of Quality bicycle shockFrom Ulrich and Eppinger

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Metrics also can protect you

• What if the customer is unhappy with the thing you produce which meets all the specifications (list of metrics)

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Non-standard metrics

• “The system needs 3 different diameter wheels”– Yes/no– Spread in diameters

• “The product must instill pride in the user”– Subjective– Focus groups/ surveys

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Caution!• Try not to spec. your project so that:

– It is impossible (no solutions)– It requires costly exotic materials (unless needed)– There is only a single solution– It requires too much time to analyze or build– It requires fabrication processes that we don’t have

access to– It is exceedingly dangerous or risky– It is not challenge at all

• It’s ok to have 1 or 2 “reach” specs but not all of them

• Specifications can drastically change the outcome

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Simple initial hand calculations

• It’s very easy to set up an “impossible” set of metrics to be met

• Weight: < 0.01 g• Volume: > 10 m^3• Load carrying capacity: > 10 kN

• Engineering analysis will help you determine a reasonable set of specifications

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Exercise

• Mass of shopping cart: < 2 kg– Is this a reasonable spec?

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Shopping cart initial analysis

• Load bearing capacity• Mass of cart• Frictional losses• Power consumption• Refueling times• Cost• Can you come up with a design that you can

show will meet the specifications you list?

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Negotiation

• What if you agree to meet an impossible specification?

• How do you deal with creeping elegance?• What is creeping elegance?• Types of customers that you may have to

manage.

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Next week

• Continue specifications