mechanical engineering department voice of the engineer (voe) function trees fall 2012-1
TRANSCRIPT
Mechanical Engineering Department
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
Mechanical Engineering Department
Step 1: Formulate – Identify Core Functions
Shopping carts
That leaves us with…
1. Function 1: Handle Products2. Function 2: Transport Products
Mechanical Engineering Department
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.
Mechanical Engineering Department
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
Mechanical Engineering Department
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
Mechanical Engineering Department
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)
Mechanical Engineering Department
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
Mechanical Engineering Department
Functions interrelate
• Flow of power (mechanical, electrical)• Flow of information (signals, sensors, actuators)• Flow of material (water, widgets)
Mechanical Engineering Department
Functions (focus of brainstorming)
• Brainstorming focuses on ways to achieve the functions
Mechanical Engineering Department
Specifications
• Objective• Can be measured
– Practical (test costing $10,000 won’t work)– Need to be measured
• Complete - Relate to the customer needs
Mechanical Engineering Department
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
Mechanical Engineering Department
Specifications cover all needs
• “House of Quality”• Some needs are covered by more than one
metric• Some metrics cover more than one need
Mechanical Engineering Department
Metrics also can protect you
• What if the customer is unhappy with the thing you produce which meets all the specifications (list of metrics)
Mechanical Engineering Department
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
Mechanical Engineering Department
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
Mechanical Engineering Department
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
Mechanical Engineering Department
Exercise
• Mass of shopping cart: < 2 kg– Is this a reasonable spec?
Mechanical Engineering Department
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?
Mechanical Engineering Department
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.