Dr. Tarek A. Tutunji Product functions
Functional Modeling Basics
All products do something
That is why they exist!
A function of a product is a clear relationship between its
inputs and desired outputs
Product function is the overall intended function of the
product: what does it do
Make copies
Listen to music
Clip nails
Functional Modeling Basics
Functions can, and often is, divided into sub-functions
A sub-function is a component of a product function
The relationship between sub-functions and the overall function
is governed by input-output relationship and/or constraints.
A constraint is a criteria that must be satisfied
Why Functional Decomposition?
Functions are directly related to customer needs
Functional models organize the design team, tasks, and
process
Concentrate on what rather than how
Creativity is enhanced
More solutions can be generated
Function Trees
Basic approach is to decompose the main function into sub-
functions
Function trees
Functional Analysis System Technique
Top-down approach
Subtract and Operate Procedure
Bottom-up approach
Top-down vs. Bottom-up
Top-down
Start with main function
Decompose into sub-functions
Bottom-up
Start with smallest functions
Combine to make function tree structure
Functional Analysis System Technique
(FAST)
Top-down approach
Used to define, analyze, and understand product functions
and how they are related
Brainstorm all the functions that the product does from the
customer’s point of view
Identify the basic function
FAST Summary
Construct two vertical-dashed lines
Place the main function to the extreme left
Generate functions to the right by asking “how?” until you
reach an external function outside the line boundary
Connect these functions to create the critical path
Generate other parallel secondary functions
FAST Example: Coffee Mill
Coffee mills act to grind coffee
beans to the desired consistency
for brewing
SOP Summary
Disassemble one component
Operate the system
Analyze the effect
Deduce the sub-function
Replace the component and repeat
Translate information gathered into a functional tree
Definitions
System: an entity with clear boundary that is connected to
its environment by inputs and outputs
Energy: electrical, kinetic, magnetic, heat
Material: gas, liquid, solid, dust, work pieces
Information: signals