# Developing a Function-Means Tree

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11/5/2012
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```							                Developing a
Function-Means Tree

What functions will the design
have? By what means will those
functions be achieved?

Taken from engineering design: a project-based introduction by dym & little
It helps to go beyond the terminology and to
know what you’re really trying to do.
• Think of the “functions” as what you must do.

• Think of the “means” as how you might do it.

• The Function-Means Tree is a tool for listing the
primary functions of a design and various means of
achieving those functions.

• The Function-Means Tree should flow out of the
Attributes List, PCC, Objectives-Constraints Tree,
and Design Specifications.
Before you start too far down the path of
“brainstorming” various design alternatives…
• Determine the primary functions that are required.
– Show these on the top level of the tree
• List various means by which each function may be
implemented.
– Show these on the next level of the tree
• Determine secondary functions that would result
from implementing each of the means.
– Show these on the next level of the tree
• The tree continues to alternate between means and
functions until you reach a reasonable termination
point.
Here is a partial Function-Means Tree for a
cigarette lighter.
IGNITE
Primary function                                                             LEAFY
MATERIALS

Secondary functions                          Electrically                                                                                 Possible means of achieving
Focused
Heated
Wire
Sunlight
Laser                Flame                       the primary function

Apply heat         Generate                         Convert              Protect                           Control                                       Supply fuel
users from            Store fuel                 Ignite fuel
to leafy           electric                       electricity                                              flame                                         for flame
materials           current                         to heat             post-usage
burns

Butane             Gasoline

Miniature            Resistive
heat pump              wire
Electrical
Spark              resistance
Wall-outlet-                 Battery-based
based system                     system                         Secondary means

Control                                    Convert chemical
Store
electrical                                      energy to                                                 Protect
electricity
current                                    electrical current                                            electric              Generate
current from         electric current
flame
Function
Tertiary functions
Means

```
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