Developing a Function-Means Tree

							                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