Page 263 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

232 Chapter Nine

functions; it protects the automobile from corrosion and rust, as well
as creating a sleek look for the car.
Besides secondary useful functions, there are two other types of functions:
1. Supporting function: This function supports the main basic function
or another useful function. A supporting function results from the
specific design approach to achieve the main basic function or other
useful functions. As the design approach to achieve the main basic
function and other useful functions changes, supporting functions may
also change. There are at least two kinds of supporting functions,
assisting functions and correcting functions.
• Assisting functions: These functions assist other useful functions.
For example, the engine suspension system provides the function of
locking the position of the engine in the automobile so that the
engine can provide power without falling off the car.
• Correcting functions: These functions correct the negative effects
of another useful function. For example, the main basic function of
the water pump in the automobile internal combustion engine is to
circulate water in the engine system in order to cool it off; it is a cor-
recting function for the automobile engine. The main basic function
of the engine is to provide power for the automobile, but the internal
combustion engine also creates negative effects, such as heat. A
water pump’s function is to correct this negative effect. If we change
the design and use electricity as the power source of the automobile,
the function of a water pump will no longer be needed.
2. Harmful function: This is an unwanted, negative function caused by
the method used to achieve useful functions. For example, an internal
combustion engine not only provides power; it also generates noise,
heat, and pollution, and these are harmful functions.
In summary, the main basic function and secondary useful functions provide
benefits for the customer. Supporting functions are useful, at least they are
not harmful, but they do not provide benefits directly to the customer and do
incur costs. Harmful functions are not useful and provide no benefits at all.

Functional Statement
A function can be usually fully described in three parts: a subject, a verb,
and an object. For example, for the automobile, its main basic function can
be described as
Car moves people
(Subject) (Verb) (Object)