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

The FAST diagram

FAST Example: Coffee Mill

Coffee mills act to grind coffee

beans to the desired consistency

for brewing

FAST Example: Coffee Mill

Subtract and Operate Proc. (SOP)

Bottom-up approach

Principle: remove a part and see what happens

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

SOP Example: Coffee Mill

SOP Example: Coffee Mill

Creating a Function Structure

Inputs OutputsSystem

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

Example: finger nail clipper