ENGR 1100

Functional Decomposition

Defining Function

Function is the logical flow/transfer of energy

or static forces, material or information

between objects or the change of state of an

object caused by one or more flows

Change of state

Transformations of energy, material

properties, form (eg. shape, configuration,

position)

Defining Function vs Form

Function

What the product must do

Form

What is the shape of the product?

Which follows which?

Types of Energy

Mechanical system (typically)

Electrical, Fluid, mechanical, thermal

Actions

transformed, stored, transferred, supplied,

dissipated

Material

Through-flow (material conserving):

position, lift, translate, rotate, hold,

support, move, guide

Diverging-flow (dividing material)

: disassemble, separate

Converging-flow:

mix, attach, position relative to

Information functions

Mechanical signals, electrical signals,

software

Generally, information is part of an automatic

control or to interface with a human operator

Functional Decomposition

Step 1: For the whole device, examine

Interfaces with other objects

Step 3: Examine each interface of the

component to find the flow of energy,

information or materials

Step 2: Remove a component for more

detailed study

Stapler

The energy into the stapler is from the user’s hand

pushing on top and, for equilibrium, the desk

pushing back on the bottom. The information flow

is back to the user to tell them when to stop

pushing. Staples and paper flow into device and

stapled paper flows out.

Stapler

1) The interface between the user’s hand and top of

stapler. Energy flows from users hand.

2) The interface to the shaft at the pivot point: Limits

top assembly to 1 DOF motion-rotation about the

shaft. Energy flows here to keep the top

assembly aligned with rest of paper.

Stapler

3) The interface to staple at end of spring: Energy flows between spring and staple to push the staple into the paper.

4) The interface with the guide channel on the sides

of the spring: The structure that guides also

supports spring so it cannot buckle.

Stapler

5) The interface with base structure: The same spring material that pushes the staple also pushes the top assembly to its original position. Energy flows from base to top through the spring.

Typical Mechanical Design Functions

Guidelines

Energy Must be Conserved

Material Must be Conserved

All Interfacing objects and known fixed parts must be

identified

Ask the question, How will customer know if the system

is performing

Use action verbs to convey flow

1. Find the overall function that needs to be accomplished

Guidelines

2. Create Subfunction Descriptions

•Consider what, not how

•Break the function down as finely as possible

•Consider all operational sequences

•Use standard notation when possible

Guidelines

3. Order the Subfunction

•Flows must be logical or temporal

•Identify redundant functions and combine

•Functions not within system boundary must be

eliminated

Guidelines

4. Refine Subfunction

•What has to happened to enable subfunction?

•Continue asking for each subfunction!

Functional Decomposition

Stores

and releases

energy!

Support load

Interface with hands

How do you know its

working as it should?

i.e. how is condition

communicated?

How evaluate performance?

Consistency

Robustness

Function Tree Example for Pole Vault

Questions

Why do a function tree?

Design of individual components

Problem understanding i.e. design intent

Explore combining components to save money,

time, enhance performance

Sequence of operations

Function Block Diagram

Now we want to explore HOW the functions are related to each other

A function block diagram relates functions in the form of an operational flow

chart

Function Block Diagram for Autonomous Mine

Detector