
\chapter{Establishing Functional Structure}


In the older design philosophies, once a need is identified a concept is
directly developed into a product. However, this is a weak philosophy and
does not lead to quality designs nor foster the use of latest
technologies. Designers have a tendency to take their first idea and keep
refining towards a product design. Recall that, If you generate one idea,
it is probably a poor idea; if you generate twenty you might have one good
one. Since most of the customers need is based on meeting a functional
need, we need to generate a functional decomposition tree from the problem
statement based on the objective tree.

Functional decomposition supports the divergent-convergent design
philosophy concept. This concept requires that a design problem be
expanded into many solutions before it is narrowed to one final solution.
All design problem should be decomposed into the design of functionally
independent sub-systems. In this chapter, we will develop techniques for
decomposing any problem into smaller, more easily manageable parts by
understanding the functions required of the device and treating each
function as a separate sub-system.

Solution principles or designs based on conventional methods does not
provide optimum designs when new technologies, and discoveries are to be
used. The crux of the problem should be expressed as a requirement list of
the required function and essential constraints.
Once the problem statement is defined, the next step is to determine the
overall function, sub function and sub sub function of the design problem.
A given function can be represented in a block diagram based on the flow
of energy, materials and information. The diagram expresses the
relationship between inputs and outputs regardless of the solution within
the box.

A complex overall function describing the problem statement can be broken
into a number of sub-functions, and many of the sub-functions divided into
sub-sub functions. The division depends on the type of design system being
considered. In original designs, neither the individual  sub-functions,
nor their relationships are clearly known. Hence in this case a strong
effort is needed to  search for and establish an optimum function
structure. However, in adaptive designs, general function structure and
the functional relationships between various components and systems are
usually well established.
The lower levels of functions carry  less levels of complexity, and should
be simple to be designed. Function structures are of great importance in
the development of modular designs. An important advantage of a function
structure is that each of the component and system can be examined
individually and modified if needed. Function structures are very useful
when designing using design catalogs, since for every function task
specific component or system can be identified.

An example of function structure for a tensile testing machine is shown in
Figure \ref{overall}. A typical testing machine is shown in Figure \ref{comp}

\begin{figure}
\vspace{3in}
\caption{(a) Overall Function (b)  Subfunctions  of a testing machine}
\label{overall}
\end{figure}
\begin{figure}
\vspace{3in}
\caption{Completed function structure for the overall function set out in
figure \ref{overall}}
\label{comp}
\end{figure}
Now let us look at an example of determining the functional structure of
an existing design. Consider the case of a flow control valve. Each of the
component of the valve, e.g., the spindle, the bearing bush, sealing bush,
housing and threaded bearing bush can be identified from the engineering
drawing. The specific task of each of the component can be identified.
Either individually or collectively the components serve a specific
sub-functions and a main function as seen in the following figure.

\begin{figure}
\vspace{5in}
\caption{Analysis of a flow control valve in respect of its function structure}
\end{figure}


Some of the basic points in generating functional diagrams are as follows.
\begin{enumerate}
\item From the requirements list, establish the main function and a few
sub-functions and some sub-sub functions for each of the sub-functions. A
step by step break down at each level is needed.
\item Arrange the sub-function such that there is some relationship between
them. Do not worry about the physical or logical relationship at this
stage.
\item Determine the flow of energy, materials, and information. Find the main
and auxiliary flow of these three items.
\item Establish a structure such that main function is top of the tree and
branches into sub functions and repeats to sub-sub functions.
\item Function structures should be kept as simple as possible. Simplicity
leads to a simple and economical solutions
\end{enumerate}
The primary purpose of function structures is to facilitate the discovery
of solutions. Though the structure should not presuppose any solution, it
is legitimate to conceive of a preliminary solution and abstract the
solution. However, through a process of iteration the structure should be
made generic so as not to preclude new and innovative solutions.




Some task specific functions are
\begin{itemize}
\item Conversion of energy:
 \begin{itemize}
 \item Changing energy -e.g., electrical to mechanical energy
 \item Varying energy components- e.g. increasing speed, torque
 \item Storing energy- e.g. Storing potential or kinetic energy
\item Connecting energy with information- Switch to start a motor
\end{itemize}

\item Conversion of materials
\begin{itemize} \item Changing matter -  e.g., melting (solid to liquid)
 \item Connecting matter with energy - e.g. moving parts
\item  Rearranging materials  - e.g. mixing or separation
\item  Storing materials- e.g. storing material in a silo
\end{itemize}

\item Conversion of information

\begin{itemize} \item  Changing signals- e.g. mechanical to electrical
 \item Connecting information with energy- e.g. amplifying signals
 \item Connecting information with matter - e.g. marking metals
\item  Storing signals - e.g. data banks
\end{itemize}
\end{itemize}
\section{Procedure}
\begin{enumerate}

\item  Express the overall function for the design in terms of conversion of
inputs and outputs.

The key is to determine what needs to be achieved by the new design, and
how it is to be achieved. This can be done by representing the product or
device to be designed as simply a  black box which converts a given inputs
to desired outputs. The black box specifies the all the functions required
to convert the input into output. It is important not to place any
restrictions on the function. Such restrictions limits the solution space
or system boundary. For example the function  push from A to B, restricts
the solutions of ejecting, throwing, rolling, lifting, or even catapulting
the object from A to B. Thus it is important to widen the solution space
or system boundary as much as possible.

It is important to try to ensure that all the relevant inputs and outputs
are listed clearly. As mentioned earlier they can be classified as flows
of materials, energy and information.

\item  Break down the overall function into  a set of essential sub-functions.

The conversion of  the set of inputs into set of outputs at the main
function level is usually very complex. Thus the black box needs to be
broken into sub-tasks or sub-functions. The break up depends on the
experience of the designer, availability of components capable of
performing specific tasks, and latest technologies. In specifying
sub-functions, it is necessary to express the task as a verb plus a noun-
e.g., amplify signal, count items, decrease speed, increase diameter. Each
sub-function has its own input(s) and output(s).

\item  Draw  a block diagram showing the interactions between sub-functions.

A block diagram consists of all sub-functions separately identified
enclosing them in boxes and linked together by their inputs and outputs so
as to satisfy the overall function of the product or device that is being
designed. In  other words, the original black box of the overall function
is redrawn as a transparent box in which the necessary sub-functions and
their links can be seen

\begin{figure}
\vspace{4 in}
\caption{The box diagram}
\end{figure}
In drawing this diagram we decide how the internal inputs and outputs of
the sub-functions are linked together so as to make a feasible working
system. We may find that inputs and outputs may  have to be juggled and
perhaps redefined, and some sub-functions reconnected. It is advised that
different type of lines, continuous, dotted and dashed lines be drawn to
show the flow of material, energy and information within the block
diagram.

\item  Draw the system boundary

In drawing the block diagram we also need to make decisions about the
precise extent and location  of the system boundary. For example, there
can be no loose inputs or outputs in the diagram except that cross the
system boundary.

It may be that the boundary now has to be narrowed again, after its
earlier broadening during consideration of inputs, outputs and overall
function. The boundary has to be drawn around a sub-set of the functions
that have been identified in order to define a feasible product. It is
also possible that this drawing of the system boundary is not something in
which the designer has complete freedom, since it may be restricted by the
customer.

 \item Search for appropriate components for performing each sub-functions and
their interactions.

If the sub-functions have been defined adequately and at an appropriate
level, then it should be possible to identify a suitable component for
each sub-function. The identification of component will depend on the
nature of the product or device. For example, a component can be a
mechanical, electrical or a combination device. A microprocessor based
electronic device can substitute some older versions of electro-mechanical
devices. Since function analysis method focuses on functions leaving the
means to achieve them, even at later stage of design or development new
devices can be substituted.
\end{enumerate}
\subsection{Example of a washing machine}

A simple example of the use of function analysis method is the design of
domestic washing machine. The overall function of the machine is to
convert an input of soiled clothes into an output of clean clothes, as
shown in figure 38.
\begin{figure}
\vspace{8in}
\caption{Function analysis of washing machine} 
\end{figure}


Inside the black box there must be a process that separates the dirt from
the clothes, and so the dirt itself must also be a separate output. We
know that the conventional process involves water as a means of achieving
this separation. Thus a further stage must be added to convert clean but
wet clothes to clean and dry clothes. Even further stages involve pressing
and sorting clothes.

The essential sub-functions together with the conventional means of
achieving them, for converting soiled clothes into clean, pressed clothes
would therefore be as follows.
Essential sub functions	 Means of achieving sub functions
\[\begin{array}{ll}\\	
\mbox{Loosen dirt}&	\mbox{Add water and detergent}\\
\mbox{Separate dirt from clothes}&	\mbox{Agitate}\\
\mbox{Remove dirt}	&\mbox{Rinse}\\
\mbox{Remove water}	&\mbox{Spin}\\
\mbox{Dry clothes}	&\mbox{Blow with hot air}\\
\mbox{Smooth clothes}	&\mbox{Press}\\
\end{array}\]

The development of washing machine involves progressively widening the
system boundary, as shown in the figure. Early washing machines simply
separated dirt from clothes, but did nothing to remove excess water from
the clothes. This was left to the human operator for wringing the clothes.
The inclusion of a spin-drying function removed excess water, but still
left a drying process. This is now incorporate in a washer-drier system.
Perhaps smoothing of clothes should be incorporated in future designs from
the current practice.

\section{Functions}
\textbf{Some guidelines on identifying certain functions}

Functions should consider what and not how, Break the functions down as
fine as possible. Functional decomposition is represented as \\
 a box\\
 an action-verb\\
 an object on which action-verb takes place (verb-noun combination)\\
 known flow of materials, energy and information\\
\subsection{Some examples of overall function}
Consider the function of splash guard of a bicycle. The most important
function is to\\
 protect rider from water and dirt. The primary  function of a chair is to
seat a person.


\textbf{Some of the essential features that should be considered are}
 List all the alternative functions\\
 Include all the inputs and outputs\\
 For redesign problems, disassemble the sample to find functions and all

\section{sub-function}
 The flow should be in a logical or temporal order\\
 Identify redundant functions and combine them\\
 Functions not within the system should be eliminated\\

Specifically, there are flows associated with materials, energy and
information. Functions associated with the flow of materials are:
\begin{enumerate}
\item  Material can be designed to alter its position or shape. Usual action
verbs are lift, position, hold, support, move, translate, rotate and
guide.
\item  Material can be divided into two or more bodies. The action-verbs are
disassemble, separate.
\item  Material assembly. Usual terms are mix, attach, position relative to..
\end{enumerate}
Functions associated with the flow of information are usually in the form
of mechanical or electrical signals or software. 

Functions concerned with the flow of energy
The type of energy normally identified with electromagnetic system are
mechanical, electrical, fluid and thermal. Any of this type of energy can
be supplied, stored, transformed, or dissipated.
\section{Example}
Lets refer to our example of automatic can crusher. The design team reviewed the
objective tree and their finding on market analysis before they start
structuring a function tree.  They kept their minds open to all possible methods
of a complishing the stated goals.   The function tree is shown in the figure
below \ref{funb}
\begin{figure}[ht]
\vspace{7in}
\caption{Function tree for the automatic can crusher}
\label{funb}
\end{figure}
As shown in figure \ref{funb} the input is the aluminum cans and energy to crush
the cans.  The output of the system is crushed cans.  A loader is utilized to
input the cans into the system.  The aligner will position the cans inside the
device for crushing. A holder will fix the can in place duringthe crushing.  An
actuator will send a signal to the crushing device.  Then after the crusher an
ejector to renmove the cans from the system.


\section{Problems}
\subsection{Team Activities}

 Develop a function tree to produce a device that is capable of 
converting wood
chips to fire logs.
\begin{enumerate}
 
\item Express the overall function for the system 
 \item Break down the over all function into a set of subfunctions 
\item  Draw a block diagaram shwoing the interactions between the subfunctions 
 \item Draw the system boundary 
\end{enumerate}
\subsection{Individual Activities}

\begin{enumerate}
\item Generate a function tree for a coin sorter device?
\item Generate a function tree for a leaf removing device?
\end{enumerate}

   


