\chapter{Establishing Functional Structure}


In the older design philosophies, once a need was identified a concept was
directly developed into a product. However, this rather weak philosophy did
not lead to quality designs, nor did it foster the use of the 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 customer's 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 problems 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 do not
provide optimum designs when new technologies and discoveries are to be
used. The crux of a problem should be expressed as a list of
the required functions 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 can be 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 such a case, a strong
effort to search for and establish an optimum function
structure is required. 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 smaller levels of complexity, and should
be simple to design. Function structures are of great importance in
the development of modular designs. An important advantage of a function
structure is that each of the components and systems can be examined
individually and modified if needed. Function structures are very useful
when designing and using design catalogs, because for every function, a 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}.


\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/5-1.eps}
\caption{(a) Overall Function (b)  Sub-functions of a testing machine}
\label{overall}
\end{figure}


\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/5-2.eps}
\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
components 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 components can be identified.
Either individually or collectively, the components serve a specific
sub-function and a main function, as seen in the following figure.


\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/5-3.eps}
\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, 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-functions so 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 the main function is on top of the tree, 
branches into sub-functions and then repeats to sub-sub functions.
\item Function structures should be kept as simple as possible. Simplicity
leads to 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 to prevent precluding 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 accomplished by representing the product or
device (to be designed) simply as a black box which converts given inputs
to desired outputs. The black box specifies all the functions required
to convert the input into output. It is important not to place any
restrictions on the function. Such restrictions limit the solution space
or system boundary. For example, the function push from A to B, restricts
the solutions from 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 the 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 the 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 by
enclosing them in boxes. They are linked together by their inputs and outputs in order 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.

\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/5-4.eps}
\caption{The box diagram}
\end{figure}


When drawing this diagram we decide how the internal inputs and outputs of
the sub-functions are linked together so that we may make a feasible working
system. We may find that inputs and outputs may have to be juggled and
perhaps redefined, and some sub-functions may need to be reconnected. It is advised that
different types of lines (continuous, dotted and dashed lines) be drawn to
indicate the different types of flows (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 those that cross the
system boundary.

The boundary now needs to be narrowed again because of its
earlier broadening during the 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 the designer may not have complete freedom when drawing the system, since it may be restricted by the
customer.

 \item Search for appropriate components for performing each sub-function and
its 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 a 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, new
devices can be substituted even at later stages of design or development.
\end{enumerate}
\subsection{Example of a washing machine}

A simple example of the use of function analysis method is the design of the 
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 5.5.
\begin{figure}
\epsffile{../figures/5-5.eps}
\caption{Function analysis of washing machine} 
\end{figure}


Inside the black box a process that separates the dirt from
the clothes must occur, and 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 the 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. The process of wringing the clothes dry was left to the human operator.
The inclusion of a spin-drying function removed excess water, but still
left a drying process. This process is now incorporated into a washer-dryer system.
Perhaps the smoothing and ironing of clothes should be incorporated in future designs, in addition to the current process.

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

Functions should consider what and not how, and they should break the functions down as
finely as possible. Functional decomposition is represented as: \\
 a box\\
 an action-verb\\
 an object on which the action-verb takes place (verb-noun combination)\\
 known flow of materials, energy and information\\
\subsection{Some examples of overall function}
Consider the function of a splash guard system on a bicycle. The most important
function is to:\\ protect the 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.

\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. Some 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, and separate.
\item  Material assembly. Usual terms are mix, attach, and 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. Energy of this type of can
be supplied, stored, transformed, or dissipated.
\section{Example}
Let's refer to our example of an automatic can crusher. The design team reviewed the
objective tree and their market analysis findings before they started
structuring a function tree.  They kept their minds open to all possible methods
for accomplishing the stated goals.   The function tree is shown in the figure
below. \ref{funb}


\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/5-6.eps}
\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 during the crushing.  An
actuator will send a signal to the crushing device.  Then, after the crusher, an
ejector must remove 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 sub-functions. 
\item  Draw a block diagaram showing 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}

   


