\chapter{Specifications}
Specifications are highly important in order to provide a successful design.  All
engineering design problems are set within certain limits.  Once a problem is
defined and recognized clearly via the objective tree and the function
structures, the development of detailed specifications becomes vital.  The
development of specifications may be considered the last step in defining the
problem.  The objective tree defines the vague statements that are generally
introduced by the customer. But the objective tree and the structural functions
do not set specific limits on the different functions and objectives.  The
objective tree or function structures are statements of what a design must
achieve or do, but they are not normally set in terms of precise limits, which is
what a performance specification does.  For
example, an objective may be stated to develop a product which has low weight. 
Yet, the term "low weight" is not clearly defined. Does it mean 20 lb or 100 lb as low
weight?

Based on the customer, the requirement may be well defined and the specifications well set.
An example of such is found in the announcement from the National Inventors Council to design a
stair climbing wheel chair.  The announcement is as follows:

\begin{center}
NATIONAL INVENTORS COUNCIL\\
U. S. DEPARTMENT OF COMMERCE\\
WASHINGTON, D. C. 20550
\end{center}
 \vspace{0.5in}
 There is a great need for a STAIR-CLIMBING WHEEL CHAIR.  The objective of such a chair is to
 give an active handicapped individual an additional range of mobility.  The desired design
 should enable the individual to cope with the usual problems he or she might encounter when traveling to and from
 work, moving about industrial buildings, and the like.  It must be remembered that the chair
 will perform the usual wheel chair function approximately 95% of the time; therefore, little of the 
 conventional wheel chair's versatility and convenience should be sacrificed
 in order to provide the climbing function.  In this connection, it might be valuable to point out that
 many active handicapped persons are able to fold a conventional wheel chair, put it in an automobile
 and drive to work.  If this cannot be accomplished with a climbing chair, the overall
 objectives of providing the handicapped with independent mobility will not be achieved.  The
 following factors are to be taken into consideration:
 \begin{enumerate}
 \item WEIGHT OF OCCUPANT: Assumed to be 200 pounds.
 \item WEIGHT OF CHAIR: 50 to 75 pounds, maximum.
 \item COLLAPSIBILITY: Capable of being folded by user and stowed in the interior of a standard
 automobile or taxi cab. Special loading ramps which are not carried as a part of the chair
 system, or special modifications to the automobile to accommodate chairs will not be considered.
 \item WIDTH of CHAIR: 25 inches maximum.  The American Standards Association utilized this
 width as the maximum for standard wheel chairs, when establishing architectural standards
 which provide the physically handicapped with freedom of movement in buildings and other
 structures.  However, a lesser width for a chair, or a means of temporarily reducing the full
 open width for passage through narrow doorways, would provide a definite asset for negotiating door
 openings in private homes or other structures which do not conform the new standards.
 \item TURNING ABILITY: The turning radius should be held to a bare minimum.  Turning should
 be accomplished without damage to floors or carpets.  Chair must be able to negotiate an L
 or a U type stair landing.  Ability to negotiate an L-type Landing as small as 3 ft by 3 ft
 would be considered an asset.
 \item CLIMBING ABILITY: The chair should be able to negotiate street curbing and any stair with
 average height risers and depth tread that is found in office buildings and homes.  Ascent should
 be performed in presence of litter and moisture without damaging stair treads and risers. 
 Any transition or adjustments required between normal and ascending and descending functions
 must be accomplished in a minimum time to eliminate delays at street curbing and stairways.
 \item PROPULSION SYSTEM: The chair may be propelled by the occupant or by a motorized unit; however,
 total cost, weight, and collapsibility requirements are the same for either type of drive. 
 If self-driven, a minimum arm strength of 10 pounds may be used in devising drive mechanism.
 \item CHAIR SAFETY: The presence of an attendant, though undesirable, is permissible during
 ascent or descent.  However, the chair occupant should always be in a reasonable state of
 balance, so that no more than 15 to 25 pounds of weight will be transferred to the attendant.  The
 chair must be "fail safe" to prevent uncontrolled descent in the event something happens to the
 occupant, attendant, or mechanism.
 \item COST: In order for the maximum number of handicapped persons to be able to purchase a
 stair-climbing wheel chair, every effort should be made to keep its cost at a bare minimum. 
 The retail cost should be no more than \$200.  Current models of standard tubular frame
 folding wheel chairs are priced at approximately \$150.
 \item OTHER CONSIDERATIONS: Chair should be capable of performing all its normal functions
 without undue josting or jouncing of the occupant.  Since most paraplegics have little
 control of the lower limbs, a method of retaining them in position is often required.  The
 foot rests should be movable in order to enable the occupants to raise themselves to a standing position
 on the floor.
 \item The chair should not require the installation of special ramps, mechanical
 contrivances, or electrical outlets in buildings.
 \end{enumerate}
 
 
 The above example has a clear statement with a clear set of requirements. Therefore, an objective tree,
 a function structure and even the market analysis may not be required because all necessary details and
 specific requirements are spelled out in the statement.  This is not always the case, as a
 matter of fact 80-90\% of the time, the statement given to the design engineer is very
 vague. For instance, it may simply say, "design a stair climbing wheelchair."  In this case an objective tree, functional
 analysis and market analysis are needed to clarify the statement.  The ability to write a
 good set of engineering specifications is proof that the design team understands the
 problem.  There are many techniques for generating engineering specifications. Hubka
 \cite{hubka} separates the properties affected by the constraints into categories based on
 operational, ergonomic, aesthetic, distribution, delivery, planning, design, production and
 economic factors.  Pahl and Beitz \cite{pahl} based the specifications on the fulfillments of
 the technical functions, the attainment of economic feasibility and the observance of safety
 requirements for the human and environment.  
 
 The approach that will be followed here to develop a set of requirements will be based on the
 performance specification method and the quality function deployment method.  In the
 performance  specification method, the specification defines the required performance instead of
 the required product. It also describes the performance that a design solution has to achieve,
 but not any particular physical component which may constitute a means of achieving that performance.
  In the quality function deployment method, the attributes of a required performance are
  translated into engineering characteristics.
  
  \section{Procedure for Performance Specification Method}
  The following are the steps in producing a set of specifications using the performance
  specifications method:
  \begin{enumerate}
  \item Consider the different levels of generality of solution which might be applicable:
  
  Specifications that are set at a too-high level of generality may allow inappropriate solutions
  to be suggested. However, too-tight specifications may remove all of the designer's freedom and
  creativity for the range of acceptable solutions.
  This level of limitation may also be connected with the definition of the customer you are dealing with, because the customer may
  also limit the class and the set of specifications.  For example, designing a space shuttle
  puts the designer on a tighter limit of specification.  Another example that may 
  demonstrate this point involves the design of an air jet for civilian use. Such a design has a different
  set of requirements than designing an air jet for military use.  Recognizing the customer's needs
  is an important factor in defining the range for the set of requirements.
  
  Different types of generality levels can be listed from the most general to least
  general, and may be demonstrated as:
  \begin{itemize}
  \item product alternatives
  \item product types
  \item product features
  \end{itemize}
  Let us consider an example to illustrate these levels. Suppose that the product in question is a
  domestic aluminum can disposal.  At the highest level of generality, the designer
  would be free to propose alternative ways of disposing of aluminum cans such as, crushing,
  melting, tearing, chemical deposing, etc.   There might even be freedom to move from the
  concept of one-can to multi-can, or from domestic to factory.  At the intermediate level,
  the designer would have much more limited freedom, and might only be concerned with
  different types of can crushers such as foot operated, or automatic can crushers. At the
  lowest level of generality, the designer would be constrained to only consider different features within a
  particular type of crusher, such as if it hangs on the wall or is self standing, processes one or multi-cans in
  one step, etc.
  
  \item Determine the level of generality at which to operate:  In general the
  customer/client determines the level of generality at which the designer may operate. For
  example, the customer may ask the designer to design a safe, reliable aluminum can crusher. Here, the
  type of product has already been established by the customer, and the constrain is already placed on the
  type of aluminum can disposable unit: it must be a crusher.  Hence, the set of requirements will
  follow for a can crusher, not a can disposable unit.  
  
  \item Identify the required performance attributes.
 For clarifying the customer statement, the objective trees, function analysis and market
 analysis are used.  The objective trees and functional analysis determine the performance
 attributes of the product. Some of the requirements in the customer statement are "must meet,"
 (called Demands) and others are "desirable" (called wishes).  Solutions that do not meet the
 demands are not acceptable solutions, whereas wishes are requirements that should be taken
 into consideration whenever possible.  Pahl and Beitz \cite{pahl} developed a checklist that
 can be used to derive attributes beside the objective trees and the function analysis.  The
 checklist can be seen in figure \ref{checkl}.
 
 \def \epsfsize#1#2{0.7#1}
 \begin{figure}
\epsffile{../figures/6-1.eps}
 \caption{Checklist for drawing up a requirement list}
 \label{checkl}
 \end{figure}


 Once the attributes are listed, it is recommended to distinguish whether the attribute is a
 demand or a wish, and then to tabulate the requirements.
 \item State succinct and precise performance requirements for each attribute: The attributes
 that can be written in quantified terms must be identified.  The performance limit should
 be attached to the attribute.  The limits may be set from the customer statement of  the
 federal and government agency standard offices. These attributes may include, but are not limited
 to maximum weight, power output, size, volume flow rate, etc.
 
 For the wishes, which cannot have a number attached to them, we use the quality function 
 deployment method.  The next section describes the quality function deployment method.
 \end{enumerate}
 \subsubsection{Example: Water Tap}
 Design a one-handed water mixing tap with the following requirements:
 \begin{itemize}
 \item flow-rate :10 l/min
 \item maximum pressure:  6 bar
 \item normal pressure : 2 bar
 \item hot water temperature: 60$^{o}C$
 \item connector size: 10 mm
 \end{itemize}
 Attention must be paid to appearance.  The firm's trade mark-e should be prominently displayed. 
 Finished product should be marketed in two years time.  Manufacturing costs should not exceed \$30,
 each at a production rate of 3000 taps per month.
 The specifications are shown in figure \ref{mixtap}.
 
 \def \epsfsize#1#2{0.7#1}
 \begin{figure}
 \epsffile{../figures/6-2.eps}
 \caption{Specification for a one-handed mixing tap}
 \label{mixtap}
 \end{figure}
 
 This example is a specification for a domestic water mixing tap that can be operated with
 one hand.  The initial statement has been considerably expanded.  Some details in the
 statement have been changed, for example, the maximum pressure as a result of establishing
 the national standards that apply to such a product.  The range of users has also been taken
 into account, as have safety considerations.  The demands (D) and wishes (W) have been
 distinguished in the left column.

 \section{Example: Automatic can crusher}
In the design process, after the designers have created the objective tree and the function tree, it is
important that the designers complete a table of specification.   The designers must decide on the
level of generality of the  specifications.  Market analysis results should be reviewed at this time.
From the need statement, the specifications that {\it must} be met are:
\begin{enumerate}
\item The design of the crushing mechanism is not to exceed $1.5 \times 1.5 \times 1 ft^{3}$ in the
total size.
\item The can crusher must have a continuous feed mechanism.  
\item The cans must be crushed to $\frac{1}{5}$ of its original volume.
\item It must operate safely.  It will be used by children.
\item The device is fully automatic.
\end{enumerate}
 
 The designers came up with specifications that were ranked as wishes.  Not all wishes have the same
 level of importance.  Because of that, the design team gave a number for the rank of wishes.  The figure
 below shows the specification table that the design team came up with for the automatic can crusher.
 
 \def \epsfsize#1#2{0.7#1}
 \begin{figure}
 \epsffile{../figures/6-4.eps}
 \caption{Specifcation table for automatic can crusher}
 \label{canspec}
 \end{figure}
 
 
 \def \epsfsize#1#2{0.7#1}
 \begin{figure}
 \epsffile{../figures/6-4b.eps}
 \caption{Specification table (cont.)}
 \end{figure}
 
 \section{Quality Function Deployment Method (QFD)}
 The QFD method was first developed in JAPAN in the mid 1970's, and used in the United States
 in the late 1980's.  Through the use of the QFD method, Toyota was able to reduce the cost of
 bringing a new car model to the market by more than 60\%, and the time was reduced by about
 33/%. 
 The quality function deployment method is defined as the strategic arrangement (deployment) throughout
 all aspects of a product (function) of appropriate characteristics (quality), according to
 customer demands.
 Because the QFD recognizes that the person who buys a product is the most important person in
 determining the commercial success of a product, the QFD is essentially concerned with the
 translation of the customer requirements into engineering characteristics.  Although the
 QFD method can be used for the whole design process, it will be used here for the wishes 
 in the requirement list.  The QFD method procedure is as follows:
 \begin{enumerate}
 \item Identify the customer requirements in terms of product attributes.  This can be done
 through market research techniques such as:
 \begin{itemize}
 \item Product clinics: Customers are quizzed in depth about what they like and
 dislike about a particular product.
 \item Hall test: Various competing products are arranged on display and customers are asked
 to inspect the products and give their actions.
 \end{itemize}
 In the QFD, consumers are the most important factor and the design should be arranged in
 a manner to meet their satisfaction.  The Kano model can be used to measure customer
 satisfaction.  In the Kano model, customer satisfaction is measured by the product function
 as shown in figure \ref{kano}.
 
 \def \epsfsize#1#2{0.7#1}
 \begin{figure}
 \epsffile{../figures/6-5.eps} 
 \caption{Kano Model for customer satisfaction}
 \label{kano}
 \end{figure}
 
 
 In the Kano model, there are three different types of product quality that give customer
 satisfaction: basic quality, performance quality and excitement quality.
With basic quality, customers' requirements are not verbalized because they specify
assumed functions of the device.  The only time a customer will mention them if they are
missing.  If they are not fully implemented in the final product the customer will be
disgusted with it.  If they are included,  the customer will be neutral.  An example is the
requirement that a bicycle should have brakes.
The performance quality refers to customers' requirements that are verbalized in the form that indicates,
the better the performance, the better the product.  The excitement quality involves those
requirements that are often unspoken because the customer does not expect them to be met in the
product. If they are absent, customers are neutral. However, if the customers' reaction to
the final product contains surprise and delight at the additional functions, then the product's
chance of success in the market is high.
\item Determine the relative importance of the attributes:
The demands are absolute requirements.  The wishes, however, are not in the same order of importance.
The customers are asked to rank these requirements in order, and hence generate an ordered list
of required wishes.  Then the design team allocates points to the various attributes.
\item Evaluate the attributes of competing products:  The objective here is to determine how
the customer perceives the competition's ability to meet each of the requirements.  Usually
the customers make the judgments about the product in terms of comparison with other
products.  This step is very important because it shows opportunities for product improvement.
\item Draw a matrix of product attributes against engineering characteristics:
Attributes are in general vague and general, the characteristics are measurable, real and
quantitative.  
\item Identify the relationship between the engineering characteristics and the product
attributes:  Each cell in the table represents how an engineering characteristic relates to
the customer requirement.  Many characteristics will measure more than one customers'
requirements.  The strength of the relationship can vary, with some engineering parameters
providing strong measures for customers' requirements and others providing no measure at
all.  The relation is conveyed through numerical values such as:
\begin{itemize}
\item 9=strong relationship
\item 3=medium relationship
\item 1=weak relationship
\item blank=no relationship
\item x=demand
\end{itemize}
\item Identify any relevant interactions between engineering characteristics: Engineering
characteristics may have relationships between each other. For example, a powerful engine is
also likely to be a heavier engine.  This interaction is added as a roof to the matrix.  This is called
the house of quality.
\item Set target figures to be achieved for the engineering characteristics:  to improve over
competitors. The market analysis may be important at this stage to identify the market limits.
\end{enumerate}
\subsubsection{Example : Splashgard}
This example is of a relatively simple product. Yet, it illustrates that considerable effort can be
necessary in designing, in order to satisfy customer requirement, even for a simple product.  The design
team identified three important customers for the product: the rider, the mechanic and the
marketing.  The mechanics are considered customers because they will sell, and perhaps install, the
Splashgard. Marketing is added to the customer list to ensure capture of production and
marketing needs.  Figure \ref{requir} shows a mountain bicycle and the customer's list of requirements
for the Splashgard.

\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/6-6.eps}
\caption{Requirements for Splashgard}
\label{requir}
\end{figure}


Figure \ref{house} shows the house of quality that is developed based on the QFD method for a
Splashgard.

\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/6-7.eps}
\caption{House of quality for the Splashgard}
\label{house}
\end{figure}

\section{Example: Automatic can crusher}

The design team has taken the wishes and objectives from the specification table and the objective
tree and placed them into the house of quality.  Because of the large number of wishes they listed
on their table, they were unable to show the house of quality in one figure. However, two tables are
shown below that represent the house of quality.  On the first table, the wishes are placed with
the engineering chracteristics, while on the second table, the engineering characteristics are
evaluated against each other. The engineering characteristics are obtained by including a metric, a
value and a unit.  Numerical values between (1) and (9) are assigned between each wish and
engineering characteristic to rank the corrolation between them. One is a very low corrolation and nine
is a very high corrolation. Blank spaces correspond to no correlation.  

\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/6-8a.eps}
\caption{House of Quality}
\end{figure}

\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/6-8b.eps}
\caption{House of Quality (cont.)}
\end{figure}

\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{../figures/6-8c.eps}
\caption{House of Quality (cont.)}
\end{figure}


\def \epsfsize#1#2{0.7#1}
\begin{figure}
\epsffile{..figures/6-9.eps}
\caption{Engineering Characteristics}
\end{figure}

\section{Problems}
\subsection{Team activities}
\begin{enumerate}
\item Given the following need statement: Design a domestic heating appliance.
 Generate different levels of generality of solutions. 
 \begin{enumerate}
 \item Alternatives
 \item Types
 \item Features
 \end{enumerate}
 \item Generate engineering characteristics for the following:
 \begin{enumerate}
 \item Easy to hold
 \item Cost effective
 \item Safe for the environment
 \item Easy to maintain
 \end{enumerate}
 \item Consider the statement you worked on previously during an in-class team activity. 
 By looking at your objective tree, generate a list of specifications and house
 of quality for the statement.
 
 {\it
 If you drive in the state of Florida, you notice some traffic congestion due to the trees being trimmed on the state roads and the
     freeways. Assume that the Florida Department of Transportation is the client. Usually, branches 6 inches or less in diameter are
     trimmed. The allowable horizontal distance from the edge of the road to the branches is 6ft. The material removed from the trees must
     be collected and removed from the roadside. To reduce the cost of trimming, a maximum of only 2 workers can be assigned for each
     machine. The overall cost, which includes equipment, labor, etc. needs to be reduced by at least 25\% from present cost. The state claims
     that the demand for your machines will follow the price reduction, i.e.,
      if you are able to reduce the cost by 40\%, the demand will
     increase by 40\%. Allowable working hours depend on daylight 
     and weather conditions}.   

\end{enumerate}

\subsection{Individual Activities}
 A specification consists of a metric and a value.  For example, "average
time to assemble" is a metric, while "less than 75 seconds" is the value of
this metric.  Note that the value may take on several forms, including a
particular number, a range or an inequality.  Values are always labeled with
the appropriate units.  Together, the metric and value form a specification. 
The product specifications are simply the set of the individual specifications.
\begin{enumerate}
\item Develop a list of specifications for the following objectives.  The table should
include metrics, the corresponding values (assume a value) and units.
\begin{enumerate}
\item easy to install
\item reduces vibration to the hand
\item is not contaminated by water
\item lasts a long time
\item is safe in a crash
\item allows easy replacement of worn parts
\end{enumerate}
\item List a set of metrics corresponding to the need that a pen writes
smoothly.
\item Devise a metric and a corresponding set for the need that a roofing
material lasts many years.
\item How might you establish precise and measurable specifications for
intangible needs such as, "The front suspension looks great?"
\item Can poor performance relative to one specification always be compensated
for with high performance on the other specifications? Give examples.
\item Develop a house of quality for the following need statment:
" We have a mountain size pile of wood chips that we want processed into home use fire logs. We are located in Tallahassee, Florida. We can have a
continuous supply of wood chips through out the year. We should be able to produce 50 fire logs per minute. The share holders require us to
have a large profit margin, and our prices should be lower than our competition for the same size logs. Needless to say the logs should preduce
enough heat to keep our customers faithful, and have environmentally clean exhaust.

\end{enumerate}




 
  
 
 
 
