\chapter{Specifications}
Specifications are highly important to provide a successful design.  All
engineering design problems are set within ceratin 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 as the last step in defining the
problem.  The objective trees defines the vague statements that is generally
introduced by the cutomer. but the objective trees 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 ste in terms of precise limits, which
what a performance specification does.  For
example, an objective may be stated to develop a product which has low weight. 
The word low weight is not clearly defined doest mean 20 lb or 100 lb as low
weight.

Based on the cutomer the requirement may be well defined and the specifications are well set,
an example of that is the announcement from the National Inventors Council to design a a
stair climibing 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 him to cope with the usual problems he might encounter 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, not
 too much of the conventional wheel chair's versatility and convenience should be sacrificed
 in providing the climbing function.  In this connection it might be well to point out that
 many active handicapped 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 acheived.  The
 following factors are to be taken into considerations:
 \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 ans stowed in the interior of standard
 automobile or taxi cab. Special loading ramps which are not carried as a part of the chair
 system or special modifications to automobile to accomodate chairs will not be considered.
 \item WIDTH of CHAIR: 25 inches maximum.  The AMerican Standards Associations utilized this
 width, as the maximum for standard wheel chairs, in establishing architectural standards
 which will provide the physical handicapped with freedom of movement in buildings and other
 structures.  However, a lsesser width fo a chair or a means of temorarily reducing the full
 open width fo passage through narrow doorways would be a definite asset in 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: Chair should be able to negotiate street curbings and any stair with
 average height risers and depth tread as found in office buildings and homes.  Ascent should
 be performed in presence of litter and moisture without damaging stiar 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 curbings and stairways.
 \item PROPULSION SYSTEM: Chair may be propelled by occupant or by a motorized unit, hoever
 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 permissable during
 ascent or descent.  However, the cahir ocuupant should always be in a reasonable state of
 balance so no more than 15 to 25 pounds of weight will be transferred at attendant.  The
 chair must be "fail safe" to prevent uncontrolled descent in the event something happens to
 occupant, attendant, or mechanism.
 \item COST: In order for the maximum number of handicapped 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 approxomatley \$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 moveable to enable the occupant to raise himself to a standing position
 on the floor.
 \item The cahir should not require the installation of special ramps, mechanical
 contrivances, or electrical oulets in buildings.
 \end{enumerate}
 
 
 The above example has clear statement with clear set of requirements, an objective tree and
 a function structure and even the market analysis may not be required because al 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 times the statement that given to the design engineer is very
 vauge, like desig a stair climbing wheel chair.  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 in generating engineering specifications. Hubka
 \cite{hubka} separates the properties affected by the constraints into catgories based on
 operational, ergonomic, aesthetic, distribution, delievry, planning, design, production and
 economic factors.  Pahl and Beitz \cite{pahl} based the specifications on the fulfilments of
 the technical functions, the attainment of economic feasibility and the observance of sfetey
 requirements for human and environment.  
 
 The approach that will be followed here to develop a set of requirement will be based on the
 performance specification method and the quilty function deployment method.  In the
 performance  specification method  the specification defines the required performance not
 the required product also it describes the performance that a design solution has to achieve
 and not any particular physical component which may be a mean of achieving that performance.
  In the quality function deployment method the attributes of a arequired 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:
  
  A specifications that set at too high level of generality may allow inapproporiate solutions
  to be suggested, whereas too tight specifications will remove all deisgners freedom and
  creativity for the range of acceptable solutions.
  This may also be connected in definning the customer you are dealing with, because that may
  also limit the class and the set of specifications.  For example, designing a space shuttle
  put the designer on the tighter limit of specification.  Another example that may be used
  here to demonstarte the point is the design of an air jet for civelian use has different
  set of requirement than design an air jet for the military use.  Recognizing the customer
  is an important factor in defining the range at which the set of requirement can be.
  
  Different types of the level of generality can be lsited from the most general to least
  general my be demonstrated as:
  \begin{itemize}
  \item product alternatives
  \item product types
  \item product features
  \end{itemize}
  as an example to illustatrte thease levels, suppose that the product in question is a
  demostic aluminium can desposal usint.  At the highest level of generality the designer
  would be free to propose alternative ways of desposing alumnium cans such as, crushing,
  melting, tearing, chemical desposing,.. etc.   There might even be freedom to move from the
  concept of one can to multi can from the deomstic to factory.  At the intermediate level,
  the designer would have a much more limited freedom, and might only be concerened with
  different types of can crushers such as foot operated, or automatic can crushers. At the
  lowest level the designer would be constrained to consdiereing different features within a
  aprticular type of crushers such as if it hang on the wall or loos, one or multi cans in
  one step, etc.
  
  \item Determine the level of generality at which to operate:  In general the
  customer/client determine the level of generality at which the designer to operate, for
  example the customer may ask to design a safe, reliable alumnium can crusher.  In here the
  type of product already established by the customer and the constrain already placed on the
  type of alumnium can desposable unit to be a crusher.  Hence the set of requirement will
  follow a can crusher not a can desposable unit.  
  
  \item Identify the required performance attributes
 In clarifying the customer statement the objective trees, functiona analysis and market
 anaysis are used.  The objective trees and functional analysis detremine the performance
 attributes of the product. Some of the requirments in the custmer statement are must meet
 (called Demands) and others are desirable (called wishes).  Solutions that do not meet the
 demands are not acceptable solutions, wheras wishes are requirements that should be taken
 into consideration whenever possible.  Pahl and Beitz \cite{pahl} developed a chicklist taht
 can be used to derive attributes beside the objective trees and the function analysis.  The
 chicklist can be seen in figure 5.1.
 \begin{figure}
 \vspace{6in}
 \caption{Checlist for drawing up a requirement list}.
 \end{figure}
 Onc the attributes are listed it is recommended to distinguish wether if the attribute is a
 demand or a wish and tabulate the requirements.
 \item State succinct and precise performance requirements for each attribute: The attributes
 that can be written in quantified terms must be idenitified.  The performance limit should
 be attached to the attribute.  The limits may be set from the cutomer statement of  the
 fedral and government agancy standard offices. These  attribute may include but not limited
 to maximum weight, power output, size, volume flow rate, .. etc.
 
 For the wishes which cannot have a number attached to it we use the quality function 
 deployment method.  next section describes the quality function deployment method.
 \end{enumerate}
 \subsubsection{Example: Water Tap}
 Design one-handed water mixing tap with the following requirements:
 \begin{itemize}
 \item flowrate :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 to be paid to appearance.  The firm's trade marke to be prominently displayed. 
 Finished product to be marketed in two years time.  Manufacturing costs not to exceed \$30
 each at a production rate of 3000 taps per month.
 The specifications are shown in figure 5.2.
 \begin{figure}
 \vspace{7in}
 \caption{Specification for a one-handed mixing tap}
 \end{figure}
 This example is a sepcification 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 benn 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 saftey considerations.  The demand (D) and wishes (W) have been
 distingushed in the left colomn.
 \section{Quality FUnction Deployment Method (QFD)}
 The QFD method was fisrt developed in JAPAN in the mid 1970, and used in the United States
 in the late 1980.  Through the use of the QFD method Toyota was able to reduce the cost of
 bringing a new car model to the market by over 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 approporiate characteristics (quality)  according to
 customer demands.
 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 concerened with the
 translation of the customer requirements into engineering charactersistics.  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 are 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: in which cutomers 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 cutomers are asked
 to inspect the products and give their actions.
 \end{itemize}
 In the QFD the cunsumer is the most imporatnt factor and the design should be arranged in
 amaner to meet his satisfaction.  The Kano model can be used to measure the customer
 satisfaction.  In the Kano model the customer satsfaction measured by the product function
 as shown in figure 5.3.
 \begin{figure}
 \vspace{3in} 
 \caption{Kano Model for cutomer satisfaction}
 \end{figure}
 In the Kano model there are three different types of product quality that give customer
 satisfaction: basic quality, performance quality and excitment quality.
In the basic quality the cutomers requirements that are not verbalized as they specify
assumed functions of the device.  The only time a cutomer 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 cutomer will be neutral.  An example is the
requirement that a bicycle should have brakes.
The performance quality refers to cutomers' requirements that are verbalized in the form that
the better the performance, the better the product.  The excitment quality are the these
requirements that are often unspoken because the customer do not expect them to be met in the
product, if they are absent the cutomers are neutral. However, if the cutomers' reaction to
the final product is surprise and delight at the additional functions, then the product's
chance of success in the market are high.
\item Determine the relative importance of the attributes:
The demands are absolute requirements.  The wishes are not in the same order of importance.
The cutomers are asked to rank these requirements in order and hence generate an ordered list
of required wishes.  Then the design team allocate points to the varoius attribute.
\item Evaluste the attributes of competing products:  The objective here is to determine how
the cutomer preceives the competition's ability to meet each of the requirements.  Usually
the cutomers maks the judgements about the product in terms of comaprison with other
products.  This step is very important as it shows opportunities for product improvement.
\item Draw a matrix of product attributes against engineering charactersitics:
Attributes are in general vague and general, the characteristics are measurable, real and
quantitative.
\item Identify the relationship between the engineering caharacteristics 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 cutomers'
requirement.  The strength of the realtionship can vary, with some engineering parameters
providing strong measures for a customers' requirement and others providing no measure at
all.  The relation is conveyed through numerical values as:
\begin{itemize}
\item 9=strong relationship
\item 3=medium relationship
\item 1=weak relationship
\item blank=norelationship
\item x=demand
\end{itemize}
\item Identify any relevant interactions between engineering chracteristics: Engineering
characteristics may have relation ships bewteen each other as an example a powerful engin is
also likely to be heavier.  This interaction is added as aroof to the matrix.  This is called
the house of quality.
\item Set target figures to be achieved for the engineering chracteristics:  to improve over
competitors. The market analysis may be important at this tage to identify the market limits.
\end{enumerate}
\subsubsection{Example : Splashgard}
This example is a relatively simple product, but it illustrate how considerable effort can be
necessary in designing to satisfy cutomer requirement even for simple product.  The design
tema identifys three important cutomers for the product. the rider, the mechanic and the
marketing.  The mechanics are considerd as cutomers as they will sell and may be install the
splshgard.  The marketing are added to the cutomer list to ensure captur of production and
marketing needs.  Figure 5.4 shows a mountain bicycle and the cutomers list of requirements
for the splashgard.
\begin{figure}
\vspace{8in}
\caption{Requirments for splashgard}
\end{figure}
Figure 5.5 shows the house of quality that is developed based on theQFD method for a
splashgard.
\begin{figure}
\vspace{8in}
\caption{House of quality for the splashgard}
\end{figure}
  
 
 
 
