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Chapter: Mechanical : Computer Aided Design : Fundamentals of Computer Graphics

Fundamentals of Computer Graphics

Product Life Cycle (PLC), Product Life Cycle (PLC) For Continuous Improvement, Technology Development Cycle, The Design Process - Introduction, Morphology Of Design, Design Process Models, Sequential Engineering Design, Concurrent Engineering Design, Role Of Computers In Design, Cad System Architecture, Computer Aided Engineering – CAD/CAM, Application Of Computers To Design, Benefits Of CAM, Reasons For Implementing CAM, Computer Graphics, Co-Ordinate Systems, 2 – D Display Control Facilities, 2– D Transformations, Homogeneous Co-Ordinates, 3 – D Transformations, Line Drawing Algorithms.





Every product goe s through a cycle from birth, followed by an initial growth stage, a relatively stable matured period, and finally into a declining stage that eventually ends in the death of the product as shown schematically in Figure.

Figure.1.1. Product Life Cycle


3.5.   Introduction stage: In this stage the product is new and the customer acc eptance is low and hence the sales are low.


3.6.   Growth stage: Knowledge of the product and its capabilities reaches to a g rowing number of customers.


3.7. Maturity stage: The produ ct is widely acceptable and sales are now stable , and it grows with the same rate as the econ omy as a whole grows.


3.8.                     Decline stage: At some p oint of time the product enters the decline st age. Its sales start decreasing because of a n ew and a better product has entered the market to fulfill the same customer requirements.





Figure.1.2. Prod uct Life Cycle for continuous Improvement ( Basic)

Figure.1.3. Produc t Life Cycle for continuous Improvement (D etailed)





The development of a new technology follows a typical S-shaped curve. In its early stage, the progress is limited by the lack of ideas. A single good idea can make several other god ideas possible, and the rate of progress is exponential. Gradually the growth becomes linear when the fundamental ideas are in place and the progress is concerned with filling the gaps between, the key ideas.


 It is during this time when the commercial exploitation flourishes. But with time the technology begins to run dry and increased improvements come with greater difficulty. This matured technology grows slowly and approaches a limit asymptotically.


  The success of a technology based company lies in its capabilities of recognizing when the core technology on which the company’s products are based begin to mature and through an active R&D program, transfer to another technology growth curve which offers greater possibilities.


Figure.1.4. Schematic outline of Technology Development Curve



Figure.1.5. Improved program to develop new technology before the complete extinct of existing technology





The Engineering Design Process is the formulation of a plan to help an engineer build a product with a specified performance goal. This process involves a number of steps, and parts of the process may need to be repeated many times before production of a final product can begin.


It is a decision making process (often iterative) in which the basic sciences, mathematics, and engineering sciences are applied to convert resources optimally to meet a stated objective. Among the fundamental elements of the design process are the establishment of objectives and criteria, synthesis, analysis, construction, testing and evaluation.


The Engineering Design process is a multi-step process including the research, conceptualization, feasibility assessment, establishing design requirements, preliminary design, detailed design, production planning and tool design, and finally production.


1. Steps involved in Enginee ring Design process

Figure.1.6. Engineering Design Process


Conceptual Design


It is a process in which we in itiate the design and come up with a number of design concepts and then narrow down to the singl e best concept. This involved the following step s.


         Identification of customer needs: The mail objective of this is to completely understand the customers’ needs and to c ommunicate them to the design team


         Problem definition: The mail goal of this activity is to create a statement that describes what all needs to be accomplished to meet the needs of the customers’ requirem ents.


         Gathering Information: In this step, we collect all the information that can be helpful for developing and translating the customers’ needs into engineering design.


         Conceptualization: In thi s step, broad sets of concepts are generated th at can potentially satisfy the problem statem ent


(5) Concept selection: The main objective of this step is to evaluate the various design concepts, modifying and evolving into a single preferred concept.

Embodiment Design


It is a process where the structured development of the design concepts takes place. It is in this phase that decisions are made on strength, material selection, size shape and spatial compatibility. Embodiment design is concerned with three major tasks – product architecture, configuration design, and parametric design.


a.         Product architecture: It is concerned with dividing the overall design system into small subsystems and modules. It is in this step we decide how the physical components of the design are to be arranged in order to combine them to carry out the functional duties of the design.


b.      Configuration design: In this process we determine what all features are required in the various parts / components and how these features are to be arranged in space relative to each other.


c.       Parametric design: It starts with information from the configuration design process and aims to establish the exact dimensions and tolerances of the product. Also, final decisions on the material and manufacturing processes are done if it has not been fixed in the previous process. One of the important aspects of parametric designs is to examine if the design is robust or not.


Detail Design


It is in this phase the design is brought to a state where it has the complete engineering description of a tested and a producible product. Any missing information about the arrangement, form, material, manufacturing process, dimensions, tolerances etc of each part is added and detailed engineering drawing suitable for manufacturing are prepared.


2. Models of the Design Process


Designers have to:


Explore - the problem ‘territory’


Generate - solution concepts


Evaluate - alternative solution concepts


Communicate - a final proposal


A simple model of the design process, derived from what designers have to do


3. New Design Procedures



4. Need for Applying Technoology in the Design Process


Design is the essence o f engineering


Starts with recognition of some need


Progresses to physical implementation


Results may be simple or complex


Design can be of two k ind:


O  Something com pletely new , or


          An improved f orm of something already in existence





The consideration of the product life from its conception to retire ment.....

Anatomy of Design


Detailed examination of th e engineer’s actions as he/she identifies and solves the problem:



1.Needs Analysis


Creation begins by recognizing a need


O  Apparent fr om observation


O  Results of a detailed study


O  A specific s et of circumstances


Results in a primiti ve statement


O  Fact or opi nion


O  Does the ne ed exist and is it realistic?


O  Does it exis t now or will it exist in the future?


O  Is it a new need? (new material or physical principle)


Often depends on c ircumstances



Needs analysis once through the Anatomy provides a good star ting point for the Feasibility Study


2.  Feasibility Study



Designs can be futile unless satisfying the original need is feasible


At this stage, the product appears in abstract forms, but is they feasible???


Alternative solutions must be subjected to physical and economic analyses and be realizable from both


The Feasibility Study using analysis of several alternatives establishes the design concept as something which can be realised and accepted


Some examples.....


(i) A building must be comfortable to live in:


Heating, ventilation and air conditioning are required. Specify limits of temperature, humidity, velocity and fresh air constituency.


(ii) National fossil fuel supplies are low:


Alternative forms of energy supply are required. Specify amount and where they are needed, and any restrictions of space, time or pollution levels.


3.Preliminary Design


Main purpose is selection of the best possible solution from a choice of alternatives Make comparisons against given criteria & constraints

Must maintain an open mind; use your judgement.


4.Detailed design


Aim is to produce a complete set of working drawings which are then transmitted to the manufacturer


This stage of design is far less flexible than those previous


Design should now reflect all of the planning both for manufacture and consumption stages Construction/testing of various components may be required


Prototype building ....is it what was expected?




Here, the device or system is actually constructed, and planning for this should have been incorporated into the design


Knowledge of the capability of the machines is required, since it must be possible to build and assemble the components as specified


Special jigs, fixtures and even machines may be required


Planning is vital; including quality control hold points, methods of inspection, standards for comparison etc...

Timing of construction may be important eg. Climatics




Transportation of the ma nufactured article, complete or in subassem ly form must be anticipated in the design


Packaging, availability of vehicles, regulations for use of thoroughfares , shelf/component life, warehouse storage f acilities, special handling, environmental contr ol of temperature and humidity may need to be addressed



The product is now used by the consumer


If the design is effect, it w ill have met the need


The design may yet no t be complete; redesigns and modifications may be required depending on field trials or consumer feedback


May need to consider maintenance of components and supply of spare parts or subassemblies




The product will be discarded as its life cycle terminates


It may have become obsol ete whilst still serviceable and therefore the design may not have been fully economical


Disposal and recovery of u seful materials should have been included in the design Threats to safety should bee guarded against




1.Shigley Model



2.Ohsuga Model

3.Earle Model









With today's marketplace becoming more and more competitive, there is an ever-increasing pressure on companies to respond quickly to market needs, be cost effective, reduce lead-times to market and deliver superior quality products.



Traditionally, design has been carried out as a sequential set of activities with distinct non-overlapping phases. In such an approach, the life-cycle of a product starts with the identification of the need for that product. These needs are converted into product requirements which are passed on to the design department. The designers design the product's form, fit, and function to meet all the requirements, and pass on the design to the manufacturing department.


After the product is manufactured it goes through the phases of assembly, testing, and installation. This type of approach to life-cycle development is also known as `over the wall' approach, because the different life-cycle phases are hidden or isolated from each other. Each phase receives the output of the preceding phase as if the output had been thrown over the wall. In such an approach, the manufacturing department, for example, does not know what it will actually be manufacturing until the detailed design of the product is over.


Figure.1.8.Over the Wall Engineering (Sequential Engineering)


There are a lot of disadvantages of the sequential engineering process. The designers are responsible for creating a design that meets all the specified requirements. They are usually not concerned with how the product will be manufactured or assembled. Problems and inconsistencies in the designs are therefore, detected when the product reaches into the later phases of its life-cycle. At this stage, the only possible option is to send the product back for a re-design. The whole process becomes iterative and it not until after a lot of re-designs has taken place that the product is finally manufactured. Because of the large number of changes, and hence iterations, the product's introduction to market gets delayed. In addition, each re-design, re-work, re-assembly etc. incurs cost, and therefore the resulting product is costlier than what it was originally thought to be. The market share is lost because of the delay in product's introduction to market, and customer faith is lost. All this is undesirable.

Concurrent Engineering is a dramatically different approach to product development in which various life-cycle aspects are considered simultaneously right from the early stages of design. These life-cycle aspects include product's functionality, manufacturability, testability, assimilability, maintainability, and everything else that could be affected by the design.


In addition, various life-cycle phases overlap each other, and there in no "wall" between these phases. The completion of a previous life-cycle phase is not a pre-requisite for the start of the next life-cycle phase. In addition, there is a continuous feedback between these life-cycle phases so that the conflicts are detected as soon as possible.

The concurrent approach results in less number of changes during the later phases of product life-cycle, because of the fact that the life-cycle aspects are being considered all through the design. The benefits achieved are reduced lead times to market, reduced cost, higher quality, greater customer satisfaction, increased market share etc. Sequential engineering is the term used to describe the method of production in a linear format. The different steps are done one after another, with all attention and resources focused on that one task. After it is completed it is left alone and everything is concentrated on the next task.

In concurrent engineering, different tasks are tackled at the same time, and not necessarily in the usual order. This means that info found out later in the process can be added to earlier parts, improving them, and also saving a lot of time. Concurrent engineering is a method by which several teams within an organization work simultaneously to develop new products and services and allows a more stream lined approach. The concurrent engineering is a non-linear product or project design approach during which all phases of manufacturing operate at the same time - simultaneously. Both product and process design run in parallel and occur in the same time frame.


Product and process are closely coordinated to achieve optimal matching of requirements for effective cost, quality, and delivery. Decision making involves full team participation and involvement. The team often consists of product design engineers, manufacturing engineers, marketing personnel, purchasing, finance, and suppliers.


Figure.1.9. Sequential and Concurrent Engineering















       Modeling of the D esign


       Engineering design and analysis


       Evaluation of Prot otype through Simulation and Testing


•    Drafting and Desig n Documentation






            Productivity Improvem ent in Design Depends on Comp lexity of drawing,


Degree of repetitiveness of features in the designed parts, Degree of symmetr y in the parts,


Extensive use of li brary of user defined shapes and commonly use d entities


            Shorter Lead Times


            Flexibility in Design


            Design Analysis


            Fewer Design Error


            Standardization of Des ign, Drafting and Documentation



7.     Drawings are more understandable


8.     Improved Procedures of Engineering Changes


9.     Benefits in Manufacturing :


a.     Tool and fixture design for manufacturing


b.     Computer Aided process planning


c.      Preparation of assembly lists and bill of materials


d.     Computer aided inspection


e.      Coding and classification of components


f.       Production planning and control


g.     Preparation of numerical control programs for manufacturing the parts on CNC machines


h.     Assembly sequence planning





       To increase the productivity of the designer


       To improve the Quality of Design


       To improve Documentation


       To create a Database for manufacturing





Computer Graphics is defined as creation, storage, and manipulation of pictures and drawings by means of a digital computer


It is an extremely effective medium for communication between people and computers


Computer graphics studies the manipulation of visual and geometric information using computational techniques


It focuses on the mathematical and computational foundations of image generation and processing rather than purely aesthetic issues


In Interactive Computer Graphics (ICG) the user interacts with the compute and comprises the following important functions:

Modeling, which is concerned with the description of an object in terms of its spatial coordinates, lines, areas, edges, surfaces, and volume


Storage, which is concerned with the storage of the model in the memory of the computer



Manipulation, which is used in the construction of the model from basic primitives in combination with Boolean algebra



Viewing, in the case the computer is used to look at the model from a specific angle and presents on its screen what it sees.

Typical Hardware setup of a Graphic System


Work Station: A workstation comprises of the devices that allow the user to create and design objects, using both graphic and non-graphic instructions and data. A Stand alone workstation refers to CAD workstations that can process data and output information independent of other computer systems or workstations. It includes its own software, hardware, and peripherals.






A coordinate system is o ne which uses one or more numbers, or coordinates, to uniquely determine the position of a poi nt or other geometric element on a manifold such as Euclidean space.


Common coordinate systems are:


Number line


The simplest exam ple of a coordinate system is the identification of points on a line with real numbers using the number line. In this system, an arbitrary point O (the origin) is chosen o n a given line. The coordinate of a point P is de fined as the signed distance from O to P, where the signed distance is the distance ta ken as positive or negative dependin g on which side of the line P lies. Each point is given a unique coordinate and each real number is the coordinate of a unique point


Cartesian coordin ate system [ (x,y) and (x,y,z) ]



Polar coordinate system (ρ,θ)


Another co mmon coordinate system for the plane is the polar coordinate system. A point is chosen as the pole and a ray from this point is taken as the polar axis.


For a given angle θ, there is a single line through the pole whose angle with the polar axis is θ ( measured counter clockwise from the axis to the line). Then there is a unique point on this line whose signed distance from the or igin is r for given number r. For a gi ven pair of coordinates (r, θ) there is a single p oint, but any point is represented by many pairs of coordinates. For example (r, θ), (r, θ+2π) and (−r, θ+π) are all po lar coordinates for the same point. The pole is represented by (0, θ) for any value of θ.


Cylindrical Coord inate systems


A cylindrical coordinate system is a three-dimensional coordinate system that specifies point positions by the distance from a chos en reference axis, the direction from the axis relative to a chosen reference directio n, and the distance from a chosen reference plane perpendicular to the axis. The latter distance is given as a positive or n egative number depending on which side of t he reference plane faces the point.


The origin of the system is the point where all three coordinates can be given as zero. This is the intersection between the reference plane and the axis.


The axis is variously called the cylindrical or lon gitudinal axis, to differentiate it fro m the polar axis, which is the ray that lies in th e reference plane, starting at the origin and pointing in the reference direction.

The distanc e from the axis may be called the radial distance or radius, while the angular coord inate is sometimes referred to as the angular position or as the azimuth.


Spherical Coordi nate systems

 A spherical c oordinate system is a coordinate system for three-dimensional space where the positi on of a point is specified by three numbers: the radial distance of that point from a fixe d origin, its polar angle measured from a fixe d zenith direction, and the azimuth angl e of its orthogonal projection on a reference plane that passes through the origin an d is orthogonal to the zenith, measured from a fixed reference direction on that plane .


The radial dist ance is also called the radius or radial coordinate. The polar angle may be called co-latitu de, zenith angle, normal angle, or inclination angle

Homogeneous coo rdinate system


Three dimensional representation of a two di mensional plane is called Homogeneo us Co-ordinates. The respective system is called Homogeneous coordinate system.





The essential steps for 2D graphics are:


1.     Convert the ge ometric representation of the model to lines (ter med Vectors)


2.     Transform the lines from the model coordinate system to the screen coordinate system (termed windowing)


Select those lin es that are within the part of the model that it is wished to display known as the c lipping step

4. Instruct the display device to draw the vectors The Stages in graphics pipeline are shown.


1.  Vector Generation


The aim of vector display of a curve is to use sufficient vectors for the curve to appear smooth. The number needed is controlled by the display tolerance, which is maximum deviation of the vector representation from the true curve shape.


2.  Windowing Transformation


When it is necessary to examine in detail a part of a picture being displayed, a window may be placed around the desired part and the windowed area magnified to fill the whole screen and multiple views of the model may also be shown on the same screen.


The window is a rectangular frame or boundary through which the user looks onto the model. The viewport is the area on the screen in which the contents of the window are to be presented as an image.

3.     Clipping Transformation

The clipping is an operation to plot part of a picture within the given window of the plotting area and to discard the rest.

4.  Reflection Transformation


Reflection about any axis

5.  Zooming


This transformation is carried out to provide enlarged or shrunk view of a picture detail







i.     Translation


ii.     Scaling


iii.     Reflection with mirror


iv.    Rotation













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