Design and Fabrication of a Robot for Training Essays

Design and Fabrication of a Robot for Training Essays Design and Fabrication of a Robot for Training Essay Design and Fabrication of a Robot for Training Essay MOI UNIVERSITY SCHOOL OF ENGINEERING DEPARTMENT OF MECHANICAL AND PRODUCTION ENGINEERING COURSE CODE: PRD5 80 COURSE TITLE: FINAL YEAR PROJECT PROJECT TITLE: DESIGN AND FABRICATION OF A ROBOT FOR TRAINING PRESENTED BY: Dennis Chesire PRESENTED TO: DR. A. N. MAYAKA Submitted To The Department Of Mechanical And Production Engineering In Partial Fulfillment Of The Requirements For The Award Of Bachelor Of Technology Degree In Mechanical And Production Engineering Academic year 2007/2008 DECLARATION I hereby declare that this is my original work and has not been submitted for any award in any institution or university. SIGN †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ DATE †¦ Dennis Chesire CERTIFICATION I have read this project report and approved its presentation for examination. SIGN †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ DATE †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦ Supervisor DEDICATIONS I dedicate this design work to my family and all my friends for their inspiration and assistance even in times of difficulty. ACKNOWLEDGEMENT The completion of this project would have been impossible without the help received from many people. First I would like to thank the Almighty Father in heaven for having brought me this far. To God be glory forever and ever. I would also like to thank Dr. A. N. Mayaka for the priceless moral and technical advice he gave throughout the design process of this project. Thank you for the shared documents and materials and the precious time you gave, out of your ever busy schedule. I acknowledge the assistance of the Head of Department, Dr. Boaz Korir for coming to my aid when Dr. A. N. Mayaka was away. I would like to acknowledge all my lecturers for the tireless effort they have put in my training. Mr. Kimutai the effort you put towards this project cannot go unmentioned. I want to also extend my sincere appreciation to all the Mechanical Engineering Department technicians, specially mentioning Mr. Akwiri and Mr. Oduor My parents, I will not forget your self sacrifice in an effort to support me all through my college life. Last but not least, all my classmates, I am very grateful. May God bless you all. ABSTRACT In this project an introduction on the need of adequate training on automation in higher learning institutions is looked into in a systematic way. First there is a general introduction of robotics in chapter one, robot classifications and robot applications is in chapters three and four. Chapter five consists of the design alternatives and their analysis. General introduction on component manufacture is given in chapter six. Cost analysis and the conclusion and recommendations are done in chapters seven and eight. TABLE OF CONTENTS DECLARATIONi Supervisor DEDICATIONSi DEDICATIONSii ACKNOWLEDGEMENTiii ABSTRACTiv TABLE OF FIGURESviii LIST OF TABLESix LIST OF APPENDICESx 1. 0 CHAPTER ONE1 1. 1 GENERAL INTRODUCTION1 1. 2 PROBLEM STATEMENT2 1. 3 JUSTIFICATION3 1. 4 SCOPE5 1. 5 OBJECTIVES6 1. 5. 1 General objective6 1. 5. 2 Specific objectives6 1. 6 METHODOLOGY7 1. 6. 1 Source of data7 1. 6. 2 Target market for design7 1. . 3 Viability7 CHAPTER TWO8 2. 0 LITERATURE REVIEW8 2. 1 Background8 2. 1. 1 What is a Robot? 8 2. 2 ROBOT GENERATIONS10 2. 3 Robot systems10 2. 4 CLASSIFICATION OF ROBOTS11 2. 4. 1 Classification based on structural configuration and robot motion. 11 2. 4. 1. 1 Revolute (jointed arm) robot12 2. 4. 1. 2. Polar (spherical) robot13 2. 4. 1. 3 Cylindrical ro bot14 2. 4. 1. 4 Cartesian (rectangular) robot, sliding type14 2. 4. 1. 5 Cartesian (rectangular) robot, gantry-type14 2. 4. 1. 6. SCARA- type robot15 2. 4. 2 Basic robot motions16 2. 4. 2. 1 Six degrees of freedom16 2. 4. 3 Classification based on path control17 2. 4. 3. Point-to-point (PTP) control17 2. 4. 3. 2Continuous path (CP) control18 CHAPTER THREE19 3. 0 ROBOT APPLICATIONS19 3. 1 General application characteristics19 3. 2 APPLICATION AREAS OF INDUSTRIAL ROBOTS20 3. 2. 1 Material Transfer21 3. 2. 2 Machine Loading21 3. 2. 3 Welding23 3. 2. 3. 1Spot welding23 3. 2. 3. 2 Arc welding24 3. 2. 4 Spray Coating25 3. 2. 5 Processing Operations27 3. 2. 6 Assembly28 3. 2. 7 Inspection29 CHAPTER FOUR31 4. 0TRAINING31 4. 1 INTRODUCTION31 4. 2 APPLICATION OF ACQUIRED SKILLS31 4. 2. 1 Middle managers31 4. 3 TREND IN KENYA31 4. 4 REASONS WHY KENYAN FIRMS NEED WELL TRAINED GRADUATES FROM LEARNING INSTITUTIONS33 4. TYPES OF TRAINING34 5. 0 DESIGN ANALYSIS36 5. 1 DESIGN ALTERNATIVES36 5. 1. 1 Comparison of alternatives38 5. 2 SPECIFICATIONS39 5. 2. 1 Task Specifications39 5. 2. 1. 1 Performance Specifications39 5. 2. 1. 2 Design Specifications39 5. 2. 1. 3 Dimensional Specifications40 5. 3 EXTENT OF THE ANALYSIS42 5. 4 GRIPPER MECHANISM ANALYSIS43 5. 4. 1 Gripping Force44 5. 4. 2 Torque required to produce desired clamping force-Power screws46 5. 4. 3 Power Required49 5. 4. 4 Pins50 5. 5 HOLLOW SECTIONS51 5. 6 BELT51 5. 6. 1 Dimensions of belt cross sections52 5. 7 FASTENERS53 5. 8 WASHERS54 5. 9 COUPLINGS54 5. 9. 1 Flange coupling54 5. . 2 Derivation of flange coupling formula55 5. 10 SAFETY FACTORS57 5. 11 KEYS AND KEY-WAYS58 5. 11. 1Wood ruff key58 CHAPTER SIX59 6. 0COMPONENT PRODUCTION59 6. 1 PARAMETERS FOR OPTIMUM PRODUCTION59 6. 1. 1 Product Analysis59 6. 1. 2 Operation Analysis59 6. 1. 3 Machine Analysis59 6. 1. 4 Operator Analysis59 6. 2 RESOURCE REQUIREMENT59 6. 2. 1 Capital Resources60 6. 2. 2 Tooling Resources60 6. 2. 3 Material Resources60 6. 2. 4 Human Reso urces60 6. 2. 5 Service Resources60 CHAPTER SEVEN61 7. 0 COST ANALYSIS61 CHAPTER EIGHT63 8. 0 CONCLUSION AND RECOMMENDATIONS63 8. 1 CONCLUSION63 8. 2. 1 Recommendations for the Government65 8. 2. Recommendations for the university66 REFERENCES67 TABLE OF FIGURES Figure 1. 0: CAD/CAM layout 6 Figure 2. 1: Revolute Robot 14 Figure 2. 2: Cylindrical and Polar Robot 15 Figure 2. 3: Cartesian Robot17 Figure 2. 4: Basic Robot Motions18 Figure 2. 5: Typical Wrist Articulations19 Figure 5. : Alternative Design 138 Figure 5. 2: Alternative Design 239 Figure 5. 3: Shape of Object to be grasped40 Figure 5. 4: Determination of Principal Dimensions41 Figure 5. 5: Gripper mechanism44 Figure 5. 6: End section of Gripper45 Figure 5. : Power Screw Motions48 Figure 5. 8: Woodruff Key59 LIST OF TABLES Table 7. 1 Cost analysis 62 LIST OF APPENDICES APPENDIX I: Glossary Of Robotic Terms APPENDIX II: Nominal cross-sectional dimensions of Standard V-belts APPENDIX III: Typical coefficients of static frict ion values (Dry conditions) APPENDIX IV: Chain Dimensions and Breaking Loads of Base Chains APPENDIX V: Woodruff Keys APPENDIX VI: Straight Sided Splines for Machine Tools-4 splined APPENDIX VII: Single Thrust Ball Bearings 1. 0 CHAPTER ONE 1. 1 GENERAL INTRODUCTION Robotics is a term describing a new academic and industrial discipline. Robotics is now a well established field of endeavor both in industry and research laboratories. There is a danger that the word may be used even in areas where it is inappropriate, so knowing precisely what a robot is, how it is controlled and how it may be used in specific applications is of the highest importance. As a result of the great advances of the last few years many industrial processes have become largely automated, with the human operator playing an ever decreasing role. The fully automated and unmanned factory is probably now only a few decades away. 1. 2 PROBLEM STATEMENT Many institutions of higher learning in Kenya have incorporated studies on automation in their teaching curricular for example CAD/CAM. Proper grasp of the underlying principles are best demonstrated to the students within a laboratory. It is in pursuance of this need that an effort is being made through this project to produce an automated cylindrical configuration robot model. 1. 3 JUSTIFICATION In the recent past there has been increasing world-wide competitions and many companies see, the use of computer-assisted production systems as giving them a chance of resolving the conflict of objectives between productivity and flexibility by introducing automation in a flexible manner. But it is not only the production techniques that are undergoing a process of change. Computers are also used to assist the functions that precede, accompany or follow production. The key words of this trend are: Computer Aided Design (CAD), Computer Aided Planning (CAP) and Computer Aided Manufacturing (CAM). CAM means the integration of all planning, controlling, executing and monitoring functions of the production process on the basis of a computer network. Efforts directed towards automation and integration change the work content and working conditions of production. However, the success of a company’s commitment will be determined not only by selecting and applying the best technology but also ensuring that people and machines work together in the best possible manner. It is in this context that training is of paramount importance. There is therefore a need to introduce robotics to all practicing and training engineers so that the technology may be embraced in Kenya to aid in the attainment of Vision 2030. To attain this, a design of a simple configuration robot to aid in the displaying of the basic principles of robotics to training engineers is of great import. It is with this intention that this project is carried out as a follow up to what has been done previously on the subject. [pic] Figure 1: CAD/CAM Layout (courtesy of Robotics for Engineers Pg 308) 1. SCOPE The project will be limited to the design and fabrication of a pick-and-place robot of the cylindrical configuration type because of its relative simplicity. 1. 5 OBJECTIVES 1. 5. 1 General objective To supplement lecture room discussions on â€Å"automated industrial operations† with laboratory work. 1. 5. 2 Specific objectives i. To study the application of robots world wide ii . To develop and design a model of a simple cylindrical configuration robot for training sessions in the School of Engineering of Moi university iii. To fabricate a model of a simple cylindrical configuration robot using cheap available material 1. 6 METHODOLOGY 1. 6. 1 Source of data Development and design of the cylindrical robot is based on: Study of the available automated systems Review of related literature Inspection of layout of mechanical engineering laboratories at Moi University for compatible principal dimensions of the design Insight into the University curricular for suitability of the design needs 1. 6. 2 Target market for design Universities in Kenya Other higher learning institutions including polytechnics . 6. 3 Viability The completed design is intended for installation at the Moi university laboratories for use in demonstrations to augment theoretical lectures on automation. Other institutions should initially see the need to attach their students at Moi University before eventually buying the product to cut down on their training costs. CHAPTER TWO 2. 0 LITERATURE REVIEW 2. 1 Background The word robot exis ts in many languages an evidence of its recent coinage. The term first came in use during the 1920s and 1930s, following the appearance of a play by the Czech author Karel Capek, called R. U. R. (Rossums Universal Robots), in the play small artificial anthropomorphic creatures strictly obeyed their masters orders. These creatures were called ‘robots’, a word derived from the Czech robota, meaning ‘forced labour’. 2. 1. 1 What is a Robot? A wide spectrum of definitions exists though few manufacturers or users will agree on any. In fact none has been accepted as standard. Since there is no standard for defining or for describing the functions of a robot, it would be helpful if consideration is given to the attempts that have been made to provide one. The British Robot Association (BRA) has defined the industrial robot as A reprogrammable device with a minimum of four degrees of freedom designed to both manipulate and transport parts, tools or specialized manufacturing implements through variable programmed motions for the performance of the specific manufacturing task (Chirouze, 1988 pg 17). The Robotics Institute of America (RIA) defines the robot as A reprogrammable, multi-functional manipulator designed to move material, parts, tools or specialized devices through variable programmed motions for the performance of a variety of tasks. Japan Industrial Robot Association (JIRA) and the Japanese Industrial Committee in the ‘Glossary of terms for industrial robots’ defines the robot at various levels as Manipulator: a machine which has functions similar to those of the human upper limbs, and moves the object spatially, from one location to the other. Playback robot: a manipulator which is able to perform an operation by reading off the memorized information for an operating sequence, including positions and the like, which it learned by being taken manually through the routine beforehand. Intelligent robot: a robot which can determine its own behaviour /conduct through its functions of sense and recognition (Chirouze op cit). Computer Aided Manufacturers International (CAM-I) in the USA defines the humanoid aspects of the industrial robot as A device that performs functions ordinarily ascribed to human beings, or operates with what appears to be almost human intelligence. The definition supplied by the Concise Oxford Dictionary is ‘Apparently human automaton, intelligent and obedient but impersonal machine. ’ Another suggestion defines a robot in its developed form as An automatic machine with a certain degree of autonomy, designed for active interaction into the environment (Francis Sieglera, 1987 pg 2-4). 2. 2 ROBOT GENERATIONS There are several more or less clearly distinguished generations of industrial robots. The first generation robots are fixed-sequence robots which can repeat a sequence of operations once they have been programmed to do so. To carry out a different job, they have to be reprogrammed, often by â€Å"training† or â€Å"education† The second-generation robots are equipped with sensory devices which allow a robot to act in a not-completely defined environment, e. g. ick up a part that is misplaced from its ideal position, pick up a needed part from a batch of mixed parts, recognize a need to switch from one succession of motions to another etc. The third-generation robots which are emerging now have the intelligence to allow them to make decisions, such as ones necessary in assembly operations (assembling a prop er combination of parts; rejecting faulty parts; selecting necessary combinations of tolerances etc. ) Robots of first and so called â€Å"1. 5† generation (with some sensing devices) constitute the overwhelming majority of robots now in use and production (Francis Sieglera op cit). . 3 Robot systems However, regardless of the generation, industrial robots are built of three basic systems: The â€Å"mechanical structure† consisting of the mechanical linkages and joints capable of various movements. Additional movements are made possible by end effectors fitted at the arm end. The â€Å"control system† which can be of â€Å"fixed† or â€Å"servo† type. Robots with fixed control systems have fixed (but, possibly, adjustable) mechanical stops, limit switches, etc. , for positioning and informing the controller. Servo-controlled robots can be either point to point (PTP), where only specified point coordinates are under control and not the path between them, or continuous path (CP) controlled, thus achieving a smooth transition between the critical points. The â€Å"power unit(s),† which can be hydraulic, pneumatic, electrical, or their combination, with or without mechanical transmissions. 2. 4 CLASSIFICATION OF ROBOTS Robot classification may be considered on the following basis: 1. Structural configuration and robot motion 2. Trajectories based on motion control 3. Performance characteristics of the robot. 2. 4. Classification based on structural configuration and robot motion. For this classification, three basic motions in the operation of robots need to be distinguished. Swivel motion- This is a rotation about the longitudinal axis of a link between two joints. Bending motion-this is a rotation about the transverse axis in the joint. Prismatic motion-this is a linear motion in t he direction of the longitudinal axis, either extensional or constructional (Eugene, 1988 pg 127-128). According to robots joint movements there are the following well distinguished basic robot configurations: i. Revolute (jointed arm) robot i. Polar (spherical)robot iii. Cylindrical robot iv. Cartesian (rectangular) robot, sliding-type v. Cartesian (rectangular) robot, gantry-type vi. SCARA- type robot 2. 4. 1. 1 Revolute (jointed arm) robot This is the type that best simulates a human arm, and is often referred to as an anthropomorphic robot. Because of this it is more easily adapted to an existing human workstation than any other type of robot. [pic] Figure 2. 1: Revolute Robot (Courtesy of; Reinventing Man, Pg 48) The revolute robot consists of three major rotary joints acting as the waist and elbow mounted at the end of the shoulder link. A typical example is Asea (IRb-6 Sweden) 2. 4. 1. 2. Polar (spherical) robot This robot rotates about the axis of its waist on the base. The second axis is a horizontal rotary joint, allowing the arm to rotate in a vertical plane. Making use of all the axes, the arm can sweep through a partial sphere. This mathematically corresponds to a polar coordinate system, thus this kind of robot is classified as polar. The third degree of freedom is provided by a prismatic joint built into the arm which allows it to move in and out. The robot can sweep through partial spheres of radii depending on the length of the prismatic joint. A typical example is Unimation (series 1000, 2000, 4000, US). [pic] Figure 2. 2: Cylindrical and Polar robot (Courtesy of; Reinventing Man, Pg 47) 2. 4. 1. 3 Cylindrical robot This robot consists of a base, a horizontal arm and a prismatic joint built into the horizontal arm. The whole base can move up and down. The horizontal arm swivels around the vertical column, describing a partial cylinder in space. This mathematically corresponds to a cylindrical coordinate system, thus this kind of robot is classified as cylindrical. A typical example is Prab (Model E, FA, FB, FC and Model G Series, Norway). 2. 4. 1. Cartesian (rectangular) robot, sliding type There are three perpendicular traversing axes, realized by an up/down, a left/right, and a forward/backward moving prismatic joint. This mathematically corresponds to a Cartesian coordinate system, thus this kind of robot is classified as Cartesian. Despite the fact that this robot is of high precision, it is not referred for many appli cations because of its difficult adaptability to the existing human- operated workstations. A typical example is DEA robot (Digital Electronic Automation SpA, Model Pragma A3000, Italy). 2. 4. 1. 5 Cartesian (rectangular) robot, gantry-type This type of robot has the same structure as the sliding type Cartesian robot. The only difference is that it has a gantry for keeping the robot in sliding operation. A typical example is IBM (7565, US) [pic] Figure 2. 3: Cartesian robot (Courtesy of; Reinventing Man, Pg 46) 2. 4. 1. 6. SCARA- type robot New robot kinematic configurations can be obtained by combining the properties of the basic robot representatives outlined above. For instance if the revolute and cylindrical robot kinematics are combined, the result will be a new type of robot called SCARA, where SCARA stands for Selective Compliance Assembly Robot Arm. Its rotary joints have vertical axes, allowing movement in a horizontal plane, which corresponds to both revolute and cylindrical coordinates. The SCARA configuration has vertical major axis rotations for which the gravitational load, Coriolis and centrifugal forces do not stress the structures as much as they would if the axes were horizontal. This advantage is very important at high speeds and high precision. The best examples are IBM (7535 and 7545. US), Meta Machines (adept one, UK) 2. 4. 2 Basic robot motions Whatever the configuration, the purpose of the robot is to perform a useful task. To accomplish the task, an end effector, or hand, is attached to the end of the robot’s arm. It is this end effector which adapts the general-purpose robot to a particular task. To do the task, the robot arm must be capable of moving the end effector through a sequence of motions and/or positions. [pic] Figure 2. 4: Basic robot motions (courtesy of An Introduction To Robot Technology pg 12) 2. 4. 2. 1 Six degrees of freedom There are six basic motions, or degrees of freedom, which provide the robot with the capability to move the end effector through the required sequence of motions. These six degrees of freedom are intended to emulate the versatility of movement possessed by the human arm. Not all robots are equipped with the ability to move in all six degrees. The six basic motions consist of three arm and body motions and three wrist motions, as illustrated in the figure below for a polar –type robot. These motions are described as follows: Arm and body motions: 1. vertical transverse: up-and-down motions of the arm, caused by pivoting the entire arm about a horizontal axis or moving the arm along a vertical slide 2. radial transverse: extension and retraction of the arm (in-and-out movement) 3. otational transverse: rotation about the vertical axis (right or left swivel of the robot arm) Wrist motions: 4. wrist swivel: rotation of the wrist 5. Wrist bend: up-or-down movement of the wrist, which also involves a rotational movement. 6. Wrist yaw: right- or- left swivel of the wrist. [pic] Figure 2. 5: Typical Wrist Articulations (Courtesy of; Reinventing Man, Pg 49) 2. 4. 3 Classification based on path control There are two basic forms of robot path control: 1. Point-to-point (PTP) control With point-to-point control the robot is programmed to pause at each point to plan the next step in a predetermined manner. Despite the fact that the motion is not controlled between the set points, it usually occurs along a natural path, depending upon the kinematic geometry of the robot. On the other hand the robot under continuous control can follow any arbitrary path accurately. A point-to-point controlled robot offers greater precision in terms of accuracy and repeatability. 2. 4. 3. 2Continuous path (CP) control The continuous path control results in a smoother movement along the defined trajectory but there is a speed penalty, which is a function of the step sizes computed by the master computer in real time using interpolation methods. The penalty may be a 15-25 % speed reduction, resulting in uneconomic control of the process, i. e. the efficiency will be lower compared with the same robot operating in point-to-point control mode. CHAPTER THREE 3. 0 ROBOT APPLICATIONS 3. 1 General application characteristics There are certain general characteristics of an industrial situation which tend to make the installation of a robot economical and practical (Poole, 1989). These include the following. ? Hazardous or uncomfortable working conditions. In job situations where there are potential dangers or health hazards due to heat, radiation, or toxicity, or where the workplace is uncomfortable and unpleasant, a robot should be considered as a substitute for the human worker. This sort of application has a high probability for worker acceptance of the robot. Examples of these job situations include hot forging, die casting, spray painting and foundry operations. ? Repetitive tasks If the work cycle consists of a sequence of elements which do not vary from cycle to cycle, it is possible that a robot could be programmed to perform the task. This is especially likely if the task is accomplished within a limited workspace. Pick and place operations and machine loading are obvious examples of repetitive tasks. ? Difficult handling If the work part or tool involved in the operation is awkward or heavy, it might be possible for a robot to perform the task. Operations involving the handling of heavy work parts are a good example of this case. A human worker would need some form of mechanical assistance to lift the part, which would add to the production cycle time. Some industrial robots are capable of lifting payloads weighing several hundreds (or even more than a thousand) pounds. Multishift operation If the initial investment cost of the robot can be spread over two or three shifts, the labor savings will result in a quicker payback. This could mean the difference between whether or not the investment can be justified. Plastic injection moulding and other processes which must be operated continuously are examples of multis hift robot applications. 3. 2 APPLICATION AREAS OF INDUSTRIAL ROBOTS Industrial robots have been applied to a great variety of production situations (Groover Zimmer, 1984 pg 257). These applications can be divided into the following seven categories: 1. Material transfer 2. Machine loading . Welding 4. Spray coating 5. Processing operations 6. Assembly 7. inspection 3. 2. 1 Material Transfer Material transfer applications are those in which the robot is used to move workparts from one location to another. In some cases a reorientation of the part may be required in this material handling function. Examples of material transfer robot operations include the following: Simple pick and place operations Transfer of workparts from one conveyor to another conveyor (basically a pick and place task) Palletizing operations, in which the robot takes parts from a conveyor and loads them onto a pallet in a required attern and sequence Stacking operations similar to palletizing Loading part s from a conveyor into cartons or boxes (similar to palletizing) Depalletizing operations, in which the robot takes parts which are arranged on a pallet and loads them onto a conveyor Material transfer operations are often among the easiest and most straightforward of robot applications (e. g. pick and place, transfer from conveyor to conveyor). Robots used for these tasks usually possess a relatively low level of technological sophistication. However in other cases the motion pattern can become somewhat complicated. . 2. 2 Machine Loading Machine loading applications are material handling operations in which the robot is required to supply a production machine with raw work parts and/or to unload finished parts from a machine. Machine loading is distinguished from material transfer operation by the fact that the robot works directly with the processing equipment. In material transfer functions it does not. In the typical application the robot will grasp a raw work part from a conv eyor and load it into a machine. In some cases, the robot holds the part in position during processing. When processing is completed, the robot unloads the part from the machine and places it onto another conveyor. Production operations in which robots have been successfully applied to perform the machine loading and unloading function include the following: Die casting Injection moulding Transfer moulding Hot forging Upsetting or upset forging Stamping press operations Machining operations such as turning and milling In die casting and plastic moulding, the robot only unloads the finished parts. For machining processes, the robot both loads and unloads the machine tool. In upsetting and stamping operations, the robot holds the work part while it is being processed by the machine. Some machine loading applications consist of several processing machines in a manufacturing cell, with the robot tending two, three, or even four separate machines. One of the more recent innovations in machine loading applications is to form a flexible manufacturing system using several robots to augment the conveyor system normally used in these production cells. 3. 2. 3 Welding The welding processes are very important application area for industrial robots. The applications logically divide into two basic categories, spot welding and arc welding. 3. 2. 3. 1Spot welding Spot welding is a process in which metal parts (sheets or plates) are fused together at localized points by passing a large electric current through the two parts at the points of contact. The process is implemented by means of electrodes which squeeze the parts together and conduct the current to the point of contact. The typical pair of electrodes have the form of tongs, which can conveniently be mounted on a large robots wrist as the end effector. Using the welding â€Å"gun,† as the electrode assembly is sometimes called; the robot accomplishes a spot weld by means of the following sequence: 1) Position the welding gun in the desired location against the two pieces 2) Squeezing the two electrodes against the mating surfaces 3) Weld and hold, when the current is applied to cause heating and fusion of the two surfaces in contact 4) Release and cool. The electrodes open and sufficient time is allowed to cool the electrodes in anticipation of the next spot weld This is the sequence that has been an ideal task for a point-to- point robot. pot welding has become one of the largest application areas for industrial robots, especially in the automotive industry. 3. 2. 3. 2 Arc welding Several types of continuous arc welding processes can be accomplished by industrial robots capable of continuous-path operation. These processes include gas metal arc welding and gas tungsten arc welding. These kinds of operations are traditionall y performed by welders, who must often work under conditions which are hot, uncomfortable, and sometimes dangerous. Such conditions make this a logical candidate for the application of industrial robots. However, there are several problems associated with arc welding that have hindered the widespread use of robots in this process. First arc welding is a fabrication process often used on low volume products. Hence the economics involved in these cases make the use of any automation difficult, robots included. Second, dimensional variations in the components being arc welded are common. Human welders can compensate for these variations. Robots can not, at least with current technology. Third, human welders are often required to perform their trades in areas which are difficult to access (inside vessels, tanks, ship hulls, etc. . Forth and finally, sensor technologies capable of monitoring the variations in the arc welding process have not yet been fully developed. As a result of these problems, robot arc welding applications have been fairly limited to operations involving high or medium volumes where the components can be conveniently handled and the dimensional variations can be reas onably managed. A typical robotic arc welding station would consist of the following components: A robot capable of continuous path control A welding unit consisting of the welding tool, power source, and the wire feed system A work part manipulator, which fixtures the components and positions than for welding The work station controller is equipped to control the wire feed and arc voltage with the robot’s arm movement the activities of the work part must also be coordinated by the controller. A human worker would be used to load and unload the work parts from the manipulator. There are several advantages attributed to a robot welding station compared with its manually operated counterpart. Among these are the following: Higher productivity Improved safety More consistent welds 3. 2. 4 Spray Coating Many large consumer products and most industrial products require the application of some form of paint. When human workers apply this paint, the most common method is spray painting. However the spray painting process poses certain health hazards to the human operator. Among these are: 1) Fumes and mist from the spr aying operation these create an uncomfortable and sometimes toxic atmosphere 2) Noise from the spray nozzle. This noise is loud and prolonged exposure can impair hearing. 3) Fire hazard. The mist of paint in the air within the factory can result in flash fires. 4) Possible cancer dangers. Certain of the ingredients used in the paint are suspected of being carcinogenic. Because of these health hazards, human workers are unenthusiastic about being exposed to the spray painting environment, and companies have been forced by law enforcement agencies to construct elaborate ventilating systems to protect their workers. For these and other reasons, specialized industrial robots are being used more and more frequently to perform spray painting and related processes. Spray painting requires a robot capable of executing a smooth motion pattern which will apply the paint or other fluid evenly and avoid rums. To accomplish this, the robot is equipped with continuous-path control. The paint spray nozzle becomes the end effector. To teach the robot, the walk through method is commonly employed. An operator-programmer manually leads the robot’s end effector through the desired paint spray path. This defines the motion sequence and relative speed for the work cycle. During playback, the robot repeats the cycle to accomplish the paint spray operation. Among the many advantages of using robots for spray coating applications are the following: 1. Safety: The many safety hazards encountered when human operators perform the spray painting process are reduced. 2. Coating consistency: Once the program is established, the robot will deposit the paint or other coating with the same speed, pattern and spray rate on every cycle. 3. Lower material usage: The robot’s repeatability and consistency reduce wasted paint. Savings in this category seem to range between 10 and 50%. 4. less energy used. This results from reduced ventilation requirements since the human operator is removed from the actual process. 5. Greater productivity: The paint spraying robot can perform the operation faster than its human counterpart. It can also be used at this faster pace for three shifts per day. 3. 2. 5 Processing Operations This is a miscellaneous category in which the robot is used to perform some manufacturing process other than welding or spray painting. Assembly and inspection operations are also excluded, and they are covered in the following sections. Just as in welding and spray painting, the processing operation is performed by specialized tool attached to the robot’s wrist as its end effector. The end effector is typically a powered spindle which holds and rotates a tool such as a drill. The robot will be used to bring the tool into contact with a stationary workpart during processing. In some applications which we will include within this category, the robot’s hand is used for gripping the workpart and bringing it into contact with a tool held in a fixed position. In the latter case, we begin to overlap with the types of machine loading applications covered earlier in this case. Some of the processing operations which have been performed by industrial robots include drilling, riveting, grinding, polishing, deburring, wire brushing, and water jet cutting. 3. 2. 6 Assembly Assembly operations are seen as an area with big potential for robot applications. Batch-type assembly operations seem to offer operations seem to offer the most promise for using robots. The reason for this is based on economics and the technological capabilities of the robot. For mass production assembly, the most economical method involves fixed automation, where the equipment is designed specifically to produce the particular product. A robot would probably be too slow for mass production, and one of the robot’s most important attributes, its programmability, would hardly be used. In batch assembly, there are variations in products and the demand for each product is significantly lower than in mass production. Consequently, the assembly line in batch manufacturing must be capable of dealing with this product variation and the line changeovers that are necessitated. What is basically required for batch production is a flexible assembly system. The term that some companies use for such a system is adaptable-programmable assembly system (APAS), and robot-type arms constitute and important component of these systems. The APAS will be composed of both conventional material handling devices (conveyors, parts feeders, etc) and robot arms probably in an inline arrangement. The robot arms will be used for some parts handling duties, but its main function will be assembly. Robot assembly operation would typically require an extension of the robots material transfer capability. Many sub-assemblies consist of a stack of components on top of a base part. To put together the sub assembly requires the placement of one part on top of the base and then the other part on top of that, and so forth. The robot is certainly capable of this sort of work cycle. Assembly tasks requiring a special skill or judgment which the robot is not capable, would be performed by human workers. The feature of an industrial robot that make it suitable as a component of an APAS line are its programmability and its adaptability. Programmability is required so that a relatively complex motion cycle can be carried out during the assembly operation. Also, the APAS must be capable of storing multiple program sets to facilitate the differences in products assembled on the line. On this sense the system the system would be adaptable to changes in product style. Adaptability is also required in the sense that the assembly system would have to compensate for changes in the environment. These environmental variations include: Variations in the position and orientation of assembly components Out – of- tolerance and defective parts The current state of completion of the sub assembly Detection of human beings or objects intruding on the robot work volume 3. 2. 7 Inspection Like assembly, inspection is a relatively new area for the application of industrial robots. Traditionally, the inspection function has been a very labor intensive activity. The activity is slow, tedious, and boring, and is usually performed by human beings on a sampling basis rather than by 100% inspection. With ever increasing emphasis on quality in manufacturing, there is a trend toward automating the inspection process and toward the use of 100% inspection by machines instead of sampling inspection by human beings. An important role in this area of inspection automation will be played by industrial robots. Robots equipped with mechanical probes, optical sensing capabilities, or other measuring devices can be programmed to perform dimensional checking and other forms of inspection operations. CHAPTER FOUR 4. TRAINING 4. 1 INTRODUCTION General education is received by all during the years spent in school. This is intended to form a basis on which people can build further levels of education and training to suit specific work roles (Timings et al, 1999). As a graduate trainee having first obtained an honours degree in Engineering, on joining a medium or large firm that has suitable training schemes ‘on job’ training will be done and several years of study and training are required so as to attain very high standards. A way needs to be sought to help shorten this period. 4. 2 APPLICATION OF ACQUIRED SKILLS The qualifications and skills gained through the right and relevant training can be applied to various roles of administration in the manufacturing industry. For example; 4. 2. 1 Middle managers These are professionally trained people who are still gaining management training. They are usually university graduates in various disciplines who have passed the qualifying examination of their appropriate professional institution. They assist senior managers by heading the divisions within departments and are to continually update their knowledge of changes in technology 4. 3 TREND IN KENYA In Kenya programmable automation is still at a relatively early stage of development and an even earlier stage of application, but then there is already a discernible trend away from the fragmentation of tasks towards a broadening of technical skills. This trend with the right and timely kind of training will grow stronger and stronger. Among the already discernible trend we have: a) The elimination of the distinction between manual and intellectual work. What is emerging is a division between high-skilled and low-skilled work. b) Need for further training due to the higher skill requirements and the need for flexibility c) Change of manager’s job from one of close supervision of personnel to that of overseeing a complex network of interrelationships within a department and between other departments. d) Decentralization of the functions of management and production control. The work group is being seen as the more desirable form of organization. The challenge in Kenya now lies with the introduction of broad based training at all levels. This will help develop compatible work organization that will bring together programmable automation technology on the one hand and graduates with a broad, general understanding of the production process on the other hand. Graduates need to be well equipped to be able to carry out the challenging tasks, they will find in working environments they will end up in considering the rate at which improved technology is being embraced. 4. REASONS WHY KENYAN FIRMS NEED WELL TRAINED GRADUATES FROM LEARNING INSTITUTIONS The vision 2030 can only be attained if among other reasons, our country can be in a position to manufacture and sell products within and outside the country and still withstand the various forms of competition from products from the economic giants like China and India. Because emphasis has always been on small an d medium sized companies, use of programmable automation needs to be embraced to help these companies to be motivated principally by a desire to keep with technical change so as to remain competitive. This can also help improve technical quality of products and also ensure faster production. Because of new technology and the economic situation, training methods that have been normal practice are gradually disappearing for example lengthy apprenticeships and in-house training. This now calls for many people, particularly the young people to enter into new areas of study either just at the start or throughout the course of their whole career in educational institutions. This will ensure that future recruits to any job won’t need much in-house training. The current needs’ qualifications and skills will gradually decline as well as the current training methods and career opportunities, therefore educational institutions need to ensure that they don’t just end up in redundancy. Training needs also to be done so as to be an assurance of safety. The number of accidents may fall due to improved technology but the severity i. e. the risk of untrained personnel is greater especially during repairing or maintaining of robots. Most future employees need to fully realize all the benefits envisaged from the implementation of new systems all based on technological advancement. This is with the sole objective of attaining improved productivity and efficiency which might not be attained with the conventional manual methods. This sounds a warning to all trainees that no employee will wish to recruit someone with the full knowledge that one is not having, even in the least, knowledge on the latest technology of automation. 4. 5 TYPES OF TRAINING There are different types of training that can be performed about improved technology. These are: awareness training, basic user training, advanced application user training, manager and supervisor training and system management training. At whatever capacity in industry, knowledge is very important. After college people end up being either direct users of technology e. g. drafters, designers or managers and supervisors working in different areas such as mechanical engineering, electronic engineering, hydraulic and electric circuit design, NC part programming, sheet metal development, piping layout among others. To be fitted for such fields enough training needs to be done in depth and broadly with the knowledge that training is a practical exercise involving real people in the real world and not a theoretical exercise carried out with perfect students having identical and complete knowledge, experience and skills (Stark, 1988). The cheapest source of training is the one offered at educational institutions though the skill gained can range from poor to excellent. To equip the students or trainees with awareness on technology, the following can be used: Journals and magazines, Exhibitions, Conferences and seminars, Courses, Consultants, Open-learning- which allows the trainee the opportunity to learn wherever, whenever and at whatever pace. Awareness programs of seminars, literature, videos sponsored by industry associations, government departments and educational institutions. To offer effective result, coupling all these sources of awareness with practical and hands-on experience is of paramount importance. If one of the main aims of teaching is to build confidence, and confidence is acquired as a result of experience, then it follows that for any teaching process to be effective it has to be about promoting and extending opportunities to experience the subject. CHAPTER FIVE 5. 0 DESIGN ANALYSIS 5. 1 DESIGN ALTERNATIVES Alternative 1 Figure 5. 1 Alternative design 1 Figure 5. 2 Alternative design 2 5. 1. 1 Comparison of alternatives |Parameters |Alternative 1 |Alternative 2 | |1. Complexity of mechanism |simple |complex | |2. Cost at a glance |expensive |cheaper | |3. Technology of part production |involving |simple | |4. Power transmission |Adequate access |Limited means | |5. Safety |safer |Less safe | |6. Gripper mechanism | Simple and efficient |Simple and efficient | |7. Size |smaller |small | |8. Efficiency |More efficient |Less efficient | |9. Performance |excellent |good | |10. Reliability |excellent |good | From this comparison alternative 1 was chosen. Though the cost at a glance is high and technology of part production is involving and a little bit costly, it’s chosen because it is superior in the other comparison parameters. 5. 2 SPECIFICATIONS 5. 2. 1 Task Specifications 5. 2. 1. 1 Performance Specifications The designed system is to grasp a box of shape shown below, from a working table [pic] Figure 5. 3 Shape of object to be grasped Lift it up to gain a clearance from the working table surface Carry it through the required angle to some new position on another table. The load or box should then be brought to the surface of the new table after which the load is released. After release the arm moves to the initial position ready to repeat the sequence. 5. 2. 1. 2 Design Specifications Grasping of box or load is achieved through the gripper shown below. The gripper is operated by a chain and sprocket mechanism which is powered by a motor. The lifting action is achieved through a rack and pinion arrangement. The pinion is driven by a motor via a belt arrangement. Rotation is achieved through a motor driven gearbox. This motion is transmitted to the rotating member (shaft) through a flange coupling and to the entire design through a woodruff key. After rotating, reverse rotation of the motor helps give reverse rotation of the pinion. This helps lower the load to the surface of the second work table. Release of the load is through reverse in rotation of the motor driving the chain and sprocket arrangement. A reverse in the rotation of reduction gearbox helps the entire system back ti the initial position ready for the next task. 5. 2. 1. 3 Dimensional Specifications Figure 5. 4 Determination of principal dimensions Maximum height-1m Maximum reach-0. 5m Maximum lift of beam-0. 4m Maximum opening of gripper-50mm 5. 3 EXTENT OF THE ANALYSIS The more detailed parts of the analysis have been confined to the gripper mechanism. Other design features concerned with functional efficiency are examined and commented on in less detail. Comments on the belts, hollow sections, chains, and sprockets, fasteners, washers, couplings, safety actors, keys and keyways are confined to general descriptive notes. Finally an assessment is made of the whole machine in relation to functional, aesthetic and ergonomic criteria. 5. 4 GRIPPER MECHANISM ANALYSIS [pic]Figure 5. 5 Gripper mechanism 5. 4. 1 Gripping Force Consider the end section of the gripper with all forces indicated as shown below. [pic] Figure 5. 6 End section of gripper Let Mg-weight of object being picked P1 – Gripping force –acting on both sides to ensure no slip. They share the weight of the object. P1 = µN Where N- normal reaction that is perpendicular to the surface of the object  µ-coefficient of friction NB: N=P2 From balancing of forces in the y-direction 2P2 = Mg P2 = [pic]=N Since P1 =  µN Then P1 = [pic] Let the mass of the object = 10Kg. The mass of Most of the components that can be handled in the mechanical engineering workshops during laboratories range between 1Kg and 10Kg. the higher value is taken to even cater for the intermediate weights. From appendix of typical coefficient of static friction values for various material combinations: The value of coefficient of friction,  µ, will range from 0. 30-0. 60 i. e. For steel-woven asbestos. Taking the lower  µ then,  µ=0. 30 P1 = [pic] = [pic] = 14. 715N Total clamping force = P1+ P1 = 29. 3 N 5. 4. 2 Torque required to produce desired clamping force-Power screws Standard bolts with 60? threads are widely used to impart a clamping force T= W [[pic][pic] Where T= torque applied to turning screw W= load parallel to screw axis rm= mean thread radius rc= effective radius of rubbing surface against which load bears, called collar ra dius f= coefficient of friction between screw and sprocket gripper threads fc= coefficient of friction at collar ? = helix angle of thread at mean radius ?n = angle between tangent to tooth profile (on the loaded side) and a radial line, measured in plane normal to thread helix at mean radius. Illustration of edge [pic] Figure 5. 7 Power screw motions Alternatively, The average value of the tightening or clamping Torque, T can be shown to be: For, Course thread,  µ = 0. 15 T= 0. 195dw Course thread,  µ = 0. 10 T= 0. 135dw Fine thread,  µ = 0. 15 T= 0. 189dw Fine thread,  µ = 0. 10 T= 0. 130dw Diameter, d in these equations is the major or nominal diameter (illustration above) Values of coefficient of friction for the threads of translation screws have been determined by investigations and have been found to depend on the quality of materials, workmanship in cutting threads, degree of â€Å"running in† of the threads and lubrication. Published articles on experiments for screw-thread friction indicate that the following values would be a good estimate of the coefficient of friction. * Mean value of  µ = 0. 15 Range of variation  ± 33% Let the nominal diameter = 0. 5† T= 0. 195 x d x w = 0. 195x 0. 5 x29. 43 = 2. 87 Nm The screw threads are on two sides Therefore Total torque =2T = 2x 2. 87 = 5. 74 Nm *Lambert, T. H. , â€Å"Effects of Variations in the Screw –Thread Coefficient of Friction on the Clamping Force of Bolted Connections,† J. Mech. Eng. Sci. , 4, 1962, P. 401. 5. 4. 3 Power Required Let the gripper grip the object in 2seconds Let the smallest component it can hold be 50mm Therefore from the plan view of the gripper above (fig. ) the distance, s it is supposed to cover to clamp the load is: s= [pic] =75mm Since the power screw is double-threaded. Linear speed, ? = [pic] = [pic] = [pic] = 0. 0375 m/s Let the pinion diameter = 20mm Then from, ? =? r ? = [pic] =3. 75 rads/sec Since both sides move. Number of revolutions ?= [pic] [pic] = [pic] =35. 81 r. p. m Power, P P= T ? = 5. 74 x35. 81 = 205. 5W 5. 4. 4 Pins Two pins are used in the knuckle joint connecting the bars of the gripper that is in tension. 5. 5 HOLLOW SECTIONS Hollow sections are used in this design. These sections are more recent than channels, tees and angles. The chief advantage of the hollow form lies in the combination of rigidity, strength and lightness resulting from the metal being distributed around rather than on the axes of the section. Hollow circular sections give great torsional rigidity because of the relatively high polar second moment of area, and equal resistance to bending in all planes because of the symmetry of the cross-section. Another advantage of the hollow section is the smaller external surface area requiring painting (about 30-40% less than an equivalent rolled steel solid section. and hence the lower maintenance costs involved. Also, the convex surface of a tube does not provide recesses in which moisture can be retained, so reducing the possibility of corrosion on the outside. The joining of hollow structural members too, is easy through welding (metal arc welding) 5. 6 BELT A V-belt was chosen for this design because of these advantages: Compactnes s of design-the center distance in this particular design is small. Smoothness which is possible because the V-belt is endless. Bearing life-because of lower belt tensions, lower bearing loads are possible. Also, since this type of belt readily absorbs shock, bearing life is lengthened. Dependability- Maintenance- except for occasional tightening of the drive(required to correct stretching and creeping), little maintenance is required. 5. 6. 1 Dimensions of belt cross sections The V-belt must fit the pulley so that it does not make contact with the bottom of the groove. This arrangement avoids any radially outward reaction from the groove bottom, and eliminates the possible formation of a cushion of air being entrained at high belt speeds, either of which would tend to force the belt away from the groove sides and so slip. Belt dimensions corresponding to their cross section symbols are given in appendix II 5. 7 FASTENERS Fasteners are devices that permit one machine part to be joined to the second part. Hence, fasteners are involved in almost all designs; this design being no exception. The acceptability of any product depends not only on the selected components but also on the means by which they are fastened together. The principal purposes of fasteners are to provide the following design features: ? Disassembly for inspection and repair ? Modular design where a product consists of a number of sub-assemblies. There are three main classifications of fasteners: Removable- this type permits the pars to be readily disconnected without damaging the fastener. An example is the ordinary nut and bolt fastener. Semi-permanent- for this type the parts can be disconnected but some damage usually occur to the fastener. One such example is a cotter pin. Permanent- this type is used when it is intended that the parts will never be disassembled for example rivets. The following factors were taken into consideration in the selection of fasteners for this application: i. Primary function of fastener ii. Appearance iii. A large number of small-size fasteners versus a small number of large-size fasteners ( an example is bolts) iv. Operating conditions such as vibration loads and temperature v. Frequency of disassembly vi. Adjustability in the location of parts vii. Types of materials to be joined viii. Consequences of failure or loosening of the fastener. 5. 8 WASHERS Washers are frequently used with bolted fasteners. The most common type is the plain washer. Such a washer increases the bearing area under the nut or head of a bolt. Hence, plain washers are used to protect mating surfaces of bolted parts. They are especially needed when the parts are made of soft metals that can be easily damaged by a turning nut or bolt head during tightening. Lock washers are used to keep bolted fasteners from loosening. One type provides a spring force that helps maintain the desired bolt tension. In another type the lock washer has protruding teeth that dig into the fastener and mating parts and prevents loosening. Sometimes it is absolutely necessary that a bolted fastener not come loose even as a result of vibration. In such cases, a positive type lock washer is used. This type of washer contains a tab that is bent up against the flat portion of the nut or bolt head. The tab prevents rotational motion of the nut or bolt head. 5. 9 COUPLINGS Coupling refers to a device used to join two shafts. Shaft couplings are also required to couple machines manufactured separately e. g. electric motors with pumps. 5. 9. 1 Flange coupling This is the one that has been used in this design. This is a rigid type of coupling used for connecting shafts; 18-200mm diameter. Two flanges are used to join coaxial shafts; two cast iron flanges keyed to the ends of shafts, fastened together by means of a number of tight fitting bolts. Advantages Simple in design Cheap Dependable Require less maintenance Can transmit high torques The torque is transmitted by frictional forces acting between the faces of the coupling halves or it is transmitted by the connection bolts which are subjected to shear. The bolts work in shear only when they are precisely fitted without any clearance in the mounting holes. Disadvantages Unsuitable for absorbing shock loads No flexibility- incapable of equalizing effects of misalignment Difficult to loosen hence, wheels, pulleys and other mounted parts have to be in two parts. 5. 9. 2 Derivation of flange coupling formula First, it is assumed that none of the torque is transmitted as a result of friction between the interface of two flanges. This assumption is conservative because the clamping force of the bolts is quite large . However, frictional forces are unpredictable especially if the bolts undergo relaxation. We are therefore assuming that all the torque is transmitted through the bolts. For equilibrium, the summation of each bolt shear force multiplied by its moment arm to the centre of rotation equals to the torque, T. The torque is given by: T =Fb xZx [pic] =Ab x ? x Z x [pic] Where Fb –circumferential force on each bolt Z- Number of bolts K- Bolt circle diameter Ab –x-sectional area of each bolt The equation assumes that the load is equally shared by each bolt. That is each bolt must fit tightly in each hole without any radial clearance. The shear stress ? is taken to be 0. 25 the yield strength of the bolt material For calculation purposes, an Impact Factor is taken into account. This is given by: Tmax= C x Tnom Where Tmax -maximum torque Tnom -nominal torque C- Impact Factor 5. 10 SAFETY FACTORS Allowable stress This is the safe limiting stress, which is predetermined by taking cognizance of the operating conditions of the designed part. This strength criterion is also sometimes called working stress or permissible stress. Normally, to safeguard against permanent set or plastic deformation, the allowable stress is kept well within the elastic limit or yield point The following are relations for the static working conditions: Ductile material Allowable stress = [pic] Brittle material Allowable stress = [pic] Where F-factor of safety scf- stress concentration factor The factor of safety is a design criterion. The selection is at the discretion of the designer based on experience, authorities, and level of knowledge. The safety factor is very important as it is used to account for the unknown aspects and the various uncertainties. In this design a factor of safety of 1. 25 has been taken. 5. 11 KEYS AND KEY-WAYS A key is a rigid connector between a shaft and the hub of another component such as a pulley. A key helps prevent relative rotation between the parts. If a key is to be used a key seat must be provided in the shaft and a keyway in the hub of the other part. A key seat weakens the shaft and this forces a reduction in the design stress. 5. 11. 1Wood ruff key This is a spherical type of sunk key. It is semi circular in shape and is cut from a round bar or disk. The key seat in the shaft is also semi-circular in shape in which the key fits. The top of the key fits into a plain rectangular keyway in the hub and the key seat is equal to the thickness of the key. The key way is just half key seat. The key can be easily adjusted in the recess. It is largely used on machine tools and automobile work. It accommodates itself to any taper in the hub of the mating surface. It is used on tapering shaft ends. Figure 5. 8 Woodruff key CHAPTER SIX 6. 0COMPONENT PRODUCTION 6. 1 PARAMETERS FOR OPTIMUM PRODUCTION Optimum production is associated to the following parameters; 6. 1. 1 Product Analysis The elements of product analysis that should be taken into account are: i. Nature, kind and properties of raw materials i. Quality specifications and tolerances iii. Quantity to produce 6. 1. 2 Operation Analysis On the basis of tentative ideas of product analysis operation analysis is done. For operation analysis it is necessary to decide: i. what operation should be done ii. sequence to follow so that the desired product could be made economically 6. 1. 3 Machine Analysis It is necessary to know which machine should be used for a particular operation so that economy of production is maintained 6. 1. 4 Operator Analysis On the basis of the tentative ideas of machine analysis, operator analysis is done. For handling different machines different type of operator is needed. This may be skilled, semi-skilled or unskilled. 6. 2 RESOURCE REQUIREMENT The following resources are needed for the production exercise: 6. 2. 1 Capital Resources The available capital resources include machinery and manufacturing equipment in the mechanical engineering department workshops. These include: lathe machines, drilling machine, milling machine 6. 2. 2 Tooling Resources The available tooling resources are the consumables like the cutting tools which include; drills, lathe tools, milling cutters and the specific jigs and fixtures for machining and/or welding. 6. 2. 3 Material Resources The materials required in the manufacture include: Raw materials like metal bars and metal sheets Standardized finished components such as nuts and bolts, washers, bushes, bearings Subassemblies like the electric motors 6. 2. 4 Human Resources The technicians in the mechanical and production workshops are to be involved directly or ind