UNIVERSITY OF PUNE A PROJECT REPORT ON AN INNOVATIVE MULTI-DOF ROBOTIC ARM ASSEMBLY FOR PRESS SHOPS SUBMITTED BY MANDAR HARSHE COLIN MENEZES BHUSHAN WALZADE B3320815 B3320828 B3320850 UNDER GUIDANCE OF PROF. L. G. NAVALE DEPARTMENT OF MECHANICAL ENGINEERING MODERN EDUCATION SOCIETY’S COLLEGE OF ENGINEERING PUNE- 411001 YEAR 2006-2007 Modern Education Society’s College Of Engineering Pune – 411001 CERTIFICATE THIS IS TO CERTIFY THAT THE PROJECT REPORT AN INNOVATIVE MULTI-DOF ROBOTIC ARM ASSEMBLY FOR PRESS SHOPS SUBMITTED BY ENTITLED MANDAR HARSHE COLIN MENEZES BHUSHAN WALZADE B3320815 B3320828 B3320850

IN PARTIAL FULFILLMENT FOR THE AWARD OF DEGREE OF B. E. (MECHANICAL ENGINEERING) OF THE UNIVERSITY OF PUNE, PUNE IS APPROVED. PROF. L. G. NAVALE Project Guide Mech. Engg. Dept. PROF. V. N. CHOUGULE H. O. D. Mech. Engg. Dept DR. L. G. NAVALE Principal MESCOE, Pune. EXAMINER Acknowledgements We would like to express our sincere thanks to Mr. Hemachandra Shrotri, M. D. of Nirmiti Stampings Pvt Ltd, for giving us an opportunity to work on this project. His vast experience and guidance have been especially valuable to us. We are also grateful to Prof. L. G. Navale for his inspiration and guidance. Prof.

K. H. Munde helped us in the initial stages of the work, and his inputs resulted in the publication of a paper in the International Conference on Advances in Machine Design and Industry Automation 2007. We are extremely grateful for his help. We would like to thank Prof. V. N Chougule, the head of the Mechanical Department, for allowing us to undertake this project and provide us the necessary help. We received valuable help on the electrical and electronics aspects of the project from Prof. Aasma Shaikh of the Electronics & Telecommunication Department, Prof. Mrs. Dharmadhikari and Prof. B. H.

Deshmukh of the Electrical Department. Prof. V. Sugur and Prof A. Mitra of the Mechanical Department helped us in matters concerning their specializations. Details and technical support on the various products available in the market are especially hard to come by. In this regard, we thank the technical staff of Srijan Control Drives Ltd, Festo Controls Pvt. Ltd, Albro iii Engineers and Armatech Pvt. Ltd for their help and patience in explaining the various products available and helping us select those suitable for our application requirements. We would like to thank Mr. Satish Nikam of Nirmiti Stampings Pvt.

Ltd, who was in charge of the manufacturing works of the project. A project of such a wide spectrum requires inputs from numerous ? elds. We are thankful to the faculty of our department and also to all our colleagues who helped us with their inputs at various stages of the project. Finally, we would like to thank our colleagues Mr. Parikshit Dhodapkar, Mr. Gaurav Kakati and Mr. Paresh Panditrao,of the E&TC Department, who worked on the electronic controls of the robot and Mr. Nitant Harani of the Mechanical Department for helping us in Finite Element Analysis of the manipulator. Mandar Harshe Colin Menezes

Bhushan Walzade iv CONTENTS v Contents Certi? cate Acknowledgements List of Figures List of Tables Abstract I Company Pro? le II Problem Analysis Problem Description i iii viii xii 1 2 11 12 Robot Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1 Literature Survey 14 1. 1 Robotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1. 1. 1 1. 1. 2 1. 1. 3 Robot Anatomy . . . . . . . . . . . . . . . . . . . . . . . 15 Robot Motions . . . . . . . . . . . . . . . . . . . . . . . . 15 Work Volume . . . . . . . . . . . . . . . . . . . . . . . . . 19 CONTENTS 1. 1. 4 1. 1. 5 1. 1. 6 1. . 7 1. 1. 8 vi Robot Drive System . . . . . . . . . . . . . . . . . . . . . 19 Control Systems . . . . . . . . . . . . . . . . . . . . . . . 21 End Effectors . . . . . . . . . . . . . . . . . . . . . . . . 21 Grippers . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Robotic Sensors . . . . . . . . . . . . . . . . . . . . . . . 25 1. 2 Stepper Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1. 2. 1 1. 2. 2 1. 2. 3 1. 2. 4 1. 2. 5 1. 2. 6 De? nition of a Stepper Motor . . . . . . . . . . . . . . . 27 Step Angle ? s : . . . . . . . . . . . . . . . . . . . . . . . . 28 Steps/Revolution (Z): . . . . . . . . . . . . . . . . . . . 28 Step Angle Accuracy: . . . . . . . . . . . . . . . . . . . . 31 Static Characteristics: . . . . . . . . . . . . . . . . . . . 31 Dynamic Characteristics: . . . . . . . . . . . . . . . . . 34 1. 3 Pneumatics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1. 3. 1 1. 3. 2 1. 3. 3 1. 3. 4 1. 3. 5 1. 3. 6 1. 3. 7 Features of Pneumatics . . . . . . . . . . . . . . . . . . 34 Basic Pnuematic System . . . . . . . . . . . . . . . . . . 36 Pipe Materials . . . . . . . . . . . . . . . . . . . . . . . . 37 Air Compressor . . . . . . . . . . . . . . . . . . . . . . . 8 FRL Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Pneumatic Cylinders . . . . . . . . . . . . . . . . . . . . 40 Direction Control Valve . . . . . . . . . . . . . . . . . . . 41 43 2 Initial Ideas – Alternate Designs 2. 1 Cartesian Con? guration . . . . . . . . . . . . . . . . . . . . . . . 43 2. 2 Spherical Con? guration . . . . . . . . . . . . . . . . . . . . . . . 44 2. 3 Planar Con? guration with Pulleys . . . . . . . . . . . . . . . . . 46 2. 4 End Effectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3 Final Mechanism Description 48 CONTENTS vii III Robot Design 4 First Arm 1 52 4. 1 Prototype 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4. 1. 1 4. 1. 2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Component Design . . . . . . . . . . . . . . . . . . . . . 54 4. 2 Prototype 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4. 2. 1 4. 2. 2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Component Design . . . . . . . . . . . . . . . . . . . . . 57 72 5 Second Arm 5. 1 Prototype 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 5. 1. 1 5. 1. 2 Components and Design . . . . . . . . . . . . . . . . . 76 Design Analysis . . . . . . . . . . . . . . . . . . . . . . . 76 5. 2 Prototype 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5. 2. 1 5. 2. 2 6 Third Arm Components and Design . . . . . . . . . . . . . . . . . . 85 Design Analysis . . . . . . . . . . . . . . . . . . . . . . . 86 104 6. 1 Initial Proposals . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 6. 2 Final Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6. 3 Components Design and Actuator Selection . . . . . . . . . . . 106 7 Electronics and Control 8 Manufacturing Drawings & Process Sheets 121 124

IV Discussion & Conclusions References 152 161 List of Figures 1 2 3 4 5 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 1. 7 1. 8 1. 9 Shop Floor Layout . . . . . . . . . . . . . . . . . . . . . . . . . Shop Floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 7 8 9 Company Products . . . . . . . . . . . . . . . . . . . . . . . . . 250 Ton Pneumatic Press . . . . . . . . . . . . . . . . . . . . . Tooling used for the Pneumatic Press . . . . . . . . . . . . . . Basic robot anatomies . . . . . . . . . . . . . . . . . . . . . . . 16 Types of joints in robots . . . . . . . . . . . . . . . . . . . . . 18 DOFs associated with polar robots . . . . . . . . . . . . . . . 18 Three degree of freedoms associated with the robot wrist. . . 20 Work volumes for robot anatomies . . . . . . . . . . . . . . . . 20 Cost vs. size for electric drive and hydraulic drive . . . . . . . 22 Venturi actuated suction cups . . . . . . . . . . . . . . . . . . 26 Positional Accuracy . . . . . . . . . . . . . . . . . . . . . . . . 32 Torque Angle Curve . . . . . . . . . . . . . . . . . . . . . . . . 32 1. 10 PM Hybrid Motor Torque and Detente Torque Pro? les . . . . 33 1. 11 Torque-Current Curve . . . . . . . . . . . . . . . . . . . . . . 33 1. 12 Torque-Speed Characteristics . . . . . . . . . . . . . . . . . . 35 1. 13 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . 35 1. 14 FRL unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 1. 15 FRL unit: Symbol . . . . . . . . . . . . . . . . . . . . . . . . . 39 1. 16 Double Acting Cylinder . . . . . . . . . . . . . . . . . . . . . . 42 1. 17 5/2 D. C. valve . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 viii LIST OF FIGURES 2. 1 2. 2 3. 1 4. 1 4. 2 4. 3 4. 4 4. 5 4. 6 4. 7 4. 8 4. 9 ix Cartesian con? guration . . . . . . . . . . . . . . . . . . . . . 45 Spherical con? guration . . . . . . . . . . . . . . . . . . . . . . 45 Block Diagram of robotic assembly . . . . . . . . . . . . . . . 49 Lifting arm: First Design . . . . . . . . . . . . . . . . . . . . . 53 Lifting Arm: Final Design . . . . . . . . . . . . . . . . . . . . . 56 Pneumatic Circuit for Gripper . . . . . . . . . . . . . . . . . . 58 Stress Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Vacuum generator . . . . . . . . . . . . . . . . . . . . . . . . . 64 Velocity and Acceleration experienced by Gripper . . . . . . . 67 Force and moments experienced by Gripper . . . . . . . . . 68 Suction Gripper . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Push-in Y connector . . . . . . . . . . . . . . . . . . . . . . . . 70 4. 10 Socket Connector Cable . . . . . . . . . . . . . . . . . . . . . . 70 5. 1 5. 2 5. 3 5. 4 5. 5 5. 6 5. 7 5. 8 5. 9 Path travelled by transferring arm . . . . . . . . . . . . . . . . 73 Transferring arm, ? rst design . . . . . . . . . . . . . . . . . . 81 Joint Displacements . . . . . . . . . . . . . . . . . . . . . . . . 81 Joint Velocities . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Joint Accelerations . . . . . . . . . . . . . . . . . . . . . . . . 82 Transferring arm, ? nal design . . . . . . . . . . . . . . . . . . 84 Meshing for Bracket . . . . . . . . . . . . . . . . . . . . . . . . 87 Boundary conditions for bracket analysis . . . . . . . . . . . 88 Stress Distribution in Bracket . . . . . . . . . . . . . . . . . . 88 5. 10 Joint Displacements . . . . . . . . . . . . . . . . . . . . . . . . 92 5. 11 Joint Velocities . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 5. 12 Joint Accelerations . . . . . . . . . . . . . . . . . . . . . . . . . 102 5. 13 Joint Torques & Velocity . . . . . . . . . . . . . . . . . . . . . 03 LIST OF FIGURES 6. 1 6. 2 6. 3 6. 4 6. 5 6. 6 6. 7 6. 8 6. 9 x Unloading Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Pneumatic Circuit for Unloader . . . . . . . . . . . . . . . . . 108 Pneumatic Cylinder . . . . . . . . . . . . . . . . . . . . . . . . 108 Solenoid Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Solenoid Coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Foot mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Mounting Kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Proximity Sensors . . . . . . . . . . . . . . . . . . . . . . . . 114 Push-in Fitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 . . . . . . . . . . . . . . . . 120 6. 10 Cylinder speed/position Vs Time 6. 11 Cylinder acceleration/pressure Vs Time . . . . . . . . . . . . 120 8. 1 8. 2 8. 3 8. 4 8. 5 8. 6 8. 7 8. 8 8. 9 First Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 First Arm – Part List . . . . . . . . . . . . . . . . . . . . . . . . 126 Lead Screw for First Arm . . . . . . . . . . . . . . . . . . . . . 127 Support Bush for First Arm . . . . . . . . . . . . . . . . . . . 127 Nut for Lead Screw of First Arm . . . . . . . . . . . . . . . . 128 Bearing Cap for First Arm . . . . . . . . . . . . . . . . . . . . . 128 Base for First Arm . . . . . . . . . . . . . . . . . . . . . . . . . 129 Base Frame of First Arm . . . . . . . . . . . . . . . . . . . . . 130 Translating Beam of First Arm . . . . . . . . . . . . . . . . . . 131 8. 10 Suction Cup holder of First Arm . . . . . . . . . . . . . . . . . 132 8. 11 Second Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 8. 12 Part list for Second Arm . . . . . . . . . . . . . . . . . . . . . . 134 8. 13 Base Plate of Second Arm . . . . . . . . . . . . . . . . . . . . 135 8. 14 Lead Screw of Second Arm . . . . . . . . . . . . . . . . . . . . 136 8. 15 Nut for Lead Screw of Second Arm . . . . . . . . . . . . . . . . 136 8. 16 Support Rod & Bush of Second Arm . . . . . . . . . . . . . . 137 8. 17 Arm Platform of Second Arm . . . . . . . . . . . . . . . . . . . 138 LIST OF FIGURES xi 8. 18 Top Plate of Second Arm . . . . . . . . . . . . . . . . . . . . . 138 8. 19 Bracket for motor in Second Arm . . . . . . . . . . . . . . . . 139 8. 20 Bracket for motor of Second Arm . . . . . . . . . . . . . . . . 140 8. 21 Clamp for magnet holder of Second Arm . . . . . . . . . . . 140 8. 22 Magnet holder of Second Arm . . . . . . . . . . . . . . . . . . 141 8. 23 Third Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 8. 24 Part List for Third Arm . . . . . . . . . . . . . . . . . . . . . . 143 8. 25 Lifter Assembly of Third Arm . . . . . . . . . . . . . . . . . . . 144 8. 26 Square Nut of Third Arm . . . . . . . . . . . . . . . . . . . . . 145 8. 27 C plate of Third Arm . . . . . . . . . . . . . . . . . . . . . . . . 146 List of Tables 1. 1 Comparison of different drive systems . . . . . . . . . . . . . . 22 1. 2 Comparison of Stepper Motors . . . . . . . . . . . . . . . . . . 30 1. 3 Relation between ? s and Nr for PMH stepper motor . . . . . . . 32 1. 4 Pressure rating of pipe materials . . . . . . . . . . . . . . . . . . 39 4. 1 Lifting Arm – Speci? cations of ? rst prototype . . . . . . . . . . 53 4. 2 Lifting arm – Speci? cations of prototype 2 . . . . . . . . . . . . 56 4. 3 Mesh Information for Bracket . . . . . . . . . . . . . . . . . . . 63 4. 4 Stress Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4. 5 Vacuum Generator: Datasheet . . . . . . . . . . . . . . . . . . . 65 4. 6 Suction Gripper: Datasheet . . . . . . . . . . . . . . . . . . . . 69 4. 7 Push-in Y connector: Datasheet . . . . . . . . . . . . . . . . . . 70 4. 8 Socket Connector Cable: Datasheet . . . . . . . . . . . . . . . . 71 5. 1 Transferring Arm – Speci? cations . . . . . . . . . . . . . . . . . 84 5. 2 Nodal Displacement . . . . . . . . . . . . . . . . . . . . . . . . . 87 5. 3 Stress Intensity & Equivalent Stress . . . . . . . . . . . . . . . 87 5. 4 Design Constraints for motion . . . . . . . . . . . . . . . . . . . 91 6. 1 Third arm speci? cations – initial proposal . . . . . . . . . . . . 107 6. 2 Third Arm – Final Design Speci? cations . . . . . . . . . . . . 107 6. 3 Solenoid Valve: Datasheet . . . . . . . . . . . . . . . . . . . . . 112 6. 4 Solenoid Coil: Datasheet . . . . . . . . . . . . . . . . . . . . . . 113 6. 5 Proximity sensors: Datasheet xii . . . . . . . . . . . . . . . . . . . 117 LIST OF TABLES xiii 8. 1 Cost of raw materials . . . . . . . . . . . . . . . . . . . . . . . . 154 8. 2 Costs of machining . . . . . . . . . . . . . . . . . . . . . . . . . 155 . . . . . . . . . . . . 155 8. 3 Cost of standard components – First Arm 8. 4 Cost of standard components – Second Arm . . . . . . . . . . . 156 8. 5 Cost of standard components – Third Arm . . . . . . . . . . . 157 8. 6 Time study for manual loading and unloading of press . . . . . 159 8. 7 Expected robot times for loading and unloading of press . . . . 159 Abstract Repetitive tasks and high accuracy have become the two contradictory needs of any industrial process. By introducing autonomous robotic applications, simple repetitive tasks can be accomplished keeping the demands of the accuracy and speed in mind. However, developing these applications for industries speci? c to countries like India, where cheap labour is available, becomes a major problem to be tackled in terms of cost.

This project deals with the design, fabrication and control of a robotic arm used to load metal sheets into a press. Two stepper motors control the motion of the arm while one controls the orientation of the wrist. The arm works in tandem with other arms, to be used to lift the sheets and ? nally unload them. The sheet size is expected to vary and the arm must cope up to these differing sizes. The original position of sheet will vary as per the sheet size while the arm will be programmed to place it at the die center. Robot motion is controlled using proximity sensors placed at suitable locations on the machine press itself.

The motor control is achieved using a microcontroller. The end effector of the transferring and unloading arm will be magnetic, while that of the lifting arm will use vacuum cups. Thus we have designed an assembly of three arms – 1 DOF Lifting Arm; 3 DOF Transfering Arm; 2 DOF Unloading Arm. 1 Part I Company Pro? le 2 Nirmiti Stampings Pvt. Ltd Nitmiti Stamplings Pvt. Ltd is an ISO/TS 16949 Certi? ed company which is a manufacturer of Sheet Metal Components, Assemblies and Press Tools. It is located in a prime industrial area of Pune, which is the automotive hub of India. The company was incorporated in the year 1995.

What started as a small enterprise with only one staff member, 6 workers and with a turnover of Rs 3. 3 million (US $ 0. 07 million) has today grown into an organization with a total strength of 70 members and a turnover of Rs 80 million (US $1. 77 Million) servicing both national and international clients. The company is certi? ed for TS 16949 by BVQI. Company Statement • Vision – Leadership in our respective product range – Move up the value chain and provide our customers ready to use products – Be the preferred supplier in our product range – Be a global player in our product range – Maintain a growth rate of atleast 30% • Mission 3 – To supply our products at the ? right time ? right price ? right quality – Train and motivate our employees to achieve our vision – Delight the customer-internal and external always • Values – Respect your customers, associates and employees – Promote the highest ethical standards – Promote teamwork and increase participation of all employees – Be accountable – Create an excitement and satisfaction for all Customers, Suppliers & Employees – Honour our commitments to the society Product Range • Press Tools – Compound, Progressive – Upto 1000 x 1200 mm – For all metals, hylam, plastics, gaskets • Sheet Metal Components – Automotive Figure 1: Shop Floor Layout Figure 2: Shop Floor 6 ? Ride control ? Parking brake system ? Gear shifters ? Cable clamps ? Radiator Supports – Electronic/White Goods ? Speaker Baskets, Bottom & Top Plates, Hylam Parts, Audio Panels/Refrigerator parts – Others ? Meters, Padlocks, Night latches, ? Petrochemical components • Assemblies – Gear shift lever – Ride control – Gas Lamps Machinery • Presses – 250 Ton Pneumatic with die cushion (Bed Size 1500 x 1200) – 150 Ton Mechanical – 75 Ton Mechanical (3 Nos) – 63 Ton Pneumatic with die cushion – 50 Ton Pneumatic with die cushion 7 Figure 3: Company Products 8

Figure 4: 250 Ton Pneumatic Press 9 Figure 5: Tooling used for the Pneumatic Press 10 – 50 Ton Mechanical – 35 Ton Mechanical – 20 Ton Pneumatic – 20 Ton Mechanical • Welding – Mig Welding 1 No – Capacitance Discharge Welding 25 KVA 1 No Major Customers • Gabriel India Ltd. • LG Electronics Ltd. • Tata Ficosa Automotive Systems Ltd. • Tata Toyo Radiators Ltd. • Fleetguard Filters Pvt. Ltd. • Renowned Auto Mfgrs Ltd. • Spicer India Ltd. • Behr India Ltd (E O U). • Piaggio Vehicles Pvt. Ltd. Part II Problem Analysis 11 Problem Description A press shop which manufactures components for automobiles is expected to deal in large volumes.

Most components are small in size and are precision jobs. Hence, loading the raw material into the press becomes critical, and the rate of production depends entirely on the loading and unloading speed. An operator designated for this job will frequently experience boredom and exhaustion, each of which affects the productivity of the plant. This menial job is best left to an automated process and the operator can be assigned to more ? tful jobs where his skills are best utilized. Thus, the task at hand was to design a robotic arm to perform the necessary pick and place actions for loading the raw material (metal sheets) and unloading the ? ished components. The task entails analysis, design and fabrication of the robot. We will install the robot at Nirmiti Stampings Pvt. Ltd, Bhosari. Robot Features For the purposes listed previously, integrating a standard manipulator for pick-and-place tasks is quite impractical. This is essentially due to the constraints imposed by the press and die on which the job is to be placed. In most cases, the vertical space (i. e. the distance between punch and die 12 13 mounted in the press) available is limited (to the order of about 150 mm), and this puts a constraint on the end-effector to be compact.

This prevents the ? nal joints from being prismatic. The mechanism to be used must be such that it does not take up additional space or cause any hinderance to already installed machines. The metal sheets (used as raw material) are generally stacked vertically and hence, a pick-and-place mechanism cannot be just a planar mechanism. The guideposts on the die and features on the press also put in constraints on the path that can be traced while loading and unloading of sheets. The robot arm assembly that has to be developed must be designed as a stand-alone machine and must be integrated into an existing press.

Since sheet size and the component manufactured on the press change, the robot must be programmable. This is mainly to accommodate for the changes in absolute locations where the sheets or components may be held. The machine has to be developed to be extremely simple to control and program as the robot will not be operated by skilled technicians. Thus, the robot must take in a minimum number of inputs from the operator, plan a path based on this data and perform the loading and unloading operations. This control and path planning has to be done by the robot itself, in the sense that no external interfacing to computers is possible.

This need arises from the fact that it would be extremely impractical in terms of cost to equip a shop ? oor with a computer dedicated to controlling a single robot. The robot thus needs to perform simple motions in order to allow easy control by a simple micro-controller based system. Chapter 1 Literature Survey 1. 1 Robotics [5] Automation is de? ned as a technology that is concerned with the use of mechanical, electronic, and computer-based systems in the operation and control of production. This technology includes transfer lines, mechanized assembly machines, feedback control systems, and robots.

There are three broad classes of industrial automation: ? xed automation, programmable automation, and ? exible automation. Of these three types, robotics coincides most closely with programmable automation. The robot can be programmed to move its arm through a sequence of motions in order to perform some useful task. It will repeat that motion pattern over and over again until reprogrammed to perform some other task. Hence the programming feature allows robots to be used for a variety of different industrial operations, many of which involve the robot working together with other pieces of automated or semiautomated equipment.

These operations include machine loading and unloading, spot welding, and spray painting. 14 CHAPTER 1. LITERATURE SURVEY 15 The of? cial de? nition of an industrial robot as provided by the Robotics Industries Association (RIA) is : An industrial robot is a reprogrammable, multifunctional manipulator designed to move materials, parts, tools, or special devices through variable programmed motions for performance of a variety of tasks. 1. 1. 1 Robot Anatomy Common Robot Con? gurations The vast majority of today’s commercially available robots possess one of the four basic con? gurations: • Polar con? guration • Cylindrical con? uration • Cartesian coordinate con? guration • Jointed-arm con? guration These basic con? gurations are illustrated in Fig. 1. 1 1. 1. 2 Robot Motions The robots movement can be divided into two general categories: arm and body motions, and wrist motions. The individual joint motions associated with these two categories are sometimes referred to by the term “degrees of freedom”, and a typical industrial robot is equipped with 4 to 6 degrees of freedom. CHAPTER 1. LITERATURE SURVEY 16 Figure 1. 1: The four basic robot anatomies: (a) polar, (b) cylindrical, (c) cartesian, (d) jointed arm CHAPTER 1. LITERATURE SURVEY 7 The robot motions are accomplished by means of powered joints. Connecting the various manipulator joints together are rigid members that are called links. The joints used in the design of industrial robots typically involve a relative motion of the adjoining links that is either linear or rotational. Linear joints involve a sliding or translational motion of the connecting links. This motion can be achieved in a number of ways (e. g. , by a piston, a telescoping mechanism, and relative motion along a linear track or rail). There are at least three types of rotating joint that can be distinguished in obot manipulators. The three types are shown in Fig. 1. 2. The arm and body joints are designed to enable the robot to move its end effector to a desired position within the limits of the robots size and joint movements. For robots of polar, cylindrical, or jointed-arm con? guration, the 3 degrees of freedom associated with the arm and body motions are (Fig. 1. 3 ): 1. Vertical traverse : This is the capability to move the wrist up or down to provide the desired vertical attitude. 2. Radial traverse : This involves the extension or retraction (in or out movement) of the arm from the vertical center of the robot. . Rotational traverse : This is the rotation of the arm about the vertical axis. The wrist movement is designed to enable the robot to orient the end effector properly with respect to the task to be performed. To solve the orientation problem, the wrist is normally provided with up to 3 degrees of freedom. (Fig. 1. 4) CHAPTER 1. LITERATURE SURVEY 18 Figure 1. 2: Several types of joints used in robots: (a) rotational joint with rotation along an axis perpendicular to arm member axis, (b) rotational joint with twisting action, (c) linear motion joint, usually achieved by a sliding action

Figure 1. 3: Three degree of freedoms associated with arm and body of a polar coordinate robot. CHAPTER 1. LITERATURE SURVEY 19 1. Wrist roll : Also called wrist swivel, this involves rotation of the wrist mechanism about the arm axis. 2. Wrist pitch : Given that the wrist roll is in its center position, the pitch would involve the up or down rotation of the wrist. 3. Wrist yaw : Again, given that the swivel is in the center position of its range, wrist yaw would involve the right or left rotation of the wrist. 1. 1. 3 Work Volume

Work volume is the term that refers to the space within which the robot can manipulate its wrist end. The work volume is determined by the following physical characteristics of the robot: 1. The robots physical con? guration 2. The sizes of the body, arm, and wrist components 3. The limits of the robots joint movements. The in? uence of the physical con? guration on the shape of the work volume is shown in Fig 1. 5. The size of each work volume shape is in? uenced by the dimensions of the arm components and by the limits of its joint movements. 1. 1. 4 Robot Drive System

The drive system determines the speed of the arm movements, the strength of the robot, and its dynamic performance. To some extent, the drive system determines the kinds of applications that the robot can accomplish. Commercially available industrial robots are powered by one of three types of drive systems. These three systems are : CHAPTER 1. LITERATURE SURVEY 20 Figure 1. 4: Three degree of freedoms associated with the robot wrist. Figure 1. 5: Work volumes for various robot anatomies: (a) polar, (b) cylindrical; and (c) cartesian CHAPTER 1. LITERATURE SURVEY 1. Hydraulic drive 2. Electric drive 3.

Pneumatic drive The three systems are compared in Table 1. 1 21 1. 1. 5 Control Systems In order to operate, a robot must have a means of controlling its drive system to properly regulate its motion. Commercially available industrial robots can be classi? ed into four categories according to their control systems. The four categories are: 1. Limited-sequence robots 2. Playback robots with point-to-point control 3. Playback robots with continuous path control 4. Intelligent robots 1. 1. 6 End Effectors In robotics, the term end effectors is used to describe the hand or tool that is attached to the wrist.

The end effector represents the special tooling that permits the general-purpose robot to perform a particular application. This special tooling must be designed speci? cally for the application. End effectors can be divided into two categories: grippers and tools. Grippers could be utilized to grasp an object, usually a workpart, and hold it during the robot work cycle. There are a variety of holding methods CHAPTER 1. LITERATURE SURVEY 22 Electrical Actuators Hydraulic Actuators Pneumatic tors Actua- Moderate payload capacity High Power to weight ratio Highly accurate and precise Highly reliable and

High Payload capacity Low Payload capacity Moderate Power to Low Power to weight ratio weight ratio Moderate accuracy Low accuracy and and precision Low reliability and requires high maintenance High Cost Moderate speed range of precision Moderate reliability requires low maintenance Low cost Can work in narrow speed range and requires moderate maintenance Moderate cost Wide speed range Table 1. 1: Comparison of different drive systems Figure 1. 6: Cost vs. size for electric drive and hydraulic drive CHAPTER 1. LITERATURE SURVEY 23 that can be used in addition to the obvious mechanical means of grasping the art between two or more ? ngers. These additional methods include the use of suction cups, magnets, hooks, and scoops. A tool would be used as an end effector in applications where the robot is required to perform some operation on the workpart. These applications include spot welding, arc welding, spray welding, and drilling. In each case, the particular tool is attached to the robots wrist to accomplish the application. 1. 1. 7 Grippers Grippers are end effectors used to grasp and hold objects. The objects are generally work parts that are to be moved by the robot.

These part handling applications include machine loading and unloading, picking parts from a conveyor, and arranging parts into a pallet. Depending on the mechanism used for the purpose of gripping they can be classi? ed as: 1. Mechanical Grippers 2. Adhesive Grippers 3. Hooks, Scoops etc 4. Vacuum Cups 5. Magnetic Grippers Magnetic Grippers Electromagnetic grippers are easier to control, but require a source of dc power and an appropriate controller unit. As with any other roboticgripping device, the part must be released at the end of the handling cycle. CHAPTER 1. LITERATURE SURVEY 24

This is easier to accomplish with an electromagnet than with a permanent magnet. When the part is to be released, the controller unit reverses the polarity at a reduced power leave before switching off the electromagnet. This procedure acts to cancel the residual magnetism in the work piece and ensure a positive release of the part. The advantages of magnetic grippers in material handling applications are: • Pickup times are faster • Variations in part size can be tolerated. The gripper does not have to be designed for one particular work part. • They have the ability to handle metal parts with holes (not possible with vacuum grippers. • They require only one surface for gripping. A disadvantage of magnetic grippers is the problem of picking up only one sheet from a stack. The magnetic attraction tends to penetrate beyond the top sheet in the stack resulting in the possibility that more than a single sheet will be lifted by the magnet. This problem can be confronted in several ways: • The magnetic grippers can be designed to limit the effective penetration to the desired depth, which would correspond to the thickness of the top sheet • The stacking device used to hold the sheets can be designed to separate the sheets for pickup by the robot.

One such type of stacking device is called a “fanner”. It makes use of a magnetic ? eld to induce a charge in the ferrous sheets in the stack. Each sheet towards the CHAPTER 1. LITERATURE SURVEY 25 top of the stack is given a magnetic charge, causing them to possess the same polarity and repel each other. The sheet at the top of the stack tends to rise above the remainder of the stack, thus facilitating pickup by the robot gripper. Suction Cups Suction cups are ? exible pick up devices designed for use with vacuum generator. They are made in various sizes and shapes and are used in different handling applications.

Suction cups are typically made of elastic material such as soft rubber or soft plastic a vacuum is created between the cup and the part surface with the help of a vacuum pump or a venturi. The principle of operation either involves either creation of a vacuum by a vacuum generator or use of an air ejector called a venturi. For easier control and operation reasons, the technique based on the venturi effect is used. It consists of an air ejector and suction cups. As illustrated in the Fig 1. 7, a restrictor inside the ejector causes acceleration in the ? w of air towards port R which pulls in the ambient air through port A. This causes a vacuum. The devices made on the venturi effect, enables 85 to 90% vacuum using 4 to 5 bar compressed air. 1. 1. 8 Robotic Sensors Sensors used as peripheral devices in robotics include both simple types such as limit switches and sophisticated types such as machine vision systems. Sensors are also used as integral components of the robots position feedback control system. Their function as peripheral devices in a robotic work cell is to permit the robots activities to be coordinated with CHAPTER 1. LITERATURE SURVEY 26

Figure 1. 7: (a) Schematic view of a venturi (b) Application of venturi CHAPTER 1. LITERATURE SURVEY 27 other activities in the cell. The sensors used in robotics include the following general categories: 1. Tactile sensors: These are sensors which respond to contact forces with another object. Some of these devices are capable of measuring the level of force involved. 2. Proximity and range sensors: A proximity sensor is a device that indicates when an object is close to another object but before contact has been made. When the distance between the objects can be sensed, the device is called as range sensor. . Miscellaneous types: The miscellaneous category includes the remaining kinds of sensors that are used in robotics. These include sensors for temperature, pressure, and other variables. 4. Machine vision: A machine vision system is capable of viewing the workspace and interpreting what it sees. These systems are used in robotics to perform inspection, parts recognition, and other similar tasks. Sensors are an important component in work cell control and in safety monitoring systems. 1. 2 Stepper Motors [1] 1. 2. 1 De? nition of a Stepper Motor The de? nition of stepper motor given in British Standard Speci? ation is “A stepper motor is a brushless DC motor whose rotor rotates in discrete angular increments when its stator winding are energized in a programmed manner. Rotation occurs because CHAPTER 1. LITERATURE SURVEY of magnetic interaction between rotor poles and poles of the sequentially energized stator windings. The rotor has no electrical windings , but has salient and/or magnetized poles. ” 28 A stepper motor is a digital actuator whose input is in the form of programmed energization of the stator windings and whose output is in the form of discrete angular rotation.

It is, therefore, ideally suited for use as an actuator in computer control systems, digital control systems, etc. Control systems employing stepper motors as actuators are known as incremental motion control systems (IMCS). 1. 2. 2 Step Angle ? s : This is the angle through which an unloaded stepper motor rotates for every step of the energisation sequence. It is determined by the number of teeth on the rotor and stator, as well as the number of steps in the energisation sequence. 1. 2. 3 Steps/Revolution (Z): It is given by Z = 360? /? For permanent magnet hybrid ( PMH ) step motors, ? s = 360? /(Nr ? Kws ) = 360? /Z Where Nr = no. of teeth on rotor discs 4 for 4-step sequence (i. e. 1 phase on amd 2 phase on) = 8 for 8-step (i. e. 1-2 or hybrid) sequence of energisation of stator windings. (1. 2) (1. 1) & Kws = CHAPTER 1. LITERATURE SURVEY 29 Motor Type Stepper Motors Advantages Disadvantages Can be driven open loop without feedback No accumulative position error Responds directly to digital control signals; so stepper Fixed step angle; no ? exibilty in step resulotion Low ef? iency with ordinary controller high overshoot and oscillation in step response motors are natural choice for digital computer control Mechanically simple; requires little or no maintenance Free from contamination Limited ability to handle high inertia load Friction load increases position error, but error is not accumulative Can be repeatedly stalled Limited available output and sizes without damage Relatively rugged and durable Variable Reluctance Stepper Motors Low rotor interia High torque to inertia ratio No detente torque available with windings de-energized Exhibits mid-range reso- ance at some stepping rates under some drive conditions Capable of high stepping rate; high speed slewing capability Ability to freewheel Normally available in 3. 6 to 30 deg. step angles Low ef? ciencies at low voltages and stepping rates CHAPTER 1. LITERATURE SURVEY Light weight 3,4 and 5 phase, single and multi-stack models available Permanent Magnet Hybrid Motors Less tendency to resonate Performance affected Provides detente torque with windings de-energized 30 Higher inertia and weight due to presence of rotor magnet by hange in magnet strength Higher holding torque capabilty Better damping due to presence of rotor magnet High stepping rate capability High ef? ciency at lower speeds and lower stepping rates Electrohydraulic Motor Very ratio Can handle high inertia load well Capable rates Less tendency to oscillate and resonate Table 1. 2: Comparison of Stepper Motors of high stepping high torque-to-inertia Very high holding toque capability Requires high pressure hydraulic supply in addition to electric supply More complex construction and operation CHAPTER 1. LITERATURE SURVEY 31 1. 2. 4 Step Angle Accuracy:

Is usually ±5% of ? s ; in a few cases, we can get accuracy of 3%. In certain exceptional cases, it is possible to get an accuracy of ±1 Typical accuracy curve for a stepper motor is shown in Fig 1. 8. Observe that the positioning error is non-cumulative. Consequently positioning error at that end of N step will be the same as that for a single step, viz. ±5% of ? s . Further as the motor is loaded, the positioning error increases. 1. 2. 5 Static Characteristics: Torque-Angle Curve: It is shown in Fig. 1. 9 . It is seen that the torque increases, almost sinusoidally, with angle ? rom the equilibrium position. Holding Torque (Th ): It is the maximum load torque which the energized stepper motor can withstand without slipping from equilibrium position. If the holding is exceeded, the motor suddenly slips from the present equilibrium position and goes to the next stable equilibrium position. Detente Torque (Td ): It is the maximum load torque which is unenergized stepper motor can withstand without slipping. Detente torque is due to residual magnetism, and is, therefore, available only in PM and hybrid stepper motor. It is about 5 – 10 % of holding torque.

It is typically a fourth harmonic torque as shown in Fig. 1. 10. It is also known as cogging torque. Torque Current Curve: A typical torque current for a stepper motor is shown in Fig 1. 11 . It is seen that the curve is initially linear but, later on, its slope progressively decreases as the magnetic circuit of the motor saturates. Torque Constant (Kt ): Torque constant of a stepper motor is de? ned as the initial slope of the torque-current (T-I) curve of the stepper motor. It is CHAPTER 1. LITERATURE SURVEY 32 Nr Kws = 4 Z ? s (? ) 15. 0 10. 0 7. 5 6. 0 3. 6 3. 0 1. 8 1. 2 Kws = 8 Z 48 72 96 120 200 240 400 600 ? (? ) 7. 5 5. 0 3. 75 3. 0 1. 8 1. 5 0. 9 0. 6 6 9 12 15 25 30 50 75 24 36 48 60 100 120 200 300 Table 1. 3: Relation between ? s and Nr for PMH stepper motor Figure 1. 8: Positional Accuracy Figure 1. 9: Torque Angle Curve CHAPTER 1. LITERATURE SURVEY 33 Figure 1. 10: PM Hybrid Motor Torque and Detente Torque Pro? les Figure 1. 11: Torque-Current Curve CHAPTER 1. LITERATURE SURVEY also known as torque sensitivity. 34 1. 2. 6 Dynamic Characteristics: These are presented by torque-stepping rate curves for the motor as shown in Fig 1. 12. The two torque-stepping rate curves shown in ? are pull-in and pull-out curves. Their signi? cance is as follows: Pull-in Curve: Corresponds to the so-called start-stop or single stepping mode of stepper motor operation as shown in Fig. 1. 13(a). In this mode, the rotor comes to rest after moving through one step. Consequently, the rotor will not move any further as soon as you stop energizing the motor winding in the given programmed sequence. The motor can, therefore, start or stop with each individual pulse i. e. respond to each individual pulse. Pull-out Curve: Corresponds to slewing mode of stepper motor operation as shown in Fig. . 13(b). In this mode, the rotor is still moving in response to the previous pulse when the next pulse comes. Consequently, the motor can run at a much faster rate in slewing mode than in start-atop mode. However, the motor cannot start slewing from rest; nor can it stop immediately when you stop applying pulses. The motor will over-run by several steps before it comes to rest. 1. 3 Pneumatics [7] 1. 3. 1 Features of Pneumatics The following features are notable: 1. Wide availability of air. CHAPTER 1. LITERATURE SURVEY 35 Figure 1. 12: Torque-Speed Characteristics

Figure 1. 13: Modes of Operation CHAPTER 1. LITERATURE SURVEY 2. Compressibility of air. 36 3. Easy transportability of compressed air in pressure vessels, containers, and in long pipes. 4. Fire-proof characteristics of the medium. 5. Simple construction of pneumatic elements and easy handling. 6. High degree of controllability of pressure, speed and force. 7. Easier maintenance. Compared to hydraulic system, pneumatic system has better operational advantages but it cannot replace hydraulic system so far as power requirement and accuracy of operations is concerned. . 3. 2 Basic Pnuematic System The basic system requirements for introducing pneumatics in one’s plant is listed below: 1. Compressor Plant : The production plant using pneumatic tools, etc. should be equipped with the compressed air plant of appropriate capacity to meet the compressed air needs of the systems. 2. Pipeline : A well-laid compressed air pipeline system should be drawn from the compressor plant to the consumption point of pneumatic energy in various sections of the plant where pneumatic gadgets and systems are to be introduced. 3.

Control Valves : Various types of control valves are used to regulate, control, and monitor the air energy, for control of direction, pressure, ? ow, etc. CHAPTER 1. LITERATURE SURVEY 37 4. Air Actuator : Various types of air cylinders or air motors are used to perform the useful work for which the pneumatic system is designed like using cylinders for linear movement of jigs, ? xtures, raw materials feeding, etc. 5. Auxiliary Appliances : Various types of auxiliary equipment may have to be used in pneumatic system for effecting better performance, easy controllability and higher reliability. . 3. 3 Pipe Materials If the system pressure is quite high, materials of pipes and their physical and metallurgical properties become an important parameter and for their correct selection. But as pneumatic system usually works at a much lower pressure in comparison to hydraulic system, one may not need super high strength material for pneumatic pipelines and ? ttings. Materials which are mostly used for pneumatic pipes and tubes are listed below : 1. Galvanised iron pipes. 2. Cast iron pipes. 3. Copper tubes. 4. Aluminium tubes. 5. Rubber hose. 6. Plastic and nylon hose. . High strength steel pipe. 8. Brass tube. 9. Reinforced rubber or plastic hose, etc. CHAPTER 1. LITERATURE SURVEY 38 1. 3. 4 Air Compressor Though not directly connected to the pneumatic system, the air compressor plays a vital role in the overall system performance. Various types of air compressors are used in the industry. But positive displacement compressors are more popular. Positive displacement compressors are classi? ed as rotary type, e. g. screw, lobe, vane compressors and reciprocating type, e. g. piston type air compressor. 1. 3. 5 FRL Unit

The air that is sucked by the air compressor is not clean because of the presence of various types of contaminants in the atmosphere. Moreover, the air that is supplied to the system from the compressor is further contaminated by virtue of generation of contaminants downstream. The pressure of the air does not remain stable due to the possibility of line ? uctuations. Hence to enable supply of clean, pure and contamination free compressed air, the air requires to be ? ltered. The system performance and accuracy depends much on the pressure-stability of the air supply. An air line ? ter and a pressure regulator, therefore, are indispensible along with a third component — an airline lubricator. The main function of the lubricator is to provide the air with a lubricating ? lm of oil. These three units together are called service unit of FRL unit. Air-Filter Air-? lters are used in pneumatic systems to perform the following main functions: • To prevent entrance of solid contaminants to the system. CHAPTER 1. LITERATURE SURVEY 39 S. No 1 2 3 4 5 6 7 8 Pipe Material Copper Aluminium Brass Stainless steel Polythene at 80? C Nylon 100? C Vinyl at 25? C Rubber at 80? C

Maximum pressure (bar) 250 125 200 2500–4500 12-15 7–10 8–10 3–7 Table 1. 4: Pressure rating of pipe materials Figure 1. 14: FRL unit in combination: 1. Filter 2. Regulator 3. Lubricator Figure 1. 15: FRL unit: Symbol CHAPTER 1. LITERATURE SURVEY 40 • To condense and remove the water vapour that is present in the air passing through it. • To arrest any submicron particles that may pose a problem in the system components. The main component of the ? lter is the ? lter cartridge, which is made mostly of sintered brass, or bronze but other materials are also used. Pressure Regulator The main function of the ressure regulator is to regulate the incoming pressure to the system so that the desired air pressure is capable of ? owing at steady condition. It is done by using various valves and spring force. Lubricator The compressed air is ? rst ? ltered and then regulated to the speci? c pressure and made to pass through a lubricator in order to form a mist of oil and air for the sole purpose of providing lubrication to the mating components of the valves, cylinders etc. All lubricators follow the principle of venturimeter. 1. 3. 6 Pneumatic Cylinders The pneumatic power is converted to straight line reciprocating motion by pneumatic cylinders.

The various industrial applications for which air cylinders are used can be divided dutywise into three groups — light duty, medium duty and heavy duty. But according to the operating principle, air cylinders can be sub-divided as single acting and double acting cylinders. Single Acting Cylinder In a single acting cylinder, the compressed air is fed only in one side. Hence, this cylinder can produce work only in CHAPTER 1. LITERATURE SURVEY 41 one direction. The return movement of the piston is effected by a built-in spring or by application of an external force.

Double Acting Cylinder In a double acting cylinder, the force exerted by the compressed air moves the piston in either of the two directions. They are used particularly when the piston is required to perform work not only on the advance movement but also on the return. In principle, the stroke length is unlimited, although buckling and bending must be considered before we select a particular size of piston diameter, rod length and stroke length. 1. 3. 7 Direction Control Valve In certain designs of direction control valves, 5 openings are preferred instead of 4 openings. This ensures easy exhausting of the valve.

The Fig. 1. 17 shows a 5/2 direction control valve – spool type design. The spool slides inside the main bore and according to the spool position, the ports gets connected or disconnected. The working peinciple is as follows: Position 1 When the spools is actuated towards outer direction, port P gets connected to ‘B’ and ‘S’ remains closed while A gets connected to ‘R’. Position 2 When the spool is pushed in the inner direction, port ‘P’ and ‘A’ get connected to each other and ‘B’ to ‘S’ while port ‘R’ remains closed. CHAPTER 1. LITERATURE SURVEY 42 Figure 1. 16: Double Acting Cylinder: 1. Tube 2.

Piston 3. Piston Rod 4. Double O-ring packing on piston 5. O-ring for piston rod 6. End cover 7. Bush 8. Cushion Assembly Figure 1. 17: 5/2 D. C. valve Chapter 2 Initial Ideas – Alternate Designs The problems faced in implementing any standard available robots have already been discussed. Initially we proposed some ideas for the mechanism, but which had to be discarded. The ideas, along with their drawbacksm are discussed in this chapter. 2. 1 Cartesian Con? guration The idea of using pneumatic cylinders in a con? guration similar to that of a cylindrical con? guration was initially considered.

There would be a base cylinder which would provide for the vertical motion for the lifting that was required. Another cylinder perpendicular to that would give the necessary horizontal motion for receiving the sheets and loading them into the press. There would be another cylinder mounted to provide the third linear motion (Fig 2. 1). In this case we had the advantage of the fact that we were working on a pneumatic press and that the necessary air supply was readily available. There would have been no need for a separate compressor unit, as in the 43 CHAPTER 2. INITIAL IDEAS – ALTERNATE DESIGNS ase of the third arm that has been implemented. 44 The problem faced with this was that pneumatic cylinders are very bulky. For a given stroke length the total length of the cylinder is at least twice of this. The restriction of the ram in its downward stroke leaves only 450 mm gap between the bed and the ram. The pneumatic cylinder would have to work as cantilever with heavy loads attached or a separate supporting frame would have to be made to guide the piston rod, all making the assembly very complicated. This full arrangement would have had to be mounted on the bed and the surrounding area fenced out to avoid any mishaps.

Stacking a fresh bunch of sheets will be quite dif? cult too. Hence, this idea was discarded. 2. 2 Spherical Con? guration Another idea was to use a motor at the shoulder joint as in a spherical con? guration. In this, we would have one base motor for rotation of the entire assembly. A separate motor at the shoulder, for lifting, and a pneumatic cylinder, for the necessary linear motion for collecting and placing the sheet in the die would be used (Fig 2. 2). The major drawback of this was that since the weight of the entire assembly is more than 25 kg, the base motor would have to be very large.

The motor at the shoulder had to pick up the sheet against gravity with the load of the arm and the pneumatic cylinder, all of which calls for another big motor. The precise control of a D. C. or A. C. induction motor is not quite possible and the cost of a stepper motor or servo motors of a large CHAPTER 2. INITIAL IDEAS – ALTERNATE DESIGNS 45 Figure 2. 1: Cartesian con? guration Figure 2. 2: Spherical con? guration CHAPTER 2. INITIAL IDEAS – ALTERNATE DESIGNS torque capacity is very high. As a result, this idea too was discarded. 46 2. 3 Planar Con? guration with Pulleys for lifting The third attempt at trying to ? d a solution saw us trying to use a pulley arrangement instead of the motor at the shoulder as in the previous case. The arrangement would be quite similar, with the base motor to rotate the assembly and the pneumatic cylinder for transferring. The shoulder motor would be replaced by telescopic chutes at the end. With the help of steel cord running all along the robot from the base, the three chutes would be lowered or raised. There would be a motor at the base which would wind the cords on pulleys. The problem encountered in this arrangement was that this would make the assembly quite bulky requiring a lot of tubing.

Apart from that there was also a possibility of the cords not being wound on the pulleys evenly causing angular tilt of the sheet or sudden seizure in the motion. 2. 4 End Effectors In all of the above designs the possibility of using suction cups or electro magnets was thought of. Suction cups had an advantage that the pneumatic power required for it was easily available. However the sheets have to be greased with a particular liquid before loading, which is done manually. This would call for additional ? ltering units for the cups, which increased costs considerably. The sheets which were to be loaded are always M.

S. or of an EN series. Hence using electromagnets was a cheaper and favorable alternative. The CHAPTER 2. INITIAL IDEAS – ALTERNATE DESIGNS 47 only problem with these is that it is dif? cult to lift only one sheet from the stack using electromagnets. Thus, it is only for this application that we must use suction gripper, and use electromagnets for other tasks. Chapter 3 Final Mechanism Description After considering all the ideas that we had initially proposed, we arrived at a ? nal set of mechanisms that would work in tandem to perform the required tasks of loading and unloading the press.

The robot consists of 3 separate arms – each for performing a different role. The different tasks to be performed will be: (Fig. 3. 1) 1. Lifting the sheet 2. Planar transfer of sheet up to the die 3. Unloading of ? nished product The ? rst arm to come in contact with the plates (raw material) is the lifting arm. The lifter arm, driven by a DC motor, uses suction cups to grasp the sheets and a lead screw type arrangement to lift them to desired height. As the screw rotates, the nut is displaced either up or down depending on the direction of rotation of the screw.

This lifter is equipped with proximity switches that sense the height at which the next sheet is and also ? x the height of vertical travel. This travel limit is set by the operator. 48 CHAPTER 3. FINAL MECHANISM DESCRIPTION 49 Figure 3. 1: Block Diagram of robotic assembly CHAPTER 3. FINAL MECHANISM DESCRIPTION 50 When the lifting arm reaches the topmost position with the plate, it waits at the position until a second arm, the transferring arm, takes over. The transferring arm is a 3 DOF planar arm, which transfers the plate along a plane parallel to the horizontal. The end effector is electromagnetic.

This arm moves along a ? xed path, set by the operator during the programming mode. The start point coincides with the topmost position of the lifting arm and the ? nal position is the die center. The electromagnets of the arm switch on, gripping the plate, following which the lifting arm releases the plate. As a result, the plate is now manipulated by the transferring arm. It transfers the plate to the die center, and upon reaching this location, switches off the electromagnets. The height of the two arms are so set that the plate is around 5 mm above the die when the magnets are switched off.

This height difference is suf? cient to allow for the plates to fall onto the die without any misalignment. After the sheet has been loaded, the robot sends a signal to the press and the punch starts its descent. Once the sheet has been worked upon, a signal is sent to the robot controller which activates the unloading mechanism. The unloading mechanism is a 2 DOF arm with one linear actuator — a pneumatic piston-cylinder, and one motor, driving a rack. The height of arm from the bed is manually adjustable. The pneumatic cylinder pushes the piston out and positions the electromagnet over the ? ished product. The motor then drives the rack vertically downwards, to get the electromagnets in contact with the job. The arm picks up the job, and each motion is reversed in opposite sequence and the job is dropped into a container by switching off the magnets. This entire assembly is thus a set of 3 arms — a 1 DOF lifting arm, a 3 DOF transferring arm and a 2 DOF unloading arm. Part III Robot Design 51 Chapter 4 First Arm 4. 1 Prototype 1 4. 1. 1 Features The design of this arm, as described earlier, uses a lead screw mechanism to achieve vertical lifting of the metal sheet.

This lead screw is driven by a motor, coupled by a gear drive. In this design, the motor selected was a 1-Phase AC motor. The motor was coupled using a spur gear pair with a gear ratio of 1:1. As direction reversal of 1- Phase AC motors is not possible, the motor was connected to an Electromagnetic Double Clutch – Brake system. The end of travel in upward direction was speci? ed by adjusting the height of the sensor plate, on which the proximity switches would be mounted. (Fig 4. 1) 52 CHAPTER 4. FIRST ARM 53 Figure 4. 1: Lifting arm: First Design Components Actuator Speci? ations Permanent Magnet DC Motor 2000rpm; 100Watt ;6Kg-cm Transmission Drive Spur Gears (m=2; z=58; G 1:1) Lead Screw (Acme Thread; M22; P=5) End Effector Degree of Freedom Lifter Beam Brackets Sensor Mount Sensing Elements 2 Electormagnets (? 50? 20mm) only 1 D. o. f. 50? 50? 200mm 5? 10? 150mm Horizontal above lifter beam 2 Proximity Sensors Table 4. 1: Lifting Arm – Speci? cations of ? rst prototype CHAPTER 4. FIRST ARM 54 4. 1. 2 Component Design Lead Screw The lead screw used to lift the central beam needs to lift a total weight of about 5 kg. Thus the minimum allowable core diameter is given by W =?

Thus we get minimum dc = 0. 79 mm. As we need a pitch of 5 mm, we choose trapezoidal threads having dc do Area of core Ac = = 16. 5 mm 22 mm ? 2 d 4 c (4. 1) = 214 mm2 Calculation of driving torque 22 + 16. 5 = 19. 25 d= 2 tan(? ) = ? ? = 4. 726? µ1 = µc = 0. 1242 cos ? (4. 3) (4. 4) nP ? d (4. 2) ? = tan? 1 (µ1 ) = 7. 08? Torque required to rotate screw in nut d = 98. 55N ? mm 2 T1 = W tan(? + ? ) (4. 5) Torque required to overcome collar friction at base 3 2 R 3 ? Ri ) = 59. 1543N ? mm T2 = µW ( o 2 2 3 Ro ? Ri (4. 6) T = T1 + T2 = 157. 7 N-mm CHAPTER 4. FIRST ARM 55

However, an AC motor with speed reversal is not available and additional components like Electromagnetic Double Clutch -Brake is needed. This increases the costs and complication of the part considerably. Hence, this design was discarded. 4. 2 Prototype 2 4. 2. 1 Features As in the previous design we continue to use a lead screw but the drawbacks of the A. C. motor concerning direction reversal are overcome by using a stepper motor. This gives us a slower speed of about 100rpm with reasonably high torque. Thus, to achieve the required motion of 320mm in 2 sec we change the gear ratio of 1:1 to 5:1.

The speed is further increased by using a lead screw with a pitch of 5mm and four starts and an overall lead of 20mm. The need of any breaking system was not felt due to the ability of precise braking of the stepper motor when driven at 100 rpm. A proximity sensor is mounted on side sensor mount instead of a top sensor mount. This change was done as the central beam might collide with the top sensor plate. On sensing the beam, it sends a signal to the stepper motor which switches off. (Fig 4. 2) The pneumatic circuit for this arm is shown in Fig 4. 3. CHAPTER 4. FIRST ARM 56 Figure 4. 2: Lifting Arm: Final Design

Components Actuator Speci? cations DC Stepper Motor 500rpm; 17Kg-cm Transmission Drive Spur Gears (G 1:1; m=2; zp =30; zg =150) Lead Screw (Trapizoidal Thread; M22; P=5; Lead=20mm) End Effector Degree of Freedom Lifter Beam Brackets Sensor Mount Sensing Elements 2 Vacuum Grippers (? 50mm) only 1 D. o. f. 25? 60? 200mm 6? 12? 150mm Vertical parallel to lifter beam 2 Proximity Sensors Table 4. 2: Lifting arm – Speci? cations of prototype 2 CHAPTER 4. FIRST ARM 57 4. 2. 2 Component Design (a) Lead Screw The lead screw used to lift the central beam needs to lift a total weight of about 5 kg.

Thus the minimum allowable core diameter is given by dc = 0. 79mm. As we need a pitch of 5 mm and 4 starts, we choose trapezoidal threads having dc do Area of core Ac = 16. 5 mm = = 22 mm 214 mm2 Calculation of driving torque 22 + 16. 5 d= = 19. 25 2 tan(? ) = nP ? d ? ? = 18. 299? µc = 0. 1242 cos ? µ1 = ? = tan? 1 (µ1 ) = 7. 08? Torque required to rotate screw in nut d = 223. 71N-mm T1 = W tan(? + ? ) 2 Torque required to overcome collar friction at base 3 2 R3 ? Ri ) = 59. 1543 N-mm T2 = µW ( o 2 2 3 Ro ? Ri CHAPTER 4. FIRST ARM 58 Figure 4. 3: Pneumatic Circuit for Gripper CHAPTER 4. FIRST ARM T = T1 + T2 = 282. 7 N-mm Design of nut The bearing pressure is: Pb = W (? /4)(d2 ? d2 )Z o c 59 (4. 7) For high rubbing speed with steel screw and PB nut, Pb = 1 to 1. 5 N/mm2 . Setting Pb = 1 gives, h Z = = 0. 2949 p ? h = 1. 47 mm We select a screw with height h = 30 mm. (b) Gear Design We require a gear ratio of 1:5. Thus, we use standard gears from Albro Engineers available for this gear ratio. The pinion is with dimensions dp = 150mm, Zp = 75mm and m= 2 and the gear with dg = 30mm, Zg = 15mm and m= 2 The face width of these is b= 15mm The material used for these gears is EN8D with tensile strength Sut = 700 N/mm2 and hardness of 460BHN (case hardened)

We check these gears for their strength and evaluate the factor of safety. CHAPTER 4. FIRST ARM Beam Strength Sut 700 = = 233. 33N/mm2 3 3 60 ?bg = ? bp = (4. 8) Assuming a 20? full depth involute tooth system, Yg = 0. 484 ? 2. 87 = 0. 2926 Zg 2. 87 Yp = 0. 484 ? = 0. 4457 Zp (4. 9) (4. 10) where Yg is the Lewis form factor. ? ? bg Yg < ? bp Yp Thus, we check only the gear for safety. The Lewis equation for beam strength of spur gear tooth is Fb = = Wear Strength Ratio factor, Q = = Load stress factor, 2Zg Zg + Zp 1. 667 BHN 2 ) 100 3. 3856 ? yg b m Yg 2048. 17 N (4. 11) (4. 12) (4. 13) K = 0. 16 ( = (4. 14)

The Buckingham’s equation for wear strength of a gear tooth is Fw = = dp b Q K 2544. 27 N (4. 15) As Fb < Fw , the gear pair is weaker in bending and hence it should be checked for safety against failure in bending. CHAPTER 4. FIRST ARM Precise Estimation of Dynamic Load by Buckigham’s Equation 61 The Buckigham’s equation for the dynamic load in the tangential direction is given by Fd = Ftmax = 21V (bc + Ftmax ) 21V + bc + Ftmax (4. 16) where max. tangential force = Ka Km Ft Taking Ka = 1. 5 (application factor for electric motor with moderate shock) & Km = 2. 2 (load distribution factor for non-precise gear)

Theoretical tangential force Ft = = ? Ftmax = 86. 295N V = pitch line velocity in m/s ? dg N = 60 ? 1000 = 0. 785 p Tg = v dg /2 26. 16 N (4. 17) (4. 18) c = 11500 e N/mm (4. 19) deformation factor for steel pinion and steel gear. e = 21. 31 ? 10? 3 mm for given gear pair. ? c = 245. 075N/mm ? Fd = 796. 97N CHAPTER 4. FIRST ARM Estimating Factor of Safety Fef f = = Nef f Ka Km Ft + Fd 883. 27 N = Fb Fef f 62 (4. 20) ? (4. 21) = 2. 31 Thus, the gears used are safe against failure. (c) Bracket The brackets on which the suction cups are attached is held only at one end and the entire load of the plates is borne by it.

We designed a bracket and checked it by loading each bracket of the arm by a load of 20 N. This is almost twice the load that will be experienced by each bracket. The analysis was done on the software CosmosExpress, the results of which are given in Table 4. 3, Table 4. 4 and Fig 4. 4. (d) Vacuum Generator Together with the corresponding suction grippers and suction cups, vacuum generators are capable of picking up and retaining workpieces with smooth, impervious surfaces. Workpieces can be picked up in any position. The air supply of hese vacuum generators is controlled by the built-in solenoid valve. After switching supply power on, th