Project Number: ECC - JOIN Design of Low Cost Modular Robotic Manipulator Joints A Major Qualifying Project Report Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE in partial fulfillment of the requirements for the Degree of Bachelor of Science in Mechanical Engineering by __________________________ __________________________ Jonathan Baldiga Shivahn Fitzell __________________________ __________________________ Colin McCarthy Thomas Watson Date: April 28th, 2009 Approved: __________________________ Prof. Cobb, Major Advisor __________________________ Prof. Looft, Co-Advisor __________________________ Prof. Looft, Co-Advisor Keywords: 1. Modular joints 2. Inexpensive robotics 3. Infinite rotation Abstract The goal of this project was to design and manufacture robotic joints that are inexpensive and capable of being used in a variety of applications. In order to maximize the number of applications in which our design could be utilized, research was done on optimal strength, size, communications, modularity, and price. This project includes the research and design development necessary to engineer such a joint, including part selection, motor control, manufacturing processes, and strength analysis. Two Joints were constructed and tested: a rotator joint and a elbow-joint. The joints performed well under testing conditions and overall prices were kept low. With future development, these joints could be used in fields where size and price are critical. i Acknowledgements We would like to thank the following individuals for their contributions to this report: Professor Cobb (ME) For his assistance and feedback throughout the project Professor Looft (ECE) For his motivation and creation of this project Professor Padir (RBE) For his contributions and dedication to feedback Professor Ciaraldi (CS) For his wealth of fresh ideas and extensive help with programming Adam Sears For machining many of our parts Neil Whitehouse For aiding in the construction of our prototypes Russ Morin For his help with rapid prototyping and Solidworks expertise ii Contents ABSTRACT ................................................................................................................................................. I ACKNOWLEDGEMENTS ............................................................................................................................ II 1 INTRODUCTION ............................................................................................................................... 7 1.1 MODULARITY.................................................................................................................................. 7 1.2 COST VS CAPABILITY ......................................................................................................................... 8 1.3 GOAL............................................................................................................................................ 9 2 BACKGROUND............................................................................................................................... 11 2.1 MOTION OF JOINTS ........................................................................................................................ 11 2.1.1 RoboFlex .......................................................................................................................... 12 2.1.2 Robotic Wrist Patent ........................................................................................................ 13 2.1.3 Double Universal Joint ...................................................................................................... 14 2.1.4 Ultrasonic Motors ............................................................................................................ 16 2.2 MODULARITY AND COMMUNICATION ................................................................................................. 18 2.2.1 Development of Modular Robot Joint ............................................................................... 18 2.2.2 Unidrive Modular Joint ..................................................................................................... 20 2.2.3 Snake Robot ..................................................................................................................... 22 2.2.4 Electrical Component/Communication Research ............................................................... 23 2.2.5 Manipulability and Redundancy Control of Robotic Mechanisms ....................................... 23 2.3 MARKET FEASIBILITY ....................................................................................................................... 24 2.3.1 PowerCube....................................................................................................................... 24 2.3.2 Research Robotics ............................................................................................................ 25 2.3.3 Unimate Mark II PUMA Robot .......................................................................................... 26 3 PROJECT OBJECTIVES .................................................................................................................... 33 4 DESIGN SPECIFICATIONS ............................................................................................................... 34 5 PRELIMINARY DESIGN CONCEPTS ................................................................................................. 35 5.1 ELBOW-JOINT ITERATION 01 ............................................................................................................ 37 5.1.1 .............................................................................................................................................. 37 5.1.2 Kinematics ....................................................................................................................... 38 5.1.3 Iteration 01 Torque Analysis ............................................................................................. 39 5.1.5 Iteration 01 Stress Analysis ............................................................................................... 41 5.1.6 Iteration 01 Part Selection ................................................................................................ 51 5.1.7 Iteration 01 Discussion ..................................................................................................... 54 5.2 ROTATOR-JOINT ITERATION 01 ......................................................................................................... 55 5.2.1 Kinematics ....................................................................................................................... 55 5.2.2 Iteration 01 Components .................................................................................................. 56 5.2.3 Iteration 01 Inertia Calculations and Motor Selection........................................................ 57 5.2.4 Iteration 01 Stress Analysis ............................................................................................... 57 5.2.5 Iteration 01 Part Selection ................................................................................................ 62 5.3 ELECTRICAL SYSTEMS ITERATION 01 ................................................................................................... 64 5.4 ELBOW-JOINT PRE-PROTOTYPING ...................................................................................................... 67 5.5 ELBOW-JOINT ITERATION 02 ............................................................................................................ 69 5.5.1 Kinematics ....................................................................................................................... 70 5.5.2 Iteration 02 Stress Analysis ............................................................................................... 70 5.5.3 Iteration 02 Part Selection ................................................................................................ 76 5.5.4 Construction of Prototype................................................................................................. 78 5.5.5 Iteration 02 Discussion ..................................................................................................... 78 5.6 ROTATOR-JOINT ITERATION 02 ......................................................................................................... 79 5.6.1 Kinematics ....................................................................................................................... 80 5.6.2 Iteration 02 Components .................................................................................................. 80 5.6.3 Iteration 02 Stress Analysis ............................................................................................... 81 5.6.4 Iteration 02 Part Selection ................................................................................................ 86 1 5.6.6 Construction of Prototype................................................................................................. 88 5.7 ELECTRICAL SYSTEMS ITERATION 02 ................................................................................................... 90 6 DETAILED DESIGN ......................................................................................................................... 93 6.1 ELBOW-JOINT ITERATION 03 ...........................................................................................................