NASA-CR-2057q6 _:L,I Department of AERONAUTICS and ASTRONAUTICS STANFORD UNIVERSITY ./ SUDAAR 631 [?/J - . EXPERIMENTS IN NONLINEAR ADAPTIVE CONTROL OF MULTI-MANIPULATOR, FREE-FLYING SPACE ROBOTS Vincent Wei-Kang Chen Department of Electrical Engineering Stanford University Stanford, California 94305 Research supported by AFOSR contract F33615-85-C-5106 and NASA contract NCC 2-333-14 December 1992 EXPERIMENTS IN NONLINEAR ADAPTIVE CONTROL OF MULTI-MANIPULATOR, FREE-FLYING SPACE ROBOTS A DISSERTATION SUBMITTED TO THE DEPARTMENT OF ELECTRICAL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY By Vincent Wei-Kang Chen December 1992 Copyright © 1992 by Vincent Wei-Kang Chen All Rights Reserved. This dissertation was typeset using the I6TEX document preparation system in conjunction with emTEX running under MS-DOS ®. Figures were created with CorelDRAW!. TM 3.0 running under Microsoft ® Windows TM 3.1 on a 486-based PC. Images were produced using a Hewlett-Packard ScanJet IIc with DeskScan II scanning software also running under Windows. Plots were generated from data collected with Real Time Innovations StethoScope TM and processed using MATLAB TM, a product of The MathWorks, Inc. All figures, images, and plots were incorporated as Encapsulated Postscript ® files resulting in a completely electronically reprodudble document. The final version was produced on a HP LaserJet III printer with the LaserMaster WinJetTM800 accelerator board to achieve PostScript outputs at 800dpi resolution. ii I certify that I have read this dissertation and that in my opinion it is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Robert H. Cannon, Jr. Department of Aeronautics and Astronautics (Principal Adviser) I certify that I have read this dissertation and that in my opinion it is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Gene E Franklin Department of Electrical Engineering I certify that I have read this dissertation and that in my opinion it is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Stephen M. Rock Department of Aeronautics and Astronautics Approved for the University Committee on Graduate Studies: °°. 111 iv Abstract Sophisticated robots can greatly enhance the role of humans in space by relieving astronauts of low level, tedious assembly and maintenance chores and allowing them to concentrate on higher level tasks. Robots and astronauts can work together efIiciently, as a team; but the robot must be capable of accomplishing complex operations and yet be easy to use. Multiple cooperating manipulators are essential to dexterity and can broaden greatly the types of activities the robot can achieve; adding adaptive control can ease greatly robot usage by allowing the robot to change its own controller actions, without human intervention, in response to changes in its environment. Previous work in the Aerospace Robotics Laboratory (ARL) have shown the usefulness of a space robot with cooperating manipulators. The research presented in this dissertation extends that work by adding adaptive control. To help achieve this high level of robot sophistication, this research made several advances to the field of nonlinear adaptive control of robotic systems. A nonlinear adaptive control algorithm developed originally for control of robots, but requiring joint positions as inputs, was extended here to handle the much more general case of manipulator endpoint-position commands. A new system modelling technique, called system concatenation was developed to simplify the generation of a system model for complicated systems, such as a free-flying multiple-manipulator robot system. Finally, the task-space concept was introduced wherein the operator's inputs specify only the robot's task. The robot's subsequent autonomous performance of each task still involves, of course, endpoint positions and joint configurations as subsets. The combination of these developments resulted in a new adaptive control framework that is capable of continuously providing full adaptation capability to the complex space-robot system in all modes of operation. The new adaptive control algorithm easily handles free-flying systems with multiple, interacting manipulators, and extends naturally to even larger systems. The new adaptive controller was experimentally demonstrated on an ideal testbed in the AR/.,--a first-ever experimental model of a multi-manipulator, free-flying space robot that is capable of capturing and manipulating free-floating objects without requiring human assistance. A graphical user interface enhanced the robot usability: it enabled an operator situated at a remote location to issue high-level task description commands to the robot, and to monitor robot activities as it then carried out each assignment autonomously. vi To my grandmother, whom I have known all my life, but never really knew. To my parents, who have strived always to provide me with the _eedom to choose my own path. To my wife, _r her boundless understanding and wisdom. vii VIII Acknowledgements I wish to thank my principal advisor, Professor Robert H. Cannon, Jr., for his enthusiastic support and guidance. His energetic efforts in recruiting outstanding students and his exceptional ability for securing funding for the Aerospace Robotics Laboratory (ARL) foster an unsurpassed research environment. Professor Cannon's desire to provide the best tools makes performing research in ARL fun. To Professor Gene E Franklin, I wish to extend my gratitude for the stimulating conversations and his insights into adaptive control and beyond. I also thank Professor Stephen M. Rock for his refreshing points of view and encouragement. This research would not have been possible without the Multiple-Manipulator Free-Flying Space Robot, designed and constructed by Marc Ullman and Ross Koningstein. I am grateful also for the friendship of Marc, not to mention his assistance and counsel. Thanks, too, are due to Stan Schneider for developing the software environment for real-time control; Bill Dickson for willingly assuming the responsibility of the maintenance chores for the robots; Howard Wang for updating the graphical user- interface; Rob Zanutta, Larry Alder, Chris Uhlik, and Dan Rovner for delving into adaptive control discussions; Dennis Morse for his photographic skill and the voluminous pictures of the experimental hardware; Denny, Dave Meer, Steve Ims, and Howard Wang for keeping our computers running; Bill Ballhaus, Edward Wilson, and Richard Marks for providing on-line entertainment. I also wish to thank Gad Shelef for the mechanical design of the payload, Tom Hasler for his expert workmanship, and Godwin Zhang for the construction of the analog electronics. Finally, I wish to express my appreciation for the Air Force Office of Scientific Research (AFOSR) and the National Aeronautics and Space Administration (NASA) for providing funding for this research. ix Contents Abs_ct iv Ackno_edgements vi List of Figures xu"l'" List of Symbols xvi 1.2stof Acronyms xix 1 Introduction 1 1.1 Motivation ..................................... 1 1.1.1 What is Adaptive Control? ......................... 1 1.1.2 What is Task-Space Control? ........................ 2 1.2 Research Goals ................................... 3 1.3 Contributions ................................... 5 1.4 Review of Related Research ............................. 6 1.4.1 Object-Based Cooperative Manipulation .................. 8 1A.2 Nonadaptive Space Robotics Research ................... 8 1.4.3 Nonlinear Adaptive Robot Control ..................... 9 1.5 Reader's Guide ................................... 11 2 Modelling 13 2.1 System Model ................................... 13 2.2 Alternate Parameterization ............................. 16 xi 2.3 Summary ...................................... 18 Control Approach 19 3.1 A Specific Adaptive Control Algorithm ....................... 19 3.2 Controller Properties ................................ 21 3.3 Lyapunov Proof ................................... 23 3.3.1 Proof Outline ............................... 23 3.3.2 Proof Details ................................ 25 3.3.3 Adaptive Controller Stability ........................ 32 Adaptive Control Extensions 33 4.1 Extension to Generalized Speeds .......................... 34 4.1.1 Transforming Equations of Motion ..................... 35 4.1.2 Stability Proof ............................... 36 4.2 Extension to Endpoint Control ........................... 37 4.2.1 Endpoint Jacobian ............................. 37 4.2.2 Endpoint Adaptive Control ......................... 40 4.2.3 Stability Proof ............................... 41 The Task-Space Concept 48 5.1 Task-space Adaptive Controller--Single-Arm Case ................. 50 5.1.1 Proof .................................... 53 5.2 Generalized Relationships .............................. 53 5.2.1 Generalized Speeds ............................. 53 5.2.2 Partial Velocities .............................. 54 5.2.3 Generalized Active Forces .......................... 56 5.2.4 Equations of Motion ............................ 58 5.2.5 Task-Space Control Law Revisited ..................... 60 5.3 Control in a Noninertial Reference Frame ...................... 61 5.3.1 Adaptive Endpoint Control in Noninertial Frame .............. 62 5A Space-Robot Control--Single