45695Siegwart 6/10/04 3:17 PM Page 1 Introduction to Autonomous Mobile Robots to Introduction Roland Siegwart and Illah R. Nourbakhsh Roland SIEGWART Mobile robots range from the teleoperated Sojourner on the Mars Pathfinder mission to cleaning robots in the Paris Metro. Introduction to Autonomous Illah R. NOURBAKHSH Mobile Robots offers students and other interested readers an overview of the Autonomous Mobile Robots technology of mobility—the mechanisms that allow a mobile robot to move through a real world environment to perform its tasks—including locomotion, sensing, localization, and motion planning. It discusses all facets of mobile robotics, including hardware design, wheel design, kinematics analysis, sensors and per- ception, localization, mapping, and robot control architectures. The design of any successful robot involves the integration of many different disciplines, among them kinematics, signal analysis, information theory, artificial intelligence, and probability theory. Reflecting this, the book presents the tech- niques and technology that enable mobility in a series of interacting modules. Each chapter covers a different aspect of mobility, as the book moves from low- level to high-level details. The first two chapters explore low-level locomotory ability, examining robots’ wheels and legs and the principles of kinematics. This is followed by an in-depth view of perception, including descriptions of many “off- the-shelf” sensors and an analysis of the interpretation of sensed data. The final two chapters consider the higher-level challenges of localization and cognition, discussing successful localization strategies, autonomous mapping, and navigation competence. Bringing together all aspects of mobile robotics into one volume, Introduction to Autonomous Mobile Robots can serve as a textbook for course- work or a working tool for beginners in the field. Introduction to Autonomous Roland Siegwart is Professor and Head of the Autonomous Systems Lab at the Swiss Federal Institute of Technology, Lausanne. Illah R. Nourbakhsh is Associate Professor of Robotics in the Robotics Institute, School of Computer Science, at SIEGWART andSIEGWART NOURBAKHSH Mobile Robots Carnegie Mellon University. “This book is easy to read and well organized. The idea of providing a robot functional architecture as an outline of the book, and then explaining each component in a chapter, is excellent. I think the authors have achieved their goals, and that both the beginner and the advanced student will have a clear idea of how a robot can be endowed with mobility.” —Raja Chatila, LAAS-CNRS, France Intelligent Robotics and Autonomous Agents series A Bradford Book 0-262-19502-X The MIT Press Massachusetts Institute of Technology Cambridge, Massachusetts 02142 ,!7IA2G2-bjfach!:t;K;k;K;k http://mitpress.mit.edu Introduction to Autonomous Mobile Robots Intelligent Robotics and Autonomous Agents Ronald C. Arkin, editor Robot Shaping: An Experiment in Behavior Engineering, Marco Dorigo and Marco Colombetti, 1997 Behavior-Based Robotics, Ronald C. Arkin, 1998 Layered Learning in Multiagent Systems: A Winning Approach to Robotic Soccer, Peter Stone, 2000 Evolutionary Robotics: The Biology, Intelligence, and Technology of Self-Organizing Machines, Stefano Nolfi and Dario Floreano, 2000 Reasoning about Rational Agents, Michael Wooldridge, 2000 Introduction to AI Robotics, Robin R. Murphy, 2000 Strategic Negotiation in Multiagent Environments, Sarit Kraus, 2001 Mechanics of Robotic Manipulation, Matthew T. Mason, 2001 Designing Sociable Robots, Cynthia L. Breazeal, 2002 Introduction to Autonomous Mobile Robots, Roland Siegwart and Illah R. Nourbakhsh, 2004 Introduction to Autonomous Mobile Robots Roland Siegwart and Illah R. Nourbakhsh A Bradford Book The MIT Press Cambridge, Massachusetts London, England © 2004 Massachusetts Institute of Technology All rights reserved. No part of this book may be reproduced in any form by any electronic or mechan- ical means (including photocopying, recording, or information storage and retrieval) without permis- sion in writing from the publisher. This book was set in Times Roman by the authors using Adobe FrameMaker 7.0. Printed and bound in the United States of America. Library of Congress Cataloging-in-Publication Data Siegwart, Roland. Introduction to autonomous mobile robots / Roland Siegwart and Illah Nourbakhsh. p. cm. — (Intelligent robotics and autonomous agents) “A Bradford book.” Includes bibliographical references and index. ISBN 0-262-19502-X (hc : alk. paper) 1. Mobile robots. 2. Autonomous robots. I. Nourbakhsh, Illah Reza, 1970– . II. Title. III. Series. TJ211.415.S54 2004 629.8´92—dc22 2003059349 To Luzia and my children Janina, Malin and Yanik who give me their support and freedom to grow every day — RS To my parents Susi and Yvo who opened my eyes — RS To Marti who is my love and my inspiration — IRN To my parents Fatemeh and Mahmoud who let me disassemble and investigate everything in our home — IRN Slides and exercises that go with this book are available on: http://www.mobilerobots.org Contents Acknowledgments xi Preface xiii 1 Introduction 1 1.1 Introduction 1 1.2 An Overview of the Book 10 2 Locomotion 13 2.1 Introduction 13 2.1.1 Key issues for locomotion 16 2.2 Legged Mobile Robots 17 2.2.1 Leg configurations and stability 18 2.2.2 Examples of legged robot locomotion 21 2.3 Wheeled Mobile Robots 30 2.3.1 Wheeled locomotion: the design space 31 2.3.2 Wheeled locomotion: case studies 38 3 Mobile Robot Kinematics 47 3.1 Introduction 47 3.2 Kinematic Models and Constraints 48 3.2.1 Representing robot position 48 3.2.2 Forward kinematic models 51 3.2.3 Wheel kinematic constraints 53 3.2.4 Robot kinematic constraints 61 3.2.5 Examples: robot kinematic models and constraints 63 3.3 Mobile Robot Maneuverability 67 3.3.1 Degree of mobility 67 3.3.2 Degree of steerability 71 3.3.3 Robot maneuverability 72 viii Contents 3.4 Mobile Robot Workspace 74 3.4.1 Degrees of freedom 74 3.4.2 Holonomic robots 75 3.4.3 Path and trajectory considerations 77 3.5 Beyond Basic Kinematics 80 3.6 Motion Control (Kinematic Control) 81 3.6.1 Open loop control (trajectory-following) 81 3.6.2 Feedback control 82 4 Perception 89 4.1 Sensors for Mobile Robots 89 4.1.1 Sensor classification 89 4.1.2 Characterizing sensor performance 92 4.1.3 Wheel/motor sensors 97 4.1.4 Heading sensors 98 4.1.5 Ground-based beacons 101 4.1.6 Active ranging 104 4.1.7 Motion/speed sensors 115 4.1.8 Vision-based sensors 117 4.2 Representing Uncertainty 145 4.2.1 Statistical representation 145 4.2.2 Error propagation: combining uncertain measurements 149 4.3 Feature Extraction 151 4.3.1 Feature extraction based on range data (laser, ultrasonic, vision-based ranging) 154 4.3.2 Visual appearance based feature extraction 163 5 Mobile Robot Localization 181 5.1 Introduction 181 5.2 The Challenge of Localization: Noise and Aliasing 182 5.2.1 Sensor noise 183 5.2.2 Sensor aliasing 184 5.2.3 Effector noise 185 5.2.4 An error model for odometric position estimation 186 5.3 To Localize or Not to Localize: Localization-Based Navigation versus Programmed Solutions 191 5.4 Belief Representation 194 5.4.1 Single-hypothesis belief 194 5.4.2 Multiple-hypothesis belief 196 Contents ix 5.5 Map Representation 200 5.5.1 Continuous representations 200 5.5.2 Decomposition strategies 203 5.5.3 State of the art: current challenges in map representation 210 5.6 Probabilistic Map-Based Localization 212 5.6.1 Introduction 212 5.6.2 Markov localization 214 5.6.3 Kalman filter localization 227 5.7 Other Examples of Localization Systems 244 5.7.1 Landmark-based navigation 245 5.7.2 Globally unique localization 246 5.7.3 Positioning beacon systems 248 5.7.4 Route-based localization 249 5.8 Autonomous Map Building 250 5.8.1 The stochastic map technique 250 5.8.2 Other mapping techniques 253 6 Planning and Navigation 257 6.1 Introduction 257 6.2 Competences for Navigation: Planning and Reacting 258 6.2.1 Path planning 259 6.2.2 Obstacle avoidance 272 6.3 Navigation Architectures 291 6.3.1 Modularity for code reuse and sharing 291 6.3.2 Control localization 291 6.3.3 Techniques for decomposition 292 6.3.4 Case studies: tiered robot architectures 298 Bibliography 305 Books 305 Papers 306 Referenced Webpages 314 Interesting Internet Links to Mobile Robots 314 Index 317 Acknowledgments This book is the result of inspirations and contributions from many researchers and students at the Swiss Federal Institute of Technology Lausanne (EPFL), Carnegie Mellon Univer- sity’s Robotics Institute, Pittsburgh (CMU), and many others around the globe. We would like to thank all the researchers in mobile robotics that make this field so rich and stimulating by sharing their goals and visions with the community. It is their work that enables us to collect the material for this book. The most valuable and direct support and contribution for this book came from our past and current collaborators at EPFL and CMU. We would like to thank: Kai Arras for his con- tribution to uncertainty representation, feature extraction and Kalman filter localization; Matt Mason for his input on kinematics; Nicola Tomatis and Remy Blank for their support and assistance for the section on vision-based sensing; Al Rizzi for his guidance on feed- back control; Roland Philippsen and Jan Persson for their contribution to obstacle avoid- ance; Gilles Caprari and Yves Piguet for their input and suggestions on motion control; Agostino Martinelli for his careful checking of some of the equations and Marco Lauria for offering his talent for some of the figures. Thanks also to Marti Louw for her efforts on the cover design. This book was also inspired by other courses, especially by the lecture notes on mobile robotics at the Swiss Federal Institute of Technology, Zurich (ETHZ).