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TheRoboticsPrimer

TheRoboticsPrimerMaja J MatarićIllustrations by Nathan KoenigThe MIT PressCambridge, MassachusettsLondon, England

2007 Massachusetts Institute of TechnologyAll rights reserved. No part of this book may be reproduced in any form by anyelectronic or mechanical means (including photocopying, recording, or informationstorage and retrieval) without permission in writing from the publisher.Typeset in 10/13 Lucida Bright by the authors using LATEX 2ε .Printed and bound in the United States of America.Library of Congress Cataloging-in-Publication InformationMatarić, Maja JThe robotics primer / Maja J Matarić ; illustrations by Nathan Koenig.p. cm. (Intelligent robotics and autonomous agents series)Includes bibliographical references and index.ISBN 978-0-262-63354-3 (pbk. : alk. paper) 1. Robotics I. TitleTJ211.M3673 2007629.8’92—dc222007000981

To Helena and Nicholas, who teach me what matters, every day.

Brief Contents1What Is a Robot?Defining Robotics12Where Do Robots Come From?A Brief but Gripping History of Robotics3What’s in a Robot?Robot Components4Arms, Legs, Wheels, Tracks, and What Really Drives ThemEffectors and Actuators295Move It!Locomotion719476Grasping at StrawsManipulation597What’s Going On?Sensors698Switch on the LightSimple Sensors819Sonars, Lasers, and CamerasComplex Sensors9710Stay in ControlFeedback Control12111The Building Blocks of ControlControl Architectures13512What’s in Your Head?Representation145

viiiBrief Contents1314151617181920212223Think Hard, Act LaterDeliberative Control151Don’t Think, React!Reactive Control161Think and Act Separately, in ParallelHybrid Control177Think the Way You ActBehavior-Based Control187Making Your Robot BehaveBehavior Coordination207When the Unexpected HappensEmergent Behavior215Going PlacesNavigation223Go, Team!Group Robotics233Things Keep Getting BetterLearning255Where To Next?The Future of Robotics269Glossary293

ContentsPreface12What Is a Robot?Defining Robotics2.3Control Theory7Cybernetics82.2.1Grey Walter’s Tortoise2.2.2Braitenberg’s VehiclesArtificial Intelligence13What’s in a Robot?Robot Components3.13.23.33.43.541Where Do Robots Come From?A Brief but Gripping History of 24Brains and BrawnAutonomy2625Arms, Legs, Wheels, Tracks, and What Really Drives ThemEffectors and Actuators294.14.24.3Active vs. Passive Actuation30Types of Actuators31Motors324.3.1Direct-Current (DC) Motors32

xContents4.45Move ation60Why is Manipulation Hard?62Levels of Processing73Switch on the LightSimple Sensors818.18.28.38.49Stability48Moving and Gaits51Wheels and Steering53Staying on the Path vs. Getting ThereWhat’s Going On?Sensors697.1847Grasping at ervo Motors37Degrees of Freedom38Passive vs. Active Sensors81Switches82Light Sensors848.3.1Polarized Light868.3.2Reflective Optosensors868.3.3Reflectance Sensors888.3.4Infra Red Light898.3.5Modulation and Demodulation of Light8.3.6Break Beam Sensors908.3.7Shaft Encoders91Resistive Position Sensors948.4.1Potentiometers95Sonars, Lasers, and CamerasComplex Sensors979.1Ultrasonic or Sonar Sensing979.1.1Sonar Before and Beyond Robotics10090

xiContents9.29.39.1.2Specular Reflection101Laser Sensing104Visual Sensing1079.3.1Cameras1089.3.2Edge Detection1109.3.3Model-Based Vision1129.3.4Motion Vision1139.3.5Stereo Vision1149.3.6Texture, Shading, Contours9.3.7Biological Vision1169.3.8Vision for Robots11710 Stay in ControlFeedback Control11512110.110.210.310.4Feedback or Closed Loop Control121The Many Faces of Error122An Example of a Feedback Control RobotTypes of Feedback Control12610.4.1 Proportional Control12610.4.2 Derivative Control12810.4.3 Integral Control12910.4.4 PD and PID Control13010.5 Feedforward or Open Loop Control13111 The Building Blocks of ControlControl Architectures13511.1 Who Needs Control Architectures?11.2 Languages for Programming Robots11.3 And the Architectures are.13911.3.1 Time14111.3.2 Modularity14111.3.3 Representation14213513712 What’s in Your Head?Representation14512.1 The Many Ways to Make a Map12.2 What Can the Robot Represent?12.3 Costs of Representing14813 Think Hard, Act Later146147124

xiiContentsDeliberative Control15113.1 What Is Planning?13.2 Costs of Planning14 Don’t Think, React!Reactive Control15115416114.1 Action Selection16614.2 Subsumption Architecture16914.3 Herbert, or How to Sequence Behaviors Through theWorld17215 Think and Act Separately, in ParallelHybrid Control17715.115.215.315.4Dealing with Changes in the World/Map/TaskPlanning and Replanning180Avoiding Replanning181On-Line and Off-Line Planning18216 Think the Way You ActBehavior-Based Control17918716.1 Distributed Representation19216.2 An Example: Distributed Mapping19316.2.1 Toto the Robot19416.2.2 Toto’s Navigation19416.2.3 Toto’s Landmark Detection19616.2.4 Toto’s Mapping Behaviors19716.2.5 Path Planning in Toto’s Behavior Map16.2.6 Toto’s Map-Following20220017 Making Your Robot BehaveBehavior Coordination20717.1 Behavior Arbitration: Make a Choice17.2 Behavior Fusion: Sum It Up20920718 When the Unexpected HappensEmergent Behavior21518.118.218.318.4An Example: Emergent Wall-Following215The Whole Is Greater Than the Sum of Its PartsComponents of Emergence218Expect the Unexpected218216

xiiiContents18.5 Predictability of Surprise21918.6 Good vs. Bad Emergent Behavior22018.7 Architectures and Emergence22119 Going Search and Path PlanningSLAM229Coverage23020 Go, Team!Group Robotics22823320.120.220.320.4Benefits of Teamwork234Challenges of Teamwork236Types of Groups and Teams237Communication24120.4.1 Kin Recognition24620.5 Getting a Team to Play Together24720.5.1 I’m the Boss: Centralized Control24720.5.2 Work It Out as a Team: Distributed Control20.6 Architectures for Multi-Robot Control24920.6.1 Pecking Orders: Hierarchies25021 Things Keep Getting BetterLearning25521.121.221.321.4Reinforcement Learning256Supervised Learning260Learning by Imitation/From DemonstrationLearning and Forgetting26522 Where To Next?The Future of Robotics22.122.222.322.422.522.622.7261269Space Robotics273Surgical Robotics274Self-Reconfigurable Robotics276Humanoid Robotics277Social Robotics and Human-Robot InteractionService, Assistive and Rehabilitation RoboticsEducational Robotics283278280248

xivContents22.8 Ethical ImplicationsBibliography28923 Glossary293285

PrefaceUpon arriving at USC in 1997 as an assistant professor in Computer Science, Idesigned the Introduction to Robotics course (http://www-scf.usc.edu/ csci445). The highlights of the course were the intensive hands-on LEGO roboticslab, team projects, and the end-of-semester contest held at the nearby California Science Center. I posted my lecture notes on the web, for students’convenience, and found that, over the years, a growing number of facultyand K-12 teachers around the world contacted me about using those in theircourses and getting additional materials from me. In 2001, shortly after receiving tenure, being promoted to rank of associate professor, and expectingour second child, perhaps influence of the euphoria of it all, I had a deceptively simple thought: why not turn all those course notes into a book?As I started converting my sometimes-cryptic lecture notes into book chapters, I realized the true magnitude of the challenge I had set up for myself,that of writing a textbook for an audience that intended to span K-12 and university educators and students, as well as robotics enthusiasts who wantedto go beyond the popular press and get under the surface of the topic. Thereaders of the book would (hopefully) span the ages of early adolescence toretirement, and education levels of elementary school to PhD. This was notgoing to be easy.My motivation came from the fact that robotics is a wonderful field ofstudy. I am not a typical engineer; instead of making robots out of oldwatches and radios in my parent’s basement as a kid, I was interested inart and fashion design. I discovered the field late in college, through extracurricular reading while majoring in computer science; back then there wereno robotics courses at the University of Kansas. Upon entering graduateschool at MIT, I serendipitously chose robotics as my direction of study,based mostly on the charisma of my PhD advisor, Rodney Brooks, who wasthe first to make a compelling case for it. The goal of this book is to make acompelling case for studying robotics to a wide variety of readers, because

xviPrefacethe substance of robotics, while challenging, is incredibly interesting.Creating intelligent machines can fuel our imagination, creativity, and desire to make a difference. Robotics technology will play a key role in thefuture of humanity, and we are currently very directly shaping that future inthe research labs and classrooms around the country and the world. Mostimportantly, however, studying robotics early on can help the student to establish a foundation for a better understanding of science, technology, engineering, and math (STEM) topics. This is why I would love to see all childrenwork with robots in school, starting in elementary school (5th grade is certainly old enough, and earlier is possible), and continuing throughout highschool. Getting hooked on creative robotics opens the students’ minds andbuilds their confidence for a great variety of topics and eventually, careersin STEM. Without such fun, mind-opening learning and discovery, studentsoften incorrectly judge STEM as either uncool or unattainable. The goal ofthis book is to teach something real and true about robotics and its potential,while staying interesting and engaging.I’m amazed at how long it took to write this book. My son, who was aboutto be born when the book idea occurred to me, just turned five. All kindsof good things have happened in my career also, which slowed down thewriting. Eventually, I realized that life would just keep getting busier andthat there would never come "a great time to finish the book." Instead, timehad to be grabbed, borrowed, and stolen to get it done. My thanks go to myeditor at MIT Press, Bob Prior, who patiently reminded me of the importanceof finishing my first book, and is willing to work with me on a second.In the (long) course of writing this book, many wonderful K-12 and university educators provided feedback on the drafts. I listened to all of them. Thestudents and instructors of the Intro to Robotics course I mentioned aboveused drafts of the book, putting up with missing chapters and non-existentfigures. Marianna O’Brien, who teaches 8th grade science at Lincoln MiddleSchool in Santa Monica, was an angel: she spent over a year reading drafts,making numerous notes and improving suggestions, and helping me to geta glimpse at what it takes to be an effective pre-university teacher and howto write a book that could help. I owe Marianna a huge thank you for hertireless enthusiasm and detailed and encouraging comments! I am gratefulto Nate Koenig, a USC PhD student from my group who made the greatfigures for the book, and then got pulled into doing the formatting, the copyright permissions, the index, and the references, as well as making what nodoubt seemed to be an endless stream of small fixes in the last few months.The book owes its good looks to Nate.

xviiI am grateful to Helen Grainer and Rodney Brooks of iRobot Corp., whoagreed to sponsor a free web-based robot programming workbook companion for this book, found at http://roboticsprimer.sourceforge.net/workbook.The workbook, which I developed with my PhD students Nate Koenig andDavid Feil-Seifer, provides step-by-step guidance, example exercises, and solutions that should make real robot programming accessible to the readers ofthis book and anybody else interested in robotics.Role models are incredibly important. My mother, who has written numerous short story, essay, and poetry books, was an inspiration; she madethe endeavor seem readily within my reach. One of the goals of this book isto get people of all ages interested in robotics, so that we can create numerous role models, and never have to see kids avoid robotics (and STEM topicsin general) from ignorance, peer pressure, or lack of confidence.Above all, I am grateful to my family, who put up with some grabbed andborrowed (but never stolen) time needed to write this book. My husbandprovided moral support throughout and knew how to say "I don’t knowhow you do it" in a way that inspired and encouraged me to figure out howto do it. Finally, my two kids are the ones who motivated me the most towrite the book, since they will shortly be part of the intended audience. Ifthey and their peers think robotics is cool (and thereby Mom is cool as well),and consider taking up creative endeavors in science and engineering, thenI’ve done something good.South Pasadena, California, April 2007

1What Is a Robot?Defining RoboticsWelcome to The Robotics Primer! Congratulations, you have chosen a verycool way to learn about a very cool topic: the art, science, and engineeringof robotics. You are about to embark on a (hopefully fun) ride that will endwith your being able to tell what is real and what is not real in movies andarticles, impress friends with cool facts about robots and animals, and muchmore, most important of which is being able to better build and/or programyour own robot(s). Let’s get started!What is a robot?This is a good question to ask because, as with any interesting area of scienceand technology, there is a lot of misunderstanding about what robots are andare not, what they were and were not, and what they may or may not becomein the future. The definition of what a robot is, has been evolving over time,as research has made strides and technology has advanced. In this chapter,we will learn what a modern robot is.The word ”robot” was popularized by the Czech playwright Karel Capek(pronounced Kha-rel Cha-pek) in his 1921 play Rossum’s Universal Robots(R.U.R.). Most dictionaries list Capek as the inventor of the word “robot,”but more informal sources (such as the Web) say that it was actually hisbrother, Josef, who made up the term. In either case, the word “robot” resulted from combining the Czech words rabota, meaning “obligatory work”and robotnik, meaning “serf.” Most robots today are indeed performing suchobligatory work, in the form of repetitive and fixed tasks, such as automobileassembly and DNA sequencing. However, robotics is about much more thanobligatory labor, as you will see.The idea of a robot, or some type of machine that can help people, is mucholder than the Capek brothers. It is not possible to pin point where it orig-

21What Is a Robot?Defining Roboticsinated, because it is likely that many clever engineers of the past thoughtof it in some form. The form changed over time, as science and technologyadvanced, and made many of the previously unachievable dreams of robotsbecome a reality or at least enter the realm of possibility.With the advancement of science and technology, the notion of a robothas become more sophisticated. In the past, a robot was defined as a machine that was, basically, a clever mechanical device. Examples of such devices, even extremely sophisticated ones, can be found throughout history,and they go way back. As long as 3000 years ago, Egyptians used humancontrolled statues; and more recently, in the seventeenth and eighteenth century Europe, various clockwork-based “lifelike” creatures were constructedthat could sign, play the piano, and even “breathe.” But, as we will see, thosewere not really robots, not by our current definition and understanding ofwhat a robot is.While original notions of robots were really of clever mechanical automatons, as computational machinery developed (and in particular when it shrankin size sufficiently to be imaginable within a robot’s body), the notions ofrobots started to include thought, reasoning, problem-solving, and even emotions and consciousness. In short, robots started to look more and more likebiological creatures, ranging from insects to humans.These days we have (or should have) a very broad idea of what a robot canbe, and do not need to limit ourselves by what is currently possible mechanically or computationally. However, it is still hard to anticipate how our ideasof what a robot is and can be will evolve as science and technology advance.So back to the question: what is a robot? What makes the machine infigure 1.1 a robot, but those in figure 1.2 merely robot wannabes?R OBOTA robot is an autonomous system which exists in the physicalworld, can sense its environment, and can act on it to achievesome goals.This may seem like a very broad definition, but actually each of its parts isimportant and necessary. Let’s take it apart to see why.A robot is an AUTONOMOUS systemA UTONOMOUST ELEOPERATEDAn autonomous robot acts on the basis of its own decisions, and is not controlled by a human.There are, of course, plenty of examples of machines that are not autonomous,but are instead externally controlled by humans. They are said to be teleop-

3Figure 1.1 An example of a robot.erated; tele means “far” in Greek, so teleoperation means operating a systemfrom afar.These machines, however, are not true robots. True robots act autonomously. They may be able to take input and advice from humans, but are notcompletely controlled by them.A robot is an autonomous system which exists in the PHYSICALWORLDExisting in the physical world, the same world that people and animalsand objects and trees and and weather and many other things exist in, is afundamental property of robots. Having to deal with that physical world,and its unbendable physical laws and challenges, is what makes roboticswhat it is: a real challenge. Robots that exist on the computer are simulations; they do not really have to deal with true properties of the physicalworld, because simulations are never as complex as the real world. Therefore, although there are a lot of simulated robots in cyberspace, a true robotexists in the physical world.A robot is an autonomous system which exists in the physicalworld, can SENSE its environment

41What Is a Robot?Defining RoboticsFigure 1.2 Examples of non-robots. On the left is a system that does not exist in thephysical world; on the right, a system that is not autonomous. These robot wannabesare not the real thing.S ENSORSSensing the environment means the robot has sensors, some means of perceiving (e.g., hearing, touching, seeing, smelling, etc.) in order to get information from the world. A simulated robot, in contrast, can just be given theinformation or knowledge, as if by magic. A true robot can sense its worldonly through its sensors, just as people and other animals do. Thus, if a system does not sense but is magically given information, we do not considerit a true robot. Furthermore, if a system does not sense or get information,then it is not a robot, because it cannot respond to what goes on around it.A robot is an autonomous system which exists in the physicalworld, can sense its environment, and can ACT ON ITTaking actions to respond to sensory inputs and to achieve what is desiredis a necessary part of being a robot. A machine that does not act (i.e., doesnot move, does not affect the world by doing/changing something) is not arobot. As we will see, action in the world comes in very different forms, andthat is one reason why the field of robotics is so broad.A robot is an autonomous system which exists in the physicalworld, can sense its environment, and can act on it to ACHIEVESOME GOALS.Now we finally come to the intelligence, or at least the usefulness, of arobot. A system or machine that exists in the physical world and senses it,

5R OBOTICSbut acts randomly or uselessly, is not much of a robot, because it does not usethe sensed information and its ability to act i

The Future of Robotics 269 22.1 Space Robotics 273 22.2 Surgical Robotics 274 22.3 Self-Reconfigurable Robotics 276 22.4 Humanoid Robotics 277 22.5 Social Robotics and Human-Robot Interaction 278 22.6 Service, Assistive and Rehabilitation Robotics 280 22.7 Educational Robotics 283

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