Real-Time Control of Walking

168 Pages·1987·5.278 MB·English

by  Marc D. Donner

Progress in Computer Science
Volume 7
Series Editors
J. Bentley
E. Coffman
R. Graham
D. Kuck
N. Pippenger
Marc D. Donner
Real-Time Control
of Walking
With 88 Illustrations
1987 Birkhauser
Boston . Basel . Stuttgart
Marc D. Donner
International Business Machines
Thomas J. Watson Research Center
Yorktown Heights, NY 10598
U.S.A.
Library of Congress Cataloging in Publication Data
Donner, Marc D.
Real-time control of walking.
(Progress in computer science; vol. 7)
Bibliography: p.
Includes index.
1. Robotics. 2. Locomotion. 3. Real-time data
processing. 1. Title. II. Series
TJ21l.D66 1986 629.8'92 86-20586
CIP-KUlztitelaufnahme der Deutschen Bibliotbek
Donner, Marc D.:
Real-time control of walkinglMarc D. Donner.-I
Boston; Basel; Stuttgart: Birkhiiuser, 1986.-1
(Progress in computer science ; Vol. 7)
ISBN-13: 978-0-8176-3332-5 e- ISBN-13: 978-1-4612-4990-0
001: 10.1007/978-1-4612-4990-0
NE:GT
All rights reserved. No part of this publication may be reproduced, stored in a retrieval
system, or transmitted, in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise, without prior permission of the copyright owner.
© Birkhauser Boston, 1987
Softcoverreprint of the hardcover 1st edition 1987
ISBN-13: 978-0-8176-3332-5
Printed and bound by R. R. Donnelley & Sons, Harrisonburg, Virginia.
9 8 7 6 5 4 3 2 J
Preface
I wonder whether Karel Capek imagined in 1923 that by his use of the Czech word
for forced labor, rohota, to name the android creations of Mr. Rossum he was naming
an important technology of his future. Perhaps it wasn't Capek's work directly, but
rather its influence on Lang's movie Metropolis in 1926 that introduced the term to
the popular consciousness. In the public mind ever since a robot has been a me
chanical humanoid, tireless and somewhat sinister.
In the research community the field of robotics has recently reached large size and
respectability, but without answering the question, "What is robotics?" or perhaps,
"What is a robot?"
There is no real consensus for a precise definition of robotics. I suppose that
Capekian mechanical men, if one could build them, are robots, but after that there
is little agreement. Rather than try to enumerate all of the things that are and are
not robots, I will try to characterize the kinds of features that make a system a robot.
A candidate definition of a robot is a system intended to achieve mechanical action,
with sensory feedback from the world to guide the actions and a sophisticated con
trol system connecting the sensing and the actions.
The intent of the system must be mechanical action, so interactive graphics is not
robotics. The sensing must be of or closely related to the mechanical action, so check
printing and other traditional information processing activities are out, although the
output devices are mechanical. The actions of the system must admit change based
on the sensor data. So far the robot systems described here are not far from classical
control systems. This is true, but the domain of robotics typically involves systems
of sufficient complexity or nonlinearity of function or control that the traditional
techniques of control theory fail or are inadequately powerful.
Certainly by this definition of robotics it is possible to claim that a numerically con
trolled machine tool is a robot, though the sensing requirement must be examined
closely. The automatic fuel control system for a modern car qualifies, as does the
Preface v
autopilot of a plane. Even a clothes washer, able to sense the amount of water in the
tub and its temperature and act accordingly, can be considered to be a robot, though
it isn't a very interesting one. On the other hand, many current industrial robot sys
tems fail this test, lacking any sensory capabilities. So you can see the dilemma that
one faces when trying to provide a definition of robotics.
In some sense a robot is all of the above systems with the proviso that the program
ming of the machine's behavior is under the control of the user rather than the man
ufacturer. Certainly this excludes things like washers and dryers, which we
intuitively reject, from the field of robotics.
Having failed to define the field of robotics, in which the research reported in this
book fits, let's go on to examine the field and identify the general research themes.
There are four major areas in robotics, of various sizes and ages: manipulation,
locomotion, sensing, and control.
Manipulation is by far the oldest area of robotics research and the largest. It is con
cerned with issues in the design and programming of robots intended to sit reason
ably still and push and pull on the world around them. So called "robot arms" are
the most common artifacts in this area. Commonly these systems are fairly stiff, so
that dynamic effects can be neglected in modelling them. This permits planning to
be used as the basic tool for motion design.
Locomotion is a fairly new area of research, concerned with robots that move
around. The artifacts that researchers in this area work on are of two kinds; wheeled
rovers with various sensors designed to navigate in a fairly conventional flat-floored
environment and legged machines designed to deal with difficult terrain. The subject
of this book is the control of one such legged machine.
The third major area of activity in robotics research is in technology for sensors. This
is one of the places where the state of the art is quite weak and where progress is
being made. There has been a lot of work in computer vision in recent years, both
directed toward identifying and locating objects in a camera's visual field and for
navigation of a moving robot in a complex environment. Tactile sensing has become
an exciting area of work recently, with several research groups designing and con
structing tactile sensor arrays. Sensing is an area where a lot of the progress is still
to be made in the basic technology rather than in computer system design and pro
gramming.
The final major area of robotics research is control, how to connect the sensors and
actuators together with a computer and get the whole mess to do something inter
esting. In this area there are several main thrusts, one of which is real time systems
and the other of which is system modelling and planning. System modelling and
planning are techniques that permit computer programs to predict the behavior of
an actual robot interacting with the world so that decisions can be made as far in
vi Real-time control of walking
advance as possible. The work in real time systems assumes that sufficient computer
power is available with the robot to eliminate the need for modelling and planning,
though of course this is never completely true. This book describes work in the de
sign of tools like programming languages and operating systems directed at easing the
design and implementation job for high performance robots.
Acknowledgements
The number of people who have contributed to making this work possible or to my
enjoyment of the process of doing it or both is truly stunning. By tradition, only the
author of a dissertation is honored publicly; the rest of those who made it possible
are repaid simply with private gratitude. In token of my gratitude, I mention here
some of the people who have helped and hint at their contributions. The first five,
Ivan Sutherland, Raj Reddy, Marc Raibert, Mary Shaw, and Rick Dill, served on my
thesis committee. The rest are presented in no particular order at all.
Ivan Sutherland designed and constructed the walking machine and offered me the
opportunity to program it. He encouraged me when I decided to take a radical ap
proach to the control problem. He taught me the meaning of courage and helped
me recover it on the many occasions when I lost it.
Raj Reddy opened my eyes to the idea that good scholarship need not be narrow,
dry, or uncreative.
Marc Raibert taught me that there are no boundaries or territories in science. When
the interesting idea goes over there, follow it, even if you wander beyond the edges
of your field. He also tried to instill a measure of scientific care and discipline in my
work ... and almost succeeded, despite my best efforts.
Mary Shaw spent a lot of her time discussing language design with me, patiently
making the effort to understand the half-baked ideas I was scattering about and
asking the careful questions that helped me understand what I was doing.
Rick Dill taught me about intellectual honesty and good engineering. He has never
failed to recognize and reward real achievement nor to ridicule silly pretension.
James Gosling and I spent a lot of time eating and drinking and discussing Life, the
Universe, and Everything. Everything included my work, and James patiently suf
fered a great deal of earbending by me about OWL and walking.
Wes Clark took the effort to understand what I was doing and asked, in the most
gentle manner imaginable, some of the hardest questions that I had ever avoided.
He supervised the writing of the first walking program and provided the grapes that
I consumed while doing so.
Preface vii
Chris Stephenson provided intense intellectual challenges and a great deal of stimu
lating argument. He listened to me and made several important comments about the
design of OWL.
To Bill Wulf lowe my understanding of what a thesis is and, most importantly, the
realization that OWL could be compiled instead of interpreted.
Peter Capek, in addition to being one of the most impressive programmers of my
acquaintance, provided challenge and inspiration and unfailing hospitality. A better
friend would be hard to come by.
To the members of HA lowe lots of things, including many improvements in my
programming style and quite a few enjoyable evenings spent reading code and
drinking wine. HA included Ed Smith, James Gosling, Bob Sidebotham, Dave
Rosenthal, Ivor Durham, Mike Kazar, Mahadev Satyanarayanan (Satya), David
Nichols, and Larry Matthies, among others.
I must thank the house at 1014 Flemington for many hours of diversion during the
writing of this dissertation. When my brain began to overheat, I could always count
on remodeling projects there to provide me with walls to tear down and other forms
of useful destruction.
I am grateful for the quotation from Karn Evil 9 by Emerson, Lake and Palmer,
copyright 1973 Manticore Music Limited, reprinted with the permission of their
agents, George Carter and Company. I am also grateful to Claude Shannon for
permission to reprint the poem included as Appendix D.
Special thanks are due to the people who helped with the publication of this book,
including George Adelman, Carol Munroe, Elise Oranges, Geoff Bartlett, Maureen
Ruskie, David Jameson, and Jon Bentley.
Jim Kocher's help with videotaping was so important and so cheerful that it cannot
be forgotten. The assistance that Jim McQuade provided with the 68000 C compiler
was invaluable ... particularly the time he helped me patch a running program in order
to salvage a day's worth of data. Mike Ullner wrote the I/O routines that serviced
the OWL runtime system ... he provided some of the most reliable code I have ever
dealt with. David Douglas kept the machine functioning, bringing it back to life after
broken legs and other disasters that I feared were terminal. Jenise Tamaki kept the
lab functioning with a thousand different contributions. Sharon Burks, the CSD den
mother, was wonderful.
Finally, my friends who kept me happy and sane during my time in Pittsburgh:
Satish, Larry, James, Robin, Bob, Dave, Satya, Jenise, Peg, Ed, Sarah, Carl, Lynn,
Ed, Nathaniel, Trina, and others. It wouldn't have been worth it without you.
viii Real-time control of walking
Table of Contents
1.0 Introduction •...•••.•.••.•.•.•...••..••.••...•....•......•... 1
Part One - Machine and animal walking •..••.....•••.•.••..•..•.•..... 5
2.0 Animal walking .•...•••....•.•..•.••..•.•...•.•.•..•.••....... 7
2.1 Locality of control ............................................ 7
2.1.1 The insect nervous system .................................. 7
2.1.2 Insect experiments ........................................ 8
2.1.3 The spinal cat ............................................ 9
2.1.4 Reflexes versus patterns .................................... 9
2.2 Rear-to-front waves ......................................... 10
2.3 Why insect gaits are not discrete ................................ 14
2.4 Summary .................................................. 14
3.0 Other walking work ......•.•.......•.....••..•...........•... 17
3.1 Static stability .............................................. 18
3.2 Dynamic stability ............................................ 20
3.3 Summary .................................................. 21
4.0 SSA walking machine ••.......•..•..•..•...............•.....• 23
4.1 Mechanical overview ......................................... 23
4.2 Valve settings .............................................. 26
4.2.1 Hip control ............................................. 26
4.2.2 Knee control ............................................ 27
4.2.3 Valve switching time ...................................... 28
4.3 Control computers ........................................... 29
4.4 Hydraulic system ............................................ 30
4.4.1 Pumps ................................................. 31
4.4.2 Cylinders............................................... 31
4.4.3 Valves ................................................. 33
4.5 Summary .................................................. 35
Table of Contents ix