Contact Modeling and Directional Adhesion for Climbing Robots

166 Pages·2010·13.68 MB·English

CONTACT MODELING AND DIRECTIONAL ADHESION FOR
CLIMBING ROBOTS
A DISSERTATION
SUBMITTED TO THE DEPARTMENT OF MECHANICAL
ENGINEERING
AND THE COMMITTEE ON GRADUATE STUDIES
OF STANFORD UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
Daniel Oliveira Santos
October 2007
UMI Number: 3292413
Copyright 2008 by
Santos, Daniel O.
All rights reserved.
INFORMATION TO USERS
The quality of this reproduction is dependent upon the quality of the copy
submitted. Broken or indistinct print, colored or poor quality illustrations and
photographs, print bleed-through, substandard margins, and improper
alignment can adversely affect reproduction.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if unauthorized
copyright material had to be removed, a note will indicate the deletion.
®
UMI
UMI Microform 3292413
Copyright 2008 by ProQuest Information and Learning Company.
All rights reserved. This microform edition is protected against
unauthorized copying under Title 17, United States Code.
ProQuest Information and Learning Company
300 North Zeeb Road
P.O. Box 1346
Ann Arbor, Ml 48106-1346
© Copyright by Daniel Oliveira Santos 2008
All Rights Reserved
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.
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.
Waldron)
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.
^ C ^
P-Sac*"* g>
(Oussama Khatib)
Approved for the University Committee on Graduate Studies.
in
Abstract
Climbing robots have the potential to perform a variety of useful tasks including main-
tenance, exploration, and search and rescue. Unfortunately, current climbing robots
have not achieved robust performance in unstructured real-world environments, ex-
cept when tasked with very limited and specific goals. Examples from Nature, such as
the gecko lizard, can provide insight for achieving a new level of robot performance,
potentially able to climb a wide range of surfaces and materials.
Developing such robots requires a detailed understanding of the interaction be-
tween the feet and the climbing substrate. Climbing is a relatively new challenge for
legged robots and there has been little previous work on adhesion models specifically
for climbing. The adhesive characteristics of the contact govern the magnitudes of
forces that can be applied at the feet without them popping off or slipping along the
surface. Classical contact and adhesion models between elastic materials, as well as
most synthetic adhesives, are not able to describe the adhesion systems observed in
animals such as the gecko lizard.
The gecko lizard is able to climb vertical and even overhanging surfaces composed
of materials ranging from glass to painted wallboard. Its adhesion system contains an
important property necessary for robust climbing — directionality. A new adhesion
model, termed Frictional Adhesion, captures the directionality of the gecko's adhesive
system. This model differs from many previous adhesive models and provides distinct
advantages for climbing vertical surfaces.
A new synthetic adhesive is presented that duplicates the directionality of the
gecko adhesion system. Directional adhesives present new challenges when testing
and characterizing their adhesive qualities compared to non-directional adhesives.
IV
A custom experimental setup and procedures used for testing this adhesive are de-
scribed. Results characterizing the adhesive are given and its ability to duplicate the
directionality of the gecko adhesion system is discussed.
The nature of directional adhesion also presents new considerations for the de-
sign and control of climbing robots. Simplified two- and three-dimensional analyses
highlight the differences between non-directional and directional adhesion models. In
many cases the optimal force control and foot orientation strategies are quite differ-
ent when using directional adhesion as opposed to conventional, isotropic adhesion.
These simple models also explain some of the climbing behaviors seen in gecko lizards.
Directional adhesion enables control of the adhesion forces, which in turn facil-
itates smooth attachment and detachment of feet and robust climbing. However,
appropriate use of directional adhesion necessitates added consideration of the force
distribution to and orientation of the feet. With proper application, directional ad-
hesion can greatly improve overall performance in climbing robots.
v
Para os mens pais,
Fernando Bastos dos Santos e Ilda Marques de Oliveira Santos
VI
Acknowledgment
I would not have been able to complete this dissertation without support from the
people in my life.
I would like to thank the following people who have helped make this possible:
First and foremost, my adviser, Prof. Mark Cutkosky, who gave me the opportunity
and guidance necessary to pursue this research. Prof. Kellar Autumn for many
useful collaborations and discussions on the gecko adhesion system. My reading
committee members, Prof. Kenneth Waldron and Prof. Oussama Khatib. Sangbae
Kim, for providing me with many samples of synthetic directional adhesives to test.
All of the current and past members of BDML. Dr. Noe Lozano and the Dean's
Doctoral Diversity Fellowship for funding during my Masters degree. Prof. Channing
Robertson, Prof. Jim Swartz, and the NIH-Stanford Biotechnology Training Grant
for funding during my Doctoral degree.
Most importantly, I would like to thank my family, especially mom and dad, for
their love and support, as well as all the friends I have been lucky to have over the
years.
vn
Contents
Abstract iv
Acknowledgment vii
1 Introduction 1
1.1 Motivation 1
1.2 Thesis Outline 2
1.3 Contributions 3
2 Background Literature 5
2.1 Contact Modeling 6
2.1.1 Hertz Contact Theory 6
2.1.2 Coulomb Friction 8
2.2 Adhesion Modeling 12
2.2.1 Early Work 12
2.2.2 Johnson-Kendall-Roberts Model 14
2.2.3 Savkoor-Briggs and Other Advances 17
2.2.4 Kendall Peel Model 19
2.2.5 Summary 20
2.3 The Gecko Adhesive System 22
2.4 Gecko-Inspired Synthetic Adhesives 27
2.4.1 Theoretical Considerations 28
2.4.2 Experimental Examples 30
2.5 Directional Adhesion for Climbing 34
vm
2.6 Summary 37
3 Experimental Investigation 39
3.1 Design and Fabrication of a Directional Adhesive 40
3.1.1 Design Parameter Effects 40
3.1.2 Directional Polymer Stalks 44
3.2 Experimental Apparatus 46
3.2.1 Mechanical Setup 47
3.2.2 Electronic Setup 49
3.2.3 Software Control and Data Acquisition 50
3.2.4 System Characterization 51
3.3 Experimental Procedure 53
3.3.1 Sample Preparation and Alignment 53
3.3.2 General Procedure Description 54
3.3.3 Discussion of Raw Data 55
3.4 Adhesion Results 58
3.4.1 Adhesive Pulloff Forces 59
3.4.2 Effect of Preload Magnitude 61
3.4.3 Effect of Preload Trajectory 63
3.4.4 Rate Dependence of Adhesion 67
3.4.5 Coefficient and Work of Adhesion 69
3.4.6 2D and 3D Directional Adhesion Limit Surface 75
3.4.7 Combining Limit Surfaces from Different Contacts 84
3.5 Summary 86
4 Climbing Analysis 89
4.1 Two-Dimensional Force Analysis 90
4.1.1 Model and Analysis Description 90
4.1.2 Example Analysis Using Coulomb Friction 97
4.1.3 Comparison of Isotropic and Anisotropic Contact 101
4.2 Three-Dimensional Force Analysis 108
4.2.1 Model and Analysis Description 108
IX