electroactive polymer (eap) actuators as artificial muscles

Electroactive Polymer (EAP)Actuators as Artificial Muscles

Reality, Potential, and Challenges

SECOND EDITION

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SPIE PRESSA Publication of SPIE—The International Society for Optical Engineering

Bellingham, Washington USA

Electroactive Polymer (EAP)Actuators as Artificial Muscles

Reality, Potential, and ChallengesSECOND EDITION

Yoseph Bar-CohenEditor


Library of Congress Cataloging-in-Publication Data Electroactive polymer (EAP) actuators as artificial muscles : reality, potential, and challenges / Yoseph Bar-Cohen, editor. – 2nd ed.

p. cm. – (SPIE Press monograph) Includes bibliographical references and index. ISBN 0-8194-5297-1 1. Polymers in medicine. 2. Conducting polymers. 3. Muscles. I. Bar-Cohen, Yoseph. II. Series.

R857.P6E43 2004

610'.28–dc022 2004002977

Published by SPIE—The International Society for Optical Engineering P.O. Box 10 Bellingham, Washington 98227-0010 USA Phone: +1 360 676 3290 Fax: +1 360 647 1445 Email: [email protected] Web: http://spie.org Copyright © 2004 The Society of Photo-Optical Instrumentation Engineers All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means without written permission of the publisher. The content of this book reflects the work and thought of the author(s). Every effort has been made to publish reliable and accurate information herein, but the publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon. Printed in the United States of America. PDF ISBN: 9780819481122


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Contents Preface / xiii Topic 1 Introduction Chapter 1 EAP History, Current Status, and Infrastructure / 3 Yoseph Bar-Cohen 1.1 Introduction / 4 1.2 Biological Muscles / 8 1.3 Historical Review and Currently Available Active Polymers / 8 1.4 Polymers with Controllable Properties or Shape / 10 1.5 Electroactive Polymers (EAP) / 22 1.6 The EAP Roadmap––Need for an Established EAP Technology

Infrastructure / 39 1.7 Potential / 41 1.8 Acknowledgments / 42 1.9 References / 43 Topic 2 Natural Muscles Chapter 2 Natural Muscle as a Biological System / 53 Gerald H. Pollack, Felix A. Blyakhman, Frederick B. Reitz, Olga V. Yakovenko, and Dwayne L. Dunaway 2.1 Conceptual Background / 53 2.2 Structural Considerations / 56 2.3 Does Contraction Involve a Phase Transition? / 59 2.4 Molecular Basis of the Phase Transition / 62 2.5 Lessons from the Natural Muscle System That May Be Useful for the

Design of Polymer Actuators / 68 2.6 References / 70 Chapter 3 Metrics of Natural Muscle Function / 73 Robert J. Full and Kenneth Meijer 3.1 Caution about Copying and Comparisons / 74 3.2 Common Characterizations—Partial Picture / 75 3.3 Work-Loop Method Reveals Diverse Roles of Muscle Function during

Rhythmic Activity / 79 3.4 Direct Comparisons of Muscle with Human-Made Actuators / 85


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3.5 Future Reciprocal Interdisciplinary Collaborations / 86 3.6 Acknowledgments / 87 3.7 References / 87 Topic 3 EAP Materials Topic 3.1 Electric EAP Chapter 4 Electric EAP / 95 Qiming Zhang, Cheng Huang, Feng Xia, and Ji Su 4.1 Introduction / 96 4.2 General Terminology of Electromechanical Effects in Electric EAP / 96 4.3 PVDF-Based Ferroelectric Polymers / 103 4.4 Ferroelectric Odd-Numbered Polyamides (Nylons) / 114 4.5 Electrostriction / 119 4.6 Field-Induced Strain Due to Maxwell Stress Effect / 132 4.7 High Dielectric Constant Polymeric Materials as Actuator Materials /133 4.8 Electrets / 137 4.9 Liquid-Crystal Polymers /141 4.10 Acknowledgments / 142 4.11 References / 142 Topic 3.2 Ionic EAP Chapter 5 Electroactive Polymer Gels / 151 Paul Calvert 5.1 Introduction—the Gel State / 151 5.2 Physical Gels / 152 5.3 Chemical Gels / 152 5.4 Thermodynamic Properties of Gels / 154 5.5 Transport Properties of Gels / 155 5.6 Polyelectrolyte Gels / 156 5.7 Mechanical Properties of Gels / 156 5.8 Chemical Actuation of Gels / 157 5.9 Electrically Actuated Gels / 158 5.10 Recent Progress / 162 5.11 Future Directions / 164 5.12 References / 165 Chapter 6 Ionomeric Polymer-Metal Composites / 171 Sia Nemat-Nasser and Chris W. Thomas 6.1 Introduction / 172 6.2 Brief History of IPMC Materials / 173 6.3 Materials and Manufacture / 175 6.4 Properties and Characterization / 178 6.5 Actuation Mechanism / 196


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6.6 Development of IPMC Applications / 219 6.7 Discussion: Advantages/Disadvantages / 220 6.8 Acknowledgments / 223 6.9 References / 223 Chapter 7 Conductive Polymers / 231 José-María Sansiñena and Virginia Olazábal 7.1 Brief History of Conductive Polymers / 231 7.2 Applications of Conductive Polymers / 233 7.3 Basic Mechanism of CP Actuators / 236 7.4 Development of CP Actuators / 241 7.5 Advantages and Disadvantages of CP Actuators / 249 7.6 Acknowledgments / 252 7.7 References / 252 Chapter 8 Carbon Nanotube Actuators: Synthesis, Properties, and

Performance / 261 Geoffrey M. Spinks, Gordon G. Wallace, Ray H. Baughman, and Liming Dai 8.1 Introduction / 261 8.2 Nanotube Synthesis / 262 8.3 Characterization of Carbon Nanotubes / 266 8.4 Macroscopic Nanotube Assemblies: Mats and Fibers / 269 8.5 Mechanical Properties of Carbon Nanotubes / 270 8.6 Mechanism of Nanotube Actuation / 275 8.7 Experimental Studies of Carbon Nanotube Actuators/ 279 8.8 Conclusions and Future Developments / 288 8.9 References / 288 Topic 3.3 Molecular EAP Chapter 9 Molecular Scale Electroactive Polymers / 299 Michael J. Marsella 9.1 Introduction / 299 9.2 Intrinsic Properties and Macroscale Translation / 301 9.3 Stimulus-Induced Conformational Changes within the Single Molecule / 303 9.4 Final Comments / 311 9.5 References / 311 Topic 4 Modeling Electroactive Polymers Chapter 10 Computational Chemistry / 317 Kristopher E. Wise 10.1 Introduction / 317 10.2 Overview of Computational Methods / 318


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10.3 Quantum Mechanical Methods / 320 10.4 Classical Force Field Simulations / 328 10.5 Mesoscale Simulations / 332 10.6 References / 333 Chapter 11 Modeling and Analysis of Chemistry

and Electromechanics / 335 Thomas Wallmersperger, Bernd Kröplin, and Rainer W. Gülch 11.1 Introduction / 335 11.2 Chemical Stimulation / 337 11.3 Electrical Stimulation / 342 11.4 Conclusion / 360 11.5 References / 360 Chapter 12 Electromechanical Models for Optimal Design and Effective

Behavior of Electroactive Polymers / 363 Kaushik Bhattacharya, Jiangyu Li, and Yu Xiao 12.1 Introduction / 363 12.2 Introduction to Finite Elasticity / 364 12.3 Optimal Design of Electrostatic Actuators / 369 12.4 Models of Ionomer Actuators / 374 12.5 Reduced Models / 379 12.6 Conclusion / 382 12.7 Acknowledgment / 383 12.8 References / 383 Chapter 13 Modeling IPMC for Design of Actuation Mechanisms / 385 Satoshi Tadokoro, Masashi Konyo, and Keisuke Oguro 13.1 Models and CAE Tools for Design of IPMC Mechanisms / 386 13.2 A Physicochemical Model Considering Six Phenomena / 388 13.3 Gray-Box Macroscopic Model for Mechanical and Control Design / 396 13.4 Simulation Demonstration by Models / 402 13.5 Applications of the Model / 406 13.6 References / 425 Topic 5 Processing and Fabrication of EAPs Chapter 14 Processing and Fabrication Techniques / 431 Yoseph Bar-Cohen, Virginia Olazábal, José-María Sansiñena, and Jeffrey Hinkley 14.1 Introduction / 431 14.2 Synthesis and Material Processing / 462 14.3 Fabrication and Shaping Techniques / 434 14.4 Electroding Techniques / 441 14.5 System Integration Methods / 449


Contents ix

14.6 EAP Actuators / 452 14.7 Concluding Remarks / 453 14.8 References / 454 Topic 6 Testing and Characterization Chapter 15 Methods of Testing and Characterization / 467 Stewart Sherrit, Xiaoqi Bao, and Yoseph Bar-Cohen 15.1 Introduction / 468 15.2 Characterization of EAP with Polarization-Dependent Strains / 468 15.3 Characterization of Ionic EAP with Diffusion-Dependent Strain / 498 15.4 Summary of Test Methods / 516 15.5 Conclusion / 516 15.6 Acknowledgments / 518 15.7 References / 518 Topic 7 EAP Actuators, Devices, and Mechanisms Chapter 16 Application of Dielectric Elastomer EAP Actuators / 529 Roy Kornbluh, Ron Pelrine, Qibing Pei, Marcus Rosenthal, Scott Stanford, Neville Bonwit, Richard Heydt, Harsha Prahlad, and Subramanian V. Shastri 16.1 Introduction / 530 16.2 Dielectric Elastomer EAP—Background and Basics / 535 16.3 Actuator Design Issues / 539 16.4 Operational Considerations / 546 16.5 Examples of Dielectric Elastomer EAP Actuators and Applications / 551 16.6 Artificial Muscles and Applications to Biologically Inspired Devices / 552 16.7 General Purpose Linear Actuators / 566 16.8 Planar and Other Actuator Configurations / 567 16.9 Motors / 573 16.10 Generators / 574 16.11 Sensors / 575 16.12 Summary and Future Developments / 576 16.13 Acknowledgments / 577 16.14 References / 577 Chapter 17 Biologically Inspired Robots / 581 Brett Kennedy, Chris Melhuish, and Andrew Adamatzky 17.1 Introduction / 583 17.2 Biologically Inspired Mechanisms and Robots / 584 17.3 Aspects of Robotic Design / 584 17.4 Active Polymer Actuators in a Traditional Robotic System / 594 17.5 Using Rapid Prototyping Methods for Integrated Design / 596 17.6 Evolutionary Design Algorithms (Genetic Algorithm Design) / 598 17.7 EAP Actuators in Highly Integrated Microrobot Design / 602 17.8 Solving the Power Problem—Toward Energetic Autonomy / 614


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17.9 The Future of Active Polymer Actuators and Robots / 616 17.10 References / 617 Chapter 18 Applications of EAP to the Entertainment Industry / 621 David Hanson 18.1 Introduction / 622 18.2 Entertainment and Its Shifting Significance / 626 18.3 Technical Background to Entertainment Application of EAP / 627 18.4 The Craft of Aesthetic Biomimesis in Entertainment / 637 18.5 A Recipe for Using EAP in Entertainment / 647 18.6 Facial Expression Robot–Practical Test Bed for EAP / 647 18.7 Conclusion / 655 18.8 Acknowledgment / 655 18.9 References / 655

Chapter 19 Haptic Interfaces Using Electrorheological Fluids / 659 Constantinos Mavroidis, Yoseph Bar-Cohen, and Mourad Bouzit 19.1 Introduction / 659 19.2 Electrorheological Fluids / 661 19.3 Haptic Interfaces and Electrorheological Fluids / 666 19.4 MEMICA Haptic Glove / 668 19.5 ECS Element Model Derivation / 673 19.6 Parametric Analysis of the Design of ECS Elements / 677 19.7 Experimental ECS System and Results / 679 19.8 Conclusions / 682 19.9 Acknowledgments / 682 19.10 References / 683 Chapter 20 Shape Control of Precision Gossamer Apertures / 687 Christopher H. M. Jenkins 20.1 Introduction / 687 20.2 Shape Control of PGAs / 691 20.3 Shape Control Methodologies Involving Electroactive Polymers / 697 20.4 Conclusions / 702 20.5 Nomenclature / 703 20.6 Acknowledgments / 703 20.7 References / 704 Topic 8 Lessons Learned, Applications, and Outlook Chapter 21 EAP Applications, Potential, and Challenges / 709 Yoseph Bar-Cohen 21.1 Introduction / 710 21.2 Lesson Learned Using IPMC and Dielectric EAP / 711 21.3 Summary of Existing EAP Materials / 717 21.4 Scalability Issues and Needs / 718 21.5 Expected and Evolving Applications / 719


Contents xi

21.6 EAP Characterization / 746 21.7 Platforms for Demonstration of EAP / 748 21.8 Future Expectations / 749 21.9 Acknowledgments / 751 21.10 References / 752 Index / 757


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Preface

This book reviews the state of the art of the field of electroactive polymers (EAPs), which are also known as artificial muscles for their functional similarity to natural muscles. This book covers EAP from all its key aspects, i.e., its full infrastructure, including the available materials, analytical models, processing techniques, and characterization methods. This book is intended to serve as reference tool, a technology users’ guide, and a tutorial resource, and to create a vision for the field’s future direction. In preparing this second edition, efforts were made to update the chapters with topics that have sustained major advances since the first edition was prepared three years ago. Following the reported progress and milestones that were reached in this field has been quite heartwarming. These advances are bringing the field significantly closer to the point where engineers consider EAPs to be actuators of choice. In December 2002, the Japanese company Eamex produced a robot fish that swims in a water tank without batteries or a motor. For power, the robot fish uses an inductive coil that is energized from the top and bottom of the tank. Making a floating robot fish may not be an exciting event, but this is the first commercial product to use an EAP actuator.

EAPs are plastic materials that change shape and size when given some voltage or current. They always had enormous potential, but only now is this potential starting to materialize. Advances reported in this second edition include an improved understanding of these materials’ behavior, better analytical modeling, as well as more effective characterization, processing, and fabrication techniques. The advances were not only marked with the first commercial product; there has also been the announcement by the SRI International scientists who are confident they have reached the point that they can now meet the challenge posed by this book’s editor of building a robot arm with artificial muscles that could win an arm wrestling match against a human. This match may occur in the coming years, and the success of a robot against a human opponent will lead to a new era in both making realistic biomimetic robots and implementing engineering designs that are currently considered science fiction.

For many years the field of EAP has received relatively little attention because the number of available materials and their actuation capability were limited. The change in this view occurred in the early 1990s, as a result of the development of new EAP materials that exhibit a large displacement in response to electrical stimulation. This characteristic is a valuable attribute, which enabled myriad potential applications, and it has evolved to offer operational similarity to biological muscles. The similarity includes resilient, damage tolerant, and large


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actuation strains (stretching, contracting, or bending). Therefore, it is natural to consider EAP materials for applications that require actuators to drive biologically inspired mechanisms of manipulation, and mobility. However, before these materials can be applied as actuators of practical devices their actuation force and robustness will need to be increased significantly from the levels that are currently exhibited by the available materials. On the positive side, there has already been a series of reported successes in demonstrating miniature manipulation devices, including a catheter steering element, robotic arm, gripper, loudspeaker, active diaphragm, dust-wiper, and many others. The editor is hoping that the information documented in this book will continue to stimulate the development of niche applications for EAP and the emergence of related commercial devices. Such applications are anticipated to promote EAP materials to become actuators of choice in spite of the technology challenges and limitations they present.

Chapter 1 of this book provides an overview and background to the various EAP materials and their potential. Since biological muscles are used as a model for the development of EAP actuators, Chapter 2 describes the mechanism of muscles operation and their behavior as actuators. Chapter 3 covers the leading EAP materials and the principles that are responsible for their electroactivity. Chapter 4 covers such fundamental topics as computational chemistry and nonlinear electromechanical analysis to predict their behavior, as well as a design guide for the application of an example EAP material. Modeling the behavior of EAP materials requires the use of complex analytical tools, which is one of the major challenges to the design and control of related mechanisms and devices. The efforts currently underway to model their nonlinear electromechanical behavior and develop novel experimental techniques to measure and characterize EAP material properties are discussed in Chapter 6. Such efforts are leading to a better understanding of the origin of the electroactivity of various EAP materials, which, in turn, can help improve and possibly optimize their performance. Chapter 5 examines the processing methods of fabricating, shaping, electroding, and integrating techniques for the production of fibers, films, and other shapes of EAP actuators. Generally, EAP actuators are highly agile, lightweight, low power, mass producible, inexpensive, and possess an inherent capability to host embedded sensors and microelectromechanical systems (MEMS). Their many unique characteristics can make them a valuable alternative to current actuators such as electroactive ceramics and shape memory alloys. The making of miniature insectlike robots that can crawl, swim and/or fly may become a reality as this technology evolves as discussed in Chapters 7 and 8. Processing techniques, such as ink-jet printing, may potentially be employed to make complete devices that are driven by EAP actuators. A device may be fully produced in 3D detail, thereby allowing rapid prototyping and subsequent mass production possibilities. Thus, polymer-based EAP-actuated devices may be fully produced by an ink-jet printing process enabling the rapid implementation of science-fiction ideas (e.g., insectlike robots that become remotely operational as soon as they emerge from the production line) into engineering models and


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commercial products. Potential beneficiaries of EAP capabilities include commercial, medical, space, and military that can impact our life greatly.

In order to exploit the greatest benefit that EAP materials can offer, researchers worldwide are now exploring the various aspects of this field. The effort is multidisciplinary and cooperation among scientists, engineers, and other experts (e.g., medical doctors) are underway. Experts in chemistry, materials science, electro-mechanics, robotics, computer science, electronics, and others are working together to develop improved EAP materials, processing techniques, and applications. Methods of effective control are addressing the unique and challenging aspects of EAP actuators. EAP materials have a significant potential to improving our lives. If EAP materials can be developed to the level that they can compete with natural muscles, drive prosthetics, serve as artificial muscle implants into a human body, and become actuators of various commercial products, the developers of EAP would make tremendously positive impact in many aspects of human life.

Yoseph Bar-Cohen

February 2, 2004


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ACKNOWLEDGMENTS

The research at Jet Propulsion Laboratory (JPL), California Institute of Technology, was carried out under a contract with National Aeronautics and Space Administration (NASA) and Defense Advanced Research Projects Agency (DARPA). The editor would like to thank everyone who contributed to his efforts, both as part of his team advancing the technology as well as those who helped with the preparation of this book. The editor would like to thank the team members of his task LoMMAs that was funded by the Telerobotic and the Cross-Enterprise Programs of the NASA Code S. The team members included Dr. Sean Leary, Mark Schulman, Dr. Tianji Xu, and Andre H Yavrouian, JPL, Dr. Joycelyn Harrison, Dr. Joseph Smith, and Ji Su, NASA LaRC; Prof. Richard Claus, VT; Prof. Constantinos Mavroidis and Charles Pfeiffer, Rutgers University. Also, the editor would like to thank Dr. Timothy Knowles, ESLI, for his assistance with the development of the EAP dust-wiper mechanism using IPMC. Thanks to Marlene Turner, Harry Mashhoudy, Brian Lucky, and Cinkiat Abidin, former graduate students of the Integrated Manufacturing Engineering (IME) Program at UCLA, for helping to construct the EAP gripper and robotic arm. A special thanks to Dr. Keisuke Oguro, Osaka National Research Institute, Japan, for providing his most recent IPMC materials; and to Prof. Satoshi Tadokoro, Kobe University, Japan, for his analytical modeling effort. Prof. Mohsen Shahinpoor is acknowledged for providing IPMC samples as part of the early phase of the LoMMAs task. The editor would like also to thank his NDEAA team members Dr. Virginia Olazábal, Dr. José-María Sansiñena, Dr. Shyh-Shiuh Lih, and Dr. Stewart Sherrit for their help. In addition, he would like to thank Prof. P. Calvert, University of Arizona, for the information about biological muscles. Thanks to Dr. Steve Wax, DARPA’s EAP program Manager, and Dr. Carlos Sanday, NRL, for their helpful comments related to the development of EAP characterization methods. A specific acknowledgement is made for the courteous contribution of graphics for the various chapters of this book; and these individuals and organizations are specified next to the related graphics or tables.

The editor would like to acknowledge and express his appreciation to the following individuals, who took the time to review various book chapters of the first edition and particularly those who where not coauthors of this book. Their contribution is highly appreciated and it helped to make this book of significantly greater value to the readers:

Aluru Narayan, University of Illinois/Urbana-Champaign Paul Calvert, University of Arizona, Sia Nemat-Nasser, Dr. Chris Thomas and Mr. Jeff McGee, University of

California, San Diego Christopher Jenkins, and Dr. Aleksandra Vinogradov, South Dakota School

of Mines and Technology Kenneth Johnson, Brett Kennedy, Shyh-Shiuh Lih, Virginia Olazabal, José-

María Sansiñena, and Stewart Sherrit, Jet Propulsion Laboratory


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Giovanni Pioggia and Danilo de Rossi, University of Pisa, Italy Elizabeth Smela, University of Maryland Gerald Pollack, Washington University Hugh Brown, Paul Keller, Geoff Spinks, and Gordon Wallace, University of

Wollongong, Australia Jeffrey Hinkley, Ji Su, and Kristopher Wise, NASA LaRC Jiangyu Li, Caltech Michael Marsella, University of California, Riverside Miklos Zrinyi, Budapest University of Technology and Economics, Hungary Mourad Bouzit and Dinos Mavroidis, Rutgers University Peter Sommer-Larsen, Risoe Research Center, Denmark Mary Frecker and Qiming Zhang, Pennsylvania State University Robert Full, University of California, Berkeley, Roy Kornbluh and Ron Pelrine, SRI International Satoshi Tadokoro, Kobe University, Japan, Also, the editor would like to acknowledge and express his appreciation to

the following individuals who took the time to review the 12 chapters that were revised in this second edition and particularly those who where not coauthors of this book. Their contribution is highly appreciated and it helped making this book of significantly greater value to the readers:

Ahmed Al-Jumaily, Wellesley Campus, Auckland, New Zealand Narayan Aluru, University of Illinois/Urbana-Champaign Andy Adamatzky,

University of the West of England, Bristol, England Mary Frecker, Penn State University Kaneto Keiichi, Kyushu Institute of Technology, Japan David Hanson, University of Texas at Dallas and Human Emulation Robotics,

LLC Roy Kornbluh, SRI International, CA Don Leo, Virginia Polytechnic Institute and State University John Madden, University of British Columbia, Canada Chris Melhuish, University of the West of England, UK Walied Moussa, University of Alberta, Canada José-María Sansiñena, Los Alamos National Laboratory (LANL) Stewart Sherrit, Jet Propulsion Laboratory, CA Peter Sommer-Larsen, Risoe Research Center, Denmark Geoffery Spinks, University of Wollongong, Australia Ji Su, NASA Langley Research Center (LaRC), VA Minuro Taya, University of Washington Aleksandra Vinogradov, Montana State University Eui-Hyeok Yang, Jet Propulsion Laboratory, CA


electroactive polymer (eap) actuators as artificial muscles

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