ARTIFICIAL MUSCLE (with emphasis on Electroactive Polymers)

1
ARTIFICIAL MUSCLE(with emphasis on Electroactive
Polymers)

• By
• Bharath Ramaswamy
• Department of Electrical Computer Engineering
• Utah State University

ECE 5320 Mechatronics
2
Introduction

• Artificial Muscles are synthetic materials that
  behave like biological muscles.
• Active materials have shown to behave
  macroscopically similar to some of the processes
  taking place in biological muscle fibers.
• Artificial muscles are made up of materials which
  dramatically swell and shrink under chemical
  and/or electrical stimuli.
• Eventually, artificial muscles can be "packaged
  into virtually any shape or size and muscle for
  use in human applications could become a reality.

Ref http//mmadou.eng.uci.edu/ResearchDevelopment
/ArtificialMuscle.htm
3
Artificial vs. Natural muscle

• Artificial actuators cannot and should not be
  exactly like natural muscle in all aspects.
• power source
• environmental conditions
• materials and microstructure
• response to stimulation
• Fatigue
• Actuators should reproduce only those
  characteristics of muscle that are beneficial for
  the application.

Ref http//bees.jpl.nasa.gov/BEES2000/BEES-Flex.p
df
4
Basic Principle

• Bundles of fibers made from polymer gels would
  shrink when immersed in acidic solution, then
  swell significantly with addition of a base to
  the immersion solution.
• Immersed in acid solution, negative ions of the
  polymer were attracted to positive ions from the
  acid that permeated the gel, which resulted in
  contraction.
• Immersed in alkaline solution, the gel's negative
  ions were repulsed by negative ions from the
  solution, causing the polymer to expand.
• The mechanical effect was similar to the action
  of natural muscle tissue.
• In addition to exposing polymer gels to specific
  solutions to cause them to flex and contract,
  passing an electric current through a material
  can induce a similar effect.

Ref http//www.devicelink.com/mddi/archive/99/08/
004.html
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Enhancing Polymer Response

• Electron bombardment enhances polymer response by
  altering the materials molecular conformation and
  created new chemical bonds.
• It inserts defects into the material, making it
  more compliant and flexible. The process also
  increases the material's dielectric constant.
• By infusing polymer gel with electrorheological
  fluid (ERF), which stiffens to a solid in
  response to an electric field the polymers
  response time to electric impulses was quickened
  from 3 seconds to 100 milliseconds.

Ref http//www.devicelink.com/mddi/archive/99/08/
004.html
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Increasing Strength

• Fibers heated to 4500F to form cross-links and
  boiled in sodium hydroxide to make them elastic.
  This process binds the fiber within a gelatinous
  mass. The mass is then encapsulated in latex and
  bathed in water. The ionic-polymer fibers,
  encased within the latex shield, are bathed in a
  chemical solution and contract or expand in
  response to changes in the solution's pH.
• Adding sodium hydroxide or another base causes
  the fibers to stretch to as much as twice their
  original length. Acid results in the fibers
  contracting nearly as fast as human muscles and
  with twice the strength.
• Use of computer-controlled pumps that regulate
  the flow of acid and base into the muscle make it
  possible to regulate and program the muscle's
  activity.

Ref http//www.devicelink.com/mddi/archive/99/08/
004.html
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Important Actuator Characteristics

• Energy (the most fundamental)
• Energy density
• Energy efficiency
• Speed of response
• Force vs. Stroke
• Environmental Tolerance
• Power Supply Requirements
• Reliability and Robustness
• Passive or open-loop characteristics
• Elasticity
• Energy absorption motor and a brake
• Perturbation response preflex
• Back-drivability

Ref http//bees.jpl.nasa.gov/BEES2000/BEES-Flex.p
df
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Requirements of Material

• High dielectric constant, or ability to resist
  the flow of electric charge
• Elasticity and Non-linear behavior
• Large Displacement Response
• Low Density
• Large Strain Capability

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Terminology

• Electrostriction - the non-linear reaction of
  ferroelectric EAP
• EAP - general term describing polymers that
  respond to electrical stimulation
• Electronic EAP - polymer that change shape or
  dimensions due to migration of electrons in
  response to electric field (usually dry)
• Ionic EAP - polymer that change shape or
  dimensions due to migration of ions in response
  to electric field (usually wet and contains
  electrolyte)
• Longitudinal EAP - polymer that responds with
  change in length
• Bending EAP - polymer that responds with bending
  

Ref http//ndeaa.jpl.nasa.gov/nasa-nde/lommas/eap
/EAP-web.htm
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Materials

• Ionic polymer-Metal Composites (IPMC)
• Shape Memory Alloys (SMA)
• Electroactive Ceramics (EAC)
• Electroactive Polymers (EAP)
• Rubber
• Carbon Nanotubes

Ref http//www.unm.edu/amri/paper.html
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Materials (contd.)

• Ionic EAP
• Ionic Gels (IGL)
• Ionic Polymer-Metal Composites (IPMC)
• Conductive Polymers (CP)
• Electrorheological fluids (ERF)
• Electronic EAP
• Ferroelectric polymers
• Dielectric EAP or ESSP
• Electrostrictive Graft Elastomers
• Liquid Crystal Elastomers

Ref http//kasml.konkuk.ac.kr/image/Artificial20
Muscle.ppt
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Comparison of Properties

 
http//ndeaa.jpl.nasa.gov/nasa-nde/lommas/eap/spie
-eap.html
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Electroactive Polymer ArtificialMuscle (EPAM)

• Electroactive polymers are plastics that expand
  or contract in the presence of an electric field.

Ref http//bees.jpl.nasa.gov/BEES2000/BEES-Flex.p
df
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Basic components of an EAP-driven system
Ref ndeaa.jpl.nasa.gov/ndeaa-pub/NSMMS/EAP-NSMMS-
2000.pdf
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Muscle vs. Artificial Muscle
Ref http//bees.jpl.nasa.gov/BEES2000/BEES-Flex.p
df
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Muscle vs. Artificial Muscle
Ref http//bees.jpl.nasa.gov/BEES2000/BEES-Flex.p
df
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Sources of Excitation

• Pneumatic (ex. McKibben muscle actuators)
• Hydraulic (Electrorhological fluids)
• Heat (Shape Memory Alloys)
• Chemical
• Electrical

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Challenges to EAP

• Force actuation and mechanical energy density of
  EAPs are relatively low limiting the potential
  applications
• Low Response
• High Voltages required for Actuation
• No effective and robust EAP material is currently
  available commercially.
• No established database that documents the
  properties of the existing EAP materials.

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EAP Infrastructure Areas needing attention
Ref http//ndeaa.jpl.nasa.gov/ndeaa-pub/EAP/EAP-r
obotics-2000.pdf
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A note on Carbon Nanotubes

• Described as an extended buckminsterfullerene
  molecule, or "buckyball," the spherical molecule
  constructed solely from 60 carbon atoms.
• Composed entirely of carbon atoms and, because of
  their molecule structure, provide exceptional
  strength.
• Provide higher work densities per cycle
• Energy needed for the nanotube actuator is a full
  order of magnitude lower than that of polymer gel

Ref http//www.devicelink.com/mddi/archive/99/08/
004.html
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Applications

• Balloon used to cushion the deployment of the
  Mars Pathfinder
• Inflatable telescopes
• Biomimetic robots - highly maneuverable,
  noiseless and agile, with various shapes to
  emulate capabilities of terrestrial creatures
  with integrated multidisciplinary capabilities
  like soft-landing, hopping, digging and operating
  cooperatively.
• Prosthetic Limbs
• Artificial sphincters for treatment of
  incontinence
• Method for encasing the heart with synthetic
  muscle in lieu of transplant procedures

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References

• SRI International
• http//bees.jpl.nasa.gov/BEES2000/BEES-Flex.pdf
• Konkuk University, Artificial Structures
  Materials lab
• http//kasml.konkuk.ac.kr/image/Artificial20Muscl
  e.ppt
• Ionic Polymer-Metal Composites (IPMC) As
  Biomimetic Sensors, Actuators Artificial
  Muscles - A Review, M. Shahinpoor(a), Y.
  Bar-Cohen(b), J.O. Simpson(c) and J. Smith
• http//www.unm.edu/amri/paper.html
• Electroactive Polymers (EAP) Low Mass Muscle
  Actuators, Y. Bar-Cohena, T. Xuea, B. Joffea,
  S.-S. Liha, M. Shahinpoorb, J. Simpsonc, J.
  Smithc, and P. Willisa
• Electroactive Polymers As Artificial Muscles -
  Capabilities, Potentials And Challenges, Yoseph
  Bar-Cohen1
• http//ndeaa.jpl.nasa.gov/ndeaa-pub/EAP/EAP-roboti
  cs-2000.pdf