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Electric Flex
• Electric Flex
by Yoseph Bar Cohen
IEEE spectrum, June 2004
• Artificial Muscles
by Steven Ashley
Scientific American, October 2003
A Challenge to Artificial muscle
community
Human Muscle:
Contracts up to 50%
of their length
Force(max.)= 350 kilopascal
(@ 35% strain)
Max. power density (at a
Point) ~ 150 to 225 watts
Plan of the Talk & Introduction
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Introduction to muscles
How it works
Artificial Muscle
Applications
Muscles
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Muscles turn energy in to Motion
Efficient,
long lasting
self healing and
grow stronger with use (practice)
Muscles - Types
• Skeletal Muscle ( Striated muscle)
Comes in Pairs, contract voluntarily
single contraction( twitch ) and
sustained contraction ( tetanous )
• Smooth Muscle
ability to stretch and maintain tension
contracts involuntarily
• Cardiac Muscle
Only in Heart, endurance and consistency
twitch muscle only and contracts involuntarily
Skeletal (Striated) Muscle
Muscles of the human
body.
Cross section of skeletal muscle (200x)
Muscle fibers- red and the fat cells -white
How muscles work?
- Basic action is Contraction
- A bundle of cells called Fibers
Fibers
Fibers : cylinders
1 to 40 microns long
10 to 100 microns in diameter
Contracting Muscle
Thin filaments slide past the thick filaments shortening Saromere
Myosin molecule
Bonds with actin
Molecule:
Crossbridge
Myosin releases
ADP(adenosine
diphosphate) and
Pi(inorganic phosPate)
Muscles create force by cycling cross-bridges
Contraction of muscles : Triggered
1 Hz
5 Hz
by electrical impulses
10 Hz
50 Hz
Some facts:
Minimum unit of contraction in a muscle is called Motor
Unit
Size of the motor unit (number of fibers/motor neuron)
Muscles controlling eye motion ~ 10
Muscles controlling Larynx
2 to 3
Calf muscles
1000 to 2000
Motor unit is digital
Strength α to the number of motor units activated
Artificial Muscles
• Electroactive polymers(EAP)
• First artificial muscle:
Using natural rubber was demonstrated
by
Wilhelm Konrad Rontgen ( X – rays)
Artificial muscles-classification
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5.
Electronic
Passive dielectrics
Piezoelectric
polymers
Graft elastomers
Liquid crystals
Electrostrictive paper
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Ionic
Polymer gels
Polymer metal
composites
Conductive polymers
Carbon nanotubes
Electrorheological
liquids
Electronic polymers
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Electronic polymers react in µs
Higher energy density
Can operate in open air
Needs strong electric fields (150 V/µm)
(very close to dielectric breakdown)
Electronic polymers-cont.
• Passive dielectric – simplest and robust
SRI has achieved 8 M Pascal ( factor of 30 >)
• Piezoelectric polymers
small strain and force
improves to 4% strain and G Pascal
needs high voltages
• Graft elastomers
a long molecule is engrafted with elements
that respond to electric field ~ 4% strain
Electronic polymers-cont.
• Liquid crystals- with ferroelecric materials:
undergoes phase change from ordered
crystalline phase to disordered phase when
heated electrically.
• Electrostrictive paper
serendipitous discovery
cellophane tape sandwiched between two
silver tapes
low cost and has sufficient force with multiple
layers
Loudspeakers
Ionic muscles
• Efficiency less than 30% as compared to
80% for the electronic muscles
• Low drive voltages 1 to 5 V
• Need to enclose liquid or gel and is this
makes it more difficult to handle as
compared to electronic polymers
A comparison
Passive dielectric artificial
muscle
SRI International
Ionic polymer metal composites
Breakthroughs in electronic
polymers
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Soft silicones: ~10 to 30% strain
(SRI calls them dielectric elastomers or electric field
activated polymers)
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More strain : carbon particle in elastometric matrix
Streching polymers: increased dielectric strength
and strain (1 to 5 kV)
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Edisonian approach:
380% linear strain with
acrlyic elastomer
Applications
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Linear actuators
Loudspeakers: flat panel speakers
Pumps
Sensors
Smart surfaces: reduce drag
Power generators (~ 1 Watt in shoes)
Small winged plane: for survilence