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EAP - ElectroActive Polymers
A Short Introduction to Robotics Applications
Ing. Paolo Belluco
AIRLab - Artificial Intelligence and Robotics Lab
Politecnico di Milano
http://www.airlab.elet.polimi.it/
February 2007
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Introduction to EAP
Focus: Emulate the biological muscle
Most conventional mechanisms are driven by actuators requiring gears,
bearings and other components.
EAPs are plastic materials that change size and shape when given
some voltage or current.
EAPs behave very similarly to biological muscle and mimic their
mechanism.
EAPs acquired the moniker ”Artificial Muscle”.
Development of biologically inspired system(biomimetic) They are:
lightweight, low power, inexpensive, resilient, damage tolerant, noiseless,
agile.
Emulating the muscles can be able various new manipulation capabilities.
Muscle is multifunctional, i.e. in locomotion muscle often acts as an
energy absorber, variable stiffness suspension element or position sensor
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Skeletal muscle: biological linear Electro-Active actuator
Molecular motion on the order of nm distances is converted into the
macroscopic movements.
Structural hierarchy of
skeletal muscle
Myofibrils are simply a string
of sarcomeres: the functional
unit of muscle contraction.
Muscles also exhibit the
property of scale invariance:
their mechanism works
equally efficiently at all sizes,
which is why fundamentally
the same muscle tissue
powers both insects and
elephants.
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Part I
EAP Classification
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Smart Materials
EAP
Ionic EAP
-Ionic polymer metal
composites(IPMC)
-Carbon nanotubes(CNT)
-Ionic polymers Gels(IPG)
Conductive polymers(CP)
-Electrorheological Fluid
Electronic EAP
-Piezoelectric polymers
-Electro-strictive polymers
-Dielectric elastomer
-Liquid crystal
elastomer(LCE)
Ferroelectric Polymers
Piezo
Piezoelectric
ceramics
Piezolectric
composites
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EAP - ElectroActive Polymers
Other
Shape memory
metal and alloys
Shape memory
polymers
Magneto and
Electro-strictive
materials
Magneto and
Electrorheological
fluids
Electronic EAP
Advantages
Disadvantages
Can operate in room
condition for a long time
Rapid response (msec
level)
Can hold strain under
DC activation
Induces relatively large
actuation force
Ing. Paolo Belluco
Requires HV on the order of 150
MV/m (Ferroelectric 20 MV/m)
Compromise between strain and stress
Glass transition temperature is
inadequate for low-temperature
actuation task
High temperature applications are
limited by Curie temperature
Mostly, monopolar actuation,
independent of the voltage polarity
EAP - ElectroActive Polymers
Ionic EAP
Advantages
Disadvantages
Produce large bending
displacements
Requires low voltage
Natural bi-directional
actuation that depends
on the voltage polarity
Ing. Paolo Belluco
Except for CPs and NTs, Ionic do not
hold strain under DC voltage
Slow Response (fraction of a second)
Bending EAPs induce a relatively low
actuation force
Except for CPs, it is difficult to
produce a consistent material
(particularly IMPC)
In aqueous system the materials
sustain electrolysis over 1.23V
Need for an electrolyte and
encapsulation
Low electromechanical coupling
efficiency
EAP - ElectroActive Polymers
How Dielectric EAP work
The EAP basic architecture is made up of a
film of an elastomer dielectric material that
is coated on both sides with another
expandable film of a conducting electrode.
When voltage is applied to the two
electrodes a Maxwell pressure is created
upon the dielectric layer. The elastic
dielectric polymer acts as an incompressible
fluid which means that as the electrode
pressure causes the dielectric film to become
thinner, it expands in the planar directions.
Electrical force is converted to mechanical
actuation and motion.
Ing. Paolo Belluco
EAP - ElectroActive Polymers
How IPMC work
Ionomeric polymer-metal composite is an EAP that bends in response to
an electrical activation as a result of mobility of cations in the polymer
network or negative ions on interconnected clusters. Electrostatic forces
and mobile cation are responsible for the bending.
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Part II
Robotic Application
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Significant EAP proprieties
Stress (MPa)
Strain (%)
Drive voltage (V)
Bandwidth (Hz) or Response rate (sec)
Power density (W /cm3 )
Efficiency (%)
Lifetime (cycles)
Density (g /cm3 )
Operating Environment (Temperature, pressure, humidity, etc...)
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Fields of application
Mechanisms
Robotics, Toys and Animatronics
Human-machine Interfaces
Planetary applications
Medical applications
Liquid and Gases Flow Control
Control Weaving
MEMS
EM Polymer Sensor and Transducers
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Robotics, Toys and Animatronics
Figure: Flex2, robot using rolled DE EAP
actuators(Eckerle et.al 2000)
Ing. Paolo Belluco
Figure: Artificial face, mount
on Albert Hubo(Korea
Advanced Institute of Science
and Technology
(KAIST),Hanson Robotics)
EAP - ElectroActive Polymers
Human-machine Interfaces
Figure: Haptic glove 3D model
Ing. Paolo Belluco
Figure: Memica: Remote-Manipulator
Forces, damping or resistance would be
controlled electronically(JPL/Caltech,
Rutgers University, NASA JSC,
Harbor-UCLA Medical Center)
EAP - ElectroActive Polymers
Medical applications
Figure: Catheter activation by an IPMC type
bending EAP(Osaka National Research
Institute)
Ing. Paolo Belluco
Figure: A photographic view of
a human hand and skeleton as
well as an emulated structure
for which EAP actuators are
being sought(Graham Whiteley,
Sheffield Hallam University,
UK)
EAP - ElectroActive Polymers
Part III
Research problems
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Research problems
Developing and applying EAP materials and mechanisms involves
interdisciplinary expertise in chemistry, materials science, electronics,
computer science and others. It’s possible to divide the problems in two
group:
Mechanism understanding
EAP processing
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Mechanism understanding
Nonlinear electromechanical modeling
Materials properties characterization
Computational chemistry
New materials synthesis
Ing. Paolo Belluco
EAP - ElectroActive Polymers
EAP processing
Material fabrication techniques
Shaping (films, sheet, fibers, etc.)
Microlayering (ISAM, ink jet printing)
Support processes and integration (conductive and protective
coating, bonding, electroding, etc.)
Miniaturization techniques.
Ing. Paolo Belluco
EAP - ElectroActive Polymers
Find more info
http://www.airlab.elet.polimi.it/.../belluco
http://eap.jpl.nasa.gov/
Yoseph Bar-Cohen ”Electroactive Polymer (EAP)Actuators as artificial
muscle, reality, potential and challenges”, SPIE PRESS
[email protected]
Ing. Paolo Belluco
EAP - ElectroActive Polymers