EAP - ElectroActive PolymersA Short Introduction to Robotics Applications
Ing. Paolo Belluco
AIRLab - Artificial Intelligence and Robotics LabPolitecnico 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 givensome voltage or current.
EAPs behave very similarly to biological muscle and mimic theirmechanism.
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 anenergy 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 themacroscopic movements.
Structural hierarchy ofskeletal muscle
Myofibrils are simply a stringof sarcomeres: the functionalunit of muscle contraction.Muscles also exhibit theproperty of scale invariance:their mechanism worksequally efficiently at all sizes,which is why fundamentallythe same muscle tissuepowers both insects andelephants.
Ing. Paolo Belluco EAP - ElectroActive Polymers
Smart Materials
EAP
Ionic EAP-Ionic polymer metalcomposites(IPMC)-Carbon nanotubes(CNT)-Ionic polymers Gels(IPG)Conductive polymers(CP)-Electrorheological Fluid
Electronic EAP-Piezoelectric polymers-Electro-strictive polymers-Dielectric elastomer-Liquid crystalelastomer(LCE)Ferroelectric Polymers
Piezo
Piezoelectricceramics
Piezolectriccomposites
Other
Shape memorymetal and alloys
Shape memorypolymers
Magneto andElectro-strictivematerials
Magneto andElectro-rheologicalfluids
Ing. Paolo Belluco EAP - ElectroActive Polymers
Electronic EAP
Advantages
Can operate in roomcondition for a long time
Rapid response (mseclevel)
Can hold strain underDC activation
Induces relatively largeactuation force
Disadvantages
Requires HV on the order of 150MV/m (Ferroelectric 20 MV/m)
Compromise between strain and stress
Glass transition temperature isinadequate for low-temperatureactuation task
High temperature applications arelimited by Curie temperature
Mostly, monopolar actuation,independent of the voltage polarity
Ing. Paolo Belluco EAP - ElectroActive Polymers
Ionic EAP
Advantages
Produce large bendingdisplacements
Requires low voltage
Natural bi-directionalactuation that dependson the voltage polarity
Disadvantages
Except for CPs and NTs, Ionic do nothold strain under DC voltage
Slow Response (fraction of a second)
Bending EAPs induce a relatively lowactuation force
Except for CPs, it is difficult toproduce a consistent material(particularly IMPC)
In aqueous system the materialssustain electrolysis over 1.23V
Need for an electrolyte andencapsulation
Low electromechanical couplingefficiency
Ing. Paolo Belluco EAP - ElectroActive Polymers
How Dielectric EAP work
The EAP basic architecture is made up of afilm of an elastomer dielectric material thatis coated on both sides with anotherexpandable film of a conducting electrode.When voltage is applied to the twoelectrodes a Maxwell pressure is createdupon the dielectric layer. The elasticdielectric polymer acts as an incompressiblefluid which means that as the electrodepressure causes the dielectric film to becomethinner, it expands in the planar directions.Electrical force is converted to mechanicalactuation and motion.
Ing. Paolo Belluco EAP - ElectroActive Polymers
How IPMC work
Ionomeric polymer-metal composite is an EAP that bends in response toan electrical activation as a result of mobility of cations in the polymernetwork or negative ions on interconnected clusters. Electrostatic forcesand mobile cation are responsible for the bending.
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 EAPactuators(Eckerle et.al 2000)
Figure: Artificial face, mounton Albert Hubo(KoreaAdvanced Institute of Scienceand Technology(KAIST),Hanson Robotics)
Ing. Paolo Belluco EAP - ElectroActive Polymers
Human-machine Interfaces
Figure: Haptic glove 3D model
Figure: Memica: Remote-ManipulatorForces, damping or resistance would becontrolled electronically(JPL/Caltech,Rutgers University, NASA JSC,Harbor-UCLA Medical Center)
Ing. Paolo Belluco EAP - ElectroActive Polymers
Medical applications
Figure: Catheter activation by an IPMC typebending EAP(Osaka National ResearchInstitute)
Figure: A photographic view ofa human hand and skeleton aswell as an emulated structurefor which EAP actuators arebeing sought(Graham Whiteley,Sheffield Hallam University,UK)
Ing. Paolo Belluco EAP - ElectroActive Polymers
Research problems
Developing and applying EAP materials and mechanisms involvesinterdisciplinary expertise in chemistry, materials science, electronics,computer science and others. It’s possible to divide the problems in twogroup:
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 protectivecoating, bonding, electroding, etc.)
Miniaturization techniques.
Ing. Paolo Belluco EAP - ElectroActive Polymers
Find more info
http://www.airlab.elet.polimi.it/.../bellucohttp://eap.jpl.nasa.gov/
Yoseph Bar-Cohen ”Electroactive Polymer (EAP)Actuators as artificialmuscle, reality, potential and challenges”, SPIE PRESS
Ing. Paolo Belluco EAP - ElectroActive Polymers