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

Part I

EAP Classification

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

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 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

Part III

Research problems

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

belluco@elet.polimi.it

Ing. Paolo Belluco EAP - ElectroActive Polymers