Dielectric elastomer actuators

7/28/2019 Dielectric elastomer actuators

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Electroactive Polymer (EAP) ActuatorsResearch Group of Laboratory for Materials and Engineering

Gabor Kovacs, Silvain Michel, Christian Drager, Urs Hintermller, Alfred Schmidlin,Michael Wissler, Patrick Lochmatter and Rui Zhang

Main Project Partners

ETH Zurich, Institute of Mechanical Systems (IMES): Centre of Mechanics and Centre of Structure TechnologiesETH Zurich, Institute of Machine Tools and ManufacturingEMPA, Laboratory for Functional PolymersSwiss National Science Foundation: National Centre of Competence in Research CO-ME

Electroactive Polymer Technology

Contact: Gabor Kovacs [email protected] +41 (0)44 823 40 63 Silvain Michel [email protected] +41 (0)44 823 45 88

Working Princ iple of Dielectric Electroactive Polymers

Electroactive polymers (EAP) are promising as actuators in intelligent materialsystems, where large deformations are required. Electromagnetic, piezoelectricor shape memory alloy actuators are either too heavy, too complex or too slowfor such applications. EAP however are relatively lightweight, rather simple andfast enough.In particular, dielectric electroactive polymers were shown to have good overallperformances. Since their capabilities correspond to the performance of naturalmuscles, dielectric EAP actuators are often referred to as artificial muscles.

Arm wrestling competition: EAP-activated robot versus

human at the SPIE Symposium in March, 2005.

A dielectric EAP actuator is basically a compliantcapacitor, where a thin elastomer film is sandwichedbetween two compliant electrodes. When a high DC

voltage (kV) is applied to the electrodes, the arisingelectrostatic pressure squeezes the elastomer film inthickness and thus the film expands in planar directions.When the voltage is switched off, the elastic film returnsto its original shape.

C

+Q

-Q

A

d

Activated

UU

Co

Q=0 Ao do

Deactivated

Dielectric EAP actuator in deactivated (left) and activated state (right).

Characteristics of Empa spring roll actuators

Free strain: 35 %

Blocked force: 7 N Specific work output: 4.3 mJ /g

Activation cycles: 500

Possible Actuator Configurations

Various actuator designs are possible such as:

Single-layer or multilayer planar actuators

Spring roll actuators (electroactive polymer

wrapped around a coil spring)

Shell-like actuators (bending actuators)

Spring roll actuator.

Bending actuator in deactivated (left) and activated state (right).

Configurations and Characterist ics of Dielectric Electroactive Polymers

10 mm


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Modeling and Simulation of Dielectric

Elastomer ActuatorsMichael Wissler1,2, Dr. Gabor Kovacs1, Prof. Dr. Mehdi Farshad1, Prof. Dr. Edoardo Mazza2,1

1Empa, Laboratory for Materials and Engineering, CH-8600 Dubendorf, Switzerland2ETH Zurich, Center of Mechanics, CH-8092 Zurich, Switzerland

Goal

The goal is to model the electromechanical behavior of dielectricelastomer actuators in agreement with experiments. The models will allowsimulating the behavior of geometrically complex actuators, to optimizethe design and to ensure their reliability. New materials may besynthesized based on results generated with this model.

References

[1] M. Wissler, E. Mazza, Modelingof a pre-strained circular actuator made of dielectric elastomer actuators, Sensors and Actuators A, vol. 120, pp. 184 192, 2005

[2] M. Wissler, E. Mazza, Modelingand simulation of dielectric elastomer actuators, Smart Materials and Structures, vol. 14, pp. 1396 1402, 2005.

[3] M. Wissler et al, Circular pre-strained dielectric elastomer actuator: modeling, simulation and experimental verification, Proc. SPIE, vol. 5759, pp. 182 193, 2005.

[4] M. Wissler, E. Mazza, Modeling and Finite Element Simulation of Dielectric Elastomer Actuators, NAFEM Seminar, 2005, Wiesbaden, Germany.

Contact: Michael Wissler [email protected] +41 (0)44 823 47 87

Experiments and Finite Element Models

Results and Conclusion

Mechanical behavior: Characterization and modeling of the passivemechanical properties of the film (constitutive equations)

Characterization of the electrical properties of the film

Electromechanical coupling: Experimental and numerical investigationof planar actuators

Analyzing geometrical complex actuators (spring roll actuators)

Figure 2: Finite element model of the circular actuator.Figure 1: Experimental setup of the circular actuator.

Research Approach

Several experiments at different prestrain levels have been performed. A

constant voltage between 2 and 3.5 kV has been applied.

Voltage on Voltage off

The constitutive mechanical model is a quasilinear visco-hyperelastic

model. This model is implemented in a finite element model (see figure 2)for calculation of the behavior of the circular actuator.

In figure 3 the radial strain is plotted against time for a circular actuatorwith a biaxial prestretch of 3x3. The experiments are indicated as redcurves and the simulations as blue curves. For the hyperelastic part of theconstitutive model the Yeoh strain energy form is used. For theviscoelastic part the Prony series (exponential series) are applied. Theresults show an excellent agreement between simulation and experimentfor 2 and 2.5 kV, a good agreement for 3 kV and a satisfactory agreementfor 3.5 kV.

Voltage on Voltage off

Figure 3: Comparison between experiments and simulations.

0 250 500 750 1000

0

5

10

15

20

25

3.5 kV

3 kV

2.5 kV

2 kVRadialStrain

[%]

Time [s]

Results and Conclusion


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Spring Roll Dielectric Elastomer Actuators

for a Portable Force Feedback Device

Rui Zhang1, Dr. Gabor Kovacs1, Dr. Andreas Kunz2, Prof. Dr. Konrad Wegener2

1 Empa, Laboratory for Materials and Engineering, CH-8600 Dubendorf, Switzerland2 ETH Zurich, Institute of Machine Tools and Manufacturing, CH-8092 Zurich, Switzerland

The aim of this project is to develop a forcefeedback device, which provides satisfying touchsensations to the operator, moreover, which isportable, powerful, lightweight, and non-obstructive.

The focus is mainly on the development ofdielectric elastomer (DE) actuators and further, ontheir implementation into a force feedbackinterface.

References and Funding[1] A. Mazzone, R. Zhang, Virtual Reality Software and Technology Conference, Osaka J apan, 2003, pp. 196 204

[2] R. Zhang, A. Kunz, The 4th European Conference on Haptics, Munich Germany, J une 2004, pp. 300-307

[3] R. Zhang, A. Kunz, P. Lochmatter, G. Kovacs, 14th Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, part of IEEE Virtual Reality 2006Arlington, Virginia, USA, pp. 347-353

[4] R. Zhang, P. Lochmatter, A. Kunz, G. Kovacs, 8th SPIE Conference - EAP Actuators & Devices (EAPAD), 2006, San Diego, CA, USA (accepted)

The study is part of the National Centre of Competence in Research CO-ME, which is funded by Swiss National Science Foundation.

Contact: Rui Zhang [email protected] +41 (0)44 823 46 25

Fig. 1 Schematic of a force feedback interface. Red rectangular area includes the focus of this thesis.

Concept Study of the Force Feedback Device

To generate a resultant force on the fingertips, theactuators can be either located on the dorsal side,in the palm, between or around the fingers. Ourevaluation of 22 concepts showed that actuatorbetween the fingers is the most promisingconcept since it has

Development of the DE Actuators

Design

The spring roll DE actuator consists of a biaxiallypre-stretched DE film, which is wrapped around afully compressed spiral spring. By implementing atelescopic guidance the actuator is able to executelinear movements and to hold axial compressiveloads introduced by the fingers.

a compact and effective design,

a realistic force distribution, which is normal tothe fingertips,

and no unnecessary counter forces acting onthe hand.

Fig. 2Arts of the actuator attachment on the handare divided into four categories.

Experiments

Isometric tests were carried out to characterize the

actuator force-displacement behavior underactivation. The actuator executed a maximumblocking force of 7.2 N and a maximum elongationof 5 mm under a driving voltage of 3.5 kV.

Due to the high driving voltage, electrical safetyissues have been studied in order to providesufficient safety to human operators.

To demonstrate the proposed application, theactuator was finally implemented into a forcefeedback interface as described in figure 1.

Fig. 4 Construction of the spring roll push-pull actuator.

Fig. 6 Specification of the spring roll pull-push DE

actuator.

ValueSpecification

8 gWeight

1 hourProduction time

16 1840 mmElectrode area

about 60Layers

=12 mm, L=45 mmDimensions

VHB 4910 (3M)Material

Goal

Fig. 3 The envisioned device approach is to attach DEactuators between the fingers.

Fig. 5 Desktop demonstrator, by which a user can

feel the actuator.

Fig. 7 The actuator characteristics under isometric

tests.

6%

6%

32%

On the dorsal side

On the palmar side

Between the fingers

Around the fingers

Attachment A

Attachment B

FdeviceActuator

Actuator

Force transmission

Attachment A

Attachment B

FdeviceActuator

Actuator

Force transmission

0 1 2 3 4 5 6 7 8-10

-5

0

5

10

15

20

Force[N]

Displacement [mm]

0 kV1 kV

2 kV3 kV

Electrical Voltage

CyberGloveR

Force feedback

Visual feedback

Fingerposition

measuring

Fingerposition signal

3D Graphics

Actuatorcontrolling

Human operator in Virtual Reality

Force feedback device3D simulation andcollision detection

Biaxially prestretched,coated DE film

Telescopic guidanceCast-end

Working direction

Compressed coil spring


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Development of a Shell-like

Electroactive Polymer (EAP) ActuatorPatrick Lochmatter1,2, Dr. Gabor Kovacs1, Prof. Dr. Paolo Ermanni2

1Empa, Laboratory for Materials and Engineering, CH-8600 Dubendorf, Switzerland2ETH Zurich, Centre of Structure Technologies, CH-8092 Zurich, Switzerland

Goal

The goal of this PhD thesis is to build a shell-like actuator based on dielectric elastomers(DE), which is capable to perform complexout-of-plane deformations.

The aimed shapes of the actuator should bemaintained by a control system even whenexternal loads act upon its surface.

References

[1] P. Lochmatter, and G. Kovacs, Concepts for the reduction of the wind-induced oscillation of continuous aerial ropeway gondolas, submitted to J ournal of Wind

Engineering and Industrial Aerodynamics.

[2] P. Lochmatter, S. Michel, and G. Kovacs, in Smart Structures andMaterials 2006: Electroactive Polymer Actuators and Devices (EAPAD), 2006, San Diego, USA.

[3] P. Lochmatter, G. Kovacs, and S. Michel, Characterization of DE actuators based on an elastic film model, submitted to Sensors and Actuators A.

[4] P. Lochmatter, G. Kovacs, and M. Wissler, Characterization of DE actuators based on a viscoelastic film model, submitted to Smart Materials and Structures.

[5] Swiss Patent No. 6602005, S. Michel, G. Kovacs, and P. Lochmatter, Antrieb freinenLeichter-als-Luft-Flugapparat.

Contact: Patrick Lochmatter [email protected] +41 (0)44 823 43 27

Figure 1: The deactivated shell-like actuator (left) takes a specific shape when activated (right).

Potential Applications

Shell-like actuators may be used as adaptiveelements to generate a specific interactionbetween the structure and the environment,e.g. for

Results

Modeling

A novel model for the visco-hyperelasticbehavior of the acrylic film VHB 4910 (3M)was developed.

Therewith, the performance (energy density,efficiency) of selected planar DE actuatorconfigurations was estimated.

F(x,t)

on

Shell-like Actuator

Control andEnergy Supply

30 cm

30 cm

off

Ropeway Gondolas AerospaceActive Blimp

Propulsion

drag / oscillation-reduction of fluid-exposedstructures (left),

propulsion of vehicles through fluids (center),

continuous adjustment of surfaces (right).

Figure 2: Numerous promising applications are possible for shell-like actuators.

Experimental

Inspired by the biological agonist-antagonistprinciple of operation uni- and biaxial bendingactuators based on dielectric elastomerswere manufactured and will be characterized.

( )x t

( )y t( ) ( )z elt p t =

V

( )p t

( )xL t

( )yL t

( )zL t

DE Actuator(Capacitor)

VoltageSource

OverallResistance

4 kV 4 kV

4 kV 4 kV

Figure 3: DE actuator in an electrical circuit (left) and viscoelastic film model (right).

Figure 4: Uni- (left) and biaxial (right) bending actuator based on dielectric elastomers.

Documents

Dielectric elastomer actuators