Modellierung, Entwurf und automatisierte Herstellung von ...

Modellierung, Entwurf und automatisierte

Herstellung von Multilayer-Polymeraktoren

Modeling, design and automated fabrication of polymer-based

multilayer actuators

Thorben Hoffstadt, Dominik Tepel und Jürgen Maas

VDI GMA-FA 4.16 “Unkonventionelle Aktorik”

21. Sitzung am 23.-24. Oktober 2014 in Saarbrücken

Vortrag im Rahmen des

Workshop der Nachwuchswissenschaftler

2

Outline

1. Introduction

2. Modelling of DEAP-based multilayer actuators

3. DEAP stack-actuator design

4. Automated manufacturing process

5. Conclusion

(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators

0zl l

pv

0l

l

3

1. Electroactive Polymers – Introduction


Fundamental design of a DEAP transducer

polymer (e.g. silicone, poly-

urethane, acrylic) compliant

electrodes

Functional principle is based on the electrostatic pressure that results when the

DEAP is charged:

Considered will be electronic EAPs and in particular dielectric electroactive

polymer transducers denoted as DEAP transducers.

2

2

0 0

p

el r r

vE

t

0Vpv 0Vpv E

4

1. Properties of DEAP-based transducers


Polymer acts as a dielectric

capacitance Cp

Parasitics of polymer and electrode

loss resistances Rp and Re

Electrical

Energy Mechanical

Energy

electrical behavior

mechanical behavior electrical stimuli

mechanical stimuli

actuation

sensing

Electrical Parameters depend on the mechanical state

Due to the electromechanical coupling DEAP transducer can be

used as actuators, sensors and generators

eR

pR

pC

pv

DEi

i

DEv

5

1. DEAPs as sensors and generators


DEAP as sensor

Electrical parameters depend

on mechanical state λ

Identification of at least

one electrical parameter

~ vSens

vAct

iDE

vDE

iDE

vAct vDE vSens ~

iDE

iDE

Sensor-based

concepts

DEAP exclusively

used as sensor

Sensor-less

concepts

DEAP transducer

is simultaneously

used as sensor

DEAP as (electrostatic) generator

initia

l syste

m

0

min

imu

m

stra

in

3

ma

xim

um

stra

in

1

ma

xim

um

field

stre

ngth

2

stre

tch

DE

G

Charge

DEG

rela

x D

EG

Discharge

DEG 4

eR

pR

pC

pv

DEi

i

DEv

6 (C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators

1. DEAP Multilayer Actuators for pulling and pushing

Actuation in direction of the electric field

Compression of the polymer in z-direction

Pulling force in z-direction

z

x

Actuation perpendicular to the electric field Elongation of the polymer in z-

direction

Pushing force in z-direction

0VDEv

1zl

DEAP stack-actuator

Multilayer increasing the absolute

deformation l

DEAP roll-actuator

Multilayer increasing the

pushing force

0VDEv

1zl

pv

pv

Hoffstadt, T.; Graf, C.; Maas, J.: Modeling of Roll-Actuators based on

Electroactive Polymers. Proceedings of SPIE Smart Structures/NDE, San

Diego, USA, Vol. 8687, S. 8687-31, 2013.

Tepel, D.; Graf, C.; Maas, J.: Modeling of mechanical properties of stack

actuators based on Electroactive polymers. Proceedings of SPIE Smart

Structures/NDE, San Diego, USA, Vol. 8687, S. 8687-28, 2013.

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010104

http://dx.doi.org/10.1117/12.2010104

http://dx.doi.org/10.1117/12.2010104

http://dx.doi.org/10.1117/12.2010104

http://dx.doi.org/10.1117/12.2010104

7 (C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators

0DEv 0DEv

DEAP actuators are predestined for position

applications in small devices

Promising technology e.g. for automation

applications, haptic feedback…

electrical

contactors

force feedback glove [R. Zhang, P. Lochmatterg, A. Kunz and G.

Kovacs: “Spring Roll Dielectric Elastomer

Actuators for a Portable Force Feedback Glove”,

Proc. of SPIE Vol. 6168, 61681T-1, 2006]

pneumatic valves &

gripper [M.Giousouf: „Dielectric Elastomer

Actuators – Potential Use in Automation

Technology“, ACTUATOR 2012, pp.

358-361, 2012]

www.dielastar.de

1. Applications of DEAP multilayer actuators

8

1. DEAP Roll-actuator with polymer core

New roll-actuator design

Bi-axially prestretched active material is winded up around compressed

polymer core.

Prestretched polymer core must support the force in the operating point of

the actuator caused by the prestretched DEAP material.


prestretch

λz,core,0 prestretch

λz,EAP,0

prestretch λz,EAP,0

prestretch

λγ,EAP,0

prestretch

λγ,EAP,0

prestretch

λz,core,0

0t

0 2w

DEAP material

polymer core

0l

polymer core

polymer electrode

z r

Hoffstadt, T.; Graf, C.; Maas, J.: Modeling of Roll-Actuators based on Electroactive Polymers. Proceedings of SPIE Smart Structures/NDE,

San Diego, USA, Vol. 8687, S. 8687-31, 2013.

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

http://dx.doi.org/10.1117/12.2010093

9

1. DEAP Roll-actuator with polymer core


No-load-strain behavior of the realized prototype:

polymer core

inactive area

electrode

contact

0l l

0 0.5 1 1.5 2 2.5 31

1.01

1.02

1.03

1.04

1.05

1.06

voltage vDE

in kV

no

-lo

ad s

trai

n

z,n

l

simulation

measurement

λz

@ F

z,lo

ad =

0

Parameters of the prototype:

0 0 , ,0

, ,

31mm; 40μm; 20; 5mm

1,07; 1,2; 4,5MPa; 1MPa

o N

z EAP EAP EAP core

l t N r

Y Y

10

2. Modelling of DEAP-based multilayer actuators


Stack-actuator: actuator films are

mechanically connected in series

electrically connected in parallel

zy

xE

pv

elelast

0 zA A Electrode

Polymer

loadF

0zt t

2

20 0

0 2

1

3act el elast r z

z z z

A E YF A λ

λ λ

one actuator film describes the

stretch-force-behavior of the

whole actuator

i i

i

Wp

2

0el r E electromechanical coupling:

hyperelastic material behavior: (using Neo-Hookean approach, equi-

biaxial deformation in x- and y-direction)

0.90.910.920.930.940.950.960.970.980.9910

2

4

6

8

10

12

14

Stretch z

Pullin

g f

orc

e F

z,load in N

E0 = 10 V / µm

E0 = 20 V / µm

E0 = 30 V / µm

E0 = 40 V / µm

E0 = 50 V / µm

E0 = 60 V / µm

Y = 3MPa; εr= 7; A0 = 64mm²

Current limit under

consideration of

the lifetime Hoffstadt, T.; Tepel, D.; Maas, J.: Model-based Design Optimization Rules of

DEAP Actuators. 14th International Conference on New Actuators -

ACTUATOR 14, Bremen, June 2014.

11

Optimizing the actuator based on a dimensionless, normalized stretch-force-

behavior

energy density uc stored in the (constant) DEAP capacitance:

substitution of the electrostatic pressure:

normalizing the force and the energy density a dimensionless charateristic

results:


2. Stretch-force-behavior of a DEAP stack-actuator

2

2

0

1

2 2 2

p pc elc r

C vUu E

V V

20 12

3act c z

z z

A YF u

2

0

21 1 1

3

act cz

z z

F u

A Y Y

T. Hoffstadt and J. Maas: Model-based Optimization and Characterization of DEAP Stack-Actuators,

SMASIS 2014-7690, SMASIS 2014.

12

Operation with constant energy density equals operation with constant

electric field


2. Stretch-force-behavior of a DEAP stack-actuator

0.60.650.70.750.80.850.90.951-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

stretch z

norm

aliz

ed f

orc

e F

act /

(A

0 Y

)

uc / Y = 0.05

uc / Y = 0.1

uc / Y = 0.15

uc / Y = 0.2

pulling force

pushing force

0. .pc

p z

vuconst E const v E t

Y t

13

Stretch-force-behavior has two

characteristics

Blocking-force (obtained if the

actuator cannot deform)

No-load-stretch (obtained if the

actuator generates no force

free stroke)


2. Design Optimization

0.650.70.750.80.850.90.9510

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

stretch z

norm

aliz

ed f

orc

e F

act /

(A

0 Y

)

uc / Y = 0.05

uc / Y = 0.1

uc / Y = 0.15

uc / Y = 0.2

zy

x

No-Load-Stretch

Blocking-Force

pv

actF

,0 0

const.

zl l

0zl l

pv

0l

l

14

Operating the actuator at a constant stretch λz,0

the resulting force is linearly increased with the

electrical energy density:

If a pre-stretch (load) λz,0 is applied the

blocking-force results to:


2. Design Optimization – Blocking-Force Blocking-Force

pv

actF

,0 0

const.

zl l

0 0.05 0.1 0.15 0.20

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

energy ratio uc / Y

norm

aliz

ed B

lockin

g-F

orc

e F

act /

(A

0Y

)

z,0

= 1

z,0

= 0.9

z,0

= 0.8

,0

2

z

,0 2

0 ,0 ,0

2 1 1

3

act cz

z z

F u

A Y Y

0 ,0

2act c

z

F u

A Y Y

Blocking-Force is scalable by

cross-sectional area A0 but is

independent from the

Young‘s modulus Y

Slope is adjustable by

applied pre-load λz,0

15

The no-load-stretch is obtained if no force is

exerted:

Using a linear-elastic approach a comparable

equation results:


2. Design Optimization – No-Load-Stretch No-Load-Stretch

0zl l

pv

0l

l

0 0.05 0.1 0.15 0.2

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

energy ratio uc / Y

No-L

oad-S

tretc

h

z @

Fact =

0

hyper-elastic model

linear-elastic model

0 2act c elastF u 3

33

2 1,

8 1 1with =

4 2

cz

c

u

Y

u

Y

1 2elast z z cY Y u

21 1c

z

u

Y

No-Load-Stretch is independent from the geometry but decreases with increasing Young‘s modulus Y:

16

Optimization of mechanical work density with respect to the applied

electrical energy

Instantaneous mechanical work:

This also yields to a normalized

mechanical energy density:

Operating point with maximum

electromechanical coupling:


2. Design Optimization – Coupling Coefficient

21 1 12

3

cz

z

z z

uw

Y Y

0

1act act

z

F l FWw

V V A

3 4!

,3

2 1 6 20

3

z c z z

z opt

z z

u Yd w Y

d

0.650.70.750.80.850.90.9510

0.01

0.02

0.03

0.04

0.05

stretch z

norm

aliz

ed e

nerg

y w

/ Y

uc / Y = 0.05

uc / Y = 0.1

uc / Y = 0.15

uc / Y = 0.2

0.650.70.750.80.850.90.9510

0.05

0.1

0.15

0.2

0.25

0.3

stretch z

couplin

g c

oeff

ecie

nt

cu Y

cu Yc

w

u

17

Operating the stack-actuator with a constant voltage a corresponding initial

energy density results:

Effect of electromechanical instability1 occurs if:

Instability limits the

maximum stretch

depending on the

generated

force


2. Performance Limitations

,0 2

,0

0

p p

z c c z

v vu u

t t

1 Zhao, X., and Suo, Z., 2007. “Method to analyze electromechanical

stability of dielectric elastomers”. Applied Physics Letters, 91, p. 061921.

,02

c elast loadu F

Y Y A Y

0 0.02 0.04 0.06 0.08 0.10.4

0.5

0.6

0.7

0.8

0.9

1

initial energy ratio uc,0

/ Y

str

etc

h

z

Fact

/(A0Y) = -0.1

Fact

/(A0Y) = -0.05

Fact

/(A0Y) = 0

Fact

/(A0Y) = 0.05

Fact

/(A0Y) = 0.1

instable

region

stable region

0

loadF

A Y

limit of elec-

tromechanical

instability

load

load

load

load

load

18

Electromechanical instability

limits the

Maximum No-Load-Stretch

Maximum Blocking-Force

Depending on the exerted force the critical stretch and corresponding energy

vary


2. Performance Limitations

-0.3 -0.2 -0.1 0 0.1 0.2 0.30.4

0.6

0.8

1

Fact

/(A0 Y)

cirtical str

etc

h

z,c

rit

-0.3 -0.2 -0.1 0 0.1 0.2 0.30.05

0.1

0.15

Fact

/(A0 Y)c

irtical in

itia

l energ

y r

atio u

c,0

,crit/Y

stable region

stable region

instable region

instable region

31

,

3,0,

20 0.63

2

0 20.079

16

z crit act

c crit act

F

u F

Y

,

0

,0, ,

1 1

3

1 1

6

act z crit

c crit z crit

F

A Y

u

Y

pulling force pushing force

19

Blocking-Force No-Load-Stretch

with with

with

(A0: free design parameter)

with

(Y: material parameter

l0: free design parameter)

Electromechanical Instability

with

with

optimal operation point

maximum electromechanical coupling

Based on the static model of a DEAP stack-actuator the Blocking-Force

and No-Load-Stretch were investigated

2. Design Optimizations – Conclusion


0

,1

3act z crit

A YF

,

0 0.63z crit act

F

actF lc

uc

u

actF

0A l 0

,Y l

,1

act z critF

0,A Y l

0l

0zl l

pv

0l

01 zl l actF

0 zA A

,

c

z opt

f u

0.650.70.750.80.850.90.9510

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

stretch z

norm

aliz

ed f

orc

e F

act /

(A

0 Y

)

uc / Y = 0.05

uc / Y = 0.1

uc / Y = 0.15

uc / Y = 0.2

01 zl l

20

Increase of absolute deformation and force multilayer actuator

By stacking the actuator films to the designated height and alternating the direction of the contact tab, the DEAP stack-actuator is obtained.

3. DEAP stack-actuator design

DEAP actuator

film

DEAP

contacting film

end caps

(optional)

x y

z

DEAP contacting film

contacting electrode

contact

tabs

polymer

electrode

contact

Tepel, D., Hoffstadt, T., Graf, C., Cording, D., Krause, J., Wagner, J., and Maas, J., 2013. “Development of an automated manufacturing

process for DEAP stack-actuators”. EuroEAP2013. (C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators

2

0 2

p

el r

v

t

electrost. pressure

voltage

thickness

permittivity

+ -

21

Dry deposition process:

divided into several processing steps

fabricate stack-actuators with reproducible

and homogeneous properties


4. Manufacturing of DEAP Stack-Actuators

Tepel, D.; Hoffstadt, T.; Maas, J.: Actuator Design and Automated

Manufacturing Process for DEAP Multilayer Stack-Actuators. ACTUATOR 2014

www.dielastar.de

22

Sub-process 2: applying electrodes and folding



DEAP film is fixed on the

vacuum folding table

a nozzle is positioned

over several sectors and

electrodes are applied

DEAP film with the

applied structured

electrodes is folded

a mask is positioned

over the elastomer

after 4 spraying and 3 folding processes an actuator module is created whose thickness is 8 times higher than the single film

due to the very thin DEAP films, the films are folded to facilitate the handling

23

Sub-process 3: stacking of DEAP sub-modules to designated height



folded DEAP film

module is lifted by the

vacuum gripper

folded DEAP film

module is stacked and

laminated on top of each

other

folded DEAP film

module is transported to

the film carrier of the

rotary index table

24

Sub-process 4: cutting by a ultrasonic knife to separate DEAP stack-

actuators



stacked DEAP film

module is fixed and

transported by the film

carrier of the rotary

index table

individual actuator

modules are seperated

individual actuator

modules are cutted out

25

To realize a transition from the elastic DEAP to the stiff wiring of the power

electronics, a DEAP contacting film is used, which does not harm the actuation.

To protect the DEAP stack-actuator against environmental influences, the actuator is

encapsulated by winding a polymer film around the stack-actuator.

4. Contacting of the DEAP stack-actuator module


end cap

encapsulation material

stacked DEAP

actuator module contacting

pins

a) contacting pins

are rolled into the

contacting film

b) winded around the

actuator module in a

pre-stretched condition

c) end cap with

grooves is applied to

fix the contacting pins

d) a polymer film

is winded around

the stack-actuator

contacting

electrode

polymer

polymer

DEAP

contacting

film

end cap

DEAP

contacting

film

Hoffstadt, T.; Tepel, D.; Maas, J.: Structured electrode design for DEAP transducer with integrated safety mechanisms. EuroEAP 2014, Linköping, Sweden, Juni 2014.

26

encapsulation

material stacked DEAP

actuator module

DEAP

contacting film contacting pin

4. Experimental validation of the actuator design

DEAP stack-actuator

0 10 20 30 40 500.94

0.95

0.96

0.97

0.98

0.99

1

electrical field in V/µm

No-L

oad-S

tretc

h

calculation

measurement

0

0.1

0.2

0.3

0.4

0.5

com

pre

ssio

n

z in m

m

“No-Load-Stretch” behavior of the produced

DEAP stack-actuator:

Parameters of the stack-actuator:

t0 = 50μm; Y = 3MPa; εr= 7: N = 160


end cap

27

DEAP transducer can be used as actuators, sensors and generators

Based on an analytical model of a DEAP stack-actuator design rules can be

obtaiend

DEAP technology is an energy efficient alternative for conventional actuators

with further excellent properties.

However, concerning the material and the manufacturing a lot of R&D has to

be done.


5. Conclusion

0zl l

pv

0l

l

0.650.70.750.80.850.90.9510

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

stretch z

norm

aliz

ed f

orc

e F

act /

(A

0 Y

)

uc / Y = 0.05

uc / Y = 0.1

uc / Y = 0.15

uc / Y = 0.2

No-Load-Stretch

Blo

ckin

g-F

orc

e

28

Acknowledgement

This contribution is accomplished within the project "Dielastar - Dielektrische

Elastomere für Stellaktoren“ (Dielectric Elastomer Actuators), funded by the

Federal Ministry of Education and Research (BMBF) of Germany under grant

number 13X4011, see www.dielastar.de.


http://www.dielastar.de/

Thanks for your kind attention!

Thorben Hoffstadt

Ostwestfalen-Lippe University of Applied Sciences

Department of Electrical Engineering and Computer Science

Control Engineering and Mechatronic Systems

[email protected]

Phone: +49 (0)5261 702-5487

Jürgen Maas




[email protected]

Phone: +49 (0)5261 702-5871

Dominik Tepel




[email protected]

Phone: +49 (0)5261 702-5067

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