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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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.
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.
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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.
9
1. DEAP Roll-actuator with polymer core
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP 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:
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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)
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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:
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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:
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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:
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
4. Manufacturing of DEAP Stack-Actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
4. Manufacturing of DEAP Stack-Actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
4. Manufacturing of 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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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.
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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.
(C) Control Engineering and Mechatronic Systems - Prof. Dr.-Ing. Jürgen Maas, Thorben Hoffstadt Modeling, design and fabrication of DEAP actuators
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
Phone: +49 (0)5261 702-5487
Jürgen Maas
Ostwestfalen-Lippe University of Applied Sciences
Department of Electrical Engineering and Computer Science
Control Engineering and Mechatronic Systems
Phone: +49 (0)5261 702-5871
Dominik Tepel
Ostwestfalen-Lippe University of Applied Sciences
Department of Electrical Engineering and Computer Science
Control Engineering and Mechatronic Systems
Phone: +49 (0)5261 702-5067