Development of Dielectric Elastomer Actuators and their Implementation in a Novel Force ...

214 Pages·2007·13.16 MB·English

Diss. ETH No. xxxx
Development of Dielectric Elastomer
Actuators and their Implementation in a
Novel Force Feedback Interface
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH
for the degree of
Doctor of Technical Sciences
presented by
RUI ZHANG
M. Sc. Mech. Eng.
born 04. February 1974
in Heilongjiang, China
accepted on the recommendation of
Prof. Dr. Konrad Wegener, examiner
Prof. Dr. habil. Andreas Kunz, co-examiner
Dr. Gabor Kovacs, co-examiner
2007

To Patrick
and my family.
In commemoration of Mom and Markus.

Contents
List of Symbols xi
List of Abbreviations xiii
1 About the thesis 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Related work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Force feedback devices . . . . . . . . . . . . . . . . . . . 2
1.2.2 Soft dielectric EAP . . . . . . . . . . . . . . . . . . . . . 8
1.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Requirements of a FFD 11
2.1 Sense of touch. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.1 Sensing characteristics . . . . . . . . . . . . . . . . . . . 13
2.1.2 Control capabilities. . . . . . . . . . . . . . . . . . . . . 14
2.2 Types of Grasping . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Grasping in VR . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3 Concept study on portable FFDs 21
3.1 The concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.1 Actuators on the dorsal side. . . . . . . . . . . . . . . . 21
3.1.2 Actuators on the palmar side . . . . . . . . . . . . . . . 27
3.1.3 Actuators around the fingers . . . . . . . . . . . . . . . 29
3.2 Evaluation of the concepts . . . . . . . . . . . . . . . . . . . . . 30
3.3 Requirements on the DE actuators . . . . . . . . . . . . . . . . 32
4 Dielectric Elastomer (DE) Actuators 35
4.1 Selection of an actuator technology . . . . . . . . . . . . . . . . 35
4.2 Soft dielectric EAPs . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2.1 Structure and principle of operation . . . . . . . . . . . 37
4.2.2 Working directions . . . . . . . . . . . . . . . . . . . . . 40
vi Contents
4.2.3 Components . . . . . . . . . . . . . . . . . . . . . . . . 41
4.3 Actuators based on soft dielectric EAPs . . . . . . . . . . . . . 47
4.3.1 Components . . . . . . . . . . . . . . . . . . . . . . . . 47
4.3.2 Types of actuators . . . . . . . . . . . . . . . . . . . . . 49
5 Planar DE actuators 55
5.1 Design and principle of operation . . . . . . . . . . . . . . . . . 55
5.2 Manufacturing process . . . . . . . . . . . . . . . . . . . . . . . 56
5.3 Experimental characterization . . . . . . . . . . . . . . . . . . . 60
5.3.1 Setups . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.2 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4 Discussion and conclusions. . . . . . . . . . . . . . . . . . . . . 62
6 Rolled DE Actuator with a Coil Spring Core 65
6.1 Design and principle of operation . . . . . . . . . . . . . . . . . 65
6.2 Theoretical considerations . . . . . . . . . . . . . . . . . . . . . 71
6.2.1 Blocking force under isometric activation . . . . . . . . 72
6.2.2 Film thickness distribution under isotonic activation . . 75
6.3 Manufacturing process . . . . . . . . . . . . . . . . . . . . . . . 78
6.4 Experimental characterization . . . . . . . . . . . . . . . . . . . 83
6.4.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.4.2 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.5 Discussion and conclusions. . . . . . . . . . . . . . . . . . . . . 87
7 Optimization of the Rolled DE Actuator 91
7.1 Failure analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.2 Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.2.1 Dielectric film. . . . . . . . . . . . . . . . . . . . . . . . 94
7.2.2 Electrode . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.2.3 Actuator core . . . . . . . . . . . . . . . . . . . . . . . . 96
7.2.4 Manufacturing process . . . . . . . . . . . . . . . . . . . 101
7.3 Experimental characterization . . . . . . . . . . . . . . . . . . . 101
7.3.1 Setups . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.3.2 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.4 Discussion and conclusions. . . . . . . . . . . . . . . . . . . . . 107
8 Rolled DE Actuators with an Improved Spring Core 109
8.1 Design and principle of operation . . . . . . . . . . . . . . . . . 109
8.2 Theoretical considerations . . . . . . . . . . . . . . . . . . . . . 111
Contents vii
8.2.1 Blocking force under isometric activation . . . . . . . . 111
8.2.2 Thickness distribution under isotonic activation . . . . . 111
8.3 Selection of a core geometry . . . . . . . . . . . . . . . . . . . . 112
8.4 Manufacturing process . . . . . . . . . . . . . . . . . . . . . . . 117
8.4.1 Magazine spring core. . . . . . . . . . . . . . . . . . . . 118
8.4.2 Square spring core . . . . . . . . . . . . . . . . . . . . . 118
8.5 Experimental characterization . . . . . . . . . . . . . . . . . . . 120
8.5.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
8.5.2 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.6 Discussion and conclusions. . . . . . . . . . . . . . . . . . . . . 128
9 Electrical properties of the rolled DE actuators 131
9.1 Electrical model of the human-FFD interface . . . . . . . . . . 131
9.2 Electrical properties of the components . . . . . . . . . . . . . 132
9.2.1 Electrical resistance of human beings . . . . . . . . . . . 132
9.2.2 Electrical properties of rolled DE actuators . . . . . . . 134
9.3 Failure cases of the interface . . . . . . . . . . . . . . . . . . . . 137
9.4 Determination of the physiological impacts . . . . . . . . . . . 140
9.4.1 Simulink Model . . . . . . . . . . . . . . . . . . . . . . . 140
9.4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
9.5 Protective measures . . . . . . . . . . . . . . . . . . . . . . . . 144
9.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
10 Design and Control of the Force Feedback Interface 147
10.1 Mechatronic description . . . . . . . . . . . . . . . . . . . . . . 147
10.1.1 Wearable force feedback device II . . . . . . . . . . . . . 147
10.1.2 Rolled DE actuators . . . . . . . . . . . . . . . . . . . . 149
10.1.3 Position sensing . . . . . . . . . . . . . . . . . . . . . . 149
10.2 Electronic architecture . . . . . . . . . . . . . . . . . . . . . . . 151
10.2.1 Interface card . . . . . . . . . . . . . . . . . . . . . . . . 151
10.2.2 Current amplifier . . . . . . . . . . . . . . . . . . . . . . 151
10.2.3 Voltage amplifier . . . . . . . . . . . . . . . . . . . . . . 152
10.3 Software description-the gripper simulation software . . . . . . 153
10.3.1 Calculation of the fingers’ positions. . . . . . . . . . . . 154
10.3.2 Collision detection . . . . . . . . . . . . . . . . . . . . . 154
10.3.3 Calculation of the interaction forces . . . . . . . . . . . 156
10.3.4 Calculation of the fingers’ distances . . . . . . . . . . . 157
10.3.5 Actuator calibration . . . . . . . . . . . . . . . . . . . . 157
10.3.6 Converting the virtual distance to real one . . . . . . . 158
10.3.7 Calculation of the driving voltages . . . . . . . . . . . . 158
10.3.8 Converting and Output . . . . . . . . . . . . . . . . . . 158
viii Contents
10.4 Results and discussions . . . . . . . . . . . . . . . . . . . . . . 158
10.5 Demonstrators . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
10.5.1 Desk-top demonstrator. . . . . . . . . . . . . . . . . . . 160
10.5.2 Wearable force feedback device I . . . . . . . . . . . . . 160
11 Conclusion and Outlook 163
11.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
11.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
Appendix 169
A Theoretical considerations on soft dielectric EAPs 171
A.1 Energy consideration . . . . . . . . . . . . . . . . . . . . . . . . 171
A.2 Electromechanical coupling . . . . . . . . . . . . . . . . . . . . 173
A.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
B Additional Information 181
Bibliography 187
List of Symbols
−−→
xyz CoordinatesoftheDIPjointoftheindexfingerincartesian
index
coordinates, page 157
−−→
xyz CoordinatesoftheDIPjointofthethumbincartesiancoor-
thumb
dinates, page 157
I Maximum discharging current, page 135
max
d ThedistancebetweentheDIPsofthethumbandthemiddle
cartesian
or index finger., page 157
C The capacity of a DE actuator, page 134
a
R The discharging resistance of a DE actuator, page 134
s
R The serial resistance of a DE actuator, page 134
a
R The measurement resistance in the discharging circuit for
m
measuring the electrical properties of the rolled DE actua-
tors, page 135
R Overalldischargingresistanceinadischargingcircuit,page135
d
k Stiffness of the virtual object, page 157
virtualobject
x Deformation(displacement)ofanelasticvirtualobject(spring),
displacement
page 157
F Interaction force of a collision, page 157
interaction
A The cross-sectional area of the elastomer to the direction z,
film,z
page 74
A Planar area of a parallel-plate capacitor, page 172
C Electric capacitance, page 172
Q Amount of charges in a rolled DE actuator, page 141
c
L Threedimensionsj =1,2,3incartesiancoordinates,page174
j
E Deformationenergyinahyperelasticdielectricfilm,page172
deform
E Electric field energy, page 172
field
I Effective current of a discharging current, page 141
eff
F Compressive blocking force of the rolled DE actuator under
com
isometric activations, page 72
F Forceofthepre-stretchedfilminthedirectionzincylindrical
film,z
coordinates, page 74
F Forces applied by a FFD to one’s fingertips, page 18
device
x Contents
F The grasping force applied by an user to his target object,
grasp
page 18
F Reaction forces arising from an object when grasped by an
object
user, page 18
F Axial force of the coil spring, page 74
spring
p Hydrostatic pressure., page 45
h
Z The internal impedance of the human body, page 132
i
Z , Z The impedance of the skin, page 132
s1 s2
Z The total impedance of the human body, page 132
T
Z The partial internal impedance of one extremity, page 133
ip
l j =1,2,coatedareaoftheVHB4910filmforonerolledDE
j,electrode
actuator, page 83
L Inthedirection1ofacartesiancoordinate,lengthofasingle
1,electrode
electrode, page 112
L Inthedirection1ofacartesiancoordinate,lengthofthefirst
1,0
passive zone, page 112
L In the direction 1 of a cartesian coordinate, length of the
1,n
n−1 passive zone, page 112
L Inthedirection1ofacartesiancoordinate,lengthofthelast
1,n+1
passive zone, page 112
L(o) Initialdimensionj =1,2,3incartesiancoordinates,page173
j
l j =1,2,totaldimensionsoftheVHB4910filmusedforone
j,total
coil spring DE actuator, page 83
M Overall weight of DE actuators, page 69
actuator
O i=0,1,...4 refers to the thumb, the index, middle, ring and
i3
little finger respectively. O refers to the PIP joints of the
i3
fingers, page 15
O and O i=0,1,...4 refers to the thumb, the index, middle, ring and
i0 i1
little finger respectively. O and O refer to the MCP (or
i0 i1
the TM) joints of the fingers (the thumb), page 15
O i=0,1,...4 refers to the thumb, the index, middle, ring and
i2
little finger respectively. O refers to the PIP joints of the
i2
fingers, page 15
p Effective compressive stress arising from the electric field in
e
a compliant capacitor., page 39
p Electrostatic pressure in the direction 3, page 178
3
p Electrostatic pressure arising in conventional rigid parallel-
conv
plate capacitor, page 173
p EquivalentelectrostaticpressurearisinginsoftdielectricEAPs,
eq
page 173
Q Electrical charges, page 172