Download Lecture 15 - People @ EECS at UC Berkeley

Design Realization
lecture 15
John Canny / Jeremy Risner
10/9/03
Last Time
 Composites: Fiberglass, carbon fiber and
kevlar.
 Hierarchical materials.
 Cellular materials, honeycomb and foam.
This time
 Polymers for actuation
“Wet” versus “Dry” actuation
 “Wet” – Ionic actuators. Utilize mobility or
diffusion of ions.
 polymer-metal composites
 conductive polymers
 others . . .
 “Dry” – Electronic actuators. Utilize Coulomb
forces.
 dielectric elastomers
 electrostrictive polymers
 others . . .
Polymer-Metal Composites
 Ionic Polymer Metal Composites (IPMC)
 ion exchange polymer membrane – selectively
pass ions of a single charge - Dupont Nafion
 gold plated electrodes on either side
 applied voltage induces movement of ions and
water – causes expansion on one side
 bending movement
Polymer-Metal Composites
 performance of IPMC
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strain: 3%
energy density: 0.01-0.1 J/cm3
speed: 100 Hz
output pressure: 10-30 MPa
drive voltage: 1-2 V
Polymer-Metal Composites
 work best in aqueous environments
 robot fish in tank
EAMEX, Japan
Conductive Polymers
 Polypyrrole (PPy)– conductive polymer
 oxidation-reduction reaction when voltage is
applied
 redox induces ion flow into or out of polymer
 flow in = expansion
 requires electrolyte
Conductive Polymers
 performance for PPy bilayer actuator
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strain: 12.4%
energy density: 0.040 J/g
speed: <1Hz
output pressure: 22 MPa
drive voltage: +/- 1V
Conductive Polymers
 attach polymer to a unstretchable film (gold)
to create unimorph actuator
Electrostricted Polymers
 Electrostricted graft elastomers
 motion achieved through electrostriction
 applied electric field induces a change from one
polarized direction to another, or one phase to
another.
flexible backbone
polarized chain
Electrostricted Polymers
 performance
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strain: 4%
energy density: 0.245 J/g
speed: 10 kHz
output pressure: 22 MPa
drive voltage: 2 – 3 KV
Dielectric Elastomers
 elastomer film is sandwiched between
compliant electrodes
 apply electric field: E = V/m
 Maxwell pressure: p = ee0E2
 electrodes squeeze elastomer in thickness
apply voltage
V+
Dielectric Elastomers
 materials available off-the-shelf
 3M VHB acrylic tape
 various silicone elastomers
 desired features
 high dielectric constant and breakdown strength
 low elastic modulus – high % elongation
 thin film
Dielectric Elastomers
 increase performance through prestrain
 stretch elastomer film in one planar direction
 fix motion in prestrained direction
 allow expansion in other planar direction during
activation
electrode
1
2
3
4
V+
dielectric elastomer
rigid constraints
Dielectric Elastomers
 performance
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strain: >200%
energy density: 0.75 – 3.4 J/cm3
speed: 10Hz - 20kHz
output pressure: 3.0 – 7.2 MPa
drive voltage: 5kV
Dielectric Elastomers
 morphologies
 planar actuators
• butterfly/bowtie
 unimorphs/bimorphs
 rolls
 bellows/speakers
Actuator Comparison
Actuator Work
Actuator Power