Design Realization lecture 15

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Design Realization lecture 15

• John Canny / Jeremy Risner
• 10/9/03

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Last Time

• Composites Fiberglass, carbon fiber and kevlar.
• Hierarchical materials.
• Cellular materials, honeycomb and foam.

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This time

• Polymers for actuation

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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 . . .

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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

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Polymer-Metal Composites

• performance of IPMC
• strain 3
• energy density 0.01-0.1 J/cm3
• speed 100 Hz
• output pressure 10-30 MPa
• drive voltage 1-2 V

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Polymer-Metal Composites

• work best in aqueous environments
• robot fish in tank

EAMEX, Japan
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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

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Conductive Polymers

• performance for PPy bilayer actuator
• strain 12.4
• energy density 0.040 J/g
• speed lt1Hz
• output pressure 22 MPa
• drive voltage /- 1V

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Conductive Polymers

• attach polymer to a unstretchable film (gold) to
  create unimorph actuator

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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
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Electrostricted Polymers

• performance
• strain 4
• energy density 0.245 J/g
• speed 10 kHz
• output pressure 22 MPa
• drive voltage 2 3 KV

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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
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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

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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
V
dielectric elastomer
rigid constraints
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Dielectric Elastomers

• performance
• strain gt200
• energy density 0.75 3.4 J/cm3
• speed 10Hz - 20kHz
• output pressure 3.0 7.2 MPa
• drive voltage 5kV

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Dielectric Elastomers

• morphologies
• planar actuators
• butterfly/bowtie
• unimorphs/bimorphs
• rolls
• bellows/speakers

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Actuator Comparison
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Actuator Work
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Actuator Power