Herbert Shea Institute of Microengineering EPFL Switzerland

Miniaturized Dielectric Elastomer Actuators for Smart Machines

Herbert Shea

Institute of Microengineering

EPFL

Switzerland

http://lmts.epfl.ch/DEA

Nadine Besse

Alexis Marette Sam Schlatter

Samuel Rosset

Alexandre Poulin

Matthias Imboden

Herbert Shea Francesca Sorba

Seun Araromi David Mccoul

Xioabin Ji

Many thanks to my team

J. Shintake

What does it take to make a smart soft machine?

Need Flexible or even stretchable:

– Electronics (control, react)

– Actuation

– Sensing

– Energy Harvesting

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Scuola Superiore Sant'Anna in Pisa, Italy R. F. Shepherd, PNAS 2011, 20400–20403,

doi: 10.1073/pnas.1116564108

Monolithic actuator + sensor +

structure consisting of:

– soft dielectric (elastomer) and

– compliant electrodes

When kV voltage is applied, the elastomer is

squeezed by the electrostatic force

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Dielectric Elastomer Actuators

Dielectric Elastomer Actuators (DEA) are awesome

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• Large strain:

• over 1600% area strain demonstrated,

• 30% to 80% for long-term operation

• Soft: Young’s modulus ≈ 1 MPa

• Performance comparable to human

muscles

Soft robotics

Interaction with soft tissue

Tunable optics…

• Can add intelligence through

self-sensing and self-switching

S. Ashley, Scientific American 289, p.52 2003

EMPA’s (Zurich) 7m long blimp: “swims”

through the air using 4 artificial muscles SRI, circa 2006 http://goo.gl/14KR0

Miniaturized reliable DEAs at EPFL-LMTS. Some examples

7 Details & movies: http://lmts.epfl.ch/DEA

100 µm

Biological cell stretcher Foldable actuators Grippers for soft robotics

Stretchable soft sensors 30 GHz phase shifter

Stack of 128 layers

5 mW in 1 cm3

Soft Energy harvester

© 2013 DreamWorks Animation

CAN SOFT MACHINES BE FAST?

• Electrical time constant ≈ RC

• Mechanical resonance ≈

• Viscoelasticity

m

k

Need conductive soft electrodes

Need good elastomer with low

mechanical loss

Need good design

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U. Auckland, New Zealand, Biomimetics Lab

Acrylic-based DEAs are slow (but easy to make)

Using silicones allows for kHz operation (and long lifetime)

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High-speed rotary motor (rotates at 25 Hz, 1500 rpm),

driven at 760 Hz by 25 µm thick silicone DEA

Flexible lens that can change its focal length in 200 µs

1 cm

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Maffli, L. et al. Advanced Functional Materials, vol. 25, num. 11, p. 1656-1665, (2015)

Lens is driven by DEAs which expand to change lens curvature

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O2 plasma bonding of two silicone membranes

encapsulating an optical liquid

Focal length is reduced when DEA is activated

For speed: silicone used as: • Dielectric membrane

• Optical membrane

• Optical liquid

• Electrode

This lens concept was first reported

with acrylic materials by Carpi, F. et al.

Advanced Functional Materials, 2011,

21, 4152-4158

Stable operation for

over 400 million

cycles

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Soft can be fast if the right materials are chosen Silicone lens: 1000x larger bandwidth than acrylic

Optical response to a periodic signal for a silicone and VHB (acrylic) lens

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Silicone lens: nearly flat response up

to 1 kHz. Clear resonance peak

VHB lens: decrease in amplitude

even at low frequency. No

resonance.

3 orders of magnitudes

MULTI SEGMENT SOFT GRIPPER (DIELECTRIC ELASTOMER MINIMUM ENERGY

STRUCTURES)

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A. Araromi et al, “Roll-able multisegment dielectric elastomer minimum energy structures for a deployable

microsatellite gripper ”, IEEE Transactions on Mechatronics vol. 20, num. 1, p. 438, (2015).

Space Debris

Is this really a problem??

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Need an End-effector (grabber) for the Active Debris Remover

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DEA Advantages:

• Compact

• Light weight

• No complicated

mechanical parts

• Adaptable to the

shape of the debris

• Radiation tolerant

Robotic Arms

Dielectric Elastomer Minimum Energy

Structures (DEMES)

Ion Beam Shepard Harpoon or Nets

G. Kofod et al., Applied

Physics letters, 2007

CleanSpace One – a small Swiss satellite to remove space debris (which it needs to grab)!

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High Conformity to many shapes Simple control

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DEMES Actuation principle

Holding force limited by stiffness of substrate (PET or PDMS)

Routes to increasing holding force:

- Phase change material: SMP or low-melting point metal

- Electro-adhesion

Flexible substrate

DEMES Actuation principle

Flexible substrate

DEA+Electro-adhesion for soft robotics: 1-gram actuator picks up a 60-gram egg

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Collaboration with lab of prof. Floreano, EPFL

J. Shintake et al, Advanced Materials, online 2015 (front cover 2-2016) doi:10.1002/adma.201504264

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J. Shintake et al, Advanced Materials, online 2015

doi:10.1002/adma.201504264

FOLDABLE ACTUATOR FOR FOLDABLE MICRO AERIAL VEHICLES

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Collaboration with prof. D. Floreano’s lab at EPFL http://lis.epfl.ch

First step: fixed wings, foldable actuators (elevons)

Wing span: 40 cm

Mass: 127 g

Airframe material: Styrofoam

Flight speed: 7.2 m/s

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J. Shintake et al, IEEE Transactions on Mechatronics (2015)

doi:10.1109/TMECH.2014.2359337

Foldable DEA Elevon

Dimension: 130 mm * 70 mm

Weight: 14.4 g

Measured performance:

– Stroke angle: ±28°

– Torque: 2 N*mm

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TOWARDS TRULY SMART SOFT MACHINES

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1. Adding intelligence to the DEAs (making the “smart”

material actually smart)

a. Incorporating strain/position/proximity sensors

b. Printing TFTs on elastomer (500V)

this will enable devices with intelligence built-in

2. Lower DEA voltage to sub 100V

3. Increasing holding force by combining with Shape

Memory Polymers for tactile display and variable stiffness

robotics

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• Fast! (with right materials & electrodes)

• Manufacturable: batch-produced, repeatable

• Soft: good interface to biological tissues

• Reliable: long lifetime

• enabling for very wide range of applications

With dielectric elastomer transducers one

can combine:

– energy harvesting,

– Self-sensing

– distributed actuation

Add flexible electronics to create:

intelligent artificial soft machines

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Dielectric Elastomer Actuators

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Contact Info:

Herb Shea ([email protected])

EPFL-LMTS

Rue de la Maladière 71b, CP 526

CH-2002 Neuchâtel

Switzerland

Details & movies: http://lmts.epfl.ch/DEA

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Financial Support from:

• Swiss National Science Foundation

• European Space Agency

• EPFL

• ESNAM

• FP7 Blindpad

•NCCR robotics