Electric Flex by Yoseph Bar Cohen IEEE spectrum, June 2004 Artificial Muscles by Steven Ashley...

Electric Flex

• Electric Flexby Yoseph Bar Cohen

IEEE spectrum, June 2004

• Artificial Musclesby Steven Ashley

Scientific American, October 2003

A Challenge to Artificial muscle community

Human Muscle:

Contracts up to 50%of their length

Force(max.)= 350 kilopascal(@ 35% strain)

Max. power density (at a Point) ~ 150 to 225 watts

Plan of the Talk & Introduction

• Introduction to muscles

• How it works

• Artificial Muscle

• Applications

Muscles

• Muscles turn energy in to Motion

• Efficient,

• long lasting

• self healing and

• grow stronger with use (practice)

Muscles - Types

• Skeletal Muscle ( Striated muscle)Comes in Pairs, contract voluntarily single contraction( twitch ) andsustained contraction ( tetanous )

• Smooth Muscle ability to stretch and maintain tension contracts involuntarily

• Cardiac Muscle Only in Heart, endurance and consistency

twitch muscle only and contracts involuntarily

Skeletal (Striated) Muscle

Cross section of skeletal muscle (200x)Muscle fibers- red and the fat cells -white

Muscles of the human body.

How muscles work?

- Basic action is Contraction

- A bundle of cells called Fibers

Fibers

Fibers : cylinders1 to 40 microns long10 to 100 microns in diameter

Contracting Muscle

Thin filaments slide past the thick filaments shortening Saromere

Muscles create force by cycling cross-bridges

Myosin molecule Bonds with actin Molecule:

Crossbridge

Myosin releasesADP(adenosine diphosphate) and

Pi(inorganic phos-Pate)

Contraction of muscles : Triggered by electrical impulses

1 Hz 5 Hz 10 Hz 50 Hz

Some facts:

Minimum unit of contraction in a muscle is called Motor Unit

Size of the motor unit (number of fibers/motor neuron)

Muscles controlling eye motion ~ 10Muscles controlling Larynx 2 to 3 Calf muscles 1000 to 2000

Motor unit is digital Strength α to the number of motor units activated

Artificial Muscles

• Electroactive polymers(EAP)

• First artificial muscle:

Using natural rubber was demonstrated by

Wilhelm Konrad Rontgen ( X – rays)

Artificial muscles-classification

Electronic1. Passive dielectrics

2. Piezoelectric polymers

3. Graft elastomers

4. Liquid crystals

5. Electrostrictive paper

Ionic

1. Polymer gels

2. Polymer metal composites

3. Conductive polymers

4. Carbon nanotubes

5. Electrorheological liquids

Electronic polymers

• Electronic polymers react in µs

• Higher energy density

• Can operate in open air

• Needs strong electric fields (150 V/µm)

(very close to dielectric breakdown)

Electronic polymers-cont.

• Passive dielectric – simplest and robust SRI has achieved 8 M Pascal ( factor of 30 >)

• Piezoelectric polymers small strain and force improves to 4% strain and G Pascalneeds high voltages

• Graft elastomersa long molecule is engrafted with elements

that respond to electric field ~ 4% strain

Electronic polymers-cont.• Liquid crystals- with ferroelecric materials:

undergoes phase change from ordered crystalline phase to disordered phase when heated electrically.

• Electrostrictive paper serendipitous discoverycellophane tape sandwiched between two silver tapeslow cost and has sufficient force with multiple layers Loudspeakers

Ionic muscles

• Efficiency less than 30% as compared to 80% for the electronic muscles

• Low drive voltages 1 to 5 V

• Need to enclose liquid or gel and is this makes it more difficult to handle as compared to electronic polymers

A comparison

Passive dielectric artificial muscle

SRI International

Ionic polymer metal composites

Breakthroughs in electronic polymers

• Soft silicones: ~10 to 30% strain(SRI calls them dielectric elastomers or electric field activated polymers)

• More strain : carbon particle in elastometric matrix

• Streching polymers: increased dielectric strength and strain (1 to 5 kV)

• Edisonian approach: 380% linear strain with acrlyic elastomer

Applications

• Linear actuators

• Loudspeakers: flat panel speakers

• Pumps

• Sensors

• Smart surfaces: reduce drag

• Power generators (~ 1 Watt in shoes)

• Small winged plane: for survilence