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Competing With Nature: Smart Muscles. Mr. Alvin Quiambao , Air Force Office of Scientific Research. Group 8: Alejandra Europa, Leigh Martin, Nidia Selwyn, Jack Bobzien. Texas A&M University Chen 313 – Special Project Spring 2013.

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competing with nature smart muscles
Competing With Nature:Smart Muscles

Mr. Alvin Quiambao, Air Force Office of Scientific Research

Group 8: Alejandra Europa, Leigh Martin, Nidia Selwyn, Jack Bobzien

Texas A&M University

Chen 313 – Special Project

Spring 2013

dynamic presentation
Dynamic Presentation
  • Please visit the following link to view the dynamic version of this presentation

muscle power
Muscle Power
  • A muscle is a bundle of many cells called fibers whose function is to produce force and cause motion.
  • Efficient at turning fuel into motion
  • Long-lasting
  • Self-healing
  • Able to grow stronger with practice
  • Basic action is contraction

artificial muscles
Artificial Muscles
  • Artificial muscles are man’s attempt to duplicate, improve or simply replace the role of natural muscles
  • A “muscle” is anything which accomplishes actuation/contractionunder the command of a stimulus.
  • First artificial muscle developed in the 1950's by American physician Joseph L. McKibbenoriginally intended to actuate artificial limbs for amputees

Rehabilitation glove with artificial muscles.




Improved mechanical technology

currently implemented
Currently Implemented

  • Mechanical artificial muscles are contractile or extensional devices operated by pressurized air filling a pneumatic bladder, using motors or hydraulics

  • A shape-memory alloyis an alloy that "remembers" its original, cold-forged shape: returning to it when heated.
  • Electroactive Polymers, or EAPs, are polymers that exhibit a change in size or shape when stimulated by an electric field.
    • Dialectric Elastomer
    • IMPC’s
    • Carbon Nanotubes
basic principles

Contraction & Expansion of the Natural Muscle K

  • Muscles are the "engine" that your body uses to propel itself.
  • Turn energy into motion.
  • Contractions of muscles are triggered by electrical impulses or a stimulus
    • Nerve cells
    • Internal or external stimuli

Triggered nerve cells.

natural muscles
  • Long-lasting and Self-healing
  • Grow stronger with repetitive use
  • Allows for work cycles of more than 20%
  • Alter strength and stiffness when needed
  • Generate stresses up to about .35 MPa
  • Contract at 50% per second
  • Can transform ATP into fuel, if needed

artificial muscles1
Artificial Muscles
  • Materials that change size and shape when activated by a stimulus
  • Mimic natural body functions
  • Provide large force and motion while being lightweight and not very dense
  • Allow for more delicate movements than machines can achieve

Early McKibben Arm

Muscle of a Rubber Tube

current technology


  • External, lower-extremity orthotic and prosthetic (O&P) devices have been around for centuries
  • Made from crude materials
    • Wood and leather
    • Heavy, non-adaptive, and difficult to use
  • 1970s: Actively controlled knee dampers
    • Advantage over mechanically passive knee systems
    • More control & stability
  • Recently: Computer-controlled adaptive knee orthotic
    • Offers only locking and unlocking controllability

Prosthetic toe: 950 and 710 B.C.

This prosthetic toe dates back to between 950 and 710 B.C.

  • 1988:Popovicand Schwirtlich
    • Amputees using a powered knee prosthesis could walk at faster speeds
    • Improved metabolic economy compared to conventional knees
  • Knee design was never commercialized
  • Problems occurred with the mechanical system
    • Inadequate cycle life
    • Excessive mechanism noise
    • Limited battery life

current devices
Current Devices
  • Contemporary O&P limbs cannot yet perform as well as their biological counterparts,
    • Stability
    • Power generation
    • Efficiency
    • Cycle life
  • Current prosthetic and orthotic devices are separate, lifeless mechanisms
  • Robotic limbs are bulky and do not yet mimic the natural movement of the body
  • Devices today have no real neurological or intimate connection with the human body

  • Most devices in use today employ a force- controllable actuator
  • Comprised of an electric motor and a mechanical transmission
    • Heavy, bulky, and noisy mechanism
  • Lower-extremity O&P devices cannot modulate spring stiffness and motive force needed for normal leg movement
    • Fit/Sizing
    • Balance
    • Easily fatigued

  • The actuator and transmission play a dominant role in determining the dynamic performance of O&P devices
  • In trying to duplicate the form and function of a limb, actuators that are similar to natural muscle are needed
  • Desired changes:
    • Lighter
    • Simpler
    • More natural looking
    • Quiet operation
    • Comfortable attachment
    • Lower cost

  • For artificial appendages to truly mimic biological function, even during level ground ambulation, O&P actuators must control both joint impedance and motive force
  • Artificial muscles offer considerable advantages to the physically challenged, allowing for
    • joint impedance
    • Motive force controllability
    • Noise-free operation

current research


Picture taken from Clip Art

properties needed
Properties Needed
  • Generate large strains rather than high force
    • Fractional changes of muscle length
    • ~ 20 %
  • High response rate
  • High output power at low strain

how can this be accomplished
How can this be accomplished?
  • Do not want to mimic nature
    • Large macroscopic strains
    • Combining effects of trillions of molecular actuators
  • Take advantage of material deformations
  • Different types exist
    • Use distinct actuators / driving factors

Different contractions levels of an air muscle designed by the Schadow Robot Company.

types of actuators

Shape Memory Alloys

  • Electroactive Polymers
    • Dielectric Elastomers
    • IPMCs
    • Carbon Nanotubes

Types of Actuators

Taken from Clip Art

shape memory alloys
Shape-Memory Alloys
  • Commercially important
  • Generate strains of up to 8%
  • Require energy conversion
    • Electrical  thermal  mechanical
    • Inefficient

Shape-Memory Alloy

  • All previously mentioned artificial muscles provide high-strain
  • But all have a disadvantage
    • Inefficient energy conversion
    • Low response rate
    • High voltages
    • Etc.
  • Need for a new design

electroactive polymers eaps
Electroactive Polymers EAPs
  • Exhibit change in size or shape when exposed to an electric field
  • Use electronically conducting polymers
    • Polyaniline and polypyrrole
  • High-strain actuators

  • Solvated dopant ions inserted into a conducting-polymer electrode
  • Similar to a battery
  • Operate at a few volts
  • Generates high strains: 26%
  • High strain rates: 11%/sec
  • Large stresses: 7 to 34 MPa

(a) EAP gripping device.(b) A voltage is applied and the EAP fingers deform in order to surround the ball.(c) When the voltage is removed the EAP fingers return to their original shape and grip the ball.


Electroactive Polymer for a Robot Head

dielectric elastomers
Dielectric Elastomers
  • One type of EAP
  • Resemblance to silicone rubbers in sealants
  • Considered a capacitor
    • Better than a battery
  • Used by Artificial Muscle Inc.

Dielectric Elastomer

Compresses with applied voltage

dielectric elastomers1
Dielectric Elastomers
  • Driven by Maxwell Stress
    • Attraction between charges of opposite capacitor electrodes
    • Repulsion between like charges
  • High strains: 120%
  • Large stresses: 3.2 MPa
  • Peak strain rate: 34,00% / sec for 12% strain

problems limitations
Problems & Limitations
  • As elastomerstiffness decreases, maximum stress generation decreases
    • Maximum actuator stroke and work-per-cycle increases
  • Main limitation
    • High operating voltage needed
ipmc s
  • Ionic polymer/metal composite actuator
    • Amplifies low strains using the cantilever effect
    • Environmental Robots Inc.
  • Two metal-nanoparticle electrodes
    • Filled & separated with a solid electrolyte

EAP Bending

ipmc s1
  • Actuators act as super capacitors
  • Applied electrode potential injects electronic charges into the high surface area electrodes
  • Solvated ions migrate between the electrodes
    • One electrode expands

IPMC for sting ray robot

- Motion under water

  • Tensile strength of 40%
  • Actuation results from a local pH change cause by electrolysis of the electrolyte and transport of ions
  • Limitations
    • Low actuation rate
    • Low energy conversion efficiency
carbon nanotubes artificial muscles
Carbon Nanotubes Artificial Muscles
  • Low voltage
  • Low-strain actuators
  • Use electrochemical charge injection into nanostructured electrode
    • Electrostatically driven electrode expansion

how it w orks
How it works
  • Yarns made from sheets of carbon nanotubes
  • Solid guest or filler material in between
    • Replacing liquid electrolytes
  • Melting and solidifying the wax twists or untwist the yarn
    • Generation of motion
    • Actuated by heating

how it w orks1
How it works
  • Heat causes a phase transition and volume expansion of wax
  • Yarn provides good electrical conductivity
    • Control of heating and actuation

  • 100 times the stress of natural muscles
  • Comparable actuation rates
  • Actuator strain is at best 2%
  • Outperforms existing muscles
    • Allows for linear and rotary motions

Bundle of Carbon Nanotubes

  • Lacks biocompability
    • To replace biological muscle
  • Forces generated are limited
    • Need to keep the wax within the yarn
    • Tensile strength of the yarn material
  • Needs better constrain of volume expansion
  • Few defects can reduce strength
    • Can be fixed with thermal annealing

Performance of carbon nanotubes


Carbon nanotubes have the brightest future in the artificial muscle world.

It allows for the largest variety of movement while maintaining a high durability.

  • Very advanced technology but still behind
    • Nature provides high-strain muscles
  • Things to remember:
    • Fuel cells provide more power than batteries
    • Need to optimize synthesis conditions of carbon nanotubes: longer
  • Compatibility
    • Use same fuel and fuel delivery system as natural muscles

  • Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles. MárcioD. Lima et al. Science 338, 928 (2012);
  • Speeding Up Artificial Muscles. Mark Schulz. Science 16 November 2012: 338 (6109), 893-894.
  • Playing Nature's Game with Artificial Muscles. Ray H. Baughman. Science 1 April 2005: 308 (5718), 63-65.;308/5718/63
  • Torsional Carbon Nanotube Artificial Muscles. JavadForoughi. et al. Science 28 October 2011: 334 (6055), 494-497.;334/6055/494