Artificial Muscle

1
Artificial Muscle

• Kori Brabham
• Misti Marr
• Andy Smith
• Paul Lee

2
Natural vs. Artificial Muscle

• What does a natural muscle do?
• It is a contractile organ.
• It consists of fibers which actuate force and
  motion in response to nervous stimulation.
• How does it work?
• Muscles contract by the chemo-mechanical action
  of the proteins actin and myosin.
• Joints of the body are arrayed such that they
  comprise muscles which oppose each other.

3
Natural vs. Artificial Muscle

• How can we develop replacements for the natural
  muscle?
• Develop biomimetic actuators.
• Emphasis on implantable technologies (not on the
  the forefront now).
• What do we have to work with?
• Electrical/pneumatic servos (robotic limbs, late
  1940s-present).
• New materials.
• Synthetic polymers
• Carbon

4
What constitutes a muscle?

• Any system or combination of sub-systems can be
  considered a muscle
• hydraulic/pneumatic cylinder.
• electromagnetic servo.
• biological muscle tissue.
• In short, anything which accomplishes actuation
  under the command of a stimulus.
• Muscles primarily exert energy (ATP) to bring
  about
• motion, acceleration (?v/ ?t or ?2x/ ?t2).
• force application (Fm.a).

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Muscles Revisited

• Muscle cells are highly specialized for
  contraction.
• ONLY contract and relax
• Abduction and adduction
• Actin and myosin vary in amounts and
  configuration, depending on cell function.

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Three types

• Skeletal voluntary and striated
• Cardiac involuntary, striated, and branched
• Smooth involuntary and unstriated

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The Design of Natural Muscle

• Muscles are simply transducers
• They change the chemo-electric signal from nerves
  to mechanical energy.
• Artificial muscles should be similar in
  resilience and in the ability to produce large
  actuation strains
• http//www.unm.edu/amri/protect/

8
Brief Timeline

• 1619 - Descartes postulated that sensory impulses
  activated muscle (reflection)
• 1780 - Galvani noticed frog muscles would
  contract with electrical apparatus

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Brief Timeline (contd)

• 1968 Rubber artificial muscle
• Involved several thread running along a
  longitudinal axis
• Compressed air is injected

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Brief Timeline (contd)

• 1968 - Model Postural Control
• A biped walking machine is required to maintain
  its balance while standing and walking

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Artificial MuscleAn Overview

• Many types of artificial muscle.
• McKibbin muscle actuators
• Inflatable air tubes, delivering large force at a
  low frequency.
• PAN-chemically stimulated by pH change.
• Electrically Stimulated Tissues
• IPMC
• Solenoids (not presented)
• Piezo-active polymers and ceramics (not presented)

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A Review of Current Technology
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The McKibben Artificial Muscle
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History

• First developed in the 1950's by American
  physician Joseph L. McKibben
• originally intended to actuate artificial limbs
  for amputees
• More recently was commercialized in the 1980's by
  Bridgestone Rubber Company of Japan
• patented and called Rubbertuator
• Presently the Shadow Robot Group of England
  manufactures these actuators for robotic
  applications

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How its made

• Consists of an internal bladder
• Bladder is covered by a braided mesh shell
• Attached at either end to tendon-like structures

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How it works

• Internal bladder is pressurized
• Bladder expands in a balloon-like manner against
  the braided shell
• Shell constrains the expansion to maintain a
  cylindrical shape
• As the volume of the bladder increases due to the
  increase in pressure, the actuator shortens and
  produces tension

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Advantages of the McKibben Artificial Muscle

• High force to weight ratio
• Lightweight
• Low Cost
• Smooth

• Size availability
• Flexible
• Powerful
• Damped
• Effective

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Comparison to biological muscle

• Force-length properties are reasonably close
• Force-velocity properties are not close
• a device called a hydraulic damper that operates
  in parallel with the McKibben muscles has been
  created
• McKibben muscles are attached to a spring-like
  device that simulates the tendon properties and
  energy storage of a real muscle

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Ionic Polymer-Metal Composite
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How its made

• Composed of a perfluorinated ion exchange
  membrane
• Consist of a polymer matrix that is coated on the
  outer surface with platinum in most cases (silver
  and copper have also been used)
• coating aids in the distribution of the voltage
  over surface
• Made into sheets that can be cut into different
  shapes and sizes as needed

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How it works

• Uses electricity (electrodes, conductors, etc.)
  to operate
• A circuit is connected to surface to produce
  voltage difference, causing bending
• Strips can bend and flap dramatically which
  allows movement

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Advantages of IPMC

• Light
• Compact
• Driven by low power
• and low voltage
• Large strain capability

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Comparison to biological muscle

• High fracture tolerance
• Large actuation strain
• Inherent vibration damping
• Responds to electricity with elasticity and
  responsiveness similar to those shown to
  biological muscle

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Nanotube Artificial Muscle

• Invented by Max Plank Institute, produced by
  AlliedSignal.
• Based on Carbon nanotubes (bucky tubes).
• Sub-microscopic Carbon sheets (formed into tubes)
  filled with electrolytes.

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Nanotube Artificial Muscle (contd)

• When a voltage is applied the sheets contract to
  do work.
• Possible limitation electrically actuated.
• Being investigated by Defense Advanced Research
  Projects Agency (DARPA) as bucky paper.

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Polyacrylonitrile (PAN)

• Combination of gel and plastic. Tough.
• Contracts under pH changes.
• Contraction occur in 20 ms to a -20 strain.
• Very similar to human muscle in speed, exceeds
  human muscle in max force per cm2 (2x).

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Polyacrylonitrile (PAN) (cont)

• Must be surrounded by solutions in latex tubes.
• Some models have been developed which simulate
  muscle movement.
• University of NM project.

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Electro-active Muscle Transducers

• Uses compliant electrodes to electrically
  stimulate electro-active elastomeric materials.
• Produce strains in excess of 100, and pressures
  greater that 100 psi.
• Spherical joints have been developed based on the
  actuator.
• Developed by SRI International, Inc.

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Electro-active Muscle Transducers (contd)

• AKA Electrostrictive or dielectric elastomer.
• Exhibit a mechanical strain when subjected to an
  electrical field.
• Striction capability exceeds piezoelectric
  ceramics.
• Most common are PMMA-based.
• Produce a positive force/expansion.
• Use tiny robotic muscles.

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A Novel Use for AM

• Smart implants with tiny perforations that
  contain a pharmaceutical, plugged by artificial
  muscles.
• The implant has tiny sensors which sense blood
  concentrations of certain chemicals.

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A Novel Use for AM (contd)

• The artificial muscle then will shrink to allow a
  drug to pass freely.
• When concentrations of the sensed chemical rises
  in the blood, the muscle then relaxes to plug the
  holes a gain.

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Honorable Mention Replacement Prosthetic Limbs

• Started as passive replacements to fill clothing
  or act as support.
• Archeological evidence of prostheses in ancient
  India and Egypt--Queen Vishpla, Elis.
• Infection and blood loss.
• 1600s-1800s
• Great increase in health technology styptic
  antibiotics, anesthetics, blood clotting
  chemicals.
• Prosthetic units were developed with lighter
  weight and greater articulation (motion learned
  and controlled by amputee).
• 1940s-1980s Emphasis on actuation.
• 1980s-Present Emphasis on realism.

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Replacement Prosthetic Limbs (contd)

• Number of Companies that specialize in
  prosthesis/orthotics
• North Shore Orthotics-Prosthetics, Inc.
• Ohi, SCOPe, many others.
• Limb replacements are actuated
• By other existing muscles directly.
• By EMG generated by nearby existing muscles
• Balance.

34
Artificial Muscle

• Applications in Robots

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Types of Robots

• Miniature robots
• Wall climbers
• Exploring rovers

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Miniature Robots

• Submersible bots with plastic muscles
• Ability to someday pick up single cells
• Positive and negative ions shrink and swell the
  polymer

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Wall Climbers

• Air Rubbertuator
• Capable of difficult inspections
• Aircraft
• Bridges
• Nuclear power plants
• Obstacles, inclines, stairs, vertical movement.

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Robots in Space

• Ability to probe, dig, photograph and analyze
• No gears or complex mechanical systems
• Lighter and less complex robots
• Smaller
• Not sensitive to dust

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Capabilties

• Grasping
• Wiping
• Muscle groups working together

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Grasping

• Electric charge applied to plastic ribon
• Charged particles pushed to one side lengthens
  that side

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Wipers

• Two-way wiping motion produced
• Applications onto cameras or sensors

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Muscles Working Together

• Creates more than one motion
• Bionic men and women???
• Could replace human muscles

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Legs and Wheels

• Able to handle most terrain
• Durable
• Reliable
• Not as good as four legs

44
A Way of the Future

• Cheap
• Durable
• Lightweight
• Conserve Power

45
References

• Electroactive Polymer Actuators webpage
• Artificial Muscle Research Institute
• SRI International, Inc.
• Opthalmatronix, Inc.
• Ohio State University
• www.spacedaily.com
• Max Planck Society
• University of New Mexico -- cape.uwaterloo.ca
• BBC News
• Science Daily
• Discovery Channel