Transcript Foot Stabilization Air Muscle Attachment

P13001 Active Ankle
Foot Orthotic: Air
Muscle Tethered
Nate Couper, Bob Day, Patrick Renahan, Patrick Streeter
Project Description
• Create a tethered active ankle foot orthotic that utilizes a
terrain sensing system (already produced by Christopher
Sullivan, an RIT Master’s student) integrated with the use of
air muscles
• Tethered implies the AFO will be connected to a computer for
terrain sensing, electrical power and air supply
• The device must use air muscles to actuate the user’s foot in
place to avoid foot drop during the swing phase of the gait
cycle, while also interpreting terrain data to release the foot at
the proper time and rate to prevent a sensation of falling
forward or foot slap
• An existing AFO frame should be selected and modified to
accommodate the design intent
Background Information
Bio-Insipired Active Soft Orthotic
Device for Ankle Foot Pathologies
•Used Soft braces
•Mounted circuitry to leg, but not air
supply
•Mimicked actual muscles and tendon
attachment points
•Used ligaments to keep tendons against
brace
•Pressure sensors on bottom of sole
•Strain sensor on front surface of ankle to
determine foot angle
•Can tilt foot from side to side for uneven
terrain
Park, Yong-Lae, Bor-rong Chen, Diana Young, Leia Stirling, Robert J. Wood, Eugene Goldfield, and Radhika
Nagpal. Bio-inspired Active Soft Orthotic Device for Ankle Foot Pathologies. IEEE, 25 Sept. 2011. Web. 16
Sept. 2012. <micro.seas.harvard.edu/papers/Park_IROS11.pdf>.
An improved powered ankle–foot orthosis using proportional
myoelectric control – Ferris, et. all
• Discusses an improvement to a
previously designed air muscle
powered AFO by adding a plantar
flexion muscle
• Design features a dorsi- and
plantar-flexion muscle air muscle
• Feel that a plantar flexion muscle
is important because: “plantar
flexion muscles perform more
positive mechanical work than
the knee or hip during walking”
• Design flaws: It is difficult to get
in and out of, and takes a lot of
time, and hand tools to do so
• Discusses the forces attributed
through each “percentage of the
gait cycle”
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1351122/
and
http://edge.rit.edu/content/R12000/public/An%20improved%20powered
%20ankle%20foot%20orthosis%20using%20proportional%20myoelectric%
20control.pdf
Air Muscle Technology and our
System
• Limited commercial suppliers
• Shadow Robotics
• Festo Fluidic Muscles
• We will base our designs off of previous RIT and commercial
successes to provide the patient with as natural of a gait as possible
• This will be done through replicating natural dorsi-flexion and
plantar-flexion
Advantages of Air Muscles
•
•
•
•
Light Weight
High force output
Ease of attachment
Work well underwater for therapeutic use
Challenges of Air Muscles
• Non linear force characteristics
• Limited travel
• Limited pressure capacity
Functional Decomposition
Assist individuals
who experience
drop foot
Actuate the
Individual’s foot
appropriately
Accept the
individuals leg
Functional Decomposition
Actuate the
Individual’s foot
appropriately
Determine required
foot movement
Adjust foot
position
Functional Decomposition
Determine required
foot movement
Determine terrain
geometry
Determine current
foot position
Functional Decomposition
Adjust foot
position
Manually control
gait
Control gait via
sensor interface
Physical Decomposition
Tethered Ankle-Foot Orthotic (AFO)
AFO (the orthotic itself)
Air Regulation System
Computer Control System
Physical Decomposition
AFO
Molded Case
Foot bed
Calf cradle
Hinge
Straps
Air Muscles
Physical Decomposition
AFO
Molded Case
Foot bed
Calf cradle
Hinge
Straps
Air Muscles
Physical Decomposition
AFO
Molded Case
Air Muscles
Bladder
Sheath
Fittings
Tendons
Clamps
Physical Decomposition
Tethered Ankle-Foot Orthotic (AFO)
AFO (the orthotic itself)
Air Regulation System
Computer Control System
Physical Decomposition
Air Regulation System
Regulator
Air Source
Tubes
Fittings
Physical Decomposition
Tethered Ankle-Foot Orthotic (AFO)
AFO (the orthotic itself)
Air Regulation System
Computer Control System
Physical Decomposition
Computer Control System
Air Regulation Controls
Control Outputs
Control Inputs
Macro Design
AFO Type
• Rigid Construction
• Solid mounting
• Provide reference for
terrain sensors
• Soft Construction
• Comfortable
• Poor reference for terrain
sensors
• Hybrid
• Comfortable
• Would this provide
necessary support to air
muscles?
Air Muscle
Configuration
• Dorsiflexion Only
• Relies on passive
plantarflexion
• Plantarflexion Only
• Relies on passive
dorsiflexion
• Both
• Control over all flexion
• Offers more control and
adjustability than passive
actuation
Dorsi-flexion air muscles and attachments
Plantar-flexion air muscles and attachments
Ankle hinge
Foot stabilization
Air Muscle attachment
Traction
Toe Extension
DESIGN CONCEPT INITIAL IDEAS
Dorsi Flexion Air Muscles
and Attachments
• Two muscles running
along lateral and medial
aspects of calf
• The muscles will stop
before reaching the
ankle joint
• Tendons will run from
the bottom of the air
muscle to the
attachment point along
the side of the foot
• Normal human range of
motion is 15-20°
Plantar Flexion Air Muscle
and Attachment
• Two air muscles attached
on the posterior aspect
of the lower leg
• The muscles will run
from roughly the top of
the calf to above the
ankle joint
• Tendons will run from
the bottom of the air
muscles to a calcaneus
attachment point
• Normal human range of
motion is 50°
Initial Design Ideas Continued
Foot Stabilization
Note: Also drawn on “Dorsi Flexion Air
Muscles and Attachment slide”
Air Muscle Attachment
Toe Extension Mechanism
• Needed to keep toes raised during walking
• Allows individual to go onto the ball of the
foot
• Utilizes both Passive and Active mechanisms
• Elastomer Hinge keeps foot flat when toes not
flexed.
• Air Muscles induce tension to overcome elastomer,
and lift toes up during dorsiflexion
• During beginning of stride, change in center of mass
during plantar flexion overcomes elastomer
resistance.
• Necessary to decrease “foot-slap”
• Necessary to hold toes up when walking on
inclined surface
• Allows for an overall more natural motion of
the foot