P13001 Active Ankle Foot Orthotic: Air Muscle Tethered
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Transcript of P13001 Active Ankle Foot Orthotic: Air Muscle Tethered
P13001 Active Ankle Foot Orthotic: Air Muscle TetheredNate 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 proportionalmyoelectric 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/andhttp://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
Challenges of Air Muscles
• Light Weight• High force output• Ease of attachment• Work well underwater for therapeutic use
Advantages of Air Muscles
• Non linear force characteristics• Limited travel• Limited pressure capacity
Functional Decomposition
Assist individualswho experience
drop foot
Actuate theIndividual’s footappropriately
Accept theindividuals leg
Functional Decomposition
Actuate theIndividual’s footappropriately
Determine requiredfoot movement
Adjust footposition
Functional Decomposition
Determine requiredfoot movement
Determine terraingeometry
Determine currentfoot position
Functional Decomposition
Adjust footposition
Manually controlgait
Control gait viasensor interface
Physical Decomposition
Tethered Ankle-Foot Orthotic (AFO)
AFO (the orthotic itself)
Air Regulation System
Computer Control System
Physical DecompositionAFO
Molded Case
Air Muscles
Foot bed
Calf cradle
Hinge
Straps
Physical DecompositionAFO
Molded Case
Air Muscles
Foot bed
Calf cradle
Hinge
Straps
Physical DecompositionAFO
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 DecompositionAir 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 DecompositionComputer Control System
Air Regulation Controls
Control Outputs
Control Inputs
Macro DesignAFO 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
DESIGN CONCEPT INITIAL IDEAS
Dorsi-flexion air muscles and attachmentsPlantar-flexion air muscles and attachmentsAnkle hingeFoot stabilizationAir Muscle attachmentTractionToe Extension
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 Air Muscle Attachment
Note: Also drawn on “Dorsi Flexion Air Muscles and Attachment slide”
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