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