P13001 Active Ankle Foot Orthotic: Air Muscle Tethered

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, LeiaStirling, Robert J. Wood, Eugene Goldfield, and RadhikaNagpal. 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/ 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

Challengesof Air Muscles Advantages of Air Muscles • Light Weight • High force output • Ease of attachment • Work well underwater for therapeutic use • Non linear force characteristics • Limited travel • Limited pressure capacity

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 Functional 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 Air Muscles Bladder Sheath Fittings Tendons Clamps Physical Decomposition

Air Regulation System Regulator Air Source Tubes Fittings Physical Decomposition

Computer Control System Air Regulation Controls Control Outputs Control Inputs Physical Decomposition

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 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

P13001 Active Ankle Foot Orthotic: Air Muscle Tethered