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

Challenges of Air Muscles 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 Air Muscles Foot bed Calf cradle Hinge Straps

Physical Decomposition AFO Molded Case Air Muscles Foot bed Calf cradle Hinge Straps Footbed: Arch, pads Hinge: Screws, elastomer Straps: rivets, velcro

Physical Decomposition AFO Molded Case Air Muscles Bladder Sheath Fittings Tendons Clamps Fittings: bladder attachment, tendon attachment Tendons: cable, housing

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 Control Outputs: necessary connections to send signals to air muscles Control Inputs: necessary connections to accept terrain sensing device (for future)

Air Muscle Configuration Macro Design AFO Type Rigid Construction Solid mounting Provide reference for terrain sensors Soft Construction Comfortable Poor reference for terrain sensors Hybrid 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 Choosing to actuate both plantar and dorsiflexion with air muscles was also related to our decision to consider our target patient to have lost plantar and dorsiflexion control.

DESIGN CONCEPT INITIAL IDEAS 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