Active Ankle-Foot Orthotic Air Muscle Tethered Team P13001 Nathan Couper, ME Bob Day, ME Patrick Renahan, IE Patrick Streeter, ME This material is based upon work supported by the National Science Foundation under Award No. BES Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

Agenda Project Description –Problem Description –Assumptions and Project Scope –Customer Needs –Engineering Specifications Design Process –Functional Decomposition –Morphological Design Process Solution Demonstration Testing Results Project Results Future Work

Problem Description Foot Drop –Caused by nerve damage in the lower leg or brain Strokes, ALS, MS, Car Accidents, Other Trauma –Loss of muscle control prevents patient from dorsi-flexing the foot while walking, as well as extending the toes –AFOs are current solution Generally rigid support that lifts the foot to a proper angle Shortcomings of AFOs –Do not allow for smooth gait cycle –Inhibit plantar flexion –Descending stairs and ramps is very difficult without plantar flexion

Assumptions and Project Scope Client maintains zero muscle control over dorsi-flexion, plantar- flexion, and toe extension The system is designed to be used in a clinical setting –Tethered System Client has the ability to use a dorsi-flex assist AFO AFOs will continue to be custom made for each client Control method for system should be adaptable to previously designed terrain sensing system

Customer Needs Objective Number Customer Objective DescriptionComment/Status S4no sharp protrusions Attachments designed to be flush inside AFO FT1 support regular gait cycle System designed for responsiveness necessary for normal gait FT2 hold foot up when stepping forward Dorsi-assist AFO design has been proven successful FT2 range of motion to allow full dorsiflexion and plantar flexion Tamarac joint allows flexion of joint. Hard stops of AFO prevent over flexion FT5 operate smoothly/simulate normal muscle behavior Regulation of air muscles will allow for adjustment on patient by patient basis ST1b allow natural movement down stairs and ramps Air muscle system will provide proper plantar flexion during gait cycle

Engineering Specifications Engineering Specification Number Engineering Specification Description Units Initial Value Designed Value Method of Validation Comments s1Torque on FootN-m≥±1.5 F muscle = N Test s2Air muscle fill timeMs<150<400Test Based on descending stairs gait analysis s10 Allowable range of motion between foot and shin Deg to Range of 47.4 Test Research found that on average, a healthy individual uses 47.4 degrees of motion when descending stairs s26 Noise Level (at ears of user) dB6080 Test OSHA uses 85 dB as the threshold for measurable noise dose s31a Minimum life until failure air muscle steps>4180Test Calculated for 95% uptime. Assuming 5 minute replacement, and 44 contractions/min during Use s31b Minimum life until failure: Attachment Points steps 5.5 million >5000Test 100 steps (50 contractions), twice a week for three years

Agenda Project Description –Problem Description –Assumptions and Project Scope –Customer Needs –Engineering Specifications Design Process –Functional Decomposition –Morphological Design Process Solution Demonstration Testing Results Project Results Future Work

Functional Decomposition

Morphological Design Considerations AFO actuation Concept What motions are air muscles responsible for? Air Muscle Connection How are air muscles attached to AFO? Tendon Design How does force from Air Muscle actuate AFO? Air Supply How will air muscles be filled and regulated AFO Construction Type What construction style will the AFO have? Traction What will keep the AFO from slipping?

ABCD AFO actuation Concept (Reference) Passive Dorsi Assist No Plantar Assist Passive Dorsi Assist Active Plantar Assist Active Dorsi Assist Passive Plantar Assist Active Dorsi Assist Active Plantar Assist Air Muscle Connection (Reference) No Air Muscle Rigid Anchor to AFOCable Attachment AFO snaps into Air muscle Construct Tendon Design (Reference) No Air Muscle Air muscle Direct mount Cable and housing Steel leader (see Crab) Air Supply (Reference) No Air Muscle Compressed air tankCompressor Regenerative automatic foot pump AFO Construction Type (Reference) Hard shell (hinged)Soft shell Fully rigid hinge- Less Hybrid (hard foot bed, soft calf sleeve) Traction (Reference) Shoe reliant Knurled AFO bottom Rubberized AFO bottom

Solution: Passive Dorsi-Assist, Active Plantar-Assist Air muscle powers plantar flexion Elastomer passively causes dorsiflexion (dorsi-assist) Does not disturb positive attributes of dorsi-assist device Easier for clients to use than an air muscle that actuates in both dorsi- and plantarflexion

Testing Results Air Muscle Fill Time –Used a high speed camera (120 fps) –Verified air muscle inflated fast enough for natural gait Decibel Testing –Inflation and deflation of air muscle produced acceptable decibel levels

Testing Results Lifetime Testing –All tested air muscles lasted significantly longer than required for specifications –No failure or fatigue was observed in testing of attachment points Range of Motion –Found to be adjustable up to 64 o when descending stairs –Average healthy person uses 48 o when descending stairs

Project Results Successfully combined an AFO and air muscle system to facilitate more natural movement in the ankle joint.

Future Work Combine air muscle system with existing terrain sensing system Human trials: test functionality of device on clients who have foot drop Neuroplasticity: study effects of device from a rehabilitation standpoint rather than an aid

Demonstration

Questions