Active Ankle-Foot Orthotic: Tethered Air Muscle

P13001Project Members:Nathan Couper- Mechanical EngineeringBob Day- Mechanical EngineeringPatrick Renahan- Industrial EngineeringPatrick Streeter- Mechanical EngineeringDr. Beth DeBartolo- Faculty Guide

Project Customer:Dr. Beth DeBartolo

Project Sponsor:This material is based upon work supported by the National Science Foundation under Award No. BES-0527358. 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.

Background InformationThe aim of this project is to develop an air muscle powered ankle foot orthotic that address the symptom of foot drop. Foot drop is a very common condition present in patients who are suffering from degenerative nerve diseases (ALS, MS), stroke, or trauma to the Peroneal Nerve, and ultimately leads to an inability to dorsiflex the foot while walking. Current technology in the form of ankle-foot orthotics (AFOs) is available to aid clients, however these devices are restrictive and make navigating stairs and ramps especially difficult. This is due to a restricted ability to plantarflex the foot and “point” the toes. Our focus will be to modify an existing dorsi-assist orthotic to include a controlled, air muscle-actuated, plantarflexion when navigating uneven terrain.

Customer Requirements:

Acknowledgements:We would like to thank the following people for their generous donations, cooperation, and assistance: Dr. Kathleen Lamkin-Kennard, Dr. J.J. Mowder-Tinney and Nazareth College Physical Therapy Clinic, The National Science Foundation, Gordon Potter Jr. C.O., Cayuga Orthotics and Prosthetics Inc., Rochester Orthopedic Labs, Inc., Colton Scott, and Christopher Sullivan

System Level Physical Decomposition

Input from Terrain Sensing System

Flat terrainAscending terrain

(up stairs/up ramp)

Descending terrain (down

stairs/down ramp)

Relax air muscleRelease air

Ankle angle at foot strike = -

44.96 deg

Gait speed info from sensors.

Ankle angle at foot strike = -

14.65 deg

Gait speed info from sensors

Future Interaction with Terrain Sensing System (above)

In addition to the above Customer needs, there were several engineering specifications that involved Sensory Information (i.e. measure angle of foot or accept input from terrain sensing mechanism), Movement specifications (i.e. foot position and gate speed), Force specifications (i.e. torque on foot and force to secure orthotic), and Safety specifications (i.e. harm to equipment and harm to user).

Patient AssumptionsIn order to define the scope of this project, several patient assumptions were made: The patient was assumed to maintain zero muscle control over both dorsi- and plantarflexion, was not prone to “tone-lock,” had an an appropriately calibrated dorsi-assist AFO to hold their foot above 90º when in mid-stride, and lastly, due to the nature of a tethered system, that they would use the orthotic in a clinical setting (i.e. pool or treadmill). To perform our calculations, Anthropometric Data from the ANSUR database was used for a 50th percentile male and there were no resistive or friction forces in the joints.

CategoryObjective Number

1 - 9 rating of importance Customer Objective Description

Safe

S1 9 follow safety guidelines and standardsS3 9 energy stored safelyS4 8 no sharp protrusionsS5 6 allergy conscious

Flat Terrain

FT1 5 support regular gait cycleFT2 9 hold foot up when stepping forwardFT2 3 range of motion to allow full dorsiflexion and plantar flexionFT4 6 resist foot slapFT5 7 operate smoothly/simulate normal muscle behaviorFT6 7 allow for extended use without straining leg from weight

Comfort

CF2 9 non-invasiveCF3 8 secure foot in orthoticCF4 8 non-abrasiveCF6 5 allow normal cooling of legCF7 5 allow bending of kneeCF8 3 allow toes to flex upCF9 7 keep toes from curling down

CF11 4 low noise

Special Terrain

ST1 8 allow natural movement up and down stairs and rampsST2 5 adapt to different terrainsST3 5 fast system response between sensing and doingST4 7 correctly interprets sensor informationST5 8 support foot drop over obstacles

Model of Dorsi-assist AFO (Pictured Left)

Distal Muscle Attachment Assembly, excluding AFO (Pictured Right)

Detailed Design Concepts

Exploded Proximal Attachment (Pictured Far Right)

Un-Actuated air muscle with dorsi-assist AFO holding foot 90 degrees from floor (Top Left)

Actuated air muscle with foot fully plantarflexed (Top Right)

While the average person experiences 47 degrees of motion while walking down stairs, our AFO is capable of achieving up to 64 degrees and is customizable based on the specific client. (Right)