Active Ankle-Foot OrthoticAir 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-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.

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 NeedsObjective Number

Customer Objective Description Comment/Status

S4 no sharp protrusionsAttachments designed to be flush inside AFO

FT1support regular gaitcycle

System designed for responsiveness necessary for normal gait

FT2hold foot up when stepping forward

Dorsi-assist AFO design has been proven successful

FT2range of motion to allow fulldorsiflexion and plantar flexion

Tamarac joint allows flexion of joint.Hard stops of AFO prevent overflexion

FT5operate smoothly/simulatenormal muscle behavior

Regulation of air muscles will allow foradjustment on patient by patient basis

ST1ballow natural movement down stairs and ramps

Air muscle system will provide properplantar flexion during gait cycle

Engineering SpecificationsEngineeringSpecification

Number

EngineeringSpecificationDescription

UnitsInitialValue

DesignedValue

Method ofValidation

Comments

s1 Torque on Foot N-m ≥±1.5Fmuscle =

53.10 NTest

s2 Air muscle fill time Ms <150 <400 TestBased on descending stairs gaitanalysis

s10Allowable range of

motion betweenfoot and shin

Deg.94.5 to137.7

Range of 47.4

Test

Research found that on average,a healthy individual uses 47.4degrees of motion whendescending stairs

s26Noise Level (atears of user)

dB 60 80  TestOSHA uses 85 dB as thethreshold for measurable noisedose

s31aMinimum life untilfailure air muscle

steps >4180 Test

Calculated for 95% uptime.Assuming 5 minute replacement,and 44 contractions/min duringUse

s31bMinimum life until

failure:Attachment Points

steps  5.5

million>5000 Test

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

Functional Decomposition

Morphological Design Considerations

AFO actuationConcept What motions are air muscles responsible for?Air MuscleConnection 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 regulatedAFOConstructionType What construction style will the AFO have?

Traction What will keep the AFO from slipping?

  A B C D

AFO actuationConcept

(Reference)Passive Dorsi Assist

No Plantar Assist

Passive DorsiAssist

Active PlantarAssist

Active DorsiAssist

Passive PlantarAssist

Active DorsiAssist

Active PlantarAssist

Air MuscleConnection

(Reference)

No Air MuscleRigid Anchor to

AFO Cable Attachment

AFO snaps intoAir muscleConstruct

Tendon Design(Reference)

No Air Muscle

Air muscle Direct mount

Cable andhousing

Steel leader (seeCrab)

Air Supply(Reference)

No Air Muscle

Compressed airtank Compressor

Regenerativeautomaticfoot pump

AFOConstructionType

(Reference) Hard shell (hinged) Soft shell

Fully rigid hinge-Less

Hybrid (hard footbed, soft calf

sleeve)

Traction (Reference) Shoe reliant

Knurled AFObottom

Rubberized AFObottom  

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 64o when

descending stairs– Average healthy person uses 48o 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