Active Ankle-Foot Orthotic
description
Transcript of Active Ankle-Foot Orthotic
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