Active Ankle-Foot Orthotic - PowerPoint Presentation

Active Ankle-Foot Orthotic Air Muscle Tethered Team P13001Nathan Couper, MEBob Day, MEPatrick Renahan, IEPatrick 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 Assumptions Customer NeedsEngineering SpecificationsTest PlanMechanical AnalysisProximal AttachmentStatic AnalysisFatigue Analysis Distal Attachment Static Analysis Fatigue Analysis Air Muscle Testing Transient Flow Muscle Contractions Risk Assessment Proposed Schedule Questions and Criticism

Assumptions and Project Scope Patient maintains zero muscle control over dorsi-flexion, plantar-flexion, and toe extension This product is designed to be used on a treadmill in a clinical setting; but can be incorporated into an aquatic settingTethered SystemThe elastomer can be adjusted on a patient basis so that when the patient’s full weight is applied on the AFO, the foot rests at angle slightly above 90 degrees with respect to the patient’s lower limbDesigned patient has the ability to use a dorsi-flex assist AFO without receiving tone-lock spasmsFor calculations: Anthropometric Data is from the ANSUR (military) Database Based on the 50th percentile man 2D system no resistive forces/friction associated with the joints a normal gait cycle time of 1.2 to 1.5 steps per second is assumed Isotropic, Elastic Materials

Customer Needs Objective Number Customer Objective Description Comment/Status S1 follow safety guidelines and standards   S3 energy stored safely Air source designed for specified pressure S4 no sharp protrusions Attachments designed to be flush inside AFO S5 allergy conscious No new materials to be in contact with user 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 FT4 resist foot slap Dorsi-assist AFO design has been proven successful FT5 operate smoothly/simulate normal muscle behavior Regulation of air muscles will allow for adjustment on patient by patient basis FT6 allow for extended use without straining leg from weight   CF2 non-invasive Designed to not interfere with normal fit of AFO CF3 secure foot in orthotic Existing orthotic attachment is unchanged CF4 non-abrasive No new materials to be in contact with user CF6 allow normal cooling of leg This is a challenge with existing orthotics: vent holes will be drilled into orthotic CF7 allow bending of knee Orthotic will stop below the knee CF8 allow toes to flex up Toe flexion will not be hampered by air muscle device

ST1b allow natural movement down stairs and ramps Air muscle system will provide proper plantar flexion during gait cycle ST2 adapt to different terrains Terrain sensing system will be compatible with air muscle control ST3 fast system response between sensing and doing Low computative demands on system. Concern is with actuation speed. Intial testing suggests system has responsiveness required ST4 correctly interprets sensor information Sensor integration with team 13002 is pending ST5 support foot drop over obstacles Dorsi-assist AFO design has been proven successful

Engineering Specs Engineering Specification Number Engineering Specification Description Units Nominal Value* Ideal Value ** Method of ValidationCommentss1Torque on FootN-m≥±1.5Fmuscle =53.10 NTestForce represents requirement for 50th percentile males2Air muscle fill timeMs<150<200TestBased on descending stairs gait analysiss3predicts step upyes/noyesx-No terrain sensings4predicts step downyes/noyesx-No terrain sensings5predict flat yes/noyesx-No terrain sensings6predicts ramp upyes/noyesx-No terrain sensings7predicts ramp downyes/noyesx-No terrain sensings8predicts speed of personm/s±0.1x-No terrain sensings9measure angle of footDegrees±5x-Not necessary for system operation *Nominal value represents the initial target value for specifications. **Ideal value represents the adjusted target value for specifications based on research and adjusted objectives.

Engineering Specs s10 allowable range of motion between foot And shin degrees 94.5 to 137.7 72 to 116 with shin as reference Test Equivalent to dorsi assist AFO. Measured angle between calf of AFO and bottom of AFOs11follow safety standardsyes/no- - s14fits calf (diameter)mm292 to433 -Use of custom orthotics15fits foot (length)mm212 to317 -Use of custom orthotics17force to secureconstraintsN< 80 N TestOnly air muscle system considereds18force to removeconstraintsN< 80 N TestOnly air muscle system considereds21monitoring/display ofenergy levelyes/noyes -Pressure gauge on air tanks22error statusyes/noyes - 

Engineering Specs s23 radius of edges/corners on AFO mm 0.5mm   -   s25 Harm to user (survey) scale -  survey user s26Noise Level (at ears ofuser)dB60 Test s27Moving devices andelectronics use standarddust and water shieldingyes/noyes - s31aMinimum life untilfailure air musclesteps>18000testCalculated for 95% uptime. Assuming 20minute replacement, and 44 contractions/minduring uses31bMinimum life untilfailure: Attachmentpointssteps  5.5million>15,000test100 steps (50 contractions), twice a weekfor three yearss32Allowable toeextension/flexionDegrees0-50 test 

Testing Plan – Required Tests Engr. Spec. # Specification (description) Unit of Measure Marginal Value Comments/Status ES26 Noise level (at ears of user) dB <60 Decibel testing ES2 Flow rate – time to inflateSec<.20Initial testing indicates good performanceES1 Torque on FootN-m>=1.5Force of air muscle*moment armES31Lifetime – Air Muscle% uptime>95%Time in use versus time replacing air muscleES31Lifetime – AFO FixturesSteps>15,000Use of air muscles in clinic must not affect full life of AFOES17,18Force to secure/remove constraintN<80Velcro straps pre-existing, and test force to secure muscle (4)Clamping force: cable to air muscle Nm.358Verify clamping force is sufficient to hold cable

Testing Plan – Required Equipment Engr. Spec. # Instrumentation or equipment not available (description) ES31 Polymer to simulate AFO for lifetime analysis

Gait Analysis Stairs: Descending Percent Gait Cycle Event mean s. d. Foot Off 15% 3% Foot Strike 56% 3% Bovi, et. all Based on 88 cycles per minute: 0.30 seconds from foot off to foot strike.

Assumed AFO Design Designs based around AFO of this structure Design is flexible so it will be able to work on many different AFO designs and shapes Assumed material =

Proximal Muscle Attachment Key Components: Weld NutExterior threading for nut Secures device to AFO Screw clamps air inlet and muscle attachment to weld nut Nozzle screws into block Relatively simple components Low Profile Strong Removable

Weld Nut Uses 5/16” Nut to secure against AFO Note external threads not shown 316 Stainless Steel Allows for easy removal of device Stress Calculations: Treated like a cantilever beam 130 N force (Max force air muscle can apply) Max Bending Stress: 57.45 Mpa Shear Stress: 7.49 MPa

Proximal Anchor and Air Inlet Houses weld nut and exterior nut Applies force on weld nutAlso clamped on by ¼-20 screw1/4-inch air inlet channel Threaded hole for nozzle insertion 316 Stainless Steel

Proximal Anchor and Air Inlet Element Type: Solid 10node187 (tetrahedral) Max Stress: 45 MPa

All displacement is about 0 meters Proximal Anchor and Air Inlet

Nozzle Proposed Materials: Delrin or Stainless Steel ThreadingExternal Threading not pictured Screws into Proximal Anchor to allow air supply to muscle Air muscle clamps on to cylinder Max Stress: 2.85 Mpa Yield Stress: 63 MPa (Delrin) 290 Mpa (316)

Fatigue Analysis   316 Stainless Steel Properties:Endurance Limit (Se): 270 MPaUltimate Strength (Sut): 579 MPa Fatigue Results: (Using an applied force of 53 N rather than 130N) Weld Nut FOS=15.53 Proximal Anchor FOS=20.46 Nozzle (316 Stainless Steel) FOS=316.9 Nozzle ( Delrin ) FOS=37.6Delrin Properties:Endurance Limit (Se): 32 MPaUltimate Strength (Sut): 69 MPa

Distal Muscle Attachment Assembly

Tendon Cable Use 1.5 mm diameter cable Will use bicycle brake cableBraided Stainless Steel cableTension can be easily adjustedPreliminary calculations make us believe this solution will be more durable than previous air muscle tendon materials Maximum stress = 100.2 MPa ; yield stress = 290 Mpa Factor of Safety = 11.5 Maximum Deformation = 0.233 mm

Distal Muscle Plug Presses against Distal Muscle Plug Plate with slot for tendon cable to rest inPlugs distal end of air muscle No air nozzle needed at the distal end Proposed Material = Delrin

Maximum Stress = 8.5 MPa Yield Stress = 63 MPa

Distal Muscle Plug Plate Presses against Distal Muscle Plug Creates friction on tendon cable, Allows for tension in tendon cable to be easily adjusted Proposed Material = 316 Stainless Steel Necessary Screw Clamping Force = 0.358 N-m

Heel Cable Attachment Point Attaches distal end of tendon cable to AFO heel protrusion Held in place by 10-24 screw at distal end, Heel Cable Attachment Pin at proximal end Allows for: full range of motion of tendon cable ease of cable changeover Proposed Material = 316 Stainless Steel

ANSYS Simulation

Fatigue Analysis Analyzed with stresses from 53 N force as opposed to 130 N This will be more realistic to values seen during normal operation Ultimate Strength = 579 MPa Endurance Strength = 270 MPa Factor of Safety = 36.8

Heel Cable Attachment Pin Proposed Material = 316 Stainless Steel

Air Muscle Construction Outer SleeveInner TubeClampEnd

Muscle Testing Goal of .1 sec inflation time, max of .2 sec, estimated via gait analysisFunction of pressure and flow rate4.45cm contraction required for full range of motion Function of muscle construction

Transient testing Started by calculating the theoretical flowRealized this is questionably accurate and very complexDecided it would be easier and more accurate to directly measure inflation time Took video of the muscle inflating and counted the number of frames it took to move.

Transient testing 5 video tests

Muscle Contraction The muscle was loaded with 53N and inflated

Transient results

Programming Flow Chart Input from Terrain Sensing System Flat terrain Ascending terrain (up stairs/up ramp) Descending terrain (down stairs/down ramp) Relax air muscle Release 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

Test Plan https://edge.rit.edu/edge/P13001/public/WorkingDocuments/Project%20Management See Edge:

Updated Risk Assessment

Bill of Materials

Schedule for MSD II Reference EDGE website for working, detailed project schedule: Planning and Execution – Project Plans and Schedules – “Schedule of Action Items”http://edge.rit.edu/edge/P13001/public/Planning%20%26%20Execution

Questions?