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  • Designing a 3D-printed Methodology · the forces that arise upon heel contact. Methodology Results - ICR Results (FEA) Conclusion Designing a 3D-printed prosthe'c knee I’d like
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Upon ini'al heel contact, the ICR of the knee is located well behind the load line. Stability during heel contact is cri'cal to maintaining normal walking kinema'cs. As the knee flexes aBer ini'al heel contact, the load line is located slightly anterior to the load line, but within a reasonable range to s'll offer stability. Following this, the ICR is located well behind the load line, therefore con'nuing to provide stability to the user. Finally, shortly before toe-off, it is found that the ICR is not located in a posi'on that would offer the user stability, yet this frame is the least important as the user’s weight will already have started transferring to the other limb by this 'me. The finite element analysis of the prosthe'c knee shows that the connec'ons between components would fail first given an excessive load. When subjected to the forces that arise during normal gait condi'ons, however, this simula'on shows that the maximum stress in this knee mechanism is 9.983 MPa. Since the yield strength of ABS, a commonly-used 3D- printable material, is 34 MPa [3], it is reasonable to conclude that the knee is capable of suppor'ng its user’s weight. The design of high-quality prostheses is both costly and 'me consuming. Due to the lack of access to prosthe'c clinics for lower-limb amputees in developing countries, it is desirable to formulate a method of designing func'onal prosthe'c knees at a rela'vely low cost. While many factors must be considered to accurately analyze the performance of a prosthe'c knee, this project examines the feasibility of a 3D-printed knee with respect to its stability. A finite element analysis of the 3D-printed knee is also used to iden'fy the regions of the knee most suscep'ble to failure. Design a prosthe'c knee that: - Can be rapidly produced at a low-cost - Can be easily customized - Is rela'vely stable (as a mechanically- passive knee) - Provides its user with an acceptable range of mo'on (see image on right) Introduc'on Main Goals The func'onality of the knee is directly related to the lengths of the links that make up the four-bar knee mechanism. Using SolidWorks and MATLAB in conjunc'on with experimental gait data, the link lengths of this knee mechanism were op'mized in order to provide knee stability, par'cularly during ini'al heel contact. Unlike a simple hinge joint, the point about which a knee joint rotates changes as an individual ambulates. This changing center of rota'on, or Instantaneous Center of Rota.on (ICR), is one of the primary determinants of knee stability. When designing a four-bar mechanism knee, it is important that the ICR of each knee remains posterior to the load line as its respec've limb contacts the ground (see above image). The image to the leB shows the four-bar knee mechanism and its ICR (outlined by a circle) in four different posi'ons. If the ICR is located posterior to (in this image, to the leB of) the load line (in red), the knee can be considered stable. Finite Element Analysis (FEA) is a popular tool used to visualize the different stresses that will arise in an object upon being subjected to applied forces. If this knee prosthesis is to be manufactured using 3D printers, it is necessary to ensure it can withstand the forces that will be applied to it during normal walking condi'ons. To the right is a visual representa'on of the stresses that are present in this knee prosthesis when it is subjected to the forces that arise upon heel contact. Methodology Results - ICR Results (FEA) Conclusion Designing a 3D-printed prosthe'c knee I’d like to thank Dr. Marc Doumit for all of his guidance, encouragement, and inspira'on. Addi'onally, I’d like to thank Dr. Ahsan Ahmed and Sco^ Pardoel for taking the 'me to meet with me. The help that all of you offered was incredibly useful and very much appreciated. - Kieran Eveleigh, KEVEL040@uo^awa.ca - Use the results of the FEA to minimize the overall size of the prosthesis without hindering its func'onality. - Adjust the link lengths of four-bar knee mechanism to create a design that offers more support. - Mechanically test the performance of the knee prosthesis. Future Work [1] Rose, Jessica, and James G. Gamble. Human Walking. Philadelphia: Lippinco^ Williams & Wilkins, 2006. Print. [2] Radcliffe, CW. Four-bar linkage prosthe.c knee mechanisms: kinema.cs, alignment and prescrip.on criteria. Prosthe'cs and Ortho'cs Int. 1994; 18: 168. [3] “Acrylonitrile Butadiene Styrene (ABS) Typical Proper'es.” Prospector. UL, 2017. Web. 07 Mar. 2017. [1] [2] Kieran Eveleigh, Dr. Marc Doumit Department of Mechanical Engineering, University of O^awa

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Page 1: Designing a 3D-printed Methodology · the forces that arise upon heel contact. Methodology Results - ICR Results (FEA) Conclusion Designing a 3D-printed prosthe'c knee I’d like

Uponini'alheelcontact,theICRofthekneeislocatedwellbehindtheloadline.Stabilityduringheelcontactiscri'caltomaintainingnormalwalkingkinema'cs.AsthekneeflexesaBerini'alheelcontact,theloadlineislocatedslightlyanteriortotheloadline,butwithinareasonablerangetos'llofferstability.Followingthis,theICRislocatedwell

behindtheloadline,thereforecon'nuingtoprovidestabilitytotheuser.Finally,shortlybeforetoe-off,itisfoundthattheICRisnotlocatedinaposi'onthatwouldoffertheuserstability,yetthisframeistheleastimportantastheuser’s

weightwillalreadyhavestartedtransferringtotheotherlimbbythis'me.

Thefiniteelementanalysisoftheprosthe'ckneeshowsthattheconnec'onsbetweencomponentswouldfailfirstgivenanexcessiveload.Whensubjectedtotheforcesthatariseduringnormalgaitcondi'ons,however,thissimula'onshowsthatthemaximumstressinthiskneemechanismis9.983MPa.SincetheyieldstrengthofABS,acommonly-used3D-printablematerial,is34MPa[3],itisreasonabletoconcludethatthekneeiscapableofsuppor'ngitsuser’sweight.

Thedesignofhigh-qualityprosthesesisbothcostlyand'meconsuming.Duetothelackofaccesstoprosthe'cclinicsforlower-limbamputeesindeveloping

countries,itisdesirabletoformulateamethodofdesigningfunc'onalprosthe'ckneesatarela'velylowcost.

Whilemanyfactorsmustbeconsideredtoaccuratelyanalyzetheperformanceofaprosthe'cknee,thisprojectexaminesthefeasibilityofa3D-printedkneewithrespecttoitsstability.Afiniteelementanalysisofthe3D-printedkneeisalso

usedtoiden'fytheregionsofthekneemostsuscep'bletofailure.

Designaprosthe'ckneethat:-  Canberapidlyproducedatalow-cost

-  Canbeeasilycustomized-  Isrela'velystable(asamechanically-

passiveknee)-  Providesitsuserwithanacceptablerangeofmo'on(seeimageonright)

Introduc'on

MainGoals

Thefunc'onalityofthekneeisdirectlyrelatedtothelengthsofthelinksthatmakeupthefour-barkneemechanism.Using

SolidWorksandMATLABinconjunc'onwithexperimentalgaitdata,thelinklengthsofthiskneemechanismwereop'mizedinordertoprovidekneestability,par'cularlyduringini'alheel

contact.

Unlikeasimplehingejoint,thepointaboutwhichakneejointrotateschangesasanindividualambulates.Thischangingcenterofrota'on,orInstantaneousCenterofRota.on(ICR),isoneoftheprimarydeterminantsofkneestability.Whendesigningafour-barmechanismknee,itisimportantthattheICRofeachkneeremainsposteriortotheloadlineasitsrespec'velimb

contactstheground(seeaboveimage).

TheimagetotheleBshowsthefour-barkneemechanismanditsICR(outlinedbyacircle)infourdifferentposi'ons.IftheICRislocatedposteriorto(inthisimage,totheleBof)theloadline(in

red),thekneecanbeconsideredstable.

FiniteElementAnalysis(FEA)isapopulartoolusedtovisualizethedifferentstressesthatwillariseinanobjectuponbeingsubjectedto

appliedforces.Ifthiskneeprosthesisistobemanufacturedusing3Dprinters,itisnecessarytoensureitcanwithstandtheforcesthatwill

beappliedtoitduringnormalwalkingcondi'ons.Totherightisavisual

representa'onofthestressesthatarepresentinthiskneeprosthesiswhenitissubjectedto

theforcesthatariseuponheelcontact.

Methodology

Results-ICR

Results(FEA)

Conclusion

Designinga3D-printedprosthe'cknee

I’dliketothankDr.MarcDoumitforallofhisguidance,encouragement,andinspira'on.Addi'onally,I’dliketothankDr.AhsanAhmedandSco^Pardoelfortakingthe'metomeetwithme.Thehelpthatallofyouofferedwasincredibly

usefulandverymuchappreciated.-  KieranEveleigh,KEVEL040@uo^awa.ca

-UsetheresultsoftheFEAtominimizetheoverallsizeoftheprosthesiswithouthinderingitsfunc'onality.-Adjustthelinklengthsoffour-barkneemechanismtocreateadesignthatoffersmoresupport.

-Mechanicallytesttheperformanceofthekneeprosthesis.

FutureWork

[1]Rose,Jessica,andJamesG.Gamble.HumanWalking.Philadelphia:Lippinco^Williams&Wilkins,2006.Print.[2]Radcliffe,CW.Four-barlinkageprosthe.ckneemechanisms:kinema.cs,alignmentandprescrip.oncriteria.Prosthe'csandOrtho'csInt.1994;18:168.

[3]“AcrylonitrileButadieneStyrene(ABS)TypicalProper'es.”Prospector.UL,2017.Web.07Mar.2017.

[1]

[2]

KieranEveleigh,Dr.MarcDoumitDepartmentofMechanicalEngineering,UniversityofO^awa

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