淮海工学院毕业设计翻译Word文档下载推荐.docx
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淮海工学院毕业设计翻译Word文档下载推荐.docx
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MrDanielJohnClarke
infulfilmentoftherequirementsof
CoursesENG4111andENG4112ResearchProject
towardsthedegreeof
BachelorofEngineering(Mechanical)
Submitted:
November,2006
6.5ParallelogramMechanism........................................................................................46
6.6SpringDesign...........................................................................................................49
6.7Designofcastorframe.............................................................................................54
6.8Hubdesignandwheelselection...............................................................................56
6.9Spoolvalvecontrol...................................................................................................60
6.10Spoolvalveselection...............................................................................................63
ABSTRACT
Thepurposeofthisprojectwastodesignaheightcontrolsystemthatcouldbeappliedto
aThreePointLinkagemountedimplement.Severalmethodsofachievingthisgoalwereinvestigated.Thetwomethodsthatwereinvestigatedindetailwereanelectricaloverhydraulicsystemandamechanicaloverhydraulicsystem.
Theuniqueoperationofthethreepointlinkageimplementswhenliftassistisusedpresentsproblemswhenaccurateframeheightisrequired,suchaswhenseedingoperationsarebeingperformed.Thesystemhasbeendesignedsothatitisconstantlysensingtheheightoftheframeatbothendsoftheimplement.Theoutputfromthissensingisusedtocontrolahydraulicvalvemechanicallyorelectrically.Ifaheightdiscrepancybetweenthefrontandrearoftheimplementisdetected,thisvalvewillbe
activatedtoallowaflowofhydraulicoiltotheliftassistsystem,levellingtheimplement.
Theinvestigationoftheelectricalcontrolsysteminvolvedconstructingaprototype
circuitthatwasbasedonaPICAXEmicrocontrollertoprovidecomputingpower.This
chipwasprogrammedtoreadtheoutputfromtwovariableresistorsanddetectanyheightdiscrepancies.Whenadiscrepancywasdetected,themicrocontrolleractivatedaservomechanismthatusedmechanicalmotiontocorrectthepositionofoneoftheresistor
tomatchthemechanicalpositionofthetworesistors,thusprovingtheconceptofmechanicalheightcontrol.
Themechanicalsystemwasdesignedsothattheoutputfromtwoheightsensingwheelswasmechanicallyinputintothehydraulicvalvetoactuateitwhenthewheelssensedthat
therewasaheightdiscrepancy.Thissystemwasmodelledusingthesolidmodelling
packageSolidWorksandbasicengineeringanalysiswasperformedonthedesign.
FacultyofEngineeringandSurveying
ENG4111ResearchProjectPart1&
ENG4112ResearchProjectPart2
6.5ParallelogramMechanism
Figure6.5:
Imageshowingthefinalparallelogramdesign
Theparallelogrammechanismwasbuilttocombinemanyfunctionsinthesameunit.
Figure6.5showsanimageofthesolidmodelofthemechanism.Backingplate(A)actsas
aninterfacebetweenthemechanismandtheimplementframe.ThisissecuredtotheframewiththeU-bolts(B).Notethattherearefourdifferentheightsettingsthatareavailable
fromthetwelveholesinthebackingplate.Thisallowstheheightsensingmechanismtobe
adaptedtosuittheheightofmostimplements.Theframeintheimageismadeofsimple4”
squarerolledhollowsection(RHS),althoughadapterblockswillbesuppliedwiththedevicetofittheseU-boltstoavarietyofdifferentframesizes.Theheightsettingshown
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showsthecorrectsettingtosuita(lowered)frameheightof800mm,asmaybefoundon
largetrailingimplements.Thelargeheighttravelrangeofthemechanismcoupledwiththefourheightsettingsensuresthatthisdevicecanbefittedtomostthreepointlinkageandtrailingimplementsifthisisnecessary.
Thelowerlink(D)andupperlink(E)aremadeof50x63mmRHSwitha3mmwall
thickness.Notethatthesedimensionscorrespondto2x2½
”,whichisacommonRHSsize.Botharefittedateachendwithgreasablebearingtubesasdescribedpreviouslythatareweldedontothewallsofthesection.Fourofthesemakeupthepivotingpointsforthemechanism.Theupperandlowerlinksarebothfittedwith20mmshafts(FandG)thatprotrudefromthelinksandprovidemountingpointsfortheshockabsorber(I)andspringmechanism.ItemCformsthefourthsegmentoftheparallelogram,andisthepartthat
holdsthecastorframewhichinturnholdsthewheel.Thecastorpivot(H)ismadeofanothergreasablebearingtubethatissizedtofita30mmshaft.Fulldetailofallofthesepartsarcanbefoundintheappendices.
Theshockabsorberisfittedtotheframetodampexcessmotionresultingfromrough
terrain.Ifthiswasnotdone,therewouldbealmostconstantactivationofthespoolvalveineventhesmoothestterrain,resultinginerraticheightcontrolandexcesswearofthespoolvalveandlinkages.Theshockabsorberspecifiedforthisapplicationisaunitfromtherear
ofaNissanPatrolFourwheeldrive,partnumberIA30.Thisunitwasdesignedforaheavyvehicle,sooffersahighamountofenergyabsorptioncapacity,aswellasalonglifeandreliability.Thestrokeofthisunitismeasuredat230mm,whichifthegeometryissetcorrectlyisenoughforthisapplication.
Thegeometryofthefinaldesignofthemechanismmeansthatthegreatestdampingforceoccursattheworkingheightwhereitismostneeded,andalmostnodampingforceispresentwhentheframeisfullyextendedanddampingisnotascritical.Thismethodof
designmeansthatthedampingforcecanbeadjustedbychangingtheheightsettingofthe
U-boltsthatsecurethebackingplatetotheframe.Usingtheupperboltholeswillincrease
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thedampingforcebyraisingthewheel,whereasusingthelowerboltholeswillreducethe
dampingforcebyeffectivelyloweringthewheel.
Aviewoftheothersideofthemodelisshowninfigure6.6.Thisshowsthemechanismthatmountsaspringtothemechanism.Thisspringisnecessarytoprovideforcetopushthewheeldowntoprovideanaccuratecontourfollowingability.Theotherjobthatthe
springmustperformistoforcethewheeltotraveldownwardsfastenoughsothateveninarapidliftingphase,thewheelremainsincontactwiththeground.Thismeansthatthe
springmusthaveenoughforcetoextendtheshockabsorberatthecorrectspeedtokeepthewheeltouchingtheground.
Figure6.6:
Secondaryimageofthefinalparallelogramdesign
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Thespringholderworksbyprovidingtwoplates(FandE)thatpressoneitherendofthe
springandcontainit.These
platesmoverelativetoeachotherastheframemoves
vertically,keepingthespringcompressedandprovidingdownwardforcetothewheel.TheplatesarealignedwithashaftBthatisconnectedtobossassemblyGandslidesrelativetoalignmentbossA.Theslidingshaftisalsolocatedcoaxiallyinsidethecoilsofthespring,thereforecontainingitbetweenthetwoplates.Thealignmentbossisheldontheupper
20mmshaftbyasplitpinandawasher(D)insteadofacollarandbolt(C).Thisisbecausetheslidingshaftistooclosetothepivotshafttoallowacollarandbolttobeused.
6.6SpringDesign
Asthespringholderandtheshockabsorbersharethesamemountingpointstopand
bottom,theextensionforceontheshockabsorberduringliftingoftheimplementisequal
tothecompressionforcefromthespringminustheforcethatthespringisexertingonthegroundthroughthetyre.Thefastertheliftingaction,themoreofthespring’sforceisgoingintoextendingtheshockabsorber.Thereforethespringshouldbeabletoexertenough
forcetoextendtheshockabsorberatafastenoughratetokeepupwitharapidliftandprovideenoughadditionalforcetokeepthetyreincontactwiththegroundatthesametime.
Theshockabsorberunitthatwasobtainedformodellingpurposeswaswornout,sothecompressiondampingforcethatwasmeasuredwasnotrepresentativeofanewunit.Theextensiondampingforcefeltalotstrongerhowever,andwasenoughtoprovidearough
guidetotheexpansiondampingfactorofanewunit.Thisisthecriticaldampingfactorthatwouldgovernthedesignofthespring.Togetafeelforthedampingfactor,anextension
forceofanestimated20kgwasappliedtotheshockabsorberbyhandandtheextension
ratewasestimated.Thetestingprocedurewasonlyanapproximationbecauseasmentionedpreviouslythetestunitwaswornoutandcouldonlyprovidearoughguideanyway.
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Thistestindicatedthataforceof20kgwouldresultinanextensionspeedofapproximately
20mm/second.Itisestimatedbyvisualobservationthatthemaximumexpectedliftrateof
athreepointlinkageimplementisapproximately100mm/second.Notethatthisdeviceisnotbeingcustomisedtofitonetractor;
itisdesignedtobeuniversallyusedonawide
varietyoftractor/implementcombinations.Thustheaimofthisdesignprocessistocome
upwithamaximumfeasibleliftratefigurethatcouldbeencounteredanddesignaspring
thatwillbeabletoextendtheshockabsorberatthecorrectrateandatthesametimesupplysufficientforcetopressthetyreintotheground.Thusbasedontheobservationsoftheoperationofthreepointlinkagesystems,itisdecidedtodesignthespringtolowerthe
wheelatarateof200mm/s.Thisspeedis
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