Ngày tải lên :
17/12/2013, 11:15
... N
d1
l
d1
l
n1
tan
2
f and N
n2
¼
N
d
r
d2
r
n2
¼ N
d
l
d 2
l
n2
tan
2
f
ð3-1Þ
where r
d1
and r
nl
are the radii of the driver and driven cones, respectively, at
point 1, r
d 2
and r
n2
are driver and driven ... Inc.
setofunitstobeusedforeachratio,andtheresultingratiosareindependent
oftheunitsused.
Relativelybroadcurvesareshowninthefollowingcomputer-generated
graphsforeasyreadingtoshowcharacteristicbehaviorandtoprovide
contrastagainstthegridlines.Associatedroutines,suchasMathcadTrace,
appeartoreadthemfromtheoriginatingdata,therebyeliminatingtheread-
ingerrorsassociatedwithtracewidths.
I.BELTDRIVES
Equipmentusingnonmetallicbeltdrivesmayincludetheclutchcapabilityby
mountingthemotor(becauseitisusuallysmallerthanthedrivenmachine)
eitheruponahingedbaseoruponaslidingbasefittedwithaleveroralinkage
thatpermitsthemotortobemovedtoandfromthedrivenmachineinorder
toapplyandrelievethebelttensionandtherebygiveclutching(applyingbelt
tension)anddeclutching(relievingbelttension)capability.
Thesedesignseliminatetheneedforamechanicalclutch.Theirsim-
plicityisachieved,however,attheriskofintroducingthepossibilitythat
frictionalheatingofthebeltduringidling,whenthebelt(orbelts)mayreston
themotor’srotatingsheave(pulley).Thatmaygenerateenoughheattocause
beltingmaterialstoslowlyshrink.Thisreductioninthecenterdistance
betweenthedrivinganddrivenpulleys,orsheaves,maybegreatenoughto
causeanunintendedre-engagementofthemotorandthedrivenmachine.It
mayalsoinhibittheirdisengagement.Consequently,somebeltmanufacturers
producebeltsthatresistshrinkageduetoheatingforuseintheseclutching
anddeclutchingapplications.
Torquecapabilityforthesedrivesisaseparatecalculationtobe
performedaccordingtotheproceduresgivenbythebeltmanufacturers.
Therefore,itwillnotbeconsideredinthefollowingdiscussion.
A.HingedBase
Atfirstglanceitmayappearthatmovingamotorbymountingiteitherona
hingedbaseoronaslidingbaseissosimplethatnoanalysisisnecessary.An
analysis,however,doesbringforthseveralconsiderationsthatmaybemissed
inselectingthedimensionsofthebaseplate,inlocatingthepositionofthe
baseplatehinge,orindesigningthelinkagefortheslidingbaseplate.
Twosimilar,butdistinct,mountingdesignsforhingedbaseswillbe
considered.Intheseconfigurationsitistheweightofthemotoralonethat
providesthebelttension.ThetensionvectorshowninFigure1(a )and( b)
acting ... Inc.
maximuminFigure16,setg=13.52j,asreadusingtheMathcadTrace
feature.Evaluationofequation(1-13)forn=0.2,g=180,U=0.3,a=14j,
andh=20foru=13.52jandforu=20jgivesadetentforceof4.544lb,
whichiswithintheacceptablerange.Substitutionofg=180andq=1/32in.
intoa=gq=180/32=5.625in.enablesdeterminationofrfromr=Ua=
0.(5.625)=1.688in.Withlengthlgivenbyl=r/n=1.688/0.2=8.44in.,it
followsthattheclearancegivenbylÀr=8.440À1.688=6.752in.exceeds
thatspecified.
Thisclearancerequirementmaybesatisfiedbyincreasingthemagni-
tudeofnandreducingthemagnitudeofg.Thus,ifn=0.28andg=150,the
detentforcebecomes4.702lb,aisreducedto4.688in.,andrbecomes1.406in.
Thesevaluesgivel=5.021in.,sotheclearanceis5.021À1.406=3.615in.,
whichiswithinthedesiredrange.
VI.EXAMPLE3:CONEDRIVE
Selectaconedriveforacombinationgolfcardandaproposedcongestedarea
commutercartforuseincommunitiesthatacceptthem.Analysisoftorque
transmissiononthebasisofthedynamiccoefficientsoffrictionforacceptable
liningsindicatesthata2.00-in.overlapwouldbesufficient.
Forcomparison,consideronedesignwiththedriverconehavingan
apexhalf-angleof40janddrivenconeshavingapexhalf-anglesof50janda
seconddesigninwhichboththedriveranddrivenconeshaveapexhalf-angles
of45j.Inbothcasesinitiallyselectaconegeneratorlengthof6.00in.toallow
theoverlaptobegreaterthan2.00in.intheeventthattheprototypeshould
requiremodification.
Beginwiththe40j,50jcombinationandturntoFigure11toselectthe
dimensionsoftheconesbyenteringthecurveatz=6andreadinguptothe
40jline.Theprincipalradiusofcurvatureatthatpointis5.0346.Sincezis
measuredininches,theprincipalradiusofcurvatureis5.0346in.Readingto
theleftatthisvalueofUyieldsthatatz=4.25in.,theprincipalradiusof
curvatureofthe50jhalf-angleconeis5.0650in.Aplotofthex-dimensionfor
eachcone,showninFigure17(a),confirmsthatthetwoconesshouldroll
without...