机械原理考题020.docx
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机械原理考题020.docx
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机械原理考题020
Testpaperof《MMT》forGrade02.July,04,2004
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1.Mixedproblems(19%)
(1).Thepropermeshingconditionsforaexternalhelicalgearpairwithparallelshaftsare_mn1=mn2=standardvalue__、_n1=n2=n1=20__and1=-2,thecenterdistanceofanexternalhelicalgearpairwithoutaddendummodificationisa=mn(Z1+Z2)/(2cos)。
(4%)
(2).Thepropermeshingconditionsforaspurbevelgearpairaremn1=mn2(largeend)_、_1=2=20_andR1=R2.Thestandardparametersofawormgearingaredefinedonthemid-plane.Toensuretherotatingrelationshipofthewormandwormwheelasshowninthefigure,thewormshouldbe_left-handed(right-handedorleft-handed).(4%)
(3).Amongtheintermittentmechanisms(orstepmechanisms),thereexistsrigidimpulsein_Ratchet_mechanismandtherotatingangleoftheoutputlinkofthe_Geneva_mechanisminaworkingcyclecan’tbechanged.
_Differential__screwmechanismscanbeusedasfinemeasuringinstruments.__Compound__screwmechanismscanbeusedtomovethecomponentsquickly.(4%)
(4).Inamechanicalsystemrunningatastablespeedwiththeperiod2,arotatinglinkisselectedastheequivalentlink.TheequivalentresistantmomentMristhefunctionoftherotatingangleasshowninthefigurewhiletheequivalentdrivingmomentMdisconstant.TheequivalentmomentofinertiaJeisconstant.ThentheequivalentdrivingmomentMd=50_Nm.ThemaximumincrementofworkWmax=_50__Nm.Themaximumspeedoftheequivalentlinkmaxappearsat=,whiletheminimumspeedoftheequivalentlinkminappearsat=3/2.(7%)
2.
Drawthekinematicdiagramofthemechanism.(4%)
3.Calculatethedegreeoffreedomofthemechanismshowninthefigure.Addtheserialnumberstothelinksandindicatecompoundhinges,passiveDOF,redundantconstraintsbeforethecalculationandtheformulashouldbegiven.(5%)
Solution:
F=3n-2pL-pH
=3×6-2×8-1
=1
4.
Locateallinstantcentersofthelinkagemechanismforthepositionshown.(4%)
5.Intheoffsetslider-crankmechanismABC,crankABisthedriver.(6%)
(1)GivethelengthconditionsothatlinkABcanbeacrank.
(2)Usinggraphicalmethod,determinethemaximumpressureangleMAX.
(3)
DeterminethestrokeHoftheslider.
6.Inarevolutefour-barlinkageABCD,sidelinkABisthedriver.ThepositionsofsidelinkCDandthelinesegmentAEonthesidelinkABcorrespondingtotwopositionsofthelinkageareknown.Thefirstpositionofthelinkageisalsoadeadpoint.FindthefirstpositionB1oftherevoluteB.Describebrieflythedrawingsteps.(7%)
Solution:
(1)连接AC2和C2E2
(2)作AC2’E1AC2E2且字母旋向相同,得C2’
(3)作C1C2’的中垂线,与DC1的延长线交于B1。
7.Inacammechanismwithoscillatingrollerfollowershownbelow,thecamcontourisacirclecenteredatpointC.Drawandindicatethefollowing:
(8%)
a)Thepitchcurveofthecamanditsprimecirclewiththeradiusrp;
b)Camangleforrise0,camangleforouterdwellS,camangleforreturn0',camangleforinnerdwellS'.
c)Theangularliftofthefollowermax;
d)Thepressureangleofthemechanismatthepositionshown.
8.ShownareapairofinvoluteprofilesC1andC2withthecommonnormaln-npassingthroughthecontactpointK.Drawinthefigureandpointoutthefollowing:
(6%)
(1)Twopitchcircles.
(2)TheactuallineofactionB1B2.
(3)PointM2ontheprofileC2whichwillengagewithpointM1ontheprofileC1.
9.Apairofexternalspurgearshavetheparametersas:
ha*=1,c*=0.25,Z1=25,i12=3,α=20˚,workingcenterdistancea'=300mm ,rb1=70.477mm,rf1=69.90mm.Findthefollowing:
(12%)
1)Themodulemofthegearpairandthemodificationcoefficientx1ofthepinion;
2)Whattypeofcorrectedgearpairdoesitbelongto?
Why?
3)Parametersx2、ra2、αa2、ρa2ofthegear2.
Solution:
Itbelongstothecorrectedgearpairwithreferencecenterdistance,becausea=a’.
10.Inthegeartrainshownbelow,Z1=Z2=20,Z4=Z5=30,n4=2000r/min.Allgeardrivesarestandardgeardrives.Findbothmagnitudeandthedirectionofn1.(10%)
Solution:
Sinceallgeardrivesarestandardgeardrives,
r3=r1+2r2,Z3=Z1+2Z2=20+2×20=60
r6=r4+2r5,Z6=Z4+2Z5=30+2×30=90
Intheordinarygeartrain1-2-3,
Inthedifferentialgeartrain4-5-6-1,
Thedirectionofn1isthesameasn4.
11.Inthegear-linkageshownbelow,thecrankABisadriver.Theoutputpinion5islocatedontheshaftA.Analyzethemotiontransmissionrouteanddrawitsstructuralblockdiagram.Whatisthecombinationpatternofthecombinedmechanism?
(5%)
12.Therearethreeunbalancedmassesm1,m2andm3onthreetransverseplanesoftherotorasshownbelow.Theirmass-radiusproductsare:
m1r1=2kgmm、m2r2=6kgmm、m3r3=3kgmm.Theirlocationsareshowninthefigure.Therotoristobebalanceddynamicallybytwomassesonplane1andplane3.Determinetheamountsandangularlocationsofthetwobalancingmass-radiusproducts.(6%)
13.ThefirstlineofthesubroutineLINK,RRP,andRPRis:
SUBLINK(XA,YA,VAX,VAY,AAX,AAY,Q,W,E,LAB,XB,YB,VBX,VBY,ABX,ABY)
SUBRRP(M,YB,LAB,YA,VAY,AAY,QAB,WAB,EAB)
SUBRPR(M,XA,YA,VAX,VAY,AAX,AAY,XC,YC,VCX,VCY,ACX,ACY,LAB,QBD,WBD,EBD)
respectively.
Inthesix-barmechanismshownbelow,XA=0,YA=0,LAB=28mm,LBC=66mm,DBC=60,LBD=33mm,XE=94mm,YE=15mm,LEF=120mm.ThecrankABrotatesataconstantspeedof10rad/sec.AmainprogramisrequiredtoanalyzetheoutputmotionsofpointF.ThemechanismwillbeanalyzedforthewholecyclewhendriverABrotatesfrom0to360withastepsizeof5.(8%)
FORI=0TO360STEP5
Q1=I*PI/180
CALLLINK(0,0,0,0,0,0,Q1,10,0,28,XB,YB,VBX,VBY,ABX,ABY)
CALLRRP(+1,0,66,YB,VBY,ABY,QBC,W2,E2)
CALLLINK(XB,YB,VBX,VBY,ABX,ABY,QBC+PI/3,W2,E2,33,XD,YD,VDX,VDY,ADX,ADY)
CALLRPR(0,94,15,0,0,0,0,XD,YD,VDX,VDY,ADX,ADY,0,QEF,W6,E6)
CALLLINK(94,15,0,0,0,0,QEF,W6,E6,120,XF,YF,VFX,VFY,AFX,AFY)
PRINTI,XF,YF,VFX,VFY,AFX,AFY
NEXTI
END
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