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时间:2017-12-07
《机械原理(双语)试卷1答案》由会员上传分享,免费在线阅读,更多相关内容在行业资料-天天文库。
1、机械原理(双语)试卷答案一、Checkpoint(markyouranswerontheanswersheetbyTrueorFalse)(20points2points/each)1.ThegradeofamechanismisdefinedasthehighestgradeofAssurgroupinthemechanism.(T)2.AnymechanismwhichhasdeterminedmotionscanbeassembledfromabasicmechanismbyconnectingAssurgrouptothedeterminedl
2、inksusingouterpairs,groupbygroup.Thisisthecompositionprincipleofmechanism(T)3.Inversionofamechanismcanchangetherelativemotionbetweenitslinks(F)4.Ifamechanismhasquickreturncharacteristics,thenweshouldsetthefasterstrokeasworkingstroke.(F)5.Inacammechanism,thesineaccelerationmotion
3、curvewouldproducesoftimpulse(F)6.Arotorisdynamicallybalancedifithasbeenstaticallybalanced.(F)7.Ifcrank-rockermechanism(rockerisdriver)reachit’sdeadpoint,thentransmissionangleγisequaltozero.(T)8.Iftheefficiencyofmechanismη≤0,thenthemechanismisself-lockmechanism.(T)9.Thepressurean
4、gleremainsthesameatallpointsonthetoothprofilesoftherack(ak=a),whichisalsocalledthenormalpressureangle.(T)10.Thepropermeshingconditionsforexternalhelicalgearismn1=mn2=mn,an1=an2=anandβ1=-β2(T)二.CalculatethedegreeoffreedomofthemechanismasshowninFig(10points)Solution:A:passiveDOFn=
5、8,pl=11,ph=1F=3n-2Pl-Ph(3points)=3x8-2x11-1=1(7points)三.InthecammechanismwithinlinetranslatingFlat-facedfollowershowninFig,thecamisacirculardisk(Theradiusofthecirculardiskr=50mm).lA0=202mmSupposingthattheangularvelocityω1ofthecamisknown,ω1=10rad/s,thevelocityV2ofthefollower2isto
6、befoundwhenθ=45°byinstantcentermethod.(15points)Solution:BecausepointcisinstantcentrebetweenCam1andfollower2,(6points)2then:BVC2=VC1=ω1.LAC=10x202x2/2=200mm/S(6points)Becausefollower2isatranslatingfollowerThen:1OV2=VC2=200mm/S(3points)θcA四.Anoffsetslider-crankmechanismisasshowni
7、nFig.Supposingthatthelengtha=120mm,b=600mm,offsete=120mm.findoutthecoefficientKoftravelspeedvariationandTheworkingstrokeHbygraphicmethod(15points)Solution:Selectul=1/10,drawouttwolimitingpositions(AC1,AC2)ofslider-crankmechanismAeC2C1AC1=AB+BCAC2=BC-BC(6points)0THENθ=∠C1AC2=4.9(
8、3points)K=(180+θ)/(180-θ)=1.06(3points)H=C1C2/u
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