机械原理(双语)试卷2答案.pdf

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1、《机械原理（双语）》课程试卷2答案一、Checkpoint(markyouranswerontheanswersheetbyTrueorFalse)(20points2points/each)1．ThelinkswithinamechanismcanhavedeterminedrelativemotionsifandonlyiftheDOFofthemechanismisgreaterthanzeroandequaltothenumberofthedrivinglinks(T)2.Duringthegroupdividingofmechanism,iftheDOFofthegroupisze

2、ro,thenthegroupiscalledAssurgroup(F)3.Anythreeindependentlinksingeneralplanemotionmusthavethreeinstantcentres,thethreeinstantcentresmaylieonacommonstraightline.(F)4.IfamechanismcomplywiththeGrashof’scriterion,thenthemechanismmusthaveacrank.(F)5.Arotorisstaticallybalancedifithasbeendynamicallybalanc

3、ed.(T)6.Inthevelocitypolygon,Thevectorconnectingtheanytwopointsexceptpointprepresentsrelativevelocitybetweenthemandthedirectionisoppositetothevelocity’symbol(T)7.Theanalysiswithdynamicstaticisanalysisofthemechanismforcewithexceptionoftheinertiaforce,applyingintothecaseoflowvelocitymechanism.(F)8.In

4、acrank-rockermechanism,therockerDCreachesitstwolimitingpositionsDC1andDC2.ifthecrankABisadriver,thenthelimitingpositionsarecalleddeadpoints.(F)9.Thepressureangleremainsthesameatallpointsonthetoothprofilesoftherack(ak=a),whichisalsocalledthenormalpressureangle.(T)10.Thetransmissionratioofwormgearing

5、(wormisdriver)canbecalculatedbytheformulai12=d2/d1(F)二.CalculatethedegreeoffreedomofthemechanismshowninFig(10points)solution:A:passiveDOFB:compoundhingeBn=9,PL=12,PH=21F=3n-2PL-PH(3points)=3×9-2×12-2=1(7points)三.FortheplatecammechanismwithtranslatinginlinerollerfollowerasshowninFig,thecamcontourisc

6、ircle(theradiusr=100mm),theradiusofrollerrR=10mm,OC=20mm,thecamrotatesatanticlockwise.1).Drawoutthepitchcurveofthecammechanism2).Findouttheradiusofprimecirclerp=?3).Findouttheliftoffollowerh=?4).Forthepositionshown,indicatepressureangleα5).Forthepositionshown,indicatedisplacements(20points)solution

7、:1).thepitchcurveofthecammechanismAsshowninFigdottedcircle(2points)2).rp=r-OC+rT=90mm(2points)O3).h=2OC=40mm(2points)C4).AsshowninFig(2points)5).AsshowninFig(2points)ω2四.Designanoffsetslider-crankmechanismb