机械原理李璨

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1、第五章作业5.1Youaregiventwosetsoflinks.Selectfourlinksfromeachsetsuchthatthecouplercanrotatefullywithrespecttotheothers.Sketchthelinkageandidentifythetypeoffour-barmechanism.(1)L1=50mm,L2=80mm,L3=150mm,L4=190mm,andL5=280mm(2)L1=50mm,L2=20mm,L3=40mm,L4=35mm,andL5=25mmSolution(1)∵LMAX+

2、LMIN=L1+L5≤L3+L4Crank-rockermechanismDouble-crankmechanismDouble-rockermechanism(2)∵LMAX+LMIN=L1+L2≤L3+L4Crank-rockermechanismDouble-crankmechanismDouble-rockermechanism5.2Inafour-barlinkagemechanismshowninFig.5-39,thelengthsofeachlinkare:l1=28mm,l2=52mm,l3=50mm,l4=72mm,trytodet

3、erminethefollowingquantities:(1)Iflink4isgroundlink,theimbalanceangleθ,themaximumandminimumvaluesoftransmissionangleγminandγmax,andtimeratio.(2)Iflink1isgroundlink,identifythetypeoffour-barlinkage.(3)Iflink3isgroundlink,identifythetypeoffour-barlinkage.Solution(1)由图可知θ=19ºγmin=5

4、1ºγmax=157ºk=(180º+θ)/(180º-θ)=1.236024845(2)∵L1=LminandL1istheframe.∴Themechanismisadouble-crankmechanism.(3)∵L1istheshortestlinkandisthecouplerlink∴themechanismisadouble-rockermechanism5.5Designafour-barlinkagetomoveitscouplerthroughthethreepositionsshowninFig.5-41usingpointsA

5、andBasmovingpoints.AB=4cm.Solution5.7Repeatproblem5.6withaquick-returnlinkageforatimeratioof1:1.14.(Usinggraphicalmethod)Solution∵k=(180º+θ)/(180º-θ)=1:1.14∴θ=‐33.65ºthatis,θ=33.65º如图所示