《机械原理（英汉双语）（第2版）》 课件Chapter 12、13 Fluctuation and Regulation in Speed of Machines； Balance of Machinery.pptx

Chapter12FluctuationandRegulationinSpeedofMachines

1.ForcesActingonaMachine(1)WorkingresistanceWorkingresistancereferstothetypesofmachines.

(2)DrivingforceThedifferentprimemotorshavedifferentoperatingpeculiarities.Therelationshipbetweenthedrivingforceanditsspeedisoftenrepresentedbythepeculiarcurveofamachine.Fig.12-1ashowsapeculiarcurveofaninternalcombustionengine,andFig.12-1bshowsapeculiarcurveofanACelectromotor.12.1OperatingAnalysisofMachineryFig.12-1Mechanicalbehaviorcurveofprimemachines(原动机的机械特性曲线图)

2.OperatingProcessofMachines(1)StartupperiodTherunningspeedofamachineisfromzerotoworkrunningspeedinthisperiod,andtheworkdonebythedrivingforceisgreaterthantheworkdonebytheresistance.

(2)SteadyrunningperiodInthesteadyrunningperiod,theworkdonebythedrivingforceisequaltotheworkdonebytheresistanceinaperiod.Theincrementofthekineticenergyiszero.

(3)StoppingperiodInthestoppingperiod,thedrivingforcewillceasetowork,thusWd=0.Themotioncontinuesforacertaintimeowingtotheinertiakineticenergyofthemachine.

Fig.12-2Crankpunch(曲柄压力机)Fig.12-3Operatingprocessofmachinery(机械的运转过程)

12.2EquivalentKineticModelofMechanismSystems1.TheMethodofResearchingRunningProcessofMachines

Fig.12-4Forceanalysisofacrankpunch

(曲柄压力机的受力分析)InordertofindtheactualmotionofamechanismshowninFig.12-4,wemustsolvethedrivingtorqueactingonthelink1andtheangularvelocity.Thedynamicforceanalysisoftheslidercrankmechanismhasalargenumberofunknownstosolve.

Weoftenselecttherotatinglinkorreciprocatinglinkasanequivalentlink.Fig.12-5showsthoseequivalentlinks.Fig.12-5Equivalentlinks(等效构件)

(1)RotatingequivalentlinkWhentheequivalentlinkisrotatingaboutanaxiswithaconstantangularvelocity,thekineticenergyisasfollow