54883《機(jī)械原理（英語）（第2版）》（基本課件）Chapter 1 Introduction

TheoryofMachinesandMechanismsChapter1Introduction1.

TheConceptofMachinery1.1GeneralInformation(1)MechanismAmechanismisadevice,whichproducesspecificmechanicalmotions.Thus,thefunctionofamechanismistotransmitandmodifyamotion.Weoftenuseadrawingwithsomesimplelinesandsymbolstodescribethemechanism,anditiscalledkinematicaldiagram.

(2)MachineAmachineisadevicewhichproducesspecificmechanicalmotions,anditcantransmitormodifymechanicalenergy,materialsandinformation.Amachinemaybeamechanismoracombinationofmechanismscapableoftransmittingormodifyingmotionandmechanicalenergy.

(3)MachineryIntheviewpointofkinematics,mechanismandmachinehavenodifference，somechanismsandmachinesaregenerallycalledmachineryinmechanicalengineering.Thereisnoenergytransformingandmodifyinginamechanism,forexample,mechanicalwatchisamechanismbutnotamachine,becauseitcannottransformenergy.Fig.1-1Internalcombustionengineandscheme(內(nèi)燃機(jī)及其機(jī)構(gòu)簡圖)

1—piston(活塞)2—coupler(連桿)3—crankshaft(曲軸)4、5、6—gear(齒輪)7—cam(凸輪)

8—follower(推桿)9—lever(杠桿)10—valve(氣門)11—frame(缸體)2.CompositionofMachinesFig.1-2Compositionofmachine(機(jī)器組成示意圖)

Amachineconsistsofprimepower,transmission

systemandworkingsystem.Amodernmachinealsocontainsacontrolsystem.Fig.1-2showstheblockdiagramofcompositionofamachine.Fig.1-3Automaticgate(電動大門示意圖)

1—driver(驅(qū)動器)2—gate(大門)3—electromotor(電動機(jī))4—reducer(減速器)

5—chaindriver(鏈傳動)6—rollers(滾輪)

Fig.1-3bshowsadiagramofanautomaticgate.Fig.1-3ashowsthecompositionofthedriver.Theprimepoweriselectromotor3whichhasahighspeed.Butgate2needsalowspeedtowork,sowehavetoinstallgearmechanismsandchainmechanismstomodifythespeedofelectromotor3.Thereducer4andchaindriver5aretransmissionsystem.Gate2consistingoftheparallellinkagesiscalledworkingsystem.Fig.1-4Constituteofthecoupler(連桿的組成)

1—bodyofthecoupler(連桿體)2—bearing(小端軸承)3—bearingbush(軸瓦)

4—headofthecoupler(連桿頭)5—bolt(螺栓)6—nut(螺母)7—washer(墊圈)1.2TeachingContentandObjectoftheCourse1.ResearchObjectoftheCourse

Theresearchobjectofthecourseisthetheoryofmachinery,andmachinerycontainsmechanismsandmachines.Therefore,thetheoryofmechanismsandmachinesistheimportantcontentofthiscourse.

Thepiston,coupler,crank,cam,gearandsoonshowninFig.1-1aresmallestmotionunits,andtheyarecalledlinks.Themotionoflinksisanimportantcontentforus.

2.ContentofThisCourse(1)StructuralanalysisofmechanismsItinvolvesthecompositionofmechanism,kinematicaldiagram,calculationofdegreeoffreedomandanalysisofmechanism.

(2)KinematicsofmechanismsItdealswiththerelativemotionsoflinksandforcesactingonthelinks,thusitinvolvesthevelocityanalysis,accelerationanalysis,forceanalysisandsynthesisofmechanism.

(3)DynamicsofmachineryItinvolvestheinertiaforcesbalancingandthefluctuationinspeedandregulation.1.Purpose

Themachineryiscloselyrelatedtohumanlife,economicconstruction,andnationaldefenseconstruction,somechanicalindustrycanreflectaindustrylevelofacountryandalevelofscienceandtechnology.Althoughtherearealotofmachines,themechanismsconsistingmachinesarefinite.Soonthebasisoffinitemechanismstodesignsomenewmachineisacreativework.Itisalsothepurposeofthiscourse.Thiscourseisthebasisofsomeothersubsequentcourses,suchasMachineryDesign,AdvancedKinematicsandDynamicsofMechanisms,MechanicalManufacture,etc.Sothepurposeofthiscourseisalsotolaythefoundationforthefurthermachinedesign.1.3PurposeofThisCourse2.Conclusion1)Machineryisveryimportanttodeveloptheeconomy.2)TheoryofMechanismandMachinesisveryusefultodesignmachines.3)Mechanismisadevicewhichcantransmitandmodifymotion.4)Thekinematicaldiagramisasimpleformtodescribethemechanisms.5)Amachinemaybeamechanismorcombinationofmechanismscapableoftransmittingormodifyingmotionandmechanicalenergy.6)Machineryisthegenerictermofmechanismsandmachines.7)Alinkisasma