Chapter10SpatialMechanismsandRoboticMechanisms1.SpatialKinematicalPairs(1)ClassⅠkinematicpairsAsphereisplacedonanevenplaneshowninFig10-1a.

(2)ClassⅡkinematicpairsEachclassⅡkinematicpairofferstwoconstraintsandhasfourdegreesoffreedom.Fig.10-1bshowsacylinderplanepairwhichconstrainsthetranslationalmotionalongthezaxisandtherotationalmotionaboutthexaxis.

10.1IntroductionofSpatialMechanismsFig.10-1Spatialkinematicpairs1(空間運(yùn)動(dòng)副1)(3)ClassⅢkinematicpairsEachclassⅢkinematicpairoffersthreeconstraintsandthreedegreesoffreedom.Fig.10-2ashowsasphericalpairwhichconstrainstranslationalmotionsalongthex,yandzaxeswhileoffersthreerotationalmotionsabouttheseaxes,denotedasS.Fig.10-2bshowsthesketchdiagramofthesphericalpair.Thispairiswidelyusedinspatialmechanisms.

Fig.10-2Spatialkinematicpairs2(空間運(yùn)動(dòng)副2)(4)ClassⅣkinematicpairsEveryclassⅣkinematicpairoffersfourconstraintsandtwodegreesoffreedom.Fig.10-3ashowsaspherepinpairwhichhasonlytworotationaldegreesoffreedombecauseoftheconstraintofthepin.ThespherepinpairisdenotedasS′.Fig.10-3bisitssketchdiagram.Fig10-cshowsacylinderpairwhichpermitsthetranslationalmotionalongitsaxesandtherotationalmotionaboutthesameaxis.Fig10-dshowsitssketchdiagramanddenotedasC.

Fig.10-3Spatialkinematicpairs3(空間運(yùn)動(dòng)副3)(5)ClassⅤkinematicpairsAclassⅤkinematicpairoffersfiveconstraintsandonedegreeoffreedom.Fig10-4ashowsarevolutepairwhichhasonlyonerotationaldegreeoffreedom.Fig10-4bisitssketch,denotedasR.Fig10-4cshowsaprismaticpairwhichhasonlyonedegreeoffreedomthatpermitsittoexecutetranslationalmotionalongtheaxes,denotedasP.Fig.10-4dshowsitssketch.Fig10-4eshowsahelicalpairwhichpermitsthetranslationalmotionalongitsaxisandtherotationalmotionaboutthesameaxis.Fig.10-4Spacialkinematicpairs4(空間運(yùn)動(dòng)副4)2.DegreesofFreedomofSpatialMechanismsWeassumethatthereareclassⅠkinematicpairsofp1,sotheycanofferconstraintsof1p1.Similarly,classⅡkinematicpairsofp2canofferconstraintsof2p2,classⅢkinematicpairsofp3canofferconstraintsof3p3,classⅣkinematicpairsofp4canofferconstraintsof4p4,andclassⅤkinematicpairsofp5canofferconstraintsof5p5.Therefore,thedegreeoffreedomofspatialmechanismscanbewrittenasfollows:Fig.10-5Aircraftundercarriage(飛機(jī)起落架)3.ClassificationofSpatialMechanism(1)ExpressionofspatialmechanismTheplanarmechanismsarenamedbytheirkinematicalcharacters,suchascrankrockermechanism,slidercrankmechanism,doublecrankmechanismandsoon.Generally,wenamethespatialmechanismsbythenamesoftheirkinematicpairs.Thefirstalphabetisthesymbolofthekinematicpairwhichconnectsthedrivinglinkandframe,thenwecanarrangethesymbolsofotherkinematicpairsorderly.Fig.10-5showsanaircraftundercarriagewhichcanbenamedasthespatialmechanismofSPSR.

(2)ClassificationofspatialmechanismsThespatialmechanismsareclassifiedasclosedchainmechanismsandopenchainmechanisms,accordingtothekinematicalchainisclosedoropen.Theopenchainmechanismsarewidelyappliedtotherobotfield.Fig.10-6ashowsaRSSRmechanism,inwhichlinks1,2,3andthefixedlink4areconnectedbyrevolutepairsandsphericalpairs.Itisaclosedspatialmechanism.Fig.10-6bshowsa4Ropenchainmechanisminwhichthefixedlink1andlinks2,3,4,5areconnectedbyfourrevolutepairs,anditisanunclosedspatialmechanism.Fig.10-6Classificationofspatialmechanisms(空間機(jī)構(gòu)分類)Example10-1Fig.10-7ashowsaR3Cmechanism.Calculatethedegreesoffreedomofthemechanism.Fig.10-7D.O.Fofspatialmechanisms(空間機(jī)構(gòu)的自由度)4.DegreesofFreedomofSpatialMechanismsExample10-2Fig.10-7bshowsaRSSRmechanism.Calculatethedegreesoffreedomofthismechanism.Example10-3Fig.10-8showsaopenlinkrobotmechanism.Calculatethedegreesoffreedomofthismechanism.Fig.10-8Openlinkrobotmechanism

(開鏈機(jī)器人機(jī)構(gòu))1.TandemRobotMechanismsFig.10-9Tandemrobotmechanism(串聯(lián)機(jī)器人機(jī)構(gòu))

1—Wristjoint(腕關(guān)節(jié))2—Elbowjoint(肘關(guān)節(jié))3—Shoulderjoint(肩關(guān)節(jié))

4—Waistjoint(腰關(guān)節(jié))5—Base(底座)10.2IntroductionofRoboticMechanisms

Fig.10-9ashowsa3Rrobot,whichconsistsofthreerevolutepairsandthreelinks.Atandemrobotusuallyhasfiveparts;theyarebase,waist,shoulder,elbowandwrist.Accordingly,therearefourkinematicpairswhichcontainwaist,shoulder,elbowandwristjoint.Fig.10-9bisthesketchdiagram.2.ParallelRobotMechanismsFig.10-10Parallelrobotmechanisms(并聯(lián)機(jī)器人機(jī)構(gòu))Fig.10-10ashowsaplanarparallelmechanisminwhichthreeinputlinksdrivethemovingplatform1toperformdesiredmotion.Thisiscalled3RRRplanarparallelmechanism,andithasawidelyuseinmicromechanisms.Fig.10-10bshowsaspatialparallelrobotmechanism.Itiscalled3RPSparallelrobotmechanism.Thereisonedegreeoffreedomineverybranch.Comparedwiththetandemrobot,thisparallelrobothasabetterrigiditybutitsworkspaceissmaller.3.ApplicationsofRobotictMechanisms

Robotsaretypicalelectromechanicalproductswhichhaveaverywidelyapplication.Robotscanbeclassifiedbytheirworkingpurposes,suchasindustrialrobots,medicalrobots,servicerobots,militaryrobots,toyrobotsandsoon.Industrialrobotshavebeenusedinautomaticproductionfield.Medicalrobotshavebeenwidelyusedinsurgery.Chapter11DesignofMechanismSystems1.SimpleMechanismSystemConsistingofaSingleMechanism11.1IntroductionofMechanismSystems

Whendesigningasimplemechanismsystem,methodsofevolutionandmutationcouldprovideanapproachforcreatingnewmachines.Forexample,Fig11-1ashowsthesketchdiagramofashearingmachine.ThepinoftherevolutepairBandthedimensionoftheprismaticpairCareenlargedenoughtoobtainashearingmachineshowedinFig11-1b.Fig.11-1Shearingmachine

(剪床機(jī)構(gòu))2.ComplexMechanismSystemConsistingofIndependentMechanismsFig.11-2Motionharmonizationofmechanism

(機(jī)構(gòu)運(yùn)動(dòng)的協(xié)調(diào))Fig.11-2showsahydraulicmechanismsysteminwhichthehydrocylinder1and2willoperateindependently.Thehydrocylinder1willtransferaworkpiecefromposition1toposition2,thenhydrocylinder2willtransfertheworkpiecetoposition3.Atthistimehydrocylinder1mustgobacktoitsinitialposition.3.ComplexMechanismSystemConsistingofMechanismsConnectedbyEachOther

Fig11-3showsacomplexmechanismsystem,inwhichbeltmechanism,wormmechanism,cammechanism,linkagemechanismareconnectedinseries.Itcouldclipandfeedautomatically.

Fig.11-3Automaticfeedingmachine

(自動(dòng)送料機(jī))1.MotionHarmonizationofaMechanismSystemFig.11-4Punchingmechanism

(壓力機(jī)機(jī)構(gòu))11.2HarmonizationDesignofMechanismMotions

Fig.11-4showsapunchingmachineinwhichtheactionoftheslidercrankmechanismABCisusedtopunchandtheslidercrankmechanismFGHisusedtofeed.Whenthepunchingheadgoesupafterfinishingapunchingprocess,thefeedingmechanismstartstofeed.Besides,thefeedingmechanismmustcompletefeedingandreturntoitsinitialposition,andthenthepunchingheadwillbegintopunch.2.DesignofMotionCirculationDiagram

Fig.11-5showsthemotioncirculationdiagramofapunchingmechanism.Inthefigure,theabscissaaxisindicatesthemotioncycleoftheactuatorsandtheordinateaxisindicatesthemotionstatusoftheactuators.Everymotionstatusofmechanismscanbeexpressedinthismotioncirculationdiagram.

Fig.11-5Motioncirculationdiagramofapunchingmachine

(壓力機(jī)機(jī)構(gòu)的運(yùn)動(dòng)循環(huán)圖)3.KeyPointsforDesigningMechanismSystems1)Choosesimplemechanismstosatisfythemechanicalfunctions.2)Sketchupthemotioncirculationdiagram.3)Synthesizethesimplemechanisms,anddeterminetheirdimensions.4)Determinetheconnectionmethodsandsizesofallmechanisms.5)Simulateandinspectthereliabilityofmotionharmonization.6)Optimizethesizesandthepositionsofthemechanismsrepeatedly,untiltheycansatisfytherequirements.1.ConnectionBasicLinkGroupsFig.11-6Connectingbasiclinkgroups(基本桿組)11.3CombinedMethodsofMechanismSystemsInFig11-6a,theoutsidepairsBandDoftheclassⅡlinkgroupBCDareconnectedtothedrivinglinkABandtheframe,andweobtainafourbarlinkageABCD.IftheoutsidepairsEandFofanotherclassⅡlinkgroupareconnectedtothelinkDCandtheframe,asixlinkmechanismwouldbeobtainedshowedinFig11-6a.IftheoutsidepairsBandDareconnectedtotwodrivinglinks,wecangetaparallelmechanismwithtwodegreesoffreedomshowninFig11-6b.

2.TandemConnectionofSimpleMechanismsFig.11-7Mechanismsintandemconnection1(機(jī)構(gòu)的串聯(lián)組合1)

Fig11-7ashowsagearlinkagesystem,inwhichthedrivengearisconnectedrigidlytothedrivingcrankofthecrankrockermechanism.Thismechanismsystemcanreducethespeedofthelinkagemechanism.Fig11-7bshowsanothergearlinkagesystem,inwhichtheinternalgearofthegearsisconnectedrigidlytothecoupleroftheparallelogrammechanismABCD.Fig.11-8Mechanismsintandemconnection2(機(jī)構(gòu)的串聯(lián)組合2)

Fig11-8ashowsatandemmechanismsysteminwhichtheguiderofthecrankguiderbarmechanismisconnectedtothecrankoftheslidercrankmechanism.Thesliderwouldhaveaspecialmotioncharacteristic.Fig.11-8bshowsatandemsystemconsistingofagearmechanismandacammechanism.3.ParallelConnectionofSimpleMechanismsParallelconnectionsarewidelyusedinengineering.InFig.11-9a,twoparallelhydrauliccylindermechanismsdriveadumpbucketofatrucktogether.Fig.11-9bshowsaparallelgearmechanisminwhichthemotionofdrivingshaftisresolvedintothemotionsofshaftsⅠ,Ⅱ,Ⅲ,Ⅳ,ⅤandⅥ.

Fig.11-9Mechanismsinparallelconnection1(機(jī)構(gòu)并聯(lián)組合1)Fig.11-10ashowsaninternalcombustionengine,inwhichtheslidercrankmechanismsareinlinearrangementtoV.Thepistonsaredrivinglinksanddrivethecrankshafttorotate.Fig.11-10bshowsanothercombustionengine,inwhichtheslidercrankmechanismsareradialarrangement.Fourslidercrankmechanismsdrivethecrankshafttorotate.Fig.11-10Mechanismsinparallelconnection2(機(jī)構(gòu)并聯(lián)組合2)Fig.11-11Mechanismsinparallel

connection3(機(jī)構(gòu)并聯(lián)組合3)InFig.11-11,themotionoftheelectricmotorisseparatedintotwobranches;intheendtheywillbesynthesizedtobeonerotationofthewormgearagain.Thisparallelmechanismcanenhancetheoutputcapacityofthewormgear.Inengineering,weusuallytaketandemmechanismsasthebranchesofparallelmechanismsystems.Fig.11-11showsanexamplethatbothgearmechanismsaretandemconnections.Combinationsoftandemconnectionsandparallelmechanismsareverycommoninmechanismsystems.4.SuperpositionofSimpleMechanismsFig.11-12Mechanismsinsuperposedconnection1(機(jī)構(gòu)疊加組合1)Fig.11-12ashowsahydraulicexcavator,inwhichaguiderbarmechanismislocatedontheturntable1.Arm4isdrivenbyhydrauliccylinder2androd3.Anotherhydraulicmechanismissu