虎小奇翻译1.docx
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虎小奇翻译1.docx
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虎小奇翻译1
TSINGHUASCIENCEANDTECHNOLOGY
ISSN1007-0214
17/19
pp105112
Volume8,Number1,February2003
*
LIUXinjun(刘辛军),WANGJinsong(汪劲松),LITiemin(李铁民)
**
DUANGuanghong(段广洪)
ManufacturingEngineeringInstitute,DepartmentofPrecisionInstrumentsandMechanology,
TsinghuaUniversity,Beijing100084,China
Abstract:
Parallelmanipulatorsforthemachinetoolindustryhavebeenstudiedextensivelyforvarious
industrialapplications.However,limitedusefulworkspaceareas,thepoormobility,anddesigndifficultiesof
morecomplexparallelmanipulatorshaveledtomoreinterestinparallelmanipulatorswithlessthansixdegrees
offreedom(DoFs).Severalparallelmechanismswithvariousnumbersandtypesofdegreesoffreedomare
describedinthispaper,whichcanbeusedinparallelkinematicsmachines,motionsimulators,andindustrial
robots.
Keywords:
parallelmanipulator;parallelkinematicmachine;degreeoffreedom;robot
Introduction
Mechanicalsystemsthatallowarigidbodyto
movewithrespecttoafixedbaseplayavery
importantroleinnumerousapplications.Arigid
bodycanmoveinvarioustranslationalorrotational
directionswhicharecalleddegreesoffreedom
(DoFs).Thetotalnumberofdegreesoffreedom
forarigidbodycannotexceedsix,forexample,
three-translationmotionsalongmutually
orthogonalaxesandthree-rotationalmotionsabout
theseaxes.Arobotincludesasystemtocontrol
severaldegreesoffreedomofanend-effector.
Thelastfewyearshavewitnessedimportant
developmentsintheuseofindustrialrobots,
mainlyduetotheirflexibility.However,the
Mechanicalarchitectureofthemostcommonrobots
isnotwelladaptedtocertaintasks.Othertypesof
architectureshave,therefore,recentlybeen
developedforindustrialuse,includingparallel
manipulators.
Aparallelmanipulator,whichisaclosed-loop
mechanism,typicallyconsistsofamoving
platformthatisconnectedtoafixedbaseby
Received:
2001-10-11;revised:
2002-05-28
*SupportedbytheNational973ProgramofChina
(No.G1998030607)
**Towhomcorrespondenceshouldbeaddressed.
E-mail:
litm@pim.tsinghua.edu.cn;
severallimbsorlegs.Typically,thenumberof
limbsisequaltothenumberofdegreesoffreedom
suchthateverylimbiscontrolledbyoneactuator
andalltheactuatorscanbemountedatornearthe
fixedbase.Forthisreason,parallelmanipulators
aresometimescalledplatformmanipulators.
Becausetheexternalloadcanbesharedbythe
actuators,parallelmanipulatorstendtohavea
largeload-carryingcapacity.Parallelmanipulators
arealwayspresentedashavingverygood
performanceintermsofaccuracy,rigidityandthe
abilitytomanipulatelargeloads.Theyhavebeen
usedinalargenumberofapplicationsrangingfrom
astronomytoflightsimulators,andarebecoming
increasinglypopularinthemachine-toolindustry.
Theconceptualdesignofparallelmanipulators
canbedatedbackto1947,whenGough
establishedthebasicprinciplesofamechanism
[1]
thepositionandorientationofamovingplatform
totesttirewearanddamage.Hebuiltaprototype
[2]
ahexagonalplatformwhoseverticeswereall
connectedtolinksbyball-and-socketjoints.The
otherendofthelinkwasattachedtothebasebya
universaljoint.Sixlinearactuatorsmodifiedthe
totallinklength.Stewartdesignedaplatform
[3]
(Fig.1b),inwhichthemovingelementwasa
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86-10-62773375
triangular
platform
whosevertices
wereall
并行机制有两个或三个自由度
withaclosed-loopkinematicstructure
tocontrol
in1955
(Fig.1a)wherethemovingelementwas
manipulatorasanaircraftsimulatorin1965
106
TsinghuaScienceandTechnology,February2003,8
(1):
105112
connectedbyball-and-socketjointstosupport
mechanismseachconstitutingoftwojacks,also
parallelmanipulators,withtheplanarthree-RPS
parallelmanipulatorasatypicalexample.Since
placedinatriangle.In1978,Hunt
[4]
madea
then,parallelmanipulatorshavebeenstudied
systematicstudyofthekinematicstructureof
extensivelybynumerousresearchers.
Fig.1 Earlydesignsofparallelmanipulators
Mostofthesix-DoFsparallelmanipulators
studiedtodatehaveincludedsixextendiblelimbs.
Theseparallelmanipulatorspossesstheadvantages
ofhighstiffness,lowinertia,andlargepayload
capacity.However,theysuffertheproblemsof
relativelysmallusefulworkspaceanddesign
difficulties.Furthermore,theirdirectkinematicsis
numberofdegreesoffreedomoftheend-effector.
●Themobilityofthemanipulatoriszerowhen
theactuatorsarelocked.
Parallelmechanismsareofinterestforthe
followingreasons:
●Theloadcanbedistributedonthemultiple
linkages.
verydifficulttoanalyze.Therefore,parallel
manipulatorswithlessthansixDoFshave
●Fewactuatorsareneeded.
●Whentheactuators
are
locked,
the
increasingly
attracted
attention
for
industry
manipulatorremainsinposition,whichisan
applications.
Thispaperintroducesparallelmanipulatorsand
theclassificationofparallelmanipulators.Three
typesofnewparallelmanipulatorsareintroduced:
aspatialthree-DoFsparallelmanipulator,atwo-
DoFsparallelmanipulator,andaplanarthree-
DoFsserial-parallelmanipulator.
1 DefinitionofaParallel
Manipulator
Aparallelmanipulatorismadeofanend-effector
withndegreesoffreedomwithafixedbaselinked
togetherbyatleasttwoindependentkinematic
linkages.Actuationtakesplacethroughn-simple
[5]
Thesemechanismshavethefollowing
characteristics:
importantsafetyconcernforcertainapplications.
Parallelmanipulatorsforwhichthenumberof
linkagesisstrictlyequaltothenumberofdegrees
offreedomoftheend-effectorarecalledfully
parallelmanipulators.
2 DegreesofFreedomofa
Mechanism
Thedegreesoffreedomofamechanismarethe
numberofindependentparametersorinputs
neededtocompletelyspecifytheconfigurationof
themechanism.However,ageneralmobility
criterioncannotbeeasilydefinedforclosed-loop
[4][6]
noted.Classicalmobilityformulaecanindeed
neglectsomedegreesoffreedom.Grubler's
[7]
●Atleasttwolinkagessupporttheend-
effector.Eachofthoselinkagescontainsatleast
onesimpleactuator.
maybewrittenas
M=d(n-g-1)+
g
∑f
i
(1)
●Thenumberofactuatorsisthesameasthe
whereMissystemmobility(degreesoffreedom);
actuators.
kinematiclinkages,asHunt
andLerbet
already
formula
isneverthelessgenerallyused,which
i=1
LIUXinjun(刘辛军)etal:
ParallelMechanismswithTwoorThreeDegreesofFreedom
disscrewsystemorder(d=3forplanarand
sphericalmotion,d=6forspatialmotion);nis
numberoflinksincludingtheframe;gisnumber
ofjoints;andfiaredegreesoffreedomassociated
withthei-thjoint.
3 ClassificationofParallel
Manipulators
Thetotalnumberofdegreesoffreedomofarigid
bodycannotexceed6;therefore,thenumberof
107
DoFsofaparallelmanipulatorwillbebetween2
and6.Sincethefirstparallelmechanismdesign,
manymechanicaldesignshavebeenproposedfor
parallelmanipulatorswith2to6DoFs.Asurvey
of87actuatorsproposedintheliteratureshowed
that40%hassixDoFs,3.5%fiveDoFs,6%four
DoFs,40%threeDoFs,andtheremainingtwo
[7]
3.1 Two-DoFsparallelmanipulators
Mostexistingtwo-DoFsparallelmanipulatorsare
planarmanipulatorswithtwo-translationalDoFs.
Suchdesignsuseonlyprismaticandrevolute
joints.McCloy[8]showedthatthereare20
differentcombinations.Thisnumberisreducedto
6asshowninFig.2iftheactuatorsareassumed
tobeattachedtotheground.Thereisnopassive
prismaticjointandnoactuatorissupportingthe
weightofanotheractuator.
Fig.2 Sixtypesoftwo-DoFsparallelmanipulators
3.2 Three-DoFsparallelmanipulators
Therearemanythree-DoFsparallelmanipulators,
soonlytheclassicaldesignswillbepresentedhere.
Oneexampleistheplanarthree-RRR(Rstands
forrevolvingjoint)parallelmanipulatorasshown
inFig.3a.Themovingplatformhasthreeplanar
DoFs,whicharetwotranslationsalongthexand
yaxesandonerotationaroundtheaxis
perpendiculartotheO-xyplane.Anotherexample
isthesphericalthree-RRRparallelmanipulatoras
showninFig.3b,inwhichallthejointaxes
intersectatacommonvertex.Themotionofany
pointinthemechanismisrotationaboutthe
vertex.Themovingplatformhasonlyrotational
[4]
three-RPSparallelmanipulatorshowninFig.3c,
Fig.3 Somethree-DoFsparallelmanipulators
DoFs.
DoFswithrespecttothebase.Hunt
presentedthe
108
TsinghuaScienceandT
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