文献翻译一种新型并联机床的尺寸公差分配Word格式.docx

文献翻译一种新型并联机床的尺寸公差分配Word格式.docx

《文献翻译一种新型并联机床的尺寸公差分配Word格式.docx》由会员分享，可在线阅读，更多相关《文献翻译一种新型并联机床的尺寸公差分配Word格式.docx（8页珍藏版）》请在冰豆网上搜索。

Theprototypeofanewtypeofparallelmachinetoolsisa6-6Stewartplatformmechanism.Comparedtothetraditionalmachinetool,aparallelmachinetoolpossessesmanyadvantages,suchashighprecision,highstructuralrigidityandhighmachiningforce/torquecapacity,etc.Currently,manyuniversitieshaveresearchonthiskindofmachinetools.AsshowninFig.1,theparallelmachinetoolcomprisesthefollowingfourparts:

afixedplatform,sixin-parallelactuators,thelengthvariationofeachactuatorisimplementedbyball-screwsandtheball-screwsaredrivenbyservomotors.Theballjointsconnectthefixedandmovingplatformswithball-screws;

aspindleisinstalledonmovingplatformbottom.Whenmachiningworkisbeingcarriedoutthevariationofthemovingplatformallowsaparallelmachinetooltomachinecomplicatedcurvedworkpiecesuchasdie,impelleretc.

ThedevelopingtendencyofmodernNCmachinetoolsishighspeedandhighprecision,andthemachinetoolerrorshavedirecteffectonmachinetoolprecision.Inordertomeettheprecisionspecified,ascientificdimensionaltoleranceallocationisurgentlyrequiredinthedesignofthiskindofmachinetool.Theerrorsofthemachinetoolincludethefollowingparts:

1）transmissionerrorintransmissionchains,i.e.,pitchcumulativeerroroftheball-screwineachactuatoranddeaddomainerrorduringstartingorreversingoperation;

2）lengthtransformerroroftheball-screwduetotheinfluenceofambienttemperature;

3）paresclearanceerrorthatconnectfixedandmovingplatform;

4）othererrors,i.e.,positioningerrorcausedbytransmissionrigidity,dynamicerrorcausedbymovingpartsmassandvelocitydamping.Theaboveerrorswillfinallyleadtoerroratthecutterheadofthemachinetool.Thispaperwillcarryoutresearchondimensionaltoleranceallocationbasedonakindofstatisticalexperimentmethod,Monte-Carlomethod.

2SOLUTIONOFINVERSEKINEMATICSFORMACHINETOOL

Thekinematicssolutionforthisparallelmachinetoolcanbeclassifiedintotwotypes.Whentheknownquantityisthelengthsofthesixactuatorsandtheorientationofthecutterhead,thisiscalleddirectkinematics;

Onthecontrary,whentheknownquantityisthepositionandtheorientationofthecutterheadandtheunknownquantityisthelengthsofthesixactuators,thisiscalledinversekinematics.Thesolutionofthedirectkinematicsofthemachinetoolisusedtomonitorwhilethesolutionoftheinversekinematicsofthemachinetoolisusedtocontrol.AsshowninFig.2,afixedcoordinateframeO-XYZisattachedtothefixedplatformandamovingcoordinateframeO’-X’Y’Z’isattachedtothemovingplatform.Thecenterofthejointconnectingtheitchactuatortothefixedplatformwillbedenotedas

whereasthecenterofthejointconnectingthesamelegtothemovingplatformwillbedenotedas

theY-axisofthefixedcoordinateframeisselectedalongthelinewhichbisectstheangle

andtheY’-axisofthemovingcoordinateframeisselectedalongthelinewhichbisectstheangle

.LetthepositionofpointO’withrespecttotheoriginofthefixedcoordinateframebedenotedbyvector

vectors

willbedefinedasthepositionvectorsofthemovingcoordinateframe,thuswecanwritethepositionvectorsofthemovingplatformjointsinfixedcoordinateframeas:

Wherematrix

istherotationmatrixdescribingtheorientationofthemovingplatformwithrespecttothefixedplatform,theelementsofmatrix

areshownbyRPYexpression.Let

beanglesthatthemovingplatformrotatesaboutX-axis,Y-axis,Z-axisofthefixedcoordinateframe,andthenwecanobtain:

Letvectors

bethepositionvectorsoftheplatformjointswithrespecttothefixedcoordinateframe,thenthelengthofeachactuatorcanbewrittenas:

3DIMENSIONALTOLERANCEALLOCATIONSWITHMONTE-CARLOMETHOD

2.1DeterminationofTotalDimensionalChainErroroftheMachineToolLinks

Inordertocarryoutdimensiontoleranceallocation,thevariationfeaturebetweentheerrorsofthein-parallellinksandorientationerrorofthecutterhead（orthecenterpointofthemovingplatform）needtoknow.Thedirectkinematicsisusedtoderivethecutterheaderrorfromthelinkerrorsofthemachinetool.Itisdifficulttoobtainanalyticalsolutionbydirectkinematics.Soaninverseerrorestimationmethodbywhichthelinkerrorscanbederivedfromthepositionandorientationerrorsofthecutterheadisadopted.

Thekeytothedimensionaltoleranceallocationistodeterminethetotaldimensionalchainerrorofthemachinetoollinks.Monte-Carlomethodisanumeralmethodtosolvemathematicsbasedonrandomsampling.Inthisparallelanevenly-distributedMonte-Carlorandomsimulationmethodon