>> P.226
Ⅲ-6PreloadLoadfactorLoadappliedtoalinearmotionrollingguidecanbelargerthantheoreticalloadduetomachinevibrationorshock.Generally,theappliedloadisobtainedbymultiplyingitbytheloadfactorindicatedinTable3.Table3LoadfactorOperatingconditionsfwSmoothoperationfreefromshock1～1.2Normaloperation1.2～1.5Operationwithshockload1.5～3ObjectivesofpreloadInsomecases,thelinearmotionrollingguideisusedwithclearancegiventothelinearmotionrollingguidewhenlightmotionwithsmallloadisrequired.However,forsomeapplicationsitmaybeusedwithplayintheguidingmechanismremovedorwithpreloadtoincreaserigidity.Preloadisappliedtothecontactpartsofaracewayandrollingelementswithinternalstressgeneratedinadvance.Whenaexternalloadisappliedonthepreloadedlinearmotionrollingguide,shockabsorbingwiththisinternalstressmakeselasticdeformationsmaller,anditsrigidityisincreased.(SeeFig.4)PreloadsettingPreloadamountisdeterminedbyconsideringthecharacteristicsofthemachinesorequipmentsonwhichthelinearmotionrollingguideismountedandthenatureofloadactingonthelinearmotionrollingguide.Thestandardamountofpreloadforlinearmotionrollingguidesis,ingeneral,approx.1/3ofloadwhentherollingelementsareballs(steelballs)andapprox.1/2ofloadwhentheyarerollers(cylindricalrollers).Ifthelinearmotionrollingguidesarerequiredtohaveveryhighrigiditytowithstandvibrationorfluctuatingload,alargerpreloadmaybeapplied.PrecautionforpreloadselectionEvenwhenhighrigiditymustberequired,excessivepreloadshouldbeavoided,becauseitwillproduceanexcessivestressbetweenrollingelementsandraceways,andeventuallyresultinshortlifeoflinearmotionrollingguides.Itisimportanttoapplyaproperamountofpreload,consideringtheoperationalconditions.Whenusingwithalargepreload,contactIKO.LinearBushingandStrokeRotaryBushingshouldneverbegivenalargeamountofpreload.Table4StaticsafetyfactorSeriesOperationalconditionandstaticsafetyfactorOperationwithvibrationand/orshockHighoperatingperformanceNormaloperatingconditionsCrossedRollerWay4～63～52.5～3LinearSlideUnit3～52～41～3LinearBallSpline5～74～63～5LinearBushing2.521.5StrokeRotaryBushing2.521.5RollerWay&FlatRollerCage4～63～52.5～3Ball(withoutpreload)Roller(withoutpreload)Roller(withpreload)Ball(withpreload)201510500100020003000LoadNElasticdeformationmBalldiameter10mmPreloadload:0.05×C0equivalentDiameterandlengthofroller10mm×10mmFigure4PreloadandelasticdeformationbehaviorStaticsafetyfactorGenerally,basicstaticloadratingandstaticmomentrating(orstatictorquerating)isconsideredasloadattheallowablelimitfornormalrollingmotion.However,staticsafetyfactormustbeconsideredaccordingtooperatingconditionsandrequiredperformanceofthelinearmotionrollingguide.StaticsafetyfactorcanbeobtainedbythefollowingequationandtypicalvaluesareindicatedinTable4.Equation(4)isarepresentativeequationformomentloadortorque.Staticmomentratingandmaximummomentloadineachdirectionisappliedforthecalculation.fS=C0―P0(3)fS=T0―M0(4)where,fS:StaticsafetyfactorC0:Basicstaticloadrating,NP0:taticequivalentload,N(Orappliedload(maximumload))T0:taticmomentrating,N・m(Orstatictorquerating)M0:omentloadortorqueineachdirection,N・m(Maximummomentloadormaximumtorque)
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