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Contents

BasicsofMechanicalDesign2

（机械设计基础）2

AGuidetotheSelectionofLinearActuatorsforpositioningsystems（高小飞）2

Howtogetbettermotionwithplasticparts（王佳鹏）4

Hydraulicdrivescleanerair（杨海迎）7

Suppressioncircuitsforclutchesandbrakes（李慎龙）10

GettingENERGYSAVINGSfrompneumaticsystems（赵春）11

MechanicalManufacture&

Automation15

（机械制造与自动化）15

Whathappenswhenautomationsystemsfail?

（赵方英）15

Teamdevelopsrobotsystemstoremoveaircraftcoatings（赵方英）16

Machineinsertsdifferent-sizedpinsinthesameassembly（李臣光）17

WorldwideCNCMarketReturnsBig（李臣光）18

EasierMachineVision（李臣光）18

Mechatronics（机电一体化）20

Howtoavoidelectricalhazardswithairlogic（钟雨锋）20

What’supwithmodel-basedengineering?

（许博）22

Researcherslooktosimplifydynamicsystemsdesign（许博）23

Metal-facedinductivesensorsfordurability（张应志）24

Aerospace、MarineTech&

Application24

（海空技术与应用）24

Boeingcompletes737MAXconceptdevelopmentphase（张应志）25

Softwarecouldenablechangesearlyinaircraftdesignprocess（李帅）25

RockwellAutomationtosupplyPACsanddrivestoUSNavy（李帅）26

BasicsofMechanicalDesign

（机械设计基础）

AGuidetotheSelectionofLinearActuatorsforpositioningsystems（高小飞）

Specifyinglinearmotionsystemsisn’ttheblackartmanyengineersthinkitis.Thisarticleprovidessomeusefultipsandguidanceforengineersonhowtoselectthemostsuitablelinearactuatorsforsingleandmulti-axispositioningsystems.

Manyengineersarestillnotconfidentwhenitcomestoselectingsuitablelinearmotionsystemsforanapplication.Someengineersavoidlinearmotionsystemsaltogetherandreverttotheirtraditionalcomfortzoneofspecifyingrotaryalternatives,evenifthatmeansover-engineeringasolution.Inrealitythough,specifyinglinearmotionsystemsisnotthe‘blackart’thatmanyengineersthinkitis.

Onmostoccasions,ifengineersjustpickupthephoneanddiscusstheirapplicationwithalinearsystemssupplier,potentialissuescanusuallyberesolvedandasuitablesolutionfound.Bytalkingthroughtheirconcernswithanexperiencedlinearapplicationengineer,companiescanoftensavethemselvesalotofwasteddesigneffortorpreventthesystemfrombeingtoocostly（i.e.over-engineered）.Thesuppliercanalsoinformthecustomerexactlywhatisandwhatisn’tpossibleintermsoflinearmotionsystemsandcanprovidevaluableadviceandguidanceonintegrateddrives,mountingarrangementsandfixings.

Inselectinglinearactuatorsforsingleandmulti-axishandling&

positioningsystems,terminologycanbeconfusing.Manyengineerscommonlyrefertolinearactuatorsas‘linearmodules’,‘drivenlinearsystems’or‘linearX-Ytables’.Thesetypesofsystems,whichwewillrefertoaslinearmodules,normallyincorporateanumberofdifferentlineardrivesandactuators,includingbelt-drivenlinearactuators,ballscrew-drivenlinearactuators,lineartablesandlinearmotors.

Thefactorsbelowneedcarefulconsiderationwhenselectingasuitablelinearmoduleforasingle-axis,two-axisorthree-axispositioningsystem:

SystemConfiguration

Systemconfiguration,includingthenumberofaxesofmotion,isoftenthefirstfactorthatneedscarefulthought.Themostcommonaretwo-axis（X-Y）configurations,butlesscomplexsingle-axisapplicationsandthree-axisconfigurationsarealsopossible.

Orientation&

Mounting

Systemorientationandmountingarealsokeyfactors.Inasingleaxislinearsystem,thisisfairlystraightforward,butinmultipleaxissystems,thisbecomesmorecomplex.Factorstoconsiderhereincludethedirectionoftravelofeachaxis.Doestheloadneedtobemovedsimultaneouslyinmultipleaxesordoeseachaxismoveindividually?

Doesthesystemrequireamovingcarriage（standard）oramovingrail?

Aretheaxesvertical,horizontalorinclined?

Arethemountingpositionsofeachactuatorat0,90or180degreestothehorizontal?

Otherfactorstoconsiderincludethespacingbetweensupportpointsinthesystem,aswellashowrigidandflatthesupportingsurfaceisfortheentirelinearpositioningsystem.

Mass&

CentreofGravity

Themass（andgeometry）oftheobjecttobemovedandthepositionofitscentreofgravityasitmovesrelativetoacoordinateordatumpointoneachaxismustalsobecalculated.Clearly,asamassisacceleratedordeceleratedalongmultipleaxesoftravel,thepositionofitscentreofgravityrelativetoeachaxiswillchange.Thisneedscarefulconsiderationsothatthemomentloadsatmultiplepointsinthesystemcanbeestablished.Often,calculatingthebestandworst-casescenarios（usingdesigncalculationsoftwaresuchasSchaeffler’sLinearEasySolution）andthenaveragingtheseissufficientformostapplications.

Otherquestionshereincludewhethersufficientloadcarryingcapacity（includingstaticsafetyfactors）hasbeenallowedinthesystemtocaterforinstantaneousmomentloads?

Also,arethereareanyoverhungloadsinthesystem,includingdrives,electricmotorsormotorisedgearboxes?

StrokeLengths

The‘effective’and‘total’strokelengthforeachaxisisalsocritical.Withballscrewdrivenlinearactuators,forexample,thestrokelengthislimitedtothelengthoftheballscrewitself.Therefore,maximumstrokelengthstendtobearound3metres.Butwithbelt-drivensystems,therearenosuchrestrictionsandsostrokelengthscanbehigherthanthis,uptoasmuchas20metresifrequired.Iflinearmotorsarespecified,intheory,strokelengthisunlimited,butinreality,lengthsabove10metresarerare.

Accuracy&

Repeatability

Dependingontheapplication,accuracyandrepeatabilitywilldiffergreatlybetweenapplications.Mostcustomersknowwhattheiraccuracyrequirementsarewhentheycontactus.Forexample,iftheactuatorisforanautomatedpick-and-placemachine,thenitislikelythathighrepeatabilityandaccuracyarerequired.Typically,theaccuracyofaballscrew-drivenlinearactuatoris0.16mmpermetrewithrepeatabilityof+/-0.01mm.Forbelt-drivenactuators,typicalaccuracyisaround0.5mmpermetre,withrepeatabilityof+/-0.10mm.

TraverseSpeeds&

Accelerations

Thelimitingfactorsfortraversespeedsandtraversetimesaretheballscrewsand/orthebearings.Typically,withballscrew-drivenactuators,maximumspeedsof3m/sarepossible.Forbelt-drivenactuatorswithtrackrollerguidancesystems,themaximumspeedisaround8-9m/s.Ifrecirculatinglinearbearingsareusedwithbelt-drivenactuators,maximumspeedsaresimilartotheirballscrewequivalents（i.e.3m/s）.

Accelerationitselfisnotnormallythedefiningissueinmulti-axispositioningsystems.Itistheloadsduetotheseaccelerationsinthesystemthatarecritical.Thehighestaccelerationofanylinearactuatortodateisaround40m/s2,althoughtypicallyaccelerationsaremorelikelytobemuchlessthanthis,oftenbetween0.5m/s2and5m/s2.Decelerationisalsoimportant,particularlyifthereareemergencystopsrequiredinthesystem.

Cycletimerequirements

Cycletimesdictatethelifeofalinearsystem.Forexample,apositioningsystemsuchasatoolchangeronamachinetoolmightchangethetoolfivetimesperhour.Howisthiscycletimegoingtovaryfromday-to-dayandhowwillthisaffectthefatiguelifeofthelinearcomponentswithinthesystem?

Ifthecustomerneedsthesystemtolastforaminimumof10years,changingthetoolfivetimeseveryhourmaynotbeanissue.Butifthetoolischanged10timesperhour,adifferenttypeoflinearsystemmayberequiredinordertoguaranteea10-yearoperatinglife.

ExternalLoads&

Forces

Thisincludesexternalimpactforcesonthesystemsuchasstopsorhumaninterventions.Issomethingpushingorpullingontheloadtobemovedordoestheloadtobebroughtquicklytoastopattheendofitstravel?

Forexample,adrivemaybringthelinearactuatortoastopora‘home’datumposition.Howthisisachievedandhowthisaffectstheloadsonthemasstobemovedarekeyconsiderations.Asafetystrokefactormayalsoberequiredhere.

EnvironmentalFactors

Environmentalfactorssuchastemperature,humidityandcontamination（i.e.dust,oil,water,washdowns,chemicalsandcoolants,etc.）willalsoaffectthechoiceoflinearsystem.Adustyworkingenvironmentmayrequirethecustomertoimplementexternalbellowsordustextractiondevicesforthelinearsystem.Linearactuatorscanbeprotectedfromtheenvironmentbyincorporatingspecialseals,corrosion-resistantmaterialsandcoatings,specialgreasesorbyusingplasticpartswherenecessary.

Inmedicalapplications,theoverallnoiseofthesystemmaybeafactorthatneedsaddressing.Alowerspeedlinearactuatormaybethesolutionhere,butifhighspeedsneedtobemaintained,specialcomponents,materialsorcoatingsmayneedtobespecifiedinordertominimisenoiselevels.

ElectricalConsiderations

Formulti-axispositioningsystems,drivesandotherelectricalsystemsareoftencomplexandthereforerequirecarefulconsideration.Amulti-axislinearmoduleislikelytoincorporateelectricmotors,controllers,geareddrives,cables,grippers,limitswitches,encoders,brakesandothercontroldevices.

Howtogetbettermotionwithplasticparts（王佳鹏）

Polymerbearingsurfacesresistwear,don’tneedmaintenance,andcanrunsurprisinglyfast.

Engineersmightonlyglanceatthedimensionsandloadcapacitiesofrollerandcamfollowerstoensuretheywillfitintheirdesignbeforeplacinganorder.Buttheyshouldpaycloserattentionbecausethesecomponentscanmakeorbreaktheperfor