机械专业文献翻译传感器.docx

机械专业文献翻译传感器.docx

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机械专业文献翻译传感器

Whatisasmartsensor

Oneofthebiggestadvancesinautomationhasbeenthedevelopmentandspreadofsmartsensors.Butwhatexactlyisa"smart"sensor?

Expertsfromsixsensormanufacturersdefinethisterm.

Agoodworking"smartsensor"definitioncomesfromTomGriffiths,productmanager,HoneywellIndustrialMeasurementandControl.Smartsensors,hesays,are"sensorsandinstrumentpackagesthataremicroprocessordrivenandincludefeaturessuchascommunicationcapabilityandon-boarddiagnosticsthatprovideinformationtoamonitoringsystemand/oroperatortoincreaseoperationalefficiencyandreducemaintenancecosts."

Nofailuretocommunicate

"Thebenefitofthesmartsensor,"saysBillBlack,controllersproductmanageratGEFanucAutomation,"isthewealthofinformationthatcanbegatheredfromtheprocesstoreducedowntimeandimprovequality."DavidEdeal,Temposonicsproductmanager,MTSSensors,expandsonthat:

"Thebasicpremiseofdistributedintelligence,"hesays,isthat"completeknowledgeofasystem,subsystem,orcomponent'sstateattherightplaceandtimeenablestheabilitytomake'optimal'processcontroldecisions."

AddsJohnKeating,productmarketingmanagerfortheCheckermachinevisionunitatCognex,"Fora（machinevision）sensortoreallybe'smart,'itshouldnotrequiretheusertounderstandmachinevision."

Asmartsensormustcommunicate."Atthemostbasiclevel,an'intelligent'sensorhastheabilitytocommunicateinformationbeyondthebasicfeedbacksignalsthatarederivedfromitsapplication."saysEdeal.ThiscanbeaHARTsignalsuperimposedonastandard4-20mAprocessoutput,abussystem,orwirelessarrangement.AgrowingfactorinthisareaisIEEE1451,afamilyofsmarttransducerinterfacestandardsintendedtogiveplug-and-playfunctionalitytosensorsfromdifferentmakers.

Diagnose,program

Smartsensorscanself-monitorforanyaspectoftheiroperation,including"photoeyedirty,outoftolerance,orfailedswitch,"saysGEFanuc'sBlack.Addtothis,saysHelgeHornis,intelligentsystemsmanager,Pepperl+Fuchs,"coilmonitoringfunctions,targetoutofrange,ortargettooclose."Itmayalsocompensateforchangesinoperatingconditions."A'smart'sensor,"saysDanArmentrout,strategiccreativedirector,OmronElectronicsLLC,"mustmonitoritselfanditssurroundingsandthenmakeadecisiontocompensateforthechangesautomaticallyoralertsomeoneforneededattention."

Manysmartsensorscanbere-rangedinthefield,offering"settableparametersthatallowuserstosubstituteseveral'standard'sensors,"saysHornis."Forexample,typicallysensorsareorderedtobenormallyopen（NO）ornormallyclosed（NC）.Anintelligentsensorcanbeconfiguredtobeeitheroneofthesekinds."

Intelligentsensorshavenumerousadvantages.Asthecostofembeddedcomputingpowercontinuestodecrease,"smart"deviceswillbeusedinmoreapplications.Internaldiagnosticsalonecanrecovertheinvestmentquicklybyhelpingavoidcostlydowntime.

Sensors:

GettingintoPosition

Asthesayinggoes,'Nomatterwhereyougo,thereyouare.'Still,mostapplicationsrequireabitmoreprecisionandrepeatabilitythanthat,sohere'sadviceonhowtoselectandlocatepositionsensors.

Thearticlecontainsonlineextramaterial.

What'stherightpositionsensorforaparticularapplication?

Itdependsonrequiredprecision,repeatability,speed,budget,connectivity,conditions,andlocation,amongotherfactors.Youcanbetthattakingtherightmeasurementisthefirststeptoclosingthelooponanysuccessfulapplication.

Sensortechnologiesthatcandetectpositionarenearlyasdiverseasapplicationsinprovidingfeedbackformachinecontrolandotheruses.Spatialpossibilitiesarelinear,area,rotational,andthree-dimensional.Insomeapplications,they'reusedincombination.Sensingelementsareequallydiverse.

KenBrey,technicaldirector,DMCInc.,aChicago-basedsystemintegrator,outlinedsomethefollowingposition-sensingoptions.

Thinkdigitally

Fordigitalpositionfeedback:

∙Incrementalencodersaresupportedbyallmotioncontrollers;comeinrotaryandlinearvarietiesandinmanyresolutions;aresimulatedbymanyotherdevices;andrequireahomingprocesstoreferencethemachinetoaphysicalmarker,andwhenpoweristurnedoff.

∙Absoluteencodersarenativelysupportedbyfewermotioncontrollers;canbeusedbyallcontrollersthathavesufficientavailabledigitalinputs;reportacompletepositionwithintheirrange（typicallyonerevolution）;anddonotrequirehoming.

∙Resolversaremoreimmunetohigh-levelnoiseinweldingapplications;comestandardonsomelargermotors;simulateincrementalencoderswhenusedwithappropriateservoamps;andcansimulateabsoluteencoderswithsomeservoamps.

∙Dual-encoderfeedback,generallyunder-used,isnativelysupportedbymostmotioncontrollers;usesoneencoderattachedtothemotorandanotherattacheddirectlytotheload;andisbeneficialwhenthemechanicalconnectionbetweenmotorandloadisflexibleorcanslip.

∙Visionsystems,usedwidelyforinspection,canalsobeusedforpositionfeedback.Suchsystemslocateobjectsinmultipledimensions,typicallyX,Y,androtation;frequentlyfindpartsonaconveyor;andareincreasinginspeedandsimplicity.

Ametalrolling,stamping,andcut-offapplicationprovidesanexampleofdual-encoderfeedbackuse,Breysays.'Itrequiredrapidandaccurateindexingofmaterialthrougharollmillforastampingprocess.Therollmillcreatesaninconsistentamountofmaterialstretchandrollerslip,'Breyexplains.

'Byusingtheencoderontheoutgoingmaterialaspositionfeedbackandthemotorresolverasvelocityfeedbackinadual-loopconfiguration,thesystemwastunedstableandasingleindexmoveprovidedanaccurateindexlength.Itwasmuchfasterandmoreaccuratethanmakingaprimarymove,measuringtheerror,thenhavingtomakeasecondcorrectionmove,'hesays.

Creative,economical

SamHammond,chiefengineer,Innoventor,aSt.Louis,MO-areasystemintegrator,suggeststhattheapplication'spurposeshouldguideselectionofpositionsensors;measurementsandfeedbackdon'thavetobecomplex.'Creativeimplementationscanprovidesimple,economicalsolutions,'hesays.Forinstance,forsequencing,proximitysensorsservewellinmanyinstances.

RecentsensorapplicationsincludetheAGVmentionedinleadimageandthefollowing.

∙Inamachinetoapplythetopsealstoteacontainers,proximityandthrough-beamsensorslocateincomingpackages.NationalInstrumentsvisionsystemimagesareprocessedtofindlocationofabarcodeonapre-appliedlabel,andthengiveappropriatemotorcommandstoachievethedesiredposition（rotation）settingtoapplyoneof125labeltypes.Twotypesofpositionsensorswereused.Onewasasimpleinductiveproximitysensor,usedtomonitormachinestatustoensurevariousmotioncomponentswereintherightpositionformotiontooccur.Thecameraalsoservedasapositionsensor,chosenbecauseofitsmultipurposeuse,featurelocation,andabilitytoreadbarcodes.

∙Aprogressive-diestampingmachineoperatesinclosedloop.Alinearoutputproximitysensorprovidescontrolfeedbackforoptimizingdieoperation;aservomotoradjustsdiepositioninthebendstage.Alinearproximitysensorwasselectedtogiveadimensionalreadoutfromthemetalstampingoperation;dataareusedinaclosed-loopcontrolsystem.

∙Partinspectionusesalaserdistancemeasurementdevicetodeterminesurfaceflatness.Sensormeasuresdeviationinreturnbeams,indicatingdifferentsurfaceattributesto10micronsinsize.Anencoderwouldn'thaveworkedbecausedistancewasmorethanameter.Lasermeasurementwasthetechnologychosenbecauseithadveryhighspatialresolution,didnotrequiresurfacecontact,andhadaveryhighdistanceresolution.

Anautomotivekeyandlockassemblysystemusesaproximitysensorfordetectingacapinthereadyposition.Alaserprofilesensorappliedwitharobotmeasuresthekeyprofile.

Whattouse,where?

Sensormanufacturersagreethatmatchingadvantagesinherenttocertainpositionsensingtechnologiescanhelpvariousapplications.

DavidEdeal,productmarketingmanager,MTSSensorsDiv.,says,forharshfactoryautomationenvironments,'themostsignificantfactorsevenabovespeedandaccuracyincustomer'smindsareproductdurabilityandreliability.Therefore,productswithinherentlynon-contactsensingtechnologies（inductive,magnetostrictive,laser,etc.）haveasignificantadvantageoverthosethatrelyonphysicalcontact（resistive,cableextension,etc.）'

Otherimportantfactors,Edealsays,areproductrangeofuseandapplicationflexibility.'Inotherwords,technologiesthatcanaccommodatesignificantvariationsinstrokerange,environmentalconditions,andcanprovideawiderangeofinterfaceoptionsareofgreatvaluetocustomerswhowouldprefertoavoidsourcingalargevarietyofsensortypes.Alltechnologiesareinherentlylimitedwithrespecttotheserequirements,whichiswhytherearesomanyoptions.'

Edealsuggestthathighercostoffittingsometechnologiestoacertainapplicationcreatesalimitation,suchaswithlinearvariabledifferentialtransformers.'Forexample,LVDTswithstrokelengthslongerthan12inchesarerarebecauseofthelargerproductenvelope（abouttwicethestrokelength）andhighermaterialandmanufacturingcosts.Ontheotherhand,magnetostrictivesensingtechnologyhasalwaysrequiredconditioningelectronics.WiththeadventofmicroelectronicsandtheuseofASICs,wehaveprogressedtoapointwhere,today,awiderangeofprogrammableoutputtypes（suchasanalog