What exactly is a safety light curtain? | SICK

The simplest function of a light curtain is when light beams are obstructed and the outputs turn off, which signals a stop to the associated ... Home SICKSensorBlog Whatexactlyisasafetylightcurtain? Home SICKSensorBlog Whatexactlyisasafetylightcurtain? Whatexactlyisasafetylightcurtain? Dec8,2020 Thesafetylightcurtainisreliedontoprotectthesafetyoffactorypersonnelallovertheworld.Yet,althoughthetechnologywasdevelopedalmost70yearsago,manyapplicationsmaystillnotbemakingfulluseofitscapabilities.Ihavetriedtore-appraisewhatlightcurtainscouldbecontributingtoyourmachinerysafety,factorycontrol,andproductivitywithabreakdownofthefunctionsandfeaturesthatarecurrentlyavailable.Thelightcurtainhasbecomesoubiquitous,thatitisalltooeasytoregarditasasimpleon/offdevice-afail-safe,fit-and-forgetsubstituteforprotectivefencing.However,anexpandingandversatilerangeoflightcurtainshasevolvedtoperformmultiplefunctionsandtheycancontributepositivelytoproductivityandintegratewithfactorylocalareanetworkstosupportbetterplant-wideautomation. HistoryofthelightcurtainIn1951,ErwinSickpresentedthefirstwoodenmodelofhislightcurtaintothe“GermanInventorandNewDevelopmentTradeFair”inMunich.Laterthesameyearapatentregistrationofthelightcurtainbasedontheautocollimatorprinciplewasregardedasthetechnicalbreakthroughthatbeganthedevelopmentoftechnologyweknowtoday–onethathassavedcountlesspeoplefrominjuryanddeathatthehandsofdangerousmachinery.Sincethattime,hardwareandsoftwaredevelopmenthavetransformedtheversatilityanduseofsafetylightcurtains.Thekeyattributesoflightcurtainsremainthesame,buttheirpotentialmaystillbeunder-exploited. LightcurtainspecificationsTherereallyisnosuchthingasastraightlike-for-likeofftheshelf‘menu’ofsafetylightcurtainssinceallmanufacturersoffertheirownrangesincludingdifferentsizes,shapes,andresolutionsetc.However,thestartingpointofanysafetyapplicationisalwaysthedangeryouwanttoguardagainstandthespacethatitisin.Basedonthis,therearedifferentattributestoconsiderregardingthephysicalpropertiesofthelightcurtain.Currently,thedocumentENISO13855istheharmonizedstandardforpositioningSafetylightbeamsystems,anditcanassistindeterminingwhichofthesephysicalattributestogoforandinthissectionIhavetriedtoexplainthemainspecificationstoconsider.However,therearealsoadditionalpropertiessuchasIPrating,currentconsumption,visibleindicationsetc.thatarenotcoveredhere.ScanningrangeTherangeisthemaximumdistancebetweensenderandreceiver.Incaseofactive/passiveunitsthedistancebetweentheactivepartandthepassivepartiscalledscanningrange,too.Productsareavailablewitheitherafixedrange,aselectablerange(e.g.low/high)ortheyhaveanauto-adjustingrange(atstart-up,thesensitivityisadjustedbasedonthedistancebetweensenderandreceiver).ChoosingthecorrectrangeensuresthattheSafetylightbeamsystemsisbestfitfortheapplication,forexample,ifahighpower,longrange,deviceisusedoverashortdistance,reflectionsoffnearbysurfacesmaymaketheinstallationunsafe.Ontheotherhand,alongrangedevicemayberequiredforprotectinglargeareaswhichrequirehighbeam.ProtectiveFieldHeightTheheightofaSafetylightbeamsystemmustbechosenbasedontheaccesstothehazard.Forexampleifalightcurtainisprotectingagainst"pointprotection"thenthelightcurtainmustcoverthewholeaperture.However,iftheSafetyproductisforaccessprotectionthendifferentheightscanbeusedbasedonthenumberofbeamsrequiredandtheheightfromthefloorpluspossiblereachover. Figure1:Pointandaccessprotection Figure1:Pointandaccessprotection ResolutionTheresolutionofalightcurtaincanalsoaffectthemountingpositionwithrespecttothehazard.Theterms“fingerprotection”and"handprotection"areoftenusedwhichrefertoresolutionsof14mmand30mmrespectively.However,lightcurtainsandmultiplebeamsystemscanalsohavedifferentresolutionsorbeamseparations(e.g.20mm,40mm,200mmetc.).Thehighertheresolution,thenthebetterthedetectioncapabilityisforasafetylightcurtainandthereforethedevicecanbemountedclosertoahazard(i.e.a14mmlightcurtaincanbemountedcloserthana30mmlightcurtain).ENISO13855containslotsofdifferentcalculationsformountingdistancesandresolutioncanhavealargeimpactbutthebasicequationis,figure2: Figure2:Calculationofminimumdistancetohazardouspoint Figure2:Calculationofminimumdistancetohazardouspoint Thestandardalsocoversadditionalthingssuchasdirectionofapproach,possiblereachoveretc.Forlargerdistancesandaccessprotectionabeamseparationof400mmisnormallysufficient,butthenadditionaldevicesmayberequiredforpresencedetectionifthemachinecanberesetwhilstapersonisbehindthelightcurtainormultiplelightbeamsafetydevice.AthoroughriskassessmentaccordingtotheharmonizedstandardENISO12100shouldbeperformedtotakethesepointsintoconsideration.Higherresolutionlightcurtainsareusuallymoreexpensivethanlowerresolutions,butswitchingtoalowerresolutionmeansthatthedistancebetweenthesafetylightcurtainandthehazardneedstobeincreasedwhichmaybeimpracticalornotpossibleonthefactoryfloor.TypeWhenchoosingasafetydeviceforanapplication,theharmonizedstandardENISO13849orIEC62061canbeusedtodesignthesafetyrelatedpartsofthecontrolsystem(SRP/CS).Followingthedefinitionofasafetyfunction(e.g.initiatingastopusingasafetylightcurtain)itisimportanttodeterminewhatperformancelevel(PL)orsafetyintegritylevel(SIL)thattheassociatedSRP/CSshouldachievebasedontherisk.Iwillnotgointodetailaboutfunctionalsafetyherebutforelectrosensitiveprotectiveequipment,theSafetylightbeamsystemsaccordingtoIEC61496isdirectlyrelatedtowhatPL/SILthatthesafetyfunctioncanachieve.Thefollowingfigurereflectstherelationship,figure3. Figure3:RelationshipbetweenESPETypeandPL/SIL Figure3:RelationshipbetweenESPETypeandPL/SIL ThereforeifPLe/SIL3isrequired,forexampleforprotectingpowerpresses,atype4devicewouldberequired.Active/passivesystemsTosaveonwiringandtokeepcostsdownforaccessprotectionapplications,activepassivesystemscanbeused.Anactive/passivesystemconsistsoftwodevices.Onedevicecontainsbothemittingelementsandreceivingelementsandtheotherdevicecontainse.g.mirrorsthatareusedtodeflectthebeamsbacktothereceivers,figure4.Mirrorsreducethestrengthofalightbeamandthereforeactive/passivesystemswillnormallyhaveamuchshorterdistancethansender/receiversystems. Figure4:Active/Passivesystem Figure4:Active/Passivesystem  ESPEFunctionsofSafetylightbeamsystemsThesimplestfunctionofalightcurtainiswhenlightbeamsareobstructedandtheoutputsturnoff,whichsignalsastoptotheassociatedhazardousmovement(s).Ifnoincidenthasoccurredandtheareaissafe,aresetcanbeperformed.Thisstop/startstyleofsafeoperationcanbedisruptivetofactoryflowandproductivityandthereforethelightcurtainhasevolvedoverthelasthalfcenturytoperformmultiplefunctionssuchasinternalreset,externaldevicemonitoring(EDM),beamcoding,muting,blanking,patternrecognitionandbeamcoding.RestartinterlockThetwomaininterlockingmodesthatcanbesetinareautomated–Outputsafetyswitchingdevice(OSSD’s)gohighwhenthebeamsarefree.Manual–OSSD’sgohighwhenthebeamsarefreeandthenaresetbuttonispressed.Itisimportantthatanautomatedrestartcanonlybeusedinspecificcasewhenitisnotpossibletostandbehindthelightcurtainwithoutbeingdetected(e.g.smallpresswitharmonlyaccess),figure5.Furtherrequirementsmayalsoapply. Figure5:Smallpresswithpointprotection Figure5:Smallpresswithpointprotection Amanualresetcanbeperformedusingeitheranexternalsafetyrelay,safetyPLCorinternallyiftheSafetylightbeamsystemshasthecapability.BeforesafetyPLC/Relaystheresetwasperformedusingrelaylogic.EternalDeviceMonitoring(EDM)Thelevelofsafetyperformanceforasafetyfunctioncanbeincreasediffaultdetectionisimplemented.TheharmonizedstandardENISO13849,whichisusedforcalculatingperformancelevelofaSRP/CSdescribesthetermdiagnosticscoverage(DC)whichmeasuredthiscapability.Itisameasureofhowmanydangerousfailuresaredetected.Onemethod,listedinthesestandardsandusedextensivelyinindustry,hasadiagnosticscoverageof99%(candetect99%ofdangerousfailures)andiscalledExternalDeviceMonitoring(EDM)or“checkback.”Thismonitoringfunctionisameansinwhichasafetydeviceactivelymonitorsthestateofexternaldevicesthatitcontrolssuchasmachineprimarycontrolelements(MPCEs),contactors,orrelays.Thisisneededbecausetheexternaldevicesusuallyhavenodiagnosticsoftheirown.Ifanunsafestateisdetectedintheexternaldevicethenthesafetydevicecanlockout.Thisisperformedbymonitoringcomplimentarychannelsoftheexternaldeviceswhicharephysicallylinkedinternally.Iftheoutputsofasafetydevicegohigh,thereturningEDMsignalfromthefinalswitchingdevicesmustgolowifthesystemisinasafecondition.Otherwise,thereisafault.SeeFigure6forexamplesofimplementationinasafetyrelayanddirectlyinasafetylightcurtain. Figure6:TwoexamplesoftheimplementationofEDM Figure6:TwoexamplesoftheimplementationofEDM BlankingInsomeapplications,itmightbedesirabletopermitcertainobjectstoprotrudethroughthelightcurtainfieldwithoutsignalinganobstructionofthedetectionzone.Forexample,whenusingasupporttableorrackrequiredtofeedthemachinewithaheavywork-piece,ablankingfeaturecanbeappliedtomodifythedetectioncapabilityofthelightcurtainandnotinterrupttheworkflow.Theblankingcaneitherbefixedorfloatingtoallowavariablepositionfortheobject.SeeFigure7. Figure7:Exampleoffixedblanking Figure7:Exampleoffixedblanking EnablingMaterialThroughput-MutingInmanyapplicationsofSafetylightbeamsystems,thesafetydevicemustbeabletoallowobjectsthroughwhilststillreactingtopresenceofpeople.Thisisparticularlyimportantonconveyinglineswithgoodspassingfromoneareaofproductiontoanotherorinautomatedwarehousingoperationswherestaffareexcludedfromtheautomatedstackingandshelvingareas.Sensorscanbeusedtoidentifytheobject(suchasacarbody)andallowpassageintoahazardzoneduetotheshapeandsize,whilestilldetectingpresenceofaperson.Thisisautomaticandknownasmuting.Thetwomostpopularmethodsofmutingarecrossbeamandfoursensormuting,asshowninFigure8. Figure8:Crossbeamandfoursensormuting Figure8:Crossbeamandfoursensormuting However,therearemanydifferentmethodsofmutingincludingtheuseofphotocells,groundinductiveloops,theuseofsafetylaserscanners,partialmuting(partialblanking)etc.ThetechnicalspecificationIEC/TS62046canassistintheapplicationofprotectivedevicestodetectpersons.Itisimportanttounderstandthoughthatmutingisnotthesameasbypass-mutingisautomatedwhilstbypassisamodeselectedbyanoperatorwhilstotherprotectionmeasures(e.g.enablingdevice)i.e.manual.Anothertermrelatedtomutingis"override"whichisamanualtriggeringofthemutingafteranerrorinthemutingconditions.Thisisneededtomakeasystemclearforexamplewhenapalletisstuckinasafetylightcurtainwhichhasstoppedtheconveyorandtheconveyortemporarilyneedspowertoremovethepallet.EnablingMaterialThroughput-PatternRecognitionTherearesomesafetylightcurtainsthatcanperformcomplexalgorithmsonindividualbeams.Thismeansthatnotonlycanitdetectifthebeamsareobstructedornot,butalsowhichbeamsandinwhichsequence.Thelightcurtaincansafelydetectpatterns,objects,anddirection,maintainingthesafetywhilestillallowingknownpatternstoenterandleavethedetectionzoneofthelightcurtain.Furthermore,itdoesnotrequireanyadditionalsensorsorcontrol.Thispowerfulfunctioncandramaticallyincreaseavailabilityandincreasesafetywhileatthesametimeasallowingmaterialtopassthrough.TheC4000Fusionisanexampleofsuchadevice.SeeFigure9. Figure9:Objectpatternrecognition Figure9:Objectpatternrecognition BeamcodingBecauseandmultiplebeamsystemsworkoversimilaropticalfrequencyintheInfraRedspectrum,ifseveralsafetylightcurtainsareusedincloseproximityinterferencecanoccurbetweenthesystems.Thiscouldcauseadangeroussituation.Toovercomethissomesafetylightcurtainsofferbeamcodingsothatareceivercandistinguishthebeamsfromaspecificsenderandnotbeaffectedbyanotherdeviceincloseproximity.Whenbeamcodingisactivatedthough,thismayaffecttheresponsetimeand/orrangeofthesafetylightcurtainandshouldbetakenintoaccountasthismayaffectthemountingdistance.  Summary:WhataresafetylightcurtainsandmultiplelightbeamsafetydevicesToday’sSafetydeviceinstallationsaremuchmoreattunedtoproductionneeds,capableofawiderangeofmanualandautomatedactionsthatensureaSafetylightbeamsystemsassistssafetyandproductivityratherthansacrificingefficiency.However,itisimportanttoknowwhatfeaturesandfunctionsareavailableonasafetylightcurtainandalsoiftheapplicationrequiresthemornot?Safetylightbeamsystems.TheapplicationofaSafetyproductisnotalwaysasstraightforwardasstickingitinfrontofanaccesspointandfurtherthoughtmayberequired.  Safetymultibeamsensors Safetymultibeamsensorsareelectro-sensitiveprotectivedeviceswithtwoormorelightbeams.Whenatleastoneofthelightbeamsisinterrupted,aswitch-offsignalisdeliveredtothe... Safetylightcurtains Safetylightcurtainsprovidereliableandcost-effectiveaccessprotectionforhazardouspointsandhazardousareas.Dependingonthevariant,differentmachinefunctionsareintegratedorcan... VIDEO:#40SecondsOfSafety:Alignyoursafetylightcurtainin5simplesteps VIDEO:#40SecondsOfSafety:Alignyoursafetylightcurtainin5simplesteps  Readmore Playingitsafe:SwissdesignengineerschooseSICKsafetysolutions  more Safeandrugged:ExpertsatMAN,HELLERandSICKperfectthedeTecsafetylightcurtain more Quickdiagnosticsviaapp-deTec4safetylightcurtains more SICKSensorBlog SICKSensorBlog Allarticles MartinKidman ProductSpecialistMachinerySafetySICK(UK)Ltd.MartinKidmangainedhisPh.D.attheUniversityofLiverpoolin2010andhasbeeninvolvedinIndustrialAutomationsince2006workingforvariousmanufacturersofsensors.HehasbeenatSICKUKLtd.since2013asaproductspecialistformachinerysafetyprovidingservices,supportandconsultancyforindustrialsafetyapplications.HeisalsoacertifiedFunctionalSafetyEngineer(TUVRheinland,#13017/16). Doyouhaveanyquestions?Contactourexperts Increaseyourproductivity–withsafetysolutionsfromSICK Pleasewaitamoment... Yourrequestisbeingprocessedandmaytakeafewseconds. Loading...