汽车英文文献.docx

汽车英文文献.docx

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汽车英文文献

Ahighspeedtri-visionsystemforautomotiveapplications

MarcAnthonyAzzopardi&IvanGrech&JacquesLeconte

Abstract

PurposeCamerasareexcellentwaysofnon-invasivelymonitoringtheinteriorandexteriorofvehicles.Inparticular,highspeedstereovisionandmultivisionsystemsareimportantfortransportapplicationssuchasdrivereyetrackingorcollisionavoidance.Thispaperaddressesthesynchronisationproblemwhichariseswhenmultivisioncamerasystemsareusedtocapturethehighspeedmotioncommoninsuchapplications.MethodsAnexperimental,high-speedtri-visioncamerasystemintendedforreal-timedrivereye-blinkandsaccademeasurementwasdesigned,developed,implementedandtestedusingprototype,ultra-highdynamicrange,automotive-gradeimagesensorsspecificallydevelopedbyE2V（formerlyAtmel）GrenobleSAaspartoftheEuropeanFP6project-SENSATION（advaneedsensordevelopmentforattentionstress,vigilanceandsleep/wakefulnessmonitoring）.ResultsThedevelopedsystemcansustainframeratesof59.8Hzatthefullstereovisionresolutionof1280480butthiscanreach750Hzwhena10kpixelRegionofInterest（ROI）isused,withamaximumglobalshuttespeedof1/48000sandashutterefficiencyof99.7%.ThedatacanbereliablytransmitteduncompressedoverstandardcopperCamera-Link?

cablesover5metres.Thesynchronisationerrorbetweentheleftandrightstereoimagesislessthan100psandthishasbeenverifiedbothelectricallyandoptically.Synchronisationisauto-maticallyestablishedatboot-upandmaintainedduringresolutionchanges.Athirdcamerainthesetcanbeconfiguredindependently.Thedynamicrangeofthe10bitsensorsexceeds123dBwithaspectralsensitivityextendingwellintotheinfra-redrange.ConclusionThesystemwassubjectedtoacomprehensivetestingprotocol,whichconfirmsthatthesalientrequire-mentsforthedrivermonitoringapplicationareadequatelymetandinsomerespects,exceeded.Thesynchronizationtechniquepresentedmayalsobenefitseveralotherauto-motivestereovisionapplicationsincludingnearandfar-fieldobstacledetectionandcollisionavoidance,roadconditionmonitoringandothers.

KeywordsSynchronisation.High-speedautomotivemultivision.Activesafety.Drivermonitoring.Sensors

1Introduction

Overthecomingyears,oneoftheareasofgreatestresearchanddevelopmentpotentialwillbethatofautomotivesensorsystemsandtelematics1[,2].Inparticular,thereisasteeplygrowinginterestintheutilisationofmultiplecameraswithinvehiclestoaugmentvehicleHuman-MachineInterfacing（HMI）forsafety,comfortandsecurity.

Forexternalmonitoringapplications,camerasareemergingasviablealternativestosystemssuchRadio,SoundandLight/LaserDetectionandRanging（RADAR,SODAR,LADAR/LIDAR）.Thelatteraretypicallyrathercostlyandeitherhavepoorlateralresolutionorrequiremechanicalmovingparts.

Forvehiclecabinapplications,camerasoutshineothertechniqueswiththeirabilitytocollectlargeamountsofinformationinahighlyunobtrusiveway.Moreover,camerascanbeusedtosatisfyseveralapplicationsatoncebyre-processingthesamevisiondatainmultipleways,therebyreducingthetotalnumberofsensorsrequiredtoachieveequivalentfunctionality.However,automotivevisionstillfacesseveralopenchallengesintermsofoptoelectronic-performance,size,reliability,powercon-sumption,sensitivity,multi-camerasynchronisation,inter-facingandcost.

Inthispaper,severaloftheseproblemsareaddressed.Asanexample,driverheadlocalisation,pointofgazedetectionandeyeblinkratemeasurementisconsideredforwhichthedesignofadash-board-mountableautomotivestereovisioncamerasystemispresented.ThiswasdevelopedaspartofalargeFP6IntegratedProject-SENSATION（AdvancedSensorDevelopmentforAttention,Stress,VigilanceandSleep/WakefulnessMonitoring）.Theoverarchinggoalofextendabletomultivisionsystems5-8].

Thecamerasystemisbuiltaroundamatchedsetofprototype,ultra-highdynamicrange,automotive-grade,imagesensorsspecificallydevelopedandfabricatedbyE2VGrenobleSAforthisapplication.Thesensorwhichisanoveltyinitsownright,istheAT76C410ABACMOSmonochromeautomotiveimagesensor.Thissensorimple-mentsaglobalshuttertoallowdistortion-freecaptureoffastmotion.Italsoincorporatesanon-chipMulti-ROIfeaturewithuptoeightRegionsOfInterest（ROI）withpre-programmingfacilityandallowsfastswitchingfromoneimagetoanother.Inthisway,severalreal-timeparallelimagingprocessingtaskscanbecarriedoutwithonesensor.EachROIisindependentlyprogrammableon-the-flywithrespecttointegrationtime,gain,sub-sampling/binning,position,widthandheight.

Afairlycomprehensiveseriesof“benchtestswe”reconductedinordertotestthevalidityofthenewconceptsandtoinitiallyverifythereliabilityofthesystemacrossvarioustypicalautomotiveoperatingconditions.Additionalrigoroustestingwouldofcoursebeneededtoguaranteeameantimebeforefailure（MTBF）andtodemonstratetheefficacyoftheproposeddesigntechniquesoverstatisticallysignificantproductionquantities.

2Applicationbackground

Thesetofconceivableautomotivecameraapplicationsisanever-growinglistwithsomemarketresearchreportsclaimingover10cameraswillberequiredpervehicle[9].Theincompletelistincludesoccupantdetection,occupantclassification,driverrecognition,drivervigilanceanddrowsinessmonitoring[10],roadsurfaceconditionmoni-toring,intersectionassistance[11],lane-departurewarning[12],blindspotwarning,surroundview,collisionwarning,mitigationoravoidance,headlampcontrol,accidentrecord-ing,vehiclesecurity,parkingassistance,trafficsigndetection[13],adaptivecruisecontrolandnight/syntheticvision（Fig.1）.

2.1Costconsiderations

Theautomotivesectorisaverycost-sensitiveoneandthemonetarycostpersubsystemremainsanoutstandingissuewhichcouldverywellbethebiggesthurdleinthewayoffulldeploymentofautomotivevision.Thesupply-chainindustryhasbeenactivelyaddressingthecostdilemmabyintroducingFieldProgrammableGateArray（FPGA）visionprocessingandbymovingtowardsinexpensiveimagesensorsbasedonComplementaryMetalOxideSemiconductor（CMOS）technology[14].Muchhasbeenborrowedfromotherverylargeembeddedvisionmarketswhicharealsohighlycost-sensitive:

Thesearemobiletelephonyandportablecomputing.However,automotivevisionpushesthebarsubstantiallyhigherintermsofperformancerequirements.Themuchwiderdynamicrange,higherspeed,globalshuttering,andexcellentinfra-redsensitivityarejustafewofthecharacteristicsthatsetmostautomotivevisionapplicationsapart.Thisaddedcomplex-ityincreasescost.However,astheproductionvolumepicksup,unitcostisexpectedtodropquitedramaticallybyleveragingontheexcellenteconomiesofscaleaffordedbytheCMOSmanufacturingprocess.

Somegroupshavebeenactivelydevelopingandpro-motingwaysofreducingthenumberofcamerasrequiredpervehicle.Someofthesemethodstrytocombinedisparateapplicationstore-usethesamecameras.Othertechniques（andproducts）haveemergedthattrade-offsomeaccuracyandreliabilitytoenabletheuseofmonocularvisioninscenarioswhichtraditionallyrequiredtwoormorecameras10,15,16].Distaneeestimationfor3Dobstaclelocalisationisonesuchexample.Suchtacticswillservewelltocontaincostintheinterim.However,itisexpectedthatthecostoftheimagingdeviceswilleventuallydroptoalevelwhereitwillnoIongerbethedeterminingfactorintheoverallcostofautomotivevisionsystems.Atthispoint,wearguethat

Fig.1Someautomotivevisionapplications

reliability,performaneeandaccuracyconsid-erationswillagainreachtheforefront.

Inthispaperthecostissueisaddressed,butinadifferentway.Ratherthandiscardingstereo-andmulti-visionaltogether,alow-cost（butstillhigh-performanee）techniqueforsynchronouslycombiningmultiplecamerasispre-sented.Cablingrequirementsarelikewiseshared,resultinginareductioninthecorrespondingcostandcableharnessweightsavings.

2.2Theroleofhighspeedvision

Anumberofautomotivevisionapplicationsrequirehighframe-ratevideocapture.Externalapplicationsinvolvinghighrelativemotionsuchastrafficsign,oncomingtrafficorobstacledetectionareobviouscandidates.Theneedforhighspeedvisionisperhapslessobviousintheinteriorofavehicle.However,somedrivermonitoringapplicationscangetquitedemandinginthisrespect.Eye-blinkandsaccademeasurement,forinstanee,isoneofthetechniquesthatmaybeemployedtomeasureadriver'sstateofvigilaneeandtodetecttheons[et0?

f16]eepsohappensthatthesearealsosomeofthefastestofallhumanmotionandaccuraterateofchangemeasurementsmayrequireframeratesrunninguptoseveralhundredhertz.Otherapplica-tionssuchasoccupantdetectionandclassificationcanbeaccommodatedwithmuchlowerframeratesbutthenthesamecamerasmayoccasionallyberequiredtocapturehighspeedmotionforvisual-servoingsuchaswhenmodulatingairbagreleaseorseatbelttensioningduringacrashsituation.

2.3Acontinuedcaseforstereovision/multivision

Severaloftheapplicationsmentioned,standtobenefitfromtheuseofstereovisionormultivisionsetsofcamerasoperatingintandem.Thismaybenecessarytoextendthefieldofviewortoincreasediversityandruggednessandalsotoallowaccuratestereoscopicdepthestimation1[1].Then,ofcourse,multivisionisindeedoneofthe