1AUTOMATICSTEERINGSYSTEMFORROTARYSNOWREMOVERSHirofumiHIRASHITA,TakeshiARAI,TadashiYOSHIDAAdvancedTechnologyResearchTeam,PublicWorksResearchInstitute1-6,Minamihara,TsukubaCity,Ibaraki-Pref,Japan,305-8516Tel:+81-298-79-6757Fax:+81-298-79-6732E-mail:hirasitapwri.go.jp,arai0333pwri.go.jp,yoshidapwri.go.jpABSTRACT:IncoldandsnowypartsofJapan,mostsnowisremovedfromroadsbymechanicalsnowremovers,andtodealwithroadsideconditionsandguaranteesafeoperation,thesemachinesarenormallyoperatedbytwopeople:anoperatorandanassistant.Workisinprogresstodevelopautomaticsteeringsystemsforsnowremoversinordertolightentheburdenonsnowremoveroperatingstaffandtoreducefuturelaborrequirements.Thisreportdescribesanautomaticsteeringsystemthatincorporatesthreetechnologies:thelanemarkersystemthathasbeendevelopedinrecentyearsasanITStechnology,RTK-GPStechnology,andGIStechnology.Thissteeringsystemhasbeendevelopedforrotarysnowremovers:thetypeofsnowremoverconsideredtobethemostdifficulttooperate.Thereportalsoevaluatesthethreecontrolmethodsbasedontheresultsofcorroborativetestingdoneusingactualsnowremoversandoutlinesproblemswiththesecontrolsystemsthatmustbeovercometoestablishaworkingsystem.KEYWORDS:Rotarysnowremover,automaticsteering,ITS,lanemarker,GIS,GPS1.INTRODUCTIONIncoldsnowypartsofJapan,snowisremovedfromroadsbymechanicalmeanstoguaranteesmoothwinterroadtraffic.Toguaranteethatmechanicalsnowremovalisperformedappropriatelyaccordingtothestateofsnowaccumulationonroadsurfaces,acarefullyplannedattendancecontrolmethodmustbeestablishedandthemachinerymustbeoperatedcorrectly.Theautomaticsteeringsystemthathasbeendevelopedisintendedforuseonrotarysnowremovers:atypewithanoperatingmethodmorecomplexthanthatofothertypesofsnowremovers.Ithasbeendevelopedtoreducetheburdenonsnowremoveroperatorsandtolowerfuturelaborrequirements.2.BACKGROUNDTOTHEDEVELOPMENTArotarysnowremoverisoperatedbytwopeople:anoperatorwhodrivestheremoverandanassistantwhocontrolstheejectionofthesnow.Theoperatordrivesthemachinealongthecurbontheshoulderoftheroadwhilewatchingoutformanholesorotherleveldifferencesonitssurface.Theassistantejectsthesnowwhileavoidingprivateproperty,homes,andotherareaswheresnowdisposalisforbidden(Photo1).Thegoalistoautomatepartofthevehicleoperatingworknowperformedbytheoperatorstoallowthemtocontrolthesnowejectionnowdonebytheassistants,permittingtheintroductionofone-manoperationinthefuture.Thisreportintroducespositioningtechnologyandcontroltechnologythatformthefoundationoftheautomaticsteeringsystemthathasbeendeveloped,andpresentsanevaluationofthesystembasedontheresultsofcorroborativetestingperformedwithanactualsnowremoveranddescribesproblemstobeovercometocompleteaworkingsystem.Photograph1.InsideofaRotarySnowRemover23.AUTOMATICSTEERINGSYSTEMTheautomaticsteeringsystemthathasbeendevelopedautomatestherotarysnowremoversteeringoperationthatisoneofthetasksoftheoperator.3.1SteeringcontrolofarotarysnowremoverThesteeringmechanismofarotarysnowremoverdiffersfromnormalvehiclesinthatthefrontandbackpartsarelinkedbypinsandarticulatingmechanismsareinstalledsothatthevehiclecanbendatthepins.Thesteeringiscontrolledbytheexactlinearizationmethodandbytimescaletransformationthatareeffectivewaystocontrolthecourseofamovingvehicle1).Thiscontrolmethodisrepresentedbyanequationofmotionsubjecttonon-holonomicconstraintandisbasedonnon-linearcontroltheory.Butasnowremoverslideslaterally,becauseasitremovessnow,itissubjectedtolateralreactionforcefromthesnowembankmentasshownbyPhotograph2.Sidewaysslidingiscontrolledbyusingtheintegratedservosystemdescribedbelowtotreatthisslidingasanexternaldistur-bance.(1)CoursetrackingcontrolFig.1showsamodelofthesnowremoversteeringmechanism.Inthisfigure,thedistancesfromtheconnectingpinofthesnowremovertothefrontwheelsandtotherearwheelsarerepresentedbyL.Whenthesteeringangleisrepresentedby2,thecoursefollowedbythesnowremoverisanarcwithradiusR=L/tan.WhenthecoursetangentdirectionspeedvectoratthecenterpointPofthefrontwheelsisrepresentedbyandthetangentdirectionangleby,theequationofmotionofthepointPcanbewrittenasfollows.cosvx=G6sinvy=G6LvRvtan=G6(1)Ifexactlinearizationandtimescaletransformationaredoneforequation(1)toperformstatusfeedbackcontrol,thequantityofsteeringofthesnowremoverthatis1/2ofthesteeringangleisdefinedbythefollowingequation.()3211costanfftanLy+=(2)Inequation(2),lateralslidingisnotconsidered.Inordertoeliminatethesteady-statedeviationcausedbylateralsliding,iftheintegratedservosystemisused,thequantityofsteeringisrepresentedbythefollowingequation.()GbbGbbGbcGbaGabGabGacGaaGbfGbeGbdGafGaeGad+=Gb3tanffdtcosfcostan210ref331yvyyLt(3)Thesymbolfisthecontrolgain,andbasedonequation(3),f1representsproportionalgain,f2representsderivativegain,andf3representsintegralgain.PIDcontrolwasusedtoconstructthesystem.Figure2.IntegratedServoSystemControlBlockDiagram212vRLLxyXYPFigure1.CoordinateSystem(ModelofaSnowRemover)tan-1f1f2Lcos3tanycmdcosf3vs1yrefSnowremoverPhotograph2.RotarySnowRemoverRemovingSnow33.2PositioningmethodItisnecessarytodetectavehiclespresentpositionandtohaveinformationthatdeterminesthedirectiontosteeritinordertoperformautomaticsteering.Thesystemthathasbeendevelopedisequippedwithtwofunctions:theguidancemethodthatuselanemarkersensorstodetectthevehiclespositionandthesteeringmethodthatusesGPSandGIStodetectthevehiclesposition.3.3LanemarkersensorguidancemethodAlanemarkersensorisabasictechnologyoftheAdvancedCruise-AssistHighwaySystem(AHS)developedforuseaspartoftheIntelligentTransportationSystem(ITS).Thistechnologyincludeslanemarkersburiedatintervalsunderaroadsurfaceandvehiclemountedsensorsthatdetectsignalstransmittedbytheselanemarkerstoguidethevehiclealongthecourseformedbythemarkers.Therearetwoversionsofthissystem:theradiowavemethodandthemagneticmethod.(1)SteeringanglecalculationlogicItisassumedthatthedistancebetweenthelanemarkerswillnotbeconstant,butcanbevariedaccordingtotheshapeoftheroadanddemandsofthesensorside.Therefore,thissystemisequippedwithtworowsofsensorssothatcontrolcanbeperformedevenwhenthelanemarkerinstallationintervalisnotknownuntiltherotarysnowremoverpassesoverthem(Fig.3).Tocontrolsteeringwithasinglerowofsensors(Fig.3ontheleft),thelateraldifferentialandtheazimuthaldifferentialymandmthatarenecessaryforcontrolbythetargetcoursecoordinatesystem(xy)requireinformationabouttheintervalbetweenthemarkersinadditiontothesensorsignalym1thatismeasuredbythefrontvehiclefixedcoordinatesystemf(xfyf).Butwithtworowsofsensors(Fig.3ontheright),thesystemcancalculatethelateraldifferentialandtheazimuthaldifferentialymandmofthetargetcoursecoordinatesystem(xy)byhavingtwoopposedsensorsholdthetwosensorsignalsym1andym2measuredbythefrontvehiclefixedcoordinatesystemf(xfyf)asitpassedamarkeruntiltheypassthenextmarker,sothatsteeringcontrolcanbeperformedeveniftheintervalbetweenmarkerswasunknown.(2)RadiowavemarkersensorpositioningmethodWiththeradiowavemethod,anantennainsidethesensoronthevehicletransmitsa227.5kHsradiowavetowardstheroadandwhenaradiowavemarker(Photo3)receivesthistransmission,itreturnsasignalofdoublefrequencyof455kHz.Areceivingantennainsidethesensorreceivesthisreturnradiowavetodetectthevehiclesposition(Fig.6).Thesystemdetectsthelocationsofthemarkersinthetravelingdirectionbypassingthroughthepeakvalue.Itdetectsthepositioninthelateraldirectionbycalculatingthedistancebetweentheantennasbythetriangulationmethodbasedonthedifferenceinthereceivedstrengthofthereturnradiowavessensedbythetworeceivingantennas2).Photograph3.RadioWaveMarkerPhotograph4.RadioWaveMarkerSensorFigure3.LaneMarkerSensorGuidanceMethodmtan-1（ym1ym2）/Lmymym1Lo（ym1ym2）/LmcosmLm：1.34m、Lo：-1.0mym目標(biāo)軌道No.1No.2ym1ym2LmmLoyfxfmsin-1（ym1ym1b）/2.0ymym1Lo（ym1ym1b）/2.0cosmLo：-1.0mym目標(biāo)軌道No.1ym1ym1b2mmLoyfxfNo.1前回検出値ym目標(biāo)軌道No.1No.2ym1ym2LmmLoyfxf敷設(shè)TargetcourseTargetcourseBuriedmarkerFrontpartofthesnowremoverFrontwheeltiresValuepreviouslydetectedbytheNo.1sensor4(3)MagneticmarkersensorpositioningmethodWiththemagneticmethod,magneticmarkerspermanentferritemagnets(Photo5)undertheroadsurfaceproducemagneticfieldsandamagneticsensorthatdetectsmagneticfielddensityinstalledonthevehicledeterminesthepositionofthevehiclebasedonthestrengthofeachmagneticfield.Themagneticfielddistributionofthemagneticmarkershowstheunimodalitythattreatsthecenterofthemarkerasthemaximummagneticfieldstrength.Themagneticfluxdensitiesoftheverticalcomponent(Bz)andthevehiclewidthdirectioncomponent(Bx)ofthismagneticfieldaredetectedbythemagneticsensorandthelocationofthemarkerisdetectedbycalculatingthedistancebetweenthesensorandthemarkerbasedonthepreviouslystipulatedBx/Bzrelationalequation(Fig.4)3).3.4GPS/GISpositiondetectionmethodAsystembasedonGPS/GISpositioningdetectsthepositionofthevehicletocontrolitsoperationbycomparingrotarysnowremoverpositioncoordinatedatareceivedfromaGPSsatellitewithpositioncoordinatesoflineardatafortheroadprovidedinadvancebyroadGIS.(1)RoadGISRoadGISisadatabaseofinformationconcerningstructuresandtrafficmanagementusedforroadmaintenance.Todevelopthissystem,rotarysnowremovertargetcourseinformationwascreatedsothatitcanbehandledasGISdata.Operatorsofrotarysnowremoversremovesnowtowidenthebareroadbydrivingtheirvehiclesguidedbythesnowremovaledge(Fig.5)Becausethesnowremovaledgeisoftenthecurbofthesidewalkalongthesidesoftheroad,theGISdatathatwasusediscurbdata.(2)RTK-GPSRTK-GPS,asystemcapableofhigh-precisionpositioning(errorradiusbetween2and3cm),consistsoftwoGPSreceivingantennae,oneafixedstation