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SICE-ICASEInternationalJointConference2006Oct.18-21,2006inBexco,Busan,KoreaImprovedDesignandControlExperimentsofanUnderwaterElectricManipulatorQifengZhang2,AiqunZhang,KuichenYanShenyangInstituteofAutomation,ChineseAcademyofSciences,Shenyang,China2GraduateSchooloftheChineseAcademyofSciences,Beijing,China(Tel:+86-024-23970731;E-mail:zqfW,,)Abstract:Autonomous/Semi-autonomousworkingunderwatervehicleisadevelopmenttrendofunderwatervehicles.Thispaperbrieflyanalyzestherequirementsofunderwaterelectricmanipulatortobeequippedonautonomousunderwatervehicles,anddesignsathree-functionunderwaterelectricmanipulatortest-bed.Thetest-bedhasthecharacteristicsofcompactconfiguration,completefunctionandwithbigmomentoutput.Butexteriorcablelayoutincreasesthepossibilitytoarisemalfunctionespeciallywhenthemanipulatorworkinginwater.Animproveddesignofthemanipulatorwithinnercablelayoutisalsopresentedinthispaper.Basedonthefrequencycharacteristicsoftherotaryjointdrivenmodule,thePIcorrectionisdesignedtocontroltheshoulderandelbowjointsangularrate.ThentheangleerrorisregardedastheinputofangularratecontrolloopafteraPIDController,andaNon-regressorAdaptiveController,whichhasbeenwidelyadoptedasaneffectivemeansinunderwatervehiclecontrol,isalsousedtocontrolthemanipulatorasaselectivemethod.ExperimentresultsdemonstratethegoodeffectofthePIDandtheadaptivecontrollersincontrollingjointangle,andwiththeinnercontrolloop,theNon-regressorAdaptiveControllerismorerobustthanthatwithoutinner-loop,anditisamoreappropriatecontrollerthanPIDcontrollerespeciallyinprotectingthemanipulatorsmotorsfromsaturatedvoltage.Keywords:underwaterelectricmanipulator;autonomousunderwatervehicles;adaptivecontroller.1.INTRODUCTIONInrecentyears,underwatervehiclesbecomeanincreasinginterestofresearchcommunityandindustry.Today,itiscommontousemannedunderwatervehiclestoaccomplishmissionsatseabottom,butitisofenormouscostandriskinsuchadangerousenvironment.Scientistswishtoperformunderwatermissionsinacompletelyautonomousway,sooneresearchfocusofthisfieldisontheautonomous/semi-autonomousunderwatervehicle-manipulatorsystem.Becauseofenergy,powerandefficiency,underwaterelectricmanipulatorisabsolutelyanecessityforautonomous/semi-autonomousunderwatervehicle-manipulatorsystem.Thedesignofunderwaterelectricmanipulatorandcoordinatedcontrolbetweenitandvehicleareimportantjobbeingdonebyseveralinstitutes.Forexample,theinteractionbetweenaone-linkmanipulatorandOTTERAUVisstudiedinStanforduniversityfrom19951,SAUVIMP2,asemi-autonomousvehiclewitha7-DOFelectricmanipulatorisunderdevelopmentattheAutonomousSystemLaboratoryofUniversityofHawaii,asemi-autonomousunderwatervehicleforevaluationofmanipulatortechnologyhasbeendevelopedinKoreaOceanResearchandDevelopmentInstitute3,andanunderwaterelectricmanipulatordrivenbymagnetcouplingtobeequippedforTwin-BurgerAUVhasbeendesignedbyKyushuInstituteofTechnologywithotherInstitutes4.Asacomponentofautonomous/semi-autonomousunderwatervehicle-manipulatorsystem,mediumandsmall-sizedunderwaterelectricmanipulatorismuchmoredexterousandeasytoproducethanhydraulicmanipulator,sousingunderwaterelectricmanipulatortoexploitoceanismuchmorepromising.Thethree-functionunderwaterelectricmanipulator89-950038-5-598560/06/$10C2006ICASEtest-beddesignedinthispaperistobeequippedwithaSmallAutonomous-RemotelyOperatedVehicle(SARV),whichisatest-beddesignedbyShenyangInstituteofAutomation,theChineseAcademyofSciences.ItisavehicleforevaluationofbothAUVandROVtechnologies.Lightworkinginscientificapplicationwithfiber,visionandmanipulatormoduleisoneoftheimportanttechnologiestobestudied.Inthispaper,wefirstgivethedesignofthemanipulatortest-bed,animproveddesignoftherotarymoduleisthenpresented,basedonthefrequencycharacteristicofrotarymodulebeingtested,weadoptaPIcontrollertoregulatetheangularrateofthetwojoints,andPID,Non-regressorAdaptiveControllers5areusedtocontrolthejointangle.Theexperimentresultswiththecontrollersareanalyzedatlast.2.UNDERWATERELECTRICMANIPULATORTEST-BEDDESIGN2.1MechanismDesignAccordingtotheSmallAutonomous-RemotelyOperatedVehicle,thethree-functionunderwatermanipulatorisdesignedasshowninfigure1.Themanipulatorcomposesofaclawandtwoswingjoints.Theclawisasimplebindinymechanismdrivenbyaninsidestepmotor.Theshoulderjointandelbowjointaredrivenbysamerotarymodule,whichcanprovidemuchmoremomentthanthatneededintheworkingstatusbeingdesigned.Byexchangingtheinstallationpositionofthejointlink,thearmcanrotateorpivot.TherotarymoduleincludesaDCtorque motor,aharmonic-drivereducer,afail-safebrakeandanincrementalrotaryencoder.Tocompactthestructureoftherotarymoduleandminimizeitsdimensionandweight,thetorquemotorandharmonic-drivereducerarecoreparts,and3089withtheencoder,theyhavethesamerotaryaxis,thetorquesupportpolecanpreventtheencoderbodyfromrotatingwiththeaxis.linkllink2soulderjointrivenmoduleelowjointdvenawdrivenmodulemotorFig.1Theunderwaterelectricmanipulator.Fig.2Rotaryjointdrivenmodule.2.2ElectronicDesignTwoPWMservoamplifiers,aMicroSteppingChopperDrivesareselectedtodrivetheDCmotorandstepmotor.ThePWMservoamplifiersarefullyprotectedagainstover-voltage,over-current,over-heatingandshort-circuitacrossmotor,groundandpowerleads,voltageoperatingmodeisusedtodriveDCmotor.Tosatisfytheunderwaterworkingenvironmentandbeinstalledinthevehiclestightly,amicro-computerPC-104ischosenasthecontrollerofthesystemandADT650,theextendedcardofPC-104,isusedasthedatasamplingcard.Thecardcontainsa12bitA/D,aD/Aconverter,a16bitcounter/timer,a24linesDigital1O,whichcanaccomplishallworkincludingmonitorcurrent,outputvoltage,sampleencodersignal,drivestepmotor,controlbrakeandcheckwaterproof.2.3SoftwareDesignTheQNXoperatingsystemandCprogramminglanguageareappliedtothePC-104.Thefollowingaremaincontentsofsoftwaredesign.1.DCmotorcurrentmonitoringTomonitortheDCmotorstatusandtoprotectthePWMservoamplifier.2.DCmotorvoltagecontrolToregulatetheanalogsignalstoPWMsoastocontroltheDCmotorsvoltagesupply.3.EncodersignalssamplingToreadthecountnumberof82C54counterofADT650tocalculatetheangularrateofrotaryjoint,andtoestimatethedirectionofjointrotatingbytheDigitalI/0interfacewiththedirectionsignalofencoder.4.StepmotordriveTosendpulsesignalstotheSteppingChopperDrivestocontrolthespeedanddirectionofthestepmotor,andtoenablethesignalstobecontrolledbyDigitalI/0.5.WaterproofdetectionTodetectthevoltageofdetectingpointsplacedatsealspositionbyDigitalI/0.6.RotatingrangelimitToavoidinterferencebetweenmanipulatoritselfandbetweenthevehicleandmanipulator,andtolimittherotatingrangeofeachjoint.7.ControllerdesignDesigncontrollertomakethemanipulatorswingaccordingtothecommand.3.ANIMPROVEDDESIGNOFROTARYJOINTDRIVENMODULELargenumbersofunderwaterexperimentshavebeendoneuptonowandtheexperimentsvalidatethefeasibilityandreliabilityofourdesignasatest-bed.Buttheexteriorcablelayoutisahiddentroubleweworryabout.Toovercometheproblem,aselectiveimprovingdesignoftherotaryjointdrivenmodulewithinnercablelayoutismadeasshowninfigure3.Noadditionalcomponentsareaddedtotheimproveddesign.Fig.3Improveddesignofrotaryjointdrivenmodulewithinnercablelayout.4.ANGULARRATECONTROLOFSHOULDERANDELBOWJOINTS4.1FrequencycharacteristictestingexperimentTheDCmotorsvoltagesupplyrangesfrom-24Vto+24V,andthegainofPWMservoamplifieris4.8.GiveinputsignaltoPWMasVoltagePWM=5sinwt(V)(1)Theangularrate(rad/s)ofrotarymoduleshouldbe3090Angle_ratejoint=A(co)sin(ca+qp)(rad/s)(2)DefineL(0)=20A(w)/51asthemagnitude-frequencycharacteristic,bymeasuringA(S)andqwithdifferenta;andcalculatingL(S),wegetthebodediagramofthesystemasshowninfigure4.coj=8andcw2=30aretwoinflexionofmagnitude-frequencycharacteristiccurve,mechanismresonanceoccurswhencw=55and=-1800here,sowecangetatwo-ranktransferfunction,whichcanbeusedtoanalyzethesystem.G(s)=0.174031(0.125s+1)(0.033s+i)(3-120101010Fig.4Bodediagramofrotarymodulewithno-load.4.2ANGULARRATECONTROLANDEXPER-IMENTOFTHETWOJOINTSOnland,themanipulatorswingsintheverticalplane,thesametestingmethodisadoptedtoanalyzetheshoulderandelbowfrequencycharacteristics.Testresultsshowthattheelbowjointfrequencycharacteristicsareclosetothatoftherotarymodulebuttheshoulderjointsisdifferentinsomesort.Stillcol=8isthefirstinflexionofshoulderjointsmagnitude-frequencycharacteristiccurveandcocorrespondingto=-1800iscloseto50,butthesecondinflexionofshoulderjointsmagnitude-frequencycharacteristiccurveisnotclear,sowithdifferentelbowjointangle.Tocontroltheangularrateofthemanipulatorjoint,thefirstcontrollerwethinkofisaPIDcontroller.Sincederivativeactionrequiresgoodaccelerationfeedbacksignalthattheencodercantsupply,wedesignthesamePIcontrollerKp(i+is)toanalyzeandcontrastthetwojointsresponse.Givestepsignalro=0.7(rad/s)asangularratecommand.Whent=0,jointangularratea=0,errore=roandtheintegraldoesnotact,thePWMvoltagesupplyVoltagepwM=KpXrO(4)WechooseKp=4.4atthebeginningandthePWMvoltagesupplyis3VandtheDCmotorvoltagesupplyis14.4V,whichisoutofthesystemsdeadzoneanddoesntexceedthelimitofpowersupply.TheopenlooptransferfunctionwithPIcorrectionisC(s)-0.77(1+1/Ts)s(0.125s+l)(T2s+1)whereT2=1/w2,w2,take7=0.125canmaximizethefrequencywidthofintermediatefrequency6.Thesecularequationofthesystemsclose-looptransferfunctionwithPIcontrollerisA(s)=Ts2+s+6.16(6)Thecontrolsystemsframeworkisasfigure5.controllermanipulatorjointangularrateFig.5Frameworkoftheangularratecontrolsystem.Figure6showstheresponsecurveofthetwojointwithPIcontroller.Theelbowjointangleiszerowhencontrollingangularrateoftheshoulderjoint.Goodresultisobtainedincontrollingelbowjointsangularrate.However,sincethegravitymomentvariestoomuch,thePIcontrollerwiththesameparametersdoesntactshoulderjointsangularratewell.Figures7and8aretheexperimentcurveofangularratecontrolofelbowjointandshoulderjointrespectively.Contrastexperimentsbetweenunderwaterandonlandarepresented.Resultsshowthattheresponsecurveismuchmoresmoothandofhighprecisionwhenthemanipulatorisinwater.5040302010angularratecommand(deg/s)-angularrateofshoulderjoint(deg/s)angularrateofelbowjoint(deg/s)l.-ITime(s)01234567Fig.6StepresponseofshoulderandelbowjointangularratewiththesamePIcontroller.13F-0.50.3011elbowangularratecomunderwaterverticalplane-underwaterhorizontalplane,verticalplaneonlandTime(s)3456Fig.7Stepresponsecurvesofelbowjointangularrateunderdifferentconditions.13Fm&-0.503-shoulderangularrate_comunderwaterhorizontalplanemmImunderwaterverticalplaneverticalplaneonlandTime(s)123456Fig.8Stepresponsecurvesofshoulderjointangularrateunderdifferentconditions.3091-LL-Li5.ANGLECONTROLOFSHOULDERANDELBOWJOINTS5.1PIDcontrollerBasedontheangularratecontrolofthetwojoints,thePIDcontrollerisalsoadoptedincontrollingjointangle,andtheframeworkofthecontrolsystemisshowninfigure9.Figures10and11arethestepresponsecurvesofthetwojoints,theProportionalandIntegralgainoftheinner-loopisthesameastheangularratecontrol.TheProportionalgainofouterloopis20andtheDifferentialandIntegralgainsarezero.Onejointanglevariesfrom00to500atthesametimeanotherjointangleiszero.Experimentsunderdifferentconditionsarecarriedouttovalidatetheperformanceofthecontroller.Figures10and11showthatthecontrollerisofgoodrobustness.Thecontrolerrorofelbowandshoulderangleisabout0.26%and0.50Orespectivelywhentheresponsetimeis15s.Th7JIJ-PWmmotorloadicontrollericontrollermanipulatorjointangularrateangleFig.9FrameworkofthePIDanglecontrolsystem.1.10.907-Elbowanglecommand0.5Underwaterhorizontalplane05-mUnderwaterverticalplane03Verticalplaneonland0.1Time(s)-0.1D246810121416Fig.10StepresponseofelbowjointanglewithPIDcontroller.1.10.90 7-Shoulderanglecommand05-VerticalplaneonlandMENEEMImUnderwaterverticalplane030.3nomommam=Underwaterhorizontalplane0.1Time(s)-0.16246810121416Fig.11StepresponseofshoulderjointanglewithPIDcontroller.asfollows:r=Kld+Kl+K3+K4e+K5e=YKioDi=l(7)wheredisthedesiredvalueofjointangle0andeisthetrackingerrordefinedase=d-0(8)Accordingto57,thetrackingerrorewillasymptoticallyconvergetozerowiththefollowingadaptivecontroller:KiforIlil|4Ki=Aiaifor|e|i|i=1,.,5(9)K,fe1)forIll11I)-,i=1,.,15(5;(10)wheref,ando5arepositiveconstants,andee+e(11)whereaisapositiveconstant.InPIDcontrolexperiments,wefindthatitismuchmorerobustandwithhighprecisionwhenwithinner-loop.Onereasonisthatthevoltagedeadzoneofthejointmotorisabout-5V-+5V,soinadaptivecontrol,withandwithoutinner-looparebothexperimented.Whenwithoutinner-loop,tomakethesystemresponsemorequickly,+5visaddedtotheoutputofcontrollertoovercomethedeadzone.Figure12istheframeworkofadaptivecontrolwithinner-loop,andtheinner-loopsparametersarethesameasthoseofthePIDcontroller.hX+WroadaptivemtolacontrollercOntrllej it-2imanipulatorJointangularrateangleFig.12Frameworkoftheadaptiveanglecontrolsystemwithinner-loop.0.2-ElbowanlgecommandElbowanlgeresponsewithoutinnerloop-ElbowanlgeresponsewithinnerloopTime(s)02.557.51012.51517.5205.2ExperimentswithAdaptivecontrollerAlthoughresultswithhighprecisionisachievedwithPIDcontroller,therealsoexitsaproblemthattheinvariablePIDparameterscantmeetallconditionswell,especiallyinthebeginningofstepresponsewhenthejointanglewarpisthebiggest,overshootandvoltagesaturationwilloccur.Thevariousangle,loadandenvironmentchangesneedamoreadaptiveandrobustcontroller.TheadaptivecontrollerexperimentedinthispaperisbasedontheadaptivecontrolwithboundestimationdevelopedbyYuh57.ThecontrollawisexpressedFig.13Stepresponseofelbowjointanglecontrastbetweenwithandwithoutinner-loop.Theelbowjointsstepresponseexperimentcurveofadaptivecontrollerisshowninfigure13.Elbowjointanglescontrolrangeis500inhorizontalplaneofunderwater,wehaveresultsasfollows:whenwithsameparametersofadaptivecontroller,itresponsesmorequicklyandwithhigherprecisionintheconditionofwithinner-loop.Thecontrolerrorofwithandwithoutinner-loopisabout0.25%and0.40orespectivelywhenresponsetimeis15s.3092A=fiIlillllq)i11,i=11.55.3ExperimentscontrastbetweenPIDandAdaptivecontrollerAsmentionedinabovepart,PIDcontrollerwithinvariableparametershasproblemsincontrollingthemanipulator,oneoftheimportantisthatinthebeginningofresponse,voltagesaturationoccursandwilldamagetheDCmotor.Thisproblemiswellsolvedbyadaptivecontroller.Atthesametime,otherperformancesdontdescend.Theelbowjointangleresponse,elbowjointangleerrorandmotorcontrolvoltage(/24v)curvesofthetwodifferentcontrollersareshowninfigure14.angleadaptive1.2-avoltageaaaptveErroradlaptive0.806-0.4-0.2I,0123456-0.2-langlePID-voltagePID-ErrorPID4M.Ishitsuka,S.SagaraandK.Ishii,DynamicsAnalysisandResolvedAccelerationControlofanAutonomousUnderwaterVehicleEquippedwithaManipulator,ProceedingsofUT04,pp.277-280,2004.5J.Yuh,