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SICE-ICASEInternationalJointConference2006 Oct.18-21,2006inBexco,Busan,Korea ImprovedDesignandControlExperimentsofanUnderwaterElectricManipulator QifengZhang2,AiqunZhang,KuichenYan ShenyangInstituteofAutomation,ChineseAcademyofSciences,Shenyang,China 2GraduateSchooloftheChineseAcademyofSciences,Beijing,China (TelE-mail:zqfW,) Abstract:Autonomous/Semi-autonomousworkingunderwatervehicleisadevelopmenttrendofunderwatervehicles. Thispaperbrieflyanalyzestherequirementsofunderwaterelectricmanipulatortobeequippedonautonomous underwatervehicles,anddesignsathree-functionunderwaterelectricmanipulatortest-bed.Thetest-bedhasthe characteristicsofcompactconfiguration,completefunctionandwithbigmomentoutput.Butexteriorcablelayout increasesthepossibilitytoarisemalfunctionespeciallywhenthemanipulatorworkinginwater.Animproveddesignof themanipulatorwithinnercablelayoutisalsopresentedinthispaper. Basedonthefrequencycharacteristicsoftherotaryjointdrivenmodule,thePIcorrectionisdesignedtocontrolthe shoulderandelbowjointsangularrate.Thentheangleerrorisregardedastheinputofangularratecontrolloopaftera PIDController,andaNon-regressorAdaptiveController,whichhasbeenwidelyadoptedasaneffectivemeansin underwatervehiclecontrol,isalsousedtocontrolthemanipulatorasaselectivemethod.Experimentresults demonstratethegoodeffectofthePIDandtheadaptivecontrollersincontrollingjointangle,andwiththeinnercontrol loop,theNon-regressorAdaptiveControllerismorerobustthanthatwithoutinner-loop,anditisamoreappropriate controllerthanPIDcontrollerespeciallyinprotectingthemanipulatorsmotorsfromsaturatedvoltage. Keywords:underwaterelectricmanipulator;autonomousunderwatervehicles;adaptivecontroller. 1.INTRODUCTION Inrecentyears,underwatervehiclesbecomean increasinginterestofresearchcommunityandindustry. Today,itiscommontousemannedunderwatervehicles toaccomplishmissionsatseabottom,butitisof enormouscostandriskinsuchadangerous environment.Scientistswishtoperformunderwater missionsinacompletelyautonomousway,soone researchfocusofthisfieldisontheautonomous/ semi-autonomousunderwatervehicle-manipulator system.Becauseofenergy,powerandefficiency, underwaterelectricmanipulatorisabsolutelyanecessity forautonomous/semi-autonomousunderwatervehicle- manipulatorsystem.Thedesignofunderwaterelectric manipulatorandcoordinatedcontrolbetweenitand vehicleareimportantjobbeingdonebyseveral institutes.Forexample,theinteractionbetweena one-linkmanipulatorandOTTERAUVisstudiedin Stanforduniversityfrom19951,SAUVIMP2,a semi-autonomousvehiclewitha7-DOFelectric manipulatorisunderdevelopmentattheAutonomous SystemLaboratoryofUniversityofHawaii,a semi-autonomousunderwatervehicleforevaluationof manipulatortechnologyhasbeendevelopedinKorea OceanResearchandDevelopmentInstitute3,andan underwaterelectricmanipulatordrivenbymagnet couplingtobeequippedforTwin-BurgerAUVhasbeen designedbyKyushuInstituteofTechnologywithother Institutes4.Asacomponentofautonomous/semi- autonomousunderwatervehicle-manipulatorsystem, mediumandsmall-sizedunderwaterelectric manipulatorismuchmoredexterousandeasyto producethanhydraulicmanipulator,sousing underwaterelectricmanipulatortoexploitoceanis muchmorepromising. Thethree-functionunderwaterelectricmanipulator 89-950038-5-598560/06/$10C2006ICASE test-beddesignedinthispaperistobeequippedwitha SmallAutonomous-RemotelyOperatedVehicle(SARV), whichisatest-beddesignedbyShenyangInstituteof Automation,theChineseAcademyofSciences.Itisa vehicleforevaluationofbothAUVandROV technologies.Lightworkinginscientificapplication withfiber,visionandmanipulatormoduleisoneofthe importanttechnologiestobestudied. Inthispaper,wefirstgivethedesignofthe manipulatortest-bed,animproveddesignoftherotary moduleisthenpresented,basedonthefrequency characteristicofrotarymodulebeingtested,weadopta PIcontrollertoregulatetheangularrateofthetwo joints,andPID,Non-regressorAdaptiveControllers5 areusedtocontrolthejointangle.Theexperiment resultswiththecontrollersareanalyzedatlast. 2.UNDERWATERELECTRIC MANIPULATORTEST-BEDDESIGN 2.1MechanismDesign AccordingtotheSmallAutonomous-Remotely OperatedVehicle,thethree-functionunderwater manipulatorisdesignedasshowninfigure1.The manipulatorcomposesofaclawandtwoswingjoints. Theclawisasimplebindinymechanismdrivenbyan insidestepmotor.Theshoulderjointandelbowjointare drivenbysamerotarymodule,whichcanprovidemuch moremomentthanthatneededintheworkingstatus beingdesigned.Byexchangingtheinstallationposition ofthejointlink,thearmcanrotateorpivot.Therotary moduleincludesaDCtorque motor,aharmonic-drive reducer,afail-safebrakeandanincrementalrotary encoder.Tocompactthestructureoftherotarymodule andminimizeitsdimensionandweight,thetorque motorandharmonic-drivereducerarecoreparts,and 3089 withtheencoder,theyhavethesamerotaryaxis,the torquesupportpolecanpreventtheencoderbodyfrom rotatingwiththeaxis. linkl link2 soulderjoint rivenmodule elowjointdven awdriven module motor Fig.1Theunderwaterelectricmanipulator. Fig.2Rotaryjointdrivenmodule. 2.2ElectronicDesign TwoPWMservoamplifiers,aMicroStepping ChopperDrivesareselectedtodrivetheDCmotorand stepmotor.ThePWMservoamplifiersarefully protectedagainstover-voltage,over-current,over- heatingandshort-circuitacrossmotor,groundand powerleads,voltageoperatingmodeisusedtodrive DCmotor.Tosatisfytheunderwaterworking environmentandbeinstalledinthevehiclestightly,a micro-computerPC-104ischosenasthecontrollerof thesystemandADT650,theextendedcardofPC-104, isusedasthedatasamplingcard.Thecardcontainsa12 bitA/D,aD/Aconverter,a16bitcounter/timer,a24 linesDigital1O,whichcanaccomplishallwork includingmonitorcurrent,outputvoltage,sample encodersignal,drivestepmotor,controlbrakeand checkwaterproof. 2.3SoftwareDesign TheQNXoperatingsystemandCprogramming languageareappliedtothePC-104.Thefollowingare maincontentsofsoftwaredesign. 1.DCmotorcurrentmonitoring TomonitortheDCmotorstatusandtoprotectthe PWMservoamplifier. 2.DCmotorvoltagecontrol ToregulatetheanalogsignalstoPWMsoasto controltheDCmotorsvoltagesupply. 3.Encodersignalssampling Toreadthecountnumberof82C54counterof ADT650tocalculatetheangularrateofrotaryjoint,and toestimatethedirectionofjointrotatingbytheDigital I/0interfacewiththedirectionsignalofencoder. 4.Stepmotordrive TosendpulsesignalstotheSteppingChopper Drivestocontrolthespeedanddirectionofthestep motor,andtoenablethesignalstobecontrolledby DigitalI/0. 5.Waterproofdetection Todetectthevoltageofdetectingpointsplacedat sealspositionbyDigitalI/0. 6.Rotatingrangelimit Toavoidinterferencebetweenmanipulatoritselfand betweenthevehicleandmanipulator,andtolimitthe rotatingrangeofeachjoint. 7.Controllerdesign Designcontrollertomakethemanipulatorswing accordingtothecommand. 3.ANIMPROVEDDESIGNOFROTARY JOINTDRIVENMODULE Largenumbersofunderwaterexperimentshavebeen doneuptonowandtheexperimentsvalidatethe feasibilityandreliabilityofourdesignasatest-bed.But theexteriorcablelayoutisahiddentroubleweworry about.Toovercometheproblem,aselectiveimproving designoftherotaryjointdrivenmodulewithinnercable layoutismadeasshowninfigure3.Noadditional componentsareaddedtotheimproveddesign. Fig.3Improveddesignofrotaryjointdrivenmodule withinnercablelayout. 4.ANGULARRATECONTROLOF SHOULDERANDELBOWJOINTS 4.1Frequencycharacteristictestingexperiment TheDCmotorsvoltagesupplyrangesfrom-24Vto +24V,andthegainofPWMservoamplifieris4.8.Give inputsignaltoPWMas VoltagePWM=5sinwt(V)(1) Theangularrate(rad/s)ofrotarymoduleshould be 3090 Angle_ratejoint=A(co)sin(ca+qp)(rad/s)(2) DefineL(0)=20A(w)/51asthe magnitude- frequencycharacteristic,bymeasuringA(S)andq withdifferenta;andcalculatingL(S),wegetthe bodediagramofthesystemasshowninfigure4.coj=8 andcw2=30aretwoinflexionofmagnitude-frequency characteristiccurve,mechanismresonanceoccurswhen cw=55and=-1800here,sowecangetatwo-rank transferfunction,whichcanbeusedtoanalyzethe system. G(s)=0.174031 (0.125s+1)(0.033s+i)(3 -120 101010 Fig.4Bodediagramofrotarymodulewithno-load. 4.2ANGULARRATECONTROLANDEXPER- IMENTOFTHETWOJOINTS Onland,themanipulatorswingsintheverticalplane, thesametestingmethodisadoptedtoanalyzethe shoulderandelbowfrequencycharacteristics.Test resultsshowthattheelbowjointfrequency characteristicsareclosetothatoftherotarymodulebut theshoulderjointsisdifferentinsomesort.Stillcol=8 isthefirstinflexionofshoulderjoints magnitude-frequencycharacteristiccurveandco correspondingto=-1800iscloseto50,butthe secondinflexionofshoulderjointsmagnitude- frequencycharacteristiccurveisnotclear,sowith differentelbowjointangle. Tocontroltheangularrateofthemanipulatorjoint, thefirstcontrollerwethinkofisaPIDcontroller.Since derivativeactionrequiresgoodaccelerationfeedback signalthattheencodercantsupply,wedesignthesame PIcontrollerKp(i+is)toanalyzeandcontrastthe twojointsresponse. Givestepsignal ro =0.7(rad/s)as angularrate command.Whent=0,jointangularratea=0,error e=roandtheintegraldoesnotact,thePWMvoltage supply VoltagepwM=KpXrO(4) WechooseKp=4.4atthebeginningandthePWM voltagesupplyis3VandtheDCmotorvoltagesupply is14.4V,whichisoutofthesystemsdeadzoneand doesntexceedthelimitofpowersupply.Theopen looptransferfunctionwithPIcorrectionis C(s)-0.77(1+1/Ts) s(0.125s+l)(T2s+1) whereT2=1/w2,w2,take7=0.125can maximizethefrequencywidthofintermediate frequency6.Thesecularequationofthesystems close-looptransferfunctionwithPIcontrolleris A(s)=Ts2+s+6.16(6) Thecontrolsystemsframeworkisasfigure5. controller manipulatorjoint angularrate Fig.5Frameworkoftheangularratecontrolsystem. Figure6showstheresponsecurveofthetwojoint withPIcontroller.Theelbowjointangleiszerowhen controllingangularrateoftheshoulderjoint.Good resultisobtainedincontrollingelbowjointsangular rate.However,sincethegravitymomentvariestoo much,thePIcontrollerwiththesameparameters doesntactshoulderjointsangularratewell. Figures7and8aretheexperimentcurveofangular ratecontrolofelbowjointandshoulderjoint respectively.Contrastexperimentsbetweenunderwater andonlandarepresented.Resultsshowthatthe responsecurveismuchmoresmoothandofhigh precisionwhenthemanipulatorisinwater. 50 40 30 20 10 angularratecommand(deg/s) -angularrateofshoulderjoint(deg/s) angularrateofelbowjoint(deg/s) l.-I Time(s) 01234567 Fig.6Stepresponseofshoulderandelbowjoint angularratewiththesamePIcontroller. 13 F 1.1 0.9 0.7- 0.5 0.3 01 1 elbowangularratecom underwaterverticalplane -underwaterhorizontalplane ,verticalplaneonland Time(s) 3456 Fig.7Stepresponsecurvesofelbowjointangularrate underdifferentconditions. 13 Fm (10) where f, ando5arepositiveconstants,and ee+e(11) whereaisapositiveconstant. InPIDcontrolexperiments,wefindthatitismuch morerobustandwithhighprecisionwhenwith inner-loop.Onereasonisthatthevoltagedeadzoneof thejointmotorisabout-5V-+5V,soinadaptivecontrol, withandwithoutinner-looparebothexperimented. Whenwithoutinner-loop,tomakethesystemresponse morequickly,+5visaddedtotheoutputofcontroller toovercomethedeadzone.Figure12istheframework ofadaptivecontrolwithinner-loop,andtheinner-loops parametersarethesameasthoseofthePIDcontroller. hX+W ro adaptivemtola controllercOntrlle j it-2imanipulatorJoint angularrate angle Fig.12Frameworkoftheadaptiveanglecontrolsystem withinner-loop. 0.8 0.6 0.4 0.2 -Elbowanlgecommand Elbowanlgeresponse withoutinnerloop -Elbowanlgeresponse withinnerloop Time(s) 02.557.51012.51517.520 5.2ExperimentswithAdaptivecontroller Althoughresultswithhighprecisionisachievedwith PIDcontroller,therealsoexitsaproblemthatthe invariablePIDparameterscantmeetallconditionswell, especiallyinthebeginningofstepresponsewhenthe jointanglewarpisthebiggest,overshootandvoltage saturationwilloccur.Thevariousangle,loadand environmentchangesneedamoreadaptiveandrobust controller. Theadaptivecontrollerexperimentedinthispaperis basedontheadaptivecontrolwithboundestimation developedbyYuh57.Thecontrollawisexpressed Fig.13Stepresponseofelbowjointanglecontrast betweenwithandwithoutinner-loop. Theelbowjointsstepresponseexperimentcurveof adaptivecontrollerisshowninfigure13.Elbowjoint anglescontrolrangeis500inhorizontalplaneof underwater,wehaveresultsasfollows:whenwithsame parametersofadaptivecontroller,itresponsesmore quicklyandwithhigherprecisionintheconditionof withinner-loop.Thecontrolerrorofwithandwithout inner-loopisabout0.25%and0.40orespectivelywhen responsetimeis15s. 3092 A = fiIlillllq)i11,i=11 .5 5.3ExperimentscontrastbetweenPIDandAdaptive controller Asmentionedinabovepart,PIDcontrollerwith invariableparametershasproblemsincontrollingthe manipulator,oneoftheimportantisthatinthe beginningofresponse,voltagesaturationoccursand willdamagetheDCmotor.Thisproblemiswellsolved byadaptivecontroller.Atthesametime,other performancesdontdescend.Theelbowjointangle response,elbowjointangleerrorandmotorcontrol voltage(/24v)curvesofthetwodifferentcontrollersare showninfigure14. angleadaptive 1.2-avoltageaaaptve Erroradlaptive 0.8 06- 0.4- 0.2 I, 0123456 -0.2- langlePID -voltagePID -ErrorPID 4M.Ishitsuka,S.SagaraandK.Ishii,Dynamics AnalysisandResolvedAccelerationControlofan AutonomousUnderwaterVehicleEquippedwitha Manipulator,ProceedingsofUT04,pp.277-280, 2004. 5J.Yuh,J.NieandC.S.G.Lee,ExperimentalStudy onAdaptiveControlofUnderwaterRobots, Proceedingsofthe1999IEEEInternational ConferenceonRobotics&Autmation,Vol.1,No.1, pp.393-398,1999.