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SICE ICASEInternationalJointConference2006 Oct 18 21 2006inBexco Busan Korea ImprovedDesignandControlExperimentsofanUnderwaterElectricManipulator QifengZhang2 AiqunZhang KuichenYan ShenyangInstituteofAutomation ChineseAcademyofSciences Shenyang China 2GraduateSchooloftheChineseAcademyofSciences Beijing China Tel 86 024 23970731 E mail zqfW Abstract Autonomous Semi autonomousworkingunderwatervehicleisadevelopmenttrendofunderwatervehicles Thispaperbrieflyanalyzestherequirementsofunderwaterelectricmanipulatortobeequippedonautonomous underwatervehicles anddesignsathree functionunderwaterelectricmanipulatortest bed Thetest bedhasthe characteristicsofcompactconfiguration completefunctionandwithbigmomentoutput Butexteriorcablelayout increasesthepossibilitytoarisemalfunctionespeciallywhenthemanipulatorworkinginwater Animproveddesignof themanipulatorwithinnercablelayoutisalsopresentedinthispaper Basedonthefrequencycharacteristicsoftherotaryjointdrivenmodule thePIcorrectionisdesignedtocontrolthe shoulderandelbowjoint sangularrate Thentheangleerrorisregardedastheinputofangularratecontrolloopaftera PIDController andaNon regressorAdaptiveController whichhasbeenwidelyadoptedasaneffectivemeansin underwatervehiclecontrol isalsousedtocontrolthemanipulatorasaselectivemethod Experimentresults demonstratethegoodeffectofthePIDandtheadaptivecontrollersincontrollingjointangle andwiththeinnercontrol loop theNon regressorAdaptiveControllerismorerobustthanthatwithoutinner loop anditisamoreappropriate controllerthanPIDcontrollerespeciallyinprotectingthemanipulator smotorsfromsaturatedvoltage 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 Stanforduniversityfrom1995 1 SAUVIMP 2 a semi autonomousvehiclewitha7 DOFelectric manipulatorisunderdevelopmentattheAutonomous SystemLaboratoryofUniversityofHawaii a semi autonomousunderwatervehicleforevaluationof manipulatortechnologyhasbeendevelopedinKorea OceanResearchandDevelopmentInstitute 3 andan underwaterelectricmanipulatordrivenbymagnet couplingtobeequippedforTwin BurgerAUVhasbeen designedbyKyushuInstituteofTechnologywithother Institutes 4 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 regressorAdaptiveControllers 5 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 controltheDCmotor svoltagesupply 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 TheDCmotor svoltagesupplyrangesfrom 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 theshoulderjoint sisdifferentinsomesort Stillcol 8 isthefirstinflexionofshoulderjoint s magnitude frequencycharacteristiccurveandco correspondingto 1800iscloseto50 butthe secondinflexionofshoulderjoint smagnitude frequencycharacteristiccurveisnotclear sowith differentelbowjointangle Tocontroltheangularrateofthemanipulatorjoint thefirstcontrollerwethinkofisaPIDcontroller Since derivativeactionrequiresgoodaccelerationfeedback signalthattheencodercan tsupply wedesignthesame PIcontrollerKp i is toanalyzeandcontrastthe twojoints response 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 whichisoutofthesystem sdeadzoneand doesn texceedthelimitofpowersupply Theopen looptransferfunctionwithPIcorrectionis C s 0 77 1 1 Ts s 0 125s l T2s 1 whereT2 1 w2 w2 take7 0 125can maximizethefrequencywidthofintermediate frequency 6 Thesecularequationofthesystem s close looptransferfunctionwithPIcontrolleris A s Ts2 s 6 16 6 Thecontrolsystem sframeworkisasfigure5 controller manipulatorjoint angularrate Fig 5Frameworkoftheangularratecontrolsystem Figure6showstheresponsecurveofthetwojoint withPIcontroller Theelbowjointangleiszerowhen controllingangularrateoftheshoulderjoint Good resultisobtainedincontrollingelbowjoint sangular rate However sincethegravitymomentvariestoo much thePIcontrollerwiththesameparameters doesn tactshoulderjoint sangularratewell 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 loop s parametersarethesameasthoseofthePIDcontroller hX W ro adaptive mtola 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 invariablePIDparameterscan tmeetallconditionswell especiallyinthebeginningofstepresponsewhenthe jointanglewarpisthebiggest overshootandvoltage saturationwilloccur Thevariousangle loadand environmentchangesneedamoreadaptiveandrobust controller Theadaptivecontrollerexperimentedinthispaperis basedontheadaptivecontrolwithboundestimation developedbyYuh 5 7 Thecontrollawisexpressed Fig 13Stepresponseofelbowjointanglecontrast betweenwithandwithoutinner loop Theelbowjoint sstepresponseexperimentcurveof adaptivecontrollerisshowninfigure13 Elbowjoint angle scontrolrangeis500inhorizontalplaneof 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 performancesdon tdescend 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 4 M Ishitsuka S SagaraandK Ishii Dynamics AnalysisandResolvedAccelerationControlofan AutonomousUnderwaterVehicleEquippedwitha Manipulator ProceedingsofUT 04 pp 277 280 2004 5 J Yuh J NieandC S G Lee ExperimentalStudy onAdaptiveControlofUnderwaterRobots Proceedingsofthe1999IEEEInternational ConferenceonRobotics Autmation Vol 1 No 1 pp 393 398 1999