-SPEED-ADAPTEDTRAJECTORIESINTHECASEOFINSUFFICIENTYDRAULICRESSUREFORTHEFOUR-LEGGEDLARGE-SCALEWALKINGVEHICLEALDUROABSTRACTWhenoperatingwalkingmachines,onlyacoordinatedmovementofallcylindersand/ormotorscanleadtosafe,stablewalking.ThelargehydraulicallydrivenwalkingmachineALDURO,whichisinvestigatedinthispaper,hasnoexternalpowersupply,andthereforethesizeoftheon-boardhydraulicpowerpackanditsdieselengineislimitedbyitsweight.Whenmovingseveralcylinderswithhighspeed,thehydraulicsupplycanbecomeinsufficientandtheresultingtrajectoriesoffeetandplatformcanbecomeunpredictable.WhentheALDUROisnearitsstabilitylimitsuchbehaviourcanleadtoinstabilityandtopplingofthesystem.Theproposedsolutionunderdiscussionhereistoobservethepositionerrorsandtimederivativesforthecylindersandbasedonthisreducethespeedwhennecessary.1.INTRODUCTIONThesysteminvestigatedinthispaperistheAnthropomorphicallyLeggedandWheeled-DuisburgRobot(ALDURO).Itconsistsofaplatformof2.0mby2.2mwithacabinfortheoperatorandfourlegs,each1.8mlong.Theestimatedweightis1200kg.Itcanbeusedasaquadrupedwalkingmachine(Fig.2),andbyreplacingthetwohindfeetwithwheels,itcanalsobeusedasacombinedleggedandwheeledvehicle(Fig.1).Thelattercombinestheadvantagesofawalkingmachine-highmobility-withthestabilityandspeedofwheeledvehicles2.Whenoperatinginsteepanddangerousterrain,safetyplaysanimportantrole.Itmustbeguaranteedthatthecylindersfollowthecalculatedtrajectoriesexactlysinceawrongmovementmightcausetherobottobecomeinstable.ALDUROslegsarehydraulicallydriven,withanopenhydraulicsystem.Normally,whenplanninghydraulicsystems,lowweighthasnohighpriority1.ForthewalkingmachineALDUROtheratiopowerperweightwasoptimized.Fig.1:CombinedLeggedFig.2:WalkingMachineandWheeledVehicleWhileactuatingseveralcylinderssimultaneouslyormovingveryfast,thevolumeflowofthehydraulicsupplybecomesinsufficientandtheresultingmovementsuncontrollable.Theproposedsolutionunderdiscussionhereisadecreaseinspeedofallcalculatedtrajectories.Thisisadmissibleaslongastherobotisstaticallystableatanymoment.Byobservingthepositionerrorsofthecylindersandtheirtimederivatives,adecisionistakenonwhethertodecreaseorincreasethespeedalongthetrajectories.Toensurethatallmovementsareinfluencedsimultaneously,themodel-time,uponwhichallcalculationsdepend,issloweddown.Thuswecanguaranteethatlegsandplatformcananddofollowtheprescribed-trajectories.ThisstrategyisbeingtestedonavirtualmodeloftheALDUROandisbeingtestedonavirtualmodeloftheALDUROandateststandinthelaboratory,consistingofasingleleginscale1:1,givingverygoodresults.Fig.3:Experimentalsetup2.EXPERIMENTALSETUPThelegoftheALDUROisanthropomorphic,i.e.itisbasedonthegeometryandfunctionofthehumanleg.Thehipjointisasphericalballjointwiththreedegreesoffreedom(d.o.f.)andthekneearevolutejointwithoned.o.f.Thesejointsareactuatedwithhydrauliccylinders(Fig.4),whereasthetwoadditionald.o.f.ofthefootarepassive.Tomakesolutionoftheexplicitinversekinematicspossiblewelockoneofthehipcylinders.Theexplicitsolutionofthedirectandinversekinematicsisshownindetailin4.Toexaminethedynamicbehaviouroftheleg,andtotestdifferentcontrolschemes,anexperimentalsetupforafullysizedlegwasdevelopedandbuilt(seeFig.3).ItincludesallthehydrauliccomponentsthatwillbeusedonthefirstprototypeALDUROandisdrivenbyastationaryhydraulicpowerpackinthelaboratory.Theexperimentalset-upisequippedwithanopenhydraulicsystemwitha15kWelectricalmotorandanaxialpistonpumpproducingavolumeflowof40l/minat200bar.Thisissmallerthanwhatwillbeusedontherealsystem,-whichwillbepowerdbya27kWdieselengine.Fortestswithaninsufficienthydraulicflow,asecondsetoffourhydrauliccylinders(asusedtomoveoneleg)ismountedonthefloornexttotheteststand.Anopticalfieldbusforthetransferofthesensorandactuatordatabetweentheteststandandthecontrolcomputer(withreal-timeoperatingsystem)isalsoinstalled.Thehydrauliccylindersincludepositionandpressuresensorsthatareusedascontrollerinputs.Thusdynamictestscanbecarriedouttoexaminetheco-operationbetweenthemechanicalandhydrauliccomponentsandtheelectroniccontrolsystem.Thehipplateoftheexperimentalset-upismountedonapairoflinearbearings,andthusismobileinverticaldirection.Whencombinedwiththefoot,asshowninFig.3,orthepassivewheelusedonthehindlegofthecombinedleggedandwheeledsystem,thisallowsloadingtestsonthelegwhileperformingwalkingmotions.Mechan