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.AutomationinConstruction71998401–411AconceptofdigitalcontrolsystemtoassisttheoperatorofhydraulicexcavatorsL.Płonecki),W.Tra˛mpczynski,J.Cendrowicz´AbstractAconceptofdigitalcontrolsystemtoassisttheoperatorsofhydraulicexcavatorsispresentedanddiscussed.Then,controlsystembasedondescribedideaswasmountedonaspecialnumericallycontrolledstand,equippedwithDrAandArDconverters,wheresmallhydraulicbackhoeexcavatorK-111fixtureswereused.Experimentalresultsshowsthatitfulfilsalldescribedrequirementsandcanbeusedasthemachineoperatorassist.Itenablesforprecisiontoolguidance,.automaticrepetitionofrealizedmovements,realizationofspecifictooltrajectoriesincludingenergeticallyoptimalpathsandautomaticimprovementoroptimizationofrealizedpaths.Tooltrajectoriescanalsobeprescribedusingthesettingmodel,makingexcavatorthemachineofteleoperatorclass.Presentedsystemcanbeusedasabasisforrealmachinecontrolsystem.q1998ElsevierScienceB.V.Allrightsreserved.Keywords:Digitalcontrolsystem;Hydraulicexcavators;Tooltrajectories1.IntroductionTheautomationofheavymachines,includinghy-draulicexcavators,beganinmid-1970sandwaspossibleduetoinventionofrealtimecontrollersandhydraulicelementswithgooddynamicproperties.Thefirstexcavatorequippedwithseveralmechatron-icssystems,whichwasshownasaworkingmodel,wastheexcavatorFUTUREpreparedbyOrensteinandKoppelforBAUMA’83Fairs.Sincethattime,machinesequippedwithsystemsautomatingtheen-gineoperation,pumpsoperation,machinefixtures,machinediagnostic,etc.,arepresentedandoffered.Suchsystemsbringrealhelptotheoperatorandcleareconomicalprofit.Forexample,LIEBHERRR902excavatorequippedwithLITRONICSystem.hasforatrenchdiggingtheefficiency40%higher)Correspondingauthor.andunitcosts30%lower,thansimilarmachinewithoutsuchautomaticsystem.Althoughautomation.insomecase,optimizationofseveralmachinesys-temsdevelopsquitefast,themainmachineprocess—theshovingprocess—hasnoproperunderstandinganddescriptionuntilnow.Itsautomationisquitelimitedtosystemsrepeatingalreadyperformed.movements,laserlevellingsystems,etc.andsys-temsoptimizingsuchprocessesarenotdevelopedyet.Quitenewexperimentalresultsshowclearideaforenergeticallyoptimaltooltrajectoriesinthecaseofcohesivematerials.Thetooltiphastobeguidedalongsliplines,whicharegeneratedfromthetiptoolduringthepreviousstageoftheshovingprocess.Torealizesuchtrajectoriesforpracticalpurposeandrealmachines,itisnecessarytobuildaspecialcontrolsystemforthetoolmotion,whichenablesautomaticrealisationofsuchtrajectoriesaswellasrealisationofothertasksthathelptheoperator.0926-5805r98r$19.00q1998ElsevierScienceB.V.Allrightsreserved..PIIS0926-58059800045-4()L.Płoneckietal.rAutomationinConstruction71998401–411402Takingintoaccountup-to-dayheavymachinesde-velopment,suchsystemhastofitfordigitallycon-trolledelectro-hydraulicdrives.Theconceptofsuchcontrolsystem,andverifyingexperimentalresults,arepresentedinthispaper.2.TheoptimizationoftooltrajectorieswxItwasexperimentallyfound1,2thatinthecaseofearth-movingprocessduetoheavymachinetools,thecohesivematerialdeformstogeneraterigidzones.slidingalongthesliplineswellvisiblecracksalongwhichthematerialsubstantiallychangesitsparame-terstheinitialcohesioncdecreasestotheresidual.valueclosetocs0.Inthecaseofthesimpletoolrpushingprocessperpendicularwall,theforce-dis-placementrelationshowsthatthehorizontalforcegrowsastheprocessadvances,butinanunstablemanner.Themomentofreductionoftheforcecoin-cideswithcreationofakinematicalmechanismorig-inatingfromthetoolend.Suchmechanismsarecreatedperiodicallyandcanbedescribedtheoreti-callyusingkinematicallyadmissiblemechanismsofwx.thetheoryofplasticity4–8Fig.1.Alotofeffortwasmadetodescribethesoilcuttingprocesswithinthetheoryofplasticity,wheretheproblemofactivepressureexertedbyarigidwallonagranularmediumunderplanestraincondi-.tioncanbeassumedasasimplifiedmodelforsoilshoving.Insuchcase,themethodofcharacteristicswxwasused3,9andseveraltheoreticalsolutionsfor.staticsandkinematicswereobtainedundertheas-sumptionofrigid-perfectlyplasticsoilbehavior.Al-thoughanumberofboundaryvalueproblemsweresolvedinthismanner,thereexistseverallimitationsinobtainingcompletesolutionsoreventhekinemati-wxcallyadmissibleones9,particularlyinthecaseofmoreadvancedearthcuttingprocesses.Anotherapproach,basedonkinematicallyadmis-wxsiblemechanisms,wasproposedlater5andappliedforthedescriptionofmoreadvancedearthshovingwxprocesses6,7,10–12.LetusdiscusstheproblemofplanestrainrigidwallshovingpresentedschematicallyinFig.1.As-sumingthematerialtoberigid-perfectlyplasticandtoobeytheCoulomb–Mohryieldcriterion:11sysqsyssinyccoss01...121222where:c—materialcohesion,w—internalfrictionangle.Theflowruletakestheform:EGs.ij˙«sl2.˙ijEsij.whereGsrepresentsaplasticpotential.ijInthecasewhenpotentialisdescribedbythe..yieldcriterionEq.1,theassociatedflowruleisassumed,whenanotherfunctionistaken,theflowruleisnon-associated.Usingthisapproachandassumingachangeofwxmaterialparameterswithintheslipline6,7,theFig.1.Typicaldeformationofcohesivesoilinthecaseoftheadvancedshovingprocessrealisedbythehorizontaltoolmotiontheoretica