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'IE458CAMComputerAidedManufacturingPart-5RoboticSystemsIndustrialEngineeringDepartmentKingSaudUniversity Contents·Whatisanindustrialrobot?ThebasiccomponentsofarobotPowersourcesforrobotsHydraulicdriveElectricdrivePneumaticdriveRobotsensorsThehandofarobot(end-effector)RobotMovementandPrecisionTherobotjointsRobotclassificationPhysicalclassificationControlclassificationRobotreachRobotmotionanalysisandcontrolRobotProgrammingandLanguagesRobotSelectionRobotapplicationsRobotEconomicwww.hygy1688.com衬塑复合管涂塑复合管钢塑复合管消防涂覆钢管 Whatisanindustrialrobot?Theword"robot"isderivedfromasatiricalfantasyplay,"Rossum"sUniversalRobots,"writtenbyKarelCapekin1921.Inhisplay,Capekusedthewordtomean,"forcedlabor."TheRoboticsIndustriesAssociation(RIA),formerlyknownastheRoboticsInstituteofAmerica,definesrobotinthefollowingway:Anindustrialrobotisaprogrammablemulti-functionalmanipulatordesignedtomovematerials,parts,tools,orspecialdevicesthroughvariableprogrammedmotionsfortheperformanceofavarietyoftasks. Anindustrialrobotconsistsofanumberofrigidlinksconnectedbyjointsofdifferenttypes,controlledandmonitoredbyacomputer.Toalargeextent,thephysicalconstructionofarobotresemblesahumanarm.Thelinkassemblymentionedaboveisconnectedtothebody,whichisusuallymountedonabase.Thislinkassemblyisgenerallyreferredtoasarobotarm.Awristisattachedtothearm.Tofacilitategrippingorhandling,ahandisattachedattheendofthewrist.Inroboticsterminology,thishandiscalledanend-effector.Thecompletemotionoftheend-effectorisaccomplishedthroughaseriesofmotionsandpositionsofthelinks,joints,andwrist.Atypicalindustrialrobotwithsix-degreesoffreedomisshownin.Figure1 ThewidespreaduseofCNCinmanufacturingisidealfortheuseofindustrialrobotstoperformrepetitivetasks.Suchtasksmayinvolvehandlingheavyandsometimeshazardousmaterials.SophisticatedCNCmachiningcenterscancontainpalettechangersandspecialinterfacesthatcaneasilyaccommodateindustrialrobots. Specializedrobotscanassistinbothassemblyandinspectionprocesses. Materialhandlingrobotsareusedinmanyindustries.Itmaybesurprisingtofindsuchrobotsusedeveninthefastfoodindustry. Thismaterialhandlingrobotisusedinpreparingpalettesforshipping. Repetitivetasksareidealtobeperformedbysuchmachines. ShownisaFanucM-16iRoboticArmusedinaprecisiongrindingprocessonautomotiveparts. ShownisaFanucRobotarmliftingthreeheavyboxesatonce. Inusingrobotics,humansafetyfactorsinsuchataskarecompletelyeliminated.Thisalsogreatlyreducestherisksofrepetitivestressinjuriestofactoryworkers. HandlingofdangerousmaterialsisanimportanttaskforRobotstoperform. Thesizeandweightofsomeautomotivepartsmaybetoocumbersomeandhazardousforhumanstomanipulateincertainprocesses. Shownisaroboticarmusedinconjunctionwithasmallpunchpress.Togetherthesetwomachinescouldcompriseasmallmanufacturingcell.TheuseofRoboticsinsuchasetupcangreatlyreducethechanceofhumanerrorandinjury. Itisnowcommonplacetofindautomotivemanufacturersusingroboticsinmanyphasesoftheautomotiveassemblyline. HereanautomotivesprayboothutilizesaFanucRobotarmisusedtopreciselydepositpaintonthiscarbody. Theuseofroboticscanimprovethequalityofcertainmanufacturedgoods. HereaFanucS-420Wmaterialhandlingrobotisusedintheelectronicappliancesindustry. Youwillnoteseveralothersinthebackgroundusedinotherstepsofthemanufacturingprocess. AnotherFanucA-510robotarmusedinthefoodindustry.Improvedproductivityisanimportantfactorinusingroboticequipmentisrepetitiveproductionlineoperations.Itcangreatlyreducethehumanfactorswhichcanleadtoerrorsandriskofinjury. ShownaretwoFanuchRobotarmsemployedtoperformprecisionweldingtasks.Thistypeofprocesswouldbeextremelydifficulttoachievebyhumans. THEBASICCOMPONENTSOFAROBOTThebasiccomponentsofarobotincludethemanipulator,thecontroller,andthepowersupplysources.Thetypesandattributesofthesecomponentsarediscussednext.PowerSourcesforRobotsAnimportantelementofarobotisthedrivesystem.Thedrivesystemsuppliesthepower,whichenablestherobottomove.Thedynamicperformanceoftherobotisdeterminedbythedrivesystemadopted,whichdependsmainlyonthetypeofapplicationandthepowerrequirements.Thethreetypesofdrivesystemsaregenerallyusedforindustrialrobots:HydraulicdriveElectricdrivePneumaticdrive HydraulicDriveAhydraulicdrivesystemgivesarobotgreatspeedandstrength.Thesesystemscanbedesignedtoactuatelinearorrotationaljoints.Themaindisadvantageofahydraulicsystemisthatitoccupiesfloorspaceinadditiontothatrequiredbytherobot.Problemsofleaks,makingthefloormessy.Becausetheyprovidehighspeedandstrength,hydraulicsystemsareadoptedforlargeindustrialrobots.Hydraulicrobotsarepreferredinenvironmentsinwhichtheuseofelectric-driverobotsmaycausefirehazards,forexample,inspraypainting. ElectricDrivesComparedwithahydraulicsystem,Anelectricsystemprovidesarobotwithlessspeedandstrength.Electricdrivesystemsareadoptedforsmallerrobots.Robotssupportedbyelectricdrivesystemsaremoreaccurate,exhibitbetterrepeatabilityCleanertouse. PneumaticDrivePneumaticdrivesystemsaregenerallyusedforsmallerrobots.Theserobots,withfewerdegreesoffreedom,carryoutsimplepick-and-placematerial-handlingoperations,suchaspickingupanobjectatonelocationandplacingitatanotherlocation.Theseoperationsaregenerallysimpleandhaveshortcycletimes.Pneumaticrobotsarelessexpensivethanelectricorhydraulicrobots.Mostpneumaticrobotsoperateatmechanicallyfixedendpointsforeachaxis.Abigadvantageofsuchrobotsistheirsimplemodularconstruction,usingstandardcommerciallyavailablecomponents.Thismakesitpossibleforafirmtobuilditsownrobotsatsubstantialcostsavingsforsimpletaskssuchaspickandplace,machineloadingandunloading,andsoforth. RoboticSensorsThemotionofarobotisobtainedbyprecisemovementsatitsjointsandwrist.Whilethemovementsareobtained,itisimportanttoensurethatthemotionispreciseandsmooth.Thedrivesystemsshouldbecontrolledbypropermeanstoregulatethemotionoftherobot.Alongwithcontrols,robotsarerequiredtosensesomecharacteristicsoftheirenvironment.Thesecharacteristicsprovidethefeedbacktoenablethecontrolsystemstoregulatethemanipulatormovementsefficiently.Sensorsprovidefeedbacktothecontrolsystemsandgivetherobotsmoreflexibility.Sensorssuchasvisualsensorsareusefulinthebuildingofmoreaccurateandintelligentrobots.Thesensorscanbeclassifiedinmanydifferentwaysbasedontheirutility.Inthissectionwediscussafewtypicalsensorsthatarenormallyusedinrobots:Positionsensors.Theyareusedtomonitorthepositionofjoints.Rangesensors.Rangesensorsmeasuredistancesfromareferencepointtootherpointsofimportance.Velocitysensors.VelocitysensorsareusedtoestimatethespeedwithwhichamanipulatorismovedProximitysensors.Proximitysensorsareusedtosenseandindicatethepresenceofanobjectwithinaspecifieddistanceorspacewithoutanyphysicalcontact TheHandofaRobot:End-EffectorsTheend-effectors(commonlyknownasrobothand)mountedonthewristenablestherobottoperformspecifiedtasks.Varioustypesofend-effectorsaredesignedforthesamerobottomakeitmoreflexibleandversatile.End-effectorsarecategorizedintotwomajortypes:1.Grippers:2.Tools. Grippersaregenerallyusedtograspandholdanobjectandplaceitatadesiredlocation.Gripperscanbeclassifiedas:Mechanicalgrippers,Vacuumorsuctioncups,Magneticgrippers,Adhesivegrippers,Hooks,Scoops,Others.Grippersusuallyoperateinjawtypefashionbyhavingfingerswhicheitherattachtothegripper,orarepartoftheconstruction,openandclose.Theattachedfingerscanbereplacedwithnewordifferentfingers,allowingforflexibility,seeFigure2.Gripperscanoperatewithtwofingersormore.Figure2 Attimes,arobotisrequiredtomanipulateatooltoperformanoperationonaworkpart.Spot-weldingtools,arc-weldingtools,spray-paintingnozzles,androtatingspindlesfordrillingandgrindingaretypicalexamplesoftoolsusedasend-effectors.End-effectors-Tools Gripperdesigns:Therearemanyapproachestogripperdesigns.TheseFiguresshowsthevariouslinkageswhichresultinpivotingactionforgripping. RobotMovementandPrecisionSpeedofresponseandstabilityaretwoimportantcharacteristicsofrobotmovement.Speeddefineshowquicklytherobotarmmovesfromonepointtoanother.Stabilityreferstorobotmotionwiththeleastamountofoscillation.Agoodrobotisonethatisfastenoughbutatthesametimehasgoodstability.Theprecisionofrobotmovementisdefinedbythreebasicfeatures:highresolutionAccuracyRepeatability 1.SpatialResolutionThespatialresolutionofarobotisthesmallestincrementofmovementintowhichtherobotcandivideitsworkvolume.Itdependson:thesystem"scontrolresolutionandtherobot"smechanicalinaccuracies.Thecontrolresolutionisdeterminedbytherobot"spositioncontrolsystemanditsfeedbackmeasurementsystem.Thecontrollerdividesthetotalrangeofmovementsforanyparticularjointintoindividualincrementsthatcanbeaddressedinthecontroller.Thebitstoragecapacityofthecontrolmemorydefinesthisabilitytodividethetotalrangeintoincrements.Foraparticularaxis,thenumberofseparateincrementsisgivenbyNumberofincrements=2nwherenisthenumberofbitsinthecontrolmemory. EXAMPLEArobot"scontrolmemoryhas8-bitstoragecapacity.IthastworotationaljointsandonelinearjointDeterminethecontrolresolutionforeachjoint,ifthelinearlinkcanvaryitslengthfromasshortas0.2mtoaslongas1.2m.SolutionControlmemory=8bitFromtheequationabove,numberofincrements=28=256(a)Totalrangeforrotationaljoints=360Controlresolutionforeachrotationaljoint=360/256=1.40625(b)Totalrangeforlinearjoint=1.2-0.2=1.0mControlresolutionforlinearjoint=1/256=0.003906m=3.906mm 2.AccuracyAccuracycanbedefinedastheabilityofarobottopositionitswristendatadesiredtargetpointwithinitsreach.Intermsofcontrolresolution,theaccuracycanbedefinedasone-halfofthecontrolresolution.3.RepeatabilityRepeatabilityreferstotherobot"sabilitytopositionitsend-effectorsatapointthathadpreviouslybeentaughttotherobot.Therepeatabilityerrordiffersfromaccuracyasdescribedbelow LetpointAbethetargetpointasshowninFigurea.Becauseofthelimitationsofspatialresolutionandthereforeaccuracy,theprogrammedpointbecomespointB.ThedistancebetweenpointsAandBisaresultoftherobot"slimitedaccuracyduetothespatialresolution.WhentherobotisinstructedtoreturntotheprogrammedpointB,itreturnstopointCinstead.ThedistancebetweenpointsBandCistheresultoflimitationsontherobot"srepeatability.However,therobotdoesnotalwaysgotopointCeverytimeitisaskedtoreturntotheprogrammedpointB.Instead,itformsaclusterofpoints.Thisgivesrisetoarandomphenomenonofrepeatabilityerrors.Therepeatabilityerrorsaregenerallyassumedtobenormallydistributed.Ifthemeanerrorislarge,wesaythattheaccuracyispoor.However,ifthestandarddeviationoftheerrorislow,wesaythattherepeatabilityishigh.WepictoriallyrepresenttheconceptoflowandhighrepeatabilityaswellasaccuracyinFigureb,c,d,ande.Considerthecenterofthetwoconcentriccirclesasthedesiredtargetpoint.Thediameteroftheinnercirclerepresentsthelimitsuptowhichtherobotend-effectorcanbepositionedandconsideredtobeofhighaccuracy.Anypointoutsidetheinnercircleisconsideredtobeofpoororlowaccuracy.Agroupofcloselyclusteredpointsimplieshighrepeatability,whereasasparselydistributedclusterofpointsindicateslowrepeatability. Figurea. Figure(a)Accuracyandrepeatability;(b),highaccuracyandhighrepeatability;(c)highaccuracyandlowrepeatability;(d)lowaccuracyandhighrepeatability;(e)lowaccuracyandlowrepeatability. THEROBOTICJOINTSArobotjointisamechanismthatpermitsrelativemovementbetweenpartsofarobotarm.Thejointsofarobotaredesignedtoenabletherobottomoveitsend-effectorsalongapathfromonepositiontoanotherasdesired.Thebasicmovementsrequiredforthedesiredmotionofmostindustrialrobotsare:Rotationalmovement.-Thisenablestherobottoplaceitsarminanydirectiononahorizontalplane.Radialmovement.Thisenablestherobottomoveitsend-effectorsradiallytoreachdistantpoints.Verticalmovement.Thisenablestherobottotakeitsend-effectortodifferentheights. Thesedegreesoffreedom,independentlyorincombinationwithothers,definethecompletemotionoftheend-effector.Thesemotionsareaccomplishedbymovementsofindividualjointsoftherobotaim.Thejointmovementsarebasicallythesameasrelativemotionofadjoininglinks.Dependingonthenatureofthisrelativemotion,thejointsareclassifiedasprismaticorrevolute.Prismaticjointsarealsoknownasslidingaswellaslinearjoints.Theyarecalledprismaticbecausethecrosssectionofthejointisconsideredasageneralizedprism.Theypermitlinkstomoveinalinearrelationship.Revolutejointspermitonlyangularmotionbetweenlinks. Thefivejointtypesare:Linearjoint(L).Therelativemovementbetweentheinputlinkandtheoutputlinkisalinearslidingmotion,withtheaxesofthetwolinksbeingparallel.Orthogonaljoint(O).Thisisalsoalinearslidingmotion,buttheinputandoutputlinksareperpendiculartoeachotherduringthemove.Rotationaljoint(R).Thistypeprovidesarotationalrelativemotionofthejoints,withtheaxisofrotationperpendiculartotheaxesoftheinputandoutputlinks.Twistingjoint(T).Thisjointalsoinvolvesarotarymotion,buttheaxisofrotationisparalleltotheaxesofthetwolinks.Revolvingjoint(V).INthisjointtype,theaxisoftheinputlinkisparalleltotheaxisofrotationofthejoint,andtheaxisoftheoutputlinkisperpendiculartotheaxisofrotation. twoformsoflinearjoint-typeL;twoformsoforthogonaljoint-typeO;rotationaljoint-typeR;twistingjoint-typeT;revolvingjoint-typeV. Example: Atypicalrobotmanipulatorcanbedividedintotwosections:Abody-and-armassembly,andAwristassembly.Thereareusually3degreesoffreedomassociatedwiththebody-and-arm,andeither2or3degreesoffreedomusuallyassociatedwiththewrist.Attheendofthemanipulator"swristisanobjectthatisrelatedtothetaskthatmustbeaccomplishedbytherobot.Forexample,theobjectmightbeaworkpartthatistobeloadedintoamachine,oratoolthatismanipulatedtoperformsomeprocess.Thebody-and-armoftherobotisusedtopositiontheobjectandtherobot"swristisusedtoorienttheobject.Toestablishthepositionoftheobject,thebody-and-armmustbecapableofmovingtheobjectinanyofthefollowingthreedirections:Verticalmotion(z-axismotion)Radialmotion(in-and-outory-axismotion)Right-to-leftmotion(x-axismotionorswivelaboutaverticalaxisonthebase) YawToestablishtheorientationoftheobject,wecandefine3degreesoffreedomfortherobot"swrist.Thefollowingisonepossibleconfigurationfora3d.o.f.wristassembly:Roll.Thisd.o.f.canbeaccomplishedbyaT-typejointtorotatetheobjectaboutthearmaxis.Pitch.Thisinvolvestheup-and-downrotationoftheobject,typicallydonebymeansofatypeRjoint.Yaw.Thisinvolvesright-to-leftrotationoftheobject,alsoaccomplishedtypicallyusinganR-typejoint.ThesedefinitionsareillustratedinthefollowingTypicalconfigurationofa3-degree-of-freedomwristassemblyshowingroll,pitch,andyaw. ROBOTCLASSIEFICATIONANDROBOTREACHNormallyrobotsareclassifiedonthebasisoftheirphysicalconfigurations.Robotsarealsoclassifiedonthebasisofthecontrolsystemsadopted.ClassificationBasedonPhysicalConfigurationsFourbasicconfigurationsareidentified:Cartesianconfiguration;Cylindricalconfiguration;Polarconfiguration;Jointed-armconfiguration. CartesianConfigurationRobotswithCartesianconfigurations,consistoflinksconnectedbylinearandorthogonaljoints(LandO).Theconfigurationoftherobot"sarmcanbedesignatedasLOO.Becausetheconfigurationhasthreeperpendicularslides,theyarealsocalledrectilinearrobots. Cartesiancoordinatebody-and-armassembly(LOO). CylindricalConfigurationInthecylindricalconfiguration,asshowninFigure7,robotshaveonetwisting(T)jointatthebaseandlinear(L)jointssucceedtoconnectthelinks.TherobotarminthisconfigurationcanbedesignatedasTLO.Thespaceinwhichthisrobotoperatesiscylindricalinshape,hencethenamecylindricalconfiguration. Cylindricalbody-and-armassembly(TLO) PolarConfigurationPolarrobots,asshowninFigure8,haveaworkspaceofsphericalshape.Generally,thearmisconnectedtothebasewithatwisting(T)jointandrotatory(R)and/orlinear(L)jointsfollow.ThedesignationofthearmforthisconfigurationcanbeTRLorTRR.RobotswiththedesignationTRLarealsocalledsphericalrobots.ThosewiththedesignationTRRarealsocalledarticulatedrobots. Polarcoordinatebody-and–armassembly(TRL). Jointed-ArmConfigurationThejointed-armconfiguration,isacombinationofcylindricalandarticulatedconfigurations.Thearmoftherobotisconnectedtothebasewithatwistingjoint.Thelinksinthearmareconnectedbyrotatoryjoints. Jointed-armbody-and-armassembly(TRR). ClassificationBasedonControlSystemsBasedonthecontrolsystemsadopted,robotsareclassifiedintothefollowingcategories:Point-to-point(PTP)controlrobotContinuous-path(CP)controlrobotControlled-pathrobot Point-to-Point(PTP)ThePTProbotiscapableofmovingfromonepointtoanotherpoint.Thelocationsarerecordedinthecontrolmemory.PTProbotsdonotcontrolthepathtogetfromonepointtothenextpoint.Theprogrammerexercisessomecontroloverthedesiredpathtobefollowedbyprogrammingaseriesofpointsalongthepath.Commonapplicationsincludecomponentinsertion,spotwelding,holedrilling,machineloadingandunloading,andcrudeassemblyoperations.Continuous-Path(CP)TheCProbotiscapableofperformingmovementsalongthecontrolledpath.WithCPcontrol,therobotcanstopatanyspecifiedpointalongthecontrolledpath.Allthepointsalongthepathmustbestoredexplicitlyintherobot"scontrolmemory.Straight-linemotionisthesimplestexampleforthistypeofrobot.Somecontinuous-pathcontrolledrobotsalsohavethecapabilitytofollowasmoothcurvepaththathasbeendefinedbytheprogrammer.Insuchcasestheprogrammermanuallymovestherobotarmthroughthedesiredpathandthecontrollerunitstoresalargenumberofindividualpointlocationsalongthepathinmemory.Typicalapplicationsincludespraypainting,finishinggluing,andarcweldingoperations. Controlled-PathRobotIncontrolledpathrobots,thecontrolequipmentcangeneratepathsofdifferentgeometrysuchasstraightlines,circles,andinterpolatedcurveswithahighdegreeofaccuracy.Goodaccuracycanbeobtainedatanypointalongthespecifiedpath.Onlythestartandfinishpointsandthepathdefinitionfunctionmustbestoredintherobot"scontrolmemory.Itisimportanttomentionthatallcontrolled-pathrobotshaveaservocapabilitytocorrecttheirpath. RobotReachRobotreach,alsoknownastheworkenvelopeorworkvolume,isthespaceofallpointsinthesurroundingspacethatcanbereachedbytherobotarmorthemountingpointfortheend-effectorsortool.Theareareachablebytheend-effectorsitselfisnotconsideredpartoftheworkenvelope.Reachisoneofthemostimportantcharacteristicstobeconsideredinselectingasuitablerobotbecausetheapplicationspaceshouldnotfalloutoftheselectedrobot"sreach.RobotreachforvariousrobotconfigurationsisshowninthefollowingFigureForaCartesianconfigurationthereachisarectangular-typespace.Foracylindricalconfigurationthereachisahollowcylindricalspace.Forapolarconfigurationitispartofahollowsphericalshape.Forajointed-armconfigurationdoesnothaveaspecificgeometricshape. Robotreach(workenvelope):(a)polar;(b)cylindricalrobot;(c)Cartesian. Robotreach(workenvelope):Jointarm(revolute)robot. RobotMotionAnalysisandControl AFour-JointedRobotinThreeDimensions:Mostrobotspossessaworkvolumewiththreedimensions.Considerthefourdegree-of-freedomrobotinFigure7.18.ItsconfigurationisTRL:R.Joint1(typeT)providesrotationaboutthezaxis.Joint2(typeR)providesrotationaboutahorizontalaxiswhosedirectionisdeterminedbyjoint1.Joint3(typeL)isapistonthatallowslinearmotioninadirectiondeterminedbyjoints1and2.Andjoint4(typeR)providesrotationaboutanaxisthatisparalleltotheaxisofjoint2.Thevaluesofthefourjointsare,respectively,1,2,3and4.Giventhesevalues,theforwardtransformationisgivenby:Figure7.18AfourdegreerobotwithconfigurationTRL:R. Theprimaryobjectiveofrobotprogrammingistomaketherobotunderstanditsworkcycle.Theprogramteachestherobotthefollowing:ThepathitshouldtakeThepointsitshouldreachpreciselyHowtointerpretthesensordataHowandwhentoactuatetheend-effectorHowtomovepartsfromonelocationtoanother,andsoforthROBOTPROGRAMMINGANDLANGUAGES Programmingofconventionalrobotsnormallytakesoneoftwoforms:Teach-by-showing,whichcanbedividedinto:PoweredleadthroughordiscretepointprogrammingManualleadthroughorwalk-throughorcontinuouspathprogramming(2)TextuallanguageprogrammingInteach-by-showingprogrammingtheprogrammerisrequiredtomovetherobotarmthroughthedesiredmotionpathandthepathisdefinedintherobotmemorybythecontroller.Controlsystemsforthismethodoperateineither:teachmode:isusedtoprogramtherobotrunmode:isusedtorunorexecutetheprogram. Poweredleadthroughprogrammingusesateachpendanttoinstructarobottomoveintheworkingspace.Ateachpendantisasmallhandledcontrolboxequippedwithtoggleswitches,dials,andbuttonsusedtocontroltherobot"smovementstoandfromthedesiredpointsinthespace.Thesepointsarerecordedinmemoryforsubsequentplayback.Forplaybackrobots,thisisthemostcommonprogrammingmethodused.However,ithasitslimitations:Itislargelylimitedtopoint-to-pointmotionsratherthancontinuousmovement,becauseofthedifficultyinusingateachpendanttoregulatecomplexgeometricpathsinspace.Incasessuchasmachineloadingandunloading,transfertasks,andspotwelding,themovementsofthemanipulatorarebasicallyofapoint-to-pointnatureandhencethisprogrammingmethodissuitable. Manualleadthroughprogrammingisforcontinuous-pathplaybackrobots.Inwalk-throughprogramming,theprogrammersimplymovestherobotphysicallythroughtherequiredmotioncycle.Therobotcontrollerrecordsthepositionandspeedastheprogrammerleadstherobotthroughtheoperation.Iftherobotistoobigtohandlephysically,areplicaoftherobotthathasbasicallythesamegeometryissubstitutedfortheactualrobot.Itiseasiertomanipulatethereplicaduringprogramming.Ateachbuttonconnectedtothewristoftherobotorreplicaactsasaspecialprogrammingapparatus.Whenthebuttonispressed,themovementsofthemanipulatorbecomepartoftheprogram.Thispermitstheprogrammertomakemovesofthearmthatwillnotbepartoftheprogram.Theprogrammerisabletodefinemovementsthatarenotincludedinthefinalprogramwiththehelpofaspecialprogrammingapparatus. Teach-by-showingmethodshavetheirlimitations:Teach-by-showingmethodstaketimeforprogramming.Thesemethodsarenotsuitableforcertaincomplexfunctions,whereaswithtextualmethodsitiseasytoaccomplishthecomplexfunctions.Teach-by-showingmethodsarenotsuitableforongoingdevelopmentssuchascomputer-integratedmanufacturing(CIM)systems.Thus,textualrobotlanguageshavefoundtheirwayintorobottechnology. TextuallanguageprogrammingmethodsuseanEnglish-likelanguagetoestablishthelogicalsequenceofaworkcycle.Acathoderaytube(CRT)computerterminalisusedtoinputtheprograminstructions,andtoaugmentthisprocedureateachpendantmightbeusedtodefineonlinethelocationofvariouspointsintheworkplace.Off-lineprogrammingisusedwhenatextuallanguageprogramisenteredwithoutateachpendantdefininglocationsintheprogram. ProgrammingLanguagesDifferentlanguagescanbeusedforrobotprogramming,andtheirpurposeistoinstructtherobotinhowtoperformtheseactions.Mostrobotlanguagesimplementedtodayareacombinationoftextualandteach-pendantprogramming.Someofthelanguagesthathavebeendevelopedare:WAVEVALAMLRAILMCLTL-10IRLPLAWSINGLAVALII VALIIItisoneofthemostcommonlyusedandeasilylearnedlanguages.Itisacomputer-basedcontrolsystemandlanguagedesignedfortheindustrialrobotsatUnimation,Inc.TheVALIIinstructionsareclear,concise,andgenerallyselfexplanatory.Thelanguageiseasilylearned.VALIIcomputesacontinuoustrajectorythatpermitscomplexmotionstobeexecutedquickly,withefficientuseofsystemmemoryandreductioninoverallsystemcomplexity.TheVALifsystemcontinuouslygeneratesrobotcommandsandcansimultaneouslyinteractwithahumanoperator,permittingon-lineprogramgenerationandmodification.AconvenientfeatureofVALIfistheabilitytouselibrariesofmanipulationroutines.Thus,complexoperationscanbeeasilyandquicklyprogrammedbycombiningpredefinedsubtasks. ProgrammingWithVALIIThefirststepinanyrobotprogrammingexerciseisthephysicalidentificationoflocationpointsusingtheteachpendant.Wedonothavetoteachallthepointsthattherobotisprogrammedtovisit;onlyafewkeypointshavetobeshown(e.g.,thecomerofapallet).Otherpointstowhichitcanbedirectedcanbereferencedfromthesekeypoints.Theprocedureissimple.FirstusethekeysorbuttonoftheteachpendanttodrivetherobotphysicallytothedesiredlocationandthentypethecommandHEREwiththesymbolicnameforthatlocation.Forexample,HEREP1ThiscommandwillidentifythepresentlocationasP1. Rulesforthelocationnameareasfollows:Itisanystringofletters,numbers,andperiods.hefirstcharactermustbealphabetic.Theremustbenointerveningblank.Everylocationnamemustbeunique.Theremaybealimitonthemaximumnumberofcharactersthatcanbeused.ThefollowingexampleillustratesthegeneralcommandformatforVALII:100APPROP115Inthisexample,100isthelabelthatreferstothisinstruction,APPROistheinstructiontotherobottoapproachthelocationnamedP1byadistanceof15mm. Inthefollowing,wedescribethemostcommonlyusedVALIIcommands.MOVEP1ThiscausestherobottomoveinjointinterpolationmotionfromitspresentlocationtolocationP1.MOVESP1Here,thesuffixSstandsforstraight-lineinterpolationmotion.MOVEP1VIAP2ThiscommandinstructstherobottomovefromitspresentlocationtoP1,passingthroughlocationP2.APPROP110ThiscommandinstructstherobottomoveneartothelocationP1butoffsetfromthelocationalongthetoolz-axisinthenegativedirection(abovethepart)byadistanceof10DEPART15SimilartoAPPRO,thisinstructstherobottodepartbyaspecifieddistance(15mm)fromitspresentposition.TheAPPROandDEPARTcommandscanbemodifiedtousestraight-lineinterpolationbyaddingthesuffixS. DEFINEPATH1=PATH(P1,P2,P3,P5)MOVEPATH1Thefirstcommand(DEFTNE)definesapaththatconsistsofseriesoflocationsP1,P2,P3,andP5(allpreviouslydefined).Thesecondcommand(MOVE)instructstherobottomovethroughthesepointsinjointinterpolation.AMOVEScommandcanbeusedtogetstraight-lineinterpolationABOVE&BELOWThesecommandsinstructtheelbowoftherobottopointupanddown,respectively.SPEED50IPSThisindicatesthatthespeedoftheend-effectorduringprogramexecutionshouldbe50inchpersecond(in./s).SPEED75Thisinstructstherobottooperateat75%ofnormalspeed.OPENInstructsendeffectortoopenduringtheexecutionofthenextmotion.CLOSEInstructstheend-effectortocloseduringtheexecutionofthenextmotion.OPENICausestheactiontooccurimmediately.CLOSEICausestheactiontooccurimmediately Ifagripperiscontrolledusingaservo-mechanism,thefollowingcommandsmayalsobeavailable.CLOSE40MMThewidthoffingeropeningshouldbe40mm.CLOSE3.0LBThiscauses3lbofgrippingforcetobeappliedagainstthepart..GRASP10,100Thisstatementcausesthegrippertocloseimmediatelyandcheckswhetherthefinalopeningislessthanthespecifiedamountof10mm.Ifitis,theprogrambranchestostatement100intheprogramSIGNAL4ONThisallowsthesignalfromoutputport4tobeturnedonatonepointintheprogramandSIGNAL4OFFturnedoffatanotherpointintheprogram.WAIT10ONThiscommandmakestherobotwaittogetthesignalonline10sothatthedeviceisonthere. logarithmic,exponential,andsimilarfunctions.Thefollowingrelationalandlogicaloperatorsarealsoavailable.EQEqualtoNENotequaltoGTGreaterthanGEGreaterthanorequaltoLTLessthanLELessthanorequaltoANDLogicalANDoperatorORLogicalORNOTLogicalcomplement TYPE"text“Thisstatementdisplaysthemessagegiveninthequotationmarks.Thestatementisalsousedtodisplayoutputinformationontheterminal.PROMPT"text",INDEXThisstatementdisplaysthemessagegiveninthequotationmarksonthetenninal.Thenthesystemwaitsfortheinputvalue,whichistobeassignedtothevariableINDEX.Inmostreal-lifeproblems,programsequencecontrolisrequired.Thefollowingstatementsareusedtocontrollogicflowintheprogram.GOTO10Thiscommandcausesanunconditionalbranchtostatement10. IF(Logicalexpression)THEN(Groupofinstructions)ELSE(Groupofinstructions)ENDDO(Groupofinstructions)UNTIL(Logicalexpression)Ifthelogicalexpressionistrue,thegroupofstatementsbetweenTHENandELSEisexecuted.Ifthelogicalexpressionisfalse,thegroupofstatementsbetweenELSEandENDisexecuted.TheprogramcontinuesaftertheENDstatement.ThegroupofinstructionsaftertheDOstatementmakesalogicalsetwhosevariablevaluewouldaffectthelogicalexpressionwiththeUNTILstatement.Aftereveryexecutionofthegroupofinstructions,thelogicalexpressionisvaluated.Iftheresultisfalse,theDOloopisexecutedagain;iftheresultistrue,theprogramcontinues. SUBROUTINEScanalsobewrittenandcalledinVALIIprograms.Monitormodecommandsareusedforfunctionssuchasenteringlocationsandsystemssupervision,dataprocessing,andcommunications.Someofthecommonlyusedmonitormodecommandsareasfollows:EDIT(Programname)Thismakesitpossibletoedittheexistingprogramortocreateanewprogrambythespecifiedprogramname. EXITThiscommandstorestheprogramincontrollermemoryandquitstheeditmode.STORE(Programname)Thisallowstheprogramtobestoredonaspecifieddevice.READ(Programname)Readsafilefromstoragememorytorobotcontroller.LIST(Programname)Displaysprogramonmonitor.PRINT(Programname)Provideshardcopy.DIRECTORYProvidesalistingoftheprogramnamesthatarestoredeitherinthecontrollermemoryoronthedisk.ERASE(Programname)Deletesthespecifiedprogramfrommemoryorstorage.EXECUTE(Programname)Makestherobotexecutethespecifiedprogram.ItmaybeabbreviatedasEXorEXEC.ABORTStopstherobotmotionduringexecution.STOPThesameasabort. EXAMPLE1:DevelopaprograminVALIItocommandaPUMArobottounloadacylindricalpartof10mmdiameterfrommachine1positionedatpointP1andloadthepartonmachine2positionedatP2.Thespeedofrobotmotionis40in./s.However,becauseofsafetyprecautions,thespeedisreducedto10in./swhilemovingtoamachineforanunloadingorloadingoperation. SolutionSIGNAL5SPEED40IPSOPEN100APPROPI,50SPEED10IPSMOVEPIGRASP10,100DEPARTP1,50SPEED40IPSAPPROP2,50SPEED10IPSMOVEP2BELOWOPENI100ABOVEDEPARTP2,50STOP EXAMPLE2:Supposewewanttodrill16holesaccordingtothepatternshownintheFigure.Thependantprocedurecanbeusedtoteachthe16locations,butthiswouldbequitetime-consumingandusingthesameprogramindifferentrobotinstallationswouldrequireallpointstobetaughtateachlocation.VALIIallowslocationadjustmentundercomputercontrol.Theprogramallowsallholestobedrilledgivenjustonelocation,calledSTAatthebottomright-handcornerofthediagram.Actually,twoprogramsarerequired,sinceonewillbeasubroutine. EXAMPLE3: ROBOTSELECTIONThisphenomenalgrowthinthevarietyofrobotshasmadetherobotselectionprocessdifficultforapplicationsengineers.Oncetheapplicationisselected,whichistheprimaryobjective,asuitablerobotshouldbechosenfromthemanycommercialrobotsavailableinthemarket.Thetechnicalfeaturesaretheprimeconsiderationsintheselectionofarobot.Theseincludefeaturessuchas:degreesoffreedom,controlsystemtobeadopted,workvolume,load-carryingcapacity,andaccuracyandrepeatability. Thecharacteristicsofrobotsgenerallyconsideredinaselectionprocessinclude:SizeofclassDegreesoffreedomVelocityActuatortypeControlmodeRepeatabilityLiftcapacityRight-Left-TraverseUp-down-traverseIn-Out-TraverseYawPitchRollWeightoftherobot Weelaborateonsomeofthesecharacteristics.Sizeofclass.Thesizeoftherobotisgivenbythemaximumdimension(x)oftherobotworkenvelope.Fourdifferentclassesareidentified:Micro(x<=1M)Small(15m)2.Degreesoffreedom.Thedegreesoffreedomcanbeone,two,three,andsoon.Thecostoftherobotincreaseswithincreasingnumberofdegreesoffreedom. Velocity.Velocityconsiderationsareaffectedbytherobot"sarmstructure.Therearevarioustypesofarmstructures.Forexample,thearmstructurecanbeclassifiedintothefollowingcategories:RectangularCylindricalSphericalArticulatedhorizontalArticulatedvertical4.Actuatortypes.Actuatortypeshavebeendiscussedintheearliersections.Theyare:•Hydraulic•Electric•PneumaticSometimes,acombinedelectricalandhydrauliccontrolsystemmaybepreferred. 5.Controlmodes.Possiblecontrolmodes-include:NonservoServopoint-to-point(PTP)Servocontinuouspath(CP)CombinedPTPandCPCharacteristicssuchasliftcapacity,weight,velocity,andrepeatabilityaredividedintoranges.Basedontheranges,thecharacteristicsarecategorizedinsubclasses.Forexample,liftcapacitycanbecategorizedas0-5kg,5-20kg,20-40kg,andsoforth.Asimpleapproachtoselectingarobotistoidentifyalltherequiredfeaturesandthefeaturesthatmaybedesirable. Thedesirablefeaturesmayplayanimportantroleintheselectionofrobots.Thesedesirablefeaturesinanindividualrobotmayberankedonascaleof,say,1to10andthedesirabilityofthesefeaturesitselfmaybeassignedweights.Finally,ranktheavailablerobotsthathavethesefeaturesbasedoncostandqualityconsiderations. EXAMPLEAmanufacturingcompanyisplanningtobuyarobot.Forthetypeofapplication,therobotshouldhaveatleastsixrequiredfeatures.Itwillbehelpfultohavemorefeaturesthatwouldaddsomeflexibilityinitsusagecapabilities.Thecompanyislookingatsixmoredesirablefeatures.Fiverobotsareselectedfromtheinitialeliminationprocessbasedonrequiredfeatures.TheratingscorematrixRisgivenas:Theentryinposition(i,j)representsthescoregiventotheithrobotmodelbasedonhowwellitsatisfiesthejthdesirablefeature.Thescoreisgivenonascaleof0to10.Thesescoresareassignedbytheapplicationsengineersbasedontheirexperienceandpracticalrequirements.Furthermore,iftheimportanceofdesirablefeaturesisgivenbythefollowingweightvector,determinethepriorityrankingofrobotsforthegivenapplication.W=(0.90.30.60.50.80.4) RobotApplicationsThecommonindustrialapplicationsofrobotsinmanufacturinginvolveloadingandunloadingofparts.Theyinclude:Therobotunloadingpartsfromdie-castingmachinesTherobotloadingarawhotbilletintoadie,holdingitduringforging,andunloadingitfromtheforgingdieTherobotloadingsheetblanksintoautomaticpresses,withthepartsfallingoutofthebackofthemachineautomaticallyafterthepressoperationisperformedTherobotunloadingmoldedpartsformedininjectionmoldingmachinesTherobotloadingrawblanksintoNCmachinetoolsandunloadingthefinishedpartsfromthemachinesSafetyandrelieffromhandlingheavyloadsarethekeyadvantagesofusingrobotsforloadingandunloadingoperations. ASingle-MachineRoboticCellApplicationConsideramachiningcenterwithinput—outputconveyorsandarobottoloadthepartsontothemachineandunloadthepartsfromthemachineasshownintheFigure.Atypicaloperationsequenceconsistsofthefollowingsteps:Theincomingconveyordeliversthepartstoafixedposition.Therobotpicksupapartfromtheconveyorandmovestothemachine.Therobotloadsthepartontothemachine.Thepartisprocessedonthemachine.Therobotunloadsthepartfromthemachine.Therobotputsthepartontheoutgoingconveyor.Therobotmovesfromtheoutputconveyortotheinputconveyor.Thisoperationsequenceoftheroboticcellisaccomplishedbyacellcontroller.Productionrateisoneoftheimportantperformancemeasuresofsuchcells.Weprovideanexampleofdeterminingthecycletimeandproductionrateofaroboticcell. EXAMPLEComputethecycletimeandproductionrateforasingle-machineroboticcellforan8-hshiftifthesystemavailabilityis90%.Alsodeterminethepercentutilizationofmachineandrobot.Onaverage,themachinetakes30stoprocessapart.Theotherrobotoperationtimesareasfollows:Robotpicksupapartfromtheconveyor3.0sRobotmovestheparttothemachine1.3sRobotloadsthepartontothemachinel.0sRobotunloadsthepartfromthemachine0.7sRobotmovestotheconveyor1.5sRobotputsthepartontheoutgoingconveyor0.5sRobotmovesfromtheoutputconveyortotheinputconveyor4.0s ASingle-MachineCellwithaDouble-GripperRobotAdouble-gripperrobothastwogrippingdevicesattachedtothewrist.Thetwogrippingdevicescanbeactuatedindependently.Thedoublegrippercanbeusedtohandleafinishedandanunfinishedworkpieceatthesametime.Thishelpsincreaseproductivity,particularlyinloadingandunloadingoperationsonmachines.Forexample,withtheuseofadouble-handedgripper,thefollowingrobotoperationscouldbeperformedduringthemachineoperationcycletime:1.Movetoconveyor2.Depositapartandpickupanewpart3.MovetothemachineHowever,itmustbementionedthatthisispossibleonlyifthemachineoperationcycletimeismorethanthecombinedtimeforactivities1,2,and3.Furthermore,thereisnoneedtomovetherobotarmfromtheoutputconveyortotheinputconveyor. ECONOMICJUSTIFICATIONOFROBOTSWehaveseenintheprevioussectiononrobotapplicationsthatrobotsarebeingusedinavarietyofindustrialanddomesticenvironments.Someoftheseapplicationsarejustifiedonthebasisthatthetypeofwork,suchasweldingorpainting,isdangerousandunhealthyforhumans.Itis,however,equallyimportanttostudywhethertherobotizationisalsoeconomicallyjustified.Alargenumberofmodelsforeconomicevaluationexist(fordetails,refertoWhiteetal,1989).Inthissectionweprovideasimpletreatmentbyconsideringthepaybackperiodasameasureofeconomicjustificationofrobots. PaybackPeriodMethodTheprimaryideabehindthepaybackperiodmethodistodeterminehowlongittakestogetbackthemoneyinvestedinaproject.Thepaybackperiodicanbedeterminedfromthefollowingrelation:Netinvestmentcost=totalinvestmentcostofrobotandaccessories-investmenttaxcreditsavailablefromthegovernment,ifanyNetannualcashflows=annualanticipatedrevenuesfromrobotinstallationincludingdirectlaborandmaterialcostsavings-annualoperatingcostsincludinglabor,material,andmaintenancecostoftherobotsystemnetinvestmentcost(NIC)oftherobotsystemincludingaccessoriesnetannualcashflowsn= DetroitPlasticsisplanningtoreplaceamanualpaintingsystembyaroboticsystem.Thesystemispricedat$160,000.00,whichincludessensors,grippers,andotherrequiredaccessories.Theannualmaintenanceandoperationcostoftherobotsystemonasingle-shiftbasisis$10,000.00.Thecompanyiseligiblefora$20,000.00taxcreditfromthefederalgovernmentunderitstechnologyinvestmentprogram.Therobotwillreplacetwooperators.Thehourlyrateofanoperatoris$2000includingfringebenefits.Thereisnoincreaseinproductionrate.Determinethepaybackperiodforone-andtwo-shiftoperations.Example SolutionNetinvestmentcostcapitalcost-taxcredits=$160,000-$20000.00$=140000.00Annuallaborcostoperatorrate($20/hr)Xnumberofoperators(2)Xdaysperyear(250d/yr)Xsingleshift(8h/d)=$80,000(forasingleshift)Fordouble-shiftoperation,theannuallaborcostis$160,000.00.Forasingle-shiftoperation:Annualsavings=annuallaborcost-annualrobotmaintenanceandoperatingcost=$80,000.00-$10,000.00=$70,000.00Thepaybackperiodforsingle-shiftoperationisSl40,000,00/$70,000.00=2yearsFordouble-shiftoperation,Annualsavings=$160,000.00-$20,000.00=$140,000.00.Therefore,thepaybackperiodfordouble-shiftoperationis$140,000.00/$140,000.00=1.00years.Apaybackperiodof2yearsorlessisaveryattractiveinvestment.Inthisexamplewehavenotconsideredanyproductionrateincreasewiththerobotsysteminstallation.Typically,suchasystemresultsin30to75%increaseinproductivity.Basedonthesefigures.thisisanattractiveproposal.'