外文翻译原文-精密步进电机控制器在机器人中的应用

APRECISIONSEPFERWNXFDRROBUllCAPPLICATIONSDrDineshP.Hital.HrChinTeckChaiandHrToeHyintSchoolofElectricalandElectronicsEngineeringNanyangTechnologicalInstituteSingapores!J!m!aTheobjectiveofthispaperistodevelopaprecisionsteppermotorcontrollercapableofbothindependentandsynchronizedcontrolofmultiplenumberofsteppermotors.Thecontrollerisbuiltarounda16-bitmicroprocessortoprovidefastandreliablecontroloperations.Inaddition,microsteppingtechniquesareusedtoachievehighresolutionelectronicallyandtosuppressmechanicalresonance.Thecontrolleralsoincludessixinput/outputports.Suchcontrollershavewideapplicationsinmanufacturingindustry.Forinstance,itcanbeusedtocontrolarobothavinguptosixdegreesoffreedom.Thecontrollerhasbeentestedwithasimultaneouscontrol(synchronous)ofsixsteppermotorsforaprecisiontrajectorycontrolapplications.IKI7HIwCTIoNConventionalsteppermotordrivesallowthemotorstobedrivenineitherthefullstepmodeorhalfstepmode.Theperformanceofsuchdrivesystemsareusuallylimitedbythemechanicalresonanceofthesteppermotor.Microsteppingdrivesystemsovercomethisproblembypropercontrolofcurrentineachphasel.61.Suchdrivesimprovetheresolutionofthemotorsbyafactorequaltothenumberofsub-stepsinafullstep.Forinstance,a200stepsperrevolutionmotorturnsintoa2.000stepsperrevolutionhasaimprovedresolutionbyafactorof10.Thepositionalaccuracyisalsoimprovedasaresultofimprovedresolution5.6.71.Althoughtheopenloopcontrolnormallyproducessatisfactoryperformanceasfaraspositionaccuracyisconcerned.someproblemsmayariseifthemotorisoperatingunderhighloadandhighaccelerationcondition.Themotormaylosestepsorovershoot.Theseconditionscanbeovercomewiththeuseofclosedloopcontrol2.3.61.Incloseloopcontrol.thegenerationofthepulsetrainisidenticaltotheopenloopsystemSI.Theonlydifferenceisthattheoutputofanopticalencoderisusedtodecrementthestepcounter.Thispaperpresentsaclosedloopmicrosteppingsteppermotorcontrollerwhichovercomestheproblemfoinstabilityandatthesametimeprovidesforhighaccuracy.Thistechniqueimproveselectronicallytheresolutionofsteppermotorsandsuppressesoscillations.Anotherkeyfeatureisthecapabilityofthecontrollertocontrolmultiplenumberofsteppermotorsforsimultaneousoperations(indpendentandlorsynchronized).Thishasgreatlyenhanceditsusefulnessinmoderncontrolapplications.Theapplicationofthiscontrollerforcontrollingasixdegreesoffreedomisoneoftheexamples.Thecontrolledrobotiscapableofveryaccurate.point-to-pointtrajectorycontrol.Basically,thecontrollerisusedinconjunctionwithstandardsteppermotordrivessuchasSGSL297andL7180.OPERATINGPRINCIPLEThedesignofthecontrollercatersforbothopenloopandclosedloopoperations.Themostattractivefeatureisitsabilitytopositiontherotoraccuratelywhichallowsthecontrolsystemwithhighdegreeofaccuracy.Undernormalconditionstheperformanceissatisfactorywithopenloopcontrol,butproblemsmayarise,ifthemotorisoperatingunderhighloadandaccelerationconditions.Themotormaylosestepswhileacceleratingorovershotwhiledeceleratingduetoloadinertia.Thusundertheseconditions,itisdesirabletohaveclosedloopcontrolforpositionverification.ClosedLoor,ControlInclosedloopcontrolscheme,theinstantaneousrotorpositionisdetectedandfedbacktothecontrolunit.Eachstepcomdisissuedonlywhenthemotorhasrespondedsatisfactorilytothepreviouscommndandsothereisnopossibilityofmotorlosingthesynchronization.AblockdiagramofthefeedbackschemeisgiveninFigure1.Withpositiondetectorfeature,theaccelerationisalsoautomaticallyadjusted.Anopticalencodingdeviceisusedforthepositionfeedback.MotionProfileEachsteppermotorhasamaximumstartingandstoppingspeedwhichisafunctionoftheloadinertia.Hence,itcannotbestartedorstoppedabovethemaximumspeedwithoutlosingsteps.However,itwouldbeawastetocarryouttheentiremotionataslowpace.Hence,anoptimumvelocityprofilehastobegenerated.AtypicalprofileisshowninFigure2.AprogrammabletimerisusedforthispurposeandapossibleschemeisshowninFigure3.Theprogrammabletimerisusedtogenerateapulsetrainwhosefrequencydependsontimerpreloadregister.Numberofstepsineachtimeslotduringacceleratioddecelerationisgivenbyi=1.2.nV:id.=A=Acceleration(orV=maximumvelocitydeceleration)duringaccelerationordecelerationn=numberofdiscretestepsThesestepsarecontrolledbythemicroprocessor.Numberoftimestepsnshouldbelargeenoughsothatthestepchangeinvelocityisnottoolarge.Authorizedlicenseduselimitedto:HuaiyinInstituteofTechnology.DownloadedonMarch13,2010at05:49:39ESTfromIEEEXplore.Restrictionsapply.Duringtheconstantvelocityperiod.thetotalnumberofstepsisgivenbyd=D-2(d,+d,+.+dn-1)whereD=totalnumberofstepstomoveSimultaneousControlofItultiDleNumberofMotorsWeseethatmicroprocessorisidleformostofthetime.Itisusedtoloadandpreloadregisterswiththevectornumbereachtime.Thistaskcanbedonewithinashortperiodoftime.Hence,itispossibletocontrolmultiplenumberofsteppermotorswithonemicroprocessor.Theonlyproblemisthesynchronizationofthemotors.Thelimittothenumberofmotors.whichcanbecontrolleddependsonlyonthespeedoftheprocessor.Atanaveragepulserateof2kHzwithadistanceof100substepsbetweenspeedchanges,itispossibletocontrol400motors(theortically).Practicalnumberis6-10.Synchronizationproblemariseswhentwomotorsarerequiredtostarttogetheroronehastowaitforothertostopbeforeitmakesitsownmove.Tosolvethis.aclearsetofsoftwarecommandsaredefined.Eachcommanddefinesaparticulartasktobeperformedbytheprocessor(e.g.WaitforXmillisec.Runpredefinedprofile#n.WaitforMotorktofinishconmnand#m).Theseconnnandsarecombinedtogethertoformasequencebufferwhichrepresentsaseriesofactionstobecarriedoutbythemotor.Thereareatotalof6sequencebuffers.Eachofthesedefinesasequenceforamotor.Whenacommandisreceivedtorunthesequencebuffer.theprocessorwillcontinuouslypollthestatusofeverymotorandupdatethestatusflags.andcheckifanyserviceisrequired.Ifyes.anappropriateservicewillbegiven,andtheactionwillproceedtothenextmotor.Itcontinuesuntilastopsequencecommandisexecuted.HARDWAREThevariousmodulesintheproposedcontrollersare:68OOOCPUwithRAMandROMSteppulsegenerator(velocityanddistancecounters)forthreemotorsOpticalshaftencoderforfeedbackcircuitinterface60generalbitI/OportsVMEBusinterfaceTheschematicblockdiagramofthecontrollerisshowninthefigure4.Inrealtimeapplications,themotorsareusedtodriveroboticjointsandX.Ytablecontrol.Thesenormallyhavecontrollingdevicessuchassensors,limitswitchesetc.ForCPUtointerfacewiththesedevices,60generalpurpose110bitsareavailableinthecontrolboard.-681andMC68230wereusedforserialandparallelinterfaceandfour7-191werecascadedtoform16-bitvelocitytimerforgeneratingsteppulseswithvariablefrequency.rateis20MHz.ThebackplaneusesthestandardEurocardindirect%-wayplug41612connector.Thecurrentratingpercontactis1.5amps.Expansioncardsformemory.VMEbusandsteppulsegeneratorsformoremotorscanbeplugged-in,ifrequired.Althoughsteppingmotorsnormallyperformsatisfactorilywithopen-loopcontrol,anencodercircuitwasdevelopedforobtainingfeedbackonexactposition.Alo00lineopticalshaftencoderwasusedforeachmotor.Thedirectiondecoderalsoverifiesthatthemotorisrotatinginthespecifieddirection.ThesignalENCDIRNisinterpretedashighforclockwisedirection.ThisisillustratedinFigure5.Undertheclosedloopcontrol,thedecodeddirectionsignaliscomparedwiththedirectionsignalsenttothemicrosteppingdrive.Iftheyaredifferent.aninterruptissenttothemicroprocessor.A24-bitprogrammablecounterisusedasadistancecountertocountthenumberofsteppulsesgeneratedbythevelocitycounter.Ithasa24-bitpreloadregisterwhichisusedtostorethenextstepcountwhilethecurrentcountisdecremented.Eachtimewhentimercountstozero.apulseisproduced.whichisusedtocontrolstepsforthesteppingmotor.Thevelocitytimerwillrepeatthecycleandgenerateastreamofpulsesattheoutput.TheHewlett-PackardLogicDevelopmentSystem-HP64000andMC68000emulatorwereusedasthedevelopmenttoolsfortestingandtroubleshootingoftheprototype.ThemaximumclockAssemblylanguageprograrmningwasusedbecausecodingismorecompactandefficientinthesensethatitrequireslessexecutiontime.therefore.moremotorscanbecontrolledwithasinglecontroller.Figure6showstheblockdiagramofthemaincontrolprogram.Thismoduleconsistsofthevariousfunctionsubprogramsthatareusedtodefineprofile.runprofile,definesequence.runsequenceandstopmotion.Therearesomedeviceswhichmustbeinitializeduponpower-uporhardwarereset;namelytheparallelinterface,theasynchronoustransmitterreceiverandtheprogrammabletimer.SomeoftheimportantsoftwaremodulesusedintheMainControlprogramare:DefineProfileTherearebasically4parametersneededtobespecified.thoseare:velocity,acceleration,distance.anddirection.Fromtheseparameters.theprocessorwillgenerateanaccelerationtableandreturntothemainprogram.RunProfileThemodulepreloadsthetimerandcounterfromaccelerationtable.Whenthecountercountstozero.itinterruptstheprocessorforloadingnextsetofnumbers.StatusofChannelxindicatesthestatusoftheprofile687Authorizedlicenseduselimitedto:HuaiyinInstituteofTechnology.DownloadedonMarch13,2010at05:49:39ESTfromIEEEXplore.Restrictionsapply.DefineSeauenceThisisaprogramtoinputaseriesofconurandsandsaveinthesequencebuffer.ThefollowingconmnandsareallowedPX:RunProfilexDn:DelaybynunitsWx:WaitforChannelxRunSeauenceTheprocessorfetchescurrentcommandfromthesequencebufferandcomparesitwithallthecorrnrandsavailable.Ifnoneofthemmatches.itgeneratesanerrorflagandreturnstothemainprogram.Wheneitheronematches.itexecutestheconnnandaccordingly.Uponcompletion.itincrementsthesequencecommandpointertopointstothenextconurand.Theprocessorprocessesonechannelatatime.TheblockdiagramforthismoduleisshowninFigure7.ProfileGenerationUserspecifiesthedirectionofrotation,angulardistanceandtimeofthemotion.Otherparametersofinterestbutnotsocriticalareaccelerationandmaximummotorspeed.Normally,distanceistakentobemostimportantparameter.Wehaveadoptedaconstantaccelerationprofile.Thestepchangeinspeedisfixedat500Hz.Thenumberofmicrostepstobemovedisspecifiedbytheuser.Thetimetakentoturnthatmanymicrostepsislongeratlowerspeedthanathigherone.EXPERIrnAL,RESULTSTheproposedsystemwastestedextensivelyfortheprecisionofthepositionalaccuracy.Themotorcontrollerisdesignedtointerfacetoanysteppermotordrivewhichacceptsdigitalstepsanddirectioncomnands.Fortestingpositioningaccuracy,aprofileisset.Therearethreeparameterstoset;namely,velocity,accelerationanddistance.Thedistanceparameteristhenumberofsteppulsesthatthecontrollerhastooutput.Aseriesoftestswerecarriedoutwithdifferenttestparameters.TheresultsareshowninTable1.Thepositionalaccuracyhasbeenexcellentwithoutanyerrorcount.Afurthertestwascarriedouttotestforthesimultaneouscontrolof6steppingmotorsforindependentandsynchronizedmovement.Nodatawasrecorded85such.Thedigitalpulsecounterwasusedtoverifythatthepositionalaccuracyismaintainedwhilemultiplenumberofchannelsarecontrolledsimultaneously.Themotorswereplacedadistanceawayfromtheelectroniccircuittoreducetheinterference.Propershieldinglaterwouldnotcauseanyinterferenceproblem.Differencesequencesandprofileswereexecuted.Thecontrollerhadabsolutelynoproblemsatallandthesamepositionalaccuracyismaintained.Theresolutionofsteppingmotorcanbeincreasedbyprovidingahigherpulserate.Themaximumpulserateforthecontrollerisspecifiedat100kHzusingthetimer-counterapproachtogeneratethepulsetrain,theinputfrequencytothetimermustbegreaterthan100kHz.amcurSIONTheimplementationofclosedloopmicrosteppingcontrollerforstandardsteppermotorsispresentedinthispaper.Thekeyfeaturesofthiscontrollerlieinitsflexibilitytoprovideforhighpositionalresolutionoperationofagivensteppingmotorcontrolsystem.Thecontrollerhasbeenextensivelytestedforitsaccuracy.Therehadbeenabsolutelynomissingstepproblemduringthetesting.Thecontrolleriscapableofcontrollinguptosixsteppingmotorswithoutsacrificingpositionalaccuracy.Theproposedsystemhasbeentestedforroboticcontrolofmultipleaxes.Theresultshavebeenexcellent.ThiscontrollercanalsobeusedfortrajectorycontrolforroboticapplicationandX.Ytablecontrol...ArnoldJr.,MicrosteppingaStepperMotorforGreaterPositionalResolution.ControlEngineering.Vol.32.pp.111-113.1985.TakashiK.SteppingMotorsandTheirMicroprocessorControl.ClarendonPress,Oxford,1984.TakashiK.andTakaharaT.MicroprocessorUseinMotorControlCircuits.IEE.pp.61-63.1984.KleingeldP.DriveStepperMotorWithoutMissingSteps.EDN.pp.156-158.1985.LakshminarayanV.ControlofaBi-directional4-PhaseStepperMotor.EXN,pp.306-309.1985.KuoB.,IncrementalMotionControl.Vol.2.SRL,Illinois,1979.LeenthoulltsA.,SteppingMotorsinIndustrialMotionControl.ProceedingsoftheInternationalMotorcon81.Vol.1.pp.97-105.1981.ShaughnessyW.OptimisingSteppingMotorControlParameterstoMi.nimiseProcessTime.ProceedingsoftheInternational.Motorcon81.Vol.1.pp.83-96.1981.688Authorizedlicenseduselimitedto:HuaiyinInstituteofTechnology.DownloadedonMarch13,2010at05:49:39ESTfromIEEEXplore.Restrictionsapply.TABLE1POSITIONINGERROREXPE