Introduction
Digitalcontrolsystemisalsocalledcomputercontrolsystem,whichisproducedonthebasisoftherapiddevelopmentofautomaticcontroltechnologyandcomputertechnology.Inthemid-1950s,theclassicalcontroltheoryhasbeendevelopedverymaturely,andithasbeensuccessfullyappliedinmanyfieldsofengineeringtechnology.Specifically,adigitalcontrolsystemreferstoanautomaticcontrolsystemthatusesdigitaltechnologytoachievevariouscontrolfunctions.Itsmaintypesarecomputer-centriccontrolsystems,includingcomputermonitoringsystems,directdigitalcontrolsystems,computermulti-levelcontrolsystems,anddistributedcontrolsystems.
Numericalcontrolsystems(numericalcontrolsystems)refertodigitalcontrolsystemsthatusedigitalcodesrepresentingtheprocessingsequence,processingmethodsandprocessingparametersascontrolinstructions.TheabbreviateddigitalprogramcontrolsystemiscalledNumericalControl(NC)system.Thenumericalcontrolsystemisusuallyequippedwithadedicatedelectroniccomputer,andtheprocessinginformationreflectingtheprocessingtechnologyandoperationstepsispre-recordedonthepunchedtape,punchedcard,magnetictapeordiskwithadigitalcode.Whenthesystemisworking,thereadingmechanismsequentiallysendsthecodestothecomputerandconvertsthemintocorrespondingformsofelectricalpulses,whichareusedtocontroltheworkingmachinerytocompletethevariousprocessingprocessesinorder.TheCNCsystemhashighprocessingaccuracyandprocessingefficiency,andisespeciallysuitableforsingle-pieceorsmallbatchproductionwithcomplexprocesses.Itiswidelyusedintoolmanufacturing,machining,automobilemanufacturingandshipbuildingindustries.
Development
Intheearlydays,hard-wirednumericalcontrolsystemswithfixedwiringweremostlyused,andadedicatedcomputerwasusedtocontrolapieceofequipment.Later,amicrocomputerwasusedtoreplaceaspecialcomputer,anddifferenttypesofprogramsoftwarewereusedtoachievedifferenttypesofcontrol,whichcanenhancethecontrolfunctionandflexibilityofthesystem,whichiscalledacomputernumericalcontrolsystem(CNC)orasoft-wirenumericalcontrolsystem.Lateritdevelopedintoacomputertodirectlymanageandcontrolagroupofnumericalcontrolequipment,calledcomputergroupcontrolsystemordirectnumericalcontrolsystem(DNC).IthasfurtherdevelopedintoanetworkcomposedofmultipleCNCandNCequipmentandDNCcomputerstoachievemulti-levelcontrol.Inthe1980s,itdevelopedintoagroupofmachinetoolsthatcooperatedwithworkpieces,tools,fixtures,andautomaticprocessingtransmissionlines,managedandcontrolledbyacomputer,toformacomputergroupcontrolautomaticline,calledaflexiblemanufacturingsystem(FMS).Thehigherstageofthenumericalcontrolsystemistheintegrationofdesignandmanufacturinginthemachinerymanufacturingindustry,whichcombinescomputer-aideddesign(CAD)withcomputer-aidedmanufacturing(CAM)torealizeacompleteautomationsystemforproductdesignandmanufacturingprocesses.
Composition
Thenumericalcontrolsystemiscomposedofinformationcarrier,numericalcontroldevice,servosystemandcontrolledequipment.Theinformationcarrierusespapertape,magnetictape,magneticcardordisk,etc.,tostoreprocessinginformationsuchasprocessingparameters,actionsequence,strokeandspeed.Thenumericalcontroldeviceisalsocalledtheinterpolator,whichsendsoutapulsesequenceaccordingtotheinputprocessinginformation.Eachpulserepresentsanincrementofdisplacement.Theinterpolatorisactuallyaspecial-purposecomputerwithsimplefunctions,andamicrocomputercanalsobeuseddirectly.Theincrementalpulseoutputbytheinterpolatoractsonthecorrespondingdrivemachineryorsystemtocontrolthemovementoftheworktableortool.Ifasteppingmotorisusedasthedrivingmechanism,thenumericalcontrolsystemisopen-loopcontrol.Forprecisionmachinetools,aclosed-loopcontrolmethodisrequired,withaservosystemasthedrivesystem.
Thedigitalcontrolsystemconsistsofacomputer,externalequipment,console,inputchannel,outputchannel,detectiondevice,actuator,controlledobjectandcorrespondingsoftware.
1.Computer
Thecomputeristhecoreofthedigitalcontrolsystem.Throughtheinterface,variouscontrolcommandscanbeissuedtoeachpartofthesystem,andtheThecontrolledparametersoftheobjectaredetectedandprocessedinrealtime.Itsfunctionistocompleteprogramstorage,numericalcalculation,logicjudgment,anddataprocessing.
2.Processinputandoutputchannels
Processinputandoutputchannelsaretheconnectionchannelsforinformationtransmissionandconversionsetupbetweenthecomputerandthecontrolledobject.Theinputchannelconvertsthecontrolledparametersofthecontrolledobjectintodigitalcodesthatthecomputercanrecognize,whichgenerallyrequiresthreestepsofsampling,quantizationandencoding.Theoutputchannelconvertsthecontrolinstructionsanddataoutputbythecomputerintoacontrolsignalthatcancontrolthecontrolledobject.Inputandoutputchannelsgenerallyinclude:analoginputchannels,analogoutputchannels,digitalinputchannels,anddigitaloutputchannels.
3.Externaldevices
Externaldevicesaredevicesthatexchangeinformationbetweenthecomputerandtheoutsideworld,referredtoasperipherals.Externalequipmentincludesman-machinecommunicationequipment,inputandoutputequipment,andexternalstorage.
Inputdevices:keyboards,scanners,photoelectricinputmachines,etc.,usedtoinputprogramsanddata.
Outputdevices:printers,recorders,displays,etc.,whicharemainlyusedtoprovideinformationanddatatooperatorsinordertounderstandthecontrolprocessintime.
Externalstorage:includingtapes,disks,etc.,usedtostoresystemprogramsanddata.
4.Detectiondevice
Inordertocontrolthecontrolledobject,thecontrolledparametersofthecontrolledobjectmustbecollectedfirst,suchastemperature,Pressure,liquidlevel,speed,etc.,arecompletedbythedetectiondevice.Thedetectiondeviceisthesensor,whichcanconvertnon-electricityparametersintoelectricityparameters,andthensendthemtothecomputer.
5.Actuator
Actuatorisanimportantpartofacomputercontrolsystem.Itistheexecutorofcontroltasks,suchasmotors.[1)Displaydevice:displayscreen,fluorescentdigitaldisplay,displaycontentandalarmsignalrequiredbytheoperator.
(2)Functionkeys:resetkey,startkey,printkey,displaykey,interruptkey.
(3)Numberkeys:inputsomedataormodifysomeparametersofthecontrolsystem.
7.Software
Softwareisaprogramthatcancompletevariousfunctionsofacomputercontrolsystem.Itisthecentralnerveofthecomputercontrolsystem.Underthecommandofthesoftware,theentiresystemiscoordinated.Thesoftwareincludessystemsoftwareandapplicationsoftware.
1.Systemsoftware.Itisageneraltermforprogramsthataredesignedtoimprovetheefficiencyofcomputeruse,expandfunctions,andprovideconvenientprogramsforuserstouse,maintain,andmanagecomputers.Thesystemsoftwareincludesanoperatingsystem,alanguageprocessingsystemandadiagnosissystem.Ithasacertainversatilityandisgenerallyprovidedbythecomputermanufactureralongwiththehardware.
2.Applicationsoftware.Variousprogramswrittenbytheuseraccordingtotheactualproblemtobesolved.Inthecomputercontrolsystem,itreferstotheprogramthatcompletesthevarioustasksofthesystem.Forexample,controlprocedures,dataacquisitionandprocessingprocedures,patrolinspectionandalarmprocedures.
8.Thecontrolledobject
Anactualcontrolledobjectcanhavevariousforms,butifitisabstractedintoamathematicalmodel,itcanbeThefollowingtypicaltransferfunctionsareusedtoexpress:
(1)Enlargementlink:
(2)Inertiallink:
(3)Integrallink:
(4)Differentiallink:
(5)Purelaglink:
(6)Amplification/inertia/integrationlink:
(7)Amplification/inertia/integrationSection:
(8)Amplification/inertia/integrationsection:.
Mainfunctions
Themainfunctionsofthedigitalcontrolsystemareasfollows:
1.Informationprocessing.Foracomplexcontrolsystem,theinputsignalandthecalculationoftheerroraccordingtotherequirementsofthecontrolalgorithmrequirealargeamountofcalculation.Therequiredaccuracycannotbeachievedbyusingananalogsolutiondevice,andcomputerprocessingisrequired.
2.Real-timecontrol.Thecomputercontrolsystemrealizessystemcontrolthroughsoftwareprograms,andcontinuouslycorrectsthesystemtoachievetherequireddynamiccharacteristics.
3.Complexcalculations.Thecomputerhasthefunctionofquicklyrealizingcomplexcalculations,soitcanrealizethesystem'soptimalcontrol,adaptivecontrolandotheradvancedcontrolfunctionsandmulti-functionalcalculationadjustments.
Controlprocess
Thecontrolprocessofthedigitalcontrolsystemcanbedividedintothreeparts:
1.Collectdatainrealtime.Thecontrolledparametersofthecontrolledobjectaredetectedinrealtimeandtransmittedtothecomputerforprocessingatthesametime.
2.Real-timedecision-making.Analyzethecollectedstatequantityofthecontrolledparameter,andcalculatethecontrolquantityaccordingtoacertaincontrolalgorithmtodeterminethenextcontrolprocess.
3.Real-timecontrol.Accordingtothedecision,itsendscontrolsignalstotheactuatorinrealtime.
"Real-time"meansthattheinput,calculation,andoutputofthesignalmustbecompletedwithinthesamplinginterval.Thiscontrolfunctionofthecomputercontrolsystemisconstantlyrepeated,sothattheentiresystemcanworkaccordingtocertaindynamicqualityindicators,andtheentirecontrolsystemcanachievetherequiredperformanceindicators;atthesametime,theabnormalstateofthecontrolledparametersandtheequipmentitselfAbletomonitorandprocess.
Design
Therearetwomethodsfordesigningdigitalcontrolsystems:theclassicalmethodbasedonfrequencydomaindiagramsandthestatevariablemethodbasedonstatevariables.Thedesignofthedigitalcontrolsystemneedstomeetthegivenindicators,namely:steady-stateaccuracy,transientaccuracy(dynamicresponse),stability,sensitivitytoparameterchanges,andabilitytosuppressdisturbances.Theseperformanceindicatorsdonotexistinisolation,andtheyrestricteachother.Therefore,whendesigningadigitalcontrolsystem,itisnecessarytocomprehensivelyconsiderallgivenperformanceindicatorssothateachitemcanbemet.