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Digital control system



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.

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