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院（系）：

电子工程与自动化学院

专业：

测控技术与仪器

学生姓名：

李XX

学号：

XXX

指导教师单位：

电子工程与自动化学院

指导教师：

职称：

2013年5月20日

InformationControl

AutomaticControl

Automaticcontrolhasplayedavitalroleintheadvanceofengineeringandscience.Inadditiontoitsextremeimportanceinspace-vehiclesystems,missile-guidancesystems,roboticsystems,andthelike,automaticcontrolhasbecomeanimportantandintegralpartofmodernmanufacturingandindustrialprocesses.Forexample,automaticcontrolisessentialinthenumericalcontrolofmachinetoolsinthemanufacturingindustries,inthedesignofautopilotsystemsintheaerospaceindustries,andinthedesignofcarsandtrucksintheautomobileindustries.Itisalsoessentialinsuchindustrialoperationsascontrollingpressure,temperature,humidity,viscosity,andflowintheprocessindustries.

Sinceadvancesinthetheoryandpracticeofautomaticcontrolprovidethemeansforattainingoptimalperformanceofdynamicsystems,improvingproductivity,relievingthedrudgeryofmanyroutinerepetitivemanualoperations,andmore,mostengineersandscientistsmustnowhaveagoodunderstandingofthisfield.

Controlengineeringisbasedonthefoundationsoffeedbacktheoryandlinearsystemanalysis,anditintegratestheconceptsofnetworktheoryandcommunicationtheory.Thereforecontrolengineeringisnotlimitedtoanyengineeringdisciplinebutisequallyapplicabletoaeronautical,chemical,mechanical,environmental,civil,andelectricalengineering.Forexample,acontrolsystemoftenincludeselectrical,mechanical,andchemicalcomponents.Furthermore,astheunderstandingofthedynamicsofbusiness,social,andpoliticalsystemsincreases,theabilitytocontrolthesesystemswillalsoincrease.

Acontrolsystemisaninterconnectionofcomponentsformingasystemconfigurationthatwillprovideadesiredsystemresponse.Thebasisforanalysisofasystemisthefoundationprovidedbylinearsystemtheory,whichassumesacause-effectrelationshipforthecomponentsofasystem.Thereforeacomponentorprocesstobecontrolledcanberepresentedbyablock,asshowninFigure8.1.Theinput-outputrelationshiprepresentsthecause-and-effectrelationshipoftheprocess,whichinturnrepresentsaprocessingoftheinputsignaltoprovideanoutputsignalvariable,oftenwithapoweramplification.

Ingeneral,controlsystemscanbecategorizedasbeingeitheropen-looporclosed–loop.Thedistinguishingfeaturebetweenthesetwotypesofcontrolsystemsistheuseoffeedbackcomparisonforclosed-loopoperation.

1．Open-loopControlSystem

Anopen-loopcontrolsystemutilizesacontrollerorcontrolactuatortoobtainthedesiredresponse,asshowninFigure8.2.Anopen-loopsystemisasystemwithoutfeedback,simplestformofcontrollingdevices.Figure8.3illustratesasimpletank-levelcontrolsystem.WewishtoholdthetanklevelhwithinreasonableacceptablelimitseventhoughtheoutletflowthroughvalueV1isvaried.ThiscanbeachievedbyirregularmanualadjustmentoftheinletflowratebyvalveV2.Thesystemisnotaprecisionsystem,asitdoesnothavethecapabilityofaccuratelymeasuringtheoutputflowratethroughvalveV1,theinputflowratethroughvalveV2,orthetanklevel.Figure8.4showsthesimplerelationshipthatexistsinthissystembetweentheinput（thedesiredtanklevel）andtheoutput（theactualtanklevel）.Thiscontrolsystemdoesnothaveanyfeedbackcomparison,andthetermopenloopisusedtodescribethisabsence.

Figure8.3Tank-levelcontrolsystem

Output（actualtanklevel）

Ouput

Input

Figure8.1Processtobecontrolled

2．Closed-loopControlSystem

Incontrasttoanopen-loopcontrolsystem,aclosed-loopcontrolsystemutilizesanadditionalmeasureoftheactualoutputtocomparetheactualoutputwiththedesiredoutputresponse.Themeasureoftheoutputiscalledthefeedbacksignal.Asimpleclosed-loopfeedbackcontrolsystemisshowninFigure8.5.Afeedbackcontrolsystemisacontrolsystemthattendstomaintainaprescribedrelationshipofonesystemvariabletoanotherbycomparingfunctionsofthesevariablesandusingthedifferenceasameansofcontrol.

Output

Closed-loopcontrolsystemsderivetheirvaluableaccuratereproductionoftheinputfromfeedbackcomparison.Anerrordetectorderivesasignalproportionaltothedifferencesbetweentheinputandoutput．Theclosed-loopcontrolsystemdrivestheoutputuntilitequalstheinputandtheerroriszero．Anydifferencesbetweentheactualanddesiredoutputwillbeautomaticallycorrectedinaclosed-loopcontrolsystem．Throughproperdesignthesystemcanbemaderelativelyindependentofsecondaryinputsandchangesincomponentcharacteristics．Figure8.6illustratesanautomatictank-levelcontrolversionofthesystemshowninFigure8.3.ItcanmaintainthedesiredtanklevelhwithinquiteaccuratetoleranceseventhroughtheoutputflowratethroughvalueV1isvaried.Ifthetanklevelisnotcorrect,anerrorvoltageisdeveloped．ThisisamplifiedandappliedtoamotordrivethatadjustsvalueV2inordertorestorethedesiredtanklevelbyadjustingtheinletflowrate．AblockdiagramanalogoustothissystemisshowninFigure8.7.Becausefeedbackcomparisonispresent,thetermclosed-loopisusedtodescribethesystem’soperation.

Input（desired

tanklevel）

Duetotheincreasingcomplexityofthesystemundercontrolandtheinterestinachievingoptimumperformance,theimportanceofcontrolsystemengineeringhasgrowninthepastdecade.Furthermore,asthesystembecomemorecomplex,theinterrelationshipofmanycontrolledvariablesmustbeconsideredinthecontrolscheme.AblockdiagramdepictingamultivariablecontrolsystemisshowninFigure8.8.

Theintroductionoffeedbackenablesustocontroladesiredoutputandcanimproveaccuracy,butitrequiresattentiontotheissueofstabilityofresponse.

Microcontroller

Amicrocontroller（sometimesabbreviatedµ

C,uCorMCU）isasmallcomputeronasingleintegratedcircuitcontainingaprocessorcore,memory,andprogrammableinput/outputperipherals.ProgrammemoryintheformofNORflashisalsooftenincludedonchip,aswellasatypicallysmallamountofRAM.Microcontrollersaredesignedforembeddedapplications,incontrasttothemicroprocessorsusedinpersonalcomputersorothergeneralpurposeapplications.

Microcontrollersareusedinautomaticallycontrolledproductsanddevices,suchasautomobileenginecontrolsystems,implantablemedicaldevices,remotecontrols,officemachines,appliances,powertools,toysandotherembeddedsystems.Byreducingthesizeandcostcomparedtoadesignthatusesaseparatemicroprocessor,memory,andinput/outputdevices,microcontrollersmakeiteconomicaltodigitallycontrolevenmoredevicesandprocesses.Mixedsignalmicrocontrollersarecommon,integratinganalogcomponentsneededtocontrolnon-digitalelectronicsystems.

Somemicrocontrollersmayusefour-bitwordsandoperateatclockratefrequenciesaslowas4kHz,forlowpowerconsumption（milliwattsormicrowatts）.Theywillgenerallyhavetheabilitytoretainfunctionalitywhilewaitingforaneventsuchasabuttonpressorotherinterrupt;

powerconsumptionwhilesleeping（CPUclockandmostperipheralsoff）maybejustnanowatts,makingmanyofthemwellsuitedforlonglastingbatteryapplications.Othermicrocontrollersmayserveperformance-criticalroles,wheretheymayneedtoactmorelikeadigitalsignalprocessor（DSP）,withhigherclockspeedsandpowerconsumption.

Embeddeddesign

Amicrocontrollercanbeconsideredaself-containedsystemwithaprocessor,memoryandperipheralsandcanbeusedasanembeddedsystem.Themajorityofmicrocontrollersinusetodayareembeddedinothermachinery,suchasautomobiles,telephones,appliances,andperipheralsforcomputersystems.Thesearecalledembeddedsystems.Whilesomeembeddedsystemsareverysophisticated,manyhaveminimalrequirementsformemoryandprogramlength,withnooperatingsystem,andlowsoftwarecomplexity.Typicalinputandoutputdevicesincludeswitches,relays,solenoids,LEDs,smallorcustomLCDdisplays,radiofrequencydevices,andsensorsfordatasuchastemperature,humidity,lightleveletc.Embeddedsystemsusuallyhavenokeyboard,screen,disks,printers,orotherrecognizableI/Odevicesofapersonalcomputer,andmaylackhumaninteractiondevicesofanykind.

1．Interrupts

Microcontrollersmustproviderealtime（predictable,thoughnotnecessarilyfast）responsetoeventsintheembeddedsystemtheyarecontrolling.Whencertaineventsoccur,aninterruptsystemcansignaltheprocessortosuspendprocessingthecurrentinstructionsequenceandtobeginaninterruptserviceroutine（ISR,or“interrupthandler”）.TheISRwillperformanyprocessingrequiredbasedonthesourceoftheinterruptbeforereturningtotheoriginalinstructionsequence.Possibleinterruptsourcesaredevicedependent,andoftenincludeeventssuchasaninternaltimeroverflow,completingananalogtodigitalconversion,alogiclevelchangeonaninputsuchasfromabuttonbeingpressed,anddatareceivedonacommunicationlink.Wherepowerconsumptionisimportantasinbatteryoperateddevices,interruptsmayalsowakeamicrocontrollerfromalowpowersleepstatewheretheprocessorishalteduntilrequiredtodosomethingbyaperipheralevent.

2．Programs

Microcontrollerprogramsmustfitintheavailableon-chipprogrammemory,sinceitwouldbecostlytoprovideasystemwithexternal,expandable,memory.Compilersandassemblersareusedtoconverthigh-levellanguageandassemblerlanguagecodesintoacompactmachinecodef