可编程逻辑控制器外文文献资料.docx
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可编程逻辑控制器外文文献资料.docx
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可编程逻辑控制器外文文献资料
可编程逻辑控制器外文文献资料
可编程逻辑控制器(外文文献资料)
ProgrammableLogicControllers
S.BrianMorriss
AutomatedManufacturingSystems:
Actuators,Controls,Sensors,andRoboticsS.布莱恩。
莫利斯自动化制造系统:
执行器,控制器,传感器和机器人
1.DevelopmentofPLC
Therewasquitealongdelaybeforedigitalcomputercontrolofmanufacturingprocessesbecamewidelyimplemented.Lackofstandardizationwastheproblem.NCequipmentshowedupasthefirstrealapplicationofdigitalcontrol.ThesuppliersofNCequipmentbuilttotallyenclosedsystems,evolvingawayfromanalogcontroltowarddigitalcontrol.WithlittleneedforinterconnectionoftheNCequipmenttoothercomputercontrolleddevices,thesuppliersdidnothavetoworryaboutlackofstandardsincommunication.EarlyNCequipmentreadpunchedtapeprogramsastheyran.EventhepapertapepunchersweresuppliedbytheNCequipmentsupplier.Meanwhile,largecomputermanufacturers,suchasIBMandDEC,concentratedoninterconnectingtheirownproprietaryequipmenttotheirownproprietaryofficeperipherals.(Interconnectioncapabilitywaspooreventhere.)Threeadvanceseventuallyopenedthedoorforautomatedmanufacturingbyallowingeasierinterfacingofcontrollers,sensorsandactuators.Oneadvancewasthedevelopmentoftheprogrammablecontroller,thecalleda“PC,”nowcalleda
“PLC”(programmablelogiccontroller).PLCscontaindigitalcomputers.Itwasamajorstepfromsequencingautomationwithrotatingcamsorwithseriesofelectricalrelayswitches,tousingmicroprocessor-basedPLCsequencers.Withmicroprocessors,thesequencerscouldbeprogrammedtofollowdifferentsequencesunderdifferentconditions.
ThephysicalstructureofaPLC,asshowninfigure1.8,isasimportantafeatureasitscomputerizedinnards.Thecentralcomponent,calledtheCPU,containsthedigitalcomputerandplugsintoabusorarack.OtherPLCmodulescanbepluggedintothesamebus.Optionalinterfacemodulesareavailableforjustaboutanytypeofsensororactuator.ThePLCuserbuysonlythemodulesneeded,andthusavoidshavingtoworryaboutcompatibilitybetweensensors,actuatorsandthePLC.MostPLCsoffercommunicationmodulesnow,sothatthePLCcanexchangedatawithatleastotherPLCsofthesamemake.Figure1.9showsaPLCasitmightbeconnectedforaposition-controlapplication:
readingdigitalinputsensors,controllingACmotors,andexchanginginformationwiththeoperator.
Anotheradvancewhichmadeautomationpossiblewasthedevelopmentoftherobot.AvariationonNCequipment,therobotinfigure1.10isaself-enclosedsystemofactuators,sensorsandcontroller.Compatibilityofrobotcomponentsistherobotmanufacturer?
sproblem.Arobot
includesbuilt-inprogramsallowingtheuserto“teach”positionstothearm,andtoplay-back
moves.Robotprogramminglanguagesaresimilartoothercomputerprogramminglanguages,likeBASIC.Eventheearlyrobotsallowedconnectionofcertaintypesofexternalsensorsandactuators,socompleteworkcellscouldbebuiltaround,andcontrolledby,therobot.Modernrobotsusuallyincludecommunicationports,sothatrobotscanexchangeinformationwithothercomputerizedequipmentwithsimilarcommunicationports.
Thethirdadvancewastheintroduction,byIBM,ofthepersonalcomputer(PC).(IBM?
suseofthe
name“PC”forcedthesuppliersofprogrammablecontrollerstostartcallingtheir„PC?
sby
anothername,hencethe“PLC.”)IBM?
sPCincludedafeaturethencalledopenarchitecture.Whatthismeantwasthatinsidethecomputerboxwasacomputeronasingle“mother”circuit-board
andseveralslotsonthis“motherboard.”Eachslotisastandardconnectorintoastandardbus(setofconductorscontrolledbythecomputer).Thisarchitecturewascalled“open”becauseIBMmadeinformationavailablesothatothermanufacturerscoulddesigncircuitboardsthatcouldbepluggedintothebus.IBMalsoprovidedinformationontheoperationofthemotherboardsothatotherscouldwriteIBMPCprogramstousethenewcircuitboards.IBMundertooktoavoidchangestothemotherboardthatwouldobsoletetheimportantbusandmotherboardstandards.BoardscouldbedesignedandsoftwarewrittentointerfacetheIBMPCtosensors,actuators,NCequipment,PLCs,robots,orothercomputers,withoutIBMhavingtodothedesignorprogramming.CoupledwithIBM?
sperceiveddependability,this“openarchitecture”providedthestandardthatwasmissing.Mowcomputerizationofthefactoryfloorcouldproceed.Standardsforwhatformthesignalsshouldtakeforcommunicationbetweencomputersarestilllargelymissing.ThePLC,robot,andcomputermanufacturershaveeachdevelopedtheirownstandards,butonesupplier?
sequipmentcan?
tcommunicateveryeasilywithanother?
s.Mostsuppliersdo,atleast,builttheirstandardsaroundaverybasicsetofstandardswhichdatesbackseveraldecadestoth
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