电气系统可编程序控制器毕业论文中英文资料外文翻译文献.docx

电气系统可编程序控制器毕业论文中英文资料外文翻译文献.docx

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电气系统可编程序控制器毕业论文中英文资料外文翻译文献

电气系统可编程序控制器

中英文资料外文翻译文献

英文原文

Programmablecontrollerdesignedforelectro-pneumaticsystems

Thisprojectdealswiththestudyofelectro-pneumaticsystemsandtheprogrammablecontrollerthatprovidesaneffectiveandeasywaytocontrolthesequenceofthepneumaticactuatorsmovementandthestatesofpneumaticsystem.Theprojectofaspecificcontrollerforpneumaticapplicationsjointhestudyofautomationdesignandthecontrolprocessingofpneumaticsystemswiththeelectronicdesignbasedonmicrocontrollerstoimplementtheresourcesofthecontroller.

1.Introduction

Theautomationsystemsthatuseelectro-pneumatictechnologyareformedmainlybythreekindsofelements:

actuatorsormotors,sensorsorbuttonsandcontrolelementslikevalves.Nowadays,mostofthecontrolelementsusedtoexecutethelogicofthesystemweresubstitutedbytheProgrammableLogicController（PLC）.Sensorsandswitchesarepluggedasinputsandthedirectcontrolvalvesfortheactuatorsarepluggedasoutputs.Aninternalprogramexecutesallthelogicnecessarytothesequenceofthemovements,simulatesothercomponentslikecounter,timerandcontrolthestatusofthesystem.

WiththeuseofthePLCtheprojectwinsagility,becauseitispossibletocreateandsimulatethesystemasmanytimesasneeded.Therefore,timecanbesaved,riskofmistakesreducedandcomplexitycanbeincreasedusingthesameelements.

AconventionalPLC,thatispossibletofindonthemarketfrommanycompanies,offersmanyresourcestocontrolnotonlypneumaticsystems,butallkindsofsystemthatuseselectricalcomponents.ThePLCcanbeveryversatileandrobusttobeappliedinmanykindsofapplicationintheindustryorevensecuritysystemandautomationofbuildings.

Becauseofthosecharacteristics,insomeapplicationsthePLCofferstomuchresourcesthatarenotevenusedtocontrolthesystem,electro-pneumaticsystemisoneofthiskindofapplication.TheuseofPLC,especiallyforsmallsizesystems,canbeveryexpensivefortheautomationproject.

Analternativeinthiscaseistocreateaspecificcontrollerthatcanoffertheexactlysizeandresourcesthattheprojectneeds[3,4].Thiscanbemadeusingmicrocontrollersasthebaseofthiscontroller.

Thecontroller,basedonmicrocontroller,canbeveryspecificandadaptedtoonlyonekindofmachineoritcanworkasagenericcontrollerthatcanbeprogrammedasausualPLCandworkwithlogicthatcanbechanged.Allthesecharacteristicsdependonwhatisneededandhowmuchexperiencethedesignerhaswithdevelopinganelectroniccircuitandfirmwareformicrocontroller.Butthemainadvantageofdesignthecontrollerwiththemicrocontrolleristhatthedesignerhasthetotalknowledgeofhiscontroller,whichmakesitpossibletocontrolthesizeofthecontroller,changethecomplexityandtheapplicationofit.Itmeansthattheprojectgetsmoreindependencefromothercompanies,butatthesametimetheresponsibilityofthecontrolofthesystemstaysatthedesignerhands

2.Electro-pneumaticsystem

Onautomationsystemonecanfindthreebasiccomponentsmentionedbefore,plusalogiccircuitthatcontrolsthesystem.Anadequatetechniqueisneededtoprojectthelogiccircuitandintegrateallthenecessarycomponentstoexecutethesequenceofmovementsproperly.

Forasimpledirectsequenceofmovementanintuitivemethodcanbeused[1,5],butforindirectormorecomplexsequencestheintuitioncangenerateaverycomplicatedcircuitandsignalmistakes.Itisnecessarytouseanothermethodthatcansavetimeoftheproject,makeacleancircuit,caneliminateoccasionalsignaloverlappingandredundantcircuits.

Thepresentedmethodiscalledstep-by-steporalgorithmic[1,5],itisvalidforpneumaticandelectro-pneumaticsystemsanditwasusedasabaseinthiswork.Themethodconsistsofdesigningthesystemsbasedonstandardcircuitsmadeforeachchangeonthestateoftheactuators,thesechangesarecalledsteps.

Fig.1.Standardcircuitforthepneumaticsystem.

Fig.2.Standardcircuitfortheelectro-pneumaticsystem.

Thefirstpartistodesignthosekindsofstandardcircuitsforeachstep,thenexttaskistolinkthestandardcircuitsandthelastparttoconnectthecontrolelementthatreceivesignalsfromsensors,switchesandthepreviousmovementandgivetheairorelectricitytothesupplylinesofeachstep.InFigs.1and2thestandardcircuitsaredrawnforpneumaticandelectro-pneumaticsystem[8].Itispossibletoseetherelationswiththepreviousandthenextsteps.

3.Themethodappliedinsidethecontroller

Theresultofthemethodpresentedbeforeisasequenceofmovementsoftheactuatorthatiswelldefinedbysteps.Itmeansthateachchangeonthepositionoftheactuatorsisanewstateofthesystemandthetransitionbetweenstatesiscalledstep.

Thestandardcircuitdescribedbeforehelpsthedesignertodefinethestatesofthesystemsandtodefinetheconditiontoeachchangebetweenthestates.Intheendofthedesign,thesystemisdefinedbyasequencethatneverchancesandstatesthathavetheinputsandtheoutputswelldefined.Theinputsaretheconditionforthetransitionandtheoutputsaretheresultofthetransition.

Alltheconfigurationofthosestepsstaysinsideofthemicrocontrollerandisexecutedthesamewayitwasdesigned.Thesequencesofstringsareprogrammedinsidethecontrollerwith5bytes;eachstringhastheconfigurationofonestepoftheprocess.Therearetwobytesfortheinputs,onebytefortheoutputsandtwomorefortheotherconfigurationsandauxiliaryfunctionsofthestep.Afterprogramming,thissequenceofstringsissavedinsideofanon-volatilememoryofthemicrocontroller,sotheycanbereadandexecuted.

ThecontrollertaskisnottoworkinthesamewayasaconventionalPLC,butthepurposeofitistobeanexampleofaversatilecontrollerthatisdesignforanspecificarea.AconventionalPLCprocessthecontrolofthesystemusingacyclewhereitmakesanimageoftheinputs,executealltheconditionsdefinedbytheconfigurationprogrammedinside,andthenupdatethestateoftheoutputs.Thiscontrollerworksinadifferentway,whereitreadtheconfigurationofthestep,waittheconditionofinputstobesatisfied,thenupdatethestateortheoutputsandafterthatjumptothenextstepandstarttheprocessagain.

Itcangeneratesomelimitations,asthefactthatthiscontrollercannotexecute,insidetheprogram,movementsthatmustberepeatedforsometime,butthisproblemcanbesolvedwithsomeexternallogiccomponents.Anotherlimitationisthatthecontrollercannotbeappliedonsystemsthathavenosequence.Theselimitationsareacharacteristicofthesystemthatmustbeanalyzedforeachapplication.

4.Characteristicsofthecontroller

ThecontrollerisbasedontheMICROCHIPmicrocontrollerPIC16F877[6,7]with40pins,andithasalltheresourcesneededforthisproject.Ithaenoughpinsforallthecomponents,serialcommunicationimplementedincircuit,EEPROMmemorytosavealltheconfigurationofthesystemandthesequenceofsteps.Fortheexecutionofthemainprogram,itofferscompleteresourcesastimersandinterruptions.

Thelistofresourcesofthecontrollerwascreatedtoexploreallthecapacityofthemicrocontrollertomakeitascompleteaspossible.Duringthestep,theprogramchooseshowtousetheresourcesreadingtheconfigurationstringofthestep.Thisstringhastwobytesfordigitalinputs,oneusedasamaskandtheotheroneusedasavalueexpected.Onebyteisusedtoconfiguretheoutputsvalue.Onebytesmoreisusedfortheinternaltimer,theanaloginputortime-out.TheEEPROMmemoryinsideis256byteslengththatisenoughtosavethestringofthesteps,withthischaracteristicitispossibletosavebetween48steps.

Thecontrollerhasalsoadisplayandsomebuttonsthatareusedwithaninteractivemenutoprogramthesequenceofstepsandotherconfigurations.

4.1.Interactioncomponents

Fortherealapplicationthecontrollermusthavesomeelementstointeractwiththefinaluserandtoofferacompletemonitoringofthesystemresourcesthatareavailabletothedesignerwhilecreatingthelogiccontrolofthepneumaticsystem:

.Interactivemodeofwork;functionavailableonthemainprogramfordidacticpurposes,theusergivesthesignaltoexecutethestep.

.LCDdisplay,whichshowsthestatusofthesystem,valuesofinputs,outputs,timerandstatisticsofthesequenceexecution.

.Beeptogiveimportantalerts,stop,startandemergency.

.Ledstoshowpoweronandotherstoshowthestateofinputsandoutputs.

4.2.Security

Tomakethefinalapplicationworksproperty,acorrectconfigurationtoexecutethestepsintherightwayisneeded,butmorethenthatitmustoffersolutionsincaseofbadfunctioningorproblemsintheexecutionofthesequence.Thecontrolleroffersthepossibilitytoconfiguretwointernalvirtualcircuitsthatworkinparalleltotheprincipal.Thesetwocircuitscanbeusedasemergencyorresetbuttonsandcanreturnthesystemtoacertainstateatanytime[2].Therearetwoinputsthatworkwithinterruptiontogetanimmediateaccesstothesefunctions.Itispossibletoconfiguretheposition,thebuttonsandthevalueoftime-outofthesystem.

4.3.Userinterface

Thesequenceofstringscanbeprogrammedusingtheinterfaceelementsofthecontroller.Acomputerinterfacecanalsobeusedtogeneratetheuserprogrameasily.Withagooddocumentationthefinalusercanusetheinterfacetoconfigurethestringsofbytesthatdefinethestepsofthesequence.Butitispossibletocreateaprogramwithvisualresourcesthat