Model-Driven Evolution of Software Architectures - Software and ...
Model-Driven Evolution of Software Architectures - Software and ...
Model-Driven Evolution of Software Architectures - Software and ...
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7.3. MigrationContext 135<br />
waferhasbeenexposed,<strong>and</strong>thestageshaveswapped,thewafermustbe<br />
unloadedfromitsstage.Inturn,theseactivitiesarerequestsforalowerlevelSMCcomponent.<br />
Inthischapterwewillusethe‘processwafer’<strong>and</strong><br />
‘unloadwafer’requestsasillustrativeexamples.<br />
7.3.3 ConcernsforSupervisoryMachineControlSystems<br />
Inadvancedmanufacturingmachines,multiplemanufacturingactivities<strong>and</strong>sequenceshere<strong>of</strong>-mayfulfilaparticularrequest<strong>and</strong>,inturn,multiplemechatronicsubsystemsmaybeavailabletoperformaparticularactivity.Thatis,multiplealternativesexistthatrequiretheselection<strong>of</strong>aspecificsubset<strong>of</strong>bothmanufacturingactivities<strong>and</strong>mechatronicsubsystems<br />
t<strong>of</strong>ulfilagivenmanufacturingrequest. Forinstance,whenconsidering<br />
Figure7.2,removingawaferfromDUcanbedoneusingeitherURorLR.<br />
Forsupervisorycontrol<strong>of</strong>advancedmanufacturingmachinesingeneral,<br />
thefollowingkeyconcernsareidentified.<br />
Theexecution<strong>of</strong>anactivityonaselectedsubsystemimpliesaspecific<br />
physicalstatetransition<strong>of</strong>thatsubsystem. Theselectedsequence<strong>of</strong>activitiesforasubsystemrequiresmatchingendstates<strong>and</strong>beginstates<strong>of</strong><br />
consecutivestatetransitions. Whenthesestatesdonotmatch,anadditionaltransition,asetup,hastobeexecutedbetweenconsecutiveactivities.<br />
Forinstance,whenURisidleatPA,arotationhastobeperformed<br />
beforeawafercanbeunloaded. InSMC,thesesequence-dependentsetups<br />
arecommon.<br />
Intuitively,controlledusage<strong>of</strong>mechatronicsubsystemsisanotherimportantconcern.Thecontrolsystemgenerallycheckstheavailability<strong>of</strong>a<br />
subsystemthatisrequiredforamanufacturingactivity. Onceavailable,<br />
thesubsystemshouldbeeffectivelyclaimedforthegivenactivity. When<br />
anactivityhasbeen(co)performedbyclaimedmechatronicsubsystem(s),<br />
allshouldbeunclaimedorreleased. Inourwaferscannerexample,the<br />
unloading<strong>of</strong>awaferrequiresbothUR<strong>and</strong>,forinstance,WS:0.<br />
Inordertotakefulladvantage<strong>of</strong>installedcapacity,concurrentexecution<strong>of</strong>activitiesisdonewherepossible.Inpractice,activitiescanbeexecutedconcurrentlyunlessthisisexplicitlyprohibitedbyprecedence(sequence)relationsbetweenmanufacturingactivitiesorusage<strong>of</strong>therequired<br />
mechatronicsubsystems.Inourwaferscannerexample,onewafercanbe<br />
measured<strong>and</strong>preparedforexposurewhileanotherwaferisbeingexposed.<br />
Synchronousexecutionisanothercommonconcern.Thisnotonlyrefers<br />
tosynchronisation<strong>of</strong>activitiessuchthattheyareexecutedoneafterthe<br />
other(e.g.,loadawaferbeforeprocessingit). Italsoappliestosynchronisation<strong>of</strong>specificsubsystemstatetransitionsrelatedtotwoactivities.Forinstance,physicalspaceis<strong>of</strong>tenlimited,resultinginmultiplemechatronicsubsystemsthatsimultaneouslyoperatewithinaconfinedspace.
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