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ADDRESSINGPROCESSPLANNINGANDVERIFICATIONISSUES
WITHMTCONNECT
AthulanVijayaraghavan,LucieHuet,andDavidDornfeld
DepartmentofMechanicalEngineering
UniversityofCalifornia
Berkeley,CA94720-1740
WilliamSobel
ArtisanalSoftware
Oakland,CA94611
BillBlomquistandMarkConley
RemmeleEngineeringInc.
BigLake,MN
KEYWORDS
Processplanningverification,machinetool
interoperability,MTConnect.
ABSTRACT
Robustinteroperabilitymethodsareneededin
manufacturingsystemstoimplementcomputeraided
processplanningalgorithmsandtoverify
theireffectiveness.Inthispaperwediscuss
applyingMTConnect,anopen-sourcestandard
fordataexchangeinmanufacturingsystems,in
addressingtwospecificissuesinprocess
planningandverification.Weusedatafroman
MTConnect-compliantmachinetooltoestimate
thecycletimerequiredformachiningcomplex
partsinthatmachine.MTConnectdataisalso
usedinverifyingtheconformanceoftoolpathsto
therequiredpartfeaturesbycomparingthe
featurescreatedbytheactualtoolpositionsto
therequiredpartfeaturesusingCADtools.We
demonstratethecapabilitiesofMTConnectin
easilyenablingprocessplanningandverification
inanindustrialenvironment.
INTRODUCTION
Automatedprocessplanningmethodsarea
criticalcomponentinthedesignandplanningof
manufacturingprocessesforcomplexparts.This
isespeciallythecasewithhighspeed
machining,asthecomplexinteractionsbetween
thetoolandtheworkpiecenecessitatescareful
selectionoftheprocessparametersandthe
toolpathdesign.However,toimprovethe
effectivenessofthesemethods,theyneedtobe
integratedtightlywithmachinesandsystemsin
industrialenvironments.Toenablethis,weneed
robustinteroperabilitystandardsfordata
exchangebetweenthedifferententitiesin
manufacturingsystems.
Inthispaper,wediscussusingMTConnect–an
opensourcestandardfordataexchangein
manufacturingsystems–toaddressissuesin
processplanningandverificationinmachining.
WediscusstwoexamplesofusingMTConnect
forbetterprocessplanning:
inestimatingthe
cycletimeforhighspeedmachining,andin
verifyingtheeffectivenessoftoolpathplanning
formachiningcomplexfeatures.AsMTConnect
standardizestheexchangeofmanufacturing
processdata,processplanningapplicationscan
bedevelopedindependentofthespecific
equipmentused(Vijayaraghavan,2008).This
allowedustodeveloptheprocessplanning
applicationsandimplementtheminanindustrial
settingwithminimaloverhead.Theexperiments
discussedinthispaperweredevelopedatUC
BerkeleyandimplementedatRemmele
EngineeringInc.
Thenextsectionpresentsabriefintroductionto
MTConnect,highlightingitsapplicabilityin
manufacturingprocessmonitoring.Wethen
discusstwoapplicationsofMTConnect–in
computingcycletimeestimatesandinverifying
toolpathplanningeffectiveness.
MTCONNECT
MTConnectisanopensoftwarestandardfor
dataexchangeandcommunicationbetween
manufacturingequipment(MTConnect,2008a).
TheMTConnectprotocoldefinesacommon
languageandstructureforcommunicationin
manufacturingequipment,andenables
interoperabilitybyallowingaccessto
manufacturingdatausingstandardized
interfaces.MTConnectdoesnotdefinemethods
fordatatransmissionoruse,andisnotintended
toreplacethefunctionalityofexistingproducts
and/ordatastandards.Itenhancesthedata
acquisitioncapabiltiiesofdevicesand
applications,movingtowardsaplug-and-play
environmentthatcanreducethecostof
integration.MTConnectisbuiltuponprevalent
standardsinthemanufacturingandsoftware
industry,whichmaximizesthenumberoftools
availableforitsimplementationandprovidesa
highlevelofinteroperabilitywithotherstandards
andtoolsintheseindustries.
MTConnectisanXML-basedstandardand
messagesareencodedusingXML(eXtensible
MarkupLanguage),whichhasbeenused
extensivelyasaportablewayofspecifyingdata
interchangeformats(W3C,2008).Amachinereadable
XMLschemadefinestheformatof
MTConnectmessagesandhowthedataitems
withinthosemessagesarerepresented.Atthe
timeofpublication,thelatestversionofthe
MTConnectstandarddefiningtheschemais
(MTConnect,2008b).
TheMTConnectprotocolincludesthefollowing
informationaboutadevice:
Identityofadevice
Identityofalltheindependentcomponentsof
thedevice
Designcharacteristicsofthedevice
Dataoccurringinrealornearreal-timebythe
devicethatcanbeutilizedbyotherdevicesor
applications.Thetypesofdatathatcanbe
addressedincludes:
Physicalandactualdevicedesigndata
Measurementorcalibrationdata
Near-realtimedatafromthedevice
Figure1showsanexampleofadatagathering
setupusingMTConnect.Dataisgatheredin
near-timefromamachinetoolandfromthermal
sensorsattachedtoit.Thedatastoredbythe
MTConnectprotocolforthissetupisshownin
Table1.Specializedadaptorsareusedtoparse
thedatafromthemachinetoolandfromthe
sensordevicesintoaformatthatcanbe
understoodbytheMTConnectagent,whichin
turnorganizesthedataintotheMTConnectXML
schema.Softwaretoolscanbedevelopedwhich
operateontheXMLdatafromtheagent.Since
theXMLschemaisstandardized,thesoftware
toolscanbeblindtothespecificconfigurationof
theequipmentfromwherethedataisgathered.
FIGURE1:
MTCONNECTSETUP.
TABLE1:
MTCONNECTPROTOCOLINFORMATION
FORMACHINETOOLINFIGURE1.
Deviceidentity“3-AxisMillingMachine”
Device
components
1XAxis;
1YAxis;
1ZAxis;
2ThermalSensors
Devicedesign
characteristics
XAxisTravel:
6”
YAxisTravel:
ZAxisTravel:
12”
MaxSpindleRPM:
24000
Dataoccurring
indevice
Toolposition:
(0,0,0);
SpindleRPM:
1000
AlarmStatus:
OFF
TempSensor1:
90oF
TempSensor2:
120oF
AnaddedbenefitofXMListhatitisa
hierarchicalrepresentation,andthisisexploited
bydesigningthehierarchyoftheMTConnect
schematoresemblethatofaconventional
machinetool.Theschemaitselffunctionsasa
metaphorforthemachinetoolandmakesthe
parsingandencodingofmessagesintuitive.
Dataitemsaregroupedbasedontheirlogical
organization,andnotontheirphysical
organization.Forexample,Figure2showsthe
XMLschemaassociatedwiththesetupshownin
Figure1.Althoughthetemperaturesensors
operateindependantofthemachinetool(withits
ownadaptor),thedatafromthesensorsare
associatedwithspecificcomponentsofthe
machinetool,andhencethetemperaturedatais
amemberofthehierarchyofthemachinetool.
ThenextsectiondiscussesapplyingMTConnect
inestimatingcycletimeinhigh-speed
machining.
ACCURATECYCLETIMEESTIMATES
Inhighspeedmachiningprocessestherecanbe
discrepanciesbetweentheactualfeedrates
duringcuttingandtherequired(orcommanded)
feedrates.Thesediscrepanciesaredependent
onthedesignofthecontrollerusedinthe
machinetoolandthetoolpathgeometry.While
therehavebeeninnovativecontrollerdesigns
thatminimizethefeedratediscrepancy(Sencer,
2008),mostmachinetoolsusedinconventional
industrialfacilitieshavecommercialoff-the-shelf
controllersthatdemonstratesomediscrepancies
inthefeedrates,especiallywhenmachining
complexgeometriesathighspeeds.Thereisa
needforsimpletoolstoestimatethe
discrepancyinthesemachiningconditions.
Apartfrominfluencingthesurfacequalityofthe
machinedparts,feedratevariationcanleadto
inaccurateestimatesofthecycletimeduring
machining.Accurateestimatesofthecycletime
isacriticalrequirementinplanningforcomplex
machiningoperationsinmanufacturingfacilities.
Thecycletimeisneededforbothschedulingthe
partinajobshop,aswellasforcostingthepart.
Inaccuratecycletimeestimates(especially
whenthefeedisoverestimated)canleadto
uncompetitiveestimatesforthecostofthepart
andunrealisticestimatesforthecycletime.
RelatedWork
deSouzaandCoelho(2007)presenteda
comprehensivesetofexperimentsto
demonstratefeedratelimitationsduringthe
machiningoffreeformsurfaces.Theyidentified
thecausesoffeedratevariationasdynamic
limitationsofthemachine,blockprocessingtime
FIGURE2:
MTCONNECTHIERARCHY.