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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.