On Modeling and Diagnosis of Friction and Wear in Industrial Robots

157 Pages·2011·2.49 MB·English

Linköpingstudiesinscienceandtechnology. Thesis.
No.1516
On Modeling and Diagnosis of
Friction and Wear in Industrial Robots
André Carvalho Bittencourt
REGLERTEKNIK
AUTOMATIC CON T R O L
LINKÖPING
DivisionofAutomaticControl
DepartmentofElectricalEngineering
LinköpingUniversity,SE-58183Linköping,Sweden
http://www.control.isy.liu.se
[email protected]
Linköping2012
ThisisaSwedishLicentiate’sThesis.
SwedishpostgraduateeducationleadstoaDoctor’sdegreeand/oraLicentiate’sdegree.
ADoctor’sDegreecomprises240ECTScredits(4yearsoffull-timestudies).
ALicentiate’sdegreecomprises120ECTScredits,
ofwhichatleast60ECTScreditsconstituteaLicentiate’sthesis.
Linköpingstudiesinscienceandtechnology. Thesis.
No.1516
OnModelingandDiagnosisofFrictionandWearinIndustrialRobots
AndréCarvalhoBittencourt
[email protected]
www.control.isy.liu.se
DepartmentofElectricalEngineering
LinköpingUniversity
SE-58183Linköping
Sweden
ISBN978-91-7519-982-5 ISSN0280-7971 LiU-TEK-LIC-2012:1
Copyright©2012AndréCarvalhoBittencourt
PrintedbyLiU-Tryck,Linköping,Sweden2012
Tothememoryofmybrother.

Abstract
Industrialrobotsaredesignedtoendureseveralyearsofuninterruptedoperation
andthereforeareveryreliable. However,noamountofdesigneffortcanprevent
deterioration over time, and equipments will eventually fail. Its impacts can,
nevertheless,beconsiderablyreducedifgoodmaintenance/servicepracticesare
performed. Thecurrentpracticeforserviceofindustrialrobotsisbasedonpre-
ventive and corrective policies, with little consideration about the actual condi-
tionofthesystem. Inthecurrentscenario,theserviceabilityofindustrialrobots
canbegreatlyimprovedwiththeuseofconditionmonitoring/diagnosismethods,
allowingforcondition-basedmaintenance(cbm).
Thisthesisaddressesthedesignofconditionmonitoringmethodsforindustrial
robots. The main focus is on the monitoring and diagnosis of excessive degra-
dations caused by wear of the mechanical parts. The wear processes may take
several years to be of significance, but can evolve rapidly once they start to ap-
pear. An early detection of excessive wear levels can therefore allow for cbm,
increasing maintainability and availability. Since wear is related to friction, the
basicideapursuedistoanalyzethefrictionbehaviortoinferaboutwear.
To allow this, an extensive study of friction in robot joints is considered in this
work. The effects of joint temperature, load and wear changes to static friction
in robot a joint are modeled based on empirical observations. It is found that
theeffectsofloadandtemperaturetofrictionarecomparabletothosecausedby
wear. Jointtemperatureandloadaretypicallynotmeasured,butwillalwaysbe
presentinapplications. Therefore,diagnosissolutionsmustbeabletocopewith
them.
Differentmethodsareproposedwhichallowforrobustwearmonitoring. First,a
wearestimatorissuggested. Wearestimatesaremadepossiblewiththeuseofa
test-cycleandafrictionmodel. Second,amethodisdefinedwhichconsidersthe
repetitive behavior found in many applications of industrial robots. The result
of the execution of the same task in different instances of time are compared to
provide an estimate of how the system changed over the period. Methods are
suggestedthatconsiderchangesinthedistributionofdataloggedfromtherobot.
Itisshownthroughsimulationsandexperimentsthatrobustwearmonitoringis
madepossiblewiththeproposedmethods.
v

Populärvetenskaplig sammanfattning
Modernaindustrirobotarkonstruerasförattkunnaarbetaoavbrutetunderflera
år och är därför väldigt pålitliga. Det är dock omöjligt att förhindra att roboten
slits, att prestanda försämras och att slutligen fel uppstår. Effekterna kan dock
reducerasmedhjälpavrutinerförserviceochunderhåll.Förnärvarandebygger
dessarutineroftastpåförebyggandeunderhåll,därrelativtlitenhänsyntastill
det faktiska tillståndet hos roboten. Situationen kan dock förbättras genom att
istörreutsträckninganvändametoderförövervakningochdiagnosavsystemet
ochdärmedkantillämpaenhögregradavtillståndsbaseratunderhåll.
Dennaavhandlingbehandlarutformningmetoderförtillståndsövervakningsför
industrirobotar. Arbetet behandlar främst övervakning och diagnos av försäm-
radeprestandapågrundavförslitningavmekaniskadelar.Förslitningenkanta
fleraårförattbörjautvecklas,mendärefterkanförloppetgåsnabbt.Omförslit-
ningenupptäcksitidkantillståndsbaseratunderhålltillämpas,vilketkanförhin-
drafelochökatillgänglighetenhosroboten.Eftersomförslitningärnärarelater-
ad till friktion är därför grundidén att studera friktion för att dra slutsatser om
förslitningen.
Förattmöjliggöradettaharenomfattandestudieavfriktionhosindustrirobotar
genomförts. Inverkan av temperatur och belastning har studerats och modeller-
atsutgåendefrånomfattandeexperimentellaförsök.Dessaharvisatatteffekter-
naavbelastningochtemperaturpåfriktionenäristorlekjämförbaramedförslit-
ningensinverkan.Eftersomsåvältemperatursombelastningvarierarnärroboten
arbetar,meningenavdemnormaltbrukarmätasmåsteendiagnosmetodkunna
hanteradessavariationer.
Avhandlingenföreslårtvåolikametoderförrobustövervakningochdiagnosav
förslitning,därdenförstametodeninnebärattmanskattarförslitningengenom
att använda en så kallad testcykel och en skattad friktionsmodell. Den andra
metodenutnyttjarattenindustrirobotoftaarbetarrepetitivtdärenvissrörelse
upprepas. Beteendena hos roboten då samma rörelse upprepas hos roboten vid
olikatillfällenjämförsochanvändsförattbedömahurrobotensegenskaperförän-
drats. Metoden baseras på förändringar i fördelningen hos uppmätta data, t. ex.
moment,frånroboten.Simuleringarochexperimentindikerarattdetärmöjligt
attskaparobustametoderförövervakningochdiagnosavförslitninghosindus-
tribotar.
vii

Acknowledgments
First, I would like to thank my supervisor Prof. Svante Gunnarsson for the ex-
cellentguidancethroughtheseyears,forkeepingmemotivated,fortheconstant
supportandforalwaysfinding(quickandaccurate)solutionstomyworries. Per-
hapsifitwasnotforDr.ShivaSander-TavallaeyIwouldnothavetakenthisjour-
ney, thank you for inviting me to graduate education and for all your guidance;
thanks also to Prof. Lennart Ljung and Prof. Svante Gunnarsson for accepting
me into the group. Special thanks to the valuable input I received from my co-
supervisorsDr. ErikWernholtandProf. MikaelNörloff.
Beingagraduatestudentattheisy/rtgrouphasbeenaremarkableexperience.
IfeelextremelyprivilegedforthethingsIhavelearned,taughtandthepeopleI
havemet. Suchexcellenceistheresultofseveralyearsofdedicatedwork,andI
wouldliketoexpressmygratitudetoeveryonebehindourorganizationalstruc-
ture. Tomentionsome,thankyouProf. LennartLjungandProf. SvanteGunnars-
sonforyourleadership;UllaSalaneck,ÅsaKarmelindandnowNinnaStensgård
fortheadimistrativesupport;allofourgurus,speciallytheonesbehindthisnice
LATEXthesistemplate,Dr. GustafHendebyandDr. HenrikTidefelt. Thequality
ofthisthesiswasalsoconsiderablyimprovedwiththecommentsIreceivedfrom
Prof. SvanteGunnarsson,Prof. MikaelNörloff,Dr. TorgnyBroghård,PatrikAx-
elssonandDr. ShivaSander-Tavallaey; thankyouforyourtime. Thanksalsoto
Dr. ErikFriskfortheinterestingdiscussionsondiagnosis.
Thisworkwouldnothavebeenthesameifitwasnotfortheclosecollaboration
with abb. abb not only supported me financially, via vinnova’s Industry Ex-
cellenceCenterlink-sic,butalsowithpricelessexpertiseandguidance. Thank
youDr.ShivaSander-TavallaeyandLic.NiclasSjöstrandforgivingmeaccessto
resourcesandfortheconstantinterestinmywork. ThankyouDr. ShivaSander-
Tavallaey,Dr. KarinSaarinen,MSc. HansAndersson,Dr. StigMobergandmany
others for all the valuable input and for helping me feel home at abb. Special
thankstoDr. TorgnyBroghård,whohasactedindifferentlevelsforthesuccess
ofthiscollaboration,fromhisroleinthelink-sicboardtothedetailedreviews
of my work; thanks for your guidance, expertise, and humbleness. I was intro-
duced to diagnosis of industrial robots already in 2007 when I took an “exjobb”
atabb. Thisisprobablywheremyjourneytoapostgraduateeducationstarted.
Special thanks to Lic. Niclas Sjöstrand and Prof. Bo Wahlberg who acted as my
supervisorsbackthen. ThanksalsotoProf.AlfIsakssonwithwhomIworkedin
otherprojectsrelatedtoabb.
Theenduranceofthelong-dark-coldwintersandthebrief-bright-warmsummers
ofSwedenwasmademuchmoreenjoyablewiththepresenceofgoodfriendsin
mylive.WithDanielAnkelhedIhavesharedmostofmytimeattheoffice;thanks
foryourpatience,company,andmusicknowledgeexchanges. SinaKosh···kazad
is probably the best host in the world, thanks for all the nice time we shared.
ThankyouFredrkLindsten,KarlGranström,EmreOzkan,TohidArdeshiri,Hen-
rikOhlsson,PeterRosander,CarstenFritsche,PatrikAxelsson,LubosVáci,Saikat
ix
x Acknowledgments
Saha,TianshiChen,ZoranSjanic,YlvaJung,JessicaEscobarandeveryoneelsefor
all the nice moments we shared. Thank you all for helping me counterbalance
thestressloadsofthePhDeducationwithgood-humoreddiscussionsduringour
w-fika-o-fika-r-fika-kroutine, mopedraces, ilkrakens, galadinnerfrenzies, fly-
inglimones, giantmozzarellas, pinkelephants, climbingandkitesurfingadven-
tures, (icy/bloody)barbecues, Peruviangiraffes, andsomuchmore. Imustalso
mention my friends from college, with whom I shared my first experiences in
Engineering. Specially those of the legendary 031 class of Automatic Control,
peteel and more. Thank you all for the Linguições, churrascos, Oktobers, peli-
cancompetitions,etc. Icanonlyhopethatwewillalwayskeepintouch.
ThankyouAlíciaforyourloveandpresence inmylife. Iwillalwaysbegrateful
foralltheeffortsyouhavemadeforourrelationship. Iamsorrythatithasmeant
thatyouhadtointerruptyourstudiesinBrazil,saygoodbyetoyourfamily,learn
a foreign language, freeze, and so many other things that happened and will
happen;IcanonlyhopethatIwillalwaysbeworthy.Thankyouforyourpatience,
yourcosycompanywhenhavingabeer,relaxingathome,goingonunforgettable
climbingadventures,andsomuchmore. IloveyouBosa.
Acima de tudo eu gostaria de agradecer ao suporte e amor incondicionais da
minhafamília. Detodososaprendizadosqueeuacumulei,osmaisimportantes
foramvocêsquemensinaram. Obrigadopeladedicaçãoeamorsemprepresentes
em minha vida. Obrigado pelo suporte que recebi e recebo desde que chegou a
hora de buscar meus sonhos, mesmo que isso resultasse em nos separarmos ge-
ograficamente. Peçodesculpaspelasminhasfalhasemmantermaiorfrequência
nocontatoeporsertãoesquecido. Comamor,
AndréCarvalhoBittencourt,
Linköping,January2012.