An Additive Manufacturing Path Generation Method Based on CAD Models for Robot Manipulators

110 Pages·2017·7.6 MB·English

by  Ingrid Fjordheim Onstein

An Additive Manufacturing Path
Generation Method Based on CAD Models
for Robot Manipulators
Ingrid Fjordheim Onstein
Master of Science in Cybernetics and Robotics
Submission date: May 2018
Supervisor: Jan Tommy Gravdahl, ITK
Co-supervisor: Linn Danielsen Evjemo, ITK
Norwegian University of Science and Technology
Department of Engineering Cybernetics

Problem description
Mainobjectivesforthisthesis:
1. Doaliteraturereviewonthestate-of-the-artoflarge-scaleadditivemanufactur-
ing.Considerthebenefitsandchallengesofusinga6DOFindustrialrobotas
opposedtousingatraditional3DOFtranslation-onlyset-up.
2. Presentthemethodsandsoftwarecurrentlyusedforgeneratingtrajectoriesfor
extrusionbasedAMbasedonCADmodels.
3. Improvethemethodfromthepreliminaryprojectthatusedavailablesoftwareto
generateatrajectoryforprintingasimplegeometricalform.Evaluatewhether
ornotthisimprovedmethodissuitableforfurtherworkonlarge-scaleAMwith
a6DOFrobot.
4. Developanewmethodtogenerateapathforprintingsimplegeometricalforms
usingrobotmanipulatorsthattakesadvantageoftherobots6DOF.Thisincludes
generatingapaththatreducetheneedforsupportstructuresandthatcanprint
alongcurvedcontours.
i
Abstract
TraditionalextrusionbasedAdditiveManufacturing(AM)isrealizedusinga3Degrees
ofFreedom(DOF),translationonly,3Dprinter.Here,theprintermustbelargerthan
the printed part. One way of enabling AM in large-scale is to combine AM with
robotics.Byusinga6DOFrobotmanipulatortoextrudeafast-curingmaterial,the
workspaceofthebuildwouldbegreatlyexpandedanditwouldbepossibletoincrease
theflexibilityofthebuildingprocessitselfsincethestructurewouldnolongerhave
tobebuiltfromthebottom-upapproachwhichisnecessaryformostexistingforms
of AM. This could possibly reduce the need for support structures to the point of
onlyrelyingofanchoringandstabilizing. Inthisthesis,amethodforgeneratinga
path for AM using robot manipulators that takes advantages of the robots DOF is
presented.ThepathisgeneratedbasedonsimplesurfacesinCADmodels.First,the
surface(s)issampledandthesamplesaregatheredinapointcloud. Then,apathis
generatedbasedonthepointcloudusingapathgenerationalgorithm.Threedifferent
pathgenerationalgorithmswasimplementedandtested: greedychoice, weighted
greedychoiceandTravellingSalesmanProblem(TSP).Outofthethreealgorithms,
theweightedgreedychoicealgorithmshowsthemostpromise.Withthisalgorithm,
pathsthatenableprintingalongcurvedsurfacesandreducingtheneedforsupport
structureswasgenerated.Themethodiseffective,andbyinterfacingwithFreeCAD,it
iseasytoreviewthegeneratedpathsthroughvisualaids.Itis,however,importantto
mentionthatthemethodonlygeneratespathsbasedonsimplesurfacesandisbased
ontheassumptionoffast-curingmaterialenablingmid-airprinting.
ii
Sammendrag
Tiltradisjonell3D-printingbrukes3D-printeremed3frihetsgrader.Dettemedfører
atprinterenmåværestørreenndelensomskalprintes.3D-printingistorskalakan
muliggjøresvedåkombinere3D-printingogrobotikk.Vedåbrukeenrobotmanipulator
med6frihetsgradertilåekstrudereetmaterialesomherderraskt,kanarbeidsområdet
blikraftigutvidetogdetvilværemuligåøkeflesibilitetentilbyggeprosessen.Dette
ersidenstrukturenikkelengermåbyggeslagforlagfrabunnenavsomernødvendig
fordeflesteeksisterendeløsningerinnen3D-printing.Dettekanreduserebehovetfor
støttestrukturertilkunåværeavhengigavforankringogstabilisering.
Idenneavhandlingen,vilenmetodeforågenererebanertil3D-printingforen
robotmanipulatorblipresentert. Måletmedmetodeneråutnytteallede6frihets-
gradene.DegenerertebaneneerbasertpåenkleoverflateriCAD-modeller.Detførste
stegetiprosesseneråsampledevalgteoverflateneogsamleallepunkteneienfelles
punktsky.Derettervilenenbanebligenerertbasertpådennepunktskyenvedhjelp
avenalgoritme.Treforskjelligealgoritmererimplementertogtestet,herundergrådig
algoritme, vektet grådig algoritme og travelling salesman problem (TSP). Blant de
tre algoritmene er det vektet grådig som viser mest potensiale. Denne algoritmen
generererbanersommuliggjør3D-printinglangskurvedeoverflaterogsomreduserer
behovetforstøttestrukturer.MetodenereffektivoggjennomFreeCADerdetlettå
vurderedegenerertebanenevedhjelpavvisuelleverktøy. Deterviktigånevneat
metodenkungenerererbanerbasertpåenkleoverflater,ogerbasertpåantagelsen
ommaterialesomherderhurtig.
iii
Preface
ThisthesisiswrittenaspartofaMaster’sdegreeinEngineeringCyberneticsatthe
DepartmentofEngineeringCyberneticsattheNorwegianUniversityofScienceand
Technology (NTNU). The project was carried out from January 2018 to June 2018.
This thesis is based on the work done in the specialization project performed by
thestudentwiththetitle"Additivemanufacturingbyrobotmanipulator:Amethod
forgeneratingrobottrajectorybasedonCADmodelusingexistingsolutions". The
task was formulated as an open problem and the student has chosen method and
softwareindependently.GuidancewasreceivedfromsupervisorJanTommyGravdahl,
co-supervisorLinnDanielsenEvjemoandfromMathiasHauanArbo,allatNTNU.
Acknowledgements
Iwouldliketothankmysupervisorandco-supervisoratNTNU,JanTommyGravdahl
andLinnDanielsenEvjemo,fortheirhelpandguidancethroughoutthisproject. I
wouldalsoliketothankMathiasHauanArboatNTNUfordiscussingtheprojectwith
mewhenneeded.Finally,Iwouldliketothankmybrother,HåkonFjordheimOnstein,
forprovidingmewithCADmodelsonrequest.
iv
Contents
Problemdescription i
Abstract ii
Sammendrag iii
Preface iv
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Literaturereview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Literaturestudy 5
2.1 Additivemanufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Using3Dprinters . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2 Usingindustrialrobots . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3 Existingsolutions . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Computer-AidedDesign . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.1 Boundaryrepresentation . . . . . . . . . . . . . . . . . . . . . 16
v
2.2.2 TheSTEPstandard . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.3 Stereolithography. . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.4 FreeCAD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3 AMprocessingpipeline . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.1 Tessellationofmodel . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.2 Slicingalgorithm . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.3 Supportstructures . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.4 Machineinstructions . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.5 AMsoftware . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.4 Robotcontrol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.4.1 RobotStudio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.2 RobotOperatingSystem . . . . . . . . . . . . . . . . . . . . . 34
2.5 Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.5.1 Dynamicprogramming . . . . . . . . . . . . . . . . . . . . . 36
2.5.2 Greedychoicealgorithms . . . . . . . . . . . . . . . . . . . . 36
2.5.3 TravellingSalesmanProblem . . . . . . . . . . . . . . . . . . 37
3 Preliminaryproject 39
3.1 Furtherwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4 AMPathgeneration 45
4.1 Choiceofsolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 AMPathgenerationsystem . . . . . . . . . . . . . . . . . . . . . . . 48
4.3 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.3.1 Sampleobject . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3.2 Samplingofsubobject . . . . . . . . . . . . . . . . . . . . . . 50
4.3.3 Calibrationofstep . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3.4 Generatingpointcloud . . . . . . . . . . . . . . . . . . . . . . 52
4.4 Pathgeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.4.1 Requirementsofpath . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
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4.4.3 Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5 Results 59
5.1 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.1.1 Shoehornmodel . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.1.2 Propellerblademodel . . . . . . . . . . . . . . . . . . . . . . 62
5.2 Pathgeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.2.1 Greedychoicealgorithm . . . . . . . . . . . . . . . . . . . . . 67
5.2.2 Weightedgreedyalgorithm . . . . . . . . . . . . . . . . . . . 69
5.2.3 TravellingSalesmanProblemalgorithm . . . . . . . . . . . . 76
6 Discussion 81
6.1 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.2 Pathgeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.2.1 Greedychoicealgorithm . . . . . . . . . . . . . . . . . . . . . 83
6.2.2 Weightedgreedychoicealgorithm . . . . . . . . . . . . . . . 84
6.2.3 TSPalgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.2.4 Comparingthealgorithms . . . . . . . . . . . . . . . . . . . . 88
6.3 Pathgenerationsystem . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7 Conclusion 91
7.1 Prospectforfuturework . . . . . . . . . . . . . . . . . . . . . . . . . 92
References 93
vii
List of Figures
2.1 TheBOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 NewStory+ICON:3Dprintedhouse . . . . . . . . . . . . . . . . . . 9
2.3 TheMataerialprojectenablesAMalongdoublecurvedlinesinmid-air 10
2.4 MX3DBridgeProject-Robotonbridge . . . . . . . . . . . . . . . . . 11
2.5 MX3DBridgeProject-Completespan . . . . . . . . . . . . . . . . . 11
2.6 PartprintedbytheRobotComposite3DDemonstrator . . . . . . . . 12
2.7 Atypicalaerospacecomponent-materialdepositionandremoval . . 14
2.8 Pathcomparisononabowl-likesurface . . . . . . . . . . . . . . . . . 15
2.9 B-repmodels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.10 ABéziercurveanditscontrolpolygon . . . . . . . . . . . . . . . . . 18
2.11 Schematicofthecontrolnetfora4x4Béziersurface . . . . . . . . . . 20
2.12 Bi-cubicBéziersurfaces . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.13 3Dmodelofcylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.14 TypicalprocessplanningphasesinAM . . . . . . . . . . . . . . . . . 24
2.15 Staircaseeffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.16 Slicingoftrianglemeshprocess . . . . . . . . . . . . . . . . . . . . . 26
2.17 Imageofslopedregionsofsimplemanufacturedexample . . . . . . . 27
2.18 Multi-directionalslicing. . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.19 Structuresrequiringsupportstructures . . . . . . . . . . . . . . . . . 29
2.20 DirectionparallelandcontourparallelinfillpatternsforAM . . . . . 30
3.1 ResultfromtheslicingprocessusingCraftWare . . . . . . . . . . . . 40
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