Reliability Assessment for Low-cost Unmanned Aerial Vehicles

122 Pages·2014·16.55 MB·English

Reliability Assessment for Low-cost Unmanned Aerial Vehicles
ADISSERTATION
SUBMITTEDTOTHEFACULTYOFTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFMINNESOTA
BY
PaulMichaelFreeman
INPARTIALFULFILLMENTOFTHEREQUIREMENTS
FORTHEDEGREEOF
DOCTOROFPHILOSOPHY
GaryJ.Balas,co-advisor
PeterJ.Seiler,co-advisor
November2014
©PaulMichaelFreeman 2014
ALLRIGHTSRESERVED
Acknowledgements
Personal: TBD
This material is based upon work supported by the National Science Foundation under
GrantNo. 0931931entitledCPS:EmbeddedFaultDetectionforLow-Cost, Safety-CriticalSys-
tems;Dr. TedBaker,ProgramManager. Anyopinions,󰅮indings,andconclusionsorrecommen-
dations expressed in this material are those of the author and do not necessarily re󰅮lect the
viewsoftheNationalScienceFoundation.
i
Dedication
TBD
ii
Abstract
Existinglow-costunmannedaerospacesystemsareunreliable,andengineersmustblendreli-
abilityanalysiswithfault-tolerantcontrolinnovelways. ThisdissertationintroducestheUni-
versityofMinnesotaunmannedaerialvehicle󰅮lightresearchplatform,acomprehensivesim-
ulationand󰅮lighttestfacilityforreliabilityandfault-toleranceresearch. Anindustry-standard
reliabilityassessmenttechnique,thefailuremodesandeffectsanalysis,isperformedforanun-
manned aircraft. Particular attention is afforded to the control surface and servo-actuation
subsystem. Maintainingeffectorhealthisessentialforsafe󰅮light;failuresmayleadtolossof
controlincidents. Failurelikelihood,severity,andriskarequalitativelyassessedforseveralef-
fectorfailuremodes. Designchangesarerecommendedtoimproveaircraftreliabilitybasedon
thisanalysis. Mostnotably,thecontrolsurfacesaresplit,providingindependentactuationand
dual-redundancy. Thesimulationmodelsforcontrolsurfaceaerodynamiceffectsareupdated
tore󰅮lectthesplitsurfacesusinga󰅮irst-principlesgeometricanalysis.
Thefailuremodesandeffectsanalysisisextendedbyusingahigh-󰅮idelitynonlinearaircraft
simulation. Atrimstatediscoveryisperformedtoidentifytheachievablesteady,wings-level
󰅮light envelope of the healthy and damaged vehicle. Tolerance of elevator actuator failures
is studied using familiar tools from linear systems analysis. This analysis reveals signi󰅮icant
inherent performance limitations for candidate adaptive/recon󰅮igurable control algorithms
used for the vehicle. Moreover, it demonstrates how these tools can be applied in a design
feedbacklooptomakesafety-criticalunmannedsystemsmorereliable.
Controlsurfaceimpairmentsthatdooccurmustbequicklyandaccuratelydetected. This
dissertation also considers fault detection and identi󰅮ication for an unmanned aerial vehicle
usingmodel-basedandmodel-freeapproachesandappliesthosealgorithmstoexperimental
faultedandunfaulted󰅮lighttestdata. Flighttestsareconductedwithactuatorfaultsthataffect
theplantinputandsensorfaultsthataffectthevehiclestatemeasurements. Amodel-based
detectionstrategyisdesignedandusesrobustlinear󰅮ilteringmethodstorejectexogenousdis-
turbances,e.g. wind,whileprovidingrobustnesstomodelvariation. Adata-drivenalgorithm
isdevelopedtooperateexclusivelyonraw󰅮lighttestdatawithoutphysicalmodelknowledge.
Thefaultdetectionandidenti󰅮icationperformanceofthesecomplementarybutdifferentmeth-
odsiscompared. Together,enhancedreliabilityassessmentandmulti-prongedfaultdetection
andidenti󰅮icationtechniquescanhelptobringaboutthenextgenerationofreliablelow-cost
unmannedaircraft.
iii
Contents
Acknowledgements i
Dedication ii
Abstract iii
ListofTables vii
ListofFigures viii
1 Introduction 1
2 UMNFlightResearchPlatform 4
2.1 ExperimentalFlightTestHardware . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 AirframesandR/CComponents . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Avionics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.4 GroundStation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 SoftwareandSimulationPackage . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 NonlinearSimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Software-in-the-LoopSimulation . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Hardware-in-the-LoopSimulation . . . . . . . . . . . . . . . . . . . . . . 12
2.3 FRPContributiontoResearchCommunity . . . . . . . . . . . . . . . . . . . . . . 12
3 FailureModesandEffectsAnalysis 13
3.1 FMEAOverview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 IbisHardwareElements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.1 AirframeSubsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
iv
3.2.2 PowerplantSubsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.3 EffectorsSubsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2.4 AvionicsandSensorsSubsystem . . . . . . . . . . . . . . . . . . . . . . . 17
3.3 FailuresModesandEffectsAnalysisofIbisUAV . . . . . . . . . . . . . . . . . . . 18
3.3.1 EvaluationMetrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.2 Airframe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3.3 Powerplant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3.4 AvionicsandSensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.5 Effectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 RedesigningIbisforImprovedReliability 25
4.1 Baldr: Reliability-focusedIbisVariant. . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.1 IncreasedPhysicalRedundancy . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.2 OtherModi󰅮icationsduetoSplittingSurfaces . . . . . . . . . . . . . . . . 28
4.2 BaldrSimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.1 OriginalIbisAerodynamicModel . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.2 EnhancedBaldrAerodynamicModel . . . . . . . . . . . . . . . . . . . . 31
5 ReliabilityAssessmentUsingTrimStateDiscovery 45
5.1 TrimStateDiscoveryMethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.2 AchievableSteadyWings-levelFlightEnvelopeforIbis . . . . . . . . . . . . . . . 48
5.3 LinearAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.3.1 Open-loopAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6 FaultDetectionandIsolationforControlSurfaceImpairments 60
6.1 ExperimentalScope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.2 FaultScenariosConsidered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.3 FlightTesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.4 Model-basedFaultDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.4.1 DesignConsiderations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.4.2 𝐻 FDIFormulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
∞
6.5 Data-drivenAnomalyDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
6.6 FlightTestExperimentalResults . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.6.1 LinearUAVSimulationPerformance . . . . . . . . . . . . . . . . . . . . . 73
6.6.2 Data-drivenvsModel-basedDetectorPerformance . . . . . . . . . . . . 74
v
7 ConclusionandDiscussion 79
Bibliography 81
AppendixA. FailureModesandEffectsAnalysisSummary 86
vi
List of Tables
3.1 IbisUAVHardwareSubsystemsandComponents . . . . . . . . . . . . . . . . . . 20
3.2 FailureLikelihoodCategories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3 FMEARiskMatrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.1 ModeledForceandMomentCoef󰅮icientsforIbis/FASERControlEffects . . . . . 30
4.2 Coef󰅮icientsinOriginal(Maroon)andEnhanced(Gold)AerodynamicModels . 44
6.1 ExperimentalFDIPerformanceMetrics . . . . . . . . . . . . . . . . . . . . . . . 78
A.1 FailureModes,Effects,andCriticalitySummary . . . . . . . . . . . . . . . . . . . 87
vii
List of Figures
1.1 Boeing777󰅮lightcontrolsurfaces. Theunderlyingcomputation,electrical,and
hyraulicsubsystemsaretripleredundant. . . . . . . . . . . . . . . . . . . . . . . 2
2.1 UltraStick120‘Ibis’UAVat󰅮lighttestinglocation. Thelandinggearwheelscan
beswappedwithapairofskisfor󰅮lighttestingduringthewintermonths. . . . 5
2.2 Ultra Stick 120 UAV with Ultra Stick 25e models. The department maintains
severalofthesmallerUltraStick25etestUAVs. . . . . . . . . . . . . . . . . . . . 6
2.3 MiniUltraStickmountedonstingduringexperimentsinUMNLow-SpeedWind
Tunnel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 CoreUAVavionicsarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.5 GoldyFlightControlSystemavionicspallet. . . . . . . . . . . . . . . . . . . . . . 9
3.1 FlowchartoftypicalFMEAprocedures . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 IbisUAVin󰅮light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 Reliabilityblockdiagramforpowerplantcomponents. . . . . . . . . . . . . . . . 17
3.4 Reliabilityblockdiagramforeffectorscomponents. . . . . . . . . . . . . . . . . 18
3.5 Reliabilityblockdiagramforavionicsandsensorscomponents. . . . . . . . . . 19
4.1 RudderandverticalstabilizeronUltraStick120(nottoscale). Thedirections
ofthebody-󰅮ixedaxesareindicated. . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2 Rudder splitting with a candidate cut line and computed mean aerodynamic
chords(MAC)fortheresultantpartitions. . . . . . . . . . . . . . . . . . . . . . . 27
4.3 Bodyandstabilityframede󰅮initionsforexampleaircraft. . . . . . . . . . . . . . 29
4.4 Dragforcecoef󰅮icientforleftelevator(𝐶 ). Thecoef󰅮icientfortherightele-
𝐷
𝛿𝑒𝐿
vatorisidentical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.5 Dragforcecoef󰅮icientforleft󰅮lap(𝐶 ). Thecoef󰅮icientsfortheright󰅮lap,left
𝐷
𝛿𝑓𝐿
aileron,andrightaileronareidentical. . . . . . . . . . . . . . . . . . . . . . . . . 33
4.6 Sideforcecoef󰅮icientfortoprudder(𝐶 ). Thecoef󰅮icientforthebottomrud-
𝑌
𝛿𝑟𝑇
derisidentical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
viii