PIEZOELECTRIC HYDRAULIC HYBRID ACTUATOR FOR A POTENTIAL SMART ROTOR

317 Pages·2002·4.53 MB·English

ABSTRACT
TitleofDissertation: PIEZOELECTRICHYDRAULICHYBRID
ACTUATORFORAPOTENTIALSMARTROTOR
APPLICATION
JayantSirohi,DoctorofPhilosophy,2002
Dissertation directedby: ProfessorInderjitChopra
DepartmentofAerospaceEngineering
A piezoelectric hydraulic hybrid actuator is proposed as a potential actuator for a
trailing edge flap on a smart rotor. Piezoceramics are very attractive for the smart rotor
conceptduetotheirhighenergydensityandelectro-mechanicalcoupling. Tooptimally
designsystemsbasedonpiezoceramicactuatorsandsensors,accuratepredictionoftheir
response and power consumption is necessary. However, at present, experimental data
aswell as analytical tools in this regardare limited. Additionally,actuation capabilities
ofconventionalpiezoceramicactuatorsareoftenlimitedbytheirsmallstroke.
In order to address this issue, detailed experiments were conducted on PZT-5H
piezoceramicsheetelementstoidentifytheiractuation,sensingandpowerconsumption
characteristics. The response of PZT-5H sheet actuators was measured under a variety
of mechanical loadings and electrical conditions. Using this experimental data, a
simple empirical model predicting the hysteretic free strain behavior of a PZT-5H
sheet was developed. Calibration of piezoelectric strain sensors was performed along
with the theoretical derivation and experimental validation of shear lag and transverse
sensitivity correction factors. Power consumption of piezoceramic actuators was
modeled and experimentally validated. Empirical correction factors to account for the
nonlinear variation of material properties with applied electric field were identified.
Additionally,thepossibilityofreducingthemagnitudeofcurrentdrawnbytheactuator
wasinvestigatedinconjunctionwiththenoveluseofapseudo-inductor.
Inordertoobtainhigheroutputstrokelevelsthanthatofconventionalpiezoceramic
actuators, a hybrid device combining piezoceramic actuation and hydraulic power
transmission was investigated. A prototype was designed to meet the requirements of
a trailing edge flap on a section of a full scale MD900 rotor blade. The prototype was
fabricated and tested, specifically concentrating on high pumping frequency operation.
ThedevicewasactuatedbytwoP-804.10piezostacksinseries,whichhadatotallength
of 36 mm and cross-sectional area 10 mm2. The device was tested up to a pumping
frequency of 1 kHz, and achieved its maximum flow rate at a frequency of 300 Hz.
Under uni-directional actuation, a blocked force of 33 lbs and a no-load velocity of
1.2 in/sec was measured. Under bi-directional actuation, at a frequency of 5 Hz, the
amplitude of the output displacement was measured to be 32 mils under no external
load, dropping to 15 mils under an external spring load of 180 lbs/in. The no-load
outputdisplacementamplitudedropsto12milsatafrequencyof10Hz.
It can be concluded that while the present prototype meets the requirements for a
trailing edge flap actuator in terms of blocked force and quasi-static stroke, it does not
have adequate bandwidth. In order to satisfy the bandwidth requirements, the flow rate
athighpumpingfrequenciesneedstobeimproved.
PIEZOELECTRICHYDRAULICHYBRIDACTUATORFORAPOTENTIAL
SMARTROTORAPPLICATION
by
JayantSirohi
DissertationsubmittedtotheFacultyoftheGraduateSchoolofthe
UniversityofMaryland,CollegeParkinpartialfulfillment
oftherequirementsforthedegreeof
DoctorofPhilosophy
2002
AdvisoryCommittee:
ProfessorInderjitChopra,Chair/Advisor
AssociateProfessorDarryllJ.Pines
AssociateProfessorNormanM.Wereley
AssistantProfessorChrisCadou
ProfessorAmrM.Baz,Dean’sRepresentative
(cid:176)c Copyrightby
JayantSirohi
2002
DEDICATION
ThisworkisdedicatedtoLordGanapathi,andtomyGrandparents,who
couldnotwaittoseeitcomplete
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ACKNOWLEDGEMENTS
I would like to express my gratitude to my advisor, Professor Inderjit Chopra for his
patient and inspiring guidance over the course of my graduate study. While giving
me enormous freedom to conduct my research, he also never hesitated to point out
the correct way to do things, and to provide important inputs when I did not see my
way clearly. It is to this combination of freedom and direction that I attribute the large
amountofknowledgeIhavegainedoverthepastfewyears.
Iamalsogreatlyindebtedtotheothermembersofmythesiscommittee: Dr. Darryll
Pines,Dr. NormanWereley,Dr. AmrBazandDr. ChrisCadoufortheirtimeandeffort,
andforprovidingvaluableinsightsintomyresearch. SpecialthanksareduetoDr. Pines
andDr. Wereleyfortheencouragementtheyhavegivenmeoverthepastfewyears.
I am very thankful for the existence of my ’family away from home’: Anand,
Kashyap, Nagarajan, Nitin, Prakash and Lakshmi for their companionship and for
everythingelse;someofthemhavebeenwithmeeversinceIstartedgraduateschool.
I have also benefitted greatly from the excellent companionship of my colleagues
at the Alfred Gessow Rotorcraft Center. Many thanks to the old-timer Paul and not-
quite-as-old-timers Ashish and Harsha for all our enlightening technical discussions,
as well as the good times spent together both inside and outside the Patterson building.
JinhyeongYoo,TaeohLee,AndyBernhardandNikhilKoratkarwereinvaluablesources
ofinformation,helpandsupport,andIlearntalotfromthem. Manythanksarealsodue
toBernieLaFranceandMr. LeeoftheMachineShopforalltheirhelpandenthusiasm.
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I would also like to add that I can never really acknowledge my parents adequately,
especially in such a short space. Suffice to say that they are really the reason for the
existence of this work, and also for what I am today. Without them, I would have
probablybeeninanentirelydifferentprofession.
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TABLEOFCONTENTS
ListofTables 10
ListofFigures 11
Chapter1 Introduction 1
1.1 Backgroundandproblemstatement . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Helicoptervibrationandnoise. . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Passiveisolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.2 Activevibrationcontrolschemes . . . . . . . . . . . . . . . . . . . 5
1.2.3 Activevibrationcontrol: Controlsurfaces . . . . . . . . . . . . . 8
1.2.4 Primaryflightcontrols: Swashplatelessrotor. . . . . . . . . . . . 10
1.3 Smartrotorconcept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.1 Roleofsmartstructuresandactivematerialsinthesmartrotor 13
1.3.2 Activematerialactuatorsandsensors . . . . . . . . . . . . . . . . 13
1.4 Smartactuatorsusedinactiverotors . . . . . . . . . . . . . . . . . . . . . . 17
1.4.1 Modelscaleactiverotors . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4.2 Fullscaleactiverotors . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.5 Motivationofthepresentresearch . . . . . . . . . . . . . . . . . . . . . . . 23
1.6 Objectivesofthepresentresearch . . . . . . . . . . . . . . . . . . . . . . . 28
1.7 Outlineofthedissertation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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1.8 Contributionsofthepresentwork . . . . . . . . . . . . . . . . . . . . . . . 31
Chapter2 PiezoceramicSheetActuators 41
2.1 Basicactuationmechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.2 Piezoelectricconstitutiverelations . . . . . . . . . . . . . . . . . . . . . . . 44
2.3 Experimentalsamplepreparationandcycling . . . . . . . . . . . . . . . . 47
2.4 Behaviorunderstaticexcitationfields . . . . . . . . . . . . . . . . . . . . . 49
2.4.1 Staticfreestrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.4.2 Effectofexternalstresses . . . . . . . . . . . . . . . . . . . . . . . 50
2.4.3 Drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.5 Behaviorunderdynamicexcitationfields . . . . . . . . . . . . . . . . . . . 55
2.5.1 Strainhysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.5.2 Dynamicstrainresponse . . . . . . . . . . . . . . . . . . . . . . . . 57
2.5.3 EffectofDCbias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2.6 Depolingbehavioranddielectricbreakdown . . . . . . . . . . . . . . . . . 60
2.7 Summaryandconclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Chapter3 PiezoelectricSensors 77
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2 Basicsensingmechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.2.1 PZTsensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.2.2 PVDFsensors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.3 SensorCalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
3.3.1 Experimentalsetup . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
3.3.2 Conversionofvoltageoutputtostrain . . . . . . . . . . . . . . . . 83
3.3.3 Signalconditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.4 Correctionfactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
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3.4.1 Poisson’sratioeffect . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.4.2 Shearlageffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.5 Experimentalresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.6 Generaloperatingconsiderations . . . . . . . . . . . . . . . . . . . . . . . . 93
3.6.1 Effectofsensortransverselength . . . . . . . . . . . . . . . . . . . 93
3.6.2 Effectoftemperatureonsensorcharacteristics. . . . . . . . . . . 94
3.7 Summaryandconclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Chapter4 PowerConsumptionofPiezoelectricActuators 105
4.1 Electro-mechanicalimpedanceapproach . . . . . . . . . . . . . . . . . . . 106
4.1.1 Electricalimpedanceofafreeactuator . . . . . . . . . . . . . . . 106
4.1.2 Electro-mechanicalimpedanceoftheactuator . . . . . . . . . . . 108
4.1.3 Mechanicalimpedanceofthestructure . . . . . . . . . . . . . . . 109
4.1.4 Electro-mechanical impedance of the actuator-structure
combination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.2 TheoryofL-Coscillatorcircuits . . . . . . . . . . . . . . . . . . . . . . . . 113
4.3 Developmentofnon-idealcircuitbehavior . . . . . . . . . . . . . . . . . . 115
4.3.1 Case(I): R =R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
l c
4.3.2 Case(II): R =0,R (cid:54)=0 . . . . . . . . . . . . . . . . . . . . . . . . 119
l c
4.3.3 Case(III): R (cid:54)=R (cid:54)=0 . . . . . . . . . . . . . . . . . . . . . . . . . 119
c l
4.4 Implementationofthecurrentreductioncircuit . . . . . . . . . . . . . . . 120
4.5 Implementationofapseudo-inductor . . . . . . . . . . . . . . . . . . . . . 122
4.6 Experimentalresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.7 Summaryandconclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Chapter5 PiezoelectricHydraulicHybridActuator: DesignandDevelopment 144
5.1 Piezoelectrichydraulicactuationconcept . . . . . . . . . . . . . . . . . . . 146
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