Advances in Gyroscope Technologies PDF
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Advances in Gyroscope Technologies M. N. Armenise (cid:2) C. Ciminelli (cid:2) F. Dell’Olio (cid:2) V. M. N. Passaro Advances in Gyroscope Technologies 123 M.N.Armenise F. Dell’Olio Dipartimentodi Elettrotecnica Dipartimentodi Elettrotecnica ed Elettronica ed Elettronica Politecnico diBari Politecnico diBari Via Re David200 Via Re David200 70125Bari, Italy 70125Bari, Italy e-mail: [email protected] V.M.N.Passaro C. Ciminelli Dipartimentodi Elettrotecnica Dipartimentodi Elettrotecnica ed Elettronica ed Elettronica Politecnico diBari Politecnico diBari Via Re David200 Via Re David200 70125Bari, Italy 70125Bari, Italy ISBN 978-3-642-15493-5 e-ISBN 978-3-642-15494-2 DOI 10.1007/978-3-642-15494-2 SpringerHeidelbergDordrechtLondonNewYork LibraryofCongressControlNumber:2010936445 (cid:2)Springer-VerlagBerlinHeidelberg2010 Thisworkissubjecttocopyright.Allrightsarereserved,whetherthewholeorpartofthematerialis concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting,reproductiononmicrofilmorinanyotherway,andstorageindatabanks.Duplication ofthispublicationorpartsthereofispermittedonlyundertheprovisionsoftheGermanCopyrightLaw of September 9, 1965, in its current version, and permission for use must always be obtained from Springer.ViolationsareliabletoprosecutionundertheGermanCopyrightLaw. Theuseofgeneraldescriptivenames,registerednames,trademarks,etc.inthispublicationdoesnot imply, even in the absence of a specific statement, that such names are exempt from the relevant protectivelawsandregulationsandthereforefreeforgeneraluse. Coverdesign: eStudioCalamarS.L. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface The gyroscope, which measures angular rotation around a fixed axis with respect toaninertialspace,isakeysensorinmodernnavigationsystemsenablingtoplan, record and control the movement of a vehicle from one place to another. This devicehasawidespectrumofapplicationsinspaceengineering,aeronauticaland military industry, automotive, medicine and so on. For these reasons gyro archi- tectures and technologies have been investigated by very important research groups in USA, Europe and Asia. National space agencies of a number of Countries have invested significant financial resources for developing innovative gyroscope technologies. Results ofthis intense research effort have been reported in a large number of scientific papers and patents. The purpose of the book is to collect and critically review the main results obtained by the scientific community in advanced gyroscope technologies. Architectures,designtechniquesandfabricationtechnologyofangularratesensors proposedinliteraturearedescribed.Futureresearchtrendsaimedtocoverspecial applications are also considered. ThebookisintendedforresearchersandPh.D.studentsinterestedinmodelling, design and fabrication of gyros. It may be a useful education support in some university courses focused on gyro technologies. In recent years the authors have spent an intense research effort on optical angular velocity sensors working on some specific projects supported by some space agencies. They use their deep know–how on different gyroscope technolo- gies to offer to the readers a wide vision about the book subject. The book includes seven chapters. First two chapters introduce the topic and brieflydescribephysicaleffectsexploitedingyroscopetechnologies.Chapters3,4 and 5 are focused on optical gyros. State-of-the-artof ring laser gyros, fiber optic gyros andintegratedoptical gyros is accuratelyreviewed. Vibratory gyrosand,in particular, MEMS gyros are the topic of Chap. 6, where MOEMS gyros are also introduced. Finally, the book topic is summarized in Chap. 7 that offers also an v vi Preface overview of the most innovative technologies for angular rate sensors with out- standing performance. Bari, May 2010 M. N. Armenise C. Ciminelli F. Dell’Olio V. M. N. Passaro Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Overview of Gyroscope Technologies . . . . . . . . . . . . . . . . . . . 1 1.2 Gyro Performance Parameters. . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Gyro Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 Physical Effects in Gyroscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1 Sagnac Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Coriolis Force Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3 He–Ne and Solid-State Ring Laser Gyroscopes . . . . . . . . . . . . . . . 17 3.1 He–Ne RLG Architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.2 Error Sources in He–Ne RLGs . . . . . . . . . . . . . . . . . . . . . . . . 20 3.2.1 Null Shift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.2 Lock-in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.3 Scale Factor Variation. . . . . . . . . . . . . . . . . . . . . . . . . 24 3.3 Quantum Noise in He–Ne RLGs. . . . . . . . . . . . . . . . . . . . . . . 24 3.4 Solid-State RLGs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4 Fiber Optic Gyroscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.1 Interferometric Fiber Optic Gyros (IFOGs). . . . . . . . . . . . . . . . 30 4.2 Resonant Fiber Optic Gyros (RFOGs) . . . . . . . . . . . . . . . . . . . 37 4.2.1 Phase Modulation-Based Read-Out Technique . . . . . . . . 40 4.2.2 Frequency Modulation-Based Read-Out Technique. . . . . 43 4.2.3 Resonator Length Modulation-Based Read-Out Technique . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.2.4 Critical Aspects of RFOGs. . . . . . . . . . . . . . . . . . . . . . 45 4.3 Optical Gyros Based on a Fiber Ring Laser . . . . . . . . . . . . . . . 47 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 vii viii Contents 5 Integrated Optical Gyroscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 5.1 Active Integrated Optical Gyros . . . . . . . . . . . . . . . . . . . . . . . 52 5.1.1 Integrated Ring Lasers. . . . . . . . . . . . . . . . . . . . . . . . . 52 5.1.2 Fully Integrated Active Optical Gyros. . . . . . . . . . . . . . 58 5.2 Passive Integrated Optical Gyros. . . . . . . . . . . . . . . . . . . . . . . 62 5.2.1 Passive Integrated Optical Gyros Based on a Ring Resonator . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.2.2 Passive Integrated Optical Gyros Based on Coupled Ring Resonators . . . . . . . . . . . . . . . . . . . . 73 5.2.3 Passive Integrated Optical Gyros Based on a Photonic Crystal Cavity . . . . . . . . . . . . . . . . . . . . 76 6 MEMS Gyroscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.1 Fabrication Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 6.2 Research Prototypes and Commercially Available Devices. . . . . 86 6.2.1 z-Axis MEMS Gyros. . . . . . . . . . . . . . . . . . . . . . . . . . 87 6.2.2 Lateral-Axis MEMS Gyros. . . . . . . . . . . . . . . . . . . . . . 95 6.2.3 Dual-Axis MEMS Gyros . . . . . . . . . . . . . . . . . . . . . . . 96 6.2.4 Summary of MEMS Gyros Performance . . . . . . . . . . . . 97 6.2.5 Open Issues and Design Criteria. . . . . . . . . . . . . . . . . . 97 6.3 MOEMS Gyros. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 7 Emerging Gyroscope Technologies . . . . . . . . . . . . . . . . . . . . . . . . 103 7.1 Performance of Commercial Gyroscopes . . . . . . . . . . . . . . . . . 103 7.2 New Concepts of Gyros. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 7.2.1 Nuclear Magnetic Resonance Gyroscope . . . . . . . . . . . . 104 7.2.2 Gyro Based on Atom Interferometer . . . . . . . . . . . . . . . 106 7.2.3 Superfluid Gyroscope . . . . . . . . . . . . . . . . . . . . . . . . . 106 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Chapter 1 Introduction Inertial sensors, which allow to measure linear acceleration and angular velocity, are emerging as a crucial class of sensors and their applications are continuously increasing. They were first developed for aerospace and military systems but currently are extensively used in a wide spectrum of applications, such as auto- motive, medicine, consumer electronics and so on. Inertial Measurement Units (IMUs) enabling the measurement of acceleration along three axes and angular velocity around the same three axes are very sophisticated systems whose development in terms of cost reduction and perfor- mance improvement is considered an important task for naval, defense and aerospace industry. Innovative space-qualified IMUs having reduced weight, low powerconsumption,highsensitivity,andgoodreliabilityareneededfornewspace missions. IMU worldwide market, which is currently around 2 billion dollars, is expected to significantly grow up in the next few years. Gyroscope(alsonamedgyro)measurestheangularratearoundafixedaxiswith respect to an inertial space. In the last four decades an intense research effort has beendevotedtodesign,optimizeandfabricatedifferentkindsofgyrosessentially basedonangularmomentumconservation,SagnacandCorioliseffects.Inthelast few years development of innovative gyros has been focused on micro-photonics and micro-electro-mechanics technologies. In this chapter main technologies and applications of angular rate sensors are briefly discussed. Performance parameters allowing the comparison of different gyros are defined, too. 1.1 Overview of Gyroscope Technologies Itispossibletorecognizethreedifferentkindsofgyroscopes:spinningmassgyros, optical gyros and vibrating gyros. In the first category all the devices having a massspinningsteadilywithrespecttoafreemovableaxisfall.Opticalgyroscopes are based on Sagnac effect which states that phase shift between two waves counter-propagating in a rotating ring interferometer is proportional to the loop M.N.Armeniseetal.,AdvancesinGyroscopeTechnologies, 1 DOI:10.1007/978-3-642-15494-2_1,(cid:2)Springer-VerlagBerlinHeidelberg2010 2 1 Introduction angular velocity. Vibrating gyros are based on Coriolis effect that induces a coupling between two resonant modes of a mechanical resonator. Thebasicconfigurationofgyroscopeexploitstheinertialpropertiesofawheel (orrotor)spinningathighspeed,whichtendstokeepthedirectionofitsspinaxisby virtue of the tendency of a body to resist to any change in the direction of its moment.Inthe1960sDynamicallyTunedGyroscope(DTG),whichisbasedonthis physicalprinciple,wasdeveloped[1].DTGwasusedformanyyearsinaerospace andmilitaryindustryanditwasincludedintheIMUoftheSpaceShuttle. One of the most successful spinning mass gyroscope is the Control Moment Gyroscope (CMG) [2] which is widely used for satellites stabilization [3]. It consists of a spinning rotor and one or more motorized gimbals that tilt the rotor angular moment. As the rotor tilts, the changing angular moment causes a gyro- scopic torque that rotates the spacecraft. CMGs were used for decades in large spacecraft, including Skylab, Mir Space Station and the International Space Station. Miniaturization of spinning mass gyros is very difficult and their consequent decline has created interesting business opportunities for vibrating and optical gyros that can be effectively miniaturized by MEMS and integrated optical technologies, respectively. Inthe1980s, ahighlyperformingvibrating gyro, theHemispherical Resonator Gyro(HRG),wasdeveloped.HRGsensingelementisafusedsilicahemispherical shell (diameter around 30 mm) covered by a thin metal film [4]. This device is a very sensitive and expansive gyro and it was used in some space missions, including the Near Earth Asteroid Rendezvous and the Cassini ones. Silicon and quartz MEMS gyros are innovative miniaturized vibrating angular ratesensors.Theyassurelowcostandperformancewhichisconstantlyincreasing. MEMSgyrosmarketisquicklygrowingupandisreaching800millionsdollarsin 2010 [5]. Since1963whenthefirstRingLaserGyroscope(RLG)basedonSagnaceffect was fabricated [6], a number of photonic gyroscopes have been proposed and demonstrated, including Fiber Optic Gyroscopes (FOGs) and integrated-optics gyroscopes [7, 8]. In the 1990s, the first FOG in space was used in X-ray Timing Explorer mission [9]. Recently, other very sophisticated technologies for future gyros have been demonstrated, including the nuclear magnetic resonance gyro [10] and the superfluid gyro [11]. Some reviews on gyro technology are reported in literature [12–15], while the most recent advances are in this book. 1.2 Gyro Performance Parameters Different gyro technologies are usually compared in terms of cost, power consumption, reliability, weight, volume, thermal stability, immunity to external 1.2 GyroPerformanceParameters 3 disturbance andothervery important performance parametersdescribingthe gyro behavior when it is set up in a more complex system. Starting from gyroscope static input–output characteristic a number of gyro performanceparameterscanbedefinedsuchasscalefactor,bias,inputandoutput range, full range, resolution, dynamic range and dead band [16]. Gyroscalefactorisdefinedastheratiobetweenthechangeinsensoroutputand the relevant angular velocity variation. It is usually evaluated as the slope of the straight line that can be obtained by linear fitting input–output data. Biasisdefinedastheaverage,overaspecifiedtimeinterval,ofgyrooutputthat hasnocorrelationwitheitherinputrotationoracceleration.Biasismeasuredin(cid:3)/h or (cid:3)/s. Inputrangeistherangeofinputvaluesinwhichthegyroperformancematches a specified accuracy. Output range is the product between input range and scale factor. The algebraic difference between the upper and lower values of the input range is called full range. Minimal detectable angular rate or resolution (expressed in (cid:3)/h or (cid:3)/s) is the minimumangularvelocitythatcanbedetectedbyagyroscope.Theratiobetween full range and resolution is called dynamic range (dimensionless quantity). Finally,deadbandisarangebetweentheinputlimitswithinwhichvariationsin the input produce output changes less than 10% of those expected. Gyro frequency response or step response allow to calculate gyroscope band- width and response time. Main noise contributions in gyroscope are: • quantization noise, • bias instability (or bias drift), • angle random walk. Quantization noise is mainly due to analog-to-digital conversion of the gyro output signal whereas the cause of other noise contributions depends on the gyro operating principle. Bias instability is the peak-to-peak amplitude of the bias long term drift. It is expressed in (cid:3)/s or (cid:3)/h. Angle random walk (ARW) is a noise contribution to the rotation angle value obtainable by integrating the angular velocity. Standard deviation of noise observed in rotation angle estimation can be written as: p ffiffi r ¼W t ð1:1Þ rw ARW whereW istheanglerandomwalkcoefficient,usuallyexpressedin(cid:3)/Hhor(cid:3)/Hs. ARW Differentnoisecontributionscanbeestimatedbymodelingthenoiseinangular ratemeasurementbyastochasticprocess[17].Astochasticprocessu(t)consistsof a family of time dependent real functions u(t,r), each of them associated to an elementrofaprobabilityspace<.Therealfunctionu(t,r)(alsodenotedasu(t))is called trajectory of the stochastic process. If we consider a stationary stochastic process, its autocorrelation is given by:
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