An Adaptive Observer-based Robust Estimator of Multi-sinusoidal Signals

This paper presents an adaptive observer-based robust estimation methodology of the amplitudes, frequencies and phases of biased multi-sinusoidal signals in presence of bounded perturbations on the measurement. The parameters of the sinusoidal components are estimated on-line and the update laws are individually controlled by an excitation-based switching logic enabling the update of a parameter only when the measured signal is sufficiently informative. This way doing, the algorithm is able to tackle the problem of over-parametrization (i.e., when the internal model accounts for a number of sinusoids that is larger than the true spectral content) or temporarily fading sinusoidal components. The stability analysis proves the existence of a tuning parameter set for which the estimator\u2019s dynamics are input-to-state stable with respect to bounded measurement disturbances. The performance of the proposed estimation approach is evaluated and compared with other existing tools by extensive simulation trials and real-time experiments

Suprajohtavien kvantti-inferferenssilaitteiden älykäs digitaalinen ohjaus ultramatalan kentän magneettikuvauksessa

Ultra-low-field magnetic resonance imaging (ULF MRI) studies the inner structure of matter by exciting nuclear spins using microtesla-range magnetic fields. The weak spin-induced magnetic signals are received with highly sensitive superconducting-quantum-interference-device-based (SQUID) sensors that act as flux-to-voltage converters. Because of the physical nature of the SQUID, its response to magnetic flux is periodic. To make the measurements easier, the response is linearized with a special feedback scheme. In the measurement setup used in this work, the SQUID feedback is realized with digital signal processors so that the response of the system can be manipulated using computer software. The software is designed for magnetoencephalography, which measures magnetic signals generated by the neuronal currents. These signals are in both amplitude and frequency smaller than those encountered in ULF MRI. In this thesis, new software for the needs of ULF MRI was developed. For example, a method to measure the feedback-to-input response and a new feedback reset algorithm tailored for ULF MRI were designed and implemented. The reset algorithm was designed to reactivate the flux dams in the SQUID input circuits and to reduce the signal transient after the reset. The feedback-to-input response measurements revealed a notable delay in the feedback, which degrades the frequency response of the whole system. It was shown that the frequency response can be improved by an additional digital compensation based on the measured feedback-to-input response.Ultramatalan kentän magneettikuvauksessa tutkitaan aineen rakennetta virittämällä atomiytimien spinejä mikroteslaluokan magneettikentillä. Spinien tuottamat heikot magneettiset signaalit vastaanotetaan erittäin herkillä suprajohtaviin kvantti-interferenssilaitteisiin (SQUID) perustuvilla antureilla, jotka muuntavat magneettivuon jännitteeksi. SQUIDin vaste magneettivuohon on luonnostaan periodinen. Mittausten helpottamiseksi se linearisoidaan kytkemällä mitattu signaali takaisin SQUIDiin. Tässä työssä käytetyssä mittausjärjestelmässä SQUIDien takaisinkytkentä on toteutettu digitaalisten signaaliprosessoreiden avulla, minkä ansiosta systeemin vastetta voidaan muokata tietokoneohjelmistolla. Ohjelmisto on kuitenkin suunniteltu magnetoenkefalografiaa varten. Magnetoenkefalografiassa mitatut signaalit ovat niin taajuudeltaan kuin amplitudiltaan huomattavan pieniä verattuna magneettikuvaukseen. Tämän diplomityön tarkoituksena oli kehittää uutta ohjelmistoa ultramatalan kentän magneettikuvauksen tarpeisiin. Ohjelmistoa kehitettiin esimerkiksi mittaamaan takaisinkytkentävasteita sekä kontrolloimaan vuosignaalia uudella tavalla takaisinkytkennän resetoinnin aikana. Uusi resetointialgoritmi pyrkii ohjaamaan SQUIDien vastaanottopiirien vuopatoja suprajohtavaan tilaan sekä vähentämään signaalitransienttia takaisinkytkennän resetoinnin jälkeen. Takaisinkytkennässä havaittiin viivettä, joka heikentää koko systeemin taajuusvastetta. Taajuusvasteen osoitettiin kohentuvan, kun signaalia kompensoitiin digitaalisesti hyödyntäen tietoa mitatusta takaisinkytkentävasteesta

The use of distributed sensor arrays in electrical and electromagnetic imaging

Electrical methods for exploring the earth, such as direct current resistivity, induced polarization and electromagnetism are used for numerous exploration, engineering and environmental applications. Common to all these applications is the desire to obtain the clearest possible image of the target. This thesis analyses and develops methods for improving signal to noise ratio for electrical methodsThe ability to recover subsurface information from electrical exploration methods is dependent on the limits of signal detection which is strongly influenced by instrumentation and the conductivity structure of the Earth. Multiple sensors can be used to collect data efficiently over a survey area. Such multi-receiver arrays can improve the signal-to-noise ratio. However, the use of multiple sensors can also be exploited to improve the signal fidelity from each sensor, which may then translate to more accurate geological models and/or greater depth of investigation. In this thesis a two step algorithm for the removal of harmonic noise and atmospheric transients is presented. The first step is the removal of harmonic noise from each sensor using a non-linear single value decomposition (SVD) inversion technique to model a modulated sinusoid to narrow band noise sources. The second step is spherics attenuation using an iterative technique of signal stripping then removing residual coherent noise across the array combined with robust statistical measures in the tacking process. I show that this approach can recover signals otherwise buried in noise and that under certain conditions, signal to noise ratio can be improved by more than 46 dB. The algorithms designed here are applicable to any type of electrical or time domain electromagnetic survey conducted with a multi-receiver array

34th Midwest Symposium on Circuits and Systems-Final Program

Organized by the Naval Postgraduate School Monterey California. Cosponsored by the IEEE Circuits and Systems Society. Symposium Organizing Committee: General Chairman-Sherif Michael, Technical Program-Roberto Cristi, Publications-Michael Soderstrand, Special Sessions- Charles W. Therrien, Publicity: Jeffrey Burl, Finance: Ralph Hippenstiel, and Local Arrangements: Barbara Cristi

Phase estimation in a navigation receiver

Tässä lisensiaatintutkimuksessa esitetään menetelmä näytteistetyn sinimuotoisen signaalin vaiheen estimointiin silloin, kun taajuus on tunnettu. Menetelmän nimi on vaihekorjattu korrelaatio (PCC) ja sillä voi estimoida vaiheen myös niissä tapauksissa, joissa signaalista ei ole kokonaisluvullista määrää jaksoja mittausvälissä. PCC-vaihe-estimaatin suorituskykyä tutkitaan vertaamalla sen neliösummavirhettä (MSE) Cramér-Rao alarajaan (CRLB). Jotta menetelmän analysointi ja vertailu läheisten menetelmien kanssa olisi helpompaa, signaalimallina on yksi sinimuotoinen signaali valkoisessa Gaussisessa kohinassa. Työssä esitetään lisäksi kaksi menetelmää häiriöisen signaalin vaihe-estimaatin neliösummavirheen pienentämiseen. Tyypillisiä häiriölähteitä ovat salamat ja läheisellä taajuudella toimivat lähettimet; menetelmät ovat vastaavasti nimeltään purskehäiriöiden poisto ja virheellisten ositteiden poisto. PCC-taajuusestimaatti saadaan seuraamalla signaalin vaiheen muuttumista peräkkäisissä mittausväleissä ja sen suorituskykyä sekä laskentakuormaa verrataan Interpoloituun DFT:hen (IDFT). Menetelmän sovellusalue on meteorologinen luotausjärjestelmä, joka käyttää VLF-navigointiverkkoja yläilmakehän tuulenmittaukseen. Estimointiongelmana on arvioida Doppler-ilmiön aiheuttama pienenpieni taajuussiirtymä. Venäläisen Alpharadionavigointiverkon lähetystaajuudet ovat erityisen haasteellisia, koska käytetyssä 400 ms:n mittausvälissä ei ole kokonaisluvullista määrää signaalin jaksoja. Useimmat taajuuden- ja vaiheenestimointimenetelmät eivät ole soveliaita tähän estimointiongelmaan. IDFT saattaisi olla käyttökelpoinen ja siksi sitä on käytetty vertailukohtana. Tietokonesimulaatioin osoitetaan, että vaihe-estimaatin MSE on lähellä CRLB:tä. Sama koskee taajuusestimaatteja, jotka on saatu seuraamalla signaalin vaiheen muuttumista peräkkäisissä mittausväleissä. Simulaatiot osoittavat myös, että PCC-taajuusestimaatin MSE on lähempänä CRLB:tä kuin IDFT-taajuusestimaatin MSE. Koska PCC saavuttaa tämän suorituskyvyn pienemmällä laskentakuormalla, se on soveliaampi kyseiseen sovellukseen. Lisäksi osoitetaan, että vaihe-estimaatin MSE pienenee, kun näytteenottotaajuutta tai mittausväliä kasvatetaan, tai kun salamoiden ja läheisellä taajuudella toimivien lähettimien aiheuttamat häiriöt poistetaan purskehäiriöiden poisto ja virheellisten ositteiden poisto -algoritmeilla. Lopuksi esitetään muutamia signaaliprosessoritoteutukseen (DSP) liittyviä yksityiskohtia, joilla voidaan pienentää laskentakuormaa.This thesis proposes a new method for estimating the unknown phase of a sampled sinusoid of known frequency. The method is called phase corrected correlation (PCC) and it is targeted specifically for the case, when there is a non-integer number of cycles in the measurement interval. Performance of the PCC phase estimate is studied by comparing its mean squared error (MSE) with the Cramér-Rao lower bound (CRLB). In order to simplify analysis and comparison with related methods, the selected signal model is a single sinusoid in additive white Gaussian noise. Two additional algorithms, burst noise removal and partition outlier removal, are proposed for decreasing the MSE of phase estimates in the presence of disturbances such as lightnings and interfering transmitters. PCC frequency estimate is obtained by observing signal phase change in consecutive measurement intervals. Frequency estimation performance and computational burden of the PCC is compared with Interpolated DFT (IDFT). The application domain is a meteorological sounding system for upper-air wind finding using Very Low Frequency (VLF) navigation systems. The problem is to estimate a minute frequency offset caused by the Doppler effect. Frequencies transmitted especially by the Russian Alpha radionavigation system are challenging: the estimation algorithm must be able handle a non-integer number of signal cycles in the 400 ms measurement interval. Most of the related frequency and phase estimation methods are not applicable to this estimation problem. Interpolated DFT (IDFT) may be feasible and therefore it is used as a benchmark. It is shown with computer simulations, that MSE of the phase estimate is close to the CRLB. The same applies to frequency estimates obtained by observing signal phase change in consecutive measurement intervals. Comparison with IDFT shows, that MSE of the PCC frequency estimate is closer to the CRLB as MSE of the IDFT frequency estimate. Moreover, PCC achieves this performance with lower computational burden, making it the preferred choice in this application. It is also shown that MSE of the phase estimate decreases as sampling rate or measurement interval is increased, and that MSE of the phase estimate decreases when interference is removed using burst noise removal and partition outlier removal algorithms. Finally, to achieve a computationally efficient digital signal processor (DSP) implementation, a number of implementation issues are covered

Detection of oscillatory actuator failures in passenger airliners

Thesis (MEng)--Stellenbosch University, 2019.ENGLISH ABSTRACT: This project investigates and develops techniques to detect oscillatory failure cases (OFCs) in aircraft control surface actuators. Oscillatory failures induce additional loads on the structure of the aircraft, requiring additional structural support to withstand these loads, increasing the overall mass of the aircraft. If oscillatory failures can be detected and pacified quickly, then the additional structural support would not be required, and the mass of the aircraft can be reduced, resulting in improved fuel efficiency and aircraft performance. Oscillatory failure case (OFC) detection is performed by evaluating the difference (residual) between the measured behaviour of the real actuator and the simulated behaviour of a fault-free analytically redundant actuator model running in parallel with the real actuator. An OFC detection system must generate a residual signal using the analytically redundant actuator model, and evaluate the residual signal to determine whether an oscillatory failure is present. The challenge for the residual evaluation stage is to distinguish between the components of the residual signal resulting from modelling uncertainty and sensor noise, and the components resulting from an actual oscillatory failure case. The OFC detection system must detect oscillatory failures within a maximum allowable detection time, but must not produce false alarms. Five different oscillatory failure detection techniques are investigated and developed, namely oscillation counting, integrated absolute error (IAE), discrete Fourier transform (DFT), multi-window Fourier transform (MWFT), and phase-locked loop (PLL) detection. Oscillation counting is an existing OFC detection technique that was developed by Goupil [1] and is currently in service on the Airbus A380 passenger airliner. The other four techniques are new OFC detection techniques that are developed in this project. A simulation framework is created to serve as a testbed for the training and testing of the different OFC detection techniques. The simulation framework contains models for the physical actuator, the analytically redundant actuator, the oscillatory failures (both liquid and solid failures), the flight control system, and the aircraft longitudinal dynamics. The simulation models the aircraft’s response to an oscillatory failure, since it affects the performance of the OFC detection. The five OFC detection techniques are trained and rigorously tested using training and testing data generated with the simulation framework. The detection thresholds for each technique are “trained” on fault-free data to determine the lowest detection thresholds that do not produce false alarms. The detection techniques are then tested using testing data to determine the smallest amplitude oscillatory failure that each technique can detect within the specified maximum allowable detection time. The number of false alarms for each technique is also determined. The results show that DFT, MWFT, and the PLL outperform oscillation counting and IAE by detecting smaller amplitude oscillatory failures and with shorter detection times, with MWFT providing the most promising results. However, oscillation counting and IAE are the most computationally efficient techniques, while DFT, MWFT, and PLL are more computationally expensive. Overall, the multi-window Fourier transform (MWFT) technique is the recommended approach for OFC detection, offering the best detection performance with only a small increase in computational complexity.AFRIKAANSE OPSOMMING: Hierdie projek ondersoek en ontwikkel tegnieke om ossillatoriese faling gevalle (OFGs) in vliegtuig beheeroppervlak aktueerders te bespeur. Ossillatoriese falings induseer bykomende ladings op die struktuur van die vliegtuig, en vereis dus bykomende strukturele ondersteuning om hierdie ladings te weerstaan, wat die algehele massa van die vliegtuig verhoog. Indien ossillatoriese falings bespeur en vinnig gepassifiseer kan word, dan sou die bykomende strukturele ondersteuning nie benodig word nie, en die massa van die vliegtuig sou verminder kon word, wat sou lei tot verbeterde brandstofverbruik en werkverrigting. Ossillatoriese faling geval (OFG) bespeuring word uitgevoer deur die verskil (residu) te evalueer tussen die gemete gedrag van die werklike aktueerder en die gesimuleerde gedrag van ’n foutvrye analities-oortollige aktueerder model wat in parallel met die werklike aktueerder uitvoer. ’n OFG bespeuringstelsel moet ’n residu sein genereer deur gebruik te maak van die analitiese-oortollige aktueerder model, en moet die residu evalueer om te bepaal of daar ’n ossillatoriese faling teenwoordig is. Die uitdaging vir die residu evaluasie stadium is om te onderskei tussen die komponente van die residu sein wat afkomstig is van model onsekerheid en sensor ruis, en die komponente wat afkomstig is van ’n werklike ossillatoriese faling geval. Die OFG bespeuringstelsel moet ossillatoriese falings bespeur binne ’n maksimum toelaatbare bespeuringstyd, en moet nie vals alarms gee nie. Vyf verskillende ossillatoriese faling bespeuringstegnieke word ondersoek en ontwikkel, naamlik ossillasie telling, geïntegreerde absolute fout (IAE), diskrete Fourier transform (DFT), multi-venster Fourier transform (MWFT), en fase-sluit lus (PLL) bespeuring. Ossillasie telling is ’n bestaande OFG bespeuring tegniek wat ontwikkel is deur Goupil [1] en word tans gebruik op die Airbus A380 passassiersvliegtuig. Die ander vier tegnieke is nuwe OFG bespeuringstegnieke wat ontwikkel is in hierdie projek. ’n Simulasie raamwerk is geskep om te dien as ’n toetsplatform vir die opleiding en toets van die verskillende OFG bespeuringstegnieke. Die simulasie raamwerk bevat modelle vir die fisiese aktueerder, die analities-oortollige aktueerder, die ossillatoriese falings (beide vloeibare en soliede falings), die vlugbeheerstelsel, en die vliegtuig se longitudinale vlugdinamika. Die simulasie modelleer die vliegtuig se reaksie op die ossillatoriese faling, aangesien dit die prestasie van die OFG bespeuring beïnvloed. Die vyf OFG bespeuringstegnieke is opgelei en volledig getoets deur gebruik te maak van opleiding en toets data wat genereer is met die simulasie raamwerk. Die bespeuring drempels vir elke tegniek is “opgelei” op foutvrye data om te bepaal wat die laagste bespeuringsdrempel is wat nie vals alarms gee nie. Die bespeuringstegnieke is dan getoets op toets data om te bepaal wat die kleinste amplitude ossillatoriese faling is wat elke tegniek kan bespeur binne die maksimum toelaatbare bespeuringstyd. Die aantal vals alarms vir elke tegniek is ook bepaal. Die resultate wys dat die DFT, MWFT, en PLL tegnieke oortref die ossillasie telling en IAE tegnieke deur kleiner amplitude ossillatoriese falings te bespeur in korter bespeuringstye, met die MWFT wat die mees belowende resultate lewer. Die ossillasie telling en IAE tegnieke bly egter die mees berekeningsdoeltreffende tegnieke, terwyl die DFT, NWFT, en PLL meer berekeningskoste dra. Algeheel, word die multi-venster Fourier transform (MWFT) tegniek aanbeveel as die voorkeurtegniek, omdat dit die beste bespeuringsprestasie bied met net ’n klein verhoging in berekeningskoste

분산 제약하에서 원격 제어되는 다수의 논홀로노믹 이동형 로봇 대형 재구성 제어

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2019. 2. 이동준.본 논문에서는 변화하는 주행 환경에서 분산 제약 하에 다수의 원격으로 제어되는 논홀로노믹 이동형 로봇 대형 재구성 제어에 대한 새로운 프레임워크를 제시하였다. 센싱과 컴퓨팅 능력이 갖추어진 온보드 시스템 로봇들을 활용하여 최근 개발된 예측 디스플레이 기법을 적용, 효율적인 군집 로봇의 원격 제어가 가능하도록 하였다. 잘 알려진 논홀로노믹 패시브 디컴포지션 기법을 기반으로 대형 변경이 가능하도록 새로운 파라미터를 추가, 대형 변경간 발생할 수 있는 문제들에 대해 파악하고 이를 해결하기 위해 포텐셜 필드를 활용하였다. n대의 로봇으로 다양한 대형 변경이 가능토록 시뮬레이션 환경을 조성, 39대의 탱크를 이용하여여 5가지의 각기 다른 대형으로의 변환을 새로이 제시한 알고리즘을 적용하여 구현하였다. 또한 실제 로봇 3대를 활용하여 알고리즘의 효용성에 대한 실험을 필두로 좁은 길목, 개활지 등 연속적으로 변화하는 환경 속에서의 구동을 통해 최종적으로 제시한 프레임워크의 타당성에 대해 검증하였다.We propose a novel framework for formation reconguration of multiple nonholonomic wheeled mobile robots (WMRs) in the changing driving environment. We utilize an onboard system of WMRs with the capability of sensing and computing. Each WMR has the same computing power for visualizing the driving environment, handling the sensing information and calculating the control action. One of the WMRs is the leader with the FPV camera and SLAM, while others with monocular cameras with limited FoV, as the followers, keep a certain desired formation during driving in a distributed manner. We set two control objectives, one is group driving and the other is holding the shape of the formation. We have to capture the control objectives separately and simultaneously, we make the best use of nonholonomic passive decomposition to split the WMRs' kinematics into those of the formation maintaining and group driving. The repulsive potential function to prevent the collision among WMRs and attractive potential function to restrict the boundary of follower WMRs' moving space due to limited FoV range of the monocular cameras while switching their formation are also used. Simulation with 39 tanks and experiments with three WMRs are also performed to verify the proposed framework.Acknowledgements iii List of Figures vii Abbreviations ix 1 Introduction 1 2 Formation Reconguration Control Design 5 2.1 Nonholonomic Passive Decomposition . . . . . . . . . . . . . . . 5 2.2 Attractive and Repulsive Potential Function . . . . . . . . . . . . 10 2.3 Control Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3 Estimation and Predictive Display 20 3.1 Distributed Pose Estimation . . . . . . . . . . . . . . . . . . . . . 20 3.1.1 EKF Pose Estimation of Leader WMR . . . . . . . . . . . 20 3.1.2 EKF Pose Estimation of Follower WMRs . . . . . . . . . 22 3.2 Predictive Display for Distributed WMRs Teleoperation . . . . . 23 4 Experiment 27 4.1 Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.2 Demonstrate the Proposed Algorithm . . . . . . . . . . . . . . . 30 4.3 Teleoperation Experiment with the Algorithm . . . . . . . . . . . 33 5 Conclusion 40Maste