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Low-cost navigation and guidance systems for Unmanned Aerial Vehicles. Part 2: Attitude determination and control

Sabatini R., Rodriguez L., Kaharkar A., Bartel C., Shaid T., Zammit-Mangion D.

Annual of Navigation

2013

No. 20

97--126

This paper presents the second part of the research activity performed by Cranfield University to assess the potential of low-cost navigation sensors for Unmanned Aerial Vehicles (UAVs). This part focuses on carrier-phase Global Navigation Satellite Systems (GNSS) for attitude determination and control of small to medium size UAVs. Recursive optimal estimation algorithms were developed for combining multiple attitude measurements obtained from different observation points (i.e., antenna locations), and their efficiencies were tested in various dynamic conditions. The proposed algorithms converged rapidly and produced the required output even during high dynamics manoeuvres. Results of theoretical performance analysis and simulation activities are presented in this paper, with emphasis on the advantages of the GNSS interferometric approach in UAV applications (i.e., low cost, high data-rate, low volume/weight, low signal processing requirements, etc.). The simulation activities focussed on the AEROSONDE UAV platform and considered the possible augmentation provided by interferometric GNSS techniques to a low-cost and low-weight/volume integrated navigation system (presented in the first part of this series) which employed a Vision-Based Navigation (VBN) system, a Micro-Electro-Mechanical Sensor (MEMS) based Inertial Measurement Unit (IMU) and code-range GNSS (i.e., GPS and GALILEO) for position and velocity com-putations. The integrated VBN-IMU-GNSS (VIG) system was augmented using the intefero-metric GNSS Attitude Determination (GAD) sensor data and a comparison of the performance achieved with the VIG and VIG/GAD integrated Navigation and Guidance Systems (NGS) is presented in this paper. Finally, the data provided by these NGS are used to optimise the design of a hybrid controller employing Fuzzy Logic and Proportional-Integral-Derivative (PID) techniques for the AEROSONDE UAV.

Artykuł przedstawia drugą część badań wykonanych na Uniwersytecie Cranfield dla oszacowania potencjalnych możliwości tanich czujników nawigacyjnych dla bezzałogowych obiektów latających (UAVs). Ta część skupia się na pomiarach fazowych w globalnych nawigacyjnych systemach satelitarnych (GNSS) dla określenia orientacji przestrzennej i sterowania małego lub średniego UAV. Zastosowano rekurencyjne algorytmy optymalnej estymacji dla łącznego przetwarzania różnorodnych pomiarów otrzymanych za pomocą systemu wielkoantenowego testowanego w różnorodnych warunkach wynikających z ruchu obiektu. Zaproponowane algorytmy okazały się zbieżne i zapewniły oczekiwane rezultaty nawet w warunkach bardzo dynamicznych manewrów. Przedstawiono wyniki analiz teoretycznych oraz symulacji, zwracając uwagę na zalety podejścia interferometrycznego w technice GNSS zastosowanej w warunkach wynikających z cech UAV (niski koszt, wysoka szybkość transmisji danych, niska waga i objętość, niewielkie wymagania odnośnie przetwarzania sygnału itd.). Symulacje odniesiono do UAV typu AEROSONDE z zamiarem poszerzenia możliwości systemu w efekcie zastosowania technik interferometrii GNSS, łącznie z tanimi i niewielkimi zintegrowanymi systemami nawigacyjnymi (przedstawionymi w pierwszej części badań w poprzednim artykule) zbudowanymi na systemach optycznych oraz systemie inercjalnym opartym na sensorach klasy MEMS, współpracującym z kodowym systemem GNSS. W artykule przedstawiono szczegółową analizę własności systemu zintegrowanego, łączącego techniki optyczne z GNSS i inercjalnymi, dodatkowo wspartego technikami interferometrycznymi GNSS dla określenia orientacji przestrzennej obiektu (GNSS Attitude Determination — GAD) oraz porównania z różnymi kombinacjami tych modułów. Ponadto podjęto próbę zastosowania danych dostarczonych przez opisany system NGS do zoptymalizowania mieszanego kontrolera wykorzystującego logikę rozmytą i klasyczny regulator PID do sterowania bezzałogowcem AEROSONDE.

Low-cost navigation and guidance systems for Unmanned Aerial Vehicles. Part 1: Vision-based and integrated sensors

Sabatini R., Bartel C., Kaharkar A., Shaid T., Rodriguez L., Zammit-Mangion D., Jia H.

Annual of Navigation

2012

No. 19, part 2

71--98

In this paper we present a new low-cost navigation system designed for small size Unmanned Aerial Vehicles (UAVs) based on Vision-Based Navigation (VBN) and other avionics sensors. The main objective of our research was to design a compact, light and relatively inexpensive system capable of providing the Required Navigation Performance (RNP) in all phases of flight of a small UAV, with a special focus on precision approach and landing, where Vision Based Navigation (VBN) techniques can be fully exploited in a multisensor integrated architecture. Various existing techniques for VBN were compared and the Appearance-Based Approach (ABA) was selected for implementation. Feature extraction and optical flow techniques were employed to estimate flight parameters such as roll angle, pitch angle, deviation from the runway and body rates. Additionally, we addressed the possible synergies between VBN, Global Navigation Satellite System (GNSS) and MEMS-IMU (Micro-Electromechanical System Inertial Measurement Unit) sensors, as well as the aiding from Aircraft Dynamics Models (ADMs). In particular, by employing these sensors/models, we aimed to compensate for the shortcomings of VBN and MEMS-IMU sensors in high-dynamics attitude determination tasks. An Extended Kalman Filter (EKF) was developed to fuse the information provided by the different sensors and to provide estimates of position, velocity and attitude of the UAV platform in real-time. Two different integrated navigation system architectures were implemented. The first used VBN at 20 Hz and GPS at 1 Hz to augment the MEMS-IMU running at 100 Hz. The second mode also included the ADM (computations performed at 100 Hz) to provide augmentation of the attitude channel. Simulation of these two modes was accomplished in a significant portion of the AEROSONDE UAV operational flight envelope and performing a variety of representative manoeuvres (i.e., straight climb, level turning, turning descent and climb, straight descent, etc.). Simulation of the first integrated navigation system architecture (VBN/IMU/GPS) showed that the integrated system can reach position, velocity and attitude accuracies compatible with CAT-II precision approach requirements. Simulation of the second system architecture (VBN/IMU/GPS/ADM) also showed promising results since the achieved attitude accuracy was higher using the ADM/VBS/IMU than using VBS/IMU only. However, due to rapid divergence of the ADM virtual sensor, there was a need for frequent re-initialisation of the ADM data module, which was strongly dependent on the UAV flight dynamics and the specific manoeuvring transitions performed.