Disseny d’un sistema d’estabilització de càmeres de baix cost mitjançant la implementació d’un “Gimbal analític”

Image stabilization of photos or video is important on different applications such as search-and-rescue or electrical power line inspection. Any motion creates a change on camera orientation, which can be balanced using complex image algorithms (perspective change, resizing, etc.). Nowadays, two opposite options have been applied. The first one, uses a complex platform with sensors and actuators that are able to, in real-time, correct non-desired motions and vibrations or aim to a specific target. They are called gimbals. They are expensive, big and heavy. The second one, uses image processing techniques (such as pattern recognition algorithms), that are able to process images until an image stabilization effect is obtained. This software approach requires powerful computers, because of the big amount of data from each frame or image. The approach presented in this project, uses an inertial sensor (IMU) connected to a CPU. It is able to, in real-time, record inertial data and in parallel, or in post-processing, correct images using this data (analytical solution). A commercial camera is used. The entire system is controlled by the CPU. Therefore, the main purpose of the project is the design, implementation and verification of a low cost image stabilization system by implementing an analytical gimbal. The system is composed by a small and portable computer responsible of image acquisition control and synchronism. Image stabilization is done in post-processing, reducing execution time considerably if compared with image processing techniques previously commented. It works with a low cost commercial camera and a low cost IMU, reducing overall cost. To work properly, it is critical a synchronism between data and image acquisition. The system performance is verified and validated on different scenarios. Finally, the results obtained and some future improvements or possible applications are presented.Català: L’estabilització de seqüències d’imatges o vídeo és important en diferent tipus d’aplicacions com la cerca de persones o l’inspecció de línees elèctriques. Qualsevol moviment implica un canvi en l’orientació de la càmera, requerint de rectificacions, a vegades complexes, d’imatge (com per exemple, un canvi de perspectiva). Es poden destacar dues solucions totalment oposades. Per una banda, s’han desenvolupat plataformes complexes amb sensor inercials i actuadors mecànics que estabilitzen contínuament la càmera (anomenats gimbals). Aquests sistemes acostumen a ser grans, pesats i cars. Per altra banda, hi ha una gran varietat de programaris, que per mitjà, exclusivament, del processat d’imatges permeten estabilitzar-les. Aquests programaris acostumen a requerir d’un elevat temps de processat i de potents ordinadors degut a la gran quantitat de dades que representa cada imatge. El projecte presenta la possibilitat de fer servir uns sensors inercials (a vegades ja presents, como en un UAV) però sense actuar sobre el moviment de la càmera. Les imatges son processades i estabilitzades fent servir les dades obtingudes pels sensors inercials. L’objectiu d’aquest projecte és dissenyar i implementar un sistema gimbal analític d’estabilització de baix cost. El nou sistema utilitza una càmera digital de consum i una unitat amb sensors inercials (IMU), ambdós productes de baix cost comparats amb les solucions actuals. Un ordinador petit i de baix cost s’encarrega del control del sistema i es rectifiquen les imatges per mitjà del processat de les dades obtingudes pels sensors inercials (pero això es una sol·lució analítica, a diferencia de les solucions on la rectificació fa servir tècniques de processat d’imatges o actuadors). S’aconsegueix reduir significativament els recursos requerits per al seu processat i alhora evitar els complexos sistemes d’actuadors mecànics. Les tasques principals a realitzar han sigut el disseny e implementació del hardware i software necessari per a l’adquisició de les dades i posterior estabilització de les imatges. Per a que tot el sistema funcioni correctament, esdevé clau el sincronisme de les dades entre la càmera i la IMU (per això s’ha desenvolupat una estratègia per a garantir els sincronisme de les dades). Posteriorment, s’han estudiat e implementat diferents algoritmes d’orientació i rectificació d’imatges, continuant amb la verificació i validació del sistema. Finalment, s’inclouen les conclusions del treball i algunes futures millores o possibles aplicacions

Low-Cost Inertial Measurement Unit Calibration with Nonlinear Scale Factors

Inertial measurement units (IMUs) have been widely used to provide accurate location and movement measurement solutions, along with the advances of modern manufacturing technologies. The scale factors of accelerometers and gyroscopes are linear when the range of the sensors are reasonably small, but the factor becomes nonlinear when the range gets much bigger. Based on this observation, this article presents a calibration method for low-cost IMU by effectively deriving the nonlinear scale factors of the sensors. Two motion patterns of the sensor on a rigid object are moved to collect data for calibration: One motion pattern is to upcast and rotate the rigid object, and another pattern is to place the rigid object on a stable base in different attitudes. The rotation motion produces centripetal and Coriolis force, which increases the measurement range of accelerometers. Four cost functions with different weight factors and two sets of data are utilized to optimize the IMU parameters. The weight factor comes from derived formula with input values which are the variance of the noise of the sampled data. The proposed approach was validated and evaluated on both synthetic and real-world data sets, and the experimental results demonstrated the superiority of the proposed approach in improving the accuracy of IMU for long-range use. In particular, the errors of acceleration and angular velocity led by our algorithm are significantly smaller than those resulted from the existing approaches using the same testing data sets, demonstrating a remarkable improvement of 64.12% and 47.90%, respectively

Circles within spirals, wheels within wheels; Body rotation facilitates critical insights into animal behavioural ecology

How animals behave is fundamental to enhancing their lifetime fitness, so defining how animals move in space and time relates to many ecological questions, including resource selection, activity budgets and animal movement networks. Historically, animal behaviour and movement has been defined by direct observation, however recent advancements in biotelemetry have revolutionised how we now assess behaviour, particularly allowing animals to be monitored when they cannot be seen. Studies now pair ‘convectional’ radio telemetries with motion sensors to facilitate more detailed investigations of animal space-use. Motion sensitive tags (containing e.g., accelerometers and magnetometers) provide precise data on body movements which characterise behaviour, and this has been exemplified in extensive studies using accelerometery data, which has been linked to space-use defined by GPS. Conversely, consideration of body rotation (particularly change in yaw) is virtually absent within the biologging literature, even though various scales of yaw rotation can reveal important patterns in behaviour and movement, with animal heading being a fundamental component characterising space-use. This thesis explores animal body angles, particularly about the yaw axis, for elucidating animal movement ecology. I used five model species (a reptile, a mammal and three birds) to demonstrate the value of assessing body rotation for investigating fine-scale movement-specific behaviours. As part of this, I advanced the ‘dead-reckoning’ method, where fine-scale animal movement between temporally poorly resolved GPS fixes can be deduced using heading vectors and speed. I addressed many issues with this protocol, highlighting errors and potential solutions but was able to show how this approach leads to insights into many difficult-to-study animal behaviours. These ranged from elucidating how and where lions cross supposedly impermeable man-made barriers to examining how penguins react to tidal currents and then navigate their way to their nests far from the sea in colonies enclosed within thick vegetation

Concept definition for space station technology development experiments. Experiment definition, task 2

The second task of a study with the overall objective of providing a conceptual definition of the Technology Development Mission Experiments proposed by LaRC on space station is discussed. During this task, the information (goals, objectives, and experiment functional description) assembled on a previous task was translated into the actual experiment definition. Although still of a preliminary nature, aspects such as: environment, sensors, data acquisition, communications, handling, control telemetry requirements, crew activities, etc., were addressed. Sketches, diagrams, block diagrams, and timeline analyses of crew activities are included where appropriate

A Direct Comparison of Small Aircraft Dynamics between Wind Tunnel and Flight Tests

The miniaturization of embedded electronics and sensors driven by the rapid development of mobile devices has enabled powerful avionics systems for very small aircraft. This enables a potential step forward in accurate flight data gathering for vehicles weighing 5 kg or less. Being able to flight test a small platform like this also allows the comparison of the results with reference data from ground testing in a standard sized wind tunnel of an identical airframe. With this process, the following questions can be answered: Firstly, would such a system then be able to collect accurate flight data for system identification (ID)? Is it possible at all to fly a small, remotely piloted aircraft precisely enough to record the required data, given its sensitivity to atmospheric turbulence, airframe noise, limitations of the remote piloting and so on? And secondly, if accurate data has been obtained, how well do the two experiments match? The small scale might potentially result in previously unknown or at least insignificant physical phenomena, which need to be taken into account when flight testing such a small platform. The changes in the inertial properties of the platform due to the added mass effect is one of these phenomena, which can typically be ignored for full scale aircraft. However, this has proven to be critically important for the successful analysis and comparison of the flight- and wind tunnel data obtained throughout this project. The avionics suite designed for this research was developed in house, since the weight restrictions of the small platform excluded any commercially available flight data recording packages. The suite features an lightweight airdata probe, control surface feedback sensors, a custom designed GPS receiver and many other advanced components previously not possible at this scale. A commercial reference INS was used to benchmark the system. The UAVmainframe also provides basic flight control functionality to aid the pilot in obtaining the required trim conditions and turbulence mitigation. Extensive data compatibility analysis and calibrations were performed on the recorded data using an Extended Kalman Filter (EKF) and various other methods to ensure the best possible data quality. The inertial properties of the test aircraft were determined by swing tests. The significance of the added mass contributions was discovered during these tests, which added up to 25% onto the `true' airframe inertial properties. In an effort to estimate these added mass terms, it has been found that the methods presented in literature to determine the corrections for full scale aircraft do not give the correct results for the small scale aircraft under consideration. Swing tests of a flat plate model of the test aircraft also did not capture the magnitude of the phenomenon correctly, which led to swing tests with a geometrically similar 3-d object of known inertial properties to successfully estimate the added mass corrections. Static derivatives were obtained from conventional wind tunnel testing, in conjunction with a high fidelity three dimensional inviscid solution using the PanAir code. A dynamic test rig was used in the wind tunnel to determine the dynamic derivatives. It allowed the instrumented airframe to rotate freely on a three axis gimbal, essentially 'fly' in the tunnel. The aerodynamic derivatives from these 3 DoF tests were estimated by performing system ID on the recorded data, where the model structures were modified for the reduced set of motion variables. Extensive flight testing was performed at the university's flight test centre. These tests showed the difficulty of testing such a small and light airframe due to wind and airframe noise, as well as the limitations due to lack of feedback received by the remote pilot. The pilot was aided by the flight control system to achieve a good trim condition, and pre-recorded input sequences, similar to the dynamic wind tunnel tests, were used to excite the longitudinal and lateral dynamics of the aircraft. One particular finding during the test campaign was that there is no such thing as totally calm conditions for this scale of airframe. Other findings include a high correlation between the pitch damping term and the pitching moment due to elevator, making it impossible to determine both at the same time, and that in flight the inertial properties of the test aircraft change to the values that include the added mass components, as compared to the dynamic wind tunnel tests, where the `true' inertias are used. By including these findings in the data processing, close agreement between flight and ground test data has been achieved

CubeSat Attitude System Calibration and Testing

This thesis concentrates on the development of Aalto-2 CubeSat attitude system calibration and testing methods. The work covers the design and testing phase of the calibration algorithms to the analysis of experimental data in order to verify the performance of the attitude instruments. The instruments under test are two-axis digital Sun sensor, three-axis magnetometer, three-axis gyroscope, and three-axis magnetorquer. These devices are all commercial off-the-shelf components which are selected for their cost-to-performance efficiency. The Sun sensor and gyroscope were calibrated with linear batch least squares method and the results showed that only minor corrections were required for the Sun angle and angular velocity readings, while the brightness readings from the Sun sensor required more corrections. For magnetometer calibration, a specific particle swarm optimization algorithm was developed with novel approach to estimate the full calibration parameters, without having to simplify the sensor model. The calibration results were evaluated with simulation data with satisfying results, while the results from experimental data itself showed heading error improvement from \SIrange[range-phrase=--]{5.24}{13.24}{\degree} to \SIrange[range-phrase=--]{1.9}{7.3}{\degree} for unfiltered data. Besides the magnetometer calibration parameters estimation, the magnetic properties of the spacecraft were also analyzed using inverse multiple magnetic dipole modeling approach, where multiple magnetic dipoles positions and moments are estimated using particle swarm optimization from the magnetic field strength readings around the spacecraft. The estimated total residual magnetic moment of the spacecraft is \SI{58.5}{\milli\ampere\square\meter}, lower than the maximum magnetorquer moment which is \SI{0.2}{\ampere\square\meter} in each axis. The magnetorquer was tested for verifying the validity of magnetic moment generated by the magnetorquer. The result shows that the magnetorquer moment is nonlinear, in contrast to the linear theoretical model

Robot Navigation in Distorted Magnetic Fields

This thesis investigates the utilization of magnetic field distortions for the localization and navigation of robotic systems. The work comprehensively illuminates the various aspects that are relevant in this context. Among other things, the characteristics of magnetic field environments are assessed and examined for their usability for robot navigation in various typical mobile robot deployment scenarios. A strong focus of this work lies in the self-induced static and dynamic magnetic field distortions of complex kinematic robots, which could hinder the use of magnetic fields because of their interference with the ambient magnetic field. In addition to the examination of typical distortions in robots of different classes, solutions for compensation and concrete tools are developed both in hardware (distributed magnetometer sensor systems) and in software. In this context, machine learning approaches for learning static and dynamic system distortions are explored and contrasted with classical methods for calibrating magnetic field sensors. In order to extend probabilistic state estimation methods towards the localization in magnetic fields, a measurement model based on Mises-Fisher distributions is developed in this thesis. Finally, the approaches of this work are evaluated in practice inside and outside the laboratory in different environments and domains (e.g. office, subsea, desert, etc.) with different types of robot systems

The development of an adaptive and reactive interface system for lower limb prosthetic application

Deep tissue injury (DTI) is a known problem correlating to the use of a prosthetic by a transtibial amputee (TTA), causing ulcer-like wounds on the residual limb caused by stress-induced cell necrosis. The magnitude of these stresses at the bone tissue interface has been identified computationally, far exceeding those measured at the skin's surface. Limited technology is available to directly target and reduce such cellular loading and actively reduce the risk of DTI from below-knee use. The primary aim of this project was to identify whether a bespoke prosthetic socket system could actively stiffen the tissues of the lower limb. Stabilising the residual tibia during ambulation and reducing stress concentrations on the cells. To achieve this, a proof-of-concept device was designed and manufactured, a system that allowed the change in displacement of a magnet to be responded to by counterbalancing load. The device was evaluated through experimentation on an able-bodied subject wearing an orthotic device designed to replicate the environment of a prosthetic socket. The chosen sensor effector system was validated against vector data generated by the Motek Medical Computer Assisted Rehabilitation Environment (CAREN.) The project explored a new concept of reactive loading of a below-knee prosthesis to reduce tibial/socket oscillation. The evaluation of the device indicated that external loading of the residual limb in such a manner could reduce the magnitude of rotation about the tibia and therefore minimise the conditions by which DTIs are known to occur. Efforts were made to move the design to the next iteration, focusing on implementing the target demographic.Deep tissue injury (DTI) is a known problem correlating to the use of a prosthetic by a transtibial amputee (TTA), causing ulcer-like wounds on the residual limb caused by stress-induced cell necrosis. The magnitude of these stresses at the bone tissue interface has been identified computationally, far exceeding those measured at the skin's surface. Limited technology is available to directly target and reduce such cellular loading and actively reduce the risk of DTI from below-knee use. The primary aim of this project was to identify whether a bespoke prosthetic socket system could actively stiffen the tissues of the lower limb. Stabilising the residual tibia during ambulation and reducing stress concentrations on the cells. To achieve this, a proof-of-concept device was designed and manufactured, a system that allowed the change in displacement of a magnet to be responded to by counterbalancing load. The device was evaluated through experimentation on an able-bodied subject wearing an orthotic device designed to replicate the environment of a prosthetic socket. The chosen sensor effector system was validated against vector data generated by the Motek Medical Computer Assisted Rehabilitation Environment (CAREN.) The project explored a new concept of reactive loading of a below-knee prosthesis to reduce tibial/socket oscillation. The evaluation of the device indicated that external loading of the residual limb in such a manner could reduce the magnitude of rotation about the tibia and therefore minimise the conditions by which DTIs are known to occur. Efforts were made to move the design to the next iteration, focusing on implementing the target demographic

Estudio de la dinámica de sedimentos cohesivos en el Río de la Plata.

Sediment transport processes at the muddy bottom site near Montevideo bay were examined by observing the near seabed cohesive sediment and water velocity. Wave, currents and turbulent components of the water ow were obtained with an acoustic Doppler velocimeter located 30 cm above the seabed, while sediment concentration profiles of the lowest 40 cm were estimated with a multi-frequency acoustic backscatter sensor. Exhaustive laboratory testing of the sediment extracted from the deployment site indicated that occulation expected in the field did not affect the acoustic estimation of sediment concentration. However, special attention was required during strong agitation since with concentrations of sands under 5 % granulometry of the sediment in motion was modified, leading to unrealistic estimations of higher sediment concentration. A new acoustic multifuequency technique was implemented in order to avoid this bias. The field data collected during almost six months indicated that a highly concentrated sediment layer near the bottom was kept in motion during moderate and strong waves and would remain for more than one day. Its height was 1 dm and its concentration over 100 kg/m3. Currents caused this layer to travel and this phenomena was calculated with a simplified self-stratified wavecurrent-sediment coupled analytical model. The associated sediments travel as well and this explains the actual siltation rates in the navigation channels of Montevideo Port.En esta tesis se presentan mediciones de campo de sedimento cohesivo cercano al lecho y velocidades del flujo de agua. Estos datos fueron usados para comprender los procesos de transporte de sedimentos en un sitio con fondo de barro cercano a la bahía de Montevideo. El oleaje, las corrientes y las componentes turbulentas del flujo de agua fueron obtenidas usando un velocímetro acústico Doppler (ADV por sus siglas en inglés) ubicado a unos 30 cm encima del lecho. Mediante la utilización de un sensor de retrodispersión acústica multifrecuencia (ABS por sus siglas en inglés) se estimaron también los perfiles de concentración de sedimento de los últimos 40 cm. Se realizaron intensos trabajos de laboratorio con sedimento extraído del sitio de medición, los cuales indicaron que la oculación esperada en el campo no genera sesgos en la estimación de la concentración de sedimentos. De todas maneras, es necesario tomar ciertas precauciones en momentos de gran agitación puesto que la presencia de menos de 5 % de arenas cambian la granulometría del sedimento en movimiento, induciendo mayores estimaciones de concentración de sedimento que las reales. Una nueva técnica de inversión acústica multifrecuencia fue implementada para evitar estos sesgos. La información recolectada en el campo durante cinco meses y medio muestra que durante oleaje moderado y fuerte, una capa de gran concentración de sedimento cercana al fondo es capaz de mantenerse en movimiento por más de un día. Con espesores cercanos al decímetro y concentraciones mayores a 100 kg/m3, el transporte de esta capa debido a las corrientes pudo ser calculada con un modelo analítico que acopla la interacción entre oleaje, corrientes y la autoestratificación debida a sedimentos. La estimación del sedimento transportado mediante este mecanismo permite explicar las tasas de sedimentación reportadas en los canales de acceso del puerto de Montevideo