Control System Development for small UAV Gimbal

The design process of unmanned ISR systems has typically driven in the direction of increasing system mass to increase stabilization performance and imagery quality. However, through the use of new sensor and processor technology high performance stabilization feedback is being made available for control on new small and low mass stabilized platforms that can be placed on small UAVs. This project develops and implements a LOS stabilization controller design, typically seen on larger gimbals, onto a new small stabilized gimbal, the Tigereye, and demonstrates the application on several small UAV aircraft. The Tigereye gimbal is a new 2lb, 2-axis, gimbal intended to provided high performance closed loop LOS stabilization through the utilization of inertial rate gyro, electronic video stabilization, and host platform state information. Ground and flight tests results of the LOS stabilization controller on the Tigereye gimbal have shown stabilization performance improvements over legacy systems. However, system characteristics identified in testing still limit stabilization performance, these include: host system vibration, gimbal joint friction and backlash, joint actuation compliance, payload CG asymmetry, and gyro noise and drift. The control system design has been highly modularized in anticipation of future algorithm and hardware upgrades to address the remaining issues and extend the system\u27s capabilities

Line-of-sight-stabilization and tracking control for inertial platforms

Nowadays, line of sight stabilization and tracking using inertially stabilized platforms (ISPs) are still challenging engineering problems. With a growing demand for high-precision applications, more involved control techniques are necessary to achieve better performance. In this work, kinematic and dynamic models for a three degrees-of-freedom ISP are presented. These models are based in the vehicle-manipulator system (VMS) framework for modeling of robot manipulators operating in a mobile base (vehicles). The dynamic model follows the Euler-Lagrange formulation and is implemented by numeric simulations using the iterative Newton-Euler method. Two distinct control strategies for both stabilization and tracking are proposed: (i) computed torque control and (ii) sliding mode control using the recent SuperTwisting Algorithm (STA) combined with a High-Order Sliding Mode Observer (HOSMO). Simulations using data from a simulated vessel allow us to compare the performance of the computed torque controllers with respect to the commonly used P-PI controller. Besides, the results obtained for the sliding mode controllers indicate that the Super-Twisting algorithm offers ideal robustness to the vehicle motion disturbances and also to parametric uncertainties, resulting in a stabilization precision of approximately 0,8 mrad.Hoje em dia, a estabilização e o rastreamento da linha de visada utilizando plataformas inerciais continuam a constituir desafiadores problemas de engenharia. Com a crescente demanda por aplicações de alta precisão, técnicas de controle complexas são necessárias para atingir melhor desempenho. Neste trabalho, modelos cinemáticos e dinâmicos para uma plataforma mecânica de estabilização inercial são apresentados. Tais modelos se baseiam no formalismo para sistemas veículo-manipulator para a modelagem de manipuladores robóticos operando em uma base móvel (veículo). O modelo dinâmico apresentado segue a formulação analítica de Euler-Lagrange e é implementado em simulações numéricas através do método iterativo de Newton-Euler. Duas estratégias de controle distintas para estabilização e rastreamento são propostas: (i) controle por torque-computado e (ii) controle por modos deslizantes utilizando o recente algoritmo Super-Twisting combinado com um observador baseado em modos deslizantes de alta ordem. Simulações utilizando dados de movimentação de um navio simulado permitem comparar o desempenho dos controladores por torque computado em relação a um tipo comum de controlador linear utilizado na literatura: o P-PI. Além disso, os resultados obtidos para o controle por modos deslizantes permitem concluir que o algoritmo Super-Twisting apresenta rejeição ideal a perturbações provenientes do movimento do veículo e também a incertezas paramétricas, resultando em precisão de estabilização de aproximadamente 0,8 mrad

A Uniform Method of Mechanical Disturbance Torque Measurement and Reduction for the Seeker Gimbal in the Assembly Process

In the manufacturing process of seekers, the reduction of disturbance torques (DTs) is a critical but time-consuming work. The innovation of the paper is to present a uniform method to measure and reduce mechanical DTs during gimbal’s assembly process. Firstly, the relationships between assembly parameters and DTs are established and analyzed by theoretical model. And then, a measuring system is established to measure the driven torque of the gimbal’s torque motor. With the goal of stabilizing and minimizing the driven torque, all assembly parameters relating to DTs could be adjusted. Through the proof of a lot of experiments, this proposed method could reduce the bias and fluctuation of these mechanical DTs. This method could also be used for the mechanical DTs reduction of most similar productions and improve the quality and efficiency during their system assembly process

Gyroless line-of-sight stabilization for pointing and tracking systems

A new platform stabilization approach is described where miature, low-cost, linear accelerometers are used (instead of gyroscopes) for line-of-sight (LOS) stabilization. This is accomplished by placing the accelerometers at strategic locations and combining their outputs so that angular motion is determined from linear acceleration measurements. The control system uses the sensed angular accelerations to generate movement commands for the gimbal servomotors in the stabilization platform. This counterrotates the imaging device to stabilize its LOS. The use of accelerometers allows the servo system to operate in an acceleration control mode, which is more desirable than position or velocity control modes, typical of gyro-based systems, since this increases stabilization bandwidth. Substituting gyros with accelerometers provides the additional benefits of lower sensor cost, weight, and power consumption, better temperature characteristics, more robustness, and higher shock resistance

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 203

This bibliography lists 150 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1980

Sustaining Growth in a Resource-Based Economy: The Main Issues and the Specific Case of Russia

This paper argues that the challenges posed by resource dependence, which include an increased vulnerability to external shocks, the risk of Dutch disease and the risk of development specific institutional pathologies, can be overcome, or at least very substaintially mitigated, if accompanied by the right economic policies.Russia, resource abundance, dutch disease, economic growth

Land markets and agrarian backwardness (Spain, 1900-1936)

To what extent were land markets the cause of Spanish agrarian backwardness? This paper uses new provincial data on average real land prices, together with provincial level variation in land productivity, to analyse land markets efficiency. To address this unresolved issue, we test whether land markets were spatially integrated and whether their prices can be explained with the present value model. Our results suggest that land prices converged across provinces and that variations were driven by fundamentals. In consequence, we conclude that institutional failure in land markets was not the cause of the relatively poor productivity performance of Spanish agricultur

Non-Baryonic Dark Matter in Cosmology

This paper is a broad-band review of the current status of non-baryonic dark matter research. I start with a historical overview of the evidences of dark matter existence, then I discuss how dark matter is distributed from small scale to large scale, and I then verge the attention to dark matter nature: dark matter candidates and their detection. I finally discuss some of the limits of the $\Lambda$CDM model, with particular emphasis on the small scale problems of the paradigm.Comment: 62 pages; 58 figure

Spatial clustering in the ESO-Sculptor Survey: two-point correlation functions by galaxy type at redshifts 0.1 - 0.5

We calculate the spatial two-point auto and cross-correlation functions for the 765 galaxies with Rc<21.5 and 0.1<z<0.51 in the ESO-Sculptor survey, and explore the segregation effects among the populations of giant (early-type, late spiral) and dwarf (dE, dI) galaxies. At separation of 0.3 h^-1 Mpc, pairs of early-type galaxies dominate the clustering over all the other types of pairs. At intermediate scales, 0.3-5 h^-1 Mpc, mixed pairs of dwarf and giant galaxies contribute equally as pairs of giant galaxies, whereas the latter dominate at ~10 h^-1 Mpc. We detect the signature of the transition between the 1-halo and 2-halo regimes which is expected in the scenario of galaxy formation by hierarchical merging of dark matter halos. The early-type galaxies largely outdo the late spiral galaxies in their 1-halo component, whereas the 2-halo components of both giant populations are comparable. The dwarf galaxies have an intermediate 1-halo component between the 2 giant galaxy types, and their 2-halo component is weak and consistent with null clustering. The present analysis indicates that the early-type galaxies are preferentially located near the centers of the most massive halos, whereas late spiral galaxies tend to occupy their outskirts or the centers of less massive halos. This analysis also unveils new results on the spatial distribution of dwarf galaxies: at the scale at which they significantly cluster inside the halos (<0.3 h^-1 Mpc), they are poorly mixed with the late spiral galaxies, and appear preferentially as satellites of early-type galaxies.Comment: Astronomy & Astrophysics, in press. 29 pages, 15 color figures, 3 table

Navigation/traffic control satellite mission study. Volume 2 - Systems analyses

Systems analysis of spacecraft network for transoceanic traffic contro