An FPGA-based Design Approach for Microsatellites Telemetry Subsystem

The Tele-command and Telemetry (TT&C) subsystems are one of the vital components in satellites. Commanding, managing and data sampling from different sections of the satellite are performed through the TT&C subsystem. The telemetry and Tele-command parts of this subsystem could be implemented cooperatively with or separately from each other. Based on the satellite requirements, its mission and orbital lifetime and cost various approaches may be used in order to implement this subsystem. Furthermore, nowadays, the development of satellite subsystems based on commercial devices because of their low cost and accessibility is more attractive. However, their endurance for harsh space environment remains as a severe challenge. The Field Programmable Gate Arrays (FPGAs), one of the best-developed commercial devices, are most successfully option in this application field. Nevertheless, the system designing methodology and the reliability of the implemented system on FPGAs remain as two major concerns. In this paper designing method and implementation result of Telemetry subsystem on field programmable gate array (FPGA) is presented. The implemented subsystem successfully passed environmental test according to ECSS standard. Furthermore, flight data confirm the feasibility of the presented FPGA based design methodology

Output feedback image-based visual servoing control of an underactuated unmanned aerial vehicle

In this article, image-based visual servoing control of an underactuated unmanned aerial vehicle is considered for the three-dimensional translational motion. Taking into account the low quality of accelerometers' data, the main objective of this article is to only use information of rate gyroscopes and a camera, as the sensor suite, in order to design an image-based visual servoing controller. Kinematics and dynamics of the unmanned aerial vehicle are expressed in terms of visual information, which make it possible to design dynamic image-based visual servoing controllers without using linear velocity information obtained from accelerometers. Image features are selected through perspective image moments of a flat target plane in which no geometric information is required, and therefore, the approach can be applied in unknown environments. Two output feedback controllers that deal with uncertainties in dynamics of the system related to the motion of the target and also unknown depth information of the image are proposed using a linear observer. Stability analysis guarantees that the errors of the system remain uniformly ultimately bounded during a tracking mission and converge to 0 when the target is stationary. Simulation results are presented to validate the designed controllers. © IMechE 2014

AN ADAPTIVE SCHEME FOR IMAGE-BASED VISUAL SERVOING OF AN UNDERACTUATED UAV

An image-based visual servoing (IBVS) method is proposed for controlling the 3D translational motion and the yaw rotation of a quadrotor. The dynamic model of this unmanned aerial vehicle (UAV) is considered at the design stage to account for its underactuation. In contrast with previous IBVS methods for underactuated UAVs, which used spherical image moments as visual features, the proposed controller makes use of appropriately defined perspective moments. As a consequence, we gain a clear improvement in performance, as satisfactory trajectories are obtained in both image and Cartesian space. In addition, an adaptation mechanism is included in the controller to achieve robust performance in spite of uncertainties related to the depth of the image features and to the dynamics of the robot. Simulation results in both nominal and perturbed conditions are presented to validate the proposed method

Design of a novel control algorithm for a 6 D.O.F. mobile manipulator based on a robust observer

In this paper a control algorithm based on a design technique named "Robust Damping Control" is introduced. A robust observer is further shown to overcome the problem of using velocity sensors that may degrade the system performance. The proposed controller uses only position measurements and is capable of disturbance rejection in the presence of unknown bounded disturbances without requiring the knowledge of its bound. Moreover, we propose an accurate and fast time integration method to solve the dynamic equations of the mobile manipulator system. The simulation results of a 6 D.O.F. mobile manipulator illustrate the effectiveness of the presented algorithm

Development of prediction models for shear strength of SFRCB using a machine learning approach

© 2015, The Natural Computing Applications Forum. In this study, new design equations were derived for the assessment of shear resistance of steel fiber-reinforced concrete beams (SFRCB) utilizing multi-expression programming (MEP). The superiority of MEP over conventional statistical techniques is due to its ability in modeling of mechanical behavior without a need to pre-define the model structure. The MEP models were developed using a comprehensive database obtained through an extensive literature review. New criteria were checked to verify the validity of the models. A sensitivity analysis was carried out and discussed. The MEP models provide good estimations of the shear strength of SFRCB. The developed models significantly outperform several equations found in the literature