arXiv subjects

Francesco Sanfedino

Publications and source records attributed to Francesco Sanfedino.

23 records · Page 2Linked to original sources

arXiv2022

Linear Fractional Transformation modeling of multibody dynamics around parameter-dependent equilibrium

This paper proposes a new Linear Fractional Transformation (LFT) modeling approach for uncertain Linear Parameter Varying (LPV) multibody systems with parameter-dependent equilibrium. Traditional multibody approaches, which consist in building the nonlinear model of the whole structure and linearizing it around equilibrium after a numerical trimming, do not allow to isolate parametric variations with the LFT form. Although additional techniques, such as polynomial fitting or symbolic linearization, can provide an LFT model, they may be time-consuming or miss worst-case configurations. The proposed approach relies on the trimming and linearization of the equations at the substructure level, before assembly of the multibody structure, which allows to only perform operations that preserve the LFT form throughout the linearization process. Since the physical origin of the parameters is retained, the linearized LFT-LPV model of the structure exactly covers all plants, in a single parametric model, without introducing conservatism or fitting errors. An application to the LFT-LPV modeling of a robotic arm is proposed; in its nominal configuration, the model obtained with the proposed approach matches the model provided by the software Simscape Multibody, but it is enhanced with parametric variations with the LFT form; a robust LPV synthesis is performed using Matlab robust control toolbox to illustrate the capacity of the proposed approach for control design.

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arXiv2022

Sub-Structuring Modeling of Large Space Truss Structures for Structure/Control Optimization in Presence of Parametric Uncertainties

Modern and future high precision pointing space missions face increasingly high challenges related to the widespread use of large flexible structures. The development of new modeling tools which are able to account for the multidisciplinary nature of this problem becomes extremely relevant in order to meet both structure and control performance criteria. This paper proposes a novel methodology to analytically model large truss structures in a sub-structuring framework. A three dimensional unit cube element has been designed and validated with a Finite Element commercial software. This model is composed by multiple two-dimensional sub-mechanisms assembled using block-diagram models. This constitutes the building block for constructing complex truss structures by repetitions of the element. The accurate vibration description of the system and its minimal representation, as well as the possibility of accounting for parametric uncertainties in its mechanical parameters, make it an appropriate tool to perform robust Structure/Control co-design. In order to demonstrate the strengths of the proposed approach, a co-design study case is proposed by combining a multidisciplinary optimization approach based on particle swarm algorithm and multiple structured robust Hinf-synthesis. This has been used to optimize the pointing performances of an high pointing antenna, minimizing the perturbations coming from the Solar Array Mechanisms (SADM) of two solar panels, performing active control by means of multiple proof mass actuators, and simultaneously reduce the mass of the truss-structure which connects the antenna to the main spacecraft body.

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arXiv2021

Robust line-of-sight pointing control on-board a stratospheric balloon-borne platform

This paper addresses the lack of a general methodology for the controller synthesis of an optical instrument on-board a stratospheric balloon-borne platform, such as a telescope or siderostat, to meet pointing requirements that are becoming more and more stringent in the context of astronomy missions. Most often in the literature, a simple control structure is chosen, and the control gains are tuned empirically based on ground testings. However, due to the large dimensions of the balloon and the flight chain, experimental set-ups only involve the pointing system and the platform, whereas flight experience shows that the pointing performance is essentially limited by the rejection of the natural pendulum-like oscillations of the fully deployed system. This observation justifies the need for a model that predicts such flight conditions that cannot be replicated in laboratory, and for an adequate methodology addressing the line-of-sight controller design. In particular, it is necessary to ensure robust stability and performance to the parametric uncertainties inherent to balloon-borne systems, such as complex balloon's properties or release of ballast throughout the flight, especially since experimental validation is limited. In this paper, a dynamical model of the complete system is proposed, based on a multibody approach and accounting for parametric uncertainties with Linear Fractional Transformations. The comparison with flight data shows that the frequency content of the platform's motion is accurately predicted. Then, the robust control of the line-of-sight is tackled as a $\mathcal H_{\infty}$ problem that allows to reach the performance objectives in terms of disturbance rejection, control bandwidth and actuators limitations.

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arXiv2021

Worst-Case Pointing Performance Analysis for Large Flexible Spacecraft

This paper presents a tool, PELIB, developed in MATLAB /SIMULINK environment to perform pointing performance analysis based on European pointing standards. PELIB is designed as an extension of the Satellite Dynamics Toolbox (SDT), which derives the Linear Fractional Transformation (LFT) models of flexible space structures. The addition of PELIB will allow the users of SDT to perform pointing performance analysis of real mission scenarios in the same environment used for control synthesis. PELIB offers as well the possibility to take into account uncertainties in the system. This feature represents an enhancement to the current verification tools available in the European space industry community by providing the worst-case pointing budget. The capabilities of PELIB were demonstrated in a case study involving a spacecraft model with two flexible solar arrays. Several error sources, as well as uncertain parameters, were included in this model. The nominal performance has been investigated using PELIB and compared with the current European reference tool. The worst-case performance is also investigated with the new feature of PELIB to obtain the worst-case performance budget

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arXiv2021

Integrated modelling of microvibrations induced by Solar Array Drive Mechanism for worst-case end-to-end analysis and robust disturbance estimation

Modern and future observation Space missions face increasingly more demanding pointing performance requirements. This is accompanied with the development of larger lightweight flexible structures. This paper outlines a methodology for modeling a generic multi-body flexible spacecraft in an end-to-end fashion within the Two-Inputs Two-Outputs Port framework: from disturbance all the way to pointing performance by tacking into account all the uncertainties of each sub-system. A particular focus is dedicated to a novel generic model for Solar Drive Array Mechanisms and its harmonic disturbances produced by the micro-stepping driver and the gearbox imperfections. The proposed model is validated with the on-board telemetries of a European spacecraft. Moreover this paper shows how the proposed model-based approach can be easily used for control design and closed-loop robust performance analysis. Worst-case scenarios of mechanical parameters combination are investigated to provide robust performance certificate of the reference study case. A Linear Parameter-Varying observer, scheduled by the solar array rotor angle, is finally proposed in order to estimate the disturbance torques induced by the gearbox imperfections just using the measurements coming from a classical attitude control system: a star tracker and a gyrometer.

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