Une nouvelle approche pour la détection en présence de paramètres inconnus

Nous considérons le problème de détection de défaillances dans les systèmes linéaires en présence de paramètres inconnus. Deux méthodes nouvelles basées sur des critères classiques d'optimisation en détection sont formulées. La position du problème est une transposition directe du problème du jeu à deux joueurs dans la théorie de la décision. De nouveaux critères d'évaluation des performances d'une décision en présence de nuisances déterministes sont élaborés. Ils conduisent à des solutions moins conservatives que les approches minmax classiques. Un exemple est étudié

Diagnosis and Fault-tolerant Control, 3rd Edition

Fault-tolerant control aims at a gradual shutdown response in automated systems when faults occur. It satisfies the industrial demand for enhanced availability and safety, in contrast to traditional reactions to faults, which bring about sudden shutdowns and loss of availability. The book presents effective model-based analysis and design methods for fault diagnosis and fault-tolerant control. Architectural and structural models are used to analyse the propagation of the fault through the process, to test the fault detectability and to find the redundancies in the process that can be used to ensure fault tolerance. It also introduces design methods suitable for diagnostic systems and fault-tolerant controllers for continuous processes that are described by analytical models of discrete-event systems represented by automata. The book is suitable for engineering students, engineers in industry and researchers who wish to get an overview of the variety of approaches to process diagnosis and fault-tolerant control. The authors have extensive teaching experience with graduate and PhD students, as well as with industrial experts. Parts of this book have been used in courses for this audience. The authors give a comprehensive introduction to the main ideas of diagnosis and fault-tolerant control and present some of their most recent research achievements obtained together with their research groups in a close cooperatio n with European research projects. The third edition resulted from a major re-structuring and re-writing of the former edition, which has been used for a decade by numerous research groups. New material includes distributed diagnosis of continuous and discrete-event systems, methods for reconfigurability analysis, and extensions of the structural methods towards fault-tolerant control. The bibliographical notes at the end of all chapters have been up-dated. The chapters end with exercises to be used in lectures

Nonlinear Fault Detection for Hydraulic Systems

One of the most important areas in the robotics industry is the development of robots capable of working in hazardous environments. As humans cannot safely or cheaply work in these environments, providing a high level of robotic functionality is important. Our work in this area focuses on a fault detection method known as analytical redundancy, or AR. In this paper we discuss the application to a hydraulic servovalve system of our novel rigorous nonlinear AR technique. AR is a model-based state-space technique that is theoretically guaranteed to derive the maximum number of independent tests of the consistency of sensor data with the system model and past control inputs. Conventional linear AR is only valid for linear sampled data systems. However, our new nonlinear AR (NLAR) technique maintains traditional linear AR’s mathematical guarantee to generate the maximum possible number of independent tests in the nonlinear domain. Thus NLAR allows us to gain the benefits of AR testing for nonlinear systems with both continuous and sampled data

Isotropic three-dimensional T₂ mapping of knee cartilage: Development and validation.

1) To implement a higher-resolution isotropic 3D T <sub>2</sub> mapping technique that uses sequential T <sub>2</sub> -prepared segmented gradient-recalled echo (Iso3DGRE) images for knee cartilage evaluation, and 2) to validate it both in vitro and in vivo in healthy volunteers and patients with knee osteoarthritis. The Iso3DGRE sequence with an isotropic 0.6 mm spatial resolution was developed on a clinical 3T MR scanner. Numerical simulations were performed to optimize the pulse sequence parameters. A phantom study was performed to validate the T <sub>2</sub> estimation accuracy. The repeatability of the sequence was assessed in healthy volunteers (n = 7). T <sub>2</sub> values were compared with those from a clinical standard 2D multislice multiecho (MSME) T <sub>2</sub> mapping sequence in knees of healthy volunteers (n = 13) and in patients with knee osteoarthritis (OA, n = 5). The numerical simulations resulted in 100 excitations per segment and an optimal radiofrequency (RF) excitation angle of 15°. The phantom study demonstrated a good correlation of the technique with the reference standard (slope 0.9 ± 0.05, intercept 0.2 ± 1.7 msec, R <sup>2</sup> ≥ 0.99). Repeated measurements of cartilage T <sub>2</sub> values in healthy volunteers showed a coefficient of variation of 5.6%. Both Iso3DGRE and MSME techniques found significantly higher cartilage T <sub>2</sub> values (P < 0.03) in OA patients. Iso3DGRE precision was equal to that of the MSME T <sub>2</sub> mapping in healthy volunteers, and significantly higher in OA (P = 0.01). This study successfully demonstrated that high-resolution isotropic 3D T <sub>2</sub> mapping for knee cartilage characterization is feasible, accurate, repeatable, and precise. The technique allows for multiplanar reformatting and thus T <sub>2</sub> quantification in any plane of interest. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:362-371