Jean-Philippe Cassar

Generation of Optimal Structured Residuals in the Parity Space

Abstract This paper proposes an approach for the improvement of the performances of Failure Detection and Isolation (FDI) systems Structural specifications of the expected results lead to optimize the robustness of the system with respect to the modelling uncertainties and unknown inputs. Most of the solutions of this optimization problem have been developed through the transformation of an observer - based or a parity space approach We show in this paper how the parity space approach allows the direct generation of residuals which respond to the given specifications.

In situ microscopic cytometry enables noninvasive viability assessment of animal cells by measuring entropy states

Current state of the art to determine the viability of animal cell suspension cultures is based on sampling and subsequent counting using specific staining assays. We demonstrate for the first time a noninvasive in situ imaging cytometry capable of determining the statistics of a morphologic transition during cell death in suspension cultures. To this end, we measure morphometric inhomogeneity—defined as information entropy—in cell in situ micrographs. We found that the cells are partitioned into two discrete entropy states broadened by phenotypical variability. During the normal course of a culture or by inducing cell death, we observe the transition of cells between these states. As shown by comparison with ex situ diagnostics, the entropy transition happens before or while the cytoplasmatic membrane is loosing its ability to exclude charged dyes. Therefore, measurement of morphometric inhomogeneity constitutes a noninvasive assessment of viability in real time. Biotechnol. Bioeng. 2011;108: 2884–2893.

Hierarchical Data Validation in Control Systems using Smart Actuators and Sensors

Abstract The distribution of the intelligence among all the components of the automation system allows to consider them as a connexion of a number of intelligent objects which produce or consume informations via a communication system associated with global management rules. The exchanges between components require the validation of the transmitted or received data. The functional validation is based on the physical or analytical redundancy of available information which are transmitted via a direct link or via a field bus. It is achieved by a Fault Detection and Isolation algorithm. This paper presents a hierarchical decomposition of this algorithm and shows how it can then be implemented into smart components.

Identification of MIMO Takagi-Sugeno model of a bioreactor

The main contribution of this paper is to provide an identification method to a single MIMO (multiple-input multiple-output) Takagi-Sugeno (TS) model for nonlinear MIMO systems. The methods proposed in the literature identify several TS MISO models and this needs the outputs to be separable. But this condition is not necessary in the proposed method. The TS identification method proposed uses the general principle of TS identification method which consist to decomposed a nonlinear system into a set of less complex model. Therefore, the nonlinear systems are decomposed into a set of linear systems and the contribution of each local model is expressed by a weighting function.

Criteria for the Evaluation of F.D.I. Systems Application to Sensors Location

Abstract This paper first presents an algorithm which gives sensors locations allowing to detect and to isolate the failures of system components defined in the specifications. The proposed approach uses the structural analysis of the system modelling and a bipartite graph representation of its structure. A generalised definition of the failures and a structuration of the residuals establish criteria of failures detectability and isolability. The algorithm generally gives several configurations of sensors. Hence, two additional criteria are introduced to evaluate F.D.I. systems in terms of cost and sensitivity to failures.

Vibration-based fault detection of sharp bearing faults in helicopters

Many signal processing tools have been developed by the mechanical and signal processing community to find the characteristic symptoms of sharp bearing faults (like localized spalling) from vibratory analysis. However the context of helicopter imposes a limited sampling frequency regarding the observed phenomena, many noisy vibrations and flight regimes. The performances of the classical methods are limited in such an environment mainly in identifying fault frequencies. Local bearing faults induce temporal periodic and impulsive patterns that produce redundant harmonics in the spectral domain. In this article four methods are proposed to take advantage of that redundancy. These methods provide an estimator of the fault frequency and an indicator of the quality of that estimation. These indicators are used to assess the severity of the fault. The four methods are then tested on synthesized and flight data in order to illustrate and discuss their efficiency.

Vibration-Based Fault Detection of Accelerometers in Helicopters

Vibration-based monitoring is an approach for health analysis of helicopters. However, accelerometers and other sub-elements that convert and transmit vibrations to the recording system must not corrupt the signal. These elements are prone to defects because of external injuries during flights or maintenance. This paper will deal with a method to tackle problems of loosening and mechanical shocks. The objective is to perform a passive detection of accelerometer failures from the vibrations without knowledge of previous recordings. Experiments of mechanical failures have been carried out on a shaker to reproduce in flight vibrations, and it appears that the loosening and mechanical shocks introduce asymmetry and random peaks in the temporal vibrations. Loosening was successfully detected but mechanical shocks were much harder to detect as a result of strong dependences in the vibratory environment. Loosening data sets from flights confirm experimental observations and the proposed detection method allows for the detection of the fault with better performance than standard indicators.

On the Input-Output Distinguishability of Single Output Continuous Linear Time-Invariant Systems

This note addresses the distinguishability problem for continuous linear time-invariant systems using their input and output data. The proposed approach is based on the characterization of the class of initial state vectors and control input signals that make the outputs of different continuous linear time-invariant systems indistinguishable. This class is defined here as the “indistinguishability zone.” From this characterization, a simple necessary and sufficient condition for the distinguishability of single-input, single-output systems is established. Furthermore, it is shown that multiple-input, single-output systems are never distinguishable.

Operating modes distinguishability condition in switching systems

In this paper, we consider a switching system with several operating modes which represent normal or faulty behavior. The objective is to find a necessary and sufficient condition to distinguish these modes through the input/output data. If faulty operation modes are considered the distinguishability condition corresponds to a fault detectability condition. As in [1], we define in this paper two notions of distinguishability: the distinguishability through the input/output data of the system and the distinguishability through the parity residuals of each mode. The Necessary and Sufficient Condition (NSC) of distinguishability through parity-space residuals in [1] was obtained in the case where the parity-space orders are identical in all modes. Here a more generalized NSC of distinguishability is provided for systems which could have different parity-space orders. We show in this context two main results: a NSC of distinguishability through parity residuals which generalizes the NSC in [1] and the equivalence between the two notions of distinguishability. We also demonstrate that the distinguishability definition in [1] is linked to the notion of equivalent representations used in the theory of realization.

Conditions for strict distinguishability of single-output nonlinear control-affine systems

Abstract Strict distinguishability is the property of two systems to generate identical output signals only for the zero control input and the zero initial state vector. The objective of this paper is to characterize this property for single-output nonlinear control-affine systems. In this context, we first introduce the indistinguishability zone of the systems. This zone represents the set of control inputs and initial state vectors that make the output signals of the systems indistinguishable. The explicit identification of the elements of this set is proposed in the paper. From this result, necessary and sufficient conditions for strict distinguishability are then established under suitable assumptions.