Incorporation of Robustness Properties into the Observer Based Anti-Windup Scheme in the Case of Actuator Uncertainties

Abstract-Saturation is a very common nonlinearity in control systems and may produce serious performance deterioration or even loss of stability. To cope with saturation, several anti-windup (AW) schemes have been developed over a long time. Unfortunately, they are based on the assumption that there is a static nonlinearity between the output of the controller and the plant input, which, in many situations, is not the case, because of an actuator dynamics. Against this background we provide a design procedure for the design of the AW-compensator that guarantee stability of the observer based anti-windup to face unmodeled actuator dynamics and guarantee a certain level of performance. This mixed performance method is later extended for systems with unmeasurable actuator outputs by the use of an unknown input observer (UIO). The effectiveness of the presented algorithm is demonstrated on an engine test-bench simulator. I. INTRODUCTION S result of physical limitations, the output of actuators is always limited in amplitude and rate, such as maximum or minimum torque in an engine or the maximum safe pitch rate in an aircraft. Such limits must be taken in account in the control design, otherwise the controller output will be different from the plant input, leading to wrong update of the controller states and to consequences ranging from performance deterioration over large overshoots and sometimes even to limit cycles or stability loss. Therefore, this phenomenon -usually called "controller windup" -has a paramount practical relevance and therefore many existing techniques address this problem of actuator constraints, e.g. the "Model Predictive Control" (MPC) Among the many contributions to handle input constraints for this class of problems, we recall the recent surveys of Galeani [3], Tarbouriech and Turner [4] about early and recent anti-windup research. The observer-based antiwindup design goes back to the publications of Åström and Hägglund Martin Bruckner and Luigi del Re are with the Institute for Design and Control of Mechatronical Systems (e-mail: [email protected]; [email protected]). In the case of actuator or plant uncertainties there are only a few contributions, such as the approach of Teel In this paper based on the Integral-Quadratic-Constraints (IQCs) framework we extend the observer-based antiwindup design procedure to handle actuator uncertainties and present a design procedure that allows tuning the AW for performance requirements. To this end two weighting matrices are introduced in the performance criteria. In addition some nicely interpretable rules are provided for choosing the weighting matrices. In the case, where the true plant input can't be measured the closed-loop system is extended with an unknown input observer (UIO). To the best of our knowledge, we are not aware of any work in the literature dealing with a mixed performance AW-design, jointly tackling both, unmeasurable actuator outputs and dynamic actuator uncertainty. All these algorithms are tested on an engine test-bench simulation example. The paper is structured as follows: first we introduce the observer based anti-windup compensator and present some robust stability considerations in the case of actuator uncertainties based on the IQC-framework. Afterwards an UIO is introduced to keep the performance in the case, when the output of the actuator isn't available for measurement. Finally the method is tested on a test-bench simulator. II. OBSERVER BASED ANTI-WINDUP DESIGN For reasons of global stability, throughout the paper the plant P of order n is assumed to be stable, and that the controller ( , , , ) c c c c A B C D stabilizes the system when the saturation is not active. The plant is described by the standard equations: is the state-space realization of the controller and L is the desired feedback matrix of the antiwindup compensator (se

A Study of Brain Networks Associated with Swallowing Using Graph-Theoretical Approaches

Functional connectivity between brain regions during swallowing tasks is still not well understood. Understanding these complex interactions is of great interest from both a scientific and a clinical perspective. In this study, functional magnetic resonance imaging (fMRI) was utilized to study brain functional networks during voluntary saliva swallowing in twenty-two adult healthy subjects (all females, 23.1±1.52 years of age). To construct these functional connections, we computed mean partial correlation matrices over ninety brain regions for each participant. Two regions were determined to be functionally connected if their correlation was above a certain threshold. These correlation matrices were then analyzed using graph-theoretical approaches. In particular, we considered several network measures for the whole brain and for swallowing-related brain regions. The results have shown that significant pairwise functional connections were, mostly, either local and intra-hemispheric or symmetrically inter-hemispheric. Furthermore, we showed that all human brain functional network, although varying in some degree, had typical small-world properties as compared to regular networks and random networks. These properties allow information transfer within the network at a relatively high efficiency. Swallowing-related brain regions also had higher values for some of the network measures in comparison to when these measures were calculated for the whole brain. The current results warrant further investigation of graph-theoretical approaches as a potential tool for understanding the neural basis of dysphagia. © 2013 Luan et al

Using the Gene Ontology to Annotate Key Players in Parkinson's Disease

The Gene Ontology (GO) is widely recognised as the gold standard bioinformatics resource for summarizing functional knowledge of gene products in a consistent and computable, information-rich language. GO describes cellular and organismal processes across all species, yet until now there has been a considerable gene annotation deficit within the neurological and immunological domains, both of which are relevant to Parkinson's disease. Here we introduce the Parkinson's disease GO Annotation Project, funded by Parkinson's UK and supported by the GO Consortium, which is addressing this deficit by providing GO annotation to Parkinson's-relevant human gene products, principally through expert literature curation. We discuss the steps taken to prioritise proteins, publications and cellular processes for annotation, examples of how GO annotations capture Parkinson's-relevant information, and the advantages that a topic-focused annotation approach offers to users. Building on the existing GO resource, this project collates a vast amount of Parkinson's-relevant literature into a set of high-quality annotations to be utilized by the research community

Predatory Bacteria: A Potential Ally against Multidrug-Resistant Gram-Negative Pathogens

Multidrug-resistant (MDR) Gram-negative bacteria have emerged as a serious threat to human and animal health. Bdellovibrio spp. and Micavibrio spp. are Gram-negative bacteria that prey on other Gram-negative bacteria. In this study, the ability of Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus to prey on MDR Gram-negative clinical strains was examined. Although the potential use of predatory bacteria to attack MDR pathogens has been suggested, the data supporting these claims is lacking. By conducting predation experiments we have established that predatory bacteria have the capacity to attack clinical strains of a variety of ß-lactamase-producing, MDR Gram-negative bacteria. Our observations indicate that predatory bacteria maintained their ability to prey on MDR bacteria regardless of their antimicrobial resistance, hence, might be used as therapeutic agents where other antimicrobial drugs fail. © 2013 Kadouri et al

Coherent motion of stereocilia assures the concerted gating of hair-cell transduction channels

The hair cell's mechanoreceptive organelle, the hair bundle, is highly sensitive because its transduction channels open over a very narrow range of displacements. The synchronous gating of transduction channels also underlies the active hair-bundle motility that amplifies and tunes responsiveness. The extent to which the gating of independent transduction channels is coordinated depends on how tightly individual stereocilia are constrained to move as a unit. Using dual-beam interferometry in the bullfrog's sacculus, we found that thermal movements of stereocilia located as far apart as a bundle's opposite edges display high coherence and negligible phase lag. Because the mechanical degrees of freedom of stereocilia are strongly constrained, a force applied anywhere in the hair bundle deflects the structure as a unit. This feature assures the concerted gating of transduction channels that maximizes the sensitivity of mechanoelectrical transduction and enhances the hair bundle's capacity to amplify its inputs.Comment: 24 pages, including 6 figures, published in 200

Using Bars As Signposts of Galaxy Evolution at High and Low Redshifts

An analysis of the NICMOS Deep Field shows that there is no evidence of a decline in the bar fraction beyond z~0.7, as previously claimed; both bandshifting and spatial resolution must be taken into account when evaluating the evolution of the bar fraction. Two main caveats of this study were a lack of a proper comparison sample at low redshifts and a larger number of galaxies at high redshifts. We address these caveats using two new studies. For a proper local sample, we have analyzed 134 spirals in the near-infrared using 2MASS (main results presented by Menendez-Delmestre in this volume) which serves as an ideal anchor for the low-redshift Universe. In addition to measuring the mean bar properties, we find that bar size is correlated with galaxy size and brightness, but the bar ellipticity is not correlated with these galaxy properties. The bar length is not correlated with the bar ellipticity. For larger high redshift samples we analyze the bar fraction from the 2-square degree COSMOS ACS survey. We find that the bar fraction at z~0.7 is ~50%, consistent with our earlier finding of no decline in bar fraction at high redshifts.Comment: In the proceedings of "Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork strikes a New Note

Evaluating the use of Apo-neocarzinostatin as a cell penetrating protein.

Protein-ligand complex neocarzinostatin (NCS) is a small, thermostable protein-ligand complex that is able to deliver its ligand cargo into live mammalian cells where it induces DNA damage. Apo-NCS is able to functionally display complementarity determining regions loops, and has been hypothesised to act as a cell-penetrating protein, which would make it an ideal scaffold for cell targeting, and subsequent intracellular delivery of small-molecule drugs. In order to evaluate apo-NCS as a cell penetrating protein, we have evaluated the efficiency of its internalisation into live HeLa cells using matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry and fluorescence microscopy. Following incubation of cells with apo-NCS, we observed no evidence of internalisation

Incremental bounded model checking for embedded software

Program analysis is on the brink of mainstream usage in embedded systems development. Formal verification of behavioural requirements, finding runtime errors and test case generation are some of the most common applications of automated verification tools based on bounded model checking (BMC). Existing industrial tools for embedded software use an off-the-shelf bounded model checker and apply it iteratively to verify the program with an increasing number of unwindings. This approach unnecessarily wastes time repeating work that has already been done and fails to exploit the power of incremental SAT solving. This article reports on the extension of the software model checker CBMC to support incremental BMC and its successful integration with the industrial embedded software verification tool BTC EMBEDDED TESTER. We present an extensive evaluation over large industrial embedded programs, mainly from the automotive industry. We show that incremental BMC cuts runtimes by one order of magnitude in comparison to the standard non-incremental approach, enabling the application of formal verification to large and complex embedded software. We furthermore report promising results on analysing programs with arbitrary loop structure using incremental BMC, demonstrating its applicability and potential to verify general software beyond the embedded domain