A Measurement‐Based Approach for Designing Fixed‐Order Controllers for Unknown Closed‐Loop Architecture

This paper presents a new technique to design fixed‐structure controllers for linear unknown systems using a set of measurements. In model‐based approaches, the measured data are used to identify a model of the plant for which a suitable controller can be designed. Due to the fact that real processes cannot be described perfectly by mathematical models, designing controllers using such models to guarantee some desired closed‐loop performance is a challenging task. Hence, a possible alternative to model‐based methods is to directly utilize the measured data in the design process. We propose an approach to designing structured controllers using a set of closed‐loop frequency‐domain data. The principle of such an approach is based on computing the parameters of a fixed‐order controller for which the closed‐loop frequency response fits a desired frequency response that describes some desired performance indices. This problem is formulated as an error minimization problem, which can be solved to find suitable values of the controller parameters. The main feature of the proposed control methodology is that it can be applied to stable and unstable plants. Additionally, the design process depends on a pre‐selected controller structure, which allows for the selection of low‐order controllers. An application of the proposed method to a DC servomotor system is presented to experimentally validate and demonstrate its efficacy.     

Low speed lifting cable diagnosis using instantaneous angular speed

Journal of Mechanical Science and Technology - This paper describes an experimental study of lifting cable fault diagnostic based on instantaneous angular speed (IAS) technique. During the study...     

A Nonparametric Approach to Design Fixed-order Controllers for Systems with Constrained Input

International Journal of Control, Automation and Systems - This paper presents an approach for designing fixed-structure controllers for input-constrained linear systems using frequency domain...     

Interval force/position modeling and control of a microgripper composed of two collaborative piezoelectric actuators and its automation

This paper deals with the modeling and control of a microgripper devoted to micromanipulation and microassembly applications and tasks. Based on two collaborative piezoelectric actuators, the microgripper is typified by a high sensitivity to the environment, in particular a high sensitivity to the properties of the manipulated objects. This sensitivity makes the behavior of the microgripper variable and uncertain versus the environment and consequently makes the tasks lose performances. A possible way to overstep that problem is to model the microgripper behavior and its dependency with the environment as perfect as possible and then calculate a controller from this. However, such model is complex to handle and the yielded controllers are often very complex for implementation. In this paper, we propose to use interval models to describe the behavior of the piezoelectric actuators that compose the microgripper. Then a controllers synthesis consisting in combining interval techniques and classical control theory is proposed. Both the position and the force raised in the microgripper are considered. The main advantages of the proposed technique are: 1) ease and natural way to model the uncertainties, 2) the robustness of the synthesized controllers, 3) and the derivation of low order controllers that are easier for implementation relative to those of classical robust control techniques. Finally, the paper presents the application of the controlled microgripper to an automated pick-transport-andplace task of micro-objects. This automated task demonstrates the efficiency of the control technique in micromanipulation and microassembly applications.     

Prévision du comportement en flexion de consoles courtes en béton armé. Prise en compte de l'endommagement du béton

Résumé Nous montrons par une analyse expérimentale que le comportement mécanique global des consoles courtes en béton armé est linéaire jusqu'au début de l'endommagement de la section d'encastrement. Pour les consoles réalisées et testées au laboratoire, la rupture finale se produit à l'encastrement, par la plastification du tirant sous l'effet de la traction développée par la flexion, ou à la diagonale par le cisaillement du béton. Nous proposons un modèle du comportement en flexion de la section d'encastrement fondé sur une méthode heuristique. Dans un premier lieu, le comportement de la section d'encastrement est déterminé dans le cadre de la théorie générale des poutres fléchies, en tenant compte des armatures réparties et en considérant le béton comme élastique endommageable et l'acier des armatures comme élasto-plastique parfait. Ensuite, le comportement, ainsi obtenu, est corrigé à partir des comparaisons calcul-expérience. Ce modèle permet de reproduire assez fidèlement le comportement expérimental du tirant à l'encastrement.

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Prévision du comportement en flexion de consoles courtes en béton armé. Prise en compte de l'endommagement du bétonFluxural behaviour prediction of reinforced concrete corbels, taking in account the concrete damage

An experimental analysis shows that the global mechanical behaviour of the corbels is linear until the beginning of interface corbel-column damage. For the corbels carried out and tested at the laboratory, the ultimate failure occurs at the interface corbel-column after extensive yielding of the tension reinforcement developed by the bending or at the diagonal by the shearing of concrete. A model of the bending behaviour of the interface corbel-column is proposed. This model is based on a heuristic method. First, the interface corbel-column behaviour is determined by the conventional flexural beam theory taking account of the stirrups and considering concrete as an elastic-damaging material and the steel of the reinforcements perfectly elasto-plastic. Then, the behaviour, thus obtained, is corrected using the calculation-experiment comparisons. This model gives a good agreement with the experimental results.

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Editorial Note Prof. Buyle-Bodin is a RILEM Senior Member.     

A measurement-based approach for designing reduced-order controllers with guaranteed bounded error

The objective of this paper is to present a measurement-based control-design approach for single-input single-output linear systems with guaranteed bounded error. A wide range of control-design approaches available in the literature are based on parametric models. These models can be obtained analytically using physical laws or via system identification using a set of measured data. However, due to the complex properties of real systems, an identified model is only an approximation of the plant based on simplifying assumptions. Thus, the controller designed based on a simplified model can seriously degrade the closed-loop performance of the system. In this paper, an alternative approach is proposed to develop fixed-order controllers based on measured data without the need for model identification. The proposed control technique is based on computing a suitable set of fixed-order controller parameters for which the closed-loop frequency response fits a desired frequency response that meets the desired closed-loop performance specifications. The control-design problem is formulated as a nonlinear programming problem using the concept of bounded error. The main advantages of our proposed approach are: (1) it guarantees that the error between the computed and the desired frequency responses is less than a small value; (2) the difficulty of finding the globally optimal solution in the error minimisation problem is avoided; (3) the controller can be designed without the use of any analytical model to avoid errors associated with the identification process; and (4) low-order controllers can be designed by selecting a fixed low-order controller structure. To experimentally validate and illustrate the efficacy of the proposed approach, proportional-integral measurement-based controllers are designed for a DC (direct current) servomotor.     

The Oil from Mentha rotundifolia as Green Inhibitor of Carbon Steel Corrosion in Hydrochloric Acid

The corrosion inhibition potentials of Mentha rotundifolia oil on carbon steel in 1 M HCl was studied at different concentrations via gravimetric, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Polarization curves reveal that Mentha rotundifolia oil is a mixed-type inhibitor. Changes in impedance parameters (charge transfer resistance R_t, and double-layer capacitance C_dl) were indicative of adsorption of Mentha rotundifolia on the metal surface, leading to the formation of a protective film. The effect of the temperature on the corrosion behavior with addition of the optimal concentration of Mentha rotundifolia oil was studied in the temperature range 308 and 338 K. Adsorption of oil on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Attempts to explain the inhibitory action were carried out using density functional theory (DFT) at B3LYP/6-31G(d,p) level. Quantum chemical parameters most relevant to its potential action as corrosion inhibitor such as E_HOMO (highest occupied molecular orbital energy), E_LUMO (lowest unoccupied molecular orbital energy), energy gap (ΔE), and Mulliken charges have been calculated and discussed. The theoretical results were found to be consistent with the experimental data.     

Taxonomy of quality metrics for assessing assurance of security correctness

Assurance is commonly considered as “something said or done to inspire confidence” (Webster dictionary). However, the level of confidence inspired from a statement or an action depends on the quality of its source. Similarly, the assurance that the deployed security mechanisms exhibit an appropriate posture depends on the quality of the verification process adopted. This paper presents a novel taxonomy of quality metrics pertinent for gaining assurance in a security verification process. Inspired by the systems security engineering capability maturity model and the common criteria, we introduce five ordinal quality levels for a verification process aimed at probing the correctness of runtime security mechanisms. In addition, we analyse the mapping between the quality levels and different capability levels of the following verification metrics families: coverage, rigour, depth and independence of verification. The quality taxonomy is part of a framework for the Security Assurance of operational systems. These metrics can also be used for gaining assurance in other areas such as legal and safety compliance. Furthermore, the resulting metrics taxonomy could, by identifying appropriate quality security requirements, assist manufacturers of information technology (IT) in developing their products or systems. Additionally, the taxonomy could also empower consumers in IT security product selection to efficaciously and effectively match their organisational needs, while IT security evaluators can use it as a reference point when forming judgments about the quality of a security product. We demonstrate the applicability of the proposed taxonomy through access control examples.     

Design of a Fixed‐Order RST Controller for Interval Systems: Application to the Control of Piezoelectric Actuators

This paper presents a technique for designing a robust polynomial RST controller for parametric uncertain systems. The uncertain parameters are assumed to be bounded by intervals. The computation of the controller is addressed by introducing the interval arithmetic. The controller synthesis is formulated as a set inversion problem that can be solved using the SIVIA algorithm. The proposed method is afterwards applied to design a robust controller for a piezoelectric microactuator. The experimental results show the efficiency of the proposed method. Finally, a fine stability analysis is performed to analytically prove the robustness of the designed controller.