A model-based approach to camera’s auto exposure control

A fast and robust camera’s auto exposure (AE) technique is proposed in this work. It is achieved by modeling the luminance characteristics of the imaging sensor as a concave or convex function of a control parameter (e.g., exposure time or speed) and the optimal control parameter is computed using a modified secant algorithm with fast convergence. Furthermore, the proposed solution is able to adjust the control parameter automatically in the presence of erroneous exposure. Its superior performance is confirmed by experimental results.     

Robust stabilization of singular systems withH ∞-bounded uncertainty

In this paper the problem of robust stabilizing a linear, time-invariant singular system is studied. The characterization is given in terms ofH -bounded perturbations to the numerator and denominator factors of its normalized left coprime factorization. An optimal stability margin is provided in terms of the definition of the Hankel norm of a singular system. The Hankel norm is computed using two generalized Lyapunov equations.This research was supported by the Defense Advanced Research Projects Agency under contract MDA-972-93-1-0032 and MDA-972-95-3-0016.     

Envelope-constrained IIR filter design: An LMIH ∞ optimization approach

In this paper, we consider envelope-constrained (EC) infinite impulse response (IIR) filtering problems. The aim is to design an IIR filter such that theH norm of the filtering error transfer function is minimized subject to the constraint that the estimation error with a given input to the linear dynamic system is contained or bounded in a prescribed envelope. The filter design problem is formulated as a standard optimization problem in linear matrix inequalities (LMIs).     

On modelling mechatronics systems—a geometrical approach

The paper proposes a procedure to apply a geometrical based approach to model mechatronics systems. A brief survey of the geometrical based approach of modelling with illustrative examples is presented here to enable the reader to understand the terminology of the procedure. In this procedure, first, two geometrical based models for both the physical and logical properties of a mechatronics system are established, second, the interconnection between these two models is determined, third, a total model is built up from these two models. The utilization of the procedure is demonstrated for achieving synchronization of multiple independent servo motors in an automated material transfer system which includes two conveyers.     

H∞ control of electrorheological suspension system subjected to parameter uncertainties

Vehicle suspension is normally used to attenuate unwanted vibration from various road conditions. The successful suppression of the vibration leads to the improvement of ride comfort as well as steering stability of the vehicle. One of attractive candidates to formulate successful vehicle suspension is to use electrorheological (ER) damper. This paper presents robust control performances of ER suspension system subjected to parameter uncertainties associated with sprung mass of the vehicle and time constant of the ER damper. After identifying dynamic bandwidth of a cylindrical ER damper operated with two different ER fluids (one has fast response characteristic, while the other slow response characteristic), a quarter car model is established by incorporating with time constant of the damping force. A robust H_∞ controller, which compensates the sprung mass and time constant uncertainties, is designed in order to suppress unwanted vibration of the vehicle. Control responses such as vertical acceleration of the sprung mass are presented in time and frequency domains. In addition, the effect of time constant of the damping force on the vibration control performance is investigated by undertaking a comparative work between fast and slow dynamic characteristics of the ER damper.     

H∞ loop shaping for the torque-vectoring control of electric vehicles: Theoretical design and experimental assessment

This paper presents an H_∞ torque-vectoring control formulation for a fully electric vehicle with four individually controlled electric motor drives. The design of the controller based on loop shaping and a state observer configuration is discussed, considering the effect of actuation dynamics. A gain scheduling of the controller parameters as a function of vehicle speed is implemented. The increased robustness of the H_∞ controller with respect to a Proportional Integral controller is analyzed, including simulations with different tire parameters and vehicle inertial properties. Experimental results on a four-wheel-drive electric vehicle demonstrator with on-board electric drivetrains show that this control formulation does not need a feedforward contribution for providing the required cornering response in steady-state and transient conditions.     

A co-operative environment for local government: an Internet–Intranet approach

In this paper we present a Web-based, database oriented CSCW system to support information dispersal between different Local Government authorities (Region, Prefecture and Municipalities) and the citizens. The system is implemented around the `shared workspace' notion, a group of directories and files controlled by the users of the workspace. Intranet and Extranet technologies are exploited to enable asynchronous and synchronous co-operation, manipulation of information from heterogeneous sources, security and easy administration, providing in parallel advanced communication facilities.We propose an innovative approach for the development of shared workspaces over WWW, based on state-of-the-art software platforms, integrating WWW and database technologies. The whole system was developed under a project funded by the Greek General Secretariat of Research and Technology and aims in the efficient distribution and management of information between and within different types of local authorities (Municipalities, Prefectures).     

H2/H∞ control for grid-feeding converter considering system uncertainty

Three-phase grid-feeding converters are key components to integrate distributed generation and renewable power sources to the power utility. Conventionally, proportional integral and proportional resonant-based control strategies are applied to control the output power or current of a GFC. But, those control strategies have poor transient performance and are not robust against uncertainties and volatilities in the system. This paper proposes a H₂/H_∞-based control strategy, which can mitigate the above restrictions. The uncertainty and disturbance are included to formulate the GFC system state-space model, making it more accurate to reflect the practical system conditions. The paper uses a convex optimisation method to design the H₂/H_∞-based optimal controller. Instead of using a guess-and-check method, the paper uses particle swarm optimisation to search a H₂/H_∞ optimal controller. Several case studies implemented by both simulation and experiment can verify the superiority of the proposed control strategy than the traditional PI control methods especially under dynamic and variable system conditions.     

H∞ control of a flexible gantry robot arm using smart actuators

This paper presents new feedback actuators to achieve an accurate position control of a flexible gantry robot arm. The translational motion in the plane is generated by two d.c. motors and controlled by electro-rheological (ER) clutch actuators. The generated motion can be continuously controlled by controlling the intensity of electric fields imposed to the ER fluid domains of bi-directional rotating ER clutches. On the other hand, during control action of the translational motion, a flexible arm attached to the moving part produces undesirable oscillations due to its inherent flexibility. The oscillations are actively suppressed by employing feedback voltage to the piezoceramic actuator bonded on the surface of the flexible arm. Consequently, an accurate position control at the end-point of the flexible arm can be achieved. In order to accomplish this control target, the governing equations of the proposed system are derived and rewritten as transfer functions to design a robust H_∞ controller. The control electric fields to be applied to the ER clutch and the control voltage for the piezoceramic actuator are determined via the loop shaping design procedures (LSDP) in the H_∞ control technique. Control results of position regulating and tracking are provided to evaluate the effectiveness of the proposed methodology.     

MA‐WATM: A new approach towards an adaptive wireless ATM network

In a cellular multimedia network like wireless ATM (WATM), self control seems primordial. Our new approach is based on the application of DAI (distributed artificial intelligence) techniques in order to build a selfadaptive network within random nonuniform traffic conditions. Attempting to achieve a high network capacity in terms of resource allocation and air interface BER (bit error rate), we propose to apply intelligent agent features to enhance the architecture of WATM systems. In fact, the intelligent platform MAWATM (multiagent wireless ATM) is used to provide a flexible integration of the multiagent technique in wireless entities, BSs (base stations), MSs (mobile stations) and MSCs (mobile switching centers). Two applications are investigated and explored by simulations in order to bear out the feasibility of the multiagent approach.     

Experimental modeling of hysteresis in stage systems: A Maxwell–Iwan approach

Dynamic links of high-precision stage systems consist of wires and hoses that are used for example to transport electrical current to the actuators and sensors or cooling liquids to the stages. During stage motion, these dynamic links typically express complex hysteretic behavior due to internal friction and viscoelastic properties. As such, dynamic links give rise to unwanted disturbances acting on the high-precision stage systems. This paper presents a simple but accurate physics-based and experimental modeling procedure. The generalized Maxwell model and a modification of the Iwan model are combined in parallel to capture both frequency dependencies by viscoelastic effects and amplitude dependencies by friction-based effects. The modified and physically meaningful Iwan model is shown to be equivalent to the well-known Bouc–Wen model. A so-called normalized dissipation factor is introduced to quickly recognize frequency and/or amplitude dependent behavior using measured data. Using this information, a well-founded choice for an (initial) model structure to be identified can be made. Subsequently, an identification procedure is proposed to estimate values of the model parameters again using the measured data. A simulated experiment is used to show the use of the normalized dissipation factor and validate the identification procedure. Finally, the validity and usefulness of the Maxwell–Iwan modeling approach is demonstrated by experimental results obtained from an industrial wafer stage system.     

Modulated–demodulated control: Q control of an AFM microcantilever

We outline the application of modulated–demodulated control to the quality (Q) factor control of an atomic force microscope microcantilever. We review the modulated–demodulated control technique, emphasize its linear time invariant nature and develop state space representations of the controller for design and analysis. The modulated–demodulated controller can be configured as both positive position feedback (PPF) and resonant controllers, which are effective in the control of negative imaginary systems. Negative imaginary systems theory has important application in the control of collocated mechanical systems and we briefly summarize the key relevant results. A high-frequency, tunable modulated–demodulated controller, designed specifically for MHz operation, was developed for experimental validation. The modulated–demodulated controller enables the use of a low-bandwidth baseband controller in the configuration of a high-bandwidth controller, thus simplifying the implementation of high-bandwidth controllers. We outline the controller characterization and demonstrate closed-loop control of a Bruker DMASP microcantilever. We also present AFM images highlighting the improvements in scan speed and image quality achieved as a result of Q control. Modulated–demodulated control appears well suited to the control of high-frequency resonant dynamics. In addition to high-speed atomic force microscopy, we believe this control technique may find applications in high-frequency microelectromechanical systems (MEMS).     

Conception approach of access control in heterogeneous information systems using UML

The development of the information systems should answer more and more to the problems of federated data sources and the problems with the heterogeneous distributed information systems. The assurance of data access security realized in the cooperative information systems with loose connection among local data sources is hard to achieve mainly for two reasons: the local data sources are heterogeneous (i.e. data, models, access security models, semantics, etc.) and the local autonomy of systems does not allow to create a global integrated security schema. The paper proposes to use one common set of access control concepts to support the access control management in security of heterogeneous information systems. The UML (Unified Modeling Language) concepts can be used to define and implement the most popular access control models, such as DAC, MAC or RBAC. Next, the concepts derived from different models can be joined to use one common approach comprehensible for each administrator of each cooperative information system in the federation.     

Digital natives’ snack content consumption and their goals: A means-end chain approach

This study explores digital natives’ consumption of snack contents, which are short-form digital contents that reflects on the emerging trend of snack culture, referring to the participative, multi-tasking, and shortened consumption of digital contents. Specifically, employing goal theory and a means-end chain approach, this study investigates digital natives’ snack content consumption behaviors and the goals they pursue through those behaviors. Data were collected using laddering interviews, a type of semi-structured interview, and the results of the analyses were presented in a hierarchical goal map that identified four attributes and 14 goals associated with snack content consumption. The findings show that information acquisition, sense of accomplishment, fun, and restorative are the main four values users obtain through the usage of snack contents. This empirical study enhances the understanding of digital natives’ goals in consuming snack contents and provides insights into the current trend of digital content consumption.