Showing papers in "IEEE Control Systems Magazine in 2001"
TL;DR: This work model NCSs with packet dropout and multiple-packet transmission as asynchronous dynamical systems and analyze their stability using stability regions and a hybrid systems technique, and discusses methods to compensate network-induced delay.
Abstract: First, we review some previous work on networked control systems (NCSs) and offer some improvements. Then, we summarize the fundamental issues in NCSs and examine them with different underlying network-scheduling protocols. We present NCS models with network-induced delay and analyze their stability using stability regions and a hybrid systems technique. Following that, we discuss methods to compensate network-induced delay and present experimental results over a physical network. Then, we model NCSs with packet dropout and multiple-packet transmission as asynchronous dynamical systems and analyze their stability. Finally, we present our conclusions.
3,467 citations
TL;DR: A conceptual framework for addressing infrastructure interdependencies is presented that could serve as the basis for further understanding and scholarship in this important area and is used to explore the challenges and complexities of interdependency.
Abstract: The notion that our nation's critical infrastructures are highly interconnected and mutually dependent in complex ways, both physically and through a host of information and communications technologies (so-called "cyberbased systems"), is more than an abstract, theoretical concept. As shown by the 1998 failure of the Galaxy 4 telecommunications satellite, the prolonged power crisis in California, and many other recent infrastructure disruptions, what happens to one infrastructure can directly and indirectly affect other infrastructures, impact large geographic regions and send ripples throughout the national a global economy. This article presents a conceptual framework for addressing infrastructure interdependencies that could serve as the basis for further understanding and scholarship in this important area. We use this framework to explore the challenges and complexities of interdependency. We set the stage for this discussion by explicitly defining the terms infrastructure, infrastructure dependencies, and infrastructure interdependencies and introducing the fundamental concept of infrastructures as complex adaptive systems. We then focus on the interrelated factors and system conditions that collectively define the six dimensions. Finally, we discuss some of the research challenges involved in developing, applying, and validating modeling and simulation methodologies and tools for infrastructure interdependency analysis.
2,341 citations
TL;DR: In this article, the authors show that standard PBC is stymied by the presence of unbounded energy dissipation, hence it is applicable only to systems that are stabilizable with passive controllers.
Abstract: Energy is one of the fundamental concepts in science and engineering practice, where it is common to view dynamical systems as energy-transformation devices. This perspective is particularly useful in studying complex nonlinear systems by decomposing them into simpler subsystems that, upon interconnection, add up their energies to determine the full system's behavior. The action of a controller may also be understood in energy terms as another dynamical system. The control problem can then be recast as finding a dynamical system and an interconnection pattern such that the overall energy function takes the desired form. This energy-shaping approach is the essence of passivity-based control (PBC), a controller design technique that is very well known in mechanical systems. Our objectives in the article are threefold. First, to call attention to the fact that PBC does not rely on some particular structural properties of mechanical systems, but hinges on the more fundamental (and universal) property of energy balancing. Second, to identify the physical obstacles that hamper the use of standard PBC in applications other than mechanical systems. In particular, we show that standard PBC is stymied by the presence of unbounded energy dissipation, hence it is applicable only to systems that are stabilizable with passive controllers. Third, to revisit a PBC theory that has been developed to overcome the dissipation obstacle as well as to make the incorporation of process prior knowledge more systematic. These two important features allow us to design energy-based controllers for a wide range of physical systems.
865 citations
TL;DR: In this article, it is demonstrated how dispensing with queues and dynamically scheduling control traffic improves closed-loop performance.
Abstract: The defining characteristic of a networked control system (NCS) is having one or more control loops closed via a serial communication channel Typically, when the words networking and control are used together, the focus is on the control of networks, but in this article our intent is nearly inverse, not control of networks but control through networks NCS design objectives revolve around the performance and stability of a target physical device rather than of the network The problem of stabilizing queue lengths, for example, is of secondary importance Integrating computer networks into control systems to replace the traditional point-to-point wiring has enormous advantages, including lower cost, reduced weight and power, simpler installation and maintenance, and higher reliability In this article, in addition to introducing networked control systems, we demonstrate how dispensing with queues and dynamically scheduling control traffic improves closed-loop performance
813 citations
TL;DR: Three network types are compared: the Ethernet bus, with carrier sense multiple access with collision detection, token-passing bus, and controller area network bus, which can be used as a communication backbone for a networked control system connecting sensors, actuators, and controllers.
Abstract: Many different network types have been promoted for use in control systems. In this article, we compare three of them: the Ethernet bus, with carrier sense multiple access with collision detection, token-passing bus (e.g., ControlNet), and controller area network bus (e.g., DeviceNet). We consider how each control network can be used as a communication backbone for a networked control system connecting sensors, actuators, and controllers. A detailed discussion of the medium access control sublayer protocol for each network is provided. For each protocol, we study the key parameters of the corresponding network when used in a control situation, including network utilization, magnitude of the expected time delay, and characteristics of time delays. Simulation results are presented for several different scenarios, and the advantages and disadvantages of each network are summarized.
616 citations
TL;DR: The number of ways of measuring complexity has grown even faster. as discussed by the authors presents an incomplete categorization and tabulation of measures of complexity, which represent variations on a few underlying themes.
Abstract: The world has grown more complex recently, and the number of ways of measuring complexity has grown even faster. This multiplication of measures has been taken by some to indicate confusion in the field of complex systems. In fact, the many measures of complexity represent variations on a few underlying themes. This column presents an (incomplete) categorization and tabulation of measures of complexity. An historical analog to the problem of measuring complexity is the problem of describing electromagnetism before Maxwell’s equations. In the case of electromagnetism, quantities such as electric and magnetic forces that arose in different experimental contexts were originally regarded as fundamentally different. Eventually it became clear that electricity and magnetism were in fact closely related aspects of the same fundamental quantity, the electromagnetic field. Similarly, contemporary researchers in architecture, biology, computer science, dynamical systems, engineering, finance, game theory, etc., have defined different measures of complexity for each field. Because these researchers were asking the same questions about the complexity of their different subjects of research, however, their answers have much in common. Three questions that are frequently posed when attempting to quantify the complexity of the thing (house, bacterium, problem, process, investment scheme) under study are 1) How hard is it to describe? 2) How hard is it to create? 3) What is its degree of organization? I use these questions to group measures of complexity. Measures within a group are typically closely related quantities.
334 citations
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TL;DR: The influence model is constructed to represent in a tractable way the dynamics of networked and interacting Markov chains, and the generalizations embodied in the influence model could prove to be important degrees of freedom in particular applications.
Abstract: This article describes what we have termed the influence model, constructed to represent in a tractable way the dynamics of networked and interacting Markov chains. The constraints imposed on the influence model may restrict its modeling ability but permit explicit and detailed analysis and computation and still leave room for rather richly structured and novel behavior. We focus on the dynamic evolution of the system. The influence matrix H, in both the homogeneous and general cases, bears further study as an interesting generalization of familiar stochastic matrices. The influence model may also find use as a representation for stochastic signals of various kinds. The influence model is evidently related to other models of networked stochastic automata in the literature, but the details of the relationships remain to be worked out more explicitly in many cases. The generalizations embodied in the influence model could prove to be important degrees of freedom in particular applications.
206 citations
TL;DR: In this paper, the authors present some essential ingredients for Six Sigma implementation, generated from a pilot survey conducted in UK manufacturing and service organisations, and identify the critical success factors that will make the application successful.
Abstract: For the effective implementation of Six Sigma projects, organisations must understand the critical success factors that will make the application successful. Critical success factors represent the essential ingredients without which a project stands little chance of success. The authors present some essential ingredients for Six Sigma implementation, generated from a pilot survey conducted in UK manufacturing and service organisations.
203 citations
TL;DR: In this article, the double integrator plant is considered, which is one of the most fundamental systems in control applications, representing single degree-of-freedom translational and rotational motion.
Abstract: We deal with a form of controller evaluation that may be called naive control In naive control, a control algorithm derived under nominal (or ideal) conditions is evaluated by analytical or numerical means under off-nominal (or nonideal) conditions that were not assumed in the formal synthesis procedure Under such nonideal conditions, the controller may or may not perform well This approach is distinct from robust control, which seeks to accommodate off-nominal perturbations in the synthesis procedure We consider the double integrator plant, which is one of the most fundamental systems in control applications, representing single degree-of-freedom translational and rotational motion Applications of the double integrator include low-friction, free rigid-body motion, such as single-axis spacecraft rotation and rotary crane motion The double integrator plant considered includes a saturation nonlinearity on the control input
156 citations
151 citations
TL;DR: An open-control software infrastructure that gives an open control platform (OCP) for complex systems that coordinates distributed interaction among diverse components and supports dynamic reconfiguration and customization of the components in real time is described.
Abstract: Advances in software technology have the potential to revolutionize control system design. Component-based architectures encourage flexible "plug-and-play" extensibility and evolution of systems. Distributed object computing allows interoperation. Advances are being made to enable dynamic reconfiguration and evolution of systems while they are still running. Technologies are being developed to allow networked, embedded devices to connect to each other and self-organize. This article describes a software infrastructure that gives an open control platform (OCP) for complex systems that coordinates distributed interaction among diverse components and supports dynamic reconfiguration and customization of the components in real time. Its primary goals are to accommodate rapidly changing application requirements, incorporate new technology (such as hardware platforms or sensors), interoperate in heterogeneous environments, and maintain viability in unpredictable and changing environments. The next section describes the current practice in control system implementation and discusses features of a complex control system architecture. It is followed by a description of the desired features a software infrastructure must have to promote new advances in control system design. We then describe an open-control software infrastructure to support these desired features, followed by a brief overview of a first-generation prototype of this infrastructure that has been developed for an autonomous aerial vehicle control.
TL;DR: The authors argues that the facts do not support the belief that congestion occurs because demand exceeds capacity, so they support initiatives to build additional highway capacity or curtail highway travel demand, and they support proposals to make transit more attractive or automobile use more costly.
Abstract: People believe congestion occurs because demand exceeds capacity, so they support initiatives to build additional highway capacity or curtail highway travel demand Politicians work to bring highway construction projects into their districts; environmentalists support proposals to make transit more attractive or automobile use more costly This article argues that the facts do not support the belief that congestion occurs because demand exceeds capacity
TL;DR: In this paper, an improved global sliding-mode control (GSMC) was proposed for controlling second-order time-varying systems with bounded uncertain parameters and disturbances, and the proposed controller drove the system states along the minimum time trajectory within the input torque limit.
Abstract: An improved global sliding-mode control (GSMC) was proposed for controlling second-order time-varying systems with bounded uncertain parameters and disturbances. The proposed controller drives the system states along the minimum time trajectory within the input torque limit. If the reference input and the bounds of the uncertain parameters and disturbances are specified, the minimum arrival time and the acceleration are expressed in closed-form equations. The proposed controller was applied to the brushless DC motor with uncertain loads. Experimental results of the proposed controller are quite similar to simulation and closed-form equation results and showed the best performance compared with other SMC. The closed-form equation can be used for designing motor-based actuators for mechanical systems without simulation and experiments.
TL;DR: Recent advances in motor control and learning are introduced, namely, the role of the basal ganglia in acquisition of goal-directed behaviors, learning of internal models by the cerebellum, and decomposition of complex tasks by the competition of predictive models.
Abstract: A new theory was postulated that the cerebellum, the basal ganglia, and the cerebral cortex have evolved to implement different kinds of learning algorithms: the cerebellum for supervised learning, the basal ganglia for reinforcement learning, and the cerebral cortex for unsupervised learning. Here, we introduce recent advances in motor control and learning, namely, the role of the basal ganglia in acquisition of goal-directed behaviors, learning of internal models by the cerebellum, and decomposition of complex tasks by the competition of predictive models.
TL;DR: Control theoretic design tools can be effectively used in designing high-performance algorithms in the context of ATM ABR congestion control, which can adapt to the variations in the number of sources sharing a switch.
Abstract: We present a control-theoretic approach to designing available bit rate (ABR) congestion control algorithms. ATM networks deal with different types of traffic. Among the several services offered by ATM, the ABR service plays a central role in regulating the network traffic, as it is the only service category that uses explicit feedback from the network. We present several algorithms for ABR congestion, which can adapt to the variations in the number of sources sharing a switch. These properties make this algorithm easier to apply in volatile networks, where both the network delay and the number of active sessions are not known or cannot be predicted accurately beforehand. In summary, we strongly believe that control theoretic design tools can be effectively used in designing high-performance algorithms in the context of ATM ABR congestion control.
TL;DR: In this paper, the authors use the example of wireless networking, an area of great interest in the emerging field of information technology, to illustrate it and provide a profusion of practical examples of problems that may have sometimes abstractly engaged our attentions in the past.
Abstract: Over the past four decades, the field of control has woven a rich tapestry of a larger systems theory, with sustained investigations into fundamental issues such as control, estimation, stability, optimality, adaptation, and decentralization. These issues are the fundamental ingredients in many new proposed technologies, which are now within our collective purview. They provide a profusion of practical examples of problems that may have sometimes abstractly engaged our attentions in the past and offer a wealth of opportunities for imaginative solutions. The opportunities are ours to seize. That is the central thesis of this article, and the author uses the example of wireless networking, an area of great interest in the emerging field of information technology, to illustrate it.
TL;DR: In this article, a robust force controller for a hydraulic actuator interacting with an uncertain environment via quantitative feedback theory (QFT) is presented. But the authors do not consider the impact of environmental variability and variations in hydraulic component parameters.
Abstract: The article presents the design of a robust force controller for a hydraulic actuator interacting with an uncertain environment via quantitative feedback theory (QFT). After the derivation of a realistic nonlinear differential equation model, a linearized plant transfer function is developed. The effects of nonlinearities are accounted for by describing the linearized model parameters as structured uncertainty. The impact of environmental variability as well as variations in hydraulic component parameters are also included as uncertainty in the model. The QFT design procedure is carried out to design a robust controller that satisfies performance specifications for tracking and disturbance rejection. The designed controller enjoys the simplicity of fixed-gain controllers, is easy to implement, and at the same time is robust to the variation of hydraulic functions as well as environmental stiffness. The controller is implemented on an industrial hydraulic actuator equipped with a low-cost proportional valve. The experimental results show that robust stability against system uncertainties and under varying conditions is achieved and the performance goals are satisfied.
TL;DR: In this paper, the authors consider a special structure of dynamic system model that admits a very tractable inclusion of element failure phenomena, for which a global system Lyapunov function can be constructed.
Abstract: We consider a special structure of dynamic system model that admits a very tractable inclusion of element failure phenomena, for which a global system Lyapunov function can be constructed This class includes Hamiltonian systems as a special case, with a wide class of R-L-C circuits and mechanical spring-mass-damper systems in which branch failures are induced by exceeding thresholds of inductor current or spring force magnitude Using a detailed R-L-C circuit as our illustrative example, this article describes how geometric features of the global Lyapunov function constructed, along with partial trajectory information from time domain simulations, can be used to more efficiently predict which branches are subject to failure in a specific disturbance scenario The underlying concepts are closely related to techniques of merging families of Lyapunov functions in hybrid system analysis It is hoped that these techniques will add to the set of tools available for predicting and preventing cascading failure in large scale networks
TL;DR: In this paper, a scale vehicle testbed has been developed for use as an evaluation tool to bridge the design gap between simulation studies and full-sized hardware, and a yaw rate vehicle controller is introduced to exemplify the type of investigations that can be conducted with the IRS.
Abstract: To circumvent the cost and inherent danger in testing aggressive vehicle controllers using full-sized vehicles, a scale vehicle testbed has been developed for use as an evaluation tool to bridge the design gap between simulation studies and full-sized hardware. We describe vehicle dynamic models of the IRS simulation system, along with experimental verification using frequency response and parameter measurements. The next section provides a detailed discussion of dynamic similitude via the Buckingham pi theorem (1914), as well as a graphical comparison between distributions of dynamic scale parameters of scaled and full-sized vehicles. Following that, a yaw rate vehicle controller is introduced to exemplify the type of investigations that can be conducted with the IRS. The controller uses differential torque and brake inputs to assist the driver to control the yaw rate of the vehicle and is designed to achieve model tracking while allowing the driver to maintain control over the front wheels of the vehicle.
TL;DR: In this paper, a nonlinear controller for coupled air temperature and humidity, with various methods of feedback and feedforward control appropriate for this system, is presented to demonstrate key characteristics of greenhouse environment control.
Abstract: Plant production systems have become more sophisticated. Climate control has changed over the past several decades from manual to digital operations, and control computers have become faster and more capable. The paper focuses first on the environment control of plant production in commercial greenhouses and plant growth chambers, and then contrasts that growing system with the needs for rather different control strategies to grow plants in space applications. To demonstrate key characteristics of greenhouse environment control, a nonlinear controller for coupled air temperature and humidity, with various methods of feedback and feedforward control appropriate for this system, is presented.
TL;DR: Two examples are presented that illustrate how biological motor control tasks can be investigated in varying degrees of complexity and detail and show that a model with detailed anatomical structure and dynamic properties has to be developed to investigate the detailed interactions among several sensory feedback loops in the spinal cord.
Abstract: We have been pursuing a modular approach to modeling and investigating the neural control of posture and movement. A modular approach is a practical and natural way of investigating the function and structure of the complex central nervous system (CNS). The modules can include skeletal dynamics, muscle dynamics with recruitment and force-generation characteristics, basic spinal cord neural circuits responsible for the local stretch reflex, interneuronal networks that provide modulation of various reflexes, various structures of brain circuits, and control strategy decision-making centers. The anatomical detail and complexity of each module can vary depending on the specific scientific question or motor task to be investigated and the extent of information available on the hierarchy. To demonstrate the modular approach, we present two examples that illustrate how biological motor control tasks can be investigated in varying degrees of complexity and detail. One example shows that a model with detailed anatomical structure and dynamic properties has to be developed to investigate the detailed interactions among several sensory feedback loops in the spinal cord. The other example shows that when investigating whole-body behavior, a grosser structured model with lumped components is more tractable so issues such as the interaction of spinal cord regulation and upper CNS intelligent control can be investigated.
TL;DR: The goal is to improve the efficiency of operation of agricultural enterprises, as well as the duality and consistency of products, by compensating for the vagueness and uncertainty of the environment.
Abstract: Modern agricultural business is becoming increasingly reliant on computer-based systems, automation, and robotics that are taking over many of the tedious tasks formerly performed by humans, with superior performance in most cases. To manage the increasing complexity of agricultural systems, increasingly sophisticated methodologies are required. This has given rise to the promising field of precision agriculture, where the goal is to improve the efficiency of operation of agricultural enterprises, as well as the duality and consistency of products, by compensating for the vagueness and uncertainty of the environment. Conversely, social demand has created pressure for respectful treatment of the environment and the well-being of humans. These objectives result in new and challenging problems, problems that can only be resolved by applying advanced information and control technologies to production management of processes and farms.
TL;DR: In this paper, a hybrid control methodology combining conventional and intelligent techniques has been introduced to replace human supervision for a DCS-controlled laminar cooling process, which is superior in terms of high performance, reliability, simplicity and ease of construction.
Abstract: In industrial control, it frequently happens that, while the low-level controller performs very well, high-level supervision is required to maintain good overall performance that is usually beyond the capability of direct machine control. A hybrid control methodology combining conventional and intelligent techniques has been introduced to replace human supervision for a DCS-controlled laminar cooling process. The industrial experiments show the improved performance of the proposed hybrid control model and confirm its validity in a real manufacturing environment. The results can be extended to a wide range of processes with similar features. The methodology is superior in terms of high performance, reliability, simplicity and ease of construction.
TL;DR: Findings of agriculture research conducted in Japan in three areas are presented: 1) artificial intelligence applications in agriculture and the environments: 2) intelligent environment control for plant production systems; and 3) intelligent robots in agriculture.
Abstract: The paper presents findings of agriculture research conducted in Japan in three areas: 1) artificial intelligence applications in agriculture and the environments: 2) intelligent environment control for plant production systems; and 3) intelligent robots in agriculture. The latest biosystem derived algorithms are discussed. A finite element inverse technique using a photosynthesis algorithm is described, following by a comparison of neural network (NN) training by the photosynthetic algorithm versus genetic algorithm (GA). Leaf cellular automata are introduced, and their application to optimisation problems is discussed. A decision system consisting of NNs and GAs is applied to the optimisation of plant growth under hydroponics in Japanese plant factories. In this system, the plant growth affected by nutrient concentration is first identified using NNs. Finally, recent developments in intelligent agricultural robots in Japan are introduced.
TL;DR: This article uses computer-aided design tools to develop a describing function analysis of a pendulum clock as a control system that allows the pendulum to provide the required time keeping and add enough energy to the pendula to overcome the damping caused by friction.
Abstract: This article uses computer-aided design tools to develop a describing function analysis of a pendulum clock. We design the escapement as a control system that allows the pendulum to provide the required time keeping and, at the same time, add enough energy to the pendulum to overcome the damping caused by friction. We use analysis tools in the MATLAB Control System Toolbox to accomplish the design and analysis. A by-product of our analysis is a simple MATLAB/Simulink model and a script that generates describing functions for any arbitrary nonlinear system (including systems with multiple nonlinearities and with frequency-dependent describing functions). We also develop a Simulink model of the clock to verify the results of the analysis. The analysis described here uses some object-oriented programming features of MATLAB.
TL;DR: In this paper, the authors explain sensor specifications which quantify the ability of sensor to provide measurements of physical variables, and they can be applied to all branches of science and engineering, not just control systems.
Abstract: The author explains sensor specifications which quantify the ability of sensor to provide measurements of physical variables. Sensor manufacturer typically provide information about sensor specifications in the form of a specification sheet. The concepts described will help one interpret the information on a specification sheet. They can be applied to all branches of science and engineering, not just control systems. However, the systems approach of control engineers provides a unique perspective on these topics and associated issues.
TL;DR: Strategies that have been used to control standing posture with electrical stimulation and research efforts aimed at improving the performance of stimulation systems are described.
Abstract: Describes strategies that have been used to control standing posture with electrical stimulation and reviews research efforts aimed at improving the performance of stimulation systems.
TL;DR: In this article, the authors present a typical process control curriculum and discuss how chemical process control courses can be revised to better meet the needs of a typical BSc-level chemical engineer, including case studies, distributed control systems in laboratories, identification and control simulation packages, and studio-based approaches combining lecture, simulation, and experiments in the same room.
Abstract: Chemical process control textbooks and courses differ significantly from their electrical or mechanical control equivalents. The primary goals of this article are to i) emphasize the distinctly challenging characteristics of chemical processes, ii) present a typical process control curriculum and iii) discuss how chemical process control courses can be revised to better meet the needs of a typical BSc-level chemical engineer. In addition to a review of material covered in a standard process control course, we discuss innovative approaches in process control education, including the use of case studies, distributed control systems in laboratories, identification and control simulation packages, and studio-based approaches combining lecture, simulation, and experiments in the same room. We also provide perspectives on needed developments in process control education.
TL;DR: In this article, the main aspects of the generic Data Based Mechanistic (DBM) approach to modeling stochastic dynamic systems are reviewed and applied to the analysis, forecasting, and control of environmental and agricultural systems.
Abstract: This article briefly reviews the main aspects of the generic data based mechanistic (DBM) approach to modeling stochastic dynamic systems and shown how it is being applied to the analysis, forecasting, and control of environmental and agricultural systems. The advantages of this inductive approach to modeling lie in its wide range of applicability. It can be used to model linear, nonstationary, and nonlinear stochastic systems, and its exploitation of recursive estimation means that the modeling results are useful for both online and offline applications. To demonstrate the practical utility of the various methodological tools that underpin the DBM approach, the article also outlines several typical, practical examples in the area of environmental and agricultural systems analysis, where DBM models have formed the basis for simulation model reduction, control system design, and forecasting.
TL;DR: In this article, a sequence of laboratories is presented that have been designed to maximize student involvement in the design as well as execution of the laboratory exercises, and students explore fundamental ideas of sensing, actuation, and feedback.
Abstract: A sequence of laboratories is presented that have been designed to maximize student involvement in the design as well as execution of the laboratory exercises. The first lab begins with the simplest possible model, and students explore fundamental ideas of sensing, actuation, and feedback. With the second lab, student-designed experiments are introduced. By the end of the sequence, students independently design and implement system identification, controller design, and performance assessment for high performance tracking with a motor servo. The education literature establishes the potential for discovery learning to increase learning outcomes in laboratory teaching.