Showing papers in "IEEE Control Systems Magazine in 1998"
TL;DR: An optimization approach to iterative control design and a direct optimal tuning algorithm that is particularly well suited for the tuning of the basic control loops in the process industry, which are typically PID loops.
Abstract: We have examined an optimization approach to iterative control design. The important ingredient is that the gradient of the design criterion is computed from measured closed loop data. The approach is thus not model-based. The scheme converges to a stationary point of the design criterion under the assumption of boundedness of the signals in the loop. From a practical viewpoint, the scheme offers several advantages. It is straightforward to apply. It is possible to control the rate of change of the controller in each iteration. The objective can be manipulated between iterations in order to tighten or loosen performance requirements. Certain frequency regions can be emphasized if desired. This direct optimal tuning algorithm is particularly well suited for the tuning of the basic control loops in the process industry, which are typically PID loops. These primary loops are often very badly tuned, making the application of more advanced (for example, multivariable) techniques rather useless. A first requirement in the successful application of advanced control techniques is that the primary loops be tuned properly. This new technique appears to be a very practical way of doing this, with an almost automatic procedure.
906 citations
TL;DR: An overview of the current state-of-the-art in industrial diesel control applications is given in this paper, and an outlook on possible future control issues and their role in diesel engine evolution is presented.
Abstract: This article is intended to give control engineers an overview of models and controls of diesel engines. The main emphasis is on the engine's torque generation, including all necessary ancillary devices (turbocharger, injection-system, etc.), pollutant emission and model-based controls. The paper gives a brief introduction of the basic working principles and the salient features of diesel engines and their main differences to Otto (gasoline or spark-ignited) engines are shown. The most important control tasks are then identified and their implications on engine performance are analyzed. An overview of the current state-of-the-art in industrial diesel control applications is given. It also discusses models for the simulation of transient macroscopic effects, and how these models can be simplified to be useful for controller synthesis. Finally. an outlook on possible future control issues and their role in diesel engine evolution is presented.
406 citations
TL;DR: The effectiveness of a controller architecture, which combines adaptive feedforward neural networks with feedback linearization, has been demonstrated on a variety of flight vehicles and is planned to expand and improve the applicability of the approach.
Abstract: The effectiveness of a controller architecture, which combines adaptive feedforward neural networks with feedback linearization, has been demonstrated on a variety of flight vehicles. The boundedness of tracking error and control signals is guaranteed. The architecture can accommodate both linear-in-the-parameters networks, as well as single-hidden-layer perceptron neural networks. Both theoretical and experimental research is planned to expand and improve the applicability of the approach, and to demonstrate practical utility in the areas of cost reduction and improved flight safety.
377 citations
TL;DR: In this paper, the authors describe the mathematical modeling, analysis, and simulation of a dynamic automatic manual layshaft transmission and dry clutch combination powertrain model, and corresponding coordinated control laws synthesized using a conventional SI ICE powerplant-alternator combination, a dry clutch and manual transmission/differential, variable field alternator, brakes and complete vehicle longitudinal dynamics with tire-road interface characterization.
Abstract: This paper describes the mathematical modeling, analysis, and simulation of a dynamic automatic manual layshaft transmission and dry clutch combination powertrain model, and corresponding coordinated control laws synthesized using a conventional SI ICE powerplant-alternator combination, a dry clutch and manual transmission/differential, variable field alternator, brakes, and complete vehicle longitudinal dynamics with tire-road interface characterization. The conventional power train model is validated using experimental test data confirming accurate emulation of dynamic components of the pre-hybridized vehicle. In addition, the development of dynamic series and parallel hybrid electric vehicle (HEV) powertrain models and corresponding coordinated control laws are described. A discussion of the key issues associated with coordinated control law development is provided. Simulations of the dynamic behavior of two types of series HEVs are shown.
276 citations
TL;DR: The use of randomized algorithms to solve some problems in control system designs that are perceived to be "difficult" is presented to show that the randomized approach can be quite successful in tackling a practical problem.
Abstract: The topic of the present article is the use of randomized algorithms to solve some problems in control system designs that are perceived to be "difficult". A brief introduction is given to the notions of computational complexity that are pertinent to the present discussion, and then some problems in control system analysis and synthesis that are difficult in a complexity-theoretic sense are described. Some of the elements of statistical learning theory, which forms the basis of the randomized approach, are briefly described. Finally, these two sets of ideas are brought together to show that it is possible to construct efficient randomized algorithms for each of the difficult problems discussed by using the ideas of statistical learning theory. A real-life design example of synthesizing a first-order controller for the longitudinal stabilization of an unstable fighter aircraft is then presented to show that the randomized approach can be quite successful in tackling a practical problem.
173 citations
TL;DR: There is a strong pedagogical potential for the type of tools that are proposed, which are based on objects which admit direct graphical manipulation, and which allow students to quickly gain insight and motivation.
Abstract: Experiments have shown that the time is now ripe for a new generation of interactive learning tools for control. The tools are based on objects which admit direct graphical manipulation. During manipulations, objects are updated instantaneously, so that relations between objects are maintained all the time. The tools are natural complements to traditional education, and allow students to quickly gain insight and motivation. A high degree of interactivity has been found to be a key issue in the design. Together with a high bandwidth in the man-machine interaction, this enhances learning significantly. Another nice feature is the possibility to hide minor issues and focus on the essentials. It is not easy to describe the power of these tools adequately in text. The best way to appreciate them is simply to use them. We believe that there is a strong pedagogical potential for the type of tools that we have described. We are also of the opinion that we are only at the very beginning in the development of learning tools of this type. The addition of sound and animation are interesting avenues that should be pursued.
143 citations
TL;DR: In this paper, the application of linear observer theory to engine control with a specific focus on observers based on exhaust measurements is discussed and experimental results are reported that illustrate the benefits and superior performance of the linear observer based control.
Abstract: This paper discusses the application of linear observer theory to engine control with a specific focus on observers based on exhaust measurements. The motivation for this architecture is that a direct measurement of the relevant quantity (the exhaust chemistry entering the catalyst) will typically lead to the most accurate control. A secondary motivation is the need to reduce costs. If sufficient accuracy can be obtained with the exhaust sensor providing the primary information, the cost associated with intake manifold sensors can be reduced. The basic theory is discussed and experimental results are reported that illustrate the benefits and superior performance of linear observer based control.
138 citations
TL;DR: Autonomous control as discussed by the authors is defined as a higher level of automatic control, which is defined by the need to solve complex optimization problems in the face of uncertainty, in near real time, and without human intervention.
Abstract: The main features of autonomous control systems are determined by the need to solve complex optimization problems in the face of uncertainty, in near real time, and without human intervention. In this article we define autonomous control as a higher level of automatic control. A taxonomy of current control, optimization and estimation paradigms is examined vis-a-vis the challenges of autonomous control. Also, research issues, and application areas of autonomous control, are identified. The manifold benefits it offers make the quest for autonomous control worthwhile.
130 citations
TL;DR: The use of vision-based feedback has been identified as one of the more promising approaches for controlling the microassembly process, and the field of visual servoing is discussed as discussed by the authors.
Abstract: The technology barrier that micromanipulation presents to many emerging fields requires that control and assembly issues in ultra-high precision motion control be addressed. In this article, we first discuss the important differences that exist between microassembly and traditional automatic assembly. We then overview ongoing efforts in microassembly and approaches being pursued. The use of vision-based feedback has been identified as one of the more promising approaches for controlling the microassembly process, and the field of visual servoing is discussed. Applications of the field to micropositioning are demonstrated. The importance of force in assembly is obvious, and developments in force sensing at the scales required are also discussed. As microassembly matures and robust, economical micromanipulation strategies are developed. Microelectromechanical system (MEMS) designers will envision a myriad of new hybrid MEMS devices previously thought impossible to manufacture.
122 citations
TL;DR: In this paper, the authors apply the linear H/sub/spl infin// control design technique to a PD-like control system currently applied in oil well drilling and show that the suppression of stick-slip oscillations and transient behavior can be largely improved.
Abstract: We show, applying the linear H/sub /spl infin// control design technique, that the suppression of stick-slip oscillations and transient behavior can be largely improved over a PD-like control system currently applied in oil well drilling. Using rough knowledge (e.g. size and induced oscillation frequency) of the friction disturbance, the appropriate choice of dynamic weighting functions can make the closed loop system robust toward the substantial uncertainty in the knowledge of the nonlinear friction. After an introduction to drilling engineering and a description of the drilling system, a condensed analysis of the stick-slip phenomenon in drillstrings and a brief history of control solutions for the drillstring problem are given, and H/sub /spl infin// control solutions for allied systems are described. Then, the general principles of linear H/sub /spl infin// control design are sketched. Subsequently, the H/sub /spl infin// control design technique is applied to design a controller for the system under study. Next, the improved closed-loop behavior toward stick-slip oscillations is shown in simulations and experiments. Conclusions with respect to the results are drawn.
116 citations
TL;DR: In this article, the authors explore a possible approach to the problem of designing control and diagnostic strategies for future generations of automotive engines based on the use of physical models to estimate unmeasured or unmeasurable variables and parameters.
Abstract: The aim of this article is to explore a possible approach to the problem of designing control and diagnostic strategies for future generations of automotive engines. The work described focuses on the use of physical models to estimate unmeasured or unmeasurable variables and parameters, to be used for control and diagnostic purposes. We introduce the mean value engine model used, present a conceptual strategy for combined control and diagnosis focusing mainly on the problem of air fuel ratio control, review basic concepts related to estimation in nonlinear systems, and propose various forms of the estimators that serve different objectives. We illustrate estimation problems in the context of a simplified engine model, assuming both linear and nonlinear measurement of oxygen concentration in the exhaust. Some simulation and experimental results related to estimation-based control and diagnosis are shown.
TL;DR: This work follows a model-based approach where the difference in wheel velocities of driven and non-driven wheels is used and the goal is to compute certain parameters from available standard sensors in the car, which depend directly or indirectly on the friction.
Abstract: Tire-road friction estimation has become an intense research area as the interest of information technology in vehicles increases. In this work, we follow a model-based approach where the difference in wheel velocities of driven and non-driven wheels is used. The perhaps most important feature is that only existing sensors are needed if the car is supplied with ABS brakes. The goal is to compute certain parameters from available standard sensors in the car, which depend directly or indirectly on the friction, and to find rules regarding how to evaluate the maximal friction forces that can be used for braking or cornering.
TL;DR: In this article, the authors present interactive learning tools used in courses in automatic control at Lund Institute of Technology, aimed at improving the understanding of and intuition for the abstract parts of the control courses.
Abstract: We present interactive learning tools used in courses in automatic control at Lund Institute of Technology. The learning tools are aimed at improving the understanding of and intuition for the abstract parts of the control courses. The tools, mainly dynamic interactive modules for a course in sampled-data systems, are implemented in Matlab and can be used over the Internet.
TL;DR: In this article, a single input single output (SISO) analytical model and closed-loop identification experiments are presented, with emphasis on design procedures of H/sub 2/ and H/ sub /spl infin// controllers applied to the electromagnetic levitation system.
Abstract: Many magnetically levitated transport systems have been constructed, tested, and improved. Various magnetic levitation (MagLev) system technologies are being developed, and some of them, including the prototype featured in this article, use electromagnets for vehicle levitation. Vehicle levitation is achieved by controlling the gaps of these electromagnets. The constructed prototype will have independent levitation and propulsion systems, but the focus of this article is on the levitation system only. The system is open-loop unstable, highly nonlinear, and it has a very restricted equilibrium region. A single input single output (SISO) analytical model and closed-loop identification experiments are presented, with emphasis on design procedures of H/sub 2/ and H/sub /spl infin// controllers applied to the electromagnetic levitation system. For the designs of these controllers, a special choice of weighting functions is employed to attenuate the resonance peak at low frequencies in the closed-loop system. The results show that closed-loop system responses with H/sub 2/ and H/sub /spl infin// controllers are very similar and present better performances when compared to the response obtained with a classical controller.
TL;DR: The basic structure of the Simplex architecture is introduced and the types of faults it can handle are described, and the fault detection mechanism based on the trajectories of the physical system in its state space is described.
Abstract: One of the most attractive features of computer-controlled systems should be the ease with which they can be modified to incorporate improvements and new capabilities. It would be desirable to make the software changes in a safe and reliable fashion while the system is running. The Simplex architecture, a real-time software technology developed at the Carnegie Mellon University Software Engineering Institute, is designed for this purpose. We introduce the basic structure of the Simplex architecture and describe the types of faults it can handle. We describe the fault detection mechanism based on the trajectories of the physical system in its state space, and derive the control switching logic that determines which controller is chosen to control the physical system in each sampling period.
TL;DR: In this article, an electric hydraulic mechanism is used to rotate the camshaft relative to the crankshaft in order to retard the cam timing with respect to the intake and exhaust strokes of the engine.
Abstract: This paper describe the variable cam timing (VCT) system which addresses both the drivability and emission performance by utilising an electric hydraulic mechanism to rotate the camshaft relative to the crankshaft in order to retard the cam timing with respect to the intake and exhaust strokes of the engine. By retarding the exhaust valve closing further into the intake stroke, more exhaust gas is drawn into the cylinder providing internal exhaust gas recirculation. In this manner, the amount of residual gas trapped in the cylinder at the end of the exhaust stroke is controlled by cam timing, suppressing NOx formation and reducing the pumping losses. Furthermore, this residual contains some unburned hydrocarbons; consequently, retaining it in the cylinder through two combustion cycles also reduces hydrocarbon emissions. In addition to the reduction of NOx and HC emissions, variable cam timing permits the engine designer to optimize cam timing over a wide range of engine operating conditions.
TL;DR: In this article, a run-to-run (RtR) control is integrated with the real-time control design to provide a comprehensive control design algorithm for semiconductor manufacture.
Abstract: Concerns optical measurement techniques for semiconductor manufacturing process monitoring and control. They can provide previously impossible real-time monitoring of several process variables, in-situ or ex-situ. This further enables the applications of more sophisticated real-time control algorithms, other than SPC. The SPC-based run-to-run (RtR) control, on the other hand, is still an instrumental part of the control algorithm, whenever there is a lack of real-time sensors for measuring critical process metrics. An emerging practice is to integrate RtR with the real-time control design to provide a comprehensive control design algorithm for semiconductor manufacture. The continued trend of semiconductor industry is toward an bigger wafers and smaller devices. This requires more integrated supervisory control, able to provide even tighter control, especially for photolithography, CVD, and etch processes. A unified framework needs to be established, at least for these critical processes, to facilitate and expedite systematic control design and development. In addition, as more sophisticated algorithms are being implemented, the control-related software and hardware should be user-friendly so that it can be operated by nonexpert personnel. Finally, since chip manufacturing consists of various processes, a comprehensive control algorithm on a factory-wide basis should utilize information (process-state, wafer-state, and tool-state data) from the current process as well as upstream and downstream processes.
TL;DR: In this paper, a basic study of vibration control, disturbance rejection, and friction compensation in robots with flexible drive systems is described, and a feed-forward compensation control based on a friction observer is proposed.
Abstract: Describes a basic study of vibration control, disturbance rejection, and friction compensation in robots with flexible drive systems. First, the system gain characteristic at the antiresonance frequency is introduced to evaluate the vibratory behavior of the control system. Secondly, joint torque negative feedback is discussed. While it is shown that joint torque negative feedback has a good effect on vibration suppression, the property of disturbance rejection is easily deteriorated when a high-gain joint torque feedback is used. Based on the assignment of pole-distribution, the relationships between vibration suppression and disturbance rejection are analyzed. Thirdly, a feedforward compensation control based on a friction observer is proposed. It is shown that the tracking error is effectively decreased by this friction compensation.
TL;DR: In this article, an approach is presented which integrates model-based adaptive control and reconfiguration based on fault detection/diagnosis applied to a heat exchanger plant in order to improve reliability and control performance.
Abstract: Heat exchangers play an important role in chemical and process industries. In order to improve reliability and control performance, intelligent concepts for control, supervision and reconfiguration are necessary. In the paper, an approach is presented which integrates model-based adaptive control and reconfiguration based on fault detection/diagnosis applied to a heat exchanger plant. The adaptive controller and the fault detection scheme are based on a fuzzy model of the process (Takagi-Sugeno type). The fault diagnosis is performed using a self-organizing fuzzy structure.
TL;DR: The purpose of this article is to stimulate the use of fuzzy logic to provide new control functions that are outside the domain of traditional control, where fuzzy control is likely to provide the greatest payoff.
Abstract: Fuzzy logic is used mostly to handle high-level control functions that traditional control methods do not address. This article discusses different ways that fuzzy logic can be used in high-level control functions. Specifically, we examine the use of fuzzy logic for supervisory control, for selecting discrete control actions, for identifying the operating environment, and for evaluating controller performance. The purpose of this article is to stimulate the use of fuzzy logic to provide new control functions that are outside the domain of traditional control, where fuzzy control is likely to provide the greatest payoff.
TL;DR: In this paper, a new approach to the manual flight control problem with both rate and amplitude actuator constraints, referred to as linear quadratic tracking (LQT), is outlined.
Abstract: The objectives of this article are to concisely state the tracking control problem with actuator saturation, briefly review the current literature, and formulate the problem in a manual (flight) control context. The complexity of tracking control with saturation is demonstrated via a simple example. A new approach to the manual flight control problem with both rate and amplitude actuator constraints, referred to as linear quadratic tracking (LQT), is outlined. This approach is specifically directed toward the dynamic tracking control problem subject to both displacement and rate actuator constraints, particularly for the challenging case of open-loop unstable plants, which are of current interest in flight control. At the same time, due to the low order of the simplified plant models used in flight control it is reasonable to assume full state feedback is available, although the tracked variable is a scalar, e.g., pitch rate. The saturation avoidance aspect of the proposed LQT solution is demonstrated for the simple example.
TL;DR: In this paper, the authors present a new parallel control scheme which ensures tracking of end-effector position along the unconstrained directions and tracking of contact force along the constrained direction, in spite of uncertainty on the contact stiffness.
Abstract: Force and position control strategies are aimed at handling the interaction of a robot manipulator with the environment. Among them, the parallel force/position control approach offers good performance in the face of uncertainty on the geometry of the contact surface. This article presents a new parallel control scheme which ensures tracking of end-effector position along the unconstrained directions and tracking of contact force along the constrained direction, in spite of uncertainty on the contact stiffness. The controller is of inverse dynamics type with a force feedforward action. Adaptation to the unknown stiffness coefficient is achieved by resorting to a suitable estimate update law driven by the force error. Experimental results on an industrial robot with open control architecture are reported.
TL;DR: In this article, the impact-force behavior of a 6-DOF commercial manipulator interacting with a very hard granite surface is investigated. And the authors show how to effectively employ integral control even in the transition phase, maintaining contact with the environment without bounce despite the potential problems of integrator wind-up.
Abstract: The impact-force behavior is experimentally studied on a 6-DOF commercial manipulator interacting with a very hard granite surface. It is shown that the elastic-joint robot model proposed by Spong (1987) completely explains frequency and damping of impact-force oscillations, so that oscillations can be totally ascribed to joint compliance, while links behave as rigid bodies. This article shows, through analysis and experiments, how to effectively employ integral control even in the transition phase, maintaining contact with the environment without bounce despite the potential problems of integrator wind-up. We begin by describing the experimental setup and how the manipulator model is derived. We then report the experimental results and model validation and discuss the open-loop permanent contact and impact. We also give an analysis of the wind-up problem of integral control, propose methods to avoid or counteract it, and report bounceless experimental controlled impacts.
TL;DR: In this paper, the authors describe a practical algorithm that requires only O(1) dynamic torque, which is applicable to a wide range of snake robot morphologies and can be used for climbing obstacles.
Abstract: Autonomous snake robot locomotion in rough terrain depends on the robot's ability to rise from a horizontal position to a vertical, for its ability to climb obstacles. At first sight, lifting N body segments seems to require O(N/sup 2/) dynamic torque. However, in this article we describe a practical algorithm that requires only O(1) dynamic torque. The algorithm is applicable to a wide range range of snake robot morphologies. The algorithm requires little space, and control is simple, since motion occurs only in a plane. Analysis of the algorithm reveals a strong relation between the maximum dynamic torque required and the joint pitch range. We discuss some consequences for the design of snake robots. For instance, an adjustment of the mass center of the robot's end segment can reduce the maximum dynamic torque. Implications are studied for some snake robot joint designs, including Dragon, an autonomous snake robot constructed for the study of unconventional locomotion.
TL;DR: In this article, interior point methods for linear and non-linear control problems are discussed and a review of current status and a discussion of future directions are provided. But the authors focus on the nonlinear problem of optimal control and model predictive control problems.
Abstract: Since Karmarkar's work (1984), interior point methods in linear programming have triggered a tremendous amount of activity. The applicability of interior-point methods for the efficient solution of nonlinear programming problems has also been of interest, and has shown huge potential benefits. This has tremendous impact in process control, especially since optimal control and model predictive control problems, hitherto considered unsolvable, could be solved in a realistic time. In this article, we outline some recent developments in interior point methods for the solution of linear and nonlinear programming problems followed by a summary of the recent work for applying these concepts in control. We conclude with a review of current status and a discussion of future directions.
TL;DR: Several examples of feedback control in these pumps were explored in this article, including parameter estimation for position sensing, observer based motor commutation, position control of the rigid impeller subjected to highly uncertain fluid dynamic forces, and pump discharge rate regulation.
Abstract: Artificial hearts are a commercially interesting technology which relies heavily on feedback control, particularly with centrifugal pump implementations using magnetic bearings. Several examples of feedback control in these pumps were explored in this paper, including parameter estimation for position sensing, observer based motor commutation, position control of the rigid impeller subjected to highly uncertain fluid dynamic forces, and pump discharge rate regulation (physiological control) to achieve uncertain objectives (due to insufficient experience) using difficult measurements on an extremely complex plant. Such problems are typical of an expanding range of biomedical applications for automatic control.
TL;DR: In this article, a robust controller that theoretically guarantees stability over a wide range of parameter changes is described, and the performance of the robust controller is evaluated in simulation as well as on a test vehicle.
Abstract: Vehicle lateral dynamics are affected by vehicle mass, longitudinal velocity, vehicle inertia, and the cornering stiffness of the tires. All of these parameters are subject to variation, even over the course of a single trip. Therefore, a practical lateral control system must guarantee stability, and hopefully ride comfort, over a wide range of parameter changes. This article describes a robust controller that theoretically guarantees stability over a wide range of parameter changes. The performance of the robust controller is then evaluated in simulation as well as on a test vehicle. Test results for experiments conducted on an instrumented track are presented, comparing the robust controller to a PID controller that was tuned on the vehicle.
TL;DR: In this paper, a real-time closed loop demonstration of spark advance control by interpretation of ionization current signals is presented, which leads to a clear improvement in engine efficiency compared to traditional systems using only engine speed and load.
Abstract: The paper presents a real-time closed loop demonstration of spark advance control by interpretation of ionization current signals. Such control is shown to be able to handle variations in air humidity, which is a major factor influencing burn rates, and consequently pressure buildup and useful work transferred via piston to drive shaft. This leads to a clear improvement in engine efficiency compared to traditional systems using only engine speed and load. Inspired by the type of challenges and potential usefulness in interpretation of ionization current signals, the paper focuses on closed loop ignition control by ionization current interpretation. The topics discussed include: the basics of ionization currents; spark advance control, especially principles relating pressure information to efficiency; and the structure of the ion-sense spark advance controller. The experimental demonstrations and some conclusions are presented.
TL;DR: In this article, a self-learning fuzzy logic controller (SLFLC) is proposed for the position control of a DC servo system in the presence of a gravity-dependent shaft load and fairly high static friction.
Abstract: Describes an experimental verification of a self-learning fuzzy logic controller (SLFLC). The SLFLC contains a learning algorithm that utilizes a second-order reference model and a sensitivity model related to the fuzzy controller parameters. The effectiveness of the proposed controller has been tested by experiment in the position control loop of a chopper fed DC servo system in the presence of a gravity-dependent shaft load and fairly high static friction. The experimental results prove that the SLFLC provides closed-loop behavior as desired and eliminates a steady-state position error.
TL;DR: Use of the World Wide Web to facilitate learning of basic, theoretical, technical material is described in terms of the experience in developing interactive demonstration and exercise modules focusing on Fourier analysis, convolution, the sampling theorem, and elementary control systems.
Abstract: Use of the World Wide Web to facilitate learning of basic, theoretical, technical material is described in terms of our experience in developing interactive demonstration and exercise modules focusing on Fourier analysis, convolution, the sampling theorem, and elementary control systems. Early attempts involved multimedia presentations and downloadable MATLAB M-files, or server computations initiated by CGI forms. More recently, Java applets have been used to improve immediacy and interactivity while dramatically reducing server burden. Currently we are integrating audio with the demonstrations, and developing interactive lecture modules as possible replacements of classroom lectures for certain types of material.