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This paper deals with a hydraulic servo system with compliance control for the operation in an environment with frequent machine-human interaction. The compliance is mechanically adjusted in the present hydraulic system by changing the neutral position of the bridge valves between the full opening and the full closing states. The mathematical model of the system is first derived, and the static and the dynamic behavior of the system are investigated through numerical simulation. Since the present system exhibits a strong nonlinear characteristic in the operating condition of large compliance, a nonlinear controller is designed with the feedback linearization technique. In the operating condition of small compliance, on the other hand, a conventional linear control is applicable as usual hydraulic control systems. The performance of the present control system is investigated through both numerical simulation and experiment, justifying that the present hydraulic servo system continuously adapts its performance between a rigid positioning against disturbances and a compliant positioning to prevent damage to obstacles on the path. [DOI: 10.1115/1.1433803]

Frequently, due to the irregularities in fuel properties of the wastes and variations in feed rates, the operation of a batch-fed incinerator may encounter pressure surges and transient flue gas leakages. A lumped model to simulate the flow, pressure, and temperature behavior of an incineration system was developed, according to the fundamental conservation laws governing the overall balances of flow and thermal-mechanical energies of the system components. The system dynamic responses to flow control and waste burning variations were analyzed numerically. Qualitatively, the results correctly reflected the observed operational characteristics of batch-fed incinerators. The lumped system model can serve as a tool to design control algorithms. The concepts and approaches adopted in this work can be used as the basis for further expansion in details toward the development of an incinerator system simulator for operator training purposes.

The structured singular value method is applied to continuous-time SISO repetitive control systems in order to determine their stability and performance robustness in the presence of structured parametric modeling error in the plant. Performance measures for repetitive control systems are introduced and the robust performance analysis using structured singular values is modified, taking the alternating magnitude behaviour of the sensitivity function of a repetitive control system into account. The analysis procedure is simplified considerably in the case of large time delay by noting that the upper and lower envelopes of the structured singular value plots are obtained from corresponding finite dimensional systems without any time delay. The analysis procedures developed are applied to an example on repetitive control of an electrohydraulic material testing machine, available in the literature, to demonstrate their usefulness.

Two methods of control of semi-active suspensions that specifically address the problem of structural vibrations of the vehicle body are considered. These control strategies are based on those developed for active suspension systems in Part I of this study and rely on either modifications of suspension control forces that account for body compliance or on the addition of a proof-mass actuator to reduce structural vibrations. A half-car model that includes body compliance is used to evaluate the effects of these control strategies on the performance of the suspensions with two-state and continuously modulated dampers. The performances of the systems are evaluated in both the time and frequency domains. The effect of time delays in the process of actuating the adjustable dampers is investigated. Significant reductions of structural vibrations are observed when the nodes of body beaming modes are a sufficient distance away from the suspension mounting points, and the time delays in the control system are negligible. The results deteriorate markedly when two-state dampers are used instead of continuously variable dampers or when a time delay in excess of 5 ms is present in the control loop. When the preference in suspension design shifts toward road holding it becomes increasingly difficult to improve the vehicle structural response without sacrificing other aspects of performance.

A novel nonlinear sliding mode controller has recently been developed for direct acting proportional solenoid valves. This paper presents a comparison between the valve performance using this controller, and that obtained using two alternative control strategies; state feedback and PID control. Each controller is described in turn, and experimental step response results are presented to demonstrate the validity of each strategy. These results are compared on the basis of response time, overshoot, and steady-state error. The time taken to design each controller, and the required level of knowledge of the valve dynamics, are also assessed. The ability of each controller to reject flow reaction forces is evaluated by observing the changes in the step response when oil is passed through the valve. The results demonstrate that the sliding mode controller results in a faster, more robust closed-loop response. In addition, only minimal knowledge of the valve dynamics is required in order to design the controller.

An integrated time domain state space identification technique for structural systems is presented. This technique integrates the Observability Range Space Extraction identification algorithm, Balanced Realization model reduction algorithm, and Least Square model updating algorithm to generate low order and highly accurate state space models for structural systems based upon time domain data. The algorithms are integrated in such a manner that the Observability Range Space Extraction identification algorithm is used to generate an initial overparameterized state space model and then the Balanced Realization model reduction and Least Square model updating algorithms are used to iteratively reduce and update the model to achieve minimum prediction errors in time domain. We shall present the Observability Range Space Extraction identification algorithm and the Least Square model updating algorithm and discuss the integrated identification technique. The MIT Middeck Active Control Experiment (MACE) is used as an application example. MACE is an active structure control experiment to be conducted in the Space Shuttle middeck. Results of ground experiments using this technique will be discussed.

A correlation equation is established between open-loop test data and the desired closed-loop system characteristics permitting control system synthesis to be done on the basis of a numerical approach using experimental data. The method is applicable when the system is linear-time-invariant and open-loop stable. The major merits of the algorithm are two-fold: 1) Arbitrary placement of the closed-loop system equation is possible, and 2) explicit knowledge of an open-loop system model is not needed for the controller synthesis.

Model-based monitoring systems based on state observer theory are attractive for machine monitoring because practical, inexpensive, and reliable sensors can be located remote to the signal(s) of interest. Then, a model of the machine plus an estimation algorithm are utilized to convert the output of the remote sensors to signals representing the desired local behavior. While this type of monitoring system has shown much promise in the laboratory, it has not been widely accepted by industry because, in practice, these systems often have poor performance with respect to accuracy, bandwidth, reliability (false alarms), and robustness. In this paper, the limitations of the deterministic state observer are investigated quantitatively from the machine monitoring viewpoint. The limitations in the transient and steady-state observer performance are quantified based on the estimation error bounds, and from these error bounds, performance indices are selected. Then, based on the relationships between the indices, a main index is determined in order to represent the overall observer performance. The index is the condition number of the observer eigenvectors in [L.sub.2] norm. It is shown that observers with small condition numbers are guaranteed to have small error bounds. This index can be utilized as a quality condition for any linear observer regardless of how it is designed as well as form the basis for an observer design methodology for high performance observer-based monitoring systems.

All real-world control systems have saturation nonlinearity in final control elements (including actuators). When controllers involve integral action, reset windup can cause instability as well as make system performance unsatisfactory. Based on the describing function method and the generalized Popov criterion, this paper presents analysis of the global stability of a control system having a saturating second-order plant, both with and without using a deadbeat limiting scheme to constrain its controller output. The improvement of system performance by incorporating the anti-windup feature in the controller is illustrated by computer simulations.

The fundamental concept of feedback to control dynamic systems has played a major role in many areas of engineering. Increases in complexity and more stringent requirements have introduced new challenges for control systems. This paper presents an introduction to and appreciation for intelligent control systems, their application areas, and justifies their need. Specific problem related to automated human comfort control is discussed. Some analytical derivations related to neural networks and fuzzy optimal control as elements of proposed intelligent control systems, along with experimental results, are presented. A brief glossary of common terminology used in this area is included.

In this essay, on the observance of the 50th anniversary of the founding of ASME's Dynamic Systems and Control Division, I try to connect the technology of control to the way in which control practitioners think. Despite some tension between the conclusions implied in the introductory paragraphs and conclusions drawn later in the essay, I have left them to stand in their original form to emphasize tensions in control thinking, for which the source might not be apparent. The opinions expressed here are strictly my own, but I must acknowledge the creative proddings of my colleagues in getting these thoughts recorded at all.

In this paper, a generalized design procedure for sliding mode control of nonlinear mechanical systems is proposed. The design approach combines the essential idea of the block control principle, utilizing some of the components of the state vector as a virtual control, with the basic concept of zero dynamics. For mechanical systems governed by a set of interconnected second-order equations, the block control principle cannot be directly applied. To facilitate the controller design, we assume that control systems can be transformed into a regular form consisting of second-order equations. The proposed design approach consists of reducing the original plant into the regular form, constructing a switching manifold, and enforcing sliding mode in the manifold such that the reduced order system in sliding mode has desired dynamics. Stabilization of the mechanical system with unstable zero dynamics is taken into consideration. It is shown that the approach has the advantage of decomposing the original problem into subproblems of lower dimensions, and each of them can be handled independently. As an example, control of a rotational inverted pendulum system is examined. The performance of the proposed approach is validated by both numerical and experimental results. [S0022-0434(00)01601-4] Keywords: Block Control Principle, Regular Form, Mechanical Systems, Sliding Mode Control, Rotational Inverted Pendulum, Unstable Zero Dynamics

Efficient design of high performance automatic control systems is extremely important for high technology systems. To get the best hardware cost-to-performance ratio, it is desirable to design a controller that takes full advantage of actuator capabilities, but this can lead to nonlinear behavior due to actuator saturation. The saturation nonlinearities in the system may have severe effects on system performance due to, for example, integrator windup. In this paper, a new design method is presented based on Lyapunov stability theory. By incorporating the actuator constraints directly in the design method, better utilization of the available control effort can be ensured in achieving desired system behavior. [S0022-0434(00)01801-3]