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The flywheel inverted pendulum is an underactuated mechanical system with a nonlinear model but admitting a linear approximation around the unstable equilibrium point in the upper position. Although underactuated systems usually require nonlinear controllers, the easy tuning and understanding of linear controllers make them more attractive for designers and final users. In a recent paper, a simple PID controller was proposed by the authors, leading to an internally unstable controlled plant. To achieve global stability, two options are developed here: first by introducing an internal stabilizing controller and second by replacing the PID controller by an observer-based state feedback control. Simulation and experimental results show the effectiveness of the design. [ABSTRACT FROM AUTHOR]

Highlights: [•] A Smith predictor based prediction scheme with a tuning parameter is proposed. [•] The control design is based on the delay-free model of the plant. [•] Uncertain unstable plants with large time delay are considered. [•] A tradeoff between disturbance performance and robustness can be achieved. [Copyright &y& Elsevier]

Abstract: This paper deals with the control of single-input–single-output linear time-delayed systems, when there are different delays in the output/input transfer function. The process can be disturbed and unstable. A new control structure is proposed, solving the problem in several steps. First, by using a stable predictor/observer the plant is stabilized, regardless the delays. On the stable plant, the multidelay plant model is considered as a single delay plant with additional disturbances. The problem of disturbance rejection is solved by using a disturbance observer approach. Finally, output tracking is achieved by a two degrees of freedom controller. [Copyright &y& Elsevier]

SUMMARY This paper deals with the design of optimal control for unstable time-delayed systems. Delays can be considered either at the output (measurement delays), the input (actuator delays) or both including transmission delays. The system could be unstable. The cost index weights the system state and the control input. Fully state accessibility is assumed, but the option of output dynamic feedback through an observer can be considered. This result can be split into a predictor followed by a state estimator if it is the case and state feedback. The main result is a general control law including a state feedback plus a feedforward of the delayed input. The control design technique is applied to control the pitch angle of a simulated (simplified) aircraft model. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a Non-Uniform Predictor-Observer (NUPO) based control approach in order to deal with two of the main problems related to Networked Control Systems (NCS) or Sensor Networks (SN): time-varying delays and packet loss. In addition, if these delays are longer than the sampling period, the packet disordering phenomenon can appear. Due to these issues, a (scarce) nonuniform, delayed measurement signal could be received by the controller. But including the NUPO proposal in the control system, the delay will be compensated by the prediction stage, and the nonavailable data will be reconstructed by the observer stage. So, a delay-free, uniformly sampled controller design can be adopted. To ensure stability, the predictor must satisfy a feasibility problem based on a time-varying delay-dependent condition expressed in terms of Linear Matrix Inequalities (LMI). Some aspects like the relation between network delay and robustness/performance trade-off are empirically studied. A simulation example shows the benefits (robustness and control performance improvement) of the NUPO approach by comparison to another similar proposal. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the problem of controlling MIMO plants where the pattern of measurements sampling and control actions delivering is not regular is tackled. Multirate control, time delay systems, missing data environments as well as limited computing and communication resources are on the grounds of these problems. There is an extensive literature on these topics. Different models are reviewed and, from the control viewpoint, model-based control design techniques are reported and new algorithms are proposed. Among the main challenges are the achievement of good performance and the avoidance of intersampling ripple. Both issues are considered and some results are discussed. [Copyright &y& Elsevier]

Abstract: In this paper a new dead-time-compensator to deal with unstable time delay systems is presented. The result is an extension to multiple-input multiple-output systems with multiple and different time delays of a previous result already reported for single-input single-output systems. There are two key issues: the system instability and the presence of different time delays in each signal channel. The proposed approach is developed in three steps. First, a non-delayed output plant is predicted. This predictor is a stable dead-time-compensator coping with multiple and arbitrary delays in all the signal channels. Then, a stabilizer controller is easily designed for the resulting non-delayed plant. For this stabilized plant, the control performance is improved in order to achieve some output tracking and regulation requirements. The results are illustrated by two examples showing their applicability to unstable multiple-input multiple-output multi-delayed plants, which is the main novelty of the proposed approach. [Copyright &y& Elsevier]

Abstract: In order to reduce the control design problem for input/output long-delay systems, a stable predictor is presented in this paper. The predictor is stable for stable/unstable or minimum/non-minimum phase systems. Based on the predicted undelayed output, any available control design procedure can be applied to fulfil the control requirements, the delay remaining unchanged. Disturbance rejection and robustness may be enhanced based on the estimation error. The approach is shown to work in all considered cases and comparison with other methods, when available in the literature, is reported. [Copyright &y& Elsevier]

In many industrial control applications the control action updating can be faster than the output measurement, leading to multirate controllers. In this paper, some dual rate operations are used to model the controller as well as the controlled plant. The controller design is model-bused and depends on the input to be tracked. The controller is split into two parts acting at different sampling rates and its design is approached bused on the characteristics of each available sampling rate. The control target is to reach the similar performances to those the faster single rate controller would achieve. Model-based cancellation controllers are designed using this approach and promising results are obtained. [ABSTRACT FROM AUTHOR]

Good slow disturbances attenuation in a mold level control with stopper rod is very important for avoiding several product defects and keeping down casting interruptions. The aim of this work is to improve the accuracy of the diagnosis and compensation of an adaptive mold level control method for slow disturbances related to changes of stopper rod. The advantages offered by the architecture, called Adaptive-Network-based Fuzzy Inference System, were used for training a previous model. This allowed learning based on the process data from a steel cast case study, representing all intensity levels of valve erosion and clogging. The developed model has high accuracy in its functional relationship between two compact input variables and the compensation coefficient of the valve gain variations. The future implementation of this proposal will consider a combined training of the model, which would be very convenient for maintaining good accuracy in the Fuzzy Inference System using new data from the process. [ABSTRACT FROM AUTHOR]

There are many processes with multiple time-delays. These may appear in the direct path or in some feedback path. In this paper, a pre-compensator is designed in order to convert a multiple time-delays process to one with a single time-delay in the forward path. On this simpler model, any well-established approach to design the control for input/output time-delay plants can be applied. The proposed method is directly applicable to stable plants with multiple time-delays, including in the feedback path, and it can be extended to unstable plants with some constraints. Some numerical examples and case studies are provided to illustrate the application of the proposed algorithms. [ABSTRACT FROM AUTHOR]