A discussion of identification methods employed in process control applications is carried out. The identification methods discussed range from explicit modelling techniques based on the relay experiment and the Phase-Locked Loop methods of nonparametric system identification, through to the implicit modelling techniques of subspace identification and the model-free methods used in Iterative Feedback Tuning. For a given range of gain and phase margins, graphical methods are developed that show the viable gain margin and phase margin design pairings that are achievable by the use of a PI controller as the compensation element in a closed loop control system. Two further graphical methods that allow the parameters of a PID controller to be determined such that gain and phase margin design specifications can be met are discussed. Iterative tuning methods that allow the design of PI controllers to meet gain and phase margin specifications are developed. An extension of the iterative tuning method that allows the design of PI controllers to meet maximum sensitivity and phase margin design specifications is also discussed. The Phase-Locked Loop (PLL) method of system identification is used to carry out the closed loop identification and tuning of cascade connected control systems. The closed loop identification of multivariable systems using the PLL method of system identification and the design of a decentralised control system based on an extension to the exact gain and phase margin design method is discussed. The Iterative Feedback Tuning (IFT) method of restricted structure controller design is discussed. A new method, Controller Parameter Cycling (CPC), is introduced. The CPC method of controller tuning allows the determination of both the cost function gradient and Hessian from experiments that are carried out on the closed loop system. Thus, improved numerical techniques can be used by the CPC method over those employed in the IFT method.

SINCE their invention, optical tweezers have found a host of applications, primarily as micro- manipulation tools and sensitive force transducers. The development of techniques such as holographic optical tweezers has enabled the manipulation of multiple particles in three dimensions. Recent advances in computation power and display technologies have afforded the opportunity to explore applications of real-time manipulation and particle tracking, utilising closed-loop feedback control, the principle aim of this work. We begin by investigating the use of holographic optical tweezers as an autonomous micro- fabrication device, to construct three dimensional colloidal crystals. We develop a bespoke microfluidic construction environment, and demonstrate tracking and control algorithms to iden- tify, capture and manipulate microspheres into required arrangements. Our algorithm calculates the paths of particles from any desired initial to final configurations, and avoids inter-particle collisions, and the undiffracted beam. The development of multiple trap systems has also increased interest in the trapping and tracking properties of lower symmetry structures. In this light, we investigate the behaviour of multiply trapped silica micro-rods, and demonstrate real-time tracking in two dimensions. The precision of our method is estimated, and the translational and rotational stiffness coefficients are evaluated using thermal motion analysis and Stokes' drag. We measure the variation of these stiffness coefficients relative to the displacement of the traps from the ends of the micro-rods, and find good agreement with theory. We go on to use our micro-rod probes to image the surface of an oil droplet in a manner analogous to scanning probe microscopy, with closed-loop feedback control of the micro-rod's position. As. the resolution of our surface images is limited by the tracking accuracy of the micro-rods, we investigate the imaging capability of another form of high aspect-ratio probe - a cigar shaped, silica shelled form of Diatom algae. This probe is held using two optical traps centered at least lOμm from its tip, enabling highly curved and strongly scattering samples to be imaged. We demonstrate the advantages of this technique by imaging the surface of the soft alga Pseudopediastrum, while it is alive and unadhered to the surface. The resolution is currently equivalent to confocal microscopy, but as it is not diffraction limited, there is scope for significant improvement by reducing the tip diameter and limiting the thermal motion of the probe. Motivated by improving our imaging technique, we further investigate the degree of control that can be exercised over our Diatom probe. By position clamping translational and rotational modes in different ways, we are able to dramatically improve the position resolution, with no reduction in force sensitivity. We also demonstrate control over rotational-translational coupling, and exhibit a mechanism whereby the average centre of rotation of our probe can be displaced away from its centre, a feature that could potentially be used to damp existing couplings within the motion of more complex optically trapped structures. Finally, we explore three dimensional tracking of our Diatom probes using stereo-microscopy. The full five degree of freedom stiffness matrix is used to calculate forces and torques exerted at the probe tip. Together, we hope the techniques demonstrated in this thesis. represent a step towards a novel and flexible form of all optical scanning probe microscopy.

No description available.

By considering a non-singular performance cost functional, observer backstepping designs and adaptive observer backstepping designs are compared to high-gain observer designs for an output feedback system and a parametric output feedback system. For the output feedback system, if the initial error between the initial condition of the state and the initial condition of the observer is large, the high-gain observer design has better performance than the observer backstepping design. Whilst, for the parametric output feedback system, if the a-priori estimate for the bound of the uncertain parameter is conservative, the adaptive observer backstepping design has better performance than the high-gain observer design. In the sense of gap metric robustness, by a backstepping procedure, a robust state feedback controller is developed for the nominal plant in strick-feedback form. For the closed-loop, the controller achieves gain-function stability, and stability if the initial condition is zero. By the gap metric robustness theory, the controller achieves robustness to plant perturbations which are small in gap sense. In this way, it is shown that for any perturbed plant the controller stabilizes the closed-loop in the presence of input and measurement disturbances if the gap metric distance between the nominal and perturbed plant is less than a computable constant. For output feedback control, a nominal plant in output-feedback form is considered, and the observer backstepping procedure is amended to design a robust controller and an observer in the presence of input and measurement disturbances. The closed-loop is shown to be gain-function stable, and stable if the initial condition is zero. If the nonlinearities are only locally Lipschitz continuous, the results are only local to input and measurement disturbances; if the nonlinearities are globally Lipschitz continuous, then results are global to input and measurement disturbances. By gap metric robustness theory, if the initial condition is zero the controller is shown to be robust to plant perturbations in a gap metric sense. As an application, the theory is applied to a system with time delay, and it is shown that if the time delay is suitably small, the controller is able to achieve stability of the closed-loop. To investigate the robustness of high-gain designs to loop disturbances and plant perturbations, a restricted class of nonlinear nominal plant in normal form are considered. An amended high-gain observer control design is shown to be robust to loop disturbances and has a non-zero plant perturbation margin, which is independent of the high-gain factor.

No description available.

The closed-loop control of processes over networks has in recent years become an increasingly popular research topic. This is a very viable solution for a wide variety of applications due to the rapid developments in communication network technologies and the widespread expansion of network devices and users. The convergence of communication networks technologies and advanced control methods do have a great potential to replace traditional control systems. The research programme presented in this thesis led to a development of networked predictive control algorithms over wired local area networks, general packet radio service wireless networks and wireless local area networks. Since the network is taken as a part of a control system, the network-induced time delay and data dropout are unavoidable. How to compensate for these issues is the main challenge in designing control methodologies for networked control systems. Five solutions were presented in this thesis to address these problems and were termed as recursive predictive control method I, inner loop predictive control method, outer loop predictive control method, modified generalised predictive control method and recursive predictive control method II. Irrespective of the different implementations of the networked control methods used, there is a common structure for each method which consists of a predictive control generator, a network delay compensator, a buffer and a plant output predictor. The predictive control generator and network delay compensator were used to compensate for the network delay and data dropout in the forward channel. The network delay and data dropout in the feedback channel was compensated for by using the plant output predictor, buffer and network delay compensator. The relationship between the sampling rate, packet size, network delay and data dropout were examined by using a round trip time delay method. Two network delay measurement methods were also presented and analysed in this thesis. The results of the real-time measurement of the network delay were used in an offline simulation. A networked servo system was built to test the system performance for an approximately linear, open-loop stable system and a networked inverted pendulum system was used to illustrate the system performance for an open-loop unstable system. The stability of each method was also considered. In order to simplify the software development, the Matlab/Simulink/Real-time workshop integrated development suit was used in the practical control system. The simulation block diagram in the Simulink environment was translated to the standard C language by using the real-time workshop. The ARMLINUX-GCC 3.4.4 was used to compile the generated C language file into the executable file running on an embedded board. In order to monitor the status of the control system and change the parameters of the controller, a network-based supervisory program was also developed using Microsoft Visual C++ 6.0.

Η παρούσα διδακτορική διατριβή στοχεύει στην μελέτη και ανάλυση μεταβλητών συστημάτων με απώτερο σκοπό την ανάπτυξη αλγορίθμων στο χώρο της αναγνώρισης συστημάτων, πρόβλεψης εξόδου αυτών, και δημιουργίας προσαρμοστικών ελεγκτών που θα επιδεικνύουν σθεναρότητα απέναντι στις μεταβολές των υπό μελέτη συστημάτων. Η μεταβολή στα συστήματα αυτά προκύπτει κυρίως από την εισαγωγή τυχαίων χρονικών καθυστερήσεων στην είσοδο και στην έξοδο αυτών. Οι καθυστερήσεις αυτές, είναι δυνατόν να είναι σταθερές ή μεταβαλλόμενες, γνωστές ή άγνωστες, ντετερμινιστικές ή στοχαστικές. Σαν τελικό αποτέλεσμα οι εισαγόμενες χρονοκαθυστερήσεις είναι δυνατόν να αλλάξουν την συμπεριφορά του συστήματος οδηγώντας αυτό στην αστάθεια. Στην παρούσα διδακτορική διατριβή προτείνονται μέθοδοι μοντελοποίησης αυτών των χρονοκαθυστερήσεων σε συνδυασμό με τους αλγορίθμους αναγνώρισης και πρόβλεψης εξόδου συστημάτων υποκείμενων σε αυτές τις χρονικές καθυστερήσεις. Επιπροσθέτως παρατίθενται πρότυπες και κατάλληλα διαμορφωμένες δομές προσαρμοστικού ελέγχου και μελέτης της ευστάθειας αυτών των συστημάτων. / The aim of this dissertation is the study and analysis of varying systems, as also the development of algorithms in the field of: a) system identification, b) system prediction, and c) adaptive control that will be able to be robust to the variations of the systems under study. These variations in these systems are induced mainly from the insertion of time delays in the input and output of those systems. These delays can be constant, or varying, known or unknown, deterministic or stochastic. As a final result these time delays can alter the behavior and the performance of the system while driving it to instability. In this dissertation new algorithms are proposed for the modeling of these time delays in conjunction with the algorithms for the identification and output prediction of systems with time delays. Additionally new algorithms of adaptive control and stability analysis of the controlled systems are proposed.

No description available.

With the advent and development of modern information technology, such as the Internet, the difficulty in transmitting data has been reduced significantly. This makes it easier for entities to share their experience to a larger extent than before. In this thesis, we study the design and analysis of feedback mechanisms, which are the information systems that enable entities to learn information from others' experience. We provide a framework for feedback mechanisms. We first provide an abstract model of a feedback mechanism which defines the scope of our concept and identifies the necessary components of a feedback mechanism. We then provide a framework for feedback mechanisms. This provides a global and systematic view of feedback mechanisms. We also use our model and framework to decompose and analyse several existing feedback mechanisms. We propose an electronic marketplace which can be used for trading online services such as computational resources and digital storage. This marketplace incorporates a dispute prevention and resolution mechanism that is explicitly designed to encourage the good conduct of marketplace users, as well as providing important security features and being cost-effective. We also show how to incorporate the marketplace into Grid computing for exchanging computational resources. We propose a novel feedback mechanism for electronic marketplaces. In this setting, the role of feedback is no longer a “shadow of the future”, but a “shadow of the present”. In other words, feedback directly impacts on the seller's payoff for the current transaction instead of future transactions. This changes the fundamental functionality of feedback, which solves many inherent problems of reputation systems that are commonly applied in electronic marketplaces. We provide a novel announcement scheme for vehicular ad-hoc networks (VANETs) based on a reputation system in order to evaluate message reliability. This scheme features robustness against adversaries, efficiency and fault tolerance to temporary unavailability of the central server.

Networked predictive control is a new research method for Networked Control Systems (NCS), which is able to handle network-induced problems such as time-delay, data dropouts, packets disorders, etc. while stabilizing the closed-loop system. This work is an extension and complement of networked predictive control methodology. There is always present model uncertainties or physical nonlinearity in the process of NCS. Therefore, it makes the study of the robust control of NCS and that of networked nonlinear control system (NNCS) considerably important. This work studied the following three problems: the robust control of networked predictive linear control systems, the control scheme for networked nonlinear control systems (NNCS) and the robust control of NNCS. The emphasis is on stability analysis and the design of robust control. This work adapted the two control schemes, namely, the time-driven and the event driven predictive controller for the implementation of NCS. It studied networked linear control systems and networked nonlinear control systems. Firstly, time-driven predictive controller is used to compensate for the networked-induced problems of a class of networked linear control systems while robustly stabilizing the closed-loop system. Secondly, event-driven predictive controller is applied to networked linear control system and NNCS and the work goes on to solve the robust control problem. The event-driven predictive controller brings great benefits to NCS implementation: it makes the synchronization of the clocks of the process and the controller unnecessary and it avoids measuring the exact values of the individual components of the network induced time-delay. This work developed the theory of stability analysis and robust synthesis of NCS and NNCS. The robust stability analysis and robust synthesis of a range of different system configurations have been thoroughly studied. A series of methods have been developed to handle the stability analysis and controller design for NCS and NNCS. The stability of the closed-loop of NCS has been studied by transforming it into that of a corresponding augmented system. It has been proved that if some equality conditions are satisfied then the closed-loop of NCS is stable for an upper-bounded random time delay and data dropouts. The equality conditions can be incorporated into a sub-optimal problem. Solving the sub-optimal problem gives the controller parameters and thus enables the synthesis of NCS. To simplify the calculation of solving the controller parameters, this thesis developed the relationship between networked nonlinear control system and a class of uncertain linear feedback control system. It proves that the controller parameters of some types of networked control system can be equivalently derived from the robust control of a class of uncertain linear feedback control system. The methods developed in this thesis for control design and robustness analysis have been validated by simulations or experiments.