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Control Theory and Applications, IEE Proceedings -

Issue 2 • Date Mar 1996

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Displaying Results 1 - 13 of 13
  • Analysis of stabilised output error methods

    Page(s): 209 - 216
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    In the paper, analysis of stabilised output-error methods (SOEMs) for parameter estimation of unstable aircraft is presented. These methods overcome the numerical difficulties encountered in parameter estimation of unstable systems by utilising measured states. The methods, along with the output error method and the equation error method, are briefly described for the sake of comparison. However, the main idea of the paper is to present asymptotic analysis of the SOEM. The results of application of SOEMs to simulated data of an unstable/augmented aircraft are presented View full abstract»

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  • Real-time synchronisation of multiaxis high-speed machines, from SFC specification to Petri net verification

    Page(s): 164 - 170
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    The paper considers the co-ordination and control of flexible, independently driven, multiaxis, high-speed machinery in which mechanical complexity has been exchanged for sophistication in control. The control of such machines is a hybrid control problem and the paper addresses the specification and design of the discrete event part of the controller. It focuses on the design of synchronisation logic for the event-driven real-time co-ordination and synchronisation of the machine. It proposes a method for inferring system behaviour and performing formal verification of machine systems specified using a subset of the industry standard IEC 1131 sequential function charts (SFC). It shows how an SFC-based design can be translated to an equivalent Petri net model, thereby allowing Petri net theory and analysis techniques to probe its behaviour and verify its functionality. The approach is demonstrated by considering the design of synchronisation logic for a prototype six-axis high-speed packaging machine which incorporates both time-critical and system-critical functions View full abstract»

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  • Iterative learning control for discrete-time systems with exponential rate of convergence

    Page(s): 217 - 224
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    An algorithm for iterative learning control is proposed based on an optimisation principle used by other authors to derive gradient-type algorithms. The new algorithm is a descent algorithm and has potential benefits which include realisation in terms of Riccati feedback and feedforward components. This realisation also has the advantage of implicitly ensuring automatic step-size selection and hence guaranteeing convergence without the need for empirical choice of parameters. The algorithm achieves a geometric rate of convergence for invertible plants. One important feature of the proposed algorithm is the dependence of the speed of convergence on weight parameters appearing in the norms of the signals chosen for the optimisation problem View full abstract»

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  • Integrated process improvement in design and manufacture using a systems approach

    Page(s): 171 - 185
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1684 KB)  

    The paper describes a soft-systems method for the capture, representation and analysis of process knowledge as a platform for process improvement in capital goods manufacture. It is based on the formative results of some collaborative work, funded by two EPSRC grants, between manufacturing companies, including an MNE and an SME. The paper reports on: the problem addressed by the collaborative programme; the approach taken; the results obtained thus far; and the response of the problem-owners to those results and to the prospects of future work. It proposes specific deliverables based on formative results which may enable strategists in certain manufacturing enterprises to begin to design and implement process improvement programmes based on a system approach. The paper describes a novel form of systemic diagram (systemigram) which is used as the means to capture process understanding. Process models, represented by systemigrams, have proved useful to multifunction teams charged with the responsibility of implementing concurrent engineering philosophies by their companies who are seeking significant reductions in product cycle time View full abstract»

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  • Design and analysis of neural/fuzzy variable structural PID control systems

    Page(s): 200 - 208
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (796 KB)  

    The paper describes the design method of a neural/fuzzy variable structural proportional-integral-derivative (neural/fuzzy VSPID) control system. The neural/fuzzy VSPID controller has a structure similar to that of the conventional PID. In this controller, the PD mode is used in the case of large errors to speed up response, whereas the PI mode is applied for small error conditions to eliminate the steady-state offset. A sigmoidal-like neuron is employed as a preassigned algorithm of the law of structural change. Meanwhile, the controller parameters would be changed according to local conditions. Bounded neural networks or bounded fuzzy logic systems are used for constructing the nonlinear relationship between the PID controller parameters and local operating control conditions. Flexible changes of controller modes and resilient controller parameters of the neural/fuzzy VSPID during the transient could thereby solve the typical conflict in nature between steady-state error and dynamic responsiveness. A neutralisation process is used to demonstrate the applicability of such a controller for controlling highly nonlinear processes View full abstract»

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  • Design of a distributed software architecture for an intelligent planning system

    Page(s): 125 - 131
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The paper describes the design of a distributed software architecture for an intelligent planning system based on a process model of cognitive systems (PMCS). PMCS is described in terms of its problem-solving behaviour and structure, and is illustrated through a simple case study in robotics. In the PMCS model, autonomous knowledge sources, each implementing a component of the system's functionality, co-operate by message-passing in order to maintain a distributed model of the system's environment and to synthesise decisions based on the model. Simulation tools developed at the University of Westminster for the rapid prototyping of parallel systems have been used to simulate the software architecture based on PMCS. Simulation results for the planning case study are presented in order to demonstrate the effectiveness of PMCS in solving planning problems in a distributed manner View full abstract»

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  • Guaranteed rates of convergence of a class of PD controllers for trajectory tracking problems of robotic manipulators with dynamic uncertainties

    Page(s): 186 - 190
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The paper provides a better understanding of the behaviour of a class of simple proportional plus derivative (PD) controllers applied to robotic manipulators and to highlight some useful design criteria. The stability and robustness of PD controllers for trajectory tracking problems of robotic manipulators with dynamic uncertainties is investigated. Based on Lvapunov's second method it is shown that the composite velocity and position tracking error vector is guaranteed to exponentially converge from any initial condition to a closed ball, defined by its L2 norm being less than a certain threshold provided that the PD controller gains are chosen greater than a specific bound depending on the dynamic parameters, desired trajectories and levels of external disturbances. Moreover, the size of the ball can be made arbitrarily small by increasing the controller gains wherever appropriate and possible. As a result, both transient and steady-state performance of the simple PD controllers for trajectory tracking is assured View full abstract»

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  • Hybrid position/force control of a hydraulic underwater manipulator

    Page(s): 145 - 151
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    Current generation underwater remotely operated vehicles equipped with robotic manipulators are teleoperated and consequently place a large workload burden on the human operator. A greater degree of automation could improve the efficiency and accuracy with which underwater tasks are carried out. A hybrid position/force control scheme is proposed to control an industrial hydraulic underwater manipulator, modified to include a force/torque sensor, for tasks such as weld inspection. Modelling of the hydraulic actuation mechanism is performed and the resulting model is easily incorporated in the standard robot dynamic equations. An experimental facility using a PC-based digital signal processor is used to produce practical hybrid position/force results for a Slingsby TA9 hydraulic arm. Results are presented for the manipulator sliding across a planar surface in different parts of its work envelope. Good general agreement is obtained between the simulated and practical systems. A fixed gain control strategy is shown to work well, provided it is tuned for the arm configuration when sliding occurs View full abstract»

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  • Process performance monitoring using multivariate statistical process control

    Page(s): 132 - 144
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1316 KB)  

    Statistical process control (SPC) is a tool for achieving and maintaining product quality. Classical univariate statistical techniques have focused on the monitoring of one quality variable at a time and are not appropriate for analysing process data where variables exhibit collinear behaviour. Minimal information is derived on the interactions between variables which are so important in complex manufacturing processes. These limitations are addressed through the application of multivariate statistical process control (MSPC). The bases of MSPC are the projection techniques of principal components analysis and projection to latent structures. The philosophy behind these approaches is to reduce the dimensionality of the problem by forming a new set of latent variables to obtain an enhanced understanding of the process behaviour. If the variables are highly correlated, then the process can be defined in terms of a reduced set of latent variables, which are a linear combination of the original variables. The authors present an overview of multivariate statistical process control and its nonlinear extension for process monitoring. The power of the methodology is demonstrated by application to two industrial processes View full abstract»

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  • Temporal multiresolution analysis for a quantitative/qualitative interpretation of complex dynamic processes

    Page(s): 191 - 199
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (972 KB)  

    The paper describes a qualitative reasoning approach aimed at representing and interpreting a dynamic process evolution. The problem specifically addressed is the presence of multiple time scales in complex systems. Definitions of a temporal granularity as well as related concepts are provided. For the representation of a single process, a segmentation and abstraction method is described. The identification of dynamic features at any level of abstraction then supplies a help to better choose relevant sampling frequencies of the simulated process and helps in interpreting its outputs. An example is given for a complex crop model, whose interpretation is tested expert knowledge View full abstract»

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  • Control and integration techniques in a fully automated manufacturing cell for carbon composites

    Page(s): 159 - 163
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    The paper presents a fully automated robotic manufacturing cell for assembly of composite preforms for subsequent impregnation using resin transfer moulding techniques. Computerised component design data are used to derive all key manufacturing information for the preform assembly, from material roll to finished preform. Profile cutting, lay-up of plies, inspection and fixing are performed in the multiple-robot cell under central computer control. The operation technique used for each cell component is described along with the calibration techniques required between cell components and the arbitrary axis system of the CAD data. The advantages gained by CAD control of the cell have allowed methods for manufacturing preforms for 3-dimensional components to be developed, increasing the flexibility of the manufacturing system View full abstract»

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  • A toolbox for minimal state space model realisation

    Page(s): 152 - 158
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    A new Matlab toolbox based upon the observer-Kalman filter/eigensystem realisation algorithm is presented. The paper gives a brief overview of the development of the approach followed by a concise review of the relevant theory. After a description of the toolbox functionality, an illustrative example is used to explain its successful operation View full abstract»

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  • Anytime heuristic schedule repair in manufacturing industry

    Page(s): 114 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1116 KB)  

    Although optimal schedules may be produced, the conditions under which those schedules remain optimal are unlikely to last for long, given the highly dynamic nature of the factory and the complexity of the informal, short-lived objectives and constraints which arise in practice, together with the shifting market conditions and the prevailing goal of pleasing the customer. The paper describes a software package which has been developed in collaboration with an industrial partner to permit schedule repair in response to dynamic conditions, both under the initiative of the human scheduler and automatically. A number of schedule heuristics are described to illustrate the problem of removing stockouts, together with some principles for designing repair heuristics. The performance of the heuristics is compared and a simple deliberation algorithm is presented for selecting dynamically between the heuristics depending on the rate of progress towards the goal. The results of experiments on simulated data are presented and discussed View full abstract»

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