Longitudinal control for guided transport
The thesis describes a study of automatic driving in a guided transport system. Full scale practical experiments have been carried out with the co-operation of British Railways Research & Development Division. Considerable attention is paid to the problem of line capacity with a rigorous safety constraint and operational and engineering limitations. An understanding of vehicle interactions under discontinuous and continuous signalling systems is demonstrated, leading to an explanation of why the theoretical steady state plain line capacities are not realisable. This is extended to show the importance of the vehicle trajectory and how shaping the trajectory can minimise journey time, headway, energy consumption and other performance criteria, bearing in mind the inconsistency of these aims and demonstrating the trade-offs. Some theoretical work on generalised control systems is described and this demonstrates the need for a greater understanding of practical engineering constraints. Consequently, available literature on train performance has been studied and experiments carried out with an instrumented train. The results indicate an inadequate understanding of train behaviour in much that has previously been pUblished. A mathematical model of the test train has been formulated and with the help of the Mathematics Applications Section of British Rail, this has been simulated on the computer. It is evident that railway braking systems partictilarly those employing cast iron friction blocks,introduce significant control problems. The control system of the train is demonstrated to be non-linear and subject to severe stochastic disturbances of both environmental and system parameters. Instrumentation of the system is difficult and the report goes to some length to identify the fundamental limitations of measurement of the principal state variables. A complete single vehicle control system has been realised on the British Rail Test Line at Mickleover. It is anticipated that an engineered system would be microprocessor based and experience has been gained with Intel devices in the communications system, whilst a mini-computer system was considered more appropriate as a test bed for control principle development. The results of the performance evaluation and control tests at Mickleover give significant insight into the likelihood of realisation of some of the theoretical ideals developed in the earlier study. The report includes details of some of the authors more recent work with British Rail on a project to implement pilot scheme automatic train operation. The experimental work for this project has included the implementation of a simple automatic driver on a Motorola Microprocessor.