John T. Pearson

Active stability control strategies for a high speed bogie

Abstract This paper presents a comparison of control algorithms for actively stabilised wheelsets on high speed railway vehicles. Both intuitively derived classical strategies and modern optimal strategies are considered. Computer simulations are used to assess and compare the performance of the strategies in terms of their ability to provide stability across a range of operating conditions, for a range of parameter uncertainty and also in terms of their actuator requirements. Actuator models are also developed, not only to properly assess the impact of actuator dynamics on the active stability system performance, but also to further quantify and refine the actuator requirements needed to implement the system practically. The concept has been implemented practically on a full size vehicle and some preliminary experimental results are included. Although the paper concentrates upon stability control, some observations are included regarding the integration of steering controllers.

Control system studies of an active anti-roll bar tilt system for railway vehicles:

Abstract This paper describes a theoretical study of an active anti-roll bar tilt control system for a railway vehicle. It presents the rationale behind body tilting, the advantages and disadvantages associated with body tilting and the key tilt control system requirements. The paper also describes the control modelling process and presents some simulation results from control system studies. A number of competing control systems have been designed and analysed, including both classical and optimal control strategies. The performance of the control systems for a variety of curves is considered, as well as their response to track irregularities. The results show that all the strategies provide good tilting performance, the optimal control approach being marginally better.

Adaptive schemes for the active control of helicopter structural response

This paper describes a new method for the design of an adaptive controller for the reduction of vibration in helicopter structures. Two known approaches are described which can be used to implement an active vibration control system-a frequency domain controller or a time domain controller. Both strategies have a number of advantages and disadvantages, which are discussed in the paper. A new approach to the design of an adaptive controller for the reduction of helicopter vibration is described. This new technique is a hybrid time/frequency domain solution combining the advantages from both the time domain linear quadratic feedback controller and the frequency domain quasi-static controller. Both fixed gain and adaptive control designs have been implemented, and comparisons of the performance of the various control approaches to the problem of minimizing vibration in helicopter structures is made. The hybrid strategy has been studied extensively using computer simulations and its performance has been shown to equal that of the frequency domain approach, providing up to 90 percent vibration reduction at the blade-passing frequency. Results from experimental validation on a helicopter airframe test rig confirm the effectiveness of the strategy. >

Modelling of High Redundancy Actuation Utilising Multiple Moving Coil Actuators

This paper presents the modelling of a moving coil actuator for use as an element in a High Redundancy Actuator (HRA). A single element model is derived from first principles and verified using experimental data. This model is subsequently used to describe an approach to deriving models of multi-element HRAs and determine the effect of a variety of faults, chosen to be appropriate for the electro-magnetic technology, on the behaviour of multi-element assemblies.

MAGLEV suspensions - A sensor optimisation framework

In this paper, a systematic framework for optimised sensor configurations is implemented via Hinfin loop shaping procedure. The optimisation framework, gives the sensor sets that satisfy predefined user criteria and the preset constraints required for the MAGnetic LEVitated suspension performance via evolutionary algorithms. The scheme is assessed via appropriate simulations for its efficacy.

Failure Modes and Probabilities of a High Redundancy Actuator

A high redundancy actuator (HRA) is composed of a high number of actuation elements, increasing both the travel and the force over the power of an individual element. This provides inherent fault tolerance, because when an element fails, the capabilities of the actuator may be reduced, but it does not become dysfunctional. This paper analyses the likelihood of different reductions in capabilities, based on the reliability of the actuation elements used. The result is a probability distribution that quantifies the capability of the high redundancy actuator. Together with the required capabilities, this determines the fault tolerance of the actuator.

Control Design for a Pneumatically Actuated Parallel Link Manipulator

This paper is concerned with the practical application of control to a pneumatically actuated Stewart-Gough platform with 6 Degrees of Freedom (DOF). Two control approaches for motion control of the platform are presented using a classical control technique and a modern control technique. The control schemes experimental results are compared showing that either approach is suitable but with LQG giving slightly better performance.

APPLICATION OF DIAGNOSTIC TECHNIQUES TO AN EXPERIMENTAL AIRCRAFT FUEL RIG

Abstract An important issue for Aerospace and Defence Systems providers is how to reduce the risks associated with installing a new Fault Detection Tool (FDT) on a system. It is highly desirable that some degree of assessment, selection and validation is carried out before the FDT is integrated with the system. This paper describes the initial phases of a project to investigate the processes behind the assessment and validation using an Experimental Aircraft Fuel Rig (referred to as the Advanced Diagnostic Test-bed ADT). This paper also presents results from preliminary verification and validation work that has been used on a mathematical model of the ADT, and also some results from some initial diagnostic technique assessment that has been performed using real experimental data from the ADT and simulated data from mathematical models.

Investigation of Kalman filter divergence using robust stability techniques [combat aircraft tracking/navigation system]

Presents an overview of a preliminary study into the issues associated with Kalman filter stability. Future advanced combat aircraft will require further levels of system integration it is believed that Kalman filters will play a key role in this increased integration and consequently their performance and robustness are of interest. The paper applies the /spl mu/-analysis robust stability technique to a two dimensional tracking/navigation system which requires a nonlinear or extended Kalman filter. Results show that the robust stability margins provide an indication of poor robustness, under some circumstances, but further work is required to predict instability or divergence in the extended Kalman filter.

A Petri Net Approach to Fault Verification in Phased Mission Systems using the Standard Deviation Technique

Health management systems are now standard aspects of complex systems. They monitor the behaviour of components and sub-systems and in the event of unexpected system behaviour diagnose faults that have occurred. Although this process should reduce system downtime it is known that health management systems can generate false faults that do not represent the actual state of the system and cause resources to be wasted. The authors propose a process to address this issue in which Petri nets are used to model complex systems. Faults reported on the system are simulated in the Petri net model to predict the resultant system behaviour. This behaviour is then compared to that from the actual system. Using the standard deviation technique the similarity of the system variables is assessed and the validity of the fault determined. The process has been automated and is tested through application to an experimental rig representing an aircraft fuel system. The success of the process to verify genuine faults and identify false faults in a multi-phase mission is demonstrated. A technique is also presented that is specific to tank leaks where depending on the location and size of the leak, the resulting symptoms will vary.