Improving the performance of railway track-switching through the introduction of fault tolerance

In the future, the performance of the railway system must be improved to accommodate increasing passenger volumes and service quality demands. Track switches are a vital part of the rail infrastructure, enabling traffic to take different routes. All modern switch designs have evolved from a design first patented in 1832. However, switches present single points of failure, require frequent and costly maintenance interventions, and restrict network capacity. Fault tolerance is the practice of preventing subsystem faults propagating to whole-system failures. Existing switches are not considered fault tolerant. This thesis describes the development and potential performance of fault-tolerant railway track switching solutions. The work first presents a requirements definition and evaluation framework which can be used to select candidate designs from a range of novel switching solutions. A candidate design with the potential to exceed the performance of existing designs is selected. This design is then modelled to ascertain its practical feasibility alongside potential reliability, availability, maintainability and capacity performance. The design and construction of a laboratory scale demonstrator of the design is described. The modelling results show that the performance of the fault tolerant design may exceed that of traditional switches. Reliability and availability performance increases significantly, whilst capacity gains are present but more marginal without the associated relaxation of rules regarding junction control. However, the work also identifies significant areas of future work before such an approach could be adopted in practice

Detecting Impacts on a Representative Aerospace Structure: An Implementation with Tests

This is a conference paper.Collisions with aerial objects, e.g. bird strikes, pose a threat to aircraft in flight. In conventional aircraft, the pilot(s) would typically be aware of any significant collision through control response, noise, or visual indicators, and can fulfil the regulatory requirement of reporting the incident. In a UAV (Unmanned Aerial Vehicle), there is a requirement to automate these functions. The aim of the work detailed in this paper is to demonstrate that acoustic emission sensing equipment developed in the laboratory, and described in previous literature, can also be used to detect impacts on a large scale aerospace structure. The test structure for this work is a BAE Systems HERTI (High Endurance Rapid Technology Insertion) UAV. Simulated bird strike impacts are performed along the leading edge. Measurements are transmitted from sensors mounted on the wing to a processing system that deduces the location and energy of the impact by comparing the range of acoustic signatures. It is shown that the use of an array of 3 sensors enables repeatable detection and location of low energy impacts, demonstrating that acoustic detection of impacts is possible on a representative aerospace structure

Improving the reliability and availability of railway track switching by analysing historical failure data and introducing functionally redundant subsystems

This is an Open Access Article. It is published by Sage under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/Track switches are safety critical assets that not only provide flexibility to rail networks but also present single points of failure. Switch failures within dense-traffic passenger rail systems cause a disproportionate level of delay. Subsystem redundancy is one of a number of approaches, which can be used to ensure an appropriate safety integrity and/or operational reliability level, successfully adopted by, for example, the aeronautical and nuclear industries. This paper models the adoption of a functional redundancy approach to the functional subsystems of traditional railway track switching arrangements in order to evaluate the potential increase in the reliability and availability of switches. The paper makes three main contributions. First, 2P-Weibull failure distributions for each functional subsystem of each common category of points operating equipment are established using a timeline and iterative maximum likelihood estimation approach, based on almost 40,000 sampled failure events over 74,800 years of continuous operation. Second, these results are used as baselines in a reliability block diagram approach to model engineering fault tolerance, through subsystem redundancy, into existing switching systems. Third, the reliability block diagrams are used with a Monte-Carlo simulation approach in order to model the availability of redundantly engineered track switches over expected asset lifetimes. Results show a significant improvement in the reliability and availability of switches; unscheduled downtime reduces by an order of magnitude across all powered switch types, whilst significant increases in the whole-system reliability are demonstrated. Hence, switch designs utilising a functional redundancy approach are well worth further investigation. However, it is also established that as equipment failures are engineered out, switch reliability/availability can be seen to plateau as the dominant contributor to unreliability becomes human error

Model-based controller design for a lift-and-drop railway track switch actuator

Track switches are essential in order to enable railway vehicles to change routes however they are also the largest single cause of failure on the railway network. A new generation of switching concepts are emerging from projects like In2Rail, REPOINT and S-Code that promise to improve rail network performance through the use of new mechanisms, monitoring and control systems. This paper focusses on modelling and control of a lab-demonstrator from the REPOINT project. Unlike conventional track switch machines, this actuator needs closed loop feedback control. First, a detailed simulation model of the actuator is developed and validated against experimental results. Two model-based control designs are then developed and tested: a classical cascaded P/PI controller and a modern state feedback controller. The two controllers are compared and it is found that, whilst there are some performance differences, both meet the requirements for use in a redundantly actuated REPOINT switch

Dynamic analysis and performance of a Repoint track switch

This paper is closed access until 09 May 2020.Repoint is an alternative concept for the design of track switches developed at Loughborough University. The concept, based around a stub switch, offers several improvements over current designs. Through a novel locking arrangement, it allows parallel, multi-channel actuation and passive locking functions, providing a high degree of fault tolerance. The aim of the work presented in this paper is to evaluate the dynamic interaction forces due to the passage of rolling stock over the switch and, particularly, the area of the stub rail ends, in comparison to a conventional switch. Specific behaviour and load transfer conditions from one rail to the other at the joint are analysed, as well as long term wear conditions of the rails. These evaluations are undertaken by means of multi-body dynamic simulations, leading to design refinement of the stub rail ends and the identification of further research and development requirements in their design

Rethinking rail track switches for fault tolerance and enhanced performance

© 2016, © IMechE 2016. Railway track switches, commonly referred to as ‘turnouts’ or ‘points,’ are a necessary element of any rail network. However, they often prove to be performance-limiting elements of networks. A novel concept for rail track switching has been developed as part of a UK research project with substantial industrial input. The concept is currently at the demonstrator phase, with a scale (384 mm) gauge unit operational in a laboratory. Details of the novel arrangement and concept are provided herein. This concept is considered as an advance on the state of the art. This paper also presents the work that took place to develop the concept. Novel contributions include the establishment of a formal set of functional requirements for railway track switching solutions, and a demonstration that the current solutions do not fully meet these requirements. The novel design meets the set of functional requirements for track switching solutions, in addition to offering several features that the current designs are unable to offer, in particular to enable multi-channel actuation and rail locking, and provide a degree of fault tolerance. This paper describes the design and operation of this switching concept, from requirements capture and solution generation through to the construction of the laboratory demonstrator. The novel concept is contrasted with the design and operation of the ‘traditional’ switch design. Conclusions to the work show that the novel concept meets all the functional requirements whilst exceeding the capabilities of the existing designs in most non-functional requirement areas

Repoint Track Switch Wheel-Rail Mechanical Interface Analysis

Repoint is a new concept for track switching developed at Loughborough University. Through a novel locking arrangement it allows parallel, multi-channel actuation and pas-sive locking functions, providing a high degree of fault tolerance. The concept, based around a stub switch, offers several features that current designs are unable to achieve. The aim of the work presented in this paper is to evaluate the dynamic interaction forces due to the passage of rolling stock over the switch and, particularly, the area of the stub rail ends, in comparison to a conventional switch. Specific behaviour and load transfer conditions from one rail to the other at the joint are analysed, as well as long term wear conditions of the rails. These evaluations are undertaken by means of dynamic simulations, leading to design refinement of the stub rail ends