A model of a repoint track switch for control

Track switching provides necessary flexibility to a rail network, allowing vehicles to change routes when necessary. Track switches, however, have historically been prone to failure. To increase asset reliability, a concept for a novel design of switch has been developed which allows multi-channel actuation through a novel actuation and locking mechanism, under a project titled 'Repoint'. This paper describes a mathematical model of the operation a novel Repoint track switch. The model was derived from a first principles physical analysis of the Repoint concept design. The structure of the model mimics the physical structure of the design. Each physical component has an individual sub-model. The model has been used to estimate the actuator drive requirements for a case study mainline switch installation. It has been found that a Repoint track switch could be run from an existing UK signalling power supply. It is anticipated that this model will be used as the basis for a control system design activity for a technology demonstrator installation currently under construction

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

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

Extending maintenance intervals of track switches utilising multi-channel redundancy of actuation and sensing

A concept for a novel track switch arrangement has been developed at Loughborough University, which, through a novel locking arrangement, allows parallel, multi-channel actuation and locking functions for the first time. This switch has been developed as part of the REPOINT project, and is referred to as the REPOINT switch. Existing track switches generally use a single-channel actuator and lock, and undergo an intensive maintenance and inspection regime to ensure an acceptable level of reliability/availability. This paper demonstrates, through mathematical modelling with very conservative assumptions, that an increase in switch availability is possible alongside a corresponding decrease in ongoing maintenance intensity using the REPOINT multi-channel approach. The paper firstly introduces the theory behind the design of the REPOINT switch, using a switch with 2-out-of-3 redundant actuation and sensing channels as an example. An existing switch is analysed using real-world data as a benchmark. Availability is determined by the target time in which Maintenance Teams must have replaced any failed components, expressed herein as τ. Availability measures are obtained as functions of τ which show the range of possible switch availability against maintenance response times, for the given set of assumptions. The results show that for a REPOINT installation, gains in system availability are possible even when response times are set many times longer than current standards, indicating a significant reduction in ongoing maintenance cost

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

Design, construction and operation of a REPOINT laboratory demonstrator

The REPOINT project, led by Loughborough University, has been active since March 2011. It seeks to improve the reliability, safety and maintainability of track switching technology, with the aim of increasing network capacity and lowering operating costs. To do this, the project is exploring combining mature concepts from other industries such as fault tolerance, line-replaceable units and passively safe design, with novel mechanical arrangements, in order to bring about a step change in performance. One design, based around a stub-switch arrangement, has showed particular promise and is the currently the subject of three patent applications covering the novel mode of operation. A laboratory-scale demonstrator of all key subsystems is currently under construction, under funding from the FutureRailway.org team. This is integrated with test and monitoring equipment, alongside a rapid-prototyping control system. This first-generation design will be used to prove the concept of operation and to develop the associated control and monitoring technology. The goal of this paper is to provide an overview of the REPOINT project to date, and the design and operation of the proposed novel REPOINT design. This paper firstly introduces the REPOINT project and highlights of the proposed novel design. It then discusses the simulation, modelling and design of the demonstrator rig, and the associated test and development equipment. The conclusions highlight the progress so far – on the REPOINT project and the Demonstrator rig - and comment upon potential next steps towards network deployment

Rethinking rail track switches for fault tolerance and enhanced performance

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 currently 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

Design, construction, deployment and testing of a full-scale Repoint Light track switch (I)

A novel track switch actuation method, known as Repoint Light, is under full-scale prototype design phase at loughborough University. The design concept uses parallel-channel actuation, locking and detection, allowing the switch to continue to function with no loss of performance in the event of a single channel fault. The prototype will be constructed, tested and deployed, including tests with the passage of traffic, upon a functional railway. This paper describes the design and performance challenges faced when introducing the concept into its real operating environment, as well as systems engineering processes followed in the design and considerations regarding reliability, maintainability and performance of the switch

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

Detecting impacts on a representative aerospace structure: an implementation with tests

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

Extending emergency repair response times for railway track switches through multi-channel redundancy of functional subsystems

A novel track switch concept has been developed at Loughborough University, which allows parallel-channel, fault-tolerant functions for the first time. This paper demonstrates, through mathematical modelling, real-world data and conservative assumptions, that using a multi-channel, fault-tolerant switching concept can allow an increase in switch availability over baseline scenarios. Performance of four existing switch types is analysed for baseline performance using field data. Multi-channel architectures are then analysed across a range of reactionary maintenance regimes. Availability measures are obtained which show the range of possible switch availability against maintenance response times. The most significant improvements occur when maintenance practice is also revised, the novel system offering the option to run to subsystem failure and remain functional. Results indicate that for multi-channel installations, gains in system availability are possible even when emergency response times are set orders of magnitude longer than currently achieved, indicating a signifi cant reduction in ongoing maintenance commitment. The work also demonstrates that the particular choice of subsystem architecture is of low significance