Faults tend to have significant impact on railway performance, disrupting or stopping train movement. Railway administrators make significant efforts to reduce or eliminate sources of failures. So-called ‘single point’ failures are often the most difficult to deal with as there are no work-arounds. Examples include rails and wheelsets, which are designed to have exceptionally high integrity, an aspiration that advances in materials have supported.
Other equipment is sometimes provided with dual or even triple redundancy, so that a single fault still allows traffic to flow, provided, that is, the fault becomes evident before the other components fail! A good example is the London Underground practice of using at least two air compressors on each train.
Until now, points have been safe but subject to many single point failure modes in control, actuation, detection and locking. It was in 2010 that Professor Roger Goodall of Loughborough University, working with his then colleague Professor Roger Dixon (now with the University of Birmingham), proposed some fundamental research into track switching.
Roll forward to a very cold day in January 2019 and Professor Bob Allison, Loughborough’s Vice Chancellor, and Professor Roger Goodall, Professor of Control Engineering, welcomed some 50 guests from operators, suppliers and friends to demonstrate the results of that original research – Repoint Light – at the Great Central Railway’s Quorn and Woodhouse station.
Repoint has been covered in Rail Engineer before (issue 131, September 2015 and issue 160, February 2018). Briefly, it seeks to eliminate single point (sorry) failure modes by employing gravity for locking and multiple actuators and detectors to achieve redundancy.
The full Repoint concept also included stub switches, but this feature was not included in the demonstrator, which, except for the actuators, is a standard size CVS flat bottom switch on concrete bearers. Indeed, it also included roller slide chairs, which are redundant in this application.
The switch is entirely conventional, using flat-bottom stock rails and shallow depth switch rails, and standard concrete bearers and roller base plates even though the latter have no function with these actuators. Three bearers – 1, 3 and 5 – are replaced by Repoint actuators, each one of which contains two drive motors and four Hall-effect position sensors used for detection.
The drive motors are positioned below the switch rails and are connected to cams that lift, traverse and then lower the stock rails. The motors in each bearer are synchronised electronically. The rails are not secured to the drive mechanism, which permits the rails to move if only one of the actuator pairs operates.
Each switch rail is detected in its open and closed position. Detection is arranged such that, if one rail is detected closed, the other must be detected open, and on a ‘two out of three’ voting basis based on the principles of triplicated systems used in aerospace controls. In fact, on this size switch, any one of the actuators would operate the switch and the choice of the location of the actuators was made to ensure each could raise the switch rails to clear the locking blocks of the other two.
For longer switches, the Repoint team advised that additional in-bearer actuators would be provided instead of a back-drive. As the lateral movement is twice the vertical movement (circular motion) a smaller lift would be needed to provide the appropriate lateral movement to maintain the natural line of the rails.
The semi-circular motion of the switch rails was clearly demonstrated at the test site and showed one issue for which care will be required in set up. It is a requirement that the switch rails close firmly on the stock rails and, whilst the demonstrator switch worked, it looked feasible that the switch rail could bind on the stock rail and not drop by gravity into perfect alignment. It will be important, therefore, that the detection is only proved when the switch rail is vertically in the correct position.
This is all a matter of having the right amount of adjustment; one of the reasons for having a prototype. And the Repoint team confirmed that, indeed, the detection will not activate unless the switch rails are fully in the correct location. It would not be an issue with the full Repoint system using stub rails.
The Valley of Death
It is comparatively unusual to see such a fully engineered product developed under the leadership of an academic institution (with support from RC Designs, Baker Engineering, Progress Rail and Ramboll). The Great Central Railway trial installation represented Rail Industry Readiness Level 5, whereas it would be more usual to stop at RIRL 3.
Loughborough deliberately sought to try and overcome the so-called “valley of death”, where innovations stall through lack of investors to get them into production, and to recognise that, in general, Network Rail expects new products to be at least at RIRL 6 before they can be considered for trail on the ‘big’ railway.
It was good to see that the demonstration at Quorn was attended by many potential industrial partners.
Your writer has been involved with the development of point machines before, and it is quite conceivable that a seven-digit sum can be spent developing and proving new actuators before any see more than prototype service. Unless an actuator is adopted internationally, amortising this cost can be a significant issue.
Equally, having three actuators rather than one might increase costs, albeit, the Repoint Light actuator looks less complicated than many other designs. That said, in the context of the overall cost of installing a switch, the cost of the actuators is small. However, in conversation with one of the potential industrial partners, it became apparent that the conditions of the research grants make it difficult for any one supplier to adopt Repoint exclusively.
So it was good that many former colleagues, experienced in introducing new switch mechanisms, were impressed with the concept and its presentation. They were seeing potential issues and how they might be addressed, but the prize of being able to keep a switch in service to the end of traffic, even if a component fails, is one worth working for.
Great Central Railway themselves were excellent hosts, including a Hall class locomotive, complete with a Repoint train headboard, providing an excellent trip for all the guests.