All IRSE Aspect conferences are an opportunity for airing new developments and areas of research in signalling technology. The reliability and maintenance of point operation, whilst much improved down the years, is still a cause for concern and failures when they happen often lead to significant train delays.
From the beginning of railways, points have depended on movable sliding switch rails to control the direction that trains take at diverging or converging junctions. These require periodic lubrication, a method of moving the rails and a means of proving that they are in the exact position before signals are cleared for safe train movement. These three factors are potential sources of unreliability. So what if the movement of the rails can be accomplished differently? Would reliability be improved?
The development of the clamp lock back in the 1980s was a first step in trying to improve performance, but a completely new and novel design of point mechanism has since been progressed by Loughborough University in the UK. Known as ‘Repoint’, the concept was first hinted at in 2013 (issue 101, March 2013) with a fuller description in issue 131 (September 2015) which has led to a modified design known as ‘Repoint Light’ being launched in 2016. Sam Bemment from the university described the proposal at Aspect 2017
The Repoint Light system
Instead of sliding the rails across, why not lift them away from the sleeper base and lower them into a new position? This is the principle behind the new thinking.
In simplistic terms, three modified stretcher bars between the two stock rails (the outer rails) are fitted with two positioning slots (or more depending on the type of point) into which downward facing studs fitted to three actuator bearers that connect the two switch rails are lowered. The fit of the stud to the slot has to be exact, with strict tolerances, so as to achieve a prevention of movement that effectively locks the points into position.
When the point is reversed, motorised cams in the actuator bearers lift the two switch rails out of the slots, drive the rails across to the reverse position and lower them into different slots on the stretchers linking the stock rails. The power needed for this movement is calculated as less than sliding a conventional point.
Clearly the new position has to be proven with point detection mechanisms to ensure the switch rail is tight against the stock rail. Redundancy is achieved by having the three actuator bearers, and indeed there could be more of these used for high -peed points with an extended length.
Development and refinement since 2013 has reached the stage where an operational trial on a real railway can be planned. Following Aspect, Rail Engineer has learnt that the trial will take place on the Great Central heritage railway near to Loughborough, which has lower permitted speeds than the national rail network, at some time in 2018. Many eyes will be watching to see how Repoint performs in everyday service and weather.
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