GB2420627A

GB2420627A - Void meter

Info

Publication number: GB2420627A
Application number: GB0425798A
Authority: GB
Inventors: Gillian Carol Hibbert; Simon Kay; Stephen Nicholas Kent; Paul Bewes Molyneaux-Berry
Original assignee: AEA Technology PLC
Current assignee: Ricardo AEA Ltd
Priority date: 2004-11-24
Filing date: 2004-11-24
Publication date: 2006-05-31
Also published as: GB0425798D0

Abstract

An instrument for monitoring vertical movement of a railway line relative to the supporting ballast, referred to as a void meter, consists of a shaft (14) connected at one end to a clamp (12) such as a magnetic base so it can be clamped onto a rail (30). The shaft (14) extends in a generally horizontal direction and carries a pivoted sensing member (15) for recording changes in the height of the rail (30) relative to the ballast. An indicator (26) pivots on the shaft (14), being displaced when the sensing member (15) is turned, and being held by friction.

Description

Void Meter The present invention relates to an instrument for monitoring

vertical movement of a railway line relative to the supporting ballast, such an instrument commonly being referred to as a void meter.

Railway lines are usually supported by sleepers (or ties), which rest on ballast consisting of a packed bed of angular stones. Vibration caused by the passage of trains can lead to the development of voids under the sleepers. When a train passes along the railway track, any such voids will allow vertical movement of the track and so of the train. Where such voids occur under just one end of a sleeper, this may cause the vehicles in the train to tilt or sway, and in extreme cases this can lead to derailment. Furthermore, if the vertical movement is larger than about 20 mm, this can impose excessive stresses on the rails, particularly in the vicinity of points. Accordingly, monitoring the presence and size of such voids is desirable. Similar problems can also arise where the rails are supported by a continuous support structure such as a concrete slab base rather than by conventional ballast, and it should be appreciated that

in this specification the term ballast is to be

interpreted as meaning the underlying medium that supports the rails, and above which the rails extend.

Various designs of void meter are known. For example GB 2 385 424 (Gentech International Ltd) describes a void meter including a lineside stake carrying a mounting bracket above a sleeper, the bracket supporting a spring-loaded plate pushing down on the sleeper, a movable magnet, and a displacement sensor such as a reed switch. Mechanical void meters have also been proposed, for example US 4 794 697 (Kango Wolf Power Tools) describes one with a vertical shaft extending from a baseplate that rests on the ballast, the shaft carrying a spring-loaded bracket that clamps onto the rail foot, and a collar on the shaft which is a friction fit; displacement of the rail pushes the bracket and the collar down the shaft, and the collar remains in the depressed position when the train has passed. Both these devices require some work to be done on the track, to install the lineside stake or to clear an area of ballast for the baseplate to rest respectively, and a robust, accurate void meter that could be rapidly and simply installed (and later removed) with no work on the ballast According to the present invention there is provided an instrument for monitoring vertical movement of a railway rail relative to the supporting ballast, the instrument comprising a shaft connected at one end to a clamp whereby it may be clamped onto a railway rail so that the shaft extends in a generally horizontal direction, the shaft carrying a mechanical means incorporating a pivoted sensing member for recording changes in the height of the rail relative to the ballast.

The clamp may be a mechanical clamp for attaching the instrument to the foot of the rail, and in this case is preferably one that requires a tool to release it. In this case the instrument can be installed on a railway line and left for a prolonged period, for examples several hours or even days, without the risk of trespassers removing the clamp. However, in some situations it is preferable to use a magnetic clamp, such that it may be clamped onto the side of the rail web, for example. The use of the magnetic clamp (which may be referred to as a magnetic base) ensures that the instrument can be simply and rapidly fixed in position on the rail, and equally rapidly removed, so that it is not necessary to close down operation of the railway line for any significant period of time. Such clamps are available commercially, for example from RS Components, and typically incorporate a small handle which is turned through 900 to actuate or release the clamp. They are ideal where the operation of the instrument is to be monitored by trackside staff, and the clamps need only be left in position during the passage of a single train.

Preferably the mechanical means for recording changes in height comprises a sensing member pivotally supported on the shaft and linked to a sensing foot for resting on the ballast, such that changes in height cause pivotal motion of the sensing member. To provide an indication of the magnitude of this pivotal motion, the recording means may also comprise an indicating element pivotally supported on the shaft. The indicating element may for example be held in position by friction, such that it is displaced when the sensing member moves in one direction and then stays in position. Alternatively the recording means may comprise an indicating element in the form of a paper chart and a pen which are moved relative to each other by movement of the sensing member; for example a circular paper disk might be attached to the sensing member to rotate with it, and a pen be held in a fixed position relative to the shaft, so as to mark the paper disk. Equally, the paper disk might be in a fixed position, and the pen be moved by the sensing member. In another alternative, the recording means may comprise a scribing surface covered with an indicating paint, and a scratching element that marks the paint, the scribing surface and the scratching element being moved relative to each other when the sensing member is displaced.

Preferably the sensing member is pivotally connected to a bar to the lower end of which is fixed the sensing foot, the bar being provided with a plurality of locating positions at which it. may be connected to the sensing S member to accommodate different initial heights of the rail above the ballast. For example these locating positions may be defined by holes through the bar, through which a pivot pin may be inserted to connect the bar to the sensing member. Alternatively the bar carrying the sensing foot may be slidable relative to a member pivotally connected to the sensing member, there being a clamp to secure the bar to the pivotal member, so that the length of the bar that is below the sensing member can be adjusted. In use, the sensing member is initially set up slightly below the horizontal with the sensing foot resting on the ballast, by suitable selection of the locating position at which the bar is connected to the sensing member.

Although the instrument may include resilient means for urging the sensing foot onto the ballast, preferably the sensing foot rests on the ballast by virtue of its own weight.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 shows a perspective view of a void meter of the invention; Figure 2 shows a view of the void meter in the direction of arrow A of figure 1; and Figure 3 shows a view of the void meter in the direction of arrow B of figure 1, with the void meter installed on a railway line.

Referring now to figures 1 and 2, a void meter 10 includes a magnetic base 12 with a small handle 13 which can be turned through 900 either to fix the base 12 onto a steel surface, or to release it, this magnetic base 12 supporting a shaft 14. At the other end of the shaft 14 is a sensing member 15 freely pivoted on the shaft 14, the member 15 being shaped like an upside-down T so it has three arms 16, 17 and 18. An arcuate scale 19 extends between the arms 16 and 17, the upright arm 17 having an end part l7a that extends axially onto the end of the scale 19. The arm 18 has a hole for a pivot pin at its outer end. A sensing foot 22 is integral with a support bar 23 with ten holes 24 at different heights near its upper end, and the pivot pin 20 is passed through one of these holes 24 so that the sensing foot 22 and support bar 23 hang freely. In use, the sensing foot 22 will rest on the ballast under its own weight. The void meter 10 also includes an indicator 26 whose tip is adjacent to the scale 19.

Referring now to figure 3, the void meter 10 is shown clamped onto the side of the web of a rail 30 by means of the magnetic base 12. The shaft 14 is of steel, with a threaded end portion (not shown) by which it is connected to the base 12. The shaft 14 is machined so as also to define a collar 32 of larger diameter at an intermediate position along its length, and the outer part 33 of the shaft 14 is of somewhat smaller diameter, the outermost end portion 34 also being threaded. The indicator 26 consists of a radially-extending indicator arm 35 integral with a boss 36 which is a friction fit on the outer part 33 of the shaft, these components being made of a strong, resilient and dimensionally stable polymeric material such as acrylonitrile butadiene styrene (ABS); for example the boss 36 may define a large axial hole with three or four protruberances which engage with the shaft 33. The sensing member 15 is also of this resilient polymeric material, and incorporates a hub 38 which can freely turn on the outer part 33 of the shaft.

An end cap 40 is attached to the end portion 34 of the shaft 14, and secures the hub 38 and so the sensing member 16.

Thus in use of the void meter 10 it is clamped onto the rail 30 as shown in figure 3. The pivot pin 20 is passed through one of the holes 24 such that the sensing foot 22 rests on the ballast 42 with the aligned arms 16 and 18 of the sensing member 15 tilted a few degrees away from the horizontal (say about 8 ), with the end with the pivot pin 20 slightly below the shaft 14 (as shown in figure 2) . The indicator 26 is pushed around until its tip is adjacent to the end part 17a at the top end of the scale 19.

When a train passes along the rail 30, if there is any voidage then the rail 30 will be depressed relative to the ballast 42. Consequently the sensing foot 22 is pushed up relative to the shaft 14, SO that the sensing member 15 turns, and the end part 17a pushes against the tip of the indicator 26, so the indicator 26 turns through the same angle. After the train has passed, the rail 30 returns to its original position, and so do the sensing foot 22 and the sensing member 15. The indicator 26 does not turn freely on the shaft 14, but stays in its new orientation, and the arc length along the scale 19 between the position of the tip of the indicator 26 and the end part l7a is a measure of the angle through which the sensing member 15 has turned, and is therefore also a measure of the distance that the rail 30 has been depressed, i.e. the voidage.

It will be appreciated that the scale 19 may be calibrated for example in millimetres, or alternatively the scale may indicate the quantity of ballast that must be introduced under the sleepers (if the rail 30 is indeed supported on sleepers and conventional ballast) The scale 19 is simple to read, and its reading is not affected if a succession of trains pass over the rail 30.

It will be appreciated that a void meter of the invention may differ from that described above. There are some circumstances in which the ease of removal of the void meter 10 - by simply releasing the magnetic base 12 by turning the handle 13 - may be perceived as disadvantageous, and in such circumstances the shaft 14 might instead be attached to a mechanical clamp secured to the foot of the rail 30, for example comprising a steel plate that passes under the rail 30 with curved flanges on each side, one such flange engaging one side of the foot, and the other flange carrying a bolt which can be adjusted to engage and clamp onto the foot on the opposite side of the rail 30. Such a clamp cannot be released without use of a spanner, and so is more secure against vandals.

The indicator 26 and indeed the sensing member 15 might be made of different materials. By way of example, the indicator 26 may be made of steel, turning freely on the shaft 14 but locating between two fixed flanges or bosses on the shaft, and being spring-loaded against one of them (such as the flange 32) , so that it is held by the friction with this flange. For example, part of the outer end 33 of the shaft 14 might be threaded, and carry a washer and nut, the washer acting as one of the fixed flanges and being held by the nut. The frictional force can, in this case, be adjusted by adjusting the compression of the spring.

Claims

Claims 1. An instrument for monitoring vertical movement of a railway rail

relative to the supporting ballast, the instrument comprising a shaft connected at one end to a clamp whereby it may be clamped onto a railway rail so that the shaft extends in a generally horizontal direction, the shaft carrying a mechanical means incorporating a pivoted sensing member for recording changes in the height of the rail relative to the ballast.
2. An instrument as claimed in claim 1 wherein the clamp is a mechanical clamp for attaching the instrument to the foot of the rail, and requires a tool to release it.
3. An instrument as claimed in claim 1 wherein the clamp is a magnetic clamp.
4. An instrument as claimed in any one of the preceding claims wherein the mechanical means for recording changes in height comprises a sensing member pivotally supported on the shaft and linked to a sensing foot for resting on the ballast, such that changes in height cause pivotal motion of the sensing member.
5. An instrument as claimed in claim 4 also comprising an indicating element pivotally supported on the shaft.
6. An instrument as claimed in claim 5 wherein the indicating element is held in position by friction, such that it is angularly displaced when the sensing member moves in one direction and then stays in position.
7. An instrument as claimed in any one of claims 4 to 6 wherein the sensing member is pivotally connected to a bar to the lower end of which is fixed the sensing foot, the pivotal connection being such as to accommodate different initial heights of the rail above the ballast.
8. An instrument as claimed in any one of claims 4 to 7 where-in t.he sensing foot rests on the ballast by virtue of its own weight.
9. An instrument for monitoring vertical movement of a railway line relative to the supporting ballast substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

15875 MdDe P T Mansfield

Chartered Patent Agent Agent for the Applicant