GB2385424A

GB2385424A - Railway Sleeper displacement measurement or detection

Info

Publication number: GB2385424A
Application number: GB0302625A
Authority: GB
Inventors: Peter Andrew Frank; Russell Moss; Iain Hood
Original assignee: Gentech International Ltd
Current assignee: Gentech International Ltd
Priority date: 2002-02-06
Filing date: 2003-02-05
Publication date: 2003-08-20
Also published as: GB0302625D0; GB0202740D0

Abstract

A void meter, for detecting vertical movement of a railway sleeper 20, includes a top plate 1 attached via a mounting bracket 11 to a lineside stake 22. A displacement sensor, such as a reed switch sensor 3-5, is attached to the top plate 1 with a movable magnet carrier 4 connected to a bottom plate 8 via a flexible push rod 6. A compression spring 9, mounted between the top plate 1 and the bottom plate 8, presses the bottom plate 8 against the sleeper 20. Accordingly, vertical displacement of the sleeper is transferred via the bottom plate 8 and the push rod 6 to the magnet carrier 4, that displacement being detected by the reed switch sensor.

Description

i 1 2385424

DISPLACEMENT MEASUREMENT OR DETECTION

This invention relates to the measurement or detection of displacement, and in particular to such measurement or detection in the context of movement of railway 5 sleepers. In the UK and other countries, railway track is mounted on wooden or concrete sleepers, which also act as ties. These are then bedded onto a gravel base sometimes termed ballast, the track being levelled by adjustment of this bed. Due to train vibration, settlement can occur, resulting in voids under the sleeper causing vertical 10 movement whenever a train passes.

When this movement exceeds a certain amount, typically around 2 ems, stress on the track becomes a concern, particularly adjacent to points, and can result in points failure. Points failure has been assessed to be the most common problem causing train delays. Accordingly, monitoring for such voids is highly desirable, so that appropriate 15 maintenance action can be taken as soon as possible.

The present invention provides a device for detecting vertical movement of a railway sleeper, the device comprising: a positional reference structure for providing a positional reference relative to the ground; 20 a displacement sensor attached to the positional reference structure, having a sensor housing and a relatively movable sensing member, a displacement member being connected at one end to the sensing member; a sleeper engagement means for engaging a railway sleeper, and being connected to the other end of the displacement member; and 25 resilient means connected between the positional reference structure and the sleeper engagement means so as to engage resiliently the sleeper engagement means against the sleeper, such that vertical displacement of the sleeper is transferred via the sleeper engagement means and the displacement member to the sensing member, to be detected by the displacement sensor.

30 Such a device is generally known as a void meter.

A preferred embodiment of the invention is capable of allowing for a significant degree of horizontal misalignment of the sleeper. Advantageously, this may be achieved by the lower end of a compression spring holding a base plate against the sleeper by spring tension, with a push rod coupled to a displacement sensor being 5 connected to the base plate. The upper end of the compression spring is attached to a top plate retaining the sensor housing. By virtue of the base plate being held against the sleeper by spring tension of the compression spring, the base plate and displacement sensor push rod can follow any downward movement of the sleeper.

The displacement sensor is preferably based on a reed switch ladder with 10 associated resistor network.

The device can be attached by means of a mounting bracket to a stake, such as a standard stake available from the UK railway maintenance authority, the stake being driven into the ground adjacent the sleeper being monitored so as to provide a positional reference against which sleeper displacement can be determined.

15 The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: Figure 1 is a side sectional view of a device according to an embodiment of the invention; 20 Figure 2 is a top plan view of the device of Figure 1; Figure 3 is an enlarged sectional view of the displacement sensor of Figure 1; Figure 4 is a top plan view of the sensor of Figure 3; and Figure 5 is a circuit diagram of the displacement sensor and associated detection circuitry.

25 Referring to Figures 1 and 2, the preferred device comprises a top plate 1, preferably having a circular portion, with attached flange 2 retaining a sensor housing 3 in the form of an extrusion (providing a magnet slide and printed circuit board PCB housing) within which is a magnet carrier 4 and a magnet 5. A flexible push rod 6 is connected to the magnet carrier 4, extending through an extrusion end stop 7 to a base 30 plate 8, again preferably circular. The base plate 8, as will be described, is arranged to contact the top surface of a sleeper 20 of the railway track. A compression spring 9 is disposed between the top plate 1 and the base plate 8. A protective gaiter 10 surrounds

the compression spring 9 and the remainder of the sensor assembly. The top plate 1 extends laterally from the circular portion and is provided with suitable fixing means, such as bolt apertures 16 (one or more of which may be elongate for allowing adjustment) for attachment to a mounting bracket 11. The mounting bracket 11 5 includes further fixing means, such as elongate apertures 18, for mounting to a standard stake 22 (shown by dashed lines) provided by the railway maintenance authority. Figure 1 is a section taken on line A-A in Figure 2.

Referring to Figures 3 and 4, the displacement sensor design can be seen in greater detail. Within the sensor housing 3 are located the magnet carrier 4, the 10 magnet 5 and a printed circuit board (PCB) 12 carrying the reed switch ladder 14.

Movement of the magnet carrier 4, when actuated by the push rod 6, causes the magnet 5 to move adjacent the reed switches in the reed switch ladder 14 and thereby to activate the reed switches so as to provide an indication of displacement of the magnet carrier 4 and thus also of the base plate 8. The magnet carrier 4 can move over the 15 maximum working stroke MWS as shown in Figure 3. Figure 3 is a section taken on line B-B in Figure 4.

Figure 5 shows the reed switch/resistor network and associated detection circuitry comprising a gain block 30 amplifying the displacement signal provided by the reed switch/resistor network 32, and a voltage regulator 34 for providing a stable 20 reference voltage. The preferred reed switch ladder comprises thirty-four reed switches with associated resistor network, which typically provides a stepped resistive output having a resolution of about 3 mm between adjacent switches. The resistive change from the network 32 is then converted by the gain block 30 to a displacement signal in the form of a stepped voltage output of 0.5 to 3.5 volts, which is compatible 25 with data input requirements of certain existing lineside data buses. The output of the gain block 30 may be supplied to a filter 36 located at the input to a data logger. This displacement signal can then be fed back to a central monitoring location through a data bus system provided at all points systems. Any progressive increase in detected sleeper movement adjacent particular points would then be used for predictive 30 maintenarce purposes, prior to onset offailure.

The reed switch/resistor network 32 is also connected to a reference resistor 38 which sets the scaling factor for the ladder network. When the reference resistor 38

has a resistance value of 100 k ohms, the resistance of each resistor in the ladder network can be 100 ohms, except for that of the resistor adjacent the reference resistor 38, which can be 510 ohms.

Referring back to Figures I to 4, the magnet carrier 4 is preferably made of a 5 plastics material and slides within the sensor housing 3 which is preferably an aluminium extrusion. The housing 3 also acts as the printed circuit board carrier. The printed circuit board 12, carrying all of the reed switches and associated components as shown in Figure 5, is fully encapsulated into the housing extrusion 3 for mechanical and environmental protection. The push rod 6 is flexible and is mounted to the magnet 10 carrier 4 and the base plate 8 so as to allow for some misalignment from purely vertical movement.

Since the top plate 1 and the sensor housing 3 are attached to the base plate 8 by the compression spring 9, this allows for any horizontal misalignment of the sleeper 20. Since the compression spring 9 holds the base plate 8 against the sleeper 20 by 15 spring tension, the base plate 8 and the push rod 6 therefore follow any downward movement of the sleeper 20. Another advantage of this arrangement is that the assembly does not require any separate attachment means between sleeper and base plate, the spring tension is sufficient for this purpose. In order to position the assembly, it is sufficient to drive the stake 22 into the ground adjacent the sleeper 20 20 and attach the assembly with bracket 11 so as to align the base plate 8 over the top of the sleeper 20. In this state, the spring 9 may be held partially compressed and then released so that the base plate 8 contacts the sleeper 20, enabling it to follow movement of the sleeper and to allow the required degree of displacement of the magnet carrier 4.

25 The protective gaiter 10 is preferably of rubber and surrounds the whole assembly to provide environmental protection. Exhaust vents and drainage holes may be provided for air displacement and drainage of water during flood conditions.

Although the preferred displacement sensor is based on the use of reed switches, with associated resistor network, other displacement or movement detecting 30 techniques could be used, for example accelerometer or ulrasonic position sensing.

Claims

s CLAIMS

1. A device for detecting vertical movement of a railway sleeper, the 5 device comprising: a positional reference structure for providing a positional reference relative to the ground; a displacement sensor attached to the positional reference structure, having a sensor housing and a relatively movable sensing member, a displacement member 10 being connected at one end to the sensing member; a sleeper engagement means for engaging a railway sleeper, and being connected to the other end of the displacement member; and resilient means connected between the positional reference structure and the sleeper engagement means so as to engage resiliently the sleeper engagement means 15 against the sleeper, such that vertical displacement of the sleeper is transferred via the sleeper engagement means and the displacement member to the sensing member, to be detected by the displacement sensor.

2. A device according to claim 1, wherein the resilient means is a 20 compression spring.

3. A device according to claim 2, wherein the displacement sensor and the displacement member are disposed within the compression spring.

25 4. A device according to claim 2 or claim 3, wherein the compression spring is surrounded by a protective gaiter.

5. A device according to claim 4, wherein the protective gaiter is of rubber.

6. A device according to claim 4 or claim S. wherein the protective gaiter is provided with apertures.

l 7. A device according to any one of the preceding claims, wherein the 5 sleeper engagement means comprises a surface for pressing against the sleeper.

8. A device according to claim 7, wherein the sleeper engagement means comprises a circular plate.

10 9. A device according to any one of the preceding claims, wherein the positional reference structure includes an overlying portion arranged to overly the sleeper. 1 O. A device according to claLm 9, wherein the overlying portion includes a 15 circular plate retaining the displacement sensor.

11. A device according to claim 9 or claim 10, wherein the positional reference structure includes means for attachment to a ground-mounted stake.

20 12. A device according to claim 11, wherein the attachment means comprises a mounting bracket with bolt holes, at least one of which is elongate for adjustment. 13. A device according to any one of the preceding claims, wherein the 25 displacement member is a flexible push rod.

14. A device according to any one of the preceding claims, wherein the displacement sensor comprises a plurality of reed switches, and the sensing member comprises a magnet.

15. A device according to claim 14, wherein the displacement sensor comprises a respective plurality of resistors connected to the plurality of reed switches

l so that displacement of the sensing member within the sensor housing causes a corresponding change in combined resistance value resulting from the switched resistors. 5 16. A device according to claim 15, wherein the reed switches and resistors are arranged in a ladder network.

17. A device according to claim 15 or claim 16, including means for converting the resistance value to an output voltage.

18. A device for detecting vertical movement of a railway sleeper, the device being substantially as herein described with reference to and as illustrated in the accompanying drawings.

in