GB2563909A

GB2563909A - Railway vehicle wheel detection apparatus and method

Info

Publication number: GB2563909A
Application number: GB1710447.2A
Authority: GB
Inventors: Roger Donald Brain Alex; Curtis Graham
Original assignee: Multiclip Co Ltd
Current assignee: Multiclip Co Ltd
Priority date: 2017-06-29
Filing date: 2017-06-29
Publication date: 2019-01-02
Also published as: GB201710447D0; WO2019002852A1

Abstract

The presence of a railway vehicle wheel (fig.2,60) on a section of rail (fig.2,50) supported by adjacent rail supports (fig.2,70) is determined by a wheel detector 11 and the result indicated by an output controller 13. The detector is configured to employ measurements from a Wheatstone bridge strain gauge sensor 2, obtaining measurements of shear strain in a vertical direction at a single measurement location, within or on the surface of the rail web, preferably midway between the supports, without any measurements from another location. The wheel detector may have at least one comparator. Preferably, a first comparator 111 compares the magnitude of a positive input signal with a first predetermined threshold value, and a second comparator 112 compares a negative input signal with a second threshold value, outputting the results to the output controller. The output controller may switch off respective output signals for a period should the magnitude of the input signals exceed their threshold values, and for an additional delay period after the input signal drops below the threshold value. The wheel detector may also be configured to determine the direction of travel of the train. Additional signal conditioning circuitry 12 may amplify the sensor measurement signals.

Description

RAILWAY VEHICLE WHEEL DETECTION APPARATUS AND METHOD

The present invention relates to railway vehicle wheel detection apparatus and a railway vehicle wheel detection method.

Railway networks use so-called axle counting systems to detect the passage of an axle, i.e. a pair of wheels of a railway vehicle, into or out of a section of track, to determine if that section of track is occupied by a railway vehicle or not, and/or to identify the number of vehicles occupying a section of track. Prior art axle counting systems comprise sensor “heads” that detect the passage of an axle, and an “evaluator” that determines the direction of wheel motion and increments or decrements a count of the number of axles that have passed in a given direction.

The predominant conventional means of detecting the presence of an axle is to detect the disruption of a magnetic field by the presence of a train wheel. However, this method of detection means that false activations are possible when other objects disrupt the magnetic field, such as hand tools, steel toe-capped boots or stray magnetic fields from on-train equipment. To enable false activations to be identified, two detectors are used at the same measurement location. The detectors also require removal from the track during some track maintenance activities, such as tamping and rail grinding, which is time-consuming and poses a risk to the safety of the personnel that must remove and replace the detectors.

As a train wheel passes along a section of rail supported by sleepers, the vertical shear force in the rail at a measurement point between two sleepers changes. A previously-proposed system combines the measurements from two strain gauges, positioned respectively at two measurement points, one at each end of a section of rail supported by two sleepers, to measure the shear force in the rail section between the two gauges as a wheel passes between them and thereby detect the presence of a railway vehicle. However, such strain gauge systems are generally more complex, and consume more power, than magnetic detection systems.

According to an embodiment of a first aspect of the present invention, there is provided railway vehicle wheel detection apparatus configured to detect the presence of a railway vehicle wheel on a section of railway rail supported by a pair of adjacent rail supports, the apparatus comprising: a wheel detector configured to employ measurements of shear strain in a vertical direction from a Wheatstone bridge strain gauge sensor positioned at one measurement location within or on the surface of the web of the railway rail between the pair of adjacent supports, but no shear strain measurement from another measurement location between the pair of adjacent supports, to determine whether a railway vehicle wheel is present on the railway rail at the measurement location; and an output controller configured to generate an output indicating the result of the determination.

According to an embodiment of a second aspect of the present invention, there is provided a railway vehicle wheel detection method for detecting the presence of a railway vehicle wheel on a section of railway rail supported by a pair of adjacent rail supports, the method comprising: using a Wheatstone bridge strain gauge sensor to obtain measurements of shear strain in a vertical direction at a single measurement location within the railway rail between the pair of adjacent supports; and employing the shear strain measurements from the single measurement location, but no shear strain measurement from another measurement location between the pair of adjacent supports, to determine whether a railway vehicle wheel is present on the railway rail at the measurement location.

An embodiment of the present invention uses just a single measurement position between adjacent rail supports to measure the change in force as a railway vehicle wheel approaches, passes over and moves away from the measurement position, and to use this change in force measurement to identify the presence of a wheel and/or the direction of motion of the wheel. The strain gauge system for obtaining the necessary measurements to detect trains is thereby simpler, but no less accurate, than the prior art.

In the context of this application a rail support may be a railway sleeper (rail tie) or a pedestal rail mount, which supports the rail beneath the rail foot, or discrete rail suspension assemblies from which the head of the rail is suspended.

Reference will now be made, by way of example, to the accompanying drawings, in which;

Figure 1 is a block diagram of railway vehicle wheel detection apparatus embodying the present invention;

Figure 2 is a circuit diagram of a Wheatstone bridge strain gauge sensor;

Figure 3 is (above) an illustration of a sensor positioned on a rail and (below) a diagram illustrating the vertical shear force measured by the sensor as a wheel rolls over the rail above it;

Figure 4 is a diagram illustrating the ideal vertical shear force measured by a sensor as a wheel passes over the measurement position;

Figure 5 shows a perspective view of one type of sensor; and Figure 6 is a diagram of outputs of the apparatus relative to inputs.

As shown in Figure 1, railway vehicle wheel detection apparatus 1 embodying the present invention comprises a wheel detection device (wheel detector) 11 connected to receive at least one input signal A (B) indicative of shear strain measured by a strain gauge sensor 2 positioned on the rail at a single measurement location between adjacent rail supports 70 (see Figure 3). Unlike prior art systems which require measurements from two different locations on the rail web 51, the detection device 11 of the present invention requires measurements from only one measurement location between adjacent rail supports 70 in order to accurately detect the presence of a wheel 60 on the rail 50.

The strain gauge sensor 2 is a Wheatstone bridge strain gauge sensor. For the purposes of the present invention a Wheatstone bridge strain gauge sensor is a type of strain gauge sensor which comprises two or four strain gauge elements connected in a Wheatstone bridge formation, such as elements Ri to R4 illustrated in Figure 2. Strain gauge measurement signals are typically very small and it is difficult to detect such small signals in the presence of any measurement noise (which is often significantly worse just as a train is passing). A Wheatstone bridge strain gauge sensor produces a differential signal, and any measurement noise is common to both outputs, so detection of the small measurement signal is much more straightforward. It is preferable to use a four element bridge as this arrangement provides a degree of compensation for temperature effects on the strain gauges, and also longitudinal strains.

As shown in Figure 3, the sensor 2 is attached at the measurement location to or within the web 51 of the rail 50, preferably so as to position the strain gauge elements at the vertical neutral axis of the rail. The measurement location is preferably exactly midway between adjacent rail supports 70, as shown in Figure 3, but may be slightly closer to one support than the other.

The weight of a railway vehicle on a railway rail 50 imparts a load to the rail 50, through a wheel 60 of the vehicle, which causes distortion of the rail 50. As shown in Figure 4, which depicts ideal shear force, as a wheel 60 of a railway vehicle travels on the rail 50 over the measurement location, the shear strain measured by the sensor 2 changes such that the polarity of the measurement (as compared to the amount of any shear strain experienced by the rail 50 at the measurement location when a wheel 60 is not present) reverses as the wheel 60 passes directly over the measurement location. The magnitude of the signal increases as the wheel 60 approaches the point of measurement, then decreases again as the wheel 60 moves away from the measurement point.

As shown in Figure 3, the shear strain force signal from the centrally-located sensor 2 comprises a positive and a negative triangular pulse with an asymptote between them indicating the presence of a vehicle wheel between the adjacent sleeper supports 70. Direction of travel of the vehicle may be determined by the sequence of the negative and positive pulses, i.e. by determining whether the positive pulse or the negative pulse was generated first.

The sensor 2 desirably comprises a type of sensor in which the strain gauge elements of the sensor are housed within a barrel 20 configured to be held within a correspondingly-sized hole which has been pre-drilled in the rail web 51, so that the strain gauge elements of the sensor 2 may be located at the horizontal neutral axis of the rail 50 as well as its vertical neutral axis. A sensor of this type is shown in Figure 5. However, a type of sensor in which the strain gauge elements are bonded to one surface of the rail web 51 (not shown) may be used instead.

The detection device 11 comprises at least one comparator 111(112) connected to receive the input signal A (B). The comparator 111 (112) is configured to compare the magnitude of the input signal it receives with a preset threshold value and send the result C1 (C2) of the comparison to an output controller 13 of the apparatus 1. The output controller 13 outputs an output signal X (Y). When the magnitude of the input signal A (B) exceeds the preset threshold value, the output controller 13 causes the output signal to be switched off X (Y) and does not permit the output signal X (Y) to be output again until the magnitude of the input signal A (B) has gone below the preset threshold value. In this way, the current consumption of the device is reduced when a wheel is detected. The current consumption of the device when a wheel is not present may be used as an indication that the apparatus is functioning correctly.

Desirably, as shown in Figure 1, the detection device 11 comprises a first comparator 111 and a second comparator 112 connected to receive respective first and second input signals A, B indicative of shear strain measured by the Wheatstone bridge strain sensor 2, and the output controller 13 is configured to output first and second output signals X and Y. The operation of this embodiment will now be descried with reference to the diagram of Figure 6. As mentioned above, the first input signal A has a positive value and the second input signal B has a negative value. The first comparator 111 compares the magnitude of the positive input signal A with a first preset threshold value TH1 and sends the comparison result C1 to the output controller 13. If the comparison result C1 indicates that the threshold value TH1 is exceeded, the output signal X is switched off by the output controller 13. When the magnitude of the input signal A goes below the threshold value TH1 again, the output controller 13 switches the output signal X on again. The second comparator 112 compares the magnitude of the negative input signal B with a second preset threshold value TH2 (which may or may not have the same magnitude as the first preset threshold value TH1 and sends the comparison result C2 to the output controller 13. If the comparison result C2 indicates that the threshold value TH2 is exceeded, the output signal Y is switched off by the output controller 13. When the magnitude of the input signal B goes below the threshold value TH2 again, the output controller 13 switches the output signal Y on again.

The preset threshold value(s) may be determined empirically, or may be calculated based on knowledge of the rail section, material properties, typical axle loads and strain gauge parameters that would give the output as a change of resistance for a given force in the rail.

Preferably, the output controller 13 causes the output signal corresponding to the comparison result it received first, i.e. the comparison result corresponding to the approach of the train to the sensor, to remain off for a short additional delay period D after the magnitude of the input signal A has gone below the preset threshold value TH1. Because of this short delay, the output signals X and Y will overlap slightly. The output signals X and Y are typically output to an evaluator (not shown) that uses the output signals to register the presence of a railway vehicle on that section of rail. The overlap of the output signals X and Y may be taken by the evaluator as confirmation that the output signals X and Y are not the result of a false detection. The length of the period of overlap between the output signals X and Y, i.e. delay period D, is preselected based, for example, on the expected speed of passing trains, but will typically be a few milliseconds. In practice the output controller 13 may be configured to apply the delay period to both output signals X and Y regardless of the order of receipt of the comparison results C1, C2, as shown in Figure 6.

It is usually the case that the sensor output signals a, b generated by the sensor 2 undergo some pre-processing before being input to the comparators 111, 112, so apparatus 1 embodying the invention preferably further comprises signal conditioning circuitry 12 configured to receive the sensor output signals a, b, to condition the sensor output signals a, b so as to generate the comparator input signals A, B, and to output the comparator input signals A, B to the comparators 111, 112. For example, since the magnitudes of the sensor output signals a, b are small, the conditioning is likely to comprise amplification of the signals a, b. In addition, the conditioning may position the voltage of the expected signal approximately midway between the supply voltages, so as to provide a good range for the positive and negative pulses, and ease configuration of the preset threshold values of the comparators.

Claims

1. Railway vehicle wheel detection apparatus configured to detect the presence of a railway vehicle wheel on a section of railway rail supported by a pair of adjacent rail supports, the apparatus comprising: a wheel detector configured to employ measurements of shear strain in a vertical direction from a Wheatstone bridge strain gauge sensor positioned at one measurement location within or on the surface of the web of the railway rail between the pair of adjacent supports, but no shear strain measurement from another measurement location between the pair of adjacent supports, to determine whether a railway vehicle wheel is present on the railway rail at the measurement location; and an output controller configured to generate an output indicating the result of the determination.

2. Apparatus as claimed in claim 1, wherein the wheel detector is also configured to determine the direction of travel of the detected railway vehicle from the measurements at the one measurement location.

3. Apparatus as claimed in claim 1 or 2, wherein the wheel detector comprises at least one comparator configured to compare the magnitude of an input signal, corresponding to shear strain measurements provided by the sensor, with a predetermined threshold value and to output the result of the comparison to the output controller.

4. Apparatus as claimed in claim 3, wherein the output controller is operable to switch off an output signal of the apparatus for a period when the comparator determines that the magnitude of the input signal exceeds the predetermined threshold value.

5. Apparatus as claimed in claim 1 or 2, wherein the wheel detector comprises a first comparator configured to compare a magnitude of a positive input signal, corresponding to shear strain measurements provided by the sensor, with a first predetermined threshold value and to output the result of the comparison to the output controller, and a second comparator configured to compare a magnitude of a negative input signal, corresponding to shear strain measurements provided by the sensor, with a second predetermined threshold value and to output the result of the comparison to the output controller.

6. Apparatus as claimed in claim 5, wherein the output controller is operable to switch off a first output signal of the apparatus for a period when the first comparator determines that the magnitude of the positive input signal exceeds the first predetermined threshold value, and to switch off a second output signal for a period when the second comparator determines that the magnitude of the negative input signal exceeds the second predetermined threshold value.

7. Apparatus as claimed in claim 6, wherein the output controller is operable to switch off, for an additional predetermined delay period after the magnitude of the input signal goes below the corresponding predetermined threshold value again, the output signal that corresponds to the comparison result that the output controller receives first.

8. Apparatus as claimed in any preceding claim, further comprising signal conditioning circuitry configured to amplify measurement signals generated by the sensor.

9. Apparatus as claimed in any preceding claim, wherein the measurement location is substantially midway between adjacent rail supports.

10. A railway wheel detection assembly comprising apparatus as claimed in any preceding claim and a Wheatstone bridge strain gauge sensor.

11. A railway vehicle wheel detection method for detecting the presence of a railway vehicle wheel on a section of railway rail supported by a pair of adjacent rail supports, the method comprising: using a Wheatstone bridge strain gauge sensor to obtain measurements of shear strain in a vertical direction at a single measurement location within the railway rail between the pair of adjacent supports; and employing the shear strain measurements from the single measurement location, but no shear strain measurement from another measurement location between the pair of adjacent supports, to determine whether a railway vehicle wheel is present on the railway rail at the measurement location.