GB2150298A - Method and apparatus for weighing rail wagons - Google Patents

Abstract

The weight of a railway wagon in a train is determined using a weighbridge 10 over which the train passes, the weighbridge having load measuring transducers 15-18. The weight indicated by the transducers is determined repetitively as each pair of wheels of the wagon pass over the weighbridge, the measurements being averaged in a computer 20 over a period when the measurements are within a predetermined tolerance band. Each transducer 15-18 may comprise a double strain gauge. If a discrepancy occurs between the outputs of the two strain gauges of any of the transducers, caused by a fault, the computer 20 identifies which strain gauge is faulty by comparing its output with those of other strain gauges. <IMAGE>

Description

SPECIFICATION Methods and apparatus for weighing rail wagons This invention relates to a method and apparatus for weighing rail wagons.

It is well-known to provide a weighbridge over which a train of wagons is passed, the weigh bridge having load transducers to sense the load on each pair of wheels as they pass over the weighbridge. The usual practice is to have a number of swiches (e.g. limit or proximity switches) spaced along the rails to detect the wheels. For example, six switches might be provided. The output from the load transducers can be fed to a computer which relies on the switches actuated by the wheels to determine which way the train is moving.

Any summation technique must sum the total weight for each individual wagon as all the wheels of that wagon pass over the weighbridge. It is necessary that the weighbridge should be relatively short so that it weighs only one pair of wheels. The time taken to traverse the weighbridge will depend on the speed of the train. At higher speeds, there is only a short time between the passage of successive pairs of wheels and hence measurements have to be made in this short time period. When the wheels move onto the weighbridge, oscillation of the weighbridge occurs and measurement of the load has to be made when the weighbridge has settled down.With existing devices, problems arise from the switches which have to be set very accurately and must be reliable in order to detect the wheels and to tell the computer which way the train is moving and to give a trigger signal for effecting the load measurement. These devices also have problems in that the train must be moving relatively slowly. If it is moving too fast, then it is not possible to make the weighing measurement, triggered by a switch, which will give an accurate indication of the load measurement.

It is one of the objects of the present invention to provide an improved method and apparatus for weighing rail wagons which eliminates the necessity for switches to trigger recording of a load measurement.

According to the present invention a method of determining the weight of a railway wagon in a train using a weighbridge over which the train passes, the weighbridge having load measuring transducers, comprises the steps of repetitively determining the weight as a pair of wheels move across the weigh bridge and averaging the measured load during a period when the load measurements are within a predetermined tolerance band. This technique of averaging a number of load readings enables a far more accurate determination of the load to be made than the use of a single load measurement which has to be triggered by a switch.

Provided the train moves continously across the weighbridge, the loads on successive pairs of wheels of each individual wagon may be measured in this way and may be summated in a computer.

In the simplest form, the weighbridge may have a pair of transducers, one for each rail of the track. More generally however, it is preferable to support each rail at two points spaced along the length of the rail. This leads to the use to two pairs of transducers. In such an arrangement, the loading of the individual transducers changes as the wheels move over the weighbridge; the first set of transducers, that is the transducers at or near the end at which the wagon approaches the weighbridge, will initially take a larger share of the load but this share will decrease as the wheels move towards and over the weigh bridge. Initial loading still causes oscillations in the output readings of the first set of transducers but one cannot wait until the load measurements of one set of transducers settle down to a steady value.In this arrangement it is the combined output of successive transducers on each rail which must settle down to be within a predetermined tolerance band. Checking this and then making repetitive readings for averaging can be effected by the computer. Another way however of determining when to make the readings is to compare the outputs of successive transducers on a rail and, when they are equal or substantially equal, it can be assumed that the wheels are substantially midway between the two sets of transducers. At that point, the readings can be made; the weight on each rail is the sum of the readings of all the transducers supporting that rail.

Whilst it may be possible to assume that a train moves continuously in one direction over a weighbridge, this is not always the case and it is preferable to make proper correction if a train should be reversed so that any wagon, or even a pair of wheels, passes back onto or over the weighbridge.

If it is required to detect the direction of movement of the wagons, then the signals from load measuring means on the weighbridge may be used and the direction of movement can be determined by noting which load measuring means first responds as the wheels move onto the weigh platform. In practice, each load measuring means would comprise two transducers, one on each rail. Thus, in a system having means for detecting the direction of movement as described above, four transducers would be provided in two pairs.

The total load to be measured will be the summation of the outputs of the four transducers. As is described later, each individual transducer may be a load cell having two strain gauges; this facilitates checking to see if any transducer is faulty.

For checking whether the wagon moves backward over the weighbridge, the computer may be arranged to monitor the ratio of the determined loads on the two spaced load sensing means; if these are equal, the wheels have reached the mid point between the two sensing means, which mid point would normally be the centre of the weighbridge. if the wheel rolls backward before equality of load at the two sensing means has been established, the ratio of the loads on the first and second sensing means (considered from the direction of original approach of the wagon) will increase before the sum of the sensed loads becomes zero, at which time the wheels will have moved back off the weighbridge. If a pair of wheels runs backwards onto the weighbridge, the load on the second sensing means will be initially much larger than that on the first sensing means.The computer may be arranged to sense this and count the number of times it occurs so that when the train starts up again and crosses the weighbridge in the correct direction, the pairs of wheels can be recounted until the point is reached at which the rollback started; the weighing procedure can then recommence.

in this country, it is the general practice for wagons carrying coal, minerals and the like to have two pairs of wheels. The weight of a wagon may be obtained by adding the weights of the two pairs of wheels.

This weight may be noted with the appropriate wagon number which may be fed into the computer. It will be readily apparent however that, by appropriate programming of the computer the technique may be employed for wagons having bogies, e.g. two bogies each with two or more pairs of wheels.

The velocity of a wagon can readily be determined from the sensed information by determining how long it takes for a pair of wheels to cross the weighbridge, this being done by noting the rapid increase in load as the wheels move onto the weighbridge and decrease as they move off. Knowing the length of the weighbridge, the velocity of the wagon can be determined. If the velocities for the first and second pairs of wheels differ and if the pitch between the wagon wheels is known, it is possible to find the acceleration or decleration of the wagon. Gravitational forces due to such acceleration or decleration may thus be determined to provide corrections for the wagon weight determined from the transducer outputs.

Iffourtransducers are provided as described above, the outputs of the various transducers may be compared to establish if any transducer is faulty. If a faulty transducer is discovered, the computer may be arranged to ignore the signals from that transducer and to replace them by appropriate signals from the good transducers. The comparison to determine if any transducer is faulty conveniently is carried out at the start of a measurement on a wagon.

The invention furthermore includes within its scope apparatus for carrying out the above method and comprising a weighbridge with transducers producing output signals and computing means responsive to the output signals and arranged to determine the weight of each wagon as it passes over the weighbridge.

In the following description reference will be made to the accompanying drawings in which: Figure 1 diagrammatically illustrates in side elevation a weighbridge and part of adjacent sections of rail track for weighing wagons passing along the track; Figure 2 is a plan view of the weighbridge of Figure 1 showing the locations of transducers in a preferred embodiment; Figure 3 is a diagram illustrating the amplitude of a typical loading signal from a transducer in the apparatus of Figures 1 and 2; Figure 4 are load/time and velocity/time graphs typical of the passage of wagons over the weighbridge; Figure 5 is a graphical diagram indicating measurements which might be made with a typical train; Figure 6 illustrates a modification of the arrangement of Figure 2;; Figures 7 and 8 are diagrams explaining the use of spaced transducers along the length of the weighbridge; and Figure 9 is a diagram for explaining how the direction of movement of a wagon is found.

Referring to Figures 1 and 2 there is shown a weighbridge 10 across which extends two rails 11 and 12 for carrying railway vehicles from a first section of fixed track 13 to a further section 14 on the opposite side of the weighbridge. The length of the weighbridge is such that only one pair of wheels of a wagon will rest on the weighbridge section 10 as a train passes along the track. This weighbridge section is supported by two pairs of transducers, of which a first pair 15, 16 are located near one end of the weighbridge and the other pair 17, 18 are located at the other end of the weighbridge. The two transducers of each pair support respectively the weighbridge section 10 and the two rails 11, 12 and thus the total load on the weighbridge at any one time would be indicated by the summation of the outputs of all four transducers.However when a pair of wagon wheels moves onto the weighbridge, e.g. from the left in Figures 1 and 2, and the load measurement on the first pair of transducers 15, 16 in this case increases rapidly and will be higher than the load measurement on the other pair of transducers 17, 18 until the wheels have moved beyond the centre point of the weighbridge. The transducers are disposed symmetrically in this particular embodiment, and hence the loads on the first and second pairs would be equal when the wheels are at the centre of the weighbridge. Many types of transducers or load cells are well known and, for the present purposes, it will suffice to say that each gives an electrical output signal representative of the load applied to that transducer.

The outputs from the load transducers are typically analogue electrical signals which are fed to a computer 20. In this case, each signal may be fed through a zero error and range adjust circuit 22 and then digitised in an analogue-to-digital converter 23 before being applied to the computer 20 which, in this case, is a digital computer, typically a mini or micro computer. The computer 20 is arranged to sample periodically and repetitively the signals from each of the transducers. Preferab!y these signals from all four transducers are sampled simultaneously. The computer determines the weight of each wagon in the manner to be described below and displays this information on a display unit 21 which conveniently comprises a printer on which is printed out the weight of each wagon and the wagon identification. This wagon identification might be fed into the computer manually but provision may be made automatically reading identification marks on each wagon as it passes over the weighbridge.

As a pair of wagon wheels roll onto the weighbridge, the transducers will register a rapid increase in load.

If four such transducers are employed as shown in Figure 2, the load will increase more rapidly on the nearer pair as explained later with reference to Figure 8. Figure 3 illustrates the combined output from two transducers supporting one rail on a weighbridge; the rapid increase occurs between a time T1 and a time tx.

As the wheels roll across the weighbridge, there will initially be rapid fluctuations of the output but these will gradually die down and are small, in the example shown in Figure 1, after a time ty. The digitising unit effects rapid repetitive sampling of the output from each transducer and the computer is programmed to detect when the oscillations have settled down to lie within a predetermined tolerance band which is indicated at 30 in Figure 3. When this settling down of the oscillations has been detected, the load signals are then processed. The repetitive digitised output signals from the transducers are summated and averaged until the wheels leave the weighbridge at the time T2. The load measurement falls off rapidly then and this fall off is arranged to provide the required signals for cessation of load summation and averaging.The total load on the weighbridge is obtained by summing the average outputs of the four transducers.

It will be appreciated that it would be possible to add the outputs of the four transducers before digitising or after digitising and before summating instead of averaging the output from each transducer separately and summing the averages if it is merely desired to obtain indication of the total load. However it is preferred to process the outputs of the individual transducers separately as this enables the direction of travel of the wagon to be determined as will be described below.

Referring to Figure 3 it will be noted that the computer detects the times T1 and T2 and hence it is readily possible to determine the time taken for a pair of wheels to cross the weighbridge. Since the weighbridge is of known length, it is possible from this information to determine the average velocity of each pair of wheels as it passes across the weighbridge. Figure 4 in the upper part of the diagram shows the load output summated from the transducers of a weighbridge as three wagons pass across the weighbridge. For each wagon there are two pairs of wheels and hence each wagon provides two time spaced signals of the general form discussed with regard to Figure 3. These signals are shown in the upper part of Figure 4.In the lower part, the graphical diagram contains a plot of the average velocity, determined as described above, for each pair of wheels as it passes across the weigh bridge. These points are joined by a line which thus constitutes a graphical diagram of the train velocity as it moves across the weigh bridge. From the change in velocity between the first and second pair of wheels of each wagon, the acceleration or deceleration (f) can be calculated. The area between each section of the velocity/time graph for a wagon is determinable from the graph. These areas are labelled dwn and dsn in Figure 4 where dwn is equal to the pitch between the pairs of wheels of wagon n, and dsn is the pitch between the trailing wheels of wagon n and the leading wheels of the next wagon (n + 1).This information may be obtained to verify the correct identification of wagon and to check and identify the type of locomotive pulling or pushing the train.

The equation to establish the pitch can be shown to be as follows: for a locomotive pulling the train lete = (m + 2n) where m is the number of axles on the locomotive n is the wagon number for a locomotive pushing the train e = 2n Then the pitch of the wheels of wagon n: dwn D (t2e - t2(e.1)) (t2(e-1 - t(2e.3) + t2e - t(2e.1)) 2 (t2(e.1) - t(2e3)) (t2e - t(2e.1)) and the acceleration of wagon n: fn - D ((t2(e - t(2,-3,)-(t2e-t(2,-l))) (t2e - t2(e.1)) (t2e - t(2e.1))(t2(e1 - t(2e3)) where D = the length of the weighbridge.

The weight measurement will only take place when the wheel pitch calculation is equal to the wagon wheel pitch specified. In the Figure 5 it is shown as d7 = dwi (for wagon 1), dg = dW2 (for wagon 2) etc. up to del, = dwn (for wagon n). If the locomotive is pushing the train, the above numbering will be reversed. Note the following measurements can be specified accurately for locomotive and wagon.

d5 - the distance between the locomotive driving wheels dL - the distance between the last leading and front trailing driving wheels.

dw - the distance between the wagon wheels.

The following will have to be specified within a loose tolerance due to slackness of the couplings.

dm - the distance between the last trailing drive wheel of the locomotive and the leading wheel of the first wagon.

dsn - the distance between the wheels of two adjacent wagons.

Assume that a train is approaching from the left in Figures 2,7 and 8 and that R1 is the total load sensed by the first sensors 15, 16 and R2 is the total load sensed by the second sensors 17, 18. As shown in Figure 8, there will be a slight overshoot on R1 as the wheels move onto the weighbridge but the fluctuations will die away rapidly. In the arrangement described, the magnitudes of R1 and R2 can be separately determined and hence their ratio can be found. The force readings R1 and R2 are the additional loads in addition to the deadweight of the weighbridge platform. The magnitude of this deadweight is zeroed out in the initiai calibration. If R1 is much greater than R2 at time T1, then the wheel is traversing from left to right. As the wheels move across the weighbridge, the ratio of R1 to R2 will diminish.R1 will equal R2 when the wheels are midway between the two sets of transducers at T2 and the ratio will become zero when the wheels finally ieave the weighbridge platform at T3. Hence it is readily possible from the input information fed into the computer to determine and indicate the direction of travel of the wagons. The weight of each wagon may be determined as previously described. It is likewise possible, as previously described to determine the speed of the wagons. Although the total weight determinations, as described above, is effected by averaging over a time period, in some cases it may be preferred to monitor the ratio of R1 to R2 and to effect a single weight determination at the time when R1 is equal to R2, that is to say when the wheels are in the centre of the weigh platform. The weight on those wheels is the sum of R1 and R2.

This is illustrated in Figures 7 and 8 which are explanatory diagrams. Figure 9 is a graphical diagram indicating how the direction of travel of a wagon is found using the ratio R1/R2. This Figure shows the ratios R1/R2 plotted against time as a train comprising a number of wagons moves across the weighbridge with reversals so that certain wagons move back onto the weighbridge after passing or partly passing over it.

Figure 7 shows a load moving across the weighbridge and Figure 8 shows the outputs of the load cells R1 and R2. An alternative means of obtaining the wagon wheel weight is to monitor R1/R2 and when it equais 1, R1 = R2 and, as previously explained, the wheel should be in the centre of the weigh platform (point C, time T2, Figure 8). At this moment the weight is taken as W1 = R1 + R2 Once the weight has been recorded; R1 is monitored and when R1 (atT3) = R2(atT1) (within a small tolerance band) (see Figure 8), the weighing operation is completed for that pair of wheels.However, if the wheel rolls backwards before R1 = R2 (at T1) can be established, see CD Figure 9, the position will be reached when R1/R2 > > 1 and finally R1 + R2 = 0, at which time the wheel will have run back off the weigh platform which is contrary to the first R1/R2 comparison that was made. If a second wheel runs backwards onto the weighbridge, DE Figure 9, R1/R2 < < 1, the 1,the computer 20 will be programmed to count the number of times this occurs, so that when the train starts up and crosses the weigh bridge in the correct direction, the wheels can be recounted until the point is reached at which the rollback started and the weighing procedure can recommence.

The weight of the second wagon wheel W2 is obtained in a similar manner toW1. The total wagon weight is obtained by adding W1 + W2. This weight is noted with the appropriate wagon number. The whole procedure is repeated until all of the wagons have been weighed.

If four transducers are employed, checking of the transducers or any defective transducer may be made by comparison of appropriate readings and this can be done automatically by preprogramming the computer. It is preferred however, for this purpose, to use, for each transducer, a load'cell comprising a double strain gauge. Thus there are, in such a construction, eight strain gauges. These are iilustrated in Figure 6, which is a modification of Figure 2, using the following notations. In each load cell with two strain gauges, these two gauges are labelled X and Y, and a pair of load cells across the platform at right angles to the rails can be labelled A and B and finally the pair of load cells on the leading edge of the weighbridge is numbered 1 and the trailing edge numbered 2.A checking procedure can now be carried out by the weigher computer during the weighing cycle.

Referring to Figure 7, as a wheel pair moves onto the weigh platform the time will be noted as T1.

Strain gauge 1AX is compared with 1AY and 1 BX is compared with 1 BY. These measurements should agree to within a small tolerance band. If they do, then (1AX + 1AY)/2 and (1BX + 1 BY): 2 are taken as the respective load cell measurement.The summation of these gives the reaction to the wagon wheels at each end of the weighbridge and is expressed as R1 = (1AX+ 1AY)/2+ (1BX+ 1 BY)/2 and R2 = (2AX + 2AY)/2 + (2BX + 2BY)/2 If however, a pair of strain gauges do not agree, then these pair are compared with each of those on the other load cell; i.e., 1AX is compared with 1 BX and 1 BY, and 1AY is compared with 1 BX and 1 BY and end 2 is treated in a similar manner. This should establish which strain gauge is at fault. The computer can be programmed to print out a fault message stating exactly which strain gauge and load cell is defective. An accurate weighing can still be obtained by taking the load cell measurement as being that of the good strain gauge. For example if 1AY is the defective strain gauge then the reaction at one end of the weighbridge would be: R1 = 1AX + (1BX + 1BY)/2 or an alternative way of expressing it would be to ignore the defective load cell signal and replace it by the other good strain gauge measurement. This particular comparison need only be carried out once at the start of a wagon wheel measurement to establish the effectiveness of the load cells at each end of the weigh platform.

Claims (14)

1. A method of determining the weight of a railway wagon in a train using a weighbridge over which the train passes, the weighbridge having load measuring transducers, comprising the steps of repetitively determining the weight as a pair of wheels move across the weigh bridge and averaging the measure load during a period when the load measurements are within a predetermined tolerance band.

2. A method as claimed in claim 1 wherein the loads on successive pairs of wheels of each individual wagon are measured and summated in a computer.

3. A method as claimed in either of the preceding claims wherein the weighbridge is provided with a pair of load measuring means spaced along the length of the rail track and wherein the direction of movement of the wagon is determined by noting which load measuring means first responds as the wheels move onto the weigh platform.

4. A method as claimed in any of the preceding claims wherein each load measuring means comprises two transducers for each rail.

5. A method as claimed in claim 4 wherein, for checking whether the wagon moves backward over the weighbridge, the computer is arranged to monitor the ratio of the determined loads on the two spaced load sensing means.

6. A method as claimed in any of the preceding claims and wherein the weighbridge is provided with a pair of load measuring means spaced along the length of the rail track, each load measuring means having separate load sensors for each rail, the sum of the loads of the sensors supporting that rail when the sum is within a predetermined tolerance band.

7. A method as claimed in any of claims 1 to 5 and wherein the weighbridge is provided with a pair of load measuring means spaced along the length of the track and wherein the weighing is effected when the determined loads on the two spaced sensing means are approximately equal.

8. A method of determining the weight of railway wagons in a train substantially as hereinbefore described with eference to the accompanying drawings.

9. Apparatus for carrying out the method of any of the preceding claims and comprising a weigh bridge with transducers producing output signals and computing means responsive to the output signals and arranged to determine the weight of each wagon as it passes over the weighbridge.

10. Apparatus for determining the weight of a railway wagon in a train, which apparatus comprises a weighbridge having load measuring transducers and means for repetitively determining the weight as a pair of wheels of the wagon move across the weigh bridge and means averaging the measured loads when the load measurements are in a predetermined tolerance band.

11. Apparatus as claimed in claim 10 and having, for each rail, two transducers spaced along the length of the rail.

12. Apparatus as claimed in claim 11 and including means for determining or responsive to the ratio of the loads determined by the spaced transducers for each rail.

13. Apparatus as claimed in any of claims 10 to 12 wherein each transducer comprises two load sensors and wherein means are provided for comparing the outputs of the two sensors in each transducer.

14. Apparatus for weighing railway wagons substantially as hereinbefore described with reference to the accompanying drawings.