This invention relates to railway track maintenance utilising a track maintenance machine which runs on the track. More particularly, but not exclusively, the invention relates to railway track maintenance by the so- called stoneblowing method •

In known track maintenance methods data is obtained from a stretch of track to be maintained either by a separate survey (two pass operation) or during the maintenance run (single pass operation) and from the data obtained the necessary adjustments to be made to the track to achieve an improved vertical track geometry (i.e a design profile in the case of two pass and smoothing in the case of single pass) calculated. In stoneblowing the adjustment values necessary are translated into predetermined quantities of stone or other packing material (hereafter_included in the term "stone") to be injected under the individual sleepers. In tamping the adjustments are translated into relative heights to which the track at successive sleepers is to be lifted.

During a stoneblowing operation individual sleepers are overlifted from their premaintenance level and the predetermined stone quantities injected into the x ^τ oid created under the sleeper soffit. The level to which the sleeper is overlifted must be adequate to allow injection of all the desired stone for the optimum long term track quality. Generally for 20mm sized stone the overlift must be at least 40mm. Following stone injection the sleeper wi___L settle on to the stone as the track is lowered. his settlement will take place under the weight of the sleeper and by the passage of the machine over it. However the track, as left by the machine will generally still be higher than its design height, typically 25 mm higher. This residual overlift is eliminated by the subsequent passage of traffic which will consolidate the injected stone so that the track adopts substantially the design profile. In practice it has been found that there is some scatter in the initial settlement of the track following

aintenance and that this can result in the track not achieving an optimum profile immediately behind the maintenance machine, i.e. immediate post maintenance.

In the case of tamping the track can also be purposely overlifted in a controlled manner and tamped. The overlift is then eliminated by the action of subsequent traffic and/or a track stabilisation device to its design height. When the track stabilisation device is mounted on the machine to act immediately after tamping the track immediate post maintenance should be at its design height. Otherwise there will be a residual overlift as in the case of stoneblowing. in practice the immediate post maintenance level is somewhat unpredictable.

The aim of the present invention is to improve the control of the immediate post maintenance track geometry.

According to the present invention a method of track maintenance utilising a track maintenance machine which runs on the track and which has track lifting equipment and stone injection or stone tamping or other stone packing equipment and also has a measuring system for monitoring the lifting of the track by the track lifting equipment, the method comprising determining the necessary adjustments to be made to achieve a design profile and then as the machine progresses along the track overlifting the track at selected sleepers and injecting or tamping stone under the sleepers,is characterised in that the said measuring system is arranged to measure the lift achieved at an immediate post maintenance position to the rear of the machine with reference to the level of unmaintained track to the front of the machine as the machine progresses along the track.

In further development of the invention the overlifting of the track is controlled in part in dependence upon the measured immediate post maintenance lift.

Advantageously the overlifting is controlled in dependence upon the mean of the the measured immediate post maintenance lift at a number of preceding sleepers

A correction factor for controlling the overlift at

future sleepers may be obtained by determining the relationship of the applied lift to the immediate post maintenance lift at a number of sleepers

Advanrageously the overlift is controlled in the sense to maintain the track immediate post maintenance substantially smooth.

Said measuring system may comprise at least one straight reference line extending from a front feeler located forwardly of the track maintenance machine on uncorrected track to a rear feeler located at said immediate post maintenance position and sensor means measure the vertical offsets of the track from said line at predetermined points along said line and comprise a first sensor for measuring the offsets at a position forward of the lifting equipment on uncorrected track and a second sensor for measuring the offset of the track adjacent the track lifting equipment. The reference line may be a wire but it could be a beam of electromagnetic radiation such as a laser beam.

Exemplary embodiments of the invention will now be described with reference to the accompanying diagrammatic drawings, in which:

Figures 1 serves to explain a double pass stoneblowing method, and

Figure 2 serves to explain a single pass stoneblowing method.

Referring now to Figure 1, a section of railway track is shown at 1 on which a stoneblowing machine 2 is located, which during a maintenance run travels in the direction of arrow 3. The stoneblowing machine is represented in the drawing by foremost and rearmost load bearing bogies 4 and 5 respectively. The bogie 4 has wheelsets 6 and 7 and the bogie 5 has wheelsets 8 and 9.

Feelers are guided along the track and contact the track at points A,B,C and D, which have a fixed spacing from each other along the machine. The wheelset : constitutes the feeler guided on the track at point C and the further feelers 11 to 13 guided on the track at points

A,B and D are in the form of trollies having flanged wheels running on the track. The feelers 11 and 13 support the ends of a wire 14 extending between them, the wire 14 constituting a measuring reference system. The wheelset 6 supports a sensor 15 for determining the vertical offset of the track from the wire 14 at point C and the feeler 12 supports a sensor 16 for determining the vertical offset of the track from the wire 14 at point B. The track maintenance machine 2 also has distance measuring equipment (not shown) to determine the position of the machine on the track

Track lifting eσuipment of known form is represented at 18 and stone injection equipment of known form is represented at 19. An on-board computer (not shown) is provided to record the measurements made by the sensors 15 and 16 and the distance measuring equipment and to provide data processing utilising these measurements in order ,inter alia, to calculate the stone quantities to be placed under the sleepers. Under control of the computer the stone quantities are automatically delivered in known manner from a hopper (not shown) to the stone injection equipment 19 at the appropriate time as the machine progresses along the track.

In carrying out a track maintenance operation using the machine of Figure 1, a preliminary measuring run is first carried out over the length of track to be maintained. During the preliminary measuring run the offsets of the point B from the wire 14 are measured at stepped intervals along the track using sensor 16 and recorded in the on-board computer. From these measurements the original track profile represented by the dotted line passing through points A,B,C and D is calculated. By running a track design algorithm over this profile the design profile represented by the dashed line passing through D" and the design lift DD" for each sleeper and hence the stone quantities to be injected under each sleeper can be calculated. Also during this run the offsets of the track at point C from the wire 14 are

measured using the sensor 15 and recorded in the on-board computer. Since the measurement at point C is for loaded track and the measurement at point B is for unloaded track a difference value can be obtained representing the void beneath any given sleeper and can be used in determining sleeper height adjustments to achieve the design level if the chosen method requires it. As an alternative to supporting the sensor 15 on the wheeelset 6 it could be mounted on a separate feeler positioned adajacent a wheelset in order to obtain a loaded measurement If a loaded measurement is not required then instead of using a loaded wheelset 6 to support the sensor 15, a further feeler similar to the feelers 11 to 13 could be provided and positioned between the wheelset 6 and the feeler 11.

Then a maintenance run is carried out during which the machine travels in the 'direction of arrow 3. During the maintenance run the track is overlifted by equipment 18 at selected sleepers such that the maximum lift BB'is given to the sleeper to be stone injected. The predetermined quantities of stone are then injected by injection equipment 19 at the selected sleepers. Following stone injection as the machine progresses along the track the track behind the injection equipment settles onto the stone under the weight of the sleepers and the passage of the rear of the machine over it. Hence during a maintenance run the track beneath the machine is represented by the full line A,C,B',D'. The point D' indicates the level of the track immediately after the machine has passed, i.e. the immediate post maintenance level.

During the maintenance run the sensor 16 monitors the height to which the track is lifted to control the track lifting equipment 18 to achieve the desired overlift. This is done by comparing the height of point B' relative to points A and C with the height measured for point B during the preliminary measuring run using the outputs of sensors 15 and 16. The feeler 12 supporting the sensor 16 is positioned as close as practical to the sleepers that are to be stone injected. Also during the maintenance run.

the sensor 15 measures the offsets of the track at point C from the wire 14. Since the levels of points A and C remain the same during both the preliminary measuring run and the maintenance run, the change in offset DD' at point D, i.e. the immediate post maintenance lift and hence the residual overlift D'D" can be calculated. Thus from the geometry of the measuring system, the change in the output of the sensor 15 between the preliminary measuring run and the maintenance run gives an indication of the change in the height of the wire 14 caused by the track at feeler 13 changing from D to D' .

If therefore:

0j5 = output from sensor 15 on preliminary run

0^5'= output from sensor 15 on maintenance run <_>i6 = output from sensor 16 on preliminary run (Dig'= output from sensor 16 on maintenance run movement of the sensors in the direction of track lift increases the output movement of the sensors in the direction of track lowering decreases the output the sensor output is scaled in units of length

Then: the lift given to each sleeper immediately following the passage of the machine, i.e. the lift at point D immediate post maintenance is given by;

DD'=(0 ₁₅ ' - 0 ₁₅ )*AD/AC the residual overlift is given by;

D"D' = DD' - DD" where DD"is the design lift

Therefore the residual overlift can be derived from;

D"D' = (Oi5' - 0 ₁₅ )*AD/AC - DD"

The lift given to each sleeper at the time of overlift is given by;

BB' =(0 ₁₆ ' - 0 ₁₆ ) - (0 ₁₅ ' - 0 ₁₅ )*AB/AC

Advantageously for the purposes of calculation:

AB = BD, and

AC is a sub-multiple of the distance AB

The optimum situation will be the one that operates with the smallest value of residual overlift D"D' and where the residual absolute height of D' is the same at each sleeper so that the track immediate post maintenance is smooth. Experience shows that there is a correlation between the value of immediate post maintenance lift DD' and the actual lift BB' given to each sleeper during stoneblowing but that this relationship varies from site to site. Therefore by comparing the lift DD' with the actual lift BB' that was given to each sleeper the relationship for the site being maintained can be calculated. This information can then be used to control future lifts at subsequent sleepers such that the residual overlift D"D' is kept to a controlled value.

The correction to the overlift can be applied on a sleeper by sleeper basis but an improvement will probably result if the correction is made on the mean result from a number of sleepers. If the mean value of the immediate post maintenance lift is taken from say the last ten sleeper positions recorded then the system will adapt to any underlying trends in the track whilst being resistant to any freak individual results. With experience the number of sleepers over which to take the average can be optimised. The machine can thus be built to "learn" the characteristics of each individual site and adapt itself to it.

As the settlement is likely to be influenced by features such as rail section, sleeper type, sleeper spacing, etc. this data can be recorded in a data base. At the commencement of work at each site, if the key characteristics are fed in to the machine's control system, the machine can be programmed to choose the most suitable lift/settlement characteristics to be used at the commencement of maintenance. These values, if wrong, will rapidly converge to the optimum values as the adaptive system derived from the measurement of immediate post mainte lance lift as described above takes control. hen the machine is first used a value of constant

overlift can be used on the first few sleepers. The machine will then adapt these values to achieve the optimum result.

With experience the lift values of the stoneblowing machine will be able to be adjusted such that the value of the immediate post maintenance lift DD' can be kept to a minimum thus fulfilling the desired objectives of achieving a smooth post maintenance geometry and a minimum immediate post maintenance lift whilst achieving an adequate overlift

10 at each sleeper to accept the injected stone.

The method described above uses sensors 15 and 16 measuring offsets from a wire chord 14 as its measuring system. A method using an alternative measuring system, such as beams of light and optical sensors to perform the

15 same measurements of track levels would work equally well.

Referring now to Figure 2, a machine capable of carrying out a single pass stoneblowing operation is shown. The machine is similar to that of Figure 1 and the same reference numerals have been used to designate ² corresponding items. The differences from the machine of Figure 1 are at the front end of the machine where further feelers 21, 22 and 23 contact the track 1 at points E, F and G and further sensors 23, 24 and 25 are provided on feelers 11, 21 and 22. Also the wire chord is extended to

?5 be supported by the feeler 23. These additional items measure the versines of the track profile ahead of the machine.

In the arrangement shown the dimensions are such that AD = AG

30 AF = FG = AB = BD

AE is a sub-multiple of the distance AF AC is a sub-multiple of the distance AF From the versine measured at E by the sensor 24 in relation to A and G measured from the outputs of sensors 23

35 and 24, a correction for the track geometry can be derived. The output of sensor 15 can be used to adjust for the loaded track profile. The versine at point F is measured in relation to points A and G as the machine progresses

- Q _

along the track from the outputs of sensors 23 and 25. From the versines that, were measured at F the premaintenance shape of the track at points B and E in relation to points A, F and G can be derived. The outputs at 23 can be used to determine the immediate post maintenance lift DD' at point D. The lift at point B is controlled from the output of the sensor 15.

This is one example of a system for carrying out the track geometry corrections in a single pass over the track.

10 Other dimensions could be used on the chord arrangement.

Another method to derive the control information would be to use an inclinometer attached to a track measuring trolley pushed ahead of the machine to record the premaintenance track geometry. Such a system is described

15 in UK Patent GB 2085825B.

The system could either use the lost motion device described in this Patent to index the track geometry measuring trolley along the track or the indexing could be achieved by the track maintenance machine itself as it

20 p αses at the sleepers to carry out the maintenance.

Other measuring systems could use a combination of inclinometer measurements and versine measurements

The method described with reference to Figures 1 and 2 would be equally applicable to methods using other types of

_* -_ track correction tools, such as tamping equipment. It would be particularly suitable for methods of track tamping where significant settlement of the track is expected to occur following maintenance either under the action of traffic or from a track stabilisation device. In this

³⁰ case the value of DD" that the machine was programmed to achieve would be optimised to suit the expected degree of settlement. Such an arrangement would be particularly advantageous where the maintenance is being carried out with large lifts. 35