GB2268780A

GB2268780A - Mining apparatus

Info

Publication number: GB2268780A
Application number: GB9213453A
Authority: GB
Inventors: Colin Gordon Michael Merriman
Original assignee: Gullick Dobson Ltd
Current assignee: Gullick Dobson Ltd
Priority date: 1992-06-24
Filing date: 1992-06-24
Publication date: 1994-01-19
Also published as: AU4145893A; GB9213453D0

Abstract

Method and apparatus for enabling movement of a section (18-24) of a mining conveyor in at least two separate modes. In the first movement mode the conveyor section (21, 22) is advanced by a first distance (x) which corresponds to the full stroke of a hydraulic ram associated with the conveyor section and in the second mode the conveyor section (18-20, 22,-24) is advanced by a distance (a-e) less than the first distances (x). In the first movement mode hydraulic pressure to the ram is maintained subsequent to movement of the conveyor section, and in the second mode this pressure is not maintained. The invention includes a computer system for calculating the require movement distances for a number of different conveyor sections, as well as a kit of parts and modified rams for modifying existing systems to enable them to function according to the described method. <IMAGE>

Description

MINING APPARATUS The present invention relates to mining apparatus.

Figure 1 shows a plan view of a coal face 1. Modern mining techniques utilise automated cutting machines 2 for making a straight cut parallel to the coal face 1. Rotating blades 3 mounted on the machines cut away a slice of the coal face, the depth of the slice "A" being known as the "web", and deposit the coal onto a conveyor 4. The conveyor acts as the track for the cutting machine and runs parallel to the coal face between two access tunnels 5,6, one on either side of the coal face and perpendicular to it.

The conveyor 4, which is normally a limited chain of straight sections, feeds the cut coal onto conveyors in the service tunnels for delivery to the surface.

Roof supports 9 are provided and these form a safe area under which miners can work.

The roof supports and conveyor are linked by hydraulic rams 10.

After a cut has been made along the length of the coal face in one direction (shown as from left to right in the figure) the conveyor and cutting machine are pushed forward as a unit and then the roof supports are pulled forward, usually one at a time, by the web distance so that the cutting machine may then move back along the coal face to cut out a section of the face in the other direction.

Movement of the conveyor, cutter and roof supports is achieved by means of the rams 10.

As the roof supports are stepped forward, the now unsupported roof section is allowed to fall in behind them.

A variety of techniques are known for controlling the hydraulic advance of the conveyor and roof supports. A first system, known as "latch push" uses the full stroke of the hydraulic rams to push the conveyor forward and maintains the hydraulic pressure subsequent to movement of the rams to ensure that the pistons remain at the end of their stroke. Maintenance of the pressure in this manner is advantageous in that if a fall in should occur in front of the conveyor the ram will resist being pushed back by the weight of the coal. Other causes of "push back" such as conveyor movement due to the cutting action are also resisted.

A second, analogue, technique is known. This technique involves a transducer for sensing the position of the hydraulic rams and driving the rams until a predetermined position is reached. The analogue technique is an open loop control system, since the hydraulic pressure within the rams is not maintained once the desired position has been attained. The control of the pistons by an analogue system enables the web distance to be varied. The disadvantages of this technique are twofold : firstly, that a solenoid valve is required to turn the flow of hydraulic fluid on and off, each solenoid having a substantial power requirement; and secondly, the fact that hydraulic pressure is not maintained allows "push back" of the rams.

Even a closed loop analogue system would exhibit this disadvantage, since once a ram has been pushed back by a cave-in the coal in front of the ram will prevent any correctional movement.

In addition, because the conveyor is essentially made up of a number of rigid sections it is necessary for the entire length of the conveyor to be advanced substantially simultaneously. To perform this advance with the conventional analogue technique would require a large number of solenoid valves to operate at the same time and a very substantial power supply would be required. For this reason an analogue advance is more commonly used for advancing the roof supports, as this may be done one support at a time, than for advancing the conveyor.

Variation of the normally constant web may be necessary for a number of reasons. For instance, geological variations in the strata of the coal face may necessitate a smaller web, cave-ins may cause variations in the normally straight cutting face and the rotation of the cutting blades may cause movement of the conveyor.

Another phenomenon called "pull-back", is illustrated in Figure 2 which is a schematic plan view of the conveyor showing movement of the roof supports. Subsequent to the conveyor advance, each roof support is moved forward one at a time. As each support 9 is moved forward in the direction of the arrow "A" by the ram 10 there is an opposing reaction "B" as the conveyor tries to pull the conveyor out of line.

Because of the varying conditions it is therefore occasionally necessary to re-align the conveyor to compensate for these effects.

Since the roof supports and conveyor are linked by hydraulic rams the web distance is a function of both the support advance and the conveyor advance.

The solutions to the problem of conveyor realignment currently in use fall into two categories (i) A first solution is to use a latch conveyor push system and an analogue support advance - the latch conveyor push giving the advantages of low power consumption and resistance to "push back" and the analogue technique for support advance allowing easy variation of the web.

Because the supports may be advanced one at a time power consumption by the solenoid valves is not excessive. However, as the variable length stroke of the analogue technique is being applied to the support advance, which is a rapid movement, and the turn on/turn off of the solenoid valves is slow, accuracy of advance is lost.

(ii) Secondly, an analogue system is used on both conveyor and support advance with the solenoid valve being "on" throughout the ram stroke.

This method allows reasonably accurate ram positioning.

Unfortunately, since the conveyor is relatively inflexible, all the hydraulic rams need to be operated at once, thus necessitating the solenoid valves to all be "on" at the same time and creating the need for a very substantial power supply. In addition, the problems of push back of the conveyor are not adequately dealt with as explained above.

Up until now, combining latch push and analogue technique in a single hydraulic ram for conveyor advance has not been achieved, as the two traditional systems of latch push and the analogue techniques are generally thought to be incompatible.

There is therefore a need to provide a satisfactory system for the control and implementation of the cutter advance, particularly in situations where the web distance needs to be varied, or where a web requires straightening.

According to a first aspect of the present invention a method is provided for moving a mining conveyor, wherein a plurality of roof supports are connected to the conveyor by a plurality of hydraulic rams and each roof support is connected to a section of the mining conveyor by at least one hydraulic ram, the rams being used to move the conveyor and wherein two separate modes of movement are provided for advancement of the conveyor section a first movement mode wherein the conveyor section is advanced by the ram by a first distance substantially perpendicular to the line of the conveyor under hydraulic pressure and the hydraulic pressure is maintained even after the ram has moved the conveyor section by the first distance; and a second movement mode wherein the conveyor section is advanced by the ram by a second distance, substantially perpendicular to the line of the conveyor, under hydraulic pressure, and the hydraulic pressure on the ram is not maintained after the ram has moved the conveyor section by the second distance.

The first distance preferably corresponds to a distance moved by the conveyor section when the hydraulic ram has reached the end of its stroke.

The second distance is preferably less than the first distance.

Preferably, the same hydraulic ram that is used for moving the conveyor section is also used to advance the roof support.

The second distance may vary from one conveyor section to another according to necessity.

Any combination of the first and second modes can be used for advancement of the conveyor sections i.e. some, none or all of the hydraulic rams may operate in the first mode and the remainder, if any, dperate in the second mode according to necessity.

The decision as to which conveyor sections are to be advanced in the first mode and which are to be advanced in the second mode may be made by an operator. Alternatively, a computer control system may be used to select which of the conveyor sections are to be advanced in which-mode at any given time.

An operator may set the required second distances for each conveyor operating in the second mode by adjusting the ram operation for each individual conveyor section at each of the associated roof supports in turn.

Alternatively, a system may be provided for interlinking the rams such that an operator may set the required second distances for each conveyor section operating in the second mode by adjusting the ram operation for each individual conveyor section in turn by entering the required movement data at a single location. The location may be at or adjacent to one of the roof supports or alternatively at a remote position. The system for interlinking the rams may form part of a computer control system.

The computer control system may provide a facility for automatically setting the distances by which some or all of the conveyor sections advance when operating in the second mode.

When the conveyor advance is to be used to straighten a coal face, the computer control system may calculate a "best fit" distance for advancing each of the conveyor sections and control the individual rams accordingly.

The best fit may be achieved by means of a computer program and calculated on the basis of just one or more manual or computer measurements overestimates of distance between the conveyor and coal face.

According to a second aspect of the present invention apparatus is provided for moving a mining conveyor including a plurality of roof supports connected to the conveyor by a plurality of hydraulic rams, each roof support being connected to a section of the mining conveyor by at least one hydraulic ram, the rams being used to move the conveyor, wherein each roof support includes means for advancing its associated conveyor section in either one of two separate modes of movement, the two modes comprising: a first movement mode wherein the conveyor section is advanced by the ram by a first distance substantially perpendicular to the line of the conveyor under hydraulic pressure and the hydraulic pressure is maintained even after the ram has moved the conveyor section by the first distance; and a second movement mode wherein the conveyor section is advanced by the ram by a second distance, substantially perpendicular to the line of the conveyor, under hydraulic pressure and the hydraulic pressure on the ram is not maintained after the ram has moved the conveyor section by the second distance.

Preferably, the means for advancing the conveyor section in the first mode of movement includes a first hydraulic valve for controlling hydraulic fluid flow such that when the valve is in a first state hydraulic fluid pressure causes advancement of the conveyor section, by the ram, by the first distance and the valve remains in the first state even after the ram has moved the conveyor by first distance.

Preferably, the means for advancing the conveyor section in the second mode of movement includes the first hydraulic valve for controlling hydraulic fluid flow such that when the valve is in the first state hydraulic pressure causes advancement of the conveyor section, by the ram, until the ram has moved the conveyor by the second distance whereupon a second hydraulic valve is controlled in such a manner that the hydraulic pressure is no longer maintained causing the conveyor section to stop moving.

Preferably, the second hydraulic valve is controlled to either cut off or reduce hydraulic fluid flow to the ram. The second hydraulic valve may be controlled to divert the hydraulic fluid flow away from the ram.

Preferably the first and second valves are triggered by a signal so as to pass from a second state to a first state.

Preferably, the first state allows hydraulic fluid to flow through the valves.

Preferably hydraulic fluid pressure is operable to maintain the valves in the first state, after they have been triggered such that maintenance of the trigger signal is not necessary.

Preferably the trigger signal is an electrical signal.

Preferably, the ram is equipped with positional sensing means.

Alternatively, the conveyor section may be provided with positional sensing means.

When operating in the second mode of movement the positional sensing means is used to detect when the conveyor has been moved by the second distance.

According to a third aspect of the invention a kit of parts is provided for modifying a roof support and hydraulic ram to permit operation in both the first and second modes of movement as described in relation to the first and second aspects of the invention.

The kit may include any combination of a hydraulic valve, a manifold and positional sensing means.

According to a fourth aspect of the invention a computer system is provided arranged in use, to calculate the degree of movement required by at least some of a plurality of conveyor sections in order to move from an initial conveyor configuration to a desired second configuration.

Preferably, in the second configuration the conveyor sections interact to form a substantially straight line.

Preferably the second configuration is chosen such that none of the conveyor sections need to move by more than a maximum distance to reach it from their initial configuration.

The maximum distance preferably corresponds to the distance moved by a conveyor section when propelled by a hydraulic ram and wherein the ram performs a full stroke.

Preferably positional data concerning the initial configuration is entered into the computer system and the computer uses this data to calculate the movement required by each section to achieve the desired second configuration.

Preferably, the positional data concerning the initial configuration is obtained from positional sensing means which is associated with each conveyor section or with hydraulic rams associated to the conveyor sections.

Alternatively, the positional data may be obtained by manual or automatic measurement or estimation.

Preferably, the computer system may utilise second data to calculate the degree of movement required by each of the conveyor sections to attain the second configuration.

Preferably, the second data is based upon a series of measurements proportional to the distance between each of the conveyor sections and a coal face.

Alternatively, the second data may be obtained from a sample of measurements proportional to the distance between a selected number of conveyor sections and a coal face and interpolating between the samples.

Interpolating may be by means of a "best-fit" curve algorithm, or by straight line interpolation.

Preferably the sample of measurements is taken at points of interest along the length of the coal face. The number of samples may be varied according to the profile of the coal face and the initial configuration of the conveyor.

A fifth aspect of the invention provides a hydraulic ram for operation in either one of two modes: a first mode in which the ram is arranged to propel a first member by a first distance under hydraulic pressure and maintains the hydraulic pressure even when the first distance has been attained; and a second mode in which the ram is arranged to propel a first member by a second distance under hydraulic pressure but does not maintain the pressure once the second distance has been attained.

Preferably, the first member is arranged to be a section of a mining conveyor.

Preferably, the first distance corresponds to a distance moved by the first member when the hydraulic ram performs a full stroke and the second distance is less than the first distance.

Preferably, the hydraulic ram is equipped with positional sensing means and at least two hydraulic valves, the first hydraulic valve being used for operation in the first mode and the first and second hydraulic valves being used for operation in the second mode.

By way of example, specific embodiments of the invention will now be described, with reference to the accompanying drawings in which: Figure 3 is a schematic block diagram showing a computer control system for use with the present invention: Figure 4 shows a mis-aligned mining conveyor, and Figure 5 is a flow diagram illustrating the method of the present invention.

The present invention provides a method and apparatus for moving a mining conveyor and combining the advantages of latch push and the analogue technique for conveyor advance on a single system by the provision of an extra hydraulic circuit for halting a latch push operation after a predetermined ram position has been attained.

Known latch push systems utilise a hydraulic valve system for the hydraulic ram fluid which, once initiated electrically, is hydraulically self sustaining. This type of valve is convenient for latch push systems as the hydraulic ram is always pushed to the end of its stroke and maintained there by the pressure of the hydraulic fluid. The momentary action necessary to turn it "on" means that its electrical power requirements are very much less than that of the solenoid valves required for conventional analogue push systems.

The apparatus of the invention uses a modified version of the latch push system. But instead of having a single electrically triggered hydraulically self sustaining valve, a second valve is incorporated into each ram system together with positional sensing means in the form of a transducer mounted on the ram. The inventive method uses essentially the conventional latch push system for situations where a fuil web advance is required, i.e. triggering the first valve to allow hydraulic fluid to flow under pressure and propel the ram to the end of its stroke and maintaining the hydraulic pressure even after reaching the end of its stroke.But upon encountering the need for reducing the web (e.g. in order to straighten the conveyor) a second mode of operation is used whereby the first valve is triggered, as before, to propel the ram and the conveyor but as soon as the transducer on the ram signals that the desired web has been reached the second hydraulic valve is triggered so as to either cut-off, reduce or divert the hydraulic fluid flow to the ram and stop the conveyor advance.

Because the valves used are of the electrically triggered but hydraulically self sustaining type, all the rams may be operated at substantially the same time for conveyor advance without the need for a substantial power supply.

The extra hydraulic circuitry necessary for the implementation of the present invention is, in its most basic form, a small bolt-on manifold incorporating the additional hydraulic valve plus a ram having a transducer for positional sensing.

In this manner, the benefits of flexibility of the analogue push systems are attained.

The necessity for a substantial electrical power supply is removed, since the electrical triggering signals are only momentary.

Where the full web distance is required only one of the two valves is in use and the system operates in a latch push mode.

In a first embodiment of the invention, if the web has to be varied, a desired stroke distance is entered manually into each support. When the transducer on the ram indicates that the desired distance has been attained a trigger signal is sent to the second hydraulic valve to stop the ram movement i.e. an analogue push.

Alternatively, in a second preferred embodiment shown schematically in Figure 3, the roof support/conveyor movement system is computer controlled and the supports interlinked. In the figure, each roof support has an associated control unit 11 for controlling the movement of a conveyor section, and the roof support itself, by means of one or more hydraulic rams (not shown). Sensors 12, in the form of transducers associated to hydraulic rams, output electrical signals dependent on the position of the rams to the control units. Each control unit triggers its associated hydraulic valves 13 at the correct instant dependent upon the transducer outputs and the desired operating mode (latch push or analogue). Input/output interfaces 15 are provided at each control unit to input instructions to and output data from the unit.A supervisory computer 16 can control the whole system via a bus 14 and control access to the bus for exchanges of information between the control units. The computer may also perform various support functions to be described in greater detail hereinafter.

The computer control system shown in Figure 3 has a great deal of operational flexibility. Variation of the web distance may be achieved in a variety of ways: Firstly, because the control units are interlinked by the bus system 14, the desired stroke distance (or the web) for each of the conveyor movement rams can be entered, by an operator, into any one of the input/output interfaces 15 associated to the control units. As the desired web distance may be different for each of the conveyor movement rams the data input by the operator may be quite complex. This operational mode allows a faster set-up of the movement systems than the manual system, by avoiding the need for walking to each roof support in turn. but still leaves the operator in control.

Secondly, the web distances can be varied from a location remote from the coal face by including extra interfaces at any location with access to the bus.

Thirdly, the computer 16 can perform an automatic control of the hydraulic ram units and advance the conveyor. cutter and roof supports by the full web automatically at the end of each cutter pass of the coal face. The computer may also be connected to receive inputs from operators or from sensors which indicate the actual configuration of the conveyor such that the computer is informed as to how much, if at all, the conveyor is out of line and the computer may instruct variation of the web accordingly.

The computer system provides additional support by including analytical programs. One of these programs may be for interpolation such that an operator may take a few strategic measurements of the conveyor position with regard to the coal face and the computer will interpolate between them (e.g. by using a so-called "best-fit curve" program) to instruct the degree of conveyor advancement for the conveyor movement rams between those which have been measured.

To illustrate the procedure for straightening the line of a conveyor Figures 4 and 5 will now be referred to.

Figure 4 shows part of a conveyor of which only the sections, 18 to 24, surrounding a disturbed area are shown. The broken line (---) shows the conveyor as it would appear if it were not disturbed.

Assume now that the cutter has reached the edge of the coal face and that the conveyor is due to advance.

A full web advance by latch push for each section would move the correctly aligned sections, 18 and 24 to line 1 on the figure, but would move the most severely disturbed sections. 21 and 22. to line 2 and would obviously not correct the disturbance.

Therefore, in order to correct the disturbance and advance the conveyor as far as possible, the best solution is to move sections 21 and 22 by the full web and decrease the advance for the other sections to re-align the conveyor along line 2.

To achieve realignment it is necessary to know how far each section requires to be moved (i.e. a, b, c, d and e of Figure 4). These distances may be either: all measured manually, measured automatically by a sensor or estimated by an experienced operator. Alternatively some of the distances may be measured and the other distances interpolated as already described.

Once the required advance for one or more of the conveyor section is known that data may be input into the control units either automatically (if fully computer controlled) or by means of one or more of the I/O interfaces or remotely as already discussed.

Having input all the data the conveyor can now be advanced.

Referring to Figure 5 all the hydraulic rams are initiated in the "latch push" mode (by opening their "first" hydraulic valves) and each hydraulic ram is monitored by one of the control units. If a particular ram is actually being used in the "analogue" mode the control unit will monitor the distance moved, as indicated by the hydraulic ram sensor and once the distance reaches its particular desired value, the movement is stopped. This is achieved by operating the second valve on the ram which is effectively a "latch push cancel" valve. When all the conveyor sections have stopped moving the conveyor will be aligned with line 2 of Figure 4.

The roof supports can now be advanced in conventional fashion.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method for moving a mining conveyor, wherein a plurality of roof supports are connected to the conveyor by a plurality of hydraulic rams and each roof support is connected to a section of the mining conveyor by at least one hydraulic ram, the rams being used to move the conveyor and wherein the method provides two separate modes of movement for advancement of conveyor sections: a first movement mode wherein the conveyor section is advanced by the or each ram by a first distance relative to the roof support under hydraulic pressure and the hydraulic pressure is maintained even after the or each ram has moved the conveyor section by the first distance; and a second movement mode wherein the conveyor section is advanced by the or each ram by a second distance relative to the roof support under hydraulic pressure, and the hydraulic pressure on the or each ram is not maintained after the conveyor section has moved by the second distance.

2. The method according to claim 1, wherein the first distance corresponds to a distance moved by the conveyor section when the or each hydraulic ram has reached the end of its stroke.

3. The method according to claim 1 or claim 2, wherein the second distance is less than the first distance.

4. The method according to any of the preceding claims, wherein the same hydraulic ram or rams that are used for moving the conveyor section are also used to advance the roof support.

5. The method according to any of the preceding claims, wherein the second distance varies from one conveyor section to another according to necessity.

6. The method according to any of the preceding claims, wherein any combination of the first and second modes can be used for advancement of the individual conveyor sections.

7. The method according to claim 6, wherein a decision as to which conveyor sections are to be advanced in the first mode and which are to be advanced in the second mode is made by an operator.

8. The method according to claim 6, wherein a computer control system is used to select which of the conveyor sections are to be advanced in the first mode and which are to be advanced in the second mode at any given time.

9. The method according to any one of claims 6, 7 or 8, wherein the required second distances for each conveyor section operating in the second mode are settable by adjusting the ram operation for each individual conveyor section at each of the associated roof supports in turn.

10. The method according to any one of claims 6, 7 or 8, wherein a system is provided for interlinking the rams such that the required second distances for each conveyor section operating in the second mode are settable by adjusting the ram operation for each individual conveyor section by entering the required movement data at a single location.

11. The method according to claim 10, wherein the location is at or adjacent to one of the roof supports.

12. The method according to claim 10, wherein the location is at a remote position from the supports.

13. The method according to any one of claims 10, 11 or 12, wherein the system for interlinking the rams forms part of a computer control system.

14. The method according to claim 13, wherein the computer control system provides a facility for automatically setting the distances by which some or all of the conveyor sections advance when operating in the second mode.

15. The method according to claim 13 or 14, wherein when the conveyor advance is to be used to straighten a coal face, the computer control system calculates a "best fit" distance for advancing each of the conveyor sections and controls the individual rams accordingly.

16. The method according to claim 15, wherein the best fit is achieved by means of a computer program and calculated on the basis of one or more manual or computer measurements or estimates of distance between the conveyor and coal face.

17. Apparatus for moving a mining conveyor, the apparatus including a plurality of roof supports connected to the conveyor by a plurality of hydraulic rams, each roof support being connected to a section of the mining conveyor by at least one hydraulic ram, the rams being used to move the conveyor, wherein each roof support includes means for advancing its associated conveyor section in either one of two separate modes of movement, the two modes comprising: a first movement mode wherein the conveyor section is advanced by the or each ram by a first distance relative to the roof support under hydraulic pressure and the hydraulic pressure is maintained even after the or each ram has moved the conveyor section by the first distance; and a second movement mode wherein the conveyor section is advanced by the or each ram by a second distance relative to the roof support under hydraulic pressure and the hydraulic pressure on the or each ram is not maintained after the conveyor section has moved by the second distance.

18. The apparatus according to claim 17, wherein the means for advancing the conveyor section in the first mode of movement includes a first hydraulic valve for controlling hydraulic fluid flow such that when the valve is in a first state hydraulic fluid pressure causes advancement of the conveyor section, by the or each ram, by the first distance and the valve remains in the first state even after the or each ram has moved the conveyor by the first distance.

19. The apparatus according to claim 18, wherein the means for advancing the conveyor section in the second mode of movement includes the first hydraulic valve for controlling hydraulic fluid flow such that when the valve is in the first state hydraulic pressure causes advancement of the conveyor section, by the or each ram, until the or each ram has moved the conveyor section by the second distance whereupon a second hydraulic valve is controlled in such a manner that the hydraulic pressure is no longer maintained causing the conveyor section to stop moving.

20. The apparatus according to claim 19, wherein the second hydraulic valve is controlled to either cut off or reduce hydraulic fluid flow to the or each ram.

21. The apparatus according to claim 19 or 20, wherein the second hydraulic valve is controllable to divert hydraulic fluid flow away from the ram.

22. The apparatus according to claims 19, 20 or 21, wherein the first and second valves are triggered by a trigger signal so as to pass from a second state to a first state.

23. The apparatus according to claim 22, wherein the first state allows hydraulic fluid to flow through the valves.

24. The apparatus according to claim 22 or 23, wherein hydraulic fluid pressure is operable to maintain the valves in the first state, after they have been triggered such that maintenance of the trigger signal is not necessary.

25. The apparatus according to claim 22, 23 or 24, wherein the trigger signal is an electrical signal.

26. The apparatus according to any one of claims 17 to 25, wherein the or each ram is equipped with positional sensing means.

27. The apparatus according to any one of claims 17 to 25, wherein conveyor sections are provided with positional sensing means.

28. The apparatus according to claim 26 or 27, wherein when operating in the second mode of movement the positional sensing means is used to detect when the conveyor sections have been moved by their required second distances.

29. A kit of parts for modifying a roof support and one or more hydraulic rams associated with the roof support and connected to a section of mining conveyor, the kit permitting the modified roof support and the or each hydraulic ram associated therewith to operate in either one of two modes of movement for advancement of the conveyor section, the modes comprising: a first movement mode wherein the conveyor section is advanced by the or each ram by a first distance relative to the roof support under hydraulic pressure and the hydraulic pressure is maintained even after the or each ram has moved the conveyor section by the first distance; and a second movement mode wherein the conveyor section is advanced by the or each ram by a second distance relative to the roof support under hydraulic pressure, and the hydraulic pressure on the or each ram is not maintained after the conveyor section has moved by the second distance.

30. The kit according to claim 29, wherein the kit includes any combination of one or more hydraulic valves, a manifold and positional sensing means.

31. A computer system arranged, in use, to calculate a degree of movement required by at least some of a plurality of mining conveyor sections in order to move from an initial conveyor configuration to a desired second configuration.

32. The computer system according to claim 31, wherein in the second configuration the conveyor sections interact to form a substantially straight line.

33. The computer system according to claim 31 or 32, wherein the second configuration is chosen such that none of the conveyor sections need to move by more than a maximum distance to reach it from their initial configuration.

34. The computer system according to claim 33, wherein the maximum distance corresponds to a distance moved by a conveyor section when propelled by a hydraulic ram associated with the conveyor section when the ram performs a full stroke.

35. The computer system according to any of claims 31 to 34, wherein positional data concerning the initial configuration is entered into the computer system and the computer uses this data to calculate the movement required by each section to achieve the desired second configuration.

36. The computer system according to claim 35, wherein the positional data concerning the initial configuration is obtained from positional sensing means which is associated with each conveyor section or with hydraulic rams associated to the conveyor sections.

37. The computer system according to claim 35, wherein the positional data is obtained by manual or automatic measurement or estimation.

38. The computer system according to any one of claims 31 to 37, wherein movement data is utilised to calculate the degree of movement data required by each of the conveyor sections to attain the second configuration.

39. The computer system according to claim 38, wherein the movement data is based upon a series of measurements proportional to the distance between each of the conveyor sections and a coal face.

40. The computer system according to claim 38, wherein the movement is obtained from a sample of measurements proportional to the distance between a selected number of conveyor sections and a coal face and interpolating between the samples.

41. The computer system according to claim 40, wherein the interpolating is performed by means of a "best-fit" curve algorithm, or by straight line interpolation.

42. The computer system according to claim 40 or claim 41, wherein the sample of measurements is taken at points of interest along the length of the coal face.

43. the computer system according to claim 40, claim 41 or claim 42, wherein the number of samples can be varied according to the profile of the coal face and the initial configuration of the conveyor.

44. A hydraulic ram for operation in either one of two modes: a first mode in which the ram is arranged to propel a first member by a first distance under hydraulic pressure, such hydraulic pressure being maintained even when the first distance has been attained; and a second mode in which the ram is arranged to propel a first member by a second distance under hydraulic pressure, but such hydraulic pressure is not maintained once the second distance has been attained.

45. The hydraulic ram according to claim 44, wherein the first member is arranged to be a section of a mining conveyor.

46. The hydraulic ram according to claim 44 or 45, wherein the first distance corresponds to a distance moved by the first member when the hydraulic ram performs a full stroke and the second distance is less than the first distance.

47. The hydraulic ram according to any one of claims 44, 45 or 46, wherein the ram is equipped with positional sensing means and at least two hydraulic valves, the first hydraulic valve being used for operation in the first mode and the first and second hydraulic valves being used for operation in the second mode.

48. A method for moving a mining conveyor substantially as herein described with reference to Figures 3, 4 and 5.

49. A kit of parts for modifying a roof support and one or more hydraulic rams associated with the roof support, the modified support and ram(s) enabling movement of a section of a mining conveyor according to the method of claim 48.

50. A hydraulic ram for enabling movement of a section of a mining conveyor according to the method of claim 48.

51. Apparatus for moving a mining conveyor substantially as herein described with reference to Figures 3, 4 and 5.

52. A computer system substantially as herein described with reference to Figures 4 and 5.