CA1134610A - Method of and apparatus for monitoring movement of a mine conveyor - Google Patents

Abstract

ABSTRACT

The longitudinal slippage or creep or a mine conveyor is monitored optically with a view to saving production. The method involves transmitting an optical signal from a primary source in the mine roadway to a reflector on the conveyor and receiving the reflected signal with a receiver adjacent to the primary source and reducing the angular movement of the re-flector and line creep of the conveyor. An optical method is used to calculate the distance between the primary source and conveyor by measuring the time taken for a light signal to travel from the source to the reflector and back again. Alternatively or additionally, cord transducer is used to measure the distance.
Processing circuitry calculates the conveyor creep from the angle and distance measurements.
The invention provides apparatus for carrying out the above method.

Description

~ 3~610 CA~E 37~7 This invention rel~tPs to a ~ethod ~f and apparatus for moni~oring ~ove~ent of a mine con-vevor, ~he invention finds particular application in an underground coal mine emplo,ying a longwall mining system.
In such a longwall coal mining system, coal is won from an underground coal seam by a mining machine which traverses to and fro along an exposed face of the seam and which is mounted upon an armoured face conve~or, As coal is won from the seam by a traverse of the mining machine, the coalface advances into the seam and the armoured face conveyor is moved t~wards the newl,y exposed coalface in a snake-like manner so that the mining machine can win further coal from the seam on a subsequent traverse, Mine roof neighbouring the coalface is supported by mine roof supports arranged adjacent to the armoured face conveyor on a side away from the coalface. Double acting h~draulic rams connect the armoured face conveyor to the mine roof supports and are adapted to cause relative movement therebetween. Mine roof rearward of the roof supports is allowed to col]apse to form an area known as the goaf.
The coalface~ w'nich is typically of the order of two hundred metres long, is serviced by two mine roadwa~s which intersect the coelf ce at opposite ends respectivelv, 3C It is desirable, dl~rlng operaticn of the ~ ~ 3~10 longwall coal minin~ system that the direction of advance of the coalface further into the seam is consistent (the direction lsually being normal ~, to the coalface). V~riation in the direction of advance occurs when the ends of the coalface change their relative advancement.
If-such variation occurs, the armoured face conveyor tends to 'creep' or slide in its entirety along the coalface from one end thereof to the other. Occurence of such 'cree~ing' is un-desira~le beca~se c~al production is lost as 'creeping' necessitates the time consuming transfer of sections of the armoured face c~n-ve~or from said ~ther end of the face t~ said one end. C~n;Teyor 'creeping' can also occur even if the direction of the coalface remains consistent, the mere 'snake-like' advancing of the conveyor tending to cause such creeping.
Conveyor 'creep' becomes an even more acute problem in a sloping coal seam, wherein the con-veyor tends to creep from a high to a lower end of the coalface. Hitherto, the problem of con-veyor creep in a sloping seam has been mitigated by deliberately angling the coalface away from orthogonality with respect to the coal seam so as to tend to counteract the slope of the seam and the consequent 'creep'.
It is an object of 'he present invention to tend to overcome the problem of c~nve~or creep and thereb~ tend to avoi~ time consumin~ transfer 1~3~ 0 of sections of an armoured ~face convcyor.
According to a first aspect of the present invention, a method of continuously monitoring thc movement o-f a mine conveyor comprising receiving an optical signal with a fixed optical receiver, the optical signal being pro-jected from an optical source attachable to the conveyor, measuring angles subtended at the receiver by said source with first means associated with the receiver, measuring distances between the source and the receiver with second means associated with the receiver and calculating from the measured angles and distances movement of the mine conveyorO
The method may also include determining distances between the source and receiver to give a quantitative value of the movement.
The optical signal is preferably received from a reflector, in which case an optical signal is transmitted from a primary source adjacent to the receiver and reflected by the reflectorO The reflector is preferably a retro-reflector.
The term "optical" as used in this specification applies to any visible or invisible radiation having optical properties and thus includes, for example, infra red and ultra violet light.
The distances between the source and receiver is conveniently deter-mined by optical means. Alternatively or additionally, cord transducer meansmay determine the distancesu According to another aspect of the present invention, apparatus for continuously monitoring the movement of a mine conveyor comprising a fixed optical receiver, an optical source attachable to the conveyor, the receiver being responsive to light projected from the optical source, first means as-sociated with the receiver for measuring angles subtended at the receiver by said optical source, second means associated with the receiver for determining distances between said source and said receiver and processing circuitry for calculating from said measured angles and distances movement of the mine con-veyorO

1~.3~

A quantitativc valuc oE thc movcmen1: can hc found by the processing circuitry iF the apparatus includcs me~ s for detcrmining distances between said sourcc and said receiver.
Preferably, the optical source is a reElector in which case an optical signal is transmitted from a primary source adjacent to the receiver and reflected by the reflector~ The reElector is preferably a retro-reflector.
The means for determining distances between the source and receiver conveniently comprises an optical means~ The optical means is located adja-cent to the receiver and transmits an optical signal to the reflector and receives the reflected signal. The optical means comprises a Kerr cell and oscillator.
Alternatively or additionally, the means for determining distances between the source and receiver comprises cord transducer means.
An embodiment of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is an incomplete diagr3mmatic view of a longwall minin~ s~stem, Figure 2 is a plan of an optical source/
receiver module, Figure 3 is an elevation of an optical source/receiver module, Figure 4 is an incomplete diagrammatic view of a means for determining distances, Figure 5 is a ~raph showing values of electrical signal occurring in the means of ' Figure 4, Figure 6 is a more detailed view of Figure 4, and Figure 7 is an enlarged view of part of Figure 1.
Referring to Figure 1, an underground coal seam is generally indicated b~ 1, a coalface buv

2, and an area around the coalface by 3. Mine roof over the coalface area 3 is supported b~
mine roof supports (not shown), but mine roof rearward of the coalface area 3 is allowed to collapse to form a goaf area 4. An armoured face conveyor 5 is arranged in the coalface area

3 s~,bstantiall~ parallel to the coalface 2, and h~draulic rams (not shown) inter-connect the armoured face conve~or 5, and the previousl~
mentioned mine roof supports.
A min1n~ m~ch.i.ne (not shown) is adaptea to traverse to and fro along the armoured face con-ve~or 5, winning coal on e~ch traverse. After ;3'~

passage of the mining ~achine past a part of the coalface 2, tne armoured face conveyor 5 is advanced in a snake like manner, so that the mining machine can win coal from the part of the coalface on a subse~llent tr~verse. Mine road-ways 8, 9 service the coalface area 3, the mine roadways intersec-ting the coalface area at opposite ends 11, 12, respectively.
It can be seen in the Figure tha-t the face ends 11, 12 have been differentially advanced, since the mine roadway 9 and its associated face end 12 are advanced farther into the coal seam 1 than the mine roadway 8 and its respective face end 11. During the course of differential ad-vancement, the conveyor 5 has moved, slid or crept in its entirety in the coalface area 3 towards the face end 11. If the seam is sloped, then gravity can enhance the creeping motion of the conveyor.
Successive actuations of the hydraulic rams to advance the conveyor cause a cumulative move-ment of the conveyor in response to the component and consequently the conve~or creeps towards the less advanced face end 11.
An optical reflector 14 is mounted on an end of the conveyor towards the face end 11. An optical source 1~ and receiver 18 are arranged in the vicin ty of the end of the coalface 11 along a line which is generally perpendicular to the conveyor 5 and whicn extends rearwardly l`cl~ n b~ eons~`J~ ot~ s ~n ~s ~ O~of~`~/so4r~

v of the conve~or. An optical s~gnal path be-tween .he source, reflector and receiver is shol~n at 22 in a diagrammatic fo-rm. The optical path length is tvpicall~1 about 4G metres. The optical receiver 18 is conveniently re~erred to as a detector.
The reflector 14 is a retro-reflector of the single-corner cube type of prism form giving internal reflections from externally mirrored surfaces. It will be explained subsequently with reference to Figures 2 and 3 that the optical source and detector are adjacent but not coincident so that the apex area of the prism, which merely returns the beam to the source is not employed. The prism can therefore be flattened at its apex by reducing its dimensions.
The actual light path and flattening of the apex are not shown in the drawings which are of a simplified nature but the actual path and flattening are clear to those skilled in the art from the above description.
The size of the prism is dictated by the size of the detector window and the spacing between the centres of the source and detector ]enses. It may be seen that the reflected patch of light, ignoring blurring, is twice the size of the reflector, irrespective of range. The reflected patch of light 'nas to encompass the detector wiDdow between the centre and the periphery of the patch so that the reflector 2 must be of co~p~r~r~e size lo the ~e~ector window, which, as will be seen, is ~ effect the obJective lens o~ the receiver o~tic~l system.
There are v~rious ~1~ernati1re reflectors which ~ay possibly be used but which are, in general, ma~kedly inferior t~ the sin~le-corner cube prism reflector. The nearest is perhaps the corner cube arra~ which has an advantage in reduced depth but it still provides a light patch of only twice the size of one corner element (acting, in fact, like a concave mirror with the source near the centre of curvature) and produces a net reflected beam much weaker than the angle corner prism. Other alternatives include 'cats eves' as used on roads, an~ light scattering surfaces of the kind employing a multitude of ver~ small glass beads adhering to a stick~ tape.
The optical source 16 and detector 18 must be positioned so that the~ do not obstruct operation of other mining equipment and of course so that other mining e~uipment does not impair their own operation.

C Optical means 30 is associated with the r~eas~ eS
receiver 18 and this optical means m~asu~c~
distances between the receiver 18 arld -the reflector 14. The optical means 3C is described in more detail below with reference to Figures - ~, 5 and 5. A cord transducer means is shown at 19 and 20 but this will be referred to in more detail belo~ data processin~ and display means 2~ and a computer means 28 shown ln Figure 1 wi].l be described with reference to operation in ~igure 7 below.
Turning now to Figures 2 and 3, the optical source 16 and receiver 18 are described in more detail.
c~ pr~
-~ Fi~ure 3 shows ~e optical source and re-ceiver as seen from the retro-reflector 14. The prlnn~r~
optical source ~U~ is mounted closely beneath a lens 82 alcting as receiver obaective lens. The source ~e~is a gallium arsenide light emitting diode (~ED) which can be operated at low voltage and is robust and suited to the mine environment.
~he power limitations of the source are overcome to a large extent by pulsing it at a low dut~
ratio. It is arranged to have a beam spread sufficient to embrace angular movement of the reflector 14 and may typically provid.e a 25 horizontal fan beam by means of a lens (not shown). A significant advantage of the ~ED as a source is that its output is in the near infra-red region at about 0.9 ~. The spectral efficiency of silicon photo-diodes used in the detector at this wavelength is improved sub-stantially as compared for example with the output o.f a tungs-ten lamp. In addition the detector can use a filter to select this radiation amongst substantial visible and other 'noise' radiation in the environment. The latter may be caused by i~.lumin~tion in the coalface area, miners lamps, reflec-tions off od.d surfaces etc.
Referring to Figure 2, a detector array 83 is placed approximately at the focal length of the objective lens 82. A cylindrical lens 84 is positioned, with its axis horizontal, between the lens 82 and the detector array 83 to produce a vertical spread of the field of view and so ensure that any vertical undulations in the position adopted b~ the retro-reflector 14 do not cause the image to miss the detector array 83. The resulting vertical extent of the image is several times the horizontal extent.
The detector array 83 consists of 256 photo-diode el'ements arranged in a basic situationt horizontally through the optical axis of the receiver. ~he image of the retro-reflector 14 projected onto the array will illuminate one or two photo-diode elements at a lateral position corresponding to the angle of the retro-reflector off the optical axis.
~urning now to Figures 4 and 5, the optical ~eans 30 is described in principle. An optical source of polarized li.2ht is shown at 31. The o~tical source 31 includes a Kerr ceil, and polarized li~ht anal~;ser which controls -t,'ne inter..-,ity of an optic~l signal fro~ the source in response to a ~odulatir~ signal a~,pl.ied b,y a crystal oscillator 32. A Kerr cell essentially ~;3~0 comprises a material such as nit:robenzene placed in a cell, the material al-tering its optica.l transmission properties in response to an applied electric ~ield ~cross the cell. The signal from the source 31 is reflected by a reflector 33 (in some embodiments this could be the retro-reflector 14 referred to above) and received by a phototube 34.
The phototube receives its operating voltage from the oscillator 32. Thus the sensitivity of the phototube varies with the same frequency as the intensity of the light reflected by the reflector 33. Mirrors 3~ are shown adjacent to the source 31 and phototube 34, which mirrors merely tend to preserve the integrity of the optical signal.
Delay coils 37, which are described below are inserted between the oscillator 32 and the phototube 34.
In operation of the means 30, the maximum of light intensity can be arranged to coincide with the maximum of sensitivity of the phototube.
Consequently, it will be apparent in this case that an intensity maximum will arrive at the phototube 34 at a time when the phototube is at high or low sensitivity, de~ending upon the optical path length trave]led by the optica].
signal, wh1ch in practice depends upon the dist~nce between the reflector 33 ~n~ 'he s~ rce and phototub~.
Conse~uently, the photo-electric current derived by the phototube will vary with said o distance. ~eferring to ~igure 5, a curve 38 shows the variations of pho-toelectric current with distance, photoelectric current beinO
plotted as ordina-te and dlstance as abcissa.
Suppose, now, that similar ~eans to the optical means 30 were t~ be positioned in -the p~ace of the means 30, the only difference bein~ that the maximum of the source intensity coincided with the minimum of the phototube sensitivit,y. In such a case, a curve 39 would correspond to the curve 38 in Figure 5. If both signals are then passed in opposite dir~ections through a measuring instrument 35, aJdifference curve 40 is produced.
It is naturally impossible to arrange two identical means 30 in the manner outlined above, it is however possible to make one means fulfil both functions. This can be done by periodicall~y reversing the phase of the light modulation by the Kerr cell relative to that of the phototube, the period being long in comparison with the period of the modulating signal from the oscillator but short in comparison with the response time of the measuring instrument 35.
~he phase of light mo~ulation is simp],y reversed by reversing the direction of ~he ~odulating voltage applied to the Kerr cell.
50nse~uentl~y, wher the m"easuring instrument 35 indicates a zero ~Talue of photocurrent, this will indicate a series of closely defined points where the reflector 33 may be situated. The ~ ~3~

separation bet~reen successi-~e zero points of the reflector de?ends upon the ~odulatin~
fre~uency with which rhe Kerr cell causes flashes of li~ht fro~ the so-~rce 31, i.e. upon the modulatin~ fre~uency o~ the oscillator 32. The modulating fre~uency can be a~justed to any desired value appropriate -to the distance between the means 30 and the reflector 33. For example, ten million flashes per second corresponds to a distance of about 7.5 metres calculated as follows; light has a velocity of about 3 x 1C8 metres per second, ten million flashes corresponds to a radio wavelength of about 30 metres and so the peri.od of change corresponds to 15 metres and two zero points in a period gives 7.5 metres.
In practice, a zero adjustment of the position of the reflector 33 is difficult to achieve and consequently, the modulatin7 signal from the oscillator 33 is delayed in the coil~ 37 so that for zero points the li~ht flashes must be delayed equally long. Gonsequently alteration of the delay in the coils 37 alters the separation of the zero polnts and hence the apparent di.stan.ce travelled b~ the li~ht beam.
The reqllired distance is then, for the above fre~uency, an even multiple of 7.5 plus the distar.ce to the first zero point~ de~ending upon the electrical delav in the coils 37. The electrica' delay is interna~ly ca1ibrated in the optical means 30 and can be converted to an _~4_ ~ ~3'~

equivalent op~ical ler.,~,,th.
The multiple of 7.5 can be cle~ermine~ by changin~ the modu~tin~ frequenc,~r so that another len~th such as 7.4 or 7.~; is ~he separation of the zero photocurrent values.
Consequentl~, three separate equations in-volvin~ n1, n2 and n3 where n1, n2 and n3 arethe multiples of the 7.5, 7.4 and 7.6 separation respectively can be set up. As the velocit~ of light is accuratel~ known, solution of these equations by computer means 28 as described below, give a value for the separation of the means 30 and reflector 33.
The optical means 30 is shown in more detail in Figure 6. The same reference numerals are used where appropriate. The distance between the source 31 and reflector 33 is out of scale with the distance between the source and photo-tube 34 so,that the path of the light is shown 2~ dotted where it goes over a long distance. In Figure 6, the Kerr cell is shown at 41 and an oscillator for changin~ the direction of the modulating signal applied to the Kerr cell is shown at 42. A reverser mechanism 43 is con-trolled by the oscillator 42 so that when thedirection of the mod1llating voltage is changed, the direction of the photo-current is reversed.
The source 31 and phototube 34 have various optical components associated with them to ensure that the optical signal transmitted and ~;3~

received is of the correct type. S~me of these

4 ~
componen~s comprise lenses s~own at ~ and . "
mirrors shown at 45.
Referrin~ back to ~igu-re 1, an al~ernative or additional method and apparatus for measuring the distance from the optical source 16 and receiver 18 to the reflector 14 is described. A
cord transducer 19, of the kind described in our British Patent ~peci~ication Serial No. 1 475 755 is fixedly attached to the optical receiver 18 or to a member (not shown) attaChed to the optical receiver 18. The cord transducer 19 (not shown in detail in the drawings) comprises a container which contains a flexible elongate member such as string or wire wound upon a spool. As the string or wire is pulled from the spool, the spool rotates. The spool is mechanicall.y linked to an electric.al transducer. The transducer r~
is adapted to derive an electri.cal si~nal as the spool rotates, which electrical signal is in-dicative of extension o~ the wire or cord from the container. Extended cord is indicated by 20 in Figure 1. The cord or wire is tensioned by spring means which tend t.~ rotate the spool in an opposite sense so as to pull the cord or wire back into the container. The transducer ~ t;~C
thus derives an electrical signal -LlldU~ of how much cord is pulled back within the container.
The cord transducer extended cord 20 is fixedl~y attached to the conveyor adjacent to tke bl i sbe~ 1 -16-~13~tj3 V

reflector 14. The electrical signal derived b~ , the cord transdllcer gives a continuous indication of dist~nce between the optica1 receiver or detec or ~3 and the reflector 14 since the distance is e~ual to the extension of the cord.
As explained above, therefore, the following signals are derived:
a) a signal representing angular dis-placement, which is derived by the optical receiver or detector 18, b) a signal representing the distance between the detector 18 and the reflector 14 which may be derived b~
either or both of the optical means 30 and/or the cord transducer 19.
It should be appreciated that the signals mentioned in a, b above require processing before the information the~ carr~ can be deduced from them. ~hus the signal from the detector 18 has to be processed so that an angular position for the retro-reflector 14 can be deduced from wh;ch photodiode is illuminated;
the signal from the optical means 30 has to be processed so that equations can be solved to deduce the ~ctual separation of the reflector 14 and detector 1&; the signal from the cord transducer has to be anal~sed so that the distance can be deduced whether the cord hac wound in or out. It should be appreciated that in some applications distance measuring is ~ffecte~ ~y '.he opt,ic~ eans 3~ al~ne and in others by the c~rd trans~ c~r 19 ~l,one.
Dupl,ication and checking can be provi~1e~ by usin~ both in unison.
Cperation is now described with reference to Figure 7. In this Figure, ~ first configur-ation of the source 16 optical receiver 18 and reflector 14 is shown in full lines and a second configuration is shown dotted. The reflector position are separated by a distance d, and by an angular separation indicated by an angle shown at 25. The first configuration may represent a desired alignment, in which case the conveyor 5 has crept a distance d out of align-ment.
During operation of the mining installation and the invention, the reflector 14 can move fr~m the first configuration to the second configuration dependent upon mine conveyor creep. It should, however, be appreciated that creep of the con-veyor is a dynamic or continuous process and that conse~uently the two configurations shown in Figure 2 are by way of illustration only, since in practice the conveyor will creep into many configurations with respect to the source and detector, most of which configurations will be of a transient or temporary nature.
The data processing means 26 which comprises pre-processing circuitry, receives the signals ~entioned at a and b above. The pre-processing _18-~ (3 circuitry 2~ converts the signal from the detector 12 concerning ~hich photodiode is illuminated into a first out?ut signal which is directly related to the angular position (such as 25) of the reflector 14 with respect to the detector. ~he pre-processing circuitry 26 also receives an electrical signal concerning wave-forms of the sk~t shown at 40 in ~igure 5 and fed to the measuring instrument 35 and solves equations to provide a second output signal which is directl~ related to the distance of the reflector from the optical means 30. Alter-natively or additionallv to the last operation, the pre-processing circuitry 26 receives the signal from the cord transducer 19 and converts this to a third output signal which indicates the distance between the detector 18 and reflector 14.
The first ou~put signal and either or both of the second and third output signals from the preprocessing circuitry 26 are fed to the computer means 28. The computer means 28 can comprise a microprocessor. In any event, it is able to deduce frcm the signal provided by the pre-processing circuitry, by making trigonometric calculation the creep of the convevor i.e.
distances such as d mentioned above.
The computer means 28 can be located at any convenien~ position in the under~round in-stallation or indeed at the mine surface.

The co~pu-ter means derives an ellt;put signal which is indicative of the contirluous or dynamic creep of the conve,yor (such as d) and this output signal may be utilised to differentially advance the ends ~1, 12 of the coalface 3 so that the con~7e~yor can be caused to creep towards a desired position.
~uch utilisation col~ld be effected directly b~ an operator who w~uld display the information on the screen and act upon i~ as explained below or it could be done b~y a further controllin~
computer (not shown) which w~uld take similar action.
Thus on the example shown in ~igure 1, the face end 11 would be advanced further than the face end 12 by controlling the forward advance of the mine conveyor 5.
~he invention could find other applicatior in a sloping seam. In such a seam, the invention would be used to enable a tendency of the conveyor to slide under gravity to be reduced by differentially advancing the face ends to reduce the slope and to attempt to induce creep opposite to the slope.
~rom the above description, it can be seen that the inventlon tends to overcome problems associated with conve,yor creep and thereb,v enable the time consuming transfer of conve~70r section to be avoided.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of continuously monitoring the movement of a mine conveyor comprising receiving an optical signal with a fixed optical receiver, the optical signal being projected from an optical source attachable to the conveyor, measuring angles subtended at the receiver by said source with first means associated with the receiver, measuring distances between the source and the receiver with second means associated with the receiver and calculating from the measured angles and distances movement of the mine conveyor.

2. A method as claimed in Claim 1 wherein the optical signal is received from a primary source adjacent to the receiver after being reflected by a reflector comprising the said optical source.

3. A method as claimed in Claim 1 wherein the distances are measured by optical and cord transducer means.

4. Apparatus for continuously monitoring the movement of a mine conveyor comprising a fixed optical receiver, an optical source attachable to the conveyor, the receiver being responsive to light projected from the optical source, first means associated with the receiver for measuring angles subtended at the receiver by said optical source, second means associated with the receiver for determining distances between said source and said receiver and processing circuitry for calculating from said measured angles and distances movement of the mine conveyor.

5. Apparatus as claimed in Claim 4 wherein a primary optical source is mounted adjacent the receiver.

6. Apparatus as claimed in Claim 5 wherein the optical source is a reflector for reflecting light from the primary optical source.

7. Apparatus as claimed in Claim 4 wherein the optical source is a retro-reflector.

8. Apparatus as claimed in Claim 4 wherein the second means associated with the receiver for determining distances between said source and said receiver is an optical and cord transducer means.

9. Apparatus as claimed in Claim 8 wherein the optical means is located adjacent to the receiver and transmits a further optical signal to the reflector and receives the further signal after it is reflected by the reflector.