CA1124053A - System for surveying the profile of a surface - Google Patents
System for surveying the profile of a surfaceInfo
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- CA1124053A CA1124053A CA298,605A CA298605A CA1124053A CA 1124053 A CA1124053 A CA 1124053A CA 298605 A CA298605 A CA 298605A CA 1124053 A CA1124053 A CA 1124053A
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- receiver
- sources
- coalface
- reflectors
- optical
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Abstract
ABSTRACT
A survey system for determining the shape of a fixed path along which there may be no line of sight from end to end. The system comprises a mobile optical detector adapted to travel along the path and a plurality of optical sources which can be arranged along the path. As it moves along, the detector receives optical signals from consecutive groups of the sources and processing circuitry in the system deduces the angular positions of the sources and hence the shape of the path. In a coal mine, the optical sources are positioned on mine roof supports and the detector on a mining machine which traverses to and fro along the coalface. The system then determines the shape of the coalface. The frequency with which the detector and processing circuitry scan the sources is compatible with the mining machine. The sources can be retro-reflectors, in which case a primary optical source is mounted adjacent to the detector.
A survey system for determining the shape of a fixed path along which there may be no line of sight from end to end. The system comprises a mobile optical detector adapted to travel along the path and a plurality of optical sources which can be arranged along the path. As it moves along, the detector receives optical signals from consecutive groups of the sources and processing circuitry in the system deduces the angular positions of the sources and hence the shape of the path. In a coal mine, the optical sources are positioned on mine roof supports and the detector on a mining machine which traverses to and fro along the coalface. The system then determines the shape of the coalface. The frequency with which the detector and processing circuitry scan the sources is compatible with the mining machine. The sources can be retro-reflectors, in which case a primary optical source is mounted adjacent to the detector.
Description
Cece ~21 : , B~CKGRCU~TD 0~ TE~ I~JE~TION
.. 1~ Field of the inventlon ~:! The present invention relates to surve~ s~stems for determinin~ the shape of a fixed path and . 5 particlllarly for determinin~ such shape l.~hen the fixed path defines the profile of an ext.ended surface. ~he invention is particularly, though not excl.usively, suitable for use in an under-ground mining installation, wherein coal is won . , .
from a lon~wall coalface.
.~ Such an installation includes a coal mining machine adapted to traverse to and fro along an armoured face conve~or comprising a plurality of SeGtionS or pans extending along the longwall ~: 15 coalface, a pluralit~ of self advancing roof .~ supports arranged along the armoured face con-. veyor on a side awa~ from the coalface and double actin~ hydraulic rams correcting -the roof supports : to the conve70r. As coal is won~ the coalface equipmerlt i~ advanced further into the coal seam towards remaining coal, and the mine roof over ; worked out parts of the coal seam behind the roof supports is allowed to col1apse. Advance of the conveyor 15 effected in a snake-like manner, whereb~ after passage of the mining machine on a traverse, the sections are pushed up to the newly : exposed coalface b~ the double actin~, rams, After the sections have been pushed to the coalface the ~ roof supports are one b~ one lowered pulled up to the conve~or b~ the rams and t,hen reset to the ;~ -2-~.
roof.
; During normal working of the coal mining installation, it is desirable that the coalface is maintained substantiall~ straight, since face curvat~re tends to increase stresses upon and wear rate of the mining e~nipment, thereby causing a greater frequency of breakdown of the mining equi~ment. ~uch breakdowns are costl~ in terms of lost production. Additionally, since the roof which collapses behind the roof support ` tends to fracture along straight lines, curvature of the face tends to cause falling of the roof in advance of intended points resulting in dis-ruption of normal working and requiring manual ` 15 shoring up.
It is also desirable that the direction of advance of the coalface further into the seam is consistent (the direction usuall~ being normal to the coalface) since otherwise the conveyor tends to move in its entiret~ towards one end of the face. ~uch movement of the c~nve~or necessitates time consl~ing transfer of c~nveyor sections from one end of the face to the other. ~he movement -; of the conveyor becomes an even more serious problem in an inclined sea~, where gravit~ tendsto enhance such move~ent. Moreover, in an inclined seam, the coalface is frequently deliberately angled with respect to a line substantially orthogonal to the coal seam in order to reduce the incline and the movement.
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5;3 Maintenance of a particul.ar direction of advance of the coal ace also ensures that the total face length Le.between parallel erld tunnels or 'gates' does not vary significantl.y so that no changes in the number of conve.yor secti.ons o.r roof supports is necessar~.
.. 1~ Field of the inventlon ~:! The present invention relates to surve~ s~stems for determinin~ the shape of a fixed path and . 5 particlllarly for determinin~ such shape l.~hen the fixed path defines the profile of an ext.ended surface. ~he invention is particularly, though not excl.usively, suitable for use in an under-ground mining installation, wherein coal is won . , .
from a lon~wall coalface.
.~ Such an installation includes a coal mining machine adapted to traverse to and fro along an armoured face conve~or comprising a plurality of SeGtionS or pans extending along the longwall ~: 15 coalface, a pluralit~ of self advancing roof .~ supports arranged along the armoured face con-. veyor on a side awa~ from the coalface and double actin~ hydraulic rams correcting -the roof supports : to the conve70r. As coal is won~ the coalface equipmerlt i~ advanced further into the coal seam towards remaining coal, and the mine roof over ; worked out parts of the coal seam behind the roof supports is allowed to col1apse. Advance of the conveyor 15 effected in a snake-like manner, whereb~ after passage of the mining machine on a traverse, the sections are pushed up to the newly : exposed coalface b~ the double actin~, rams, After the sections have been pushed to the coalface the ~ roof supports are one b~ one lowered pulled up to the conve~or b~ the rams and t,hen reset to the ;~ -2-~.
roof.
; During normal working of the coal mining installation, it is desirable that the coalface is maintained substantiall~ straight, since face curvat~re tends to increase stresses upon and wear rate of the mining e~nipment, thereby causing a greater frequency of breakdown of the mining equi~ment. ~uch breakdowns are costl~ in terms of lost production. Additionally, since the roof which collapses behind the roof support ` tends to fracture along straight lines, curvature of the face tends to cause falling of the roof in advance of intended points resulting in dis-ruption of normal working and requiring manual ` 15 shoring up.
It is also desirable that the direction of advance of the coalface further into the seam is consistent (the direction usuall~ being normal to the coalface) since otherwise the conveyor tends to move in its entiret~ towards one end of the face. ~uch movement of the c~nve~or necessitates time consl~ing transfer of c~nveyor sections from one end of the face to the other. ~he movement -; of the conveyor becomes an even more serious problem in an inclined sea~, where gravit~ tendsto enhance such move~ent. Moreover, in an inclined seam, the coalface is frequently deliberately angled with respect to a line substantially orthogonal to the coal seam in order to reduce the incline and the movement.
--3~
5;3 Maintenance of a particul.ar direction of advance of the coal ace also ensures that the total face length Le.between parallel erld tunnels or 'gates' does not vary significantl.y so that no changes in the number of conve.yor secti.ons o.r roof supports is necessar~.
2. Description of the Prior Art In the kind of mining installation described it has been usual for an operator to advance the conveyor towards the newl~ exposed coalface in order to attempt to keep the coalface straight and to keep the direction of advance of the coal-face substantiall~ constant. However, as it is difficult to determine relative positions of conveyor sections throughout the conve~or length which extends alon~ a coalface of t~picall~ two ` hundred metres, the operator has either to guess ~ when he feels an7 conveyor section is advanced .; sufficiently or e].se advance the section as far - 20 as possible towards the coalface. The mine roof .` supports are then advanced. up to the conve~or.
Consequentl~, if lumps of coal or other n-on uniformities prevent either the conve~or section coming into abutment with the coalface or the full advance of the roof support, then the coalface becomes misaligned on the current or subsequent .; traverses of the coal winning machine.
It is known for lasers to be used to measure the direction of advance of the coalface and also for lasers to be used to provids a straight line -4_ 4~;3 along which rock tunnelling maehines can steer.
SUMMARY OF THE INVENTION
` According to the principles of the present invention a survey system is provided whereby the profile of the coalface may be determined even where there may be no line of sight from end to end of the coalface. A mobile receiver on the mining machine is provided which receives optical signals from points along the coalface and deduces the coalface profile from the :~ signals together with a signal indicating the machine's position the deduction being effected with processing circuitry. The ` detector periodically scans the sources and the processing cir-euitry solves equations to determine their position.
In accordance with the present invention there is provided a survey system comprising a mobile optical receiver .- adapted to travel in a fixed path, a series of optical sources ~ adapted to be positioned in a line generally along said path, sa~d the receiver being responsive to light projected by ~ optical sources visible to the reeeiver to determine the relative angul-ar positions of said sourees, the system ineluding control cir-cuitry for effecting such souree angle determinations periodieal-ly, eaeh time in respeet of a predetermined minimum group of said sourees and at sueh intervals in relation to the speed of the mobile receiver that a plurality of angle determinations are made on each group of sources as they become visible to the re-ceiver, the system further ineluding processing circuitry adap-ted to correlate the different angular measurements involving the same sourees and to derive therefrom information identifying the shape of said fixed path.
~RIBF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic plan view of a section through the coalface showing the face profile in an exaggerated form;
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Figure 2 shows a plan view of one en~ of khe coalface with coal cutting machine and survey system in operation;
Figure 3 is a diagrammatic perspective view along the coalface showing the pit props in position;
Figure 4(a) and (b) are plan and elevation of an optical source/.receiver module;
Figure 5 is a block diagram of the signal processiny circuitry of the survey systems.
Figure 6 shows a plan view of part of a ,, ;' -5a-~?~4~3 coalface installation including a second embodiment of surve,v s~s~em; and Figure 7 shows a block diagr?Am of a signal source, detector and processing circuitry of the embodiment of Figure 6.
DESCRIPTION OF THE PREFERRED EMBO~IMENTS
Referring to Figure, 1 there is shown a coalface 1 extending across a coal seam 6 for, t~pically, a few hundred metres. The coalface is serviced b~ mine roadways 2 and 3 known as the main gate and the return gate. It is ~ ' means of these roadwa~s that men and equipment ~, can be transported to and from the coalface and won coal transported therefrom.
Where the coal seam is horizontal from side to side the desired direction of advance is parallel to the 'gates' 2 and 3. An ideal profile for the coalface is therefore normal to this direction and parallel to straight lines such as 4 and 5. In general it is satisfactor~ if the c~alface profile lies for the whole of its length between the parallel lines 41 5 spaced at about one metre apart for a coalface length of, sa~
three hundred metres.
Reference now to Figure 2 shows a mining ' machine 10 which traverses to and fro along the coalface with a cutting drum 11 winning coal during the traverse to a depth into the coalface of about sixt~ centimetrss, The mining machine is electricall~ powered and runs on rail portions . .
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of a conveyor which comprises a plurality of sections movable towards the coalface in a snake-like manner as previously explained. The general line of the conveyor, however1 follows tbe profile of the coalface.
~ urning now also to Figure 3 retro-reflectors 12 9 some of whic~ are a]so shown in ; Fig~re 2 can be seen positioned on vertical sections (~e.legs) of roof supports 17 at fixed intervals,e.g.every fifth supp~rt. Figure 3 also shows alternative positîons for the reflectors on horizontal arms or canopies 18 and on o-ther oblique portions of the supports but these can `~ provide difficulties and a loss of accuracy. In any case however, retro-reflectors are placed in identical positions on the selected props. An optical source and detector unit 16, which co-oper~tes with the retro-reflectors is mounted on the machine. ~he unit 16 is also shown in Figure 4a and 4b and is described subsequentl~.
Spacing of the retro-reflectors is affected by a number of fsctors. A sin~le set of obser-vation involves simultaneous or substantially simultaneous responses from several reflectors.
The gre~ter the range disparity between the nearest and the farthest the more accurate are the results. However, this must be balanced against other factors~ ~he greater the beam path the greater the likelihood of obstruction ~0 b~ variations in the face and by dust etc.,in ':' ~.'' s~
the air. In addition~ the greater the range of the optical system the greater has ~he power of the source to be. Safet~ requirements put severe restrictions on volta~es than can be used so that power requirements of the equipment generally are of major importance.
In the light of the above factors a reflector spacing of five metres is found sat-isfactor~, giving a maximum reflector range of about 20 metres, which does of course impl~ an optical path le~gth of 40 met~es.
The reflectors themselves are of the single-corner cube type of prism form giving internal reflections from externall~ mirrored surfaces.
It will be explained subsequently that the optical source and detector are adjacent but not co-incident so that the apex area of the prism, which merel~ returns a beam directl~ to the source, is not emploved, The prism can therefore be flattened at its apex to re~uce its dimensions.
The size of the prism is dictated b~ the size of the detector window and the spacing between the centres oi the source and detector lenses, It ma~ be seen that the reflected patch of ligh~, ignorin~ blurrin~ is twice the size of the reflector, irrespective of range. ~he reflected patch of light has to encompass the detector window between the centre and the peripher~ of the patch so that the reflector must be of comparable size to the detector window, --which, as will be seen, is in effect the objective lens of the receiver optical system.
There are various alternative reflectors which may possibly be used but which are, in general, markedly inferior to the single-corner cube prism reflector. The nearest is perhaps the corner cube array which has an advantage in reduced depth but it still provides a light patch of only twice the si~e 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 single-corne~ prism. Other alternatives include 'cats-eyes' as used on roads, and light-scattering surfaces of the kind employing a multitude of ; very small glass beads adhering to a sticky tape.
In addition to the reflector angle information that is derived, a distance transducer (shown in Figures 5 and 7) is mounted on the cutting machine to indicate the distance travelled by the receiver. This distance is, of course, measured along the conveyor profile. The distance transducer typically comprises pulse counter odometer means which senses movement of a mechanical component d~ on the machine and derives electrical pulses in proportion to said movement.
Referring again to Figure 2 in addition to the series of retro reflectors 12, mounted on the props, a single reflector 13 is positioned at the 9 _ ,"~,,.";p.
,~ , extreme end of the coalface and directed also towards the receiver mounted on the cutting machine 10~ This reflector 13 is on the optical axis of -the receiver when the minin~ m~chine is correctl~ positioned both in distance from the coalface and in heading across it. I-t ma~ be, of course 9 that the desired heading is not normal to the side gates but is slewed from this direction to counteract the effect of a non-horizontal seam, ~,to bias the advancing direction of t'ne roof supports slightl~ up hill. In an~ event, when the mining ~achine is correctly located, the ~ angle of the beam reflected from the reflector 13, with respect to the receiver optical axis, is zero~ ~his facilit~ provides a direct indication of the mining machine heading and : also facilitates initial set up, but it suffers from the basic disadvantages of a long beam path : system in that gross errors ma~ cause interruption of the line of sight and the effects of dust are accentuated.
.~ ~he reflector 1~, is a retro-reflector in the horizontal plane onl,y, consisting of a long triangular section prism the axis of which is , 25 vertical. A beam will therefore be returned.
irrespective of mining machine heading and the height of tne reflector will take account of - vertical undulatlons of t,he mine floor in the vicinity of the coalface.
Referring now to Figure 4(a) and (b), there ..
i3 is shown the layout of the source/receiver unit 16 mounted on the mining machine. Figure 4(b) shows the module as seen from the rear of the mining machine. The optical source 21 is mounted closely beneath the receiver objective lens 22, The source 21 is a gallium-arsenide ]ight-emittin~-diode (LED) which can therefore be operated at low voltage and is robust and 9 Ui ted to the envirQnment. The power limitations of ; 10 this source are overcome to a large extent b~
pulsing it at a low duty ratio. It is arranged ; to have a beam spread sufficient to embrace a minimum group of reflectors 12 within a range of twent~ metres and ma~ typically provide a 25 horizontal fan beam by means of a lens now shown.
~he number of reflectors in a group is determined by various factors as will be explained. In an alternative arrangement two source beams are ; produced, one o~ fairly wide angle for the near reflectors of the group, and one narrow angle for the more distant ones of the group. The narrow angle then compensates for the long path.
A significant advantage of the LED as a source is that its output is in the near infra-red region at about 0.9~ . The ~pectralefficiency of silicon photo-diodes used in the detector at this wavelength is improved sub-stantially as compared with the output of a tungsten lamp (which although of high power has other disadvantages in addition). In addition .
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the detector can use a filter to detect this ., ;
radiation amongst substantial visible and other 'noise' radiation in the environment. ~he latter may be caused by deliberate illumination of the coalface, ~iners' lamps, reflections off odd surfaces etc.
Referring now to ~igure 4(a), a detector arra~ 23 is placed approximatel~ a' the focal length of the ob~ective lens 22. A cylindrical lens 24 is positioned, with its axis horizontal, between the lens 22 and the detector array 23~
to produce a vertical spread of the field of view and so ensure that any vertical und~lations in the positions of the retro-reflectors 12, or elsewhere, do not cause the image to miss the detector array 23. The resulting vertical extent of the image is several times the horizontal extent.
The detector array 23 consists of a line of ~ 20 256 photo-diode elements arranged, in a basic i situation, horizontàll~ through the optical axis of the receiver. The image of a retro-reflector 12 projected on to the array will illuminate one or two photo-diode elements at a lateral position ;~ 5 corres?onding to the angle of the retro-reflector off the optical a~is. In the situation described, ; the reflectors 12 are above the height of the receiver and consequently the image of a line of reflectors is inclined. The array 23 is therefore inclined correspondingly, ., .
, ,, ...
Several images of retro-reflectors will be present simultaneously and these will sweep slowly over the array as the coal cutting machine trav~
erses the coalface.
Figure 5 shows the basic arrangement for identifying the image posi-tions on the array and computing the output values accordingly. The diode array 23 is coupled to a shift register 26. A '1' state is shifted through the register 26 by a clock pulse train, producing an interrogating pulse for ; each diode element of the array in passing. Output current pulses are thus produced serially from those diodes illuminated. The current pulses are con-verted to video output pulses for further conversion to digital format in known manner. The data processing is then performed in two stages by process-ing circuitry 27, comprising firstly a pre-processor 28 which extracts merely the relative angular positions of the nearest group of retro-reflectors and secondly a further microprocessor 29, which performs the remainder of the ;~ computation. The further microprocessor 29 also receives a distance signal from the previously mentioned distance transducer which is now shown at 30.
. A display 31 i.s connected to the output of the further microprocessor. The pre-processor 2~ may be a microprocessor of the type sold under the trade mark Intersil/Harris 6100. The microprocessor 29 may be of the type sold 2~ by Marconi Space and Defence Systems Limited under the trade mark MC 1~00.
The process of computing the face profile has to take account of a number of indeterminate factors. Thus, the reflectors are assumed to be :.
randoml~ offset fro~. tneir nominal position. The line of the reflec~ors is not therefore a true co?v of the face profil.e. The heading of the cutting machine i.e.the direction of the optic~l axis is i~ genera~. not known in view of local variations in the convevor path. In the worst case the d.istance tr~velled alon~ the fixed path of the conve~or b.y the cutting machine and the receiver is not known. The principle of the computatlon is therefore to measure the angular :~: relationship of a group of the reflectors G
number of times ideally a ~reat number of times throughout the period in which they are visible to the receiver and by correlating the sets of - 15 values for the same group of reflectors taken at ;~ different positions of the receiver the relative positions of the reflectors of this group can be determined in terms of x and. y co-ordinates of a pre-determined reference. Each set of angle ~ 20 values for a group in effect provides an eauation relating the positions of the reflectors of that group to each other and to the receiver position .
at the instant of taking the angle values. A
sufficient number of sets of values will therefore .~
enable the equations to be solved for x and y. A
surplus of such sets of values can be assessed on a statistical basis to provide the best values for x and y As the receiver travels along the face one reflector will pass from view and another will come into view. ~ach reflector will there-., :
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fore feature in a number of successive ~,roups and multip]e angle determinations will be made in respect of each group that a reflector fe~tures in. ~he statistic`al data are thus increased accordingl~. The mathematical processes involved in the extraction of x and y in a situation of this kind are well known an~ emplo~ the Kalman filtering process. ~his operates by iterative adjustment of a mathematical model of the reflector dispositions to minimise the difference between the observed angular position of a reflector as presented by the microprocessor and an estimated value of that angular position, with respect to the variables: y displacement of detector arra~
from x axis; x position of each particular reflector; y position of each particular reflector;
distance in x moved b~ the detector array; and the skew angle of the receiver optical axis to the x axis.
On a first run the mathem~tical model relies on data fed in : nominal interval between reflectors;
~umber--of reflectors; mean distance between receiver and line of reflectors etc. However, after the first run, each estimated profile and reflector disposition can be used for the next run, since each profile will be fairly closel~
related to the next.
During a run, for each set of observations, :...
or 'scan', the estimated values of the reflector ,, .
angle off the optical axis are calculated for .,~
, .':
~l~2~ 3~3 each reflector, using the previously estimated reflector positions and the assumed new position of the mining machine and receiver. The differences between these estimated values and ~he currently observed angles are used to adjust the estimated machine position and the reflector positions so as to minimise the mean square error between estimated and measured angles over all scans.
A convenient reference line at least for the first run is taken to be the line through the first two reflectors, this then bein~ the x axis referred to above.
There is a minimum number of reflectors that can feature in a ~roup,i.~.of simultaneous angle determinations~ for the extraction of the co-ordinates of the reflectors and the receiver to be possible. If there are absolutel~ no other ref-erences than the angular displacements of the reflectors in a group, then four reflectors is a minimum group. If, however, a further reference is supplied, in the form of the distance travelled by the receiver, for example, or the range of each reflector, then the minimum number can be reduced.
~he greater the number in a group however, the greater the amount of statistical information available and the more accurate the results.
Since the positions of the reflectors transverse to the coal face cannot be relied upon,~for reasons explained above~ the final ~0 layout of these reflectors is of secondary -16~
.
,4~i;3 importance compared to the path of the receiver~
which, as mentioned, moves in and out transversely in synchronism with the coalface. The reflectors therefore provide a set of temDorary reference points for the location of this fixed path, the lack of prior knowledge of the positions of these reference points being compensated by the multi-plicity of angle determinations taken.
~he micro processor determining the observed reflector angles is mounted on the cutting machine. ~he main processor, which analyses the observations and calculates the estimated dispositions, is mounted, together with the display 31 ln the gate.
~he output is then displayed at the machine in the following form (a) A small number (e.g.4) indicator lamps indicating such things as: c~mputer running; self-check O~Ko; input data validity; power supply levels correctO
(b) A digital (LED) display showing, on demand, any of the data words normally output on the data link. Thus for example, with the machine stationary, the angles of the nearest retro-reflectors can be displayed in turn and checked against ~easurements taken by surveying methods.
(c) An analog display of face profile.
~his is of most interest to the miners ., ~ 17-, ' 5;3 working at the face. A row of (parallel) linear LED displa,ys gives a long rect-angular dot matrix on wbich the current or previous profile is graphically displayed.
~he 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.
Various modifications of the system are possible. Thus the reflectors fitted to the roof ~ supports may be replaced by lamps or other sources ; so obviatin~ the primary source on the receiver module. The reflector arr~ngement does however have the advantage that the active devices are all kept in one place rather than distributed along -the coalface with the attendant disadvantages of suppl~ cables.
In Figures ~ and 7 which should now be referred to the same reference numerals are used where appropriate. ~he previously mentioned . .
armoured face conveyor is now shown at 32 in ~ Flgure 6. A primary source 33 emits a laser beam ,~ 25 of fan shape extended in the vertical direction and swept horizontally, broadside as it were, so ; as to intercept the reflectors sequentially. I~
Figure 6 for example, the laser beam intercepts ~ retro-reflector 12a~ then 12b and then 12c. ~he `- 30 vertical extension ensures that undulations from , ~
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the horizon-tal do not prevent the reflectors from seeing the laser beam. A receiver s`~own at 34 is a localised wide angle optical detector, instead of array as described in the previous embodiment, the angular displacement of each reflector from the last being indicated by the time interval between reception of the reflected beams. The processing circuitry 27 is then adapt;ed to measure these time intervals by utilisation of a modified pre-processor 3~.
Instead of a linear array of optical detectors~ a rectangular array may be used to give an equivalent vertical sp~ead to the field of view in the absence of the cy]indrical lens.
Charge cnupled devices can also be used as ` combined optical detectors and analog shift registers in place of the standard optical elements proposed.
The profile display may be provided by an electroluminescent panel or liquid crystal panel.
In an alternative mounting arr ngement for the reflectors they could be positioned on a spill plate portion of the conveyor, so that, being fixed with respect to the conveyor the~
.~ 25 define the face profile exactly. Although this would simplify the calculations by the removal of a variable, it would mean that the reflectors were low down and vulnerable to damage of dis-; placement.
Z0 It will be clear t;hat, although tha syste~
;, ' ;;3 described is particularly suited to a mining operation, the inver.tion is also applic~ble to the survey of any extended surface or path to which a mobile receiver can be constrained, whether above or be]ow ground.
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Consequentl~, if lumps of coal or other n-on uniformities prevent either the conve~or section coming into abutment with the coalface or the full advance of the roof support, then the coalface becomes misaligned on the current or subsequent .; traverses of the coal winning machine.
It is known for lasers to be used to measure the direction of advance of the coalface and also for lasers to be used to provids a straight line -4_ 4~;3 along which rock tunnelling maehines can steer.
SUMMARY OF THE INVENTION
` According to the principles of the present invention a survey system is provided whereby the profile of the coalface may be determined even where there may be no line of sight from end to end of the coalface. A mobile receiver on the mining machine is provided which receives optical signals from points along the coalface and deduces the coalface profile from the :~ signals together with a signal indicating the machine's position the deduction being effected with processing circuitry. The ` detector periodically scans the sources and the processing cir-euitry solves equations to determine their position.
In accordance with the present invention there is provided a survey system comprising a mobile optical receiver .- adapted to travel in a fixed path, a series of optical sources ~ adapted to be positioned in a line generally along said path, sa~d the receiver being responsive to light projected by ~ optical sources visible to the reeeiver to determine the relative angul-ar positions of said sourees, the system ineluding control cir-cuitry for effecting such souree angle determinations periodieal-ly, eaeh time in respeet of a predetermined minimum group of said sourees and at sueh intervals in relation to the speed of the mobile receiver that a plurality of angle determinations are made on each group of sources as they become visible to the re-ceiver, the system further ineluding processing circuitry adap-ted to correlate the different angular measurements involving the same sourees and to derive therefrom information identifying the shape of said fixed path.
~RIBF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic plan view of a section through the coalface showing the face profile in an exaggerated form;
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Figure 2 shows a plan view of one en~ of khe coalface with coal cutting machine and survey system in operation;
Figure 3 is a diagrammatic perspective view along the coalface showing the pit props in position;
Figure 4(a) and (b) are plan and elevation of an optical source/.receiver module;
Figure 5 is a block diagram of the signal processiny circuitry of the survey systems.
Figure 6 shows a plan view of part of a ,, ;' -5a-~?~4~3 coalface installation including a second embodiment of surve,v s~s~em; and Figure 7 shows a block diagr?Am of a signal source, detector and processing circuitry of the embodiment of Figure 6.
DESCRIPTION OF THE PREFERRED EMBO~IMENTS
Referring to Figure, 1 there is shown a coalface 1 extending across a coal seam 6 for, t~pically, a few hundred metres. The coalface is serviced b~ mine roadways 2 and 3 known as the main gate and the return gate. It is ~ ' means of these roadwa~s that men and equipment ~, can be transported to and from the coalface and won coal transported therefrom.
Where the coal seam is horizontal from side to side the desired direction of advance is parallel to the 'gates' 2 and 3. An ideal profile for the coalface is therefore normal to this direction and parallel to straight lines such as 4 and 5. In general it is satisfactor~ if the c~alface profile lies for the whole of its length between the parallel lines 41 5 spaced at about one metre apart for a coalface length of, sa~
three hundred metres.
Reference now to Figure 2 shows a mining ' machine 10 which traverses to and fro along the coalface with a cutting drum 11 winning coal during the traverse to a depth into the coalface of about sixt~ centimetrss, The mining machine is electricall~ powered and runs on rail portions . .
4~53 .
of a conveyor which comprises a plurality of sections movable towards the coalface in a snake-like manner as previously explained. The general line of the conveyor, however1 follows tbe profile of the coalface.
~ urning now also to Figure 3 retro-reflectors 12 9 some of whic~ are a]so shown in ; Fig~re 2 can be seen positioned on vertical sections (~e.legs) of roof supports 17 at fixed intervals,e.g.every fifth supp~rt. Figure 3 also shows alternative positîons for the reflectors on horizontal arms or canopies 18 and on o-ther oblique portions of the supports but these can `~ provide difficulties and a loss of accuracy. In any case however, retro-reflectors are placed in identical positions on the selected props. An optical source and detector unit 16, which co-oper~tes with the retro-reflectors is mounted on the machine. ~he unit 16 is also shown in Figure 4a and 4b and is described subsequentl~.
Spacing of the retro-reflectors is affected by a number of fsctors. A sin~le set of obser-vation involves simultaneous or substantially simultaneous responses from several reflectors.
The gre~ter the range disparity between the nearest and the farthest the more accurate are the results. However, this must be balanced against other factors~ ~he greater the beam path the greater the likelihood of obstruction ~0 b~ variations in the face and by dust etc.,in ':' ~.'' s~
the air. In addition~ the greater the range of the optical system the greater has ~he power of the source to be. Safet~ requirements put severe restrictions on volta~es than can be used so that power requirements of the equipment generally are of major importance.
In the light of the above factors a reflector spacing of five metres is found sat-isfactor~, giving a maximum reflector range of about 20 metres, which does of course impl~ an optical path le~gth of 40 met~es.
The reflectors themselves are of the single-corner cube type of prism form giving internal reflections from externall~ mirrored surfaces.
It will be explained subsequently that the optical source and detector are adjacent but not co-incident so that the apex area of the prism, which merel~ returns a beam directl~ to the source, is not emploved, The prism can therefore be flattened at its apex to re~uce its dimensions.
The size of the prism is dictated b~ the size of the detector window and the spacing between the centres oi the source and detector lenses, It ma~ be seen that the reflected patch of ligh~, ignorin~ blurrin~ is twice the size of the reflector, irrespective of range. ~he reflected patch of light has to encompass the detector window between the centre and the peripher~ of the patch so that the reflector must be of comparable size to the detector window, --which, as will be seen, is in effect the objective lens of the receiver optical system.
There are various alternative reflectors which may possibly be used but which are, in general, markedly inferior to the single-corner cube prism reflector. The nearest is perhaps the corner cube array which has an advantage in reduced depth but it still provides a light patch of only twice the si~e 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 single-corne~ prism. Other alternatives include 'cats-eyes' as used on roads, and light-scattering surfaces of the kind employing a multitude of ; very small glass beads adhering to a sticky tape.
In addition to the reflector angle information that is derived, a distance transducer (shown in Figures 5 and 7) is mounted on the cutting machine to indicate the distance travelled by the receiver. This distance is, of course, measured along the conveyor profile. The distance transducer typically comprises pulse counter odometer means which senses movement of a mechanical component d~ on the machine and derives electrical pulses in proportion to said movement.
Referring again to Figure 2 in addition to the series of retro reflectors 12, mounted on the props, a single reflector 13 is positioned at the 9 _ ,"~,,.";p.
,~ , extreme end of the coalface and directed also towards the receiver mounted on the cutting machine 10~ This reflector 13 is on the optical axis of -the receiver when the minin~ m~chine is correctl~ positioned both in distance from the coalface and in heading across it. I-t ma~ be, of course 9 that the desired heading is not normal to the side gates but is slewed from this direction to counteract the effect of a non-horizontal seam, ~,to bias the advancing direction of t'ne roof supports slightl~ up hill. In an~ event, when the mining ~achine is correctly located, the ~ angle of the beam reflected from the reflector 13, with respect to the receiver optical axis, is zero~ ~his facilit~ provides a direct indication of the mining machine heading and : also facilitates initial set up, but it suffers from the basic disadvantages of a long beam path : system in that gross errors ma~ cause interruption of the line of sight and the effects of dust are accentuated.
.~ ~he reflector 1~, is a retro-reflector in the horizontal plane onl,y, consisting of a long triangular section prism the axis of which is , 25 vertical. A beam will therefore be returned.
irrespective of mining machine heading and the height of tne reflector will take account of - vertical undulatlons of t,he mine floor in the vicinity of the coalface.
Referring now to Figure 4(a) and (b), there ..
i3 is shown the layout of the source/receiver unit 16 mounted on the mining machine. Figure 4(b) shows the module as seen from the rear of the mining machine. The optical source 21 is mounted closely beneath the receiver objective lens 22, The source 21 is a gallium-arsenide ]ight-emittin~-diode (LED) which can therefore be operated at low voltage and is robust and 9 Ui ted to the envirQnment. The power limitations of ; 10 this source are overcome to a large extent b~
pulsing it at a low duty ratio. It is arranged ; to have a beam spread sufficient to embrace a minimum group of reflectors 12 within a range of twent~ metres and ma~ typically provide a 25 horizontal fan beam by means of a lens now shown.
~he number of reflectors in a group is determined by various factors as will be explained. In an alternative arrangement two source beams are ; produced, one o~ fairly wide angle for the near reflectors of the group, and one narrow angle for the more distant ones of the group. The narrow angle then compensates for the long path.
A significant advantage of the LED as a source is that its output is in the near infra-red region at about 0.9~ . The ~pectralefficiency of silicon photo-diodes used in the detector at this wavelength is improved sub-stantially as compared with the output of a tungsten lamp (which although of high power has other disadvantages in addition). In addition .
,:
:
.
the detector can use a filter to detect this ., ;
radiation amongst substantial visible and other 'noise' radiation in the environment. ~he latter may be caused by deliberate illumination of the coalface, ~iners' lamps, reflections off odd surfaces etc.
Referring now to ~igure 4(a), a detector arra~ 23 is placed approximatel~ a' the focal length of the ob~ective lens 22. A cylindrical lens 24 is positioned, with its axis horizontal, between the lens 22 and the detector array 23~
to produce a vertical spread of the field of view and so ensure that any vertical und~lations in the positions of the retro-reflectors 12, or elsewhere, do not cause the image to miss the detector array 23. The resulting vertical extent of the image is several times the horizontal extent.
The detector array 23 consists of a line of ~ 20 256 photo-diode elements arranged, in a basic i situation, horizontàll~ through the optical axis of the receiver. The image of a retro-reflector 12 projected on to the array will illuminate one or two photo-diode elements at a lateral position ;~ 5 corres?onding to the angle of the retro-reflector off the optical a~is. In the situation described, ; the reflectors 12 are above the height of the receiver and consequently the image of a line of reflectors is inclined. The array 23 is therefore inclined correspondingly, ., .
, ,, ...
Several images of retro-reflectors will be present simultaneously and these will sweep slowly over the array as the coal cutting machine trav~
erses the coalface.
Figure 5 shows the basic arrangement for identifying the image posi-tions on the array and computing the output values accordingly. The diode array 23 is coupled to a shift register 26. A '1' state is shifted through the register 26 by a clock pulse train, producing an interrogating pulse for ; each diode element of the array in passing. Output current pulses are thus produced serially from those diodes illuminated. The current pulses are con-verted to video output pulses for further conversion to digital format in known manner. The data processing is then performed in two stages by process-ing circuitry 27, comprising firstly a pre-processor 28 which extracts merely the relative angular positions of the nearest group of retro-reflectors and secondly a further microprocessor 29, which performs the remainder of the ;~ computation. The further microprocessor 29 also receives a distance signal from the previously mentioned distance transducer which is now shown at 30.
. A display 31 i.s connected to the output of the further microprocessor. The pre-processor 2~ may be a microprocessor of the type sold under the trade mark Intersil/Harris 6100. The microprocessor 29 may be of the type sold 2~ by Marconi Space and Defence Systems Limited under the trade mark MC 1~00.
The process of computing the face profile has to take account of a number of indeterminate factors. Thus, the reflectors are assumed to be :.
randoml~ offset fro~. tneir nominal position. The line of the reflec~ors is not therefore a true co?v of the face profil.e. The heading of the cutting machine i.e.the direction of the optic~l axis is i~ genera~. not known in view of local variations in the convevor path. In the worst case the d.istance tr~velled alon~ the fixed path of the conve~or b.y the cutting machine and the receiver is not known. The principle of the computatlon is therefore to measure the angular :~: relationship of a group of the reflectors G
number of times ideally a ~reat number of times throughout the period in which they are visible to the receiver and by correlating the sets of - 15 values for the same group of reflectors taken at ;~ different positions of the receiver the relative positions of the reflectors of this group can be determined in terms of x and. y co-ordinates of a pre-determined reference. Each set of angle ~ 20 values for a group in effect provides an eauation relating the positions of the reflectors of that group to each other and to the receiver position .
at the instant of taking the angle values. A
sufficient number of sets of values will therefore .~
enable the equations to be solved for x and y. A
surplus of such sets of values can be assessed on a statistical basis to provide the best values for x and y As the receiver travels along the face one reflector will pass from view and another will come into view. ~ach reflector will there-., :
i:
;~' ,, .
fore feature in a number of successive ~,roups and multip]e angle determinations will be made in respect of each group that a reflector fe~tures in. ~he statistic`al data are thus increased accordingl~. The mathematical processes involved in the extraction of x and y in a situation of this kind are well known an~ emplo~ the Kalman filtering process. ~his operates by iterative adjustment of a mathematical model of the reflector dispositions to minimise the difference between the observed angular position of a reflector as presented by the microprocessor and an estimated value of that angular position, with respect to the variables: y displacement of detector arra~
from x axis; x position of each particular reflector; y position of each particular reflector;
distance in x moved b~ the detector array; and the skew angle of the receiver optical axis to the x axis.
On a first run the mathem~tical model relies on data fed in : nominal interval between reflectors;
~umber--of reflectors; mean distance between receiver and line of reflectors etc. However, after the first run, each estimated profile and reflector disposition can be used for the next run, since each profile will be fairly closel~
related to the next.
During a run, for each set of observations, :...
or 'scan', the estimated values of the reflector ,, .
angle off the optical axis are calculated for .,~
, .':
~l~2~ 3~3 each reflector, using the previously estimated reflector positions and the assumed new position of the mining machine and receiver. The differences between these estimated values and ~he currently observed angles are used to adjust the estimated machine position and the reflector positions so as to minimise the mean square error between estimated and measured angles over all scans.
A convenient reference line at least for the first run is taken to be the line through the first two reflectors, this then bein~ the x axis referred to above.
There is a minimum number of reflectors that can feature in a ~roup,i.~.of simultaneous angle determinations~ for the extraction of the co-ordinates of the reflectors and the receiver to be possible. If there are absolutel~ no other ref-erences than the angular displacements of the reflectors in a group, then four reflectors is a minimum group. If, however, a further reference is supplied, in the form of the distance travelled by the receiver, for example, or the range of each reflector, then the minimum number can be reduced.
~he greater the number in a group however, the greater the amount of statistical information available and the more accurate the results.
Since the positions of the reflectors transverse to the coal face cannot be relied upon,~for reasons explained above~ the final ~0 layout of these reflectors is of secondary -16~
.
,4~i;3 importance compared to the path of the receiver~
which, as mentioned, moves in and out transversely in synchronism with the coalface. The reflectors therefore provide a set of temDorary reference points for the location of this fixed path, the lack of prior knowledge of the positions of these reference points being compensated by the multi-plicity of angle determinations taken.
~he micro processor determining the observed reflector angles is mounted on the cutting machine. ~he main processor, which analyses the observations and calculates the estimated dispositions, is mounted, together with the display 31 ln the gate.
~he output is then displayed at the machine in the following form (a) A small number (e.g.4) indicator lamps indicating such things as: c~mputer running; self-check O~Ko; input data validity; power supply levels correctO
(b) A digital (LED) display showing, on demand, any of the data words normally output on the data link. Thus for example, with the machine stationary, the angles of the nearest retro-reflectors can be displayed in turn and checked against ~easurements taken by surveying methods.
(c) An analog display of face profile.
~his is of most interest to the miners ., ~ 17-, ' 5;3 working at the face. A row of (parallel) linear LED displa,ys gives a long rect-angular dot matrix on wbich the current or previous profile is graphically displayed.
~he 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.
Various modifications of the system are possible. Thus the reflectors fitted to the roof ~ supports may be replaced by lamps or other sources ; so obviatin~ the primary source on the receiver module. The reflector arr~ngement does however have the advantage that the active devices are all kept in one place rather than distributed along -the coalface with the attendant disadvantages of suppl~ cables.
In Figures ~ and 7 which should now be referred to the same reference numerals are used where appropriate. ~he previously mentioned . .
armoured face conveyor is now shown at 32 in ~ Flgure 6. A primary source 33 emits a laser beam ,~ 25 of fan shape extended in the vertical direction and swept horizontally, broadside as it were, so ; as to intercept the reflectors sequentially. I~
Figure 6 for example, the laser beam intercepts ~ retro-reflector 12a~ then 12b and then 12c. ~he `- 30 vertical extension ensures that undulations from , ~
:"
the horizon-tal do not prevent the reflectors from seeing the laser beam. A receiver s`~own at 34 is a localised wide angle optical detector, instead of array as described in the previous embodiment, the angular displacement of each reflector from the last being indicated by the time interval between reception of the reflected beams. The processing circuitry 27 is then adapt;ed to measure these time intervals by utilisation of a modified pre-processor 3~.
Instead of a linear array of optical detectors~ a rectangular array may be used to give an equivalent vertical sp~ead to the field of view in the absence of the cy]indrical lens.
Charge cnupled devices can also be used as ` combined optical detectors and analog shift registers in place of the standard optical elements proposed.
The profile display may be provided by an electroluminescent panel or liquid crystal panel.
In an alternative mounting arr ngement for the reflectors they could be positioned on a spill plate portion of the conveyor, so that, being fixed with respect to the conveyor the~
.~ 25 define the face profile exactly. Although this would simplify the calculations by the removal of a variable, it would mean that the reflectors were low down and vulnerable to damage of dis-; placement.
Z0 It will be clear t;hat, although tha syste~
;, ' ;;3 described is particularly suited to a mining operation, the inver.tion is also applic~ble to the survey of any extended surface or path to which a mobile receiver can be constrained, whether above or be]ow ground.
. .
., . ~ .
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,, .
,, ,,
Claims (13)
1. A survey system comprising a mobile optical receiver adapted to travel in a fixed path, a series of optical sources adapted to be positioned in a line generally along said path, the receiver being responsive to light projected by said optical sources visible to the receiver to determine the relative angular positions of said sources, the system including control cirsuitry for effecting such source angle determinations periodically, each time in respect of a predetermined minimum group of said sources and at such intervals in relation to the speed of the mobile receiver that a plurality of angle determinations are made on each group of sources as they become visible to the receiver, the system further including processing circuitry adapted to correlate the different angular measurements involving the same sources and to derive therefrom information identifying the shape of said fixed path.
2. A survey system according to Claim 1, including means providing an indication of distance travelled by said mobile receiver along said fixed path, this distance indication being supplied to said processing circuitry as a factor in the determination of said fixed path.
3. A survey system according to Claim 1 wherein said sources are refletors and a primary source is mounted adjacent the receiver.
4. A survey system according to Claim 2, wherein said sources are reflectors and a primary source is mounted adjacent the receiver.
5. A survey system according to Claim 3, wherein said reflectors are retro-reflectors.
6. A survey system according to Claim 5 wherein said primary source has a beam width sufficient to illuminate said minimum group of sources.
7. A system according to Claim 1, wherein said receiver comprises an array of photo-electric elements which are activated selectively according to the angle of an incident beam of light relative to an optical axis of the receiver.
8. A system according to Claim 7 wherein said array is a linear array responsive to the position of said sources in a plane containing said array.
9. A system according to Claim 8 wherein said linear array consists of photo-diodes which are coupled to the stages of a shift register to permit serial interrogation and serial read-out of beam-incidence information, the relative spacing of stored charge in said array of photo-diodes providing an output dependent upon the angles of incidence of respective beams.
10. A system according to Claim 5 wherein said primary source has a beam of substantially line section, the primary source being adapted to make a broadside sweep so as to scan said reflectors, the receiver including circuit means for processing signals resulting from sequential reception of plural beams.
11. A system according to Claim 10 wherein said primary source is a laser and the receiver comprises a localised photo-electric element having a wide angle of view, said circuit means being responsive to the time lapse between successive beam receptions to provide an output dependent upon the angles of incidence of the respective beams.
12. A survey system according to Claim 1, for use in determining the profile of a coalface, said mobile receiver being mounted on a coal winning machine so that the coalface is parallel to said fixed path, said sources being mounted in similar positions on mine roof supports.
13. A system according to Claim 12, wherein a reflector is mounted on the required optical axis of the receiver at one end of the coalface to provide a direct reading of heading error of the coalface throughout the travel of the receiver.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,605A CA1124053A (en) | 1978-03-09 | 1978-03-09 | System for surveying the profile of a surface |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,605A CA1124053A (en) | 1978-03-09 | 1978-03-09 | System for surveying the profile of a surface |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1124053A true CA1124053A (en) | 1982-05-25 |
Family
ID=4110951
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA298,605A Expired CA1124053A (en) | 1978-03-09 | 1978-03-09 | System for surveying the profile of a surface |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1124053A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10724861B2 (en) * | 2015-08-03 | 2020-07-28 | Commonwealth Scientific And Industrial Research Organisation | Monitoring systems and methods |
| CN117348500A (en) * | 2023-12-04 | 2024-01-05 | 济南华科电气设备有限公司 | Automatic control method and system for fully-mechanized coal mining face |
-
1978
- 1978-03-09 CA CA298,605A patent/CA1124053A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10724861B2 (en) * | 2015-08-03 | 2020-07-28 | Commonwealth Scientific And Industrial Research Organisation | Monitoring systems and methods |
| CN117348500A (en) * | 2023-12-04 | 2024-01-05 | 济南华科电气设备有限公司 | Automatic control method and system for fully-mechanized coal mining face |
| CN117348500B (en) * | 2023-12-04 | 2024-02-02 | 济南华科电气设备有限公司 | Automatic control method and system for fully-mechanized coal mining face |
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