Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 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:
-- 5 --
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
-13-
~ ~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
-15-
~;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.
-19-
1 01
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.
-20-
