Note: Descriptions are shown in the official language in which they were submitted.
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GEOSIEERING OF SOLID MINERAL MINING MACHINES
BACKGROUND
[0002] The present invention generally relates to a method and apparatus
for
detecting the presence of rock during coal or ore mining operations.
[0003] A more effective way to control solid mineral mining equipment, or
miners, has
been greatly desired by the mining industry. Many concepts have already been
tried, over
a period of many years, to improve mining controls to increase the amount of
coal, or
other mineral, cut by the mining equipment and to decrease the amount of
undesirable
rock cut by the mining equipment. Many of these concepts involve "guidance"
systems
that direct or point the miner where to cut, based on predictions or
assumptions related to
the location of the mineral-rock interface. These predictions or assumptions
are typically
based on data or information obtained from the experience of the mining
equipment from
previous cuts.
[0004] One seemingly simplified approach employs repetitive cycles. A
computer is
instructed by the miner operator to perform specific cycles or the control
system is
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programmed to memorize operator actions over a cycle and duplicate them. This
approach does not work well because of the high variability of the rock and
mineral
formations and operational considerations. This approach is particularly
ineffective
when applied to continuous miners, because the miner rides on the floor that
has
been cut resulting in cutting errors (e.g., leaving an excessive layer of coal
on the
floor, or cutting excessively down into the rock on the floor) for one cut
tending to
be amplified for subsequent cuts.
[0005] In the case of long-wall mining there is some opportunity to utilize
what
has been learned on one pass along the mineral face to improve upon cutting
strategy
for the next pass along the face. One approach utilizes a memory system to log
the
profiles of the rock face at the floor and roof on one pass and then to use
this
knowledge to influence the cutting as the cutters pass along the same face,
going in
the opposite direction. This approach has been of only limited success because
the
rock face profile on one pass does not exactly reflect the needed rock face
profile of
the next pass and because there is much variability in the formations and
mining
operations. Consequently, such equipment and operation are limited in their
efficiency in cutting to the rock-coal interface using guidance strategy.
[0006] Gamma detectors have, over the years, shown promise in detecting the
location of the rock-wall interface for both continuous miners and long wall
miners,
but typically have not been effective because they have been installed so as
to measure
where the mining equipment has been rather than where the cutter is going. One
reason that
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gamma detectors have often been used in a non-effective manner is that the
detectors
could not physically survive if subjected to the environment in locations
where they
would be most effective.
[0007] Numerous other approaches have already been conceived and tested over
the years for directing or guiding mining equipment. Most of these concepts
have
not proven to be commercially successful due to technical deficiencies,
implementation problems, and cost. Many types of sensors have been
incorporated
into control systems to monitor the shape, profile and characteristics of the
formations through which the mining equipment is cutting and to make cutting
decisions on where to point subsequent cuts based on this information. Thus,
these
approaches fail not only due to practical implementation problems but also
because
of a fundamental flaw with the concept. Knowledge about the shapes, profiles,
or
characteristics of the formation being passed through does not provide
accurate
information about the formation just ahead, for which the cutting decisions
must be
made.
[0008] In most of the examples above, the control systems employed have been
complex and expensive. A typical approach is to use a gravity-referenced or
inertial-
referenced control system, with various other sensors added. Some of these
control
concepts have been referred to as "horizon control systems." A horizon control
system typically uses the gravity-referenced sensors or inertial-referenced
sensors that
keep track of the orientation of the continuous miner and the profile of the
roof and
floor.
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[0009] In principle, the horizon control system approach is to control the
mining
equipment by use of guidance systems adapted to mining applications. However,
as
discussed above, guidance systems cannot generate accurate information about
the
formation to be cut because the historical information that they log in detail
is not a valid
indicator of what is ahead. Moreover, these guidance systems are complex and
costly.
[0010] It is described in U.S. application publication no. US 2002-0056809
in
underground coal mining, a properly designed and properly positioned, forward-
looking
armored gamma detector, in combination with a suitable control system, can be
effective for
reducing the amount of rock taken while extracting an increased amount of coal
or other
mineral. A mining control system that incorporates such forward-looking
detectors is
referred to as a "rock avoidance system." The use of rock avoidance systems
can help cut
the floor of the mine very smoothly and simplify the job of the operator. Rock
avoidance
systems allow continuous miner operators to be positioned further from the
coal face, thus
reducing health hazards.
[0011] However, even when used with forward-looking rock detectors as
described in U.S.
application publication no. US 2002-0056809, these horizon control systems do
not
utilize the data generated by the rock detectors as fully as it could be used,
because
the systems are conceived and designed to guide or point, determining the
direction
to
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move, rather than being appropriately responsive to sources of external
intelligence
such as armored gamma detectors. In addition, inertial or gravity referenced
systems
are not typically designed to provide precision and timely measurements of
cutter
movements that will allow a rock detector to achieve maximum sensing accuracy.
[0012] Rock avoidance systems that rely upon complex guidance systems are
costly and, complicated and have some inherent inefficiency resulting from
their
methodology. A need now exists to provide an accurate rock avoidance system
that
is simple, economical and easy to install and operate. There is also a need
for such a
rock avoidance system for use on long-wall mining equipment as well as
continuous
mining equipment.
SUMMARY
[0013] These deficiencies are alleviated to an extent by the present invention
which in one aspect provides a rock avoidance system for solid mineral mining
using
a forward looking rock/mineral interface detector and controlling the miner to
cut to
the detected rock/mineral interface.
[0014] In another aspect, vertical movements of the cutting mechanisms are
measured for the purpose of being used by the rock detector to make more
accurate
mathematical calculations of the location of the coal-rock interface.
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[0015] In another aspect, a method is provided for improving accuracy by
incorporating a device within an armored rock detector to sense angular
movements
of the cutter boom and to correlate changes in gamma radiation to the angular
movements, within selected energy ranges. An armored rock detector, so
configured,
can make effectively accurate cutting decisions under a wide range of mining
conditions without support from complex control systems. Cutting decisions
from
the rock detector are transmitted directly to the miner control system to slow
or stop
the movement of the cutter toward the coal-rock interface or to a control and
display
panel where other constraints and logic may be applied.
[0016] In another aspect, the change in attenuation is determined, and the
thickness of the remaining coal is calculated by measuring the rate at which
the
gamma radiation increases. Greater accuracy in the calculations is achieved by
measuring the relative changes in gamma counts for various energy levels.
Quick
response is achieved so that the cutter of a continuous miner moving toward
the rock
on each cut may be stopped before reaching the rock by employing curve-fitting
techniques that correlate the gamma ray measurements with incremental
movements
of the cutters. The rock detector is outfitted with the required logic
elements and
algorithms.
[0017] In yet another aspect, a method of geosteering is provided on a
continuous
miner is for a shearing down to be slowed slightly as the floor is approached.
Control of
the shearing is accomplished by signals from the rock detector which operate
the
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solenoids that control the hydraulic system. Following the shearing stroke,
the miner
is placed in reverse for a short distance in order to remove the small cusp
left behind
the cutter. During this backing up, the rock detector will maintain the boom
at
constant angle so that the floor will be cut level. Next, the operator moves
the miner
forward slowly, simultaneously shearing up, to sump to approximately fifty
percent
the diameter of the cutter. If a rock detector is used at the roof, it will
slow the cut
slightly before reaching the rock interface and then stop the cut. While the
boom is
being held at a constant angle by the rock detector, the operator drives the
miner
forward to a full sump. At this point, the operator is ready to start the
shear down to
repeat the cycle.
[0018] In another aspect, the rock detector is placed near the cutter on a
continuous miner, so that it can detect the radiation passing through the coal
in front
of the advancing cutter. When cutting at the floor, the detector moves with
the
advancing cutter such that the angular size of the field of view is not
reduced as the
cutter moves down toward the bottom portions of the miner.
[0019] In another aspect, the rock detector is placed near the cutter on a
long-
wall miner When geosteering the trailing drum, the divergence rock detector is
positioned within a few feet of the bottom edge of the picks so that a
divergence
between the tips of the picks and the rock will be detected before coal is
left
unmined. Also, the divergence rock detector is positioned close to the picks
so that
the cutter can be biased toward divergence without concern for leaving coal
unmined. In another aspect, a
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convergence rock detector is used on the trailing drum, and positioned close
enough
to the cutter to be able to detect rock that is being mined and then mixed
with the
coal. In a preferred embodiment a geosteering system is provided that includes
an
armored rock detector, positioned on the boom of a continuous miner to view
the
area where coal is being cut, to measure the changes in gamma radiation as a
result of
the coal being cut away, to correlate the changes in gamma radiation with
incremental changes in the position of the cutter, and to make logical
decisions when
to slow and/or to stop the cutter before cutting into the rock. In order to
obtain
precise measurements of rotation of the cutter boom or of the vertical
movements of
the cutter, an accelerometer is incorporated into the rock detector.
[0020] In another preferred embodiment, the geosteering system includes a
control and display panel that keeps the operator informed about the cutting
progress, particularly in regard to cutting at the roof. This panel accepts
data and
decisions from the rock detectors and also displays the position of the cutter
relative
to the most recent cuts at the floor. A solid-state accelerometer, in the form
of a
micro-chip, is included as part of the electronics. This accelerometer
acquires
additional information on the instantaneous motion of the continuous miner and
sends that information to the rock detector so that the rock detector can
subtract
errors resulting from motion of the miner from the measured incremental
movement
of the cutter and rock detector. In a typical application, gamma data is
correlated to
the incremental movements of the cutter and this information is retained
within the
control and display panel for at least ten cutting
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cycles. Detailed, automatic analysis of this data allows refinement of the
logical
decisions to be made for future cutting cycles.
[0021] In another embodiment, an encoder and/or a potentiometer are provided
to instantly measure and report to the rock detector, the movement of the
boom, on
which the cutter is attached. Such substantially instant, precise data allows
the rock
detector to make fast, accurate measurements. When rock detectors are being
used
for controlling cutting at the roof, in addition to controlling cutting at the
floor,
such auxiliary devices provide supporting information to the rock detector, to
the
miner control system, and to the operator. This preferred embodiment includes
a
cutter motion indicator, containing an optical encoder and a potentiometer, at
the
pivot point of the boom. By combining this precise, high-speed data with the
expanded computational capabilities of other preferred embodiments, advanced
automation at higher speeds of operation are made possible.
[0022] In yet another embodiment, rock detectors are used to steer the cutting
of
a long-wall mining system. In some applications, both the leading drum and the
trailing drum of a long-wall shearing system are geo-steered by use of rock
detectors.
Whenever the mining equipment reverses direction, the leading drum becomes the
trailing drum. The armored rock detector is placed near the bottom of the cowl
for
the trailing drum and allows direct view of the surface being cut by the drum.
The
rock detector begins by slowly raising the drum until the rock detector
determines
that coal is being left unmined. Raising and lowering of the drum by the rock
detector is accomplished by
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operating the solenoids that control the hydraulic system. Upon recognition
that a
small amount of coal is being left over the rock, the rock detector quickly
lowers the
drum by approximately two inches. The amount that the drum is lowered will
depend upon the miner and mining conditions. In one aspect, the rock detector
continues to steer the drum so that the cutting operation cycles between three
conditions (1) removal of only a small amount of rock, (2) preferable removal
of all
coal and no rock, and (3) leaving up to one or two inches of coal over the
rock. In
the case where the coal bonds well to the rock, typically fire clay, the
maximum
amount of coal occasionally left will preferably be less than two inches. The
preferable result is that for most of the cut along the face, almost no floor
rock is
mined and very little coal is left un_mined. For the case where soft coal is
not bonded
to the fire clay, preferably substantially all of the coal will be removed
substantially all
of the time.
[0023] These and other objects, features and advantages of the invention will
be
more clearly understood from the following detailed description and drawings
of
preferred embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic view of a continuous miner including a pair of
rock
detectors constructed in accordance with a preferred embodiment of the
invention.
[0025] FIG. 2 is a graph showing a typical equilibrium energy spectrum for a
homogenous rock formation above and below a coal vein.
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[0026] FIG. 3 is a graph showing the effects of coal on a typical equilibrium
energy spectrum for a homogenous rock formation.
[0027] FIG. 4 is a partial cross-sectional view of one of the armored rock
detectors
of FIG. 1.
[0028] FIG. 5 is a cross-sectional view of one of the rock detectors of FIG.
4.
[0029] FIG. 6 is a view taken along section line VI-VI of FIG. 5, at the
scintillation element.
[0030] FIG. 7 is a view taken along section line VII-VII of FIG. 5, at the
photo-
multiplier tube.
[0031] FIG. 8 is a view taken along section line VIII-VIII of FIG. 5, at the
accelerometer.
[0032] FIGS. 9a and 9b are graphs of gamma ray counts versus time and versus
change of cutter boom angle.
[0033] FIG. 10 is a schematic drawing of a logic element used with a rock
detector constructed in accordance with an embodiment of the invention.
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[0034] FIG. 11 is a schematic drawing of a logic element and digital signal
processor used with a rock detector constructed in accordance with an
embodiment
of the invention.
[0035] FIG. 12 is a schematic drawing of a logic element and digital signal
processor used with a pair of rock detectors constructed in accordance with an
embodiment of the invention.
[0036] FIG. 13 is a schematic drawing of a junction box and cables used in an
embodiment of the invention.
[0037] FIG. 14 is a schematic drawing of a control and display panel and
cables
used in an embodiment of the invention.
[0038] FIG. 15 is a schematic drawing of a control and display panel,
accelerometer and cables used in an embodiment of the invention.
[0039] FIG. 16a is a view of a cutter motion indicator used with a rock
detector in
accordance with an embodiment of the invention.
[0040] FIG. 16b is a cross-sectional view of the cutter motion indicator of
FIG.
16a.
[0041] FIG. 17 is a cross-sectional view of a linkage mechanism used with
cutter
motion indicator of FIG. 16a.
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[0042] FIG. 18 is a schematic view of a longwall shearing system in accordance
with an embodiment of the invention.
[0043] FIG. 19 is a schematic of a pair of rock detectors on the trailing
shear of
the long-wall miner of FIG. 18.
[0044] FIG. 20 is a graph of predicted and measured floor depth versus
distance
traveled.
[0045] FIG. 21 is a graph of detected gamma ray counts versus coal/rock
interface depth.
[0046] FIG. 22 is a graph like FIG. 21.
[0047] FIG. 23 is a graph like FIG. 21.
[0048] FIG. 24 is a cross-sectional view of a rock detector constructed in
accordance with another embodiment of the invention.
[0049] FIG. 25 is a cross-sectional view taken along line XXV-XXV of FIG. 24.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] The present invention provides a more accurate and faster solid mineral
mining by use of a rock avoidance system that applies a new methodology called
geosteering to solid mineral mining.
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[0051] Geosteering techniques have been used in oilfield applications as
exemplified in US patents 5,230,386, RE 035,386, and 5,812,068. With
geosteering, the distance to the oilfield bed boundary is measured while in
the
formation, and the drill string is steered by direct measurements of the
formation so
that it stays in the mineral vein. This technology has advanced to the point
where
horizontal wells in excess of one mile are routinely drilled. Further, these
wells can
now be drilled with the drill string staying in the reservoir formation
throughout the
horizontal section. Such geosteering for oilfield applications was recognized
as an
important new methodology and a substantial advance over directional drilling
techniques exemplified by US patents 3,982,431 and 4,905,774.
[0052] The "directional drilling" approach to horizontal drilling in oil and
gas
wells is somewhat analogous to currently-used "horizon control" that has been
used
for mining applications. In both cases of directional-based controls, for oil
and for
coal, independent attitudinal and/or inertial reference systems provide the
basis for
guiding or pointing the machinery. In each application, the extent and profile
of a
solid mineral vein to be mined is not predictable. Indeed, the problem is more
critical in coal mining
than in oil well drilling, because the mining operation needs to be accurate
to within
inches compared to the accuracy of feet typically required in oil wells.
[0053] Guidance or pointing based on an inertial or gravity based reference
system does not provide the intelligence needed to accurately make the next
cut.
The control functions at any moment must be accomplished by signals from
sensors
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that are measuring relevant parameters for the formation just ahead, where the
cutting will occur. Directional control systems, such as horizon control, used
in solid
mineral mining have not produced the successes achieved with directional
drilling in
horizontal oil wells. Thus, implementation of geosteering to solid mineral
mining
represents an even greater opportunity for improvement than did the
implementation
of geosteering for drilling oil and gas wells.
[0054] The principle of geosteering for continuous miners is to keep the
cutter
moving between the boundaries of the coal vein and letting the continuous
miner
follow the cutter through the geologic formation. Geosteering is more
straightforward than conventional approaches, and is fundamentally simpler in
concept. The actual profile of the tunnel being cut through the earth during
mining,
the vertical excursions of the tunnel, and the slope of the floor and roof of
the tunnel
are not primary the primary objective of geosteering. These parameters can be
derived from data acquired while performing geosteering, and may be of some
interest, but such data are the consequence of geosteering rather than being
the
guide for cutting.
[0055] Coal is located in a formation between other materials, generally
classified
as rock. An example would be a coal seam having black marine shale at the roof
and
fire clay, another form of shale, at the floor. In this example, the shale has
a
significantly higher level of natural radiation than the coal. As the shale
radiation
passes through the coal from the rock, it is attenuated. The thickness of the
coal is
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reduced as a continuous miner removes the coal. Reduction in the thickness of
the
coal results in less attenuation so that the gamma radiation reaching the
detector
increases as the coal is cut away. At the point of contact between the cutter
and the
rock, there is no attenuation by coal and the gamma radiation is at a maximum.
By
measuring the rate at which the gamma radiation increases, the change in
attenuation
can be determined, and the thickness of the remaining coal can be calculated.
[0056] Greater accuracy in the calculations is achieved by measuring the
relative
changes in gamma counts for various energy levels. Quick response is required
because the cutter of a continuous miner is moving rapidly toward the rock on
each
cut and should be stopped before reaching the rock. Since the cutter picks are
on a
rotating drum, the advancing face of the cutter is a curve. As the first picks
along the
centerline of the drum begin to enter the rock, bare rock is exposed and
pieces of
rock are cut away and dragged on top of the coal pile behind the cutter. If
the
cutters actually enter the rock, it is desirable to immediately stop the
advance of the
cutter to save wear on the picks and avoid cutting undesirable rock. To
achieve faster
response and higher
accuracy, curve-fitting techniques are employed by correlating the gamma
measurements with incremental movements of the cutters. The system includes
associated logic elements and algorithms.
[0057] Geosteering, which relies primarily upon measurements of natural gamma
radiation, can only be properly implemented by understanding the physics of
the
processes and physical phenomena involved in making and interpreting the gamma
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measurements. Physical characteristics of the formations and their radiation
properties are reviewed below. The logic elements included in the preferred
embodiments have been created to accomplish the required decision-making,
taking
advantage of this understanding of the physics involved, within the confines
of the
protected environment provided within the rock detector.
[0058] Radiation flux from coal/rock usually originates from trace levels of
radioactive potassium, uranium, or thorium that are within the rock. In a
typical
case, a discrete spectrum of gamma rays is produced by the radioactive decay
of the
trace elements. These gamma rays are transported through the formation, losing
energy through Compton scattering (and possibly pair production), until they
are
finally photo-electrically absorbed. Within the rock, an equilibrium spectrum
is soon
established reflecting a balance between the production of gamma rays in
radioactive
decays, the downscattering of gamma rays to lower energy, and the absorption
of
gamma rays through photoelectric absorption.
=
[0059] When the flux enters the coal region, this equilibrium is upset. The
production of gamma rays in coal is much lower, reflecting a significantly
lower level
of potassium, uranium, and thorium. Since the higher energy regions of the
radiation flux are not replenished, the spectrum shifts to lower energies as
the gamma
rays are down-scattered and decreases in magnitude as the gamma rays are
absorbed.
[0060] The inverse of this process is observed as coal is mined. First, the
gamma
flux is low in magnitude and energy, reflecting the extensive absorption by
the thick
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layer of coal. Then, as coal is removed, the magnitude of the flux increases,
and the
mean energy of the flux increases.
[0061] A typical equilibrium spectrum for a homogeneous rock formation above
and below a coal vein is shown in FIG. 2. The broad peak at about 100 key is
the
down-scatter peak. Most of the gamma radiation under this peak has lost energy
through Compton scattering. If Compton scattering were the only physical
process
involved, a 1/E2 distribution would be seen, instead of the down-scatter peak.
However, as gamma rays lose energy, their cross-section for photoelectric
absorption
increases. This absorption results in the gamma radiation having the lower
energy,
producing the backscatter peak that is observed in FIG. 2.
[0062] The formula for the photoelectric cross-section is given as:
rz)3.6
Li0)
Pe 0 .01barnes I electronEq. 1
\ 3.15
E '
132 kev
where Z is the average atomic number of the formation. The denominator in this
formula shows the strong energy dependence of the cross-section, and explains
the
existence of the backscatter peak. The numerator gives the dependence of the
cross-
section on the lithology of the formation.
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[0063] An oilfield convention for describing this dependence is to consider
the
photoelectric cross section at E=30.6 key. At this energy, the numerator =
0.01 and
we have:
Pe . (¨z\3.6 barnes I electron Eq. 2
10j
[0064] Using this convention, the photoelectric cross-section of coal is found
to
range from about 0.1 to about 0.3 bames/electron, while the rock above and
below
the coal typically ranges from 2-5 bames/electron. As a result, of this
difference in
the
photoelectric cross-section, the down-scatter peak for the rock above and
below the
coal is at a higher energy than the down-scatter peak for coal.
[0065] It is somewhat easier to visualize these parameters by starting with
only
rock and adding coal on top of the rock, as happens when steering the trailing
shearing drum of a long-wall miner. If the drum is raised, a thin layer of
coal is
added on top of the rock and the spectrum is shifted to lower energies. Gamma
rays
from the rock lose energy as they are Compton-scattered in the coal. The
higher
energy regions of the flux are not replenished, because the natural
radioactivity of the
coal is much lower than that of the rock. As more coal is added, the gamma
rays are
shifted to sufficiently low energies to allow absorption to be a significant
factor again.
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The reverse of this description then applies to the removal of coal by the
cutters on a
continuous miner.
[0066] FIG. 3 shows an example of this phenomenon, presenting the spectrum at
the surface of bare rock (0 cm) and at the surface of a coal layer on top of
that rock at
distances of 10 cm and 20 cm from that rock. From the plots on FIG. 3, it is
clear
that the percent of flux per energy unit is greater at the rock -face than
that observed
through a layer of coal.
[0067] Geosteerin.g accomplishes the steering for solid mineral mining through
direct measurements made on the formation in the region where the cutting is
being
performed. Inertial reference systems, attitudinal reference systems or
guidance
systems
are not required for geosteering. The steering is accomplished using rock
detectors
that follow the mineral formation.
[0068] In conventional systems, the vertical movements of the cutter are
controlled to be in conformance to a complex profile of the movements and/or
attitudinal parameters of the continuous miner and of the tunnel through which
it is
moving. Conventional systems have been arranged primarily to track where the
miner has been, and then attempts to adjust the direction and actions, and
point the
cutter based on what is learned during cutting. Geosteering, in contrast,
simply
follows the mineral vein within the formation.
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[0069] Another preferred embodiment includes increasing the computational
capabilities within the rock detector so as to be able to perform more complex
calculations for making better cutting decisions. Statistical analyses are
performed to
determine the probable accuracy of the decisions made by the rock detector.
Data
from this expanded capability supports higher level analyses. This is depicted
in FIG.
20. FIG. 20 shows the estimates of the position of the coal/rock interface at
the
floor for previous cutting cycles, as well as predictions for the next cutting
cycle. This
prediction is used as the "0" reference for the next measured cycle. The
position of
the regular measurement of the counts is given in terms of the distance to the
predicted coal/rock interface. A typical measurement is depicted in FIG. 21.
It
shows the counts measured in a time interval of 0.25 seconds as a function of
depth.
(This time interval is not unique but is given as a typical example.) When
these data
points are analyzed, the
predicted rock interface is at -1.67 inches, not 0.0 inches. However, that is
not an
error. To illustrate the ability of this technique to pick out changes in
slope, the
model formation incorporated a change in slope at 275 inches, which resulted
in the
coal/rock interface being 1.5 inches lower than predicted. The measured data
were
sufficient to determine this change.
[0070] This measurement will be added to the earlier measurements, the
expanded set of measurements will be fitted, and a prediction will be made for
the
next cut. Also, the measurement can be used to extend the present cut to the
newly
measured boundary. Immediate use within a pass requires quick decision-making
during the sweep down, since an entire sweep down can occur in just two or
three
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seconds. The processing capability described in this invention (including PICs
and a
DSP) have the speed and capability needed to determine the boundary in
sufficient
time to affect the cut.
[0071] Another feature that should be noted is the ability of such a system to
"learn" from previously obtained data. An example of this would be the
observed
count rates as a function of the distance to the interface. As long as the
radiation
from the rock above and below the coal is constant, and the thickness of the
coal vein
is constant, this function will remain the same. But, as these variables
change, so will
the function.
[0072] Typically, these changes occurs at a much slower rate than the change
in
the position of the floor. Thus, over the interval used to predict the next
floor
position, the
response function can be assumed to be a constant. But, over longer periods, a
change in this function can be noted. Generally, it can be assumed to be
constant
over about ten to fifteen mining passes, which should be sufficient to
determine the
position of the boundary at the next cut. But, over longer intervals, such as
a day of
making cuts, the coal thickness and or the level of radioactivity in the rock
above and
below the coal can vary.
[0073] The change in the response pattern produces a signal that can be
distinguished from the signal produced by changes in the position of the
coal/rock
interface. There are two ways in which this difference can be observed. First,
the
ratio of the count rates in various energy regions changes with the distance
to the
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boundary. An increase in the level of radioactivity will have minimal effect
on this
ratio. Second, there is a unique signature when the miner breaks through the
coal/rock interface and start mining into the rock. This signature will be
considered
in some detail in the next example.
[0074] When a change in the thickness of the coal, or the level of
radioactivity in
the formation above or below the coal crosses a threshold of significance, the
system
is capable of performing two actions. First, it can alert the person
supervising the
mining activities of the change in the conditions. This is done through the
use of the
control and display panel. This affords him the opportunity to manually change
the
actions of the miner. Second, it can alter the pattern it uses to determine
the interface
to reflect the new conditions.
[0075] Another preferred embodiment involves a system with two detectors: one
for the roof and one for the floor. An example is pictured in Fig. 1. In this
example,
the roof rock is five times as hot as the floor rock. Examples of the relative
signals for
the roof and the floor are shown in Fig. 22, which gives the count rate as a
function
of the distance from the miner to the floor.
[0076] The response of the floor detector is much flatter than the response of
the
roof detector, as well as much flatter than the floor detector response in the
prior
example. This is a result of the heightened background cause by the roof being
five
times as radioactive as the floor.
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[0077] Even with shielding, the floor detector still has some sensitivity to
the
radiation from the roof. When, as in the prior example, the roof radiation is
comparable to the floor radiation, the effects of this sensitivity are
relatively small.
But, when the roof is five times as hot as the floor, the effects become
noticeable.
[0078] Note that the background radiation level from the roof is not a
constant.
As the process of mining down towards the floor rock begins, the boom
containing
the cutter and the armored rock detectors is typically level or tilted
slightly upwards.
As the mining progresses, it tilts down towards the floor. With this motion,
there is
maximum sensitivity to the roof radiation at the start of the process, and a
reduction
in sensitivity as the miner tilts toward the floor. This results in a decrease
in the
=
count rates due to
the roof radiation, which partially offsets the increase in the count rate
that result
from the removal of coal from the floor and the flattened response seen in
Figs. 22-
23.
[0079] This reduction in signal combined with an increase in the statistical
uncertainty due to the higher background from the roof results in
significantly
greater uncertainty in determining the floor coal/rock interface from
measurements
made while cutting coal than from establishing the roof coal/rock interface
from
measurements made while cutting coal. Given this difference, one might think
that
the floor detector will not add to the accuracy of the measurement.
[0080] There is, however, a very significant bed boundary signal that is
unique to
the floor detector. It is a significant rise in the count rate as the miner
reaches the
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floor. An example of this is shown in FIG. 23, which shows a step function
change in
count rate at the coal/rock interface.
[0081] The reason for this change is that, when the miner reaches the
boundary, it
starts mining the radioactive rock instead of the coal. The surface of the
coal pile is
quicldy covered with shale. Since the coal pile is very close to the detector,
the
higher radiation from this region results in a significant increase in the
detector count
rate.
[0082] A similar signal is not seen at the roof. When the miner breaks through
the
coal/rock interface at the roof, the shale falls to the floor. The roof
armored rock
detector is shielded from the floor signal, so it does not show a marked
increase right
at the boundary.
[0083] Armored rock detectors may be used for geosteering at the floor and at
the
roof of a mining operation. FIG. 1 shows a continuous miner 10 that has been
configured with two armored rock detectors 20, 120. The primary function of
these
detectors 20, 120 is to determine when the cutter picks 14 are approaching the
coal-
rock interface 15, 16, to slow the movement of the boom 11, and to stop the
movement of the boom 11 whenever all of the coal 18 has been removed.
[0084] Each of these detectors 20, 120 has been strategically positioned to
allow
it to receive gamma radiation from the rocks at the coal-rock interface 15, 16
in front
of the advancing cutter picks 14, as well as directly behind the cutters. To
reach the
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rock detectors 20, 120, some of the radiation 28 passes between the picks 14.
In the
event that the cutter picks 14 overshoot the interface 15 at the floor, and
enter the
floor rock 26, the picks will throw rock on top of the coal pile 21 behind the
cutter.
This sudden exposure of the rock surface and the loose rock added on top of
the coal
pile 21 behind the cutter gives an immediate rise in gamma counts, an
indication that
the cutter 12 has gone too far and the shearing is stopped before a
significant amount
of rock 26 is removed. By making the rock detectors 20, 120 faster and more
accurate, the cutter 12 can be stopped before cutting into the coal-rock
interface 15.
A variety of techniques are employed to increase the accuracy and speed of the
detectors 20, 120.
[0085] Many functional elements are required to make effective the rock
detectors
20, 120. As can be seen in FIGS. 1 and 4, the rock detectors 20, 120 are
protected
by armor 70 that surrounds, shields, and supports them at a critical location
near the
cutter picks 14. A challenge in designing the armored rock detector 20, 120 is
the
simultaneous provision of effective protection from the harsh environment and
of an
unobstructed path for the gamma rays 28 to enter the scintillation element 50
with as
little attenuation as possible. Windows are provided in each portion of the
structure
to prevent obstruction of the gamma rays 28 trying to enter the scintillation
element
50. FIGS. 6-8, which are cross-sectional views of FIG. 5, show the various
elements
that protect the scintillation element 50, the electronics 57 and other
sensors. These
multiple levels of protection are described in detail below.
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[0086] Gamma rays 28 entering the armored rock detector 20, 120, shown in
FIG. 4, pass through a non-metallic window 71, preferably formed of poly-
ether,
ether, ketone (PEEK), in order to reach the scintillation element 50 within
the rock
detector 20, 120. Other windows 65 have been cut into a rigid dynamic
enclosure
80 which surrounds the scintillation element 50. A gap 65' is provided in a
flexible
support sleeve 68 within the rigid dynamic enclosure 80 and a gap 64 is
provided in
the flexible support sleeve 61 surrounding the scintillation element 50,
inside the
scintillation shield 63. The gaps 65', 64 are aligned to minimize the amount
of metal
in the path of the
gamma rays 28, except for the scintillation shield 63, which has been made as
thin as
possible.
[0087] Next, with reference to FIG. 5, will be described the general
functioning
of the detectors 20, 120. A scintillation element 50 responds to gamma rays 28
that
have been emitted from the rock 26 above or below the unmined coal 18. The
response is to produce a tiny pulse of light that travels to a window 52 at
the window
end of the scintillation element 50 or is reflected into the window 52 by a
reflector
67 (FIG. 6) that is wrapped around the scintillation element 50. The light
pulse
travels through an optical coupler 51, through the window 52, and through a
second
optical coupler 53 into the faceplate of a Light detecting element, shown here
as a
photo-multiplier tube 55. An electrical pulse is generated by the photo-
multiplier
tube 55 and sent to electronics element 57. The photo-multiplier tube 55, the
electronics element 57 and an accelerometer 60 are located in an assembly
called a
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photo-metric module 58. Since components within the photo-metric module 58
utilize electricity, it is necessary that it be enclosed in an explosion-proof
housing 59
to avoid accidental ignition of gas or dust that may be in the vicinity of the
continuous miner 10 on which the armored rock detector 20, 120 is installed.
In
addition to satisfying the explosion-proof safety requirements of the Mine
Safety and
Health Administration, the explosion-proof housing 59 also serves as an
effective
barrier that protects the electrical elements 56, 57 and the accelerometer 60
from the
strong electromagnetic fields generated by the heavy electrical equipment on
the
miner 10.
[0088] Better details of the protective elements are shown in FIGS. 6-8. The
first
view in FIG. 6 shows a flexible support sleeve 61 surrounding the
scintillation
element 50, which protects it from high levels of lower frequency vibrations.
The
tight fitting sleeve 61 firmly and uniformly supports the fragile
scintillation element
50 at flat portions 63 of the sleeve 61 and provides a high resonant frequency
so that
it will not resonate with lower frequency vibrations that pass through the
outer
support system. The outer support system consists of the flexible support
sleeve 68
inside of the rigid enclosure 80 and a rigid elastomeric shock absorbing
sheath 81
which surrounds the enclosure 80. A typical size scintillation element 50 for
this
application is 1.4 inches in diameter by 10 inches in length, but may be as
large as 2
inches in diameter. The resonant frequency of these outer support elements 68,
81,
80 protect against shock and isolate the scintillation element 50 from high
frequencies.
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[0089] FIG. 7 illustrates a view of the photo-multiplier tube 55, which is
inside
the photo-metric module 58, which in turn is within the explosion-proof
housing 59.
A flexible support sleeve 75 surrounds the photo-multiplier tube 55, another
flexible
sleeve 69 surrounds the photo-metric module 58, and the flexible sleeve 68
extends
the full length of the rigid dynamic enclosure 80 over the explosion-proof
housing
59. Likewise, the elastomeric shock-absorbing sheath 81 fully covers the
entire rigid
dynamic enclosure 80. It should be noted that this sheath 81 serves other
useful
purposes. It provides good mechanical compliance with the armor 70. This is
particularly important
during installation in which dust and particles will be present. Another
purpose of
the sheath 81 is to prevent water or dust from entering through the window in
the
enclosure 80.
[0090] FIG. 8 illustrates the accelerometer module 60, which is afforded the
same
critical protection from the harsh environment as the photo-multiplier tube
55.
Installation of the rock detector 20, 120 into the armor 70 includes rotating
the
detector so that an axis of sensitivity 83 of the accelerometer 60 is
approximately
parallel with the floor plane of the miner 10, defined by the surface upon
which the
miner 10 crawler travels. This alignment does not have to be exact since the
primary
objective is to provide incremental motion information, not absolute
orientation or
position. It is the use of this incremental motion information by the rock
detector
20, 120 that assists the geosteering concept to be effective by enabling
faster and
more accurate cutting decisions required to stay within the coal vein. This is
better
explained below.
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[0091] If the advance of the cutter picks 14, due to the lowering or raising
of the
boom 11 to which the rotating cutter 12 is attached, is at a constant rate,
then the
gamma data could be correlated with time. However, there are many operational
reasons why the rate of movement of the boom 11 is not constant. Another
choice
available is to correlate the gamma data with the actual incremental movement
of the
boom, which can be measured. Movement of the boom directly relates to the
movement of the cutter, though there are potential errors.
[0092] Gamma counts correlated to time might appear as curve 1 in FIG. 9a.
Notice that there is considerable scatter in the data in addition to some
erratic trends
within the data set. The general scatter is a result of gamma radiation being
statistical
in nature. There is no way to predict when a piece of the formation vvill
issue the
next gamma ray. Averaging the data over time is essential. Since the rate of
the
gamma counts is increasing as the rock interface is approached, in addition to
the
statistical variations, it is useful to use a well-known method for making
predictions
based on well behaved data that has a statistical component; that is, to
correlate the
data to an independent variable that is controllable. The change in the count
rate is a
result of the cutter removing the coal. A challenge, and an objective of this
invention, is to provide a means to derive an accurate measurement of cutter
motion,
over short increments of time. Motion is the cause of the change in count
rates as
cutting continues, and precise increments of motion can be used to correlate
the
count rates for curve-fitting purposes.
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[0093] When correlated with actual incremental movements of the cutter (or the
boom), the same data may produce a more useful curve such as curve 2 in FIG.
9b.
The value of the better behaved curve 2 is that it can be used to predict the
point at
which a value will be reached that corresponds to the value expected at the
point
when the cutter picks 14 reach the coal-rock 15 interface. By plotting
multiple
curves for each energy range and by applying algorithms to these curves, more
accurate predictions are possible, even for variable operating conditions.
[0094] A logic element 57 is functionally depicted in FIG. 10. As explained
earlier, this critical element is well protected from the harsh environment by
an
explosion-proof housing 59 that is dynamically isolated by a support system.
The
metallic housing 59 also protects against electromagnetic interference with
the miner
electrical systems 55, 56, 57. The logic element 57 receives electrical pulses
from an
amplifier 91 after being generated by the photo-multiplier tube 55. The
electrical
pulses from the photo-multiplier tube 55 may have amplitudes as low as 30 mV,
and
the duration may be as small as a few hundred nanoseconds. They are routed
through the buffer 90, which isolates the input signal from the logic element
57
circuitry to prevent degradation to the signal. The amplifier 91 increases the
amplitude and inverts the signal from a negative aperiodic pulse to a positive
aperiodic pulse. The amplifier gain may be on the order of twenty. The actual
gain
value is dependent upon the voltage range of the input signal, the range and
resolution of an analog-to-digital converter 92, the supply voltages, and the
slew rate
of the amplifier 91. The amplified signal may serve as a trigger signal to
inform the
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microcontroller 93 that a new pulse is ready for processing. Since the pulse
is
aperiodic and short in duration, it is necessary to sample and hold the peak
amplitude
of the amplified pulse until the microcontroller 93 can act on the trigger
signal and
read the amplitude via the analog-to-digital converter 92.
[0095] Once the amplified pulse amplitude has been sampled, the
microcontroller
93 resets the sample-and-hold peak detector of the sampled pulse, while
maintaining
a
running count and/or average count over a given period of time. The pulse
counts
may be grouped into two or more energy ranges to form an energy spectrum. In
particular, the counts in each energy spectrum, for each segment of time, such
as
0.10 seconds, are correlated with the motion of the cutter since the last time
segment. Discrimination and pattern recognition techniques are then used to
characterize and predict the thickness of the coal, and thus the distance from
the
picks 14 to the rock 26. By applying various algorithms to the relationships
that
correlate counts with measured incremental movement within the energy
spectrums
and the gross counts, higher accuracy can be achieved under variable operating
conditions.
[0096] A power supply 56 provides high voltage to the photo-multiplier tube
55.
Noise is easily introduced into high impedance circuitry such as is required
for the
high voltage photo-multiplier tube 55. Having the power supply 56 inside the
explosion-proof housing 59 protects the circuitry from electrically induced
noise
from the large motors and other machinery on the miner 10. The housing 59 also
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protects against this high voltage accidentally igniting gas and/or coal dust
in the
vicinity of the miner 10. Provisions are made for the microcontroller 93 to
control
the voltage from the power supply 56 to the photo-multiplier tube 55 to
control its
gain.
[0097] Provisions are made in the logic element 57 to continuously communicate
with a miner control system 100 or a control and display panel 130 (FIG. 13).
Most
of the information is transferred in a serial data stream to minimize the
number of
wires. The protocol for the data stream can be changed by selection of
components
and
programming to be RS-232, RS-485, IEEE 1394 or other serial communication
standards as may be available. Decisions to stop or pause the cutter 12 are
included
in the data stream, though a separate wire 204 and 205, respectively (FIG.
13). The
data stream includes a time stamp, gross counts per time increment, a running
average of the counts over a periods of time such as 0.5 seconds and two
seconds,
motion per time increment, and a data scatter/accuracy probability
coefficient.
Functional, logical, and manual override capability at the control and display
panel
130 or in the miner control center 100 can be provided as desired. The control
and
display panel 130 may also be used to track the stop positions of the cutter
12 at the
floor and the roof to produce a profile of the tunnel being produced by the
miner for
historical purposes.
[0098] If the cutter 12 overshoots the interface 15 and actually enters the
rock 26,
it is important that the cutting be stopped immediately. This is accomplished
by
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keeping a running count over a period of time between 2.0 seconds and 4.0
seconds.
A sudden increase in gross counts above the previous running average produces
a
stop signal along the stop wire 204. Occasionally, there may be dislocated
radioactive Materials inside the coal vein 24. If this happens and the cutter
12 is
stopped too early, the operator can override by releasing a shear control
switch (not
shown) on the miner 10 controls and immediately turn it on again. If precise
cutter
motion information is available so that the logic can determine that the stop
decision
is not reasonable, it can issue a decision to slow the cutting.
[0099] One benefit of introducing precision geosteering technology into coal
mining is that doing so lays the groundwork for an almost boundless future
growth
of software techniques, algorithms, and generally smarter controls for use on
mineral
mining equipment. Given that the operator is so intimately connected with the
minute-by-minute operation of a continuous miner, the need and opportunity for
continual enhancements in coal mining may be greater in some respects than for
oil
well drilling.
[0100] In order to allow for growth in computational capability, a more
powerful
processor, such as a digital signal processor 104 (FIGS. 11-12) can be used. A
greater number of algorithms may be stored and executed with greater speed. By
adding larger program and data memory in the ROM 110 and RAM 108,
respectively, the digital signal processor 104 can execute multiple algorithms
in
parallel to calculate coal thickness and do so at greatly increased speed than
the
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microcontroller 93 alone. If the accuracy coefficient indicates that the data
is
inconclusive, the processor can call up other algorithms and take other
actions before
making a final decision. Digital signal processors, currently available,
require a larger
footprint than the microcontroller 93. As such, only rock detectors having
scintillation elements that are 1.75 inches in diameter or greater will have
sufficient
space in the explosion-proof housing. Typically, a digital signal processor
using
current technology can perform 80 million instructions per second (MIPS) or
more.
The microcontroller 93 is generally limited by current
technology to 10 MIPS or less and is further limited by its inability to
access large
amounts of ROM or RAM without additional circuitry.
[0101] The armored rock detectors 20, 120 can be accommodated electronically
and logically by connecting the logic element 57 of the first detector 120 to
the
digital signal processor 104 in the second rock detector 20. Electrical
junctions
between the two detectors 20, 120 are accomplished in a small, standard
explosion-
proof junction box 211.
[0102] Use of a rock detector 120 at the roof not only allows faster, more
accurate cutting decisions at the roof but the information from the roof
detector 120
can be used to support a higher level of logical decision-making. For example,
it is
known that the thickness of the coal seam varies more slowly than the
elevation of
the floor or roof. Therefore, if anomalies exist such that the accuracy
probability
coefficient produced by the floor rock detector 20 is unsatisfactory,
reflecting a high
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level of scatter in the data, the decision on that cut can be based on the
last cut at the
roof less the thickness of the coal on the last cut. Or, if the logic element
57 cross-
checks a decision and determines that the decision is not consistent with
other known
data from the other detector, the logic element 57 can elect to slow down the
cut in
order to obtain more accuracy or can alert the operator to the condition,
giving the
operator the opportunity to override. Fortunately, these situations are
anomalies and
do not all have to be solved in an ideal manner, but provide opportunities to
make
future improvements to further the
efficiency of the operation. As the miners become increasingly more automated,
having a variety of software routines that can be called into play will be an
asset.
[0103] Actual incremental movements of the cutter 12 toward or away from the
rock interfaces 15, 16 can be determined in various ways. A vertical
displacement
sensor may be used to determine actual incremental vertical movements of the
rock
detector, by measuring the change in distance of the cutter 12 or the boom 11
from
a known position on the floor, roof or wall. Such a sensor might be a
mechanical
displacement, optical, acoustic or other gauge. The rock detector performance
and
the geosteering control system strategy are not dependent upon the source of
the
measurements of the incremental movement.
[0104] Some of the operational aspects of preferred embodiments will now be
discussed in more detail. An object is to utilize an accelerometer design that
has
been proven over many years in rugged and demanding environments, such as
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directional drilling for oil. The accelerometer 60, shown in FIG. 8, is
oriented so
that whenever the tips of the cutter picks 14 are at a nominal floor position,
on a
level floor, the direction of sensitivity of the accelerometer would be
parallel to the
floor, in the same direction as the forward advance of the continuous miner.
In that
configuration, the accelerometer. 60 would ideally indicate a zero reading.
However,
if the boom 11 is raised or lowered, a component of gravity is measured
against the
axis of sensitivity 83 of the accelerometer 60. The measurement of the change
in
angle can be made very precisely by this method.
[0105] In actual operation, the floor will generally not be level and so the
nominal
zero position of the accelerometer 60 would not produce a zero reading. This
is not
a problem since the objective is to measure the change in position, or
relative
movement and not the absolute position. Changes M gamma measurements relative
to actual incremental changes in position will produce a curve similar to
curve 2 in
FIG. 9b.
[0106] There are operational considerations that must be addressed in order to
achieve a high degree of precision from the accelerometer 60. One is
vibration. As
the cutter 12 rotates to cut the coal, vibrations are induced into the boom
11.
Vibrations in the vertical direction, generally perpendicular to the axis of
sensitivity
83 of the accelerometer 60, have only a secondary, small effect on the
accuracy of the
accelerometer 60. However, vibrations and movements back and forth are also
experienced and such movements are interpreted by the accelerometer 60 as
rotation
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of the boom 11 and vertical movement of the cutter 12. Another effect of the
operation on the accuracy of the accelerometer 60 is that of the vertical
movement of
the front of the miner 10 as a result of the force being applied to the cutter
12 by the
hydraulic cylinders (not shown) connecting the boom 11 to the body of the
miner
10. If left unadjusted, the data would be in error by the amount of vertical
movement of the miner 10 that occurs during the shearing stroke. Both of these
sources of error are addressed below.
[0107] Referring back to FIG. 8, three elements serve to isolate the
accelerometer
60 from damaging shock and high frequency vibrations resulting from the miner
10
mechanisms and from impacts by materials being thrown against the armored rock
detector 20, 120 by the rotating cutter picks 14. These three elements are (1)
elastomeric ridges 82 on the enclosure 81, (2) the flexible support sleeve 68
positioned between the dynamic housing 80 and the explosion-proof housing 59,
and (3) the flexible support sleeve 61 between the accelerometer module 60 and
the
explosion-proof housing 59. Lower frequencies will pass through all three
levels of
isolation. The effects of the lower frequencies on the data are minimized by
software
techniques. However, the operational methodology that will now be described
greatly reduces these effects before they enter into the data stream.
[0108] There are many situations faced during the operation of continuous
miners
so that they cannot all be discussed. Fortunately, an operator can be quickly
trained on how to utilize the geosteering system to simplify his job and to be
more
=
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effective in most of the situations that he encounters. A typical example of
the
procedure for cutting at the coal face 17 (FIG. 1) is to first sump the cutter
12 into
the face near the roof and then to raise the cutter picks 14 to the coal-rock
interface
16. Next, the boom 11 is lowered so that the cutter 12 shears down toward the
rock
interface 15 at the floor. In most coal formations, this shearing process can
be
performed faster than the gathering arms and conveyor on the continuous miner
10
can carry away the coal. It is not
unusual for the operator to temporarily stop or pause the shearing for two or
three
seconds to allow the coal handling equipment to carry away some coal before
cutting
the rest of the way to the floor. This temporary pause, whether performed
manually
by the operator or automatically by the geosteering system, is an opportunity
to
establish a precise reference position for starting the data correlation
process.
[01.091 The logic element 57 (FIGS. 10-12) issues a pause command when the
boom 11 reaches a desired angular position, even if the operator does not do
so. In
either case, the logic element 57 recognizes that the boom 11 has stopped
moving
and quickly determines the precise angle of the accelerometer 60, and thus the
rock
detectors 20, 120. It is important to note that it is a simple arithmetic
calculation to
convert the angle measured by the accelerometer 60 to a linear distance
perpendicular to the plane of the continuous miner 10 by use of the formula Lx
sin
(theta) where L is the length of the boom 11 and theta is the angle measured
by the
accelerometer 60 in the rock detector 20, 120. Further, determining the
"height" of
the cutter 12 relative to the plane on which the crawler is theoretically
advancing is
not of any significant value to the objective of correlating gamma data being
taken by
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the rock detector 20, 120. The primary objective is to correlate the gamma
counts
with precise motion that corresponds to the changes in gamma counts, not
necessarily the measure of absolute "height" above some reference. Therefore,
the
incremental change in the angle of the rock detector, which does directly
relate to the
"height" of the rock detector 20, 120, may be chosen as the parameter which is
used
to correlate changes in gamma measurements to produce
the curve 2 shown in FIG. 9b. It is the incremental change in gamma counts
versus
an incremental change in angle that is analyzed to predict the intercept of
the cutter
picks 14 with the coal-rock interface 15, 16, through curve fitting
techniques.
[0110] After the first pause in the shear down stroke is achieved at a
selected angle
which might correspond to the cutter 12 being in the range of 6-10 inches
above the
nominal zero position, a precise measurement of the angle is made. If the
operator
feels that the pause is being commanded too early or too late, he can select a
different
setting. Provisions are made for the operator to be able to adjust the
duration of
this first pause if desired, and the operator also can override simply by
resuming the
down shear. As the selected angle is achieved and motion is stopped, the logic
element 57 acquires gamma counts at intervals of approximately 0.1 seconds.
While
loose coal, such as the coal found in the coal pile 21, is fairly transparent
to radiation,
it does affect gamma radiation readings. Thus, it may be necessary to pause
the sump
midway through the sump to enable the rotating picks to clear away the coal.
[0111] Upon the initiation of the pause command, a solenoid that controls the
hydraulic system on the miner 10 closes to stop fluid flow. However, if the
operator
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has driven the cutter 12 hard into the coal, there will be some pre-load taken
by the
structure and the hydraulics so that the shear down will not stop instantly.
In some
cases, the front of the miner 10 may be raised a few inches due to the high
force
being applied to the cutter 12 so that the cutter is physically higher than
the angle
indicated by the accelerometer 60. Fortunately, this tends to be a self-
correcting
problem because
the cutter 12 will continue to lower, after hydraulic flow has stopped, until
the pre-
load has been relieved and the front of the miner 10 has returned to its
unloaded
state.
[0112] Once the cutter 12 has essentially stopped moving down, the logic
element 57 will record the angle and begin accumulating gamma counts. The
difference between this angle and the angle at which the last cutting sequence
was
stopped is determined and the number and duration of the expected shearing
pulses
is calculated. The actual number of pauses will depend on where the interface
is
actually located. The rock detector will calculate the approximate number of
shearing pulses, based on the position of the cutter 12 relative to the
previous shear
down. Pulses of approximately 0.25 second duration will result in the cutter
12
being lowered approximately 1.5 inches. At the end of the pulse, the cutter 12
will
not yet have traveled the full 1.5 inches but will continue for a short time.
After the
pulse stops and the solenoid controlling the hydraulics closes, the cutter 12
will
complete its travel and stop. Some vibration will continue due to rotation of
the
drum 12 and incidental contact with the formation. As soon as the
accelerometer 60
determines that vertical movement has essentially stopped, a precise
determination of
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the movement since the last stop is calculated. It is this precise incremental
movement against which the gamma counts are correlated.
[0113] As the cutter 12 nears the angle at which the shearing command was
issued on the last shearing stroke, the duration of the pulses may be reduced,
depending upon the accuracy coefficient that is being continuously calculated.
Data
collected between
these pause points will be assigned a position value between the position
corresponding to the pause points. Through this methodology, very little time
will
be consumed in the pauses. The operator cannot actually see a stop in motion
of the
boom. Since the cutter 12 can usually extract coal faster than the miner 10
can carry
it away, the addition of pauses does not slow the mining process. The cutter
will
continue to remove coal as fast as the rest of the system can remove and
transport it.
Instead, the effect is to increase speed because only coal is being mined. By
not
mining rock, room is made available on the conveyor and in shuttle cars for
more
coal. Total coal production is increased while the mining of rock is reduced.
[0114] As data is accumulated, the logic element 57 develops a curve and
begins
to make a prediction as to the location of the coal-rock interface 15, 16.
Upon
reaching the angle associated with the location of the coal-rock interface 15,
16, the
logic element 57 will issue a stop command and signal the operator that the
shearing
stroke has been concluded. In a more automated arrangement, such as for high-
wall
mining, this stop signal can, instead, be sent to the automated control
system.
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[0115] The rotating drum 12 that supports the cutter picks 14 on the front of
a
continuous miner, is supported on a boom 11 that moves up and down in order to
force the picks 14 into the coal being cut. During the shearing stroke, the
miner 10
frame is not moving forward. By precisely measuring the rotation of the boom
relative to the stationary miner 10, this angular measurement can be used to
correlate
gamma counts to the incremental motion. A source of error is that the miner 10
frame itself may move
away from the floor due to the high forces exerted by the continuous miner as
it
forces the cutter 12 down into the coal. As the miner 10 moves, it changes the
vertical position of the pivot point for the boom 11. When the control process
described above is used, this motion has no effect on the results. If the coal
is very
hard and the cutting is very fast, it may be desirable to compensate for this
motion in
other ways as described below.
[0116] Although the miner control center 100 can be configured to respond to
the cutting decisions from the rock detector 20, 120, the addition of the
control and
display panel 130 is desirable (S. 13, 15, 16). If a control and display panel
130 is
provided for the rock detector, a small acceleration micro-chip 131 may be
included
to automatically correct for errors that result from vertical movement of a
pivot pin
22 (FIG. 1) about which the cutter boom 11 rotates. The small solid-state
accelerometer 131 is mounted on a small circuit board that measures the tilt
of the
miner 10. By measuring the amount that the miner 10 is tilted, and
transmitting this
information to the rock detector 20, 120, the rock detector 20, 120 will
adjust the
data to remove the error.
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[0117] First, the angular measurements by the accelerometer in the rock
detector
are converted to linear height numbers by the simple calculation of Lx
sin(theta),
where L is the length of the boom and theta is the angle measured by the
accelerometer 60 in the armored rock detector 20. Then, the vertical movement
of
the pivot pin 22 on the miner frame is calculated by the same equation, except
that
the length is the distance from the pivot pin 22 to the point on the crawler
about
which the frame pivots and the
angle is the tilt of the miner frame as measured by the accelerometer 131 in
the
control and display panel 130. This error number is sent to the rock detector
20,
120 where it is subtracted from the height calculated using the accelerometer
angle
of the rock detector 20, 120 and boom 11. Making these adjustments permits the
incremental movements to be accurately measured even when the pivot pin 22 is
moving.
[0118] The control and display panel 130 may be configured as needed for the
type of machine and the specific operational requirements for a specific mine.
It may
include a liquid crystal display (LCD), light emitting diodes (LED), and/or
incandescent bulbs. Typically an LCD would display system parameters, such as
gamma counts, boom movements, coal thickness calculations and system status
= information. LEDs would provide visual indication of the miner status
such as
calibrating, cutting, start, pause, stop and rock contact warning.
Furthermore, the
operator can change system settings and access data and parameters as needed.
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[0119] Due to the electrical components in the control and display panel 130,
it
must be enclosed in an explosion-proof housing (not shown). Since operational
needs and preferences are subject to change, particularly in a rapidly
advancing
technology such as this, there is a need for the control and display panel 130
to be
re-configurable in various ways without having to re-certify the design for
Mine
Safety and Health Administration requirements. Frequent re-certification can
be
avoided by eliminating penetrations through the pressure proof window or
housing,
for switches or controls. Penetrations, other than for standard cable entries,
can be
eliminated by use of
electromagnetic switches that are activated by a magnetic wand that that will
work
through a certified pressure proof window. Whenever the magnetic wand is moved
on the outside surface of the window, near a switch that is located on the
inside of
the window, the switch will trip. Switches may be momentary or may toggle
on/off.
Easier to use configurations include incorporation of the wand into a compound
lever so that it can be simply moved to operate a switch and then be returned
to a
stowed location. The control and display panel may also be operated remotely
by an.
RE link as is routine for the miner control center 100.
[0120] The various embodiments described above produce a faster, more accurate
system, that is simpler and less costly that conventional systems previously
used.
However, other important improvements can be made as described below.
Specifically, a separate cutter motion indicator can be added to the system to
provide
very accurate, almost instantaneous measurements of cutter movements.
CA 02441621 2012-10-26
[01211 Every mining company is constantly looking for ways to advance the
miners
at a faster rate in order to mine more coal. Great improvements have, in fact,
been
made during recent years, thus helping to keep the cost of mining coal in
check. This
has contributed somewhat to the problem of mining more rock. As the miner is
moved more quickly, cutting errors are more difficult to avoid by the
operator. With
experience, the operators do improve. But, as new operators must be added over
time, loss of production and undesirable mining of rock, a real problem at all
times,
is made worse with inexperienced operators. Therefore, a challenge is to make
cutting decisions more accurate and quicker. As the miner 10 is then able to
advance
faster, more improvements are, again, needed. Some conventional systems employ
inclinometers that respond too slowly to allow the accuracy and speed that is
desired.
Even the very precise accelerometers described in the earlier embodiments,
though
significant improvements, may place some limits on speed in some conditions.
As
miners generally become more automated, speed and robust control become more
important requirements. A separate cutter motion indicator 300 (FIGS. 16a,
16b, 17)
can be added to the system to provide almost instantaneous measurements of
cutter
movements. The indicator 300 is positioned at the pivot of the boom.
[0122] The cutter motion indicator 300 can be configured in different ways,
depending upon the configuration of the mining equipment and the operational
requirements. When using a cutter motion indicator 300, an accelerometer 60 is
not
required inside the rock detector 20,120. The space normally occupied by the
accelerometer 60 may be used for other purposes.
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[0123] An explosion proof housing 302 is used to contain an optical encoder
303
and electronics 320 to ensure that those components will not be able to ignite
gas or
dust in the vicinity of the miner 10. Thick steel walls 319 of the enclosure
302 are
capable of withstanding considerable impact without losing pressure integrity.
An 0-
ring seal (not shown) provides the primary seal between the lid 304 and the
housing
walls 319. Multiple seals 311, 312, 313, 317 ensure pressure integrity around
a shaft
321 that transmits the rotation of the boom 11 to the optical encoder 303
inside the
enclosure 300. Dual seals 312 preferably are high pressure seals made of PEEK.
In
addition, a bushing 317 around the shaft 321 is provided as added protection.
The
dimensions of the shaft 321 and the bushing 317 are controlled such that the
maximum clearance is 0.002 inches. This small gap ensures that even if gas is
able to
pass around the non-metallic seals 312, the amount of escaping gas will be so
small
so that it will not be hot enough upon exiting the gap to ignite any gas or
dust that
might be around the enclosure 302.
[0124] Rotation of the boom 11 is transferred into rotation of the shaft 321
which in turn drives the optical encoder 303. The optical encoder 303
indicates
rotation of the shaft 321 by emitting pulses, a single pulse representing a
specific
amount of rotation. Provision is made to indicate the direction of rotation as
well.
Optical encoders, such as the optical encoder 303, are commercially available
that are
very precise, accurately indicating rotation of small fractions of a degree.
Pulses from
the optical encoder 303 representing the amount of rotation are received by a
counter and adder assembly 320. The number of pulses are added and subtracted
as
the boom 11 rotates. Incremental movement of the cutter 12 toward the rock
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interface 15, 16 is calculated by determining the product of the length of the
boom
11 and the arc-sine of the angle rotated.
[0125] Though very precise, the optical encoder 303 does not indicate the
actual
distance of the cutter 12 above the rock interface 15, only the amount of
rotation per
increment of time, typically 0.10 seconds. It should be remembered that it is
the
actual distance of the cutter 12 to the rock, or equivalently, the thickness
of the coal
that is not
known. If the distance to the rock could be known with sufficient accuracy,
without
the use of the armored gamma detector 20, 120, the detector would not be
needed.
Therefore, the information that can be known to high precision through the use
of
the cutter motion indicator 300 is the incremental changes in position as
determined
by the optical encoder 303. With this precise data on incremental changes, the
armored gamma detector 20, 120 determines the distance to the rock 15, 16
through the interpretation of the gamma radiation 28 as it relates to these
incremental changes in position.
[0126] Motion of the miner 10 frame during the cutting process, as explained
earlier, is a source of error in the cutter motion data being provided to the
armored
rock detector 20, 120 by the cutter motion indicator 300. Accelerometers are
incorporated inside cutter tools for drilling oil wells for the purpose of
determining
angle relative to gravity to a high degree of accuracy. The accelerometer 60
is such a
device. The accelerometer 60 determines if its angle relative to gravity
changes,
which is a measurement of any change of the angle of the miner 10 frame
relative to
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the gravity vector. It is also simple to then calculate the instantaneous
change in
height of the boom pivot pin 22 that results from this rotation. These
calculations
are performed by the counter and adder assembly 320.
[0127] Once precise cutter motion data is available, along with cutting
control
decisions from the armored rock detector, additional information can be
derived.
Typically, this would be accomplished in the control and display panel 130 or
within
the
control system provided by the continuous miner. For example, the cutter 12
motion for each cut, including the point at which the armored rock detector
issued a
stop command, the actual position that the stop occurred, any indications of
contact
with rock, and other information is readily available for historical storage
and/or
further evaluation or use. Since the stop position at the floor and the roof
are known
each cut, relative to the previous cut, tracking these stop points in the
control and
display panel would provide a contour of the floor and the roof. Decisions can
be
made in the control and display panel 130 to override the rock detector 20,
120 or
decisions can be made independent of the rock detector under certain special
conditions. For example, suppose that a cut is stopped at a particular
position.
Then, suppose on the next cut the detector gives a false indication due to an
anomaly
in the coal vein, and issues a command to stop the cutter six inches above the
position of the previous cut. Logic can be included in the control and display
panel
130 that would override or ignore the armored detector 20 decision. The
decision
could be made to stop the cutter 12 at the same height as the last cut,
relying upon
the knowledge that the formations will not change six inches over the distance
of one
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cut. Or, alternately, the decision could be to slow the cutter until the rock
detector
20, 120 detects that the rock has been contacted, indicated in a sudden jump
in gross
gamma counts.
[0128] A suitable structure must be provided for transferring the rotation of
the
boom into the shaft 321 in the cutter motion indicator 300. If a continuous
miner is
configured such that the pivot pin 22 rotates with the boom 11, then a
connection
can
be made directly at the center of the pivot pin 22. However, for this
configuration,
there are some mechanical challenges. The cutter motion indicator 300 is a
precise
instrument. Its shaft 321 must be mechanically attached to the boom 11 so that
any
rotation of the boom 11 is transmitted to the encoder. However, it is
difficult to
locate the cutter motion indicator 300 at a precise distance from the pivot
pin 22.
Further, due to the large forces endured by the miner components, some
relative
linear motion between the cutter motion indicator 300 and the pivot pin 22
must be
tolerated. This has been accomplished by the use of a spline 342 (FIG. 17).
Similarly, it is not practical to provide an exact alignment of the cutter
motion
indicator 300 and the pivot pin 22 to which it must be attached. To overcome
this
obstacle, a dual universal joint 340, 341 is provided. With these joints 340,
341, 342
in the drive train assembly, linear motion perpendicular to the drive train
assembly
will not induce forces into the drive train assembly. Similarly, small angular
misalignments between the drive train assembly and the axis of the pivot pin
22
around which the boom 11 is rotating will not induce forces into the drive
train
assembly.
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[0129] Addition of the dual universal joints 340, 341 and spline 342 may
introduce a possible backlash problem. Addition of an anti-backlash spring 316
eliminates backlash by removing slack in the universal joints 340, 341 and the
spline
342.
[0130] There are multiple methods for obtaining angular rotation of the boom
relative to the frame. One method is to attach a shaft at the center of the
pin upon
which the boom is hinged. However, some miners are designed such the boom
bearing
rotates on the pivot pin 22 such that the pin 22 itself does not rotate. A
lever (not
shown) can be attached to the boom 11 that transfers the boom rotation to a
point
that is along the bearing axis. Also, the pivot pin 22 on which the boom 11
hinges
usually wears so that it becomes loose. The combination of the spline 342,
dual
joints 340, 341, and anti-backlash spring 316 prevent these undesirable linear
movements from entering into the rotational measurement.
[0131] On many miners, the pivot pin 22 does not rotate with the boom 11, the
bearings being on the boom 11 side of the pivot pin 22. In this case, a lever
must be
added to the boom 11 to transfer the boom 11 rotation to a point along the
axis of
the pivot pin 22 on which it is rotated. The provisions within the drive train
assembly discussed above are effective for relieving relative linear motion
and
misalignments on this miner configuration as well.
[0132] Calibration of the optical encoder 303 may be accomplished occasionally
if
needed. This would typically be performed at the beginning of a shift and
during
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major moves of the miner within the mine. To accomplish a calibration, the
continuous miner 10 is driven up to the face of the coal at a location where
the floor
is flat, not necessarily level, prior to start of the cutting operation. The
cutter 12 is
then lowered to the floor.
[0133] A calibration command is sent to the cutter motion indicator 300 from
the
control and display panel 130 through wire 206. This calibration command would
also be forwarded to the armored rock detector 20, 120 so that gamma readings
can
be
recorded as well. The counter and adder assembly 320 in the cutter motion
indicator
300 reads the optical encoder 303 and the accelerometer 60 and accepts that
reading
as the zero position. The cutter 12 then is raised to the roof and the
calibration is
repeated and this reading is taken as the zero roof position. During the next
cut, the
readings will be referenced to this starting reading. The second cut will be
referenced
to the first cut, etc.
[0134] The primary source of motion information is from the optical encoder
303. This encoder 303 has a disk with holes that move past a light source as
it is
turned by the boom motion through the drive train assembly described earlier.
The
holes in the disk are spaced to provide a certain degree of angular
resolution.
Typically, the angular resolution of a commercially available encoder is on
the order
of 0.06 . The output signals, A and B, from the optical encoder 303 are pulses
that
can be counted by the microcontroller 93 or other logic. Furthermore, if the
pulse
from A leads the pulse from B, then the rotation is clockwise. Thus, the
running
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count of pulses is incremented by one. If the pulse from A lags the pulse from
B,
then the rotation is counter-clockwise. Thus, the running count of pulses is
decremented by one. At any given time, the number of pulses counted can be
converted to an angle measurement simply by multiplying the current pulse
count by
the angular resolution, thereby giving the angle of the boom 11.
[0135] To sense the tilt of the miner 10 frame, an accelerometer 60 is used
inside
the cutter motion indicator 300. An accelerometer 60 can measure angle based
on a
change
in orientation with respect to the gravity vector. The gravity vector is the
same all
over the earth; it points toward the center of the earth. With the
accelerometer 60
fixed to the miner 10 frame, the orientation of the accelerometer 60 changes
as the
miner 10 tilts up or down. The output signal from the accelerometer 60 is
typically
an analog voltage, or current, which can be converted to voltage, that varies
as the G
force varies according the resolution of the device. Typically, a commercially
available accelerometer has a resolution of 1 micro-G. The output voltage can
be
sampled by an analog-to-digital converter 92. The sampled value can be
converted
to angle by referencing it to a G force of 1 and taking the arc-sine. Thus,
the tilt of
the miner 10 frame is measured during the shearing stroke and the vertical
movement of the pivot is measured, subtracted from the measurement made by the
optical encoder 303, and the difference is reported to the rock detector 20.
[0136] Another preferred embodiment applies geosteering to long-wall shearing
systems. Long-wall miners have two shearing drums 412, 413, as shown in FIG.
18.
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When moving one direction, the cutting drum 413 is in the front and is
referred to as
the leading drum. It cuts at the coal/rock interface 16 at the roof and the
second
drum 412, referred to as the trailing drum, cuts at the floor interface 15.
Typically,
one operator positions himself near the front of the miner and visually
controls the
height of the leading drum 413 so as to remove all the coal 18 and to remove
as little
rock 26 above the coal 18 as practical. A second operator controls the
vertical
position of the trailing drum 412 that is located approximately 40 feet behind
the
leading drum 413.
Visibility of the trailing drum 412 is usually severely limited due to the
shearing
assembly being filled with coal. In some operations, rock may fall from the
roof,
obscuring the cutter 412. Coal and rock roll behind a cowl 404 so that the
exposed
cut 415 is quickly covered in the region a few feet behind the cowl.
Fortunately, the
exposed cut immediately behind and somewhat under the cowl 404 remains free
from debris which is useful.
[0137] Geosteering is accomplished for the trailing drum 412 by placing a rock
detector 401 on the back of the cowl 404 such that it can view the surface
that has
just been cut by the cutter drum 412. The purpose of this rock detector 401 is
to
differentiate between the condition when the cutter drum 412 is cutting into
the
floor rock, typically fire clay, from the condition when picks 407 of the drum
412
(FIG. 19) are above the floor so that coal is being left unmined. The rock
detector
401 also can calculate the thickness of the coal being left. In effect, this
rock
detector 401 is measuring the distance that the cutter is separating from the
coal/rock interface, or the amount of divergence between them. For that
reason,
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this detector is referred to as the divergence rock detector 401. If the
cutter is
beginning to cut into the floor, indicating that the cutter 412 and the floor
are
moving toward each other, the detector 410 detects the rock that is being
mined and
mixed with the coal. This detector is referred to as the convergence rock
detector
410.
[0138] The cowl 404 may be located close to the cutter picks 407, as close as
three inches. In such a circumstance, the divergence rock detector 401 may
actually
be
vertically beneath the cutter picks 407, thereby in a position between the
picks and
the coal.
[0139] As the miner moves forward, the cowl 404 drags on the newly cut surface
415, thus removing lumps of coal or rock and all but a small amount of coal
dust. If
the cutter 412 is cutting into the rock 26, the divergence detector 401 will
not be
able to measure any change in gamma readings. Therefore, the detector 401 will
begin to raise the cutter 412 in small steps. For example, the rock detector
401 may
give a command each 10 seconds to raise the cutter by 0.5 inches. If the miner
10 is
moving at the rate of 30 fpm, then the cutter 412 will be raised approximately
0.1
inches for each foot of travel. Once the cutter tips 407 are raised above the
coal/rock interface 15, no rock is being mined.
[0140] If the cutter 412 rises above the rock 26, coal will be left behind,
unmined. Once the coal is approximately one inch thick, the divergence
detector
401 will detect the layer of coal and stop raising the cutter 412. The
detector will
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measure the thickness of the coal and then lower the cutter 412 by that
amount.
After 10 seconds, it will begin to raise the cutter 412 as before, in 0.5"
steps, each 10
seconds and repeat the process.
[0141] Unless a convergence rock detector 410 is being used, the divergence
rock
detector 401 will continue to raise the drum 412 by 0.5 inches each 10
seconds.
During this time, the coal/rock interface 15 may be rising either toward or
dropping
away from the cutter drum 412 and movements of the miner either add or
subtract
from these relative movements. These possible relative movements must be
considered in selecting the rate at which the divergence rock detector 401
raises the
drum 412. If the drum 412 is raised too rapidly, the cutter tips will quickly
be
sufficiently above the rock interface 15 so that coal is left unmined. If the
drum is
raised too slowly, at a time when there is rapid convergence between the
cutter 412
and the floor interface 15, the cutter 412 may dig into the rock 26 faster
than it is
being raised out of the rock 26, until the rate of convergence decreases.
Fortunately,
this would be a rare condition, for a reasonable set of control parameters.
[0142] Floor conditions vary from mine to mine. Control parameters in the rock
detector 401 are set to best fit the range of conditions that exist in each
mine. Some
floor conditions are very favorable for geosteering even though they may have
traditionally been considered to be poor floor conditions for other types of
mining
systems. For example, in some mines, the coal is soft and is not bonded to the
fire
clay in the floor. As a result, whenever the cutter 412 is raised out of the
floor, such
that the picks 407 do not reach into the fire clay, the coal will continue to
break away
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from the fire clay so that no coal is left unmined. This zone of cutting is
called the
break away zone. This condition may continue even when the cutter picks 407
are
two inches or more above the fire clay, meaning that the break away zone may
be as
much as two inches or more.
[0143] Geosteering can mine almost all the coal and little or none of the rock
when the breakaway zone is greater than one inch. If the cutter 412 is either
cutting
into the rock 26 or leaving coal unmined, there is a procedure employed by the
rock
detector 401 to recognize this condition and to return the cutter 412 to cut
in the
break away zone. Once in the break away zone, the accelerometer 60 inside the
rock
detector 401 monitors the angle of the cowl 404 so that any vertical movements
of
the cutter 412 are detected. The cowl 404 is riding on the top of the fire
clay such
that the position of the cutter 412 can be controlled relative to the fire
clay. The
rock detector 401 opens solenoid valves as required to raise or lower the
cutter 412
in order to keep the tips of the picks 407 inside the break away zone. For
each
movement of the cutter 412, the rock detector 401 pulses the solenoids for a
length
of time that is calculated by the rock detector depending upon the response
rate of
the hydraulic system.
[0144] Unusual situations may arise from time to time. The geosteering must be
robust to respond to these situations or, at least, quickly recover from any
disruptions
in the normal process. For example, the cutter 412 might move up more than
commanded so that the soft coal is no longer being broken away from the fire
clay,
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or the coal might have hard spots so that it remains bonded to the fire clay
even
though it is being cut very thin. In these cases, the divergence detector 401
will
recognize a sudden change in gamma readings and respond by lowering the cutter
by
the thickness of the coal that it reads. Also, the accelerometer 60 will
respond by
reporting a change in the height of
the cowl as it climbs upon the coal that is beginning to be left. This event
can also
be included in the logic.
[0145] The more difficult condition to protect against is for the cutter 412
to
begin entering the rock 26 because the divergence detector 401 does see a
change in
gamma readings because it is already looking at fire clay with only a little
dust on top.
This is solved by performing repetitive cycling once the picks 407 have
entered the
breakaway zone. First, the cutter 412 is raised 0.5 inches. The accelerometer
60
immediately registers the cutter 412 being raised. After approximately six
seconds
the cowl 404 is seen, by the accelerometer 60, to be lifted up if the cutter
412 was in
fire clay 26. If so, two seconds later, the rock detector 401 issues a command
to raise
by one inch. If, after approximately six seconds the cowl 404 jumps up again,
reported by accelerometer 60, the detector 401 issues another up command. It
would have to be a very unusual situation for this process to continue for
very many
steps. However, eventually the cutter 412 will be out of the rock and into the
breakaway zone, even if the cutter 412 found itself a few inches in the fire
clay. Once
=
entering the breakaway zone, the next step up does not produce a change in the
cowl
404 angle so that the rock detector 401 knows that it is in the breakaway zone
of the
formation. At this point, repetitive cycling occurs--once up by 0.5 inches
followed
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by down by 0.5 inches. So long as the accelerometer 60 confirms that the
cutter is in
the desired breakaway zone, the cycling continues. Once the cowl 404
determines
that the cutter 412 has exited the breakaway zone, and is in the fire clay
again, the
above sequence is repeated. Meanwhile, if control
is temporarily lost and the cutter 412 begins leaving coal, the accelerometer
60
reports this condition, which is confirmed and corrected by the divergence
detector
401, as explained earlier. The rock detector 410 has enough inputs and enough
logic
to regain control even if it is lost temporarily due to unusual events or
conditions.
[0146] By this geosteering process, the rock detector keeps the drum adjusted
at a
height so that little or no rock is mined and little or no coal is left except
for unusual,
anomalous conditions. Note that the basis for control is a direct measurement
of the
formation being mined and the response by the rock detector is a direct result
of the
measurements. A guidance system for the long-wall shearing machine is not
required, nor could it ever be nearly as accurate.
[0147] One significant benefit from geosteering the trailing cutter is that
the need
for an operator to steer the cutter is eliminated. Whenever the cutting system
is
reversed, the one operator that was controlling the leading cutting drum moves
to
the other end of the machine to control what was the trailing drum but is then
the
leading drum.
[0148] Under certain dynamic circumstances, the coal/rock interface 406 and
the
cutter picks 407 may converge quickly, resulting in more rock 405 being taken.
If a
particular mine faces this undesirable condition, a convergence rock detector
410
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may be added to detect whenever large amounts of rock are being cut and mixed
with the coal 411. Detection of this condition will result in the convergence
rock
detector 410 alerting the divergence rock detector 401 which will quickly
raise the
cutter picks 407.
Since there is the possibility, in some mine conditions, for large amounts of
rock to
fall from the roof, the divergence detector 401 will override the convergence
rock
detector 410 in the event of a false signal.
[01491 Routing and protection of a power and signal cable to the divergence
detector 401 is difficult due to the continual impact from rock and coal. To
solve
this problem, a battery 408 is installed in the cowl 404 to supply power to
the
divergence detector 401. Signals are transmitted to the miner control center
by a
radio link inside the detector 401 (not shown). A receiver module (not shown)
in
the miner control center translates the signals to open a solenoid to raise
the cutter
412 or to open the solenoid to lower the cutter 412, as needed.
[0150] Since the cowl 404 is free to rotate 360 degrees so that it can be
reversed
whenever the machine is reversed, the divergence rock detector 401 must be
disabled
whenever the cowl 404 is rotated into the leading drum position. An
accelerometer
60 is incorporated into the photometric module 58 that detects the orientation
of
the detector and disables its control capability once the detector 401 is
rotated out of
its operating position. Whenever the detector 401 is returned to the proper
position
for steering the trailing cutter 412 at the floor, the detector 401 reads the
output of
the accelerometer 60 and automatically activates the controls once the
detector 401
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has returned to its operating position.
[0151] It should be pointed out that in some cases, the accelerometer 60 may
be a
small solid state device that is incorporated within the electronics 57 inside
the
photometric module 58.
[0152] FIG. 24 illustrates a rock detector 220 constructed in accordance with
another embodiment of the invention. Previously described rock detectors 20,
120
include an accelerometer 60 or a cutter motion indicator 300. The
accelerometer 60
determines the angle of the boom 11 relative to gravity and therefore assists
in
determining the movement of the boom 11. The cutter motion indicator 300, with
the optical encoder 303, determines the angular movement of the boom 11. The
rock detector 220 includes the accelerometer 60 as well as a rate gyro 222
(FIGS. 24
and 25).
[0153] As described above, curve fitting of gamma radiation readings are an
important aspect of the invention. The gamma radiation readings taken by the
rock
detectors are correlated with measurements of incremental movements of the
cutter
12 toward the rock interfaces 15, 16. Since changes in the position of the
cutter 12
can be equated with changes in the thickness of uncut coal in front of the
advancing
cutter 12, changes in the gamma radiation readings may be correlated to
changes in
position of the cutter 12. The rate gyro 222 measures incremental movements of
the
cutter 12. Specifically, the rate gyro 222 measures the rotation of the rock
detector
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220, and since
the rock detector is mounted on the boom 11 the rotation of the rock detector
220
is the same as the rotation of the boom 11. The distance from the pivot pin 22
and
the axis of the cutter 12 is fixed and so the movement of the rock detector
220 can
be calculated. By integrating the output of the rate gyro 222 with other
measured
information, changes in the position of the cutter 12 and changes in the
thickness of
the uncut coal can be known.
[0154] An advantage of the rate gyro 222 is that its output is relatively
insensitive
to most vibrations. Only rotational vibration is measured, not lateral
vibration, and
rotational vibration can be easily filtered out of the output. Nonetheless,
since the
rate gyro 222 is unable to make an independent measurement of the actual
orientation of the boom and since a rate gyro 222 accumulates errors over
time, it
may be used in conjunction with the accelerometer 60, as illustrate in FIG.
24.
During brief periods of time when lateral vibration is minimal, the
accelerometer 60
is used to determine actual orientation of the boom 11 relative to gravity.
Then, the
rate gyro 222 is used to determine angular rotation from that position, even
under
high vibration conditions.
[0155] The combination of the rate gyro 222 and the accelerometer 60 allows
precise measurement of boom 11 movement over short periods of time, such as
0.1
seconds, and also allows determination of position over long periods of time
as well.
Short duration measurements allow the gamma radiation readings to be
accurately
correlated to incremental position changes so that curve fitting procedure is
not
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[0156] One methodology for the use of the rate gyro 222 includes
automatically
pausing the movement of the boom 11 when the cutter 12 has been determined to
be
only a few inches from the predicted location of one of the rock interfaces
15,16. By
pausing movement, the mechanical dynamics of the mining equipment are
minimized
for a moment of time. Excess coal is cleared away, the mining equipment
settles to
its nominal position, and the accelerometer 60 establishes the position of the
boom
11 relative to the previous cutting stroke. From that point, the rate gyro
222, in
combination with the accelerometer 60, accurately tracks the cutter 12 as it
moves
toward the rock interface 15, 16.
[01571 Although not illustrated, a second accelerometer 60 may be used in
conjunction with the rock detector 220. The first accelerometer 60, within the
rock
detector 220, is utilized to measure the movement of the boom 11 relative to
gravity.
The second accelerometer 60, positioned on the mining equipment, is utilized
to
measure the angular movement of the mining equipment.
[0158] The scope of the claims should not be limited by the preferred
embodiments
set forth in the examples, but should be given the broadest interpretation
consistent
with the description as a whole. For example, although there are significant
technical
and practical benefits derived from incorporating the logic elements within
the
explosion-proof housing of the rock detector, it should be understood that
this
element of the geosteering system could be re-located into the control and
display
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panel, or into the miner control system, or chosen places on the continuous
miner.
64
