U.S. patent number 4,968,098 [Application Number 07/405,365] was granted by the patent office on 1990-11-06 for coal seam discontinuity sensor and method for coal mining apparatus.
This patent grant is currently assigned to Atlantic Richfield Company. Invention is credited to Amjad A. Bseisu, Robert L. Hirsch, Fred W. Ng.
United States Patent |
4,968,098 |
Hirsch , et al. |
November 6, 1990 |
Coal seam discontinuity sensor and method for coal mining
apparatus
Abstract
A continuous mining apparatus such as a coal milling or shearing
machine includes sensors mounted on the machine frame or on the
cutter bits, including an accelerometer and one or more strain
gauges, for sensing vibrations and stresses exerted on the cutter
bits during operation of the machine. A signal conditioning and
amplification circuit provides an audio and/or visual display
indicating when the cutter is moving outside of the coal seam
and/or is cutting along a cleat or other joint to improve
excavation rates while maintaining or lowering stress levels on the
cutter bits. The display enables the machine operator to keep from
penetrating the roof or floor of the coal seam and to position the
cutter to take advantage of natural fracture lines in the seam. The
frequency spectrum of the sensor signals is determined to
distinguish vibrations caused by bit interaction with the material
being cut.
Inventors: |
Hirsch; Robert L. (Dallas,
TX), Ng; Fred W. (Dallas, TX), Bseisu; Amjad A.
(Dallas, TX) |
Assignee: |
Atlantic Richfield Company (Los
Angeles, CA)
|
Family
ID: |
23603407 |
Appl.
No.: |
07/405,365 |
Filed: |
September 11, 1989 |
Current U.S.
Class: |
299/1.1;
73/579 |
Current CPC
Class: |
E21C
35/10 (20130101); E21C 39/00 (20130101) |
Current International
Class: |
B23Q
17/09 (20060101); E21C 35/10 (20060101); E21C
35/00 (20060101); E21C 39/00 (20060101); E21C
035/24 () |
Field of
Search: |
;299/1,79,91
;73/579,594 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
253712 |
|
Jan 1970 |
|
SU |
|
976074 |
|
Nov 1982 |
|
SU |
|
1002571 |
|
Mar 1983 |
|
SU |
|
1145130 |
|
Mar 1985 |
|
SU |
|
Primary Examiner: Novosad; Stephen J.
Assistant Examiner: Bagnell; David J.
Attorney, Agent or Firm: Martin; Michael E.
Claims
What is claimed is:
1. A method for operating a continuous mining apparatus for mining
a seam of a mineral value such as coal and the like, said seam
having one or more cleats forming a discontinuity in said seam,
said apparatus including cutter means supported thereon for cutting
said mineral value from said seam, and said apparatus includes
sensor means mounted thereon for generating a signal related to at
least one of stresses exerted on said cutter means and vibrations
of said cutter means, said method including the steps of:
engaging said cutter means with said seam and traversing said
cutter means along said seam to cut said mineral value, generating
signals related to said at least one of vibrations and stresses on
said cutter means while cutting said mineral value, generating a
signal related to signals from said sensor means to indicate when
said cutter means is cutting along said discontinuity in said seam,
and adjusting the position of said cutter means relative to said
discontinuity to advance along said discontinuity to maximize the
extraction of said mineral value from said seam.
2. The method set forth in claim 1 wherein:
said sensor means comprises accelerometer means mounted on said
cutter means and the step of generating said signal comprises
generating signals related to vibrations of said cutter means as
sensed by said accelerometer means and generating an audible signal
corresponding to the signal provided by said accelerometer means
and which is indicative of a change in the material being cut by
said cutter means.
3. The method set forth in claim 1 wherein:
said sensor means comprise strain gauges mounted on said cutter
means for sensing stresses exerted on said cutter means in at least
two directions and, adjusting the position of said cutter means
relative to said seam to reduce stresses exerted on said cutter
means.
4. The method set forth in claim 1 including the step of:
determining a selected frequency spectrum of signals generated by
said sensor means and detecting a signal at a frequency which is
related to the cutting effort of said cutter means.
5. The method set forth in claim 4 wherein:
the step of determining the frequency spectrum of said signal from
said sensor means includes performing Fourier transform analysis on
a set of multiple time records of the signals produced by said
sensor means; and
determining the auto spectra of said transformed time records.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a system and method for sensing
the limits of and discontinuities in underground coal seams for
optimizing mining of the coal with coal milling machines and the
like.
2. Background
In the automated mining of coal using coal milling and shearing
machines, the quality of the coal and the rate of excavation can be
improved if the limits of the coal seam can be detected and if the
coal can be mined along surfaces which exhibit minimum strength
such as along cleats, cross-cleats and slips. Conventional practice
in coal milling and shearing requires the machine operator to
follow strata maps and to visually notice a change in the milling
characteristics of the machine to detect penetration of the milling
cutters out of the coal seam or to determine discontinuities in the
seam. The ability to accurately detect the seam limits and surfaces
which present minimum cutting resistance is highly dependent on the
experience and alertness of the operator as well as the comparative
structural differences between the coal seam and the adjacent
formation material.
Accordingly, a system which could automatically detect the movement
of the milling cutter out of the coal seam would greatly reduce the
amount of foreign material mined with the coal and improve the
quality of the coal product. Moreover, the ability to detect the
presence of discontinuities or fractures in the coal seam can be
used to improve the rate of excavation by adjusting the cutters to
mill along the surfaces which define the discontinuity or fracture
in the seam. For example, if the presence and direction of cleats
or slips in the seam can be detected, the attitude of the milling
cutter may be adjusted to take advantage of the discontinuity in
the seam provided by these faults to increase the rate of coal
production at reduced stress levels on the mining equipment. To
this end the present invention has been developed with a view to
improving the quality and rate of excavation of coal and similar
minerals which are mined by automated or semiautomated machines
which effect milling or mechanical cutting of the product.
SUMMARY OF THE INVENTION
The present invention provides a system and method for detecting a
change in milling or similar cutting operations for the mining of
coal and similar minerals. In accordance with one aspect of the
present invention, there is provided a system associated with a
coal milling or shearing machine which detects strains and
vibrations of the machine cutting elements to provide a signal
indicating a change in the cutting forces exerted on the coal seam
to minimize the excursion of the cutting machine out of the coal
seam. The system of the present invention is also operable to
detect the relative resistance to the cutting effort whereby the
cutting operation may be conducted along faults or discontinuities
in the seam such as are formed by cleats or slips to improve the
rate of excavation of the coal and minimize the stresses imposed on
the cutting equipment.
In accordance with another aspect of the present invention, a
system is provided for a coal mining machine which produces both
audible and visual signals indicating the penetration of the
machine cutters out of the coal seam or out of a cutting plane
which produces the optimal cutting rate of the machine. In
accordance with one embodiment of the invention, sensors such as
strain gauges and/or accelerometers are mounted on or adjacent to
the cutting elements of a coal milling or shearing machine and the
output signals from the strain gauges or accelerometers are
conditioned and used to furnish an audible signal or a visual
display indicating a change in the cutting forces by the machine
due to movement of the cutter out of the coal seam or out of an
optimal cutting angle or cutting plane. The sensors may be mounted
elsewhere on the machine if convenient to do so.
In accordance with yet another aspect of the present invention,
there is provided a method for detecting certain vibrations in a
coal mining apparatus which are indicative of a change in the
cutting characteristics such as might be experienced by moving the
cutters out of the coal seam or along or out of a discontinuity in
the coal seam. The method of the invention includes providing
certain vibration or strain measuring sensors on the apparatus at
selected locations and analyzing selected parts of the frequency
spectrum of the signals generated by the sensors to determine
changes in signal frequency and/or amplitude of signals of a
particular frequency which may indicate a change in the material
being cut or a change in resistance to cutting of a particular
material. The method of the present invention detects certain
frequencies of interest while precluding false readings from
nonessential signals or "noise".
Advantages of the present invention reside in the ability to mine
coal and other minerals with mechanical cutting equipment in an
improved manner which reduces the presence of contaminants in the
coal, improves the excavation rate, reduces stresses on the cutting
machine and thereby provides for faster and more efficient
production of quality coal and similar minerals.
Those skilled in the art will further appreciate the
above-mentioned advantages and superior features of the present
invention together with other aspects thereof upon reading the
detailed description which follows in conjunction with the
drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of a coal shearing machine utilizing
the system of the present invention and shown cutting along a face
in an underground coal seam;
FIG. 2 is a detail view showing one arrangement for transmitting
signals from sensors on the coal cutting elements to a signal
conditioning and display circuit mounted coal cutting machine;
FIG. 3 is a detail view of a coal shearing cutter showing the 1,
cation of strain gauge and accelerometer type sensors on a cutting
member;
FIG. 4 is a schematic diagram of the signal treating circuit for
the system of the present invention; and
FIG. 6 is a diagram of a frequency spectrum of the output signal of
one of the sensors.
DESCRIPTION OF A PREFERRED EMBODIMENT
In the description which follows, like parts are marked throughout
the specification and drawing with the same reference numerals,
respectively. The drawing figures are not to scale and certain
features are shown in schematic form in the interest of clarity and
conciseness.
Referring to FIG. 1, there is illustrated a continuous long-wall
mining apparatus generally designated by the numeral 10 and
sometimes known in the art as a shearer. The shearer 10 is
exemplary of so-called continuous miners which mechanically cut or
excavate the mineral being mined such as the coal seam 12. The coal
seam 12 has upper and lower bedding surfaces 14 and 16 and a
plurality of cleats 18 which are generally vertical as illustrated.
The direction of the coal seam 12 is for illustrative purposes only
as are the specific directions and locations of the cleats 18.
Those skilled in the art will appreciate that the bedding planes or
surfaces defining the coal seam 12 may extend in different
directions as may the cleats 18.
The shearer 10 includes a support frame 20 and a drum support arm
22 which houses suitable drive mechanism for rotating a cutting
drum or wheel 24. The cutting drum 24 is fitted with a plurality of
cutter elements 26 in the form of bits or picks which are supported
in respective socket members 28 about the periphery of the drum 24.
The drum 24 may have a spiral configuration on which additional
cutters 26, not shown, may be disposed. The drum 24 is supported
for rotation on the support arm 22 and is driven by suitable motor
means and drive mechanism, also not shown. The shearer 10 is of
conventional construction except for the modifications to be
described herein and illustrated in the drawing figures. The
shearer 10 is provided with a suitable operator control station 21,
also of conventional configuration. The shearer 10 is also
supported on elongated haulage support rails 30 for traversal along
the coal seam 12 to cut coal from the face 13 in a conventional
manner through rotation of the drum 24 and haulage of the machine
along the supports by conventional mechanism, also not shown.
Although the system of the present invention is shown associated
with the shearer 10, those skilled in the art will recognize that
the advantages and superior features of the present invention may
also be implemented on other types of coal cutting machines such as
universal type cutting machines, ripping type continuous miners,
boring type continuous miners and milling type continuous miners.
Moreover, it is contemplated that the present invention may also be
utilized on long-wall plow type miners.
In the illustration of FIG. 1, conventional coal conveying
equipment for removing coal from the floor 17 adjacent the face 13
has been omitted in the interest of clarity and since such
apparatus forms no part of the present invention. The shearer 10 is
of the type which may be adjusted vertically to cut the face 13
which has a height greater than the sweep of the cutter drum 24 by
making multiple passes of the drum across the face.
Referring now to FIGS. 2 and 3, and as shown in FIG. 3 by way of
example, the drum 24 is fitted with a plurality of
circumferentially spaced support sockets 28, one shown, for
supporting the cutters 26. The cutter 26 may be one of several
types used in conjunction with continuous mining machines of the
type described above. In accordance with the present invention, one
or more of the cutters 26 is fitted with a vibration sensor in the
form a piezoelectric accelerometer 40. In FIG. 3 the accelerometer
40 is illustrated disposed within the cutting element 26 to
minimize the prospect of damage to the accelerometer.
Alternatively, the accelerometer could be mounted on the support
socket 28 also in a protected manner. The cutter 26 is also
preferably fitted with one or more piezoelectric strain gauges 42
and 44 which may be disposed to measure strains on the cutter in
one or more planes for determining the direction of the resultant
load on the cutter as it performs its cutting action against the
coal face. The strain gauges 42 and 44 may also be imbedded in the
body of the cutter 26 to prevent damage thereto during operation.
As further illustrated in FIG. 3, each of the sensors comprising
the accelerometer 40, and the strain gauges 42 and 44 includes a
signal conductor extending therefrom, respectively, and indicated
in FIG. 3 by the numerals 41, 43, and 45. These conductors may also
be suitably protected from exposure to abrasion and damage during
operation of the drum 24. The exemplary arrangement of sensors 40,
42 and 44 for the cutter 26 as shown in FIG. 3 may be repeated for
a selected number of cutters 26 on the periphery of the drum
24.
Signals from each of the sensors 40, 42 and 44 may be transmitted
to a suitable signal-receiving, conditioning and amplification
circuit as illustrated in FIG. 4 and generally designated by the
numeral 50. Signals from the strain gauges 42 and 44 and the
accelerometer 40 are transmitted by way of their respective
conductors through a conventional multiconductor slipring assembly
52 to the circuit 50. FIG. 2 illustrates the arrangement of the
cutter drum 24 which is supported for rotation with respect to a
stationary hub 54 disposed on the support arm 22. The slipring
assembly 52 includes a conventional stator member 56 supported by
the hub 54 and a rotor member 58 supported on the drum 24.
Referring again to FIG. 4, the circuit 50 is adapted to provide a
signal to an audio signal generator or speaker 60 which is suitably
disposed in proximity to the operator control station 21 so that an
operator controlling the mining machine 10 may detect a change in
an audible signal which is correlated with a change in the stresses
or vibrations imposed on the cutters 26 due to cutting action such
as would occur if the cutters were moving away from the seam 12
either above the seam through the bedding surface 14 or below the
seam through the bedding surface 16. Since the stresses on the
cutters 26 would normally change if the cutters started penetrating
different earth material above the surface 14 or below the surface
16 the operator could adjust the position of the arm 22 to bring
the cutters 26 back into cutting only the coal material. Moreover,
the stresses on the cutters 26 are also related to the cutting
effort, which effort is minimized if the cutters are operating
parallel to and generally coplanar with a cleat 18 or a similar
fracture line in the coal seam 12. Since the stress levels
encountered by the cutters 26 are lower if the cutters are
operating in a plane which includes the joint or cleat 18, these
stress levels would be indicated by readings from the strain gauges
42 and 44. Moreover, the direction of the relative stresses
indicated by the strain gauges 42 and 44 may also indicate an
optimum angle for the cutting plane of the drum 24 or an optimum
cutting angle for the cutters 26, which, in some instances, may be
adjustable relative to the plane of rotation of the drum 24. Still
further, as previously mentioned, the amplitude as well as possibly
the frequency of vibrations of the cutters 26, for a given
operating speed of the drum 24, would vary in accordance with the
type of material being penetrated by the cutters and these
vibration characteristics can be measured and provided as an output
signal to indicate to the operator of the machine 10 when the
cutters are penetrating material other than coal. As shown in FIG.
4, a visual display 62 may also be provided for receiving suitable
output signals from the circuit 50 to indicate the stress levels
encountered by the cutters 26 and the vibrational characteristics
sensed by the accelerometer 40.
The sensors 40, 42 and 44 may not require to be located on the
cutting elements 26 or even on the rotating drum 24. Indeed, it may
be preferable to avoid placing the sensors 40, 42 and 44 on the
cutting elements 26 to preclude damage to the sensors. Referring to
FIG. 1, there is illustrated an alternate arrangement wherein a
sensor in the form of an accelerometer 70 is mounted on the support
arm 22 and yet a third sensor in the form of an accelerometer 72 is
mounted on the machine frame 20. The sensors 70 and 72 are to some
extent more likely to sense vibrations other than the vibrations of
the cutting elements 26 as the cutting elements encounter the coal
seam 12. However, in accordance with a preferred method of
analyzing the signals produced by the sensors 40, 42, 44, 70 and
72, the vibrations of the cutting elements and their amplitude
and/or frequency may be distinguished from other vibrations of the
machine caused by the motor and drive mechanism, for example, and
certain machine structure response to such vibrations. For example,
referring to FIG. 5, there is illustrated a plot of a selected
frequency spectrum of the signals sensed by the accelerometer 40
during operation to cut the coal seam 12. The diagram of FIG. 5 is
a plot of a selected range of frequencies on the abscissa versus
signal amplitude in decibels on the ordinate. In FIG. 5, the solid
line frequency signal characteristic 79 indicates a peak amplitude
signal at point 80 with additional peak amplitude signals of
somewhat lower intensity at points 82 and 84, which lower peak
amplitude signals are multiples of the frequency of the signal 80.
The signal 80 is a frequency which is a multiple of the number of
cutters times the rotational speed of the drum 24 while the signals
82 and 84 are second and third multiples or harmonics of the
frequency of the signal 80.
If the cutters 26 move out of the coal seam 12 into material of
greater or lesser hardness, the amplitude of the stresses or
vibrations encountered by the cutters 26 may be greater or less,
respectively. Accordingly, the dashed line 85 in the diagram of
FIG. 5 also shows peak intensity signals at 86, 88 and 90
corresponding to the peak amplitudes at the fundamental frequency
as indicated by the point 80 and multiples of that frequency as
indicated by the points 82 and 84. Accordingly, by measuring the
frequency spectrum of the signals generated by the accelerometer 40
or the strain gauges 42 or 44 or the accelerometers 70 or 72, it is
possible to analyze such frequency spectrum to determine a change
in certain signals which are related to the cutting effort of the
apparatus 10.
The frequency spectrum illustrated in FIG. 5 may be obtained by
subjecting a plurality of multiple point consecutive time records
of the output signals from the sensors 40, 42, 44, 70 or 72 to fast
Fourier transform analysis of the time domain data to produce auto
spectra values comprising the magnitude of the Fourier transforms
squared or the product of the Fourier transform and its complex
conjugate, preferably as running average values, respectively.
These values are used to provide the plot of the respective
frequency spectrum lines 79 and 85 of FIG. 5. Moreover, by plotting
the frequency spectrum of the signals sensed by the sensors 70 and
72, in particular, the amplitude of the signals at the frequency of
the number of teeth in the cutting drum 24 times the speed of
rotation of the drum, for example, may indicate, for different
cutting conditions, a signal amplitude change which may be sensed
on a continuous basis and used to adjust the position of the cutter
drum relative to the seam 12. These signals may be easily
distinguished from random or apparatus structure response
vibrations as a result of the spectral analysis. The frequency
spectrum of the signals produced by the sensors 40, 42, 44, 70 or
72 may be carried out by a suitable frequency spectrum analyzer
included in the signal conditioner and amplification circuit
50.
The operation of the apparatus 10 in conjunction with the circuit
illustrated in FIG. 4 is believed to be understandable to those of
ordinary skill in the art from the foregoing description. However,
briefly, the apparatus 10 is advanced through a coal seam 12 by
operating the cutter drum 24 to shear the coal along the face 13 by
vertical adjustment of the arm 22 to maintain the cutter in a
position which will not cut into the earth material above the
surface 14 or below the surface 16. If the depth of cut permits
movement of the drum 24 to a position intersecting or aligned with
the cleats 18 then, by shearing along the plane of the cleat, the
stresses exerted on the apparatus 10 are reduced and the excavation
rate for a given power input may be increased. If the seam 12
changes its course, the vibration of the cutters 26, as they
penetrate material other than the coal, will change and the
accelerometers 40, 70 or 72 will sense such a change to produce a
different output signal which may be identified by an audio
signal-generating device 60 or visual display 62. Accordingly, the
operator may adjust the height of the arm 22 or the advance
position of the machine 10 toward the face 13 as required to keep
the cutter drum 24 operable to cut only the coal material intended
for excavation. In this way greater production of cleaner coal may
be obtained than relying solely on visual inspection of the seam
during the continuous mining operation.
Although a preferred embodiment of the present invention has been
described herein, those skilled in the art will also recognize that
various substitutions and modifications may be made to the
embodiment described without departing from the scope and spirit of
the invention as recited in the appended claims.
* * * * *