Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~OREHOL~ LAS~R CAVITY MONITORING SYSTEM
This invention relates to a system for
measuring, through a borehole, the dimensions of a mined
stope, or any other underground cavity in development or
once terminated, or to evaluate the stage of a mining
development such as a raise or a drift. ~.
There is no system to date permitting to measure ~
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rapidly and with precision the dimensions and volume of a
mined stope or any other underground cavity through a
borehole. The evaluation of such data would permit to
estimate the efficiency of a mining method. -
Actually, the efficiency of a mining method may
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be estimated by evaluating the dilution originating from
the back breaks of mined walls and roof, by estimating the
damages caused by blasting and by observing the size and
type of the broken rock in the mine drawpoints. All these
evaluations are, however, based on visual observations and
on the experience of an operator or miner. These
measurements are thus not very objective and vary greatly.
Other methods permit to obtain a more precise
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measurement of what has been mined in the stope. The
measurement of the output tonnage and of the tonnage
treated by the concentrator in comparison to what has been
planned permits to obtain a good estimate of the
situation. However, this method has several disadvantages
such as: (1) it is necessary to wait several days or weeks
before obtaining the tonnage from the mill, (2) the values
obtained are only qualitative and no information
concerning the source or origin of the dilution or of the
blasts back breaks may be obtained. Furthermore, little
information helping to optimise future planning may be
derived.
An apparatus using ultrasonic waves has been
recently developed by Noranda Inc. (US Patent No.
4,845,990 granted July 11, 1989). However, several
disadvantages have been experienced during use of such an
apparatus such as: (1) the apparatus may not be
effectively used for measuring distances over 55 feet, ~2)
the measurements are inaccurate when the surfaces to be
measured are inclined with respect to the apparatus
resulting in false results, (3) its orientation during
measurement is often inaccurate, and (4) the weight and
size of the apparatus are not well suited to be used
underground.
For some years, another measurement technique
originating from a sophisticated surveying apparatus
(called total station) seems to have gained a certain
interest for some mining operations. This apparatus is a
prismless laser theodolite called EDM (Electronic Distance
Measurement) which permits to measure the distance
separating such apparatus from the wall or the roof of a
mined stope as well as the angle of sight. However, this
apparatus has the following disadvantages: (1) the
apparatus is sensible to the mining environment, (2) the
apparatus must be installed on a tripod base in a safe
area away from the underground cavity, which reduces even
more its field of sight, (3) many accesses to the mined
stope must be available (which is rarely the case in a
mine) to be able to cover the full underground cavity, and
(4) for some mining methods such as the well known VCR
(Vertical Craters Retreat) mining method, there is no
access to the mined stope except through blasting
boreholes and such apparatus cannot therefore be used.
Furthermore, the apparatus does not work automatically
following a pattern of laser measurement permitting to
calculate the volume and to rapidly interpret the
measurements.
It is therefore the object of the present
invention to provide a system which would permit to
rapidly measure the dimensions and determine the shape
and volume of an underground cavity through a borehole
leading to such cavity without the disadvantages of the
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above mentioned apparatus.
The system in accordance with the present
invention comprises a probe adapted to be lowered by means
of a cable into a borehole leading to an underground
cavity and having a fixed portion attached at one end to
the cable and a rotary head located at the other end. The
probe contains a navigation module for providing a signal
representing the orientation of the probe with respect to
a reference position, a laser rangefinder mounted in the
rotary head for generating data signals representing
distance measurements to obtain the shape and volume of
the cavity, a micro-processor for controlling the
operation of the rotary head and for collecting the data
generated by the navigation module and the rangefinder,
and a communication interface for transmitting the output
signals collected by the micro-processor over the cable
and for receiving control signals transmitted from the
collar of the borehole over the cable for controlling the
operation of the micro-processor. A control unit is
located at the collar of the borehole and includes a host
computer which generates the above mentioned control
signals and a second communication interface linking the
host computer to the probe. Such second communication
interface includes means for transmitting the control
signals over the cable and means for receiving the output
signals transmitted over the cable. A depth counter is
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located at the collar of the borehole and connected to the
host computer for providing information relating to the
depth of the laser rangefinder with respect to the upper
edge of the borehole.
The probe further comprises drive means for ~ ;
rotating the laser head 360 around the axis of the probe,
a motion encoder mounted on the laser head for detecting
the angular rotation of the laser head and a rotating disk :~
supporting the laser rangefinder and adapted for rotation
around an axis perpendicular to the axis of the probe,
such rotating disk permitting to direct the laser
rangefinder at the wall of the cavity at angles varying
from 0 to 145 from the axis of the probe to scan
concentric circles on the wall of the cavity permitting to
take series of distance measurements to obtain the shape
and volume of the cavity.
The navigation module comprises two
inclinometers mounted 90 from each other and a gyroscope
for measuring the axial rotation of the probe, the
integration of the signals of the two inclinometers, the
gyroscope and the depth counter permitting to determine
the exact position of the probe with respect to the collar ::
of the borehole. :
Proximity switches are installed at different
locations on the probe and connected to the micro-
processor to inform a user of the position of the probe
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with respect to the lower end of the borehole. A CCD
(Charge Coupled Device) camera is located at the end of
the laser head for viewing the condition of the borehole
during lowering of the probe so as to avoid the
possibility of the probe getting jammed in a damaged
borehole.
The communication interface of the probe
includes bi-directional speed adapters used to adapt the
speed of the signals from and to the micro-processor to a
suitable transmission speed.
The communication interface of the control unit
comprises a serial transmitter for transmitting the
control signals over the cable and a serial receiver for
passing the output signals of the micro-processor to the
host computer.
The invention will now be disclosed, by way of
example, with reference to the accompanying drawings in
which:
Figures 1, la and lb illustrate an overall view
of the borehole laser cavity monitoring system in
accordance to the present invention;
Figure 2 is a block diagram of the control unit
of the borehole laser cavity monitoring system;
Figure 3 is a drawing showing the different
parts of the probe of the borehole laser cavity monitoring
system;
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Figure 4 is a view showing the end of the probe
partly out of a borehole in its scanning position; '~
Figure 5 is a block diagram of the probe control '
circuit; and
Figures 6a and 6b are block diagrams of the
communication interfaces of the probe and the control
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Referring to Figures 1, la and lb, the borehole
laser c,avity monitoring system comprises a probe 10
adapted to be lowered into a borehole 11 leading to a
mined stope 12 by means of a single communication cable 13
containing several mini-coaxial cables for data and video
transmission, and containing also suitable wiring for
power transmission. The communication cable is reinforced
with a Kelvar (trademark) cord for providing good tensile
strength in case the probe is jammed into the borehole.
The user of the borehole laser cavity monitoring system is
usually located in a drift 14 just over the mined stope or
any underground cavity to be surveyed. The probe is
lowered using the communication cable 13 to the position ' ,'~
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shown in Figure 1. The cable is normally rolled on a reel ~ ,,
15 for easy manipulation and transportation. The cable , ,,~
passes through a depth counter 16 fixed to a holder-17
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installed at the collar of the borehole. The depth ';~
counter is usually a wheel in contact with the cable and ,'~
is used for providing'a digital signal to measure the ,'
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length of cable paid off into the borehole.
Located in the drift at the collar of the hole
is a control unit 18 which is connected to cable 13 wound
on reel 15. As shown in Figure 2, the control unit
includes a communication interface 20 linking the probe to
a host computer 22 with a key board 24 and a screen 26.
The depth counter 16 is connected to the host computer 22
via a suitable interface 27. A video output jack 28 is
also provided on the control unit for viewing video
signals from a CCD camera located on the probe ~to be
disclosed later). A separate power battery pack 32
provides dc voltage to the system.
Referring to Figure 3, probe 10 is made of two
detachable parts A and B joined together by clamps 34 for
easy transportation. A survey pointer 36 is mounted on
part A to align the probe toward a surveyed target located
in the drift 14 (not shown) before lowering the instrument
into the borehole. Mounted on a printed circuit board
(PCB) inside the probe is a communication interface 38 to
be disclosed later. Also mounted on a printed circuit
board inside the probe is a navigation module 40 of
conventional type and including two inclinometers 42
mounted 90 from each other, and a gyroscope 44 for
measuring the axial rotation of the probe. By integrating
the signals of the two inclinometers 42, the gyroscope 44
and the depth counter 16 (shown in Figure 2) the exact
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position of the probe with respect to the collar of the
borehole may be derived. Three sets of proximity switches
46 are also installed at different locations on the probe -~
to inform the user of the position of the probe with
respect to the end or the toe of the borehole. A laser
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head 48 is mounted on a rotating joint 50 at the lower end
of the probe. The rotating joint is operated by a motor
52 which allows the laser head to turn 360 around the
axis of the probe. The laser head 48 contains a motion
encoder 54 to detect the angular rotation of the laser
head, a CCD camera 56 for viewing the condition of the
borehole during lowering of the probe and a rotary disk 58
supporting a laser rangefinder 60 including transmitter
and receiver optics. The rotary disk is operated by a
motor 62. Rotation of the disk 62 is sensed by an encoder
64. The laser rangefinder is controlled by a probe
control circuit board 66 including a micro-processor 68
and a motion controller 70 to be discloser later (see
Figure 5).
The laser rangefinder is a known instrument
permitting to measure distances on natural surfaces
(prismless) like rock faces. Based on time of flight
technology, the transmitter optic pulses a signal toward
an opposite wall of the cavity and the receiver optic
receives the echo signal. The time taken by the signal to
travel toward the rock face and return to the receiver is
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converted to distance reading in known manner.
As shown in Figure 4, the probe is lowered until
it is located partly outside of the borehole toe in
position to scan the cavity. The fixed part of the probe
10 is maintained in position during the scanning process.
The rotating head 48 is pivoted 360 around the axis "Y"
of the probe while the rotary disk 58 suppor~ing the laser
rangefinder optics turn 145 around the ~X~ axis of the
probe. The combination of these two motions allows the
laser rangefinder to take series of distance measurements
to obtain the shape and volume of the cavity. The data
may be transferred to any CAD system for processing.
As shown in Figure 5, the operation of motor 52
which drives the laser head is controlled by micro~
processor 68 through motion controller 70 which is
connected to motor 52. Motion controller 70 also drives,
through slip ring 72, motor 62 which is coupled to rotary
disk 58 supporting the laser rangefinder optics.
Horizontal motion encoder 54 which is coupled to
motor 52 provides an output signal representing the
horizontal position of the laser head around the "y" axis
(Figure 4). This signal is fed to micro-processor 68 for
transmission to the communication interface. Similarly,
vertical motion encoder 64 which is coupled to the rotary
disk of the laser head provides a signal representing the
position of the rotary disk 58 around axis '~x~' (Figure 4).
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This signal is fed to the micro-processor 68 through
motion controller 70 for transmission to the communication
interface.
The data generated by the rangefinder optics is
fed to the micro-processor 68 for transmission to the
communication interface.
The signals generated by the proximity switches
46 located on the fixed part of the probe are fed directly
to the micro-processor while the signals generated by the
proximity switches located on the rotating part of the
probe are fed to the micro-processor through the slip ring
72.
The data signals generated by the navigation
module 40 are also fed to the micro-processor 68 for
lS transmission to the communication interface 38.
Referring to Figure 6a, the data signals
originating from the micro-processor 68 (see Figure 5) are
fed to the communication interface 38. The video signal
originating from the camera 56 (see Figure 5) is also fed
to the communication interface. The communication
interface includes bi-directional speed adaptors 74 and 76
both used to adapt a high speed serial communication link
to a lower suitable transmission speed. The signals
originating from the micro-processor 68 pass through the
serial speed adaptor 74 prior to being fed to a buffer 78
and transmitted over the cable 13. In the reverse
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direction, the signals originating from the control unit
communication interface 20 and transmitted over the
coaxial cable are passed through a buffer 80 prior to
being fed to the serial speed adaptor 76. The probe
communication interface 38 further comprises a buffer 82
to adapt the video signal originating from the probe
camera 56 for transmission over the cable. In the control
unit, the communication interface 20 is used to link the
probe to the host computer.
Referring to Figure 6b, the signals including
the data from the probe micro-processor (laser
rangefinder, orientation module and proximity switches)
which are carried over the cable 13 pass through a
receiving buffer 84 in order to adapt the signal
amplitudes. The buffered signals pass through the serial
receiver 86 prior to being fed to the host computer 22.
In the same way, the control signals from the host
computer 22 pass through the serial transmitter 88 prior
to being passed through a buffer 90 and carried over the
cable. The communication interface of the control unit 20
also includes a buffer 92 to adapt the video signal
originating from the probe camera 56 (see Figure 5). The
video signal is fed to a video output jack 28 which is
also shown in Figure 2.
Although the invention has been disclosed, by
way of example, with reference to a preferred embodiment,
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it is to be understood that it ~is not limited to such
embodiment and that other alternatives, within the scope
of the claims, are also envisaged.
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