Another problem involved cutouts within the stope. To
simulate a cutout or void in the stope wall, a piece of foam
rubber approximately 5 ft wide, 4 ft high, and 2 in thick
was placed against the inside of one of the stope walls
about midway between the muckpile and dumping bin.

Tramming path

Figure 10.—Oscillations in tramming path.

The foam rubber absorbed enough of the sound waves
transmitted by the sensors to simulate the absence of a
wall. In the tests, the minimucker stayed near the center
of the stope until it encountered the perceived void in the
wall, at which point it tried to center itself between the
wall and the void (fig. 11). Because it could not correct
itself in time, it collided with the wall where the foam
rubber ended.

After testing several different guidance schemes, re-
searchers determined that this problem could not be cor-
rected with the existing system and would require addi-
tional forward- and reverse-looking sensors that would
recognize a large void in the stope wall. Figure 12 shows
one possible sensor layout. This system will be the subject
of later work and was not addressed in the algorithms
discussed in the following section.

A third problem was that the steering reaction speed
depended on hydraulic fluid temperature. Much of the
work done in the test stope was done during cold weather
when temperatures were around 40° F. As the mini-
mucker warmed up, the operation of the system improved,
but if the machine was run in the automatic guidance
mode while it was cold, the system was unreliable. This
problem was solved by allowing the minimucker to warm
up for 30 min before testing began. In most underground
environments, cold temperatures would not be a problem.

Figure 11.—Centering at cutout.


Abstract
Introduction
Acknowledgments
Initial design and testing ... .
Computer-based, radio-remote-control system . .

Automatic guidance system

Summary

CONTENTS

Transmitter 2.0.6... 6. cee eee eee eee
Receiver ...... :
Computer system ......
Test setup and results .. .

Sensor selection»... 00.00. eee eee eee ee eee eeeees
Original system operation ......
Testing original guidance system .
Alternate algorithm .......

Minimucker as originally designed
Minimucker with bucket and slide mechanism modifications
Components of radio-remote-control system
Remote-control pendant
Test stope layout 2.6.2.0... 6. cee cece e ee eee ees
Concrete test stope and festoon system.............04%
Ultrasonic ranging sensor mounted on minimucker .
Sensor layout........... .
Original guidance system operation

Oscillations in tramming path
Centering at cutout 6.0... cee cece eee eet e eee teeeeetenees
Addition of forward- and reverse-looking sensors to recognize cutouts . .
Limiting sensing distance ... . . .
Operation of alternate guidance algorithm

Minimucker specifications 0.00.00. 00.00. cceeeeeeeeeeeenees
Agastat ultrasonic sensor specifications

Beouaaauuseannne

Page

WOCBDHDIADANUUAAYWY


COMPUTER-BASED, RADIO-REMOTE-CONTROL SYSTEM

To eliminate the need for a tether in remote-control
operations, both infrared remote control and radio-
frequency remote control were considered. Infrared
remote control was eliminated as an option in this situa-
tion because of its susceptibility to interference from heavy
dust and because the operator has to be within the line of
sight of the machine. While radio-remote-control systems
are more costly than infrared control systems, they are not
susceptible to interference from dust. Also, radio-remote-
control communications are omnidirectional and while they
do have some line-of-sight restrictions, the placement of
the transmitter and the receiver is not as critical.

Recent developments in computer-based, radio-remote
controls allowed the needed improvements to be imple-
mented with one system. Programmable, computer-based
radio control systems developed by Blackbox Controls,
Ltd.,‘ had been installed on LHD’s in several mines in the
United States, so this system was chosen to be retrofitted
to the minimucker. The system consisted of a control
pendant and transmitter, receiver, microprocessor, and
control electronics (figs. 3-4). Rather than the control
outputs being connected directly to the servovalves and
other machine devices, the radio control system interfaced
with the electronics originally used for the tether-remote-
control operation. This simplified installation and allowed
the option of using cither radio-remote or tether-remote
control.

TRANSMITTER

The system’s transmitter is located within the control
pendant, Commands that can be sent include motor on

“Blackbox Controls, Ltd. (Glen Williams, Ontario, ON). Operations
and Maintenance Manual for IQ Series Remote Controls. 1989, 35 pp.

Figure 3.—Components of radio-remote-control syste!
enclosure, computer and receiver, power supply enclosur.

and off, open and close tailgate, raise and lower bucket,
set and release brakes, turn rear and front lights on and
off, learn and repeat, and tram forward, reverse, left, or
right. Radio transmissions of command signals are sent
out in 15-ms bursts, and the radio transmitter is turned on
only for the time of the transmission. Idle time varies be-
tween 240 and 50 ms, depending on the amount of activity
of the controls. This discontinuous transmission has the
advantage of prolonging the transmitter’s battery life.

Along with the control command signals, a code unique
to the system on each machine is transmitted; this feature
allows the same radio frequency to be used by more than
one machine. The modulation scheme uses narrow-band
FM, pulse width modulation at 450 to 470 MHz and is
transmitted at 0.2 to 0.4 W. The transmitter requires a
12-V, nickel-cadmium rechargeable battery. If transmis-
sions stop or become blocked or if the pendant is tilted
over 40° off vertical, the minimucker shuts off and the
brakes are set.

RECEIVER

The receiver portion of the system is located on the
exterior of the minimucker in a steel enclosure. A 6-in
monopole, whip-type antenna is also mounted on the
exterior of the machine. Commands received from the
transmitter initiate software routines that execute the
desired function. All functions are controlled by relay
or on-off switches except the tramming controls, which
are proportional, The tramming outputs from the radio
receiver are intended to drive electrohydraulic controls
directly. However, since the output is interfaced to the
original control electronics, isolated proportional potenti-
ometers are required to convert the pulse width modulated

waeege

Figure 4.—Remote-control pendant.


DEVELOPMENT AND TESTING OF A COMPUTER-ASSISTED REMOTE-
CONTROL SYSTEM FOR THE COMPACT LOADER-TRAMMER

By T. M. Ruff*

ABSTRACT

A prototype mucking machine designed to operate in narrow-vein stopes was developed by Foster-
Miller, Inc., Waltham, MA, under contract with the U.S. Bureau of Mines. The machine, called a
compact loader-trammer, or minimucker, was designed to replace slusher muckers in narrow-vein
underground mines. The minimucker is a six-wheel-drive, skid-steered, load-haul-dump (LHD) machine
that loads muck at the front with a novel slide-bucket system and ejects it out the rear so that the
machine does not have to be turned around. To correct deficiencies of the tether-remote-control
system, a computer-based, radio-remote-control system was retrofitted to the minimucker. Initial tests
indicated a need to assist the operator in guiding the machine in narrow stopes. An automatic guidance
system that used ultrasonic ranging sensors and a wall-following algorithm was installed. Additional
tests in a simulated test stope showed that these changes improved the operation of the minimucker.
The design and functions of the minimucker and its computer-based, remote-control system are
reviewed, and an ultrasonic-sensor-based guidance system is described.

Electrical engineer, Spokane Research Center, U.S. Bureau of Mines, Spokane, WA.


°F

ft

MHz

min

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

degree Fahrenheit

foot

hour
horsepower
hertz

inch
kilohertz
pound
pound (force)
meter
milliampere
megahertz

minute

mph

st

st/h

Vac

Vde

yd?

yd?/h

mile per hour
millisecond
percent

second

short ton

short ton per hour
volt

volt, alternating current
volt, direct current
watt

cubic yard

cubic yard per hour



A typical mucking cycle requires the following steps:
(1) tram to the muck pile, (2) load the minimucker by
crowding the pile and retracting the bucket to place the
load of muck on the deck (it takes approximately four
bucket loads to fill the machine), (3) tram backwards to
the dumpsite and position the tailgate over the ore pass,
(4) open the tailgate and retract the bucket fully until all
the muck is ejected, and (5) close the tailgate and lower
the bucket to repeat the cycle.

On the original system, the operator used a control
pendant that was physically connected to the machine by
a 30-ft-long multiconductor tether. This required the
operator to follow the machine during the mucking proc-
ess and to keep the tether from being run over during
machine operations.

With the cooperation of Homestake Mining Co., Bu-
reau researchers conducted an underground test when the
prototype minimucker was completed. At the testsite, the
machine shuttled waste to a 5-ft-diam borehole 20 ft from
the waste pile. Approximately 75 st was moved. The fol-
lowing difficulties were noted by one of Homestake’s
mining engineers:

1. The channel-and-roller power cable festoon system
recommended in the contract report could not be used
because it was difficult to install and because it was sus-
ceptible to damage from nearby blasting.

2. The bucket was not very efficient during digging
because of its straight leading edge.

3. Bucket cycle speeds were slow because of the slow
speed of the three-stage telescopic cylinders.

4. The tether remote control made operation awkward
and, in some situations, unsafe.

The only modification made after the initial test was to
redesign the bucket. This included changing the shape of
the leading edge of the bucket and improving the mech-
anism for holding the bucket against the machine body

Figure 1.—Minimucker as originally designed.

while digging. Following these changes, a second test
was run in which 125 st of waste was moved. The bucket
redesign improved digging efficiencies. However, modifi-
cations were still needed to improve the speed of bucket
movement and so the three-stage telescopic cylinders used
for bucket movement were replaced by a chain-actuated,
single-stage-cylinder slide mechanism (fig. 2). Although
loading times were projected to be half the original times,
Homestake was not able to resume testing after this
modification.

The overall results from these preliminary tests were
promising. Noted advantages included the following:

1, The minimucker was casy to maneuver because of
its small turning radius.

2. Overall dimensions allowed the minimucker to fit
into any area of the mine and made interlevel relocation
simple.

3. The machine had powerful crowding capabilities for
loading muck.

4, The modified bucket improved cycling times.

Disadvantages included the following:

1. The machine was unable to load ore cars.

2. The low dump gate clearance made maneuvering
over the dump point difficult.

3. The tether remote control still made operation cum-
bersome and unsafe.

The minimucker was delivered to the Bureau’s Spo-
kane Research Center (SRC) in 1988. After reviewing the
underground test results and operating the machine at
SRC, project personnel determined two ways in which the
minimucker could be improved: eliminate the need for
the tether cable and incorporate computer-based technol-
ogy into the control system.

emt

Figure 2,—Minimucker with bucket and slide mechanism
modifications.


RI| 9431 REPORT OF INVESTIGATIONS /1992

Development and Testing of a Computer-
Assisted Remote-Control System for the
Compact Loader-Trammer

By T. M. Ruff

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF MINES



Tests in the simulated stope also showed that the
operators became extremely fatigued as they attempted
to keep the minimucker from hitting the stope walls.
Because avoiding collisions was impossible, machine wear

was also excessive. It was evident that some type of
assistance was needed to guide the minimucker through
the stope. Collision avoidance would become even more
critical in a dark, underground environment.

AUTOMATIC GUIDANCE SYSTEM

SENSOR SELECTION

Several different options for automatic guidance were
evaluated, including the use of ultrasonic ranging sensors,
wires embedded in the stope floor, and optical path fol-
lowing. Ultrasonic ranging was chosen for the following
reasons: (1) The tramming path of the minimucker in a
narrow stope was scen as relatively simple; that is, the
minimucker had only one possible tramming path, which
would be relatively straight with no complex turns or
direction changes, (2) in a narrow stope, the walls would
be close to the machine and would be, in most situations,
continuous, (3) the costs of using ultrasonic ranging
sensors and the existing computer system were much
cheaper than costs of the other alternatives, and (4) the
sensory system could be totally contained on the mini-
mucker so that no additional preparation in the stope
would be required.

The ultrasonic ranging sensors needed to be small to fit
on the machine, but they only needed to measure short
distances (under 3 ft), making them relatively inexpensive.
At the same time, they had to be rugged and waterproof.
The sensors finally chosen were selected because of their
low cost, small size, ruggedness, water resistance, and
availability. Specifications of the sensors used are shown
in table 2.

Table 2.—Agastat ultrasonic sensor specifications

Dimensions, in:

Diameter . 1.2
Length .. 28
Input voltage 10 to 30
Maximum current drain. 50
Output, V de:
inimum distance . . 0
Maximum distance 5
Operating frequency .. 210

Beam width ...... . 10

Sensing distance 4 to 30
Response speed . 50
Temperature rating . -40 to 122
Humidity ...... . 0 to 95
Waterproof enclosure io)
Cost (ai te : $260

‘Front transmitting surface must be dried before operation.

ORIGINAL SYSTEM OPERATION

One ultrasonic ranging sensor was mounted on each
of the four corners of the minimucker. A 0- to 5-V
analog signal is sent to an onboard computer, where it is
digitized. This signal is proportional to the distance
between the sensor and the stope wall. Figure 7 shows a
sensor mounted in a protective case and bolted to the
minimucker frame. Figure 8 shows the layout of the sen-
sors. When the machine is tramming forward, the outputs
from the front left (V,,) and right (Vag) sensors are used;
when tramming in reverse, the outputs from the rear left
(Vig) and right (Vag) sensors are used.

an
Sensor

Figure 8.—-Sensor layout.


input from the radio transmitter to a signal that simulates
the potentiometer system used in the original tramming
controls. Thus, movements of the tramming joystick allow
the operator to increase or decrease the speed of the mini-
mucker in proportion to the amount of deflection of the
joystick.

COMPUTER SYSTEM

The computer portion of the remote-control system
consists of an INTEL 8031 microprocessor and removable
battery SRAM modules that contain the operations pro-
grams. A command transmitted from the control pendant
initiates the portion of the software that controls the func-
tion for that command. For example, moving the tram-
ming joystick forward at half full scale would initiate a
program that controls the servovalves that govern forward
movement of the minimucker. The half full-scale deflec-
tion corresponds to a variable gain value set within the
program that corresponds to the joystick position trans-
mitted, causing the minimucker to travel at half of full
speed.

This system is similar to a programmable controller and
allows customized programs and sensor input to be used
in the control of the minimucker. To enter customized
programs or modify existing ones, a personal computer or
dumb terminal can be connected using serial (RS232)
communication.

Along with customized programs, a learn-and-repeat
mode allows automation concepts to be tested. That is,
the minimucker can be "taught" to execute a serics of
commands automatically by memorizing the commands in
"learn" mode. Memorization is accomplished by going
through the steps of the operation one at a time. After
these commands have been stored by the microprocessor,
depressing the repeat switch on the control pendant causes
the minimucker to repeat the commands. This can be
useful in decreasing the time required to execute a simple
repetitive action that would normally take several separate
commands to achieve—for instance, unloading the mini-
mucker. However, the learn-and-repeat system is time
based and unintelligent. For instance, the system mem-
orizes the amount of time the output for the "raise bucket"
command was on. When the repeat system is activated,
the bucket is raised for the memorized amount of time
whether the bucket is at the end of its travel or not.
Feedback from sensors indicating the position of the
bucket can be added to make the system position-based.

TEST SETUP AND RESULTS

Full-cycle tests were conducted to evaluate the radio-
remote-control system and bucket modifications on the

minimucker. A simulated stope 6 ft wide by 100 ft long
was constructed of reinforced concrete to represent a
narrow drift with a muckpile and an ore pass. A festoon
system for handling the power cable was also constructed
from 3/8-in-diam wire rope suspended between two posts
across the entire 100-ft length of the simulated stope. The
power cable was connected to pulleys suspended from the
wire rope, which allowed the pulleys to roll as the mini-
mucker pulled the power cable. Figures 5 and 6 show the
simulated stope and festoon system.

The cycling tests involved running the minimucker
through a complete mucking cycle while all operations of
the cycle were timed. The operator of the minimucker
stood behind the dumping bin with a maximum distance
of 125 ft between him or her and the machine. Four
hours of continuous mucking were monitored. The tests
showed that the load, haul, dump, and return cycle took an
average of 2.2 min, and with an average load of 1.6 yd,
the minimucker could haul an estimated 59 st/h. Tests of
the original minimucker, as described in the contract
report, showed a cycle time of 2.9 min and a capacity of
44 st/h (table 1). These original tests were conducted
under similar conditions and with a 100-ft tramming dis-
tance, but were not conducted in the simulated stope.

Recessed

a | oe >

Is) conn = t
Concrete walls q “Muck pile

Ramp (8m

Figure 5.—Test stope layout.

Figure 6.—Concrete test stope and festoon system.


INTRODUCTION

Current methods of mucking narrow stopes involve the
use of slushers, overshot loaders, or small load-haul-dump
(LHD) units. A safer and more productive means of
moving material from the face while working within the
physical constraints of a narrow stope has been a popular
topic among companies involved in this type of mining.
With this goal in mind, Foster-Miller, Inc., Waltham, MA,
under contract with the U.S, Bureau of Mines,” developed
a compact loader-trammer, or minimucker? The mini-
mucker is a six-wheel-drive, skid-steered, LHD machine
that can be operated in stopes as narrow as 5 ft. Its
unique loading and dumping mechanism allows the
machine to tram between an ore pass and a muckpile

without turning around. The development of the proto-
type was completed in 1984, after which the minimucker
was sent to the Homestake Mining Co. in Lead, SD, for
underground testing.

Following these underground tests, it was decided that
a computer-based, radio-remote-control system would
allow the operator to remain in a safe location while
operating the machine. Such a system would also allow
automation techniques to be studied. Using ultrasonic
sensors and a simple guidance algorithm, a guidance
system was developed that improved the operation of the
minimucker by decreasing operator fatigue and machine
wear,

ACKNOWLEDGMENTS

The author would like to express his appreciation to
Ron Patey, chief engineer, Blackbox Controls Ltd., Glen
Williams, Ontario, ON, for his assistance in installing the

radio-remote-control system and programming the guid-
ance algorithms.

INITIAL DESIGN AND TESTING

The objective of the contract work done by Foster-
Miller was to develop a compact LHD unit to replace the
existing methods of mucking narrow stopes in metal-
nonmetal mines. The first task was to determine if there
was a need for such a machine, after which exact specifi-
cations could be determined. The response to a survey
of mining operations was positive, and the important pa-
rameters for the machine’s design were laid out. These
parameters included the following:

1. Dimensions should be a maximum of 4.5 ft wide, 7 ft
high, and 12 ft long.
2. The average pay load should be 0.75 to 1.25 yd?.
3. The machine should be powered by air or electr
4, The machine should be controlled remotely.

Table 1 lists the exact specifications of the minimucker
as determined by the survey, and figure 1 shows the mini-
mucker as originally designed. As seen in the figure, the
minimucker uses a slide bucket to load muck onto the
loading deck and push it out through the tailgate at the
rear of the machine. Because the machine does not have

?Tallone, T. Compact Loader-Trammer for Underground Metal and
Nonmetal Mines. General and Design Review (contract JO205037,
Foster-Miller, Inc.) BuMines OFR 10A-86, v. I, 1985, 93 pp.

3Reference to specific products does not imply endorsement by the
U.S. Bureau of Mines.

to be turned around to be unloaded, it is ideal for narrow
stopes.

Table 1.—Minimucker specifications

Dimensions, in:

Mucking length . 163
Tramming length 152
Mucking height . 57
Tramming height 87
Dumping height . 61
Width .. 54
Turning radius . 160
Net weight . 7,800
Performance:

Traction motor output . 2x25
Pay load capacity . 15/8
Rated load capacity : 4,500
Cycle time (200 ft round trip) . 29
Net hauling capacity . : 32
Do. ....... 44
Tramming speed 3
Breakout force . . 3,000 to
6,000

Electrical system:
Motor flange (TEFC *D") 50
Motor flange (3-phase, 60 Hz) Vac. . 460
Lights and solenoids (1-phase, 60 Hz) .. Vac. . 115
Controls (tethered pendant) . . 7 12/24



Abstract
Introduction
Acknowledgments
Initial design and testing ... .
Computer-based, radio-remote-control system . .

Automatic guidance system

Summary

CONTENTS

Transmitter 2.0.6... 6. cee eee eee eee
Receiver ...... :
Computer system ......
Test setup and results .. .

Sensor selection»... 00.00. eee eee eee ee eee eeeees
Original system operation ......
Testing original guidance system .
Alternate algorithm .......

Minimucker as originally designed
Minimucker with bucket and slide mechanism modifications
Components of radio-remote-control system
Remote-control pendant
Test stope layout 2.6.2.0... 6. cee cece e ee eee ees
Concrete test stope and festoon system.............04%
Ultrasonic ranging sensor mounted on minimucker .
Sensor layout........... .
Original guidance system operation

Oscillations in tramming path
Centering at cutout 6.0... cee cece eee eet e eee teeeeetenees
Addition of forward- and reverse-looking sensors to recognize cutouts . .
Limiting sensing distance ... . . .
Operation of alternate guidance algorithm

Minimucker specifications 0.00.00. 00.00. cceeeeeeeeeeeenees
Agastat ultrasonic sensor specifications

Beouaaauuseannne

Page

WOCBDHDIADANUUAAYWY


ALTERNATE ALGORITHM

The test results indicated that the algorithm should be
modified to dampen, if not eliminate, the path oscillations.
Several solutions were studied, including limiting the
sensing distance of the ultrasonic sensors to 8 in so that
the minimucker would base its path corrections on its dis-
tance from one wall at a time and also correct its steering
according to distances measured simultaneously at the
front and rear of the machine.

The first attempt to dampen the oscillations in the
tramming path involved limiting the sensing distance of the
ultrasonic sensors to 8 in so that objects outside of this
8-in zone did not affect the sensor output (fig. 13). How-
ever, this modification alone did not correct the problems
satisfactorily because this distance did not allow enough
time for the minimucker to correct its position, resulting
in collisions with the wall. Also, because only the front
sensors were used in forward travel, when the machine
was close to the wall, large corrections caused the front to
move away from the wall but the rear to collide with the
wall. When tramming in reverse, the reaction was the
same but at opposite ends.

To correct the problem and dampen oscillations in
the tramming path, information from all the sensors was
used simultancously. When tramming forward, the front
sensors were monitored and the computer program deter-
mined which wall was closest to the minimucker. This
determined which rear sensor was used to set the amount

Figure 12.—Addition of forward- and reverse-looking sensors
to recognize cutouts.

that the minimucker should turn. For example, if the
minimucker was traveling forward, close to the left-hand
wall (fig. 14), the guidance software would subtract the
value from the right front sensor, Var, from the value of
the left front sensor, V,,. All these values would be
complemented so that small voltage signals relating
to the proximity of the sensors to the wall would be
converted to large hexadecimal values. V,. would then
be subtracted from the value of V,,, and this value

Figure 13.—Limiting sensing distance.

Figure 14.—Operation of alternate guidance algorithm.


Library of Congress Cataloging in Publication Data:

Ruff, T. M.
Development and testing of a computer-assisted remote-control system for the
compact loader-trammer / by T.M. Ruff.
p. cm. — (Report of investigations; 9431)
Includes bibliographical references.
Supt. of Docs. no.: I 28,23:9431.
1. Mineral industries—Waste disposal. 2. Mine haulage—Automation. 3. Naviga-

tion—Data processing. I. Title. II. Series: Report of investigations (United States.
Bureau of Mines); 9431.

TN23.U43 [TD893.6.M5] 622 s—de20 [622’.2] 92-16025 CIP



Report of Investigations 9431

Development and Testing of a Computer-
Assisted Remote-Control System for the
Compact Loader-Trammer

By T. M. Ruff

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
T S Ary, Director


The computer scans the appropriate pair of sensors
10 times per second. After the signals are digitized, the
binary values are complemented so that small voltages
relating to close distances to the wall result in large hexa-
decimal values. To correct the machine’s position, values
from the left and right sensors are subtracted from one
another, resulting in zero if the machine is in the center of
the stope or in a negative or positive nonzero value (AV)
if the machine is not centered in the stope (fig. 9). If the
resulting signal is nonzero, the computer corrects the
machine’s position by causing the right or left drive motor
to slow down momentarily, steering the machine away
from the wall until the signal is once again zero. The
amount the machine is turned is determined by the mag-
nitude of the resulting subtracted value.

Operation of the guidance system is controlled with the
existing pendant. A switch turns the automatic guidance
system on or off, When on, pushing the tramming control
full forward or full reverse causes the minimucker to move
forward or reverse at full speed while the guidance system
automatically corrects the machine’s path to keep it away
from the walls. The guidance system only affects tram-
ming and does not alter the operation of the other manual
controls. The automatic guidance system can be turned
off when muck is being cleaned up next to the walls;
otherwise, the system can be left on, and loading and

Tramming
direction

Vis —Vep = AV
AV>0 Steer right
AV=0 Stay same
AV <0 Steer left

Stope walls

Figure 9.—Original guidance system operation.

dumping can continue as described in the section "Initial
Design and Testing.”

TESTING ORIGINAL GUIDANCE SYSTEM

One concern with ultrasonic sensors was that accurate
operation depends on the surface that is reflecting the
sound waves. Optimum conditions require that the
reflecting surface be flat and perpendicular to the incident
sound waves. Smooth, flat surfaces at angles close to 45°
relative to the sound waves will reflect the waves away
from the sensors so that the sensors detect no object in
the sensing zone. However, the concrete walls of the test
stope (and walls in a mine) are not perfectly smooth.
Bumps and depressions provide enough surface area to
reflect at least a portion of the sound waves so that
accurate measurements can be made’

To test the effect of large irregularities in the simulated
stope walls, a portion of the concrete wall was lined with
corrugated steel; after the cement dried, the steel was
removed, leaving a wavelike pattern in the wall. These
irregularities did not adversely affect the accuracy of the
sensors.

Several mucking cycles were run in which the gain of
the steering correction was altered to optimize the reaction
speed of the minimucker. These preliminary tests showed
that the effort required to keep the minimucker from
hitting the stope walls decreased. The machine traveled at
full speed (3 mph) in both forward and reverse for the
100-ft length of the stope and at the same time corrected
its position so that it remained in the center.

In doing this, however, the minimucker’s tramming path
oscillated from one side of the stope to the other (fig. 10).
In some instances, the oscillations became too large and
occurred too frequently, and the machine could not correct
its position fast enough to avoid colliding with the wall.
Additional tests showed that the oscillations resulted from
the combined effects of two characteristics of the algo-
rithm. First, the algorithm adjusted the position of the
minimucker using the monitored distance from both walls.
If the machine was tramming at a position in the stope
where it was an adequate distance from the walls, it would
still correct its position so that it would be centered in the
stope. This caused the minimucker to correct its position
constantly even if it was following a safe path. Second,
when correcting the path, the algorithm sent a signal to
one drive motor to slow down so that the minimucker
would turn away from the wall. The minimucker would
then head for the other wall, a problem inherent with skid
steering.

King, RH, P. J. A. Lever, W. Strickland, and J. D. Lane.
Ultrasonic Rangers for Underground Mine Equipment Navigation.
Paper in Proceedings of the Ist International Symposium on Mine
Mechanization and Automation (Golden, CO, June 10-13, 1991). CO
Sch. Mines, Golden, CO. V. 1, 1991, pp. 6-31 to 6-44.


10

would be multiplied by a software adjustable constant, K.
These two values would then be subtracted, resulting
in the correction factor that controlled the amount the
machine turned away from the wall. Thus,

G = (Vir ~ Var) ~ KVR - Vin),

where G = path correction gain.

If the front of the machine was closer to the wall than
the rear, (Viz - Viz) <0, then the second term of the
equation would be multiplied by K and the steering cor-
rection would be increased. If the rear of the machine
was closer to the wall, (Vip - Viz) >0, then the machine
would already be correcting its position and the second

term would be ignored. Similar but opposite operations
would take place when the machine was tramming in
reverse.

The new algorithm was tested by operating the mini-
mucker in the simulated stope. Several values of K were
tried; a value of 2.0 gave the best results, Oscillations in
the tramming path were dampened with this version and
tramming was greatly improved—there were no collisions
with the wall. During cycling tests, no large improvements
were seen in hauling capacity. However, machine wear
was greatly reduced because collisions with the stope walls
were avoided and the machine could be controlled easily
in the narrow confines of the stope, which made the tram-
ming portion of the mucking cycle essentially effortless.

SUMMARY

The minimucker shows potential as an alternative
machine for mucking narrow stopes. Tether remote con-
trol that requires the operator to follow the machine is not
acceptable for long tramming distances, so a wireless
method of directing the equipment is required. A radio-
remote-control system was recommended for controlling
this machine in narrow stopes. However, because of the
difficulty in maneuvering a rubber-tired vehicle in a narrow
stope, some type of assistance was needed to keep the
machine from hitting the stope walls.

Computer-assisted guidance using ultrasonic ranging
sensors was implemented using the computer and controls
of a radio-remote-control system. A simple algorithm was
tested that allowed the minimucker to follow the walls of
the stope while avoiding collisions. The first attempt used

only two of the four sensors to monitor the minimucker’s
distance from the walls. Oscillations in the tramming path
made this algorithm unacceptable. The operation of the
guidance system was improved by using all four sensors to
determine position and control the minimucker. While
this modification dampened path oscillations, it did not
solve the problem of wall collisions when large voids or
cutouts in the stope walls were passed. Solving this prob-
lem may require additional sensors and may be the focus
of later work, Although the automatic guidance system
did not significantly improve mucking cycle times for con-
tinuous mucking over a 2-h period, the system did reduce
machine wear and operator fatigue, making long periods
of mucking more productive when considering ergonomics
and maintenance.