Progress Toward a Reduced Exposure Mining System

George H. Schnakenberg, Jr.

U.S. Bureau of Mines

Pittsburgh, Pennsylvania
1

Abstract. In 1986 the U.S. Bureau of Mines (USBM) NEW APPROACH

embarked on a major research effort to develop

technology that can substantially reduce worker exposure

to face hazards simply by relocating the equipment

operators to an area of relative safety. This reduced

exposure mining system (REMS) research effort enhances

the USBM ongoing health and safety research efforts to

reduce and control dust and noise and to reduce accidents

through training and better mining practices. This paper

reports progress of the research that is developing and will

demonstrate the technologies required for the computerassisted tele-remote operation of continuous mining

machines, haulage systems, and roof bolting machines.

NEED FOR RESEARCH

Coal is the United States’ most abundant fossil energy appropriately, renamed "the reduced exposure mining

resource constituting over 82% of all domestic system" or "REMS" (McClelland, et. al., 1994).

nonrenewable energy reserves. At the present

consumption rate, recoverable reserves of coal will last The USBM research focuses on developing the critical

240 years. Today, about 80% of all coal mined in the technology—in a practical and transferrable form—that

United States is used to generate over half (55%) of the will enable what are now the most hazardous activities of

electricity consumed by the Nation. This situation will equipment operation to be performed in safety from a

continue beyond the year 2010, with the demand for nearby control station. We at the Bureau have progressed

electricity expected to increase by 22% by that time. Of a long way along the path to reach that goal.

that increase, 95% will come from coal. Since so much in

our lives depends upon electricity, an uninterrupted flow Our research originated with the continuous mining

of affordable coal, mined with minimal risk to workers, is machine and now includes, in addition to the continuous

essential to maintaining this nation’s vitality. miner, a continuous haulage system, a roof bolter, and

Today, face workers in underground room-and-pillar

mines experience disproportionate health and safety

hazards compared to their coworkers elsewhere in the RESEARCH ACTIVITIES

mine. Operators of roof bolting and continuous mining

equipment comprise one-fifth of the workforce yet

accounted for two-fifths of the deaths and lost-time

injuries during 1986-1992. Shuttle car haulage is also

burdened with hazards.

Facing us is the inevitable—that coal will become

more difficult and potentially more hazardous to mine as

miners are forced to tap into deeper and thinner seams.

Safer and more efficient mining systems will be needed to

improve worker safety and control energy costs. It is

imperative that the U.S. Bureau of Mines (USBM) utilize

advanced technology to minimize worker risks and

improve mining methods. The nature of the coal industry

in this country encumbers the USBM with this research

responsibility. The Bureau’s research on a computerenhanced mining system under its Equipment Safety

division of the Health and Safety Research program,

provides an essential component to safely satisfy the coal

needs of our nation.

In 1986, the USBM concluded that advances in

automation technologies could be used to significantly

enhance underground worker safety and health and

potentially provide a foundation for new mining methods.

It was thought possible that equipment operators could

successfully operate their machines without being located

in the face area with them, thus greatly reducing, if not

eliminating, their exposure to dust, noise, machine and

geological hazards. Having recognized this possibility,

USBM researchers were obligated to pursue the research.

Thus a new research approach was added to the USBM

research arsenal attacking present and future health and

safety hazards affecting coal mine workers. The

computer-assisted mining system research program was

thus conceived. It was recently, and perhaps more

ventilation.

Research is being conducted at two USBM research

centers—one, the lead center, near Pittsburgh,

Pennsylvania, and one in Spokane, Washington. The

Spokane Research Center's effort concentrates entirely on

developing the automated drilling and bolting module for

the roof bolter. All other research and the technical

project coordination are conducted at Pittsburgh. The

current research schedule plan calls for a convincing

demonstration of the technology by September 1997.

Much of our work has been reported at prior SMEAIME annual meetings and elsewhere (Schnakenberg and

Sammarco, 1991). The essence of the research stems

from the need to use sensors and computers for much of

the machine control because the safest position for the

machine operator is not within a direct line of sight of the

machine. Thus, the research consists of six major areas:

(1) The machine or equipment itself. It must be

equipped with position sensors on its moving parts

so that the control system gets the feedback it

needs for closed-loop control. In the special case

of the roof bolter, this research area includes the
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design of a module which can perform drop loops formed by supporting the cable and hose

automated drilling and bolting. bundle by a ring, which freely slides on a runner attached

(2) Navigation and guidance systems; provide the provide the 3.5 m of slack needed to allow freedom of

control system with data on the position and movement between the two machines. Two chains also

orientation of the machine. connect the two machines to prevent inadvertent strain on

(3) Coal-rock interface detection; provides the

means to keep the mining machine within the Roof bolter: The roof bolter provides the greatest

desired part of the coal seam. challenge to automate. The drilling, installation, and

(4) Data communications; the link between the human operation. The USBM purchased a Fletcher Model

activities of the machine and a computer HDDR-13, C-F (WATER) roof bolting machine to support

located at a convenient control station. the research effort. The research team at Pittsburgh has

(5) Control software; its architecture must be such accept computer control. The research team at Spokane

that the program code runs quickly and has written the control software and is continuing to

predictably and is easily understood, modified, design and build an automated roof drilling and bolting

and documented. module. Although the objective is total hands-off drilling

(6) Visualization and operator interface; they injury-saving goal of line-of-sight, remote-controlled

provide the means for the operator to bolting requires an automated drilling and bolting module.

understand what is going on with the mining

machine—visualization—and the facility to Ventilation: Ventilation methods and equipment for

control machine actions—the operator REMS will not greatly differ from that being developed

interface. and used for normal and extended-cut continuous mining.

Areas (4), (5), and (6) influence the selection of the paused while the curtain is advanced. When using

computer hardware as well. continuous haulage, the haulage system can support the

Machine al, 1992). Current research is showing that a properly

Continuous Mining Machine: We started with a

continuous mining machine that was on hand, a Joy

16CM, and then a new machine, a Joy 14CM. We added

sensors to report appendage positions, motor currents, and

hydraulic pressure, the sensors being most important for

machine control. Since the mining machine is working

with continuous haulage, we thought it best if the haulage

system would carry the supply cables and hoses to the Because remote manual control over a mining machine

machine. We then devised a method for easily is challenging even when the operator has a view of the

disconnecting the power, water, and communications from machine, it is best if the machine motion control is done

the miner. A means for supporting the cables that with the help of a computer. To do this, the computer

provides sufficient slack between the haulage system and must know where the machine is, the direction it is

the continuous mining machine was also devised. Our heading and the boundaries of the coal seam, i.e., coal

work on the continuous mining machine is essentially interface detection, which will be discussed in the next

complete. section. One way to determine machine position is to

Continuous Haulage: The greatest safety gains of REMS to use an inertial guidance system that can report its

will be realized when continuous haulage is employed. position accurately. While we experimented with

The continuous haulage system must be coordinated with alternative systems (Anderson, 1989 and 1992; Jobes,

the actions of the mining machine. We purchased a short 1991 and 1993), an inertial navigation system using three

(18 m) section of a Joy 3FCT that nevertheless represents orthogonal laser gyroscopes and accelerometers was being

all the components of a full system. We attached a sensor perfected for military applications by Honeywell Military

to indicate the steering angle of the wheels of the hopper Avionics Division. Several years ago, we obtained a

car and modified the haulage system to carry the power Honeywell system and have worked with the

and communication cables and the water hose for the manufacturer to fine tune it for use on a continuous

continuous mining machine. Quick disconnects and two mining machine (Sammarco, 1993). This sensor, renamed

to the conveyor boom (tail) of the mining machine,

the continuous miner cables.

setting of roof bolts are largely a mechanically-assisted,

completed a major effort to prepare the bolter chassis to

and bolting of a 15- to 20-m mine entry, even the highly

If line curtains are used, the machine activities can be

fan and tubing for blowing ventilation systems (Taylor, et

functioning dust scrubber integral with the mining machine

is a substantial contributor to good face ventilation for

methane control. A sensor that monitors the status of

loading the dust scrubber filter of the continuous miner

has been developed and reports to the control system.

Navigation

reference its position from the mine geometry; the other is
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the Honeywell Ore Recovery and Tunneling Aid naturally occurring gamma radiation emanating from the

(HORTA) for mining applications, is mounted on the host strata can be used (Mowrey, 1991a, 1991b;

mining machine and reports machine orientation and Maksimovic and Mowrey, 1993). When coal thicknesses

position. As a result of our application and test results, the greater than 0.6 m are required or geological conditions

HORTA is presently being aggressively marketed for are not favorable, natural gamma methods will not work.

mining machine guidance systems especially for highwall For these instances, we are evaluating using commercial

applications. As of this writing (August 1995), the ground-penetrating radar to measure coal thickness. The

accuracy of the HORTA has not been fully determined. USBM has also developed a highly unique spatial domain

The only true test of the accuracy is to subject it to the radar system that can, among other uses, determine the

mining conditions under which it is to operate (including distances from the air-coal interface to the roughly planar

vibration, machine motions, and time), namely on the boundaries of the layers of strata for depths of a few

miner for highwall and room-and- pillar mining. We plan meters (Chufo and Johnson, 1991). Within the next

to conduct tests in an open-pit coal mine because we need couple of years, this radar system will be able to produce

to be able to compare position and orientation data from 3-D images of hidden strata.

the HORTA against accurate transit data. At this time a

test site in an open-pit mine appears likely. For those situations when no coal is to be left on the

The guidance of the continuous haulage system is when the bits of the continuous miner touch the overlying

another task that is nearing completion. The objective is strata. This system uses an infrared (surface temperature

to keep the position of the conveyor discharge (tail) of the sensitive) imaging video (TV) camera that detects the

mining machine over the center of the hopper of the immediate heating of the bits, rock surface, and dust,

continuous haulage system while coal is being discharged caused by friction with the harder overburden. A simple

from the miner. At other times, the hopper car must be video alarm system, normally used to detect intruders by

positioned to receive coal or to avoid stressing the cables sensing movements in a stationary video scene, is used to

of the mining machine. Our control program restricts the detect the increased thermal activity the instant it occurs.

movements of the mining machine to those which the As the control computer raises the boom toward the roof,

haulage system can follow. We have used three string it monitors the signal from the video alarm and stops

potentiometers mounted on the front of the hopper car raising the boom when the alarm signal is detected

with the free ends of the strings attached to the rear of the (Mowrey and Ganoe, 1995).

continuous mining machine. Triangulation calculations

applied to these data provide the haulage control computer Communication and Computers

with the orientation and position of the hopper relative to

the mining machine. The controller (detailed below)

interprets this information and uses it to steer the guide

wheels of the hopper and to move the haulage system

forward and backward as necessary.

Coal Rock Interface Determination

One of the most difficult problems that the USBM transmits it over a twisted-pair data link to the control

faces in developing computer-assisted mining is keeping station. On a separate twisted pair, machine commands

the cutting head of a mining machine within the desired that turn the motors or hydraulic valves on or off are sent

boundaries of a coal seam, whatever the type of geology to a second microcontroller card onboard the machine

encountered. Two in-seam guidance situations are usually (Schiffbauer, 1994). The USBM empirically determined

encountered. One is the desire to extract all the coal to appendage motion response characteristics and devised

the seam boundary; the other is the need to leave a layer the appropriate servo control algorithms. Control delays

of coal on the floor or roof or both for reasons of ground are essentially those of the machine hydraulics.

stability or coal quality. Furthermore, properties of

overlying or supporting strata vary from seam to seam. The HORTA is connected to its own controlling

Techniques useful in one seam may not be useful in offboard computer by two twisted-pair wires. All four

others. The USBM has put extensive research effort into twisted pairs are bundled and enclosed in hydraulic hose

these problems (Mowrey, 1991a, 1991b, and 1992; conduit and bound to the machine power cable.

Maksimovic and Mowrey, 1993; Pazuchanics and

Mowrey, 1991 and 1993). In the case of the continuous haulage system, we

When some thickness of coal is to be left on the roof much as possible. We worked with the manufacturer to

and/or the floor, a commercially available coal-thickness enable us to connect our steering-wheel angle sensors and

sensor that uses the ability of the coal to attenuate the string potentiometers for guidance directly into their

roof, we have developed a sensing system that detects

Sensor data and commands must quickly and

confidently flow between the mining equipment and the

machine control computer outby. In an effort to keep the

systems onboard the machine as simple as possible, we

chose Intel’s Bitbus, a network of microcontrollers. One

microcontroller card gathers all the sensor data (except

that from the HORTA) and repeatedly and continuously

wanted to utilize the manufacturer’s control system as
4

system. We used their current-loop communication these pictures in concert with machine actions or

network to pass the status and sensor data into and pass environmental changes. We have developed two

commands from our control computer. prototype visualization concepts. In one case we show

The outby control station for REMS, intended to be coal, the mining machine, the continuous haulage machine

located near the power center in room-and-pillar and our research control hut. As the machine or its

operations, contains 3-4 single-board PC’s, an associated appendages move, the picture of the machine on the

shared monitor, and a keyboard. Microcontroller cards monitor also moves. Moreover, the operator can zoom in

reside in one PC to communicate with the mining machine on the machine or view it from any angle, including from

and haulage system. Another PC exclusively operates the underneath the ground. In another instance, which was

HORTA. A third PC runs our control software—software developed for highwall mining, we provide simultaneous

that interprets the data from the machines and issues top, side, and end views as “flat” drawings (orthographic

commands that turn motors and control hydraulic valve on projections). In the side view, we show the mining

or off to perform mining and haulage tasks. A Silicon machine in profile, the coal that is extracted, and the coal

Graphics workstation and monitor displays the workface thickness left on roof and floor using readings obtained

with the machines in action, and serves also as the from the coal thickness sensors. This information for the

operator interface where the machine operator observes current cut is overlaid on a similar picture of the previous

what is happening and can intervene if necessary. All of cut. These X-Ray-like views provide machine operators

the mentioned computers are interconnected so that they with a better “view” than if they were there with the

can immediately share sensor and control data. The machine. Using these views, they can optimize the

hardware described fits into a single compact frame inside extraction by using knowledge of the previous cut to

a control hut that advances with the section. adjust roof or floor height to take or leave more coal. A

Machine Controller Software views a projected path of the miner to see whether the

The USBM chose to use a hierarchical, real-time

control system to integrate and manage computer-assisted

machine control. The system we developed is modeled

after that developed by the National Institute of Standards

and Technology (NIST) (Quintero and Barbera, 1992) and

is the practical implementation of NIST's NASREM

architecture developed and adopted for the NASA space

program (Albus, et al, 1989). This form of control

programming was selected because it claimed the

advantages of ease of understanding, readability,

modification, and a deterministic and well-understood

behavior. We have found these claims to be true and

useful. The programming language used is C and runs in

MS-DOS on one PC. The structure of the software is a

hierarchy of tasks with the higher level tasks being

composed of a parallel and serial combination of more

simple tasks. With this structure, tasks can be easily

added or modified. Our controller provides a

“researchers” interface featuring pull-down menus that

allow selected issuing of task commands at any level or

direct control over each machine actuator. Although this

interface is handy for the researchers, it is inappropriate as

an operator interface.

Visualization and Operator Interface

Because the machine operators will not be within line

of sight of the machine they are controlling, and because

TV cameras (which will probably always be present)

cannot always provide the best perspective, we have

developed an alternative. The basic research objective is

to develop meaningful (information conveying) pictures of

the machine in its working area and animate or update

our indoor research area consisting of a block of artificial

top view allows a view of the pillar (web) width, and

pillar is narrowing or getting wider. Steering corrections

can be made manually if needed. The visualization system

does not have to be used with a computer-controlled

mining system, but it does need to be able to get

navigational and appendage data from the mining

machine.

The visualization system described above could also

depict a longwall shearer, the seam boundaries, and the

shield supports and their movements, and thereby could

enhance development and use of automated longwall

mining.

We are currently developing an operator interface for

the continuous mining machine and continuous haulage

element of REMS. The objective of an operator interface

is to quickly inform the operator of the status of the

machine operation at all times and permit facile manual

control of machine tasks or actuators whenever it becomes

necessary. The design is a particularly difficult task since

the USBM does not have continual access to a mine in

which we can operate REMS so that we can experience

real mining scenarios and develop the appropriate

informative interface from those experiences. However,

we are developing the basic structure and components that

should allow easy reconfiguration and prototyping. A

preliminary interface is under development.

FUTURE RESEARCH
5

At the present time (August 1995), the USBM is Determination of a Continuous Mining Machine Using

planning to conduct challenging tests of the continuous an Angular Position-Sensing System. BuMines

mining machine using open pit and highwall mines. The IC 9222,* 8 pp.

accuracy of the HORTA will be determined by performing

full-scale highwall mining scenarios in an open-pit mine. Anderson, D. L. (1992). Underground Test Results of a

Absence of overburden provides researchers access to Laser-Based Continuous Miner Tram Control System.

measure machine position using surveying equipment. BuMines RI (in publication), available from author,

The open-pit site will offer opportunities to test and refine Bureau of Mines, P.O. Box 18070, Pittsburgh, PA

automatic mining scenarios such as two-pass advances and 15236, USA.

turning crosscuts; the radar system for maintaining web

thickness in highwall; evaluation of the visualization Chufo, R. L., and Johnson, W. J. (1991). A Radar Coal

system; and will provide an opportunity to get the Thickness Sensor. Conference Record of the 1991

operating time that is needed to improve the designs of an IEEE Industry Applications Society Annual Meeting.

operator interface. A highwall mine will provide a test site Dearborn, MI, pp. 1182-1191.

for the coal interface detection systems as they are

integrated into the control system. Jobes, C. C. (1991). Utilizing Mechanical Linear

The combination of successful open pit and highwall Machine's Position and Heading. BuMines RI 9364,* 19

mining tests should spark the interest of the highwall and pp.

underground mining industry and thereby provide the

incentive for equipment manufacturers to use USBM Jobes, C. C. (1993). Mechanical Sensor Guidance of a

technology. Mining Machine. IEEE Transactions of Industry

The roof bolter, when ready in a year or so, will be

tested in an underground mine in an area of previously Maksimovic, S., and Mowrey, G. L. (1993). Basic

bolted roof. Geological and Analytical Properties of Selected Coal

SUMMARY

The USBM is engaged in a research program that

utilizes advances in machine control technology to

improve worker safety and health in underground coal

mines. Sensors and computer technology can now allow

remote operation of the continuous mining machine,

continuous haulage system, and roof bolter, from a nearby

safe location during the most hazardous tasks of cutting

and hauling coal and bolting the roof. Substantial progress

has been made and components of the REMS, such as

coal interface detection and visualization, can be utilized

individually in today’s mining systems to increase safety.

Provided the resources are available, the performance of

the system can be tested and demonstrated using test sites

of open pit and highwall mines. The demonstration should

convince industry and equipment manufacturers that

REMS can improve the bottom line substantially by

reducing injuries and fatalities, and their associated costs.

REFERENCES

Albus, J. S., McCain, H. G., and Lumia, R. (1989).

NASA/NBS Standard Reference Model for Telerobot

Control System Architecture (NASREM). NIST

(formerly NBS) Technical Note 1235, April 1989

Edition.

Anderson, D. L. (1989). Position and Heading

Transducers for the Determination of a Mining

Applications, Vol. 29, No. 4, pp. 755-761.

Seams for Coal Interface Detection. BuMines IC 9296,*

58 pp.

McClelland, J. J., R. F. Randolph, G. H. Schnakenberg,

Jr., and R. S. Fowkes. (1994) Safety Breakthrough—Reduced Exposure Mining System (REMS).

BuMines SP-26-94,* 38 pp.

Mowrey, G. L. (1991a). Promising Coal Interface

Detection Methods. Mining Engineering, Vol. 43, No. 1,

pp. 134-138.

Mowrey, G. L. (1991b). Horizon Control Holds Key to

Automation (Part 1). Coal magazine, pp. 44-48.

Mowrey, G. L. (1992). Horizon Control Holds Key to

Automation (Part 2). Coal magazine, pp. 47-51.

Mowrey, G. L., and Ganoe, C. W. (1995). An InfraredBased Coal Interface Detection System, Proceedings,

Third International Symposium on Mine Mechanization

and Automation, Golden, CO, June 12-14, 1995, Ed. L.

Ozdemir and K. Hanna, pp. 3-21 to 3-31.

Pazuchanics, M. J., and Mowrey, G. L. (1991). Use of

Adaptive Signal Processing Techniques to Discriminate

Between Coal Cutting and Rock Cutting. BuMines

IC 9269,* 13 pp.

Pazuchanics, M. J., and Mowrey, G. L. (1993). Recent

Progress in Discriminating Between Coal Cutting and
6

Rock Cutting with Adaptive Signal Processing Schiffbauer, W. H. (1994). A Distributed

Techniques. BuMines RI 9475,* 15 pp. Communications and Real-Time Control Network for

Quintero, R., and Barbera, A. J. (1992). A Real-Time Conference on Robotics for Challenging Environments,

Control System Methodology for Developing Intelligent Albuquerque, NM.

Control Systems. NISTIR 4936. U.S. Department of

Commerce, National Institute of Standards and Schnakenberg, Jr., G. H., and Sammarco, J. J. (1991).

Technology, Robot Systems Division, Gaithersburg, MD Overview of the Bureau of Mines Computer-Assisted

20899, 84 pp. Mining Research Program. Proceedings of the

Sammarco, J. J. (1993). Field Evaluation of the Modular Automation, Golden, CO, pp. 9-9 to 9-29.

Azimuth and Positioning System (MAPS) for a

Continuous Mining Machine. BuMines IC 9354,* Taylor, C. D., Goodman, G. V. R., and Vincze, T. (1992).

14 pp. Extended Cut Face Ventilation for Remotely Controlled

Robotic Mining. Proceedings of the ACE Specialty

International Symposium on Mine Mechanization and

and Automated Mining Systems. Proceedings of SME

1992 Annual Meeting, 11 pp.

*All U.S. Bureau of Mines publications available from the

National Technical Information Service, Springfield, VA

22161, (703) 487-4650; FAX (703) 321-8547.